JP5710537B2 - Endless band evaluation method and solution casting method - Google Patents

Description

The present invention relates to an endless band evaluation method and a solution casting method .

  With the increase in the screen size of a liquid crystal display (LCD), an optical film used for the LCD is also required to have a large area. The optical film is manufactured in a long length and then cut into a predetermined size according to the dimensions of the LCD. Therefore, in order to manufacture an optical film having a larger area, it is necessary to manufacture a long optical film having a width larger than that of the conventional one.

  As a typical method for producing a long optical film, there is a solution casting method. In the solution casting method, a dope is prepared by dissolving a polymer in a solvent. The dope is cast on a moving casting support, and a casting film is formed on the casting support by the dope. And after evaporating a solvent to such an extent that it has a self-supporting property and drying a cast film, it peels from a cast support body. The peeled wet film is biaxially stretched with a tenter as necessary, and further dried to obtain a product film.

  As the casting support, a metal endless band stretched around a plurality of metal drums is used. The maximum width of the film that can be produced by the solution casting method is limited by the width of the endless band. Therefore, a larger width endless band is required to produce a larger width film. However, until now, the limit was an endless band with a width of about 2 m. This is related to a metal strip manufacturing facility that is an endless band material, and a new manufacturing facility is required to manufacture a metal strip having a wider width than before. Therefore, it is difficult to widen the metal strip itself.

  Therefore, in Patent Document 1, an endless band having a wider width than the conventional one is obtained by welding in the longitudinal direction a central member that is a central portion in the width direction and a pair of side members that are each side portion. Yes.

Korean Patent Publication No. 2009-0110082

  With an endless band as described in Patent Document 1, paying attention to smoothing the projections of the vertical weld line by polishing and finishing the endless band itself to a mirror surface, the endless band is also fixed to a certain level by precision inspection or precision polishing. If the degree was obtained, it was regarded as an acceptable product. However, it has been found that even when a solution film is formed using such an endless band having a certain smoothness, a slight thickness unevenness occurs in the film portion corresponding to the longitudinal weld line. When such a film is wound up in a roll form, this slight thickness unevenness occurs only in the longitudinal weld line, so it concentrates at a fixed position in the roll form and can be visually observed as a black streak.

  The black streaks extend in the circumferential direction so as to go around the film roll and are recognized on both sides of the film roll. The so-called black streak failure in which black streaks are recognized in this way is small as a thickness unevenness of the film itself and does not pose a serious problem, but has been demanded for improvement because it is visually recognized as a black streak. In addition, depending on the degree of black streaks, not only the commercial value on the appearance surface is lowered, but also when coating film is formed on the film by applying a coating solution, uneven coating that makes the coating uneven may appear. There is also. Furthermore, depending on the LCD or the like that will be required to have a high resolution in the future, this thickness unevenness may become a problem.

  Therefore, there is a need for a new evaluation standard that does not cause black streak failure, as well as an endless band evaluation standard in which the surface is finished to a mirror surface by precision polishing and smoothness is within a certain range by precise inspection.

The present invention has been made to solve such problems, and an object thereof is to provide an evaluation method and a solution casting method of the endless band so as to eliminate the occurrence of temperature unevenness in the endless band.

  As a result of the inventor's earnest study, the smoothness of the endless band alone is not sufficient, the contact pressure distribution between the endless band and the drum is important, and the contact pressure distribution and the temperature distribution of the endless band are correlated. Focusing on the fact that the temperature distribution is non-uniform in the part where the contact pressure is high compared to other parts, a new evaluation standard for the endless band was determined.

  The evaluation method of an endless band of the present invention is a method for evaluating whether or not a metal endless band that runs between a pair of metal drums and runs in a rotating manner is appropriate as a casting band, A pressure-sensitive film whose color density changes according to pressure is inserted between the drum and the endless band, and the contact pressure distribution of the endless band to the drum is measured from the color density of the pressure-sensitive film. In this case, the endless band is evaluated as appropriate as a casting band. The pressure-sensitive film preferably has a total thickness of 50 μm or more and 400 μm or less.

  Moreover, you may use the temperature sensitive liquid crystal film affixed on the surface of the endless band instead of using a pressure sensitive film. In this case, the temperature distribution between the pair of drums is given, and the temperature distribution before the temperature distribution in the width direction of the endless band becomes constant due to the change in the color of the temperature-sensitive liquid crystal film passing on one drum. When the measured temperature distribution is within a certain range, the endless band is evaluated as appropriate as a casting band.

