Hot Melt Adhesive with Low Blocking Force
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Solution Overview
Problem
Conventional hot melt adhesives face challenges in achieving low viscosity, fast set speed, superior adhesion, and reduced cold flow and/or blocking, which are often mutually exclusive properties, particularly when used with thin or porous substrates like nonwovens in disposable diapers.
Innovation Solution
A hot melt adhesive composition comprising an ethylene vinyl acetate copolymer, a hydrogenated styrenic block copolymer, a tackifying resin, and a liquid plasticizer, optimized to provide superior hot tack, adhesion, resistance to blocking and cold flow, and fast set speed, with specific weight percentages and properties of each component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional hot melt adhesives increase adhesion properties, then superior adhesion is achieved, but cold flow and blocking increase
Solution Approach 1:
The patent employs a composite adhesive formulation combining four distinct polymer systems: EVA copolymer (30-70 wt%), HSBC (10-50 wt%), tackifying resin (10-40 wt%), and liquid plasticizer (5-30 wt%). Each component contributes specific properties that collectively achieve superior adhesion while suppressing cold flow and blocking through synergistic interactions among the materials.
Solution Approach 2:
The patent systematically adjusts formulation parameters including polymer ratios, molecular weights, vinyl acetate content (8-28%), and processing conditions (temperature, shear rate) to optimize the balance between adhesion strength and resistance to cold flow. The viscosity is controlled within 500-5000 cP at application temperature through these parameter modifications.
2Loss of time
If conventional hot melt adhesives achieve fast set speed, then rapid bonding is obtained, but adhesion properties deteriorate
Solution Approach 1:
The adhesive formulation exhibits spatially varying properties through the synergistic combination of components: HSBC provides rapid initial tack for fast set speed, while EVA and tackifying resin contribute to ultimate adhesion strength. The liquid plasticizer ensures proper flow and distribution during the brief setting period, enabling both fast initial bonding and strong final adhesion.
3Force
If conventional hot melt adhesives reduce viscosity, then low viscosity is achieved, but cold flow increases
Solution Approach 1:
The adhesive formulation exhibits dynamic rheological behavior where viscosity is highly temperature-dependent. At application temperature (melting point +20°C to melting point +50°C), the viscosity is low (500-5000 cP) for easy application. As the adhesive cools below its melting point, the viscosity increases dramatically, preventing cold flow. This dynamic viscosity change is achieved through the crystalline structure of EVA and HSBC combined with the amorphous tackifying resin matrix.
Data Source
AI summary
A hot melt adhesive composed of an ethylene vinyl acetate copolymer, a hydrogenated styrenic block copolymer, a tackifying resin, and a liquid plasticizer. The preferred ethylene vinyl acetate copolymer has a vinyl acetate content between 8 and 28 percent by weight, and the preferred hydrogenated styrenic block copolymer is a styrene-ethylene-butylene-styrene having about 30% styrene content and essentially no diblock. The hot melt gives excellent peel strength when used as a construction adhesive for disposable nonwoven articles. It can also be formulated to exhibit very low bleed through and blocking characteristics when used on low basis weight nonwoven fabrics.