KR102226092B1 - Polarizing plate and liquid crystal display - Google Patents

Abstract

The polarizing plate 5 is formed by laminating a first protective film (optical film 12), a polarizer 11, and a second protective film (optical film 13) in this order. The retardation value Ro in the in-plane direction of the second protective film and the retardation value Rt in the thickness direction are within a predetermined range. Of the first protective film and the second protective film, only the second protective film contains an ultraviolet absorber. The 2nd protective film contains the polyester diol whose both ends of a main chain are hydroxyl groups. The 2nd protective film is a laminated film containing a core layer and two skin layers containing microparticles|fine-particles.

Description

Polarizing plate and liquid crystal display

The present invention relates to a polarizing plate and an IPS (In Plane Switching) type liquid crystal display device provided with the polarizing plate.

Conventionally, as a technique for improving display unevenness in a liquid crystal display device, there is one disclosed in Patent Document 1, for example. In Patent Document 1, when an optical film is applied to a thin liquid crystal display device (for example, an IPS type liquid crystal display device), an aliphatic dicarboxylic acid and The optical nonuniformity is improved by using a polycondensation ester of an aliphatic diol as a plasticizer and containing 10% by mass or more of the plasticizer with respect to a polymer (preferably cellulose acylate) forming an optical film.

On the other hand, as the glass substrate of the liquid crystal cell becomes thinner with the thinning of the liquid crystal display device used as a large-sized television, the polarizing plate located on the viewing side with respect to the liquid crystal cell causes a dimensional change due to absorption and bends (bending deformation). Concomitantly, a bend of a liquid crystal cell or an image non-uniformity (bend non-uniformity) due to the bend occurs. For this reason, conventionally, in the polarizing plate, by configuring the protective film located on the visible side with respect to the polarizer with a film having low moisture permeability, absorption of the polarizing plate is reduced to suppress dimensional change, thereby suppressing the bend of the liquid crystal cell. I was doing it. Further, examples of the film having low moisture permeability include resin films such as PET (polyethylene terephthalate) and acrylic. These films are formed by, for example, a melt casting film forming method.

Japanese Patent Laid-Open Publication No. 2013-254190 (see claims 9, 10, 23, paragraphs [0037] to [0043], [0215], etc.)

Here, for convenience of explanation below, in the polarizing plate located on the viewing side with respect to the liquid crystal cell, the protective film located on the viewing side with respect to the polarizer is also referred to as a T1 film, and the protective film located on the liquid crystal cell side with respect to the polarizer , Also referred to as a T2 film.

In a liquid crystal display device, in order to prevent deterioration of a liquid crystal cell due to sunlight (especially ultraviolet rays), a function of absorbing ultraviolet rays is required for a polarizing plate disposed on the viewing side with respect to the liquid crystal cell. Such an ultraviolet absorbing function can be imparted, for example, by adding an ultraviolet absorber to the T1 film.

However, when the above-described low moisture permeable film (film containing PET or acrylic) is used as the T1 film, since additives such as an ultraviolet absorber are melted by heat in the melt-casting film forming method, conditions suitable for melting are precisely irradiated to Since it is necessary to form a film under conditions, it is generally not easy to add an additive, and therefore, the productivity of the film decreases and the production cost increases. In addition, when the additive is excessively added, bleed-out (leaching of the additive) occurs, and when the film formed into a film is applied to the polarizing plate, there is a concern that the quality of the polarizing plate may be impaired.

Therefore, in the polarizing plate on the viewing side with respect to the liquid crystal cell, the inventor of the present application studied that by adding an ultraviolet absorber to the T2 film, the T2 film has an ultraviolet absorbing function to prevent deterioration of the liquid crystal cell. However, it has been found from various studies that when an ultraviolet absorber is added to the T2 film, bend unevenness occurs due to the addition or the durability of the T2 film is deteriorated. For this reason, it is desired to realize a polarizing plate capable of suppressing bend unevenness and deterioration in durability. In particular, in an IPS type liquid crystal display device equipped with a high transmittance panel, since the amount of transmitted light is large, display unevenness is easily recognized, and it is important to suppress bend unevenness.

In addition, about the expression principle of bend nonuniformity, it estimates as follows. In the film-forming process of the film, since the compatibility between the ultraviolet absorber and the resin constituting the film (for example, a cellulose ester resin) is poor, cracks occur inside the film formed into the film. Moisture that has permeated even a little through the T1 film having low moisture permeability tends to accumulate in the cracked portion of the T2 film, and the T2 film causes dimensional variation due to the accumulated moisture. For this reason, a bend occurs in the liquid crystal cell, and image non-uniformity (bend non-uniformity) occurs due to the bend.

In addition, about the deterioration of the durability of the T2 film, it is considered as follows. In general, fine particles (mat agents) are added to the film in order to provide unevenness to the film surface at the time of film formation to ensure slipperiness and to ensure a stable winding shape. When an ultraviolet absorber is further added to the film (dope) during film formation, aggregation of the fine particles and the ultraviolet absorber proceeds in the film forming process. In particular, in the film formation of a single layer film, since the fine particles are uniformly dispersed throughout the film, the agglomeration is performed over the entire film. As a result, the haze of the entire film is deteriorated, and the durability of the T2 film (for example, the haze after the moist heat durability test) is also deteriorated.

The present invention has been made to solve the above problem, and its object is to suppress the bend unevenness that occurs when applied to an IPS type liquid crystal display device, and the durability of the protective film (T2 film) on the liquid crystal cell side of the viewing side polarizing plate. It is to provide a polarizing plate capable of suppressing deterioration of and a liquid crystal display device provided with the polarizing plate.

The above object of the present invention is achieved by the following manufacturing method.

That is, the polarizing plate according to one aspect of the present invention is a polarizing plate in which a first protective film, a polarizer, and a second protective film are laminated in this order,

In the second protective film, the retardation value Ro(nm) in the in-plane direction of the film defined by the following formula (i) and the retardation value Rt(nm) in the thickness direction of the film defined by the following formula (ii) are , Satisfying the conditions defined by the following formulas (iii) and (iv),

(i) Ro=(nx-ny)×d

(ii) Rt=((nx+ny)/2-nz)×d

(In the formula, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is the refractive index in the thickness direction of the film (refractive index is 23°C, under an environment of 55% RH, at a wavelength of 590 nm) Measurement), d represents the thickness (nm) of the film.)

(iii) 0nm≤Ro≤10nm

(iv) |Rt|≤25nm

Of the first protective film and the second protective film, only the second protective film contains an ultraviolet absorber,

The second protective film contains a polyester diol in which both ends of the main chain are hydroxyl groups,

The second protective film is a laminated film comprising a core layer and two skin layers containing fine particles, positioned on the front and back sides of the core layer.

In addition, a liquid crystal display device according to another aspect of the present invention,

The above polarizing plate,

Including an IPS type liquid crystal cell in which a liquid crystal layer is sandwiched by a pair of substrates,

The polarizing plate is disposed on the viewing side with respect to the liquid crystal cell, and the second protective film is disposed on the side of the liquid crystal cell with respect to the polarizer.

Since the 2nd protective film which comprises a polarizing plate contains the polyester diol whose both ends of a main chain are hydroxyl groups, at the time of film formation of a 2nd protective film, compatibility between an ultraviolet absorber and a resin can be improved. Thereby, it is possible to suppress the occurrence of cracks in the inside of the film formed into a film, and it is possible to suppress the occurrence of dimensional variation in the second protective film due to the accumulation of moisture in the cracked portion. As a result, when the polarizing plate is particularly applied to an IPS-type liquid crystal display device, the bend of the liquid crystal cell caused by the dimensional variation of the second protective film can be suppressed, and image non-uniformity (bend non-uniformity) can be suppressed.

Moreover, the 2nd protective film is comprised from a laminated film, and the fine particle is contained in the outermost layer (skin layer). For this reason, at the time of forming the second protective film, the fine particles and the ultraviolet absorber are aggregated only in the skin layer (not aggregated over the entire film), and deterioration of haze in the entire film can be suppressed. Thereby, the durability of the 2nd protective film can be improved.

1 is a cross-sectional view showing a schematic configuration of an IPS type liquid crystal display device according to an embodiment of the present invention.

An embodiment of the present invention will be described below based on the drawings. In addition, in the present specification, when a numerical range is expressed as A to B, the values of the lower limit A and the upper limit B are included in the numerical range. In addition, the present invention is not limited to the following contents.

The polarizing plate of this embodiment is a polarizing plate in which a first protective film, a polarizer, and a second protective film are laminated in this order. In the second protective film, the retardation value Ro(nm) in the in-plane direction of the film defined by the following formula (i) and the retardation value Rt(nm) in the thickness direction of the film defined by the following formula (ii) are And the conditions defined by the following formulas (iii) and (iv) are satisfied.

(i) Ro=(nx-ny)×d

(ii) Rt=((nx+ny)/2-nz)×d

(In the formula, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is the refractive index in the thickness direction of the film (refractive index is 23°C, under an environment of 55% RH, at a wavelength of 590 nm) Measurement), d represents the thickness (nm) of the film.)

(iii) 0nm≤Ro≤10nm

(iv) |Rt|≤25nm

Of the first protective film and the second protective film, only the second protective film contains an ultraviolet absorber,

The second protective film contains a polyester diol in which both ends of the main chain are hydroxyl groups,

The second protective film is a laminated film comprising a core layer and two skin layers containing fine particles, positioned on the front and back sides of the core layer.

In the polarizing plate which laminated the 1st protective film, the polarizer, and the 2nd protective film in this order, as for the 2nd protective film, Ro and Rt defined by Formulas (i) and (ii) are formula (iii) and (iv) ) Is a so-called zero retardation film. When a polarizing plate of such a structure is applied to, for example, a viewing side polarizing plate of an IPS type liquid crystal display device, the second protective film is positioned on the liquid crystal cell side with respect to the polarizer.

In this embodiment, since an ultraviolet absorber is contained in the 2nd protective film, the kind of additive used for film formation of a 1st protective film can be reduced. Thereby, it becomes possible to easily form the 1st protective film into a film by the melt-casting film forming method, and it becomes possible to apply the film-formed 1st protective film to a polarizing plate. Further, of course, it is also possible to form a film of the first protective film by the solution casting film forming method. Further, by arranging the polarizing plate on the visible side of the liquid crystal cell, since ultraviolet rays are absorbed by the second protective film (ultraviolet ray absorber), deterioration of the liquid crystal cell due to ultraviolet rays can be prevented. In addition, it becomes possible to suppress deterioration of the second protective film itself due to ultraviolet rays and to improve its durability.

Moreover, the 2nd protective film which comprises a polarizing plate contains the polyester diol whose both ends of a main chain are hydroxyl groups. Thereby, even if the 2nd protective film is a structure containing an ultraviolet absorber like this embodiment, at the time of film formation of a 2nd protective film, the ultraviolet absorber and the resin which comprises a 2nd protective film (for example, cellulose ester Resin) can be improved. Thereby, it is possible to suppress the occurrence of cracks in the inside of the film-formed film.

Therefore, even if moisture in the air permeates the first protective film, it is possible to suppress that the moisture accumulates in the crack portion of the second protective film and causes dimensional variation of the second protective film. As a result, in particular, in the IPS type liquid crystal display device, bending of the liquid crystal cell caused by dimensional variation of the second protective film can be suppressed, and image non-uniformity (bend non-uniformity) can be suppressed.

Moreover, the 2nd protective film is comprised from a laminated film containing a core layer and two skin layers, and the said skin layer contains fine particles. Therefore, as in the present embodiment, even if the second protective film contains an ultraviolet absorber, at the time of forming the second protective film, aggregation of the fine particles and the ultraviolet absorber occurs only in the skin layer, and the entire film Doesn't happen over. Thereby, deterioration of haze in the whole film can be suppressed, and deterioration of durability (for example, haze after a moist heat endurance test) of the second protective film can be suppressed.

It is preferable that the said ultraviolet absorber is contained in both the said core layer and said two skin layers in the said 2nd protective film. In this case, ultraviolet rays are absorbed in the entire second protective film (laminated film), so that deterioration of the liquid crystal cell due to ultraviolet rays and deterioration of the second protective film itself due to ultraviolet rays can be reliably prevented.

The polyester diol is preferably contained in both the core layer and the two skin layers in the second protective film. By including the polyester diol in the core layer and the skin layer containing the ultraviolet absorber, compatibility between the ultraviolet absorber and the resin may be improved over the entire core layer and the skin layer. Thereby, it is possible to suppress occurrence of cracks in both the core layer and the skin layer, thereby suppressing dimensional variation of the second protective film and bend unevenness resulting from it.

In the second protective film, the core layer and the two skin layers may contain a resin containing a cellulose ester. A film containing a cellulose ester resin can be formed by a solution-casting film forming method in which additives are relatively easy to add, and in addition, three layers including a core layer and two skin layers can be easily formed by co-rolling. . Thereby, the 2nd protective film which is a laminated film and the polarizing plate provided with it can be realized easily.

It is preferable that the first protective film contains a resin containing polyethylene terephthalate (PET). In this case, the moisture permeability of the first protective film is lowered to reduce the absorption of the polarizing plate, and the bend of the polarizing plate due to absorption and the bend unevenness resulting from it can be suppressed. In addition, since the second protective film becomes less susceptible to moisture, it is also effective in improving the durability of the second protective film.

The liquid crystal display device of this embodiment includes the polarizing plate of this embodiment described above, and an IPS type liquid crystal cell in which a liquid crystal layer is sandwiched by a pair of substrates, and the polarizing plate is disposed on a viewing side with respect to the liquid crystal cell, In addition, the second protective film is disposed on the side of the liquid crystal cell with respect to the polarizer. In this case, in the IPS type liquid crystal display device, the bend of the substrate and the resulting bend unevenness can be suppressed.

In particular, the IPS type liquid crystal display device is susceptible to bend unevenness due to the characteristics of the liquid crystal cell. For this reason, the polarizing plate configuration of the present embodiment that suppresses bend unevenness becomes very effective when the liquid crystal cell is an IPS type.

[IPS type liquid crystal display device]

Hereinafter, a specific configuration of the liquid crystal display device of the present embodiment will be described. 1 is a cross-sectional view showing a schematic configuration of an IPS type liquid crystal display device 1 according to the present embodiment. The liquid crystal display device 1 includes a liquid crystal display panel 2 and a backlight 3. The backlight 3 is a light source for illuminating the liquid crystal display panel 2.

The liquid crystal display panel 2 is configured by arranging a polarizing plate 5 on the viewing side of the IPS type liquid crystal cell 4 and arranging the polarizing plate 6 on the backlight 3 side. The liquid crystal cell 4 is formed by sandwiching a liquid crystal layer with a pair of glass substrates (not shown).

The polarizing plate 5 is provided with a polarizer 11 and an optical film 12·13. The polarizer 11 transmits a predetermined linearly polarized light. The optical film 12 is a first protective film (also referred to as a T1 film) disposed on the visible side of the polarizer 11. The optical film 13 is a second protective film (also referred to as a T2 film) disposed on the side of the liquid crystal cell 4 of the polarizer 11, that is, on the side opposite to the viewing side with respect to the polarizer 11. The optical film 12 may also be referred to as a counter film because it is disposed to face the optical film 13 through the polarizer 11. The polarizing plate 5 is attached to the visible side of the liquid crystal cell 4 through an adhesive layer 7. That is, the polarizing plate 5 is positioned on the viewing side with respect to the liquid crystal cell 4, and is bonded to the liquid crystal cell 4 so that the optical film 13 is on the side of the liquid crystal cell 4 with respect to the polarizer 11 .

