JP2011195605A - Resin film, method for producing resin film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin film excellent in weather resistance, such as little dimensional change due to changes in temperature and relative humidity.SOLUTION: The resin film is used, which has Martens hardness of 165-350 MPa obtained by measuring at least either one of the surfaces by Nano-indentation method with a measurement depth of 1 μm and relaxation modulus of 3,800-6,000 MPa obtained by measuring at least either one of the surfaces by Nano-indentation method with a measurement depth of 1 μm.

Description

  The present invention relates to a resin film, a method for producing the resin film, a polarizing plate using the resin film as a transparent protective film, and a liquid crystal display device including the polarizing plate.

  Resin films are used in various fields, such as liquid crystal display devices, in view of their chemical characteristics, mechanical characteristics, electrical characteristics, and the like. Specifically, various resin films, such as a transparent protective film for protecting the polarizing element of the polarizing plate, are disposed in the image display area of the liquid crystal display device. As such a resin film, for example, a resin film excellent in transparency such as a cellulose ester film is used.

  In addition, the resin film is required to have excellent weather resistance such as a small dimensional change due to temperature and humidity changes. Specifically, for example, in the case of a liquid crystal display device including a polarizing plate using a resin film as a transparent protective film for protecting the polarizing element of the polarizing plate, the dimension of the resin film attached to the polarizing element changes. As a result, stress was generated between the polarizing element and the resin film, and the transparent protective film might be peeled off from the polarizing element. In addition, the polarizing plate provided with the resin film is warped due to the dimensional change of the resin film, and the warping may be peeled off from the liquid crystal cell of the liquid crystal display device.

  In addition, the fields of use of liquid crystal display devices are diversifying, and the use of liquid crystal display devices is not limited to indoor use but is also increasing outdoors. Specifically, for example, it may be used as an advertising medium instead of a poster by displaying video or information on a liquid crystal display device, that is, used as a digital signage. In such a case, the liquid crystal display device may be used in a poor environment such as under hot weather or under high temperature and high humidity, and the resin film provided in the liquid crystal display device may be used in such a poor environment. Even so, it is required to have excellent weather resistance capable of suppressing dimensional changes.

  Examples of the resin film provided in the liquid crystal display device include those described in Patent Document 1 and Patent Document 2.

  In Patent Document 1, the film length method and the elongation at break in the width direction are both 5% or more and 150% or less, the in-plane retardation Ret is 10 nm or less, and the thickness direction retardation Rth is −. An acrylic film having a thickness of 10 to 10 nm and having a film surface hardness of 0.2 GPa (200 MPa) to 0.35 GPa (350 MPa) measured by a nano-indentation method is described.

  Patent Document 2 describes a plastic film for fixing liquid crystal molecules on the surface, and having a relaxation elastic modulus of 3.5 GPa or more on the surface.

JP 2008-101202 A JP 2008-281758 A

  The present inventor paid attention to the hardness of the surface of the resin film and the like in order to obtain a resin film having a small dimensional change due to temperature and humidity changes as described above. Specifically, attention was paid to the Martens hardness and relaxation modulus of the surface of the resin film measured at a measurement depth of 1 μm by the nanoindentation method.

  And as a method of adjusting the hardness of the surface of the resin film, etc., the method of increasing the polarity of the resin constituting the resin film, the method of increasing the molecular weight of the resin, the method of aligning the orientation of the resin molecules, and the resin film Although the method of hardening the surface of a resin film etc., such as a method of containing a crosslinking agent, can be considered, each has the following drawbacks.

  When the polarity of the resin constituting the resin film is increased, the crystallization of the resin proceeds and the optical properties such as the refractive index of the resin film tend to change. For this reason, it was not preferable to use the resin film for optical applications.

  Moreover, when the resin constituting the resin film has a high molecular weight, it tends to be difficult to orient the resin molecules. For this reason, since the orientation of the resin molecules is low, the surface hardness cannot be sufficiently increased unless the molecular weight is very high. In addition, since the orientation of the resin molecules becomes low, it is difficult to use in combination with a method for aligning the orientation of the molecules. Furthermore, if the resin is made to have a high molecular weight, the cost tends to increase.

  In addition, examples of a method for aligning the orientation of resin molecules include a method of stretching a resin film, and the like. However, if the stretching rate is increased in order to increase the orientation of the resin molecules, the resin film may be broken. was there. Therefore, in order to enhance the effect of improving the orientation of the resin molecules by stretching, it is conceivable that the resin film contains a low molecular weight component such as a plasticizer. However, when a low molecular weight component such as a plasticizer is contained in the resin film, the fluidity of the resin molecules is increased and the resin film tends not to be sufficiently hard.

  Further, in the method of incorporating a crosslinking agent into the resin film, it is difficult to uniformly disperse the crosslinking agent unless the crosslinking agent to be contained is sufficiently high in compatibility with the resin constituting the resin film. Moreover, it is difficult to control the crosslinking reaction by the crosslinking agent, and there is a tendency that the quality of the obtained resin film is uneven. In particular, when it is used as an optical film provided in a liquid crystal display device corresponding to a large screen, it is not preferable because it has a large area and requires uniform hardness.

  Therefore, it is positively adjusted that the Martens hardness and relaxation modulus of the surface of the resin film measured at a measurement depth of 1 μm by the nanoindentation method can sufficiently suppress the dimensional change due to temperature and humidity changes. Otherwise it was difficult.

  Patent Document 1 only discloses an acrylic film having a film surface hardness of 200 MPa or more and 350 MPa or less measured by a nanoindentation method, and the acrylic film has a low elastic modulus and is restored from deformation. For example, there is a tendency that handling properties at the time of manufacture are not good.

  Patent Document 2 describes a material having a surface relaxation elastic modulus of 3.5 GPa or more. Here, the surface relaxation elastic modulus is measured at a measurement depth of 200 nm in the nanoindentation method. It is the value. The surface relaxation modulus of the same film measured at a measurement depth of 1 μm by the nanoindentation method was actually about 3 GPa, and the surface relaxation modulus was too low.

  From the above, the films described in Patent Document 1 and Patent Document 2 are easily plastically deformed, and when the dimensions change due to the stress generated during transport or bonding of the resin film, the film is deformed as it is. There is a tendency for dimensional changes due to temperature and humidity changes to increase. In addition, it is difficult to make the surface hardness and relaxation elastic modulus within a predetermined range by simply stretching, and it is difficult to make the dimensional change due to temperature and humidity changes sufficiently small. .

  This invention is made | formed in view of this situation, Comprising: It aims at providing the resin film excellent in weather resistance, such as a small dimensional change by a temperature / humidity change. Moreover, it aims at providing the manufacturing method of a resin film, the polarizing plate which used the said resin film as a transparent protective film, and the liquid crystal display device provided with the said polarizing plate.

  The resin film according to one embodiment of the present invention has a Martens hardness of 165 to 350 MPa measured at least one surface at a measurement depth of 1 μm in the nanoindentation method, and has a measurement depth in the nanoindentation method. The relaxation elastic modulus measured at least one of the surfaces at 1 μm is 3800 to 6000 MPa.

  According to such a configuration, by setting the Martens hardness and the relaxation elastic modulus of the surface of at least one of the resin films within the above ranges, respectively, the weather resistance, such as small dimensional change due to temperature and humidity changes, is achieved. An excellent resin film can be provided. Moreover, since this resin film has the surface Martens hardness and the relaxation elastic modulus in the said range, respectively, it is excellent also in mechanical strength.

  This is presumed as follows.

  If the Martens hardness of the surface of at least one of the resin films is within the above range, the surface is sufficiently hard, and is not easily deformed by the stress generated when the resin film is transported or bonded, and is flexible. It is considered that the dimensional change due to the temperature and humidity change can be suppressed by holding. If the relaxation elastic modulus of the surface of at least one of the resin films is within the above range, the elastic recovery and plastic deformation of the resin film work favorably with respect to minute dimensional changes due to temperature and humidity changes. It is thought that the force which returns a dimension works, suppressing the further dimensional change by a humidity change.

