JP2015072376A - Retardation film and production method of the same, and circularly polarizing plate including the retardation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long retardation film having a slow axis in an oblique direction with excellent accuracy of the axis and having an extremely large value of birefringence.SOLUTION: The retardation film is a long film, comprising a polyester resin selected from polyethylene terephthalate, modified polyethylene terephthalate, and their blends. The modified polyethylene terephthalate contains any of a repeating unit derived from cyclohexane dimethanol, a repeating unit derived from diethylene glycol, and a repeating unit derived from isophthalic acid. The retardation film shows directions of the slow axis in a range from 30° to 60° with respect to the longitudinal direction over the entire region in a width direction of the film, and a birefringence Δnof 0.085 or more.

Description

  The present invention relates to a retardation film, a method for producing the same, and a circularly polarizing plate including the retardation film.

  In so-called mobile devices such as mobile phones and tablet terminals, liquid crystal display devices and organic electroluminescence (EL) panels are used as image display devices. Due to the image forming method of liquid crystal display devices and organic EL panels, polarizing plates are arranged in mobile devices. Such mobile devices often view the display screen outdoors because of their product characteristics. However, when trying to watch a mobile device wearing polarized sunglasses, light may be absorbed by the sunglasses of the polarizing plate depending on the angle due to the influence of the polarizing plate, and the image may not be visible.

  In order to solve such a problem, a technique for arranging a retardation film having a very large in-plane retardation on the outermost surface of an image display device has been proposed. According to this technique, even if a change in phase difference occurs depending on the viewing angle, the phase difference of the entire retardation film is very large, so that the effect on visibility can be reduced. As such a retardation film having a very large in-plane retardation, a stretched film of polyethylene terephthalate (PET) is used. Such a retardation film needs to be arranged so as to form an angle of 45 ° with respect to the absorption axis of the polarizing plate. However, in a retardation film, it is extremely difficult to precisely control the axial accuracy and develop the slow axis in an oblique direction. As a result, in many cases, such a retardation film is punched in an oblique direction from a roll-shaped film having a slow axis in the longitudinal direction and bonded to a polarizing plate. In such a case, there exists a problem that the manufacturing efficiency of bonding of a polarizing plate and retardation film is low. Alternatively, when a retardation film is produced by transverse stretching, only the portion (lateral end portion) having a slow axis in the oblique direction of the film may be used by utilizing bowing that occurs during transverse stretching. In this case, since only the end portion of the film can be used, it is industrially unacceptable and impractical.

  As described above, there is a strong demand for a long retardation film having a slow axis in an oblique direction with excellent axial accuracy and a very large in-plane retardation.

Japanese Patent No. 3105374

  The present invention has been made in order to solve the above-described conventional problems. The object of the present invention is to have a slow axis in an oblique direction with excellent axial accuracy and a very large birefringence (as a result). An object of the present invention is to provide a long retardation film having an in-plane retardation. Another object of the present invention is to provide a method capable of producing such a retardation film with high production efficiency. Still another object of the present invention is to provide a long circularly polarizing plate including such a retardation film.

The retardation film of the present invention is long. This retardation film is composed of a polyester resin selected from polyethylene terephthalate, modified polyethylene terephthalate, and blends thereof. The modified polyethylene terephthalate is a repeating unit derived from cyclohexanedimethanol, a repeating unit derived from diethylene glycol, And any repeating unit derived from isophthalic acid. In this retardation film, the direction of the slow axis is in the range of 30 ° to 60 ° with respect to the longitudinal direction over the entire width direction, and the birefringence Δn _xy is 0.085 or more.
In one embodiment, the retardation film has a dimensional shrinkage ratio of 2.0% or less after being heated at 80 ° C. for 240 hours.
In one embodiment, the retardation film has a crystallinity measured by X-ray diffraction (XR) of 25% or more.
In one embodiment, the retardation film has an in-plane retardation Re (590) of 3000 nm or more.
According to another situation of this invention, the manufacturing method of said retardation film is provided. In this method, the left and right end portions of the film are respectively held by variable pitch type left and right clips whose longitudinal clip pitches change; the film is preheated; the clip pitches of the left and right clips are independent of each other And then obliquely stretching the film; after the oblique stretching, the film is crystallized by heat treatment with the clip pitch of the left and right clips kept constant; and Releasing the gripping clip.
In one embodiment, the said heat processing is performed at the temperature of 100 to 280 degreeC.
In one embodiment, the oblique stretching includes (i) increasing the clip pitch of one of the left and right clips and decreasing the clip pitch of the other clip; and (ii) Increasing the reduced clip pitch to the same pitch as the enlarged clip pitch, and setting the clip pitch of each clip to a predetermined pitch.
According to another situation of this invention, a elongate circularly-polarizing plate is provided. This circularly polarizing plate includes the above-described long retardation film and a long polarizer disposed on one side of the retardation film.

  According to the present invention, a long shape having a slow axis in an oblique direction with excellent axial accuracy and having a very large birefringence (resulting in in-plane retardation), which has been difficult to produce in the past. A retardation film can actually be obtained. Such a retardation film can be obtained by appropriately combining the type of polyester resin and the oblique stretching treatment.

It is a schematic plan view explaining the whole structure of an example of the extending | stretching apparatus which can be used for manufacture of the retardation film of this invention. It is a principal part schematic plan view for demonstrating the link mechanism which changes a clip pitch in the extending | stretching apparatus of FIG. 1, and shows the state where a clip pitch is the minimum. It is a principal part schematic plan view for demonstrating the link mechanism which changes a clip pitch in the extending | stretching apparatus of FIG. 1, and shows a state with the largest clip pitch. It is a schematic diagram explaining one embodiment of the diagonal stretch in manufacture of the phase difference film of this invention. It is a graph which shows the relationship between each zone of the extending | stretching apparatus in the case of the diagonal extending | stretching shown in FIG. 4, and a clip pitch. It is the schematic explaining the bonding method of the retardation film and polarizing plate of this invention.