The polarizing plate 6 includes a polarizer 14 and an optical film 15·16. The polarizer 14 transmits a predetermined linearly polarized light. The optical film 15 is a third protective film (also referred to as a T3 film) disposed on the visible side (liquid crystal cell 4 side) of the polarizer 14. The optical film 16 is a fourth protective film (also referred to as a T4 film) disposed on the backlight 3 side (a side opposite to the viewing side) of the polarizer 14. This polarizing plate 6 is attached to the backlight 3 side of the liquid crystal cell 4 through an adhesive layer 8. Further, the optical film 15 on the viewing side may be omitted, and the polarizer 14 may be brought into direct contact with the adhesive layer 8. The polarizer 11 and the polarizer 14 are arranged to be in a cross Nicol state.

[Second protective film]

Next, the 2nd protective film of a polarizing plate on a viewer side is demonstrated. In addition, the configuration of the second protective film shown below is also applicable to the third protective film of the polarizing plate on the backlight side. However, the ultraviolet absorber included in the second protective film may or may not be included in the third protective film.

The second protective film of this embodiment is a so-called zero retardation film. That is, in the second protective film, the retardation value Ro(nm) in the in-plane direction of the film defined by the following formula (i) and the retardation value Rt(nm) in the thickness direction of the film defined by the following formula (ii) Satisfies the conditions defined by the following formulas (iii) and (iv).

(i) Ro=(nx-ny)×d

(ii) Rt={(nx+ny)/2-nz}×d

(In the formula, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction (orthogonal to the ground axis) in the film plane), and nz is the refractive index in the thickness direction of the film (refractive index is 23°C, 55%) In the environment of RH, measured at a wavelength of 590 nm), d represents the thickness (nm) of the film.)

(iii) 0nm≤Ro≤10nm

(iv) |Rt|≤25nm

The retardation value Ro·Rt can be measured according to a known method. Specifically, the retardation value Ro · Rt is a three-dimensional refractive index at a wavelength of 590 nm in an environment of 23°C and 55% RH using an automatic birefringence meter Axo Scan (manufactured by Axo Scan Mueller Matrix Polarimeter). It can be measured and calculated from the obtained refractive indices nx, ny, and nz.

When the polarizing plate is bonded to the liquid crystal cell from the side of the second protective film by making the retardation value Ro Rt of the second protective film almost zero (by satisfying the conditions specified by formulas (iii) and (iv)), Light leakage during black display in a liquid crystal display device can be effectively prevented. Further, since the thickness of the second protective film can be reduced, it is possible to further reduce the thickness of the polarizing plate and the liquid crystal display device, which is preferable.

It is preferable that the 2nd protective film is a light-transmitting film whose light transmittance at 380 nm is less than 50%. The light transmittance at a wavelength of 380 nm of the second protective film can be measured and determined using, for example, an ultraviolet-visible spectrophotometer (manufactured by Nippon Bunko Corporation, product name: V7100). The light transmittance at 380 nm is preferably less than 25%, more preferably less than 10%.

In the second protective film, as a method of reducing the light transmittance at 380 nm to less than 50%, an additive having light absorption at 380 nm is added to the film, and in particular, an ultraviolet absorber having strong absorption in the ultraviolet region is added. It is valid to do.

Hereinafter, the details of the second protective film will be further described.

(Laminated film)

The second protective film of the present embodiment includes a core layer containing cellulose acylate as a cellulose ester resin, a first skin layer containing cellulose acylate on the front side of the core layer, and a cellulose acyl on the back side of the core layer. It has a second skin layer comprising a rate. In addition, in this embodiment, a "core layer" refers to a layer with the thickest film thickness, and a "skin layer" refers to a layer having a thinner film thickness than the core layer and in contact with the front and back of the core layer.

As will be described later, the second protective film can be prepared by simultaneously or sequentially casting a dope containing cellulose acylate on a support by multi-layer casting to form a film, but even in that case, each layer is mixed with each other to form a clear interface. It may not be in a state.

Moreover, even if only one type of cellulose acylate is used in each layer, a plurality of cellulose acylates may be mixed in one layer, but the cellulose acylate in each layer is preferably one type.

(Film thickness)

The thickness of the entire second protective film is preferably 3 µm or more and 50 µm or less, more preferably 5 µm or more and 47 µm or less, and still more preferably 7 µm or more and 45 µm or less. When the film thickness is set to 3 µm or more, the strength as a film can be secured, so it is preferable. Further, by setting the film thickness to 50 µm or less, it is easy to cope with changes in humidity and easy to maintain optical properties.

The thickness of the first skin layer and the second skin layer is preferably 0.3 µm or more and 3 µm or less, more preferably 0.4 µm or more and 2.5 µm or less, and still more preferably 0.5 µm or more and 2.0 µm or less. In addition, the film thickness can be measured with an electron micrometer K402B manufactured by Anritsu Corporation, for example.

(Cellulose acylate)

The cellulose acylate used for the core layer and the skin layer of the second protective film is not particularly limited. As raw materials for cellulose acylate, there are cotton linters and wood pulp (hardwood pulp, softwood pulp), and the like, and cellulose acylate obtained from any raw material may be used. In some cases, cellulose acylate obtained from a plurality of raw materials may be mixed. You can use it.

The β-1,4 bonded glucose units constituting cellulose have free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer obtained by acylating some or all of these hydroxyl groups by acyl groups. The average degree of acyl substitution means the ratio in which the hydroxyl groups of the cellulose positioned at the 2nd, 3rd and 6th positions are acylated (100% of acylation is substitution degree 1).

The method of measuring the degree of acetyl substitution can be carried out according to D-817-91 of ASTM (American Association of Testing Materials).

In this embodiment, the average acyl substitution degree of the cellulose acylate of the core layer and the average acyl substitution degree of the cellulose acylate of the first skin layer and the second skin layer are each independently 2.00 to 3.00, preferably 2.50 to 3.00.

The acyl group having 2 or more carbon atoms of the cellulose acylate may be an aliphatic group or an allyl group, and is not particularly limited. These are, for example, alkylcarbonyl esters, alkenylcarbonyl esters, aromatic carbonyl esters, aromatic alkylcarbonyl esters and the like of cellulose, and may each have a further substituted group. Preferred examples of these are acetyl group, propionyl group, butanoyl group, heptanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecano Diary, isobutanoyl group, tert-butanoyl group, cyclohexane carbonyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group, and the like. Among these, an acetyl group, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a tert-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and particularly preferably An acetyl group, a propionyl group, and a butanoyl group (when the acyl group has 2 to 4 carbon atoms), and more particularly preferably an acetyl group (when the cellulose acylate is cellulose acetate).

Specifically, as the cellulose acylate, for example, cellulose acetate (for example, diacetyl cellulose, triacetyl cellulose), cellulose acetate butyrate, or cellulose acetate propionate can be used.

In the acylation of cellulose, when an acid anhydride or an acid chloride is used as the acylating agent, an organic acid such as acetic acid or methylene chloride is used as the organic solvent serving as the reaction solvent. As the catalyst, when the acylating agent is an acid anhydride, a protic catalyst such as sulfuric acid is preferably used, and when the acylating agent is an acid chloride (eg, CH ₃ CH ₂ COCl), a basic compound is used.

The most common industrial synthesis method of mixed fatty acid ester of cellulose is a method of acylating cellulose with a mixed organic acid component containing fatty acids (acetic acid, propionic acid, valeric acid, etc.) corresponding to acetyl groups and other acyl groups, or their acid anhydrides. .

(additive)

<Polyester diol>

It is preferable that the 2nd protective film contains polyester diol as an additive. The said polyester diol is suitably selected so that an additive compatible with a cellulose acylate dope or a cellulose acylate film exhibits a desired characteristic, and its structure, molecular weight, and addition amount are suitably selected.

In the polyester diol used in the present embodiment, it is preferable that both ends of the main chain are alcoholic hydroxyl groups, from the viewpoint of compatibility between the cellulose acylate dope or the cellulose acylate film and the additive, and the control of optical properties. In particular, it is necessary to make the addition amount of the polyester diol into 5 mass% or more with respect to the cellulose acylate, it is preferable to set it as 9 to 40 mass %, and it is more preferable that it is 10 to 30 mass %.

In the second protective film containing cellulose acylate, for controlling optical anisotropy, it is important to keep the hydroxyl value (OHV) and molecular weight of the polyester diol in a certain range in order to keep the quality constant. In particular, the hydroxyl value is also preferable for quality control. For the measurement of the hydroxyl value, the acetic anhydride method described in Japanese Industrial Standard JIS K 1557-1:2007 can be applied.

The hydroxyl value is preferably 40 mgKOH/g or more and 170 mgKOH/g or less, more preferably 60 mgKOH/g or more and 150 mgKOH/g or less, and particularly preferably 90 mgKOH/g or more and 140 mgKOH/g or less. When the hydroxyl value is too large, the molecular weight is small, the amount of the low molecular weight component increases, and the volatilization property tends to be large, which is not preferable. Moreover, when the hydroxyl value is too small, the solubility in a solvent and compatibility with a cellulose acylate deteriorate, and there exists a tendency which is not preferable.

The number average molecular weight (Mn) of a polyester diol can be calculated from a value of a hydroxyl value or a measurement of GPC (gel permeation chromatography). As the value of the molecular weight, it is preferably 650 or more and 2800 or less, more preferably 700 or more and 2000 or less, and particularly preferably 800 or more and 1250 or less. Further, in order to be optically isotropic, those having a molecular weight of 800 or more and 1200 or less are particularly suitably used.

The polyester diol can be produced by a known method such as a dehydration condensation reaction of a dibasic acid and a glycol, or addition of an anhydrous dibasic acid to a glycol and a dehydration condensation reaction.

Here, examples of the dibasic acid constituting the polyester diol include succinic acid, glutaric acid, adipic acid, maleic acid, and the like, and these are used alone or in combination of two or more. Dipic acid or mixtures thereof and the like are preferably used.

The number of carbon atoms of the dibasic acid is preferably 4 to 8, preferably 4 to 6, and particularly preferably 6. The smaller the number of carbon atoms can lower the moisture permeability of the cellulose acylate film, and is suitable also from the point of compatibility, and the number of carbon atoms is preferably 6 from the viewpoint of cost and handling properties of the polyester diol.

In addition, as the glycol constituting the polyester diol, suitable ones can be selected from various glycols such as ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, and butylene glycol. Those having 2 to 4 are preferred, and ethylene glycol having 2 carbon atoms is particularly preferred. This is because the less carbon number is excellent in compatibility with a cellulose ester dope or a cellulose ester film, and is excellent in bleed-out resistance by moist heat thermostat.

<fine particles>

Fine particles (mat agents) can be added to the second protective film. The mat agent is not particularly limited as long as it is a material exhibiting a function of preventing scratches or deterioration in transportability during handling, and an inorganic compound or an organic compound mat agent may be used.

As a preferable specific example of the mat agent of the inorganic compound, an inorganic compound containing silicon (e.g., silicon dioxide, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, etc.), titanium oxide, zinc oxide, aluminum oxide, oxide Barium, zirconium oxide, strontium oxide, antimony oxide, tin oxide, tin oxide antimony, calcium carbonate, talc, clay, calcined kaolin, calcium phosphate, etc. are preferable, and more preferably inorganic compounds containing silicon or zirconium oxide. , Since the turbidity of the cellulose acylate film can be reduced, silicon dioxide is particularly preferably used. As the fine particles of the silicon dioxide, for example, a commercial product having a brand name such as Aerosil (registered trademark) R972, R974, R812, 200, 300, R202, OX50, TT600 (manufactured by Nippon Aerosil Co., Ltd.) can be used. have. As the zirconium oxide fine particles, commercially available ones such as Aerosil R976 and R811 (above made by Nippon Aerosil Co., Ltd.) can be used.

As a preferable specific example of the mat agent of an organic compound, a polymer, such as a silicone resin, a fluororesin, and an acrylic resin, is preferable, for example, and silicone resin is used especially preferably. Among the silicone resins, it is particularly preferable to have a three-dimensional network structure, and for example, Toss Pearl (registered trademark) 103, Toss Pearl 105, Toss Pearl 108, Toss Pearl 120, Toss Pearl 145, Toss Pearl 3120 and Toss Pearl 240 ( A commercial item having a brand name such as Toshiba Silicone Co., Ltd. can be used.

The method of adding the mat agent to the cellulose acylate solution is not particularly limited. For example, an additive (mat agent) may be contained in the step of mixing the cellulose acylate and the solvent, or after preparing a mixed solution of the cellulose acylate and the solvent, the additive may be added. In addition, the mat agent may be added and mixed immediately before casting the dope, and the mixing can be performed by installing a screw-type mixer online. Specifically, a static mixer such as an in-line mixer is preferable. In addition, as the in-line mixer, for example, a static mixer SWJ (Toray stationary in-pipe mixer Hi-Mixer) (manufactured by Toray Engineering) or the like is preferable. The preferable form of mixing of the mat agent is as described in paragraph number 0127 of Japanese Unexamined Patent Application Publication No. 2013-75401.

In the present embodiment, the fact that the matting agent is contained in at least one of the two skin layers of the second protective film is abrasion resistance due to reduction of the friction coefficient of the film surface, and pulling deformation that occurs when the wide-width film is wound in a long length ( It is preferable from the viewpoint of prevention of straining) or cracking, and prevention of film breakage. In particular, it is particularly preferable to contain a mat agent on both sides of the two skin layers from the viewpoint of effectively reducing scratch resistance, pulling deformation, and cracking. In addition, of the skin layer and the core layer of the second protective film, since the matting agent is dispersed only in the skin layer and is not dispersed throughout the film, aggregation with the ultraviolet absorber is prevented. It is not performed in, and is preferable.

The content of the mat agent is preferably 0.01 to 5.0% by mass, more preferably 0.03 to 3.0% by mass, and particularly preferably 0.05 to 1.0% by mass. By setting it as the said range, the effect of reducing pulling deformation and cracking, and abrasion resistance can be realized without increasing the haze of the optical film.

<Retardation lowering agent 1: sugar ester>

It is preferable that the 2nd protective film contains a retardation reducing agent together with cellulose acylate.

As a retardation reducing agent, a compound (A) having one furanose structure or a pyranose structure, or a compound (B) in which at least one of two or more or 12 or less of a furanose structure or a pyranose structure is bonded. A sugar ester or a sugar ester compound, which is a compound obtained by esterifying all or part of the OH groups in an aliphatic acyl group, may be included.

Examples of preferred compounds (A) and (B) include compounds shown below, but the present invention is not limited thereto.

Examples of the compound (A) include glucose, galactose, mannose, fructose, xylose, and arabinose. Further, the compound (A) also includes maltitol obtained by hydrogenating maltose at high pressure to reduce it.

Further, examples of the compound (B) include lactose, sucrose, cellobiose, maltose, cellotriose, maltotriose, raffinose, and kestose. Among these compounds (A) and (B), it is particularly preferable to have both a furanose structure and a pyranose structure. Sucrose is mentioned as an example.

There is no restriction|limiting in particular as a monocarboxylic acid used when synthesizing a sugar ester, A well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, etc. can be used. The carboxylic acid to be used may be one or a mixture of two or more.

As a preferable aliphatic monocarboxylic acid, for example, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, Undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecyl acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachinic acid, behenic acid, lignoceric acid, serotic acid, hep And saturated fatty acids such as tacosic acid, montanic acid, melisic acid, and lactic acid, undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid, and octenic acid.

Examples of preferred alicyclic monocarboxylic acids include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, or derivatives thereof.

