U.S. patent application number 10/462599 was filed with the patent office on 2004-12-23 for crosslinked solid type pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet comprising the composition, and pressure-sensitive adhesive sheet for waterproofing/airproofing comprising the sheet.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Fujiwara, Shuzo, Hirose, Isao, Ina, Yasunobu, Kitamura, Yoshihiro, Yamaguchi, Tomoo.
Application Number | 20040258936 10/462599 |
Document ID | / |
Family ID | 33516953 |
Filed Date | 2004-12-23 |
United States Patent
Application |
20040258936 |
Kind Code |
A1 |
Yamaguchi, Tomoo ; et
al. |
December 23, 2004 |
Crosslinked solid type pressure-sensitive adhesive composition,
pressure-sensitive adhesive sheet comprising the composition, and
pressure-sensitive adhesive sheet for waterproofing/airproofing
comprising the sheet
Abstract
A solid type pressure-sensitive adhesive composition capable of
being applied without the necessity of using an organic solvent or
water and a pressure-sensitive adhesive sheet, which are excellent
in both adhesive force and holding power and, in particular,
undergo no decrease in low-temperature adhesive force even when the
adhesive layer thickness is small. The crosslinked solid type
pressure-sensitive adhesive composition comprising (a) a rubbery
polymer, (b) a tackifier, and (c) a crosslinking agent comprising
at least one member selected from the group consisting of thiuram
vulcanizing agents, quinoid vulcanizing agents, quinone dioxime
vulcanizing agents, and maleimide vulcanizing agents.
Inventors: |
Yamaguchi, Tomoo;
(Ibaraki-shi, JP) ; Ina, Yasunobu; (Ibaraki-shi,
JP) ; Hirose, Isao; (Ibaraki-shi, JP) ;
Fujiwara, Shuzo; (Ibaraki-shi, JP) ; Kitamura,
Yoshihiro; (Ibaraki-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
NITTO DENKO CORPORATION
|
Family ID: |
33516953 |
Appl. No.: |
10/462599 |
Filed: |
June 17, 2003 |
Current U.S.
Class: |
428/500 ;
525/332.5 |
Current CPC
Class: |
C08F 8/00 20130101; Y10T
428/2852 20150115; C09J 7/383 20180101; B32B 25/04 20130101; Y10T
428/31855 20150401; Y10T 442/2754 20150401; C08F 210/12 20130101;
C08F 8/00 20130101; C08F 2810/20 20130101 |
Class at
Publication: |
428/500 ;
525/332.5 |
International
Class: |
C08F 008/00; B32B
007/12; B32B 015/04; B32B 027/00 |
Claims
1. A crosslinked solid type pressure-sensitive adhesive composition
comprising (a) a rubbery polymer, (b) a tackifier, and (c) a
crosslinking agent comprising at least one member selected from the
group consisting of quinoid vulcanizing agents and quinone dioxime
vulcanizing agents.
2. The composition as claimed in claim 1, wherein the rubbery
polymer (a) is a butyl rubber.
3. The composition as claimed in claim 1, wherein the rubbery
polymer (a) is a regenerated butyl rubber.
4. The composition as claimed in claim 1, wherein the rubbery
polymer (a) has a Mooney viscosity ML.sub.1+4(100.degree. C.) of
from 20 to 100.
5. The composition as claimed in claim 1, wherein the tackifier (b)
is a resin compatible with the rubbery polymer.
6. The composition as claimed in claim 1, wherein the tackifier (b)
is used in an amount of from 20 to 200 parts by weight per 100
parts by weight of the rubbery polymer.
7. The composition as claimed in claim 1, wherein the crosslinking
agent (c) is used in an amount of from 0.5 to 20 parts by weight
per 100 parts by weight of the rubbery polymer.
8. A pressure-sensitive adhesive sheet comprising a substrate and
formed thereover a pressure-sensitive adhesive layer comprising a
crosslinked solid type pressure-sensitive adhesive composition
comprising (a) a rubbery polymer, (b) a tackifier, and (c) a
crosslinking agent comprising at least one member selected from the
group consisting of quinoid vulcanizing agents and quinone dioxime
vulcanizing agents.
