U.S. patent application number 14/115744 was filed with the patent office on 2014-03-27 for water-dispersed pressure-sensitive adhesive composition, pressure-sensitive adhesive and pressure-sensitive adhesive sheet.
This patent application is currently assigned to NITTO DENKO CORPORATION. The applicant listed for this patent is Chie Kitano, Mika Okada. Invention is credited to Chie Kitano, Mika Okada.
Application Number | 20140088239 14/115744 |
Document ID | / |
Family ID | 48467429 |
Filed Date | 2014-03-27 |
United States Patent
Application |
20140088239 |
Kind Code |
A1 |
Okada; Mika ; et
al. |
March 27, 2014 |
WATER-DISPERSED PRESSURE-SENSITIVE ADHESIVE COMPOSITION,
PRESSURE-SENSITIVE ADHESIVE AND PRESSURE-SENSITIVE ADHESIVE
SHEET
Abstract
The present invention makes a water-dispersed PSA composition
capable of forming a PSA that exhibits good adhesiveness to a
non-polar adherend such as polyethylene and polypropylene at a low
temperature. The water-dispersed PSA composition comprises a
(meth)acrylic polymer obtained by polymerizing a monomer
composition comprising as a primary component an
alkyl(meth)acrylate having an alkyl group with 1 to 18 carbon
atoms, and a latex containing a rubber component that is immiscible
with the (meth)acrylic polymer, the (meth)acrylic polymer and the
latex being mixed at a weight ratio ((meth)acrylic polymer/rubber
latex) within a range of 95/5 to 25/75 based on solid contents;
wherein a storage modulus in a range of -15.degree. C. to
25.degree. C. is 1 MPa or smaller, the storage modulus being
determined by a dynamic viscoelastic measurement in which shear
strain is applied at a frequency of 1 Hz, the measurement being
taken with respect to the water-dispersed PSA composition dried at
100.degree. C. for 3 minutes.
Inventors: |
Okada; Mika; (Ibaraki-shi,
JP) ; Kitano; Chie; (Ibaraki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Okada; Mika
Kitano; Chie |
Ibaraki-shi
Ibaraki-shi |
|
JP
JP |
|
|
Assignee: |
NITTO DENKO CORPORATION
Ibaraki-shi, Osaka
JP
|
Family ID: |
48467429 |
Appl. No.: |
14/115744 |
Filed: |
April 24, 2012 |
PCT Filed: |
April 24, 2012 |
PCT NO: |
PCT/JP2012/060944 |
371 Date: |
November 5, 2013 |
Current U.S.
Class: |
524/523 |
Current CPC
Class: |
C08L 9/00 20130101; C09J
7/385 20180101; C09J 121/02 20130101; C09J 133/064 20130101; C08L
33/08 20130101; C09J 2433/00 20130101; C09J 2421/00 20130101; C09J
133/04 20130101; C09J 133/08 20130101; C09J 2301/312 20200801; C08L
7/00 20130101; C09J 2301/302 20200801; C09J 133/08 20130101; C08L
7/00 20130101; C09J 133/08 20130101; C08L 9/00 20130101; C09J
121/02 20130101; C09J 2421/00 20130101; C09J 2433/00 20130101; C08L
33/08 20130101; C09J 2421/00 20130101; C09J 2433/00 20130101 |
Class at
Publication: |
524/523 |
International
Class: |
C09J 7/02 20060101
C09J007/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 26, 2011 |
JP |
2011-117951 |
Jul 22, 2011 |
JP |
2011-160387 |
Feb 17, 2012 |
JP |
2012-033057 |
Claims
1. A water-dispersed pressure-sensitive adhesive composition
comprising: a (meth)acrylic polymer obtained by polymerizing a
monomer composition comprising, as a primary component, an
alkyl(meth)acrylate having an alkyl group with 1 to 18 carbon
atoms; and a latex containing a rubber component that is immiscible
with the (meth)acrylic polymer; a weight ratio ((meth)acrylic
polymer/rubber latex) of the (meth)acrylic polymer and the latex
being within a range of 95/5 to 25/75 based on solid contents,
wherein a storage modulus in a range of -15.degree. C. to
25.degree. C. is 1 MPa or smaller, the storage modulus being
determined by a dynamic viscoelastic measurement in which shear
strain is applied at a frequency of 1 Hz, the measurement being
taken with respect to the water-dispersed pressure-sensitive
adhesive composition dried at 100.degree. C. for 3 minutes.
2. The water-dispersed pressure-sensitive adhesive composition
according to claim 1, wherein the latex has a loss tangent peak
temperature of -5.degree. C. or below, the loss tangent peak
temperature being determined by a dynamic viscoelastic measurement
in which shear strain is applied at a frequency of 1 Hz.
3. The water-dispersed pressure-sensitive adhesive composition
according to claim 1, further comprising a tackifier that is
miscible with the rubber component, but immiscible with the
(meth)acylic polymer.
4. The water-dispersed pressure-sensitive adhesive composition
according to claim 3, comprising the tackifier in an amount within
a range above 0 part by weight up to 100 parts by weight relative
to 100 parts by weight of solid contents of the latex.
5. The water-dispersed pressure-sensitive adhesive composition
according to claim 3, wherein the tackifier has a softening point
of 80.degree. C. to 150.degree. C.
6. The water-dispersed pressure-sensitive adhesive composition
according to claim 1, wherein the rubber component is at least one
species selected from a group consisting of natural rubber,
synthesized polyisoprene rubber, polybutadiene rubber, and
styrene-butadiene rubber.
7. A pressure-sensitive adhesive formed with the water-dispersed
pressure-sensitive adhesive composition according to claim 1.
8. A pressure-sensitive adhesive sheet comprising a
pressure-sensitive adhesive layer formed with the water-dispersed
pressure-sensitive adhesive composition according to claim 1.
9. The water-dispersed pressure-sensitive adhesive composition
according to claim 2, further comprising a tackifier that is
miscible with the rubber component, but immiscible with the
(meth)acylic polymer.
10. The water-dispersed pressure-sensitive adhesive composition
according to claim 9, comprising the tackifier in an amount within
a range above 0 part by weight up to 100 parts by weight relative
to 100 parts by weight of solid contents of the latex.
11. The water-dispersed pressure-sensitive adhesive composition
according to claim 9, wherein the tackifier has a softening point
of 80.degree. C. to 150.degree. C.
12. The water-dispersed pressure-sensitive adhesive composition
according to claim 2, wherein the rubber component is at least one
species selected from a group consisting of natural rubber,
synthesized polyisoprene rubber, polybutadiene rubber, and
styrene-butadiene rubber.
13. A pressure-sensitive adhesive formed with the water-dispersed
pressure-sensitive adhesive composition according to claim 2.
14. A pressure-sensitive adhesive sheet comprising a
pressure-sensitive adhesive layer formed with the water-dispersed
pressure-sensitive adhesive composition according to claim 2.
15. The water-dispersed pressure-sensitive adhesive composition
according to claim 4, wherein the tackifier has a softening point
of 80.degree. C. to 150.degree. C.
16. The water-dispersed pressure-sensitive adhesive composition
according to claim 3, wherein the rubber component is at least one
species selected from a group consisting of natural rubber,
synthesized polyisoprene rubber, polybutadiene rubber, and
styrene-butadiene rubber.
17. A pressure-sensitive adhesive formed with the water-dispersed
pressure-sensitive adhesive composition according to claim 3.
18. A pressure-sensitive adhesive sheet comprising a
pressure-sensitive adhesive layer formed with the water-dispersed
pressure-sensitive adhesive composition according to claim 3.
19. The water-dispersed pressure-sensitive adhesive composition
according to claim 10, wherein the tackifier has a softening point
of 80.degree. C. to 150.degree. C.
20. The water-dispersed pressure-sensitive adhesive composition
according to claim 4, wherein the rubber component is at least one
species selected from a group consisting of natural rubber,
synthesized polyisoprene rubber, polybutadiene rubber, and
styrene-butadiene rubber.
Description
TECHNICAL FIELD
[0001] The present invention relates to a water-dispersed
pressure-sensitive adhesive composition used for pressure-sensitive
adhesives, etc., as well as a pressure-sensitive adhesive and a
pressure-sensitive adhesive sheet each formed of the composition.
The present application claims priority to Japanese Patent
Application No. 2011-117951 filed on May 26, 2011, Japanese Patent
Application No. 2011-160387 filed on Jul. 22, 2011, and Japanese
Patent Application No. 2012-033057 filed on Feb. 17, 2012, and the
entire contents of these applications are incorporated in the
present application as reference.
BACKGROUND ART
[0002] In recent years, from the standpoint of environmental
stress, reduction of organic solvent usage has been desired. With
respect to a pressure-sensitive adhesive (PSA) composition
laminated on a PSA sheet, it has been also underway to shift from
solvent-based PSA compositions where an organic solvent is used as
the solvating media to water-dispersed PSA compositions where water
is used as the dispersion media.
[0003] As such a PSA, an acrylic PSA has been widely used because
of its versatility. However, there exists a problem such that an
acrylic PSA, in general, is poorly adhesive to a non-polar adherend
such as polyethylene and polypropylene.
[0004] In order to solve this kind of problem, in a disclosed
method, a tackifying resin having a high softening point is added
(e.g., see Patent Document 1). Also disclosed is a PSA that
comprises an acrylic polymer and a rubber-based PSA, and further
comprises a rosin-based tackifying resin, whereby the PSA exhibits
good adhesiveness to a non-polar adherend even at a low temperature
(e.g., see Patent Document 2).
