JP2013186367A - Method for manufacturing polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a thin-wall polarizing plate with favorable external appearance.SOLUTION: The method includes for manufacturing a thin-wall polarizing plate 4 with the thickness of 105 μm or less by bonding protective films 2a and 2b on one face or both faces of a polarizing film 1 via adhesive and drying them. Pinch rolls 6 for clamping both-side ends of the polarizing plate 4 are installed, as widening rolls, near at least an inlet part in a drying furnace 5 through which the polarizing plate 4 obtained by bonding the polarizing film 1 and the protective films 2a and 2b passes. Therefore, when drying the polarizing plate 4, the polarizing plate is widened by the pinch rolls 6.

Description

  The present invention relates to a method for producing a thin polarizing plate in which a protective film is bonded to one side or both sides of a polarizing film.

  A polarizing plate is widely used as a polarized light supplying element and a polarized light detecting element in a liquid crystal display device. As such a polarizing plate, one having a protective film bonded to both sides of a polarizing film is generally used. However, in recent years, liquid crystal display devices have been developed for mobile devices such as notebook personal computers and mobile phones. Is required to be thinner and lighter with the development of large-screen TVs. For this reason, various attempts have been made to reduce the thickness of the polarizing plate by bonding a protective film to only one surface of the polarizing film or using a thin protective film (see, for example, Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 2007-292287 JP 2009-181042 A

  However, the thin polarizing plate dried in a drying furnace by bonding a protective film only to one surface of the polarizing film has wavy wrinkles and the like, and has a problem in appearance. In particular, this problem was remarkable in a thin polarizing plate having a thickness of 105 μm or less.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method of manufacturing a thin polarizing plate having a good appearance without wavy wrinkles or the like.

As a result of intensive studies to solve the above-described problems, the present inventors have found a solution means having the following configuration and have completed the present invention.
(1) A method of manufacturing a thin polarizing plate having a thickness of 105 μm or less by bonding a protective film to one or both sides of a polarizing film via an adhesive and drying the polarizing film, the polarizing film and the protective film A method for producing a thin polarizing plate, wherein the polarizing plate obtained by laminating is dried with a widening roll when the polarizing plate is dried.
(2) The said widening roll is a manufacturing method of the polarizing plate as described in said (1) installed in the at least entrance part vicinity in the drying furnace through which the said polarizing plate passes.
(3) The said widening roll is a manufacturing method of the polarizing plate as described in said (1) or (2) with which two or more said widening rolls are installed along the conveyance path of a polarizing plate in the drying furnace through which the said polarizing plate passes.
(4) The widening roll is a pinch roll that sandwiches a side end portion of the polarizing plate, and the pinch roll is installed at both side end portions in the width direction of the conveyance path of the polarizing plate. The manufacturing method of the polarizing plate in any one of-(3).
(5) The widening roll is a curved roll (1) to (3) in which a central portion in the width direction orthogonal to the conveyance direction of the polarizing plate is higher than both side end portions in the width direction. The manufacturing method of the polarizing plate in any one of.

  According to the present invention, when a thin polarizing plate in which a protective film is bonded to one or both sides of a polarizing film is dried, the polarizing plate is widened with a widening roll, so that the appearance is not larger than 105 μm. Can be obtained.

It is the schematic which shows the drying furnace in one Embodiment of this invention which used the pinch roll as a widening roll. (A) is a perspective view between the adjacent guide rolls in embodiment shown in FIG. 1, (b) is a top view for demonstrating the installation angle of the pinch roll shown to (a). It is the perspective view which showed the other example of the widening roll used suitably for the manufacturing method of this invention.

Hereinafter, an embodiment of the production method of the present invention will be described with reference to FIGS.
FIG. 1 is a schematic view showing a drying furnace in an embodiment of the present invention using a pinch roll 6 as a widening roll, and FIG. 2 (a) is a view between adjacent guide rolls 7 and 7 in the embodiment. FIG. 2B is a plan view for explaining the installation angle of the pinch roll 6.

  In the embodiment shown in FIG. 1, a polarizing plate 4 is obtained by laminating and integrating a first protective film 2 a and a second protective film 2 b with a nip roll 3 on both surfaces of a polarizing film 1. Then, it is conveyed into the drying furnace 5. In the drying furnace 5, the polarizing plate 4 is conveyed by the guide roll 7 while being widened by the pinch roll 6. Thus, the dried polarizing plate 4 is obtained by passing through the drying furnace 5.

