WO2011096161A1 - Process for producing resin film, resin film, polarizer, and liquid-crystal display device - Google Patents

Abstract

Disclosed is a process for producing a resin film through solution casting, the process including a casting step in which a resin solution (dope) (16) is ejected from the orifice (21b) of a casting die (20) and cast on an endless-belt support (11) and, simultaneously therewith, a solvent in which the transparent resin as a component of the dope is soluble is caused to flow down from both longitudinal ends of the orifice (21b) of the casting die (20). The process satisfies relationship (1): -5 < T2 - T1 < 5 (1) (wherein T1 indicates the temperature [ºC] of the solvent which has just left the orifice, and T2 indicates the temperature [ºC] of the solvent which has just reached to the support).

Description

Manufacturing method of resin film, resin film, polarizing plate, and liquid crystal display device

The present invention relates to a resin film manufacturing method, a resin film obtained by the manufacturing method, a polarizing plate using the resin film as a transparent protective film, and a liquid crystal display device including the polarizing plate.

Resin films are used in various fields, such as liquid crystal display devices, in view of their chemical characteristics, mechanical characteristics, electrical characteristics, and the like. Specifically, various resin films, such as a transparent protective film for protecting the polarizing element of the polarizing plate, are disposed in the image display area of the liquid crystal display device. As such a resin film, for example, a resin film excellent in transparency such as a cellulose ester film is widely used.

A resin film such as a cellulose ester film can be produced using a resin solution (dope) obtained by dissolving a raw material resin such as a cellulose ester resin in a solvent. Specific examples of a method for producing a resin film using such a dope include a solution casting film forming method. The solution casting film forming method is a method of casting a dope on a traveling support to form a casting film, drying it to a peelable extent, peeling it from the support as a film, and peeling it. This is a method for producing a long resin film by drying, stretching, and the like while the film is conveyed by a conveyance roller.

When a resin film was produced by the solution casting film forming method as described above, when the casting film was peeled off from the support as a film, the end in the width direction of the film was sometimes difficult to peel off. In addition, when the film remains on the support due to this peeling failure, the film that remains without being peeled is mixed as a foreign substance into a resin film that is manufactured later, or has an adverse effect. Had to do. Therefore, when a peeling defect occurs, there is a problem that the resin film cannot be stably manufactured. Furthermore, when peeling failure occurs, there is a problem that retardation and orientation in the width direction of the obtained resin film become non-uniform and optical characteristics are deteriorated.

Further, when a resin film is produced by the solution casting film forming method as described above, a coating based on the dope is formed in the vicinity of both longitudinal ends of the discharge port of the casting die for casting the dope on the traveling support. Was sometimes formed. This film was formed by drying the solvent of the dope, and was gradually grown by the production of the resin film. And this film had the problem of disturbing the flow of the dope which casts and inhibiting manufacture of a resin film.

Further, in the production of a resin film by a solution casting film forming method, as a method for suppressing the formation of a film as described above, for example, a method described in Patent Document 1 can be mentioned. Patent Document 1 includes a method in which a solvent is allowed to flow from the outside of both ends of a lip (discharge port) of a casting die when a resin film is manufactured.

JP 2002-337173 A

The present invention suppresses the formation of a film in the vicinity of both ends in the longitudinal direction of the discharge port of the casting die, further suppresses film peeling failure, and stably manufactures a resin film having excellent optical characteristics. An object of the present invention is to provide a method for producing a resin film. Moreover, it aims at providing the liquid crystal display device provided with the resin film obtained by the said manufacturing method, the polarizing plate which used the said resin film as a transparent protective film, and the said polarizing plate.

One aspect of the present invention is a casting process in which a casting solution is formed by casting a resin solution containing a transparent resin from a casting die on a traveling support, and the casting film is used as the support. And a drying step for drying the peeled cast film. In the casting step, the resin solution is discharged from a discharge port of the casting die and cast onto the support. And a solvent capable of dissolving the transparent resin is allowed to flow down from both longitudinal ends of the discharge port of the casting die to satisfy the following formula (1).

−5 <T2−T1 <5 (1)
(In the formula, T1 indicates the temperature [° C.] of the solvent immediately after the solvent flows down from the discharge port, and T2 indicates the temperature [° C.] of the solvent when the solvent reaches the support. Is shown.)

Another aspect of the present invention is a resin film obtained by the method for producing a resin film.

Another aspect of the present invention is a polarizing plate comprising a polarizing element and a transparent protective film disposed on the surface of the polarizing element, wherein the transparent protective film is the resin film. This is a characteristic polarizing plate.

Another aspect of the present invention is a liquid crystal display device including a liquid crystal cell and two polarizing plates arranged so as to sandwich the liquid crystal cell, and at least one of the two polarizing plates. Is a liquid crystal display device characterized by being the polarizing plate.

The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

It is the schematic which shows the basic composition of the manufacturing apparatus of the resin film in one Embodiment of this invention. It is a schematic perspective view which shows the periphery of the casting die 20 in one Embodiment of this invention. It is a side view of the casting die | dye seen from the running direction downstream of the endless belt support body 11 in one Embodiment of this invention. FIG. 4 is a cross-sectional view of the casting die as seen from the section line VI-VI in FIG. 3.

The present inventor has inferred that the peeling failure occurring at the end portion in the width direction of the film is due to the fact that the drying of the end portion proceeds more than the drying of other portions. In addition, since the formation of the film also occurs in the vicinity of both ends of the discharge port of the casting die, the drying of the end portion of the casting film cast from the casting die proceeds more than the drying of other portions. I guessed it. From these things, this inventor guessed that formation of the said film | membrane and the said peeling defect are related. Therefore, in order to suppress the separation failure and the film formation, it was considered that a method of increasing the solvent concentration at the end in the width direction of the casting film discharged from the casting die can be applied. Specifically, for example, it was considered that a method of flowing a solvent from the outside of both ends of the discharge port of the casting die as in Patent Document 1 can be applied.

However, the method described in Patent Document 1 is a method that focuses on suppressing the formation of a film based on the dope in the vicinity of both ends of the discharge port of the casting die. Therefore, according to the study of the present inventor, even if this method is simply used, it is likely to be affected by the environmental change around the casting die and the like, and in fact, the peeling failure may not be sufficiently suppressed.

The present inventor has paid attention to the influence of the environmental change around the casting die, and as a result of earnestly examining conditions that can suppress film formation and film peeling failure, it has been found that the above object is achieved by the present invention described below. It was.

Hereinafter, embodiments according to the method for producing a resin film of the present invention will be described, but the present invention is not limited thereto.

The method for producing a resin film according to the present embodiment forms a casting film (web) by casting a resin solution (dope) obtained by dissolving a transparent resin in a solvent from a casting die on a traveling support. The production method includes a casting process, a peeling process for peeling the cast film from the support, and a drying process for drying the peeled cast film. For example, it is performed by a resin film manufacturing apparatus using a solution casting film forming method as shown in FIG. In addition, as a manufacturing apparatus of a resin film, it is not limited to what is shown in FIG. 1, The thing of another structure may be sufficient.

And the manufacturing method of the resin film which concerns on this embodiment discharges the said resin solution from the discharge port of the said casting die in the said casting process, and while casting on the said support body, the said casting die A solvent capable of dissolving the transparent resin is allowed to flow down from both longitudinal ends of the discharge port to satisfy the following formula (1).

−5 <T2−T1 <5 (1)
In the formula, T1 indicates the temperature [° C.] of the solvent immediately after the solvent flows down from the discharge port, and T2 indicates the temperature [° C.] of the solvent when the solvent reaches the support. Show.