CITATION LIST
[Patent Literatures]
[0005] [Patent Document 1] Japanese Patent Application Publication
No. H3-34786
[Patent Document 2] Japanese Patent Application Publication No.
2008-163095
SUMMARY OF INVENTION
Technical Problem
[0006] What has been desired is, however, a water-dispersed PSA
composition capable of forming a PSA having yet better adhesive
strength to a non-polar adherend at a low temperature than the
emulsion-based PSA's described in Patent Documents 1 and 2.
[0007] An objective of the present invention is to provide a
water-dispersed PSA composition capable of forming a PSA that
exhibits greater adhesiveness to a non-polar adherend such as
polyethylene and polypropylene at a low temperature.
Solution to Problem
[0008] The present inventors have earnestly researched in order to
solve the problem. As a result, they discovered that with a
water-dispersed PSA composition formed to comprise a (meth)acrylic
polymer and a latex that is immiscible with the (meth)acrylic
polymer at a prescribed weight ratio so that the PSA after dried
would exhibit a prescribed storage modulus, a PSA exhibiting good
adhesiveness to a non-polar adherend at a low temperature could be
formed; and completed the present invention.
[0009] It is considered that since the water-dispersed PSA
composition according to Patent Document 2 uses a rubber component
that exhibits a high modulus of elasticity in a low temperature
range, its storage modulus exceeds 1 MPa in a range of -15.degree.
C. to 25.degree. C., resulting in insufficient wettability to
adherends; and therefore, it exhibits poorer adhesiveness.
[0010] More specifically, the water-dispersed PSA composition
according to the present invention comprises a (meth)acrylic
polymer obtained by polymerizing a monomer composition comprising
as a primary component an alkyl(meth)acrylate having an alkyl group
with 1 to 18 carbon atoms, and a latex containing a rubber
component that is immiscible with the (meth)acrylic polymer, the
(meth)acrylic polymer and the latex being mixed at a weight ratio
((meth)acrylic polymer/rubber latex) within a range of 95/5 to
25/75 based on solid contents, wherein a storage modulus in a range
of -15.degree. C. to 25.degree. C. is 1 MPa or smaller, the storage
modulus being determined by a dynamic viscoelastic measurement in
which shear strain is applied at a frequency of 1 Hz, the
measurement being taken with respect to the water-dispersed PSA
composition dried at 100.degree. C. for 3 minutes.
[0011] In the water-dispersed PSA composition according to the
present invention, the latex containing the rubber component
preferably has a loss tangent peak temperature of -5.degree. C. or
below when determined by a dynamic viscoelastic measurement in
which shear strain is applied at a frequency of 1 Hz.
[0012] It is preferable that the water-dispersed PSA composition
according to the present invention further comprises a tackifier
that is miscible with the rubber component, but immiscible with the
(meth)acylic polymer.
[0013] The water-dispersed PSA composition according to the present
invention comprises the tackifier preferably in an amount within a
range above 0 part by weight up to 100 parts by weight relative to
100 parts by weight of solid contents of the rubber latex.
[0014] In the water-dispersed PSA composition according to the
present invention, the tackifier preferably has a softening point
of 80.degree. C. to 150.degree. C.
[0015] In the water-dispersed PSA composition according to the
present invention, it is preferable that the rubber component
contained in the latex is at least one species selected from a
group consisting of natural rubber, synthesized polyisoprene
rubber, polybutadiene rubber, and styrene-butadiene rubber.
[0016] The PSA according to the present invention is characterized
by being formed with a water-dispersed PSA composition according to
the present invention described above.
[0017] The PSA sheet according to the present invention is
characterized by comprising a PSA layer formed with a
water-dispersed PSA composition according to the present invention
described above.
Advantageous Effects of Invention
[0018] According to the present invention, can be provided a
water-dispersed PSA composition capable of forming a PSA that
exhibits good adhesiveness to a non-polar adherend such as
polyethylene and polypropylene at a low temperature.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 shows a graph indicating the evaluation results on
the miscibility of the (meth)acrylic polymer and the rubber
component used in Example 3.
[0020] FIG. 2 shows a TEM image of the PSA sheet obtained in
Example 3.
[0021] FIG. 3 shows cross-sectional diagrams schematically
illustrating outline configurations of PSA sheets according to some
embodiments of the present invention.
EMBODIMENTS OF INVENTION
[0022] Particulars of the present invention are described
below.
[0023] It is noted that "A to B" indicating a range means "A or
greater, but B or smaller" and various physical properties given in
the present description refer to values measured by the methods
described in Examples described later unless otherwise noted. In
the present description, "(meth)acryl" in "(meth)acrylic polymer"
and the like means "acryl and/or methacryl". In addition,
"water-dispersed" in the present description refers to a state
where components are at least partially dispersed in water; and for
instance, "water-dispersed PSA composition" refers to a composition
comprising a PSA composition and water and being in a state where
the PSA composition is partially dispersed in water. It is noted
that the term "dispersed" refers to a state where at least part of
components are not dissolved in water, including also a suspended
state and an emulsified state.
(I) Water-Dispersed PSA Composition
[0024] The water-dispersed PSA composition according to the present
invention comprises a (meth)acrylic polymer obtained by
polymerizing a monomer composition comprising as a primary
component an alkyl(meth)acrylate having an alkyl group with 1 to 18
carbon atoms, and a latex containing a rubber component that is
immiscible with the (meth)acrylic polymer. In the water-dispsersed
PSA composition according to the present invention, the
(meth)acrylic polymer and the latex are mixed at a weight ratio
((meth)acrylic polymer/rubber latex) within a range of 95/5 to
25/75 based on solid contents. It has a storage modulus of 1 MPa or
smaller when determined by a dynamic viscoelastic measurement in
which shear strain is applied at a frequency of 1 Hz, with the
measurement being taken with respect to the water-dispersed PSA
composition dried at 100.degree. C. for three minutes.
[0025] The respective components are described below.
[0026] (i) (Meth)acrylic Polymer
[0027] The (meth)acrylic polymer can be obtained by polymerizing a
monomer composition comprising, as a primary component, an
alkyl(meth)acrylate having an alkyl group with 1 to 18 carbon
atoms. The monomer composition may comprise, as desired, a
functional-group-containing unsaturated monomer or an unsaturated
monomer copolymerizable with the alkyl(meth)acrylate or the
functional-group-containing unsaturated monomer.
[0028] The alkyl(meth)acrylate having an alkyl group with 1 to 18
carbon atoms includes compounds represented by the following
general formula (1):
[Chem. 1]
H.sub.2C.dbd.CR.sup.1COOR.sup.2 (1)
(in general formula (1), R.sup.1 is a hydrogen atom or a methyl
group and R.sup.2 is an straight-chained or branched alkyl group
having 1 to 18 carbon atoms.)
[0029] Specific examples of R.sup.2 in general formula (1) include
methyl group, ethyl group, propyl group, isopropyl group, butyl
group, isobutyl group, sec-butyl group, t-butyl group, pentyl
group, neopentyl group, isoamyl group, hexyl group, heptyl group,
octyl group, 2-ethylhexyl group, isooctyl group, nonyl group,
isononyl group, decyl group, isodecyl group, undecyl group, dodecyl
group, tridecyl group, tetradecyl group, pentadecyl group,
hexadecyl group, heptadecyl group, octadecyl group, and so on.
[0030] Specific examples of the alkyl(meth)acrylate represented by
general formula (1) include methyl(meth)acrylate,
ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate,
butyl(meth)acrylate, isobutyl(meth)acrylate,
sec-butyl(meth)acrylate, t-butyl(meth)acrylate,
pentyl(meth)acrylate, neopentyl(meth)acrylate,
isoamyl(meth)acrylate, hexyl(meth)acrylate, heptyl(meth)acrylate,
octyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,
isooctyl(meth)acrylate, nonyl(meth)acrylate,
isononyl(meth)acrylate, decyl(meth)acrylate,
isodecyl(meth)acrylate, undecyl(meth)acrylate,
dodecyl(meth)acrylate, tridecyl(meth)acrylate,
tetradecyl(meth)acrylate, pentadecyl(meth)acrylate,
hexadecyl(meth)acrylate, heptadecyl(meth)acrylate,
octadecyl(meth)acrylate, and so on. These alkyl(meth)acrylates can
be used singly or in combination of two or more kinds.
[0031] The number of carbon atoms of the alkyl group in the
alkyl(meth)acrylate is preferably 2 to 18, or more preferably 4 to
12.
[0032] The amount of the alkyl(meth)acrylate to be added can be,
for instance, 60 to 99.5 parts by weight or preferably 70 to 99
parts by weight relative to 100 parts by weight of a total amount
of the monomer composition.
[0033] Examples of the functional-group-containing unsaturated
monomer include carboxyl-group-containing unsaturated monomers.
[0034] Carboxyl-group-containing monomers include unsaturated
carboxylic acids such as (meth)acrylic acid, itaconic acid, maleic
acid, fumaric acid, crotonic acid, cinammic acid, etc.; monoesters
of unsaturated dicarboxylic acids such as monomethyl itaconate,
monobutyl itaconate, 2-acryloyloxyethyl phthalate, etc.; monoesters
of unsaturated tricarboxylic acids such as 2-methacryloyloxyethyl
trimellitate, 2-methacryloyloxyethyl pyromellitate, etc.;
carboxyalkyl acrylates such as carboxyethyl acrylates
(.beta.-carboxyethyl acrylate, etc.), carboxypentyl acrylates,
etc.; acrylic acid dimer, acrylic acid trimer; anhydrides of
unsaturated dicarboxylic acids such as itaconic acid anhydride,
maleic acid anhydride, fumaric acid anhydride, etc.; and so on.
