KR20160083003A - Method for producing laminated optical film - Google Patents

Abstract

A bonding step of bonding the first film and the second film via an adhesive layer formed so that the thickness after curing is not more than 2.5 占 퐉 and a curing step of curing the adhesive layer after bonding the first film and the second film, Wherein at least one of the first film and the second film is an optical film and the viscosity of the adhesive layer when the first film and the second film are bonded in the bonding step is 60 cP or less.

Description

METHOD FOR PRODUCING LAMINATED OPTICAL FILM [0002]

The present invention relates to a method for producing a laminated optical film, and more particularly, to a method for producing a laminated optical film including a step of bonding a film through an adhesive layer.

A variety of laminated optical films are used for optical devices such as image display devices (liquid crystal display devices, organic EL display devices, etc.), and one typical example thereof is a polarizing plate used for a liquid crystal display device or the like. In the present specification, the laminated optical film is a laminate composed of a plurality of films, and at least one of films constituting the laminate is an optical film. The optical film refers to a film used for optical use, such as being used as a member of an optical device.

The polarizing plate is usually produced by bonding a protective film to one side or both sides of a polarizing film using an adhesive. For example, Japanese Patent Application Laid-Open No. 2010-230806 (Patent Document 1) discloses a method for producing a polarizing plate in which a polarizing film and a protective film are bonded to each other through an adhesive layer made of an ultraviolet curable adhesive, and then the ultraviolet rays are irradiated to cure the adhesive layer .

Patent Document 1: JP-A-2010-230806

In recent years, an optical device is required to be further thinned, and accordingly, a laminated optical film such as a polarizing plate incorporated therein is required to be further thinned. For this reason, when an adhesive is used for film bonding for producing a laminated optical film, it is desired that the thickness of the adhesive layer made of the adhesive is as small as possible.

However, it has been clarified by the inventors of the present invention that small bubbles are formed in the entire adhesive layer when the thickness of the adhesive layer is made smaller. Since this bubble, even if it is very small, scatters light transmitted through the laminated optical film, the optical function of the laminated optical film may be affected unexpectedly.

It is therefore an object of the present invention to provide a method for producing a laminated optical film which enables film bonding without causing air bubbles in the adhesive layer even when the thickness of the adhesive layer interposed between the films is made smaller.

The present invention provides a method for producing the following laminated optical film.

[1] A process for producing a cured product, comprising: a bonding step of bonding a first film and a second film to each other through an adhesive layer formed so that a thickness after curing is not more than 2.5 m; Process,

Wherein at least one of the first film and the second film is an optical film,

Wherein the viscosity of the adhesive layer when the first film and the second film are bonded in the bonding step is not more than 60 cP.

[2] The method for producing a laminated optical film according to [1], further comprising a heating step of heating the adhesive layer to adjust its viscosity to 60 cP or less before the bonding step.

[3] The method for producing a laminated optical film according to [2], wherein in the heating step, the adhesive layer is heated by irradiation of infrared rays.

[4] The method for producing a laminated optical film according to [2] or [3], wherein the adhesive layer is heated to 40 ° C or higher in the heating step.

[5] The method for producing a laminated optical film according to any one of [1] to [4], wherein the adhesive constituting the adhesive layer is a curable adhesive for a solventless formulation.

[6] The method for producing a laminated optical film according to [1], wherein the adhesive layer has a viscosity at the time of bonding the first film and the second film to 60 cP or less by containing a solvent.

[7] The method for producing a laminated optical film according to any one of [1] to [6], wherein the adhesive constituting the adhesive layer is an active energy ray curable adhesive.

[8] A method for producing a laminated optical film while continuously conveying a long film of the first film and a long film of the second film so that the longitudinal direction thereof is in the carrying direction,

An application step of continuously applying an adhesive to the bonding surface of the first film or the second film to form an adhesive layer;

Wherein the first film and the second film are passed between a pair of bonding rolls so that their transport directions become parallel,

(1) to (7).

[9] The method for producing a laminated optical film according to [8], wherein the angle formed by the first film and the second film passed between the pair of bonding rolls is 60 ° or less.

[10] The method for producing a laminated optical film according to [8] or [9], wherein the conveying speed of the first film and the second film passed between the pair of bonding rolls is 10 m / min or more.

[11] The method for producing a laminated optical film according to any one of [8] to [10], wherein the widths of the first film and the second film are 0.4 to 2 m.

[12] The method for producing a laminated optical film according to any one of [1] to [11], wherein the first film is a polarizing film and the second film is a protective film.

According to the method of the present invention, a laminated optical film can be produced without generating air bubbles in the adhesive layer even when the thickness of the adhesive layer interposed between the films is as small as 2.5 占 퐉 or less.

Fig. 1 is a side view schematically showing an example of a manufacturing method of a laminated optical film and a manufacturing apparatus used therefor according to the present invention.
2 is a side view schematically showing another example of a manufacturing method of a laminated optical film and a manufacturing apparatus used therefor according to the present invention.

The present invention relates to a method for producing a laminated optical film by bonding a first film and a second film using a curable adhesive. At least one of the first and second films is an optical film, and typically both films are optical films. The laminated optical film obtained by the method of the present invention is an optical member used as one member of an optical device such as an image display device (liquid crystal display device or the like), and one typical example thereof is a polarizing plate.

The polarizing plate has at least a polarizing film as a first film which is an optical film and a protective film as a second film which is laminated and bonded to one side of the polarizing film through an adhesive layer. The polarizing plate may further include a protective film as a third film laminated and bonded to the other side of the polarizing film through an adhesive layer.

Hereinafter, a method for producing a laminated optical film according to the present invention will be described in detail with reference to embodiments. On the other hand, in the following, an embodiment in which the first film is a polarizing film and the second film is a protective film and the laminated optical film to be produced is a polarizing plate will be described, but a problem to be solved by the present invention is, The same can be applied to other laminated optical films which are subjected to film bonding, so that the present invention can be suitably applied to the production of other laminated optical films.

In one embodiment, the method for producing a laminated optical film according to the present invention comprises the steps of:

A coating step of applying an adhesive to the bonding surface of the first film or the second film to form an adhesive layer,

A bonding step of bonding the first film and the second film through an adhesive layer, and

Curing process for curing the adhesive layer

In this order. Hereinafter, each step will be described in detail with reference to FIG. Fig. 1 is a side view schematically showing an example of a manufacturing method of a laminated optical film and a manufacturing apparatus used therefor according to the present invention. 1 shows an example of producing a polarizing plate by bonding a protective film 20 (second film) to one surface of a polarizing film 10 (first film). Generally, as shown in Fig. 1, a laminated optical film such as a polarizing plate is continuously produced as a long product by carrying out processing in each process while continuously feeding a long film and transporting it . However, the production method of the present invention is not limited to continuous production using such a long film, but may be a method using a single sheet film.

<Coating Step>

1, in this step, rolls (wound products) of elongated polarizing film 10 and rolls of elongate protective film 20 are first prepared, and they are continuously unwound While the film is transported. Each film is transported so that its longitudinal direction is the transport direction. A guide roll 60 for supporting a running film is provided on the conveying path of the film appropriately. The arrows in Fig. 1 indicate the transport direction of the film or the rotation direction of various rolls.

The transport path of the protective film 20 is disposed on the bonding surface side (upper side in Fig. 1) of the polarizing film to which the protective film 20 is to be bonded. Normally, the carrying direction (film length direction) of the polarizing film 10 and the carrying direction (film length direction) of the protective film 20 are parallel. 1, an example in which the protective film 20 is bonded to one side of the polarizing film 10 is shown, but a protective film (third film) 21 is also provided on the other side of the polarizing film 10 In this case, a transport path of the protective film 21 (third film) is further formed on the lower side of the polarizing film 10 as shown in Fig. On the other hand, when a film other than the second film is further bonded to the first film using a curable adhesive, such as the third film, the other film is preferably bonded according to the method of the present invention, It is also possible to use a bonding method.