  That is, if the Martens hardness and the relaxation modulus of the surface of at least one of the resin films are within the above ranges, the resin constituting the resin film is suitably oriented, and the polarity of the resin is increased, It is considered that the surface hardness can exhibit excellent weather resistance such as a small dimensional change due to temperature and humidity changes without increasing the molecular weight of the resin.

  From the above, by setting the Martens hardness and relaxation modulus of the surface of at least one of the resin films within the above ranges, a resin film having excellent weather resistance such as a small dimensional change due to temperature and humidity changes is obtained. It is thought that it can be provided.

  Moreover, it is preferable that the absolute value of the difference of the Martens hardness which measured one surface and the Martens hardness which measured the other surface is 10 Mpa or less. According to such a configuration, a smaller dimensional change due to temperature and humidity changes can be obtained. Moreover, the obtained resin film can suppress the curvature (curl) which generate | occur | produces when the dimensional change by a temperature / humidity change differs by the one surface and the other surface.

  Moreover, it is preferable that the absolute value of the difference of the relaxation elastic modulus which measured one surface and the relaxation elastic modulus which measured the other surface is 200 Mpa or less. According to such a configuration, a smaller dimensional change due to temperature and humidity changes can be obtained. That is, since the dimensional change is different when the relaxation elastic modulus is different, the difference in dimensional change due to the temperature and humidity change is reduced between one surface and the other surface. Therefore, the obtained resin film can suppress warpage (curl) caused by a difference in dimensional change.

  Moreover, it is preferable to contain at least one of a cellulose resin and a cellulose resin derivative. According to such a configuration, it is possible to provide a resin film having excellent weather resistance such as small dimensional change due to temperature and humidity changes and high transparency.

  Moreover, the method for producing a resin film according to another aspect of the present invention is the method for producing the resin film, wherein both end portions in the width direction of the long film are gripped by a plurality of pairs of gripping portions. However, the gripping part includes a stretching process in which the gripping part moves in the longitudinal direction of the film and moves in the direction of gradually increasing the distance between the gripping parts in the width direction of the film. It is carried out in the presence of a poor solvent vapor.

  According to such a structure, the resin film excellent in weather resistance and mechanical strength as described above can be easily produced.

  This is presumed as follows.

  Since the film is stretched in the presence of the vapor of the poor solvent, it is easier to stretch than stretching in the presence of dry air, and it is considered that the occurrence of breakage and the like can be suppressed even when stretched at a high stretch rate. Further, when stretching is performed in the presence of a good solvent vapor, it is necessary to increase the uniformity of temperature and solvent concentration in a region (stretching zone) where the stretching process is performed to a level where it is difficult to achieve. In such a case, it becomes difficult to maintain uniformity and unevenness in temperature and solvent concentration occurs, and the resin film partially dissolves due to reasons such as the resin film partially dissolving due to this unevenness. And it is thought that the property of the resin film obtained cannot be ensured by the melt | dissolution. Further, when the film is stretched at a high stretch rate in the presence of a good solvent vapor, it is considered that the resin film tends to break due to partial dissolution of the resin film.

  Therefore, by performing stretching in the presence of the poor solvent vapor of the film, it is possible to stretch at a high stretch while suppressing the occurrence of breakage of the resin film, etc., so the Martens hardness and relaxation of the surface of the resin film It is thought that it can extend | stretch so that an elasticity modulus may become in the said range, respectively.

  And since the Martens hardness and the relaxation elastic modulus of the surface of the resin film are each stretched so as to be within the above ranges, the resin constituting the resin film is preferably oriented, and the polarity of the resin is increased. It is considered that the surface hardness can exhibit excellent weather resistance such as a small dimensional change due to a change in temperature and humidity without increasing the molecular weight of the resin.

  As mentioned above, the resin film excellent in the weather resistance and mechanical strength as described above can be easily produced.

  Moreover, it is preferable that the density | concentration of the vapor | steam of the poor solvent in the said extending process is 5-20 volume%. According to such a structure, the resin film excellent in weather resistance and mechanical strength can be manufactured more easily. This is considered to be a suitable concentration at which the concentration of the poor solvent vapor can be stretched with high stretching while suppressing the occurrence of breakage of the resin film.

  Moreover, it is preferable to provide the heating process which heats the said film in at least one before and behind the said extending process. According to such a structure, the resin film excellent in weather resistance and mechanical strength can be manufactured more easily.

  Moreover, the polarizing plate according to another aspect of the present invention is a polarizing plate comprising a polarizing element and a transparent protective film disposed on at least one surface of the polarizing element, wherein the transparent protective film is It is the said resin film, It is characterized by the above-mentioned. According to such a configuration, as a transparent protective film of a polarizing plate, a resin film having excellent weather resistance, for example, a small dimensional change due to temperature and humidity changes is applied. For example, when applied to a liquid crystal display device A polarizing plate capable of suppressing the occurrence of peeling from the liquid crystal cell or the like is obtained. Furthermore, since the resin film used as a transparent protective film of a polarizing plate has high mechanical strength, the obtained polarizing plate is excellent in mechanical strength.

  The liquid crystal display device according to another aspect 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, the two polarizing plates. At least one of the plates is the polarizing plate. According to such a configuration, since the polarizing plate having a resin film having excellent weather resistance, for example, a small dimensional change due to changes in temperature and humidity is used, the occurrence of peeling from a liquid crystal cell or the like is suppressed. A liquid crystal display device with high performance can be provided. Furthermore, the liquid crystal display device obtained also has high product stability also from the point that the mechanical strength of the polarizing plate provided is high.

  ADVANTAGE OF THE INVENTION According to this invention, the resin film excellent in weather resistance, such as a small dimensional change by a temperature / humidity change, can be provided. Moreover, the manufacturing method of a resin film, the polarizing plate which used the said resin film as a transparent protective film, and the liquid crystal display device provided with the said polarizing plate are provided.

1 is a schematic diagram showing a configuration of a stretching device 11. FIG. It is the schematic which shows the basic composition of the manufacturing apparatus 21 of the resin film by a solution casting film forming method. It is the schematic which shows the fundamental structure of the manufacturing apparatus 31 of the resin film by a melt casting film forming method.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

[Resin film]
The resin film according to the present embodiment has a Martens hardness (HMT 115) measured at least one surface at a measurement depth of 1 μm in the nanoindentation method of 165 to 350 MPa, and is measured in the nanoindentation method. The relaxation elastic modulus (Eit) measured at least one of the surfaces at a depth of 1 μm is 3800 to 6000 MPa.

  As described above, the present inventor has obtained a surface of a resin film measured at a measurement depth of 1 μm by a nano-indentation method in order to obtain a resin film having excellent weather resistance such as a small dimensional change due to a change in temperature and humidity. We focused on the Martens hardness and relaxation elastic modulus.

  And as a method of adjusting the hardness of the surface of the resin film, generally, a method of increasing the polarity of the resin constituting the resin film, a method of increasing the molecular weight of the resin, a method of aligning the orientation of the resin molecules, In addition, a method of hardening the surface of the resin film, such as a method of adding a crosslinking agent to the resin film, can be considered, but there are disadvantages as described above. In other words, it was difficult to make the surface Martens hardness and relaxation modulus of the resin film measured at a measurement depth of 1 μm in the nano-indentation method within the above range unless positively adjusted. .

  Therefore, the resin film according to the present embodiment has a temperature and humidity by making the Martens hardness and relaxation elastic modulus measured at least one surface at a measurement depth of 1 μm in the nanoindentation method within the above ranges, respectively. It is possible to provide a resin film having excellent weather resistance, such as a small dimensional change due to change. Moreover, since this resin film has the surface Martens hardness and the relaxation elastic modulus in the said range, respectively, it is excellent also in mechanical strength.

