TWI686629B - Polarizing plate and method for producing the same - Google Patents

Abstract

The present invention provides a polarizing plate including a polarizer, an adhesive layer, and a brightness enhancement film in this order and the surface of the brightness enhancement film in the adhesive layer side is treated with surface activation treatment, and method for producing the polarizing plate. The surface active treatment is preferably a corona treatment.

Description

Polarizing plate and its manufacturing method

The present invention relates to a polarizing plate including a polarizing plate and a brightness enhancement film laminated thereon and a manufacturing method thereof.

In recent years, with the increase in the size of LCD mobile terminals represented by smartphones, in order to achieve long-term driving with limited battery capacity, the use of brightening films can improve the efficiency of backlight utilization. On the other hand, from the aspect of design and portability, the demand for thinning of liquid crystal mobile terminals is increasing, and even for the polarizing plates used therefor, further thinning and lightening are required.

The brightness enhancement film is a backlight of a liquid crystal display device, and when reflected light is incident, it has a property of reflecting linear polarized light of a specified polarizing axis or circular polarized light of a specified direction and transmitting other light. For example, on the backlight side of the polarizer (absorption linear polarizer) arranged on the backlight side of the liquid crystal cell, by configuring the brightness enhancement film, when the backlight enters the brightness enhancement film, only the specified polarization state (the polarized light that can pass through the polarizer) is transmitted State) light is supplied to the polarizer, and on the other hand, it does not transmit light other than the specified polarization state and reflects it. A reflective layer, etc., which is arranged on the back side of the brightness enhancement film. The light reflected on the surface of the brightness enhancement film is reversed by the reflective layer and can enter the brightness enhancement film again. Part or all of the emitted light can be supplied to the polarizer through the brightness enhancement film through the light in the specified polarization state.

As such, if a brightness enhancement film is used, the polarized light absorbed by the polarizer is reflected without passing through the polarizer side, and by repeatedly reflecting and reversing between the brightness enhancement film and the reflective layer, the polarized light is converted into a transparent polarizer The polarized light can be supplied to the polarizer. As a result, the use efficiency of the backlight can be improved, and power consumption may be reduced. In addition, when the same power consumption (backlight light amount) is compared, the screen may become brighter than when the brightness enhancement film is not used (for example, Japanese Patent Laid-Open No. 11) -248941, JP 11-248942, JP 11-64840 and JP 11-64841).

In the specification of Japanese Patent No. 5332599, a polarizing plate with a brightness enhancement film with a thickness of 40 to 100 μm interposed by an adhesive layer (pressure-sensitive adhesive layer) on a polarizer is disclosed.

A polarizer with a brightness enhancement film attached to the polarizer through an adhesive layer is required to withstand the durability of a humid and hot environment. Traditional polarizers, such as 60°C and 90% RH, are used in the polarizer’s durability test. At the end, there is a problem of peeling at the interface of the brightness enhancement film and the adhesive layer. This problem is more pronounced as the thickness of the brightness enhancement film is smaller.

The object of the present invention is to provide a polarizing plate comprising a polarizer, an adhesive layer and a brightness enhancement film in sequence, which is not likely to cause peeling between the adhesive layer and the brightness enhancement film in a hot and humid environment, and has a high humidity and heat durability, and Its manufacturing method.

The present invention provides the following polarizing plate, its manufacturing method, and liquid crystal display device.

[1] A polarizing plate comprising a polarizer, an adhesive layer and a brightness enhancement film in sequence; wherein the surface on the adhesive layer side of the brightness enhancement film is subjected to surface activation treatment.

[2] The polarizing plate according to [1], wherein the adhesive layer is in contact with the brightness enhancement film.

[3] The polarizing plate according to [1] or [2], wherein the polarizer is in contact with the adhesive layer.

[4] The polarizing plate according to any one of [1] to [3], wherein the surface activation treatment is corona treatment.

[5] The polarizing plate according to any one of [1] to [4], wherein the thickness of the brightness enhancement film is 10 to 30 μm.

[6] The polarizing plate according to any one of [1] to [5], wherein the thickness of the polarizer is 15 μm or less.

[7] The polarizing plate according to any one of [1] to [6], wherein the storage elastic modulus of the adhesive layer in the temperature range of 23 to 80° C. is 0.15 to 1 MPa, and the thickness thereof is 3 to 20 μm.

[8] The polarizing plate according to any one of [1] to [7], further comprising a protective film laminated on the surface of the polarizer opposite to the adhesive layer.

[9] The polarizing plate according to [8], wherein the protective film is made of polyolefin resin or cellulose resin.

[10] A liquid crystal display device comprising: a liquid crystal cell And the polarizing plate as described in any one of [1] to [9].

[11] A method of manufacturing a polarizing plate, which is a method of manufacturing a polarizing plate sequentially including a polarizer, an adhesive layer, and a brightness enhancement film, including: implementing a surface on the surface of the brightness enhancement film on the side of the adhesive layer The step of activation treatment; and the step of depositing the adhesive layer on the surface after the surface activation treatment.

According to the present invention, even if the thickness of the brightness enhancement film is small, it is not easy to cause peeling between the adhesive layer and the brightness enhancement film in a humid and hot environment, and the polarizing plate with excellent humid and heat durability. The polarizing plate of the present invention can be suitably applied to image display devices typified by liquid crystal display devices, particularly liquid crystal display devices for small and medium-sized mobile terminals (tablet computers, smart phones, etc.).

1‧‧‧ Polarizer

10‧‧‧ Polarizer

20‧‧‧1st adhesive layer

30‧‧‧Brightening film

40‧‧‧Protection film

50‧‧‧ 2nd adhesive layer

60‧‧‧Partition

70、80‧‧‧Partition

90‧‧‧Surface protective film

100, 200, 300 ‧‧‧ laminate

Fig. 1 is a schematic cross-sectional view showing an example of the layer configuration of the polarizing plate of the present invention.

