JP2004163981A - Manufacturing method of retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a high-molecular retardation film that is small in thickness, retardation range, and a retardation spot in a minute range, that has also small, improved, and excellently uniform lagging axis size, and that has excellent transparency, is free from scratches or abrasion, and is suitable for optical use. <P>SOLUTION: A high molecular solution is made to flow on a substrate to form a fluid film. It is then separated from the substrate, dried, uniaxially stretched, and cooled to form the retardation film. In this manufacturing method, the uniaxial stretching is performed through a first stage stretching and a second stage stretching. Also, the second stage stretching is performed at a temperature 1-20°C higher than in the first stage stretching to produce the retardation film. <P>COPYRIGHT: (C)2004,JPO

Description

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

  BACKGROUND ART A retardation plate made of a thermoplastic polymer film having optical transparency and birefringence has been widely used as an anti-glare material and as a retardation compensator 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 for manufacturing the retardation plate, a method for manufacturing various polymer films by uniaxial stretching has already been 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 production method thereof. If these are compared with the main technical issues, they can be summarized as follows.

  Patent Document 1 discloses that the ratio of the length in the direction orthogonal to the stretching axis to the length before stretching is 1/1, mainly on a polycarbonate resin film or sheet under the condition that the distance between rolls is 5 times or more the film width. The square root of the stretching ratio to 1 / the cube root of the stretching ratio, that is, the neck-in ratio is (1-1 / square root of the stretching ratio) × 100% to (1-1 / the cube root of the stretching ratio) × 100%. As described above, a method of stretching using a biaxial stretching machine capable of performing a constant shrinkage in the width direction, or a method of stretching vertically and uniaxially with a free width has been 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.

  Further, Patent Document 2 discloses a method for producing a retardation film formed by longitudinally and uniaxially stretching a polycarbonate polymer film, wherein a temperature from a glass transition temperature of the film to a temperature lower by 10 ° C. than the glass transition temperature in the stretched region. A method for producing a retardation film having a viewing angle characteristic and a good flatness having a thermal relaxation region 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 a large stretching apparatus is required, which greatly restricts equipment. Further, in this manufacturing method, the stretching region has a thermal relaxation region which 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, Patent Literature 3 proposes a method which can easily manufacture 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 a specific temperature and magnification condition. In this manufacturing method, when the film is subjected to uniaxial stretching, 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. Also, at the stretching starting point, stretching tension is applied and the width shrinks, so that vertical wrinkles are formed in the film width direction (inwardly obliquely at the end in the width direction and almost parallel to the vertical direction near the center). This causes a portion where film contact with the roll surface becomes poor. As a result, there is a problem that uneven stretching of the retardation value and unevenness of the angle of the slow axis tend to occur as a result of uneven stretching having a temperature difference in the width direction. Further, a so-called bowing phenomenon occurs in which the stretched line is bent in the width direction of the film (stretching in 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 (to the both ends of the film). There are problems such as the occurrence of spots (in which the angle becomes larger toward the front) and the variation of the retardation value in the range of the retardation value or the minute range.

  Further, Patent Document 4 discloses a method for producing a retardation plate for longitudinally and uniaxially stretching a film, 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, 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 conditions 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.

  Furthermore, 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, Patent Document 5, Patent Document 6, and Patent Document 7 can be cited. In these methods, uniaxial stretching is performed with a relatively large amount of solvent. According to these methods, the apparent glass transition temperature decreases according to the amount of the contained solvent, and therefore, there is an advantage that the stretching can be performed at a relatively low temperature.

  Patent Document 5 discloses a method for producing a retardation film, which regulates the tension applied to the film and the drying temperature under conditions that are equal to or lower than the yield value of the film determined by the residual solvent and the temperature. This method is to provide 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, since it is difficult to make the stretching start line straight in the width direction, retardation unevenness in the width direction is reduced. There are problems that can easily arise.

