Title of Invention

ACRYLIC PRESSURE-SENSITIVE ADHESIVE COMPOSITION FOR POLARIZING FILM

Abstract The present invention provides an acrylic pressure-sensitive adhesive composition for a polarizing film comprising a) 100 parts by weight of a (meth)acrylic copolymer having a high molecular weight, which is copolymerized from a (meth)acrylic acid ester monomer and a vinylic and/or an acrylic monomer having a functional group capable of crosslinking with a multifunctional crosslinking agent and has a weight- average molecular weight of at least 1,000,000; b) 5-20 parts by weight of a (meth)acrylic copolymer having a low molecular weight, which comprises the same monomer of the main chain of a) the (meth)acrylic copolymer having a high molecular weight, has a weight-average molecular weight of 2,000-30,000 and comprises 0.01-1 monomer, per one molecule of the copolymer on average, having a functional group capable of reacting with the crosslinking agent of c); and c) 0.01-10 parts by weight of a multifunctional crosslinking agent. A polarizing film comprising the composition and a liquid crystal display device comprising the same can minimize the light leakage problem with good stress-relaxation ability, while maintaining such major characteristics as adhesion durability, even under thermal and humidity conditions.
Full Text Technical Field
[1] The present invention relates to an acrylic pressure-sensitive adhesive composition
for a polarizing film, more particularly to a pressure-sensitive adhesive composition for a polarizing film capable of solving the light leakage problem, a polarizing film prepared therefrom and a liquid crystal display device using the same.
Background Art
[2] In general a liquid crystal cell containing liquid crystals and a polarizing film are
basically needed to manufacture a liquid crystal display device. An adequate adhesive layer or a pressure-sensitive adhesive layer is required to join them. In addition, a phase retardation film, a compensation film for wide view angle, a brightness enhancement film, etc. may be further joined to the polarizing film in order to improve the performance of a liquid crystal display device.
[3] Typically, a liquid crystal display comprises a uniformly aligned liquid crystal
layer; a polarizing film comprising a liquid crystal ceil, which consists of a transparent glass plate or a plastic plate including a transparent electrode layer and an adhesive layer or a pressure-sensitive adhesive layer; a phase retardation film; and additional functional film layers,
[4] The polarizing film contains regularly aligned iodine compounds or dichromic
polarizing materials and has a multi-layer structure to protect these polarizing elements by forming protecting films made of triacetyl cellulose (TAC), etc. on both sides of the film. The polarizing film may further comprise a phase retardation film having an anisotropic molecular alignment, a compensation film for wide view angle such as an optically designed liquid crystal film, etc.
[5] Because these films are made of materials having different molecular structures and
compositions, they have different physical properties. Especially, under a specific thermal and/or humidity condition, materials having an anisotropic molecular alignment shrink or expand, which causes the lack of dimensional stability. As a result, if the polarizing film is fixed by a pressure-sensitive adhesive, a shear stress caused (he thermal and/or humidity condition remains, so that light leakage occurs at the region where the stress is concentrated.
[6] One way to solve the problem of light leakage is to reduce the shrinkage of the
polarizing film at the thermal and/or humidity condition. However, if is very difficult to remove the stress applied to a liquid crystal panel to which a polarizing film consisting of different materials has been attached.
[7] Rubbers, acryls and silicones are commonly used as pressure-sensitive adhcsives.
Among these, acrylic pressure-sensitive adhesives are used the most widely in manu­
facturing high performance pressure-sensitive adhesive compositions. Molecular char­
acteristics of adhesive materials, such as molecular weight and distribution, cross
linking density, and composition, mainly influence the durability of pressure-sensitive
adhesives, which may be controlled by the high adhesive strength and cohesive
strength.
[8] However, when a polarizing film manufactured using such a pressure-sensitive
adhesive is used for a long time under a specific thermal and/or humidity condition in a liquid crystal display, stress tends to concentrate because of the shrinkage of the polarizing film. To solve this problem, the adhesive layer needs to have a stress relaxation ability.
(9) For this purpose, Japan Patent Publication No. Hei 1-66283 disclosed a polarizing
film employing an acrylic pressure-sensitive adhesive layer mainly comprising
(meth)acrylic acid alkyl ester having alkyl groups with 1-12 carbon atoms, in which
the pressure-sensitive adhesive layer comprises the polymer constituent having a
weight-average molecular weight of at most 100,000 in less than 15 wi% and the
polymer constituent having a weight-average molecular weight of at least 1,000,000 in
more than 10 wt%. Although the polarizing film employing the adhesive comprising a
lot of polymer constituent having a high molecular weight has good adhesion
durability, it is difficult to relax the stress caused by the dimensional change of the
polarizing film because the adhesive has large cohesive force (elasticity).
[10] Korea Patent Publication No. 1998-079266 attempted to solve the problem of light
