TWI739751B - Manufacturing method of polarizing film - Google Patents

Abstract

The present invention is a method for manufacturing a polarizing film, which includes: a width restriction step of contacting the above-mentioned polyvinyl alcohol resin film after contacting the treatment liquid with at least one free roller with a diameter of more than 150 mm to be restricted in the width direction; And a drying step is to dry the polyvinyl alcohol-based resin film after the width restriction step.

Description

Manufacturing method of polarizing film

The present invention relates to a method for manufacturing a polarizing film that can be used as a component of a polarizing plate.

Regarding the polarizing film, it was previously used for uniaxially stretched polyvinyl alcohol resin film to adsorb and align dichroic pigments such as iodine or dichroic dyes. The polarizing film is usually formed by bonding the protective film on one or both sides with an adhesive to make a polarizing plate, which is used in image display devices such as liquid crystal display devices such as LCD TVs, personal computer monitors, and mobile phones. In recent years, with the thinning of liquid crystal display devices, thinner polarizing films have been required.

Generally, the polarizing film is manufactured by applying various treatments such as swelling, dyeing, crosslinking, and stretching to a continuously conveyed long polyvinyl alcohol resin film in a bath, followed by washing treatment and drying (for example, (Refer to Japanese Patent Laid-Open No. 2009-48179).

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2009-48179

In order to perform the stretching treatment, the polyvinyl alcohol resin film used in the drying step shrinks in the width direction when the moisture is removed by the drying step, and the thickness tends to increase due to the shrinkage in the width direction, which cannot meet the requirements for thinning. Require.

In Patent Document 1, it is described that in the drying step, by making a polyvinyl alcohol-based resin The film is dried by contacting a plurality of heat rollers, and the shrinkage in the width direction in the drying step is suppressed, and a thin polarizing film is provided. However, when a polyvinyl alcohol-based resin film with a high water content is brought into contact with a heat roll and restrained in the width direction, there is a problem that the polyvinyl alcohol-based resin film is easily broken.

On the other hand, since the water content of the polyvinyl alcohol-based resin film is low to some extent, a method of suppressing the shrinkage in the width direction by performing a drying step is also considered. However, if this method is used, the polyvinyl alcohol-based resin film The friction between the resin film and the roller is reduced. Therefore, if the polyvinyl alcohol-based resin film is only brought into contact with the roller, the width direction cannot be sufficiently restrained, and the width direction must be mechanically fixed with a tenter cloth. The problem that the polyvinyl alcohol resin film is easily broken.

The object of the present invention is to provide a method for manufacturing a polarizing film, which can suppress the breakage of the polyvinyl alcohol-based resin film while suppressing the shrinkage in the width direction to produce a thin polarizing film with a small shrinkage force.

The present invention provides a method for manufacturing the polarizing film shown below.

[1] A method of manufacturing a polarizing film, comprising: a width restraint step of contacting at least one free roller with a diameter of 150 mm or more on the polyvinyl alcohol-based resin film after contacting the treatment liquid to restrain in the width direction; and The drying step is to dry the polyvinyl alcohol-based resin film after the width restriction step.

[2] The method for producing a polarizing film as described in [1], wherein in the width restriction step, the polyvinyl alcohol-based resin film is in contact with a plurality of rollers including the free roller, from the first roller to At least 40% of the time between when the last roller is released is in contact with any roller.

[3] The method for producing a polarizing film as described in [1] or [2], wherein the polyvinyl alcohol-based resin film is in contact with the above-mentioned width within 20 seconds after the end of contact with the above-mentioned treatment liquid. The first roller in the binding step.

[4] The method for producing a polarizing film as described in any one of [1] to [3], wherein the water content of the polyvinyl alcohol-based resin film at the point when it comes into contact with the first roll in the width restriction step is 30 weight %above.

According to the method of the present invention, the breakage of the polyvinyl alcohol-based resin film can be suppressed while the shrinkage in the width direction can be suppressed, and a thin polarizing film with a small shrinkage force can be produced.

10‧‧‧Material film containing polyvinyl alcohol resin

11‧‧‧Raw material sheet roll

13‧‧‧Swelling bath

15‧‧‧Dyeing bath

17‧‧‧Cross-linked bath

19‧‧‧Clean bath

21‧‧‧Drying furnace

23‧‧‧Polarizing Film

30‧‧‧Guide roller

31‧‧‧Guide roller

32‧‧‧Guide roller

33‧‧‧Guide roller

34‧‧‧Guide roller

35‧‧‧Guide roller

36‧‧‧Guide roller

37‧‧‧Guide roller

38‧‧‧Guide roller

39‧‧‧Guide roller

40‧‧‧Guide roller

41‧‧‧Guide roller

50‧‧‧nip roller

51‧‧‧Pinch roller

52‧‧‧Nip roller

53‧‧‧Pinch roller

54‧‧‧Pinch roller

60‧‧‧Guide roller

61‧‧‧Guide roller

70‧‧‧Width restraint

71‧‧‧Free Roll

72‧‧‧Free Roll

73‧‧‧Free Roll

74‧‧‧Hot air dryer

74a‧‧‧The components of hot air dryer

74b‧‧‧The components of the hot air dryer

75‧‧‧Hot air dryer

75a‧‧‧The components of hot air dryer

75b‧‧‧The components of the hot air dryer

76‧‧‧Hot air dryer

76a‧‧‧The components of hot air dryer

76b‧‧‧The components of hot air dryer

81‧‧‧Guide roller

82‧‧‧Nip roller

83‧‧‧Nip roller

90‧‧‧Drying furnace

711‧‧‧Free Roll

712‧‧‧Free Roll

713‧‧‧Free Roll

721‧‧‧Free Roll

722‧‧‧Free Roll

723‧‧‧Free Roll

731‧‧‧Free Roll

732‧‧‧Free Roll

733‧‧‧Free Roll

741‧‧‧Free Roll

P1‧‧‧Location

P2‧‧‧Location

P3‧‧‧Location

P4‧‧‧Location

FIG. 1 is a cross-sectional view schematically showing an example of the manufacturing method of the polarizing film of the present invention and the polarizing film manufacturing apparatus used therefor.

