JP2010271690A - Method for producing retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem when a film is produced from a ring structure-introduced acrylic polymer that the heat resistance of the film is improved but the film becomes brittle, the flexibility of the film intends to be deteriorated, the stretched film has flexibility but a uniaxial stretched film being a vertically-stretched film produced in an actual film formation line is torn easily and therefore the film is broken frequently during the time to transport the film and at a horizontal stretching step and the handleability of the film is poor in the film formation line. <P>SOLUTION: The method for producing a retardation film comprising the steps of: vertically stretching the film composed of the acrylic polymer to the flow direction of the film; and horizontally stretching the vertically-stretched film to the width direction thereof, in the concrete, includes the steps of: vertically stretching the film so that ¾Rth¾/¾R0¾ (wherein ¾Rth¾ is the absolute value of thickness retardation, and ¾R0¾ is the absolute value of in-plane retardation) becomes 0.6-2.0; and horizontally stretching the vertically-stretched film to the width direction thereof. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a method for producing a retardation film comprising an acrylic polymer. In particular, the present invention relates to a method for stably producing an acrylic polymer, which is generally considered to have low flexibility, as a retardation film having excellent optical properties without causing film breakage.
Specifically, in the longitudinal stretching step, the longitudinal value ratio (| Rth | / | R0 |) of the in-plane retardation R0 and the thickness retardation Rth is such that the longitudinal ratio is 0.6 or more and 2.0 or less. The present invention relates to a method for producing a sequential biaxially stretched retardation film, characterized by performing transverse stretching after stretching.

Acrylic polymers represented by PMMA are well known to have excellent optical properties, and have been applied to various applications as optical materials having high light transmittance, low birefringence, and low phase difference. . However, since an acrylic polymer has low retardation development performance, it is difficult to obtain a necessary retardation value even if it is stretched. Further, while the use environment of the liquid crystal display device becomes severe, the demand for heat resistance of the optical film has increased, but it is difficult to impart sufficient heat resistance to the stretched film of PMMA.
For this reason, studies have been made to improve the heat resistance by introducing various ring structures into the acrylic polymer. However, if the heat resistance is improved, the resin becomes brittle and the flexibility of the film tends to decrease. there were.
Thus, there is disclosed a retardation film that achieves both heat resistance and flexibility by subjecting a heat-resistant acrylic polymer film having various ring structures to longitudinal and transverse biaxial stretching (see Patent Document 1). ). However, although improvement in flexibility can be confirmed with a lab stretching machine, film breakage occurred during film transport before stretching or stretching in the actual machine, and it was difficult to stably obtain a long roll.
In the field of optical films, oven longitudinal stretching having an annealing zone as described in Patent Document 2 is common. This stretching method is generally a method of stretching in a long stretching zone while being heated in an oven. Unlike roll longitudinal stretching, it is free-end uniaxial stretching, so that it is easy to obtain an optically uniform one. . Furthermore, sequential biaxial stretching by oven longitudinal stretching + tenter transverse stretching is the mainstream in sequential biaxially stretched films (see Patent Document 3). However, heating in an oven is inferior in heat conduction compared to roll stretching conveyed while touching a heating roll, which is disadvantageous in terms of productivity and cost associated with the recent drop in the price of display image devices. In addition, a film that has been uniaxially stretched at the free end in the longitudinal direction of the oven is easy to tear in the flow direction of the film. Therefore, in the case of a low flexibility film such as an acrylic polymer, the longitudinal tearing during transverse stretching becomes remarkable. There was a problem that stable production was difficult.
Furthermore, Patent Document 4 introduces a sequential biaxially stretched film that combines longitudinal stretching and lateral stretching, and a method in which lateral stretching is performed at a higher temperature than longitudinal stretching. However, in this method, due to the heating in the tenter performed at a high temperature, a force that is drawn into the furnace of the tenter is applied to the film when the orientation imparted by the longitudinal stretching is relaxed. For this reason, a film having low flexibility such as an acrylic polymer has a problem that the film is frequently broken and stable production is difficult.
As a method of longitudinal stretching, there is a method called roll longitudinal stretching machine with respect to oven longitudinal stretching machine. This method shortens the interval between two stretching rolls having different peripheral speeds, passes several heating rolls arranged in front of the stretching section, heats the film, raises the temperature, It is the method of extending | stretching as extending | stretching temperature. According to this method, there is no need for a large heat-retaining furnace or heating furnace, which is advantageous not only in terms of equipment introduction, but also because the film is heated while in contact with the heating roll, so that it is more thermally conductive than heating in the oven. Is also advantageous. In other words, the production speed can be increased, and the productivity and cost are advantageous as the price of display image devices in recent years declines. However, the film suddenly thermally expands on the surface of the heating roll and wrinkles are generated, or the film floats from the roll and temperature unevenness occurs, which causes a disadvantage that the phase difference after stretching does not become uniform. .
On the other hand, as described in Patent Documents 5 and 6, attaching a device for blowing hot air to the heating roll of the roll longitudinal stretching machine, adding a mechanism for blowing hot air from the guide roll having a vent, etc. A method of modifying the device has been proposed. However, this method cannot take advantage of the advantage that the roll longitudinal stretching apparatus is lower in equipment cost than the oven longitudinal stretching apparatus.
As described above, in order to cope with the recent decline in the price of display image devices, a method of stably biaxially stretching a film having low flexibility such as an acrylic polymer into a retardation film in a stable and inexpensive manner. Although it was hoped for, it was not fulfilled at present.

