JP2014145985A - Polarizing diffusion film, method for manufacturing polarizing diffusion film, and liquid crystal display device including polarizing diffusion film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film having polarization selectivity and diffusivity as well as shape stability, and to provide a liquid crystal display device including the film as a polarizing diffusion film.SOLUTION: A polarizing diffusion film is provided, which comprises substantially one crystalline resin having an intrinsic birefringence of 0.1 or more, and the film has a total ray transmittance of 50 to 90% for visible rays, a transmission haze of 12 to 90% for visible rays, and a transmissive polarization degree of 20 to 90% for visible rays. A product of E and T, where E is a tensile elastic modulus measured at a stretching rate of 20% per minute at 70°C in a direction parallel to a reflection axis of the film, and T is an average film thickness, is 350 GPa μm or more. When the film is stretched at a rate of 20% per minute at 70°C in a direction perpendicular to the reflection axis, fracture elongation thereof, measured at 23°C and a rate of 20%/minute in a direction perpendicular to the reflection axis and parallel to the major surface of the film, is 5% or more.

Description

  The present invention relates to a polarizing diffusion film, a method for producing a polarizing diffusion film, and a liquid crystal display device including the polarizing diffusion film, and particularly relates to a polarizing diffusion film suitable for a liquid crystal display device.

  Liquid crystal display devices are widely used as display devices for computers, televisions, mobile phones, and the like, but there is a demand for further improvement of display characteristics and reduction of power consumption. As means for satisfying these requirements, there is a case where light from the light source is appropriately diffused and light use efficiency of the light source is improved. When the light from the light source is appropriately diffused, the viewing angle of the liquid crystal display device can be increased, and in-plane uniformity such as luminance can be increased. Further, when the light use efficiency of the light source is increased, it is possible to increase the overall luminance of the liquid crystal display device to obtain a bright image quality and to reduce power consumption.

  A reflective polarizer that transmits polarized light a while reflecting polarized light b orthogonal to polarized light a and a liquid crystal display device including the reflective polarizer are disclosed (see Patent Document 1). The liquid crystal display device includes a liquid crystal cell, a reflective polarizer, a backlight, and a diffuse reflector in order from the display surface side.

  Of the light emitted from the backlight of the liquid crystal display device, the polarized light a is transmitted through the reflective polarizer to become display light, while the polarized light b is reflected by the reflective polarizer to become reflected light. The polarized light b reflected by the reflective polarizer is reflected by the diffuse reflector, and the polarization state is randomized to become light including the polarized light a and the polarized light b. Of the randomized light, the polarized light a passes through the reflective polarizer and becomes display light, and the polarized light b becomes reflected light again. In this way, the utilization efficiency of the light emitted from the backlight is increased. This reflective polarizer is a multilayer film in which a film A made of polyethylene naphthalate and a film B made of copolyester using naphthalenedicarboxylic acid, terephthalic acid or the like as an acid component are laminated in multiple layers.

  As another reflective polarizer, a sheet in which the second transparent resin is dispersed in the form of particles or a predetermined shape in a continuous phase composed of the first transparent resin, transmits the polarized light a, and transmits the polarized light a A sheet that reflects polarized light b orthogonal to is disclosed (see Patent Documents 2 and 9). This sheet is obtained by extruding a mixture of two different resins.

  Moreover, the film and sheet | seat for light guides which provided the haze anisotropy are disclosed (refer patent documents 3-5). Of the non-polarized light incident from the end face of the film, only the specific polarized light is scattered and emitted, so that the utilization efficiency of the light irradiated from the end face of the film can be improved. This film is obtained by uniaxially stretching a film such as polyethylene naphthalate containing a filler or not containing a filler.

  Furthermore, a method is described in which a crystallized unoriented resin (polyethylene terephthalate resin or the like) is biaxially stretched and oriented to obtain a resin article for container use (see Patent Document 6).

  On the other hand, one of the important characteristics for a liquid crystal display device is front luminance. As means for improving the front luminance, it is known to adjust the emission angle from the film surface by changing the surface shape of the optical film (for example, a reflective polarizer) to a prism shape (see Patent Documents 7 and 8). ).

Japanese National Patent Publication No. 9-506985 JP 2003-075643 A JP 11-281975 A JP 2001-264539 A JP 2001-49008 A JP-T-2005-531445 JP 2007-272052 A JP 2007-20669 A Special Table 2000-506989

  Since the reflective polarizer described in Patent Document 1 is a laminate in which a film A and a film B having a different chemical structure are laminated in multiple layers, the manufacturing method is complicated and the cost can be reduced. It was difficult. Moreover, in order to provide diffusion performance, it was necessary to further form a member or layer having a diffusion function by bonding or painting. Further, since the sheets described in Patent Documents 2 and 9 are manufactured by polymer alloy, the manufacturing method is complicated, and it is difficult to precisely control the polarization characteristics and the diffusion performance.

  Although the film or sheet described in Patent Documents 3 to 5 can be manufactured by a method in which the optical characteristics are relatively easy to control, it is a member for guiding light incident from the end face of the film or sheet. Therefore, the sheet | seat described in patent documents 3-5 does not have the performance which permeate | transmits specific polarization | polarized-light among the light which injects from a sheet | seat surface, and does not have the function to diffuse the transmitted light. The reason is that the degree of crystallinity of the film before stretching is small and the transmission haze is also small.

  In Patent Document 6, the crystallized resin is stretched to increase its transparency, but the polarization and diffusibility are insufficient.

  Since the films described in Patent Documents 7 and 8 are obtained from two different types of resins, the manufacturing method is complicated, and it is difficult to precisely control the polarization characteristics and diffusion performance.

  That is, conventionally, a film that transmits linearly polarized light in a specific direction out of light incident from the film surface, efficiently reflects linearly polarized light orthogonal thereto (that is, has “polarization selectivity”), and has a diffusive property. It was desired. However, no satisfactory film is provided in terms of both performance and manufacturability.

  In addition, when a film is used for a liquid crystal display device, the film is heated by a light source of the display device, etc., so that wrinkles or the like are generated on the film and the display property may be lowered. On the other hand, if the rigidity of the film is increased in order to suppress such wrinkles, the film may be easily broken when the film is cut into a predetermined size after production.

  Accordingly, the present invention provides a film that has polarization selectivity and diffusivity, and is excellent in shape stability that does not generate wrinkles even when exposed to heat of a liquid crystal display device, and means for easily manufacturing the film. The purpose is to do.

  Thereby, the film of the present invention can be used as a polarizing diffusion film that can withstand the heat of the liquid crystal display device, and the front luminance of the liquid crystal display device can be increased.

The first of the present invention relates to the following polarizing diffusion film.
[1] A polarizing diffuser film consisting essentially of a crystalline resin having one kind of intrinsic birefringence of 0.1 or more, having a total light transmittance of 50 to 90% for visible light, and transmitting for visible light Tensile modulus E measured at a rate of 20% / min at a rate of 20% / min at 70 ° C. in the direction parallel to the reflection axis, having a haze of 12 to 90%, a transmission polarization degree to visible light of 20 to 90%, and the film The product with the average thickness T is 350 GPa · μm or more, and is perpendicular to the reflection axis and parallel to the main surface of the film when stretched at a rate of 20% / min at 70 ° C. in the direction parallel to the reflection axis. A polarizing diffuser film having an elongation at break measured at a rate of 20% / min at 23 ° C. of 5% or more.
[2] The crystallinity of the polarizing diffusion film is 8 to 40%, and the polarizing diffusion film is composed of a uniaxially stretched resin film of a crystalline resin having an intrinsic birefringence of 0.1 or more, The uniaxially stretched resin film has a transmission haze with respect to visible light of 5 to 90% when the film thickness is 100 μm, and a TEM image (imaging image) of a cut surface perpendicular to the stretch direction of the uniaxially stretched resin film. A bright and dark structure is observed when the distance in the film thickness direction of the range is 0.1 μm and the imaging area is 120 μm 2), and the bright and dark portions of the bright and dark structure are composed of substantially the same composition [1] The polarizing diffuser film described.
[3] The polarizing diffuser film according to [1] or [2], wherein the transmission polarization degree is 16 to 90% when the film thickness is 100 μm.
[4] The polarizing diffuser film according to any one of [1] to [3], wherein the crystallinity is 8 to 35%.
[5] The polarizing diffusion film according to any one of [1] to [4], wherein the crystalline resin is a polyester resin, an aromatic polyether ketone resin, or a liquid crystalline resin.
[6] The polarizing diffuser film according to [5], wherein the crystalline resin is a polyethylene terephthalate resin.
[7] The polarizing diffuser film according to any one of [1] to [6], wherein at least one surface of the polarizing diffuser film has a light collecting function and / or a light diffusing function.
[8] At least one surface of the polarizing diffusion film has a shape selected from the group consisting of a one-dimensional prism, a two-dimensional prism, a microlens, a lenticular lens, and an irregular concavo-convex shape. Polarizing diffusion film.
[9] Polarized light having the polarizing diffusing film according to any one of [1] to [7] and a resin layer, and the resin layer having a light collecting function and / or a light diffusing function. Diffusion film laminate.
[10] The resin layer having a condensing function and / or a light diffusion function has a shape selected from the group consisting of a one-dimensional prism, a two-dimensional prism, a microlens, a lenticular lens, and an irregular concavo-convex shape, [9 ] The polarizing diffuser film laminated body of description.
[11] The polarizing diffuser film laminate according to [9] or [10], wherein the resin layer contains particles.

2nd of this invention is related with the manufacturing method of the following polarizing diffusion films.
[12] A method for producing a polarizing diffuser film according to any one of [1] to [8],
A step of heating an amorphous sheet made of a crystalline resin having an intrinsic birefringence of 0.1 or more to obtain a crystallized sheet, and a step of obtaining a stretched film by stretching the crystallized sheet mainly in a uniaxial direction. And, without substantially fixing the stretched film, at a temperature equal to or higher than the glass transition temperature of the stretched film, the relaxation rate in the stretch direction and / or the main surface of the film orthogonal to the stretch direction And heating until the relaxation rate in the parallel direction is 0.3% or more.
[13] In the step of obtaining the crystallized sheet, the amorphous sheet is heated at a temperature T represented by the following formula (I) until the crystallinity becomes 2% or more. Manufacturing method of polarizing diffuser film.

Tc−40 ° C. ≦ T <Tm−10 ° C. (I)
(In formula (I), Tc represents the crystallization temperature of the crystalline resin, and Tm represents the melting point of the crystalline resin)
[14] The method for producing a polarizing diffuser film according to [12], wherein the crystallized sheet has a transmission haze with respect to visible light of 2 to 70% and a crystallinity of 2 to 20%.

