JP5451215B2 - Film for polarizer support substrate - Google Patents

Description

  The present invention relates to a film for a polarizer support substrate. More specifically, it is possible to ensure the stability of the optical axis that can prevent the color shift and color spot of the liquid crystal display, and also has excellent adhesion to the polarizer, and the polarization that can make the polarizer durable for a long time The present invention relates to a child support base film.

  The liquid crystal display adjusts the amount of emitted light by changing the polarization direction of incident light by changing the phase difference of the liquid crystal layer by controlling the orientation of liquid crystal molecules between polarizing plates arranged orthogonally. Therefore, in order to obtain good display image quality, it is required that the polarization direction of light incident on the liquid crystal layer is stable.

  The polarizing plate used in many liquid crystal displays is of the absorption film type, and consists of a structure in which a dichroic molecule is uniaxially oriented in a matrix and the polarizer is sandwiched between transparent substrates. . In many cases, a uniaxially stretched poly (vinyl alcohol) film impregnated with iodine as a polarizer is used as a dichroic molecule.

  Further, in most cases, a cellulose triacetate (TAC) film is currently used as a supporting substrate for protecting the polarizer. The TAC film, which is a material with excellent transparency, has excellent optical isotropy and has almost no phase difference in the plane. Therefore, the vibration direction of the incident linearly polarized light is hardly changed. Although it is a suitable material, it is disadvantageous in terms of cost because it can be produced only by the solution casting method with the current technology. Depending on the application used, the TAC film may not have sufficient moisture resistance and heat resistance.

Aromatic polyester films such as polyethylene terephthalate are excellent in transparency, heat resistance and mechanical strength, and are inexpensive compared to TAC. Therefore, polyethylene terephthalate has been used as a polarizer support substrate in place of TAC film in the past. Various attempts have been made.
A film having excellent optical isotropy, such as a TAC film, was used as a support substrate so that the vibration direction of incident linearly polarized light was not changed by the support substrate of the polarizer, whereas an aromatic polyester film was In addition, since the molecular chain has an aromatic ring with a high polarizability, the intrinsic birefringence is extremely large, and the film birefringence accompanies the orientation of the molecular chain by stretching treatment to give excellent transparency, heat resistance, and mechanical strength. Is likely to occur, and luminance spots and color shifts are likely to occur. Therefore, the following studies have been made to use a polyester film as a supporting substrate.

  For example, in Patent Document 1, in a display panel including a polarizer and a pair of substrates made of a uniaxially stretched plastic film in contact with the polarizer, the angle formed by the optical principal axis direction of the uniaxially stretched plastic film and the polarization axis direction of the polarizer is It is disclosed that the angle is approximately ± 3 degrees or less, and it is described that a uniaxially stretched polyester film is used as the uniaxially stretched film. According to Patent Document 1, if the angle between the optical principal axis direction of the uniaxially stretched film and the polarization axis direction of the polarizer is not appropriate, an interference color due to the birefringence phenomenon occurs, the contrast ratio decreases, and the display quality decreases. It is disclosed that it decreases.

  Further, in a polyester film that is particularly strongly stretched in one direction parallel to the film surface, a film satisfying a specific relational expression between the refractive index in the main stretching direction and the refractive index in the vertical direction is an adhesive on at least one surface of the polarizing film. A polarizing plate pasted through these layers is disclosed in Patent Document 2, and it is described that color spots do not occur when such a film is used.

  Further, for example, Patent Document 3 discloses a uniaxially stretched polyester film as a surface protective film for a polarizing film, and as a polyester film particularly advantageous for use under harsh conditions such as in-vehicle use, only a longitudinal or lateral direction is disclosed. In other words, it is preferable to stretch at least 5%, practically 50 to 800%, and heat set at about 100 ° C. for 60 minutes to about 280 ° C. for 5 minutes.

  In Patent Document 4, a uniaxially stretched polyester film is used as a transparent support substrate for a polarizer, and the uniaxially stretched hydrophilic polymer film and the uniaxially stretched polyester film are pasted so that the stretching direction is parallel or orthogonal. It is disclosed that the smaller the angle deviation at that time, the more preferable in terms of light transmittance. Further, a uniaxially stretched polyester film having a retardation value of 8000 nm is disclosed.

  As described above, the use of a uniaxially stretched polyester film and the elimination of color spots and the like by reducing the difference between the principal axis direction and the polarization axis direction of the polarizer have been studied. On the other hand, the accuracy of the uniformity of the alignment direction required for the polarizer support substrate is very high, and it is difficult to obtain the stability of the optical axis that can withstand practical use even in the peripheral part of the film simply by stretching in the uniaxial direction. there were. In addition, with the increase in the size of liquid crystal screens, the support substrate is required to have a large area, and uniform performance is required in the area to be used. For polyester films that have a large increase in birefringence due to stretching. Thus, there is a demand for a film that does not cause color shift and color spots including both ends of the film.

  Furthermore, since a polarizer support base material is bonded to a polarizer to form a polarizing plate, excellent adhesiveness with a polyvinyl alcohol film generally used as a polarizer is required. This is because a polarizer using a polyvinyl alcohol film has poor moisture resistance, and the polarization function deteriorates over time unless the adhesiveness to the support substrate is sufficient. However, stretched molecular oriented polyester films generally have poor adhesion to other materials, and particularly low adhesion to polyvinyl alcohol. Therefore, when stretched oriented polyester films are used as polarizer support substrates, Improvement of adhesiveness with a polarizer is desired.

JP 58-143305 A JP-A-60-26304 JP 61-241703 A JP 63-226603 A

  The object of the present invention is a uniaxially oriented polyester film, which has a high degree of optical axis stability in which the orientation direction is uniformly controlled even at both ends of the film, where the orientation direction of the film has been apt to be non-uniform in the past. A polarizer that can prevent color shifts and color spots of a liquid crystal display even when used as a supporting substrate up to both ends, and further has excellent adhesion to the polarizer and can make the polarizer durable for a long period of time. It is providing the film for support base materials.

  As a result of intensive studies to solve the above problems, the present inventor has uniformly controlled the orientation direction of the film to both ends of the film due to the bowing phenomenon that occurs during film formation in the conventional uniaxially stretched polyester film. However, it was difficult to use at a practical level while being proposed for use as a polarizer support substrate. In the present invention, the clip portion is slit by controlling the drawing speed and tension during the drawing process. Has found that a film having a stable optical axis can be obtained by uniformly controlling the orientation direction of the film up to both ends of the film, and can be used as a film for a polarizer support substrate. In addition, excellent adhesion to the polarizer can be obtained by forming a coating layer in which a certain amount of copolymerized polyester having an optimized glass transition point and polyvinyl alcohol having a high degree of saponification is present on the surface of the polyester film. The present inventors have found that a polyester film suitable for a polarizer support substrate can be provided.

That is, an object of the present invention is a method for producing a uniaxially oriented aromatic polyester film in which an aromatic polyester resin composition is melt-extrusion cast, stretched in the MD direction and TD direction, and heat-set. The draw ratio (R ^MD ) in the MD direction is in the range of 0.7 to 2.0, and the draw ratio in the TD direction and the MD direction (R ^TD / R ^MD ) exceeds 3.0. The range is 0 or less, the stretching speed in the TD direction is 300% / min or more, the transport speed before stretching in the TD direction is 0.995 to 0.998 of the transport speed in the TD direction stretching, and TD The film take-up conveyance speed after completion of the direction stretching is 1.003 to 1.010 of the TD direction stretching conveyance speed, and in the heat setting treatment, the heat setting temperature is the aromatic polyester resin composition. Higher than the glass transition point of the aromatic polyester constituting, in the range of (melting point -15 ° C.) or less, uniaxially oriented aromatic polyester film obtained is more than 75 mol% of the monomer units of the aromatic polyester be ethylene terephthalate , The degree of orientation of the PET crystal (−105) plane in the film TD direction obtained by wide-angle X-ray diffraction measurement, the angle α between the in-plane slow axis and the film TD direction, and the in-plane slow axis and the film TD direction Satisfying the following formulas (1) and (2):
fc _TD (−105) ≧ 0.35 (1)
(In formula (1), fc _TD (−105) represents the degree of orientation of the PET crystal (−105) plane in the film TD direction obtained by wide-angle X-ray diffraction measurement)
0 ≦ α + β ≦ 15 ° (2)
(In the formula (2), α represents an angle formed by the in-plane slow axis of the film and the film TD direction, and an average of 10 points measured at 100 points every 100 mm in the MD direction for both ends of the film using an ellipsometer. Β represents the variation in the angle between the in-plane slow axis of the film and the film TD direction, and 10 points measured at 5 points every 100 mm in the MD direction at both ends of the film using an ellipsometer. (Represented by 3 times the standard deviation)
Copolymer polyester having a glass transition point of 20 to 90 ° C. on at least one surface of the film is 40% by weight to 80% by weight based on the weight of the binder component and polyvinyl alcohol having a saponification degree of 80% by mole to 90% by mole as a binder component. This is achieved by a method for producing a uniaxially oriented aromatic polyester film for a polarizer support substrate , which is provided with a coating layer containing 20% by weight or more and 60% by weight or less based on weight.

