High-Viscosity Polyolefin Dispersion Coating for Soft Tissue Webs
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Solution Overview
Problem
Existing methods for producing high-strength, soft, and absorbent tissue products face challenges as increasing one property often adversely affects others, such as softness and strength, especially when applying aqueous polyolefin dispersions to non-creped webs, which tend to penetrate and reduce mass efficiency, leading to stiff products.
Innovation Solution
A method involving the application of a high viscosity aqueous polyolefin dispersion with specific properties, including a viscosity calculated by the equation y = 40e^0.07x, where x is the percentage of emulsifier content, to the surface of a web with greater than 50% cellulosic fibers, without penetration, and drying at temperatures below the melting point of the base polymer to maintain morphological structure and enhance softness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If aqueous polyolefin dispersion is applied to non-creped web surface, then softness is improved, but dispersion penetrates the web and reduces mass efficiency leading to stiff product
Solution Approach 1:
The patent changes the viscosity parameter of the aqueous polyolefin dispersion by adjusting emulsifier content according to the equation y = 40e^0.07x, where y is viscosity and x is emulsifier percentage. This parameter change prevents penetration while maintaining softness improvement.
Solution Approach 2:
The patent uses an emulsifier as an intermediary substance to control the interaction between the polyolefin dispersion and the web. The emulsifier content is specifically controlled to achieve the desired viscosity that prevents penetration while allowing surface coating for softness.
2Ease of operation
If fiber bonding is reduced to increase softness, then softness is improved, but strength of the tissue web is adversely affected
Solution Approach 1:
The patent applies polyolefin dispersion only to the surface of the web rather than throughout the bulk. This local application provides softness at the surface while leaving the internal fiber bonding intact to maintain strength.
Solution Approach 2:
The patent creates a composite structure with cellulosic fibers providing strength and polyolefin dispersion providing surface softness. The two materials work together with the polyolefin coating on the surface while the fiber matrix maintains structural integrity.
3Ease of manufacture
If dispersion is applied before drying when web is still wet, then application is simplified, but dispersion penetrates the web and forms hydrogen bonds creating stiff product
Solution Approach 1:
The patent applies the polyolefin dispersion to the web surface before the web is completely dried, but at a stage when the surface is ready to accept coating. The high viscosity prevents penetration even during this intermediate wet state, allowing simplified application while maintaining product flexibility.
4Loss of substance
If high viscosity dispersion is used to prevent penetration, then mass efficiency is improved, but phase inversion may occur affecting coating stability
Solution Approach 1:
The patent carefully controls the viscosity parameter within a specific range defined by the equation y = 40e^0.07x to prevent penetration while avoiding phase inversion. The emulsifier content is adjusted to achieve the optimal viscosity that balances penetration prevention with coating stability.
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 effectively retains the dispersion on the web surface, preventing phase inversion and enhancing the hand feel and softness of the tissue while maintaining or improving tensile strength, resulting in a stronger and softer product.
Implementation Method 1
the aqueous polyolefin dispersion has a viscosity of equal to or greater than a value calculated by an equation of y = 40 e 0.07x
Implementation Method 2
drying at temperatures below the melting point of the base polymer to maintain morphological structure
Implementation Method 3
the remaining polymer dispersion beads melt to form a film
Implementation Method 4
it tends to penetrate the web, reduce mass efficiency, and form hydrogen bonds between pulp fibers
Data Source
Figure 1A~2B
Figure 1C~2D
Figure 3
AI summary
Sheet-like products, such as tissue products made from a low-density web, are disclosed containing an additive composition. The additive composition, for instance, comprises an aqueous dispersion containing an alpha-olefin polymer, and an ethylene-carboxylic acid copolymer. The additive composition may be applied to the surface of the web so that it does not thoroughly or even substantially penetrate the web. For instance, the additive may be applied to one or both surfaces of the web by gravure printing, press coating, spraying or the like. The additive composition may improve the strength of the tissue web and/or improve the perceived softness of the web.