Aqueous Polyurethane Dispersion Adhesion to Plastic Substrates
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Solution Overview
Problem
Aqueous polyurethane coatings exhibit excellent mechanical and chemical resistance but struggle with adhesion, particularly on plastic substrates, necessitating an improvement in coating compositions to enhance adhesive properties without compromising resistance.
Innovation Solution
An aqueous polyurethane dispersion comprising at least two polyurethanes with specific molar masses, hydroxyl group content, and branching, utilizing hydroxy-functional polycarbonates and controlled polyol fractions, along with a multifunctional isocyanate or aminoplast crosslinker, to optimize film formation and substrate adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molar mass polyurethanes (Mw > 20 kg/mol) are used to achieve good mechanical and chemical resistance, then coating film strength is improved, but adhesion to substrates deteriorates
Solution Approach 1:
The invention divides the polyurethane system into two segments: a high molar mass polyurethane (U1, Mw ≥ 10 kg/mol) providing mechanical strength and chemical resistance, and a low molar mass polyurethane (U2, Mw < 10 kg/mol) with high hydroxyl group content providing adhesion. This segmentation allows each component to fulfill its specific function without compromise.
Solution Approach 2:
The invention creates a composite aqueous polyurethane dispersion combining two polyurethanes with different molar masses and functional characteristics. The high molar mass polyurethane U1 and low molar mass polyurethane U2 work synergistically to achieve both strong adhesion and excellent mechanical/chemical resistance in the coating film.
2Reliability
If low molar mass polyurethanes with high hydroxyl group content are used to improve adhesion, then substrate bonding is enhanced, but mechanical resistance may be compromised
Solution Approach 1:
The invention divides the polyurethane system into two segments: a high molar mass polyurethane (U1, Mw ≥ 10 kg/mol) providing mechanical strength and chemical resistance, and a low molar mass polyurethane (U2, Mw < 10 kg/mol) with high hydroxyl group content providing adhesion. This segmentation allows each component to fulfill its specific function without compromise.
Solution Approach 2:
The invention creates a composite aqueous polyurethane dispersion combining two polyurethanes with different molar masses and functional characteristics. The high molar mass polyurethane U1 and low molar mass polyurethane U2 work synergistically to achieve both strong adhesion and excellent mechanical/chemical resistance in the coating film.
3Ease of manufacture
If conventional chain extenders (diamines or dihydrazides) are used to form polyurethane dispersions, then film formation is achieved, but adhesion to plastic substrates deteriorates
Solution Approach 1:
The invention changes the molar mass parameter and hydroxyl group content parameter of the polyurethane components. By using a low molar mass polyurethane U2 with high hydroxyl group content (1.4-4.0 mol/kg) derived from polycarbonate polyols, the system achieves both proper film formation and improved adhesion to plastic substrates.
Solution Approach 2:
The invention creates a composite aqueous polyurethane dispersion combining two polyurethanes with different molar masses and functional characteristics. The high molar mass polyurethane U1 and low molar mass polyurethane U2 work synergistically to achieve both strong adhesion and excellent mechanical/chemical resistance in the coating film.
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 solution significantly improves adhesion to plastic substrates while maintaining mechanical and chemical resistance, as demonstrated by enhanced solvent and hot water resistance in coating films.
Implementation Method 1
chain extending an isocyanate-functional prepolymer in the aqueous phase by means of polyfunctional compounds of low molar mass dissolved in water, referred to as chain extenders, such as diamines or dihydrazides which react with the isocyanate groups of the prepolymer
Implementation Method 2
hydroxy-functional polycarbonates of formula III HO - (X - O - CO - O -)m - X - OH are used in the synthesis of U1 and U2
Implementation Method 3
one pack systems are known which dry physically by evaporation of water
Implementation Method 4
the film formation optionally being supported by addition of thermally activated crosslinking agents such as melamine formaldehyde crosslinker resins or blocked isocyanates which initiate curing at temperatures above 100 °C
Data Source
AI summary
The invention relates to an aqueous polyurethane dispersion U comprising at least two aqueously dispersed polyurethanes whereof at least one is an aqueously dispersible polyurethane U1having a mass-average molar mass Mw1of at least 10 kg/mol, and at least one is an aqueously dispersible polyurethane U2having a mass-average molar mass Mw2of less than 10kg/mol, a process for the preparation thereof, and a method of use thereof.