Article comprising light absorbent composition to mask visual haze and related method   

Abstract: A transparent article includes a continuous polyester matrix having at least one incompatible filler dispersed therein. The incompatible filler provides domains in the polyester matrix, each domain having a particular dimension, thus providing a range of dimensions for the domains in the article. To create haze, the dimensions are within the range of from about 380 nm to about 720 nm. Once the range of dimensions is determined, a light absorbent composition can be found which absorbs light at a range of wavelengths that at least substantially covers the range of dimensions of the domains. In doing so, it has been found that the haze of the article can be substantially masked. Method for producing the article and for masking the haze are also provided.

This application is a continuation of U.S. patent application Ser. No. 12/823,447 filed on Jun. 25, 2010 which is a continuation of U.S. patent application Ser. No. 10/769,167 filed on Jan. 30, 2004 and is now granted U.S. Pat. No. 7,833,595 and claims the benefit of U.S. Provisional Application Ser. No. 60/44,313, filed on Jan. 31, 2003. The teachings of all of which are incorporated in their entirety. Other related Applications are application Ser. No. 11/618,437, which is a divisional of Ser. No. 10/769,167 and is now granted U.S. Pat. No. 8,052,917; application Ser. No. 11/617,248, which is a continuation of Ser. No. 10/769,167 and is now granted U.S. Pat. No. 7,438,960; application Ser. No. 12/823,306, which is a continuation of Ser. No. 10/769,167 and is now granted U.S. Pat. No. 8,053,050; application Ser. No. 12/823,422, which is a continuation of Ser. No. 10/769,167 and is now granted U.S. Pat. No. 8,067,074; and application Ser. No. 12/823,486, which is a continuation of Ser. No. 10/769,167 and is now granted U.S. Pat. No. 8,057,874.

BACKGROUND OF THE INVENTION

This invention relates to the production of a transparent article and, more particularly, to the production of a shaped, transparent thermoplastic article, such as a container or bottle, having an incompatible filler, preferably a gas barrier strengthening filler dispersed therein, wherein the light absorption of the article has been altered to effectively mask or reduce the visual haze of the article.

Thermoplastic polymers, such as polyesters, have long been used in the production of packaging materials, including preforms which are then blown or otherwise oriented into a desired form as necessary for the production of plastic articles such as containers and/or bottles for food and beverage storage and delivery. Among the most preferred and cost-effective thermoplastic polymers used for this purpose are poly(ethylene phthalate) resins. Poly(ethylene terephthalate) (PET), as well as other polyesters, when processed properly under the right conditions and oriented into a desired shape, provides a high clarity, low haze article. Consequently, the plastic bottling industry has used PET and similar polyesters for several years in its production of plastic containers and bottles for food and beverages.

Unfortunately, while plastic containers made from polyester, provide excellent high strength containers having excellent gas barrier properties for most foods and beverages, they are presently not suitable as beer containers or other food containers where extremely low gas permeability is required. It will be appreciated that when oxygen and other air gases come into contact with certain foods and beverages, such as beer for example, the beer oxidizes or otherwise becomes stale. Consequently, attempts have been made heretofore to reduce the oxygen/gas permeability of the container or, stated another way, to increase the gas barrier strength of the container.

One known way to reduce oxygen/gas permeability or to increase the gas barrier strength of the container is to blend certain gas barrier strengthening fillers with the polyester in the container. For instance, certain polyamides, such as polyxylylene amides, are well known in the art to provide improved gas barrier strength to polyester containers. To produce these containers, the filler is typically blended or dispersed in the polyester by processes known in the art and then the article is manufactured. In some instances, the containers may be molded as by injection molding and the like. In other instances, preforms of the containers are prepared such as by injection molding or extrusion, and are then blown or otherwise oriented into the desired size and shape.

Various patents and patent publications have taught the use of polyester/polyamide blend compositions for forming an article having low haze and reduced gas permeability compared to polyester alone. In at least one patent publication, in order to provide a low haze/low gas permeability container, it is stated that the blend composition employ a polyamide having a number average molecular weight of less than 15,000. That patent publication further makes it clear that blends of higher molecular weight polyamides with polyester are known to have high haze values which limit their practical use in the food and beverage container industry.

In other words, heretofore, few, if any, blends of polyester and these gas barrier strengthening fillers, such as higher molecular weight polyamides, have been used in the plastic container or bottling industry, or any industry where transparent, high clarity articles are desired, because it is a well-known fact that, upon orienting or stretching an article containing a blend of polyester and polyamide, the article loses much of its clarity and transparency, i.e., becomes visually cloudy or hazy. This characteristic is known in the industry as haze.

Haze, as described in most of the patent literature, can be measured, much like any other physical property. Measurements to determine the level or amount of haze may be obtained using a colorimeter (e.g., Hunter Lab Color Quest) and following ASTM D1003. Haze is typically reported as a percentage based upon the thickness of the article and can be calculated by the equation

Haze   % = T Diffuse T Total × 100

where Haze % equals transmittance haze, TDiffuse equals diffuse light transmittance, and TTotal equals total light transmittance. A 4% haze measurement in a container sidewall approximately 15 mils thick is normally visible to the naked eye. Generally, when testing containers made from different blends of polyester and polyamides, haze values have been measured in the 15% to 35% range for these 15 mil thick containers. For purposes of this invention, this type of haze will often be referred to hereinafter as “physical haze” or “measured haze.”

Moreover, as the amount of gas barrier strengthening filler used in the polyester/filler blend increases, the physical haze value also increases. In fact, it has been found by others that effective blend ratios of polyester (e.g., PET) and aromatic polyamides (e.g., poly(m-xylylene adipamide) commonly referred to as MXD6) provide for physical haze values in the 20% to 30% range upon orienting the polymers into the form of a container again having a wall thickness of about 15 mils.

Heretofore, efforts have focused on reducing the gas permeability of the article by addition of gas barrier strengthening fillers, while, at the same time, trying to reduce the amount of physical haze produced upon orientation of the article. Such efforts, where successful, have generally found that to reduce physical haze, the size of the molecules of the filler had to be significantly small. Generally, it is understood, as stated above, that polyamides having a number average molecular weight of less than 15000 in a concentration of less than 2 percent by weight are needed to sufficiently reduce physical haze. Alternatively, it has been found that, where polyamide domains in the polyester have been limited to an average number size of from 30 to 200 nanometers, physical haze will also be reduced or limited. At least one theory for this phenomenon is that the polyamide particles are so small that they fail to scatter light, particularly in the visible spectra, i.e., the particles do not reflect light to the observer in a manner detectable to the naked eye. Moreover, in measuring the physical haze using machines such as a colorimeter, it is clear that the physical haze measured has been reduced or potentially even eliminated.

Based upon this theory, it should be understood then that, where those particles or domains surrounding the filler are much larger than 200 nanometers, say on the order of 400 to 700 nanometers, the haze of the article is not only physically measurable, but also may be visible to the ordinary observer. In fact, at least one journal article expressly recognizes that the number and size of the dispersed particles does create measured haze. It is further noted therein that stretching makes for even more measured haze because, firstly, stretching increases the size of the dispersed particles in a sheet plane and, secondly, the difference in the anisotropic refractive indices of the matrix and the dispersed phase increases. Thus, some patents have attempted to prevent the stretching or reorienting of the MXD6 domains, for example, by producing bottles of PET and MXD6 when the polymer is in its molten state.

Hence, all of the prior art has focused on the physical haze phenomenon and the reduction or elimination thereof. In contrast, the present invention focuses on the visual aspect of the haze property since it is this characteristic which is believed to be detrimental to the cosmetic appearance and practical use of the article, not the physical haze of the article.

