Process using a paint composition for automotive weather strips

Abstract: A process for producing an automotive weather strip. The process comprises the steps of applying a urethane-based aqueous paint onto a semi-finished product of an automotive weather strip; drying and curing the paint-applied product in a heating furnace; and applying a silicone compound having an amino group onto the semi-finished product. This process does not require complete curing of the as-applied aqueous paint in the drying step but allows complete curing by the heat inertia of the drying step, enabling shorter drying times or lower drying temperatures to be employed.

Description: The present invention relates to a processes for producing automotive weather strips. Most 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 process for producing automotive weather strips which does not require the as-applied coat to be cured completely in a drying oven but which permits it to be cured completely by the heat inertia of the drying step and which can also shorten the length of the drying oven or lower the drying temperature. The object of the invention can be attained by a process for producing automotive weather strips which comprises the steps of extruding a semi-finished product of automotive weather strip while it is continuously coated with a urethane-based aqueous paint, then drying and curing the product in a heating furnace, or comprises extruding a semi-finished product of automotive weather strip, heating it, immediately followed by continuous application of a urethane-based aqueous paint, then drying and curing the product in a heating furnace, or comprises unrolling a semi-finished extruded product of automotive weather strip while it is continuously coated with a urethane-based aqueous paint, then drying and curing the extruded product in a heating furnace, wherein a silicone compound having an amino group is applied to the coated surface of the semi-finished product or extruded product after it leaves the heating furnace, or wherein a silicone compound having an amino group is incorporated in the urethane-based aqueous paint. 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. 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 y-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-methacryloxypropylmethyldiethoxysilane 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. The following is the description of a mode for carrying out the invention as it relates to a process for producing automotive weather strips. The substrate of automotive weather strips is not limited in any particular way but thermoplastic elastomers are preferably used. The urethane-based aqueous paint may be a urethane-based emulsion paint which typically uses an isocyanate-, melamine-, epoxy- or carbodiimide-based curing agent. 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. If the silicone compounds having an amino group is to be applied to the coated surface of the substrate as it emerges from the drying oven, it may be diluted with water. The application method is in no way limited and spraying and brushing may be mentioned as typical examples. 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 EXAMPLES 1 AND 2 The data in Table 1 demonstrates the advantages of the process for producing an automotive weather strip according to the invention. Extruded, heated and later cooled automotive weather strips were coated with two samples of urethane-based aqueous paint containing γ-aminopropyltrimethoxysilane as a silicone compound having an amino group, thereby preparing weather strip products, which were tested for wear resistance. The results are shown in Table 1 together with those of two comparative products. Ex. 1 Ex. 2 Comp. 1 Comp. 2 Treatment with silicon compound yes yes no no Drying/curing conditions 200°C x 10 min 80°C x 10 min 200°C x 10 min 80°C x 10 min Wear resistance (cycles) EPDM rubber 20,000 20,000 10,000 5,000 TPO 5,000 5,000 2,000 100 The processes for producing automotive weather strips according to the present invention do not require the as-applied coat to be cured completely in a drying oven but they permit it to be cured completely by the heat inertia of the drying step and they can also shorten the length of the drying oven or lower the drying temperature. The improvement in productivity is particularly noticeable if thermoplastic elastomers such as TPO are used as the substrate of automotive weather strips.

Claims: A process for producing an automotive weather strip, comprising: applying a urethane-based aqueous paint onto a semi-finished product of an automotive weather strip; drying and curing the paint-applied product in a heating furnace; and applying a silicone compound having an amino group onto the semi-finished product. The process according to claim 1, wherein said silicone compound is applied onto the urethane-based aqueous paint surface after said drying step. The process according to claim 1 or 2, wherein said automotive weather strip has a substrate comprising a thermoplastic elastomer. The process according to any one of the preceding claims, wherein said silicone compound having an amino group is contained in said urethane-based aqueous paint.

Inventors: MATSUMOTO KEOGO, SATO NOBUMASA, TOMOHIRO SEI, MATSUMOTO, KEOGO, SATO, NOBUMASA, TOMOHIRO, SEI, Matsumoto, Keogo, Nishikawa Rubber Co. Ltd., Sato, Nobumasa, Nishikawa Rubber Co. Ltd., Tomohiro, Sei, Nishikawa Rubber Co. Ltd.
Applicants: NISHIKAWA RUBBER CO LTD, NISHIKAWA RUBBER CO., LTD.
Application year: 2001
Main classification: C08K5
IPC codes: C09D175, C08G18, C08K5