(Polarizing film 1)
The polarizing film 1 is a polarizing film made of a polyvinyl alcohol resin. The polyvinyl alcohol-based resin is usually obtained by saponifying a polyvinyl acetate-based resin. The saponification degree of the polyvinyl alcohol-based resin is usually about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% to 100 mol%. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. Specific examples of the copolymer of vinyl acetate and other monomers copolymerizable therewith include ethylene-vinyl acetate copolymer. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1000 to 10000, preferably about 1500 to 5000.

  The polyvinyl alcohol resin may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like modified with aldehydes may be used. Usually, an unstretched polyvinyl alcohol-based resin film having a thickness of about 20 μm to 100 μm, preferably about 30 μm to 80 μm is used as a starting material in the production of a polarizing film. Industrially, the width of the film is practically about 1500 mm to 4000 mm, but is not limited thereto. This unstretched film is processed in the order of swelling treatment, dyeing treatment, boric acid treatment, and water washing treatment, then subjected to boric acid treatment or uniaxial stretching in the previous step, and finally dried to obtain a polyvinyl alcohol polarizing film. The thickness of is, for example, about 1 μm to 40 μm.

  The method for producing the polarizing film 1 is not particularly limited. For example, (i) the unstretched polyvinyl alcohol-based resin film is uniaxially stretched in air or an inert gas, then subjected to swelling treatment, dyeing treatment with a dichroic dye, boron A method of treating in the order of acid treatment and water washing treatment, and finally drying, (ii) treating the unstretched polyvinyl alcohol resin film in the order of swelling treatment, dyeing treatment with dichroic dye, boric acid treatment and water washing treatment. The boric acid treatment step and / or the previous step may be performed by wet uniaxial stretching and finally drying.

  In any of the above methods (i) and (ii), uniaxial stretching may be performed in one step, or may be performed in two or more steps, but may be performed in a plurality of steps. preferable. As a stretching method, a known method can be adopted, for example, a roll-to-roll stretching method in which stretching is performed with a difference in peripheral speed between two nip rolls that transport a film; a heat as described in Japanese Patent No. 2731813 Roll stretching method; tenter stretching method and the like. The order of the steps is basically as described above, but there is no restriction on the number of treatment baths, treatment conditions, and the like. Moreover, you may add the process which is not described in the method of said (i) and (ii) as needed. Examples of such steps include immersion treatment with an aqueous iodide solution not containing boric acid (iodide treatment) or immersion treatment with an aqueous solution containing zinc chloride not containing boric acid (zinc treatment) after boric acid treatment, etc. Is mentioned.

  The swelling treatment step is performed for the purpose of removing foreign matter from the film surface, removing the plasticizer in the film, imparting easy dyeability in the next step, and plasticizing the film. The treatment conditions are determined within a range in which these objects can be achieved and within a range in which problems such as extreme dissolution and devitrification of the polyvinyl alcohol-based resin film do not occur. When the film previously stretched in the gas is swelled as in the method (i) above, the film is immersed in water or an aqueous solution of, for example, about 15 ° C to 70 ° C, preferably about 30 ° C to 60 ° C. Thus, the swelling treatment is performed. The immersion time of the film is about 30 seconds to 300 seconds, preferably about 60 seconds to 240 seconds. When the polyvinyl alcohol-based resin film is swollen in an unstretched state as in the method (ii) above, the film is placed in water or an aqueous solution of, for example, about 10 ° C to 50 ° C, preferably about 20 ° C to 40 ° C. It is performed by dipping. The immersion time of the film is about 30 seconds to 300 seconds, preferably about 60 seconds to 240 seconds.

  A preferable swelling degree in the swelling treatment is 1.05 to 2.5 times. Here, the degree of swelling is defined as the mass after swelling / the mass before swelling. If the degree of swelling is small, plasticizer removal in the polyvinyl alcohol-based resin film is often insufficient, and if the degree of swelling is large, uneven dyeing tends to occur in the dyeing process performed after the swelling process. .

  In the method (ii), a uniaxial stretching process may be performed during the swelling process. In this case, the draw ratio is preferably 3 times or less. The stretch ratio is defined as the length after stretching / the length in the initial state. If the stretch ratio here is high, uneven dyeing tends to occur in the dyeing process.

