Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-12-08
2002-06-25
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S231000, C526S318420, C526S320000, C526S329600, C523S201000
Reexamination Certificate
active
06410655
ABSTRACT:
The present invention relates to a resin composition for an aqueous paint, which contains substantially no volatile organic compound (hereinafter referred to as “VOC”) and has excellent freezing-thawing stability and low temperature film-formability and forms a film excellent in anti-blocking property and water resistance.
Recently, environmental regulations became stricter with regard to reduction of toxicity and a VOC, and also from a 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 business. Its typical paint is an aqueous emulsion paint, but since the aqueous emulsion paint employs water as a solvent, there are problems that its dispersion state is changed by freezing-thawing cycle during storage and freezing-thawing stability is poor due to viscosity rise or coalescing. Therefore, it is heretofore general to employ an organic solvent including ethylene glycol as a freeze-proofing agent, thereby improving freezing-thawing stability.
Also, an aqueous emulsion resin has an inherent minimum film-forming temperature (hereinafter referred to as “MFT”), and when a surface to be coated has a temperature of lower than MFT, it was necessary to blend an organic solvent as a coalescing agent for film-formation. Thus, the aqueous emulsion paint contains a considerable amount of a VOC, and when drying of a coated film is insufficient, there are problems of adversely affecting water resistance and anti-blocking property by the presence of the remaining VOC.
Therefore, it has been studied to reduce VOC as much as possible from an aqueous emulsion paint in order to solve environmental problems, to save resources and to prevent orders. For example, there has been developed a paint having a VOC reduced by using a low MFT aqueous emulsion resin, but the paint using a low MFT aqueous emulsion resin is poor in water resistance and anti-blocking property and provides a problem that a coated film strength is poor. Also, an aqueous emulsion paint having a low VOC amount, which is improved in freezing-thawing stability, is disclosed, for example, in JP-A-8-302238.
However, when this paint is stored in a frozen state for a long term, the freezing-thawing stability becomes poor and a coated film obtained provides problems that anti-blocking property and water resistance become poor.
The present invention has been made by taking these prior arts into consideration. Thus, an object of the present invention is to provide a resin composition for an aqueous paint for forming a coating film having excellent anti-blocking property and also having excellent freezing-thawing stability and low temperature film-formability, without using a VOC as a coalescing agent and an anti-freezing agent which are resources of providing environmental pollution and odor, or with only a very small amount of these additives.
In order to solve the above problems, the present inventors have intensively studied, and have discovered that the above problems are surely solved by providing the following constitution. The present invention is based on this discovery.
That is, the present invention relates to a resin composition for an aqueous paint, containing different phase structure emulsion particles obtained by multi-stage emulsion polymerization as a binder, wherein the different phase structure emulsion particles have an outermost phase formed by an emulsion polymer of an ethylenic unsaturated monomer having a glass transition temperature of from −50° C. to 10° C., and satisfy the following conditions (1) to (3):
(1) the emulsion polymer forming the outermost phase contains from 1 to 20 mass % of an ethylenic unsaturated monomer having at least one of a polyethylene glycol chain and a polypropylene glycol chain,
(2) at least one phase present in the inside from the outermost phase of the different phase structure emulsion particles comprises an emulsion polymer of an ethylenic unsaturated monomer having a glass transition temperature of from 30° C. to 110° C., and
(3) the binder has a minimum film-forming temperature of at most 10° C.
Hereinafter, the present invention is described in more details.
A resin composition for an aqueous paint of the present invention employs different phase structure emulsion particles prepared by multi-stage emulsion polymerization of an ethylenic unsaturated monomer in water as a binder.
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, and the emulsion polymer of an ethylenic unsaturated monomer thus formed constitutes different phase structure emulsion particles comprising the outermost phase and at least one phase of inner phases.
A typical example of the multi-stage emulsion polymerization process includes a process of 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 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 polyoxynonylphenylether sulfonate, polyoxyethylene polyoxypropylene glycol ether sulfuric acid salt, a reactive emulsifier such as a monomer having a sulfonic acid group or a sulfuric ester group, and other anionic surfactants; a polyoxyethylene alkylether, polyoxynonylphenylether, a sorbitan aliphatic acid ester, a polyoxyethylene aliphatic acid ester, a polyoxyethylene-polyoxypropylene block copolymer, a reactive nonionic surfactant and other nonionic surfactants; an alkylamine salt, a quaternary ammonium salt and other cationic surfactants; (modified)polyvinyl alcohol, and the like.
Examples of the polymerization initiator include those generally used for radical polymerization, and among them, a water-soluble material is preferable, examples of which include persulfates such as potassium persulfate and ammonium persulfate, azo type compounds such as 2,2′-azobis(2-amidinopropane)hydrochloride, 4,4′-azobis-cyanovaleric acid, 2,2′-azobis(2-methylbutaneamidoxime)dihydrochloride tetrahydrate and the like, aqueous hydrogen peroxide, t-butylhydroperoxide and other peroxides. Further, a redox type compound including a combination of ferrous sulfate and a reducing agent such as L-ascorbic acid and sodium thiosulfate are also usable.
Examples of the chain transfer agent include long chain alkylmercaptans such as N-dodecylmercaptan, aromatic mercaptans, hydrogenated hydrocarbons and the like.
Examples of the emulsion stabilizer include polyvinyl alcohol, hydroxylethylcellulose, polyvinylpyrrolidone and the like.
The emulsion polymerization is carried out by a one time-charging method of charging a monomer one time, 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 containing an ethylenic unsaturated monomer having at least one of a polyethylene glycol chain and a polypropylene glycol chain in an amount of from 1 to 20 mass %, preferably from 5 to 15 mass %, of the total ethylenic unsaturated monomers in such a manner as to provide the outermost phase comprising an emulsion polymer having a glass transition temperature (hereina
Okubo Masayoshi
Sakaguchi Shinya
Sasaki Hiroharu
Takamatsu Atsushi
Tsuneta Kazuyoshi
Asinovsky Olga
Dai Nippon Toryo Co., Ltd.
Seidleck James J.
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