U.S. patent application number 13/695580 was filed with the patent office on 2013-05-09 for adhesive composition.
This patent application is currently assigned to NITTO DENKO CORPORATION. The applicant listed for this patent is Takuya Mori, Tatsuki Nagatsuka, Miki Okamoto, Kentarou Takeda. Invention is credited to Takuya Mori, Tatsuki Nagatsuka, Miki Okamoto, Kentarou Takeda.
Application Number | 20130114026 13/695580 |
Document ID | / |
Family ID | 44861048 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130114026 |
Kind Code |
A1 |
Okamoto; Miki ; et
al. |
May 9, 2013 |
ADHESIVE COMPOSITION
Abstract
An adhesive composition which allows for preventing misalignment
when mutually laminating adherends, mutually strongly bonding the
adherends when correction of lamination is not required, as well as
peeling the adherends without causing any damage thereto when
correction of lamination is required. The adhesive composition
includes an adhesive base agent consisting of a monomer and a
polymerization initiator. Adhesive strength of the adhesive
composition changes to take a local maximum value, a local minimum
value and a value greater than the local maximum value along with
increase of irradiation amount of the electromagnetic wave or
particle beam irradiated to the adhesive composition under a
predetermined temperature environment.
Inventors: |
Okamoto; Miki; (Osaka,
JP) ; Mori; Takuya; (Osaka, JP) ; Takeda;
Kentarou; (Osaka, JP) ; Nagatsuka; Tatsuki;
(Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Okamoto; Miki
Mori; Takuya
Takeda; Kentarou
Nagatsuka; Tatsuki |
Osaka
Osaka
Osaka
Osaka |
|
JP
JP
JP
JP |
|
|
Assignee: |
NITTO DENKO CORPORATION
Ibaraki-shi, Osaka
JP
|
Family ID: |
44861048 |
Appl. No.: |
13/695580 |
Filed: |
April 30, 2010 |
PCT Filed: |
April 30, 2010 |
PCT NO: |
PCT/JP2010/057647 |
371 Date: |
January 9, 2013 |
Current U.S.
Class: |
349/96 ; 522/167;
522/168; 522/170; 522/173; 522/177; 522/182 |
Current CPC
Class: |
C09J 5/00 20130101; B32B
38/10 20130101; C09J 133/24 20130101; C09J 4/00 20130101; C09J
133/14 20130101; B32B 38/0008 20130101; C09J 133/26 20130101; C09J
133/02 20130101; C09J 137/00 20130101; G02F 1/133528 20130101; C09J
139/04 20130101; C09J 133/20 20130101 |
Class at
Publication: |
349/96 ; 522/173;
522/182; 522/177; 522/167; 522/170; 522/168 |
International
Class: |
C09J 139/04 20060101
C09J139/04; G02F 1/1335 20060101 G02F001/1335; C09J 133/20 20060101
C09J133/20; C09J 137/00 20060101 C09J137/00; C09J 133/26 20060101
C09J133/26; C09J 133/02 20060101 C09J133/02 |
Claims
1. An adhesive composition which intervenes between at least two
adherends and develops adhesive strength for mutually laminating
the at least two adherends by irradiation of electromagnetic wave
or particle beam, comprising: (a) an adhesive base agent consisting
of at least one type of monomer; and (b) at least one type of
polymerization initiator for generating polymerization of the
adhesive base agent, wherein the adhesive strength changes to take
a local maximum value, a local minimum value and a value greater
than the local maximum value along with increase of irradiation
amount of the electromagnetic wave or particle beam irradiated to
the adhesive composition under a predetermined temperature
environment.
2. An adhesive composition which intervenes between at least two
adherends and develops adhesive strength for mutually laminating
the at least two adherends by irradiation of electromagnetic wave
or particle beam, comprising: (a) an adhesive base agent consisting
of at least one type of monomer; and (b) at least one type of
polymerization initiator for generating polymerization of the
adhesive base agent, wherein the adhesive strength changes to take
a local maximum value and a local minimum value along with increase
of irradiation amount of the electromagnetic wave or particle beam
irradiated to the adhesive composition under a predetermined
temperature environment, and wherein the adhesive changes to take a
value greater than the local maximum value by further maintaining
the adhesive composition under a temperature environment higher
than the predetermined temperature environment after the adhesive
strength taking the local minimum value.
3. An adhesive composition as defined claim 1, the adhesive
composition indicates viscoelastic state which develops adhesive
strength by pressure when the adhesive strength is at least the
local maximum value, and indicates cured state which is sufficient
to allow for peeling at least one of the at least two adherends and
a layer consisting of the adhesive composition at an interface
therebetween without damaging the adherends when the adhesive
strength is at least at the local minimum value.
4. An adhesive composition as defined by claim 1, wherein time
required for the adhesive strength reaching to the local maximum
value, time required for the adhesive strength changing from the
local maximum value to the local minimum value and time required
for the adhesive strength changing from the local minimum value to
the value greater than the local maximum value is shortened along
with increase of irradiation intensity of electromagnetic wave or
particle beam and/or rise of temperature for adhesion.
5. An adhesive composition as defined by claim 1, the adhesive
composition is fluid when electromagnetic wave or particle beam has
not been irradiated under the predetermined temperature
environment.
6. An adhesive composition as defined by claim 1, wherein the at
least one type of monomer included in the adhesive base agent is a
photo-polymerizing vinyl monomer having at least one of hydroxyl
group, carboxyl group, cyano group, amino group, alicyclic
hydrocarbon group, heterocyclic group, amido group or carboxylate
ester group.
7. An adhesive composition as defined by claim 1, wherein the at
least one type of polymerization initiator is a
photo-polymerization initiator.
8. An adhesive composition as defined by claim 7, wherein
electromagnetic wave absorption wavelength of the
photo-polymerization initiator is a wavelength of electromagnetic
wave which transmits through either one of the at least two
adherends.
9. An adhesive composition as defined by claim 1, wherein the
adhesive strength decreases to a value at least smaller than the
local maximum value when the adhesive composition is immersed in
water after the adhesive strength increased the value greater than
the local maximum value.
10. An adhesive composition as defined by claim 1, wherein one of
the at least two adherends is an optical film and the other of the
at least two adherends is a substrate.
11. An adhesive composition as defined by claim 1, wherein one of
the at least two adherends is an optical film and the other of the
at least two adherends is a glass substrate or a plastic
substrate.
12. An adhesive composition as defined by claim 1, wherein both of
the at least two adherends are optical films.
13. An adhesive composition as defined by claim 1, wherein both of
the at least two adherends are glass substrates or plastic
substrates.
14. An adhesive composition as defined by claim 10, wherein the
optical film is a polarizing film, a polarizer, an anti-glare film,
a hard-coat film, an anti-reflection film, an optical compensation
film, a conductive film, a UV-cut film, a diffusion film, a
prismatic film, a light distribution film, a heat ray cut film, a
hand-cut filter or an electromagnetic wave shield film.
15. A viscoelastic body adapted to develop adhesive strength by
pressure along with increase of irradiation amount of
electromagnetic wave or particle beam irradiated to the adhesive
composition defined by claim 1 under a predetermined temperature
environment.
16. An optical film wherein a layer of the adhesive composition
defined by claim 1 is provided on at least one of surfaces
thereof.
17. A polarizing film wherein a layer of the adhesive composition
defined by claim 1 is provided on at least one of surfaces
thereof.
18. A panel for an optical display unit wherein a layer of the
adhesive composition defined by claim 1 is provided on at least one
of surfaces thereof.
19. A liquid crystal cell wherein a layer of the adhesive
composition defined by claim 1 is provided on at least one of
surfaces thereof.
20. An optical display unit comprising: a layer of the adhesive
composition defined by claim 1; an optical film bonded to one of
surfaces of the layer and a panel for an optical display unit
bonded to the other of the surfaces of the layer by irradiation of
electromagnetic wave or particle beam under a predetermined
temperature environment.
21. An optical display unit defined by claim 20, wherein the
optical film is a polarizing film and the panel for an optical
display unit is a liquid crystal cell.
22. An optical display unit defined by claim 21, wherein a
protection film of a polarizer of the polarizing film is laminated
on a surface opposite to the surface which the layer of the
polarizing film is bonded thereto.
Description
TECHNICAL FIELD
[0001] The present invention relates to adhesive composition. In
particular, the present invention relates to adhesive composition,
for example used for mutually laminating two adherends, a substrate
and a polarizing film, for manufacturing a liquid-crystal display
unit, which develops adhesive strength by irradiation of
electromagnetic wave or particle beam and allows for preventing
misalignment when laminating and for peeling easily where
necessary.
[0002] A liquid-crystal display unit used for a liquid-crystal
television is, in general, what a driving circuit, a printed
circuit board for driving and, where necessary, a back-light are
mounted on a liquid-crystal panel. The liquid-crystal panel is
configured by laminating sheet-like polarizing films to both
surfaces of a rectangular liquid-crystal cell which the
configuration elements thereof are a liquid-crystal layer, two
glass substrates sandwiching the liquid-crystal layer, transparent
electrodes and/or a color filter. A hard-coat layer and/or an
anti-glare layer may be provided on a surface of a polarizing film
which has not been laminated to a liquid-crystal cell of a
liquid-crystal panel. A polarizing film is, in general, what a
transparent protection film made from triacetyl cellulose (TAC) is
laminated on both surfaces of a polarizer produced from polyvinyl
alcohol (PVA) film. As another form of a polarizing film, it may be
manufactured by laminating a protection film only on one of the
surfaces of the polarizer and laminating a film having optical
compensation such as a phase contrast film on the other surface
thereof. On a polarizing film, generally, a surface protection film
for protecting the polarizing film, an adhesive layer for
laminating the polarizing film and the liquid-crystal cell and a
releasable film for protecting the adhesive layer until laminating
the polarizing film to the liquid-crystal cell. A laminate in which
a polarizing film is provided with a surface protection film, an
adhesive layer and a releasable film is called an optical film
laminate. A polarizing film is, in general, included in a
sheet-like optical film laminate cut out from a web-like optical
film laminate such that the size of the sheet corresponds to the
size of the liquid-crystal cell.
[0003] Generally, a liquid-crystal panel of a liquid-crystal
display unit is manufactured by laminating a protection film
included in a polarizing film and a glass substrate included in a
liquid-crystal cell via an adhesive layer. Adhesive used for
laminating the liquid-crystal cell and the polarizing film may be
defined as having the following properties. [0004] It is a
semi-solid material with high viscosity and low elastic modulus,
and adhered to an adherend by pressurizing [0005] It is peelable
from an adherend even after adhesion [0006] State of the adhesive
does not change in adhering process.
[0007] An adhesive having such properties is one type of adhesives
in a broad sense, and is called a pressure-sensitive adhesive
(hereinafter, PSA) because it intervenes between two adherends and
develops adhesive strength by being pressurized. Herein, an
adhesive means a PSA.
[0008] A technique for laminating a polarizing film and a
liquid-crystal cell using a PSA has the following merits. Since a
PSA is highly viscous, it allows for preventing misalignment
between the liquid-crystal cell and the polarizing film when
laminating. In addition, when it is required to correct alignment
or lamination, it allows for peeling the polarizing film from the
liquid-crystal cell.
[0009] On the other hand, the technique for laminating a polarizing
film and a liquid-crystal cell using a PSA has the following
demerits.
1. Degradation of Brightness Uniformity and View Angle
Characteristics
[0010] As described in above, a PSA is a semi-solid material with
high viscosity and low elastic modulus, and the status thereof does
not change during laminating. Thus, it is difficult to control
change of the size of the polarizing film in an environment where a
size of a polarizing film changes by heating or moisturizing after
laminating the polarizing film and a liquid-crystal cell via a PSA
layer. If the size of the polarizing film changes, it could cause
unevenness in brightness within a surface of a liquid-crystal
panel. Unevenness of brightness may be noticeable at peripheries
and/or at corners of a display surface of the liquid-crystal panel.
In addition, it could cause degradation of view angle
characteristics in that a contrast is degraded when the
liquid-crystal panel is viewed at an oblique angle. These demerits
may be further noticeable along with upsizing of liquid-crystal
panels in coming days.
2. Generation of Cracks in a Polarizing Film which a Protection
Film is Laminated Only on One of Surfaces Thereof
[0011] Conventional polarizing film is what protection films are
laminated on both surfaces of a polarizer. If the protection film
is laminated only on one of the surfaces, it allows for making a
polarizing film thinner. Since thin polarizing film allows for
reducing materials and thus manufacturing cost, using such thin
polarizing films in manufacturing liquid-crystal panels is very
advantageous for environmental consideration and cost-effectiveness
today when liquid-crystal panels are becoming larger and thinner.
However, when a thin polarizing film is laminated with a
liquid-crystal cell using a PSA, a change in size of the thin
polarizing film due to heating, moisturizing or an abrupt
temperature change may cause cracks therein. Because of this, in a
present liquid-crystal panel manufacturing technique using a PSA, a
thin polarizing film having a protection film laminated only on one
of the surfaces of a polarizer has not been put into practical
use
3. Scratches on a Surface of a Polarizing Film
[0012] A PSA is a material with low elastic modulus. Thus, when a
force is applied to a surface of a polarizing film, the polarizing
film itself may be deformed even when a hard coat layer is
laminated on the surface thereof because repulsive force of the PSA
is weak, and a dent and/or a collapse may be generated on the
surface of the polarizing film and/or the hard coat layer. This
problem may be particularly serious when using a thin polarizing
film which seems to be promising in coming days.
4. Difficulty in Re-Working
[0013] When a misalignment of laminating position of a liquid
crystal cell and a polarizing film or a trapping of foreign item or
air bubble is occurred while laminating the polarizing film and the
liquid crystal cell using a PSA, it is necessary to peel the
polarizing film from the liquid crystal cell. However, since
adhesion between the polarizing film and the liquid crystal cell
via a PSA may be strong enough to maintain a liquid crystal panel
as a product, a large force is required to actually peel the
polarizing film from the liquid crystal cell. But, applying a large
force to peel the polarizing film from the liquid crystal cell may
adversely affect the liquid crystal cells. And, a part of the
polarizing film or the PSA may not be completely peeled and may
remain on the liquid crystal cell. In such a case, removing process
of the remaining polarizing film is complex.
[0014] A part of those demerits of the technique for laminating a
polarizing film and a liquid crystal cell using a PSA is considered
to be solvable by laminating a polarizing film and a liquid crystal
cell using a conventional adhesive in place of a PSA. The technique
therefor has been proposed in, for example, the Patent Document 1
and the Patent Document 2.
[0015] The technique disclosed in the Patent Document 1 is a method
for manufacturing a liquid crystal panel by laminating an optical
film and a liquid crystal cell, wherein the optical film is first
laminated with a substrate in a weak adhesion state, then is
brought to a final adhesion state only when the liquid crystal
panel is determined to be defect-free under an inspection. The
adhesive used in the technique may be, for example, an acrylic
ultraviolet ray-curing adhesive or a heat-curing adhesive. In the
technique, ultraviolet ray is irradiated to a degree not to fully
cure the adhesive so that it is in a weak adhesion state. When the
liquid crystal panel is determined to be defect-free under an
inspection, ultraviolet ray is irradiated again so that the optical
film is fully bonded with the substrate. If the liquid crystal
panel is determined to be defective under the inspection, since the
adhesive layer is in a weak adhesion state, the optical film may be
easily peeled without adversely affecting the product.
