Clear Coating Composition Balancing High Solids and Color Shift

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Solution Overview

Problem

Existing clear coating compositions struggle to achieve high solid content while maintaining resistance to color shift and coating workability, as well as ease of cleaning, to meet consumer demands for higher designability and appearance.

Innovation Solution

A clear coating composition comprising a combination of primary and secondary hydroxy group-containing acrylic resins with specific molecular weights and acid values, along with an organic solvent system, including alcohols and ketones, to control reaction rates and inhibit permeation, thereby enhancing pot life, resistance to color shift, and cleaning ease.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the solid concentration of the coating composition is increased to reduce VOC emission, then environmental performance is improved, but coating workability and ease of cleaning deteriorate

Engineering Contradiction:

ImproveVOC emissionVSAvoidcoating workability

Core Design Contradiction:

Object-affected harmful factorsVSEase of operation

Solution Approach 1:

The patent applies parameter changes by precisely controlling the molecular weights of primary and secondary hydroxy group-containing acrylic resins within specific ranges (primary: 2,000-6,000, secondary: 6,000-20,000). This molecular weight optimization enables the coating composition to maintain appropriate viscosity and reactivity at high solid concentrations (55% or more), thereby preserving coating workability while reducing VOC emission.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If the solid concentration of the coating composition is increased to reduce VOC emission, then environmental performance is improved, but ease of cleaning deteriorates

Engineering Contradiction:

ImproveVOC emissionVSAvoidease of cleaning

Core Design Contradiction:

Object-affected harmful factorsVSEase of repair

Solution Approach 1:

The patent utilizes parameter changes by optimizing the molecular weight parameters of the acrylic resins and the equivalent ratio of isocyanate groups to hydroxy groups (0.9-1.2). These parameter optimizations control the curing reaction kinetics, ensuring that the coating maintains workability during application while achieving proper cure characteristics that facilitate ease of cleaning, even at high solid concentrations.

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If high solid content coating composition is used to reduce VOC, then environmental performance is improved, but resistance to color shift becomes insufficient

Engineering Contradiction:

ImproveVOC emissionVSAvoidresistance to color shift

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent applies composite materials by formulating a complex coating composition that includes primary hydroxy group-containing acrylic resin, secondary hydroxy group-containing acrylic resin, polyisocyanate compound, and specific organic solvents. This composite formulation synergistically achieves high solid content (55% or more) while maintaining resistance to color shift, thereby resolving the contradiction between environmental performance and reliability.

Inventive Principle:

Principle #40Composite materials

4Ease of operation

If the molecular weight of acrylic resin is decreased to improve coating workability, then coating workability is improved, but resistance to color shift deteriorates

Engineering Contradiction:

Improvecoating workabilityVSAvoidresistance to color shift

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent applies segmentation by dividing the hydroxy group-containing acrylic resin into two distinct components with different molecular weight ranges and functions: primary hydroxy group-containing acrylic resin (lower molecular weight: 2,000-6,000) for coating workability, and secondary hydroxy group-containing acrylic resin (higher molecular weight: 6,000-20,000) for resistance to color shift. This segmentation allows each component to optimize its specific function while working synergistically.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by assigning different molecular weight characteristics to different resin components based on their specific functions. The primary hydroxy group-containing acrylic resin has lower molecular weight localized for improving coating workability and reactivity, while the secondary hydroxy group-containing acrylic resin has higher molecular weight localized for enhancing resistance to color shift and film integrity.

Inventive Principle:

Principle #3Local quality

5Reliability

If the molecular weight of acrylic resin is increased to improve resistance to color shift, then resistance to color shift is improved, but coating workability deteriorates

Engineering Contradiction:

Improveresistance to color shiftVSAvoidcoating workability

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

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 composition provides a coating film with superior resistance to color shift, improved coating workability, and enhanced cleaning ease, while maintaining a high solid content and smoothness.

Implementation Method 1

a hydroxy group-containing acrylic resin (A); a polyisocyanate compound (B)... simultaneously curing the uncured base coating film and the uncured clear coating film

Methodology Applied

Scientific EffectPolymerization reaction: Photopolymerisation

Implementation Method 2

the organic solvent (C) includes at least one alcohol solvent selected from the group consisting of linear primary alcohols having 1 to 8 carbon atoms, branched primary alcohols having 3 to 8 carbon atoms, linear secondary alcohols having 1 to 8 carbon atoms, and branched secondary alcohols having 3 to 8 carbon atoms

Methodology Applied

Scientific EffectEvaporation: Evaporation

Implementation Method 3

inhibit permeation, thereby enhancing pot life, resistance to color shift

Methodology Applied

Scientific EffectPermeation barrier: Permeation

Data Source

PatentEP4431575B1Clear coating composition and method for producing coated article

Publication Date: 2026.02.25 NIPPON PAINT AUTOMOTIVE COATINGS

AI summary

Provided is a clear coating composition which affords a coating film having superior resistance to color shift and is superior in coating workability while having a high solid content. A clear coating composition including a hydroxy group-containing acrylic resin (A), a polyisocyanate compound (B), and an organic solvent (C), wherein the hydroxy group-containing acrylic resin (A) includes a primary hydroxy group-containing acrylic resin (A1) and a secondary hydroxy group-containing acrylic resin (A2), the primary hydroxy group-containing acrylic resin (A1) has a weight average molecular weight of 6000 or less, the secondary hydroxy group-containing acrylic resin (A2) has a weight average molecular weight of 6000 or more, the organic solvent (C) includes a specific primary alcohol and/or secondary alcohol, and the clear coating composition has a solid concentration of 55% by mass or more at a time of coating.