  Hereinafter, although preferable embodiment of this invention is described, this invention is not limited to these embodiment.

(I) Retardation film The retardation film by embodiment of this invention is elongate. In the present specification, the “long shape” refers to an elongated shape having a ratio of length to width of 10 or more. The ratio of the length to the width of the retardation film is preferably 30 or more, more preferably 100 or more. In one embodiment, the retardation film is wound in a roll shape.

  The retardation film has a slow axis direction in the range of 30 ° to 60 °, preferably in the range of 38 ° to 52 °, more preferably in the range of 43 ° to 47 ° with respect to the longitudinal direction over the entire width direction of the film. More preferably, the slow axis direction forms an angle of about 45 ° with respect to the longitudinal direction. According to the present invention, in the long retardation film, the direction of the slow axis can be precisely controlled in a predetermined direction with respect to the long direction. As a result, it is not necessary to cut each sheet in an oblique direction in bonding with the polarizing plate, and bonding can be performed by so-called roll-to-roll, so that manufacturing efficiency can be significantly improved. In addition, since the direction of the slow axis is precisely controlled, it is possible to finally realize an image display device (for example, a mobile device) having excellent visibility even through polarized sunglasses. Thus, it is one of the achievements of the present invention to actually produce a long retardation film having a slow axis in an oblique direction with very excellent axial accuracy.

  The in-plane retardation Re (590) of the retardation film is 3000 nm or more, preferably 4000 nm or more, more preferably 5000 nm or more. The upper limit of the in-plane retardation Re (590) is, for example, 15000 nm. According to the present invention, a retardation film having such a large in-plane retardation can be obtained without breaking the film. By arranging the retardation film having such an in-plane retardation on the outermost surface of the image display device, even if the phase difference changes depending on the viewing angle, the retardation of the entire retardation film is very large. The influence on visibility can be reduced. As a result, an image display device (for example, a mobile device) having excellent visibility even through polarized sunglasses can be realized by the synergistic effect with the above excellent axial accuracy. The in-plane retardation Re (λ) is an in-plane retardation of the film measured with light having a wavelength of λ nm at 23 ° C. Thus, for example, Re (590) is the in-plane retardation of the film measured with light having a wavelength of 590 nm. Re (λ) is determined by the formula: Re (λ) = (nx−ny) × d, where d (nm) is the thickness of the film. Here, nx is the refractive index in the direction in which the in-plane refractive index is maximum (that is, the slow axis direction), and ny is the refractive index in the direction perpendicular to the slow axis in the plane.

The birefringence Δn _xy of the retardation film is 0.085 or more, preferably 0.09 or more, more preferably 0.10 or more. The upper limit of the birefringence Δn _xy is, for example, 0.15. According to the present invention, a retardation film having such a large birefringence can be obtained without breaking the film. As a result, the retardation film having a very large in-plane retardation as described above. Can be obtained. The birefringence Δn _xy is obtained by the formula: Δn _xy = nx−ny.

  The retardation film preferably has a dimensional shrinkage after heating for 240 hours at 80 ° C. of 2.0% or less, and more preferably 1.0% or less. According to the present invention, it is possible to realize a retardation film having such a small dimensional change and excellent axial accuracy as described above.

  The retardation film preferably has a crystallinity measured by X-ray diffraction (XRD) of 25% or more, more preferably 30% or more. The upper limit of the crystallinity is, for example, 70%. When the crystallinity is in such a range, there is an advantage that the film does not shrink when the stretched film is heated, and optical properties such as retardation and orientation angle are hardly changed.

  The thickness of the retardation film can vary depending on the purpose and desired in-plane retardation. The thickness of the retardation film is typically 10 μm to 200 μm, preferably 20 μm to 130 μm.

  The retardation film is made of a polyester resin. By using a polyester resin, a retardation film having a very large in-plane retardation can be obtained. Furthermore, a retardation film having a slow axis in an oblique direction can be obtained with excellent axial accuracy by applying a production method including oblique stretching described later. Any appropriate polyester resin can be adopted as the polyester resin as long as such an effect is obtained. The polyester resin can be obtained by condensation polymerization of a carboxylic acid component and a polyol component.

  Examples of the carboxylic acid component include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, benzylmalonic acid, 1,4-naphthalic acid, diphenic acid, 4,4′-oxybenzoic acid, and 2,5-naphthalenedicarboxylic acid. Examples of the aliphatic dicarboxylic acid include malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, trimethyladipic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid, zebacic acid, fumaric acid, Maleic acid, itaconic acid, thiodipropionic acid, diglycolic acid are mentioned. Examples of the alicyclic dicarboxylic acid include 1,3-cyclopentane dicarboxylic acid, 1,2-cyclohexane dicarboxylic acid, 1,3-cyclopentane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, and 2,5-norbornane dicarboxylic acid. Examples include acids and adamantane dicarboxylic acids. The carboxylic acid component may be a derivative such as ester, chloride, or acid anhydride. For example, dimethyl 1,4-cyclohexanedicarboxylate, dimethyl 2,6-naphthalenedicarboxylate, dimethyl isophthalate, dimethyl terephthalate And diphenyl terephthalate. A carboxylic acid component may be used independently and may use 2 or more types together.