Details of the method for producing these compounds are described in, for example, Japanese Patent Application Laid-Open No. 8-245678.

In addition to the esterified compounds of the compounds (A) and (B), the esterified compounds of oligosaccharides can be applied as a compound in which 3 to 12 of at least one of a furanose structure or a pyranose structure are bonded.

Oligosaccharides are prepared by reacting enzymes such as amylase on starch and sucrose. Examples of oligosaccharides applicable to this embodiment include maltooligosaccharides, isomaltooligosaccharides, fructooligosaccharides, galactooligosaccharides, and xylooligosaccharides. Oligosaccharides can also be acetylated in the same manner as in the above compounds (A) and (B).

Next, an example of a production example of a sugar ester is shown. Acetic anhydride (200 ml) was added dropwise to a solution in which pyridine (100 ml) was added to glucose (29.8 g, 166 mmol), and reacted for 24 hours. After that, the solution was concentrated by evaporation and added to ice water. After allowing to stand for 1 hour, it was filtered through a glass filter to separate the solid and water, and the solid on the glass filter was dissolved in chloroform, and the mixture was separated with cold water until it became neutral. After separating the organic layer, it was dried over anhydrous sodium sulfate. After the anhydrous sodium sulfate was removed by filtration, chloroform was removed by evaporation, and then glycospentaacetate (58.8 g, 150 mmol, 90.9%) was obtained by drying under reduced pressure. Further, instead of the acetic anhydride, the monocarboxylic acid described above can be used.

Below, although a specific example of the sugar ester compound of this embodiment is given, this invention is not limited to this.

The 2nd protective film contains the said sugar ester compound in the range of 1 to 35 mass %, especially 5 to 30 mass% in a film in order to suppress deterioration of a polarization function and stabilize a display quality. It is desirable. Within this range, the excellent effect of the present embodiment is exhibited, and there is no bleed-out during storage of the fabric, and it is preferable. Moreover, you may use together the sugar ester compound which esterified all OH groups, and the sugar ester compound in which one or more OH groups remain. For example, a mixture of sucrose octaacetate, sucrose heptaacetate, and sucrose hexaacetate may be mentioned. The mixing ratio is not particularly limited, but for example 30:30:30, 40:30:30, 40:50:10, 50:30:20, 60:30:10, 80:10:10, 90: And combinations such as 7:3, 95:5:0, and the like. These may be controlled by adjusting the reaction time or the addition amount of the monocarboxylic acid to be reacted with the sugar at the time of esterification of the sugar, or may be mixed with each.

<Retardation reducing agent 2: acrylic polymer>

The second protective film may contain an acrylic polymer having a number average molecular weight of 500 or more and 30000 or less as a retardation reducing agent. As such an acrylic polymer, those described in paragraphs [0059] to [0093] of WO08/044463 are preferably used.

<Retardation reducing agent 3: Polyester>

The 2nd protective film may contain polyester represented by the following general formula (B1) or (B2) as a retardation reducing agent. This is a monocarboxylic acid B _1, or polyester obtained from a carbon number of 1 B monoalcohol of 1 to 12 ₂ ester having 2 to 12 carbon atoms a divalent alcohol G and having 2 to 12 dibasic acids, having 1 to 12 carbon atoms in the.

General formula (B1)

B ₁ -(GA-) _m GB ₁

In the general formula (B1), B ₁ represents a monocarboxylic acid having 1 to 12 carbon atoms, G represents a divalent alcohol having 2 to 12 carbon atoms, and A represents a dibasic acid having 2 to 12 carbon atoms. It is particularly preferable that B ₁ , G and A all have a small proportion of an aromatic ring or do not contain them. m represents the number of repetitions.

General formula (B2)

B ₂ -(AG-) _n AB ₂

In the general formula (B2), B ₂ represents a monoalcohol having 1 to 12 carbon atoms, G represents a dihydric alcohol having 2 to 12 carbon atoms, and A represents a dibasic acid having 2 to 12 carbon atoms. It is particularly preferable that B ₂ , G and A all have a small proportion of an aromatic ring or do not contain them. n represents the number of repetitions.

The _{monocarboxylic acid represented by B 1} is not particularly limited, and a known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, or the like can be preferably used.

Examples of preferable monocarboxylic acids include the following, but the present invention is not limited thereto.

As the aliphatic monocarboxylic acid, a fatty acid having a linear or branched chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it has 1 to 20 carbon atoms, and it is particularly preferable that it has 1 to 12 carbon atoms. When acetic acid is contained, compatibility with the cellulose ester is increased, so it is preferable, and it is also preferable to mix and use acetic acid and other monocarboxylic acids.

Preferred aliphatic monocarboxylic acids include, for example, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, and unde Silic acid, lauric acid, tridecyl acid, myristic acid, pentadecyl acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachnoic acid, behenic acid, lignoceric acid, serotic acid, heptaco Saturated fatty acids such as acidic acid, montanic acid, melisic acid, and lactic acid, undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, and unsaturated fatty acids such as arachidonic acid.

The _{monoalcohol component represented by B 2} is not particularly limited, and known alcohols can be used. For example, an aliphatic saturated alcohol or an aliphatic unsaturated alcohol having a linear or branched chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it has 1 to 20 carbon atoms, and it is particularly preferable that it has 1 to 12 carbon atoms.

Examples of the divalent alcohol component represented by G include the following, but the present invention is not limited thereto. For example, ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1 ,5-pentanediol, 1,6-hexanediol, 1,5-pentylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, etc. are mentioned. Among these, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol , Diethylene glycol and triethylene glycol are preferred, and 1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexanediol, and diethylene glycol are preferably used.

As the dibasic acid (dicarboxylic acid) component represented by A, an aliphatic dibasic acid and an alicyclic dibasic acid are preferable. For example, as an aliphatic dibasic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, etc., in particular As the aliphatic dicarboxylic acid, one having 4 to 12 carbon atoms and at least one selected from these are used. That is, you may use in combination of 2 or more types of dibasic acids. In that case, aromatic dicarboxylic acids, such as phthalic acid, isophthalic acid, and terephthalic acid, can also be used together.

Each of m and n represents the number of repetitions, and is preferably 1 or more and 170 or less.

The number average molecular weight of the polyester is preferably 20000 or less, and more preferably 10000 or less. Particularly, a polyester having a number average molecular weight of 500 to 10000 has good compatibility with a cellulose ester, and neither evaporation nor volatilization occurs in the film formation, and thus, it is preferable.

Polycondensation of polyester is performed by a conventional method. For example, by direct reaction of the dibasic acid and glycol, the dibasic acid or alkyl esters thereof, for example, the methyl ester of dibasic acid and the polyesterization reaction of glycols or transesterification reaction to heat-melt condensation It can be easily synthesized by a legal method or any method of dehalogenation reaction of an acid chloride of these acids and glycol. It is preferable that the number average molecular weight is not that large by direct reaction. The polyester having a high distribution on the low molecular weight side has very good compatibility with the cellulose ester, and after film formation, the moisture permeability is also small, and a second protective film excellent in transparency can be obtained.

The method for adjusting the molecular weight may be a conventional method without any particular limitation. For example, depending on the polymerization conditions, in the method of blocking the molecular ends with a monovalent acid (monocarboxylic acid) or a monohydric alcohol (monoalcohol), the molecular weight can be adjusted by controlling the amount of these monovalent compounds added. . In this case, a monovalent acid is preferable from the viewpoint of stability of the polymer.

For example, as a monovalent acid, acetic acid, propionic acid, butyric acid, etc. are mentioned as a preferable example. During the polycondensation reaction, ones that are easily distilled off are selected when they are not distilled out of the system but are stopped and the monovalent acid is removed from the reaction system, but these may be mixed and used. In the case of direct reaction, the number average molecular weight can be adjusted also by measuring the timing of stopping the reaction according to the amount of water distilled off during the reaction. In addition, it can be done by biasing the number of moles of the glycol or dibasic acid to be added, and can be adjusted even if the reaction temperature is controlled.

It is preferable to contain 1-40 mass% of polyester of this embodiment with respect to the 2nd protective film, It is more preferable to contain 2-30 mass %, It is especially preferable to contain 3-15 mass %.

By using the acrylic polymer or the film to which polyester is added, a polarizing plate with little deterioration due to high temperature and high humidity can be obtained. Moreover, by using this polarizing plate, contrast and viewing angle stability are maintained for a long time, and an IPS type liquid crystal display device excellent in surface planarity can be obtained.

<plasticizer>

The second protective film may contain a plasticizer if necessary. The plasticizer is not particularly limited, but is preferably selected from polyhydric carboxylic acid ester plasticizers, glycolate plasticizers, phthalic acid ester plasticizers, fatty acid ester plasticizers and polyhydric alcohol ester plasticizers, polyester plasticizers, acrylic plasticizers, etc. . In addition, these plasticizers may act as retardation reducing agents.

The glycolate plasticizer is not particularly limited, but alkylphthalylalkylglycolates can be preferably used. Examples of the alkylphthalylalkylglycolates include methylphthalylmethylglycolate, ethylphthalylethylglycolate, propylphthalylpropylglycolate, butylphthalylbutylglycolate, octylphthalyloctylglycolate, and methylphthalyl Ethyl glycolate, ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl phthalyl ethyl glycolate, propyl phthalyl butyl Glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycolate, octyl phthalyl methyl glycolate, octyl phthalyl ethyl glycolate, and the like.

As a phthalic acid ester plasticizer, for example, diethylphthalate, dimethoxyethylphthalate, dimethylphthalate, dioctylphthalate, dibutylphthalate, di-2-ethylhexylphthalate, dioctylphthalate, dicyclohexylphthalate, dicyclohexyltere And phthalate.

As a citric acid ester plasticizer, acetyl trimethyl citrate, acetyl triethyl citrate, acetyl tributyl citrate, etc. are mentioned, for example.

Examples of the fatty acid ester plasticizer include butyl oleate, methyl acetyl ricinoleate, dibutyl sebacate, and the like.

Examples of the phosphate ester plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, and tributyl phosphate.

Examples of the polyhydric carboxylic acid ester compound include esters of divalent or more, preferably di- to 20-valent polyhydric carboxylic acids and alcohols. In addition, the aliphatic polyhydric carboxylic acid is preferably 2 to 20 valent, and in the case of an aromatic polyhydric carboxylic acid or an alicyclic polyhydric carboxylic acid, it is preferably trivalent to 20 valent.

Polyhydric carboxylic acid is represented by the following general formula (C).

General formula (C)

R ₂ (COOH) _m (OH) _n

In the general formula (C), R ₂ is a (m+n) valent organic group, m is a positive integer of 2 or more, n is an integer of 0 or more, the COOH group represents a carboxy group, and the OH group represents an alcoholic or phenolic hydroxy group.

Examples of preferred polyhydric carboxylic acids include the following, but the present invention is not limited thereto. Trivalent or higher aromatic polyhydric carboxylic acids such as trimellitic acid, trimesic acid, pyromellitic acid, or derivatives thereof, aliphatic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid, fumaric acid, maleic acid, and tetrahydrophthalic acid Oxypolyhydric carboxylic acids such as polyhydric carboxylic acid, tartaric acid, tartronic acid, malic acid, and citric acid can be preferably used. In particular, it is preferable to use an oxypolycarboxylic acid from the viewpoint of improving retention properties.

There is no restriction|limiting in particular as alcohol used for polyhydric carboxylic acid ester, Well-known alcohol and phenols can be used. For example, an aliphatic saturated alcohol or an aliphatic unsaturated alcohol having a linear or branched chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it has 1 to 20 carbon atoms, and it is particularly preferable that it has 1 to 10 carbon atoms. Further, alicyclic alcohols such as cyclopentanol and cyclohexanol or derivatives thereof, aromatic alcohols such as benzyl alcohol and cinnamyl alcohol, or derivatives thereof, and the like can be preferably used.

When an oxypolyhydric carboxylic acid is used as the polyhydric carboxylic acid, the alcoholic or phenolic hydroxy group of the oxypolyhydric carboxylic acid may be esterified using a monocarboxylic acid. Examples of preferable monocarboxylic acids include the following, but the present invention is not limited thereto.

As the aliphatic monocarboxylic acid, a fatty acid having a linear or branched chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it has 1 to 20 carbon atoms, and it is particularly preferable that it has 1 to 10 carbon atoms.

Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, and lauric acid. , Tridecyl acid, myristic acid, pentadecyl acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachnic acid, behenic acid, lignoceric acid, serotic acid, heptaconic acid, montanic acid, And unsaturated fatty acids such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

Examples of preferred alicyclic monocarboxylic acids include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, or derivatives thereof.

Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two benzene rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralinecarboxylic acid. And aromatic monocarboxylic acids or derivatives thereof having the above. In particular, acetic acid, propionic acid, and benzoic acid are preferable.

The molecular weight of the polyhydric carboxylic acid ester is not particularly limited, but it is preferably in the range of 300 to 1000, and more preferably in the range of 350 to 750. The larger one is preferable from the viewpoint of improving retention, and the small one is preferable from the viewpoint of moisture permeability and compatibility with a cellulose ester.

The number of alcohols used for the polyhydric carboxylic acid ester may be one or a mixture of two or more.

The acid value of the polyhydric carboxylic acid ester is preferably 1 mgKOH/g or less, and more preferably 0.2 mgKOH/g or less. By setting the acid value in the above range, environmental fluctuations of retardation are also suppressed, which is preferable.

The acid value refers to the number of milligrams of potassium hydroxide required to neutralize the acid (carboxyl group present in the sample) contained in 1 g of a sample. The acid value was measured according to JIS K0070.

An example of a particularly preferable polyhydric carboxylic acid ester compound is shown below, but the present invention is not limited thereto. For example, triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, acetyl tribenzyl citrate, Dibutyl tartrate, diacetyl dibutyl tartrate, tributyl trimellitate, tetrabutyl pyromellitate, and the like.

The polyester plasticizer is not particularly limited, but a polyester plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be used. Although it does not specifically limit as a polyester plasticizer, For example, an aromatic terminal ester plasticizer represented by the following general formula (D) can be used.

General formula (D)

B-(G-A)n-G-B

In the general formula (D), B is a benzene monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms , A represents an alkylenedicarboxylic acid residue having 4 to 12 carbon atoms or an aryldicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.

The compound represented by the general formula (D) is a benzene monocarboxylic acid residue represented by B and an alkylene glycol residue or an oxyalkylene glycol residue or an aryl glycol residue represented by G, and an alkylenedicarboxyl represented by A. It is composed of an acid residue or an aryldicarboxylic acid residue, and is obtained by the same reaction as a conventional polyester plasticizer.

As the benzene monocarboxylic acid component of the polyester plasticizer, for example, benzoic acid, paratertiary butylbenzoic acid, orthotoluic acid, metatoluic acid, paratoluic acid, dimethylbenzoic acid, ethylbenzoic acid, normal propylbenzoic acid, aminobenzoic acid, ace Oxybenzoic acid and the like, and these can be used as one type or a mixture of two or more types, respectively.

Examples of alkylene glycol components having 2 to 12 carbon atoms in the polyester plasticizer include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, and 1,2-propane. Diol, 2-methyl1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2-diethyl- 1,3-propanediol (3,3-dimethylol pentane), 2-n-butyl-2-ethyl-1, 3 propanediol (3,3-dimethylolheptane), 3-methyl-1,5-pentane Diol 1,6-hexanediol, 2,2,4-trimethyl 1,3-pentanediol, 2-ethyl 1,3-hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1 ,10-decanediol, 1,12-octadecanediol, and the like, and these glycols are used as one or a mixture of two or more. In particular, alkylene glycols having 2 to 12 carbon atoms are particularly preferred because they have excellent compatibility with cellulose esters.