[0016] The technique disclosed in the Patent Document 2 is a liquid
crystal display device having an ultraviolet ray-curing adhesive
layer and a method for manufacturing the same. In the technique, a
polarizing film is temporarily laminated with a liquid crystal cell
via an ultraviolet ray-curing adhesive, and then the polarizing
film is fully bonded to the liquid crystal cell by curing the
ultraviolet ray-curing adhesive under a irradiation of ultraviolet
ray, after inspecting for misalignment and trapping of foreign item
or air bubble. If any abnormality such as misalignment of the
polarizing film is found in the inspection, the adhesive is removed
from the polarizing film except when the polarizing film itself is
defective. The polarizing film which the adhesive is removed
therefrom is re-used.
[0017] Generally, such conventional adhesive may be defined as a
material with the following properties. [0018] It is originally a
fluid with liquidity and low viscosity which allows for sufficient
application to enlarge contact area when applied to an adherend,
and then adheres to the adherend by curing under light irradiation
or heating [0019] Increase in amount of light irradiation or
heating changes the adhesive to a fully cured state from a weak
adhesion state [0020] It is impossible to peel the polarizing film
from the liquid crystal cell without cohesion failure of the
adherends and/or the adhesive even after the adhesive is fully
cured [0021] State of the adhesive irreversibly changes over an
adhesion process (changes from fluid to solid).
[0022] An adhesive having such properties may be called an energy
sensitive adhesive (hereinafter, ESA) which develops adhesive
strength by curing under provided energy such as light or heat, and
may be called as an ultraviolet ray-curing adhesive or a
heat-curing adhesive depending on a type of provided energy.
PRIOR ART DOCUMENT
[0023] The prior art documents referred to in the above and
following descriptions are listed below. Patent Document 1:
Japanese Patent: JP3115116B
[0024] Patent Document 2: Laid-Open Japanese Patent Application
Publication JP10-333140A
[0025] Patent Document 3: Laid-Open Japanese Patent Application
Publication JP2008-31214A
[0026] Patent Document 4: Laid-Open Japanese Patent Application
Publication JP2007-212995A
[0027] Patent Document 5: Laid-Open Japanese Patent Application
Publication JP2006-316181A
[0028] Patent Document 6: Laid-Open Japanese Patent Application
Publication JP2008-189838A
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0029] As described in above, a conventional ESA is in fluid state
before absorbing energy such as ultraviolet ray for example, and
develops adhesive strength for laminating adherends by absorbing
the energy to be cured. Thus, for example, in a case where
laminating a polarizing film and a liquid crystal cell using a
conventional ESA, the polarizing film and the liquid crystal cell
may mutually slip before the ESA is cured and the alignment
accuracy may be degraded. In addition, adhesive strength of a
conventional ESA in fluid state is very weak. Thus, until the ESA
is cured after laminating a polarizing film and a liquid crystal
cell, the polarizing film may be partially peeled from the liquid
crystal cell due to curling caused by contraction stress of the
polarizing film. The thinner the polarizing film is, the more
noticeable the demerit becomes. Further, the conventional ESA
cannot be removed from the adherend once cured. This means that if
laminating the polarizing film and the liquid crystal cell is
failed, the polarizing film cannot be removed from the liquid
crystal cell, and it is impossible or extremely difficult at best
to re-use the liquid crystal cell.
[0030] The technique disclosed in the Patent Document 1 and the
Patent Document 2 is for firstly laminating a polarizing film and a
liquid crystal cell via an adhesive layer at a weak adhesion state,
inspecting whether or not it is required to correct the lamination,
and then, laminating them at a strong adhesion state by irradiating
ultraviolet ray. The technique disclosed in either Patent Document
requires a certain degree of peeling force even at a weak adhesion
state when it is necessary to peel the polarizing film from the
liquid crystal cell to correct the lamination therebetween, and
presents a risk of causing the same problem with the PSA described
above. Also, if the polarizing film is peeled from the liquid
crystal cell at a weak adhesion state, the ESA at a weak adhesion
state may remain on the liquid crystal cell after peeling. Since
removal of the remaining ESA from the liquid crystal cell requires
a solvent, the work for removal becomes complex and an
environmental load therefrom becomes larger.
[0031] The present invention aims at providing adhesive composition
which allows for: preventing misalignment when laminating
adherends; strongly bonding of the adherends when a correction of
lamination is not required; and easily peeling the adherends
without any damage thereto when a correction of lamination is
required.
Means to Solve the Problem
[0032] The inventors of the present invention have completed the
invention based on a finding that adhesive strength between
adherends laminated via an adhesive composition and state of the
adhesive composition may be controlled by precisely controlling
irradiation intensity and irradiation amount of electromagnetic
wave or particle beam to the adhesive composition, and temperature
environment when the electromagnetic wave or particle beam is
irradiated to the adhesive composition.
[0033] In a first aspect, the present invention provides adhesive
composition which intervenes between at least two adherends and
develops adhesive strength for laminating the adherends by
irradiating electromagnetic wave or particle beam. The adhesive
composition defined by the present invention is at fluid state or a
highly viscous fluid state at least when the electromagnetic wave
or particle beam has not been irradiated, and the adhesive strength
thereof for laminating the adherends is very small. The adhesive
strength of the adhesive composition may be increased or reduced by
irradiating the electromagnetic wave or particle beam at intensity
lower than the critical irradiation intensity defined herein and by
extending and/or shortening irradiation time of the electromagnetic
wave or particle beam via a layer of an intervening film under a
predetermined temperature environment. According to the present
invention, by providing the irradiation intensity of the
electromagnetic wave or particle beam lower than that used for
curing the conventional ESAs, the adhesive strength between the
adherends via the adhesive composition may be arbitrarily
controlled.
[0034] An adhesive composition according to the present invention
comprises adhesive agent consisting of at least one type of monomer
and at least one type of polymerization initiator for generating
polymerization of the adhesive agent. The adhesive composition
according to the present invention is used for mutually laminating
at least two adherends. Adhesive strength of the adhesive
composition increases to a local maximum value, then decreases to a
local minimum value, and then, increases to a value greater than
the local maximum value along with increase in irradiation amount
of electromagnetic wave or particle beam, irradiated at intensity
lower than critical irradiation intensity defined herein under a
predetermined temperature environment.
[0035] According to the present invention, when laminating the two
adherends with the adhesive composition, the adherends may be
laminated in a state where positions thereof are not misaligned by
increasing the adhesive strength to at least the local maximum
value by irradiating the electromagnetic wave or particle beam with
an appropriate intensity for a predetermined time. Here, at least
the local maximum value means any value in a predetermined range
with the local maximum value as the greatest value. The state of
the adhesive composition at the value is viscoelastic where
adhesive strength is developed by pressure.
[0036] When it is necessary to peel the two adherends, the
adherends may be easily peeled by reducing the adhesive strength to
at least the local minimum value under irradiation of the
electromagnetic wave or particle beam with an appropriate intensity
for a predetermined time. Here, at least the local minimum value
means any value in a predetermined range where the local minimum
value is the smallest value. The state of the adhesive composition
at the value is cured to a degree where at least one of the at
least two adherends and the layer of the adhesive composition may
be peeled at an interface therebetween without damaging the
adherends. Here, "may be peeled at an interface therebetween
without damaging the adherends" includes not only a case where the
layer of the adhesive composition and the adherend may be peeled at
the interface therebetween without causing cohesion failure of the
layer of the adhesive composition and the adherend, but also a case
where the adhesive composition and the adherend may be peeled at
the interface therebetween at a state where a part of the adhesive
composition is remaining on the adherend after being peeled.
[0037] Adhesive strength of the adhesive composition according to
the present invention decreases to the local minimum value after
taking the local maximum value, and then, increases to a value
greater than the local maximum value along with increase in
irradiation amount of electromagnetic wave or particle beam
irradiated at intensity lower than critical irradiation intensity.
According to the present invention, the adherends may be laminated
without any position misalignment by increasing the adhesive
strength of the adhesive composition to at least the local maximum
value by irradiating the electromagnetic wave or particle beam with
an appropriate intensity for a predetermined time under a first
predetermined temperature environment. When a correction of the
lamination is not required, the two adherends may be bonded at a
final strong adhesion by increasing the adhesive strength to a
value greater than the local maximum value by further irradiating
the electromagnetic wave or particle beam with an appropriate
intensity under the first predetermined temperature environment for
the predetermined time. The state of the adhesive composition then
is cured at the same degree when the adhesive strength is at the
local minimum value or is further cured, and if it is attempted to
peel the two adherends, cohesion failure may occur in the layer of
the adhesive composition and/or within the adherends.
[0038] The adhesive composition according to the present invention
allows for increasing the adhesive strength to a value greater than
the local maximum value by maintaining the adhesive composition
under a second predetermined temperature environment higher than
the first predetermined temperature environment for a time equal to
or longer than the predetermined time, after the adhesive strength
decreased to the local minimum value after taking the local maximum
value, by irradiating the electromagnetic wave or particle beam
under the first predetermined temperature environment. In this
case, the adherends may be laminated without position misalignment
by increasing the adhesive strength to at least the local maximum
value. When a correction of the lamination is not required, the two
adherends may be bonded at final strong adhesion by increasing the
adhesive strength to a value greater than the local maximum value
by maintaining the adherends under the second predetermined
temperature environment for a time equal to or longer than the
predetermined time. The state of the adhesive composition then is
cured at the same degree when the adhesive strength is at the local
minimum value or is further cured, and if it is attempted to peel
the two adherends, cohesion failure may occur in the layer of the
adhesive composition and/or within the adherends.
[0039] Adhesive strength of the adhesive composition according to
the present invention may be reduced to a value smaller than at
least the local maximum value by immersing the adhesive layer in
water after the adhesive strength increases to a value greater than
the local maximum value along with increase in irradiation amount
of electromagnetic wave or particle beam. According to the present
invention, when it is necessary to peel the two adherends laminated
via the adhesive composition after reaching to the final strong
adhesion state, the two adherends may be easily peeled by immersing
the laminate consisting of the two adherends and the adhesive
composition in water to swell the adhesive composition.
[0040] In the adhesive composition according to the present
invention, increase of the irradiation intensity of the
electromagnetic wave or particle beam and/or increase of the
temperature reduces time necessary for the adhesive strength
increasing to the local maximum value, decreasing from the local
maximum value to the local minimum value, and increasing to a value
greater than the local maximum value from the local minimum value.
According to the present invention, appropriate selection of the
irradiation intensity of the electromagnetic wave or particle beam
and the temperature for bonding allows for arbitrarily controlling
time for the adhesive composition reaching to a certain adhesive
strength and state and controlling time to maintain the state.
Thus, use of the adhesive composition according to the present
invention allows for higher degree of freedom in process to
laminate the adherends with the adhesive composition.
[0041] The at least one type of monomer contained in an adhesive
base agent is: preferably a photopolymerizing vinyl monomer having
at least one of hydroxyl group, carboxyl group, cyano group, amino
group, alicyclic hydrocarbon group or heterocyclic group;
preferably an acryloyl group-containing monomer or a
photopolymerizing vinyl monomer having carboxyl group, cyano group,
amino group or heterocyclic group; preferably a (meth)acryloyl
group-containing monomer; more preferably a monofunctional
(meth)acryloyl group-containing monomer; and more preferably a
monofunctional (meth)acryloyl group-containing monomer having a
polar group. The polar group is preferably a monofunctional
(meth)acryloyl group-containing monomer having at least one of
hydroxyl group, carboxyl group, cyano group, amino group, alicyclic
hydrocarbon group, heterocyclic group, and the at least one monomer
is preferably a hydroxyalkyl (meth)acrylamide, a hydroxyalkyl
(meth)acrylate, a N,N-dialkyl (meth)acrylamide, or a N-alkyl
(meth)acrylamide.
[0042] In one embodiment of the present invention, the
polymerization initiator is preferably a photo-polymerization
initiator. Absorption wavelength of the photo-polymerization
initiator is preferably a wavelength that transmits through either
one of the at least two adherends.
[0043] It is preferable that the adhesive composition according to
the present invention is used as an ESA for laminating an optical
film with another optical film or an optical film with a substrate.
It is also preferable that the adhesive composition according to
the present invention is used as an ESA for manufacturing a liquid
crystal display unit, a plasma display unit, and an organic
electroluminescence (EL) display unit.
[0044] In manufacturing a liquid crystal display unit, one of the
two adherends to be laminated may be a polarizer, a protection film
laminated on a polarizer for protection thereof or an optical
compensation film using a phase contrast film. The other of the two
adherends may be a glass substrate or a plastic substrate included
in a liquid crystal cell.
[0045] In manufacturing a plasma display unit, one of the two
adherends to be laminated may be a plasma display panel or a
protection substrate thereof, and the other of the two adherends
may be a ultraviolet (UV)-cut film, an anti-glare film, an
anti-reflection film, an anti-crack film, an electromagnetic wave
shield film, a band-pass film or a hard-coat film.
[0046] In manufacturing an organic EL display unit, one of the two
adherends to be laminated may be an organic EL display panel or a
protection substrate thereof, and the other of the two adherends
may be a UV-cut film, an anti-glare film, an anti-reflection film,
an anti-crack film, a circular polarizing plate for anti-reflection
or a hard-coat film.
[0047] According to another aspect, the present invention provides
a viscoelastic body which develops adhesive strength by pressure in
a predetermined temperature environment along with increase of
irradiation amount of the electromagnetic wave or particle beam
irradiated to the adhesive composition according to the present
invention.
[0048] According to another aspect, the present invention provides
an optical film or a panel for an optical display unit which is
provided on one of the surfaces therewith the adhesive composition
according to the present invention, or the viscoelastic body which
develops adhesive strength by pressure in a predetermined
temperature environment along with increase in irradiation amount
of the electromagnetic wave or particle beam irradiated to the
adhesive composition according to the present invention. That is,
in this aspect, a layer of the adhesive composition or a layer of
the viscoelastic body according to the present invention is formed
on one of the surfaces of the optical film or the panel for optical
display unit. The optical film may be formed in sheets or a web.
According to one embodiment of the present invention, the optical
film may be a polarizing film and the panel for an optical display
unit may be a liquid crystal cell.
[0049] In another aspect, the present invention provides an optical
display unit comprising an optical film laminated with a layer of
the adhesive composition and the panel for an optical display unit
according to the present invention. In the present invention, the
optical film and the layer of the adhesive composition are bonded
by irradiating the electromagnetic wave or particle beam to the
adhesive composition contacting the optical film at intensity lower
than the critical irradiation intensity for a certain time under a
predetermined temperature environment. Similarly, the panel for the
optical display unit and the layer of the adhesive composition are
bonded by irradiating the electromagnetic wave or particle beam to
the adhesive composition contacting the panel for the optical
display unit at intensity lower than the critical irradiation
intensity for a certain time under a predetermined temperature
environment. When manufacturing an optical display unit, the layer
of the adhesive composition may be initially formed on the optical
film, formed on the panel for optical display unit, or formed on a
transferrable substrate and then transferred onto the panel for the
optical display unit or the optical film at fluid state or
viscoelastic state. According to one embodiment of the present
invention, the optical film may be a polarizing film and the panel
for the optical display unit may be a liquid crystal cell. As for
the polarizing film, one which a protection film for a polarizer is
laminated only on a surface opposite to the surface that the layer
of the adhesive composition is bonded thereon, or, one which a
protection film is laminated only on a surface that the layer of
the adhesive composition is bonded thereon, may be used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] FIG. 1 is a schematic diagram showing change of adhesive
strength of the adhesive composition according to the present
invention.
[0051] FIG. 2 is a schematic diagram showing change of adhesive
strength of conventional adhesive composition.
[0052] FIG. 3 is a table showing test result for change of adhesive
strength to glass when irradiation amount of electromagnetic wave
or particle beam is changed.
[0053] FIG. 4 is a table showing elasticity of the adhesive
composition according to the present invention at PSA-like state,
easy-to-peel state, and strong adhesion state.
[0054] FIG. 5 is a diagram showing change of state of the adhesive
composition according to irradiation intensity of the
electromagnetic wave or particle beam.
