METHOD FOR LUBRICATING TIRE-MOLDING BLADDERS

Abstract: A tire-molding bladder is treated with a lubrication/­ release composition to provide lubrication between and/or release of the bladder and a tire molded therewith. The lubrication/release composition contains an aqueous emul­ sion of an organopolysiloxane bearing one or more silicon-­ bonded amino-substituted hydrocarbon radicals and cures on and adheres to the surface of the bladder, particularly when heated. Bladder life is extended and multiple moldings without recoating of the bladder is provided.

Description: METHOD FOR LUBRICATING TIRE-MOLDING BLADDERS Background of the Invention This invention concerns a lubricant composition for tire-molding bladders. In the vulcanization molding of unvulcanized crude tires, a bag, a so-called "bladder," is usually inserted into the tire and expanded with hot water or steam followed by molding in the metal mold. When the bladder expands, good lubrication must be present between the interior of the crude tire and the bladder. Moreover, after vulcanization, there must be good release between the bladder and the interior surface of the vulcanized tire. Accordingly, a mixture of silicone release oil, mica powder and talc powder (usually referred to as inner surface release, inner surface paint, green inner paint or BPL), dissolved and dispersed in rubber volatile oil, etc., is sprayed and dried on the inner surface of each crude tire and the bladder is then inserted and the tire is then vulcanised and molded. However, the mica powder and talc powder tend to fall off the surface of the crude tire, becoming attached to the outer surface of the tire and producing a soilage or stain. As a result, the inner surface of each tire must be dried after spraying, which complicates the process and reduces the productivity. For this reason, methods and compositions have been proposed in which a release agent or lubricant is applied to the bladder's surface instead of the previous application of inner surface paint to the inner surface of the crude tire. Japanese Kokai Patent 57-111394 (Great Britain 2087914) discloses a mixture of polydimethylsiloxane, alkoxysilane and zinc catalyst; however, the working time (pot life) is short as a result. Adhesion to the bladder is also weak and not long lasting. Japanese Kokai Patent 57-119992 (Great Britain 2088898) and Japanese Kokai Patent 57-111393 (Great Britan 2087913) discloses polyethylene glycol- and/or polypropylene glycol-containing compositions which, accordingly, have an inferior heat resistance. Due to their thermal decomposition, the polydimethylsiloxane and bentonite clay on the bladder's surface readily come off, resulting in poor durability. Brief Description of the invent ion The above noted drawbacks of the prior art are resolved by the improvement offered by the present invention which, briefly stated, comprises applying to the tire-contacting surface of a tire-molding bladder a lubrication/release composition comprising a curable organopolysiloxane, in aqueous emulsion, and then curing the applied organopolysiloxane by way of one or more silicon-bonded, amino-substituted hydrocarbon radicals. Curing of the organopolysiloxane is preferably accelerated by heating the applied composition. It is also an object of this invention to provide an improved process for molding tires with the aid of a tire-molding bladder wherein the bladder can be used repeatedly without the necessity of recoating the bladder. Detailed Description of the Invention Specifically, the present invention relates to an improved process for molding a tire, said process comprising applying a lubricant/release composition to at least the tire-contacting surface of a tire-molding bladder to improve the lubrication between the bladder and a tire being molded therewith and/or to improve the release of the bladder from a tire molded therewith, the improvement comprising (i) applying, as said lubricant/release composition, a lubricant/release composition comprising an aqueous emulsion of an organopolysiloxane component containing an average of at least one silicon-bonded, amino-substituted hydrocarbon radical per molecule thereof having the formula -R1 (NHCH2CH2)aNHR2 wherein R1 denotes a divalent a n hydrocarbon radical, R2 denotes a radical selected from the group consisting of hydrogen and monovalent hydrocarbon radicals and a denotes a number having a value of from 0 to about 10 and (ii) thereafter curing the applied composition. by way of further explanation, the organopolysiloxane containing at least one radical with the formula 1 2 -Rl(NHCH2CH2)aNHR2 bonded to silicon in each molecule is the principal material of the present composition and imparts durable release and lubricity. It undergoes self-crosslinking into a rubber by atmospheric carbon dioxide after evaporation of the water component and then strongly adheres to the bladder's surface. In the formula R1 is a divalent hydrocarbon radical and examples thereof are alkylene radicals having the formula -CnH2n-, such as -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2CH(CH3)CH2- and -(CH2)4- and alkylene arylene radicals such as -(CH2)2C6H4#. Among these, the propylene radical is the most common. R is a hydrogen atom or a monovalent hydrocarbon group. Examples of the latter are methyl, ethyl, propyl, hexyl and phenyl; a is a number with the value of O to 10, preferably 0 or 1. The other silicon-bonded radicals in the organopolysiloxane can be alkyl radicals such as methyl, ethyl, propyl, butyl and pentyl; substituted alkyl radicals such as 2-phenylethyl, 2-phenylpropyl and 3,3,3, -trifluoropropyl; aryl and substituted aryl radicals as phenyl, tolyl and xylyl; alkenyl radicals such as vinyl, allyl and propenyl; alkoxy radicals such as methoxy, ethoxy, propoxy and methoxyethoxy; and hydroxyl group. The organopolysiloxane component must contain at least one siloxane unit possessing the group with 1 2 the formula -R (NHCH2CH2)aNHR bonded to silicon. It is possibly constituted only of such a siloxane unit or may also contain other organosiloxane units. In such other organosiloxane units, the silicon-bonded radicals can be an alkyl radical such as methyl, ethyl, propyl, butyl and pentyl; substituted alkyl radicals such as 2-phenylethyl, 2-phenylpropyl and 3,3,3-trifluoropropyl; aryl or substituted aryl radicals such as phenyl, tolyl and xylyl; alkenyl radicals such as vinyl, allyl and propenyl; alkoxy radicals such as methoxy, ethoxy, propoxy and methoxyethoxy, or the hydroxyl radical. From the standpoint of releasability, the siliconbonded radicals preferably are at least 20 mol % alkyl radicals. The molecular structure of this organopolysiloxane may be either straight chain, branched, cyclic or network. The organopolysiloxane component preferably has a straight chain molecular structure having the formula EMI4.1 1 2 wherein R1 R and a are as noted above and A denotes a chain terminating radical selected from the group consisting of hydroxy; monovalent hydrocarbon, such as methyl, vinyl or phenyl; alkoxy, such as methoxy or ethoxy; and -Rl(NHCH2CH2)aNHR such as -CnH2n(NHCH2CH2)aNH2 where n: is three or four and a is zero or one; and x and y denote numbers having a value of zero or more. From the standpoint of ease of emulsification the viscosity is preferably 10 to 10,000 centistokes (cS) at 25 C. A nonionic or cationic surfactant is necessary for emulsifying the organopolysiloxane component. Examples of the nonionic surfactants are polyoxyalkylene alkyl ethers, polyoxyalkylene alkylphenol ethers, polyoxyalkylene alkyl esters, sorbitan alkyl esters, polyoxyalkylene sorbitan alkyl esters. etc. Examples of the cationic surfactants are aliphatic amine salts, quaternary ammonium salts, alkylpyridinium salts, etc. One or more than one of these species can be used. The surfactant is added in the amount necessary for the emulsification of the organopolysiloxane component. Usually, 1 to 50 weight parts are used per 100 weight parts of organopolysiloxane. Water is used to produce the emulsion of the present composition. There is no specific requirement on its quantity. To produce the lubricant/release composition, the surfactant component and the water component are added to the organopolysiloxane component and this is then emulsified using an emulsifying device such as a colloid mill, homogenizer, homomixer, etc. Colorants, preservatives, trimethylsilyl-terminated