U.S. patent application number 15/529624 was filed with the patent office on 2017-09-14 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 | 20170260425 15/529624 |
Document ID | / |
Family ID | 56123122 |
Filed Date | 2017-09-14 |
United States Patent
Application |
20170260425 |
Kind Code |
A1 |
YAMAMOTO; Shuuhei ; et
al. |
September 14, 2017 |
PRESSURE-SENSITIVE ADHESIVE SHEET
Abstract
Provided is a PSA sheet with which good air release properties
can be obtained while whose quality can be further enhanced. 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 further comprises a coating layer partially covering the
PSA layer surface. The PSA sheet's adhesive is formed of the PSA
layer and the coating layer. The coating layer has a linearly
extending part running from one edge to another edge of the
adhesive face. The linearly extending part has a first face forming
the PSA sheet's adhesive face and a second face located on the PSA
layer side relative to the first face. The second face of the
linearly extending part forms an overall gently curved line in a
cross section perpendicularly intersecting the length direction of
the linearly extending part.
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.: |
15/529624 |
Filed: |
November 27, 2015 |
PCT Filed: |
November 27, 2015 |
PCT NO: |
PCT/JP2015/083444 |
371 Date: |
May 25, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 29/007 20130101;
B32B 2255/00 20130101; B32B 2307/538 20130101; B32B 15/12 20130101;
C09J 7/22 20180101; C09J 2301/206 20200801; C09J 2301/21 20200801;
B32B 7/12 20130101; B32B 2255/102 20130101; B32B 2266/0207
20130101; C09J 133/14 20130101; B32B 27/34 20130101; B32B 2266/0242
20130101; C09J 2203/326 20130101; B32B 3/00 20130101; B32B 15/09
20130101; B32B 29/005 20130101; B32B 2266/0257 20130101; B32B
2266/0264 20130101; C09J 2493/00 20130101; B32B 2405/00 20130101;
B32B 2255/10 20130101; B32B 2307/748 20130101; B32B 2250/02
20130101; B32B 2255/02 20130101; C09J 2301/414 20200801; B32B 25/06
20130101; B32B 2255/26 20130101; C09J 2467/006 20130101; B32B 7/14
20130101; B32B 27/40 20130101; B32B 2255/06 20130101; C09J 133/08
20130101; B32B 2309/105 20130101; B32B 27/36 20130101; B32B 2250/03
20130101; C09J 2301/122 20200801; C09J 2475/005 20130101; B32B 5/18
20130101; B32B 2250/24 20130101; B32B 2266/025 20130101; C09J
2203/318 20130101; C09J 2433/006 20130101; B32B 2307/412 20130101;
C09J 7/38 20180101; C09J 2301/124 20200801; B32B 27/08 20130101;
B32B 27/32 20130101; B32B 2250/26 20130101; B32B 2266/0228
20130101; C09J 2423/006 20130101; B32B 27/281 20130101; B32B 25/08
20130101; B32B 27/10 20130101; B32B 27/12 20130101; C09J 2301/16
20200801; B32B 15/08 20130101; B32B 2307/50 20130101; C09J 2301/302
20200801; B32B 2255/12 20130101; B32B 2255/28 20130101; B32B 27/065
20130101; B32B 27/304 20130101; B32B 2307/72 20130101; B32B
2266/0278 20130101; B32B 7/06 20130101; C09J 2301/204 20200801;
B32B 27/306 20130101; B32B 2266/0235 20130101; B32B 2307/414
20130101; C09J 2400/243 20130101; C09J 2433/00 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 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2014 |
JP |
2014-242183 |
Aug 21, 2015 |
JP |
2015-164269 |
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
surface of the pressure-sensitive adhesive layer, the
pressure-sensitive adhesive sheet has an adhesive face formed of
the pressure-sensitive adhesive layer and the coating layer, the
coating layer has a linearly extending part that runs from one edge
to another edge of the adhesive face, the linearly extending part
has a first face forming the adhesive face of the
pressure-sensitive adhesive sheet and a second face located on the
pressure-sensitive adhesive layer side relative to the first face,
and the second face of the linearly extending part forms an overall
gently curved line in a cross section that perpendicularly
intersects the length direction of the linearly extending part.
2. The pressure-sensitive adhesive sheet according to claim 1,
wherein, in the cross section that perpendicularly intersects the
length direction of the linearly extending part, the second face of
the linearly extending part has a segment that starts from one edge
of the linearly extending part and runs towards the middle in a
gently curved line in the depth direction of the pressure-sensitive
adhesive layer.
3. The pressure-sensitive adhesive sheet according to claim 1,
wherein, in the cross section that perpendicularly intersects the
length direction of the linearly extending part, the second face of
the linearly extending part has an inclined segment that runs from
one edge of the linearly extending part in the depth direction of
the pressure-sensitive adhesive layer and a flat segment that
includes the deepest point of the linearly extending part and runs
mostly parallel to the adhesive face.
4. The pressure-sensitive adhesive sheet according to claim 3,
wherein the inclined segment is curved, convex on the
pressure-sensitive adhesive layer side.
5. The pressure-sensitive adhesive sheet according to claim 1,
wherein the linearly extending part has a thickness T and a width W
with a W/T ratio of 50 or higher.
6. The pressure-sensitive adhesive sheet according to claim 1,
wherein the linearly extending part has a width of 100 .mu.m or
greater.
7. 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.
8-11. (canceled)
12. The pressure-sensitive adhesive sheet according to claim 7,
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.
13. The pressure-sensitive adhesive sheet according to claim 7,
wherein the pressure-sensitive adhesive layer comprises an
isocyanate-based crosslinking agent and/or an epoxy-based
crosslinking agent.
14. The pressure-sensitive adhesive sheet according to claim 7,
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.
15. The pressure-sensitive adhesive sheet according to claim 1,
wherein the coating layer comprises a transparent resin.
16. (canceled)
17. The pressure-sensitive adhesive sheet according to claim 1,
wherein the coating layer comprises a polyurethane-based resin.
18. The pressure-sensitive adhesive sheet according to claim 1,
wherein the coating layer is of a two-component part
polyurethane-based resin that is curable upon mixing.
19. (canceled)
20. The pressure-sensitive adhesive sheet according to claim 1,
wherein the substrate film is a polyester film.
21-22. (canceled)
23. The pressure-sensitive adhesive sheet according to claim 1,
wherein the substrate film is a foam film.
24. The pressure-sensitive adhesive sheet according to claim 23,
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.
25. The pressure-sensitive adhesive sheet according to claim 23,
wherein the foam film is an acrylic resin foam or a polyolefinic
resin foam.
26-38. (canceled)
39. 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.
40. The release liner-backed pressure-sensitive adhesive sheet
according to claim 39, wherein the release liner has a smooth
surface on the adhesive face side.