  The dyeing process is performed for the purpose of adsorbing and orienting the dichroic dye on the polyvinyl alcohol-based resin film. The treatment conditions are determined within a range in which these objects can be achieved and within a range in which problems such as extreme dissolution and devitrification of the polyvinyl alcohol-based resin film do not occur. When iodine is used as the dichroic dye, for example, iodine / potassium iodide / water = about 0.003 to about 0.003 to about 0.13 in a mass ratio under a temperature condition of about 10 ° C. to 45 ° C., preferably about 20 ° C. to 35 ° C. The immersion treatment is performed for about 30 seconds to 600 seconds, preferably about 60 seconds to 300 seconds, using an aqueous solution having a concentration of 2 / about 0.1 to 10/100. Instead of potassium iodide, other iodides such as zinc iodide may be used alone, or other iodides and potassium iodide may be used in combination. Furthermore, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc. may coexist. In addition, the dyeing | staining process in the case of adding a boric acid is distinguished from the following boric acid process by the point containing an iodine. Any dye containing about 0.003 parts by mass or more of iodine with respect to 100 parts by mass of water can be regarded as a dyeing treatment bath.

  When a water-soluble dichroic dye is used as the dichroic dye, for example, about 20 ° C. to 80 ° C., preferably about 30 ° C. to 70 ° C. The dyeing treatment is performed by immersing in an aqueous solution having a concentration of 0.001 to 0.1 / 100 for about 30 seconds to 600 seconds, preferably about 60 seconds to 300 seconds. The aqueous solution of the dichroic dye to be used may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant or the like. The dichroic dye may be used alone, or two or more dichroic dyes may be used in combination.

  The boric acid treatment step is generally performed by immersing a polyvinyl alcohol resin film dyed with a dichroic dye in an aqueous solution containing about 1 to 10 parts by mass of boric acid with respect to 100 parts by mass of water. When the dichroic dye is iodine, it is preferable to contain about 1 to 30 parts by mass of iodide with respect to 100 parts by mass of water. Examples of iodide include potassium iodide and zinc iodide. Further, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may coexist.

  Here, the boric acid treatment step is carried out for water resistance due to crosslinking, hue adjustment (preventing bluishness, etc.) and the like. When boric acid treatment is performed for water resistance by crosslinking, a crosslinking agent such as glyoxal or glutaraldehyde can be used together with boric acid as necessary. In addition, the boric acid treatment for water resistance may be referred to by names such as water resistance treatment, crosslinking treatment, and immobilization treatment. In addition, boric acid treatment for hue adjustment may be referred to by a name such as complementary color treatment or re-dyeing treatment.

  In the boric acid treatment process, boric acid treatment for water resistance and boric acid treatment for color adjustment are not particularly distinguished, but depending on the purpose, the concentration of boric acid and iodide, the temperature of the treatment bath Is preferably changed as appropriate. For example, as in the above method (ii), the unstretched polyvinyl alcohol-based resin film is subjected to a boric acid treatment after being subjected to a swelling treatment and a dyeing treatment, and the boric acid treatment is aimed at water resistance by crosslinking. In this case, a boric acid treatment bath containing about 3 to 10 parts by weight of boric acid and about 1 to 20 parts by weight of iodide is used with respect to 100 parts by weight of water, usually about 50 to 70 ° C., preferably Is carried out at a temperature of about 55 ° C to 65 ° C. The immersion time is usually about 30 to 600 seconds, preferably about 60 to 420 seconds, and more preferably about 90 to 300 seconds. When the polyvinyl alcohol resin film that has been subjected to the swelling treatment, the dyeing treatment and the stretching treatment is treated with boric acid for the purpose of water resistance by crosslinking as in the method (i) above, the temperature of the boric acid treatment bath is used. Is usually about 50 ° C to 85 ° C, preferably about 55 ° C to 80 ° C. Others may be performed in the same manner as the boric acid treatment after the above-described unstretched polyvinyl alcohol-based resin film is swollen and dyed.

  You may make it perform the boric-acid process for hue adjustment after the boric-acid process for water resistance. For example, when the dichroic dye is iodine, as boric acid treatment for water resistance, boric acid containing about 1 to 5 parts by mass of boric acid and about 3 to 30 parts by mass of iodide with respect to 100 parts by mass of water. Using an acid treatment bath, boric acid treatment is usually performed at a temperature of about 10 ° C to 45 ° C. The immersion time is usually about 3 to 300 seconds, preferably about 10 to 240 seconds. Subsequent boric acid treatment for hue adjustment is usually performed at a lower boric acid concentration, a higher iodide concentration, and a lower temperature than boric acid treatment for water resistance.