leakage by offering a stress-relaxation property to the pressure-sensitive adhesive composition, which comprises 100 parts by weight of a high molecular weight acrylic copolymer having a weight-average molecular weight of at least 1,000,000,20-200 parts by weight of a low molecular weight acrylic copolymer having a weight-average molecular weight of at most 30,000 and 0.005-5 parts by weight of a multifunctional crosslinking agent. However, because of the too high content of the low molecular weight acrylic copolymer having a molecular weight of at most 30,000 and lack of compatibility, it is difficult to ensure durability as bubble and edge lifting at high temperature and high humidity. In particular, the patent did not mention the method of preventing the durability problem caused by surface transference of the material having a low molecular weight after a considerable lapse of time.
[11] Japan Patent Publication No, 2002-47468 attempted to offer stress-relaxation with a
pressure-sensitive adhesive composition for a polarizing film comprising 100 parts by weight of a high molecular weight acrylic copolymer having a weight-average
molecular weight ranging from 800.000 lo 2,000,000, 5-50 parts by weigh! of a low molecular weight acrylic copolymer having a with no functional groups and weight-average molecular weight of at most 50,000 or having a degree of dispersion ranging from 1.0 lo 2.5 and having no functional groups, a crosslinking agent and a silane compound. However, it did not mention the problems of non-homogeneous adhesion strength and durability after a prolonged time due to surface transference of the ma terial having a low molecular weight and compatibility with the material having a high molecular weight.
[12) Japan Patent Publication No. 2003-49141 attempted to solve the problem of light
leakage by offering stress-relaxation with a pressure-sensitive adhesive composition for a polarizing film comprising a high molecular weight acrylic copolymer having a weight-average molecular weight ranging from 1,000,000 to 2,000,000 and having functional groups, a medium molecular weight acrylic copolytncr having a weight-average molecular weight ranging from 30,000 to 300,000 and having less than two functional groups, a low molecular weight acrylic copolymer having a weight-average molecular weight ranging from 1,000 lo 20.000 (degree of dispersion = 1.0-2.5) and having no functional groups and a crosslinking agent. While this patent employs the acrylic copolymer having a medium molecular weight and having functional groups, the acrylic copolymer having a low molecular weight and having no functional groups may cause durability problem after a prolonged time because of .surface transference. To solve this problem, the acrylic copolymer having a high molecular weight and the acrylic copolymer having a low molecular weight should be compatible with each other. However, this patent did not mention it.
[ 131 It is also possible to control (he crosslinking density by chemical bonding in order
to offer stress-relaxation to the pressure-sensitive adhesive. However, it is insufficient to solve the stress concentration problem of the polarizing film. Moreover, if the crosslinking density is too low, the durability problem may occur.
[14] Accordingly, a novel pressure-sensitive adhesive for a polarizing film capable of
solving the light leakage problem while maintaining major characteristics of the polarizing film even at high temperature and humidity conditions and after a prolonged time and a polarizing film using the same are urgently needed, Disclosure of Invention Technical Solution
[ 15] It is an object of the present invention to provide an acrylic pressure-sensitive
adhesive composition for a polarizing film capable of solving the light leakage problem while maintaining such major characteristics as adhesion durability under high temperature and high humidity conditions.
[16] It is another object of the present invention to provide a polarizing film using the
acrylic pressure-sensitive adhesive composition.
[17J It is still another object of the present invention to provide a liquid crystal display
device comprising the polarizing film prepared with the acrylic pressure-sensitive adhesive composition.
[18] The above objects of the present invention can be attained by the present invention.
[19] In order to attain the objects, the present invention provides an acrylic pressure-
sensitive adhesive composition for a polarizing film comprising a) 100 parts by weight of a high molecular weight (meth)acrylic copolymer copolymerized from a (meth)acrylic acid ester monomer and a vinylic and/or an acrylic monomer crosslinkable with a mutifunctional crosslinking agent and having a weight-average molecular weight of at least 1,000,000; b) 5-20 parts by weight of a low moleculer weight (meth)acrylic copolymer comprising the same monomer comprised in the main chain of the high moleculer weight (meth)acrylic copolymer of a), having a weight-average molecular weight ranging from 2,000 to 30,000 and comprising 0.01-1 monomer, per one molecule of the copolymer on average, having a functional group capable of reacting with the crosslinking agent of c); and c) 0.01-10 parts by weight of a mutifunctional crosslinking agent.
wherein the multifunctional crosslinking agent is at least one selected from the group consisting of an isocyanate compound, an epoxy compound, an aziridine compound and a metal chelate compound.
[20] The present invention also provides polarizing film comprising an adhesive layer of
the acrylic pressure-sensitive adhesive composition on one or both sides of the polarizing film.
[21] The present invention further provides a liquid crystal display device comprising a
liquid crystal panel, in which the pressure-sensitive adhesive polarizing film is joined on one or both sides of the liquid crystal cell,
[22] Hereunder is gi ven a detailed description of the present invention,
[23] Conventionally, in order to solving the light leakage problem, a plasticizer or,