41. 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, 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 first face located on the releasable face side and a second
face forming the outer surface on the releasable face, and the
second face of the linearly extending part forms an overall gently
curved line in a cross section that perpendicularly intersects the
length direction of the linearly extending part.
42-44. (canceled)
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. 2015-164269 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 Documents 1 and 2.
CITATION LIST
Patent Literature
[0004] [Patent Document 1] Japanese Patent Application Publication
No. 2006-70273 [0005] [Patent Document 2] Japanese Patent
Application Publication No. 2000-160117
SUMMARY OF INVENTION
Technical Problem
[0006] 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,
there is a known technique by which ridges are formed on the
surface of a release liner that protects the adhesive face of a PSA
sheet and the ridges are used to form grooves in the PSA layer
surface (Patent Document 1). Air and the like that are to remain
between the adhesive face and the adherend can be eliminated
through the grooves formed in the surface of the PSA layer. Methods
by which grooves are formed in the PSA layer surface as described
in Patent Document 1 have a problem that depending on the thickness
of the PSA layer, the depth of the grooves serving as pathways for
air and the like is limited; and after removal of the release liner
and the like to expose the adhesive face, if it takes time before
its application to an adherend, the viscoelasticity of the PSA
layer causes the grooves to fade or be lost, whereby no air release
properties are obtained. In addition, when the PSA sheet is peeled
off the adherend, there may be a tendency for the occurrence of
leftover adhesive residue with the grooves serving as initiation
points. Patent Document 2 discloses partial lamination of a
non-adhesive layer on the PSA layer surface and the use of the
non-adhesive layer surface as a passageway for air and the like to
ensure air release properties. However, it does not examine the
state of contact between the non-adhesive layer and the PSA layer
or how the state of contact would affect the quality of the PSA
sheet.
[0007] The present inventors examined how the quality can be
improved for a PSA sheet that comprises a coating layer partially
covering a PSA layer surface and have completed the present
invention with focus on the coating layer's shape (cross-sectional
shape) in the depth direction. The present invention is thus
related to improvement of a PSA sheet that has a coating layer as
an air releasing means placed partially on the PSA layer surface,
with an objective to provide a PSA sheet that comprises a coating
layer having a novel cross-sectional shape likely to fit with PSA
whereby good air release properties are obtained and the quality
can be further enhanced.
Solution to Problem
[0008] 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 further comprises a coating layer
that partially covers the surface of the PSA layer. The adhesive
face of the PSA sheet is formed of the PSA layer and the coating
layer. The coating layer has a linearly extending part that runs
from one edge to another edge of the adhesive face. The linearly
extending part has a first face forming the adhesive face of the
PSA sheet and a second face located on the PSA layer side relative
to the first face. The second face of the linearly extending part
forms an overall gently curved line in a cross section that
perpendicularly intersects the length direction of the linearly
extending part.
[0009] The viscoelastic material forming the PSA layer is likely to
fit with the coating layer having such a cross-sectional shape.
Even with respect to coating layers having the same surface pattern
and the same thickness, when the coating layer has a
cross-sectional shape as described above, the surface condition of
the PSA layer and the tightness of adhesion between the PSA layer
and the coating layer can be superior as compared to when the
coating layer does not have such a cross-sectional shape. According
to this embodiment, in the PSA sheet comprising the coating layer
that partially covers the PSA layer surface, good air release
properties are obtained while the quality can be further enhanced.
While no particular limitations are to be imposed, the effects of
this invention are obtained through the novel cross-sectional shape
of the coating layer. Thus, the PSA components and the coating
layer material are not limited. This may be effective in removing
limitations to the materials used such as the use of a relatively
hard material as the PSA to maintain the groove shape in Patent
Document 1.
[0010] Herein, "forming an overall gently curved line" means that
it draws an overall gently curved line which may partially include
a straight line (e.g. at the bottom of the coating layer, etc.). It
also means being entirely free of corners when observed at
10000.times. magnification (in particular, when observing an SEM
(scanning electron microscopy) or TEM (transmission electron
microscopy) cross-sectional image of a linearly extending part of
the coating layer at 10000.times. magnification). In other words,
it means being free of corners at the submicroscopic (0.1 .mu.m)
level and preferably being free of inflection points.
[0011] In a preferable embodiment of the PSA sheet disclosed
herein, in the cross section that perpendicularly intersects the
length direction of the linearly extending part, the second face of
the linearly extending part has a segment that starts from one edge
of the linearly extending part and runs towards the middle in a
gently curved line in the depth direction of the PSA layer. The one
edge is typically each edge. In other words, the segment that runs
in a gently curved line in the depth direction of the PSA layer
refers to one edge portion or each of the two end portions (each of
the two ends). When the edges of the width direction of the
linearly extending part are in such an embodiment, the PSA fits
well with the coating layer. The edge portions can basically form
the adhesive face of the PSA sheet, high quality of the edge
portions leads to high quality of the adhesive face.
[0012] Herein, that it "starts from one edge of a linearly
extending part and runs towards the middle in a gently curved line
while sinking in the depth direction of the PSA layer" is not
limited to a specific slope or curved shape. In typical, the
concept includes having a gentle slope such that it always
satisfies that, in a cross section perpendicularly intersecting the
length direction of a linearly extending part, on the line of the
second face of the linearly extending part, at X .mu.m towards the
middle from one edge of the linearly extending part, the second
face has a depth less than 1/ 2X .mu.m (preferably less than 1/ 3X
.mu.m, more preferably less than 1/2X .mu.m, e.g. less than 1/3X
.mu.m). The depth of the second face of the linearly extending part
refers to the depth of the second face relative to the outer
surface of the PSA layer (precisely, relative to the imaginary flat
surface formed with the outer surface of the PSA layer). X is a
positive integer and its upper limit is a half the width of the
linearly extending part. For instance, when a linearly extending
part of the coating layer has a thickness less than 3 .mu.m, at X
in a range of 10 .mu.m or less (more restrictedly in a range of 5
.mu.m or less), on the line formed by the second face of the
linearly extending part, at X .mu.m towards the middle from one
edge of the linearly extending part, it is preferable that the
second face always has a depth less than 1/ 3X .mu.m (preferably
less than 1/2X .mu.m, more preferably less than 1/3X .mu.m, e.g.
less than 1/4X .mu.m).
[0013] In a preferable embodiment of the PSA sheet disclosed
herein, in the cross section that perpendicularly intersects the
length direction of the linearly extending part, the second face of
the linearly extending part has an inclined segment that runs from
one edge of the linearly extending part in the depth direction of
the PSA layer and a flat segment that includes the deepest point of
the linearly extending part and runs mostly parallel to the
adhesive face. With the inclusion of the inclined segment, the
effects of this invention are preferably realized. It is noted that
the one edge is typically each edge; and in this case, the inclined
segment is present at each end of the width direction of the
linearly extending part.
