JP2010014994A - Method of manufacturing phase-difference film - Google Patents

Abstract

A retardation film having a Re as high as 40 or higher and a haze as low as 0.5% or less is produced.
A cellulose acylate film is heated to reach 190 ° C. This heating step is performed with the clip tenter 18 while holding the both sides of the cellulose acylate film 11 with the clip 13. In the clip tenter 18, after the heating process, a temperature lowering process for lowering the cellulose acylate film to a temperature lower than the crystallization temperature Tc and a widening process for expanding the width are performed in this order. The temperature of the cellulose acylate film 11 at the time of widening is higher than the glass transition point Tg and lower than Tc. The widening ratio in the widening step is 1.1 or more, and the retardation film 17 is obtained by this widening step.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a retardation film.

  Liquid crystal display devices are widely used in monitors for personal computers and portable devices, and for television applications because of their various advantages, such as low voltage and low power consumption, enabling miniaturization and thinning. In such a liquid crystal display device, various modes have been proposed depending on the alignment state of the liquid crystal in the liquid crystal cell. Conventionally, the TN has an alignment state twisted by about 90 ° from the lower substrate to the upper substrate of the liquid crystal cell. The mode was mainstream.

  In general, a liquid crystal display device includes a liquid crystal cell, an optical compensation sheet, and a polarizer. The optical compensation sheet is used for eliminating image coloring or expanding the viewing angle, and a stretched birefringent film or a film obtained by applying a liquid crystal to a transparent film is used.

  For example, Patent Document 1 discloses a technique for applying an optical compensation sheet in which a discotic liquid crystal is applied on a triacetyl cellulose film, aligned, and fixed to a TN mode liquid crystal cell to widen the viewing angle. However, a television-use liquid crystal display device that is expected to be viewed from various angles on a large screen has a strict requirement for viewing angle dependency, and even with the above-described method, the requirement cannot be satisfied. Therefore, liquid crystal display devices different from the TN mode, such as an IPS (In-plane Switching) mode, an OCB (Optically Compensatory Bend) mode, and a VA (Vertically Aligned) mode, have been studied. In particular, the VA mode is attracting attention as a liquid crystal display device for TV because of its high contrast and relatively high manufacturing yield.

  Optical retardation (high retardation value) is required for a retardation film of a liquid crystal display device. In particular, an optical compensation sheet for VA requires in-plane retardation (Re) of 40 nm or more.

  The retardation film converts the elliptically polarized light after passing through the liquid crystal layer into a state close to linearly polarized light by matching with the retardation of the liquid crystal layer in the liquid crystal display. The phase difference of the liquid crystal layer is not uniform but varies. Therefore, it is necessary to select a retardation film to be combined according to the liquid crystal layer to be used.

There are various types of polymer films used as retardation films, and typical examples include films made of cellulose acylate. The cellulose acylate film is converted into a retardation film through a stretching process in which the cellulose acylate film is pulled in a predetermined direction. In the case of producing a long retardation film, for example, the side end portion of the cellulose acylate film is held by holding means such as a clip, and tension is applied in the width direction to widen the width. By this stretching step, the surface direction retardation Re is increased. Note that Re is a retardation value in a direction orthogonal to the thickness direction of the film, that is, in the film surface direction, and is obtained by the following equation (1). Nx is the refractive index in the X axis, which is the slow axis direction on the surface of the retardation film, Ny is the refractive index in the Y axis, which is the fast axis direction, and d is the thickness (nm) of the film.
Re = (Nx−Ny) × d (1)

In some cases, a cellulose acylate film having a high retardation Rth in the thickness direction is desired. Rth is obtained by the following equation. Nz is a refractive index in the Z axis, which is the thickness direction of the retardation film.
Rth = {(Nx + Ny) / 2−Nz} × d (2)

  Non-Patent Document 1 discloses a cellulose acetate film having a high retardation value. On page 29 of Non-Patent Document 1, a method for producing a cellulose acylate phase difference plate that is stretched at 30 to 160 ° C. in a uniaxial direction or a biaxial direction at a temperature equal to or lower than the glass transition point is disclosed. It is preferable that the film forming step and the stretching step are performed sequentially or continuously, and the film is stretched in a state where the solvent remains in the film.

  In Patent Document 2, in order to achieve a high retardation value with cellulose triacetate, an aromatic compound having at least two aromatic rings, particularly a compound having a 1,3,5-triazine ring, is added and subjected to stretching treatment. Cellulose triacetate is generally a polymer material that is difficult to stretch, and it is known that it is difficult to increase the birefringence, but it is necessary to increase the birefringence by simultaneously orienting the additives in the stretching process. To achieve a high retardation value. Since this film can also serve as a protective film for the polarizing plate, there is an advantage that an inexpensive and thin liquid crystal display device can be provided.

  Patent Document 3 discloses a cellulose ester optical biaxial film that is stretched 1.2 to 4.0 times in at least one direction at a temperature of 15 to 160 ° C. within a residual solvent amount of 10 to 100% by mass.

Patent Document 4 discloses a tenter heated from 140 ° C. to 180 ° C. after a roll film having a residual solvent amount of less than 3% is fed from a feeding device, preheated at a temperature 10 ° C. to 40 ° C. lower than the stretching temperature. An optical cellulose acylate film characterized by being stretched 1.1 to 1.6 times in the width direction in an apparatus is disclosed.
Japanese Patent No. 2587398 European Patent Application No. 91656 JP 2002-187960 A JP 2006-83203 A Invention Association Open Technique 2001-1745

  In order to obtain a retardation film having a high retardation value by the methods of Non-Patent Document 1 and Patent Documents 1 to 4, stretching at a higher magnification is required, but the retardation film obtained by these methods has a haze value. The liquid crystal display device using these retardation films becomes high in contrast, and the contrast is lowered. Furthermore, the retardation film obtained by these methods tends to deteriorate in dimensional stability over time, and the liquid crystal display device using the retardation film tends to cause light leakage at the outer periphery and corners of the display screen. was there.

  Therefore, in the present invention, in view of the above problems, a retardation film capable of producing a retardation film having a small haze of 0.5% or less and a small dimensional change rate even though Re is as high as 40 or more. It aims at providing the manufacturing method of.

  In order to solve the above-mentioned problems, the method for producing a retardation film of the present invention is a method of heating the cellulose acylate film so as to reach 190 ° C. while holding both sides of the long cellulose acylate film. And a widening step of widening the cellulose acylate film that has undergone the heating step in a state where the cellulose acylate film is maintained at a temperature of less than 190 ° C. to form a retardation film.

  In the manufacturing method, when the width of the cellulose acylate film before the widening step is L1, the width after the widening step is L2, the crystallization temperature of the cellulose acylate is Tc, and the glass transition point is Tg, The cellulose acylate film is preferably widened so that L2 ≧ 1.1 × L1 while maintaining the temperature in a range higher than Tg and lower than Tc.

  The method for producing a retardation film further includes a casting step in which a dope in which cellulose acylate is dissolved in a solvent is continuously cast on a traveling support to form a casting film, and a flow including the solvent. It is preferable to have a peeling step of peeling the cast film as a wet film from the support and a drying step of drying the wet film until the residual solvent ratio reaches 2% to obtain the cellulose acylate film.

