Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-06-24
2004-08-24
Tucker, Philip (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S412000, C525S174000, C525S177000
Reexamination Certificate
active
06780902
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aqueous coating composition, in particular a novel aqueous coating composition free of the problems of environmental hormones and suitable for coating the inner surfaces of cans.
BACKGROUND OF THE INVENTION
In order to solve the problem of global environmental pollution caused by the evaporation of organic solvents, aqueous coating compositions have been replacing organic solvent-based coating compositions in the field of coating compositions for the inner surfaces of cans such as food cans. Japanese Examined Patent Publication No. 1988-41934 and Japanese Unexamined Patent Publication No. 1995-138523 propose, as the aqueous coating compositions, compositions comprising an epoxy-modified acrylic resin prepared by reacting or mixing an epoxy resin with a carboxyl-containing acrylic resin.
In these known aqueous coating compositions, a high-molecular-weight epoxy resin obtained by reacting a low-molecular-weight epoxy resin with bisphenol A is generally used as the starting epoxy resin, in order to achieve good application workability and high film performance. As a result, unreacted bisphenol A remains in the compositions and causes the problem of environmental hormones. However, if a low-molecular-weight epoxy resin in which no bisphenols are detected is used as the starting epoxy resin to avoid the problem, the resulting aqueous coating composition is poor in application workability and film performance characteristics such as adhesion to substrates, flavor protecting properties, etc., and thus is unsuitable as a coating composition for the inner surfaces of cans.
Therefore, no fundamental solution has been proposed so far to avoid the problem of environmental hormones caused by bisphenols in aqueous coating compositions comprising an epoxy-modified acrylic resin.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a novel aqueous coating composition free of the problems of the prior art.
Another object of the invention is to provide a novel aqueous coating composition which is free of the problem of environmental hormones caused by bisphenols while having good application workability and high film performance.
Other objects and features of the invention will be apparent from the following description.
The present invention provides an aqueous coating composition comprising a carboxyl-containing, acrylic-modified polyester resin (B) neutralized and dispersed in an aqueous medium, the polyester resin (B) being obtainable by reacting a carboxyl-containing acrylic resin (c) and an epoxy-modified polyester resin (A) prepared by esterification of a carboxyl-containing polyester resin (a) having a number average molecular weight of 1,000 to 30,000 and an acid value of 5 to 200 mg KOH/g with a 1,2-epoxy-containing low-molecular-weight epoxy compound (b) having a number average molecular weight of 1,200 or less.
The inventors carried out extensive research to develop an aqueous coating composition which is free of the problem of environmental hormones caused by bisphenols and which is suitable for coating the inner surfaces of cans. As a result, the inventors found that when an aqueous coating composition is prepared by neutralizing and dispersing a resin obtained by sequentially reacting a specific carboxyl-containing polyester resin, a specific low-molecular-weight epoxy compound in which no bisphenols are detected, and a carboxyl-containing acrylic resin as starting materials, the aqueous coating composition contains no free bisphenols and is capable of achieving the same application workability and film performance as attained by known aqueous coating compositions comprising an epoxy-modified acrylic resin. The present invention has been accomplished based on these new findings.
The epoxy-modified polyester resin (A) in the aqueous coating composition of the invention is prepared by esterification of a carboxyl-containing polyester resin (a) having a number average molecular weight of 1,000 to 30,000 and an acid value of 5 to 200 mg KOH/g, and a 1,2-epoxy-containing low-molecular-weight epoxy compound (b) having a number average molecular weight of 1,200 or less.
It is essential that the carboxyl-containing polyester resin (a) have a number average molecular weight of 1,000 to 30,000, and an acid value of 5 to 200 mg KOH/g. If the number average molecular weight is less than 1,000 or the acid value exceeds 200 mg KOH/g, side reactions are likely to occur at the time of addition reaction of the carboxyl group and the epoxy group of the epoxy compound (b), increasing the viscosity of the resulting resin (A) and thereby making the production of the composition difficult. On the other hand, a number average molecular weight exceeding 30,000 or an acid value less than 5 mg KOH/g makes it difficult to disperse the polyester resin (B) in an aqueous medium in the following step. Thus, molecular weights and acid values outside the above-specified range are undesirable.
Preferably, the carboxyl-containing polyester resin (a) has a number average molecular weight of 2,000 to 10,000, and an acid value of about 20 to 150 mg KOH/g.
The polyester resin (a) is prepared by polycondensation of a polyhydric alcohol with a polybasic acid. Polyhydric alcohols are polyols such as alkane polyols, oxyalkylene polyols, polyoxyalkylene polyols, alicyclic polyols and the like. Typical examples of polyhydric alcohols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, neopentyl glycol, glycerin, 2-methylglycerin, trimethylolpropane, trimethylolethane, pentaerythritol and like alkane polyols; diethylene glycol, dipropylene glycol and like oxyalkylene polyols; triethylene glycol, tetraethylene glycol, polyethylene glycol, tripropylene glycol, polypropylene glycol and like polyoxyalkylene polyols; 1,4-cyclohexane dimethanol and like alicyclic polyols; etc. Examples of polybasic acids include adipic acid, sebacic acid, glutaric acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, succinic acid, pimelic acid, azelaic acid, dodecanedioic acid, cyclohexanedicarboxylic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, endomethylene-tetrahydrophthalic acid, methylendomethylene-tetrahydrophthalic acid, hexahydrophthalic acid, naphthalenedicarboxylic acid, trimellitic acid, butanetricarboxylic acid, anhydrides of these acids, and the like.
In the polycondensastion of a polyhydric alcohol with a polybasic acid, a strong protonic acid, a heavy metal oxide or the like can be used as a polycondensation catalyst. Examples of strong protonic acids include sulfuric acid, benzenesulfonic acid, p-toluenesulfonic acid and the like. Examples of heavy metal oxides include tetrabutyl titanate, dibutyltin oxide, antimony trioxide, manganese dioxide and the like.
The polyester resin (a) can be prepared by subjecting a polyhydric alcohol and a polybasic acid to condensation so as to introduce carboxyl groups into the resin molecule and thereby impart the specific acid value required for the invention. Alternatively, the resin (a) may be obtained by first preparing a hydroxyl-containing polyester resin, followed by addition of an acid anhydride to the hydroxyl groups to impart the specific acid value. Examples of the acid anhydrides include phthalic anhydride, trimellitic anhydride, succinic anhydride, maleic anhydride, hexahydrophthalic anhydride, pyromellitic anhydride and the like.
It is essential that the 1,2-epoxy-containing low-molecular-weight epoxy compound (b) have a number average molecular weight of 1,200 or less. The low-molecular-weight epoxy compound, in which no unreacted bisphenols are detected, is used to modify the carboxyl-containing polyester resin (a). As a result, an aqueous coating composition can be obtained which contains no free bisphenols while having good application workability and high film performance. Therefore, the obtained aqueous coating compo
Hirose Yuji
Nakai Noboru
Nishida Reiziro
Numa Nobushige
Aylward D.
Kansai Paint Co. Ltd.
Tucker Philip
LandOfFree
Water-based coating composition does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Water-based coating composition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Water-based coating composition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3316099