Paint composition and its use

Abstract: A paint composition for automotive weather strips and glass runs which comprises a curable urethane-based emulsion paint having added to it either at least two silane coupling agents or a reaction product obtained by previously mixing at least two silane coupling agents. The silane coupling agents are a silane coupling agent having an amino group, a silane coupling agent having an epoxy group, a silane coupling agent having a methacryloxy group, or a silane coupling agent having an acryloxy group. Also discloses are processes for producing automotive weather strips.

Description: The present invention relates to a paint composition for automotive weather strips and glass runs. Most automotive weather strips and glass runs (which are hereunder sometimes referred to simply as "automotive weather strips") are coated with curable urethane―based paints on the surface of the substrate to impart it special functions such as wear resistance and slip property (sliding property) or provide it with better appearance. Conventionally, curable urethane-based paints of a solvent type have been used in the manufacture of automotive weather strips; however, with the recent concern over the global environment and the health of working personnel, a need has arisen for a shift toward aqueous and other paints of a non-solvent type. However, water which is the medium for paints of the aqueous type have more latent heat of evaporation than solvents, so the aqueous paints require more heat than paints of the solvent type in order to dry up the water after application. In addition, unlike solvent-type paints that allow adjustment of volatilization temperature and rate by combining several kinds of solvents, aqueous-type paints require preliminary drying in order to prevent "flashing" due to nearly instantaneous volatilization of water. As a result, longer drying times are required by the aqueous paints and in order to deal with this low productivity problem, it becomes necessary to build a new drying oven for shifting from the solvent-type paint to the aqueous type. Most automotive weather strips use substrates that are made of thermosetting elastomers such as EPDM rubber (ethylene propylene rubber) or thermoplastic elastomers such as TPO (thermoplastic polyolefins). If thermoplastic elastomers are used as the substrate, drying should be carried out at a low temperatures of 150 °C or below to prevent thermal deformation that would otherwise occur during post-application drying; however, if the paint applied is of the aqueous type, the drying operation is not highly productive since water is very difficult to dry. The EPDM rubber as an exemplary thermosetting elastomer is nonpolar and has low sticking property and it is also hydrophobic; hence, aqueous paints cannot produce a more adhesive coat than solvent-type paints. With a view to solving this problem, pretreatments such as corona discharge and primer application are conventionally applied to the substrate surface but problems still remain, such as high initial cost and the difficulty involved in performing positive pretreatments on complexly shaped articles. Therefore, an object of the invention is to provide a paint for automotive weather strips that is free from the above-mentioned defects of the prior art and which can achieve strong adhesion to the EPDM rubber without corona discharge, primer application or other pretreatments on the substrate surface while exhibiting high wear resistance. As a result of the extensive studies made in order to attain the above-mentioned object, the present inventors found that the object of the invention could be attained by adding at least two specified silane coupling agents or a product of premixing reaction between said at least two silane coupling agents to a curable urethane- based emulsion paint. Thus, the present invention relates to a paint composition for automotive weather strips comprising a curable urethane-based emulsion paint having added thereto either at least two silane coupling agents selected from the group consisting of a silane coupling agent having an amino group, a silane coupling agent having an epoxy group, a silane coupling agent having a methacryloxy group . and a silane coupling agent having an acryloxy group, or a reaction product obtained by previously mixing said at least two silane coupling agents. Particular embodiments and examples in accordance with this invention will now be described with reference to the accompanying drawing; in which: Fig. 1 is a schematic representation of an abrasion tester according to a method specified by the Japan Society for Promotion of Scientific Research; Fig. 2 is an illustration of a glass run product; Fig. 3 is an illustration of another type of glass run product; and Fig. 4 illustrates how a glass run product is subjected to an abrasion test or a sliding resistance test. The following is the description of a mode for carrying out the invention as it relates to a