  The nano-indentation method uses an ultra-micro hardness tester to push an indenter consisting of a diamond tip with a regular triangular pyramid shape (Berkovic type) into a flat sample surface (here, a resin film), and load / unload tests And the elastic modulus and hardness are measured from the load / unload response at that time. Specifically, a test force (load) -indentation depth curve is created by the load / unload test, and the hardness and elastic modulus are obtained from the curve. Specifically, the test force (load) -indentation depth curve is created by performing the following operations. First, the indenter is pushed into the sample while increasing the load at a constant speed until the indenter reaches a predetermined pushing depth from the sample surface. Then, after the indenter is pushed down to a predetermined pushing depth, it is held for a predetermined time with a constant load. At that time, the indenter gradually sinks into the sample. Then, after the holding is completed, the indenter is pulled out from the sample so that the load decreases at a constant speed. At that time, even if the indenter is returned to the position immediately before being pushed into the sample, the indenter and the sample are separated by the amount of deformation caused by the pushing of the indenter. Such an operation is performed to create the test force (load) -indentation depth curve. As the ultra-micro hardness meter, specifically, for example, Shimadzu dynamic ultra-micro hardness meter DUH-211S manufactured by Shimadzu Corporation can be used.

  And the Martens hardness (HMT 115) measured in the nanoindentation method is a hardness measured in a state where a test force (load) is applied. Specifically, the load F is calculated by dividing the load F by the surface area As intruded by the indenter from the surface of the sample from the relationship of the load-indentation depth curve measured when the load increases. More specifically, when a regular triangular pyramid indenter having an inter-ridge angle (opposite ridge angle) of 115 ° is used, it is calculated from the following formula (1).

HM = F / As = F / (26.43 × h ² ) (1)
In the formula (1), HM represents Martens hardness (MPa), F represents load (N), As represents surface area (mm ² ), and h represents indentation depth (mm). ).

  Therefore, the Martens hardness measured on the surface at a measurement depth of 1 μm in the nanoindentation method is the hardness calculated from the above formula (1) when the indentation depth h is 1 μm (0.001 mm). is there. In addition, the Martens hardness can measure the hardness of a thin film and a higher elastic force than the Vickers hardness which measures only plastic deformation from the deformation trace.

  The relaxation elastic modulus (Eit) measured in the nanoindentation method is calculated from the following formula (2) using the test force (load) -indentation depth curve created by the load / unload test. Is the elastic modulus.

1 / Er = (1-Vs ² ) / Eit + (1-Vi ² ) / Ei (2)
In the above formula (2), Er represents a converted elastic modulus (MPa) by indentation contact, Vs represents a Poisson's ratio of the sample, Eit represents a relaxation elastic modulus (MPa), and Vi represents an indenter. The Poisson's ratio is shown, and Ei is the Young's modulus (MPa) of the indenter. And Er is computable from following formula (3). Vs is a value obtained by dividing lateral strain (%) by longitudinal strain (%). For example, strain (elongation) (lateral strain (%) and longitudinal strain (%)) when a resin film is pulled at a constant speed with a tensile tester can be measured and calculated from these strains. More specifically, for example, it can be measured by a Poisson's ratio measuring device (for example, Tensilon RTA-100 manufactured by Orientec Co., Ltd.). Vi is 0.07. Ei is 1.14 × 10 ⁶ MPa.

S = 2 × Er × Ap ^0.5 / π ^0.5 (3)
In the above formula (3), S represents the inclination at the start of unloading in the test force (load) -indentation depth curve (the inclination of the approximate curve (dF / dh)), and Er is converted by indentation contact. The elastic modulus (MPa) is indicated, and Ap is the projected contact area (mm ² ). Ap is calculated from the following equation (4).

^{Ap = 23.96 × hc 2 (4} )
In the above formula (4), Ap represents the contact projected area (mm ² ), and hc represents the contact depth (mm). And hc is calculated from the following equation (5).

hc = hmax−0.75 × (hmax−hr) (5)
In the above formula (5), hc represents the contact depth (mm), hmax represents the indentation depth (maximum depth) (mm) at the maximum test force Fmax, and hr represents the test force. (Load) —The intercept (mm) at which the tangent line of the unloading curve at the maximum test force Fmax of the indentation depth curve intersects the depth axis.

  Therefore, the relaxation modulus measured on the surface at a measurement depth of 1 μm in the nanoindentation method is that the indentation depth (maximum depth) hmax at the maximum test force Fmax is 1 μm (0.001 mm). Sometimes the elastic modulus is calculated from the above formulas (2) to (5). As described above, this relaxation elastic modulus depends on the slope at the start of unloading in the test force (load) -indentation depth curve (the slope of the approximate curve (dF / dh)), and the plastic deformation of the sample. It becomes an index indicating ease of use, difficulty of elastic recovery, and the like.

  The Martens hardness is 165 to 350 MPa on at least one surface, and the relaxation modulus may be 3800 to 6000 MPa on at least one surface, but both surfaces are within the above range. It is preferable.

  Moreover, as for the said Martens hardness, at least any one surface is 165-350 MPa, and it is preferable that it is 180-350 MPa. Moreover, it is more preferable that the both surfaces are within the above range. If the Martens hardness is too small, the size tends to change due to changes in temperature and humidity. Moreover, when too large, there exists a tendency for a resin film to become easy to receive damage, such as a fracture | rupture. Specifically, for example, when producing a resin film, the film tends to break, for example, when stretched, or when the resin film is attached to a polarizing element. That is, if the Martens hardness of the surface of at least one of the resin films is within the above range, the surface is sufficiently hard, and the dimensions are less likely to change due to changes in temperature and humidity. It is considered that the occurrence of the above-described problems is suppressed.

  And the absolute value of the difference between the Martens hardness measured on one surface and the Martens hardness measured on the other surface, for example, the absolute value of the difference in Martens hardness between the A surface and the B surface of the resin film is 10 MPa or less. It is preferable that it is 5 Mpa or less. If the difference is too large, the difference in dimensional change caused by the stress generated during transport or bonding of the resin film is large between one surface and the other surface. ). Therefore, when the absolute value of the difference in Martens hardness is 10 MPa or less, a dimensional change due to a change in temperature and humidity is smaller.

  In addition, A surface and B surface show the following surfaces. As for the surface of the resin film, the upper surface is referred to as “A surface” and the lower surface is referred to as “B surface” in a stretching process in a stretching apparatus described later. In addition, when the stretching step is performed in the solution casting film forming method or the melt casting film forming method described later, the surface that is in contact with the support (support surface) is the B surface and is not in contact with the support. The surface (air surface) is the A surface.

  In addition, the relaxation elastic modulus of at least one of the surfaces is 3800 to 6000 MPa, and preferably 4200 to 6000 MPa. Moreover, it is more preferable that the both surfaces are within the above range. If the relaxation elastic modulus is too small, it is difficult to be plastically deformed, and on the contrary, there is a tendency that a dimensional change due to temperature and humidity changes tends to occur. Moreover, when the relaxation elastic modulus is too small, it tends to be soft, and it is difficult to make the Martens hardness within the above range. On the other hand, if the relaxation elastic modulus is too large, plastic deformation is likely to occur, and the force to return the dimensions tends to be difficult to work. That is, when the relaxation modulus of the surface of at least one of the resin films is within the above range, the elastic recovery and plastic deformation of the resin film work favorably with respect to minute dimensional changes due to temperature and humidity changes. It is thought that the force which returns a dimension works, suppressing the further dimensional change by a humidity change. The dimensions change slightly due to changes in temperature and humidity, and it is difficult for plastic deformation, and it is considered that the changes in dimensions due to changes in temperature and humidity can be reduced.

  And, the absolute value of the difference between the relaxation elastic modulus measured on one surface and the relaxation elastic modulus measured on the other surface, for example, the absolute value of the difference in relaxation elastic modulus between the A and B surfaces of the resin film is The pressure is preferably 200 MPa or less, and more preferably 100 MPa or less. If the difference is too large, there is a large difference in dimensional change due to temperature and humidity changes between one surface and the other surface, and the resin film tends to warp (curl). Therefore, when the absolute value of the difference between the relaxation elastic moduli is 200 MPa or less, a dimensional change due to a change in temperature and humidity is smaller.

  From the above, when the Martens hardness and the relaxation modulus of the surface of the resin film are within the above ranges, the resin constituting the resin film is preferably oriented, increasing the polarity of the resin or increasing the molecular weight of the resin. It is considered that the surface hardness can exhibit excellent weather resistance, such as a small dimensional change due to temperature and humidity changes, without being changed. And, when the Martens hardness and the relaxation elastic modulus of the surface of the resin film are within the above ranges, respectively, it is possible to provide a resin film excellent in weather resistance such as a small dimensional change due to temperature and humidity changes. Conceivable.