This onset Ming also, as a preferred embodiment, the uniaxially oriented aromatic polyester film obtained, 10 wt% or more of an acrylic resin having further oxazoline groups and polyalkylene oxide chains in the coating layer based on the weight of the binder component 20 The obtained uniaxially oriented aromatic polyester film has an in-plane retardation of the polyester film of 1000 nm or more and a variation of 100 nm or less, and the obtained uniaxially oriented aromatic polyester film. The film has a crystal size of the PET crystal (100) plane of the polyester film satisfying the following formula (3), and the haze value of the film is 7% or less,
3.0 nm ≦ χc _P (100) ≦ 4.5 nm (3)
(In formula (3), χc _P (100) represents the crystal size [nm] of the PET crystal (100) plane of the film obtained by wide-angle X-ray diffraction measurement)
In uniaxial oriented aromatic polyester film obtained copolymerized polyester in the coating layer, it dicarboxylic acid component having a sulfonate group is a copolyester containing 1 to 16 mol% per total carboxylic acid component, the resulting uniaxially In the oriented aromatic polyester film, the surface energy of the coating layer surface is 50 to 65 dyne / cm, and the resulting uniaxially oriented aromatic polyester film has a film shrinkage ratio after 120 minutes of non-restraining heat treatment at 120 ° C. direction, 5% or less in any of the film TD direction, also include those comprising at least any one.

  According to the present invention, the angle between the film in-plane slow axis and the film TD direction and the variation thereof at the both ends of the film are small, and an advanced optical axis capable of preventing color shift and color spot of a liquid crystal display. In addition, it is possible to provide a film for a polarizer support base material that can secure the stability of the polarizer and is further excellent in adhesiveness with a polarizer and can make the polarizer long-term durability. A polarizing plate using such a film can provide a liquid crystal display product excellent in display image quality free from color shifts and color spots at a low cost, and can cope with an increase in size.

The present invention will be described in detail below.
<Aromatic polyester>
In the aromatic polyester constituting the uniaxially oriented aromatic polyester film of the present invention, 75 mol% or more of the monomer units is ethylene terephthalate. By using such polyester, the degree of orientation in the main alignment axis direction is increased by orientation crystallization having a main alignment axis in one direction, and a film having a refractive index characteristic suitable as a support substrate for a polarizer can be obtained. A film having high heat resistance and mechanical strength can be obtained. The monomer unit component is more preferably 80 mol% or more, further preferably 90 mol%, particularly preferably 95 mol% or more.

  Aromatic polyester, if it contains a subordinate component, such as diethylene glycol, neopentyl glycol, polyalkylene glycol and the like diol components, adipic acid, sebacic acid, phthalic acid, isophthalic acid, naphthalene dicarboxylic acid, 5-sodium sulfoisophthalic acid, etc. Examples include dicarboxylic acid components.

<Uniaxially oriented aromatic polyester film>
The aromatic polyester film of the present invention is a uniaxially oriented aromatic polyester film. Here, the definition of “uniaxial orientation” in the present invention includes not only a uniaxially oriented film stretched only in one direction but also a film having a large difference in orientation degree between the main orientation direction and its orthogonal direction among films stretched in two directions. Any film having uniaxial orientation satisfying the degree of orientation of the PET crystal (−105) plane described below is included in this definition.

(Crystal orientation)
In the uniaxially oriented aromatic polyester film of the present invention, the degree of orientation of the PET crystal (−105) plane in the film TD direction obtained by wide-angle X-ray diffraction measurement needs to satisfy the following formula (1).
fc _TD (−105) ≧ 0.35 (1)
(In formula (1), fc _TD (−105) represents the degree of orientation of the PET crystal (−105) plane in the film TD direction obtained by wide-angle X-ray diffraction measurement)
The film of the present invention is a uniaxially oriented film, and the molecular orientation obtained by stretching can be confirmed by observing the orientation crystallization behavior of the obtained film by wide-angle X-ray diffraction measurement.
Specifically, by wide-angle X-ray diffraction measurement, a sample fixed at a Bragg angle corresponding to the crystal plane to be observed is rotated over the whole globe, and an X-ray diffraction pole figure is measured. It is obtained by calculating the degree of orientation.
Here, the degree of crystal orientation fc takes a value of -0.5 to 1, and as fc is closer to 1, the normal vector of the measured crystal plane and the direction in which the evaluation is parallel are more distributed, and fc is- The closer to 0.5 the more normal vectors and evaluation directions are orthogonal.
The normal vector of the PET crystal (−105) plane is substantially along the molecular chain, and if the fc _TD (−105) satisfies the range of the formula (1), the molecular chain is in the film main stretching direction. In the present invention, the direction is the film TD direction (hereinafter sometimes referred to as the width direction or the lateral direction).

The uniaxially oriented aromatic polyester film of the present invention is oriented crystallized in the range of the degree of orientation in the film TD direction, thereby having a main orientation axis highly oriented in the TD direction, and supporting this film with a polarizer. When laminating with a polarizer as a substrate, it is possible to suppress the occurrence of color shifts and color spots associated with changes in the polarization state of polarized light by this film. Here, the main orientation axis direction of the film corresponds to a slow axis from the viewpoint of the vibration behavior of light, and is sometimes referred to as a film in-plane slow axis.
The directionality of laminating the polarizer support substrate and the polarizer is such that color shift and color unevenness are achieved if the main orientation axis of the polarizer support substrate and the transmission axis of the polarizer are either orthogonal or parallel. Can be suppressed. On the other hand, in order to obtain a high degree of optical axis stability in which the orientation direction is uniformly controlled for both end portions of the film, a method of stretching so that the TD direction becomes the main orientation in the film forming process is necessary and obtained. The main direction of the degree of crystal orientation of the film is the TD direction.

  In addition, from the viewpoint that the polarizer and the polarizer support substrate can be continuously produced, the polarizer is referred to as a film MD direction (hereinafter sometimes referred to as a continuous film forming direction, a longitudinal direction, or a longitudinal direction) and a light absorption axis of the polarizer. Are preferably laminated in parallel with each other, and the linearly polarized light and the polarizer transmission axis obtained are preferably in the film TD direction.

The degree of crystal orientation represented by fc _TD (−105) is more preferably 0.38 or more, further preferably 0.40 or more, and particularly preferably 0.43 or more. The higher the degree of crystal orientation, the better, but the upper limit is preferably 0.55 or less, or 0.50 or less in consideration of polymer characteristics and manufacturable film production.
On the other hand, when the fc _TD (−105) of the film is less than the lower limit, the difference between the polarizer transmission axis and the film molecular orientation angle is large, color shifts and color spots occur, and the display image quality deteriorates.

In order to obtain a film having such a degree of crystal orientation, the draw ratio (R ^TD / R ^MD ) in the film TD direction and the film MD direction exceeds 3.0 and is 7.0 or less, as will be described in detail in the film manufacturing method. perform stretching treatment within an amount of, after obtaining the uniaxially oriented polyester film by performing at a draw ratio (R ^MD) range below 2.0 times 0.7 times or more such films MD direction, the glass of the polyester By performing heat setting treatment in the range of not lower than the transition point and not higher than (melting point−15 ° C.), when performing such stretching, the tension in the MD direction is moderately increased, and the stretching speed in the TD direction is increased. Achieved.

(Slow axis angle α and slow axis angle variation β)
In addition, the uniaxially oriented aromatic polyester film of the present invention includes an angle α (hereinafter sometimes referred to as a slow axis angle α) formed by the in-plane slow axis of the film and the film TD direction, and an in-plane slow axis of the film. The relationship of the angle variation β (hereinafter sometimes referred to as the slow axis angle variation β) with the film TD direction needs to satisfy the following formula (2).
0 ≦ α + β ≦ 15 ° (2)
(In the formula (2), α represents an angle formed by the in-plane slow axis of the film and the film TD direction, and an average of 10 points measured at 100 points every 100 mm in the MD direction for both ends of the film using an ellipsometer. Β represents the variation in the angle between the in-plane slow axis of the film and the film TD direction, and 10 points measured at 5 points every 100 mm in the MD direction at both ends of the film using an ellipsometer. (Represented by 3 times the standard deviation)
When the value represented by (α + β) exceeds this range, not only a color shift occurs at both ends of the film, but also color spots occur.
The value of the slow axis angle α alone is preferably 15 ° or less, more preferably 10 ° or less, still more preferably 8 ° or less, particularly preferably 5 ° or less, and most preferably 3 ° or less. Further, the value of the slow axis angle variation β alone is preferably 5 ° or less, more preferably 2 ° or less, further preferably 1 ° or less, particularly preferably 0.5 ° or less, and most preferably 0 °. It is. A preferable range of (α + β) represented by the formula (2) is derived from the preferable ranges of α and β, particularly preferably 5 ° or less, and most preferably 3 ° or less.