dimethylpolysiloxane oil or protective colloids such as poly(vinyl alcohol), methylcellulose, etc., to improve the emulsion 5 storage stability and dilution stability may be added to the composition, if desired. The lubricant composition for tire-molding bladders is then uniformly sprayed onto the surface of the bladder and dried. Upon heating at 130 to 2000C for 30 to 10 minutes, the organopolysiloxane component in the composition undergoes self-crosslinking together with atmospheric carbon dioxide gas. A rubber film with a durable lubrication and releasability is thus obtained. If the lubrication or releasability deteriorates during tire-molding operations, the composition of the present invention can be applied to the same bladder again in order to use the bladder repeatedly. The improved process of this invention will now be further explained by the disclosure of examples which illustrate, but do not limit, the invention. All parts and percentages are by weight unless otherwise indicated. Viscosities were measured at 250 C. Me denotes the methyl radical. Example 1 Octamethylcyclotetrasiloxane, 94.16 parts; CH3(CH30)2Si(CH2)3NHCH2CH2NH2, 5.33 parts; hexamethyldisiloxane, 0.51 par as the end-blocking agent and 0.02 part potassium hydroxide as the catalyst are mixed and an equilibration reaction is carried out at 1300C for 10 hours to yield an amino groupcontaining organopolysiloxane (1,450 cS viscosity) with the formula EMI7.1 A uniform emulsion starting solution is prepared from 30 parts of this organopolysiloxane, 3 species of polyoxyethylene nonylphenol ethers with different HLB values as the surfactant and 67 parts water. The surface of a butyl rubber bladder is completely cleaned with a toluene-containing cloth to remove all the oily stains, etc., and then uniformly sprayed with the usual spray gun with the emulsion starting solution diluted 3-fold with water. After drying, this is heated at 170 C for 30 minutes. The composition of the invention becomes a rubber which is tightly adhered to the bladder's surface. The bladder is inserted into a BAG-O-MATIC vulcanizer for the repeated vulcanization molding of crude tires into radial tires for passenger cars. Good molding without inner paint (BPL or green inner paint) is continued up to the 14th cycle. Due to the decline in releasability, the emulsion starting solution diluted 3-fold with water is sprayed again and molding may again be repeated 14 times. For comparison, a 30% emulsion (solution (a)) of a trimethylsilyl-terminated dimethylpolysiloxane (viscosity. 350 cS) is used in the same molding experiment Only 3 tires could be molded. Example 2 An amino group-containing organopolysiloxane with a 3,500 cS viscosity is prepared by reacting a mixture of 100 parts hydroxyl-terminated dimethylpolysiloxane with a viscosity of 80 cS, 1.2 parts CH3(CH30)2Si(0H2)3NHCH2CH2NH2, 0.3 parts (CH30)3Si(CH2)3NHCH2CH2NH2 and 0.08 par potassium hydroxide at 130 C for 3 hours. Using this amino group-containing organopolysiloxane, an emulsion starting solution is prepared as in Example 1. To 100 parts of this emulsion are added 20 parts of solution (a) used for comparison in Example I and this is then diluted 4-fold with water. This is then applied to a bladder's surface as in Example 1 and heated. The organopolysiloxane on the bladder's surface is then a rubber and forms a highly lubricating film. This bladder can be used to mold 16 tires and the releasability is good. Example 3 Sodium hydroxide, 100 ppmt as the catalyst is added to 495 parts hydroxyl-terminated dimethylpolysiloxane with a viscosity of 90 cS and 5 parts of the hydrolysis condensation product (viscosity, 530 cS) of the silane with the formula CH3(CH30)2Si(CH2)3NHCH2CH2NH2. An equilibration reaction is carried out at 90 C for 10 hours followed by neutralization with 150 ppm acetic acid to provide a hydroxyl group-terminated organopolysiloxane (viscosity, 3,750 cS) which contains amino groups. To 30 parts of this organopolysiloxane are added 5 parts polyoxyethylene nonylphenol ether surfactant, 1 part cationic surfactant with the formula (CH3)3(C12H25)N+C1 and 64 parts water This is then emulsified using a colloid mill