T1 and T2 can be measured using a non-contact temperature detection device such as an infrared thermography. In addition, the solvent discharged from the longitudinal direction both ends of the discharge port of the casting die gradually permeates the ribbon-shaped resin solution (casting ribbon) discharged from the discharge port of the casting die. Non-contact temperature detection devices such as infrared thermography can measure the temperature of the surface, so by measuring using a non-contact temperature detection device such as infrared thermography, casting before penetrating the casting ribbon. The temperature of the solvent remaining on the ribbon can be measured.

FIG. 1 is a schematic view showing a basic configuration of a resin film manufacturing apparatus 1 by a solution casting method using an endless belt support 11. The resin film manufacturing apparatus 1 includes an endless belt support 11, a casting die 20, a peeling roller 13, a drying device 14, a winding device 15, and the like. The casting die 20 discharges a resin solution (dope) 16 in which a transparent resin is dissolved in a solvent in the form of a ribbon and casts it on the surface of the endless belt support 11. The endless belt support 11 is supported to be drivable by a pair of driving rollers and driven rollers, and forms a casting film (web) made of the resin solution 16 cast from the casting die 20 while being conveyed, It is dried to such an extent that it can be peeled by the peeling roller 13. The peeling roller 13 peels the dried cast film from the endless belt support 11. The peeled cast film is further dried by the drying device 14, and the dried cast film is wound around the winding device 15 as a resin film.

As shown in FIG. 1, the endless belt support 11 is a metal endless belt having a mirror surface and traveling infinitely. As the belt, for example, a belt made of stainless steel or the like is preferably used from the viewpoint of peelability of the cast film. The width of the casting film cast by the casting die 20 is preferably 80 to 99% with respect to the width of the endless belt support 11 from the viewpoint of effectively utilizing the width of the endless belt support 11. . In order to finally obtain a resin film having a width of 1500 to 4000 mm, the width of the endless belt support 11 is preferably 1800 to 4500 mm. Further, instead of the endless belt support, a rotating metal drum (endless drum support) having a mirror surface may be used.

FIG. 2 is a schematic perspective view showing the periphery of the casting die 20. FIG. 3 is a side view of the casting die 20 as viewed from the downstream side in the running direction of the endless belt support 11. FIG. 4 is a cross-sectional view of the casting die 20 as seen from the section line VI-VI in FIG.

The casting die 20 includes a casting die body 21, a dope supply pipe 22, a side plate 23, and a solvent supply pipe 24, as shown in FIGS. As shown in FIG. 4, the dope supply pipe 22 is connected to the upper end portion of the casting die body 21 and supplies the dope 16 into the casting die body 21. As shown in FIG. 4, the casting die body 21 includes a manifold portion 21 a for stably casting the dope 16 onto the endless belt support 11, and discharging the dope 16 into the endless belt 16. And a discharge port 21 b for casting on the belt support 11. The side plates 23 are provided at both ends of the casting die main body 21 in the longitudinal direction (direction substantially orthogonal to the conveying direction of the endless belt support 11). As shown in FIG. 3, the distance between the side plates 23 provided at both ends in the longitudinal direction of the casting die body 21 is the length in the longitudinal direction of the discharge port 21b of the casting die body 21, that is, a ribbon-like shape. The length of the resin solution 16 in the width direction is defined. The solvent supply pipe 24 is installed on the side plate 23 on the downstream side in the traveling direction of the endless belt support 11, that is, on the downstream side surface in the traveling direction of the dope 16, and is a solvent 35 that can dissolve the transparent resin. Is supplied into the side plate 23. A flow rate detection device 31, a liquid feeding device 32, a valve 33, and a solvent storage tank 34 are connected to the solvent supply pipe 24 in this order from the downstream side in the solvent flow direction. The solvent storage tank 34 stores a solvent 35 that can dissolve the transparent resin. The valve 33 is opened to start distribution of the solvent 35 stored in the solvent storage tank 34 into the solvent supply pipe 24. The liquid feeding device 32 feeds the solvent 35 in the solvent supply pipe 24 toward the side plate 23. The flow rate detection device 31 detects the flow rate of the solvent 35 flowing through the solvent supply pipe 24. And based on the detection result, you may control the output of the said liquid feeding apparatus 32. FIG. By doing so, as shown in FIG. 3, the solvent 35 supplied into the side plate 23 flows through the side plate 23 and flows down from both longitudinal ends of the discharge port 21b. That is, the solvent 35 is caused to flow down on both ends of the casting film 16.

At that time, the environment around the casting die 20 is set to an environment satisfying the above formula (1). By doing so, it is possible to stably produce a resin film that suppresses poor peeling of the film (casting film) and has excellent optical characteristics such as retardation and orientation.

Further, when a resin film is produced by the solution casting film forming method, a film based on the dope may be formed in the vicinity of both ends of the discharge port of the casting die. And this membrane | film | coat is formed when the solvent of dope dries and grows gradually by manufacture of a resin film. And this film had the problem of disturbing the flow of the dope which casts and inhibiting manufacture of a resin film. Furthermore, there has been a problem that the film detached from the casting die damages the resin film or the like. According to this embodiment, not only the film peeling failure can be suppressed, but also the film formation can be suppressed. Moreover, this film formation is considered to have a correlation with the peelability of the film. Therefore, in this embodiment, it can be considered that the film peeling failure can be suppressed because it is possible to suppress the formation of a film in the vicinity of both ends in the longitudinal direction of the discharge port of the casting die.

On the other hand, if the temperature change of the solvent from being discharged from the discharge port until reaching the support is too large, the solvent is less effective to improve the peelability of the cast film from the support, There was a tendency for the casting film to fail to peel off. Specifically, when T1 is too high as compared with T2, moisture in the atmosphere tends to precipitate on the surface of the solvent discharged from the discharge port, that is, the solvent on the casting ribbon. For this reason, there was a tendency for the casting film to fail to peel off. Further, when T2 is too high as compared with T1, the solvent is excessively volatilized, and the solvent is caused to flow down to the casting film, thereby improving the peelability of the casting film from the support. There was a tendency that the effect could not be sufficiently exhibited, and this caused a tendency to cause peeling failure of the cast film.

Also, the relationship between T1 and T2 varies depending on the environment around the casting die 20. Specifically, for example, the type of the solvent, the ambient temperature, the temperature of the casting ribbon discharged from the discharge port, the flow rate of the solvent, the flow rate of the solvent, the resin discharged from the discharge port from the discharge port By the distance to the location where the solution reaches the support, the presence or absence of the air blown to the resin solution or solvent discharged from the discharge port, the amount of the air, heating or cooling the solvent discharged from the discharge port, etc. Change. As a method of heating the solvent, for example, a heater is embedded in the solvent until the solvent discharged from the discharge port reaches the support, and the solvent flows on the heater. Examples thereof include a method of heating the solvent and a method of applying infrared rays or hot air to the solvent discharged from the discharge port. Examples of the method for cooling the solvent include a method of applying cold air to the solvent discharged from the discharge port.

T1 and T2 may satisfy the above relationship, but T1 and T2 are preferably 15 to 30 ° C., respectively. If T1 and T2 are too low or too high, the temperature difference between the solvent and the casting film becomes large, and this temperature difference causes either one of the surfaces of the casting film to shrink and the end portion to There is a tendency to break easily.

Further, the environment around the casting die 20 is preferably an environment that satisfies the following formula (2), and more preferably an environment that satisfies the following formula (3). By doing so, the peeling defect of a film (casting film) can be suppressed more.

10 ⁻⁷ <W2 / W1 <10 ⁻⁵ (2)
3 × 10 ⁻⁷ <W2 / W1 <10 ⁻⁶ (3)
In the formula, W1 represents the supply amount [ml] of the solvent, and W2 represents the loss amount [ml] of the solvent.

