CN113825619B

CN113825619B - Method and apparatus for producing optical film

Info

Publication number: CN113825619B
Application number: CN201980096483.0A
Authority: CN
Inventors: 安藤卓也; 高桥英史; 网谷圭二
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2019-06-04
Filing date: 2019-12-11
Publication date: 2024-05-28
Anticipated expiration: 2039-12-11
Also published as: TW202112524A; JP7454937B2; WO2020246061A1; KR20220016893A; CN113825619A; JP2020201471A

Abstract

The method for producing an optical film (4) according to one embodiment of the present invention is a method for producing an optical film by subjecting a long film (2) to N treatments (N is an integer of 1 or more), wherein N treatments are performed while conveying the film, the width of the film is continuously measured at each of a plurality of positions (20) during the conveyance, and the rate of change in the width of the film is calculated based on the measurement result of the upstream position and the measurement result of the downstream position among two positions selected from the plurality of positions, which are obtained at the same timing.

Description

Method and apparatus for producing optical film

Technical Field

The present invention relates to a method and an apparatus for manufacturing an optical film.

Background

In general, an optical film is manufactured by performing at least one treatment for imparting desired optical characteristics while conveying the film. For example, when the optical film is a polarizing film, at least one treatment is performed to impart linear polarization characteristics to the film as optical characteristics. In the case of manufacturing an optical film as described above, the width of the film varies in the process of manufacturing an optical film from the film. When the film is conveyed, the rate of change between the width of the film on the upstream side and the width of the film on the downstream side is known as the shrinkage rate (see patent document 1). In the process of manufacturing an optical film, when the shrinkage ratio of the film deviates from a preset allowable range (management width), the film may break, or the thickness of the film deviates from a desired thickness. Therefore, in order to properly manufacture an optical film, management of the shrinkage is important.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 8-226811

Disclosure of Invention

Technical problem to be solved by the invention

In the technique described in patent document 1, the width of the film is measured at an upstream side measurement point and a downstream side measurement point in order to calculate the shrinkage. However, in patent document 1, the width of the film is measured at the upstream side measurement point and the downstream side measurement point at the same portion of the film (sheet in patent document 1), that is, at the portion of the film measured at the upstream side measurement point, when passing through the downstream side measurement point. Therefore, it is not possible to confirm whether or not the shrinkage ratio deviates from the allowable range while the film moves from the upstream side measurement point to the downstream side measurement point.

Accordingly, an object of the present invention is to provide a method and an apparatus for producing an optical film, which can efficiently measure the shrinkage, have stable quality, and can reduce the material cost.

Technical scheme for solving technical problems

Method for producing optical film according to one aspect of the present invention

In the method for producing an optical film, N is an integer of 1 or more, the N treatments are performed while the film is being conveyed, the width of the film is continuously measured at a plurality of positions during the conveyance, and the change rate of the width of the film is calculated based on the measurement result of the upstream position and the measurement result of the downstream position among two positions selected from the plurality of positions, which are obtained at the same timing.

An apparatus for producing an optical film according to another aspect of the present invention includes: n processing units for performing a process of imparting at least optical characteristics to the film, wherein N is an integer of 1 or more; a conveying mechanism for conveying the film; a plurality of width measuring devices which are arranged at a plurality of positions on the conveying mechanism and continuously measure the width of the film conveyed by the conveying mechanism at the plurality of positions; and a calculating unit that calculates a rate of change in the width of the film based on a measurement result obtained at the same timing from among measurement results of the upstream width measuring device and measurement results of the downstream width measuring device among the two width measuring devices selected from the plurality of width measuring devices.

In the above-described manufacturing method and the above-described manufacturing apparatus, the width of the film is measured at a plurality of locations. This enables the width of the film to be measured continuously while the film is being conveyed. The rate of change in the width of the film is calculated based on the measurement results of the width of the film measured at the same timing at the upstream and downstream portions among the widths of the films measured continuously at the plurality of portions. Therefore, the shrinkage can be measured efficiently, the quality is stable, and the material cost of the optical film can be reduced.

In the above manufacturing method, the upstream portion may be a position before one of the N processes is performed, and the downstream portion may be a position after the one process is performed.

In the manufacturing apparatus, the upstream-side width measuring device may be disposed before one of the N processing units, and the downstream-side width measuring device may be disposed after the one processing unit.

The width of the film is easily changed when each of the N processes is performed. Therefore, in the above configuration, the rate of change in the width of the film can be calculated at the portion where the width of the film is easily changed.

In the above manufacturing method, the N processes may include an i-1 process, an i process, and an i+1 process, wherein i is an integer of 2 or more, the upstream portion is between the i-1 process position and the i process position, and the downstream portion is between the i process position and the i+1 process position.

In the manufacturing apparatus, the N-th processing unit may include an i-1 th processing unit, an i-th processing unit, and an i+1 th processing unit, wherein i is an integer of 2 or more, the upstream-side width measuring device may be disposed between the i-1 th processing unit and the i-th processing unit, and the downstream-side width measuring device may be disposed between the i-th processing unit and the i+1 th processing unit.

The width of the film is easily changed when the film is subjected to treatment. Therefore, with the above configuration, the rate of change in the width of the film can be calculated at the portion where the width of the film is easily changed. In the above configuration, when the rate of change of the width of the film exceeds the allowable range, it is considered that the rate of change of the width is caused by the ith process or the state of the film before the ith process is changed, and therefore, by adjusting the rate of change of the width of the film to be within the allowable range, it is possible to prevent the occurrence of a defect.

In the above manufacturing method, the N processes may include an i-1 process and an i-1 process, wherein i is an integer of 2 or more, the upstream portion is located between the i-1 process position and the i-1 process position, and the downstream portion is located between the i-1 process position and the i-1 process position, and the upstream portion and the downstream portion may be located between the i-1 process position and the i-1 process position, or the upstream portion may be a position before the i-1 process position and the downstream portion may be the i-1 process position.

In the manufacturing apparatus, the N process units may include an i-1 process unit and an i-1 process unit, wherein i is an integer of 2 or more, the upstream width measuring device may be disposed at a position of the i-1 process unit and the downstream width measuring device may be disposed between the i-1 process unit and the i-1 process unit, the upstream width measuring device and the downstream width measuring device may be disposed between the i-1 process unit and the i-1 process unit, respectively, or the upstream width measuring device may be disposed before the i-1 process unit and the downstream width measuring device may be disposed at a position of the i-1 process unit.

With the above configuration, the rate of change of the width when the film is subjected to the treatment or the rate of change of the width between the end of one treatment and the next treatment can be calculated.

In the above-described manufacturing method, the width of the film may be measured by acquiring an image of at least an end portion of the film by an imaging unit during the conveyance.

In the manufacturing apparatus, at least one of the plurality of width measuring devices may include an imaging unit that images at least an end portion of the film.

In this case, the width of the film can be calculated using the image acquired by the imaging unit.

In the above manufacturing method, the width of the film may be measured based on the brightness of at least one of the reflected light reflected from the film by the light incident on the film and the transmitted light transmitted through the film during the conveyance.

In the manufacturing apparatus, at least one of the plurality of width measuring devices may include a light detecting unit for detecting at least one of reflected light reflected from the film and transmitted light transmitted through the film, the light being incident on the film.

In the manufacturing apparatus, at least one of the plurality of width measuring devices may have a light irradiation unit that irradiates light onto the film. For example, when the difference in brightness between the light transmitted through the film and the surrounding environment is small, the brightness of the surrounding environment can be increased by the light from the light irradiation section. As a result, the width of the film is easily measured.

