Kaolin and Calcium Carbonate Coating Composition for Paperboard
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Solution Overview
Problem
Coated paper and paperboard products face significant challenges with cracking and flaking when subjected to creasing and folding operations due to the strain applied, which compromises their mechanical strength and barrier properties.
Innovation Solution
A coating composition comprising kaolin with a shape factor of less than 70 and calcium carbonate with a d50 of at least 2.4 microns and a steepness factor of at least 30, combined with a thickener, is used to enhance the modulus and stiffness of the coating, thereby reducing flaking and cracking at folds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If coating layers with higher stiffness are used, then superior strength is provided, but cracking or flaking severity increases at folded edges
Solution Approach 1:
The patent changes the physical and chemical parameters of the coating composition by incorporating specific additives (silane-modified polymers, titania, zinc stearate) and controlling particle size distributions of pigments. These parameter changes modify the coating's mechanical properties to achieve optimal balance between strength and flexibility, reducing cracking and flaking while maintaining superior strength.
Solution Approach 2:
The patent creates a composite coating material combining multiple components: kaolin, calcium carbonate, silane-modified polymers, titania, and zinc stearate. This composite structure leverages the complementary properties of each component - the inorganic pigments provide strength and stiffness while the silane-modified polymer matrix provides flexibility and adhesion, resolving the contradiction between strength and cracking resistance.
2Quantity of substance
If stiffer coating layers are applied, then fiber usage reduction is achieved, but coating layer rupture occurs at folded edges
Solution Approach 1:
The patent modifies the coating composition parameters by incorporating zinc stearate as a lubricant and controlling the particle size distribution of calcium carbonate (d50 of at least 2.4 μm). These changes reduce the coating's brittleness and improve its ability to withstand folding stresses, maintaining coating integrity while achieving fiber usage reduction through the high pigment concentration formulation.
Solution Approach 2:
The silane-modified polymer acts as an intermediary between the inorganic pigment particles and the substrate. Its modified surface chemistry improves adhesion and stress distribution, allowing the coating to maintain integrity during folding operations while still providing the stiffness needed to reduce fiber usage in the substrate.
3Strength
If higher stiffness coating is used, then mechanical strength is improved, but barrier properties are compromised due to cracking
Solution Approach 1:
The composite coating structure with silane-modified polymer matrix and dispersed inorganic pigments (kaolin, calcium carbonate, titania) creates a cohesive network that maintains barrier continuity. The polymer matrix fills gaps between pigment particles and provides flexibility, preventing crack formation that would compromise barrier properties while maintaining mechanical strength.
Solution Approach 2:
The patent controls the particle size distribution of calcium carbonate (d50 ≥ 2.4 μm, steepness factor ≥ 30) and incorporates zinc stearate to optimize packing density and reduce void spaces. These parameter changes enhance both mechanical strength and barrier properties simultaneously by creating a dense, crack-resistant coating structure.
Data Source
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AI summary
A coating composition may include kaolin having a shape factor less than about 70 and calcium carbonate, wherein less than about 90% by weight and greater than about 60% by weight of particles of the calcium carbonate have an equivalent spherical diameter (esd) less than 2 microns. The coating composition may include a thickener present in an amount ranging from about 0.1% to about 0.9% by active dry weight of the composition. A coating composition may include kaolin having a shape factor less than about 70 and calcium carbonate having a mean particle size (dso) of at least about 2.4 microns and a steepness factor of at least about 30. The coating composition may be a paper basecoat composition or a paperboard basecoat composition. A paper or paperboard product may include the coating composition on at least one surface of the paper product or paperboard product.