JP5051916B2 - Manufacturing method of laminate film - Google Patents

Description

  The present invention relates to a method for producing a laminate film in which a plastic film is bonded to one side or both sides of a wet film via an adhesive layer.

  The production method of the present invention can be applied to the production of various types of laminate films. For example, it is used in a method of producing a polarizing plate using a polarizer as a wet film and a transparent protective film for a polarizer as a plastic film. Can do. In addition, examples of the wet film include cellophane films, polyvinyl alcohol films, and the like, and the production method of the present invention can be applied to the production of laminate films used for packaging foods, medical devices and the like.

  Conventionally, a water-based adhesive is usually used to produce a laminate film by laminating a plastic film on one or both sides of a wet film. As the bonding method, for example, a wet film is transported between a pair of pressure-bonding rolls, and a plastic film is transported on both sides of the film, and the plastic film is simultaneously bonded, and a wet film is transported between a pair of pressure-bonding rolls. In addition, a sequential lamination method is adopted in which a plastic film is transported and bonded to one side, and then the plastic film is bonded to the other side of the wet film.

  However, when a wet film and a plastic film are bonded together by the above-described laminating method, foreign matter bites and bubbles are generated between the wet film and the plastic film in the obtained laminate film. In particular, with the increase in the bonding speed, the generation of bubbles becomes remarkable. In addition, wrinkles are generated, and streaky unevenness is generated.

  To solve the above-mentioned problems related to the generation of wrinkles, a method of bonding a wet film (polyvinyl alcohol film having a water content of 0.1 to 20% by weight) and a plastic film (cellulose film) at a predetermined nip pressure is proposed. (Patent Document 1). However, even with this method, bubbles generated between the wet film and the plastic film in the laminate film cannot be sufficiently suppressed. On the other hand, by increasing the pressure of the nip roll when laminating the wet film and the plastic film, it is possible to reduce bubbles, but if the pressure of the nip roll is increased, film meandering, wrinkles, dents, scratches, There are problems such as the occurrence of rust and the early wear of the roll (rubber roll).

In addition, when producing a laminate using a film other than a wet film, air bubbles are generated at the time of pressure bonding. Therefore, a method for suppressing the generation of air bubbles has also been proposed in producing the laminate. For example, in a manufacturing method of manufacturing a laminate by niping a support and a resin film of a thermoplastic resin, a gas having permeability to the resin film is blown with entrained air accompanying the nip point. (Patent Document 2), a method of reducing bubble entrainment during laminating by blowing gas onto the surface of the resin film immediately before pressure bonding when continuously laminating a metal strip and a resin film with a pressure roll (Patent Document 3) ), A method of suppressing the entrainment of air bubbles in the laminate by spraying heated gas into the space between the film and the metal band in the pressure-bonding roll part when continuously laminating the metal band and the resin film (Patent Document 4). Has been. However, even when these methods are used, air bubbles in producing a laminate film from a wet film and a plastic film cannot be sufficiently suppressed.
Japanese Patent Laid-Open No. 10-166519 JP 2002-283451 A Japanese Patent Laid-Open No. 10-16050 JP 7-125169 A

  The present invention provides a method for producing a laminate film by laminating a plastic film to a wet film, and the production method is capable of suppressing air bubbles generated between the wet film and the plastic film in the obtained laminate film. For the purpose.

  The present inventors diligently studied to solve the above problems, and found that the object can be achieved by a method for producing a laminate film described below, and have completed the present invention.

The present invention provides a pair of wet films having a moisture content of 10 to 60% by weight on one or both sides of a plastic film having a moisture content of 0.1 to 5% by weight via an adhesive layer provided on the plastic film. In the method for producing a laminate film to be bonded by a pressure roll,
At least air entrained on the surface of each film from the film joining portion where the wet film and the plastic film are bonded together by the pair of pressure-bonding rolls to the introduction portion of each film in each pressure-bonding roll,
Purging with a replacement gas having a solubility in water of 0.1 cm ³ / cm ³ H ₂ O (20 ° C., 1 atm) or more,
The present invention relates to a method for producing a laminate film, wherein the bonding is performed in a state where each film surface is replaced with the replacement gas.

  In the method for producing the laminate film, carbon dioxide, ammonia, water vapor, or a mixed gas thereof is suitable as the replacement gas.

  In the method for producing a laminate film, it is preferable that purging with a replacement gas is performed under conditions where the Reynolds number of the replacement gas is in the range of 3000 to 20000.

  The manufacturing method of the laminate film is effective when the transport speed of each film is 2 to 50 m / min.

  The method for producing the laminate film is preferably applied when the wet film is a polarizer, the plastic film is a transparent protective film for the polarizer, and a polarizing plate is produced as the laminate film.

  In the production of a conventional laminate film, bubbles are generated due to the accompanying air that moves by adhering to the film surface due to the viscosity of the air when bonded. On the other hand, in the method for producing a laminate film of the present invention, the entrained air on the surface of each film to be bonded is purged with a replacement gas having a predetermined solubility or more to forcibly replace, and each film is bonded. The generation of bubbles is suppressed. When bubbles are generated on the bonding surface by entrained air as in the past, it is difficult to eliminate the bubbles composed of air, but in the present invention, the replacement gas used has a high solubility in water. Therefore, even when bubbles are generated on the bonding surface, the gas constituting the bubbles (substitution gas) is quickly absorbed into the wet film. As a result, the inside of the bubble is evacuated, and the evacuated bubble disappears due to the atmospheric pressure. Therefore, according to the method for producing a laminate film of the present invention, a laminate film in which bubbles generated between the wet film and the plastic film are suppressed can be produced. According to the production method of the present invention, even when the conveyance speed of each film (speed of the pressure-bonding roll) is increased, a laminate film with suppressed bubbles can be produced, and the production speed of the laminate film production line is high. It can be applied to

  Further, Patent Documents 2 to 4 propose that turbulent flow is generated by strongly blowing a replacement gas similar to that of the present invention onto the film surface to suppress entrainment of bubbles in the entrained gas laminate. However, when a laminate film is produced with a wet film and a plastic film as in the present invention, the following adverse effects occur when turbulent flow occurs on the wet film surface. For example, when strong turbulence occurs, drying of moisture on the surface of the wet film is promoted, and the flexibility of the surface is impaired, resulting in an increase in bonded bubbles, or absorption of gas (substitution gas) on the surface of the wet film. Is promoted to form a saturated layer (with respect to gas absorption) on the surface of the wet film, and the absorption of the bonded air bubbles into the wet film is hindered and increased. On the other hand, when the amount of gas spray is insufficient, the entrained air on the wet film surface forms a laminar flow, and it is difficult to perform sufficient replacement with the target gas (substitution gas). In the method for producing a laminated film of the present invention, since the entrained air on each film surface to be bonded is purged with a replacement gas having a predetermined solubility or more, the films are bonded together. Only the replacement gas is present, and bonding can be performed while appropriately generating turbulent flow on the wet film surface, and there is no problem caused by strongly blowing the replacement gas.

