The coloration of EVA

Transcription

1 The coloration of EVA Public

2 2 Introduction EVA is a commodity polyethylene copolymer. The vinyl acetate group is bulky and polar, which therefore imparts high flexibility and transparency to the polyethylene backbone. EVA grades can contain from 2% to 50% vinyl acetate, but most grades contain 10-25%. As the level of vinyl acetate in the copolymer increases, the level of crystalline is reduced. This yields in products ranging from similar to low density polythene to flexible rubbers. Clarity, flexibility, toughness and solvent solubility also increase with increasing vinyl acetate content. Although it has elastomeric properties and can be melt processed, it is not classified as an TPE. Processing is done relatively low temperatures of ºC as the melting point is ~80ºC and the glass transition temperature around -40ºC (depending on the grade).

3 3 EVA / applications EVA comes close to plasticized PVC in its properties of economy and flexibility and can therefore be used for similar applications. A key difference between soft PVC and EVA is that EVA does not contain any plasticizer to create flexibility, which can migrate. Therefore EVA is used in the medical and food packaging industry. EVA is also used as part of multi layer films to impart toughness. The addition of foaming agent creates products with good insulating and shock absorbing properties, which are highly suitable

4 4 EVA slipper and shoe sole production EVA can be processed by conventional thermoplastic methods including foam molding. Conventional rubber processing techniques such as internal mixers, two roll mills may also be used. Typical melt temperatures for EVA during extrusion and molding should not exceed 220C. During the processes, blowing agents can be applied

5 EVA coloration Public

6 6 EVA / Coloration EVA is a PE copolymer; processing and coloration is similar to LDPE. - Heat stability - Processing temperatures C - Select heat stable pigments - Potentially no use of diarylide pigments - Light stability - Selection depends on customer requirement - Migration stability - Potential color migration between materials should be considered - Dispersion - Easy to disperse pigments - Non dispersed agglomerates negatively impact rub fastness - Regulatory status - Consumer goods regulations

7 7 EVA coloration / Migration fastness Color migration has to be considered in shoe applications. Although color migration in EVA is not very strong, contact with other layers of different materials and colors could create issues. Certain pigments have a tendency to migrate. This is related to its pigment stability but also application conditions. The material, additives and usage conditions can all have an influence on the migration fastness.

8 8 EVA coloration / Migration fastness Unfortunately there is no universal test method for bleeding. A very aggressive test is the white vinyl test or called sandwich method - A layer of 0.1% colored plasticized PVC is placed between two layers of white plasticized PVC. - Different times and temperatures are used. - Short test : 140C/2h - Long test : 80C/24h - Year test : 25C/1 year

9 9 EVA coloration / Solutions Red E4G

10 10 EVA coloration / Solutions

11 11 EVA coloration / Pigment solubility

12 12 EVA coloration / Pigment solubility

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