If the amount of W2 is too small relative to W1, the volatility of the solvent is too low, and it is difficult to evaporate even on the support and the like, and there is a tendency for film peeling failure to occur. Moreover, when there is too much W2 with respect to W1, there exists a tendency for a solvent to evaporate too much and for a solvent to suppress the peeling defect of a film.

Also, the relationship between W1 and W2 varies depending on the environment around the casting die 20. Specifically, for example, the presence of a film formed near both ends of the discharge port of the casting die, inhibition by impurities present in the solvent, the type of solvent, the ambient temperature, and the casting discharged from the discharge port Ribbon temperature, solvent flow rate, solvent flow rate, distance from the discharge port to the location where the resin solution discharged from the discharge port reaches the support, resin solution discharged from the discharge port, It varies depending on the presence / absence of the air blown on the solvent, the amount of air flow, and heating or cooling the solvent discharged from the discharge port. Note that W1 varies depending on the output of the liquid feeding device 32. Examples of the method for heating or cooling the solvent include the same methods as described above.

Note that W1 is the amount of the solvent flowing down. W2 is obtained by measuring the amount of solvent reaching the support and calculating the difference between W1 and the amount of solvent reaching the support. The amount of the solvent reached on the support is measured by measuring the gas concentration volatilized from the solvent until the solvent discharged from the discharge port reaches the support every unit time. It can be calculated by integrating the amount of time it takes for the solvent to circulate.

The discharge port 21b is formed on a ridge line on the endless belt support 11 side of the casting die body 21 as shown in FIG. As shown in FIG. 3, the ridge line extends in a direction substantially orthogonal to the traveling direction of the endless belt support 11. The distance A between the discharge port 21b and the endless belt support 11 is preferably 200 to 5000 μm. If the distance A is too narrow, the casting die 20 and the endless belt support 11 may come into contact with each other. If the distance A is too wide, the casting ribbon tends to be easily influenced by external factors such as wind.

As shown in FIG. 3, the dope supply pipe 22 branches into three and is connected to the casting die main body 21. However, the number is not limited to this number. It may be. The number of dope supply pipes 22 is preferably about 2 to 4 from the viewpoint of stably supplying the dope 16 to the casting die body 21.

When there are a plurality of dope supply pipes 22, the center-to-center distance (pitch) C of the adjacent dope supply pipes 22 connected to the casting die body 21 is determined from the viewpoint of stable supply of the dope 16. The width is preferably about 10 to 25% with respect to the width (width of the casting ribbon) B of the outlet 21b. Moreover, it is preferable that the intervals C between adjacent dope supply pipes 22 are all equal.

Also, as shown in FIGS. 2 to 4, it is preferable that the dope supply pipe 22 is smoothly bent rather than bent at a right angle after the branching or abruptly bent such as having a small curvature radius. If it bends sharply, the dope flow may stagnate, and contamination tends to occur.

Further, a slit 21c is formed between the lower end portion of the manifold portion 21a and the discharge port 21b. The width (slit width) D of the discharge port 21b can be adjusted according to the thickness of the resin film to be manufactured, and is preferably adjusted to about 100 to 1000 μm, for example. If the width D is too narrow, the liquid feeding pressure of the dope 16 is increased, and when a minute foreign matter is mixed into the dope 16, the foreign matter is clogged by the slit 21c, and a streak-like defect may occur in the casting film. There is. Moreover, when the width D is too wide, it tends to be difficult to produce a thin resin film.

The ratio (E / D) of the distance E of the slit (between the lower end of the manifold portion 21a and the discharge port 21b) to the width (slit width) D of the discharge port 21b is about 100 to 400. Preferably there is. If the E / D is too small, the time for the dope 16 to pass through the slit becomes too short, and it tends to be difficult to control the discharge amount (casting amount) of the dope 16. On the other hand, if the E / D is too large, the time for the dope 16 to pass through the slit becomes too long, and the dope tends to be contaminated.

Further, the casting die 20 is not limited to the shape shown in FIGS. 2 to 4, and may be any environment as long as the environment around the casting die 20 satisfies the above formula (1). A simple casting die can be used.

Then, a resin film can be produced from the cast film (web) formed on the endless belt support 11 by a peeling process or a drying process using the peeling roller 13, the drying device 14, the winding device 15, and the like. The process described below is not particularly limited and can be adopted as long as it is a general process. Specifically, for example, the following steps are performed. In addition, this invention is not limited to the following processes.

First, while the formed cast film (web) is conveyed by the endless belt support 11, the solvent in the dope is dried. The drying is performed, for example, by heating the endless belt support 11 or blowing heated air on the web. At that time, although the temperature of the web varies depending on the dope solution, it is preferably in the range of −5 ° C. to 70 ° C. in consideration of the conveyance speed accompanying the evaporation time of the solvent, the degree of dispersion of the fine particles, the productivity, and the like. A range of from 0 to 60 ° C. is more preferable. The higher the temperature of the web, the faster the solvent can be dried. However, when the temperature is too high, the web tends to foam or the flatness tends to deteriorate.

When the endless belt support 11 is heated, for example, a method of heating the web on the endless belt support 11 with an infrared heater, a method of heating the front and back surfaces of the endless belt support 11 with an infrared heater, the endless belt Examples include a method of heating by heating air on the back surface of the belt support 11, and the method can be appropriately selected as necessary.

Further, when the heated air is blown, the wind pressure of the heated air is preferably 50 to 5000 Pa in consideration of the uniformity of solvent evaporation, the degree of dispersion of fine particles, and the like. The temperature of the heating air may be dried at a constant temperature, or may be supplied in several steps in the running direction of the endless belt support 11.

The time from casting the dope onto the endless belt support 11 to peeling the web from the endless belt support 11 varies depending on the film thickness of the resin film to be produced and the solvent used. In consideration of the peelability from the endless belt support 11, it is preferably in the range of 0.5 to 5 minutes.

The traveling speed of the endless belt support 11 is preferably about 50 to 300 m / min, for example. The ratio (draft ratio) of the traveling speed of the endless belt support 11 to the flow rate of the dope discharged from the casting die 20 is preferably about 0.5 to 2. When the draft ratio is within this range, the cast film can be stably formed. For example, if the draft ratio is too large, there is a tendency to cause a phenomenon called neck-in in which the cast film is reduced in the width direction, and if so, a wide resin film cannot be formed.

The peeling roll 13 is disposed near the surface of the endless belt support 11 on the side where the dope 16 is cast, and the distance between the endless belt support 11 and the peeling roller 13 is 1 to 100 mm. It is preferable. The dried cast film (web) is peeled off as a film by pulling the dried cast film (web) with tension using the peeling roller 13 as a fulcrum. When the film is peeled from the endless belt support 11, the film is stretched in the film transport direction (machine direction: MD direction) by the peeling tension and the subsequent transport tension. For this reason, it is preferable that the peeling tension and the conveying tension when peeling the film from the endless belt support 11 are 50 to 400 N / m.

Moreover, the residual solvent rate of the film when peeling the film from the endless belt support 11 is the peelability from the endless belt support 11, the residual solvent rate at the time of peeling, the transportability after peeling, and after transporting and drying. Considering the physical properties of the resulting resin film, it is preferably 30 to 200% by mass. The residual solvent ratio of the film is defined by the following formula (I).

Residual solvent ratio (mass%) = {(M ₁ −M ₂ ) / M ₂ } × 100 (I)
Here, M ₁ is shows the mass at any point in the film, M ₂ shows the mass after drying for 1 hour at 115 ° C. The film was measured M _1.

