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
2002-10-31
2004-10-26
Niland, Patrick D. (Department: 1714)
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...
C523S400000, C524S508000, C524S514000, C524S538000, C524S540000, C525S064000, C525S065000, C525S066000, C525S068000, C525S069000, C525S124000, C525S454000, C525S455000, C525S902000
Reexamination Certificate
active
06809147
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a thermosetting composition, and more particularly a thermosetting composition which comprises an acrylic plastisol of acrylic resin particles having a gradient-type structure having a certain thermosetting material formulated therein and thereby has enhanced storage stability and solid physical properties (elongation, strength) and is useful as, such as, automotive body sealers or undercoats.
BACKGROUND ART
In the prior art, polyvinyl chloride (PVC) plastisols comprising a plasticizer having PVC particles dispersed therein have been utilized in various fields, since they have excellent storage stability (particularly viscosity stability) and solid physical properties and any plasticizer of which rarely bleeds. However, since a generation of hydrogen chloride gas due to PVC at incinerating brings a destruction of ozon layer, a cause of acid rain, a cause of dioxin, etc., it has been growing strong that PVC plastisols are replaced by acrylic plastisols comprising a plasticizer having acrylic resin particles and a filler dispersed therein.
However, the prior acrylic plastisols are likely to be affected by the type of plasticizer to be used and thus cannot be compatible with development of sufficient solid physical properties by heating gelation and storage stability (particularly viscosity stability) at paste state. Further, when a cheap and all-purpose plasticizer (e.g., diisononyl phthalate) is used, the plasticizer may easily bleed since sufficient gelation cannot be obtained by heating, which may result in a surface contamination or inferior appearance.
So, there has been suggested an acrylic plastisol using acrylic resin particles having a gradient-type structure, that is, in which the monomer unit proportion changes from the core to the shell multistep-wise or continuously (gradient-type acrylic resin particles), which may prevent a plasticizer bleeding with sufficient solid (gelation) properties, even if an all-purpose plasticizer is used; and which aims at a progress of solid physical properties (see Japanese Patent Laid-Open Publication No. 295850/1996).
This acrylic plastisol using the gradient-type acrylic resin particles bears comparison with the prior PVC plastisols in the points of solid physical properties and prevention of a plasticizer bleeding after gelation; and can be said to have fully a value as a replacement, but in case of supposing such as an application to a body sealer used for a connecting part or gap part in automotive assembly line, it is necessary to change the type of plasticizer and/or to increase the amount of the gradient-type acrylic resin particles in order to obtain sufficiently satisfactory physical properties of sealant for attaining an original air- and water-tight sealing, which may be deteriorated the storage stability and increased the viscosity, which be effected the workability.
DISCLOSURE OF INVENTION
When the present inventors made intense studies for the purpose of modifying the physical properties of an acrylic plastisol using such gradient-type acrylic resin particles, they found that if said acrylic plastisol is formulated with an polyisocyanate component wherein free isocyanate group(s) (NCO) has been blocked and a latent curing agent therefor as a thermosetting material, the physical properties of their expected objective are more improved without deterioration of storage stability, that is, the physical properties can be designed to tough strength and excellent elongation and include excellent adhesion to a painted plate or a metal surface, and hence, they completed the present invention.
Thus, according to the present invention there is provided a thermosetting composition which comprises an acrylic plastisol consisting of a plasticizer having acrylic resin particles having a gradient-type structure in which the monomer unit proportion changes from the core to the shell multistep-wise or continuously and a filler dispersed therein and therewith formulated, as thermosetting material, a blocked urethane prepolymer wherein free NCO groups of a terminal NCO-containing urethane prepolymer have been blocked or a blocked polyisocyanate compound and a latent curing agent therefor.
The above-described gradient-type acrylic resin particles in the present invention contain, as monomer unit, at least one selected from ethyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, sec-butyl methacrylate, t-butyl methacrylate, ethylhexyl methacrylate, ethyl acrylate, n-butyl acrylate, sec-butyl acrylate and t-butyl acrylate [hereinafter referred to as “A monomer”]; and a mixture of at least one selected from methyl methacrylate and benzyl methacrylate with at least one selected from methacrylic acid, acrylic acid, itaconic acid and crotonic acid [hereinafter referred to as “mixture B monomer”]. Such gradient-type acrylic resin particles can be produced by polymerizing A monomer (described above) and mixture B monomer (also described above) while changing the ratio (proportion) of the former to the latter multistep-wise or continuously. In this case, the proportion of A monomer will be gradually reduced from the core toward the shell, while that of mixture B monomer will be gradually increased from the core toward the shell. Typically, one may use an acrylic resin particle having an average molecular weight of 1,000-2,000,000 and a particle diameter of the primary particle and/or the secondary particle (which consists of aggregated primary particle) of 0.1-100 &mgr;m. For example, “DIANAL” which is commercially available from Mitsubishi Rayon Co., Ltd. is known.
Examples of filler in the present invention include, for example, clay, calcium carbonate (e.g., heavy-duty calcium carbonate, precipitated calcium carbonate, surface treated calcium carbonate, etc.), magnesium carbonate, titanium oxide, calcined plaster, barium sulfate, zinc white, silicic acid, mica powder, talc, bentonite, silica, glass powder, red iron oxide, carbon black, graphite powder, alumina, silas balloon, ceramic balloon, glass balloon, plastic balloon, metal powder, and the like.
Examples of plasticizer in the present invention include, for example, phthalate ester such as di(2-ethylhexyl) phthalate, butyl benzyl phthalate (high polar plasticizer), dinonyl phthalate, diisononyl phthalate, diisodecyl phthalate, diundecyl phthalate, diheptyl phthalate, butyl phthalyl butyl glycolate; aliphatic dibasic acid ester such as dioctyl adipate, didecyl adipate, dioctyl sebacate; polyglycol benzoate such as polyoxyethylene glycol dibenzoate, polyoxypropylene glycol dibenzoate; trimellitate; pyromellitic acid ester; phosphates such as tributyl phosphate, tricresyl phosphate; hydrocarbons such as alkyl-substituted diphenyl, alkyl-substituted terphenyl, partially hydrogenated alkyl terphenyl, aromatic process oil, pine oil; and the like. One or admixture of two or more selected from the group consisting of these plasticizers may be suitably selected and used depending on the type of the gradient-type acrylic resin particle. Particularly, diisononylphthalate which is inexpensive and for all-purpose can be used.
Examples of blocked urethane prepolymer in the present invention can be prepared according to the following procedure:
i) First, polyol is allowed to react with an excess amount of polyisocyanate compound to obtain terminal NCO-containing urethane prepolymer.
Examples of polyol include, for example, polyether polyol including polyoxyalkylene polyol (PPG), modified polyether polyol, polytetramethylene ether glycol; polyester polyol including condensation polyester polyol, lactone polyester polyol, polycarbonate diol; polybutadiene polyol; polyolefin polyol; polymer polyol obtained by polymerizing or graft-polymerizing acrylonitrile alone or a mixture monomer of acrylonitrile with at least one selected from the group consisting of styrene, acrylamide, acrylic ester, methacrylic ester and vinyl acetate; and the like.
Examples of the above-described polyisocyanate compound include trimethylene diisocyanate, te
Minamihori Takashi
Nakayama Kenta
Ohno Hitoshi
Jacobson & Holman PLLC
Niland Patrick D.
Sunstar Giken Kabushiki Kaisha
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