  A typical example of the polyol component is a dihydric alcohol. Examples of the dihydric alcohol include aliphatic diols, alicyclic diols, and aromatic diols. Examples of the aliphatic diol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2, 2-dimethyl-1,3-propanediol (neopentyl glycol), 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3- Examples include butadiol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethyl-1,6-hexanediol. It is done. Examples of the alicyclic diol include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecane dimethanol, adamantanediol, 2,2,4 , 4-tetramethyl-1,3-cyclobutanediol. Examples of the aromatic diol include 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4 '-(2-norbornylidene) diphenol, 4,4'-dihydroxybiphenol, o-, m- and p-dihydroxybenzene, 4,4'-isopropylidenephenol, 4,4'-isopropylidenebis (2,6-cyclophenol) 2,5-naphthalenediol and p-xylenediol. A polyol component may be used independently and may use 2 or more types together.

  Preferred carboxylic acid components include terephthalic acid, isophthalic acid, and 2,5-naphthalenedicarboxylic acid. Preferred polyol components include ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol. Accordingly, preferred polyester resins include, for example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polycyclohexylene terephthalate, and copolymers, blends and modified products thereof. It is done. By using such a polyester-based resin and applying a production method including oblique stretching described later, a retardation film having a more preferable in-plane retardation and having a better axial accuracy is obtained. Can do. In one embodiment, the polyester-based resin can be a modified PET containing repeating units derived from cyclohexanedimethanol. In this case, the ratio of cyclohexanedimethanol in the polyol component is preferably more than 0 mol% and 10 mol% or less, more preferably more than 0 mol% and 3 mol% or less. In another embodiment, the polyester-based resin can be a modified PET containing repeating units derived from isophthalic acid. In this case, the proportion of isophthalic acid in the carboxylic acid component is preferably more than 0 mol% and 20 mol% or less, more preferably more than 0 mol% and 10 mol% or less. Needless to say, these embodiments may be combined.

  The glass transition temperature of the polyester resin is preferably 65 ° C to 80 ° C, more preferably 70 ° C to 75 ° C. If the glass transition temperature is too low, the desired dimensional shrinkage rate may not be obtained. If the glass transition temperature is excessively high, the molding stability at the time of film molding may deteriorate, and the transparency of the film may be impaired. The glass transition temperature is determined according to JIS K 7121 (1987).

  The weight average molecular weight of the polyester resin is preferably 10,000 to 100,000, more preferably 15,000 to 50,000. If it is such a weight average molecular weight, the handling at the time of shaping | molding is easy, and the film which has the outstanding mechanical strength can be obtained.

  The polyester resin can be formed into a film by any appropriate method. The retardation film of the present invention can be obtained by subjecting the obtained polyester resin film to a production method including oblique stretching described later.

(II) Retardation Film Manufacturing Method A retardation film manufacturing method according to an embodiment of the present invention is a variable-pitch left and right clip in which the vertical clip pitch changes at the left and right ends of the film to be stretched. (Step A: gripping step); preheating the film (step B: preheating step); changing the clip pitch of the left and right clips independently and stretching the film diagonally ( Step C: Stretching step); If necessary, the film is heat-treated and crystallized in a state where the clip pitch of the left and right clips is constant (Step D: Crystallization step); and Releasing the gripping clip (step E: release step); Hereinafter, each process is demonstrated in detail about an example which produces the said phase difference film from the said polyester-type resin film.

A. First, a stretching apparatus that can be used in the manufacturing method of the present invention including this process will be described with reference to FIGS. FIG. 1 is a schematic plan view illustrating the overall configuration of an example of a stretching apparatus that can be used in the production method of the present invention. 2 and 3 are schematic plan views of main parts for explaining a link mechanism for changing the clip pitch in the stretching apparatus of FIG. 1, respectively, FIG. 2 shows a state in which the clip pitch is minimum, and FIG. Indicates the maximum clip pitch. The stretching device 100 has an endless loop 10L and an endless loop 10R having a large number of clips 20 for gripping the film on both the left and right sides in a plan view. In this specification, the left endless loop as viewed from the film entrance side is referred to as the left endless loop 10L, and the right endless loop is referred to as the right endless loop 10R. The clips 20 of the left and right endless loops 10L and 10R are guided by the reference rail 70 and move in a loop. The left endless loop 10R moves in a counterclockwise direction, and the right endless loop 10R moves in a clockwise direction. In the stretching apparatus, a gripping zone A, a preheating zone B, a stretching zone C, a crystallization zone D, and a release zone E are sequentially provided from the inlet side to the outlet side of the sheet. Each of these zones means a zone where a film to be stretched is substantially gripped, preheated, obliquely stretched, crystallized and released, and does not mean a mechanically and structurally independent section. Absent. It should also be noted that the length ratio of each zone is different from the actual length ratio.

  In the gripping zone A and the preheating zone B, the left and right endless loops 10R and 10L are configured to be substantially parallel to each other at a separation distance corresponding to the initial width of the polyester resin film. In the stretching zone C, the distance between the left and right endless loops 10R, 10L gradually increases from the preheating zone B side toward the crystallization zone D until it corresponds to the width after stretching of the film. In the illustrated example, in the crystallization zone D, the left and right endless loops 10R and 10L are configured to be substantially parallel to each other at a separation distance corresponding to the width after stretching of the film. In the crystallization zone D, the left and right endless loops 10R, 10L may be configured to gradually expand or contract from the width after stretching of the film (not shown).

