Patent Publication Number: US-2013244017-A1

Title: Plastisol for spray-molded plastic articles

Description:
CLAIM OF PRIORITY 
     This application claims priority from U.S. Provisional Patent Application Ser. No. 61/419,290 bearing Attorney Docket Number 12010008 and filed on Dec. 3, 2010, which is incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a plastisol for making spray-molded polyvinyl chloride plastic articles, particularly suited for use in lower temperature conditions as an alternative to a slush molding using plastisol dry blend powders. 
     BACKGROUND OF THE INVENTION 
     U.S. Patent Application Publication 20040054085 (Tansey) describes a problem in the art of making instrument panel coverstocks that are designed to tear at specific locations in order to permit release of airbags from their compartments. Low temperatures can embrittle PVC or PVC alloys used as such coverstock for instrument panels, creating the possibility of fragments of coverstock causing injury to passengers during deployment of an airbag. 
     Tansey attempts to solve the embrittlement problem by dispersing a melt processible partially crosslinked rubber into a PVC matrix. However, the dispersion of a partially crosslinked rubber into a polymer does not assist the overall thermoplastic nature of the alloy. Indeed, a crosslinked elastomer, i.e., a rubber can inhibit melt processibility of the alloy during the formation of the final form of the thermoplastic product. Also, a rubber can reduce the cold temperature performance of the alloy and elevate the melt viscocity of the polymer. 
     U.S. Patent Application Publication US 20090239984 (Horton et al.) describes a thermoplastic alloy comprising poly(vinyl halide) and an olefin-based uncrosslinked elastomer having thermoplastic properties. The alloy could be made into a polymeric skin using slush molding techniques. 
     Others use a dry blend of PVC particles in slush molding to make plastic articles such as instrument panels. These dry blends can not use higher molecular weight resins and higher levels of plasticizers, which assist in low temperature air bag deployment through instrument panel polymer skins, because the resulting dry blend powder is not properly flowable for pouring that powder into a slush mold and melting the powder at a reasonable temperature. Therefore, the dry blend must be used without the higher molecular weight resins and higher levels of plasticizer. 
     As explained in U.S. Pat. No. 6,129,175 (Tutor et al.), slush-molding is a process where one end of the mold is open. The plastisol is poured into the open end of the mold, and the mold is then cooled from the outside in using cold water. Satisfactory gelation properties are very important in slush molding. 
     SUMMARY OF THE INVENTION 
     The present invention solves the problem by finding a suitable plastisol for making slush molded plastic articles with good low temperature performance properties. 
     One aspect of the present invention is a spray molded plastic article comprising plastisol liquid fused into a solid after being sprayed in a thin layer on to a surface of a female form mold, wherein the plastisol comprises poly(vinyl halide), a trimellitate plasticizer, and a second plasticizer, wherein the trimellitate plasticizer comprises between about 60 and about 90 weight percent of total plasticizer in the article. 
     For purposes of this invention, “thin” means from about 0.04 to about 0.30 and preferably from about 0.06 to about 0.20 cm. For purposes of this invention, a “female form mold” can be a slush mold, or any other open cavity mold. 
     One advantage of the invention is that the plastisol can be processed to form a polymeric skin by spray application of the plastisol onto a female form mold cavity. 
    
