Silicone rubber composition for treatment of fiber structures

Abstract: The silicone rubber compositions of the present invention for treatment of fiber structures are cured by a condensation reaction and are thus free from drawbacks of addition reaction curing type. The compositions contain mercaptoalkyl group-containing di-or trialkoxysilanes and aliphatic monohydroxy alcohols. As a result, even when inorganic filler content is increased in dispersion, viscosity stability was excellent, and high-strength films are readily obtained. Condensation reaction-curable silicone rubbers for treatment of fiber structure are provided which have excellent abrasion resistance and a pot life above 8 hours.

Description: The present invention concerns silicone rubber compositions for treatment of fiber structures, such as woven fabric, knit fabric, nonwoven fabric, etc. More specifically, the present invention relates to silicone rubber compositions for treatment of fiber structures, having long pot life and imparting films of excellent tensile strength, tear strength, and abrasion resistance. Fiber structures, such as woven fabrics, knit fabrics and nonwoven fabrics, treated (especially coated) with conventional silicone rubbers are soft with excellent water- repellency, water-pressure resistance and also high moisture permeability. Thus they have been widely used in diaper covers, snow wear, mountain wear, sports wear, raincoats, tents, etc. The silicone rubbers used for coating fiber structures are, e.g., addition reaction-curable silicone rubbers (Japanese Kokai Patents Nos. Sho 58(1983)-171937, Sho 60(1985)-51754 and Sho 57(1982)-165069) and condensation reaction-curable silicone rubber (Japanese Kokai Patent No. Sho 53(1978)-94693). However, the silicone rubbers have some strong points and also some weak points, and both long pot life and desirable physical properties cannot be obtained at the same time. For example, addition reaction-curable silicone rubbers form films with good tensile strength, tear strength, abrasion resistance, etc., while their adhesion to fiber structure is weak, and curing may be adversely affected by small amounts of surfactants and other impurities of phosphorus, nitrogen, sulfur compounds adhered to the fiber during processing of fibers or fabrics. On the other hand, the condensation reaction-curable silicone rubbers show good adhesion to the fiber structure, while tensile strength, tear strength and abrasion resistance are not sufficient. In the case of condensation reaction-curable silicone rubbers based on hydroxy-terminated organopolysiloxanes and organohydrogenpolysiloxanes, such drawbacks may be overcome by compounding inorganic reinforcing fillers such as finely powdered silica; while with increasing silica content, pot life decreases, and gelation occurs within 30 minutes, thus coating workability is poor. It is an object of the present invention to overcome the above-noted problems and provide condensation reaction- curable silicone rubbers for treatment of fiber structure, having excellent abrasion resistance and a pot life above 8 hours. Such objectives can be attained by a silicone rubber composition for treatment of fiber structures comprising: (A) 100 parts by weight of an essentially linear organopolysiloxane represented by the formula HO(R₂SiO) n H, wherein R is a substituted or unsubstituted monovalent hydrocarbon group and the subscript n is a number of 50 - 10 000, (B) 0-50 parts by weight of an alkenyl group-terminated organopolysiloxane, (C) 3-100 parts by weight of an inorganic filler, (D) 0.1-20 parts by weight of an organohydrogenpolysiloxane of units of general formula R a H b SiO (4-a-b)/2 , wherein R is a substituted or unsubstituted monovalent hydrocarbon group, a is 1 - 3, b is 0,5 - 1, containing at least 3 hydrogen atoms bonded to different silicon atoms, (E) 0.1-20 parts by weight of a di- or trialkoxysilane containing a mercaptoalkyl group, (F) 0.1-30 parts by weight of an aliphatic monohydroxy alcohol, (G) 0.1-20 parts by weight of a curing catalyst, and (H) an appropriate amount of solvent. The organopolysiloxane used for the component A is the main component of the coating materials of the present invention and is essentially a linear polysiloxane represented by the general formula HO(R₂SiO) n H wherein R is a substituted or unsubstituted monovalent hydrocarbon group and the subscript n is a