[0035] Examples of the functional-group-containing unsaturated
monomer other than the carboxyl-group-containing unsaturated
monomers include hydroxyl-group-containing unsaturated monomers
such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate,
4-hydroxybutyl acrylate, etc.; amide-group-containing unsaturated
monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide,
N,N-diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide,
N-butyl(meth)acrylamide, N-methoxymethyl(meth)acrylamide,
N-methylol(meth)acrylamide, N-methylolpropane(meth)acrylamide,
etc.; amino-group-containing unsaturated monomers such as
aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate,
t-butylaminoethyl(meth)acrylate, etc.; glycidyl-group-containing
unsaturated monomers such as glycidyl(meth)acrylate,
methylglycidyl(meth)acrylate, etc.; cyano-group-containing
unsaturated monomers such as (meth)acrylonitrile, etc.;
maleimide-group-containing monomers such as N-cyclohexyl maleimide,
N-isopropyl maleimide, N-lauryl maleimide, N-phenyl maleimide,
etc.; itaconimide-group-containing monomers such as N-methyl
itaconimide, N-ethyl itaconimide, N-butyl itaconimide, N-octyl
itaconimide, N-2-ethylhexylitaconimide, N-cyclohexyl itaconimide,
N-lauryl itaconimide, etc.; succinimide-group-containing monomers
such as N-(meth)acryloyloxymethylene succinimide,
N-(meth)acryloyl-6-oxyhexamethylene succinimide,
N-(meth)acryloyl-8-oxyoctamethylene succinimide, etc.;
vinyl-group-containing heterocyclic compounds such as
N-vinylpyrrolidone, N-(1-methylvinyl) pyrrolidone, N-vinylpyridine,
N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine,
N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole,
N-vinylmorpholine, (meth)acryloylmorpholine, etc.;
sulfonate-group-containing unsaturated monomers such as styrene
sulfonate, allylsulfonate, 2-(meth)acrylamide-2-methyl propane
sulfonate, (meth)acrylamide propane sulfonate,
sulfopropyl(meth)acrylate, (meth)acryloxynaphthalene sulfonate,
etc.; phosphate-group-containing unsaturated monomers such as
2-hydroxyethylacryloyl phosphate, etc.; functional monomers such as
2-methacryloyloxyethyl isocyanate, etc.; as well as N-vinyl
carboxylic acid amides, and so on.
[0036] The amount of the functional-group-containing unsaturated
monomer to be added is, for instance, 0.5 to 12 parts by weight or
preferably 1 to 10 parts by weight relative to 100 parts by weight
of a total amount of the monomer composition.
[0037] Examples of an unsaturated monomer copolymerizable with the
alkyl(meth)acrylate and the functional-group-containing unsaturated
monomers include vinylester-group-containing monomers such as vinyl
acetate, etc.; unsaturated aromatic monomers such as styrene,
vinyltoluene, etc.; (meth)acrylic acid alicyclic hydrocarbon ester
monomers such as cyclopentyl di(meth)acrylate,
isobornyl(meth)acrylate, etc.; alkoxy-group-containing unsaturated
monomers such as methoxyethyl(meth)acrylate,
ethoxyethyl(meth)acrylate, etc.; olefinic monomers such as
ethylene, propylene, isoprene, butadiene, isobutylene, etc.;
vinyl-ether-based monomers such as vinyl ether, etc.;
halogen-atom-containing unsaturated monomers such as vinyl
chloride, etc.; and others such as
tetrahydrofurfuryl(meth)acrylate, heterocyclic compounds of
fluoro(meth)acrylates, etc., acrylic-acid-ester-based monomers
containing a halogen atom, and so on.
[0038] The monomer composition may further comprise a
multi-functional monomer. Examples of the multi-functional monomer
include (mono or poly)ethylene glycol di(meth)acrylates such as
ethylene glycol di(meth)acrylate, diethylene glycol
di(meth)acrylate, triethylene glycol di(meth)acrylate,
trimethylolpropane tri(meth)acrylate, tetraethylene glycol
di(meth)acrylate, etc.; (mono or poly)alkylene glycol
di(meth)acrylates such as (mono or poly)propylene glycol
di(meth)acrylates, etc., such as propylene glycol di(meth)acrylate,
etc.; as well as (meth)acrylic acid esters of polyols such as
neopentyl glycol di(meth)acrylate, 1,6-hexane-diol
di(meth)acrylate, tetramethylolmethane tri(meth)acrylate,
pentaerythritol di(meth)acrylate, trimethylolpropane
tri(meth)acrylate, pentaerythritol tri(meth)acrylate,
dipentaerythritol hexa(meth)acrylate, etc.; divinylbenzene; and so
on. Other Examples of the multi-functional monomer include epoxy
acrylates, polyester acrylates, urethane acrylates and the
like.
[0039] The monomer composition may further comprise an
alkoxysilyl-group-containing vinyl monomer. The
alkoxysilyl-group-containing vinyl monomer includes silicone-based
(meth)acrylate monomers, silicone-based vinyl monomers, and so
on.
[0040] Examples of the silicone-based (meth)acrylate monomer
include (meth)acryloxyalkyl-trialkoxysilanes such as
(meth)acryloxymethyl-trimethoxysilane,
(meth)acryloxymethyl-triethoxysilane,
2-(meth)acryloxyethyl-trimethoxysilane,
2-(meth)acryloxyethyl-triethoxysilane,
3-(meth)acryloxypropyl-trimethoxysilane,
3-(meth)acryloxypropyl-triethoxysilane,
3-(meth)acryloxypropyl-tripropoxysilane,
3-(meth)acryloxypropyl-triisopropoxysilane,
3-(meth)acryloxypropyl-tributoxysilane, etc.; (meth)acryloxyalkyl
alkyl-dialkoxysilanes such as
(meth)acryloxymethyl-methyldimethoxysilane,
(meth)acryloxymethyl-methyldiethoxysilane,
2-(meth)acryloxyethyl-methyldimethoxysilane,
2-(meth)acryloxyethyl-methyldiethoxysilane,
3-(meth)acryloxypropyl-methyldimethoxysilane,
3-(meth)acryloxypropyl-methyldiethoxysilane,
3-(meth)acryloxypropyl-methyldipropoxysilane,
3-(meth)acryloxypropyl-methyldiisopropoxysilane,
3-(meth)acryloxypropyl-methyldibutoxysilane,
3-(meth)acryloxypropyl-ethyldimethoxysilane,
3-(meth)acryloxypropyl-ethyldiethoxysilane,
3-(meth)acryloxypropyl-ethyldipropoxysilane,
3-(meth)acryloxypropyl-ethyldiisopropoxysilane,
3-(meth)acryloxypropyl-ethyldibutoxysilane,
3-(meth)acryloxypropyl-propyldimethoxysilane,
3-(meth)acryloxypropyl-propyldiethoxysilane, etc.; and their
corresponding (meth)acryloxyalkyl-dialkyl(mono)alkoxysilanes; and
so on.
[0041] Examples of the silicone-based vinyl monomer include
vinyltrialkoxysilanes such as vinyltrimethoxysilane,
vinyltriethoxysilane, vinyltripropoxysilane,
vinyltriisopropoxysilane, vinyltributoxysilane, etc.; their
corresponding vinylalkyldialkoxysilanes and
vinyldialkylalkoxysilanes; vinylalkyltrialkoxysilanes such as
vinylmethyltrimethoxysilane, vinylmethyltriethoxysilane,
.beta.-vinylethyltrimethoxysilane,
.beta.-vinylethyltriethoxysilane,
.gamma.-vinylpropyltrimethoxysilane, vinylpropyltriethoxysilane,
.gamma.-vinylpropyltripropoxysilane,
.gamma.-vinylpropyltriisopropoxysilane,
.gamma.-vinylpropyltributoxysilane, etc.; and their corresponding
(vinylalkyl)alkyldialkoxysilanes and
(vinylalkyl)dialkyl(mono)alkoxysilanes; and so on.
[0042] By using an alkoxysilyl-group-containing vinyl monomer,
alkoxysilyl groups are introduced into the polymer chains and
reactions among the silyl groups allow formation of a crosslinked
structure. These alkoxysilyl-group-containing vinyl monomers can be
used singly or in combination, as appropriate.
[0043] The amount of these alkoxysilyl-group-containing vinyl
monomers to be added is, for instance, within a range greater than
0 part by weight up to 40 parts by weight or preferably within a
range greater than 0 part by weight up to 30 parts by weight
relative to 100 parts by weight of the alkyl(meth)acrylate.
[0044] The (meth)acrylic polymer according to the present invention
can be obtained, for instance, by polymerizing the monomer
composition described above by a polymerization method such as
emulsion polymerization, etc.
[0045] In emulsion polymerization, for instance, polymerization is
carried out by suitably mixing in water a polymerization initiator,
an emulsifier, and as necessary a chain transfer agent, etc., along
with the monomer composition. More specifically, for example, can
be employed a known emulsion polymerization method such as
all-at-once supply method (one batch polymerization method),
monomer dropping method, monomer emulsion dropping method, etc. In
monomer dropping method, can be suitably selected either continuous
dropping or portionwise dropping. Although the reaction conditions,
etc. can be appropriately selected, the polymerization temperature
is, for instance, 20.degree. C. to 100.degree. C.
