JPH1119954A - Preparation of phase contrast film and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of retardation spots and others by orienting a polymer film uniaxially in the machine direction by a method in which a uniaxial orientation process includes the first stage orientation and the second stage orientation, and the second stage orientation is done at a temperature which is by specified degrees higher than that of the first stage orientation. SOLUTION: Uniaxial orientation is done by the first stage orientation and the second stage orientation, and the second stage orientation is done at a temperature which is by 1-20 deg.C higher than that of the first stage orientation. By doing the uniaxial orientation at temperatures of two stages, a film can be made in which the generation of retardation (the product of a double- refractive index and thickness) spots (color spots in a phase difference compensation film, spots characteristic to a view angle) is prevented. By setting up the orientation temperatures in this way, by the free shrinkage in the width direction of the film in the uniaxial orientation, the decrease in the main refractive index in the direction perpendicular to the orientation direction and the increase in the refractive index in the thickness direction are induced, with the contribution of longitudinal slackening, to improve view angle characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a retardation film by uniaxially stretching a polymer film by a casting method and an apparatus therefor. More specifically, the polymer film is uniaxially stretched in the running direction, and unevenness of retardation (product of birefringence and thickness) (color unevenness when viewing as a retardation compensation film, unevenness of viewing angle characteristics), and the like. The present invention relates to a method and an apparatus for producing a film which does not generate any film.

[0002]

2. Description of the Related Art A retardation plate made of a light-transmitting and birefringent thermoplastic polymer film has been widely used as an anti-glare material and as a retardation compensating plate in an F-STN type liquid crystal display device. ing. 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 been already known. Generally, a uniaxially stretched polycarbonate resin having a large intrinsic birefringence is used. 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. If these are compared with the main technical issues, they can be summarized as follows.

[0003] Japanese Patent Application Laid-Open No. 2-191904 mainly discloses a polycarbonate resin film or sheet.
Under the condition that the distance between the rolls is 5 times or more the film width, the ratio of the length in the direction perpendicular to the stretching axis to the length before stretching is 1 / the square root of the stretching ratio to 1 / the 3rd root of the stretching ratio, ie, the neck In-rate is (1-1 / square root of stretching ratio) × 100% or more
A method of stretching using a biaxial stretching machine capable of performing constant shrinkage in the width direction so as to be (1-1 / third root of stretching ratio) × 100%, or a method of stretching uniaxially with a free width in a longitudinal direction. Proposed. However, in this manufacturing method, it is necessary to set the distance between the rolls to 5 times or more, so a huge stretching apparatus is required, and there are restrictions on facilities such as a need for a free roll for guiding between the stretching rolls. There is a problem that it is large.

Japanese Unexamined Patent Publication (Kokai) No. 3-235902 discloses a method for producing a retardation film by longitudinally and uniaxially stretching a polycarbonate polymer film. A method for producing a retardation film having a flattened film with improved viewing angle characteristics and a good flatness, which has a thermal relaxation region up to a temperature lower by 10 ° C., is described. It also describes a method in which the ratio between the distance between two pairs of rolls for stretching and the film width is 5 or more. This method also has a problem in that the equipment is largely restricted in that a huge stretching apparatus is required. In this manufacturing method, the stretching region has a thermal relaxation region that is a temperature from the glass transition temperature of the film to a temperature lower by 10 ° C. than the glass transition temperature. Since the condition is a temperature lower than the glass transition temperature, there is a problem that the time required for relaxation is extremely long, and there is still a problem in producing a retardation film having excellent viewing angle characteristics. I have.

Focusing on this point, Japanese Patent Laid-Open No. 5-15011
No. 5 proposes a method of easily producing a polycarbonate-based retarder having a wider viewing angle with less restrictions on facilities such as requiring a huge facility. In this method, the length of the film between the nip rolls at the time of stretching is smaller than that of a known document, is set to be 1 to 3 times the film width, and is uniaxially stretched under specific temperature and magnification conditions. In this manufacturing method, when the film is uniaxially stretched, the film may slip at the nip roll portion, and the film surface may be scratched. To prevent this, the nip position is finely adjusted or the temperature of the heating roll before stretching is adjusted to finely control the stretching point (or stretching line) so that the stretching point does not ride on the roll. Otherwise, there is a problem that a scratch is likely to occur. At the stretching start point, stretching tension is applied,
Wrinkles in the film width direction due to width shrinkage (inward diagonally at the end in the width direction, almost parallel to the vertical direction near the center), causing poor film contact with the roll surface Is generated. As a result, there is a problem that uneven stretching with a temperature difference in the width direction results in unevenness of the retardation value and unevenness of the angle of the slow axis. Furthermore,
The so-called bowing phenomenon occurs in which the stretching line is bent in the width direction of the film (stretching at the center in the width direction is delayed and both ends are advanced), and the angle of the slow axis is changed in the width direction of the film (toward both ends of the film). There are problems such as the occurrence of spots (such as an increase in the angle), and the problem that the dispersion of the retardation value in the range of the retardation value or the minute range becomes large.

