Grafted Rubber Polymer Dispersion for Pressure Sensitive Adhesives
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Solution Overview
Problem
Existing pressure-sensitive adhesives (PSAs) based on natural rubber have low stability and high coagulum formation during emulsion polymerization, leading to unstable dispersions and loss of adhesive properties due to crosslinking, which limits their use in commercial applications, especially on low surface tension substrates like polypropylene.
Innovation Solution
A specific emulsion polymerization process is developed to create a hybrid aqueous polymer dispersion by grafting acrylic monomers onto natural or synthetic rubber polymers, using a redox initiator system and maintaining a pH above 7 to prevent crosslinking, resulting in a stable dispersion with low coagulum and high adhesive performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If natural rubber is used as base polymer in emulsion polymerization, then adhesive properties and soft touch are improved, but stability and coagulum formation worsen
Solution Approach 1:
The patent creates a hybrid polymer system combining natural rubber particles with acrylic copolymer particles in a single aqueous dispersion. This composite approach allows the natural rubber to provide adhesive properties and soft touch while the acrylic component contributes to stability and prevents coagulum formation, resolving the contradiction between adhesive performance and dispersion stability.
2Reliability
If acrylic monomers are grafted onto rubber polymer, then adhesion on low surface tension substrates is improved, but crosslinking and coagulum formation increase
Solution Approach 1:
The patent segments the polymer system into distinct rubber polymer particles and acrylic copolymer particles within the aqueous dispersion, preventing unwanted crosslinking between them. This segmentation allows the acrylic monomers to be incorporated in a controlled manner that improves adhesion on low surface tension substrates without causing excessive crosslinking and coagulum formation.
Solution Approach 2:
The patent carefully controls the grafting parameters including monomer ratio, initiator concentration, and reaction conditions to optimize the balance between achieving good adhesion on low surface tension substrates through acrylic monomer incorporation and preventing harmful crosslinking and coagulum formation.
3Reliability
If emulsion polymerization is used to produce hybrid copolymer, then adhesive performance is improved, but dry coagulum formation increases
Solution Approach 1:
The patent uses an aqueous medium as an intermediary to carry out the emulsion polymerization process, which allows for controlled polymerization and reduces the formation of dry coagulum. The aqueous environment provides better control over the polymerization reaction compared to organic solvents, maintaining high adhesive performance while minimizing substance loss through coagulum formation.
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 process produces a PSA with improved cohesive strength, adhesion on low surface tension substrates, and maintains the soft touch characteristic of natural rubber-based adhesives, while preventing crosslinking and coagulum formation, ensuring stability and effectiveness in commercial applications.
Implementation Method 1
using a redox initiator system
Implementation Method 2
specific process of emulsion polymerization of said monomeric composition in the presence of said aqueous rubber dispersion
Implementation Method 3
polymeric particles of rubber polymer, in particular natural rubber polymer modified, in particular grafted with a monomeric composition comprising specific acrylic monomers
Data Source
AI summary
The invention relates to an aqueous polymer dispersion comprising:a) an aqueous polymer dispersion comprising grafted rubber polymeric particles from rubber polymer being selected from natural or synthetic rubber,b) an aqueous polymer dispersion with polymeric particles of a second polymer comprising monomeric units derived front a monomeric composition b) comprising:b1) a (meth)acrylate of a linear or branched alcohol in C4 to C10 or a mixture of such (meth)acrylates, said (meth)acrylate having Tgb1 lower than −30° C.,b2) optionally, at least one comonomer having Tgb2 higher than −30° C.,with said grafted rubber polymeric particles being grafted in an aqueous dispersion by a part of said monomeric composition b) as defined above. The invention covers a process of preparation of said dispersion, an adhesive composition comprising said dispersion, the use of said dispersion in pressure sensitive adhesives, and the resulting adhesive.