The third aspect of the present invention relates to a liquid crystal display device using a polarizing diffusion film.
[15] (A) a surface light source for a liquid crystal backlight, (B) at least one optical element and / or an air gap, (C) the polarizing diffuser film according to any one of [1] to [8] [9] to [11] The polarizing diffuser film laminate according to any one of [9] to [11], and (D) at least a liquid crystal panel in which a liquid crystal cell is sandwiched between two or more polarizing plates, The liquid crystal display device in which each member of (D) is arrange | positioned in said order.
[16] The liquid crystal display device according to [15], wherein the (C) polarizing diffusion film is disposed adjacent to the (D) liquid crystal panel.
[17] The liquid crystal display device according to [16], wherein the (C) polarizing diffusion film also serves as a light source side protective film of a polarizing plate constituting the liquid crystal panel (D).
[18] The reflection axis of the (C) polarizing diffuser film and the absorption axis direction of the polarizing plate (D) constituting the liquid crystal panel and disposed on the light source side are substantially the same. , [16] The liquid crystal display device.

  According to the present invention, a film having polarization selectivity and diffusibility and having shape stability can be provided. The film of the present invention can be used as a polarizing diffusion film for a liquid crystal display device.

It is an example of the cross-sectional TEM image parallel to the extending | stretching direction of the polarizing diffuser film of this invention. It is an example of the cross-sectional TEM image perpendicular | vertical to the extending | stretching direction of the polarizing diffuser film of this invention. It is a perspective view including the film cross section which shows the 1st example of the surface shape of the polarizing diffuser film of this invention. It is a perspective view including the film cross section which shows the 2nd example of the surface shape of the polarizing diffuser film of this invention. It is the top view and sectional drawing which show the 3rd example of the surface shape of the polarizing diffuser film of this invention. It is a figure which shows an example of a structure of a liquid crystal display device. It is a figure which shows the other example of a structure of a liquid crystal display device. It is a figure explaining the display mechanism of a liquid crystal display device.

1. Polarizing diffusion film A polarizing diffusion film is a film having both “polarization selectivity” and “diffusivity”. Polarization selectivity refers to the property of transmitting more linearly polarized light in a specific direction than linearly polarized light orthogonal to the specific direction and reflecting more linearly polarized light orthogonal to the linearly polarized light in a specific direction. On the other hand, diffusibility refers to the property of diffusing transmitted light. That is, the polarizing diffuser film transmits and diffuses the linearly polarized light in a specific direction, but the linearly polarized light orthogonal to this can be reflected and returned to the light incident side.

  The polarizing diffuser film has a total light transmittance with respect to visible light of a certain level or more. The total light transmittance with respect to visible light of the polarizing diffusion film of the present invention is preferably 50% or more, and more preferably 65% or more. The higher the total light transmittance, the better. However, since surface reflection occurs on both sides of the film, it is usually 90% or less. However, the total light transmittance can be further increased by providing an antireflection film or the like.

  By setting the total light transmittance to 50% or more, the brightness of the liquid crystal display device including the polarizing diffusion film of the present invention is not significantly impaired, and the effect of polarization selectivity (polarization reflection property) and diffusibility is increased. Brightness can be achieved.

  The total light transmittance for visible light in the present application is a visual average value of the total light transmittance, and can be obtained by the following procedure.

1) A depolarization plate is set in front of the test piece installation part on the beam entrance side of the integrating sphere of the spectrophotometer so that light can be incident from the normal direction of the surface of the depolarization plate. This makes it possible to enter non-polarized light from the normal direction of the film surface as the test piece. Light having a wavelength range of 380 to 780 nm transmitted through the depolarizing plate is incident on the film surface, and the total light transmittance is measured every 10 nm.
2) Based on JIS R-3106, the total light transmittance Ttotal of the visual average value is calculated from the total light transmission data obtained in 1).
3) The calculated total light transmittance Ttotal may be converted into a value (Ttotal @ 100 μm) when the film thickness t is 100 μm. Specifically, it may be applied to the following expression.

By using the depolarizing plate in this way, even if the spectrophotometer's spectroscopic light is polarized to some extent, it can be corrected and the original characteristics of the film can be evaluated. Or when not using a depolarizer, total light transmittance Ttotal can also be measured as follows.
1) The film surface is irradiated with light having a wavelength range of 380 to 780 nm, and the total light transmittance is measured every 10 nm.
2) The film of 1) is rotated 90 degrees in a plane including the film surface, and the total light transmittance is measured in the same manner as 1).
3) An average value at each wavelength of the total light transmittance data measured in the above 1) and 2) is obtained, and averaged total light transmission data is obtained. From the averaged total light transmission data, the total light transmittance Ttotal of the visual average value is calculated.

  One example of an index indicating the polarization selectivity of the polarizing diffusion film is “transmission polarization degree”. The transmission polarization degree of the film is an index indicating the property of selectively transmitting either the polarized light V or the polarized light P orthogonal to the polarized light V. That is, the polarizing diffusion film of the present invention includes a uniaxially stretched resin film as will be described later, and polarized light V perpendicular to the stretching direction (stretching axis) is polarized parallel to the stretching direction (stretching axis). It has the property of being selectively transmitted over P. The “reflection axis” is an axis that selectively reflects polarized light parallel to the axis and polarized light perpendicular to the axis.

  The transmitted polarization degree is expressed by the following formula. In the following formula, “Tv” indicates the total light transmittance (%) of the film with respect to the polarized light V perpendicular to the stretching axis. On the other hand, “Tp” indicates the total light transmittance (%) of the film with respect to the polarized light P parallel to the stretching axis.

  The transmission polarization degree with respect to visible light of the polarizing diffusion film of the present invention is preferably 20% or more, more preferably 30% or more, and further preferably 40% or more. Further, the transmission polarization degree is 90% or less in consideration of diffusibility.

For the polarizing diffusion film of the present invention, “transmission polarization degree of the film per unit thickness” is also an important parameter. If the transmission polarization degree of the film per unit thickness is too low, it may be necessary to make the film extremely thick in order to ensure the performance of the polarizing diffusion film. Therefore, it is not preferable from the viewpoint of film handling and resin requirement. Accordingly, the transmission polarization degree (transmission polarization degree @ 100 μm) when the film thickness is 100 μm is preferably 16% or more, more preferably 20% or more, and more preferably 30% or more. Preferably, it is preferably 90% or less.
The transmission polarization degree when the film thickness t is 100 μm is calculated from the formulas (3) and (4) as Tv and Tp (Tv @ 100 μm and Tp @ 100 μm) when the film thickness t is 100 μm. Then, the calculated Tv @ 100 μm and Tp @ 100 μm may be obtained by applying the equation (5).

  In particular, when the polarizing diffuser film is applied to a liquid crystal display device, the total light transmittance Tv of the film with respect to the polarized light V is preferably higher by 10% or more than the total light transmittance Tp of the film with respect to the polarized light P. . Thereby, excellent display characteristics can be imparted to the liquid crystal display device.

The measurement of the transmission polarization degree may be performed according to the following procedure.
1) A polarizing plate is set in front of the test piece installation part of the integrating sphere of the spectrophotometer so that light can be incident from the normal direction of the set polarizing plate surface. Thereby, linearly polarized light perpendicular to the absorption axis of the polarizing plate can be incident on the test piece.
2) A film as a test piece is set in close contact with the polarizing plate, and the total light transmittance with respect to the polarized light is measured.
3) First, the stretching axis of the film as the test piece is made parallel to the polarization direction of the incident linearly polarized light. Irradiate linearly polarized light in the wavelength range of 380 to 780 nm, and measure the total light transmittance for each wavelength of 10 nm. The measured value is divided by the total light transmittance of the polarizing plate, and the total light transmittance Tp of polarized light parallel to the stretching axis is obtained based on JIS R-3106. The obtained Tp may be converted to Tp @ 100 μm.
4) Next, the film as the test piece is rotated 90 degrees in a plane including the film surface, and the stretching axis of the film as the test piece is made perpendicular to the polarization direction of the incident linearly polarized light. Similarly to 3), linearly polarized light with a wavelength range of 380 to 780 nm is irradiated, and the total light transmittance is measured every 10 nm. Similarly to 3), the measured value is divided by the total light transmittance of the polarizing plate, and the total light transmittance Tv of polarized light perpendicular to the stretching axis is obtained based on JIS R-3106. The obtained Tv may be converted into Tv @ 100 μm.
5) The obtained total light transmittances Tp and Tv, or Tp @ 100 μm and Tv @ 100 μm are applied to the formula (2) or formula (5) to calculate the transmission polarization degree.

  On the other hand, one example of an index indicating the diffusibility of the polarizing diffusion film is “transmission haze”. The transmission haze with respect to visible light of the polarizing diffusion film of the present invention is preferably 12% or more, and more preferably 25% or more. This is because when applied to a light diffusion film of a liquid crystal display device, the device is provided with reduced unevenness and uniform brightness. The transmission haze is preferably 90% or less. This is because a film having an excessively high transmission haze has high diffusibility but lowers the luminance of the liquid crystal display device due to light loss or the like.

  The “transmission haze of the film per unit thickness” is also an important parameter for the polarizing diffusion film of the present invention. If the transmission haze of the film per unit thickness is too low, it may be necessary to make the film extremely thick in order to ensure the performance of the polarizing diffusion film. Therefore, it is not preferable from the viewpoint of film handling and resin requirement. On the other hand, if the transmission haze of the film per unit thickness is too high, the transmission haze of the film having a desired thickness becomes too high, and the brightness of the liquid crystal display device may be lowered due to light loss or the like. Therefore, the transmission haze (transmission haze @ 100 μm) when the film thickness is 100 μm is preferably 5 to 90%, and more preferably 10 to 80%.

The measurement of transmission haze and transmission haze @ 100 μm may be performed according to the following procedure.
If the surface of the polarizing diffusion film to be measured has a surface shape having a light collecting function and / or a light diffusing function such as a one-dimensional prism described later, in order to eliminate the influence of transmission haze due to the surface shape, It is preferable to measure the transmission haze after applying highly transparent oil or the like to the surface of the film.

1) A depolarization plate is set in front of the test piece installation part at the light entrance of the spectrophotometer so that light can be incident from the normal direction of the surface of the depolarization plate. This makes it possible to enter non-polarized light from the normal direction of the film surface as the test piece. The film surface is irradiated with light having a wavelength range of 380 to 780 nm, and the parallel light transmittance is measured for each wavelength of 10 nm.
2) From the parallel light transmission data obtained in the above 1), the parallel light transmittance Tpara of the visual average value is calculated based on JIS R-3106.
3) From the parallel light transmittance Tpara calculated in the above 2) and the total light transmittance Ttotal, the transmission haze is calculated from the following equation (6).
4) The parallel light transmittance Tpara calculated in the above 2) is converted into a value (Tpara @ 100 μm) when the film thickness t is 100 μm. Specifically, it may be applied to the following formula (7).
5) Parallel light transmittance (Tpara @ 100 μm) when the film thickness t calculated in 4) is 100 μm and total light transmittance (Ttotal @ 100 μm) when the film thickness t is 100 μm. From the following equation (8), the transmission haze (transmission haze @ 100 μm) when the film thickness t is 100 μm is calculated.