In the above-described manufacturing method, the film may be conveyed by a conveying roller, the film on the conveying roller may be irradiated with the light, and the width of the film may be measured by detecting an end portion of the film based on a difference between a brightness of the reflected light of the film generated by the irradiation of the light and a brightness of the reflected light of the conveying roller.

In the above-described manufacturing apparatus, the conveying mechanism may include a conveying roller, the light irradiation unit may irradiate light onto the film on the conveying roller, and at least one of the plurality of width measuring units may measure the width of the film based on a difference between a brightness of the reflected light of the film generated by the light irradiated from the light irradiation unit onto the film on the conveying roller and a brightness of the reflected light of the conveying roller.

In this case, the end portion of the film is easily determined by the luminance difference between the reflected light reflected from the film and the reflected light reflected from the conveying roller. As a result, the width of the film can be calculated more accurately based on the position of the end portion. In the case where the reflected light reflected from the film has sufficient brightness by regular reflection, measurement is not limited to the conveyance roller.

In the above-described manufacturing method, the transmitted light may be transmitted through the film by light incident on the film through a polarizing filter. Alternatively, in the above-described manufacturing method, the width of the polarizing film may be measured based on the brightness of light obtained by passing the transmitted light through the film.

In one embodiment of the manufacturing apparatus, a polarizing filter may be provided between the light irradiation unit and the film. Alternatively, an embodiment of the manufacturing apparatus may have a polarizing filter between the light detection unit and the film.

For example, in the case where the film has linear polarization characteristics, the polarization filter is arranged in a crossed nicols state with respect to the film, whereby the width of the film can be easily measured.

In the above-described production method, the N treatments may include at least one of a swelling treatment, a dyeing treatment, a crosslinking treatment, a stretching treatment, and a drying treatment.

In the above manufacturing apparatus, the N treatment units may include at least one treatment unit selected from a swelling treatment unit, a dyeing treatment unit, a crosslinking treatment unit, a stretching treatment unit, and a drying treatment unit.

An example of the above-mentioned optical film is a polarizing film.

Effects of the invention

According to the present invention, it is possible to provide a method for producing an optical film and an apparatus for producing an optical film, which can efficiently measure the shrinkage, have stable quality, and can reduce the material cost.

Drawings

Fig. 1 is a schematic diagram for explaining a method of manufacturing an optical film according to an embodiment.

Fig. 2 is a diagram for explaining a change in the width of the film in the method of manufacturing an optical film.

Fig. 3 is a diagram for explaining the width measuring instrument and the calculating unit.

Fig. 4 is a diagram for explaining an example of the width detector included in the width measuring device.

Fig. 5 is a diagram for explaining another example of the width detector included in the width measuring instrument.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals, and repetitive description thereof will be omitted. The dimensional ratios in the drawings are not necessarily consistent with the dimensional ratios described.

Fig. 1 is a schematic diagram for explaining an embodiment of the present invention. Hereinafter, a case where a polarizing film is produced as an optical film will be described.

In the present embodiment, a polarizing film (optical film) 4 is produced by sequentially subjecting the film 2 being conveyed to N (N is an integer of 1 or more) treatments while conveying the long film 2. The N treatments are treatments for imparting at least linear polarization characteristics to the film 2 as optical characteristics. The upper limit of N is not particularly limited, and N is usually an integer of 30 or less, may be an integer of 25 or less, may be an integer of 20 or less, or may be an integer of 10 or less.

When linear polarization characteristics are imparted to the film 2, the film 2 functions as a polarizing film 4. Since linear polarization characteristics are substantially imparted before all of the N processes are completed, in the method for manufacturing the polarizing film 4 using the film 2, the film 2 has a function as the polarizing film 4 during the manufacturing process. However, for convenience of explanation, unless otherwise specified, the film 2 after all of the N treatments are completed is referred to as a polarizing film 4, and the film before all of the N treatments are referred to as a film 2. In the case of manufacturing the polarizing film 4, the film 2 is generally subjected to a swelling treatment, a dyeing treatment, a crosslinking treatment, a stretching treatment, and a drying treatment. The stretching treatment may be performed on the film 2 in any of the treatments (for example, crosslinking treatment), or may be performed on the film 2 in parallel while performing a plurality of treatments.

The film 2 is a polyvinyl alcohol resin film. Examples of the length of the film 2 in the longitudinal direction are in the range of 1000m to 30000m, preferably 1000m to 20000 m. An example of the length in the width direction (direction orthogonal to the longitudinal direction) of the film 2 is 1300mm to 5000mm. Examples of the thickness of the film 2 before the N treatments are 10 μm to 100 μm. The film 2 is produced by a known method such as a melt extrusion method or a solvent casting method. The film 2 may be a purchased film or a film subjected to a treatment such as stretching or lamination in advance. Fig. 1 shows a case where a film 2 is prepared as a blank roll 6, and N treatments are applied to the film 2 fed out from the blank roll 6 to obtain a polarizing film 4. In the case of producing the film 2 by the above-described method (melt extrusion method, solvent casting method, etc.), for example, the film 2 produced by the above-described method (melt extrusion method, solvent casting method, etc.) may be continuously transported, and the above-described N treatments may be performed during the transport.

The polarizing film 4 manufacturing apparatus 10 includes a plurality of nip rollers 11, a plurality of guide rollers 12, a swelling treatment section 13 ₁, a dyeing treatment section 13 ₂, a crosslinking treatment section 13 ₃, a cleaning treatment section 13 ₄, and a drying treatment section 13 ₅.

The plurality of pinch rollers 11 and the plurality of guide rollers 12 are included in the conveying mechanism of the film 2, and are conveying rollers for conveying the film 2. The plurality of nip rollers 11 and the plurality of guide rollers 12 are appropriately arranged to constitute a conveying path for the film 2.

The pinch roller 11 has a function of imparting a rotational force of the pinch roller 11 to the film 2 by sandwiching and pressing the film 2. The pinch roller 11 also has a function of changing the conveying direction of the film 2. In the conveying direction of the film 2, for example, a circumferential speed difference is applied to the adjacent two pinch rollers 11, whereby the film 2 conveyed between the adjacent two pinch rollers 11 is subjected to a stretching process (for example, a uniaxial stretching process). Fig. 1 illustrates a case where the manufacturing apparatus 10 has 6 nip rollers 11. In the case where 6 pinch rollers 11 are described differently, as shown in fig. 1, 6 pinch rollers 11 are referred to as pinch rollers 11 ₁～11₆.

The guide roller 12 has a function of supporting the film 2 and changing the conveying direction of the film 2. Fig. 1 illustrates a case where the manufacturing apparatus 10 has 12 guide rollers 12. In the case of distinguishing the 12 guide rollers 12, as shown in fig. 1, the 12 guide rollers 12 are referred to as guide rollers 12 ₁～12₁₂.

The swelling portion 13 ₁ is a portion for swelling the film 2. The swelling portion 13 ₁ has a treatment tank in which a treatment liquid for swelling treatment is stored. The membrane 2 is subjected to swelling treatment by impregnating the membrane 2 with the treatment liquid provided in the swelling treatment portion 13 ₁. In the present embodiment, a film conveying path for immersing the film 2 in the processing liquid is formed by the pinch roller 11 ₁ and the guide roller 12 ₁～12₃. In this configuration, the pinch roller 11 ₁ and the guide roller 12 ₃ are disposed before and after the swelling treatment by the swelling treatment portion 13 ₁ (in other words, before and after the swelling treatment portion 13 ₁) is performed on the film 2.

