U.S. patent application number 14/189470 was filed with the patent office on 2014-08-28 for polarizing plate.
This patent application is currently assigned to LG CHEM, LTD.. The applicant listed for this patent is LG CHEM, LTD.. Invention is credited to Sae Han CHO, Eun Soo HUH, Ki Ok KWON, Min Ki LEE, In Kyu PARK, Sung Soo YOON.
Application Number | 20140240647 14/189470 |
Document ID | / |
Family ID | 47898475 |
Filed Date | 2014-08-28 |
United States Patent
Application |
20140240647 |
Kind Code |
A1 |
HUH; Eun Soo ; et
al. |
August 28, 2014 |
POLARIZING PLATE
Abstract
Provided are a polarizing plate and a liquid crystal display
device. The polarizing plate has lighter weight, a smaller
thickness, and excellent physical properties such as durability,
water resistance, workability, and light leakage preventing
ability. In addition, the polarizing plate prevents curling
occurring in the polarizing plate or a polarizer in formation
thereof, and has excellent thermal resistance or thermal shock
resistance.
Inventors: |
HUH; Eun Soo; (Daejeon,
KR) ; KWON; Ki Ok; (Daejeon, KR) ; PARK; In
Kyu; (Daejeon, KR) ; YOON; Sung Soo; (Daejeon,
KR) ; LEE; Min Ki; (Daejeon, KR) ; CHO; Sae
Han; (Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG CHEM, LTD. |
Seoul |
|
KR |
|
|
Assignee: |
LG CHEM, LTD.
Seoul
KR
|
Family ID: |
47898475 |
Appl. No.: |
14/189470 |
Filed: |
February 25, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14183120 |
Feb 18, 2014 |
|
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14189470 |
|
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PCT/KR2012/006578 |
Aug 17, 2012 |
|
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14183120 |
|
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Current U.S.
Class: |
349/96 ;
359/507 |
Current CPC
Class: |
G02B 1/105 20130101;
C09J 133/10 20130101; C09J 133/00 20130101; Y10T 428/1041 20150115;
C09K 2323/05 20200801; Y10T 428/1077 20150115; C09J 133/06
20130101; C09K 2323/055 20200801; G02B 5/3033 20130101; C09K
2323/035 20200801; Y10T 428/105 20150115; C09J 133/04 20130101;
G02F 1/133528 20130101; C09K 2323/059 20200801; G02B 1/14 20150115;
C09K 2323/031 20200801; C09K 2323/057 20200801; Y10T 428/1082
20150115; C09J 133/12 20130101; Y10T 428/1059 20150115; B32B
2457/202 20130101; Y10T 428/1073 20150115 |
Class at
Publication: |
349/96 ;
359/507 |
International
Class: |
G02B 1/10 20060101
G02B001/10; G02F 1/1335 20060101 G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 19, 2011 |
KR |
10-2011-0082852 |
Aug 19, 2011 |
KR |
10-2011-0082860 |
Aug 17, 2012 |
KR |
10-2012-0089887 |
Claims
1. A polarizing plate, comprising: a polarizer; an active energy
beam-curable adhesive layer; and a pressure-sensitive adhesive
layer, which are sequentially disposed, wherein the
pressure-sensitive adhesive layer includes a first
pressure-sensitive adhesive layer forming a first surface; and a
second pressure-sensitive adhesive layer forming a second surface,
and the first and second surfaces include pressure-sensitive
adhesive layers having different tensile modulus.
2. The polarizing plate according to claim 1, wherein the adhesive
layer is directly attached to at least one surface of the
polarizer, and the first surface of the pressure-sensitive adhesive
layer is directly attached to the adhesive layer.
3. The polarizing plate according to claim 2, wherein the first
surface has a higher tensile modulus than the second surface.
4. The polarizing plate according to claim 1, wherein the polarizer
is a polyvinylalcohol-based polarizer.
5. The polarizing plate according to claim 1, wherein the first
surface has a tensile modulus at 25.degree. C. of 1 to 1,000
MPa.
6. The polarizing plate according to claim 1, wherein the second
surface has a tensile modulus at 25.degree. C. of 0.01 to 1.0
MPa.
7. The polarizing plate according to claim 1, wherein the first
pressure-sensitive adhesive layer includes a crosslinked structure
of an acryl polymer crosslinked by a multifunctional crosslinking
agent and a crosslinked structure of polymerized multifunctional
acrylate.
8. The polarizing plate according to claim 1, wherein the adhesive
layer includes an adhesive composition including an epoxy compound
and/or an acryl-based monomer in a cured state.
9. The polarizing plate according to claim 8, wherein the epoxy
compound includes an alicyclic epoxy compound and/or a glycidyl
ether-type epoxy compound.
10. The polarizing plate according to claim 8, wherein the epoxy
compound has a weight average molecular weight of 1,000 to
5,000.
11. The polarizing plate according to claim 8, wherein the
acryl-based monomer is a hydrophilic acryl-based monomer or a
hydrophobic acryl-based monomer.
12. The polarizing plate according to claim 11, wherein the
hydrophilic acryl-based monomer has a hydroxyl group, a carboxyl
group or an alkoxy group.
13. The polarizing plate according to claim 8, wherein the adhesive
composition further includes 1 to 40 parts by weight of a reactive
oligomer.
14. The polarizing plate according to claim 8, wherein the adhesive
composition is a non-solvent type composition.
15. The polarizing plate according to claim 8, wherein the adhesive
composition has a viscosity at 25.degree. C. of 5 to 1,000 cps.
16. The polarizing plate according to claim 1, further comprising:
a protective film attached to a surface of the polarizer opposite
to the surface to which the pressure-sensitive adhesive layer is
attached.
17. The polarizing plate according to claim 16, wherein the
protective film is a cellulose film, a polyester film, a
polycarbonate film, a polyethersulfone film, an acryl film or a
polyolefin film.
18. The polarizing plate according to claim 1, further comprising:
at least one layer selected from the group consisting of an
anti-reflection layer, an anti-glare layer, a phase retardation
plate, a wide viewing angle compensation film and a brightness
enhancement layer.
19. A liquid crystal display device, comprising: a liquid crystal
panel; and the polarizing plate according to claim 1 attached to
one or both surfaces of the liquid crystal panel.
20. The device according to claim 19, wherein the liquid crystal
panel is attached to the second pressure-sensitive adhesive
layer.
21. (canceled)
Description
[0001] This application is a continuation of U.S. application Ser.
No. 14/183,120, filed Feb. 18, 2014, which is a bypass continuation
of International Application No. PCT/KR2012/006578, filed Aug. 17,
2012, and claims priority to and the benefit of Korean Application
No. 10-2011-0082852, filed on Aug. 19, 2011, Korean Application No.
10-2011-0082860, filed on Aug. 19, 2011, and Korean Application No.
10-2012-0089887, filed on Aug. 17, 2012, the disclosure of which
are incorporated herein by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present application relates to a polarizing plate and a
liquid crystal display device.
[0004] 2. Discussion of Related Art
[0005] A polarizing plate is an optically functional film applied
to a device such as a liquid crystal display (LCD) device.
[0006] The polarizing plate may include a polarizer, which is a
functional sheet capable of extracting light vibrating in only one
direction from incident light vibrating in several directions, and
protective films usually attached to both surfaces of the
polarizer. The polarizing plate may further include a
pressure-sensitive adhesive layer formed under the protective film
and used to attach a liquid crystal panel to the polarizing plate,
and a releasing film formed under the pressure-sensitive adhesive
layer. In addition, the polarizing plate may include an additional
functional film such as an anti-reflection film or a phase
retardation film.
SUMMARY OF THE INVENTION
[0007] The present application is directed to a polarizing plate
and a LCD device.
[0008] In one aspect, an exemplary polarizing plate includes: a
polarizer, an active energy beam-curable adhesive layer, and a
pressure-sensitive adhesive layer, which are sequentially disposed.
The pressure-sensitive adhesive layer has first and second
surfaces, which have different tensile modulus.
[0009] In the specification, "at least two elements sequentially
disposed," for example, the term "A and B" sequentially disposed
means that the elements A and B are disposed in sequence as
described above, and another element C may be interposed between A
and B, for example, A, C and B may be disposed in order as
described above.
[0010] In addition, in the specification, when two elements are
described as being attached or directly attached to each other, for
example, "B is directly attached to A," may mean that no other
element may be disposed on at least one main surface of A, and B
may be directly attached thereto.
[0011] The exemplary polarizing plate includes a polarizer, an
adhesive layer and a pressure-sensitive adhesive layer, which are
sequentially disposed. In another example, in the polarizing plate,
the adhesive layer may be directly attached to the polarizer, and
the pressure-sensitive adhesive layer may also be directly attached
to the adhesive layer. FIG. 1 shows a structure 1 of an exemplary
polarizing plate, in which a polarizer 11, an adhesive layer 12 and
a pressure-sensitive adhesive layer 13 are sequentially
disposed.
[0012] Since the polarizer is usually manufactured of a hydrophilic
resin such as polyvinylalcohol, it is generally vulnerable to
moisture. In addition, since an extension process is generally
performed in the manufacture of the polarizer, contraction easily
occurs under a humid condition, and thus optical characteristics of
the polarizing plate are degraded. Accordingly, to reinforce
physical properties of the polarizing plate, a protective film
represented by a triacetylcellulose (TAC) film is generally
attached to both surfaces of the polarizer, and when there is no
protective film, due to poor dimensional stability of the
polarizer, durability and optical properties are greatly degraded,
and water resistance is dramatically decreased.
[0013] To this end, in one exemplary structure of the polarizing
plate of the present application, since a protective film is not
attached to at least one main surface of the polarizer, a thinner
and lighter structure and a structure in which an adhesive layer
and a pressure-sensitive adhesive layer are directly and
continuously attached to the main surface of the polarizer not
having the protective film are employed. In addition, as the
exemplary polarizing plate of the present application allows both
main surfaces of the pressure-sensitive adhesive layer to have
different peel strengths, a problem caused by poor dimensional
stability of the polarizer may be solved. In the specification, the
polarizing plate in which attachment of the protective film is
omitted from at least one surface of the polarizer as described
above may be referred to as a thin polarizing plate.
[0014] As the polarizer, one conventionally used in the art may be
used without particular limitation. As a polarizer, for example, a
polyvinylalcohol-based polarizer may be used. Such a polarizer may
be formed by adsorbing and aligning a dichroic pigment on a
polyvinylalcohol-based resin film. A polyvinylalcohol-based resin
constituting the polarizer, for example, may be obtained by
gelating a polyvinylacetate resin. As the polyvinylacetate resin, a
homopolymer of vinyl acetate; and a copolymer of vinyl acetate and
a different monomer polymerizable with the vinyl acetate may be
used. An example of the monomer copolymerizable with vinyl acetate
may be unsaturated carbonic acids, olefins, vinyl ethers,
unsaturated sulfonic acids or acrylamides having an ammonium group,
which are used alone or in combination of at least two thereof.
However, the present application is not limited thereto. A degree
of gelation for a polyvinyl alcohol resin may be usually about 85
to 100 mol %, for example, 98 mol % or more. The polyvinylalcohol
resin may further be modified, and for example, polyvinylformal or
polyvinylacetal modified with aldehydes may be used.