  When the width of the wet film when the solvent residual ratio is 60% is L3 and the width when the solvent residual ratio is 10% is L4, the drying process is performed while the solvent residual ratio decreases from 60% to 10%. It is preferable to have a drying and widening step of widening the film so that L4 ≧ 1.1 × L3.

  According to the present invention, although the Re is as high as 40 or more, a retardation film having a small haze of 0.5% or less and a small dimensional change rate can be produced.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments described here.

As the polymer film used for producing the retardation film, a cellulose acylate film made of cellulose acylate is used. Among cellulose acylates, the ratio of esterifying the hydroxyl group of cellulose with carboxylic acid, that is, the degree of acyl group substitution (hereinafter referred to as acyl group substitution degree) satisfies all the conditions of the following formulas (I) to (III). What is satisfied is more preferable. In (I) to (III), A and B are both acyl group substitution degrees, the acyl group in A is an acetyl group, and the acyl group in B has 3 to 22 carbon atoms.
2.5 ≦ A + B ≦ 3.0 (I)
0 ≦ A ≦ 3.0 (II)
0 ≦ B ≦ 2.9 (III)

  Glucose units constituting cellulose and having β-1,4 bonds have free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer in which some or all of these hydroxyl groups are esterified, and hydrogen of the hydroxyl groups is substituted with acyl groups having 2 or more carbon atoms. Since the degree of substitution is 1 when esterification of one hydroxyl group in the glucose unit is 100%, in the case of cellulose acylate, the hydroxyl groups at the 2nd, 3rd and 6th positions are each 100% ester. The degree of substitution is 3.

  Here, the substitution degree of the acyl group at the 2-position of the glucose unit is DS2, the substitution degree of the acyl group at the 3-position is DS3, and the substitution degree of the acyl group at the 6-position is DS6. The total acyl group substitution degree determined by DS2 + DS3 + DS6 is preferably 2.00 to 3.00, more preferably 2.22 to 2.90, and even more preferably 2.40 to 2.88. . DS6 / (DS2 + DS3 + DS6) is preferably 0.32 or more, more preferably 0.322 or more, and further preferably 0.324 to 0.340.

  There may be only one kind of acyl group, or two or more kinds. When there are two or more acyl groups, it is preferable that one of them is an acetyl group. DSA + DSB, where DSA is the sum of the substitution degrees of the hydrogens of the hydroxyl groups at the 2nd, 3rd and 6th positions with the acetyl group, and DSB is the sum of the substitution degrees other than the acetyl groups at the 2nd, 3rd and 6th positions The value of is preferably 2.2 to 2.86, particularly preferably 2.40 to 2.80. DSB is preferably 1.50 or more, and particularly preferably 1.7 or more. Further, it is preferable that 28% or more of the DSB is a substituent at the 6-position hydroxyl group, more preferably 30% or more, still more preferably 31% or more, and particularly preferably 32% or more is a substituent at the 6-position hydroxyl group. Preferably there is. The 6-position DSA + DSB value of cellulose acylate is preferably 0.75 or more, more preferably 0.80 or more, and particularly preferably 0.85 or more. By using the cellulose acylate as described above, a dope having a preferable solubility and a dope having a low viscosity and a good filterability can be produced. In particular, when a non-chlorine organic solvent is used, the above cellulose acylate is preferable.

  The acyl group having 2 or more carbon atoms may be an aliphatic group or an aryl group, and is not particularly limited. For example, there are cellulose alkylcarbonyl ester, alkenylcarbonyl ester, aromatic carbonyl ester, aromatic alkylcarbonyl ester, etc., and these may each further have a substituted group. Propionyl group, butanoyl group, pentanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecanoyl group, iso-butanoyl group, t-butanoyl group, cyclohexane Examples thereof include a carbonyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, and a cinnamoyl group. Among these, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a t-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and a propionyl group and a butanoyl group are particularly preferable.

  The cellulose acylate film may contain various additives in addition to the cellulose acylate. Examples of the various additives include plasticizers, deterioration inhibitors, ultraviolet absorbers, dyes, fine particles as so-called matting agents that improve slipperiness, and retardation increasing agents for increasing Re and Rth. In the case of producing a cellulose acylate film by a solution casting method, a so-called release agent for improving the peelability from the casting support can be used, and this release agent is contained in the cellulose acylate film. It may be included.

  When the retardation increasing agent is included in the cellulose acylate film, Re and Rth of the same height are expressed even when the width-expansion rate in the manufacturing process of the retardation film described later is reduced compared to the case where the retardation increasing agent is not included. Can be made. A retardation raising agent is not specifically limited, For example, what is described in Paragraph [0030]-[0142] of Unexamined-Japanese-Patent No. 2006-235383 can be used. Among them, as a particularly preferred retardation increasing agent, a compound represented by the structural formula of Formula 1 can be exemplified.

  When the retardation increasing agent is used, the retardation increasing agent is preferably 2% or more and 10% or less, more preferably 3% or more and 10% or less with respect to the mass of the cellulose acylate. Should be used. This percentage value is a value obtained by 100 × x / y, where x is the mass of the cellulose acylate film and y is the mass of the retardation increasing agent.

  FIG. 1 is a schematic view of a retardation film manufacturing facility. The retardation film manufacturing facility 10 transports the cellulose acylate film 11 by feeding it out and holding both sides of the cellulose acylate film 11 sent from the sending device 12 by clips 13 as holding means. The clip tenter 18 which carries out the temperature control of the conveyed cellulose acylate film 11 and the widening to widen the phase difference film 17 and cuts and removes both side portions of the retardation film 17; and A temperature adjusting device 22 that adjusts the temperature of the retardation film 17 and a winding device 23 that winds the retardation film 17 are provided.

  The cellulose acylate film 11 is dried, and is produced by a solution casting method in the present embodiment, and once wound into a roll. When a cellulose acylate film produced by a solution casting method is used, it is preferable to use a film having a solvent content of at most 2% by weight, that is, 2% by weight or less. Thereby, the haze suppression effect which implements the below-mentioned heating process and widening process is heightened more.

  The roll of the cellulose acylate film 11 is unwound by the feeding device 12 and sent to the clip tenter 18. The delivery device 12 has a drive control unit (not shown) that controls the rotation of the roll of the cellulose acylate film 11, and thereby the feed rate to the clip tenter 18 is adjusted.

  The clip tenter 18 has a plurality of clips 13 that hold the side portions of the cellulose acylate film 11 on both sides of the conveyance path of the cellulose acylate film 11, and a chain that runs endlessly with the plurality of clips 13 attached thereto. (Not shown), a rail (not shown) for determining the path of the chain, and a plurality of slits extending in the width direction of the cellulose acylate film 11 in the conveying direction, and air is supplied to the cellulose acylate film 11 from these slits. A blower duct 26 that sends out air and a blower 27 that sends air to the blower duct 26 are provided. The air duct 26 is divided into a plurality of sections in the transport direction of the cellulose acylate film 11, and the slit is formed in each section so as to face the film transport path. Air that flows out from each slit is sent to the air duct 26 by a blower 27 connected to the air duct 26. The blower 27 is provided with a controller (not shown) for controlling on / off of air delivery from the slit of each section of the air duct 26, air volume, wind speed, air temperature and humidity. In addition, the temperature and humidity and the flow rate of the air sent out are controlled independently. The rail is provided with a shift mechanism (not shown). The shift mechanism moves the rail in the width direction of the cellulose acylate film 11, and thereby the chain is displaced.

