JP4242514B2 - Production equipment and production method of stretched film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a uniform and high-quality solution cast film with high productivity, and a manufacturing facility therefor. More specifically, by detecting the retardation spots generated in the film produced by casting and stretching the solution, and analyzing the image, the cause of the spots from the occurrence position, range and / or appearance of the generated retardation spots and The present invention relates to a method and apparatus for determining the degree and / or implementing measures for eliminating the spots.
[0002]
[Prior art]
As the retardation film, a stretched polymer resin, particularly a stretched polycarbonate film is used.
[0003]
In the film, one of the important characteristics is uniformity of optical characteristics. In other words, a high degree of retardation (abbreviated as Re in the present specification) is required.
[0004]
The Re value is expressed as the product (Δn * d) of birefringence (Δn) and thickness (d). Therefore, in order to make the Re value uniform and prevent optical spots from occurring, it is necessary to control and manufacture so as not to generate birefringence spots and thickness spots of the film. When analyzing the production process of the film, the thickness unevenness of the film often exists in the cast film before stretching. For example, there are those caused by vertical spots that are substantially parallel to the running direction of the film, horizontal spots called so-called horizontal spots, etc. that are substantially perpendicular to the running direction, and thickness spots that have almost no regularity such as leveling defects.
[0005]
Such thickness unevenness occurring in the film before stretching is often solved by various conventional techniques, and some of these techniques are disclosed. In other words, vertical spots are devised by extruding the lip structure of the extrusion die to control the time variation of the resin flow, and horizontal spots are the opening of the extrusion die lip, the distance between the lip tip and the support, and the flow characteristics of the resin solution. In addition, the leveling can be substantially eliminated by drying the liquid film cast on the support without causing disturbance due to a non-uniform air flow or the like.
[0006]
However, even if various spots of the film before stretching are completely eliminated, the following optical spots are further generated in the stretched film. That is, another characteristic that constitutes Re, that is, speckles may occur in birefringence.
[0007]
It has been found that birefringence spots are often related to how the film deforms during stretching.
[0008]
These spots are caused by wrinkles such as vertical wrinkles and cross-shaped wrinkles that occur during stretching, those caused by fluctuations in tension during stretching, and those caused by bending of the stretching line in the film width direction. In general, the birefringence spots generated during film stretching are such that the width direction of the film is larger than the longitudinal direction of the film (that is, the stretching direction). Unevenness due to bending of the stretched line that occurs because the tension is not uniformly applied in the width direction occurs at several points in the width direction of the stretched film as a result of the stretched line being stretched without being aligned in the width direction of the film. This is because wrinkles may cause phenomena such as movement in the width direction over time. Further, there may be a case where Re is not uniformly distributed in the width direction of the film due to a difference in the tension applied in the width direction of the film. The wavy wrinkles that occur during the longitudinal stretching are stretched all at once in the width direction immediately after the film leaves the roll surface where the stretching tension is applied, and if the stretched lines are straight, they are eliminated. This is made difficult by the slight unbalance of the stretching tension between the width direction and the running direction. Furthermore, when the film slides on the roll surface due to stretching tension, a fatal problem may occur as a retardation film that generates scratches.
[0009]
In order to impart a high degree of uniformity to the Re value, factors caused by unstretching, particularly retardation spots due to thickness spots, and retardation spots mainly caused by birefringence spots during stretching are separated. It is extremely important to control the separated spots individually to control the optical properties of the film uniformly.
[0010]
As a technique for producing a film with little thickness unevenness of the film before stretching and a technique for uniformly stretching the film, JP-A-2-59703, JP-A-2-256003, and JP-A-2-256003 are known materials that regulate film thickness unevenness and Re unevenness. JP-A-6-279598, JP-A-8-101305, JP-A-8-101308, and the like are disclosed.
[0011]
In JP-A-2-59703, a polymer film having a thickness (x) fluctuation width of 0.1X or less and a change rate of 0.015X / cm or less is uniaxially stretched to obtain a fluctuation width of the retardation value. Is 10% or less, and the manufacturing method of the retardation film whose change rate is 1.8% / cm or less is disclosed.