Fig. 2 is a cross-sectional view schematically showing an example of the roller structure in the width restricting portion.

Fig. 3 is a cross-sectional view schematically showing an example of the roller structure in the width restricting portion.

Fig. 4 is a cross-sectional view schematically showing an example of the roller structure in the width restricting portion.

Fig. 5 is a cross-sectional view schematically showing an example of the roller structure in the width restricting portion.

<Manufacturing method of polarizing film>

In the present invention, the polarizing film is a polyvinyl alcohol resin film that is uniaxially stretched to adsorb and align the dichroic dye (iodine or dichroic dye). The polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film is usually obtained by saponifying a polyvinyl acetate-based resin. The degree of saponification is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. Regarding polyvinyl acetate-based resins, for example, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, it may also be a copolymer of vinyl acetate and other monomers copolymerizable therewith. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

These polyvinyl alcohol resins can also be modified, for example, they can also be used: modified by aldehydes The polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc.

In the present invention, as the starting material for the production of the polarizing film, unstretched polyethylene having a thickness of 65 μm or less (for example, 60 μm or less), preferably 50 μm or less, more preferably 35 μm or less, and more preferably 30 μm or less is used Alcohol-based resin film (raw material film). Thereby, the polarizing film of the thin film with increasing market requirements can be obtained. Although the thinner the raw material film is, the more likely it is that the film breaks during the stretching process, but according to the present invention, even when the raw material film is thin, the film breakage can be effectively suppressed. The raw material film may be a polyvinyl alcohol-based resin film that has been stretched in the gas phase in advance.

The width of the raw film is not particularly limited. For example, it can be about 400 to 6000 mm. However, the larger the width of the film, the more likely it is to break the film during the stretching process.

In the present invention, the raw film is prepared as a roll (raw sheet roll) of a long unstretched polyvinyl alcohol-based resin film.

The polarizing film can be subjected to a processing step of unwinding the above-mentioned long raw film from the raw sheet reel and continuously transporting it along the film transport path of the polarizing film manufacturing device to make it contact with the processing liquid, and then implement the width restriction Step, after that, a drying step is performed to continuously manufacture a long polarizing film.

As the above-mentioned treatment steps, for example, it may include: a swelling treatment step, which is a step of immersing the raw film in a swelling bath and then pulling it out; a dyeing treatment step, which is a step of immersing the swelling treatment film in a dyeing bath and then pulling it out; and The linking treatment step involves immersing the dyed film in a crosslinking bath and then pulling it out. Moreover, between the series of processing steps (that is, before and after any one or more processing steps and/or during any one or more processing steps), uniaxial stretching processing is performed by wet or dry processing. If necessary, other processing steps can also be added. Each of the above-mentioned treatment steps may be the treatment of immersing the membrane in one bath, or the treatment of sequentially immersing the film in two or more baths.

The width restriction step is to make the polyvinyl alcohol resin film contacted with the treatment liquid in the treatment step contact at least one free roller with a diameter of 150 mm or more (hereinafter, also It is called "large diameter free roll") and the step of restraining in the width direction. The roller contacting the polyvinyl alcohol resin film in the width restriction step may also include one or more large-diameter free rollers, free rollers with a diameter of less than 150 mm, and driving rollers. In this specification, the contact of the polyvinyl alcohol-based resin film on the roll does not mean point contact but surface contact (the polyvinyl alcohol-based resin film has a width in the longitudinal direction and is in contact with a free roll). The surface contact constrains the polyvinyl alcohol-based resin film in the width direction.

Here, the so-called free roller refers to a roller without a drive mechanism such as a motor. By using a free roller as a mechanism for restraining the width direction of the polyvinyl alcohol-based resin film in contact with the treatment liquid as described above, the breakage of the polyvinyl alcohol-based resin film can be suppressed. In the present invention, by providing such a width restriction step, the polyvinyl alcohol-based resin film can be slowly dried in a state of being restricted in the width direction, without applying a large load to the polyvinyl alcohol-based resin film and suppressing The shrinkage in the width direction produces a thin polarizing film with a small shrinkage force.

As the above-mentioned drying step, a step of drying the polyvinyl alcohol-based resin film subjected to the width restriction step to obtain a polarizing film is a step of reducing the moisture content to less than 15% by weight, for example.

Hereinafter, referring to FIG. 1, the manufacturing method of the polarizing film of the present invention will be described in more detail. FIG. 1 is a cross-sectional view schematically showing an example of the manufacturing method of the polarizing film of the present invention and the polarizing film manufacturing apparatus used therefor. The polarizing film manufacturing apparatus shown in FIG. 1 is constructed as follows: A blank (unstretched) film 10 containing polyvinyl alcohol-based resin is continuously unwound by a raw sheet roll 11 on one side and transported along the film on the other side. It passes through the swelling bath 13, the dyeing bath 15, the cross-linking bath 17, and the cleaning bath 19 arranged on the film conveying path in sequence, then passes through the width restricting part 70, and finally passes through the drying oven 90. The obtained polarizing film can be directly transported, for example, to the next polarizing plate manufacturing step (a step of attaching a protective film to one or both sides of the polarizing film 23). The arrow in Figure 1 indicates the transport direction of the film.

Furthermore, although FIG. 1 shows an example in which a swelling bath 13, a dyeing bath 15, a cross-linking bath 17, and a cleaning bath 19 are separately provided in each tank, any more than one treatment can be performed as needed. Two baths (the baths that contain the polyvinyl alcohol-based resin film on the film transport path such as the swelling bath 13, the dye bath 15, the cross-linking bath 17, and the cleaning bath 19 are collectively referred to as the "treatment bath"). Above the slot.

The film transport path of the polarizing film manufacturing apparatus can be constructed by the above-mentioned treatment bath, width restraint 70 and drying oven 90, and also by the guide rollers 30 to 41, 60, 61, 81 and the nip rollers 50 to 54 , 82, 83 are arranged at suitable positions and constructed. Among them, the guide rollers 30~41, 60, 61, 81 can support the film being conveyed, or can change the film conveying direction; nip rollers 50~54, 82, 83 The conveyed film can be pressed and clamped to impart driving force by its rotation to the film, or the film conveying direction can be changed. Guide rollers or nip rollers can be arranged in each treatment bath, before and after the drying furnace, or in the treatment bath, whereby the film in the treatment bath can be introduced, dipped, and drawn from the treatment bath [refer to Figure 1]. For example, since one or more guide rollers are provided in each processing bath, the film can be immersed in each processing bath by conveying the film along the guide rollers.

