Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1997-05-28
2000-09-05
Reddick, Judy M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
523400, 525113, 525114, 525115, 525256, 525279, 525281, 5253261, 5253298, 5253299, 525340, 525347, 525375, 525374, 525379, 525404, 525419, 525449, 525533, C08F 2000
Patent
active
061144738
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a resin composition for powder coating utilizing a carboxyl group-containing resin and an epoxy group-containing curing agent and provided with high impact resistance, weather resistance, etc.
BACKGROUND ART
At present, as a resin for powder coating, an epoxy resin, a polyester resin, a polyacrylic resin, a polyvinyl chloride resin or a polyethylene resin is, for example, used.
In recent years, a thermosetting resin is mainly used from the viewpoint of the smoothness and physical properties of the coating film. However, a thermosetting resin has a drawback that when a condensation type resin is used or when a blocked isocyanate is used as a curing agent, a condensation-liberated component or a blocking agent will form a gas at the time of curing, which in turn forms bubbles in the coating film. Therefore, as a curing agent preferred for powder coating, a polyglycidyl compound may, for example, be mentioned which is free from a component liberated during the curing reaction. However, when a usual glycidyl compound such as a bisphenol type diglycidyl ether, is used as a curing agent, a bisphenol type diglycidyl ether of a low molecular weight type is liquid at room temperature, and if it is melt-mixed with a carboxyl group-containing resin, followed by pulverization to obtain a powder coating, it brings about a problem that the powder undergoes fusion or blocking during the storage.
On the other hand, a bisphenol type diglycidyl ether of a high molecular weight type has a less number of functional groups (epoxy groups) per unit weight, and a larger amount will be required, which is disadvantageous from the viewpoint of the cost. Further, if a bisphenol type diglycidyl ether of a high molecular weight type is incorporated in a large amount, the melt viscosity of the coating material tends to be high, thus leading to a problem that smoothness of the coating film will be impaired.
Namely, the curing agent is usually desired to be solid at room temperature and have a low melt viscosity and a large number of functional groups per unit weight. As such a curing agent, a compound having three glycidyl groups or similar functional groups per molecule, such as triglycidyl isocyanurate or tris(.beta.-methylglycidyl) isocyanurate, may, for example, be mentioned. Triglycidyl isocyanurate has high crystallizability and thus has a high melting point at a level of from 100 to 140.degree. C. Accordingly, in order to mix it uniformly with the resin containing carboxyl groups, it will be necessary to conduct the kneading at a slightly high temperature (a temperature around the melting point). In addition, this triglycidyl isocyanurate is highly reactive, and a curing reaction between carboxyl groups and glycidyl groups tends to proceed to some extent to form powder coating even at the temperature for the kneading, whereby the flow property (fluidity) at the time of baking (heat curing) tends to decrease slightly, thus leading to formation of surface roughening so-called orange peel on the surface of the coating film.
On the other hand, tris(.beta.-methylglycidyl) isocyanurate has a melting point of from 70 to 100.degree. C., and it can be uniformly kneaded with the resin containing carboxyl groups at a relatively low temperature at a level of 100.degree. C. or lower, whereby the curing reaction during the kneading can be suppressed. Therefore, it is free from the above-mentioned problem.
As a case wherein this tris(g-methylglycidyl) isocyanurate is employed, Japanese Unexamined Patent Publication No. 24244/1974 discloses a resin composition for powder coating, which comprises tris(.beta.-methylglycidyl) isocyanurate and a polyester resin having an acid value of from 30 to 200 prepared from an aromatic dicarboxylic acid or its ester, a dihydroxy alcohol and a polybasic carboxylic acid.
Japanese Unexamined Patent Publication No. 94722/1974 discloses a method for producing a resin composition for powder coating comprising a free hydroxyl group-containing polyester resin, an aci
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Hidaka Motohiko
Ikeda Hisao
Miyake Satoru
Moro Takeo
Nissan Chemical Industries Ltd.
Reddick Judy M.
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