Foamed Adhesive Viscosity Control for Oily Surfaces
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Solution Overview
Problem
Foamable adhesives struggle to provide sufficient adhesion to oily metal surfaces, often resulting in adhesive failure during metal cleaning and pre-treatment processes, and fail to maintain shape and location during heat cycles, leading to undesirable sagging and loss of the adhesive.
Innovation Solution
A hot melt adhesive formulation combining solid polymers, a thixotropic filler, a blowing agent system, and a cross-linking system with specific activation temperatures to control melt viscosity and ensure adhesion to oily surfaces, maintaining shape and developing adhesive properties at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the adhesive is applied as a hot melt with low melt viscosity for easy application, then the adhesive can be readily applied by extrusion, but the adhesive will sag and drop off the substrate during heating to the foaming temperature
Solution Approach 1:
The adhesive formulation utilizes temperature-dependent viscosity changes. At application temperature, the adhesive has low viscosity for easy extrusion. During heating to foaming temperature, the viscosity increases to prevent sagging, and at foaming temperature, the viscosity is optimized to trap gases while maintaining shape retention.
Solution Approach 2:
The adhesive exhibits dynamic rheological properties that change with temperature and shear rate. The formulation is designed to be shear-thinning during application for easy flow, then transitions to a more viscous state during heating to maintain position, and finally becomes gas-trapping at foaming temperature.
2Stability of the object's composition
If the adhesive has high melt viscosity to prevent sagging during heating, then the adhesive retains its shape and location, but the adhesive cannot be readily applied by extrusion
Solution Approach 1:
The adhesive formulation utilizes temperature-dependent viscosity changes. At application temperature, the adhesive has low viscosity for easy extrusion. During heating to foaming temperature, the viscosity increases to prevent sagging, and at foaming temperature, the viscosity is optimized to trap gases while maintaining shape retention.
3Strength
If the adhesive provides strong adhesion to oily metal surfaces, then the adhesive bonds effectively, but the adhesive may fail cohesively rather than adhesively during cleaning and pre-treatment processes
Solution Approach 1:
The adhesive is applied to the substrate before any cleaning or pre-treatment processes occur. This preliminary application ensures that the adhesive is already bonded to the surface, and subsequent cleaning processes remove contaminants rather than the adhesive itself. The formulation is designed to maintain adhesive bonding through these processes.
Solution Approach 2:
The adhesive formulation combines multiple polymer components with complementary properties. The blend includes polymers that provide adhesion to oily surfaces while maintaining cohesive strength, creating a composite material that resists both adhesive and cohesive failure modes during cleaning and pre-treatment.
4Stability of the object's composition
If the adhesive is dry to the touch after application, then the adhesive retains its shape and location, but the adhesive must be heated to the foaming temperature to activate the blowing agent
Solution Approach 1:
The adhesive undergoes phase transitions as temperature increases. Initially applied as a melt that cools to a solid, dry-to-touch state. Upon heating to the foaming temperature, the blowing agent activates and the adhesive transitions to a foamed state, providing volume expansion and additional adhesive 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
The formulation achieves strong adhesion to oily surfaces without pre-treatment, reduces sagging and adhesive failure, and ensures cohesive failure rather than adhesive failure, allowing for effective bonding in industries like automobile and aircraft manufacturing.
Implementation Method 1
a thixotropic filler (ii) in a cross-linking system
Implementation Method 2
a cross-linking system (iii) in which the cross-linking system increases the melt viscosity of the adhesive at an activation temperature within the temperature range at which the adhesive is heated up to the foaming temperature
Implementation Method 3
a blowing agent system (iv) in which the blowing agent system produces a gas at a foaming temperature within the temperature range at which the adhesive is heated up to the foaming temperature
Implementation Method 4
provides a soft flexible foamed adhesive... having good adhesion to oily surfaces
Data Source
AI summary
A foamable adhesive system is provided which can achieve necessary adhesion to an oily surface and which is not tacky to the touch once applied to the surface and has a melt viscosity in the bake phase high enough to retain its shape and adhesion to the substrate and in addition a melt viscosity sufficiently high to retain gas bubbles formed by the decomposition of the blowing agent and which also retains its shape and structure once formed by use of a polymer system containing a thixotropic filler and a two compartment (component) cross linking system.