  In the production method of the present invention, as described above, it is desirable that the bonding is performed on the wet film surface in a state where the displacing gas does not cause strong turbulence. On the other hand, in order to efficiently obtain the effect of the replacement gas, it is desired that the flow of the replacement gas is appropriately performed on each film surface. Therefore, when maintaining the state where each film surface is purged with the replacement gas, it is preferable to set the flow state of the replacement gas on each film surface to a weak turbulent flow. From this point of view, it is more preferable that the purge with the replacement gas is performed under conditions where the Reynolds number of the replacement gas is in the range of 3000 to 20000.

  Below, the manufacturing method of the laminate film of this invention is demonstrated, referring drawings. FIG. 1 shows an example of a method for producing a laminate film of the present invention. FIG. 1A is a cross-sectional view and FIG. 1B is a perspective view. In FIG. 1, a laminate film 3 is manufactured by pressing a wet film 1 and a plastic film 2 by passing between a pair of press rolls R <b> 1 and R <b> 2. An adhesive layer A is provided on the plastic film 2, and the plastic film 2 and the wet film 1 are bonded together via the adhesive layer A.

  In the bonding, at least each film (wet film 1, plastic film 2) in each of the pressure-bonding rolls R1, R2 from the film joining portion x where the wet film 1 and the plastic film 2 are bonded by the pair of pressure-bonding rolls R1, R2. The film surfaces up to y1 and y2 (the part where the film first contacts the roll) are purged with the replacement gas G. In the purged state, as shown in FIG. 1, for example, in the pressure-bonding rolls R1 and R2, the gap between the flow paths purged by the replacement gas G at the upper part of each film (wet film 1 and plastic film 2) conveyed. The purge hood F can be provided so as to form z (z1, z2). The channel gap z is usually preferably 1 to 10 mm, and more preferably 1 to 5 mm.

  The purge hood F covers at least the introduction portions y1 and y2 of the surface of each film (wet film 1, plastic film 2) to be transported back from the film joining portion x in the film transport direction. That's fine. FIG. 1 shows a case in which a purge hood F having an extra size that can sufficiently cover the introduction portions y1 and y2 is used.

  In the purge hood F of FIG. 1, a supply port b for the replacement gas G is provided above the film joining portion x (vertically above the conveying direction of the laminate film 3), and the replacement gas introduced from the supply port b. The purge is performed by G. The replacement gas G is introduced from the supply port b as needed at the time of the bonding, and a flow path is formed so as to flow in the direction opposite to the rotation direction of the pressure-bonding rolls R1 and R2 (film transport direction) according to the direction of the arrow. Has been. The replacement gas G introduced from the supply port b is discharged from the flow path gaps z1 and z2 between the respective films (wet film 1 and plastic film 2) and the purge hood ends a1 and a2. Suction means can be provided at the purge hood ends a1 and a2.

  In FIG. 1A, the pressure-bonding rolls R1, R2, the wet film 1, the plastic film 2, and the laminate film 3 are shown in cross section, but the purge hood F has at least the wet film 1 and the plastic in the longitudinal direction of the roll. It is preferable to use a film having a size that can cover the film 2 with its full width. Although not shown in FIG. 1A, the purge hood F may be formed so as to cover the side surfaces of the pressure-bonding rolls R1 and R2. According to the purge hood F that covers the side surfaces of the pressure-bonding rolls R1 and R2, the purge with the replacement gas G can be efficiently performed. In FIG. 1B, what has the side seal S on the side of the purge hood F is described.

  In addition, FIG. 1 shows a case where the purge hood F has a shape that conforms to the outer shape of the roll, but the shape of the purge hood F is not particularly limited. Further, the supply port b of the replacement gas G is also provided in the purge hood F, and the position where the supply port b is provided is not particularly limited as long as the purge can be performed. However, the structure shown in FIG. 1 is preferable in terms of the efficiency of purging with the replacement gas G.

  FIG. 2 shows a case where a purge hood F ′ different from that in FIG. 1 is used. The purge hood F ′ in FIG. 2 is not provided with the supply port b for the replacement gas G. When the purge hood F ′ of FIG. 2 is used, the replacement gas G is introduced through a gap between any film (wet film 1 or plastic film 2) and the purge hood end a1 ′ or a2 ′. It is discharged from the gap (z1 or z2) between the film on the side not present and the purge hood end a1 ′ or a2 ′. A suction means may be provided at the purge hood end a1 ′ or a2 ′ on the discharge side. In FIG. 2, the replacement gas G is introduced from the gap (z2) between the plastic film 2 and the purge hood end a2. However, the introduction of the replacement gas is performed between the opposite wet film 1 and the purge hood end a1 (z1). ) Can also be introduced.

  1 and 2 illustrate the case where the plastic film 2 is bonded to one side of the wet film 1, the plastic film 2 can be sequentially bonded to the other side of the wet film 1. . The plastic film 2 can be bonded to the other side of the wet film 1 by the same method as described above.

  Further, the plastic film 2 can be simultaneously bonded to both surfaces of the wet film 1 by the same method as described above. For example, the pressure-bonding rolls R1 and R2 and the purge hood F similar to those in FIG. 1 are used, and the plastic film 2 is transported to the pressure-bonding rolls R1 and R2 and the replacement gas is supplied from the supply port b of the replacement gas G. It can be carried out by conveying the wet film 1 together with G.

  The material of the said crimping | compression-bonding roll, a roll diameter, roll peripheral speed (conveying speed at the time of bonding), etc. are adjusted suitably.

  As the pressure-bonding roll, for example, an elastic roll in which a metal core is coated with a rubber layer or a resin layer, or a metal roll such as iron, stainless steel, titanium, or aluminum can be used.

  As the diameter of the pressure-bonding roll, the smaller the diameter, the smaller the area where the wet film 1 and the plastic film 2 are in contact with each other, so the pressure applied to the film surface is relatively high. Therefore, the roll diameter is preferably 250 mm or less, and more preferably 200 mm or less. However, if the diameter becomes too small, the roll becomes less rigid and a sufficient force cannot be applied. Therefore, it is preferable to use a roll of 50 mm or more, and more preferably a roll of 100 mm or more. The roll surface length (length in the longitudinal direction of the roll) may be equal to or greater than the width of each film (wet film 1, plastic film 2).

  Moreover, the conveyance speed of the film (the peripheral speed of the pressure-bonding roll) is not particularly limited, and is usually preferably adjusted at about 2 to 50 m / min. In the case where the film conveyance speed is 10 m / min or more, and further, in the case of a high speed of 30 to 50 m / min, since bubbles have been easily generated in the past, the present invention is particularly suitable for the case where the film conveyance speed is high. It is valid.