  The clip 20L on the left endless loop 10L (left clip) and the clip 20R on the right endless loop 10R (right clip) can each move independently. For example, the driving sprockets 11 and 12 of the left endless loop 10L are rotationally driven counterclockwise by the electric motors 13 and 14, and the driving sprockets 11 and 12 of the right endless loop 10R are clocked by the electric motors 13 and 14. It is driven to rotate around. As a result, traveling force is applied to the clip carrying member 30 of the drive roller (not shown) engaged with the drive sprockets 11 and 12. As a result, the left endless loop 10L cyclically moves in the counterclockwise direction, and the right endless loop 10R cyclically moves in the clockwise direction. By driving the left electric motor and the right electric motor independently of each other, the left endless loop 10L and the right endless loop 10R can be cyclically moved independently.

  Further, the clip (left clip) 20 of the left endless loop 10L and the clip (right clip) 20 of the right endless loop 10R are each of a variable pitch type. That is, the left and right clips 20 and 20 can independently change the clip pitch (distance between clips) in the vertical direction (MD) with movement. The variable pitch type can be realized by any appropriate configuration. Hereinafter, a link mechanism (pantograph mechanism) will be described as an example.

  As shown in FIGS. 2 and 3, an elongated rectangular clip carrying member 30 is provided in the lateral direction in plan view for carrying the clips 20 individually. Although not shown, the clip carrying member 30 is formed into a solid frame structure with a closed cross section by an upper beam, a lower beam, a front wall (wall on the clip side), and a rear wall (wall on the side opposite to the clip). The clip carrying member 30 is provided so as to roll on the traveling road surfaces 81 and 82 by the traveling wheels 38 at both ends thereof. 2 and 3, the traveling wheels on the front wall (the traveling wheels that roll on the traveling road surface 81) are not shown. The traveling road surfaces 81 and 82 are parallel to the reference rail 70 over the entire area. A long hole 31 is formed along the longitudinal direction of the clip carrying member on the rear side (the side opposite to the clip) of the upper and lower beams of the clip carrying member 30, and the slider 32 can slide in the longitudinal direction of the long hole 31. Is engaged. In the vicinity of the end portion of the clip carrying member 30 on the clip 20 side, a single first shaft member 33 is vertically provided so as to penetrate the upper beam and the lower beam. On the other hand, a single second shaft member 34 is vertically provided through the slider 32 of the clip carrying member 30. One end of a main link member 35 is pivotally connected to the first shaft member 33 of each clip carrying member 30. The main link member 35 is pivotally connected to the second shaft member 34 of the adjacent clip carrier member 30 at the other end. In addition to the main link member 35, one end of the sub link member 36 is pivotally connected to the first shaft member 33 of each clip carrying member 30. The sub link member 36 is pivotally connected at the other end to the intermediate portion of the main link member 35 by a pivot shaft 37. As shown in FIG. 2, as the slider 32 moves to the rear side of the clip carrying member 30 (opposite the clip side) by the link mechanism using the main link member 35 and the sub link member 36, the clip carrying members 30 are connected to each other. As the slider 32 moves to the front side (clip side) of the clip carrier member 30 as shown in FIG. 3, the clip pitch increases. . Positioning of the slider 32 is performed by the pitch setting rail 90. As shown in FIGS. 2 and 3, the larger the clip pitch, the smaller the separation distance between the reference rail 70 and the pitch setting rail 90. Since the link mechanism is well known in the art, a more detailed description is omitted.

  The retardation film of the present invention having a slow axis in an oblique direction (for example, a direction of 45 ° with respect to the longitudinal direction) is produced by obliquely stretching the polyester-based resin film using the stretching apparatus as described above. Can be done. First, in the gripping zone A (film entrance of the stretching apparatus 100), the left and right endless loops 10R, 10L are gripped by the clips 20 of the polyester-based resin film at a constant clip pitch equal to each other. The film is sent to the preheating zone B by the movement of the loops 10 </ b> R and 10 </ b> L (substantially, the movement of each clip holding member 30 guided by the reference rail 70).

B. Preheating process In the preheating zone (preheating process) B, the left and right endless loops 10R and 10L are basically parallel to each other at a separation distance corresponding to the initial width of the polyester resin film as described above. Specifically, neither horizontal stretching nor longitudinal stretching is performed, and the film is heated. However, the distance between the left and right clips (distance in the width direction) may be slightly increased in order to avoid problems such as film deflection due to preheating and contact with the nozzles in the oven.

  In the preheating step, the film is heated to a temperature T1 (° C.). It is preferable that temperature T1 is more than the glass transition temperature (Tg) of a film, More preferably, it is Tg + 2 degreeC or more, More preferably, it is Tg + 5 degreeC or more. On the other hand, the heating temperature T1 is preferably Tg + 40 ° C. or lower, more preferably Tg + 30 ° C. or lower. Although it changes with the kind of polyester-type resin, temperature T1 is 70 to 150 degreeC, for example, Preferably it is 80 to 130 degreeC.

  The temperature raising time to the temperature T1 and the holding time at the temperature T1 can be appropriately set according to the type of polyester resin and the production conditions (for example, the film conveyance speed). These temperature raising time and holding time can be controlled by adjusting the moving speed of the clip 20, the length of the preheating zone, the temperature of the preheating zone, and the like.

C. Stretching process In the stretching zone (stretching process) C, the clip pitch of the left and right clips 20 is changed independently, and the film is stretched obliquely. The oblique stretching can be performed while increasing the distance between the left and right clips (distance in the width direction), for example, as in the illustrated example. This will be specifically described below. In the following description, for convenience, the stretching zone C is described as being divided into an inlet-side stretching zone (first oblique stretching zone) C1 and an outlet-side stretching zone (second oblique stretching zone) C2. The lengths of the first oblique stretching zone C1 and the second oblique stretching zone C2 and the ratio of the lengths to each other can be appropriately set according to the purpose.