  When the cellulose acylate film 11 is guided by the clip tenter 18, each side portion is gripped by the clip 13 and conveyed by the travel of the clip 13. By changing the distance between one clip 13 and the other clip 13 on both sides, the tension applied in the width direction of the cellulose acylate film 11 can be changed, thereby changing the width. Details of the process in the clip tenter 18 will be described later with reference to another drawing.

  The retardation film 17 of the clip tenter 18 is guided by the edge-cutting device 21 and continuously cut and removed on both sides. Thereby, the grip location gripped by the clip 13 is separated from the central portion that is the product. The cut-out side portions are sent to a crusher 28 having a rotary cutter (not shown) and cut into fine chips.

  The temperature adjusting device 22 includes a plurality of rollers 31 that support the retardation film 17 on the peripheral surface. These rollers 31 include a driving roller that conveys the retardation film 17 by being rotationally driven in the circumferential direction. Inside the temperature adjusting device 22 is provided with an air duct 32 provided with a plurality of slits (not shown) extending in the width direction of the retardation film 17 in the transport direction, and cold air flows out from the air duct 32. By doing so, the retardation film 17 is cooled.

  The retardation film 17 cooled by the temperature adjusting device 22 is sent to the winding device 23 and wound into a roll.

  FIG. 2 is an explanatory diagram of the cellulose acylate film 11 in the clip tenter 18. The arrow line Y is the conveyance direction of the cellulose acylate film 11. In the clip tenter 18, tension is applied to the cellulose acylate film 11 in the width direction indicated by the arrows X 1 and X 2. A position where the holding of the cellulose acylate film 11 by the clip 13 (see FIG. 1) is started is a holding start position PS, and a position where the holding is released is a holding release position PE. The inlet of the clip tenter 18 is on the upstream side of the holding start position PS, and the outlet is on the downstream side of the holding release position, but is not shown in FIG.

  When the cellulose acylate film 11 enters the clip tenter 18, the cellulose acylate film 11 is heated by the air flowing out from the air duct 26, and the temperature rises. And the cellulose acylate film 11 is heated so that it may become the temperature more than the crystallization temperature Tc of a cellulose acylate. This process is referred to as a heating process. Conventionally, when heating a polymer film, conditions are set so that the polymer is not crystallized as much as possible, that is, the amorphous part is as much as possible, and the temperature condition can be suppressed to a temperature lower than the crystallization temperature Tc. I came. This is because the transparency usually falls when the polymer crystallizes. On the other hand, in the present invention, a cellulose acylate film is used as a material for the retardation film 17, and the cellulose acylate film 11 is heated to a temperature equal to or higher than the crystallization temperature Tc before the widening step described later. Perform the process. That is, the cellulose acylate film 11 is positively and intentionally heated to a temperature equal to or higher than the crystallization temperature Tc of the cellulose acylate. Thereby, the transparency of the cellulose acylate film 11 is improved, that is, the haze is lowered.

  Cellulose acylate is a typical amorphous polymer, but the crystallization temperature Tc may be detected. However, even if crystallization occurs at a temperature higher than the crystallization temperature Tc, it is considered that the volume of the crystal part is very small compared to other polymers. For this reason, even if it crystallizes, it is guessed that a crystal part does not become so large that a haze is raised, but a microcrystal area | region is scattered. Then, rather than the increase in haze that can occur due to the generation and growth of this crystal part, the effect of heating that the extremely small voids (voids) that are normally present in the cellulose acylate film 11 disappear by high-temperature heating. Therefore, it is considered that the haze as the retardation film 17 is reduced.

  The temperature at which the cellulose acylate film 11 is heated to reach the crystallization temperature Tc is terminated at the temperature holding start position P1, the temperature equal to or higher than the crystallization temperature Tc, that is, the temperature is lowered to the crystallization temperature. The position where the temperature is lower than Tc is referred to as a temperature holding end position P2. In the present embodiment, a plurality of non-contact temperature detecting means are provided along the transport path of the cellulose acylate film 11, the temperature of the transported cellulose acylate film 11 is measured at a plurality of positions, and the cellulose acylate film 11 is measured. However, the present invention is not limited to this method. For example, the relationship between the temperature of the air from the air duct 26 and the rising temperature per unit time of the cellulose acylate 11 by this air, that is, the temperature increasing speed, is obtained in advance, and the temperature and flow rate of the air from the air duct 26 The temperature holding start position P1 can be obtained from the relationship with the traveling speed of the clip 13.

  The crystallization temperature Tc includes both a temperature rising crystal and a temperature falling crystal, and the crystallization temperature Tc when the heating step is started is a temperature in the temperature rising crystal. The temperature of the temperature rising crystal can be determined by differential scanning calorimetry according to JIS K7121. Although the temperature holding start position P1 is displaced depending on the temperature and flow rate of air from the air duct 26 (see FIG. 1), it is preferable to displace the temperature holding end position P2 from the viewpoint of ease of displacement. For example, when the haze of the cellulose acylate film 11 is difficult to be reduced, the temperature and the air volume of the air from the air duct 26 are set so that the temperature holding end position P2 is on the downstream side as compared with the case where the haze is not easily reduced. Good.

The distance from the temperature holding start position P1 to the temperature holding end position P2 can be determined by the following methods (1) to (3), for example. However, the method is not limited to this method.
(1) Sampling is performed from the cellulose acylate film 11 to be the retardation film 17, and the sample is heated to a temperature equal to or higher than Ts. After heating, the haze is measured. In this way, the relationship between the temperature holding time and the haze is obtained in advance, and the distance from the temperature holding start position P1 to the temperature holding end position P2 is obtained from this relationship and the moving speed of the clip 13. In this case, it is more preferable to obtain the relationship between haze and temperature holding time with a sample stretched in one direction and spread after holding the temperature at Tc or higher.
(2) A light source that emits light toward the phase difference film 17 and a light source that is opposed to the light source through the phase difference film 17 are provided in the conveyance path on the downstream side of the clip tenter 18. The transparency of the retardation film 17 is measured by the light receiving unit to be measured, and the distance from the temperature holding start position P1 to the temperature holding end position P2 is determined according to the difference from the target transparency. If the target transparency is not reached, the distance between the positions P1 and P2 is set longer. In addition, when using this method, it is preferable to obtain | require previously the relationship between the target haze and the transparency calculated | required by the said light source and light-receiving part.
(3) Sampling is performed from the cellulose acylate film 11 to be the retardation film 17, and this sample is heated to Tc or more. The heated sample is subjected to differential scanning calorimetry (DSC) to check whether the crystallization temperature Tc is detected. When detected, the other samples are heated so that the temperature holding time becomes longer. Then, the temperature holding time is extended to such an extent that the crystallization temperature Tc is not recognized. That is, the temperature holding time at which the crystallization temperature Tc is not recognized is obtained, and the distance between the positions P1 and P2 is determined by this and the moving speed of the clip 13.

  The time for maintaining the temperature of the cellulose acylate film 11 at the crystallization temperature Tc or higher is preferably in the range of 3 seconds to 3 minutes. And it is preferable that this time continues. When the time is shorter than 3 seconds, the microscopic voids (voids) normally present in the cellulose acylate film 11 do not disappear, and therefore a retardation film having a haze of 0.5 or less cannot be obtained. There is. When the cellulose acylate film 11 contains fine particles such as silica, the haze reduction effect is noticeable by keeping the time of 3 seconds or more continuously at the crystallization temperature Tc or higher. Even if it is longer than 3 minutes, the possibility of further increase in the haze reduction effect is extremely thin, so there is almost no need to keep the temperature continuously for longer than 3 minutes. When the time is longer than 3 minutes, Re may not be increased to 40 nm or more.