The slow axis angle α in the present invention represents the angle formed between the slow axis and the film TD direction at both end portions (sometimes referred to as edge portions) of the film, and both end portions of the film using an ellipsometer. Is represented by an average value of 10 points measured every 5 points in the MD direction. The slow axis angle variation β in the present invention represents the angle variation between the film in-plane slow axis and the film TD direction at both ends of the film. Like α, an ellipsometer is used. It is represented by three times the standard deviation value of 10 points measured at 5 points every 100 mm in the MD direction for both ends of the film.
Here, the both ends of the film refer to both ends of the film after slitting the portion corresponding to the tenter clip holding portion in the film forming process, and specifically, the portion corresponding to the tenter clip holding portion in the film forming process is removed. The slit refers to both ends of the film obtained by being performed within a range of 4% to 10% from both ends of the film before the slit.

  The film obtained by stretching film formation tends to have a larger deviation between the stretching direction and the orientation axis due to the bowing phenomenon, and the slow axis angle α and the variation of the slow axis angle β tend to increase as the film reaches both ends. is there. In the present invention, by controlling the film forming method, the slow axis angle α and the slow axis angle variation β are reduced for both ends of the film obtained by slitting the clip portion, As a result, it is possible to ensure the stability of the optical axis that can prevent color shift and color spots of the liquid crystal display even when used up to both ends of the film, and there is less variation in the screen of the display image quality and higher The display image quality of performance is manifested.

In order to obtain (α + β) represented by Formula 2, the draw ratio (R ^TD / R ^MD ) in the film TD direction and the film MD direction exceeds 3.0 as described in detail in the film production method. The film is stretched in a range of 0.0 or less, and after obtaining a uniaxially oriented polyester film by performing a stretch ratio (R ^MD ) in the film MD direction in a range of 0.7 times to 2.0 times, When performing the heat setting treatment within the range of the glass transition point of the polyester to (melting point −15 ° C.) and below, and performing such stretching, the tension in the MD direction is moderately increased, and the stretching speed in the TD direction is increased. Achieved by enhancing.

(In-plane phase difference)
The uniaxially oriented aromatic polyester film of the present invention preferably has an in-plane retardation of the film of 1000 nm or more. The in-plane retardation is more preferably 3000 nm or more, further preferably 5000 nm or more, and particularly preferably 7000 nm or more.

  It is preferable that the polarizer support base material which is the use of the film of the present invention does not disturb the linearly polarized light obtained by the polarizer as much as possible. Therefore, in a TAC film or the like, the smaller the retardation of the film, that is, the product of birefringence multiplied by the film thickness, the more suitable for the polarizer support substrate. However, when an aromatic polyester is used, since it has a relatively large intrinsic birefringence due to the molecular structure, a film phase difference due to molecular chain orientation is likely to appear, and it is difficult to control this to a small value. Therefore, by making the film uniaxially oriented and making the in-plane retardation of the film within such a range, the retardation value of the film is made larger than the wavelength of visible light, and the influence on the incident linearly polarized light is reduced. The influence on the quality is so small that it can be ignored, and a better display image quality can be obtained.

  The in-plane retardation is 5 points in every 100 mm in the film-forming direction with respect to the position of 5 points in the width direction and the 5 positions in the width direction of the both ends of the obtained film, the central part, and their intermediate positions. A total of 25 samples were cut out each, measured using an ellipsometer, and represented by the average value of the maximum phase differences obtained for each sample.

Further, the variation in the in-plane retardation is preferably 100 nm or less. The variation in the in-plane phase difference is directly related to the variation in the screen of the display image quality. Therefore, the smaller the value is, the more preferable it is 50 nm or less.
These in-plane retardations are stretched in the range where the ratio of draw ratios (R ^TD / R ^MD ) in the film TD direction and the film MD direction is more than 3.0 and 7.0 or less for films having the same thickness. Achieved by doing.

(Crystal size, transparency)
The polarizer support substrate used for the film of the present invention is preferably transparent in order to increase the transmittance of linearly polarized light, and the size of the crystallization region in the film can be set to a specific size. preferable. Specifically, it is preferable that the crystal size of the PET crystal (100) plane of the polyester film satisfies the following formula (3).
3.0 nm ≦ χc _P (100) ≦ 4.5 nm (3)
(In formula (3), χc _P (100) represents the crystal size [nm] of the PET crystal (100) plane of the film obtained by wide-angle X-ray diffraction measurement)
χc _P (100) represents the crystal size [nm] of the PET crystal (100) plane of the film obtained by wide-angle X-ray diffraction measurement. Specifically, χc _P (100) using the wide-angle X-ray diffraction measurement is based on X-rays while rotating the sample and the measuring instrument so that the X-ray incident angle and the angle of the measuring instrument with respect to the film surface are always equal around the sample. Diffraction measurement is performed (2θ-θ scan), and the crystal size is calculated from the peak half-value width at the Bragg angle corresponding to the crystal plane to be monitored.
The upper limit of the crystal size represented by the formula (3) is more preferably 4.0 nm.
When the value of the formula (3) exceeds the upper limit, there are many light scattering factors based on the structural non-uniformity in the film, the transparency of the film is poor, and the haze value may be high. On the other hand, the value of formula (3) is less than 3.0 nm, although it is transparent, it may lead to a decrease in optical axis stability at both ends of the film, the crystallinity is too small, and other characteristics, In particular, it may be difficult to control the heat shrinkage rate described later to a preferable value.

  The crystal size is determined by the heat setting temperature after stretching the film, and the film after stretching is preferably subjected to heat setting in the range of the glass transition point of the polyester to (melting point −15 ° C.) or less, and further 180 ° C. It is preferably in the range of ~ 240 ° C.

As a characteristic regarding transparency of the film, the haze value of the film is preferably 7% or less, more preferably 5% or less, and particularly preferably 1.5% or less.
As a means to achieve a highly transparent film having such a haze value, the above-mentioned crystal size is made a specific size, and the film does not contain particles such as a lubricant or, if so, based on the film weight The method of using in the very small range of 0.1 weight% or less is mentioned. Moreover, since the particle content in the coating layer added for the purpose of improving slipperiness also affects the haze value, the haze value can be lowered by using it within a certain content range.

(Heat shrinkage)
In the uniaxially oriented aromatic polyester film of the present invention, the film shrinkage ratio after non-restraining heat treatment at 120 ° C. for 30 minutes is preferably 5% or less in both the film MD direction and the film TD direction, more preferably It is 3% or less, and particularly preferably 2% or less.

  Since the film of the present invention passes through many steps to be heated, such as the production of a polarizing plate or the step of compositing the obtained polarizing plate with a liquid crystal cell, good dimensional stability is required. By having this, the thermal contraction rate difference with a member to be bonded such as a polarizer after the processing step is small, and warpage or the like hardly occurs. On the other hand, when the value of the heat shrinkage rate exceeds the upper limit, warpage or the like may occur.

  As a means for obtaining these heat shrinkage characteristics, it is preferable to perform heat setting treatment on the stretched film in the range of not less than the glass transition point of the polyester and not more than (melting point−15 ° C.). Moreover, you may attach toe-in within the range by which the optical axis stability of the both ends of a film is not impaired by a bowing phenomenon.

<Coating layer>
The film for a polarizer supporting substrate of the present invention is a copolymer polyester having a glass transition point of 20 to 90 ° C. on at least one surface of a uniaxially oriented aromatic polyester film and is 55% by weight or more and 85% by weight or less based on the weight of the binder component. A coating layer containing 15 to 45% by weight of polyvinyl alcohol having a saponification degree of 80 to 90 mol% based on the weight of the binder component is provided. Further, it is preferable that the coating layer further contains an acrylic resin having an oxazoline group and a polyalkylene oxide chain in an amount of 5 wt% to 25 wt% based on the weight of the binder component.
The constituent components of the coating layer are described below.