Japanese Unexamined Patent Publication (Kokai) No. 8-101306 discloses a method for producing a retardation plate in which a film is longitudinally and uniaxially stretched, wherein a temperature gradient is provided in the width direction of the thermoplastic resin film and the film is longitudinally and uniaxially stretched. I have. Although this method is considered to be effective, it is necessary to finely adjust the temperature gradient according to the properties of the film before stretching, and in fact, there is a problem that the manufacturing restrictions are greatly increased. That is, even if the temperature in the width direction of the film can be delicately controlled, the factor that determines the unevenness of the retardation value is also in the unevenness in the width direction of the film thickness. However, there is a problem that complicated operations such as fine control of the temperature in the film width direction 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.

Japanese Patent Application Laid-Open No. 4-282212 discloses a method for producing a retardation film, wherein the tension applied to the film and the drying temperature are regulated under a condition not more than the yield value of the film determined by the residual solvent and the temperature. Is described. This method provides a method for producing a retardation film by a casting film forming method having an appropriate retardation without requiring a heat treatment step. This method is a method of stretching (starting) using the difference in the yield value of the contained solvent film. In this method, it is difficult to make the stretching start line straight in the width direction. There are problems that can easily arise.

Japanese Unexamined Patent Publication (Kokai) No. 4-204503 discloses a retardation film of good quality with little unevenness, characterized in that the film is stretched with the solvent content of the film just before stretching being 2 to 10% based on the solid content. Is described. This was invented as a result of the finding that the optical unevenness of the retardation film can be eliminated by regulating the amount of the solvent contained in the casting film during the stretching step. In this method, since the amount of the residual solvent before the stretching is large, there is a problem that in order to achieve the target amount of the residual solvent after the stretching, it is inevitable that the drying equipment becomes huge or the production rate is significantly reduced. Since a film having a large solvent content is stretched, it is difficult to adjust a retardation value to a desired value and to control minute retardation spots. If the drying ability is low, the solvent content is non-uniform in the film plane, causing a partial difference in stretchability, which causes birefringence unevenness after stretching.

Japanese Patent Application Laid-Open No. 5-113506 discloses that when the solvent content is in the range of 3 to 10% based on the solid content,
A method for producing a retardation film having excellent viewing angle characteristics to be stretched in an atmosphere of 55 ° C. or more and 175 ° C. or less is described.

However, in this method, since the amount of the solvent in the film at the time of stretching is large, the solvent rapidly evaporates due to heating in the stretching step, and there is a problem that fine bubbles are generated. Not only is it not easy to control the target uniformity), but also the residual solvent tends to remain even after the stretching treatment, and this residual solvent may adversely affect the production of parts for liquid crystal display devices. In order to further reduce the amount of residual solvent after stretching, there is a problem that a step for drying needs to be added. In addition, the viewing angle characteristics are also improved, but since the film is stretched in a state where the amount of the remaining solvent is large, the retardation value is hardly increased due to the plasticizing effect of the solvent, and the improvement of the viewing angle characteristics is also insufficient. is there. Among them, a particularly serious problem is that local unevenness (retardation value unevenness, minute retardation value unevenness, slow axis unevenness) tends to occur locally.

JP-A-8-212224 proposes a technique for stretching in a state where the solvent content is less than 2% by weight. This method is intended to improve the drawability of the polymer and the orientation of the polymer after stretching due to the difference in stretchability due to the inclusion of a high concentration of solvent, that is, unevenness in birefringence. . However, even if the film is stretched with the content of the solvent reduced, it is extremely difficult to produce a film with uniform properties unless the film is stretched by strictly controlling the retardation value or the angle of the slow axis of the film before stretching. . Unless longitudinal wrinkles occurring in the film at the stretching start point are prevented, retardation unevenness occurs in a minute range, and there is still a problem in producing a high-quality retardation film.