[0015] An active energy beam-curable adhesive layer is disposed at
one side of the polarizer. The adhesive layer may play a critical
role in ensuring physical properties of the polarizing plate when
the polarizing plate is a thin polarizing plate. For example, the
pressure-sensitive adhesive layer has first and second surfaces,
and in one example, the first surface may have a higher tensile
modulus than the second surface and be attached to the adhesive
layer. In this case, since the first surface has a lower peel
strength than the second surface, it may be easily peeled-off from
the polarizer. However, in the present application, since the
adhesive is disposed between the polarizer and the
pressure-sensitive adhesive and cured after a single-molecular
reactive material of the adhesive is penetrated or diffused into
the pressure-sensitive adhesive before the adhesive layer is cured,
the adhesive may allow the first surface of the pressure-sensitive
adhesive layer to be swollen or may increase roughness of the
surface. Thus, cohesion between the pressure-sensitive adhesive
layer and the polarizer is ensured, and the polarizing plate can
have excellent physical properties. In addition, since the active
energy beam-curable adhesive is used instead of a water-based
adhesive, curling of the polarizing plate caused by transformation
of the polarizer and protective film due to heat generated in a
thermal drying and curing operation of the water-based adhesive in
an operation of manufacturing the polarizing plate may be
prevented, and the polarizer may be effectively protected. As a
result, cracks to be generated in the polarizer may be prevented
even under a thermal resistant or thermal shock condition.
[0016] In the specification, the term "curing of an adhesive
composition or pressure-sensitive adhesive composition" refers to
an operation of changing an adhesive or pressure-sensitive adhesive
composition to express adhesive or pressure-sensitive adhesive
characteristics by a physical action or chemical reaction of
components of the composition. In addition, in the specification,
the term "active energy beam" may refer to microwaves, IR rays, UV
rays, X rays, .gamma. rays, or particle beams such as a particle
beams, proton beams, neutron beams and electron beams, and
conventionally UV rays or electron beams. In addition, the term
"active energy beam-curable" used herein may mean that the curing
may be induced by radiation with active energy beams. In one
example, curing of the adhesive composition may be executed by a
free radical polymerization or cationic reaction due to the
radiation with active energy beams, for example, by simultaneously
or sequentially performing the free radical polymerization and
cationic reactions.
[0017] The adhesive layer may include a composition including an
epoxy compound or an acryl-based monomer in a cured state, for
example, a composition including an epoxy compound and an
acryl-based monomer in a cured state. For example, the adhesive
composition may include 5 to 80 parts by weight of the epoxy
compound and 10 to 200 parts by weight of the acryl-based monomer,
for example, 15 to 60 parts by weight of the epoxy compound and 20
to 150 parts by weight of the acryl-based monomer. When the epoxy
compound and the acryl-based monomer are included within the
content ranges described above, more effective curing of an
adhesive composition may be induced, and physical properties may be
enhanced by more effectively performing curing due to living
characteristics of the cationic reaction which may induce a dark
reaction in a state in which the radiation with active energy beams
is finished. The unit "parts by weight" used herein refers to a
weight ratio between components. An adhesive composition having
excellent curing efficiency and physical properties after curing
may be provided by controlling the ratio of the components of the
adhesive composition.
[0018] The term "epoxy compound" used herein may refer to at least
one or at least two of monomeric, oligomeric or polymeric compounds
including epoxy groups.
[0019] The epoxy compound may enhance the physical properties of
the adhesive layer such as water resistance and adhesive
strength.
[0020] For example, as the epoxy compound, the epoxy compound which
can be crosslinked or polymerized by a cationic reaction may be
used.
[0021] In one example, as the epoxy compound, an epoxy resin having
a weight average molecular weight (Mw) of 1,000 to 5,000 or 2,000
to 4,000 may be used. In the specification, the weight average
molecular weight refers to a conversion value for reference
polystyrene measured by gel permeation chromatography (GPC), and
unless specifically defined otherwise, the term "molecular weight"
refers to the "weight average molecular weight." When the molecular
weight of the epoxy resin is 1,000 or more, the durability of the
adhesive layer may be suitably maintained, and when the molecular
weight of the epoxy resin is 5,000 or less, workability, such as
coatability of the composition may be effectively maintained.
[0022] In one example, as the epoxy compound, an alicyclic epoxy
compound or glycidyl ether-type epoxy compound may be used, for
example, a mixture of the alicyclic epoxy compound and the glycidyl
ether-type epoxy compound may be used.
[0023] The term "alicyclic epoxy compound" used herein may refer to
a compound including at least one epoxylated aliphatic ring, and
the term "glycidyl ether-type epoxy compound" may refer to a
compound including at least one glycidyl ether group.
[0024] As the alicyclic epoxy compound is included in the epoxy
compound, a glass transition temperature of the adhesive
composition is increased, and thus the adhesive layer has
sufficient durability. Therefore, even when the protective film is
formed on only one surface of the polarizer, occurrence of cracks
in the polarizer may be prevented even under a thermal resistant or
thermal shock condition.
[0025] In the alicyclic epoxy compound including an epoxylated
aliphatic ring, for example, the epoxylated aliphatic ring may
refer to a compound having an epoxy group formed in an alicyclic
ring. Here, a hydrogen atom constituting the alicyclic ring may be
optionally substituted with a substituent such as an alkyl group.
As the alicyclic epoxy compound, for example, a compound to be
specifically exemplified below may be used, but a kind of the epoxy
compound capable of being used herein is not limited to the
following example.
[0026] As the alicyclic epoxy compound, first, an
epoxycyclohexylmethyl epoxycyclohexanecarboxylate-based compound
represented by Formula 1 may be used:
##STR00001##
[0027] In Formula 1, R.sub.1 and R.sub.2 are each independently
hydrogen or an alkyl group.
[0028] The term "alkyl group" used herein, unless specifically
defined otherwise, may refer to a linear, branched or cyclic alkyl
group having 1 to 20, 1 to 16, 1 to 12, 1 to 8, or 1 to 4 carbon
atoms, and the alkyl group may be unsubstituted or optionally
substituted with at least one substituent.
[0029] As an another example of the alicyclic epoxy compound, an
epoxycyclohexane carboxylate-based compound of alkane diol
represented by Formula 2 may be used:
##STR00002##
[0030] In Formula 2, R.sub.3 and R.sub.4 are each independently
hydrogen or an alkyl group, and n represents an integer between 2
and 20.
[0031] In addition, as still another example of the alicyclic epoxy
compound, an epoxy cyclohexylmethyl ester-based compound of
dicarboxylic acid represented by Formula 3 may be used:
##STR00003##
[0032] In Formula 3, R.sub.5 and R.sub.6 are each independently
hydrogen or an alkyl group, and p represents an integer between 2
and 20.
[0033] As yet another example of the alicyclic epoxy compound, an
epoxycyclohexylmethyl ether-based compound of polyethyleneglycol
represented by Formula 4 may be used:
##STR00004##
[0034] In Formula 4, R.sub.7 and R.sub.8 are each independently
hydrogen or an alkyl group, and q is an integer between 2 and
20.
[0035] As yet another example of the alicyclic epoxy compound, an
epoxycyclohexylmethyl ether-based compound of alkane diol
represented by Formula 5 may be used:
##STR00005##
[0036] In Formula 5, R.sub.9 and R.sub.10 are each independently
hydrogen or an alkyl group, and r is an integer between 2 and
20.
[0037] As yet another example of the alicyclic epoxy compound, a
diepoxytrispiro-based compound represented by Formula 6 may be
used:
##STR00006##
[0038] In Formula 6, R.sub.11 and R.sub.12 are each independently
hydrogen or an alkyl group.
[0039] As yet another example of the alicyclic epoxy compound, a
diepoxymonospiro-based compound represented by Formula 7 may be
use:
##STR00007##
[0040] In Formula 7, R.sub.13 and R.sub.14 are each independently
hydrogen or an alkyl group.
[0041] As yet another example of the alicyclic epoxy compound, a
vinylcyclohexene diepoxide compound represented by Formula 8 may be
used:
##STR00008##
[0042] In Formula 8, R.sub.15 is hydrogen or an alkyl group.
[0043] As yet another example of the alicyclic epoxy compound, an
epoxycyclopentyl ether compound represented by Formula 9 may be
used:
##STR00009##
[0044] In Formula 9, R.sub.16 and R.sub.17 are each independently
hydrogen or an alkyl group.
[0045] As yet another example of the alicyclic epoxy compound, a
diepoxy tricyclodecane compound represented by Formula 10 may be
used:
##STR00010##
[0046] In Formula 10, R.sub.18 is hydrogen or an alkyl group.
[0047] In further detail, the alicyclic epoxy compound may be, but
is not limited to, an epoxycyclohexylmethyl epoxycyclohexane
carboxylate compound, an epoxycyclohexane carboxylate compound of
alkane diol, an epoxycyclohexylmethyl ester compound of
dicarboxylic acid or an epoxycyclohexylmethyl ether compound of
alkane diol, for example, at least one selected from the group
consisting of an esterification product of
7-oxabicyclo[4,1,0]heptane-3-carboxylic acid and
(7-oxa-bicyclo[4,1,0]hepto-3-yl)methanol (a compound of Formula 1
in which R.sub.1 and R.sub.2 are hydrogen); an esterification
product of 4-methyl-7-oxabicyclo[4,1,0]heptane-3-carboxylic acid
and (4-methyl-7-oxa-bicyclo[4,1,0]hepto-3-yl)methanol (a compound
of Formula 1 in which R.sub.1 and R.sub.2 are 4-CH.sub.3); an
esterification product of 7-oxabicyclo[4,1,0]heptane-3-carboxylic
acid and 1,2-ethanediol (a compound of Formula 2 in which R.sub.3
and R.sub.4 are hydrogen, and n is 1); an esterification product of
(7-oxabicyclo[4,1,0]hepto-3-yl)methanol and adipic acid (a compound
of Formula 3 in which R.sub.5 and R.sub.6 are hydrogen, and p is
2); an esterification product of
(4-methyl-7-oxabicyclo[4,1,0]hepto-3-yl)methanol and adipic acid (a
compound of Formula 3 in which R.sub.5 and R.sub.6 are 4-CH.sub.3,
and p is 2); and an esterification product of
(7-oxabicyclo[4,1,0]hepto-3-yl)methanol and 1,2-ethanediol (a
compound of Formula 5 in which R.sub.9 and R.sub.10 are hydrogen,
and r is 1).
[0048] In addition, as the glycidyl ether-type epoxy compound is
included in the epoxy compound, a glycidyl ether functional group
may form a soft chain having polarity in the adhesive layer after a
curing reaction, and thus adhesive strength of the adhesive layer
with respect to a PVA polarizer may be enhanced.
[0049] In one example, the glycidyl ether-type epoxy compound may
include, for example, aliphatic polyhydric alcohol or alkyleneoxide
thereof, for example, polyglycidyl ether of an ethyleneoxide or
propyleneoxide addition product.