[0046] The polymerization initiator is not particularly limited and
a polymerization initiator usually used in emulsion polymerization
can be used. Examples include azo-based initiators such as
2,2'-azobisisobutyronitrile,
2,2'-azobis(2-methylpropionamidine)disulfate salt,
2,2'-azobis(2-methylpropionamidine)dihydrochloride salt,
2,2'-azobis(2-amidinopropane)dihydrochloride salt,
2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate,
2,2'-azobis(N,N'-dimethylene isobutylamidine),
2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride salt,
etc.; persulfate salt-based initiators such as potassium
persulfate, ammonium persulfate, etc.; peroxide-based initiators
such as benzoyl peroxide, t-butyl hydroperoxide, hydrogen peroxide,
etc.; substituted ethane-based initiators such as
phenyl-substituted ethane, etc.; carbonyl-based initiators such as
aromatic carbonyl compounds, etc.; redox-based initiators such as a
combination of a persulfate salt and sodium hydrogen sulfite, a
combination of a peroxide and sodium ascorbate, etc.; and so
on.
[0047] These polymerization initiators are used singly or in
combination, as appropriate. Although the amount of the
polymerization initiator to be added can be suitably selected, it
is, for instance, 0.005 to 1 part by weight or preferably 0.01 to
0.8 part by weight relative to 100 parts by weight of a total
amount of the monomer composition.
[0048] The emulsifier is not particularly limited and an emulsifier
usually used in emulsion polymerization can be used. Examples
include anionic emulsifiers such as sodium lauryl sulfate, ammonium
lauryl sulfate, sodium dodecyl benzene sulfonate, sodium
polyoxyethylene lauryl sulfate, sodium polyoxyethylene alkyl ether
sulfates, ammonium polyoxyethylene alkyl phenyl ether sulfates,
sodium polyoxyethylene alkyl phenyl ether sulfates, sodium
polyoxyethylene alkyl sulfosuccinates, etc.; non-ionic emulsifiers
include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl
ethers, polyoxyethylene aliphatic acid esters,
polyoxyethylene-polyoxypropylene block polymers, etc.; and so on.
Alternatively, may be used radically polymerizable (reactive)
emulsifiers (e.g., HS-10 (available from Dai-Ichi Kogyo Seiyaku
Co., Ltd.)) having structures of these anionic emulsifiers or
non-ionic emulsifiers in which radically polymerizable (reactive)
groups such as propenyl group, ally ether group, etc., have been
introduced.
[0049] These emulsifiers can be used singly or in combination, as
appropriate. The amount of the emulsifier to be added is, for
instance, 0.2 to 10 parts by weight or preferably 0.5 to 5 parts by
weight relative to 100 parts by weight of a total amount of the
monomer composition.
[0050] A chain transfer agent adjusts the molecular weight of a
polymer as necessary and a chain transfer agent usually used in
emulsion polymerization is used. Examples include mercaptans such
as 1-dodecanethiol, mercaptoacetic acid, 2-mercaptoethanol,
2-ethylhexyl thioglycolate, 2,3-dimethylmercapto-1-propanol, and so
on. These chain transfer agents are used singly or in combination,
as appropriate. The amount of the chain transfer agent to be added
is, for instance, 0.001 to 0.5 part by weight relative to 100 parts
by weight of a total amount of the monomer composition.
[0051] In order to increase the stability of the (meth)acrylic
polymer, for instance, with aqueous ammonia, etc., it can be
adjusted to, for example, pH 7 to 9 or preferably to pH 7 to 8.
[0052] (ii) Latex Containing a Rubber Component
[0053] The water-dispersed PSA composition according to the present
invention comprises a latex containing a rubber component that is
immiscible with the (meth)acrylic polymer (which hereinafter may be
referred to as "rubber-based latex").
[0054] The rubber component preferably has a loss tangent peak
temperature of -5.degree. C. or below when determined by a dynamic
viscoelastic measurement in which shear strain is applied at a
frequency of 1 Hz. The loss tangent peak temperature of the rubber
component is more preferably -10.degree. C. or below, even more
preferably -15.degree. C. or below, even more preferably
-20.degree. C. or below, particularly preferably -25.degree. C. or
below, or most preferably -30.degree. C. or below. By adjusting the
loss tangent peak temperature to be within the range described
above, the modulus of elasticity at a low temperature can be
decreased and the adhesive strength at a low temperature can be
increased. Although the lower limit is not particularly limited for
the loss tangent peak temperature of the rubber component, it can
be, for instance, -130.degree. C. or above, preferably -120.degree.
C. or above, or more preferably -110.degree. C. or above.
[0055] It is noted that the dynamic viscoelastic measurement
performed with shear strain applied at a frequency of 1 Hz can be
carried out by the same method as in the "(5) Dynamic viscoelastic
measurement of PSA sheet" in Examples described later.
[0056] Examples of the rubber-based latex include natural rubber
latex and synthetic rubber-based latex. Natural rubber latex can be
modified natural rubbers obtained by grafting an
alkyl(meth)acrylate, etc., on a natural rubber.
[0057] Synthetic rubber-based latex is an aqueous dispersion of a
synthetic polymer. The variety of synthetic polymers include
polyisoprenes, styrene-butadiene copolymers (SBR),
styrene-butadiene-vinylpyridine-based polymers, polybutadiene-based
polymers, methyl-methacrylate-butadiene-based copolymers,
acrylonitrile-butadiene-based polymers (NBR), polychloroprenes
(CR), and so on.
[0058] It is noted that a person of ordinary skill in the art can
figure out how to obtain a latex containing a rubber component that
has a loss tangent peak temperature within the range described
above and is immiscible with the (meth)acrylic polymer, by
modifying the composition through adjustment of the compositional
ratio (copolymerization ratio) of the rubber component based on the
contents of description of the present application including the
specific examples described later as well as general technical
knowledge such as solubility parameter (sp) values, etc.
[0059] As such a rubber-based latex, a commercial product can be
used. Examples of a styrene-butadiene latex include products
available from Zeon Corporation (NIPOL series), JSR Corporation,
Asahi Kasei Chemicals Corporation, DIC Corporation (LACSTAR
series), Nippon A&L Inc. (NALSTAR series), etc. Examples of
styrene-butadiene-vinylpyridine latex include products available
from Zeon Corporation (NIPOL series), Nippon A&L Corporation
(PYRATEX series), etc. Examples of polybutadiene latex include
products available from Zeon Corporation (NIPOL series). Examples
of MMA-polybutadiene latex include products available from Nippon
A&L Corporation (NALSTAR series), etc. Examples of
acrylonitrile-butadiene latex include products available from Zeon
Corporation (NIPOL series), Nippon A&L Corporation (CYATEX
series), DIC Corporation (LACSTAR series), etc. Examples of
chloroprene latex include products available from Showa Denko K. K.
(SHOPRENE series), Tosoh Corporation (SKYPRENE series), etc.
[0060] Either one of these rubber-based latexes can be used as long
as its rubber component is immiscible with the (meth)acrylic
polymer.
[0061] In a PSA formed of the water-dispersed PSA composition
according to the present invention, the (meth)acrylic polymer and
the rubber component exist in immiscible phases. The miscibility of
the (meth)acrylic polymer component and the rubber component can be
evaluated by the peaks of the (meth)acrylic polymer component and
the peaks of the rubber component in the loss modulus curve and the
loss tangent curve obtained by a dynamic viscoelastic measurement.
More specifically, for instance, as shown in FIG. 1, when two peaks
are present corresponding to a peak of a (meth)acrylic polymer and
a peak of a rubber component in the loss modulus (G'') curve or in
the loss tangent (tan .delta.) curve obtained by a dynamic
viscoelastic measurement, it indicates that the (meth)acrylic
polymer component and the rubber component are immiscible with each
other.
[0062] It is noted that when the rubber component of the
rubber-based latex and the (meth)acrylic polymer are present in
immiscible phases, in a dried PSA, the acrylic phase formed
primarily of the (meth)acrylic polymer and the rubber phase formed
primarily of the rubber component form a sea-island structure. Such
a structure can be visually confirmed, for instance, as shown in
FIG. 2, by observing a section of dried PSA with a transmission
electron microscope (TEM).
[0063] Hence, when the (meth)acrylic polymer peak and the rubber
component peak overlap with each other in the loss modulus curve
and the loss tangent curve obtained by a dynamic viscoelastic
measurement, the miscibility can be evaluated by determining
whether a sea-island structure has been formed or not. For this
case, in the present invention, as long as a sea-island structure
is formed to some extent, even if there is a miscible region, it is
judged to be immiscible.
[0064] The weight ratio of such a (meth)acrylic polymer to the
rubber-based latex ((meth)acrylic polymer/rubber-based latex) is
preferably 95/5 to 25/75 or preferably 90/10 to 30/70 based on
their solid contents. When the amount of the rubber component is
smaller than the aforementioned range, the adhesive strength to a
non-polar adherend and the adhesive strength at a low temperature
will decrease. When the amount of the acrylic polymer component is
smaller than the aforementioned range, sufficient adhesive strength
to a polar adherend such as SUS, etc., may not be obtained.
[0065] (iii) Tackifier
[0066] The water-dispersed PSA composition according to the present
invention preferably comprises a tackifier (typically a tackifying
resin) that is miscible with the rubber component, but immiscible
with the (meth)acrylic polymer.