number in the 50-10,000 range. R represents an alkyl group such as methyl, ethyl, propyl, butyl, octyl, etc.; an alkenyl group such as vinyl, allyl, etc.; an aryl group such as phenyl, tolyl, etc.; a substituted alkyl group such as 3,3,3-trifluoropropyl, 3- chloropropyl, etc. While n is in the range of 50-10,000, those values of n above 1,000, known as organopolysiloxane rubbers, are preferred. Essentially linear means that unless there are some adverse effects, branched, cyclic and three-dimensional structures may be present. All R groups may be same or different; however, it is preferred that a majority of the R be alkyl, most preferably methyl. Organopolysiloxane A may be a homopolymer, a copolymer, or mixtures of two or more polymers. The alkenyl group-terminated organopolysiloxane of component B is not an essential component; however, it enhances the elongation of the film when cured together with the component A. A vinyl group is especially preferred for alkenyl group. Other organic groups include those given for R above. As with component A, the degree of polymerization is preferably above 50, more preferably above 1,000, namely, organopolysiloxane rubber. Based on 100 parts by weight of component A, the amount of component B added is 0-50 parts by weight, preferably 5-30 parts by weight. The inorganic fillers used as component C are needed for enhancing tensile strength, tear strength and abrasion resistance of cured film. While fumed silica is preferred, dry-process silica, wet-process silica, finely powdered quartz, titanium dioxide, calcium carbonate, kieselguhr, carbon black, etc., can be also be used. They may be use as mixtures of two or more, and they may be surface-treated with silanes, silazanes, low-molecular-weight polysiloxanes, organic compounds, etc. Based on 100 parts by weight of component A, the amount of component C added is 3-100 parts by weight, preferably 5-50 parts by weight. The organopolysiloxane used as component D in the present invention is the crosslinking agent for component A and is linear, branched, or cyclic organohydrogenpolysiloxane of units of general formula R a H b SiO (4-a-b)/2 wherein R is substituted or unsubstituted monovalent hydrocarbon group as defined above; a is 1-3; b is 0.5-1, containing at least 3 hydrogen atoms bonded to different silicon atoms. Preferred are linear, branched and cyclic methylhydrogenpolysiloxanes, dimethyl-co-methylhydrogenpolysiloxanes, methylphenyl-co-methylhydrogen polysiloxanes, etc., with a degree of polymerization 4-50. Based on 100 parts by weight of component A, the amount of component D used is 0.1-20 parts by weight, preferably 0.5-10 parts by weight. The mercaptoalkyl group-containing di- or trialkoxysilane used as component E in the present invention is needed for pot life extension and can be represented by the general formula HS(CH₂) d Si(R) e (OR¹) 3-e wherein R is a substituted or unsubstituted monovalent hydrocarbon group as given above; R¹ is an alkyl group of 1-5 carbon atoms; d is 2-6; e is 0 or 1. Preferably, d is 3, and R or R¹ is an alkyl group of 1-3 carbon atoms. Specific examples include HS(CH₂)₃Si(CH₃)(OCH₃)₂, HS(CH₂)₃Si(CH₃)(OC₂H₅)₂, HS(CH₂)₃Si(CH₃)(OC₃H₇)₂, HS(CH₂)₃Si(OCH₃)₃, HS(CH₂)₃Si(OC₂H₅)₃, HS(CH₂)₃Si(OC₃H₇)₃, HS(CH₂)₅Si(OCH₃)₃, HS(CH₂)₃Si(CH₃)(OC₄H₉)₂, etc. Based on 100 parts by weight of component A, the amount of component E used is 0.1-20 parts by weight, preferably 0.5-10 parts by weight. The aliphatic monohydroxy alcohol used as component F is also a pot life-extending component used with component E; aliphatic monohydroxy alcohols of 1-5 carbon atoms are preferred. Especially, for component F, monohydroxy alcohols of 1-3 carbon atoms are preferred because they are readily evaporated upon heating without leaving any residues on fibers or any odor. Ethyl alcohol is most preferred. Based on 100 parts by weight of component A, the amount of component F used is 0.1-30 parts by weight, preferably 0.5-20 parts by weight. The curing catalyst used for component G is a condensation reaction catalyst and promotes reaction between component A (also component B if present) and component D. The condensation reaction catalysts are organometallic catalysts and amine catalysts. Organometallic catalysts are metal salts of organic acids, e.g., dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin dioctoate, zinc naphthenate, tin octylate, cobalt