[0050] In one example, when a mixture of an alicyclic epoxy
compound and a glycidyl ether-type epoxy compound is used as the
epoxy compound, the alicyclic epoxy compound may be
3,4-epoxycyclohexylmethyl, 3,4-epoxycyclohexanecarboxylate,
bis(3,4-epoxycyclohexylmethyl)adipatedicyclopentadienedioxide,
limonenedioxide or 4-vinylcyclohexenedioxide, and the glycidyl
ether-type epoxy compound may be an epoxy compound having an epoxy
group other than the alicyclic epoxy group. That is, the glycidyl
ether-type epoxy compound may be novolac epoxy, bisphenol A-based
epoxy, bisphenol F-based epoxy, brominated bisphenol epoxy, n-butyl
glycidylether, aliphatic glycidylether (12 to 14 carbon atoms),
2-ethylhexylglycidyl ether, phenyl glycidyl ether, o-cresyl
glycidyl ether, nonyl phenyl glycidyl ether, ethyleneglycol
diglycidylether, diethyleneglycol diglycidylether, propyleneglycol
diglycidylether, tripropyleneglycol diglycidylether,
neopentylglycol diglycidylether, 1,4-butanediol diglycidylether,
1,6-hexanediol diglycidylether, trimethylolpropane
triglycidylether, trimethylolpropane diglycidylether,
trimethylolpropane polyglycidylether, polyethyleneglycol
diglycidylether, or glycerin triglycidylether, And the glycidyl
ether-type epoxy compound may be, for example, glycidyl ether
having a cyclic aliphatic backbone such as
1,4-cyclohexanedimethanol diglycidyl ether or a hydrogenated
compound of an aromatic epoxy compound. In one example, the
glycidyl ether-type epoxy compound may be, glycidyl ether having a
cyclic aliphatic backbone. The glycidyl ether having a cyclic
aliphatic backbone may have 3 to 20 carbon atoms, 3 to 16 carbon
atoms or 3 to 12 carbon atoms. However, the present application is
not limited thereto.
[0051] In this case, the epoxy compound may include 5 to 40 parts
by weight of the alicyclic epoxy compound and 5 to 30 parts by
weight of the glycidyl ether-type epoxy compound, for example, 15
to 40 parts by weight of the alicyclic epoxy compound and 15 to 30
parts by weight of the glycidyl ether-type epoxy compound or 20 to
30 parts by weight of the alicyclic epoxy compound and 20 to 30
parts by weight of the glycidyl ether-type epoxy compound. When the
alicyclic epoxy compound is included at 5 parts by weight or more,
the sufficient durability of the adhesive layer may be ensured, and
when the alicyclic epoxy compound is included at 40 parts by weight
or less, the adhesive strength to the PVA polarizer is not
decreased. When the glycidyl ether-type epoxy compound is included
at 5 parts by weight or more, the adhesive strength is increased,
and when the glycidyl ether-type epoxy compound is included at 30
parts by weight or less, the durability of the adhesive layer is
not decreased.
[0052] Here, the alicyclic epoxy compound and the glycidyl
ether-type epoxy compound may be included in a weight ratio of 3:1
to 1:3, and within this range, an effect of enhancing the
durability of the adhesive layer and the adhesive strength of the
adhesive layer with respect to the PVA polarizer may be
maximized.
[0053] The adhesive composition further includes a radical
polymerizable compound. For example, the radical polymerizable
compound may be an acryl-based monomer. The term "radical
polymerizable compound" used herein may refer to a compound
including at least one polymerizable functional group capable of
participating in a crosslinking reaction in a molecular structure,
for example, a free radical polymerization reaction. The
polymerizable functional group may be, but is not limited to, an
allyl group, an allyloxy group, an acryloyl group, a methacryloyl
group or acrylonitrile.
[0054] In one example, the acryl-based monomer may include a
hydrophilic acryl-based monomer or a hydrophobic acryl-based
monomer. For example, the acryl-based monomer may include a mixture
of a hydrophilic acryl-based monomer and a hydrophobic acryl-based
monomer.
[0055] For example, to enhance the adhesive strength of the
adhesive layer to the PVA polarizer, the hydrophilic acryl-based
monomer may be included in the acryl-based monomer.
[0056] Here, the term "hydrophilic acryl-based monomer" may refer
to an acryl-based monomer having hydrophilicity, simultaneously
including a polymerizable functional group and a polar functional
group in a molecular structure, and the polar functional group may
be, but is not limited to, a hydroxyl group, a carboxyl group or an
alkoxy group.
[0057] For example, the hydrophilic acryl-based monomer may be at
least one of the compounds represented by Formulas 11 to 13. For
example, the hydrophilic acryl-based monomer may be the compound
represented by Formula 11, but the present application is not
limited thereto.
##STR00011##
[0058] In Formula 11, R.sub.19 is hydrogen or an alkyl group, A and
B are each independently an alkylene group or an alkylidene group,
and n is a number between 0 and 5.
##STR00012##
[0059] In Formula 12, R is hydrogen or an alkyl group, and R.sub.20
is hydrogen or -A.sub.3-C(.dbd.O)--OH, in which A.sub.3 is an
alkylene group or an alkylidene group.
##STR00013##
[0060] In Formula 13, R is hydrogen or an alkyl group, R.sub.21 is
an alkyl group, and A.sub.1 and A.sub.2 are each independently an
alkylene group or an alkylidene group.
[0061] The term "alkylene group or alkylidene group" used herein
may be a substituted or unsubstituted linear, branched or cyclic
alkylene or alkylidene group, which has 1 to 20, 1 to 16, 1 to 12,
1 to 8, or 1 to 4 carbon atoms. For example, the alkylene or
alkylidene group may be a linear or branched alkylene or alkylidene
group having 1 to 12, 1 to 8 or 1 to 4 carbon atoms.
[0062] In Formula 11, n is a number between 0 and 3, and more for
example, between 0 and 2.
[0063] In addition, in the compound of Formula 12, R.sub.20 is
hydrogen or --(CH.sub.2).sub.m--C(.dbd.O)--OH (m is an integer
between 1 and 4).
[0064] In addition, in the compound of Formula 13, R.sub.21 may be
alkyl having 1 to 4 carbon atoms, and A.sub.1 and A.sub.2 may be
each independently alkylene having 1 to 4 carbon atoms.
[0065] The compound of Formula 11 may be 2-hydroxyethyl
(meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl
(meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl
(meth)acrylate, 2-hydroxyethyleneglycol (meth)acrylate or
2-hydroxypropyleneglycol (meth)acrylate, the compound of Formula 12
may be acrylic acid, methacrylic acid or .beta.-carboxyethyl
(meth)acrylate, and the compound of Formula 13 may be
2-(2-ethoxyethoxy)ethyl (meth)acrylate, but the present application
is not limited thereto.
[0066] In one example, the hydrophilic acryl-based monomer may be
the compound represented by Formula 11.
[0067] The acryl-based monomer may include 10 to 80 parts by weight
of the hydrophilic monomer or 20 to 60 parts by weight of the
hydrophilic monomer. When the hydrophilic monomer is included in
the above range, adhesive strength of the pressure-sensitive
adhesive layer with respect to the PVA polarizer may be
enhanced.
[0068] In addition, in one example, the acryl-based monomer may
include at least one hydrophobic acryl-based monomer to control
attachment strength, compatibility and glass transition
temperature.
[0069] Here, the hydrophobic acryl-based monomer may be, for
example, an acrylic acid ester of an aromatic compound, a
methacrylic acid ester of an aromatic compound, alkyl acrylate or
alkyl methacrylate having a long chain alkyl group, for example, an
alkyl group having 9 or more carbon atoms, for example, 9 to 15
carbon atoms, or acrylic acid ester or methacrylic acid ester of an
alicyclic compound.
[0070] In one example, the hydrophobic acryl-based monomer may be a
compound represented by Formula 14 and/or a compound represented by
Formula 15.
##STR00014##
[0071] In Formula 14, R.sub.22 is hydrogen or an alkyl group, D is
an alkylene group or an alkylidene group, Q is a single bond, an
oxygen atom or a sulfur atom, Ar is an aryl group, and p is a
number between 0 and 3.
##STR00015##
[0072] In Formula 15, R is hydrogen or an alkyl group, and R.sub.23
is a monovalent residue derived from an alkyl group having 9 or
more carbon atoms or a monovalent residue derived from an alicyclic
compound.
[0073] In Formula 14, the term "single bond" means that there is no
separate atom in the part represented by Q, and D or a carbon atom
of C(.dbd.O) is directly connected to Ar.
[0074] In addition, in Formula 14, an aryl group refers to a
monovalent residue derived from a compound including a structure
including benzene or a structure in which at least two benzenes are
connected to each other or condensed, or a derivative thereof. The
aryl group, for example, may be an aryl group having 6 to 22 carbon
atoms, 6 to 16 carbon atoms or 6 to 13 carbon atoms, and for
example, a phenyl group, a phenylethyl group, a phenylpropyl group,
a benzyl group, a tollyl group, a xylyl group or a naphthyl
group.
[0075] In addition, in Formula 14, p is 0 or 1.
[0076] In addition, in the compound of Formula 15, R.sub.23 is a
monovalent residue derived from an alicyclic compound having 3 to
20 carbon atoms, for example, 6 to 15 carbon atoms, or R.sub.23 is
an alkyl group having 9 to 15 carbon atoms.
[0077] The compound of Formula 14 may be, but is not limited to,
phenoxy ethyl (meth)acrylate, benzyl (meth)acrylate,
2-phenylthio-1-ethyl (meth)acrylate, 6-(4,6-dibromo-2-isopropyl
phenoxy)-1-hexyl (meth)acrylate, 6-(4,6-dibromo-2-sec-butyl
phenoxy)-1-hexyl (meth)acrylate, 2,6-dibromo-4-nonylphenyl
(meth)acrylate, 2,6-dibromo-4-dodecyl phenyl (meth)acrylate,
2-(1-naphthyloxy)-1-ethyl (meth)acrylate, 2-(2-naphthyloxy)-1-ethyl
(meth)acrylate, 6-(1-naphthyloxy)-1-hexyl (meth)acrylate,
6-(2-naphthyloxy)-1-hexyl (meth)acrylate, 8-(1-naphthyloxy)-1-octyl
(meth)acrylate or 8-(2-naphthyloxy)-1-octyl (meth)acrylate,
conventionally phenoxy ethyl (meth)acrylate, benzyl(meth)acrylate
2-phenylthio-1-ethyl acrylate, 8-(2-naphthyloxy)-1-octyl acrylate
or 2-(1-naphthyloxy)-ethyl acrylate. For example, the compound of
Formula 14 may be phenoxy ethyl (meth)acrylate or benzyl
(meth)acrylate.
[0078] The compound of Formula 15 may be, but is not limited to,
isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, norbornanyl
(meth)acrylate, norbornenyl (meth)acrylate, dicyclopentadienyl
(meth)acrylate, ethynylcyclohexane (meth)acrylate,
ethynylcyclohexene (meth)acrylate or ethynyldecahydronaphthalene
(meth)acrylate. For example, the compound of Formula 15 may be
isobornyl (meth)acrylate.
[0079] As the acryl-based monomer, the hydrophobic acryl-based
monomer may be used, for example, at 60 parts by weight or less,
for example, 10 to 60 parts by weight. When the hydrophobic
acryl-based monomer is included at less than 10 parts by weight,
the number of hydrophilic functional groups is more than that of
hydrophobic functional groups, and thus a water resistant
characteristic of the polarizing plate may be degraded. When the
hydrophobic acryl-based monomer is included at more than 60 parts
by weight, the attachment strength to the PVA polarizing element
may be degraded.
[0080] In addition, for example, when the compound of Formula 14 is
used as the hydrophobic compound, the compound may be included, for
example, at 0 to 40 parts by weight or 10 to 30 parts by weight. In
addition, when the compound of Formula 15 is used as the
hydrophobic compound, the compound may be included, for example, at
0 to 30 parts by weight or 5 to 20 parts by weight. In such a
weight ratio, the attachment strength to a base, for example, an
acryl protective film to be described below, may be maximized.
[0081] In one example, the adhesive composition may further include
a reactive oligomer. The term "reactive oligomer" refers to a
compound formed by polymerizing at least two monomers, and includes
all compounds having a polymerizable functional group capable of
participating in a crosslinking reaction, for example, the kind of
polymerizable functional group previously described in the
description of the radical polymerizable compound.