  Moreover, the laminating pressure between rolls at the time of bonding is not particularly limited and is appropriately set. The laminating pressure is preferably about 2 MPa or more and 5 MPa or less, more preferably 3 MPa or more and 4 MPa or less from the viewpoint of easy adjustment and productivity of the laminated film. When the laminating pressure is less than 2 MPa, sufficient pressing cannot be performed, and bubbles are generated between the films. On the other hand, if the laminating pressure is higher than 5 MPa, the roll and the apparatus are excessively loaded, causing damage. Lamination pressure was measured using a pressure-sensitive paper “Prescale” manufactured by Fuji Photo Film Co., Ltd., and the color change of the pressure-sensitive paper was binarized by computer image processing. It is calculated from the approximate expression of

As the replacement gas used for purging the entrained air in the present invention, one having a solubility in water of 0.1 cm ³ / cm ³ H ₂ O (20 ° C., 1 atm) or more is used. The solubility of the replacement gas is preferably 0.5 cm ³ / cm ³ H ₂ O (20 ° C., 1 atm) or more, more preferably 0.8 cm ³ / cm ³ H ₂ O (20 ° C., 1 atm) or more. If the solubility of the replacement gas is less than 0.1 cm ³ / cm ³ H ₂ O (20 ° C., 1 atm), bubbles generated in the laminate film cannot be sufficiently suppressed. Examples of the replacement gas satisfying the solubility include acetylene (1.03: the unit is the same as described above), ammonia (702), sulfur dioxide (39), ethylene (0.122), hydrogen chloride (442 ), Chlorine (2.30), carbon dioxide (0.88), hydrogen sulfide (2.58), and the like. These replacement gases can be used as a mixed gas. The replacement gas is preferably carbon dioxide from the viewpoint of ease of handling and safety. The solubility is a volume when a gas of 1 atm = 101325 Pa is dissolved in 1 cm ^{3 of} water at 20 ° C. Specifically, this is based on values measured by the measurement method described in the Science Chronology 2001 (Physics / Chemicals, Product 154 (578)).

  Moreover, the introduction amount of the replacement gas is usually preferably 1 to 50 liters / min, and more preferably 10 to 30 liters / min.

  The purge with the above replacement gas is preferably performed under conditions where the Reynolds number (Re number) of the replacement gas is in the range of 3000 to 20000. The Reynolds number (Re number) is a dimensionless number defined by the ratio of inertial force to viscous force. By controlling the Reynolds number (Re number) within the above range, the flow state of the replacement gas on the wet film surface Can be set in the transition region from laminar to turbulent flow. The Reynolds number (Re number) is more preferably 5000 to 15000, and still more preferably 8000 to 13000.

The Reynolds number (Re number) is represented by the following formula.
Re = U ・ L ・ ρ / μ (Dimensionless number)
U = relative speed (m / s). In the present invention, relative speed = gas flow velocity (m / s) + film transport speed (roll peripheral speed) (m / s). Gas flow rate (m / s) = gas introduction amount (m ³ / s) × (1 / roll surface length) × (1 / channel gap). The roll surface length (m) indicates the length in the longitudinal direction of the pressure-bonding roll that conveys each film. The channel gap (m) indicates the gap between the wet film and the purge hood (z1, z2 in FIG. 1). In FIG. 1, since the gas introduced from the supply port b is released from the two gaps (assuming that each release amount is equal), the gas introduction amount for calculating the gas flow rate is as follows. It is calculated as ½ of the gas introduction amount supplied from b. That is, in FIG. 1, gas flow rate = gas introduction amount × 1/2 × (1 / roll surface length) × (1 / channel gap).
L = Running section (m). In FIG. 1, it is a partial circumferential length from the film joining portion x to the introduction portion y1 (purge release portion) of the wet film 1 in the pressure-bonding roll R1, and L = running section is 1/4 of the circumference of the pressure-rolling roll R1. It corresponds to. In FIG. 2, the flow of the replacement gas is disturbed because the flow path is bent sharply at the film joining portion x. Therefore, in FIG. 2, L = the run-up section is the partial circumferential length from the film joining portion x to the introduction portion y1 (purge release portion) of the wet film 1 in the pressure-bonding roll R1, and the plastic in the pressure-bonding roll R2 from the film joining portion x. It is not the sum of the peripheral lengths up to the introduction part y2 (purge release part) of the film 2, but the partial peripheral length from the film joining part x to the introduction part y1 (purge release part) of the wet film 1 in the press roll R1. This corresponds to 1/4 of the circumference of the pressure roll R1. ρ = gas density (kg · m ³ ), μ = gas viscosity (Pa · s), both measured values at 20 ° C.

  The wet film used in the method for producing a laminate film of the present invention has a moisture content of 10 to 60% by weight. The moisture content of the wet film is suitably applied to the present invention when it is 15 to 50% by weight, and further 20 to 40% by weight. On the other hand, the moisture content of the plastic film is 0.1 to 5% by weight. The moisture content of the plastic film is suitably applied to the present invention when it is 1 to 3% by weight. In addition, when bonding a plastic film on both surfaces of a wet film, the material of a plastic film may be the same and may differ. Moreover, the moisture content may be the same or different. In the method for producing a laminate film, the material for forming the adhesive layer is appropriately determined according to the wet film and plastic film to be used.

  The following describes the case where a polarizing plate is manufactured by using a polarizer as a wet film and using a transparent protective film for a polarizer as a plastic film and bonding them together via an adhesive layer.

  As the polarizer, a polymer film such as a polyvinyl alcohol (PVA) film that is dyed with a dichroic substance such as iodine or a dichroic dye and uniaxially stretched is usually used. The thickness of such a polarizer is not particularly limited, but those having a thickness of about 5 to 80 μm, preferably 40 μm or less are used.

  As optical properties of the polarizer, the single transmittance when measured with a single polarizer is preferably 40% or more, and more preferably in the range of 42 to 45%. In addition, it is preferable that the orthogonal transmittance measured by superposing two polarizers so that the absorption axes of the two polarizers are 90 ° with each other is smaller, and practically 0.00% The content is preferably 0.050% or less and more preferably 0.030% or less. The degree of polarization is preferably 99.90% or more and 100% or less for practical use, and particularly preferably 99.93% or more and 100% or less. Even when measured as a polarizing plate, it is preferable to obtain optical characteristics substantially equivalent to this.

  As a polymer film which forms a polarizer, various things can be used without being specifically limited. For example, PVA dehydration is applied to hydrophilic polymer films such as polyvinyl alcohol (PVA) film, polyethylene terephthalate (PET) film, ethylene / vinyl acetate copolymer film, partially saponified film, and cellulose film. Examples thereof include polyene-based oriented films such as treated products and polyvinyl chloride dehydrochlorinated products. Among these, since it is excellent in the dyeability by dichroic substances, such as an iodine, it is preferable to use a PVA-type film.

  The degree of polymerization of the polymer film material is generally 500 to 10,000, preferably in the range of 1000 to 6000, and more preferably in the range of 1400 to 4000. Furthermore, in the case of a saponified film, the saponification degree is preferably 75 mol% or more, more preferably 98 mol% or more, for example, from the viewpoint of solubility in water, and 98.3 to 99.8 mol. % Is more preferable.

