Urea-Modified Paper Coating Slips for Viscosity and Drying Energy Reduction
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Solution Overview
Problem
The paper production process is energy-intensive, particularly in drying paper coated with aqueous paper coating paint, and there is a limit to increasing the solids content of coating paints due to viscosity issues, which affects processability and paper quality, including smoothness and calcium ion stability.
Innovation Solution
Incorporating urea into the aqueous paper coating paint compositions to increase the solids content while reducing viscosity, using a binder with a glass transition temperature below 50°C and high inorganic pigments, along with optional additives, to enhance energy efficiency and paper quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the solids content of coating paint is increased to reduce drying energy, then the energy required for drying is reduced, but the viscosity increases sharply and processability is lost
Solution Approach 1:
The patent introduces urea as a chemical additive that changes the physical-chemical parameters of the coating composition. Urea modifies the water-binder-pigment interactions, allowing the system to maintain low viscosity even at high solids content (up to 80% or more), thereby resolving the contradiction between energy efficiency and processability
Solution Approach 2:
The patent creates a composite aqueous composition containing urea, water, binder, and pigment in specific proportions. This composite structure allows the system to achieve both high solids content and acceptable rheological properties, as urea acts as a dispersing and thickening agent that prevents viscosity buildup
2Quantity of substance
If the solids content of coating paint is increased to reduce drying energy, then the amount of water to be evaporated is reduced, but the drying energy requirement increases due to higher viscosity
Solution Approach 1:
By adding urea, the patent changes the evaporative properties and flow characteristics of the coating. Urea reduces the energy required for water evaporation by modifying the binding properties and allowing for more efficient drying kinetics, thus resolving the contradiction between reducing water content and minimizing drying energy
3Productivity
If the solids content is increased to improve paper quality, then the coating efficiency is improved, but the viscosity increases and smoothness deteriorates
Solution Approach 1:
Urea addition changes the rheological parameters of the coating, maintaining low viscosity at high solids content. This allows the coating to flow smoothly during application and level out properly, achieving both high coating efficiency and excellent surface smoothness simultaneously
4Loss of time
If the solids content is increased to reduce drying time, then the production speed is improved, but the viscosity increases and calcium ion stability decreases
Solution Approach 1:
Urea modification changes the chemical environment in the coating, enhancing calcium ion stability even at high solids content. This allows for faster drying times without compromising the stability of the binder dispersion, resolving the contradiction between production speed and composition 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
This approach allows for higher energy efficiency in paper drying, improved smoothness of coated paper, and enhanced calcium ion stability, enabling higher solids content without increased viscosity, thus optimizing paper production.
Implementation Method 1
urea, especially when used in larger amounts, preferably in an amount of up to 100% of the maximum amount soluble in the respective composition, can be used to increase the solids content to reduce the amount required for drying amount of energy required for paper coated with aqueous paper coating paint and/or to reduce the viscosity of paper coating paint
Implementation Method 2
urea, especially when used in larger amounts, preferably in an amount of up to 100% of the maximum amount soluble in the respective composition, can be used to increase the solids content
Implementation Method 3
at least one polymer suitable as a binder for paper coating paints with a glass transition temperature Tg of less than 50 ° C
Implementation Method 4
at least 60% by weight of inorganic pigments based on the total solids content
Implementation Method 5
there is a need to further improve the calcium ion stability, i.e. the prevention of coagulation caused by calcium ions, in binder dispersions for paper coating paints
Data Source
AI summary
A description is given of the use of urea for reducing the amount of energy required to dry paper coated with an aqueous papercoating slip, and/or for reducing the viscosity of papercoating slips. A description is also given of aqueous compositions suitable for use in accordance with claim 1, in the form of aqueous papercoating slips, aqueous, pigment-free binder dispersions, aqueous, binder-free pigment suspensions and aqueous, pigment-free starch solutions containing urea H2N-CO-NH2 in an amount in each case of preferably 1-100% of the maximum amount soluble in the composition in question.