JP5104154B2 - Method for producing retardation film - Google Patents

Description

  The present invention relates to a method for producing a retardation film, a retardation film, a polarizing plate using the same, and a liquid crystal display device.

  Various retardation films are used in liquid crystal display devices.

  The retardation film is produced by molecular alignment by liquid crystal stretching, liquid crystal alignment, and the like. However, in order to give in-plane retardation in a single film, it is necessary to use the former stretching method.

  For such a polymer retardation film, a method called a melt casting method in which a polymer material is melted and formed into a film shape, or a solution casting method in which it is dissolved in a solvent and formed into a film is used. The film produced by the melt casting method has no phase difference in the so-called original fabric in a state where the film is not stretched, and the phase difference generated by the tension acting in the conveyance direction in the conveyance process when producing a long base material. It is only born. Therefore, as a retardation film that can be produced by stretching this melt casting film, Nz = (nx−nz) / (nx−ny) (nx is the refractive index in the slow axis direction in the film plane, ny is The Nz value defined by the refractive index in the fast axis direction, nz being the refractive index in the film thickness direction) is in the range of Nz ≦ 0 or 1 ≦ Nz. On the other hand, in solution casting, in the process of drawing a solution on a drum or belt support in the form of a film and peeling off from the substrate after the solvent is dried to some extent, the raw material polymer is dried and contracted on the support, and the polymer is in-plane. Therefore, a phase difference is always generated in the film thickness direction. Therefore, in general, the absolute value of the Nz value of a retardation film that can be produced by solution casting can be produced only in a range larger than that of a retardation film that can be produced by melt casting.

On the other hand, as a method for reducing the phase difference in the film thickness direction in the solution casting method, for example, a method of adding positive and negative birefringent materials as in Patent Document 1, and specifically in Patent Document 2 for cellulose ester. A method as disclosed in US Pat. However, in such a film, even if the film is stretched so as to generate a desired phase difference thereafter, the phase difference is hardly exhibited. Furthermore, when a film that can be produced by solution casting is stretched in the conveying direction as it is, there is a problem that the film becomes cloudy and the contrast is lowered. Further, as disclosed in Patent Document 3, when the film is stretched at a temperature much higher than the glass transition temperature (Tg) of the film, there is a problem that the film material is decomposed and yellowed. The method disclosed in No. 4 has a problem that a sufficient phase difference cannot be obtained, and stretching itself is difficult, resulting in an optically nonuniform film.
JP-A-8-110402 JP 2003-12859 A JP 2007-86755 A JP 2007-93936 A

Accordingly, an object of the present invention (object) is to express the desired phase difference, turbidity (haze) and yellowing or unevenness without Rukoto Kyosu Hisage manufacturing method according to a solution casting method of high phase difference film contrast It is.

  The above object of the present invention is achieved by the following configurations.

1. At least, comprising a casting step of forming a web by casting a dope prepared by dissolving a resin in a solvent in the belt support or drum, a separation step of separating the web, and a drying process by a roll conveyor In the method for producing a retardation film by a solution casting method ,
Above the boiling point of the solvent used the web to dope while dried at glass transition temperature (Tg) of the temperature of the film after drying, 30% to 3% or more the web in the conveying direction, a direction orthogonal to the transport direction The film is subjected to heat shrinkage at a shrinkage rate of 1% to 10%, the in-plane retardation Ro represented by the following formula is 26 nm to 300 nm, and the thickness direction retardation Rth is used to express A retardation film having an absolute value of the Nz coefficient determined by the step of 0.5 or more and 4 or less is obtained.

Ro = (nx−ny) × d
Rth = {(nx + ny) / 2−nz} × d
Nz = Rth / Ro + 0.5
(However, the refractive index in the slow axis direction in the retardation film surface is nx, the refractive index in the fast axis direction is ny, the refractive index in the film thickness direction is nz, and the film thickness is d (nm) . )
2. 2. The method for producing a retardation film according to claim 1, wherein the Nz coefficient is adjusted by stretching and heating shrinkage so that the absolute value of the Nz coefficient is 0.5 or more and 4 or less.
3 . The method for producing a retardation film according to claim 1 or 2, wherein the distance between the rolls in the roll conveyance is adjusted to 0.8 to 4 times the web width and the web is conveyed.

4 . The method for producing a retardation film according to any one of Items 1 to 3, wherein the process of shrinking the web is performed at a conveyance tension of 0.5 N / cm to 1.0 N / cm. .

5 . The method for producing a retardation film according to any one of Items 1 to 4, wherein a process of shrinking the web is performed by gradually increasing a conveyance tension.

6 . The phase difference film according to any one of claims 1 to 5 , wherein the web is stretched or held in a direction orthogonal to a conveyance direction before the step of shrinking the web. Production method.

The present invention, express the desired retardation, clouding (haze) and yellowing or unevenness without cut with a manufacturing method according to a solution casting method of high phase difference film contrast.

  The best mode for carrying out the present invention will be described in detail below, but the present invention is not limited thereto.

The method for producing a retardation film of the present invention includes a casting step in which a dope obtained by dissolving a raw material resin in a solvent is cast from a die onto an endless belt support, and a web is formed. In the method for producing a retardation film, after the peeling, a thin film retardation film is produced by a solution casting production apparatus having a stretching process, at least a drying process by roll conveyance, and a winding process.
While the web is dried at a temperature not lower than the boiling point of the solvent used for the dope and not higher than the glass transition temperature (Tg) of the dried film, the web is not less than 3% and not more than 20% in the transport direction, in a direction perpendicular to the transport direction. Heat shrinkage is performed at a shrinkage rate of 1% or more and 10% or less, the in-plane retardation Ro represented by the above formula is 26 nm or more and 300 nm or less, and the thickness direction retardation Rth is used in the above formula. A retardation film having an absolute value of Nz required of 0.5 or more and 4 or less is obtained.

  Here, the shrinkage rate referred to in the present invention is determined by the following equation (1).

Formula (1) Shrinkage (%) = (1−Vertical or horizontal dimension of the web at the exit of the drying step (cm) / Vertical or horizontal dimension of the web before entering the drying step (cm)) × 100
As the measurement method for the above dimensions, the vertical or horizontal actual dimension is measured by marking the marked length in the transport direction with an ink jet printer at the time of peeling, winding the film, and measuring the marked part. The shrinkage rate can be calculated.

  As a result of intensive studies in view of the above problems, the present inventors express a desired retardation, have no cloudiness or yellowing, and in order to produce a high-contrast retardation film, in addition to the production conditions of the stretching step, It has been found that this can be achieved by highly controlling the drying conditions and shrinkage conditions of the film in the web drying process, and the present invention has been achieved.

  That is, in the invention of claim 1, the drying step by roll conveyance conveys the web while drying the web at a temperature not lower than the boiling point of the solvent used for the dope and not higher than the glass transition temperature (Tg) of the dried film. It is characterized in that heat shrinkage is performed at a shrinkage rate of 3% or more and 30% or less in the direction (also referred to as MD direction) and 1% or more and 10% or less in the direction orthogonal to the transport direction (also referred to as TD direction).

  In the present invention, the web formed in the casting step is gradually removed in the drying step, and the web having the total residual solvent amount of 15% by mass or less is referred to as a film.

The invention according to claim 2 is characterized in that the Nz coefficient is adjusted by stretching and heating shrinkage so that the absolute value of the Nz coefficient is 0.5 or more and 4 or less.
The invention according to claim 3 is characterized in that the distance between the rolls in the roll conveyance is adjusted to 0.8 to 4 times the web width and the web is conveyed.

The invention of claim 4 is characterized in that the process of shrinking the web is performed at a conveying tension of 0.5 N / cm to 1.0 N / cm.

The invention according to claim 5 is characterized in that the process of shrinking the web is performed by gradually increasing the conveyance tension.

The invention of claim 6 is characterized in that, before the process of shrinking the web, the web is stretched or held in a direction perpendicular to the conveying direction.

The retardation film produced by the inventions according to claims 1 to 6 expresses a desired retardation, has no white turbidity or yellowing, is a retardation film having a high contrast, a polarizing plate using the retardation film, and a liquid crystal The display device has excellent visibility.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1, but the aspect of the present invention is not limited to this.