  When a PVA-based film is used as the polymer film, the PVA-based film can be formed by any method such as a casting method in which a stock solution dissolved in water or an organic solvent is cast, a casting method, an extrusion method, or the like. Can be used as appropriate. The phase difference value at this time is preferably 5 nm to 100 nm. Moreover, in order to obtain an in-plane uniform polarizer, it is preferable that the retardation difference in the PVA film is as small as possible, and the in-plane retardation of the PVA film is 10 nm or less at a measurement wavelength of 1000 nm. Preferably, it is 5 nm or less.

  The moisture content of the polarizer when laminating the polarizer and the transparent protective film is not particularly limited as long as the moisture content is 10 to 60% by weight. If the moisture content is too high, a long drying time is required and excessive drying equipment is required. Therefore, the moisture content of the polarizer when the transparent protective film is bonded to the polarizer is preferably 15 to 50% by weight, and more preferably 20 to 40% by weight. The moisture content of such a polarizer can generally be adjusted by the conditions of the drying process during the polarizer manufacturing process, but if necessary, a separate moisture conditioning process is provided, soaking in a water bath, spraying water droplets, or again Heat drying or reduced pressure drying may be performed.

  The method for producing the polarizer is not limited to this, but can generally be roughly classified into a dry stretching method and a wet stretching method. As a manufacturing process of a polarizer by a wet stretching method, an appropriate method can be used depending on the conditions. For example, the polymer film includes swelling, dyeing, crosslinking, stretching, washing with water, and a drying treatment process. A method of manufacturing by a series of manufacturing steps is common. In each of these treatment steps except the drying treatment step, each treatment is performed while being immersed in a bath made of various solutions. The order, number of times, and presence / absence of each treatment of swelling, dyeing, crosslinking, stretching, washing and drying in each treatment step are not particularly limited, and several treatments are performed simultaneously in one treatment step. It is not necessary to perform some processes. For example, the stretching process may be performed after the dyeing process, or may be performed simultaneously with the swelling or the dyeing process, or may be performed after the stretching process. Furthermore, it is also preferable to perform the crosslinking treatment before and after the stretching treatment. Moreover, as an extending | stretching process, although an appropriate method can be used without being limited, For example, in the case of roll extending | stretching, the method of extending | stretching by the peripheral speed difference of the roll between rolls is used. Furthermore, additives such as boric acid, borax or potassium iodide may be added to each treatment as appropriate. Therefore, the polarizer may contain boric acid, zinc sulfate, zinc chloride, potassium iodide and the like as necessary. Furthermore, in some of these processes, the film may be stretched in the flow direction or the width direction as appropriate, and a water washing process may be performed for each process.

  As the swelling treatment step, for example, the polymer film is immersed in a treatment bath (swelling bath) filled with water. As a result, the polymer film is washed with water, and the surface of the polymer film can be cleaned of stains and anti-blocking agents, and the effect of preventing unevenness such as uneven dyeing can be expected by swelling the polymer film. The polymer film may be stretched in this swelling bath.

  Examples of the dyeing process include a method of dyeing the polymer film by immersing it in a treatment bath (dye bath) containing a dichroic substance such as iodine or an organic dye. The polymer film may be stretched in the dyeing bath, and the cumulative draw ratio integrated with the draw ratio in the previous treatment step is about 1.1 to 3.5 times. When iodine is used as the dichroic substance, it is preferable to further add iodide to the dyeing bath because the dyeing efficiency can be further improved. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Etc. In addition to the method of immersing in a dyeing bath, the dyeing treatment may be, for example, a method of applying or spraying an aqueous solution containing a dichroic substance onto the polymer film. A method of mixing in advance may be used.

  In the crosslinking treatment step, for example, the polymer film is immersed in a treatment bath (crosslinking bath) containing a crosslinking agent. A conventionally known substance can be used as the crosslinking agent. Examples thereof include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. One kind of these may be used, or two or more kinds may be used in combination. Iodide may be added to the crosslinking bath from the viewpoint of obtaining uniform characteristics in the plane of the polarizer. Similarly to the dyeing treatment, the crosslinking treatment may be performed by applying or spraying a solution containing a crosslinking agent, or may be subjected to a stretching treatment simultaneously with the crosslinking treatment. The cumulative draw ratio at this time is about 1.1 to 3.5 times.

  As the stretching treatment step, in the case of the wet stretching method, stretching is performed so that the cumulative stretching ratio is about 2 to 7 times in a state of being immersed in a treatment bath (stretching bath). As the solution for the stretching bath, a solution obtained by adding various metal salts and iodine, boron or zinc compounds in a solvent such as water, ethanol or various organic solvents is preferably used.

  In the water washing treatment step, for example, by immersing the polymer film in a treatment bath (water washing bath), unnecessary residues such as boric acid attached in the previous treatment can be washed away. Iodide may be added to the aqueous solution. For example, sodium iodide or potassium iodide is preferably used. The temperature of the washing bath is about 10 to 60 ° C. The number of times of the water washing treatment is not particularly limited and may be carried out a plurality of times, and it is preferable to appropriately adjust the type and concentration of the additive in each water washing bath.

  In addition, when pulling up the polymer film from each treatment bath, in order to prevent the occurrence of dripping, a conventionally known liquid break roll such as a pinch roll may be used, or the liquid is scraped off with an air knife, etc. Excess water may be removed by this method.

  As the drying treatment step, a conventionally known drying method such as natural drying, blow drying, or heat drying can be used. For example, in heat drying, the heating temperature is about 20 to 80 ° C., and the drying time is about 1 to 10 minutes. Moreover, it can extend | stretch suitably also in this drying process process.

  Furthermore, the final draw ratio (total draw ratio) of the polarizer obtained by the treatment step is preferably 3 to 7 times. If the total draw ratio is less than 3 times, it is difficult to obtain a polarizer with a high degree of polarization, and if it exceeds 7 times, the film tends to break.

  Moreover, the manufacturing method of a polarizer is not limited to the said manufacturing method, You may manufacture a polarizer using another manufacturing method, if the moisture content of 10 to 60 weight% is satisfied. For example, a dichroic substance may be kneaded into a polymer film such as a dry stretching method or polyethylene terephthalate (PET), formed into a film, and stretched, or uniaxially oriented liquid crystal is used as a host. O type using a chromatic dye as a guest (US Pat. No. 5,523,863, JP-T-3-503322), E type using dichroic lyotropic liquid crystal (US) Patent No. 6,049,428).

As the transparent protective film, a film excellent in transparency, mechanical strength, thermal stability, isotropy and the like is preferable for the purpose of protecting the polarizer. The thickness of the transparent protective film is generally about 1 to 300 μm, and more preferably about 5 to 100 μm. In addition, the surface of the transparent protective film is subjected to surface modification treatment by corona treatment, plasma treatment, flame treatment, ozone treatment, primer treatment, glow treatment, saponification treatment, etc. from the viewpoint of improving polarization characteristics, durability, and adhesive properties. Also good. Among these surface modification treatments, saponification treatment with an alkali or the like is preferable. The moisture permeability of such a transparent protective film is about 0.5 to 5000 g / m ² · 24 h according to the measurement according to JIS Z0208 (cup method) at a temperature of 40 ° C. and a relative humidity of 90%.

