JP2010184408A - Method for producing optical film, optical film, polarizing plate and liquid crystal display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an optical film, in which the optical film having such retardations sufficiently close to zero can be obtained even if the optical film is stretched that the in-plane direction retardation is 0-5 nm and the thickness direction retardation is -5 to 5 nm. <P>SOLUTION: The method for producing the optical film comprises: a flow casting step of flow-casting a resin solution, which is obtained by dissolving a transparent resin and a compound having negative orientational birefringence in a solvent, on a traveling support to form a flow casting film; an exfoliation step of exfoliating the flow casting film from the support as a film; a drying step of drying the solvent in the exfoliated film; and a stretching step of stretching the film having ≤1 mass% residual solvent rate at the temperature higher than the glass transition temperature of the film by 30-100°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical film manufacturing method, an optical film obtained by the manufacturing method, a polarizing plate using the optical film as a transparent protective film, and a liquid crystal display device including the polarizing plate.

  Liquid crystal display devices, plasma display devices, and the like are widely used for reasons such as space saving and energy saving. Moreover, as an optical film used for various image display apparatuses, such as a liquid crystal display device and a plasma display apparatus, the resin film excellent in translucency, such as a cellulose ester film, is used, for example. Such a resin film is manufactured by, for example, a solution casting film forming method. The solution casting film forming method is a method in which a resin solution obtained by dissolving a raw material resin in a solvent is cast on a traveling support, and the film obtained by drying to some extent is peeled off from the support, and the peeled film This is a method for producing a resin film by carrying out drying, stretching and the like while carrying the film with a carrying roller. This method is preferably used because a uniform film thickness is easily obtained and the composition of the obtained film is easily adjusted.

  An image display device, particularly a liquid crystal display device used as a television receiver, is required to have a large screen and high image quality. For this reason, not only the further improvement of the visibility in the optical film used as a phase difference film is calculated | required, but manufacture of the wide wide film is calculated | required. In order to produce a wide film by the solution casting film forming method as described above, a method of widening the width of the casting film itself using a wide support or a transport roller, a method of stretching the film, etc. Can be mentioned.

  The method of increasing the width of the casting film itself has a problem in that it requires a change in equipment and a new establishment of a factory every time the required width of the optical film changes, which increases costs.

  Moreover, as a method of stretching the film, for example, when using polyethylene terephthalate (PET) or polyvinyl alcohol as a raw material resin, it is possible to stretch the film to about 2 to 4 times the width of the film, A wide resin film can be obtained. However, in the case of a cellulose ester resin film that can be used as a transparent protective film for a polarizing plate or a retardation film, when it is highly stretched, not only there is a risk of breakage, but the haze increases and it can be used as an optical film. There was a problem of disappearing. In addition, as a retardation film, particularly a retardation film for IPS (in-plane switching), the retardation is required to be an optical value close to 0. However, in order to obtain a wide film, the retardation is obtained by performing high stretching. It was difficult to obtain an optical value close to 0.

  Examples of the retardation film for IPS are listed in Patent Document 1. In Patent Document 1, the in-plane direction retardation (Ro) is 0 nm or more and 5 nm or less, the thickness direction retardation (Rt) is −5 nm or more and 5 nm or less, the film thickness is 20 to 50 μm, and the surface to be bonded to the polarizer is used. A polarizing plate protective film having a water contact angle of 30 to 45 degrees is disclosed.

JP 2008-112127 A

  According to Patent Document 1, it is disclosed that the feeling of roughness, the contrast ratio in the oblique direction, and the color shift amount in the oblique direction are improved. However, in order to obtain a wide film, it is difficult to make the retardation near 0 when the film is stretched to a high degree. Accordingly, it has been difficult to obtain a wide film capable of exhibiting the above effects by highly stretching the film.

  The present invention has been made in view of such circumstances. Even when the film is stretched, the in-plane retardation is 0 nm or more and 5 nm or less, the thickness direction retardation is −5 nm or more and 5 nm or less, and the retardation is sufficiently close to 0. It aims at providing the manufacturing method of the optical film which can obtain a film. Moreover, it aims at providing the liquid crystal display device provided with the optical film obtained by the manufacturing method of such an optical film, the polarizing plate which used the said optical film as a transparent protective film, and the said polarizing plate.

  The method for producing an optical film according to one embodiment of the present invention is a method for producing an optical film having an in-plane retardation of 0 nm or more and 5 nm or less, and a thickness direction retardation of −5 nm or more and 5 nm or less. A casting process in which a casting solution is formed by casting a resin solution in which a compound having negative orientation birefringence is dissolved in a solvent on a traveling support, and the casting membrane is used as the film. A peeling step for peeling from the body, a drying step for drying the solvent in the peeled film, and a temperature 30 to 100 ° C. higher than the glass transition temperature of the film after the residual solvent ratio of the film is 1% by mass or less. And a stretching step of stretching the film.

  According to said structure, even if a film is extended | stretched, both the in-plane direction retardation and the thickness direction retardation can manufacture the optical film close | similar to 0 sufficiently. That is, it is possible to produce an optical film having a retardation sufficiently close to 0 and capable of being used as a retardation film for IPS, for example.

  This is presumed to be due to the following.

  First, a film containing a compound having negative orientation birefringence is stretched so that the degree of orientation in the in-plane direction is the same by stretching the film with a small amount of residual solvent. It is thought. Therefore, it is thought that it can suppress that the in-plane direction retardation by extending | stretching of a film leaves | separates from 0.

  And it is thought that the orientation in the thickness direction can be thermally relaxed by setting the film at a predetermined temperature higher than the glass transition temperature of the film during stretching, and the retardation in the thickness direction due to stretching of the film can be suppressed from leaving 0. It is done.