JP 2005-162835 A JP 2003-131033 A JP-A-6-337313 JP 2006-309029 A JP-A-9-76343 Japanese Patent Laid-Open No. 9-230137

The inventors of the present invention, for example, have a tendency that, in an acrylic polymer into which various ring structures are introduced in order to improve heat resistance, the heat resistance is improved but the film becomes brittle and the flexibility of the film is lowered. In order to improve the flexibility, it has been confirmed that it is effective to perform longitudinal and transverse biaxial stretching.
However, if it is a stretched film, it has flexibility, but in the actual film production line, due to the ease of tearing the uniaxially stretched film after longitudinal stretching, film breakage frequently occurs during film transport and in the transverse stretching process, There was a problem with handling in the film production line.
Accordingly, the present inventors have developed a biaxially stretched phase difference film using an acrylic polymer having low flexibility, which cannot be achieved by the above-described conventional technology, with roll longitudinal stretching and tenter transverse, which are superior in terms of equipment. The inventors have found a method of producing by sequential biaxial stretching of the stretching and have arrived at the present invention.

In view of the above circumstances, the present inventors have studied the initial technology of film production, and as a result, the following method is used in a state where there is no problem with a biaxially stretched retardation film using an acrylic polymer having low flexibility. The manufacturing method which manufactures continuously for a long time was discovered.
That is,
[1] In a method for producing a retardation film, in which an acrylic polymer film is longitudinally stretched in the film flow direction and then laterally stretched in the film width direction, an in-plane retardation R0 and a thickness retardation Rth The successive biaxially characterized by stretching in the width direction of the film after longitudinal stretching so that the ratio of each absolute value (| Rth | / | R0 |) is 0.6 or more and 2.0 or less A method for producing a stretched retardation film.
[2] The method for producing a retardation film according to [1], wherein in the longitudinal stretching step, stretching is performed so that an in-plane retardation R0 is 50 to 500 nm.
[3] In the longitudinal stretching step, when the distance between the roll center on the inlet side and the roll center on the outlet side is defined as the stretching section length A and the film width before longitudinal stretching is B, A / B is 0.05 or more and 0.00. The method for producing a retardation film according to any one of [1] and [2], wherein the retardation film is 5 or less.
[4] The retardation according to any one of [1] to [3], wherein in the longitudinal stretching step, the film is stretched after being heated by contact with at least 5 hot rolls. A method for producing a film.
[5] The method for producing a retardation film as described in [4], wherein any one heating method selected from an IR heater, a ceramic heater, and a hot air heater is used in combination in the longitudinal stretching step.

  According to the present invention, a biaxially stretched retardation film using an acrylic polymer having low flexibility can be prepared by sequential biaxial stretching of roll longitudinal stretching and tenter transverse stretching, which are superior in terms of equipment. .

The present invention is described in detail below. In the present specification, the “main component” is intended to contain 50% by weight or more. In addition, “a to b” indicating the range indicates a range from a to b.
The method for producing a retardation film using the acrylic polymer of the present invention is effective for all acrylic polymers that can be formed into a film by a known method. The production method of the present invention is suitable for a retardation film having a film thickness of 5 μm to 600 μm, preferably 10 μm to 400 μm.
Next, the acrylic polymer used in the present invention will be described.
The acrylic polymer used in the present invention is a resin obtained by polymerizing acrylic acid, methacrylic acid and derivatives thereof as a main component and derivatives thereof. For example, the general formula (1)