  Examples of the material for forming the transparent protective film include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, acrylic polymers such as polymethyl methacrylate, polystyrene, acrylonitrile and styrene. Examples thereof include styrene-based polymers such as copolymers (AS resins) and polycarbonate-based polymers. In addition, polyethylene, polypropylene, polyolefins having a cyclo or norbornene structure, polyolefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers , Polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or the above Polymer blends and the like are also examples of polymers that form the protective film. One or more kinds of arbitrary appropriate additives may be contained in the transparent protective film. Examples of the additive include an ultraviolet absorber, an antioxidant, a lubricant, a plasticizer, a release agent, a coloring inhibitor, a flame retardant, a nucleating agent, an antistatic agent, a pigment, and a coloring agent. The content of the thermoplastic resin in the transparent protective film is preferably 50 to 100% by weight, more preferably 50 to 99% by weight, still more preferably 60 to 98% by weight, and particularly preferably 70 to 97% by weight. . When content of the said thermoplastic resin in a transparent protective film is 50 weight% or less, there exists a possibility that the high transparency etc. which a thermoplastic resin originally has cannot fully be expressed.

  Moreover, as a transparent protective film, the polymer film as described in Unexamined-Japanese-Patent No. 2001-343529 (WO01 / 37007), for example, (A) thermoplastic resin which has a substituted and / or unsubstituted imide group in a side chain, ( B) Resin compositions containing thermoplastic resins having substituted and / or unsubstituted phenyl and nitrile groups in the side chains. A specific example is a film of a resin composition containing an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. As the film, a film made of a mixed extruded product of the resin composition or the like can be used. Since these films have a small phase difference and a small photoelastic coefficient, problems such as unevenness due to the distortion of the polarizing plate can be eliminated, and since the moisture permeability is small, the humidification durability is excellent.

  When this protective film is bonded to both sides of the polarizer, one having different characteristics may be used on each side. Examples of the characteristics include thickness, material, light transmittance, tensile elastic modulus, presence / absence of an optical functional layer, and the like.

  As the transparent protective film of the present invention, at least one selected from cellulose resin (polymer), polycarbonate resin (polymer), cyclic polyolefin resin (cycloolefin or polyolefin having norbornene structure) and (meth) acrylic resin is used. Is preferred. The effect of the present invention is particularly remarkable when a protective film made of triacetyl cellulose is used.

  Cellulose resin is an ester of cellulose and fatty acid. Specific examples of the cellulose ester resin include triacetyl cellulose, diacetyl cellulose, tripropionyl cellulose, dipropionyl cellulose and the like. Among these, triacetyl cellulose is particularly preferable. Many products of triacetylcellulose are commercially available, which is advantageous in terms of availability and cost. Examples of commercially available products of triacetyl cellulose include trade names “UV-50”, “UV-80”, “SH-80”, “TD-80U”, “TD-TAC”, and “UZ” manufactured by Fujifilm Corporation. -TAC "and" KC series "manufactured by Konica. In general, these triacetyl celluloses have an in-plane retardation (Re) of almost zero, but a thickness direction retardation (Rth) of about 60 nm.

  In addition, the cellulose resin film with a small thickness direction phase difference is obtained by processing the said cellulose resin, for example. For example, a base film such as polyethylene terephthalate, polypropylene, and stainless steel coated with a solvent such as cyclopentanone and methyl ethyl ketone is bonded to a general cellulose film and dried by heating (for example, at 80 to 150 ° C. for about 3 to 10 minutes). ) And then peeling the base film; a solution obtained by dissolving norbornene resin, (meth) acrylic resin, etc. in a solvent such as cyclopentanone, methyl ethyl ketone, etc. is applied to a general cellulose resin film and dried by heating ( For example, a method of peeling the coated film after 80 to 150 ° C. for about 3 to 10 minutes is mentioned.

  Moreover, as a cellulose resin film with a small thickness direction retardation, the fatty acid cellulose resin film which controlled the fat substitution degree can be used. Generally used triacetyl cellulose has an acetic acid substitution degree of about 2.8. Preferably, the Rth can be reduced by controlling the acetic acid substitution degree to 1.8 to 2.7. Rth can be controlled to be small by adding a plasticizer such as dibutyl phthalate, p-toluenesulfonanilide, acetyltriethyl citrate to the fatty acid-substituted cellulose resin. The addition amount of the plasticizer is preferably 40 parts by weight or less, more preferably 1 to 20 parts by weight, and still more preferably 1 to 15 parts by weight with respect to 100 parts by weight of the fatty acid cellulose resin.

  Specific examples of the cyclic polyolefin resin are preferably norbornene resins. The cyclic olefin-based resin is a general term for resins that are polymerized using a cyclic olefin as a polymerization unit, and is described in, for example, JP-A-1-240517, JP-A-3-14882, JP-A-3-122137, and the like. Resin. Specific examples include ring-opening (co) polymers of cyclic olefins, addition polymers of cyclic olefins, cyclic olefins and α-olefins such as ethylene and propylene (typically random copolymers), And graft polymers obtained by modifying them with an unsaturated carboxylic acid or a derivative thereof, and hydrides thereof. Specific examples of the cyclic olefin include norbornene monomers.

  Various products are commercially available as the cyclic polyolefin resin. As specific examples, trade names “ZEONEX” and “ZEONOR” manufactured by ZEON CORPORATION, product names “ARTON” manufactured by JSR Corporation, “TOPAS” manufactured by TICONA, and product names manufactured by Mitsui Chemicals, Inc. “APEL”.

  The (meth) acrylic resin preferably has a Tg (glass transition temperature) of 115 ° C. or higher, more preferably 120 ° C. or higher, still more preferably 125 ° C. or higher, and particularly preferably 130 ° C. or higher. When Tg is 115 ° C. or higher, the polarizing plate can be excellent in durability. Although the upper limit of Tg of the (meth) acrylic resin is not particularly limited, it is preferably 170 ° C. or less from the viewpoint of moldability. From (meth) acrylic resin, a film having in-plane retardation (Re) and thickness direction retardation (Rth) of almost zero can be obtained.

  As the (meth) acrylic resin, any appropriate (meth) acrylic resin can be adopted as long as the effects of the present invention are not impaired. For example, poly (meth) acrylic acid ester such as polymethyl methacrylate, methyl methacrylate- (meth) acrylic acid copolymer, methyl methacrylate- (meth) acrylic acid ester copolymer, methyl methacrylate-acrylic acid ester- (Meth) acrylic acid copolymer, (meth) methyl acrylate-styrene copolymer (MS resin, etc.), polymer having an alicyclic hydrocarbon group (for example, methyl methacrylate-cyclohexyl methacrylate copolymer, Methyl methacrylate- (meth) acrylate norbornyl copolymer, etc.). Preferably, poly (meth) acrylate C1-6 alkyl such as poly (meth) acrylate methyl is used. More preferred is a methyl methacrylate resin containing methyl methacrylate as a main component (50 to 100% by weight, preferably 70 to 100% by weight).