2 (a) and (b) are schematic cross-sectional views showing an example of a method of manufacturing a polarizing plate of the present invention.

Figs. 3 (a) and (b) are schematic cross-sectional views showing another example of the method of manufacturing the polarizing plate of the present invention.

Hereinafter, the present invention will be described in detail while showing an embodiment.

<Polarizer>

(1) Structure of polarizing plate

Fig. 1 is a schematic cross-sectional view showing an example of the layer configuration of the polarizing plate of the present invention. The polarizing plate of the present invention as the polarizing plate 1 shown in FIG. 1 includes a polarizer 10, a first adhesive layer 20, and a brightness enhancement film 30 in this order. The polarizing plate of the present invention may further include other films and layers. For example, the polarizing plate 1 shown in FIG. 1 includes: a protective film 40 deposited on the surface of the polarizer 10 opposite to the first adhesive layer 20; The second adhesive layer 50 laminated on the outer surface of the protective film 40; the partition member 60 laminated on the outer surface of the second adhesive layer 50. The second adhesive layer 50 is used to attach the polarizing plate to other members (such as liquid crystal cells and other optical films). The partition member 60 is a film temporarily attached to protect the surface of the second adhesive layer 50 before being attached to other members.

The surface of the brightness enhancement film 30 on the side of the first adhesive layer 20 is subjected to surface activation treatment. As a result, peeling between the first adhesive layer 20 and the brightness enhancement film 30 is less likely to occur in a hot and humid environment, and it can become a polarizing plate with good damp and heat durability. Corona treatment is ideal for surface activation treatment.

(2) Polarizer

The polarizer 10 is an absorption type polarizer that absorbs linear polarized light having a vibration plane parallel to its absorption axis and penetrates the linear polarized light having a vibration plane perpendicular to the absorption axis (parallel to the transmission axis), and can be suitably used The dichroic dye adsorbs and aligns the polarizing film of the polyvinyl alcohol-based resin film. The polarizer 10 can be manufactured by, for example, including the following steps: a polyvinyl alcohol-based resin film The step of performing uniaxial extension; the step of dyeing the polyvinyl alcohol-based resin film with a dichroic pigment to adsorb the dichroic pigment; the step of treating the polyvinyl alcohol-based resin film with the adsorbed dichroic pigment with an aqueous solution of boric acid; and borrowing Water washing step after treatment with boric acid aqueous solution.

As the polyvinyl alcohol-based resin, a saponified polyvinyl acetate-based resin can be used. As the polyvinyl acetate-based resin, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, a copolymer of vinyl acetate and other monomers copolymerizable therewith can be used. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, (meth)acrylamides having ammonium groups, and the like. In this specification, "(meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid.

The saponification degree of the polyvinyl alcohol-based resin is usually about 85 to 100 mol%, and more preferably 98 mol% or more. The polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formaldehyde or polyvinyl acetal modified with aldehydes may be used. The average degree of polymerization of the polyvinyl alcohol-based resin is usually about 1,000 to 10,000, and more preferably about 1,500 to 5,000. The average degree of polymerization of the polyvinyl alcohol-based resin can be determined in accordance with JIS K 6726.

Such a polyvinyl alcohol-based resin film maker can use a raw material film as the polarizer 10 (polarizing film). The method of forming a polyvinyl alcohol-based resin film is not particularly limited, and a conventional method can be used. The thickness of the polyvinyl alcohol-based raw material film is not particularly limited. In order to make the thickness of the polarizer 10 be 15 μm or less, it is preferable to use about 5 to 35 μm. More preferably, it is 20 μm or less. The polyvinyl alcohol-based raw material film with an extended thickness of more than 35 μm is used to obtain For the polarizer 10 having a thickness of 15 μm or less, the stretch magnification must be increased. Even when the thickness of the polarizer 10 is 15 μm or less, the dimensional shrinkage in a high-temperature environment becomes large. In addition, when the thickness is less than 5 μm, the operability at the time of stretching is low, and the defect of cutting is likely to occur when the polarizer is manufactured.

The uniaxial extension of the polyvinyl alcohol-based resin film can be performed before, simultaneously with, or after the dyeing of the dichroic pigment. When the uniaxial stretching is performed after dyeing, the uniaxial stretching can be performed before or during boric acid treatment. Moreover, one-axis extension can be performed in these plural stages.

When one axis is extended, one axis can be extended between rollers with different rotation speeds, or one axis can be extended using hot rollers. The uniaxial stretching may be dry stretching in the atmosphere, or wet stretching using a solvent to stretch the polyvinyl alcohol-based resin film in a swollen state. The stretch magnification is usually about 3 to 8 times.

As a method of dyeing the polyvinyl alcohol-based resin film with a dichroic dye, for example, a method of immersing the film in an aqueous solution containing a dichroic dye is used. As a dichroic dye system, iodine or a dichroic organic dye is used. Furthermore, the polyvinyl alcohol-based resin film is preferably subjected to water immersion treatment before dyeing treatment.

As a dyeing treatment by iodine, a method of immersing a polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide is generally used. The content of iodine in the aqueous solution is about 0.01 to 1 part by weight per 100 parts by weight of water. The content of potassium iodide may be about 0.5 to 20 parts by weight per 100 parts by weight of water. Moreover, the temperature of the aqueous solution may be about 20 to 40°C. On the other hand, as a dyeing treatment by a dichroic organic dye, a method of immersing a polyvinyl alcohol-based resin film in an aqueous solution containing a dichroic organic dye is generally used. Aqueous solutions containing dichroic organic dyes may contain inorganic salts such as sodium sulfate as dyeing aids. The content of the dichroic organic dye in the aqueous solution may be about 1×10 ^-4 to 10 parts by weight per 100 parts by weight of water. The temperature of the aqueous solution may be around 20 to 80°C.