In this step, a curable adhesive is applied to the bonding surface of the polarizing film 10 or the bonding surface of the protective film 20 by using the adhesive coating device 30 to form an adhesive layer (not shown). In the example of Fig. 1, a curable adhesive is applied to the protective film 20 side. The means for applying the curable adhesive to the bonding surface is not particularly limited, and various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be used. When the protective film 21 (third film) is also bonded to the other side of the polarizing film 10, a curable adhesive for bonding the protective film 20 (second film) and a protective film 21 3 film) may be homogeneous or heterogeneous, but they are preferably the same in terms of production efficiency.

The curable adhesive is applied so that the thickness when used as a polarizing plate, that is, the thickness after curing is 2.5 m or less. The reason why the thickness of the adhesive layer in the present invention is set to 2.5 占 퐉 or less is that a problem such as generation of air bubbles occurs only when such a very thin adhesive layer is formed. Therefore, the method of the present invention is a particularly effective means for reducing the thickness of the adhesive layer to as small as 2.5 占 퐉 or less. According to the present invention, even when the thickness of the adhesive layer is 2.0 占 퐉 or less, Can be effectively prevented or suppressed. On the other hand, the thickness of the adhesive layer can be measured according to the method described in the embodiment of the later-described examples. The thickness of the adhesive layer after curing is usually 0.5 占 퐉 or more.

The environmental temperature at which the application process is carried out and the temperature of the curable adhesive at the time of application are not particularly limited. These temperatures may be, for example, about 10 to 35 DEG C (about 25 DEG C or the like).

Next, the polarizing film 10, the protective film 20 and the curable adhesive will be described.

(1) polarizing film

The polarizing film 10 as the first film may be one in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin and suitably used in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film .

As the polyvinyl alcohol-based resin constituting the polarizing film 10, a saponified polyvinyl acetate-based resin can be used. As the polyvinyl acetate resin, a copolymer of vinyl acetate and other monomers copolymerizable therewith may be mentioned in addition to polyvinyl acetate as a homopolymer of vinyl acetate. Examples of other monomers copolymerizable with vinyl acetate include acrylamides having unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids and ammonium groups.

The degree of saponification of the polyvinyl alcohol-based resin is generally about 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol-based resin may be modified. For example, polyvinyl formal and polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the polyvinyl alcohol-based resin is usually from about 1,000 to 10,000, preferably from about 1,500 to 5,000.

Such a polyvinyl alcohol-based resin is used as the original film of the polarizing film 10. The method of forming the polyvinyl alcohol-based resin is not particularly limited, and a known method is employed. The thickness of the polyvinyl alcohol-based original film is, for example, about 10 to 150 占 퐉.

The polarizing film usually has a step of uniaxially stretching the original film made of the polyvinyl alcohol-based resin, a step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye and adsorbing the dichroic dye, A step of treating the vinyl alcohol resin film with an aqueous solution of boric acid, and a step of washing with water after treatment with an aqueous solution of boric acid.

The uniaxial stretching of the polyvinyl alcohol based resin film can be performed before, simultaneously with, or after dyeing the dichroic dye. When uniaxial stretching is performed after dyeing, the uniaxial stretching may be performed before the boric acid treatment or during the boric acid treatment. In addition, uniaxial stretching may be performed in a plurality of such steps.

During uniaxial stretching, stretching may be uniaxially stretched between rolls having different peripheral velocities, or uniaxial stretching may be performed using hot roll. The uniaxial stretching may be dry stretching in which drawing is performed in the atmosphere, or wet stretching in which a polyvinyl alcohol based resin film is stretched by using a solvent. The stretching magnification is usually about 3 to 8 times.

As a method of dyeing a polyvinyl alcohol-based resin film with a dichroic dye, for example, a method of immersing a polyvinyl alcohol-based resin film in an aqueous solution containing a dichroic dye is employed. Specific examples of the dichroic dye include iodine and dichroic dyes. On the other hand, it is preferable that the polyvinyl alcohol-based resin film is subjected to immersion treatment in water before the dyeing treatment.

When iodine is used as the dichroic dye, a method in which a polyvinyl alcohol resin film is dipped in an aqueous solution containing iodine and potassium iodide is generally employed. The content of iodine in this aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water. The content of potassium iodide is usually about 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the aqueous solution used for dyeing is usually about 20 to 40 占 폚. The immersion time (dyeing time) in this aqueous solution is usually about 20 to 1800 seconds.

On the other hand, when a dichroic dye is used as the dichroic dye, a method of dying and dyeing the polyvinyl alcohol resin film into an aqueous solution containing a water-soluble dichroic dye is generally employed. The content of the dichroic dye in the aqueous solution is generally about 1 × 10 ^-4 to 10 parts by weight per 100 parts by weight of water and preferably about 1 × 10 ^-3 to 1 part by weight. The aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the dichroic dye aqueous solution used for dyeing is usually about 20 to 80 ° C. The immersion time (dyeing time) in this aqueous solution is usually about 10 to 1800 seconds.

The boric acid treatment after dyeing with a dichroic dye is usually carried out by immersing the dyed polyvinyl alcohol resin film in an aqueous solution containing boric acid.

The amount of boric acid in the boric acid-containing aqueous solution is usually about 2 to 15 parts by weight and preferably 5 to 12 parts by weight per 100 parts by weight of water. When iodine is used as the dichroic dye, it is preferable that the aqueous solution containing boric acid contains potassium iodide. The amount of potassium iodide in the boric acid-containing aqueous solution is generally about 0.1 to 15 parts by weight, preferably about 5 to 12 parts by weight, per 100 parts by weight of water. The immersion time in the boric acid-containing aqueous solution is usually about 60 to 1200 seconds, preferably about 150 to 600 seconds, more preferably about 200 to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually 50 占 폚 or higher, preferably 50 to 85 占 폚, and more preferably 60 to 80 占 폚.

The polyvinyl alcohol-based resin film after treatment with boric acid is usually subjected to water washing treatment. The water washing treatment can be carried out, for example, by immersing the boric acid-treated polyvinyl alcohol resin film in water. The water temperature in the water washing treatment is usually about 5 to 40 占 폚. The immersion time is usually about 1 to 120 seconds.

After washing with water, drying treatment is carried out to obtain the polarizing film 10. The thickness of the polarizing film 10 is usually about 1 to 80 占 퐉, and preferably about 5 to 40 占 퐉. The drying treatment can be performed using a hot-air dryer or a far-infrared heater. The temperature of the drying treatment is usually about 30 to 100 占 폚, preferably 50 to 80 占 폚. The drying treatment time is usually about 60 to 600 seconds, preferably 120 to 600 seconds.

By the drying treatment, the water content of the polarizing film 10 is reduced to practical use. The water content thereof is usually 5 to 20% by weight, preferably 8 to 15% by weight. If the moisture content is less than 5 wt%, the flexibility of the polarizing film 10 is lost, and the polarizing film 10 may be damaged or broken after drying. If the moisture content exceeds 20% by weight, the thermal stability of the polarizing film 10 may be poor.

The film width of the long polarizing film 10 is not particularly limited and may be usually about 0.2 to 2 m. However, it has been clarified by the inventors of the present invention that as the film width becomes larger, the adhesive layer tends to contain bubbles. Therefore, the method of the present invention is particularly effective when the film width is large, for example, when the width of the first film is 0.4 to 2 m.

(2) Protective film

The protective film 20 as the second film is stacked on the polarizing film 10 to at least partly protect the polarizing film 10. The protective film 20 is not particularly limited as long as it has translucency (preferably transparency), and may be a film made of a thermoplastic resin film or a glass material. Examples of the film made of a glass material include glass films described in Japanese Patent Application Laid-Open Nos. 12-247785, 12/090693, 08-283041, and the like.