  The boric acid treatment step may consist of a single step or a plurality of steps, but is usually performed in steps 2 to 5. In this case, the aqueous solution composition and temperature of each boric acid treatment bath used in each step may be appropriately adjusted, and may be the same or different within the above range. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment may be performed in a plurality of steps, respectively.

  After the boric acid treatment step, a water washing treatment is performed. The water washing treatment is performed, for example, by immersing a polyvinyl alcohol-based resin film treated with boric acid for water resistance and / or hue adjustment in water, spraying water as a shower, or using both immersion and spraying. The water temperature in the water washing treatment is usually about 2 to 40 ° C., and the immersion time is preferably about 2 to 120 seconds.

  Finally, after the water washing process, a drying process is performed. The drying process is preferably performed in a large number of stages by changing the tension little by little, but is usually performed in 2 to 5 stages due to restrictions on equipment. When performed in two stages, the tension in the front stage is preferably set in the range of 600 to 1500 N / m, and the tension in the rear stage is preferably set in the range of 300 to 1200 N / m. If the tension becomes too large, the polyvinyl alcohol-based resin film breaks more, and if it becomes too small, the generation of wrinkles increases, which is not preferable. Moreover, it is preferable to set the drying temperature of a front | former stage in the range of 30-90 degreeC, and the drying temperature of a back | latter stage in the range of 50-100 degreeC. If the temperature is too high, the polyvinyl alcohol-based resin film will be ruptured, the optical properties will be lowered, and if the temperature is too low, streaks will increase, which is not preferable. The drying time can be 60 to 600 seconds, for example, and the drying time in each stage may be the same or different. If the time is too long, it is not preferable in terms of productivity, and if the time is too short, drying is insufficient, which is not preferable.

Through the above steps, a polarizing film 1 made of a polyvinyl alcohol-based resin film that is uniaxially stretched and adsorbed and oriented with a dichroic dye is obtained.
The thickness of the polarizing film 1 will not be specifically limited if the sum total with the protective film bonded on both surfaces of this polarizing film 1 is 105 micrometers or less, Usually, it is about 1-40 micrometers.

  The moisture content of the polarizing film 1 after a drying process becomes like this. Preferably it is 3-14 mass%, More preferably, it is 3-10 mass%, More preferably, it is 3-8 mass%. If the moisture content exceeds 14% by mass, the polarizing film 1 tends to shrink in a dry heat environment. In addition, the moisture content of the polarizing film 1 is calculated | required from the weight change before and behind hold | maintaining under 105 degreeC dry heat for 1 hour.

(Protective film)
A protective film is laminated | stacked and bonded to the single side | surface or both surfaces of the polarizing film 1 mentioned above through the adhesive bond layer. The first protective film 2a and the second protective film 2b may be the same or different protective films.
Examples of protective films include cycloolefin resin films such as norbornene resins; cellulose acetate resin films; polyester resin films such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polycarbonate resin films; acrylic resin films. A film that has been widely used in the art, such as a polypropylene-based resin film.

  Cycloolefin resins are commercially available products such as Topas (manufactured by Ticona), Arton (manufactured by JSR), ZEONOR (manufactured by Nippon Zeon), ZEONEX (manufactured by Nippon Zeon Co., Ltd.). ) And Apel (Mitsui Chemicals) can be preferably used. When such a cycloolefin-based resin is formed into a film, a known method such as a solvent casting method or a melt extrusion method is appropriately used. In addition, for example, a film of a cycloolefin resin film formed in advance such as Essina (manufactured by Sekisui Chemical Co., Ltd.), SCA40 (manufactured by Sekisui Chemical Co., Ltd.), ZEONOR film (manufactured by ZEON CORPORATION) Commercial products may be used.

  The cycloolefin resin film may be uniaxially stretched or biaxially stretched. By stretching, an arbitrary retardation value can be given to the cycloolefin-based resin film. Stretching is usually performed continuously while unwinding the film roll, and the film is stretched in a heating furnace in a roll traveling direction, a direction perpendicular to the traveling direction, or both. As the temperature of the heating furnace, a range from the vicinity of the glass transition temperature of the cycloolefin resin to [glass transition temperature + 100 ° C.] is usually employed. The draw ratio is usually 1.1 to 6 times, preferably 1.1 to 3.5 times.