  Accordingly, the in-plane direction retardation and the thickness direction retardation are sufficiently close to 0, with the in-plane direction retardation ranging from 0 nm to 5 nm and the thickness direction retardation ranging from -5 nm to 5 nm, depending on the residual solvent ratio and the temperature of the film during stretching. Can be controlled.

  Moreover, in the said manufacturing method, it is preferable that the said extending process extends the said film above 200 degreeC after the residual solvent rate of the said film becomes 0.5 mass% or less. According to such a configuration, an optical film having in-plane direction retardation and thickness direction retardation closer to 0 can be obtained.

  The film before the stretching step preferably has an in-plane retardation of 0 nm or more and 5 nm or less, and a thickness direction retardation of −5 nm or more and 5 nm or less. According to such a configuration, both the in-plane direction retardation and the thickness direction retardation can be stretched to produce an optical film that is close to 0, and a wider optical film can be obtained.

  The transparent resin is preferably a cellulose ester resin. According to such a structure, it is preferable at the point from which an optical film with high translucency is obtained. Moreover, since the optical film containing a cellulose ester resin can be used as a transparent protective film for a polarizing plate or a retardation film, both functions can be achieved with a single film.

  The compound having negative orientation birefringence is preferably an acrylic resin. According to such a configuration, an optical film having in-plane direction retardation and thickness direction retardation closer to 0 can be obtained.

  Moreover, it is preferable that the width | variety of the said optical film is 1000-3000 mm. When trying to produce such a wide optical film, the retardation of the optical film is generally easily separated from 0, but according to the above production method, the retardation can be suppressed from separating from 0. Accordingly, it is possible to obtain a wide optical film having a retardation sufficiently close to 0.

  The optical film which concerns on another one aspect | mode of this invention is obtained by the said manufacturing method, It is characterized by the above-mentioned. According to such a configuration, a wide optical film having a retardation sufficiently close to 0 and a wide width can be obtained. For this reason, it can apply to image display apparatuses, such as a liquid crystal display device, as a phase difference film for which retardation is calculated | required sufficiently close to 0, especially a phase difference film for IPS.

  The polarizing plate which concerns on the other one aspect | mode of this invention is a polarizing plate provided with a polarizing element and the transparent protective film arrange | positioned on the surface of the said polarizing element, Comprising: The said transparent protective film is the said optical film. It is characterized by this.

  According to such a configuration, an optical film having a retardation sufficiently close to 0 is applied as the transparent protective film of the polarizing element. For example, when applied to a liquid crystal display device, a liquid crystal display excellent in contrast and the like. A polarizing plate capable of realizing high image quality of the apparatus is obtained. Furthermore, when a wide optical film is used as an optical film used as a transparent protective film of a polarizing element, it can be applied to a liquid crystal display device having a large screen.

  A liquid crystal display device according to another embodiment of the present invention is a liquid crystal display device including a liquid crystal cell and two polarizing plates arranged so as to sandwich the liquid crystal cell, and the two polarizing plates At least one of them is the polarizing plate.

  According to such a configuration, since the polarizing plate provided with the optical film whose retardation is sufficiently close to 0 is used, high image quality of the liquid crystal display device excellent in contrast and the like can be realized. Furthermore, when a wide optical film is used as the transparent protective film for the polarizing plate, a large screen can be realized.

  According to the present invention, even when the film is stretched, an optical film having an in-plane retardation of 0 nm to 5 nm and a thickness direction retardation of -5 nm to 5 nm can be obtained.

It is the schematic which shows the basic composition of the manufacturing apparatus 11 of the optical film by a solution casting film forming method.

  Hereinafter, although the embodiment concerning the manufacturing method of the optical film of the present invention is described, the present invention is not limited to these.

  In the method for producing an optical film (resin film) according to this embodiment, a resin solution (dope) in which a transparent resin and a compound having negative orientation birefringence are dissolved is cast on a traveling support. A casting process for forming a cast film (web), a peeling process for peeling the cast film from the support as a film, a drying process for drying the peeled film, and a stretching process for stretching the film. It is a manufacturing method by a so-called solution casting film forming method. For example, it is performed by an optical film manufacturing apparatus using a solution casting film forming method as shown in FIG. The film here refers to a film after a cast film (web) made of a dope cast on a support is dried on the support and can be peeled off from the support. In addition, as an optical film manufacturing apparatus, it is not limited to what is shown in FIG. 1, The thing of another structure may be sufficient.

  FIG. 1 is a schematic diagram showing a basic configuration of an optical film manufacturing apparatus 11 by a solution casting method. The optical film manufacturing apparatus 11 includes an endless belt support 12, a casting die 13, a peeling roller 14, a drying device 15, a stretching device 16, a winding device 17, and the like. The casting die 13 casts a resin solution (dope) 19 in which a transparent resin is dissolved on the surface of the endless belt support 12. The endless belt support 12 is drivably supported by a pair of driving rollers and driven rollers, and forms a web made of the resin solution 19 cast from the casting die 13 and is dried while being conveyed. A film. The peeling roller 14 peels the film from the endless belt support 12. The drying device 15 dries the peeled film while being transported by a transport roller. The stretching device 16 stretches the film under the conditions described later. And the said winding apparatus 17 winds up the dried and stretched film, and makes it a film roll.

  As shown in FIG. 1, the casting die 13 is supplied with a dope 19 from a dope supply pipe connected to the upper end of the casting die 13. Then, the supplied dope is discharged from the casting die 13 to the endless belt support 12, and a web is formed on the endless belt support 12.