Specific examples of the thermoplastic resin constituting the protective film 20 include a chain polyolefin resin (polypropylene resin film, polyethylene resin film, etc.), a cyclic polyolefin resin (norbornene resin) The same polyolefin-based resin; Polyester-based resins such as polyethylene terephthalate; (Meth) acrylic resins such as methyl methacrylate resins; Cellulosic resins such as cellulose triacetate and cellulose diacetate; Polycarbonate resin; Polyvinyl alcohol-based resin; Polyvinyl acetate resin; Polyarylate resins; Polystyrene type resin; Polyether sulfone type resin; Polysulfone resins; Polyamide based resin; Polyimide resin; And mixtures or copolymers thereof. The protective film 20 may have a multilayer structure of a resin layer made of a thermoplastic resin.

The cyclic polyolefin-based resin is a resin having a unit of a cyclic olefin-based monomer such as norbornene or a polycyclic norbornene-based monomer, and examples thereof include hydrogenated products of the ring-opening polymer of the cyclic olefin, (Styrene,? -Methylstyrene, nuclear alkyl-substituted styrene, etc.) and the like having a cyclic olefin and a chain olefin (ethylene, propylene, etc.) and / or a vinyl group.

The (meth) acrylic resin constituting the (meth) acrylic resin film may be a resin mainly composed of a methacrylic resin (containing not less than 50% by weight), preferably a methacrylic resin. By using the (meth) acrylic resin film as a protective film, it is possible to further improve the humidity resistance and mechanical strength of the polarizing plate and the liquid crystal panel obtained by bonding it to the liquid crystal cell. (Meth) acrylate refers to methacrylate and / or acrylate, and (meth) acrylate refers to methacrylate and / or acrylate, and (meth) acrylic acid means methacrylic acid and / or acrylic acid .

The methacrylic resin is a polymer mainly containing methacrylic acid ester (containing 50% by weight or more). The methacrylic resin may be a homopolymer of one kind of methacrylic acid ester or may be a copolymer of methacrylic acid ester and other methacrylic acid ester or acrylic ester or the like. Examples of the methacrylic acid esters include alkyl methacrylates such as methyl methacrylate, ethyl methacrylate and butyl methacrylate, and the number of carbon atoms of the alkyl group is usually about 1-4. As the acrylic acid ester copolymerizable with the methacrylic acid ester, alkyl acrylate is preferable, and examples thereof include methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. The number of carbon atoms of the alkyl group is usually 1 ~ 8. In addition to these, an aromatic vinyl compound such as styrene which is a compound having at least one polymerizable carbon-carbon double bond in the molecule, or a vinyl cyan compound such as acrylonitrile may be contained in the copolymer.

The (meth) acrylic resin film preferably contains acrylic rubber particles in terms of impact resistance and film formability of the film. The amount of the acrylic rubber particles that can be contained in the (meth) acrylic resin is preferably 5% by weight or more, more preferably 10% by weight or more, based on 100% by weight of the (meth) acrylic resin. The upper limit of the amount of the acrylic rubber particles is not critical, but if the amount of the acrylic rubber particles is too large, the surface hardness of the film is lowered, and when the film is subjected to the surface treatment, the solvent resistance to the organic solvent . Accordingly, the amount of the acrylic rubber particles that can be contained in the (meth) acrylic resin is preferably 80% by weight or less, and more preferably 60% by weight or less.

The acrylic rubber particles are particles composed mainly of an acrylate ester (containing not less than 50% by weight) of an elastomer as an essential component, and may be of a single-layer structure consisting essentially of only this elastomer, May be used. Specific examples of the elastomer include a copolymer of 50 to 99.9% by weight of alkyl acrylate, 0 to 49.9% by weight of at least one other vinyl monomer copolymerizable therewith, and 0.1 to 10% by weight of copolymerizable crosslinkable monomer A crosslinked elastic copolymer obtained by polymerization of a monomer is preferably used.

Examples of the alkyl acrylate include methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. The alkyl group usually has about 1 to 8 carbon atoms. Examples of other vinyl monomers copolymerizable with the alkyl acrylate include compounds having one polymerizable carbon-carbon double bond in the molecule, and more specifically, methacrylic acid esters such as methyl methacrylate, styrene , Vinyl cyan compounds such as acrylonitrile, and the like. Examples of the crosslinkable monomer as the copolymerizable compound include crosslinkable compounds having at least two polymerizable carbon-carbon double bonds in the molecule, and specific examples thereof include ethylene glycol di (meth) acrylate and butanediol di (Meth) acrylate such as poly (meth) acrylate, alkenyl esters of (meth) acrylic acid such as allyl (meth) acrylate and methallyl methacrylate, and divinylbenzene.

The protective film 20 may contain various additives, if necessary. Specific examples of the additives include fluorescent whitening agents, dispersants, surfactants, heat stabilizers, light stabilizers, ultraviolet absorbers, infrared absorbers, antistatic agents, antioxidants, lubricants, organic dyes, pigments and inorganic pigments.

The thickness of the protective film 20 is usually about 2 to 300 占 퐉, preferably 10 占 퐉 or more, more preferably 200 占 퐉 or less, more preferably 150 占 퐉 or less, further preferably 100 占 퐉 or less. The film width of the elongate protective film 20 is not particularly limited, but is generally the same as that of the polarizing film 10 to be bonded. Even when the widths of both the polarizing film 10 and the protective film 20 are as large as 0.4 to 2 m, the method of the present invention can effectively prevent or suppress the generation of bubbles.

The protective film 20 may be obtained by subjecting the thermoplastic resin film to stretching treatment. An arbitrary retardation value can be given by stretching. A protective film having a predetermined retardation property is also referred to as an optical compensation film or a retardation film. Examples of the stretching treatment include uniaxial stretching and biaxial stretching. Examples of the stretching direction include a machine direction MD of the unstretched film, a direction perpendicular to the MD, and a direction oblique to the machine direction MD. The biaxial stretching may be simultaneous biaxial stretching in which two stretching directions are simultaneously performed, or may be sequential biaxial stretching after stretching in a predetermined direction and then stretching in other directions.

The protective film 20 may have a surface treatment layer such as a hard coat layer, an antiglare layer, an antistatic layer, an antireflection layer, and an antifouling layer on the surface opposite to the bonding surface with the polarizing film 10.

Further, in order to improve the adhesion with the polarizing film 10, it is preferable that the bonding surface of the protective film 20 is subjected to surface activation treatment before application of the curable adhesive. Specific examples of the surface activation treatment include plasma treatment, corona treatment, ultraviolet ray irradiation treatment, flame (flame) treatment, saponification treatment (immersion in an aqueous alkaline solution such as sodium hydroxide or potassium hydroxide). The bonding surface of the polarizing film 10 may be subjected to a surface activation treatment instead of the bonding surface of the protective film 20 or together with the bonding surface of the protective film 20. [

As for the protective film 21 as the third film to be bonded to the other surface of the polarizing film 10 shown in the example of Fig. 2, the above description about the protective film 20 is cited. The second film (protective film 20) and the third film (protective film 21) may be the same kind of film or different kinds of films.

(3) Curable adhesive

The curable adhesive used in the present invention is an adhesive that can be cured by irradiation of active energy rays such as ultraviolet rays, visible rays, electron rays, X-rays, or by heat. Of these, as the curable adhesive, an active energy ray-curable adhesive can be preferably used because it has excellent adhesiveness, transparency, mechanical strength, thermal stability, and the like, and an active energy It is possible to more suitably use the ray-curable adhesive. The epoxy compound referred to herein means a compound having an average of at least one, preferably two or more epoxy groups in the molecule. The epoxy compound may be used alone, or two or more epoxy compounds may be used in combination.

From the viewpoints of weatherability, refractive index, cationic polymerizability and the like, it is preferable that the epoxy compound contained in the curable adhesive such as an active energy ray-curable adhesive is an epoxy compound which does not contain an aromatic ring in the molecule. As such an epoxy compound, a hydrogenated epoxy compound (glycidyl ether of a polyol having an alicyclic ring), an aliphatic epoxy compound, and an alicyclic epoxy compound can be exemplified.