[0012]
JP-A-8-101305 discloses a polymer film having birefringence, characterized in that the difference in thickness from a point 1 cm away from an arbitrary point in the film plane is 0.3 μm or less. In JP-A-8-101308, the thickness difference of an unstretched film is 0.5 μm or more and 3 μm in thickness difference between adjacent thick and thin portions in both the film transport direction and the width direction. In the following, a raw film having a wavy variation with a pitch of 1 mm to 40 mm or less is stretched uniaxially or biaxially, and the retardation value between any two points separated from each other by 10 cm within the film plane. There has been proposed a retardation plate characterized in that the difference is 5 nm or less.
[0013]
JP-A-2-256003 discloses an optical film in which the thickness unevenness of the film is regulated. When the thickness unevenness is measured continuously in the extrusion direction, the thickness amplitude is 50 mm or less. It is specified that a polymer film having a sinusoidal thickness variation of 0.5 μm or more does not exist. Japanese Patent Application Laid-Open No. 6-279598 discloses a heat-resistant transparent film which is a polymer film having a thickness of 200 μm or less and whose thickness change in the vicinity thereof is 0.5% or less of the average thickness of the film.
[0014]
Japanese Patent Application Laid-Open No. 10-300925 discloses a method for making Re spots uniform in the stretching step. This is a method for producing a retardation film formed by uniaxially stretching a resin film. In the method for producing a retardation film, the fluctuation in tension applied to the film being stretched is controlled within a range of ± 1%. This is a technique for controlling fluctuations to be small.
[0015]
JP-A-8-101306 discloses a method of longitudinally uniaxially stretching by providing a stretching temperature gradient in the width direction of the film. This is a technique for correcting the U-shaped distribution of the retardation value in the width direction, which occurs due to the proximity roll stretching, because the neck-in situation differs between the both ends and the center in the film width direction. These techniques are techniques for eliminating comparatively gentle retardation spots such as a U-shape in the width direction.
[0016]
JP-A-8-327820 discloses a uniform retardation film in which the film is uniformly heated and stretched so that the temperature difference between any two points 1 cm apart from the film is 0.3 ° C. or less. Techniques for making are disclosed.
[0017]
In JP-A-9-230137, in a method for producing a retardation film, a film heated at the time of stretching is pressed against the surface of a stretching roll with heated air to prevent the film from lifting and wrinkles are generated in the film. A method for obtaining a retardation film with little variation in retardation is disclosed.
[0018]
JP-A-9-304616 discloses a method for producing a retardation film by uniaxially stretching a resin film, wherein the thickness of the stretched film is thicker as it approaches the center from both ends. A manufacturing method is disclosed.
[0019]
Summarizing these methods, it is now possible to keep the thickness unevenness present in the film before stretching sufficiently small depending on the preferred design of the extrusion die and the film forming conditions of the cast. That is, as described above, the retardation unevenness caused by the thickness unevenness before stretching of the film can be solved by various techniques.
[0020]
On the other hand, retardation spots caused by birefringence spots generated during film stretching have not been sufficiently improved by the above-described technique, and there are still problems to be solved.
[0021]
[Problems to be solved by the invention]
Therefore, the inventors of the present application have made extensive studies on the method of detecting and eliminating Re spots. As a result, the Re spots on the film are obtained as an image, image analysis is performed, and the results are fed back to the manufacturing facility. The present invention has been found out that it can be easily solved. In the present invention, “obtaining as an image” includes not only direct observation with the naked eye but also acquisition as video data by an optical or electronic method.
[0022]
[Means for Solving the Problems]
  The present invention is as follows.
  1.A stretched film production facility comprising the following means (a), (b), (c), and (e):
(A) means for projecting light that has passed through a polarizing plate from a direction perpendicular to the film surface, detecting the transmitted light through the polarizing plate, and obtaining retardation spots of the film;
(B) means for obtaining digital data from the image of the retardation spots,
(C) By analyzing the digital data, the degree of retardation spots should be determined from the position, range and / or appearance of the retardation spots generated on the film, and should be changed from the data on the degree of retardation spots. Means for determining film heating conditions; and
(E) Means for changing the optical spots of the film by feeding back the film heating condition to be changed in (c) and controlling the film heating condition.
[0023]
  2.2. The stretched film production facility according to 1 above, wherein the film heating conditions to be changed are fed back and the film heating conditions are controlled in the stretching step.
[0024]
3. 3. The film production facility according to 1 or 2 above, wherein the film is a polymer film.
[0025]
4). 3. The film production facility according to 1 or 2 above, wherein the film is a polycarbonate film.