[0082] The reactive oligomer may be, but is not limited to, a
photo-reactive oligomer known in the art, urethane acrylate,
polyester acrylate, polyether acrylate or epoxy acrylate. For
example, the reactive oligomer may be urethane acrylate.
[0083] In the adhesive composition, the reactive oligomer may be
included, for example, at 1 to 40 parts by weight or 5 to 20 parts
by weight. In such a weight ratio, a synergistic effect of the
glass transition temperature of the adhesive layer may be
maximized.
[0084] The adhesive composition may further include a cationic
initiator as an initiator for starting a curing reaction. As the
cationic initiator, any one starting a cationic reaction by
application or radiation of light without particular limitation,
for example, a cationic photoinitiator for starting a cationic
reaction by radiation with active energy beams, may be used.
[0085] In one example, the cationic photoinitiator may be an onium
salt- or organometallic salt-based ionic cationic initiator, or a
non-ionic cationic photoinitiator such as an organic silane- or
latent sulfonic acid-based cationic photoinitiator or other
non-ionic compounds. The onium salt-based initiator may be
diaryliodonium salt, triarylsulfonium salt or aryldiazonium salt,
the organometallic salt-based initiator may be iron arene, the
organic silane-based initiator may be o-nitrobenzyl triaryl silyl
ether, triaryl silyl peroxide or acyl silane, and the latent
sulfonic acid-based initiator may be .alpha.-sulfonyloxy ketone or
.alpha.-hydroxymethylbenzoin sulfonate. However, the present
application is not limited thereto. In addition, as the cationic
initiator, a mixture of an iodine-based initiator and a
photosensitizer may be used.
[0086] The cationic initiator is an ionized cationic
photoinitiator, for example, an onium salt-based ionized cationic
photoinitiator. In one example, the cationic initiator is a
triacrylsulfonium salt-based ionized cationic photoinitiator.
However, the present application is not limited thereto.
[0087] The adhesive composition may include 0.01 to 10 parts by
weight, for example, 0.1 to 5 parts by weight of the cationic
initiator. In this range, the adhesive composition may have
excellent curing efficiency and physical properties after
curing.
[0088] The adhesive composition may further include a
photoinitiator as a radical initiator capable of starting a
polymerization or crosslinking reaction of an acryl-based monomer.
For example, the photoinitiator may be an initiator such as
benzoin-based photoinitiator, a hydroxyketone compound, an
aminoketone compound or a phosphine oxide compound. In one example,
the photoinitiator may be a phosphine oxide compound. In detail,
the photoinitiator may be, but is not limited to, benzoin, benzoin
methylether, benzoin ethylether, benzoin isopropylether, benzoin
n-butylether, benzoin isobutylether, acetophenone, dimethylamino
acetophenone, 2,2-dimethoxy-2-phenylacetophenone,
2,2-diethoxy-2-phenylacetophenone,
2-hydroxy-2-methyl-1-phenylpropane-1-one, 1-hydroxy
cyclohexylphenylketone,
2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-one,
4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone, benzophenone,
p-phenylbenzophenone, 4,4'-diethylamino benzophenone, dichloro
benzophenone, 2-methylanthraquinone, 2-ethylanthraquinone,
2-t-butylanthraquinone, 2-aminoanthraquinone, 2-methyl
thioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone,
2,4-dimethylthioxanthone, 2,4-diethylthioxanthone,
benzyldimethylketal, acetophenone dimethylketal, p-dimethylamino
benzoic acid ester,
oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone],
bis(2,4,6-trimethylbenzoyl)-phenyl-phosphineoxide or
2,4,6-trimethylbenzoyl-diphenyl-phosphineoxide.
[0089] In the adhesive composition, the photoinitiator may be
included at 0.1 to 10 parts by weight, for example, 0.5 to 5 parts
by weight, and in this range, effective polymerization and
crosslinking may be induced, and degradation in physical properties
due to reaction residues may be prevented.
[0090] The adhesive composition may also use an initiator
generating a radical by absorbing active energy beams having a long
wavelength, that is, a long-wavelength photoinitiator, as a radical
initiator. Such an initiator may be used alone or in combination
with a different kind of initiator.
[0091] That is, in the protective film included in the polarizing
plate, a UV protector may be mixed to protect the polarizer from UV
rays. In this case, when electromagnetic waves are radiated to cure
the adhesive composition, electromagnetic waves having a short
wavelength, for example, a wavelength of approximately 365 nm or
less, are absorbed by the protective film, and thus the suitable
curing reaction may not progress. To prevent this problem, the
radical initiator may include an initiator capable of generating
radicals by absorbing electromagnetic waves having a long
wavelength, for example, a wavelength of approximately 365 nm or
more.
[0092] The long-wavelength photoinitiator may be, for example,
diphenyl(2,4,6-trimethylbenzoyl)-phosphineoxide, or
bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide. For example, the
long-wavelength photoinitiator may be Darocur TPO or Irgacure 819
produced by Ciba Specialty Chemicals, Switzerland, but the present
application is not limited thereto.
[0093] The adhesive composition may further include an additive
such as a photosensitizer, an antioxidant or an attachment
enhancing agent, or a known oligomer component to control adhesion
performance and brittleness when necessary.
[0094] In one example, the adhesive composition may be formulated
in a non-solvent type. The non-solvent type composition may mean a
kind of adhesive composition not including an organic or
water-based solvent component used to dilute components
constituting the adhesive composition. As the adhesive composition
is formulated in a non-solvent type, a volatilization process for a
solvent is not necessary in the formation of the adhesive layer,
thickness uniformity may be effectively maintained, and curling of
the polarizer may be effectively prevented.
[0095] The adhesive composition may have a viscosity at 25.degree.
C. of 5 to 1,000 cps, for example, 10 to 100 cps. As the viscosity
is controlled in this range, process efficiency, ease of
controlling a thickness and thickness uniformity may be ensured,
and the physical properties such as the adhesive characteristic may
be effectively maintained.
[0096] A method of forming the adhesive layer on the polarizer
using the composition is not particularly limited, and thus, for
example, a method of coating an adhesive composition on the
polarizer and curing the composition, or coating the adhesive
composition on the polarizer, laminating the pressure-sensitive
adhesive layer again and curing the coated adhesive composition,
may be used. In this case, the curing of the adhesive composition
may be executed by a method of radiating active energy beams having
a suitable intensity to induce a polymerization or crosslinking
reaction of the component in consideration of each component.
[0097] The adhesive layer may have a thickness of 0.1 to 30 .mu.m,
0.5 to 15 .mu.m, or 1 to 10 .mu.m. As the thickness of the adhesive
layer is controlled to 0.1 .mu.m or more, the water resistance of
the polarizing plate may be excellently maintained, and when the
thickness of the adhesive layer is controlled to 30 .mu.m or less,
the thin polarizing plate having a uniform adhesive layer and
excellent physical properties may be formed.
[0098] The pressure-sensitive adhesive layer included in the
polarizing plate has first and second surfaces which have different
tensile modulus. In one example, the first surface has a higher
tensile modulus than the second surface and is directly attached to
the adhesive layer, and the second surface may be a
pressure-sensitive adhesive surface to attach the polarizing plate
to a liquid crystal panel.
[0099] FIG. 2 exemplifies a pressure-sensitive adhesive layer 2
having first and second surfaces 21 and 22.
[0100] As described above, in the pressure-sensitive adhesive
layer, when the first surface attached to the adhesive layer is set
to have a higher tensile modulus than that of the second surface,
contraction or expansion of the polarizer under a severe condition
such as a high temperature or high humidity condition may be
effectively inhibited. In addition, as the second surface attaching
the polarizing plate to a glass substrate of the liquid crystal
panel is set to have a lower tensile modulus than the first
surface, excellent wettability may be ensured.
[0101] In one example, the first surface may have a tensile modulus
at 25.degree. C. of 1 to 1,000 MPa, 10 to 900 MPa or 250 to 500
MPa. In addition, in one example, the second surface may have a
tensile modulus at 25.degree. C. of 0.01 to 1.0 MPa, 0.02 to 0.8
MPa or 0.03 MPa to 0.7 MPa. As the tensile modulus of the first and
second surfaces are controlled within the above-mentioned ranges,
the pressure-sensitive adhesive layer may effectively inhibit the
contraction or expansion of the polarizer under a severe condition,
and have excellent wettability to the adherent such as the glass
substrate.
[0102] A method of constituting the pressure-sensitive adhesive
layer having different tensile modulus on both surfaces is not
particularly limited. In one example, the pressure-sensitive
adhesive layer may be a multi-layered pressure-sensitive adhesive
layer constituted by stacking at least two kinds of
pressure-sensitive adhesive layers having different tensile
modulus.
[0103] For example, as shown in FIG. 3, the pressure-sensitive
adhesive layer 3 may include a first pressure-sensitive adhesive
layer 31 forming a first surface 21, and a second
pressure-sensitive adhesive layer 32 forming a second surface 22,
and tensile modulus of the respective pressure-sensitive adhesive
layers 31 and 32 may be differently controlled, thereby realizing a
pressure-sensitive adhesive layer having different tensile modulus
on both surfaces. The pressure-sensitive adhesive layer may be
formed in a multi-layered structure such as a double-layered
structure as shown in FIG. 3, or at least triple-layered structure
in some cases.
[0104] The pressure-sensitive adhesive layer may have a total
thickness of, for example, approximately 10 to 80 .mu.m, 20 to 60
.mu.m or 30 to 50 .mu.m. As the total thickness of the
pressure-sensitive adhesive layer is controlled as described above,
the polarizing plate may have a small thickness and excellent
physical properties such as durability under a severe condition. In
addition, when the pressure-sensitive adhesive layer is formed in a
double-layered structure as shown in FIG. 3, the first
pressure-sensitive adhesive layer may have a thickness of 4 to 50
.mu.m, and the second pressure-sensitive adhesive layer may have a
thickness of 5 to 50 .mu.m. As the thickness of the first
pressure-sensitive adhesive layer is controlled within a range of 4
to 50 .mu.m, the contraction or expansion of the polarizer may be
effectively prevented. In addition, as the second
pressure-sensitive adhesive layer is controlled within a range of 5
to 50 .mu.m, the wettability of the pressure-sensitive adhesive
layer or the durability of the polarizing plate may be effectively
maintained. Although the pressure-sensitive adhesive layer is
formed in a multi-layered structure, a sum of the thicknesses of
the first and second pressure-sensitive adhesive layers may satisfy
the above-mentioned range of the total thickness.
[0105] A method of forming the pressure-sensitive adhesive layer is
not particularly limited. For example, the pressure-sensitive
adhesive layer may be formed by curing a conventional room
temperature-curable, moisture-curable, heat-curable or photocurable
pressure-sensitive adhesive composition. In addition, to realize
the multi-layered pressure-sensitive adhesive layer, a method of
subsequently repeating coating and curing processes of the
pressure-sensitive adhesive composition, or laminating separately
manufactured pressure-sensitive adhesive layers to each other may
be used.
[0106] In one example, when the pressure-sensitive adhesive layer
is formed in a multi-layered structure, the pressure-sensitive
adhesive layer disposed at a side of the polarizer, for example,
the first pressure-sensitive adhesive layer in the double-layered
structure, may be a pressure-sensitive adhesive layer composed of a
photocurable pressure-sensitive adhesive composition, but the
present application is not limited thereto. The term "photocurable
pressure-sensitive adhesive composition" may refer to a
pressure-sensitive adhesive composition which may be cured by
inducing a polymerization or crosslinking reaction by radiation
with electromagnetic waves, for example, UV rays or electron
beams.
