JPH1119955A - Manufacture of phase difference film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a phase difference film adapted to an optical application of satisfactory quality with particularly extremely small speckle of retardation value by eliminating phase difference speckle of an infinitesimal range. SOLUTION: The method for manufacturing a phase difference film made of polymer by casting polymer solution on a support, drying the resultant film and then orienting it comprises the steps of releasing the film containing 8 to 20 wt.% of solvent from the support, then grasping the film by a pin tenter so that a length of the film of a direction perpendicular to an orientation axis becomes 99 to 105%, drying it until the containing solvent amount of the film becomes 2.0 wt.% or less, and further uniaxially orienting the film 1.1 to 3.2 times in a feeding direction of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a retardation film by stretching a solution cast polymer film. More specifically, the present invention relates to a method for producing a retardation film that does not cause retardation unevenness (accordingly, color unevenness and viewing angle characteristic unevenness when a retardation compensation film is formed) by stretching a polymer film. .

[0002]

2. Description of the Related Art A retardation plate made of a thermoplastic polymer film has been widely used as an anti-glare material and as a retardation compensation plate in an F-STN type liquid crystal display device. A retardation plate of a polymer film utilizes birefringence generated by molecular orientation by stretching. As a method of manufacturing the retardation plate, a method of manufacturing various polymer films by uniaxial stretching has already been known. Generally, a uniaxially stretched polycarbonate resin having a large intrinsic birefringence is used. The following four points are specially described as characteristics to be provided by the phase difference plate.

1) In addition to being excellent in transparency, the film must have good flatness without appearance defects such as scratches, scratches, and waving of the film.

2) The range of change of the retardation value and the range of change of the angle of the slow axis are small. With the enlargement of the liquid crystal display screen, various problems have become apparent due to the necessity of increasing the size of the members. . That is, even in a small range of a film, the characteristic value which can be relatively easily controlled is increased, and uniformity of characteristics in a wider and larger film is required. For example, if the difference between the retardation values of two points 10 cm apart from each other in the plane of the retardation film exceeds 5 nm, color spots generated on the liquid crystal display device can be recognized by the naked eye, and the liquid crystal display device cannot be used as a liquid crystal display device. Have been. Thus, the range of the retardation value in the width direction and the length direction of the sheet-like film or the film wound in a roll was 5 nm regardless of the measured position.
It is required that: Similarly, the slow axis is required to be uniform no matter where the member is cut on the film roll. When the slow axes are not uniformly distributed, there is a problem that the alignment becomes complicated when the retardation films are used in combination with each other or with other members.

[0005] 3) Small spots of retardation in a minute range. A small area, for example, 10
It is required that the difference between the retardation values at points separated by mm is 1.5 nm or less. If this value is exceeded, color spots may be detected when the film is sandwiched between polarizing plates, and a phase difference plate or a plurality of phase difference plates and a polarizing plate may be overlapped with each other. When used as a display element, unevenness of the retardation value may be added, which is a problem because it is detected as a color unevenness.

4) To maximize viewing angle characteristics. Even when the viewing angle is increased, it is necessary to make the display of the liquid crystal display device look good. As the size of the screen of the liquid crystal display device increases, the size of the retardation film used therein also increases, which inevitably increases the demand for uniformity of characteristic values on a larger surface.

[0007] As a conventional technique, several techniques have been proposed for a retardation film by a longitudinal uniaxial stretching method and a method for producing the same. For example, Japanese Patent Application Laid-Open No. 8-101306 discloses a method for producing a retardation plate in which a film is longitudinally and uniaxially stretched, in which a temperature gradient is provided in the width direction of the thermoplastic resin film and the film is longitudinally and uniaxially stretched. Although this method is considered to be effective, there is also a need to finely adjust the temperature gradient according to the properties of the film before stretching, and in fact, there is a problem in that the production conditions are greatly increased. That is, even if the temperature in the width direction of the film can be finely controlled, the factor that determines the distribution of the retardation value is also in the width direction distribution of the film thickness. (The retardation value is determined by the birefringence Δn and the film thickness. Each time the original film is changed, there is a problem that complicated operations such as finely controlling the temperature in the film width direction in accordance with the thickness unevenness of the film are required.