  FIG. 1 is a schematic view of an apparatus for producing a retardation film by a solution casting method in which an endless belt support is used and a first drying process and a second drying process are arranged by a roll conveyance method. Fig. 1 (a) uses an endless belt support that, after casting, is stretched by a tenter device, then undergoes a process of shrinking the web in a first drying process by a roll conveyance method, and then performs a main drying in a second drying process. It is a schematic perspective view of the manufacturing apparatus of the phase difference film by the solution casting method. In the present invention, while the web is dried at a temperature equal to or higher than the boiling point of the solvent used for the dope and equal to or lower than the glass transition temperature (Tg) of the dried film, 3% to 20% in the web transport direction, The process of performing heat shrinkage at a shrinkage rate of 1% or more and 10% or less in the orthogonal direction is preferably performed in the first drying step, but in the first drying step, the web is pre-dried and within the second drying step. The web may be contracted. Further, both the first drying step and the second drying step may be performed. In the first drying step, the web is shrunk in the conveyance direction, and then in the second drying step, the web is shrunk in a direction perpendicular to the web conveyance direction. It is also preferable to do this.

  FIG. 1B is a schematic cross section taken along the line AA ′ of FIG.

  In the figure, reference numeral 1a denotes a production apparatus for a solution casting method of a retardation film. The manufacturing apparatus 1a includes a casting step 101, a stretching step 103, a first drying step 102, a second drying step 104, and a winding step 105.

  The casting step 101 includes a mirror endless belt support 101a, a die 101b for casting a dope 2 in which a resin is dissolved in a solvent, and a heating device 101c. The endless belt support 101a is held by a roll 101a1 and a roll 101a2, and can be rotated (in the direction of the arrow in the figure).

  Reference numeral 3 denotes a peeling roll for peeling the web in a state where the dope casted on the endless belt support 101a is solidified, and 4 denotes the peeled web. The thickness of the web 4 can be set as necessary so that the thickness of the retardation film recovered in the winding process 105 becomes the set film thickness.

  The dope 2 is produced using a resin material for a retardation film using a mixed solvent composed of a good solvent and a poor solvent. In the present invention, what dissolves the resin used alone is called a good solvent, and what swells or does not dissolve alone is called a poor solvent.

  The heating device 101c is disposed to remove the solvent so that the dope 2 cast on the endless belt support 101a can be peeled from the endless belt support 101a.

  The heating device 101c includes a heated air supply pipe 101e and an exhaust pipe 101d. Although the heating apparatus 101c shown in this figure shows the case where heating air is used, the heating means is not particularly limited. In addition to this, for example, a method of heating the dope surface on the endless belt support 101a with an infrared heater A method of blowing warm air to the back surface of the endless belt support 101a and heating from the back surface side can be mentioned, and it can be appropriately selected as necessary.

  The endless belt support 101a is provided with measurement means (not shown) and display means (not shown) so that the temperature of the surface of the endless belt support 101a can be measured. The measuring means is not particularly limited, and examples thereof include a non-contact type thermometer and a contact type thermometer, and can be appropriately selected as necessary. The display means is not particularly limited, and examples thereof include a liquid crystal display device, and can be appropriately selected as necessary.

  The time between casting and peeling varies depending on the film thickness of the retardation film to be produced and the solvent used, but in the range of 0.5 to 5 minutes in consideration of peelability from the endless belt support 101a. preferable.

  As the endless belt support 101a to be used, one having a mirror-finished surface is preferable. For example, a metal belt having a surface plated with a casting is preferably used. The width of the endless belt support 101a is preferably 1700 mm to 3500 mm. The casting width is preferably 80% to 99% with respect to the width of the endless belt support 101a.

  The surface temperature of the endless belt support 101a in the casting process is preferably set to 20 ° C. to a temperature at which the solvent does not boil and foam. A higher temperature is preferable because the web can be dried faster, but if the temperature is too high, the web may foam or the flatness may deteriorate.

  The surface of the endless belt support 101a is preferably set so that the temperature at the center in the width direction is higher than the temperature at the end in the width direction. More preferably, the surface of the endless belt support 101a has a releasability from the endless belt support, a residual solvent amount at the time of peeling, It is preferable that the temperature is set to be higher by 1 ° C. to 30 ° C. in consideration of the transport properties and the physical characteristics of the film obtained after transport and drying.

  In addition, the edge part of the surface of the endless belt support body 101a means the range of 50 mm-500 mm in the width direction on the basis of the edge of the surface of the endless belt support body 101a. The central portion of the surface of the endless belt support 101a refers to a portion excluding the range of both ends from the entire width of the endless belt support 101a.

  The residual solvent amount of the web 4 when the web 4 is peeled from the endless belt support 101a is 70% by mass or more in consideration of curl stability at the end, conveyance stability, gripping ability with a tenter device, stretch rate, and the like. 170 mass% is preferable. Moreover, the ratio of the good solvent amount to the total residual solvent amount is such that the peelability of the web from the endless belt support, the curl stability of the end portion, the strength strength of the end portion by stabilizing the residual of the poor solvent, Considering gripping suitability and the like, 10% to 70% is preferable. Preferably it is 5%-60%, More preferably, it is 5%-30%. The solvent to be used will be described later.

  The concentration of the resin for forming the retardation film of the dope 2 is preferably higher because the drying load after casting on the endless belt support can be reduced, but the concentration of the resin for forming the retardation film is too high. And the load at the time of filtration increases, and the filtration accuracy deteriorates. The concentration for achieving both of these is preferably 10% by mass to 35% by mass, and more preferably 15% by mass to 25% by mass.

  When the web 4 is peeled from the endless belt support 101a, the web 4 is stretched in the MD (Machine Direction) direction due to the peeling tension and the subsequent conveying tension. Therefore, in the present invention, the web is peeled from the endless belt support 101a. In this case, it is preferable that the peeling and conveying tension be 1 N / cm to 4 N / cm.

  The stretching step 103 includes an outer box 103a having a dry air intake port 103b and a discharge port 103c, and a tenter stretching device 103d placed in the outer box 103a. The tenter used in the tenter stretching apparatus 103d is not particularly limited, and examples thereof include a clip tenter and a pin tenter, which can be selected and used as necessary. In the tenter stretching apparatus 103d, the web 4 can be stretched or held in width in the transport direction (MD direction) of the web 4 or in a direction perpendicular to the transport direction (TD direction) as necessary.

  It is also common to divide the tenter into several temperature zones in the direction of travel of the base. The temperature during stretching is selected so that desired physical properties and planarity can be obtained, but the temperature in the drying zone before and after the tenter is also selected from a temperature different from the temperature during stretching for various reasons. Sometimes. For example, if the atmospheric temperature in the drying zone before the tenter is different from the temperature in the tenter, the temperature in the zone near the tenter entrance is set to an intermediate temperature between the temperature in the drying zone before the tenter and the temperature in the center of the tenter. It is generally done. Similarly, when the temperature in the tenter is different from that in the tenter, the temperature in the zone near the tenter outlet is set to an intermediate temperature between the temperature after the tenter and the temperature in the tenter. As an example, when the residual solvent amount before the tenter in the cellulose ester film production process is 20% or more and 50% or less, the temperature of the drying zone before and after the tenter is generally 30 to 120 ° C, preferably 50 to 100 ° C, The temperature of the stretching portion is 50 to 180 ° C., preferably 80 to 140 ° C., and the temperature of the tenter inlet or outlet is appropriately selected from the intermediate temperatures.

  The pattern of stretching, i.e. the trajectory of the gripping clip, is selected from the optical properties and flatness of the film as well as the temperature, and varies. A retained pattern is often used. In the vicinity of the end of clip holding near the tenter exit, the width is generally relaxed in order to suppress the base vibration by releasing the holding.

  The drawing pattern is also related to the drawing speed, but the drawing speed is generally 10 to 1000 (% / min), preferably 100 to 500 (% / min). This stretching speed is not constant when the clip trajectory is a curve, and gradually changes in the base traveling direction.

  The tenter can also shrink the web. In order to shrink the web in the MD direction, for example, a method in which the film is shrunk by temporarily clipping out the width stretching and relaxing in the MD direction or by gradually narrowing the interval between adjacent clips of the transverse stretching apparatus. There is. The latter method can be performed by using a general simultaneous biaxial stretching apparatus, and by gradually and gradually narrowing the interval between adjacent clips in the longitudinal direction by driving the clip portion by, for example, a pantograph method or a linear drive method. it can.