[0107] In one example, the pressure-sensitive adhesive layer may
include a so called interpenetrating polymer network (hereinafter
referred to as "IPN"). The term "IPN" may refer to a state in which
at least two kinds of crosslinking structures are present in the
pressure-sensitive adhesive layer, and in one example, the
crosslinking structure may be present in an entangled, linked or
penetrated state. When the pressure-sensitive adhesive layer
includes the IPN, a polarizing plate having excellent durability
under a severe condition, and excellent workability, optical
characteristics and a light leakage preventing ability.
[0108] When the pressure-sensitive adhesive layer includes the IPN
structure, the first pressure-sensitive adhesive layer may include,
for example, a crosslinking structure of an acryl polymer
crosslinked by a multifunctional crosslinking agent and a
crosslinking structure of a polymerized multifunctional
acrylate.
[0109] Here, as the acryl polymer crosslinked by the
multifunctional crosslinking agent, for example, an acryl polymer
having a weight average molecular weight (Mw) of 500,000 or more
may be used. When the weight average molecular weight (Mw) of the
polymer is 500,000 or more, a pressure-sensitive adhesive layer
having excellent durability under a severe condition may be formed.
The upper limit of the molecular weight is not particularly
limited, and for example, in consideration of the durability of the
pressure-sensitive adhesive or coatability of the composition, the
molecular weight may be controlled within a range of 2,500,000 or
less.
[0110] In one example, the acryl polymer may be a polymer including
a (meth)acrylic acid ester-based monomer in a polymerization
unit.
[0111] As the (meth)acrylic acid ester-based monomer, for example,
alkyl (meth)acrylate may be used, and in consideration of cohesive
strength, glass transition temperature or pressure-sensitive
adhesion of the pressure-sensitive adhesive, alkyl (meth)acrylate
including an alkyl group having 1 to 14 carbon atoms may be used.
Such a monomer may be methyl (meth)acrylate, ethyl (meth)acrylate,
n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl
(meth)acrylate, t-butyl (meth)acrylate, sec-butyl (meth)acrylate,
pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-ethylbutyl
(meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate,
isononyl (meth)acrylate, lauryl (meth)acrylate or tetradecyl
(meth)acrylate, which may be used alone or in combination of at
least two thereof.
[0112] The polymer may further include a crosslinkable monomer in a
polymerization unit. The polymer is a polymer including 50 to 99.9
parts by weight of the (meth)acrylic acid ester-based monomer and
0.1 to 50 parts by weight of the crosslinkable monomer in a
polymerized form. Here, the "crosslinkable monomer" refers to a
monomer capable of being copolymerized with the (meth)acrylic acid
ester-based monomer, which may provide a crosslinkable functional
group to a side chain or terminal end of the polymer after
copolymerization.
[0113] As the crosslinkable monomer, a monomer which may serve to
control the durability, pressure-sensitive adhesive strength and
cohesive strength of the pressure-sensitive adhesive, and to
provide, for example, a hydroxyl group, a carboxyl group, an epoxy
group, an isocyanate group or a nitrogen-containing functional
group such as an amino group to the polymer, and may be
copolymerizable with the (meth)acrylic acid ester-based monomer.
Various monomers serving as described above are known in the art,
and herein all of them may be used. In detail, the crosslinkable
monomer may be, but is not limited to, a monomer having a hydroxyl
group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl
(meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl
(meth)acrylate, 8-hydroxyoctyl (meth)acrylate,
2-hydroxyethyleneglycol (meth)acrylate or 2-hydroxypropyleneglycol
(meth)acrylate, a monomer having a carboxyl group such as
(meth)acrylic acid, 2-(meth)acryloyloxy acetic acid,
3-(meth)acryloyloxy propylic acid, 4-(meth)acryloyloxy butyric
acid, acrylic acid dimer, itaconic acid, maleic acid or maleic
anhydride, a monomer having an epoxy group such as glycidyl
(meth)acrylate, or a monomer having nitrogen such as
(meth)acrylamide, N-vinyl pyrrolidone or N-vinyl caprolactame,
which may be used alone or in combination of at least two
thereof.
[0114] The acryl polymer may further include a monomer represented
by Formula 16 in a polymerized form when necessary. Such a monomer
may be added to control a glass transition temperature and provide
other functionalities.
##STR00016##
[0115] In Formula 16, R.sub.25 and R.sub.27 are each independently
hydrogen or alkyl, R.sub.28 is a cyano group; phenyl group which is
unsubstituted or substituted with alkyl; an acetyloxy group; or
COR.sub.29 in which R.sub.29 is a glycidyloxy, group, or an amino
group which is unsubstituted or substituted with alkyl or
alkoxyalkyl.
[0116] The monomer of Formula 16 may be included at 20 parts by
weight or less based on the weight of the (meth)acrylic acid
ester-based monomer or crosslinkable monomer, but the weight ratio
may be changed according to the purpose.
[0117] The acryl polymer may be prepared by applying a conventional
polymerization method such as solution polymerization,
photopolymerization, bulk polymerization, suspension polymerization
or emulsion polymerization to a mixture of monomers having
respective components described above.
[0118] As a multifunctional crosslinking agent crosslinking the
acryl polymer in the pressure-sensitive adhesive layer, for
example, a general crosslinking agent such as an isocyanate
crosslinking agent, an epoxy crosslinking agent, an aziridin
crosslinking agent, or a metal chelate crosslinking agent may be
used. For example, an isocyanate crosslinking agent is used, but
the present application is not limited thereto. As the isocyanate
crosslinking agent, a multifunctional isocyanate compound such as
tolylene diisocyanate, xylene diisocyanate, diphenylmethane
diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate,
tetramethylxylene diisocyanate or naphthalene diisocyanate, or a
compound prepared by reacting the multifunctional isocyanate
compound with a polyol compound such as trimethylol propane may be
used. As the epoxy crosslinking agent, at least one selected from
the group consisting of ethyleneglycol diglycidylether,
triglycidylether, trimethylolpropane triglycidylether,
N,N,N',N'-tetraglycidyl ethylenediamine and glycerin
diglycidylether may be used, and as the aziridine crosslinking
agent, at least one selected from the group consisting of
N,N'-toluene-2,4-bis(1-aziridine carboxamide),
N,N'-diphenylmethane-4,4'-bis(1-aziridine carboxamide),
triethylenemelamine, bisisoprothaloyl-1-(2-methylaziridine) and
tri-1-aziridinyl phosphine oxide may be used, but the present
application is not limited thereto. In addition, as the metal
chelate crosslinking agent, a compound in which a polyvalent metal
such as aluminum, iron, zinc, tin, titanium, antimony, magnesium or
vanadium is coordinated to acetyl acetone or ethyl acetoacetate may
be used, but the present application is not limited thereto.
[0119] The multifunctional crosslinking agent may be included in
the pressure-sensitive adhesive, for example, at 0.01 to 10 parts
by weight or 0.01 to 5 parts by weight based on 100 parts by weight
of the acryl polymer described above. In this range, the
pressure-sensitive adhesive may maintain excellent cohesive
strength and durability.
[0120] The multifunctional crosslinking agent may crosslink the
polymer by reaction with a crosslinkable functional group of the
acryl polymer in the formation of the pressure-sensitive adhesive
layer such as an aging process.
[0121] In the pressure-sensitive adhesive layer having the IPN
structure, a crosslinking structure realized by polymerized
multifunctional acrylate may be included together with a
crosslinking structure realized by an acryl polymer crosslinked by
the multifunctional crosslinking agent.
[0122] As the multifunctional acrylate, a compound having at least
two (meth)acryloyl groups in a molecule may be used without
limitation. For example, the multifunctional acrylate may be a
difunctional acrylate such as 1,4-butanediol di(meth)acrylate,
1,6-hexanediol di(meth)acrylate, neopentylglycol di(meth)acrylate,
polyethyleneglycol di(meth)acrylate, neopentylglycol adipate
di(meth)acrylate, hydroxypivalic acid neopentylglycol
di(meth)acrylate, dicyclopentanyl di(meth)acrylate,
caprolactone-modified dicyclopentenyl di(meth)acrylate,
ethyleneoxide-modified di(meth)acrylate, di(meth)acryloxy ethyl
isocyanurate, allylated cyclohexyl di(meth)acrylate,
tricyclodecanedimethanol (meth)acrylate, dimethylol dicyclopentane
di(meth)acrylate, ethyleneoxide-modified hexahydrophthalic acid
di(meth)acrylate, tricyclodecane dimethanol(meth)acrylate,
neopentylglycol-modified trimethylpropane di(meth)acrylate,
adamantane di(meth)acrylate, or
9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorine; a trifunctional
acrylate such as trimethylolpropane tri(meth)acrylate,
dipentaerythritol tri(meth)acrylate, propionic acid-modified
dipentaerythritol tri(meth)acrylate, pentaerythritol
tri(meth)acrylate, propyleneoxide-modified trimethylolpropane
tri(meth)acrylate, trifunctional urethane (meth)acrylate, or
tris(meth)acryloxyethylisocyanurate; a tetrafunctional acrylate
such as diglycerin tetra(meth)acrylate or pentaerythritol
tetra(meth)acrylate; a pentafunctional acrylate such as propionic
acid-modified dipentaerythritol penta(meth)acrylate; or a
hexafunctional acrylate such as dipentaerythritol
hexa(meth)acrylate, caprolactone-modified dipentaerythritol
hexa(meth)acrylate, or urethane (meth)acrylate (e.g. a reaction
product of an isocyanate monomer and trimethylolpropane
tri(meth)acrylate). In some cases, the multifunctional acrylate may
be a photocurable oligomer known in the art, which may be any kind
of urethane acrylate, polycarbonate acrylate, polyester acrylate,
polyether acrylate or epoxy acrylate.
[0123] The multifunctional acrylate may be used alone or in
combination of at least two thereof. The acrylate having a
molecular weight of less than 1,000 and at least trifunctional
acrylate be used in an aspect of realizing durability, but the
present application is not limited thereto.
[0124] The multifunctional acrylate may include a ring structure in
a backbone structure. As such acrylate is used, the contraction or
expansion of the polarizer may be more effectively inhibited, and
the light leakage inhibition effect may be enhanced. The ring
structure included in the multifunctional acrylate may be a
carbocyclic or heterocyclic structure, or a monocyclic or
polycyclic structure. The multifunctional acrylate may be, but is
not limited to, a monomer having an isocyanurate structure such as
tris(meth)acryloxy ethyl isocyanuarate or hexafunctional acrylate
such as isocyanate-modified urethane (meth)acrylate (e.g. a
reaction product of an isocyanate monomer and trimethylolpropane
tri(meth)acrylate).
[0125] The multifunctional acrylate may be included in the
pressure-sensitive adhesive layer at 20 to 200 parts by weight
based on 100 parts by weight of the acryl polymer, and thus may
more effectively control the tensile modulus of the
pressure-sensitive adhesive layer and maintain excellent
durability.