In addition, examples of the oxyalkylene glycol component having 4 to 12 carbon atoms of the aromatic terminal ester include, for example, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol, and these glycols are one type. Alternatively, it may be used as a mixture of two or more.

Examples of the alkylenedicarboxylic acid component having 4 to 12 carbon atoms of the aromatic terminal ester include succinic acid, maleic acid, fumaric acid, glutal acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and the like, Each of these is used as one or a mixture of two or more. Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5 naphthalenedicarboxylic acid, and 1,4 naphthalenedicarboxylic acid.

The polyester plasticizer preferably has a number average molecular weight in the range of 300 to 1500, more preferably 400 to 1000. Further, the acid value thereof is 0.5 mgKOH/g or less, the hydroxy value is 25 mgKOH/g or less, more preferably the acid value is 0.3 mgKOH/g or less, and the hydroxy value is 15 mgKOH/g or less.

Hereinafter, the synthesis example of the aromatic terminal ester plasticizer which can be used in this embodiment is shown.

<Sample No. 1 (aromatic terminal ester sample)>

410 parts of phthalic acid, 610 parts of benzoic acid, 737 parts of dipropylene glycol, and 0.40 parts of tetraisopropyl titanate as a catalyst were collectively added to the reaction vessel, and the excess monohydric alcohol was refluxed using a reflux condenser under stirring in a nitrogen stream. , Heating was continued at 130 to 250° C. until the acid value became 2 or less, and the water produced was continuously removed. ^{Subsequently, the effluent was removed under reduced pressure of 1.33×10 4} Pa to finally 4×10 ² Pa or less at 200 to 230°C, and then filtered to obtain an aromatic terminal ester plasticizer having the following properties.

Viscosity (25° C., mPa·s); 43400

Acid value; 0.2

<Sample No. 2 (aromatic terminal ester sample)>

In the reaction vessel, except for using 410 parts of phthalic acid, 610 parts of benzoic acid, 341 parts of ethylene glycol, and 0.35 parts of tetraisopropyl titanate as a catalyst, Sample No. In exactly the same manner as in 1, an aromatic terminal ester having the following properties was obtained.

Viscosity (25° C., mPa·s); 31000

Acid value; 0.1

<Sample No. 3 (aromatic terminal ester sample)>

In the reaction vessel, except for using 410 parts of phthalic acid, 610 parts of benzoic acid, 418 parts of 1,2-propanediol, and 0.35 parts of tetraisopropyl titanate as a catalyst, Sample No. In exactly the same manner as in 1, an aromatic terminal ester having the following properties was obtained.

Viscosity (25° C., mPa·s); 38000

Acid value; 0.05

<Sample No. 4 (aromatic terminal ester sample)>

In the reaction vessel, except for using 410 parts of phthalic acid, 610 parts of benzoic acid, 418 parts of 1,3-propanediol, and 0.35 parts of tetraisopropyl titanate as a catalyst, Sample No. In exactly the same manner as in 1, an aromatic terminal ester having the following properties was obtained.

Viscosity (25° C., mPa·s); 37000

Acid value; 0.05

Below, although the specific compound of the aromatic terminal ester plasticizer which can be used in this embodiment is shown, this invention is not limited to this.

<Ultraviolet absorber>

It is preferable that the 2nd protective film contains an ultraviolet absorber which has an ultraviolet absorption function. The ultraviolet absorber is the most effective means for making the light transmittance at 380 nm less than 50%. The ultraviolet absorber is preferably contained in at least any layer of the second protective film which is a laminated film, but it is preferably contained in both the core layer and the two skin layers.

The ultraviolet absorber can improve durability by absorbing ultraviolet rays of 400 nm or less, and prevent deterioration of the liquid crystal cell due to ultraviolet rays. In particular, the transmittance at a wavelength of 380 nm is preferably 25% or less, more preferably 10% or less, and still more preferably 5% or less.

Although the ultraviolet absorber to be used is not particularly limited, for example, an oxybenzophenone compound, a benzotriazole compound, a salicylic acid ester compound, a benzophenone compound, a cyanoacrylate compound, a triazine compound, a nickel complex salt compound, Inorganic powder, etc. are mentioned.

As an ultraviolet absorber applicable to this embodiment, for example, 5-chloro-2-(3,5-di-sec-butyl-2-hydroxylphenyl)-2H-benzotriazole, (2-2H-benzotria Zol-2-yl)-6-(straight and branched dodecyl)-4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, etc., and Tinuvin 109 , Tinuvin 171, Tinuvin 234, Tinuvin 326, Tinuvin 327, Tinuvin 328, Tinuvin 928 and the like, and these are all commercially available products manufactured by BASF Japan, and can be preferably used.

Ultraviolet absorbers used more preferably are benzotriazole-based compounds, benzophenone-based compounds, and triazine-based compounds, particularly preferably benzotriazole-based compounds and benzophenone-based compounds.

For example, as the benzotriazole-based compound, a compound represented by the following general formula (b) can be used.

In the general formula (b), R ₁ , R ₂ , R ₃ , R ₄ and R ₅ may be the same or different, and hydrogen atom, halogen atom, nitro group, hydroxy group, alkyl group, alkenyl group, aryl group, alkoxy Group, acyloxy group, aryloxy group, alkylthio group, arylthio group, mono or dialkylamino group, acylamino group or 5 to 6 membered heterocyclic group, and R ₄ and R ₅ are ring-closed and 5 to 6 membered You may form a carbocyclic ring. In addition, these groups described above may have arbitrary substituents.

Below, although the specific example of a benzotriazole type compound is given, this invention is not limited to these.

UV-1: 2-(2'hydroxy-5'-methylphenyl)benzotriazole

UV-2: 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)benzotriazole

UV-3: 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)benzotriazole

UV-4: 2-(2'-hydroxy-3',5'di-tert-butylphenyl)-5-chlorobenzotriazole

UV-5: 2-(2'-hydroxy-3'-(3",4",5",6"-tetrahydrophthalimidomethyl)-5'-methylphenyl)benzotriazole

UV-6: 2,2-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol)

UV-7: 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole

UV-8: 2-(2H-benzotriazol-2-yl)-6-(straight and branched dodecyl)-4-methylphenol (TINUVIN171)

UV-9: octyl-3-[3-tert-butyl-4-hydroxy-5-(chloro-2H-benzotriazol-2-yl)phenyl]propionate and 2-ethylhexyl-3-[3 mixture of -tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl]propionate (TINUVIN109)

In addition, as the benzophenone-based compound, a compound represented by the following general formula (c) is preferably used.

In the general formula (c), Y represents a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, an alkoxy group or a phenyl group, and these alkyl, alkenyl and phenyl groups may have a substituent. A represents a hydrogen atom, an alkyl group, an alkenyl group, a phenyl group, a cycloalkyl group, an alkylcarbonyl group, an alkylsulfonyl group or a -CO(NH) _{n -1} -D group, and D represents an alkyl group, an alkenyl group, or a phenyl group which may have a substituent. . m and n represent 1 or 2.

In the above, the alkyl group represents, for example, a linear or branched aliphatic group having up to 24 carbon atoms, the alkoxy group represents, for example, an alkoxy group having up to 18 carbon atoms, and the alkenyl group is, for example, an alkenyl group having up to 16 carbon atoms. And represents an allyl group, a 2-butenyl group, and the like. In addition, as a substituent for an alkyl group, an alkenyl group, and a phenyl group, a halogen atom, for example, a chlorine atom, a bromine atom, a fluorine atom, etc., a hydroxy group, a phenyl group (an alkyl group or a halogen atom may be substituted for this phenyl group), and the like. have.

Specific examples of the benzophenone compound represented by the general formula (c) are shown below, but the present invention is not limited thereto.

UV-10: 2,4-dihydroxybenzophenone

UV-11: 2,2'-dihydroxy-4-methoxybenzophenone

UV-12: 2-hydroxy-4-methoxy-5-sulfobenzophenone

UV-13: bis(2-methoxy-4-hydroxy-5-benzoylphenylmethane)

In addition, discoid compounds (triazine-based compounds), such as a compound having a 1,3,5 triazine ring, are also preferably used as an ultraviolet absorber.

In this embodiment, as an ultraviolet absorber, especially "2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3) shown below. ,3-tetramethylbutyl)phenol" is preferably used since it not only makes the ultraviolet absorption property of the 2nd protective film and low retardation compatible, but also can provide a thin film.

The 2nd protective film of this embodiment may contain 2 or more types of ultraviolet absorbers.

Further, as the ultraviolet absorber, a polymer ultraviolet absorber can also be preferably used, and in particular, the polymer type ultraviolet absorber described in Japanese Patent Application Laid-Open No. Hei 6-148430 is preferably used.

The ultraviolet absorber is added to the dope after dissolving the ultraviolet absorber in an alcohol such as methanol, ethanol, butanol, a solvent such as methylene chloride, methyl acetate, acetone, or dioxolane, or a mixed solvent thereof, or direct dope composition. You may add it in. What is not dissolved in an organic solvent like inorganic powder is added to the dope after dispersing it in an organic solvent and a cellulose ester using a dissolver or a sand mill.

The amount of the ultraviolet absorber used is not uniform depending on the type of the ultraviolet absorber, the conditions of use, etc., but when the dry film thickness of the second protective film is 10 to 100 µm, 0.5 to 10 mass% relative to the second protective film is preferable. And 0.6 to 4% by mass is more preferable.

(Production method of the second protective film)

The second protective film of this embodiment is for forming a core layer containing a cellulose ester resin, a dope for forming a first skin layer containing a cellulose ester resin, and a second skin layer containing a cellulose ester resin It can form a film by making all dope cast on a support body. In this case, the three kinds of dope may be simultaneously or sequentially multilayered on the support. In the present embodiment, the covalently rolled dope is dried to form a film, the film is peeled from the support, and the film after the peeling may be stretched.

<Preparation of Dope>

In this embodiment, the 2nd protective film can be manufactured using the solution (dope) which melt|dissolved cellulose acylate in an organic solvent by the solution casting film forming method.

The organic solvent preferably contains a solvent selected from an ether having 3 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms, an ester having 3 to 12 carbon atoms, and a halogenated hydrocarbon having 1 to 6 carbon atoms . Ether, ketone, and ester may have a cyclic structure. A compound having two or more of the functional groups of ethers, ketones and esters (ie, -O-, -CO- and -COO-) can also be used as an organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having a certain functional group.

Examples of ethers having 3 to 12 carbon atoms include diisopropyl ether, dimethoxy methane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetol do.

Examples of the ketone having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone.

Examples of esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate.

Examples of the organic solvent having two or more types of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol, and 2-butoxyethanol.

The number of carbon atoms in the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. It is preferable that the halogen of the halogenated hydrocarbon is chlorine. The ratio of the hydrogen atom of the halogenated hydrocarbon substituted with the halogen is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, still more preferably 35 to 65 mol%, and 40 to 60 mol% It is most preferred. Methylene chloride is a representative halogenated hydrocarbon.

You may mix and use two or more types of organic solvents.

The preparation of the solution can be carried out using a method and apparatus for preparing dope in an ordinary solution film forming method. Further, in the case of a general method, it is preferable to use a halogenated hydrocarbon (especially methylene chloride) as the organic solvent.

It is preferable to adjust the amount of cellulose acylate so that it may contain 10-40 mass% in the solution obtained, and it is more preferable that it is 10-30 mass %. In the organic solvent, you may add arbitrary additives.

The solution can be prepared by stirring the cellulose acylate and an organic solvent at room temperature (0 to 40°C). The high concentration solution may be stirred under pressure and heating conditions. Specifically, the cellulose acylate and the organic solvent are put in a pressurized container, sealed, and stirred under pressure while heating at a temperature above the boiling point of the solvent at room temperature and within a range at which the solvent does not boil. The heating temperature is usually 40°C or higher, preferably 60 to 200°C, and more preferably 80 to 110°C.

Each component may be roughly mixed in advance and then put into a container, or may be sequentially introduced into the container. The container needs to be configured to be able to stir. The container can be pressurized by injecting an inert gas such as nitrogen gas. Further, an increase in the vapor pressure of the solvent by heating may be used. Alternatively, after sealing the container, each component may be added under pressure.

In the case of heating, it is preferable to heat from the outside of the container. For example, a jacket type heating device can be used. Further, a plate heater is provided outside the container, and the entire container can be heated by piping to circulate the liquid.

It is preferable to provide a stirring blade inside the container, and to stir using this. It is preferable that the stirring blade has a length reaching the vicinity of the wall of the container. It is preferable to provide scraping blades at the ends of the stirring blades in order to renew the liquid film on the container wall.

Instruments, such as a pressure gauge and a thermometer, may be installed in the container. Each component is dissolved in a solvent in a container. The prepared dope may be taken out from the container after cooling, or may be taken out and then cooled using a heat exchanger or the like.

<Shared performance>

From the prepared cellulose acylate solution (dope), a cellulose acylate film can be produced by a solution film forming method.

The dope is cast on a drum or band and the solvent is evaporated to form a film. It is preferable to adjust the concentration of the dope before casting so that the solid content is 10 to 40% by mass. It is preferable to finish the surface of the drum or band in a mirror-finished state. As for the casting and drying method in the solution casting film forming method, U.S. Patent No.2336310, U.S. Patent No.2367603, U.S. Patent No. 2492078, U.S. Patent No.2492977, U.S. Patent No.2492978, U.S. Patent No.2607704, U.S. Patent No.2739069, U.S. Patent No.2739070, British Patent No.640731, British Patent No.736892, Japanese Patent No.45-4554, Japanese Patent No.49-5614 Japanese Patent Application Laid-Open No. 60-176834, Japanese Patent Laid-Open No. 60-203430, and Japanese Patent Laid-Open No. 62-115035 have descriptions.

In this embodiment, the obtained cellulose acylate solution (dope) can be cast and formed on a smooth band or drum as a support. In the production of the second protective film, a known covalent rolling method can be used. For example, a film may be produced by flexing and laminating a cellulose acylate solution from a plurality of studies arranged at intervals in the traveling direction of the metal support, respectively. For example, Japanese Unexamined Patent Publication No. 61-158414, Japanese Patent The method described in Unexamined Publication No. Hei1-122419, Japanese Unexamined Patent Publication No. 11-198285, and the like can be used. Further, a film may be formed by casting a cellulose acylate solution from two research studies. For example, Japanese Patent Publication No. 60-27562, Japanese Patent Publication No. 61-94724, and Japanese Patent Publication No. 61-947245 , Japanese Patent Application Laid-Open No. 61-104813, Japanese Patent Laid-Open No. 61-158413, and Japanese Patent Laid-Open No. 6-134933. In addition, the flow of the high viscosity cellulose acylate solution described in Japanese Patent Laid-Open No. 56-162617 is wrapped with a low viscosity cellulose acylate solution, and the high viscosity and low viscosity cellulose acylate solution are simultaneously extruded. It may be a method. In addition, it is also preferable that the outer solution described in JP 61-94724 A and JP 61-94725 A contains more alcohol components which are poor solvents than the inner solution.

In addition, a film can also be produced by peeling the film molded on the metal support body by using two flow studies and performing second casting on the side in contact with the metal support surface (for example, Japanese Patent Publication No. 44-20235).

In this embodiment, a cellulose acylate solution can be co-rolled to produce a cellulose acylate film of a skin layer/core layer/skin layer. In addition, the covalently rolled dope can be dried and peeled off from the support as a film.