    
     EMBODIMENTS OF THE INVENTION 
     Poly(Vinyl Halide) 
     Polyvinyl halides are polymers containing a vinyl moiety and one or more halides bonded thereto. Commercially accepted polyvinyl halides are poly(vinyl chloride) (“PVC”) and chlorinated poly(vinyl chloride) (“CPVC”) due to availability and cost. 
     PVC is essentially a homopolymer of vinyl chloride with minor amounts of other co-monomers, if any. 
     Poly(vinyl chloride) comprises polymerized vinyl chloride monomer where preferred polymers are essentially homopolymerized vinyl chloride with little or no copolymerized co-monomers. Useful co-monomers if desired include mono-unsaturated ethylenically unsaturated monomer copolymerizable with vinyl chloride monomer by addition polymerization. Useful co-monomers include other vinyl monomers such as vinyl acetate, ethers, and vinylidene chloride. Other useful co-monomers comprise mono-ethylenically unsaturated monomers including acrylics such as lower alkyl acrylates or methacrylates, acrylic and methacrylic acid, lower alkenyl olefins, vinyl aromatics such as styrene and styrene derivatives, and vinyl esters and ethers. Typical useful commercial co-monomers include acrylonitrile, 2-ethylhexyl acrylate, vinylidene chloride, and isobutyl ether. Useful PVC copolymers can contain from about 0.1% to about 10% or 15%, preferably from about 0.5% to about 5%, by weight of copolymerized co-monomer. 
     Preferred PVCs are suspension polymerized vinyl chloride although less preferred mass (bulk) polymerized can be useful. 
     The PVCs of this invention have a K-value from about 50 to about 90 and preferably from about 60 to about 85, as measured by using 0.2 grams of resin in 100 ml of cyclohexanone at 30° C. by ASTM D 1243. 
     Plasticizer 
     The poly(vinyl halide) used in the present invention needs to be flexible. Plasticizers are added to poly(vinyl halide) to form flexible thermoplastic polymers. 
     Plasticizers which perform at lower temperatures, between about −25° C. and about −55° C., are needed for use in the invention because plastic articles such as polymer skins used as instrument panel coverings need to perform at such temperatures in order for air bag deployment to perform properly as a required safety feature in passenger vehicles. 
     Trimellitate plasticizers are capable of performance at temperatures ranging from about −10° C. to about −30° C. and preferably from about −10° C. to about −25° C. Non-limiting examples of trimellitate plasticizers include trimethyl trimellitate (TMTM), Tri-(2-ethylhexyl) trimellitate (TEHTM-HG or TOTM), Tri-(n-octyl, n-decyl) trimellitate (ATM), Tri-(heptyl,nonyl) trimellitate (LTM), and n-octyl trimellitate (NOTM). Of these plasticizers, NOTM is preferred because of the combination of its low temperature performance and plasticizer absorption during dryblend processing. 
     PolyOne Corporation of Avon Lake, Ohio is a manufacturer of Synplast™ trimellitate plasticizers and offers for sale the following grades which qualify as low temperature performing plasticizers: Synplast NOTM and Synplast 810TM. 
     A second plasticizer is needed in the plastisols of the present invention. Plasticizers which perform at the lower temperatures identified above are useful to supplement the trimellitate plasticizer described above because they provide additional low temperature performance to meet cold deployment requirements. 
     Non-limiting examples of the second plasticizer are a straight chain dibasic acid ester plasticizer (such as dioctyl adipate, or dioctyl sebacate) Dioctyl Azelate (DOZ), Diisodecyl adipate (DIDA), Diisononyl sebacate (DINS), and Diisodecyl sebacate (DIDS). 
     Commercially available plasticizers are Plasthall DIDS from Hallstar, and Synplast DIDA, Synplast DOS, Synplast DOA from PolyOne, among others. 
     The amount of trimellitate plasticizer to total plasticizer content is significant to the present invention. Via experimentation with trimellitate and sebacate plasticizers, it has been determined that too little trimellitate plasticizer in the plastisol compound permits exudation, probably sebacate plasticizer. However too much trimellitate plasticizer reduces physical property performance at low temperatures such as −30° C. Table 1 below identifies acceptable, desirable, and preferred ranges of the percentage of trimellitate plasticizer to total plasticizer content in the plastisol compound. 
     Optional Additives 
     The compound of the present invention can include conventional plastics additives suitable for plastisols in an amount that is sufficient to obtain a desired processing or performance property for the compound. The amount should not be wasteful of the additive nor detrimental to the processing or performance of the compound. Those skilled in the art of thermoplastics compounding, without undue experimentation but with reference to such treatises as  Plastics Additives Database  (2004) from Plastics Design Library (www.williamandrew.com), can select from many different types of additives for inclusion into the compounds of the present invention. 
     Non-limiting examples of optional additives include adhesion promoters; biocides (antibacterials, fungicides, and mildewcides), anti-fogging agents; anti-static agents; bonding, blowing and foaming agents; dispersants; fillers and extenders; fire and flame retardants and smoke suppressants; impact modifiers; initiators; lubricants; micas; pigments, colorants and dyes; plasticizers; processing aids; release agents; silanes, titanates and zirconates; slip and anti-blocking agents; stabilizers; stearates; ultraviolet light absorbers; viscosity regulators; waxes; and combinations of them. 
     Table 1 shows acceptable, desirable, and preferred ingredients for the plastisols of the present invention. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Ingredient (Weight 
                   
                   
                   
               
               
                 Percents) 
                 Acceptable 
                 Desirable 
                 Preferred 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Low Fog PVC Resin 
                 42-52 
                 45-49 
                 46.93 
               