optionally, a copolymer having a low molecular weight was added to a copolymer having a high molecular weight to offer stress-relaxation ability to a pressure-sensitive adhesive. The existence of the copolymer having a low molecular weight in the network formed by the copolymer having a high molecular weight increases fluidity and relaxes the stress concentrated by shrinkage or expansion of the polarizing film, thereby solving the light leakage problem. However, the copolymer having a low molecular weight may cause the durability problem after a prolonged lime because of surface transference.
[24] The present invention attempts to improve compatibility with the copolymer having
a high molecular weight in order to solve the durability problem caused by surface transference of the copolymer having a low molecular weight. That is, the monomer constituting the main chain of the copolymer having a low molecular weight should be
equal to thai of the copolymer having a high molecular weight. Since the copolymer
having a low molecular weight has 0.01-1 functional group, per one molecule on
average, capable of reacting with the multifunctional crosslinking agent, the durability
problem due to surface transference of the copolymer having a low molecular weight
docs not occur. Also, because the copolymer having a low molecular weight does not
form a network structure, concentration of stress can he effectively prevented. Con­
sequently, durability and the light leakage problem can be improved simultaneously.
[25] The pressure-sensitive adhesive composition of the present invention comprises a
(meth)acrylic copolymer having a high molecular weight, a (meth)acrylic copolymer having a low molecular weight and a multifunctional crosslinking agent. The (meth) acrylic copolymer having a low molecular weight comprises the same (meth}acrylic monomer having a reactive functional group as that of the (meth)acrylic copolymer having a high molecular weight. That is to say, since the (melh)acrylic copolymer having a low molecular weight has 0.01-1 functional group on average per one molecule, surface transference of Ihe copolymer having a low molecular weight can be prevented. Thus, the light leakage problem is solved by the stress-relaxation ability, while satisfying the adhesion durability.
[26] The adhesive composition of the present invention can be used in a variety of
pressure-sensitive adhesives or adhesives for optical purposes without limitation, including acryls, silicons, ruhberys, urcthanes, polyesters and epoxy compounds, Among these, the acrylic adhesive is preferable.
(27] Hereunder is given a specific description of each component of the pressure-
sensitive adhesive composition.
|28J a) The (meth)acrylic copolymer having a high molecular weight is a copolymer
comprising a (rneth}acrylic acid ester monomer as main constituent and a vinylic and/
or an acrylic monomer having a functional group crosslinkable with a multifunctional
crosslinking agent. It comprises 91.0-99.9 parts by weight of the (meth)acrylic acid
ester monomer and 0.1-9 parts by weight of the vinylic and/or the acrylic monomer
having a functional group crosslinkable with a multifunctional crosslinking agent.
[29] If the alkyl group of the (meth)acrylic acid ester monomer, which is the base
monomer of a) the (meth)acrylic copolymer, has the form of a long chain, cohesive force of the adhesive decreases at high temperature. Thus, the (meth)acrylk acid ester monomer preferably has an alkyl group having 1-12 carbon atoms, in order to maintain good cohesive force at high temperature. More preferably, it is an alkyl ester having 2-8 carbon atoms, such as butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (melh)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylatc, 2-ethyIbutyl benzyl acrylate. These monomers can be used alone or in combination,
[30] Preferably, the (meth)acrylic acid ester monomer is comprised in 91,0-99.9 parts by
weight. If the content is below 91.0 parts by weight, adhesive strength with the
polarizing film may worsen. Otherwise, if it exceeds 99.9 parts by weight, the
durability may worsen because of low cohesive force.
[31) The vinylic monomer and/or the acrylic monomer having a functional group
capable of crosslinking reacts with the crosslinking agent and offers cohesive force or adhesion strength by chemical bonding, so that the cohesive force of the adhesive does not decrease at high temperature and high humidity. The monomer having a functional group capable of crosslinking may be the one having a hydroxy group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxyethylene glycol (meth)acrylate and 2-hydroxypropylene glycol (meth)acrylate, or the one having a carboxyl group, such as acrylic acid, meihacrylic acid, acrylic acid dimer, itaconic acid, maleic acid and maleic acid anhydride, but k not limited to them. These monomers may be used alone or in combination.
[32] Preferably, the vinylic monomer and/or the acrylic monomer having a functional
group capable of crosslinking or the mixture thereof is comprised in 0.1-9 parts by weight. If the content of (he monomer having a functional group capable of crosslinking is below 0.1 parts by weight, cohesive failure tends to occur at high temperature and/or high humidify conditions and improvement of adhesive strength is only slight. Otherwise, if if exceeds 9 parts by weight, the compatibility decreases, so that surface transference becomes severe, thereby impairing fluidity and reducing stress-relaxation ability due to increased cohesive force.
[33J Preferably, a) the (meth)acrylic copolymer having a high molecular weight has a
weight-average molecular weight of ai least 1,000,000, more preferably ranging from 1,000,000 to 2,000,000. If the weight-average molecular weight is smaller than 1,000,000, durability problem as bubble or edge lifting may occur under high temperature and/or high humidity conditions because of insufficient cohesive force. Otherwise, if it exceeds 2,000,000, the ability of relaxing stress concentration is lowered.
