|
Hydrogenated hydrocarbon tackifier resins are the preferred resin choice for many formulators in major adhesive industries due to their water-white, crystal-like appearance and excellent thermal stability. These resins are used mainly in hot melt adhesives for the hygiene industry, plastic modification, and in other demanding applications where a very light color is required.
The selection of the right tackifier resin system is critical for the performances of hot melt. As discussed in ”Tackifier Selection”, resin compatibility that can be adjusted by the chemical structure, the degree of hydrogenation, and the molecular weight is an important consideration.
For example, fully hydrogenated hydrocarbon resins like Regalite™ S1100, have good compatibility with the mid-block of a styrenic block copolymer and provide very good adhesion to the substrate. Unfortunately, these resins produce poor application characteristics when spray coating of the adhesive is attempted.
Partially hydrogenated hydrocarbon resins such as Regalite™ S5100 have good compatibility with styrenic blocks and reduce the viscosity to provide excellent coating ability for the hot melt, however the adhesion is poor.
A combination of a fully hydrogenated and a partially hydrogenated hydrocarbon resin provides a synergistic effect, compared with a single hydrogenated hydrocarbon resin of intermediate degree of hydrogenation. Each resin contributes its best adhesive performance properties, resulting in overall superior adhesive performance as compared with a single resin having the same degree of hydrogenation.
The combination of two resins in various concentrations allows adhesive formulators to "fine-tune" adhesive properties without having to consider other resin types.
To illustrate this, Table 2 shows the performances of hot melt containing a combination of Regalite™ S1100 and Regalite™ S5100 at different ratios.
Table 1: Basic Test Formulation
| SIS linear block copolymer 30% Sty, 17% diblock, MFI=8 |
25 wt%
|
| Regalite™ blend |
62.5 wt%
|
| Paraffinic white oil |
12.5 wt%
|
Since the results of dynamic mechanical analysis (DMA) predicted similar adhesive performance, the two adhesives were coated and various adhesive performance parameters were measured. The formulations were coated onto polypropylene film using a Meltex C200 coater, at a approximately 37 g/m2 coating weight. Standard pressure sensitive adhesive (PSA) test methods were used to evaluate the coatings; the needle penetration was measured, and viscosity curves were determined between 120°C and 180°C.
Table 2: Adhesive Performance Data
| Regalite™ S1100 / Regalite™ S5100 ratio |
250/0
|
187.5/62.5
|
125/125
|
62.5/187.5
|
0/250
|
|
| Coating weight (gsm) |
37
|
37
|
37
|
37
|
37
|
37
|
| Peel to steel, N/25mm |
32.9
|
32.2
|
34.7
|
36.3
|
11
|
20.8
|
| Peel to P.E., N/25mm |
10.2
|
4.9
|
8.8
|
10.6
|
4.7
|
2.1
|
| 23°C shear to steel, 2.5 kg, min |
5262
|
>10k
|
>10k
|
>10k
|
>10k
|
>10k
|
| 40 C shear to steel, 2.5 kg, min |
110
|
165
|
384
|
671
|
222
|
598
|
| 40°C shear to P.E., 1 kg, min |
21651
|
28671
|
>48k
|
>48k
|
>48k
|
>48k
|
| 70°C shear to steel, 0.5 kg, min |
136
|
187
|
202
|
160
|
40
|
136
|
| SAFT (°C) to steel, 0.5 kg |
88
|
90
|
89
|
86
|
77
|
83
|
| Loop tack to steel (N/25mm) |
47.9
|
50.2
|
46.2
|
34.5
|
15.9
|
24.3
|
| Loop tack to P.E. (N/25mm) |
12.4
|
18.7
|
14.8
|
8.7
|
3.2
|
6.6
|
| Needle penetration, mm |
102
|
105
|
107
|
103
|
88
|
97
|
Viscosity (mPa•s)
120°C
140°C
160°C
180°C |
2823
83.20
7.96
1.92
|
552
26.05
4.90
1.81
|
153.60
15.90
4.36
1.75
|
70.50
12.10
4.15
1.90
|
52.20
11.60
4.083
1.76
|
82.50
14.20
4.62
2.07
|
The data shows that the performance of both adhesives was very similar, but the two resin mix had better results in certain tests. There were significant improvements in:
- Peel resistance and loop tack properties to steel and to polyethylene indicating better adhesion, especially to polyethylene.
- Overall lower viscosity values in the viscosity curve for improved coatability (sprayability) and for coating at lower temperatures.
- Needle penetration (higher), indicating a softer adhesive.
- Cohesion at higher temperatures, as determined by 40°C and 70°C shear resistance to steel and shear adhesion failure temperature (SAFT) values for better creep resistance.
|