[0026]
5). 3. The film production equipment according to 1 or 2 above, wherein the film is a film produced by means of casting a polymer solution on a support, separating after drying and producing a cast film.
[0027]
6). 3. The film production equipment according to 1 or 2 above, wherein the film is a film produced by means of casting a polycarbonate solution on a support, peeling off after drying, and producing a cast film.
[0028]
7. The manufacturing method of the stretched film which uses the manufacturing equipment in any one of said 1-6.
[0029]
Here, 7 “a method for producing a stretched film using any one of production facilities 1 to 6 above” means more specifically the following invention.
[0030]
  8).The manufacturing method of the stretched film characterized by including each process of following (f)-(i).
(F) projecting light passing through the polarizing plate from a direction perpendicular to the film surface, detecting the transmitted light through the polarizing plate, and obtaining retardation spots of the film;
(G) obtaining digital data from the image of the retardation spots,
(H) By analyzing the image of this digital data, the degree of retardation spots should be determined from the position, range and / or appearance of the retardation spots generated on the film and changed from the data on the degree of retardation spots. Determining film heating conditions; and
(I) A step of changing the optical spots of the film by feeding back the film heating condition to be changed in (h) and controlling the film heating condition.
[0031]
  9.9. The method for producing a stretched film as described in 8 above, wherein the film heating conditions to be changed are fed back and the film heating conditions are controlled in the stretching step.
[0032]
10. 10. The method for producing a film as described in 8 or 9 above, wherein the film is a polymer film.
[0033]
11. 10. The method for producing a film as described in 8 or 9 above, wherein the film is a polycarbonate film.
[0034]
12 10. The method for producing a film as described in 8 or 9 above, wherein the film is a film prepared by casting a polymer solution on a support, drying and then peeling to produce a cast film.
[0035]
13. 10. The method for producing a film as described in 8 or 9 above, wherein the film is a film produced by casting a polycarbonate solution on a support, drying and then peeling to produce a cast film.
[0036]
The present invention will be described in detail below.
All resins that can be manufactured by casting can be applied to the present invention. For example, a cellulose resin, a polycarbonate resin, a polyarylate resin, a polyolefin resin, a polystyrene resin, a vinyl chloride resin, an acrylic resin, a polysulfone resin, a polyethersulfone resin, and a mixture of two or more of these Examples include copolymerization.
[0037]
The polymer resin particularly preferably applicable is an aromatic polycarbonate type. The polycarbonate will be described in detail below, but the present invention is not limited to this.
[0038]
a) Aromatic polycarbonate and viscosity average molecular weight
The aromatic polycarbonate used in the present invention is not particularly limited as long as it is an aromatic polycarbonate capable of obtaining desired film properties. In general, a polymer material generally called an aromatic polycarbonate means a material obtained by polycondensation of a phenol derivative and phosgene, diphenyl carbonate or the like. Usually, an aromatic polycarbonate represented by a repeating unit having 2,2-bis (4-hydroxyphenyl) propane, which is called bisphenol A, as a bisphenol component (in this specification, this bisphenol A is a bisphenol component) Aromatic polycarbonate is referred to as bisphenol A polycarbonate), but the aromatic polycarbonate copolymer is formed by selecting various other bisphenol derivatives together with 2,2-bis (4-hydroxyphenyl) propane. can do.
[0039]
Examples of such copolymer components include bis (4hydroxyphenyl) methane, 1,1-bis (4-hydroxyphenyl) cyclohexane (also referred to as bisphenol-Z), and 9,9-bis (4-hydroxyphenyl) fluorene (bisphenol). FL), 1,1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 9,9-bis (3-methyl-4-hydroxyphenyl) fluorene, 2,2-bis ( 4-hydroxy-3-methylphenyl) -2-phenylethane, 2,2-bis (4-hydroxyphenyl) -1,1,1,3,3,3-hexafluoropropane, bis (4-hydroxyphenyl) Diphenylmethane, bis (4-hydroxyphenyl) sulfide, bis (4-hydroxyphenyl) sulfide Bis (4-hydroxyphenyl) sulfone and the like. Moreover, it is also possible to use the polyester carbonate which contains a terephthalic acid and / or isophthalic acid component in the carbonic acid component in part. Thus, by substituting bisphenol A and a part of the carbonic acid component with other structural units, the properties of the aromatic polycarbonate such as heat resistance and solubility can be improved.