Heretofore, however, this “visual haze” or “visible haze” of an article has never been considered separate and apart from the physical haze of the article, as it is generally immeasurable by traditional physical testing of the article. By “visual haze” or “visible haze,” it is meant that haze which can be observed optically or visually by a person in ordinary direct or indirect light. It is the haze that is visible to the naked eye of the observer, presumably due to the reflectance or transmittance of the light from the filler domains present in the article. It is believed that the visual masking of the physical haze phenomenon results in the elimination or reduction of this “visual haze,” and can provide an article suitable for commercial use. To that end, it will be understood that “visual haze” is not a measured physical property to the same extent that the physical haze of an article is determinable on a colorimeter or the like, and eliminating or reducing visual haze may or may not reduce the measured physical haze of the article.

Accordingly, eliminating or reducing the “visual haze” of an article, regardless of the physical haze measurements, is seen as highly desirable to the art, particularly to the plastic container and bottling industry. Thus, there remains a need to provide a process by which to mask the visible haze of a transparent article made from polyester blended with a gas barrier strengthening filler, as well as for transparent, preferably oriented, articles comprising a polyester/filler blend that is aesthetically and visually acceptable to the plastic container and bottling industry.

SUMMARY

Broadly, the present invention is directed to the production of a transparent article such as a plastic container or bottle made from a major component of thermoplastic polymer and a minor component of an incompatible filler. Such an article, particularly when oriented or stretched, will typically produce a haze. It has been unexpectedly found that the haze of the transparent article visible to the naked eye may be substantially masked or, put another way, the visible haze of the article may be eliminated or substantially reduced (not necessarily on physical terms, but on visibility terms), by altering the light absorption of the article at wavelengths that at least substantially correlate with the size dimensions of the domains in the thermoplastic polymer formed upon formation of the article. Importantly, the particular dimensions with which the wavelengths are to be correlated are those in the axial plane of the article. It will be understood that, by the term “substantially masked,” it is meant that the alteration of the light absorption of the article does not necessarily affect the measured physical haze of the article, but does substantially reduce or nearly eliminate that haze visible to the naked eye. The measured physical haze of the article may not be affected by the light absorbent composition at all, may be affected by the composition by only slightly reducing the measured haze in the article, or may be affected significantly by the light absorbent composition, depending upon the actual light absorbent composition and the amount employed. In any event, the visually observable haze of an article is “substantially masked” or substantially undetectable to the naked eye of the ordinary observer, but physical haze is still generally measurable by a colorimeter to be above ordinarily acceptable limits.

One manner of altering the light absorption of the article is to employ an effective amount of one or more light absorbing compositions known to absorb light at wavelengths which at least substantially cover, and more preferably, at least substantially correlate to most, if not all, of the dimensions of the domains found in the axial plane of the article. It will be appreciated that, for purposes of this invention, at least some, and more preferably, at least a majority of these dimensions of the domains will necessarily have a size falling within the range from about 400 nm to about 700 nm, which substantially corresponds to the visible spectrum (i.e., from about 380 nm to about 720 nm). By utilizing a light absorbing composition, such as a colorant, that has a known region of absorption at wavelengths within the visible spectrum, one can substantially correlate the wavelengths, in nanometers, within the region of absorption of the composition to the dimensions, also in nanometers, of the filler domains found in the article. By using one or more particular light absorbing compositions having a region of absorption that at least substantially covers the range of dimensions of the domains containing the filler found in the thermoplastic filler that fall within the visible spectrum, it has been found that “visual haze,” as defined herein above, is substantially reduced, if not eliminated, and physical haze is masked in the article.

Furthermore, experimentation has provided a more detailed approximation of the amount of light absorbing composition required to “substantially cover” the range of dimensions of the domains containing the filler. More particularly, a composition that absorbs light such that X is less than 9.6 in the equation

X=Σ(1−Ai)×(Ni)

where Ai is the percent of light absorbed at a wavelength i and Ni is the number of domains per hundred square microns at wavelength i, and where i ranges from 400 nm to 700 nm, is considered to substantially cover the domains and at least start to reduce the visual haze of an article. It will be recognized that an alternative expression of this equation is

X=Σ(Li)×(Ni)

where Li is the percent of light not absorbed (i.e. that is available to reflect) at a wavelength i.

The advantages of the present invention over existing prior art relating to transparent articles employing polyester and incompatible fillers, which shall become apparent from the description and drawings that follow, are accomplished by the invention as hereinafter described and claimed.

In general, one or more aspects of the present invention may be achieved by a transparent article comprising a thermoplastic polymer matrix; a plurality of domains, each encompassing at least one incompatible filler, dispersed in the polyester matrix, the domains having a range of dimensions in an axial plane of the article, wherein the dimensions of at least some of the domains in the axial plane of the article fall within a range of from about 400 nm to about 700 nm; and an effective amount of at least one light absorbent composition, wherein the at least one light absorbent composition absorbs light in a region of the visible spectrum at wavelengths that at least substantially covers the range of dimensions of the domains in the article, to substantially mask any visual haze of the transparent article.

One or more other aspects of the present invention may be accomplished by a process for the production of a transparent article made of a blend of a major component of polyester, a minor component of at least one incompatible filler dispersed therein, and at least one light absorbent composition, comprising blending the filler into the polyester; forming an article into a desired size and shape, wherein domains comprising the incompatible filler are created in the polyester upon formation of the article; determining a range of dimensions in the axial plane of the article for the domains in the polyester, at least some of the dimensions falling within a range of from about 400 nm to about 700 nm; finding a light absorbent composition that absorbs light in a region of the visible spectrum at wavelengths that at least substantially covers the range of dimensions of the domains in the polyester; and adding an effective amount of the light absorbent composition to the polyester and the incompatible filler and forming a different, transparent container into the same desired size and shape, to substantially mask any visual haze in the article.

Still one or more other aspects of the present invention may be achieved by a transparent article comprising a thermoplastic polymer matrix; a plurality of domains, each encompassing at least one incompatible filler, dispersed in the polyester matrix, the domains having a range of dimensions in an axial plane of the article, wherein the dimensions of at least some of the domains in the axial plane of the article fall within a range of from about 400 nm to about 700 nm; and at least one light absorbent composition, wherein the at least one light absorbent composition absorbs light in a region of the visible spectrum such that X is less than 9.6 in an equation

X=Σ(1−Ai)×(Ni)

where Ai is the percent of light absorbed at a wavelength i, where Ni is the number of domains per hundred square microns at wavelength i, and where i ranges from 400 nm to 700 nm.

Yet one or more other aspects of the present invention may further be achieved by a process for the production of a transparent article made of a blend of a major component of polyester, a minor component of at least one incompatible filler dispersed therein, and at least one light absorbent composition, comprising blending a selected amount of the filler into the polyester; forming an article into a desired size and shape, wherein domains comprising the incompatible filler are created in the polyester upon formation of the article; determining a range of dimensions in the axial plane of the article for the domains in the polyester, at least some of the dimensions falling within a range of from about 400 nm to about 700 nm; blending a selected amount of light absorbent composition into the polyester to determine that the light absorbent composition absorbs light in a region of the visible spectrum such that X is less than 9.6 in the equation

X=Σ(1−Ai)×(Ni)

where Ai is the percent of light absorbed at a wavelength i and Ni is the number of domains per hundred square microns at wavelength i, and where i ranges from 400 nm to 700 nm; and adding that selected amount of the light absorbent composition to the polyester and the selected amount of incompatible filler and forming a different, transparent container into the same desired size and shape, thereby substantially masking any visual haze in the article.