The drying device 14 includes a plurality of transport rollers, and dries the film while transporting the film between the rollers. In that case, you may dry using heating air, infrared rays, etc. independently, and you may dry using heating air and infrared rays together. It is preferable to use heated air from the viewpoint of simplicity. The drying temperature varies depending on the amount of residual solvent in the film. However, the drying temperature is appropriately selected depending on the residual solvent ratio in the range of 30 to 180 ° C. in consideration of drying time, unevenness of shrinkage, stability of the amount of expansion and contraction, etc. That's fine. Further, it may be dried at a constant temperature, or may be divided into two to four stages of temperature and may be divided into several stages of temperature. Further, the film can be stretched in the MD direction while being transported in the drying device 14.

The residual solvent ratio of the film after the drying treatment in the drying device 14 is preferably 0.001 to 5% by mass in consideration of the load of the drying process, the dimensional stability expansion / contraction ratio during storage, and the like. In the present embodiment, a film in which the solvent is gradually removed in the drying step and the total residual solvent amount is 15% by mass or less is referred to as a resin film.

The winding device 15 winds the resin film having a predetermined residual solvent ratio on the winding core to a required length by the drying device 14. In addition, it is preferable that the temperature at the time of winding is cooled to room temperature in order to prevent abrasion, loosening, and the like due to shrinkage after winding. The winder to be used can be used without particular limitation, and may be a commonly used one. Specifically, it can be wound using, for example, a winder using a constant tension method, a constant torque method, a taper tension method, a program tension control method with a constant internal stress, or the like.

In addition, the manufacturing apparatus of a resin film is not limited to the thing of said structure, For example, you may provide the extending | stretching apparatus etc. separately. Examples of the stretching device include a stretching device that stretches the film peeled from the endless belt support 11 in a direction (Transverse Direction: TD direction) orthogonal to the film transport direction.

Hereinafter, the composition of the resin solution (dope) used in the present embodiment will be described.

The resin solution used in this embodiment is obtained by dissolving a transparent resin in a solvent.

The transparent resin is not particularly limited as long as it is a resin having transparency when formed into a substrate by a solution casting film forming method or the like, but is easily manufactured by a solution casting film forming method or the like. It is preferable that the adhesive property with other functional layers such as a hard coat layer is excellent and that it is optically isotropic. Here, the transparency means that the visible light transmittance is 60% or more, preferably 80% or more, and more preferably 90% or more.

Specific examples of the transparent resin include cellulose ester resins such as cellulose diacetate resin, cellulose triacetate resin, cellulose acetate butyrate resin, and cellulose acetate propionate resin; polyethylene terephthalate resin and polyethylene naphthalate resin. Acrylic resins such as polymethyl methacrylate resins; Polysulfone (including polyether sulfone) resins, polyethylene resins, polypropylene resins, cellophane, polyvinylidene chloride resins, polyvinyl alcohol resins, ethylene vinyl alcohol resins, Shinji Vinyl resins such as tactic polystyrene resins, cycloolefin resins and polymethylpentene resins; polycarbonate resins; polyarylate trees ; It can be mentioned fluorine-based resin or the like; polyether ketone resins; polyether ketone imide resin; polyamide resin. Among these, cellulose ester resins, cycloolefin resins, polycarbonate resins, and polysulfone (including polyethersulfone) resins are preferable. Furthermore, cellulose ester resins are preferred, and among cellulose ester resins, cellulose acetate resins, cellulose propionate resins, cellulose butyrate resins, cellulose acetate butyrate resins, cellulose acetate propionate resins, and cellulose triacetate resins are preferred, Cellulose triacetate resin is particularly preferred. Moreover, the said transparent resin may use the transparent resin illustrated above independently, and may use it in combination of 2 or more type.

Next, the cellulose ester resin will be described.

The number average molecular weight of the cellulose ester-based resin is preferably 30,000 to 200,000 in that the mechanical strength is high when it is molded into a resin film, and an appropriate dope viscosity is obtained in the solution casting film forming method. The weight average molecular weight (Mw) / number average molecular weight (Mn) is preferably in the range of 1 to 5, more preferably in the range of 1.4 to 3.0.

Further, the average molecular weight and molecular weight distribution of a resin such as a cellulose ester resin can be measured using gel permeation chromatography or high performance liquid chromatography. Therefore, the number average molecular weight (Mn) and the weight average molecular weight (Mw) can be calculated using these, and the ratio can be calculated.

The cellulose ester resin preferably has an acyl group having 2 to 4 carbon atoms as a substituent. As the substitution degree, for example, when the substitution degree of the acetyl group is X and the substitution degree of the propionyl group or butyryl group is Y, the total value of X and Y is 2.2 or more and 2.95 or less, X is preferably more than 0 and 2.95 or less.

Further, the portion not substituted with an acyl group usually exists as a hydroxyl group. These cellulose ester resins can be synthesized by a known method. The method for measuring the substitution degree of the acyl group can be measured in accordance with the provisions of ASTM-D817-96.

The cellulose that is the raw material of the cellulose ester-based resin is not particularly limited, and examples thereof include cotton linter, wood pulp (derived from coniferous tree, derived from broadleaf tree), kenaf and the like. The cellulose ester resins obtained from them can be mixed and used at an arbitrary ratio, but it is preferable to use 50% by mass or more of cotton linter. When the acylating agent is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), these cellulose ester resins use an organic acid such as acetic acid or an organic solvent such as methylene chloride, It can be obtained by reacting with a cellulose raw material using such a protic catalyst.

The solvent used in the present embodiment can be a solvent containing a good solvent for the transparent resin. The good solvent varies depending on the transparent resin used. For example, in the case of a cellulose ester resin, the good solvent and the poor solvent change depending on the acyl group substitution degree of the cellulose ester. For example, when acetone is used as the solvent, the cellulose ester acetate ester (acetyl group substitution degree 2.4), cellulose Acetate propionate is a good solvent, and cellulose acetate (acetyl group substitution degree 2.8) is a poor solvent. Therefore, since the good solvent and the poor solvent differ depending on the transparent resin used, the case of a cellulose ester resin will be described as an example.

Examples of good solvents for cellulose ester resins include organic halogen compounds such as methylene chloride, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dioxolane derivatives, cyclohexanone, Ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3- Hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, etc. Can be mentioned. Among these, organic halogen compounds such as methylene chloride, dioxolane derivatives, methyl acetate, ethyl acetate, acetone and the like are preferable. These good solvents may be used alone or in combination of two or more.

The dope may contain a poor solvent as long as the transparent resin does not precipitate. Examples of poor solvents for cellulose ester resins include alcohols having 1 to 8 carbon atoms such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, methyl ethyl ketone, and methyl isobutyl. Examples include ketones, propyl acetate, monochlorobenzene, benzene, cyclohexane, tetrahydrofuran, methyl cellosolve, and ethylene glycol monomethyl ether. These poor solvents may be used alone or in combination of two or more.

The resin solution used in this embodiment may contain other components (additives) other than the transparent resin and the solvent as long as the effects of the present invention are not impaired. Examples of the additive include fine particles, plasticizers, antioxidants, ultraviolet absorbers, heat stabilizers, conductive substances, flame retardants, lubricants, and matting agents.

The fine particles are appropriately selected according to the purpose of use. Specific examples of the purpose of use include, for example, a case where visible light is scattered by being contained in a transparent resin, a case where slipperiness is imparted, and the like. By containing, both the scattering of visible light and the improvement of slipperiness can be improved. Moreover, in any case, it is necessary to adjust the particle size and content of the fine particles to such an extent that the transparency of the film is not impaired. The fine particles may be inorganic fine particles such as silicon oxide or organic fine particles such as acrylic resin.