  The measurement of the transmission polarization degree, the transmission haze, and the total light transmittance described above may be performed using, for example, a spectrophotometer U-4100 manufactured by Hitachi High-Technologies Corporation and a 150φ integrating sphere attachment device as necessary.

  As described above, the polarizing diffusion film of the present invention can be characterized mainly by three optical characteristics of “total light transmittance”, “transmission polarization degree”, and “transmission haze” with respect to visible light. . That is, in the polarizing diffusion film of the present invention, the three optical characteristics are balanced in a high dimension. In particular, there is an advantage in coexistence of “transmission haze per unit thickness” and “transmission polarization degree”. This advantage is that the degree of crystallinity of the film, which will be described later, and “parts with relatively high crystallinity and relatively strong molecular orientation” and “parts with relatively low crystallinity and relatively weak molecular orientation” It can be considered that it is realized by the mixed state of.

  In the polarizing diffuser film of the present invention, the product of the tensile elastic modulus E measured at 70 ° C. parallel to the reflection axis and the average thickness T of the film is 350 GPa · μm or more. The larger this product is, the higher the rigidity of the film is, and even when the film is exposed to heat, wrinkles are more difficult and the shape stability is higher.

The tensile elastic modulus E can be obtained by the following method. A dumbbell test piece (total length: 120 mm, parallel part length: 50 mm, parallel part width: 10 mm, chuck part width: 25 mm) was prepared so that the reflection axis of the film of the present invention and the long axis of the dumbbell were parallel, stretching temperature 70 ° C., preheating Time 2 minutes, stretching speed 10 mm / min. That is, 20% of the length in the stretching direction of the dumbbell specimen before stretching can be stretched at a rate of stretching in 1 minute, and the tensile elastic modulus E can be measured.
The polarizing diffuser film of the present invention has a breaking elongation perpendicular to the reflection axis and parallel to the main surface of the film when stretched at a rate of 20% / min at 70 ° C. in the direction parallel to the reflection axis. 5% or more.

  The elongation at break can be determined by the following method. A dumbbell test piece (total length 120 mm, parallel part length 50 mm, parallel part width 10 mm, chuck part width 25 mm) was prepared so that the reflection axis of the film of the present invention and the long axis of the dumbbell were perpendicular to each other. Speed 10 mm / min. That is, the elongation at break can be measured by stretching 20% of the length in the stretching direction of the dumbbell specimen before stretching at a rate of stretching in 1 minute.

  When the elongation at break is greater than or equal to the above, when the film of the present invention is produced and processed into a predetermined size, the film is less likely to break or crack.

  The polarizing diffusion film of the present invention includes a resin film of a crystalline resin, and preferably includes a uniaxially stretched resin film of a crystalline resin. The polarizing diffusion film of the present invention further preferably includes substantially one type of uniaxially stretched resin film of crystalline resin. This is because if the uniaxially stretched resin film is a resin alloy composed of a plurality of different resins, an interface is formed between the different types of resins and phase separation is likely to occur. In particular, when the compatibility between a plurality of types of resins is low, the adhesive force at the interface is weak, so that the interface is peeled off during stretching and voids are likely to occur. When a void occurs, light scattering in the void becomes too strong, causing light loss and making it difficult to control light diffusibility.

  A crystalline resin is a resin containing a crystalline polymer, and is a resin material in which many crystalline regions are formed. Here, the intrinsic birefringence of the crystalline resin is preferably a certain value or more.

Intrinsic birefringence is a “parameter indicating the height of molecular orientation of a polymer” and is represented by the following equation. In Formula (9), Δn ^o is intrinsic birefringence; and alpha ₂ is the molecular chain; n is an average refractive index; N _A is Avogadro's number; [rho is the density; M is the molecular weight; alpha ₁ is the polarizability of the molecular chain direction The polarizability in the vertical direction is shown.
(Equation 5)
^{Δn o = (2π / 9)} {(n 2 +2) 2 / n} (N A · ρ / M) (α 1 -α 2)
Formula (9)
A resin having a high intrinsic birefringence has a characteristic that, when processed by stretching or other means, the molecules are oriented to increase the birefringence.

  The intrinsic birefringence of various resins is described in, for example, JP-A-2004-35347. The intrinsic birefringence of the crystalline resin of the uniaxially stretched resin film contained in the polarizing diffusion film of the present invention is preferably 0.1 or more. Examples of crystalline resins having an intrinsic birefringence of 0.1 or more include polyester resins, aromatic polyetherketone resins, and liquid crystalline resins.

  Specific examples of the polyester-based resin having an intrinsic birefringence of 0.1 or more include polyethylene terephthalate, polyethylene-2,6-naphthalate, polypropylene terephthalate, polybutylene terephthalate, and the like, preferably polyethylene terephthalate or polyethylene-2. , 6-Naphthalate. Specific examples of the polyester resin having an intrinsic birefringence of 0.1 or more include 0.1 mol of a copolymer of the polyester resin, 0.1 mol of isophthalic acid, cyclohexanedimethanol, dimethyl terephthalate, and the like as a comonomer in the polyester resin. % Resin is also included.

  Specific examples of the aromatic polyetherketone resin having an intrinsic birefringence of 0.1 or more include polyetheretherketone. Specific examples of the liquid crystalline resin having an intrinsic birefringence of 0.1 or more include a polycondensate of ethylene terephthalate and p-hydroxybenzoic acid.

  The main component of the crystalline resin having an intrinsic birefringence of 0.1 or more is preferably polyethylene terephthalate. Examples of the polyethylene terephthalate include a polycondensate (homopolymer) containing terephthalic acid and ethylene glycol as monomer components; and a copolymer (copolymer) further containing a comonomer component other than terephthalic acid and ethylene glycol.

  Examples of comonomer components in polyethylene terephthalate copolymers include diol components such as diethylene glycol, neopentyl glycol, polyalkylene glycol, 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol; adipic acid , Carboxylic acid components such as sebacic acid, phthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid; and ester components such as dimethyl terephthalate.

  The content of the comonomer component in the polyethylene terephthalate copolymer is preferably 5% by weight or less. In general, the comonomer component tends to inhibit crystallization, but if it is within the above range, it does not inhibit the formation of a light-dark structure described later. Since the comonomer component tends to inhibit crystallization, the comonomer component may be contained in a relatively dark portion having low crystallinity. In addition, content, such as a comonomer component contained in a dark part and a bright part, respectively, may differ.

  Examples of polyethylene terephthalate include, as a mixture of the same kind of resin, a mixture of the homopolymer and the copolymer; a mixture of the homopolymers having different molecular weights; a mixture of the copolymers having different molecular weights.

  The polyethylene terephthalate may contain a different kind of resin that is compatible with the polyethylene terephthalate as long as the effects of the present invention are not impaired. Examples of such different kinds of resins include polyethylene naphthalate and polybutylene terephthalate. However, phase separation may occur if too many different types of resins are added. For this reason, it is preferable that content of different kind of resin is 5 weight% or less with respect to a polyethylene terephthalate. In order to reliably suppress the formation of phase separation by mixing different types of resin and polyethylene terephthalate, it is preferable to copolymerize a small amount of naphthalenedicarboxylic acid or the like as a comonomer component.

  Polyethylene terephthalate may contain other components such as a low molecular weight wax, a plasticizer, a higher fatty acid, and a metal salt thereof as long as the effects of the present invention are not impaired. Polyethylene terephthalate is a crystal nucleating agent, heat stabilizer, antioxidant, antistatic agent, lubricant, light-proofing agent, anti-blocking agent, thickener, UV absorber, fluorescent whitening agent, pigment in the polymerization stage or after polymerization. Various additives such as a flame retardant may be included.

  Crystal nucleating agents can primarily control the crystallization rate or crystal size, which affects the mechanical properties of the film. That is, the crystallinity of polyethylene terephthalate is almost determined by the type of resin, and is not greatly influenced by various additives such as a crystal nucleating agent. Examples of the crystal nucleating agent include phosphoric acid, phosphorous acid and esters thereof, inorganic particles such as silica, kaolin, calcium carbonate, titanium dioxide, barium sulfate, talc, and alumina; various organic particles.

  The amount of other components and various additives added is preferably 5% by weight or less based on polyethylene terephthalate. Other components and various additives may not necessarily have compatibility with polyethylene terephthalate when only a small amount such as ppm order is contained.

  The polarizing diffuser film of the present invention adjusts the image quality of a known ultraviolet absorber for cutting ultraviolet rays, a known flame retardant for improving flame retardancy, a known light resistant agent for improving light resistance, and a display device. An appropriate amount of a coloring agent for the purpose may be included.

  In order to preferentially obtain the shape stability of the polarizing diffusion film of the present invention, the crystallinity is preferably 8 to 40%; in order to preferentially obtain a high transmission polarization degree, it is 8 to 35. % Is preferred. Moreover, it is more preferable that it is 20 to 35%. This is because the desired total light transmittance, transmission haze, and polarization selectivity described above are obtained.

  The crystallinity can be determined from the measurement by the density method or the measurement by the X-ray diffraction method, but the crystallinity in the present invention is measured by the density method. The density method is a method for obtaining the crystallinity from the density of the resin. The density of the reference resin is described in the following literature, for example.

R.de.P.Daubeny, CWBunn, CJBrrown, Proc.Roy.Soc., A226,531 (1954)
A preferable example of the measurement of the density of the resin includes measurement by a density gradient tube method. The density gradient tube method is defined in JIS-7112, and can be performed according to JIS-7112 except for the preparation of the measurement solution. The density measurement by the density gradient tube method may be performed using, for example, a density gradient tube method specific gravity measurement water tank (OMD-6 / Ikeda Rika Kogyo Co., Ltd.).

  In addition, a crystalline phase and an amorphous phase are mixed in the polarizing diffusion film of the present invention. In the polarizing diffuser film of the present invention, the mixed state of “parts having relatively high crystallinity” and “parts having relatively high amorphous properties and relatively low crystallinity” is obtained by thinning the film. It can be observed by an observed transmission electron microscope (TEM) image. The mixed state can be observed as a “light / dark structure” by a TEM image obtained by observing a thin slice of the film.

  The light and dark structure observed by TEM is a structure in which “bright parts” and “dark parts” are mixed in a TEM image; specifically, a structure in which “bright parts” and “dark parts” form sea islands. Say. The comparison of crystallinity between “bright” and “dark” in the TEM image was confirmed by scanning the Raman spectrum and scanning both the bright and dark areas by microscopic Raman analysis (resolution: 1 μm) described later. sell.

  The bright part and the dark part are made of substantially the same resin composition. “The bright part and the dark part are composed of a resin having substantially the same composition” means that “the dark part composed of resin particles or filler having a composition different from that of the bright part” in the “resin constituting the bright part”. Means that the components constituting both are substantially the same resin component.