Other aspects of the present invention may be still further achieved by a method for masking visual haze in a transparent article made from a major component of thermoplastic polymer and a minor component of at least one incompatible filler, comprising altering light absorption of the transparent article at wavelengths that at least substantially correlates with dimensions, in the axial plane of the article, of domains in the thermoplastic polymer created upon formation of the article and containing the incompatible filler.

DETAILED DESCRIPTION

FIG. 1 is a representative sectional, perspective view of a part of an oriented article illustrating domains containing an incompatible filler dispersed within a thermoplastic polymer matrix;

FIG. 2 is a representative cross-sectional view of a shaped, oriented article also illustrating domains containing an incompatible filler dispersed within a thermoplastic polymer matrix;

FIG. 3 is an enlarged sectional view of one domain within the thermoplastic polymer matrix of FIG. 2;

FIG. 4 is an enlarged sectional view of the domain of FIG. 3 taken along line 4-4 in FIG. 3;

FIG. 5 is a photomicrograph of a portion of a transparent article prior to orientation;

FIG. 6 is a photomicrograph of the same portion of the transparent article of FIG. 5 after orientation to a desired shape and size;

FIG. 7 is a representative graph of the data obtained from analysis of the dimensions of the MXD-6 domains of a 500 ml bottle prepared from polyester and MXD-6;

FIGS. 8A, 8B, and 8C are representative absorption spectra of various yellow, red, and blue colorants, respectively;

FIGS. 9A, 9B, 9C, and 9D are representative absorption spectra of various green, orange, purple and pink colorants, respectively;

FIG. 10 is a representative comparison graph comparing the plot of the number of domains per hundred square microns present in an article based upon its size in nanometers with the % of light absorbed of a particular green colorant designated Sprite Green, over that a range of wavelengths in nanometers for the same article;

FIG. 11 is a representative comparison graph comparing the plot of the number of domains per hundred square microns present in an article based upon its size in nanometers with the % light absorbed of various green and red colorants over a range of wavelengths in nanometers for the same article; and

FIG. 12 is a representative comparison graph comparing the plot of the number of domains per hundred square microns present in an article based upon its size in nanometers with the % light absorbed of various blue and red colorants over a range of wavelengths in nanometers for the same article.

DETAILED DESCRIPTION

In accordance with the present invention, shaped transparent articles comprising thermoplastic polymer and at least one incompatible filler dispersed therein are provided wherein haze in the article, normally visible to the naked eye of the ordinary observer, and produced most commonly by stretching or orienting the thermoplastic polymer and filler blend during production of the article, has been substantially masked. Such articles are especially useful in the packaging industry when in the form of a container or bottle.

The present invention solves the haze problem in a manner heretofore never contemplated. It masks haze that is visible to the naked eye of the observer of the article and does not require the use of low molecular weight fillers or fillers having domain dimensions in the article of less than about 200 nm or otherwise below the lowest wavelengths of the visible spectrum (i.e., less than about 380-400 nm), so as to produce an article having reduced physical haze below about 4% per 15 mil thickness of the article. Instead, the present invention masks any visible haze by altering the light absorption of the article at wavelengths that at least substantially covers the range of the dimensions of the filler domains in the axial plane of the article.

By the phrase “at least substantially covers” and the phrase “at least substantially correlates” also used herein, both of which can be used interchangeably, it is meant that the range of wavelengths, in nanometers, at which the light absorbent composition employed absorbs light in the visible spectrum is approximate to or is greater than the range of dimensions of the filler domains in the axial plane of the article, to the extent that those dimensions are somewhere between about 400 nm and about 700 nm, i.e., are in the visible spectrum. Thus, it will be appreciated that the range of dimensions of the filler domains does not have to completely cover the entire visible spectrum. It will also be appreciated that the range of wavelengths need not necessarily cover the entire range of dimensions of the filler domains provided in the article to mask the haze, but rather that they cover enough of the range of dimensions to substantially mask the haze. For instance, it is possible that the range of dimensions of the filler domains provided in the article is greater than or at least partially falls outside of the visible range. The range of wavelengths of the light absorbent composition need only substantially cover that range of dimensions that falls within the visible spectrum for the present invention. In another instance, if a light absorbent composition is capable of absorbing light in all but a very small region where only a few domains exist, it has been determined that the observer would not be able to see the haze of the container or bottle regardless of the fact that the light at a particular wavelength is not absorbed where a few domains may exist. That is, the remaining existence of a few particular domains having dimensions that do not correspond (i.e., fall outside the range of) to light absorbing wavelengths of the light absorbent composition employed is seen as de minimus to the present invention, and will not prevent substantial masking of the visual haze in the article. For practical purposes, masking of the visual haze will be deemed sufficient if the cosmetic appearance of the article having substantially masked haze is acceptable to the interested industry, in particular the container and bottling industry, as a transparent article that can be practically used in commerce.

In further defining the phrases “at least substantially covers” and “at least substantially correlates” above, it will also be appreciated that the greater the number of domains having a particular dimension in the axial plane of the article, desirably the greater the light absorption at the matching wavelength should be. However, it has been found that there need not necessarily be a one to one or greater correspondence between the intensity (i.e., amount) of the absorption for the light absorbent composition and the number of domains having a particular dimension. If substantial light is absorbed by the light absorbent composition at a wavelength that correlates to a particular dimension for a domain in the article, then it is believed that at least significant masking of the haze will occur.

More particularly, it has been found that a light absorbent composition that absorbs light in the visible spectrum such that X is less than 9.6 in the equation

X=Σ(1−Ai)×(Ni)

where Ai is the percent of light absorbed at a wavelength i and Ni is the number of domains per hundred square microns (108 nm2) at wavelength i, and where i ranges from 400 nm to 700 nm (i.e., the visible spectrum), is considered to substantially cover the domains and will at least start reducing the visual haze of an article.

Stated another way, to reduce visual haze of an article, a light absorbent composition must be included in the relevant part of an article, typically the single continuous portion of the article where haze is noticed such as the sidewall of a container or bottle. That light absorbent composition must be capable of absorbing light in the visible spectrum of that single, continuous portion of the article such that, when absorbance is determined on that single continuous portion of the article without an incompatible filler present, X is less than 9.6 in the equation

X=Σ(L1)×(Ni)

where Li is the percent of light not absorbed (i.e. that is available to reflect) at a wavelength i, and Ni is the number of domains per hundred square microns (108 nm2) at wavelength i, and where i ranges from 400 nm to 700 nm (i.e., the visible spectrum) If X is less than 9.6, then the ordinary observer will at least begin to see a reduction in the visual haze of the article.

Moreover, as X gets smaller, the visual haze of the article will be further reduced. Thus, while X must be less than 9.6 in the above equation for a reduction in visual haze to start to be noticed, X less than 9.5 is preferred, and X less than 9 is more preferred, and X less than 7.5 is even more preferred. It will be appreciated that where no domains are present (i.e., N=0), X will necessarily be 0, and no haze will be encountered. Likewise, where the colorant or light absorbent composition has absorbed most of the light available for reflection over a range of wavelengths, then the percent of light transmitted or reflected is low (i.e., L approaches 0) and therefore, X will be low unless there is an unusually high number of domains of the same size as those wavelengths. In other words, the total amount of relative light available for reflectance (i.e., that is not absorbed) across the entire visible spectrum, from about 400 nm to about 700 nm, must be less than 9.6. The “total amount of relative light” is calculated as the sum of all the light at each wavelength between about 400 nm and about 700 nm with a greater amount of light required for each wavelength having domains at that wavelength. Thus, the relative amount of light required to be absorbed is weighted toward the number of domains present in the wavelength.