[0067] Examples of such a tackifier include tackifying resins, with
examples including rosin-based resins such as rosin esters,
hydrogenated rosin esters, disproportionated rosin esters,
polymerized rosin esters, etc.; coumarone-indene-based resins such
as coumarone-indene resins, hydrogenated coumarone-indene resins,
phenol-modified coumarone-indene resins, epoxy-modified
coumarone-indene resins, etc.; terpene-based resins such as
.alpha.-pinene resins, .beta.-pinene resins, polyterpene resins,
hydrogenated terpene resins, aromatic modified terpene resins,
terpene phenolic resins, etc.; petroleum-based resins such as
aliphatic petroleum resins, aromatic petroleum resins, aromatic
modified aliphatic petroleum resins, etc.; and so on. These can be
used singly or in combination of two or more kinds. Particularly
preferable are rosin-based resins, terpene-based resins, and
coumarone-indene resins.
[0068] The tackifier is miscible with the rubber component, but
immiscible with the (meth)acrylic polymer. Thus, it is considered
that with the tackifier being miscible with the rubber component,
the modulus of elasticity of the rubber phase decreases, and as a
result, with the increasing wettability to an adherend allows the
adhesive strength to increase.
[0069] The miscibility of a tackifier can be evaluated by the
presence of haze in a PSA sheet after dried. More specifically, it
is evaluated based on the methods for "(2) Evaluation of the
miscibility of rubber component and tackifier" and "(3) Evaluation
of the miscibility of (meth)acrylic polymer and tackifier" in
Examples described later.
[0070] The amount of the rubber-component-miscible tackifier to be
added is, for instance, within a range above 0 part by weight up to
100 parts by weight, preferably 5 to 100 parts by weight, or more
preferably 10 to 90 parts by weight relative to 100 parts by weight
of solid contents of the rubber-based latex. When this amount is
within this range, the modulus of elasticity of the rubber phase
will be sufficiently reduced, and the wettability to an adherend
will be increased to a greater degree. Since the glass transition
temperature of the rubber phase will decrease and become able to
suppress an increase in the modulus of elasticity at a low
temperature, sufficient wettability to an adherend can be obtained
at a low temperature.
[0071] The rubber-component-miscible tackifier has a softening
point of preferably 80.degree. C. to 150.degree. C. or more
preferably 90.degree. C. to 140.degree. C. When it is below this
range, the cohesive strength of the PSA will decrease. When it is
above this range, the low temperature adhesive strength is likely
to decrease.
[0072] It is noted that the softening point of a tackifying resin
can be measured based on, for instance, the ring-and-ball method
(BS K-5902).
[0073] Although the mode of addition of a tackifying resin is not
particularly limited, it is usually preferable that the tackifying
resin is added in a water dispersion form where it is pre-dispersed
in water. As such a water dispersion of a tackifying resin, a
commercial product can be used. Alternatively, can be used a
desired tackifier forced to disperse in water by a disperser.
[0074] In the water-dispersed PSA composition according to the
present invention, in addition to the tackifier miscible with the
rubber component, may be used a tackifier (typically a tackifying
resin) miscible with the (meth)acrylic polymer. By using such a
tackifier in combination, can be produced an effect of further
increasing the adhesive strength at room temperature.
[0075] Examples of such a tackifying resin miscible with the
(meth)acrylic polymer include rosin-based resins such as rosin
esters, hydrogenated rosin esters, disproportionated rosin esters,
polymerized rosin esters, etc.; coumarone-indene-based resins such
as coumarone-indene resins, hydrogenated coumarone-indene resins,
phenol-modified coumarone-indene resins, epoxy-modified
coumarone-indene resins, etc.; terpene-based resins such as
.alpha.-pinene resins, .beta.-pinene resins, polyterpene resins,
hydrogenated terpene resins, aromatic modified terpene resins,
terpene phenolic resins, etc.; petroleum-based resins such as
aliphatic petroleum resins, aromatic petroleum resins, aromatic
modified aliphatic petroleum resins, etc.; and so on. Rosin
ester-based resins are particularly preferable. These can be used
singly or in combination of two or more kinds.
[0076] It is noted that as the tackifying resins of terpene-based,
rosin-based, etc., various tackifying resins having a wide range of
sp values are available (e.g., see "Handbook of Pressure-Sensitive
Adhesive (3rd ed.)" (published by Japan Adhesive Tape Manufacturers
Association)). A person of ordinary skill in the art may figure out
how to obtain a tackifying resin that is miscible with the rubber
component, but immiscible with the (meth)acrylic polymer based on
the contents of description of the present application including
the specific examples described later as well as general technical
knowledge such as sp values, etc.
[0077] The amount of the (meth)acrylic-polymer-miscible tackifying
resin to be added is, for instance, within a range greater than 0
part by weight up to 20 parts by weight or preferably 1 to 10 parts
by weight relative to 100 parts by weight of solid contents of the
(meth)acrylic polymer. When it is above this range, the glass
transition temperature of the acrylic phase formed primarily of the
(meth)acrylic polymer increases and the modulus of elasticity at a
low temperature increases, whereby, at a low temperature,
sufficient wettability to an adherend may not be obtained, causing
the adhesive strength to decrease.
[0078] In the water-dispersed PSA composition according to the
present invention, in addition to the aforementioned tackifiers,
may be used a tackifying resin in a liquid state at room
temperature.
[0079] Although the mode of addition of a tackifying resin in a
liquid state at room temperature is not particularly limited, the
tackifying resin in a liquid state at room temperature is
preferably added as a dispersion where it has been pre-dispersed in
water. As a water dispersion of such a liquid-at-room-temperature
tackifying resin, a commercial product can be used. Alternatively,
can be used a desired tackifying resin forced to disperse in water
by a disperser. Tackifying resin in a liquid state at room
temperature refers to a tackifying resin having a softening point
of 25.degree. C. or below before dispersed as an emulsion. In the
present invention, of these resins, low molecular weight polymers
of rosin esters and/or terpene are particularly preferable.
[0080] The tackifying resin in a liquid state at room temperature
is preferably miscible with the rubber component. With the
tackifying resin in a liquid state at room temperature being
miscible with the rubber component, the modulus of elasticity of
the rubber phase decreases and the wettability to an adherend
increases, allowing the adhesive strength to increase.
[0081] The amount of the liquid-at-room-temperature tackifying
resin to be added is, for instance, within a range greater than 0
part by weight up to 50 parts by weight or preferably 1 to 40 parts
by weight relative to 100 parts by weight of solid contents of the
rubber-based latex. When it is above this range, the cohesive
strength of the PSA will decrease.
[0082] (iv) Other Components
[0083] To the water-dispersed PSA composition according to the
present invention, in accordance with its purpose and application,
as necessary, a crosslinking agent can be added. Examples of the
crosslinking agent include isocyanate-based crosslinking agents,
epoxy-based crosslinking agents, oxazoline-based crosslinking
agents, aziridine-based crosslinking agents, metal chelate-based
crosslinking agents, and so on.
[0084] These crosslinking agents are not particularly limited, and
an oil-soluble or a water-soluble crosslinking agent can be used.
These crosslinking agents can be used singly or in combination, as
appropriate. Its amount to be added is, for instance, 10 parts by
weight or smaller, preferably 0.01 to 10 parts by weight, or more
preferably 0.02 to 5 parts by weight relative to 100 parts by
weight of the (meth)acrylic polymer.
[0085] Examples of an isocyanate-based crosslinking agent include
lower aliphatic polyisocyanates such as 1,2-ethylene diisocyanate,
1,4-butylene diisocyanate, 1,6-hexamethylene diisocyanate, etc.;
alicyclic polyisocyanates such as cyclopentylene diisocyanate,
cyclohexylene diisocyanate, isophorone diisocyanate, hydrogenated
tolylene diisocyanate, hydrogenated xylene diisocyanate, etc.; and
aromatic polyisocyanates such as 2,4-tolylene diisocyanate,
2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate,
xylylene diisocyanate, etc.; and so on. As the isocyanate-based
crosslinking agent, for example, can also be used commercial
products including an adduct of trimethylolpropane and tolylene
diisocyanate (trade name "CORONATE L" available from Nippon
Polyurethane Industry Co., Ltd.), an adduct of trimethylolpropane
and hexamethylene diisocyanate (trade name "CORONATE HL" available
from Nippon Polyurethane Industry Co., Ltd.), an adduct of
trimethylolpropane and xylylene diisocyanate (trade name "TAKENATE
D-110N" available from Mitsui Chemicals, Inc.), and so on.
[0086] Examples of an epoxy-based crosslinking agent include
N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline,
1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol
diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene
glycol diglycidyl ether, propylene glycol diglycidyl ether,
polyethylene glycol diglycidyl ethers, polypropylene glycol
diglycidyl ethers, sorbitol polyglycidyl ethers, glycerol
polyglycidyl ethers, pentaerythritol polyglycidyl ethers,
polyglycerol polyglycidyl ethers, sorbitan polyglycidyl ethers,
trimethylolpropane polyglycidyl ethers, diglycidyl adipate,
o-diglycidyl phthalate, triglycidyl
tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether and
bisphenol-S diglycidyl ether; as well as epoxy-based resins having
two or more epoxy groups per molecule. As the epoxy-based
crosslinking agent, can also be used, for example, commercial
products such as trade name "TETRAD C" available from Mitsubishi
Gas Chemical Company, Inc., and so on.
[0087] Examples of an oxazoline-based crosslinking agent include
those listed as examples in Japanese Patent Application Publication
No. 2009-001673. In particular, it can be a compound having a main
chain of an acryl structure or a styrene structure as well as an
oxazoline group as a side chain of the main chain, or preferably an
oxazoline-group-containing acrylic polymer having a main chain of
an acryl structure and an oxazoline group as a side chain of the
main chain.