  The upper limit value of the temperature to be held (hereinafter referred to as the holding temperature) is not particularly limited except for the point of considering the thermal degradation of cellulose acylate and the type of additive contained in cellulose acylate film 11. When the additive cannot be identified, the upper limit value may be Tc + 50 ° C. That is, the holding temperature of the cellulose acylate film 11 in the heating step is preferably in the range of Tc or more (Tc + 50 ° C.). In addition, as long as it exists in this range continuously for the above-mentioned time, holding temperature does not need to be constant and may change. That is, the temperature of the cellulose acylate film 11 in the conveyance section from the temperature holding start position P1 to the temperature holding end position P2 may change within the above temperature range.

  Since the crystallization temperature Tc of the cellulose acylate varies depending on the type of acyl group and the acyl group substitution degree, it is preferable to actually measure the crystallization temperature Tc for each cellulose acylate film 11 to be used. However, the cellulose acylate film 11 may be heated so as to reach 190 ° C. in the heating step without actually measuring, and the holding temperature is preferably in the range of 190 ° C. or higher and 240 ° C. or lower, and 200 ° C. or higher and 220 ° C. or lower. It is more preferable to set the temperature within a range of ° C. If the holding temperature is lower than 190 ° C., for example, depending on the type of cellulose acylate and the properties of the cellulose acylate film 11, the effect of reducing haze may not be sufficiently obtained. That is, it cannot be said that there is no case where the haze is larger than 0.5. On the other hand, when the holding temperature is higher than 240 ° C., the low molecular compound additive contained in the cellulose acylate film 11 may be vaporized, and when the holding temperature is higher than 250 ° C., the cellulose acylate is decomposed. It may end up.

  Besides cellulose acetate (TAC) in which the crystallization temperature Tc is detected, some cellulose acylates do not detect the crystallization temperature Tc due to the type of acyl group. Examples of such cellulose acylate include cellulose acetate propionate (CAP) having both an acyl group and a propionyl group as acyl groups. It has not been confirmed whether CAP has a lower melting point than TAC and is partially crystallized. However, even in the case of cellulose acylate in which the crystallization temperature Tc is not detected in this way, a heating step is performed, and the cellulose acylate film 11 may be heated to reach 190 ° C. in this heating step, and the holding temperature is It is preferable to set it as the range of 190 to 240 degreeC, and it is more preferable to set it as the range of 200 to 220 degreeC.

  In order to maintain the temperature of the cellulose acylate film 11 in the above range, the air from the air duct 26 is maintained so that the temperature of the transport path of the cellulose acylate film 11 is maintained in the range of 190 ° C. or higher and 240 ° C. or lower. It is preferable to control the temperature and flow rate.

  The heating step is preferably carried out without widening the cellulose acylate film 11, that is, with non-widening, and more preferably with the width kept constant. That is, it is most preferable to run the clip 13 so as to keep the first width L1 at the holding start position P2 constant without increasing or decreasing the width (decreasing the width). In FIG. 2, reference numeral KL represents the position of the cellulose acylate film 11 held by the clip 13 on the most central side in the width direction of the cellulose acylate film 11, and the cellulose acylate film 11. The width of the retardation film 17 is the distance between the holding target lines KL on both sides.

  In the clip tenter 18, a widening step is performed in which the cellulose acylate film 11 that has passed through the heating step is widened while being held at a temperature lower than Tc or lower than 190 ° C. The position at which widening is started is referred to as widening start position P3, and the position at which widening ends is referred to as widening end position P4. Prior to this widening step, it is more preferable to carry out a temperature lowering step for lowering the temperature of the cellulose acylate film 11 after the heating step to a temperature lower than Tc. This is because the widening is preferably started after the temperature of the cellulose acylate film 11 becomes lower than Tc, and it is preferable in terms of production efficiency that the widening start position P3 is as upstream as possible. .

  By setting the temperature of the air from the air duct 26 in the conveyance path downstream of the temperature holding end position P2 lower than that on the upstream side of the temperature holding end position P2, the temperature lowering step can be performed.

  By this temperature lowering step, the temperature of the cellulose acylate film 11 is lowered to a temperature lower than Tc. When the temperature in the temperature rising crystal and the temperature in the temperature falling crystal are different from each other with respect to the crystallization temperature of the cellulose acylate, the temperature in the temperature rising crystal may be regarded as Tc as in the heating step.

  When the glass transition point of the cellulose acylate contained in the cellulose acylate film 11 is defined as Tg, the temperature of the cellulose acylate film 11 is maintained in a range higher than Tg and lower than Tc in the widening step which is a subsequent step. Since it is preferable to widen in a state, it is preferable to adjust the temperature of the cellulose acylate film 11 with air from the air duct 26 so that the cellulose acylate film 11 is in a temperature range higher than Tg and lower than Tc. Tg can be measured by differential scanning calorimetry according to JIS K7121.

  If these are not measured in advance, such as when Tg and Tc cannot be measured, the temperature of the cellulose acylate film 11 may be lowered so as to be higher than 150 ° C. and lower than 190 ° C. in the temperature lowering step. More preferably, the temperature is in the range of 160 ° C. or higher and 180 ° C. or lower. This is because at 190 ° C. or higher, even if the widening step is performed, the retardation may not rise to a sufficient extent to be used as a retardation film. On the other hand, when the temperature of the cellulose acylate film 11 is lowered to a temperature lower than 150 ° C. and the process proceeds to the widening process as it is, the cellulose acylate film 11 may be torn due to the application of tension in the widening process, or the phase difference. The effect of the heating process described above may be diminished, such as an increase in the haze of the film 17. Therefore, in the temperature lowering step, heating by blowing air from the blowing duct 26 may be performed so that the temperature is not lower than 150 ° C.

  The position at which the temperature of the cellulose acylate film 11 reaches Tc is measured by measuring the temperature of the cellulose acylate film 11 conveyed by non-contact temperature detecting means provided in plural along the conveyance path of the cellulose acylate film 11. , And this can be set as the temperature lowering end position P5, but is not limited to this method. For example, as in the case of obtaining the temperature holding start position P1, the relationship between the temperature of the air from the air duct 26 and the descending temperature per unit time of the cellulose acylate 11 by this air, that is, the temperature descending speed, is obtained in advance. The temperature lowering end position P5 can be obtained from the relationship between the temperature and flow rate of air from the air duct 26 and the traveling speed of the clip 13.

  Similarly to the heating step, it is preferable that the temperature lowering step is not widened and the first width L1 is maintained.

  The cellulose acylate film 11 that has been subjected to a temperature lowering step and having a temperature lower than Tc, preferably 150 ° C. or higher and 190 ° C. or lower, is subjected to a widening step for developing a retardation value as the retardation film 17. During the widening step, it is more preferable to keep the temperature of the cellulose acylate film 11 in the above temperature range and keep it in the range of 160 ° C. or higher and 180 ° C. or lower. Thereby, both the increase of the retardation value in the case of widening with the below-mentioned widening rate and the effect of preventing the cellulose acylate film 11 from tearing are further improved.