It will be appreciated that the determination of whether a light absorbent composition will absorb light for a particular article below an X threshold is relatively simple and can be determined without undue experimentation. Ai is the percent of light absorbed by the article having the colorant without the incompatible filler at wavelength i; Li is the percent of light available to reflect at wavelength i, where i is 400 nm to 700 nm. These percentages can be calculated upon measuring the absorbance of the composition, it being understood that Ai+Li=1. In most instances, Li will be 1 minus the percent absorbed, or the percent of light available for reflectance. These measurements can be obtained using the process described below. Ni is the number of domains per hundred square microns at wavelength i, where i is 400 nm to 700 nm. Ni can be measured by SEM and normalized to square microns.

The intensity of the light at wavelength i may be pertinent in some instances, and can be factored into the equation as Ii as follows

X=300Σ(Li)×(Ni)×(Ii)

where Ii is the intensity of a source of light at the wavelength divided by the total light between 400 nm to 700 nm. Where a spectrophotometer that measures the percent light is used, Ii is 1/300 and, therefore, multiplying by 300 normalizes the light to a common standard.

In essence, it has been found that employing a higher concentration of light absorbent composition to the article may help to more fully mask the visible haze in the article where the light absorbent composition absorbs light at a particular wavelength less intensely than at other wavelengths and/or where a great number of domains exist at a particular dimension corresponding to that particular wavelength. It is believed that any required intensity of the light absorbed can be calculated or predetermined without undue experimentation based upon the concentration of the light absorbent composition, the thickness of the article and other known parameters and coefficients according to the law of Beer-Lambert-Bouguer.

Referring now to the drawings, a section of a shaped, transparent article, generally indicated by the numeral 10 in FIG. 1, is illustrated. As shown, the section 10 has been oriented or stretched in all directions within the axial plane of the article, including both the radial (X) and axial (Y) directions, as indicated by the arrows. By the term “axial plane,” it is meant that the general plane of the article is essentially parallel to the surface of the article, or put another way, that the general plane of the article is substantially perpendicular to the line of sight of the observer.

The section 10 comprises a thermoplastic polymer matrix 12 having discrete particles 14 of an incompatible filler dispersed therein and, where the incompatible filler is not extensible or deformable like polyester and other thermoplastic polymers (e.g., clay particles), voids 16 encompass the particles 14. Assuming the use of spherical filler particles 14 upon blending in the polymer matrix 12, and where the particles have been dispersed uniformly and an article has been oriented evenly in all directions within the axial plane, a cross-section of the voids 16 would be, in theory, circular, as shown here and in FIG. 4, when viewed perpendicular to the axial plane. In practice however, dispersion of the filler and stretching of the article is not precise, and irregular-shaped voids are most often created, having various length, width and height dimensions.

It will be understood that the incompatible filler may be extensible and deformable like the thermoplastic polymer as well. Such fillers may themselves include various thermoplastic polymers, like polyamides. In the case of a polyester matrix, the incompatible filler would stretch like the polyester and form a stretched, discrete minor phase 17 within the polyester matrix. This phase 17 will essentially include not only the particles 14 but also the voids 16 in FIG. 1. Thus, the extensible filler will be stretched to fill-in all of the voids. In FIG. 1, the minor phase 17 of the filler will compass the entire circle identified by the numeral 16 as well as the circle therein identified by the numeral 14.

It is also known that, oftentimes, given the irregular shapes that may form, two or more of these discrete minor phases of the filler may come together to form one larger structure. For purposes of this invention, numerals 17 and 27 in FIGS. 1-4 will be referred to hereinafter as “the discrete phases” or “the minor phases” of the filler, unless otherwise stated, and shall include the area or volume denoted by both the numerals 16 and 14 in FIG. 1, and the numerals 26 and 24 in FIGS. 2-4, respectively. This language associates the present invention with the use of extensible thermoplastic polymers as the incompatible filler, but should not necessarily be limited in scope thereto, the present invention being set forth by the scope and spirit of the attached claims.

Unlike the representative drawing, sectioning the article along any one specific axial plane will penetrate the discrete minor phases 17 at various places through the height of each phase unless, as shown here, all minor phases 17 are evenly parallel on the specific axial plane. Thus, some discrete phases should appear smaller than others on any one specific axial plane. Likewise, cutting the article along any one specific transverse plane will penetrate the discrete phases at various places through the length and/or width of each discrete phase unless the phases are unidirectionally stacked on each other within that plane. Thus, some discrete phases should appear longer than others on any one specific axial plane.

In FIG. 2, a section of a wall of a shaped article, generally indicated by the numeral 20, is illustrated. Such an article may be a plastic container or bottle. As described previously for FIG. 1 above, this section 20 of the article includes a thermoplastic polymer matrix 22 having discrete particles 24 of an incompatible filler dispersed therein and surrounded by voids 26. Based upon the FIGS. 3 and 4, it will be appreciated that this article 20 is also oriented or stretched in all directions within the axial plane of the article, in a manner similar to that shown in FIG. 1.

FIGS. 3 and 4 are sectional views illustrating enlargement of a section of the shaped article of FIG. 2, wherein the filler particle 24 is contained in the void 26 and is entrapped within the continuous thermoplastic polymer matrix 22. Again, where the filler is an extensible, deformable thermoplastic polymer, the entire area or volume denoted by the numerals 24 and 26 is the minor phase 27 of the filler. These phases 27 result from the shaped article being stretched as discussed herein above.

Upon formation of the article, a domain 28 is created in the polymer matrix 22 which essentially includes both the discrete particle 24 and void 26, or the entire minor phase 27 of the incompatible filler. Where the incompatible filler used in the present invention is moldable and stretchable like the polymer employed in the article, orientation or stretching of the article will cause the incompatible filler, like the polymer, to spread along the axial plane of the article and to narrow in the transverse plane of the article as the wall of the article becomes thinner. However, in instances where the filler is not stretchable like the polymer, a void or voids 26 may be left between the filler and the polymer. Where a polyamide and another thermoplastic polymer other than the thermoplastic polymer employed as the matrix polymer, e.g., polyester, are utilized as the filler, the void left, if any, will generally be de minimus since both of the thermoplastic polymers are stretchable and deformable. Thus, the domains created in the matrix polymer are essentially the volume of the minor phases themselves. Nevertheless, for purposes of this invention, it will be understood that, where non-deformable filler particles are utilized, a domain 28 includes not only the volume of the filler particle 24, but also any additional volume in the article of any void 26 between the filler particle 24 and the polymer 22. Where the article has not been stretched, the domain will match the volume of the filler particle.

The present invention is particularly concerned with those domains having a dimension in the axial plane of the article within the range of from about 400 nm to 700 nm. Referring to FIGS. 3 and 4, the dimension of a domain is the diameter of the domain. Thus, in FIG. 3, the dimension can be seen as extending from one end 29 to the other end 29′ of the domain. In FIG. 4, the dimension of the domain shown is any diameter of the circle. However, it will be appreciated that more often the domain in the axial plane of the article will be ellipsoidal in nature and will have a longer diameter in one direction, say the Y direction, than in another, say the X direction. In this instance, the dimensions of relevance may be the longest diameter of the domain (i.e., the major axis of the domain which, in this scenario, is in the axial Y direction), or the diameter of the dimension perpendicular to the longest diameter in the axial plane (i.e., the minor axis of the domain which is in the radial (X) direction). It has been found that domains having dimensions of between about 400 nm and about 700 nm show up in the article as visual haze. Not coincidentally, this range is also the range of the visible spectrum. Thus, any domain having a dimension falling within the range of the visible spectrum might be visible as haze.

It will also be understood that not all domains must necessarily have dimensions that fall within the range of the visible spectrum, but it is only those domains with which the present invention is concerned. In theory, if a sufficient number of domains having dimensions in the visible spectrum are found, then the container will have haze regardless of the number of domains that do not have dimensions falling within the visible spectrum.