[ 34] b) The (meth)acrylic copolymer having a low molecular weight is prepared from
the same monomer that is used to prepare the (niem)acryHc copolymer having a high
molecular weight. It should have polymer 0.01-1 functional group, per one molecule of
the polymer on average, capable of reacting with a multifunctional crosslinking agent
[35) That is to say, the (meth)acrylic copolymer having a low molecular weight should
comprise the same monomer that is used to prepare the (meth)aerylic copolytncr having a high molecular weight in order to solve the durability problem related with surface transference. And, it should have 0.01-1 functional group, per one molecule of
the copolymer on average, capable of reacting with a multifunctional crmslinking
agent, so thai concentration of stress can be effectively prevented without the
copolymer having a low molecular weight forming a network structure, Resultanily,
the problems of durability and light leakage can be improved simultaneously.
[?6| Preferably, the (meih)acrylic copolymcr having a low molecular weighl has a
weight-average molecular weighl ranging from 2,000 to 30,000. If the weight-average
molecular weighl is smaller than 2,000, the adhesion durability may worsen.
Otherwise, if il exceeds 30,000, the flexibility worsens, so that if becomes difficult lo
solve the light leakage problem.
[371 Preferably, the (meth)acryJic copolymer having a low molecular weighl is
comprised in 5-20 parts by weight per 100 parts by weighl of a) the (meth)acrylic
copolymer having a high molecular weight, If the content is below 5 parts by weight,
concentration of stress is not sufficiently relaxed. Otherwise, if it exceeds 20 parts by
weighl, the cohesive force worsens, and thus the durability problem may occur.
(38) The method of preparing a) the (meth)acrylic copolymer having a high molecular
weighl or b) (he (meth)acrylic copolymer having a low molecular weight is not par-licularly limited. They can be prepared, for example, by solution polymerization, pho-topolymerization, bulk polymerization, suspension polymerization, emulsion poly­merization, etc. Particularly, it is preferable to prepare the acrylic copolymcr of the present invention by solution polymerization at a polymerization temperature of 50 "C-140 CC. Also, it is preferable to add a polymerization initiator when the monomers are mixed uniformly.
[39] The polymerization initiator may be an azo based polymerization initiator such as
azobisisobufyronitrile and azobiscyclohexanecarbonitrile, a peroxide such as benzoyl
peroxide and acelyl peroxide or a mixture thereof.
[40] Also, a chain transfer agent like mercaptan, such as lauryl mercaptan, n-dodecyl
mercaplan and n-oclyl mercaptan, or a-methyLstyrcne dimer can be used along with the
polymerization initiator in preparing the copolymer having a low molecular weight.
[41) c) The multifunctional crosslinking agent reacts with the carboxyl group or the
hydroxy group lo increase cohesive force of the adhesive.
[42] The crosslinking agent may be an isocyanate compound, an epoxy compound, an
aziridine compound or a metal chelate compound Particularly, an isocyanate compound is preferable considering easiness of use. The isocyanate compound may he tolylenc diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, hex-amcthylene diisocyanate, isoform diisocyanate, tetramethylxylcne diisocyanate, naphthalene diisocyanate or reaction products of these with such polyol as trimethy-lolpropane. The epoxy compound may be ethylene glycol diglycidyl ether, triglycidyl ether, trimeihylolpropane triglycidyl ether, N,N,N',N'-tetraglycidylethylene diamine,
glcyerine diglycidyl ether, etc. The aziridine compound may be N,N' -toluene-2,4-bLs( 1 -aziridinecarboxide),
N,N'-dSphenylmethane-4,4^bis(l-aziridinecarboxide), trielhylene melarnine, bisiso-
prothaloyl-l-(2-mcthylaziridine), tri-1-aziridinylphosphine oxide, etc. The metal
chelate compound may be the one in which a rnultivalent metal element such as
aluminum, iron, zinc, tin, titanium, antimony, magnesium and vanadium is coordinated
with acetylaceione or ethyl acetoacciate.
[43] Preferably, the crosslink! ng agent is comprised in O.01-10 parts by weight per 100
pans by weight of the (meth)acrylic copolymer having a high molecular weight,
[44] The method of preparing the adhesive composition is not particularly limited. It can
be obtained by mixing the acrylic copolymer and the crosslinking agent by the con­
ventional method.
[45] It is required that the multifunctional crosslinking agent not participate in
crosslinking white it is mixed to form an adhesive layer in order to obtain a uniform
coating. Following the coaling process, an elastic, crosslinked adhesive layer with a
strong cohesive force is obtained by drying and aging. The strong cohesive force of the
adhesive contributes to improving adhesion and cutting properites.
(46] Preferably, the acrylic pressure-sensitive adhesive composition of the present
invention has a crosslinking density of 5-95 %, more preferably 15-80 %, considering
the optimum physical property balance. Here, the crosslinking density refers the
crosslinked portion in wt% of the acrylic adhesive undissolved by the solvent in the gel
content measuring method. If the pressure-sensitive adhesive has a crosslinking density
less than 5 %, the cohesive force of the adhesive decrease and such adhesion durability
problem as bubble or edge lifting may occur. Otherwise, if it exceeds 95 %, stress con-
centration by contraction of the polarizing film is not sufficiently relaxed.
[47] The acrylic pressure-sensitive adhesive composition of the present invention may
further comprise a silane coupling agent, which improves heat and moisture resistance by improving adhesion stability, when attached to a glass plate. Particularly, the silane coupling agent improves adhesion reliability when the adhesive is kept under high temperature and high humidity conditions for a long time.