(Polymer binder)
As a polymer binder component constituting the coating layer, it is necessary to contain a copolyester having a glass transition point of 20 to 90 ° C. and polyvinyl alcohol having a saponification degree of 80 to 90 mol%.
The content of the polymer binder is preferably 30% by weight or more and 90% by weight or less based on the weight of the coating layer. The content of the polymer binder is more preferably 50% by weight or more and 80% by weight or less, and further preferably 60% by weight or more and 75% by weight or less.
When the content of the polymer binder is in such a range, the adhesiveness with the polarizer can be strengthened, and the polarizer can be made long-term durable.

(Copolymerized polyester)
The glass transition point (hereinafter sometimes abbreviated as Tg) of the copolymerized polyester is 20 to 90 ° C, preferably 25 to 80 ° C. If the glass transition point is less than the lower limit value, the films block each other. On the other hand, if the glass transition point exceeds the upper limit value, the adhesion with the polarizer is reduced.

  The content of the copolyester is 40 to 80% by weight based on the weight of the binder component. The content of the copolyester is preferably 40 to 70% by weight. If the content of the copolyester is less than the lower limit, the adhesion with the polyester film is not sufficient. Moreover, when content of copolyester exceeds an upper limit, adhesiveness with a polarizer will fall.

Examples of the copolyester include polyesters obtained from the following polybasic acids or ester-forming derivatives thereof and polyols or ester-forming derivatives thereof. At least one of the polybasic acid and polyol contains two or more components. .
As polybasic acid component of copolymer polyester, terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid, pyro A merit acid, a dimer acid, 5-sodium sulfo isophthalic acid etc. can be mentioned. These acid components are preferably two or more types of copolyester. The polyester may contain an unsaturated polybasic acid component such as maleic acid or itaconic acid, or a hydroxycarboxylic acid component such as p-hydroxybenzoic acid, as long as it is in a slight amount.

  Polyol component of polyester resin includes ethylene glycol, 1,4-butanediol, diethylene glycol, dipropylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, xylene glycol, dimethylolpropane, poly (ethylene oxide) glycol And poly (tetramethylene oxide) glycol.

The copolyester preferably contains 1 to 16 mol% of a dicarboxylic acid component having a sulfonate group per total carboxylic acid component. As the dicarboxylic acid component, 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, Examples include 5-potassium sulfoterephthalic acid.
The amount of the dicarboxylic acid component having a sulfonate group is more preferably 1.5 to 14 mol%. When such a component is less than the lower limit, the hydrophilicity of the copolyester may be insufficient. On the other hand, when such a component exceeds the upper limit, the moisture resistance of the coating layer is lowered, and the function of the polarizer may be lowered.

  The range of the glass transition point of the copolyester can be obtained by making the copolymerization ratio of the above components moderate. Specifically, regarding the upper limit of the glass transition point, for example, by using an aromatic dicarboxylic acid component such as 2,6-naphthalenedicarboxylic acid so as not to exceed 80 mol% based on the total acid component of the copolymerized polyester, It is possible to prevent the transition point from exceeding the upper limit of such a range. In addition, by making the alicyclic diol and aromatic diol components such as 1,4-cyclohexanedimethanol and bisphenol A ethylene oxide adduct not exceed 60 mol% based on the total diol components of the copolymerized polyester, It is possible to prevent the glass transition point from exceeding the upper limit of the range.

  On the other hand, the lower limit of the glass transition point of the copolyester is long chain fat such as 1,4-butanediol, diethylene glycol, 1,6-hexanediol, poly (ethylene oxide) glycol, poly (tetramethylene oxide) glycol. By making the group diol component not exceed 60 mol% based on the total diol component of the copolymer polyester, the glass transition point can be prevented from falling below the lower limit of the range.

  In the present invention, when the coating layer is formed on the film, the coating layer composition is dissolved or dispersed in water or an aqueous solution containing some organic solvent. Alternatively, the polyester is preferably soluble or dispersible in an aqueous solution containing some organic solvent. In order to improve water dispersibility, it is preferable that a copolymer component having a functional group with a high degree of ionization such as a sulfonate and a highly hydrophilic copolymer component such as a polyalkyl ether are included.

(Polyvinyl alcohol)
As the polyvinyl alcohol of the present invention, polyvinyl alcohol having a saponification degree of 80 to 90 mol% is used. Examples of such polyvinyl alcohol include vinyl alcohol-vinyl acetate copolymer, vinyl alcohol-vinyl butyral copolymer, and ethylene-vinyl alcohol copolymer. Among these, vinyl alcohol-vinyl acetate copolymer, ethylene-vinyl alcohol A copolymer is preferred. Usually, the copolymerization ratio of vinyl alcohol is represented by the degree of saponification.

The polyvinyl alcohol of the present invention is characterized by a considerably high saponification degree, and by using the polyvinyl alcohol in the range of such a saponification degree, strong adhesiveness with a polarizer made of a polyvinyl alcohol film is expressed.
When the saponification degree is less than 80 mol%, the adhesiveness with the absorbent polarizing film is lowered, and when it exceeds 90 mol%, the moisture resistance of the easy-adhesion layer is lowered.

  The content of polyvinyl alcohol is 20 to 60% by weight based on the weight of the binder component. The content of polyvinyl alcohol is preferably 20 to 50% by weight. If the content of polyvinyl alcohol is less than the lower limit, the adhesiveness with the polarizer is lowered. Moreover, when content of polyvinyl alcohol exceeds an upper limit, adhesiveness with a polyester film is not enough.

(acrylic resin)
Moreover, it is preferable to contain the acrylic resin which has an oxazoline group and a polyalkylene oxide chain in addition to said copolymer polyester and polyvinyl alcohol as a polymer binder component which comprises the coating layer of this invention. Since the polyvinyl alcohol component tends to become brittle over time, the strength of the coating layer may decrease over time although the adhesiveness with the polarizer increases. Therefore, by further containing an acrylic resin having an oxazoline group, the resin can self-crosslink to form a network structure, and the coating layer strength can be maintained over time. The strength of the coating layer can also be improved by using a cross-linking agent as will be described later, but in many cases, it is cross-linked by reacting with the OH group of the polyvinyl alcohol component, so that the adhesiveness may be inferior.

  The content of the acrylic resin having an oxazoline group and a polyalkylene oxide chain is preferably 0% by weight to 20% by weight, more preferably 10% by weight to 20% by weight, based on the weight of the polymer binder component. It is. If the content of the acrylic resin is less than the lower limit, the coating layer strength may decrease with time. On the other hand, when the content of the acrylic resin exceeds the upper limit value, the ratio of the copolymerized polyester component and the polyvinyl alcohol component becomes relatively small, so that the adhesiveness may be inferior.

The acrylic resin having an oxazoline group and a polyalkylene oxide chain is preferably an acrylic resin that is soluble or dispersible in water or an aqueous system containing a small amount of an organic solvent.
Specifically, it is a copolymer containing a monomer component having an oxazoline group, a monomer component having a polyalkylene oxide chain, and other copolymerization monomer components.

As monomers having an oxazoline group, 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2- Examples thereof include isopropenyl-4-methyl-2-oxazoline and 2-isopropenyl-5-methyl-2-oxazoline, and one or a mixture of two or more thereof can be used. Among these, 2-isopropenyl-2-oxazoline is preferred because it is easily available industrially. By using an acrylic resin having an oxazoline group, the coating layer strength can be improved, and the durability of the coating layer can be further increased.
The monomer component having an oxazoline group is preferably 5 mol% or more and 80 mol% or less, more preferably 10 mol% or more and 50 mol% or less, based on the repeating unit of the acrylic resin.

Examples of the monomer having a polyalkylene oxide chain include those obtained by adding polyalkylene oxide to an ester part of acrylic acid or methacrylic acid. Examples of the polyalkylene oxide chain include polyethylene oxide, polypropylene oxide, and polybutylene oxide. The repeating unit of the polyalkylene oxide chain is preferably 3 to 100.
By using an acrylic resin having a polyalkylene oxide chain, the compatibility between the polyester resin and the acrylic resin in the coating layer is better than that of an acrylic resin not containing a polyalkylene oxide chain, and the transparency of the coating layer is improved. be able to.
When the number of repeating units of the polyalkylene oxide chain is less than 3, the compatibility between the polyester resin and the acrylic resin is lowered, and the transparency of the coating layer may be lowered. If the repeating unit of the polyalkylene oxide chain is larger than 100, the wet heat resistance of the coating layer is lowered, and the durability of the coating layer may be lowered at high humidity and high temperature.