Referring to FIGS. 5 and 6, photomicrographs of a transparent article before (preform) and after orientation (container), respectively, show that the domains created in a polyester during formation, and here, orientation, of the article, and containing the incompatible filler, indeed increase in size upon orientation. In the transparent, non-hazy preform, the domains are on the order of about 200 nm or less, well below the visible spectrum. However, in FIG. 6, the stretching process during orientation of the container has increased the size of the domains. As shown, the length dimensions of the domains are well within the visible spectrum.

Also, the domains does not have to cover the entire visible spectrum. The domains\' dimensions may comprise a range that extends into the region of the visible spectrum, i.e., the range of dimensions exceeds 400 nm or starts below 700 nm, or may fall only within a particular range within the region of the visible spectrum, e.g., range from about 450 nm to about 580 nm.

Once the range of dimensions of the filler domains is determined or otherwise found, a light absorbent composition can be found which absorbs light at wavelengths in the region of the visible spectrum that at least substantially covers the range of dimensions of the domains or, stated another way, that provides for X being less than 9.6 in the equation

X=Σ(1−Ai)×(Ni)

where Ai is the percent of light absorbed at a wavelength i and Ni is the number of domains per hundred square microns (108 nm2) at wavelength i, and where i ranges from 400 to 700. However, determining the range of dimensions of the filler domains does not have to be done experimentally or by measurement. All that is required is that it be determined that a substantial number of domains have dimensions falling within the visible spectrum, i.e., from about 400 nm to about 700 nm. This can be as simple as determining that the container or other article has physical haze that is visible to the naked eye. It is believed that if the article has “visual haze,” it necessarily has domains having dimensions falling in the region of the visible spectrum.

The light absorption of the light absorbent composition is often known to those skilled in the art, and may be found or determined by any manner known in the art. One method for determining the light absorption of a light absorbent composition is to analyze the absorption spectra of the composition. Once the region of absorption for that spectrum of the composition is known, that spectrum can be considered in view of the range of dimensions of the filler domains present, and/or can be used to calculate the percent of light available for reflecting at any of a selected wavelength. If the light absorption spectrum at least substantially covers the range of dimensions, or if X is less than 9.6, more preferably less than 9.5, even more preferably less than 9 and most preferably less than 7.5, then the composition can be used in the article. When the article is oriented or stretched, it has been unexpectedly found that the composition in the article absorbs light in a manner that substantially masks the haze of the article.

Turning to the components of the article, the present invention includes a thermoplastic polymer matrix having an incompatible filler dispersed therein. The incompatible filler is preferably present in an amount of about 0.5 to about 50 percent by weight based on the weight of polymer. In one embodiment, a polyester, preferably PET, may comprise from about 99.5 to about 50 percent by weight of the article as the major component and the incompatible filler, preferably MXD-6, may comprise from about 0.5 to about 50 percent by weight of the article as the minor component.

It will be understood that the thermoplastic polymer suitable for use in the present invention can be made into a film or sheet. The present invention is not, however, limited to films and sheets. The article of the present invention also includes containers, bottles, trays, bases, lids, etc. Such article may be manufactured or formed into a desired size and shape using any processing techniques known in the art, including blow molding, injection molding, extrusion, and the like. Articles of the present invention may also include a wall of a larger article. Moreover, the article of the present invention is desirably transparent. By “transparent,” it is meant that one can see through the article, i.e. is not opaque. It will be understood that the transparent article may be colored, but that one can clearly see through at least one wall or sheet of the article.

The major component of the article of the present invention is the thermoplastic polymer matrix. Suitable thermoplastic polymers for use in the present invention include any thermoplastic homopolymer, copolymer, terpolymer, or blend. Examples of thermoplastic polymers include polyamides, such as nylon 6, nylon 66 and nylon 612, linear polyesters, such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene isophthalate, and polyethylene naphthalate, branched polyesters, polystyrenes, polycarbonate, polyvinyl chloride, polyvinylidene dichloride, polyacrylamide, polyacrylonitrile, polyvinyl acetate, polyacrylic acid, polyvinyl methyl ether, ethylene vinyl acetate copolymer, poly(3-phenyl-1-propene), poly(vinylcyclohexane), ethylene methyl acrylate copolymer, and low molecular weight polyolefins having 2 to 20 carbon atoms, such as polyethylene, polypropylene, ethylene-propylene copolymers, poly(1-hexene), poly(4-methyl-1-pentene), poly(1-butene), and poly(3-methyl-1-butene). Preferably, the thermoplastic polymer used in the present invention comprises a polyester polymer or copolymer.

The polyester phase may be any article-forming polyester or copolyester such as a polyester capable of being cast, extruded or molded into an article. The polyesters should have a glass transition temperature between about 50° C. and about 150° C., preferably about 60°-100° C., should preferably be orientable, and have an I.V. of at least 0.55, preferably 0.6 to 1.0 deciliters/gram, as determined by ASTM D-4603-86 at 30° C. in a 60/40 by weight mixture of phenol and tetrachloroethane. Suitable polyesters include those produced from aromatic, aliphatic or cycloaliphatic dicarboxylic acids of from 4 to about 40 carbon atoms and aliphatic or alicyclic glycols having from 2 to about 24 carbon atoms.

Polyesters employed in the present invention can be prepared by conventional polymerization procedures well known in the art. The polyester polymers and copolymers may be prepared, for example, by melt phase polymerization involving the reaction of a diol with a dicarboxylic acid, or its corresponding diester. Various copolymers resulting from use of multiple diols and diacids may also be used. Polymers containing repeating units of only one chemical composition are homopolymers. Polymers with two or more chemically different repeat units in the same macromolecule are termed copolymers. The diversity of the repeat units depends on the number of different types of monomers present in the initial polymerization reaction. In the case of polyesters, copolymers include reacting one or more diols with a diacid or multiple diacids, and are sometimes referred to as terpolymers.

As noted herein above, suitable dicarboxylic acids include those comprising from about 4 to about 40 carbon atoms. Specific dicarboxylic acids include, but are not limited to, terephthalic acid, isophthalic acid, naphthalene 2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4′-dicarboxylic acid, 1,3-phenylenedioxydiacetic acid, 1,2-phenylenedioxydiacetic acid, 1,4-phenylenedioxydiacetic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and the like. Specific esters include, but are not limited to, phthalic esters and naphthalic diesters.

These acids or esters may be reacted with an aliphatic diol preferably having from about 2 to about 24 carbon atoms, a cycloaliphatic diol having from about 7 to about 24 carbon atoms, an aromatic diol having from about 6 to about 24 carbon atoms, or a glycol ether having from 4 to 24 carbon atoms. Suitable diols include, but are not limited to, 1,4-butenediol, trimethylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, resorcinol, and hydroquinone.

Polyfunctional comonomers can also be used, typically in amounts of from about 0.1 to about 3 mole percent. Suitable comonomers include, but are not limited to, trimellitic anhydride, trimethylopropane, pyromellitic dianhydride (PMDA), and pentaerythritol. Polyester-forming polyacids or polyols can also be used. Blends of polyesters and copolyesters may also be useful in the present invention.

One preferred polyester is polyethylene terephthalate (PET) formed from the approximate 1:1 stoichiometric reaction of terephthalic acid, or its ester, with ethylene glycol. Another preferred polyester is polyethylene naphthalate (PEN) formed from the approximate 1:1 to 1:1.6 stoichiometric reaction of naphthalene dicarboxylic acid, or its ester, with ethylene glycol. Yet another preferred polyester is polybutylene terephthalate (PBT). Copolymers of PET, copolymers of PEN, and copolymers of PBT are also preferred. Specific copolymers and terpolymers of interest are PET with combinations of isophthalic acid or its diester, 2,6 naphthalic acid or its diester, and/or cyclohexane dimethanol.

