U.S. patent application number 15/529634 was filed with the patent office on 2017-09-21 for pressure-sensitive adhesive sheet.
This patent application is currently assigned to Nitto Denko Corporation. The applicant listed for this patent is Nitto Denko Corporation. Invention is credited to Kiichiro MATSUSHITA, Shuuhei YAMAMOTO.
Application Number | 20170267897 15/529634 |
Document ID | / |
Family ID | 56123122 |
Filed Date | 2017-09-21 |
United States Patent
Application |
20170267897 |
Kind Code |
A1 |
YAMAMOTO; Shuuhei ; et
al. |
September 21, 2017 |
PRESSURE-SENSITIVE ADHESIVE SHEET
Abstract
Provided is a PSA sheet capable of showing high long-term
adhesive strength and good air release properties between the PSA
sheet and an adherend. This invention provides a PSA sheet
comprising a substrate film and a PSA layer provided to at least
one face of the substrate film. The PSA sheet comprises a coating
layer partially covering the PSA layer surface, whereby the PSA
layer surface has a coating layer-bearing area and a coating
layer-free area. The coating layer-free area occupies 70% or more
of the PSA layer surface. In a top view of the PSA layer surface,
the coating layer-bearing area has a linearly extending part
running from one edge to another edge of the PSA layer. The
linearly extending part has a width in a range of 0.1 mm to 2
mm.
Inventors: |
YAMAMOTO; Shuuhei;
(Ibaraki-shi, Osaka, JP) ; MATSUSHITA; Kiichiro;
(Ibaraki-shi, Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nitto Denko Corporation |
Ibaraki-shi, Osaka |
|
JP |
|
|
Assignee: |
Nitto Denko Corporation
Ibaraki-shi, Osaka
JP
|
Family ID: |
56123122 |
Appl. No.: |
15/529634 |
Filed: |
November 27, 2015 |
PCT Filed: |
November 27, 2015 |
PCT NO: |
PCT/JP2015/083445 |
371 Date: |
May 25, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09J 7/38 20180101; C09J
133/14 20130101; B32B 3/00 20130101; B32B 2255/28 20130101; B32B
2266/0278 20130101; B32B 7/14 20130101; C09J 2203/326 20130101;
B32B 27/281 20130101; B32B 2250/26 20130101; B32B 2266/0228
20130101; B32B 2266/0242 20130101; C09J 133/08 20130101; B32B
2307/748 20130101; C09J 2493/00 20130101; B32B 27/36 20130101; B32B
27/34 20130101; B32B 7/06 20130101; B32B 2309/105 20130101; B32B
2405/00 20130101; C09J 2301/16 20200801; B32B 27/40 20130101; C09J
7/22 20180101; B32B 2255/102 20130101; B32B 2307/414 20130101; C09J
2301/122 20200801; B32B 27/10 20130101; B32B 2266/0207 20130101;
C09J 2467/006 20130101; B32B 15/12 20130101; B32B 5/18 20130101;
B32B 27/12 20130101; B32B 2307/50 20130101; C09J 2203/318 20130101;
C09J 2475/005 20130101; B32B 2255/06 20130101; B32B 2250/24
20130101; C09J 2400/243 20130101; B32B 27/306 20130101; B32B 27/32
20130101; B32B 2250/03 20130101; B32B 2307/412 20130101; B32B 7/12
20130101; B32B 25/08 20130101; B32B 2255/26 20130101; C09J 2301/204
20200801; B32B 29/005 20130101; B32B 2266/0235 20130101; C09J
2301/302 20200801; B32B 2255/02 20130101; C09J 2301/124 20200801;
B32B 25/06 20130101; C09J 2301/206 20200801; B32B 2255/10 20130101;
B32B 2307/538 20130101; C09J 2301/21 20200801; B32B 2255/12
20130101; B32B 2255/00 20130101; B32B 2266/025 20130101; C09J
2423/006 20130101; B32B 29/007 20130101; C09J 2433/006 20130101;
B32B 15/08 20130101; B32B 27/304 20130101; B32B 2266/0257 20130101;
C09J 2301/414 20200801; B32B 15/09 20130101; B32B 27/065 20130101;
B32B 27/08 20130101; C09J 2433/00 20130101; B32B 2250/02 20130101;
B32B 2266/0264 20130101; B32B 2307/72 20130101; C08F 220/1804
20200201; C08F 220/1808 20200201; C08F 220/06 20130101; C08F 220/20
20130101; C08F 220/1804 20200201; C08F 220/1808 20200201; C08F
220/06 20130101; C08F 220/20 20130101 |
International
Class: |
C09J 7/02 20060101
C09J007/02; B32B 7/14 20060101 B32B007/14; B32B 7/06 20060101
B32B007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2014 |
JP |
2014-242183 |
Aug 21, 2015 |
JP |
2015-164270 |
Claims
1. A pressure-sensitive adhesive sheet comprising a substrate film
and a pressure-sensitive adhesive layer provided to at least one
face of the substrate film, wherein the pressure-sensitive adhesive
sheet further comprises a coating layer that partially covers the
pressure-sensitive adhesive layer surface, whereby the
pressure-sensitive adhesive layer surface has a coating
layer-bearing area and a coating layer-free area, the coating
layer-free area occupies 70% or more of the pressure-sensitive
adhesive layer surface, in a top view of the pressure-sensitive
adhesive layer surface, the coating layer-bearing area has a
linearly extending part that runs from one edge to another edge of
the pressure-sensitive adhesive layer, the linearly extending part
has a width in a range of 0.1 mm to 2 mm.
2. The pressure-sensitive adhesive sheet according to claim 1,
wherein the pressure-sensitive adhesive layer surface is provided
with a plurality of the linearly extending parts among which the
linearly extending parts in a group are placed at intervals
arranged in the width direction, whereby the coating layer-bearing
area has a stripe pattern.
3. The pressure-sensitive adhesive sheet according to claim 2,
wherein the coating layer-bearing area comprises a first stripe
pattern and a second stripe pattern that is placed to intersect the
first stripe pattern, whereby the coating layer-bearing area has a
lattice pattern.
4. The pressure-sensitive adhesive sheet according to claim 2,
wherein, in the coating layer-bearing area, the intervals between
the plurality of the linearly extending parts forming the stripe
pattern are in a range of 1.0 mm to 10 mm.
5. The pressure-sensitive adhesive sheet according to claim 1,
having an adhesive surface on which the coating layer is partially
placed, the adhesive face exhibiting a 180.degree. peel strength
after 24-hour adhesion of 13 N/25 mm or greater.
6. The pressure-sensitive adhesive sheet according to claim 1,
wherein the pressure-sensitive adhesive layer comprises an acrylic
polymer that accounts for more than 50% by weight of all polymers
in the pressure-sensitive adhesive layer, with the acrylic polymer
comprising, as a monomer, more than 50% by weight alkyl
(meth)acrylate represented by a formula (1):
CH.sub.2.dbd.C(R.sup.1)COOR.sup.2 (1) wherein R.sup.1 is a hydrogen
atom or a methyl group; R.sup.2 is an acyclic alkyl group with 1 to
20 carbon atoms.
7-9. (canceled)
10. The pressure-sensitive adhesive sheet according to claim 6,
wherein a carboxy group-containing monomer is copolymerized in the
acrylic polymer, the copolymerization ratio of the carboxy
group-containing monomer being 0.1% to 10% by weight to all
monomers used in the synthesis of the acrylic polymer.
11. The pressure-sensitive adhesive sheet according to claim 6,
wherein a hydroxy group-containing monomer is copolymerized in the
acrylic polymer, the copolymerization ratio of the hydroxy
group-containing monomer being 0.001% to 10% by weight to all
monomers used in the synthesis of the acrylic polymer.
12. The pressure-sensitive adhesive sheet according to claim 6,
wherein the pressure-sensitive adhesive layer comprises an
isocyanate-based crosslinking agent and/or an epoxy-based
crosslinking agent.
13. The pressure-sensitive adhesive sheet according to claim 6,
wherein the pressure-sensitive adhesive layer comprises a tackifier
resin with a softening point of 100.degree. C. to 140.degree. C. in
an amount of 30 parts to 60 parts by weight to 100 parts by weight
of the acrylic polymer, and the tackifier resin is at least one
species selected from the group consisting of a rosin-based
tackifier resin, a terpene-based tackifier resin and a
hydrocarbon-based tackifier resin.
14. The pressure-sensitive adhesive sheet according to claim 1,
wherein the coating layer comprises a transparent resin.
15. (canceled)
16. The pressure-sensitive adhesive sheet according to claim 1,
wherein the coating layer is of a polyurethane-based resin.
17. The pressure-sensitive adhesive sheet according to claim 1,
wherein the coating layer is of a two-component polyurethane-based
resin that is curable upon mixing.
18. (canceled)
19. The pressure-sensitive adhesive sheet according to claim 1,
wherein the substrate film is a polyester film.
20. (canceled)
21. The pressure-sensitive adhesive sheet according to claim 1,
wherein the substrate film exhibits a total light transmittance of
80% or higher.
22. The pressure-sensitive adhesive sheet according to claim 1,
wherein the substrate film is a foam film.
23. The pressure-sensitive adhesive sheet according to claim 22,
wherein the foam film has a mean pore diameter of 10 p.m to 200 p.m
and a density of 0.01 g/cm.sup.3 to 0.7 g/cm.sup.3.
24. The pressure-sensitive adhesive sheet according to claim 22,
wherein the foam film is an acrylic resin foam or a polyolefinic
resin foam.
25. A release liner-backed pressure-sensitive adhesive sheet
comprising the pressure-sensitive adhesive sheet according to claim
1, and a release liner that protects the adhesive face of the
pressure-sensitive adhesive sheet wherein the release liner has a
smooth surface on the adhesive face side.
26. A release liner for a pressure-sensitive adhesive sheet, the
release liner comprising a releasable support having at least one
releasable face, wherein the releasable face of the releasable
support is provided with a coating layer capable of being
transferred onto the pressure-sensitive adhesive sheet, whereby the
releasable surface has a coating layer-bearing area and a coating
layer-free area, the coating layer-free area occupies 70% or more
of the pressure-sensitive adhesive layer surface, the coating layer
has a linearly extending part that runs from one edge to another
edge of the releasable face, the linearly extending part has a
width in a range of 0.1 mm to 2 mm.
Description
TECHNICAL FIELD
[0001] The present invention relates to a pressure-sensitive
adhesive sheet.
[0002] This application claims priority to Japanese Patent
Application No. 2014-242183 filed on Nov. 28, 2014 and Japanese
Patent Application No. 2015-164270 filed on Aug. 21, 2015; the
entire contents thereof are incorporated herein by reference.
BACKGROUND ART
[0003] In general, pressure-sensitive adhesive (or PSA; the same
applies hereinafter) has characteristics to be in a soft solid
(viscoelastic) state in a room temperature range and easily adhere
to adherend with some pressure. With the benefit of such
properties, PSA is widely used in forms of substrate-supported PSA
sheets having a PSA layer at least on one face of the substrate for
purposes including fastening and surface protection of various
articles and obtaining desirable appearances such as for decorative
purposes. Documents disclosing these types of conventional art
include Patent Document 1.
CITATION LIST
Patent Literature
[0004] [Patent Document 1] Japanese Patent Application Publication
No. 2000-160117
SUMMARY OF INVENTION
Technical Problem
[0005] With respect to conventional PSA sheets, when the PSA sheets
are adhered to adherends, there have been cases where a fluid
substance such as air is left between the PSA sheets and the
adherends to form bubbles and the like (trapped air, etc.), thereby
causing degradation of the appearances. Such bubbles and the like
are not desirable, either, in view of their negative impact on the
adhesive properties such as reduced adhesive strength. To prevent
formation of the bubbles and the like or to provide features (or
air release properties) to eliminate the sort of bubbles if formed,
a technique of partial lamination of a non-adhesive layer on the
PSA layer surface is suggested (Patent Document 1). However, with
respect to the art according to Patent Document 1, because the
non-adhesive layer occupies a large portion of the PSA layer
surface, the art has not been satisfactory in dealing with the
influence on the adhesive properties, resulting in reduced adhesive
strength, etc. The studies by the present inventors have revealed
that it does not serve as a highly reliable bonding means
particularly in an application that continues to require high
adhesive strength after adhesion.