[0040]
The aromatic polycarbonate used in the present invention has a viscosity average molecular weight of 20,000 or more and 200,000 or less. A viscosity average molecular weight of less than 20,000 is not preferable because the viscosity of the solution is too low to control the film thickness. On the other hand, when the viscosity average molecular weight exceeds 200,000, the solution viscosity becomes too high and it becomes difficult to control the film thickness. A particularly preferable viscosity average molecular weight is 30,000 or more and 70,000 or less.
[0041]
b) Dissolution process
Examples of the solvent used for dissolving the aromatic polycarbonate in the present invention include conventionally known solvents mainly composed of methylene chloride or 1,3-dioxolane. For example, a solvent in which the content of methylene chloride or 1,3-dioxolane is 98.0 to 100% by weight and the content of a mixture of ethanol and pentanol is 0.0 to 2.0% by weight is an example. .
[0042]
c) Casting process
Film production in the case of aromatic polycarbonate includes, for example, the following steps.
That is, the obtained solution can be cast and formed on a support such as a steel belt, a drum, or a support film (generally a biaxially oriented film of polyester) by a known method. Immediately after casting, it is preferable that the liquid film be uniformly dried without unevenness so that external force such as wind force is not received as much as possible, and after the second half is in a semi-solidified state, hot air is blown to promote drying.
[0043]
The film obtained by evaporating a predetermined amount of the solvent by drying in this way is peeled from the support under the conditions that the residual solvent amount of the film is 21 to 25% by weight and the support temperature is 0 to 14 ° C., for example. .
[0044]
The temperature of the support at this time is the surface temperature immediately after peeling the film. This can be measured with a contact or non-contact thermometer. At the time of peeling, the temperature of the film is adjusted by blowing hot air or the like so that the surface temperature of the support and the temperature of the film become substantially equal. If the solvent content at the time of peeling and the temperature of the support deviate from the specified conditions, the film tends to be deformed at the time of peeling and the transparency is lowered, which is not preferable.
[0045]
d) Stretching process
The film after peeling is preliminarily dried and simultaneously stretched. In this lateral stretching, the film is stretched 3 to 20% (1.03 to 1.20 times) in the width direction by a so-called pin tenter that holds both ends in the film width direction with pins. By this transverse stretching, so-called vertical streak-like thickness spots generated in the running direction of the film are remarkably reduced, and the contribution of thickness spots in the unstretched film to Re spots is remarkably reduced. The film after transverse stretching is dried with a roll-suspended dryer or the like until the residual solvent amount is, for example, 0.1% by weight to 2.0% by weight. More preferably, drying is performed so that the concentration is 0.1% by weight to 1.5% by weight. When the amount of residual solvent is 0.1% by weight or less or exceeds 2.0% by weight, it is not preferable because the effect of homogenizing optical properties during uniaxial stretching is small.
[0046]
In the step of stretching the film, uniaxial stretching is performed in the longitudinal direction. Detailed description will be given below with reference to the drawings.
FIG. 1 shows a preheating zone 1 which is a part of a preheating device before stretching, and a subsequent stretching zone 2.
[0047]
The transport roller 3 is for guiding the film 4 to the stretching zone 2 by running the film 4 with good flatness. The hot air blowing nozzle 5 is used to uniformly heat the hot air blowing film 4 at a high speed at which the wind speed at the nozzle tip is about 10 m / sec to 30 m / sec, and is arranged orthogonal to the film running direction. . The distance between the tip of the nozzle outlet and the film 4 is preferably set in the range of 5 to 20 mm.
[0048]
In the present invention, a radiant heating device 6 is disposed between the hot air blowing nozzle 5 and another hot air blowing nozzle 5 adjacent thereto. This apparatus is for heating the film 4 by radiant heat. The radiant heating device 6 disposed between the hot air blowing nozzles 5 is divided into blocks in the width direction of the film 4 as shown in the perspective view of FIG. 2, and is installed along the width direction of the film to be stretched. Each radiant heating device 6 is accompanied by a device 7 for adjusting the distance from the heating surface to the film surface. Further, a power supply line is individually connected to the radiant heating device 6 so that the heating amount can be adjusted. The amount of heating of the film is adjusted by individually adjusting the surface temperature of the radiant heating device 6. This surface temperature is adjusted by changing the output power amount according to the information detected by the Re spot (color spot) detection device 8 shown in FIG. The radiant heating device 6 is installed above and below the film 4. The distance from the heating surface of the radiant heating device 6 to the film surface can be changed within a range of 20 to 150 mm. The radiant heating device 6 has a size of approximately 120 mm * 120 mm, 120 mm * 60 mm or the like, and a known device can be used as necessary. The surface temperature of the heating device is preferably one that can be heated to about 400 ° C. although it depends on the required heating amount of the film. When viewed in the width direction of the film, the heating devices are preferably arranged in a staggered manner from one row and the next row.