The polarizing film manufacturing device shown in Figure 1 is equipped with nip rolls (nip rolls 50 to 54) before and after each treatment bath, so that the roll-to-roll extension can be implemented. The roll-to-roll extension is in any more than one treatment bath. A peripheral speed difference is applied between the nip rollers arranged in the front and rear to perform longitudinal uniaxial extension. Hereinafter, each step will be described.

(Steps for swelling treatment)

The swelling treatment step is performed for the removal of foreign matter on the surface of the raw film 10, the removal of the plasticizer in the raw film 10, the impartment of dyeability, and the plasticization of the raw film 10, etc. The processing conditions are determined in a range that can achieve the purpose and in a range that does not cause extreme dissolution or devitrification of the raw material film 10.

1, the swelling treatment step can be implemented as follows: while unwinding the raw film 10 using the raw sheet roll 11 continuously, while transporting the raw film 10 along the film transport path, and placing the raw film 10 in the swelling bath 13 Soak for a specific time, and then pull it out. In the example of FIG. 1, from unwinding the raw film 10 to immersing in the swelling bath 13, the raw film 10 can be guided along the path The film conveying path constructed by the rollers 60 and 61 and the nip roller 50 is conveyed. In the swelling process, the film is transported along the film transport path constructed by the guide rollers 30 to 32.

As the swelling liquid of the swelling bath 13, in addition to pure water, boric acid (Japanese Patent Laid-Open No. 10-153709), chloride (Japanese Patent Laid-Open No. 06-281816), inorganic acid, inorganic salt can also be used. , Water-soluble organic solvents, alcohols, etc. are added in the range of about 0.01-10% by weight to form an aqueous solution.

The temperature of the swelling bath 13 is, for example, about 10-50°C, preferably about 10-40°C, and more preferably about 15-30°C. The immersion time of the raw film 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. Moreover, when the raw material film 10 is a polyvinyl alcohol-based resin film stretched in gas in advance, the temperature of the swelling bath 13 is, for example, about 20 to 70°C, preferably about 30 to 60°C. The immersion time of the raw film 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

In the swelling treatment, the raw film 10 swells in the width direction and wrinkles are easily generated on the film. As a method for removing the wrinkles and transporting the film on the other side, it can be enumerated that the guide rollers 30, 31, and/or 32 use a widening roller such as a widening roller, a spiral roller, a middle-high roller, or a guide roller. Other expansion devices for cloth rolls, bending rolls, and stenter cloth clips. Another method to suppress the generation of wrinkles is to implement extension processing. For example, the difference in peripheral speed between the nip roll 50 and the nip roll 51 can be used to perform uniaxial stretching in the swelling bath 13.

In the swelling treatment, since the film swells and expands in the conveying direction of the film, when the film is not actively stretched, in order to eliminate the slack of the film in the conveying direction, for example, it is preferable to: 13 The speeds of the nip rollers 50 and 51 arranged before and after are controlled. In addition, in order to stabilize the transport of the film in the swelling bath 13, the water flow in the swelling bath 13 is controlled by an underwater sprinkler, or an EPC device (Edge Position Control) device: detects the end of the film to prevent Membrane meandering device) etc. are also useful.

In the example shown in Figure 1, the film drawn from the swelling bath 13 sequentially passes through the guide roller 32, the clamp The roller 51 is introduced into the dyeing bath 15.

(Dyeing processing steps)

The dyeing treatment step is performed for the purpose of adsorbing the dichroic dye on the polyvinyl alcohol resin film after the swelling treatment, and aligning it. The processing conditions are determined in the range that can achieve the purpose, and in the range that does not produce the extreme melting or devitrification of the film. 1, the dyeing treatment step can be implemented by the following method: transport along the film transport path constructed by the guide rollers 33 to 35 and the nip roller 51, the swelling process of the film in the dyeing bath 15 (contained in the dyeing Soak in the treatment solution of the tank for a specific time, and then pull it out. In order to improve the dyeability of dichroic pigments, the film used in the dyeing treatment step is preferably a film that has undergone at least a certain degree of uniaxial stretching treatment, or it is preferable to replace the uniaxial stretching treatment before the dyeing treatment, or to remove In addition to the uniaxial stretching treatment before the dyeing treatment, the uniaxial stretching treatment is performed during the dyeing treatment.

In the case of using iodine as a dichroic pigment, the dyeing solution of the dyeing bath 15 can be, for example, an aqueous solution whose concentration is iodine/potassium iodide/water=about 0.003~0.3/about 0.1~10/100 in terms of weight ratio. Instead of potassium iodide, other iodides such as zinc iodide can be used, or potassium iodide and other iodides can be used in combination. In addition, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc., may coexist. In the case of adding boric acid, in terms of containing iodine, it is distinguished from the following cross-linking treatment. As long as the aqueous solution contains about 0.003 parts by weight or more of iodine relative to 100 parts by weight of water, it can be regarded as dyeing bath 15. The temperature of the dyeing bath 15 when dipping the film is usually about 10~45°C, preferably 10~40°C, more preferably 20~35°C, and the immersion time of the film is usually about 30~600 seconds, preferably 60~ 300 seconds.

When a water-soluble dichroic dye is used as the dichroic pigment, the dyeing solution of the dyeing bath 15 can be an aqueous solution with a concentration of dichroic dye/water=about 0.001 to 0.1/100 in a weight ratio, for example. In this dyeing bath 15, a dyeing auxiliary agent etc. may coexist, for example, an inorganic salt, such as sodium sulfate, or a surfactant, etc. may be contained. Only one kind of dichroic dye may be used alone, or two or more dichroic dyes may be used in combination. The temperature of dyeing bath 15 when dipping the membrane For example, it is about 20 to 80°C, preferably 30 to 70°C, and the immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds.

As described above, in the dyeing treatment step, the film can be stretched uniaxially in the dyeing bath 15. The uniaxial stretching of the film can be performed by a method such as applying a peripheral speed difference between the nip roll 51 and the nip roll 52 arranged before and after the dyeing bath 15.