9. The pressure-sensitive adhesive sheet as claimed in claim 8,
wherein the pressure-sensitive adhesive layer has a thickness of
from 50 to 500 .mu.m.
10. The pressure-sensitive adhesive sheet as claimed in claim 8,
which is for use as a pressure-sensitive adhesive sheet for
waterproofing and/or airproofing.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a crosslinked solid type
pressure-sensitive adhesive composition which does not
substantially contain a solvent, and a pressure-sensitive adhesive
sheet (including a tape, film and other form) obtained by applying
the composition with heating to a substrate. The invention further
relates to a pressure-sensitive adhesive sheet for
waterproofing/airproofing comprising the pressure-sensitive
adhesive sheet.
DESCRIPTION OF THE RELATED ART
[0002] Due to the enforcement of the Housing Quality Security
Promotion Law, it is desired to completely eliminate the leaking of
rain in houses, and various waterproof sheets are used. Recently,
various airproof sheets also have been used with the demand for
highly airtight, highly heat-insulated houses, which are highly
effective in energy saving. Conventional pressure-sensitive
adhesive sheets for use as such waterproof or airproof
pressure-sensitive adhesive sheets employ a pressure-sensitive
adhesive comprising a rubber-asphalt, butyl rubber or acrylic
polymer as the base. The butyl rubber pressure-sensitive adhesive
has an actual durability of 30 years and shows relatively
satisfactory adhesiveness at high temperatures and low
temperatures. With respect to the mode of failure in peeling from
adherends, which is a factor important for the function of
waterproofing, the butyl rubber pressure-sensitive adhesive shows
cohesive failure. Pressure-sensitive adhesive sheets in which the
adhesive does not show cohesive failure upon peeling are
undesirable because a space is formed between the adherend and the
pressure-sensitive adhesive to pose the possibility that water
might penetrate into the space to impair waterproofing. On the
other hand, the rubber-asphalt pressure-sensitive adhesive has a
durability as short as about 10 years and shows poor adhesiveness
at high temperatures and low temperatures. The acrylic
pressure-sensitive adhesive, which has been marketed recently, is
less apt to show cohesive failure upon peeling from adherends and
whether or not this pressure-sensitive adhesive retains a
sufficient waterproofing function over many years has not been
demonstrated.
[0003] As described above, the butyl rubber pressure-sensitive
adhesive is superior in properties to other pressure-sensitive
adhesives for waterproofing/airproofing. However, the butyl rubber
pressure-sensitive adhesive is required to adhere to various
adherends including wood plates, plywoods, and
moistureproof/waterproof sheets so as to adhere to all adherends
among recent new house building materials and retain
waterproofing/airproofing properties over a long period of time.
Furthermore, the pressure-sensitive adhesive is desired to adhere
even at high temperatures and low temperatures as in midsummer and
midwinter. Thus, the butyl rubber pressure-sensitive adhesive is
required to be further improved in performance.
[0004] A solid type pressure-sensitive adhesive has hitherto been
used in pressure-sensitive adhesive sheets for
waterproofing/airproofing. A solid type pressure-sensitive adhesive
composition is a solvent-free and non-aqueous pressure-sensitive
adhesive composition which contains neither any organic solvent
causative of environmental pollution nor water, which necessitates
much energy for drying. It is generally produced by incorporating a
tackifier into a rubbery polymer, represented by natural rubber, as
the main ingredient, adding thereto a filler, e.g., fine calcium
carbonate particles, softener, e.g., an oil, antioxidant, and the
like, in appropriate proportions, and kneading this mixture with a
kneader, Banbury mixer, mixing rolls, or the like with heating to
obtain a pressure-sensitive adhesive composition which is solid at
ordinary temperature.