               
                 Low Fog Barium-Zinc 
                 0-5 
                 3-4 
                 3.75 
               
               
                 Stabilizer 
               
               
                 Amine Scavenger 
                 0-1 
                 0.5 
                 0.47 
               
               
                 Low Temp Trimellitate 
                 22-37 
                 25-35 
                 30.03 
               
               
                 Plasticizer 
               
               
                 Polyol 
                 0-3 
                 1-3 
                 1.88 
               
               
                 Mold Release 
               
               
                 Low Temp Sebacate 
                  5-20 
                  7-12 
                 9.85 
               
               
                 Plasticizer 
               
               
                 UV Stabilizer 
                 0-3 
                 1-3 
                 2.35 
               
               
                 Epoxidized Soybean Oil 
                  0-10 
                 3-6 
                 4.69 
               
               
                 Heat Stabilizer 
               
               
                 Fumed Silica Thickener 
                 0.0.1 
                   0-0.1 
                 0.05 
               
               
                 Percentage of 
                 62-88 
                 67-83 
                 75.3 
               
               
                 Trimellitate Plasticizer to 
               
               
                 Total Plasticizer 
               
               
                   
               
            
           
         
       
     
     Processing 
     The preparation of compounds of the present invention is uncomplicated. The compound of the present can be made in a batch operation. 
     Mixing in a batch process typically occurs in a low shear mixer with a prop-type blade operating at a temperature below 37° C. to avoid plastisol gelation. The mixing speeds range from 60 to 1000 rpm. The output from the mixer is a liquid dispersion ready for later spraying on a mold to form a plastic article. 
     The plastisol is a thick or viscous liquid, flowable for use in later molding operations. 
     Subsequent molding techniques are well known to those skilled in the art of thermoplastics polymer engineering. Without undue experimentation but with such references as “Handbook of Molded Part Shrinkage and Warpage”; “Specialized Molding Techniques”; and “Rotational Molding Technology”, all published by Plastics Design Library (www.williamandrew.com), one can make articles of any conceivable shape and appearance using plastisols of the present invention. 
     After mixing to form the plastisol, preferably, female form molds such as slush molds can be used to form useful plastic articles. Slush molding utilizes an open-end mold design for forming articles (e.g., vehicle instrument panels) as a polymeric skin. One skilled in the art can understand the principles of slush molding by referring to U.S. Pat. No. 6,797,222 (Hausmann et al.) and U.S. Pat. No. 2,736,925; U.S. Pat. No. 3,039,146; European Patent Publication 0 339 222, European Patent Publication 0 476 742 and PCT Patent Publication WO 0207946, in addition to those documents identified above in the Background section. 
     Briefly, traditional slush molding generally involves the following steps: a) an open-air tank is first filled with a suitable polymer powder in a sufficient quantity and with grain sizes typically below 500 micrometers; b) a mold, usually electroplated with nickel, is then heated to a given temperature; c) the tank and the mold are then coupled in a closed system with suitable coupling means; d) the system is moved so that the tank transfers the powder onto the mold, thus obtaining a uniform layer of partially or completely melted powder which adheres to the mold; e) the closed system is then opened after being brought to the initial conditions again; at this stage the possible excess polymer powder deposits again into the tank and can thus be regenerated; f) the mold can now be heated in order to complete the melting; g) the mold is then cooled with suitable cooling means; and h) the formed sheet is stripped off as a semi-finished product which can then be assembled with a support in order to obtain the finished product in the form of instrument panels, door panels, etc. for the upholstery of cars. 
     The plastisols of the present invention are particularly suitable to spray the plastisol onto a slush mold surface, otherwise used with slush molding plastisol powders, using an airless spray equipment system. This ability to spray a liquid, as opposed to dispersing a powder into a slush mold, can minimize the “runs” and “drips” which sometimes appear in a plastisol molded plastic article made using the slush process. The spray application also allows for selective skin thickness levels on the part, which allows for lower part weight on non-deployable areas. This is difficult to obtain with a powder. 
     Therefore, while a slush mold can be used, the molding of a polymeric skin using plastisol of the present invention can significantly reduce the traditional processing steps for slush molding. A preferred method of molding comprises the steps of (a) spraying a surface of a female form mold cavity, preferably a cold nickel slush mold cavity, with plastisol to obtain a layer of plastisol which adheres to the surface of the mold; (b) heating a mold to a temperature of about 160° C. to about 230° C. to gel and fuse the plastisol to form a polymeric skin on the mold; (c) cooling the mold with suitable cooling means; and (d) removing the formed polymeric skin from the mold. Not only is the final polymeric skin product improved but the processing to make the polymeric skin is rendered less complicated. 
     USEFULNESS OF THE INVENTION 
     Plastisols of the present invention are particularly suitable for use in the spraying of thin polymeric film products as an alternative to slush molding for simulated leather, simulated cloth, and other goods used in residential and vehicular upholstery which exhibit improved low temperature and mechanical properties. For example, a “polymeric skin” can be formed using slush molding from plastisols of the present invention. This polymeric skin has a very large aspect ratio of length or width to thickness and can mimic the shape of the mold to create random or repeating patterns of the appearance of grain in leather, wood, or other naturally-occurring items. 
     EXAMPLES 
     Table 2 identifies the ingredients used in the Examples. Table 3 identifies the formulations. Table 4 identifies the processing conditions. Table 5 shows the results of performance testing. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Ingredient 
                 Brand 
                 Maker 
               
