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Kristalex hydrocarbon resins are thermoplastic resins derived largely from pure aromatic monomers like a-methylstyrene and styrene. Coupled with the low viscosity (relative to polymers), superior color, and narrow molecular weight distribution inherent to most pure monomer hydrocarbon resins, Kristalex hydrocarbon resins have exceptional all-round properties.
In addition to an excellent high temperature performance Kristalex hydrocarbon resins also provide a special balance of mechanical strength, set-speed, and low-temperature flexibility. Examples of the formulations are listed in Table 1. In this table Kristalex hydrocarbon resin represents both Kristalex resin grades Kristalex F85 and Kristalex F100. They are evaluated against Picco HM100 hydrocarbon resin and Foralyn 90 ester of hydrogenated rosin. Table 1: Evaluated Hot Melt Adhesive Formulations
| Formulation |
1 |
2 |
3 |
4 |
5 |
6 |
| Evatane 28/40 ethylene vinyl acetatea |
17.5 |
17.5 |
17.5 |
– |
– |
– |
| Evatane 28/400 ethylene vinyl acetatea |
17.5 |
17.5 |
17.5 |
– |
– |
– |
| Lotryl 35 BA40 ethylene butyl acrylatea |
– |
– |
– |
17.5 |
17.5 |
17.5 |
| Lotryl 35 BA320 ethylene butyl acrylatea |
– |
– |
– |
17.5 |
17.5 |
17.5 |
| Kristalex hydrocarbon resinsb |
40 |
– |
– |
40 |
– |
– |
| Foralyn 90 ester of hydrogenated rosinb |
– |
– |
40 |
– |
– |
40 |
| Paraffin wax 68/70 |
10 |
10 |
10 |
10 |
10 |
10 |
| Sasolwaks C80 waxc |
5 |
5 |
5 |
5 |
5 |
5 |
| Irganox 1076 antioxidantd |
0.2 |
0.2 |
0.2 |
0.2 |
0.2 |
0.2 | aArkema Chemical Company
bEastman Chemical Company
cSasol Wax Company
dCiba Specialty Chemicals Company
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Outstanding Low Temperature Flexibility
Bending the test specimen over a mandrel at -5°C and -15°C provides a good indication of the low temperature flexibility of the hot melt adhesive. Superior flexibility manifests itself by small mandrel diameters. The diameter of the smallest mandrel over which the sample does not break is shown in Figure 1.
Both Kristalex hydrocarbon resins display almost equal results thereby outperforming the other two resins significantly. Since Kristalex F100 has a softening point 15°C higher than Kristalex F85 it would be expected to reduce low temperature flexibility. The comparatively lower compatibility of Kristalex F100, however, offsets this effect providing similar system flexibility using either tackifier.
Figure 1: Low Temperature Flexibility - Effect of Resin
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Exceptional Low Temperature Performance
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Tensile properties at -30°C are presented in Figure 2. Systems formulated with Kristalex F85 hydrocarbon resin clearly show superior low temperature tensile properties in all cases. The remarkably high tensile and elongation properties of the formulations with Kristalex F85 indicate excellent impact resistance of the finished adhesive. In this respect, Kristalex hydrocarbon resins undoubtedly offer a unique balance of properties compared with the other two resins.
The low temperature performance of ethylene butyl acrylate (EBA) systems is much better in comparison with EVA. This is due to the lower Tg of EBA copolymer, albeit that its lower degree of compatibility towards Kristalex hydrocarbon resins contributes to low temperature flexibility as well.
Figure 2: Low Temperature Tensile Properties
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Rheological Evaluation
In Figure 3, a comparison is made of the viscoelastic response of three EBA-based hot melt adhesives. G' and Tan delta values of formulations containing Kristalex F85, Picco HM100, and Foralyn 90 are displayed. The G' curves run from the upper left corner of the figure downwards to the right. The Tan d curves start from the lower left hand part of the figure and end at the upper right corner.
Figure 3: Viscolastic Response Comparison
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| For polymers, the peak in the Tan delta curves demonstrates the temperature at which the individual segments of the polymer become mobile. On this basis the Tan d peak temperature can be related to the glass transition temperature of the polymer. EVA polymers have a more random character in comparison with EBA's and hence have a sharper Tg; around -34°C. As stated earlier, the Tg of EBA is considerably lower, about -52°C, which indicates superior low temperature flexibility. The test results presented here confirm this.
Note: Eastman Chemical Company produces Kristalex hydrocarbon resins in two locations: Jefferson, PA USA and Middleburg, NL. The properties of the products from each plant are nearly identical. The source of the product can be determined by the grade nomenclature: the US-produced materials are identified by a four digit code (Kristalex 3085) and the European products have a combination of letters and numbers (Kristalex F85). The results here were obtained using European Kristalex products, however, the results with the North American materials should be comparable. |