The swelling treatment is performed for the purposes of removing foreign matter from the surface of the film 2, removing a plasticizer in the film 2, imparting dyeing easiness in the subsequent steps, plasticizing the film 2, and the like. The conditions for the swelling treatment may be determined within a range that can achieve these objects and within a range that does not cause any adverse effects such as extreme dissolution and devitrification of the film 2. In the swelling portion 13 ₁, the membrane 2 is immersed in a treatment liquid at a temperature of, for example, 10 to 50 ℃, preferably 20 to 50 ℃ to perform swelling treatment. The swelling treatment time is about 5 to 300 seconds, preferably about 20 to 240 seconds. An example of the treatment liquid in the swelling treatment section 13 ₁ is water. Therefore, the swelling treatment can also be used as the water washing treatment of the membrane 2.

The dyeing section 13 ₂ is a section for dyeing the film 2. The dyeing section 13 ₂ has a treatment tank in which a treatment liquid for dyeing treatment is stored. The film 2 is dyed by immersing the film in the processing liquid provided in the dyeing unit 13 ₂. In the present embodiment, a film conveying path for immersing the film 2 in the processing liquid is formed by the pinch roller 11 ₂ and the guide roller 12 ₄～12₆. In this configuration, the pinch roller 11 ₂ and the guide roller 12 ₆ are disposed before and after the film 2 is subjected to the dyeing process by the dyeing process portion 13 ₂ (in other words, before and after the dyeing process portion 13 ₂).

The treatment liquid provided in the dyeing treatment unit 13 ₂ in the present embodiment is an aqueous solution of a dichroic dye, and the film 2 is dyed with the dichroic dye in the dyeing treatment. The dyeing treatment of the conventional dichroic dye is performed for the purpose of adsorbing the dichroic dye to the film 2. The processing conditions are determined according to the desired optical characteristics within a range that can achieve such a purpose and within a range that does not cause any adverse effects such as extreme dissolution and devitrification of the film 2. Examples of dichroic dyes used for dyeing are iodine and dichroic dyes.

In the case of using iodine as a dichroic dye, the film 2 is subjected to dyeing treatment by immersing it in an aqueous solution containing 0.003 to 0.2 parts by weight of iodine and 0.1 to 10 parts by weight of potassium iodide with respect to 100 parts by weight of water at a temperature of, for example, 10 to 50 ℃, preferably 15 to 40 ℃ for 10 to 600 seconds, preferably 30 to 300 seconds. Instead of potassium iodide, other iodides may be used, such as zinc iodide. Other iodides may also be used in combination with potassium iodide. In addition, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride, and the like may be allowed to coexist. When the treating liquid contains iodine in an amount of 0.003 parts by weight or more per 100 parts by weight of water, the treating liquid can be regarded as a treating liquid for dyeing.

In the case of using a water-soluble dichroic dye as the dichroic dye, the film 2 is immersed in an aqueous solution containing 0.001 to 0.1 parts by weight of the dichroic dye relative to 100 parts by weight of water at a temperature of, for example, 20 to 80 ℃, preferably 30 to 60 ℃ for 10 to 600 seconds, preferably 20 to 300 seconds, to perform dyeing treatment. The aqueous solution of the dichroic dye to be used may contain a dyeing auxiliary or the like, or may contain an inorganic salt such as sodium sulfate, a surfactant or the like. The dichroic dye may be used alone, or two or more kinds of dichroic dyes may be used together according to a desired color tone.

The crosslinking unit 13 ₃ is a unit for crosslinking the film 2. The crosslinking treatment section 13 ₃ has a treatment tank in which a treatment liquid for crosslinking treatment is stored. The film 2 is subjected to a crosslinking treatment by immersing the film in the treatment liquid provided in the crosslinking treatment section 13 ₃. In the present embodiment, a film conveying path for immersing the film 2 in the processing liquid is formed by the pinch roller 11 ₃ and the guide roller 12 ₇～12₉. In this configuration, the pinch roller 11 ₃ and the guide roller 12 ₉ are disposed before and after the film 2 is subjected to the crosslinking treatment by the crosslinking treatment section 13 ₃ (in other words, before and after the crosslinking treatment section 13 ₃).

The crosslinking treatment is a treatment performed for the purpose of imparting water resistance, adjusting color tone (preventing the film 2 from being colored with cyan or the like) and the like by crosslinking.

The treatment liquid used in the crosslinking treatment section 13 ₃ is, for example, an aqueous solution containing, for example, about 1 to 10 parts by weight of boric acid relative to 100 parts by weight of water. When the dichroic dye used in the dyeing treatment is iodine, the treatment liquid used in the crosslinking treatment unit 13 ₃ preferably contains an iodide in addition to boric acid, and the amount thereof is, for example, 1 to 30 parts by weight relative to 100 parts by weight of water. Examples of the iodide include potassium iodide and zinc iodide. Compounds other than iodide may be allowed to coexist, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, and the like.

In the crosslinking treatment of the crosslinking treatment section 13 ₃, the concentration of boric acid and iodide and the temperature of the treatment liquid can be appropriately changed according to the purpose.

For example, when the purpose of the crosslinking treatment is to sequentially perform the swelling treatment, the dyeing treatment, and the crosslinking treatment on the polyvinyl alcohol resin film based on the hydration resistance of the crosslinking, the crosslinking agent-containing liquid of the treatment liquid is, for example, an aqueous solution having a concentration of boric acid/iodide/water=3 to 10/1 to 20/100 in terms of weight ratio. If necessary, other crosslinking agents such as glyoxal and glutaraldehyde may be used instead of boric acid, and boric acid and other crosslinking agents may be used in combination. The temperature of the treatment liquid at the time of impregnating the film 2 is usually 50 to 70 ℃, preferably 53 to 65 ℃, and the impregnation time of the film 2 is usually 10 to 600 seconds, preferably 20 to 300 seconds, more preferably 20 to 200 seconds. When the pre-stretched film 2 is subjected to dyeing treatment and crosslinking treatment in this order before the swelling treatment, the temperature of the treatment liquid is usually about 50 to 85 ℃, preferably about 55 to 80 ℃.

When iodine is used as a dichroic dye for the purpose of color tone adjustment in the crosslinking treatment, a crosslinking agent-containing liquid having a concentration of boric acid/iodide/water=1 to 5/3 to 30/100 in terms of weight ratio can be used as the treatment liquid. The temperature of the treatment liquid at the time of impregnating the membrane 2 is usually 10 to 45 ℃, and the impregnation time of the membrane 2 is usually 1 to 300 seconds, preferably 2 to 100 seconds.

The cleaning section 13 ₄ is a section for performing cleaning treatment on the film 2 after the crosslinking treatment. The cleaning processing unit 13 ₄ has a processing tank in which a processing liquid for cleaning processing is stored. The membrane 2 is immersed in the treatment liquid provided in the cleaning treatment section 13 ₄, thereby performing a cleaning treatment on the membrane 2. In the present embodiment, a film conveying path for immersing the film 2 in the processing liquid is formed by the pinch roller 11 ₄ and the guide roller 12 ₁₀～12₁₂. In this configuration, the pinch roller 11 ₄ and the guide roller 12 ₁₂ are disposed before and after the film 2 is subjected to the cleaning process by the cleaning process portion 13 ₄ (in other words, before and after the cleaning process portion 13 ₄). Examples of the treatment liquid in the washing treatment include water, an aqueous solution containing potassium iodide, and an aqueous solution containing boric acid. The temperature of the treatment liquid is usually 2 to 40 ℃, and the treatment time is usually 2 to 120 seconds.

The cleaning treatment in the cleaning treatment section 13 ₄ may be performed by spraying the treatment liquid, or by a combination of dipping and spraying.