  The width of the retardation film 17 obtained by the widening step, that is, the width of the retardation film 17 at the widening end position P4 is referred to as a second width L2. The widening is preferably performed so that the widening ratio obtained by L2 / L1 is 1.1 or more, that is, L2 ≧ 1.1 × L1. The widening is more preferably performed so that 2.0 × L1 ≧ L2 ≧ 1.1 × L1, and more preferably 1.7 × L1 ≧ L2 ≧ 1.1 × L1. When the widening ratio is smaller than 1.1, the retardation value, particularly Re, may not be sufficiently high as a retardation film even when a retardation increasing agent is used. On the other hand, if the widening ratio is larger than 2.0, the temperature of the cellulose acylate film 11 may have to be increased to Tc or more in order to prevent the cellulose acylate film 11 from being torn, Even when a retardation increasing agent is added, the retardation may not be sufficiently increased.

  By carrying out the above heating step and the widening step after the heating step on the cellulose acylate film, a retardation film having a low haze of 0.5 or less despite a high retardation of 40 or more. It can be made from a cellulose acylate film. The obtained retardation film further has a high Rth of 70 or more.

  According to the above method, regardless of whether or not the cellulose acylate film 11 is widened in the solution casting process, that is, even if a non-widened cellulose acylate film 11 is used, high Re and low haze are used. Can be produced. Further, in the case of performing the widening of the predetermined condition even in the solution casting process, the haze is lowered and the heating process for reducing the haze is performed, thereby causing the widening in the solution casting process. Therefore, a retardation film having improved dimensional stability, that is, a smaller dimensional change rate can be produced. Below, it demonstrates per aspect combined with the solution casting process.

[Dope raw material and production method]
When the cellulose acylate film 11 is produced by a solution casting method, a dope in which cellulose acylate is dissolved in a solvent is produced. The aforementioned various additives are also included in this dope.

  Liquids that dissolve cellulose acylate and become a solvent component of the dope include aromatic hydrocarbons (eg, benzene, toluene, etc.), halogenated hydrocarbons (eg, dichloromethane, chlorobenzene, etc.), alcohols (eg, methanol, ethanol, etc.) , N-propanol, n-butanol, diethylene glycol, etc.), ketones (eg, acetone, methyl ethyl ketone, etc.), esters (eg, methyl acetate, ethyl acetate, propyl acetate, etc.) and ethers (eg, tetrahydrofuran, methyl cellosolve, etc.). Illustrated. Some additives may be used without being dissolved in these additives.

  Among the above solvents, halogenated hydrocarbons having 1 to 7 carbon atoms are preferable, and dichloromethane is most preferable. And from the viewpoints of the solubility of cellulose acylate, the peelability of the cast film from the casting support, the mechanical strength of the retardation film, the optical properties of the retardation film, etc., the alcohol having 1 to 5 carbon atoms It is preferable to use one or several of these in a mixture with dichloromethane. At this time, the content of the alcohol is preferably 2% by weight to 25% by weight and more preferably 5% by weight to 20% by weight with respect to the whole solvent. Preferable specific examples of the alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol, etc. Among them, methanol, ethanol, n-butanol, or a mixture thereof is preferably used.

  For the purpose of minimizing the influence on the environment, the dope may be manufactured without using dichloromethane. As the solvent in this case, an ether having 4 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms, and an ester having 3 to 12 carbon atoms are preferable, and these may be appropriately mixed and used. These ethers, ketones and esters may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —O—, —CO— and —COO—) can also be used as a solvent. The solvent may have another functional group such as an alcoholic hydroxyl group in the chemical structure.

  Various additives and solvents are described in detail in paragraphs [0196] to [0516] of JP-A-2005-104148, and the various additives and solvents described therein are also applicable to the present invention. Can do.

  The manufacturing method of the dope to be cast is not particularly limited, and a known manufacturing method may be applied. However, in the case of the so-called cooling casting in which the cast film made of the cast dope is solidified by cooling and stripped, the cellulose is more than the dope in the case of the so-called dry casting in which the cast film is dried and stripped. It is preferable to manufacture the dope so that the concentration of solids such as acylate is high. As a method for increasing the solid content concentration, a so-called flash concentration method is preferably used. The flash concentration method is a method in which a dope having a concentration lower than a target concentration is once produced and a part of the solvent is evaporated by blowing out the dope 51 with a known flash device.

  The dope to be cast preferably has a cellulose acylate concentration of 5 to 40% by weight, more preferably 15 to 30% by weight, and more preferably 17 to 25% by weight. The following range is more preferable.

[Film production equipment and method]
FIG. 3 is a schematic view of a production facility for the retardation film 17 including a solution casting part. In the retardation film manufacturing facility 50 in FIG. 3, the same devices and members as those in the retardation film manufacturing facility 10 in FIG.

  The phase difference film manufacturing facility 50 includes a solution film forming unit 52 that forms the cellulose acylate film 11 from the dope 51, and an optical control unit 53 that uses the cellulose acylate film 11 obtained by the solution film forming unit 52 as the phase difference film 17. With. The retardation film manufacturing facility 50 is provided with a solution film forming section 52 instead of the delivery device 12 of the retardation film manufacturing facility 10 of FIG. That is, the clip tenter 18 of the retardation film manufacturing facility 10 is connected to the downstream side of the solution film forming unit 52, and the optical control unit 53 is downstream from the clip tenter 18.

  A casting film 58 for forming a casting film 56 by casting the dope 51 and a wet film 57 containing a solvent, and both end portions of the wet film 57 are held in the solution casting part 52. The clip tenter 62 that widens the wet film 57 by being held by the clip 61, the edge cutting device 87 that cuts off both end portions of the wet film 57, and the wet film 57 that is spread over a plurality of rollers 66 and dried. Thus, a drying chamber 67 serving as the cellulose acylate film 11 is sequentially provided from the upstream side.

  In the casting chamber 58, a casting die 71 that continuously flows out the guided dope 51, an endless band 72 that is provided to face the dope outlet of the casting die 71, and a band 72 are passed over. And two backup rollers 73 for continuously running the same.

  A temperature controller (not shown) for controlling the temperature of the casting die 71 is attached to the casting die 71 so that the temperature of the dope 51 flowing out toward the band 72 is maintained at a predetermined temperature. At least one of the two backup rollers 73 is rotated in the circumferential direction by a driving means (not shown). By continuously flowing out the dope 51 from the casting die 71 onto the traveling band 72, the dope 51 is cast on the band 72 to form a casting film 56.

  The backup roller 73 is provided with a heat transfer medium circulation device 76 that supplies a heat transfer medium having a predetermined temperature to the backup roller 73 and controls the peripheral surface temperature of the backup roller 73. A flow path (not shown) for the heat transfer medium is formed inside the backup roller 73, and the peripheral surface temperature of the backup roller 73 is set to a predetermined value by passing the heat transfer medium through the flow path. The temperature of the band 72 that is held at the value and contacts the backup roller 73 is controlled. The temperature of the band 72 is appropriately set according to the type of solvent, the type of solid component, the concentration of the dope 51, and the like.

  A decompression chamber 77 for sucking air is provided on the upstream side of the casting die 71 in the traveling direction of the band 72. By sucking air by the decompression chamber 77, the upstream area of the dope 51 that has flowed out as a bead is decompressed to a pressure lower than that of the downstream area.