Diagonal stretching typically involves (i) increasing the clip pitch of one of the left and right clips and decreasing the clip pitch of the other clip, and (ii) the decreased clip Increasing the pitch to the same pitch as the enlarged clip pitch, and setting the clip pitch of each clip to a predetermined pitch. This will be specifically described with reference to FIG. 4 and FIG. First, in the preheating zone B, the right and left clip pitch are both set to P _1. P ₁ is the clip pitch at the time of gripping the film. Next, as soon as the film enters the first oblique stretching zone C1, the clip pitch of one (right side in the illustrated example) starts to increase, and the clip pitch of the other (left side in the illustrated example) Start decreasing. In the first oblique stretching zone C1, it increases the clip pitch of the right clip to the P _2, to reduce the clip pitch of the left clip to the P _3. Therefore, the end portion of the first oblique stretching zone C1 in (beginning of the second oblique stretching zone C2), left clip moves the clip pitch P _3, right clip is a moving clip pitch P ₂ ing. Next, as soon as the film enters the second oblique stretching zone C2, the clip pitch of the left clip starts to increase. In the second oblique stretching zone C2, increases the clip pitch of the left clip to the P _2. On the other hand, the clip pitch of the right clip is maintained at P2 in the _second oblique stretching zone C2. Therefore, the end portion of the second oblique stretching zone C2 in (end of extension zone C), the left clip and right clips together, there is a moving clip pitch P _2. In the illustrated example, for the sake of simplicity, both the clip pitch decrease start position of the left clip and the clip pitch increase start position of the right clip are both set as the start portion of the first oblique stretching zone C1. It can be set to any suitable position in the zone. For example, the position at which the clip pitch of the left clip starts to decrease may be the intermediate portion of the first oblique stretching zone C1, and the position at which the clip pitch of the right clip begins to increase may be the intermediate portion of the first oblique stretching zone C1. Good. Needless to say, the position at which the clip pitch of the left clip starts to increase may be the intermediate portion of the first oblique stretching zone C1 or the intermediate portion of the second oblique stretching zone C2. The clip pitch ratio can generally correspond to the clip moving speed ratio. Therefore, the ratio of the clip pitch of the left and right clips can generally correspond to the ratio of the stretching ratio in the MD direction between the right side edge and the left side edge of the film.

  As described above, the clip pitch can be adjusted by positioning the slider by adjusting the distance between the pitch setting rail of the stretching device and the reference rail.

The clip pitch change rate (P ₂ / P ₁ ) is preferably 1.2 to 1.9, and more preferably 1.4 to 1.7. When P ₂ / P ₁ is in such a range, there is an advantage that the film can be prevented from being broken. Furthermore, the clip pitch change rate (P ₃ / P ₁ ) is preferably 0.5 to 0.9, and more preferably 0.6 to 0.8. If P ₃ / P ₁ is in such a range, there is an advantage that wrinkles are unlikely to enter the film.

  In the oblique stretching in the method for producing a retardation film of the present invention, the clip pitch change rate of one clip and the clip pitch change of the other clip at the end of the first oblique stretching (stretching in the first oblique stretching zone C1). The product with the rate is preferably 1.0 to 1.7. If the product of the rate of change is within such a range, a retardation film having excellent axial accuracy and small dimensional change can be obtained.

  The oblique stretching can typically be performed at a temperature T2. The temperature T2 is preferably Tg-20 ° C to Tg + 30 ° C, more preferably Tg-10 ° C to Tg + 20 ° C, and particularly preferably about Tg, with respect to the glass transition temperature (Tg) of the polyester resin film. Although it changes with the kind of polyester-type resin film, temperature T2 is 70 to 110 degreeC, for example, Preferably it is 80 to 100 degreeC. The difference (T1-T2) between the temperature T1 and the temperature T2 is preferably ± 2 ° C. or more, more preferably ± 5 ° C. or more. In one embodiment, T1> T2, and thus the film heated to temperature T1 in the preheating step can be cooled to temperature T2.

The oblique stretching described above may include stretching in the lateral direction, and may not include stretching in the lateral direction. In other words, the width of the film after oblique stretching may be larger than the initial width of the film, or may be substantially the same as the initial width. Needless to say, the illustrated example shows an embodiment including transverse stretching. When the oblique stretching includes lateral stretching as in the illustrated example, the transverse stretching ratio (ratio W ₂ / W ₁ between the initial width W ₁ of the film and the width W ₂ of the film after oblique stretching) is preferably 1 It is 0.0-4.0, More preferably, it is 1.3-3.0. If the draw ratio is too small, tin-like wrinkles may occur in the resulting retardation film. When the draw ratio is too large, the biaxiality of the obtained retardation film is increased, and the viewing angle characteristics may be deteriorated when applied to an image display device or the like.

D. Crystallization Step In the crystallization zone (crystallization step) D, the diagonally stretched polyester resin film is crystallized by heat treatment in a state where the clip pitch of the left and right clips 20 is constant. Specifically, in a state where the clip pitches of the left and right clips 20 were both P _2, it is heated while conveying the film. The crystallization step can be performed as necessary.

  The heat treatment can typically be performed at a temperature T3. The temperature T3 can vary depending on the type of polyester resin and the desired crystallinity. T3 is typically higher than the stretching temperature T2 (that is, T2 <T3), and is, for example, 100 ° C. to 280 ° C. The difference (T3-T2) between T3 and T2 is preferably 20 ° C to 150 ° C. The heat treatment time is typically 10 seconds to 10 minutes. The heat treatment time can be controlled by adjusting the length of the heat treatment zone and / or the film transport speed.