  When the cycloolefin-based resin film is stretched, the stretching direction is arbitrary, but those that are 0 °, 45 °, and 90 ° with respect to the flow direction of the film are common. The retardation characteristics of a film having a stretching direction of 0 ° are often uniaxial, and the retardation characteristics of films having 45 ° and 90 ° are often weakly biaxial. The characteristics affect the viewing angle of the display device, but may be appropriately selected depending on the type of liquid crystal display device to be applied and the type of composite polarizing plate. As the phase difference value, what is usually called λ / 4, λ / 2, or the like is often used. In many cases, the phase difference range is 90 to 170 nm for λ / 4 and 200 to 300 nm for λ / 2.

  In addition, since the cycloolefin resin film generally has poor surface activity, the surface to be bonded to the polarizing film 1 is subjected to surface treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, and saponification treatment. It is preferred to do so. Among these, plasma treatment and corona treatment that can be performed relatively easily are preferable.

  The cellulose acetate-based resin that can be used for the protective film is a cellulose part or a complete acetate ester, and examples thereof include triacetyl cellulose, diacetyl cellulose, and cellulose acetate propionate.

  As such a cellulose ester-based resin film, an appropriate commercially available product such as “KC4UY” (manufactured by Konica Minolta Opto Co., Ltd.) can be preferably used.

  In addition, a cellulose acetate-based resin film imparted with a retardation property is also preferably used. As a commercially available cellulose acetate-based resin film imparted with such a retardation property, “WV BZ 438” (manufactured by Fuji Film Co., Ltd.) ), “KC4FR-1” (manufactured by Konica Minolta Opto) and the like. Cellulose acetate is also called acetyl cellulose or cellulose acetate.

  In particular, when the cellulose resin film is laminated with the polarizing film 1 using an aqueous adhesive, the cellulose resin film is subjected to a saponification treatment in order to enhance the adhesiveness with the polarizing film 1. As the saponification treatment, a method of immersing in an aqueous solution of an alkali such as sodium hydroxide or potassium hydroxide can be employed.

  When the protective film as described above is in a roll state, the films tend to adhere to each other and easily cause blocking. Therefore, usually, the roll end is subjected to uneven processing, a ribbon is inserted into the end, A roll of a protective film is used.

  The thickness of the protective film is not particularly limited as long as the sum of the polarizing film 1 described above and the protective film bonded to both surfaces of the polarizing film 1 is 105 μm or less, and a thin one is preferable, but if it is too thin, The strength is lowered and the processability is inferior. On the other hand, when it is too thick, problems such as a decrease in transparency, a longer curing time after bonding, and a customer request for thinning arise. Therefore, the suitable thickness of a protective film is 1-50 micrometers, for example, Preferably it is 5-40 micrometers.

<Bonding process of polarizing film 1 and protective film>
The polarizing film 1 and the protective film are bonded and integrated by the nip roll 3 before being transported into the drying path 5 to become the polarizing plate 4.

  The total thickness (after drying) of the polarizing film 1 and the protective film bonded to both surfaces of the polarizing film 1 is 105 μm or less, preferably 10 μm or more and 105 μm or less, more preferably 50 μm or more and 105 μm or less. .

  Bonding integration of the polarizing film 1 and the protective film may be performed by simultaneously bonding the polarizing film 1 and the protective film with the nip roll 3, or the protective film is bonded to one surface of the polarizing film 1 with the nip roll. Then, the protective film may be bonded to the other surface of the polarizing film 1 by a nip roll, and the polarizing film 1 and the protective film may be sequentially bonded.

Before bonding the polarizing film 1 and the protective film, an adhesive is applied to at least one of the polarizing film 1 and the protective film so that the polarizing film 1 and the protective film can be bonded.
It does not specifically limit as an adhesive agent coating apparatus, For example, a roll coating apparatus, a gravure coating apparatus, a spray coating apparatus etc. are mentioned.

  As the adhesive, for example, an aqueous adhesive, that is, an adhesive in which an adhesive component is dissolved or dispersed in water; a thermosetting adhesive or the like can be used.