The drying unit 13 ₅ is a unit for drying the film 2. In the present embodiment, the drying unit 13 ₅ is a drying device. In the drying unit 13 ₅, the film 2 after the cleaning process by the cleaning unit 13 ₄ is carried in, and the film 2 is dried while the film 2 passes through the drying unit 13 ₅. In the present embodiment, a film conveying path for immersing the film 2 in the processing liquid is formed by the nip roller 11 ₅、11₆. The guide roller 12 may be appropriately disposed in the drying processing unit 13 ₅ for supporting and conveying the film 2. Drying by the drying treatment section 13 ₅ is performed in the drying treatment section 13 ₅ maintained at a temperature of about 40 to 100 ℃ for about 30 to about 600 seconds. In fig. 1, the drying process section 13 ₅ is schematically shown. The drying unit 13 ₅ is not particularly limited as long as it can dry the moisture adhering to the film 2, and may be a known technique generally used in the production of a polarizing film.

In the manufacturing apparatus 10, a stretching process for uniaxially stretching the film 2 is performed using a circumferential speed difference of at least two pinch rollers 11 (the pinch roller 11 on the upstream side and the pinch roller 11 on the downstream side) among the plurality of pinch rollers 11. In this case, the two pinch rollers 11 contributing to the uniaxial stretching process described above function as stretching process sections.

For example, the stretching treatment of the uniaxial stretching treatment may be performed by using the circumferential speed difference between the grip roller 11 ₃ arranged before the crosslinking treatment section 13 ₃ and the grip roller 11 ₄ arranged after the crosslinking treatment section 13 ₃. In this case, since the stretching process is performed in parallel with the crosslinking process, the crosslinking process unit 13 ₃ also functions as a stretching process unit. The stretching treatment is also effective for suppressing the generation of wrinkles.

The stretching treatment may be mainly performed by two pinch rollers 11 disposed before and after one treatment section (for example, the crosslinking treatment section 13 ₃ described above), while the stretching treatment may be further performed gradually by other pinch rollers 11.

The manufacturing apparatus 10 may further include a stretching unit for performing the stretching process. In this case, the stretching unit is disposed, for example, in the subsequent stage of the crosslinking unit 13 ₃ (for example, between the crosslinking unit 13 ₃ and the cleaning unit 13 ₄).

The manufacturing apparatus 10 may include at least one of the swelling treatment section 13 ₁, the dyeing treatment section 13 ₂, the crosslinking treatment section 13 ₃, the cleaning treatment section 13 ₄, and the drying treatment section 13 ₅. For example, the manufacturing apparatus 10 may have a plurality of crosslinking treatment sections 13 ₃. In the same manner as in the case where the manufacturing apparatus 10 includes the stretching unit, the manufacturing apparatus 10 may include a plurality of stretching units, for example.

In the case of producing the polarizing film 4 by using the production apparatus 10, first, the film 2 is paid out from the blank roll 6, and the film 2 is conveyed in the longitudinal direction along a conveying path formed by the plurality of pinch rollers 11 and the plurality of guide rollers 12. The transport speed may be 1 to 60 m/min or 1.5 to 50 m/min. On the transport path of the film 2, from the web 6 side, a swelling treatment section 13 ₁, a dyeing treatment section 13 ₂, a crosslinking treatment section 13 ₃, a cleaning treatment section 13 ₄, and a drying treatment section 13 ₅ are provided. As described above, at least two pinch rollers 11 also function as stretching sections. Therefore, the transported film 2 is subjected to swelling treatment, dyeing treatment, crosslinking treatment, cleaning treatment, and drying treatment, and also to stretching treatment. Thus, linear polarization characteristics (optical characteristics) are imparted to the film 2, and a polarizing film 4 is obtained.

The polarizing film 4 obtained by the drying treatment section 13 ₅ is used for manufacturing a polarizing plate including the polarizing film 4, for example. For example, the polarizing plate is manufactured by performing a lamination step of laminating a protective film on one or both surfaces of the polarizing film 4. The polarizing film 4 obtained by the drying unit 13 ₅ may be continuously fed for producing the polarizing plate, or may be wound into a roll form at one time.

As shown in fig. 2, in the process of manufacturing the polarizing film 4 by performing N processes while conveying the film 2, the length of the film 2 in the width direction varies. The width of the film 2 at a position on the upstream side (hereinafter referred to as "upstream position") among any two positions in the conveyance of the film 2 is referred to as W1, the width of the film 2 at a position on the downstream side (hereinafter referred to as "downstream position") from the upstream position is referred to as W2, and the rate of change in the width of the film 2 between the upstream and downstream positions is referred to as the shrinkage (%), and in this case, the shrinkage is defined by the following equation.

The internal shrinkage= ((W1-W2)/W1) ×100

In one embodiment of the present invention, the method further comprises a monitoring step of monitoring the shrinkage. In the monitoring step, as shown in fig. 1, the width of the film 2 is continuously measured at a plurality of measurement points 20 (a plurality of positions) in the film 2 being conveyed. In fig. 1, a plurality of measurement points 20 of the width of the film 2 are shown with arrows. In the case of distinguishing between the plurality of measurement points 20, the plurality of measurement points 20 will be referred to as measurement points 20 ₁～20₁₂.

The measurement point 20 may be a point at which the width of the film 2 wound around the pinch roller 11 or the guide roller 12 is measured, or may be a point at which the width of the film 2 not wound around the pinch roller 11 or the guide roller 12 is measured. The measurement point 20 shown in fig. 1 is an example, and for example, the measurement point 20 ₁ may be a position for measuring the width of the film 2 fed from the pinch roller 11 ₁, and the measurement point 20 ₄ may be a position for measuring the width of the film 2 wound around the guide roller 12 ₆ (the film 2 on the guide roller 12 ₆).

Preferably, the measurement point 20 ₁～20₃ before the film 2 is dyed is a point at which the width of the film 2 wound around the pinch roller 11 or the guide roller 12 is measured. On the other hand, after the measurement point 20 ₄, the relationship between the pinch roller 11 or the guide roller 12 and the film 2 is not generally limited.

The measurement point 20 can be arranged before and after one of the N treatments is performed on the film 2. For example, the measurement point 20 ₁ is a point at which the state of being wound around the pinch roller 11 ₁ or the width of the film 2 immediately after being sent out from the pinch roller 11 ₁ is measured in fig. 1, and is a measurement point before the swelling treatment is performed. The measurement point 20 ₂ is a point at which the width of the film 2 on the guide roller 12 ₃ or immediately after being sent out from the guide roller 12 ₃ is measured.

Thus, the measurement point 20 ₁、20₂ is a measurement point of the width of the film 2 before and after the swelling treatment is performed on the film 2. In this way, the measurement points before and after one treatment (before and after immersing the film in the treatment liquid of a certain treatment section) are also measurement points before and after the treatment section that performs the treatment.

Another example of such a measurement point 20 is measurement point 20 ₃、20₄, measurement point 20 ₅、20₇, measurement point 20 ₈、20₁₀, and measurement point 20 ₁₁、20₁₂. The measurement points 20 ₃、20₄, 20 ₅、20₇, and 20 ₈、20₁₀ are measurement points of the width of the film 2 before and after the swelling treatment, dyeing treatment, crosslinking treatment, and cleaning treatment. The measurement point 20 ₁₁、20₁₂ is a measurement point of the width of the film 2 before and after the drying treatment.