In the dyeing process, in order to remove the wrinkles of the film while conveying the polyvinyl alcohol resin film in the same way as the swelling process, the guide rolls 33, 34 and/or 35 can be used such as spreading rolls, spiral rolls, and medium-high rolls. Rolls with widening function, or other widening devices such as cloth guide rollers, bending rollers, and tenter cloth clips can be used. One method for suppressing the generation of wrinkles is to perform the stretching treatment in the same way as the swelling treatment.

In the example shown in FIG. 1, the film drawn from the dyeing bath 15 is introduced into the cross-linking bath 17 through the guide roller 35 and the nip roller 52 in this order.

(Cross-linking processing steps)

The cross-linking treatment step is a treatment performed for water resistance or hue adjustment (to prevent the film from resembling cyan, etc.) by cross-linking. 1, the cross-linking treatment can be implemented by the following way: along the film conveying path constructed by the guide rollers 36 to 38 and the nip roller 52, in the cross-linking bath 17 (the cross-linking liquid contained in the cross-linking tank In ), the dyed film is immersed for a specific time, and then pulled out.

The crosslinking liquid of the crosslinking bath 17 may be an aqueous solution containing, for example, about 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water. Regarding the cross-linking solution, when the dichroic dye used in the dyeing treatment is iodine, it is preferable to contain iodide in addition to boric acid, and the amount can be set to, for example, 1 to 100 parts by weight of water. 30 parts by weight. Examples of iodides include potassium iodide and zinc iodide. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc., may coexist.

In the cross-linking treatment, the concentration of boric acid and iodide and the temperature of the cross-linking bath 17 can be appropriately changed according to the purpose. For example, the purpose of cross-linking treatment is through the resistance of cross-linking For hydration, when the polyvinyl alcohol resin film is sequentially subjected to swelling treatment, dyeing treatment and cross-linking treatment, the cross-linking agent-containing liquid of the cross-linking bath can be boric acid/iodide/ in weight ratio. Water = 3~10/1~20/100 aqueous solution. If necessary, other crosslinking agents such as glyoxal or glutaraldehyde may be used instead of boric acid, and boric acid and other crosslinking agents may also be used in combination. The temperature of the cross-linking bath when dipping the film is usually about 50-70°C, preferably 53-65°C, and the immersion time of the film is usually about 10-600 seconds, preferably 20-300 seconds, and more preferably 20- 200 seconds. In addition, when the polyvinyl alcohol resin film stretched before the swelling treatment is sequentially dyed and cross-linked, the temperature of the cross-linking bath 17 is usually about 50 to 85°C, preferably 55 to 80 ℃.

In the cross-linking treatment for the purpose of hue adjustment, for example, when iodine is used as a dichroic pigment, the concentration can be used in a weight ratio of boric acid/iodide/water = 1~5/3~30/100 Liquid containing crosslinking agent. The temperature of the cross-linking bath when immersing the film is usually about 10 to 45°C, and the immersion time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

The cross-linking treatment can also be carried out multiple times, usually 2 to 5 times. In this case, the composition and temperature of each crosslinking bath used may be the same or different as long as they are within the above-mentioned range. The cross-linking treatment for water resistance by cross-linking and the cross-linking treatment for hue adjustment can also be performed in a plurality of steps, respectively.

It is also possible to perform uniaxial stretching treatment in the cross-linking bath 17 by using the difference in peripheral speed between the nip roll 52 and the nip roll 53.

In the cross-linking treatment, in order to remove the wrinkles of the film while conveying the polyvinyl alcohol resin film in the same way as the swelling treatment, the guide rollers 36, 37, and/or 38 can be used such as spreading rollers, spiral rollers, and medium-high rollers. Rolls with widening function, or use other widening devices such as cloth guide rollers, bending rollers, and tenter cloth clips. Another method for suppressing the generation of wrinkles is to perform the stretching treatment in the same way as the swelling treatment.

In the example shown in FIG. 1, the film drawn from the cross-linking bath 17 is introduced into the film cleaning bath 19 through the guide roller 38 and the nip roller 53 in this order.

(Cleaning process steps)

The manufacturing method of the present invention may include a cleaning treatment step after the cross-linking treatment step. The cleaning treatment is performed to remove excess agents such as boric acid or iodine adhering to the polyvinyl alcohol-based resin film. The cleaning treatment can be performed by, for example, immersing the crosslinked polyvinyl alcohol-based resin film in the film cleaning bath 19, or spraying the film as a shower with a film cleaning solution, or using these in combination.

FIG. 1 shows an example of a case where a polyvinyl alcohol-based resin film is immersed in a cleaning bath 19 to perform cleaning treatment. The temperature of the membrane cleaning bath 19 in the membrane cleaning process is usually about 2~40℃, and the immersion time of the membrane is usually about 2~120 seconds.

Furthermore, in the cleaning process, in order to remove wrinkles and transport the polyvinyl alcohol resin film at the same time, the guide rollers 39, 40, and/or 41 can be used such as widening rollers, spiral rollers, and medium-high rollers with widening function. Roller, or other spreading devices such as cloth guide roller, bending roller, and stenter clip can be used. In addition, in order to suppress the generation of wrinkles in the film cleaning treatment, stretching treatment may be performed.

(Extended processing steps)

As described above, the raw film 10 is between the above-mentioned series of processing steps (that is, before and after any one or more processing steps and/or during any one or more processing steps), uniaxially performed by wet or dry processing. Extension processing. The specific method of uniaxial stretching treatment can be, for example, between the rollers for longitudinal uniaxial stretching by applying a circumferential speed difference between two nip rollers (for example, two nip rollers arranged before and after the treatment bath) constituting the film conveying path Stretching, such as hot roll stretching and tenter stretching described in Patent No. 2731813, is preferably stretch between rolls. The uniaxial stretching treatment step can be carried out multiple times from the raw film 10 to the polarizing film 23 being obtained. As mentioned above, the stretching treatment is also beneficial to suppress the generation of wrinkles in the film.

The final cumulative extension ratio of the polarizing film 23 based on the raw film 10 is usually about 4.5 to 7 times, preferably 5 to 6.5 times.