<Drying process>

A method of drying the peeled film after being dried on a drum or belt will be described. The film peeled off at the peeling position immediately before the drum or belt is conveyed by passing alternately through a group of rolls arranged in a zigzag shape, or a method of non-contact conveying by holding both ends of the peeled film with a clip or the like It is conveyed by etc. Drying can be performed by a method of blowing air of a predetermined temperature on both sides of the film during transport, or a method of using a heating means such as a microwave. Rapid drying may damage the flatness of the film to be formed, and in the initial stage of drying, it is preferable to dry at a temperature such that the solvent does not foam, and to dry at a high temperature after drying proceeds.

In the drying step after peeling from the support, the film attempts to shrink in the longitudinal direction or the width direction due to evaporation of the solvent. The shrinkage increases with drying at high temperatures. Drying while suppressing this shrinkage as much as possible is preferable because the flatness of the film is improved. In this respect, for example, as disclosed in Japanese Patent Laid-Open Publication No. 62-46625, a method in which the entire process or part of the drying process is performed while holding the width of both ends of the web with clips or pins in the width direction (tenter Mode) is preferred. It is preferable that the drying temperature in the said drying process is 100-145 degreeC. Although the drying temperature, the amount of drying air, and the drying time are different depending on the solvent to be used, it may be appropriately selected according to the type and combination of the solvent to be used.

<stretching>

In this embodiment, after the dope which has been covalently rolled is dried and peeled from the support, the film can be stretched.

In the present embodiment, stretching may be carried out in either direction of the film conveyance direction (hereinafter, also referred to as the film MD direction) and the direction orthogonal to the film conveyance direction (hereinafter, also referred to as the film TD direction), but at least stretching in the film TD direction , From the viewpoint of expressing a desired retardation. Further, biaxial stretching in combination with stretching in a direction not coincident with the film TD direction (for example, the film MD direction) may be used. In addition, stretching may be performed in one stage or in multiple stages.

When performing biaxial stretching, it is preferable to stretch in the film TD direction (transport direction and a perpendicular direction) after extending|stretching in the film MD direction (transport direction). When extending|stretching, a residual solvent may be contained, and you may extend|stretch in the state which does not contain a residual solvent. In the case of containing a residual solvent, it is preferable that the amount of the solvent is stretched between 0.1% by weight and 50% by weight based on the weight of the solid content of the film.

The draw ratios in the biaxial directions orthogonal to each other are preferably in the range of 1.0 to 2.0 times in the film MD direction and 1.01 to 2.5 times in the film TD direction, respectively, and 1.01 to 1.5 times in the film MD direction, the film It is preferably in the range of 1.05 to 2.0 times in the MD direction. By performing such stretching, the expression property of retardation Ro·Rt is adjusted, and the zero retardation film of the present embodiment can be realized.

The film surface temperature at the start of stretching is preferably 100°C or more and 220°C or less, and more preferably 120°C or more and 200°C or less.

In addition, in this embodiment, as a method of extending|stretching in the film TD direction, it is preferable to extend|stretch using a tenter device.

When stretching in the film TD direction, the residual solvent amount of the film at the time of starting of stretching is preferably 0% by mass or more and 3% by mass or less, more preferably 0% by mass or more and 2.3% by mass or less, and 0% by mass or more and 2.1% by mass It is more preferable that it is the following. In addition, the amount of residual solvent is represented by the following formula.

Residual solvent amount (mass%) = {(M-N)/N}×100

Here, M is the mass of the film (web) at an arbitrary point in time, and N is the mass of the film measured for M when dried at 110°C for 3 hours.

The film elastic modulus at the time of stretching in the film TD direction is preferably 100 MPa or more and 1500 MPa or less, more preferably 100 MPa or more and 1000 MPa or less, still more preferably 100 MPa or more and 500 MPa or less, and particularly preferably 100 MPa or more and 300 MPa or less. .

The film elastic modulus was cut from the center of the film 15 seconds before stretching to be 10 mm in the film MD direction and 130 mm in the film TD direction, and using a Tensilon universal testing machine RTF series (manufactured by Orientech), the distance between the chuck was 100 mm, and the tensile speed. It can measure by performing a tensile test at 100 mm%/min.

[First protective film]

Next, the 1st protective film of a polarizing plate on a viewer side is demonstrated. In addition, the structure of the 1st protective film shown below is applicable also to the 4th protective film of the polarizing plate on the backlight side.

The first protective film may be composed of an acrylic film, or may be composed of a polyester film containing a polyester resin (eg PET resin). Acrylic resins and polyester resins have low moisture permeability and can be suitably used as resins constituting the first protective film from the viewpoint of suppressing the moisture content of the film. Incidentally, the moisture permeability of acrylic is, for example, 200 g/m ² ·day in the case of a thickness of 40 µm, and the moisture permeability of PET resin is, for example, 20 g/m ² ·day in the case of 80 µm in thickness. In addition, the measurement conditions of the moisture permeability are 40 degreeC and 90%RH.

(Polyester film)

The 1st protective film may be a polyester film which has super birefringence in a plane and has a light transmittance of 50% or more at a wavelength of 380 nm. Here, the in-plane superbirefringence means that the retardation Ro in the in-plane direction is 8000 nm or more. The light transmittance at a wavelength of 380 nm in the first protective film is preferably 60 to 95%, more preferably 70 to 95%, and even more preferably 80 to 95%.

In the first protective film, as a method of making the light transmittance at a wavelength of 380 nm 50% or more, it is effective not to add an additive that absorbs light near a wavelength of 380 nm to the first protective film, and particularly absorbs ultraviolet rays. It is preferable not to add an ultraviolet absorber.

The polyester film of this embodiment is a stretched polyester film, and it is preferable that it is 8000 nm, and it is more preferable that it is 10000 nm, from the viewpoint of expressing super birefringence, as for the lower limit of the retardation Ro. On the other hand, the upper limit of the retardation Ro of the stretched polyester film is, even if a film having a retardation Ro higher than that is used, the effect of improving the visibility further is not substantially obtained. Since the thickness also tends to increase, it is preferable to set it to 30000 nm from the viewpoint that it may be contrary to the request for thinning, and from the viewpoint of deteriorating the handling properties as an industrial material.

Moreover, when an ultraviolet absorber is contained in a polyester film, birefringence will fall. In order to maintain the super birefringence, it is necessary to increase the draw ratio when producing the polyester film, to adjust the draw temperature, and the like. However, applying these means increases haze and lowers the contrast of the display device. In addition, there is also a means of increasing the birefringence value by increasing the film thickness of the polyester film, but weight and thickness increase while weight reduction and thin film reduction are required as the display device becomes larger. In addition, when the polyester film becomes thick, it may be a cause of manufacturing troubles or failures due to a decrease in handling properties when manufacturing a polarizing plate or a display device. In this embodiment, since the ultraviolet absorber is not added to the first protective film (polyester film), the above problem does not occur.

In the stretched polyester film, the value of the ratio (Ro/Rt) of the retardation Ro in the in-plane direction and the retardation value Rt in the thickness direction is preferably 0.2 or more, more preferably 0.5 or more, further preferably It is more than 0.6.

The maximum value of Ro/Rt is 2.0 (that is, a completely uniaxially symmetric film), but as the film approaches a completely uniaxially symmetrical film, the mechanical strength in a direction orthogonal to the orientation direction tends to decrease. Therefore, the upper limit of Ro/Rt of the polyester film is preferably 1.2 or less, and more preferably 1.0 or less.

Polyester, which is a raw material resin for a stretched polyester film, has excellent transparency, excellent thermal and mechanical properties, and can easily control retardation by stretching. Among polyester, polyethylene terephthalate or polyethylene naphthalate is preferable. Polyester typified by polyethylene terephthalate and polyethylene naphthalate is preferable because it has a large intrinsic birefringence and relatively easily obtains a large retardation even if the film has a thin thickness. In particular, polyethylene naphthalate is suitable for particularly high retardation or thin film thickness while maintaining high retardation, since it has a large intrinsic birefringence among polyesters.

(Method for producing stretched polyester film)

Below, the outline of the manufacturing method of a stretched polyester film is demonstrated.

The polyester film can be obtained by condensing an arbitrary dicarboxylic acid and a diol. As dicarboxylic acid, for example, terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5 -Naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3- Cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2, 2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecadicarboxylic acid, and the like.

Examples of the diol include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1 ,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, and the like.

As a dicarboxylic acid component and a diol component which comprise a polyester film, you may use 1 type or 2 or more types, respectively. Specific polyester resins constituting the polyester film include, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and the like, preferably polyethylene terephthalate (PET) and polyethylene. Naphthalate (PEN), more preferably polyethylene terephthalate (PET). The polyester resin may contain other copolymerization components as necessary, and in terms of mechanical strength, the proportion of the copolymerization component is preferably 3 mol% or less, preferably 2 mol% or less, more preferably 1.5 mol% or less. to be. These resins have excellent transparency and excellent thermal and mechanical properties. In addition, these resins can easily control retardation by stretching.

The polyester film can be obtained according to a general manufacturing method. Specifically, the polyester resin is melted, and the non-oriented polyester extruded into a sheet is stretched in the longitudinal direction using the difference in speed of the roll at a temperature equal to or higher than the glass transition temperature, and then in the transverse direction by a tenter. The melt casting method etc. which produce a stretched polyester film by extending|stretching, performing heat treatment, and relaxation treatment as needed are mentioned. The stretched polyester film may be a uniaxially stretched film or a biaxially stretched film.

Production conditions for obtaining a polyester film can be appropriately set according to a known method. For example, the longitudinal stretching temperature and the transverse stretching temperature are usually 80 to 130°C, and preferably 90 to 120°C. The vertical draw ratio is usually 1.0 to 3.5 times, preferably 1.0 to 3.0 times. In addition, the transverse draw ratio is usually 2.5 to 6.0 times, and preferably 3.0 to 5.5 times.

Controlling the retardation in a specific range can be performed by appropriately setting the draw ratio, the draw temperature, and the thickness of the film. For example, the higher the difference in draw ratio between vertical stretching and transverse stretching, the lower the stretching temperature, and the thicker the film, the easier it is to obtain a high retardation. Conversely, the lower the difference in the draw ratio between the longitudinal stretching and the transverse stretching, the higher the stretching temperature, and the thinner the film thickness, the easier it is to obtain a lower retardation. Further, the higher the stretching temperature and the lower the total stretching ratio, the easier it is to obtain a film with a low ratio (Ro/Rt) between the retardation value and the retardation value in the thickness direction. Conversely, the lower the stretching temperature and the higher the total stretching ratio, the higher the ratio of the retardation value and the thickness direction retardation value (Ro/Rt) is obtained. In addition, the heat treatment temperature is usually preferably in the range of 140 to 240°C, and more preferably in the range of 170 to 240°C.

The temperature of the relaxation treatment is usually in the range of 100 to 230°C, more preferably in the range of 110 to 210°C, and even more preferably in the range of 120 to 180°C. In addition, the amount of relaxation is usually in the range of 0.1 to 20%, preferably in the range of 1 to 10%, and more preferably in the range of 2 to 5%. It is preferable that the temperature and the amount of relaxation of this relaxation treatment are set such that the heat shrinkage rate at 150°C of the polyester film after the relaxation treatment is 2% or less.

In addition, in the uniaxial stretching and biaxial stretching treatment, after lateral stretching, in order to alleviate the deformation of the orientation principal axis typified by Boeing, a heat treatment may be performed again or an stretching treatment may be performed. The maximum value of the deformation of the orientation main axis by the bowing with respect to the stretching direction is preferably within 30°, more preferably within 15°, and even more preferably within 8°. When the maximum value of the deformation of the orientation main axis exceeds 30°, when a polarizing plate is formed in a subsequent step and sheet flies, non-uniformity in optical properties may occur between the sheet flies. Here, the orientation main axis means the molecular orientation direction in an arbitrary point on a stretched polyester film. In addition, the deformation|transformation of an orientation principal axis with respect to the extending|stretching direction means the angle difference between an orientation principal axis and a stretching direction. In addition, the maximum value means the maximum value of the value in the direction perpendicular to the long direction. The orientation main axis can be measured using, for example, a retardation film/optical material inspection device RETS (manufactured by Otsuka Electric Corporation) or a molecular alignment meter MOA (manufactured by Oji Keisoku Co., Ltd.).

In order to suppress the fluctuation of retardation in a polyester film, it is preferable that the thickness nonuniformity of a film is small. If the vertical draw ratio is lowered in order to produce a retardation difference, the value of the vertical thickness non-uniformity (hereinafter, also referred to as "thickness non-uniformity") may increase. Since there is a region where the value of the vertical thickness non-uniformity is very high in a certain range of the draw ratio, it is preferable to set the film forming conditions outside such a range.

The thickness unevenness of the stretched polyester film is preferably 5.0% or less, more preferably 4.5% or less, still more preferably 4.0% or less, and particularly preferably 3.0% or less. The thickness non-uniformity of a film can be measured by arbitrary means. For example, a continuous tape-like sample (length 3 m) in the film conveyance direction was taken, and a commercially available measuring instrument, for example, ``Electronic Micrometer Millitron 1240'' manufactured by Seiko EM Co., Ltd., was used, The thickness of 100 points is measured at 1 cm pitch, the maximum value (dmax), the minimum value (dmin), and the average value (d) of the thickness are obtained, and the thickness non-uniformity (%) can be calculated by the following equation.

Thickness unevenness (%)=((dmax-dmin)/d)×100

The thickness of the stretched polyester film is arbitrary, for example, it can be appropriately set in the range of 15 to 300 µm, preferably in the range of 30 to 200 µm, particularly in the range of 60 to 80 µm, thinning and good visibility It is preferable from the viewpoint of making it compatible.

You may have various functional layers on at least one surface in a stretched polyester film. As such a functional layer, for example, a hard coating layer (also referred to as an ultraviolet curing resin layer), an antiglare layer, an antireflection layer, a low reflective layer, a low reflective antiglare layer, an antireflective antiglare layer, an antistatic layer, a silicone layer, an adhesive layer, an antifouling layer, At least one selected from the group consisting of a fingerprint layer, a water repellent layer, and a blue cut layer may be used. In this embodiment, it is preferable to set it as the structure which has an ultraviolet curable resin layer on the visible side of the stretched polyester film which is a 1st protective film. In addition, by providing an anti-glare layer, an anti-reflection layer, a low-reflection layer, a low-reflection anti-glare layer, and an anti-reflection anti-glare layer, an effect of further improving color unevenness when observed from an oblique direction can also be expected.

When providing various functional layers, it is preferable to provide an easy-adhesion layer on the surface of a stretched polyester film. At that time, from the viewpoint of suppressing interference due to reflected light, it is preferable to adjust the refractive index of the easily bonding layer to be near a rising average of the refractive index of the functional layer and the refractive index of the alignment film. The adjustment of the refractive index of the easy-to-adhesion layer can employ a known method, and can be easily adjusted by, for example, containing titanium, zirconium, or other metal species in the binder resin. The coating liquid used for formation of the easily bonding layer is preferably an aqueous coating liquid containing at least one of a water-soluble or water-dispersible copolymer polyester resin, an acrylic resin, and a polyurethane resin. As these coating liquids, for example, Japanese Patent Publication No. Hei 6-81714, Japanese Patent No. 3200929, Japanese Patent No. 3632044, Japanese Patent No. 4547644, Japanese Patent No. 4770971, Japanese Patent No. 3567927 A water-soluble or water-dispersible copolymerized polyester resin solution, acrylic resin solution, polyurethane resin solution disclosed in Japanese Patent Publication No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, Japanese Patent No. 4150982, etc. And the like.

