UV-Curable Pressure Sensitive Adhesive Uniform Tack
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Solution Overview
Problem
UV-curable pressure sensitive acrylic adhesives exhibit uneven tack and properties on both sides after curing, with one side being strongly exposed to UV light, leading to inadequate adhesion in transfer processes and double-sided tapes, and require higher UV doses, affecting productivity.
Innovation Solution
The development of UV-curable pressure sensitive acrylic adhesives using specific acrylic monomers with pendant reactive functional groups, such as cycloaliphatic epoxides and oxetanes, reacted with cationic photoinitiators, which allows for uniform tack and properties on both sides after curing, reducing the required UV dose and enhancing productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional UV-curable pressure sensitive acrylic adhesives are cured with medium pressure mercury lamps, then the adhesive side exposed to UV light achieves sufficient curing, but the opposite side facing the release liner has strongly reduced tack and inadequate adhesion
Solution Approach 1:
The patent applies local quality by using a multi-layer adhesive structure where the first adhesive layer (in contact with release liner) has different composition and properties than the second adhesive layer (exposed to UV light). The first layer is formulated to maintain high tack and adhesion to release liner, while the second layer is optimized for UV curing and bonding to final substrate. This resolves the contradiction by giving each side locally optimized properties rather than uniform composition throughout.
Solution Approach 2:
The invention employs asymmetry by creating an asymmetric adhesive structure with two distinct adhesive layers having different formulations, thicknesses, and functional characteristics. The layer configuration and composition are deliberately asymmetric to match the asymmetric curing conditions (one side exposed to UV, one side protected), thereby achieving uniform performance on both sides despite asymmetric processing.
2Reliability
If higher UV doses are applied to ensure adequate curing of the adhesive, then curing completeness improves, but line speed decreases and productivity is reduced
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition and photoinitiator system of the adhesive to achieve curing at lower UV doses. Specifically, the adhesive contains cationic photoinitiators and reactive functional groups (epoxide, oxetane, or vinyl) that enable efficient cationic polymerization upon UV exposure. This chemical optimization allows complete curing at reduced UV energy input, thereby maintaining reliability while improving productivity through higher line speeds.
3Quantity of substance
If solvent borne or water based acrylic adhesives are used, then higher coat weights can be applied in a single step, but the need for solvent or water removal adds process complexity and waste
Solution Approach 1:
The invention applies the taking out principle by completely removing the solvent or water component from the adhesive formulation, using instead a 100% solids content UV-curable acrylic adhesive. This eliminates the need for drying or evaporation steps to remove solvents, reducing process complexity and waste while maintaining the capability to apply higher coat weights in a single step. The UV-curable chemistry enables direct curing of high-solids formulations without liquid carriers.
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 solution achieves uniform tack and improved performance on both sides of the adhesive, requiring lower UV doses, increasing line speed and productivity, and eliminating the need for solvent removal, enabling higher coat weights and reduced waste.
Implementation Method 1
UV-curable pressure sensitive acrylic adhesives which are obtainable by reacting a specific acrylic monomer with at least one monomer which comprises a pendant reactive functional group selected from cycloaliphatic epoxides, oxetanes, mono-substituted oxiranes or mixtures in a first step and then reacting the obtained mixture with at least one cationic photoinitiator
Data Source
AI summary
The present invention relates to an UV-curable pressure sensitive acrylic adhesive obtainable by reacting in a first step a mixture comprising: (i) at least one acrylic monomer of formula (I)wherein R1 is H or CH3; and wherein R2 and R3 are both H or both CH3; and n is an integer from 0 to 22; or mixtures thereof; and (ii) at least one monomer which comprises a pendant reactive functional group selected from cycloaliphatic epoxides, oxetanes, mono-substituted oxiranes or mixtures thereof; and in a second step reacting the obtained mixture from the first step with (iii) at least one cationic photoinitiator; and (iv) optionally further additives. An article comprising this adhesive, and a method of manufacturing the article.