BEST MODE FOR CARRYING OUT THE INVENTION
[0055] The present invention is particularly described in the
following.
<Adhesive Base Agent>
[0056] The adhesive composition according to the present invention
comprises: (a) an adhesive base agent consisting of at least one
type of monomer and (b) at least one type of polymerization
initiator for initiating polymerization of the adhesive base agent.
The at least one type of monomer is a material which becomes a
polymer by polymerization under an action of the polymerization
initiator. Glass transition temperature of the adhesive base agent,
after polymerization, is preferably 50.degree. C. or higher, when
the adhesive base agent is used for laminating a polarizing film
and a substrate of a liquid crystal panel. Glass transition
temperature of 50.degree. C. or higher allows for reducing
unevenness of display by reducing deformation of a polarizing film
even when heat generates distortion in a liquid crystal panel or
the polarizing film in, for example, a liquid crystal display unit.
When the adhesive composition according to the present invention is
used as an adhesive for panels for vehicles, it also improves
durability of the panels under heat because adhesive strength of
the adhesive composition may be maintained even when a temperature
in a car cabin becomes high.
[0057] It is preferable that refraction index of the adhesive base
agent after polymerization is close to that of two adherends to be
laminated via a layer of the adhesive composition. It is most
preferable that the refraction index of the adhesive base agent
after polymerization is intermediate of those of the two adherends.
Use of the adhesive composition comprising such adhesive base agent
allows for improving efficiency of use of light and visibility
because reflection at an interface between the layer of the
adhesive composition and the adherends is reduced.
[0058] The material usable as a monomer for an adhesive base agent
for the adhesive composition according to the invention is
preferably a photo-polymerizing vinyl monomer having at least one
of hydroxyl group, carboxyl group, cyano group, amino group, amido
group, carboxylate ester group, alicyclic hydrocarbon group or
heterocyclic group; and, in particular for bonding a glass
substrate and a polarizing film, preferably an acryloyl
group-containing monomer or a photo-polymerizing vinyl monomer
having carboxyl group, cyano group, amino group, amido group or
heterocyclic group; preferably a (meth)acryloyl group-containing
monomer; more preferably a monofunctional (meth)acryloyl
group-containing monomer; and more preferably a monofunctional
(meth)acryloyl group-containing monomer having a polar group.
[0059] The acryloyl group-containing monomer may include a
(meth)acrylamide monomer, a (meth)acrylate monomer, and the like.
It may also include an acryloyl group-containing monomer having a
polar group such as heterocyclic group, hydroxyl group and amino
group.
[0060] The acrylamide monomer may include, for example,
hydroxymethyl acrylamide, hydroxyethyl acrylamide, hydroxypropyl
acrylamide, dimethyl acrylamide, diethyl acrylamide, N-methyl
acrylamide and the like. The acrylamide monomer is preferable
because: it has a polar group; owing to the polar group, hydrogen
bonding capacity to the surface of glass substrate is improved;
glass transition temperature is often a room temperature or higher;
adhesive strength can be reduced by immersing in water so that it
is easily recycled; and adhesive strength can be reduced without
using various organic solvents so that environmental load is
reduced.
[0061] The (meth)acrylate monomer may include a (meth)acrylate
monomer having hydroxyl group, heterocyclic group or alicyclic
hydrocarbon group.
[0062] The (meth)acrylate monomer having hydroxyl group may
include, for example, hydroxyethyl acrylate, hydroxyethyl
methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate,
hydroxybutyl acrylate and hydroxybutyl methacrylate. The
(meth)acrylate monomer having hydroxyl group is preferable because
it has a polar group, and owing to the polar group, hydrogen
bonding capacity to the surface of glass substrate is improved.
[0063] The (meth)acrylate monomer having heterocyclic group may
include, for example, glycidyl methacrylate and tetrahydrofurfuryl
methacrylate. The (meth)acrylate monomer having heterocyclic group
is preferable because it has a polar group, and owing to the polar
group, hydrogen bonding capacity to the surface of glass substrate
is improved.
[0064] The (meth)acrylate monomer having alicyclic hydrocarbon
group may include, for example, dicyclopentenyl acrylate, isobornyl
acrylate, and cyclohexyl methacrylate. Since the (meth)acrylate
monomer having alicyclic hydrocarbon group has no polar group, it
is suitable for laminating with substrates having no polar group or
week polarity, such as cycloolefinic substrates.
[0065] Other polar group-containing monomer may include, for
example, acryloylmorpholine, acrylic acid, acrylamide, and
acrylonitrile. The other polar group-containing monomer is
preferable because it has a polar group, and owing to the polar
group, hydrogen bonding capacity to the surface of glass substrate
is improved.
[0066] The adhesive base agent of the adhesive composition
according to the present invention may be what two or more of the
above monomers are combined therein. Also, the adhesive base agent
may be what any of the above monomers is a base component and a
monomer other than the above monomers is a sub-component. In this
case, it is preferable that a ratio of the above monomer in the
adhesive base agent is greater than 50%. The adhesive composition
according to the present invention is in fluid state when the
electromagnetic wave or particle beam has not been irradiated under
a predetermined temperature environment for curing the adhesive
composition. Herein, the fluid state includes highly viscous fluid
state. For the adhesive composition to be in fluid state, the
adhesive base agent of the adhesive composition needs to be fluid
or dissolved in fluid material under a predetermined temperature
environment for curing the adhesive composition.
<Polymerization Initiator>
[0067] Any publicly-known polymerization initiator may be used as a
polymerization initiator of the adhesive composition according to
the present invention. A polymerization initiator is a material
that can absorb energy to produce active species. Polymerization of
an adhesive base agent is initiated when active species produced by
the polymerization initiator is added to unsaturated bond of the
adhesive base agent, and proceeds as active species of the adhesive
base agent is added to unsaturated bond of the adhesive. It is
preferable to use a photo-polymerization initiator as a
polymerization initiator in the present invention. Use of a
photo-polymerization initiator allows for generating polymerization
by light to facilitate control of adhesive strength and state of
the adhesive composition according to the present invention and to
avoid deterioration or failure of the adhesive. Examples of
photo-polymerization initiator may include alkylphenone
photo-polymerization initiator, acylphosphine oxide
photo-polymerization initiator, titanocene photo-polymerization
initiator, and cation photo-polymerization initiator. Examples of
photo-polymerization initiator using ultraviolet may include
various photo-polymerization initiators such as benzoin
photo-polymerization initiator, benzophenon photo-polymerization
initiator, anthraquinones photo-polymerization initiator, xanthone
photo-polymerization initiator, tioxanthone photo-polymerization
initiator, ketal photo-polymerization initiator.
[0068] Specific examples of the photo-polymerization initiator may
include acetophenone compounds such as 4-(2-hydroxyethoxy)phenyl
(2-hydroxy-2-propyl) ketone,
.alpha.-hydroxy-.alpha.,.alpha.'-dimethyl acetophenone, methoxy
acetophenone, 2,2-dimethoxy-2-phenyl acetophenone, 2,2-diethoxy
acetophenone, 1-hydroxycyclohexyl phenyl ketone, and
2-methyl-1-[4-(methylthio)-phenyl]-2-morpholinopropane-1-one;
benzoin ether compounds such as benzoin ethyl ether, benzoin
isopropyl ether, and anisoin methyl ether; a-ketol compounds such
as 2-methyl-2-hydroxypropiophenone; ketal compounds such as benzyl
dimethyl ketal; aromatic sulfonyl chloride compounds such as
2-naphthalenesulfonyl chloride; photo-active oxime compounds such
as 1-phenone-1,1-propanedione-2-(O-ethoxycarbonyl)oxime;
benzophenone compounds such as benzophenone, benzoylbenzoic acid,
3,3'-dimethyl-4-methoxy-benzophenone, and 3,3',4,4'-tetra(t-butyl
peroxycarbonyl)benzophenone.
[0069] Energy necessary for a polymerization initiator to produce
active species is generally provided through either one of two
adherends to be laminated via the adhesive composition. Thus, when
a photo-polymerization initiator is used as a component of the
adhesive composition, it is preferable that light absorption
wavelength of a usable photo-polymerization initiator is a
wavelength that transmits through adherends to be laminated. For
example, when the adhesive composition according to the present
invention is used for laminating a liquid crystal cell and a
polarizing film which a TAC film is used as a protection film
thereof, it is preferable to use a photo-polymerization initiator
having light absorption at wavelength longer than about 380 nm that
transmits through a polarizing film so that irradiated light is not
absorbed by light absorber contained in the TAC.
[0070] In the present invention, as electromagnetic wave or
particle beam for irradiation, it is preferable to use
electromagnetic wave having wavelength of ultraviolet ray or that
in vicinity thereof. If visible light is used, polymerization may
proceed under effect of surrounding light to make control of
reaction difficult, and absorption of visible light by residual of
the polymerization initiator may color the adhesive composition. If
infrared ray is used, polymerization may proceed under effect of
heat to make control of reaction difficult.
[0071] In the present invention, it is preferable that a
photo-polymerization initiator, after reacting by light, has no or
low absorption in a range of wavelength of visible light.
Particularly, when the adhesive composition according to the
present invention is used for a liquid crystal display unit, it is
preferable that a photo-polymerization initiator has no or low
absorption in vicinity of 440 nm, 530 nm and 610 nm which are the
peaks of an emission line of a backlight so that it does not affect
hue when viewing.
<Mixing Ratio of Adhesive Base Agent and Polymerization
Initiator in the Adhesive Composition>
[0072] Mixing ratio of adhesive base agent and polymerization
initiator in the adhesive composition according to the present
invention is not particularly specified. However, if a ratio of the
polymerization initiator is too high, it may raise problems such as
reaction control is difficult because speed of polymerization is
too fast, the adhesive composition is colored and dispersion of the
polymerization initiator is deteriorated. If the ratio of the
polymerization initiator is too low, productivity of a process of
laminating the adherends using the adhesive composition is reduced
and is not preferable. For example, when hydroxyethyl acrylamide
(HEAA) is used as an adhesive base agent and acylphosphine oxide
photo-polymerizing initiator is used as a polymerization initiator,
it is preferable that the adhesive composition according to the
present invention contains 0.3 to 3 parts of the polymerization
initiator to 100 parts of HEAA in the adhesive composition.
<Change of Adhesive Strength and State of the Adhesive
Composition According to Irradiation Intensity of Electromagnetic
Wave or Particle Beam>
[0073] The adhesive composition according to the present invention
may be used for mutually laminating two adherends by intervening
therebetween. In the present invention, the adhesive strength
between the adherends via the adhesive composition and the state of
the adhesive composition according to the present invention may be
controlled by controlling temperature environment where the
adhesive composition is exposed so that the temperature of the
adhesive composition is maintained at a certain degree for a
predetermined time, as well as by maintaining irradiation intensity
of the electromagnetic wave or particle beam irradiated to the
adhesive composition smaller than the irradiation intensity defined
herein for curing conventional adhesives.
[0074] When mutually laminating at least two adherends using the
adhesive composition according to the present invention,
electromagnetic wave or particle beam is irradiated from a side of
one of the adherends of the laminate consisting of the at least two
adherends and the adhesive composition and reaches to the adhesive
composition through the one of the adherends. Therefore, the
irradiation intensity and the irradiation amount of the
electromagnetic wave or particle beam to the laminate (i.e. the
irradiation intensity and the irradiation amount of the
electromagnetic wave or particle beam measured between the
irradiation source and the laminate, hereinafter referred as
"measured irradiation intensity and irradiation amount"), and the
actual irradiation intensity and the actual irradiation amount of
the electromagnetic wave or particle beam to the adhesive
composition itself (hereinafter referred as "theoretical
irradiation intensity and irradiation amount") are different.
Herein, when irradiation intensity and irradiation amount of the
electromagnetic wave or ultraviolet is referred, it means the
measured irradiation intensity and irradiation amount, not the
actual irradiation intensity and irradiation amount. For example,
since light transmissivity at wavelength of 400 nm by a polarizing
film from Nitto Denko Corporation (product code VEGQ5724DU) is
about 30%, light intensity and amount absorbed by the adhesive
composition through this polarizing film (the theoretical
irradiation intensity and irradiation amount) may be about 30% of
the irradiation intensity and the irradiation amount of the light
source (the measured irradiation intensity and irradiation
amount).
[0075] Adhesive strength F for laminating an adherend 1 and an
adherend 1' via a layer 2 of the adhesive composition is defined as
the smallest of the following f1, f1', f2, f3 and f3':
[0076] Interface adhesive strength f1, f1': adhesive strength
working between the adherend 1 or the adherend 1' and the layer
2;
[0077] Cohesion of the adhesive composition f2: force working
between molecules of the adhesive composition within the layer
2;
[0078] Cohesion of adherends f3, f3': force working between
molecules within the adherend 1 and the adherend 1'.
[0079] Relationship of magnitude among the f1, f1', 12, 13 and f3'
determines where state of adhesion fails, such as, at an interface
between the adherend 1 and the adherend 1', the layer 2, or the
adherend 1, 1' and the layer 2. The state of adhesion between the
adherend 1 and the adherend 1' fails at where the above forces are
the smallest. The failure is classified as cohesion failure of the
adherends 1, 1', interface failure between the adherends 1, 1' and
the layer 2, cohesion failure of the layer 2 of the adhesive
composition, and the mixture failure thereof. Generally, since it
is difficult to measure adhesive strength, peeling force is
evaluated as the adhesive strength. The peeling force takes a value
including a force required for plastic deformation of the layer 2
of the adhesive composition and a force smaller of the interface
adhesive strength f1, f1'.
[0080] Use of the adhesive composition according to the present
invention allows for arbitrarily controlling of adhesive strength
for mutually laminating adherends (F in the above definition of
adhesive strength (hereinafter, the symbol for adhesive strength is
that used in the above definition)) and state of the adhesive
composition.
(Fluid State)
[0081] The layer 2 of the adhesive composition according to the
present invention is in fluid state with liquidity when the
electromagnetic wave or particle beam has not been irradiated and
under at least the first predetermined temperature environment, as
for the conventional adhesives according to the above definition.
In this state, the adhesive strength F is very small and the
lamination position of the two adherends 1, 1' via the layer 2 may
be easily displaced. At this point, the cohesion f2 is very small
compared with f1, f1', f3 and f3'.
(PSA-Like State)
[0082] If the electromagnetic wave or particle beam with an
appropriate intensity is irradiated to the layer 2 under the first
predetermined temperature environment, the adhesive strength F
increases along with the increase of the irradiation amount thereof
(i.e. the cohesion f2 becomes larger). If the irradiation amount
further increases, the adhesive strength F reaches to the local
maximum value and then starts decreasing. The state of the layer 2
when the adhesive strength F takes a value in a predetermined range
including the local maximum value is similar to a state of the
conventional adhesives according to the above definition (i.e.
PSA), that is viscoelastic body which is not fully cured and with
high viscosity and low elastic modules. When the layer 2 is at such
state, the layer 2 develops adhesive strength by pressure and may
reduce misalignment of the two adherends 1, 1' laminated via the
layer 2 by preventing displacement between the two adherends 1, 1'.
At this point, the cohesion f1 has a sufficient magnitude not to
generate any displacement by a force in shearing direction at
laminating.
[0083] If a peeling force is applied between the two adherends 1,
1' while the adhesive strength F is taking a value in the
predetermined range including the local maximum value, the layer 2
deforms to stretch, and when the peeling forces becomes larger than
a force that is a sum of the interface adhesive strength f1 or f1'
and a force required for the layer 2 to deform to stretch (a force
required for plastic deformation of the layer 2 at the state of
viscoelastic body), one of the adherends 1 and 1' is peeled from
the layer 2. Whether the one of the adherends 1 and 1' is peeled
from the layer 2 at the interface between the adherend 1 and the
layer 2 or at the interface between the adherend 1' and the layer 2
depends on the magnitude of f1 and f1'. In the above, since the 12
is greater than the f1 or f1', cohesion failure of the adhesive may
be prevented. If the one of the adherends 1 and 1' is peeled from
the layer 2, since the layer is at the similar state as PSA
according to the above definition, they may be re-bonded.