  The casting chamber 58 is provided with a temperature control device 78 for keeping the internal temperature at a predetermined value, and a condenser (condenser) 81 for condensing and recovering the solvent evaporated from the dope 51 and the casting film 56. It is done. A recovery device 82 for recovering the condensed and liquefied solvent is provided outside the casting chamber 58.

  The clip tenter 62 provided downstream of the casting chamber 58 has the same configuration as the clip tenter 18 of the optical control unit 53. That is, the clip tenter 62 extends in the transport direction of the wet film 57, and the temperature-controlled air is supplied to the wet film 57. Are provided with a blower duct 83 for sending air from above and a blower 86 for sending air to the blower duct 83.

  The ear clip device 87 has the same configuration as the ear clip device 21 of the optical control unit 53, and cuts out both sides of the wet film. The ear-cutting device 87 includes a crusher 88 for finely cutting the side edge scraps of the wet film 17 that has been cut off.

  An adsorption recovery device 91 that adsorbs and recovers the solvent evaporated from the wet film 57, that is, the solvent gas, is connected to the drying chamber 67.

  Next, an example of a method for manufacturing the retardation film 17 by the retardation film manufacturing facility 50 will be described. The dope 51 is cast from a casting die 71 to a band 72 cooled by a heat transfer medium. The temperature of the dope 51 at the time of casting is preferably constant in the range of 30 to 35 ° C., and the surface temperature of the band 72 is preferably constant in the range of 35 to 40 ° C. The temperature of the casting chamber 58 is preferably set to 30 ° C. to 35 ° C. by the temperature control device 78. The solvent evaporated inside the casting chamber 58 is recovered by the recovery device 82 and then regenerated and reused as a solvent for dope production.

  A casting bead is formed from the casting die 71 to the band 72, and a casting film 56 is formed on the band 72. In order to stabilize the state of the casting bead, the upstream area of the bead is controlled by the decompression chamber 77 so as to have a predetermined pressure value. The pressure in the upstream area with respect to the bead is preferably 2000 Pa to 10 Pa lower than the downstream area. It is preferable to attach a jacket (not shown) to the decompression chamber 77 so that the internal temperature is kept at a predetermined temperature. This temperature is preferably equal to or higher than the condensation point of the dope solvent.

  The cast film 56 is dried to a degree sufficient to peel off the band 72. Drying can be performed by providing an air duct (not shown) in the vicinity of the band 72 and sending air from the air duct to the casting film 56. The stripping is performed by pulling the wet film 57 from the downstream side of the band 72 and supporting the wet film 57 by a roller 92 provided in the conveyance path. The solvent residual ratio of the cast film at the time of peeling is preferably 20% or more and 100% or less. In this specification, the solvent residual ratio (unit:%) is a value based on the dry amount, and specifically, when the weight of the solvent is x and the weight of the casting film 56 is y, {x / (y −x)} × 100.

  When the wet film 57 peeled off from the band 72 in a state containing the solvent is guided by the clip tenter 62, both end portions thereof are held by the clips 61 as holding means and conveyed downstream. During this conveyance, the wet film 57 is recommended to be dried by the air sent from the air duct 83.

  The temperature of the wet film 57 is controlled by the air that flows out from the air duct 83. The slit of the air duct 83 is provided in the vicinity of the conveyance path of the wet film 57, and the temperature of the air that flows out and the temperature of the wet film 57 may be regarded as the same temperature. The temperature of the wet film in the clip tenter 62 will be described later with reference to another drawing.

  In the clip tenter 62, the residual solvent rate of the wet film 57 gradually decreases as the wet film 57 advances downstream. Therefore, air having a higher temperature may be sent out from the blower duct 83 so that the temperature of the wet film 57 becomes higher as it goes downstream. The wet film 57 is further dried by the clip tenter 62 until the solvent residual rate reaches 10%. Therefore, even if the solvent residual ratio becomes lower than 10%, the clip tenter 62 may continue drying.

  In the clip tenter 62, the wet film 57 is pulled in the width direction. The wet film 57 may shrink in the width direction as the solvent decreases, that is, the wet film 57 may shrink. However, the clip tenter 62 may perform any one of the contraction width, the width maintenance, and the widening, as will be described later. Moreover, it is more preferable to carry out the widening step under predetermined conditions.

  In the case of carrying out cooling casting instead of dry casting, it is preferable to use a known so-called pin tenter in which the holding means is a pin instead of the clip tenter 62.

  The wet film 57 from the clip tenter 62 is cut and removed by the edge-cutting device 87 at both side ends held by the pins. The separated both ends are sent to a crusher 88 by a cutter blower (not shown). The crusher 88 pulverizes the side edges to form chips. Since this chip is reused for dope manufacturing, the raw material can be effectively used.

  On the other hand, the wet film 57 from which both end portions have been cut off is sent to the drying chamber 67 and further dried. This drying is performed until the solvent residual rate reaches 2%, that is, until the solvent residual ratio is in the range of 0 to 2%, and the cellulose acylate film 11 is obtained by this drying. In the drying chamber 67, the wet film 57 is conveyed while being wound around the roller 66. Although the internal temperature of the drying chamber 67 is not specifically limited, It is preferable to set it as 50-160 degreeC. The drying chamber 67 is more preferably divided into a plurality of sections in the transport direction of the wet film 57 in order to change the blowing temperature. In addition, when a preliminary drying chamber (not shown) is provided between the ear opener 87 and the drying chamber 67 to preliminarily dry the retardation film 17, the temperature of the retardation film 17 may rapidly increase in the drying chamber 67. Therefore, the change in the shape of the wet film 57 in the drying chamber 67 can be suppressed.

  The solvent gas generated by evaporation in the drying chamber 67 is adsorbed and recovered by the adsorption recovery device 91. The air from which the solvent component has been removed is sent again as dry air into the drying chamber 67.

  The cellulose acylate film 11 having a solvent residual ratio in the range of 0 to 2% is sent to the clip tenter 18 of the optical control unit. And the retardation film 17 is manufactured through the process similar to the case where the retardation film manufacturing equipment 10 of FIG. 1 is used.

  From casting die, decompression chamber, support structure, peeling method, stretching, drying conditions for each process, handling method, curling, winding method after flatness correction, solvent recovery method, film recovery method, etc. The details are described in paragraphs [0617] to [0889] of JP-A-2005-104148, and these descriptions can be applied to the present invention.

  FIG. 4 is an explanatory view of the wet film 57 from when the clip tenter 62 starts to be held by the clip 61 (see FIG. 3) until it is released. The arrow line Y is the conveyance direction of the wet film 57. In the clip tenter 62, tension is applied to the wet film 57 in the width direction indicated by the arrows X1 and X2. In the clip tenter 62, a position where the clip 61 starts to be held is a holding start position PS, a position where the holding is released is a holding releasing position PE, and a position where the clip 72 is peeled off from the band 72 is a peeling position PP. The inlet of the clip tenter 62 is on the upstream side of the holding start position PS, and the outlet is on the downstream side of the holding release position PE, but the illustration is omitted in FIG.

  The solvent gradually evaporates from the wet film 57 until it reaches the holding start position PS after being peeled off from the band 72 at the stripping position PP, and further evaporated by the outflow of dry air from the air duct 83 in the clip tenter 62. The solvent residual ratio of the wet film 57 is further lowered. The position at which the solvent residual ratio is 60% by weight is defined as the 11th position P11, and the position at which 10% by weight is defined as the 12th position P12.

