Page 86 - Handbook of Surface Improvement and Modification

6.1 Methods and mechanisms of tack enhancement 81

Phase behavior of poly(styrene-b-isoprene-b-styrene)/tackifier resin blends was
investigated by thermal analysis, morphological observations, and cloud point measure-
10
ments. Phase transition temperatures were different on heating and cooling (on heating:
lower critical solution temperature phase transition was 150 and upper critical solution
o
temperature 200 C; on the cooling process, only upper critical solution temperature at
o
10
200 C was observed). The properties of the pressure-sensitive adhesive were changed
10
along with annealing temperature corresponding to the phase behavior.
The adhesive behavior of the polymer was controlled by chain stretching during the
11
unloading process. The chain elongation contributed substantially to dissipation during
11
the debonding process at all velocities. The adhesive performance of the tackifier-
11
enriched surface was determined by loading velocity and contact time.
Rubber-based pressure-sensitive adhesives (three packing tapes) were exposed to
12
sunlight for 6 months to accelerate the oxidation of the adhesives. Natural rubbers and
12
aliphatic petroleum resins decomposed completely during of deterioration process. Cou-
marone resins, aromatic petroleum resins and β-pinene resins have higher resistance to
12
oxidation than natural rubbers and aliphatic petroleum resins. These tackifiers can be
identified by pyrolysis-gas chromatography/mass spectrometry even after the deteriora-
12
tion.
The photochemical stability of conservation adhesive (BEVA 371) was studied using
Fourier transform infrared spectroscopy, size exclusion chromatography, and solubility
13
tests. The polycyclohexanone tackifying resin was the least stable component of conser-
13
vation adhesives. Many of its
oxidation products were identi-
13
fied in the aged samples. Works
are in progress to select more UV-
resistant tackifier for the adhe-
13
sive.
The role of tackifier in a
pressure-sensitive adhesive tape
Figure 6.11. Rolling tack tester. [Adapted, by permission, from was investigated using pressure-
Nakamura, Y, Adachi, M; Tachibana, Y; Sakai, Y; Nakano, S; Fujii, sensitive adhesive prepared from
S; Sasaki, M; Urahama, Y, Int. J. Adh. Adh., 29, 806-11, 2009.] an acrylic block copolymer con-
sisting of polymethylmethacrylate
and poly(butyl acrylate) as base polymer and a tackifier; the poly(butyl acrylate) oligomer
14
was used as a diluent to compare the effect on the adhesion properties. Tack was mea-
sured using a rolling tack tester in wide temperature and rolling rate ranges (Figure
14
6.11). The tack increased and the failure mode varied from cohesive failure to interfacial
14
failure with an increase in the rolling rate. The tack value and the failure mode strongly
14
depended upon the viscoelastic properties of adhesive. Both tackifier and oligomer
improved the mobility of base polymer, but only tackifier increased the cohesive strength
14
of the base polymer.
The dependence of peel strength and shear strength of epoxidized natural rubber-
based pressure-sensitive adhesive on molecular weight and the rate of testing was investi-
15
gated using coumarone-indene as the tackifying resin. The peel and shear strength
4 15
increased up to an optimum molecular weight of 6.5x10 . In the case of peel strength,