[0084] As described above, the state of the adhesive composition
when it becomes a viscoelastic body which develops the adhesive
strength F by pressure is herein referred as "PSA-like" state, and
in the PSA-like state, the adhesive strength F takes a value in a
predetermined range where the local maximum value is the greatest
value. The local maximum value of the adhesive strength F and the
predetermined range including the local maximum value when the
adhesive composition is in the PSA-like state vary depending on
conditions including a type of the adhesive base agent, a type and
a dose of the photo-polymerization initiator, irradiation intensity
and wavelength of the electromagnetic wave or particle beam, and
temperature environment.
[0085] After the adhesive composition reaching to the PSA-like
state, the state may be maintained for a certain period by shading
the adhesive composition from further irradiation of the
electromagnetic wave or particle beam and by maintaining the
temperature lower than the first predetermined temperature
environment.
[0086] For example, a case where one of the at least two adherends,
the adherend 1, is a polarizing film and the other, the adherend
1', is a glass of a liquid cell is considered. The polarizing film
is a laminate which protection films consisting TAC are laminated
on both surfaces thereof. Although the detail of experiments will
be later described in Example 1, the layer 2 came to "PSA-like"
state when: an adhesive composition containing 100 parts of HEAA
monomer and 1 part of acylphosphine oxide photo-polymerizing
initiator was applied on a glass to form the layer 2; a polarizing
film was laminated on the layer 2; and, while the obtained laminate
was heated at 70.degree. C. from the glass side, light with energy
of 15 to 35 mJ/cm.sup.2 with the wavelength of 405 nm was
irradiated from the polarizing film side at the irradiation
intensity of 7 mW/cm.sup.2. The local maximum value of the adhesive
strength was 12 N/25 mm. And the proportion of the reacted monomer
when the adhesive strength was at the local maximum value was about
57%.
(Easy-to-Peel State)
[0087] After the adhesive strength F reached to the local maximum
value, if the electromagnetic wave or particle beam with an
appropriate intensity is further irradiated to the layer 2 under
the first predetermined temperature environment, the adhesive
strength F decreases to the local minimum value along with the
increase of the electromagnetic wave or particle beam and then
starts to increase again. The state of the layer 2, when the
adhesive strength F takes a value in a predetermined range
including the local minimum value, is not fully cured, though the
layer 2 is further cured than it was at the PSA-like state. While
the layer 2 is in such state, the two adherends 1, 1' may be easily
peeled from the layer 2 with a little force. Thus, the laminated
two adherends 1, 1' may be peeled without giving damage thereto. At
this point, the cohesion f2 is larger than when the layer 2 was at
the PSA-like state and either of the interface adhesive strength f1
or f1' is considered to be far smaller than the f2. Since the layer
2 is cured, the adhesive strength F is very small and the adhesive
composition hardly spreads onto the adherends, and thus, once the
adherend 1 or 1' is peeled from the layer 2, it is not possible to
re-bond them with adhesive strength sufficient to maintain at least
the state of lamination as a product.
[0088] As described in the above, the state of cure when at least
one of the adherends 1, 1' and the layer 2 may be peeled at the
interface therebetween without damaging the adherends is herein
referred as "easy-to-peel" state, and the adhesive strength F at
the state takes a value in a predetermined range where the local
minimum value is the smallest value. The local minimum value of the
adhesive strength F and the predetermined range including the local
minimum value when the adhesive composition is at the easy-to-peel
state vary depending on conditions including a type of the adhesive
base agent, a type and a dose of the photo-polymerization
initiator, irradiation intensity and wavelength of the
electromagnetic wave or particle beam, and temperature
environment.
[0089] In the same Example 1, for example, when light having energy
of 35 to 150 mJ/cm.sup.2 was irradiated from the polarizing film
side, the state of the layer 2 became "easy-to-peel" state, and the
local minimum value of the adhesive strength then was 0.5 N/25 mm,
and the proportion of the reacted monomer when the adhesive
strength was at the local minimum value was about 87%.
(Strong Adhesion State)
[0090] After the adhesive strength F started increasing again after
taking the local minimum value, if the electromagnetic wave or
particle beam with an appropriate intensity is continued to be
irradiated to the layer 2 under the first predetermined temperature
environment, the adhesive strength F increases along with the
increase of the irradiation amount of the electromagnetic wave or
particle beam and finally reaches to a value at least greater than
the local maximum value. At this point, the polymerization of the
adhesive base agent in the layer 2 is almost completed and the
layer 2 is at a same cured state as it was at the easy-to-peel
state or is further cured, and thus the two adherends 1, 1'
strongly adhere via the layer 2. The cohesion f2 at this point is
same as or greater than the f2 at the easy-to-peel state, and the
interface adhesive strength f1 and f1' are greater than the f2 in
the PSA-like state. Already at this point, the two adherends 1, 1'
may not be peeled, and if they are forced to be peeled, cohesion
failure occurs in either of the adherend 1 or the adherend 1' or
the layer 2 depending on the magnitude relationship between the f2,
f3 and f3'.
[0091] As described in above, the state of the adhesive composition
when it is at a same cured state as it was at the easy-to-peel
state or is further cured is herein referred as "strong adhesion"
state, and the adhesive strength F at the state takes a value
greater than the local maximum value. The smallest value of the
adhesive strength F when the adhesive composition is in the strong
adhesion state (i.e. the local minimum value in a range greater
than the local maximum value) varies depending on conditions
including a type of the adhesive base agent, a type and a dose of
the photo-polymerization initiator, irradiation intensity and
wavelength of the electromagnetic wave or particle beam, and
temperature environment.
[0092] In the same Example 1, for example, when light having energy
greater than 150 mJ/cm.sup.2 was irradiated from the polarizing
film side, the layer 2 became "strong adhesion" state, and the
maximum value of the adhesive strength then was greater than the
cohesion of the protection film included in the polarizing film and
the interface adhesive strength between the protection film and the
polarizer. And the proportion of the reacted monomer when the
irradiation amount was at 300 mJ/cm.sup.2 was about 89%.
(Summary on Change of Adhesive Strength and State of the Adhesive
Composition)
[0093] As described in above, when the electromagnetic ware or
particle beam is irradiated at intensity lower than that used for
the conventional adhesive composition under a predetermined
temperature environment, the value of the adhesive strength F of
the adhesive composition according to the present invention changes
as shown in FIG. 1 along with the increase of the irradiation
amount of the electromagnetic ware or particle beam. It is possible
to increase the adhesive strength F to the local maximum value,
then to decrease to the local minimum value, and then, to increase
again to a value greater than the local maximum value along with
the increase in the irradiation amount of the electromagnetic wave
or particle beam. The state of the adhesive composition when the
adhesive strength F takes a value in the predetermined range
including the local maximum value is the above described PSA-like
state, the state thereof when it takes a value in the predetermined
range including the local minimum value is the easy-to-peel state,
and the state thereof when it takes a value greater than the local
maximum value is the strong adhesion state. When the adhesive
composition is in the easy-to-peel state, it has almost cured and
has sufficient cohesion but has not reached to the strong adhesion
state, and thus, the adhesive composition may be peeled from the
adherend at the interface therebetween with a small force.
[0094] On the other hand, a value of adhesive strength F of the
conventional adhesive composition increases along with the increase
of the electromagnetic wave or particle beam without taking a local
maximum value or a local minimum value, as shown in FIG. 2. This
means that the state of the conventional adhesive composition
changes from the PSA-like state directly to the strong adhesion
state along with the increase of the irradiation amount of the
electromagnetic wave or particle beam, and does not pass the
easy-to-peel state where the adhesive strength increases to the
local maximum value, then decreases to allow for easy peeling of
the adherends.
(Critical Irradiation Intensity)
[0095] Irradiation intensity of the electromagnetic wave or
particle beam for changing the adhesive strength and the state of
the adhesive composition according to the present invention as
shown in FIG. 1 is far smaller than intensity used for changing the
adhesive strength of the conventional adhesive composition as shown
in FIG. 2. Herein, the greatest value of the irradiation intensity
of the electromagnetic wave or particle beam for changing the
adhesive strength F of the adhesive composition according to the
present invention as shown in FIG. 1 is referred as "critical
irradiation intensity." When the electromagnetic wave or particle
beam with intensity greater than the critical irradiation intensity
is irradiated, the adhesive strength F of the adhesive composition
changes as shown in FIG. 2 without taking the local maximum value
and the local minimum value.
[0096] For example, although the detail of experiments will be
later described in Example 2, when the electromagnetic wave or
particle beam with intensity greater than 41 mW/cm.sup.2 at
wavelength of 405 nm was irradiated to the adhesive composition
consisting of 100 parts of HEAA and 0.5 part of a
photo-polymerization initiator, the adhesive strength of the
adhesive composition increased without taking a local maximum or a
local minimum value along with the increase of the irradiation
amount, and the state thereof changed from the PSA-like state
directly to the strong adhesion state without being the
easy-to-peel state. On the other hand, when the electromagnetic
wave or particle beam with intensity of 41 mW/cm.sup.2 or less was
irradiated to the same adhesive composition, the adhesive strength
increased with taking the local maximum and the local minimum
values along with the increase of the irradiation amount, and the
state thereof changed from the PSA-like state to the strong
adhesion state via the easy-to-peel state. As described, the
critical irradiation intensity then was 41 mW/cm.sup.2 (refer to
FIG. 3). In the above example, since the light was irradiated
through the polarizing film (VEGQ5724DU from Nitto Denko
Corporation), the light actually reached to the adhesive
composition was considered to be about 30% of the irradiation
intensity. The critical irradiation intensity varies depending on
conditions including a type of the adhesive base agent, a type and
a dose of the photo-polymerization initiator, temperature
environment, and wavelength of the irradiated light.
(Elastic Modulus)
[0097] FIG. 4 shows elastic modulus for the adhesive composition
according to the present invention when it is in the PSA-like
state, the easy-to-peel state and the strong adhesion state. The
values of elastic modulus shown in FIG. 4 are those when the
electromagnetic wave or particle beam was irradiated with the
method shown in Example 1, and the method and the conditions of
measurement of the elastic modulus are as shown in Example 1.
Elastic modulus of the above-defined conventional adhesive
composition (i.e. the PSA) has been described in the patent
documents such as the Patent Document 3, the Patent Document 4, the
Patent Document 5, and the Patent Document 6. The method and the
conditions of measurement of the elastic modulus are different
between the adhesive composition according to the present invention
and the conventional PSAs according to the above described Patent
Documents. The elastic modulus of the adhesive composition
according to the present invention is tensile elastic modulus
measured with the method of the later-described Example 1. Since
the elastic modulus of the conventional PSAs according to the above
described Patent Documents is too low to measure by applying
tensile stress to a sample in a form of a sheet, stored elastic
modulus is measured by applying twisted shear stress. Although the
elastic modulus of the adhesive composition according to the
present invention should not be directly compared with that of the
conventional PSAs, it is in general possible to convert as tensile
elastic modulus/3=shear elastic modulus. If numbers of digits of
the elastic modulus are different therebetween, it is considered as
possible to understand the difference of the elastic modulus as a
clear difference of physical properties.
[0098] When the elastic modulus of the adhesive composition
according to the present invention is compared with that of the
conventional PSAs according to the Patent Documents from the above
standpoint, it is understood as that the physical properties of the
adhesive composition according to the present invention are totally
different from those of the conventional PSAs. Since the elastic
modulus of the adhesive composition according to the present
invention is higher than that of the conventional PSAs, when a
polarizing film having a protection film laminated only on one of
surfaces of a polarizer is laminated with a liquid crystal cell via
the adhesive composition according to the present invention,
expansion and shrinkage of the polarizer under heating and cooling
in a reliability test (heat-shock test) may be prevented to provide
the polarizer with an excellent durability with anti-crack
property. On the other hand, since the elastic modulus of the
conventional PSAs is low, expansion and shrinkage of the polarizer
under heating and cooling in the reliability test may not be
prevented so that cracking occurs in the polarizer.
[0099] In addition, since the elastic modulus of the conventional
PSAs is low, repulsion thereof is small. Therefore, when the
conventional PSA is used for laminating the polarizing film and the
liquid crystal cell, application of force onto a surface of the
polarizing film may deform the polarizing film itself to cause dent
or collapse on the surface thereof even if the polarizing film has
a hard-coat layer. On the contrary, since the elastic modulus of
the adhesive composition according to the present invention is
high, repulsion thereof is large. Therefore, when the adhesive
composition according to the present invention is used for
laminating the polarizing film and the liquid crystal cell,
application of force onto a surface of the polarizing film does not
deform the polarizing film itself, and dent or collapse on the
surface thereof may be prevented.
[0100] When durability of a polarizing film is considered, it is
preferable that glass transition temperature Tg of the adhesive
composition is high. High Tg of the adhesive composition raises
fusing temperature and deforming temperature of the adhesive
composition to allow for preventing expanding or shrinking of a
polarizer to avoid cracking thereof.
(Control of Adhesive Strength and State by Irradiation Intensity of
Electromagnetic Wave or Particle Beam)
[0101] Irradiation amount of electromagnetic wave or particle beam
may be expressed as product of intensity and time of irradiation.
Thus, the adhesive strength and state of the adhesive composition
according to the present invention may be arbitrarily changed by
controlling irradiation intensity of the electromagnetic wave or
particle beam. Thus, when the irradiation intensity of the
electromagnetic wave or particle beam is raised within a range
lower than the above defined critical irradiation intensity, it
allows for shortening time required for the adhesive strength
reaching to the local maximum value (or, time for the state of the
adhesive composition becoming to the PSA-like state), time required
for the adhesive strength decreasing from the local maximum value
to the local minimum value (or, time for the state of the adhesive
composition becoming to the easy-to-peel state) and time required
for the adhesive strength increasing from the local minimum value
to the greatest value (or, time for the state of the adhesive
composition becoming to the strong adhesion state). For example, by
doubling the irradiation intensity of the electromagnetic wave or
particle beam, the adhesive strength may be changed, within time
half of that before raising the irradiation intensity, from the
local maximum value (the state of the adhesive composition at this
point is the PSA-like state) to the local minimum value (the state
of the adhesive composition at this point is the easy-to-peel
state) and then to the greatest value (the state of the adhesive
composition at this point is the strong adhesion state). FIG. 5 in
the later described Example 3 shows this phenomenon.
[0102] However, even with irradiation intensity lower than the
above mentioned critical irradiation intensity, the reaction
proceeds faster along with the increase of the irradiation
intensity of the electromagnetic wave or particle beam to make the
control of the local maximum and the local minimum values of the
adhesive strength difficult. Particularly, there rises an issue
that freedom for stopping the reaction at the PSA-like state after
the adhesive strength taking the local maximum value may be
reduced. On the other hand, even with irradiation intensity lower
than the above mentioned critical irradiation intensity, the
reaction proceeds slower as the decrease of the irradiation
intensity of the electromagnetic wave or particle beam to result in
reduction of productivity. Therefore, practically, it is necessary
to select irradiation intensity of the electromagnetic wave or
particle beam that satisfies both of facilitating the control of
the polymerization reaction and maximizing the productivity.