  Moreover, it is preferable that the width | variety of the said resin film is 1000-4000 mm. Such a wide resin film is preferable from the viewpoint of use in a large liquid crystal display device, use efficiency of a film during polarizing plate processing, and production efficiency when used as an optical film. Moreover, it is preferable that the film thickness of the said resin film is 20-100 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 the thickness is measured at 20 to 200 locations in the width direction of the resin film with a contact-type film thickness meter manufactured by Mitutoyo Corporation, and the average of the measured values. Values are shown as film thickness.

  Moreover, when using the said resin film as optical films, such as a transparent protective film of a polarizing plate, it is preferable to contain transparent resin as resin which comprises a resin film. The transparent resin is not particularly limited as long as it is a resin having transparency when formed into a film or a substrate by a solution casting film forming method or a melt casting film forming method. It is preferable that film formation by a film method, a melt casting film formation method, or the like is easy, that the adhesiveness with a hard coat layer or the like 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 resins; cellulose resin derivatives such as cellulose ester resins such as cellulose diacetate resin, cellulose triacetate resin, cellulose acetate butyrate resin, and cellulose acetate propionate resin. Polyester resins such as polyethylene terephthalate resin and polyethylene naphthalate resin; acrylic resins such as polymethyl methacrylate resin; polysulfone resins such as polyethersulfone resin; polyethylene resins, polypropylene resins, cellophane, polyvinylidene chloride resins; Vinyl based resins such as polyvinyl alcohol resin, ethylene vinyl alcohol resin, syndiotactic polystyrene resin, cycloolefin resin and polymethylpentene resin Fats; polycarbonate resins; polyarylate resin; polyether ketone resins; polyether ketone imide resin; polyamide resin; fluorine-based resins. Among these, a cellulose resin and a cellulose resin derivative are preferable. That is, the resin film preferably contains at least one of a cellulose resin and a cellulose resin derivative. By doing so, it is possible to provide a resin film having excellent weather resistance, such as small dimensional change due to temperature and humidity changes, and high transparency. Further, the transparent resin is more preferably a cellulose ester resin, and among the cellulose ester resins, cellulose acetate resin, cellulose propionate resin, cellulose butyrate resin, cellulose acetate butyrate resin, cellulose acetate propionate. Resin and cellulose triacetate resin are preferable, and cellulose triacetate resin is particularly preferable. 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 in view of high mechanical strength when formed into a resin film and an appropriate dope viscosity in the solution casting film forming method. Further, the closer the number average molecular weight (Mn) / weight average molecular weight (Mw) is to 1, the more uniform the molecular weight is, and it is more preferable that the molecular weight is in the range of 0.3 to 1.0.

  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.

[Production method of resin film]
Next, the manufacturing method of the resin film which concerns on this embodiment is demonstrated.

  The method for producing a resin film according to the present embodiment is a method for producing the resin film, wherein the gripping portion is gripped by a plurality of pairs of gripping portions while gripping both end portions in the width direction of the long film. A stretching step of moving in the longitudinal direction of the film and moving in the direction of gradually increasing the distance between the gripping portions in the width direction of the film, wherein the stretching step includes presence of vapor of a poor solvent for the film It is characterized by the following. And if the manufacturing method of the resin film which concerns on this embodiment is equipped with the said extending process and manufactures the said resin film, it will not specifically limit, The film before extending | stretching is not specifically limited. Specifically, for example, as a method for producing a resin film according to the present embodiment, as a stretching step in a solution casting film forming method, a melt casting film forming method, or the like, a method in which the above-described stretching step is performed, etc. Examples of the film before stretching include a film before becoming a final product resin film in the solution casting film forming method and the melt casting film forming method. Moreover, a film refers to the film before extending | stretching and the film in the said extending process here, and a resin film refers to the film after giving the said extending process. And the width direction of a film is a direction orthogonal to the longitudinal direction (conveying direction) of a long film.

(Stretching process)
First, the said extending process is demonstrated.

  As described above, in the stretching step, the gripping portion moves in the longitudinal direction of the film while gripping both side ends in the width direction of the long film with a plurality of pairs of gripping portions. It is a step of moving in the direction of gradually increasing the distance between the gripping portions in the width direction of the film, and is performed in the presence of a poor solvent vapor for the film. Specifically, for example, it is performed by a stretching apparatus as shown in FIG. Moreover, as an extending | stretching 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 view showing the configuration of the stretching apparatus 11. The stretching device 11 stretches the film 17 in a direction (Transverse Direction: TD direction) orthogonal to the transport direction, and includes a first rail 12, a second rail 13, a plurality of clips 14, and a first air curtain forming unit. 15 and the second air curtain forming part 16 and the like. Specifically, as shown in FIG. 1, the film 17 is stretched in the TD direction by gripping both end portions in the width direction with the clips 14 that are gripping portions and increasing the distance between the opposing clips 14. It is something to be made.

  The first rail 12 extends along one end of the film 17 and defines the traveling direction of the clip 14 as will be described later. The second rail 13 extends along the other end of the film 17 and defines the traveling direction of the clip 14 as will be described later. There are a plurality of the clips 14, and each clip grips both end portions in the width direction of the film 17, and the film 17 is placed on the first rail 12 and the second rail 13 while holding the film 17. Travel sequentially in the transport direction. The clip 14 is omitted in FIG. 1 and is actually disposed on the first rail 12 and the second rail 13 at a predetermined interval. The first air curtain forming part 15 and the second air curtain forming part 16 each form an air curtain. The first air curtain forming part 15 and the second air curtain forming part 16 are arranged so as to sandwich the first rail 12, the second rail 13 and the clip 14 in the front and rear in the transport direction of the film 17. Has been.

  The traveling direction of the clip 14 by the first rail 12 and the second rail 13 is determined as follows. First, in the region A2, the clip 14 is gripped by a plurality of clips 14 while holding both side ends in the width direction of the film 17 after passing through the air curtain formed by the first air curtain forming portion 15. Along the side edges of the film 17, the distance between the clips 14 is run with little change. Next, in the region A3, the clip 14 moves in the longitudinal direction of the film 17 while holding the both end portions in the width direction of the film 17 with the plurality of clips 14, and the width direction of the resin film 17 Then, the vehicle travels so as to move in the direction of gradually increasing the distance between the clips 14. Finally, in the region A4, the clip 14 is held in the width direction of the film 17 with a plurality of clips 14, and the clip 14 in the region A3 along the both side ends. Drive with little change in the distance between. Further, the clip 14 in the region A4 releases the grip of the film 17, and then returns to the region A2. The film 17 released from the gripping of the clip 14 is conveyed toward the second air curtain forming portion 16 and passes through the air curtain formed by the second air curtain forming portion 16.

  The film 17 is stretched in the TD direction by running the clip 14 as described above.

  The angle θ formed by the moving direction of the clip 14 in the region A2 and the moving direction of the clip 14 in the region A3 is preferably 0.01 to 5 °, and is preferably 0.1 to 3 °. It is more preferable. If the angle θ is too small, it is necessary to lengthen the region (stretching zone) in which the stretching process is performed in order to increase the final stretching ratio, the economic load is large, and the surface Martens hardness and relaxation elastic modulus are in the above ranges. Tends to be difficult to adjust within. In addition, if the angle θ is too large, the production rate tends to decrease in order to secure the relaxation time necessary for resin orientation, and the film 17 may be broken from the portion gripped by the clip 14. is there.

  Moreover, it is preferable that the extending | stretching rate of the TD direction of the said film 17 is 15 to 60%, and it is more preferable that it is 20 to 50%. If the stretching ratio is too low, it tends to be difficult to adjust the surface Martens hardness and relaxation elastic modulus within the above ranges. On the other hand, if the stretching ratio is too high, the film 17 may be broken from the portion gripped by the clip 14. In addition, a draw ratio is defined by following formula (6).

