Polyvinyl Acetate Photopolymer for Screen Printing Stencils
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Solution Overview
Problem
Conventional photosensitive compositions for screen printing stencils and photolithography face issues such as limited shelf life, sensitivity to oxygen and moisture, slow photoreaction speed, and poor water resistance, particularly due to the use of dichromate and diazo resins, which require multiple components and lead to instability and reduced image resolution.
Innovation Solution
A photosensitive polymer composition based on non-hydrolyzed polyvinyl acetate (PVAc) with styrylpyridinium and/or styrylquinolinium groups, which allows for efficient photo-crosslinking with minimal photodimerizable groups, resulting in a water-resistant and abrasion-resistant hardened product with high photo-sensitivity and image resolving power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If dichromate sensitized water-soluble emulsions are used, then photosensitivity is achieved, but shelf life is limited due to dark reaction making unexposed areas insoluble
Solution Approach 1:
The patent extracts the problematic dichromate component from the system and replaces it with a photodimerizable compound (cinnamoyl group) that does not undergo dark reactions. This removal of the harmful element (dichromate) while retaining the useful function (photosensitivity) resolves the contradiction between achieving photosensitivity and maintaining shelf life.
Solution Approach 2:
The patent changes the chemical parameter of the sensitizer from dichromate to a photodimerizable compound with cinnamoyl groups. This parameter change fundamentally alters the chemical behavior, eliminating the dark reaction while preserving photosensitivity, thereby extending shelf life without sacrificing photosensitivity.
2Illumination intensity
If diazo resins are used for photosensitization, then photosensitivity is achieved, but photoreaction speed is slow
Solution Approach 1:
The patent changes the chemical structure of the photosensitizer from diazo resin to photodimerizable compounds (cinnamates, chalcones, stilbenes, coumarins). These compounds have different photoreaction mechanisms that proceed faster upon UV exposure, thereby increasing photoreaction speed while maintaining adequate photosensitivity.
3Strength
If high levels of cinnamoyl groups are added for crosslinking, then photo-crosslinking efficiency is improved, but water developability decreases
Solution Approach 1:
The patent optimizes the concentration parameter of cinnamoyl groups, finding that low levels (0.05-0.5 mole%) are sufficient for effective crosslinking. This parameter optimization achieves crosslinking efficiency without excessive cinnamoyl content, thereby preserving water developability of the emulsion system.
Solution Approach 2:
The patent applies partial action by using minimal amounts of photodimerizable groups (0.05-0.5 mole%) rather than high levels. This partial action is sufficient to achieve the desired crosslinking effect while avoiding the negative consequence of reduced water developability that would occur with excessive cinnamoyl content.
4Strength
If free radical initiated systems are used, then photopolymerization is achieved, but oxygen and moisture sensitivity increases
Solution Approach 1:
The patent substitutes the free radical initiation mechanism with a photodimerization mechanism. Instead of using oxygen-sensitive free radical initiators, the system uses UV-induced photodimerization of cinnamoyl groups, which is not sensitive to oxygen or moisture. This mechanism substitution maintains polymerization capability while significantly improving stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composition achieves faster photoreaction speeds, higher water resistance, and improved image resolution, maintaining stability and functionality for extended periods without phase separation, outperforming traditional polyvinyl alcohol-based systems.
Implementation Method 1
a photosensitive polymer composition in the form of an aqueous emulsion comprising a non-hydrolyzed or non-saponified vinyl acetate polymer (polyvinyl acetate) added with a styrylpyridinium and/or styrylquinolinium group
Data Source
AI summary
The present invention discloses a photosensitive composition, comprising polyvinyl acetate (0% saponified) having a styryl type nitrogen-containing heterocyclic groups such as a styrylpyridinium or/and styrylquinolinium that possesses high UV light energy sensitivity with a small photosensitive group content, high solid content, high water resistance, and very sharp imaging characteristics and produced therefrom photosensitive compositions such as a photo-resist, photolithographic plates, screen printing stencil emulsion and film, and abrasion resistant photosensitive emulsion and film, and other photosensitive compositions being used for commercial and industrial applications.