JP-A-4-84106 discloses a method for producing a retardation film in which a polycarbonate film is uniaxially stretched between rolls at a glass transition temperature or lower and within an elastic deformation limit. Japanese Patent Application Laid-Open No. 4-84107 describes a method for producing a retardation film in which a polycarbonate film is stretched uniaxially in multiple stages such that the stretching ratio per stage is 3% or less between two or more pairs of rolls having different peripheral speeds. ing. In the former method of uniaxially stretching between rolls at a temperature equal to or lower than the glass transition temperature, the film slides on the roll surface immediately before stretching because the tensile stress becomes extremely high,
There is a problem that slip scratches easily occur. Also, in the latter case of multi-stage uniaxial stretching, sliding scratches due to high stretching stress are less likely to occur, but it is necessary to slightly change the speed of each stretching roll for multi-stage stretching according to a change in film thickness, etc. There is a problem that the operation becomes complicated.

[0014]

The technical problems in the production of a retardation film and the characteristics to be provided by the retardation plate are summarized as follows.

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

2) The range of the change of the retardation value and the range of the change of the angle of the slow axis are small. As the size of the liquid crystal display screen increases, various problems have become apparent because the size of the members must be increased. That is, even in the small range of the film, the characteristic value which can be controlled relatively easily is required to be uniform in a wider and larger film as the size is increased. 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. Accordingly, it is required that the range of the retardation value is 5 nm or less even if the retardation value is measured at any position in the width direction and the length direction of the film wound in a roll shape. Similarly, the slow axis is required to be uniform no matter where the member is cut on the film roll.

3) The retardation of a small range is small. 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 superimposed on a liquid crystal display. When used as an 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.

[0019]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies on the mechanism of uniaxial stretching of a solution cast film and obtained the following findings, and reached the present invention.

In the present invention, (1) the polymer solution is cast on a support, (2) the formed liquid film is peeled off from the support, (3) after drying, (4) uniaxial stretching And in the method for producing a retardation film, the uniaxial stretching step (4)
Is performed in the first-stage stretching and the second-stage stretching, and the second-stage stretching is performed at a temperature lower than the temperature of the first-stage stretching by 1 to 1.
Perform at a temperature 20 ° C. higher to produce a retardation film.

The polymer used in the present invention is not particularly limited as long as 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 used in which a polycondensation reaction is used and a main chain is 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 (4hydroxy-3-methylphenyl) propane, 2,2-bis (4hydroxyphenyl) -2-phenylethane, 2,2bis (4hydroxyphenyl) 1,2
1,1,3,3,3 hexafluoropropane, bis (4
(Hydroxyphenyl) diphenylmethane, bis (4hydroxyphenyl) sulfide, bis (4hydroxyphenyl) sulfone, and the like. 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 polycarbonate resin used in the present invention has a viscosity average molecular weight of 1 determined by viscosity measurement in a methylene chloride solution having a concentration of 0.5 g / dl at 20 ° C.
0000 or more and 200,000 or less, preferably 20,
The range from 000 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.

As the solvent system used in the polymer solution of the present invention, a solvent mainly composed of methylene chloride or 1,3-
Solvents mainly comprising dioxolane are exemplified.

As a specific method for preparing a polycarbonate solution, there is a method in which the polycarbonate is poured into methylene chloride and dissolved by stirring. If necessary, 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. The solution thus obtained is cast on a steel belt, a drum, or a support film (generally, a biaxially oriented polyester film) surface or the like by a known method, and dried to obtain a semi-dry state ( At this time, the content of the solvent is about 20 wt% or less).

Similarly, for polysulfone, polyethersulfone, polyarylate, polystyrene, and triacetylcellulose solutions, 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.

In the present invention, the drying step (3) comprises:
It is preferable to include (3-1) a step of drying while holding the film with a pin tenter, and (3-2) a step of drying using a roll hanging type drying apparatus.

In the drying step (3-1), the solvent-containing film obtained by peeling from the support is continuously held in a state where both ends thereof are gripped by a pin tenter (usually pierced with pins and fixed and transported). Can be dried by heating.
The film shrinks because a large amount of solvent evaporates in this step. A shrinkage stress is generated corresponding to the shrinkage, and a retardation value and a spot of a slow axis are generated, so that the film width and the hot air temperature at the time of holding the pin tenter are adjusted to desired set values so as to reduce the shrinkage stress. Is preferred.

