Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-03-29
2001-07-24
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S414000, C524S418000, C524S425000, C524S437000, C524S445000, C524S451000, C524S492000, C524S494000
Reexamination Certificate
active
06265467
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an acrylic SMC (sheet molding compound) or PMC (bulk molding compound) of which controllability of thickening speed is excellent and which has excellent handling property, molding processability and storage stability, and a method for producing the same; a method for producing acrylic artificial marble which gives high productivity and has excellent appearance and hot water resistance; and a thickening agent which has excellent thickening property and hot water resistance.
BACKGROUND ART
Acrylic artificial marble prepared by compounding inorganic fillers such as aluminum hydroxide and the like into an acrylic resin has various prominent functions and properties such as excellent mold appearance, soft feeling, weatherability and the like, and is widely used for counters such as a kitchen counter and the like, washing and dressing stands, waterproof pan, an other architectural uses. These are usually produced by a casting method in which a so-called premix prepared by dispersing inorganic fillers into an acrylic syrup is filled into a mold, and this is cured and polymerized at relatively lower temperature. However, since this acrylic syrup has a lower boiling point, the curing temperature has to be lowered and consequently the molding time becomes longer, therefore, productivity decreases. Further, since the filling property of the premix into a mold is not successful, the shape of a molded article is restricted.
For improving these defects, there has been conventionally effected investigation for producing acrylic artificial marble by heat and compression molding of BMC obtained by thickening a resin syrup with a thickening agent.
For example, Japanese Patent Application Laid-Open (JP-A) No. 5-32720 discloses an acrylic BMC for artificial marble excellent in handling property and molding property, prepared by compounding inorganic fillers and a crosslinked resin power having specific degree of swelling obtained by suspension polymerization into an acrylic syrup obtained by previously dissolving an acrylic polymer in an acrylic monomer.
Further, JP-A No. 6-298883 discloses an acrylic BMC for artificial marble excellent in low constriction property in heat-curing, prepared by compounding organic fillers and a thermoplastic acrylic resin powder into an acrylic syrup obtained by previously dissolving an acrylic polymer in an acrylic monomer, the thermoplastic acrylic resin powder being poor soluble in the syrup.
Further, JP-A No. 6-313019 discloses an acrylic BMC for artificial marble of which cracking in molding is prevented and appearance of the resulting molded article and thickening stability thereof are improved, prepared by compounding a resin powder obtained by spray-drying treatment of a crosslinked polymer obtained by emulsion polymerization into an acrylic syrup obtained by previously dissolving an acrylic polymer in an acrylic monomer.
Further, Japanese Patent Application Publication (JP-B) No. 5-13899 discloses an acrylic BMC for artificial marble of excellent in heat resistance, prepared by compounding inorganic fillers and an acrylic resin powder having a specific molecular weight into an acrylic monomer containing a specific amount of a crosslinking agent.
However, in the methods disclosed in JP-A Nos. 5-32720, 6-298883 and 6-313019, since an acrylic polymer is dissolved in an acrylic monomer to prepare a syrup, number of processes is large and production cost tends to increase. Further, when resin powders disclosed in these publications are used as thickening agents, there is a tendency that aging of a premix for obtaining an acrylic BMC requires a long period of time (about 24 hours) and productivity decreases.
On the other hand, in the method disclosed in JP-B No. 5-13899, an acrylic BMC is obtained directly by mixing an acrylic monomer, inorganic filler and polymer powder not via an acrylic syrup. However, since the mixture is kneaded at a temperature of 60° C. for 30 minutes or more for dissolving the polymer powder and thickening the mixture, long period heat history is required for obtaining the acrylic BMC and storage stability of the resulting acrylic BMC deteriorates. Further, when a grain-like acrylic BMC is going to be obtained by compounding a colored resin particle in this method, the colored resin particle is dissolved during kneading and grain pattern becomes extremely unclear or grain pattern disappears, leading to poor appearance.
To solve these problems, the present inventors have found that when a polymer powder having certain oil absorption, certain degree of swelling and certain specific surface area is used as a thickening agent, there is obtained an acrylic BMC which exhibits high thickening speed, requires no aging and provides clear grain pattern (International Publication WO97/40098).
DISCLOSURE OF INVENTION
The present invention has been accomplished for further improving hot water resistance of the resulting molded article and controllability of thickening speed regarding the above-described thickening agent found by the present inventors.
Namely, an object of the present invention is to provide an acrylic SMC or BMC which is useful for producing a molded article such as acrylic artificial marble and the like excellent in appearance and hot water resistance, and excellent in controllability of thickening speed, handling property, molding processability and storage stability, and a method for producing the same; a method for producing acrylic artificial marble which has high productivity and has excellent appearance and hot water resistance; and a thickening agent which is suitable for them.
The present inventors have investigated for attaining the above-described object, and as a result, have found that acrylic artificial marble excellent in hot water resistance can be produced by using a specific thickening agent, that thickening speed can be controlled and an acrylic SMC or BMC excellent in handling property can be produced by using a specific thickening agent together with other components, and that an acrylic SMC or BMC which has excellent storage stability and exhibits clear grain pattern can be produced continuously with high productivity by kneading a specific thickening agent under specific conditions, completing the present invention.
Namely, the present invention relates to:
An acrylic SMC or BMC comprising an acrylic monomer or acrylic monomer mixture (A), an inorganic filler (B) and a polymer powder (C) having a bulk density in the range from 0.1 to 0.7 g/ml, an oil absorption of linseed oil in the range from 60 to 200 ml/100 g, a degree of swelling by methyl methacrylate is 16-fold or more and a specific surface area in the range from 1 to 100 m
2/
g, further, optionally an inorganic filler-containing resin particle (E),
wherein the polymer powder (C) contains a polymer powder (C
1
) containing no surfactant and/or a polymer powder (C
2
) containing as a constituent component a reactive surfactant;
or wherein the polymer powder (C) contains at least two components selected from a non-crosslinked polymer powder (C
3
) having a weight-average molecular weight in the range from 100,000 to 2,500,000, a non-crosslinked polymer powder (C
4
) having a weight-average molecular weight in the range from 2,500,000 to 5,000,000 and a crosslinked polymer powder (C
5
);
An acrylic SMC or BMC comprising an acrylic monomer or acrylic monomer mixture (A), an inorganic filler(B), a polymer powder (C) having a bulk density in the range from 0.1 to 0.7 g/ml, an oil absorption of linseed oil in the range from 60 to 200 ml/100 g, a degree of swelling by methyl methacrylate is 16-fold or more and a specific surface area in the range from 1 to 100 m
2
/g and a polymer powder (D) having a specific surface area in the range from 0.01 m
2/
g to 1 m
2
/g, further, optionally an inorganic filler-containing resin particle (E);
A method for producing an acrylic SMC or BMC comprising mixing uniformly the above-described component (A), component (B) and component (C), further, optionally the component (E) and
Hayashi Kentaro
Kishimoto Yuichiro
Koyanagi Seiya
Nakahara Yoshihito
Saiki Shinji
Cain Edward J.
Mitsubishi Rayon Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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