[0088] Examples of an aziridine-based crosslinking agent include
trimethylolpropane tris[3-(1-azyridinyl)propionate] and
trimethylolpropane tris[3-(1-(2-methyl)azyridinyl propionate].
[0089] Examples of a metal chelate-based crosslinking agent include
those listed in Japanese Patent Application Publication No.
2007-063536. In particular, examples include aluminum chelate-based
compounds, titanium chelate-based compounds, zinc chelate-based
compounds, zirconium chelate-based compounds, iron chelate-based
compounds, cobalt chelate-based compounds, nickel chelate-based
compounds, tin chelate-based compounds, manganese chelate-based
compounds, and chromium chelate-based compounds.
[0090] To the water-dispersed PSA composition according to the
present invention, as necessary, can be added additives usually
added to PSA such as thickeners, release adjusting agents,
plasticizers, softening agents, fillers, colorants (pigments, dyes,
etc.), anti-aging agents, surfactants, leveling agents,
anti-foaming agents, and so on. The amounts of these additives to
be added are not particularly limited and can be suitably
selected.
[0091] The thickener can be an acrylic alkaline thickening type, a
urethane-based associative type, a clay-based one, a
cellulose-based one, a polyamide-based one, and so on. For example,
it can be added in an amount of 0.01 to 1% by weight of the
water-dispersed PSA composition. By using a thickener within such a
range, the water-dispersed PSA composition can be adjusted to have
applicable viscosity and a PSA sheet free of air spots and grooves
can be obtained.
[0092] The water-dispersed PSA composition according to the present
invention has a storage modulus of 1 MPa or smaller over a range of
-15.degree. C. to 25.degree. C., or preferably 0.9 MPa or smaller,
when determined by a dynamic viscoelastic measurement in which
shear strain is applied at a frequency of 1 Hz after a PSA is
formed. When it is above this range, the wettability to an adherend
turns out insufficient and the adhesive strength decreases.
Although the lower limit is not particularly limited, it can be,
for instance, 0.01 MPa or greater.
[0093] It is noted that a person of ordinary skill in the art will
be able to adjust the storage modulus at -15.degree. C. to
25.degree. C. determined by a dynamic viscoelastic measurement
performed with shear strain at a frequency of 1 Hz to be within the
range described above by modifying the composition based on the
contents of the present description including specific examples
described later as well as technical common knowledge.
(II) PSA Sheet
[0094] The PSA sheet according to the present invention comprises a
PSA layer formed of the water-dispersed PSA composition described
above.
[0095] The PSA sheet according to the present invention may have a
configuration of an on-substrate PSA sheet where such a PSA layer
is provided on either face or each face of a substrate (support)
sheet, or it may have a configuration of a substrate-free PSA sheet
where the PSA layer is held on a release sheet (which may be a
substrate sheet having a release surface). The concept of the PSA
sheet referred to here encompasses those called as PSA tapes, PSA
labels, PSA films, and so on.
[0096] Although the PSA layer is typically formed in a continuous
manner, it is not limited to such a form and it can be formed into,
for example, a regular or random pattern of dots, stripes, and so
on. The PSA sheet provided by the present invention may be in a
roll or in a flat sheet. Alternatively, the PSA sheet can be
processed into various other forms.
[0097] The PSA sheet according to the present invention can be made
to have the respective cross-sectional structures schematically
illustrated in FIG. 3(a)-(c).
[0098] FIG. 3(a) shows a configuration example of an on-substrate
PSA sheet of an adhesively single-faced kind, in which PSA layer 2
is provided on one face of substrate 1. For example, such a PSA
sheet can be made into a roll by winding it so that, with substrate
1 having a release surface on its face opposite to the face having
PSA layer 2, as shown in FIG. 3(a), the release surface of
substrate 1 laminated with PSA layer 2 comes in contact with PSA
layer 2 laminated on substrate 1.
[0099] The PSA sheet shown in FIG. 3(b) has a configuration where
PSA layer 2 is protected with release sheet 3 having a release
surface at least on the PSA layer side and it can also be made into
a roll by winding it.
[0100] The PSA sheet shown in FIG. 3(c) has a configuration where
PSA layer 2 is provided on each face of substrate 1 and each of
these PSA layers 2 is protected with release sheet 3 having a
release surface at least on the PSA layer side. The PSA sheet shown
in FIG. 3(c) can be made into a roll, for instance, by pre-forming
PSA layers 2 on release sheets 3 and adhering these to each of the
front and back faces of substrate 1, and winding the resultant.
[0101] In the PSA sheet shown in FIG. 3(c), PSA layers 2 are
provided on each face of substrate 1. These PSA layers 2 may be
formed of a PSA having the same composition or may be formed
respectively of PSA's having different compositions.
[0102] Examples of a material forming the substrate include
polyolefin-based films such as polyethylenes, polypropylenes,
ethylene-propylene copolymers, etc.; polyester-based films such as
polyethylene phthalate, etc.; plastic films such as polyvinyl
chloride, etc.; papers such as Kraft papers, Washi papers, etc.;
fabrics such as cotton fabrics, staple cloth fabrics, etc.;
non-woven fabrics such as polyester non-woven fabrics, vinylon
non-woven fabrics, etc.; and metal foils.
[0103] The plastic films may be non-stretched films, or stretched
(uni-axially stretched or bi-axially stretched) films. To the
substrate surface to be provided with a PSA layer, can be given a
surface treatment such as primer coating, corona discharge
treatment, and so on.
[0104] The PSA layer can be obtained by applying the
water-dispersed PSA composition described above to a substrate by a
known coating method followed by drying. The method for applying
the water-dispersed PSA composition to a substrate is not
particularly limited and it can be carried out using, for instance,
a gravure roll coater, a reverse roll coater, a kiss roll coater, a
dip roll coater, a bar coater, a knife coater, a spray coater, a
fountain dye coater, a closed edge dye coater, and so on.
[0105] The PSA layer can be formed by transferring to a substrate a
PSA layer pre-formed by applying the water-dispersed PSA
composition to a release sheet.
[0106] The thickness of the PSA layer after dried is not
particularly limited, and it is, for instance, 500 .mu.m or
smaller, or preferably within a range of 5 .mu.m to 200 .mu.m.
Although the drying temperature may depend on the kind of the
substrate, it can be, for instance, within a range of 40.degree. C.
to 120.dbd. C.
[0107] From the standpoint of providing a PSA sheet that exhibits
good adhesiveness to a non-polar adherend at a low temperature, the
PSA sheet according to the present invention has preferably an
adhesive strength to a polypropylene (PP) plate at -5.degree. C. of
3.0 N/20 mm or greater and an adhesive strength to a PP plate at
-15.degree. C. of 2.5 N/20 mm or greater, more preferably an
adhesive strength to a PP plate at -5.degree. C. of 3.5 N/20 mm or
greater and an adhesive strength to a PP plate at -15.degree. C. of
3.0 N/20 mm or greater, or even more preferably an adhesive
strength to a PP plate at -5.degree. C. of 4.0 N/20 mm or greater
and an adhesive strength to a PP plate at -15.degree. C. of 3.5
N/20 mm or greater.
[0108] From the standpoint of providing a PSA sheet that maintains
its properties even at a low temperature, besides satisfying the
adhesive strength described above, it has preferably an adhesive
strength to a SUS plate at -5.degree. C. of 4.0 N/20 mm or greater
and an adhesive strength to a SUS plate at -15.degree. C. of 4.0
N/20 mm or greater, more preferably an adhesive strength to a SUS
plate at -5.degree. C. of 4.5 N/20 mm or greater and an adhesive
strength to a SUS at -15.degree. C. plate of 4.5 N/20 mm or
greater, or even more preferably an adhesive strength to a SUS
plate at -5.degree. C. of 5.0 N/20 mm or greater and an adhesive
strength to a SUS plate at -15.degree. C. of 5.0 N/20 mm or
greater.
EXAMPLES
[0109] The present invention is described more specifically with
examples and comparative examples below. However, the present
invention is not limited to the following examples and comparative
examples. In the following descriptions, "part" and "%" are based
on the weight unless otherwise specified.
Synthesis Example 1
Synthesis of a Water-Dispersed (Meth)Acrylic Polymer (A)
[0110] To a reaction vessel equipped with a condenser, a nitrogen
inlet tube, a thermometer and a stirrer, were added 96 parts of
butyl acrylate (BA), 4 parts of acrylic acid (AA), 0.08 part of
t-dodecanethiol (chain transfer agent), 2 parts of sodium
polyoxyethylene lauryl sulfate (emulsifier) and 153 parts of
ion-exchanged water as an emulsified mixture (i.e., an emulsion of
starting monomers); and the resulting mixture was stirred under
nitrogen gas for one hour.
[0111] Then, it was heated to 60.degree. C., and to this, was
added, based on solid contents, 0.1 part of
2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate
(polymerization initiator) (trade name "VA-057" available from Wako
Pure Chemical Industries, Ltd.) prepared as a 10% aqueous solution,
and the polymerization was carried out for 3 hours. To this, was
added 10% aqueous ammonia to adjust it to pH 7.5 and was obtained a
water-dispersed (meth)acrylic polymer (A).
Synthesis Example 2
Synthesis of a Water-Dispersed (Meth)Acrylic Polymer (B)
[0112] In the same manner as Synthesis Example 1 except that
2-ethylhexyl acrylate (2-EHA) was used in place of butyl acrylate
(BA), was obtained a water-dispersed (meth)acrylic polymer (B).