Examples of the inorganic fine particles include silicon oxide, titanium oxide, aluminum oxide, zirconium oxide, magnesium oxide, calcium carbonate, strontium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, and aluminum silicate. And fine particles such as magnesium silicate and calcium phosphate. Among these, fine particles such as silicon oxide, titanium oxide, aluminum oxide, zirconium oxide, and magnesium oxide are preferably used.

Examples of the organic fine particles include acrylic resins such as polymethyl methacrylate resin, acrylic styrene resins, silicone resins, polystyrene resins, polycarbonate resins, benzoguanamine resins, melamine resins, polyolefin resins, polyester resins, Fine particles composed of polyamide-based resin, polyimide-based resin, polyfluorinated ethylene-based resin, and the like can be given. Among these, crosslinked polystyrene particles, acrylic resin fine particles of polymethyl methacrylate particles, and the like are preferable.

Further, as the fine particles, the fine particles exemplified above may be used alone, or two or more kinds may be used in combination.

The average particle diameter of the fine particles is preferably 0.1 to 10 μm, and more preferably 0.3 to 5 μm. If the average particle size of the fine particles is too small, the functionality due to the fine particles tends not to be sufficiently exhibited. On the other hand, if it is too large, not only the functionality due to the fine particles cannot be sufficiently exhibited, but also the translucency of the resin film tends to be lowered. In addition, although the average particle diameter of microparticles | fine-particles can be measured also by TEM observation of the cross section of a resin film, it can also be measured using a laser diffraction type particle size distribution measuring apparatus etc.

The content of the fine particles is preferably 0.01 to 35% by mass, and more preferably 0.05 to 30% by mass with respect to the transparent resin. If the content of the fine particles is too small, the functionality due to the fine particles tends to be insufficient. Moreover, when there is too much, there exists a tendency for the translucency of a resin film to fall.

The shape of the fine particles is not particularly limited, and examples thereof include a spherical shape, a flat plate shape, and a needle shape, and a spherical shape is preferable.

The plasticizer can be used without particular limitation, for example, phosphate ester plasticizer, phthalate ester plasticizer, trimellitic ester plasticizer, pyromellitic acid plasticizer, glycolate plasticizer, Examples include citrate plasticizers and polyester plasticizers. When the plasticizer is contained, the content thereof is preferably 1 to 40% by mass, preferably 3 to 20% by mass with respect to the cellulose ester resin in view of dimensional stability and processability. More preferably, it is 4 to 15% by mass. If the content of the plasticizer is too small, a smooth cut surface cannot be obtained when slitting or punching, and there is a tendency for generation of chips. That is, the effect of including a plasticizer cannot be sufficiently exhibited.

The antioxidant can be used without any particular limitation, and for example, a hindered phenol compound is preferably used. When the antioxidant is contained, the content of the antioxidant is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the cellulose ester resin.

The resin film produced by the production method according to the present embodiment can be used for a polarizing plate or a liquid crystal display member because of its high dimensional stability. In this case, deterioration prevention of the polarizing plate or the liquid crystal is possible. Therefore, an ultraviolet absorber is preferably used.

As the ultraviolet absorber, those having excellent absorption ability of ultraviolet rays having a wavelength of 370 nm or less and having little absorption of visible light having a wavelength of 400 nm or more are preferably used from the viewpoint of good liquid crystal display properties. Specifically, the transmittance at 380 nm is preferably less than 10%, more preferably less than 5%. Specific examples of the UV absorber include oxybenzophenone compounds, benzotriazole compounds (benzotriazole UV absorbers), salicylic acid ester compounds, benzophenone compounds (benzophenone UV absorbers), and cyanoacrylates. Compounds, nickel complex compounds, triazine compounds, and the like. In these, a benzotriazole type ultraviolet absorber and a benzophenone type ultraviolet absorber are preferable. The content of the ultraviolet absorber is preferably from 0.1% by mass to 2.5% by mass, considering the effect as an ultraviolet absorber, transparency, etc., and from 0.8% by mass to 2.0% by mass. % Is more preferable.

Examples of the thermal stabilizer include kaolin, talc, diatomaceous earth, quartz, inorganic fine particles such as calcium carbonate, barium sulfate, titanium oxide, and alumina, and salts of alkaline earth metals such as calcium and magnesium.

The conductive material is not particularly limited, and examples thereof include ionic conductive materials such as anionic polymer compounds, conductive fine particles such as metal oxide fine particles, and antistatic agents. By containing the conductive substance, a resin film having a preferable impedance can be obtained. Here, the ion conductive substance is a substance that shows electric conductivity and contains ions that are carriers for carrying electricity.

Next, as an example of a method for preparing a dope, a case where a cellulose ester resin is used as a transparent resin will be described.

The method for dissolving the cellulose ester resin when preparing the dope is not particularly limited, and a general method can be used. By combining heating and pressurization, it is possible to heat above the boiling point of the solvent at normal pressure, and it is possible to dissolve the cellulose ester resin in the solvent above the boiling point at normal pressure. It is preferable from the viewpoint of preventing the occurrence of. In addition, a method in which a cellulose ester resin is mixed with a poor solvent and wetted or swollen, and then a good solvent is added and dissolved is also preferably used.

The pressurization may be performed by a method in which an inert gas such as nitrogen gas is injected, or a method in which a solvent is heated in a sealed container and the vapor pressure of the solvent is increased by the heating. The heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

A higher solvent temperature (heating temperature) for dissolving the cellulose ester-based resin is preferable from the viewpoint of solubility of the cellulose ester. However, when the heating temperature is increased, the pressure in the container is increased by the pressurization. Productivity must be reduced. Therefore, the heating temperature is preferably 45 to 120 ° C. The pressure is adjusted to a pressure at which the solvent does not boil at the set temperature. Alternatively, a cooling dissolution method is also preferably used, whereby the cellulose ester resin can be dissolved in a solvent such as methyl acetate.

Next, the obtained cellulose ester resin solution is filtered using an appropriate filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like. However, if the absolute filtration accuracy is too small, there is a problem that the filter medium is likely to be clogged. Therefore, a filter medium having an absolute filtration accuracy of 0.008 mm or less is preferable, and a filter medium having a 0.001 to 0.008 mm is more preferable.

There is no restriction | limiting in particular in the material of a filter medium, A normal filter medium can be used. For example, a plastic filter material such as polypropylene or Teflon (registered trademark), a filter paper using cellulose fiber or rayon, or a metal filter material such as stainless steel is preferable because the fiber does not fall off. It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose ester resin solution by filtration. The bright spot foreign matter is a state where two polarizing plates are placed in a crossed Nicols state, a resin film is placed between them, light is applied from one polarizing plate side, and observation is performed from the other polarizing plate side. It is a point (foreign matter) where light from the opposite side appears to leak, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less.

The filtration is not particularly limited and can be carried out by a usual method, but the method of filtration while heating at a temperature not lower than the boiling point of the solvent at normal pressure and at which the solvent does not boil under pressure may be performed before and after the filtration. The increase in the difference in filtration pressure (referred to as differential pressure) is small and preferable. The temperature is preferably 35 to 60 ° C. The filtration pressure is preferably smaller, for example, 1.6 MPa or less.

When each of the above additives is contained, for example, the additive may be dissolved in an organic solvent such as alcohol, methylene chloride, dioxolane and the like, or may be added to the dope or directly during the dope composition. In addition, for inorganic powders that do not dissolve in organic solvents, the additive and cellulose ester resin are added to the dope using a dissolver or sand mill with the additive dispersed in the cellulose ester resin. It is preferable.

The fine particles are dispersed in the obtained cellulose ester resin solution. The method for dispersing is not particularly limited, and can be performed, for example, as follows. For example, first, a dispersion solvent and fine particles are stirred and mixed, and then dispersed using a disperser. This is a fine particle dispersion. The fine particle dispersion is added to the cellulose ester resin solution and stirred.

