Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-06-25
2003-09-16
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C522S116000, C522S120000, C522S123000, C427S214000, C428S403000, C428S407000
Reexamination Certificate
active
06620887
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a resin composition useful as a radiation curable resin composition, a thermosetting resin composition, and to a resin composition that has a low viscosity, a low shrink property and a rapid-curability, unlike a conventional curable resin composition.
(2) Description of the Related Art
Radical-polymerization type radiation curable resin compositions are utilized in the field of surface fabrication because they are rapidly curable at low temperatures, and the cured coating films have excellent scuff and chemical resistance. However, the radiation curable resin compositions, usually tend to have high viscosities at room temperature. Therefore, it is necessary to reduce the viscosities in order to facilitate their application.
The use of organic solvents or diluent monomers having low viscosities are necessary for viscosity reduction of the curable resin compositions. As a result, environmental concerns such as increased volatile organic compound (VOC) contents, skin irritation caused by the diluent monomers, along with the decreased curing rates of the resin compositions are observed.
In general, radiation curable resin compositions shrink remarkably in volume upon curing, therefore, a method comprising the addition of a high-molecular weight oligomer or polymer is adopted to reduce the percentage of shrinkage. However, when this method is adopted, the viscosity of the resin is increased; the coating properties are deteriorated; and further the coating curability is deteriorated by the decrease in resin concentration at the reaction site.
In the field of film coating materials, for example, radiation curable resin compositions draw attention. For instance, JP-A-3-252460 discloses a composition for coating material which comprises an ethylenic unsaturated compound having a molecular weight of 500 or less, a styrene-based polymer having a softening point of 70° C. or higher, and a photopolymerization initiator which has excellent adhesive properties to various substrates, high gloss, blocking resistance, scratch resistance, water resistance, etc.
However, since the aforesaid composition contains a styrene-based polymer having no photo-reactivity, its viscosity becomes so high that the coatability is poor depending on the amount of the styrene-based polymer added. Moreover, since a large amount of the photopolymerization initiator must be incorporated into the composition in order to attain a high productivity, a large amount of the photopolymerization initiator remains in the cured coating film, resulting in a film product having the unpleasant odor of the photopolymerization initiator. Thus, a product having satisfactory overall performance characteristics could not be obtained.
In the field of coating materials for wood coatings, rapid-curing radiation curable compositions have come to be extensively used which entail a low energy cost and are good in productivity. Of these radiation curable compositions, those that contain an unsaturated polyester resin, inter alia, have been extensively used because they give a cured coating film that is excellent in finished appearance involving gloss and feeling of fleshiness, and they are inexpensive.
However, in the case of coating films having such a composition, the surface curing speed is lower than the in-depth curing speed, resulting in insufficient productivity of the applied and cured product. Moreover, since the internal strain of the cured coating film is increased by the cure shrinkage of one or more monomers and oligomers contained in the composition, the composition has the disadvantage in that the cured coating film tends to be cracked by repeated heating and cooling.
To overcome these problems, JP-A-4-202213 discloses a composition using a maleic acid-based unsaturated polyester containing a specific glycol component, and JP-A-5-202163 discloses a composition using an epoxy acrylate, a specific acryl polyol component and an isocyanate compound.
The composition disclosed in JP-A-4-202213 requires the use of styrene monomer as a diluent to improve the coating efficiency. The use of styrene monomer deteriorates the surface curability, however, and the work environment is harmed by odor from the volatilization of the styrene monomer. The composition disclosed in JP-A-5-202163 also fails to improve the work environment because it has a high viscosity and hence requires the use of a diluent, such as an organic solvent, to improve the coating work efficiency required for practical use.
In recent years, printing inks that can be cured by active energy rays such as electron rays, ultraviolet rays, visible rays, etc. have been increasingly substituted for common oil inks, because of their many advantages, such as faster printing and delivery, hygienic properties, etc. These printing inks comprise a composition containing a radical-polymerizable monomer, an oligomer and a coloring agent such as a pigment. As specific examples of the printing inks, the composition systems which also use in combination a diallyl phthalate-based polymer disclosed in, for example, JP-B-61-4861 and JP-A-3-212460 have been extensively used from the viewpoint of printability, curability, mar resistance, etc. These composition systems, however, involve the following problems. Since the diallyl phthalate-based polymer has no photo-reactivity, a photopolymerization initiator should be used in said composition systems in a larger amount than in composition systems composed of a radical-polymerizable monomer and an oligomer in order to attain a practical curing rate. In addition, when a large amount of the aforesaid diallyl phthalate-based polymer is added to control the polymerization shrinkage and improving the adhesive properties to a substrate, the viscosity is extremely increased, so that the printability, leveling properties, appearance and the like are deteriorated.
When the composition system disclosed is used as colored printing ink, its curing rate tends to decrease compared to an uncolored composition because of the remarkable light absorption by a dye or pigment for the coloring. Therefore, a larger amount of a photopolymerization initiator is necessary in order to attain a practical curing rate.
Moreover, when the amount of the photo-polymerization initiator is increased in order to improve the curability, the surface curability is improved, but the in-depth curability was not sufficient owing to remarkable light absorption in the surface layer, with the result that that the adhesive properties of the resulting coating film to a substrate are deteriorated.
Thus, it has been difficult to obtain all three conflicting characteristics, i.e., low viscosity, low shrink properties and rapid curability in a solvent-free radiation curable resin composition in all applications of the resin composition. To solve this problem, a method of foaming the resin composition during curing in order to prevent cure shrinkage, and a method of adding solid fine particles as disclosed in JP-A-7-228644, etc. have been proposed. These methods, however, have the disadvantage in that when the obtained resin composition is used as a coating material, the resulting cured coating film has an unsatisfactory appearance.
The reactive microgels disclosed in Japanese Patent No. 2703125 and JP-B-6-25210 are crosslinked fine particles with a small particle size and reactivity and, hence, do not undesirably influence the coating appearance, so they might be capable of solving the above problems. However, although these microgels are suitable for use inca resist composition for lithographic plates, they cannot achieve the low viscosity intended according to the present invention, for the following reason. The crosslinking density of particles of the microgel is so low that a solvent-free coating material cannot be obtained by mixing fine particles of the microgel with another radical-polymerizable monomer because the fine particles are swelled by the radical polymerizable monomer during mixing. The low v
Fujimoto Juichi
Fukushima Hiroshi
Nushi Seiji
Mitsubishi Rayon Co. Ltd.
Nutter Nathan M.
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