As long as the extension processing step is before the width constraint step, any of the above can also be used When two or more processing steps are used to perform the extension processing, the extension processing can also be performed using any one processing step.

(Width constraint step)

After the cleaning treatment step, the polyvinyl alcohol-based resin film is brought into contact with at least one large-diameter free roller with a diameter of 150 mm or more to restrain the width direction width restraint step.

In the width restraint step, the polyvinyl alcohol-based resin film does not need to be in constant contact with the roller, but from the viewpoint of effective width restraint, it is preferably 0.5 seconds or more, and more preferably 2 seconds or more The continuous contact time. The present invention includes at least one large-diameter free roller with a diameter of 150 mm or more as the roller used in the width restriction step. With the large-diameter free roller, it becomes easy to ensure the continuous contact time as described above. The diameter of the large-diameter free roller is preferably 200 mm or more, and more preferably 300 mm or more. The diameter of the large-diameter free roller is preferably less than 450 mm. When the diameter is 450 mm or more, a load is applied to the polyvinyl alcohol-based resin film due to free roll rotation resistance, and the polyvinyl alcohol-based resin film may be easily broken. In the width restriction step, it is preferable to include two or more large-diameter free rollers.

The rollers used in the width restraint step can adjust the conveying direction of the polyvinyl alcohol-based resin film and can be forcedly curled, preferably including a plurality of the above-mentioned large-diameter free rollers, and more preferably 3 or more and 5 Below. In the case of using a plurality of rollers, the polyvinyl alcohol-based resin film is preferably in contact with any roller for at least 40% of the time between the contact with the first roller and the release of the last roller in the width restriction step. By making the time of contact with the roller more than 40%, a sufficient width restraint effect can be obtained. The time of contact with the roller is more preferably 70% or more. The time of contact with the rollers can be adjusted by the number of rollers, the position of the rollers, and the surrounding angle of each roller. In addition, from the viewpoint of effective width restriction, the continuous time during which the polyvinyl alcohol-based resin film does not contact the roll is preferably 2 seconds or less.

Furthermore, in this manual, the first roller will be contacted in the width restriction step. The point is used as the lead-in point of the width constraint step, and the point released from the last roller is the lead-out point of the self-width constraint step. When there is one roller used in the width restriction step, the first roller and the last roller become the same roller. The time from the beginning to the end of the width restriction step is preferably more than 5 seconds. Furthermore, the time from the beginning to the end of the width restriction step is preferably less than 60 seconds. In the case of more than 60 seconds, the drying of the polyvinyl alcohol-based resin film in the width restriction step will proceed more than necessary, and the polyvinyl alcohol-based resin film may be broken in the subsequent drying step.

In the width restraint step, the polyvinyl alcohol-based resin film can be slowly dried in a state restrained in the width direction, without applying a large load to the polyvinyl alcohol-based resin film, suppressing the shrinkage in the width direction, and manufacturing thin and shrinking Polarizing film with less power. In order to control the drying state in the width restriction step, for example, a method of drying with a hot air dryer, an infrared heater, or a combination of these is preferable. In the width restriction step, the maximum temperature reached by the polyvinyl alcohol-based resin film is, for example, 30-100°C, preferably 50-80°C.

In FIG. 1, the width restriction step is implemented in the width restriction portion 70. In the width restricting portion 70 shown in FIG. 1, there are provided three free rollers 71, 72, 73, and hot air dryers 74, 75, 76 arranged to face each other by the rollers 71, 72, 73. . Each hot air dryer 74, 75, 76 has the following components: components 74a, 75a, 76a, which are outlets for sending hot air from the upstream side to the downstream direction are arranged on the line in the width direction; and components 74b, 75b , 76b, which is the outlet for sending out hot air from the downstream side to the upstream direction and is arranged on the line in the width direction. The hot air sent from the hot air dryers 74, 75, 76 blows the polyvinyl alcohol resin film contacting the opposite free rollers 71, 72, 73 to suppress the drying of the polyvinyl alcohol resin film in the width restriction step state. The three free rollers 71, 72, and 73 are all large-diameter free rollers. In the width restricting portion 70 shown in FIG. 1, the point where the polyvinyl alcohol-based resin film contacts the free roller 71 is the lead-in point of the width restricting step, and the point released by the free roller 73 is the leading-out point of the width restricting step.

The configuration of the rollers in the width restricting portion 70 is not limited to the configuration shown in FIG. 1. In Figure 2~ In FIG. 5, another form in the width restricting portion 70 is schematically shown. In FIGS. 2 to 5, the conveying path of the polyvinyl alcohol-based resin film 10 in the width restriction step is represented by a solid line, and the conveying path of the polyvinyl alcohol resin film 10 before and after the width restriction step is represented by a broken line. The conveying direction is indicated by an arrow. In addition, as in FIG. 1, the guide roller immediately before the introduction of the width restraint step is referred to as the guide roller 54, and the guide roller immediately after the exit from the width restraint step is referred to as the guide roller 81. Although the conveying direction of the polyvinyl alcohol-based resin film before and after the width restraining step and the width restraining step are not necessarily the same as the example shown in FIG. 1, the conveying direction can be appropriately adjusted by using a guide roller or the like.

In the example shown in FIG. 2, three free rollers 711, 712, and 713 with a diameter of 300 mm are arranged. After the polyvinyl alcohol-based resin film comes into contact with the free roller 711 at P11 and is introduced into the width restriction step, it is released by the free roller 711 at P12. After that, it contacts the next free roller 712 at P13, and is released by the free roller 712 at P14. In addition, it contacts the last free roller 713 at P15, is released by the free roller 713 at P16, and is derived from the width restriction step. In the example shown in Figure 2, if the transport speed of the film is set to 10m/min, the time required for transport between locations becomes 2.83 seconds for P11~P12, 1.8 seconds for P12~P13, and P13~P14 It is 2.83 seconds, P14~P15 is 1.8 seconds, P15~P16 is 2.83 seconds, respectively, the rollers 711, 712, 713 and the front and rear guide rollers are arranged. In this case, the time required for the width restriction step was 12.09 seconds, and the time for the polyvinyl alcohol-based resin film to contact the roller was 8.49 seconds. Therefore, 70% of the time of the width restriction step is in contact with any roller.

