Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-08-18
2001-05-01
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S223000, C524S387000, C524S388000, C524S728000, C524S765000
Reexamination Certificate
active
06225389
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a water-free, water-washable, energy-curable, polymer-forming composition, especially useful as a print screen coating, and a method for applying same.
2. Background of the Art
In silk screen printing, the ink is forced onto a printing substrate through a stencil, or “mask”, having a porous screen area configured in the shape of the indicia to be printed, such as letters or graphic images. The printing substrate can be paper, textile, metal, ceramic, polymer film, and the like. The screen can be a gauze or mesh fabricated from metal, textile fabric such as silk or cotton, or various polymer materials.
The mask is generally prepared by coating a screen with a curable composition, curing the composition, and then engraving the indicia. The engraved areas are porous, thereby permitting ink to be forced through the screen onto the printing substrate to print the indicia.
After printing, the ink on the substrate is cured or hardened by any of several methods such as, for example, exposure of the ink to energy such as heat or radiation (e.g. ultraviolet, electron beam, and the like), evaporation of a solvent in the ink composition, or oxidation hardening of drying oil components (e.g linseed oil, tung oil), and the like.
The three main technologies being practiced today which make up the bulk of the coatings and inks include solvent borne, water borne, and zero volatile organic compounds (VOC). Solvent borne and water borne systems produce coatings which are washable. Water washability is a desired feature of a coating composition since the coating application equipment needs to be cleaned for reuse. However, there has been a technological push to eliminate organic solvents and water in such compositions. Organic solvents present environmental health concerns. And both solvent based and water based systems are energy intensive, requiring drying ovens to remove the solvent or water. For example, thermally induced drying and curing of coated screen fabric typically requires about 7,000 to 12,000 kilojoules of energy per kilogram of fabric as well as a long curing time, typically several hours. Consequently, what is desired is a waterless, yet water-dispersible, zero VOC composition which would be particularly useful as a coating for a print screen.
SUMMARY OF THE INVENTION
In accordance with the present invention, a substantially water-free, water-washable, energy-curable, polymer-forming composition is provided which comprises:
a) an oligomer selected from the group consisting of epoxy oligomer and urethane oligomer, said oligomer having at least two polymerizable ethylenically unsaturated moieties;
b) at least one alkoxylated polyol monomer having at least two polymerizable ethylenically unsaturated moieties and capable of being copolymerized with oligomer component (a) to provide a solid cured polymer when exposed to energy-polymerizing conditions; and,
c) at least one surface active agent capable of being integrated into the molecular structure of the polymer resulting from the copolymerization of (a) and (b) either by covalent bonding or by hydrogen bonding, and further capable of rendering said composition water-dispersible.
Also provided herein is a method for coating a screen with the aforementioned composition employing applicator means which can be washed with water.
The foregoing composition contains substantially no VOCs and is readily dispersible in water. Another advantage of this composition is that it significantly reduces the amount of energy and time required to effect curing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
While the present invention is particularly applicable to coatings for print screens, it should be understood that any coating application or substrate, for printing or non-printing purposes, is within its scope. Percentages of materials are by weight unless stated otherwise. Note that all quantities appearing hereinafter shall be understood to be modified by the term “about” except in the Examples and unless indicated otherwise.
The substantially water-free, water-washable, energy-curable, poly-forming composition herein includes an epoxy oligomer and/or urethane oligomer having at least two polymerizable ethylenically unsaturated moieties, an alkoxylated polyol monomer having at least two ethylenically unsaturated moieties and a surface active agent which is copolymerizable with the oligomer and/or monomer.
An aliphatic and/or aromatic urethane oligomer may optionally be employed instead of, or in addition to, the epoxy oligomer. The urethane oligomer component is preferably a urethane acrylate such as, for example, PHOTOMER® 6008 available from Henkel Corporation. However, the epoxy oligomer is preferred.
Also, the epoxy oligomer may optionally be accompanied by polyester acrylate oligomer, trimethylol propane dimerester tetraacrylate oligomer, or dipolyoxypropylene glycerol adipate oligomer.
Generally, the energy-curable composition of the present invention includes the following component weight percentages:
Oligomers
30%-70%
Monomers
30%-70%
Surfactants
0.1% to about 20%
Photoinitiators
0-10%
The epoxy oligomer can be prepared by reacting an epoxide with an unsaturated acid such as acrylic or methacrylic acid, optionally in the presence of a polyamide derived from a polymerized fatty acid.
In one embodiment the epoxy acrylate oligomer is derived from a compound having the formula:
R
1
—[—CH
2
—CHOH—CH
2
—O(O)C—CH═CH
2
]
n
wherein R
1
is an aliphatic, aromatic or arene moiety having at least two carbon atoms and at least two oxido residues, and n is an integer of from 2 to 6.
Useful epoxides include the glycidyl ethers of both polyhydric phenols and polyhydric alcohols, epoxidized fatty acids or drying oil acids, epoxidized diolefins, epoxidized di-unsaturated acid esters, as well as epoxidized unsaturated polyesters, preferably containing an average of more than one epoxide group per molecule. The preferred epoxy compounds will have a molecular weight of from 300 to 600 and an epoxy equivalent weight of between 150 and 1,200.
Representative examples of the epoxides include condensation products of polyphenols and (methyl)epichlorohydrin. For the polyphenols, there may be listed bisphenol A, 2,2′-bis(4-hydroxyphenyl)methane (bisphenol F), halogenated bisphenol A, resorcinol, hydroquinone, catechol, tetrahydroxyphenylethane, phenol novolac, cresol novolac, bisphenol A novolac and bisphenol F novolac. There may also be listed epoxy compounds of the alcohol ether type obtainable from polyols such as alkylene glycols and polyalkylene glycols, e.g. ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, glycerine, diglycerol, trimethylolpropane, pentaerythritol, inositol, sorbitol, polyethylene glycol, polypropylene glycol, polytetrahydrofuran, (i.e., poly(1,4-butanediol), which is obtainable under the designation TERATHONE® from DuPont), and alkylene oxide-adduct of bisphenols, and (methyl)epichlorohydrin; glycidyl amines obtainable from anilines such as diaminodiphenylmethane, diaminophenylsulfone and p-aminophenol, and (methyl)epichlorohydrin; glycidyl esters based on acid anhydrides such as phthalic anhydride and tetrahydro- or hexahydro-phthalic anhydride; and alicyclic epoxides such as 3,4-epoxy-6-methylcyclohexylmethyl and 3,4-epoxy-6-methylcyclohexyl carboxylate.
Glycidyl polyethers of polyhydric phenols are made from the reaction of a polyhydric phenol with epihalohydrin or glycerol dihalohydrin, and a sufficient amount of caustic alkali to combine with the halogen of the halohydrin. Glycidyl ethers of polyhydric alcohols are made by reacting at least about 2 moles of an epihalohydrin with 1 mole of a polyhydric alcohol such as ethylene glycol, pentaerythritol, etc., followed by dehydrohalogenation.
In addition to polyepoxides made from alcohols or phenols and an epihalohydrin, polyepoxides made by the known peracid methods are also suitable. Epoxides of unsaturated es
Drach John E.
Henkel Corp.
Moore Margaret G.
Trzaska Steven J.
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