Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2000-04-20
2001-10-23
Ashton, Rosemary (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S284100, C430S910000, C522S088000
Reexamination Certificate
active
06306557
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for preparing water dispersible negative-type photosensitive compositions. Particularly, the water dispersible negative-type photosensitive compositions prepared by the process of the present invention have low solvent content and are useful as resists for forming printed circuits, printing plates or solder masks.
2. Description of the Related Arts
Photosensitive material used in the process of manufacturing printed circuit board may be classified into 3 categories: photoresist for etching, dielectric for build-up processes and solder resist. The photoresist for etching is used in the etching of copper-conductor circuits and should be stripped from the surface of copper-conductor circuits after etching. The dielectric for build-up processes is used for the insulation of layers of copper-conductor circuits. The solder resist is applied onto partial circuits after the manufacturing of copper-conductor circuits has been finished. In addition, the photosensitive material can be classified liquid type or dry film type according to their outward appearance. The liquid type photosensitive material is usually coated onto circuit boards by screen printing, roller coating, curtain coating or dip coating. Dry film type photosensitive material is first applied onto a transparent polyester substrate, then the photosensitive layer is heated and laminated to the circuit board substrate.
Further, photosensitive material can also be classified as solvent-developable or alkaline aqueous-developable according to the pattern of development. The former uses organic solvent as developing solution, which is a potential irritant and harmful to staff during operation. Further, contamination arising from evaporation increases the recovery costs. Thus, solvent-developable photosensitive material is gradually being replaced by alkaline aqueous-developable material. The developing solution used in the alkaline aqueous-developable material is mostly sodium carbonate aqueous solution. Because the binder is present in the photosensitive composition contains carboxyl groups, it can be neutralized by sodium carbonate to form salts during development. This causes the photosensitive composition which has not been exposed to be emulsified and dispersed in the water. Thus, the purpose of the development is achieved.
The components of the photosensitive composition include binder, photomonomer, photoinitiator, thermal inhibitor, storage stabilizer, plasticizer and other additives. Because the components are not completely compatible each other, the addition of 30-70% of organic solvents to dissolve and disperse each component is necessary. See, e.g. U.S. Pat. Nos. 4,418,138, 4,537,855, 4,604,343, 5,364,737, 5,393,643, 5,387,494, 5,389,495 and 5,411,837. The type of organic solvents depends on the purpose of the photosensitive composition, including dichloromethane, chloroform, tetrachloromethane, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, 2-butyl alcohol, isobutyl alcohol, n-pentyl alcohol, 2-methyl-1-butanol, isopentyl alcohol, n-hexyl alcohol, propyleneglycol monomethyl ether, dipropyleneglycol monomethyl ether, carbitol, acetone, methyl ethyl ketone and propyleneglycol monomethyl ether acetate, etc.
The bulk use of organic solvents is potentially risky for the operators and increases the recovery costs, thus decreasing the competitiveness of this material. The photosensitive compositions prepared by the methods of the prior art contain at least 20%-30% of organic solvents (See, e.g. Barr, U.S. Pat. No. 5,389,495 and Bttomley et al, U.S. Pat. No. 5,411,837). Thus, the present invention aims to replace organic solvents with water while maintaining the desired properties of a photosensitive composition for making electric circuit substrates.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to provide a process for preparing a water-dispersible photosensitive composition, comprising the steps of: (a) adding an unsaturated photomonomer and/or a plasticizer to a carboxyl-group bearing acrylic resin solution which contains at least an organic solvent; (b) distilling and removing said organic solvent to form a resin paste; (c dissolving a photoinitiator and an alkaline into said resin paste; (d) adding deionized water and mixing thoroughly to form an emulsion; and (e) adjusting the viscosity of said emulsion with a water-soluble resin.
The novelty of the present invention is the first step, in which a photomonomer and/or a plasticizer is dissolved in an acrylic resin solution containing an organic solvent (this acrylic resin bears carboxyl groups). The organic solvent in the mixture mentioned above is then removed in a distillation manner arid circulated for reuse. Therefore, the solvent content of the produced photosensitive composition can be reduced to a relatively low level, and the solvent used can be circulated for reuse so that the production costs (e.g. the treatments of waste liquid and waste air) can be decreased.
The present invention will be more fully understood and further advantages will become apparent when reference is made to the following description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process for preparing a water-dispersible photosensitive composition, comprising the steps of: (a) adding an unsaturated photomonomer and/or a plasticizer to a carboxyl-group bearing acrylic resin solution which contains at least an organic solvent; (b) distilling and removing said organic solvent to form a resin paste; (c) dissolving a photoinitiator and an alkaline into said resin paste; (d) adding deionized water and mixing thoroughly to form an emulsion; and (e) adjusting the viscosity of said emulsion with a water-soluble resin.
In the process of the present invention, the binder (acrylic resin) in step (a) is synthesized from the solution polymerization of an acrylic monomer in the presence of an organic solvent. Suitable acrylic monomer is selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, fumaric acid, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, hexyl acrylate, hexyl methacrylate, acrylamide, cyanoacrylate and styrene. The introduction of carboxyl-group bearing acrylic acid or methacrylic acid can cause the photosensitive composition to meet the requirements of alkaline aqueous development and increase the hydrophilicity. Optionally, the introduction of another acrylic monomer can easily adjust the hydrophilicity and the glass transition temperature (T
g
) of the acrylic resin. The greater hydrophilicity of the acrylic resin, the more compatible with all the components in the photosensitive composition with water and the greater the developing effect. However, the adhesion of the photosensitive composition will be lower. The T
g
will affect the viscosity of the photosensitive composition after heating. The lower T
g
makes the photosensitive layers wet and sticky, and thus not appropriate for the operation of image transfer.
Generally, acrylic resin may be synthesized by way of solution polymerization in the presence of organic solvent. Suitable solvent includes dichloromethane, chloroform, tetrachloromethane, acetone, methyl ethyl ketone, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, diethyl ketone, propyleneglycol monomethyl ether and propyleneglycol monomethyl ether acetate. The reaction temperature is based on the thermal polymerization initiator. If the reaction temperature is higher than the boiling point of the solvent, then the polymerization has to be performed under pressure, otherwise solvent evaporation will occur during the reaction. The common polymerization temperature ranges from 70° C. to 130° C. Two or more solvents described above may be used ac
Jeng Jauder
Lin Hsien Kuang
Ashton Rosemary
Christensen O'Connor Johnson & Kindness PLLC
Industrial Technology Research Foundation
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