The esterification or polycondensation reaction of the carboxylic acid or ester with glycol typically takes place in the presence of a catalyst. Suitable catalysts include, but are not limited to, antimony oxide, antimony triacetate, antimony ethylene glycolate, organomagnesium, tin oxide, titanium alkoxides, dibutyl tin dilaurate, and germanium oxide. These catalysts may be used in combination with zinc, manganese, or magnesium acetates or benzoates. Catalysts comprising antimony are preferred. Another preferred polyester is polytrimethylene terephthalate (PTT). It can be prepared by, for example, reacting 1,3-propanediol with at least one aromatic diacid or alkyl ester thereof. Preferred diacids and alkyl esters include terephthalic acid (TPA) or dimethyl terephthalate (DMT). Accordingly, the PTT preferably comprises at least about 80 mole percent of either TPA or DMT. Other diols which may be copolymerized in such a polyester include, for example, ethylene glycol, diethylene glycol, 1,4-cyclohexane dimethanol, and 1,4-butanediol. Aromatic and aliphatic acids which may be used simultaneously to make a copolymer include, for example, isophthalic acid and sebacic acid.

Preferred catalysts for preparing PTT include titanium and zirconium compounds. Suitable catalytic titanium compounds include, but are not limited to, titanium alkylates and their derivatives, titanium complex salts, titanium complexes with hydroxycarboxylic acids, titanium dioxide-silicon dioxide-co-precipitates, and hydrated alkaline-containing titanium dioxide. Specific examples include tetra-(2-ethylhexyl)-titanate, tetrastearyl titanate, diisopropoxy-bis(acetyl-acetonato)-titanium, di-n-butoxy-bis(triethanolaminato)-titanium, tributylmonoacetyltitanate, triisopropyl monoacetyltitanate, tetrabenzoic acid titanate, alkali titanium oxalates and malonates, potassium hexafluorotitanate, and titanium complexes with tartaric acid, citric acid or lactic acid. Preferred catalytic titanium compounds are titanium tetrabutylate and titanium tetraisopropylate. The corresponding zirconium compounds may also be used.

The polymer of this invention may also contain small amounts of phosphorous compounds, such as phosphates, and a catalyst such as a cobalt compound, that tends to impart a blue hue. Also, small amounts of other polymers such as polyolefins can be tolerated in the continuous matrix.

The melt phase polymerization described above may be followed by a crystallization step, then a solid phase polymerization (SSP) step to achieve the intrinsic viscosity necessary for the manufacture of certain articles such as bottles. The crystallization and polymerization can be performed in a tumbler dryer reaction in a batch-type system. Alternatively, the crystallization and polymerization can be accomplished in a continuous solid state process whereby the polymer flows from one vessel to another after its predetermined treatment in each vessel. The crystallization conditions preferably include a temperature of from about 100° C. to about 150° C. The solid phase polymerization conditions preferably include a temperature of from about 200° C. to about 232° C., and more preferably from about 215° C. to about 232° C. The solid phase polymerization may be carried out for a time sufficient to raise the intrinsic viscosity to the desired level, which will depend upon the application. For a typical bottle application, the preferred intrinsic viscosity is from about 0.65 to about 1.0 deciliter/gram, as determined by ASTM D-4603-86 at 30° C. in a 60/40 by weight mixture of phenol and tetrachloroethane. The time required to reach this viscosity may range from about 8 to about 21 hours. In one embodiment of the invention, the article-forming polyester of the present invention may comprise recycled polyester or materials derived from recycled polyester, such as polyester monomers, catalysts, and oligomers.

Suitable fillers for the present invention include, but are not necessarily limited to, those polymers, clays, minerals, and other compounds known to be chemically unreactive with the thermoplastic polymer matrix so as to provide discrete domains within the polymer matrix. Typically, such fillers will be provided in order to improve a physical or mechanical property of the polyester for a desired purpose. For example, in many food and beverage packaging applications, reducing gas permeability of the container or bottle in which the food or beverage is stored is often desired. Thus, gas barrier strengthening fillers are added to improve the container\'s ability to prevent oxygen or other gases from passing through the container wall and into the container or bottle, thereby possibly spoiling the food or beverage inside.

The incompatible fillers of the present invention are on the order of from about 10 nanometers to less than about 1 micron in diameter. While there are many larger particles which may increase the gas barrier strengthening properties of the container or bottle, the present invention refers to those particle fillers which create domains having dimensions of from about 10 nanometers up to about 1 micron, and which, more particularly, create domains having dimensions of from about 400 nanometers to about 700 nanometers. Thus, fillers having particle sizes higher or lower than the about 400 to about 700 nanometer range may be employed so long as at least some of the domains created upon orientation fall within that range, even if other domains are created that fall outside of that range.

The most preferred incompatible fillers are polyamides. Suitable polyamides include aliphatic, cycloaliphatic and aromatic polyamides. As noted above, the amount of polyamide to be blended with the polyester is preferably from about 0.5 to about 50 weight percent, more preferably from about 3 to about 15 weight percent. Also preferred incompatible fillers are nanoclays, glass beads, and fibers.

Where a polyamide is employed as the incompatible filler, the polyamide component of the present invention may be represented by repeating unit A-D, where A is the residue of a dicarboxylic acid including adipic acid, isophthalic acid, terephthalic acid, 1,4-cyclohexanedicarboxyolic acid, resorcinol dicarboxylic acid, naphthalene-2,6-dicarboxylic acid or a mixture thereof, and D is the residue of a diamine including m-xylylene diamine, p-xylylene diamine, hexamethylene diamine, ethylene diamine, 1,4-cyclohexanedimethylamine or a mixture thereof. Preferred polyamides that can be used in this invention includes poly(m-xylylene adipamide) or a copolymer thereof, isophthalic or terephthalic acid-modified poly(m-xylylene adipamide), nylon 6, nylon 6,6 or a mixture thereof, poly(hexamethylene isophthalamide), poly(hexamethylene adipamide-co-isophthalamide), poly(hexamethylene adipamide-co-isophthalamide, poly(hexamethylene adipamide-co-terephthalamide) or poly(hexamethylene isophthalamide-co-terephthalamide).

Suitable polyamides may also contain small amounts of trifunctional or tetrafunctional comonomers including trimellitic anhydride, pyromellitic dianhydride or other polyamide forming polyacids and polyamines known in the art.

The I. V. for the polyamides to be blended with the polyester is preferably less than about 1.0 deciliters/gram, and most preferably less than about 0.7 deciliters/gram as determined by ASTM D-4603-86 at 25° C. in a 60/40 by weight mixture of phenol and tetrachloroethane at a concentration of 0.5 g/100 ml (solvent).

The preparation of polyamides and polyester/polyamide blend compositions is well known in the art and any methods for obtaining these compositions may be employed.

In one embodiment of the present invention, the preferred polyamide is poly(m-xylylene adipamide), also often referred to as MXD-6. MXD-6 is preferably used in an amount ranging from about 1 to about 30 percent by weight relative to the polyester resin. Also preferred are other MXDs, wherein all or part of the units derived from adipic acid are replaced by units derived from dicarboxylic acid with 6 to 24 carbon atoms other than adipic acid, such as for example, sebacic, azelaic, and dodecanoic acid, may be employed.

The invention does not require but may include the use or addition of any of a plurality of organic or inorganic materials, such as but not limited to, anti-blocks, anti-stats, plasticizers, stabilizers nucleating agents, etc. These materials may be incorporated into the polymer matrix, into the dispersed minor phase, or may exist as separate dispersed phases.

