Nanoparticle based inks and methods of making the same

This application claims priority to Provisional Application Ser. No. 60/237,142, filed Oct. 2, 2000, and Ser. No. 60/243,022, filed Oct. 25, 2000, the entirety of which are incorporated herein by reference.

The present invention relates to recording mediums, inks, ink compositions, methods of making recording mediums and inks, nanoparticles and methods of making nanoparticles.

Typically, colorants tend to fade when exposed to electromagnetic radiation such as sunlight or artificial light and the like. It is believed that most of the fading of colorants when exposed to light is due to photodegradation mechanisms. These photodegradation mechanisms include oxidation or reduction of the colorants depending upon the environmental conditions in which the colorant is placed. Fading of colorants also depends upon the substrate upon which they reside.

Product analysis of stable photoproducts and intermediates has revealed several important modes of photodecomposition. These include electron ejection from the colorant, reaction with ground-state or excited singlet state oxygen, bond cleavage to form various products, reduction to form colorless leuco dyes and electron or hydrogen atom abstraction to form radical intermediates.

Various factors such as temperature, humidity, gaseous reactants, including O₂, O₃, SO₂, and NO₂, and water soluble, nonvolatile photodegradation products themselves have been shown to influence fading of colorants. The factors that effect colorant fading appear to exhibit a certain amount of interdependence. It is due to this complex behavior that observations for the fading of a particular colorant on a particular substrate cannot be applied to colorants and substrates in general.

Under conditions of constant temperature it has been observed that an increase in the relative humidity of the atmosphere increases the fading of a colorant for a variety of colorant-substrate systems (e.g., McLaren, K., J. Soc. Dyers Colour, 1956, 72, 527). For example, as the relative humidity of the atmosphere increases, a fiber may swell because the moisture content of the fiber increases. This aids diffusion of gaseous reactants through the substrate structure.

The ability of a light source to cause photochemical change in a colorant is also dependent upon the spectral distribution of the light source, that is, the proportion of radiation of wavelengths most effective in causing a change in the colorant and the quantum yield of colorant degradation as a function of wavelength. On the basis of photochemical principles, it might be expected that light of higher energy (short wavelengths) would be more effective at causing fading than light of lower energy (long wavelengths). Studies have revealed that this is not always the case. Over 100 colorants of different classes were studied and found that generally the most unstable were faded more efficiently by visible light while those of higher lightfastness were degraded mainly by ultraviolet light (McLaren, K., J. Soc. Dyers Colour, 1956, 72, 86).

The influence of a substrate on colorant stability can be extremely important. Colorant fading may be retarded or promoted by chemical groups within the substrate. Such groups can be a ground-state species or excited-state species. The porosity of the substrate is also an important factor in colorant stability. A high porosity can promote fading of a colorant by facilitating penetration of moisture and gaseous reactants into the substrate. A substrate may also act as a protective agent by screening the colorant from light of wavelengths capable of causing degradation.

The purity of the substrate is also an important consideration whenever the photochemistry of dyed technical polymers is considered. For example, technical-grade cotton, viscose rayon, polyethylene, polypropylene, and polyisoprene are known to contain carbonyl group impurities. These impurities absorb light of wavelengths greater than 300 nm, which are present in sunlight, and so, excitation of these impurities may lead to reactive species capable of causing colorant fading (van Beek, H. C. A., Col. Res. Appl., 1983, 8(3), 176).

In addition to fading, colorants tend to bleed when applied to fabrics. Accordingly, a colorant system that exhibits enhanced stability and color fastness when printed or applied to any type of fabric is desired.

What is needed in the art is a colorant system that not only provides increased light fastness and better color stability, but also one which is capable of being printed on fabrics without special treatment or other limitations. In addition, a superior textile printing ink with substrate independent durability performance is needed. There also exists a need for methods and compositions which are capable of stabilizing a wide variety of colorants from the effects of electromagnetic radiation, such as sunlight and artificial light.

The present invention is directed to, among other things, new recording mediums, new inks, ink compositions, nanoparticles, methods of making and using nanoparticles, methods for stabilizing colorants against photodecomposition, and methods for stabilizing colorants against oxidation or reduction. In accordance with the present invention such recording mediums, when applied to substrates, exhibit improved water and detergent resistance. The present invention includes methods for enhancing the substrate independent durability performance of inks and methods to stabilize colorants against fading due to interactions with a substrate, as well as methods for color density control. By employing a nanoparticle template upon which to bind a colorant and/or charged polymer-colorant layer(s), this invention provides new recording mediums and ways to control their stability, durability and color intensity.

In general, the following discussion relates to particles having a diameter less than about 1,000 nanometers. However, the present invention is also directed towards particles having a diameter greater than 1,000 nanometers. The present invention is directed to recording mediums comprising particles or nanoparticles with a colloidal inner core which is used as a particle template surface. One aspect of the present invention is multiple, alternating layers of charged polymer-colorant (or polyelectrolyte-colorant) being assembled on the nanoparticle template core surface. Because these layers are characterized by alternating charges, layer integrity is maintained by a variety of chemical and physical forces, including coulombic forces, van der Waals forces and others. Different colorants may be used in sequential charged polymer-colorant layers to afford unusual or hard-to-obtain colors. Additionally, charged polymer-colorant layers may alternate with layers of charged polymer void of colorant (“void charged polymer” layers), in order to protect the colorant below the void charged polymer layers, to manipulate particle charge, or to alter its surface characteristics. Charged polymer layers may also contain “functional additives” such as UV or visible radiation filter molecules or substances to protect dyes from harmful radiation, leuco dyes or colorless predyes that develop color upon irradiation, or reactive species generators that react to fade colors upon irradiation. A final outside layer, comprised of a protective stratum of transparent charged polymer, may optionally be added to the nanoparticle. When assembled in this fashion, the final charge of this protective outer layer (zeta potential) is employed to enhance the adherence of the dye particle to the fabric surface during printing. Thus, by matching the nanoparticle charge to the opposite charge of the printing substrate or textile coating, strong coulombic attraction can be achieved, in addition to van der Waals and other physical and chemical forces. One aspect of the present invention includes the nanoparticle comprising a silica particle. However, other inorganic nanoparticles as well as organic and organometallic nanoparticles may be employed herein, the selection of which will be apparent to one of ordinary skill in the relevant art.

The present invention is also directed to nanoparticles that contain more than one colorant and optionally contain colorant stabilizers. The nanoparticles may comprise a charged polymer membrane or coating which prevents materials or reactants which might degrade the colorant from interacting with the colorant. The present invention is directed to nanoparticles with a colloidal inner core that is used as a template surface upon which to bind a series of functional layers. The nanoparticles may be incorporated into a variety of liquid mediums to form colorant compositions, including inks in ink jet processes.

The present invention is further directed to a method of stabilizing a colorant by assembling charged polymer layers, including multiple, alternating layers of charged polymer-colorant and colorless charged polymer, on a nanoparticle surface. In one aspect of the present invention, one or more colorant stabilizers are also incorporated in the charged polymer layers, thereby providing multiple levels of colorant protection from photodegradation mechanisms.

The present invention is also directed to recording mediums containing the above-described nanoparticles. The recording mediums may be applied to any substrate to impart a color to the substrate. One aspect of the present invention is that, a colorant composition comprising the nanoparticles described above, a liquid medium and a pre-polymer is coated onto a substrate and subsequently exposed to radiation to fix the nanoparticle to the substrate via the polymerization of the pre-polymer.

Another aspect of the present invention is the above described nanoparticles being present in a polymer coating of a heat transfer product, such as is used for transferring graphic images onto clothing.