[0014] In a preferable embodiment of the PSA sheet disclosed
herein, the inclined segment is curved, convex on the PSA layer
side. Such an embodiment preferably brings about the effects of
this invention.
[0015] In a preferable embodiment of the PSA sheet disclosed
herein, the linearly extending part has a thickness T and a width W
with a W/T ratio of 50 or higher. With respect to such an
embodiment, the effects of this invention are more preferably
produced.
[0016] In a preferable embodiment of the PSA sheet disclosed
herein, the linearly extending part has a width of 100 .mu.m or
greater. With respect to such an embodiment, the effects of this
invention are more preferably produced.
[0017] The present invention also provides a release liner-backed
PSA sheet comprising a PSA sheet disclosed herein and a release
liner that protects an adhesive face of the PSA sheet. Of the
surfaces of the release liner, the adhesive face-side surface is
preferably 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.
[0018] 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 is provided with a coating layer that can be transferred
onto a PSA sheet. 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 first face located on the releasable
face side and a second face forming the outer surface on the
releasable face. The second face of the linearly extending part
forms an overall gently curved line in a cross section that
perpendicularly intersects the length direction of the linearly
extending part. With the use of such a release liner to transfer
the coating layer onto the PSA layer surface of the PSA sheet, a
high-quality PSA sheet having good air release properties can be
made.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 shows a schematic top view of the PSA sheet according
to an embodiment.
[0020] FIG. 2 shows a cross-sectional diagram at line II-II in FIG.
1.
[0021] FIG. 3 shows a cross section of a linearly extending part
(perpendicularly intersecting the length direction) of the coating
layer according to an embodiment in an enlarged schematic
cross-sectional view.
[0022] FIG. 4 shows the left edge of the coating layer in FIG. 3 in
a further enlarged schematic cross-sectional view.
[0023] FIG. 5 shows the right edge of the coating layer in FIG. 3
in a further enlarged schematic cross-sectional view.
[0024] FIG. 6 shows a schematic cross-sectional diagram of the
release liner-backed PSA sheet according to an embodiment.
[0025] FIG. 7 shows a schematic cross-sectional diagram of the
release liner-backed PSA sheet according to another embodiment.
[0026] FIG. 8 shows a schematic cross-sectional diagram of the
release liner for the PSA sheet according to an embodiment.
[0027] FIG. 9 shows an SEM cross-sectional image of the PSA sheet
of a working example.
[0028] FIG. 10 shows an SEM cross-sectional image of the PSA sheet
of the working example, showing one edge (left edge) of the coating
layer in FIG. 9 in an enlarged view.
[0029] FIG. 11 shows an SEM cross-sectional image of the PSA sheet
of the working example, showing a flat segment at the center of the
coating layer in FIG. 9 in an enlarged view.
[0030] FIG. 12 shows an SEM cross-sectional image of the PSA sheet
of the working example, showing the other edge (right edge) of the
coating layer in FIG. 9 in an enlarged view.
DESCRIPTION OF EMBODIMENTS
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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. When PSA sheet 1 is
applied to an adherend, the coating layer 30 forms pathways for air
and the like between the PSA sheet 1 and the adherend, whereby air
release properties are provided.
[0036] The coating layer 30 has a prescribed pattern (coating layer
pattern) 40 on the adhesive face 1A of the PSA sheet 1. In this
embodiment, the coating layer 30 is in a lattice pattern 40. In
particular, the lattice pattern 40 of the coating layer 30 is
formed of the first stripe pattern 42 and the second stripe pattern
44 that is placed to intersect the first stripe pattern 42.
[0037] The first stripe pattern 42 is formed of parts 50 (linearly
extending parts, bands in this embodiment) that run straight from
one edge to another edge of the adhesive face 1A. These linearly
extending parts 50 are placed in parallel, spaced at intervals
arranged in the width direction. In this embodiment, the linearly
extending parts 50 are placed at an angle such that their length
directions intersect the edges (ends, limits) of the width
direction of PSA sheet 1, with each part reaching two edges (two
sides) of the adhesive face 1A.
[0038] Similarly to the first stripe pattern 42, the second stripe
pattern 44 is also formed of parts 50 (linearly extending parts,
bands in this embodiment) that run straight from one edge to
another edge of the adhesive face 1A. These linearly extending
parts 50 are placed in parallel at intervals arranged in the width
direction. In this embodiment, the linearly extending parts 50 are
placed at an angle such that their length directions intersect the
edges of the width direction of PSA sheet 1, with each part
reaching two edges (two sides) of the adhesive face 1A. In this
embodiment, the linearly extending parts 50 are straight bands, but
are not limited thereto. Each linearly extending part may be
curvilinear. In such an embodiment, the several linearly extending
parts may form a wavy stripe pattern, etc. The number of the
linearly extending parts (the number of lines) may depend on the
shape, size, etc., of the adhesive face of the PSA sheet; and
therefore, it is not limited to a particular number.
[0039] In this embodiment, the first stripe pattern 42 and the
second stripe pattern 44 intersect each other so that the linearly
extending parts 50 of the first stripe pattern 42 and the linearly
extending parts 50 of the second stripe pattern 44 cross one
another almost perpendicularly. Thus, the linearly extending parts
50 of the first stripe pattern 42 partially overlap the linearly
extending parts 50 of the second stripe pattern 44.
[0040] 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 linearly extending 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 linearly
extending parts may be partially connected to one another. From the
standpoint of the air release properties, the coating layer
preferably comprises one, two or more stripe patterns. The coating
layer pattern (typically a lattice pattern) may include a third
stripe pattern.
[0041] Described next is a cross-sectional shape of the coating
layer 30. FIG. 3 shows a cross section of a linearly extending part
(the cross section perpendicularly intersecting the length
direction) of the coating layer according to an embodiment in an
enlarged schematic cross-sectional view. FIG. 4 shows the left edge
of the coating layer in FIG. 3 in a further enlarged schematic
cross-sectional view. FIG. 5 shows the right edge of the coating
layer in FIG. 3 in a further enlarged schematic cross-sectional
view.
[0042] As shown in FIG. 3, a linearly extending part 50 of the
coating layer 30 is in a thin layer laminated partially on the
surface 20A of the PSA layer 20 and has a first face 52 that forms
the adhesive face 1A of the PSA sheet 1 and a second face 54
located on the PSA layer 20 side relative to the first face 52. In
particular, the surfaces of the linearly extending part 50 are
formed with the first face (outer surface) 52 and the second face
(inner surface) 54 as the back face of the first face 52.
