Stain resistant cover composition

Abstract: A stain resistant cover composition of the invention for a coloured rubber part of a tire comprises 100 parts by weight of water, 1.0 to 50 parts by weight of polyvinyl alcohol, 15 to 150 parts by weight (solid content) of a vinyl acetate resin emulsion, 0.5 to 5.0 parts by weight of a surfactant, and 0.5 to 5.0 parts by weight of a silicon oil. A stain resistant protective film of the present invention is used for a coloured portion in the side wall part of a tire, wherein the protective film comprises polyvinyl alcohol, a vinyl acetate resin emulsion, a surfactant, and a silicon oil. The present invention can provide a stain resistant cover composition for a coloured rubber part of a tire used for preventing the coloured part (side wall) of a tire from being stained by antioxidants bleeding from other tires, or dust, and from being scratched by contact with other tires when rubber tires are stacked while being transported or stored.

Description: The present invention relates to a stain resistant cover composition (hereinafter called merely "cover composition") for a coloured rubber part of a tire used for preventing a coloured part (side wall) of a tire from being stained by antioxidants bleeding from other tires, or dust and being scratched by contact with tires when rubber tires are transported or stored as they are piled up and to a protective film therefor. There has so far been a problem that tires for automobiles (so-called white letter tires or white line tires) provided with white rubber in a circular form on a side wall part for decoration or a white rubber part showing thereon a manufacturer name are scratched by contact with other tires or stained in a coloured (white) rubber part by antioxidants bleeding from adjacent tires, dust, rubbish and the like and discoloured when the tires are transported or stored as they are piled up. Known as conventional techniques for preventing a coloured rubber part from being partially lost or discoloured by the scratches and staining described above are: (1) a method in which a tire is wrapped with a synthetic paper; (2) a method in which a soft plastic film is adhered to a tire (refer to, for example, Japanese Patent Publication No. Sho 64-3682); (3) a method in which a tire is wrapped with an LDPE film coated with PVA as an adhesive; (4) a method in which a tire is wrapped with a film obtained by applying a pressure sensitive adhesive prepared by blending natural rubber or SBR with other elastomers and a hydrogenated petroleum resin on a polyvinyl chloride series resin film (Japanese Patent Application Laid-Open No. Hei 4-183768); and (5) a method in which a film coated with blue paint is formed on a tire and removed by washing with water upon using. However, in the preceding method (1) in which a tire is wrapped with a synthetic paper, the synthetic paper is expensive and has to be removed when the tire is built in a rim in automobile manufacturers. Further, a problem is involved in the disposition of the removed synthetic paper, such as wasting it as rubbish. The preceding method (2) in which a soft plastic film is adhered to a tire is a method effective enough to solve the problem in the preceding wrapping method with a synthetic paper. However, the adhesive tape itself does not have a sufficiently high strength, and an additional step in which the white letter part of a tire is subjected in advance to thin film treatment is needed. The above wrapping method (3) with an LDPE film has a problem in respect of the strength and the weatherability of LDPE. The method (4) in which a tire is wrapped with a polyvinyl chloride series resin film coated thereon with a pressure sensitive adhesive has the problem that the film is liable to peeling off upon moving such as transporting. Further, in peeling off, the adhesive remains in some cases,and there is the problem that rinsing with a solvent and washing with water have to be repeated in order when the adhesive remains. The method (5) has the problems that it takes a long time for drying and the thickness of a coated film is not fixed. Overall investigation of the processability and the cost in the conventional methods (1) to (5) described above shows that the method (5) in which a film coated with blue paint is formed on a tire is effective. As described above, however, the method (5) has the problems that it takes a long time for drying and the thickness of a coated film is not fixed and that if the thin film is tried to form so that the film can be dried in a short time, a coating solution is repelled. An object of the present invention is to provide a stain resistant cover composition for a coloured rubber part of a tire, and a protective film thereof, which can be achieved substantially by a method obtained by improving the preceding method in which a film coated with blue paint is formed on a tire, wherein the composition has a good processability and is dried for a short time after applying; the thickness of the coated film thereof is regularized; the film is provided with such durability that it does not peel off in transporting or handling the tires; and it does not damage the appearance and can easily be removed by washing. Intensive investigations made by the present inventors regarding the components incorporated into the cover composition have resulted in successfully obtaining a stain resistant