The hydrogenated epoxy compound is obtained by reacting epichlorohydrin with an alicyclic polyol obtained by hydrogenating an aromatic ring of an aromatic polyol. Examples of the aromatic polyol include bisphenol-type compounds such as bisphenol A, bisphenol F, and bisphenol S; Novolak type resins such as phenol novolak resins, cresol novolak resins, and hydroxybenzaldehyde phenol novolac resins; And polyfunctional compounds such as tetrahydroxydiphenylmethane, tetrahydroxybenzophenone, and polyvinylphenol. Of the hydrogenated epoxy compounds, diglycidyl ethers of hydrogenated bisphenol A can be mentioned.

Examples of the aliphatic epoxy compound include polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof. More specifically, diglycidyl ether of 1,4-butanediol; Diglycidyl ether of 1,6-hexanediol; Triglycidyl ether of glycerin; Triglycidyl ether of trimethylolpropane; Diglycidyl ether of polyethylene glycol; Diglycidyl ether of propylene glycol; And polyglycidyl ethers of polyether polyols obtained by adding one or more alkylene oxides (ethylene oxide or propylene oxide) to aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol or glycerin.

The alicyclic epoxy compound is an epoxy compound having at least one epoxy group bonded to an alicyclic ring in the molecule. The "epoxy group bonded to the alicyclic ring" means a bridging oxygen atom -O- in the structure represented by the following formula. In the formula, m is an integer of 2 to 5.

The compound in which one or more hydrogen atoms of the (CH ₂ ) _m in the above formula are removed from other groups in the chemical structure may be an alicyclic epoxy compound. (CH ₂ ) _m may be appropriately substituted with a straight chain alkyl group such as a methyl group or an ethyl group. Among the alicyclic epoxy compounds, an epoxy compound having an oxabicyclohexane ring (m = 3 in the above formula) or an oxabicycloheptane ring (m = 4 in the above formula) (10) and the protective film (20). Hereinafter, the alicyclic epoxy compound preferably used is specifically exemplified, but the present invention is not limited to these compounds.

(a) epoxycyclohexylmethyl epoxycyclohexanecarboxylates represented by the following formula (I):

In the formula (I), R ¹ and R ² independently represent a hydrogen atom or a straight chain alkyl group having 1 to 5 carbon atoms.

(b) epoxycyclohexanecarboxylates of an alkanediol represented by the following formula (II):

In the formula (II), R ³ and R ⁴ independently represent a hydrogen atom or a straight chain alkyl group of 1 to 5 carbon atoms, and n represents an integer of 2 to 20.

(c) epoxycyclohexylmethyl esters of dicarboxylic acids represented by the following formula (III):

In the formula (III), R ⁵ and R ⁶ independently represent a hydrogen atom or a straight chain alkyl group having 1 to 5 carbon atoms, and p represents an integer of 2 to 20.

(d) epoxycyclohexyl methyl ethers of polyethylene glycol represented by the following formula (IV):

In the formula (IV), R ⁷ and R ⁸ independently represent a hydrogen atom or a straight chain alkyl group of 1 to 5 carbon atoms, and q represents an integer of 2 to 10.

(e) epoxycyclohexyl methyl ethers of alkane diols represented by the following formula (V):

In the formula (V), R ⁹ and R ¹⁰ independently represent a hydrogen atom or a straight chain alkyl group of 1 to 5 carbon atoms, and r represents an integer of 2 to 20.

(f) a diepoxy trispyro compound represented by the following formula (VI):

In the formula (VI), R ¹¹ and R ¹² independently represent a hydrogen atom or a straight chain alkyl group having 1 to 5 carbon atoms.

(g) a diepoxy monospiro compound represented by the following formula (VII):

In the formula (VII), R ¹³ and R ¹⁴ independently represent a hydrogen atom or a straight chain alkyl group having 1 to 5 carbon atoms.

(h) vinylcyclohexene epoxides represented by the following formula (VIII):

In the formula (VIII), R ¹⁵ represents a hydrogen atom or a straight chain alkyl group of 1 to 5 carbon atoms.

(i) epoxycyclopentyl ethers represented by the following formula (IX):

In formula (IX), R ¹⁶ and R ¹⁷ independently represent a hydrogen atom or a straight chain alkyl group of 1 to 5 carbon atoms.

(j) diepoxytricyclodecane represented by the following formula (X):

In the formula (X), R ¹⁸ represents a hydrogen atom or a straight chain alkyl group of 1 to 5 carbon atoms.

Among the above-exemplified alicyclic epoxy compounds, the following alicyclic epoxy compounds are commercially available, or the like, and are more preferably used because they are relatively easy to obtain.

(A) an esterified product of 7-oxabicyclo [4.1.0] heptane-3-carboxylic acid with (7-oxa-bicyclo [4.1.0] hept- , R &^lt; ¹ &gt; = R &lt; ² &gt; = H]

(B) An ester with 4-methyl-7-oxabicyclo [4.1.0] heptane-3-carboxylic acid and (4-methyl-7-oxa-bicyclo [4.1.0] hept- Cargo [compound wherein R ¹ = 4-CH ₃ and R ² = 4-CH ₃ in the formula (I)],

(C) an esterified product of 7-oxabicyclo [4.1.0] heptane-3-carboxylic acid and 1,2-ethanediol [wherein R ³ = R ⁴ = H, n = 2 compound],

(D) (7-oxabicyclo [4.1.0] hept-3-yl) methanol and adipic acid [compound of formula (III) wherein R ⁵ = R ⁶ = H, p = 4] ,

(E) (4-methyl-7-oxabicyclo [4.1.0] hept-3-yl) methanol and adipic acid [wherein R ⁵ = 4-CH ₃ , R ⁶ = 4-CH ₃ , p = 4]

(F) (7-oxabicyclo [4.1.0] hept-3-yl) methanol and 1,2-ethanediol [wherein R ⁹ = R ¹⁰ = H, r = 2].

The epoxy equivalent of the epoxy compound is usually in the range of 30 to 3000 g / equivalent, preferably 50 to 1500 g / equivalent. When the epoxy equivalent is less than 30 g / equivalent, the flexibility of the adhesive layer after curing may be lowered or the adhesive strength may be lowered. On the other hand, if it exceeds 3000 g / equivalent, compatibility with other components contained in the adhesive may be lowered.

The curable adhesive containing the epoxy compound as a curable component preferably contains a cationic polymerization initiator. When the active energy ray curable adhesive is used, it preferably contains a cationic polymerization initiator. The cationic polymerization initiator is to initiate a polymerization reaction of an epoxy group by generating a cationic species or a Lewis acid by irradiation or heat of an active energy ray such as visible light, ultraviolet ray, X-ray or electron ray, A cationic species or a Lewis acid is generated by irradiation of an energy ray to initiate the polymerization reaction of the epoxy group.

The method of curing the adhesive by irradiation of an active energy ray using a cationic ion polymerization initiator enables curing at room temperature and reduces the need to consider deformation due to heat resistance or expansion of the polarizing film 10, It is advantageous in that it can be adhered well. In addition, since the photocationic polymerization initiator acts catalytically by light, it is excellent in storage stability and workability even when mixed with an epoxy compound.

Examples of the photocationic polymerization initiator include aromatic diazonium salts; Onium salts such as aromatic iodonium salts and aromatic sulfonium salts; Iron-arene complexes and the like.

Examples of the aromatic diazonium salt include benzene diazonium hexafluoroantimonate, benzene diazonium hexafluorophosphate, and benzene diazonium hexafluoroborate.

Examples of the aromatic iodonium salt include diphenyl iodonium tetrakis (pentafluorophenyl) borate, diphenyl iodonium hexafluorophosphate, diphenyl iodonium hexafluoroantimonate, di (4-nonyl Phenyl) iodonium hexafluorophosphate, and the like.