  Further, a heat transfer coefficient distribution in the width direction of the endless band may be obtained from the obtained width direction temperature distribution, and may be evaluated as appropriate as the casting band when the heat transfer coefficient distribution is within a certain range. The endless band preferably has a weld line in the longitudinal direction. Further, it is preferable that a peak in the distribution is obtained from any one of the contact pressure distribution, the temperature distribution, and the heat transfer coefficient distribution, and is evaluated as appropriate when the numerical value representing the peak is within a certain range.

  Further, in the solution casting method of the present invention, an endless band evaluated as appropriate by the above-described endless band evaluation method is used, and a dope containing a polymer and a solvent is poured onto the endless band from a casting die. A film is formed, and the solvent is evaporated from the cast film to peel it off as a wet film.

  According to the present invention, it is possible to appropriately evaluate an endless band used in solution casting in consideration of a factor of black streak failure that cannot be found by conventional precision inspection.

It is a perspective view which shows the method of spanning the wide endless band by longitudinal welding between drums, and measuring contact pressure distribution. It is a flowchart which shows the evaluation method of the endless band of this invention. It is a graph for demonstrating specification and determination of the peak from contact pressure distribution. It is a graph which shows an example of the contact pressure distribution calculated | required with the pressure sensitive film. It is a graph which similarly shows an example of contact pressure distribution of another site | part. It is a graph which shows an example of the heat transfer coefficient distribution in the width direction of the endless band calculated | required using the temperature-sensitive liquid crystal film. It is a graph which similarly shows an example of heat transfer coefficient distribution. It is a perspective view which shows the method of measuring the width direction temperature distribution of an endless band using a temperature-sensitive liquid crystal film. It is a graph which shows an example of the width direction contact pressure distribution of the endless band evaluated as the pass by the evaluation method of this invention. It is a graph which shows an example of the heat transfer coefficient distribution in the width direction of the endless band evaluated as the pass by the evaluation method of the present invention. It is a side view which shows the other evaluation installation which calculates | requires the width direction contact pressure distribution in the perimeter of an endless band using a roll-shaped pressure sensitive film. It is a flowchart which shows the evaluation method of the endless band of this invention using a temperature sensitive liquid crystal film. It is a side view which shows the outline | summary of the solution film-forming equipment using the endless band evaluated with the evaluation method of this invention.

(Endless band)
As shown in FIG. 1, the endless band 10 is obtained by joining a central member 11 and a side member 12 by vertical welding and widening in the width direction. The endless band 10 is mirror-finished by precision polishing or the like on the front and back surfaces of the entire circumference including the vertical weld line 13 (which is actually impossible to see, but is indicated by a two-dot chain line for explanation). It has been. In the mirror finish, the polishing of the endless band 10 is finished in a state where the surface roughness is 0.05 μm or less and the smoothness is confirmed.

(Endless band evaluation method)
As shown in the flowchart of FIG. 2, after the endless band 10 is accepted by mirror finishing, an evaluation test is performed to determine whether or not the endless band 10 is suitable as a casting support for solution casting. In the evaluation test, as shown in FIG. 1, the endless band 10 is spanned between a pair of drums 15 and 16, and the contact pressure distribution is measured. For this reason, the pressure-sensitive film (pressure measurement film) 20 is set on the band entering side of the first drum 15 and the endless band 10 is rotated at a predetermined traveling speed. The pressure-sensitive film 20 is sandwiched between the first drum 15 and the endless band 10 as the endless band 10 travels. Thereafter, the clamping is released at the band outlet of the first drum 15 and discharged. The discharged pressure sensitive film 20 is collected, and a contact pressure distribution is obtained from the pressure sensitive film 20. Since the surfaces of the drums 15 and 16 are already finished smoothly and the same contact pressure distribution is exhibited regardless of which of the drums 15 and 16 is used, in this embodiment, between the first drum 15 and the endless band 10. The contact pressure at is measured. Of course, the contact pressure with the second drum 16 may be measured. In the present embodiment, the first drum 15 is a driving drum and the second drum 16 is a driven drum.