Stretch rate (%) = {(L ₂ −L ₁ ) / L ₁ } × 100 (6)
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 film 17 is stretched in the presence of a poor solvent vapor for the film 17. Specifically, the regions of the first air curtain forming part 15 and the second air curtain forming part 16 (extension zones) A2 to A4 are filled with the vapor of the poor solvent. By doing so, it can suppress that the vapor | steam of the said poor solvent aggregates, becomes liquid, adheres to a resin film, and the trace by the adhered solvent is formed on a resin film.

  And, as described above, by stretching in the presence of a poor solvent vapor for the film, it is easier to stretch than stretching in the presence of dry air, and even if stretched at a high stretch rate, breakage or the like occurs Can be suppressed. In addition, when stretched in the presence of a good solvent vapor, the resin film is partially dissolved for reasons such as partially dissolving the resin film, and the properties of the resulting resin film are ensured by the dissolution. It is thought that it is not possible. Further, when the film is stretched at a high stretch rate in the presence of a good solvent vapor, it is considered that the resin film tends to break due to partial dissolution of the resin film.

  Therefore, as described above, by stretching in the presence of the poor solvent vapor of the film, it is possible to stretch at a high stretch while suppressing the occurrence of breakage of the resin film, etc. It is considered that the Martens hardness and the relaxation elastic modulus can be stretched so as to be within the above ranges, respectively.

  And since the Martens hardness and the relaxation elastic modulus of the surface of the resin film are each stretched so as to be within the above ranges, the resin constituting the resin film is preferably oriented, and the polarity of the resin is increased. It is considered that the surface hardness can exhibit excellent weather resistance such as a small dimensional change due to a change in temperature and humidity without increasing the molecular weight of the resin.

  As mentioned above, the resin film excellent in the weather resistance and mechanical strength as described above can be easily produced.

  Moreover, as a density | concentration of the said poor solvent, it is preferable that it is 5-20 volume%, and it is more preferable that it is 6-15 volume%. When the concentration is too low, the above-described effects due to stretching in the presence of a poor solvent vapor tend to be reduced, and the surface Martens hardness and relaxation elastic modulus tend to be difficult to adjust within the above range. If the concentration is too high, the resin film surface is not uniformly stretched, the surface of the resin film is wavy, it takes time to dry, and the surface Martens hardness and relaxation elastic modulus tend to be difficult to adjust within the above range. .

Here, the poor solvent is a solvent having a permeability of 10 g / (m ² · min) or less with respect to a film obtained by the permeability test shown below.

<Penetration test>
The permeability test is a test for examining the permeability of a liquid per predetermined time and predetermined area.

  Specifically, first, the weights of the glass tube and lids that can be attached and detached by sliding are measured on both side ends of the glass tube. And the lid | cover which can be attached or detached by a slide is mounted | worn to the both ends of a glass tube so that it may be in the state with which 1 kg (within +/- 50g) of the liquids which are osmosis | permeability measurement objects was enclosed. The glass tube filled with the liquid is brought into an upright state, the upper lid is removed at that time, and the opened upper end is covered with a film.

  Next, the glass tube covering the film is turned upside down so that the liquid comes into contact with the film, and then the other upper lid is removed and the side opposite to the side covered with the film is removed. Open the end of. In this state, it is left for a predetermined measurement time.

  When the measurement time has elapsed, a lid is attached to the upper end, the glass tube with the lid is turned upside down, and then the film is removed. Then, a lid is attached to the other end (the end on the side covered with the film), and the weight at that time is measured. From the mass, the weight of the reduced liquid is calculated.

And the value which remove | divided the weight (g) of the reduced liquid with the area (m < ² >) and the measurement time (minute) which were contacting the liquid of the film is the permeability (g / (m < ² > * min>) with respect to a film. )). In addition, the area which was in contact with the liquid of the film can be calculated from the inner diameter of the glass tube.

  The material of the glass tube and the lid used for this permeability test is not particularly limited as long as it is not affected by the liquid to be measured, but preferably has a small volume change due to temperature or the like. In general, this permeability evaluation is performed under the condition that the film as a sample is not deformed or broken. When the penetrability test is performed, if the liquid dissolves in the film within one minute and a hole is opened, accurate penetrability evaluation is impossible and measurement is impossible.

  The poor solvent varies depending on the transparent resin. For example, when a cellulose ester resin is used as the transparent resin, alcohol having 1 to 4 carbon atoms such as methanol and ethanol, water, and the like are used. Can be mentioned.

  Moreover, it is preferable that the poor solvent content rate of the said film 17 at the time of extending | stretching is 1-15 mass%, and it is more preferable that it is 3-10 mass%. If the content of the poor solvent is too low, the above-mentioned effect due to stretching in the presence of the vapor of the poor solvent is reduced, and it becomes difficult to adjust the surface Martens hardness and relaxation elastic modulus within the above range. There is. Further, if the content of the poor solvent is too high, it is not uniformly stretched, the resin film surface is wavy, it takes time to dry, and it becomes difficult to adjust the surface Martens hardness and relaxation elastic modulus within the above ranges. Tend. The poor solvent content is calculated as follows. First, the mass (mass before stretching) of the film 17 is measured. Thereafter, the film 17 is allowed to stand for the same time as the time required for the stretching step in an environment where the conditions and specifically the concentration and temperature of the poor solvent vapor are the same as those when the stretching step is performed. The mass of the film 17 (the mass after stretching) is measured. And a poor solvent content rate (mass%) is computed using following formula (7).

Poor solvent content = (mass after stretching−mass before stretching) / mass after stretching × 100 (7)
Further, when the film 17 is stretched, the film 17 is usually heated. Although the heating of the film 17 is not particularly limited, specifically, for example, the film 17 may be heated by spraying the vapor of the poor solvent onto the film 17, or separately heated air is blown. The film 17 may be heated by spraying on the film 17. And the temperature of the said film 17 is below a glass transition temperature (Tg), Comprising: It is preferable that it is 100 degreeC or more, It is Tg or less, It is more preferable that it is 130 degreeC or more.

  Moreover, it is preferable to provide the heating process which heats the said film 17 in at least one before and behind the said extending process. By doing so, the resin film excellent in weather resistance and mechanical strength can be manufactured more easily. Specific examples of the heating step include the following first heating step and second heating step.

  Before passing through the first air curtain forming portion 15, specifically, it is preferable to include a first heating step of heating the film 17 in the region A1 shown in FIG. And it is preferable that the temperature of the film 17 here is higher than the temperature of the film at the time of the said extending | stretching process, specifically, it is Tg or less, for example, it is preferable that it is 105 degreeC or more, and it is Tg or less. And it is more preferable that it is 135 degreeC or more. By doing so, a film can be heated before the said extending process, and the said extending process can be performed suitably. Therefore, it becomes easy to adjust the surface Martens hardness and relaxation elastic modulus within the above ranges, and a resin film excellent in weather resistance and mechanical strength can be produced more easily.

  In addition, after passing through the second air curtain forming part 16, specifically, it is preferable to include a second heating step of heating the film 17 in a region A5 shown in FIG. And it is preferable that the temperature of the film 17 here is higher than the temperature of the film at the time of the said extending | stretching process, specifically, it is Tg or less, for example, it is preferable that it is 105 degreeC or more, and it is Tg or less. And it is more preferable that it is 135 degreeC or more. By doing so, the orientation of the resin constituting the film 17 can be stabilized. Therefore, it becomes easy to adjust the surface Martens hardness and relaxation elastic modulus within the above ranges, and a resin film excellent in weather resistance and mechanical strength can be produced more easily.

  The method for producing a resin film according to the present embodiment is not particularly limited as long as it includes the stretching step and produces the resin film, and specifically, for example, a solution casting film forming method and a melt flow Examples of the stretching process in the film-forming method include those that are subjected to the stretching process as described above. Hereinafter, the solution-casting film-forming method and the melt-casting film-forming method will be described as examples.

(Solution casting film forming method)
First, the manufacturing method of the resin film by the solution casting film forming method is demonstrated.