The heating temperature is from temperature (Tg ₂ +10) to
It is preferable to control the temperature to (Tg ₂ +90) ° C. (Tg
₂ (° 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. Specifically, in the case of a polycarbonate solution, it is preferable to control the temperature to 90 to 130 ° C.

The hot air temperature of the pin tenter is (Tg ₂ +1)
0) When the temperature is lower than 0 ° C., since the solvent is not sufficiently dried, the characteristics of the film immediately before stretching may not be controlled due to the effect of the solvent contained in the subsequent drying step in the roll hanging type drying apparatus. In addition, the hot air temperature is (Tg ₂ +
If the temperature exceeds 90) ° C., the optical characteristics (retardation value, slow axis, and distribution thereof) may deviate from desired values.

Further, a polymer film is formed with a pin tenter,
It is preferable to control the distance between the pins so that the distance between the pins after gripping, that is, the length of the film in the direction perpendicular to the stretching axis is reduced by 2 to 5%. When the amount of reduction in the distance between the pins for holding the polymer film of the pin tenter is less than 2%,
Since the shrinkage stress due to the evaporation of the solvent is large, the retardation value and the size and distribution of the slow axis may not be the desired values. If the reduction amount of the inter-pin distance is set to more than 5%, the film sags during running in the pin tenter, resulting in poor flatness and poor running in the next step, thereby achieving the object of the present invention. May not be possible. At the exit of the pin tenter, the structure can be fixed by cooling the film to room temperature with cold air.

The characteristic value of the polymer film after the drying step in the pin tenter of the above (3-1) is such that the residual solvent amount is 3.5 to 4.5 wt. %, Retardation value 10-1
It is preferable to satisfy 5 nm and an angle of the slow axis of -10 to +10 degrees.

Subsequently, it is preferable to cut off both edges of about 50 mm gripped by the pins of the pin tenter. If both edges are not cut off, the pierced portion of the pin is uneven and the film does not run smoothly on the roll surface for transport to the next process, or white powder (pin) generated from the pierced hole of the pin May be attached to and contaminate the film product.

Next, it is preferable that the film is passed through a roll hanging drier, and further dried in the drying step (3-2) using a roll hanging drier.
This step also serves as a pre-heat treatment step for the film before stretching.

The drying conditions of the roll hanging type drying apparatus are as follows:
Temperature (Tg ₃ -20) to (Tg ₃ +10) ° C., tension 1
About 2.5 kg / cm ² is preferable. (Tg ₃ (° C.) is a glass transition temperature of a polymer film containing a solvent,
This temperature increases with decreasing residual solvent content as drying proceeds. )

Desirable characteristic values of the film subjected to the uniaxial stretching step after the drying treatment in the roll hanging type drying apparatus of the above (3-2) are, particularly, those containing a solvent content of 0.5 from a polycarbonate solution. ~ 2.0 wt. %,
More preferably, 0.5 to 1.6 wt. %. Retardation value: 10 to 20 nm, more preferably 10 to 15 n
It is desirable to control so as to simultaneously satisfy m and the angle of the slow axis: -7 to +7 degrees. When these characteristic values are out of the above ranges, good conditions cannot be found in the next stretching step, and it is difficult to produce a retardation film having excellent characteristics.

The polymer film wound around the roll subjected to the uniaxial stretching step is preferably held down by a nip roll. It is preferable that the stretching does not substantially occur on the nip roll or the pinch roll immediately before the stretching, and starts immediately after the film leaves the nip roll. It is preferable to start stretching such that the stretch line (stretch start line) of the film does not bend (so-called bowing) across the width direction of the film.

In the above (4) uniaxial stretching step, the polymer film is uniaxially stretched at a predetermined magnification. In the present invention, the uniaxial stretching is performed by a first stage stretching and a second stage stretching.
Further, the second stage of stretching is performed at a temperature higher by 1 to 20 ° C. than the temperature of the first stage of stretching. By performing uniaxial stretching at two temperatures, a film is produced which does not cause unevenness of retardation (product of birefringence and thickness) (colored unevenness when viewed as a retardation compensation film, unevenness of viewing angle characteristics) and the like. be able to.

