Process for producing vulcanized rubber-synthetic resin composite structure

Abstract: An improved process for producing a vulcanized rubber-synthetic resin composite structure by injecting a molten synthetic resin into a mold in which a vulcanized rubber molding has been disposed, wherein said improvement comprises (I) chlorinating the surface of the vulcanized rubber molding which comes into contact with the synthetic resin, and forming on the chlorinated surface a curable adhesive layer composed mainly of resol-type phenolic resin and aldehyde-modified polyvinyl alcohol, or (II) forming a curable adhesive layer composed mainly of chlorosulfonated polyethylene on the surface of the vulca­ nized rubber molding which comes into contact with the synthetic resin, and injecting the molten synthetic resin while keeping the vulcanized rubber molding heated.

Description: The present invention relates to a process for producing a vulcanized rubber-synthetic resin composite structure, and more particularly, to a process for producing a vulcanised rubber-synthetic resin composite structure in which the vulcanised rubber and the synthetic resin are bonded extremely firmly to each other. Industrial rubber products are often used in the form of rubber-metal composite structure. Recently, metals for this purpose are being supplanted by the recently developed engineering plastics which have outstanding mechanical strength, heat resistance, oil resistance, and creep resistance. As a result, new application areas are being opened up by the rubber-synthetic resin composite structure. An example of such application areas is the automotive suspension rod. The conventional metal rod with rubber bushings is being supplanted by the plastics rod with rubber bushings whose plan view is shown in Fig. 1 and whose sectional view taken through section II-II of Fig. 1 is shown in Fig. 2. There are shown a rod proper 2 made of plastics (such as polyamide resin), a bushing 3 made of vulcanized rubber, and a steel bearing 4. The rubber bushings 3 attached to both ends of the rod 1 are intended to reduce the torsional rigidity, and the rod 1 is joined to the automotive body through the bushings 3 and steel bearings 4. The rubber-synthetic resin composite structure is usually produced by curing a desired part of unvulcanized rubber in contact with the surface of the synthetic resin moldings to which a chlorine-containing vulcanizable adhesive has been applied. According to the disclosure of Japanese Patent Laid-open No. 104717/1987, the plastics rod with rubber bushings as shown in Figs. 1 and 2 is produced by disposing the bushings of vulcanized rubber in a mold and injecting a melt of a synthetic resin into the mold. GB-691252 discloses a process for making composite articles which comprises subjecting the surface of a soft-vulcanised rubber component to chemical modification, bringing said modified surface into contact with a rigid component with a bonding layer therebetween and hardening the bonding layer whilst pressing the rubber component against the rigid component. Needless to say, firm bonding between rubber and resin is very important for the rubber-resin composite structure. In the case of the plastics rod with rubber bushings, the plastics rod proper and the rubber bushing should be bonded extremely firmly to each other. Unfortunately, adhesion between rubber and plastics is poor, and a sufficient bond strength is not achieved by simply injecting a molten resin into a cavity surrounding the bushing of vulcanized rubber, as disclosed in the above-mentioned Japanese Patent Laid-open No. 104717/1987. A high adhesion strength is obtained when bonding is performed by curing unvulcanized rubber in contact with a synthetic resin molding. However, this bonding method has a disadvantage that the physical properties of the synthetic resin molding might be deteriorated by the heat history encountered in the curing step. Moreover, a resin molding having a low melting point might be deformed by the curing heat. An additional disadvantage is a comparatively high production cost. Therefore, the above-mentioned method is inefficient for the production of a composite structure (having a rubber bushing embedded in plastics) as shown in Figs. 1 and 2. The present invention provides a process for producing a vulcanized rubber-synthetic resin composite structure which comprises chlorinating the surface of the vulcanized rubber molding which comes into contact with the synthetic