Examples of the dispersion solvent include lower alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, and butyl alcohol. Moreover, although it does not specifically limit to lower alcohol, It is preferable to use the thing similar to the solvent used when preparing the solution of a cellulose-ester-type resin.

The disperser can be used without particular limitation, and a general disperser can be used. Dispersers can be broadly divided into media dispersers and medialess dispersers. Medialess dispersers are preferred from the viewpoint of lower haze (higher translucency). Examples of the media disperser include a ball mill, a sand mill, and a dyno mill. Examples of the medialess disperser include an ultrasonic type, a centrifugal type, and a high pressure type, and a high pressure type dispersing device is preferable. The high-pressure dispersion device is a device that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube. Examples of the high-pressure dispersing device include an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation, a nanomizer manufactured by Nanomizer, and the like, and other examples include a Manton Gorin type high-pressure dispersing device. Examples of the Menton Gorin type high-pressure dispersing device include a homogenizer manufactured by Izumi Food Machinery, UHN-01 manufactured by Sanwa Machinery Co., Ltd., and the like.

Further, as the solvent that flows down from both ends of the discharge port of the casting die, the same solvent as the resin solution (dope) can be used. Specifically, a good solvent for the transparent resin may be contained, and a poor solvent may be contained as necessary.

According to the manufacturing method according to the present embodiment as described above, it is possible to suppress a film peeling failure, and thus a resin film excellent in optical properties with high uniformity such as retardation and orientation can be obtained. Moreover, according to the manufacturing method according to the present embodiment, it is possible to suppress the occurrence of dope contamination and the formation of a film in the vicinity of both ends of the discharge port. can get.

The width of the resin film obtained here is preferably 1500 to 2500 mm from the viewpoint of use in a large liquid crystal display device, use efficiency of the film during polarizing plate processing, and production efficiency.

The film thickness of the resin film is preferably 20 to 70 μm from the viewpoint of thinning the liquid crystal display device and stabilizing the production of the resin film. Here, the film thickness is an average film thickness. The film thickness is measured at 20 to 200 locations in the width direction of the resin film with a contact-type film thickness meter manufactured by Mitutoyo Corporation, and the average value of the measured values. Is shown as the film thickness.

(Polarizer)
The polarizing plate which concerns on this embodiment is equipped with a polarizing element and the transparent protective film arrange | positioned on the surface of the said polarizing element, and the said transparent protective film is the said resin film. The polarizing element is an optical element that emits incident light converted to polarized light.

As the polarizing plate, for example, a completely saponified polyvinyl alcohol aqueous solution is used on at least one surface of a polarizing element produced by immersing and stretching a polyvinyl alcohol film in an iodine solution, and the resin film or What laminated | stacked the said laminated | multilayer film is preferable. Further, the resin film may be laminated on the other surface of the polarizing element, or a transparent protective film for another polarizing plate may be laminated. As the transparent protective film for the polarizing plate, for example, as a commercially available cellulose ester film, KC8UX2M, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC8UY-HA, KC8UX-RHA (above, manufactured by Konica Minolta Opto) Is preferably used. Or you may use resin films, such as cyclic olefin resin other than a cellulose-ester film, an acrylic resin, polyester, a polycarbonate. In this case, since the saponification suitability is low, it is preferable to perform an adhesive process on the polarizing plate through an appropriate adhesive layer.

As described above, the polarizing plate uses the resin film as a protective film laminated on at least one surface side of the polarizing element. In that case, when the said resin film works as a phase difference film, it is preferable to arrange | position so that the slow axis of a resin film may be substantially parallel or orthogonal to the absorption axis of a polarizing element.

Further, specific examples of the polarizing element include, for example, a polyvinyl alcohol polarizing film. Polyvinyl alcohol polarizing films include those obtained by dyeing iodine on polyvinyl alcohol films and those obtained by dyeing dichroic dyes. As the polyvinyl alcohol film, a modified polyvinyl alcohol film modified with ethylene is preferably used.

The polarizing element is obtained as follows, for example. First, a film is formed using a polyvinyl alcohol aqueous solution. The obtained polyvinyl alcohol film is uniaxially stretched and then dyed or dyed and then uniaxially stretched. And preferably, a durability treatment is performed with a boron compound.

The film thickness of the polarizing element is preferably 5 to 40 μm, more preferably 5 to 30 μm, and even more preferably 5 to 20 μm.

When a cellulose ester resin film is laminated on the surface of the polarizing element, it is preferably bonded with a water-based adhesive mainly composed of completely saponified polyvinyl alcohol. Moreover, in the case of resin films other than a cellulose ester-based resin film, it is preferable to perform adhesion processing on the polarizing plate through an appropriate adhesive layer.

The polarizing plate as described above uses the resin film according to this embodiment as a transparent protective film. Since this resin film is excellent in optical properties with high uniformity such as retardation and orientation, when the obtained polarizing plate is applied to, for example, a liquid crystal display device, the contrast of the liquid crystal display device is improved. High image quality can be achieved.

(Liquid crystal display device)
The liquid crystal display device according to this embodiment includes a liquid crystal cell and two polarizing plates arranged so as to sandwich the liquid crystal cell, and at least one of the two polarizing plates is the polarizing plate. . Note that the liquid crystal cell is a cell in which a liquid crystal substance is filled between a pair of electrodes, and by applying a voltage to the electrodes, the alignment state of the liquid crystal is changed and the amount of transmitted light is controlled. Such a liquid crystal display device uses the polarizing plate as a transparent protective film for the polarizing plate. By doing so, a high-quality liquid crystal display device with improved contrast and the like can be obtained.

As mentioned above, although embodiment which concerns on this invention was described in detail, above-described description is an illustration in all the situation, Comprising: This invention is not limited to these. It is understood that countless variations that are not illustrated can be envisaged without departing from the scope of the present invention.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[Example 1]
(Preparation of dope)
First, a cellulose acetate propionate resin (acetyl group substitution degree: 1.2, propionyl group substitution degree: 1.2, total acyl) as a transparent resin in a dissolution tank containing 300 parts by mass of methylene chloride and 52 parts by mass of ethanol. Group substitution degree: 2.4) 100 parts by mass are added, and further 5 parts by mass of triphenyl phosphate, 5 parts by mass of ethylphthalylethyl glycol, and 0.2 parts by mass of silica particles (primary particle size: 12 nm) are added. did. And after raising the liquid temperature to 80 ° C., the mixture was stirred for 3 hours. By doing so, a cellulose acetate propionate resin solution was obtained. Then, stirring was complete | finished and it was left until the liquid temperature became 43 degreeC. Then, the obtained resin solution was filtered using a filter paper having a filtration accuracy of 0.005 mm. Air bubbles in the resin solution were degassed by allowing the resin solution after filtration to stand overnight. Using the resin solution thus obtained as a dope, a resin film was produced as follows.

(Manufacture of resin film)
First, the temperature of the obtained dope was adjusted to 35 ° C., and the temperature of the endless belt support was adjusted to 25 ° C. Then, using a resin film production apparatus as shown in FIG. 1, a dope was cast from an casting die onto an endless belt support made of stainless steel and polished to a super mirror surface at a conveyance speed of 60 m / min. . At that time, a mixed solvent of 95% by mass of methylene chloride and 5% by mass of methanol was allowed to flow down from both ends of the discharge port of the casting die as a solvent. Then, before the solvent discharged from the discharge port reaches the support, a heater is embedded in the solvent, and the solvent flows through the heater so that the solvent is heated. The temperature, supply amount, and loss amount of the solvent flowing down from both ends of the discharge port of the die were adjusted to the temperatures, supply amounts, and loss amounts shown in Table 1. Then, the web was peeled from the endless belt support as a film, and the peeled film was stretched 15% in the TD direction while holding both ends of the film with clips using a stretching device (tenter). Then, the stretched film was wound up with a winder, and the resin film wound up in roll shape was obtained.