Further, as a method for eliminating optical spots generated at the time of stretching, a method of defining the amount of a solvent in a film at the time of stretching is disclosed. As these known documents, Japanese Patent Laid-Open No.
No. 82212, JP-A-4-204503, JP-A-5-113506 and the like. In these methods, uniaxial stretching is performed with a relatively large amount of solvent. According to these methods, the apparent glass transition temperature is lowered in accordance with the amount of the solvent contained, so that there is an advantage that the stretching can be performed at a relatively low temperature.

The method disclosed in Japanese Patent Application Laid-Open No. 4-282212 is a method in which stretching is performed by utilizing the difference in the yield value of the solvent film contained. In this method, it is difficult to make the stretching start line straight in the width direction. It is difficult to fix the stretching point (stretching line) in the running direction, and there is a problem that retardation unevenness in the width direction and the running direction is easily generated.

Japanese Patent Application Laid-Open No. 4-204503 discloses a method of stretching a film immediately before stretching by setting the solvent content to 2 to 10% on a solid content basis (the amount of a solvent contained in a dried solute (solid content)). JP-A-5-113506 discloses that when the solvent content is in the range of 3 to 10% based on the solid content, the film has excellent viewing angle characteristics in an atmosphere of 155 ° C. or more and 175 ° C. or less. A method for producing a retardation film is described.

In these methods, since a film having a large solvent content is stretched, a difference in stretchability is likely to occur partially, which causes a problem of birefringence unevenness after stretching, and the retardation value is set to a desired value. It is difficult to adjust the temperature and to control minute retardation spots. Further, since the amount of the solvent in the film at the time of stretching is large, the remaining solvent tends to remain even after the stretching treatment. The residual solvent may have an adverse effect during processing when producing a component for a liquid crystal display device. To further reduce the amount of residual solvent after stretching,
There is also a problem that it is necessary to add a drying step, and in such a case, the heated molecular weight of the drying causes relaxation of the oriented molecular chains, making it difficult to adjust the characteristics to a desired retardation value.

As a method of improving the stretching method when a large amount of residual solvent is contained, a technique of uniaxial stretching with a smaller solvent content has been proposed. Japanese Patent Application Laid-Open No. H08-212224 discloses a technique for stretching in a state where the solvent content is less than 2% by weight. However, this method partially causes a difference in stretchability due to a high concentration of a solvent. This is for improving unevenness in the film thickness after stretching and the orientation of the polymer, that is, birefringence. Certainly, it seems that this method can reduce the range of the retardation value over a wide area of the film, among the characteristics that the retarder should have. However, unevenness of the retardation value in a minute range at a point separated by about 10 mm on the film surface could not be eliminated.

Further, a phase difference value representing a retardation, △
Paying attention to the fact that n * d is determined by the product of the birefringence value Δn and the film thickness d, the retardation plate or the non-stretched film that defines the thickness unevenness in the minute range has a small range within the film plane. A technique has been proposed in which the difference in retardation is reduced by controlling the thickness difference to suppress coloring spots and phase difference spots.

Japanese Unexamined Patent Publication (Kokai) No. 2-59703 discloses that the deflection width of the thickness (x) is 0.1x or less and the rate of change thereof is 0.1.
A method for producing a retardation film in which a polymer film having a width of 015x / cm or less is uniaxially stretched, and a deflection width of the retardation is 10% or less and a rate of change thereof is 1.8% / cm or less is disclosed. .

Japanese Patent Application Laid-Open No. 8-101305 discloses a polymer film having birefringence, wherein a difference in thickness at a position 1 cm away from an arbitrary point in the film plane is 0.3 μm.
It is reported that the object can be achieved by a retardation plate characterized by the following.

Japanese Patent Application Laid-Open No. 8-101308 discloses that the thickness of an unstretched film changes in the thickness direction between a thick portion and a thin portion adjacent to each other in the length direction and the width direction in a range from 0.5 μm to 3 μm. Is a uniaxially or biaxially stretched raw film having a wave variation of 1 mm to 40 mm or less, and arbitrary 2 cm apart from each other in the film plane.
A retardation plate characterized in that the difference in retardation value between points is 5 nm or less has been proposed.

[0017] By forming a fine wavy thickness variation in the raw film as described above, a raw film having countless thin portions in the film plane can be obtained. It is said that the stretching start points are innumerable in the film surface, so that large stretching unevenness does not occur, but it is actually extremely difficult to make such a thickness variation uniformly over the film surface. There is.