The measurement point 20 may be a point at which the width of the film 2 is measured during a step of performing one treatment on the film 2. An example of such a measurement point 20 is measurement point 20 ₆、20₉. The measurement point 20 ₆ is a measurement point on the way of the film 2 being conveyed between the guide roller 12 ₇ and the guide roller 12 ₈. Similarly, the measurement point 20 ₉ is a measurement point on the way of the film 2 being conveyed between the guide roller 12 ₁₀ and the guide roller 12 ₁₁. At measurement point 20 ₆、20₉, the width of film 2 in the treatment liquid is measured.

In the monitoring step, the shrinkage ratio is calculated based on the measurement results measured at the same timing (i.e., simultaneously) at the two positions among the measurement results of the width of the continuous measurement film 2 at each of the two positions (upstream and downstream positions) selected in advance from the plurality of measurement points 20. The same timing (i.e., simultaneous) described above may also be deviated in several ways within the scope of the gist of the present invention. The time difference between the measurement at the upstream portion and the measurement at the downstream portion is not particularly limited, and may be 1 minute or less, 30 seconds or less, 20 seconds or less, or 10 seconds or less. The monitoring process is preferably automated.

In the example of the upstream and downstream portions, the upstream portion is one of N processes (hereinafter referred to as "predetermined process") and the downstream portion is after the predetermined process. For example, when the predetermined process is a dyeing process, the upstream part is before the dyeing process, and the downstream part is after the dyeing process. The terms "before the predetermined process" and "after the predetermined process" also include cases where other processes are performed between the upstream portion, the downstream portion, and the "predetermined process" described above.

When any two adjacent processes among the N processes are referred to as an i-1 process and an i process (i is an integer of 2 or more), and the corresponding process units are referred to as an i-1 process unit and an i process unit, the upstream portion and the downstream portion may be any one of configuration examples 1 to 3 below.

Configuration example 1

The upstream portion is located at a position in the i-1 th process (i-1 th process portion position) and the downstream portion is located between the i-1 th process (i-1 th process portion) position and the i-th process (i-th process portion) position. For example, in the case where the i-1 th process is a crosslinking process, among the plurality of measurement points 20 shown in fig. 1, examples of the upstream and downstream sites are the measurement points 20 ₆ and the measurement points 20 ₇.

Configuration example 2

The upstream portion and the downstream portion are respectively located between the position of the i-1 th process (i-1 th process section) and the position of the i-th process (i-th process section). For example, in the case where the i-1 th process is a crosslinking process, among the plurality of measurement points 20 shown in fig. 1, examples of the upstream and downstream sites are the measurement points 20 ₇ and the measurement points 20 ₈.

Configuration example 3

The upstream portion is the position before the i-1 th process (i-1 th process portion) and the downstream portion is the position in the i-1 th process (i-1 th process portion). For example, in the case where the i-1 th process is a crosslinking process, among the plurality of measurement points 20 shown in fig. 1, examples of the upstream and downstream sites are the measurement points 20 ₅ and the measurement points 20 ₆.

When i is an integer of 2 or more, the process next to the ith process is referred to as the ith+1 process, and the corresponding process unit is referred to as the ith+1 process unit, examples of the upstream portion and the downstream portion may be the following configuration example 4.

Configuration example 4

The upstream portion is between the position of the i-1 th process (i-1 th process portion) and the position of the i-th process (i-th process portion), and the downstream portion is between the position of the i-th process (i-th process portion) and the position of the i+1 th process (i+1-th process portion). For example, in the case where the i-1 th process is a crosslinking process, among the plurality of measurement points 20 shown in fig. 1, examples of the upstream and downstream sites are the measurement points 20 ₇ and the measurement points 20 ₁₀.

As the group of the upstream portion and the downstream portion, for example, a group of two measurement points 20 which are not adjacent may be used such that the upstream portion is the measurement point 20 ₁ and the downstream portion is the measurement point 20 ₈.

In the case where the manufacturing apparatus 10 includes at least one of the swelling treatment section 13 ₁, the dyeing treatment section 13 ₂, the crosslinking treatment section 13 ₃, the cleaning treatment section 13 ₄, and the drying treatment section 13 ₅, the upstream portion and the downstream portion may be portions that are treated for the same purpose, or may be portions that are treated for different purposes. For example, in the case where the manufacturing apparatus 10 has two or more swelling treatment sections 13 ₁ and two swelling treatment sections 13 ₁ are referred to as swelling treatment sections 13 ₁-a、13₁ -b, the upstream portion may be the position (or before or after) of the swelling treatment section 13 ₁ -a, the downstream portion may be the position (or before or after) of the swelling treatment section 13 ₁ -b, the upstream portion may be the position (or before or after) of the swelling treatment section 13 ₁ -a or the swelling treatment section 13 ₁ -b, and the downstream portion may be the position (or before or after) of the dyeing treatment section 13 ₂. The same applies to the case of having a plurality of stretching portions.

The shrinkage may be calculated by a plurality of groups of the upstream portion and the downstream portion selected from the plurality of measurement points 20. For example, the shrinkage may be calculated based on the measurement result at the measurement point 20 ₁ and the measurement result at the measurement point 20 ₂, and the shrinkage may be calculated based on the measurement result at the measurement point 20 ₅ and the measurement result at the measurement point 20 ₇. Among the plurality of groups of the upstream portion and the downstream portion, the upstream portion or the downstream portion may be a common group. For example, the shrinkage may be calculated based on the measurement result of the measurement point 20 ₁ and the measurement result of the measurement point 20 ₂, and the shrinkage may be calculated based on the measurement result of the measurement point 20 ₁ and the measurement result of the measurement point 20 ₄. Similarly, the shrinkage may be calculated based on the measurement result of the measurement point 20 ₅ and the measurement result of the measurement point 20 ₇, and the shrinkage may be calculated based on the measurement result of the measurement point 20 ₆ and the measurement result of the measurement point 20 ₇.

In order to calculate the shrinkage ratio, the optical film manufacturing apparatus 10 includes a plurality of width measuring devices 30 and a calculating unit 40 as shown in fig. 3.

Each width measuring device 30 is a device for continuously measuring the width of the film 2. The plurality of width measuring instruments 30 are arranged one-to-one with the plurality of measuring points 20. That is, one width measuring instrument 30 is disposed at one measuring point 20. Fig. 3 schematically illustrates two width measuring instruments 30 selected for calculating the shrinkage ratio among the plurality of width measuring instruments 30 (i.e., an upstream width measuring instrument 30 _UP disposed at an upstream portion and a downstream width measuring instrument 30 _DOWN disposed at a downstream portion), and a calculating unit 40.

The width measuring instrument 30 has two end detectors 31. One of the two end detectors 31 is a detector for detecting one end 2a of the film 2 in the width direction, and the other is a detector for detecting the other end 2b (the end opposite to the end 2 a) of the film in the width direction. The width measuring device 30 is configured to detect the end portions 2a, 2b of the film 2 based on the state of the film 2 at the measurement point 20. Therefore, the configuration of the width measuring instrument 30 may be different for each measurement point 20. However, the two end detectors 31 (the two end detectors 31 disposed at the one measurement point 20) included in the one width measuring instrument 30 have the same configuration.

Fig. 4 is a schematic diagram for explaining a schematic configuration of an end detector 31A as an example of the end detector 31. The end detector 31A is a detector suitable for measuring the width of the film 2 on the conveying roller R. The conveying roller R is a pinch roller 11 or a guide roller 12 shown in fig. 1.

Two end detectors 31A are disposed on the film 2 to detect the end portions 2a and 2b, respectively. As described above, the end detector 31A has the same structure, and thus the case where the end detector 31A detects the end 2a will be described.

The end detector 31A has a light irradiation section 32 and a light detection section 33. Fig. 4 illustrates a case where the film 2 is disposed on the conveying roller R.

