Multi-Layer Paper Adhesion via Polymer Spray
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Solution Overview
Problem
Current methods for producing multi-layer paper do not fully meet the requirements for improved strength, especially under shear forces, heat, and moisture, and often result in weak layer adhesion and brittleness.
Innovation Solution
A process involving dewatering two aqueous fibrous suspensions to form fibrous webs, spraying one web with a water-soluble polymer solution, joining the webs under pressure, and drying with heat to create a multi-layer paper, where the polymer solution contains monomers polymerized from formula I, optionally with subsequent hydrolysis to form primary amino or amidine groups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If adhesive starches or starch derivatives are sprayed onto a paper web to increase layer adhesion, then layer adhesion is improved, but the starch composite becomes partially or completely irreversibly brittle upon subsequent heat exposure
Solution Approach 1:
The patent changes the chemical parameters of the adhesive by using polymers with specific functional groups (carboxyl, hydroxyl, amino, amidine, or isocyanate groups) instead of traditional starch. These polymers can be applied at controlled pH values (3-10) and form adhesives through chemical reactions with fiber surfaces, providing heat stability that starch cannot achieve. The molecular weight, charge density, and functional group composition are specifically controlled to optimize both adhesion and heat resistance.
Solution Approach 2:
The patent creates a composite adhesive system by combining polymers with multiple functional groups that can interact with both cellulose fibers and provide heat stability. The composite nature of these polymers (containing multiple types of functional groups in specific ratios) allows simultaneous achievement of strong layer adhesion and resistance to heat-induced brittleness, overcoming the limitations of single-component starch adhesives.
2Strength
If native starch is used as an adhesive with high viscosity in aqueous solution, then layer adhesion can be achieved, but only a low solids content can be used
Solution Approach 1:
The patent fundamentally changes the adhesive material from starch to synthetic or semi-synthetic polymers with tunable properties. These polymers can be formulated with much higher solids contents (5-50% or more) while maintaining appropriate viscosity for spraying. The molecular weight, charge density, and functional group composition can be adjusted to achieve the desired balance between adhesion performance and applicability at high solids content, eliminating the low solids content limitation of starch.
3Adaptability or versatility
If increased amounts of recycled raw material are used, then environmental sustainability is improved, but fiber lengths become shorter and paper strength decreases
Solution Approach 1:
The patent uses polymer adhesives as intermediary substances that bridge the gap between short recycled fibers and the requirement for strong paper. These polymers adsorb onto fiber surfaces through chemical and physical interactions, creating strong bonding points that compensate for the reduced fiber length. The polymers act as mediators that transfer and distribute stresses across the fiber network, maintaining paper strength even when fibers are short and cannot provide sufficient mechanical interlocking alone.
4Shape
If increasingly voluminous fiber blends are used to increase bending stiffness, then bending stiffness is improved, but layer adhesion requirements increase
Solution Approach 1:
The patent employs polymers with specifically controlled molecular weights, charge densities, and functional group compositions to achieve optimal layer adhesion for voluminous fiber blends. The high molecular weight provides long-range bridging between fibers, while charged groups (positive or negative) enhance electrostatic interactions with fiber surfaces. Functional groups like carboxyl, hydroxyl, amino, and isocyanate groups provide multiple bonding mechanisms, ensuring strong adhesion even in challenging voluminous fiber structures where traditional adhesives fail.
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 process enhances the strength and durability of multi-layer paper, improving layer adhesion and resistance to splitting, while maintaining strength under varying conditions of heat and moisture.
Implementation Method 1
spraying at least one fiber web with an aqueous spray solution or spray suspension
Implementation Method 2
The polymers mentioned in the examples also include a polyallylamine and polymers obtained by polymerization of N-vinylformamide and subsequent, at least partial, hydrolysis of the formamide groups
Implementation Method 3
dewatering the partially dewatered laminate by applying heat to produce a multi-layer paper
Implementation Method 4
dewatering the partially dewatered laminate by applying heat
Implementation Method 5
In the drying section of a paper machine, this results in gelatinization and thus strengthening
Implementation Method 6
dewatering the laminate under pressure to produce a partially dewatered laminate
Implementation Method 7
joining the two fiber webs to form a laminate, dewatering the laminate under pressure
Implementation Method 8
These polymers are obtained by polymerization of at least 5 wt% (meth)acrylic acid and are applied, among other methods, by spraying onto a paper layer
Data Source
AI summary
The invention relates to a method for producing dried multi-layer paper, comprising the following steps: (A) dewatering a first aqueous fibrous material suspension, whereby a first fibrous material web is produced having a dry content of between 14 wt.-% and 25 wt.-%; (B) dewatering a second aqueous fibrous material suspension, whereby a second fibrous material web is produced having a dry content between 14 wt.% and 25 wt.%; (C) spraying at least one flat side of the first fibrous material web, the second fibrous material web or the first fibrous material web and the second fibrous material web with a spraying solution or spraying suspension, whereby at least one sprayed fibrous material web having a sprayed flat side is produced; (D) joining the first fibrous material web to the second fibrous material web, at least one of the above two being a sprayed fibrous material web, such that a layer composite is produced; (E) dewatering the layer composite by pressing, such that a partially dewatered layer composite is produced; (F) dewatering the partially dewatered layer composite with the application of heat, such that the dried multi-layer paper is produced; wherein the spraying solution or spraying suspension contains (c-a) water and (c-b) at least one water-soluble polymer P, which can be obtained by the polymerisation of (i) 40 to 85 mol.% of a monomer of formula I, in which R1 = H or C1-C6-alkyl, (ii) 15 to 60 mol.% of one or more ethylenically unsaturated monomers that are different from a monomer of formula I, wherein the total quantity of all monomers (i) and (ii) is 100 mol.%, and optionally by a subsequent partial or complete hydrolisation of the units of the monomers of formula (I) polymerised into the polymer P with the formation of primary amino groups or amidine groups, the proportion of water being at least 75 wt.% relative to the spraying solution or the spraying suspension.