[0043] The first face 52 of the linearly extending part 50 is flush
with or protrudes slightly from the outer surface of the PSA layer
20. From the standpoint of the air release properties, it is
preferable that the first face 52 of the linearly extending part 50
protrudes slightly from the outer surface of the PSA layer 20. The
height of the protruding portion of the first face of the linearly
extending part (the height relative to the outer surface of the PSA
layer (precisely, relative to the imaginary flat surface formed
with the outer surface of the PSA layer)) is preferably less than
30% (e.g. less than 10%) of the thickness of the linearly extending
part. It is noted that the thickness of the linearly extending part
is basically identical to the thickness of the coating layer.
[0044] The second face 54 of the linearly extending part 50 forms
an overall gently curved line in a cross section that
perpendicularly intersects the length direction of the linearly
extending part 50. In particular, as shown in FIG. 4, in the cross
section, the second face 54 of a linearly extending part 50 has a
segment that starts from one edge 56 (the left edge in the drawing)
of the linearly extending part 50 and runs towards the middle in a
gently curved line while sinking in the depth direction (the
thickness direction) of the PSA layer 20. Similarly, as shown in
FIG. 5, the second face 54 of a linearly extending part 50 has a
segment that starts from the other edge 58 (the right edge in the
drawing) of the linearly extending part 50 and runs towards the
middle in a gently curved line while sinking in the depth direction
(the thickness direction) of the PSA layer 20. The one edge 56 and
the other edge 58 correspond to the two edges of the width
direction of the linearly extending part 50.
[0045] More specifically, the second face 54 of a linearly
extending part 50 has an inclined segment 60 and a flat segment 62
that continues from the inclined segment 60. In the cross section,
the inclined segment 60 has a shape that runs from the one edge 56
of the linearly extending part 50 in the depth direction of the PSA
layer 20. The flat segment 62 of the second face 54 is a range that
includes the deepest portion of the linearly extending part 50. In
this embodiment, in the cross section, it runs mostly parallel to
the adhesive face 1A of the PSA sheet 1.
[0046] In this embodiment, the inclined segment 60 is formed in an
area running from the one edge 56 of the width direction of the
linearly extending part 50 to about 10 .mu.m towards the middle in
the width direction, and an area running from the other edge 58 of
the width direction of the linearly extending part 50 to about 10
.mu.m towards the middle in the width direction. The rest of the
second face 54 (i.e. the bottom of the coating layer 30) forms the
flat segment 62. The inclined segment 60 is curved, convex on the
PSA layer 20 side.
[0047] The range to which the inclined segment is formed is not
limited to those described above. When a linearly extending part of
the coating layer has a maximum depth of D .mu.m, the inclined
segment can be formed in a range that runs from one of the two
edges of the width direction of the linearly extending part to 10D
.mu.m (typically 7D .mu.m, e.g. 4D .mu.m) towards the middle in the
width direction. For instance, when the linearly extending part of
the coating layer has a maximum depth in a range of 0.5 .mu.m to 2
.mu.m, the inclined segment may be formed in a range that runs from
one of the two edges of the width direction of the linearly
extending part up to 20 .mu.m (typically 14 .mu.m, e.g. 8.0 .mu.m)
or up to 5.0 .mu.m (typically 3.5 .mu.m, e.g. 2.0 .mu.m) towards
the middle in the width direction. The depth of the linearly
extending part is the depth of the second face of the linearly
extending part, referring to the depth of the linearly extending
part relative to the outer surface of the PSA layer (precisely,
relative to the imaginary flat surface formed with the outer
surface of the PSA layer). The same is true with the maximum depth
(the depth of the deepest point).
[0048] From the one edge 56 or the other edge 58 of the width
direction of the linearly extending part 50 up to at least about 1
.mu.m (e.g. 2 .mu.m, typically 3 .mu.m) towards the middle in the
width direction, the inclined segment 60 has a slope that can be
confirmed in a cross-sectional image (e.g. an SEM cross-sectional
image) at 10000.times. magnification (specifically, a slope that
has, in the cross section, an angle of, for instance, 5.degree. or
greater, typically 10.degree. or greater between the adhesive face
1A and the inclined segment 60). The slope of the inclined segment
60 is suitably in a range such that the angle between the adhesive
face 1A and the inclined segment 60 in the cross section is about
60.degree. or less (e.g. 45.degree. or less, typically 30.degree.
or less).
[0049] In this embodiment, the maximum depth of the linearly
extending parts 50 of the coating layer 30 is about 1.5 .mu.m, but
the maximum depth is not limited to this. The maximum depth of the
linearly extending parts of the coating layer 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, the maximum depth of the linearly
extending parts 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).
The maximum depth is 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). When the first face of the coating layer is almost flush
with the outer surface of the PSA layer, the maximum depth of the
linearly extending parts of the coating layer is about the same as
the thickness of the coating layer. The maximum depth of a linearly
extending part of the coating layer can be obtained by SEM or TEM
analysis.
[0050] The width (W1) of each linearly extending part 50 of the
coating layer 30 is about 200 .mu.m in the present embodiment, but
is not limited to this. In a preferable embodiment, the width (W1)
of each linearly extending part of the coating layer is 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 width (W1) of the linearly extending part is more
preferably 0.2 mm or greater, yet more preferably 0.3 mm or
greater, or particularly preferably 0.5 mm or greater. In another
preferable embodiment, the width (W1) of each linearly extending
part of the coating layer is about 10 .mu.m or greater. From the
standpoint of the air release properties, the width (W1) of each
linearly extending part of the coating layer is preferably 50 .mu.m
or greater, more preferably 100 .mu.m or greater, or yet more
preferably 150 .mu.m or greater. From the standpoint of the
adhesive strength, the appearance, etc., the width (W1) of the
linearly extending part is more preferably 12 mm or less, yet more
preferably 1.0 mm or less, even more preferably 0.7 mm or less,
particularly preferably 0.5 mm or less, or most preferably 0.4 mm
or less. The width (W1) of a linearly extending part of the first
stripe pattern can be equal to or different from the width (W1) of
a linearly extending part of the second stripe pattern.
[0051] In a preferable embodiment, from the standpoint of the air
release properties, a linearly extending part has a ratio (W/T) of
its width W to its thickness T of about 50 or higher. The ratio
(W/T) is more preferably about 80 or higher, or yet more preferably
100 or higher (typically 120 or higher). From the standpoint of the
balance between air release properties and adhesion, the ratio
(W/T) is preferably about 500 or lower (e.g. 200 or lower,
typically 165 or lower).
[0052] The intervals (W2) between the linearly extending parts 50
forming the first stripe pattern 42 of the coating layer 30 are
about 18 mm in this embodiment and the same applies to the
intervals (W2) between the linearly extending parts 50 forming the
second stripe pattern 44, but neither is limited to this. The
intervals (W2) between the linearly extending parts forming the
first stripe pattern are preferably in a range of 1.0 mm to 10 mm.