(Acrylic film)

The 1st protective film of this embodiment may be a film (acrylic film) containing an acrylic resin. A methacrylic resin is also contained in an acrylic resin. The acrylic film can be produced by, for example, a solution casting film forming method similarly to a cellulose ester film.

As the (meth)acrylic resin, Tg (glass transition temperature) is preferably 115°C or higher, more preferably 120°C or higher, still more preferably 125°C or higher, and particularly preferably 130°C or higher. When Tg is 115°C or higher, the durability of the film is improved. The upper limit of the Tg of the (meth)acrylic resin is not particularly limited, but from the viewpoint of moldability and the like, it is preferably 170°C or less.

As the (meth)acrylic resin, any suitable (meth)acrylic resin can be employed within a range that does not impair the effects of the present embodiment. For example, poly(meth)acrylic acid esters such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymerization, methyl methacrylate-(meth)acrylic acid ester copolymer, methyl methacrylate-acrylic acid ester- (Meth)acrylic acid copolymer, methyl (meth)acrylate-styrene copolymer (MS resin, etc.), polymers having an alicyclic hydrocarbon group (e.g., methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate) -(Meth)acrylate norbornyl copolymer, etc.) are mentioned. Preferably, poly(meth)acrylate C1-6 alkyl such as poly(meth)acrylate is used. More preferably, a methyl methacrylate-based resin containing methyl methacrylate as the main component (50 to 100% by mass, preferably in the range of 70 to 100% by mass) is used.

As a specific example of a (meth)acrylic resin, for example, Acripet VH, Acripet VRL20A, Dianal BR52, BR80, BR83, BR85, BR88 (manufactured by Mitsubishi Rayon Co., Ltd.), KT75 (Denki Chemical Co., Ltd.) (Note)), Delpet 60N, 80N (manufactured by Asahi Kasei Chemicals Co., Ltd.), (meth)acrylic resin having an intramolecular ring structure described in Japanese Patent Laid-Open No. 2004-70296, intramolecular crosslinking or intramolecular cyclization The high Tg (meth)acrylic resin system obtained by reaction is mentioned.

As the (meth)acrylic resin, it is also preferable to use a (meth)acrylic resin having a lactone ring structure. As (meth)acrylic resins having a lactone ring structure, Japanese Patent Laid-Open No. 2000-230016, Japanese Patent Laid-Open No. 2001-51814, Japanese Patent Laid-Open No. 2002-120326, and Japanese Patent Laid-Open No. 2002-254544 Those described in Gazette, Japanese Patent Laid-Open No. 2005-146084, and the like are mentioned.

Further, as the (meth)acrylic resin, an acrylic resin having a structural unit of an unsaturated carboxylic acid alkyl ester and a structural unit of a glutaric anhydride can be used. As the acrylic resin, Japanese Patent Application Laid-Open No. 2004-70290, Japanese Patent Laid-Open No. 2004-70296, Japanese Patent Laid-Open No. 2004-163924, Japanese Patent Laid-Open No. 2004-292812, Japanese Patent Laid-Open No. 2005 -314534, JP 2006-131898, JP 2006-206881, JP 2006-265532, JP 2006-283013, JP 2006 Those described in Japanese Patent Application Laid-Open No. -299005 and Japanese Patent Application Laid-Open No. 2006-335902, etc. are mentioned.

Further, as the (meth)acrylic resin, a thermoplastic resin having a glutarimide unit, a (meth)acrylic acid ester unit, and an aromatic vinyl unit can be used. As the said thermoplastic resin, JP 2006-309033 A, JP 2006-317560 A, JP 2006-328329 A, JP 2006-328334 A, JP 2006 -337491, JP 2006-337492 A, JP 2006-337493 A, JP 2006-337569 A, etc. are mentioned.

(Ultraviolet ray curing resin layer)

In this embodiment, it is preferable that the 1st protective film is a structure which has an ultraviolet-curable resin layer (hereafter also called a hard coating layer).

The hard coat layer is a layer for imparting hard coatability to the surface of the first protective film, and for example, a composition for forming a hard coat layer containing an ultraviolet curing resin and a photopolymerization initiator is used, and after formation of a coating film, irradiation of ultraviolet rays is performed. It is a layer formed by curing an ultraviolet-curable resin.

The ultraviolet curable resin applicable to the present embodiment is not particularly limited as long as it is a resin component having a property cured by ultraviolet rays, but as a representative resin material, it has one or two or more unsaturated bonds such as a compound having an acrylate-based functional group. And compounds. Examples of the compound having one unsaturated bond include ethyl (meth)acrylate, ethylhexyl (meth)acrylate, styrene, methylstyrene, and N-vinylpyrrolidone. As a compound having two or more unsaturated bonds, for example, polymethylolpropane tri(meth)acrylate, tripropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate )Acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, neo Pentyl glycol di (meth) acrylate, and the like, and polyfunctional compounds modified with ethylene oxide (EO) or the like, or reaction products such as the polyfunctional compound and (meth) acrylate (e.g., polyhydric alcohol (Meth)acrylate ester) etc. are mentioned. In addition, "(meth)acrylate" refers to a methacrylate and an acrylate.

In addition to the above compounds, polyester resins, polyether resins, acrylic resins, epoxy resins, urethane resins, alkyd resins, spiro resins of relatively low molecular weight (number average molecular weight 300 to 80,000, preferably 400 to 5000) having an unsaturated double bond An acetal resin, a polybutadiene resin, a polythiol polyene resin, and the like can also be used as the ultraviolet curable resin. In addition, the resin in this case includes all dimers, oligomers, and polymers other than monomers.

As a preferable compound in this embodiment, the compound which has 3 or more unsaturated bonds is mentioned. When such a compound is used, the crosslinking density of the hard coat layer to be formed can be increased, and the hardness of the coating film can be increased.

Specifically, pentaerythritol triacrylate, pentaerythritol tetraacrylate, polyester polyfunctional acrylate oligomer (3 to 15 functional), urethane polyfunctional acrylate oligomer (3 to 15 functional), etc. are appropriately used in combination. It is desirable.

The ultraviolet curable resin can also be used in combination with a solvent drying resin (a resin capable of forming a film by only drying a solvent added to adjust the solid content at the time of coating). By using a solvent-dried resin together, it is possible to effectively prevent a film defect on the coated surface. The solvent-dried resin that can be used in combination with the ultraviolet curing resin is not particularly limited, and a general thermoplastic resin can be used.

The photoinitiator is not particularly limited, and known ones can be used. For example, as the photoinitiator, acetophenones, benzophenones, Michler benzoyl benzoate, α-amyloxime ester, thioxanthones, propiophenones , Benzyls, benzoins, and acylphosphine oxides. Moreover, it is preferable to mix and use a photosensitizer, and specific examples thereof include n-butylamine, triethylamine, poly-n-butylphosphine, and the like.

As the photoinitiator, when the ultraviolet curing resin is a resin having a radically polymerizable unsaturated group, it is preferable to use acetophenones, benzophenones, thioxanthones, benzoin, benzoin methyl ether, etc. alone or in combination. . In addition, when the ultraviolet curing resin is a resin system having a cationic polymerizable functional group, as the photoinitiator, an aromatic diazonium salt, an aromatic sulfonium salt, an aromatic iodonium salt, a metallocene compound, a benzoin sulfonic acid ester, etc. may be used alone or as a mixture. It is preferable to use.

As a photoinitiator, in the case of an ultraviolet curing resin having a radically polymerizable unsaturated group, 1-hydroxy-cyclohexyl-phenyl-ketone (trade name: IRGACURE 184, manufactured by BASF Japan) is compatible with ultraviolet curing resins and yellowing. It is preferable because it is also small.

The content of the photoinitiator in the composition for forming a hard coat layer is preferably in the range of 1.0 to 10 parts by mass per 100 parts by mass of the ultraviolet curing resin. If the added amount is 1.0 parts by mass or more, the hardness of the hard coating layer can be set to a desired condition, and if it is 10 parts by mass or less, ionizing radiation reaches the deep part of the coated film, promoting internal hardening, and the desired surface of the hard coating layer. It is preferable from the point that pencil hardness can be obtained.

A more preferable lower limit of the content of the photopolymerization initiator is 2.0 parts by mass, and a more preferable upper limit is 8.0 parts by mass. When the content of the photopolymerization initiator is in this range, hardness distribution does not occur in the film thickness direction, and uniform hardness as a hard coating layer is easily achieved.

The composition for forming a hard coat layer may contain a solvent. As the solvent, it can be appropriately selected and used according to the kind and solubility of the ultraviolet curable resin component to be used. For example, as a solvent, ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, diacetone alcohol, etc.), ethers (e.g., dioxane, tetrahydrofuran, propylene glycol Monomethyl ether, propylene glycol monomethyl ether acetate, etc.), aliphatic hydrocarbons (eg, hexane, etc.), alicyclic hydrocarbons (eg, cyclohexane, etc.), aromatic hydrocarbons (eg, toluene, xylene, etc.) Etc.), halogenated carbons (e.g., dichloromethane, dichloroethane, etc.), esters (e.g., methyl acetate, ethyl acetate, butyl acetate, etc.), water, alcohols (e.g., ethanol, isopropanol, Butanol, cyclohexanol, etc.), cellosolves (e.g., methyl cellosolve, ethyl cellosolve, etc.), cellosolve acetates, sulfoxides (e.g., dimethyl sulfoxide, etc.), amides ( For example, dimethylformamide, dimethylacetamide, etc.) etc. can be illustrated, and a mixed solvent of these can also be used. In particular, it is preferable to include at least any of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, or a mixture thereof in a ketone solvent, because of its excellent compatibility with an ultraviolet curing resin and excellent coating properties.

In addition, the composition for forming a hard coating layer includes increasing the hardness of the hard coating layer, suppressing curing shrinkage, preventing blocking, controlling the refractive index, imparting anti-glare properties, or controlling the properties of particles or the surface of the hard coating layer. Depending on the purpose, conventionally known organic fine particles, inorganic fine particles, dispersants, surfactants, antistatic agents, silane coupling agents, thickeners, color inhibitors, colorants (pigments, dyes), antifoaming agents, leveling agents, flame retardants, adhesion imparting agents, polymerization prohibited Agents, antioxidants, surface modifiers, and the like may be added. Further, the composition for forming a hard coating layer may contain a photosensitizer, and specific examples thereof include n-butylamine, triethylamine, poly-n-butylphosphine, and the like.

The method for preparing the composition for forming the hard coat layer is not particularly limited, as long as the respective constituents can be uniformly mixed, and for example, each constituent component is prepared by using a known device such as a paint shaker, a bead mill, a kneader, or a mixer. It can be prepared by mixing or dissolving.

In addition, a method of applying the composition for forming a hard coating layer on the first protective film is not particularly limited, and for example, a spin coating method, an immersion method, a spray method, a die coating method, a bar coating method, a roll coater method, Well-known wet coating methods, such as a meniscus coater method, a flexo printing method, a screen printing method, and a feed coater method, are mentioned.

[Physical properties of the first protective film]

The retardation Ro in the in-plane direction of the first protective film may be 350 nm or less. Further, the retardation Rt in the thickness direction of the first protective film may be 350 nm or less. In this case, for example, a film containing an acrylic resin (including an acrylic-styrene polymer) can be used as the first protective film.

The retardation Ro in the in-plane direction of the first protective film may be 8000 nm or more. Further, the retardation Ro in the thickness direction of the first protective film may be 8000 nm or more. In this case, for example, a film containing a polyethylene terephthalate resin can be used as the first protective film.

It is preferable that the 1st protective film contains a polyethylene terephthalate resin or an acrylic resin. In this case, the first protective film having a moisture permeability of 200 g/m ² ·day or less can be reliably realized.

It is preferable that the thickness of the 1st protective film is 10 micrometers or more and 40 micrometers or less. The use of the thin first protective film can contribute to realization of a thin polarizing plate.

[Polarizer]

In the polarizing plate of this embodiment, the first protective film and the second protective film described above are bonded to both surfaces of a polarizer using an ultraviolet curable adhesive or a water-based adhesive. When the polarizing plate is used as a polarizing plate on the viewing side, it is preferable to provide an antiglare layer or a clear hard coating layer, an antireflection layer, an antistatic layer, an antifouling layer, and the like in the protective film for a polarizing plate.

(Polarizer)

The polarizer, which is the main constituent element of the polarizing plate, is an element that allows only light of a polarization surface in a predetermined direction to pass, and a representative polarizer currently known is a polyvinyl alcohol-based polarizing film. Polyvinyl alcohol-based polarizing films include those obtained by dyeing a polyvinyl alcohol-based film with iodine and dyeing a dichroic dye.

As a polarizer, a polyvinyl alcohol aqueous solution is formed into a film, and it is uniaxially stretched and dyed, or, after dyeing and then uniaxially stretched, a polarizer that is preferably subjected to durability treatment with a boron compound can be used. The film thickness of the polarizer is preferably 2 to 30 µm, and particularly preferably 2 to 15 µm.

In addition, ethylene-modified polyvinyl having a content of 1 to 4 mol%, a polymerization degree of 2000 to 4000, and a saponification degree of 99.0 to 99.99 mol%, as described in Japanese Patent Laid-Open No. 2003-248123, Japanese Patent Laid-Open No. 2003-342322, etc. Alcohol is also preferably used. Among them, an ethylene-modified polyvinyl alcohol film having a hot water cutting temperature of 66 to 73°C is preferably used. The polarizer using this ethylene-modified polyvinyl alcohol film is not only excellent in polarization performance and durability performance, but also has little color unevenness, and is particularly preferably used for a large-sized liquid crystal display device.

(Manufacture of polarizing plate)

The polarizing plate of this embodiment can be manufactured by a general method. Specifically, the side of the polarizer-facing surface of the first protective film is appropriately surface-treated, and bonded to one surface of a polarizer produced by immersion stretching in an iodine solution using an ultraviolet curable adhesive or a water-based adhesive described later. Then, the second protective film is bonded to the other surface of the polarizer.

As for the direction of bonding with a polarizer, it is preferable that the absorption axis of a polarizer and the slow axis of each protective film are orthogonally bonded, for example.

(UV curable adhesive)

In the polarizing plate of the present embodiment, it is preferable that the protective film and the polarizer are adhered by an ultraviolet curable adhesive. By applying an ultraviolet curable adhesive to the bonding of the protective film and the polarizer, even a thin film can obtain a polarizing plate having high strength and excellent planarity.

<Composition of UV-curable adhesive>

As an ultraviolet-curable adhesive composition for a polarizing plate, a photo-radical polymerization-type composition using photo-radical polymerization, a photo-cationic polymerization-type composition using photo-cationic polymerization, and a hybrid composition in which photo-radical polymerization and photo-cationic polymerization are used in combination are known.

Examples of the photo-radical polymerizable composition include a radical polymerizable compound containing a polar group such as a hydroxy group or a carboxyl group described in Japanese Patent Laid-Open No. 2008-009329 and a composition containing a radical polymerizable compound not containing a polar group in a specific ratio. Is known. In particular, the radical polymerizable compound is preferably a compound having an ethylenically unsaturated bond capable of radical polymerization. Preferred examples of the compound having an ethylenically unsaturated bond capable of radical polymerization include a compound having a (meth)acryloyl group. Examples of the compound having a (meth)acryloyl group include an N-substituted (meth)acrylamide compound, a (meth)acrylate compound, and the like. (Meth)acrylamide means acrylamide or methacrylamide.