  Specific examples of (meth) acrylic resins include (meth) acrylic resins having a ring structure in the molecule described in, for example, Acrypet VH and Acrypet VRL20A manufactured by Mitsubishi Rayon Co., Ltd., and JP-A-2004-70296. And a high Tg (meth) acrylic resin system obtained by intramolecular crosslinking or intramolecular cyclization reaction.

  As the (meth) acrylic resin, a (meth) acrylic resin having a lactone ring structure can also be used. It is because it has high mechanical strength by high heat resistance, high transparency, and biaxial stretching.

Examples of the (meth) acrylic resin having a lactone ring structure include JP 2000-230016, JP 2001-151814, JP 2002-120326, JP 2002-254544, and JP 2005. Examples thereof include (meth) acrylic resins having a lactone ring structure described in Japanese Patent No. 146084.

  As the transparent protective film, one having a front phase difference of less than 40 nm and a thickness direction retardation of less than 80 nm is usually used. The front phase difference Re is represented by Re = (nx−ny) × d. The thickness direction retardation Rth is represented by Rth = (nx−nz) × d. The Nz coefficient is represented by Nz = (nx−nz) / (nx−ny). [However, the refractive indexes in the slow axis direction, the fast axis direction, and the thickness direction of the film are nx, ny, and nz, respectively, and d (nm) is the thickness of the film. The slow axis direction is the direction that maximizes the refractive index in the film plane. ]. In addition, it is preferable that a transparent protective film has as little color as possible. A protective film having a thickness direction retardation value of −90 nm to +75 nm is preferably used. By using a film having a thickness direction retardation value (Rth) of −90 nm to +75 nm, the coloring (optical coloring) of the polarizing plate caused by the transparent protective film can be almost eliminated. The thickness direction retardation value (Rth) is more preferably −80 nm to +60 nm, and particularly preferably −70 nm to +45 nm.

  On the other hand, as the transparent protective film, a phase difference plate having a phase difference with a front phase difference of 40 nm or more and / or a thickness direction retardation of 80 nm or more can be used. The front phase difference is usually controlled in the range of 40 to 200 nm, and the thickness direction phase difference is usually controlled in the range of 80 to 300 nm. When a retardation plate is used as the transparent protective film, the retardation plate functions also as a transparent protective film, so that the thickness can be reduced.

  The retardation plate may have an appropriate retardation according to the purpose of use, such as those for the purpose of compensating for various wavelength plates or birefringence of liquid crystal layers and compensation of viewing angle, etc. It may be one in which retardation plates are stacked and optical characteristics such as retardation are controlled.

  The transparent protective film can be appropriately selected according to the applied liquid crystal display device. For example, in the case of VA (including Vertical Alignment, MVA, and PVA), it is desirable that at least one of the polarizing plates (cell side) has a retardation. As specific phase differences, it is desirable that Re = 0 to 240 nm and Rth = 0 to 500 nm. In terms of the three-dimensional refractive index, nx> ny = nz, nx> ny> nz, nx> nz> ny, nx = ny> nz (uniaxial, biaxial, Z-ized, negative C-plate) is desirable. When polarizing plates are used above and below the liquid crystal cell, both the upper and lower sides of the liquid crystal cell may have a phase difference, or any one of the upper and lower transparent protective films may have a phase difference.

  For example, in the case of IPS (including In-Plane Switching, FFS), both cases where the transparent protective film on one side of the polarizing plate has a phase difference and does not have a phase difference can be used. For example, when there is no phase difference, it is desirable that the liquid crystal cell does not have a phase difference both above and below (cell side). When the liquid crystal cell has a phase difference, it is desirable that the liquid crystal cell has a phase difference on both the upper and lower sides. No phase difference, A-plate on the top, positive C-plate on the bottom). When it has a phase difference, it is desirable that Re = −500 to 500 nm and Rth = −500 to 500 nm. In terms of the three-dimensional refractive index, nx> ny = nz, nx> nz> ny, nz> nx = ny, nz> nx> ny (uniaxial, Z-ized, positive C-plate, positive A-plate) are desirable.

  In addition, the film which has the said phase difference can be bonded together separately to the transparent protective film which does not have a phase difference, and can provide the said function.

  The adhesive layer used for laminating the polarizer and the transparent protective film is not particularly limited as long as it is optically transparent, and water-based, solvent-based, hot-melt-based, and radical-curing types are used. A water-based adhesive is preferred.

  Although it does not specifically limit as a water-system adhesive agent which forms an adhesive bond layer, For example, a vinyl polymer type | system | group, a gelatin type, a vinyl type latex type, a polyurethane type, an isocyanate type, a polyester type, an epoxy type etc. can be illustrated. Such an adhesive layer composed of an aqueous adhesive can be formed as an aqueous solution coating / drying layer, etc., but when preparing the aqueous solution, a catalyst such as a crosslinking agent, other additives, and an acid can be used as necessary. Can be blended. As the water-based adhesive, an adhesive containing a vinyl polymer is preferably used, and the vinyl polymer is preferably a polyvinyl alcohol resin. The polyvinyl alcohol-based resin can contain a water-soluble crosslinking agent such as boric acid, borax, glutaraldehyde, melamine, or oxalic acid. In particular, when a polyvinyl alcohol polymer film is used as the polarizer, it is preferable from the viewpoint of adhesiveness to use an adhesive containing a polyvinyl alcohol resin. Furthermore, an adhesive containing a polyvinyl alcohol-based resin having an acetoacetyl group is more preferable from the viewpoint of improving durability.

  The polyvinyl alcohol-based resin is not particularly limited, but an average degree of polymerization of about 100 to 3000 and an average degree of saponification of about 85 to 100 mol% are preferable from the viewpoint of adhesiveness. Further, the concentration of the aqueous adhesive solution may be appropriately determined according to the target thickness of the adhesive layer, and is not particularly limited, but is preferably 0.1 to 15% by weight, More preferably, it is 0.5 to 10% by weight. If this solution concentration is too high, the viscosity will increase too much, and streaky unevenness will tend to occur. If the solution concentration is too low, the coating properties will be poor and unevenness will tend to occur.

  Polyvinyl alcohol resin is polyvinyl alcohol obtained by saponifying polyvinyl acetate; a derivative thereof; a saponified product of a copolymer of vinyl acetate and a monomer having copolymerizability; Examples thereof include modified polyvinyl alcohols that have been converted into ethers, ethers, grafts, or phosphoric esters. Examples of the monomer include (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, unsaturated carboxylic acids such as (meth) acrylic acid and esters thereof; α-olefins such as ethylene and propylene, (meth) Examples include allyl sulfonic acid (soda), sulfonic acid soda (monoalkyl malate), disulfonic acid soda alkyl maleate, N-methylol acrylamide, acrylamide alkyl sulfonic acid alkali salt, N-vinyl pyrrolidone, N-vinyl pyrrolidone derivatives, and the like. . These polyvinyl alcohol resins can be used singly or in combination of two or more.