  Patent Document 6 describes a method for producing a good-quality retardation film with little unevenness, characterized in that the film is stretched by setting the solvent content of the film immediately before stretching to 2 to 10% based on the solid content. I have. 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 the retardation value to a desired value and to control minute retardation spots. If the drying ability is low, the solvent content is not uniform in the plane of the film, causing a difference in stretchability partially, thereby causing birefringence unevenness after stretching.

  Patent Document 7 discloses a method for producing a retardation film having excellent viewing angle characteristics, which is stretched in an atmosphere of 155 ° C. or more and 175 ° C. or less when the solvent content is in a range of 3 to 10% on a solid content basis. Is described.

  However, in this method, the amount of the solvent in the film at the time of stretching is large, so that the solvent rapidly evaporates due to heating in the stretching process, causing a problem that fine bubbles are generated, and the uniformity of the stretched film (optical uniformity). Not only is it not easy to control), but also the residual solvent tends to remain after the stretching process, 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 must 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 large problem is that local unevenness (retardation value irregularity, minute retardation value irregularity, slow axis irregularity) tends to occur locally.

  Patent Document 8 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 partial difference in stretchability caused by the inclusion of the high concentration solvent, that is, the occurrence of unevenness in birefringence. . However, it is extremely difficult to produce a film with uniform properties unless the film is stretched by reducing the amount of the contained solvent and the film is stretched by strictly controlling the retardation value and 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, phase difference unevenness occurs in a minute range, and there is still a problem in producing a high quality phase difference film.

  Patent Document 9 describes a method for producing a retardation film in which a polycarbonate film is uniaxially stretched between rolls at a temperature equal to or lower than a glass transition temperature and within an elastic deformation limit. Patent Document 10 describes a method for producing a retardation film in which a polycarbonate film is stretched uniaxially in two or more steps between two or more rolls having different peripheral speeds so that the stretching ratio per step is 3% or less. In the former method, in which the film is uniaxially stretched between rolls at a temperature lower than the glass transition temperature, the tensile stress becomes extremely high, so that the film slides on the roll surface immediately before stretching, and thus there is a problem in that a sliding scratch is easily generated. In the case of the latter multi-stage uniaxial stretching, sliding scratches due to high stretching stress are unlikely 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 operation becomes complicated.

JP-A-2-191904 JP-A-3-235902 JP-A-5-150115 JP-A-8-101306 JP-A-4-282212 JP-A-4-204503 JP-A-5-113506 JP-A-8-212224 JP-A-4-84106 JP-A-4-84107

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

  1) In addition to being excellent in transparency, the film has 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. As the size of the liquid crystal display screen increases, various problems have become evident since the members need to be increased in size. That is, even in the small range of the film, the characteristic value which can be relatively easily controlled 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 with the naked eye, and cannot be used as a liquid crystal display device. Have been. Accordingly, it is required that the range of the retardation value be 5 nm or less, regardless of the position in the width direction and the length direction of the film wound in a roll. Similarly, the slow axis is required to be uniform no matter where the member is cut on the film roll.

  3) Small spots of retardation in a minute range. It is required that the difference in retardation value in a minute range, for example, at a point separated by 10 mm on the film surface 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 the 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 in the liquid crystal display device also increases, and the demand for uniformity of characteristic values on a larger surface inevitably increases.

  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 as a result, obtained the following findings, and reached the present invention.

  In the present invention, (1) a solution comprising polycarbonate and methylene chloride is cast on a support, (2) the formed liquid film is peeled off from the support, and (3) after drying, (4) In the method for producing a retardation film composed of polycarbonate by uniaxially stretching, the uniaxial stretching step (4) is performed by a first stage stretching and a second stage stretching, and the second stage stretching is performed by the first stage stretching. At a temperature higher by 1 to 20 ° C. than the stretching temperature to produce a retardation film made of polycarbonate.