  Gripping and stretching with a tenter can be performed anywhere from 50 to 150% by mass of the residual solvent amount of the film immediately after peeling to 0% by mass of the substantial residual solvent immediately before winding. It is preferred to introduce the shrinking process according to the invention.

  The dry air intake port 103b and the discharge port 103c may be reversed. Although the case where heated air is used as the solvent removing means in the stretching step 103 is shown, the solvent removing means is not particularly limited, and other examples include infrared rays.

  The total residual solvent amount of the web at the start of stretching in the stretching step 103 is 10% by mass to 30% by mass in consideration of the curl stability at the end, the gripping ability with the tenter device, the conveyance stability, the stretch rate, and the like. It is preferable to do. In addition, the ratio of the good solvent amount to the total residual solvent amount is preferably 5% to 50% in consideration of gripping suitability with a tenter device, conveyance stability, and the like. Preferably, it is 5% to 40%. More preferably, it is 5% to 30%.

  The first drying step 102 includes a drying device 102a. It has a heated air supply pipe 102c disposed in the drying apparatus 102a, a discharge port 102b, and a transport roll 102d for transporting the web 4. The heated air supply pipe 102 c controls the temperature of the surface of the web 4 sent from the casting process 101. It is possible to adjust the amount of solvent contained in the web 4 before entering the stretching step 103 in the first drying step 102.

  In the case of the manufacturing apparatus shown in the figure, the web is peeled from the endless belt support 101a, and used for the dope in the drying process (in the figure, the first drying process 102 or the second drying process 104) by roll conveyance. While drying the web at a temperature not lower than the boiling point of the solvent and not higher than the glass transition temperature (Tg) of the dried film, the web is not less than 3% and not more than 30% in the conveying direction, and not less than 1% and not less than 10% in the direction perpendicular to the conveying direction. By performing heat shrinkage at a shrinkage rate of not more than%, a desired retardation can be expressed, and a retardation film having high contrast without white turbidity or yellowing can be obtained. For web shrinkage, it is preferable from the viewpoint of stability and reproducibility to use a longitudinal stretching machine having a plurality of rolls capable of changing the peripheral speed.

  In the present invention, in order to achieve the object, since the web is dried while being conveyed in a roll, it is very important to control the temperature in the drying process. By carrying out drying in a state in which the conditions are appropriately controlled, the aggregation and orientation state of the polymer can be appropriately controlled, so that the desired optical characteristics can be achieved. The temperature measuring means is not particularly limited, and includes the above-described non-contact type thermometer, contact type thermometer, and the like, and can be appropriately selected as necessary.

  Drying in the drying step may be heating air, infrared rays, etc. alone or in combination with heating air and infrared drying. It is preferable to use heated air in terms of simplicity. This figure shows the case where heated air is used.

  The drying temperature varies depending on the amount of residual solvent in the web when entering the stretching step, but the adjustment of the stretch ratio of the web according to the present invention, condensation on the surface of the web as the solvent evaporates, the amount of residual solvent, and foaming of the solvent In view of the above, it is necessary to dry the web at a temperature not lower than the boiling point of the solvent used for the dope and not higher than the glass transition temperature (Tg) of the dried film. The drying temperature is preferably 40 ° C. or more lower than the glass transition temperature and higher than the boiling point of the solvent.

Here, the boiling point of the solvent is a boiling point under a pressure of 1 atm, that is, 1.013 × 10 ⁵ N / m ² . For the measurement of the boiling point, a known technique can be applied, and in the case of a simple substance, values described in documents such as a chemical handbook can also be referred to. When a plurality of solvents are used, the weighted average boiling point is determined by the following formula using the mass% of each solvent as a weight.

(How to find the weighted average boiling point)
When the boiling point data x _{i of} each solvent and the weight w _i are used, the weighted average boiling point (° C.) is obtained by the following formula.

  The glass transition temperature (Tg) of the film can be determined by the method described in JIS K7121. Specifically, a film sample is cut into a round shape, 10 mg is sealed in an aluminum sample pan, vacuum-dried for 24 hr or more, and then subjected to differential scanning calorimetry (DSC) (DSC8230, manufactured by Rigaku Corporation) at 10 ° C. / The temperature is raised from room temperature to 300 ° C. in a nitrogen gas atmosphere in minutes, and the glass transition temperature (Tg) is measured. Tg is obtained by taking the temperature at which the DSC curve begins to deviate from the baseline.

  Further, this drying process is divided into a plurality of sections such as a first section, a second section, a third section, etc., and it is preferable to divide the conditions depending on the residual solvent amount in each process. Specifically, a partition that divides the temperature condition is provided for independent control, or a plurality of drive rolls (feed rolls) are provided so that the tension in each part is different, so that the contraction condition for the rotational speed is independent. Appropriately, the tension should be taken independently. As the amount of residual solvent decreases, it is preferable to raise the temperature and increase the tension.

  The distance between the rolls in the roll conveyance is preferably adjusted to 0.8 to 4 times the web width to carry the web. In general, in the longitudinal stretching step, the shrinkage in the width direction is suppressed by shortening the distance between the rolls with respect to the web width. However, in the present invention, the distance between the rolls may be long in order to shrink particularly in the transport direction. Although it is preferable, in order to appropriately maintain the shrinkage balance in the direction orthogonal to the conveyance direction, the distance between the rolls with respect to the web width is preferably 0.8 times or more and 4 times or less.

  FIG. 2 is an enlarged schematic view of the roll conveyance portion of the roll conveyance / drying process. In the figure, F indicates the distance between the contact point of the upper transporting roll 102d 'with which the web 4 is in contact and the contact point of the lower transporting roll 102d with which the web 4 is in contact. The interval between the upper conveyance roll 102d 'and the lower conveyance roll 102d can be freely set. The transport speed of the roll transport unit is also independent and variable. In the roll conveyance / drying step, the drying shrinkage rate in the film conveyance direction can be changed as necessary depending on the distance F between the roll contacts and the conveyance speed in addition to the drying temperature and time.

  It is preferable to perform the process of shrinking the web at a conveyance tension of 0.5 N / cm to 1.0 N / cm. This is for maintaining the smoothness of the film and obtaining a desired amount of shrinkage.

  Moreover, it is preferable that the process of shrinking the web is performed by gradually increasing the conveyance tension. In the present invention, the film is shrunk during the course of drying, but the more solvent in the film, the smaller the degree of shrinkage of the film at the same tension. In order to appropriately shrink the film without impairing the flatness of the film, it is preferable to increase the transport tension compared to the initial stage of the shrinking process. It is also effective to raise the temperature.

  The second drying step 104 includes a drying box 104a having a drying air intake port 104b and a discharge port 104c, an upper conveyance roll 104d that conveys the web 4, and a lower conveyance roll 104e. The upper conveyance roll 104d and the lower conveyance roll 104e are a set of upper and lower, and are configured by a plurality of sets. The number of transport rolls disposed in the second drying step 104 varies depending on the drying conditions, the method, the length of the retardation film to be manufactured, and the like, and is set as appropriate. The upper conveyance roll 104d and the lower conveyance roll 104e are free rotation rolls that are not rotationally driven by a drive source. In addition, between the drying process and the winding process, a transport roll that freely rotates is not used. Usually, one to several transport drive rolls (roll driven to rotate by a drive source) are installed. Need. Basically, the purpose of the transport drive roll is to transport the resin film by its drive, so the transport of the resin film and the rotation of the drive roll are synchronized by nip or suction (air suction). With the mechanism.

In the retardation film of the present invention, the refractive index in the slow axis direction in the film plane is nx, the refractive index in the fast axis direction is ny, the refractive index in the film thickness direction is nz, and the film thickness is d (nm). The retardation Ro in the in-plane direction represented by the above formula is 26 nm or more and 300 nm or less, and the absolute value of the Nz coefficient obtained by the above formula using the retardation Rth in the thickness direction is 0.5. It is 4 or less.

  The retardation of the retardation film of the present invention is preferably adjusted by combining stretching and shrinkage according to the present invention. Stretching and shrinkage are performed by a tenter stretching apparatus, a first drying step, a second drying step, etc., but it is also preferable to perform stretching and free end stretching. The free end stretching means uniaxial stretching without supporting both ends in the direction orthogonal to the stretching direction.

