Ethylenvinylacetat

A group of copolymers is called ethylene vinyl acetate (EVA).

The basic material for hot-melt adhesive preferably copolymers with fractions of 18% to 33% of vinyl acetate are used.
The density is 0.93 to 0.96 g / cm ³, the melting range between 60 ° and 95 ° C.  EVA copolymers have different melt flow indices which allow conclusions on the molecular weight.

Type Selection

The type selection is simplified if one sums up the products into four groups:

18% vinyl acetate
This relatively low-priced products are designed for hot melt adhesive systems, which are primarily selected due to surface gloss, hardness and anti-blocking tendency.  They are also used for adhesion of porous materials.
25% vinyl acetate
The materials have been developed in terms of optimum use of hot melt adhesive systems.
28% vinyl acetate
You will find a wide range of applications. The products made from it are characterized by toughness, flexibility and improved adhesion.
33% vinyl acetate
These products are preferably used in hot melt adhesives for non-porous support materials. It is often advantageous to use combinations to meet the requirements at the lowest cost needs. For example, create a blend of  EVA grades with high and low melt index values, it will result in viscosities and technical properties whose values lie between those of the two starting materials.

Melt Flow Index (MFI 190 ° C) and vinyl acetate content (% VA)

Both the melt flow index (MFI) and the vinyl acetate content (% VA) have a significant impact on property profiles and processing parameters.
The following chart shows some of these property profiles:

Table: variations of VA content and MFI values in relation to  physical properties

VA % MFI
(190°C/10min) 
Tensile strenght
(kg)
Softening Point (°C) Shore A
 18  2  175  185  92
 24  3  140  175  81
 28  5  140  155  82
 24  20  88  130  85
 28  20  85  115  81
 18  150  108  100  83
 28  150  76  88  68
 24  400  70  84  76
 28  400  67  84  67

Below diagramm shows some of the properties:




The table shows that for example for the same VA content (VA 28%) with increasing MFI value (MFI 5 to 400) the softening temperature and the tensile strength are decreasing.

Typical applications for EVA hot melt adhesives due to their low processing temperatures are:

Competence

We are happy to advise you further. Contact our experienced technicians.

ROWAK AG