octylate, diisooctyltin dioctylate, zirconium naphthenate, zirconium octylate, tetrabutyl orthotitanate, etc. Amine catalysts are, e.g., di- and triethanolamine. Based on 100 parts by weight of component A, the amount of component G used is 0.1-20 parts by weight, preferably 0.5-10 parts by weight. The solvents used as component H in the present invention are used in making the compositions of the present invention into dispersions for easy application on fiber structure, e.g., aromatic hydrocarbon solvents such as toluene, xylene, benzene, etc.; chlorine-containing solvents such as carbon tetrachloride, trichloroethylene, 1,1,1- trichloroethane, tetrachloroethylene, etc.; aliphatic hydrocarbon solvents such as hexane, heptane, etc. Among them, aromatic solvents and chlorine solvents are preferred. While the amount of component H used varies as needed for ease of coating application, it is usually 50-2,000 parts by weight, preferably 100-1,000 parts by weight based on 100 parts by weight of component A. In the present invention, beside components A-H, various additives may be added, such as various silane couplers for enhanced adhesion, hydroxy-terminated low-molecular-weight organopolysiloxanes as plasticizers, triorganosilyl group-terminated silicone oils for imparting lubricity and softness to the film, pigments, dyes, antimildew agents, etc. The fiber structures are woven, knit, nonwoven fabrics, etc., of natural fibers such as cotton, jute, wool, silk, etc., regenerated fibers such as rayon, semisynthetics such as acetate, etc., synthetic fibers such as nylons, polyesters, acrylics, vinyl chloride, polyethylene, polypropylene, Spandex, etc., and their blends. The mode of application on fiber structures is not restricted in any particular way, while in a preferred process, films are formed by gravure or knife coating on the fiber structure and cured by heat. If desired, a silicone rubber composition of the present invention is coated on a Teflon sheet, etc., adhered to a fiber structure and heat- cured for adhesion of the silicone rubber to the fiber structure. Depending on the applications, immersion or spray method may be used. After solvents are evaporated, the treated fiber structures are heated at 100-200°C for 1-5 min to form a silicone rubber film on the fiber structure, with good toughness and moisture permeability. The fiber structure treated with the silicone rubber compositions of the present invention have good toughness and moisture permeability, thus are useful for diaper covers, snow wear, mountain wear, sports wear, raincoat, tent, etc. Next, the present invention is explained with examples. In the examples, parts and % are by weight. Application Examples 1 & 2 In a kneader mixer, 100 parts of hydroxy-terminated dimethylpolysiloxane of molecular weight about 520,000, 9 parts of hydroxy-terminated dimethylpolysiloxane plasticizer with degree of polymerization 10, and 30 parts of fumed silica (Aerosil 300, product of Nippon Aerosil Co.) of specific surface area 300 m²/g were kneaded sufficiently and heated at 180°C for 4 h to give a rubber base (I). Using a stirrer 100 parts of this rubber base (I) were compounded with 3.2 parts of trimethylsilyl-terminated methylhydrogenpolysiloxane with degree of polymerization about 50 and 246.8 parts of toluene to give dispersion (I). This dispersion was rapidly stir-mixed with 1.0 part of HS(CH₂)₃Si(CH₃)(OCH₃)₂, 1.5 parts of methyl alcohol or 1.5 parts of isopropyl alcohol, 1.0 part of dibutyltin di(2-ethylhexoate) catalyst, and 25 parts of toluene for viscosity control. Then changes in viscosity with elapse of time was measured using a single cylinder rotating viscometer, Bisumetoron VG-A (product of Seiki Industrial Co., Ltd.). After 10 h, the dispersion was coated on a polytetrafluoroethylene (Teflon) film using a 100-µm applicator, and the ease of coating application was examined. Next, most of toluene was removed by blowing hot air, and a nylon taffeta was spread on the coating. Then, the silicone rubber was cured by heating in a hot-air circulation oven at 150°C for 5 min. The assembly was then cooled to room temperature, and the Teflon film was peeled from the silicone rubber-coated nylon taffeta. The silicone coating film was examined. For comparison, the experiment was repeated without methyl alcohol or HS(CH₂)₃Si(CH₃)(OCH₃)₂ or both. In all cases, gelation occurred quickly, while the composition