Example 1
[0113] Both based on solid contents, were mixed 70 parts of the
water-dispersed (meth)acrylic polymer (A) obtained in Synthesis
Example 1 and 30 parts of a synthetic polyisoprene latex (trade
name "SEPOLEX IR-100K" available from Sumitomo Seika Chemicals Co.,
Ltd.) to prepare a water-dispersed PSA composition.
[0114] Subsequently, the resulting water-dispersed PSA composition
was mixed with 0.5 part of an acrylic alkali thickener (trade name
"ARON B-500" available from Toagosei Co., Ltd.) to increase the
viscosity. The thickened water-dispersed PSA composition was
applied to coat a 25 .mu.m thick polyethylene terephthalate
substrate (trade name "LUMIRROR S-10" available from Toray
Industries, Inc.) so as to obtain a thickness of 60 .mu.m after
dried, and this was allowed to dry at 100.degree. C. for 3 minutes
to prepare a PSA sheet.
Example 2
[0115] A PSA sheet was prepared in the same manner as Example 1
except that the water-dispersed (meth)acrylic polymer (A) and the
synthetic polyisoprene latex (trade name "SEPOLEX IR-100K"
available from Sumitomo Seika Chemicals Co., Ltd.) were mixed at a
modified ratio shown in Table 4.
Example 3
[0116] Both based on solid contents, 70 parts of the
water-dispersed (meth)acrylic polymer (A) obtained in Synthesis
Example 1 and 30 parts of a synthetic polyisoprene latex (trade
name "SEPOLEX IR-100K" available from Sumitomo Seika Chemicals Co.,
Ltd.) were mixed. To this, based on solid contents, was then added,
as a tackifier, 6 parts (20 parts relative to 100 parts of solid
contents of the rubber latex) of an aromatic modified terpene resin
emulsion (trade name "NANOLET R-1050" available from Yasuhara
Chemical Co., Ltd., softening point 100.degree. C.) to prepare a
water-dispersed PSA composition.
[0117] Then, the resulting water-dispersed PSA composition was
mixed with 0.5 part of an acrylic alkali thickener (trade name
"ARON B-500" available from Toagosei Co., Ltd.) to increase the
viscosity, and the thickened water-dispersed PSA composition was
applied to coat a 25 .mu.m thick polyethylene terephthalate
substrate (trade name "LUMIRROR S-10" available from Toray
Industries, Inc.) so as to obtain a thickness of 60 .mu.m after
dried and this was allowed to dry at 100.degree. C. for 3 minutes
to prepare a PSA sheet.
Examples 4, 6, 8-10, Comparative Examples 1-11
[0118] PSA sheets were prepared in the same manner as Example 3
except that the species and the ratios of (meth)acrylic polymer,
rubber component and tackifier were as shown in Table 4.
Example 5
[0119] A PSA sheet was prepared in the same manner as Example 3
except that the amount of the tackifier was 18 parts (60 parts
relative to 100 parts of solid contents of the rubber latex)
instead of 6 parts and 0.035 part of an epoxy-based crosslinking
agent (trade name "TETRAD-C" available from Mitsubishi Gas Chemical
Company, Inc.) was further added to prepare the water-dispersed PSA
composition.
Examples 7, 11
[0120] PSA sheets were prepared in the same manner as Example 5
except that the species and the ratios of (meth)acrylic polymer,
rubber component and tackifier as well as the amounts of the
crosslinking agent added were as shown in Table 4.
<Evaluations>
(1) Evaluation of the Miscibility of (Meth)Acrylic Polymer and
Rubber Component
[0121] Both based on solid contents, were mixed 70 parts of a
water-dispersed (meth)acrylic polymer and 30 parts of a latex to
prepare a water-dispersed PSA composition.
[0122] Then, the resulting water-dispersed PSA composition was
mixed with 0.5 part of an acrylic alkali thickener (trade name
"ARON B-500" available from Toagosei Co., Ltd.) to increase the
viscosity and the thickened water-dispersed PSA composition was
applied to coat a release sheet (trade name "DIAFOIL MRF-38"
available from Mitsubishi Plastics, Inc.) so as to obtain a
thickness of 60 .mu.m after dried and this was allowed to dry at
100.degree. C. for 3 minutes to prepare a PSA sheet.
[0123] The PSA sheet was released from the release sheet and PSA
layers were laminated to prepare a laminate of about 2 mm thick and
from this, a 7.9 mm diameter measurement sample was cut out. The
measurement sample was placed between 7.9 mm diameter parallel
discs, and using a dynamic viscoelastic measurement device
("Advanced Rheometric Expansion System" available from Rheometric
Scientific, Inc.), while applying shear strain at a frequency of 1
Hz, at a heating rate of 5.degree. C./min, were measured the
storage modulus (G') and the loss modulus (G'') over a range of
-70.degree. C. to 100.degree. C. Based on the storage modulus (G')
and the loss modulus (G''), the loss tangent tan .delta. was
calculated by the following equation:
Loss tangent tan .delta.=G''/G'
[0124] The calculated loss tangent (tan .delta.) values were
plotted against the temperature to obtain a loss tangent curve and
the presence of a (meth)acrylic polymer peak and a rubber component
peak were checked. When the two peaks were not present, it was
determined to be miscible (M) and when both of the peaks were
present, it was determined to be immiscible (IM). Table 1 shows the
results of the evaluation of the miscibilities of the (meth)acrylic
polymers and the rubber components used in Examples and Comparative
Examples described above.
[0125] In addition, as an example, FIG. 2 shows a graph exhibiting
the results of the evaluation on the miscibility of the
(meth)acrylic polymer and the rubber component used in Example
3.
TABLE-US-00001 TABLE 1 Water-dispersed (meth)acrylic polymer Trade
name A B Latex IR-100K IM IM SB-0561 IM -- SB-0589 IM -- SB-0533 IM
-- SB-0568 IM -- SB-2877A IM -- MG-25 IM --
(2) Evaluation of the Miscibility of Rubber Component and
Tackifier
[0126] To 100 parts of solid contents of the latex, was added,
based on solid contents, 20 parts of the tackifier to prepare a
water-dispersed PSA composition. Then, the resulting
water-dispersed PSA composition was mixed with 0.5 part of an
acrylic alkali thickener (trade name "ARON B-500" available from
Toagosei Co., Ltd.) to increase the viscosity and the thickened
water-dispersed PSA composition was applied to coat a release sheet
(trade name "DIAFOIL MRF-38" available from Mitsubishi Plastics,
Inc.) so as to obtain a thickness of 60 .mu.m after dried and this
was allowed to dry at 100.degree. C. for 3 minutes to prepare a PSA
sheet.
[0127] To one face of the prepared PSA sheet, was adhered a glass
slide ("Glass Slide White Ground Edges" available from Matsunami
Glass Ind., Ltd.; 1.3 mm thick), and from this, the release sheet
was removed to prepare a sample for evaluation. The haze of this
sample was measured with a haze meter "HM-150" (available from
Murakami Color Research Laboratory Co., Ltd.), and based on JIS
K7136, the value was calculated by the equation: haze
(%)=Td/Tt.times.100 (Td: diffuse transmittance, Tt: total
transmittance). When the calculated haze value was 50% or smaller
(0 to 50%), it was determined to be miscible and when it was
greater than 50%, it was determined to be immiscible.
[0128] It is noted that regarding the evaluation of the
miscibility, with respect to the prepared PSA sheet, it is
preferable to determine it to be miscible when its haze value is
45% or smaller and immiscible when it is greater than 45%, or it is
more preferable to determine it to be miscible when its haze value
is 40% or smaller and immiscible when it is greater than 40%.
[0129] Table 2 shows the evaluation results of the haze values with
respect to the pairs of the rubber component and the tackifier used
in Examples and Comparative Examples described above.
TABLE-US-00002 TABLE 2 Haze value (%) Tackifying resin R-1050
NS-100H Latex IR-100K 4.6 70.3 SB-0561 39.2 -- SB-0589 2.2 --
SB-0533 1.0 -- SB-0568 1.8 -- SB-2877A 17.1 -- MG-25 5.5 --
(3) Evaluation of the Miscibility of (Meth)Acrylic Polymer and
Tackifier
[0130] To 100 parts of solid contents of the (meth)acrylic polymer,
was added, based on solid contents, 20 parts of the tackifier to
prepare a water-dispersed PSA composition. Then, the resulting
water-dispersed PSA composition was mixed with 0.5 part of an
acrylic alkali thickener (trade name "ARON B-500" available from
Toagosei Co., Ltd.) to increase the viscosity and the thickened
water-dispersed PSA composition was applied to coat a release sheet
(trade name "DIAFOIL MRF-38" available from Mitsubishi Plastics,
Inc.) so as to obtain a thickness of 60 .mu.m after dried and this
was allowed to dry at 100.degree. C. for 3 minutes to prepare a PSA
sheet.
[0131] To one face of the prepared PSA sheet, was adhered a glass
slide ("Glass Slide White Ground Edges" available from Matsunami
Glass Ind., Ltd.; 1.3 mm thick), and from this, the release sheet
was removed to prepare a sample for evaluation. The haze of this
sample was measured with a haze meter "HIM-150" (available from
Murakami Color Research Laboratory Co., Ltd.), and based on JIS
K7136, the value was calculated by the equation: haze
(%)=Td/Tt.times.100 (Td: diffuse transmittance, Tt: total
transmittance). When the calculated haze value was 50% or smaller
(0 to 50%), it was determined to be miscible and when it was
greater than 50%, it was determined to be immiscible.
