Multilayer Coating Film Formation on Thermally Expandable Bases
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Solution Overview
Problem
Conventional methods for forming multilayer coating films on thermally expandable/shrinkable bases, such as automobile bodies, often result in coating film defects like creases and cracks due to thermal expansion/shrinkage, and sagging during the application of intermediate coating compositions, which affects the smoothness and durability of the final coating.
Innovation Solution
A method involving the application of an aqueous intermediate coating composition preheated to 60-90°C, followed by an aqueous base coating composition, and a clear coating composition, all applied in an uncured state and then baked together, using a specific resin composition with an acrylic resin emulsion and a fatty acid diester compound as a film formation auxiliary agent to enhance flexibility and prevent sagging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an intermediate coating composition is applied and preheated to form an uncured intermediate coating film, then the coating film appearance is improved and sagging is prevented, but the process time and energy consumption increase
Solution Approach 1:
The intermediate coating composition is preheated to 60-90°C before applying the base and clear coating compositions. This preliminary heating action prevents sagging during subsequent coating applications and maintains coating film appearance quality throughout the multilayer coating process
Solution Approach 2:
The patent combines multiple coating compositions (intermediate, base, and clear coating compositions) into a single multilayer coating process with one final curing step. This merging of operations reduces the total number of separate heating and curing cycles, thereby reducing overall energy consumption and process time while maintaining coating quality
2Loss of energy
If multiple coating compositions are applied one after another in an uncured state, then energy consumption is reduced, but coating film defects such as creases and cracks occur on thermally expandable/shrinkable bases
Solution Approach 1:
The patent specifies precise temperature ranges (60-90°C) and time periods (3-10 minutes) for preheating the intermediate coating composition. These controlled parameter changes ensure the coating film has sufficient flexibility during thermal expansion/shrinkage of the base, preventing creases and cracks while maintaining the energy-efficient one-baking process
Solution Approach 2:
The intermediate coating composition uses a composite resin system combining acrylic resin emulsion with specific glass transition temperature range (-50 to 20°C) and fatty acid diester compound. This composite material provides both the flexibility needed to accommodate base thermal expansion/shrinkage and the adhesion required to prevent coating defects
3Manufacturing precision
If the viscosity of intermediate coating composition is controlled to prevent sagging, then coating film appearance is improved, but the ease of application is reduced
Solution Approach 1:
The patent controls the viscosity of the intermediate coating composition within specific ranges (100-500 cP at 20°C) and adjusts it dynamically through temperature control during application. This parameter optimization prevents sagging and maintains coating appearance while ensuring easy and uniform application
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
This approach ensures a smooth, chipping-resistant multilayer coating film with improved physical properties by maintaining the softness of the coating film and preventing sagging, thereby achieving a high-quality appearance and strength on thermally expandable/shrinkable bases.
Implementation Method 1
preheating the applied aqueous intermediate coating composition at 60 to 90° C. for 3 to 10 minutes
Implementation Method 2
preheating the applied aqueous base coating composition at 60 to 90° C. for 3 to 10 minutes
Implementation Method 3
baking and curing the uncured intermediate coating film, base coating film and clear coating film at a time to form a multilayer coating film
Data Source
AI summary
The coating film formed on an automobile body has softness during a film formation even on a thermally expandable/shrinkable base, and the cured film has an excellent appearance.Provided is a method for forming a multilayer coating film, the method comprises: applying an aqueous intermediate coating composition and preheating the applied composition at 60 to 90° C. to form an uncured film;preheating to form an uncured base coating film and a clear coating film; andbaking and curing these uncured films to form a multilayer coating film,wherein the aqueous intermediate coating composition comprises (a) an acrylic resin emulsion having a specific properties, and (b) a film formation auxiliary agent that is a fatty acid diester compound having a boiling point of 280° C. to 350° C., anda cured film comprising (a) and (b) at a mass ratio of 3:1 has a rupture elongation of 1% or more.