Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-06-19
2003-03-25
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C523S201000, C523S335000, C525S376000, C528S363000
Reexamination Certificate
active
06538062
ABSTRACT:
The present invention relates to a room temperature curable resin composition for an aqueous paint, which contains substantially no volatile organic compound (hereinafter referred to as “VOC”) and which, while having a low minimum film-forming temperature (hereinafter referred to as “MFT), forms a film having an excellent anti-blocking property and being excellent in various physical properties such as water resistance, smoothness and weather resistance.
In recent years, environmental regulations have become stricter with regard to reduction of toxicity and VOC, and also from the viewpoint of saving resources, it is demanded to use water in place of an organic solvent as a solvent for a paint in the field of paint industry. As a typical paint, an aqueous emulsion paint may be mentioned which employs an aqueous emulsion resin as a binder.
However, the aqueous emulsion resin has a specific MFT, and when the temperature of the surface to be coated was lower than MFT, it was necessary to blend an organic solvent as a coalescing agent for film-formation.
On the other hand, in order to prevent blocking which is likely to occur when coated plates are piled, it is necessary to use a resin of high hardness as a binder. However, a composition employing a resin of high hardness has a high MFT, and it is again necessary to blend a coalescing agent in a large amount. Thus, even an aqueous emulsion paint contained a substantial amount of VOC, and when drying of the coated film was inadequate, there was a problem that the anti-blocking property or water resistance tended to be poor due to the remaining VOC.
Further, with respect to an aqueous emulsion paint, a study has been made on a paint having both properties of a low temperature film-forming property and an anti-blocking property. As a result, as shown in JP-A-2-175742, JP-A-7-26196, JP-A-11-349828, etc., a paint having a good anti-blocking property has been developed which comprises an emulsion resin having carbonyl groups, having a relatively low MFT, and a compound having hydrazide groups, wherein particles are crosslinked to one another to improve the anti-blocking property. However, there has been a problem that, although a certain level of an anti-blocking property can be obtained only by such crosslinking of particles, the anti-blocking property is inadequate under severe conditions.
The present invention has been made in view of such problems of the prior art, and it is an object of the present invention to provide a resin composition for an aqueous paint which is excellent in the low temperature film-forming property and which forms a coating film excellent in the anti-blocking property and in the water resistance, smoothness, weather resistance, etc., without using VOC such as coalescing agent which is likely to cause environmental pollution or bad odor, or by an addition of a small amount of VOC, if used.
In order to accomplish the above object, the present inventors have conducted an extensive study and as a result, they have found it possible to certainly accomplish the above object by the following construction and have arrived at the present invention.
Namely, the present invention provides a resin composition for an aqueous paint, which comprises (a) a binder composed of different phase structure emulsion particles obtained by multi-stage emulsion polymerization, and (b) a compound having at least two hydrazide groups in its molecule, wherein the different phase structure emulsion particles have an outermost phase formed of an emulsion polymer which is an emulsion polymer of an ethylenic unsaturated monomer, having a glass transition temperature of from −50° C. to 15° C., and the following conditions (1) to (3) are satisfied:
(1) the emulsion polymer forming the outermost phase contains from 1 to 25 mass % of an ethylenic unsaturated monomer having a carbonyl group,
(2) at least one phase located inside the outermost phase of the different phase structure emulsion particles, is formed of an emulsion polymer of an ethylenic unsaturated monomer, having a glass transition temperature of from 50° C. to 150° C., and
(3) the binder has a minimum film-forming temperature of at most 30° C.
Now, the present invention will be described in detail.
The binder (a) constituting the resin composition for an aqueous paint of the present invention is one composed of different phase structure emulsion particles prepared by multi-stage emulsion polymerization of an ethylenic unsaturated monomer in water.
The multi-stage emulsion polymerization is carried out by at least 2 stages, usually from 2 to 5 stages of emulsion polymerization of an ethylenic unsaturated monomer in water in accordance with a well known emulsion polymerization process, so that the emulsion polymer of an ethylenic unsaturated monomer thereby formed constitutes different phase structure emulsion particles comprising the outermost phase and one or more inner phases.
A typical example of the multi-stage emulsion polymerization process may be a process comprising a plurality of steps of repeating emulsion polymerization of an ethylenic unsaturated monomer at an elevated temperature of from 60 to 90° C. in the presence of an emulsifying agent and a polymerization initiator, and further optionally a chain transfer agent and an emulsion stabilizer.
Examples of the emulsifier include anionic surfactants, such as an aliphatic acid salt such as sodium lauryl sulfate, a higher alcohol sulfuric acid ester salt, an alkylbenzene sulfonate such as sodium dodecylbenzene sulfonate, a polyoxyethylenealkylether sulfuric acid salt, ammonium polyoxyethylenephenylether sulfonate, polyoxyethylene polyoxypropylene glycol ether sulfuric acid salt, and a so-called reactive emulsifier having a sulfonic acid group or a sulfuric ester group and a polymerizable carbon—carbon unsaturated double bond in its molecule; nonionic surfactants, such as a polyoxyethylene alkylether, polyoxynonylphenylether, a sorbitan aliphatic acid ester, a polyoxyethylene aliphatic acid ester, a polyoxyethylene-polyoxypropylene block copolymer, and a reactive nonionic surfactant having the above-mentioned group and polymerizable carbon—carbon unsaturated double bond in its molecule; cationic surfactants such as, an alkylamine salt and a quaternary ammonium salt; and (modified)polyvinyl alcohol.
Examples of the polymerization initiator include those generally used for radical polymerization, and among them, a water-soluble material is preferable. For example, persulfates such as potassium persulfate and ammonium persulfate, azo type compounds such as 2,2′-azobis(2-amidinopropane)hydrochloride, 4,4′-azobis-cyanovaleric acid and 2,2′-azobis (2-methylbutaneamidoxime)dihydrochloride tetrahydrate, and peroxides such as aqueous hydrogen peroxide and t-butylhydroperoxide, may be mentioned. Further, a redox type compound including a combination of ferrous sulfate with a reducing agent such as L-ascorbic acid and sodium thiosulfate, is also useful.
Examples of the chain transfer agent include long chain alkylmercaptans such as N-dodecylmercaptan, aromatic mercaptans and halogenated hydrocarbons.
Examples of the emulsion stabilizer include polyvinyl alcohol, hydroxylethylcellulose and polyvinylpyrrolidone.
The emulsion polymerization is carried out by a one time-charging method of charging a monomer all at once, a monomer-dropping method of continuously dropping a monomer, a preemulsion method of previously mixing and emulsifying a monomer, water and an emulsifier and dropping the emulsified product, or a combination of these methods.
According to the present invention, in the preparation of different phase structure emulsion particles as a binder in accordance with the above-mentioned methods, as an ethylenic unsaturated monomer which is added at the final stage of multi-stage emulsion polymerization and forms the outermost phase, it is necessary to use an ethylenic unsaturated monomer having a carbonyl groups in an amount of from 1 to 25 mass %, preferably from 5 to 20 mass %, of the total ethylenic unsatu
Sakaguchi Shinya
Sasaki Hiroharu
Takamatsu Atsushi
Tsuneta Kazuyoshi
Dai Nippon Toryo Co., Ltd.
Lee Rip
Wu David W.
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