[0103] In addition, for example, when the electromagnetic wave or
particle beam is irradiated until the state of the adhesive
composition becomes the PSA-like state (or, until the adhesive
strength takes the local maximum value) and then stopped, the
adhesive composition may stay in the PSA-like state. Then, by
restarting the irradiation of the electromagnetic wave or particle
beam, the state of the adhesive composition may be changed to the
easy-to-peel state and then to the strong adhesion state. As such,
the adhesive composition may maintain the adhesive strength and the
state at when the irradiation of the electromagnetic wave or
particle beam is stopped. Therefore, by irradiating the
electromagnetic wave or particle beam to the adhesive composition
applied to the adherends at an appropriate intensity for an
appropriate time, the state of the adhesive composition may be
changed to the PSA-like state, the adhesive composition may be
stored in the state, and, a process of irradiating again the
electromagnetic wave or particle beam may be adopted for adhering
another adherend to the adhesive composition at a certain point of
time later, to allow for structuring a manufacturing process with
high degree of freedom.
[0104] When the adhesive composition is applied to an adherend and
stored in the PSA-like state, the layer of the adhesive composition
may be formed on sheets of polarizing film, on a web of polarizing
film to be wound or on a substrate for storing. For transferring to
the adherend, the layer of the PSA-like adhesive composition may be
formed on sheets of releasable liners and stored as sheets, or the
layer of the PSA-like adhesive composition may be formed on a web
of releasable sheets and wound the web for storing.
(Control of Reaction Speed by Temperature Environment)
[0105] As described in above, the adhesive strength and the state
of the adhesive composition according to the present invention may
be changed depending on the irradiation amount of the
electromagnetic wave or particle beam irradiated at intensity lower
than the critical irradiation intensity under a predetermined
temperature environment. Speed of the change of the adhesive
strength and the state may be accelerated by changing the
temperature environment where the adhesive composition is placed.
That is, raising the temperature of the adhesive composition while
the polymerization thereof proceeds under irradiation of the
electromagnetic wave or particle beam allows for shortening time
required for the adhesive strength reaching to the local maximum
value, time required for the adhesive strength decreasing from the
local maximum value to the local minimum value and time required
for the adhesive strength increasing from the local minimum value
to the greatest value.
[0106] However, as for controlling the adhesive strength by the
irradiation intensity, if the speed of the reaction is too fast,
the control of the local maximum and the local minimum value may be
difficult, and if the speed of the reaction is too slow, the
productivity may be reduced. Also, if the temperature for
laminating is too high, films or display units may be destructed.
Therefore, practically, it is necessary to select temperature
environment that satisfies both of facilitating the control of the
polymerization reaction and maximizing the productivity.
[0107] The predetermined temperature environment according to the
present invention is referred as a temperature environment where
calorie calculated as dissipated calorie from the adhesive
composition deducted from a sum of calorie provided to the adhesive
composition and calorie generated by the polymerization thereof is
maintained at a predetermined calorie or higher at least for a
predetermined time. Therefore, when it is referred as "under a
predetermined temperature environment", it means that the adhesive
composition is placed in an environment where it may be heated at a
predetermined temperature for a certain period of time, which the
heating temperature and the heating environment thereof are
considered. For example, when a laminate which two adherends are
laminated therein via the adhesive composition is heated in an open
system which has dissipation of heat, the laminate requires to be
heated at a higher temperature for a certain period of time than in
a closed system which does not have dissipation of heat, in order
to provide for the adhesive strength to change while taking the
local maximum and the local minimum values. The temperature of the
adhesive composition when placed under the predetermined
temperature environment is required to be in vicinity of or higher
than the glass transition temperature of the adhesive
composition.
(Control of Adhesive Strength and State by Temperature
Environment)
[0108] As described in above, the adhesive strength and the state
of the adhesive composition according to the present invention may
be changed depending on the irradiation amount of the
electromagnetic wave or particle beam irradiated at intensity lower
than the critical irradiation intensity under a predetermined
temperature environment. That is, the adhesive strength of the
adhesive composition according to the present invention changes to
the local maximum value, then to the local minimum value and then
to a value greater than the local maximum value along with the
increase of the irradiation amount of the electromagnetic wave or
particle beam irradiated thereto under the predetermined
temperature environment.
[0109] On the other hand, the adhesive strength and state of the
adhesive composition may be changed by changing the temperature
environment where the adhesive composition is placed at halfway of
reaction without irradiating the electromagnetic wave or particle
beam. For example, the adhesive strength may be increased from the
local minimum value to a value greater than the local maximum value
by maintaining the adhesive composition under the second
temperature environment for a certain period of time or longer,
which the temperature thereof is higher than that of the first
temperature environment, after the adhesive strength of the
adhesive composition taking the local minimum value after taking
the local maximum value by the irradiation of the electromagnetic
wave or particle beam under the first temperature environment. Or,
the adhesive strength may be increased from the local maximum value
directly to a value greater than the local maximum value by
maintaining the adhesive composition under the second temperature
environment for a certain period of time or longer, which the
temperature thereof is higher than that of the first temperature
environment, after the adhesive strength of the adhesive
composition taking the local maximum value by the irradiation of
the electromagnetic wave or particle beam under the first
temperature environment. In either case, the temperature of the
adhesive composition is required to be in vicinity of or higher
than the glass transition temperature of the adhesive
composition.
[0110] In the present invention, the temperature of the second
temperature environment needs to be higher than that of the first
temperature environment. That is, when the adhesive strength of the
adhesive composition is at the local minimum value (the
easy-to-peel state), curing thereof is almost completed and the
curing does not much proceed even if the electromagnetic wave or
particle beam is further irradiated thereto. However, raising the
temperature of the adhesive composition to the glass transition
temperature or higher thereof allows for reducing stress at the
interface between the adherends and the adhesive composition to
improve the adhesive strength. Thus, in order to raise the
temperature of the adhesive composition in a state where the
electromagnetic wave or particle beam is not irradiated, i.e.
without influence of heat generated by the adhesive composition
absorbing the electromagnetic wave or particle beam or of radiation
heat, it is necessary to raise the temperature of a temperature
environment higher than that of the temperature environment where
the electromagnetic wave or particle beam was irradiated.
<Recyclability>
[0111] It is required to crush glass of a liquid crystal panel and
to collect used rare metal when disposing a liquid crystal display
unit. Optical films such as a polarizing film laminated to the
liquid crystal panel may be an obstacle when disposing a liquid
crystal display unit and should be peeled therefrom. It is
preferable to remove optical films such as a polarizing film to
reduce weight when recycling. But, when a PSA is used to laminate
optical films such as a polarizing film to a liquid crystal cell,
adhesive strength thereof increases along with time. Thus, at a
time to dispose a liquid crystal panel, the adhesive strength of
the PSA is too large so that the laminated optical films are prone
to break and peeling thereof is very difficult. In addition, along
with upsizing of liquid crystal panels, force necessary to peel
optical films from liquid crystal cells becomes larger, but,
glasses are thinner and prone to break when peeling, which makes
peeling more difficult. The adhesive composition according to the
present invention allows for solving such problem in recycling
because the adhesive strength thereof is significantly reduced only
by immersing in water even after the adhesive strength reaching to
the strong adhesion state.
[0112] As described in above, once the adhesive strength reaches to
the strong adhesion state along with the increase of the
irradiation amount of the electromagnetic wave or particle beam
irradiated to the adhesive composition at intensity lower than the
critical irradiation intensity under the predetermined temperature
environment, the adhesive composition may not be peeled from the
adherends at the interface therebetween, and if they are forced to
be peeled, cohesion failure occurs within the adhesive composition
or the adherends. However, immersion of the adhesive composition
according to the present invention in water swells itself to reduce
either of the interface adhesive strength f1, f1' or the cohesion
12 of the adhesive composition so that the adhesive strength F
thereof is reduced to facilitate peeling at the interface between
the adherends and the adhesive composition. The adhesive strength F
at this point is at least greater than the local maximum value
described above. By making the adherends and the adhesive
composition peelable, the adhesive composition may be easily peeled
from the liquid crystal cell when recycling the liquid crystal
television to reduce environmental load and recycling cost.
Temperature of water for immersing the adhesive composition to
swell to peel is not questioned, but the higher the temperature of
water for immersing, the shorter the time to reduce the adhesive
strength for making the adhesive composition peelable.
(Other Additives Which can be Added)
[0113] The adhesive composition according to the present invention
may contain additives other than the adhesive base agent and the
polymerization initiator, as described in the following. For
example, various Si coupling agents or cross-linking agents may be
added to the adhesive composition according to the present
invention to improve adhesive strength between a substrate of a
liquid crystal cell and a polarizing film. Also, a polymerization
inhibitor may be added to the adhesive composition from a view
point of preventing dark reaction or prolonging usable life.
Further, the effect of the present invention may be achieved even
when a polymerization initiator having light absorption wavelength
different from the transmitting wavelength of the polarizing film
is used by adding a photo-sensitizer adjusted to the transmitting
wavelength of the polarizing film to the adhesive composition
according to the present invention. Also, electric conductive
material for providing conductivity, fine particles having
birefringence for providing phase difference, or surfactant for
improving leveling property of a surface may be added to the
adhesive composition. Various curing agent may also be added to the
adhesive composition. Curing agents may include phenolic plastic,
various imidazole compounds and their derivatives, hydrazide
compound, dicyandiamide, isocyanate compound and microencapsulation
thereof. For example, when phenolic plastic is added as a curing
agent, phosphorous compound such as triphenylphosphin may be
combined as a curing accelerator.
<Use of the Adhesive Composition According to the Present
Invention>
[0114] The adhesive composition according to the present invention
may be used to mutually laminate two adherends. The two adherends
may be two optical films or an optical film and a substrate. It is
preferable that the adhesive composition according to the present
invention may be used as an adhesive for manufacturing a liquid
crystal display unit, a plasma display unit and/or an organic EL
display unit.
[0115] In manufacturing a liquid crystal display unit, one of the
two adherends to be laminated may be a polarizer, a protection film
laminated on a surface of the polarizer for protection thereof
and/or an optical compensating film using a phase difference film.
The other of the two adherends may be a glass substrate or a
plastic substrate included in a liquid crystal cell.
[0116] In manufacturing a plasma display unit, one of the two
adherends to be laminated may be a plasma display panel and/or a
protection substrate thereof, and the other of the two adherends
may be a UV-cut film, an anti-glare film, an anti-reflection film,
an anti-crack film, an electromagnetic wave shield film, a
band-pass film or a hard-coat film.
[0117] In manufacturing an organic EL display unit, one of the two
adherends to be laminated may be an organic EL display panel or a
protection substrate thereof, and the other of the two adherends
may be a UV-cut film, an anti-glare film, an anti-reflection film,
an anti-crack film, a circular polarizing plate for anti-reflection
or a hard-coat film.
[0118] As described in above, the adhesive strength of the adhesive
composition according to the present invention for laminating two
adherends via the adhesive composition may be arbitrarily
controlled by irradiating electromagnetic wave or particle beam
with intensity lower than the critical irradiation intensity
defined herein under a predetermined temperature environment.
According to the present invention, the adhesive strength of the
adhesive composition may be controlled as the adhesive strength
increases to the local maximum value along with the increase of the
irradiation amount thereto, then decreases to the local minimum
value along with the further irradiation of the irradiation amount
that reduces the adhesive strength, and then increases again to a
value greater than the local maximum value by further increasing
the irradiation amount. Thus, using the adhesive composition
according to the present invention achieves a lamination method,
wherein, the lamination is inspected after laminating the adherends
after or while changing the state of the adhesive composition to
the PSA-like state, and if it is found that correction of
lamination is not required, the adherends are fully bonded by
changing the state of the adhesive composition to the strong
adhesion state, and if the correction of lamination is required,
the adhesive composition is maintained in the easy-to-peel state to
allow for easy peeling of the adhesive composition and the
adherends at the interface therebetween.
[0119] Also, by changing at halfway the temperature environment
where the adhesive composition according to the present invention
is placed, the adhesive and the state thereof may be changed
without irradiating the electromagnetic wave or particle beam.
Thus, for example, the lamination is inspected after mutually
laminating the adherends with the adhesive composition in the
PSA-like state under the first temperature environment, and if the
correction of the lamination is not required, the adherends may be
fully bonded with the adhesive composition in the strong adhesion
state by maintaining the adhesive composition under the second
temperature environment for a predetermined time period or
longer.
[0120] The lamination method using the adhesive composition
according to the present invention includes, in particular, the
following steps. Firstly, the electromagnetic wave or particle beam
with intensity lower than the critical irradiation intensity
defined herein is irradiated under a predetermined temperature
environment. By increasing the irradiation amount, the state of the
adhesive composition changes to the PSA-like state which develops
adhesive strength by pressure. The adhesive strength at this point
takes a value within a predetermined range including the local
maximum value. Two adherends are mutually temporality laminated by
pressure with the adhesive composition in the PSA-like state
intervening therebetween. The order of the step of irradiating the
electromagnetic wave or particle beam to the adhesive composition
to change the state thereof to the PSA-like state and the step of
laminating the at least two adherends and the adhesive composition
is not questioned. For example, the state of the adhesive
composition may be changed to the PSA-like state by irradiating the
electromagnetic wave or particle beam after applying the adhesive
composition in fluid state to one of the at least two adherends and
overlapping the other adherend on the adhesive composition. Or, the
other adherend may be overlapped onto the adhesive composition in
the PSA-like state and bonded thereto after applying the adhesive
composition in fluid state to one of the at least two adherends and
irradiating the electromagnetic wave or particle beam thereto.
[0121] The method and order of the step of applying the adhesive
composition to the adherends and the step of irradiating the
electromagnetic wave or particle beam to the adhesive composition
to change the state thereof to the PSA-like state is not
questioned. For example, the adhesive composition may be
transferred to one of the at least two adherends after applying the
adhesive composition onto a releasable liner and changing the state
of the adhesive composition to the PSA-like state by irradiating
the electromagnetic wave or particle beam. Or, the state of the
adhesive composition may be changed to the PSA-like state by
irradiating the electromagnetic wave or particle beam after
applying the adhesive composition onto a releasable liner and
overlapping a layer of the adhesive composition onto one of the at
least two adherends.
[0122] As another method, the adhesive composition in the PSA-like
state may be transferred to one of the at least two adherends after
applying the adhesive composition onto a releasable liner, changing
the state of the adhesive composition to the PSA-like state by
irradiating the electromagnetic wave or particle beam, laminating
another releasable liner on the adhesive composition as the
PSA-like state and peeling one of the releasable liners. Or, the
adhesive composition may be transferred to one of the at least two
adherends after applying the adhesive composition onto a releasable
liner, overlapping another releasable liner on the adhesive
composition, changing the state of the adhesive composition to the
PSA-like state by irradiating the electromagnetic wave or particle
beam, and peeling one of the releasable liners.
[0123] The laminate of the adhesive composition in the PSA-like
state and one of the at least two adherends, or, the laminate of
the adhesive composition in the PSA-like state and a releasable
liner may be used in a form of a sheet, a wound roll or be
laminated on a substrate.
[0124] The state of lamination of the adherends is inspected after
temporary bonding the at least two adherends. When a correction of
the lamination is required as a result of the inspection, for
example, when misalignment of lamination position or trapping of
foreign item or air bubble occurred, the adherends and the adhesive
composition need to be peeled. It is not preferable to peel while
the adhesive composition is in the PSA-like state, because large
force is necessary for peeling and the adhesive composition at the
PSA-like state may stay on the adherends. For example, a glass for
a current liquid crystal cell is thinner and the size thereof is
larger than before. Because of this, when the adhesive strength of
the adhesive composition is large, the glass may break when peeling
the polarizing film laminated on the liquid crystal cell. And,
upsizing of the liquid crystal cell requires a large force to peel
the polarizing film from the liquid crystal cell even under the
same adhesive strength, because an area of lamination therebetween
is large, and this presents a risk of damaging the liquid crystal
cell when peeling. Thus, in the lamination method using the
adhesive composition according to the present invention, when
peeling of the adhesive composition and the adherends is required,
the electromagnetic wave or particle beam with intensity lower than
the critical irradiation intensity is further irradiated to the
adhesive composition under a predetermined temperature environment.
