Method for treating plastic, leather or rubber substrates

Abstract: There is disclosed a method for treating and protecting a substrate, said method comprising coating the surface of said substrate with a composition comprising a blend of (A) a polydimethylsiloxane polymer having a viscosity at 25°C. of 5 to 100,000 mm 2 /s (cS); and (B) a polyisobutylene oligomer having a number average molecular weight of 200 to 550. The treatment imparts an aesthetically pleasing appearance to the surfaces of plastic, rubber or leather substrates whereby surface gloss is enhanced, but not excessively, as is the case for a prior art all-silicone treating agent.

Description: The present invention relates to a method for treating plastic, leather or rubber substrates with a composition comprising a polyisobutylene (PIB) oligomer and a polydimethylsiloxane (PDMS) fluid. Synthetic leathers based on poly (vinyl chloride) resins (PVC), and polymer alloys thereof, are extensively used in the automotive and furniture markets due to their low cost and durability relative to natural leathers (including resistance to ozone, ultraviolet radiation and burning). Protective treatments have been developed for the purpose of cleaning, preserving, and conditioning the surfaces of these PVC products, as well as those fabricated from various organic rubbers and natural leathers. Specifically, PDMS oils have been used as treating agents for plastics and rubbers. Such treatments impart improved gloss, restore the appearance, and protect the surfaces against grease, dirt, water, UV radiation, thermal degradation and ozone. Thus, US-A 3,956,174 discloses a process for protecting, preserving and renewing surfaces, such as rubber or polymer surfaces. The process comprises applying an emulsion of a polydimethylsiloxane fluid to the surface, allowing the fluid to penetrate the surface for a given time and then reiterating the application at least one more time. Preferred treating emulsions of this patent include a polyol compound, such as diethylene glycol or glycerin. US Patent No. 4,232,869 is directed to a pick up cartridge comprising a cantilever having a stylus and a damper material. The damper material of this reference is formed of an elastomer comprising a polymer blend of a silicone rubber polymer and polyisobutylene. The polyisobutylene has a viscosity average molecular weight between 5,000 and 50,000. JP-A-6155159 relates to compositions for coating automobile doors which form weatherproofed and easily removable films. The coatings comprise oxygen-containing wax, polybutylene having an average molecular weight of between 300 to 30,000, and silicon oil. Unfortunately, treatment with silicone compositions typically also has an undesirable side effect. These materials impart a "greasy" feel to be treated substrate. This greasiness is believed to be due to residual materials which do not penetrate the surface and which subsequently attract dirt or dust. Another problem with silicone formulations is the high gloss imparted to the treated surface. This is especially problematic in automobiles and minivans which have large dashboards and windscreens. Excessive gloss of the treated surfaces can result in hazardous driving conditions due to associated glare. This is especially true during daylight hours when bright sunlight reflects off the treated dashboard, resulting in visual "washout" or temporary "blinding" of the driver. Although the glare issue in critical automotive applications has been addressed by making use of plastic materials having lower gloss or matte finishes, these materials still require some aftermarket care in order to protect the original finish and to restore the appearance of aged components. Contrastingly, a slight enhancement of gloss is desired since this provides an immediate visual indication of the applied treatment for the consumer. Thus, a successful treating composition must have a delicate balance of gloss augmentation. Our invention overcomes the above mentioned disadvantages and provides a treating composition, and a method of treatment therefor, which imparts an aesthetically pleasing appearance to the surfaces of plastic, rubber or leather substrates. The gloss of the treated substrate is enhanced, but not excessively, as is the case for a prior art all-silicone treating agent. Further, substrates treated with the instant compositions have a significantly reduced degree of greasiness relative to those treated with a typical silicone oil. Moreover, the treatment compositions of our invention provide improved protection against various environmental factors, particularly thermal degradation of a plastic (e.g., due to the loss of plasticizer which occurs when an automobile is exposed to direct sunlight). The present