[Example 2]
As the solvent that flows down from both ends of the discharge port of the casting die, a mixed solvent of 80% by mass of methylene chloride and 20% by mass of methanol is used instead of the mixed solvent of 95% by mass of methylene chloride and 5% by mass of methanol. The temperature, supply amount, and loss amount of the solvent flowing down from both ends of the discharge port of the casting die are adjusted by adjusting the flow rate of the air blown to the resin solution and solvent discharged from Example 1 is the same as Example 1 except that the loss is adjusted.

[Example 3]
Instead of a mixed solvent of 95% by mass of methylene chloride and 5% by mass of methanol, a mixed solvent of 80% by mass of methylene chloride, 5% by mass of methanol and 15% by mass of cyclohexane was used as a solvent to flow down from both ends of the discharge port of the casting die. Use, adjust the distance from the discharge port to the location where the resin solution discharged from the discharge port reaches the support, thereby supplying the temperature and supply of the solvent flowing down from both ends of the discharge port of the casting die Example 1 is the same as Example 1 except that the amount and loss amount are adjusted to the temperature, supply amount, and loss amount shown in Table 1.

[Example 4]
Instead of a mixed solvent of 95% by mass of methylene chloride and 5% by mass of methanol as a solvent that flows down from the both ends of the casting die of the casting die, methylene chloride is used, and hot air is applied to the solvent discharged from the outlet. As in Example 1, except that the temperature, supply amount and loss amount of the solvent flowing down from both ends of the casting die of the casting die were adjusted to the temperatures, supply amounts and loss amounts shown in Table 1. It is.

[Comparative Example 1]
By adjusting the distance from the discharge port to the location where the resin solution discharged from the discharge port reaches the support, the temperature of the solvent that flows down from both ends of the discharge port of the casting die, the supply amount, and Example 1 is the same as Example 1 except that the loss amount is adjusted to the temperature, supply amount, and loss amount shown in Table 1.

[Comparative Example 2]
The temperature, supply amount, and loss amount of the solvent that flows down from both ends of the discharge port of the casting die by applying hot air to the solvent discharged from the discharge port are shown in Table 1. It is the same as that of Example 2 except having adjusted so that it may become.

[Comparative Example 3]
Before the solvent discharged from the discharge port reaches the support, a heater is embedded in the solvent, and the solvent flows through the heater so that the solvent is heated. Example 3 is the same as Example 3 except that the temperature, supply amount, and loss amount of the solvent flowing down from both ends of the discharge port are adjusted to the temperature, supply amount, and loss amount shown in Table 1.

[Comparative Example 4]
By adjusting the amount of air blown to the resin solution or solvent discharged from the discharge port, the temperature, supply amount and loss amount of the solvent flowing down from both ends of the discharge port of the casting die are shown in Table 1, Example 4 is the same as Example 4 except that the supply amount and the loss amount are adjusted.

The resin films (Examples 1 to 4 and Comparative Examples 1 to 4) obtained as described above were evaluated as follows, and the results are shown in Table 1.

(Number of foreign objects)
The obtained resin film is placed between two polarizing plates in an orthogonal (crossed Nicols) state, light is applied from one polarizing plate side, and the other polarizing plate side is used with a transmission microscope. And observed at a magnification of 50 times. At that time, the number of foreign matters having a size of 50 μm or more recognized in the polarization crossed Nicol state in an area of 25 cm ² was counted, and the value converted into the number per 1 cm ² was defined as the number of foreign matters.

If the number of foreign substances is 0.15 or less, it is evaluated as “◎”, and if it exceeds 0.15 and is 0.20 or less, it is evaluated as “◯”, and 0.20 If it exceeds 0.25, it is evaluated as “Δ”. If it exceeds 0.25 and is 0.35 or less, it is evaluated as “X”. If it exceeds 0.35, “XX” is evaluated. ".

Here, the foreign matter is a foreign matter recognized in the polarization crossed Nicol state, and in the polarized crossed Nicol state, only the location of the foreign matter is observed in the dark field, so that the number can be easily measured. it can.

(transparency)
The haze of the obtained resin film was measured according to JIS K7105-1981. Specifically, 10 samples were cut out at equal intervals in the width direction of the obtained resin film, and the haze of the cut out sample was measured using a haze meter (NDH manufactured by Nippon Denshoku Industries Co., Ltd.). The average value of the measured haze was evaluated as a transparency index. If the haze is 0.1 or less, it is evaluated as “◎”, and if it exceeds 0.1 and is 0.2 or less, it is evaluated as “◯”, and if it exceeds 0.2 and is 0.5 or less. , “△” was evaluated, and when it exceeded 0.5 and 1.0 or less, it was evaluated as “X”, and when it exceeded 0.1, “XX” was evaluated.

(optical properties)
The in-plane direction retardation Ro and the slow axis angle θ of 10 samples used in the evaluation of the transparency were measured using an automatic birefringence measuring apparatus (KOBRA-21ADH manufactured by Oji Scientific Instruments).

Specifically, first, using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), in the environment of a temperature of 23 ° C. and a humidity of 55% RH, the retardation of each sample was measured at a wavelength of 590 nm. The angle θ of the axis, the refractive index Nx in the slow axis direction, and the refractive index Ny in the fast axis direction were measured. Next, the film thickness d of the resin film was measured using a contact-type film thickness meter manufactured by Mitutoyo Corporation. And from each measured value obtained, in-plane direction retardation Ro of each sample was calculated using the following formula (4).

Ro = (Nx−Ny) × d (4)
In the formula, Nx represents the refractive index in the slow axis direction of the resin film, Ny represents the refractive index in the fast axis direction, and d represents the film thickness (nm) of the film.

First, if the difference between the maximum value Romax and the minimum value Romin in the in-plane direction retardation Ro of each obtained sample is 1.0 or less, it is evaluated as “◎”, exceeds 1.0, and exceeds 2. If it is 0 or less, it is evaluated as “◯”, and if it exceeds 2.0 and 4.0 or less, it is evaluated as “Δ”, and if it exceeds 4.0 and 5.0 or less, “×” is evaluated. If it exceeded 5.0, it was evaluated as “XX”.

Next, if the difference between the maximum value θmax and the minimum value θmin among the slow axis angles θ of the obtained samples is 0.2 or less, it is evaluated as “◎” and exceeds 0.2. If it is 0.3 or less, it is evaluated as “◯”, and if it exceeds 0.3 and 0.4 or less, it is evaluated as “Δ”, and if it exceeds 0.4 and 0.5 or less, “×” ", And if it exceeded 0.5, it was evaluated as" XX ".

(Peelability)
After peeling the casting film from the support, visually check whether the casting film remains on the support, and if the casting film remains cannot be confirmed, it is evaluated as `` ○ '' If the cast film remained, it was evaluated as “x”.

(Film formation)
After the resin film was formed as described above, it was visually observed whether or not a film was formed on the surface of the casting die. And when formation of the film could not be confirmed, it was evaluated as “◯”, and when formation of the film was confirmed, it was evaluated as “x”.

Table 1 shows the evaluation results of the above evaluations.

 

As can be seen from Table 1, when T1 and T2 are such that T2-T1 exceeds −0.5 and less than 0.5 (Examples 1 to 4), T1 that does not satisfy the above relationship From the case of T2 (Comparative Examples 1 to 4), a resin film having not only excellent releasability but also few foreign substances, excellent transparency, and excellent uniform optical properties such as retardation was obtained. Further, in the case of Examples 1 to 4, even when the resin film was manufactured, the formation of a film on the casting die was suppressed. From this, it is considered that the resin films according to Examples 1 to 4 suppress the occurrence of defects due to film formation. Moreover, it is thought that suppression of this film formation has contributed to the improvement of peelability.

