hydrofluoropropene blowing agents for thermoplastics   

The present invention relates to blowing agent compositions comprising at least one hydrochlorofluoroolefin (HCFO) used in the preparation of foamable thermoplastic compositions. The HCFOs of the present invention include, but are not limited to, 1-chloro-3,3,3-trifluoropropene (HCFO-1233zd), particularly the trans-isomer, 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf), dichloro-fluorinated propenes, and mixtures thereof. The blowing agent compositions of the present invention are preferably used with coblowing agents including carbon dioxide, atmospheric gases, hydrofluorocarbons (HFC), hydrofluoroolefins (HFO), alkanes, hydrofluoroethers (HFE), and mixtures thereof. Preferred HFCs used as coblowing agents in the present invention include, but are not limited too, 1,1,1,2-tetrafluoroethane (HFC-134a); 1,1-difluoroethane (HFC-152a); 1,1,1-trifluoroethane (HFC-143a); pentafluorethane (HFC-125); and difluoromethane (HFC-32). The blowing agent compositions are useful in the production of low density insulating foams with improved k-factor.

With the continued concern over global climate change there is an increasing need to develop technologies to replace those with high ozone depletion potential (ODP) and high global warming potential (GWP). Though hydrofluorocarbons (HFC), being non-ozone depleting compounds, have been identified as alternative blowing agents to chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) in the production of thermoplastic foams, they still tend to have significant GWP.

It was discovered that blowing agent compositions comprising a hydrochlorofluorolefin, particularly HCFO-1233zd, HCFO-1233xf, dichloro-fluorinated propenes, and mixtures thereof can permit the production of lower density, closed-cell foam and good k-factor which will be particularly useful for thermal insulating foams. This invention may also permit the production of low density, closed-cell foams with enlarged, controlled cell size.

WO 2004/037913, WO 2007/002703, and US Pat. Publication 2004119047 disclose blowing agents comprising halogenated alkenes of generic formula that would include numerous HCFOs, among many other materials including brominated and iodinated compounds and HFOs. Specific HCFOs for use in thermoplastic foaming are not disclosed nor are the benefits of using the HCFOs in terms of increasing the foam cell size as discovered in the present invention. HCFO-1233zd is disclosed for use in polyurethane foaming, however it is not obvious to one skilled in the art that a blowing agent for polyurethane foaming would be particularly good for thermoplastic foaming.

GB 950,876 discloses a process for the production of polyurethane foams. It discloses that any suitable halogenated saturated or unsaturated hydrocarbon having a boiling point below 150° C., preferably below 50° C., can be used as the blowing agent. Trichlorofluoroethene, chlorotrifluoroethene, and 1,1-dichloro-2,2-difluoroethene are disclosed in a list of suitable blowing agents. Hydrochlorofluoropropenes are not specifically disclosed nor are longer chain HCFOs. There is no disclosure related to blowing agents for thermoplastic foaming nor are the benefits of HCFOs in thermoplastic foaming mentioned nor preferred combinations of HCFOs with other coblowing agents.

CA 2016328 discloses a process for preparing closed-cell, polyisocyanate foam. Disclosed are organic compound blowing agents including halogenated alkanes and alkenes, where the alkene is propylene, and the halogenated hydrocarbons can be chlorofluorocarbons. Among the many exemplary compounds listed are specific chlorofluoroethylenes containing 1 chlorine and from 1 to 3 fluorines. Hydrochlorofluoropropenes are not specifically disclosed nor are longer chain HCFOs. There is no disclosure related to blowing agents for thermoplastic foaming nor are the benefits of HCFOs in thermoplastic foaming mentioned nor preferred combinations of HCFOs with other coblowing agents.

The present invention relates to the use of blowing agents with negligible ozone-depletion and low GWP comprising a hydrochlorofluoroolefin (HCFO) used with an additional blowing agent. The present invention discloses blowing agent and foamable resin compositions useful for the production of foams with decreased density, enlarged cell size, and improved k-factor that can be used as insulating foams. In a preferred embodiment of this invention the HCFO is 1-chloro-3,3,3-trilfluoropropene (HCFO-1233zd), preferably the trans isomer; 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf), and mixtures thereof. Preferred coblowing agents to be used with the HCFO include hydrofluorocarbons (HFC), preferably 1,1,1,2-tetrafluoroethane; 1,1-difluoroethane (HFC-152a); pentafluoroethane (HFC-125); 1,1,1-trifluoroethane (HFC-143a); difluoromethane (HFC-32); hydrofluoroolefins (HFO), preferably 3,3,3-trifluoropropene (HFO-1243zf); 1,3,3,3-tetrafluoropropene (HFO-1234ze), particularly the trans isomer; 2,3,3,3-tetrafluoropropene (HFO-1234yf); (cis and/or trans)-1,2,3,3,3-pentafluoropropene (HFO-1225ye); carbon dioxide; alkanes, preferably a butane or a pentane, and mixtures thereof.