  A method for producing a resin film by a solution casting film forming method includes a casting step of casting a resin solution (dope) containing the transparent resin on a traveling support, and forming the film. A peeling process for peeling from the support, a stretching process for stretching the peeled film, and a drying process for drying the stretched film are provided, and the stretching process as described above is performed as the stretching process. For example, it is performed by a resin film manufacturing apparatus using a solution casting film forming method as shown in FIG. In addition, as a manufacturing apparatus of a resin film, if the said each process is performed, it will not be limited to what is shown in FIG. 2, The thing of another structure may be sufficient. Here, the film means a film after a cast film (web) made of a dope cast on a support is dried on the endless belt support and can be peeled from the endless belt support. .

  FIG. 2 is a schematic diagram showing a basic configuration of a resin film manufacturing apparatus 21 by a solution casting method. The resin film manufacturing apparatus 21 includes an endless belt support 22, a casting die 23, a peeling roller 24, a stretching device 11, a drying device 25, a winding device 26, and the like. The casting die 23 casts a resin solution (dope) 28 in which the transparent resin is dissolved onto the surface of the endless belt support 22. The endless belt support 22 is supported to be drivable by a pair of driving rollers and driven rollers, and forms a web made of the resin solution 28 cast from the casting die 23, and is dried while being conveyed. The film 17 is used. The peeling roller 24 peels the film 17 from the endless belt support 22. The stretching device 11 stretches the film 17 under the aforementioned conditions. The drying device 25 dries the stretched film 17 while being transported by a transport roller. And the said winding apparatus 26 winds up the stretched and dried film 17, and makes it a film roll.

  Each of the above-described configurations, for example, each configuration of the endless belt support 22, the casting die 23, the peeling roller 24, the drying device 25, the winding device 26, etc. The same as described in Japanese Unexamined Patent Application Publication No. 2008-307730 and Japanese Unexamined Patent Application Publication No. 2009-73154.

  Moreover, the residual solvent rate of the film at the time of manufacture is defined by following formula (8).

Residual solvent ratio (mass%) = {(M ₁ −M ₂ ) / M ₂ } × 100 (8)
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.

(Melt casting method)
Next, the manufacturing method of the resin film by the melt casting film forming method is demonstrated.

  A method of producing a resin film by a melt casting film forming method includes a casting step of casting a resin melt obtained by melting the transparent resin on a traveling support to form a casting film, A cooling step of cooling the cast film to form a film, a peeling step of peeling the film from the support, a transporting step of transporting the peeled film by a plurality of transport rollers, and a stretching step of stretching the film. The stretching process as described above is performed as the stretching process. For example, it is performed by a resin film manufacturing apparatus using a melt casting film forming method as shown in FIG. The resin film manufacturing apparatus is not particularly limited to the one shown in FIG. 3 as long as it performs each of the above steps, and may have other configurations. Here, the film means 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.

  FIG. 3 is a schematic diagram showing a basic configuration of a resin film manufacturing apparatus 31 by a melt casting film forming method. The resin film manufacturing apparatus 31 includes a first cooling roller 32, a casting die 33, a touch roller 34, a second cooling roller 35, a third cooling roller 36, a peeling roller 37, a conveying roller 38, a stretching apparatus 11, and a winding device. The apparatus 39 etc. are provided.

  The casting die 33 casts a resin melt (dope) obtained by melting the transparent resin onto the surface of the first cooling roller 32. The first cooling roller 32 forms a casting film made of a dope cast from the casting die 33, cools the casting film while transporting it, and transports the casting film to the second cooling roller 35. At that time, the thickness of the casting film is adjusted and the surface is smoothed by the touch roller 34 provided in contact with the first cooling roller 32. The second cooling roller 35 cools the cast film while transporting it, and transports the cast film to the third cooling roller 36. By so doing, the cast film is used as a film. The peeling roller 37 peels the film from the third cooling roller 36. The conveyance roller 38 extends in the MD direction while conveying the peeled film. The stretching device 11 stretches the film 17 in the TD direction under the above-described conditions. The winding device 39 winds up the cooled and solidified and stretched film to form a film roll.

  The casting die 33 has the same configuration as the casting die 23 except that a resin melt is discharged as a dope instead of a resin solution.

  The first cooling roller 32, the second cooling roller 35, and the third cooling roller 36 are metal rollers having a mirror surface. As each of the rollers, for example, a roller made of stainless steel or the like is preferably used from the viewpoint of peelability of a cast film or a film. The width of the cast film cast by the casting die 33, the transport speed of the cast film by the first cooling roller 32, the second cooling roller 35, and the third cooling roller 36, etc. It is the same as the case by.

  The touch roller 34 has an elastic surface, and is deformed along the surface of the first cooling roller 32 by a pressing force to the first cooling roller 32, and between the first cooling roller 32, Form a nip. The touch roller 34 can be used without particular limitation as long as it is a touch roller conventionally used in the melt casting film forming method. Specifically, the thing made from stainless steel is mentioned, for example.

  The peeling roller 37 is in contact with the third cooling roller 36, and the film is peeled by applying pressure.

  The conveyance roller 38 is composed of a plurality of conveyance rollers, and can be stretched in the MD direction of the film by setting a different rotation speed for each conveyance roller.

  The stretching device 11 has the above-described configuration shown in FIG. 1 and stretches the film 17 in a direction (Transverse Direction: TD direction) orthogonal to the web conveyance direction.

  The winding device 39 has the same configuration as the winding device 26 when the solution casting film forming method is used.

  Hereinafter, the composition of the resin solution (dope) used in the method for producing a resin film by the melt casting method will be described.

  If the said transparent resin can be heated and fuse | melted, the thing similar to the case by the said solution casting film forming method can be used. In addition, the same composition as in the case of the solution casting film forming method can be used except that no solvent is used.

(Polarizer)
The polarizing plate according to the present embodiment includes a polarizing element and a transparent protective film disposed on the surface of the polarizing element, and the transparent protective film is a resin film according to the present embodiment. The polarizing element is an optical element that emits incident light converted to polarized light.

  As the polarizing plate, for example, a completely 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. A laminate is preferred. Further, the resin film may be laminated on the other surface of the polarizing element, or a transparent protective film for another polarizing plate may be laminated. As the transparent protective film for the 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) Is 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 resin film as a protective film laminated on at least one surface side of the polarizing element. In that case, when the said resin film works 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.

  Since the polarizing plate as described above uses the resin film according to this embodiment as a transparent protective film for the polarizing element, the resin film is excellent in weather resistance, for example, the dimensional change due to temperature and humidity changes is small. For example, when applied to a liquid crystal display device, a polarizing plate capable of suppressing the occurrence of peeling from the liquid crystal cell or the like is obtained. Furthermore, since the resin film used as a transparent protective film of a polarizing plate has high mechanical strength, the obtained polarizing plate is excellent in mechanical strength.

(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. In such a liquid crystal display device, the resin film according to the present embodiment is used as a transparent protective film for a polarizing plate, so that the resin film has excellent weather resistance, for example, a dimensional change due to temperature and humidity changes is small. Therefore, it is possible to provide a liquid crystal display device with high product stability in which occurrence of peeling from a liquid crystal cell or the like is suppressed. Furthermore, the liquid crystal display device obtained also has high product stability also from the point that the mechanical strength of the polarizing plate provided is high.

  Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto. In particular, the necessary stretching conditions vary depending on the raw materials.

[Example A]
(Examples 1-12 and Comparative Examples 1-16)
First, 100 parts by mass of cellulose triacetate resin (number average molecular weight Mn: 160000, weight average molecular weight Mw: 310000, Mw / Mn: about 1.94) is added to a dissolution tank containing 440 parts by mass of methylene chloride and 40 parts by mass of ethanol. As a plasticizer, 8 parts by mass of triphenyl phosphate and 2 parts by mass of ethyl phthalyl ethyl glycolate were added. And after raising the temperature until the liquid temperature reached 90 ° C., the mixture was stirred for 2 hours. By doing so, a resin solution was obtained.

  Then, stirring was complete | finished and it was left to stand until the liquid temperature became 40 degreeC. And the obtained resin solution was filtered using the filter paper (Azumi filter paper No.244 by Azumi filter paper Co., Ltd.). 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 the first dope to produce a resin film as follows.

(Preparation of second dope)
Instead of cellulose triacetate resin (number average molecular weight Mn: 160000, weight average molecular weight Mw: 310000, Mw / Mn: about 1.94), cellulose triacetate resin (number average molecular weight Mn: 180000, weight average molecular weight Mw: 300000, Mw) / Mn: about 1.67) was used, and it was manufactured in the same manner as the first dope.

