Pressure-Sensitive Adhesive Mastication Using Fatty Acids
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Solution Overview
Problem
Existing continuous extrusion processes for producing pressure-sensitive adhesives from high-molecular-weight natural rubber face challenges in maintaining productivity and adhesion properties, often requiring longer residence times or chemical peptizers, which can disrupt adhesive aging and leave residue on substrates.
Innovation Solution
A two-step continuous process using a single- or twin-screw extruder with mild temperatures and the addition of C12-C24 fatty acids to facilitate mastication of natural rubber, reducing viscosity and improving adhesion without the need for peptizers or high-temperature processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If high-molecular-weight natural rubber (TSR grade) is used in continuous extrusion process, then production cost is reduced and capital investment is lowered, but longer residence times are needed which sacrifices high throughput rates
Solution Approach 1:
A peptizer is introduced as an intermediary substance to facilitate the mastication of high-molecular-weight natural rubber during continuous extrusion. The peptizer chemically assists in breaking down the rubber molecules, enabling adequate mastication without extending residence time, thus maintaining high throughput rates while using cost-effective TSR grade rubber
Solution Approach 2:
The molecular weight parameters of the natural rubber are changed by introducing a peptizer that catalyzes the breakdown of polymer chains. This parameter modification allows high-molecular-weight TSR rubber to be processed effectively in continuous extrusion without sacrificing productivity
2Productivity
If chemical peptizers are added to facilitate rubber breakdown, then throughput rates are maintained, but residual peptizer disrupts aging properties of the adhesive
Solution Approach 1:
The chemical composition parameters of the peptizer are optimized to achieve effective rubber mastication with minimal residual impact on adhesive aging. By carefully selecting and dosing the peptizer, adequate molecular breakdown is achieved while limiting disruption to the adhesive's long-term performance
3Manufacturing precision
If longer residence times are used in extruder, then adequate mastication of high-molecular-weight rubber is achieved, but high throughput rates are sacrificed
Solution Approach 1:
A peptizer is used as a chemical intermediary to accelerate the mastication process. This mediator enables adequate molecular breakdown of high-molecular-weight rubber without requiring extended residence time in the extruder, thus maintaining high throughput rates while achieving proper mastication quality
Solution Approach 2:
The mechanical mastication process is supplemented or replaced by chemical action of the peptizer. Instead of relying solely on mechanical shear forces that require long residence times, the peptizer provides chemical assistance that speeds up molecular breakdown, enabling shorter residence times while maintaining mastication quality
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 enables the production of pressure-sensitive adhesives with improved adhesion to steel and enhanced clean removability from difficult substrates like marble and ceramic tile, maintaining adhesive properties and reducing residue, while maintaining high throughput rates.
Implementation Method 1
The high molecular weight of natural rubber is usually reduced by mastication in a batch process using a Banbury or similar mixer
Implementation Method 2
The natural rubber has a Mooney viscosity within the range of 85 to 100... The product is a homogeneous pressure-sensitive adhesive having a viscosity, measured at 150° C. and a shear rate of 5000 s−1, at least 15% lower than the viscosity of a pressure-sensitive adhesive prepared by a similar process without the added C12-C24 fatty acid
Implementation Method 3
A first step comprises masticating in a single- or twin-screw extruder a mixture comprising natural rubber, a tackifier, a filler, and an added C12-C24 fatty acid
Implementation Method 4
The mastication is performed in a first section of the extruder at a temperature within the range of 10° C. to 45° C. In a second step, mastication of the mixture continues in at least one subsequent extruder section at a temperature within the range of 45° C. to 100° C.
Implementation Method 5
a rubber adhesive that can penetrate openings in the scrim and bond the scrim to the backing layer... The process enables the production of pressure-sensitive adhesives with improved adhesion to steel
Data Source
AI summary
A continuous process for making a pressure-sensitive adhesive is disclosed. A mixture comprising natural rubber having a Mooney viscosity of 85 to 100, a tackifier, a filler, and 0.1 to 5 wt. % of an added C12-C24 fatty acid based on the amount of mixture is masticated in a first section of a single- or twin-screw extruder. Mastication of the mixture continues in at least one subsequent extruder section in the presence of additional tackifier. The product is a homogeneous, reduced-viscosity pressure-sensitive adhesive. The minor proportion of added C12-C24 fatty acid aids mastication of the rubber and enables high throughput without addition of peptizers. Duct tapes made from the adhesives display improved adhesion to steel, better adhesion bond strength, and enhanced seven-day clean removability from even difficult substrates such as marble or ceramic tile.