As a boric acid treatment after being dyed with a dichroic dye, a method of immersing the dyed polyvinyl alcohol-based resin film in an aqueous solution containing boric acid is generally used. When iodine is used as the dichroic dye, the aqueous solution containing boric acid preferably contains potassium iodide. The amount of boric acid in the aqueous solution containing boric acid may be about 2 to 15 parts by weight per 100 parts by weight of water. The amount of potassium iodide in the aqueous solution may be about 0.1 to 15 parts by weight per 100 parts by weight of water. The temperature of the aqueous solution may be above 50°C, for example from 50 to 85°C.

The polyvinyl alcohol-based resin film after boric acid treatment is usually washed with water. The water washing treatment can be performed, for example, by immersing the boric acid-treated polyvinyl alcohol-based resin film in water. The temperature of the water for washing treatment is usually about 5 to 40°C.

After washing with water, a drying process is performed to obtain polarizer 10. Drying can be done with hot air dryer and far infrared heater. The thickness of the polarizer 10 is preferably 15 μm or less, and more preferably 10 μm or less. The thickness of the polarizer 10 is 15 μm or less, which is advantageous in the thinning of the polarizing plate and the liquid crystal display device. The thickness of the polarizer 10 is usually 4 μm or more.

(3) The first adhesive layer

The first adhesive layer 20 is a layer existing between the polarizer 10 and the brightness enhancement film 30. The first adhesive layer 20 is typically directly laminated on the polarizer 10 with the polarizer 10 in contact with the first adhesive layer 20. For example, when a protective film is attached to the polarizer 10 and the first adhesive layer 20 is deposited thereon, it is learned that peeling between the adhesive layer and the brightness enhancement film is not likely to occur even in a hot and humid environment. The first adhesive layer 20 may be composed of an adhesive composition mainly composed of resins such as (meth)acrylic, rubber, urethane, ester, polysiloxane, and polyvinyl ether resins. . Among them, a (meth)acrylic resin having excellent transparency, weather resistance, and heat resistance is suitable as the adhesive composition of the matrix polymer. The adhesive composition may be active energy ray hardening type or thermosetting type.

As the (meth)acrylic matrix polymer, for example, butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate are suitably used (Meth)acrylate-based matrix polymers of esters, and copolymerized matrix polymers using two or more of these (meth)acrylates. For matrix polymers, it is more desirable to copolymerize polar monomers. As polar monomers, for example, (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, (meth)acrylic acid N,N-di A monomer having a carboxyl group, a hydroxyl group, an amide group, an amine group, an epoxy group, etc. of methylaminoethyl ester and glycidyl (meth)acrylate.

The adhesive composition usually contains a crosslinking agent. As a cross-linking agent, for example, a metal ion having a valence of 2 or more forms a metal salt of a carboxylic acid with a carboxyl group; a polyamine compound forms an amide bond with a carboxyl group; polycyclic Oxygen compounds or polyols form ester bonds with carboxyl groups; polyisocyanate compounds form amide bonds with carboxyl groups. Among them, polyisocyanate compounds are more desirable.

The so-called active energy ray-curable adhesive composition refers to the property that it is hardened by being irradiated with active energy rays such as ultraviolet rays and electron beams. It is also adhesive before being irradiated with active energy rays, and can adhere to adherends such as films It is hardened by the irradiation of active energy rays and has an adhesive composition with properties that can adjust the adhesive force. The active energy ray-curable adhesive composition is preferably ultraviolet-curable. The active energy ray-curable adhesive composition may contain an active energy ray polymerizable compound in addition to the matrix polymer and the cross-linking agent. Furthermore, if necessary, it may contain a photopolymerization initiator, a photosensitizer, and the like.

The adhesive composition may include fine particles for imparting light scattering properties; beads; resins other than the matrix polymer; adhesive imparting agents; fillers; antioxidants; ultraviolet absorbers; pigments; and additives such as colorants.

The first adhesive layer 20 can be formed by applying an organic solvent dilution liquid of the adhesive composition to a substrate and drying it. The base material may be the polarizer 10, the brightness enhancement film 30, the partition member, and the like. When an active energy ray-curable adhesive composition is used, the formed adhesive layer can become a desired hardened material by irradiating the active energy ray.

The first adhesive layer 20 preferably has a storage elastic modulus of 0.15 to 1 MPa in a temperature range of 23 to 80°C. In this way, in a hot and humid environment, it is possible to suppress the scale that easily occurs with the shrinkage of the polarizer 10 The change in size can improve the durability of the polarizing plate. Moreover, when a liquid crystal display device equipped with a polarizing plate (for example, a liquid crystal display device for small and medium-sized mobile terminals) is placed in a hot and humid environment, the movement of the polarizing plate is suppressed, and the reliability of the liquid crystal display device can be improved.

The so-called "storage elastic modulus showing 0.15 to 1 MPa in a temperature range of 23 to 80°C" refers to any temperature in this range, and the storage elastic modulus is a value within the above range. The storage elastic modulus usually decreases with increasing temperature. Therefore, as long as the storage elastic modulus at 23°C and 80°C is within the above range, the temperature within this range can display the storage elastic modulus within the above range. The storage elastic modulus of the first adhesive layer 20 can be measured using a commercially available viscoelasticity measuring device, for example, a viscoelasticity measuring device "DYNAMIC ANALYZER RDA 11" manufactured by REOMETRIC Corporation shown in the examples described later.

As a method of adjusting the storage elastic modulus to the above range, for example, an adhesive composition containing a matrix polymer and a crosslinking agent is further added with an oligomer, specifically an amine (meth)acrylate oligomer, Becomes an active energy ray-curable adhesive composition (ideally an ultraviolet-curable adhesive composition). It is more desirable to irradiate active energy rays to harden the adhesive layer moderately.