Another embodiment of this invention are foamable resin compositions containing greater than about 1 parts per hundred (pph) and less than about 100 pph of the blowing agent composition with respect to resin, preferably greater than about 2 pph and less than about 40 pph, more preferably greater than about 3 pph and less than about 25 pph, and even more preferably greater than about 4 pph and less than about 15 pph of the blowing agent composition with respect to resin.

The process for preparing a foamed thermoplastic product is as follows: Prepare a foamable polymer composition by blending together components comprising foamable polymer composition in any order. Typically, prepare a foamable polymer composition by plasticizing a polymer resin and then blending in components of a blowing agent composition at an initial pressure. A common process of plasticizing a polymer resin is heat plasticization, which involves heating a polymer resin enough to soften it sufficiently to blend in a blowing agent composition. Generally, heat plasticization involves heating a thermoplastic polymer resin near or above its glass transition temperature (Tg), or melt temperature (Tm) for crystalline polymers.

A foamable polymer composition can contain additional additives such as nucleating agents, cell-controlling agents, dyes, pigments, fillers, antioxidants, extrusion aids, stabilizing agents, antistatic agents, fire retardants, IR attenuating agents and thermally insulating additives. Nucleating agents can include, among others, materials such as talc, calcium carbonate, sodium benzoate, and chemical blowing agents such azodicarbonamide or sodium bicarbonate and citric acid. IR attenuating agents and thermally insulating additives can include carbon black, graphite, silicon dioxide, metal flake or powder, among others. Flame retardants can include, among others, brominated materials such as hexabromocyclodecane and polybrominated biphenyl ether.

Foam preparation processes of the present invention include batch, semi-batch, and continuous processes. Batch processes involve preparation of at least one portion of the foamable polymer composition in a storable state and then using that portion of foamable polymer composition at some future point in time to prepare a foam.

A semi-batch process involves preparing at least a portion of a foamable polymer composition and intermittently expanding that foamable polymer composition into a foam all in a single process. For example, U.S. Pat. No. 4,323,528, incorporated herein by reference, discloses a process for making polyolefin foams via an accumulating extrusion process. The process comprises: 1) mixing a thermoplastic material and a blowing agent composition to form a foamable polymer composition; 2) extruding the foamable polymer composition into a holding zone maintained at a temperature and pressure which does not allow the foamable polymer composition to foam; the holding zone has a die defining an orifice opening into a zone of lower pressure at which the foamable polymer composition foams and an openable gate closing the die orifice; 3) periodically opening the gate while substantially concurrently applying mechanical pressure by means of a movable ram on the foamable polymer composition to eject it from the holding zone through the die orifice into the zone of lower pressure, and 4) allowing the ejected foamable polymer composition to expand to form the foam.

A continuous process involves forming a foamable polymer composition and then expanding that foamable polymer composition in a non-stop manner. For example, prepare a foamable polymer composition in an extruder by heating a polymer resin to form a molten resin, blending into the molten resin a blowing agent composition at an initial pressure to form a foamable polymer composition, and then extruding that foamable polymer composition through a die into a zone at a foaming pressure and allowing the foamable polymer composition to expand into a foam. Desirably, cool the foamable polymer composition after addition of the blowing agent and prior to extruding through the die in order to optimize foam properties. Cool the foamable polymer composition, for example, with heat exchangers.

Foams of the present invention can be of any form imaginable including sheet, plank, rod, tube, beads, or any combination thereof. Included in the present invention are laminate foams that comprise multiple distinguishable longitudinal foam members that are bound to one another.

Examples 1-7

The solubility and diffusivity of gases in polystyrene resin was measured using capillary column inverse gas chromatography (cc-IGC) as described in: Hadj Romdhane, Ilyess (1994) “Polymer-Solvent Diffusion and Equilibrium Parameters by Inverse Gas-Liquid Chromatography” PhD Dissertation, Dept. of Chem. Eng., Penn State University. and Hong S U, Albouy A, Duda J L (1999) “Measurement and Prediction of Blowing Agent Solubility in Polystyrene at Supercritical Conditions” Cell Polym 18 (5):301-313.