By irradiating the electromagnetic wave or particle beam for more
than the amount necessary to change the state of the adhesive
composition to the PSA-like state, the adhesive composition may be
cured to a degree where at least one of the at least two adherends
and the adhesive composition may be peeled at the interface
therebetween without damaging the adherends. At this point, the
adhesive strength takes a value in a predetermined range including
the local minimum value.
[0125] When correction of the lamination is not required as a
result of the inspection after temporary bonding, the at least two
adherends are fully bonded. Thus, in the lamination method using
the adhesive composition according to the present invention, the
electromagnetic wave or particle beam with intensity lower than the
critical irradiation intensity is further irradiated to the
adhesive composition in the PSA-like state under a predetermined
temperature environment. By irradiating the electromagnetic wave or
particle beam for more than the amount necessary to change the
state of the adhesive composition to the easy-to-peel state, the
adhesive composition may be fully cured to fully bond the at least
two adherends and the adhesive composition. Or, the electromagnetic
wave or particle beam with intensity lower than the critical
irradiation intensity is further irradiated to the adhesive
composition in the PSA-like state under a predetermined temperature
environment to change the state of the adhesive composition to the
easy-to-peel state, and then maintain the adhesive composition
under a temperature environment which the temperature thereof is
higher than that of the predetermined temperature environment to
fully cure the adhesive composition to fully bond the at least two
adherends and the adhesive composition. At this point, the adhesive
strength takes a value at least greater than the local maximum
value.
EXAMPLES
Example 1
[0126] One part of a photo-polymerization initiator (Irgacure819
from Ciba Japan K.K.) was added to 100 parts of
N-(2-hydroxyethyl)acrylamide monomer (from Kohjin Co., Ltd.) and
dissolved to prepare adhesive composition. To accelerate rate of
dissolution, ultrasonic wave was applied while heating at
50.degree. C. One milliliter of the adhesive composition was
dropped onto a plate glass with a dropping pipette, a polarizing
film (VEGQ5724DU from Nitto Denko Corporation) was overlapped
thereon, and the polarizing film was pressed with a hand-roller to
laminate the polarizing film and the plate glass. The thickness of
the adhesive composition was adjusted to 10 .mu.m. Glass transition
temperature (Tg) of the adhesive composition was 98.degree. C. The
size of the plate glass was 150.times.50 mm and that of the
polarizing film was 140.times.40 mm.
[0127] Since TAC which an ultraviolet absorber is added thereto is
used for a protection film of the polarizing film, light with
wavelength of 380 nm or less hardly transmits therethrough. Thus,
Irgacure819 having absorption of visible light in vicinity of 400
nm was selected as the photo-polymerization initiator. The plate
glass laminated with the polarizing film was placed as the glass
facing downward onto a hot plate (HHP-411 from As One Corporation)
heated to 70.degree. C., and light was irradiated from the
polarizing film side with an ultraviolet irradiator (UBX0801-01
from Eye Graphics Co., Ltd., a high voltage mercury lamp with
output of 8 kW). For preventing the temperature of the polarizing
film or the plate glass overheated than necessary, a heat ray cut
filter was mounted between the ultraviolet irradiator and the
polarizing film.
[0128] Irradiation intensity of the light (measured irradiation
intensity) was measured with a measuring device having the
wavelength of 405 nm in the measurement range (Eye UV Meter UVPF-A1
from Eye Graphics Co., Ltd.). The irradiation intensity was
adjusted so that the irradiation intensity at the wavelength of 405
nm was 7 mW/cm.sup.2, which was measured between the irradiation
source and the polarizing film. Since the light reaches to the
adhesive composition passing through the polarizing film while a
part of the light is absorbed by the polarizing film, the
irradiation intensity of the light irradiated to the adhesive
composition (theoretical irradiation intensity) may be about 30% of
the measured irradiation intensity. Thus, the irradiation intensity
to the adhesive composition (the theoretical irradiation intensity)
is theoretically calculated as 7 mW/cm.sup.2.times.30%=about 2
mW/cm.sup.2. The relationship between the measured irradiation
intensity and the theoretical irradiation intensity is similarly
applied in the following Examples and Comparative Examples.
[0129] Adhesive strength was measured with a tensile testing
machine (AG-IS, an autograph from Shimadzu Corporation).
Electromagnetic wave or particle beam was irradiated to bond the
polarizing film and the glass substrate laminated as described
above, and then, a 180-degree peel value (peeling force) was
measured at room temperature (25.degree. C.) while peeling at a
tensile speed of 300 mm/min with the tensile testing machine, and
the value was considered as the adhesive strength. Adhesive
strength in Examples and Comparative Examples herein was measured
similarly.
(1) PSA-Like State
[0130] By irradiating light to the adhesive composition in fluid
state for 2 seconds from the polarizing film side, the state of the
adhesive composition changed to the PSA-like state. The PSA-like
state remained for 5 seconds from starting irradiation and 3
seconds from beginning of the PSA-like state. Measured irradiation
amount of light from the beginning to the end of the PSA-like state
was from 15 to 35 mJ/cm.sup.2, and the local maximum value of the
adhesive strength was 12 N/25 mm.
(2) Easy-to-Peel State
[0131] By irradiating light to the adhesive composition in the
PSA-like state for 3 seconds or longer from the polarizing film
side, the state of the adhesive composition changed to the
easy-to-peel state. The easy-to-peel state remained for 21 seconds
from starting irradiation (i.e. the fluid state) and 16 seconds
from the beginning of the easy-to-peel state. Measured irradiation
amount of light from the beginning to the end of the easy-to-peel
state was from 35 to 150 mJ/cm.sup.2, and the local minimum value
of the adhesive strength was 0.5 N/25 mm.
(3) Strong Adhesion State
[0132] By irradiating light to the adhesive composition in the
easy-to-peel state for 16 seconds or longer from the polarizing
film side, the state of the adhesive composition changed to the
strong adhesion state. By irradiating for 21 seconds or longer from
starting irradiation, the state changed to the strong adhesion
state. Measured irradiation amount of light at the beginning of the
strong adhesion state was 150 mJ/cm.sup.2.
[0133] FIG. 4 shows elastic modulus of the adhesive composition in
the PSA-like state, the easy-to-peel state and the strong adhesion
state. The elastic modulus of the adhesive composition according to
the present invention is high. There was found a problem in the
adhesive composition according to the present invention that shear
stress was not measurable when applied because of slippage between
a torque sensor of the device and the adhesive composition. To
address this, in the adhesive composition according to the present
invention, a sample was cut in sheets to apply tensile stress to
measure elastic modulus. The elastic modulus was measured with
solid viscoelasticity measuring device RSAIII, a dynamic mechanical
analyzer from TA Instruments Japan Inc. Conditions for measurement
were as follows.
Deformation mode: tension
Frequency: 1 Hz
[0134] Initial strain: 0.1%
Temperature: -60.degree. C..about.300.degree. C.
Example 2
Measurement of Critical Irradiation Intensity
[0135] A half part of a photo-polymerization initiator (Irgacure819
from Ciba Japan K.K.) was added to 100 parts of
N-(2-hydroxyethyl)acrylamide monomer (from Kohjin Co., Ltd.) and
dissolved to prepare adhesive composition. To accelerate rate of
dissolution, ultrasonic wave was applied while heating at
50.degree. C. One milliliter of the adhesive composition was
dropped onto a plate glass with a dropping pipette, a polarizing
film (VEGQ5724DU from Nitto Denko Corporation) cut in sheets having
a width of 25 mm was laminated therewith. The thickness of the
adhesive composition was adjusted to 10 .mu.m. The plate glass
laminated with the polarizing film was placed in an oven heated to
40.degree. C., and light was irradiated from the polarizing film
side with an ultraviolet irradiator (UBX0801-01 from Eye Graphics
Co., Ltd., a high voltage mercury lamp with output of 8 kW). For
preventing the temperature of the polarizing film or the plate
glass overheated than necessary, a heat ray cut filter was mounted
between the ultraviolet irradiator and the polarizing film. Glass
transition temperature (Tg) of the adhesive composition was
98.degree. C.
[0136] The measured irradiation intensity of the light was adjusted
so that the intensity at wavelength of 405 nm was varied in 8 cases
as 7 mW/cm.sup.2, 14 mW/cm.sup.2, 21 mW/cm.sup.2, 25.4 mW/cm.sup.2,
32.5 mW/cm.sup.2, 41 mW/cm.sup.2, 60 mW/cm.sup.2 and 80mW/cm.sup.2.
FIG. 3 shows test results for the adhesive strength against glass
when irradiation time was varied at different irradiation
intensity.
[0137] From the table in FIG. 3, it is understood as that the
adhesive strength changed to take the local maximum value, then the
local minimum value and then a value greater than the local maximum
value along with the increase of the irradiation time when the
measured irradiation intensity is 41 mW/cm.sup.2 or lower. However,
as the irradiation intensity becomes higher, the irradiation time
for the adhesive strength to take the local minimum value becomes
shorter to make control of the adhesive strength more difficult. It
is preferable that the irradiation intensity is 32.5 mW/cm.sup.2 or
lower to facilitate control of the adhesive strength. When the
measured irradiation intensity is 32.5 mW/cm.sup.2, the light
intensity actually reached to the adhesive composition is
considered to be about 10 mW/cm.sup.2. When the measured
irradiation intensity was 60 mW/cm.sup.2 or higher, the adhesive
strength increased along with the increase of the irradiation time,
and did not take the local maximum value or the local minimum
value.
Example 3
Control of Adhesive Strength and State by Irradiation Intensity of
Electromagnetic Wave or Particle Beam
[0138] For the same adhesive strength composition in Example 1,
change of state of the adhesive composition depending on the
irradiation time when varying the irradiation intensity was
observed under the same conditions as Example 1 except the
irradiation intensity of light. The irradiation intensity at the
wavelength of 405 nm was varied in a range from 1.5 to 35
mW/cm.sup.2. The result is shown in FIG. 5, where a cross (x) shows
that the adhesive composition was at fluid state, a triangle
(.DELTA.) shows that the adhesive composition was at PSA-like
state, a circle (.largecircle.) shows that the adhesive composition
was at easy-to-peel state, and a double circle (.circleincircle.)
shows that the adhesive composition was at strong adhesion state.
From FIG. 5, it is understood that time for the state of the
adhesive composition changing to the PSA-like state, time to the
easy-to-peel state and time to the strong adhesion state was
shortened along with the increase of the irradiation intensity.
Example 4
[0139] A half part of a photo-polymerization initiator (Irgacure819
from Ciba Japan K.K.) was added to 100 parts of
hydroxymethylacrylamide monomer (from Tokyo Chemical Industry Co.,
Ltd.) and dissolved to prepare adhesive composition. To accelerate
rate of dissolution, ultrasonic wave was applied while heating at
50.degree. C. One milliliter of the adhesive composition was
dropped onto a plate glass with a dropping pipette, a polarizing
film (VEGQ5724DU from Nitto Denko Corporation) was overlapped
thereon, and the polarizing film was pressed with a hand-roller to
laminate the polarizing film and the plate glass. Reason for
selecting Irgacure819 is the same as in Example 1. The plate glass
laminated with the polarizing film was placed as the glass facing
downward onto a hot plate (HHP-411 from As One Corporation) heated
to 60.degree. C., and light was irradiated from the polarizing film
side with an ultraviolet irradiator (UBX0801-01 from Eye Graphics
Co., Ltd., a high voltage mercury lamp with output of 8 kW). For
preventing the temperature of the polarizing film or the plate
glass overheated than necessary, a heat ray cut filter was mounted
between the ultraviolet irradiator and the polarizing film.
Irradiation intensity of the light was measured with a measuring
device having the wavelength of 405 nm in the measurement range
(Eye UV Meter UVPF-A1 from Eye Graphics Co., Ltd.). The irradiation
intensity was adjusted so that the irradiation intensity at the
wavelength of 405 nm was 14 mW/cm.sup.2.
[0140] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
1.5 seconds, the state of the adhesive composition changed to the
PSA-like state. By further irradiating light for 10 seconds, the
state of the adhesive composition changed to the easy-to-peel state
and remained for 50 seconds from the beginning thereof. Then, by
raising the temperature of the hot plate to 120.degree. C. and
further irradiating light for 60 seconds or longer, the state of
the adhesive composition changed to the strong adhesion state.
Example 5
[0141] Conditions for Example 5 were the same as Example 4 except
that hydroxymethylacrylamide monomer (from Tokyo Chemical Industry
Co., Ltd.) in Example 4 was changed to hydroxyethylacrylamide
monomer (from Kohjin Co., Ltd.) to prepare adhesive
composition.
[0142] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
2 seconds, the state of the adhesive composition changed to the
PSA-like state. By further irradiating light for 10 seconds, the
state of the adhesive composition changed to the easy-to-peel state
and remained for 50 seconds from the beginning thereof. Then, by
further irradiating light for 60 seconds or longer, the state of
the adhesive composition changed to the strong adhesion state. The
Tg of the adhesive composition was 98.degree. C.
[0143] In Example 5, by irradiating light to the laminate of the
polarizing film and the plate glass via the adhesive composition in
fluid state for 2 seconds, the state of the adhesive composition
changed to the PSA-like state. By further irradiating light for 30
seconds, the state of the adhesive composition changed to the
easy-to-peel state. Then, by raising the temperature of the hot
plate to 100.degree. C. and continued heating for 300 seconds
without irradiating light, the state of the adhesive composition
changed to the strong adhesion state.
[0144] In Example 5, by irradiating light to the laminate with the
irradiation intensity changed from 14 mW/cm.sup.2 to 80 mW/cm.sup.2
but the other conditions maintained as Example 5, the adhesive
composition in the fluid state changed to the strong adhesion state
in 1.5 seconds and remained at the strong adhesion state even after
extending the irradiation time.
Example 6
[0145] A half part of a photo-polymerization initiator (Irgacure819
from Ciba Japan K.K.) was added to 100 parts of
hydroxypropylacrylamide monomer (from Fluka) and dissolved to
prepare adhesive composition. To accelerate rate of dissolution,
ultrasonic wave was applied while heating at 50.degree. C. One
milliliter of the adhesive composition was dropped onto a plate
glass with a dropping pipette, and the plate glass was placed on a
hot plate (HHP-411 from As One Corporation) heated to 100.degree.
C. to evaporate moisture. After moisture evaporated, a polarizing
film (VEGQ5724DU from Nitto Denko Corporation) was overlapped on
the adhesive composition on the plate glass, and the polarizing
film was pressed with a hand-roller to laminate the polarizing film
and the plate glass. The plate glass laminated with the polarizing
film was placed as the glass facing downward onto the hot plate,
and light was irradiated from the polarizing film side with an
ultraviolet irradiator (UBX0801-01 from Eye Graphics Co., Ltd., a
high voltage mercury lamp with output of 8 kW). For preventing the
temperature of the polarizing film or the plate glass overheated
than necessary, a heat ray cut filter was mounted between the
ultraviolet irradiator and the polarizing film. Irradiation
intensity of the light was measured with a measuring device having
the wavelength of 405 nm in the measurement range (Eye UV Meter
UVPF-A1 from Eye Graphics Co., Ltd.). The irradiation intensity was
adjusted so that the irradiation intensity at the wavelength of 405
nm was 14 mW/cm.sup.2.