Techniques for producing a film having a small thickness unevenness in a film before stretching are particularly suitable for a minute range of thickness unevenness, for example, a narrow lip streak continuous in the film running direction or a thin streak generated intermittently in the running direction. However, the problem that it is difficult to eliminate the thickness unevenness of the present invention has not been solved. At present, such thickness unevenness often remains after uniaxial stretching and impairs the quality of the retardation film.

As described above, of the characteristics that the retardation plate should have, the retardation unevenness in a relatively large area (item (2) above)
Has been greatly improved by the prior art. However, there is still a problem to be solved with respect to a technique for resolving retardation unevenness in a fine range on the film surface (item 3).

[0020]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a sufficiently small phase difference unevenness, particularly, a viewing angle in which a minute range of phase difference unevenness has been eliminated. An object of the present invention is to provide a method for manufacturing a high-performance phase difference compensator having excellent characteristics.

[0021]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively studied the stretching mechanism of a solution cast film and have reached the present invention. That is, the present invention
In order to uniformize the range of the retardation value, the minute retardation value and the distribution of the slow axis, the film is treated with a tensile force in the transverse direction with a pin tenter in a state containing a specified amount of a solvent, and the thickness unevenness (especially It has been found that the object can be achieved by reducing the size of the streak-like minute unevenness in thickness) and then uniaxially stretching the film in the running direction under specified conditions, thereby achieving the present invention. When a slight tension is applied to the film in a state where the solvent is contained at a high concentration, a portion of the film containing more solvent than the surroundings in the film surface, and therefore, a band-like or streak-like appearance in which the thickness is locally thicker than the surroundings. Tg '(Tg'
(° C.) is the glass transition temperature of the solvent-containing polymer film, and this temperature increases as the drying proceeds, with the residual solvent content decreasing. ) Is stretched locally. As a result, thickness unevenness can be reduced.

Further, the phase difference of the belt-like or streak-like portions thicker than the surroundings hardly changes even after the tension is applied in the width direction of the film. The retardation was measured for that portion, but no particular increase in molecular orientation was found. It is presumed that the structural change of the band-like or streak-like portion due to stretching has not substantially occurred, and it will be so small that it cannot be detected by a normal method. In addition, the result that the molecular orientation was particularly increased in this portion was not obtained. That is, it has been found that if tension is applied to the film under specified conditions (solvent content, temperature, elongation rate), the thickness unevenness can be reduced without substantially changing the molecular orientation structure.

With respect to the dependence of the retardation value on the stretching temperature during uniaxial stretching of polycarbonate, for example, polycarbonate (trade name: Panlite C, manufactured by Teijin Chemicals Ltd.)
When a retardation film is made by stretching a film containing no solvent of -1400 QJ), increasing the stretching temperature by 1 ° C. reduces the retardation value by about 30 nm, and stretching a film containing methylene chloride as a solvent contained. When the solvent is increased by 0.1% by weight, the retardation value decreases by about 9 nm. In this case, when the solvent is increased by 0.1% by weight, the apparent glass transition temperature and Tg ″ of the film are 1.4 ° C. Lowering (Japanese Unexamined Patent Publication No.
-299828).

From these facts, to control the unevenness of the retardation, it is necessary to precisely control the stretching temperature (in both the width direction and the length direction). Also, when a solvent is contained, the apparent glass transition temperature Tg 'changes remarkably with a trace amount of the solvent, so that it is necessary to control the content of the solvent to be as uniform as possible during stretching. .

That is, the method of the present invention is a method for producing a polymer retardation film by casting a polymer solution on a support, drying the obtained film, and stretching it. 1. A film having a solvent content of 8 to 20% by weight is peeled from the support, and The length of the film in the direction perpendicular to the stretching axis is 99% or more
2. The film is gripped by a pin tenter so that the film content becomes 105%. Film ambient temperature (Tg '+ 10) to (Tg' +
90) At 90 ° C., the solvent content of the film is 2.0
3. Drying to less than% by weight (Tg ′ (° C.) is the glass transition temperature of the solvent-containing polymer film, and this temperature increases with decreasing residual solvent content as drying proceeds). Further, the film was subjected to (Tg "+10) to (Tg" +4
5) The present invention has been completed by finding out that this can be achieved by a method for producing a retardation film, which is characterized in that the film is uniaxially stretched 1.1 to 3.2 times in the running direction of the film at a temperature of ° C. (Tg ″ (° C.) is the glass transition temperature of the solvent-containing polymer film, and this temperature rises as drying proceeds, with a decrease in residual solvent content.)