A 15 m long, 0.53 mm diameter GC capillary-column was prepared with a 3 micron thick polystyrene internal film coating. The column was installed into a Hewlet Packard 5890 Series II Gas Chromatograph with flame ionizer detector. Elution profiles for gases being tested were analyzed according the method outlined in the reference, using methane as the reference gas. The results give the diffusion coefficient of the gas through the polymer, Dp, and the solubility of the gas in the polymer in terms of the partition coefficient, K, which is the ratio of the concentration of the gas in the polymer phase to the concentration in the vapor phase. As such, the greater the value of K for a particular gas in the resin the greater its solubility in that resin.

Table 1 shows the partition coefficient and diffusivity values for several gases in polystyrene at 140° C. Comparative examples 1-5 show the solubility and diffusivity of HCFC-142b (1-chloro-1,1-difluoroethane), HFC-152a (1,1-difluoroethane), HFC-134a (1,1,1,2-tetrafluoroethane), HFC-32 (difluoromethane), and HFC-245fa (1,1,1,3,3-pentafluoropropane) in polystyrene (PS). Examples 6 and show the solubility and diffusivity of trans-HCFO-1233zd (1-chloro-3,3,3-trifluoropropene) and HCFO-1233xf (2-chloro-3,3,3-trifluoropropene).

These examples show that HCFO-1233zd and HCFO-1233xf have sufficient solubility and diffusivity in polystyrene resin to be effective blowing agents or as useful coblowing agents with other blowing agents such as HFCs or carbon dioxide. HCFO-1233xf, for instance, was found to have a solubility comparable to that of HCFC-142b. The diffusivities of HCFO-1233zd and HCFO-1233xf were found to be low, indicating that should be useful in providing foams with improved k-factor.

TABLE 1 Partition Coefficient and Diffusivity of Gases in Polystyrene at 140° C. by Inverse Gas Chromatography Bp Mw Dp Example Gas (° C.) (g/mol) K (cm²/s) 1 HCFC-142b −9.8 100.5 1.249 2.61E−08 2 HFC-152a −24.1 66.05 0.734 9.49E−08 3 HFC-134a −26.1 102.02 0.397 3.40E−08 4 HFC-32 −51.7 52.02 0.436 1.95E−07 5 HFC-245fa 15.1 134.05 0.639 2.05E−08 6 HCFO-1233zd 20.5 130.5 2.326 1.72E−08 7 HCFO-1233xf 15 130.5 1.475 1.67E−08

Extruded polystyrene foam was produced using a counter-rotating twin screw extruder with internal barrel diameters or 27 mm and a barrel length of 40 diameters. The screw design was suitable for foaming applications. The pressure in the extruder barrel was controlled with the gear pump and was set high enough such that the blowing agent dissolved in the extruder. The extruder die for examples 9-20 was an adjustable-lip slot die with a gap width of 6.35 mm. For example 1, the die was a 2 mm diameter strand die with a 1 mm land length. Two grades of general purpose polystyrene were used for the extrusion trials and fed to the extruder at rates of either 2.27 or 4.54 kg/hr (5 or 10 lb/hr). Blowing agents were pumped into the polystyrene resin melt at a controlled rate using high pressure delivery pumps. In the extruder, the blowing agent is mixed and dissolved in the resin melt to produce an expandable resin composition. The expandable resin composition is cooled to an appropriate foaming temperature and then extruded from the die where the drop in pressure initiates foaming. Talc was used as a nucleating agent and was pre-blended with polystyrene to make a masterbatch of 50 wt % talc in polystyrene. Beads of this masterbatch were mixed with polystyrene pellets to achieve 0.5 wt % talc in each experiment.

The density, open cell content, and cell size was measured for foam samples collected during each run. Density was measured according to ASTM D792, open cell content was measured using gas pychnometry according to ASTM D285-C, and cell size was measured by averaging the cell diameters from scanning electron microscope (SEM) micrographs of foam sample fracture surfaces. SEM images are also used to observe the cell structure and qualitatively check for open cell content.

Table 2 shows data for examples 8 through 20, including the loading of each blowing agent in the formulation, the resin feed rate, melt flow index of the resin, the expandable resin melt temperature, and the density, cell size, and open cell content of the resulting foamed product.