Other copolymer components that constitute the acrylic resin include alkyl acrylate, alkyl methacrylate; hydroxyl group-containing monomers such as 2-hydroxyalkyl acrylate and 2-hydroxyalkyl methacrylate; epoxy groups such as glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether Monomers: Monomers having carboxyl groups or salts thereof such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrene sulfonic acid and salts thereof; acrylamide, methacrylamide, N-alkylacrylamide, N-alkyl Methacrylamide, N, N-dialkylacrylamide, N, N-dialkylmethacrylamide, N-alkoxyacrylamide, N-alkoxymethacrylate Monomers having an amide group such as amide, N, N-dialkoxyacrylamide, N, N-dialkoxymethacrylamide, acryloylmorpholine, N-methylolacrylamide, N-methylolmethacrylamide, N-phenylacrylamide, N-phenylmethacrylamide Monomers of acid anhydrides such as maleic anhydride and itaconic anhydride; vinyl isocyanate, allyl isocyanate, styrene, α-methyl styrene, vinyl methyl ether, vinyl ethyl ether, vinyl trialkoxysilane, alkyl maleic acid monoester, alkyl fumarate Examples include acid monoesters, alkyl itaconate monoesters, acrylonitrile, methacrylonitrile, vinylidene chloride, ethylene, propylene, vinyl chloride, vinyl acetate, and butadiene. It is done.
Among these copolymer components, examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a 2-ethylhexyl group, and a cyclohexyl group. . Examples of the alkoxy group include a methoxy group, an ethoxy group, a butoxy group, and an isobutoxy group.

(particle)
The coating layer preferably contains 3 to 25 parts by weight of particles based on the weight of the coating layer for the purpose of imparting film slipperiness. The content of the particles is more preferably 5 to 20 parts by weight. If the content of the particles is less than the lower limit, the slipperiness of the film, that is, the transportability may be insufficient. On the other hand, if it exceeds the upper limit, the haze value of the film may be lowered and may not be used for display applications. .

  Examples of such particles include calcium carbonate, magnesium carbonate, calcium oxide, zinc oxide, magnesium oxide, silicon oxide, sodium silicate, aluminum hydroxide, iron oxide, zirconium oxide, barium sulfate, titanium oxide, tin oxide, antimony trioxide, Examples thereof include inorganic fine particles such as carbon black and molybdenum disulfide, and organic fine particles such as acrylic cross-linked polymers, styrene cross-linked polymers, silicone resins, fluororesins, benzoguanamine resins, phenol resins, and nylon resins. Among these, for the water-insoluble solid substance, it is preferable to select particles whose specific gravity does not exceed 3 in order to avoid sedimentation in the aqueous dispersion. Moreover, it is preferable that the average particle diameter of particle | grains is 20-80 nm.

(Crosslinking agent)
The coating layer preferably further contains 5 to 20 parts by weight of a crosslinking agent represented by the following formula (I) based on the weight of the coating layer.

  By using such a compound as a crosslinking agent, it is possible to further strengthen the adhesion between the coating layer and a polarizer comprising a polyvinyl alcohol film. However, if the cross-linking agent exceeds the upper limit value, the blocking resistance may deteriorate and the adhesion to the polyester film may decrease.

  For the purpose of ensuring adhesiveness with a polarizer and rollability of a film, a copolymerized polyester, polyvinyl alcohol, a coating layer containing particles and a crosslinking agent, or an acrylic resin having a copolymerized polyester, polyvinyl alcohol, an oxazoline group, Examples such as a coating layer containing particles and a crosslinking agent are exemplified.

(Surface energy of coating layer)
The surface energy of the coating layer surface is preferably 50 to 65 dyne / cm, more preferably 52 to 60 dyne / cm. If the surface energy is less than the lower limit, the adhesion with a hydrophilic polarizer may not be sufficient. On the other hand, if the surface energy exceeds the upper limit value, the adhesion with the polyester film may be insufficient, or the moisture resistance of the coating film may be insufficient.
The surface energy can be obtained by laminating a coating layer composed of the above-described components with a thickness of, for example, 0.01 to 1 μm. The thickness of the coating layer is preferably in the range of 0.01 to 0.3 μm, more preferably 0.02 to 0.25 μm. If the coating layer is too thin, the adhesive force may be insufficient. Conversely, if the coating layer is too thick, blocking may occur or the haze value may increase.

(Surface roughness of coating layer)
The surface center line average roughness (Ra) of the coating layer is preferably in the range of 10 nm to 250 nm because the blocking resistance and transportability of the film are improved.

(Formation method of coating layer)
The composition used for coating the coating layer is used in the form of an aqueous coating solution such as an aqueous solution, aqueous dispersion or emulsion to form a coating layer (hereinafter sometimes referred to as “coating film”). It is preferable. In order to form a coating film, other components other than the composition, such as an antistatic agent, a colorant, a surfactant, and an ultraviolet absorber, can be added as necessary.

  The solid content concentration of the aqueous coating liquid used in the present invention is usually 20% by weight or less, but is preferably 1 to 10% by weight. If this ratio is less than the lower limit, the applicability to the polyester film may be insufficient. On the other hand, if the ratio exceeds the upper limit, the stability of the coating liquid and the appearance of the coating layer may be deteriorated.

Application of the aqueous coating liquid to the polyester film can be carried out at any stage, but it is preferably carried out during the production process of the polyester film, and further applied to the polyester film before the completion of orientational crystallization. preferable.
Here, the polyester film before the crystal orientation is completed is an unstretched film described later, a uniaxially oriented film in which the unstretched film is oriented in either the longitudinal direction or the transverse direction, and further in the longitudinal direction and the transverse direction. And those obtained by orientation at low magnification in two directions (referring to a biaxially stretched film before final reorientation in the machine direction or transverse direction to complete orientation crystallization).
In particular, it is preferable to apply the aqueous coating liquid of the above composition to an unstretched film or a uniaxially stretched film oriented in one direction, and perform longitudinal stretching and / or lateral stretching and heat setting as it is.

  When applying an aqueous coating liquid to a film, as a pretreatment for improving the coating property, the film surface is subjected to physical treatment such as corona surface treatment, flame treatment, plasma treatment, etc., or chemically combined with the composition. It is preferable to use an inert surfactant in combination.

  Such a surfactant promotes the wetting of the aqueous coating liquid onto the polyester film. For example, polyoxyethylene alkylphenyl ether, polyoxyethylene-fatty acid ester, sorbitan fatty acid ester, glycerin fatty acid ester, fatty acid metal soap, Examples include anionic and nonionic surfactants such as alkyl sulfates, alkyl sulfonates, and alkyl sulfosuccinates. The surfactant is preferably contained in an amount of 1 to 10% by weight in the composition forming the coating film.

  As a coating method, any known coating method can be applied. For example, a roll coating method, a gravure coating method, a roll brush method, a spray coating method, an air knife coating method, an impregnation method, a curtain coating method and the like can be used alone or in combination. In addition, a coating film may be formed only in the single side | surface of a film as needed, and may be formed in both surfaces.

(Film thickness)
The film thickness of the uniaxially oriented aromatic polyester film of the present invention is preferably in the range of 10 μm to 250 μm, more preferably 20 μm to 100 μm. When the film thickness is less than the lower limit, a sufficient function as a support substrate may not be exhibited when used as a polarizer support substrate. Moreover, in order to reduce the display thickness of a liquid crystal display, the member used is calculated | required more thinly within the range which expresses a function, and it is preferable that the upper limit of film thickness is this range.

<Film production method>
(Melt extrusion casting)
The uniaxially oriented film of the present invention is obtained by forming an aromatic polyester resin composition by melt extrusion casting and then stretching it in at least one direction. In addition, the formation time and formation method of a coating layer follow the formation method of the above-mentioned coating layer.

  A conventionally known technique can be used for melt extrusion. Specifically, the dried aromatic polyester resin composition pellets are supplied to an extruder, a molten resin is extruded from a slit die such as a T die, and a vent device is set in the extruder supplied with resin pellets. In addition, there is a method of extruding a molten resin from a slit die such as a T die while discharging moisture and various gas components generated during melt extrusion.

  The molten resin extruded from the slit die is cast and cooled and solidified. The cooling and solidification method may be any conventionally known method, but a method of casting a molten resin on a rotating cooling roll and forming a sheet is exemplified.

  The surface temperature of the cooling roll is preferably set in the range of (Tg-100) ° C. to (Tg + 20) ° C. with respect to the glass transition point (Tg) of the resin composition. The surface temperature of the cooling roll is more preferably set in the range of (Tg−70) ° C. to (Tg−5) ° C. with respect to the glass transition point (Tg) of the resin composition. When the surface temperature of the cooling roll exceeds the upper limit, the molten resin may stick to the roll before solidifying. Further, when the surface temperature of the cooling roll is less than the lower limit, solidification is too fast and the roll surface slides, and the flatness of the obtained sheet may be impaired.

  When casting on the chill roll, a metal wire is stretched near the position where the molten resin lands on the chill roll, and an electric field is generated by passing an electric current to charge the resin, and the chill roll is placed on the metal surface. Increasing the adhesion is also effective from the viewpoint of increasing the flatness of the film. In that case, you may add an electrolyte substance in the resin composition in the range which does not exceed the meaning of this invention.