In the present invention, the temperature of the first stage stretching is preferably (Tg ₁ +10) ° C. to (Tg ₁ +35) ° C. Further, the temperature of the second-stage stretching is preferably 5 to 10 ° C. higher than the first-stage stretching temperature. (Here, Tg ₁ is the glass transition temperature when a solvent is contained, and this temperature increases as the drying proceeds, as the residual solvent content decreases.) The stretching temperature is set in this manner. the free shrink in the width direction of the film in a uniaxial stretching by the main refractive index in the stretching direction n _x, the main refractive index in the direction perpendicular to the stretching direction n _y,
Easily occurs increase of n _y drop and n _z of when the refractive index in the thickness direction is n _z, also be worked contribution of longitudinal relaxation,
The viewing angle characteristics can be improved. If the stretching temperature is (Tg ₁ +10) ° C. or less, the relaxation of the molecular chains in the longitudinal and transverse directions is unlikely to occur. In such a case, it is necessary to take a longer time for the relaxation. The length is increased, or a step for thermal relaxation is separately required.

The stretching temperature in the first stage is (Tg ₁ +35) ° C.
If the molecular weight is higher, it is difficult to increase the orientation of the molecular chain, and the resulting film may have an uneven retardation value. The stretching temperature may be set to a relatively high temperature in the above temperature range 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 and improve the viewing angle characteristics. preferable.

The stretching in the first stage is performed at a stretching ratio of 1.1 to 3.2.
And the second stage of stretching has a stretching ratio of 1.01 to 1.2.
It is preferably 0 times. The stretching ratio referred to here means the stretching ratio with respect to the original length before stretching in both the first stage and the second stage.

The film is heated by an air jet between the stretching roll and the roll after the completion of the stretching to perform the first-stage stretching.
It is preferable that the air jet is blown immediately after the film leaves the stretching roll by a slit nozzle in which hot air is uniformly generated in the width direction so that stretching is started. The speed of the hot air jet is preferably in the range of 15 to 30 m / sec in order to maximize the heat transfer coefficient to the film.
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.

The stretching in the second stage can be carried out using an apparatus such as an air-jet type heating stretching method similar to the first stage, or a film wound around rolls and stretched. In particular, it is preferably used in view of the uniformity of the optical characteristics of the film obtained by the air jet heating and drawing method and the absence of surface defects.

In the first stage of stretching, it is preferable to strictly control the stretching temperature and the length between rolls (stretching span). The length from the start point (or stretching start line) of the first stage to the end of stretching, especially when a nip roll is provided during the second stage of stretching, the stretching start point (or the stretching start line)
And the length between the stretching nip rolls is preferably 1.5 times or more and 4.0 times or less with respect to the width of the film to be stretched.

If the inter-roll length (stretching span) is at least 1.5 times the film width before stretching, the film is stretched and the film width and thickness can be freely changed (width and thickness) while the end point of stretching is between them. Thickness). In other words, free-width uniaxial stretching and free-thickness uniaxial stretching provide an ideal uniaxially stretched structure in which the refractive indices _ny and _nz are equal, and the viewing angle characteristics are improved.

When the inter-roll length (stretching span) is 1.5 times or less with respect to the film width, rotation of the polymer chain along the stretching axis due to free shrinkage in the film width direction hardly occurs. The optical structure of the film may be fixed while the so-called plane orientation is large (the refractive index in the thickness direction is small). That is, the uniaxial stretching in which the refractive indexes _ny and _nz are equal to each other is not achieved, and the viewing angle characteristics may not be improved.

The film may be nipped with a nip roll at the end point of the stretching in the first stage, or may be nipped without the nip.
Stepwise stretching may be performed. When the nip is performed at the end point of the stretching in the first stage, if the nip is performed while the temperature of the film is high, small-pitch wavy spots generated at the time of stretching may be held down by rolls, and wrinkles may be fixed. If the temperature of the nip roll system is too low as compared with the temperature of the stretching in the first stage, the thermally expanded film shrinks and the film may be wrinkled. Therefore, it is preferable to adjust the temperature of the nip roll system so as to be 5 ° C. to 100 ° C. lower than the temperature of the first stage stretching.

It is preferable that the film after the completion of the second-stage stretching is then cooled to room temperature. At this time, if the film temperature is rapidly cooled from the stretching temperature to the room temperature, so-called quenching may result in a wrinkled retardation film. 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 will enter. The wrinkles due to the expansion and contraction are fixed as they are when they are rapidly cooled, and remain as so-called wavy wrinkles in a corrugated shape substantially parallel to the longitudinal direction. The corrugated plate-like wrinkles may cause the stretched film to be 100 to 1
The problem can be solved by contacting the rolls at a temperature of 50 ° C. or by air heat treatment between the rolls and then cooling to room temperature.