[0006] The present invention has been made in view of these
circumstances with an objective to provide a PSA sheet capable of
exhibiting high long-term adhesive strength as well as good air
release properties between the PSA sheet and an adherend.
Solution to Problem
[0007] The present invention provides a PSA sheet comprising a
substrate film and a PSA layer provided to at least one face of the
substrate film. The PSA sheet comprises a coating layer that
partially covers the PSA layer surface, whereby the PSA layer
surface has a coating layer-bearing area and a coating layer-free
area. The % surface area of the coating layer-free area in the PSA
layer surface is 70% or higher. When the PSA layer surface is seen
from the top, the coating layer-bearing area has a linearly
extending part that runs from one edge to another edge of the PSA
layer. The linearly extending part has a width in a range of 0.1 mm
to 2 mm.
[0008] As a general tendency, with respect to a PSA sheet, with
decreasing surface area of the adhesive face, the adhesiveness
proportionally decreases as well. When a coating layer is placed on
the adhesive face of the PSA sheet, the exposed surface area of the
adhesive face will decrease by as much as the portion covered by
the coating layer; and therefore, a similar tendency may be seen.
In fact, in the working examples described later, with increasing
surface area of the coating layer and decreasing exposed surface
area of the PSA layer in the PSA layer surface, the initial
adhesive strength immediately after application decreased in a
proportional manner. However, studies by the present inventors have
revealed that the long-term adhesive strength shows a tendency
different from the initial adhesive strength. In particular, it has
been found that, in the embodiment where the coating layer is
partially placed on the PSA layer surface, when the % surface area
of the coating layer-free area in the PSA layer surface was less
than 70%, the adhesive strength hardly increased from the level
immediately after it was applied; and there was a higher tendency
for insufficient long-term adhesive strength as compared to when
the % surface area was 70% or higher (see Examples described
later). In the art disclosed herein, high long-term adhesive
strength is obtained when the coating layer-free area occupies 70%
or more surface area. Naturally, however, with increasing surface
area of the coating layer-free area, the surface area of the
coating layer-bearing area decreases in relation. Thus, the primary
effect of the coating layer to provide air release properties to
the interface between the PSA sheet and an adherend may quite
possibly be impaired. Thus, in the art disclosed herein, the
coating layer is placed so that, when the PSA layer surface is seen
from the top, it has a linearly extending part that runs from one
edge to another edge of the PSA layer; and the width of the
linearly extending part is set in the range of 0.1 mm to 2 mm. By
this, in the PSA sheet capable of showing high long-term adhesive
strength, good air release properties can be realized. The linearly
extending part has a width of preferably 0.2 mm or greater (e.g. 0
3 mm or greater, or even 0.5 mm or greater), and preferably 1.2 mm
or less (more preferably 0.7 mm or less, or yet more preferably 0.4
mm or less). Herein, the long-term adhesive strength refers to the
adhesive strength at 24 hours after the PSA sheet is applied to an
adherend.
[0009] In a preferable embodiment of the PSA sheet disclosed
herein, the PSA layer surface is provided with a plurality of the
linearly extending parts. Among the plurality of the linearly
extending parts, two or more linearly extending parts in a group
are placed at intervals arranged in the width direction, whereby
the coating layer-bearing area has a stripe pattern. In such an
embodiment, through the two or more linearly extending parts in the
stripe pattern, air and the like to remain between the adherend
surface and the adhesive face are efficiently eliminated.
[0010] In a preferable embodiment of the PSA sheet disclosed
herein, the coating layer-bearing area comprises a first stripe
pattern and a second stripe pattern that is placed to intersect the
first stripe pattern, whereby the coating layer-bearing area has a
lattice pattern. In such an embodiment, air and the like to remain
between the adherend surface and the adhesive face are efficiently
eliminated.
[0011] In a preferable embodiment of the PSA sheet disclosed
herein, in the coating layer-bearing area, the two or more linearly
extending parts in the stripe pattern have intervals in a range of
1.0 mm to 10 mm. In such an embodiment, high long-term adhesive
strength and good air release properties are combined in a
well-balanced manner. The intervals between the linearly extending
parts are more preferably 1 5 mm to 8 mm, or yet more preferably
2.5 mm to 5 mm.
[0012] In a preferable embodiment, the PSA sheet disclosed herein
has an adhesive surface on which the coating layer is partially
placed and that exhibits a 24-hour 180.degree. peel strength of 13
N/25 mm or greater. According to the art disclosed herein, in the
embodiment where the coating layer is provided, such peel strength
can be obtained.
[0013] The present invention also provides a release liner-backed
PSA sheet comprising a PSA sheet disclosed herein and a release
liner that protects the PSA layer surface in the PSA sheet. Of the
surfaces of the release liner, the PSA layer-side surface is formed
smooth. In such an embodiment, greater adhesive properties tend to
be obtained. According to the art disclosed herein, in this
embodiment, when the release liner is used as a coating
layer-transferring film, a good transfer of the coating layer can
be obtained.
[0014] The present invention also provides a release liner for PSA
sheets, the release liner comprising a releasable support having at
least one releasable face. The releasable face of the releasable
support in the release liner is provided with a coating layer that
can be transferred onto a PSA sheet, whereby the releasable face
has a coating layer-bearing area and a coating layer-free area. The
% surface area of the coating layer-free area in the releasable
face is 70% or greater. The coating layer further has a linearly
extending part that runs from one edge to another edge of the
releasable face. The linearly extending part has a width in a range
of 0.1 mm to 2 mm. By transferring the coating layer onto the PSA
layer surface of the PSA sheet using such a release liner, it is
possible to preferably make a PSA sheet that combines high
long-term adhesive strength and good air release properties at a
high level.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 shows a schematic top view of the PSA sheet according
to an embodiment.
[0016] FIG. 2 shows a cross-sectional diagram at line II-II in FIG.
1.
[0017] FIG. 3 shows a schematic cross-sectional diagram of the
release liner-backed PSA sheet according to an embodiment.
[0018] FIG. 4 shows a schematic cross-sectional diagram of the
release liner-backed PSA sheet according to another embodiment.
[0019] FIG. 5 shows a schematic cross-sectional diagram of the
release liner for the PSA sheet according to an embodiment.
DESCRIPTION OF EMBODIMENTS
[0020] Preferred embodiments of the present invention are described
below. Matters necessary to practice this invention other than
those specifically referred to in this description may be
comprehended by a person of ordinary skill in the art based on the
instruction regarding implementations of the invention according to
this description and the common technical knowledge in the
pertinent field. The present invention can be practiced based on
the contents disclosed in this description and common technical
knowledge in the subject field. In the drawings referenced below, a
common reference numeral may be assigned to members or sites
producing the same effects, and duplicated descriptions are
sometimes omitted or simplified. The embodiments described in the
drawings are schematized for clear illustration of the present
invention, and do not necessarily represent the accurate sizes or
reduction scales of the PSA sheet of the present invention provided
as an actual product.
[0021] The concept of PSA sheet herein encompasses so-called PSA
tapes, PSA labels, and PSA films The PSA sheet disclosed herein can
be in a roll form or in a flat sheet form. Alternatively, the sheet
may be further processed into various forms.
[0022] FIG. 1 shows a schematic top view of the PSA sheet according
to an embodiment. FIG. 2 shows a cross-sectional diagram at line
II-II in FIG. 1. With reference to the drawings, the PSA sheet in
this embodiment is described.
[0023] As shown in FIGS. 1 and 2, PSA sheet 1 according to this
embodiment has a layered structure formed of a substrate film 10
and a PSA layer 20. Substrate film 10 supports the PSA layer 20. In
PSA sheet 1, the surface 20A on the PSA layer 20 side forms an
adhesive face 1A. The other face 1B (the surface on the film
substrate 10 side) of PSA sheet 1 is a non-adhesive face.
[0024] On the surface 20A of the PSA layer 20, a coating layer 30
is partially placed. In other words, the PSA layer surface 20A is
partially covered with the coating layer 30, and has a coating
layer-bearing area 50 where the coating layer 30 is placed and a
coating layer-free area 51 where the coating layer 30 is not placed
and the PSA layer 20 is exposed on the surface. When the PSA sheet
1 is applied to an adherend, the coating layer 30 forms pathways
for air and the like at the interface between the PSA sheet 1 and
the adherend, thereby providing air release properties. The surface
of the coating layer 30 may be flush with the PSA layer surface 20A
or may protrude at least partially in the thickness direction from
the PSA layer surface 20A.
[0025] When the PSA layer surface 20A is seen from the top, the
coating layer-bearing area 50 is in a certain pattern (coating
layer pattern) 60. In the present embodiment, the coating
layer-bearing area 50 shows a lattice pattern 60. In particular,
when the PSA layer surface 20A is seen from the top, the lattice
pattern 60 of the coating layer 30 is formed of a first stripe
pattern 70 and a second stripe pattern 80 that is placed to
intersect with the first stripe pattern 70.
[0026] The first stripe pattern 70 is formed of a plurality of long
parts (bands) 75A, 75B and 75C that extend straight from one edge
to another edge of the PSA layer 20. The plurality of the long
parts 75A, 75B and 75C are placed in parallel at intervals arranged
in the width direction. In this embodiment, the long parts 75A, 75B
and 75C are placed at an angle such that their length directions
intersect the edges (ends, limits) of the width direction of the
PSA sheet 1, with each long part reaching two edges (two sides) of
the PSA layer 20. Herein, the term "long part" means a part having
a length direction and a width direction (a direction
perpendicularly intersecting the length direction) (i.e. a part
having a length and a width), typically referring to a long band
regardless of whether it is straight or curved. In the other words,
the long part can be described as a linearly extending part.
[0027] Similarly to the first stripe pattern 70, the second stripe
pattern 80 is also formed of a plurality of long parts (bands) 85A,
85B and 85C that extend straight from one edge to another edge of
the PSA layer 20. The plurality of the long parts 85A, 85B and 85C
are placed in parallel at intervals arranged in the width
direction. In this embodiment, the long parts 85A, 85B and 85C are
placed at an angle such that their length directions intersect the
edges (ends, limits) of the width direction of the PSA sheet 1,
with each long part reaching two edges (two sides) of the PSA layer
20. In this embodiment, the long parts 75A, 75B, 75C, 85A, 85B and
85C are straight, but are not limited thereto. Each long part may
be curvilinear. In such an embodiment, a plurality of the long
parts may form a wavy stripe pattern, etc.
[0028] In this embodiment, the first stripe pattern 70 and the
second stripe pattern 80 intersect each other so that the long
parts 75A, 75B and 75C of the first stripe pattern 70 and the long
parts 85A, 85B and 85C of the second stripe pattern 80 cross one
another almost perpendicularly. Thus, the long parts 75A, 75B and
75C of the first stripe pattern 70 partially overlap the long parts
85A, 85B and 85C of the second stripe pattern 80.
[0029] Herein, the lattice pattern typically refers to a pattern
that includes two stripe patterns intersecting each other and
encompasses not only a rhombic lattice as in the present
embodiment, but also various lattice shapes such as a square
lattice and a triangular lattice. When the long parts are straight,
the angle (the acute angle) at an intersection of the two stripe
patterns can be in a range from 10.degree. to 90.degree.
(preferably 45.degree. to 90.degree., typically 60.degree. to
90.degree.). The lattice pattern disclosed herein also encompasses
a pattern that includes a stripe pattern formed of several linearly
extending parts with repeated bending, for instance, a pattern such
as a hexagonal lattice. In such a pattern, adjacent long parts may
be partially connected to one another. From the standpoint of the
air release properties, the coating layer-bearing area preferably
comprises one, two or more stripe patterns. Thus, the coating
layer-bearing area (typically in a lattice pattern) may include a
third stripe pattern.