[0126] The pressure-sensitive adhesive layer may further include a
silane coupling agent. The silane coupling agent serves to enhance
the cohesion and adhesion stability of the pressure-sensitive
adhesive, improve thermal resistance and humidity resistance, and
enhance adhesion reliability even when the pressure-sensitive
adhesive is left for a long time under a severe condition. For
example, the silane coupling agent may be, .gamma.-glycidoxypropyl
triethoxy silane, .gamma.-glycidoxypropyl trimethoxy silane,
.gamma.-glycidoxypropyl methyldiethoxy silane,
.gamma.-glycidoxypropyl triethoxy silane, 3-mercaptopropyl
trimethoxy silane, vinyltrimethoxysilane, vinyltriethoxy silane,
.gamma.-methacryloxypropyl trimethoxy silane, .gamma.-methacryloxy
propyl triethoxy silane, .gamma.-aminopropyl trimethoxy silane,
.gamma.-aminopropyl triethoxy silane, 3-isocyanatopropyl triethoxy
silane, .gamma.-acetoacetatepropyl trimethoxysilane,
acetoacetatepropyl triethoxy silane, .beta.-cyanoacetyl trimethoxy
silane, .beta.-cyanoacetyl triethoxy silane, or
acetoxyacetotrimethoxy silane, which may be used alone or in
combination of at least two thereof. In the present application, a
silane-based coupling agent having an acetoacetate or
.beta.-cyanoacetyl group may be used, but the present application
is not limited thereto. In the pressure-sensitive adhesive layer,
the silane coupling agent may be included at 0.01 to 5 parts by
weight, and preferably 0.01 to 1 part by weight based on 100 parts
by weight of the acryl polymer, and thus the pressure-sensitive
adhesive strength and durability may be effectively maintained.
[0127] The pressure-sensitive adhesive layer may further include a
tackifier resin. The tackifier resin may be a hydrocarbon-based
resin or a hydrogenated product thereof, a rosin resin or a
hydrogenated product thereof, a rosin ester resin or a hydrogenated
product thereof, a terphene resin or a hydrogenated product
thereof, a terphene phenol resin or a hydrogenated product thereof,
a polymerized rosin resin and a polymerized rosin ester resin,
which may be used alone or in combination of at least two thereof.
The tackifier resin may be included at 1 to 100 parts by weight
based on 100 parts by weight of the acryl polymer.
[0128] The pressure-sensitive adhesive layer may further include at
least one additive selected from the group consisting of an epoxy
resin, a curing agent, a UV stabilizer, an antioxidant, a coloring
agent, a reinforcing agent, a filler, a foaming agent, a surfactant
and a plasticizer as long as it does not affect the desired
effect.
[0129] A method of forming the pressure-sensitive adhesive layer is
not particularly limited. In one example, the pressure-sensitive
adhesive layer may be formed by a method of preparing a
pressure-sensitive adhesive composition by mixing the components
described above, coating the pressure-sensitive adhesive
composition on a suitable process base using a conventional means
such as a bar coater or a comma coater, and curing the composition.
In addition, a method of curing the pressure-sensitive adhesive
composition is not particularly limited, and for example, the
composition may not be cured by sequentially or simultaneously
performing a method of aging the composition at a suitable
temperature such that a crosslinking reaction of the acryl polymer
and the multifunctional crosslinking agent may progress and a
process of radiating electromagnetic waves to enable the
multifunctional acrylate to be polymerized. The radiation of the
electromagnetic waves may be performed using a means such as a high
pressure mercury lamp, an electrodeless lamp or a xenon lamp. In
addition, conditions for radiating electromagnetic waves are not
particularly limited, as long as the conditions are controlled to
appropriately execute the polymerization of the multifunctional
acrylate without degrading all the physical properties. For
example, the radiation of electromagnetic waves may be performed
for a suitable time by controlling a luminance to 50 to 2,000
mW/cm.sup.2 and an intensity of radiation of 10 to 1,000
mJ/cm.sup.2.
[0130] Meanwhile, in consideration of the efficiency of the curing
process by the radiation of the electromagnetic waves, a
photoinitiator may be included in the pressure-sensitive adhesive
composition. As the photoinitiator, any one that can generate
radicals by the radiation of electromagnetic waves and start the
curing reaction may be used without particular limitation. For
example, the photoinitiator may be benzoin, benzoin methylether,
benzoin ethylether, benzoin isopropylether, benzoin n-butylether,
benzoin isobutylether, acetophenone, dimethylamino acetophenone,
2,2-dimethoxy-2-phenylacetophenone,
2,2-diethoxy-2-phenylacetophenone,
2-hydroxy-2-methyl-1-phenylpropane-1-one,
1-hydroxycyclohexylphenylketone,
2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-one,
4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone, benzophenone,
p-phenylbenzophenone, 4,4'-diethylaminobenzophenone,
dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone,
2-t-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone,
2-ethylthioxanthone, 2-chlorothioxanthone,
2,4-dimethylthioxanthone, 2,4-diethylthioxanthone,
benzyldimethylketal, acetophenone dimethylketal, p-dimethylamino
benzoic acid ester,
oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone] or
2,4,6-trimethylbenzoyl-diphenyl-phosphineoxide, which may be used
alone or in combination of at least two thereof, but the present
application is not limited thereto.
[0131] The photoinitiator may be included at 0.2 to 20 parts by
weight, 0.2 to 10 parts by weight, or 0.2 to 5 parts by weight
based on 100 parts by weight of the acryl polymer. The
photoinitiator may be included at 0.2 to 20 parts by weight based
on 100 parts by weight of the multifunctional acrylate. According
to such control, the reaction of the multifunctional acrylate may
be effectively induced, and degradation in physical properties of
the pressure-sensitive adhesive due to remaining components after
curing may be prevented.
[0132] The pressure-sensitive adhesive layer may also be formed
using a heat-curable or room temperature-curable pressure-sensitive
adhesive composition, and in this case, the pressure-sensitive
adhesive layer may include an acryl polymer crosslinked by a
multifunctional crosslinking agent.
[0133] Similar to the photocurable composition described above, the
acryl polymer may be a polymer having a molecular weight of 500,000
to 2,500,000, and including a (meth)acrylic acid ester-based
monomer and a crosslinkable monomer in a polymerization unit, or a
polymer including 80 to 99.9 parts by weight of a (meth)acrylic
acid ester-based monomer and 0.1 to 20 parts by weight of a
crosslinkable monomer in a polymerization unit. Here, specific
kinds of the (meth)acrylic acid ester-based monomer and the
crosslinkable monomer or the method of preparing the polymer are
the same as described above. In addition, the polymer may also
include a functional monomer represented by Formula 16.
[0134] In addition, as the multifunctional crosslinking agent
crosslinking the acryl polymer in the pressure-sensitive adhesive
layer, an isocyanate crosslinking agent, an epoxy crosslinking
agent, an aziridine crosslinking agent or a metal chelate
crosslinking agent may also be used as described above. Such a
crosslinking agent may be included at a suitable content within a
range of 0.01 to 10 parts by weight, for example, 0.01 to 5 parts
by weight based on 100 parts by weight of the acryl polymer in
consideration of the tensile modulus, durability and cohesion of
the pressure-sensitive adhesive layer.
[0135] The above method of forming the pressure-sensitive adhesive
layer is similar to that for the photocurable pressure-sensitive
adhesive described above, except that the curing process by the
radiation of electromagnetic waves is not performed. That is, the
pressure-sensitive adhesive layer may be formed by preparing the
pressure-sensitive adhesive composition by suitably mixing
necessary components, coating the composition on a suitable base,
and curing the composition. The heat-curable pressure-sensitive
adhesive composition may further include at least one additive
selected from the group consisting of a silane coupling agent, a
tackifier resin, an epoxy resin, a curing agent, a UV stabilizer,
an antioxidant, a coloring agent, a reinforcing agent, a filler, a
foaming agent, a surfactant and a plasticizer when necessary.
[0136] When the pressure-sensitive adhesive layer is formed in a
multi-layered structure such as at least double-layered structure,
the pressure-sensitive adhesive layer constituting the
multi-layered structure may be formed using suitable kinds, for
example, the same or different kinds of the heat-curable, room
temperature-curable, moisture-curable and photocurable adhesive
compositions.
[0137] In one example, when the pressure-sensitive adhesive layer
includes a first pressure-sensitive adhesive layer forming a first
surface, and a second pressure-sensitive adhesive layer forming a
second surface, and the first surface is attached to the polarizer,
the pressure-sensitive adhesive layer may be formed using a
pressure-sensitive adhesive composition realizing an IPN structure
as the first photocurable pressure-sensitive adhesive composition.
Therefore, in one example, the first pressure-sensitive adhesive
layer may include a crosslinking structure including an acryl
polymer crosslinked by a multifunctional crosslinking agent and a
crosslinking agent including polymerized multifunctional
acrylate.
[0138] The polarizing plate may further include a protective film
attached to one or both surfaces, for example, one surface,
specifically, a surface of the polarizer opposite to the surface on
which the adhesive layer and the pressure-sensitive adhesive layer
are sequentially disposed. As the protective film, a
cellulose-based film such as a TAC film, a polyester-based film
such as a poly(ethylene terephthalate)) (PET) film, a
polycarbonate-based film, a polyestersulfone-based film, or a
polyolefin-based film such as an acryl-based and/or a polyethylene
film, a polypropylene film, a cyclic polyolefin film or polyolefin
film having a norbornene structure or an ethylene-propylene
copolymer film may be used, but the present application is not
limited thereto. The protective film may be attached to the
polarizer by means of, for example, an adhesive layer
conventionally used to attach the protective film.
[0139] The polarizing plate may further include a releasing film
attached under the pressure-sensitive adhesive layer. As the
releasing film, a conventional component known in the art may be
employed.
[0140] The polarizing plate may further include at least one
functional layer selected from the group consisting of an
anti-reflection layer, an anti-glare layer, a phase retardation
plate, a wide viewing angle compensation film and a brightness
enhancement film when necessary.
[0141] The exemplary LCD device of the present application may
include a liquid crystal panel and the polarizing plate attached to
one or both surfaces of the liquid crystal panel.
[0142] The kind of the liquid crystal panel included in the LCD
device is not particularly limited. For example, a known panel such
as a passive matrix-type panel such as a twisted nematic (TN),
super twisted nematic (STN), ferroelectric (F) or polymer dispersed
(PD) panel, an active matrix-type panel such as a two or three
terminal panel, an in-plane switching (IPS) panel or a
vertically-aligned (VA) panel may be used without limitation.
[0143] In addition, kinds of other components constituting the LCD
device, for example, upper and lower substrates (e.g., a color
filter substrate or an array substrate), are not particularly
limited either, and any components known in the art may be employed
without limitation.
Advantageous Effect
[0144] One exemplary polarizing plate has lighter weight, a smaller
thickness, and excellent physical properties such as durability,
water resistance, workability, and light leakage preventing
ability. In addition, one exemplary polarizing plate does not
induce curling occurring in the polarizing plate or a polarizer in
formation thereof, and has excellent thermal resistance or thermal
shock resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0145] FIG. 1 is a diagram illustrating a structure of an exemplary
polarizing plate;
[0146] FIGS. 2 and 3 are cross-sectional views illustrating
exemplary pressure-sensitive adhesive layers of the present
application; and
[0147] FIG. 4 is a schematic diagram illustrating a method of
evaluating a curling characteristic.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0148] Hereinafter, the present application will be described with
reference to Examples according to the present application and
Comparative Examples not according to the present application in
detail. However, the scope of the present application is not
limited to the following Examples.
Preparation Example 1
Preparation of Acryl Polymer (A)
[0149] 98 parts by weight of n-butyl acrylate (n-BA) and 2 parts by
weight of 2-hydroxyethyl acrylate (2-HEA) were put into a 1 L
reactor refluxing nitrogen gas and equipped with a cooling device
to facilitate temperature control. Subsequently, 180 parts by
weight of ethyl acetate (EAc) was put as a solvent into the
reactor, which was purged with the nitrogen gas for 60 minutes to
remove oxygen. Afterwards, the temperature was maintained at
67.degree. C., 0.05 parts by weight of azobisisobutyronitrile
(AIBN) was put into the reactor as a reaction initiator, and the
reaction was carried out for 8 hours. After the reaction, the
reaction product was diluted with ethyl acetate, and thus an acryl
polymer (A) having a solid content of 30 wt %, a weight average
molecular weight of 1,000,000, and a distribution of molecular
weight of 4.9 was prepared.