[0005] Such solid type pressure-sensitive adhesive compositions are
uncrosslinked compositions which have poor cohesive force
especially at high temperatures and hence have often caused
positional shifting. Furthermore, waterproof/airproof tapes should
adhere to various adherends, and most of these have had an adhesive
layer thickness as large as about from 0.2 to 0.5 mm because
reduced adhesive layer thicknesses, in particular, result in a
considerably reduced adhesive force at low temperatures. Because of
this, there has been a desire for a pressure-sensitive adhesive
sheet which, even when the adhesive layer thickness is small, can
exhibit the same functions as pressure-sensitive adhesive sheets
heretofore in use so as to reduce the amount of the
pressure-sensitive adhesive composition used.
SUMMARY OF THE INVENTION
[0006] The present invention has been made under these
circumstances.
[0007] Accordingly, one object of the invention is to provide a
crosslinked solid type pressure-sensitive adhesive composition
capable of being applied without the necessity of using an organic
solvent or water, which is excellent in both adhesive force and
holding power and, in particular, undergo no decrease in
low-temperature adhesive force even when the adhesive layer
thickness is small.
[0008] Another object of the invention is to provide a
pressure-sensitive adhesive sheet using the composition.
[0009] Still another object of the invention is to provide a
pressure-sensitive adhesive sheet for waterproofing/airproofing,
using the sheet.
[0010] It is thought that a solid type pressure-sensitive adhesive
composition comprising a rubbery polymer as the main ingredient can
be made to have an enhanced cohesive force by crosslinking with a
crosslinking agent as in the case of ordinary rubber products, and
the problems described above can be thus avoided. Crosslinked
rubber products other than pressure-sensitive adhesives are mostly
produced by a method in which a crosslinking agent is incorporated
beforehand into a rubbery polymer through kneading and the
resultant composition is formed into a sheet or another desired
shape before being crosslinked. In constant, in the case of
pressure-sensitive adhesive sheets employing a solid type
pressure-sensitive adhesive, a pressure-sensitive adhesive
composition capable of being crosslinked in the step of kneading a
rubbery polymer together with materials such as a tackifier and a
softener is thought to be optimal from the standpoint of production
steps because the process for producing these pressure-sensitive
adhesive sheets does not include a heating step in which the
pressure-sensitive adhesive composition applied is heated. In this
case, the practical kneading temperature during the kneading is
about 180.degree. C. at the most, and it is considerably difficult
to heat the composition to, for example, 200.degree. C., which is
necessary for the crosslinking reaction with sulfur generally used
for the crosslinking of butyl rubbers. In addition, although
crosslinking with sulfur generally requires about 20 to 30 minutes,
such long-term kneading with heating cuts molecular chains of the
rubbery polymer due to heat and shear force and thereby reduces
rather than increases the cohesive force. Consequently, the time
period of the kneading step is about from 5 to 20 minutes at the
most. Because of these, it was thought that a crosslinking agent
which undergoes a crosslinking reaction at a relatively low
temperature in a short time period should be used in the
invention.
[0011] Based on the idea described above, the present inventors
selected a crosslinking agent capable of reacting with a
rubber-based pressure-sensitive adhesive during kneading. They have
found that when a rubber-based pressure-sensitive adhesive is
kneaded together with this crosslinking agent with heating while
monitoring the kneading torque and suitably regulating the kneading
temperature and kneading time, then the crosslinking agent can be
evenly dispersed in the material without causing the rubbery
polymer to undergo a molecular weight decrease due to molecular
chain cutting. As a result, the desired crosslinking can be
realized and the cohesive force can be enhanced. The invention has
thus been completed.
[0012] The crosslinked solid type pressure-sensitive adhesive
composition according to the invention comprises (a) a rubbery
polymer, (b) a tackifier, and (c) a crosslinking agent comprising
at least one member selected from the group consisting of thiuram
vulcanizing agents, quinoid vulcanizing agents, quinone dioxime
vulcanizing agents, and maleimide vulcanizing agents (claim 1).
[0013] In a preferred embodiment, the rubbery polymer (a) is a
butyl rubber.