(In the formula, R 1 and R 2 each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. Specifically, the organic residue is a linear or branched chain having 1 to 20 carbon atoms. Preferred examples of the compound (monomer) having a structure represented by a chain or cyclic alkyl group, acrylic acid, methacrylic acid and derivatives thereof include methyl (meth) acrylate, (meth ) Ethyl acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, n-hexyl (meth) acrylate, 2-chloroethyl (meth) acrylate, (Meth) acrylic acid 2-hydroxyethyl, (meth) acrylic acid 3-hydroxypropyl, (meth) acrylic acid 2,3,4,5,6-pentahydroxyexyl and (meth) acrylic acid Such as Le acid 2,3,4,5-hydroxypentyl and the like. Among these, only 1 type may be used and 2 or more types may be used together. Of these, methyl (meth) acrylate is most preferred because of its excellent thermal stability.
The acrylic polymer may be copolymerized with N-substituted maleimides such as phenylmaleimide, cyclohexylmaleimide and methylmaleimide from the viewpoint of heat resistance, or in the molecular chain (in the main skeleton or in the polymer). A lactone ring structure, a glutaric anhydride structure, a glutarimide structure, or the like may be introduced into the main chain). Especially, the structure which does not contain a nitrogen atom from the point of the difficulty of coloring (yellowing) of a film is preferable. Moreover, the thing which has a lactone ring structure in a principal chain from the point which is easy to express a positive birefringence (positive phase difference) is preferable. Regarding the lactone ring structure in the main chain, a 4- to 8-membered ring may be used, but a 5- to 6-membered ring is more preferable, and a 6-membered ring is particularly preferable in terms of the stability of the structure. As described above, examples of the case where the lactone ring structure in the main chain is a 6-membered ring include a general formula (2) described later and a structure represented in Japanese Patent Application Laid-Open No. 2004-168882. When synthesizing a polymer before introducing a lactone ring structure into the polymer, it is possible to obtain a polymer having a high polymerization yield, a polymer having a high content of lactone ring structure with a high polymerization yield, methyl methacrylate, etc. It is preferable that it is a structure represented by General formula (2) at a point with good copolymerizability with (meth) acrylic acid ester. Further, these acrylic polymers may have a unit obtained by copolymerizing other monomer components that can be copolymerized within a range not impairing heat resistance.

(In the formula, R 3, R 4 and R 5 each independently represents a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom.)
Specific examples of other monomer components that can be copolymerized include aromatic vinyl monomers such as styrene and α-methylstyrene, nitrile monomers such as acrylonitrile, vinyl esters such as vinyl acetate, and the like. Can be given. The weight average molecular weight of the above acrylic polymer is preferably in the range of 1,000 to 2,000,000, more preferably in the range of 5,000 to 1,000,000, and still more preferably 10, It is in the range of 000 to 500,000, particularly preferably in the range of 50,000 to 500,000.
As the method for producing the above acrylic polymer, JP-A-2005-146084, JP-A-2006-96960, JP-A-2006-171464, JP-A-2008-9378, JP-A-2008-231748. What is necessary is just to superpose | polymerize the monomer composition containing (meth) acrylic acid ester using well-known methods, such as a gazette.
Moreover, you may use together the other thermoplastic resin which can be used together with the acrylic polymer used for this invention. As another thermoplastic resin that can be used in combination, a thermoplastic resin that is thermodynamically compatible with the acrylic polymer is preferable. For example, a copolymer containing a vinyl cyanide monomer unit and an aromatic vinyl monomer unit, specifically 50 wt.% Of an acrylonitrile-styrene copolymer, a polyvinyl chloride resin, or a methacrylic ester. % Or more of the polymer. In addition, it can be confirmed by measuring the glass transition point of the thermoplastic resin composition obtained by mixing these that the acrylic polymer and the other thermoplastic resin are thermodynamically compatible. it can. Specifically, only one point of the glass transition point measured by the differential scanning calorimeter is observed for the mixture of the lactone ring-containing polymer and the other thermoplastic resin, so that the thermodynamic compatibility is achieved. I can say that.
In addition, the acrylic polymer used in the present invention includes UV absorbers, antioxidants, lubricants and plasticizers, malleability improvers such as rubber particles, mold release agents, and coloring, as long as the object of the present invention is not impaired. An additive such as a colorant such as an inhibitor, a flame retardant, an antistatic agent, and a pigment may be optionally added. However, in light of the characteristics required by the application to be applied, it is necessary to add in a range that does not adversely affect the purpose.
As a method for forming a film, a conventionally known method can be used, and examples thereof include a solution casting method (solution casting method) and a melt extrusion method, and any of them can be employed. However, the melt extrusion method that does not require drying or recovery of the solvent is advantageous in terms of equipment and is preferred in the present invention.
When trying to obtain a film using the solution casting method (solution casting method), stir and mix the thermoplastic resin, which is the main component, and other polymers and other additives, if necessary, in a good solvent. It is possible to obtain a uniform mixed solution, cast onto a support film or drum and pre-dried until it has self-supporting properties, and then peel off from the support film or drum and dry. Solvents used in the solution casting method (solution casting method) include, for example, chlorinated solvents such as chloroform and dichloromethane; aromatic solvents such as toluene, xylene, benzene, and mixed solvents thereof; methanol, ethanol, and isopropanol And alcohol solvents such as n-butanol and 2-butanol; methyl cellosolve, ethyl cellosolve, butyl cellosolve, dimethylformamide, dimethyl sulfoxide, dioxane, cyclohexanone, tetrahydrofuran, acetone, ethyl acetate, and diethyl ether. These solvents may be used alone or in combination of two or more.
Examples of the apparatus for performing the solution casting method (solution casting method) include a drum-type casting machine and a belt-type casting machine.
When trying to obtain a film using the melt extrusion method, a thermoplastic resin from an extruder equipped with a T-type die or the like, or a thermoplastic resin kneaded in advance with other polymers and other additives as necessary Can be made into a film having an arbitrary thickness by extruding by heating and melting and pulling the obtained film with a cooling drum. In the method for producing an acrylic film according to the present invention, the extruder includes a polymer filter between the screw portion and the die, and further, a gas generated along with melt-kneading of the acrylic polymer. It is desirable to have a devolatilizing means for sucking the water.
The melt extrusion temperature for producing the film of the present invention is preferably 150 to 350 ° C, more preferably 200 to 300 ° C.
The acrylic film according to the present invention may be a single layer film or a laminated film, and in the case of a laminated film, a method of discharging using a T-die die after lamination using a pinol or a feed block. A conventionally known method such as a method of stacking and discharging using a multi-manifold type die can be used.
As the dice for producing the film of the present invention, conventionally known dice can be used. For example, a manifold die, a fish tail die, a coat hanger die, or the like can be used. The acrylic polymer discharged from the die can be cooled and solidified on a casting drum to form a film. At this time, a known method of closely contacting the cooling roll with wire pinning, a vacuum chamber or the like may be used together, or a touch roll forming method, specifically, a press roll method, an elastic metal nip roll, a metal endless belt, etc. It may be a method in which an unstretched film is obtained by tightly cooling and solidifying to a cooling medium and rapidly cooling to a glass transition temperature (Tg) or lower.