The polymer used in the present invention is not particularly limited as long as the desired properties of the film can be obtained. Examples of the polymer include a conventionally known polymer such as polycarbonate, polysulfone, polyethersulfone, polyarylate, polystyrene, and triacetylcellulose, which can be formed by a solution casting method. That is, any polymer solution that forms a solution having the concentration and viscosity necessary for the solution casting method can be applied to the method of the present invention. Of these, polycarbonate is particularly preferred.

In general, a polymer material generally referred to as a polycarbonate is a material generally produced by a polycondensation reaction and having a main chain connected by a carbon bond. Among these, those obtained by a polycondensation reaction from a bisphenol derivative and phosgene or diphenyl carbonate are meant.
Aromatic polycarbonate represented by a repeating unit containing 2,2 bis (4-hydroxyphenyl) propane as a bisphenol component, which is called bisphenol A in terms of economy and physical properties, is preferably used, and various bisphenol derivatives are appropriately selected. By doing so, a polycarbonate copolymer can be formed.

As such copolymerization components, bis (4hydroxyphenyl) methane, 1,1-bis (4hydroxyphenyl) cyclohexane, 9,9-bis (4hydroxyphenyl) fluorene, 1,1-bis (4hydroxyphenyl) -3,3,5 trimethylcyclohexane, 2,2
-Bis (4-hydroxy-3-methylphenyl) propane,
2,2-bis (4-hydroxyphenyl) -2phenylethane, 2,2bis (4-hydroxyphenyl) 1,1,
Examples thereof include 1,3,3,3 hexafluoropropane, bis (4hydroxyphenyl) diphenylmethane, bis (4hydroxyphenyl) sulfide, and bis (4hydroxyphenyl) sulfone. Furthermore, those in which the hydrogen group of these phenyl groups is partially substituted with a methyl group or a halogen group are also included.

In general, it is also possible to use a polyester carbonate containing a terephthalic acid and / or isophthalic acid component. By using such a constituent unit as a part of the constituent component of the polycarbonate composed of bisphenol A, the properties of the polycarbonate, for example, heat resistance and solubility can be improved, but such a copolymer is also used in the present invention. Can be used.

The molecular weight of the polycarbonate resin used in the present invention is 10,000 to 200,000, preferably 10,000 to 200,000, as the viscosity average molecular weight determined by measuring the viscosity at 20 ° C. in a methylene chloride solution having a concentration of 0.5 g / dl. 2
The range from 0000 to 120,000 is preferably used. When a resin having a viscosity average molecular weight lower than 10,000 is used, the mechanical strength of the obtained film may be insufficient. On the other hand, when the molecular weight is 200,000 or more, the viscosity of the dope becomes too high, which causes problems in dissolution and handling in the casting step, which is not preferable.

The solvent used in the present invention includes a solvent mainly composed of methylene chloride and a solvent mainly composed of 1,3-dioxolane.

As a specific method for preparing a polycarbonate solution, the polycarbonate is put into methylene chloride and dissolved by stirring. If necessary, a method may be used in which a predetermined amount of ethanol is mixed in advance as methylene chloride in methylene chloride, and then polycarbonate is added thereto and dissolved by stirring at room temperature.

Similarly, for each solution of polysulfone, polyether sulfone, polyarylate, polystyrene, and triacetyl cellulose, these resins are dissolved in a solvent mainly composed of methylene chloride or a solvent mainly composed of 1,3-dioxolane. Can be prepared.

In the present invention, the concentration of the polymer solution is 10 to
By adjusting the amount to 30% by weight, more preferably 15 to 25% by weight, a film can be suitably formed by a solution casting method.

The solution thus obtained is applied to a steel belt, a drum or a support film (generally, a biaxially oriented polyester film) by a known method.
It is cast, dried and peeled from the support in a semi-dry state.

The solvent content of the film after peeling is 8 to 20.
Adjust by weight just before feeding into the pin tenter so that the weight% is obtained. In the method of the present invention, drying can be performed at a temperature of room temperature to 80 ° C. between the guide rolls immediately after the cast peeling and the entrance of the pin tenter.