[0014] The pressure-sensitive adhesive sheet in sheet or tape form
according to the invention comprises a substrate and formed
thereover a pressure-sensitive adhesive layer comprising the
crosslinked solid type pressure-sensitive adhesive composition
having the constitution described above.
[0015] The pressure-sensitive adhesive sheet is used as a
pressure-sensitive adhesive sheet for waterproofing and/or
airproofing.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The crosslinked solid type pressure-sensitive adhesive
composition of the invention comprises (a) a rubbery polymer, (b) a
tackifier, and (c) a crosslinking agent comprising at least one
member selected from the group consisting of thiuram vulcanizing
agents, quinoid vulcanizing agents, quinone dioxime vulcanizing
agents, and maleimide vulcanizing agents. The rubbery polymer (a)
used in the invention preferably is a butyl rubber from the
standpoints of durability and weatherability. Most preferred butyl
rubber is a regenerated butyl rubber, which has excellent
processability. The rubbery polymer (a) preferably has a Mooney
viscosity ML.sub.1+4(100.degree. C.) of from 20 to 100. Besides
butyl rubbers, rubbery polymers which may be used according to need
are synthetic rubbers such as butadiene rubbers, isoprene rubbers,
polyisobutylene and blends of two or more of these.
[0017] The tackifier (b) used in the invention serves not only to
impart tackiness but to facilitate thermal softening. Examples of
this tackifier include various resins compatible with the rubbery
polymer, such as petroleum resins, phenolic resins, rosin resins,
and terpene resins. Such a tackifier is used in an amount of from
20 to 200 parts by weight, preferably from 30 to 150 parts by
weight, per 100 parts by weight of the rubbery polymer.
[0018] The crosslinking agent (c) used in the invention is a
crosslinking agent comprising at least one member selected from the
group consisting of thiuram vulcanizing agents, quinoid vulcanizing
agents, quinone dioxime vulcanizing agents, and maleimide
vulcanizing agents.
[0019] Examples of the thiuram vulcanizing agents include
tetramethylthiuram disulfide, tetraethylthiuram disulfide,
tetrabutylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram
disulfide, dipentamethylenethiuram tetrasulfide, and
tetramethylthiuram monosulfide.
[0020] Examples of the quinoid vulcanizing agents include
poly-p-dinitrosobenzene.
[0021] Examples of the quinone dioxime vulcanizing agents include
p-quinone dioxime and p,p'-dibenzoylquinone dioxime.
[0022] Examples of the maleimide vulcanizing agents include
N,N'-m-phenylenedimaleimide, N,N'-p-phenylenedimaleimide, and
N,N'-ethylenedimaleimide.
[0023] Those crosslinking agents have common properties, i.e., they
can be used for crosslinking at low temperatures (e.g., 180.degree.
C. or lower) and have a high crosslinking rate. These crosslinking
agents are used in an amount of generally from 0.5 to 20 parts by
weight, preferably from 0.5 to 10 parts by weight, per 100 parts by
weight of the rubbery polymer.
[0024] Examples of compounding agents for use in the invention as
optional ingredients include fillers such as calcium carbonate,
talc, and magnesium oxide, softeners such as polybutene and process
oil, antioxidants, and plasticizers. The amounts of such
ingredients used per 100 parts by weight of the rubbery polymer are
as follows. The amount of the filler is up to 200 parts by weight,
preferably from 10 to 150 parts by weight, the amount of the
softener is up to 150 parts by weight, preferably from 5 to 100
parts by weight, and the amount of the antioxidant is up to 5 parts
by weight, preferably from 0.5 to 5 parts by weight, more
preferably from 1 to 3 parts by weight.
[0025] In the invention, the rubbery polymer and tackifier
described above are heated and kneaded as essential ingredients
together with any of those optional ingredients without using any
organic solvent or water at all, and the crosslinking agent is
further added thereto. The resulting mixture is continuously heated
and kneaded to thereby uniformly disperse the crosslinking agent in
the mixture and simultaneously react it uniformly with the rubbery
polymer. Thus, a pressure-sensitive adhesive composition is
obtained which has a structure in which the rubbery polymer has
been moderately crosslinked.