In the example shown in FIG. 3, three free rollers 721, 722, and 723 with a diameter of 150 mm are arranged. After the polyvinyl alcohol-based resin film comes into contact with the free roller 721 at P21 and is introduced into the width restriction step, it is released by the free roller 721 at P22. After that, it contacts the next free roller 722 at P23, and is released by the free roller 722 at P24. In addition, it contacts the last free roller 723 at P25, is released by the free roller 723 at P26, and is derived from the width restriction step. In the example shown in Figure 3, if the transport speed of the film is set to 10m/min, the time required for transport between locations becomes 0.9 seconds for P21~P22, 1.59 seconds for P22~P23, and P23~P24 for 0.38 seconds, P24~P25 is 1.59 seconds, P25~P26 is 0.9 seconds, respectively, the rollers 731, 732, 733 and the front and rear guide rollers are arranged. In this case, the time required for the width restriction step was 5.36 seconds, and the time for the polyvinyl alcohol-based resin film to contact the roller was 2.18 seconds. Therefore, 41% of the time of the width restriction step is in contact with any roller.

In the example shown in FIG. 4, two free rollers 731 and 733 with a diameter of 120 mm and a free roller 732 with a diameter of 450 mm are arranged. After the polyvinyl alcohol-based resin film comes into contact with the free roller 731 at P31 and is introduced into the width restriction step, it is released by the free roller 731 at P32. After that, it contacts the next free roller 732 at P33, and is released by the free roller 732 at P34. In addition, at P35, it touches the last free roller 733, at P36, it is released by the free roller 733, and is derived from the width restriction step. In the example shown in Figure 4, if the transport speed of the film is set to 10m/min, the time required for transport between locations becomes 0.85 seconds for P31~P32, 0.88 seconds for P32~P33, and 0.88 seconds for P33~P34. It is 6.36 seconds, P34~P35 is 0.88 seconds, P35~P36 is 0.85 seconds. In this case, the time required for the width restraint step was 9.82 seconds, and the time during which the polyvinyl alcohol-based resin film was in contact with the roller was 8.06 seconds. Therefore, 82% of the time of the width restriction step is in contact with any roller.

In the example shown in Fig. 5, a free roller 741 with a diameter of 550 mm is arranged. After the polyvinyl alcohol-based resin film comes into contact with the free roller 741 at P41 and is introduced into the width restriction step, it is released by the free roller 741 at P42 and is led out from the width restriction step. In the example shown in Figure 5, if the transport speed of the film is set to 10m/min, the free roller 741 and the front and back guide rollers are arranged so that the time required for transport between locations becomes 5.18 seconds for P41~P42 . In this case, in the total time of 5.18 seconds as the time shown in the width restraint step, that is, 100% of the time of the width restraint step, contact the roll of the polyvinyl alcohol-based resin film.

The width restriction step is preferably performed immediately after the treatment step of contacting the polyvinyl alcohol-based resin film with the treatment liquid and treating it. In the example of FIG. 1, the step immediately before the width restriction step is a cleaning step, and the treatment liquid is a cleaning treatment liquid. Width constraint step The treatment liquid that contacts the polyvinyl alcohol resin film before the step can be the dyeing treatment liquid in the dyeing treatment step, the cross-linking treatment liquid in the cross-linking treatment step, or the treatment of the following other treatments (complementary color treatment or zinc treatment) liquid. The method of contacting the treatment liquid for the polyvinyl alcohol resin film is to use the previously known methods such as immersion in the treatment bath, blowing of the treatment liquid by a water jet, and coating of the treatment liquid.

The polyvinyl alcohol-based resin film is preferably introduced into the width restraint step within 20 seconds after the contact with the treatment liquid in the step immediately before the width restraint step. In the case of more than 20 seconds, the time for the polyvinyl alcohol-based resin film to slowly dry without the width restriction increases, and the width restriction effect may not be fully expressed. In addition, the time when the contact with the treatment liquid in the immediately preceding step is completed refers to the time when it is pulled out from the cleaning bath 19 in the case of the example shown in FIG. 1.

In addition, the water content of the polyvinyl alcohol-based resin film at the time of introduction to the width restriction step is preferably 30% by weight or more. When the water content of the polyvinyl alcohol-based resin film is less than 30% by weight, the width restraint effect may not be sufficiently expressed. Furthermore, in the device shown in FIG. 1, the moisture content at the time of introduction to the width restriction step can be regarded as the same as the moisture content at the position P1 immediately before the introduction to the width restriction portion 70.

In the width restriction step, the maximum temperature reached by the polyvinyl alcohol-based resin film is, for example, 30-100°C, preferably 50-80°C.

(Drying step)

After the width restriction step, a drying step of applying a drying treatment to the polyvinyl alcohol-based resin film is performed. The drying step is a step to further reduce the moisture content of the polyvinyl alcohol-based resin film, for example, a step to reduce the moisture content from 15% by weight or more and less than 30% by weight to less than 15% by weight. The method of drying treatment can be exemplified, for example, a hot air dryer, an infrared heater, or a method of drying by using these in combination.

In the drying step, the maximum temperature reached by the polyvinyl alcohol resin film is, for example, 30-100°C, preferably 50-90°C. The time of the drying step is, for example, 60~600 seconds, preferably 120~600 seconds. By having the width restriction step and the drying step as described above, it is possible to produce a thin polarizing film with a desired moisture content while suppressing the breakage of the polyvinyl alcohol-based resin film while efficiently producing it. The thickness of the polarizing film 23 obtained by the above method is, for example, about 5 to 30 μm, and the shrinkage force measured by the following method is, for example, less than 2.70 N.

(Other processing steps for polyvinyl alcohol resin film)

Processing other than the above-mentioned processing can also be added. Examples of additional treatments include: immersion treatment in a boric acid-free iodide aqueous solution (complementary color treatment) after the cross-linking treatment step, and immersion treatment in a boric acid-free aqueous solution containing zinc chloride, etc. ( Zinc treatment).