  As shown in FIG. 1, the endless belt support 12 is a metal endless belt having a mirror surface and traveling infinitely. As the belt, for example, a belt made of stainless steel or the like is preferably used from the viewpoint of peelability of the film. The width of the casting film cast by the casting die 13 is preferably 80 to 99% with respect to the width of the endless belt support 12 from the viewpoint of effectively utilizing the width of the endless belt support 12. . Further, instead of the endless belt support, a rotating metal drum (endless drum support) having a mirror surface may be used.

  And the said endless belt support body 12 dries the solvent in dope, conveying the cast film (web) formed on the surface. The drying is performed, for example, by heating the endless belt support 12 or blowing heated air on the web. At that time, although it depends on the composition of the dope, the temperature of the web is preferably in the range of −5 to 70 ° C., in the range of 0 to 60 ° C. More preferred. The higher the temperature of the web, the faster the solvent can be dried. However, when the temperature is too high, the web tends to foam or the flatness tends to deteriorate.

  When heating the endless belt support 12, for example, a method of heating the web on the endless belt support 12 with an infrared heater, a method of heating the back of the endless belt support 12 with an infrared heater, the back of the endless belt support 12 And a method of heating by blowing heated air, and the like can be selected as needed.

  In addition, when blowing heated air, the wind pressure of the heated air is preferably 50 to 5000 Pa in consideration of the uniformity of solvent evaporation and the like. The temperature of the heating air may be dried at a constant temperature, or may be supplied in several steps in the running direction of the endless belt support 12.

  The time from casting the dope on the endless belt support 12 to peeling the web from the endless belt support 12 varies depending on the film thickness of the optical film to be produced and the solvent used. In consideration of peelability from 12, it is preferably in the range of 0.5 to 5 minutes.

  The transport speed of the cast film by the endless belt support 12 is preferably about 50 to 200 m / min, for example. Moreover, it is preferable that ratio (draft ratio) of the conveyance speed of the cast film with respect to the traveling speed of the endless belt support 12 is about 0.8 to 1.2. When the draft ratio is within this range, the cast film can be stably formed. For example, if the draft ratio is too large, there is a tendency to cause a phenomenon called neck-in in which the cast film is reduced in the width direction, and if so, a wide film cannot be formed.

  The peeling roller 14 is in contact with the surface of the endless belt support 12 on which the dope 19 is cast, and the dried web (film) is peeled by applying pressure to the endless belt support 12 side. . When the film is peeled from the endless belt support 12, the film is stretched in the film conveyance direction (Machine Direction: MD direction) by the peeling tension and the subsequent conveyance tension. For this reason, it is preferable that the peeling tension and the conveyance tension when peeling the film from the endless belt support 12 are 50 to 400 N / m.

  Further, the residual solvent ratio of the film when the film is peeled off from the endless belt support 12 is the peelability from the endless belt support 12, the residual solvent ratio at the time of peeling, the transportability after peeling, and the optical completed after transporting and drying. Considering the physical properties of the film, it is preferably 30 to 200% by mass.

  The residual solvent ratio of the film is defined by the following formula (I).

Residual solvent ratio (mass%) = {(M ₁ −M ₂ ) / M ₂ } × 100 (I)
Here, M ₁ is shows the mass at any point in the film, M ₂ shows the mass after drying for 1 hour at 115 ° C. The film was measured M _1.

  The drying device 15 includes a plurality of transport rollers, and dries the film while transporting the film between the rollers. In that case, you may dry using heating air, infrared rays, etc. independently, and you may dry using heating air and infrared rays together. It is preferable to use heated air from the viewpoint of simplicity. The drying temperature varies depending on the residual solvent ratio of the film, but it is determined by appropriately selecting the drying solvent temperature in the range of 30 to 180 ° C. in consideration of drying time, shrinkage unevenness, stability of expansion and contraction, etc. That's fine. Moreover, it may be dried at a constant temperature, or may be divided into two to four stages of temperature, and may be divided into several stages of temperature. Further, the film can be stretched in the MD direction while being conveyed in the drying device 15.

  The stretching device 16 stretches the film in a direction (Transverse Direction: TD direction) orthogonal to the web conveyance direction under the following conditions. Specifically, both ends in a direction perpendicular to the film transport direction are gripped with a clip or the like, and the distance between the opposing clips is increased to extend in the TD direction.

  The film before being stretched by the stretching device 16 has a residual solvent ratio of 1% by mass or less. Here, you may adjust with the said drying apparatus 15 so that the residual solvent rate of a film may be 1 mass% or less. Moreover, the said film is extended | stretched in the state 30-100 degreeC higher than a glass transition temperature. This film may be heated, for example, by blowing heated air on the film, or may be heated by a heating device such as an infrared heater.

  Moreover, it is preferable that the film before extending | stretching with the said extending | stretching apparatus 16 is 0.5 mass% or less of residual solvent ratios, and that in-plane direction retardation (Ro) is 0 nm or more and 5 nm or less. The thickness direction retardation (Rt) is preferably -5 nm or more and 5 nm or less. And it is preferable that the temperature of the film at the time of extending | stretching is 200 degreeC or more.

  And by extending | stretching on said conditions, Ro is 0 nm or more and 5 nm or less, Rt is -5 nm or more and 5 nm or less, and both Ro and Rt can fully manufacture the optical film with retardation close | similar to 0. Ro and Rt are defined by the following formulas (II) and (III).

Ro = (Nx−Ny) × d (II)
Rt = {(Nx + Ny) / 2−Nz} × d (III)
Here, Nx represents the refractive index in the slow axis direction of the film, Ny represents the refractive index in the fast axis direction, Nz represents the refractive index in the thickness direction, and d represents the film thickness (nm). Indicates.