  The film of the present invention needs to be stretched to obtain a stretched film. However, as a stretching method for obtaining a stretched film, a longitudinal stretching machine and a lateral stretching machine are successively arranged in order from the viewpoint of the introduction cost of the apparatus. A method of performing axial stretching is preferred. For the longitudinal stretching, any conventionally known stretching method may be employed, but the roll longitudinal stretching method is preferred from the viewpoint of the introduction cost of the apparatus and the viewpoint of heat conduction. Note that the roll longitudinal stretching method means that the film is heated while being heated with a heating roll set at a predetermined temperature to raise the film temperature to a predetermined temperature, and the outlet side from the roll speed on the inlet side between the stretching rolls. It is the method of extending | stretching by enlarging the roll rotation speed of this.

In addition, the method of extending | stretching while heating in oven instead of a heating roll is described with the oven vertical stretching method distinguished from the said roll vertical stretching method.
The stretching temperature and stretching ratio of the film can be adjusted as appropriate using the mechanical strength, surface properties, and thickness accuracy of the obtained film as indices, but the film temperature at this time is the glass transition temperature of the film with a heating roll. When Tg is set, it is preferably heated to a range of Tg-10 ° C. or higher and Tg + 20 ° C. or lower, and further heated to a range of Tg or higher and Tg + 30 ° C. or lower by a preheating device provided in the stretching section. preferable. When the film heating with a heating roll is lower than Tg−10 ° C., the transparency of the film tends to deteriorate, and in the extreme case, the film tends to cause process problems such as tearing or cracking. When it is higher than Tg + 20 ° C., a trouble that the film sticks to the roll is likely to occur. In addition, when the heating in the preheating device is lower than Tg, the film is likely to be wrinkled, causing problems in the process such as tearing and cracking of the film, and when it is higher than Tg + 30 ° C., The mechanical properties such as the elongation rate, tensile strength, and flexibility of the obtained film are not improved, and the secondary workability is deteriorated. The number of heating rolls is preferably 5 or more. When the number is less than 5, the heating effect is reduced, so that the film cannot be sufficiently warmed. A method of increasing the roll diameter in order to enhance the heating effect is not preferable because the thermal expansion of the film due to heating cannot be released and wrinkles and breakage due to wrinkles are likely to occur. As the preheating device provided in the drawing section, a conventionally known method can be used, and any heating method selected from an IR heater, a ceramic heater, and a hot air heater is preferable from the viewpoint of the introduction cost of the device.
In addition, the longitudinal stretching may be performed such that the ratio of the absolute values of the in-plane retardation R0 and the thickness retardation Rth (| Rth | / | R0 |) is 0.6 or more and 2.0 or less. preferable. When it is smaller than 0.6, the uniaxial stretchability is high, so that the film is easily split in the transverse stretching step to be performed later, and the production stability is poor. On the other hand, when the ratio is larger than 2.0, the neck-in suppressing effect in the longitudinal stretching becomes too large, which is disadvantageous for the width direction retardation and thickness uniformity. More preferably, they are 0.7 or more and 1.8 or less, More preferably, they are 0.8 or more and 1.5 or less.
In addition, when the distance between the center of the roll on the inlet side (low speed roll) and the center of the roll on the outlet side (high speed roll) is A, and the film width before longitudinal stretching is B, A / B is 0.05 or more and 0. .5 or less is preferable. If it is less than 0.05, the length of the drawing section becomes too short with respect to the width of the film, and the diameter of the drawing roll needs to be reduced. In this case, since strength such as deflection of the roll is insufficient, uniform stretching cannot be performed. When the ratio is larger than 0.5, the influence of neck-in in the longitudinal stretching is exerted to the film center portion, which is disadvantageous for the retardation in the width direction and the uniformity of the thickness. More preferably, it is 0.1 or more and 0.45 or less.
Also,
For the transverse stretching, a tenter transverse stretching machine constituted by a clip traveling device for transverse stretching and an oven is preferably used. The clip travel device grips and conveys the lateral end portion of the film with the clip, and at the same time opens the guide rail of the clip travel device to extend the distance between the left and right two rows of clips. In addition, the simultaneous biaxial stretching machine which gave the expansion / contraction function of the clip also to the flow direction of the film may be used. The oven heats the film to a temperature at which the film can be stretched, and after the stretching, heat-treats the film as necessary, and then cools it. In any case, the heating of the film is preferably Tg−10 ° C. or higher and Tg + 50 ° C. or lower, more preferably Tg−5 ° C. or higher and Tg + 30 ° C. or lower, when the glass transition temperature of the thermoplastic resin film is Tg.