  The retardation film composed of the polymer of the method of the present invention has a small thickness of the retardation film in the entire width and the entire length in the winding direction of the product roll-shaped film, the range of the retardation, and the minute range of the retardation, and the size of the slow axis. It is small, good and excellent in uniformity, excellent in transparency, and free from scratches and scratches, so productivity and workability are significantly improved, and a polymer suitable for optical applications that is extremely useful industrially A retardation film can be provided.

  The polymer used in the present invention is not particularly limited as long as the desired properties of the film can be obtained. Examples thereof include conventionally known polymers 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, and polycarbonate is preferable.

  In general, a polymer material collectively referred to as polycarbonate generally refers to a material 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 referred to as 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 2,3,5 trimethylcyclohexane, 2,2-bis (4hydroxy-3-methylphenyl) propane, 2,2-bis (4hydroxyphenyl) -2phenylethane, 2,2bis (4hydroxyphenyl) 1,1,2 1,3,3,3 hexafluoropropane, bis (4hydroxyphenyl) diphenylmethane, bis (4hydroxyphenyl) sulfide, bis (4hydroxyphenyl) sulfone and the like can be mentioned. Furthermore, those in which the hydrogen groups of these phenyl groups are partially substituted with methyl groups or halogen groups are also included.

  It is also generally possible to use polyester carbonates containing terephthalic acid and / or isophthalic acid components. 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 10,000 to 200,000, preferably 20,000 or more, as determined from a viscosity measurement at 20 ° C. in a methylene chloride solution having a concentration of 0.5 g / dl. A range of 120,000 or less is preferably used. If a resin having a viscosity average molecular weight lower than 10,000 is used, the resulting film may have insufficient mechanical strength. On the other hand, if 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.

  Examples of the solvent used in the present invention include a solvent mainly composed of methylene chloride.

  As a specific method for preparing a polycarbonate solution, there is a method in which the polycarbonate is put 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 by a known method, dried, and dried to a semi-dry state ( The solvent content at this time is about 20% by weight or less).

  In the present invention, by adjusting the concentration of the solution composed of polycarbonate and methylene chloride to 10 to 30% by weight, more preferably 15 to 25% by weight, a film can be suitably formed by the solution casting method.

  In the present invention, the drying step (3) may 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. preferable.

  In the drying step (3-1), the solvent-containing film obtained by peeling off from the support is continuously heated and dried while both ends thereof are gripped by a pin tenter (usually pierced with pins and fixed and transported). can do. The film shrinks because a large amount of solvent evaporates in this step. A shrinkage stress is generated in accordance with 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.

It is preferable to control the heating temperature to a temperature of (Tg ₂ +10) to (Tg ₂ +90) ° C. (Tg ₂ (° C.) is the glass transition temperature of a film made of a polycarbonate containing a solvent, and this temperature increases with the decrease in the residual solvent content as the drying proceeds.) Specifically, in the case of a polycarbonate solution, 90 ° C. It is preferable to control the temperature to 130 ° C.

When the hot air temperature of the pin tenter is lower than (Tg ₂ +10) ° C., the drying of the solvent is not sufficiently performed. You may not be able to control it. When the hot air temperature exceeds (Tg ₂ +90) ° C., the optical characteristics (retardation value, slow axis, and distribution thereof) may deviate from desired values.

  Further, it is preferable to control the distance between the pins so that the distance between the pins, that is, the length of the film in the direction perpendicular to the stretching axis, shrinks by 2 to 5% after the film made of polycarbonate is gripped by the pin tenter. If the amount of reduction in the pin-to-pin distance of the film gripping film made of polycarbonate for the pin tenter is less than 2%, the shrinkage stress due to solvent evaporation is large and the retardation value and the size and distribution of the slow axis do not become the desired values. There is. 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 film made of polycarbonate after the drying step in the pin tenter of (3-1) 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 are preferred.

  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 smoothly run on the roll surface for transporting to the next process, or white powder generated from the pierced hole of the pin May be attached to and contaminated the film product.