The apparatus for producing a retardation film in the present invention includes a cast film forming apparatus (A), a film peeling apparatus (B), a pin tenter drying apparatus (C), and a roll as shown in FIGS. 1 and 2. A hanging-type drying apparatus (D), a first-stage stretching apparatus (E), a first cooling chamber (F), a second-stage stretching apparatus (G), and a second cooling chamber (H), and these apparatuses are provided. They are arranged in this order, and the temperature condition of the second-stage stretching device is one time lower than that of the first-stage stretching device.
It is a device that is 〜20 ° C. The film can be continuously passed through this manufacturing apparatus for processing. FIG. 1 shows a case where no nip roll is provided between the first stage stretching device (E) and the second stage stretching device (G), and FIG. 2 shows a case where a nip roll is provided.

In this way, the film is formed of a polymer film which satisfies the required characteristics as a constituent element of the liquid crystal display element by the solution film forming method, has a small thickness variation width, a range of retardation value, and a retardation value. A retardation film having small viewing spots and excellent viewing angle characteristics can be manufactured.

[0054]

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

[Measurement of Retardation Value and Slow Axis Angle] The total width of the sample in the width direction of the film is KO, a trade name manufactured by Shin-Oji Paper Co., Ltd.
BRA-21SDH) to measure the retardation value at 5 mm intervals. From this data, the difference in retardation value over the entire width of the measurement sample was determined. That is, take the difference between the maximum value and the minimum value of the retardation value in the entire width range,
It was 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). If this value is large, this portion may appear as streak-like color spots when the film is sandwiched between polarizing plates.
The sample length for the measurement was the total length in the width direction, and 1 m in the length direction was the measurement length.

[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 solvent content based on solid content was determined from the weight change rate before and after drying (accurately weighed with an analytical balance). In the case of measurement in the film width direction, the measurement was performed by dividing the film into five equal parts in the width direction.

[Measurement of Viewing Angle Characteristics] Automatic birefringence index measuring device (trade name KOBRA-21AD manufactured by Shin-Oji Paper Co., Ltd.)
Using H), the retardation R in the normal direction of the film
The retardation Re (40) when obliquely incident on e (0) and the normal line of the film at a relative angle of 40 degrees was measured, and the rate of change in retardation was determined from the absolute value of the difference.

[0058]

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

[Measurement of Apparent Glass Transition Temperature Tg _1-3 (Tg of Film Containing Solvent)] About 10 mg of a film sample containing a solvent was used at a heating rate of 10 ° C./min.
In the DSC curve (DSC measurement device is DSC V4 OB
(Using DuPont 2000). The apparent glass transition temperature Tg of the falling (inflection point) portion of this curve
₁ to ₃ .

[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, dried and peeled off from the belt surface. The characteristics of the film at this time were as follows. Solvent content: 19.5 ± 1.0 wt. % (Total width of film) Glass transition temperature Tg ₂ : 45 ° C. Film thickness: 70 μm, film width: 1500 mm,
Thickness unevenness: 1 μm (full width of film)

The film was then passed through a pin tenter, which divided the room into six zones. At this time, the width of the entrance of the pin tenter was 1500 mm, and the width was gradually reduced as it proceeded from the entrance, and the reduction width of each zone was made linear. The fifth zone was reduced to 1448 mm (that is, 3.5%). The temperature of the dry air in the oven of the pin tenter was 110 ° C. in all six chambers. Next, the film was air-cooled to room temperature while holding the film, and both edges were cut off at the pin tenter outlet. The characteristic values of the film thus obtained were as follows. Retardation value: 10 to 15 nm (film width 14
00 mm) Slow axis value: -7 to +7 degrees (film width 1400 mm) Residual solvent amount and its distribution: 4.0 ± 0.5 wt. %
(Film width 1400 mm) Glass transition temperature Tg ₃ : 110 ° C. Thickness and thickness unevenness: 70 μm and 1.0 μm (film width 1400 mm) In this way, a non-stretched film having a thickness of 70 μm was prepared. The film was further passed through a roll-hanging drier, a stretching device and a stretching device having a cooling zone.