In addition, as a photocationic polymerization type composition, as disclosed in Japanese Patent Laid-Open No. 2011-028234, (α) cationic polymerizable compound, (β) photocationic polymerization initiator, (γ) light having a wavelength longer than 380nm The ultraviolet-curable adhesive composition containing each component of a photosensitizer which shows maximum absorption and (δ) naphthalene-type photosensitization auxiliary agent is mentioned. However, other ultraviolet curable adhesives may be used.

(1) pretreatment process

The pretreatment step is a step of performing adhesion facilitation treatment to the adhesion surface of the protective film with the polarizer. Examples of the easy adhesion treatment include corona treatment and plasma treatment.

(Application process of UV-curable adhesive)

As the application step of the ultraviolet curable adhesive, the ultraviolet curable adhesive is applied to at least one of the adhesive surface of the polarizer and the protective film for polarizing plates. When applying the ultraviolet curable adhesive directly to the surface of the polarizer or the protective film, there is no particular limitation on the application method. For example, various wet coating methods, such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater, can be used. Further, after applying an ultraviolet curable adhesive between the polarizer and the protective film, a method of uniformly pushing and spreading by pressing with a roller or the like can also be used.

(2) bonding process

After applying the ultraviolet curable adhesive by the above method, it is treated in a bonding process. In this bonding step, for example, when an ultraviolet curable adhesive is applied to the surface of the polarizer in the previous application step, a cellulose resin film is superimposed thereon. Further, in the case of a method of applying an ultraviolet curable adhesive to the surface of the first or second protective film, a polarizer is superimposed thereon. Further, when an ultraviolet curable adhesive is cast between the polarizer and the protective film, the polarizer and the protective film are overlapped in that state. And, usually, in this state, it is pressed between the pressure rollers or the like from the protective film side on both sides. As the material of the pressure roller, it is possible to use metal or rubber. The pressure rollers arranged on both sides may be of the same material or may be of different materials.

(3) curing process

In the curing step, ultraviolet rays are irradiated to the uncured ultraviolet-curable adhesive, such as a cationic polymerizable compound (for example, an epoxy compound or an oxetane compound) or a radical polymerizable compound (for example, an acrylate compound, an acrylamide compound). The ultraviolet curable adhesive layer including a compound, etc.) is cured, and the overlapped polarizer and the protective film are adhered through the ultraviolet curable adhesive. In the configuration of the present embodiment in which the protective film is bonded to both surfaces of the polarizer, irradiating ultraviolet rays while simultaneously curing the ultraviolet curing adhesive on both sides of the polarizer while overlapping the protective film through an ultraviolet curable adhesive on both surfaces of the polarizer is performed. It is advantageous.

As the irradiation conditions of ultraviolet rays, any suitable conditions can be adopted as long as the ultraviolet curable adhesive can be cured. Dose of ultraviolet rays is preferably from 50 to a range of 1500mJ / cm ² in accumulated light quantity, and is more preferably in the range of 100 to 500mJ / cm ^2. In this embodiment, it is also preferable from the viewpoint of yield improvement to irradiate with ultraviolet rays from the 1st protective film side.

In the case of performing the manufacturing process of the polarizing plate in a continuous line, the line speed depends on the curing time of the adhesive, but is preferably in the range of 1 to 500 m/min, more preferably in the range of 5 to 300 m/min, more preferably 10 To 100 m/min. When the line speed is 1 m/min or more, productivity can be ensured, or damage to a protective film can be suppressed, and a polarizing plate excellent in durability can be produced. In addition, when the line speed is 500 m/min or less, curing of the ultraviolet-curable adhesive becomes sufficient, and an ultraviolet-curable adhesive layer having a target hardness and excellent adhesion can be formed.

It is preferable that another thermoplastic resin is bonded to the polarizer on the side opposite to the side on which the protective film of the polarizer is bonded using a water paste or an ultraviolet curable adhesive. In the case of a cellulose resin film, it is preferable that the surface to be bonded to the polarizer is saponified and bonded with a polyvinyl alcohol-based water paste.

[Liquid crystal display device]

By using the above-described polarizing plate for a liquid crystal display device, a liquid crystal display device excellent in various visibility can be produced.

The polarizing plate of this embodiment can be used for a liquid crystal display device of various driving systems such as STN, TN, OCB, HAN, VA (MVA, PVA), IPS, OCB, etc., but is preferably an IPS type liquid crystal display device.

In the liquid crystal display device, two polarizing plates are usually used: a polarizing plate on the viewing side and a polarizing plate on the backlight side, but it is preferable to use the polarizing plate of the present embodiment as a polarizing plate on both the viewing side and the backlight side, and as a polarizing plate on one side. It is also preferable to use.

The bonding direction of the polarizing plate in the IPS type liquid crystal display device can be performed with reference to Japanese Unexamined Patent Application Publication No. 2005-234431.

The liquid crystal cell used in this embodiment includes a liquid crystal layer and a pair of substrates (glass substrates) sandwiching the liquid crystal layer, and the pair of substrates is a glass substrate having a thickness in the range of 0.3 to 0.7 mm. , From the viewpoint of reduction in thickness and weight of a liquid crystal display device. Further, the polarizing plate of the present embodiment can make it difficult to cause a panel bend even if the glass substrate constituting the liquid crystal cell is thinned.

Examples of the material constituting the glass substrate usable for the liquid crystal cell include soda lime glass and silicate glass, and silicate glass is preferable, and silica glass or borosilicate glass is more preferable.

The glass constituting the glass substrate is preferably an alkali-free glass that does not substantially contain an alkali component, specifically, it is preferably a glass having an alkali component content of 1000 ppm or less. It is preferable that it is 500 ppm or less, and, as for content of the alkali component in a glass substrate, it is more preferable that it is 300 ppm or less. In a glass substrate containing an alkali component, substitution of cations occurs on the film surface, and clouding is likely to occur. This is because the density of the film surface layer is liable to decrease and the glass substrate is liable to be damaged.

It is preferable that the thickness of the glass substrate of the liquid crystal cell constituting the liquid crystal display device is in the range of 0.3 to 0.7 mm. It is preferable to set it as such a thickness from the point which can contribute to thinning formation of a liquid crystal display device.

The glass substrate can be formed by a known method, for example, a float method, a downdraw method, an overflow downdraw method, or the like. Among them, the overflow down-draw method is preferred from the viewpoint of the fact that the surface of the glass substrate does not come into contact with the molding member during molding, and the surface of the obtained glass substrate is less likely to be scratched.

In addition, such a glass substrate can also be obtained as a commercial item, for example, an alkali-free glass AN100 (thickness 500 μm) manufactured by Asahi Glass, and EAGLE XG(r) Slim (thickness 300 μm, 400 μm) manufactured by Corning Corporation. ), and a glass substrate (thickness 100-200 µm) manufactured by Nippon Denki Glass Corporation.

In addition, the polarizing plate and the glass substrate constituting the liquid crystal cell are adhered through an adhesive layer. As the adhesive layer, a double-sided tape, for example, a 25-µm-thick double-sided tape (inorganic tape MO-3005C) manufactured by Lintec, or a composition used for formation of an actinic ray-curable resin layer can be applied.

By using the polarizing plate of the present embodiment, panel bends are suppressed, even if the screen is a large screen of 30 or more, and a liquid crystal display device having excellent visibility such as display unevenness and front contrast, and a thin and lightweight liquid crystal display device can be obtained. .

[Example]

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the indication of "part" or "%" is used in Examples, "part by mass" or "% by mass" is indicated unless otherwise specified.

≪Production of the second protective film≫

<Preparation of cellulose ester resin>

A cellulose ester resin was synthesized and the degree of substitution thereof was measured by the method described in Japanese Patent Application Laid-Open No. Hei 10-45804 and Japanese Patent Application Laid-Open No. 8-231761. Specifically, sulfuric acid (7.8 parts by mass per 100 parts by mass of cellulose) was added as a catalyst, and a carboxylic acid serving as a raw material for an acyl substituent was added to perform an acylation reaction at 40°C. At this time, the degree of substitution of the acyl group was adjusted by adjusting the amount of acetic acid. Further, after acylation, aging was performed at 40°C. Further, the low molecular weight component of this cellulose acetate was washed with acetone and removed. Thereby, cellulose ester resin CA1 (triacetyl cellulose (TAC), total acyl substitution degree: 2.81) was obtained.

<Preparation of polyester diol>

(Preparation of polyester diol A)

A dibasic acid and glycol were subjected to a dehydration condensation reaction to prepare a polyesterdiol A as a hydroxyl group at both ends of the main chain. At this time, adipic acid was used as the dibasic acid, and ethylene glycol was used as the glycol. The hydroxyl value of the obtained polyester diol A was measured by the acetic anhydride method described in JIS K 1557-1:2007, and as a result, it was 113 mgKOH/g.

(Preparation of polyester diol B)

A dicarboxylic acid and glycol were subjected to a dehydration condensation reaction to prepare a polyester diol B in which both ends of the main chain were sealed with an acyl group. At this time, as the dicarboxylic acid, a mixture of terephthalic acid (45 mol%), phthalic acid (5 mol%), adipic acid (20 mol%), and succinic acid (30 mol%) in the above ratio is used. Ethylene glycol was used as the glycol. As a result of measuring the number average molecular weight (Mn) of polyester diol B by GPC, it was Mn=840.

<Preparation of dope for core layer formation>

The following composition was put into a mixing tank, stirred, and each component was dissolved to prepare a dope solution C01 for forming a core layer.

(Doping composition)

100 parts by mass of cellulose ester resin CA1

20 parts by mass of polyester diol A

Ultraviolet absorber (Tinuvin 928 having a structure represented by Compound 12 (manufactured by BASF Japan) 2.4 parts by mass)

394.0 parts by mass of methylene chloride

59.0 parts by mass of methanol

<Preparation of dope for skin layer formation>

(Preparation of fine particle dispersion)

Particulate matter (Aerosil R972V Nippon Aerosil Co., Ltd. product) 11 parts by mass

89 parts by mass of ethanol

After stirring and mixing the above for 50 minutes with a dissolver, dispersion was performed with 10,000 ton Gaulin to obtain a fine particle dispersion.

(Preparation of an additive liquid for fine particles)

Based on the following composition, the microparticle dispersion was slowly added to the dissolution tank containing methylene chloride while sufficiently stirring. In addition, dispersion was performed with an attritor so that the particle diameter of the secondary particles became a predetermined size. This was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle addition liquid.

99 parts by mass of methylene chloride

5 parts by mass of fine particle dispersion

(Preparation of dope for skin layer formation)

The following composition was put into a mixing tank, stirred, and each component was dissolved to prepare a dope solution C02 for forming a skin layer.

(Doping composition)

100 parts by mass of cellulose ester resin CA1

20 parts by mass of polyester diol A

Ultraviolet absorber (Tinuvin 928 having a structure represented by Compound 12 (manufactured by BASF Japan) 2.4 parts by mass)

0.078 parts by mass of fine particle additive solution

394.0 parts by mass of methylene chloride

59.0 parts by mass of methanol

<The film formation of the 2nd protective film 2-1>

Using the core layer forming C01 and the skin layer forming dope solution C02 prepared above, a flexible band running from the casting die of the band casting machine so that a film laminated in the order of skin layer/core layer/skin layer is obtained. Each dope solution was covalently rolled (simultaneously multilayered covalently rolled) on the (support). At this time, the casting amount of each dope solution was adjusted so that each layer of the film after extending|stretching might become the film thickness shown in Table 1, and the casting film was formed on the casting band. In addition, as the dope for forming the two skin layers sandwiching the core layer, the same dope solution C02 for forming a skin layer was used.

Subsequently, the cast film was peeled off from the cast band, and the solvent was evaporated at 35°C, followed by stretching 1.25 times in the width direction by tenter stretching, followed by drying at a drying temperature of 135°C. When stretching by zone stretching was started, the residual solvent amount was 20.0%, and when stretching by the tenter was started, the residual solvent amount was 8.0%.

After stretching with a tenter, a relaxation treatment was performed at 130°C for 5 minutes, and drying was terminated while conveying the drying zone at 120°C and 140°C with a plurality of rollers. The obtained film was slit to a width of 1.5 m, and knurled with a width of 10 mm and a height of 5 µm was performed on both ends of the film, and then wound around a core to prepare a second protective film 2-1 (three-layer laminated film).

<Formation of the second protective film 2-2 to 2-5>

To obtain the composition shown in Table 1, each additive (polyester diol, ultraviolet absorber) was added to the dope solution, except that the film was formed without adding or adding it in the same manner as the film formation of the second protective film 2-1, The 2nd protective films 2-2 to 2-5 (three-layer laminated film) were formed into a film. In addition, the 2nd protective film 2-2 is the same as the 2nd protective film 2-1.

<Formation of the second protective film 2-6>

Except having used only the dope solution C02 for skin layer formation, the addition amount of the fine particle addition liquid was changed as shown in Table 1, and the film was formed by casting the dope solution so that the film thickness of the film after film formation became the value shown in Table 1. It carried out similarly to the film formation of 2nd protective film 2-1, and formed the 2nd protective film 2-6 (single layer film) into a film.

≪Measurement of retardation value Ro·Rt≫

The retardation value Ro·Rt of the second protective films 2-1 to 2-6 produced above was measured as follows. That is, using an automatic birefringence meter Axo Scan (manufactured by Axo Scan Mueller Matrix Polarimeter: Axo Scan Mueller Matrix), a three-dimensional refractive index measurement was performed at a wavelength of 590 nm in an environment of 23°C and 55% RH, and the obtained refractive indices nx, ny From, nz, the retardation value Ro·Rt of the second protective films 2-1 to 2-6 was calculated by the above-described equation.

Table 1 shows the configuration and properties of the second protective film.

≪Production of the first protective film≫

<The film formation of the 1st protective film 1-1>

(Preparation of polyester resin A)

The esterification reaction vessel was heated, 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were added at 200° C., while heating and stirring, 0.017 parts by mass of antimony trioxide as a catalyst, 0.064 parts by mass of magnesium acetate tetrahydrate, and triethyl 0.16 parts by mass of amine was added. A pressure esterification reaction was performed under conditions of a gauge pressure of 0.34 MPa and a temperature of 240°C.

Next, the esterification reaction vessel was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Further, the temperature was raised to 260°C in 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. Subsequently, after 15 minutes, dispersion treatment was performed with a high-pressure disperser, and after 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can, and a polycondensation reaction was performed at 280°C under reduced pressure.

After completion of the polycondensation reaction, filtration treatment was performed with Nathlon filter NF-05S manufactured by Nippon Seisen, extruded in a strand shape from a nozzle, and filtered in advance (pore diameter: 1 µm or less), and then using cooling water. It cooled and solidified, and the resin was cut into pellet form. The intrinsic viscosity of the obtained polyester resin A (polyethylene terephthalate resin A) was 0.62 cm ³ /g, and inert particles and internally precipitated particles were not substantially contained.

(Preparation of coating liquid for forming an adhesive modified layer)

Transesterification reaction and polycondensation reaction are performed by a conventional method, and as the dicarboxylic acid component (with respect to the entire dicarboxylic acid component) 46 mol% of terephthalic acid, 46 mol% of isophthalic acid, and 5-sulfonate isophthalic acid A water-dispersible sulfonic acid metal base-containing copolymer polyester resin having a composition of 50 mol% of ethylene glycol and 50 mol% of neopentyl glycol as a glycol component (with respect to the entire glycol component) was prepared using 8 mol% of sodium.

Then, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of a nonionic surfactant were mixed, followed by heating and stirring, and after reaching 77°C, the water dispersibility After adding 5 parts by mass of a sulfonic acid metal base-containing copolymer polyester resin, heating and stirring until the resin lump disappears, the resin aqueous dispersion is cooled to room temperature, and a homogeneous water-dispersible copolymer having a solid content concentration of 5.0% by mass A polyester resin solution was obtained.