invention, therefore, relates to a blend of (A) a polydimethylsiloxane polymer having a viscosity at 25°C. of 5 to 100,000 mm 2 /s (cS); and (B) a polyisobutylene oligomer having a number average molecular weight of 200 to 550, wherein the weight ratio of said polydimethylsiloxane (A) to said polyisobutylene (B) is 99:1 to 30:70. The invention further relates to a method for treating and protecting a substrate selected from plastic, leather and organic (i.e., non-silicone) rubber comprising coating the surface of said substrate with our blend. The polydimethylsiloxane (A) of the invention is a homopolymer or copolymer having a viscosity at 25°C. which is in the range of 5 to 100,000 mm 2 /s (cS) wherein up to 35 mole percent, preferably less than 10 mole percent, of diorganosiloxane units may be copolymerized with the dimethylsiloxane units. When the viscosity is greater than 100,000 mm 2 /s (cS) the penetration of the silicone fluids into the substrate to be protected is poor. When the viscosity is less than about 5 mm 2 /s (cS) the degree of protection provided is inadequate because this component becomes too volatile. Preferably, the viscosity of component (A) is 100 to 1,000 mm 2 /s (cS) at 25°C., most preferably 300 to 400 mm 2 /s (cS). The organic groups of the above mentioned diorganopolysiloxane units are independently selected from alkyl radicals having 1 to 16 carbon atoms, halogenated alkyl radicals having 3 to 6 carbon atoms, aryl radicals such as phenyl, aralkyl radicals, cycloaliphatic radicals or alkylene oxide groups, such as ethylene oxide, propylene oxide or copolymeric combinations thereof. The nature of the terminal groups on the PDMS of component (A) is not critical for the purposes of this invention and these may be inert groups, such as trimethylsiloxy, dimethylphenylsiloxy and diethylphenylsiloxy. They may also be illustrated by groups such as dimethylvinylsiloxy, dimethylhexenylsiloxy, dimethylhydroxysiloxy, dimethylhydrogensiloxy, dimethylalkoxysiloxy, methyldialkoxysiloxy and trialkoxysiloxy, wherein the alkoxy groups are preferably methoxy. Most preferably, component (A) is a polydimethylsiloxane homopolymer having trimethylsiloxy terminal units. Component (A) is well known in the art and is generally available commercially. Component (B) of our invention is a PIB oligomer having a number average molecular weight (MWn) of 200 to 550, preferably 300 to 550, and most preferably from 320 to 450. When the molecular weight is greater than 550, the compositions produce a film which is sticky and tacky and this, in turn, leads to excessive dirt pick-up by the treated substrate. Such oligomers are known in the art and many are available commercially in a variety of molecular weights and end group combinations. The PIB oligomer may have fully saturated end groups or it may have at least one terminal group which contains a functional group such as epoxy, methylpropenyl, halide, alkoxyphenylene, hydroxyl, carboxyl, chlorosilyl, vinyl, succinic anhydride, isocyanato, amino or amido. A preferred PIB oligomer has either two fully saturated end groups or has one epoxy end group and one saturated end group. Again, the specific polymers and oligomers described above can be prepared by methods known in the art. To prepare the compositions of this invention, the above described components are thoroughly mixed such that the weight ratio of (A) to (B) is 99:1 to 30:70. Preferably this ratio is 90:10 to 40:60, and most preferably 75:25 to 50:50. These blends are then applied to the aforementioned substrates according to our method. The compositions of this invention may be applied in the form of an aqueous emulsion, as a solution in an organic or siloxane-based solvent or as a neat blend without further dilution. Application of the neat blend is not preferred since it can result in excessive deposition of the composition. It is, however, a viable technique when the viscosity of the composition is relatively low, such as below 500 mm 2 /s (cS). An excess deposition on the substrate can overcome the benefits of reduced but acceptable gloss, not to mention the obviously undesirable waste of material. Compositions of our invention can also be applied from a solution of the PDMS/PIB blend in a volatile carrier, such as a hydrocarbon having from 6 to 16 carbon atoms in its molecule. The hydrocarbon may be a straight or branched chain compound such as heptane, decane, tetradecane and hexadecane. However, due to the existence of volatile organic compound (VOC) regulations, this is not a preferred delivery system. Alternatively, low molecular weight linear polysiloxanes having a viscosity below 5 mm 2 /s (cS) at 25°C. can be used as a solvent. Illustrative solvents are linear diorganopolysiloxanes having a degree of polymerization (DP) of 2 to 9. Cyclic diorganopolysiloxanes having a viscosity below 10 mm 2 /s (cS) at 25°C. are also suitable. Illustrative are cyclics having a DP of 4 to 6, wherein the organic groups are independently selected from alkyl radicals having 1 to 6 carbon atoms. Specific examples of the above siloxanes include hexamethyldisiloxane, octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane. Mixtures of these siloxanes may also be employed. Preferably, the compositions of this invention are applied from an aqueous emulsion. In this case, the PDMS and PIB fluids are preferably premixed and then emulsified. Alternatively, each fluid can be emulsified independently and the resulting emulsions can then be mixed. These emulsions are prepared with the aid of at least one non-ionic surfactant, and the employment of standard mixing and dispersion techniques. The preferred surfactant is an ethoxylated trimethylnonanol. Chemically, this surfactant is trimethylnonylphenyl poly(ethylene oxide). Other suitable non-ionic surfactants may be selected from modified polyethoxylated alcohols. The non-ionic surfactant can be used in combination with an anionic surfactant, such as a sodium alkylaryl ether sulfate, sodium alkylaryl polyether sulfonate, or a blend of an alkylaryl polyether alcohol with an organic sulfonate. The emulsions preferably contain 1 to 60 percent of the combined weights of components (A) and (B), most preferably 20 weight percent, the remainder being water, surfactant and an additional minor component, described infra. In this connection, commercial silicone aqueous emulsions are available which contain up to 50% silicone. In addition to components (A) and (B), the instant compositions may contain a variety of additives which are not essential or critical to performance, but may be advantageous in some applications. These materials include rust inhibitors, dyes, UV absorbers, antifoam agents and antimicrobial agents. When employed, such additives should comprise no more than 2 parts by weight for each 100 parts by weight of (A) and (B). When the compositions of the invention are to be applied from an aqueous emulsion, the additives are preferably soluble, or dispersible, in water. The method of the present invention comprises coating at least a portion of the surface of a plastic, leather or rubber substrate with the above described composition comprising components (A) and (B). The method of coating (or treating) these substrates may be any of those known in the art. Examples of suitable coating methods include wiping, spraying, pouring, brushing, rolling and dipping. Preferably, the composition is sparingly applied to the substrate and distributed over the surface thereof by rubbing with a cloth, paper towel or rag. Alternatively, the composition may be applied to the cloth, towel or rag and then rubbed over the surface of the substrate. After such an application, any water or solvent used as a carrier for component (A) and (B) is allowed to evaporate to leave a treated substrate. If desired, this treated surface may further be buffed or polished to enhance the appearance of the final finish. The plastic substrates which benefit from treatment with the instant compositions include polymers and copolymers of vinylic monomers, polyurethanes, acrylics and polyolefins, such as polypropylene and polypropylene/EPDM alloys. A preferred utility of our method is the treatment of plasticized PVC films, polymeric alloys based on PVC and PVC-coated fabrics found in automotive and furniture applications. Examples of rubbers which can be treated with our compositions include butyl, urethane and ethylene-propylene diene monomer terpolymers (EPDM). Treatment of rubber automobile tires is a preferred utility in this regard. Both natural and synthetic leathers (e.g., polyurethane leather, Naugahyde™) also benefit from treatment with the instant compositions. The following examples are presented to further illustrate the method and compositions of this invention. All parts and percentages in the examples are on a weight basis and all measurements were obtained at 25°C., unless indicated to the contrary. The following materials were employed in the examples: PDMS A = trimethylsiloxy-terminated polydimethylsiloxane having a viscosity of 350 mm 2 /s (cS). PIB A = Actipol™ E-6, described as an epoxy-terminated polyisobutylene having a number average molecular weight of 365 and a product of the Amoco Chemical Company, Chicago, IL. This oligomer has one terminal group of the structure the other terminal group being of the formula -C(CH 3 ) 3 . PIB B = Polysynlane™, described as a saturated polyisobutylene having a number average molecular weight of 320 and having one terminal group of the formula the other terminal group being of the formula -C(CH 3 ) 3 . It is a product of Polyesther Corporation, Southhampton, NY. PIB C = Indopol™ L-14, described as a vinyl-terminated polyisobutylene having a number average molecular weight of 320 and also a product of the Amoco Chemical Company, Chicago, IL. One terminal group of this oligomer has the vinyl-like structure (2-methylpropenyl)-HC=C(CH 3 ) 2 , the other terminal group having the formula -C(CH 3 ) 3 . PIB D = Actipol™ E-16, similar to PIB A but having a molecular weight of 975. PIB E = Indopol™ H-35, similar to PIB C but having a molecular weight of 660. Example 1 The above described PIB and PDMS fluids were pre-mixed in a disposable beaker, using a spatula, in the proportions shown in Table 1. Separately, trimethylnonylphenyl poly(ethylene oxide) surfactant (Tergitol™ TMN-6; Union Carbide, Danbury, CT) and deionized water were pre-mixed in a stainless steel beaker using a Cowels blade with medium agitation. Proportions of water and surfactant used are also presented in Table 1. The mixture of PIB and PDMS was then added to the surfactant-water mixture under fast agitation and the agitation was continued for approximately two minutes. The mixture was finally run through a microfluidizer until a constant particle size was achieved (at least 4 passes). Formulation PDMS A (g) PIB Used PIB (g) Surfactant (g) Water (g) Control 40.00 -- -- 2.2 157.8 1 18.75 A 6.25 1.1 78.9 2 20.00 A 20.00 2.2 157.8 3 6.25 A 18.75 1.1 78.9 4 18.75 B 6.25 1.1 78.9 5 55.00 B 55.00 6.0 434.0 6 6.25 B 18.75 1.1 78.9 7 18.75 C 6.25 1.1 78.9 8 20.00 C 20.00 2.2 157.8 9 6.25 C 18.75 1.1 78.9 All the emulsions had a non-volatile (NV) polymer content between 20% and about 24%. Example 2 The formulations of Example 1 were used to treat two different automotive vinyl substrates: Substrate A = a foam-expanded poly (vinyl chloride) (PVC); Substrate B = a PVC/ABS alloy, wherein ABS is an acrylonitrile-butadiene-styrene copolymer. Samples of Substrate A, measuring 2 inches by 3 1/2 inches (5.1 cm by 8.9 cm), were weighed and each of these was treated with 230 µl of one of the above described formulations or control. The treatment was applied directly to the substrate with a micropipet and the emulsion was wiped in a circular motion over the entire surface with a 3 x 3 inch (7.6 x 7.6 cm) cotton cloth. The substrate was allowed to air dry for 2 1/2 hours and re-weighed. In the case of Substrate B, 3 x 3 inch (7.6 x 7.6 cm) samples were weighed and treated with 300 µl of the formulations or control, in a similar manner. An objective indication of surface "greasiness" was then obtained by noting the amount of transfer of applied treatment to a paper tissue, as follows. One half of a Kimwipe™ tissue was weighed and placed on top of a treated substrate, whereupon a 100 gram weight having a diameter of approximately 1.75 inches (4.5 cm) was placed on top of the tissue and allowed to remain in contact therewith. After 30 minutes, the weight was removed and the tissue re-weighed. The weight pick-up and degree of improvement over the control was obtained with the aid of the following equations. The results are presented in Table 2. % Wt Pick-up = 100 x (final tissue weight - initial tissue weight) initial tissue weight % Improvement Relative to Control = (% Wt pick-up control - % Wt pick-up sample) % Wt pick-up control If a "% Improvement Relative to Control" of greater than 25% was obtained, it was deemed significant since this is considerably greater than experimental error (4 to 7%). Form. Wt of Trmt Substrate A (g) % Improvement Substrate A Wt of Trmt Substrate B (g) % Improvement Substrate B Control 0.0071 -- 0.0080 -- 1 0.0065 66 0.0076 47 2 0.0073 79 0.0085 58 3 0.0077 89 0.0074 66 4A 0.0060 55 0.0091 58 4B 0.0078 53 0.0083 58 5 0.0066 76 0.0071 61 6 0.0083 100 0.0083 66 7 0.0075 55 0.0083 53 8 0.0068 66 0.0085 66 9 0.0084 100 0.0083 66 All of the formulations of the invention imparted a significant "% Improvement Relative to Control", this being an indication of substantivity to the respective substrate. (COMPARATIVE) EXAMPLE 1 The procedure of Example 1 was followed using Formulations 10 through 12, as described in Table 3a. Formulation PDMS A (g) PIB PIB (g) Surfactant (g) Water (g) 10 -- D 165.00 9.0 651.0 11 -- E 165.00 9.0 651.0 12 18.75 E 6.25 1.1 98.9 These formulations had a non-volatile polymer content of 20% and were used to treat Substrate B, as described above. The visual evaluation of these samples, summarized in Table 3b, indicated that PIB having a number average molecular weight greater than 550 is not suitable for treating such substrates. Formulation Wt of Treatment Observation 10 0.0095 g Sticky, tacky to touch. 11 0.0090 g Sticky; streaked appearance. 