A) Drying conditions in a roll hanging type drying apparatus Hot air temperature: 100 ° C., tension applied to the film: 1.5 K
g / cm ² , treatment time: 30 minutes. The characteristic values of the obtained film were as follows: residual solvent amount: 1.6 ± 0.05 wt. %, Glass transition temperature Tg ₁ : 140 ° C., retardation value: 12
１５15 nm (full width of film 1400 mm), angle of slow axis: -5 to +5 degrees (full width of film 1400 mm).

B) Stretching conditions First stage Stretching temperature: 150 under air-jet heating
° C, stretching ratio: 1.26 times, span length of stretching: 1.6 times the film width before stretching. Second stage Stretching temperature: 160 under air jet heating
C., stretching ratio: 1.03 times, stretching span length: 1.6 times the film width before stretching. The film after the completion of the second-stage stretching was nipped with a nip roll maintained at a temperature of 100 ° C. Thereafter, cooling was performed in a cooling zone at 60 ° C. for 30 seconds, and then air-cooled to room temperature.

The properties of the obtained film as a retardation film were as follows. Film thickness: 54 μm, film thickness unevenness: 0.3 μ
m (total width of 1200 mm film), difference between maximum and minimum retardation values: 4 nm (1200 mm film width) Micro retardation value Maximum value: 1.1 nm (120
0 mm film width) Slow axis angle range: -1.5 to +1.5 degrees (1200 m
m film width) Viewing angle characteristics: 7.5, appearance defects: scratches, scratches,
No undulations. Table 1 shows the above results.

[0065]

[Table 1]

[Examples 2 to 4] Table 1 shows the characteristic values of the films obtained by forming stretched films in the same manner as in Example 1 except that the stretching conditions were changed as shown in Table 1. Note that the retardation of the film was about 500 n under any conditions.
m.

As shown in Table 1, stretching was carried out in Example 2 at a higher stretching temperature than in Example 1. In this case also, the obtained film had good properties and was excellent as a retardation film. Met.

As shown in Table 1, in Example 3, stretching was performed with both the stretching temperature and the stretching ratio higher than those in Example 1. As shown in FIG. 2, the stretching was performed between the stretching in the first stage and the stretching in the second stage. A method of nipping a film with a nip roll was used. At this time, the temperature of the nip roll was adjusted to 150 ° C. to 160 ° C. so as not to wrinkle the film. Also in Example 3, the properties of the obtained film were good and excellent as a retardation film.

As shown in Table 1, in the fourth embodiment, the second
The film was stretched at a higher stretching ratio than that in Example 1, but the film obtained in this case also had good properties and was excellent as a retardation film.

COMPARATIVE EXAMPLE The stretching in the first stage was carried out under the stretching conditions except that the stretching temperature was 150 ° C., the stretching ratio was 1.26 times, and the stretching in the second stage was not performed under air jet heating. A stretched film was prepared in exactly the same manner as in Example 1.
Table 1 shows the characteristic values of the obtained film as a retardation film. The film obtained here had a large range of retardation value, the maximum value of minute retardation value, the range of slow axis angle, and the like, and also had poor viewing angle characteristics. No external defects.

[0071]

The retardation film comprising the polymer of the method of the present invention has a small thickness, a range of retardation, and a small range of retardation in the entire width of the product roll film and the entire length in the winding direction, The size of the slow axis is small, good and excellent in uniformity, excellent in transparency, and free from scratches and abrasions. A suitable polymer retardation film can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the configuration of a retardation film manufacturing apparatus (a nip roll is not provided between a first-stage stretching apparatus and a second-stage stretching apparatus).

FIG. 2 is a schematic diagram illustrating the configuration of a retardation film manufacturing apparatus (a nip roll is provided between a first-stage stretching apparatus and a second-stage stretching apparatus); a cast film forming apparatus (A); and a film peeling apparatus (B). , Pin tenter drying device (C), roll hanging type drying device (D), first stage stretching device (E), first
A cooling chamber (F), a second-stage stretching apparatus (G), and a second cooling chamber (H) are provided, and these apparatuses and chambers are arranged in this order, and the film is continuously passed through the manufacturing apparatus. And process.

[Explanation of symbols]

 1: Cast film forming device 2: Film peeling device 3: Pin tenter drying device 4: Roll hanging type drying device 5: First stage stretching device 6: First cooling room 7: Second stage stretching device 8: Second cooling room 9: Film 10: Free rotating roll 11: Nip roll 12: Air jet device

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 20, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0066

[Correction method] Change

[Correction contents]

[Examples 2 to 4] Table 1 shows the characteristic values of the films obtained by forming stretched films in the same manner as in Example 1 except that the stretching conditions were changed as shown in Table 1. Implemented
The retardation of the film was set to a condition of about 500 nm under both the conditions of the example and the comparative example , and obtained.
The retardation value of the film was about 500 nm .