The thickness of the first adhesive layer 20 may be 1 to 40 μm, and from the viewpoint of suppressing the dimensional change of the polarizing plate while maintaining good workability, it is more preferably 3 to 25 μm (for example, 3 to 20 μm).

(4) Brightening film

The brightness enhancement film 30, also called a reflective polarizing film, can use a polarization conversion element having a function of separating light emitted from a light source (backlight) into transmitted polarized light and reflected polarized light or scattered polarized light. As described above, by disposing the brightness enhancement film 30 on the polarizer 10 and using the recursive light of reflected polarized light or scattered polarized light, the output efficiency of linear polarized light emitted from the polarizer 10 can be improved. The brightness enhancement film 30 is usually laminated in contact with the first adhesive layer 20.

The brightness enhancement film 30 may be, for example, an anisotropic reflective polarizer. An example of the anisotropic reflective polarizer is an anisotropic multiple film that transmits linear polarized light in one vibration direction and reflects linear polarized light in another vibration direction, and a specific example thereof is DBEF (Japanese Patent Laid-Open No. 4-268505, etc.) made by 3M ). Another example of the anisotropic reflective polarizer is a composite of a cholesteric liquid crystal layer and a λ/4 plate, and a specific example thereof is PCF manufactured by Nitto Denko (Japanese Patent Laid-Open No. 11-231130, etc.). Another example of an anisotropic reflective polarizer is a reflective grid polarizer. The specific example is a metal grid reflective polarizer (U.S. Patent No. 6,288,840, etc.) which performs fine processing on metal and emits reflective polarized light in the visible light region, A film extended by adding metal fine particles to a polymer matrix (Japanese Patent Laid-Open No. 8-184701).

An optical layer such as a hard coat layer, an anti-glare layer, a light diffusion layer, and a phase difference layer having a phase difference value of 1/4 wavelength may be provided on the surface of the brightness enhancement film 30 opposite to the first adhesive layer 20. The formation of the optical layer can improve the adhesion to the backlight tape and the uniformity of the displayed image. The thickness of the brightness enhancement film 30 may be about 10 to 100 μm. From the viewpoint of thinning of the polarizing plate, it is preferably 10 to 50 μm, and more preferably 10 to 30 μm.

In the polarizing plate of the present invention, the first adhesive on the brightness enhancement film 30 The surface on the side of the adhesive layer 20 is subjected to surface activation treatment. This surface activation treatment is performed before the brightening film 30 and the first adhesive layer 20 are bonded together. As a result, peeling between the brightness enhancement film 30 and the first adhesive layer 20 is less likely to occur in a hot and humid environment, and the polarizing plate 1 with good damp and heat durability can be obtained.

The surface activation treatment may be a hydrophilization treatment of the surface, a dry treatment, or a wet treatment. As dry treatment, for example, corona treatment, plasma treatment, discharge treatment such as glow discharge; flame treatment; ozone treatment; UV ozone treatment; ionization active ray treatment such as ultraviolet treatment, electron beam treatment, etc. As the wet treatment, for example, ultrasonic treatment of a solvent such as water or acetone, alkali treatment, anchor coating treatment, etc. are used. These treatments can be performed individually or in combination of two or more.

Among them, corona treatment and/or plasma treatment are preferable for the surface activation treatment from the viewpoint of the peeling suppression effect of the brightness enhancement film 30 in a hot and humid environment and the productivity of the polarizing plate. As long as these surface activation treatments are performed, even when the thickness of the brightness enhancement film 30 is as small as 30 μm or less in a hot and humid environment, the peeling between the first adhesive layer 20 and the brightness enhancement film 30 can be effectively suppressed. Furthermore, the surface of the first adhesive layer 20 on the side of the brightness enhancement film 30 may be combined with surface activation treatment. Even if only the surface of the brightness enhancement film 30 is subjected to surface activation treatment, sufficient effects can be obtained. . Surprisingly, on the contrary, when the surface activation treatment is performed only on the surface of the first adhesive layer 20 on the brightness enhancement film 30 side, the effect is lacking.

(5) Protective film

The protective film 40 is an arbitrary adhesive layered on the polarizer 10 and the first adhesive The film on the opposite side of layer 20. However, from the viewpoint of protecting the polarizer 10, the polarizing plate preferably includes the protective film 40. The protective film 40 is a thermoplastic resin having translucency (preferably optically transparent), such as a chain polyolefin resin (polypropylene resin, etc.), a cyclic polyolefin resin (norbornene resin, etc.) Polyolefin resin; cellulose ester resin such as cellulose triacetate and cellulose diacetate; polyester resin such as polyethylene terephthalate and polybutylene terephthalate; Polycarbonate resin; (meth)acrylic resin; polystyrene resin; polyvinyl chloride resin; acrylonitrile/butadiene/styrene resin; acrylonitrile/styrene resin; polyvinyl acetate Resins; polyvinylidene chloride resins; polyamide resins; polyacetal resins; modified polyphenylene ether resins; polyphenol resins; polyether resins; polyarylate resins; polyamides Films composed of amide imide resin; polyimide resin. Among them, polyolefin resins and cellulose resins are preferably used.

As the chain polyolefin resin, in addition to homopolymers of chain olefins of polyethylene resin and polypropylene resin, for example, copolymers composed of two or more chain olefins.

Cyclic polyolefin resin is a general term for resins polymerized by polymerization units. Specific examples of cyclic polyolefin resins include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, and copolymers of cyclic olefins and chain olefins such as ethylene and propylene ( Representatives are random copolymers) and graft polymers modified with unsaturated carboxylic acids and their derivatives, and hydrides of these. Among them, norbornene-based monomers using norbornene-based monomers such as norbornene, polycyclic norbornene-based monomers as cyclic olefins Fat is ideal.

