Plastic and nonmetallic article shaping or treating: processes – Vacuum treatment of work – To degas or prevent gas entrapment
Reexamination Certificate
1999-05-24
2001-10-30
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Vacuum treatment of work
To degas or prevent gas entrapment
C264S141000, C526S273000
Reexamination Certificate
active
06309572
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process for the preparation of a powder coating composition containing a copolymer of a glycidyl group- or methylglycidyl group-containing unsaturated monomeric compound with an ethylenically unsaturated comonomer.
Powder coating compositions are now used in a wide variety of fields in place of liquid coating compositions which cause, during coating and hardening, air pollution by the generation of organic vapors. In particular, powder coating compositions containing a glycidyl group-containing acrylic resin and a polybasic acid curing agent are advantageously used because they give coatings having a beautiful appearance and excellent weatherability.
One known method for the preparation of such a glycidyl group-containing acrylic resin powder coating composition includes suspension-, bulk- or solution-polymerizing a glycidyl group-containing unsaturated monomeric compound with an ethylenically unsaturated monomer to obtain an acrylic copolymer-containing product. The product is treated for the removal of volatile matters such as a solvent and is subsequently coarsely pulverized and then dry-mixed with a curing agent, a pigment and other additives using a mill. The milled mixture is then melted, kneaded, pelletized, ground and sieved to obtain the powder coating composition.
The known method, however, has the following drawbacks. Namely, when suspension polymerization is adopted in the above method, a large amount of a chain transfer agent must be used in order to obtain a relatively low molecular weight copolymer. When a bulk polymerization is adopted, on the other hand, there is caused a drawback that a high polymerization degree cannot be attained. With a solution polymerization using an inert solvent such as toluene or xylene, a step for removing the solvent from the polymerization product must be performed at a high temperature under a high vacuum for a long period of time.
Additionally, since the above acrylic copolymer obtained by the removal of volatile matters is in the form of a bulk at a low temperature, it is necessary to coarsely pulverize same before mixing with the curing agent, pigment and additives. Further, kneading, pelletizing and grinding of the mixture must be carried out to obtain a powder coating composition.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a process for the preparation of a powder coating composition containing a glycidyl group- or methylglycidyl group-containing acrylic resin, which is devoid of the drawbacks of the above conventional process.
Another object of the present invention is to provide an economical method for the preparation of a powder coating composition of the above-mentioned type.
In accomplishing the foregoing object, the present invention provides a process for the preparation of a powder coating composition, comprising copolymerizing 5-90% by weight of at least one monomeric compound selected from the group consisting of glycidyl group-containing unsaturated compounds and methylglycidyl group-containing unsaturated compounds with 95-10% by weight of an ethylenically unsaturated monomer in methanol to obtain a resin solution; and
spray-drying said resin solution to obtain a powdery resin.
In another aspect, the present invention provides a process for the preparation of a powder coating composition comprising the steps of:
copolymerizing 5-90% by weight of at least one compound selected from the group consisting of glycidyl group-containing unsaturated compounds and methylglycidyl group-containing unsaturated compounds with 95-10% by weight of an ethylenically unsaturated monomer in methanol to obtain a resin solution;
feeding said resin solution to an extruder having a die and a plurality of vent ports;
while removing volatile matters existing in said resin solution in said extruder from said extruder through said vent ports, extruding said resin solution through said die to obtain extrudates; and
pulverizing said extrudates.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments of the invention to follow.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The process for the preparation of a powder coating composition according to the present invention includes copolymerizing 5-90% by weight of glycidyl group-containing unsaturated compounds and/or methylglycidyl group-containing unsaturated compounds with 95-10% by weight of an ethylenically unsaturated monomer in methanol to obtain a resin solution.
The copolymerization is generally performed at a temperature of 10-150° C. under a pressure of 0-200 kgf/cm
2
. The methanol is generally used in an amount so that the content thereof in the resin solution is in the range of 5-99.99% by weight, preferably 10-80% by weight. The use of methanol as the solvent has a merit that the molecular weight of the copolymer can be controlled as desired and that the powder coating composition can give a coating having good properties such as surface smoothness and gloss.
The copolymerization in the methanol solvent is preferably carried out to provide a polymerization degree of at least 98%, more preferably at least 99%, most preferably at least 99.5% for reasons of minimizing the content of volatile matters in the powder coating composition. The copolymerization is also preferably performed so that the copolymer resin obtained has a number average molecular weight of 500-50,000, more preferably 3,000-10,000 and a glass transition point of 20-120° C., more preferably 30-100° C., most preferably 40-80° C. for reasons of obtaining a powder coating composition which has suitable storage stability and gives a coating having good smoothness and flexibility.
Any glycidyl group- and/or methylglycidyl group-containing unsaturated monomeric compound may be used for the purpose of the present invention. A glycidyl group- and/or methylglycidyl group-containing unsaturated monomeric compound giving a thermosetting resin upon copolymerization is suitably used. Illustrative of suitable glycidyl group- and/or methylglycidyl group-containing unsaturated monomeric compound are glycidyl acrylate, glycidyl methacrylate, methylglycidyl acrylate and methylglycidyl methacrylate.
The ethylenically unsaturated monomer is a monomer other than the above unsaturated monomeric compound and capable of copolymerizing with the above unsaturated monomeric compound and is preferably a monomer capable of giving a thermosetting resin upon copolymerization with the above unsaturated monomeric compound. Examples of the ethylenically unsaturated monomers include alkyl acrylates and methacrylates, such as methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, n-butyl methacrylate, n-butyl acrylate, i-butyl methacrylate, i-butyl acrylate, t-butyl methacrylate, t-butyl acrylate, 2-ethylhexyl methacrylate, 2-ethylhexyl acrylate, lauryl methacrylate, lauryl acrylate; cycloalkyl acrylates and methacrylates, such as cyclohexyl methacrylate and cyclohexyl acrylate; hydroxyalkyl acrylates and methacrylates, such as 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate; styrene; &agr;-alkylstyrenes, such as &agr;-methylstyrene; acrylonitrile; acrylamide; and methacrylamide.
In one embodiment of the present invention, the resin solution thus obtained by the above copolymerization is spray-dried to obtain a powder resin composition having any desired average particle diameter of, for example, about 1-100 &mgr;m. This method is advantageous because the removal and recovery of methanol may be performed simultaneously with the formation of the powder coating composition.
Before the spray-drying, the resin solution is preferably mixed with a curing agent, a pigment and/or any other suitable additives (any other ingredients to be added to a powder coating composition), so that a uniform powder coating composition can be easily obtained. It is also preferred that the mixing be performed by admixing the resin solution
Isozaki Tsuyoshi
Kurokawa Masahiro
Eashoo Mark
Lorusso & Loud
Mitsubishi Gas Chemical Company Inc.
Silbaugh Jan H.
LandOfFree
Process for the preparation of powder coating composition does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the preparation of powder coating composition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the preparation of powder coating composition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2606030