  In the clip tenter 62, the wet film 57 is held at a temperature lower than the crystallization temperature Tc and dried. The temperature of the wet film 57 in the clip tenter 62 is more preferably constant in the range of 100 ° C. to 160 ° C., and more preferably in the range of 110 ° C. to 150 ° C.

  As described above, the clip tenter is more preferably widened. However, this widening is performed in the range where the solvent residual ratio is 60% or more and 10% or less. That is, it is carried out on the transport path from the eleventh position P11 to the twelfth position P12. Hereinafter, this process is referred to as a drying widening process. The thirteenth position P13, which is the start position of the dry widening process, is the same as the eleventh position P11 or between the eleventh position P11 and the twelfth position P12, and the fourteenth position P14, which is the end position of the dry widening process, It is the same as the twelfth position P12 or between the thirteenth position P11 and the twelfth position P12.

  The width of the wet film 57 at the thirteenth position P13 is the third width L3, and the width at the fourteenth position is the fourth width L4. Here, FIG. 4 shows a mode in which the width of the wet film 57 is kept constant from the holding start position PS to the thirteenth position P13. In the drying and widening step, it is preferable to widen so that the widening ratio obtained by L4 / L3 is 1.1 or more, that is, L4 ≧ 1.1 × L3. The widening is more preferably performed so that 1.5 × L3 ≧ L4 ≧ 1.1 × L3, and further preferably 1.4 × L3 ≧ L4 ≧ 1.1 × L3.

  By performing this dry widening step in addition to the widening step in the optical control unit 53, the haze of the obtained retardation film 17 becomes lower, and the effect that the dimensional stability is further improved is obtained. This dimensional stability is in an environment where the temperature is 60 ° C. and the relative humidity is 90%.

  When this dry widening step is performed, the widening rate in the widening step in the clip tenter 18 of the optical control unit 53 can be further reduced. Then, when the widening ratio for expressing the predetermined Re is RA, the widening ratio in the widening step is higher than when the widening ratio L2 / L1 in the widening step is RA without performing the dry widening step. It is preferable that both L2 / L1 and the drying widening step L4 / L3 are larger than zero so that L2 / L3 becomes RA as a result. Thereby, even if Re value is equal, the retardation film 17 more excellent in the low haze and dimensional stability can be produced.

  By performing the drying and widening step at the timing and the widening rate as described above, the haze of the retardation film 17 can be further reduced and the dimensional stability can be improved.

  In this embodiment, the wet film 57 is dried in the clip tenter 62 and the drying chamber 67 so that the residual solvent ratio is 2% or less. Furthermore, in the present embodiment, two clip tenters 62 and 18 are used, but this is used as one clip tenter, and the drying process of the wet film is performed in one clip tenter without using the drying chamber 67. The drying and widening step included in the drying step, the heating step after the drying step, and the widening step may be performed.

  Moreover, although this embodiment has mentioned what connects the solution film-forming part 52 and the optical control part 53, and implements a drying process and a heating process continuously, it is not limited to this. For example, the cellulose acylate film 11 obtained in the solution casting part 52 is once wound up by a winding device, and the retardation film 17 is manufactured by the retardation film manufacturing facility 10 of FIG. Can do.

  The present invention has both the effects of haze suppression and dimensional stability when a retardation film having Re of 40 nm or more and 100 nm or less is produced according to the above aspect, and when Re is made of a retardation film of 40 nm or more and 60 nm or less. More effective. Specifically, the haze can be kept low to 0.5 or less, and further to 0.3 or less, and for dimensional stability, the dimensional change rate in the longitudinal direction of the retardation film is −0.3 to The rate of dimensional change in the width direction can be suppressed to a range of about −0.2 to +0.2 to a range of about +0.3. In addition, the present invention satisfies the above-mentioned haze and dimensional stability, and can produce a retardation film having an Rth in the range of 70 nm to 250 nm, more reliably a retardation having an Rth of 110 to 120 nm. You can make a film.

  Furthermore, in the present invention, a retardation film satisfying the above-mentioned Re, haze, and dimensional stability can be more easily obtained by using a retardation increasing agent, even if the widening rate in the widening step and the dry widening step is set smaller. Can be manufactured.

  The present invention is particularly effective when a retardation film having a width of 1400 mm to 2500 mm, particularly 1800 mm to 2500 mm, and particularly when a thin retardation film having a thickness of 20 μm to 60 μm is manufactured. effective.

A dope 51 having the following formulation was made. Solid content concentration is 19.4% by weight Cellulose acylate 100 parts by weight (Substitution degree 2.81 cellulose triacetate, viscosity average polymerization degree 305.6%, dichloromethane solution 6% by weight viscosity 350 mPa · s)
Dichloromethane (first component of solvent) 403 parts by weight Methanol (second component of solvent) 60.2 parts by weight Retardation increasing agent shown in Chemical formula 7.4 parts by weight Triphenyl phosphate 7.9 parts by weight Biphenyl diphenyl phosphate 3.9 Parts by weight

  A dope 51 was also prepared in which the amount of the retardation increasing agent was changed to 5.4 parts by weight.

  Using the dope 51, a retardation film was produced by the retardation film production equipment 50 so as to have the thickness shown in Table 1 under 12 different conditions. The production speed is 50 m / min. Each condition is shown in Table 1. “Experiment” is an embodiment of the present invention, and “comparative experiment” is a comparative example for the present invention. In addition, Experiment 1 to Experiment 3, Experiment 5 to Experiment 8, and Comparative Experiment 1 use a dope having an amount of a retardation increasing agent of 7.4 parts by weight, and other experiments and comparative experiments have an amount of the retardation increasing agent. The dope which is 5.4 weight part was used.

  The dope 51 was sent to the solution casting part 52 with a gear pump, and the resulting cellulose acylate film was wound up. The cast film was peeled off when the solvent residual ratio was 40%. And this cellulose acylate film was used as the phase difference film with the phase difference film manufacturing equipment 10.

  In both experiments and comparative experiments, the solvent residual ratio at the thirteenth position P13 is 45%, and the solvent residual ratio at the fourteenth position P14 is 25%. In the drying chamber 67, drying was performed until the solvent residual ratio became 0.2% or less, and this was wound up. When the glass transition point Tg and the crystallization temperature Tc of this cellulose acylate film were measured, the Tg was 126 ° C. and the Tc was 187 ° C.

  The wound cellulose acylate film was guided to the clip tenter 18 by the delivery device 12. And the heating process was implemented about the experiment except the comparative experiment 1, and a comparative experiment. The temperature in the “heating step” column of Table 1 is the temperature of the cellulose acylate film in this heating step. The implementation time of the heating process is 5 seconds. Moreover, the solvent residual ratio in the widening start position P1 is 0.2%. Next, the widening process was implemented about the experiment except the comparative experiment 1, and a comparative experiment.

The “widening rate” of “drying widening step” in Table 1 is a value of L4 / L3, and the “widening rate” of “widening step” is a value of “L2 / L1”. The “temperature” in the “drying widening step” and the “widening step” means the temperature of the wet film and the temperature of the cellulose acylate film, respectively.
“Wait rate” is expressed as the ratio of the tenter outlet film width to the tenter inlet film width in each stretching step. In addition, description of "-" in each column of Table 1 means that the corresponding process was not performed.