(Preparation of third dope)
As a plasticizer, instead of adding 8 parts by mass of triphenyl phosphate and 2 parts by mass of ethyl phthalyl ethyl glycolate, except adding 4 parts by mass of triphenyl phosphate and 1 part by mass of ethyl phthalyl ethyl glycolate, It manufactured like the 1st dope.

(Preparation of the fourth dope)
Instead of cellulose triacetate resin (number average molecular weight Mn: 160000, weight average molecular weight Mw: 310000, Mw / Mn: about 1.94), cellulose triacetate resin (number average molecular weight Mn: 200000, weight average molecular weight Mw: 380000, Mw) / Mn: about 1.9), instead of adding 8 parts by mass of triphenyl phosphate, it was prepared in the same manner as in the first dope except that 2 parts by mass of triphenyl phosphate was added.

(Preparation of fifth dope)
Instead of cellulose triacetate resin (number average molecular weight Mn: 160000, weight average molecular weight Mw: 310000, Mw / Mn: about 1.94), cellulose triacetate resin (number average molecular weight Mn: 200000, weight average molecular weight Mw: 380000, Mw) / Mn: produced in the same manner as the first dope except that about 1.9) was used.

(Manufacture of resin film)
First, using an apparatus for producing a resin film by a solution casting film forming method as shown in FIG. 2, an endless belt support made of an endless polished from a casting die (coat hanger die) to stainless steel and polished to a super mirror surface is used. The dope was cast. By doing so, a web was formed on the endless belt support and conveyed while drying. Then, the web is peeled from the endless belt support as a film, dried while being conveyed in a roll at 110 ° C., and when the residual solvent amount reaches a predetermined amount, the film is stretched as shown in FIG. The film was stretched in the width direction under the following conditions while holding both ends of the film with clips. Then, the area | region currently hold | gripped with the clip was cut using the cutting apparatus, and the resin film was obtained.

  The stretching apparatus includes an apparatus for dropping a poor solvent into the stretching zone, and the poor solvent is volatilized in the stretching zone so that the vapor of the poor solvent is present at a predetermined concentration. Here, methanol was used as the poor solvent dropped into the stretching zone.

  As stretching conditions in the stretching apparatus, the stretching ratio, the temperature before the stretching zone (in the region A1), the temperature in the stretching zone (regions A2 to A4), and the beginning of stretching (at the boundary between the region A2 and the region A3). Poor solvent content of film (poor solvent content at the start of stretching), concentration of poor solvent vapor in stretching zone (regions A2 to A4) (stretching zone poor solvent concentration), temperature after stretching zone (in region A5) Were adjusted so as to satisfy the conditions shown in Tables 1 to 3, respectively.

  The stretch ratio is a value calculated from the above formula (6), and the poor solvent content of the film at the start of stretching (at the boundary between the region A2 and the region A3) is calculated from the above formula (7). Is the value to be In addition, the concentration of the poor solvent vapor in the stretching zone is adjusted by the amount of heating air supplied to the stretching zone, and the concentration is obtained by collecting the gas present in the stretching zone to obtain a gas chromatograph (Shimadzu Corporation). GC-2014) manufactured by Seisakusho was used, and measurement was performed using helium as a carrier gas.

  In addition, the Martens hardness and the relaxation elastic modulus are the test force (load) -indentation depth curve measured using Shimadzu Dynamic Ultra Micro Hardness Tester DUH-211S manufactured by Shimadzu Corporation, and It calculated by the said calculation method from the Poisson's ratio measured using Tensilon RTA-100.

  About each said Example and comparative example, the following evaluation was performed.

(Evaluation of polarizing plate)
Using the obtained resin film, a polarizing plate was produced as follows, and the polarizing plate was evaluated.

  First, according to the following method, a polarizing plate was prepared using each of the resin films and one of KC8UCR5 manufactured by Konica Minolta Opto Co., Ltd., which is a cellulose ester-based optical compensation film, as a polarizing plate protective film.

(A) Production of polarizing film 100 parts by mass of polyvinyl alcohol (hereinafter abbreviated as PVA) having a saponification degree of 99.95 mol% and a polymerization degree of 2400 impregnated with 10 parts by mass of glycerin and 170 parts by mass of water Was melt-kneaded, defoamed, melt-extruded from a T-die onto a metal roll, and formed into a film. Then, it dried and heat-processed and obtained the PVA film. The obtained PVA film had an average thickness of 40 μm, a moisture content of 4.4%, and a film width of 3 m.

  Next, the obtained PVA film was continuously processed in the order of preliminary swelling, dyeing, uniaxial stretching by a wet method, fixing treatment, drying, and heat treatment to prepare a polarizing film. That is, the PVA film was pre-swelled by immersing in water at a temperature of 30 ° C. for 30 seconds, and immersed in an aqueous solution having an iodine concentration of 0.4 g / liter and a potassium iodide concentration of 40 g / liter at a temperature of 35 ° C. for 3 minutes. Subsequently, the film was uniaxially stretched 6 times in a 50% aqueous solution with a boric acid concentration of 4% under the condition that the tension applied to the film was 700 N / m, and the potassium iodide concentration was 40 g / liter and the boric acid concentration was 40 g / liter. Then, it was immersed in an aqueous solution having a zinc chloride concentration of 10 g / liter and a temperature of 30 ° C. for 5 minutes for fixing. Thereafter, the PVA film was taken out, dried with hot air at a temperature of 40 ° C., and further heat-treated at a temperature of 100 ° C. for 5 minutes. The obtained polarizing film had an average thickness of 15 μm.

(B) Preparation of polarizing plate Next, according to the following processes 1-5, the polarizing film and the protective film for polarizing plates were bonded together, and the polarizing plate corresponding to each resin film which concerns on each comparative example was produced.

  Step 1: An optical compensation film (Konica Minolta Op KKKR-5 manufactured by Konica Minolta Opto Co., Ltd.) and the resin film are immersed in a 2 mol / L sodium hydroxide solution at a temperature of 60 ° C. for 90 seconds, and then washed with water. , Dried. On one surface of each resin film, a peelable protective film (manufactured by PET) was pasted for protection. Similarly, the above-described optical compensation film was immersed in a 2 mol / L sodium hydroxide solution at a temperature of 60 ° C. for 90 seconds, then washed with water and dried.

  Process 2: The above-mentioned polarizing film was immersed in the storage tank of the polyvinyl alcohol adhesive agent solution of 2 mass% of solid content for 1-2 seconds.

  Step 3: Excess adhesive adhered to the polarizing film in Step 2 was lightly removed, and this polarizing film was sandwiched between the optical compensation film and the resin film that had been subjected to alkali treatment in Step 1, and laminated.

Process 4: The laminate was bonded at a speed of about 2 m / min at a pressure of ^{20 to} 30 N / cm ² with two rotating rollers. At this time, it was carried out with care to prevent bubbles from entering.

  Step 5: The sample prepared in Step 4 was dried in a dryer at a temperature of 80 ° C. for 2 minutes to prepare a polarizing plate.

  Next, the polarizing plate on the outermost surface of a commercially available liquid crystal display panel (VA type) was carefully peeled off, and the polarizing plate was pasted in a size of 15 cm × 15 cm. The adhesive force may be any adhesive as long as it is 10-15 N / 25 cm, and a polyvinyl alcohol-based one is used. In addition, the said adhesive force is throwing power on condition of 180 degree peeling, 300 mm / min of pulling speed, and room temperature atmosphere (temperature 25 degreeC, relative humidity 55% RH) using RTC-1225A by Orientec Co., Ltd. It confirmed by the measurement of (N / 25mm).

  The polarizing plate attached to the outermost surface of the liquid crystal display panel (VA type) was stored for 200 hours under conditions of high temperature and high humidity (temperature 60 ° C., relative humidity 95% RH). Then, it returned to room temperature and confirmed peeling of the said resin film visually.

  If the peeling is not confirmed, it is evaluated as “」 ”, if the peeling is less than 5 mm from the end, it is evaluated as“ ◯ ”, and if the peeling is 5 mm or more from the end, it is evaluated as“ x ”. did.