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

Drying conditions of the roll hanging type drying device are preferably a temperature (Tg ₃ −20) to (Tg ₃ +10) ° C. and a tension of about 1 to 2.5 kg / cm ² . (Tg ₃ (° C.) is the glass transition temperature of a film made of polycarbonate containing a solvent, and this temperature increases as the residual solvent content decreases as drying proceeds.)

  Desirable characteristic values of the film to be subjected to the uniaxial stretching step after the drying treatment with the roll hanging type drying device of the above (3-2) are as follows. . %, More preferably 0.5 to 1.6 wt. %. It is desirable to control so that the retardation value: 10 to 20 nm, more preferably 10 to 15 nm, and the angle of the slow axis: -7 to +7 degrees are simultaneously satisfied. 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.

  It is preferable that the film made of polycarbonate wound around a roll subjected to the uniaxial stretching step is 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 stretching line (stretching 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 polycarbonate 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, and the second stage stretching is performed. The stretching is performed at a temperature 1 to 20 ° C. higher than the stretching temperature in the first stage. By performing uniaxial stretching at two temperatures, a film is produced that 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.

The temperature of the first-stage stretching in the present invention is preferably (Tg ₁ +10) ° C. to (Tg ₁ +35) ° C. Furthermore, the temperature of the second-stage stretching is preferably 5 to 10 ° C. higher than the first-stage stretching temperature. (Tg ₁ as used herein refers to the glass transition temperature when a solvent is contained, and this temperature increases as the residual solvent content decreases as drying proceeds.)

The free shrink in the width direction of the film in a uniaxial stretching by setting the stretching temperature in this way, the main refractive index in the stretching direction n _x, the main refractive index in the direction perpendicular to the stretching direction n _y, the refractive index in the thickness direction When _nz is set to _nz , _ny decreases and _nz rises easily, and the contribution of the relaxation in the vertical direction is also effective, so that the viewing angle characteristics can be improved. When 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.

When the stretching temperature in the first step is higher than (Tg ₁ +35) ° C., it is difficult to increase the molecular chain orientation, 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 as much as possible and to improve the viewing angle characteristics by sufficiently relaxing the orientation of the polymer chains in the width direction. preferable.

  The stretching in the first stage preferably has a stretching ratio of 1.1 to 3.2, and the stretching in the second stage preferably has a stretching ratio of 1.01 to 1.20. The stretching ratio referred to here means the stretching ratio 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 purpose, an air-floating hot-air device can be preferably used. This method is very 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 hot air can be changed in the direction of film travel between the stretching rolls.

  The stretching in the second stage can be carried out using an apparatus such as an air jet heating stretching method similar to the first stage, or a device in which a film is stretched by winding a film between rolls. In particular, it is preferably used in view of the uniformity of the optical characteristics of the film obtained by the air jet type heating and stretching 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 starting point (or stretching start line) of the first stage to the end of stretching, especially when a nip roll is provided during stretching in the second stage, stretching from the starting point (or stretching start line) It is preferable that the length between the nip rolls is 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 (the width and thickness decrease) while the end point of stretching is in between. ) Happens. 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, it is difficult for the polymer chain to rotate along the stretching axis based on free shrinkage in the film width direction. In some cases, the optical structure of the film is fixed while the value is large (the refractive index in the thickness direction is small). That is, it is not the ideal uniaxial stretching in which the refractive indexes _ny and _nz are equal, and the viewing angle characteristics may not be improved.

  The film may be nipped by a nip roll at the end point of the first stage stretching, or the second stage stretching may be performed without the nip. 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 pressed by rolls, and wrinkles may be fixed. If the temperature of the nip roll system is too low compared to the stretching temperature 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, a wrinkled retardation film may be formed. Rapid cooling of the stretched film causes shrinkage by the amount of 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 wrinkles can be eliminated by bringing the stretched film into contact with a roll at a temperature of 100 to 150 ° C. or by air heat treatment between the rolls and then cooling to room temperature.