[48] The silane coupling agent may be y-glycidoxypropyltrimethoxysilane, y-
glycidoxypropylmethyldiethoxysilane, Y-glycidoxypropyltrie*hoxysilane, 3-mercaptopropyl trimethoxysilane, vinyltrimethoxysilane, vinyltriemoxysilane, y-methacryloxypropyltrimethoxysilane, Y-tnethacryloxypropyltriethoxysilane, y-aminopropyltrimcthoxy silane, Y-aminopropy Itriethoxy silane, 3-isocyanatepropyltriethoxysilMie, y-acetoacetatepropyltrimethoxysilane or a mixture thereof. It may be comprised hi 0.005-5 parts by weigjit per 100 parts by weight of the (meth)acrylic copolymer having a high molecular weight.
[49) The acrylic pressure-sensitive adhesive composition of the present invention may
further comprise a tackiliers. The lackifier may be a (hydrated) hydrocarbon resin, a (hydrated) rosin resin, a {hydrated) rosin ester resin, a (hydrated) terpene resin, a {hydrated) terpene phenol resin, it polymerized rosin resin, a polymerized rosin ester resin or a mixture thereof.
[50] The fackifier may be comprised in 1-100 parts by weight per 100 parts by weight of
the (meih)acrylic copolymer having a high molecular weight. If the tackifier is used in excess, compatibility or cohesive force of the adhesive may decrease.
[51[ Besides, the acrylic pressure-sensitive adhesive composition of the prasent
invention may further comprise a plasticizer, an epoxy resin, a hardener, etc. depending on purposes. Also, a UV stabilizer, an aniioxidant, u colorant, a reinforcing agent, a Tiller, a defoaming agent, a surfactant, etc. may be added.
[52] The present invention also provides a polarizing film comprising the above-
described acrylic pressure-sensitive adhesive composition as adhesive layer of (he polarizing film.
[53] The polarizing film of the present invention has an adhesive layer made of the
pressure-sensitive adhesive composition on one or both sides of the polarizing film. The polarizing material or element of the polarizing film is not particularly limited.
[54] Preferably, the polarizing film may be, for example, the one prepared by adding
such polarizing component as iodine or dichromic dye to a film made of a poly vinyl alcohol resin. The thickness of the polarizing film is not particularly limited. The poly vinyl alcohol resin may be poly vinyl alcohol, polyvinyl formal, poly vinyl acctal or gummed ethylene and vinyl acetate copolymcr.
[551 On both sides of the polarizing film, protecting films consisting of a cellulose film
made of, for example, triacetyl cellulose, a polycarbonate film, a polyester film made of, for example, polyethylene terephthakte, a polyethcr sulfone film or polyethylene, polypropylene, polyolefin having a cyclo or norbornene structure or an ethylene-propylene copolymer may be formed. The thickness of these protecting films is not particularly limited.
[56] The method of forming the adhesive layer on the polarizing fiJm is not particularly
limited. The pressure-sensitive adhesive may be directly coated on the polarizing film using a bar coater, etc, and then dried. Or, after ihe adhesive is coated on a easily-peeling substrate and then dried, the adhesive layer formed on the substrate may be transferred to the polarizing film and then aged.
[571 Also, on the polarizing film of the present invention at least one functional layers of
a protecting layer, a reflection layer, a anti-glare layer, a phase retardation film, a com­
pensation film for a wide view angle, a brightness enhancement film may be formed.
[58] The polarizing film employing the pressure-sensitive adhesive of the present
invention can be used in all common liquid crystal display devices, and the kind of the
liquid crystal panel is not particularly limited. Preferably, the adhesive polarizing film
may be attached on one or both sides of a liquid crystal panel to manufacture a liquid
crystal display device.
[59] As described above, the pressure-sensitive adhesive composition of the present
invention is advantageous in solving the problem of light leakage by relaxing the stress caused by shrinkage of the polarizing film, when used for a long time under thermal and/or humidity conditions, without sacrificing adhesion durability. Best Mode for Carrying Out the Invention
[60] Hereinafter, the present invention is described in more detail through examples.
However, the following examples are only for the underetanding of the present
invention, and the present invention is not limited to or by them.
[61] {Examples!
[62] Preparation step 1: Preparation of acrylic copolymer having high molecular weight,
H-l
[63] To a 1 L reactor equipped with a cooler enabling n itrogen gas reflux and easy
temperature control was added a mixture of monomers comprising 88 parts by weight
of n-butyl aery late (BA), 10 parts by weight of ethyl acrylate (EA) and 2 parts by
weight of acrylic acid (AA), as specified in Table 1 below. Then, 120 parts by weight
of ethyl acetate {EAc) was added as solvent. Purging was performed for 60 minutes
wilh nitrogen gas to remove oxygen. Whiling keeping the temperature at 60 °C,
reaction was performed for 8 hours by adding 0.03 part by weight of azobisisobuty-
ronhrile (AIBN), which had been diluted to 45 % in ethyl acetate, a polymerization i
niliaior. After the reaction was completed, the reaction product was diluted with ethyl
acetate (EAc) to obtain a (meth)acrylic copolymer, H-l, which had a solid content of
17 wi% and a weight-average molecular weight of 1,600,000.
[64] Preparation step 2; Preparation of acrylic copolymers having high molecular
weight, H-2 and H-3
[65] Acrylic copolymers having high molecular weight, H-2 and H-3 were prepared in
the same manner of Preparation step 1, except that the content of each constituent was
changed and 150 parts by weight of ethyl acetate was added as solvent, as specified in
Table 1. The result is shown in Table 1.
[66] Preparation step 3: Preparation of acrylic copolymer having low molecular weight,
L-l