  As the pressure-sensitive film 20, a pre-scale (trade name) 2-sheet type manufactured by Fuji Film Co., Ltd., for ultra-low pressure (LLLLW) is used. This pressure-sensitive film 20 is composed of a two-sheet type of an A film 20a and a C film 20c. The A film 20a has a thickness of 80 to 100 μm (the thickness varies depending on the type) and is contained in a black plastic bag. The A film 20a has a color former layer coated on a support made of a polyethylene terephthalate (PET) film. The color former layer includes microcapsules in which the color former is contained. The C film 20c has a thickness of 80 to 100 μm (thickness varies depending on the type) and is contained in a blue plastic bag. The C film 20c has a developer layer coated on a support made of a PET film. The developer layer contains a developer that reacts with the color former and develops a red color. In use, both the films 20a and 20c are overlapped so that the glossy and rough surfaces (coating layer surfaces) are inward, and then pressed between measurement points. The C film 20c is colored red by pressurization. And the higher the pressure, the higher the concentration. The pressure distribution can be visually inspected based on the color density of the portion where the density has changed. Further, instead of visual inspection, analysis may be performed using a dedicated contact pressure distribution analyzer.

  The pressure-sensitive film 20 preferably has a total thickness (thickness when the two films 20a and 20c are overlapped) of 50 μm or more and 400 μm or less. The total thickness of the pressure-sensitive film 20 is preferably 50 μm to 400 μm, more preferably 120 μm to 300 μm, and particularly preferably 150 μm to 250 μm. If the total thickness of the pressure-sensitive film 20 exceeds 400 μm, the smoothness of the surfaces of the band 10 and the drums 15 and 16 is adversely affected when the pressure-sensitive film 20 is added. In addition, when the total thickness of the pressure-sensitive film 20 is less than 50 μm, it becomes difficult to handle the pressure-sensitive film 20, which is not preferable. The pressure-sensitive film 20 may be a single sheet other than the two-sheet type, and a film whose density changes according to the contact pressure.

  The dedicated contact pressure distribution analyzer uses, for example, the pressure image analysis system Data Shot FPD-100 / 100S manufactured by Fuji Film Co., Ltd. for the camera type and the pressure image analysis system FPD-8010E manufactured by Fuji Film Co., Ltd. for the scanner type. Use FPD-9270. In these contact pressure distribution analyzers, for example, the contact pressure distribution in the width direction of the endless band 10 is converted based on the color density distribution for one line read from the scanner.

  Next, as shown in FIG. 3, each extreme value (indicated by a black rectangular mark) is obtained from this contact pressure distribution, and the extreme value that is the maximum value is specified as a peak. The method for specifying the peak is automatically performed based on a known numerical algorithm such as the Savitzky-Golay method instead of visual inspection or visual inspection. The numerical algorithm is described in detail in “Waveform Data Processing for Scientific Measurement Utilizing Microcomputer / PC in Measurement System” (edited by Shigeo Minami, 1986, published by CQ).

  Next, for the specified peak, whether or not these numerical values are within a certain range using numerical values (ΔP / Po) and (ΔP · W) / (Po · Wh) representing the sharpness of the peak according to the following equation (1) Thus, pass (OK) or fail (NG) is determined as the evaluation of the band. Numerical values (ΔP / Po) and (ΔP · W) / (Po · Wh) representing the sharpness of the peak are obtained based on the value of the intermediate value point (indicated by a white rectangular mark) of the contact pressure between the polar regions.

  When the numerical values (ΔP / Po) and (ΔP · W) / (Po · Wh) representing the sharpness of the peak satisfy the following expression (2), it is determined that the endless band for the casting apparatus is suitable and passed. . Further, when the following expression (2) is not satisfied, it is determined that the contact pressure distribution is defective, and the contact pressure distribution improving process is performed.

なお、上記（２）式におけるしきい値は、エンドレスバンド１０の特性等に応じて適宜変更してよい。

The threshold value in the above equation (2) may be changed as appropriate according to the characteristics of the endless band 10 and the like.

  In the contact pressure distribution improving process, the drum contact surface 10 b of the endless band 10 is improved (for example, polished) to suppress the peak of the contact pressure and make the contact pressure uniform in the width direction of the endless band 10. If necessary, the surface 10a opposite to the drum contact surface 10b is also polished.

  4 and 5 show an example of the contact pressure distribution, and it can be seen that a peak of the contact pressure occurs at the longitudinal weld line 13 of the endless band 10.

  Next, the relationship among the contact pressure distribution, the heat transfer coefficient distribution between the endless band and the drum, and the temperature distribution of the endless band will be described. A temperature-sensitive liquid crystal film (see FIG. 8) is attached to the area including the part of the endless band 10 from which the data of FIGS. 4 and 5 are obtained, and the temperature distribution in the width direction of the endless band 10 is measured. When the heat transfer coefficient α between the endless band 10 and the drum 16 is determined based on this temperature distribution, it is found that the distribution of the calculated heat transfer coefficient α and the contact pressure distribution are substantially the same.