of the present invention, using both methyl alcohol and HS(CH₂)₃Si(CH₃)(OCH₃)₂ showed stable viscosity even after 10 h with good coating workability, giving coated films free from voids. The results are given in Table I. Composition, parts Application Example Comparative Example 1 2 1 2 3 Dispersion 100 100 100 100 100 HS(CH₂)₃SiMe(OMe)₂ 1.0 1.0 - - 1.0 Methanol 1.5 - - 1.5 - Isopropanol - 1.5 - - - Properties Change of Viscosity (cP) with time 0 Hours 8200 8400 9200 8700 9050 0.5 Hours 8100 8200 gel gel 8800 1 Hours 8100 8200 - - 9000 2 Hours 8050 8200 - - 15000 3 Hours 8350 8300 - - gel 5 Hours 8350 8350 - - - 8 Hours 8350 8300 - - - 10 Hours 8400 8350 - - - State of Coating after 10 Hours good good poor poor poor Surface State of film good good - - - Application Examples 3-6 The dispersion (I) used in Application Example 1 was treated with 1.5 parts of ethyl alcohol and various amounts of HS(CH₂)₃Si(CH₃)(OCH₃)₂. Then changes in viscosity with time was measured as in Application Example 1 with observation of states of coating and film. For comparison, the process was repeated using 1.5 parts of ethyl alcohol, but without HS(CH₂)₃Si(CH₃)(OCH₃)₂. The results are given in Table II. The composition with only ethyl alcohol was found to be gelled after 30 min, while the compositions treated with both ethyl alcohol and HS(CH₂)₃Si(CH₃)(OCH₃)₂ showed stable viscosity even after 10 hours with good coatability and state of film. Composition, parts Application Example Comparative Example 3 4 5 6 4 Dispersion 100 100 100 100 100 HS(CH₂)₃SiMe(OMe)₂ .25 .50 1.0 2.0 - Ethanol 1.5 1.5 1.5 1.5 1.5 Properties Change of Viscosity (cP) with time 0 Hours 9200 9050 8400 7800 9250 0.5 Hours 9200 8750 8350 7800 gel 1 Hours 9350 8750 8350 7500 - 2 Hours 9400 8750 8500 7500 - 3 Hours 9500 8700 8400 7500 - 5 Hours 9500 8700 8350 7500 - 8 Hours 9450 8650 8350 7700 - 10 Hours 9550 8750 8500 7600 - State of Coating after 10 hours good good good good poor Surface State of film good good good good - Application Examples 7-10 Rubber base (II) was prepared under the conditions of Application Example 1, except that 90 parts of the hydroxy- terminated dimethylpolysiloxane with molecular weight 520,000 used in Application Example 1 and 10 parts of vinyl group- terminated dimethylpolysiloxane of molecular weight 55000 were used. Dispersion (II) was prepared under the same conditions of Application Example 1 from 100 parts of the rubber base (II). Then, 100 parts of dispersion (II) was treated with 1 part of dibutyltin diacetate catalyst and 25 parts of toluene as viscosity control agent. As shown in Table III, the mixture was stirred with 2 parts of HS(CH₂)₃Si(CH₃)(OCH₃)₂, 0.5, 2.5, or 5.0 parts of ethyl alcohol. Similar to Application Example 1, the change in viscosity with time was measured and coating films were prepared. An experiment was also carried out using 2.0 parts of HS(CH₂)₃Si(OCH₃)₃ and 1.0 part of ethyl alcohol. A comparative example was made using 2.0 parts of HS(CH₂)₃Si(OCH₃)₃ without ethyl alcohol. The results are given in Table III. Compared with the comparative example, the examples of the present invention showed stable viscosity even after 24 h with good state of films. Composition, parts Application Example Comparative Example 7 8 9 10 5 Dispersion (II) 100 100 100 100 100 HS(CH₂)₃SiMe(OMe)₂ 2.0 2.0 2.0 - - HS(CH₂)₃Si(OMe)₃ - - - 2.0 2.0 Ethanol 0.5 2.5 5.0 1.0 - Properties Change of Viscosity (cP) with time 0 Hours 8450 7400 6800 7880 8350 1 Hours 8450 7400 6800 7880 8660 2 Hours 8650 7300 6800 7750 12350 5 Hours 8350 7300 6950 7820 gel 10 Hours 8600 7650 6800 7950 - 24 Hours 8950 7850 7450 7980 - State of Coating after 24 hours good good good good poor Surface State of film good good good good - Application Examples 11-14 Rubber bases (III), (IV), (V), and (VI) were prepared from 90 parts of dimethyl polysiloxane having hydroxyl groups at the ends of molecular chains with molecular weight of about 520,000 used in Application Example 3, 10 parts of dimethyl polysiloxane having vinyl groups at the ends of molecular chains with molecular weight of about 55,000 used in Application Example 3, as well as 5.25 parts (5% with respect to the weight of polysiloxane), 11.11 parts (10% with respect to the weight of polysiloxane), 17.64 parts (15% with respect to the weight of polysiloxane), and 25.0 parts (20% with respect to the weight of polysiloxane) of fumed silica and a