[67] To a 1 L reactor equipped with a cooler enabling nitrogen gas reflux and easy
temperature control were added a mixture of monomers comprising 95.3 parts by weight of n-butyl acrylate, 4.0 parts by weight of ethyl acrylate and 0.7 part by weight
of acrylic acid and 2 parts by weight of dodecylmercaptan (DDM) as chain transfer agem, as specified in Table 1. Then, 120 parts by weight of ethyl acetate was added as solvent. Purging was performed for 60 minutes with nitrogen gas to remove oxygen. Whiting keeping Ihe temperature at 60 "C, reaction was performed for 8 hours by adding 0.03 part by weight of azobisisobulyronitrile, which had been diluted k> 45 % in ethyj acctale, a polymerization initiator to obtain a (meih)acrylic copolymer, L-J, which had a solid content of 45 wt% and a weight-average molecular weight of 10,000,
[68f Preparation step 4: Preparation of acrylic copolymers L-2 to L-5
[69] Acrylic copolymers having low molecular weight^ L-2 to L-5 were prepared in the
same manner of Preparation step 3, except that the content of each constituent was changed, as specified in Table 1. The result is shown in Table 1.
[70] [Examplel]
[71]
[72] 100 pans by weight molecular weight, H-l and 15 parts by weight (by solid content) of the acrylic copolymer having a tow molecular weight, L-l were mixed together. 0.5 part by weight of lolylenc diisocyanate adduct of trimeihylolpropane (TDM) was added as multifunctional crosslinkmg agent. The mixture was diluted to an adequate con­centration considering transparency, mixed homogeneously, coated on a release paper and then dried to obtain a uniform adhesive layer having a thickness of 30 microns,
[73]
[74] The adhesive layer was adhered to an iodine based polarizing film having a
thickness of 185 microns. The resultant polarizing film was cut an appropriate size for testing. The test result is given in Table 2 below.
[75] (Testing Example]
[76] Durability
[77] The polarizing film (90 mm x 170 mm) prepared in Example 1 was attached on
both sides of a glass plate (110 mm x 190 mm x 0.7 mm), wilh the light absorbing axes perpendicular to each other. In the process, a pressure of about 5 kg/cm2 was applied in a clean room, so that bubble or contamination did not occur. The samples were kept under the condition of 60 °C and 90 % R.H. for 1,000 hours. It was identified if bubble and edge lifting had occurred. Heal resistance was evaluated by observing bubble and edge lifting after keeping the samples at 80 "C for 1,000 hours. Observation was performed after keeping the samples at room temperature for 24 hours, Durability was evaluated by observing the adhesive polarizing film 5 months later. Durability evaluation standard was as follows.
[78] O: No bubbles and no edge lifting were observed
[79] A: A few bubbles and a little edge lifting were observed
180] x: A large amount of bubbles and edge lifting were observed
[81] Light transmission homogeneity (light leakage)
182] Using the same samples, it was observed if light passed through the samples using
backlight in a dark room. In the test, the polarizing films (200 mm x 200 mm) was attached on both sides of a glass plate (210 mm x 210 mm x 0,7 mm), with me light absorbing axes perpendicular to each other. The standard for light transmission ho­mogeneity was as follows.
[83] O: No light leaking was observed by the naked eye.
184] A: A little non-uniform light transmission was observed.
[85] X: A severe light leaking from the edge of polarizers was observed.
[86] [Examples 2 and 3]
[87] Mixing and lamination were performed as Example 1, as specified in Table 2.
Durabilify and light transmission homogeneity were evaluated. The result is given in Table 2.
[88] [Comparative Examples 1-6]
[89] Mixing and lamination were performed as Example i, as specified in Table 2.
Durability and light transmission homogeneity were evaluated. The result is given in Table 2.
[90] Table 1
(Table Removed)
[92] As seen in Table 2, all of Examples 1-3 showed good durability and light
transmission homogeneity. On the contrary, Comparative Example 1 (the (meth)acrylic copolynter having a weight-average molecular weight of 800,000), Comparative Example 2 (including 30 parts by weight of the (meth)acrylic copolymer having a low molecular weight) and Comparative Example 6 (in which the monomer for copolymerizing the (meth)acrylic copolymer having a high molecular weight and the one for copolymerizing the (meth)acrylic copolymer having a low molecular weight arc different) showed very poor durability. Also, Comparative Example 3 (including 2 parts by weight of the (meth)acrylic copoiymer having a low molecular weight), Comparative Exampk 4 (in which the number of the reactive functional groups of the (meth)acrylic copolymer having a low molecular weight is not 0.01-1) and Comparative Example 5 (in which the weight-average molecular weight of the (meth)acrylic copolymer having a low molecular weight falls outside 2,000-30,000) showed slight or severe light transmission non-homogeneily. Industrial Applicability
193)
(94} The present invention provides an acrylic pressure-sensitive adhesive composition
for a polarizing film capable of solving the light leakage problem by relaxing the stress caused by shrinkage of the polarizing film under thermal and humidity conditions, without sacrificing such major characteristics as adhesion durability. Accordingly, if the pressure-sensitive adhesive composition of the present invention is used for the polarizing film of a liquid crystal display device, it can prevent light leakage caused by stress concentration, even after a considerable lapse of time.
[95] While the present invention has been described with reference to the preferred em-
bodiments, those skilled in the art will appreciate that various modifications and sub­stitutions can be made thereto without deponing from the spirit and scope of the present invention as sei forth in the appended claims.