Next, the film having a solvent content of 8 to 20% by weight is gripped with a pin tenter without substantially changing the retardation, and the edge in the film width direction is gripped by the grip width (the film in the direction perpendicular to the stretching axis). 99%)
A tension is applied in the width direction of the film so as to be about 105%, and the film atmosphere temperature (Tg ′) is continuously held in a state where both ends are gripped (usually pierced with pins and fixed and conveyed).
(+10) to (Tg ′ + 90) ° C. (Tg ′ (° C.) is the glass transition temperature of a polymer film containing a solvent, and this temperature increases as the residual solvent content decreases as drying proceeds.)

By heating and drying the film having a solvent content of 8 to 20% by weight in a pin tenter as described above, thickness unevenness generated in the solution casting step can be reduced. When the solvent content is 8% by weight or less and dried by heating as described above, since the average solvent amount of the entire film is low, the difference in solvent amount between the thick and small portions of the film is small. And the shrinkage tension of the film due to the evaporation of the solvent is reduced, so that the effect of improving the uneven thickness is lost. Further, even if this film is stretched uniaxially in the longitudinal direction in a subsequent step, spots remain as they are, and it is impossible to eliminate minute spots in thickness. When the content of the solvent exceeds 20% by weight,
Since evaporation of the solvent due to drying is rapid, unevenness in thickness cannot be improved. Further, when the content of the solvent exceeds 20% by weight, fine bubbles may be generated in the film.

By heat-drying the film at an ambient temperature of (Tg ′ + 10) to (Tg ′ + 90) ° C. using a pin tenter, thickness unevenness generated in the solution casting step can be reduced. Specifically, the polycarbonate solution has a temperature of 90C to 130C, and the more preferable film atmosphere temperature is 100C to 120C.

When the film ambient temperature of the pin tenter is (T
If the temperature is lower than (g ′ + 10) ° C., the solvent may not be sufficiently dried, so that the properties of the film immediately before stretching may not be controlled due to the influence of the solvent contained in the subsequent preheating step before stretching. Further, when the film ambient temperature is (Tg ′ + 9)
0) When the temperature exceeds 0 ° C., particularly, optical characteristics (retardation value, slow axis, and distribution thereof) may deviate from desired values.

Tension is applied to the film in the film width direction by a pin tenter, and the gripping width of the film (the length of the film in a direction perpendicular to the stretching axis) is 99% to 105% (reduction amount 1% to elongation amount 5%). By controlling as described above, unevenness in thickness generated in the solution casting process can be reduced. Since the film is dried in the pin tenter, when the holding width is set to a free length without applying tension by the pin tenter, the length of the film in the direction orthogonal to the stretching axis is 96% or less (a reduction amount of 4% or more). Shrinkage occurs. 99% of the film length in the direction perpendicular to the stretching axis
(Reduction amount 1%) to 105% of the film length (elongation amount 5
%), The shrinkage stress of the film is generated as compared with the case where the holding width is set to a free length, and the thickness unevenness of the band portion or the streak portion can be improved.

When the length of the film in the direction perpendicular to the stretching axis is 105% or more (the elongation is 5% or more),
Since the shrinkage stress due to evaporation of the solvent is large, the dependence of the retardation value and the size and distribution of the slow axis in the film width direction is increased, and the object of the present invention cannot be achieved.

At the exit of the pin tenter, the film is cooled to room temperature to fix the structure of the film. Also, both edges of about 50 mm gripped by the pins of the pin tenter are cut off. If both edges are not cut off, white powder (scraped powder by the pin) generated from the pin piercing hole or the like re-adheres to the product part of the film and becomes contaminated.

Next, the film is passed through a step of drying using a roll hanging type drying apparatus. In the drying treatment process using the roll hanging type drying device, the phase difference unevenness in the next stretching process can be improved by controlling the characteristics of the film as follows. That is, the solvent content: 2.0
% By weight, preferably 0.5 to 2.0% by weight, more preferably 0.5 to 1.6% by weight. If the solvent content is outside the above range, the retardation unevenness in the next stretching step cannot be improved, and a retardation film having excellent characteristics cannot be produced.