Mixing or blending of a polyester resin and polyxylylene amide may be carried out in an extruder under known conditions of temperature and shear forces so as to ensure proper mixing and to create a fine, stable dispersion of the polyamide in the polyester matrix. In one embodiment, the polyester and filler of the present invention is generally prepared using a well known technique known as the “shake and bake” method. Typically, polyester, such as PET, and polyamide polymers, as well as the light absorbent composition when it is time, are mixed into a masterbatch, shaken until thoroughly mixed and poured into the hopper to be extruded or molded into preforms as is well known in the art. Shear rates higher than 100 s−1 may be used when melt-mixing polyamide. The melt viscosity ratio of the polyester to the polyxylylene amide, elevated at 280° C. at a shear rate of 100 s−1, is preferably between about 3:1 and 8:1.

Once blended, the blended components may then be made into a desired size and shape of an article. In one embodiment, the component can be blow molded into the shape of a bottle or other container of a particular size. Once molded, a determination that at least some of the filler domains in the article have dimensions in the axial plane of the container of from about 400 nm to about 700 nm can be made. Such a determination may be made simply by determining that the article has haze visible to the naked eye. In one embodiment, where a more precise determination is desired, the minor phase of the thermoplastic polymer filler can be dissolved out of the polyester matrix by using formic acid. Use of cold formic acid, i.e., formic acid at room temperature, is preferred. As the temperature of hot formic acid is above the Tg of polyester, it is possible that the domains could be relaxed or expanded depending upon the location of the domains. Once dissolved, a measurement of the domain dimensions can be taken as may be known in the art. For example, one method of measuring the domain dimensions is to obtain a scanning electron microscope (SEM) photomicrograph of the article and measure the domain using appropriate equipment and techniques such as by using LuciaM (available from Laboratory Imaging, Prague, Czech Republic) software on the photomicrographs realized at 5000×. It will be appreciated that, however, that the dimensions measured may not all be the longest dimensions for any one domain, although theoretically they should be. In one embodiment, measurements were taken of both the preforms and the container in both the radial and axial directions in the axial plane of the container.

Once it is determined that the range of dimensions in the axial plane of the container for the domains created in the polymer matrix after forming the container includes at least some of the dimensions falling within a range of from about 400 nm to about 700 nm, a light absorbent composition can be found that absorbs light in a region of the visible spectrum at wavelengths that at least substantially covers the range of dimensions of the domains in the container. As noted above, this can be done by any means known in the art, including experimentally by adding various compositions to a similarly blown container, experimentally by providing sleeves of colored films over the article, by review of the spectrum of the various light absorbent compositions proposed to be used, or by determining whether X in the equation

X=Σ(1−Ai)×(Ni)

where Ai is the percent of light absorbed at a wavelength i and Ni is the number of domains per hundred square microns (108 nm2) at wavelength i, and where i ranges from 400 nm to 700 nm (i.e., the visible spectrum), is less than 9.6, preferably less than 9.5, more preferably less than 9, and most preferably less than 7.5.

Preferably, these compositions will be colorants commonly used in pigmenting or dying of plastics. Essentially any colorant (either a dye or a pigment) may be employed provided it has a suitable spectrum as required for the present invention. The colorant may or may not be compatible with (i.e., hydrophilic to) the polyamide or other filler employed.

The colorant can be mixed into the polyester/filler matrix or, alternatively, can be made of a separate film overlaying the article showing visible haze. Known multi-layering techniques can be used to adhere the layers together. Generally, however, the light absorbent composition may be in a separate film overlaying a separate layer of the article comprising the polyester/filler matrix.

Thus, in a multilayer container, at least one layer of the multi-layer container may comprise the thermoplastic matrix with the dispersed incompatible filler and another, different layer may comprise the light absorbent composition.

It is also possible that the light absorbent composition can come from the polyester itself. If the range of dimensions for the domains is such that yellowing of the polyester can provide light absorption in a range that substantially covers that range of dimensions of the domains, no additional composition will be necessarily required. Hence, the yellowing component of the polyester itself may serve as the light absorbent composition.

Alternatively, and as noted above, an effective amount of the light absorbent composition may be added to the thermoplastic polymer and the incompatible filler blend in any manner known in the art. Another container may then be made using known container-making techniques such as blow molding. This new transparent container having a polyester matrix with an incompatible filler and a light absorbent composition dispersed therein should then be made into the same desired size and shape. A different size and shape may provide different dimensions to the domains found in the article and could change the range of the dimensions and thus, the light absorbent composition required. It should then be evident that the light absorbent composition can substantially mask the haze in the container.

In order to demonstrate practice of the present invention, a number of preforms were extruded from a blend of polyester, namely polyethylene terephthalate (PET) and about 5 percent by weight polyamide, namely, poly(-xylylene adipamide), commonly known as MXD-6 and available from Mitsubishi Gas Chemical (Harada, M., Plastics Engineering, 1998). The preforms also contained 0.04 percent by weight 1,2,4,5-benzenetetracarboxylic dianhydride, or pyromellitic dianhydride (PMDA). Upon extrusion, a number of bottle preforms were produced having MXD-6 dispersed within a PET matrix. Some of the preforms were then blow molded into bottles, each bottle having essentially an identical shape and a size of 500 ml\'s. Upon construction of the bottles, each was cut in both the vertical transverse plane and the horizontal transverse plane and etched in cold formic acid for about 60 minutes, the samples then were washed with water till neutral pH and then with acetone. Obtained samples were metalized (gold) with Agar Auto sputter Coater under subsequent condition: 20 mA for 20 seconds with argon flow. The longest dimensions of the remaining MXD-6 domains were measured using LuciaM software on the SEM photomicrographs realized at magnification of 5000×. The photomicrographs were obtained from cutting the bottle in the vertical and horizontal transverse planes and observing the longest dimension which necessarily was the dimension parallel to the surface of the article. In FIG. 7, the distribution of the results obtained from the measure of the longest dimension in the vertical transverse plane, i.e., the radial (X) direction based upon the Figures above, is reported.

Obtained data shows that during the blow-molding from preform to bottle, the MXD-6 domains increase in diameter. Generally, an increase of the average dimension from about 160 nm (preform average) to about 500 nm (bottle average) has been found. That is an increase factor of 3:1 in the radial direction. FIGS. 5 (preform) and 6 (oriented bottle) show this phenomena.

Based upon the data, the domains were found to range in length from about 400 nm to about 600 nm, with the greatest number of domains having a dimension of about 500 nm. This is within the visible spectrum. Viewing the visible spectrum, it can be determined that the region at about 500 nm is the green region (green 512 nm). From review of the chromatic circle, it can be seen that the complementary color which absorbs light in this same region is red. Therefore, attempts were made to find a red colorant which would absorb light in the green region corresponding to the range of dimensions of the domains. It will be appreciated that any colorant that absorbs in the region required of the article will suffice and it is not necessary to choose the color complementary to that region for absorption purposes based upon a chromatic circle.

Several spectrum were carried out on different kinds and colors of commercial colorants. In particular, the spectrum focused on the primary colors and the colors near to red or that contained red. Some spectrum were available from prior laboratory experimentation and other spectrum were available from the producers of the colorants. Of the spectrum analysis performed, all of the spectrum were carried out with a Perkin Elmer UV/VS spectrometer Lamda 2, with a scanning rate of 30 nm/minute from 250 nm to 780 nm. FIGS. 8A, 8B and 8C show spectrum for various yellow, red, and blue colorants, respectively. The spectrum are not normalized, as the interest here was to understand whether or not the region of absorption of the color was in the visible spectrum.