Examples of the aromatic sulfonium salt include triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium tetrakis (pentafluorophenyl) borate, 4,4'-bis (diphenyl Diphenylsulfide bis (hexafluorophosphate), 4,4'-bis [di (? - hydroxyethoxy) phenylsulfonio] diphenylsulfide bis (hexafluoroantimonate) Di (p-toluyl) sulfonyl] -2 (4-hydroxyphenyl) (Isopropylthioxanthone) tetrakis (pentafluorophenyl) borate, 4-phenylcarbonyl (meth) acrylate, Diphenylsulfide hexafluorophosphate, 4- (p-tert-butylphenylcarbonyl) -4'-diphenylsulfone-diphenylsulfide hexafluorophosphate, 4- (P-tert-butylphenylcarbonyl) -4'-di (p-toluyl) sulfonio-diphenylsulfide tetrakis (pentafluorophenyl) borate, and the like. .

Examples of the iron-arene complexes include xylene-cyclopentadienyl iron (II) hexafluoroantimonate, cumene-cyclopentadienyl iron (II) hexafluorophosphate, xylene-cyclopentadienyl iron (II) Tris (trifluoromethylsulfonyl) methanide, and the like.

The cationic ion polymerization initiator may be used alone or in combination of two or more. Among them, an aromatic sulfonium salt is advantageously used because it has an ultraviolet ray absorbing property even in a wavelength range of 300 nm or more, and is therefore excellent in curability and can provide a cured product having good mechanical strength and adhesive strength.

The blending amount of the photocationic polymerization initiator is usually 0.5 to 20 parts by weight, preferably 1 part by weight or more, and more preferably 15 parts by weight or less, based on 100 parts by weight of the epoxy compound. If the compounding amount of the photocationic polymerization initiator is less than 0.5 parts by weight based on 100 parts by weight of the epoxy compound, the curing becomes insufficient and the mechanical strength or the bonding strength tends to be lowered. When the blending amount of the photocationic polymerization initiator is more than 20 parts by weight based on 100 parts by weight of the epoxy compound, the ionic substance in the cured product is increased to increase the hygroscopicity of the cured product, and the durability of the polarizing plate may be lowered.

When a photocationic polymerization initiator is used, the active energy ray-curable adhesive may further contain a photosensitizer, if necessary. By using the photosensitizer, the reactivity of the cationic polymerization is improved, and the mechanical strength and adhesive strength of the cured product can be improved. Examples of the photosensitizer include a carbonyl compound, an organic sulfur compound, a persulfate, a redox compound, an azo and diazo compound, a halogen compound, a photoreducible dye, and the like.

More specific examples of the photosensitizer include benzoin derivatives such as benzoin methyl ether, benzoin isopropyl ether, and?,? -Dimethoxy-? -Phenylacetophenone; Benzophenone derivatives such as benzophenone, 2,4-dichlorobenzophenone, methyl o-benzoylbenzoate, 4,4'-bis (dimethylamino) benzophenone and 4,4'-bis (diethylamino) benzophenone; Thioxanthone derivatives such as 2-chlorothioxanthone and 2-isopropylthioxanthone; Anthraquinone derivatives such as 2-chloro anthraquinone and 2-methyl anthraquinone; Acridone derivatives such as N-methyl acridone, N-butyl acridone; Other examples include?,? - diethoxyacetophenone, benzyl, fluorenone, xanthone, uranyl compound, halogen compound and the like. The photosensitizer may be used alone, or two or more of them may be used in combination. The photosensitizer is preferably contained in the range of 0.1 to 20 parts by weight in 100 parts by weight of the curable adhesive.

The curable adhesive may further contain a compound that promotes cation polymerization such as oxetanes and polyols.

Oxetanes are compounds having a 4-membered ring ether in the molecule. Specific examples of oxetanes include 3-ethyl-3-hydroxymethyloxetane, 1,4-bis [(3-ethyl-3-oxetanyl) methoxymethyl] (3-ethyl-3-oxetanyl) methyl] ether, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane and phenol novolak oxetane. The oxetanes are contained in the curable adhesive in an amount of usually 5 to 95% by weight, preferably 30 to 70% by weight.

As the polyol, it is preferable that an acid group other than the phenolic hydroxyl group is not present. For example, a polyol compound having no functional group other than the hydroxyl group, a polyester polyol compound, a polycaprolactone polyol compound, a polyol compound having a phenolic hydroxyl group, Carbonate polyol and the like. The molecular weight of the polyol is usually 48 or more, preferably 62 or more, more preferably 100 or more, and further preferably 1000 or less. The polyols are contained in the curable adhesive in an amount of usually 50% by weight or less, preferably 30% by weight or less.

The curable adhesive may contain a cationic polymerizable curable component such as the epoxy compound described above and a (meth) acrylic compound that is subjected to radical polymerization. (Meth) acrylic compound is used in combination, the effect of increasing the hardness and the mechanical strength of the adhesive layer can be expected, and furthermore, the viscosity and the curing speed of the curable resin composition can be adjusted more easily.

The (meth) acrylic compound is obtained by reacting two or more kinds of (meth) acrylate monomers having at least one (meth) acryloyloxy group in the molecule or a functional group-containing compound, and at least two (meth) (Meth) acryloyloxy group-containing compounds such as (meth) acrylate oligomers having a silyloxy group and a silyloxy group. The (meth) acrylic compound may be used singly or in combination of two or more. When two or more (meth) acrylate monomers are used in combination, two or more (meth) acrylate monomers may be used, and two or more (meth) acrylate oligomers may be used. One or more of the oligomers may be used in combination.

(Meth) acrylate monomers include mono (meth) acrylate monomers having one (meth) acryloyloxy group in the molecule, bifunctional (meth) acrylate monomers having two (meth) acryloyloxy groups in the molecule (Meth) acrylate monomers having three or more (meth) acryloyloxy groups in the molecule.

Specific examples of monofunctional (meth) acrylate monomers include tetrahydrofurfuryl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2- or 3-hydroxypropyl (meth) (Meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (Meth) acrylate, dicyclopentenyl (meth) acrylate, benzyl (meth) acrylate, isobornyl (meth) acrylate, phenoxyethyl (meth) acrylate, dicyclopentenyloxy (Meth) acrylate, pentaerythritol mono (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, trimethylolpropane mono (meth) acrylate, ) Acrylic .

As the mono-functional (meth) acrylate monomer, a carboxyl group-containing (meth) acrylate monomer may be used. Specific examples of the carboxyl group-containing monofunctional (meth) acrylate monomers include 2- (meth) acryloyloxyethylphthalic acid, 2- (meth) acryloyloxyethylhexahydrophthalic acid, carboxyethyl (meth) (Meth) acryloyloxyethyl succinic acid, N- (meth) acryloyloxy-N ', N'-dicarboxymethyl-p-phenylenediamine, 4- (meth) acryloyloxyethyltrimellitic acid &Lt; / RTI &gt;

Specific examples of the bifunctional (meth) acrylate monomer include alkylene glycol di (meth) acrylates, polyoxyalkylene glycol di (meth) acrylates, halogen-substituted alkylene glycol di (meth) Di (meth) acrylates of aliphatic polyols, di (meth) acrylates of hydrogenated dicyclopentadiene or tricyclodecanedialanol, di (meth) acrylates of dioxane glycol or dioxanedialanol, bis (Meth) acrylates of alkylene oxide adducts of bisphenol F or bisphenol A, or di (meth) acrylates of alkylene oxide adducts of bisphenol F, and epoxy di (meth) acrylates of bisphenol A or bisphenol F.