Further, in the stretching step, the film is uniaxially stretched in a running direction of 1.1 to 3.2 times. At that time, the stretching temperature and the inter-roll length (stretching span) are strictly controlled. It is preferable that the length between the stretching nip rolls from the stretching start point (or stretching start line) to the stretching end is 1.5 times or more and 4.0 times or less with respect to the width of the film before stretching.

If the length between the rolls is 1.5 times or more and 4.0 times or less the width of the film before stretching, the film is stretched and the width and thickness of the film can be freely changed while the end point of stretching is between them. and reduction in thickness) occurs, so to speak, the free width uniaxial stretching, free thickness uniaxially stretched and turned to the principal refractive index in the stretching direction n _x, the principal refractive index n _y in orthogonal directions in the stretching direction, the main refraction in the thickness direction rate the viewing angle characteristics become uniaxially stretched structure ideal such that the n _y and n _z of when the n _z equal is improved. When the inter-roll length is not more than 1.5 times the film width, the so-called plane orientation is large (thickness) because rotation of the polymer chain along the stretching axis due to free shrinkage in the film width direction is unlikely to occur. The optical structure of the film is fixed while the refractive index in the direction is small). That is, it is not an ideal uniaxial stretching in which the refractive indexes _ny and _nz are equal, and the viewing angle characteristics are not improved.

The stretching temperature in the present invention is (Tg ″ +1)
0) ° C. to (Tg ″ +45) ° C. (Tg ″ (° C.) is the glass transition temperature of the polymer film containing the solvent, and this temperature increases as the residual solvent content decreases as drying proceeds. .) easily occurs increase of decrease and n _z of the n _y by free shrink in the width direction of the film during the uniaxial stretching by the stretching temperature is set as described above, also it is worked to some extent contributed longitudinal relaxation, field The angular characteristics can be improved. Stretching temperature is (Tg "+10) ℃
In the following cases, it is difficult to relax the molecular chains in the vertical and horizontal directions, so in such a case, it is necessary to take a longer time for the relaxation, and the length between the rolls is increased, or
Alternatively, a step for thermal relaxation is required separately. If the stretching temperature is higher than (Tg ″ +45) ° C., it is difficult to increase the orientation of the molecular chains, and the unevenness of the retardation value of the obtained film increases, which is not preferable. ) To (Tg ″ +30) ° C. The stretching temperature is set to be as low as possible in order to minimize the amount of residual solvent after stretching and to sufficiently relax the orientation of the polymer chains in the width direction to improve the viewing angle characteristics. It is preferable to use a relatively high temperature in the range.

The film wound around the roll immediately before the start of stretching is held by a nip roll. According to the conditions in the present invention, stretching can be performed without any problem. The roll at the end point of stretching also nips the film. Here, if the film is nipped at a high temperature, small pitch wavy spots generated during stretching may be pressed on the roll and wrinkles may be fixed. Therefore, it is preferable to lower the temperature of the nip roll by several degrees from the stretching temperature.

The film is stretched by heating with a jet of air between the roll before stretching and the roll after stretching. The air jet is blown immediately after the film leaves the stretching roll by a slit nozzle that allows hot air to flow uniformly in the width direction so that stretching is started. The speed of the hot air jet is 15 to 30 m / s to maximize the heat transfer coefficient to the film.
The range of ec is preferred. As a device for this, an air-floating hot-air device can be preferably used. This method is extremely convenient in that hot air is blown over the entire surface of the film being stretched, and the speed of hot air and the temperature of the hot air can be changed in the running direction of the film between stretching rolls.

Next, the film after the completion of stretching is cooled.
At this time, so-called rapid cooling in which the film temperature is rapidly lowered from the stretching temperature to room temperature must not be performed. Rapid cooling of the stretched film causes shrinkage due to thermal expansion, so even when cooling the film in space, or when contacting the film with a roll and cooling it, wrinkles parallel to the longitudinal direction of the film are generated. Many enter. The wrinkles due to the expansion and contraction are fixed as they are when they are rapidly cooled and remain as so-called wrinkles in a corrugated shape substantially parallel to the longitudinal direction, so that the flatness of the film is significantly deteriorated. The corrugated wrinkles may cause the stretched film to have a thickness of 50 to 1
The problem can be solved by contacting with a roll at a temperature of 50 ° C. and treating and cooling to room temperature.