In the crystallization step, MD contraction processing for contracting the film in the machine direction (MD) by decreasing the clip pitch of the left and right clips may be performed. By performing MD shrinkage treatment in the crystallization step, a retardation film having further excellent axial accuracy can be obtained. In MD shrinkage treatment are both reduced to P ₄ of the clip pitches of the left clip and right clip. The clip pitch change rate (P ₄ / P ₂ ) is preferably 0.7 to 0.999, more preferably 0.7 to 0.995, and further preferably 0.8 to 0.99. . The shrinkage rate in the MD shrinkage treatment is preferably 0.1% to 30%, more preferably 0.5% to 30%, and further preferably 1% to 20%.

E. Release process Finally, the clip holding the film is released to obtain a retardation film. In addition, the width W ₂ of the film after oblique stretching corresponds to the width of the obtained retardation film (FIG. 4). When the oblique stretching does not include transverse stretching, the width of the obtained retardation film is substantially equal to the initial width of the film.

(III) Bonding with polarizing plate Outline The retardation film of the present invention can be bonded to a polarizing plate with very high production efficiency. Details are as follows. The retardation film of the present invention is long and has a slow axis in an oblique direction (as described above, for example, a direction of 45 ° with respect to the long direction). In many cases, the long polarizer has an absorption axis in the longitudinal direction or the width direction. Therefore, when the retardation film of the present invention is used, the slow axis is, for example, 45 ° with respect to the absorption axis of the polarizing plate. In the case of bonding at an angle (for example, in the case of producing a circularly polarizing plate), a so-called roll-to-roll can be used, and extremely excellent production efficiency can be realized. The roll-to-roll refers to a method of continuously laminating long films while aligning their long directions while roll-feeding them.

  With reference to FIG. 6, the bonding method of retardation film and a polarizing plate is demonstrated easily. In FIG. 6, reference numerals 811 and 812 are rolls for winding the polarizing plate and the retardation film, respectively, and reference numeral 822 is a transport roll. In the illustrated example, a polarizing plate (first protective film 320 / polarizer 310 / second protective film 330) and a retardation film 340 are sent out in the direction of the arrows, and are bonded together with their respective longitudinal directions aligned. In that case, it bonds together so that the 2nd protective film 330 of a polarizing plate and the phase difference film 340 may adjoin. Thus, a retardation film and a polarizing plate can be bonded together to obtain a polarizing film with a retardation film. Although not illustrated, for example, a polarizing plate (first protective film 320 / polarizer 310) and a retardation film 340 are bonded so that the polarizer 310 and the retardation film 340 are adjacent to each other, and the retardation film 340 is formed. It can also function as a protective film.

B. Method for producing circularly polarizing plate B-1. Production of long polarizer As described above, a long circularly polarized light is obtained by laminating the long retardation film of the present invention and the long polarizer (preferably by roll-to-roll). A plate can be made. As the long polarizer, a polarizing film having an absorption axis in either the long direction or the width direction can be employed. Specifically, dichroic substances such as iodine and dichroic dyes on hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, ethylene / vinyl acetate copolymer partially saponified films, etc. And a polyene-based oriented film such as a uniaxially stretched product and a dehydrated product of polyvinyl alcohol and a dehydrochlorinated product of polyvinyl chloride. Among these, a long polarizing film in which a dichroic substance such as iodine is adsorbed on a polyvinyl alcohol film and uniaxially stretched is particularly preferable because of its high polarization dichroic ratio. The thickness of these long polarizing films is not particularly limited, but is generally about 1 to 80 μm.

  A long polarizer uniaxially stretched by adsorbing iodine to a polyvinyl alcohol film, for example, is dyed by immersing a polyvinyl alcohol meter film in an aqueous solution of iodine and stretched to 3 to 7 times the original length. Can be produced. If necessary, it may contain boric acid, zinc sulfate, zinc chloride, or the like, or may be immersed in an aqueous solution such as potassium iodide. Further, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing.

  By washing the polyvinyl alcohol film with water, not only can the surface of the polyvinyl alcohol film be cleaned and the anti-blocking agent can be washed, but also the effect of preventing unevenness such as uneven dyeing can be obtained by swelling the polyvinyl alcohol film. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. The film can be stretched in an aqueous solution of boric acid or potassium iodide or in a water bath.

B-2. Production of Circular Polarizing Plate The long retardation film of the present invention described in (I) and (II) above and the long polarizer described in B-1 above are described with reference to FIG. As described, it is continuously fed out, and then continuously bonded in a state where the respective longitudinal directions are aligned to obtain a long circularly polarizing plate. The long circularly polarizing plate thus obtained can be used after being cut into a desired dimension. Note that the long retardation film and the long polarizer can typically be bonded together via a pressure-sensitive adhesive or an adhesive. Any appropriate pressure-sensitive adhesive or adhesive can be used as the pressure-sensitive adhesive or adhesive as long as the optical properties of the obtained circularly polarizing plate are not impaired.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples. In addition, the measurement and evaluation method in an Example are as follows.