  Ro and Rt can be measured using an automatic birefringence meter. For example, using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments), it can be obtained at a wavelength of 590 nm in an environment of a temperature of 23 ° C. and a humidity of 55% RH.

  On the other hand, when the residual solvent ratio exceeds 1% by mass, the obtained optical film has a low Ro, a high Rt, and the retardation tends to depart from 0, so that an optical film having a retardation sufficiently close to 0 cannot be obtained. . This is considered to be due to the fact that the degree of orientation in the in-plane direction is strongly negative and weakly positive.

  And when the temperature of the film at the time of extending | stretching is so low that it exceeds 30 degreeC from the glass temperature of a film, Ro of the obtained optical film is low, Rt becomes high, retardation tends to leave | separate from 0, and retardation is enough. An optical film close to 0 cannot be obtained. This is considered to be due to insufficient thermal relaxation and strong orientation in the thickness direction. Moreover, when it is so high that it exceeds 100 degreeC from the glass temperature of a film, there exists a tendency for the flatness of a film to deteriorate.

  Moreover, the residual solvent rate of the film extended | stretched with the said extending | stretching apparatus 16 can be adjusted by adjusting the preparation conditions and drying conditions of a film. Moreover, in this embodiment, although the said drying apparatus 15 was provided, if the residual solvent rate of the film at the time of extending | stretching is dried to the said range, it does not need to be provided. A drying device for drying the film stretched by the stretching device 16 may be further provided.

  Further, the stretching ratio in the TD direction of the film here is preferably 15 to 50%, more preferably 25 to 45%, and still more preferably 25 to 30%. When such a high stretching is used, the retardation of the optical film is generally easily separated from 0. However, when the film is stretched under the above conditions, the retardation can be prevented from separating from 0. Accordingly, it is possible to obtain a wide optical film having a retardation sufficiently close to 0. Moreover, when the width | variety of an optical film is wide, it is preferable also from the point of use to a large sized liquid crystal display device, the use efficiency of the film at the time of polarizing plate processing, and production efficiency. In addition, an extending | stretching rate is defined by following formula (IV).

Stretch rate (%) = {(L ₂ −L ₁ ) / L ₁ } × 100 (IV)
Here, L ₁ indicates the length before stretching between the end portions at a predetermined position of the film, and L ₂ indicates the length after stretching between the end portions at the predetermined position of the film. In addition, the width | variety of a film is the value which measured the width | variety with the C-type JIS1 grade steel scale.

  The winding device 17 winds the film stretched by the stretching device 16 on a winding core to a required length. The temperature at the time of winding is preferably cooled to room temperature in order to prevent scratches and loosening due to shrinkage after winding. The winder to be used can be used without any particular limitation, and may be a commonly used one, such as a constant tension method, a constant torque method, a taper tension method, or a program tension control method with a constant internal stress. Can be wound up.

  By the process as described above, a retardation is sufficiently close to 0 and a wide optical film is obtained. For this reason, it can apply to image display apparatuses, such as a liquid crystal display device, as a phase difference film for which retardation is calculated | required sufficiently close to 0, especially a phase difference film for IPS.

  Moreover, it is preferable that the width | variety of an optical film is 1000-3000 mm. When trying to produce such a wide optical film, the retardation of the optical film generally tends to be separated from 0, but when the film is stretched under the above conditions, the retardation can be suppressed from separating from 0. Accordingly, it is possible to obtain a wide optical film having a retardation sufficiently close to 0. Moreover, when the width | variety of an optical film is wide, it is preferable also from the point of use to a large sized liquid crystal display device, the use efficiency of the film at the time of polarizing plate processing, and production efficiency. Moreover, it is preferable that the film thickness of a film is 30-90 micrometers from points, such as a viewpoint of thickness reduction of a liquid crystal display device, and the production stabilization of a film. Here, the film thickness is an average film thickness, and 20 to 200 locations in the film width direction are measured with a contact-type film thickness meter manufactured by Mitutoyo Corporation, and the average value of the measured values is calculated. Shown as film thickness.

  Hereinafter, the composition of the resin solution used in this embodiment will be described.

  The resin solution used in this embodiment is obtained by dissolving a transparent resin and a compound having negative orientation birefringence in a solvent.

  The transparent resin is not particularly limited as long as it is a resin having transparency when formed into a substrate by a solution casting film forming method or the like, but is easily manufactured by a solution casting film forming method or the like. It is preferable that the adhesive property with other functional layers such as a hard coat layer is excellent and that it is optically isotropic. Here, the transparency means that the visible light transmittance is 60% or more, preferably 80% or more, and more preferably 90% or more.

  Specific examples of the transparent resin include cellulose ester resins such as cellulose diacetate resin, cellulose triacetate resin, cellulose acetate butyrate resin, and cellulose acetate propionate resin; polyethylene terephthalate resin and polyethylene naphthalate resin. Acrylic resins such as polymethyl methacrylate resins; Polysulfone (including polyether sulfone) resins, polyethylene resins, polypropylene resins, cellophane, polyvinylidene chloride resins, polyvinyl alcohol resins, ethylene vinyl alcohol resins, Shinji Vinyl resins such as tactic polystyrene resins, cycloolefin resins and polymethylpentene resins; polycarbonate resins; polyarylate resins Polyetherketone resins; polyether ketone imide resin; can be mentioned fluorine-based resin or the like; a polyamide resin. Among these, cellulose ester resins, cycloolefin resins, polycarbonate resins, and polysulfone (including polyethersulfone) resins are preferable. Furthermore, cellulose ester resins are preferred, and among cellulose ester resins, cellulose acetate resins, cellulose propionate resins, cellulose butyrate resins, cellulose acetate butyrate resins, cellulose acetate propionate resins, and cellulose triacetate resins are preferred, Cellulose triacetate resin is particularly preferred. Moreover, the said transparent resin may use the transparent resin illustrated above independently, and may use it in combination of 2 or more type.