  As the water-based adhesive, for example, a composition in which a polyvinyl alcohol resin, a urethane resin, or the like is used as a main component and an isocyanate compound, an epoxy compound, or the like is blended in order to improve adhesiveness can be used. When such an aqueous adhesive is used, the thickness of the adhesive layer is usually 1 μm or less, and even when the cross section is observed with a normal optical microscope, the adhesive layer is practically not observed.

  When using polyvinyl alcohol resin as the main component of the adhesive, in addition to partially saponified polyvinyl alcohol and fully saponified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, methylol group-modified polyvinyl alcohol, amino group-modified A modified polyvinyl alcohol resin such as polyvinyl alcohol may be used. When such a polyvinyl alcohol resin is used, an aqueous solution of the polyvinyl alcohol resin is used as an adhesive. The density | concentration of the polyvinyl alcohol-type resin in an adhesive agent is 1-10 weight part normally with respect to 100 weight part of water, Preferably it is 1-5 weight part.

  The thickness of the adhesive layer after drying is usually about 0.001 to 5 μm, preferably 0.01 μm or more, preferably 2 μm or less, more preferably 1 μm or less. If the thickness of the adhesive layer becomes too large, the appearance of the polarizing plate tends to be poor.

<Step of drying polarizing plate 4>
The polarizing plate 4 obtained as described above is conveyed into the drying furnace 5. In the drying furnace 5, the polarizing plate 4 is conveyed along the guide roll 7 while being widened by the widening roll 6, and passes through the drying furnace 5.

  The drying furnace 5 is not particularly limited, and examples thereof include a hot air drying furnace, an infrared drying furnace, a hot air type and an infrared type combined drying furnace, and the like.

The total length of the conveyance path of the polarizing plate in the drying furnace 5 is 10 to 60 m, preferably 20 to 50 m.
The drying temperature in the drying furnace 5 is usually 30 ° C to 100 ° C, more preferably 60 ° C to 100 ° C. If the drying temperature is too high, curling is likely to occur in the polarizing plate 4, which is not preferable. On the other hand, if the drying temperature is too low, it is difficult to remove moisture when using a water-based adhesive.
The drying time, that is, the time from when the polarizing plate 4 is carried into the drying furnace 5 to when the polarizing plate 4 passes through the drying furnace 5 is usually 50 to 1200 seconds, preferably 60 to 1000 seconds, more preferably. Is 100 to 600 seconds. If the drying time is too short, the polarizing film 1 and the protective film easily peel off due to insufficient drying, and if it exceeds 1200 seconds, it is not preferable from the viewpoint of productivity.
In addition, the drying furnace 5 may be comprised from several drying furnaces from which drying temperature differs, and what is necessary is just to adjust this drying temperature suitably according to the kind etc. of adhesive agent.

  In the drying furnace 5, a guide roll 7 is installed to control the conveyance path of the polarizing plate 4, and a pinch roll 6 is installed along the conveyance path of the polarizing plate 4. The pinch roll 6 and the guide roll 7 are both driven rollers and are driven in accordance with the movement of the polarizing plate 4 conveyed by driving a take-up roller (not shown) that winds the polarizing plate 4. It is.

Since the pinch roll 6 and the guide roll 7 are in direct contact with the polarizing plate 4, it is preferable to use a metal roll such as a stainless steel polishing roll having a low thermal conductivity, a plastic roll, a rubber roll, or the like.
The stainless steel polishing roll is made of SUS304, SUS316 or the like, and the surface roughness is about 0.2 to 1 expressed by the average interval S of the local peaks of the roughness curve of JIS B 0601 (surface roughness). Those that are 0.0S are preferred.

  The size of the pinch roll 6 is not particularly limited, and the roll diameter is preferably about 10 to 50 mmφ, and the length of the pinch roll 6 is at least the length shown in FIGS. 2 (a) and 2 (b). The length W (the length with which one pinch roll 6 sandwiches the side edges of the polarizing plate 4) is preferably about 2% to 10% with respect to the entire width of the polarizing plate 4. Since both sides of the polarizing plate 4 are affected by heat and the protective film is easily shrunk in the width direction of the conveyance path, if the length of the pinch roll 6 is in the above range, the generation of wrinkles and the like is efficient. Can be suppressed. In particular, when a water-based adhesive is used as the adhesive, it is effective because moisture easily escapes from both side ends of the polarizing plate 4.

