Non-thermoplastic Pressure-sensitive Adhesive Mixing Process
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Solution Overview
Problem
The production of non-thermoplastic pressure-sensitive adhesives (PSAs) often results in thermal degradation of polymers during mixing, leading to reduced cohesion and stability due to high shear energies and temperatures, which complicates achieving high viscosity without post-crosslinking and solvent-based processes.
Innovation Solution
A method involving a two-step mixing process using a planetary roller extruder, where a processing agent with a lower boiling point is added to quench the premix between mixing steps, allowing for controlled temperature reduction and minimizing thermal degradation, enabling the production of highly cohesive PSAs without solvents or additives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high shear energies are applied during mixing to achieve homogeneous mixing of adhesive components, then mixing homogeneity is improved, but thermal degradation of polymers increases
Solution Approach 1:
The mixing process is divided into multiple stages with different intensity levels. High-shear mixing is applied first to achieve homogeneous distribution of components, followed by a low-shear finishing stage to eliminate thermal degradation effects and ensure final mixing homogeneity without excessive heat generation.
Solution Approach 2:
The mixing process uses periodic alternation between high-shear and low-shear mixing modes. Cycles of intensive mixing are followed by rest periods or gentle mixing phases, allowing heat dissipation and preventing cumulative thermal degradation while maintaining mixing effectiveness.
2Manufacturing precision
If prolonged mixing time is used to achieve homogeneous mixing, then mixing homogeneity is improved, but thermal degradation increases
Solution Approach 1:
Components are pre-prepared and pre-positioned in the mixer before the main mixing process. This preliminary preparation reduces the overall mixing time required to achieve homogeneity, thereby limiting the duration of thermal exposure and reducing polymer degradation.
Solution Approach 2:
The mixing process is enhanced by replacing purely mechanical extended mixing with controlled thermal processing or chemical activation methods. This substitution achieves homogeneous mixing more quickly without relying on prolonged mechanical shear that generates heat over extended periods.
3Ease of operation
If solvent-based processes are used to reduce viscosity during processing, then processability is improved, but additional process steps are required
Solution Approach 1:
The viscosity of the adhesive system is controlled by adjusting physical parameters such as temperature and shear rate rather than by adding solvents. During processing, temperature and shear conditions are optimized to achieve suitable viscosity levels, eliminating the need for solvent-based viscosity reduction and subsequent solvent removal steps.
Solution Approach 2:
The adhesive system exhibits self-adjusting viscosity characteristics through its rheological properties. The material automatically adapts its viscosity to processing conditions, providing ease of application without requiring external solvents or additional processing steps to modify its flow properties.
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
This method effectively reduces thermal degradation, allowing for the production of high-viscosity PSAs with larger average chain lengths, enhancing their cohesion and stability, and enabling their use in applications requiring strong adhesion and removability without post-crosslinking or solvent-based processes.
Implementation Method 1
Particularly due to the high viscosity of the non-thermoplastic components, internal mixers or extruders are often used, such as twin-screw extruders or planetary roller extruders, in order to be able to apply the high shear energies that are required for homogeneous mixing of the adhesive.
Implementation Method 2
The introduction of high shear energies into the highly viscous mixture results in the temperature of the mixture increasing
Implementation Method 3
This can be achieved by adding a processing agent 403 to the premix 402, namely before the second mixing step, which is subsequently evaporated 404 from the premix 402.
Implementation Method 4
The cooling effect of the process medium is further improved upon addition, so that particularly rapid quenching of the premix is possible
Data Source
Figure 1
AI summary
A process for producing a highly cohesive, non-thermoplastic pressure-sensitive adhesive based on elastomers is presented. This process uses neither solvents nor thermoplastic additives, yet minimizes thermal degradation during compounding. This is achieved by adding a vaporizable process agent, which is introduced into the adhesive after pre-mixing the components and evaporates rapidly, thus quenching the adhesive. Furthermore, the use of water for cooling the adhesive is proposed, and the resulting highly cohesive pressure-sensitive adhesive, as well as a pressure-sensitive tape containing this adhesive, are presented.