We claim:
1. An acrylic pressure-sensitive adhesive composition for a polarizing film comprising
a) 100 parts by weight of a (meth)acrylic copolymer having a high molecular weight, which is copolymerized from a (meth)acrylic acid ester monomer and a vinylic and/or an acrylic monomer having a functional group capable of crosslinking with a multifunctional crosslinking agent and has a weight-average molecular weight of at least 1,000,000;
b) 5-20 parts by weight of a (meth)acrylic copolymer having a low molecular weight, which comprises the same monomer comprised in the main chain of the (meth)acrylic copolymer of a), has a weight-average molecular weight of 2,000-30,000 and comprises 0.01-1 monomer, per one molecule of the copolymer on average, having a functional group capable of reacting with the crosslinking agent of c); and
c) 0.01-10 parts by weight of a multifunctional crosslinking agent,
wherein the multifunctional crosslinking agent is at least one selected from the group consisting of an isocyanate compound, an epoxy compound, an aziridine compound and a metal chelate compound.
2. The acrylic pressure-sensitive adhesive composition for a polarizing film as claimed in claim 1, wherein a) the (meth)acrylic copolymer having a high molecular weight comprises 91.0-99.9 parts by weight of the (meth)acrylic acid ester monomer and 0.1-9 parts by weight of the vinylic and/or the acrylic monomer having a functional group capable of crosslinking with a multifunctional crosslinking agent.
3. The acrylic pressure-sensitive adhesive composition for a polarizing film as claimed in claim 1, wherein the (meth)acrylic acid ester monomer of a) is at least one alkyl ester having 2-8 carbon atoms, which is selected from the group consisting of butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-octyt (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, 2-ethylbutyl (meth)acrylate and benzyl acrylate.
4. The acrylic pressure-sensitive adhesive composition for a polarizing film as claimed in claim 1, wherein the monomer having a functional group capable of crosslinking of a) is at least one selected from the group consisting of 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxyethylene glycol (meth)acrylate, 2-hydroxypropylene glycol (meth)acrylate, acrylic acid, methacrylic acid, acrylic acid dimer, itaconic acid, maleic acid and


