Hot Melt Adhesive Composition for Difficult Substrates
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Solution Overview
Problem
Conventional hot melt adhesives face challenges in maintaining adhesion to difficult substrates at both low and high temperatures, often sacrificing cohesion and experiencing brittleness at low temperatures or softening at high temperatures, leading to inadequate performance in applications like food packaging and woodworking.
Innovation Solution
A hot melt adhesive composition comprising an ethylene vinyl acetate-containing polymer, a tackifier, an antioxidant, and an adhesion promoting semi-crystalline polymer with a weight average molecular weight of 30,000 daltons or less, which enhances adhesion and cohesion across a wide temperature range by including an optional wax, particularly with maleated polymers having a SAP number equal to or greater than 20.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If hot melt adhesive based on metallocene ethylene octene copolymers is used, then low odor and high clarity are achieved, but adhesion to difficult substrates at low temperatures deteriorates
Solution Approach 1:
The patent combines metallocene ethylene octene copolymer with ethylene vinyl acetate copolymer and semi-crystalline polymer to create a composite adhesive formulation. This composite approach allows the adhesive to maintain the low odor and high clarity benefits of mEO while gaining the low-temperature adhesion properties of EVA and the crystalline structure of the semi-crystalline polymer component.
Solution Approach 2:
The patent modifies the adhesive composition by incorporating specific components with defined molecular weights (semi-crystalline polymer with Mw ≤ 30,000 daltons) and chemical characteristics (EVA with specific vinyl acetate content). These parameter changes enable the adhesive to maintain flexibility and adhesion at low temperatures while preserving the optical and sensory properties of the base mEO adhesive.
2Reliability
If hot melt adhesive based on amorphous poly-alpha-olefins is used, then adhesion to difficult substrates at elevated temperatures is improved, but viscosity control and cohesion deteriorate
Solution Approach 1:
The patent creates a composite formulation combining amorphous poly-alpha-olefin with semi-crystalline polymer and ethylene vinyl acetate copolymer. The semi-crystalline polymer component provides structural integrity and viscosity control, while the EVA component enhances cohesion. This composite structure allows the adhesive to maintain adhesion at elevated temperatures without sacrificing viscosity control or internal strength.
Solution Approach 2:
The patent introduces a low molecular weight semi-crystalline polymer (Mw ≤ 30,000 daltons) that provides localized crystalline regions within the amorphous matrix. These crystalline regions act as physical crosslinks that maintain viscosity control and cohesion at elevated temperatures, while the amorphous regions provide the adhesion properties to difficult substrates.
3Reliability
If adhesion is increased to difficult substrates, then adhesion performance is improved, but cohesion between component parts deteriorates
Solution Approach 1:
The patent carefully controls the molecular weight of the semi-crystalline polymer component (Mw ≤ 30,000 daltons) to optimize the balance between adhesion and cohesion. The low molecular weight allows sufficient chain entanglement and interfacial interaction for strong adhesion to difficult substrates, while the crystalline structure provides adequate internal strength and cohesion to prevent adhesive failure.
Solution Approach 2:
The patent formulates a composite adhesive containing multiple polymer components (mEO, EVA, and semi-crystalline polymer) in specific proportions. This composite structure distributes the functional requirements: the semi-crystalline polymer and EVA provide adhesion to difficult substrates, while the overall composite formulation maintains cohesion through the synergistic interaction of all components.
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 composition exhibits improved adhesion and cohesion properties, demonstrated by increased shear and peel adhesion failure temperatures, and enhanced performance in both cold and high-temperature applications, as shown in the examples, maintaining strength and flexibility across a broader temperature range compared to conventional adhesives.
Implementation Method 1
adhesion promoting additive comprising at least one semi-crystalline polymer
Implementation Method 2
cohesion between component parts of a composition
Data Source
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AI summary
Hot melt adhesive compositions which have enhanced adhesion to difficult substrates, particularly at refrigerator/freezer temperatures or at elevated temperatures. The inventive compositions require a base polymer comprising an ethylene vinyl acetate-containing polymer; a tackifier; an adhesion promoting additive comprising at least one semi-crystalline polymer having a weight average molecular weight of about 30,000 daltons or less; and optional wax; and an optional antioxidant. It has been found that the adhesion promoting additive of this invention enhances the adhesion properties of a hot melt adhesive composition having ethylene vinyl acetate-containing polymer, particularly at elevated temperatures or at low refrigerator and freezer temperatures where other conventional adhesives have been unsuccessful.