  As shown in FIG. 8, in the temperature distribution measurement, the endless band 10 is rotationally driven by the first drum 15. The second drum 16 is a driven drum that rotates freely, and the temperature distribution of the endless band 10 on the second drum 16 is measured by the camera 24. For this reason, the first drum 15 is set to 30 ° C. by the temperature controller 25, and the second drum 16 is set to 40 ° C. by the temperature controller 26. Then, the surface temperature distribution of the endless band 10 is measured by the camera 24.

  The temperature distribution measurement is performed using a temperature-sensitive liquid crystal film (heat distribution measurement film) 21. The temperature-sensitive liquid crystal film 21 is obtained by encapsulating liquid crystal whose color changes with temperature and applying it to a support. The temperature-sensitive liquid crystal film 21 changes color from red to green and blue as the temperature rises. For example, a product made by Nippon Capsule Product is used. Unlike the pressure-sensitive film 20, the temperature-sensitive liquid crystal film 21 is not sandwiched between the endless band 10 and the drum 16, so that the thickness is not particularly limited. It is preferable that they are 50 micrometers or more and 400 micrometers or less. A more preferable range is the same as that of the pressure-sensitive film 20. The temperature-sensitive liquid crystal film 21 changes color from red to green at 32 ° C. The color change is photographed with a camera as a moving image, and the heat transfer coefficient α between the endless band 10 and the drum is obtained by the following equation (3) based on the moving image photographing data.

なお、上記（３）式において、Tはエンドレスバンド１０の温度（℃）、T0は第２ドラム１６に接触開始した時のエンドレスバンド１０の温度（３０℃）、TDは第２ドラム１６の温度（４０℃）、tは第２ドラム１６に接触開始してからの経過時間（ｓｅｃ）、Cはエンドレスバンド１０の比熱（定数）、θはエンドレスバンド１０の厚み（定数）、ρはエンドレスバンド１０の密度（定数）、αはバンド１０と第２ドラム１６間の熱伝達係数である。感温液晶フィルム２１が緑色（Ｔ＝３２℃）になるまでの接触時間tを動画撮影データから読み取る。そして、（３）式により熱伝達係数αを逆算する。

In the above equation (3), T is the temperature of the endless band 10 (° C.), T 0 is the temperature of the endless band 10 at the start of contact with the second drum 16 (30 ° C.), and TD is the temperature of the second drum 16. (40 ° C.), t is the elapsed time (sec) from the start of contact with the second drum 16, C is the specific heat (constant) of the endless band 10, θ is the thickness (constant) of the endless band 10, and ρ is the endless band. A density (constant) of 10 and α is a heat transfer coefficient between the band 10 and the second drum 16. The contact time t until the temperature-sensitive liquid crystal film 21 becomes green (T = 32 ° C.) is read from the moving image shooting data. Then, the heat transfer coefficient α is calculated backward using equation (3).

  6 and 7 show the distribution in the width direction of the endless band 10 of the heat transfer coefficient α obtained as described above.

  The distribution of the heat transfer coefficient α as shown in FIGS. 6 and 7 and the contact pressure distribution as shown in FIGS. 4 and 5 are in a corresponding relationship, and the contact pressure is higher than that in other portions. A change in the heat transfer coefficient α appears at the high longitudinal weld line 13. It can be seen that the peak of the distribution of the heat transfer coefficient α and the peak of the contact pressure distribution are almost the same, and there is a certain relationship between them. Therefore, it can be seen that the non-uniform contact pressure distribution causes the non-uniform temperature distribution in the width direction of the endless band, resulting in uneven thickness of the cast film.

  As described above, the distribution of the contact pressure due to the color density of the pressure-sensitive film 20 and the distribution of the heat transfer coefficient α due to the discoloration of the temperature-sensitive liquid crystal film 21 change in the vertical weld line 13 in the same manner. Even if the surface is mirror-finished by precision measurement, the contact pressure distribution reaches a peak at the longitudinal weld line 13. Then, it was found that the temperature distribution of the endless band 10 also changed in the width direction at such a portion where the contact pressure reached a peak. Therefore, it is considered that only this portion is dried, for example, as compared with other portions, and as a result, a subtle difference in film thickness occurs in the cast film.

