A new development in waterborne systems is the use of natural rubber (NR) latex as the base polymer for waterborne PSA for tape applications. A special hydrocarbon-based resin dispersion, Tacolyn 5193, was developed for this application. Table 1 shows how Tacolyn 5193 can be used in combination with NR to produce a waterborne adhesive with properties similar to a traditional solventborne adhesive. In the examples shown Formula A is a simple 1:1 blend of NR latex and Tacolyn 5193 that can be compared to the commercially available solvent-based NR adhesive shown in column B. The other two formulas in columns C and D show a partial replacement of the high molecular weight NR latex with Synthomer carboxylated styrene butadiene rubber (c-SBR) latex or a low molecular weight NR latex. By using other elastomers in the system the properties can be manipulated to improve tack and peel adhesion at the expense of some loss of adhesion.
Table 1: Adhesive Performance of Natural Rubber Latex Packaging Tape
| Composition |
Formula
(Parts resin per hundred parts rubber) |
| |
A |
B |
C |
D |
| Natural rubber latex LATZ |
100 |
Commercial Solvent-Based NR Formula |
50 |
50 |
| Lo Mooney natural rubber latex |
|
|
50 |
| Tacolyn 5193 resin dispersiona |
100 |
100 |
100 |
| Synthomer 30A40, c-SBRb |
|
50 |
|
|
Test Properties |
| Peel adhesion to steel, N/25mm |
|
6-10 |
7-8 |
7-8 |
| Rolling ball tack, cm |
2-3 |
<5 |
16 |
2-3 |
| Loop tack to steel, N/25mm |
9-10 |
10-15 |
18 |
13 |
| Shear, 23°C, 2.5kg to steel minutes, |
3000 |
10000 |
1000 |
2000 |
| Shear, 40°C, 2.5kg to steel, minutes |
1200 |
1000 |
80 |
300 |
| Shear, 40°C, 1kg to cardboard, minutes |
750 |
400 |
20 |
200 |
| Flap test, minutes |
300 |
500 |
40 |
300 |
| Coating weight g/m2 |
17-19 |
17-19 |
19-20 |
19-20 |
aEastman Chemical Company
bSynthomer Ltd.