               
                   
               
             
            
               
                 Low Fog PVC Resin 
                 Geon 129 × 115 
                 PolyOne (Avon Lake, OH) 
               
               
                 Low Fog Barium- 
                 Mark 6708ACM 
                 Crompton (Cleveland, OH) 
               
               
                 Zinc Stabilizer 
               
               
                 Amine Scavenger 
                 Amfine CPS-55R 
                 Amfine Corp., Allendale, NJ 
               
               
                 Low Temp 
                 Synplast NOTM 
                 PolyOne 
               
               
                 Trimellitate 
               
               
                 Plasticizer 
               
               
                 Polyol 
                 Poly-G 2028 
                 Arch Chemical (Norwalk, CT) 
               
               
                 Mold Release 
               
               
                 Low Temp Sebacate 
                 Plasthall DIDS 
                 Hallstar (Bedford Park, IL) 
               
               
                 Plasticizer 
               
               
                 UV Stabilizer 
                 Uvinol Cyano DP 
                 BASF (Charlotte, NC) 
               
               
                   
                 Acrylate 3039 
               
               
                 Epoxidized Soybean 
                 Plas-Chek 775 
                 Ferro Corp. 
               
               
                 Oil Heat Stabilizer 
               
               
                 Fumed Silica 
                 Aerosil 200 
                 Evonik Industries 
               
               
                 Thickener 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Ingredient 
                 Comp. 
                 Comp. 
                   
                 Comp. 
                 Comp. 
                   
               
               
                 (PHR) 
                 Ex. A 
                 Ex. B 
                 Ex. 1 
                 Ex. C 
                 Ex. D 
                 Control 
               
               
                   
               
             
            
               
                 Geon 
                 100 
                 100 
                 100 
                 100 
                 100 
                 PolyOne 
               
               
                 129 × 115 
                   
                   
                   
                   
                   
                 PVC 
               
               
                   
                   
                   
                   
                   
                   
                 Powder - 
               
               
                   
                   
                   
                   
                   
                   
                 VBX3600 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Ingredient 
                 Comp. 
                 Comp. 
                   
                 Comp. 
                 Comp. 
                   
               
               
                 (PHR) 
                 Ex. A 
                 Ex. B 
                 Ex. 1 
                 Ex. C 
                 Ex. D 
                 Control 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ferro 6708 
                 8 
                 8 
                 8 
                 8 
                 8 
                   
               
               
                 CPS-55RD 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 Synplast 
                 85 
                 0 
                 64 
                 42.5 
                 21 
               
               
                 NOTM 
               
               
                 Poly-G 2028 
                 4 
                 4 
                 4 
                 4 
                 4 
               
               
                 DIDS 
                 0 
                 85 
                 21 
                 42.5 
                 64 
               
               
                 Uvinol 3039 
                 5 
                 5 
                 5 
                 5 
                 5 
               
               
                 Plas-Chek 775 
                 10 
                 10 
                 10 
                 10 
                 10 
               
               
                 Aerosil 200 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
               
               
                 Percent of 
                 100% 
                 0% 
                 75.3% 
                 50% 
                 24.7% 
                 N/A 
               
               
                 Trimellitate 
               
               
                 Plasticizer to 
               
               
                 Total 
               
               
                 Plasticizer 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Processing 
                 Comparative Examples A-D and 
                   
               
               
                 Condition 
                 Example 1 
                 Control 
               
               
                   
               
             
            
               
                 Mixing 
                 Low Shear Mixer 
                 Henschel Mixer 
               
               
                 Equipment 
               
               
                 Mixing Temp. 
                 Below 37° C. 
                 130° C. 
               