  A polyvinyl alcohol-based resin containing an acetoacetyl group is obtained by reacting a polyvinyl alcohol-based resin with diketene by a known method. For example, a method in which a polyvinyl alcohol resin is dispersed in a solvent such as acetic acid and diketene is added thereto, and a polyvinyl alcohol resin is previously dissolved in a solvent such as dimethylformamide or dioxane, and diketene is added thereto. And the like. Moreover, the method of making diketene gas or liquid diketene contact directly to polyvinyl alcohol is mentioned.

  The degree of acetoacetyl group modification of the polyvinyl alcohol-based resin containing an acetoacetyl group is not particularly limited as long as it is 0.1 mol% or more. If it is less than 0.1 mol%, the water resistance of the adhesive layer is insufficient, which is inappropriate. The degree of acetoacetyl group modification is preferably about 0.1 to 40 mol%, more preferably 1 to 20 mol%, and particularly preferably 2 to 7 mol%. When the degree of acetoacetyl modification exceeds 40 mol%, the number of reaction points with the cross-linking agent decreases, and the effect of improving water resistance is small. Such a modification degree of acetoacetyl group can be measured using a nuclear magnetic resonance apparatus (NMR).

  As a crosslinking agent, what is generally used for an adhesive can be used without any particular limitation. For example, in the case of an adhesive using a polyvinyl alcohol resin as described above, a functional group having reactivity with a polyvinyl alcohol resin. A compound having at least two groups can be preferably used. For example, ethylenediamine, triethylenediamine, hexamethylenediamine and other alkyldiamines having two alkylene groups and two amino groups; tolylene diisocyanate, hydrogenated tolylene diisocyanate, trimethylolpropane tolylene diisocyanate adduct, triphenylmethane triisocyanate, methylene bis (Isocyanates such as 4-phenylmethane triisocyanate, isophorone diisocyanate and ketoxime block product or phenol block product thereof; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin di or triglycidyl ether, 1,6-hexane Diol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycol Epoxys such as dianiline and diglycidylamine; monoaldehydes such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde; Aminoformaldehyde resins such as methylol urea, methylol melamine, alkylated methylol urea, alkylated methylol melamine, acetoguanamine, benzoguanamine and formaldehyde condensates; sodium, potassium, magnesium, calcium, aluminum, iron, nickel, etc. And divalent or trivalent metal salts and oxides thereof, among which amino-formaldehyde resins, Methylol compounds having Chiroru groups are preferred.

  The compounding amount of the crosslinking agent is generally about 0.1 to 35 parts by weight with respect to 100 parts by weight of the resin, and 10 to 25 parts by weight are preferably used. , 30 to 46 parts by weight, more preferably 32 to 40 parts by weight of a cross-linking agent in exchange for shortening the time (pot life) from preparation of the adhesive to the adhesive layer. Mixing is also effective.

  The adhesive may contain a metal compound filler. With the metal compound filler, the fluidity of the adhesive layer can be controlled, the film thickness can be stabilized, and a polarizing plate having a good appearance, uniform in-plane and no adhesive variation can be obtained.

  The adhesive layer may appropriately contain an additive if necessary. Examples of additives include sensitizers that increase the curing speed and sensitivity by electron beams typified by carbonyl compounds, coupling agents such as silane coupling agents and titanium coupling agents, and adhesion promoters typified by ethylene oxide. Additives that improve wettability with transparent protective films, acryloxy group compounds and hydrocarbons (natural and synthetic resins), and other additives that improve mechanical strength and processability, UV absorbers, aging Inhibitors, dyes, processing aids, ion trapping agents, antioxidants, tackifiers, fillers (other than metal compound fillers), plasticizers, leveling agents, foam inhibitors, antistatics, heat stabilizers, water resistance Stabilizers such as decomposition stabilizers are listed.

  A polarizing plate is obtained by attaching a transparent protective film to one or both surfaces of the polarizer via an adhesive layer. The adhesive layer is formed in advance on the transparent protective film, but an undercoat layer or an easy adhesion treatment layer may be provided between the adhesive layer and the transparent protective film. When the adhesive layer is formed of a water-based adhesive or the like, the thickness of the adhesive layer is preferably 30 to 300 nm. The thickness of the adhesive layer is more preferably 60 to 250 nm.

  The polarizing plate can be used as an optical film in which at least one optical functional layer is further laminated. Examples of the optical functional layer include a hard coat treatment layer, an antireflection treatment layer, a sticking prevention treatment layer, a surface treatment layer such as a diffusion layer or an antiglare treatment layer, and an alignment liquid crystal for the purpose of viewing angle compensation or optical compensation. Layer. Furthermore, image display devices such as polarization conversion elements, reflectors, transflective plates, retardation plates (including wavelength plates (λ plates) such as 1/2 and 1/4), viewing angle compensation films, brightness enhancement films, etc. There may be mentioned one in which one or two or more optical films used for forming are laminated. In particular, the polarizing plate is a reflective polarizing plate or a semi-transmissive polarizing plate in which a reflecting plate or a semi-transmissive reflecting plate is laminated, an elliptical polarizing plate or a circular polarizing plate in which a retardation plate is laminated, a viewing angle compensation layer, or a viewing angle. A wide viewing angle polarizing plate in which a compensation film is laminated or a polarizing plate in which a brightness enhancement film is laminated is preferably used.

  In the case of laminating the optical functional layer, generally, the surface treatment layer and the alignment liquid crystal layer may be directly laminated on a film such as a polarizing plate, but the optical functional layer composed of various films is formed by using the adhesive layer. The method of laminating through is preferably used. As the adhesive layer at this time, an adhesive layer made of an adhesive is particularly preferably used.

  The pressure-sensitive adhesive layer made of a pressure-sensitive adhesive can be formed of a suitable pressure-sensitive adhesive according to the prior art such as acrylic, silicone-based, polyester-based, polyurethane-based, polyether-based, or rubber-based. This adhesive has the following features: prevention of foaming and peeling phenomenon due to moisture absorption, deterioration of optical properties due to thermal expansion differences, prevention of warping of liquid crystal cells, and formation of a high-quality and durable image display device. It is preferable that the pressure-sensitive adhesive layer has a low moisture absorption rate and excellent heat resistance, and further, it does not require a high-temperature process for curing and drying from the viewpoint of preventing changes in optical properties such as polarizing plates. Those that do not require a long curing treatment or drying time are preferred. From such a viewpoint, an acrylic pressure-sensitive adhesive is preferably used for the polarizing plate and the optical film. Further, fine particles may be added to the pressure-sensitive adhesive to form a pressure-sensitive adhesive layer that exhibits light diffusibility.

  When the pressure-sensitive adhesive layer made of the pressure-sensitive adhesive is exposed on the surface, it is preferable to temporarily cover with a separator for the purpose of preventing contamination until the pressure-sensitive adhesive layer is put to practical use. As the separator, an appropriate film according to the above-described protective film or the like, which is provided with a release coat with an appropriate release agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide, if necessary, is used. preferable.