12 0.0087 g Sticky. Example 3 Substrate A and Substrate B were again treated according to the procedures of Example 2. In each case, the sample was weighed before treatment and again after drying in ambient air. The 85 degree gloss (per ASTM D523) was recorded using a portable micro TRI gloss meter (BYK Gardner Inc., Silver Spring, Maryland). At least five readings were taken over the surface of the substrate and these were averaged. The treated substrates were then heat aged in an oven at 120°C. After three weeks the treated substrates were allowed to cool to room temperature, re-weighed, and the 85 degree gloss was again measured. Tables 4a and 4b show the % gloss retention after heat aging for each formulation and the control. Table 5 shows the % improvement of weight change of each substrate after heat aging relative to the control, wherein the following equations were utilized: % Gloss Retention = 100 x (Final Gloss)/(Initial Gloss) % Wt Change = 100 x (final weight - initial weight) initial weight of substrate % Improvement Relative to Control = 100 x % Wt Change control - % Wt Change sample % Wt Change control (Substrate A) Formulation Initial Gloss (%) Final Gloss (%) Wt. of Trmt. (g) % Gloss Retention Control 6.7 4.1 0.0081 61 1 5.6 3.4 0.0079 61 2 4.9 3.6 0.0072 73 3 3.8 3.3 0.0075 87 4A 4.1 3.1 0.0075 76 4B 3.9 2.7 0.0088 69 5 3.5 3.0 0.0086 86 6 3.6 2.5 0.0084 69 7 5.3 3.4 0.0082 64 8 4.7 3.2 0.0075 68 9 3.5 2.5 0.0079 71 Untreated (A) 2.6 -- -- -- (Substrate B) Formulation Initial Gloss (%) Final Gloss (%) Wt. of Trmt. (g) % Gloss Retention Control 9.3 6.8 0.0089 73 1 9.0 7.4 0.0069 82 2 8.6 6.8 0.0074 79 3 8.4 6.2 0.0082 74 4A 8.2 7.0 0.0072 85 4B 7.9 6.3 0.0086 80 5 8.3 6.6 0.0070 80 6 8.7 5.9 0.0076 68 7 9.1 7.5 0.0080 82 8 8.6 6.8 0.0076 79 9 8.4 5.8 0.0079 69 Untreated (B) 3.3 -- -- -- Formulation % Improvement (Substrate A) % Improvement (Substrate B) Control -- -- 1 43 41 2 47 27 3 -25 10 4A 48 34 4B 46 29 5 52 28 6 -99 1 7 55 32 8 45 15 9 61 2 A value of % Improvement in Table 5 of greater than 25% is considered significant and highly desirable with respect to thermal stability of the treatment. Thus, preferred formulations wherein the ratio of PDMS to PIB was at least 1:1, and preferably 3:1, show enhanced stability. These formulations are not readily volatilized at elevated temperatures and therefore provide better thermal protection than an all silicone treatment or blend having a PDMS to PIB ratio of less than 1:1. (COMPARATIVE) Example 2 The procedure of Example 3 was followed using Formulations 13 and 14, as described in Table 6a. Formulation PDMS A (g) PIB PIB (g) Surfactant (g) Water (g) 13 -- A 165.00 9.0 651.0 14 -- C 165.00 9.0 651.0 These formulations had a non-volatile content of 20% and were used to treat Substrate B, as described above. The evaluation of these samples, summarized in Table 6b, indicated that these low molecular weight PIB components alone do not produce any change in the glossiness of the substrate. Formulation Wt of Treatment 85° Gloss (Initial) 13 0.0085 g 3.5 14 0.0090 g 3.4 Untreated -- 3.3

Claims: A composition comprising a blend of (A) a polydimethylsiloxane polymer having a viscosity at 25°C. of 5 to 100,000 mm 2 /s (cS); and (B) a polyisobutylene oligomer having a number average molecular weight of 200 to 550, wherein the weight ratio of said polydimethylsiloxane (A) to said polyisobutylene (B) is 99:1 to 30:70. A method for treating a substrate, said method comprising coating the surface of said substrate with the composition of claim 1. The method according to claim 2 wherein said substrate is selected from leather, organic rubbersor a plastics material. The method according to claim 3 wherein said substrate is a plastics material and is selected from a polymer or copolymer of vinyl chloride. The method according to claim 2 wherein one end group of said polyisobutylene is a saturated group and the other end group is selected from a saturated group or an epoxy group. The method according to claim 2 wherein said blend is diluted with a solvent before said coating step. The method according to claim 2 wherein said blend is dispersed in water to form an emulsion before said coating step. The method according to claim 2 wherein said polydimethylsiloxane has a viscosity of 100 to 1,000 mm 2 /s (cS) at 25°C. and said polyisobutylene (B) has a number average molecular weight of 300 to 550. The method according to claim 8 wherein the weight ratio of polydimethylsiloxane (A) to polyisobutylene (B) is 40:60 to 90:10.

Inventors: GENTLE THOMAS MATTHEW, HAUENSTEIN DALE EARL, KENNAN LINDA DENISE, POPA PAUL JOSEPH, GENTLE, THOMAS MATTHEW, HAUENSTEIN, DALE EARL, KENNAN, LINDA DENISE, POPA, PAUL JOSEPH
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1995
Main classification: C08L83
IPC codes: C14C11, C08L23, C09K3, C09D123, C08J7, C09D183, C08L83