<Measurement method>
The physical properties in the present invention are measured by the following method. The same method was used in the examples and comparative examples.
(Dealcoholization reaction rate (lactone cyclization rate))
The dealcoholization reaction rate (lactone cyclization rate) is based on the weight loss that occurs when all hydroxyl groups are dealcoholated as methanol from the polymer composition obtained by polymerization, and before the weight reduction starts in dynamic TG measurement. It calculated | required from the weight reduction by the dealcoholization reaction from 150 degreeC to 300 degreeC before decomposition | disassembly of a polymer starts.
That is, in the dynamic TG measurement of the polymer having a lactone ring structure, the weight reduction rate between 150 ° C. and 300 ° C. is measured, and the obtained actual weight reduction rate is defined as (X). On the other hand, from the composition of the polymer, all the hydroxyl groups contained in the polymer composition are involved in the formation of the lactone ring, so that it becomes an alcohol and is dealcoholized. (Y) is the weight loss rate calculated on the assumption that the% dealcoholization reaction has occurred. The theoretical weight reduction rate (Y) is more specifically the molar ratio of raw material monomers having a structure (hydroxyl group) involved in the dealcoholization reaction in the polymer, that is, the raw material unit in the polymer composition. It can be calculated from the content of the monomer. These values (X, Y) are calculated from the dealcoholization formula:
1- (actual weight reduction rate (X) / theoretical weight reduction rate (Y))
Substituting into, the value is obtained and expressed in% to obtain the dealcoholization reaction rate.
Then, assuming that the lactone cyclization reaction was performed by the amount corresponding to the dealcoholization reaction rate, the content ratio (wt%) of the following formula lactone ring = B × A × MR / Mm
(In the formula, B is the weight content ratio of the raw material monomer structural unit having a structure (hydroxyl group) involved in lactone cyclization in the polymer before lactone cyclization, and MR is the lactone ring structural unit to be generated. Mm is the molecular weight of the raw material monomer having a structure (hydroxyl group) involved in lactone cyclization, and A is the dealcoholization reaction rate)
Thus, the lactone ring content ratio can be calculated.
(Weight average molecular weight)
The weight average molecular weight of the polymer was determined by polystyrene conversion of GPC (GPC system manufactured by Tosoh Corporation, chloroform solvent).
(Thermal analysis of resin and film)
The thermal analysis of the resin and film was performed using DSC (manufactured by Rigaku Corporation, apparatus name: DSC-8230) under the conditions of about 10 mg of sample, a heating rate of 10 ° C./min, and a nitrogen flow of 50 cc / min. . The glass transition temperature (Tg) was determined by the midpoint method according to ASTM-D-3418. In addition, the measurement of the said glass transition temperature was performed in the temperature range of 30-250 degreeC. Further, when two or more glass transition temperatures (Tg) were measured, such as incompatible mixed polymers, a weighted average of glass transition temperatures (Tg) in each polymer was obtained and used.
(Melt flow rate)
The melt flow rate was measured at a test temperature of 240 ° C. and a load of 10 kg based on JIS K7210.
(Film thickness)
Measurement was performed using a Digimatic Micrometer (manufactured by Mitutoyo Corporation).
(Film temperature)
One point of the film center portion was measured using a radiation thermometer, SK-8110, manufactured by Sato Keiki Seisakusho.
(Refractive index)
In accordance with JIS K7142, the value at 23 ° C. with respect to the measurement wavelength of 589 nm was measured using a refractometer (manufactured by Atago Co., Ltd., device name: Digital Abbe refractometer DR-M2).
(Phase difference)
The in-plane retardation value (R0) and thickness direction retardation value (Rth) of the film at a wavelength of 589 nm were measured using KOBRA-WR manufactured by Oji Scientific Instruments. The thickness direction retardation value (Rth) is the average refractive index of the film measured with an Abbe refractometer, the film thickness d, the slow axis as the tilt central axis, and the incident angle of 40 °, and the in-plane retardation value. (R0), thickness direction phase difference value (Rth), phase difference value (R0 (40 °)) measured by tilting the slow axis by 40 °, and values of three-dimensional refractive indexes nx, ny, nz Was obtained from the following formula.
Thickness direction retardation Rth (nm) = d × {(nx + ny) / 2−nz}
Since the refractive index in the flow direction of the film was nx, the in-plane retardation value (R0) of the film when the slow axis was developed in the film width direction was expressed as minus.
Further, when obtaining the difference of the in-plane retardation R0 value between two points separated by 1 cm, a point 5 mm away from the center in the width direction to the end and a point 5 mm away from the opposite end were measured.
(Bending test)
In the film bending test, the film was observed to be cracked when bent at 180 ° in a bending radius of 1 mm in the film forming direction in an atmosphere of 25 ° C. and 65% RH. The test was carried out twice, and the case where both were not cracked was evaluated as “◯”, the case where it was cracked once as “Δ”, and the case where all were cracked as “x”.

