UV Curable Acrylic Hot Melt Adhesive Cohesive Strength
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Solution Overview
Problem
Current technologies for crosslinking acrylic polymers in pressure sensitive adhesives face challenges such as the need for multifunctional polyols and photopolymerizable diacrylates, which are unsuitable for hot melt adhesives, and there is a demand for UV-curable acrylic polymers that can be processed as hot melts with reduced environmental emissions.
Innovation Solution
A UV curable adhesive composition comprising a UV curable acrylic polymer with covalently bound UV-reactive groups and a cationic photoinitiator, which is coated onto a substrate and cured under UV radiation in the range of 200 to 600 nm, specifically using a cationic photoinitiator like diaryliodonium salts and photosensitizers to promote crosslinking and achieve a hot melt pressure sensitive adhesive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If very low molecular weight polymers are used to achieve sufficient fluidity at application temperatures, then the adhesive becomes easily coatable, but the cohesive strength is insufficient
Solution Approach 1:
The patent changes the molecular weight parameter of the polymer to a moderate range that provides acceptable fluidity without sacrificing cohesive strength, and introduces UV-reactive groups to enable crosslinking that compensates for the moderate molecular weight
Solution Approach 2:
The patent creates a composite system combining moderate molecular weight polymers with UV-reactive groups and cationic photoinitiators, where the UV crosslinking component provides the cohesive strength that would otherwise require high molecular weight polymers
2Strength
If very high molecular weight polymers are used to improve cohesive strength, then the adhesive gains sufficient cohesion, but the viscosity becomes too high for easy coating
Solution Approach 1:
The patent adjusts the polymer molecular weight to a moderate range that provides acceptable fluidity for coating, and introduces UV crosslinking capability to achieve the required cohesive strength without needing very high molecular weight polymers
Solution Approach 2:
The patent replaces the mechanical approach of using high molecular weight polymers to achieve cohesive strength with a chemical approach using UV-induced crosslinking of moderate molecular weight polymers with UV-reactive groups
3Ease of operation
If low molecular weight oils or resins are added to reduce viscosity for easier coating, then the adhesive becomes more fluid, but the cohesive strength and heat resistance deteriorate
Solution Approach 1:
The patent uses moderate molecular weight polymers instead of low molecular weight oils or resins to achieve acceptable fluidity, and introduces UV crosslinking capability to provide the cohesive strength and heat resistance that would otherwise require high molecular weight polymers or extensive addition of low molecular weight additives
4Strength
If photopolymerizable diacrylate is used for crosslinking, then the adhesive gains cohesive strength, but it becomes unsuitable for hot melt adhesive applications requiring post-application polymerization
Solution Approach 1:
The patent replaces radical photopolymerization of diacrylate with cationic photopolymerization of UV-reactive groups, enabling the adhesive to be processed as a hot melt and then cured under UV irradiation without requiring post-application polymerization steps
Solution Approach 2:
The patent changes the polymerization mechanism from radical to cationic, and uses moderate molecular weight polymers with UV-reactive groups instead of photopolymerizable diacrylate, enabling both hot melt processability and UV curability
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 provides a hot melt pressure sensitive adhesive with improved cohesive strength, reduced shrinkage, and enhanced adhesiveness, suitable for use in tapes and medical tapes, with a Shear Adhesion Failure Temperature (SAFT) greater than 110°C and peel adhesion, while being environmentally friendly and cost-effective.
Implementation Method 1
a UV curable adhesive composition comprising a UV curable acrylic polymer which comprises at least one covalently bound UV reactive group and a cationic photoinitiator
Implementation Method 2
Hot melt adhesives are solids at room temperature, melt at elevated temperatures to coat on a substrate
Data Source
AI summary
The present invention relates to a UV curable adhesive composition comprising a UV curable acrylic polymer comprising at least one covalently bound UV-reactive group and a cationic photoinitiator and a method of curing such composition. The invention further includes hot melt pressure sensitive adhesives comprising such cured composition and use of said hot melt pressure sensitive adhesives.