[0026] Kneading with heating can be conducted using a batch
kneading machine such as a pressure kneader, Banbury mixer or
mixing rolls, or a continuous kneading machine such as a twin-screw
kneader. In this kneading operation, a suitable kneading
temperature is selected from a range of about from 100 to
200.degree. C. according to the kind of the rubber, etc. The
kneading time is suitably selected according to the kneading
temperature so that the total kneading time for each ingredient is
in the range of from 3 to 60 minutes. During the kneading, the
kneading torque is monitored and the end point for torque increase
is judged to be the end point for the crosslinking reaction.
[0027] The solid type pressure-sensitive adhesive composition thus
crosslinked has satisfactory moldability such that it readily
softens upon heating. Consequently, when this pressure-sensitive
adhesive composition is applied with heating to a substrate such as
a fabric (e.g., cotton, rayon, artificial-fiber, or nonwoven
fabric), a paper (e.g., Japanese paper or kraft paper), a plastic
(e.g., cellophane, polyethylene, polyester, poly(vinyl chloride),
cellulose acetate, polypropylene, poly(ethylene terephthalate),
polystyrene, or polyacrylonitrile), a metal foil, or a plastic
laminate of any of these by means of calender rolls, an extruder,
or the like, then a pressure-sensitive adhesive sheet comprising
the substrate and formed thereon a layer comprising the
pressure-sensitive adhesive composition can be produced in the form
of a sheet, tape, film, or the like. Since this process does not
use any organic solvent causative of environmental pollution, or
water which necessitates much energy for drying, there is no need
of conducting a step for drying a coated substrate in a drying
oven. This process is hence friendly to the global environment and
can greatly contribute to energy saving.
[0028] The adhesive layer thickness, i.e., the thickness of the
layer comprising the pressure-sensitive adhesive composition
described above, can be regulated to a value in the wide range of
generally from 50 to 500 .mu.m, preferably from 100 to 300 .mu.m.
Even when the adhesive layer has a small thickness within this
range, the pressure-sensitive adhesive sheet does not show an
abrupt decrease in tackiness properties at low temperatures unlike
pressure-sensitive adhesive sheets heretofore in use. Consequently,
the pressure-sensitive adhesive sheet of the invention has an
effect that the adhesive layer thickness can be reduced and, hence,
application of a pressure-sensitive adhesive composition in an
unnecessarily large amount can be avoided.
[0029] The substrate may be subjected to conventional treatments in
order to improve the adhesive force (anchoring force) of the
pressure-sensitive adhesive layer. For example, that side of the
substrate which is coated with the pressure-sensitive adhesive
layer may be subjected to a surface treatment, such as a corona
treatment or plasma treatment, or coated with a primer layer. That
side of the substrate which is not coated with the
pressure-sensitive adhesive layer may be suitably coated with a
release agent represented by a silicone resin or a fluororesin in
order to facilitate the unwinding of a roll of the sheet.
[0030] The pressure-sensitive adhesive sheet of the invention thus
produced is excellent not only in adhesive force but in holding
power because of the improved cohesive force due to moderate
crosslinking. Even when the adhesive sheet is allowed to stand at
high temperatures, it retains a high cohesive force. The
pressure-sensitive adhesive sheet of the invention can hence be
used in various bonding applications. However, the adhesive sheet
is useful as a waterproof or airproof sheet or the like for the
waterproofing/airproofing of houses so as to take advantage of the
high waterproofing properties, durability, and weatherability
thereof. The adhesive sheet can be extensively utilized for the
waterproofing of buildings other than houses.
[0031] The invention will be explained below in greater detail by
reference to the following Examples, but the invention should not
be construed as being limited to these Examples in any way.
