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In most cases unmodified aliphatic resins are used for HMPSA systems. They are mid-block compatible and do not change the end-block properties of styrene isoprene styrene (SIS) block copolymer-based formulations. Oils, generally used in these systems, are partially compatible with the end-blocks and addition of such oils will decrease the "hardness" and adversely affect shear adhesion. Other resins such as rosin esters, styrene modified terpene resins, or aromatic modified aliphatic resins can be used for tackification. Generally these resins exhibit mid-block and some degree of end-block compatibility.
In HMPSA formulations, unmodified aliphatic hydrocarbon resins will give satisfactory adhesion properties, but also high viscosities at processing temperatures. As this limits the production speed of a hot melt coating unit, Piccotac 1094-E hydrocarbon resin was developed to provide similar viscosities to aromatic modified aliphatic hydrocarbon resins at elevated temperatures. Thanks to its partial compatibility with the end-blocks of SIS polymers, aromatic modified hydrocarbon resin exhibits lower viscosity levels at application temperatures. The unique chemical structure of Piccotac 1094-E combines the advantages of unmodified with modified aliphatic hydrocarbon resins in one tackifier. The resin also gives very good rolling ball tack and high affinity to cardboard.
Evaluation of Piccotac 1094-E Hydrocarbon Resin in a SIS-Based Formulation
The HMPSA formulation includes 120 parts of resin and 20 parts of a naphthenic oil (Shellflex 451 FC) per hundred parts of SIS elastomer. A thermoplastic block copolymer, an 18% styrene-containing SIS with no diblocks, was used (Kraton D-1160) to illustrate that lower MMAP values in general reduce melt viscosities.
Table 1: Formulations Based on Four Different Tackifier Resins |
| Formulation Number |
1 |
2 |
3 |
4 |
| Kraton D-1160 thermoplastic block copolymera |
100 |
100 |
100 |
100 |
| Piccotac 1095-N hydrocarbon resinb |
120 |
-- |
-- |
|
| Piccotac 1094-E hydrocarbon resinb |
-- |
120 |
-- |
-- |
| Piccotac 9095 hydrocarbon resinb |
-- |
|
120 |
-- |
| Piccotac 8095 hydrocarbon resinb |
-- |
-- |
-- |
120 |
| Shellflex 451 FC naphthenic oilc |
20 |
20 |
20 |
20 |
| Irganox 1010 hindered phenolic antioxidantd |
2 |
2 |
2 |
2 |
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| Coating weight (gm2) |
23 |
22 |
22 |
21 |
| Viscosity @ 175°C (mPa•s) |
72,400 |
48,400 |
48,300 |
47.800 |
| Substrate |
BOPP |
BOPP |
BOPP |
BOPP |
| Coater |
Meltex |
Meltex |
Meltex |
Meltex |
| Release |
Yes |
Yes |
Yes |
Yes |
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Peel adhesion to steel (N/25 mm)
Test method W102** |
17.0 |
12.7 |
17.2 |
16.0 |
Shear adhesion to steel (minutes)@ 23°C/2.5 kg;
Test method W106** |
>10K |
>10K |
>10K |
>10K |
Shear adhesion to steel (minutes) @ 40°C/2.5 kg;
Test method W106** |
171 |
800 |
448 |
279 |
Shear adhesion to cardboard (minutes) @ 40°C/1 kg;
Test method W106** |
191 |
594 |
619 |
434 |
Shear adhesion to cardboard (minutes) @ 70°C/0.5 kg;
Test method W106** |
1178 |
1889 |
1479 |
526 |
Flap test to cardboard (minutes) @ 23°C/1 kg;
Test method W100** |
130 |
253 |
171 |
193 |
Rolling ball tack (cm)
Test method W107** |
7.6 |
3.8 |
2.6 |
9.3 |
Loop tack (N/25 mm)
Test method W103** |
31.6 |
22.0 |
29.9 |
26.3 |
Shear adhesion failure temperature, 0.5 kg (°C)
Test method W126** |
101 |
98 |
102 |
91 |
aKraton Polymer Company
bEastman Chemical Company
cShell Chemical Company
dCiba Chemical Company
**Eastman Chemical Company Middleburg BV copyright test methods
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The conclusion can be made that Piccotac 1094-E (Formulation 2), just like the aromatic modified hydrocarbon resins Piccotac 9095 (Formulation 3), and Piccotac 8095 (Formulation 4) gives a much lower viscosity at 175°C than an aliphatic resin, such as Piccotac 1095-N. This is not surprising for aromatic modified resins, since the aromatic components of the resin will decrease the formation of styrene polymer endblock domain structure at high temperatures and thus creates an adhesive with a lower viscosity.
That Piccotac 1094-E produces an adhesive with a lower viscosity, equal to Piccotac 8095, is remarkable for an unmodified aliphatic hydrocarbon resin. At low temperatures, however, the resin is only compatible with the mid-block and will give optimum tack properties as shown by the low rolling ball tack values. Also, the cardboard testing shows improved performance, as is illustrated by the better shear adhesion and higher flap test values. The other properties of the Piccotac 1094-E formulation were more or less similar to Formulation 1 with Piccotac 1095-N and Formulation 3 with Piccotac 9095 hydrocarbon resin.
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