[0030] In the coating layer-bearing area 50, the widths (W1) of the
respective long parts 75A, 75B, 75C, 85A, 85B and 85C are in a
range of 0.1 mm to 2 mm. This can combine high long-term adhesive
strength (adhesive strength after aged) and good air release
properties. From the standpoint of enhancing the air release
properties, the widths W1 of the long parts are preferably 0.2 mm
or greater, more preferably 0.3 mm or greater, or yet more
preferably 0.5 mm or greater. From the standpoint of the adhesive
strength, the appearance, etc., the widths W1 of the long parts are
preferably 12 mm or less, more preferably 1.0 mm or less, yet more
preferably 0.7 mm or less, particularly preferably 0.5 mm or less,
or most preferably 0.4 mm or less.
[0031] In the coating layer-bearing area 50, the intervals W2
between the long parts 75A, 75B and 75C forming the first stripe
pattern 70 are preferably selected from a range of 1.0 mm to 10 mm.
By this, in an embodiment where the widths of the long parts are in
the range, there is a higher tendency that high long-term adhesive
strength is combined with air release properties in a well-balanced
manner. Here, the intervals W2 between the long parts refer to the
widths of spaces present between any two adjacent long parts in the
PSA layer surface. From the standpoint of increasing the long-term
adhesive strength, etc., the intervals W2 between the long parts
are more preferably 1.5 mm or greater, or yet more preferably 2.5
mm or greater. The intervals W2 between the long parts can be about
8 mm or less (e.g. 5 mm or less, typically 3 mm or less). The
intervals between the long parts forming the second stripe pattern
80 can also be preferably selected from the ranges exemplified for
the intervals between the long parts 75A, 75B and 75C. The
intervals W2 are preferably evenly spaced.
[0032] From the standpoint of combining well-balanced high
long-term adhesive strength and air release properties, the pitch
of the long parts is preferably in a range of 1 mm to 20 mm. The
pitch of the long parts is more preferably 1 5 mm or greater, yet
more preferably 2 mm or greater (e.g. 2.5 mm or greater); it is
more preferably 15 mm or less (e.g. 12 mm or less), or yet more
preferably 5 mm or less. The pitch refers to the distance
(interval) between the centerlines of the width directions (i.e.
the lengthwise centerlines) of the long parts.
[0033] Before used, as shown in FIG. 3, the PSA sheet 1 may be in a
form of a release liner-backed PSA sheet 1 where the PSA layer 20
is protected with a release liner 40 having a release face at least
on the PSA layer surface 20A side. Alternatively, it may be in a
form such that the back face (opposite from the PSA layer 20 side
surface) of substrate film 10 is a release face and the PSA sheet 1
is wound so that the back face is brought into contact with the PSA
layer 20 whereby the PSA layer 20 is protected with the back face
of the substrate film. Such an adhesively single-faced PSA sheet
(single-faced PSA sheet) having only one adhesive face is
favorable, for instance, when the surface opposite from the
adhesive surface requires features such as decoration and surface
protection, or when it is used as a paint substitute sheet.
[0034] When the PSA sheet disclosed herein is an adhesively
double-faced substrate-backed PSA sheet (a double-faced PSA sheet)
as shown in FIG. 4, the PSA sheet 2 may be in an embodiment such
that the respective faces (both non-releasable) of substrate film
10 are provided with PSA layers 21 and 22 with the PSA layers 21
and 22 protected with release liners 41 and 42, respectively, with
each liner having a release face at least on the PSA layer side. In
the PSA sheet 2, a coating layer 30 is partially placed only on the
surface of the PSA layer 21, and no coating layer is formed on the
PSA layer 22. Alternatively, although not specifically shown in a
drawing, the double-faced PSA sheet may be in an embodiment such
that PSA layers are provided to the respective faces (both
non-releasable) of the substrate film and one of the PSA layers is
protected with a release liner having a release face on each side.
By winding the PSA sheet so that the other PSA layer is brought
into contact with the back face of the release liner, this type of
PSA sheet can be made into an embodiment where the two PSA layers
are protected with the one release liner. The double-faced PSA
sheet is preferably used, for instance, for bonding/fixing
applications.
<Properties of PSA Sheet, etc.>
[0035] The PSA sheet disclosed herein is characterized by the %
surface area of the coating layer-free area in the PSA layer
surface (which can be the % surface area of the coating layer in
the adhesive face (adhesive surface) of the PSA sheet) being 70% or
higher. This can ensure high long-term adhesive strength. The %
surface area is preferably 75% or higher, or more preferably 80% or
higher; from the standpoint of obtaining good air release
properties, the % surface area is preferably 90% or lower, or more
preferably 85% or lower.
[0036] In a preferable embodiment, the adhesive surface (typically
formed of the PSA layer surface and the coating layer surface) of
the PSA sheet shows a 24-hour 180.degree. adhesive strength
(180.degree. adhesive strength after 24-hour adhesion, or a 24-hour
adhesion strength, hereinafter) of 13 N/25 mm or greater. The PSA
sheet can exhibit at least a certain level of long-term adhesive
strength (adhesive strength after aged) while having good air
release properties. The 24-hour adhesion strength is preferably 14
N/25 mm or greater (e.g. 16 N/25 mm or greater). The 24-hour
adhesion strength can be determined by the method described next.
In particular, the PSA sheet is cut to a 25 mm wide by 100 mm long
size to obtain a measurement sample; and in an environment at
23.degree. C. and 50% RH, the adhesive surface of the measurement
sample is press-bonded to the surface of a stainless steel plate
(SUS 304BA plate) with a 2 kg roller moved back and forth once.
This is left standing in the same environment for 24 hours.
Subsequently, using a universal tensile/compression tester, based
on JIS Z 0237:2000, the peel strength (N/25 mm) is determined at a
tensile speed of 300 mm/min at a peel angle of 180.degree.. More
specifically, it is determined by the method described later in
Examples.
[0037] In a preferable embodiment, the PSA sheet has transparency
(including semi-transparency). In such a PSA sheet, when bubbles
and the like are trapped between the PSA sheet and an adherend,
they are visible through the PSA sheet and are likely to degrade
the appearance. The art disclosed herein prevents formation of the
sort of bubbles between the PSA sheet and the adherend; and
therefore, an excellent appearance can be obtained in a transparent
PSA sheet. In particular, the PSA sheet may exhibit a total light
transmittance of 80% or higher (e.g. 90% or higher, typically 95%
or higher). The PSA sheet preferably has a haze value of 10% or
lower (e.g. 5% or lower). The total light transmittance and the
haze value can be determined using a commercial transmissometer
(e.g. product name HAZE METER HM-150 available from Murakami Color
Research Laboratory). The total light transmittance and the haze
value of the substrate film described later are also determined by
the same methods.
[0038] The overall thickness of the PSA sheet disclosed herein
(including the PSA layer and the substrate, but excluding the
release liner) is not particularly limited. It is suitably in a
range of about 2 .mu.m to 1000 .mu.m, or preferably 5 .mu.m to 500
.mu.m (e.g. 10 .mu.m to 300 .mu.m, typically 30 .mu.m to 100
.mu.m). The PSA sheet limited in overall thickness can be
advantageous in view of making products to which the PSA sheet is
applied smaller, lighter, resource-saving, and so on.
<Substrate Film>
[0039] Examples of the substrate film disclosed herein include
resin film, paper, cloth, rubber film, foam film, and metal foil as
well as a composite and a laminate of these. In particular, from
the standpoint of the ease of application and the appearance, it
preferably comprises a resin film layer. The inclusion of the resin
film layer is advantageous also from the standpoint of the size
stability, the accuracy of thickness, the ease of processing, the
tensile strength and so on. Examples of the resin film include
polyolefinic resin film such as polyethylene (PE), polypropylene
(PP), and ethylene/polypropylene copolymers; polyester-based resin
film such as polyethylene terephthalate (PET), polybutylene
terephthalate, and polyethylene naphthalate; vinyl chloride-based
resin film; vinyl acetate-based resin film; polyimide-based resin
film; polyamide-based resin film; fluororesin film; and cellophane.
Favorable examples include resin films formed from PE, PP and PET.
Among the resin films, polyester film is more preferable; among
them, PET film is even more preferable. The substrate film may have
a monolayer structure or a multilayer structure formed of two,
three or more layers.
[0040] In a preferable embodiment, the substrate film is a
substrate comprising a foam film (a foam-containing substrate).
This provides impact-absorbing capabilities to the PSA sheet. Here,
the foam film refers to a film structure having a part with foam
cells (a foam cell structure). The foam-containing substrate may be
a mono-layer structure formed from a foam film or a multi-layer
structure wherein at least one of whose two or more layers is
formed of a foam film (a foam layer). A configurational example of
the foam-containing substrate is a composite substrate in which a
foam film (a foam layer) and a non-foamed film (a non-foamed layer)
are laminated. The non-foamed film (non-foamed layer) refers to a
film structure that has not been subjected to a purposeful foaming
process (e.g. a process to incorporate foam cells), referring to a
film essentially free of a foam cell structure. Atypical example of
the foam film is a resin film (e.g. a polyester-based resin film
such as of PET) having an expansion rate of less than 1.1-fold
(e.g. less than 1.05-fold, typically less than 1.01-fold). When the
substrate film comprises two or more foam layers, the materials and
structures of these foam layers can be identical or different. When
the foam film has a multi-layer structure that includes a foam
layer, from the standpoint of increasing the tightness between
layers, adhesive layers may be placed between the layers.
[0041] The foam film is not particularly limited in average foam
cell diameter; it is usually suitably 10 .mu.m to 200 .mu.m,
preferably 20 .mu.m to 180 .mu.m, or more preferably 30 .mu.m to
150 .mu.m. When the average foam cell diameter is10 .mu.m or
larger, the impact-absorbing properties tend to increase. On the
other hand, when the average foam cell diameter is 200 .mu.m or
smaller, the handling properties and waterproof properties
(water-blocking properties) tend to increase.
[0042] The average foam cell diameter (.mu.m) of the foam film can
be determined, using a low-vacuum scanning electron microscope to
take an enlarged image of a cross section of the foam and
subjecting it to image analysis. About 20 to 30 foam cells can be
analyzed. As the low-vacuum scanning electron microscope, for
instance, product name S-3400N Scanning Electron Microscope
available from Hitachi High-Tech Science Systems Corporation) can
be used.
[0043] The foam film is not particularly limited in density
(apparent density); it is usually suitably 0.01 g/cm.sup.3 or
higher, preferably 0.01 g/cm.sup.3 to 0.7 g/cm.sup.3, or more
preferably 0.02 g/cm.sup.3 to 0.5 g/cm.sup.3. When the density is
0.01 g/cm.sup.3 or higher, the strength of the foam film (and even
that of the PSA sheet) will increase with a tendency toward greater
impact resistance and handling properties. On the other hand, when
the density is 0.7 g/cm.sup.3 or lower, the conformability to a
difference in level tends to increase without an excessive decrease
in flexibility.
[0044] The density (apparent density) of the foam film is
determined based on the method described in JIS K 7222:1999. In
particular, the foam film is punched out into a 100 mm by 100 mm
size to prepare a specimen and the dimensions of the specimen are
measured. Using a 1/100 dial gauge with a 20 mm diameter
measurement terminal, the thickness of the specimen is measured.
From these values, the volume of the foam film specimen is
determined The specimen is weighed on a top-loading balance
(minimum scale 0.01 g or greater). From these values, the apparent
density (g/cm.sup.3) of the foam film can be determined
[0045] The 50% compressive stress of the foam film is not
particularly limited. From the standpoint of the impact resistance,
the foam film suitably shows a 50% compressive stress of 0.1
N/cm.sup.2 or greater. When the 50% compressive stress is at or
above a certain value, for instance, even if the foam film is thin
(e.g. about 100 .mu.m thick), it can show sufficient resistance
when compressed (resilience to compression) and maintain good
impact resistance. The 50% compressive stress is preferably 0.2
N/cm.sup.2 or greater, or more preferably 0.5 N/cm.sup.2 or
greater. From the standpoint of combining flexibility and impact
resistance in a well-balanced way, the 50% compressive stress is
suitably 8 N/cm.sup.2 or less, preferably 6 N/cm.sup.2 or less, or
more preferably 3 N/cm.sup.2 or less.