cover composition for a coloured rubber part of a tire and a protective film therefor which meet the objects described above, by employing a novel composition comprising water, a specific vinyl acetate resin, polyvinyl alcohol, a surfactant, and a silicone oil, which has a good processability and is dried for a short time after applying as well as providing a coated film with a fixed thickness and which has a durability and can easily be removed by washing. Thus, the present invention has been accomplished. The present invention in aspect provides a stain resistant cover composition for a coloured rubber part of a tire, comprising 100 parts by weight of water, 15 to 150 parts by weight (solid content) of a vinyl acetate resin emulsion, 1.0 to 50 parts by weight of polyvinyl alcohol, 0.5 to 5.0 parts by weight of a surfactant, and 0.5 to 5.0 parts by weight of a silicone oil. The stain resistant cover composition according to the invention preferably further comprises a colourant and/or a softener. The invention in another aspect provides a stain resistant protective film used for a coloured portion of a side wall part of a tire, wherein said protective film comprises 15 to 150 parts by weight (solid content) of a vinyl acetate resin emulsion, 1.0 to 50 parts by weight of polyvinyl alcohol, 0.5 to 5.0 parts by weight of a surfactant, and 0.5 to 5.0 parts by weight of a silicone oil; and wherein the protective film has a thickness of 0.01 mm or more. The stain resistant protective film according to the invention preferably further comprises a colourant and/or a softener. Fig. 1 is a drawing for explaining a method for evaluating stain resistant performances in the examples, wherein the numerals show the following: 1: tire (white letter tire), 2: coloured portion in a side wall part, 3: protective film formed with the cover composition, and 4: side wall part (black rubber) on an opposite side. The stain resistant cover composition of the present invention for a coloured rubber part of a tire is a composition comprising city water (preferably purified water), a vinyl acetate resin emulsion, polyvinyl alcohol, a surfactant, and a silicone oil. The stain resistant protective film of the present invention for a coloured rubber part of a tire is formed by applying the cover composition described above on a coloured portion in the side wall part of a tire and then drying, wherein the above protective film comprises a vinyl acetate resin emulsion, polyvinyl alcohol, a surfactant, and a silicone oil. The vinyl acetate resin emulsion used in the cover composition of the present invention is incorporated in order to provide durability (stain resistant performance) and an excellent washing performance, and various emulsions can be used as long as they are vinyl acetate resin emulsions. Vinyl acetate resin emulsions having a viscosity of 10,000 to 500,000 cp (25°C) are preferably used, and aqueous (concentration: 30 %) vinyl acetate resin emulsions having the physical property described above are more preferably used in view of the handling performance. The amount of the vinyl acetate resin emulsion is 15 to 150 parts by weight (solid matter content), preferably 30 to 90 parts by weight, per 100 parts by weight of water. If a vinyl acetate resin emulsion having a concentration of 30 % is used, the amount is 50 to 500 parts by weight, preferably 100 to 300 parts by weight, per 100 weight parts of water. An amount of the vinyl acetate resin emulsion of less than 15 parts by weight (solid matter content) does not satisfy the stain resistant performance, and an amount exceeding 150 parts by weight (solid matter content) provides an insufficient elongation of the coated film and may cause film breaking due to distortion caused during transportation. Polyvinyl alcohol used in the cover composition of the present invention functions as a protective colloid for the vinyl acetate resin emulsion described above. The amount of polyvinyl alcohol is 1.0 to 50 parts by weight, preferably 5 to 10 parts by weight, per 100 parts by weight of water. An amount of polyvinyl alcohol falling in a range of 1.0 to 50 parts by weight as described above causes a stable protective layer to be formed on the vinyl acetate resin emulsion particles and can help prepare a stable and even composition, and therefore makes it possible to coat fine particles by spraying. An amount of polyvinyl alcohol of less than 1.0 part by weight leads to the formation of a protective colloid layer which is unstable to the vinyl acetate resin emulsion and makes spray coating difficult, and an amount exceeding 50 parts by weight notably increases the viscosity of the composition solution and causes drying to take time. The surfactant used in the cover composition of the present invention acts as a dispersant and is incorporated in order to improve the dispersibility of the vinyl acetate resin emulsion. There can be used as the surfactant, for example, anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, and fluorine series surfactants. Among them, the anionic surfactants are preferred. There can be used as the anionic surfactant, for example, carboxylates such as N-acylamino acid salts and alkyl ethercarboxylates, sulfonates such as alkylsulfonates and alkylbenzene- and alkylnaphthalenesulfonates, sulfuric acid ester salts such as alkylsulfates and alkyl ethersulfates, and phosphoric acid ester salts such as