Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-04-09
2003-02-04
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C525S327300, C525S386000
Reexamination Certificate
active
06515046
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a powder coating applicable to fields such as the painting of vehicle bodies and components, construction materials, and household electrical appliances. In particular, the invention relates to a method of manufacturing a powder coating by an environmentally friendly spray drying method in which the manufacturing is able to be completed easily, without a long complicated process, and with good conservation of energy.
2. Description of Related Art
Powder coatings are widely used for the general painting of metals, as environmentally friendly paints which do not release organic solvents into the atmosphere during paint application.
Normally, a powder coating is manufactured by manufacturing a main constituent resin, subjecting the resin to coarse crushing, dry blending with a hardener and various additives, and then subjecting the dry blend to extrusion, cooling, a second crushing process, and classification. Compared with solvent based paints, the manufacturing process is long and complex, and consequently the problem arises of increased manufacturing cost. In order to resolve this problem, trials are being conducted on preparing a raw materials solution by dissolving or dispersing the raw materials, namely the main constituent resin, the hardener and the various additives, in a solvent, and then removing the solvent to obtain the powder coating directly.
In such a case, in order to obtain the final product powder coating, a step for removing the solvent is necessary, although if during solvent removal the raw materials solution is heated to a high temperature, the main constituent resin and the hardener undergo a curing reaction, resulting in gelling.
Furthermore, spray drying has also been proposed as a method of removing the solvent. For example, a method is disclosed in EP0420097, wherein a powder coating raw materials solution dispersed in water is converted to powder by spray drying. However, in the case of this method, dispersants and the like are necessary for dispersing the powder coating raw materials in water, and so not only does the cost of the raw materials increase, but there is also a danger of a reduction in the storage stability of the paint, and reductions in the water resistance and chemical resistance of the formed paint film. Furthermore, because water, which has a large specific heat and a large latent heat of vaporization, is used as the medium, the thermal energy cost required in the drying process is extremely high.
In EP0312610, a method is disclosed in which a raw materials solution comprising a main constituent resin and an organic solvent is subjected to drying. However, in the case of this manufacturing method, because a high temperature solvent gas which has been heated to a superheated vapor state is used as the heat source gas, there is a danger that within the system comprising the main constituent resin and the hardener, the powder coating raw materials will be exposed to high temperatures during the drying process, causing the main constituent resin and the hardener to undergo a curing reaction which will result in a gelling of the paint, making it unusable as a powder coating.
Furthermore, in EP0962472A2, a method of manufacturing a powder coating is disclosed wherein an acrylic resin containing an epoxy group is used as the main constituent resin, and this main constituent resin is polymerized in methanol, before a hardener is added and the resulting raw materials solution is then spray dried. However in this method, because methanol, in which the main constituent resin is very insoluble, is used in the polymerization reaction of the main constituent resin, the main constituent resin is susceptible to precipitating out of the raw materials solution, and at normal temperatures it is extremely difficult to dissolve the main constituent resin uniformly in the raw materials solution, meaning the raw materials solution needs to be heated. Furthermore, because the boiling point of methanol is low, in order to cool, liquefy and recover the evaporated methanol vapor following the spray drying process, the temperature of the recovery apparatus must be kept extremely low, meaning the energy costs associated with the manufacture are high. Even in the case where the solvent is not recovered, the resultant increase in the cost of the raw materials, the cost of disposing of the evaporated methanol, and the effect on the environment mean that industrial application of the method is difficult.
BRIEF SUMMARY OF THE INVENTION
However, the inventors of the present invention commenced extensive research aimed at achieving a method of manufacturing a powder coating which would resolve the various problems and drawbacks of the conventional techniques described above, would not require a long complicated manufacturing process, could be manufactured easily and at low cost, and moreover would be in no danger of gelling during the manufacturing process.
Consequently, an object of the present invention is to provide a method of manufacturing a powder coating which is able to be manufactured easily, without a long complicated process, and with good conservation of energy, and furthermore is in no danger of gelling during the manufacturing process.
As a result of extensive research into resolving the problems described above, the inventors discovered that when a powder coating raw materials solution comprising an epoxy group containing acrylic resin (A) and a polyvalent carboxylic acid (B) dissolved in an organic solvent (C) incorporating an alcohol (C-1) of 2 to 4 carbon atoms was spray dried at a temperature at which the epoxy group containing acrylic resin (A) and the polyvalent carboxylic acid (B) underwent no substantial curing reaction, a powder coating was able to be manufactured easily and cheaply, without any danger of gelling, and this enabled the inventors to complete the present invention.
In other words, the present invention provides a method of manufacturing a powder coating in which a powder coating raw materials solution comprising as essential constituents an epoxy group containing acrylic resin (A), a polyvalent carboxylic acid (B), and an organic solvent (C) incorporating an alcohol (C-1) of 2 to 4 carbon atoms is spray dried at a temperature at which the epoxy group containing acrylic resin (A) and the polyvalent carboxylic acid (B) undergo no substantial curing reaction.
The method of manufacturing a powder coating according to the present invention is a highly practical method which does not require the type of long complicated process associated with conventional methods of manufacturing powder coatings, and which enables the manufacturing to be completed easily and at low cost, and moreover with no danger of gelling occurring during the manufacturing process.
DETAILED DESCRIPTION OF THE INVENTION
As follows is a detailed description of the specifics of the present invention.
First, the epoxy group containing acrylic resin (A), which is one of the essential constituents of the powder coating raw materials solution used in the manufacturing method of the present invention, will be described.
In order to obtain a powder coating which displays a superior balance between storage stability and external appearance of the paint film, the epoxy group containing acrylic resin. (A) should preferably have a softening point within the range from 80 to 150° C.
Known methods can be applied to the preparation of the epoxy group containing acrylic resin (A), although a method wherein an individual vinyl monomer incorporating an epoxy group, and where necessary another copolymerizable vinyl monomer, are each polymerized in an organic solvent is the most simple, and is therefore preferred. Known materials can be used for the polymerization initiator and the solvent used in this preparation method.
Examples of particularly representative vinyl monomers with an epoxy group include monomers with an epoxy group such as glycidyl (meth) acrylate, &bgr;-met
Agawa Tetsuro
Okada Katsuhiko
Aylward D.
Dainippon Ink and Chemicals Inc.
Dawson Robert
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