[0049]
The stretching of the film 4 is started in the stretching zone 2 of FIG. At this time, the film enters the zone 2 from the zone 1 and then stretching is started. Further, the second stage stretching can be carried out in the next zone.
[0050]
In this stretching zone 2, Re spots due to birefringence spots are often generated during stretching, which is a problem in the present invention. As described above, even if a film having no thickness unevenness of the film before stretching is stretched, it is difficult to eliminate the Re spots. This unevenness is caused by the fact that the stretching tension during stretching is not uniformly applied to the entire surface of the film. For example, at the end in the width direction, the film contracts in an oblique direction so that the width decreases in the running direction of the film. On the inner side in the width direction, wave-like wrinkles are generated substantially parallel to the running direction of the film as compared with the end portion. That is, when running, the flatness of the film is impaired and the film is stretched to generate spots. This phenomenon becomes generally more noticeable as the stretching tension of the film increases. That is, this phenomenon is more likely to occur as the film is stretched such that high tension stretching and low temperature stretching tend to apply tension during stretching. This wavy wrinkle also changes depending on the stretching conditions.
[0051]
When the film is observed under crossed Nicols, stretched spots are clearly detected as colored spots. In this case, the color spots do not appear at random in the width direction of the film, but often appear as a band having some regularity in the width direction.
[0052]
FIG. 3 shows the Re spot detection device 8 of the present invention. In the case of visual observation, Re spots can be detected as color spots by wearing glasses (analyzer) with polarizing plates attached from the position of the Re spot detector 8 in FIG. In the light box 9, a lamp that radiates a wide and uniform strong light is installed. Among them, it is preferable to arrange several fluorescent tubes as a light source box. A transparent glass plate or a sheet made of a transparent resin is attached to the surface of the box. Further, a light diffusing plate made of ground glass or a transparent film is installed on the surface of the transparent body. Next, a polarizing plate 10 is attached to the entire surface of the light box to obtain linearly polarized light. The surface of the light box 9 is set parallel to the traveling film surface 4 and the light from the box is projected onto the film. In the case of visual observation, the entire surface appears to be uniformly colored when there are no Re spots. On the other hand, when there are Re spots, color spots can be observed.
[0053]
FIG. 4 is a diagram showing the Re distribution in the width direction of the stretched film as color spots. In this example {circle around (1)}, a portion where Re is different from other portions, that is, a case where there are two Re spots is shown. In this example, the Re spot has a Re value larger than that of the other part, but conversely, the case where it is smaller than the other part also corresponds to the Re spot.
[0054]
The Re spots of this film are improved by radiantly heating the corresponding part. That is, the difference from other parts is reduced. In addition, when the Re value of the part with Re spots is smaller than other parts, it is improved by radiant heating weaker.
[0055]
(2) in FIG. 4 shows the Re value after this countermeasure. The degree of heating of the radiant heating device is determined by the surface temperature of the radiant heating device and the distance from the film, but the relationship between the amount of change in Re and the surface temperature of the radiant heating device and / or the distance from the film is trial and error. Can be sought.
[0056]
Thus, when Re spots as color spots are relatively large, visually observe through the analyzer to confirm the degree and location of the color spots on the film, and correspondingly, the radiation heating device of the necessary heating point The temperature and the distance from the film are changed, and the change of the temperature of the radiant heating device at the necessary heating point and the distance from the film is repeated until the color spots cannot be observed. Heating a specific part of the radiant heating device in advance to determine how much the amount of heating in the radiant heating device is changed to correct the Re spots and how much the distance between the radiant heating device and the film is changed It is desirable to obtain data on how much the amount is changed and how much the Re value fluctuates when the distance between the radiant heating device and the film is changed.