[0132] It is noted that regarding the evaluation of the
miscibility, with respect to the prepared PSA sheet, it is
preferable to determine it to be miscible when its haze value is
45% or smaller and immiscible when it is greater than 45%, or it is
more preferable to determine it to be miscible when its haze value
is 40% or smaller and immiscible when it is greater than 40%.
[0133] Table 3 shows the evaluation results of the haze values with
respect to the pairs of the (meth)acrylic polymer and the tackifier
used in Examples and Comparative Examples described above.
TABLE-US-00003 TABLE 3 Haze value (%) Water-dispersed (meth)acrylic
polymer A B Tackifying resin R-1050 68.8 70.5 NS-100H 0.8 1.2
(4) Adhesive Strength
[0134] Each of the PSA sheets obtained in Examples and Comparative
Examples was cut to a size of 20 mm by 100 mm, and under an
atmosphere at a measurement temperature (-5.degree. C., -15.degree.
C.), this was adhered to, as an adherend, a SUS304 stainless steel
plate or a polypropylene (PP) plate (trade name "PP-N-AN" available
from Shin-Kobe Machinery Co., Ltd.) and pressure-bonded with a 2 kg
roller moved back and forth once. The resultant was then left under
an atmosphere at a measurement temperature (-5.degree. C.,
-15.degree. C.) for 30 minutes, and in an atmosphere at -5.degree.
C. or -15.degree. C., it was subjected to a peel test at a peeling
angle of 180.degree. and a peeling speed of 300 mm/min to measure
the adhesive strength. The results are shown in Table 4.
(5) Dynamic Viscoelastic Measurement of PSA Sheet
[0135] Each of the water-dispersed PSA compositions obtained in
Examples and Comparative Examples was applied to coat a release
sheet (trade name "DIAFOIL MRF-38" available from Mitsubishi
Plastics, Inc.) so as to obtain a thickness of 60 .mu.m an after
dried and this was allowed to dry at 100.degree. C. for 3 minutes
to prepare a PSA sheet.
[0136] The PSA sheet was released from the release sheet and PSA
layers were laminated to prepare a laminate of about 2 mm thick and
from this, a 7.9 mm diameter measurement sample was cut out.
[0137] The measurement sample was placed between 7.9 mm diameter
parallel discs, and using "Advanced Rheometric Expansion System"
available from Rheometric Scientific, Inc., while applying shear
strain at a frequency of 1 Hz, at a heating rate of 5.degree.
C./min, the storage modulus (G') was measured over a range of
-70.degree. C. to 100.degree. C. The results are shown in Table
4.
[0138] Although Table 4 shows only the storage modulus (G') values
at -15.degree. C. and 25.degree. C., with the PSA sheets obtained
in the present Examples, as shown in FIG. 1, the G' at -15.degree.
C. has the greatest value within a range of -15.degree. C. to
-25.degree. C.; and therefore, if the G' value at -15.degree. C. is
1 MPa or smaller, the G' values over -15.degree. C. to 25.degree.
C. are 1 MPa or smaller.
TABLE-US-00004 TABLE 4 (Meth)acrylic Polymer (parts by weight of
solid contents) Rubber Component Synthesis Synthesis (parts by
weight of solid contents) Example1 Example 2 IR-100K SB 0561 SB
0589 SB 0533 SB 0568 SB 2877A MG-25 Ex. 1 70 30 Ex. 2 90 10 Ex. 3
70 30 Ex. 4 70 30 Ex. 5 70 30 Ex. 6 50 50 Ex. 7 50 50 Ex. 8 30 70
Ex. 9 70 30 Ex. 10 70 30 Ex. 11 70 30 Comparative Ex. 1 100
Comparative Ex. 2 100 Comparative Ex. 3 90 10 Comparative Ex. 4 90
10 Comparative Ex. 5 70 30 Comparative Ex. 6 70 30 Comparative Ex.
7 70 30 Comparative Ex. 8 70 30 Comparative Ex. 9 70 30 Comparative
Ex. 10 70 30 Comparative Ex. 11 70 30 Tackifier (parts Dynamic PP
Adhesive SUS Adhesive by weight of Crosslinking Agent
Viscoelasticity Strength Strength solid contents) (parts by weight)
G' (MPa) (N/20 mm) (N/20 mm) R-1050 NS-100H T/C 25.degree. C.
-15.degree. C. -5.degree. C. -15.degree. C. -5.degree. C.
-15.degree. C. Ex. 1 0 0.22 0.48 3.5 3.3 7.0 6.5 Ex. 2 0 0.19 0.60
3.6 3.2 6.8 7.6 Ex. 3 6 0.20 0.48 6.0 5.5 7.4 7.8 Ex. 4 12 0.20
0.50 5.2 5.6 6.7 7.8 Ex. 5 18 0.035 0.18 0.60 6.9 6.6 8.4 9.5 Ex. 6
10 0.25 0.47 5.2 6.5 6.0 8.0 Ex. 7 30 0.04 0.16 0.48 9.4 5.6 9.3
12.0 Ex. 8 14 0.27 0.38 6.7 8.2 6.2 8.1 Ex. 9 12 0.32 0.94 4.2 2.8
4.2 4.4 Ex. 10 12 3.5 0.2 0.8 7.1 6.2 7.3 8.9 Ex. 11 12 0.06 0.07
0.28 6.3 5.6 6.3 7.5 Comparative Ex. 1 0.18 0.60 4.4 0.8 6.7 8.1
Comparative Ex. 2 20 0.16 3.31 1.3 2.0 11.2 2.5 Comparative Ex. 3 5
0.17 1.29 4.5 1.6 5.5 6.9 Comparative Ex. 4 18 0.18 2.10 1.9 1.4
8.1 6.0 Comparative Ex. 5 14 0.24 1.20 7.1 1.8 8.2 9.8 Comparative
Ex. 6 12 .gtoreq.10 .gtoreq.10 0.3 0.2 1.3 0.1 Comparative Ex. 7 12
0.85 .gtoreq.10 0.8 0.2 1.3 0.1 Comparative Ex. 8 12 0.76
.gtoreq.10 0.5 0.2 2.2 0.2 Comparative Ex. 9 12 0.24 2.96 4.7 1.2
8.5 8.5 Comparative Ex. 10 12 0.38 2.54 3.4 1.9 5.3 6.2 Comparative
Ex. 11 14 0.32 3.9 2.7 0.7 4.4 3.8
[0139] It is noted that in Tables 1 to 4, "IR-100K" refers to a
synthetic polyisoprene latex (trade name "SEPOLEX IR-100K"
available from Sumitomo Seika Chemicals Co., Ltd.), of which the
rubber component had a loss tangent peak temperature of -53.degree.
C.; "SB0561" refers to a styrene-butadiene latex (trade name
"SB-0561" available from JSR Corporation), of which the loss
tangent peak temperature was -45.degree. C.; "SB0589" refers to a
styrene-butadiene latex (trade name "SB-0589" available from JSR
Corporation), of which the loss tangent peak temperature was
21.degree. C.; "SB0533" refers to a styrene-butadiene latex (trade
name "SB-0533" available from JSR Corporation), of which the loss
tangent peak temperature was 0.degree. C.; "SB0568" refers to
styrene-butadiene latex (trade name "SB-0568" available from JSR
Corporation), of which the loss tangent peak temperature was
-4.degree. C.; "SB2877A" refers to a styrene-butadiene latex (trade
name "SB-2877A" available from JSR Corporation), of which the loss
tangent peak temperature was -26.degree. C.; "MG-25" refers to a
MMA-grafted natural rubber latex (trade name "REGITEX MG-25"
available from Regitex Corporation), of which the loss tangent peak
temperature was -58.degree. C.
[0140] In Tables 1 to 4, "R-1050", "NS-100H", and "T/C" refer to an
aromatic modified terpene resin emulsion (trade name "NANOLET
R-1050" available from Yasuhara Chemical Co., Ltd., softening point
100.degree. C.), a rosin-based tackifier (trade name "SUPER ESTER
NS-100H" available from Arakawa Chemical Industries, Ltd.,
softening point 100.degree. C.), and an epoxy-based crosslinking
agent (trade name "TETRAD-C" available from Mitsubishi Gas Chemical
Company, Inc.), respectively.
[0141] As shown in Table 4, the PSA sheets according to the present
invention were confirmed to have an adhesive strength to a PP plate
at -5.degree. C. of 3.0 N/20 mm or greater as well as an adhesive
strength to a PP plate at -15.degree. C. of 2.5 N/20 mm or greater,
and exhibit good adhesiveness to a non-polar adherend at a low
temperature.
[0142] Additionally, the PSA sheets according to the present
invention were confirmed to have an adhesive strength to a SUS
plate at -5.degree. C. of 4.0 N/20 mm or greater as well as an
adhesive strength to a SUS plate at -15.degree. C. of 4.0 N/20 mm
or greater, and exhibit good adhesiveness also to a polar adherend
at a low temperature.
[0143] The present invention is not limited to the respective
embodiments described above and can be modified in a variety of
ways within the ranges described in the claims. The technical scope
of the present invention encompasses embodiments obtained by
suitably combining technical means disclosed respectively in the
different embodiments.
INDUSTRIAL APPLICABILITY
[0144] The water-dispersed PSA composition according to the present
invention is capable of forming a PSA that exhibits good
adhesiveness to a non-polar adherend such as polyethylene and
polypropylene at a low temperature. Therefore, it can be preferably
used for a variety of PSA sheets.
REFERENCE SIGNS LIST
[0145] 1 substrate [0146] 2 PSA layer [0147] 3 release sheet
* * * * *