alkylphosphates and alkyl etherphosphates. The amount of the surfactant is 0.5 to 5.0 parts by weight, preferably 0.7 to 1.5 part by weight, per 100 parts by weight of water. An amount of the surfactant falling in a range of 0.5 to 5.0 parts by weight as described above secures the uniform dispersibility (dispersant function) of the composition in water and turns a lipophilic property on a tire surface into a hydrophilic property (polarity change function), which improves the coating and adhesion and reduces the surface tension to prevent cissing of the coating solution from being generated and enhance the coating performance (coating function), whereby these functions can be exhibited while keeping a good balance. An amount of the surfactant of less than 0.5 part by weight causes cissing on the coated face of a tire, and an amount exceeding 5.0 parts by weight can not control defoaming and makes it impossible to coat evenly the fine particles. The silicone oil used in the cover composition is incorporated in order to regularize the film thickness and impart lubricity. Various silicone oils can be used and include, for example, polyether-modified silicone oils obtained by turning a part of dimethylsiloxane into a hydrophobic group and a part of polyether into a hydrophilic group, and polyoxyethylene alkylsiloxane. The preferred polyoxyethylene alkylsiloxane includes polyoxyethylene alkylsiloxane in which an alkyl group has 1 to 20 carbon atoms, preferably 1 to 4 carbon atoms. The amount of the silicone oil is 0.5 to 5.0 parts by weight, preferably 1.0 to 2.0 parts by weight, per 100 parts by weight of water. An amount of the silicone oil falling in a range of 0.5 to 5.0 parts by weight as described above sufficiently improves leveling and defoaming and does not cause bleeding on the surface of the coated and dried film. An amount of the silicone oil of less than 0.5 part by weight is insufficient for leveling and causes insufficient defoaming, and an amount exceeding 5 parts by weight causes the silicone oil to bleed on the surface of the coated and dried film. The cover composition of the present invention can further contain a colourant in order to enhance the appearance and provide a masking function and/or a softener in order to improve the physical properties of the protective film. Various dyes, inorganic pigments, and organic pigments can be used as the colorant, and sulfonated dyes, pigments containing less heavy metals, for example pigments for cosmetics and emulsions of pigments, and metal oxides are preferably used. They may be used alone or in combination of two or more kinds thereof. The amount of the colourant is 0 to 20 parts by weight per 100 parts by weight of water. When the amount of the colourant is 0 part by weight, a transparent cover composition and protective film are obtained. The amount is preferably 0.5 to 2.0 parts by weight. An amount of the colourant falling in a range of 0.5 to 2.0 parts by weight can provide fine colour tone. As the amount of the colourant is increased, the colour tone becomes somber, and the appearance is damaged. An amount of the colourant exceeding 20 parts by weight makes it impossible to disperse the colourant and therefore is not preferred. There can be used as the softener, for example, dimethyl phthalate (DMP), dibutyl phthalate (DBF), butylbenzyl phthalate (BBP), and among them dibutyl phthalate (DBP) is preferred. They can be incorporated alone or in combination of two or more kinds thereof. Dibutyl phthalate (DBP)is effective for film cracking particularly at low temperatures (0°C or lower). The amount of the softener is 0 to 50 parts by weight, preferably 5 to 30 parts by weight per 100 parts by weight of water. An amount of the softener falling in a range of 5 to 30 parts by weight can reduce the viscosity of the coating solution while preventing running of the coated film. An amount of the softener exceeding 50 parts by weight increases notably running of the coated film and causes deformation of the coated film to continue. In addition, it degrades the film strength and increases the rubbing wear of the film. Further, glycerin can be incorporated into the cover composition of the present invention for the purpose of further improving the film strength. The amount of glycerin is 0 to 50 parts by weight, preferably 5 to 20 parts by weight, per 100 parts by weight of water. An amount of glycerin falling in a range of 5 to 20 parts by weight improves the balance (toughness of the film) of the film hardness with the film elongation. An amount of glycerin exceeding 50 parts by weight causes film cracking and therefore is not preferred. In the present invention, in addition to water, the vinyl acetate resin emulsion, polyvinyl alcohol, the surfactant, the silicone oil, the colourant and/or the softener, a hydrophilic polymer dispersion such as a latex and an additive such as a hydrophilic colloid dispersion of a resin can suitably be incorporated according to necessity. The cover composition of the present invention is prepared by blending and stirring the additives incorporated according to necessity as well as water, the vinyl acetate resin emulsion, polyvinyl alcohol, the surfactant, the silicone oil, the colourant and/or the softener by means of a stirrer equipped with blades for a agitator, propeller blades, turbine blades, or puddle blades. The stain resistant protective film of the present