               
                 Mixing Speed 
                 &gt;500 rpm 
                 600 rpm 
               
               
                 Order of 
                 50 phr of Synplast NOTM initially, 
                 N/a 
               
               
                 Addition of 
                 then all dry ingredients, and then 
               
               
                 Ingredients 
                 once dispersed, add remaining liquid 
               
               
                   
                 components 
               
               
                 Form of 
                 Thick liquid 
                 Powder 
               
               
                 Product After 
               
               
                 Mixing 
               
               
                   
               
            
           
         
       
     
     Each of the Comparative Examples A-D and Example 1 were then tested by molding into a square skin shape having dimensions of 19.05 cm×19.05 cm×0.127 cm (7.5 inch×7.5 inch by 0.050 inch thick having a mass of 50 grams) processed in a oven heat cycle of 204° C. (400° F.) for 12 minutes with the plastisol poured into a cold mold. 
     The Dry Blend Powder Control was processed using an oven heat cycle, first preheating the 30.48 cm×30.48 cm (12 inch by 12 inch) nickel mold for 10 minutes at 327° C. (620° F.). The mold was removed and the powder was poured onto the mold when the surface temperature reached 230° C. Excess powder was removed after 10 seconds and the backside was post cured at 327° C. (620° F.) for 30 seconds. The part was quenched in a 23° C. water bath for 10 seconds. The finished part had dimensions of 30.48 cm×30.48 cm×0.127 cm (12 inch by 12 inch by 0.05 inches). 
     The molded parts were then tested using the standardized methods described in Table 5. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 Performance 
                 Comp. 
                 Comp. 
                   
                 Comp. 
                 Comp. 
                   
               
               
                 Test 
                 Ex. A 
                 Ex. B 
                 Ex. 1 
                 Ex. C 
                 Ex. D 
                 Control 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 SAE J1756 
                 71 
                 52 
                 76 
                 86 
                 68 
                 85 
               
               
                 100° C. heat, 
               
               
                 23° C. cool 1 
               
               
                 hour read 
               
               
                 SAE J1756 
                 90 
                 87 
                 93 
                 95 
                 90 
                 99 
               
               
                 100° C. heat, 
               
               
                 23° C. cool 
               
               
                 16 hour read 
               
               
                 Dynamic 
                 −42.6 
                 −69.8 
                 −50.4 
                 −56.8 
                 −62.9 
                 −49.7 
               
               
                 Mechanical 
               
               
                 Analysis 
               
               
                 Tg E″ max 
               
               
                 (° C.) 
               
               
                 Dynamic 
                 −25.9 
                 −48.7 
                 −32.7 
                 −37.7 
                 −43.4 
                 −27.0 
               
               
                 Mechanical 
               
               
                 Analysis Tg 
               
               
                 Tan δ max 
               
               
                 (° C.) 
               
               
                 ASTM D638 
                 260 
                 215 
                 294 
                 301 
                 279 
                 138 
               
               
                 @ −30° C. 
               
               
                 Elongation 
               
               
                 (%) 
               
               
                 ASTM D638 
                 2560 
                 2090 
                 2670 
                 2570 
                 2090 
                 2900 
               
               
                 @ −30° C. 
               
               
                 Tensile (psi) 
               
               
                 Exudation of 
                 None 
                 Heavy 
                 None 
                 Slight 
                 Heavy 
                 N/A 
               
               
                 Plasticizer 
               
               
                 Percent of 
                 100% 
                 0% 
                 75.3% 
                 50% 
                 24.7% 
                 N/A 
               
               
                 Trimellitate 
               
               
                 Plasticizer to 
               
               
                 Total 
               
               
                 Plasticizer 
               
               
                   
               
            
           
         
       
     
     The results of Table 5 show that trimellitate plasticizer is required for use in the present invention (Comparative Example B) and must be present in an amount greater than 50% by weight of total plasticizer in order to avoid exudation (Comparative Examples C and D). However, using only trimellitate plasticizer does not result in sufficient results comparable to the control for dynamic mechanical analysis Tg, elongation, and tensile properties (Comparative Example A). Therefore, Example 1 with trimellitate plasticizer comprising about 75% by weight of the total plasticizer present in the plastisol not only avoids exudation but also has physical properties at low temperature meeting or exceeding the physical properties of a dry blend control. 
     The invention is not limited to the above embodiments. The claims follow.