  And about 12 types of obtained retardation films, haze, Re, Rth, and the dimensional-change rate were evaluated.

The haze (unit:%) was sampled from each retardation film at a size of 40 mm × 80 mm, and each sample was subjected to JIS K-6714 with a haze meter (model: HGM-2DP, Suga test machine) at 25 ° C. and 60% RH. Measured and evaluated according to the following criteria.
◎: Very good at 0 or more and 0.3 or less ○;

The dimensional change rate was evaluated in both the longitudinal direction and the width direction of the retardation film. First, 30 mm × 120 mm is sampled from each retardation film, and two samples to be evaluated are prepared. One of the two is obtained by cutting the obtained long retardation film at 120 mm in the longitudinal direction and 30 mm in the width direction, and the other is cut at 30 mm in the longitudinal direction and 120 mm in the width direction. It is. Then, humidity was adjusted for 24 hours at 25 ° C. and 60% RH, and with a pin gauge (EF-PH manufactured by Mitutoyo Corporation), two holes with a diameter of 6 mm were opened at both ends in a direction of 120 mm at intervals of about 100 mm, The distance between the holes is L20. A sample was made by ESPEC temp. & Humid. The distance (L21) between the holes after the treatment for 24 hours at 60 ° C. and 90% RH is measured with a chamber PR-45. The dimensional change rate is a value measured up to a minimum scale of 1/1000 mm in all distance measurements. And the dimensional change rate of each sample can be calculated | required by a following formula.
Dimensional change rate of 60 ° C. and 90% RH = {(L20−L21) / L20} × 100

  The dimensional change rate can be evaluated as good when it is in the range of -0.3 to +0.3.

  A liquid crystal display device was produced by the following method using the respective retardation films obtained in the experiment of Example 1 and the comparative experiment.

[Preparation of polarizing plate]
A polyvinyl alcohol (PVA) film having a thickness of 80 μm is dyed by immersing it in an aqueous iodine solution having an iodine concentration of 0.05% by mass at 30 ° C. for 60 seconds, and then in an aqueous boric acid solution having a boric acid concentration of 4% by mass. The film was vertically stretched to 5 times the original length while being immersed for 2 seconds, and then dried at 50 ° C. for 4 minutes to obtain a polarizing film having a thickness of 20 μm.

  The retardation film obtained in Example 1 and a commercially available cellulose triacetate film (Fujitac TD80UL (manufactured by Fuji Photo Film Co., Ltd., haze 0.3%, thickness unevenness 0.7 μm)) at 1.5 mol / liter After dipping in a 55 ° C. aqueous sodium hydroxide solution, the sodium hydroxide was thoroughly washed away with water. Then, after being immersed in a diluted sulfuric acid aqueous solution at 0.005 mol / liter for 1 minute at 35 ° C., it was immersed in water to sufficiently wash away the diluted sulfuric acid aqueous solution. Finally, the retardation film and the cellulose triacetate film were sufficiently dried at 120 ° C.

  After a commercially available cellulose triacetate film subjected to saponification treatment as described above is bonded to one surface of the polarizing film using a polyvinyl alcohol-based adhesive, a retardation film subjected to saponification treatment as described above is also used. A polarizing plate was prepared by bonding to the other surface of the polarizing film. In addition, since the polarizing film, the retardation film, and the cellulose triacetate film are all produced in a roll form, the longitudinal directions of the roll films are parallel to each other and are continuously bonded. The retardation film disposed on the cell side of the polarizing film is bonded so that its slow axis and the transmission axis of the polarizer are parallel.

  An acrylic adhesive material was attached to the cell side surface of the produced polarizing plate, and a separate film was attached to the adhesive material. A protective film was attached to the surface opposite to the cell.

[Mounting on VA mode LCD panel]
The polarizing plates provided on both surfaces of the liquid crystal cell of the VA mode liquid crystal television (LC-37GX3W, manufactured by Sharp Corporation) were peeled off. And the created polarizing plate was affixed on each surface of the liquid crystal cell from which the polarizing plate was peeled off. At that time, the phase difference films produced in Experiments 1 to 8 of Comparative Example 1 and Comparative Experiments 1 to 4 are placed on the viewer side and the backlight side of the liquid crystal cell via an adhesive so that the retardation film is on the liquid crystal cell side. Twelve kinds of liquid crystal display devices were made by sticking them one by one. The experiment number and comparative experiment number in Table 2 indicate which experiment and comparative experiment of Example 1 the retardation film used was obtained. The crossed Nicols were arranged so that the transmission axis of the polarizing plate on the viewer side was in the vertical direction and the transmission axis of the polarizing plate on the backlight side was in the horizontal direction. Front contrast was obtained for the obtained liquid crystal display device. This front contrast is measured using a measuring machine (EZ-Contrast 160D, manufactured by ELDIM) at 25 ° C. and 60% RH, and the brightness in the white display state and the brightness in the black display state are measured. Obtained by calculating. Table 2 shows the values of the front contrast.

Furthermore, after standing at 60 ° C. and 90% for 500 hours, and further standing at 25 ° C. and 60% for 24 hours, the presence or absence of light leakage at the outer peripheral portion and corner portion of the display screen was evaluated by black display. did. The results are shown in Table 2. The “light leakage evaluation” column in Table 2 is a result of evaluation based on the following criteria.
“○”: No light leakage is visible at all “△”: Light leakage is slightly visible at the outer periphery and corners “X”: Light leakage is clearly visible at the outer periphery and corners

It is the schematic of the retardation film manufacturing equipment which implemented this invention. It is explanatory drawing which shows the holding state of the cellulose acylate film in a clip tenter. It is the schematic of retardation film manufacturing equipment containing a solution casting part. It is explanatory drawing which shows the holding state of the wet film in the clip tenter of a solution casting part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Phase difference film manufacturing equipment 11 Cellulose acylate film 17 Phase difference film 18 Tenta 50 Phase difference film manufacturing equipment 52 Solution film forming part 53 Optical control part 62 Clip tenter 67 Drying room

Claims (4)

A heating step of heating the cellulose acylate film so as to reach 190 ° C. while holding both sides of the long cellulose acylate film;
Widening step to widen the cellulose acylate film that has undergone the heating step in a state where the cellulose acylate film is maintained at a temperature of less than 190 ° C. to form a retardation film;
A method for producing a retardation film, comprising: When the width of the cellulose acylate film before the widening step is L1, the width after the widening step is L2, the crystallization temperature of the cellulose acylate is Tc, and the glass transition point is Tg,
2. The widening step includes widening the cellulose acylate film so that L2 ≧ 1.1 × L1 while maintaining the temperature in a range higher than Tg and lower than Tc. The method for producing a retardation film. A casting step in which the dope in which the cellulose acylate is dissolved in a solvent is continuously cast on a traveling support to form a casting film;
A peeling step of peeling off the casting film containing the solvent as a wet film from the support;
Drying the wet film until the solvent residual rate reaches 2% to form the cellulose acylate film;
The method for producing a retardation film according to claim 1, wherein: When the width of the wet film when the solvent residual ratio is 60% is L3, and the width when the solvent residual ratio is 10% is L4,
The said drying process has a drying widening process of widening the said wet film so that it may become L4> = 1.1 * L3, while a solvent residual rate reduces from 60% to 10%. The method for producing a retardation film.

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