[0051]

According to the method for producing a polymer retardation film of the present invention, a film containing a specified amount of a solvent is gripped to a specific width by applying a tension in a lateral direction by a pin tenter before longitudinal uniaxial stretching. By keeping the film atmosphere at a specific temperature to reduce thickness unevenness (especially streak-like minute thickness unevenness), then drying and stretching the film vertically and uniaxially under specific conditions, a retardation film having an extremely small unevenness in retardation value. Can be manufactured. According to the method for producing a polymer retardation film of the present invention, it is possible to produce a good-quality retardation film in which the unevenness of the retardation value is extremely small, and in particular, the unevenness of the retardation value in a minute range is eliminated. As a result, a retardation film suitable for optical applications can be provided.

[0052]

The present invention will be described below in detail with reference to examples. The measurement was performed by the following method.

1) Measurement of Retardation Value and Slow Axis Angle Regarding the total width of the sample in the width direction of the film, KOBR (trade name, manufactured by Shin-Oji Paper Co., Ltd.)
A-21SDH), and the retardation value was measured at 5 mm intervals. From this data, the difference in retardation value over the entire width of the measurement sample was determined. That is, the difference between the maximum value and the minimum value of the retardation value in the range of the entire width was taken as a measure of uniformity (unit: nm). Further, the difference between the retardation value of the value measured at 5 mm intervals with respect to the entire width of the film and the next adjacent point, that is, the difference of the retardation value between 10 mm, was measured, and the maximum value was defined as the maximum value of the retardation of the minute portion of the film. (Unit: nm). When this is large, when the film is sandwiched between polarizing plates, the portion may appear as streak-like color spots. The length of the sample in the width direction was set as the measurement length, and 1 m in the length direction was set as the measurement length.

2) Measurement of Amount of Solvent Contained in Film About 5 g of a film containing a solvent was collected, dried with a hot-air dryer at 170 ° C. for 1 hour, and then cooled to room temperature. The rate of change in weight before and after drying was precisely weighed with an analytical balance. From this, the solvent content based on the solid content was determined. In the case of measurement in the width direction, the film was measured by dividing the film into five equal parts in the width direction.

3) Measurement of viewing angle characteristics Automatic birefringence index measuring device (trade name of Shin-Oji Paper Co., Ltd.)
Using KOBRA-21ADH), the retardation Re (0) in the film normal direction and the film normal to
Retardation Re at oblique incidence at a relative angle of degrees
(40) was measured, and the rate of change in retardation was determined from the absolute value of the difference.

[0056]

[| Re (0) -Re (40) | / Re
(0)] × 100 A smaller change rate means better viewing angle characteristics.

4) Measurement of glass transition temperatures Tg ′ and Tg ″ (Tg of a film containing a solvent)
0 mg and a heating rate of 10 ° C./min. The DSC curve was obtained with. The falling (inflection point) portion of this curve was defined as the apparent glass transition temperature Tg ′, Tg ″.

Example 1 Polycarbonate manufactured by Teijin Chemicals Ltd. (trade name: Panlite C-1400QJ, viscosity average molecular weight: 38,000, Tg of polymer not containing methylene chloride was 159 ° C.). It was dissolved in methylene chloride to prepare an 18% by weight solution. This was cast on a steel belt and dried to form a film with small thickness unevenness, and peeled off from the belt surface. The characteristics of the film at this time were as follows. Content of solvent: 18 ± 1.0% by weight (total width of film) Glass transition temperature Tg ′: 45 ° C. Film thickness: 70 μm, film width: 1500 mm Thickness unevenness: 1 μm (film 1450 mm width) Fine streaky thickness unevenness: 0 3 streaks of 0.5 to 0.7 μm
Book / film 1450 mm wide.

The film was then passed through a pin tenter, which divided the room into six zones. At this time, the entrance width of the pin tenter is 1500 mm, and the length of the film in the direction perpendicular to the stretching axis is 100%, that is, the length of the film in the direction perpendicular to the stretching axis is 150% from the entrance to the sixth zone.
0 mm. The temperature of the dry air in the oven of the pin tenter was 118 ° C. in all six chambers. Next, while holding the film, the film was air-cooled to room temperature, and both edges were cut off by 50 mm at the exit of the pin tenter.