[0146] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
1 second, the state of the adhesive composition changed to the
PSA-like state. By further irradiating light for 10 seconds, the
state of the adhesive composition changed to the easy-to-peel
state. Then, by further irradiating light for 20 seconds or longer,
the state of the adhesive composition changed to the strong
adhesion state. The Tg of the adhesive composition was 74.degree.
C.
Example 7
[0147] Conditions for Example 7 were the same as Example 4 except
that hydroxymethylacrylamide monomer (from Tokyo Chemical Industry
Co., Ltd.) in Example 4 was changed to dimethylacrylamide monomer
(from Kohjin Co., Ltd.) to prepare adhesive composition.
[0148] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
1 second, the state of the adhesive composition changed to the
[0149] PSA-like state. By further irradiating light for 10 seconds,
the state of the adhesive composition changed to the easy-to-peel
state and remained for 50 seconds from the beginning thereof. Then,
by further irradiating light for 60 seconds or longer, the state of
the adhesive composition changed to the strong adhesion state. The
Tg of the adhesive composition was 119.degree. C.
Example 8
[0150] Conditions for Example 8 were the same as Example 4 except
that hydroxymethylacrylamide monomer (from Tokyo Chemical Industry
Co., Ltd.) in Example 4 was changed to diethylacrylamide monomer
(from Kohjin Co., Ltd.) to prepare adhesive composition.
[0151] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
1 second, the state of the adhesive composition changed to the
PSA-like state. By further irradiating light for 10 seconds, the
state of the adhesive composition changed to the easy-to-peel state
and remained for 20 seconds from the beginning thereof. Then, by
further irradiating light for 30 seconds or longer, the state of
the adhesive composition changed to the strong adhesion state. The
Tg of the adhesive composition was 81.degree. C.
Example 9
[0152] A half part of a photo-polymerization initiator (Irgacure819
from Ciba Japan K.K.) was added to 100 parts of acrylic acid
monomer (from Toagosei Co., Ltd.) and dissolved to prepare adhesive
composition. To accelerate rate of dissolution, ultrasonic wave was
applied while heating at 50.degree. C. Silane coupling agent (from
Shin-Etsu Chemical Co., Ltd.) was applied to a plate glass with a
spinning coater and the plate glass was heated at 100.degree. C.
for 1 minute. One milliliter of the adhesive composition was
dropped onto the plate glass with a dropping pipette, and a
polarizing film (VEGQ5724DU from Nitto Denko Corporation) was
overlapped thereon, and the polarizing film was pressed with a
hand-roller to laminate the polarizing film and the plate glass.
The plate glass laminated with the polarizing film was placed as
the glass facing downward onto a hot plate (HHP-411 from As One
Corporation) heated to 80.degree. C., and light was irradiated from
the polarizing film side with an ultraviolet irradiator (UBX0801-01
from Eye Graphics Co., Ltd., a high voltage mercury lamp with
output of 8 kW). For preventing the temperature of the polarizing
film or the plate glass overheated than necessary, a heat ray cut
filter was mounted between the ultraviolet irradiator and the
polarizing film. Irradiation intensity of the light was measured
with a measuring device having the wavelength of 405 nm in the
measurement range (Eye UV Meter UVPF-A1 from Eye Graphics Co.,
Ltd.). The irradiation intensity was adjusted so that the
irradiation intensity at the wavelength of 405 nm was 14
mW/cm.sup.2.
[0153] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
1 second, the state of the adhesive composition changed to the
PSA-like state. By further irradiating light for 10 seconds, the
state of the adhesive composition changed to the easy-to-peel state
and remained for 50 seconds from the beginning thereof. Then, by
further irradiating light for 60 seconds or longer, the state of
the adhesive composition changed to the strong adhesion state. The
Tg of the adhesive composition was 106.degree. C.
Example 10
[0154] Conditions for Example 10 were the same as Example 4 except
that hydroxymethylacrylamide monomer (from Tokyo Chemical Industry
Co., Ltd.) in Example 4 was changed to 2-hydroxyethylacrylate
monomer (from Nippon Shokubai Co., Ltd.) to prepare adhesive
composition.
[0155] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
5 seconds, the state of the adhesive composition changed to the
PSA-like state. By further irradiating light for 30 seconds, the
state of the adhesive composition changed to the easy-to-peel state
and remained for 30 seconds from the beginning thereof. Then, by
further irradiating light for 60 seconds or longer, the state of
the adhesive composition changed to the strong adhesion state. The
Tg of the adhesive composition was -15.degree. C.
Example 11
[0156] Conditions for Example 11 were the same as Example 4 except
that hydroxymethylacrylamide monomer (from Tokyo Chemical Industry
Co., Ltd.) in Example 4 was changed to acrylonitrile monomer (from
Wako Pure Chemical Industries, Ltd.) to prepare adhesive
composition.
[0157] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
1 second, the state of the adhesive composition changed to the
PSA-like state and remained for 9 seconds from the beginning
thereof. By further irradiating light for 15 seconds, the state of
the adhesive composition changed to the easy-to-peel state and
remained for 105 seconds from the beginning thereof. Then, by
further irradiating light for 120 seconds or longer, the state of
the adhesive composition changed to the strong adhesion state. The
Tg of the adhesive composition was 97.degree. C.
Example 12
[0158] Conditions for Example 12 were the same as Example 4 except
that hydroxymethylacrylamide monomer (from Tokyo Chemical Industry
Co., Ltd.) in Example 4 was changed to acryloyl morpholine monomer
(from Kohjin Co., Ltd.) to prepare adhesive composition.
[0159] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
1 second, the state of the adhesive composition changed to the
PSA-like state. By further irradiating light for 3 seconds, the
state of the adhesive composition changed to the easy-to-peel state
and remained for 57 seconds from the beginning thereof. Then, by
further irradiating light for 60 seconds or longer, the state of
the adhesive composition changed to the strong adhesion state. The
Tg of the adhesive composition was 145.degree. C.
Example 13
[0160] Conditions for Example 13 were the same as Example 4 except
that hydroxymethylacrylamide monomer (from Tokyo Chemical Industry
Co., Ltd.) in Example 4 was changed to N-methyl methacrylamide
monomer (from Tokyo Chemical Industry Co., Ltd.) and that the
heating temperature of the hot plate was raised to 120.degree. C.
from 60.degree. C. to prepare adhesive composition.
[0161] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
30 seconds, the state of the adhesive composition changed to the
PSA-like state. By further irradiating light for 90 seconds, the
state of the adhesive composition changed to the easy-to-peel
state. Then, by further irradiating light for 120 seconds or
longer, the state of the adhesive composition changed to the strong
adhesion state.
Example 14
[0162] Conditions for Example 12 were the same as Example 4 except
that hydroxymethylacrylamide monomer (from Tokyo Chemical Industry
Co., Ltd.) in Example 4 was changed to glycidyl methacrylate
monomer (from Kishida Chemical Co., Ltd.) to prepare adhesive
composition.
[0163] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
30 seconds, the state of the adhesive composition changed to the
PSA-like state and remained for 90 seconds from the beginning
thereof. By changing the temperature of the hot plate to 80.degree.
C. and further irradiating light for 30 seconds, the state of the
adhesive composition changed to the easy-to-peel state and remained
for 90 seconds from the beginning thereof. Then, by further
irradiating light for 240 seconds or longer, the state of the
adhesive composition changed to the strong adhesion state. The Tg
of the adhesive composition was 46.degree. C.
Example 15
[0164] Conditions for Example 15 were the same as Example 4 except
that hydroxymethylacrylamide monomer (from Tokyo Chemical Industry
Co., Ltd.) in Example 4 was changed to tetrahydrofurfuryl
methacrylate monomer (from Tokyo Chemical Industry Co., Ltd.) and
that the heating temperature of the hot plate was raised to
120.degree. C. from 60.degree. C. to prepare adhesive
composition.
[0165] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
30 seconds, the state of the adhesive composition changed to the
PSA-like state and remained for 30 seconds from the beginning
thereof. By further irradiating light for 60 seconds, the state of
the adhesive composition changed to the easy-to-peel state and
remained for 60 seconds from the beginning thereof. Then, by
further irradiating light for 240 seconds or longer, the state of
the adhesive composition changed to the strong adhesion state. The
Tg of the adhesive composition was 60.degree. C.
Example 16
[0166] Conditions for Example 16 were the same as Example 5 except
that hydroxyethylacrylamide monomer (from Kohjin Co., Ltd.) in
Example 5 was changed to a mixture of 50 parts of
hydroxyethylacrylamide monomer (from Kohjin Co., Ltd.) and 50 parts
of methyl methacrylate monomer (from Wako Pure Chemical Industries,
Ltd.) to prepare adhesive composition.
[0167] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
3 seconds, the state of the adhesive composition changed to the
PSA-like state and remained for 27 seconds from the beginning
thereof. By further irradiating light for 10 seconds, the state of
the adhesive composition changed to the easy-to-peel state. Then,
by further irradiating light for 20 seconds or longer, the state of
the adhesive composition changed to the strong adhesion state.
Example 17
[0168] A layer of the adhesive composition of Example 2 was formed
for a thickness of 10 .mu.m on an anti-glare film (AG150 from Nitto
Denko Corporation) using a bar coater. By irradiating light of
wavelength 405 nm to the anti-glare film with the adhesive
composition from the adhesive layer side in an oven at 40.degree.
C. for 3 seconds at irradiation intensity of 7 mW/cm.sup.2, the
state of the adhesive composition changed to the PSA-like state.
This anti-glare film with the adhesive composition in the PSA-like
state was laminated with an organic EL display (XEL-1 from Sony
Corporation) which a low-reflection film laminated on the top
surface on the viewing side with a PSA was released therefrom.
Since the lamination was performed while the adhesive composition
was in the PSA-like state, the lamination was successfully
completed without misalignment in the lamination or trapping air
bubble. By further irradiation the light for 20 seconds (23 seconds
from the beginning of the irradiation), the state of the adhesive
composition changed to the easy-to-peel state. Then, by further
irradiating light for 40 seconds (63 seconds from the beginning of
the irradiation), the state of the adhesive composition changed to
the strong adhesion state.
[0169] The anti-glare film with the adhesive composition in the
PSA-like state prepared was laminated with the organic EL display
under the same conditions. By irradiating light for 20 seconds
while heating, the state of the adhesive composition changed to the
easy-to-peel state. When the anti-glare film was peeled from the
organic EL display, it was easily peeled at an interface between
the glass of the organic EL display and the adhesive composition
without cohesion failure thereof. The organic EL display was not
damaged either. After peeling, it was not possible to laminate the
anti-glare film with the organic EL display even by
overlapping.
Example 18
[0170] A layer of the adhesive composition of Example 2 was formed
for a thickness of 10 .mu.m on a polarizing film (VEGQ5724DU from
Nitto Denko Corporation) using a bar coater. By irradiating light
of wavelength 405 nm to the polarizing film with the adhesive
composition from the adhesive layer side in an oven at 40.degree.
C. for 1 second at irradiation intensity of 30 mW/cm.sup.2, the
state of the adhesive composition changed to the PSA-like state.
This polarizing film with the adhesive composition in the PSA-like
state was laminated with a liquid crystal cell obtained by peeling
a polarizing film from a liquid crystal panel of a liquid crystal
television (LC-32DE5 from Sharp Corporation). By further
irradiating light of wavelength 405 nm from the polarizing film
side in an oven at 40.degree. C. for 20 seconds (22 seconds from
the beginning of the irradiation) at irradiation intensity of 14
mW/cm.sup.2, the state of the adhesive composition changed to the
easy-to-peel state. Then, by further irradiating light of
wavelength 405 nm from the polarizing film side in an oven at
80.degree. C. for 40 seconds (62 seconds from the beginning of the
irradiation) at irradiation intensity of 14 mW/cm.sup.2, the state
of the adhesive composition changed to the strong adhesion
state.
[0171] After the state of adhesive composition changed to the
strong adhesion state, the liquid crystal cell laminated with the
polarizing film was immersed in hot water at 60.degree. C. for 1
day. When the liquid crystal cell was taken out of hot water, the
polarizing film was easily peeled from the liquid crystal cell.
[0172] A polarizing film with the adhesive composition in the
PSA-like state prepared under the same conditions as above was
laminated with the above liquid crystal cell. Light was irradiated
while heating to change the state of the adhesive composition to
the easy-to-peel state. Then, when the polarizing film was peeled
from the liquid crystal panel, it was easily peeled from the liquid
crystal cell. There was no damage to the liquid crystal cell.
Example 19
[0173] A liquid crystal cell which a polarizing film peeled
therefrom was prepared by peeling the polarizing film from a liquid
crystal panel of a liquid crystal television (LC-32DE5 from Sharp
Corporation). Using the adhesive composition of Example 2, a layer
of the adhesive composition of Example 2 was formed for a thickness
of 10 .mu.m on each of two polarizing films (VEGQ5724DU from Nitto
Denko Corporation) using a bar coater. Light of wavelength 405 nm
was irradiated to the two polarizing films with the adhesive
composition formed thereon from the adhesive composition side in an
oven at 30.degree. C. for 1 second at irradiation intensity of 30
mW/cm.sup.2, and the state of the adhesive composition changed to
the PSA-like state. Each of the two polarizing films with the
adhesive composition in the PSA-like state was laminated to a
viewing side and a backlight side of the prepared liquid crystal
cell such that the polarizing axis was perpendicular to each other.
Then, by irradiating light of wavelength 405 nm from the polarizing
film side in an oven at 80.degree. C. for 60 seconds (61 seconds
from the beginning of the irradiation) at irradiation intensity of
14 mW/cm.sup.2, the state of the adhesive composition changed to
the strong adhesion state.
[0174] After the state of adhesive composition changed to the
strong adhesion state, the liquid crystal panel laminated with the
polarizing film was kept in an oven at 80.degree. C. for 100 hours.
Unlike later described Comparative Example 1 using a PSA,
unevenness of brightness within the surface (unwanted light
penetration at four corners) was not found. Since the adhesive
composition was hard, reduction of hardness of a liquid crystal
panel surface as one occurred when laminating with a PSA was not
found.
Example 20
[0175] A liquid crystal cell which a polarizing film peeled
therefrom was prepared by peeling the polarizing film from a liquid
crystal panel of a liquid crystal television (LC-32DE5 from Sharp
Corporation). Using the adhesive composition of Example 2, a layer
of the adhesive composition of Example 2 was formed for a thickness
of 10 .mu.m on each of two polarizing films (VEGQ5724DU and
VEGQ5724NTB-V1 from Nitto Denko Corporation) using a bar coater. A
releasable liner (MRF38 from Mitsubishi Plastics, Inc.) was
laminated with each of the two polarizing films which the layer of
the adhesive composition formed thereon. Light of wavelength 405 nm
was irradiated from the polarizing film side under a temperature
environment of 25.degree. C. for 1 second at irradiation intensity
of 10 mW/cm.sup.2, and the state of the adhesive composition
changed to the PSA-like state. The releasable liner was peeled from
each of the two polarizing films with the adhesive composition in
the PSA-like state, and each of the two polarizing films was
laminated to a viewing side and a backlight side of the prepared
liquid crystal cell such that the polarizing axis was perpendicular
to each other. By further irradiating light of wavelength 405 nm
from the polarizing film side in an oven at 40.degree. C. for 30
seconds (31 seconds from the beginning of the irradiation) at
irradiation intensity of 14 mW/cm.sup.2, the state of the adhesive
composition changed to the easy-to-peel state. Then, by further
irradiating light of wavelength 405 nm from the polarizing film
side in an oven at 80.degree. C. for 30 seconds (61 seconds from
the beginning of the irradiation) at irradiation intensity of 14
mW/cm.sup.2, the state of the adhesive composition changed to the
strong adhesion state.
[0176] When the polarizing film was peeled from the liquid crystal
cell after the state of the adhesive composition changed to the
easy-to-peel state, the peeling force was light enough not to cause
cracking or to reduce visibility of the liquid crystal cell.