More specific examples of the bifunctional (meth) acrylate monomers include ethylene glycol di (meth) acrylate, 1,3-butanediol di (meth) acrylate, 1,4-butanediol di (meth) (Meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylol propane di (meth) acrylate, pentaerythritol di (meth) acrylate, (Meth) acrylate, diethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, dipropylene glycol di ) Acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, silicone di (meth) acrylate, (Meth) acryloyloxyethoxyethoxyphenyl] propane, 2,2-bis [4- (meth) acryloyloxy Acrylate, tricyclodecane dimethanol di (meth) acrylate, 1,3-dioxane-2,5-diyl di (meth) acrylate, hydrogenated dicyclopentadienyl di (meth) Acrylate (also known as dioxane glycol di (meth) acrylate), acetal compound of hydroxypivalaldehyde and trimethylolpropane (chemical name: 2- (2-hydroxy-1,1-dimethylethyl) Di (meth) acrylate and tris (hydroxyethyl) isocyanurate di (meth) acrylate of bis (hydroxymethyl) -1,3-

Examples of the trifunctional or higher polyfunctional (meth) acrylate monomer include glycerin tri (meth) acrylate, trimethylol propane tri (meth) acrylate, ditrimethylol propane tri (meth) acrylate, ditrimethylol propane tetra (Meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, (Meth) acrylates of trifunctional or higher aliphatic polyols and tri (meth) acrylates of trifunctional or higher halogen substituted polyols, tri (meth) acrylates of alkylene oxide adducts of glycerin, trimethyl Tri (meth) acrylates of alkylene oxide adducts of olpropane, 1,1,1-tris [(meth) ) Acryloyloxyethoxyethoxy] propane, and tris (hydroxyethyl) isocyanurate tri (meth) acrylates.

On the other hand, (meth) acrylate oligomers include urethane (meth) acrylate oligomers, polyester (meth) acrylate oligomers and epoxy (meth) acrylate oligomers.

Urethane (meth) acrylate oligomer is a compound having a urethane bond (-NHCOO-) and at least two (meth) acryloyloxy groups in the molecule. Specifically, the urethane reaction product of a hydroxyl group-containing (meth) acrylate monomer having at least one (meth) acryloyloxy group and at least one hydroxyl group in the molecule and a polyisocyanate, or a reaction product of a polyol with a polyisocyanate (Meth) acrylate monomer having at least one (meth) acryloyloxy group and at least one hydroxyl group in the molecule, and the like.

Examples of the hydroxyl group-containing (meth) acrylate monomer used in the urethanization reaction include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) (Meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol penta (meth) acrylate, pentaerythritol tri (meth) acrylate, Acrylate, and the like.

Examples of the polyisocyanate to be provided in the urethane formation reaction with the hydroxyl group-containing (meth) acrylate monomer include hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, Diisocyanates (for example, hydrogenated tolylene diisocyanate, hydrogenated xylylene diisocyanate and the like) obtained by hydrogenating an aromatic isocyanate in these diisocyanates, tri- or tri-isocyanates such as triphenylmethane triisocyanate and dibenzylbenzene triisocyanate, -Isocyanate and a polyisocyanate obtained by mass-increasing the above-mentioned diisocyanate.

In addition to the aromatic, aliphatic or alicyclic polyols, polyester polyols, polyether polyols and the like can be used as the polyols used for forming the terminal isocyanate group-containing urethane compound by the reaction with the polyisocyanate. Examples of the aliphatic and alicyclic polyols include 1,4-butanediol, 1,6-hexanediol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, neopentyl glycol, trimethylolethane, trimethylolpropane, ditrimethylol Propylene, pentaerythritol, dipentaerythritol, dimethylolheptane, dimethylolpropionic acid, dimethylolbutanoic acid, glycerin, hydrogenated bisphenol A, and the like.

The polyester polyol is obtained by a dehydration condensation reaction between the polyol and the polybasic carboxylic acid or an anhydride thereof. Examples of the polybasic carboxylic acid or its anhydride include succinic acid, adipic acid, maleic acid, anhydride, itaconic acid, (anhydrous) trimellitic acid, (anhydrous) pyromellitic acid, (anhydrous) Isophthalic acid, terephthalic acid, hexahydrophthalic anhydride, and the like.

The polyether polyol may be a polyoxyalkylene-modified polyol obtained by the reaction of the aforementioned polyols or dihydroxybenzenes with an alkylene oxide in addition to the polyalkylene glycol.

The polyester (meth) acrylate oligomer is a compound having an ester bond in the molecule and at least two (meth) acryloyloxy groups. Specifically, it can be obtained by a dehydration condensation reaction of (meth) acrylic acid, a polybasic carboxylic acid or an anhydride thereof, and a polyol. Examples of the polybasic carboxylic acid or its anhydride used in the dehydration condensation reaction include succinic acid, adipic acid, maleic acid, (anhydride) itaconic acid, (anhydrous) trimellitic acid, (anhydrous) pyromellitic acid , Hexahydrophthalic anhydride (phthalic anhydride), phthalic acid (anhydride), isophthalic acid, terephthalic acid and the like. Examples of the polyol used in the dehydration condensation reaction include 1,4-butanediol, 1,6-hexanediol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, neopentyl glycol, trimethylolethane, Ditrimethylolpropane, pentaerythritol, dipentaerythritol, dimethylolheptane, dimethylolpropionic acid, dimethylolbutanoic acid, glycerin, hydrogenated bisphenol A, and the like.

The epoxy (meth) acrylate oligomer can be obtained by an addition reaction of polyglycidyl ether and (meth) acrylic acid, and has at least two (meth) acryloyloxy groups in the molecule. Examples of the polyglycidyl ether used in the addition reaction include ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, bisphenol A diglycidyl ether, and the like.

When the (meth) acrylic compound is compounded in the curable adhesive, the amount thereof is preferably 20% by weight or less, more preferably 10% by weight or less based on the total amount of the curable component. If the blending amount of the (meth) acrylic compound is increased, the adhesion between the polarizing film 10 and the protective film 20 tends to be lowered.

When the curable adhesive contains a radical polymerizable curable component such as a (meth) acrylic compound, it is preferable to blend a radical polymerization initiator. In the case of an active energy ray curable adhesive, it is preferable to incorporate a photo radical polymerization initiator Do.

Specific examples of the photoradical polymerization initiator include acetophenone, 3-methylacetophenone, benzyldimethylketal, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan- An acetophenone-based initiator such as 1- [4- (methylthio) phenyl-2-morpholinopropane-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1- Benzophenone based initiators such as benzophenone, 4-chlorobenzophenone, and 4,4'-diaminobenzophenone; Benzoin ether initiators such as benzoin propyl ether, benzoin ethyl ether; Thioxanthone initiators such as 4-isopropylthioxanthone; In addition, xanthone, fluorenone, camphorquinone, benzaldehyde, and anthraquinone are included.

The blending amount of the photo-radical polymerization initiator is usually 0.5 to 20 parts by weight, preferably 1 to 6 parts by weight, based on 100 parts by weight of the (meth) acrylic compound. If the amount of the photo radical polymerization initiator is less than 0.5 part by weight, the effect of using the (meth) acrylic compound tends to be hardly observed. If the amount of the photo-radical polymerization initiator exceeds 20 parts by weight, the durability of the resulting polarizer may be lowered.

The curable adhesive may contain additives such as an ion trapping agent, an antioxidant, a chain transfer agent, a tackifier, a thermoplastic resin, a filler, a flow regulator, a plasticizer, a defoamer, an antistatic agent and a leveling agent. Examples of the ion trap agent include inorganic compounds such as powdery bismuth, antimony, magnesium, aluminum, calcium, titanium and mixtures thereof. Examples of the antioxidant include hindered phenol antioxidants .

As described above, the curable adhesive containing an epoxy compound as at least a part of the curable component can be used as a curable adhesive for a solventless formulation substantially not containing a solvent, but may be diluted with a solvent as described later. Specific examples of the solvent include aliphatic hydrocarbons such as n-hexane and cyclohexane; Aromatic hydrocarbons such as toluene and xylene; Alcohols such as methanol, ethanol, propanol, isopropanol and n-butanol; Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; Esters such as methyl acetate, ethyl acetate and butyl acetate; Cellosolve such as methyl cellosolve, ethyl cellosolve, butyl cellosolve; And halogenated hydrocarbons such as methylene chloride and chloroform.