  Such stretching may be performed by, for example, feeding a film from a feed roll on which a film formed in a belt shape is wound, and a portion where the film is fed at a higher speed than the feed speed by a take-up roll different from the feed roll. In a stretching method (so-called roll-toe-roll stretching) in which the film is stretched in the longitudinal direction by winding the film, both ends in the width direction are not supported by clamps and the like so that no tension is applied in the width direction. Stretching method.

  By performing free end stretching in this manner, a retardation film having an Nz coefficient in the above range can be obtained more reliably without laminating a shrinkable film during stretching.

  The winding recovery step 105 includes a winding device (not shown), and winds the retardation film 5 having the residual solvent amount set in the second drying step 104 to a necessary length to be wound around the winding core. Reference numeral 105a denotes a roll-like retardation film wound around a winding core. The temperature at the time of winding is preferably cooled to room temperature in order to prevent scratches and loosening due to shrinkage after winding. The winder to be used may be a commonly used winder, and can be wound by a winding method such as a constant tension method, a constant torque method, a taper tension method, or a program tension control method with a constant internal stress.

  The stretch rate of the retardation film collected in the winding and collecting step 105 is 0% to 20% in the MD direction and the stretch rate in the TD direction in consideration of the physical characteristics of the film that is produced after transport and drying. It is preferable that it is -3%-20%.

  In addition, it is preferable to perform the process which forms an emboss in the both-sides edge part of a phase difference film with the embossing apparatus in the front | former stage introduce | transduced into a winding process with respect to the phase difference film which finished the conveyance drying process. As the embossing apparatus, for example, an apparatus described in JP-A-63-74850 can be used.

  In the method of the present invention, the film thickness of the retardation film after winding varies depending on the purpose of use, but as a finished film, the film thickness range used in the present invention is 20 to 200 μm, particularly 25 to 120 μm. Is preferred.

  The width of the retardation film of the present invention is preferably from 1.2 m to 4 m in consideration of liquid crystal screen like large TV, use efficiency of film during polarizing plate processing, workability, production efficiency, etc. It is more preferable that it is ˜3 m from the viewpoint of productivity and handling.

  FIG. 3 is a schematic view of another apparatus for producing a retardation film according to the present invention.

  This is a case where a tenter stretching apparatus 103 for a stretching process is further introduced between the first drying process 102 and the second drying process 104 in the manufacturing apparatus of FIG. After the web is shrunk in the first drying step 102, the tenter stretching device 103d can further perform stretching or shrinking in the transport direction or a direction orthogonal to the transport direction with high accuracy.

  FIG. 4 is a schematic view of another apparatus for producing a retardation film according to the present invention.

  This is a case where a stretching process 103 is introduced after the first drying process 102 in the manufacturing apparatus of FIG. It is possible to shrink the web where there is a relatively large amount of residual solvent.

(Resin material)
The resin used in the method for producing a retardation film of the present invention is not particularly limited, and a resin generally used in a solution casting method can be used. As a resin material for producing a retardation film, for example, good adhesiveness with a polarizer and optical transparency are preferable requirements. The visible light transmittance is 60% or more, preferably 80% or more, and particularly preferably 90% or more.

  The resin is not particularly limited as long as it is a resin that forms a retardation film having the above properties. For example, cellulose esters such as cellulose diacetate resin, cellulose triacetate resin, cellulose acetate butyrate resin, and cellulose acetate propionate resin. Resin, polyester resin, polycarbonate resin, polyarylate resin, polysulfone (including polyethersulfone) resin, polyethylene terephthalate resin, polyester resin such as polyethylene naphthalate resin, polyethylene resin, polypropylene resin, cellophane, polychlorinated resin Vinylidene resin, polyvinyl alcohol resin, ethylene vinyl alcohol resin, syndiotactic polystyrene resin, polycarbonate resin, cycloolefin resin, polymethyl Pentene resins, polyether ketone resins, polyether ketone imide resin, polyamide resin, fluorine resin, nylon resin, polymethylmethacrylate resin, and acrylic resin. Among these, cellulose ester resins, cycloolefin resins, polycarbonate resins, and polysulfone (including polyethersulfone) resins are preferable. In the present invention, cellulose ester resins, cycloolefin resins, and polycarbonate resins are particularly preferable in production. From the viewpoints of cost, transparency, adhesion and the like, it is preferably used.

  The cellulose ester resin used in the present invention will be described. The cellulose ester-based resin is preferably cellulose acetate resin, cellulose propionate resin, cellulose butyrate resin, cellulose acetate butyrate resin, or cellulose acetate propionate resin. Among them, cellulose acetate butyrate resin, cellulose acetate phthalate resin, cellulose acetate Propionate resin is preferably used.

  In particular, when the substitution degree of the acetyl group is X and the substitution degree of the propionyl group or butyryl group is Y, a cellulose ester resin having a mixed fatty acid ester of cellulose in which X and Y are in the following ranges is preferably used.

Formula (I) 2.0 ≦ X + Y ≦ 2.8
Formula (II) 0.1 ≦ Y ≦ 1.2
Furthermore, a cellulose acetate propionate (total acyl group substitution degree = X + Y) resin of 2.4 ≦ X + Y ≦ 2.6 and 1.4 ≦ X ≦ 2.3 is preferable. Among them, 2.4 ≦ X + Y ≦ 2.6, 1.7 ≦ X ≦ 2.3, 0.1 ≦ Y ≦ 0.9, cellulose acetate propionate resin, cellulose acetate butyrate (total acyl group substitution degree = X + Y ) Resins are preferred. 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 measuring method of the substitution degree of an acyl group can be measured according to the provisions of ASTM-D817-96.

  When a cellulose ester resin is used as the retardation film according to the present invention, the cellulose used as a raw material for the cellulose ester resin is not particularly limited, but includes cotton linter, wood pulp (derived from coniferous trees, derived from broadleaf trees), kenaf and the like. I can list them. Moreover, the cellulose ester-type resin obtained from them can be mixed and used in arbitrary ratios, respectively. 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 obtain by making it react with a cellulose raw material using such a protic catalyst.

When the acylating agent is acid chloride (CH ₃ COCl, C ₂ H ₅ COCl, C ₃ H ₇ COCl), the reaction is carried out using a basic compound such as an amine as a catalyst. Specifically, it can be synthesized with reference to the method described in JP-A-10-45804. The cellulose ester resin used in the present invention is obtained by mixing and reacting the above acylating agent amounts in accordance with the degree of substitution. In the cellulose ester resin, these acylating agents react with hydroxyl groups of cellulose molecules. To do. Cellulose molecules are composed of many glucose units linked together, and the glucose unit has three hydroxyl groups. The number of acyl groups derived from these three hydroxyl groups is called the degree of substitution (mol%). For example, cellulose triacetate has acetyl groups bonded to all three hydroxyl groups of the glucose unit (actually 2.6 to 3.0).

  As described above, the cellulose ester resin according to the present invention includes a propionate group or a butyrate group in addition to an acetyl group such as a cellulose acetate propionate resin, a cellulose acetate butyrate resin, or a cellulose acetate propionate butyrate resin. A mixed fatty acid ester of cellulose to which is bound is particularly preferably used. In addition, the cellulose acetate propionate resin containing a propionate group as a substituent is excellent in water resistance and is useful as a film for a liquid crystal image display device.

  The number average molecular weight of the cellulose ester-based resin is preferably 40000 to 200000, and has a high mechanical strength when molded, and an appropriate dope viscosity in the case of a solution casting method, and more preferably 50000 to 150,000. . The weight average molecular weight (Mw) / number average molecular weight (Mn) is preferably in the range of 1.4 to 4.5.

(Dope)
The solvent used in preparing the dope used in the solution casting method may be any solvent that can dissolve the resin, and may be mixed with other solvents even if it cannot be dissolved alone. As long as it can be dissolved, it can be used. In general, a mixed solvent composed of a good solvent and a poor solvent is 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. In the case of a cellulose ester resin, the preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent.

  Since the good solvent and the poor solvent differ depending on the resin to be used, the case of cellulose ester resin will be described. Examples of the good solvent include methylene chloride, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, 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 and the like, but organic halogen compounds such as methylene chloride, Dioxolane derivatives, methyl acetate, ethyl acetate, acetone and the like are mentioned as preferred organic solvents (that is, good solvents). That.