[0046] The 50% compressive stress (hardness) of the foam film is
determined based on JIS K 6767:1999. In particular, the foam film
is cut to 100 mm by 100 mm pieces. These pieces are layered to a
total thickness of at least 2 mm and the resultant is used as a
measurement sample. At room temperature, using a compression
tester, the measurement sample is compressed at a rate of 10
mm/min. When compressed to 50% (when compressed to 50% of its
initial thickness) and held at 50% compression for 10 seconds, the
value (resilience in N/cm.sup.2) is recorded as the 50% compressive
stress. Other conditions (e.g. jig and calculation method, etc.)
are conformed to JIS K 6767:1999.
[0047] The foam constituting the foam film disclosed herein is not
particularly limited in foam cell structure. The foam cell
structure can be a continuous foam cell structure, an isolated foam
cell structure, or a semi-continuous foam cell structure. From the
standpoint of the impact absorbing properties, continuous and
semi-continuous foam cell structures are preferable.
[0048] The material of the foam film is not particularly limited.
The foam film can be typically formed from a material comprising a
polymer component (e.g. a thermoplastic polymer). A preferable foam
film is usually formed of foam of a plastic material (plastic
foam). The plastic material (which means to include a rubber
material) for forming the plastic foam is not particularly limited;
a suitable species can be selected among known plastic materials.
For the plastic material (typically a thermoplastic polymer),
solely one species or a combination of two or more species can be
used. The primary component (typically a component accounting for
more than 50% by weight) among the polymers in the substrate film
or the foam film may be referred to as the "base polymer"
hereinafter.
[0049] Specific examples of the foam include polyolefinic resin
foam such as PE foam and PP foam; polyester-based foam such as PET
foam, polyethylene naphthalate foam and polybutylene terephthalate
foam; polyvinyl chloride-based resin foam such as polyvinyl
chloride foam; vinyl acetate-based foam; acrylic resin foam;
polyphenylene sulfide resin foam; amide-based resin foam such as
polyamide (nylon) resin foam and all-aromatic polyamide (aramide)
resin foam; polyimide-based resin foam; polyether ether ketone
(PEEK) foam; styrene-based resin foam such as polystyrene foam; and
urethane-based resin foam such as polyurethane resin foam. As the
foam, rubber-based resin foam such as polychloroprene rubber foam
can be used as well.
[0050] In a preferable embodiment, acrylic resin foam (foam formed
from acrylic resin) is used as the foam. Here, the acrylic resin
foam refers to foam comprising an acrylic polymer as the base
polymer. The acrylic polymer in this description is as defined
later. As the alkyl (meth)acrylate forming the acrylic polymer,
one, two or more species can be preferably used among alkyl
(meth)acrylates having acyclic alkyl groups with 1 to 20
(preferably 1 to 8, typically 1 to 4) carbon atoms. Preferable
examples of the alkyl (meth)acrylate include ethyl acrylate,
n-butyl acrylate and 2-ethylhexyl acrylate. The amount of the alkyl
(meth)acrylate as the primary monomer is suitably 70% by weight or
more of all monomers in the acrylic polymer, or preferably 75% by
weight or more (e.g. 80% by weight or more). The amount of the
alkyl (meth)acrylate is suitably 98% by weight or less of all the
monomers, or preferably 97% by weight or less (e.g. 96% by weight
or less).
[0051] The secondary monomer co-polymerizable with the alkyl
(meth)acrylate as the primary monomer may be useful in introducing
crosslinking points in the acrylic polymer or in increasing the
cohesive strength of the acrylic polymer. As the secondary monomer,
one, two or more species of functional group-containing monomers
can be used among, for instance, carboxy group-containing monomers,
hydroxy group-containing monomers, acid anhydride group-containing
monomers, amide group-containing monomers, amino group-containing
monomers, cyano group-containing monomers, monomers having nitrogen
atom-containing rings and the like. The secondary monomer can also
be a vinyl ester-based monomer such as vinyl acetate, an aromatic
vinyl compound such as styrene, a sulfonate group-containing
monomer, a phosphate group-containing monomer and the like. The
amount of the secondary monomer is suitably 0.5% by weight or more
of all monomers in the acrylic polymer, or preferably 1% by weight
or more. The amount of the secondary monomer is suitably 30% by
weight or less of all the monomers, or preferably 10% by weight or
less.
[0052] When the foam is formed with an emulsion-based resin
composition by a foaming method where gases including air are mixed
in mechanically such as by stirring, it is preferable that the
monomers forming the acrylic polymer comprise a nitrogen
atom-containing monomer as the secondary monomer. This facilitates
the formation of foam cells in the foaming process and may increase
the viscosity of the composition when forming the foam (typically
when drying the resin composition), whereby the foam cells are
readily kept in the foam body.
[0053] Examples of the nitrogen atom-containing monomer include
cyano group-containing monomers such as acrylonitrile and
methacrylonitrile; lactam ring-containing monomers such as
N-vinyl-2-pyrolidone; amide group-containing monomers such as
(meth)acrylamide, N-hydroxyethyl(meth)acrylamide,
N-methylolacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide
and diacetone acrylamide. These can be used solely as one species
or in a combination of two or more species. Among them, cyano
group-containing monomers such as acrylonitrile and lactam
ring-containing monomers such as N-vinyl-2-pyrolidone are
preferable.
[0054] The amount of the nitrogen atom-containing monomer is
suitably 2% by weight or more of all monomers in the acrylic
polymer, or preferably 3% by weight or more (e.g. 4% by weight or
more). The amount of the nitrogen atom-containing monomer is
suitably 30% by weight or less of all the monomers, or preferably
25% by weight or less (e.g. 20% by weight or less).
[0055] The method for obtaining the acrylic polymer is not
particularly limited. Various polymerization methods known as
procedures for the synthesis of acrylic polymer can be suitably
used, such as solution polymerization, emulsion polymerization,
bulk polymerization, suspension polymerization, active energy ray
polymerization (e.g. UV polymerization). For instance, a desirable
acrylic polymer can be obtained by dissolving or dispersing a
monomer mixture in a suitable polymerization solvent (toluene,
ethyl acetate, water, etc.) and carrying out polymerization using a
polymerization initiator such as an azo-based polymerization
initiator and a peroxide-based initiator. In view of the ease of
foaming and environmental aspects, it is preferable to use acrylic
resin foam (emulsion-based acrylic resin foam) obtained by emulsion
polymerization.
[0056] From the standpoint of increasing the cohesive strength, the
acrylic resin foam-forming composition preferably comprises a
crosslinking agent. The type of crosslinking agent is not
particularly limited. Among various crosslinking agents, one, two
or more species can be suitably selected and used. Favorable
examples of the crosslinking agent include isocyanate-based
crosslinking agents, epoxy-based crosslinking agents,
oxazoline-based crosslinking agents, carbodiimide-based
crosslinking agents, melamine-based crosslinking agents and metal
oxide-based crosslinking agents. In particular, oxazoline-based
crosslinking agents are preferable. The amount of the crosslinking
agent used is not particularly limited. To 100 parts by weight of
the acrylic polymer, it is suitably selected from a range of about
10 parts by weight or less (e.g. about 0.005 part to 10 parts by
weight, preferably about 0.01 part to 5 parts by weight).
[0057] In another preferable embodiment, polyolefinic resin foam
(resin foam formed from a polyolefin) is used as the foam. As the
plastic material forming the polyolefinic foam, various known or
commonly-used polyolefinic resins can be used without particular
limitations. Examples include polyethylene such as low density
polyethylene (LDPE), linear low density polyethylene (LLDPE), high
density polyethylene (HDPE) and metallocene catalyst-based linear
low density polyethylene; polypropylene; ethylene-propylene
copolymer; and ethylene-vinyl acetate copolymer. Among these
polyolefinic resins, solely one species or a combination of two or
more species can be used.
[0058] From the standpoint of the impact resistance, waterproof
properties, etc., favorable examples of the foam film in the art
disclosed herein include a polyethylene-based foam film essentially
formed of polyethylene-based resin foam and a polypropylene-based
foam film essentially formed of polypropylene-based resin foam.
Here, the polyethylene-based resin refers to resin formed from
ethylene as the primary monomer (i.e. the primary component among
the monomers) and may include HDPE, LDPE and LLDPE as well as
ethylene-propylene and ethylene-vinyl acetate copolymers of which
ethylene is copolymerized at a ratio above 50% by weight.
Similarly, the polypropylene-based resin refers to resin formed
from propylene as the primary monomer. As the foam film in the art
disclosed herein, a polypropylene-based foam film can be preferably
used.
[0059] The foaming method for the foam film is not particularly
limited. In accordance with the purpose, ease of procedures, etc.,
chemical procedures, physical procedures and so on can be employed
individually or in combination. From the standpoint of the
contamination, etc., physical foaming methods are preferable.
Specific examples include a foaming method where a film-forming
material is prepared to contain a foaming agent such as a low
boiling compound (e.g. a hydrocarbon) and thermally expandable
microspheres and foam cells are formed from the foaming agent, a
foaming method where gases such as air are mechanically mixed in, a
foaming method by solvent removal which takes advantage of removal
of a solvent such as water, and a foaming method using a
supercritical fluid. For instance, a method where an inert gas
(e.g. carbon dioxide) is injected into the foam film-forming
polymer under increased pressure and the resultant is placed under
reduced pressure to form a foam film By this method, the average
foam cell diameter can be easily controlled to be at or below a
certain value and the foam film can be easily made to have a lower
density.
[0060] The foam film is fabricated by employing a foaming method as
described above. The formation of the foam film is not particularly
limited. For instance, when employing a foaming method that
mechanically admixes gases such as air, a resin composition (e.g.
an emulsion-based resin composition) containing foam can be
subsequently applied over a substrate or release paper, etc., and
allowed to dry to obtain a foam film. From the standpoint of the
foam stability, etc., the drying preferably includes a preliminary
drying step at or above 50.degree. C., but below 125.degree. C. as
well as a main drying step at 125.degree. C. to 200.degree. C.
Alternatively, foam can be formed continuously into a film using a
calender, extruder, conveyer belt casting and so forth; or a method
where a kneaded mixture of foam-forming materials is foamed and
molded in a batch process can be employed. In forming the foam
film, a surface layer may be removed by slicing to adjust the film
to obtain desirable thickness and foam characteristics.
[0061] The thermoplastic polymer (e.g. a polyolefinic polymer) that
can be included in the foam film may comprise a thermoplastic
elastomer that exhibits properties of rubber at room temperature,
but shows thermoplasticity at a high temperature. From the
standpoint of the flexibility and conformability, one, two or more
species can be used among thermoplastic elastomers, for instance,
olefinic elastomers such as ethylene-propylene copolymer,
ethylene-propylene-diene copolymer, ethylene-vinyl acetate
copolymer, polybutene, polyisobutylene, and chlorinated
polyethylene; styrene-based elastomers such as
styrene-butadiene-styrene copolymer; thermoplastic polyester-based
elastomers; thermoplastic polyurethane-based elastomers; and
thermoplastic acrylic elastomers. Among them, a thermoplastic
elastomer having a glass transition temperature of room temperature
or lower (e.g. 20.degree. C. or lower). The thermoplastic elastomer
content in the foam film is preferably about 10% to 90% by weight
(e.g. 20% to 80% by weight) of the thermoplastic polymer in the
foam film.