FIG. 1A is a film cross-sectional TEM image parallel to the reflection axis; FIG. 1B is a film cross-sectional TEM image perpendicular to the reflection axis. The distance in the film thickness direction of the imaging range of FIGS. 1A and 1B is 0.1 μm, and the imaging area is 120 μm ² . In the film cross-sectional TEM image parallel to the reflection axis, islands extending in the reflection axis direction are seen (see FIG. 1A). On the other hand, in the film cross-sectional TEM image perpendicular to the reflection axis direction, an island portion with low directivity is seen (see FIG. 1B).

  The “bright part” and “dark part” in the TEM image are not necessarily clear, but it is considered that the resin density and crystallinity of the part are different. Since the density and crystallinity are different, the refractive index, orientation, and birefringence are also considered to be different.

  In the cross-sectional TEM image of the film, when the bright portion is dispersed in the dark portion, the interface reflection or light scattering of the film occurs due to the difference in the refractive index of the resin constituting each. Therefore, if a moderate amount of bright portions are dispersed in the cross-sectional TEM image of the film, the transmission haze of the film can be adjusted to a suitable range.

  The “bright part” and “dark part” in the TEM image have different orientations due to the difference in density and crystallinity of the resin, resulting in a difference in birefringence. As a result of the difference in birefringence, a difference in refractive index is generated between the direction parallel to the stretching direction and the direction perpendicular thereto. Therefore, there is a difference between reflectance and light scattering for polarized light parallel to the stretching direction and reflectance and light scattering for perpendicular polarized light. In a crystalline resin having positive birefringence, such as polyethylene terephthalate, the refractive index difference in the parallel direction to the stretching direction is larger than the refractive index difference in the vertical direction. Are more likely to be reflected and scattered.

  The more interfaces between the bright and dark parts in the cross-sectional TEM image of the film, the greater the difference in the amount of reflection and scattering between the polarized light parallel to the stretching direction and the polarized light, and the greater the degree of transmitted polarization of the film. Become. If the area of each bright part is too large, or if the bright parts are connected and not separated from each other, the interface with the dark part is reduced. On the other hand, if there are too many interfaces between the bright part and the dark part, the light will be scattered too much to increase the light loss or disturb the polarization. Therefore, it is important that the bright portions in the cross-sectional TEM image of the film are dispersed in an appropriate amount and in an appropriate shape.

  In order to obtain a TEM image of the cross section of the film, the film is first cut to obtain a thin slice sample. The cut surface is perpendicular to the direction of the reflection axis of the film and parallel to the thickness direction of the film. Thin section samples can be obtained by a general method, for example, a resin-embedded film sample is fixed to a sample holder of an ultramicrotome; trimming is performed using a razor blade; a glass knife or an artificial sapphire knife is used. It can be obtained by chamfering; cutting out a 0.1-1 μm thick slice with an ultramicrotome diamond knife.

The obtained thin slice sample may optionally be stained. For example, the section sample may be placed in a staining container containing ruthenium tetroxide crystals and vapor-stained at room temperature for about 2 hours. A cut surface of a stained or unstained thin section sample is imaged with a transmission electron microscope apparatus to obtain a TEM image (end-view image). Examples of the transmission electron microscope apparatus include H-7650 manufactured by Hitachi High-Technologies Corporation. The acceleration voltage is preferably set to about several tens to 100 kV. The observation magnification, for example, from about 1,000 to 20,000 fold with; preferably to an observation visual field range and 5～20000Myuemu ^2, and more preferably a 10 to 1000 [mu] m ^2. An image is output at about 5000 to 50000 times.

  The brightness of each pixel of the output TEM image and the average brightness of the entire image are obtained. The ratio of the number of pixels brighter than the average to the total number of pixels is defined as “bright area ratio”.

  Image processing can be performed using image analysis software that is generally used (for example, ImageJ 1.32S created by Wayne Rasband). Specifically, the TEM image is a general image digital file such as JPEG (grayscale, for example, 256 gradations); the gradation is obtained for each pixel, the number of pixels and the gradation are histogrammed, and the entire image The binarization process is performed using the average gradation as a threshold, and pixels with a gradation (bright) above the threshold are set to 1, and pixels with a gradation (dark) below the threshold are set to 0; all pixels The number of pixels of value 1 with respect to the number is calculated and used as the area fraction of the bright part.

  Note that due to factors in the TEM observation state or image output, the output image may be output as different brightness although it actually has the same brightness. For example, the left region and the right region of the image are output as different brightness although they actually have the same brightness; as they move from the left side to the right side of the image, the same brightness actually In spite of having, it may be output as a result of gradually becoming brighter. In such a case, it is preferable to calculate the area fraction of the bright part after performing background correction, and then performing histogram processing, average gradation calculation, and binarization processing.

  In the polarizing diffuser film of the present invention, the mixed state of “a portion with relatively high crystallinity” and “a portion with relatively high amorphousness and relatively low crystallinity” is the crossing of the polarizing diffuser film. It can also be observed as a “bright / dark structure” by means of a polarization microscope image under Nicol. In a polarizing microscope image under crossed Nicols, “bright part” is a part with relatively high crystallinity; “dark part” is a part with relatively low crystallinity. To compare the crystallinity and orientation of “bright” and “dark” in polarized light microscope images under crossed Nicols, scan across both bright and dark areas by micro Raman analysis (resolution: 1 μm) described later. Thus, it can be confirmed by analyzing the Raman spectrum.

  The bright part and the dark part in the polarization microscope image under crossed Nicols are composed of a resin (polymer) having substantially the same composition as in the TEM image. “The bright portion and the dark portion are composed of a resin having substantially the same composition” means that the component constituting the bright portion and the component constituting the dark portion are substantially the same resin component. To do.

  In polarized light micrographs under crossed Nicols (including crossed Nicols), portions that appear relatively bright (bright portions) tend to have higher crystallinity and orientation, and portions that appear relatively dark (dark portions) Tend to have low crystallinity and orientation. That is, the crystallinity and orientation of the bright part are higher than the crystallinity and orientation of the dark part. High crystallinity facilitates orientation; high orientation provides high birefringence. Therefore, “the crystallinity and orientation degree of the bright part are larger than that of the dark part” means that “the birefringence of the bright part is larger than that of the dark part”.

  The polarization microscope image is observed using a device: NIKON OPTIPHOT-2 in which a polarizer (polarizing film) is arranged on the incident light side and the observation light side of the transmission image. A polarized image is photographed using an imaging device: CANON POWERSHOT A650 with an objective lens of x100 and an observation magnification of 1000 times.

  A polarizing microscope image of a film can be obtained by observing the film surface as it is, but in order to obtain a polarizing microscope image with high analytical accuracy, it is preferable to obtain a thin slice sample by cutting the film. The cut surface is parallel to the reflection axis direction of the film and parallel to the thickness direction of the film. The thin slice sample can be obtained by the same general method as described above. The thickness of the section having a cut surface parallel to the stretching direction of the uniaxially stretched resin film is preferably 0.5 to 2 μm from the viewpoint of facilitating observation of the light-dark structure, and the spatial resolution of Raman analysis is 1 μm. Therefore, the thickness of the section is more preferably 1 to 2 μm, and further preferably 1 μm.

  The crossed Nicols state in the present invention refers to a state where the angles formed by the polarization axes of the two polarizers sandwiching the film sample intersect each other (a state where the Nicols are not parallel Nicols). When the polarization axes of two polarizers intersect, the angle at which these polarization axes intersect is changed to find the angle at which the contrast of light and dark becomes the highest; for example, the light and dark image can be observed at that angle (for example, 90 °). preferable.

  The polarizing diffuser film of the present invention is characterized by high shape stability, that is, wrinkles are not easily generated even when exposed to heat.

  The polarizing diffusion film of the present invention is used as an optical film in a liquid crystal display device, as will be described later. In the liquid crystal display device, the optical film is heated and heated to about 60 ° C. Therefore, even when heated at 60 ° C., it is required that there are few wrinkles.

  As described later, the shape stability of the polarizing diffuser film of the present invention can be improved mainly by adjusting the stretching treatment conditions.

2. Manufacturing method of polarizing diffuser film The manufacturing method of the polarizing diffuser film of the present invention includes (1) a step of obtaining a crystallized sheet before stretching, (2) a step of uniaxially stretching the crystallized sheet, and further if necessary. (3) A step of relaxing the stretched film (relaxation step).

(1) Step of obtaining a crystallized sheet before stretching It is important that a crystallized sheet before stretching (hereinafter also referred to as a crystallization raw fabric) has a crystallinity and a transmission haze within a predetermined range. This is for imparting both appropriate transmission haze and transmission polarization degree to the stretched film.

  The crystallinity of the crystallized sheet before stretching is preferably 2 to 20%. This is because if the crystallinity of the crystallized sheet before stretching is in such a range, the crystallinity of the resin film after stretching can be set to, for example, 8 to 40%, preferably 8 to 35%.

  When the crystallinity of the crystallized sheet before stretching is too high, the crystallized sheet becomes hard and a large stretching stress is required. For this reason, not only the portion having relatively high crystallinity but also the portion having relatively low crystallinity has a strong orientation. Moreover, when the crystallinity degree of the crystallized sheet before extending | stretching is too high, a large crystal grain may be contained. For this reason, the film obtained by uniaxial stretching may not be provided with desired optical characteristics as a polarizing diffusion film, or the crystallinity may be too high to make stretching itself difficult. On the other hand, if the crystallinity of the crystallized sheet before stretching is too low, there are few crystals to be oriented, and the stretching stress is not so much. For this reason, it becomes difficult to orient even a portion having relatively high crystallinity.

  As described above, the crystallinity of the crystallized sheet before stretching can be determined from the measurement by the density method. The size of the crystal grains can be determined by observation with a polarizing microscope.

  The transmission haze with respect to visible light of the crystallized sheet before stretching is preferably 2 to 70%, and more preferably 2 to 50%. This is for appropriately adjusting the transmission haze of the stretched film and obtaining a practical degree of polarization. The transmission haze of the crystallized sheet before stretching can be measured in the same manner as the transmission haze of the polarizing diffuser film described above. However, since the crystallized sheet before stretching has almost no optical anisotropy, the measurement of the transmission haze does not need to obtain the average value by changing the direction of the polarizing diffusion film.

  As described above, it is important to adjust the crystallinity and transmission haze of the crystallized sheet before stretching to a predetermined range; the crystallinity of the crystallized sheet before stretching is 2 to 20% and is visible. The transmission haze with respect to the light beam is preferably 2 to 70%. This is for imparting both high polarization and diffusibility to the stretched film.

  The thickness of the crystallized sheet before stretching is mainly determined by the thickness of the stretched film to be obtained by the stretching step (2) and the stretching ratio, but is preferably 50 to 2000 μm, more preferably about 80 to 1500 μm. is there.

  The crystallized sheet before stretching can be obtained by a) haze-up crystallization of a polyester resin sheet in an amorphous state, and further b) haze-up by preheating before stretching if necessary. It may be obtained by crystallization and is not particularly limited.