(1) Orientation angle (expression direction of slow axis)
Samples were prepared by cutting out the central portion of the retardation films obtained in Examples and Comparative Examples into a square shape having a width of 50 mm and a length of 50 mm so that one side thereof was parallel to the width direction of the film. This sample was measured using a Mueller matrix polarimeter (product name “Axoscan” manufactured by Axometrics), and the orientation angle θ at a wavelength of 550 nm and 23 ° C. was measured. The orientation angle θ was measured with a sample placed in parallel on a measurement table.
(2) In-plane retardation Re
In the same manner as in the above (1), measurement was performed at a wavelength of 590 nm and 23 ° C. using a product name “Axoscan” manufactured by Axometrics.
(3) Thickness It measured using the micro gauge type thickness meter (made by Mitutoyo Corporation).
(4) Dimensional change The retardation films obtained in Examples and Comparative Examples were cut into 100 mm × 100 mm. The dimensions of the cut film were accurately measured using a Mitutoyo Corporation CNC Image Measuring Machine QuickVision (QV606). Then, after putting it in a heating oven at 80 ° C. for 240 hours, the film was taken out and the dimensions were measured again accurately to determine the change in the dimensions.
(5) Crystallinity About the retardation films obtained in Examples and Comparative Examples, X-ray diffraction measurement was performed using a two-dimensional detector-mounted X-ray diffractometer (manufactured by Bruker AXS, D8 DISCOVER with GADDS). A scattering profile was obtained. The obtained scattering profile was separated into a crystalline diffraction line and an amorphous halo peak by fitting. The crystallinity Xc was determined from the following formula (1) from the integrated intensity of each peak obtained.
Xc = Ic / (Ic + Ia) × 100 (1)
Ic: Crystalline scattering intensity
Ia: Amorphous scattering intensity (6) Production of circularly polarizing plate by roll-to-roll Retardation films obtained in Examples and Comparative Examples, a long polarizer, and a long cycloolefin system obliquely stretched A long circular polarizing plate having a three-layer structure of retardation film / polarizer / cycloolefin-based film bonded to a film (manufactured by Nippon Zeon Co., Ltd., product name “ZD12-141158-E1330”) by roll-to-roll. Was made. The ones capable of producing a circularly polarizing plate by roll-to-roll were indicated as “◯”, and the ones that were not possible as “×”. In addition, the long polarizer is 6 times between rolls having different speed ratios in an aqueous solution containing boric acid after dyeing a long film made of polyvinyl alcohol resin in an aqueous solution containing iodine. It was produced by uniaxial stretching.
(7) Visibility with polarized sunglasses The circularly polarizing plate obtained in the above (6) is cut into a predetermined size, and the polarized light previously bonded to a commercially available organic EL TV (product name “15EL9500” manufactured by LG Display). After peeling off the plate, the cut out circularly polarizing plate was bonded. Bonding was performed via an acrylic pressure-sensitive adhesive applied to the cycloolefin film surface of the circularly polarizing plate. An image was output to an organic EL television with a circularly polarizing plate, and the appearance of the image was visually confirmed with commercially available polarized sunglasses. Judgment criteria are as follows.
○ ・ ・ ・ There is no color or interference fringes and can be seen normally △ ・ ・ ・ Interference fringes can be seen depending on the viewing angle of TV × ・ ・ ・ Interference fringes can be seen regardless of the angle, or images appear colored

<Example 1>
(Polyester resin film)
As the polyester-based resin film, a modified polyethylene terephthalate (PET) film (manufactured by Mitsubishi Plastics, trade name “Novaclear SI-026”, thickness 200 μm) was used. Modified PET is a copolymer containing repeating units derived from cyclohexanedimethanol.

(Diagonal stretching)
The above polyester resin film is subjected to pre-heat treatment, oblique stretching and crystallization treatment with a clip pitch profile as shown in FIG. 5 using an apparatus as shown in FIGS. 1 to 4 to obtain a retardation film. It was. Specifically, the polyester resin film (thickness 200 μm, width 550 mm) was preheated to 87 ° C. in the preheating zone of the stretching apparatus. In the preheating zone, the clip pitch of the left and right clips was 125 mm. Next, as soon as the film entered the first diagonal stretching zone C1, the clip pitch of the right clip started to increase and increased from 125 mm to 187.5 mm in the first diagonal stretching zone C1. The clip pitch change rate was 1.5. In the first oblique stretching zone C1, the clip pitch of the left clip started to decrease and decreased from 125 mm to 90 mm in the first oblique stretching zone C1. The clip pitch change rate was 0.72. Next, as soon as the film entered the second oblique stretching zone C2, the clip pitch of the left clip started to increase and increased from 90 mm to 187.5 mm in the second oblique stretching zone C2. On the other hand, the clip pitch of the right clip was maintained at 187.5 mm in the second oblique stretching zone C2. Simultaneously with the above oblique stretching, the film was stretched 2.83 times in the width direction. The oblique stretching was performed at 87 ° C.

(Crystallization treatment)
Next, crystallization treatment was performed in the crystallization zone. Specifically, heat treatment was performed at 190 ° C. for 1 minute while the clip pitches of the left clip and right clip were both maintained at 187.5 mm.

  As described above, a retardation film (thickness: 53 μm) was obtained. The obtained retardation film was subjected to the evaluations (1) to (7) above. The results are shown in Table 1.

<Example 2>
A retardation film (thickness 52 μm) was obtained in the same manner as in Example 1 except that an amorphous PET film (trade name “Novaclear SG-007”, thickness 200 μm) was used as the polyester resin film. Obtained. The obtained retardation film was subjected to the evaluations (1) to (7) above. The results are shown in Table 1.

<Example 3>
A retardation film (thickness) in the same manner as in Example 1 except that an amorphous PET film (Mitsubishi Resin Co., Ltd., trade name “Novaclear SI-026”, thickness 125 μm) having a different thickness was used as the polyester resin film 33 μm) was obtained. The obtained retardation film was subjected to the evaluations (1) to (7) above. The results are shown in Table 1.

<Comparative Example 1>
A retardation film (thickness 57 μm) was obtained in the same manner as in Example 1 except that the crystallization treatment was not performed and the stretching temperature was 92 ° C. The obtained retardation film was subjected to the evaluations (1) to (7) above. The results are shown in Table 1.

<Comparative Example 2>
A retardation film (thickness 57 μm) was obtained in the same manner as in Example 1 except that the crystallization treatment was not performed. The obtained retardation film was subjected to the evaluations (1) to (7) above. The results are shown in Table 1.

