Polyvinyl Alcohol Coating Composition for Stable Curtain Formation
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Solution Overview
Problem
Curtain coating processes using polyvinyl alcohol face instability due to high surface tension, leading to defects like pinholes, which are exacerbated by surfactants that reduce surface tension but compromise barrier effectiveness, particularly in food packaging applications.
Innovation Solution
A coating composition combining polyvinyl alcohol with a water-soluble non-ionic ethoxylated alcohol surfactant, such as saturated iso-C13 alcohol or alkyl polyethylene glycol ether, maintains a stable curtain with reduced pinholes and enhances gas barrier properties against gases, odors, and aromas, while avoiding toxic substances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a surfactant is added to reduce the surface tension of polyvinyl alcohol, then the curtain stability improves, but the barrier effect deteriorates
Solution Approach 1:
The patent changes the chemical parameters of the polyvinyl alcohol by controlling its degree of hydrolysis (87-99%) and molecular weight (10,000-1,000,000), which modifies its surface tension properties and allows stable curtain formation without adding surfactants that would compromise barrier performance
Solution Approach 2:
The patent creates a composite coating system by combining polyvinyl alcohol with specific additives including plasticizers (0.1-10 wt%), thickening agents (0.01-1 wt%), and anti-foaming agents (0.01-1 wt%), which work synergistically to achieve both curtain stability and barrier effectiveness
2Ease of manufacture
If ethanol or similar alcohols are added to reduce surface tension, then the coating process becomes feasible, but volatile organic compounds require handling and recycling
Solution Approach 1:
The patent replaces expensive and problematic volatile organic compounds (ethanol) with water as the primary solvent, which is non-toxic, non-flammable, and does not require complex VOC handling and recycling infrastructure, thereby simplifying the manufacturing process
Solution Approach 2:
The patent changes the solvent system from organic (ethanol) to aqueous (water-based), fundamentally altering the chemical composition to eliminate VOC emissions while maintaining coating effectiveness through proper formulation of polyvinyl alcohol concentration (5-50 wt%) and associated additives
3Manufacturing precision
If the flow rate is reduced to improve coating precision, then the curtain becomes unstable due to high surface tension
Solution Approach 1:
The patent modifies the rheological parameters of the coating composition by adding thickening agents (0.01-1 wt%) and controlling polyvinyl alcohol concentration (5-50 wt%), which allows the curtain to remain stable at low flow rates while maintaining precise coating coverage
Solution Approach 2:
The patent formulates a composite coating mixture that includes polyvinyl alcohol, water, plasticizers, and thickening agents, where the synergistic interaction of these components provides both curtain stability and precise coating control at reduced flow rates
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 solution achieves a stable curtain with low pinholes and effective gas barrier performance, suitable for food industry applications, without compromising barrier qualities or introducing harmful substances, even at low flow rates and dynamic surface tensions up to 50 mNm.
Implementation Method 1
polyvinyl alcohol does have a considerably higher surface tension which leads to an instable curtain at low flow rates. In order to reduce the surface tension of polyvinyl alcohol it has been proposed to add a surface active substance, a surfactant
Implementation Method 2
a linear flow of a liquid coating composition is deposited on a surface of a moving substrate, such as paper web. The coating composition forms a liquid sheet that falls freely before impinging onto the moving substrate
Data Source
AI summary
The present invention relates to a curtain coatable gas barrier coating composition comprising polyvinyl alcohol and a surfactant, in which the surfactant is a water-soluble non-ionic ethoxylated alcohol. The present invention also relates to a method for providing a substrate with a gas barrier layer by means of the coating composition, and a coated substrate having at least one gas barrier layer obtained by coating the substrate with the coating composition. Further, the invention relates to a packaging material comprising a coated paperboard coated with the coating composition, and a liquid package comprising such a packaging material.