JP5988649B2 - Manufacturing method of polarizing plate - Google Patents

Description

  The present invention relates to a method for producing a polarizing plate used as a liquid crystal display member.

  A liquid crystal panel that forms the core of a liquid crystal display device is usually configured by disposing polarizing plates on both sides of a liquid crystal cell. Generally, a polarizing plate has a structure in which a protective film made of a transparent resin is bonded to one surface of a polarizing film made of a polyvinyl alcohol resin through an adhesive. A transparent resin film is often bonded to the other surface of the polarizing film via an adhesive, and the transparent resin film on this side has only a protective function for the polarizing film, similar to the protective film on the opposite side. In addition to the protective function, it may be a so-called retardation film provided with an in-plane and / or thickness direction retardation for the purpose of optical compensation and viewing angle compensation of the liquid crystal cell. In this specification, a protective film, a retardation film, or the like that is bonded to such a polarizing film via an adhesive is referred to as an “optical film”. The adhesive used for bonding the optical film to the polarizing film is generally a liquid, and exhibits an adhesive force between the polarizing film and the optical film by the curing reaction of the liquid adhesive.

  In recent years, the price of liquid crystal display devices such as televisions has been drastically reduced, and the demand for lower prices for the members constituting the same has increased, while the demand for quality has also increased. In this trend, adhesives used in the production of polarizing plates are also active energy rays that can be applied to many types of optical films, from water-based adhesives where the types of optical films that can be applied are limited to specific resins such as cellulose resins. It is being changed to a curable adhesive. The pasting of a polarizing film and an optical film using an active energy ray curable adhesive has been proposed in, for example, Japanese Patent Application Laid-Open No. 2004-245925 (Patent Document 1).

  The active energy ray curable adhesive is prepared in liquid form, and the die coater that directly applies the liquid adhesive to the object to be coated, or the liquid adhesive that is supported on the groove formed on the surface, is applied to the surface of the object to be coated. Using a gravure roll that is transferred to the optical film, the optical film is preliminarily applied to the bonding surface to the polarizing film. And the polarizing film is piled up on the adhesive coating surface, active energy rays, such as an ultraviolet-ray and an electron beam, are irradiated, an adhesive agent is hardened, and adhesive force is expressed. The method using such an active energy ray-curable adhesive is a very effective method because there are many applicable optical films.

  As a method for producing a polarizing plate using such an active energy ray-curable adhesive, for example, in JP 2009-134190 A (Patent Document 2), a protective film is laminated on both sides of a polarizing film via an adhesive. In addition, a method is disclosed in which a laminate is obtained, and active energy rays are irradiated while the laminate is brought into close contact with the outer surface of a convex curved surface formed in an arc shape along the transport direction of the laminate. According to this method, the reverse curl and wave curl that are likely to occur in the obtained polarizing plate can be suppressed, and a polarizing plate having good performance can be produced.

  In the method of this document, the thickness of the adhesive layer formed on the protective film does not greatly affect the reverse curl and wave curl of the polarizing plate to be manufactured, so the coating thickness of the adhesive is controlled. There seems to be little need to do. However, although the thickness of the adhesive layer varies, most of the levels are not problematic, but defects such as bubbles may occur. If the defects are large, the yield of the polarizing plate is lowered. There was a thing. Furthermore, in the stable production of inexpensive and higher-performance polarizing plates, active energy ray-curable adhesives are often applied thicker than conventional aqueous adhesives, and are themselves expensive. In addition, since it is desired to reduce the thickness of the polarizing plate itself, it is desired to manage the polarizing plate so as to have a minimum necessary thickness in consideration of the deflection width.

  An infrared film thickness meter is known as a device for measuring the coating thickness in order to manage the coating thickness in-line. However, since the infrared film thickness meter has a limited resolution, the thickness of the coating layer (adhesive layer) formed on the film that is continuously transported with a thickness of about several μm, like the polarizing plate production line. It was difficult to accurately measure the thickness. Specifically, in the polarizing plate production line, as shown in FIG. 1 to be described later, the polarizing film and the optical film bonded to at least one surface thereof are each continuously without having a special support. The film is transported and bonded together, but the film that is continuously transported in this way has subtle fluctuations in the thickness direction and the direction in which tension is applied (flow direction). When trying to measure the coating layer thickness with an infrared film thickness meter in the presence of fluctuations, only an accuracy of about ± 1 μm can be obtained, and it is practically impossible to control the coating thickness based on it. Met. Also, when the thickness of the adhesive layer formed on the optical film is measured with an infrared film thickness meter, the infrared absorption peak given by the optical film and the infrared absorption peak given by the adhesive must be clearly distinguished. On the other hand, depending on the type of optical film, both peaks may overlap, and the measured value itself may not be obtained. Therefore, until now, in the production of a polarizing plate using a liquid adhesive, in-line inspection of the thickness of the liquid adhesive applied on the film has not been performed.