(Stretching)
By stretching the sheet-like material obtained by melt extrusion casting in at least one direction, the optical properties and mechanical properties of the film can be matched with the object of the present invention.
As the stretching method, a conventionally known method can be used. For example, in the case of stretching in the machine direction, a method of stretching using a peripheral speed difference of two or more rolls or a method of stretching in an oven can be mentioned. It is done.

  In the stretching method using a roll, examples of the heating method of the sheet (unstretched film) include a method of induction heating with a roll through a heating medium, and a method of heating from the outside with an infrared heater, etc. Several methods may be taken. In addition, in the method of stretching in an oven, the heating method of the sheet-like material (unstretched film) is a method of widening the clip interval according to the stretch ratio in a tenter type oven that grips both ends of the film with clips, etc., a roll system in the oven And a method of stretching the film by passing the film, and a method of stretching the film only in the oven with only the difference in speed between the inlet side and the outlet side, and may take one or a plurality of methods.

  Moreover, when extending | stretching to a horizontal direction, the method of extending | stretching a difference in the clip conveyance rail space | interval of an entrance side and an exit side in the tenter oven of the system which hold | grips an edge part with a clip etc. is mentioned. Furthermore, when extending | stretching to vertical and horizontal two directions, the method of extending | stretching both the vertical and horizontal directions sequentially is preferable. You may extend | stretch by the method of extending | stretching to the vertical and horizontal direction simultaneously, if it is a range which satisfy | fills the below-mentioned extending | stretching tension.

(Stretching temperature)
The film stretching temperature (Td) in the present invention is preferably a temperature of Tg to (Tg + 40 ° C.). When the stretching temperature of the film is less than Tg (polyester glass transition temperature), stretching itself is difficult. On the other hand, when the stretching temperature exceeds (Tg + 40 ° C.), the stress required for stretching becomes extremely low. As a result, the molecular chains are not sufficiently oriented, and the various characteristics described above may not be ensured. A more preferable range of the stretching temperature is Tg to (Tg + 20 ° C.).

(Stretch ratio)
When performing the stretching, the stretching ratio in the film TD direction and the film MD direction represented by the following formula (4) needs to be more than 3.0 and 7.0 or less.
Film stretch ratio = R ^TD / R ^MD (4)
Such a draw ratio is preferably 3.2 or more and 5.5 or less, more preferably 3.2 or more and 4.5 or less.

  In order to improve the degree of orientation in the TD direction, the slow axis angle α, and the slow axis angle variation β, it is necessary to perform stretching at a stretch ratio in such a range. When the draw ratio is less than the lower limit, these characteristics cannot be made sufficient. On the other hand, when the draw ratio exceeds the upper limit, the strength in the machine direction (MD direction) decreases and breakage occurs.

When performing the stretching, the stretching ratio in the film MD direction (R ^MD ) needs to be in the range of 0.7 to 2.0 times.
Further, the draw ratio (R ^MD ) in the film MD direction is preferably in the range of 0.95 times to 1.75 times, and more preferably in the range of 1.0 times to 1.5 times.

Film forming method for obtaining a monoaxially oriented film of the present invention, in addition to those due to uniaxial stretching or biaxial stretching, the film method made for the longitudinal shrink and also include a vertical direction if R ^MD is less than 1 It means that the film forming method is to shrink.
When ^RMD is less than the lower limit, that is, extreme shrinkage not only impairs the flatness and uniformity of the film, but also in this case, it becomes extremely brittle in the direction of lower draw ratio. When ^RMD exceeds the upper limit, the bowing phenomenon becomes excessive, and the degree of orientation in the TD direction, the slow axis angle α, and the slow axis angle variation β cannot be within the ranges defined in the present invention.
The draw ratio R ^{TD in the} film TD direction is derived from the relationship between the above-described draw ratio and the draw ratio in the film MD direction, but is preferably 3.0 times or more and 6.0 times or less.

(Stretching speed)
The stretching speed in the MD direction is preferably 5 to 500000% / min. On the other hand, in the present invention, the stretching speed in the TD direction is higher than the conventional speed so that the degree of orientation in the TD direction, the slow axis angle α, and the slow axis angle variation β are within the ranges defined in the present invention. It is necessary to carry out at 300% / min or more, more preferably 500% / min or more, further preferably 700% / min or more, and further preferably 1200% / min or more. The upper limit is at most 500000% / min depending on the type of apparatus.

(Stretch tension)
Further, in order to set the degree of orientation in the TD direction, the slow axis angle α, and the slow axis angle variation β to the ranges specified in the present invention, it is necessary to appropriately increase the MD direction tension in the stretching process. . In order to obtain a moderately high tension in the MD direction, it is effective to increase the downstream film transport speed from the upstream film transport speed in the film manufacturing process. Specifically, when biaxial stretching is sequentially performed in the order of the MD direction and the TD direction, the transport speed (transport roll rotation speed) on the most downstream side in the MD direction stretching process is set to the transport speed of the TD direction stretching (film gripping clip). (Movement speed) of 0.995 to 0.998. When uniaxial stretching is performed in the TD direction, the transport speed before stretching in the TD direction is set to 0.995 to 0.998, which is the transport speed (film gripping clip moving speed) of the TD direction stretching.
Moreover, let the conveyance speed (conveyance roll rotational speed) of the film take-up after completion | finish of TD direction extension be 1.003 to 1.010 of the conveyance speed of TD direction extending | stretching.

(Heat setting temperature)
The film obtained by this stretching method is further subjected to heat setting treatment in the range of not less than the glass transition point of the polyester and not more than (melting point−15 ° C.). The heat setting temperature is preferably in the range of 180 ° C. or higher and 240 ° C. or lower.
By performing such heat setting treatment, it is possible to obtain the degree of orientation in the TD direction, the slow axis angle α, the slow axis angle variation β, the crystal size, and the heat shrinkage characteristics of the present invention.

(Post-processing of film)
The stretched film may be subjected to post-processing such as surface activation treatment (coating, corona discharge, plasma treatment, etc.) as necessary for improving the adhesiveness during pasting with other members. This post-processing may be performed during the film stretching process or may be performed in a separate process.

<Polarizer support substrate>
The uniaxially oriented polyester film of the present invention has a high degree of orientation in the film TD direction and is useful as a polarizer support base material because the slow axis angle α and the slow axis angle variation β are small at both ends of the film. It is.

<Polarizing plate>
A polarizing plate can be produced by using the film for a polarizer support substrate of the present invention as a support substrate for a polarizer and making it composite with a polarizer. By using the film of the present invention as a support substrate for a polarizer, it is possible to prevent color shifts and color spots of a liquid crystal display while improving adhesion with the polarizer and enhancing the durability of the polarizer.

The method of compounding with the polarizer is not particularly limited, and examples thereof include bonding with a film-like polarizer in which dichroic molecules are uniaxially oriented in a matrix. The dichroic molecule is not particularly limited, but polyiodine ions are generally used. In many cases, a polyvinyl alcohol film is used as the film-like polarizer material.
About the method of compounding with a polarizer, you may use the apply | coating method other than the method of laminating | stacking with a polarizer film. Examples of the application type include a method in which liquid crystal molecules are aligned by coating shear force, and the applied reactive liquid crystal molecules are aligned and solidified by irradiation with polarized light.

More specifically, the polarizing plate is a composite of the polarizer and the uniaxially oriented aromatic polyester film of the present invention so that the transmission axis direction of the polarizer and the film TD direction of the film of the present invention are parallel to each other. In this case, the influence on the linearly polarized light by the film, that is, the change in the polarization state can be reduced.
In addition, the obtained polarizing plate can ensure the stability of the optical axis that can prevent color shift and color spot of the liquid crystal display, and there is little variation in the screen of the display image quality when incorporated in the display. Higher performance display image quality is manifested.

Moreover, in the bonding with the polarizer, the film of the present invention may be used for only one of the supporting substrates to be bonded to both sides of the polarizer, or may be used for both.
When combining the polarizer and the film of the present invention, it is preferable to directly laminate the polarizer and the film of the present invention via an easy-adhesion layer. However, the polarizer and the adhesive layer are laminated, and the adhesive layer is further laminated. And the easy-adhesion layer of the present invention may be bonded together.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited only to these Examples. Each characteristic value was measured by the following method. Moreover, unless otherwise indicated, the part and% in an Example mean a weight part and weight%, respectively.

(1) Composition and content of coating layer
^The composition and the amount of each component were specified by ¹ H-NMR measurement.