  Next, the cellulose ester resin will be described.

  The number average molecular weight of the cellulose ester-based resin is preferably 30,000 to 200,000 because the mechanical strength when molded into a resin film is strong, and is preferable in that the dope viscosity is appropriate in the solution casting film forming method. More preferably, it is 50000-150,000. Moreover, it is preferable that weight average molecular weight (Mw) / number average molecular weight (Mn) exists in the range of 1-5, and it is more preferable that it exists in the range of 1.4-3.0.

  The average molecular weight and molecular weight distribution of a resin such as a cellulose ester resin can be measured using gel permeation chromatography or high performance liquid chromatography. Therefore, the number average molecular weight (Mn) and the mass average molecular weight (Mw) can be calculated using these, and the ratio can be calculated.

  The cellulose ester resin preferably has an acyl group having 2 to 4 carbon atoms as a substituent. As the substitution degree, for example, when the substitution degree of the acetyl group is X and the substitution degree of the propionyl group or butyryl group is Y, the total value of X and Y is 2.2 or more and 2.95 or less, X is preferably more than 0 and 2.95 or less.

  In addition, the portion not substituted with an acyl group usually exists as a hydroxyl group. These cellulose ester resins can be synthesized by a known method. The measuring method of the substitution degree of an acyl group can be measured according to the provisions of ASTM-D817-96.

  The cellulose that is the raw material of the cellulose ester resin is not particularly limited, and examples thereof include cotton linters, wood pulp (derived from coniferous trees and hardwoods), kenaf and the like. The cellulose ester resins obtained from them can be mixed and used at an arbitrary ratio, but it is preferable to use 50% by mass or more of cotton linter. When the acylating agent is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), these cellulose ester resins use an organic acid such as acetic acid or an organic solvent such as methylene chloride, It can be obtained by reacting with a cellulose raw material using such a protic catalyst.

  The compound having negative orientation birefringence means a material exhibiting negative birefringence in the stretching direction of the film in the resin film. As the resin film, for example, in the case of a film made of a cellulose ester resin, specifically, for example, an acrylic resin, a polyester resin, a compound having a furanose structure or a pyranose structure, a sulfone compound, and the like can be mentioned. Of these, acrylic resins are preferably used.

  Whether or not the film has negative orientation birefringence can be determined by measuring the birefringence of the film in a system not added with the compound with a birefringence meter and comparing the difference.

  The acrylic resin is preferably an acrylic resin having a negative orientation birefringence with respect to the stretching direction and having a mass average molecular weight Mw of 500 or more and 30000 or less, and an acrylic resin having an aromatic ring in the side chain. More preferably, the resin and the acrylic resin having a cyclohexyl group in the side chain.

  In addition, as a polymerization method of the acrylic resin, for example, a method using a peroxide polymerization initiator such as cumene peroxide and t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than normal polymerization, A method using a chain transfer agent such as a mercapto compound or carbon tetrachloride in addition to the polymerization initiator, a method using a polymerization terminator such as benzoquinone or dinitrobenzene in addition to the polymerization initiator, JP 2000-128911 A Alternatively, a bulk polymerization method using a compound having one thiol group and a secondary hydroxyl group as described in JP-A-2000-344823, or a polymerization catalyst in which the compound and an organometallic compound are used in combination. Etc. In particular, the method described in JP2000-128911A or JP2000-344823A is preferably used.

  The acrylic resin preferably has a hydroxyl value measured in accordance with JIS K 0070 (1992) of 30 to 150 mgKOH / g.

  As the solvent of the resin solution, a solvent containing a good solvent for the transparent resin can be used, and a poor solvent may be contained as long as the transparent resin does not precipitate. Examples of the good solvent for the cellulose ester resin include organic halogen compounds such as methylene chloride. Moreover, as a poor solvent with respect to a cellulose-ester-type resin, C1-C8 alcohols, such as methanol, etc. are mentioned, for example.

  In addition, the resin solution used in the present embodiment is a component other than the transparent resin, the compound having negative orientation birefringence, and the solvent (additives) as long as the effects of the present invention are not impaired. ) May be contained. Examples of the additive include fine particles, plasticizers, antioxidants, ultraviolet absorbers, heat stabilizers, conductive substances, flame retardants, lubricants, and matting agents.

  The fine particles are appropriately selected according to the purpose of use, but are preferably fine particles that can scatter visible light when contained in a transparent resin. The fine particles may be inorganic fine particles such as silicon oxide or organic fine particles such as acrylic resin.

  Moreover, the solution of a cellulose-ester-type resin is obtained by mixing said each composition. The obtained cellulose ester resin solution is preferably filtered using a suitable filter medium such as filter paper.

  The plasticizer can be used without particular limitation, for example, phosphate ester plasticizer, phthalate ester plasticizer, trimellitic ester plasticizer, pyromellitic acid plasticizer, glycolate plasticizer, Examples include citrate plasticizers and polyester plasticizers. When the plasticizer is contained, the content is preferably 1 to 40% by mass, and 3 to 20% by mass with respect to the cellulose ester-based resin in consideration of dimensional stability and processability. More preferably, it is more preferably 4 to 15% by mass. If the content of the plasticizer is too small, a smooth cut surface cannot be obtained when slitting or punching, and there is a tendency for generation of chips. That is, the effect of including a plasticizer cannot be sufficiently exhibited.