  In the present invention, based on the above knowledge, when the endless band 10 is used as the casting band of the casting apparatus 31 (see FIG. 13) of the solution casting apparatus 30, the above evaluation test is performed to obtain the contact pressure distribution. A peak is not seen in the contact pressure distribution, or even if there is a peak, it is evaluated as an acceptable product when it is within a certain range. Therefore, even if it looks like a mirror-finished product, it will be evaluated in advance if the film thickness failure occurs due to non-uniform temperature distribution at the peak due to non-uniform contact pressure distribution. It is possible to select only the endless band that is optimal for the solution casting apparatus.

  As described above, since the endless band 10 free from black streak failure can be installed in the solution film-forming facility 30, black streak failure occurs after installation as in the past, and there is no need to take measures against it. Thus, it is possible to reliably perform the attaching work of the new endless band without waste.

FIG. 9 shows an example of the contact pressure distribution after the improvement process is performed so that the contact pressure distribution becomes substantially constant. FIG. 10 also shows an example of the width direction distribution of the heat transfer coefficient α obtained by measuring the temperature direction temperature distribution of the endless band 10 after the improvement process with the temperature-sensitive liquid crystal film 21. By adopting such an evaluation method, it is possible to eliminate temperature distribution unevenness due to the longitudinal weld line 13 that is difficult to find by surface inspection alone, eliminate subtle thickness unevenness failure, and wind the film into a roll form. When taken, the black streak failure caused by the vertical weld line 13 can be eliminated.

  In the above embodiment, the case where the endless band 10 having the vertical weld line 13 is used for the solution film-forming facility 30 has been described. However, the present embodiment is also applicable to a normal endless band having no vertical weld line 13. By applying the invention, the endless band may be used for solution film formation so that the film thickness unevenness does not occur. In addition, when the solution casting equipment is periodically repaired, the present invention may be applied to measure the contact pressure distribution and temperature distribution of the endless band, and the endless band may be evaluated based on this.

  In the said embodiment, the width direction contact pressure distribution is measured with the pressure-sensitive film 20 about a part of endless band 10, the peak of a contact pressure is calculated | required in this part of contact pressure distribution, and the value of a peak exceeds a fixed value. However, the endless band 10 is determined to require improvement processing. However, not only such a partial contact pressure distribution but also a plurality of locations in the circumferential direction of the endless band 10 and the contact pressure at the entire circumference. The distribution may be measured and the evaluation may be performed based on the measured distribution. For example, when the belt-shaped pressure sensitive film 20 is used, these are placed on the endless band 10 at a constant pitch, and the contact pressure between the endless band 10 and the drum 16 is measured.

  In addition, as shown in FIG. 1, instead of using the band-like pressure-sensitive film 20 extending in the width direction of the endless band 10, as shown in FIG. 11, a feeling composed of a two-sheet type A film 27a and a C film 27c. The pressure film 27 is individually made into a roll form, and the pressure-sensitive film 27 is continuously supplied between the drum 16 and the endless band 10 and is wound around the take-up shaft 28 individually or simultaneously as a roll form on the drum outlet side. You may take it. In this case, the contact pressure distribution can be obtained at once over the entire length of the endless band 10.

  In the above embodiment, the contact pressure distribution in the band width direction between the drum 16 and the endless band 10 is obtained using the pressure-sensitive film 20, and based on this, whether or not the casting band is appropriate is evaluated. As shown in the flowchart of FIG. 12, instead of the pressure-sensitive film 20, the temperature-direction liquid crystal film 21 obtains the temperature distribution in the width direction of the endless band 10, and obtains the heat transfer coefficient distribution in the width direction of the endless band 10 from this temperature distribution. When the peak of the heat transfer coefficient is within a certain range, it may be determined that the casting band is appropriate.

  In this case, in FIG. 8, the temperature adjusters 25 and 26 provided on the drums 15 and 16 are used to set the temperatures of the peripheral surfaces of the drums 15 and 16 to be different between the drums 15 and 16, respectively. , 16 is read from the color change of the temperature-sensitive liquid crystal film 21, the heat transfer coefficient distribution is obtained from the read color change, the peak in the distribution is identified, and the value of this peak It is evaluated whether it is appropriate as a casting band depending on whether or not is within a certain range. The identification of the peak and the determination of whether or not the peak value is within a certain range are performed by the same processing as the peak in the contact pressure distribution.