  The production apparatus of the retardation film made of polycarbonate according to 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. 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. The devices are arranged in this order, and 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. 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, a film made of polycarbonate that satisfies the required characteristics as a constituent element of a liquid crystal display element by a solution casting method has a small thickness variation width, a range of a retardation value, and a fine unevenness of a retardation value. A small retardation film having excellent viewing angle characteristics can be produced.

Hereinafter, the present invention will be described in detail with reference to examples. The measurement was performed by the following method.
[Measurement of retardation value and slow axis angle]
The retardation value was measured at intervals of 5 mm with respect to the entire width of the sample in the width direction of the film using a continuous retardation measuring device (trade name: KOBRA-21SDH manufactured by Shin-Oji Paper Co., Ltd.). 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 obtained and used 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 small 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 measurement sample length 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 rate of change in weight before and after drying (accurately weighed with an analytical balance). In the case of film width direction measurement, the measurement was performed by dividing the film into five equal parts in the width direction.

[Measurement of viewing angle characteristics]
Using an automatic birefringence measuring apparatus (trade name: KOBRA-21ADH, manufactured by Shin-Oji Paper Co., Ltd.), retardation Re (0) in the normal direction of the film and oblique incidence at a relative angle of 40 degrees with the normal of the film. Then, the retardation Re (40) was measured, and the rate of change of the retardation was determined from the absolute value of the difference.
[| Re (0) -Re (40) | / Re (0)] × 100
The smaller the rate of change, the better the 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. Was used to determine the DSC curve (the DSC measurement device used was DSC V4OB DuPont2000). The falling (inflection point) portion of this curve was set to the apparent glass transition temperature Tg _1-3 .

[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.) was dissolved in methylene chloride and 18% by weight. Was prepared. 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. % (Full 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. Subsequently, 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 1400 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 1400mm)
Glass transition temperature Tg ₃ : 110 ° C.
Thickness and thickness unevenness: 70 μm and 1.0 μm (film width 1400 mm)
Thus, a non-stretched film having a thickness of 70 μm was prepared.
The film was further passed through a roll-hanging dryer, a stretching device having a stretching and cooling zone.

a) Drying conditions in a roll hanging type drying apparatus 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 were as follows: residual solvent amount: 1.6 ± 0.05 wt. %, Glass transition temperature Tg ₁ : 140 ° C., retardation value: 12 to 15 nm (full width of film 1400 mm), angle of slow axis: −5 to +5 degrees (full width of film 1400 mm).

b) Stretching condition first stage Stretching temperature: 150 ° C, stretching ratio: 1.26 times, stretching span length: 1.6 times the film width before stretching under air jet heating.
Second Stage Under air-jet heating, the film was stretched at a stretching temperature: 160 ° C., a stretching ratio: 1.03 times, and a stretching span length: 1.6 times the film width before stretching.

  The film after completion of the second-stage stretching was nipped with a nip roll maintained at a temperature of 100 ° C. Thereafter, the mixture was cooled 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, unevenness of film thickness: 0.3 μm (1200 mm film width), difference between maximum and minimum retardation values: 4 nm (1200 mm film width)
Small retardation value Maximum value: 1.1 nm (1200 mm film width)
Slow axis angle range: -1.5 to +1.5 degrees (1200 mm film width)
Viewing angle characteristics: 7.5, appearance defects: no scratches, scratches, undulations, etc.
Table 1 shows the above results.

[Examples 2 to 4]
Except for changing the stretching conditions as shown in Table 1, a stretched film was prepared in the same manner as in Example 1, and the characteristic values of the obtained film are shown in Table 1. In each case, the retardation of the film was set to about 500 nm.

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

  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 film was stretched between the first stage stretching and the second stage stretching by 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 Example 4, stretching was performed at a higher stretching ratio in the second step than in Example 1, but in this case also, the characteristics of the obtained film were good, and the film for retardation was used. It was excellent.

[Comparative example]
In the stretching conditions, the stretching in the first stage was performed under the same conditions as in Example 1 except that the stretching temperature was 150 ° C. and the stretching ratio was 1.26 times under air jet heating, and the stretching in the second stage was not performed. A stretched film was made. 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.