  The amorphous polyester resin sheet may be commercially available, or may be produced by a known film forming means such as extrusion. The sheet made of polyester resin may be a single layer or a multilayer.

  The polyester resin constituting the amorphous sheet can contain a certain amount or less of a comonomer component. Since the comonomer component has a tendency to inhibit crystallization of the resin, the crystallization speed in haze-up crystallization can be precisely controlled. Furthermore, since the polyester resin containing a comonomer component has good viscosity in the molten state and flexibility in the solid state, it is excellent in moldability in the later-described (2) stretching step.

  The haze-up crystallization of the polyester resin in the amorphous state can be obtained by heating the polyester resin sheet in the amorphous state at a predetermined temperature and time. The amorphous polyester resin sheet may be heated by setting the amorphous polyester resin sheet in a stretching device (for example, a preheating zone of a tenter stretching machine) and applying a certain tension. Further, heating may be performed by heating means other than the stretching device (for example, a gear oven, a heating roll, an infrared heater, or a combination thereof).

  The heating temperature (T1) when the amorphous polyester resin sheet is heated to cause haze-up crystallization is set in the vicinity of the crystallization temperature Tc of the polyester resin. The crystallization temperature usually includes a cold crystallization temperature Tcc and a melt crystallization Thc. In the present invention, the crystallization temperature Tc means the cold crystallization temperature Tcc. The crystallization temperature Tc of the polyester resin is usually in a temperature range (Tg <Tc <Tm) between the glass transition temperature Tg and the melting temperature Tm of the polyester resin.

  In order to facilitate the haze-up crystallization of the polyester resin sheet in an amorphous state, the heating temperature (T1) is preferably “Tc−40 ° C. ≦ T1 <Tm−10 ° C.”, and “Tc−30 ° C. ≦ It is more preferable that “T1 <Tm−10 ° C.”. In the case of polyethylene terephthalate, T1 is about 105-180 ° C. Here, Tc is the crystallization temperature of the polyester resin, and Tm is the melting temperature of the polyester resin. For example, the crystallization temperature Tc of polyethylene terephthalate is about 115 to 170 ° C.

  The crystallization temperature (Tc) of the polyester resin is preferably determined by differential scanning calorimetry (DSC) of the sheet or the polyester resin that is not crystallized (in a supercooled state). Differential scanning calorimetry (DSC) may be performed in accordance with JIS K7122. The melting temperature (Tm) of the polyester resin is also preferably determined by differential scanning calorimetry according to JIS K7122.

  The heating time in the case of heating and crystallizing an amorphous polyester resin sheet is such that the crystallization sheet has a certain degree of crystallinity (for example, 2 to 20%) and transmission haze (for example, 2 to 70%). What is necessary is just to set so that it may satisfy | fill. The longer the heating time, the higher the crystallinity. On the other hand, when the heating time is short, the crystallinity is also lowered. The heating time for heating and crystallizing an amorphous polyester resin sheet is the heating temperature (T1), the thickness of the sheet, the molecular weight of the resin constituting the sheet, the types and amounts of additives and copolymers, or heating. Although depending on the method, it is 5 seconds to 20 minutes, preferably 10 seconds to 10 minutes.

  For example, when a sheet made of amorphous polyethylene terephthalate is heat-treated in a gear oven at 120 ° C., the heating time is preferably about 1.5 to 10 minutes, preferably about 1.5 to 7 minutes. Is more preferable. Moreover, when heating with a 120 degreeC heating roll, it is preferable that it is 10 to 100 second, More preferably, it is 15 to 60 second.

  However, when preheating before stretching is further performed, the crystallization sheet may be further crystallized even in this preheating. In that case, the heating time in the haze-up crystallization may be appropriately shortened in consideration of preheating before stretching.

  In any case, the heating temperature and heating time for haze-up crystallization can be appropriately adjusted in consideration of the heating method, the line speed, the amount of hot air, and the like.

  As described above, the haze-up crystallized sheet may be further preheated before stretching. The preheating before stretching is to make the sheet set in the stretching apparatus soft before the stretching to make it suitable for stretching.

  Crystallization may also proceed due to preheating before stretching. In that case, it is preferable to adjust the conditions (heating temperature and heating time) for haze-up crystallization.

  The preheating temperature (T2) in the preheating before stretching is set to a range equal to or higher than the vicinity of the glass transition temperature Tg in order to make the crystallized sheet soft enough for stretching. The preheating temperature (T2) may be the same as the stretching temperature (T3) described later. For example, in the case of a crystallized sheet made of polyethylene terephthalate, the preheating temperature (T2) is set to approximately 95 to 180 ° C., although it varies depending on the viscosity of the resin, the crystallinity of the crystallized sheet, and the line speed and air volume.

  The preheating time in preheating before stretching can be appropriately adjusted so that the crystallization sheet at the start of stretching reaches a predetermined preheating temperature. If the preheating time is too long, the crystallinity of the crystallized sheet may be excessively increased (for example, more than 30%), and stretching itself may be difficult. On the other hand, if the preheating time before stretching is too short, the temperature of the crystallized sheet at the start of stretching is not sufficiently high, so that the stretching stress is too high and stretching becomes difficult. For example, in the case of a crystallized sheet made of polyethylene terephthalate, the preheating time is preferably 0.1 to 10 minutes.

  In any case, the preheating temperature T2 and the preheating time can be appropriately adjusted in consideration of the influence of the line speed, the amount of hot air, and the like.

(2) Stretching step The stretching step is a step of stretching the “crystallized sheet before stretching”. The “crystallized sheet before stretching” may be a sheet obtained by the above-described haze-up crystallization; it may be a sheet obtained by further preheating after the haze-up crystallization; Sheets obtained by other processes may be used.

  By stretching, a film in which the transmission haze and the transmission polarization degree are controlled is obtained. The means for uniaxially stretching the crystallized sheet before stretching made of a polyester resin is not particularly limited. “Uniaxial stretching” means stretching in a uniaxial direction, but may be stretched in a direction different from the uniaxial direction to the extent that the effects of the present invention are not impaired. Depending on the stretching equipment used, even if it is intended to stretch in a uniaxial direction, it may be substantially stretched in a direction different from the uniaxial direction. The “uniaxial stretching” is understood to include such stretching.

  For example, the sheet may be stretched in a direction perpendicular to the desired stretching direction. In general, pure uniaxial stretching means that only two opposite sides of the four original sheets before stretching are fixed and stretched with both ends in a direction perpendicular to the stretching direction in a free state (“transverse free” Also referred to as “uniaxial stretching”). In transverse free uniaxial stretching, the direction perpendicular to the stretching direction contracts due to Poisson deformation along with stretching. Therefore, it is not stretched in a direction perpendicular to the stretching direction.

  On the other hand, when fixing (clamping) the four sides of the original fabric, even if the original fabric is stretched only in one direction, the ends in the direction perpendicular to the stretching direction are fixed (also referred to as “laterally fixed uniaxial stretching”). Therefore, the film could not be shrunk, and the film was substantially stretched slightly in the direction perpendicular to the stretching direction.

  The “uniaxial stretching” includes lateral free uniaxial stretching and lateral fixed uniaxial stretching. Examples of the transverse free uniaxial stretching include a roll stretching method and the like, and the transverse fixed uniaxial stretching includes lateral uniaxial stretching by a tenter method in addition to the above.

The stretching speed of uniaxial stretching is not particularly limited, but is preferably 5 to 500% / second, more preferably 9 to 500% / second, and still more preferably 9 to 300% / second. The stretching speed is represented by the following formula (10), where Lo is the initial sample length and L is the length of the stretched sample after time t. If the stretching speed is too high, the stretching stress increases and the burden on the equipment increases, and as a result, uniform stretching may be difficult. On the other hand, if the stretching speed is too slow, the production speed is extremely slow, and the productivity may be reduced.
(Equation 6)
Stretching speed (% / second) = (L−Lo) / Lo / t × 100 (10)
The stretching speed can vary depending on the crystallinity of the crystallized sheet before stretching. As the crystallinity of the crystallized sheet increases, the film becomes harder and the stretching stress increases, so the optimum stretching speed tends to decrease.

  For example, when a crystallized sheet made of polyethylene terephthalate is stretched at about 120 ° C., the stretching speed is preferably 5 to 220% / sec. Note that the stretching speed is not necessarily constant from the initial stage to the latter stage of the stretching process. For example, the stretching speed may be 25% / sec in the initial stage and 10% / sec as a whole.

  When the stretching temperature (T3) is high, the stress applied to the crystallization sheet at the time of stretching is small, so that the portion with relatively low crystallinity and not the portion with relatively low crystallinity are stretched without much orientation. When the stretching temperature (T3) is low, the stress applied to the crystallization sheet during stretching is large, so that not only a portion with relatively high crystallinity but also a portion with relatively low crystallinity is oriented. For example, when a crystallized sheet made of polyethylene terephthalate is stretched, the stretching temperature (T3) is preferably 80 to 125 ° C. The tensile modulus E measured at 70 ° C. parallel to the reflection axis (stretching axis) can be increased by lowering the stretching temperature or increasing the stretching speed. The stretching temperature (T3) may be the same as or different from the preheating temperature (T2) in the preheating step.

  The draw ratio is also selected according to the resin to be selected, and is not particularly limited. In the case of a polyester resin, 2 to 10 times is preferable. If the draw ratio is too large, the possibility of stretching breakage may increase, and if it is too small, a sufficient molecular orientation state may not be obtained.

The thickness of the stretched film obtained by the stretching step is 20 to 500 μm, preferably 30 to 300 μm. A film that is too thin does not have sufficient rigidity, makes it difficult to maintain flatness, and may be difficult to handle and incorporate into a liquid crystal display device. On the other hand, a film that is too thick may be difficult to wind in a roll form, or may increase productivity by reducing the amount of resin required.
The elongation at break can be increased by lowering the draw ratio or lowering the relaxation temperature described below.

  In the conventional film production conditions, when the original film or crystallized sheet of crystalline resin is uniaxially stretched, microcrystals (generally spherulites composed of lamellar crystals) or crystallized sheets existing in the original film stage Most of the spherulites were dismantled and molecular chains were often stretched uniformly. For this reason, the stretched film obtained had a substantially uniform orientation structure and high transparency. On the other hand, the uniaxially stretched resin film of the present invention is obtained by uniaxially stretching a crystallized sheet obtained by crystallizing a polyester resin under predetermined conditions, so that the specific light-dark structure as described above is obtained. . Thereby, the stretched film which expresses a desired optical characteristic can be obtained.

(3) Regarding Relaxation Step (2) The stretched film obtained in the stretching step is preferably relaxed. Relaxation is a process for enhancing the long-term dimensional maintenance of the film after relaxation by relaxing (shrinking) the film by heating. Although it may be relaxed in any direction, it is preferable to relax in the stretching direction. On the other hand, the film may be relaxed or not relaxed in a direction perpendicular to the stretching direction and parallel to the main surface of the film. Preferably, the film is relaxed both in the stretching direction and in a direction perpendicular to the stretching direction and parallel to the main surface of the film.