  Further, based on the temperature distribution using the temperature-sensitive liquid crystal film 21, whether or not the endless band 10 is appropriate as a casting band may be evaluated based on whether or not the temperature distribution falls within a certain range. In this case, when the endless band 10 contacts the second drum 16 and changes in temperature, for example, the contact time becomes long and the temperature distribution in the width direction of the endless band 10 is uniform. Adopt temperature distribution. Whether the endless band is appropriate as a casting band is determined by whether the temperature distribution in which the temperature unevenness in the width direction has occurred is substantially uniform in the width direction in the measurement of the temperature distribution after the improvement process. I do. And when it becomes uniform, it evaluates as appropriate (pass), and when the temperature nonuniformity still arises, it evaluates as improper (fail).

  In FIG. 8, the temperature-sensitive liquid crystal film 21 is attached to only a part of the endless band 10 in the longitudinal direction, but this may be applied over the entire length of the endless band 10. In this case, the temperature distribution in the width direction can be measured for the entire length of the endless band 10, and the width-direction heat transfer coefficient distribution for the entire length can be obtained based on this. Note that the temperature-sensitive liquid crystal film 21 may be applied along the traveling direction only on a part including the vertical weld line 13 instead of being applied to almost the entire width of the endless band. Temperature distribution can be measured. Similarly, the pressure-sensitive films 21 and 27 may be arranged along the traveling direction only in a part including the vertical weld line 13 instead of being arranged with respect to almost the entire width of the endless band.

  The central member 11 and the side member 12 constituting the endless band 10 are preferably formed from the same material, for example, stainless steel, and more preferably formed through the same raw material and forming process. As the stainless steel, for example, SUS316 is preferable. As the central member 11, a band that has been used as a conventional casting support may be used. The central member 11 is wider than the side member 12, and the width of the central member 11 in this embodiment is constant in the range of 1500 mm to 2100 mm, and the width of the side member 12 is constant in the range of 50 mm to 500 mm. is there. The width of the endless band 10 is preferably in the range of 2000 mm to 3000 mm, but may be in a range other than this.

(Solution casting equipment)
As shown in FIG. 13, the solution casting apparatus 30 includes a casting device 31, a first tenter 32, a roll drying device 33, a second tenter 34, a slitter 35, and a winding device 36 on the upstream side. Are connected in series. The kind of polymer is not particularly limited, and a known polymer that can be formed into a film by solution casting may be used. In the following embodiments, a case where cellulose acylate is used as a polymer will be described as an example.

  The casting apparatus 31 includes an endless band 10 that is stretched around drums 41 and 42, a casting die 44, a duct (membrane dryer) 45, a decompression chamber 46, and a stripping roll 47. The band 10 is an endless metal casting support body formed in an annular shape, and is stretched around the peripheral surfaces of the first drum 41 and the second drum 42. The endless band 10 is evaluated by the above evaluation method as having no unevenness in the contact pressure distribution. The first drum 41 is rotationally driven by a motor (not shown), whereby the band 10 travels in the first direction indicated by the arrow A.

  A casting die 44 is disposed above the first drum 41. The casting die 44 continuously flows the dope 50 against the traveling endless band 10. Thereby, the casting film 51 is formed on the endless band 10. The dope 50 is obtained by, for example, dissolving cellulose acylate in a solvent, manufactured by a dope manufacturing line (not shown), and supplied to the casting die 44.

  A decompression chamber 46 is provided upstream of the bead 54 from the casting die 44 in the traveling direction of the endless band 10. The decompression chamber 46 sucks the atmosphere in the upstream area of the bead 54 to decompress the area and reduce the vibration of the bead 54.

  In order to improve the production speed, the casting film 51 toward the peeling roll 47 is heated by the second drum 42 and the endless band 10. Further, at the casting position, the endless band 10 is cooled by the first drum 41 so that the temperature of the endless band 10 does not excessively increase. For this reason, each drum 41, 42 has a temperature control device (not shown).

  A plurality of ducts 45 are provided along the traveling path of the endless band 10. Each duct 45 is connected to a hot air controller (both not shown) having a blower, and blows dry air from the outlet. The hot air controller controls the temperature, humidity, and flow rate of the drying air independently. The temperature of the casting film 51 is adjusted by controlling the temperature and flow rate of the drying air and the temperature control by the temperature adjusting device of the drums 41 and 42 themselves, and the casting film 51 is dried. Then, the casting film 51 is solidified to the extent that it can be conveyed by the first tenter 32, and self-supporting property is imparted. Note that the membrane dryer may be configured by another heater or the like instead of or in addition to the duct 45.

