EVOH Resin Composition for Uniform Crystallization
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Solution Overview
Problem
Ethylene-vinyl alcohol copolymers (EVOH) used in melt molding face challenges in maintaining stability and external appearance characteristics due to nonuniform crystallization, which leads to issues like yellowing and unstable fluidity during processing.
Innovation Solution
A resin composition with a heterogeneous nucleation index (f) of less than 0.6, achieved by controlling the crystallization process through high cooling rates in differential scanning calorimetry, high degree of saponification, optimal ethylene content, low higher fatty acid amide content, and inclusion of alkali metal salts, ensures uniform crystal size and improved melt molding stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If EVOH is processed by melt molding to improve manufacturing efficiency, then productivity increases, but external appearance characteristics deteriorate due to coloration such as yellowing
Solution Approach 1:
The invention changes the chemical composition parameters of the EVOH by controlling the degree of saponification (85-99 mol%) and ethylene content (10-40 mol%). This parameter optimization allows the material to maintain stability during melt molding while preventing coloration, thus resolving the contradiction between productivity improvement and external appearance deterioration
Solution Approach 2:
The invention creates a composite resin system by blending EVOH with other polymers and additives in specific ratios. This composite approach enhances the material's resistance to thermal degradation during melt molding, preventing yellowing while maintaining high productivity benefits
2Strength
If crystallization is allowed at high temperature to form thicker crystalline lamellae, then mechanical strength improves, but nonuniformity in crystal thickness increases leading to unstable fluidity
Solution Approach 1:
The invention optimizes the crystallization temperature parameter within a specific range (90-140°C) to achieve uniform crystal thickness. This controlled parameter change ensures both adequate mechanical strength and uniform crystal structure, preventing fluidity instability during subsequent processing
3Object-generated harmful factors
If crystallization is carried out within a narrow temperature range to achieve uniform crystal thickness, then external appearance characteristics improve, but crystallization speed decreases
Solution Approach 1:
The invention introduces nucleating agents as intermediaries to facilitate crystallization at controlled temperatures. These agents provide nucleation sites that enable uniform crystal formation without requiring excessively narrow temperature ranges, thus maintaining both external appearance quality and acceptable crystallization speed
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 resin composition results in extrusion-molded, injection-molded, and blow-molded articles with superior stability and external appearance characteristics, preventing yellowing and ensuring consistent melt formability.
Implementation Method 1
the crystallization of the crystalline polymer carried out within a narrow temperature range leads to the formation of crystalline lamellae of a comparatively uniform thickness and spherulites of a comparatively uniform size
Implementation Method 2
The term 'homogeneous nucleation' as referred to herein means the mechanism in which crystal nuclei are generated according to a statistical probability by way of thermodynamic driving
Implementation Method 3
The term 'heterogeneous nucleation' as referred to herein means the mechanism in which crystal nuclei are generated through interactions of crystalline polymers with impurities and the like contained in the crystalline polymers
Implementation Method 4
A molded product from EVOH is generally formed by using a melt molding procedure
Data Source
Figure 1
AI summary
A resin composition superior in stability and external appearance characteristics during/following melt molding; and an extrusion-molded article, an injection-molded article and a blow-molded article that are formed from the resin composition are provided. The resin composition contains an ethylene-vinyl alcohol copolymer as a principle component, and has a heterogeneous nucleation index (f) of less than 0.6 as determined by formula (1) based on a differential scanning calorimetry (DSC) curve obtained by DSC in which the resin composition is cooled at a rate of 150 °C/sec from a molten state at 210 °C. In the formula (1), Qtotal represents an area of a total region surrounded by the DSC curve and a base line, and Qhetero represents an area of a heterogeneous region that is a part of the total region, falling within a range from the temperature lower than the melting point by 38 °C to a temperature lower than the melting point by 75 °C. f=Qhetero/Qtotal