specific surface area of 300 m²/g (Aerosil 300, Nippon Aerosil Co., Ltd), respectively. As a comparative example, rubber base (VII) was prepared without adding the fumed silica. For each rubber base 100 parts were taken to prepare dispersions (III)-(VII) according to Application Example 1. In Application Example 1, 25 parts of toluene were added to 100 parts of the dispersion. In this case, however, it was not added, while 1.0 part of dibutyltin di(2-ethylhexoate) as well as 2.0 part of HS(CH₂)₃Si(CH₃)(OCH₃)₂ listed in Table IV and 3.0 parts of ethyl alcohol were added. For the obtained sample, the variation in time of the viscosity was measured in the same way as in Application Example 1. The above dispersions containing HS(CH₂)₃Si(CH₃)(OCH₃)₂ and ethyl alcohol were cast into a Teflon mold of 11 x 15 x 0.5 cm and allowed to stand at room temperature for 2 days for evaporation of the solvent then heated in a circulation hot-air oven at 150°C for 5 min to obtain silicone rubber sheets. These silicone rubber sheets were made into test specimens using a dumbbell puncher. The specimens were tested for tensile strength using a tensile tester at a rate of 30 cm/min. Usually, an increase in fumed silica content results in poor viscosity stability of dispersions. However, as shown in Table IV, in the examples of the present invention, even with increased fumed silica content, the initial viscosity shows no changes even after 24 h. Since the film tensile strength increases with increasing fumed silica content, the present invention provides both stable dispersion viscosity and silicone rubber films of high strength. Composition, parts Application Example Comparative Example 11 12 13 14 6 Dispersion, 100 (III) (IV) (V) (VI) (VII) Fume Silica, % of Polysiloxane 5 10 15 20 0 HS(CH₂)₃SiMe(OMe)₂ 2.0 2.0 2.0 2.0 2.0 Ethanol 3.0 3.0 3.0 3.0 3.0 Properties Change of Viscosity (cP) with time 0 Hours 7400 9200 12250 17550 6300 1 Hours 7400 9200 12250 17550 6300 2 Hours 7300 9000 11150 16600 6100 5 Hours 7250 8600 12200 15500 6050 10 Hours 7950 8900 12250 17850 6350 24 Hours 7900 9300 11700 17200 6550 State of Coating after 10 hours good good good good good Surface State of film good good good good good Tensile Strength, kg/cm² 25.5 40.3 57.3 80.5 9.8 Overall rating as coating material The condensation reaction-curing silicone rubber compositions of the present invention containing mercaptoalkyl group-containing di- or trialkoxysilanes and aliphatic monohydroxy alcohols are free from drawbacks of addition reaction curing type and, even when inorganic filler content is increased in dispersion, viscosity stability was excellent, and high-strength films are readily obtained.

Claims: A silicone rubber composition for treatment of fiber structures comprising: (A) 100 parts by weight of an essentially linear organopolysiloxane represented by the formula HO(R₂SiO) n H, wherein R is a substituted or unsubstituted monovalent hydrocarbon group and the subscript n is a number of 50 - 10 000, (B) 0-50 parts by weight of an alkenyl group-terminated organopolysiloxane, (C) 3-100 parts by weight of an inorganic filler, (D) 0.1-20 parts by weight of an organohydrogenpolysiloxane of units of general formula R a H b SiO (4-a-b)/2 , wherein R is a substituted or unsubstituted monovalent hydrocarbon group, a is 1 - 3, b is 0,5 - 1, containing at least 3 hydrogen atoms bonded to different silicon atoms, (E) 0.1-20 parts by weight of a di- or trialkoxysilane containing a mercaptoalkyl group, (F) 0.1-30 parts by weight of an aliphatic monohydroxy alcohol, (G) 0.1-20 parts by weight of a curing catalyst, and (H) an appropriate amount of solvent. A silicone rubber composition in accordance with claim 1 wherein the component (A) is an hydroxy group terminated polymethylsiloxane rubber, component (B) is an alkenyl group-terminated polydimethylsiloxane, component (C) is finely divided silica, component (D) is a polymethylhydrogensiloxane, component (E) is methylmercaptopropyldimethoxysilane or mercaptopropyltrimethoxysilane, component (F) is an aliphatic monohydroxy alcohol of 1-3 carbon atoms and component (G) is a dibutyltin salt of an organic acid.

Inventors: ONA ISAO, OZAKI MASARU, ONA, ISAO, OZAKI, MASARU
Applicants: DOW CORNING TORAY SILICONE, DOW CORNING TORAY SILICONE COMPANY, LIMITED
Application year: 1990
Main classification: C08K13
IPC codes: C08K13, C08K5, C08L83, D06M15, D06M11, C08K3