EXAMPLES The present invention will be described in further detail below with reference to examples, but the present invention is not limited thereto.
[Production Example 1]
A 1 m2 reaction kettle equipped with a stirrer, temperature sensor, cooling pipe, and nitrogen introduction pipe is charged with 204 kg of methyl methacrylate (MMA), 51 kg of methyl 2- (hydroxymethyl) acrylate (MHMA), and 249 kg of toluene. Then, while the temperature was raised to 105 ° C. while refluxing nitrogen and refluxed, 281 g of tertiary amyl peroxyisononanoate (manufactured by Atofina Yoshitomi, trade name: Luperox 570) was added as a polymerization initiator. While a solution comprising a polymerization initiator and 5.4 kg of toluene was added dropwise over 2 hours, solution polymerization was performed under reflux (about 105 to 110 ° C.), followed by further aging for 4 hours.
To the obtained polymer solution, 255 g of stearyl phosphate / distearyl phosphate mixture (manufactured by Sakai Chemicals, trade name: Phoslex A-18) was added and cyclized under reflux (about 90 to 110 ° C.) for 5 hours. A condensation reaction was performed.
Subsequently, the polymer solution obtained by the cyclization condensation reaction was subjected to a vent having a barrel temperature of 250 ° C., a rotation speed of 150 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent of 1 and a forevent of 4 It is introduced into a type screw twin screw extruder (Φ = 42 mm, L / D = 42) at a processing rate of 15 kg / hour in terms of the amount of resin, subjected to cyclization condensation reaction and devolatilization in the extruder, and then extruded. As a result, a transparent pellet (1A) was obtained.
The obtained resin pellet (1A) had a mass average molecular weight of 132,000, a lactone ring content of 28.5%, and a glass transition temperature of 129 ° C.
[Production Example 2]
In a 1 m2 reaction vessel equipped with a stirrer, temperature sensor, cooling pipe, nitrogen gas introduction pipe, 150 kg of methyl methacrylate (MMA), 75 kg of 2- (hydroxymethyl) methyl acrylate (MHMA), n-butyl methacrylate (BMA) 25 kg and 250 kg of toluene were charged. While introducing nitrogen gas into the reaction vessel, the temperature was raised to 105 ° C. and refluxed. As a polymerization initiator, 0.15 kg of t-amyl peroxyisononanoate (manufactured by Arkema Yoshitomi Corp., Luperox 570) was added. At the same time as the addition, an initiator solution consisting of 0.30 kg of t-amyl peroxyisononanoate (manufactured by Arkema Yoshitomi Corp., Luperox 570) and 3.5 kg of toluene was added dropwise over 6 hours while refluxing (about 105 Solution polymerization was carried out at a temperature of from C. to 111.degree.
The weight average molecular weight of the obtained polymer (2A) was 195000, and the polymerization reaction rate was 96.2%. Further, the content of the structural unit of MHMA in the polymer (2A) is 30.2% by mass, the content of the MMA structural unit is 59.9% by mass, and the content of the BMA structural unit is 9.9% by mass. %Met.
To the obtained polymer solution, 0.250 kg of an octyl phosphate / dioctyl phosphate mixture (manufactured by Sakai Chemical Co., Phoslex A-8) is added as a cyclization catalyst, and the mixture is refluxed at about 85 to 105 ° C. for 2 hours. The polycondensation reaction (reaction in which the polymer is subjected to intramolecular dealcoholization reaction to form a lactone ring structure in the polymer molecule) was performed.
Next, the obtained polymer solution was heated to 220 ° C. through a heat exchanger, barrel temperature 250 ° C., rotation speed 170 rpm, degree of vacuum 13.3 hPa to 400 hPa (10 mmHg to 300 mmHg), one rear vent, Introduced into a vent type screw twin screw extruder (φ = 42 mm, L / D = 42) with a fore vent number of 4 at a processing rate of 15 kg / hour in terms of resin amount, and the cyclocondensation reaction and desorption were carried out in the extruder. Volatile treatment was performed. At that time, 9.8 parts by mass of zinc octylate (manufactured by Nippon Kagaku Sangyo Co., Ltd., Nikka Octix Zinc 18%), Irganox 1010, C.I. A solution consisting of 8 parts by mass, 0.8 parts by mass of Adeka Stub AO-412S manufactured by Asahi Denka Kogyo Co., Ltd., and 88.6 parts by mass of toluene was poured at a rate of 0.46 kg / hour. By the devolatilization operation, a transparent resin pellet (2B) was obtained. The obtained resin pellet (2B) had a weight average molecular weight of 128,000, a glass transition temperature of 133 ° C., and a melt flow rate of 12.4 g / 10 min.
[Production Example 3]
MMA 40 parts, MHMA 10 parts, toluene 50 parts, ADK STAB 2112 (manufactured by ADEKA) 0.025 part was charged into a reaction kettle equipped with a stirrer, temperature sensor, cooling pipe, and nitrogen introduction pipe, and nitrogen was passed through this at 105 ° C. When the mixture was heated to reflux and refluxed, 0.05 part of tertiary amyl peroxyisonononanoate (manufactured by Atofina Yoshitomi, trade name: Luperox 570) was added as an initiator, and at the same time, tertiary amyl peroxyisonononate 0. While dropping 1 part over 3 hours, solution polymerization was performed under reflux at about 105 to 110 ° C., and further aging was performed for 4 hours.