<Polarizer>

A polarizing plate can be obtained by attaching a protective film to at least one side of the polarizing film manufactured in the above manner through an adhesive. As the protective film, for example, a film containing acetyl cellulose resin such as triacetyl cellulose or diacetyl cellulose; containing such as polyethylene terephthalate, polyethylene naphthalate and Polybutylene terephthalate polyester resin film; polycarbonate resin film, cycloolefin resin film; acrylic resin film; chain olefin resin film containing polypropylene resin.

In order to improve the adhesion between the polarizing film and the protective film, corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. can also be applied to the bonding surface of the polarizing film and/or protective film. deal with. Examples of the adhesive used for bonding the polarizing film and the protective film include: an active energy ray curable adhesive such as an ultraviolet curable adhesive, or an aqueous solution of a polyvinyl alcohol-based resin, or a crosslinking agent blended therein The aqueous solution, such as the water-based adhesive of the urethane-based latex adhesive. The ultraviolet curing adhesive may be a mixture of an acrylic compound and a photo-radical polymerization initiator, or a mixture of an epoxy compound and a photo-cationic polymerization initiator, or the like. In addition, a cationic polymerizable epoxy compound and a radical polymerizable acrylic compound can be used together, and a photocationic polymerization initiator and a light A radical polymerization initiator is used as the initiator.

[Example]

Hereinafter, examples are given to illustrate the present invention more specifically, but the present invention is not limited by these examples. In addition, in the following examples, the film thickness and shrinkage force are measured by the following methods.

[Measurement of film thickness]

The film thickness of the polarizing film was measured with a contact film thickness meter (trade name "DIGIMICRO MH-15M" manufactured by Nikon Co., Ltd.). In addition, the film thickness of the polarizing film was measured at 15 points at different positions in the width direction, and the average value was calculated. The average value is shown in Table 1.

[Measurement of contractility]

The evaluation sample with a width of 2 mm and a length of 50 mm was cut out with a super cutter (manufactured by Ogino Seiki Seisakusho Co., Ltd.) so that the absorption axis direction (extending direction) of the polarizing film became the long axis. The shrinkage force of the obtained short strip-shaped evaluation sample was measured using a thermomechanical analysis device (manufactured by SII NanoTechnology Co., Ltd., model TMA/6100). The measurement is set as follows: carry out in a fixed size mode (set the distance between the chucks to 10mm), place the test piece in a room at 20°C for a sufficient period of time, and set the temperature in the sample room from 20°C The temperature is increased to 80°C in 1 minute, and the temperature in the sample room is maintained at 80°C after the temperature rises. After the temperature was raised and left for 4 hours, the shrinkage force in the longitudinal direction of the test piece was measured in an environment of 80°C. In this measurement, the static load is set to 0 mN, and the jig is a probe made of SUS (Steel Use Stainless).

<Example 1>

The polarizing film was manufactured using the same apparatus as the polarizing film manufacturing apparatus shown in FIG. 1. As the free rollers 71, 72, and 73 arranged in the width restricting portion 70, those having a diameter of 300 mm are used. In addition, in the drying oven 90, three hot air dryers No. 1 to No. 3 were used for drying.

(1) Swelling treatment steps

The 30μm thick polyvinyl alcohol film [trade name "Kuraray Polyvinyl Alcohol Film VF-PE#3000" manufactured by Kuraray Co., Ltd., polymerization degree 2400, saponification degree of 99.9 mol% or more] is continuously transported, and the dry method is used on the other side. The uniaxial extension is about 4 times. While the obtained stretched polyvinyl alcohol film is continuously unwound by the raw sheet roll 11, it is transported, and it is placed in a swelling bath 13 with 40°C pure water, and the stretched film is kept stretched so as not to relax the film. Immerse for 60 seconds while in the state.

(2) Dyeing process steps

Then, the film passed through the nip roller 51 was immersed in a dyeing bath 15 at 28°C with an iodine/potassium iodide/water (weight ratio) of 0.1/5/100 for 60 seconds.

(3) Cross-linking treatment steps

Then, in order to implement cross-linking treatment for water resistance, the film passing through the nip roller 52 is placed on Potassium iodide/boric acid/water (weight ratio) is 10.5/7.5/100 and immersed in the first cross-linking bath 17 at 68℃ 300 seconds.

(4) Cleaning treatment steps

The film after the second cross-linking treatment was immersed in a clean bath 19 containing pure water at 5°C.

(5) Width constraint step

Then, the film after the cleaning process is passed through the width restricting portion 70. The temperature of the hot air blown from the three hot air dryers 74 to 76 in the width restriction part 70 is set as shown in Table 1. In addition, the moisture content of the film immediately before (position P1) being introduced into the width restraining portion 70 was measured with a moisture content meter (product name: moisture meter IRMA1100, manufactured by CHINO Co., Ltd.). The results are shown in Table 1. The time from when the film is taken out from the cleaning bath 19 to when it comes into contact with the free roller 71 is 12 seconds. In addition, the time from when the film is in contact with the first free roller 71 to the release of the last free roller 73 in the width restricting portion 70 (the time of the width restricting step), and between the free roller 71 and the free roller 72, and between the free roller 72 and the free roller 72 are measured. The non-contact time between the free rollers 73. The time of the width restriction step is 8.1 seconds, the continuous time of the film not contacting the free rollers is less than 2 seconds, and the time of the film contacting the free rollers 71, 72, 73 is 78% relative to the time required for the width restriction step.

(6) Drying step

The film after passing through the width restricting portion 70 is passed through a drying oven 90 to produce a polarizing film. Set the temperature of the hot air sent from the 3 hot air dryers No. 1 to No. 3 in the drying oven 90 as shown in Table 1. In addition, the moisture content of the film immediately before being introduced into the drying furnace 90 (position P3) and immediately after being exported from the drying furnace 90 (position P4) is used with a moisture content meter (product name: moisture meter IRMA110, manufactured by CHINO Co., Ltd.) And make the measurement. The results are shown in Table 1.

<Example 2>

The temperature of the hot air sent from the three hot air dryers 74 to 76 in the width restricting part 70 was set as shown in Table 1. Except for this, a polarizing film was produced in the same manner as in Example 1. In the same manner as in Example 1, the moisture content of the film was measured immediately before introduction into the width restricting portion 70 (position P1), immediately before introduction into the drying furnace 90 (position P3), and immediately after being led out from the drying furnace 90 (position P4). The results are shown in Table 1.