  Examples of the poor solvent 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, methyl isobutyl ketone, propyl acetate, and monochloro. Examples thereof include benzene, benzene, cyclohexane, tetrahydrofuran, methyl cellosolve, ethylene glycol monomethyl ether, and the like. These poor solvents can be used alone or in combination of two or more.

  Next, a method for preparing a dope using a cellulose ester resin will be described. As a method for dissolving the cellulose ester resin when preparing the dope, a general method can be used. When heating and pressurization are combined, it is possible to heat above the boiling point at normal pressure. It is preferable to stir and dissolve while heating at a temperature that is equal to or higher than the boiling point of the solvent at normal pressure and that the solvent does not boil under pressure, in order to prevent the generation of massive undissolved materials called gels and mamacos. 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 of injecting an inert gas such as nitrogen gas or a method of increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  The heating temperature with the addition of the solvent is preferably higher from the viewpoint of the solubility of the cellulose ester, but if the heating temperature is too high, the required pressure increases and the productivity deteriorates. A preferable heating temperature is 45 to 120 ° C, more preferably 60 to 110 ° C, and still more preferably 70 ° C to 105 ° C. The pressure is adjusted so that 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, this cellulose ester resin solution is filtered using a suitable 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. For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is still more preferable.

  There are no particular restrictions on the material of the filter medium, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel do not drop off fibers. preferable. It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose ester by filtration.

A bright spot foreign substance is when two polarizing plates are placed in a crossed Nicol state, a cellulose ester film is placed between them, light is applied from the side of one polarizing plate, and observed from the side of the other polarizing plate. 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. More preferably, it is 100 pieces / cm < ² > or less, More preferably, it is 50 pieces / m < ² > or less, More preferably, it is 0-10 pieces / cm < ² > or less. Further, it is preferable that the number of bright spots of 0.01 mm or less is small.

  The dope can be filtered by a normal method, but the method of filtering while heating at a temperature not lower than the boiling point of the solvent at normal pressure and in a range where the solvent does not boil under pressure is the filtration pressure before and after filtration. The increase in the difference (referred to as differential pressure) is small and preferable. A preferred temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and still more preferably 45 to 55 ° C.

  A smaller filtration pressure is preferred. The filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and further preferably 1.0 MPa or less.

(Plasticizer)
Although it does not specifically limit as a plasticizer, Phosphate ester plasticizer, phthalate ester plasticizer, trimellitic acid ester plasticizer, pyromellitic acid plasticizer, glycolate plasticizer, citrate plasticizer Polyester plasticizers can be preferably used. Examples of the phosphate ester include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, and the like. Examples of the phthalic acid ester include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, and butyl benzyl phthalate. Examples of trimellitic acid plasticizers include tributyl trimellitate, triphenyl trimellitate, triethyl trimellitate, and the like. Examples of the pyromellitic acid ester plasticizer include tetrabutyl pyromellitate, tetraphenyl pyromellitate, and tetraethyl pyromellitate. Examples of glycolic acid esters include triacetin, tributyrin, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, and butyl phthalyl butyl glycolate. Examples of the citrate plasticizer include triethyl citrate, tri-n-butyl citrate, acetyl triethyl citrate, acetyl tri-n-butyl citrate, and acetyl tri-n- (2-ethylhexyl) citrate. As the polyester plasticizer, a copolymer of a dibasic acid such as an aliphatic dibasic acid, an alicyclic dibasic acid, or an aromatic dibasic acid and a glycol can be used. The aliphatic dibasic acid is not particularly limited, and adipic acid, sebacic acid, phthalic acid, terephthalic acid, 1,4-cyclohexyl dicarboxylic acid and the like can be used.

  As the glycol, ethylene glycol, diethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol and the like can be used. These dibasic acids and glycols may be used alone or in combination of two or more. The molecular weight of the polyester is preferably in the range of 500 to 2000 in terms of weight average molecular weight from the viewpoint of compatibility with the cellulose ester.

  In the present invention, it is particularly preferable to use a plasticizer having a vapor pressure of less than 1333 Pa at 200 ° C., more preferably a compound having a vapor pressure of 666 Pa or less, and more preferably 1 to 133 Pa. The non-volatile plasticizer is not particularly limited, and examples thereof include arylene bis (diaryl phosphate) ester, tricresyl phosphate, trimellitic acid tri (2-ethylhexyl), and the above polyester plasticizer. These plasticizers can be used alone or in combination of two or more.

  In consideration of dimensional stability and processability, the plasticizer can be added in an amount of 1 to 40% by mass, preferably 3 to 20% by mass, based on the cellulose ester resin. More preferably, it is 4 to 15% by mass. If the amount is less than 3% by mass, a smooth cut surface cannot be obtained when slitting or punching, resulting in increased generation of chips.

  It is preferable to add an antioxidant, an ultraviolet absorber or the like to the retardation film according to the present invention. As the antioxidant, a hindered phenol compound is preferably used, and 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl). -4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3 5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino) -1,3 5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octadecyl-3- ( , 5-di-t-butyl-4-hydroxyphenyl) propionate, N, N′-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 1,3,5 -Trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate Etc. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination. The amount of these compounds added is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the cellulose ester.

  In addition, heat stabilizers such as inorganic fine particles such as kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide, and alumina, and alkaline earth metal salts such as calcium and magnesium may be added. Good.

(UV absorber)
The retardation film produced by the production method of the present invention can be used for a polarizing plate or a liquid crystal display member because of its high dimensional stability. In this case, the polarizing plate or liquid crystal can be prevented from being deteriorated. Therefore, an ultraviolet absorber is preferably used.

  As the ultraviolet absorber, those excellent in the ability to absorb 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 preferably used ultraviolet absorbers include, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, triazine compounds, and the like. For example, the ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574 are preferably used. Moreover, the polymeric ultraviolet absorbers described in JP-A-6-148430 and JP-A-12-273437 are also preferably used. Or you may add the ultraviolet absorber described in Unexamined-Japanese-Patent No. 10-152568.

  Among these ultraviolet absorbers, benzotriazole ultraviolet absorbers and benzophenone ultraviolet absorbers are preferable ultraviolet absorbers. Although the specific example of a benzotriazole type ultraviolet absorber is given to the following, this invention is not limited to these.

2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) benzotriazole, 2- (2'-hydroxy-3) '-Tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy -3 '-(3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5'-methylphenyl) benzotriazole, 2,2-methylenebis (4- (1,1,3,3-tetramethyl) Butyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl)- -Chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol (TINUVIN171, manufactured by Ciba Specialty Chemicals), octyl-3- [ 3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy-5- (5- Chloro-2H-benzotriazol-2-yl) phenyl] propionate (TINUVIN109, manufactured by Ciba Specialty Chemicals)
Specific examples of the benzophenone-based ultraviolet absorber are shown below, but the present invention is not limited thereto. 2,4-dihydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane)
The ultraviolet absorber may be added by dissolving the ultraviolet absorber in an organic solvent such as alcohol, methylene chloride, dioxolane and the like, or adding it directly to the dope composition. For an inorganic powder that does not dissolve in an organic solvent, it is preferable to use a dissolver or a sand mill in the organic solvent and the cellulose ester resin to disperse it before adding it to the dope. The amount of the ultraviolet absorber used is preferably 0.1% by mass to 2.5% by mass in consideration of the effect as an ultraviolet absorber, transparency, and the like. Furthermore, Preferably, it is 0.8 mass%-2.0 mass%.

(Matting agent)
In addition, fine particles may be added to the cellulose ester resin film as a matting agent in order to prevent the films from sticking to each other or to impart slipperiness to facilitate handling. The fine particles include inorganic compound fine particles and organic compound fine particles. Inorganic compounds include silicon-containing compounds, silicon dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, etc. More preferred is an inorganic compound containing silicon or zirconium oxide, but silicon dioxide is particularly preferably used since the turbidity of the cellulose ester laminated film can be reduced.

  As fine particles of silicon dioxide, for example, AEROSIL-200, 200V, 300, R972, R972V, R974, R976, R976S, R202, R812, R805, OX50, TT600, RY50, RX50, NY50, NAX50, NA50H manufactured by Aerosil Co., Ltd. NA50Y, NX90, RY200S, RY200, RX200, R8200, RA200H, RA200HS, NA200Y, R816, R104, RY300, RX300, R106, and the like. Among these, AEROSIL-200V and R972V are preferable in terms of controlling dispersibility and particle size.

  As the fine particles of zirconium oxide, commercially available products such as Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) can be used.