  The relaxation temperature is preferably a glass transition temperature Tg or higher, and is preferably (melting temperature Tm-30) ° C. or lower. If the relaxation temperature is too high, crystallization of the resin constituting the film proceeds, and the polarization selectivity may be lowered, or the film may be easily broken.

  The relaxation is preferably performed without substantially fixing the stretched film. “Not substantially fixed” means a state in which the film can shrink. Accordingly, the film may be fixed as long as no tension is applied. For example, when relaxing in the stretching direction, the stretched film may be fixed with a width narrower than the tenter width when the tenter is stretched.

  The relaxation rate in the stretching direction by the relaxation treatment is preferably 1% or more and 20% or less. More preferably, they are 2% or more and 18% or less, More preferably, they are 2.4% or more and 15% or less. Further, the relaxation rate in the direction perpendicular to the stretching direction and parallel to the main surface of the film by the relaxation treatment is preferably 0.3% or more and 3% or less, and more preferably 0.5% or more and 3% or less.

When the relaxation rate is too large, the effective width becomes narrow, which is not desirable from the viewpoint of productivity. The relaxation rate refers to the ratio of the film length in the specific direction contracted by relaxation to the film length in the specific direction before relaxation. For example, the relaxation rate in the stretching direction refers to the ratio of the film length in the stretching direction contracted by relaxation to the film length in the stretching direction before relaxation. As a method for measuring the relaxation rate, for example, before the relaxation treatment, two benchmarks are drawn in a direction perpendicular to the stretching direction and parallel to the main surface of the film; the distance d1 between the two benchmarks is measured. Re-measure the distance d2 between the two marked lines after the relaxation treatment;
(Equation 7)
Relaxation rate (%) = 100 × (d1−d2) / d1 (11)
Thus, the relaxation rate in the stretching direction can be measured.

  By the relaxation treatment, the film can be relaxed both in the stretching direction and in a direction perpendicular to the stretching direction and parallel to the main surface of the film. The relaxation in the stretching direction and the relaxation in the direction orthogonal to the stretching direction and parallel to the main surface of the film may be performed simultaneously or sequentially. If relaxation is performed in both directions at the same time, deformation of the polarizing diffusion film due to stress caused by relaxation can be suppressed, which may be preferable. In order to perform relaxation in both directions at the same time, relaxation is performed in a state where no tension is applied (substantially not fixed) in both the stretching direction and the direction orthogonal to the stretching direction and parallel to the main surface of the film. What is necessary is just to heat a film.

  On the other hand, when heat fixing is performed in a state where the film is fixed, in order to improve long-term dimensional maintenance, it is necessary to carry out at a higher temperature than in the case of relaxation, or to carry out for a long time. Therefore, the microstructure is more likely to be disturbed and the polarization selectivity is likely to be lowered. Here, fixing the film means a state in which the film cannot freely shrink.

  The relaxation may be performed without removing the stretched film from the stretching apparatus, or the stretched film may be removed from the stretching apparatus and relaxed by a separate means.

3. Use of Polarizing Diffusion Film The polarizing diffusion film of the present invention is preferably used as an optical film of a liquid crystal display device. The surface shape of at least one surface of the polarizing diffusion film of the present invention is changed to a surface shape having a condensing function, or the polarizing diffusion film of the present invention is laminated with a resin layer having a condensing function. It is also a preferred embodiment to form a laminate. By setting it as such an aspect, when arrange | positioning in a liquid crystal display device, the brightness | luminance of a liquid crystal display device, especially front luminance can be raised.

  Further, it is more preferable that the surface shape and the resin layer having a light collecting function are provided only on one surface of the polarizing diffusion film of the present invention. For example, when the polarizing diffuser film is used as a member of a liquid crystal display device, it is preferable that the “surface on the side in contact with the polarizing plate” has a surface shape having a light collecting function or a resin layer. By making the surface of the polarizing diffusion film into a shape having a condensing function or laminating with a resin layer having a condensing function, incident light is selectively transmitted by polarization selectivity and emitted obliquely by diffusivity. Since the polarized light can be collected in the front direction, the front luminance is further improved.

  Further, at least one surface of the polarizing diffusion film of the present invention is formed into a surface shape having a light diffusing function, or the polarizing diffusing film laminate is formed by laminating the polarizing diffusing film of the present invention and a resin layer having the light diffusing function. It is also a preferred embodiment. By setting it as such an aspect, when a polarizing diffuser film is arrange | positioned in a liquid crystal display device, the dot pattern printed on the light-guide plate used for the surface light source for liquid crystal backlights can be concealed. It also conceals moiré and brightness unevenness caused by the use of optical elements such as prism sheets and microlens sheets, and more effectively prevents other optical elements and the polarizing diffuser film from coming into close contact with each other. it can.

  For example, a surface shape or a resin layer having a light collecting function and / or a light diffusing function is provided on the “surface on the side in contact with the polarizing plate” of the polarizing diffusion film of the present invention, and another optical material is provided on the other surface of the surface An embodiment having a surface shape having a light diffusing function and also having a resin layer for the purpose of preventing adhesion to the element is also a preferred embodiment. As described above, the polarizing diffuser film or the polarizing diffuser film laminate of the present invention having both the light collecting function and / or the light diffusing function and the polarized light reflection characteristic is a prism film, a microlens film, or a light used conventionally. Luminance, concealment, adhesion prevention and the like can be further improved at a lower cost than when a diffusion film or the like is combined with a polarizing diffusion film. The surface shape and the resin layer may have both a light collecting function and a light diffusing function, or may have only one of them.

  A film generally used as a prism film, a microlens film, a light diffusion film, or the like conventionally used is a film obtained by surface-treating a biaxially stretched polyethylene terephthalate (PET) film. Even if these films are combined with a polarizing diffusion film having polarization selectivity, the phase difference of the biaxially stretched PET film is large, so that when the selected polarized light passes through the biaxially stretched PET film, Disturbed. Therefore, the effect of polarization reflection is impaired. In addition, the polarizing diffusion film of the present invention can realize cost reduction and can also reduce the thickness of the liquid crystal display device as compared with the case where a prism film or microlens film and a polarizing diffusion film are used in combination. .

  Examples of surface shapes and resin layers having a condensing function or a light diffusing function include a one-dimensional prism shape (see FIG. 2), a two-dimensional prism shape (see FIG. 3), a microlens shape (see FIG. 4), and a lenticular lens. Shape, wave shape, irregular shape of irregular shape, resin layer shape containing particles, and the like, but are not particularly limited.

  The one-dimensional prism shape means a state in which a plurality of triangular prisms are arranged in a row (see FIG. 2). FIG. 2 shows a cross-sectional view of a polarizing diffuser film having a one-dimensional prism-like surface shape perpendicular to the ridge line of the prism. The prism pitch P1 may be equal or unequal, but is preferably about 1 to 200 μm, the prism apex angle θ1 is preferably about 60 to 120 degrees, and the prism height h1 is about 0.4 to It is preferable that it is 110 micrometers. It is preferable that the ridge line of the prism is parallel to or orthogonal to the reflection axis of the polarizing diffusion film. This is to increase the sheet take-up efficiency of the polarizing diffusion film.

  The two-dimensional prism shape means a state in which a plurality of quadrangular pyramids are arranged in a matrix (see FIG. 3). FIG. 3 shows a perspective view including a cross section of a polarizing diffusion film having a two-dimensional prism-like surface shape. The distance P2 between the apexes of the quadrangular pyramids may be equal or unequal, but is preferably about 1 to 200 μm; the height h2 from the bottom of the quadrangular pyramids is preferably about 0.4 to 110 μm. The prism apex angle θ2 may be about 60 to 120 degrees.

  The microlens shape means a state where a plurality of convex lenses are arranged on the film surface (see FIG. 4). The convex lenses may be arranged with regularity or may be arranged randomly. Arrangement with regularity refers to arrangement so as to be closely packed. The lens shape is not particularly limited to either a spherical surface or an aspherical surface, and the shape and size are appropriately selected according to the desired light collection performance and light diffusion performance. FIG. 4 (A) shows a top view of a polarizing diffuser film having a microlens-shaped surface shape; FIG. 4 (B) shows a cross-sectional view of the film. The lens diameter D of each microlens is preferably about 4 to 200 μm, and the lens height h ′ is preferably about 2 to 100 μm.

  The lenticular lens shape means a state in which a plurality of plano-convex cylindrical lenses are arranged in a row. The lens pitch of the plano-convex cylindrical lens may be equal or unequal, but is preferably about 1 to 200 μm, and the height of the curved surface portion of the lens is preferably about 0.5 to 100 μm. The curved portion of the cross section of the plano-convex cylindrical lens is not particularly limited to either an arc shape or a non-arc shape, and the shape and size are appropriately selected according to the desired light collection performance and light diffusion performance.

  The irregular irregular shape refers to a state in which irregularities having a random size and size are formed instead of a specific shape. The irregular irregularities only need to be formed substantially randomly, and a certain random irregular pattern may exist repeatedly. The height of the unevenness is not particularly limited, and is appropriately selected according to the desired light collecting performance and light diffusion performance, but the interval between the lowest point and the highest point of the unevenness is about 0.5 to 100 μm. preferable.

  The resin layer containing particles refers to a layer in which a resin layer mixed with particles is formed. The material, shape, and size of the particles are appropriately selected according to the desired light collecting performance and light diffusion performance, and are not particularly limited. For example, the material of the particles is preferably transparent; the shape is spherical, oval, cube The average particle size is preferably about 0.5 to 200 μm. The surface shape of the resin layer containing particles is not particularly limited, and may have irregularities along the mixed particle shape; it may be planar; one-dimensional prism shape, two-dimensional prism shape, It may be a microlens shape, a lenticular lens shape, a wave shape, an irregular shape, or the like.

  The thickness of the polarizing diffuser film having the surface shape and / or the resin layer having the light collecting function and / or the light diffusing function of the present invention is the thickness of the surface shape and the resin layer having the light collecting function and / or the light diffusing function. The total thickness is preferably 20 to 650 μm.

  As described above, the surface of the polarizing diffusion film of the present invention may have a surface shape having a light collecting function and / or a light diffusion function, but the surface shape is the surface of the uniaxially stretched resin film itself. It may be in the shape; it may be in the shape of a resin layer separately disposed on the surface of the uniaxially stretched resin film.

  A method for forming a surface shape or a resin layer having a light collecting function and / or a light diffusing function is not particularly limited, and a conventional method can be used. For example, in order to change the surface shape of the uniaxially stretched resin film itself to a surface shape having a light collecting function and / or a light diffusion function, a mold is placed on the surface of the uniaxially stretched resin film, for example, a glass transition temperature Tg or more of the resin, What is necessary is just to heat-press on the temperature conditions below crystallization temperature Tc, and to form by peeling a metal mold | die after cooling solidification. The heat press can be performed by using a method such as a roll press using a shaping roll, a double belt press, etc. in addition to a flat plate laminating press.