[0062] From the standpoint of the ease of mixing a foam-forming gas
and the foam stability, as the foaming agent, various surfactants
can be used in the foam film-forming material (e.g. an
emulsion-based acrylic resin composition), with examples including
anionic surfactants, cationic surfactants, nonionic surfactants and
amphoteric surfactants. Hydrocarbon-based and fluorine-based
surfactants can be used as well. In particular, from the standpoint
of reducing the foam cell diameters and stabilizing the foam,
anionic surfactants are preferable; ammonium salts of fatty acids
(typically ammonium salts of higher fatty acids) such as ammonium
stearate are more preferable. For the surfactant, solely one
species or a combination of two or more species can be used. The
surfactant content is preferably about 0.1 part to 10 parts by
weight (e.g. 0.5 part to 8 parts by weight) to 100 parts by weight
of the base polymer of the foam film The foaming agent in this
description includes not only an agent that shows foaming
capabilities, but also a foam cell diameter-adjusting agent to
reduce the foam diameters as well as a foam stabilizer such as a
foam-adjusting agent.
[0063] When the foam film-forming material is an aqueous dispersion
(e.g. an acrylic emulsion), it is preferable to use a
silicone-based compound as the foaming agent. By this, the recovery
of thickness (the degree and speed of recovery) after compression
tends to improve. A preferable silicone-based compound has 2000 or
fewer siloxane bonds. Examples of the silicone-based compound
include silicone oil, modified silicone oil, and silicone resin. In
particular, dimethyl silicone oil and methyl phenyl silicone oil
are preferable. As the silicone-based compound, a silicone-modified
polymer (e.g. a silicone-modified acrylic polymer, a
silicone-modified urethane-based polymer, etc.) can be used as
well. These can be used solely as one species or in a combination
of two or more species. The silicone compound content is preferably
about 0.01 part to 5 parts by weight (e.g. 0.05 part to 4 parts by
weight, typically 0.1 part to 3 parts by weight) to 100 parts by
weight of the base polymer of the foam film.
[0064] From the standpoint of stabilizing the foam and increasing
the ease of film formation, the foam film-forming material (e.g. an
emulsion-based acrylic resin composition) may comprise a thickener.
The thickener is not particularly limited. Examples include acrylic
acid-based thickeners, urethane-based thickeners and polyvinyl
alcohol-based thickeners. In particular, polyacrylic acid-based
thickeners and urethane-based thickeners are preferable. The
thickener content is preferably about 0.1 part to 10 parts by
weight (e.g. 0.1 part to 5 parts by weight) to 100 parts by weight
of the base polymer of the foam film.
[0065] When a foam-containing substrate is used as the substrate
film, the foam film preferably comprises a foam-nucleating agent
such as a metal hydroxide (e.g. magnesium hydroxide). This tends to
facilitate the adjustment of the average foam cell diameter in the
foam film to obtain desirable impact-absorbing properties,
flexibility and so on. The foam-nucleating agent can be a metal
oxide, composite oxide, metal carbonate, metal sulfate, etc. The
foam-nucleating agent content is preferably about 0.5 part to 125
parts by weight (e.g. 1 part to 120 parts by weight) to 100 parts
by weight of the base polymer of the foam film.
[0066] When using a foam-containing substrate as the substrate
film, from the standpoint of inhibiting the foam from degassing
while foam cells are being formed, the foam film preferably
comprises a degassing inhibitor such as fatty acid amides. A more
preferable fatty acid amide has a bis-amide structure. The
degassing inhibitor can be a metal salt of a fatty acid as well.
The degassing inhibitor content is preferably about 0.5 part to 10
parts by weight (e.g. 0.7 part to 8 parts by weight, typically 1
part to 6 parts by weight) to 100 parts by weight of the base
polymer of the foam film.
[0067] The substrate film (e.g. a foam film) may comprise a
softener so as to provide desirable fluidity to the film-forming
material thereby to improve properties such as flexibility. With
the inclusion of a softener in the foam film, properties such as
ease of stretching the film and expansion ratio can be preferably
adjusted. For example, one, two or more species can be preferably
used among hydrocarbon-based softeners such as liquid paraffin,
paraffin wax, micro wax and polyethylene wax; ester-based softeners
such as glyceryl stearate; and fatty acid-based softeners. The
softener content is preferably 0.5 part to 50 parts by weight (e.g.
0.8 part to 40 parts by weight, typically 1 part to 30 parts by
weight) to 100 parts by weight of the base polymer of the substrate
film (e.g. a foam film)
[0068] When emulsion-based acrylic resin foam is used, an arbitrary
anticorrosive may be included to prevent corrosion of metal parts
adjacent to the foam film. As the anticorrosive, an azole
ring-containing compound is preferable. With the use of an azole
ring-containing compound, inhibition of metal corrosion and tight
adhesion to adherends can be combined at a high level. In
particular, a compound with the azole ring forming a fused ring
with an aromatic ring such as a benzene ring is preferable;
benzotriazole-based compounds and benzothiazole -based compounds
are especially preferable. The anticorrosive content is preferably
about 0.2 part to 5 parts by weight (e.g. 0.3 part to 2 parts by
weight) to 100 parts by weight of the base polymer of the foam
film
[0069] In a preferable embodiment, the substrate film has
transparency (including semi-transparency). In the PSA sheet
comprising such a substrate film, when bubbles and the like are
trapped between the PSA sheet and an adherend, they are visible
through the PSA sheet and are likely to degrade the appearance. The
art disclosed herein prevents formation of the sort of bubbles
between the PSA sheet and the adherend; and therefore, an excellent
appearance can be obtained in an embodiment comprising a
transparent substrate. In particular, the substrate film may show a
total light transmittance of 80% or higher (e.g. 90% or higher,
typically 95% or higher). The substrate film preferably has a haze
value of 10% or lower (e.g. 5% or lower).
[0070] To obtain desirable designs and optical properties, the
substrate film (e.g. a resin film) may be colored black, white or
other with various types of colorant (e.g. pigment) content. As a
black colorant, carbon black is preferable. It is also possible to
employ a method where at least one surface (one or each face) of
the substrate film is subjected to printing to overlay one, two or
more colored layers (e.g. a black layer and a white layer).
[0071] To the substrate film (e.g. a resin substrate film, a foam
substrate film), various additives may be added as necessary, such
as filler (inorganic filler, organic filler, etc.), anti-aging
agent, antioxidant, UV ray absorber, antistatic agent, slip agent
and plasticizer.
[0072] When the PSA sheet is adhesive on one face, between the two
surfaces of the substrate film, the surface (back face) opposite
from the surface to be provided with a PSA layer is preferably made
smooth. The smooth surface may be the outer face of the PSA sheet;
and therefore, when the PSA sheet having the smooth surface is used
as, for instance, a decorative sheet or a surface protection sheet,
it may provide a better appearance (design). In a preferable
embodiment, from the standpoint of the adhesive properties and the
quality of appearance (design), the back face of the substrate film
may have an arithmetic mean surface roughness of 1 .mu.m or less
(e.g. about 0.05 .mu.m to 0.75 .mu.m, typically about 0.1 .mu.m to
0.5 .mu.m). In this description, the arithmetic mean surface
roughness can be measured using a general surface roughness gauge
(e.g. non-contact three-dimensional surface profilometer under
model name WYKO NT-3300 available from Veeco).
[0073] When an adhesively single-faced PSA sheet is wound to bring
the back face of the substrate film in contact with the PSA layer
surface, the back face (opposite from the surface to be provided
with a PSA layer) of the substrate film may be subjected as
necessary to release treatment with a silicone-based, long chain
alkyl-based, fluorine-based release agent or the like. The release
treatment brings about effects such as easier unwinding of the PSA
sheet wound in a roll. On the other hand, the PSA layer-side
surface of the substrate film may be subjected to a heretofore
known surface treatment such as corona discharge treatment and
primer coating for purposes such as increasing the tightness of
adhesion between the substrate and the PSA layer.
[0074] The thickness of the substrate film is not particularly
limited and can be suitably selected in accordance with the
purpose. In general, the substrate thickness is suitably 1 .mu.m or
larger (e.g. about 2 .mu.m to 500 .mu.m), or preferably about 5
.mu.m to 500 .mu.m (e.g. 10 .mu.m to 200 .mu.m, typically 15 .mu.m
to 100 .mu.m). It is advantageous to limit the thickness of the
substrate film in view of making the PSA sheet thinner, smaller,
lighter, resources-saving, and so on.
[0075] When the substrate film comprises a foam film, the thickness
of the foam-containing substrate (e.g. a foam substrate film) can
be suitably selected in accordance with the strength and
flexibility of the PSA sheet, intended purposes and so on. From the
standpoint of the impact-absorbing properties, etc., the
foam-containing substrate has a thickness of suitably 30 .mu.m or
larger, preferably 50 .mu.m or larger, or more preferably 60 .mu.m
or larger (e.g. 80 .mu.m or larger). From the standpoint of making
the PSA sheet thinner, smaller, lighter, resource-saving, and so
on, the thickness of the foam-containing substrate is usually
suitably 1 mm or smaller. The use of the foam film disclosed herein
can bring about excellent impact-absorbing capabilities even when
the thickness is about 350 .mu.m or smaller (more preferably 250
.mu.m or smaller, e.g. 180 .mu.m or smaller). The thickness of the
foam film (possibly a foam layer) in the foam-containing substrate
can also be preferably selected from the ranges exemplified as the
thickness of the aforementioned foam-containing substrate.
<PSA Layer>
[0076] The PSA layer disclosed herein typically refers to a layer
formed of a material (PSA) that exists as a soft solid (a
viscoelastic material) in a room temperature range and has a
property to adhere easily to adherend with some pressure applied.
As defined in "Adhesion: Fundamental and Practice" by C. A.
Dahlquist (McLaren & Sons (1966), P. 143), the PSA referred to
herein is generally a material that has a property satisfying
complex tensile modulus E*(1 Hz)<10.sup.7 dyne/cm.sup.2
(typically, a material that exhibits the described characteristics
at 25.degree. C.).
[0077] The PSA layer disclosed herein may comprise, as its base
polymer, one, two or more species among acrylic polymers,
rubber-based polymers, polyester-based polymers, urethane-based
polymers, polyether-based polymers, silicone-based polymers,
polyamide -based polymers, fluorine-based polymers, etc. From the
standpoint of the adhesive properties (e.g. peel strength,
repulsion resistance), molecular design, etc., acrylic polymers can
be preferably used. In other words, the PSA layer is preferably an
acrylic PSA layer that comprises an acrylic polymer as its base
polymer. The "base polymer" of a PSA refers to the primary
component (typically, a component accounting for more than 50% by
weight) among polymers in the PSA.
[0078] As the acrylic polymer, for example, a polymer of a
monomeric starting material comprising an alkyl (meth)acrylate as a
primary monomer and possibly comprising a secondary monomer
copolymerizable with the primary monomer is preferable. The primary
monomer herein refers to a component that accounts for higher than
50% by weight of the monomer composition in the monomeric starting
material.
[0079] As the alkyl (meth)acrylate, for instance, a compound
represented by the following formula (1) can preferably be
used:
CH.sub.2.dbd.C(R.sup.1)COOR.sup.2 (1)
[0080] Herein, R.sup.1 in the formula (1) is a hydrogen atom or a
methyl group. R.sup.2 is a acyclic alkyl group having 1 to 20
carbon atoms (hereinafter, such a numerical range of carbon atoms
may be indicated as "C.sub.1-20"). From the standpoint of the
storage elastic modulus of the PSA, etc., an alkyl (meth)acrylate
having a C.sub.1-12 (e.g. C.sub.2-10, typically C.sub.4-8) acyclic
alkyl group for R.sup.2 is preferable. For the alkyl (meth)acrylate
having a C.sub.1-20 acyclic alkyl group for R.sup.2, solely one
species or a combination of two or more species can be used.
Preferable alkyl (meth)acrylates include n-butyl acrylate and
2-ethylhexyl acrylate.