Continued on the front page (72) Inventor Ichiro Okamoto 77 Kitayoshida-cho, Matsuyama-shi, Ehime Pref.

Claims (11)

[Claims] (1) casting a polymer solution on a support,
(2) In the method of peeling the formed solvent-containing film from the support and (3) drying and then (4) uniaxially stretching to produce a retardation film, the uniaxially stretching step (4) is performed in the first step. A method for producing a retardation film, wherein the method comprises the steps of stretching in a second step and stretching in a second step, wherein the temperature of the second step is higher by 1 to 20 ° C. than the temperature of the first step. 2. The uniaxial stretching step (4) is carried out at a temperature (Tg ₁
+10) to (Tg ₁ +35) ° C. and a draw ratio of 1.1 to 1.1
The stretching in the second stage is performed at a temperature 5 to 10 ° C. higher than the stretching temperature in the first stage, and the stretching ratio is 1.
The method for producing a retardation film according to claim 1, wherein the method is performed under a condition of 01 to 1.20 times. (Tg ₁ (° C.) is the glass transition temperature of a polymer film containing a solvent, and this temperature rises as the residual solvent content decreases as drying proceeds.) 3. The method for producing a retardation film according to claim 1, wherein the polymer solution is a polycarbonate solution of 10 to 30% by weight. 4. The drying step (3) comprises (3-1) a step of drying while holding a film with a pin tenter, and (3-2) a step of drying using a roll hanging type drying apparatus. The method for producing a retardation film according to claim 1, wherein: 5. In the drying step (3-1), the film peeled from the support is gripped with a pin tenter so that the shrinkage of the film in a direction perpendicular to the running direction is 2 to 5%. While the temperature (Tg ₂ +1
0) ~ (Tg ₂ +90) ℃, method for producing a retardation film according to claim 4, characterized in that the drying. (T
g ₂ (° C.) is the glass transition temperature of the polymer film containing the solvent, and this temperature rises as the drying proceeds and the residual solvent content decreases. ) 6. The characteristic value of the film after drying in the drying step (3-1) is such that the residual solvent amount is 3.5 to 4.5 wt.
%, A retardation value of 10 to 15 nm, and an angle of the slow axis of -10 to +10 degrees.
5. The method for producing a retardation film according to any one of 5. 7. The film dried in the drying step (3-1) is further subjected to a temperature (1 to 2.5 kg / cm ² ) while applying a tension of 1 to 2.5 kg / cm ^{2 in} a film running direction using a roll hanging type drying device. _{Tg 3 -20) ~ (Tg 3} +10) method for producing a retardation film according to claim 4 for performing drying at ℃ conditions. (Tg ₃ (° C.) is the glass transition temperature of the solvent-containing polymer film, and this temperature increases with the decrease in the residual solvent content as the drying proceeds.) 8. The film subjected to the uniaxial stretching step has a characteristic value of 0.5 to 2.0 wt. %, A retardation value of 10 to 20 nm, and an angle of the slow axis of -7 to +
The method for producing a retardation film according to any one of claims 1 to 7, which satisfies 7 degrees. 9. The method according to claim 1, wherein the stretching in the first stage is carried out under the condition that the length between stretching rolls is 1.5 to 4.0 times the film width before stretching. A method for manufacturing a retardation film. 10. The method for producing a retardation film according to claim 1, wherein the method of heating the film in the first stage of stretching comprises an air jet heating method. (1) A polymer solution is cast on a support, (2) the formed solvent-containing film is peeled from the support, (3) dried, and (4) uniaxially stretched. , A retardation film producing apparatus for producing a retardation film, comprising a cast film forming apparatus (A), a film peeling apparatus (B), a pin tenter drying apparatus (C), a roll hanging type drying apparatus (D), A first-stage stretching apparatus (E), a first cooling chamber (F), a second-stage stretching apparatus (G), and a second cooling chamber (H), and these apparatuses and chambers are arranged in this order. An apparatus for producing a retardation film, wherein the temperature condition of the second-stage stretching device is higher by 1 to 20 ° C. than the temperature condition of the first-stage stretching device.