[0057]
When the Re spot detection device 8 is used, the image data taken from the Re spot detection device 8 is processed, the color difference of the color is detected, the part and the temperature of the radiation heating device 6 are designated, and the radiation heating is performed. The amount of power sent to the device can be determined. A commercially available spectroradiometer can be used for color difference detection.
[0058]
In the case of automating this operation, image data taken from the Re spot detection device 8, preferably digital data, is subjected to image analysis, whereby the retardation spot is determined from the position, range and / or appearance of the retardation spot generated on the film. The film heating condition to be changed is determined from the data of the cause and / or degree of these retardation spots, and the film heating condition to be changed is fed back to the film manufacturing facility to determine the film heating condition. The optical spots of the film can be changed by controlling the heating conditions. As described above, this film heating condition can be changed by changing the amount of electric power sent to a specific part of the radiant heating device 6. When this adjustment operation takes a long time or when Re changes in the middle and spots appear, it is preferable to control automatically.
[0059]
In the above description, the case of changing the heating of the radiant heating device 6 has been described. However, the present invention is not limited to this, and the change of heating is not limited to the film stretching step, but the film after casting. It is possible in the preheating process, the stretching process, and any subsequent stage after peeling. However, since the effect is small after unstretched and the concentration of the containing solvent is high and after stretching, it is most efficient to carry out the stretching process.
[0060]
The heating method according to the present invention includes a method by convection and heat conduction in addition to the method by radiation as illustrated. For example, hot air spraying or use of a heating roller.
[0061]
In addition, the control of the heating condition according to the present invention is a method of changing the distance between the heating device and the film in addition to the method of changing the power supply and changing the heating capacity of a specific part of the heating device as illustrated. A method of changing the amount of blowing air, a method of changing the flow rate of the supply heat medium, and the like are conceivable.
[0062]
【Example】
Examples of the present invention will be described below. The present invention is not limited by this embodiment.
The method for measuring film properties is as follows.
[0063]
[Measurement of Re spots]
The film cut out from the film forming process was measured off-line. The measuring device was measured using a birefringence measuring device KOBRA-21ADH or KOBRA-21SDH manufactured by Shin-Oji Paper Co., Ltd. As Re spots, the maximum value of Re spots per 1 m width of film (the direction perpendicular to the direction of movement of the film when the film is continuously produced) and the maximum value of Re spots between any two points 10 mm apart Asked. In addition, the maximum value of Re spots per 1 m width of the film is the continuous data when measuring Re between two points 50 cm away from the center in the width direction of the film (and thus 1 m in total). It represents the difference between the maximum value and the minimum value, and the maximum value of Re spots between any two points 10 mm apart is 201 points obtained by measuring Re at 5 mm intervals for the 1 m width. For Re, the difference in Re between all adjacent 10 mm points (becomes 199 points) was obtained, and the maximum value was obtained. Unless otherwise specified for each example, the average value of both and Re is for 20 samples measured every 10 m of production, and the Re average value is for the entire sample.
[0064]
[Example 1]
Aromatic polycarbonate resin (trade name “Panlite (registered trademark) grade C-1400QJ” manufactured by Teijin Chemicals Ltd., polymer Tg = 158 ° C.), viscosity average molecular weight 38,000 was dissolved in methylene chloride solvent, 18 A weight percent solution was made.
[0065]
This solution was passed through a filter (a filter manufactured by Advantech Co., Ltd., trade name depth cartridge filter, TCPD-05A, average pore diameter 0.5 μm) to remove internal foreign matters. Thus, a clean solution for casting was prepared. Next, the temperature of the solution and the support is adjusted to 13 ± 0.5 ° C., the thickness of the liquid film is adjusted to 75 μm after drying, and the solution is cast on the support. It was made to dry and the film was peeled off from the support body. The amount of residual solvent in the film at this time was 23% by weight.
