Radiation-Crosslinkable Hotmelt Adhesive for High Cohesion
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Solution Overview
Problem
Radiation-crosslinkable hotmelt adhesives face challenges in achieving sufficient cohesion and shear strength, particularly at elevated temperatures, due to high viscosity issues caused by polar groups, which are exacerbated by viscosity-lowering additives that compromise adhesion and cohesion.
Innovation Solution
A radiation-crosslinkable hotmelt adhesive comprising at least 60% by weight of C1 to C18 alkyl(meth)acrylates and oligo(meth)acrylates with nonacrylic C—C double bonds, along with a photoinitiator, which is either added as an additive or incorporated by copolymerization, to achieve high cohesion and low viscosity, enabling effective adhesion and cohesion through controlled crosslinking with UV light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the fraction of polar groups in acrylate polymers is increased to achieve higher cohesion, then the cohesion and shear strength are improved, but the zero-shear viscosity increases to more than 100 Pa s at coating temperature, making the adhesive difficult to apply
Solution Approach 1:
The patent changes the chemical composition parameters by incorporating specific polar groups (carboxylic acid, hydroxyl, amide, urea, carbamate) at controlled fractions (0.1-30 wt%, preferably 0.5-25 wt%, more preferably 1-15 wt%) into the poly(meth)acrylate structure. This parameter optimization allows achieving high cohesion (shear strength ≥40 min at 70°C) while maintaining manageable viscosity (<100 Pa s at 130°C) for practical coating operations.
2Ease of operation
If viscosity-lowering additives such as plasticizers, resins, and low molecular mass blending polymers are used to reduce viscosity, then the ease of coating is improved, but the cohesion and adhesion are destroyed or adversely affected due to migration and UV absorption
Solution Approach 1:
The patent extracts and eliminates the need for conventional viscosity-lowering additives (plasticizers, resins, low molecular mass blending polymers) by directly incorporating the necessary polar functional groups into the poly(meth)acrylate polymer structure itself. This extraction of harmful additives resolves the contradiction by achieving both low viscosity and high cohesion without migration or UV interference.
Solution Approach 2:
The patent creates a composite polymer structure where poly(meth)acrylate is combined with specific polar functional groups (carboxylic acid, hydroxyl, amide, urea, carbamate) to form a unified adhesive composition. This composite approach integrates viscosity control and cohesion enhancement into a single material system, eliminating the need for separate additive components that cause migration and UV absorption problems.
3Ease of manufacture
If viscosity-lowering additives are used to enable coating, then the ease of manufacture is improved, but the peel strength and adhesion are adversely affected
Solution Approach 1:
The patent changes the chemical structure parameters of the poly(meth)acrylate by incorporating polar functional groups at optimized fractions, which simultaneously improves coating processability (by reducing viscosity through molecular structure modification rather than additives) and enhances peel strength (by improving adhesion through polar interactions with substrates). This parameter optimization eliminates the need for harmful viscosity-lowering additives.
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 hotmelt adhesive with enhanced cohesion and shear strength at elevated temperatures while maintaining low viscosity, ensuring effective adhesion and cohesion without the drawbacks of conventional additives, thus suitable for various applications including adhesive tapes.
Implementation Method 1
The hotmelt adhesive comprises a photoinitiator and can be used for producing adhesive tapes. The irradiation takes place preferably with actinic radiation, preferably UV light, more particularly UV-C radiation.
Implementation Method 2
Radiation-curable PSAs, especially hotmelt PSAs free from water and solvent, generally have good adhesion. The cohesion can be enhanced by irradiation with high-energy light.
Data Source
AI summary
Described is a radiation-crosslinkable hotmelt adhesive comprising at least one radiation-crosslinkable poly(meth)acrylate formed to an extent of at least 60% by weight of C1 to C10 alkyl(meth)acrylates and at least one oligo(meth)acrylate which comprises nonacrylic C C double bonds and has a K value of less than or equal to 20. The hotmelt adhesive comprises a photoinitiator which may be present in the form of an additive not attached to the poly(meth)acrylate and/or not attached to the oligo(meth)acrylate, may be incorporated by copolymerization into the poly(meth)acrylate, and/or may be attached to the oligo(meth)acrylate. The hotmelt adhesive can be used for producing adhesive tapes.