  A stripping roll 47 is provided on the upstream side in the traveling direction of the casting die 44 of the first drum 41. The peeling roll 47 supports the casting film 51 when the casting film 51 that has been dried in a state containing a solvent is peeled from the endless band 10. The cast film 51 that has been peeled off, that is, the film 52 is guided to the first tenter 32.

  In the first tenter 32, both side edges of the film 52 are gripped by the clip 53, and a tension in the film width direction is applied while the film 52 is conveyed, thereby widening the film 52. In the first tenter 32, a preheating area, an extension area, and a relaxation area are formed in order from the upstream side. The relaxation area is provided as necessary.

  The first tenter 32 has a pair of rails and a chain (both not shown). The rails are arranged on both sides of the conveyance path of the film 52 so as to be separated at a predetermined interval. This rail interval is constant in the preheating area, gradually becomes wider in the extension area as it goes downstream, and constant in the relaxation area, or becomes gradually narrower as it goes downstream. Clips 53 are attached to the chain at regular intervals.

  The preheating area, the extension area, and the relaxation area are formed as spaces by sending dry air from the duct 45, and there is no clear boundary between these areas. From the slit of the duct 45, dry air adjusted to a predetermined temperature and humidity is sent toward the film 52.

  In the roll drying device 33, the film 52 is wound around a large number of rolls 56 and conveyed. The atmosphere inside the roll dryer 33 is adjusted by a temperature controller (not shown) such as temperature and humidity, and the solvent evaporates from the film 52 while the film 52 is being transported.

  The second tenter 34 has the same structure as the first tenter 32 and includes a clip 58 and a duct 59. The second tenter 34 stretches while holding the film 52 with a clip 58. By this stretching, a film 52 having desired optical properties is obtained. The obtained film 52 can be used, for example, as a retardation film for a liquid crystal display. Note that the second tenter 34 may not be used depending on the optical characteristics of the film 52.

  The slitter 35 cuts out the side portion including the retention marks by the clips 53 and 58 of the first tenter 32 and the second tenter 34. The film 52 whose side portions have been cut off is wound into a roll by the winding device 36. The film roll 56 obtained by the present invention can be used particularly for a retardation film and a polarizing plate protective film.

  The width of the endless band 10 is preferably 1.1 times or more and 2.0 times or less the casting width of the dope 50, for example. The length of the endless band 10 is preferably 20 m or more and 200 m or less, for example. The thickness of the endless band 10 is preferably not less than 0.5 mm and not more than 2.5 mm, for example. The uneven thickness of the endless band 10 is preferably 0.5% or less with respect to the total thickness. The surface roughness of the surface 10a on which the casting film 51 is formed is preferably 0.05 μm or less.

  The width of the film as a product is preferably 600 mm or more, and more preferably 1400 mm or more and 2500 mm or less. The present invention is also effective when the film width is greater than 2500 mm. The film thickness is preferably 20 μm or more and 80 μm or less.

(polymer)
In the said embodiment, the polymer used as the raw material of a polymer film is not specifically limited, For example, there exist a cellulose acylate, cyclic polyolefin, etc.

(Cellulose acylate)
Only one type of acyl group may be used in the cellulose acylate of the present invention, or two or more types of acyl groups may be used. When two or more kinds of acyl groups are used, it is preferable that one of them is an acetyl group. The ratio in which the hydroxyl group of cellulose is esterified with carboxylic acid, that is, the substitution degree of the acyl group satisfies all of the following formulas (I) to (III) is preferable. In the following formulas (I) to (III), A and B represent the substitution degree of the acyl group, A is the substitution degree of the acetyl group, and B is the substitution degree of the acyl group having 3 to 22 carbon atoms. It is. In addition, it is preferable that 90 weight% or more of a triacetyl cellulose (TAC) is 0.1 mm-4 mm particle | grains.
(I) 2.0 ≦ A + B ≦ 3.0
(II) 1.0 ≦ A ≦ 3.0
(III) 0 ≦ B ≦ 2.0

  The total substitution degree A + B of the acyl group is more preferably 2.20 or more and 2.90 or less, and particularly preferably 2.40 or more and 2.88 or less. Further, the substitution degree B of the acyl group having 3 to 22 carbon atoms is more preferably 0.30 or more, and particularly preferably 0.5 or more.