maleic acid anhydride.
5. The acrylic pressure-sensitive adhesive composition for a polarizing film as claimed in claim 1, wherein the acrylic copolymer is prepared by a method selected from the group consisting of solution polymerization, photopolymerization, bulk polymerization, suspension polymerization and emulsion polymerization.
6. The acrylic pressure-sensitive adhesive composition for a polarizing film as claimed in claim 1, which has a crosslinking density of 5-95 %.
7. An adhesive polarizing film comprising an adhesive layer prepared from the acrylic pressure-sensitive adhesive composition of any one as claimed in claims 1 to 6 on one or both sides of the polarizing film.
8. The adhesive polarizing film as claimed in claim 7, which further comprises at least one film selected from the group consisting of a protection film, a reflection film, a phase retardation film, a compensation film for wide view angle or a brightness enhancement film.
9. A liquid crystal display device comprising a liquid crystal panel, in which the
adhesive polarizing film as claimed in claim 7 or 8 is attached on one or both sides of a liquid
crystal cell.
10. Acrylic pressure-sensitive adhesive composition for polarizing film as claimed in
any of the above claims substantially as described in the specification and illustrated in the
accompanying drawings.



Documents:

4023-delnp-2006-abstract.pdf

4023-DELNP-2006-Assignment-(08-07-2010).pdf

4023-delnp-2006-assignment.pdf

4023-delnp-2006-Claims (27-11-2009).pdf

4023-delnp-2006-claims.pdf

4023-DELNP-2006-Correspondence-Others (27-11-2009).pdf

4023-DELNP-2006-Correspondence-Others-(08-07-2010).pdf

4023-DELNP-2006-Correspondence-Others-(27-11-2009).pdf

4023-delnp-2006-correspondence-others.pdf

4023-delnp-2006-Description (Complete) (27-11-2009).pdf

4023-DELNP-2006-Description (Complete)-(08-07-2010).pdf

4023-delnp-2006-description (complete).pdf

4023-delnp-2006-form-1.pdf

4023-DELNP-2006-Form-18.pdf

4023-delnp-2006-form-2.pdf

4023-DELNP-2006-Form-26.pdf

4023-DELNP-2006-Form-3-(27-11-2009).pdf

4023-DELNP-2006-Form-3.pdf

4023-DELNP-2006-Form-5.pdf

4023-DELNP-2006-GPA-(08-07-2010).pdf

4023-delnp-2006-pct-304.pdf

4023-DELNP-2006-Petition-137-(27-11-2009).pdf


Patent Number 241719
Indian Patent Application Number 4023/DELNP/2006
PG Journal Number 31/2010
Publication Date 30-Jul-2010
Grant Date 22-Jul-2010
Date of Filing 12-Jul-2006
Name of Patentee LG CHEM, LTD.
Applicant Address LG TWIN TOWERS, EAST TOWER 20, YEOUIDO-DONG, YEONGDEUNGPO-GU, SEOUL 150-721 (KR).
Inventors:
# Inventor's Name Inventor's Address
1 KIM, SE-RA LG CHEM. APT. 7-503, DORYONG-DONG, 381-42, YUSEONG-GU, DAEJEON 305-340 (KR).
2 CHANG, SUK-KY Lucky Hana Apt. 106-701, Sinseong-dong, Yuseong-gu, Daejeon 305-721 (KR).
3 CHO, HYUN-JU Buwon-dong 63-2, Gimhae-si, Gyeongsangnam-do 621-906 (KR).
4 LEE, JAE-GWAN 302, Jeonmin-dong 390-9, Yuseong-gu, Daejeon 305-810 (KR).
5 HAN, IN-CHEON Garak Plaza Apt. 3-901, Garak-dong 199, Songpa-gu, Seoul 138-160 (KR).
6 SEONG, HYE-RAN Dapsimni 1-dong 270-11, Dongdaemun-gu, Seoul 130-802 (KR).
PCT International Classification Number C09J 133/00
PCT International Application Number PCT/KR2005/001070
PCT International Filing date 2005-04-13
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10-2004-0028355 2004-04-23 Republic of Korea