By this, 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 linearly extending
parts refer to the widths of spaces present between any two
adjacent linearly extending parts in the adhesive face of the PSA
sheet. From the standpoint of increasing the long-term adhesive
strength, etc., the intervals (W2) between the linearly extending
parts are more preferably 1.5 mm or greater, or yet more preferably
2.5 mm or greater. The intervals (W2) between the linearly
extending parts can be about 8 mm or less (e.g. 5 mm or less,
typically 3 mm or less). The intervals (W2) between the linearly
extending parts forming the second stripe pattern can also be
preferably selected from the ranges exemplified for the intervals
(W2) between the linearly extending parts forming the first stripe
pattern. The intervals (W2) are preferably evenly spaced. The
intervals (W2) between the linearly extending parts forming the
first stripe pattern can be equal to or different from the
intervals (W2) between the linearly extending parts forming the
second stripe pattern.
[0053] From the standpoint of combining well-balanced high
long-term adhesive strength and air release properties, the pitch
the linearly extending parts is preferably in a range of 1 mm to 20
mm. The pitch of the linearly extending 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 linearly extending
parts.
[0054] With focus on the surface 20A of the PSA layer 20, the
embodiment above can be described such that the surface 20A of the
PSA layer 20 has a coating layer-bearing area 70 where the coating
layer 30 is placed and a coating layer-free area 72 where the PSA
layer 20 is exposed on the outer surface without the coating layer
30. The features (shape, arrangement, relative position, size,
etc.) of the coating layer-bearing area 70 in the PSA layer surface
20A are the same with the features of the coating layer 30 in the
adhesive face 1A of the PSA sheet 1. Thus, the coating
layer-bearing area 70 is in a pattern (a lattice pattern) that has
the same features as the coating layer pattern 40 with a first
stripe pattern having the same features as the first stripe pattern
42 and a second stripe pattern having the same features as the
second stripe pattern 44. The first stripe pattern of the coating
layer-bearing area 70 has linearly extending parts that have the
same features as the linearly extending parts 50 that the first
stripe pattern 42 has. The second stripe pattern of the coating
layer-bearing area 70 has linearly extending parts that have the
same features as the linearly extending parts 50 that the second
stripe pattern 44 has. Thus, details of the features of the coating
layer-bearing area 70 and the coating layer-free area 72 are
omitted here.
[0055] Before used, as shown in FIG. 6, the PSA sheet 1 may be in a
form of a release liner-backed PSA sheet 1 protected with a release
liner 100 having a release face on the adhesive face 1A 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 face requires features such as
decoration and surface protection, or when it is used as a paint
substitute sheet.
[0056] When the PSA sheet disclosed herein is an adhesively
double-faced substrate-backed PSA sheet (a double-faced PSA sheet)
as shown in FIG. 7, 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 101 and 102, 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.>
[0057] In the PSA sheet disclosed herein, 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 of the PSA
sheet) is preferably 70% or higher. This can ensure high long-term
adhesive strength. The % surface area is more preferably 75% or
higher, or yet 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.
[0058] In a preferable embodiment, the adhesive face (typically
formed of the outer surface of the PSA layer 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). In another
preferable embodiment, the adhesive face of the PSA sheet shows a
24-hour adhesion strength of 2 N/20 mm or greater (preferably 5
N/20 mm or greater, or more preferably 8 N/20 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 20 mm or 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 face 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/20 mm or N/25 mm) is
determined at a tensile speed of 300 mm/min at a peel angle of
180.degree..
[0059] 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. That the PSA sheet is transparent means that the
components (PSA layer, substrate film and coating layer) of the PSA
sheet are transparent. Herein, that the PSA sheet and its
components (PSA layer, substrate film and coating layer) are
transparent may mean that the PSA sheet and its components show 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.
[0060] 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). In a preferable embodiment, the PSA sheet has an overall
thickness of 50 .mu.m or less, or more preferably 30 .mu.m or less
(e.g. 15 .mu.m or less, typically 5 .mu.m or less). According to
the art disclosed herein, good air release properties can be
obtained even when the PSA sheet is limited in overall thickness as
described above. 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.
[0061] The tolerance for thickness of the PSA sheet disclosed
herein is preferably 50% or less. The PSA sheet with a small
tolerance for thickness can exhibit greater adhesive properties.
The tolerance for thickness is more preferably 40% or less, yet
more preferably 30% or less, or particularly preferably 20% or
less. The tolerance for thickness of the PSA sheet is determined by
the method described later in Examples.
<Substrate Film>
[0062] 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.
[0063] 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. A typical 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.
[0064] 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 is 10 .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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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).
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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).
[0078] 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.
[0079] 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).
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.
[0087] 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.
[0088] 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.
[0089] 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.
[0090] 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).
[0091] 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.
[0092] 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).
[0093] 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).
[0094] 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.
[0095] 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).
[0096] 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.
[0097] 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). In a preferable embodiment, the thickness of the
substrate film is about 30 .mu.m or smaller, more preferably 12
.mu.m or smaller, or yet more preferably smaller than 10 .mu.m
(e.g. smaller than 5 .mu.m, typically smaller than 3 .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.
[0098] 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>
[0099] 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.).
[0100] 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.
[0101] 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.
[0102] 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)
[0103] 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.
[0104] 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.
[0105] 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.
[0106] 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.
[0107] 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).
[0108] 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).
[0109] 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.
[0110] 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.
[0111] 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).
[0112] 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.
[0113] 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.
[0114] The PSA layer disclosed herein can be formed by a heretofore
known method. For instance, a transfer method can be preferably
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.
Alternatively, a direct method can also be employed, in which a PSA
composition is directly provided (typically applied) to a substrate
and allowed to dry to form a PSA layer. 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.
[0115] 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, comma 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.
[0116] 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.
[0117] 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). In a preferable embodiment, the thickness of the PSA layer
is 20 .mu.m or smaller, more preferably 10 .mu.m or smaller, or yet
more preferably 7 .mu.m or smaller (e.g. 5 .mu.m or smaller).
According to the art disclosed herein, even in an embodiment where
the PSA layer is limited in thickness as above, good air release
properties can be obtained. 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>
[0118] 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.
[0119] 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.
[0120] 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.
[0121] The coating layer is typically 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..
[0122] The method for placing the coating layer on the PSA layer
surface is not particularly limited. In typical, a method as
described next is 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 same
embodiment can also be obtained by forming a coating layer on a
releasable surface as described above and further forming a PSA
layer to cover the coating layer. In this case, the resulting PSA
layer is subsequently transferred onto a surface of a substrate
film. Based on technical common knowledge in the pertinent field, a
skilled person can employ a method as described above, select a
coating layer material in view of the wetting properties relative
to the releasable surface of the releasable support, adjust the
viscosity of the coating layer-forming composition to a suitable
range, and further select, for instance, a suitable printing means
to form a coating layer having a cross-sectional shape disclosed
herein.