The cellulose-based resin refers to a part or all of the hydrogen atoms of the hydroxyl group of cellulose obtained from raw cellulose such as cotton seed velvet, wood pulp (broadleaf pulp, conifer pulp), etc., through acetyl, propyl and/ Or cellulose organic acid ester substituted with butyl acetyl group or cellulose mixed organic acid ester. Examples include cellulose acetate, propionate, butyrate, and mixed esters of these. Among them, triethyl acetyl cellulose, diethyl acetyl cellulose, cellulose acetate propionate and cellulose acetate butyrate are more preferable.

It is useful to control the phase difference value of the protective film 40 to a value suitable for the liquid crystal display device. For example, in the liquid crystal display device of the horizontal alignment (IPS) mode, it is preferable to use a film having a phase difference value of substantially zero. The substantial phase difference value is 0, which means that the in-plane phase difference value at a wavelength of 590 nm is 10 nm or less, the absolute value of the thickness direction phase difference at a wavelength of 590 nm is 10 nm or less, and the absolute value of the thickness direction phase difference at a wavelength of 480 to 750 nm The value is 15 nm or less.

Depending on the mode of the liquid crystal display device, the protective film 40 is stretched and/or contracted to give a suitable phase difference value.

The thickness of the protective film 40 may be about 1 to 100 μm. From the viewpoint of strength and operability, it is preferably 5 to 60 μm, and more preferably 5 to 50 μm. As long as the thickness is within this range, the polarizer 10 can be mechanically protected. Even if it is exposed to a hot and humid environment, the polarizer 10 does not shrink and can maintain stable optical characteristics.

The protective film 40 may be attached to the polarizer 10 via an adhesive layer. As the adhesive for forming the adhesive layer, an aqueous adhesive or active Performance energy curable adhesive.

As the water-based adhesive, for example, an adhesive composed of a polyvinyl alcohol-based resin aqueous solution, an aqueous two-component urethane-based emulsion adhesive, or the like. Among them, an adhesive composed of an aqueous solution of a polyvinyl alcohol-based resin is suitably used. As the polyvinyl alcohol-based resin, in addition to the vinyl alcohol homopolymer obtained by saponification of polyvinyl acetate homopolymer polyvinyl acetate, copolymers of vinyl acetate and other monomers copolymerizable therewith can be used The polyvinyl alcohol-based copolymer obtained by the saponification treatment or the modified polyvinyl alcohol-based polymer whose hydroxyl groups are partially modified. The water-based adhesive may include crosslinking agents such as aldehyde compounds, epoxy compounds, melamine-based compounds, methylol compounds, isocyanate compounds, amine compounds, and polyvalent metal salts.

When the water-based adhesive is used, after the polarizer 10 and the protective film 40 are bonded, it is preferable to perform a drying step in order to remove the water contained in the water-based adhesive. After the drying step, for example, a curing step of curing at a temperature of about 20 to 45°C may be provided.

The above-mentioned active energy ray-curable adhesive refers to an adhesive that is hardened by irradiating active energy rays such as ultraviolet rays, and includes, for example, a polymerizable compound and a photopolymerization initiator, a photoreactive resin, and a binder. Resin and photoreactive crosslinking agent etc. Examples of the polymerizable compound include photopolymerizable monomers such as photocurable epoxy-based monomers, photocurable (meth)acrylic monomers, and photocurable amine ester-based monomers, and photopolymerizable monomers. Oligomers, etc. Examples of the photopolymerization initiator include substances that generate active species of neutral radicals, anionic radicals, and cationic radicals by irradiating active energy rays such as ultraviolet rays. As included For the active energy ray-curable adhesive of the polymerizable compound and the photopolymerization initiator, for example, those including a photocurable epoxy-based monomer and a photocationic polymerization initiator are preferably used.

When the active energy ray-curable adhesive is used, after the polarizer 10 and the protective film 40 are bonded, a drying step is performed as necessary, and then, the active energy ray-curable adhesive is hardened by irradiating the active energy ray. step. The light source of the active energy ray is not particularly limited, and is preferably an ultraviolet ray with a luminous distribution below 400 nm. Specifically, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a chemical lamp, a black light lamp, a microwave-activated mercury lamp can be used , Metal halogen lamps, etc.

When the polarizer 10 and the protective film 40 are bonded, saponification treatment, corona treatment, plasma treatment, etc. may be performed on at least one of the bonding surfaces of these.

(6) Second adhesive layer and partition member

The second adhesive layer 50 laminated on the outer surface of the protective film 40 is an arbitrary layer provided for attaching the polarizing plate to other members (for example, liquid crystal cells and other optical films). Regarding the composition of the adhesive composition constituting the second adhesive layer 50, the description on the first adhesive layer 20 is cited. The storage elastic modulus of the second adhesive layer 50 may be the same as the first adhesive layer 20 or may be different.

The partition member 60 is a film temporarily attached to protect the surface of the second adhesive layer 50 before being attached to other members. For example, a film made of a transparent resin made of polyethylene terephthalate can be used. borrow Treated by release agent such as polysiloxane. On the surface of the first adhesive layer 20, in order to protect the surface before being bonded to the brightness enhancement film, the same partition member as described above may be attached.

<Manufacturing method of polarizing plate>

The method for manufacturing a polarizing plate of the present invention is a method for manufacturing a polarizing plate including a polarizer, a first adhesive layer and a brightness enhancement film in sequence, including the following steps: on the surface of the first adhesive layer side of the brightness enhancement film , The first step of performing the surface activation treatment; and the second step of depositing the first adhesive layer on the aforementioned surface where the surface activation treatment is performed.