[0081] The secondary monomer copolymerizable with the alkyl
(meth)acrylate as the primary monomer may be useful in introducing
crosslinking points into the acrylic polymer and increasing the
cohesive strength of the acrylic polymer. As the secondary monomer,
one, two or more species can be used among functional
group-containing monomers such as carboxy group-containing
monomers, hydroxy group-containing monomers, acid anhydride
group-containing monomers, amide group-containing monomers, amino
group-containing monomers, and monomers having nitrogen-containing
rings. The secondary monomer may also be a vinyl ester-based
monomer such as vinyl acetate, an aromatic vinyl compound such as
styrene, a sulfonate group-containing monomer, a phosphate
group-containing monomer, etc. For instance, from the standpoint of
increasing the cohesive strength, an acrylic polymer in which a
carboxy group-containing monomer or a hydroxy group-containing
monomer is copolymerized as the secondary monomer is preferable.
Preferable examples of the carboxy group-containing monomer include
acrylic acid and methacrylic acid. Preferable examples of the
hydroxy group-containing monomer include 2-hydroxyethyl acrylate
and 4-hydroxybutyl acrylate.
[0082] The amount of the secondary monomer is suitably 0.5% by
weight of all monomers in the acrylic polymer, or preferably 1% by
weight or more. The amount of the secondary monomer is suitably 30%
by weight or less of all the monomers, or preferably 10% by weight
or less (e.g. 5% by weight or less). When a carboxy
group-containing monomer is copolymerized in the acrylic polymer,
from the standpoint of combining adhesive strength and cohesive
strength, the carboxy group-containing monomer content is
preferably within a range of about 0.1% to 10% by weight (e.g. 0.2%
to 8% by weight, typically 0.5% to 5% by weight) of all the
monomers used in the synthesis of the acrylic polymer. When a
hydroxy group-containing monomer is copolymerized in the acrylic
polymer, from the standpoint of combining adhesive strength and
cohesive strength, the hydroxy group-containing monomer content is
preferably within a range of about 0.001% to 10% by weight (e.g.
0.01% to 5%, typically 0.02% to 2% by weight) of all the monomers
used in the synthesis of the acrylic polymer. When a vinyl
ester-based monomer such as vinyl acetate is copolymerized as the
secondary monomer, the vinyl ester-based monomer content is
preferably about 30% by weight or less (typically 0.01% to 30% by
weight, e.g. 0.1% to 10% by weight) of all the monomers used in the
synthesis of the acrylic polymer.
[0083] The method for obtaining the acrylic polymer is not
particularly limited. Various polymerization methods known as
procedures for the synthesis of acrylic polymer can be suitably
employed, such as solution polymerization, emulsion polymerization,
bulk polymerization and suspension polymerization. It is also
possible to employ active energy ray radiation polymerization which
involves irradiation of UV etc. For instance, a desirable acrylic
polymer can be obtained by dissolving or dispersing a monomer
mixture in a suitable polymerization solvent (toluene, ethyl
acetate, water, etc.) and carrying out polymerization using a
polymerization initiator such as an azo-based polymerization
initiator and a peroxide-based initiator.
[0084] From the standpoint of combining adhesive strength and
cohesive strength in a well-balanced way, the acrylic polymer
disclosed herein preferably has a weight average molecular weight
(Mw) in a range of 10.times.10.sup.4 or higher, but
100.times.10.sup.4 or lower. An acrylic polymer whose Mw is
20.times.10.sup.4 or higher, but 70.times.10.sup.4 or lower (e.g.
30.times.10.sup.4 or higher, but 50.times.10.sup.4 or lower) may
bring about better results. In this description, Mw refers to the
value based on standard polystyrene obtained by GPC (gas permeation
chromatography).
[0085] From the standpoint of increasing the cohesive strength, the
PSA composition preferably comprises a crosslinking agent. The type
of crosslinking agent is not particularly limited; one, two or more
species can be suitably selected and used among heretofore known
crosslinking agents. Preferable examples of the crosslinking agent
include isocyanate-based crosslinking agents and epoxy-based
crosslinking agents. The amount of the crosslinking agent used is
not particularly limited. For instance, to 100 parts by weight of
the acrylic polymer, it can be selected from a range of about 10
parts by weight or less (e.g. about 0.005 part to 10 parts by
weight, preferably about 0.01 part to 5 parts by weight).
[0086] The PSA layer disclosed herein may have a composition
comprising a tackifier. The tackifier is not particularly limited.
Various tackifier resins can be used, such as rosin-based tackifier
resin, terpene-based tackifier resin, hydrocarbon-based tackifier
resin, epoxy-based tackifier resin, polyamide-based tackifier
resin, elastomer-based tackifier resin, phenolic tackifier resin,
and ketone-based tackifier resin. These tackifier resins can be
used solely as one species or in a combination of two or more
species.
[0087] The tackifier resin preferably has a softening point
(temperature of softening) of about 60.degree. C. or higher
(preferably about 80.degree. C. or higher, typically 100.degree. C.
or higher). By this, the PSA sheet can be obtained with higher
adhesive strength. The upper limit of the softening point of the
tackifier resin is not particularly limited; it can be about
180.degree. C. or lower (e.g. about 140.degree. C. or lower). The
softening point of tackifier resin referred to herein is defined as
the value measured by the softening point test method (ring and
ball method) specified either in JIS K5902:2006 or in JIS
K2207:2006.
[0088] The amount of tackifier resin can be suitably selected in
accordance with the target adhesive properties (adhesive strength,
etc.). For instance, by solid content, it is preferable to use a
tackifier at a ratio of about 10 parts to 100 parts by weight (more
preferably 20 parts to 80 parts by weight, or yet more preferably
30 parts to 60 parts by weight) relative to 100 parts by weight of
the base polymer (preferably an acrylic polymer).
[0089] The PSA composition may comprise, as necessary, various
additives generally known in the field of PSA compositions, such as
leveling agent, crosslinking accelerator, plasticizer, softening
agent, filler, anti-static agent, anti-aging agent, UV-absorbing
agent, antioxidant and photo-stabilizing agent. With respect to
these various additives, heretofore known species can be used by
typical methods.
[0090] The PSA layer disclosed herein may be formed from aqueous,
solvent-based, hot-melt, and active energy ray-curable types of PSA
composition, etc. The aqueous PSA composition refers to a PSA
composition in a form comprising PSA (PSA layer-forming components)
in a solvent whose primary component is water (in an aqueous
solvent), typically including a so-called water-dispersed PSA
composition (a composition in a form where at least part of the PSA
is dispersed in water). The solvent-based PSA composition refers to
a PSA composition in a form comprising PSA in an organic solvent.
From the standpoint of reducing environmental stress, an aqueous
PSA composition is preferable. From the standpoint of the adhesive
properties, etc., a solvent-based PSA composition is preferably
used.
[0091] The PSA layer disclosed herein can be formed by a heretofore
known method. For instance, a direct method can be preferably
employed, in which a PSA composition is directly provided
(typically applied) to a substrate and allowed to dry to form a PSA
layer. Alternatively, a transfer method can also be used, in which
a PSA composition is provided to a releasable surface (a release
face) and allowed to dry to form a PSA layer on the surface and the
PSA layer is transferred to a substrate. As the release face, a
release liner surface, the back face of a substrate treated with a
release agent, and the like can be used.
[0092] The PSA composition can be applied using a known or commonly
used coater, such as a gravure roll coater, reverse roll coater,
kiss roll coater, dip roll coater, die coater, bar coater, knife
coater, and spray coater. Alternatively, the PSA composition can be
applied by immersion, curtain coating, etc.
[0093] From the standpoint of facilitating the crosslinking
reaction, increasing the productivity, etc., the PSA composition is
preferably heated to dry. The drying temperature can be, for
instance, about 40.degree. C. to 150.degree. C., or usually
preferably about 60.degree. C. to 130.degree. C. After dried, the
PSA composition can be further allowed to age for adjustment of
migration of the components in the PSA layer, for the progress of
the crosslinking reaction, for releasing the distortion possibly
present in the substrate and PSA layer, etc.
[0094] The thickness of the PSA layer disclosed herein is not
particularly limited; it can be suitably selected in accordance
with the purpose. Usually, from the standpoint of the productivity
such as the drying efficiency, adhesive properties, etc., it is
suitably about 0.5 .mu.m to 200 .mu.m, or preferably about 2 .mu.m
to 200 .mu.m (e.g. 5 .mu.m to 100 .mu.m, typically 10 .mu.m to 50
.mu.m). It is advantageous to limit the thickness of the PSA layer
in view of making the PSA sheet thinner, smaller, lighter,
resource-saving, and so on. When the art disclosed herein is
implemented in an embodiment of an adhesively double-faced sheet
having a PSA layer on each face of a substrate, the thicknesses of
the respective PSA layers can be the same or different.
<Coating Layer>
[0095] The coating layer partially covering the PSA layer surface
is not particularly limited as long as it can provide air release
properties. A favorable example of the coating layer material is a
resin material. From the standpoint of the appearance, the coating
layer is preferably formed from a transparent or semi-transparent
resin material.
[0096] Examples of the resin material form which the coating layer
can be formed include a polyurethane-based resin, a phenolic resin,
an epoxy-based resin, a polyamide-based resin, a urea
melamine-based resin, a silicone-based resin, a polysilazane-based
resin, a fluororesin, a phenoxy resin, a methacrylic resin, an
acrylic resin, an acrylic urethane-based resin, an acrylic
styrene-based resin, a polyarylate resin, a polyester-based resin,
a polyolefinic resin, a polystyrene-based resin, polyvinyl
chloride, a vinyl chloride/vinyl acetate copolymer, polyvinyl
acetate, polyvinylidene chloride, polycarbonate, a cellulose, and a
polyacetal. The resin can be one, two or more species of resin
selected from various types of resins including a heat-curable
resin, a UV-curable resin, an electron beam-curable resin, and a
two-component resin that is curable upon mixing
[0097] The coating layer disclosed herein may comprise as necessary
various additives such as fillers, anti-aging agent, antioxidant,
UV absorber, crosslinking agent, slip agent, colorant (pigment,
dye, etc.), antistatic agent, viscosity-adjusting agent
(thixotropic agent, thickening agent, etc.), and film-forming
aid.
[0098] The coating layer is preferably non-adhesive or weakly
adhesive. This preferably brings about good air release properties.
Here, that the coating layer is non-adhesive or weakly adhesive
means that the coating layer has a 180.degree. peel strength less
than 3 N/25 mm (typically less than 1 N/25 mm, including
unmeasurably low adhesive strength). In particular, the 180.degree.
peel strength of the coating layer is determined by the following
method: The PSA sheet having a coating layer over the entire PSA
layer surface is cut to a 25 mm wide by 100 mm long size to obtain
a measurement sample; in an environment at 23.degree. C., 50% RH,
the measurement sample is press-bonded over its coating layer
surface to the surface of a stainless steel plate (SUS304BA plate)
with a 2 kg roller moved back and forth once. If it does not
adhere, it is considered non-adhesive here. The resultant is left
standing in the same environment for 30 minutes. Using a universal
tensile/compression tester, based on JIS Z 0237:2000, it is then
measured for peel strength (N/20 mm) at a tensile speed of 300
mm/min at a peel angle of 180.degree..
[0099] The method for placing the coating layer on the PSA layer
surface is not particularly limited. For instance, a method as
described next can be employed. In particular, a coating
layer-forming composition is prepared as necessary by dissolution
or dispersion in a suitable solvent. Subsequently, by employing a
suitable method among various known or commonly-used printing
methods, the composition is provided to a releasable surface of a
releasable support (or a coating layer-transferring film, typically
a release liner) and allowed to cure. The releasable support
surface on which the coating layer is formed is brought into
contact with the PSA layer surface to transfer the coating layer
onto the PSA layer surface. The coating layer is thus partially
placed on the PSA layer surface. For instance, a desirable coating
layer pattern such as a lattice pattern can be preferably formed by
employing a method such as offset printing, silk screen printing,
letterpress printing, flexographic printing, gravure printing, and
inkjet printing. From the standpoint of the air release properties,
gravure printing is more preferable. Alternatively, the coating
layer-forming composition can be directly provided to the PSA layer
surface and allowed to cure by means of, for instance, UV curing to
place a coating layer partially on the PSA layer surface.