[0066]
Thereafter, the film immediately after peeling was taken off. At that time, a take-up roller having a surface coated with a fluororesin was used. Also, the surface of the transport roller was entirely covered with a fluororesin. The surface roughness Ra of these rollers was 0.1 μm. The take-up tension was controlled by the tension applied to the dancer roller, and the film width was 5 kg / 1 m. Next, the film edge was grasped, heated to 120 ° C. to widen, and stretched in the direction perpendicular to the film traveling direction by 1.10 times. Further, the film was introduced into a roll-suspended dryer so that the residual solvent amount was 0.5% by weight or less. This film was passed through the preheating zone 1 maintained at 50 ° C. using the apparatus shown in FIG. 1, and then the hot air temperature blown from the nozzle in the stretching zone 2 was set to 152 ° C. in the running direction. The film was stretched twice. Next, the second stage stretching 1.1 times was performed at a hot air temperature of 158 ° C. in a second stage stretching zone not shown in FIG. In the first stretching zone (2 in FIG. 1), radiant heating was performed using 6- (1) and 6- (2) of the radiant heating device of FIG. The light passing through the polarizing plate is projected onto the film from the vertical direction, and the transmitted light is projected on the monitor TV screen as a color spot image through the polarizing plate as a color spot, and is detected visually while detecting each part of the radiation heating device 6. It was adjusted until the surface temperature was changed to eliminate the color spots on the entire screen. As the radiant heating device 6, a heater having a heating surface of 12 cm square was closely arranged in the width direction of the film, and the distance from the heating surface to the film surface was set to 100 mm.
[0067]
The average value of Re of the obtained film is 580 nm, the maximum value of Re spots per 1 m width of the film is within 2 nm, and the maximum value of Re spots between any two points 10 mm apart is within 0.9 nm, which is extremely uniform. A retardation film could be obtained.
[0068]
[Comparative Example 1]
A stretched film was produced in the same manner as in Example 1 except that Re spots were not controlled by a radiant heating device, and a stretching operation was performed under the same conditions (stretching temperature, stretch ratio, hot air conditions, etc.) as in Example 1. At this time, Re spots (color spots) occur especially at the edges of the film due to the influence of the vertical warp generated during stretching, and even if the stretching tension is lowered by changing the stretching temperature (hot air temperature) conditions, these spots are eliminated. could not.
[0069]
[Example 2]
In the same manner as in Example 1, a cast film was prepared and subjected to pin tenter transverse stretching and then longitudinal stretching.
[0070]
FIG. 5 schematically shows the results of testing the relationship between the arrangement of radiant heaters, heating intensity, etc., and Re spots. In other words, this test schematically shows the result of an experiment for confirming the conditions for changing the Re spots by changing the position and heating intensity of the radiant heater.
[0071]
(1) in FIG. 5 shows an example where Re is uniformly distributed and color spots are not observed. In this case, the maximum value of Re spots per 1 m width of the film is within 3 nm, the maximum value of Re spots between any two points 10 mm apart is within 1 nm, and streaky Re spots that change rapidly with a narrow width ( There was no thing resulting from the uneven thickness of an unstretched film.
[0072]
(2) in FIG. 5 is a result of radiant heating performed on the film having excellent Re uniformity in (1) by the radiant heating device 6- (1) in the stretching zone (2 in FIG. 1). In this case, when the 12 cm square radiant heating device 6- (1) is heated with the distance from the film surface being 100 mm and the surface temperature of the heater unit at this position being 200 ° C. Is shown. In this case, it was found that a low Re portion could be made over about 100 mm at the center in the width direction of the film.
[0073]
Further, (3) in FIG. 5 is one in which three heater units are closely arranged and controlled at a portion corresponding to the central portion in the width direction of the film of the 12 cm square radiant heater 6- (1). In any case, the surface temperature of the heater unit was 200 ° C., and the distance to the film surface was 100 mm. In this case, it was found that a Re distribution in which three pieces of (2) in FIG.
[0074]
As is clear from these test results, it can be confirmed that the fluctuation of the Re value of the film can be controlled by the position of the radiant heating device such as the distance to the film surface, the width direction and the arrangement in the running or stretching direction and the surface temperature. It was.
[0075]
[Example 3]
A cast film was prepared using APEC-HT (polymer Tg = 205 ° C.), which is a polycarbonate from Bayer, as a polymer raw material. Stretching was first performed by pinching the end with a pin tenter, heating to 165 ° C. and stretching in the transverse direction up to 1.04 times. Next, both end pin portions of the film were removed, and the film was lowered by a roll-suspended dryer until the residual solvent amount of the film was 0.5% by weight. This film was stretched 1.3 times by the stretching machine shown in FIG. The temperature of the air ejected from the nozzle at this time was 185 ° C. Here, as the radiant heating device, a heater unit having a width of 60 mm and a length of 120 mm was closely arranged in the film width direction so that the length direction thereof was closely aligned. The distance from the surface of the heater unit to the film was 50 mm. Next, the film was stretched 1.1 times at 200 ° C. in the next zone not shown in FIG. Control was made to change the Re spots by changing the surface temperature of each heater unit. At this time, an image obtained by the Re spot detection device 8 and a reference Re value image are copied together on a television monitor, and each heating device is set so that the color tone is as close as possible to the reference Re value image. The amount of radiant heating was adjusted to reduce color spots. The average value of Re of the stretched film thus obtained is 620 nm, the maximum value of Re spots per 1 m width of the film is within 3 nm, and the maximum value of Re spots between any two points 10 mm apart is within 0.9 nm. A stretched film with uniform Re can be produced.