Further, 3 parts by mass of the aggregated silica particles (manufactured by Fuji Silysia Co., Ltd., 310 Cyricia) were dispersed in 50 parts by mass of water. 0.54 parts by mass of an aqueous dispersion of Silysia 310 was added to 99.5 parts by mass of the water-dispersible copolymer polyester resin solution, and 20 parts by mass of water was added while stirring to prepare a coating liquid for forming an adhesive modified layer.

(Production of PET film)

The prepared polyester resin A was dried by a conventional method, fed to an extruder, melted at 285°C, and the polymer was filtered through a filter medium of a stainless steel sintered body (with a nominal filtration accuracy of 10 μm particles cut 95%), and the sheet from the detention center. After extruding as an image, it was wound around a casting drum having a surface temperature of 30°C using an electrostatic casting method, and cooled and solidified to prepare an unstretched polyester film (PET film).

Subsequently, the prepared coating solution for forming an adhesive modified layer was applied to both surfaces of the unstretched PET film by a reverse roll method so that the amount of coating after drying was 0.08 g/m ² , and then dried at 80° C. for 20 seconds.

The unstretched film on which the adhesion-improving layer was formed was guided by a tenter stretching machine, and while holding the end of the film with a clip, it was stretched four times in the width direction in a heating zone at a temperature of 125°C.

Subsequently, while maintaining the stretched width in the width direction, it is treated at a temperature of 225° C. for 30 seconds, and a 3% relaxation treatment is performed in the width direction, and a uniaxially oriented PET film having a film thickness of 60 μm ( 1 Protective film 1-1) was produced.

<The film formation of the 1st protective film 1-2>

(Synthesis of acrylic resin 1 (copolymer A1))

As a monomer, with respect to a mixture of 93.6 parts by mass (90 mol%) of styrene, 7.2 parts by mass (10 mol%) of acrylic acid, 29.4 parts by mass of ethylbenzene, and 3.3 parts by mass of 2-ethylhexanol, 2,2-bis(4) 0.04 parts by mass of ,4-di-tert butyl peroxide)propane was added, and this polymerization solution was continuously introduced into a polymerization apparatus having a 5.0 L completely mixed reactor at 1.67 L/hour. At this time, the temperature of the completely mixed reactor was adjusted to 135°C. Subsequently, the polymer solution continuously discharged from the polymerization reactor was supplied to a vent type screw extruder reduced to a pressure of 2.7 to 4.0 kPa, and volatiles were removed to obtain a pellet-shaped copolymer A1. As for the constitutional ratio of the monomer unit in the copolymer A1, the styrene monomer was 90 mol%, the acrylic acid monomer was 10 mol%, and the weight average molecular weight was 300,000.

The following components were stirred with a stirring device and sufficiently dissolved while heating to prepare dope 1.

(Composition of Dope 1)

Copolymer A1 (styrene: 90 mol%, acrylic acid: 10 mol%, weight average molecular weight: 300,000) 100 parts by mass

Fine particles (R812 manufactured by Nippon Aerosil, silica particles, average particle diameter 8 nm) 0.30 parts by mass

150 parts by mass of methylene chloride

5 parts by mass of ethanol

The prepared dope 1 was uniformly cast on a stainless steel band support at a temperature of 22°C and a width of 2 m using a belt casting apparatus. In the stainless steel band support body, the solvent was evaporated until the residual solvent amount became 50%, and the obtained film-like material was peeled from the stainless steel band support body with a peeling tension of 162 N/m.

Subsequently, the peeled film-like material was dried at a drying temperature of 135°C while evaporating the solvent at 35°C and stretching 1.25 times in the width direction by tenter stretching. When stretching by zone stretching was started, the residual solvent amount was 20.0%, and when stretching by the tenter was started, the residual solvent amount was 8.0%.

After stretching with a tenter, a relaxation treatment was performed at 130°C for 5 minutes, and drying was terminated while conveying the drying zone at 120°C and 140°C with a plurality of rollers. The obtained film was slit to a width of 1.5 m, and after knurling with a width of 10 mm and a height of 5 μm was performed on both ends of the film, it was wound around a core to prepare an acrylic film (1st protective film 1-2). The film thickness of the produced acrylic film was 40 micrometers, and the winding length was 4000 m.

≪Production of the polarizing plate≫

Using the first protective film 1-1 (PET film) and the second protective film 2-1 prepared above, a polarizing plate 101 was produced according to the following method.

<Manufacture of polarizing plate 101>

1) Fabrication of polarizer

After carrying out the dyeing treatment and 2.5 times stretching treatment by immersing in a dyeing bath (30°C) of a mixture of iodine and potassium iodide while continuously conveying a polyvinyl alcohol film with a thickness of 60 μm through a guide roll. , In an acidic bath (60°C) to which boric acid and potassium iodide were added, stretching treatment and crosslinking treatment were performed to increase total 5 times, and the obtained iodine-PVA polarizer having a thickness of 12 µm was placed in a dryer at 50° C. for 30 minutes. It dried to obtain a polarizer with a moisture content of 4.9%.

2) Preparation of UV-curable adhesive B

Each of the following components was mixed to prepare a liquid ultraviolet curable adhesive.

40 parts by mass of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate

60 parts by mass of bisphenol A type epoxy resin

Diphenyl[4-(phenylthio)phenyl]sulfoniumhexafluoroantimonate (cationic polymerization initiator) 4.0 parts by mass

3) Bonding and polarizing plate manufacturing

After corona treatment was performed on the bonding surface of the first protective film 1-1, the prepared ultraviolet-curable adhesive B was coated with a thickness of 3 µm by a coating apparatus equipped with a chamber doctor. Further, after corona treatment was performed on the bonding surface of the second protective film 2-1, the UV-curable adhesive B was similarly applied to a thickness of 3 μm.

Immediately after applying an ultraviolet curable adhesive to the first protective film 1-1 and the second protective film 2-1, immediately apply the first protective film 1-1 on one side of the polarizer prepared above, and the second protective film on the other side. Each of 2-1 was bonded by a bonding roll via the coated surface of the UV-curable adhesive B. Thereafter, at a line speed of 20 m/min, a metal halide lamp was irradiated from the side of the first protective film 1-1 so that the ^{accumulated light amount at a wavelength of 280 to 320 nm became 320 mJ/cm 2, and the adhesive on both sides was cured,} The polarizing plate 101 was obtained.

<Production of polarizing plates 102 to 106>

In the production of the polarizing plate 101, polarizing plates 102 to 106 were produced in the same manner as in production of the polarizing plate 101, except that the first protective film and the second protective film were changed to be the combination shown in Table 2.

≪Production of a liquid crystal display device≫

Using the polarizing plate 101 produced above, a liquid crystal display device 201 was produced according to the following method.

That is, as a liquid crystal cell, an IPS system liquid crystal cell having two glass substrates having a thickness of 0.5 mm and a liquid crystal layer disposed therebetween was prepared. Then, the prepared pair of polarizing plates 101·101 was bonded to each other through the adhesive layer so that the second protective film was on the side of the liquid crystal cell, thereby obtaining a liquid crystal display device 201. In the bonding, the absorption axis of the polarizer of the polarizing plate on the viewing side and the absorption axis of the polarizer of the polarizing plate on the backlight side were made orthogonal. Hereinafter, it carried out similarly, and liquid crystal display devices 202-206 were produced using polarizing plates 102-106.

≪Evaluation≫

(Bend non-uniformity)

The produced liquid crystal displays 201 to 206 were allowed to stand for 24 hours in an environment of 40°C and 95% RH. Subsequently, in a state in which the liquid crystal displays 201 to 206 were displayed in black under a dry environment at 40°C, the difference between the luminance near the 4 vertices and the luminance near the center of the display screen (image non-uniformity at the center and the periphery) was observed visually on the display screen. . And, based on the following evaluation criteria, it evaluated the bend nonuniformity.

"Evaluation standard"

◎: No bend unevenness is seen.

(Circle): Bend unevenness is slightly seen, but there is no problem in practical use.

△: Bend unevenness is seen, but the quality is acceptable for practical use.

X: A clear bend unevenness is seen, and there is a problem in practical use.

(durability)

The second protective films 2-1 to 2-6 prepared above were each cut into A4 size (210 mm×297 mm), stored for 1000 hours in a high-temperature, high-humidity thermostat at a temperature of 60°C and a humidity of 90% RH, and a wet heat treatment sample Was produced. Subsequently, the film subjected to moist heat treatment was subjected to humidity control for 24 hours under conditions of a temperature of 23°C and a relative humidity of 55% RH.

Thereafter, according to the standard of JIS K7165, a D65 light source was used, and the haze of the film was measured with a haze meter (brand name NDH2000, manufactured by Nippon Denshoku Kogyo Co., Ltd.), and durability (moist heat durability) based on the following evaluation criteria. ) Was evaluated. At this time, the thickness of the sample was evaluated by converting it into a haze value in the case of 80 µm.

"Evaluation standard"

(Double-circle): Haze is less than 0.5%.

○: Haze is 0.5% or more and less than 1.0%.

?: Haze is 1.0% or more and less than 1.5.

X: Haze is 1.5% or more.

Table 2 shows the results of the evaluation.

From Table 2, in Examples 1 to 2, bend unevenness was suppressed, and deterioration in durability was also suppressed. In Examples 1 to 2, since the second protective film constituting the polarizing plate contains polyesterdiol A, which is a hydroxyl group at both ends of the main chain, even if the second protective film contains an ultraviolet absorber, at the time of film formation. The compatibility of the ultraviolet absorber and the cellulose ester resin can be improved, and generation of cracks in the inside of the film formed film is suppressed. Thereby, it is thought that it was possible to suppress the occurrence of dimensional variation of the second protective film due to the accumulation of moisture in the cracks, suppress the bend of the liquid crystal cell, and suppress the bend unevenness.

In addition, in Examples 1 to 2, fine particles are contained only in the skin layer of the second protective film. In this configuration, even if the second protective film contains an ultraviolet absorber, at the time of forming the second protective film, aggregation of the fine particles and the ultraviolet absorber occurs only in the skin layer. Therefore, it is thought that deterioration of haze in the whole film can be suppressed and deterioration of durability of the 2nd protective film was able to be suppressed.

In particular, the evaluation of bend unevenness and durability is better in Example 1 in which the first protective film is a PET film than in Example 2 in which the first protective film is an acrylic film. Since the PET film has lower moisture permeability than the acrylic film and more suppresses moisture absorption, it is considered that it contributes to suppression of bend unevenness and also contributes to improvement of durability.

In contrast, in Comparative Example 1, since the second protective film did not contain an ultraviolet absorber, it is considered that the second protective film was deteriorated by ultraviolet rays, and the durability was deteriorated. In Comparative Example 2, the polyester diol added to the second protective film was not a polyester diol having a hydroxyl group at both ends of the main chain, and in Comparative Example 3, the polyester diol itself was not added, so the ultraviolet absorber and the resin It is considered that the compatibility of the film cannot be improved, and as a result, cracks are generated in the film-formed film, and bend unevenness has occurred. In Comparative Example 4, since the second film was composed of a single layer film, and the fine particles were dispersed throughout the film, aggregation of the fine particles and the ultraviolet absorber was carried out over the entire film, resulting in deterioration of the haze of the entire film and deterioration in durability. I think it is.

[supplement]

As described above, embodiments of the present invention have been described, but the scope of the present invention is not limited thereto, and various modifications can be made and implemented without departing from the gist of the invention.

The polarizing plate and liquid crystal display device of the present embodiment described above can be expressed as follows.

1. It is a polarizing plate which laminated a 1st protective film, a polarizer, and a 2nd protective film in this order,

In the second protective film, the retardation value Ro(nm) in the in-plane direction of the film defined by the following formula (i) and the retardation value Rt(nm) in the thickness direction of the film defined by the following formula (ii) are , Satisfying the conditions defined by the following formulas (iii) and (iv),

(i) Ro=(nx-ny)×d

(ii) Rt=((nx+ny)/2-nz)×d

(In the formula, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is the refractive index in the thickness direction of the film (refractive index is 23°C, under an environment of 55% RH, at a wavelength of 590 nm) Measurement), d represents the thickness (nm) of the film.)

(iii) 0nm≤Ro≤10nm

(iv) |Rt|≤25nm

Of the first protective film and the second protective film, only the second protective film contains an ultraviolet absorber,

The second protective film contains a polyester diol in which both ends of the main chain are hydroxyl groups,

The second protective film is a laminated film comprising a core layer and two skin layers containing fine particles located on the front side and the back side of the core layer.

2. The polarizing plate according to the above 1, wherein the ultraviolet absorber is contained in both the core layer and the two skin layers in the second protective film.

3. The said polyester diol is contained in both said core layer and said two skin layers in said 2nd protective film, The polarizing plate of said 2 characterized by the above-mentioned.

4. In the said 2nd protective film, the said core layer and said two skin layers contain a resin containing a cellulose ester, The polarizing plate in any one of said 1-3.

5. The polarizing plate according to any one of the above 1 to 4, wherein the first protective film contains a resin containing polyethylene terephthalate.

6. The polarizing plate according to any one of 1 to 5 above, and

Including an IPS type liquid crystal cell in which a liquid crystal layer is sandwiched by a pair of substrates,

The polarizing plate is disposed on a viewing side with respect to the liquid crystal cell, and the second protective film is disposed on the side of the liquid crystal cell with respect to the polarizer.

The polarizing plate of the present invention can be used, for example, for an IPS type liquid crystal display device.

1 liquid crystal display
4 liquid crystal cell
5 polarizer
11 polarizer
12 optical film (first protective film)
13 optical film (second protective film)

Claims (6)

It is a polarizing plate which laminated a 1st protective film, a polarizer, and a 2nd protective film in this order,
The first protective film is a polyester film having a light transmittance of 50% or more at a wavelength of 380 nm,
In the second protective film, the retardation value Ro(nm) in the in-plane direction of the film defined by the following formula (i) and the retardation value Rt(nm) in the thickness direction of the film defined by the following formula (ii) are , Satisfying the conditions defined by the following formulas (iii) and (iv),
(i) Ro=(nx-ny)×d
(ii) Rt=((nx+ny)/2-nz)×d
(Wherein, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is the refractive index in the thickness direction of the film. Measurement), d represents the thickness (nm) of the film.)
(iii) 0nm≤Ro≤10nm
(iv) |Rt|≤25nm
Of the first protective film and the second protective film, only the second protective film contains an ultraviolet absorber,
The second protective film contains a polyester diol in which both ends of the main chain are hydroxyl groups,
The second protective film is a laminated film comprising a core layer and two skin layers containing fine particles located on the front and back sides of the core layer. The polarizing plate according to claim 1, wherein the ultraviolet absorber is included in both the core layer and the two skin layers in the second protective film. The polarizing plate according to claim 2, wherein the polyester diol is contained in both the core layer and the two skin layers in the second protective film. The polarizing plate according to any one of claims 1 to 3, wherein in the second protective film, the core layer and the two skin layers contain a resin containing a cellulose ester. The polarizing plate according to any one of claims 1 to 3, wherein the first protective film contains a resin containing polyethylene terephthalate. The polarizing plate according to any one of claims 1 to 3, and
Including an IPS type liquid crystal cell in which a liquid crystal layer is sandwiched by a pair of substrates,
The polarizing plate is disposed on the viewing side with respect to the liquid crystal cell, and the second protective film is disposed on the side of the liquid crystal cell with respect to the polarizer.

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