resin, forming a layer of a curable adhesive on the chlorinated surface of the vulcanized rubber molding, said curable adhesive being composed mainly of resol-type phenolic resin and aldehydemodified polyvinyl alcohol, disposing the vulcanized rubber molding in a mold, injecting a molten resin into the mold, and demolding the composite structure after the setting of the injected resin. The present invention is concerned with an improved process for producing a vulcanized rubber-synthetic resin composite structure by injecting a molten synthetic resin into a mold in which a vulcanized rubber molding has been disposed, wherein the improvement comprises chlorinating the surface of the vulcanized rubber molding which comes into contact with the synthetic resin, and forming on the chlorinated surface a curable adhesive layer composed mainly of resol-type phenolic resin and aldehydemodified polyvinyl alcohol. A preferred embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a plan view showing a plastics rod with rubber bushings; Fig. 2 is a sectional view taken in the direction of the arrows along the line II-II of Fig. 1; Fig. 3 is a plan view showing a test piece prepared in Examples and Comparative Examples; and Fig. 4 is a sectional view taken in the direction of the arrows along the line IV-IV of Fig. 3. In a process in accordance with of the present invention, the vulcanised rubber molding to be disposed in the mold undergoes chlorination treatment so that at least the surface which comes into contact with the synthetic resin is chlorinated. The chlorination treatment may be accomplished by any one of the following methods. (1) by dipping the vulcanized rubber molding in an aqueous solution of sodium hypochlorite and hydrochloric acid; (2) by exposing the vulcanized rubber molding to a chlorine gas atmosphere; or (3) by coating the vulcanized rubber molding with a solvent solution containing an organic compound which gives chlorine to the vulcanized rubber. (An example of the organic compound is trichloroisocyanuric acid, and an example of the solvent is ethyl acetate.) The third method is most advantageous owing to its safety in operation and good adhesion effect. After the chlorination treatment, the chlorinated surface of the vulcanized rubber molding is coated with an adhesive layer composed of resol-type phenolic resin and aldehyde-modified polyvinyl alcohol. The resol-type phenolic resin is produced by reacting formaldehyde with a phenol in the presence of an alkaline catalyst. Examples of the phenol include phenol and derivatives thereof (such as xylenol and resorcinol) . A preferred example of the resol-type phenolic resin used in the present invention is resol-type phenol-resorcinol resin which is a cocondensate of formaldehyde and a mixture of phenol and resorcinol. The phenolresorcinol mixture should contain phenol and resorcinol at a molar ratio of 75:25 to 95:5, preferably 85:15 to 95:5. The aldehyde-modified polyvinyl alcohol is obtained by reacting polyvinyl alcohol with an aldehyde. It includes, for example, polyvinyl formal resin, polyvinyl acetal resin, and polyvinyl butyral resin. Preferable among them is polyvinyl butyral resin. According to the present invention, the resol-type phenolic resin and the aldehyde-modified polyvinyl alcohol should be used in a molar ratio of 75:25 to 99:1, preferably 85:15 to 97:3. The adhesive may be incorporated with optional components such as solvent, pigment, and suspending agent. The total amount of the optional components should be less than 85 wt% of the total weight of the adhesive. After the formation of the adhesive layer on the chlorinated surface, the vulcanized rubber molding is disposed in the mold and a molten resin is injected into the mold to make an integrated body. There are no specific limitations on the degree of chlorination of the vulcanized rubber molding and the thickness of the adhesive layer to be formed on the vulcanized rubber molding. They may be properly determined according to the product dimensions, the manufacturing conditions, and the properties required. There are no specific limitations on the rubber constituting the vulcanised rubber molding. The preferred rubber is natural rubber or synthetic rubber having a carbon-carbon double bond in the structural formula. These rubbers may be used alone or in combination with one another. The rubber is incorporated with a filler (such as carbon black, silica, calcium carbonate, and mica) and commonly used additives (such as softener, antioxidant, vulcanization accelerator, and crosslinking agent). After thorough mixing, the resulting rubber compound is cured or semicured into the vulcanized rubber molding under proper conditions. The synthetic resin used for injection molding is usually a thermoplastic resin. It includes, for example, polyamide resin, ABS resin, acetal resin, methacrylic resin, ethylene-vinyl acetate copolymer, fluoroplastics, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polypropylene, polyimide, polystyrene, polysulfone, polyphenylene sulfide, vinyl acetate resin, vinylidene chloride resin, AS resin, and vinyl chloride resin. Preferable among them are polyamide resins, especially those which have amide groups on the main chain structure. Examples of such polyamide resins include nylon-6, nylon-11, nylon-12, nylon-66, nylon-610, and copolymers and blends thereof, with the functional group partly modified or not modified. These polyamide resins may be incorporated with other thermoplastic resins and rubber components for the improvement of their physical properties. They may also be incorporated with a reinforcement (such as glass fiber, carbon fiber, and whiskers) and an inorganic filler (such as calcium carbonate and talc). According to the process of the present invention, a vulcanized rubber molding is disposed in a mold and a molten synthetic resin is injected into the mold. Therefore, the process enables the efficient production of the vulcanised rubber-synthetic resin composite structure. In addition, the vulcanized rubber molding previously undergoes special treatment for the improvement of adhesion properties. Therefore, firm bonding is established between the vulcanized rubber molding and the injected synthetic resin, and the resulting vulcanized rubber-synthetic resin composite structure has an extremely high bond strength. The process of the present invention enables the efficient production of the extremely firmly bonded vulcanized rubber-synthetic resin composite structure at a low production cost and with a high productivity without causing the deterioration and deformation of the synthetic resin by heat history. The process of the present invention will be very effective for the production of plastics rod with rubber bushings for automotive use. The invention will be understood more readily by reference to the following Examples and Comparative Examples; however, these Examples are intended to illustrate the invention and should not be construed as limiting the scope of the invention. Example 1 A vulcanized rubber test piece conforming to ASTM D429 (Method B, for 90° peel test) was prepared from the rubber compound of the formulation shown in Table 1 below. Formulation of Rubber Compound Component parts by weight Natural Rubber 50 SBR 50 Carbon black HAF 30 Zinc oxide 5 Aromatic oil 5 Stearic acid 1 Vulcanization accelerator DM 1 Sulfur 1.5 The surface of the test piece was coated by brushing with an ethyl acetate solution containing 3.5 ± 0.5 wt% of trichloroisocyanuric acid for chlorination treatment. Subsequently, the test piece was coated with an adhesive (about 5-10 µm thick) of the following formulation. Resol-type phenolic-resorcinol resin: 18 wt% (cocondensation product of formaldehyde and a 90:10 (by weight) mixture of phenol and resorcinol) Polyvinyl butyral resin: 2 wt% Filler: 16 wt% Solvent: 64 wt% The vulcanized rubber test piece which had been treated as mentioned above was disposed in a mold. The mold was filled by injection molding with completely dried nylon-66 ("CM-3001M" made by Toray Industries, Inc.). Immediately after demolding, the molding underwent post-heating in an oven at 120°C for 60 minutes. Thus there was obtained a test piece 13 of composite structure in which vulcanized rubber 11 and polyamide resin 12 are integrated as shown in Fig. 3 (plan view) and Fig. 4 (sectional view through section IV-IV of Fig. 3). Incidentally, this test piece 13 has the following dimensions. I₁ = 25.4 mm I₂ = 110 mm I₃ = 55 mm d₁ = 4 mm d₂ = 7 mm The thus obtained test piece 13 of composite structure was tested for adhesion according to ASTM D429, Method B, 90°. The results are shown in Table 2. Example 2 The same procedure as in Example 1 was repeated except that post-heating was not performed after demolding. The test piece was tested for adhesion. The results are shown in Table 2. Comparative Example 1 The same procedure as in Example 2 was repeated except that the vulcanized rubber test piece underwent