Referring to FIG. 2, an embodiment of the method for manufacturing the polarizing plate 1 shown in FIG. 1 will be described below. First, on one side of the polarizer 10, a protective film 40 is bonded via an adhesive layer, and on top of this, while the second adhesive layer 50 is stacked, the first adhesive is bonded on the other side of the polarizer 10 For layer 20, a layered product 100 having a layer structure shown in FIG. 2(a) is obtained. As shown, the partition member 60 is temporarily attached to the outer surface of the second adhesive layer 50, and the partition member 70 is temporarily attached to the outer surface of the first adhesive layer 20.

Then, from the first adhesive layer 20 of the laminate 100, the separation member 70 is peeled off, and then on the peeling surface, in the first step above, on the bonding surface (layer surface), the layer is previously subjected to surface activation treatment to increase The bright film 30 obtains the polarizing plate 1 (FIG. 2( b ), second step). Surface activation can also be performed on the bonding surface of the first adhesive layer 20 and the brightness enhancement film 30 Management.

In the production of the layered product 100, the layering sequence including the second adhesive layer 50/protective film 40/polarizer 10/first adhesive layer 20 in sequence is not limited to the above example. For example, it may be that the protective film 40 is laminated on one side of the polarizer 10, a second adhesive layer 50 is provided thereon, and then the first adhesive layer 20 is laminated on the other side of the polarizer 10; On one side of the polarizer 10, a protective film 40 is laminated, and on the other side of the polarizer 10, a first adhesive layer 20 is laminated, and then a second adhesive layer 50 is provided on the protective film 40 in this order.

The method of attaching the brightness enhancement film 30 to the first adhesive layer 20 of the laminate 100 may be a single-piece lamination method, or a sheet-roller lamination method as described in Japanese Patent Laid-Open No. 2004-262071. In addition, it can be produced in a long shape, and when the required number is large, the roller-to-roller bonding method is also useful (the same applies to the following embodiments).

Next, referring to FIG. 3, another embodiment of the method of manufacturing the polarizing plate 1 shown in FIG. 1 will be described as follows. First, on one side of the polarizer 10, a protective film 40 is bonded via an adhesive layer, and a second adhesive layer 50 is laminated thereon to obtain a layered body 200 with a layer structure shown in FIG. 3(a) . As shown in the figure, the partition member 60 may be temporarily attached to the outer surface of the second adhesive layer 50, or the surface protective film 90 may be temporarily attached to the outer surface of the polarizer 10. At least one of the bonding surface of the protective film 40 and the second adhesive layer 50, and the bonding surface of the second adhesive layer 50 and the protective film 40, and the bonding of the polarizer 10 to the surface protective film 90 At least one of the bonding surface and the bonding surface of the surface protective film 90 and the polarizer 10 can be performed Surface activation treatment such as corona treatment and plasma treatment.

On the other hand, in the first step described above, after the surface activation treatment is performed on the surface of the brightness enhancement film 30, the first adhesive layer 20 is layered on the surface area to obtain a laminate 300. The bonding surface of the first adhesive layer 20 and the brightness enhancement film 30 may also be subjected to surface activation treatment such as corona treatment and plasma treatment. As shown in the figure, the partition member 80 may be temporarily attached to the outer surface of the first adhesive layer 20.

Then, the separation member 80 is peeled off from the first adhesive layer 20 of the laminate 300, the surface protective film 90 is peeled off from the polarizer 10 of the laminate 200, and then the first adhesive layer is bonded on the polarizer 10 20. The polarizing plate 1 is obtained (Figure 3 (b), second step).

In the production of the layered body 200 provided with the surface protection film 90, the layering order is not limited to the above-mentioned in order to obtain a layer structure including the second adhesive layer 50/protective film 40/polarizer 10/surface protective film 90 in sequence. example. For example, the protective film 40 may be laminated on one side of the polarizer 10, a second adhesive layer 50 may be provided thereon, and then the surface protective film 90 may be laminated on the other side of the polarizer 10; On one side of the sheet 10, a protective film 40 is laminated, and on the other side of the polarizer 10, a surface protective film 90 is laminated, and then a second adhesive layer 50 is provided on the protective film 40 in this order.

<Liquid crystal display device>

The polarizing plate of the present invention can be applied to a liquid crystal display device. The liquid crystal display device includes a liquid crystal cell and the polarizing plate of the present invention attached to the surface thereof. The polarizing plate is attached to the liquid crystal cell with an adhesive layer (Figure 1) The second adhesive layer 50) of the polarizing plate 1 shown is performed. The polarizing plate of the present invention can generally be used as a polarizing plate disposed on the backlight side of a liquid crystal cell. The driving method of the liquid crystal cell can be any conventionally known method, and the IPS mode is more ideal. The liquid crystal display device using the polarizing plate of the present invention has good moisture and heat durability.

Examples

Examples and comparative examples are shown below, and the present invention will be described more specifically, but the present invention is not limited to these examples. In addition, the film thickness, the phase difference value, and the storage elastic modulus of the adhesive layer are measured according to the following.

(1) Thickness

It was measured using a digital micrometer "MH-15M" made by Nikon.

(2) In-plane phase difference and thickness direction phase difference

Using the "KOBRA-ADH" manufactured by the Prince Measuring Machine (Co) of the phase difference meter based on the parallel Nicol rotation method, the measurement was performed at 23°C with light having a wavelength of 590 nm, 483 nm, or 755 nm.

(3) Storage elastic modulus

The storage elastic modulus G'of the adhesive layer is measured according to (I) to (III) below.

(I) Two 25±1 mg samples were taken from the adhesive layer and formed into approximately spherical shapes.

(II) The obtained approximately spherical sample is attached to the upper and lower surfaces of the Type I fixture. Let's use an L-shaped fixture together. The composition of the measurement sample is L-shaped jig/adhesive/I-type jig/adhesive/L-type jig.