  The polarizing plate according to the present invention can be preferably used for forming an image display device such as a liquid crystal display device (LCD) or an electroluminescence display device (ELD).

  The polarizing plate can be preferably used for forming a liquid crystal display device, for example, a liquid crystal display device such as a reflective type, a semi-transmissive type, or a transmissive / reflective type in which a polarizing plate is arranged on one side or both sides of a liquid crystal cell. Can be used. The liquid crystal cell substrate may be either a plastic substrate or a glass substrate. The liquid crystal cell forming the liquid crystal display device is arbitrary. For example, an appropriate type such as an active matrix drive type represented by a thin film transistor type, a simple matrix drive type represented by a twist nematic type or a super twist nematic type, etc. A liquid crystal cell may be used.

  Moreover, when providing a polarizing plate and an optical film in the both sides of a liquid crystal cell, they may be the same and may differ. Furthermore, when forming the liquid crystal display device, for example, appropriate components such as a prism array sheet, a lens array sheet, a light diffusion plate, and a backlight can be arranged in one or more layers at appropriate positions.

  The present invention will be described more specifically with reference to the following examples and comparative examples. However, the present invention is not limited to these examples and comparative examples.

(Measurement method of moisture content of polarizer)
A sample of 180 mm × 500 mm was cut out from the obtained polarizer, and its initial weight (W (g)) was measured. The sample was left in a drier at 120 ° C. for 2 hours, and then the weight after drying (D (g)) was measured. From these measured values, the moisture content was determined by the following formula.
Moisture content (%) = {(WD) / W} × 100

(Production of polarizer)
Using a polyvinyl alcohol film having a thickness of 75 μm (manufactured by Kuraray Co., Ltd .: VF-PS7500, width 1000 mm), the film was stretched to 2.5 times the draw ratio while being immersed in 30 ° C. pure water for 60 seconds. Dyeing is performed in an aqueous iodine solution (weight ratio: pure water / iodine (I) / potassium iodide (KI) = 100 / 0.01 / 1) for 45 seconds, and the draw ratio is 5.8 in a 4% by weight boric acid aqueous solution. The film was stretched so as to be doubled, immersed in pure water for 10 seconds, and then dried at 40 ° C. for 3 minutes while maintaining the tension of the film to obtain a polarizer. The polarizer had a width of 520 mm, a thickness of 25 μm, and a moisture content of 30% by weight.

(Creation of transparent protective film with adhesive layer)
100 parts by weight of PVA resin (manufactured by Nippon Synthetic Chemical Industry Co., Ltd .: Gosenol) and 35 parts by weight of a cross-linking agent (manufactured by Dainippon Ink Chemical Co., Ltd .: Watersol) are dissolved in 3760 parts by weight of pure water to form an adhesive. Was prepared. This adhesive was applied to one side of a 80 μm-thick triacetyl cellulose (TAC) film (Fuji Photo Film Co., Ltd .: UZ-80T, moisture content 1.4 wt%) with a slot die, and then 1 ° C. at 85 ° C. The TAC film with an adhesive layer having an adhesive layer having a thickness of 0.1 μm was obtained by drying for a minute.

Example 1
(Preparation of polarizing plate)
A polarizing plate was produced by the method shown in FIG. The wet film 1 was the polarizer described above, and the plastic film 2 was the TAC film with the adhesive layer.
The replacement gas, carbon dioxide gas (solubility in water of _{^{0.88cm 3 / cm 3 H 2 O}} (20 ℃, 1atm)) was used. The density of the gas is ρ = 1.842 (kg · m ³ ) (1 atm, 20 ° C.), and the viscosity of the gas is μ = 0.000015 (Pa · s).
The amount of substitution gas introduced was 50 liters / min.
The pressure roll was a metal roll having a diameter of 200 mm and a roll surface length (length in the longitudinal direction) of 1000 mm.
The film conveyance speed (roll peripheral speed) is 30 m / min.
The purge hood used was a stainless steel plate. The purge hood was arranged such that the flow path gaps z1 and z2 were 10 mm.
Reynolds number (Re) = 10700 calculated from these.

  A TAC film with a polarizer and an adhesive layer is conveyed between the pair of pressure-bonding rolls, these are pressure-bonded, and a TAC film is bonded to one side of the polarizer to form a laminated film (laminate film 3 in FIG. 1). Got. At this time, the laminating pressure between the pressure-bonding rolls was 0.3 MPa. The obtained polarizing plate was dried at 80 ° C. for 2 minutes after bonding.

Examples 2-3 and Comparative Examples 1-5
A polarizing plate was obtained in the same manner as in Example 1, except that the type of replacement gas, the film conveyance speed (roll peripheral speed), and the amount of gas introduced were changed as shown in Table 1. In Comparative Examples 3 and 4, the replacement gas is not supplied. In Comparative Example 5, air was introduced instead of the replacement gas.

  The following evaluation was performed about the polarizing plate produced in the Example and the comparative example. The results are shown in Table 1.

(Check for bubbles)
About the obtained polarizing plate, the number (cell / m < ² >) of the bubble between a polarizer and a TAC film was confirmed.

  As is clear from the results in Table 1 above, according to the examples of the present invention, the air bubbles generated between the wet film (polarizer) and the plastic film (transparent protective film) are suppressed, and the laminate film (polarizing plate). Can be manufactured.

It is sectional drawing of the schematic which shows an example of the manufacturing method of the laminate film of this invention. It is a perspective view of the schematic which shows an example of the manufacturing method of the laminate film of this invention. It is the schematic of sectional drawing which shows the other example of the manufacturing method of the laminate film of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wet film 2 Plastic film 3 Laminate film A Adhesive layer F Purge food R1, R2 Press roll b Replacement gas supply port G Replacement gas z Channel gap S Side seal

Claims (5)

A plastic film with a moisture content of 0.1 to 5% by weight is attached to one or both surfaces of a wet film with a moisture content of 10 to 60% by weight through a pair of pressure-bonding rolls via an adhesive layer provided on the plastic film. In the manufacturing method of the laminated film to match,
At least air entrained on the surface of each film from the film joining portion where the wet film and the plastic film are bonded together by the pair of pressure-bonding rolls to the introduction portion of each film in each pressure-bonding roll,
Purging with a replacement gas having a solubility in water of 0.1 cm ³ / cm ³ H ₂ O (20 ° C., 1 atm) or more,
The method for producing a laminated film, wherein the bonding is performed in a state where each film surface is replaced with the replacement gas. The replacement gas, the manufacturing method of the laminate film according to claim 1, wherein the carbon dioxide, the ammonia flax other mixtures of these gases.   The method for producing a laminated film according to claim 1 or 2, wherein the purge with the replacement gas is performed under conditions where the Reynolds number of the replacement gas is in the range of 3000 to 20000.   The method for producing a laminated film according to any one of claims 1 to 3, wherein the conveyance speed of each film is 2 to 50 m / min.   The wet film is a polarizer, the plastic film is a transparent protective film for a polarizer, and the laminate film is a polarizing plate. The method for producing a laminate film according to any one of claims 1 to 4.

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