Multilayer Coating Film Simultaneous Curing
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Solution Overview
Problem
The existing multilayer coating film-forming methods using aqueous coating compositions often result in insufficient water resistance, smoothness, and distinctness of image, and are prone to popping due to the use of water-soluble resins and the omission of heat-curing steps, leading to adhesion issues and reduced finish quality.
Innovation Solution
A method involving the sequential application of aqueous coating compositions, where an acrylic modified polyester resin and a blocked polyisocyanate compound with specific structures are used as the first colored coating composition, followed by a clear coating composition, to form a multilayer coating film that is cured simultaneously, enhancing smoothness, distinctness, and water resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If aqueous coating compositions are used to omit heat-curing steps and save energy, then energy consumption is reduced and environmental pollution is minimized, but water resistance and smoothness of the coating film deteriorate due to formation of mixed layers
Solution Approach 1:
The patent changes the chemical parameters of the coating composition by introducing a water-soluble polyisocyanate compound with specific molecular weight range (1,000-10,000) and functional group composition. This parameter change allows the aqueous coating to achieve proper crosslinking and water resistance without requiring intermediate heat-curing steps, thus resolving the contradiction between energy savings and coating performance.
Solution Approach 2:
The patent creates a composite coating system by combining water-soluble resin, water-soluble polyisocyanate compound, and effect pigments in a specific formulation. This composite material approach enables the coating to form a unified, non-mixed layer structure that provides both smoothness and water resistance while using aqueous composition for energy efficiency.
2Object-generated harmful factors
If aqueous coating compositions are used for environmental benefits, then organic solvent volatilization is reduced, but smoothness and distinctness of image deteriorate due to mixed layer formation
Solution Approach 1:
The patent modifies the molecular weight and functional group composition of the polyisocyanate compound to achieve optimal viscosity and reactivity parameters. This allows the coating to flow smoothly and level out properly without forming mixed layers, maintaining image distinctness while using environmentally friendly aqueous composition.
Solution Approach 2:
The water-soluble polyisocyanate compound acts as an intermediary that bridges the water-soluble resin and effect pigments, preventing phase separation and mixed layer formation. This intermediary component ensures uniform distribution and proper adhesion, maintaining smoothness and image quality while using aqueous formulation.
3Reliability
If heat-curable coating composition is used, then curing is achieved, but popping occurs due to rapid solvent evaporation during heating
Solution Approach 1:
The patent changes the curing mechanism by using water-soluble polyisocyanate that can crosslink at lower temperatures with controlled rate. This parameter change in curing temperature and rate prevents rapid water evaporation that causes popping, while still achieving complete curing of the coating film.
Solution Approach 2:
The patent incorporates the water-soluble polyisocyanate compound in advance during coating application, allowing gradual crosslinking to begin before and during the final curing step. This preliminary action prevents sudden solvent evaporation and popping by establishing a controlled curing process from the outset.
4Object-generated harmful factors
If water-soluble resin is used in aqueous coating composition, then environmental benefits are achieved, but adhesion deteriorates due to insufficient crosslinking
Solution Approach 1:
The patent creates a composite chemical system combining water-soluble resin with water-soluble polyisocyanate compound to form crosslinked networks. This composite material approach maintains the environmental benefits of aqueous formulation while achieving strong adhesion through proper crosslinking density and network structure.
Solution Approach 2:
The patent optimizes the molecular weight and functional group composition of the polyisocyanate compound to achieve optimal crosslinking density. This parameter optimization ensures sufficient adhesion strength while maintaining water solubility for environmental compatibility, resolving the contradiction between green chemistry and performance.
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 method achieves a multilayer coating film with improved smoothness, distinctness of image, popping resistance, and water resistance, maintaining adhesion even after storage, and reduces the occurrence of foam-like defects.
Implementation Method 1
the aqueous first colored coating composition (X) comprising an acrylic modified polyester resin (A) and a blocked polyisocyanate compound (B) having at least one blocked isocyanate group selected from the group consisting of: a blocked isocyanate group represented by formula (I)... heating to simultaneously cure the uncured first colored coating film, uncured second colored coating film, and uncured clear coating film
Implementation Method 2
the solvent remaining inside the coating film evaporates rapidly during heating and curing to form air bubbles in the coating film... popping occurs because the solvent in the coating film rapidly evaporates during heating and curing
Data Source
AI summary
An object to be attained by the present invention is to provide a method for forming a multilayer coating film having excellent smoothness, distinctness of image, water resistance, adhesion, and popping resistance; moreover, the multilayer coating film has excellent water resistance and adhesion, even when the coating compositions are applied after being stored for a fixed period of time. The present invention provides a method for forming a multilayer coating film comprising applying an aqueous first' colored coating composition and a second colored coating composition to a substrate in this order, and heating to simultaneously cure the aqueous first colored coating film and the second colored coating film, wherein the aqueous first colored coating composition comprises an acrylic modified polyester resin and a blocked polyisocyanate compound having a specific blocked isocyanate group.