  Further, in order to form a resin layer having a light collecting function and / or a light diffusing function separately arranged on the surface of the film, for example, a gold in which a thermosetting resin or an active energy ray curable resin is injected on the surface of the film The molds are stacked and brought into close contact; the resin is cured by heating or irradiation with active energy rays; the mold may be peeled off. On the other hand, in order to form a resin layer containing particles, for example, a thermosetting resin or an active energy ray curable resin, particles, and a solvent are sufficiently mixed; The film surface is adhered and cured to form the resin; or the mixture is applied to the film surface by a method such as gravure coating; after drying at a predetermined temperature if necessary; heating or irradiation with active energy rays Then, the resin may be cured. As a method for applying the mixture, in addition to gravure coating, methods such as kiss coating, bar coating, and die coating can be used. Examples of the active energy ray curable resin include an ultraviolet ray curable resin and an electron beam curable resin.

  The surface of the polarizing diffusion film of the present invention may be subjected to known easy adhesion treatment or easy slip treatment. Further, the surface of the polarizing diffusion film may be subjected to an antireflection treatment, an anti-Newton ring treatment, an antistatic treatment or a hard coat treatment by a known treatment method.

4). Liquid crystal display device The polarizing diffusion film of the present invention is preferably used as an optical film of a liquid crystal display device. Specifically, the liquid crystal display device of the present invention comprises (A) a surface light source for a liquid crystal backlight, (B) at least one optical element and / or an air gap, (C) the polarizing diffusion film of the present invention or the present invention. A polarizing diffuser film laminate and (D) a liquid crystal panel comprising a liquid crystal cell sandwiched between two or more polarizing plates are included. Here, the members (A) to (D) are arranged in the order described above.

(A) Surface light source for liquid crystal backlight The surface light source for liquid crystal backlight is a sidelight (edge light) type surface light source in which a known light source is disposed on the side of the light guide plate, or a known light source is arranged under the diffusion plate. It can be a direct type surface light source. Examples of known light sources include cold cathode fluorescent lamps (CCFL), hot cathode fluorescent lamps (HCFL), external electrode fluorescent lamps (EEFL), flat fluorescent lamps (FFL), light emitting diode elements (LEDs), organic electroluminescent elements (OLEDs). ) Is included.

(B) Optical element and / or air gap An optical element is an element that condenses and / or diffuses light from a surface light source for a liquid crystal backlight. Examples of the optical element include a diffusion film, a prism sheet, and a microlens sheet coated with a binder containing beads or beads.

  An air gap is an air layer provided between the surface light source for liquid crystal backlights and the polarizing diffusion film of the present invention. This air layer becomes a reflective interface between the liquid crystal backlight surface light source and the polarizing reflective film, and can collect and / or diffuse light from the liquid crystal backlight surface light source. Examples of the air gap include an air layer formed in the concave portion of the prism sheet.

(D) A liquid crystal panel in which a liquid crystal cell is sandwiched between two or more polarizing plates. A liquid crystal cell is a device including liquid crystal sealed between two substrates. The substrate may be made of a known material, and examples thereof include a glass plate and a plastic film. The polarizing plate may also be made of a known material, and examples thereof include a dichroic polarizing plate using a dichroic dye. The lower polarizing plate is disposed on the (A) surface light source side; the upper polarizing plate is disposed on the display screen side. The absorption axis of the lower polarizing plate and the absorption axis of the upper polarizing plate are orthogonal to each other.

  In a liquid crystal display device having a large display screen (for example, 20 inches or more), in general, the absorption axis of the polarizing plate often coincides with the horizontal direction of the display screen. On the other hand, in a liquid crystal display device having a small and medium display screen (for example, less than 20 inches), generally, the absorption axis of the polarizing plate is often disposed at an angle of 45 ° with respect to the vertical and horizontal directions of the display screen.

  The members (A) to (D) are preferably arranged in the order of (A), (B), (C), and (D). FIG. 5 is an exploded view showing an example of the liquid crystal display device of the present invention. In FIG. 5, (A) a side light type liquid crystal backlight surface light source includes a light guide plate 50, a reflection sheet 60, and a light source 70. FIG. 5 shows (C) a polarizing diffusion film 30 and (B) an optical element 40 such as a bead-coated diffusion film. In FIG. 5, there may be a mode in which a plurality of optical elements 40 are arranged, or a mode in which no optical element 40 is arranged. (D) The liquid crystal panel includes a liquid crystal cell 10, an upper polarizing plate 20, and a lower polarizing plate 21. In addition, you may use the polarizing diffusion film laminated body of this invention for (C).

  FIG. 6 is an exploded view showing another example of the liquid crystal display device of the present invention. (A) Instead of the side light type liquid crystal backlight surface light source, (A) a direct type surface light source and a diffusion plate are arranged, and the liquid crystal display device of FIG. (A) The direct type surface light source includes a light source 70 arranged in the plane and a reflection sheet 60. The diffusing plate 80 is disposed between (A) the direct type surface light source and (B) the optical element 40 such as a diffusing film, a prism sheet, or a microlens sheet. In FIG. 6, there may be a mode in which a plurality of optical elements 40 are arranged, or a mode in which no optical element 40 is arranged.

  FIG. 7 is a view for explaining the display mechanism of the liquid crystal display device of the present invention. In FIG. 7, the extending | stretching axis | shaft of the polarizing diffuser film 30 is arrange | positioned so that it may become horizontal on the paper surface. The polarizing diffusion film 30 has a performance of transmitting polarized light perpendicular to the stretching axis and reflecting polarized light parallel to the stretching axis. The lower polarizing plate 21 is disposed so that the absorption axis is horizontal to the paper surface.

  The non-polarized light 100 emitted from the light source has polarized light P having a polarization direction parallel to the stretching axis of the polarizing diffusion film 30 and polarized light V having a polarization direction perpendicular to the stretching axis of the polarizing diffusion film 30. Most of the polarized light V included in the non-polarized light 100 passes through the polarizing diffusion film 30 and becomes polarized light V101. The polarized light V101 is transmitted without being absorbed by the lower polarizing plate 21 and becomes display light. Since most of the polarized light V101 is diffused in the light emission direction while maintaining the polarized light, it becomes display light in a wide viewing angle.

  On the other hand, a part of the polarized light P included in the non-polarized light 100 is transmitted through the polarizing diffusion film 30 and diffused to become polarized light P102. The polarized light P <b> 102 is absorbed by the lower polarizing plate 21. Further, most of the remaining polarized light P included in the non-polarized light 100 is reflected, and most of the reflected light becomes polarized light P103.

  The polarized light P <b> 103 is further reflected by an optical element and a reflection sheet (both not shown), and the polarized light is canceled to become reflected light 104. The reflected light 104 is reused as non-polarized light 100. Since the liquid crystal display device of the present invention can reuse light by such a mechanism, it is possible to increase the luminance while widening the viewing angle.

  In the apparatus shown in FIG. 7, the polarizing diffuser film 30 is such that the reflection axis of the polarizing diffuser film 30 (or the stretched axis when produced by uniaxial stretching) is substantially parallel to the absorption axis of the lower polarizing plate 21. It is preferable that it is installed in. This is because the amount of display light can be increased and the light utilization efficiency can be increased.

  In the liquid crystal display device of the present invention, it is preferable that (C) the polarizing diffusion film or the polarizing diffusion film laminate is disposed adjacent to the (D) liquid crystal panel. With such a configuration, the “upper diffusion film” disposed between (B) and (D) in the conventional liquid crystal display device may be unnecessary. That is, since the liquid crystal display device of the present invention has (C) a polarizing diffusion film or a polarizing diffusion film laminate having excellent polarization diffusivity, the luminance can be obtained without having a member such as an upper diffusion film. There is little unevenness and the luminance is improved.

  Of course, another film may be disposed between (C) the polarizing diffusion film or polarizing diffusion film laminate and (D) the liquid crystal panel. In this case, the other film is (C) The polarized light V transmitted from the polarizing diffuser film or the polarizing diffuser film laminate is preferably a film that does not disturb, reflect, or absorb much.

  As described above, when a one-dimensional prism is formed on the surface of the polarizing diffusion film or polarizing diffusion film laminate (C), the ridge line of the prism is parallel or perpendicular to the stretching direction of the uniaxially stretched resin film. It is preferable to arrange | position. On the other hand, the absorption axis of the lower polarizing plate arranged parallel to the reflection axis direction of the film of the present invention is generally a liquid crystal display device (for example, a liquid crystal television) having a large display screen (for example, 20 inches or more) as described above. ) Is often arranged parallel to the vertical direction of the display screen.

  Therefore, when the ridge line of the one-dimensional prism is arranged in parallel to the reflection axis direction of the film of the present invention, it is often parallel to the vertical direction of the display screen. When the ridge line of the one-dimensional prism is parallel to the stretching direction of the stretched resin film, an improvement in polarization selectivity is expected.

  On the other hand, when the ridge line of the one-dimensional prism is arranged perpendicular to the stretching direction of the stretched resin film, it is often parallel to the lateral direction of the display screen. When the ridge line of the one-dimensional prism is parallel to the horizontal direction of the display screen, the decrease in luminance in the oblique direction is reduced.

  In the case where the absorption axis of the polarizing plate is inclined by 45 ° with respect to the vertical and horizontal directions of the display screen, the surface of the polarizing diffusion film of the present invention is preferably a microlens shape rather than a one-dimensional prism. .

  Moreover, generally, a polarizing plate has a film in order to protect the surface. However, in the liquid crystal display device of the present invention, (C) the polarizing diffuser film or the polarizing diffuser film laminate is a polarizing plate constituting a liquid crystal panel and disposed on the light source side (lower polarizing plate). ) As a protective film. That is, the (C) polarizing diffusion film or polarizing diffusion film laminate of the present invention may be integrated with a polarizing plate to be a “polarizing plate with a polarizing diffusion function”. Usually, a polarizer of a polarizing plate is produced by uniaxial stretching, and the stretching direction is an absorption axis. Therefore, a “polarizing plate with a polarizing diffusion function” can be easily manufactured by laminating a polarizing diffusion film and a polarizer manufactured by vertical uniaxial roll stretching by roll-to-roll.

  From the above, when the (C) polarizing diffusion film or polarizing diffusion film laminate of the present invention is used, members conventionally used as constituent members of liquid crystal display devices can be omitted. The liquid crystal display device with no members is advantageous in that it is low in cost and thin.

  The conventional liquid crystal display device includes the following members between (A) and (D) in order to achieve any one or all of luminance improvement, luminance unevenness reduction, and viewing angle improvement.