[0123] The thickness of the coating layer can be designed to obtain
desirable air release properties and is not particularly limited.
From the standpoint of the smoothness of the PSA sheet's adhesive
face and the lamination on the PSA layer, it is preferable that the
thickness of the coating layer is about equal to or less than the
thickness of the PSA layer. In a preferable embodiment, the ratio
(T.sub.C/T.sub.A) of the thickness T.sub.C of the coating layer to
the thickness T.sub.A of the PSA layer is 0.75 or less, more
preferably 0.70 or less, or yet more preferably 0.5 or less (e.g.
0.4 or less). For instance, a higher degree of smoothness is
obtained in an embodiment where the PSA layer has a thickness of 1
.mu.m or greater (preferably 2 .mu.m or greater, or more preferably
3 .mu.m or greater) while satisfying the ratio (T.sub.C/T.sub.A).
In another preferable embodiment, from the standpoint of combining
air release properties and appearance, the thickness of the coating
layer is preferably up to about a half (e.g. up to one-third,
typically up to one-fifth) the thickness of the PSA layer.
[0124] From the standpoint of the air release properties,
productivity, etc., the particular 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
smoothness, the lamination and the appearance of the adhesive face
of the PSA sheet, the coating layer has a thickness of preferably
10 .mu.m or less, more preferably 5 .mu.m or less, yet more
preferably 4 .mu.m or less (e.g. less than 4 .mu.m, typically 3
.mu.m or less), or particularly preferably less than 3 .mu.m (e.g.
2 .mu.m or less). According to the art disclosed herein, even when
the coating layer is such a thin layer, good air release properties
are obtained. Such a thin coating layer is particularly preferable
for use in applications that require thinning (typically mobile
electronic applications). The thickness of the coating layer can be
obtained by SEM or TEM analysis of a cross section of the PSA
sheet.
<Release Liner>
[0125] 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 face 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.
[0126] In a preferable embodiment, the release surface (on the side
that makes contact with the PSA sheet's adhesive face) 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).
[0127] As shown in FIG. 8, 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
transferable 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 on the
adhesive face of the PSA sheet described earlier. Thus, details are
omitted. The linearly extending parts of the coating layer provided
to the release liner are also basically as described earlier,
except that the first face is on the releasable surface side and
the second face forms the outer surface on the releasable face.
Thus, details are omitted.
[0128] 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).
[0129] 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.
[0130] 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.
[0131] 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
displays (typically TV displays) 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.
[0132] 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 such as mobile phones, smartphones, tablet PCs,
notebook PCs, various wearable devices (e.g. wrist wearables put on
wrists such as wrist watches; modular devices attached to bodies
with clips, straps, etc.; eye wears including eye glass types
(monocular or binocular, including head-mounted pieces); clothing
types worn as, for instance, accessories on shirts, socks,
hats/caps, etc.; ear-mounted pieces put on ears such as earphones),
digital cameras, digital video cameras, acoustic equipment
(portable music players, IC recorders, etc.), calculators (e.g.
pocket calculators), handheld game devices, electronic
dictionaries, electronic notebooks, electronic books, vehicle
navigation devices, portable radios, portable TVs, portable
printers, portable scanners, and portable modems; 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; for fixing rim sheets, decorative panels,
batteries, and various other parts; fixing labels (including
various marks) such as logos (letter logos) and various designs
(symbols); 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.
[0133] Matters disclosed by this description include the
following:
(1) A PSA sheet comprising a substrate film and a PSA layer
provided to at least one face of the substrate film, wherein
[0134] the PSA sheet further comprises a coating layer that
partially covers the surface of the PSA layer,
[0135] the PSA sheet has an adhesive face formed of the PSA layer
and the coating layer,
[0136] the coating layer has a linearly extending part that runs
from one edge to another edge of the adhesive face,
[0137] the linearly extending part has a first face forming the
adhesive face of the PSA sheet and a second face located on the PSA
layer side relative to the first face, and
[0138] the second face of the linearly extending part forms an
overall gently curved line in a cross section that perpendicularly
intersects the length direction of the linearly extending part.
(2) The PSA sheet according to (1) above, wherein, in the cross
section that perpendicularly intersects the length direction of the
linearly extending part, the second face of the linearly extending
part has a segment that starts from one edge of the linearly
extending part and runs towards the middle in a gently curved line
in the depth direction of the PSA layer. (3) The PSA sheet
according to (1) or (2) above, wherein, in the cross section that
perpendicularly intersects the length direction of the linearly
extending part, the second face of the linearly extending part has
an inclined segment that runs from one edge of the linearly
extending part in the depth direction of the PSA layer and a flat
segment that includes the deepest point of the linearly extending
part and runs mostly parallel to the adhesive face. (4) The PSA
sheet according to (3) above, wherein the inclined segment is
curved, convex on the PSA layer side. (5) The PSA sheet according
to any one of (1) to (4) above, wherein the linearly extending part
has a thickness T and a width W with a W/T ratio of 50 or higher.
(6) The PSA sheet according to any one of (1) to (5) above, wherein
the linearly extending part has a width of 100 .mu.m or greater.
(7) The PSA sheet according to any one of (1) to (6) 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):
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). (8)
The PSA sheet according to (7) above, wherein the alkyl
(meth)acrylate is n-butyl acrylate and/or 2-ethylhexyl acrylate.
