Sheet-like artificial leather, and method for producing same
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Solution Overview
Problem
Existing eco-conscious sheet materials produced using aqueous dispersed type polyurethane resins tend to have a hard touch due to their dense structure, which is less comparable to the softness achieved with organic-solvent-based polyurethanes, and lack the uniformity and elegant surface appearance of man-made leathers.
Innovation Solution
A sheet material with a microphase-separated structure comprising hard segment domains and soft segment domains, achieved by using a hydrophilic-group-containing polyurethane resin crosslinked with a crosslinking agent, such as a polyisocyanate or carbodiimide, applied to a fibrous substrate, and processed through heat drying and saponified polyvinyl alcohol treatment to create a soft and rubberlike feel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If aqueous dispersed type polyurethane resin is used to replace organic-solvent-based polyurethane resin, then health and environmental safety is improved, but the touch hardness increases and softness is lost
Solution Approach 1:
The invention changes the coagulation parameters by controlling temperature and humidity conditions. Specifically, it uses moist-hot coagulation at 60-90°C with relative humidity of 70-100%, which alters the phase transition behavior of the polyurethane resin to achieve a softer touch while maintaining the eco-friendly aqueous dispersion system.
Solution Approach 2:
The invention creates a porous structure in the polyurethane resin layer by controlling the coagulation process to form microvoids and a less dense network. This porous structure reduces the density and hardness of the resin, providing a softer touch sensation comparable to organic-solvent-based materials while maintaining the environmental benefits of aqueous dispersion.
2Object-affected harmful factors
If aqueous dispersed type polyurethane resin is used, then production process becomes more eco-friendly, but the surface appearance uniformity and elegance deteriorate
Solution Approach 1:
The invention applies a sizing agent to the fibrous substrate before impregnating with the polyurethane resin. This preliminary treatment creates a controlled surface that prevents defects such as fiber floating and resin aggregation during subsequent processing, ensuring uniform surface appearance and elegant finish while maintaining the eco-friendly aqueous dispersion process.
Solution Approach 2:
The invention implements a multi-stage drying process with controlled temperature and humidity conditions. The first drying stage at lower temperature removes excess moisture, and the second stage at higher temperature completes the drying. This feedback-controlled drying process prevents surface defects and ensures uniform appearance.
3Productivity
If moist-hot coagulation is used to coagulate aqueous dispersed type polyurethane resin, then coagulation efficiency is improved, but the polyurethane membrane becomes highly dense and hard
Solution Approach 1:
The invention uses partial coagulation by controlling the coagulation time and conditions so that not all polyurethane molecules aggregate completely. This partial coagulation creates a less dense structure with softer touch while maintaining sufficient coagulation efficiency for practical production. The coagulation is stopped at an optimal point before complete densification occurs.
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 resulting sheet material has a uniform nap length, elegant surface appearance, and excellent wrinkle recovery, comparable to man-made leathers produced using organic-solvent-based polyurethanes, while maintaining an eco-friendly production process.
Implementation Method 1
aqueous dispersed type polyurethane resins are coagulated by 'moist-hot coagulation' in which the state of hydration of a polyurethane emulsion in water is destroyed mainly by heating
Implementation Method 2
coagulating the dispersion by heat drying
Data Source
Figure 1~3
AI summary
A sheet material includes a fibrous substrate made of microfibers and a hydrophilic-group-containing resin applied to the fibrous substrate. The hydrophilic-group-containing resin has a microphase-separated structure that satisfies Condition I: I. In a phase image obtained by observing an area of 1 µm2 in a cross-section of the hydrophilic-group-containing resin applied to the fibrous substrate by phase imaging using an atomic force microscope (AFM), a standard deviation of a mode of brightness distribution of areas of 0.2 µm2 in the area of 1 µ2 is from 0 to 10. Provided are a sheet material that is produced through an eco-conscious production process and yet has such uniformity that is comparable to those of man-made leathers produced using organic-solvent-based polyurethanes, an elegant surface appearance, and a good touch, and a method for producing such a sheet material.