[0100] The thickness of the coating layer can be designed to obtain
desirable air release properties and is not particularly limited.
From the standpoint of combining air release properties and
appearance, it is preferably up to about a half (e.g. up to
one-third, typically up to one-fifth) the thickness of the PSA
layer. In particular, from the standpoint of the air release
properties, productivity, etc., the thickness of the coating layer
is preferably 0.1 .mu.m or greater (e.g. 0.5 .mu.m or greater,
typically 1 .mu.m or greater). From the standpoint of the
appearance, the coating layer has a thickness of preferably 10
.mu.m or less, or more preferably 5 .mu.m or less (e.g. 3 .mu.m or
less, typically 2 .mu.m or less). The thickness of the coating
layer can be obtained by TEM (transmission electron microscopy)
analysis of a cross section of the PSA sheet.
[0101] The art disclosed herein is preferably implemented in an
embodiment of a release liner-backed PSA sheet that has a release
liner protecting the adhesive surface of the PSA sheet. As the
release liner, any conventional release paper or the like can be
used without any particular limitations. For example, a release
liner having a release layer on a surface of a liner substrate such
as resin film (PET, etc.) and paper; a release liner formed from a
poorly-adhesive material such as a fluorine-based polymer
(polytetrafluoroethylene, etc.) or a polyolefin-based resin (PE,
PP, etc.); or the like can be used. The release layer can be
formed, for instance, by subjecting the liner substrate to a
surface treatment with a release agent such as a silicone-based, a
long-chain alkyl-based, a fluorine-based, a molybdenum
disulfide-based release agent or the like.
[0102] In a preferable embodiment, the release surface (on the side
that makes contact with the PSA sheet's adhesive surface) of the
release liner (release film) is formed smooth. A good coating layer
transfer can be obtained when a coating layer is partially formed
on the releasable surface of such a release liner and the release
liner surface with the coating layer partially formed thereon is
brought into contact with a PSA layer to transfer the coating layer
onto the PSA layer surface (in this case, the release liner also
serves as the coating layer-transferring film (release film)) The
smooth texture of the surface of the release liner is transferred
onto the PSA layer surface, whereby the adhesive properties tend to
increase as well. Similar effects can be obtained by partially
forming a coating layer on the releasable surface of such a release
liner and further forming a PSA layer on the releasable surface
with the coating layer formed thereon so as to cover the coating
layer. In this case, the PSA layer formed is transferred to a
surface of a substrate film. For these reasons, it is preferable
that the release surface of the release liner has an arithmetic
average surface roughness of 1 .mu.m or less (e.g. about 0.05 .mu.m
to 0.75 .mu.m, typically about 0.1 .mu.m to 0.5 .mu.m).
[0103] As shown in FIG. 5, the release liner used in fabricating
the PSA sheet disclosed herein may be a coating layer-bearing
release liner 110 that comprises a releasable support 20 having a
releasable surface 120A. The releasable support 120 may have a
release layer at least on one face of a liner substrate, or it can
be a support formed from a low-adhesive material. The releasable
surface 120A of the releasable support 120 is provided with a
coating layer 30 that can be transferred to a PSA sheet. In other
words, the coating layer 30 is arranged on the releasable surface
120A in a state that it can be separated by an adhesive strength of
PSA, etc. With the use of such release liner 110 having a
transferrable coating layer 30 on the surface, the PSA sheet
disclosed herein is preferably fabricated. The features (shape,
arrangement, relative position, size, pattern, etc.) of the coating
layer provided to the releasable surface of the releasable support
are basically the same as the features of the coating layer
partially covering the PSA layer surface of the PSA sheet described
earlier. Accordingly, the constructions of the coating
layer-bearing area and the coating layer-free area as well as their
relation (including the % surface area of the coating layer-free
area) on the releasable surface are also basically the same as the
constructions of the coating layer-bearing area and the coating
layer-free area as well as their relation (including the % surface
area of the coating layer-free area) on the PSA layer surface.
Thus, details are omitted.
[0104] The thickness (overall thickness) of the release liner is
not particularly limited. From the standpoint of the ease of
removal, handling properties, strength, etc., it is preferably
about 10 .mu.m to 500 .mu.m (e.g. 15 .mu.m to 100 .mu.m).
[0105] As described above, in applying the PSA sheet disclosed
herein to an adherend, the sort of bubble formation can be
efficiently prevented at the interface with the adherend. Thus, in
either application method between application by hand (manual
application) and application with an automated applicator or the
like (automated application), the ease of application will improve.
For example, when applied by manual application, the degree of
dependence on skills of individuals can be reduced, thereby
bringing about advantages such as increases in efficiency and
quality of the application and their stabilization. When applied by
automated application, failures during application such as trapping
of bubbles and reapplication work can be reduced. Accordingly,
either by manual application or by automated application, it is
possible to bring about increases in application efficiency and
quality, stabilization of the quality and so on, thereby increasing
the productivity and quality of products made with the use of the
PSA sheet as well. The art disclosed herein can bring about more
uniform application; and therefore, it is particularly favorable as
a PSA sheet that is applied with an automated applicator.
[0106] Between the PSA sheet and the adherend, the sort of bubble
formation may occur, not just during the application, but also
after the application as the time passes. In typical, after the PSA
sheet is applied, upon storage and use in an environment at a
relatively high temperature (e.g. 35.degree. C. or higher), etc.,
aforementioned bubbles and the like may form between the PSA sheet
and the adherend, causing degradation of the appearance. For
instance, such high temperature conditions are likely to be reached
in factories and outdoor in summer, inside electronics, etc.
According to the art disclosed herein, even when used for
applications exposed to such high temperature environments, the
sort of bubble formation can be prevented.
[0107] With the benefit of the features described above, the PSA
sheet disclosed herein can be preferably used for application to
surfaces of various articles. In a preferable embodiment, it can be
used as decorative sheets and surface protection sheets of various
kinds, a fixing sheet for printing plates of flexographic printing
and the like, a light-blocking sheet, and so on. For instance, it
is preferable as a decorative sheet (typically a paint-substitute
sheet) applied to vehicle exteriors, house building materials, and
so on. It is also preferable for use inside electronics such as TVs
as a cover sheet used to increase the smoothness of the outer face
of a chassis or to cover uneven places such as of screw holes in
surfaces of various parts. The use of such a cover sheet can
decrease unevenness of the appearance of the adherend's outer
surface and make the dimensional precision uniform. It can also be
preferably used as an exterior sheet for battery packs for which
the appearance is important.
[0108] Even when made thin, with the PSA sheet disclosed herein, it
is possible to prevent degradation of appearance quality after its
application while maintaining good adhesive properties. Thus, it
can be preferably used for applications (e.g. for mobile
electronics) where a thinner build and a lighter weight are
required desirably with saving of resources. In particular, it can
be preferably used as a surface protection sheet for mobile
electronics (e.g. mobile phones, smartphones, tablet PCs, notebook
PCs); for bonding/fixing applications in liquid crystal displays of
these mobile electronics; for fixing protection panels (lenses) to
protect the displays of these mobile electronics; for fixing key
modules of mobile phones; and for like purposes. When used for the
mobile electronics, the PSA sheet may have a shape in accordance
with the purpose and so on, such as a frame shape and a ribbon
shape (a strip shape). In this description, to be "mobile," it is
not sufficient that it can be just carried, but it needs to be
mobile enough for an individual (an average adult) to be able to
carry it by hand relatively easily.
[0109] Matters disclosed by this description include the following:
[0110] (1) A PSA sheet comprising a substrate film and a PSA layer
provided to at least one face of the substrate film, wherein
[0111] the PSA sheet further comprises a coating layer that
partially covers the PSA layer surface, whereby the PSA layer
surface has a coating layer-bearing area and a coating layer-free
area,
[0112] the coating layer-free area occupies 70% or more of the PSA
layer surface,
[0113] in a top view of the PSA layer surface, the coating
layer-bearing area has a linearly extending part that runs from one
edge to another edge of the PSA layer,
[0114] the linearly extending part has a width in a range of 0.1 mm
to 2 mm [0115] (2) The PSA sheet according to (1) above, wherein
the PSA layer surface is provided with a plurality of the linearly
extending parts among which the linearly extending parts in a group
are placed at intervals arranged in the width direction, whereby
the coating layer-bearing area has a stripe pattern [0116] (3) The
PSA sheet according to (2) above, wherein the coating layer-bearing
area comprises a first stripe pattern and a second stripe pattern
that is placed to intersect the first stripe pattern, whereby the
coating layer-bearing area has a lattice pattern. [0117] (4) The
PSA sheet according to (2) or (3) above, wherein, in the coating
layer-bearing area, the intervals between the plurality of the
linearly extending parts forming the stripe pattern are in a range
of 1.0 mm to 10 mm. [0118] (5) The PSA sheet according to any one
of (1) to (4) above, having an adhesive face on which the coating
layer is partially placed, the adhesive face exhibiting a
180.degree. peel strength after 24-hour adhesion of 13 N/25 mm or
greater. [0119] (6) The PSA sheet according to any one of (1) to
(5) above, wherein the PSA layer comprises an acrylic polymer that
accounts for more than 50% (by weight) of all polymers in the PSA
layer, with the acrylic polymer comprising, as a monomer, more than
50% (by weight) alkyl (meth)acrylate represented by a formula
(1):
[0119] CH.sub.2.dbd.C(R.sup.1)COOR.sup.2 (1)
(in the formula (1), R.sup.1 is a hydrogen atom or a methyl group;
R.sup.2 is an acyclic alkyl group with 1 to 20 carbon atoms).
[0120] (7) The PSA sheet according to (6) above, wherein the alkyl
(meth)acrylate is n-butyl acrylate and/or 2-ethylhexyl acrylate.
[0121] (8) The PSA sheet according to (6) or (7) above, wherein the
acrylic polymer is an acrylic polymer in which a carboxy
group-containing monomer and/or a hydroxy group-containing monomer
is copolymerized as secondary monomer(s). [0122] (9) The PSA sheet
according to any one of (6) to (8) above, wherein the acrylic
polymer is an acrylic polymer in which at least one species of
secondary monomer selected from the group consisting of acrylic
acid, methacrylic acid, 2-hydroxyethyl acrylate and 4-hydroxybutyl
acrylate is copolymerized. [0123] (10) The PSA sheet according to
any one of (6) to (9) above, wherein a carboxy group-containing
monomer is copolymerized in the acrylic polymer, the
copolymerization ratio of the carboxy group-containing monomer
being 0.1% to 10% (by weight) to all the monomers used in
synthesizing the acrylic polymer. [0124] (11) The PSA sheet
according to any one of (6) to (10) above, wherein a hydroxy
group-containing monomer is copolymerized in the acrylic polymer,
the copolymerization ratio of the hydroxy group-containing monomer
being 0.001% to 10% (by weight) to all the monomers used in
synthesizing the acrylic polymer. [0125] (12) The PSA sheet
according to any one of (6) to (11) above, wherein the PSA layer
comprises an isocyanate-based crosslinking agent and/or an
epoxy-based crosslinking agent. [0126] (13) The PSA sheet according
to any one of (6) to (12) above, wherein the PSA layer comprises a
tackifier resin with a softening point of 100.degree. C. to
140.degree. C. in an amount of 30 parts to 60 parts by weight to
100 parts by weight of the acrylic polymer, the tackifier resin
being at least one species selected from the group consisting of a
rosin-based tackifier resin, a terpene-based tackifier resin and a
hydrocarbon-based tackifier resin. [0127] (14) The PSA sheet
according to any one of (1) to (13) above, wherein the coating
layer comprises a transparent resin. [0128] (15) The PSA sheet
according to any one of (1) to (14) above, wherein the coating
layer comprises at least one species of resins selected from the
group consisting of a polyurethane-based resin, a phenolic resin,
an epoxy-based resin, a polyamide-based resin, a urea
melamine-based resin, a silicone-based resin, a polysilazane-based
resin, a fluororesin, a phenoxy resin, a methacrylic resin, an
acrylic resin, an acrylic urethane-based resin, an acrylic
styrene-based resin, a polyarylate resin, a polyester-based resin,
a polyolefinic resin, a polystyrene-based resin, polyvinyl
chloride, a vinyl chloride/vinyl acetate copolymer, polyvinyl
acetate, polyvinylidene chloride, polycarbonate, a cellulose, and a
polyacetal. [0129] (16) The PSA sheet according to any one of (1)
to (15) above, wherein the coating layer is of a polyurethane-based
resin. [0130] (17) The PSA sheet according to any one of (1) to
(16) above, wherein the coating layer is of a two-component
polyurethane-based resin that is curable upon mixing [0131] (18)
The PSA sheet according to any one of (1) to (17) above, wherein
the substrate film is a polyolefinic resin film, a polyester-based
resin film, a vinyl chloride-based resin film, a vinyl
acetate-based resin film, a polyimide-based resin film, a
polyamide-based resin film, a fluororesin film, or a cellophane
film. [0132] (19) The PSA sheet according to any one of (1) to (18)
above, wherein the substrate film is a polyester film. [0133] (20)
The PSA sheet according to any one of (1) to (19) above, wherein
the substrate film is a polyethylene terephthalate film. [0134]
(21) The PSA sheet according to any one of (1) to (20) above,
wherein the substrate film exhibits a total light transmittance of
80% or higher. [0135] (22) The PSA sheet according to any one of
(1) to (17) above, wherein the substrate film is a foam film.