(9) The PSA sheet according to (7) or (8) 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). (10) The PSA sheet
according to any one of (7) to (9) 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. (11) The PSA sheet according to any one
of (7) to (10) 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. (12)
The PSA sheet according to any one of (7) to (11) 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. (13) The PSA sheet according to
any one of (7) to (12) above, wherein the PSA layer comprises an
isocyanate-based crosslinking agent and/or an epoxy-based
crosslinking agent. (14) The PSA sheet according to any one of (7)
to (13) 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. (15) The PSA sheet according to any one of (1) to
(14) above, wherein the coating layer comprises a transparent
resin. (16) The PSA sheet according to any one of (1) to (15)
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. (17) The PSA sheet
according to any one of (1) to (16) above, wherein the coating
layer is of a polyurethane-based resin. (18) The PSA sheet
according to any one of (1) to (17) above, wherein the coating
layer is of a two-component polyurethane-based resin that is
curable upon mixing. (19) The PSA sheet according to any one of (1)
to (18) 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. (20) The PSA sheet according to any one of (1) to
(19) above, wherein the substrate film is a polyester film. (21)
The PSA sheet according to any one of (1) to (20) above, wherein
the substrate film is a polyethylene terephthalate film. (22) The
PSA sheet according to any one of (1) to (21) above, wherein the
substrate film exhibits a total light transmittance of 80% or
higher. (23) The PSA sheet according to any one of (1) to (18)
above, wherein the substrate film is a foam film. (24) The PSA
sheet according to (23) 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. (25) The PSA sheet according to (23)
or (24) above, wherein the foam film is an acrylic resin foam body
or a polyolefinic resin foam body. (26) The PSA sheet according to
any one of (1) to (25) above, wherein the coating layer has a
thickness less than 3 .mu.m. (27) The PSA sheet according to any
one of (1) to (26) above for use in mobile electronics. (28) The
PSA sheet according to any one of (1) to (27) above, wherein the
PSA layer has a thickness of 20 .mu.m or less. (29) The PSA sheet
according to any one of (1) to (28) above, wherein the PSA layer
has a thickness T.sub.A and the coating layer has a thickness
T.sub.C with a T.sub.C/T.sub.A ratio value of 0.75 or less. (30)
The PSA sheet according to any one of (1) to (29) above,
comprising, as the PSA layers, first and second PSA layers provided
on first and second faces of the substrate film, respectively,
wherein
[0139] the coating layer is partially placed on the surface of at
least one PSA layer between the first and second PSA layers.
(31) The PSA sheet according to any one of (1) to (30) above,
wherein the substrate film has a thickness less than 5 .mu.m. (32)
The PSA sheet according to any one of (1) to (31) above having an
overall thickness of 50 .mu.m or less. (33) The PSA sheet according
to any one of (1) to (32) above, wherein the PSA layer surface has
a coating layer-bearing area and a coating layer-free area, the
coating layer-free area occupying 70% or more of the PSA layer
surface. (34) The PSA sheet according to (33) above, wherein the
linearly extending part has a width in a range of 0.1 mm to 2 mm.
(35) The PSA sheet according to (33) or (34) above, wherein
[0140] 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.
(36) The PSA sheet according to (35) 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. (37) The PSA sheet according to (35) or (36) above,
wherein, in the coating layer-bearing area, the intervals between
the plurality of the linearly extending parts forming one stripe
pattern are in a range of 1.0 mm to 10 mm. (38) The PSA sheet
according to any one of (33) to (37) 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. (39) A release liner-backed PSA sheet
comprising the PSA sheet according to any one of (1) to (38) above
and a release liner that protects an adhesive face of the PSA
sheet. (40) The release liner-backed PSA sheet according to (39)
above, wherein, of the surfaces of the release liner, the adhesive
face-side surface is formed smooth (wherein the release liner has a
smooth surface on the adhesive face side). (41) A release liner for
a PSA sheet, the release liner comprising a releasable support
having at least one releasable face, wherein
[0141] the releasable face of the releasable support is provided
with a coating layer disclosed herein that can be transferred onto
a PSA sheet.
(42) The release liner according to (40) above, wherein the coating
layer has a linearly extending part that runs from one edge to
another edge of the releasable face,
[0142] the linearly extending part has a first face located on the
releasable face side and a second face forming the outer surface on
the releasable face, and
[0143] the second face of the linearly extending part forms an
overall gently curved line in a cross section that perpendicularly
intersects the length direction of the linearly extending part.
(43) The release liner according to (41) or (42) above, wherein the
coating layer has a thickness less than 3 .mu.m. (44) A method for
producing the PSA sheet according to any one of (1) to (38) above,
the method comprising:
[0144] a step of forming a PSA layer on a releasable face of a
releasable support; and
[0145] a step of transferring the PSA layer onto a surface of a
substrate film, the method being characterized by the following
features:
[0146] a coating layer is partially formed on the releasable face
of the releasable support and the PSA layer-forming step is a step
of further forming the PSA layer on the releasable face where the
coating layer has been formed; or no coating layer is formed on the
releasable face of the releasable support, the releasable support
is removed from the PSA layer after the PSA layer-transferring
step, a coating layer-bearing releasable support having a
releasable face on which a coating layer is partially formed is
obtained, and the coating layer-bearing releasable support is
layered over the PSA layer so that the coating layer is transferred
onto the PSA layer surface.
(45) A method for producing the PSA sheet according to any one of
(1) to (38) above, the method comprising:
[0147] a step of forming a coating layer partially on a releasable
face of a releasable support;
[0148] a step of further forming a PSA layer on the releasable face
where the coating layer has been formed; and
[0149] a step of transferring the PSA layer onto a surface of a
substrate film.
[0150] 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.
Example
(Preparation of PSA Composition)
[0151] 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.
[0152] 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)
[0153] 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
(C1-CA1) available from Fujiko Co., Ltd.) to form a coating layer
(coating thickness about 1.5 .mu.m, transparent) in a lattice
pattern. A coating layer-bearing release film was thus obtained,
with the coating layer formed partially on the releasable face.
(Fabrication of PSA Sheets)
[0154] To the coating layer-bearing releasable face of the
resulting coating layer-bearing release film, the PSA composition
was applied and allowed to dry to a final thickness of 13 .mu.m to
obtain a PSA layer supported on the release film. A 4 .mu.m thick
PET substrate film (trade name LUMIRROR available from Toray
Industries, Inc.) was obtained. Onto the first face (corona
discharge-treated face) of the PET substrate, the resulting PSA
layer was transferred along with the release film supporting it.
The release film was used as it was to protect the PSA layer
surface.
[0155] To the release agent-treated face of 38 .mu.m thick release
film (trade name DIAFOIL MRF-38 available from Mitsubishi Plastics,
Inc.), the PSA composition was applied to a final thickness of 13
.mu.m and allowed to dry at 100.degree. C. for 3 minutes to obtain
a PSA layer supported on the release film. The resulting PSA layer
was transferred along with the release film supporting it onto the
second face (corona discharge-treated face) of the PET substrate.
The release film was used as it was to protect the PSA layer
surface.
[0156] By transferring the respective PSA layers onto the two faces
of the PET substrate by the methods described above, a
substrate-supported double-faced PSA sheet was fabricated, with the
first face of the PET substrate provided with the coating
layer-bearing PSA layer and the second face thereof provided with
the coating layer-free PSA layer. One of the adhesive faces of the
PSA sheet was a coating layer-bearing adhesive face where the
coating layer in the lattice pattern shown in FIG. 1 was formed,
with each coating layer band having a width (line width) of about
200 .mu.m and the coating layer bands having a pitch of about 2 mm.
The % surface area of the coating layer in the adhesive face of the
PSA sheet was 19%. FIGS. 1 to 12 show SEM cross-sectional images of
the resulting PSA sheets. These cross-sectional images were taken
from a cross section perpendicularly intersecting the length
direction of a linearly extending part of the coating layer. The
coating layer in the images shows a band in the lattice pattern.