  The antioxidant can be used without any particular limitation, but for example, a hindered phenol compound is preferably used. Moreover, when it contains the said antioxidant, it is preferable that content of antioxidant is 1 ppm-1.0% by mass ratio with respect to a cellulose-ester resin, and it is more preferable that it is 10-1000 ppm.

  The resin film produced by the production method according to the present embodiment can be used for a polarizing plate or a liquid crystal display member because of its high dimensional stability. In this case, deterioration prevention of the polarizing plate or the liquid crystal is possible. Therefore, an ultraviolet absorber is preferably used.

  As the ultraviolet absorber, those which are excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less and have little absorption of visible light having a wavelength of 400 nm or more are preferably used from the viewpoint of good liquid crystal display properties. Specifically, the transmittance at 380 nm is preferably less than 10%, more preferably less than 5%. Specific examples of the UV absorber include oxybenzophenone compounds, benzotriazole compounds (benzotriazole UV absorbers), salicylic acid ester compounds, benzophenone compounds (benzophenone UV absorbers), and cyanoacrylates. Compounds, nickel complex compounds, triazine compounds, and the like. In these, a benzotriazole type ultraviolet absorber and a benzophenone type ultraviolet absorber are preferable. The content of the ultraviolet absorber is preferably 0.1% by mass to 2.5% by mass, and 0.8% by mass to 2.0% by mass in consideration of the effect as an ultraviolet absorber, transparency, and the like. % Is more preferable.

  Examples of the heat stabilizer include kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide, inorganic fine particles such as alumina, and alkaline earth metal salts such as calcium and magnesium.

  The conductive material is not particularly limited, and examples thereof include ionic conductive materials such as anionic polymer compounds, conductive fine particles such as metal oxide fine particles, and antistatic agents. By containing the conductive substance, a resin film having a preferable impedance can be obtained. Here, the ion conductive substance is a substance that shows electric conductivity and contains ions that are carriers for carrying electricity.

  Next, as an example of a method for preparing a dope, a case where a cellulose ester resin is used as a transparent resin will be described.

  The method for dissolving the cellulose ester resin when preparing the dope is not particularly limited, and a general method can be used. By combining heating and pressurization, it is possible to heat above the boiling point of the solvent at normal pressure, and it is possible to dissolve the cellulose ester resin in the solvent above the boiling point at normal pressure. It is preferable from the viewpoint of preventing the occurrence of. In addition, a method in which a cellulose ester resin is mixed with a poor solvent and wetted or swollen, and then a good solvent is added and dissolved is also preferably used.

  The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas, or a method of heating the solvent in a sealed container and increasing the vapor pressure of the solvent by the heating. The heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  A higher solvent temperature (heating temperature) for dissolving the cellulose ester-based resin is preferable from the viewpoint of solubility of the cellulose ester. However, when the heating temperature is increased, the pressure in the container is increased by the pressurization. Productivity must be reduced. Therefore, the heating temperature is preferably 45 to 120 ° C. The pressure is adjusted to a pressure at which the solvent does not boil at the set temperature. Alternatively, a cooling dissolution method is also preferably used, whereby the cellulose ester resin can be dissolved in a solvent such as methyl acetate.

  Next, the obtained cellulose ester resin solution is filtered using a suitable filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like. However, if the absolute filtration accuracy is too small, there is a problem that the filter medium is likely to be clogged. For this reason, a filter medium with an absolute filtration accuracy of 0.050 mm or less is preferable, and a filter medium with 0.001 to 0.008 mm is more preferable.

The material of the filter medium is not particularly limited, and a normal filter medium can be used. For example, a plastic filter material such as polypropylene or Teflon (registered trademark) or a metal filter material such as stainless steel is preferable because fibers do not fall off. It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose ester resin solution by filtration. The bright spot foreign matter is when two polarizing plates are arranged in a crossed nicols state, a resin film is placed between them, light is applied from one polarizing plate side, and observed from the other polarizing plate side. It is a point (foreign matter) where light from the opposite side appears to leak, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less.

  The filtration is not particularly limited and can be carried out by a usual method, but the method of filtration while heating at a temperature not lower than the boiling point of the solvent at normal pressure and at which the solvent does not boil under pressure may be performed before and after the filtration. The increase in the difference in filtration pressure is small and preferable. The temperature is preferably 45 to 120 ° C. The filtration pressure is preferably smaller, for example, 1.6 MPa or less.

  When the additives are contained, for example, the additives may be dissolved in an organic solvent such as alcohol, methylene chloride, dioxolane, etc. and then added to the dope, or may be added directly to the dope composition. In addition, for inorganic powders that do not dissolve in organic solvents, the additive and cellulose ester resin are added to the dope using a dissolver or sand mill with the additive dispersed in the cellulose ester resin. It is preferable.

  The fine particles are dispersed in the obtained cellulose ester resin solution. The method for dispersing is not particularly limited, and can be performed, for example, as follows. For example, first, a dispersion solvent and fine particles are stirred and mixed, and then dispersed using a disperser. This is a fine particle dispersion. The fine particle dispersion is added to the cellulose ester resin solution and stirred.

  Examples of the dispersing solvent include lower alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, and butyl alcohol. Moreover, although it does not specifically limit to lower alcohol, It is preferable to use the thing similar to the solvent used when preparing the solution of a cellulose-ester-type resin.