Further, when W1 and W2 are such that W2 / W1 exceeds 10 ⁻⁷ and less than 10 ⁻⁵ (Examples 2 to 4), they are W1 and W2 that do not satisfy the above relationship (implementation). From Example 1), it was possible to obtain a resin film that was further excellent in transparency and, in some cases, had fewer foreign matters and was superior in optical properties.

This specification discloses various modes of technology as described above, and the main technologies are summarized below.

One aspect of the present invention is a casting process in which a casting solution is formed by casting a resin solution containing a transparent resin from a casting die on a traveling support, and the casting film is used as the support. And a drying step for drying the peeled cast film. In the casting step, the resin solution is discharged from a discharge port of the casting die and cast onto the support. And a solvent capable of dissolving the transparent resin is allowed to flow down from both longitudinal ends of the discharge port of the casting die to satisfy the following formula (1).

−5 <T2−T1 <5 (1)
(In the formula, T1 indicates the temperature [° C.] of the solvent immediately after the solvent flows down from the discharge port, and T2 indicates the temperature [° C.] of the solvent when the solvent reaches the support. Is shown.)

According to said structure, it suppresses that a film | membrane is formed in the longitudinal direction both ends vicinity of the discharge outlet of a casting die, Furthermore, the peeling defect of a film is suppressed and the resin film excellent in the optical characteristic is stabilized. The manufacturing method of the resin film which can be manufactured in this way can be provided.

This is thought to be due to the following.

First, at least a part of the solvent permeates the casting film on the support by flowing down a solvent capable of dissolving the transparent resin constituting the resin film from both longitudinal ends of the discharge port of the casting die. And it is thought that the solvent concentration of the width direction edge part of a casting film can be raised. That is, it is thought that it can suppress that the drying of the edge part of the casting film cast from the casting die progresses rather than the drying of other parts. Therefore, it is thought that it can suppress that a film | membrane is formed in the longitudinal direction both ends vicinity of the discharge outlet of a casting die.

Furthermore, the difference between the temperature of the solvent immediately after being discharged from both ends in the longitudinal direction of the discharge port of the casting die and the temperature of the solvent at the time of reaching the support is as follows. By adjusting so as to be small, it is considered that the evaporation of the solvent discharged from both ends in the longitudinal direction of the discharge port of the casting die can be sufficiently controlled. Specifically, it is possible to suppress the solvent from being excessively reduced by evaporation before reaching the support. Therefore, it is considered that the solvent concentration at the end portion in the width direction of the cast film can be sufficiently increased, and the peeling failure at the end portion in the width direction of the film can be sufficiently suppressed. Therefore, it is possible to sufficiently suppress the occurrence of non-uniformity such as retardation and orientation based on defective peeling. Furthermore, the washing | cleaning of the support body performed when peeling defect generate | occur | produces can be reduced, and a resin film can be manufactured stably.

Moreover, in the method for producing the resin film, it is preferable to satisfy the following formula (2).

10 ⁻⁷ <W2 / W1 <10 ⁻⁵ (2)
(W1 represents the supply amount [ml] of the solvent, and W2 represents the loss amount [ml] of the solvent.)

According to said structure, the peeling defect of a film can be suppressed more. This is considered to be because the evaporation of the solvent discharged from both ends in the longitudinal direction of the discharge port of the casting die can be controlled more. Therefore, it is considered that the solvent concentration at the end in the width direction of the cast film can be further increased.

Further, in the method for producing the resin film, it is preferable that the transparent resin is a cellulose ester resin and the solvent contains methylene chloride.

According to the above configuration, film formation and film peeling failure can be further suppressed. This is considered because the solvent flowed down from the discharge port suitably penetrates into the casting film on the support and can further increase the solvent concentration at the end in the width direction of the casting film. Furthermore, not only the occurrence of non-uniformity such as retardation and orientation based on poor peeling is sufficiently suppressed, but since the transparent resin is a cellulose ester resin, a resin film that is sufficiently excellent in transparency can be obtained. can get.

Another aspect of the present invention is a resin film obtained by the method for producing a resin film.

According to the above configuration, it is possible to provide a resin film excellent in optical characteristics with high uniformity such as retardation and orientation. This can suppress the occurrence of turbulence in the dope flow due to the film formed in the vicinity of both ends in the longitudinal direction of the discharge port of the casting die, and nonuniformity such as retardation and orientation based on separation failure that may occur during manufacturing. This is considered to be because the occurrence of sex is sufficiently suppressed.

Another aspect of the present invention is a polarizing plate comprising a polarizing element and a transparent protective film disposed on the surface of the polarizing element, wherein the transparent protective film is the resin film. This is a characteristic polarizing plate.

According to the above configuration, as a protective film for the polarizing plate, a resin film with high uniformity such as retardation and orientation and excellent optical characteristics is applied. For example, when applied to a liquid crystal display device, the contrast of It is possible to provide a polarizing plate that can improve the image quality of the liquid crystal display device such as improvement.

Another aspect of the present invention is a liquid crystal display device including a liquid crystal cell and two polarizing plates arranged so as to sandwich the liquid crystal cell, and at least one of the two polarizing plates. Is a liquid crystal display device characterized by being the polarizing plate.

According to the above configuration, since a polarizing plate including a resin film with excellent uniformity and optical properties such as retardation and orientation is used, it is possible to provide a high-quality liquid crystal display device with improved contrast and the like. it can.

According to the present invention, it is possible to suppress the formation of a film in the vicinity of both ends in the longitudinal direction of the discharge port of the casting die, further suppress the film peeling failure, and stabilize the resin film having excellent optical characteristics. A method for producing a resin film that can be produced is provided. Moreover, the resin film obtained by the said manufacturing method, the polarizing plate which used the said resin film as a transparent protective film, and the liquid crystal display device provided with the said polarizing plate are provided.

Claims (6)

1. A casting step of casting a resin solution containing a transparent resin from a casting die on a traveling support to form a casting film; and a peeling step of peeling the casting film from the support; A drying process for drying the peeled cast film,
   In the casting step, the resin solution is discharged from the discharge port of the casting die and cast on the support, and the transparent resin is poured from both longitudinal ends of the discharge port of the casting die. Let down the soluble solvent,
   The manufacturing method of the resin film characterized by satisfy | filling following formula (1).
   −5 <T2−T1 <5 (1)
   (In the formula, T1 indicates the temperature [° C.] of the solvent immediately after the solvent flows down from the discharge port, and T2 indicates the temperature [° C.] of the solvent when the solvent reaches the support. Is shown.)
2. The method for producing a resin film according to claim 1, wherein the following formula (2) is satisfied.
   10 ⁻⁷ <W2 / W1 <10 ⁻⁵ (2)
   (W1 represents the supply amount [ml] of the solvent, and W2 represents the loss amount [ml] of the solvent.)
3. The transparent resin is a cellulose ester resin,
   The method for producing a resin film according to claim 1, wherein the solvent contains methylene chloride.
4. A resin film obtained by the method for producing a resin film according to any one of claims 1 to 3.
5. A polarizing plate comprising a polarizing element and a transparent protective film disposed on the surface of the polarizing element,
   The said transparent protective film is a resin film of Claim 4, The polarizing plate characterized by the above-mentioned.
6. A liquid crystal display device comprising a liquid crystal cell and two polarizing plates arranged so as to sandwich the liquid crystal cell,
   6. The liquid crystal display device according to claim 5, wherein at least one of the two polarizing plates is the polarizing plate according to claim 5.

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