Comparative example 8 is typical for polystyrene foaming with HFC-134a, where the poor solubility and difficulties in processing tend to lead to higher density foam with smaller size and more open cells. Increasing the amount of HFC-134a in the formulation above the solubility limit, around 6.5 wt % 134a for this system, was found to lead to many problems including blow holes, defects, foam collapse, large voids, high open cell content, and others.

Comparative examples 9 and 10 show results for foaming with 3,3,3-trifluoropene (HFO-1243zf; TFP).

In examples 11 and 12, blowing agent compositions of TFP (HFO-1243zf) and HCFO-1233zd permitted production of lower density foam than achievable with TFP alone along with a beneficial enlargement in the cell size, where it was possible to produce closed-cell foam product with cell sizes greater than 0.2 mm at densities less than 53 kg/m³ and even less than 45 kg/m³. These foams would be useful as thermal insulating foams with improved k-factor.

Examples 13 through 16 were produced during the same extrusion trial. In examples 13, HFC-134a was used as the only blowing agent at a loading of 5.3 wt %. The foamed product had significant defects including blowholes and large voids. During foam extrusion there was frequent popping at the die caused by undissolved blowing agent exiting the die. Following example 13, HCFO-1233zd, predominantly the trans isomer, was added to produce example 14, which resulted in reduction of the popping at the die with a reduction in the die pressure along with reducing the number of defects in the foamed product. Then the blowing agent feeds were adjusted to generate examples 15 and 16, where there was no popping at the die and only a few defects. The foam of example 13, blown using only HFC-134a, had a very broad or bimodal cell size distribution, with cell sizes ranging from around 0.05 mm to around 1 mm, with the larger cells near the center of the sample. The foams blown with combinations of 134a and HCFO-1233zd also had non-uniform cell size distributions, with the larger cells near the core of the samples, but with much narrower distributions without the very large cells. HCFO-1233zd improved the processing of the 134a blown foams, improved the general quality of the foamed product, and permitted production of lower density foam.

Examples 17 and 18 were produced during using HFO-1234yf (2,3,3,3-tetrafluoroethane) as the only blowing agent. At a loading of 5.7 wt % 1234yf, as shown in example 18, the foamed product had very small cell size, macrovoids, blowholes, high open cell content, and frequent periods of popping at the die caused by undissolved blowing agent. Increasing the content of 1234yf made these problems worse. For examples 19 and 20, blowing agent compositions of HFO-1234yf and HCFO-1233zd permitted production of lower density foam than was produced using the HFO-1234yf alone. The foamed samples of examples 19 and 20 were of good quality, with few defects and produced without popping at the die. The HCFO-1233zd was predominantly the trans-isomer.

TABLE 2 Blowing Agent Loading Polystyrene Resin Foam Properties 134a TFP 1234yf 1233zd Feed MFI T Density Cell Size OCC Example (wt %) (wt %) (wt %) (wt %) (kg/hr) (g/10 min) (° C.) (kg/m³) (mm) (%) 8 6.4 — — — 2.27 4.0 111 60.9 0.06 23 9 — 6.6 — — 2.27 11.0 114 57.6 0.11 <5 10 — 7.2 — — 2.27 11.0 115 56.5 0.11 <5 11 — 4.1 — 6.6 4.54 11.0 113 44.3 0.29 <5 12 — 6.5 — 3.4 4.54 11.0 113 52.5 0.35 <5 13 5.3 — — — 4.54 11.0 118 76.5 defects ~10 14 5.0 — — 5.0 4.54 11.0 116 49.9 0.05. 0.20 ~10 15 4.4 — — 4.3 4.54 11.0 116 48.0 0.08. 0.25 ~10 16 4.4 — — 5.0 4.54 11.0 116 45.6 0.09. 0.16 ~10 17 4.4 — 4.54 11.0 117 90.9 0.15 5 15 — — 5.7 — 4.54 11.0 115 71.6 0.06 31.4 19 — — 4.2 4.3 4.54 11.0 114 55.2 0.12 <5 20 — — 4.9 5.0 4.54 11.0 113 53.5 0.08 <5 indicates data missing or illegible when filed

Although the invention is illustrated and described herein with reference to specific embodiments, it is not intended that the appended claims be limited to the details shown. Rather, it is expected that various modifications may be made in these details by those skilled in the art, which modifications may still be within the spirit and scope of the claimed subject matter and it is intended that these claims be construed accordingly.