EXAMPLE 1
[0032] 1,000 g of a regenerated butyl rubber (Mooney viscosity
ML.sub.1+4(100.degree. C.), 44.+-.6) was introduced into a 3 liters
pressure kneader heated to 150.degree. C. About 500 g of a calcium
carbonate powder was further introduced into the kneader. The
resulting mixture was kneaded for about 5 minutes. 400 g of
petroleum resin, "Escorez 1202", manufactured by Exxon Co., as a
tackifier was introduced into the kneader, and the resulting
mixture was kneaded for about 10 minutes. Further, 500 g of
"Polybutene HV300", manufactured by Nippon Oil Co., Ltd., as a
softener was introduced into the kneader in several portions, and
the resulting mixture was kneaded for about 10 minutes. Finally, 20
g of quinoid vulcanizing agent, "Vulnoc DNB", manufactured by
Ouchi-Shinko Chemical Industrial Co., Ltd., as a crosslinking agent
was introduced into the kneader to crosslink the mixture with
kneading for about 5 minutes. This mixture was then taken out of
the kneader. Thus, a pressure-sensitive adhesive composition was
prepared.
[0033] This pressure-sensitive adhesive composition was applied
with heating at 100.degree. C. to a substrate (0.12 mm-thick woven
fabric whose back side had been treated) by means of an 8-inch
four-roll calender so as to result in an adhesive layer thickness
of 0.25 mm. Thus, a pressure-sensitive adhesive sheet was
produced.
EXAMPLE 2
[0034] A pressure-sensitive adhesive sheet was produced in the same
manner as in Example 1, except that the adhesive layer thickness
was changed to 0.1 mm.
EXAMPLE 3
[0035] A pressure-sensitive adhesive sheet was produced in the same
manner as in Example 1, except that 20 g of thiuram vulcanizing
agent, "Nocceler TT", manufactured by Ouchi-Shinko Chemical
Industrial Co., Ltd., was used as a crosslinking agent.
EXAMPLE 4
[0036] A pressure-sensitive adhesive sheet was produced in the same
manner as in Example 1, except that 20 g of quinone dioxime
vulcanizing agent, "Vulnoc GM", manufactured by Ouchi-Shinko
Industrial Chemical Co., Ltd., was used as a crosslinking agent,
and the kneading after addition of the vulcanizing agent was
conducted at 180.degree. C. for 5 minutes.
EXAMPLE 5
[0037] A pressure-sensitive adhesive sheet was produced in the same
manner as in Example 1, except that 20 g of maleimide vulcanizing
agent, "Vulnoc PM", manufactured by Ouchi-Shinko Industrial
Chemical Co., Ltd., was used as a crosslinking agent, and the
kneading after addition of the vulcanizing agent was conducted at
180.degree. C. for 5 minutes.
COMPARATIVE EXAMPLE 1
[0038] A solid type pressure-sensitive adhesive composition was
prepared in the same manner as in Example 1, except that no
crosslinking agent was added and a crosslinking treatment was not
conducted. This composition was used to produce a
pressure-sensitive adhesive sheet in the same manner as in Example
1.
COMPARATIVE EXAMPLE 2
[0039] A pressure-sensitive adhesive sheet was produced in the same
manner as in Comparative Example 1, except that the adhesive layer
thickness was changed to 0.1 mm.
COMPARATIVE EXAMPLE 3
[0040] A solid type pressure-sensitive adhesive composition was
prepared in the same manner as in Example 1, except that 20 g of
sulfur was added as a crosslinking agent. This composition was used
to produce a pressure-sensitive adhesive sheet in the same manner
as in Example 1.
COMPARATIVE EXAMPLE 4
[0041] A solid type pressure-sensitive adhesive composition was
prepared in the same manner as in Example 1, except that no
tackifier was added. This composition was used to produce a
pressure-sensitive adhesive sheet in the same manner as in Example
1.
[0042] The pressure-sensitive adhesive sheets obtained in Examples
1 to 5 and Comparative Examples 1 to 4 were subjected to an
adhesive force test and a holding power test by the following
methods. The results of these tests are shown in the Table
below.