Schematic configuration explanatory view of a retardation film manufacturing device (without a nip roll provided between the first-stage stretching device and the second-stage stretching device) Schematic configuration explanatory view of a retardation film manufacturing apparatus (with a nip roll provided between a first-stage stretching apparatus and a second-stage stretching apparatus) Cast film forming apparatus (A), film peeling apparatus (B), pin tenter drying apparatus (C), a roll hanging type drying device (D), a first stage stretching device (E), a first cooling room (F), a second stage stretching device (G), and a second cooling room (H), And these apparatuses and chambers are arranged in this order, and the film is continuously passed through the manufacturing apparatus and processed.

Explanation of reference numerals

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: freely rotating roll 11: nip roll 12: air jet device

Claims (10)

  (1) A solution comprising polycarbonate and methylene chloride is cast on a support, (2) the formed solvent-containing film is peeled off from the support, (3) dried, and (4) uniaxially stretched. In the method for producing a retardation film made of polycarbonate, the uniaxial stretching step (4) is performed by a first stage stretching and a second stage stretching, and the temperature of the second stage stretching is the first stage stretching. A method for producing a retardation film made of polycarbonate, which is higher by 1 to 20 ° C. than a stretching temperature. The uniaxial stretching step (4) is performed under conditions of a temperature (Tg ₁ +10) to (Tg ₁ +35) ° C. and a stretching ratio of 1.1 to 3.2 times, and the second-stage stretching is performed at the first-stage stretching temperature. The method for producing a retardation film according to claim 1, wherein the method is performed at a temperature higher by 5 to 10 ° C. than at a stretching ratio of 1.01 to 1.20. (Tg ₁ (° C.) is the glass transition temperature of a film made of a polycarbonate containing a solvent, and this temperature increases as the residual solvent content decreases as drying proceeds.)   The method for producing a retardation film according to claim 1, wherein the solution is a polycarbonate solution of 10 to 30% by weight.   The drying step (3) comprises: (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. Item 4. The method for producing a retardation film according to any one of Items 1 to 3. In the drying step (3-1), while holding the film with a pin tenter so that the film has a shrinkage ratio of 2 to 5% in a direction perpendicular to the running direction, the film (Tg) is peeled from the support. ₂ +10) _{- (in} Tg 2 +90) ° C., method for producing a retardation film according to claim 4, characterized in that the drying. (Tg ₂ (° C.) is the glass transition temperature of a film made of polycarbonate containing a solvent, and this temperature rises as the residual solvent content decreases as drying proceeds.)   After drying in the drying step (3-1), the characteristic value of the film is 3.5 to 4.5 wt. %, A retardation value of 10 to 15 nm, and an angle of a slow axis of -10 to +10 degrees, the method for producing a retardation film according to any one of claims 4 to 5. The film was dried in the drying step (3-1), while applying a tension of 1~2.5Kg / cm ² in the film running direction using a roll suspension type drying apparatus, further temperature _(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 a film made of polycarbonate containing a solvent, and this temperature increases as the residual solvent content decreases as drying proceeds.)   The characteristic value of the film subjected to the uniaxial stretching step is such that the solvent content is 0.5 to 2.0 wt. %, A retardation value of 10 to 20 nm, and an angle of the slow axis of −7 to +7 degrees. The method for producing a retardation film according to claim 1.   The method for producing a retardation film according to any one of claims 1 to 8, wherein the stretching in the first stage is performed under the condition that the length between stretching rolls is 1.5 to 4.0 times the film width before stretching. .   (1) A solution comprising polycarbonate and methylene chloride is cast on a support, (2) the formed solvent-containing film is peeled off from the support, (3) dried, and (4) uniaxially stretched. A device for producing a retardation film made of polycarbonate for producing a retardation film, comprising a cast film forming device (A), a film peeling device (B), a pin tenter drying device (C), and a roll hanging type drying device (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 made of polycarbonate, 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.

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