The light irradiation section 32 irradiates light toward the film 2. The light irradiation unit 32 irradiates light to the end 2a of the film 2 and to the outside of the end 2 a. Therefore, as shown in fig. 4, when the film 2 is disposed on the conveying roller R, the light from the light irradiation section 32 also irradiates the portion of the conveying roller R that does not overlap with the film 2. The light irradiation unit 32 may be a linear light source extending in the width direction of the film 2. The light irradiation section 32 may be, for example, an LED.

The light irradiation unit 32 may be disposed in the case 34. The case 34 has a window 34a for irradiating the film 2 with light output from the light irradiation unit 32. The window portion 34a may be made of a material that transmits light output from the light irradiation portion 32. Examples of the material of the window portion 34a include polycarbonate resin, acrylic resin, vinyl chloride resin, polypropylene resin, polyethylene terephthalate resin, and glass, for example.

The light detection unit 33 detects the brightness of the light (reflected light) reflected by the film 2 from the light irradiated to the film 2 by the light irradiation unit 32. The light detection unit 33 may be an imaging unit such as a camera (for example, a CCD camera) that images at least the end portion 2a of the film 2. As shown in fig. 4, when the film 2 is disposed on the conveying roller R, the light detection unit 33 detects the brightness of the light reflected by the conveying roller R, for example, among the light irradiated from the light irradiation unit 32 to the film 2.

The light detection unit 33 may be disposed in the case 35. The case 35 has a window 35a for detecting the reflected light by the light detection unit 33. The window 35a may be made of a material that transmits the reflected light. An example of the material of the window portion 35a is the same as that of the window portion 34 a.

The measurement point 20 ₁、20₂、20₃ before the film 2 is subjected to the dyeing treatment is generally a point at which the width of the film 2 on the conveying roller R is measured. Thus, the end detector 31A is suitably adapted to the measurement point 20 ₁、20₂、20₃.

Fig. 5 is a schematic diagram for explaining a schematic configuration of an end detector 31B as another example of the end detector (width measuring device) 31. The end detector 31B is a detector suitable for a case where linear polarization characteristics are generated on the film 2 (a case where an absorption axis is formed). In general, the end detector 31B can be applied to the film 2 subjected to the dyeing process in the dyeing process section 13 ₂.

Two end detectors 31B are arranged with respect to the film 2 to detect the end portions 2a and 2B, respectively. However, as described above, the end detector 31B has the same structure, and therefore, the case where the end detector 31B detects the end 2a will be described.

The end detector 31B has a light detection section 36 and a polarizing filter 37.

The light detection unit 36 detects the brightness of light (hereinafter referred to as "light from the film 2") that enters the film 2 and passes through the film 2 in the surrounding environment of the film 2. The light detection unit 36 may be an imaging unit such as a camera (for example, a CCD camera) that images at least the end portion 2a of the film 2.

The "light of the surrounding environment of the film 2" includes illumination light from an illumination device provided in a factory for producing the polarizing film 4, light reflected by elements constituting the production apparatus 10 (for example, at least one of a side wall and a bottom wall of a processing tank provided in each processing section shown in fig. 1, a floor of the factory, and the like) such as a conveying roller R such as a pinch roller 11 and a guide roller 12. In fig. 5, the light of the surroundings of the film 2 is schematically shown by open arrows.

The polarizing filter 37 is a filter having linear polarization characteristics. The polarizing filter 37 is disposed between the light detection unit 36 and the film 2 so that the absorption axis of the film 2 and the absorption axis of the polarizing filter 37 are in a crossed nicols state. The above-described crossed nicols state is not limited to the case where the absorption axis of the film 2 and the absorption axis of the polarizing filter 37 form an angle of 90 °, and is intended to include errors of the order of ±5°, ±10°, or 15 ° with respect to 90 °, for example.

The light detection unit 36 and the polarizing filter 37 may be disposed in the case 35 having the window 35a, similarly to the light detection unit 33. The window 35a may be made of a material that transmits light from the film 2.

When only the light of the surrounding environment of the film 2 is used, the end detector 31B may have an auxiliary illumination unit (light irradiation unit) in the case where the difference between the brightness of the light from the surrounding environment and the brightness of the light transmitted through the film 2 detected by the light detection unit 36 is small. The configuration of the auxiliary illumination unit can be the same as that of the light irradiation unit 32. The auxiliary illumination unit may be smaller than the light irradiation unit 32, or may output light having a smaller power than the light output from the light irradiation unit 32. The auxiliary illumination unit may be disposed in the case 34 having the window 34a, as in the case of the light irradiation unit 32. The auxiliary illumination unit is configured to illuminate at least one of a detection region (or an imaging region) of the light detection unit 33 and the periphery thereof, and light from the auxiliary illumination unit is incident on the film 2 as ambient light.

The end detector 31B may be used to measure the width of the film 2 on the transport roller R. The end detector 31B can be used for measurement at the measurement point 20 ₅、20₈、20₁₀, for example. In this case, the conveying roller R is preferably a white roller in order to clarify the brightness difference.

The end detector 31B may be used to measure the width of the film 2 between the transport rollers R and R. The end detector 31B can be used for measuring the width of the film 2 at the measurement point 20 ₄、20₆、20₇、20₉、20₁₁、20₁₂, for example. In this case, a white plate-like member or the like may be provided on the background of the detection region (or the background of the imaging region) of the light detection unit 33 in order to clarify the luminance difference. When the auxiliary illumination unit is used for measuring the width of the film 2 between the two conveying rollers R, the auxiliary illumination unit may be disposed on the same side as the end detector 31B with respect to the film 2 or on the opposite side to the end detector 31B with respect to the film 2.

In the case of measuring the width of the film 2at the measurement point 20 ₆、20₉, the end detector 31B measures the width of the film 2 in the processing liquid. In this case, for example, as shown in fig. 5, the end detector 31B may have a housing 35, and the housing 35 may have a window 35a, and the housing 35 may be disposed so that a part of the window 35a is located in the processing liquid. When the window 35a is partially disposed in the treatment liquid, at least one of hydrophilic treatment, uneven treatment, and oblique treatment may be performed on the outer surface of the window 35 a. Thus, for example, bubbles are less likely to remain on the outer surface of the window 35a, and thus the end 2a of the film 2 is easily and accurately detected. In the case where the auxiliary illumination unit is used for measuring the width of the film 2 in the processing liquid, for example, the auxiliary illumination unit may illuminate the bottom wall of the processing tank in which the processing for the film 2 is performed. In this case, the brightness of the transmitted light irradiated from the auxiliary illumination unit, reflected by the bottom wall of the processing tank, and transmitted through the film 2 is detected by the light detection unit 36 through the polarizing filter 37.

The polarizing filter 37 of the end detector 31B may be disposed on the incident side of the light incident on the film 2, for example. For example, in the case where the end detector 31B has an auxiliary illumination portion (light irradiation portion), the polarizing filter 37 may be disposed between the auxiliary illumination portion and the film 2 without being disposed in the light detection portion 33. In this case, the polarizing filter 37 is also disposed in a crossed nicols state with the film 2.

The calculating unit 40 shown in fig. 3 to 5 is connected to the plurality of width measuring devices 30 (the width measuring devices 30 disposed at the upstream and downstream positions) in a wired or wireless manner, and calculates the shrinkage ratio based on the measurement results obtained from the plurality of width measuring devices 30.

Specifically, the calculating unit 40 determines the end portions 2a and 2b of the film 2 at the positions where the width measuring devices 30 are arranged based on the measurement results of the plurality of width measuring devices 30. The end portions 2a and 2b can be determined by a change in the luminance data as a measurement result of the width measuring device 30.