Preparation Examples 2 to 5
Preparation of Acryl Polymers (B) to (D)
[0150] Acryl polymers (B) to (D) were prepared based on the method
as described in Preparation Example 1, except that the monomer
compositions were changed as shown in Table 1. The weight average
molecular weights and distributions of molecular weight of the
prepared polymers are listed in Table 1.
TABLE-US-00001 TABLE 1 A B C D Monomer n-BA 98 98 98 80 Composition
2-HEA 2 2 -- 20 (Parts by Weight) AA -- -- 2 -- Weight Average
Molecular 100 190 100 100 Weight (10,000) Distribution of Molecular
weight 4.9 5.5 5.4 4.9 n-BA: n-butyl acrylate 2-HEA: 2-hydroxy
ethyl acrylate AA: acrylic acid
Preparation Example 6
Preparation of Adhesive Composition
[0151] An adhesive composition was prepared by mixing 55 parts by
weight of 2-hydroxyethyl acrylate (2-HEA), 20 parts by weight of
phenoxyethyl acrylate, 15 parts by weight of isobornyl acrylate and
5 parts by weight of poly[(phenyl glycidyl ether)-CO-formaldehyde],
which is a novolac epoxy resin having a molecular weight of 3000,
as an epoxy compound, and mixing 4 parts by weight of a radical
initiator (TPO, Darocure TPO) and 1 part by weight of IHT-P143 (50%
mixed triarylsulfonium hexafluorophosphate salt and 50% propylene
carbonate) as a cationic polymerization initiator with the mix.
Example 1
Preparing First Pressure-Sensitive Adhesive Layer
[0152] A first pressure-sensitive adhesive composition was prepared
by mixing 100 parts by weight of the acryl polymer (A), 3 parts by
weight of a multifunctional crosslinking agent (TDI-based
isocyanate, Coronate L, Nippon Polyurethane Industry (Japan)), 100
parts by weight of multifunctional acrylate (trifunctional urethane
acrylate, Aronix M-315), 3 parts by weight of a photoinitiator
(Irgacure 184, hydroxycyclohexylphenylketone, Ciba Specialty
Chemicals (Switzerland)) and 0.1 parts by weight of a silane
coupling agent (M812, silane coupling agent having a (3-cyanoacetyl
group, LG Chem (Korea)) in a solvent to have a solid concentration
of 30 wt %. Subsequently, the prepared pressure-sensitive adhesive
composition was coated on a releasing-treated surface of a
poly(ethylene terephthalate) (PET) releasing film (thickness: 38
.mu.m, MRF-38, Mitsubishi) subjected to releasing treatment to have
a dry thickness of 25 .mu.m, and the resulting film was dried in an
oven at 110.degree. C. for 3 minutes. Then, a releasing-treated
surface of the PET releasing film (thickness: 38 .mu.m, MRF-38,
Mitsubishi) subjected to releasing treatment, was further laminated
on the dried coating layer, and UV rays were radiated under the
following conditions, thereby forming a first pressure-sensitive
adhesive layer between two of the PET releasing films. A tensile
modulus (at 25.degree. C.) of the formed first pressure-sensitive
adhesive layer was 300 MPa. In the embodiment, the tensile modulus
was measured according to the following method.
[0153] <Conditions for UV Radiation>
[0154] UV Radiation Tool: High Pressure Mercury Lamp
[0155] Radiation Conditions: [0156] Luminance: 600 mW/cm.sup.2
[0157] Intensity of Radiation: 150 mJ/cm.sup.2
Preparing Second Pressure-Sensitive Adhesive Layer
[0158] A second pressure-sensitive adhesive composition was
prepared by mixing 100 parts by weight of the acryl polymer (A),
0.01 parts by weight of a multifunctional crosslinking agent,
(TDI-based isocyanate, Coronate L, Nippon Polyurethane Industry
(Japan)) and 0.1 parts by weight of a silane coupling agent (M812,
silane coupling agent having a .beta.-cyanoacetyl group, LG Chem
(Korea)) in a solvent to have a solid concentration of 30 wt %.
Subsequently, the prepared pressure-sensitive adhesive composition
was coated on a releasing-treated surface of a PET releasing film
(thickness: 38 .mu.m, MRF-38, Mitsubishi) subjected to releasing
treatment to have a dry thickness of 25 .mu.m, and the resulting
film was dried in an oven at 110.degree. C. for 3 minutes. Then, a
releasing-treated surface of the releasing-treated PET releasing
film (thickness: 38 .mu.m, MRF-38, Mitsubishi) was further
laminated on the dried coating layer. A tensile modulus (at
25.degree. C.) of the formed second pressure-sensitive adhesive
layer was 0.06 MPa.
[0159] Subsequently, the formed first pressure-sensitive adhesive
layer and the second pressure-sensitive adhesive layer were
laminated to each other, thereby forming a pressure-sensitive
adhesive layer having a double-layered structure.
Preparing Polarizing Plate
[0160] An acryl film (which was formed by extruding and extending a
mixture including phenoxy resin, polystyrene and
polymethylmethacrylate) was laminated as a protective film to one
surface of a polarizer formed by extending a polyvinylalcohol-based
resin film, dying the film with iodine and treating the film with a
boric acid aqueous solution using the previously prepared adhesive
composition. Subsequently, a polarizing plate was formed by
laminating the previously formed double-layered pressure-sensitive
adhesive layer to a surface of the polyvinylalcohol-based polarizer
to which the protective film was not attached using the prepared
adhesive composition. In detail, a polarizing plate was formed by
coating the adhesive composition on the polarizer, laminating the
first pressure-sensitive adhesive layer of the double-layered
pressure-sensitive adhesive layer to the coated surface, and curing
the first pressure-sensitive adhesive layer by radiation of UV rays
under the following conditions.
[0161] <Conditions for UV Radiation>
[0162] UV Radiation Tool: High Pressure Mercury Lamp
[0163] Radiation Conditions: [0164] Luminance: 800 mW/cm.sup.2
[0165] Intensity of Radiation: 2000 mJ/cm.sup.2
Examples 2 to 7 and Comparative Examples 1 to 4
[0166] A polarizing plate was formed based on the same method as
described in Example 1, except that the compositions of the first
and second pressure-sensitive adhesive layers were changed as shown
in Tables 2 and 3. However, in Comparative Examples 1 to 4, the
double-layered pressure-sensitive adhesive was not used, but a
single-layered pressure-sensitive adhesive having a first
pressure-sensitive adhesive was used.
TABLE-US-00002 TABLE 2 Example 1 2 3 4 5 6 7 First Pressure- Kind
of Acryl Polymer A B C D A A A pressure- sensitive Content of Acryl
100 100 100 100 100 100 100 sensitive adhesive Polymer adhesive
composition Content of 3 3 3 3 3 3 3 Multifunctional Crosslinking
Agent MFA1 Content 100 100 100 100 100 -- 100 MFA2 Content -- -- --
-- -- 50 -- Content of 3 3 3 3 3 3 3 Photoinitiator Content of
Silane 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Coupling Agent UV Curing Method
O O O O O O O Pressure- Thickness (.mu.m) 25 25 25 25 25 25 25
sensitive Tensile Modulus 300 300 350 850 300 400 300 adhesive
Second Pressure- Kind of Acryl Polymer A A A A A A C pressure-
sensitive Content of Acryl 100 100 100 100 100 100 100 sensitive
adhesive Polymer adhesive composition Content of 0.01 0.01 0.01
0.01 0.01 0.01 0.01 Multifunctional Crosslinking Agent MFA1 Content
-- -- -- -- 10 -- -- MFA2 Content -- -- -- -- -- -- -- Content of
-- -- -- -- 1 -- -- Photoinitiator Content of Silane 0.1 0.1 0.1
0.1 0.1 0.1 0.1 Coupling Agent UV Curing Method X X X X O X X
Pressure- Thickness (.mu.m) 25 25 25 25 25 25 25 sensitive Tensile
Modulus 0.06 0.06 0.06 0.06 0.6 0.06 0.06 adhesive composition
Content Unit: parts by weight Multifunctional Crosslinking Agent:
TDI-based isocyanate crosslinking agent (Coronate L, Nippon
Polyurethane Industry) MFA1: trifunctional urethane acrylate
(Aronix M-315, Toa Gosei K. K) MFA2: hexafunctional urethane
acrylate (UA 3061, Kyoeisha) Photoinitiator:
hydroxycyclohexylphenyl ketone (Irgacure 184, Ciba Specialty
Chemicals) Silane Coupling Agent: silane coupling agent having a
.beta.-cyanoacetyl group (M812, LG Chem) Tensile Modulus: tensile
modulus at 25.degree. C., Unit: MPa
TABLE-US-00003 TABLE 3 Comparative Example 1 2 3 4 First Pressure-
Kind of Acryl Polymer A A A A pressure- sensitive Content of Acryl
Polymer 100 100 100 100 sensitive adhesive adhesive composition
Content of 3 0.01 0.01 0.01 Multifunctional Crosslinking Agent MFA1
Content 100 -- 10 10 MFA2 Content 3 -- -- -- Content of 3 -- 1 1
Photoinitiator Content of Silane 0.1 0.1 0.1 0.1 Coupling Agent UV
Curing Method O X O O Pressure- Thickness (.mu.m) 25 25 25 50
sensitive Tensile Modulus 300 0.06 0.6 0.6 adhesive
(MPa)(25.degree. C.) composition Content Unit: partsby weight
Multifunctional Crosslinking Agent: TDI-based isocyanate
crosslinking agent (Coronate L, Nippon Polyurethane Industry) MFA1:
trifunctional urethane acrylate (Aronix M-315, Toa Gosei K. K)
MFA2: hexafunctional urethane acrylate (UA 3061, Kyoeisha)
Photoinitiator: hydroxycyclohexylphenyl ketone (Irgacure 184, Ciba
Specialty Chemicals) Silane Coupling Agent: silane coupling agent
having a .beta.-cyanoacetyl group (M812, LG Chem)
Example 8
[0167] A polarizing plate was formed based on the same method as
described in Example 1, except that an adhesive composition
prepared by mixing 44.5 parts by weight of 2-hydroxyethyl acrylate
(2-HEA), 15 parts by weight of phenoxyethyl acrylate, 9 parts by
weight of isobornyl acrylate, and 15 parts by weight of Celloxide
2021P, which is a epoxy resin and 10 parts by weight of
poly[(phenyl glycidyl ether)-CO-formaldehyde], which is a novolac
epoxy resin having a molecular weight of 3000 as epoxy compounds,
and mixing 3 parts by weight of a radical initiator (CGI 819,
bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide), 3 parts by
weight of an iodine initiator (Irgacure 250, Ciba Specialty
Chemicals) as a cationic initiator and 0.5 parts by weight of a
photosensitizer (isopropyl thioxanthone, Aldrich) with the mix was
used.