(2) Glass transition point (glass transition temperature)
A sample of 20 mg of the copolyester sample was sampled, and an aluminum pan filled was set in a DSC apparatus (DuPont Instrument 910 DSC), and the temperature was raised from room temperature at a rate of 20 ° C./min. The change in heat was recorded using an empty aluminum pan as a control, and the glass transition temperature (° C.) was read. When it was unclear, the peak of the second derivative curve of the DSC calorie change curve was taken as the glass transition temperature.

(3) Degree of crystal orientation Method of crystal plane (−105) of film by wide-angle X-ray diffraction pole measurement using X-ray diffractometer (ROTAFLEX RINT2500HL manufactured by Rigaku Corporation) and pole sample table (multipurpose sample table manufactured by Rigaku Corporation) The integral average value of the direction cosine in the TD direction of the line vector, <cos ² Φ _TD , −105>, was obtained, and the degree of crystal orientation fc _TD (−105) was obtained from the following equation (5).
fc _TD (−105) = 2/3 <cos ² Φ _TD , −105> −1/2 (5)

(4) Slow axis angle α
A 60 mm square sample parallel to MD and TD was cut out with an accuracy of 0.5 ° from the end of the obtained film. The sample is attached to a sample stage for birefringence measurement of an ellipsometer (manufactured by JASCO Corporation, device name: M-220) with an accuracy of 0.5 °, and then the maximum phase difference with respect to 550 nm incident light by automatic measurement. The rotational movement angle of the sample stage showing the above was measured, and the slow axis angle (°) was obtained. The TD direction was set to 0 °, and a positive value was taken counterclockwise.
Sampling at a total of 10 points at 5 points every 100 mm in the film forming direction at both ends was performed, and the average of the absolute values of these measured values was evaluated.

(5) Slow axis angle variation β
The standard deviation of 10 measurement results obtained according to the method of (4) was determined, and this value was multiplied by 3 to obtain β.

(6) In-plane retardation 5 points in the width direction of the two endmost parts, the center part, and their intermediate positions of the obtained film, and 5 points in the width direction, 5 points every 100 mm in the film forming direction. A total of 25 samples were cut out one by one, and the average value of all samples was obtained based on the maximum phase difference for each sample measured by the same measurement method as in (4), and the in-plane retardation of the film (nm) It was.
In addition, the difference between the maximum value and the minimum value of the maximum phase difference for each sample in the above n = 25 measurement was defined as the in-plane phase difference variation.

(7) Crystal size Using a powder X-ray diffractometer (Rigaku Corporation RINT2500HL), the crystal size was measured under the following conditions. Using CuK-α as the X-ray source, diverging slit 1/2 °, scattering slit 1/2 °, light receiving slit 0.15 mm, scanning speed 1.000 ° / min, 2θ angle 10 ° to 80 ° Measurement is performed, and a diffraction peak derived from a crystal plane, a halo derived from amorphous, and a background are separated by a multiple peak separation method using a Pseudo Voice peak model. The crystal size χc _P (100) (nm) was calculated from the half width of the diffraction peak corresponding to the crystal (100) plane among the diffraction peaks derived from the crystal plane, using Scherrer's formula (6) below.
χc _P (100) = (0.9λ) / (H cos θ) (6)
Here, λ is the X-ray wavelength (nm), H is the half width (°) of the diffraction peak, and θ is the Bragg angle (°).

(8) Haze value of film The obtained film was set in a haze meter (manufactured by Nippon Seimitsu Optical Co., Ltd., POIC haze meter SEP-HS-D1), and the haze value (%) was measured according to JISK7105. did.

(9) Thermal shrinkage ratio of film In an oven set at a temperature of 120 ° C, the film was marked in the longitudinal and transverse directions, and a 30cm square film with an accurate length measured in advance was placed under no load. After holding for 30 minutes, the sample is taken out, returned to room temperature, and the change in dimensions is read. From the length (L ₀ ) before the heat treatment and the dimensional change (ΔL) due to the heat treatment, the thermal shrinkage rates (%) in the MD direction and the TD direction were obtained from the following formula (7).
Thermal contraction rate = (ΔL / L ₀ ) × 100 (7)

(10) Surface energy A. Zisman: “Contact Augle, Wetability and Adhesion”, Am. Chem. Soc. , (1964), the surface energy was defined as the critical surface tension γc determined by measuring the obtained film.

(11) Friction coefficient (μs)
According to JIS-K7125, the static friction coefficient (μs) of the coating layer surface was measured. The measurement was performed 5 times, and the average value was used as the result.

(12) Adhesive evaluation (i) PVA film A commercially available polyvinyl alcohol film is bonded to the coating surface of the obtained film, and a cross cut (100 squares of 1 mm ² ) is performed thereon. A 24 mm wide “cellophane tape” (trade name, manufactured by Nichiban Co., Ltd.) was affixed and peeled off rapidly at a peeling angle of 180 °, and then the peeled surface was observed and evaluated according to the following criteria.
5: Peeling area is less than 10% …… Adhesion is very good 4: Peeling area is 10% or more and less than 20% …… Adhesion is good 3: Peeling area is 20% or more and less than 30% …… Adhesion is slightly good 2: Peeling Area is 30% or more and less than 40% …… Adhesive strength is poor 1: Peeling area is over 40% …… Adhesive strength is extremely poor

(13) Blocking resistance Two films were overlapped so that the coating-formed surface and the non-formed surface were in contact with each other, and this was 0.6 kg / cm ² over 17 hours in an atmosphere of 60 ° C. and 80% RH. A pressure was applied and then the film was peeled off, and the blocking resistance was evaluated according to the following criteria based on the peeling force.
◯: 98 mN / 5 cm ≦ peeling force <147 mN / 5 cm: good blocking resistance Δ: 147 mN / 5 cm ≦ peeling force <196 mN / 5 cm ·· Blocking resistance somewhat good ×: 196 mN / 5 cm ≦ peeling force Poor blocking

(14) Image quality evaluation
(Preparation of polarizing plate)
Films (A) obtained in Examples and Comparative Examples, a polyvinyl alcohol polarizing film and a commercially available TAC film (Fuji Photo Film, Fujitac, thickness 80 μm) (R) are laminated in this order to produce a polarizing plate, Its durability was evaluated.
The polyvinyl alcohol polarizing film was obtained by immersing a 120 μm-thick polyvinyl alcohol film in an aqueous solution containing 1 part of iodine, 2 parts of potassium iodide, and 4 parts of boric acid and stretching the film at 50 ° C. four times.
Moreover, the procedure for laminating the above-mentioned two kinds of films on the polarizing film to obtain a polarizing plate is as follows.
(I) Corona discharge treatment (treatment power = 800 W (200 V, 4 A), electrode to film) on the surface of each side of the above-described film (A) and film (R) cut into a rectangular shape of 40 cm × 30 cm (Distance distance = 1 mm, processing speed = 12 m / min). Here, the film (A) was cut out so as to include at least one end of both ends of the film.
(Ii) The polarizing film (polarizer) adjusted to the same size as the film (A) and the film (R) is immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.
(Iii) On the corona-treated surface of the film (A) so that excess adhesive adhering to the polarizing film (polarizer) is lightly removed, and the polarizer is placed between the film (A) and the film (R). Then, the film (R) is further laminated and disposed so that the corona-treated surface of the film (R) is in contact with the adhesive. In that case, it arrange | positions so that the MD direction of a film (A) and the extending | stretching direction of a polarizer may orthogonally cross, ie, the TD direction of a film (A) and the extending | stretching direction of a polarizer may become parallel.
(Iv) Excess adhesive and bubbles are removed and bonded from the end of the laminate composed of the film (A), the polarizing film, and the film (R) with a hand roller. The hand roller was subjected to a pressure of 20 to 30 N / cm ² and the roller speed was about 2 m / min.
(V) The sample obtained in an oven at 80 ° C. was left for 2 minutes to produce a polarizing plate (PF).