  As an organic compound, polymers, such as a silicone resin, a fluororesin, and an acrylic resin, are preferable, for example, Among these, a silicone resin is preferably used.

  Among the above-described silicone resins, those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120 and 240 (above Toshiba Silicone Co., Ltd.) ) Etc. can be used.

  The primary average particle size of the fine particles according to the present invention is preferably 20 nm or less, more preferably 5 to 16 nm, and particularly preferably 5 to 12 nm, from the viewpoint of keeping the haze low.

  The apparent specific gravity of the fine particles is preferably 70 g / liter or more, more preferably 90 to 200 g / liter, and particularly preferably 100 to 200 g / liter. Larger apparent specific gravity makes it possible to make a high-concentration dispersion, which improves haze and agglomerates, and is preferable when preparing a dope having a high solid content concentration as in the present invention. Are particularly preferably used.

  Silicon dioxide fine particles having an average primary particle diameter of 20 nm or less and an apparent specific gravity of 70 g / liter or more are, for example, a mixture of vaporized silicon tetrachloride and hydrogen burned in air at 1000 to 1200 ° C. Can be obtained. Further, for example, Aerosil 200V and Aerosil R972V (manufactured by Nippon Aerosil Co., Ltd.) are commercially available, and these can be used.

  The apparent specific gravity was calculated by the following equation by measuring a weight of silicon dioxide fine particles in a graduated cylinder and measuring the weight at that time.

Apparent specific gravity (g / liter) = Mass of silicon dioxide (g) ÷ Volume of silicon dioxide (liter)
Examples of the method for preparing a dispersion of fine particles according to the present invention include the following three types.

<< Preparation Method A >>
After stirring and mixing the solvent and the fine particles, dispersion is performed with a disperser. This is a fine particle dispersion. The fine particle dispersion is added to the dope solution and stirred.

<< Preparation Method B >>
After stirring and mixing the solvent and the fine particles, dispersion is performed with a disperser. This is a fine particle dispersion. Separately, a small amount of cellulose ester is added to the solvent and dissolved by stirring. As the cellulose ester added here, it is particularly preferable to add the solid material of the present invention.

  The fine particle dispersion is added to this and stirred. This is a fine particle addition solution. The fine particle additive solution is sufficiently mixed with the dope solution using an in-line mixer.

<< Preparation Method C >>
Add a small amount of cellulose ester to the solvent and dissolve with stirring. Fine particles are added to this and dispersed by a disperser. This is a fine particle addition solution. The fine particle additive solution is sufficiently mixed with the dope solution using an in-line mixer.

  Preparation method A is excellent in dispersibility of silicon dioxide fine particles, and preparation method C is excellent in that silicon dioxide fine particles are difficult to re-aggregate. Among them, the preparation method B described above is a preferable preparation method that is excellent in both dispersibility of the silicon dioxide fine particles and that the silicon dioxide fine particles are less likely to reaggregate.

《Distribution method》
The concentration of silicon dioxide when the silicon dioxide fine particles are mixed with a solvent and dispersed is preferably 5 to 30% by mass, more preferably 10 to 25% by mass, and most preferably 15 to 20% by mass. A higher dispersion concentration is preferable because liquid turbidity with respect to the added amount tends to be low, and haze and aggregates are improved.

  The solvent used is preferably lower alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and the like. Although it does not specifically limit as solvents other than a lower alcohol, It is preferable to use the solvent used at the time of film forming of a cellulose ester.

  The amount of silicon dioxide fine particles added to cellulose ester is preferably 0.01 to 0.3 parts by mass, more preferably 0.05 to 0.2 parts by mass, and more preferably 0.0 to 0.2 parts by mass with respect to 100 parts by mass of cellulose ester. Most preferred is 08 to 0.12 parts by mass. The larger the added amount, the better the dynamic friction coefficient, and the smaller the added amount, the lower the haze and the fewer agglomerates.

  As the disperser, a normal disperser can be used. Dispersers can be broadly divided into media dispersers and medialess dispersers. For dispersing silicon dioxide fine particles, a medialess disperser is preferred because of its low haze.

  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. In the present invention, a high pressure disperser 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. When processing with a high-pressure dispersion apparatus, for example, the maximum pressure condition inside the apparatus is preferably 9.807 MPa or more in a thin tube having a tube diameter of 1 to 2000 μm. More preferably, it is 19.613 MPa or more. Further, at that time, those having a maximum reaching speed of 100 m / second or more and those having a heat transfer speed of 420 kJ / hour or more are preferable.

  The high-pressure dispersion apparatus as described above includes an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation or a nanomizer manufactured by Nanomizer. Examples include UHN-01 manufactured by Wako Co., Ltd.

  These fine particles may be uniformly distributed in the thickness direction of the film, but it is more preferable that they are mainly distributed so as to exist mainly in the vicinity of the surface. It is preferable to add fine particles mainly to the dope arranged on the surface layer side using a dope of a seed or more because a film having high slip properties and low haze can be obtained. It is preferable to add fine particles mainly to two dopes on the surface layer side using three kinds of dopes.

(Other additives)
Moreover, the optical film which has preferable impedance can also be obtained by adding the substance which has electroconductivity to the film of this invention. Although it does not specifically limit as an electroconductive substance, The antistatic agent etc. which have compatibility with an ionic electroconductive substance, electroconductive fine particles, or a cellulose ester can be used. Here, the ion conductive substance is a substance that shows electric conductivity and contains ions that are carriers for carrying electricity, and examples thereof include ionic polymer compounds.

  Examples of the ionic polymer compound include anionic polymer compounds such as those described in JP-B-49-23828, JP-A-49-23827, and JP-A-47-28937, such as JP-B-55-734, JP-A-50- An ionene type polymer having a dissociating group in the main chain, as shown in Japanese Patent No. 54672, Japanese Patent Publication Nos. 59-14735, 57-18175, 57-18176, 57-56059, etc. No. 13223, No. 57-15376, No. Sho 53-45231, No. 55-145578, No. 55-65950, No. 55-67746, No. 57-11342, No. 57-19735, No. Sho-58- No. 56858, JP-A 61-27853, and 62-9346, a cationic pender having a cationic dissociation group in the side chain It can be mentioned door type polymers, and the like.

Examples of the conductive fine particles include conductive metal oxides. As an example of the metal oxide, ZnO, TiO ₂ , SnO ₂ , Al ₂ O ₃ , In ₂ O ₃ , SiO ₂ , MgO, BaO, MoO ₂ , V ₂ O ₅ , or a composite oxide thereof is preferable. In particular, ZnO, TiO ₂ and SnO ₂ are preferred. Examples of containing different atoms include, for example, addition of Al, In, etc. to ZnO, addition of Nb, Ta, etc. to TiO ₂ , and addition of Sb, Nb, halogen elements, etc. to SnO ₂ . Addition is effective. The amount of these different atoms added is preferably in the range of 0.01 to 25 mol%, particularly preferably in the range of 0.1 to 15 mol%.

Further, the volume resistivity of these conductive metal oxide powders is 10 ⁷ Ωcm or less, particularly 10 ⁵ Ωcm or less, the primary particle diameter is 10 nm or more and 0.2 μm or less, and the major structure has a long diameter. It is preferable that a powder having a specific structure of 30 nm or more and 6 μm or less contains 0.01% or more and 20% or less in volume fraction in at least a part of the region of the film.

  It is particularly preferable to contain an ionene conductive polymer described in JP-A-9-203810 or a quaternary ammonium cation conductive polymer having intermolecular crosslinking.

  The characteristic of the cross-linked cationic conductive polymer is the dispersible granular polymer obtained, and it can have a high concentration and high density of the cationic component in the particles, so it has not only excellent conductivity. No deterioration of conductivity was observed even under low relative humidity, and although the particles were well dispersed in the dispersed state, the adhesion of the particles was good in the film-forming process after coating, so the film strength was also low. It is strong and has excellent adhesion to other substances such as substrates, and has excellent chemical resistance.

  The dispersible granular polymer, which is a crosslinked cationic conductive polymer, generally has a particle size range of about 0.01 μm to 0.3 μm, preferably a particle size of 0.05 μm to 0.15 μm. As used herein, the term “dispersible particulate polymer” is a polymer that appears to be a clear or slightly turbid solution by visual observation but appears as a particulate dispersion under an electron microscope.