invention for a coloured rubber part of a tire can be formed as a strong protective film by applying the cover composition comprising the respective components described above to a coloured part (white rubber) in the side wall portion of a tire by hand or by means of a spray nozzle and then drying (by evaporating water contained). This protective film has a thickness of 0.01 mm or more, preferably 0.03 to 0.06 mm. A thickness of the protective film of less than 0.01 mm provides insufficient stain resistance and therefore is not preferred. In the present invention, the protective film formed on a coloured part in the side wall portion of a tire comprises polyvinyl alcohol, the vinyl acetate resin emulsion, the surfactant, and the silicone oil (further containing the colourant and/or softener described above). This protective film has a fixed thickness of the coated film. Further, the film is provided with such durability that the film does not peel off even when transporting or handling the tires. In addition, the film does not damage the appearance and has an excellent washing property capable of being easily removed by washing (this matter shall be explained in detail in the examples described later). The present invention provides a stain resistant cover composition for a coloured rubber part of a tire, and a protective film therefor, wherein the composition has a good processability and is dried for a short time after applying; the thickness of the coated film thereof is regularized; the composition is provided with such durability that it does not peel off when transporting or handling the tires; and it does not damage the appearance and can easily be removed by washing with water. The present invention is further explained below with reference to illustrative examples. The cover compositions having the blend compositions shown in the following Table 1 and Table 2 were prepared by blending the respective components with a puddle blade stirrer. Evaluated by the following evaluating methods were the stain resistant performances, washing performances, rubbing resistant performances, peeling resistant performances, anti-film cracking performances, uniform coating performances, drying performances, and appearance maintaining performances of the cover compositions obtained in Examples 1 to 7 and Comparative Examples 1 to 11. The results thereof are shown in the following Table 1. (1) Stain resistant performance: As shown in Fig. 1, a protective film was formed on coloured rubber (white rubber) of a tire of 10 x 20 mm by applying the cover composition with a spray and then drying it. A side wall portion (black rubber) having the same size as that described above was superposed on the above protective film and left standing at 60°C for one month. Then, after removing the above protective film by washing, a stain degree on the surface of the coloured rubber part (white rubber) was evaluated by visual inspection according to the following evaluation criteria. The numerals shown in Fig. 1 exhibit the following: 1: tire (white letter tire), 2: coloured part in a side wall portion, 3: protective film formed with the cover composition, and 4: side wall part (black rubber) on an opposite side. Evaluation criteria: o ○: maintaining the same whiteness as that observed before applying, ○: slightly blackened (stained pale brown), Δ: stained black. (2) Washing performance: A protective film was formed on the coloured rubber (white rubber) of a tire of 10 x 20 mm by applying the cover composition with a spray and left standing at 60°C for one month. Then, after washing the protective film with a brush such as a scrubbing brush, the washing performance was evaluated by visual inspection according to the following criteria. Evaluation criteria: o ○: no residual film; the film is easily dissolved in water, and no colour remains, ○: film partially remains, and residual colour is found, Δ: residual film and colour observed in the greater part. (3) Rubbing resistant performance: The same film as that used for evaluating the washing performance (2) described above was formed and left standing in the same manner as described above. Then, after rubbing the film surface with a tire, the rubbing resistant performance was evaluated by visual inspection according to the following criteria. Evaluation criteria: o ○: small wear loss of the film, ○: large wear loss of the film observed in part, Δ: large wear loss of the film observed in the whole part. (4) Peeling resistant performance: The same film as that used for evaluating the washing performance (2) described above was formed and left standing in the same manner as described above. Then, after rubbing the film surface with a tire, the peeling resistant performance was evaluated by visual inspection according to the following criteria. Evaluation criteria: o ○: no film peeling observed, ○: film peeling observed in part, Δ: film peeling observed in the whole part. (5) Anti-film cracking performance: The same film as that used for evaluating the washing performance (2) described above was formed in the same manner as that described above and left standing at high temperature of 60°C for a month, and then the anti-film cracking performance was evaluated by visual inspection according to the following criteria. Evaluation criteria: o ○: no film cracking observed, ○: film cracking observed in part, Δ: film cracking observed in