The comparison between the measurements performed with the SEM and the absorption spectrum of the primary colors available has led to an explanation why the red color seems to be the best color to cover the haze. At this point, however, one must again understand that the results of the SEM give the manufacturer an idea of what are the MXD-6 domain dimensions, but in this approach, the measurements are only an approximation, since it is essentially impossible to cut the sample in a manner that would provide every domain at its longest diameter. That is, at least some of the domains measured will be slightly smaller than the real diameter, since there is no way to insure that cutting of the bottle will occur in the exact middle of the domains. This issue has been addressed in detail herein above.

After viewing the spectrum, it is clear that, of the choices provided thus far, red appears to be the best candidate for covering haze, with the best choice being RENOL® Red 4 available from ColorMatrix Corp. Transparent red samples containing the red colorant were prepared and wrapped around a known bottle of the identical size and shape previously prepared. The bottle showed visual haze prior to being wrapped. Upon wrapping the bottle, substantial masking of the haze was observed. Other bottles were prepared to include various colorants. Of those, visual analysis showed that bottles including the colorant Tersar Yellow NE 1105131 available from Clariant provided substantial masking of haze at higher concentration (4%, final bottle has an orange coloration). When viewing its spectrum in FIG. 8A, it can be seen that, unlike all of the other yellow colorants with spectrum provided, the spectrum of the Tersar Yellow colorant showed at least some absorption in the region from 500 to 550 nm and even out to about 600 nm. Thus, this colorant was suitable to mask at least some of the haze (or rather the MXD domain) of the bottle. In the same manner, bottles made with about 1 percent RENOL® Blue NE 51050340 available from Clariant also showed some partial masking of the haze. In its spectrum (FIG. 8C), it can be seen that this blue can cover a zone of the MXD-6 domains. In particular, the region starting from 500 nm can be covered. Not all of the region will be masked however, and there was still some visual haze noticeable in the bottle. The same behavior can be found in using the colorant Tersar blue 40642, also available from Clariant (FIG. 8C).

FIGS. 9A, 9B, 9C, and 9D show spectra for various green, orange, purple and pink colorants, respectively. Notably, the spectrum in FIG. 9A shows that adding this particular green colorant will not effectively mask the haze of the bottle. Production of a green colored 500 ml bottle using this green colorant confirmed this, a further demonstration that in the region between 475 and 575 (the spectrum region which is not covered by the absorption of this color) there are a large number of MXD-6 domains with this dimension. It will be understood however, that other green colorants may adequately and effectively mask the haze of the bottle. Not all green colorants absorb at the same wavelengths and in the same amounts, and it is entirely possible (as shown below) that other green colorants may provide adequate masking of the visual haze for various articles including bottles.

Bottles made from Blossom orange colorant available from ColorMatrix Corp. showed very good masking of haze, but not total. In fact, upon viewing the spectrum of this color (FIG. 9B), it is possible to observe an absorption until a wavelength of about 575 nm, not enough to cover all the MXD-6 domains. Again, however, it is possible that other orange colorants may not mask the visual haze as well as this particular orange colorant, or may mask the visual haze even better.

The spectrum (FIG. 9C) of Royal Purple-1 available from ColorMatrix Corp. is seen as one of the best colorants to mask haze of the sample 500 ml bottle, although the other purple colorant, Tersar Violet 40058, available from Clairant, also appears to be suitable. The pink spectrum (FIG. 9D) also substantially masks haze in the 450 to 600 nm region.

It should thus be evident that, given the spectrum and the tests conducted above, it has been demonstrated that there is a correlation between the dimensions of the MXD-6 domains and the absorption wavelengths of various light absorbent compositions. Where the wavelengths of the region of absorption substantially cover the range of dimensions of the MXD-6 domains, substantial masking of the visual haze in the bottle occurs.

Further testing of the present invention included the preparation of additional preforms of the type described herein above (PET+0.04% PMDA+5% MXD-6) and production of additional 500 ml bottles therefrom, as well as the manufacture of other, larger preforms made for the same concentrations of minor components and larger, 1.5 L bottles molded from these larger preforms. Bottles and preforms were then cut in the manner earlier described and again analyzed at magnification of 5000×. This time, the longest direction in both the vertical and horizontal transverse planes were analyzed. It will be appreciated that the longest dimension in the horizontal transverse plane (X-Z plane) will be the same dimension as the radial (X) axis dimension in the axial plane of the article. Similarly, the longest dimension in the vertical transverse plane (Y-Z plane) will be the same dimension as the axial (Y) axis dimension in the axial plane. SEM analysis of the preforms of the 500 ml bottle showed a mean dimension of MXD-6 domains to be around 240 (radial) to about 280 (axial), while the preforms of the 1.5 L bottle showed a mean dimension of the domains to be about 300 in both the radial (X) and axial (Y) direction. In both of these preforms, the dimensions are so low that they are before, not within, the visible spectrum and therefore, no haze is seen.

However, in the oriented bottles, the mean dimension of the MXD-6 domains was about 500 nm and about 540 nm in the radial direction for the 500 cc and 1.5 L bottles, respectively, and about 1000 nm in the axial direction for both bottles. Because of the dimensions in the axial (Y) direction were greater than the visible spectrum, one would not expect to mask any haze or see any haze from that dimension. However, in the radial (X) direction, the dimensions fall within the visible spectrum, and therefore, haze is noted in the bottles.

Further testing included the production of yet another bottle having a different resin formulation and a different amount of MXD-6. In particular, a polymer matrix was made with a polyester (VFR) resin containing 10% IPA added of PET (COBITER® 80 Polyester Resin of COBARR S.p.A.) for a final formulation of 8.6% IPA. To this resin was added 9.3% of MXD-6. A 38 gram preform was extruded from which a 1.5 L bottle was made by blow molding. SEM analysis was then preformed on both the perform and the bottle from cuts providing dimensions in the radial and the axial directions. The results showed a mean dimension of the domains in the preform to be about 330 nm in the radial (X) direction and about 320 nm in the axial (Y) direction. Again, this was well below the visible spectrum.

For the 1.5 L bottle, the mean dimension of the domains was about 620 nm in the radial (X) direction and about 900 nm in the axial (Y) direction. More importantly, it was found that the range of dimensions were from about 490 nm to about 750 nm in the radial direction and from about 660 nm to about 1140 nm in the axial direction. Thus, some of the dimensions in both directions fall within the visible spectrum.

With an aim towards understanding the prior experimental data obtained, some films with different amounts of RENOL® Red-4 colorant from ColorMatrix Corp. were prepared. The experimental data obtained showed an absorbance of this colorant in essentially the same region of the MXD6 domains radial dimension distribution of the 0.5 L bottle. Samples were made of cast films with thickness of about 200 microns on a Bausano double screw extruder with PET (COBITER® 80 Polyester Resin of COBARR S.p.A.) resin adding different amount of RENOL® Red-4 at 0.05%, 0.1%, 0.2%, 0.25%, and 0.5% of weight. The blend was obtained by dry blending the right amount of colorant in 2.5 kg of PET for each test in a steel container under essentially standard conditions of temperature, pressure and screw speed.

The obtained films were then placed on the 0.5 L bottle first, and then on the other bottles, to understand if the colorant is able to mask haze, and in this case, to find the minimum amount of color required. The realized film and each film\'s capability to cover haze are summarized in the Table I below. Since visual haze can be a subjective interpretation of the eye sight of the beholder, the capability of cover haze was analyzed by asking different people to see through the bottle covered by the different cast films with different amount of colorant and report whether they can visualize any haze.

TABLE I TESTING OF INDIVIDUALS FOR PRESENCE OF VISUAL HAZE Substantially Covered Haze? (Agreement of All) Color Concentration 1.5 L, % (RENOL ® Red) 0.5 L, 5% MXD 1.5 L, 5% MXD 9.3% MXD

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