<Example 3>

The temperature of the hot air sent from the 3 hot air dryers No.1~No.3 in the drying oven 90 in the drying step was set as shown in Table 1, except for this, the polarized light was produced in the same manner as in Example 1. membrane. In the same manner as in Example 1, the moisture content of the film immediately before introduction into the width restriction step 70 (position P1), immediately before introduction into the drying furnace 90 (position P3), and immediately after being exported from the drying furnace 90 (position P4) was measured. The results are shown in Table 1.

<Example 4>

The temperature of the hot air sent from the three hot air dryers 74~76 in the width restriction part 70, and the temperature of the hot air sent from the 3 hot air dryers No.1~No.3 in the drying oven 90 in the drying step As shown in Table 1, except for this, a polarizing film was produced in the same manner as in Example 1. In the same manner as in Example 1, the moisture content of the film immediately before introduction into the width restriction step 7 (position P1), immediately before introduction into the drying furnace (position P3), and immediately after being exported from the drying furnace 90 (position P4) was measured. The results are shown in Table 1.

<Example 5>

In the structure in the width restriction part 70, the free roller 72 and the hot air dryer 75 opposite to it are not provided, and the temperature of the hot air sent from the remaining two hot air dryers 74 and 76 is set as shown in Table 1. Except for this, a polarizing film was produced in the same manner as in Example 1. In the same manner as in Example 1, the moisture content of the film was measured immediately before introduction into the width restricting portion 70 (position P1), immediately before introduction into the drying furnace 90 (position P3), and immediately after being led out from the drying furnace 90 (position P4). The results are shown in Table 1. Furthermore, the time between the inner film contacting the first free roller 71 in the width constraining portion 70 and the release of the last free roller 73 (the time of the width constraining step) and the non-contact between the free roller 71 and the free roller 73 are measured. time. The time for the width restriction step is 6.2 seconds, the continuous time that the film does not contact the free rollers is less than 2 seconds, and the time for the film to contact the free rollers 71 and 73 is 44% relative to the time required for the width restriction step.

<Example 6>

The three hot-air dryers 74 to 76 in the width restriction part 70 were not used, except that the polarizing film was produced in the same manner as in Example 1. In the same manner as in Example 1, the moisture content of the film was measured immediately before introduction into the width restricting portion 70 (position P1), immediately before introduction into the drying furnace 90 (position P3), and immediately after being led out from the drying furnace 90 (position P4). The results are shown in Table 1.

<Example 7>

The three hot air dryers 74~76 in the width restriction section 70 are not used, and the temperature of the hot air sent from the three hot air dryers No.1~No.3 in the drying oven 90 in the drying step is set as shown in the table. As shown in 1, except for this, a polarizing film was produced in the same manner as in Example 1. In the same manner as in Example 1, the moisture content of the film was measured immediately before introduction into the width restricting portion 70 (position P1), immediately before introduction into the drying furnace 90 (position P3), and immediately after being led out from the drying furnace 90 (position P4). The results are shown in Table 1.

<Comparative Example 1>

A polarizing film was produced in the same manner as in Example 1 except that the width restriction step was not performed (the width restriction portion 70 was not passed). In the same manner as in Example 1, the film immediately before being introduced into the main drying oven 90 (position P3) and immediately after being exported from the main drying oven 90 (position P4) was measured. The moisture content. The results are shown in Table 1.

10‧‧‧Material film containing polyvinyl alcohol resin

11‧‧‧Raw material sheet roll

13‧‧‧Swelling bath

15‧‧‧Dyeing bath

17‧‧‧Cross-linked bath

19‧‧‧Clean bath

23‧‧‧Polarizing Film

30‧‧‧Guide roller

31‧‧‧Guide roller

32‧‧‧Guide roller

33‧‧‧Guide roller

34‧‧‧Guide roller

35‧‧‧Guide roller

36‧‧‧Guide roller

37‧‧‧Guide roller

38‧‧‧Guide roller

39‧‧‧Guide roller

40‧‧‧Guide roller

41‧‧‧Guide roller

50‧‧‧nip roller

51‧‧‧Pinch roller

52‧‧‧Nip roller

53‧‧‧Pinch roller

54‧‧‧Pinch roller

60‧‧‧Guide roller

61‧‧‧Guide roller

70‧‧‧Width restraint

71‧‧‧Free Roll

72‧‧‧Free Roll

73‧‧‧Free Roll

74‧‧‧Hot air dryer

74a‧‧‧The components of hot air dryer

74b‧‧‧The components of the hot air dryer

75‧‧‧Hot air dryer

75a‧‧‧The components of hot air dryer

75b‧‧‧The components of the hot air dryer

76‧‧‧Hot air dryer

76a‧‧‧The components of hot air dryer

76b‧‧‧The components of hot air dryer

81‧‧‧Guide roller

82‧‧‧Nip roller

83‧‧‧Nip roller

90‧‧‧Drying furnace

P1‧‧‧Location

P2‧‧‧Location

P3‧‧‧Location

P4‧‧‧Location

Claims (4)

A method for manufacturing a polarizing film, comprising: a width restriction step, which is to make a polyvinyl alcohol resin film contacted with a treatment liquid contact at least one free roller with a diameter of 150 mm or more to restrict in the width direction; and a drying step, After the width restriction step, the polyvinyl alcohol-based resin film is dried, and the water content of the polyvinyl alcohol-based resin film after the drying step is 11% by weight or less. The method for manufacturing a polarizing film according to claim 1, wherein in the width restriction step, the polyvinyl alcohol-based resin film is in contact with a plurality of rollers including the free rollers, from contacting the first roller to releasing from the last roller At least 40% of the time is in contact with any roller. The method for producing a polarizing film according to claim 1 or 2, wherein the polyvinyl alcohol-based resin film is in contact with the first roller in the width restriction step within 20 seconds after the contact with the treatment liquid ends. The method for producing a polarizing film according to claim 1 or 2, wherein the water content of the polyvinyl alcohol-based resin film at the time when the polyvinyl alcohol-based resin film contacts the first roller in the width restriction step is 30% by weight or more.

Images