paint composition for automotive weather strips. The curable urethane-based emulsion paint which is used as the base of the paint composition is a urethane- based emulsion paint which typically uses an isocyanate-, melamine-, epoxy- or carbodiimide-based curing agent. Examples of the silane coupling agent having an amino group include γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane and N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane. Examples of the silane coupling agent having an epoxy group include -γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. Examples of the silane coupling agent having a methacryloxy group include γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropylmethyldiethoxysilafle and 3-acryloxypropylmethoxysilane. At least two of the silane coupling agents listed above or their reaction product is preferably added in an amount of 10 to 40 parts by weight per 100 parts by weight of the involatile content in the base curable urethane- based emulsion paint. In the production of automotive glass runs, if the aqueous paint containing the silicone compound having an amino group is applied to a silane-crosslinkable polyethylene coat, which is then dried and cured in a heating furnace, the water in the aqueous paint and the silicone compound having an amino group which has a catalytic action in the condensation of silane crosslinks by removal of alcohol work together to cause rapid crosslinking and curing of the applied silane-crosslinkable polyethylene coat. The silicone compound having an amino group offers the added advantage of promoting the curing of the as-applied aqueous paint film, thereby increasing its adhension to the EDPM rubber or silane-crosslinkable polyethylene. Preferred examples of the silicone compound having an amino group include aminosilane coupling agents such as γ-aminopropyltrimethoxysilane, γ- aminopropyltriethoxysilane and N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, as well as amino-modified silicone oils. The silicone compound having an amino group is preferably incorporated in amounts ranging from 2 to 15 parts by weight per 100 parts by weight of the involatile content of the aqueous paint.. EXAMPLES The present invention is illustrated in greater detail below with reference to the following Examples, but the invention should not be construed as being limited thereto. EXAMPLES 1 AND 2 AND COMPARATIVE EXAMPLE 1 The data in Table 1 demonstrates the advantages of the paint composition according to the invention. Two samples of a curable urethane polymer were mixed with two silane coupling agents to prepare two paint compositions, which were tested for adhesion, wear resistance and dynamic friction coefficient. The results are shown in Table 1 together with those of a comparative paint composition. Ex.1 Ex.2 Comp. Ex.1 Amount (parts by wt.) Curable urethane polymer 100.0 100.0 100.0 Silane A 8.0 8.0 8.0 Silane B 8.0 - - Silane C - 8.0 8.0 Adhesion (N/cm) 7.0 7.0 4.0 Wear resistance (cycles) 1 30,000 20,000 10,000 Dynamic friction coefficient (µK) ≤ 0.1 ≤ 0.1 0.2 Silane coupling agent A: γ-glycidoxypropyltrimethoxysilane (KBM-403 of Shin-Etsu Chemical Co. , Ltd.; TSL 8350 of GE Toshiba Silicone; SH-6040 of Toray Dow Silicone) Silane coupling agent B: 3-acryloxypropyltrimethoxysilane (KBM-5103 of Shin-Etsu Chemical Co., Ltd.) Silane coupling agent C: γ-aminopropyltrimethoxysilane (KBM-903 of Shin-Etsu Chemical Co. , Ltd. ; TSL 8330 of GE Toshiba Silicone) 1) Wear resistance: The coated surface was rubbed with a glass plate (see Fig. 1) until the substrate became exposed. The wear resistance of the sample was evaluated in terms of the number of cycles the glass plate was reciprocated before the substrate showed. As described on the foregoing pages, the paint composition for automotive weather strips according to the present invention can achieve strong adhesion to the EPDM rubber without corona discharge, primer application or other pretreatments on the substrate surface while exhibiting high wear resistance.

Claims: A non-solvent type paint composition for automotive weather strips and glass runs which comprises a curable urethane-based emulsion paint having added thereto either at least two silane coupling agents, or a reaction product obtained by previously mixing at least two silane coupling agents; the silane coupling agents comprising, a silane coupling agent having an amino group, a silane coupling agent having an epoxy group, a silane coupling agent having a methacryloxy group, or a silane coupling agent having an acryloxy group.

Inventors: MATSUMOTO KEIGO, SATO NOBUMASA, TOMOHIRO SEI, MATSUMOTO, KEIGO, SATO, NOBUMASA, TOMOHIRO, SEI, Matsumoto, Keigo, c/o Nishikawa Rubber Co. Ltd., Sato, Nobumasa, c/o Nishikawa Rubber Co. Ltd., Tomohiro, Sei, c/o Nishikawa Rubber Co. Ltd.
Applicants: NISHIKAWA RUBBER CO LTD, NISHIKAWA RUBBER CO., LTD.
Application year: 2001
Main classification: C08K5
IPC codes: C09D5, B05D7, B60J10, C08G18, C09D183, C08J7, C08K5, C09D175