  When the resin film is used as a retardation film, the addition of an antistatic agent or a matting agent is preferably included in the surface layer portion (portion of 10 μm from the surface) of the retardation film. It is preferable to contain an antistatic agent and / or a matting agent on the surface of the film. Specifically, a dope A containing a conductive material and / or a matting agent and a dope B substantially not containing these are used, and the dope B is cast so that the dope A is present on at least one side of the dope B. It is preferable. If necessary, an antistatic agent, a flame retardant, a lubricant, an oil agent, a matting agent, and other additives may be added.

(Functional layer)
In producing the polarizer protective film of the present invention, before and / or after stretching, an antistatic layer, a hard coat layer, an antireflection layer, a slippery layer, an easy adhesion layer, an antiglare layer, a barrier layer, an optical compensation layer, etc. The functional layer may be provided. In particular, a layer selected from an antistatic layer, a hard coat layer, an antireflection layer, an easy adhesion layer, an antiglare layer and an optical compensation layer can be provided. At this time, various surface treatments such as corona discharge treatment, plasma treatment, and chemical treatment can be performed as necessary.

(Polarizer)
The polarizing plate of the present invention will be described.

  The polarizing plate can be produced by a general method. The back surface side of the polarizer protective film of the present invention is subjected to alkali saponification treatment. The saponified polarizer protective film is preferably bonded to at least one surface of a polarizer produced by immersing and stretching a polyvinyl alcohol film in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. The polarizer protective film may be used on the other surface, or another polarizer protective film may be used. For the polarizer protective film of the present invention, the polarizer protective film used on the other surface is a cellulose acylate film having an in-plane retardation Ro of 590 nm, 0 to 10 nm, and Rth of -30 to 30 nm. It is preferable to use it. By using it in combination with the polarizer protective film of the present invention, it is possible to obtain a polarizing plate that is excellent in flatness and has a stable viewing angle expansion effect.

  As a polarizer protective film used on the back side, as a commercially available cellulose acylate film, KC8UX, KC4UX, KC5UX, KC8UCR3, KC8UCR4, KC8UCR5, KC8UY, KC4UY, KC10UDR, KC8UY-HA, KC8UX-RH OPT Co., Ltd.) is preferably used.

  The polarizer protective film of the present invention is industrially produced as a long film, and an aspect in which a polarizing plate is constituted by bonding with a polarizer produced as a long film is most useful. Moreover, it can also be used as a mere retardation film which does not have a function as a polarizer protective film, such as further bonding to a polarizing plate.

  A polarizer, which is a main component of a polarizing plate, is an element that allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is polyvinyl alcohol. There are ones in which iodine is dyed on a system film and ones in which a dichroic dye is dyed, but it is not limited to this. For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound. A polarizer having a thickness of 5 to 30 μm is preferably used.

  The polarizing plate can be configured by further bonding a protective film on one side and a separate film on the other side. The protective film and the separate film are used for the purpose of protecting the polarizing plate at the time of shipping the polarizing plate and at the time of product inspection. In this case, the protect film is bonded for the purpose of protecting the surface of the polarizing plate, and is used on the side opposite to the surface where the polarizing plate is bonded to the liquid crystal cell. Moreover, a separate film is used in order to cover the adhesive layer bonded to a liquid crystal cell, and is used for the surface side which bonds a polarizing plate to a liquid crystal cell.

(Liquid crystal display device)
Mounting of the polarizing plate to the liquid crystal display device can produce various liquid crystal display devices with excellent visibility by bonding the polarizer protective film surface according to the present invention to the liquid crystal cell side.

  As described above, the liquid crystal cell is preferably bonded using an acrylic pressure-sensitive adhesive.

  The polarizer protective film of the present invention is a reflection type, transmission type, transflective LCD or TN type, STN type, OCB type, HAN type, VA type (PVA type, MVA type: vertical alignment method), IPS type, etc. It is preferably used in a drive type LCD. In particular, it is preferably used for a VA type or IPS type liquid crystal display device. A large-screen liquid crystal display device with a 30-inch or larger screen has less color unevenness and wavy unevenness, and has an effect that eyes do not get tired even during long-time viewing.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
[Production of Retardation Film 1 of the Present Invention]
<Preparation of dope solution>
The following materials are sequentially put into a sealed container, and the temperature in the container is raised from 20 ° C. to 80 ° C., and then stirred for 3 hours while maintaining the temperature at 80 ° C. to completely dissolve the cellulose ester. A dope solution was prepared. Then, stirring was stopped and the liquid temperature was lowered to 43 ° C. This dope solution was filtered using filter paper (Azumi Filter Paper Co., Ltd., Azumi Filter Paper No. 244) to obtain Dope A.

(Dope A)
Cellulose ester (cellulose acetate propionate; acetyl group substitution degree 1.3, propionyl group substitution degree 1.1) 100 parts by weight Polymethyl acrylate 3 parts by weight Sucrose octabenzoate 5 parts by weight Silicon oxide fine particles (Aerosil R972V (Nippon Aerosil Co., Ltd.) Company-made))
0.1 parts by mass Methylene chloride 240 parts by mass Ethanol 60 parts by mass The dope A prepared as described above was cast on a 30 ° C support made of a stainless steel endless belt through a casting die kept at 30 ° C. Then, a web was formed, dried on the support, dried on the support until the residual solvent amount of the web reached 65% by mass, and then the web was peeled from the support with a peeling roll.

  Subsequently, both ends of the web were gripped with a tenter and then stretched by 3% in the width direction at 55 ° C. The residual solvent amount at the tenter outlet was 30%. After stretching with a tenter, the web was stretched by 1% in the conveying direction while drying to a residual solvent amount of 20% by mass with a drying air at a temperature of 47 ° C. in a longitudinal stretching process using a plurality of rolls arranged vertically.

  Thereafter, the web was transported and shrunk in a drying process having a first section and a second section in which a plurality of rolls were arranged vertically in the same manner as the longitudinal stretching process. The distance ratio between rolls (MD / TD) with respect to the web at this time was doubled. The temperature is set to 75 ° C. in the first section and 95 ° C. in the second section, and the web conveyance tension is 0.7 N / cm in the first section and 0.8 N / cm in the second section. Set to. At this time, the shrinkage in the conveyance direction and the width direction in the first section was 7% and 2%, respectively, and in the second section, it was 9% and 2% in the same manner.

  Thereafter, the web was wound up to obtain the retardation film 1 of the present invention. The film thickness was 84 μm and the residual solvent amount was below the measurement limit.

(Measurement of retardation value of film)
When the retardation value represented by the following formula at a wavelength of 590 nm of the obtained film was measured in an environment of 23 ° C. and 55% RH using KOBRA-21-ADH manufactured by Oji Scientific Instruments, the Rth value was 100 nm, Ro value was 40 nm, Nz value was 2.72, and the fast axis was parallel to the transport direction.

Ro = (nx−ny) × d
Rth = {(nx + ny) / 2−nz} × d
Nz = Rth / Ro + 0.5
(The refractive index in the slow axis direction in the retardation film plane is nx, the refractive index in the fast axis direction is ny, the refractive index in the film thickness direction is nz, and the film thickness is d (nm).)
(Measure haze)
When NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. was used, the haze of the film was measured according to JISK7136 and found to be 0.12%.

(Measurement of yellowness (YI))
The film transmission light spectrum was measured with a spectrophotometer U-3310 manufactured by Hitachi High-Technologies Corporation, and the yellowness YI was calculated with a D65 light source and a 2-degree field of view.

(Flatness)
When the film was placed on a black cloth and unevenness was visually evaluated under a three-wavelength fluorescent lamp, the evaluation level was 3.

  1: The presence of unevenness can be readily seen visually.

  2: Unevenness is observed when looking closely.

  3: Unevenness cannot be observed.

[Production of Retardation Films 2 to 8 of the Present Invention]
Retardation films 2 to 8 of the present invention were produced in the same manner as the retardation film 1 of the present invention except that the production conditions and film thickness were changed as described in Tables 1 and 2.

[Production of Comparative Retardation Films 1 to 4]
Comparative retardation films 1 to 4 were produced in the same manner as the retardation film 1 of the present invention except that the production conditions and film thickness were changed as described in Tables 1 and 2.