<Comparative Example 3>
Instead of the polyester resin film, a cycloolefin resin film (manufactured by Nippon Zeon Co., Ltd., trade name “ZF14-100”, thickness 100 μm, width 420 mm) was used.
The cycloolefin resin film was subjected to pre-heat treatment and oblique stretching with a clip pitch profile as shown in FIG. 5 using an apparatus as shown in FIGS. 1 to 4 to obtain a retardation film. Specifically, it was preheated to 150 ° C. in the preheating zone. In the preheating zone, the clip pitch of the left and right clips was 125 mm. Next, as soon as the film entered the first oblique stretching zone C1, the clip pitch of the right clip began to increase and increased from 125 mm to 165 mm in the first oblique stretching zone C1. The clip pitch change rate was 1.32. In the first oblique stretching zone C1, the clip pitch of the left clip started to decrease, and decreased from 125 mm to 108.75 mm in the first oblique stretching zone C1. The clip pitch change rate was 0.87. Next, as soon as the film entered the second diagonal stretching zone C2, the clip pitch of the left clip started to increase and increased from 90 mm to 165 mm in the second diagonal stretching zone C2. On the other hand, the clip pitch of the right clip was maintained at 165 mm in the second oblique stretching zone C2. Simultaneously with the oblique stretching, stretching in the width direction was doubled. In addition, the crystallization process was not performed after extending | stretching.
A retardation film (thickness 41 μm) was obtained as described above. The obtained retardation film was subjected to the evaluations (1) to (7) above. The results are shown in Table 1.

<Comparative Example 4>
A retardation film (thickness: 50 μm) was obtained in the same manner as in Example 2 except that transverse stretching (stretching ratio: 4.0 times) was performed using a tenter stretching machine instead of oblique stretching. The obtained retardation film was subjected to the evaluations (1) to (7) above. The results are shown in Table 1.

<Comparative Example 5>
Example 1 was carried out in the same manner as in Example 1 except that longitudinal uniaxial stretching (stretching ratio: 4.0 times) was performed using a heat roll instead of oblique stretching, and a film having a thickness of 100 μm before stretching was used. A retardation film (thickness 50 μm) was obtained. The obtained retardation film was subjected to the evaluations (1) to (7) above. The results are shown in Table 1.

<Comparative Example 6>
A sequential biaxially stretched PET film (trade name “T602E25N”, thickness 23 μm, manufactured by Mitsubishi Plastics, Inc.) that has been crystallized as a polyester resin film was used as a retardation film. This retardation film was subjected to the evaluations (1) to (7) above. The results are shown in Table 1.

<Evaluation>
As apparent from Table 1, according to the examples of the present invention, a specific polyester-based resin film is used, and a specific oblique stretching and crystallization treatment are combined to form an oblique direction with excellent axial accuracy. A long retardation film having a slow axis and very large birefringence could be actually produced. On the other hand, the birefringence of the retardation films of Comparative Examples 1 and 2 obtained without performing the crystallization treatment was significantly smaller than the films of the examples. The retardation film of Comparative Example 3 obtained using a cycloolefin film had a birefringence that was significantly lower than that of the film of the Example. In the retardation films of Comparative Examples 4 to 6 obtained by longitudinal stretching, lateral stretching or biaxial stretching, it was impossible to produce a circularly polarizing plate by roll-to-roll. Furthermore, as a whole, the retardation film of the comparative example was inferior to the retardation film of the example in terms of visibility with polarized sunglasses.

  The retardation film obtained by the production method of the present invention is suitably used for image display devices such as liquid crystal display devices (LCD) and organic electroluminescence display devices (OLED), and mobile devices using such image display devices. .

10L endless loop 10R endless loop 20 clip 30 clip carrying member 70 reference rail 90 pitch setting rail 100 stretching device

Claims (8)

It is composed of a polyester resin selected from polyethylene terephthalate, modified polyethylene terephthalate, and blends thereof,
The modified polyethylene terephthalate contains any one of a repeating unit derived from cyclohexanedimethanol, a repeating unit derived from diethylene glycol, and a repeating unit derived from isophthalic acid,
The direction of the slow axis is in the range of 30 ° to 60 ° with respect to the longitudinal direction over the entire width direction, and the birefringence Δn _xy is 0.085 or more.
A long retardation film.   The retardation film according to claim 1, wherein the dimensional shrinkage after heating at 80 ° C. for 240 hours is 2.0% or less.   The retardation film according to claim 1 or 2, wherein the crystallinity measured by X-ray diffraction (XRD) is 25% or more.   The retardation film according to claim 1, wherein the in-plane retardation Re (590) is 3000 nm or more.   Grasping the left and right edges of the film with variable-pitch left and right clips that change the vertical clip pitch; preheating the film; independently changing the clip pitch of the left and right clips And obliquely stretching the film; after the oblique stretching, the film is crystallized by heat treatment with the clip pitch of the left and right clips kept constant; and a clip for gripping the film The method for producing a retardation film according to claim 1, comprising: releasing.   The method for producing a retardation film according to claim 5, wherein the heat treatment is performed at a temperature of 100 ° C. to 280 ° C. The oblique stretching is
(I) increasing the clip pitch of one of the left and right clips and decreasing the clip pitch of the other clip, and (ii) making the decreased clip pitch the same as the enlarged clip pitch The method for producing a retardation film according to claim 5, comprising increasing to a pitch, and setting a clip pitch of each clip to a predetermined pitch. A long circular polarizing plate comprising the long retardation film according to claim 1 and a long polarizer disposed on one side of the retardation film.

Images