  The dispersing machine can be used without any particular limitation, and a general dispersing machine can be used. Dispersers can be broadly divided into media dispersers and medialess dispersers. Medialess dispersers are preferred from the viewpoint of lower haze (higher translucency). Examples of the media disperser include a ball mill, a sand mill, and a dyno mill. Examples of the medialess disperser include an ultrasonic type, a centrifugal type, and a high pressure type, and a high pressure type dispersing device is preferable. The high-pressure dispersion device is a device that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube. Examples of the high-pressure dispersing device include an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation, a nanomizer manufactured by Nanomizer, and the like, and a Menton Gorin type high-pressure dispersing device. Examples of the Menton Gorin type high-pressure dispersion device include Izumi Food Machinery homogenizer, Sanwa Kikai Co., Ltd. UHN-01, and the like.

  The optical film manufactured by the manufacturing method according to the present embodiment is obtained by the manufacturing method, and is a wide optical film having a retardation sufficiently close to 0 and wide. For this reason, it can apply to image display apparatuses, such as a liquid crystal display device, as a phase difference film for which retardation is calculated | required sufficiently close to 0, especially a phase difference film for IPS.

(Polarizer)
The polarizing plate which concerns on this embodiment is equipped with a polarizing element and the transparent protective film arrange | positioned on the surface of the said polarizing element, and the said transparent protective film is the said optical film. The polarizing element is an optical element that emits incident light converted to polarized light.

  As the polarizing plate, for example, a resin film or a saponified polyvinyl alcohol aqueous solution is used on at least one surface of a polarizing element produced by immersing and stretching a polyvinyl alcohol film in an iodine solution. What laminated | stacked the said laminated | multilayer film is preferable. Moreover, the said optical film may be laminated | stacked also on the other surface of the said polarizing element, and the transparent protective film for another polarizing plate may be laminated | stacked. As a transparent protective film for this polarizing plate, for example, as a commercially available cellulose ester film, KC8UX2M, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC8UY-HA, KC8UX-RHA (above, manufactured by Konica Minolta Opto Co., Ltd.) Etc. are preferably used. Or you may use resin films, such as cyclic olefin resin other than a cellulose-ester film, an acrylic resin, polyester, a polycarbonate. In this case, since the saponification suitability is low, it is preferable to perform an adhesive process on the polarizing plate through an appropriate adhesive layer.

  As described above, the polarizing plate uses the optical film as a protective film laminated on at least one surface side of the polarizing element. In that case, when the said optical film functions as a phase difference film, it is preferable to arrange | position so that the slow axis of a resin film may be substantially parallel or orthogonal to the absorption axis of a polarizing element.

  Moreover, as a specific example of the said polarizing element, a polyvinyl alcohol-type polarizing film is mentioned, for example. Polyvinyl alcohol polarizing films include those obtained by dyeing iodine on polyvinyl alcohol films and those obtained by dyeing dichroic dyes. As the polyvinyl alcohol film, a modified polyvinyl alcohol film modified with ethylene is preferably used.

  The polarizing element is obtained as follows, for example. First, a film is formed using a polyvinyl alcohol aqueous solution. The obtained polyvinyl alcohol film is uniaxially stretched and then dyed or dyed and then uniaxially stretched. And preferably, a durability treatment is performed with a boron compound.

  The thickness of the polarizing element is preferably 5 to 40 μm, more preferably 5 to 30 μm, and more preferably 5 to 20 μm.

  When the cellulose ester resin film is laminated on the surface of the polarizing element, it is preferable to bond the cellulose ester resin film with an aqueous adhesive mainly composed of completely saponified polyvinyl alcohol or the like. Moreover, in the case of resin films other than a cellulose ester-type resin film, it is preferable to carry out the adhesive process to a polarizing plate through a suitable adhesion layer.

  The polarizing plate as described above can be applied to a liquid crystal display device having a large screen by using the wide resin film according to the present embodiment as the transparent protective film.

(Liquid crystal display device)
The liquid crystal display device according to this embodiment includes a liquid crystal cell and two polarizing plates arranged so as to sandwich the liquid crystal cell, and at least one of the two polarizing plates is the polarizing plate. . Note that the liquid crystal cell is a cell in which a liquid crystal substance is filled between a pair of electrodes, and by applying a voltage to the electrodes, the alignment state of the liquid crystal is changed and the amount of transmitted light is controlled. Such a liquid crystal display device can have a large screen by using the wide optical film according to the present embodiment as a transparent protective film for a polarizing plate.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

  An optical film was produced by the following method.

(Preparation of dope)
First, cellulose triacetate resin (acyl group substitution degree: 2.5 (degree of acetylation: 61.0%), mass average molecular weight Mw as a transparent resin in a dissolution tank containing 475 parts by mass of methylene chloride and 50 parts by mass of ethanol. : 300,000, number average molecular weight Mn: 100,000) 85 parts by mass, further, 1.5 parts by mass of 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) benzotriazole, methyl methacrylate 2-hydroxyethyl acrylate copolymer (80/20 (mass ratio), mass average molecular weight Mw: 8000, number average molecular weight Mn: 4000) 8 parts by mass, methyl acrylate polymer as a compound having negative orientation birefringence (Mass average molecular weight Mw: 1000, number average molecular weight Mn: 800) 5 parts by mass were added. And after raising the liquid temperature to 80 ° C., the mixture was stirred for 3 hours. By doing so, a cellulose triacetate resin solution was obtained. Then, stirring was complete | finished and it was left until the liquid temperature became 43 degreeC. Then, the obtained resin solution was filtered using a filter paper having a filtration accuracy of 0.005 mm. Air bubbles in the resin solution were degassed by allowing the resin solution after filtration to stand overnight. The resin solution thus obtained was used as a dope to produce a resin film (cellulose triacetate film) as follows.

  In addition, the said methyl acrylate polymer was obtained by the method according to Example 3 as described in Unexamined-Japanese-Patent No. 2000-128911, Comprising: The hydroxyl value (OHV) was 50 mgKOH / g.