As shown in FIG. 2A, the pinch rolls 6 are installed at both end portions of the conveyance path from the viewpoint of obtaining the polarizing plate 4 without unevenness. At this time, as shown in FIG. 2B, the pinch roll 6 may be tilted at an angle α in the transport direction of the polarizing plate 4 or tilted at an angle α in the direction opposite to the transport direction. Also good. Incidentally, FIG. 2B shows a state in which the pinch roll 6 is inclined in the transport direction (indicated by an arrow). Specifically, the angle α is 0 to ± 45 °, preferably 0 to ± 30 °, more preferably 0 to ± 30 °, with respect to the width direction orthogonal to the longitudinal direction of the conveyance path. The angle is preferably 0 to ± 15 °, and particularly preferably 0 ° (provided that + is when in the transport direction of the polarizing plate 4 and − is when the direction is opposite to the transport direction of the polarizing plate 4). ).
Note that FIG. 2B shows only one of the pinch rolls 6 and 6 on both sides, but the other is the same.
Further, the pinch rolls 6 and 6 may be inclined in the vertical direction (vertical direction) of the transport path. In this case, the inclination angle is 0 to ± 45 ° at the tip (tip located on the center side of the polarizing plate 4) with respect to the rear end of the pinch roll 6, preferably 0 to ± 30 °, more preferably 0 to ±±. It is 15 °, and particularly preferably 0 ° (however, when the tip is above the rear end of the pinch roll 6 is +, and when it is below is-).

The pinch roll 6 is preferably installed in the drying furnace 5 at least near the entrance. Since the polarizing plate 4 immediately after being transported into the drying furnace 5 is easily affected by heat and easily contracts in the width direction, the pinch roll 6 is installed at least in the vicinity of the inlet portion in the drying furnace 5 so as to be wavy. Generation of wrinkles and the like can be effectively suppressed.
The vicinity of the entrance in the drying furnace 5 refers to a region having a length of ¼ to ３ from the entrance with respect to the entire length of the conveyance path of the polarizing plate 4 in the drying furnace 5. One or more pinch rolls 6 can be installed near the entrance.

  In this embodiment, as shown in FIG. 1, four pinch rolls 6 and four guide rolls 7 are installed in the drying furnace 5, but the pinch roll 6 is installed in the drying furnace 5. It may be installed at 1-10 locations, preferably 2-8 locations. In this way, if there are a plurality of installation locations of the pinch roll 6, it is possible to suppress the polarizing plate 4 from contracting in the width direction of the transport path due to the influence of heat, so that the generation of wavy wrinkles and the like is further effective. Can be suppressed.

FIG. 3 is a perspective view showing another example of the widening roll preferably used in the manufacturing method of the present invention.
In this embodiment, a curved roll 8 shown in FIG. 3 is used instead of the pinch roll 6 described above.

  As the bending roll 8 for widening the polarizing plate 4, for example, a metal such as stainless steel, a plastic, a rubber roll, or the like can be used.

  Moreover, in this invention, you may use together a curved roll and a pinch roll suitably as a widening roll.

(Polarizing plate 4)
By performing the widening process of the polarizing plate 4 at the time of drying as described above, the polarizing plate 4 having a good appearance without wrinkles can be obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by this Example.

<Example 1>
A polyvinyl alcohol film having a thickness of 75 μm was uniaxially stretched by a dry method, and further immersed in pure water while being kept in a tension state, and then immersed in an aqueous solution of iodine / potassium iodide / water. Then, it was immersed in an aqueous solution of potassium iodide / boric acid / water, subsequently washed with pure water, and then dried to obtain a polarizing film 1 in which iodine was adsorbed and oriented on polyvinyl alcohol. The thickness of the polarizing film 1 was 28 μm.
Separately, in 100 parts by weight of water, 3 parts by weight of a carboxyl group-modified polyvinyl alcohol (“Kuraray Poval KL318”, manufactured by Kuraray Co., Ltd.), a water-soluble polyamide epoxy resin (“Smiles Resin 650”, Sumika Chemtex) (Made by Co., Ltd.) 1.5 parts by weight of an aqueous solution having a solid content concentration of 30% was dissolved to prepare an aqueous adhesive mainly composed of a polyvinyl alcohol resin.