<Bonding Step>

In this step, the polarizing film 10 and the protective film 20 are bonded to each other through the adhesive layer formed in the coating step. As shown in Fig. 1, the bonding of the film is performed by paired polarizing films 10 and protective films 20 which are continuously conveyed and a pair of bonding rolls 40 (in the direction of conveyance) , 40, thereby pressing the laminated film by the bonding rolls 40, 40 from above and below. The pressure applied to the film by the bonding rolls 40, 40 is, for example, about 0.5 to 4 MPa.

At this time, in the present invention, the viscosity of the adhesive layer (that is, the curable adhesive constituting it) when the polarizing film 10 and the protective film 20 are bonded (when they are passed between the bonding rolls 40 and 40) 60 cP or less. By setting the viscosity of the adhesive layer at the time of film bonding to 60 cP or less, it is possible to obtain a polarizing plate free from air bubbles or greatly suppressing bubbles in the adhesive layer without deteriorating adhesiveness between the films. The viscosity value mentioned here is a value measured according to the method described in the embodiment of the later-described embodiment. In order to more effectively prevent the formation of bubbles, the viscosity of the adhesive layer is preferably 50 cP or less, more preferably 40 cP or less.

On the other hand, if the viscosity of the adhesive layer is too low, the applied curable adhesive tends to come out from the film at the time of bonding. Therefore, the viscosity of the adhesive layer at the time of film bonding is preferably 10 cP or more, more preferably 20 cP or more.

As a method for adjusting the viscosity of the adhesive layer to 60 cP or less,

1) a method of adding a solvent to a curable adhesive having a viscosity of more than 60 cP and diluting it, and applying this to the bonding surface of the polarizing film 10 or the protective film 20,

2) a method of providing a heating step of heating the adhesive layer before film bonding (before passing between the bonding rolls 40 and 40)

And the like. Among them, the method 2) is preferable in that the viscosity can be lowered without using a solvent separately.

In the method 1), after the curable adhesive such as the above-mentioned active energy ray-curable adhesive is mixed with a solvent and the diluted curable adhesive is applied in the coating step, the viscosity of the adhesive layer at the time of film bonding The bonding process should be performed with care not to exceed 60 cP. As the solvent, for example, those described above can be used. The amount of the solvent to be used is not particularly limited as long as the viscosity of the adhesive layer at the time of film bonding is 60 cP or less.

The means for heating the adhesive layer in the method 2) is not particularly limited and may be heated, for example, by irradiation with infrared rays, or by using a hot air heater or an oven. By these means, it is easy to continuously heat the entire adhesive layer of the continuously transported film. Among them, heating by infrared irradiation is advantageous in that it is possible to heat in a shorter time and that the adhesive layer can be continuously heated to a desired degree even if the film conveying speed is increased. The infrared rays may be irradiated from the side of the adhesive layer or from the back side of the film on which the adhesive layer is formed (side not having the adhesive layer), but preferably the side from the side of the adhesive layer. In the example shown in Fig. 1, the infrared ray irradiating device 70 is used to heat the adhesive layer by irradiating infrared rays from the adhesive layer side formed on the protective film 20. In the method (2), an adhesive having a low viscosity by heating is used, and for example, the above-mentioned active energy ray curable adhesive which can be used as an adhesive for a solventless formulation can be suitably used.

The infrared ray irradiating device 70 is capable of irradiating infrared rays capable of absorbing the curable adhesive. The above-mentioned active energy ray-curable adhesive containing an epoxy compound or an epoxy compound and a (meth) acrylic compound as a curable component absorbs infrared rays having a wavelength of about 6 to 12 占 퐉. Therefore, as the infrared ray irradiating device 70, an infrared ray having a wavelength of 6-12 占 퐉 can be irradiated. For example, a "far infrared ray plate heater" manufactured by Hakko Denki KK can be used.

The heating temperature of the adhesive layer is not particularly limited as long as it has a viscosity of not more than 60 cP and can function as an adhesive even at the heating temperature and varies depending on the composition of the curable adhesive used. More typically at least 50 &lt; 0 &gt; C. The heating temperature is preferably 70 DEG C or lower, more preferably 65 DEG C or lower. If the heating temperature is too high, thermal degradation may occur in the adhesive layer or the film.

1, the polarizing film 10 and the protective film 20, which are passed between the pair of bonding rolls 40 and 40, form an angle &amp;thetas; ( Is not particularly limited but may be set to, for example, not more than 60 DEG. However, the smaller the angle &amp;thetas; is, the more the air bubbles are generated in the adhesive layer easy to do. According to the present invention, even if the angle? Is 40 or less, a polarizer having no bubbles in the adhesive layer or significantly suppressing bubbles can be obtained. On the other hand, the angle? Is usually 20 degrees or more.

The passing speed (conveying speed) of the polarizing film 10 and the protective film 20 when passing between the pair of bonding rolls 40 and 40 is not particularly limited and may be, for example, 10 m / min or more , And the larger the passage speed, the more the bubble is liable to be generated in the adhesive layer. According to the present invention, even if the passing speed is 20 m / min or more, a polarizer having no bubbles in the adhesive layer or significantly suppressing bubbles can be obtained. On the other hand, the passing speed is usually 40 m / min or less.

<Curing Process>

This step is a step of curing the adhesive layer of the laminated body of the polarizing film 10 and the protective film 20 bonded together through the adhesive layer. When the adhesive layer is made of an active energy ray-curable adhesive, as shown in Fig. 1, an active energy ray irradiating device 80 is used to irradiate an active energy ray such as visible light, ultraviolet ray, X-ray, The layer can be cured. When the laminate is composed of the polarizing film 10 and the protective film 20 and does not include the third film (protective film laminated on the other side of the polarizing film 10) Or may be irradiated from the side of the polarizing film 10, as shown in Fig. 1, preferably, from the side of the protective film 20. [

The active energy ray may be visible light, ultraviolet ray, X-ray, electron beam or the like, but ultraviolet rays are preferably used from the viewpoints of ease of handling, ease of preparation of the active energy ray-curable adhesive, stability thereof and curing performance thereof. The light source of the active energy ray is not particularly limited, but a light source having a wavelength of 400 nm or less such as 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 excited mercury lamp, Can be preferably used.

The light irradiation intensity on the adhesive layer made of the ultraviolet ray-curable adhesive is determined depending on the composition of the adhesive and is not particularly limited, but it is preferable that the irradiation intensity in the wavelength range effective for activation of the polymerization initiator is 0.1 to 100 mW / cm2. The reaction time does not become excessively long and is not more than 100 mW / cm 2, so that the yellowing of the adhesive or the deterioration of the polarizing film due to the heat radiated from the light source and the heat generated upon curing of the adhesive There is less concern. The light irradiation time to the adhesive layer is also controlled depending on the composition of the adhesive, and is not particularly limited, but it is preferable that the accumulated light amount as a product of the light irradiation intensity and the irradiation time is set to 10 to 5000 mJ / m 2 . By setting the total amount of light to be 10 mJ / m &lt; 2 &gt; or more, a sufficient amount of active species originating from the polymerization initiator can be sufficiently generated to progress the curing reaction more surely. Productivity can be maintained.

A plurality of active energy ray irradiating devices 80 may be provided, and irradiation of active energy rays may be divided into a plurality of circuits.

When the adhesive layer is cured by irradiating an active energy ray, it is advantageous in that it is possible to suppress wrinkles and curls that may be produced in the obtained polarizing plate by irradiating the active energy ray in a state in which the laminate is in close contact with the convex curved surface . As the convex curved surface, the outer peripheral surface of a roll such as a guide roll or a cooling roll can be suitably used. Especially when the active energy ray is irradiated in the state of being wound around the outer peripheral surface of the cooling roll 50 appropriately cooled as in the examples of Figs. 1 and 2, the effect of suppressing wrinkles and curls is great. The temperature of the cooling roll is, for example, 10 to 30 占 폚, preferably 15 to 25 占 폚.

The polarizing plate thus obtained is usually wound in turn by a winding device (not shown) to form a film roll.

Example

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the following examples, the thickness of the adhesive layer after curing and the viscosity of the adhesive layer at the time of film bonding were measured by the following methods.

