Multilayer Coating Film Curing with Silane-Modified Polyisocyanate
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Solution Overview
Problem
Conventional multilayer coating film-forming methods for automobile bodies face issues with smoothness, distinctness of image, adhesion, and water resistance, particularly when cured at low temperatures, due to insufficient curing and mixing between aqueous coating layers.
Innovation Solution
A method involving a primer coating composition, an aqueous colored coating composition with a hydroxyl-containing resin and blocked polyisocyanate compound, and a clear coating composition, where all layers are cured together at once, using specific blocked isocyanate groups to ensure proper crosslinking and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional multilayer coating methods are used with aqueous coating compositions, then productivity is improved by eliminating intermediate heating steps, but manufacturing precision deteriorates due to mixing between layers reducing smoothness and distinctness of image
Solution Approach 1:
A silane-modified polyisocyanate compound is introduced as a crosslinking agent that reacts with hydroxyl groups in the coating layers to form a three-dimensional network structure. This intermediary chemical bonding mechanism prevents mixing between aqueous coating layers while maintaining layer adhesion, thereby preserving smoothness and distinctness of image even in simplified one-step curing processes
Solution Approach 2:
The invention changes the chemical parameters of the coating composition by incorporating specific ratios of silane-modified polyisocyanate compound (0.1-10 part by mass per 100 part by mass of coating resin solid content) and controlling moisture content (5-50 mass%). These parameter changes enable controlled crosslinking that prevents layer mixing while maintaining curing efficiency
2Use of energy by stationary object
If low temperature curing is used to improve energy efficiency, then use of energy by stationary object is reduced, but manufacturing precision deteriorates due to insufficient curing reducing adhesion and water resistance
Solution Approach 1:
The invention changes the chemical reactivity parameters by using silane-modified polyisocyanate compounds with specific NCO group contents (2-10 mmol/g) and incorporating catalysts. These parameter changes enable the crosslinking reaction to proceed effectively at lower temperatures (60-120°C), achieving sufficient curing without compromising adhesion and water resistance while reducing energy consumption
Solution Approach 2:
The invention replaces thermal energy input with chemical reactivity-driven curing. The silane-modified polyisocyanate compound reacts with hydroxyl groups and moisture to form crosslinked structures, substituting for high-temperature thermal curing and enabling effective coating curing at lower temperatures with reduced energy input
3Device complexity
If simplified one-coat or two-coat systems are used to reduce process complexity, then device complexity is reduced, but manufacturing precision deteriorates due to insufficient layer differentiation
Solution Approach 1:
The invention merges multiple coating layers (primer, base coat, clear coat) into simplified one-coat or two-coat systems while maintaining functional differentiation through chemical crosslinking. The silane-modified polyisocyanate compound enables each layer to achieve proper adhesion and properties through crosslinking with hydroxyl-containing resins, preserving manufacturing precision despite reduced process complexity
Solution Approach 2:
The invention uses composite material systems combining hydroxyl-containing resins (acrylic, polyester, polyurethane), silane-modified polyisocyanate crosslinking agents, and catalysts. This composite approach enables multi-functional performance (adhesion, smoothness, distinctness of image, water resistance) in simplified coating systems without compromising manufacturing precision
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 excellent smoothness, distinctness of image, adhesion, and water resistance, even when cured at low temperatures, by ensuring thorough crosslinking and minimizing layer mixing.
Implementation Method 1
an aqueous colored coating composition (Y1) for a base coat, to form an uncured base coat coating film thereover, step 1-3: a step of coating the article to be coated having the uncured primer coating film and uncured base coat coating film, with a clear coating composition (Z), and forming an uncured clear coating film thereover, and step 1-4: a step of curing the uncured primer coating film, the uncured base coat coating film and the uncured clear coating film by heating them
Implementation Method 2
a step of curing the uncured primer coating film, the uncured base coat coating film and the uncured clear coating film by heating them
Data Source
AI summary
An object of the present disclosure is to provide a method of forming a multilayer coating film that forms a multilayer coating film with excellent smoothness, distinctness of image, adhesion and water resistance when a plurality of uncured coating films are cured at once, and especially when they are cured at once at low temperature. The method of the present disclosure is as follows. A method of forming a multilayer coating film comprising the following steps 1-1 to 1-4: step 1-1: a step of coating an article to be coated with a primer coating composition (X) and forming an uncured primer coating film on the article to be coated, step 1-2: a step of coating the article to be coated having the uncured primer coating film with an aqueous colored coating composition (Y 1 ) for a base coat, to form an uncured base coat coating film thereover, step 1-3: a step of coating the article to be coated having the uncured primer coating film and uncured base coat coating film, with a clear coating composition (Z), and forming an uncured clear coating film thereover, and step 1-4: a step of curing the uncured primer coating film, the uncured base coat coating film and the uncured clear coating film by heating them.