Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2001-03-27
2003-09-30
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C523S406000, C523S409000, C525S329500, C525S329700, C525S379000
Reexamination Certificate
active
06627316
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to resin compositions for use in water borne coatings and a water borne coating composition comprising such resin compositions which is particularly suitable for coating the external surface of cans, and provides a coating having superior smoothness and gloss, as well as superior adhesion, film hardness, resistance to yellowing, and ease of fabrication. The present invention also relates to a method of coating film formation with the use of this water borne coating composition.
Cans, and those made from metal and alloys thereof, can be used as vessels containing various food and drink products. The external surface of such metal cans can be coated with white paints, which can be printed on with ink of a different color, and then finished by clear coating the ink imprinted white paint to prevent corrosion and protect the underlying coating, which can include product information as well as ingredient lists and trademarks or other sales related printing.
Previously, organic solvent solutions having acryl/amino resin, polyester/amino resin, or a resin system obtained by addition of epoxide resin to these resins were used as coating compositions for this kind of painting on cans. However, these coating compositions require a large quantity of solvent, resulting in vaporization when baking the coating film, an important factor of air pollution. More recently, water borne coating compositions for coating the external surface of cans were developed.
Examples of well-known water-borne vinyl polymer coatings include a resin emulsion-type coating having a polymer synthesized from monomer constituent by emulsion polymerization method using a surfactant, and a coating having a resin solubilized or emulsified by neutralization of carboxyl groups introduced in a resin.
The emulsion-type resin coating contains a surfactant. There is the problem that a coating film obtained after baking becomes inferior in water resistance because the surfactant remains in the coating film. In addition, the low coating viscosity peculiar to emulsion type resins makes the coating film difficult to apply.
Similarly, in coatings having a resin solubilized or emulsified by neutralization of carboxyl groups, there is the problem that there are a limited amount of carboxyl groups that can be introduced in the resin while still providing a water resistant coating, because the carboxyl groups can be neutralized with a suitable volatile base chemical agent, and are thus changed into being water-soluble. Accordingly, the use of considerable quantities of organic solvent becomes necessary in order to provide a stable coating, and thus it is difficult to achieve a low content of organic solvent in the coating composition.
It is important for coatings for the external surface of cans to be easy to fabricate and apply. The resulting coating should exhibit superior scratch resistance, yellowing resistance, and retort resistance. Attempts have been made to utilize a copolymer resin as a base resin, providing a coating film having the above properties, but they have been unsatisfactory. For example, Japanese Patent Laid-Open No. 239404/1993 discloses a water-borne coating composition including, as a resin composition, 20-80 parts by weight of a water-soluble acrylic resin, 20-50 parts by weight of a water-soluble amino resin and 5-30 parts by weight of an amine-modified epoxy resin which is obtained by adding an amine to epoxy compounds. However, this composition fails to provide the above qualities, and exhibits the following deficiencies: cloudiness, and isolation of components in preparing a coating composition when the coating has a low organic solvent content added into this composition.
SUMMARY OF THE INVENTION
The present invention provides a resin composition and a water-borne coating composition comprising the resin composition which can solve the above problems, while providing the above desired properties, achieving a good balance of coating film properties including appearance, adhesion, fabricability, hardness, yellowing resistance and retort resistance, in addition to good coatability, and low content of organic solvent in a coating composition.
The present invention provides a resin composition for use in a water-borne coating composition, as well as a method for forming a coating film including coating the water-borne coating composition.
The present invention provides a resin composition, which is the quaternary salt-formation reaction product, in the presence of a tertiary amine, of (a) about from 50 to 90 parts by weight of a copolymer having an acid value of about from 20 to 160 mgKOH/g and (b) about from 10 to 50 parts by weight of an amine-modified epoxide resin. The invention also provides a resin composition wherein the amine-modified epoxide resin (b) is an addition reaction product of a primary or secondary amine and an epoxy resin having an epoxy equivalent of about from 150 to 1,200. In addition, the present invention provides a resin composition wherein the copolymer (a) is the copolymerization product of at least one &agr;, &bgr;-ethylenically unsaturated carboxylic acid and at least one radically polymerizable unsaturated monomer, the unsaturated monomer being copolymerizable with the at least one unsaturated carboxylic acid.
The present invention also comprises a water-borne coating composition comprising (A) a resin composition of Claim
1
and (B) at least one amino resin, both being dissolved or dispersed in a stable aqueous medium.
Furthermore, the present invention provides a method for forming a coating film including coating the water-borne coating composition onto an external surface of a can, and a coated substrate, such as a can.
DETAILED DESCRIPTION OF THE INVENTION
Although specific embodiments of the present invention are described in detail herein, it is to be expressly understood that the invention is not limited thereto. The following detailed description of the various preferred embodiments is provided for example only and should not be construed as constituting any limitation of the invention. Modifications will be obvious to those skilled in the art, and all modifications that do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.
The resin composition of the present invention is a resin composition that can be obtained by quaternary salt-formation reaction of the following copolymer (a) and an amine-modified epoxide resin (b) in the presence of a tertiary amine.
Copolymer (a)
Copolymer (a) in the present invention is essentially based on &agr;, &bgr;-ethylenically unsaturated carboxylic acid as monomer constituents. The unsaturated carboxylic acid should be present in about from 2.5 to 20% by weight, preferably about from 5 to 15% by weight of the copolymer (a).
The unsaturated carboxylic acid described above can include, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid.
In copolymer (a), the quantity of copolymerization of &agr;, &bgr;-ethylenically unsaturated carboxylic acid should be sufficient to obtain a resulting copolymer (a) having an acid value of about from 20 to 160 mg KOH/g, preferably about from 40 to 120 mg KOH/g. When the acid value of copolymer (a) is less than 20 mg KOH/g, the quaternary salt-formation reaction with amine-modified epoxide resin is difficult to initiate and advance. Such a low acid value also makes it difficult to make the copolymer (a) water-borne, and diminishes the curability of the resulting coating film. When the acid value of copolymer (a) exceeds 160 mgKOH/g, water resistance, retort resistance and fabricability of the resulting coating film suffer.
Copolymer (a) should have a number average molecular weight of about from 8,000 to 25,000, preferably about from 10,000 to 20,000.
Representative examples of radically polymerizable unsaturated monomers copolymerizable with &agr;, &bgr;-ethylenically unsaturated carboxylic acid can include C 1-24 alkyl (meth)acrylate such as methyl (
Iwamoto Tohru
Matsuki Hiroyasu
Nishida Reijirou
Shioda Atsushi
Aylward D.
Dawson Robert
Huntley & Associates
Kansai Paint Co. Ltd.
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