The characteristic values of the film thus obtained were as follows. Retardation value: 20 to 40 nm (full width of film) Slow axis value: -30 to +30 degrees (full width of film) Content of solvent and its distribution: 4.0 ± 0.5% by weight (full width of film) Thickness unevenness: 0 3 streaks of 1 to 0.3 μm / the entire width of the film became extremely small. Thus, an unstretched film having a thickness of 70 μm was prepared. The film was further passed through a stretching apparatus having preheating, stretching, and cooling zones before stretching.

Drying using a roll hanging type dryer: hot air temperature 100 ° C., tension applied to the film 1.5 kg / cm
² , Processing time 30 minutes. The characteristic values of the obtained film are as follows: 1.5 ± 0.05% by weight of residual solvent (total width of film), glass transition temperature Tg ″ = 145 ° C., retardation value of 30 to 50 nm (total width of film), angle of slow axis -20 to +20 degrees.

Uniaxial stretching conditions: stretching temperature: 155 ° C., stretching ratio: 1.25 times, length between rolls of stretching is 1.6 times the film width before stretching. The neck-in rate of the stretched film (decrease rate of the film width due to stretching) was 13%.

Cooling conditions: cooling temperature 120 ° C., cooling time 5
Then, the film was treated with a tension of 12 kg / cm ² applied to the film during cooling, and then cooled to room temperature.

The properties of the obtained film as a retardation film were as follows, and were extremely excellent. Film thickness: 54 μm Film thickness unevenness: 0.3 μm (film overall width 1200
mm) Difference between maximum value and minimum value of retardation value: 4 nm (total width of film: 1200 mm) Maximum value of minute retardation value: 1.5 nm (total width of film: 1200 mm) Range of slow axis angle: -1.5 to +1. 5 degree viewing angle characteristics: 7.5

[Examples 2 and 3] The solvent content before treatment with a pin tenter was 10% (glass transition temperature Tg ': 6).
7 ° C.) and 15% (glass transition temperature Tg ′: 48 ° C.), and a retardation film was produced under the same conditions as in Example 1 except that the temperature was changed. Table 1 shows the characteristic values of this film. These films were extremely excellent for retardation.

[0066]

[Table 1]

[Comparative Example 1] The film length in the direction perpendicular to the stretching axis when treated with a pin tenter was 97.5.
% (The reduction amount was -2.5%), and a retardation film was prepared under the same conditions as in Example 1. The maximum value of the retardation value in a minute range of this film is 3n.
m, there are three spots in the entire width of the film, and when this film is observed between polarizing plates, streak-like color spots based on the above-mentioned retardation spots are observed, which is unsuitable as a retardation film. Was.

[Comparative Example 2] A film before being treated with a pin tenter was heated and dried with air, and the conditions were the same as in Example 1 except that the content of the solvent was reduced to 5%.
A retardation film was prepared. The maximum value of the retardation value in a minute range of this film is 3.5 nm, and there are three spots in the entire width of the film. When this film is observed between polarizing plates, streaky color spots are observed, and the phase difference is observed. It was unsuitable as a film.

Comparative Example 3 A retardation film was prepared under the same conditions as in Example 1 except that the solvent content immediately before uniaxial stretching was 4%. The range of the retardation value of this film is 7 nm (total width of the film), the maximum value of the retardation value of the minute range is 3 nm, and there are three spots in the entire width of the film. Streak-like color spots and local polarization spots were observed, and were unsuitable as a retardation film.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI B29L 11:00

Claims (1)

[Claims] 1. A method for producing a polymer retardation film by casting a polymer solution on a support, drying the obtained film, and stretching the film. 1. A film having a solvent content of 8 to 20% by weight is peeled off from the support. The length of the film in the direction perpendicular to the stretching axis is 99% or more
2. The film is gripped by a pin tenter so that the film content becomes 105%. Film ambient temperature (Tg '+ 10) to (Tg' +
90) At 90 ° C., the solvent content of the film is 2.0
3. dry to less than 4% by weight; Further, the film was subjected to (Tg "+10) to (Tg" +4
5) A method for producing a retardation film, wherein the film is uniaxially stretched 1.1 to 3.2 times in the running direction of the film at a temperature of ° C. (Tg ′, Tg ″ (° C.) are the glass transition temperatures of the polymer film containing the solvent, and this temperature increases as the residual solvent content decreases as the drying proceeds.)