  To the obtained polymer solution, 0.05 part of 2-ethylhexyl phosphate (manufactured by Sakai Chemicals, trade name: Phoslex A-8) was added, and a cyclization condensation reaction was performed at 90 to 105 ° C. under reflux for 2 hours. It was. Next, the obtained polymer solution was heated to 240 ° C. through a heat exchanger, the barrel temperature was 240 ° C., the degree of vacuum was 13.3 to 400 hPa (10 to 300 mmHg), the rear vent number was 1 and the fore vent number was 4 A side feeder is provided between the third vent and the fourth vent (referred to as the first, second, third, and fourth vents from the upstream side), and a leaf disk type polymer filter (filtered at the tip) It was introduced into a vent type screw twin screw extruder (L / D = 52) with a precision of 5 μm) at a processing rate of 70 parts / hour in terms of resin amount, and devolatilization was performed. At that time, a separately prepared mixed solution of antioxidant / cyclization catalyst deactivator was added at a rate of 1.05 parts / hour from the back of the first vent, and 1.05 parts / hour of ion-exchanged water. Were fed from behind the second and third vents, respectively. Antioxidant / cyclization catalyst deactivator mixed solution, antioxidant / cyclization catalyst deactivator mixed solution, 5 parts of antioxidant (manufactured by Ciba Specialty Chemicals, Irganox 1010), A solution in which 55 parts of zinc octylate (manufactured by Nippon Kagaku Sangyo Co., Ltd., 3.6% of Nikka octix zinc) was dissolved in 45 parts of toluene was used as a quencher. Moreover, pellets of a styrene-acrylonitrile copolymer (the ratio of styrene / acrylonitrile is 73% by mass / 27% by mass, weight average molecular weight 220,000) were charged from the side feeder at a charging rate of 30 parts / hour.

By the devolatilization operation, a pellet of the thermoplastic resin composition (3A) having negative intrinsic birefringence was obtained. The obtained resin composition had a weight average molecular weight of 146000, a glass transition temperature of 122 ° C., and a melt flow rate of 13.6 g / 10 minutes.
Example 1
The resin pellet (1A) obtained in Production Example 1 was melt-extruded at a temperature of 275 ° C. to form an unstretched film having a thickness of 165 μm, which was continuously maintained until the film temperature reached 130 ° C. by seven heating rolls. After heating, the film was heated by an IR heater to be stretched 2.0 times in the machine direction at a film temperature of 140 ° C. under the following conditions.

Longitudinal stretching method ... Roll longitudinal stretching method Distance between stretches A ... 195mm
Film width B before stretching 530mm
Furthermore, the position of 20 mm from both ends of the obtained longitudinally stretched film was continuously gripped with a 2 inch clip and supplied to the tenter, and stretched 2.0 times at 145 ° C. Thereafter, after continuously trimming to 700 mm in width with a shear cutter, a protective film made of polyethylene was pasted and wound up with a winder. A biaxially stretched film of 500 m was obtained continuously without breaking the film in the middle. The characteristics of the obtained film (1AF-2) were as follows.
Thickness (μm): 40
In-plane retardation R0 (nm): 3.0
Thickness retardation Rth (nm): 27.0
Bending test: ○
In addition, the characteristic which took out and measured the film (1AF-1) after longitudinal stretch was as follows.
Thickness (μm): 82
In-plane retardation R0 (nm): 59.1
Thickness retardation Rth (nm): 53.8
(Example 2)
The resin pellet (2B) obtained in Production Example 2 was melt-extruded at a temperature of 275 ° C. to form an unstretched film having a thickness of 300 μm, and the film was preliminarily maintained as it was by using seven heating rolls until the film temperature reached 127 ° C. After heating, the film was heated by an IR heater to be stretched 2.0 times in the machine direction at a film temperature of 140 ° C. under the following conditions.