(III) The storage elastic modulus G'of the sample prepared in this way was measured under the conditions of a temperature of 23°C, a frequency of 1 Hz, and an initial deformation of 1 N using a dynamic viscoelasticity measuring device "DVA-220" made by IT Measurement Control (Co).

(Production of polarizer A with a thickness of 7 μm)

Polyvinyl alcohol film with a thickness of 20 μm (average degree of polymerization of about 2400 and saponification degree of 99.9 mol% or more) is uniaxially stretched about 5 times by dry stretching, and further immersed in 60°C while maintaining tension After 1 minute of pure water, it was immersed in an aqueous solution having a weight ratio of iodine/potassium iodide/water of 0.05/5/100 at 28°C for 60 seconds. Then, it was immersed in an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 8.5/8.5/100 at 72°C for 300 seconds. Next, it was washed in pure water at 26°C for 20 seconds, and then dried at 65°C, to obtain a polarizing plate A having a thickness of 7 μm with iodine adsorbed on the polyvinyl alcohol film.

(Production of polarizer B with a thickness of 12 μm)

In addition to using a polyvinyl alcohol film with a thickness of 30 μm (average degree of polymerization of about 2400 and a saponification degree of 99.9 mol% or more), as in the case of polarizer A, polarized light with a thickness of 12 μm iodine adsorbed and aligned to the polyvinyl alcohol film Slice B.

(Preparation of Brightening Films C and D)

The following 2 kinds of brightening films:

‧Brightness Enhancement Film C with a thickness of 26μm; "Advanced Polarized" made by 3M Film, Version 3"

‧Brightness enhancing film D with thickness of 17μm; "Advanced Polarized Film, Version 4" made by 3M

(Preparation of protective films E and F)

The following 2 protective films:

‧Protective film E; cyclic polyolefin resin film made by Japan Zeon Co., Ltd. (thickness 23 μm, in-plane retardation value of wavelength 590 nm = 2.1 nm, thickness direction retardation value of wavelength 590 nm = 2.8 nm, wavelength 483 nm (Phase difference in thickness direction = 2.5nm, 755nm thickness phase difference value = -4.2nm)

‧Protective film F; cyclic polyolefin resin film made by Japan Zeon Co., Ltd. (thickness 13 μm, in-plane retardation value at wavelength 590 nm = 0.8 nm, thickness direction retardation value at wavelength 590 nm = 3.4 nm, wavelength 483 nm (Phase difference in thickness direction = 3.5 nm, phase difference in thickness direction at 755 nm = 2.8 nm)

(Preparation or preparation of adhesive layer)

‧The following 2 adhesive layers

‧The first adhesive layer; the copolymer of butyl acrylate and acrylic acid is added with an organic solvent solution of urethane acrylate oligomer and isocyanate-based cross-linking agent, and applied to the release-treated with a slit coater The release processing surface of the partition member made of polyethylene terephthalate with a thickness of 38 μm was dried to a thickness of 15 μm, and dried to obtain an attached The adhesive layer of the partition member (the storage elastic modulus of the adhesive layer is 0.40MPa at 23℃ and 0.18MPa at 80℃)

‧Second adhesive layer; a commercially available attachment of acrylic adhesive layer with a thickness of 25 μm is provided on the release processing surface of the partition member made of polyethylene terephthalate with a thickness of 38 μm that has undergone release treatment Adhesive layer with partitioning member (no amine acrylate oligomer. The storage elastic modulus of this adhesive layer is 0.05MPa at 23°C and 0.04MPa at 80°C)

(Preparation of water-based adhesive)

To 100 parts by weight of water, 3 parts by weight of carboxyl-modified polyvinyl alcohol ["KL-318" manufactured by Kuraray Co., Ltd.] was dissolved to prepare a polyvinyl alcohol aqueous solution. To the obtained aqueous solution, mix water-soluble polyamide epoxy resin ["SUMIREZ RESIN 650 (30)" manufactured by Taoka Chemical Industry Co., Ltd., solid content concentration 30% by weight] to 100 parts by weight of water using 1.5 parts by weight Ratio to obtain an aqueous adhesive.

<Example 1>

The polarizing plate was produced in the same order as shown in FIG. 2. First, the protective film E was bonded to one side of the polarizer A using the above-mentioned water-based adhesive. Before bonding, a corona treatment of 15.9 kJ/m ^{2 was performed} on the bonding surface of the protective film E and the polarizer A. Then, it was dried at 80°C for 5 minutes and cured at 40°C for 168 hours. Then, the first adhesive layer is bonded to the surface of the polarizer A opposite to the protective film E. Before bonding, a corona treatment of 15.9 kJ/m ^{2 was performed} on both the bonding surface of the polarizer A and the bonding surface of the first adhesive layer.

Then, the second adhesive layer is bonded to the outer surface of the protective film E. Before bonding, both the bonding surface of the protective film E and the bonding surface of the second adhesive layer were subjected to a corona treatment of 15.9 kJ/m ² . Finally, the separation member of the first adhesive layer was peeled off, and after a corona treatment of 15.9 kJ/m ^{2 was performed} on one side of the brightness enhancement film C, the brightness enhancement film C was bonded to the first adhesive with its corona treatment side The outer surface of the layer is polarized.

<Example 2>

A polarizing plate was produced in the same manner as in Example 1, except that the protective film F was used instead of the protective film E.

<Example 3>

A polarizing plate was produced in the same manner as in Example 1, except that the brightness enhancement film D was used instead of the brightness enhancement film C.

<Example 4>

A polarizing plate was produced in the same manner as in Example 1, except that polarizing plate B was used instead of polarizing plate A.

<Example 5>

A polarizing plate was produced in the same manner as in Example 3, except that polarizing plate B was used instead of polarizing plate A.