On one surface of the obtained polarizing film 1, a pre-corona-treated norbornene-based resin film (“ZEONOR FILM (registered trademark)”, manufactured by Nippon Zeon Co., Ltd., thickness: 33 μ, hereinafter sometimes referred to as “COP”) ), And a film made of triacetyl cellulose (“KC4UYW”, manufactured by Konica Minolta Opto Co., Ltd., thickness: 40 μm, hereinafter sometimes referred to as “TAC”) whose saponification treatment has been performed on the other surface respectively. The polarizing plate 4 was obtained by pasting with the nip roll 3 through the adhesive. Subsequently, the inside of the drying furnace 5 was passed and it dried at 70 degreeC for 220 second, and the polarizing plate 4 was obtained. The total thickness of the obtained polarizing plate 4 was 101 μm, and no problem was found in the visual appearance.
The drying furnace 5 is a hot air drying furnace and has a structure shown in FIG. Each pinch roll 6 has a roll diameter of 20 mmφ, and is arranged at the side end of the conveyance path with an angle α of + 10 ° as shown in FIG.
And the pinch rolls 6 and 6 were arrange | positioned in the both sides of a conveyance path so that the both-sides edge part of the polarizing plate 4 might be expanded simultaneously, and it conveyed, clamping the polarizing plate 4. FIG. At this time, the sandwiching length W of the pinch roll 6 was 4% with respect to the entire width of the polarizing plate 4.

<Examples 2 to 5>
A polarizing plate was obtained in the same manner as in Example 1 except that the first protective film, the polarizing film and the second protective film shown in Table 1 were used.

<Comparative Examples 1-5>
A polarizing plate was obtained in the same manner as in Example 1 except that the first protective film, the polarizing film and the second protective film shown in Table 1 were used and a pinch roll was not used in the drying furnace.

<Reference Example 1>
A polarizing plate was obtained in the same manner as in Example 1 except that TAC (thickness: 40 μm) was used as the first protective film.

<Reference Example 2>
A polarizing plate was obtained in the same manner as in Reference Example 1 except that no pinch roll was used in the drying furnace.

  Table 1 shows the total thickness of the polarizing plates obtained in Examples 1 to 5, Comparative Examples 1 to 5, and Reference Examples 1 and 2 and the results of visual appearance evaluation. In Table 1, “O” indicates that no abnormality such as wrinkles was observed on the appearance of the polarizing plate, and “X” indicates that abnormality such as wavy wrinkles was observed on the appearance.

As shown in Table 1, since the total thickness of the polarizing plates obtained in Reference Examples 1 and 2 was 108 μm, no problem was seen in the appearance regardless of the presence or absence of the widening treatment in the drying furnace. .
As shown in Table 1, the polarizing plates of Examples 1 to 5 had a total thickness of 101 μm or less, and were subjected to a widening process in a drying furnace, so no problem was seen in appearance.
On the other hand, as shown in Table 1, the polarizing plates of Comparative Examples 1 to 5 had a total thickness of 101 μm or less, and were not subjected to the widening process in the drying furnace, and thus there was a problem in appearance.

DESCRIPTION OF SYMBOLS 1 Polarizing film 2a First protective film 2b Second protective film 3 Nip roll 4 Polarizing plate 5 Drying furnace 6 Pinch roll 7 Guide roll 8 Curved roll

Claims (5)

A method for producing a thin polarizing plate having a thickness of 105 μm or less by bonding a protective film to one or both sides of a polarizing film via an adhesive and drying the protective film,
When drying the polarizing plate obtained by bonding the polarizing film and the protective film, the polarizing plate is widened with a widening roll.   The said widening roll is a manufacturing method of the polarizing plate of Claim 1 installed in the at least entrance part vicinity in the drying furnace through which the said polarizing plate passes.   The manufacturing method of the polarizing plate of Claim 1 or 2 with which the said widening roll is installed in multiple numbers along the conveyance path of a polarizing plate in the drying furnace which the said polarizing plate passes.   The said widening roll is a pinch roll which clamps the side edge part of the said polarizing plate, and this pinch roll is installed in the both-sides edge part of the width direction of the conveyance path of the said polarizing plate. The manufacturing method of a polarizing plate of crab.   The said widening roll is a curved roll in which the center part of the width direction orthogonal to the conveyance direction of the said polarizing plate is higher than the both-ends part of the said width direction. Manufacturing method of polarizing plate.

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