[0136] (23) The PSA sheet according to (22) above, wherein the foam
film has a mean pore diameter of 10 .mu.m to 200 .mu.m and a
density of 0.01 g/cm.sup.3 to 0.7 g/cm.sup.3. [0137] (24) The PSA
sheet according to (22) or (23) above, wherein the foam film is an
acrylic resin foam or a polyolefmic resin foam. [0138] (25) A
release liner-backed PSA sheet comprising the PSA sheet according
to any one of (1) to (24) above and a release liner that protects
the adhesive face of the PSA sheet, wherein the release liner has a
smooth surface on the adhesive face side. [0139] (26) A release
liner for a PSA sheet, the release liner comprising a releasable
support having at least one releasable face, wherein
[0140] the releasable face of the releasable support is provided
with a coating layer disclosed herein that can be transferred onto
a PSA sheet, whereby the releasable surface has a coating
layer-bearing area and a coating layer-free area,
[0141] the coating layer-free area occupies 70% or more of the PSA
layer surface,
[0142] the coating layer has a linearly extending part that runs
from one edge to another edge of the releasable surface, and
[0143] the linearly extending part has a width in a range of 0.1 mm
to 2 mm
[0144] Several Examples related to the present invention are
described below, but the present invention is not intended to be
limited to these Examples. In the description below, "parts" and
"%" are by weight unless otherwise noted.
<<Experiment 1>>
EXAMPLE 1A
(Preparation of PSA Composition)
[0145] In a reaction vessel equipped with a stirrer, thermometer,
nitrogen inlet, reflux condenser and addition funnel, were placed
70 parts of n-butyl acrylate, 30 parts of 2-ethylhexyl acrylate, 3
parts of acrylic acid, 0.05 part of 4-hydroxybutyl acrylate, 0.08
part of azobisisobutyronitrile as polymerization initiator and
toluene as the polymerization solvent. Solution polymerization was
carried out at 60.degree. C. for 6 hours to obtain an acrylic
polymer solution in toluene (viscosity 28 Pas, 40% non-volatiles).
The resulting acrylic polymer had a Mw of about
44.times.10.sup.4.
[0146] To 100 parts of the acrylic polymer in the toluene solution,
was admixed 30 parts of a polymerized rosin pentaerythritol ester
(trade name PENSEL D125 available from Arakawa Chemical Industries,
Ltd.; softening point 125.degree. C.) followed by 3 parts of an
isocyanate-based crosslinking agent (trade name CORONATE L
available from Nippon Polyurethane Industry Co., Ltd.) to prepare
an acrylic PSA composition.
(Formation of Coating Layer)
[0147] A coating layer-forming material (urethane-based,
two-component ink (curable when mixed)) was gravure-printed on the
releasable face of 75 .mu.m thick release film (trade name FMN-75WD
(C1CA1) available from Fujiko Co., Ltd.) to form a coating layer
(coating thickness 1.5 .mu.m, transparent) in a lattice
pattern.
(Fabrication of PSA Sheets)
[0148] A 75 .mu.m thick PET substrate film (trade name LUMIRROR
available from Toray Industries, Inc.) was obtained. Onto the
corona discharge-treated face of the PET substrate, the PSA
composition was applied to a thickness of 15 .mu.m (after dried)
and allowed to dry at 100.degree. C. for 3 minutes to form a PSA
layer on one face of the PET substrate film.
[0149] The coating layer-bearing release film obtained above was
brought into contact with the surface of the PSA layer to transfer
the coating layer onto the PSA layer surface. The release film was
used as it was to protect the PSA layer surface. A PSA sheet
according to this Example was thus fabricated. The PSA layer
surface of this PSA sheet had a lattice pattern formed of the
coating layer as shown in FIG. 1, with the long parts of the
coating layer-bearing area having a width (line width) of 2 mm and
intervals of 8 mm
EXAMPLE 1B
[0150] The intervals between the long parts of the coating
layer-bearing area were changed to 13 mm. Otherwise in the same
manner as Example 1A, a PSA sheet according to this Example was
fabricated.
EXAMPLE 1C
[0151] Without a coating layer, but otherwise in the same manner as
Example 1A, a PSA sheet according to this Example was
fabricated.
[180.degree. Peel Strength]
[0152] With respect to the PSA sheet according to each Example, the
to-SUS 180.degree. peel strength (adhesive strength) was tested. In
particular, the PSA sheet was cut to a 25 mm by 100 mm long size to
obtain a measurement sample. In an environment at 23.degree. C.,
50% RH, the adhesive surface of the measurement sample was
press-bonded to the surface of a stainless steel plate (SUS 304BA
plate) with a 2 kg roller moved back and forth once. This was left
standing in the same environment for 30 minutes, 24 hours, or 72
hours. Subsequently, using a universal tensile/compression tester,
based on JIS Z 0237:2000, the peel strength (N/25 mm) was
determined at a tensile speed of 300 mm/min at a peel angle of
180.degree.. Three measurements were carried out for each Example
under each condition (standing time after press-bonded) and their
average value was used. With the 180.degree. peel strength value of
Example 1C (with the coating layer-free area occupying 100% surface
area) being 100%, the 180.degree. peel strength values of Examples
1A and 1B were shown as the relative values (%) and the decreases
in adhesive strength were evaluated in association with the reduced
surface areas of their coating layer-bearing areas. The results are
shown in Table 1 with the % surface area of the coating
layer-bearing areas.
TABLE-US-00001 TABLE 1 Ex. 1A Ex. 1B Ex. 1C % Surface area of
coating layer-free area 64 75 100 Adhesive strength After 30 min
(initial) (N/25 mm) 11.4 13.5 20.9 (%) 55 65 100 After 24 hours
(N/25 mm) 12.0 17.2 22.0 (%) 55 78 100 After 72 hours (N/25 mm)
13.4 17.8 23.9 (%) 56 74 100
[0153] As shown in Table 1, with increasing surface area of the
coating layer and decreasing exposed surface area of the PSA layer,
the initial adhesive strength (at 30 minutes after adhered to the
adherend) decreased in a proportional manner. On the other hand,
with respect to the long-term adhesive strength (at 24 hours or 72
hours after adhered to the adherend), in Example 1A where the
coating layer-free area occupied 64% surface area, the adhesive
strength did not increase with aging, impairing the proportional
relationship of the initial adhesive strength and showing a value
that was significantly lower than the value expected from the
results of Examples 1B and 1C in which the coating layer-free areas
occupied 75% and 100% surface areas, respectively. These results
indicate that in an embodiment where the coating layer is partially
placed on the PSA layer surface, to obtain high long-term adhesive
strength, the coating layer-free area needs to occupy 70% or more
surface area.
<<Experiment 2>>
EXAMPLES 2A-2J
[0154] The width (mm) and intervals (mm) of long parts of the
coating layer-bearing area were set to the values shown in Table 2.
By the same method as for Example 1A, a PSA sheet according to each
Example was fabricated. Table 2 shows the 24-hour adhesion strength
(N/25 mm) determined for each Example. The measurement method is as
described above. It is noted that Examples 2A, 2I and 2J had the
same constructions as Examples 1B, 1A and 1C.
[Air Release Properties]
[0155] With respect to the PSA sheet according to each Example, the
degree of elimination of air upon application to the smooth surface
of a transparent adherend was visually inspected and graded into
the four grades shown below. The results are shown in Table 2.
[0156] A: Excellent air release properties were shown with no
bubbles left between the PSA sheet and the adherend. [0157] B:
Bubbles between the PSA sheet and the adherend were eliminated
relatively quickly, leaving no bubbles. [0158] C: Bubbles between
the PSA sheet and the adherend were eliminated relatively slowly,
leaving no bubbles. [0159] D: Bubbles were left between the PSA
sheet and the adherend.
TABLE-US-00002 [0159] TABLE 2 Ex. 2A Ex. 2B Ex. 2C Ex. 2D Ex. 2E
Ex. 2F Ex. 2G Ex. 2H Ex. 2I Ex. 2J Width (mm) 2 1.5 1.0 0.5 0.3 0.2
0.2 0.1 2 0 Interval (mm) 13 8.5 9.0 9.5 2.7 2.8 1.8 1.4 8 0 %
Surface area of 75 72 81 90 81 87 81 87 64 100 coating layer- free
area 24-h Adhesion 17.2 14.5 16.3 19.3 14.7 18.2 16.0 18.1 12.0
22.0 strength (N/25 mm) Air release properties A A A A A B B C A
D
[0160] As shown in Table 2, the PSA sheets according to Examples 2A
to 2H (each with the coating layer-free area occupying 70% or more
of the PSA layer surface and the long parts of the coating
layer-bearing area having a width in the range of 0.1 mm to 2 mm)
showed high long-term adhesive strength (24-hour adhesion strength)
and good air release properties at the interfaces between the PSA
sheets and the adherend. With respect to the PSA sheets according
to Examples 2C to 2H, after adhered to the adherend, their coating
layers were hardly visible when seen from the adherend side and
from the PSA sheet side, making great appearances. The PSA sheets
according to Examples 2C to 2G had excellent appearances and also
combined well-balanced high long-term adhesive strength and air
release properties. Among them, Examples 2E, 2F and 2G had
particularly great appearances. On the other hand, Example 2I with
the coating layer-free area occupying less than 70% surface area
showed lower long-term adhesive strength as compared to Examples 2A
to 2H. In Example 2J with no coating layer, bubbles were left
between the PSA sheet and the adherend.
[0161] Although specific embodiments of the present invention have
been described in detail above, these are merely for illustrations
and do not limit the scope of claims. The art according to the
claims includes various modifications and changes made to the
specific embodiments illustrated above.
REFERENCE SIGNS LIST
[0162] 1, 2 PSA sheets [0163] 1A adhesive surface [0164] 10
substrate film [0165] 20, 21, 22 PSA layers [0166] 20A PSA layer
surface [0167] 30 coating layer [0168] 40, 41, 42 release liners
[0169] 50 coating layer-bearing area [0170] 51 coating layer-free
area [0171] 60 coating layer pattern (lattice pattern) [0172] 70
first stripe pattern [0173] 75A, 75B, 75C long parts (linearly
extending parts) [0174] 80 second stripe pattern [0175] 85A, 85B,
85C long parts (linearly extending parts) [0176] 110 coating
layer-bearing release liner [0177] 120 releasable support [0178]
120A releasable face
* * * * *