Next, the polarizing plate (PF) is attached to one side of the liquid crystal cell so that the rubbing axis direction of the substrate surface adjacent to the liquid crystal cell and the polarizing plate transmission axis are orthogonal to each other and the polarizing plate film (PF) and the liquid crystal cell are in contact with each other. In addition, a commercially available polarizing plate was bonded to the opposite surface of the liquid crystal cell so that the absorption axis thereof was perpendicular to the absorption axis of the polarizing plate (PF), thereby producing a liquid crystal display device. The liquid crystal cell used was a commercially available LCD monitor with the polarizing plate bonded to the backlight side removed.
The obtained liquid crystal display device and the LCD monitor of the same model in which the polarizing plate on the backlight side is not exchanged, and the three primary colors of R, G, B and white (W) are simultaneously displayed on the entire monitor surface, The color difference ΔE obtained by visual observation and EZ-contrast manufactured by ELDIM was used for evaluation according to the following criteria.
○: Comparative monitor contrast, ΔE <0.5 in any of R, G, B, and W, and almost no color spots are confirmed ×: Comparative monitor contrast, 0.5 in any of R, G, B, W ≦ ΔE ≦ 1.0 or slight color spots are observed XX: Comparative monitor contrast, 0.5 ≦ ΔE ≦ 1.0 and / or remarkable in any of R, G, B, W Color spots are observed

(15) Long-term durability The sample film was evaluated in accordance with the following from the change in the degree of polarization before and after the sample film treatment when the sample film was left in an environment of 95% humidity and a temperature of 65 ° C. for 1000 hours and left flat.
○: Polarization degree after treatment is 95% or more before treatment ×: Polarization degree after treatment is less than 95% before treatment

[Example 1]
Pellets of 99.93% by weight of polyethylene terephthalate (PET) mixed with 0.07% by weight of silica particles having an average particle size of 0.15 μm (manufactured by Teijin Fibers Limited, intrinsic viscosity (o-chlorophenol, 25 ° C.)) 0.6 dl / g) was dried at 170 ° C. for 3 hours, then supplied to a single-screw kneading extruder, melted at a melting temperature of 285 ° C., filtered through a filter, and extruded from a die.
This melt was extruded onto a rotary cooling drum having a surface temperature of 25 ° C. to obtain an unstretched film having a thickness of 320 μm.
An aqueous coating solution having a concentration of 8% shown in Table 3 was uniformly applied to both surfaces of the obtained unstretched film with a roll coater. The composition for the coating layer constituting the coating agent is as shown in Table 1. In Table 1, the specific composition of the copolyester is as shown in Table 2.

  The unstretched film after coating is supplied to the tenter so that the rotation speed of the transport roll immediately before the tenter is 0.996 of the film gripping clip moving speed of the tenter, and stretched at 750% / min in the lateral direction at 85 ° C. The film was stretched 4.0 times at a speed and subsequently subjected to heat treatment at 200 ° C. for 1 minute while maintaining a constant width in the tenter. The film coming out of the tenter is taken up by a transport roll having a speed of 1.008 times the moving speed of the film gripping clip, and further slitted at a position 5% from both ends of the film to remove the tenter clip gripping portion. A stretched film having a thickness of 80 μm was obtained. The properties of the obtained film are shown in Table 3.

[Examples 2 to 12, Comparative Examples 1 to 10]
A stretched film was obtained according to Example 1 except that the composition and production conditions shown in Tables 3 and 4 were changed.

PEs 1 to 8: Copolyester PVA having a copolymer composition shown in Table 2 Polyvinyl alcohol PVA2 having a saponification degree of 86 to 89 mol%: Polyvinyl alcohol PVA3 having a saponification degree of 74 to 78 mol%: Polyvinyl having a saponification degree of 92 to 95 mol% Alcohol Ac1: An acrylic resin (Tg = 50 ° C.) composed of 30% by mole of methyl methacrylate / 2% by mole of 2-isopropenyl-2-oxazoline / 10% by mole of polyethylene oxide (n = 10) methacrylate / 30% by mole of acrylamide.
Ptcl1: Cross-linked acrylic particles having an average particle size of 40 nm

CL1: A compound represented by the following formula (II) was used as a crosslinking agent.

CL2: A compound represented by the following formula (III) was used as a crosslinking agent.

SAA: Polyoxyethylene (n = 7) lauryl ether (trade name NAROACTY N-70, manufactured by Sanyo Chemical Co., Ltd.) was used as a surfactant.

TA: terephthalic acid IA: 2,6-NDCA isophthalic acid: 2,6-naphthalenedicarboxylic acid IA-5-SO3Na: 5-sodium sulfoisophthalic acid IA-5-SO3K: 5-potassium sulfoisophthalic acid EG: ethylene glycol DEG: Diethylene glycol BD: 1,4-butanediol NPG: Neopentyl glycol

  The angle between the film in-plane slow axis and the film TD direction and the variation thereof at the both ends of the film are also small, ensuring high optical axis stability that can prevent color shift and color spot of the liquid crystal display. In addition, it is possible to provide a film for a polarizer-supporting base material that is further excellent in adhesiveness with a polarizer and can make the polarizer long-term durability. A polarizing plate using such a film can provide a liquid crystal display product excellent in display image quality free from color shifts and color spots at a low cost, and can cope with an increase in size.

Claims (7)

A method for producing a uniaxially oriented aromatic polyester film in which an aromatic polyester resin composition is melt extrusion casted, stretched in the MD direction and the TD direction, and heat-set.
In the above-described stretching, the stretching ratio in the MD direction (R ^MD ) is in the range of 0.7 times to 2.0 times, and the stretching ratio in the TD direction and the MD direction (R ^TD / R ^MD ) is 3.0. In the range of more than 7.0 and the stretching speed in the TD direction is 300% / min or more,
The transport speed before stretching in the TD direction is 0.995 to 0.998 of the transport speed of TD direction stretching, and the transport speed of the film take-up after the end of TD direction stretching is 1.003 of the transport speed of TD direction stretching. ~ 1.010,
In the heat setting treatment, the heat setting temperature is in the range of not less than the glass transition point of the aromatic polyester constituting the aromatic polyester resin composition and not more than (melting point −15 ° C.),
The resulting uniaxially oriented aromatic polyester film has 75% by mole or more of ethylene terephthalate monomer units of the aromatic polyester, and the degree of orientation of the PET crystal (−105) plane in the film TD direction obtained by wide-angle X-ray diffraction measurement The relationship between the angle α formed between the film in-plane slow axis and the film TD direction and the angle variation β formed between the film in-plane slow axis and the film TD direction satisfy the following expressions (1) and (2). ,
fc _TD (−105) ≧ 0.35 (1)
(In formula (1), fc _TD (−105) represents the degree of orientation of the PET crystal (−105) plane in the film TD direction obtained by wide-angle X-ray diffraction measurement)
0 ≦ α + β ≦ 15 ° (2)
(In the formula (2), α represents an angle formed by the in-plane slow axis of the film and the film TD direction, and an average of 10 points measured at 100 points every 100 mm in the MD direction for both ends of the film using an ellipsometer. Β represents the variation in the angle between the in-plane slow axis of the film and the film TD direction, and 10 points measured at 5 points every 100 mm in the MD direction at both ends of the film using an ellipsometer. (Represented by 3 times the standard deviation)
Copolymer polyester having a glass transition point of 20 to 90 ° C. on at least one surface of the film is 40% by weight to 80% by weight based on the weight of the binder component and polyvinyl alcohol having a saponification degree of 80% by mole to 90% by mole as a binder component. coating layer comprising 20 wt% to 60 wt% or less based on the weight is provided, the manufacturing method of the polarizer support base material for the uniaxial oriented aromatic polyester film. The obtained uniaxially oriented aromatic polyester film further comprises an acrylic resin having an oxazoline group and a polyalkylene oxide chain in the coating layer in an amount of 10 wt% to 20 wt% based on the weight of the binder component. The manufacturing method of the uniaxially-oriented aromatic polyester film for polarizer support base materials of description. Uniaxially oriented aromatic polyester film obtained is the in-plane retardation of the polyester film is 1000nm or more, and the polarizer support base material for the uniaxial oriented aromatic according to claim 1 or 2, the variation is 100nm or less A method for producing a polyester film. The obtained uniaxially oriented aromatic polyester film satisfies the following formula (3) in the crystal size of the PET crystal (100) plane of the polyester film,
3.0 nm ≦ χc _P (100) ≦ 4.5 nm (3)
(In formula (3), χc _P (100) represents the crystal size [nm] of the PET crystal (100) plane of the film obtained by wide-angle X-ray diffraction measurement)
And the haze value of a film is 7% or less, The manufacturing method of the uniaxially-oriented aromatic polyester film for polarizer support base materials in any one of Claims 1-3. In the obtained uniaxially oriented aromatic polyester film, the copolymer polyester in the coating layer is a copolymer polyester containing 1 to 16 mol% of a dicarboxylic acid component having a sulfonate group per total carboxylic acid component. The manufacturing method of the uniaxially oriented aromatic polyester film for polarizer support base materials in any one of. In the obtained uniaxially oriented aromatic polyester film, the surface energy of the coating layer surface is 50 to 65 dyne / cm. The method for producing a uniaxially oriented aromatic polyester film for a polarizer supporting substrate according to any one of claims 1 to 5. . The film shrinkage ratio after 30 minutes of unconstrained heat treatment at 120 ° C of the obtained uniaxially oriented aromatic polyester film is 5% or less in both the film MD direction and the film TD direction. The manufacturing method of the uniaxially-oriented aromatic polyester film for polarizer support base materials of description.