emulsifier to provide a homogeneous emulsion starting solution. The emulsion is then diluted 4-fold with water and applied to a bladder's surface as in Example 1 and heated. The organopolysiloxane on the bladder's surface becomes rubbery, forming a highly lubricating film. This bladder could be used to mold 11 tires and the releasability was good. Example 4 Using a colloid mill emulsifier, a homogeneous emulsion starting solution is prepared by adding 1 part nonionic surfactant with the formula C12H250(C2H40)6H, 2 parts nonionic surfactant with the formula C12H250(C2H40)8H, 0.5 part cationic surfactant with the formula (CH3)3( C12H25)N+Cl and 81.5 parts water to 15 parts of the amino group-containing organopolysiloxane (viscosity. 1650) with the formula H2NCH2CH2CH2(Me2SiO)400(MeSiO)6SiMe2CH2CH2CH2NH2 CH2CH2CH2NHCH2CH2NH2 This emulsion is then diluted 2-fold with water, applied to a bladder's surface as in Example 1 and heated. The organopolysiloxane on the bladder's surface becomes rubbery and firmly adhered to the bladder's surface. The bladder could be used to mold 14 tires and the releasability was good. As described above, this invention comprises a lubricant composition for tire-molding bladders which does not suffer from the drawbacks to the prior art. When a bladder treated with this composition is used in molding crude tires, the bladder life is significantly extended. At the same time, the tire can be molded with no stains on the surface and fewer quality problems such as exposure of tire cord or bead twist, etc. This lubricant composition for tire-molding bladders can be applied to the tires for all types of vehicles such as bicycles, motorcycles, tractors, airplaines, passenger cars, light trucks, trucks, buses, trailers, forklifts, power shovel cars, etc. It is useful regardless of the type of tire, bias or radial, etc.

Claims: CLAIMS 1. In a process for molding a tire, said process comprising applying a lubricant/release composition to at least the tire-contacting surface of a tiremolding bladder to improve the lubrication between the bladder and a tire being molded therewith and/or to improve the release of the bladder from a tire molded therewith, the improvement comprising (i) applying as said lubricant/release compositions a lubricant/release composition comprising an aqueous emulsion of an organopolysiloxane component containing an average of at least one silicon-bonded, amino-substituted hydrocarbon radical per molecule thereof having the formula -R1 (NHCH2CH2)aNHR2 wherein 1 denotes a divalent hydrocarbon radical, R2 denotes a radical selected from the group consisting of hydrogen and monovalent hydrocarbon radicals and a denotes a number having a value from 0 to 10 and (ii) thereafter curing the applied composition. 2. An improved process according to Claim 1, wherein each amino-substituted hydrocarbon radical of the organopolysiloxane component has the formula -CnH2nNHCH2CH2NH2 wherein n denotes a number having a value of 3 or 4. 3. An improved process according to Claim 2, wherein the organopolysiloxane component has a viscosity of from 10 to about 10,000 centistokes at 250C. 4. An improved process according to Claim 3, wherein at least 20 percent of the silicon-bonded organic radicals of the organopolysiloxane component are alkyl radicals. 5. An improved process according to Claim 4, wherein the organopolysiloxane component has the formula EMI12.1 wherein A denotes a terminal radical selected from the group consisting of hydroxyl, monovalent hydrocarbon, alkoxy and -CnH2n(NHCH2CH2)aNH2, and x and Z each denote, independently a number having a value of zero or more and the lubrication/release composition further comprises one or more surfactants selected from the group consisting of nonionic surfactants and cationic surfactants. 6. An improved process according to Claim 5, wherein the lubricant/release composition, applied to the tiremolding bladder, is cured by heating at l300C to 2000C for about 30 to 10 minutes, respectively.

Inventors: ONA, ISAO, USUI, KATSUTOSHI
Applicants: TORAY SILICONE COMPANY LIMITED
Application year: 1985
Main classification: B29C33
IPC codes: B29C43, B29C33, B29K21, B29C35, B29L30, B29K105, B29D30