Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
2001-01-19
2002-11-26
Yoon, Tae H. (Department: 1714)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C428S483000, C525S374000
Reexamination Certificate
active
06485837
ABSTRACT:
This invention relates to a coating composition and, more particularly, to a coating composition suitable for providing polyolefin formed products, such as polyolefin sheets, with a uniform, matte coating which exhibits good adhesion to the products, good abrasion resistance, and good chemical resistance. The invention relates also to polyolefin products coated with such coating composition.
BACKGROUND OF THE INVENTION
Soft polyvinyl chloride is frequently used for sheets, from which, for example, interior furniture of automobiles is formed. However, soft polyvinyl chloride products are disadvantageously subject to discoloration and tend to become brittle due to a large amount of plasticizer used therein for providing softness to the products.
Recently, polyolefin, e.g. olefin thermoplastic elastomer, is frequently used in place of soft polyvinyl chloride because polyolefin itself is soft and, therefore, need not be softened by use of any plasticizer. In addition, polyolefin has a smaller specific gravity than soft polyvinyl chloride, which makes it possible to provide lighter products than soft polyvinyl chloride. Furthermore, polyolefin is recyclable.
An olefin thermoplastic elastomer used for forming, for example, interior furniture of automobiles, includes an ethylene-propylene copolymer, or an ethylene-propylene-diene terpolymer consisting of an ethylene-propylene copolymer and a third component having a partial bridge structure, with an antistatic agent, a thermostabilizer, an ultraviolet absorbing agent, a pigment etc. added to it.
Generally, it is difficult to apply a coating over the surface of a product of such olefin thermoplastic elastomer, and if a coating can be provided, the coating will have poor physical properties, such as poor adhesion and poor abrasion resistance. This is because the surface of polyolefin products is inactive.
In prior art, polyolefin products are provided with a coating by first activating the surface of a product with corona discharge, then, coating the activated surface with a chlorinated polyolefin primer or a two-pack curing primer including, for example, polyester and polyisocyanate, or polyurethane and polyisocyanate, and finally providing a top coating. Such a method is disclosed in Japanese Unexamined Patent Publication Nos. SHO 63-272547 A, HEI 7-247381 A and HEI 7-247382 A.
Recently, people tend toward higher class interior furniture for automobiles, and, therefore, furniture formed simply of olefin thermoplastic elastomer is hardly seen. For example, trim panels for automobiles are frequently formed of polyolefin sheet over which fabric or the like is bonded by an adhesive. Accordingly, surface treatment of polyolefin products must provide products with resistance against solvent in the adhesive used to bond fabric to polyolefin products and creep resistance against temperature within automobiles.
Accordingly, two-pack curing type coating compositions composed of polyester and polyisocyanate or polyurethane and polyisocyanate are used in many cases. However, recently, the use of polyisocyanate curing agents has raised problems in human health and safety. Further, two-pack curing type coating compositions in which polyisocyanate is used as a curing agent have a disadvantageously short pot life because the polyisocyanate curing agent, when it is mixed, increases the viscosity of the coating compositions.
SUMMARY OF THE INVENTION
According to the present invention, a coating composition for treating the surface of a polyolefin resin product is provided. The coating composition includes a curing agent of polycarbodiimide compound. The use of polycarbodiimide compound as the curing agent can solve the above-discussed various problems, and can provide a matte, uniform coating which exhibits good adhesion to a polyolefin product, good heat resistance, and good solvent resistance.
The coating composition according to the present invention is composed of 100 parts by weight in solid content of polymer solution or water dispersion essentially consisting of a polyurethane resin or a polyester resin, and from 2 to 100 parts by weight of a polycarbodiimide compound. The polymer solution or water dispersion is referred sometimes to as main component.
The polyurethane or polyester resin may contain a carboxyl group in an amount not greater than unity (1) in terms of acid value.
According to the present invention, a polyolefin product, e.g. a polyolefin sheet is coated with the coating composition with or without a carboxyl group.
A polyolefin product may be coated with primary and secondary coatings. The primary coating is formed by applying the above-described coating composition with or without a carboxyl group, over the surface of the product, and the secondary coating is formed by applying a polyurethane solution over the primary coating.
The polyurethane resin in the secondary coating may also contain carboxyl group.
Before applying the coating composition, the surface of the polyolefin product to be coated is preferably treated with corona discharge, which increases adhesion of the coating to the product surface.
The polycarbodiimide compound used as a curing agent in the present invention is a compound which includes a highly reactive carbodiimide group expressed as —N═C═N— in its main chain. The carbodiimide group reacts with an active hydrogen group, e.g. a carboxyl group, an amino group or an hydroxyl group, to thereby provide a cross-linked structure. In particular, the polycarbodiimide compound can react with the carboxyl group at normal temperature. When a polyurethane or polyester resin containing no carboxyl group is used for the main component of the coating composition, the adhesion of the resulting coating to a polyolefin product can be provided by treating the polyolefin product with corona discharge prior to the application of the coating composition. By corona discharge, an active group, e.g. a hydroxyl group or a carboxyl group, may be produced on the surface of the polyolefin product. The carbodiimide group in the polycarbodiimide compound in the coating composition reacts with such hydroxyl group or carboxyl group or with an amino group or a hydroxyl group or water in the main component, which makes the resulting coating adhere to the surface of the polyolefin product. The coating composition composed of the main component with no carboxyl group and a polycarbodiimide compound has no pot life problem.
On the other hand, by introducing a carboxyl group into the above-described main component of the coating composition, or by using a polyurethane or polyester resin having a carboxyl group, the polyurethane or polyester resin can rapidly crosslink with the carbodiimide group. This results in a coating having good solvent resistance and good abrasion resistance. However, the resulting coating composition with a carboxyl group is more or less unstable and short in pot life.
Knowing this-fact, the inventors have found that the amount of the carboxyl group in the. main component is preferably not greater than unity (1) in terms of acid value. A coating composition composed of the main component containing a carboxyl group in this: amount and a polycarbodiimide compound is applied over the surface of a polyolefin product to form a coating. Further, this coating may be used as a primary coating, over which a secondary coating of polyurethane is disposed. The polycarbodiimide compound in the primary coating moves into the secondary coating and reacts with a carboxyl group in the secondary coating. The resulting composite coating exhibits not only good adhesion to the polyolefin product but also good solvent resistance and good abrasion resistance.
A polycarbodiimide compound commercially available from Nisshinbo Industries, Inc., Japan or from Union Carbide, Inc., U.S.A. may be used as the polycarbodiimide compound in the present invention. As for the amount of the polycarbodiimide compound, when the polycarbodiimide resin in an amount of less than 2 parts by weight to 100 parts by weight of the main component in solid
Shimizu Hidenori
Uebayashi Mitsugi
Morris LLP Duane
Seikoh Chemicals Company, Limited
Yoon Tae H.
LandOfFree
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