The other adhesive face of the PSA sheet was a coating layer-free
adhesive face.
[Air Release Properties]
[0157] One face (the coating layer-free adhesive face) of the
double-faced PSA sheet according to the present example was
exposed, backed with 25 .mu.m PET film, and cut to a 50 mm by 50 mm
square to prepare a measurement sample. The coating layer-bearing
adhesive face of the measurement sample was exposed and the
measurement sample was placed (not press-bonded) on a horizontally
laid stainless steel plate (SUS plate) as the adherend, with the
coating layer-bearing adhesive face being on the adherend side.
[0158] A bubble-forming rubber plate was then obtained, laid and
pressed over the measurement sample to form bubbles between the
adhesive face (the coating layer-bearing adhesive face) of the
measurement sample and the adherend surface. In particular, as the
bubble-forming rubber plate, was obtained a 50 mm by 50 mm square
rubber plate having a 20 mm by 20 mm square opening (through hole)
in the center of its face. The bubble-forming rubber plate was laid
over the top face (the backed face) of the measurement sample and
pressed from the top at 3 kgf for 5 seconds to press-bond the
measurement sample's adhesive face (the coating layer-bearing
adhesive face) and the adherend surface over the area corresponding
to the frame shape of the rubber plate thereby to form bubbles
between the measurement sample's adhesive face (the coating
layer-bearing adhesive face) and the adherend surface over the
non-loaded area (20 mm by 20 mm square area) corresponding to the
opening of the rubber plate.
[0159] The bubble-forming rubber plate was removed from the backed
face of the measurement sample. A 50 mm by 50 mm square rubber
plate (with no opening) was laid over the backed face of the
measurement sample and pressed from the top at 3 kgf for 15
seconds. The rubber plate was removed and the degree of elimination
of the pre-formed bubbles was visually inspected. As the rubber
plate, was used trade name NEO-200 (3 mm thick) available from
Irumagawa Rubber Co., Ltd. As the bubble-forming rubber plate, the
same type of rubber plate was processed and used.
[0160] As a result of visual inspection, no leftover bubbles were
found on the adhesive face (coating layer-bearing adhesive face) of
the PSA sheet, confirming the good air release properties of the
PSA sheet according to the present example.
[Effective Adhesive Strength (Surface Condition of Adhesive
Face)]
[0161] One face (the coating layer-free adhesive face) of the
double-faced PSA sheet according to the present example was
exposed, backed with 50 .mu.m thick PET film, and cut to a 20 mm by
100 mm size to prepare a measurement sample. Of the measurement
sample, the coating layer-bearing adhesive face was exposed. In an
environment at 23.degree. C., 50% RH, the exposed adhesive face of
the measurement sample was press-bonded to the surface of a
stainless steel plate (SUS plate) with a 5 kg roller moved back and
forth once. The resultant was 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/20 mm)
(24-hour adhesion strength) was determined at a tensile speed of
300 mm/min at a peel angle of 180.degree..
[0162] Without forming a coating layer, but otherwise in the same
manner as the present example, a PSA sheet (coating layer-free PSA
sheet) was fabricated. In the same manner as described above, the
resulting PSA sheet was adhered to the adherend and the 24-hour
peel strength P.sub.C (N/20 mm) was determined.
[0163] With the peel strength P.sub.C of the coating layer-free PSA
sheet (with 100% PSA layer and 0% coating layer in the surface area
of the adhesive face) being 100%, the % surface area of the coating
layer in the adhesive face of the PSA sheet according to the
present example was subtracted to determine the theoretical peel
strength P.sub.T (N/20 mm) of the PSA sheet according to the
present example. In the present example, the % surface area of the
coating layer in the adhesive face (coating layer-bearing adhesive
face) of the PSA sheet was 19%; from 100%-19%=81%,
P.sub.T=P.sub.C.times.0.81. When the actual measured value P.sub.M
(the peel strength of the PSA sheet according to the present
example measured under the conditions described above) is 90% or
more of the theoretical peel strength P.sub.T (i.e. when
P.sub.M.gtoreq.P.sub.T.times.0.9), it can be judged that the
coating layer formed on the PSA layer surface fit well in the PSA
layer, and the PSA sheet's adhesive face (coating layer-bearing
adhesive face) had a good surface condition to achieve a
near-theoretical value.
[0164] The PSA sheet according to the present example was tested as
described above. As a result, the actual measured peel strength
value P.sub.M was at least 90% of the theoretical peel strength
P.sub.T.
[Tolerance for Thickness]
[0165] With the PSA sheet obtained according to the present
example, using a dial gauge, at 10 points of intersection in the
coating layer lattice and 10 center points of rectangular areas
with the exposed PSA layer surrounded by the coating layer in the
lattice pattern, the thickness was measured. The maximum value
T.sub.M (.mu.m) and the standard thickness T.sub.S (.mu.m) of the
thickness values were substituted into a formula
(T.sub.M-T.sub.S)/T.sub.S.times.100 and the resulting value was
used as the tolerance (%) for thickness. With the tolerance for
thickness of the PSA sheet according to the present example being
50% or less, a Pass level grade can be given.
[0166] The PSA sheet according to the present example showed good
air release properties. It is presumed that the coating layer
formed partially on the PSA layer surface worked sufficiently as
the air releasing means. As shown in FIGS. 9 to 12, in the PSA
sheet according to the present example, a linearly extending part
(a band in the lattice pattern) had a certain cross-sectional
shape. In particular, the second face located on the PSA layer side
of the linearly extending part formed an overall gently curved line
in the cross section perpendicularly intersecting the length
direction of the linearly extending part. From the test results,
the PSA sheet with the coating layer having the cross-sectional
shape had a good surface condition on the adhesive face, showed a
small tolerance for thickness, and had high quality
[0167] These results indicate that when the coating layer has a
specific cross-sectional shape, good air release properties are
obtained and higher quality is achieved.
[0168] 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
[0169] 1, 2 PSA sheets [0170] 1A adhesive face [0171] 10 substrate
film [0172] 20, 21, 22 PSA layers [0173] 20A PSA layer surface
[0174] 30 coating layer [0175] 40 coating layer pattern (lattice
pattern) [0176] 42 first stripe pattern [0177] 44 second stripe
pattern [0178] 50 linearly extending part (band) [0179] 52 first
face [0180] 54 second face [0181] 56 one edge (left edge) of the
width direction of a linearly extending part [0182] 58 other edge
(right edge) of the width direction of a linearly extending part
[0183] 60 inclined segment [0184] 62 flat segment [0185] 70 coating
layer-bearing area [0186] 72 coating layer-free area [0187] 100,
101, 102 release liners [0188] 110 coating layer-bearing release
liner [0189] 120 releasable support [0190] 120A releasable face
* * * * *