Asymmetric Block Copolymer Hot-Melt Adhesive Viscosity Control
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Solution Overview
Problem
Hot melt adhesives used in manufacturing paper diapers and sanitary products face challenges in achieving easy application at low temperatures, maintaining a long open time, and ensuring high holding power, as existing formulations often have high melt viscosity at lower temperatures and insufficient open time.
Innovation Solution
A hot-melt adhesive composition is developed using a block copolymer composition comprising asymmetric aromatic vinyl-conjugated diene-aromatic vinyl block copolymers with specific molecular weight ratios and a tackifying resin, which maintains low melt viscosity at low temperatures and enhances holding power and open time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If aromatic vinyl-conjugated diene-aromatic vinyl block copolymer is used as base polymer, then adhesiveness to polyolefins is improved, but melt viscosity increases at lower temperatures
Solution Approach 1:
The patent uses a composite block copolymer structure consisting of a hard segment (aromatic vinyl-conjugated diene-aromatic vinyl block copolymer) and a soft segment (polybutadiene block copolymer). This composite structure allows the adhesive to maintain high adhesiveness to polyolefins while the soft segment prevents excessive viscosity increase at lower temperatures, resolving the contradiction between strength and temperature sensitivity.
2Strength
If block copolymer with two aromatic vinyl blocks of different molecular weights is used, then low temperature adhesives force is improved, but open time becomes insufficient
Solution Approach 1:
The patent changes the molecular weight parameters of the block copolymer components, specifically using a polybutadiene block copolymer with weight average molecular weight of 50,000-200,000 and controlling the aromatic vinyl monomer unit content to 30-70%. These parameter adjustments allow the adhesive to maintain low viscosity at application temperature (extending open time) while ensuring sufficient adhesives force through the asymmetric block structure.
3Ease of operation
If viscosity is lowered at relatively low temperature, then easy appliability is improved, but holding power becomes insufficient
Solution Approach 1:
The patent creates a dynamic viscosity profile through the block copolymer composition, where the adhesive exhibits low viscosity at application temperature for easy appliability, but develops high holding power as the temperature decreases and the adhesive sets. The soft segment provides initial fluidity while the hard segment ensures final bond strength.
Data Source
AI summary
Provided is a hot-melt adhesive composition which can be easily applied at a relatively low temperature, has a long open time, and also has high holding power. A hot-melt adhesive composition comprising a block copolymer composition which includes a block copolymer A and a block copolymer B, and a tackifying resin, wherein a weight ratio (A/B) of the block copolymer A and the block copolymer B is 25/75 to 90/10, and an aromatic vinyl monomer unit content of the block copolymer A is 41% or greater.