[0076]
[Example 4]
A stretched film was produced under exactly the same conditions as in Example 1, stretched under the same conditions as in Example 1, and wound up with a winder.
At this time, before the film was wound, the state of change in the Re value in the width direction of the film was measured by a Re measuring device.
A commercially available on-line phase difference measuring device was used for this measurement.
The measurement in the width direction of the film was repeated 10 times, and the profile of the Re value in the entire width direction was obtained from the average value by numerical data.
Next, the size of the Re spots, the position on the film surface, and the range are determined from the numerical data, and the heating required from the relationship between the size of the Re spots and the heating amount necessary to correct this is determined. Determined the amount.
Subsequently, this heating condition was fed back to a radiant heating apparatus which is one of the film manufacturing facilities.
By repeating such detection of Re spots in the film width direction and feedback of film heating conditions for correcting Re spots, the average value of Re is 580 nm, and the maximum value of Re spots per 1 m width of the film is within 2 nm. It was possible to obtain a uniform Re retardation film in which the maximum value of Re spots between any two points 10 mm apart was within 0.9 nm.
[0077]
【The invention's effect】
In the production of stretched film, a method of producing a film for optical application with uniform retardation by detecting Re spots mainly caused by birefringence spots generated in the stretching process and controlling to eliminate the spots. provide. According to the present invention, the uniformity of the retardation is sufficiently improved after the production of the stretched film is started, the time until stabilization is shortened, and the occurrence of retardation spots occurring during the production is promptly dealt with. In addition, the effect is exhibited when changing the conditions when producing a product with different characteristics by changing the retardation. Also, it is effective as a method for detecting and eliminating Re spots when manufacturing is continued for a long time.
[Brief description of the drawings]
FIG. 1 shows an example of a stretching apparatus according to the present invention.
FIG. 2 is a perspective view showing an example of details in a stretching apparatus according to the present invention.
FIG. 3 shows an example of a retardation spot detection unit according to the present invention.
FIG. 4 is a schematic view showing spots in the width direction of the retardation according to the present invention as color spots.
FIG. 5 is a schematic diagram showing unevenness in the width direction of the retardation for controlling the retardation distribution of the film.
[Explanation of symbols]
1. Preheating zone
2. Stretch zone
3. Film transport roller
4). the film
5). Hot air blowing nozzle
6). Radiation heating device
7. Distance change device
8). Re spot detector
9. Light source box (light box)
10. Polarizer

Claims (7)

A stretched film production facility comprising the following means (a), (b), (c), and (e):
(A) means for projecting light passing through the polarizing plate from a direction perpendicular to the film surface, detecting the transmitted light through the polarizing plate, and obtaining retardation spots of the film;
(B) means for obtaining digital data from the image of the retardation spots,
(C) The digital data should be image-analyzed to determine the degree of retardation spots from the position, range and / or appearance of the retardation spots generated on the film, and should be changed from the data on the degree of retardation spots. Means for determining film heating conditions; and
(E) Means for changing the optical spots of the film by feeding back the film heating conditions to be changed in (c) and controlling the film heating conditions. 2. The stretched film manufacturing equipment according to claim 1, wherein the film heating conditions to be changed are fed back and the film heating conditions are controlled in the stretching step. The film production facility according to claim 1, wherein the film is a polymer film. 3. The film production facility according to claim 1, wherein the film is a polycarbonate film. 3. The film production facility according to claim 1, wherein the film is a film produced by means of casting a polymer solution on a support, separating after drying and producing a cast film. . 3. The film production equipment according to claim 1, wherein the film is a film produced by means of casting a polycarbonate solution onto a support, drying and then peeling to produce a cast film. The manufacturing method of the stretched film which uses the manufacturing equipment in any one of Claims 1-6.

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