[0043] Adhesive Force Test
[0044] A pressure-sensitive adhesive sheet having a width of 25 mm
was applied to each of a stainless-steel plate and a wood plate
(hemlock). The adhesive sheet applied was peeled off at a peel
angle of 180.degree., a peel rate of 300 mm/min, and temperatures
of 0.degree. C. and 60.degree. C. to measure the adhesive force
(N/25-mm width).
[0045] Holding Power Test
[0046] A pressure-sensitive adhesive sheet having dimensions of 25
mm by 25 mm was applied to a stainless-steel plate. In a 60.degree.
C. atmosphere, a 500 g stationary load was vertically hung on one
end of the pressure-sensitive adhesive sheet, and the time (min)
required for the pressure-sensitive adhesive sheet to shift and
fall off the plate was measured. The pressure-sensitive adhesive
layer was further examined for the mode of failure.
1 TABLE Adhesive Adhesive force test [N/25 mm] Holding power layer
On stainless-steel On wood test [min]/ thickness plate plate Mode
of [.mu.m] 0.degree. C. 60.degree. C. 0.degree. C. 60.degree. C.
failure Example 1 0.25 49 10 29 11 6/cohesive failure Example 2
0.10 45 9 26 10 7/cohesive failure Example 3 0.25 43 12 30 13
5/cohesive failure Example 4 0.25 48 12 28 12 6/cohesive failure
Example 5 0.25 47 11 27 11 6/cohesive failure Comparative 0.25 40 7
29 8 2/cohesive failure Example 1 Comparative 0.10 9 6 15 7
1/cohesive failure Example 2 Comparative 0.25 41 7 28 8 2/cohesive
failure Example 3 Comparative 0.25 0 2 0 0 0/interfacial Example 4
delamination
[0047] The results in the Table above show that the
pressure-sensitive adhesive sheets obtained in Examples 1 to 5
according to the invention each were excellent both in adhesive
force at the low and high temperatures and in holding power
regardless of the adhesive layer thickness. The mode of failure of
the adhesive sheets was cohesive failure. These adhesive sheets can
hence be judged satisfactory in waterproofing properties.
[0048] Contrary to this, the pressure-sensitive adhesive sheets of
Comparative Examples 1 and 2, which had not undergone any
crosslinking treatment with a vulcanizing agent, showed a poor
holding power, and the pressure-sensitive adhesive sheet of
Comparative Example 2, which had a reduced adhesive layer
thickness, showed a considerably poor adhesive force at the low
temperature. The pressure-sensitive adhesive sheet of Comparative
Example 3, for which sulfur had been added as a vulcanizing agent,
failed to have improved properties because sufficient vulcanization
had not proceeded under the low-temperature short-duration
vulcanization conditions described in Example 1. Furthermore, the
pressure-sensitive adhesive sheet of Comparative Example 4, for
which no tackifier had been added, showed a low adhesive force and
a low holding power and failed to have the desired properties.
[0049] As described above, since the pressure-sensitive adhesive
composition of the invention is obtained by adding a tackifier to a
rubbery polymer and crosslinking the mixture with a vulcanizing
agent, it is excellent in both adhesive force and holding power
and, in particular, undergoes no decrease in low-temperature
adhesive force even when the adhesive layer thickness is small.
Furthermore, since the adhesive composition thermally softens and
can be molded easily, it can be used to produce a
pressure-sensitive adhesive sheet without the necessity of using an
organic solvent or water. In addition, since no drying step is
necessary after application, the adhesive composition can
contribute to energy saving and is desirable from the standpoint of
global environment.
[0050] It should further be apparent to those skilled in the art
that various changes in form and detail of the invention as shown
and described above may be made. It is intended that such changes
be included within the spirit and scope of the claims appended
hereto.
[0051] This application is based on Japanese Patent Application No.
2001-230730 filed Jul. 31, 2001, the disclosure of which is
incorporated herein by reference in its entirety.
* * * * *