Longitudinal stretching method: Roll longitudinal stretching method Stretching distance A: 195 mm
Film width B before stretching 530mm
Further, the position of 20 mm from both ends of the obtained longitudinally stretched film was continuously gripped with a 2 inch clip and supplied to the tenter, and stretched 2.5 times at 145 ° C. Thereafter, after continuously trimming to 700 mm in width with a shear cutter, a protective film made of polyethylene was pasted and wound up with a winder. A biaxially stretched film of 500 m was obtained continuously without breaking the film in the middle. The characteristics of the obtained film (2BF-2) were as follows.
Thickness (μm): 45
In-plane retardation R0 (nm): 50
Thickness retardation Rth (nm): 125
Bending test: ○
In addition, the characteristic which took out and measured the film (2BF-1) after longitudinal stretch was as follows.
Thickness (μm): 110
In-plane retardation R0 (nm): 250
Thickness retardation Rth (nm): 200
(Example 3)
The resin pellet (3A) obtained in Production Example 3 was melt-extruded at a temperature of 275 ° C. to form a non-stretched film having a thickness of 226 μm, and the film was preliminarily kept as it was by using seven heating rolls until the film temperature reached 125 ° C. After heating, the film was heated with an IR heater to a film temperature of 135 ° C. and stretched 2.0 times in the machine direction under the following conditions.

Longitudinal stretching method: Roll longitudinal stretching method Stretching distance A: 195 mm
Film width B before stretching 530mm
Furthermore, the position of 20 mm from both ends of the obtained longitudinally stretched film was continuously gripped with a 2 inch clip, supplied to a tenter, and stretched 2.3 times at 128 ° C. Thereafter, after continuously trimming to 700 mm in width with a shear cutter, a protective film made of polyethylene was pasted and wound up with a winder. A biaxially stretched film of 500 m was obtained continuously without breaking the film in the middle. The characteristics of the obtained film (3AF-2) were as follows.
Thickness (μm): 70
In-plane retardation R0 (nm): 69
Thickness retardation Rth (nm): −131
Bending test: ○
In addition, the characteristic which took out and measured the film (3AF-1) after longitudinal stretch was as follows.
Thickness (μm): 160
In-plane retardation R0 (nm): -155
Thickness retardation Rth (nm): -124
(Comparative Example 1)
The resin pellet (2B) obtained in Production Example 2 was melt extruded at a temperature of 275 ° C. to form a 240 μm-thick unstretched film, which was continuously stretched 1.8 times in an oven at 140 ° C. as it was.

Longitudinal stretching method ... Oven longitudinal stretching method Distance between stretching A ... 8000mm
Film width B before stretching 530mm
The characteristics of the obtained film (2BF-3) were as follows.
Thickness (μm): 180
In-plane retardation R0 (nm): 210
Thickness retardation Rth (nm): 105
Next, an attempt was made to insert the obtained film (2BF-3) into a tenter in order to transversely stretch, but the film could not be laterally stretched due to the longitudinal tearing of the film.
(Comparative Example 2)
The film was formed and stretched in the same manner as in Example 2 except that the distance A between the rolls in the longitudinal stretching was 270 mm. However, wrinkles were generated from the end of the film due to the width shrinkage due to neck-in, and this wrinkle-derived film Breaking occurred frequently and stable stretching could not be performed. In addition, the characteristic of the obtained film (2BF-4) was as follows.
Thickness (μm): 120
In-plane retardation R0 (nm): 230
Thickness retardation Rth (nm): 135

According to the film production method of the present invention, it is possible to stably form an acrylic polymer, which is generally considered to have low flexibility, as a retardation film having excellent optical properties without breaking the film for a long time. become able to. The stretched film obtained by the production method of the present invention can be suitably used as an optical film for various image display devices, particularly as a retardation film.

Claims (5)

In the method for producing a retardation film obtained by longitudinally stretching a film made of an acrylic polymer in the film flow direction and then transversely stretching in the film width direction, each of the in-plane retardation R0 and the thickness retardation Rth is absolute. A sequential biaxially stretched phase difference characterized in that the film is stretched longitudinally so that the ratio of values (| Rth | / | R0 |) is 0.6 or more and 2.0 or less and then transversely stretched in the width direction of the film. A method for producing a film.
The method for producing a retardation film according to claim 1, wherein in the longitudinal stretching step, stretching is performed so that an in-plane retardation R 0 is 50 to 500 nm.
In the longitudinal stretching step, when the distance between the roll center on the inlet side and the roll center on the outlet side is the stretch section length A and the film width before the longitudinal stretch is B, A / B is 0.05 or more and 0.5 or less. The method for producing a retardation film according to claim 1, wherein the retardation film is provided.
4. The method for producing a retardation film according to claim 1, wherein in the longitudinal stretching step, the film is stretched after being heated by contact with at least 5 hot rolls. 5.
5. The method for producing a retardation film according to claim 4, wherein in the longitudinal stretching step, any one heating method selected from an IR heater, a ceramic heater, and a hot air heater is used in combination.