Solventless Adhesive for High-Temperature Sterilization
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Solution Overview
Problem
Two-component curable solventless adhesives used in laminated composite films experience a significant decrease in adhesive strength after high-temperature sterilization, particularly when packaging foods containing acid components, leading to issues like 'pear skin' appearance and peeling of the plastic film from the metal foil.
Innovation Solution
A two-component curable solventless adhesive with a base resin containing a polyol having 30% or more secondary or tertiary terminal hydroxyl groups and a curing agent comprising isocyanate-terminated urethane prepolymer with an average functionality of 1.5 to 2.5, along with a controlled reaction to maintain adhesive strength and workability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a two-component curable solventless adhesive containing polyol and polyisocyanate is used, then workability and adhesion performance are improved, but adhesive strength drastically decreases after high-temperature sterilization treatment
Solution Approach 1:
The patent modifies the chemical parameters of the polyol by introducing acid groups through reaction with acid anhydride, and adjusts the molecular weight and hydroxyl group composition of the polyol. These parameter changes enable the adhesive to maintain stability and strength after high-temperature sterilization while preserving workability during application.
Solution Approach 2:
The patent creates a composite adhesive system combining polyol with acid groups, polyisocyanate, and acid anhydride modifiers. This composite formulation provides both immediate adhesion performance and long-term durability after sterilization, resolving the contradiction between workability and post-sterilization reliability.
2Strength
If hydroxyl groups of polyol are acid-modified with acid anhydride, then adhesion between metal foil and plastic film is improved, but viscosity increases rapidly causing deterioration of workability
Solution Approach 1:
The patent applies partial acid modification to hydroxyl groups rather than complete modification. By controlling the degree of acid anhydride reaction, the adhesive achieves sufficient adhesion enhancement without excessive viscosity increase that would compromise workability. The acid group content is optimized to balance these competing requirements.
Solution Approach 2:
The patent precisely controls the parameter of acid group content in the polyol by regulating the acid anhydride modification process. This parameter control allows the adhesive to achieve the minimum necessary adhesion improvement while maintaining viscosity within workable limits, resolving the contradiction between strength and ease of operation.
3Loss of substance
If molecular weight of adhesive components is reduced for solventless formulation, then solvent content is eliminated, but adhesive strength decreases after high-temperature sterilization
Solution Approach 1:
The patent changes the molecular weight parameter of the polyol to an optimized range that maintains solventless formulation benefits while providing sufficient adhesive strength after sterilization. The acid group introduction further modifies the chemical parameters to enhance thermal stability without requiring high molecular weight components.
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 adhesive maintains excellent appearance and adhesive strength for a long period after high-temperature sterilization, preventing peeling and ensuring interlaminar adhesion, making it suitable for packaging materials in various industrial fields.
Implementation Method 1
a two-component curable solventless adhesive comprising a base resin and a curing agent, wherein the base resin contains a polyol having an acid group and a secondary or tertiary terminal hydroxyl group
Implementation Method 2
a two-component curable solventless adhesive containing a polyol as a base resin and a polyisocyanate as a curing agent
Implementation Method 3
a method of acid-modifying hydroxyl groups of a polyol with an acid anhydride has been proposed as means for improving adhesion between the metal foil such as an aluminum foil and a plastic film
Data Source
AI summary
A two-component curable solventless adhesive which enables a laminated composite film comprising a barrier layer and a plastic film laminated with each other to maintain excellent appearance and adhesive strength for a long period even after a sterilization treatment at high temperature, and to appropriately adjust a reaction between a base resin and a curing agent during a production of the laminated composite film. The two-component curable solventless adhesive comprises a base resin and a curing agent, wherein the base resin contains a polyol having an acid group and a secondary or tertiary terminal hydroxyl group accounting for 30% or more of the entire terminal hydroxyl groups of the polyol, and the curing agent contains an isocyanate group-terminated urethane prepolymer containing at least an aralkyl polyisocyanate and/or a modified substance thereof as a raw polyisocyanate, and a content of a low molecular weight polyisocyanate is defined.