Multi-Ply Tissue Bonding Adhesive With NFC for Softness and Strength
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Solution Overview
Problem
Conventional glue-bonded multi-ply absorbent sheets face challenges in achieving optimal bonding strength and softness due to the limitations of aqueous polyvinyl alcohol (PVOH) adhesives, which often require excessive pressure, leading to compromised bulk and emboss quality.
Innovation Solution
Incorporating nanofibrillated cellulose (NFC) into the adhesive, which modifies viscosity and strengthens the fiber/polymer matrix, allowing for softer products with less glue and improved bonding strength by acting as a shear-thinning material that flows under pressure and thickens after bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional aqueous polyvinyl alcohol adhesive is used with low solids content, then the adhesive can penetrate the web, but excess glue is required to overcome excessive wicking into the web, increasing glue usage and reducing product quality
Solution Approach 1:
The patent modifies the adhesive's rheological parameters by incorporating nanofibrillated cellulose, transforming it from a Newtonian fluid to a shear-thinning non-Newtonian fluid. This parameter change allows the adhesive to exhibit different viscosity characteristics under different shear conditions, enabling controlled penetration and reduced wicking behavior
Solution Approach 2:
The patent creates a composite adhesive system by combining polyvinyl alcohol with nanofibrillated cellulose. This composite material leverages the bonding properties of PVOH and the structural reinforcement and rheological modification properties of NFC, achieving superior performance that neither component could provide alone
2Strength
If increased marrying roll pressure is used to overcome adhesive performance deficiencies, then bonding strength may improve, but bulk, softness and emboss quality suffer
Solution Approach 1:
The patent changes the adhesive's viscosity parameters through shear-thinning behavior, allowing the adhesive to remain relatively thick at rest (reducing wicking) but thin under shear stress during application (enabling penetration and bonding), thereby achieving good bonding without excessive pressure that would compromise softness
Solution Approach 2:
The adhesive's viscosity dynamically responds to shear rate conditions: high viscosity at low shear (storage condition) prevents wicking, while low viscosity at high shear (application condition) enables penetration and bonding, eliminating the need for high pressing forces
3Loss of substance
If the glue is too viscous, then excessive wicking is prevented, but the glue may not penetrate the web sufficiently, reducing bonding effectiveness
Solution Approach 1:
The patent applies parameter changes by introducing shear-thinning behavior through nanofibrillated cellulose addition, enabling the adhesive to have high viscosity at rest (preventing wicking) and low viscosity under shear (enabling penetration), thus resolving the contradiction between preventing wicking and achieving sufficient penetration
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 use of NFC in the adhesive results in increased bonding strength and reduced glue usage, enabling the production of softer multi-ply absorbent sheets with enhanced softness and adhesion properties, as demonstrated by improved Peel Test Plybond values and panel softness.
Implementation Method 1
NFC is a shear-thinning material, so it flows more as shear is applied, and recovers viscosity as shear decreases; that is, a stationary film of glue with NFC will be initially more viscous as it sits on the web surface and thin as the plies are married to enable penetration into each paper web.
Data Source
AI summary
A multi-ply absorbent sheet includes a first absorbent ply of cellulosic sheet; a second absorbent ply of cellulosic sheet; and a ply bonding adhesive interposed between the first absorbent ply and the second absorbent ply, the ply-bonding adhesive thereby adhering said absorbent plies together. The ply-bonding adhesive comprises polyvinyl alcohol and nanofibrillated cellulose. In a particularly preferred embodiment the adhesive is applied as a dilute aqueous composition to tissue plies and the nanofibrillated cellulose has a Characteristic Breaking Length of 6.5 km or above.