  The details of cellulose acylate are described in paragraphs [0140] to [0195] of JP-A-2005-104148. These descriptions are also applicable to the present invention. The same applies to additives such as solvents and plasticizers, deterioration inhibitors, ultraviolet absorbers (UV agents), optical anisotropy control agents, retardation control agents, dyes, matting agents, release agents, and release accelerators. JP-A-2005-104148 describes in detail in paragraphs [0196] to [0516].

  An experiment was conducted to confirm the effect of the evaluation method of the endless band of the present invention. In Experiment 1, as in the first embodiment, first, the endless band 10 is polished and finished so that the smoothness is within a certain range. Thereafter, the pressure-sensitive film 20 was inserted between the drum 16 and the endless band 10 and passed through the second drum 16, and the contact pressure distribution between the drum 16 and the endless band 10 at this time was obtained. And the peak was calculated | required from contact pressure distribution, and what became when this peak became in a fixed range was used as a band of a solution film-forming equipment as a pass product. In this case, a film without black streak failure was obtained. On the other hand, a black streak failure occurred when the film was formed as a solution with a surface smoothness within a certain range without passing through the evaluation method.

  In addition, in the said test, although the effect was determined by the presence or absence of the black stripe when winding a film as a film roll, you may cut out and evaluate a sample film. In this case, the sample film is cut out from the film before being wound around the winding core by the winding device 36. And when this sample film 10 is piled up and light is permeate | transmitted to the piled sample film, the shadow which appears on the surface of a sample film is observed visually. If no shadow is observed in the part of the sample film formed on the weld line, it is considered effective, and if a shadow is observed in the part of the sample film formed on the weld line, there is no effect. judge.

DESCRIPTION OF SYMBOLS 10 Endless band 11 Central member 12 Side member 13 Longitudinal weld line 15,16 Drum 21,27 Pressure sensitive film 21 Temperature sensitive liquid crystal film 30 Solution casting equipment 31 Casting device 32,34 Tenter 33 Drying device 44 Casting die 45 Duct (Membrane dryer)
51 Casting membrane

Claims (7)

In a method for evaluating whether or not a metal endless band, which is stretched between a pair of metal drums and rotates, is suitable as a casting band,
Insert a pressure sensitive film whose color density changes according to pressure between the drum and the endless band,
Measure the contact pressure distribution of the endless band to the drum from the color density of the pressure sensitive film,
An evaluation method of an endless band, wherein the endless band is evaluated as appropriate as the casting band when the contact pressure distribution is within a certain range.   The endless band evaluation method according to claim 1, wherein the pressure-sensitive film has an overall thickness of 50 μm or more and 400 μm or less. In a method for evaluating whether or not a metal endless band, which is stretched between a pair of metal drums and rotates, is suitable as a casting band,
A temperature-sensitive liquid crystal film whose color changes according to the temperature is attached to the surface of the endless band,
A temperature difference is measured between the pair of drums before a temperature distribution in the width direction of the endless band becomes constant from a change in the color of the temperature-sensitive liquid crystal film passing over one drum. ,
An evaluation method of an endless band, wherein the evaluation is made as appropriate as the casting band when the measured temperature distribution is within a certain range. In a method for evaluating whether or not a metal endless band, which is stretched between a pair of metal drums and rotates, is suitable as a casting band,
A temperature-sensitive liquid crystal film whose color changes according to the temperature is attached to the surface of the endless band,
The temperature distribution in the width direction of the endless band for each elapsed time after contact with the drum from a change in color of the temperature-sensitive liquid crystal film passing over one drum by giving a temperature difference between the pair of drums Measure and
A method of evaluating an endless band, wherein a heat transfer coefficient distribution in a width direction of the endless band is obtained from the temperature distribution, and is evaluated as appropriate as the casting band when the heat transfer coefficient distribution is within a certain range.   The endless band evaluation method according to claim 1, wherein the endless band has a weld line in a longitudinal direction.   The peak in the distribution is obtained from any one of the contact pressure distribution, the temperature distribution, and the heat transfer coefficient distribution, and is evaluated as appropriate when the numerical value representing the peak is within a certain range. The endless band evaluation method according to claim 5.   A cast film is formed by flowing a dope containing a polymer and a solvent from a casting die onto the endless band, using the endless band evaluated by the endless band evaluation method according to any one of claims 1 to 6. And then evaporating the solvent from the cast film and stripping it off as a wet film.

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