Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-10-17
2003-06-10
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S406000, C523S407000, C523S412000, C525S327400, C525S329700, C525S533000
Reexamination Certificate
active
06576689
ABSTRACT:
This application has priority benefit of Japanese Patent Application No. 00/320113, filed on Oct. 20, 2000.
BACKGROUND ART
(1) Field of the Invention
The present invention relates to a water based coating composition, a water based coating composition useful for coating the internal surface of a food can, and particularly a water based coating composition capable of forming a coating film showing a controlled eluation of bisphenol A.
(2) Description of Background Art
Recently, a water based coating composition is widely used in the art as a coating composition to be applied onto the internal surface of a can from the standpoints of working hygiene, environmental conservation and safety to fire. The water based coating composition applied onto the internal surface of the can may include ones containing mainly an esterification reaction product between an epoxy resin and a carboxyl group-containing acrylic resin as a resin component as disclosed, for example, in Japanese Patent Publication No. 41934/88 (U.S. Pat. No. 4,585,813 and U.S. Pat. No. 4,482,673) and Japanese Patent Publication No. 37026/84 (U.S. Pat. No. 4,458,040), Japanese Patent Application Laid-Open No. 329974/94, etc.
However, the above water based coating compositions use, AS A STARTING EPOXY RESIN, a high molecular weight epoxy resin obtained by reacting a low molecular weight epoxy resin with bisphenol A, resulting in that an unreacted bisphenol A remains in the coating composition. Recently, the bisphenol A causes troubles as an exogenous endcrine-disturbing chemical substance or an environmental hormone. Therefore, such a water based coating composition as to be free of bisphenol A remaining therein and as not to cause eluation of bisphenol A from a resulting coating film has been demanded. In connection therewith, the use of a bisphenols-undetected low molecular weight epoxy resin only as a starting epoxy resin may result a water based coating composition may form a coating film reduced in coating film performances such as coating workability, adhesion properties to a substrate, flavor properties and the like so as to be unsuitable as the coating composition applied onto the internal surface of the can. On the other hand, attempts to use an epoxy resin prepared by extracting and removing low molecular weight components including unreacted bisphenol A from the above high molecular weight epoxy resin as a starting epoxy resin have been made with the result that a satisfactory contact of the eluation of bisphenol A from the coating film has not been achieved.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a water based coating composition capable of forming a coating film not eluating bisphenol A therefrom without reducing coating film performances demanded on the coating film applied onto the internal surface of the can, for example, coating workability, adhesion properties, retorting resistant properties, mar resistance properties, hygienical properties, flavor properties and the like.
The present inventors made intensive studies to solve the above problems and percieved that the bisphenol A produced by thermal decomposition of the epoxy resin as a heat curing temperature of the coating film is increased may eluate from the coating film, resulting in finding out that a specified amount of the quaternary ammonium salt in the acrylic-modified epoxy resin makes it possible to form a coating film free of eluation of bisphenol A without reducing performances required for the coating film to complete the present invention.
That is, the present invention provides a water based coating composition prepared by reacting an epoxy resin (A) having a bisphenol A skeletal structure and a carboxyl group-containing acrylic resin in the presence of an amine compound to form an acrylic-modified epoxy resin (C), and neutralizing, and dispersing the acrylic-modified epoxy resin (C) into an aqueous medium, an amount of a quaternary ammonium salt in the acrylic-modified epoxy resin being in the range of 3.0×10
−4
mol or less per one gram of the resin (hereinafter may be referred to simply as 3.0×10
−4
mol/g or less).
DETAILED DESCRIPTION OF THE INVENTION
Epoxy Resin (A)
In the composition of the present invention, the epoxy resin (A) used in the preparation of the acrylic-modified epoxy resin is an epoxy resin having a bisphenol A skeletal structure, and may include the following bisphenol A based epoxy resin (a), a composite bisphenol based epoxy resin (b) having a bisphenol A skeletal structure and bisphenol F skeletal structure in one molecule, and mixture of the above (a) and (b).
Bisphenol A Based Epoxy Resin (a)
The bisphenol A based epoxy resin (a) may preferably include ones having a number average molecular weight in the range of 4,000 to 30,000, preferably 5,000 to 30,000, and an epoxy equivalent in the range of 2,000 to 10,000, preferably 2,500 to 10,000 from the standpoints of disversion stability in the aqueous medium, fabrication properties, hygienical properties and the like of the resulting coating film.
The bisphenol A based epoxy resin (a) may be prepared by one step polymerization method between bisphenol A and epichlorohydrin, or by two step polymerization method comprising adding bisphenol A to a bisphenol A based epoxy resin having a relatively low epoxy equivalent.
The relatively low epoxy equivalent bisphenol A based epoxy resin may include ones having an epoxy equivalent in the range of about 160 to about 2,000, and may include commercially available epoxy resins, for example, Epikote 828EL, Epikote 1001, Epikote 1004 and Epikote 1007 (trade names, marketed by Japan Epoxy Resin Co., Ltd. respectively); Araldite AER 250, Araldite AER 260, Araldite AER 6071, Araldite AER 6004 and Araldite AER 6007 (trade names, marketed by Asahi Kasei Epoxy Co., Ltd. respectively); Epomik R140, Epomik R301, Epomik E304 and Epomik R307 (trade names, marketed by Mitsui Chemicals, respectively); Adekaresin EP-4100 and Adekaresin EP-5100 (trade names, marketed by Asahi Denka Kogyo K.K., respectively); and the like.
The bisphenol A based epoxy resin (a) in the present invention may include commercially available ones such as Epikote 1010, Epikote 1256B40, Epikote 1256 (trade names, marketed by Japan Epoxy Resin Co., Ltd. respectively), and the like. The bisphenol A based epoxy resin (a) may also include a modified bisphenol A based epoxy resin prepared by modifying the bisphenol A based epoxy resin with a dibasic acid. The bisphenol A based epoxy resin to be reacted with the dibasic acid may preferably include ones having a number average molecular weight in the range of 2,000 to 8,000 and an epoxy equivalent in the range of 1,000 to 4,000. The dibasic acid may include a compound represented by the general formula: HOOC—(CH
2
)
n
—COOH where n is an integer of 1 to 12, specifically succinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, dodecane diaid, hexahydrophthalic acid and the like, particularly adipic acid is preferable.
The modified bisphenol A based epoxy resin may be prepared by reacting a mixture of the bisphenol A based epoxy resin with the disbasic acid in the presence of an esterifying catalyst such as tri-n-butylamine and an organic solvent at a reaction temperature of 120 to 180° C. for about 1 to 4 hours.
The modified bisphenol A based epoxy resin is such that the dibasic acid molecular chain acts as a plasticizing component and improve adhesion properties, resulting in that use of the modified epoxy resin as the bisphenol A based epoxy resin (a) is advantageous in improving fabricating properties and corrosion resistance of the resulting coating film.
Composite Bisphenol Based Epoxy Resin (b)
The composite bisphenol based epoxy resin (b) is a bisphenol based epoxy resin having a bisphenol A skeletal structure and a bisphenol F skeletal structure in one molecule. In the present specification, the bisphenol A skeletal structure is represented by the following chemical formula (1), and the bisphenol F skeletal structure is represented by the fol
Asakura Makoto
Murase Masaki
Nishida Reijiro
Noda Sumio
Aylward D.
Dawson Robert
Fisher Christen & Sabol
Kansai Paint Co. Ltd.
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