[Production of Comparative Retardation Film 5]
A Konica Minolta-tack film KC8UYW (Rth 50 nm, Ro 3 nm; manufactured by Konica Minolta Opto Co., Ltd.) was stretched by 200 ° C. and 50% in the film longitudinal direction to obtain a comparative retardation film 5. The film thickness was 80 μm, Rth 41 nm, Ro was 105 nm, and Nz 0.89.

[Production of Comparative Retardation Film 6]
<Preparation of dope solution>
The following materials were sequentially put into a sealed container, the temperature in the container was raised from 20 ° C. to 80 ° C., and the mixture was stirred for 3 hours while maintaining the temperature at 80 ° C. to completely dissolve the cellulose ester. . Then, stirring was stopped and the liquid temperature was lowered to 43 ° C. This dope was filtered using a filter paper (Azumi filter paper No. 244, manufactured by Azumi Filter Paper Co., Ltd.) to obtain a dope B.

(Dope B)
Cellulose ester (cellulose triacetate; substitution degree of acetyl group 2.87)
100 parts by mass Polymethyl acrylate 10 parts by mass Silicon oxide fine particles (Aerosil R972V (produced by Nippon Aerosil Co., Ltd.))
0.1 parts by mass Methylene chloride 270 parts by mass Ethanol 30 parts by mass The dope prepared as described above was cast on a 25 ° C. support made of a stainless steel endless belt through a casting die kept at 25 ° C. Then, the web was formed, dried on the support, dried on the support until the residual solvent amount of the web reached 95% by mass, and then the web was peeled from the support with a peeling roll.

  The web was dried at 80 ° C. while being conveyed by a roll, and then both ends of the web were held with a tenter and stretched by 3% in the width direction at 155 ° C. The residual solvent amount at the tenter outlet was 20%.

  Thereafter, the solvent was dried at 150 ° C. to the measurement limit or less and wound up to obtain a comparative retardation film 6. The film thickness was 80 μm, Rth 32 nm, Ro was 54 nm, and Nz 1.09.

  The obtained retardation films 2 to 8 of the present invention and comparative retardation films 1 to 6 were evaluated for haze, yellowness (YI), and planarity in the same manner as in Example 1 and listed in Table 3. .

  From Table 3, it can be seen that the retardation films 1 to 8 of the present invention are retardation films that are comprehensively excellent in haze, yellowness (YI), and flatness.

Example 2
Using the retardation films 2, 4, 6 and 7 of the present invention prepared in Example 1, a polarizing plate was prepared as follows, and then a liquid crystal display device was prepared using the polarizing plate.

<Production of polarizing plate>
A polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a polarizing film.

  Subsequently, according to the following processes 1-5, the polarizing film, the said phase difference film, and the cellulose-ester film on the back side were bonded together, and the polarizing plate was produced. As the polarizing plate protective film on the back side, Konica Minolta Tack KC8UX (manufactured by Konica Minolta Opto Co., Ltd.), which is a commercially available cellulose ester film, was used as a polarizing plate.

  Step 1: The film was immersed in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to obtain the saponified film to be bonded to the polarizer.

  Step 2: The polarizing film was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.

  Step 3: Excess adhesive adhered to the polarizing film in Step 2 was gently wiped, and this was placed on the film according to the present invention treated in Step 1 and laminated.

Step 4: The cellulose ester film sample, the polarizing film and the back side cellulose ester film according to the present invention laminated in Step 3 were bonded at a pressure of 20 to 30 N / cm ² and a conveying speed of about 2 m / min.

  Step 5: A sample obtained by bonding the polarizing film prepared in Step 4 to the retardation film according to the present invention and the backside cellulose ester film in a dryer at 80 ° C. was dried for 2 minutes to prepare a polarizing plate.

<Application to liquid crystal display devices>
Using the retardation film 2 of the present invention, a polarizing plate produced by making the transport direction and the absorption axis of the polarizer parallel to each other on a Sony LCD TV Bravia S1000 (40 inches) and the absorption axis of the original polarizing plate When the viewing angle was confirmed by laminating on both sides so that the retardation film of the present invention was located on the liquid crystal cell side in the same direction, good viewing characteristics were obtained.

  A polarizing plate produced using the retardation film 4 of the present invention with the transport direction and the absorption axis of the polarizer parallel to each other is the same as the absorption axis of the original polarizing plate on a BenQ liquid crystal display FP73GS (17 inches). As a result, the viewing angle was confirmed by laminating on both sides so that the retardation film of the present invention was positioned on the liquid crystal cell side, and good viewing characteristics were obtained.

  A polarizing plate produced by using the retardation film 6 of the present invention with the transport direction and the absorption axis of the polarizer perpendicular to each other is placed on the viewing side of the Hitachi liquid crystal television W17-LC50 (17 inches) and on the backlight side. The polarizing plate produced using Konica Minolta Tack KC4UEW (manufactured by Konica Minolta Opto Co., Ltd.) instead of the film is in the same direction as the absorption axis of the original polarizing plate, and the retardation film of the present invention When KV4UEW was bonded to both sides instead of being positioned on the liquid crystal cell side and the viewing angle was confirmed, good viewing characteristics were obtained.

  Using the retardation film 7 of the present invention, a polarizing plate produced by laminating the transport direction and the absorption axis of the polarizer by 45 degrees was applied to an active Clix2 (2 GB) active matrix organic EL display. When the viewing angle was confirmed by laminating the polarizing film so that the retardation film of the present invention was positioned on the liquid crystal cell side in the same direction as the absorption axis of the polarizing plate, good viewing characteristics were obtained.

It is the schematic of the manufacturing apparatus of the retardation film by the solution casting method which used the endless belt support body and arrange | positioned the 1st drying process by a roll conveyance system. It is the schematic diagram which expanded the roll conveyance part of a roll conveyance and a drying process. It is the schematic of another manufacturing apparatus of the retardation film which concerns on this invention. It is the schematic of another manufacturing apparatus of the retardation film which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b, 1c Manufacturing apparatus 101 Casting process 101a Endless belt support 101b Die 102, 102 '1st drying process 102a, 104a Drying box 102'd Tenter conveyance apparatus 103 Stretching process 103' MD stretching process 103'a Conveying part 103'b, 103'c Feed roll 103'd Heating device 103c, 102'c, 103'd1 Outer box 103d Tenter stretching device 104 Second drying step 105 Winding step 2 Dope 3 Peeling roll 4 Web 5 Phase difference film 6 , 702 Polarizing plate 601, 702a Polarizer 602, 702b Protective film 7 Liquid crystal display device 701 Liquid crystal cell

Claims (6)

At least, comprising a casting step of forming a web by casting a dope prepared by dissolving a resin in a solvent in the belt support or drum, a separation step of separating the web, and a drying process by a roll conveyor In the method for producing a retardation film by a solution casting method ,
Above the boiling point of the solvent used the web to dope while dried at glass transition temperature (Tg) of the temperature of the film after drying, 30% to 3% or more the web in the conveying direction, a direction orthogonal to the transport direction The film is subjected to heat shrinkage at a shrinkage rate of 1% to 10%, the in-plane retardation Ro represented by the following formula is 26 nm to 300 nm, and the thickness direction retardation Rth is used to express A retardation film having an absolute value of the Nz coefficient determined by the step of 0.5 or more and 4 or less is obtained.
Ro = (nx−ny) × d
Rth = {(nx + ny) / 2−nz} × d
Nz = Rth / Ro + 0.5
(However, the refractive index in the slow axis direction in the retardation film surface is nx, the refractive index in the fast axis direction is ny, the refractive index in the film thickness direction is nz, and the film thickness is d (nm) . ) The method for producing a retardation film according to claim 1, wherein the Nz coefficient is adjusted by stretching and heating shrinkage so that the absolute value of the Nz coefficient is 0.5 or more and 4 or less. The method for producing a retardation film according to claim 1 or 2, wherein the distance between the rolls in the roll conveyance is adjusted to 0.8 to 4 times the web width and the web is conveyed. The method for producing a retardation film according to any one of claims 1 to 3, wherein the process of shrinking the web is performed at a conveyance tension of 0.5 N / cm or more and 1.0 N / cm or less. The method for producing a retardation film according to any one of claims 1 to 4, wherein a process of shrinking the web is performed by gradually increasing a conveyance tension. The method for producing a retardation film according to any one of claims 1 to 5, wherein the web is stretched or held in a direction orthogonal to a conveyance direction before the step of shrinking the web. .

Images