(Tg)
The glass transition temperature (Tg) of the obtained resin film was measured in nitrogen gas using DSC (DSC8230 manufactured by Rigaku Corporation). The Tg of the resin film obtained using the first dope, the second dope, and the third dope was 126 ° C., 130 ° C., and 133 ° C., respectively, regardless of the stretching conditions.

  Said evaluation result (polarizing plate evaluation) is shown to Tables 1-3 with manufacturing conditions.

  In the table, when the resin film is broken during production (at the time of stretching), it is expressed as “break”. Further, when the surface of the produced resin film is wavy and the Martens hardness and relaxation elastic modulus cannot be measured, it is expressed as “wavy”.

  As can be seen from Tables 1 to 3, the Martens hardness measured at least one surface at a measurement depth of 1 μm in the nanoindentation method is 165 to 350 MPa, and the measurement depth is 1 μm in the nanoindentation method. When the relaxation elastic modulus measured on at least one of the surfaces is 3800 to 6000 MPa (Examples 1 to 12), both the Martens hardness and the relaxation elastic modulus are outside the above range (comparison) Compared with Examples 1-16), the resin film was difficult to peel from the polarizing plate which used the obtained resin film as a transparent protective film. From this, it was found that when the Martens hardness and the relaxation elastic modulus are within the above ranges, a resin film excellent in weather resistance such as small dimensional change due to temperature and humidity changes can be obtained.

  Further, the Martens hardness measured on both surfaces at a measurement depth of 1 μm in the nanoindentation method is 165 to 350 Mpa, respectively, and the relaxation modulus measured on both surfaces at the measurement depth of 1 μm in the nanoindentation method However, when it is 3800-6000 MPa, respectively (Examples 5-12), compared with the case where only any one side is in the said range (Examples 1-4), the obtained resin film is transparent. The resin film was more difficult to peel from the polarizing plate as the protective film. From this, it was found that the Martens hardness and the relaxation modulus on both surfaces of the resin film are preferably within the above ranges.

[Example B]
(Examples 13 to 45 and Comparative Examples 23 to 31)
Example B is the same as Example A, and the conditions shown in Tables 4 to 6 are used as the stretching conditions. In addition, Example B is an examination result in a state where the stretching ratio is high.

  The evaluation method is the same as in Example A. The evaluation results (polarizing plate evaluation) are shown in Tables 4 to 6 together with the production conditions.

  In the table, when the resin film is broken during production (at the time of stretching), it is expressed as “break”. Further, when the surface of the produced resin film is wavy and the Martens hardness and relaxation elastic modulus cannot be measured, it is expressed as “wavy”. Further, in addition to the “waving”, when a droplet trace based on a poor solvent is formed on the surface of the produced resin film, it is expressed as “waving, droplet trace”.

  From Tables 4 to 6, first, as in Tables 1 to 3, by comparing Examples 13 to 45 and Examples 17 to 25, the Martens hardness and the relaxation elastic modulus on both surfaces of the resin film are as described above. It was found that it was preferable to be within the range.

  And when extending | stretching rate was high, it turned out that extending | stretching is difficult if the density | concentration of a poor solvent is not high (Comparative Examples 18, 21, and 24). On the other hand, when the density | concentration of the poor solvent was too high, it turned out that a resin film wavy (Comparative Examples 17, 19, 20, 22, 23, 25). This is presumably due to the occurrence of uneven drying when the poor solvent exits the resin film because the droplet traces of the poor solvent are formed on the surface of the resin film.

[Example C]
(Examples 46 to 51 and Comparative Examples 26 and 27)
Example C is the same as Example A, and the conditions shown in Table 7 are used as the stretching conditions. The temperature before the stretching zone and the temperature after the stretching zone are both 150 ° C. Moreover, in the extending | stretching zone, although the temperature of the heating air sprayed on the A surface side of a resin film and the heating air sprayed on the B surface side are the same normally, it is set as the temperature shown in Table 7 in a present Example.

  The evaluation method is the same as in Example A. This evaluation result (polarizing plate evaluation) is shown in Table 7 together with manufacturing conditions.

  In the table, when the resin film is broken during production (at the time of stretching), it is expressed as “break”. Further, when the surface of the produced resin film is wavy and the Martens hardness and relaxation elastic modulus cannot be measured, it is expressed as “wavy”.

  As can be seen from Table 7, when the absolute value of the difference between the Martens hardness measured on one surface and the Martens hardness measured on the other surface is 10 MPa or less (Example 48), it exceeds 10 MPa (implementation). Compared with Examples 46 and 47), the resin film was difficult to peel from the polarizing plate using the obtained resin film as a transparent protective film. From this, it was found that the absolute value is preferably within the above range.

  In addition, when the absolute value of the difference between the relaxation modulus measured on one surface and the relaxation modulus measured on the other surface is 200 MPa or less (Examples 50 and 51), it exceeds 200 MPa (Examples). Compared with 49), the resin film was difficult to peel from the polarizing plate using the obtained resin film as a transparent protective film. From this, it was found that the absolute value is preferably within the above range.

  And when the difference of the temperature of A surface side heating air and the temperature of B surface side heating air was large, it turned out that the difference of the Martens hardness and relaxation elastic modulus of A surface and B surface becomes large. And when the temperature difference of the heating air became 60 degreeC or more, it turned out that it fractures.

[Example D]
(Examples 52-63 and Comparative Examples 28-49)
Example D is the same as Example A, using water as a poor solvent instead of methanol. In addition, the extending | stretching conditions of Example D are shown to Tables 8-10.

  The evaluation method is the same as in Example A. This evaluation result (polarizing plate evaluation) is shown to Tables 8-10 with manufacturing conditions.

  In the table, when the resin film is broken during production (at the time of stretching), it is expressed as “break”. Further, when the surface of the produced resin film is wavy and the Martens hardness and relaxation elastic modulus cannot be measured, it is expressed as “wavy”.

  As can be seen from Tables 8 to 10, it was found that even when water was used as the poor solvent (Example D), the same results as when methanol was used (Example A) were shown.

DESCRIPTION OF SYMBOLS 11 Stretching device 12 1st rail 13 2nd rail 14 Clip 15 1st air curtain formation part 16 2nd air curtain formation part 17 Film 21, 31 Production apparatus of resin film 22 Endless belt support body 23, 33 Casting die 24, 37 Peeling roller 25 Drying device 26, 39 Winding device 28 Dope 32 First cooling roller 34 Touch roller 35 Second cooling roller 36 Third cooling roller 38 Conveying roller

Claims (9)

In the nanoindentation method, the Martens hardness measured at least one surface at a measurement depth of 1 μm is 165 to 350 MPa,
A resin film having a relaxation elastic modulus of 3800 to 6000 MPa measured at least one surface at a measurement depth of 1 μm in a nanoindentation method.   2. The resin film according to claim 1, wherein the absolute value of the difference between the Martens hardness measured on one surface and the Martens hardness measured on the other surface is 10 MPa or less.   The resin film according to claim 1 or 2, wherein an absolute value of a difference between a relaxation elastic modulus measured on one surface and a relaxation elastic modulus measured on the other surface is 200 MPa or less.   The resin film according to claim 1, comprising at least one of a cellulose resin and a cellulose resin derivative. It is a manufacturing method of a resin film given in any 1 paragraph of Claims 1-4,
While gripping both side edges in the width direction of the long film with a plurality of gripping portions, the gripping portion moves in the longitudinal direction of the film and between the gripping portions in the width direction of the film. With a stretching process that moves in a direction that gradually increases the distance,
The method for producing a resin film, wherein the stretching step is performed in the presence of a poor solvent vapor for the film.   The method for producing a resin film according to claim 5, wherein the concentration of the vapor of the poor solvent in the stretching step is 5 to 20% by volume.   The method for producing a resin film according to claim 5, further comprising a heating step of heating the film on at least one of before and after the stretching step. A polarizing plate comprising a polarizing element and a transparent protective film disposed on at least one surface of the polarizing element,
The said transparent protective film is the resin film of any one of Claims 1-4, 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.

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