<Example 6>

The polarizing plate was produced in the same order as shown in FIG. 3. First, on one side of the polarizer A, the protective film E is bonded using the above-mentioned water-based adhesive. Before bonding, a corona treatment of 15.9 kJ/m ^{2 was performed} on the bonding surface of the protective film E and the polarizer A. Then, it was dried at 80°C for 5 minutes and cured at 40°C for 168 hours. Then, a surface protective film ("TORETEC 7332" manufactured by Toray Processing Co., Ltd.) was bonded to the surface of the polarizer A opposite to the protective film E. Before bonding, the bonding surface of the polarizer A was subjected to a corona treatment of 15.9 kJ/m ² . Furthermore, the second adhesive layer is attached to the outer surface of the protective film E. Before bonding, both the bonding surface of the protective film E and the bonding surface of the second adhesive layer were subjected to a corona treatment of 15.9 kJ/m ² .

Then, the first adhesive layer (with a partition member) was bonded to one side of the brightness enhancement film C. Before bonding, both the bonding surface of the brightness enhancement film C and the bonding surface of the first adhesive layer were subjected to a corona treatment of 15.9 kJ/m ² . Finally, after peeling the surface protective film of the polarizer A and the partition member of the first adhesive layer, the exposed surface (outer surface) of the polarizer A exposed by the peeling of the surface protective film was subjected to 15.9 kJ/m ² After corona treatment, the first adhesive layer was bonded to the corona treatment surface to obtain a polarizing plate.

<Example 7>

A polarizing plate was produced in the same manner as in Example 6, except that the protective film F was used instead of the protective film E.

<Example 8>

A polarizing plate was produced in the same manner as in Example 6, except that the brightness enhancement film D was used instead of the brightness enhancement film C.

<Example 9>

A polarizing plate was produced in the same manner as in Example 6, except that polarizing plate B was used instead of polarizing plate A.

<Example 10>

A polarizing plate was produced in the same manner as in Example 8 except that polarizing plate B was used instead of polarizing plate A.

<Example 11>

When bonding the first adhesive layer to the exposed surface of the polarizer A (the surface exposed by peeling of the surface protective film), except that the exposed surface of the polarizer A was not subjected to corona treatment, it was the same as Example 6. The polarizing plate was produced in the same way.

<Comparative Examples 1 to 11>

A polarizing plate was produced in the same manner as in Examples 1 to 11, except that the bonding surface of the brightness enhancing film C or D and the first adhesive layer was not subjected to corona treatment. In addition, in Comparative Examples 6 to 11, before the brightening film C or D was bonded to the first adhesive layer, although the corona treatment was not performed on the bonding surface of the brightening film C or D, it was adhered to the first The adhesive surface of the agent layer is corona treated.

[Evaluation of Damp Heat Durability]

From the obtained polarizing plate, a sample with a size of 111 mm×65 mm was cut, and it was bonded to an alkali-free glass (“Eagle XG” manufactured by Corning Corporation) via a second adhesive layer. This glass-laminated sample was subjected to a damp heat durability test for 500 hours in an oven at 60° C. and 90% RH, and the appearance of the sample after the test was visually evaluated according to the following criteria. The results are shown in Table 1. In addition, the column of “surface activation treatment” in Table 1 indicates whether the surface of the brightening film is subjected to surface activation treatment.

A: At the end of the polarizing plate, no peeling of the interface between the brightness enhancement film and the adhesive layer was observed, and the appearance was good

B: Only at the end of the polarizing plate, the above peeling was observed

C: The progress of the above peeling is observed not only at the end of the polarizing plate but up to the center

1‧‧‧ Polarizer

10‧‧‧ Polarizer

20‧‧‧1st adhesive layer

30‧‧‧Brightening film

40‧‧‧Protection film

50‧‧‧ 2nd adhesive layer

60‧‧‧Partition

Claims (11)

A polarizing plate comprising a protective film, a polarizer, an adhesive layer and a brightness enhancement film in sequence; wherein the surface on the adhesive layer side of the brightness enhancement film is subjected to surface activation treatment and the thickness of the brightness enhancement film It is 10 to 30 μm, and the protective film is laminated on the surface of the polarizer opposite to the adhesive layer via an adhesive layer. The polarizing plate as described in item 1 of the patent application scope, wherein the adhesive layer is in contact with the brightness enhancement film. The polarizing plate as described in item 1 of the patent application range, wherein the polarizer is in contact with the adhesive layer. The polarizing plate as described in item 1 of the patent application, wherein the surface activation treatment is corona treatment. The polarizing plate as described in item 1 of the patent application range, wherein the thickness of the polarizer is 15 μm or less. The polarizing plate as described in item 1 of the patent application range, wherein the storage elastic modulus of the adhesive layer in the temperature range of 23 to 80° C. is 0.15 to 1 MPa, and its thickness is 3 to 20 μm. The polarizing plate as described in item 1 of the patent application range, wherein the adhesive agent forming the adhesive agent layer is an aqueous adhesive agent or an active energy ray-curable adhesive agent. The polarizing plate as described in item 1 of the patent application range, wherein the protective film is made of polyolefin resin or cellulose resin. A liquid crystal display device includes: a liquid crystal cell and a polarizing plate as described in any one of items 1 to 8 of the patent application. A method of manufacturing a polarizing plate, the polarizing plate sequentially including a protective film, a polarizer, an adhesive layer, and a brightness enhancement film, the method of manufacturing the polarizing plate includes: implementing on the surface of the brightness enhancement film on the side of the adhesive layer The step of surface activation treatment; the step of depositing the adhesive layer on the surface after the surface activation treatment; and the adhesive layer on the surface of the polarizer opposite to the adhesive layer The step of stacking the protective film, wherein the thickness of the brightness enhancement film is 10 to 30 μm. The manufacturing method as described in item 10 of the patent application range, wherein the adhesive forming the adhesive layer is an aqueous adhesive or an active energy ray-curable adhesive.

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