Example 9
[0168] A polarizing plate was formed based on the same method as
described in Example 1, except that an adhesive composition
prepared by mixing 50 parts by weight of 2-hydroxyethyl acrylate
(2-HEA), 20 parts by weight of phenoxyethyl acrylate, 15 parts by
weight of isobornyl acrylate and 5 parts by weight of poly[(phenyl
glycidyl ether)-CO-formaldehyde], which is a novolac epoxy resin
having a molecular weight of 3000 as an epoxy compound, and mixing
4 parts by weight of a radical initiator (TPO, Darocure TPO), 3
parts by weight of an iodine initiator as a cationic initiator and
2 parts by weight of a photosensitizer (diethyl thioxanthone,
Kayacure DTEX-S, Nippon Kayaku) with the mix was used.
Comparative Example 5
[0169] A polarizing plate was formed based on the same method as
described in Example 1, except that a TAC film having a thickness
of 60 .mu.m was used as a protective film instead of the acryl
film, a water-based polyvinylalcohol-based adhesive composition
generally used to attach a protective film was coated as an
adhesive attaching the TAC film to the polarizer to have a dry
thickness of 0.1 .mu.m, the water-based polyvinylalcohol-based
adhesive composition was coated, the protective film was laminated
and dried in an oven at 80.degree. C. for 5 minutes, and a
double-layered pressure-sensitive adhesive layer was laminated
using the water-based polyvinylalcohol-based adhesive
composition.
[0170] <Evaluation of Physical Properties>
[0171] 1. Evaluation of Tensile Modulus
[0172] Herein, a tensile modulus of a pressure-sensitive adhesive
was measured by a tensile stress-strain test according to a method
defined in ASTM D638, or when it was difficult to directly measure
a tensile modulus, a storage modulus was measured by the following
method and then converted by the following Conversion Formula. In
detail, a sample having a stacked structure of a PET releasing film
(thickness: 38 .mu.m, MRF-38), a pressure-sensitive adhesive layer
and a PET releasing film (thickness: 38 .mu.m, MRF-38), formed in
Examples or Comparative Examples, was cut into a dog bone-type
specimen in a size of 7 cm (length).times.1 cm (width), both ends
of the specimen were fixed with jigs for a tensile test, and a
tensile modulus was measured according to ASTM D638. The conditions
for measuring the tensile modulus were as follows.
[0173] <Conditions for Measuring Tensile Modulus>
[0174] Measuring Tool: Universal Testing Machine (UTM)
[0175] Equipment Model: Zwick Roell Z010, Instron
[0176] Measurement Conditions: [0177] Load Cell: 500 N [0178]
Tensile Speed: 3 mm/sec
[0179] <Measurement of Storage Modulus and Conversion into
Tensile Modulus>
[0180] A pressure-sensitive adhesive layer was cut in a size of 15
cm.times.25 cm.times.25 .mu.m (width.times.length.times.thickness),
and then the cut pressure-sensitive adhesive layers were stacked in
five layers. Subsequently, after the stacked adhesive layers were
cut in a circle having a diameter of 8 mm, the cut stacked adhesive
layers are left overnight while they are pressed using glasses to
enhance wettability at an interface between the layers, thereby
removing air bubbles generated during stacking. As a result, a
specimen was prepared. Subsequently, the specimen was placed on a
parallel plate, and a gap was adjusted. Then, after Normal &
Torque was set to zero, and the stabilization of a normal force was
checked, the storage modulus was measured under the following
conditions, and a tensile modulus was calculated according to the
following Conversion Formula.
[0181] Measurement Tool and Measuring Conditions
[0182] Measurement Tool: ARES-RDA, TA Instruments Inc. with forced
convection oven
[0183] Measuring Conditions:
[0184] Geometry: 8 mm parallel plate
[0185] Gap: around 1 mm
[0186] Test Type: dynamic strain frequency sweep
[0187] Strain=10.0 [%], temperature: 30.degree. C.
[0188] Initial Frequency: 0.4 rad/s, final frequency: 100 rad/s
E=3G <Conversion Formula>
[0189] In Conversion Formula, E is a tensile modulus, and G is a
storage modulus.
[0190] 2. Evaluation of Peel Strength and Repeelability
[0191] A specimen was formed by cutting a polarizing plate in a
size of 25 mm.times.100 mm (width.times.length). Subsequently, a
PET releasing film was peeled off from the specimen, and the
specimen of the polarizing plate was attached to alkali-free glass
using a laminator by means of a pressure-sensitive adhesive layer.
Afterward, the specimen was compressed in an autoclave (50.degree.
C., 0.5 atm) for approximately 20 minutes, and stored under
constant temperature and humidity conditions (23.degree. C.,
relative humidity of 50%) for 25 hours. Then, using a texture
analyzer (TA) (Stable Micro System (United Kingdom)), the
polarizing plate was peeled off from the alkali-free glass at a
peel rate of 300 mm/min and a peel angle of 180 degrees to measure
a peel strength. In addition, repeelability was evaluated under the
following criteria:
[0192] <Criteria for Evaluation of Repeelability>
[0193] .smallcircle.: A day after attachment, the peel strength was
800 N/25 mm or less.
[0194] .DELTA.: A day after attachment, the peel strength was 1,000
N/25 mm or more.
[0195] x: A day after attachment, the peel strength was 2,000 N/25
mm or more.
[0196] 3. Evaluation of Durability and Reliability
[0197] 2 specimens were prepared by cutting a specimen prepared by
cutting a polarizing plate in a size of 90 mm.times.170 mm
(width.times.length) per Example or Comparative Example.
Subsequently, the two specimens were attached to both surfaces of a
glass substrate (110 mm.times.190 mm.times.0.7
mm=width.times.length.times.thickness) such that an optical
absorption axes crossed, thereby preparing a sample. A pressure
applied during attachment was approximately 5 kg/cm.sup.2, and the
attachment was carried out in a clean room to avoid air bubbles or
extraneous materials at an interface.
[0198] The humidity and thermal resistance of the sample was
determined by observing whether air bubbles or peeling were
generated at a pressure-sensitive adhesive interface after the
sample was left for 1,000 hours under conditions including a
temperature of 60.degree. C. and a relative humidity of 90%.
[0199] In addition, the thermal resistance was determined by
observing whether air bubbles or peeling were generated at an
adhesive interface after the sample was left at a temperature of
80.degree. C. for 1,000 hours.
[0200] The formed samples were left at room temperature for 24
hours, followed by the evaluation of the humidity and thermal
resistance or thermal resistance.
[0201] Evaluation conditions were as follows:
[0202] <Criteria for Evaluation of Durability and
Reliability>
[0203] .smallcircle.: No air bubbles and/or peeling were
generated.
[0204] .DELTA.: Air bubbles and/or peeling were somewhat
generated.
[0205] x: Air bubbles and/or peeling were considerably
generated.
[0206] 4. Evaluation of Water Resistance
[0207] Polarizing plates formed in Examples and Comparative
Examples were cut in a size of 90 mm.times.170 mm
(width.times.length), thereby forming specimens. Each specimen was
attached to a glass substrate (110 mm.times.190 mm.times.0.7
mm=width.times.length.times.thickness), thereby forming a sample. A
pressure applied during attachment was approximately 5 kg/cm.sup.2,
and the attachment was executed in a clean room to prevent bubbles
or impurities at an interface. Subsequently, the formed sample was
put into water at 60.degree. C., left for 24 hours, and it was
observed whether bubbles or peeling were generated. The water
resistance was evaluated according to the following criteria.
[0208] <Criteria for Evaluation of Water Resistance>
[0209] .smallcircle.: No air bubbles and/or peeling were
generated.
[0210] .DELTA.: Some bubbles and/or peeling were generated at an
interface.
[0211] x: Bubbles and/or peeling were considerably generated.
[0212] 5. Evaluation of Uniformity of Light Transmission
[0213] Polarizing plates formed in Examples and Comparative
Examples were attached to a 22-inch LCD monitor (LG Philips LCD) in
a state in which optical axes crossed, stored under constant
temperature and humidity conditions (23.degree. C., relative
humidity: 50%) for 24 hours, and left at 80.degree. C. for 200
hours. Subsequently, light was radiated to the monitor using a back
light in a dark room, and the uniformity of light transmission was
evaluated according to the following criteria:
[0214] <Criteria for Evaluation of Uniformity of Light
Transmission>
[0215] .circleincircle.: when non-uniformity of light transmission
was not observed in four peripheral regions of a monitor by
eyes
[0216] .smallcircle.: when non-uniformity of light transmission was
observed slightly in four peripheral regions of a monitor by
eyes
[0217] .DELTA.: when non-uniformity of light transmission was
observed somewhat in four peripheral regions of a monitor by
eyes
[0218] x: when non-uniformity of light transmission was observed
considerably in four peripheral regions of a monitor by eyes
[0219] 6. Evaluation of Weight Average Molecular Weight and
Distribution of Molecular Weight
[0220] The weight average molecular weight and the distribution of
the molecular weight of an acryl polymer were measured using GPC
under the following conditions. To draw a calibration curve,
standard polystyrene of an Agilent system was used, and measurement
results were converted.
[0221] <Conditions for Measuring Weight Average Molecular
Weight>
[0222] Measuring Tool: Agilent GPC (Agilent 1200 series, USA)
[0223] Column: two connected PL mixed B
[0224] Column Temperature: 40.degree. C.
[0225] Eluent: Tetrahydrofuran
[0226] Flow Rate: 1.0 mL/min
[0227] Concentration: .about.2 mg/mL (100 .mu.L injection)
[0228] 7. Evaluation of Curling Characteristic
[0229] A curling characteristic was evaluated according to the
following criteria by laminating a protective film cut in a size of
130 mm.times.180 mm (width direction (transverse direction
(TD)).times.length (MD direction)) with a polarizer using an
adhesive composition during an operation of forming a polarizing
plate and measuring curling occurring in the TD direction during
radiation of UV rays or drying when a water-based
polyvinylalcohol-based adhesive was used. The measurement of
curling was executed by the method illustrated in FIG. 4.
[0230] <Evaluation Criteria>
[0231] .smallcircle.: Curling occurring in the TD direction was
less than 0.5 cm.
[0232] .DELTA.: Curling occurring in the TD direction was 0.5 cm to
2.0 cm
[0233] x: Curling occurring in the TD direction was more than 2.0
cm
[0234] The measurement results are summarized and shown in Table
4.
TABLE-US-00004 TABLE 4 Kind of Curing Peel Humidity &
Uniformity of Protective Type of Kind of Strength Repeel Thermal
Thermal Water Curling Light Film Adhesive Adhesive (N/25 mm)
ability Resistance Resistance Resistance Characteristic
Transmission Example 1 Acryl UV Rays Hybrid 500 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.circleincircle. 2 Acryl UV Rays Hybrid 500 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.circleincircle. 3 Acryl UV Rays Hybrid 500 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.circleincircle. 4 Acryl UV Rays Hybrid 500 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.circleincircle. 5 Acryl UV Rays Hybrid 400 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.circleincircle. 6 Acryl UV Rays Hybrid 500 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. 7 Acryl UV Rays Hybrid 800 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. 8 Acryl UV Rays Hybrid 500 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.circleincircle. 9 Acryl UV Rays Hybrid 500 .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.circleincircle. Comparative 1 Acryl UV Rays Hybrid 30
.largecircle. X X X .largecircle. X Example 2 Acryl UV Rays Hybrid
500 .DELTA. X X X .largecircle. X 3 Acryl UV Rays Hybrid 500
.largecircle. .DELTA. X X .largecircle. X 4 Acryl UV Rays Hybrid
500 .largecircle. .DELTA. .DELTA. .DELTA. .largecircle. .DELTA. 5
TAC Water- Hybrid 500 .largecircle. .largecircle. .largecircle.
.largecircle. X .circleincircle. based Dry
* * * * *