For example, as shown in fig. 4, when the width of the film 2 in which the film 2 is disposed on the conveying roller R is measured by the width measuring device 30 including the end detector 31A, the light detecting portion 33 detects the brightness of the reflected light from the film 2 and the reflected light from the conveying roller R. Since the difference occurs between the brightness of the reflected light from the film 2 and the brightness of the reflected light from the conveying roller R, the calculating unit 40 may determine the portion where the difference occurs as the end portions 2a, 2b of the film 2.

For example, as shown in fig. 5, when the width of the film 2 is measured by the width measuring device 30 including the end detector 31B, the polarization filter 37 is in a crossed nicols state with the film 2, so that light from the film 2 is substantially blocked, and light from the outside of the film 2 is detected. Therefore, in the image formed by the luminance data detected by the light detection unit 36, a luminance difference is generated between the film 2 and the portions other than the film 2 (the film 2 side is dark and the portions other than the film 2 are bright), and therefore the calculation unit 40 may determine that the portions where the difference is generated are the end portions 2a, 2b of the film 2.

When the end portions 2a, 2B of the film 2 are specified, the calculating unit 40 calculates the width of the film 2 based on, for example, the relationship between the arrangement position of the end portion detector 31A (or the end portion detector 31B) and the positions of the end portions 2a, 2B in the detected luminance data. When the end of the transport roller R can be determined from the luminance data obtained by the end detector 31A (or the end detector 31B), for example, the width of the film 2 is calculated from the relationship between the end of the transport roller R and the positions of the ends 2a and 2B of the film 2 in the luminance data and the actual position of the end of the transport roller R.

Next, the calculating unit 40 calculates the shrinkage ratio using the width of the film 2 calculated based on the measurement results of the two width measuring instruments 30 (the upstream width measuring instrument 30U _P and the downstream width measuring instrument 30 _DOWN) respectively disposed at the upstream portion and the downstream portion, which are selected in advance from the plurality of measurement points 20. Examples of the upstream and downstream portions are as described above.

In the above-described method for producing the polarizing film 4 and the apparatus 10 for producing the polarizing film 4, the width of the film 2 is measured by the width measuring instrument 30 disposed at each of the plurality of measuring points 20 (a plurality of positions). This allows the width of the film 2 to be continuously measured while the film 2 is being conveyed. The shrinkage ratio is calculated based on the measurement results of the width of the film 2 measured at the same timing at the upstream and downstream portions among the widths of the film 2 continuously measured at the plurality of measurement points 20. Therefore, the shrinkage ratio of the film 2 can be obtained in real time during the conveyance of the film 2. That is, the shrinkage can be measured efficiently. In other words, the shrinkage can be monitored in real time.

The shrinkage represents the rate of change in the width of the film 2. Therefore, for example, when the allowable range of the shrinkage (the control width of the shrinkage) obtained in advance by experiments or simulations is exceeded in the portion where the width measurement is performed, the film 2 may be broken in the subsequent step, the thickness of the film 2 may deviate from a desired thickness (thickness in design), or a film may be produced as a defective product having a desired optical characteristic, streaks, uneven appearance, or the like.

Therefore, in the above-described method for producing the polarizing film (optical film) 4 and the apparatus 10 for producing the polarizing film 4, which can monitor the internal shrinkage in real time, when the internal shrinkage exceeds the allowable range, for example, the production of the polarizing film 4 can be interrupted. When the production is stopped, the production conditions of the polarizing film 4 (for example, the treatment liquid, the stretching conditions, etc.) may be adjusted so that the internal shrinkage is within the allowable range. For example, the manufacturing may be continued while adjusting the shrinkage ratio to be within the allowable range. This can prevent the film 2 from being broken in the subsequent steps, or can suppress the production of the polarizing film 4 that is the defective product. Accordingly, the polarizing film 4 can be manufactured in a stable process. Further, the polarizing film 4 having stable quality can be uniformly manufactured. Further, in addition, the material cost of the polarizing film 4 can be reduced. Further, since the polarizing film (optical film) 4 of a good product can be efficiently produced, the production yield of the polarizing film 4 is improved.

The width of the film 2 is easily changed by performing at least one of the N treatments on the film 2. Therefore, in the case where the upstream portion is before the predetermined process among the N processes and the downstream portion is after the predetermined process as described above, the internal shrinkage rate which brings about the defects in the production of the polarizing film 4 (for example, breakage of the film 2 in the subsequent process, deviation of the film 2 from the desired thickness, or the like) is easily monitored.

For the same reason, even in the cases of the above-described arrangement examples 1 to 4, the shrinkage rate which brings about the defects in the production of the polarizing film 4 is easily monitored. For example, it can be determined that a change in state before or after a certain process in the arrangement state, a change in state due to the process, or a change in state in the middle of the process positively affects the reduction rate. Therefore, when the shrinkage exceeds the allowable range, the manufacturing conditions can be easily adjusted.

As a result, the material cost of the polarizing film 4 can be further reduced, and the manufacturing yield of the polarizing film 4 can be further improved. In addition, the polarizing film 4 having more stable quality can be uniformly produced in a more stable process.

In the case where the width of the film 2 is measured at the measurement point 20 ₁ (before N treatments are performed), for example, linear polarization characteristics are not generated on the film 2. Thus, the film 2 is typically a transparent film having no absorption axis. In this case, the end portions 2a, 2b of the film 2 on the conveying roller R are detected by using the width measuring device 30 having the end detector 31A shown in fig. 4, whereby the end portions 2a, 2b of the film 2 can be reliably detected. As a result, the width of the film 2 can be measured more accurately. Although the case of measuring point 20 ₁ is exemplified here, measuring point 20 ₂、20₃ can also reliably detect ends 2a and 2b of film 2 using width measuring device 30 having end detector 31A shown in fig. 4.

When the film 2 is subjected to dyeing treatment and stretching treatment, linear polarization characteristics are imparted to the film 2. In the case of conveying the film 2, tension is given to the film 2 along the conveying direction of the film 2. Therefore, when the stretching treatment is gradually performed in any one of the swelling treatment, the dyeing treatment, the crosslinking treatment, and the drying treatment while the film 2 is conveyed, linear polarization characteristics are gradually imparted to the film 2 after the dyeing treatment. Further, as shown in fig. 1, the drying process is generally performed at the end of the N processes. Therefore, in the case of measuring the width of the film 2 after the dyeing process and the stretching process are performed, the width of the film 2 can be reliably detected by using the width measuring device 30 having the end detector 31B shown in fig. 5. As a result, the width of the film 2 can be measured more accurately.

As shown in fig. 4 and 5, in the case where the width measuring instrument 30 includes the cases 34 and 35, corrosion of the light irradiation unit 32 and the light detection units 33 and 36 due to iodine can be prevented. Since a treatment liquid containing iodine is used for producing the polarizing film 4, iodine is present in the production environment, and for example, the photodetection portions 33 and 36 are corroded. In contrast, by disposing the light irradiation unit 32 and the light detection units 33 and 36 in the cases 34 and 35 as shown in fig. 4 and 5, the corrosion due to iodine can be prevented. Preferably, air or the like is supplied into the housings 34 and 35 in advance to be pressurized.

Various modifications are described in conjunction with the above-described embodiments. However, the present invention is not limited to the above-described embodiments and various modifications, and is intended to have the same meaning as the embodiments and to include all modifications within the scope.

A case of manufacturing a polarizing film as an optical film is exemplified. However, the present invention can be applied to a method and an apparatus for manufacturing an optical film, which require monitoring of the shrinkage ratio in the process of manufacturing an optical film from the film. Other examples of the optical film include a protective film, a retardation film, a surface treatment film, an antireflection film, and a diffusion film.