(Thickness of the adhesive layer after curing)

The thickness of the adhesive layer after curing was measured at arbitrary five points using a spectroscopic interference film thickness meter (manufactured by Keyence), and the average value of these values was defined as the thickness of the adhesive layer.

(Viscosity of the adhesive layer at the time of film bonding)

The ultraviolet-curable adhesive is collected in a sample cup, and the temperature is adjusted to the same temperature as that at the time of film bonding. Then, the viscosity of the ultraviolet-curable adhesive is measured using "E-type viscometer" manufactured by Toki Sangyo Co., Was determined as the viscosity of the adhesive layer at the time of film bonding.

<Production Example>

(A) Production of polarizing film

A weight ratio of iodine / potassium iodide / water of 0.02 / 2 (weight ratio) was prepared by immersing the film in pure water at 30 DEG C while continuously feeding a roll-shaped polyvinyl alcohol film (thickness 75 mu m, average degree of polymerization of about 2400 and saponification degree of 99.9 mol% / 100. &Lt; / RTI &gt; Then, it was immersed in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 12/5/100 at 56.5 ° C. Subsequently, the film was washed with pure water at 8 캜, dried at 65 캜, and wound up to obtain a film roll of a polarizing film (about 30 탆 in thickness, 1300 ㎜ in width) in which iodine was adsorbed and oriented in polyvinyl alcohol. The stretching was performed mainly in a step of iodine dyeing and boric acid treatment, and the total draw ratio was 5.3 times.

(B) Production of a protective film made of a (meth) acrylic resin

(Meth) acryl-based resin, a copolymer of methyl methacrylate / methyl acrylate (weight ratio 96/4) was prepared. Further, as the acrylic rubber particles, the innermost layer is a hard polymer obtained by copolymerizing methyl methacrylate with a small amount of allyl methacrylate, and the intermediate layer contains butyl acrylate as a main component and styrene and a small amount of allyl methacrylate And an outermost layer of a three-layer structure composed of a hard polymer obtained by copolymerizing methyl methacrylate with a small amount of ethyl acrylate, wherein the elastic particles have an average particle diameter of about 250 nm when they have no outermost layer, Polymer particles were prepared.

The pellets in which the acrylic resin and acrylic rubber particles were blended at a weight ratio of 70/30 were introduced into a 65 mmφ uniaxial extruder and extruded from a T-die having a set temperature of 275 ° C. Both sides of the extruded film-like molten resin were sandwiched between two polishing rolls having a specular surface temperature set to 45 DEG C and cooled to obtain a long (meth) acrylic resin film (protective film) having a thickness of 80 mu m and a width of 1300 mm As a film roll.

&Lt; Example 1 >

Using the same polarizing plate producing apparatus as in Fig. 1, a polarizing plate was produced in the following order. The polarizing film 10 and the protective film 20 were continuously drawn from the film rolls of the polarizing film and the protective film obtained above and transported in the longitudinal direction of the polarizing film 10 and the protective film 20 (conveying speed: 30 m / minute). An ultraviolet curable adhesive A having an epoxy compound as a curable component was applied to the joint surface of the protective film 20 by using an adhesive applicator 30 (gravure coater).

Subsequently, a "far infrared ray plate heater" (infrared wavelength: 7 탆) manufactured by Hakko Denki KK was used as the infrared ray irradiating device 70 in front of the bonding rolls 40, Infrared rays are irradiated from the side of the adhesive layer to the adhesive layer side and the adhesive layer is heated to 60 DEG C and then the polarizing film 10 and the protective film 20 are stacked so as to be parallel to each other in the longitudinal direction And passed between the bonding rolls 40 and 40 to press the film, thereby performing film bonding. The angle &amp;thetas; in Fig. The passing speed of the polarizing film 10 and the protective film 20 when passing between the bonding rolls 40 and 40 was 30 m / min. The viscosity of the adhesive layer at the time of film bonding is 30 cP.

Subsequently, the laminate obtained by the film bonding was conveyed and wound around the outer circumferential surface of the cooling roll 50 set at 20 DEG C, and a D bulb manufactured by Fusion UV Systems Co., Ltd. as the active energy ray irradiating device 80 was used , And ultraviolet light was irradiated at an accumulated light quantity of 1500 mJ / cm &lt; 2 &gt; to cure the adhesive layer. Finally, the obtained polarizing plate was wound up to obtain a film roll of the polarizing plate. The thickness of the adhesive layer after curing was 1.5 占 퐉.

A quadrangular sample was cut out from the obtained polarizing plate, and the surface was observed using a reflection microscope (100-fold) from the surface thereof to confirm the presence or absence of bubbles in the cured adhesive layer. The results are shown in Table 1.

&Lt; Example 2 >

A polarizing plate was produced in the same manner as in Example 1 except that the ultraviolet curable adhesive B using an epoxy compound as a curable component was used in place of the ultraviolet curable adhesive A and the thickness of the adhesive layer after curing was as shown in Table 1 , The presence or absence of bubbles was confirmed in the same manner as in Example 1. The results are shown in Table 1.

&Lt; Comparative Example 1, Reference Example 1 >

A polarizing plate was produced in the same manner as in Example 1 except that the thickness of the adhesive layer after curing and the temperature and the viscosity of the adhesive layer at the time of film bonding were changed to those shown in Table 1. In the same manner as in Example 1, Respectively. The results are shown in Table 1. In the polarizing plate of Comparative Example 1, a large number of bubbles having a diameter of about 10 占 퐉 were found in the cured adhesive layer.

10: polarizing film 20, 21: protective film
30: adhesive applicator 40: bonding roll
50: cooling roll 60: guide roll
70: infrared ray irradiation apparatus 80: active energy ray irradiation apparatus

Claims (12)

A bonding step of bonding the first film and the second film via an adhesive layer formed so that the thickness after curing is not more than 2.5 mu m and a curing step of curing the adhesive layer after bonding the first film and the second film and,
Wherein at least one of the first film and the second film is an optical film,
Wherein the viscosity of the adhesive layer when the first film and the second film are bonded in the bonding step is not more than 60 cP. The method of manufacturing a laminated optical film according to claim 1, further comprising a heating step of heating the adhesive layer to adjust its viscosity to 60 cP or less before the bonding step. The method for producing a laminated optical film according to claim 2, wherein in the heating step, the adhesive layer is heated by irradiation of infrared rays. The method for producing a laminated optical film according to claim 2 or 3, wherein the adhesive layer is heated to 40 占 폚 or higher in the heating step. The method for producing a laminated optical film according to any one of claims 1 to 4, wherein the adhesive constituting the adhesive layer is a curable adhesive of a non-solvent type. The method for producing a laminated optical film according to claim 1, wherein the adhesive layer is adjusted to have a viscosity of not more than 60 cP by incorporating a solvent when the first film and the second film are bonded. The method for producing a laminated optical film according to any one of claims 1 to 6, wherein the adhesive constituting the adhesive layer is an active energy ray curable adhesive. The method for producing a laminated optical film according to any one of claims 1 to 7, wherein the first film and the second film are continuously transported in the longitudinal direction of the first film and the second film,
An application step of continuously applying an adhesive to the bonding surface of the first film or the second film to form an adhesive layer;
Wherein the first film and the second film are passed between a pair of bonding rolls so that their transport directions become parallel,
Wherein the laminated optical film is a laminated optical film. The method for producing a laminated optical film according to claim 8, wherein an angle formed by the first film and the second film passed between the pair of bonding rolls is not more than 60 degrees. The method for producing a laminated optical film according to claim 8 or 9, wherein the conveying speed of the first film and the second film passed between the pair of bonding rolls is 10 m / min or more. The method for producing a laminated optical film according to any one of claims 8 to 10, wherein the first film and the second film have a width of 0.4 to 2 m. The method for producing a laminated optical film according to any one of claims 1 to 11, wherein the first film is a polarizing film and the second film is a protective film.

Images