[0177] After the state of adhesive composition changed to the
strong adhesion state, the liquid crystal panel laminated with the
polarizing film was kept in an oven at 80.degree. C. for 100 hours.
Unlike later described Comparative Example 1 using a PSA,
unevenness of brightness within the surface (unwanted light
penetration at four corners) was not found. Since the adhesive
composition was hard, reduction of hardness of a liquid crystal
panel surface as one occurred when laminating with a PSA was not
found.
[0178] After laminating the polarizing film with the adhesive
composition in the PSA-like state, light of wavelength of 405 nm
was further irradiated in an oven at 80.degree. C. for 60 seconds
at irradiation intensity of 14 mW/cm.sup.2, and the state of the
adhesive composition changed to the strong adhesion state. Thus, it
is confirmed that the state of the adhesive composition changes to
the strong adhesion state by irradiating light without intermission
while the adhesive composition was in the easy-to-peel state.
Example 21
[0179] A half part of a photo-polymerization initiator (Irgacure819
from Ciba Japan K.K.) was added to 100 parts of dicyclopentenyl
acrylate monomer (from Hitachi Chemical Co., Ltd.) and dissolved to
prepare adhesive composition. To accelerate rate of dissolution,
ultrasonic wave was applied while heating at 50.degree. C. One
milliliter of the adhesive composition was dropped onto cycloolefin
film (Zeonor from Zeon Corporation), and another cycloolefin film
(Zeonor from Zeon Corporation) was overlapped thereon, and the
films were pressed to prepare a laminated film. The laminated film
was placed on a hot plate (HHP-411 from As One Corporation) heated
to 120.degree. C., and light was irradiated with an ultraviolet
irradiator (UBX0801-01 from Eye Graphics Co., Ltd., a high voltage
mercury lamp with output of 8 kW). For preventing the temperature
of the laminated film overheated than necessary, a heat ray cut
filter was mounted between the ultraviolet irradiator and the film.
The irradiation intensity was adjusted so that the irradiation
intensity at the wavelength of 405 nm was 14 mW/cm.sup.2.
[0180] By irradiating light to the laminated film for 15 seconds,
the state of the adhesive composition changed to the PSA-like
state. By further irradiating light to the laminated film for 30
seconds, the state of the adhesive composition changed to the
easy-to-peel state. By further irradiating light to the laminated
film for 120 seconds or longer, the state of the adhesive
composition changed to the strong adhesion state.
Example 22
[0181] One-side-protected polarizing film was prepared by removing
a polarizer protection film from one surface of the polarizing film
(VEGQ5724DU from Nitto Denko Corporation), and the
one-side-protected polarizing film was laminated with a liquid
crystal cell obtained by peeling a polarizing film from a liquid
crystal panel of a liquid crystal television (LC-32DE5 from Sharp
Corporation) with the same adhesive composition as Example 2. The
liquid crystal cell laminated with the one-side-protected
polarizing film was placed in an oven heated at 40.degree. C., and
light was irradiated with an ultraviolet irradiator (UBX0801-01
from Eye Graphics Co., Ltd., a high voltage mercury lamp with
output of 8 kW) from the polarizing film side. For preventing the
temperature of the polarizing film or the glass overheated than
necessary, a heat ray cut filter was mounted between the
ultraviolet irradiator and the film. Irradiation intensity of the
light was measured with a measuring device having the wavelength of
405 nm in the measurement range (Eye UV Meter UVPF-A1 from Eye
Graphics Co., Ltd.). The irradiation intensity was adjusted so that
the irradiation intensity at the wavelength of 405 nm was 14
mW/cm.sup.2.
[0182] By irradiating light to the laminate of the liquid crystal
cell and the one-side-protected polarizing film via the adhesive
composition in fluid state for 1.5 seconds, the state of the
adhesive composition changed to the PSA-like state. By further
irradiating light to the laminated film for 10 seconds, the state
of the adhesive composition changed to the easy-to-peel state and
remained for 50 seconds after the beginning thereof. By further
irradiating light to the laminated film for 60 seconds or longer,
the state of the adhesive composition changed to the strong
adhesion state.
[0183] Light was irradiated to the laminate of the liquid crystal
cell and the one-side-protected polarizing film via the adhesive
composition in fluid state for 1.5 seconds to change the state of
the adhesive composition to the PSA-like state, and the light was
further irradiated for 30 seconds to change the state of to the
easy-to-peel state. Then, when the one-side-protected polarizing
film was peeled from the liquid crystal cell, the peeling force was
light enough not to cause cracking or to reduce visibility of the
liquid crystal cell.
Example 23
[0184] One-side-protected polarizing film was prepared by removing
a polarizer protection film from one surface of the polarizing film
(VEGQ5724DU from Nitto Denko Corporation), and a layer of the
adhesive composition of Example 2 was formed thereon for a
thickness of 10 .mu.m with a bar coater. By irradiating light of
wavelength 405 nm to the one-side-protected polarizing film with
the adhesive composition from the polarizing film side in an oven
at 30.degree. C. for 1 second at irradiation intensity of 30
mW/cm.sup.2, the state of the adhesive composition changed to the
PSA-like state. The one-side-protected polarizing film with the
adhesive composition was laminated with a liquid crystal cell
obtained by peeling a polarizing film from a liquid crystal panel
of a liquid crystal television (LC-32DE5 from Sharp Corporation).
Then, by further irradiating light of wavelength of 405 nm from the
one-side-protected polarizing film side in an oven at 40.degree. C.
for 20 seconds (21 seconds from the beginning of the irradiation)
at irradiation intensity of 14 mW/cm.sup.2, the state of the
adhesive composition changed to the easy-to-peel state. By further
irradiating light of wavelength of 405 nm from the
one-side-protected polarizing film side in an oven at 80.degree. C.
for 40 seconds (61 seconds from the beginning of the irradiation)
at irradiation intensity of 14 mW/cm.sup.2, the state of the
adhesive composition changed to the strong adhesion state.
[0185] When a heat-shock test, one of durability tests for a
polarizing film, was performed on the liquid crystal panel in which
the one-side-protected polarizing film and the liquid crystal cell
were laminated in the strong adhesion state, unlike the later
described Example 2 where a PSA was used, no crack occurred in the
one-side-protected polarizing film. The heat-shock test was
performed by repeating 100 cycles of alternatively keeping the
liquid crystal panel under a temperature environment of -40.degree.
C. and that of 85.degree. C. for 30 minutes each.
[0186] Since the adhesive composition in the liquid crystal panel
was hard, reduction of hardness of a liquid crystal panel surface
as one occurred when laminating with a PSA was not found.
[0187] When the polarizing film was peeled from the liquid crystal
cell after the state of the adhesive composition changed to the
easy-to-peel state, the peeling force was light enough not to cause
cracking or to reduce visibility of the liquid crystal cell.
[0188] After laminating the one-side-protected polarizing film with
the adhesive composition in the PSA-like state and the liquid
crystal cell, by irradiating light of wavelength of 405 nm in an
oven at 80.degree. C. for 60 seconds at irradiation intensity of 14
mW/cm.sup.2, the state of the adhesive composition changed to the
strong adhesion state.
Comparative Example 1
[0189] A polarizing film (VEGQ5724DU from Nitto Denko Corporation)
which a 20 .mu.m-thick layer of acrylic PSA laminated thereon was
laminated on a plate glass with a hand roller. Light of wavelength
of 400 nm was irradiated to the laminate of the polarizing film and
the plate glass under the same conditions as Example 4. However,
the adhesive strength did not change as to take the local maximum
value or the local minimum value even by increasing the irradiation
amount.
[0190] Since a PSA was used for lamination, it was possible to peel
the polarizing film from the liquid crystal cell, but a greater
peeling force was required when compared with a case where the
adhesive composition according to the present invention was in the
easy-to-peel state. Particularly, it was necessary to peel slowly
when peeling a polarizing film from a large-size liquid crystal
panel, otherwise problems, such as cracking of the liquid crystal
cell, breakage of the polarizing film or reduction of visibility by
force applied to the liquid crystal panel might be caused. In
addition, the adhesive strength of the PSA did not decrease even by
immersing in water.
[0191] A polarizing film was peeled from a liquid crystal panel of
a liquid crystal television (Bravia KDL-40V1 from Sony Corporation)
to prepare a liquid crystal cell, and one of two polarizing films
with the adhesive composition in the PSA-like state was laminated
to a viewing side and a backlight side of the prepared liquid
crystal cell such that the polarizing axis was perpendicular to
each other. When the liquid crystal panel was heated at 80.degree.
C. for 100 hours, unevenness of brightness (unwanted light
penetration) at four corners thereof occurred. In addition, surface
hardness of the polarizing film was reduced from that of the liquid
crystal panel using the adhesive composition according to the
present invention. It was considered as that it was due to a dent
generated on the polarizing film by pushing force because the PSA
was soft.
Comparative Example 2
[0192] The one-side-protected polarizing film prepared in Example
22 was laminated to a liquid crystal cell with a 20 .mu.m-thick
acrylic PSA to form a liquid crystal panel. Since a PSA was used
for lamination, it was possible to peel the polarizing film from
the liquid crystal cell, but a greater peeling force was required
when compared with a case where the adhesive composition according
to the present invention was in the easy-to-peel state. Since a
protection film for polarizer existed on only one surface of the
polarizing film, the polarizing film was prone to break when
peeling. Particularly, it was necessary to peel slowly when peeling
a polarizing film from a large-size liquid crystal panel, otherwise
problems, such as cracking of the liquid crystal cell, breakage of
the polarizing film or reduction of visibility by force applied to
the liquid crystal panel might be caused.
[0193] When a heat shock test was performed to the liquid crystal
panel under the same conditions as Example 23, many cracks occurred
on the polarizing film.
[0194] In addition, surface hardness of the polarizing film was
reduced from that of the liquid crystal panel using the adhesive
composition according to the present invention. It was considered
as that it was due to a dent generated on the polarizing film by
pushing force because the PSA was soft. Even when compared with the
polarizing film used in Comparative Example 1 which a protection
film was laminated on both surfaces thereof, reduction of surface
hardness was large because the thickness of the polarizing film was
thin.
Comparative Example 3
[0195] A half part of a photo-polymerization initiator (Irgacure819
from Ciba Japan K.K.) was added to 100 parts of methyl methacrylate
monomer (from Wako Pure Chemical Industries, Ltd.) and dissolved to
prepare adhesive composition. To accelerate rate of dissolution,
ultrasonic wave was applied while heating at 50.degree. C. One
milliliter of methyl methacrylate monomer was dropped onto a plate
glass with a dropping pipette, and a polarizing film (VEGQ5724DU
from Nitto Denko Corporation) was overlapped thereon, and laminated
with a hand roller. The plate glass laminated with the polarizing
film was placed as the glass facing downward onto a hot plate
(HHP-411 from As One Corporation) heated to 60.degree. C., and
light was irradiated from the polarizing film side with an
ultraviolet irradiator (UBX0801-01 from Eye Graphics Co., Ltd., a
high voltage mercury lamp with output of 8 kW). For preventing the
temperature of the polarizing film or the plate glass overheated
than necessary, a heat ray cut filter was mounted between the
ultraviolet irradiator and the polarizing film. Light with
irradiation intensity of 14 mW/cm.sup.2 at wavelength of 405 nm was
irradiated from the polarizing film side.
[0196] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
3 seconds, the state of the adhesive composition changed to the
PSA-like state. By further irradiating light for 30 seconds, the
state of the adhesive composition changed to the easy-to-peel
state. Then, light was further irradiated for 210 seconds, but the
state of the adhesive composition remained in the easy-to-peel
state.
[0197] A similar test was performed with raising the temperature of
the hot plate to 80.degree. C. By irradiating light to the laminate
for 3 seconds, the state of the adhesive composition changed to the
PSA-like state. By further irradiating light for 30 seconds, the
state of the adhesive composition changed to the easy-to-peel
state. Then, light was further irradiated for 450 seconds, but the
state of the adhesive composition remained in the easy-to-peel
state.
[0198] A similar test was further performed with raising the
temperature of the hot plate to 100.degree. C. By irradiating light
to the laminate for 2 seconds, the state of the adhesive
composition changed to the PSA-like state. Then, light was further
irradiated for 480 seconds, but the state of the adhesive
composition remained in the easy-to-peel state.
Comparative Example 4
[0199] A half part of a photo-polymerization initiator (Irgacure8l9
from Ciba Japan K.K.) was added to 100 parts of dimethylaminoethyl
methacrylate monomer (from Kyoeisha Chemical Co., Ltd.) and
dissolved to prepare adhesive composition. To accelerate rate of
dissolution, ultrasonic wave was applied while heating at
50.degree. C. One milliliter of dimethylaminoethyl methacrylate
monomer was dropped onto a plate glass with a dropping pipette, and
a polarizing film (VEGQ5724DU from Nitto Denko Corporation) was
overlapped thereon, and laminated with a hand roller. The plate
glass laminated with the polarizing film was placed as the glass
facing downward onto a hot plate (HHP-411 from As One Corporation)
heated to 60.degree. C., and light was irradiated from the
polarizing film side with an ultraviolet irradiator (UBX0801-01
from Eye Graphics Co., Ltd., a high voltage mercury lamp with
output of 8 kW). For preventing the temperature of the polarizing
film or the plate glass overheated than necessary, a heat ray cut
filter was mounted between the ultraviolet irradiator and the
polarizing film. Light with irradiation intensity of 14 mW/cm.sup.2
at wavelength of 405 nm was irradiated from the polarizing film
side.
[0200] By irradiating light to the laminate of the polarizing film
and the plate glass via the adhesive composition in fluid state for
120 to 240 seconds, the state of the adhesive composition changed
to the PSA-like state. By raising the temperature of the hot plate
to 80.degree. C. and further irradiating light for 240 seconds, the
state of the adhesive composition changed to the easy-to-peel
state. But, even by irradiating light any further, the state of the
adhesive composition remained in the easy-to-peel state.
[0201] A similar test was performed with raising the temperature of
the hot plate to 80.degree. C. By irradiating light to the laminate
for 120 seconds, the state of the adhesive composition changed to
the PSA-like state. By raising the temperature of the hot plate to
100.degree. C. and further irradiating light for 120 seconds, the
state of the adhesive composition changed to the easy-to-peel
state. But, even by irradiating light any further, the state of the
adhesive composition remained in the easy-to-peel state.
[0202] A polarizing film was peeled from a liquid crystal panel of
a liquid crystal television (LC16E1 from Sharp Corporation) to
prepare a liquid crystal cell. The liquid crystal cell was
laminated with a polarizing film (VEGQ5724DU from Nitto Denko
Corporation) with a hand roller. An instant adhesive (Aron
Alpha.RTM. from Konishi Co., Ltd.) was used as an adhesive. When an
instant adhesive is used as an adhesive, it is difficult to
laminate a liquid crystal film on an entire surface thereof even
when it is small such as a 16-inch cell because the adhesive
instantaneously cures. The instant adhesive cured before it was
spread so that the adhesive was not applied to some area. Also,
since the polarizing film was instantaneously bonded with the
liquid crystal cell, initial alignment was difficult, and, once
laminated, it was not possible to peel the polarizing film from the
liquid crystal cell. Thus, a process of laminating a polarizing
film and a liquid crystal cell using such an adhesive is considered
to reduce productivity because the polarizing film may not be
peeled to allow for re-using the liquid crystal cell if air bubble
or foreign item is trapped when laminating. It was not possible
either to peel the polarizing film even after immersing in hot
water as was in Example 18. It is disadvantageous because it is not
possible to separate the polarizing film and the liquid crystal
cell for recycling the liquid crystal cell.
* * * * *