the whole part. (6) Uniform coating performance: The same film as that used for evaluating the washing performance (2) described above was formed in the same manner as that described above, wherein the coating condition after applying was evaluated by visual inspection according to the following criteria. Evaluation criteria: o ○: capable of uniformly coating thin film, ○: cissing observed in part and slightly heavy coating needed, Δ: cissing observed in large part and heavy coating needed. (7) Drying performance: The same film as that used for evaluating the washing performance (2) described above was formed at room temperature (25°C), wherein the time spent for forming the film was evaluated according to the following criteria. Evaluation criteria: o ○: dried within 30 minutes; excellent drying performance, ○: dried within 60 minutes, Δ: dried in 60 minutes or more; poor drying performance. (8) Appearance-maintaining performance: The same film as that used for evaluating the washing performance (2) described above was formed in the same manner as that described above and left standing at high temperature of 60°C for a month, and then the appearance maintaining performance was evaluated as a change in the colour tone by visual inspection according to the following criteria. Evaluation criteria: o ○: no change in colour tone, ○: partial change in colour tone (slightly somber), Δ: change in colour tone observed in the whole part (heavily somber and darkened). The results thereof are shown in the following Table 1 and Table 2. Consideration of the results summarized in Tables 1 and 2: In summary, it has been found that in Examples 1 to 7 falling in the range of the present invention, there are satisfied all performances which are required of the stain resistant protective film, that is, a stain resistant performance, a washing performance, a rubbing resistant performance, a peeling resistant performance, an anti-film cracking performance, a uniform coating performance, a drying performance, and a appearance-maintaining performance, as compared with Comparative Examples 1 to 11 falling outside the range of the present invention. Individually observing Comparative Examples 1 to 11, Comparative Example 1 is an example in which PVA (polyvinyl alcohol), the surfactant and others are not contained, and it has been found that Comparative Example 1 is inferior in stain resistant performance, rubbing resistant performance, and uniform coating performance. Comparative Example 2 is an example in which PVA (polyvinyl alcohol) and the like are not contained, and it has been found that Comparative Example 2 is inferior in stain resistant performance and uniform coating performance. Comparative Example 3 is an example in which the vinyl acetate resin emulsion, the surfactant and the silicone oil each have larger contents than the ranges of the present invention, and it has been found that Comparative Example 3 is inferior in uniform coating performance and drying performance. Comparative Examples 4 to 11 are examples in which PVA, the vinyl acetate resin emulsion, the surfactant and the silicone oil each have contents falling outside the ranges of the present invention. That is, Comparative Examples 4 and 5 are examples in which the contents of PVA fall outside the range of the present invention; Comparative Examples 6 and 7 are examples in which the contents of the vinyl acetate resin emulsion fall outside the range of the present invention; Comparative Examples 8 and 9 are examples in which the contents of the surfactant fall outside the range of the present invention; and Comparative Examples 10 and 11 are examples in which the contents of the silicone oil fall outside the range of the present invention. Considerations in comparison of Examples 1 to 7 falling in the range of the present invention with Comparative Examples 1 to 11 falling outside the range of the present invention show that the cover compositions satisfying all performances of stain resistant performance, washing performance, rubbing resistant performance, peeling resistant performance, anti-film cracking performance, uniform coating performance and drying performance.

Claims: A stain resistant cover composition for a coloured rubber part of a tire, comprising 100 parts by weight of water, 15 to 150 parts by weight (solid content) of a vinyl acetate resin emulsion, 1.0 to 50 parts by weight of polyvinyl alcohol, 0.5 to 5.0 parts by weight of a surfactant, and 0.5 to 5.0 parts by weight of a silicone oil. A stain resistant cover composition as claimed in claim 1, characterized by further comprising a colourant and/or a softener. A stain resistant protective film (3) used for a coloured portion of a side wall part (2) of a tire (1), wherein said protective film comprises 15 to 150 parts by weight (solid content) of a vinyl acetate resin emulsion, 1.0 to 50 parts by weight of polyvinyl alcohol, 0.5 to 5.0 parts by weight of a surfactant, and 0.5 to 5.0 parts by weight of a silicone oil; and wherein the protective film has a thickness of 0.01 mm or more. A stain resistant protective film as claimed in claim 3, characterized by further comprising a colourant and/or a softener.

Inventors: UCHIDA YO, YANO MASASHI, UCHIDA, YO, YANO, MASASHI
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1996
Main classification: C09D131
IPC codes: B60C1, B60C13, C09D5, G11B7, C09D129, C08L29, C09D131, C08J7, B60R21