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
1995-06-06
2003-01-07
Chu, John S. (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
C430S175000, C430S176000, C430S308000
Reexamination Certificate
active
06503683
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to polymeric preparations that can be used in screen printing processes. Further, the invention relates to a film or a liquid polymeric composition that when used in combination with aqueous alkaline liquids, such as an alkaline ink, can form sharp long-lived stencil/screen assemblies used in screen printing operations. More particularly, the invention relates to polyvinylpyridine (or pyridinium) containing films that can be cast from aqueous solutions which, after imaging and in contact with an alkaline liquid such as a screen printing ink, at a pH greater than 7, forms screen stencils with increased or improved water resistance that can be used in screen printing processes. The composition of the invention can be reclaimed from the screen using an aqueous acidic reclaiming composition.
BACKGROUND OF THE INVENTION
Images have been formed by screen printing processes for many years. In screen printing, an image is formed on a substrate by positioning a stencil comprising a given pattern in or on a finely divided mesh screen. An ink is then applied through the stencil/screen assembly onto the substrate resulting in a complementary image on the substrate. Such patterned stencils have been formed on screen constructions using a variety of techniques. Both photosensitive (negative and positive image) and non-photosensitive image forming processes have been used. The photosensitive materials used in making emulsion or film products can be solvent based or can be aqueous based. In many industries, including photostencil industries, the trend is away from solvent based materials to materials manufactured from or based on aqueous formulations. Many photosensitive film and liquid dispersions are now based on aqueous products. In a similar vein, both solvent based inks and solvent containing screen wash compositions have been used in screen printing operations. In response to demands of the market, vendors of screen printing materials have introduced water based inks. The use of water based or aqueous inks can cause images on stencils, made from water based films or aqueous emulsions, to swell or deteriorate reducing the effective lifetime of the stencil and image quality. Because these image layers formed from typically aqueous materials tend to interact with water based inks and swell, soften or otherwise deteriorate, a substantial need exists to improve the printing properties of materials derived from aqueous based systems for printing with water based inks.
BRIEF DISCUSSION OF THE INVENTION
We have found that the pH sensitivity of polymers having pendant units comprising a non-photosensitive nitrogen heterocycle, preferably a polymer comprising vinylpyridine (pyridinium), can be used to improve both photosensitive and non-photosensitive aqueous compositions and films, such as aqueous resist materials, blockout formulations and hand cut films, when used in screen printing with aqueous ink formulations. The screen printing stencil composition of the invention comprises a photosensitive polymer or photoresist material and a non-photosensitive polymer comprising pendant units comprising a nitrogen heterocycle such as a vinylpyridine and an aqueous vehicle or carrier. The invention can also be embodied in non-photosensitive compositions and methods.
Polymeric materials have been used in resist materials as both photosensitive and non-photosensitive components. Non-photosensitive components act as stabilizers, film forming agents, vehicles, pigments etc. A large variety of vinyl polymers take this role including polystyrenics, polyvinyl alcohols, polyacrylics, polyvinyl acetates; etc. In this regard pyridinium materials have also been used. Examples of photosensitive materials using pyridinium materials include the following. Leubner et al., U.S. Pat. No. 2,811,510, teach the use of light sensitive polymeric stilbazoles and salts thereof which are quaternized polyvinylpyridine materials having photopolymerizable unsaturated units. Takeda et al., U.S. Pat. No. 4,245,027, teach a light sensitive image recording material that uses a compound which on exposure to actinic radiation is capable of complexing a polyvinylpyridine material or a compound which releases a precursor capable of complexing polyvinylpyridine to form a pyridinium salt. The Takeda et al. material requires an activating exposure to appropriate wavelengths of light. Chiang et al.,
Journal of Organic Chemistry
, Vol. X, pp. 21-25 (1945) teach the light sensitivity of stilbazole nuclei. Ichimura et al.,
Journal of Polymer Science: Polymer Chemistry Edition
, Vol. 18, pp. 891-890 (1980), teach the reaction of the homopolymer of 2-chloroethyl vinyl ether and the copolymer of N-vinylpyrrolidone with stilbazole to form photosensitive polymers that can be used to immobilize enzymes. Borden, Canadian Patent No. 901,370, teaches photosensitive polymeric compositions containing vinyl styryl pyridinium materials insolubilized by the action of actinic radiation. Haas, U.S. Pat. No. 3,507,846, teaches methods for polymerizing vinylpyridine into polyvinylpyridine polymers. Yamaoka et al., U.S. Pat. No. 4,515,886, teach photosensitive materials useful as photoresists in the manufacture of semiconductors, transistors and other electrically active components in aqueous systems for photosensitive compositions. Day et al., U.S. Pat. No. 4,477,552, teach a use of a small amount of a non-photosensitive polyvinylpyridine (less than about 1 wt-%) as a stabilizer for water sensitive colloidal diazo-resin sensitizers. The pyridinium materials neither directly participate in the resist formation photoreactions nor provide any substantial properties to the stencil other than the stability of the diazo.
In a stencil or film, when in contact with acid, the pyridine polymer converts into a water soluble or dispersible pyridinium form. An opposite process can be easily performed by action of base. In contact with a base, the acid salt (quaternary) form of the polymer regenerates original polymer (in free amine form) that is inherently water insoluble. Such properties could be demonstrated with polyvinylpyridine (substituted or not in a homopolymer or copolymer form), quinolines, polyvinyl quinaldines, polyvinyl quinazolines and other polymers that have a nitrogen atom in a main chain or in a backbone.
The success of the use of the acid-base properties or pH solubility/sensitivity of the preferred non-photosensitive pyridinium materials in the resist to improve the image forming properties of the resist is a surprise. When contacted with acid, the pyridine nitrogen forms an amine salt. As shown below, the acid base reaction can be used to convert the polymer from a soluble pyridinium salt to a water insoluble free amine (pyridine) moiety. The insoluble pyridinium materials used at a concentration of greater than about 5 wt % hardens and improves the image.
The reaction of a sufficient proportion of the pyridine moieties to form the pyridinium form renders the polymer soluble or dispersible in aqueous media. When contacted with sufficient proportions of alkaline materials, the water soluble pyridinium salt is converted to the free amine form (pyridine) which is substantially water insoluble. We have found that the alkaline character of common water-based inks cooperates with the nitrogen heterocycle in the polymeric composition in the screen stencil to improve the finished stencil. In the preferred mode of the stencil composition, the polymer comprising repeating units with the nitrogen heterocycle pendant groups can have a degree of polymerization of about 50 to 100,000. The polyvinylpyridine can be a homopolymer having a molecular weight ranging from about 10
4
to 10
6
. The polymer comprising vinylpyridine can be formulated with other vinyl polymers, photosensitive compounds or compositions, surfactants, co-solvents, dyes, etc. The polyvinylpyridine can also be used in blockout formulations without a photosensitive material. These materials can be used in forming hand cut stencils from sheet stock compri
Gybin Alexander S.
Johnson Kyle K.
Komatsu Toshifumi
Vaniseghem Lawrence C.
Chu John S.
Merchant & Gould P.C.
The Chromaline Corporation
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