  One or more diffusion films; one or more diffusion films and one or more prism sheets; or one or more diffusion films, one or more prism sheets, and 1 Sheet top diffusion film.

  Moreover, the conventional liquid crystal display device may be provided with a microlens film instead of the diffusion film, and may be provided with a polarizing reflection film (DBEF manufactured by Sumitomo 3M Limited) adjacent to (D).

  On the other hand, since the liquid crystal display device of the present invention includes a film having excellent polarization diffusibility, a liquid crystal with high luminance and a wide viewing angle and less luminance unevenness is provided without a member such as a prism sheet, an upper diffusion film, or DBEF. Display device, and at a low cost.

The present invention will be described in more detail with reference to examples and comparative examples, but the scope of the present invention should not be construed as being limited thereto.
Example 1
Polyethylene terephthalate resin (homopolymer, DEG content: 1.65 ± 0.02 mol% within specification range) as raw material, with 90mmφ single screw extruder equipped with 500mm width T die, extrusion temperature 290 ° C, extrusion rate A T-die film was formed at 200 kg / hr to obtain a casting sheet having a thickness of 1000 μm.

  Next, (1) a step of obtaining a crystallized sheet before stretching was carried out. Specifically, the obtained casting sheet was heated on a heating roll having a surface temperature of 119 ° C. for 40 seconds to obtain a crystallization raw material. Next, (2) a step of uniaxially stretching the crystallized sheet was performed. Specifically, the stretched resin film was obtained by uniaxially stretching the TD direction at the time of extrusion of the heated raw fabric as the stretching direction and the stretching speed at 350% / min. The obtained stretched resin film had a thickness of 230-270 μm. The obtained stretched film was subjected to a relaxation treatment online without being taken out from the stretching apparatus. The relaxation conditions are shown in Table 1.

  The optical properties of the obtained film, that is, the total light transmittance, the transmission haze, the transmission polarization degree, and the transmission polarization degree per 100 μm were measured and calculated. These measurements were performed using a spectrophotometer U-4100 manufactured by Hitachi High-Technologies Corporation and a 150φ integrating sphere attachment device. The crystallinity of each film was also measured. Specifically, using a density gradient tube method specific gravity measurement water tank (OMD-6 / Ikeda Rika Kogyo Co., Ltd.), the density was determined according to the density gradient tube method, and the crystallinity was calculated from the obtained density. These results are shown in Table 1.

Moreover, the tensile elasticity modulus E was calculated | required with the following method.
A dumbbell test piece (total length: 120 mm, parallel part length: 50 mm, parallel part width: 10 mm, chuck part width: 25 mm) was prepared so that the reflection axis of the film of the present invention and the long axis of the dumbbell were parallel, stretching temperature 70 ° C., preheating Time 2 minutes, stretching speed 10 mm / min. That is, 20% of the length in the stretching direction of the dumbbell specimen before stretching was stretched at a rate of stretching for 1 minute, and the tensile elastic modulus E was measured.

  The elongation at break was determined by the following method. A dumbbell test piece (width 10 mm, parallel part length 50 mm, thickness 250 mm) was prepared so that the reflection axis of the film of the present invention and the long axis of the dumbbell were perpendicular to each other, with a stretching temperature of 23 ° C. and a stretching speed of 10 mm / min. That is, 20% of the length of the dumbbell specimen before stretching was stretched at a rate of stretching for 1 minute, and the elongation at break was measured.

(Examples 2-7, Comparative Examples 1-2)
About Examples 2-7 and Comparative Examples 1-2, the film was manufactured similarly to Example 1 except having changed the manufacturing conditions of Table 1 from the conditions of Example 1. Further, the optical characteristics and the like were measured in the same manner as in Example 1. The measurement results are shown in Table 1.

(Shape stability test)
The shape stability when the films obtained in Examples 1 to 7 and Comparative Examples 1 and 2 were exposed to heat was evaluated. Specifically, in the liquid crystal display (Toshiba Corp., 32ZP2), the backlight module part is placed by replacing the film cut out in the same shape as the existing film with the existing diffusion film. The entire display was heated at 60 ° C. for 3 hours in a lit state. When wrinkles occurred on the film during heating and after 3 hours, it was evaluated as x, and when wrinkles were not detected visually, it was evaluated as o. The evaluation results are shown in Table 1.

(Processability)
The processability of the films obtained in Examples 1-7 and Comparative Examples 1-2 was evaluated. Specifically, the film is bent once to 180 ° so that a crease is generated in a direction parallel to or perpendicular to the reflection axis direction of the film, and cracks are generated both in parallel and perpendicular to the reflection axis direction. The case where it did not occur was evaluated as ◯, and the case where a crack occurred was evaluated as ×.

  From Table 1, Examples 1 to 7 in which the elongation at break is 5% or more and the product of the tensile elastic modulus E and the average thickness T of the film is 350 GPa · μm or more, both in shape stability and workability. It turns out that it is excellent. On the other hand, it can be seen that Comparative Example 1 having an elongation at break of less than 5% is excellent in shape stability but not in workability. In Comparative Example 2 in which the product of the tensile modulus E and the average thickness T of the film is less than 350 GPa · μm, the shape stability is poor although the processability is excellent.

  From the above, the polarizing diffuser film of the present invention in which the product of the elongation at break, tensile modulus E and average thickness T of the film is controlled within a specific range is excellent in both shape stability and workability. I understand that.

  The polarizing diffusive film of the present invention has both polarizing properties and diffusibility, and is excellent in shape stability when exposed to heat, and therefore can be suitably used as an optical film for liquid crystal display devices.

DESCRIPTION OF SYMBOLS 10 Liquid crystal cell 20 Upper polarizing plate 21 Lower polarizing plate 30 Polarizing diffuser film 40 Optical element 50 Light guide plate 60 Reflective sheet 70 Light source 80 Diffuser plate 100 Non-polarized light from light source 101 Polarized light V
102 Polarization P
103 Polarization P
104 Reflected light P1 Prism pitch θ1, θ2 Prism apex angle h1 Prism height P2 Distance between the apexes of the quadrangular pyramid h2 Height from the bottom of the quadrangular pyramid D Spherical lens diameter h ′ Spherical height

Claims (18)

A polarizing diffuser film substantially composed of a crystalline resin having one kind of intrinsic birefringence of 0.1 or more,
The total light transmittance for visible light is 50 to 90%,
The transmission haze for visible light is 12 to 90%,
The product of the tensile elastic modulus E measured at a rate of 20% / min at 70 ° C. in the direction parallel to the reflection axis and the average thickness T of the film is 350 GPa. A speed of 20% / min at 23 ° C. perpendicular to the reflection axis and parallel to the main surface of the film when stretched at a rate of 20% / min at 70 ° C. in the direction parallel to the reflection axis. A polarizing diffuser film having an elongation at break of 5% or more as measured with 1.   The degree of crystallinity of the polarizing diffusion film is 8 to 40%, and the polarizing diffusion film is composed of a uniaxially stretched resin film of a crystalline resin having an intrinsic birefringence of 0.1 or more. The resin film has a transmission haze with respect to visible light of 5 to 90% when the film thickness is 100 μm, and a TEM image of a cut surface perpendicular to the stretching direction of the uniaxially stretched resin film (film in the imaging range) 2. The polarized light according to claim 1, wherein a light-dark structure is observed when the distance in the thickness direction is 0.1 μm and the imaging area is 120 μm 2), and the light and dark portions of the light-dark structure are composed of substantially the same composition. Sex diffusion film.   The polarizing diffuser film according to claim 1 or 2, wherein the transmission polarization degree is 16 to 90% when the film thickness is 100 µm.   The polarizing diffuser film according to any one of claims 1 to 3, wherein the crystallinity is 8 to 35%.   5. The polarizing diffusion film according to claim 1, wherein the crystalline resin is a polyester-based resin, an aromatic polyether ketone resin, or a liquid crystal resin.   The polarizing diffusion film according to claim 5, wherein the crystalline resin is a polyethylene terephthalate resin.   The polarizing diffusion film according to claim 1, wherein at least one surface of the polarizing diffusion film has a light collecting function and / or a light diffusion function.   The polarizing property according to claim 7, wherein at least one surface of the polarizing diffusion film has a shape selected from the group consisting of a one-dimensional prism, a two-dimensional prism, a microlens, a lenticular lens, and an irregular concavo-convex shape. Diffusion film.   A polarizing diffuser film laminate comprising the polarizing diffuser film according to claim 1 and a resin layer, wherein the resin layer has a light collecting function and / or a light diffusing function. .   The resin layer having a condensing function and / or a light diffusion function has a shape selected from the group consisting of a one-dimensional prism, a two-dimensional prism, a microlens, a lenticular lens, and an irregular concavo-convex shape. Polarizing diffusion film laminate.   The polarizing diffuser film laminate according to claim 9 or 10, wherein the resin layer contains particles. It is a manufacturing method of the polarization diffusion film according to any one of claims 1 to 6,
Heating an amorphous sheet made of a crystalline resin having an intrinsic birefringence of 0.1 or more to obtain a crystallized sheet;
Stretching the crystallized sheet mainly in a uniaxial direction to obtain a stretched film;
Without substantially fixing the stretched film, at a temperature equal to or higher than the glass transition temperature of the stretched film, the relaxation rate in the stretching direction and / or the direction perpendicular to the stretching direction and parallel to the main surface of the film Heating until the relaxation rate is 0.3% or more,
A method for producing a polarizing diffuser film, comprising: The polarizing property according to claim 12, wherein in the step of obtaining the crystallized sheet, the amorphous sheet is heated at a temperature T represented by the following formula (I) until the crystallinity becomes 2% or more. A method for producing a diffusion film.
Tc−40 ° C. ≦ T <Tm−10 ° C. (I)
(In formula (I), Tc represents the crystallization temperature of the crystalline resin, and Tm represents the melting point of the crystalline resin)   The method for producing a polarizing diffuser film according to claim 12, wherein the crystallized sheet has a transmission haze with respect to visible light of 2 to 70% and a crystallinity of 2 to 20%.   (A) a surface light source for a liquid crystal backlight, (B) at least one optical element and / or an air gap, (C) the polarizing diffusion film according to any one of claims 1 to 8, or claims 9 to 11. The polarizing diffuser film laminate according to any one of the above, and (D) at least a liquid crystal panel formed by sandwiching a liquid crystal cell between two or more polarizing plates, and each of the members (A) to (D) A liquid crystal display device arranged in the above order.   The liquid crystal display device according to claim 15, wherein the (C) polarizing diffusion film is disposed adjacent to the (D) liquid crystal panel.   The liquid crystal display device according to claim 16, wherein the (C) polarizing diffusion film also serves as a light source side protective film of a polarizing plate constituting the (D) liquid crystal panel.   The reflection axis of the (C) polarizing diffuser film and the absorption axis direction of the polarizing plate (D) constituting the liquid crystal panel and disposed on the light source side are substantially the same. 16. A liquid crystal display device according to 16.