The width measuring device having the end detector 31B shown in fig. 5 can be suitably applied to a case where the upstream portion is a portion for measuring the width of the film subjected to the dyeing process and the stretching process, in a case where the N processes include the dyeing process and the stretching process. In this case, when the width of the film is measured at the upstream portion, linear polarization characteristics tend to occur in the film. In the case where N treatments are performed while the film is conveyed, the stretching treatment is gradually performed on the film as described above. Therefore, the width measuring device having the end detector 31B can be suitably applied to a case where the upstream portion is a portion for measuring the width of the film subjected to the dyeing treatment.

The method for measuring the width of the film 2 is not particularly limited to the illustrated method. For example, the width may be measured by a measuring device such as a laser type displacement meter or an LED type displacement meter. The entire film 2 may be photographed by a camera or the like, and the width may be calculated from the obtained image. As shown in fig. 3, in the method of obtaining the positions of the end portions 2a and 2b of the film 2, devices for measuring the positions of the end portions 2a and 2b may be disposed at the end portions 2a and 2b of the film 2, respectively, and therefore, the method is preferable from the viewpoints of installation space and machine management (maintenance inspection, etc.).

The stretching treatment in the stretching treatment section is not limited to the wet stretching method, and a dry stretching method may be used. In the above-described embodiment, the order of the processes illustrated for producing the polarizing film may be changed or combined as appropriate within a range not departing from the gist of the present invention. The number of processing tanks in each processing unit may be one or a plurality of processing tanks. The N processes are not limited to the number of illustrated processes.

The definition of the rate of change in the width of the film (shrinkage) indicates the rate of change in the width of the film between the upstream portion and the downstream portion, and is not limited to the definition illustrated.

The above-described embodiments and various modifications may be appropriately combined within a range not departing from the gist of the present invention.

Reference numerals illustrate:

2 … membranes; 4 … polarizing films (optical films); 10 … manufacturing devices; 11 … grip rolls (conveying mechanism); 12 … guide rollers (conveying mechanism); 20 … measurement points (multiple sites); 30 … width meter; 30 _UP … upstream side width measuring device; 30 _DOWN … downstream side width measuring device; 32 … light irradiation parts; 33 … light detection sections (imaging sections); 36 … light detection section (image pickup section).

Claims

1. A method for producing an optical film by subjecting a long film to N treatments, wherein N is an integer of 1 or more,

The N treatments are performed while conveying the film,

In the conveying, the width of the film is continuously measured at a plurality of positions, and the change rate of the width of the film is calculated based on the measurement result of the upstream position and the measurement result of the downstream position among the two positions selected from the plurality of positions, which are obtained at the same timing,

In the N processes, the manufacturing can be continued while adjusting the manufacturing conditions so that the rate of change of the width of the film is within an allowable range,

The N treatments include at least one treatment selected from swelling treatment, dyeing treatment, crosslinking treatment, stretching treatment and drying treatment,

The N processes include an i-1 process, an i process, and an i+1 process, wherein i is an integer of 2 or more,

The upstream portion is between the i-1 th processing position and the i-th processing position, and the downstream portion is between the i-th processing position and the i+1-th processing position;

Or alternatively, the first and second heat exchangers may be,

The N processes include an i-1 process and an i process, wherein i is an integer of 2 or more,

The upstream portion is located at a position in the i-1 th process and the downstream portion is located between the i-1 th process and the i-1 th process, or

The upstream portion and the downstream portion are respectively between the i-1 th processing position and the i-th processing position, or

The upstream portion is a position before the i-1 th process and the downstream portion is a position in the i-1 th process.

2. The method for producing an optical film according to claim 1, wherein,

In the conveying, an image of at least an end portion of the film is acquired by an imaging unit, and the width of the film is measured.

3. The method for producing an optical film according to claim 1, wherein,

In the conveying, the width of the film is measured based on the brightness of at least one of the reflected light reflected from the film by the light incident on the film and the transmitted light transmitted through the film.

4. The method for producing an optical film according to claim 1, wherein,

The film is transported by a transport roller,

The width of the film is measured by irradiating the film on the conveying roller with the light, and detecting an end portion of the film based on a difference between a brightness of the reflected light of the film generated by the irradiation of the light and a brightness of the reflected light of the conveying roller.

5. The method for producing an optical film according to claim 3, wherein,

The transmitted light is transmitted through the film by light incident on the film through a polarizing filter.

6. The method for producing an optical film according to claim 3, wherein,

The width of the film was measured based on the brightness of the light obtained by passing the transmitted light through the polarizing film.

7. The method for producing an optical film according to any one of claims 1 to 6, wherein,

The optical film is a polarizing film.

8. An optical film manufacturing apparatus includes:

n processing units for performing a process of imparting at least optical characteristics to the film, wherein N is an integer of 1 or more;

A conveying mechanism that conveys the film;

A plurality of width measuring devices which are arranged at a plurality of positions on the conveying mechanism and continuously measure the width of the film conveyed by the conveying mechanism at the plurality of positions; and

A calculating unit that calculates a rate of change in the width of the film based on a measurement result obtained at the same timing from among measurement results of an upstream-side width measuring device and measurement results of a downstream-side width measuring device among two width measuring devices selected from the plurality of width measuring devices,

The N processing units can continue manufacturing while adjusting manufacturing conditions so that the rate of change of the width of the film is within an allowable range,

The N treatment parts comprise at least one swelling treatment part, a dyeing treatment part, a crosslinking treatment part, a stretching treatment part and a drying treatment part,

The N processing units include an i-1 processing unit, an i processing unit, and an i+1 processing unit, where i is an integer of 2 or more,

The upstream width measuring device is disposed between the i-1 th processing unit and the i-th processing unit,

The downstream-side width measuring device is disposed between the i-th processing unit and the i+1-th processing unit;

Or alternatively, the first and second heat exchangers may be,

The N processing units include an i-1 processing unit and an i processing unit, wherein i is an integer of 2 or more,

The upstream side width measuring device is disposed at a position of the i-1 th processing section and the downstream side width measuring device is disposed between the i-1 th processing section and the i-th processing section, or

The upstream-side width measuring device and the downstream-side width measuring device are disposed between the i-1 th processing unit and the i-th processing unit, respectively, or

The upstream side width measuring device is disposed before the i-1 th processing section and the downstream side width measuring device is disposed at a position of the i-1 th processing section.

9. The apparatus for producing an optical film according to claim 8, wherein,

At least one of the plurality of width measuring devices has an imaging unit that images at least an end portion of the film.

10. The apparatus for producing an optical film according to claim 8, wherein,

At least one of the plurality of width measuring devices includes a light detecting unit for detecting at least one of reflected light reflected from the film by light incident on the film and transmitted light transmitted through the film.

11. The apparatus for producing an optical film according to any one of claims 8 to 10, wherein,

At least one of the plurality of width measuring devices has a light irradiation section that irradiates light to the film.

12. The apparatus for producing an optical film according to claim 11, wherein,

The conveying mechanism is provided with a conveying roller,

The light irradiation section irradiates light to the film on the conveying roller,

At least one width measuring device among the plurality of width measuring devices measures the width of the film based on a difference between the brightness of the reflected light of the film generated by the light irradiated from the light irradiation unit to the film on the conveying roller and the brightness of the reflected light of the conveying roller.

13. The apparatus for producing an optical film according to claim 11, wherein,

A polarizing filter is provided between the light irradiation section and the film.

14. The apparatus for producing an optical film according to claim 10, wherein,

A polarizing filter is provided between the light detection section and the film.