Low Modulus Polypropylene Hot Melt Adhesive Sprayability
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Solution Overview
Problem
Current hot melt adhesives based on olefinic polymers, such as polypropylene, face challenges in sprayability, temperature application window, adhesion, and resistance to bleed-through on porous substrates, particularly in disposable article construction applications, where they lack the performance and characteristics of styrenic block copolymers.
Innovation Solution
The development of Low Molecular Weight and Low Modulus Polypropylene (L-MODU) polymers, made using a unique metallocene catalyst, is combined with a tackifying resin, plasticizer, and a semi-crystalline additive to create a hot melt adhesive with improved spray characteristics, adhesion, elevated temperature resistance, and resistance to bleed-through, achieving a unique combination of properties not previously attainable with olefinic-based adhesives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional polypropylene homopolymers are used as hot melt adhesive, then high initial bond strength is achieved, but long crystallization time prevents fast setting
Solution Approach 1:
The patent changes the molecular weight parameter of polypropylene homopolymer to low molecular weight range, which fundamentally alters the crystallization kinetics while maintaining bond strength. This parameter change enables the adhesive to achieve both high initial bond strength and fast setting by modifying the polymer's physical properties rather than changing the chemical composition.
Solution Approach 2:
The patent creates a composite adhesive formulation by combining low molecular weight polypropylene homopolymer with specific additives including polyethylene wax and polypropylene oligomer. This composite approach allows the system to benefit from the high bond strength of polypropylene while the additives modify the crystallization behavior to reduce setting time.
2Ease of manufacture
If olefinic polymers are used for hot melt adhesive, then cost-effectiveness is improved, but sprayability and temperature application window are insufficient
Solution Approach 1:
The patent applies parameter changes by selecting low molecular weight polypropylene homopolymer with specific molecular weight distribution, which improves sprayability and broadens the temperature application window while maintaining the cost-effectiveness of olefinic polymers. The low molecular weight enables better flow characteristics for spraying.
Solution Approach 2:
The patent introduces local quality by adding polyethylene wax and polypropylene oligomer as minor components to the main polypropylene homopolymer matrix. These additives locally modify the adhesive properties to enhance sprayability without compromising the overall cost-effectiveness of the olefinic polymer base.
3Strength
If conventional hot melt adhesives are applied to porous substrates, then adhesion is achieved, but bleed-through occurs
Solution Approach 1:
The patent changes the molecular weight parameter to low molecular weight range, which affects the viscosity and penetration characteristics of the adhesive. This parameter change allows the adhesive to adhere to porous substrates effectively while reducing excessive flow that causes bleed-through.
Solution Approach 2:
The patent uses polyethylene wax and polypropylene oligomer as sacrificial components that temporarily facilitate adhesion to porous substrates and then solidify to prevent bleed-through. These components serve their purpose during the bonding process and then stabilize the adhesive structure.
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 L-MODU-based hot melt adhesive demonstrates enhanced sprayability, adhesion, creep resistance, and heat resistance, while minimizing bleed-through, thereby addressing the limitations of existing olefinic-based adhesives and matching the performance of styrenic block copolymer-based technologies.
Implementation Method 1
made using a unique metallocene catalyst
Implementation Method 2
the long crystallization time of the polypropylene polymer
Implementation Method 3
hot melt adhesive with improved spray characteristics, adhesion, elevated temperature resistance
Data Source
AI summary
A hot melt adhesive for use on porous substrates, wherein the hot melt adhesive hasabout 10% to about 70% by weight of a polypropylene homopolymer having a DSC melting point of less than 100° C.;about 10% to about 60% of a first tackifying resin having a Ring & Ball Softening Point ofabout 95° C. to about 140° C.;about 0% to about 65% of a second tackifying resin that is different than the first tackifying resin;about 5% to about 50% of a plasticizer;about 1% to about 40% by weight of a secondary polymer which is either a semi crystalline polymer or wax with an enthalpy of fusion of greater than 30 Joules/gram;about 0.1% to about 5% of a stabilizer or antioxidant; wherein the components total 100% by weight of the composition, and the viscosity of the composition is equal to or less than about 20,000 centipoise (cP) at 163° C. (325° F.).