(Manufacture of cellulose triacetate film)
First, the temperature of the obtained dope was adjusted to 35 ° C., and the temperature of the endless belt support was adjusted to 25 ° C. And the dope was cast from the casting die to the endless belt support using the optical film manufacturing apparatus as shown in FIG. By doing so, the web was formed on the endless belt support, and it was conveyed while drying so that the residual solvent ratio at the time of peeling of the web (film) was 80% by mass. Then, the film was peeled from the endless belt support, and the peeled film was stretched in the TD direction under the conditions shown in Tables 1 to 3 while gripping both ends of the web with clips using a stretching device (tenter). By doing so, each cellulose triacetate film which concerns on Examples 1-27 and Comparative Examples 1-9 was manufactured. Here, a cellulose triacetate film having a width of 1000 to 2000 m can be produced when stretched at a stretch rate of 25%, and a cellulose triacetate having a width of 2000 to 2500 m when stretched at a stretch rate of 35%. When a film can be produced and stretched at a stretch rate of 45%, a cellulose triacetate film having a width of 2500 to 3000 m can be produced.

  And the glass transition temperature Tg of the obtained cellulose triacetate film was 130 degreeC. In addition, the glass transition temperature Tg of the film was measured using a differential scanning calorimeter (DSC) (DSC8230 manufactured by Rigaku Corporation).

  Each optical film (Examples 1-27 and Comparative Examples 1-9) obtained as described above was evaluated by the method shown below.

[Retardation (Ro and Rt)]
Ro and Rt of each of the optical films (Examples 1 to 27 and Comparative Examples 1 to 9) were measured using an automatic birefringence measuring apparatus (KOBRA-21ADH manufactured by Oji Scientific Instruments).

[Flatness]
The flatness of each of the optical films (Examples 1 to 27 and Comparative Examples 1 to 9) was evaluated as follows.

  First, using a one-dimensional surface roughness meter surftest SV3000 manufactured by Mitutoyo Co., Ltd., the arithmetic surface roughness Ra within a range of 10 cm × 10 cm of each film was measured at 10 locations in the width direction and 10 locations in the length direction. A total of 100 points were measured in the form of dots. Among them, when the number of locations where Ra was 0.2 μm or more was less than 10, “◯” was evaluated, and when it was 10 or more, “×” was evaluated.

  The above evaluation results are shown in Tables 1-3.

  From Tables 1 to 3, when the residual solvent ratio of the film became 1% by mass or less and the film was stretched at a temperature 30 to 100 ° C. higher than the glass transition temperature of the film (Examples 1 to 27), the film remained. When the film is stretched in a state where the solvent ratio is higher than 1% by mass (Comparative Example 1, Comparative Example 4 and Comparative Example 7), and when the film is stretched in a state not higher by 30 ° C. than the glass transition temperature of the film (Comparison) From Example 2, Comparative Example 5 and Comparative Example 8), it can be seen that Ro and Rt are both close to 0.

  When the film is stretched under the conditions where the residual solvent ratio of the film is 0.5 mass% or less and 200 ° C. or more (Example 7, Example 8, Example 16, Example 17, Example 25, and Example 26). From the other examples, it can be seen that Ro and Rt are closer to 0.

  Moreover, Examples 1-27 had the high flatness of the film. On the other hand, when it was higher than the glass transition temperature of the film by more than 100 ° C. (Comparative Example 3, Comparative Example 6 and Comparative Example 9), the flatness of the film was lowered when the film was stretched.

DESCRIPTION OF SYMBOLS 11 Optical film manufacturing apparatus 12 Endless belt support 13 Casting die 14 Peeling roller 15 Drying apparatus 16 Stretching apparatus 17 Winding apparatus

Claims (9)

An in-plane direction retardation is 0 nm or more and 5 nm or less, and a thickness direction retardation is −5 nm or more and 5 nm or less, and a method for producing an optical film,
A casting step in which a resin solution in which a transparent resin and a compound having negative orientation birefringence are dissolved in a solvent is cast on a traveling support to form a casting film;
A peeling step of peeling the cast film from the support as a film;
A drying step of drying the solvent in the peeled film;
And a stretching step of stretching the film at a temperature 30 to 100 ° C. higher than the glass transition temperature of the film after the residual solvent ratio of the film becomes 1% by mass or less. .   2. The method for producing an optical film according to claim 1, wherein in the stretching step, the film is stretched at 200 ° C. or more after the residual solvent ratio of the film becomes 0.5 mass% or less.   The optical film according to claim 1 or 2, wherein the film before the stretching step has an in-plane retardation of 0 nm to 5 nm and a thickness direction retardation of -5 nm to 5 nm. Production method.   The method for producing an optical film according to claim 1, wherein the transparent resin is a cellulose ester resin.   The method for producing an optical film according to claim 1, wherein the compound having negative orientation birefringence is an acrylic resin.   The width of the said optical film is 1000-3000 mm, The manufacturing method of the optical film of any one of Claims 1-5 characterized by the above-mentioned.   It is obtained by the manufacturing method of the optical film of any one of Claims 1-6, The optical film characterized by the above-mentioned. A polarizing plate comprising a polarizing element and a transparent protective film disposed on the surface of the polarizing element,
The said transparent protective film is an optical film of Claim 7, The polarizing plate characterized by the above-mentioned. A liquid crystal display device comprising a liquid crystal cell and two polarizing plates arranged so as to sandwich the liquid crystal cell,
A liquid crystal display device, wherein at least one of the two polarizing plates is the polarizing plate according to claim 8.

Images