no adhesive treatment. The test piece was tested for adhesion. The results are shown in Table 2. Comparative Example 2 The same procedure as in Example 2 was repeated except that the vulcanized rubber test piece underwent chlorination treatment but was not coated with the curable adhesive. The test piece was tested for adhesion. The results are shown in Table 2. Comparative Example 3 The same procedure as in Example 1 was repeated except that the vulcanized rubber test piece underwent no chlorination treatment but was coated with the curable adhesive. The test piece was tested for adhesion. The results are shown in Table 2. Comparative Example 4 The same procedure as in Example 1 was repeated except that the vulcanized rubber test piece was coated with a curable adhesive composed mainly of chlorosulfonated polyethylene. The test piece was tested for adhesion. The results are shown in Table 2. Comparative Example 5 A molding of nylon-66 ("CM-3001N" made by Toray Industries, Inc.) and an unvulcanized rubber molding of the rubber compound used in Example 1 were bonded to each other with a curable adhesive ("Chemlok 220/205" made by Lord Corp.) to give a test piece of composite structure as shown in Figs. 3 and 4. The test piece was tested for adhesion. The results are shown in Table 2. It is noted from Table 2 that the process of the present invention enables the easy and efficient production of the vulcanised rubber-synthetic resin composite structure by injection molding. The resulting product has an extremely high adhesion strength between the vulcanised rubber and the synthetic resin which is comparable to that achieved by the conventional cure adhesion method. Example No. Comparative Example No. Items 1 2 1 2 3 4 5 Chlorination treatment yes yes no yes no yes - Adhesive (a) (a) no no (a) (b) (c) Pretreatment before injection (120°C,30 min) no no no no no yes - Post-heating after demolding (120°C,60 min) yes no no no yes yes - Adhesion strength (kg/inch) 40 31 0 13 0 0 38 Peel & failure 100R 90R R/P 60 R/P R/P 95R The present invention aims to solve the problems in the prior art. Accordingly, the preferred embodiment of the present invention aims to provide a process for producing a vulcanized rubber-synthetic resin composite structure in which the vulcanized rubber and the synthetic resin are bonded extremely firmly to each other. The preferred embodiment of the present invention further aims to provide a process for producing a vulcanized rubber-synthetic resin composite structure easily and efficiently at a low production cost and with a high productivity, without causing the degradation and deformation of the synthetic resins by heat history.

Claims: A process for producing a vulcanized rubber-synthetic resin composite structure which comprises chlorinating the surface of the vulcanized rubber molding which comes into contact with the synthetic resin, forming a layer of a curable adhesive on the chlorinated surface of the vulcanized rubber molding, said curable adhesive being composed mainly of resol-type phenolic resin and aldehyde-modified polyvinyl alcohol, disposing the vulcanized rubber molding in a mold, injecting a molten resin into the mold, and demolding the composite structure after the setting of the injected resin. A process according to Claim 1, wherein the resol-type phenolic resin is a cocondensation product of formaldehyde and a phenol-resorcinol mixture. A process according to Claim 2, wherein the phenol-resorcinol mixture contains phenol and resorcinol at a molar ratio of 75:25 to 95:5. A process according to any foregoing Claim, wherein the aldehyde-modified polyvinyl alcohol is polyvinyl formal resin, polyvinyl acetal resin, or polyvinyl butyral resin. A process according to Claim 1, wherein the mixture of resol-type phenolic resin and aldehyde-modified polyvinyl alcohol contains resol-type phenolic resin and aldehyde-modified polyvinyl alcohol in a ratio of 75:25 to 99:1 by weight. A process according to any foregoing Claim, wherein the rubber component of the vulcanized rubber constituting the vulcanized rubber molding is natural rubber or synthetic rubber having a carbon-carbon double bond in the structural formula. A process according to any foregoing Claim wherein the synthetic resin is a polyamide resin.

Inventors: IIZUMI SHINGO, TAKANO KAZUYA, IIZUMI, SHINGO, TAKANO, KAZUYA
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1989
Main classification: C08J7
IPC codes: B32B25, C08J5, B29K21, B29C45, C08J7, B29L9