JP 2004-245925 A JP 2009-134190 A

  Then, the subject of this invention is managing the coating thickness of an adhesive in line, when bonding an optical film to a polarizing film through the liquid adhesive which uses an active energy ray hardening-type adhesive as a representative example. Therefore, it is intended to provide a method capable of producing a polarizing plate at a low cost while suppressing the occurrence of defects such as bubbles in the adhesive layer by reducing the thickness variation.

  As a result of diligent research to solve the above-mentioned problems, the present inventors applied a liquid adhesive on an optical film and bonded the coated layer to a polarizing film to produce a polarizing plate. By measuring the thickness of the applied adhesive by a specific method, the thickness can be accurately determined, and by controlling the adhesive application thickness during coating based on the result, adhesion The inventors have found that a polarizing plate having a uniform thickness of the agent and few defects can be produced, and the present invention has been completed.

  That is, the present invention is a method for producing a polarizing plate by bonding an optical film made of a thermoplastic resin to a polarizing film made of a polyvinyl alcohol resin through an adhesive, and the following (A), (B ), (C) and (D). A method for producing a polarizing plate comprising the steps is provided.

(A) The coating process which apply | coats said adhesive agent to the bonding surface to the polarizing film of an optical film using the coating machine which has a coating thickness control means of an adhesive agent,
(B) With the radiation film thickness meter, the thickness of the optical film is measured before the coating process, and the total thickness of the optical film and the applied adhesive is measured after the coating process. A measurement process for determining in-line the thickness of the applied adhesive from the absolute value of the measured value difference,
(C) A bonding step in which the polarizing film is applied to the adhesive surface that has been applied in the coating step and passed through the measurement step, and (D) an adhesive that is set within a range of 0.5 to 5 μm. When the ratio of the absolute value of the difference between the measured thickness X of the adhesive obtained in the measuring step and the Y with respect to the set thickness Y is a predetermined value or more, for example, 5% or more, A control step for controlling the coating thickness control means.

  According to the present invention, when an optical film is bonded to a polarizing film via an adhesive, it is formed on the optical film by measuring the film thickness before and after the coating process using a predetermined film thickness meter. The thickness of the adhesive is instantaneously measured in-line, and the result is transmitted to the adhesive application thickness control means of the coating machine to control the application thickness. A uniform polarizing plate can be produced. As a result, it is possible to suppress defects such as bubbles that are likely to occur due to variations in the thickness of the adhesive.

It is a schematic side view which shows the example of arrangement | positioning of the manufacturing apparatus used suitably for this invention. It is a block diagram which shows the relationship between each process in this invention. It is a schematic side view which shows arrangement | positioning of the manufacturing apparatus used in the Example.

  In the present invention, an optical film made of a thermoplastic resin is bonded to a polarizing film made of a polyvinyl alcohol-based resin through an adhesive to produce a polarizing plate. The optical film may be bonded only to one side of the polarizing film, or may be bonded to both sides of the polarizing film. When the optical film is bonded to both surfaces of the polarizing film, the method of the present invention may be applied to the bonding of one optical film, or the method of the present invention may be applied to the bonding of both optical films. Good.

[Polarized film]
The polarizing film is made of polyvinyl alcohol-based resin, and is a film having a property of transmitting light having a vibration surface in a certain direction among light incident on the film and absorbing light having a vibration surface perpendicular thereto. Typically, the dichroic dye is adsorbed and oriented on the polyvinyl alcohol resin. The polyvinyl alcohol resin constituting the polarizing film can be obtained by saponifying a polyvinyl acetate resin. The polyvinyl acetate resin used as a raw material for the polyvinyl alcohol resin is not only polyvinyl acetate, which is a homopolymer of vinyl acetate, but also a copolymer of vinyl acetate and other monomers copolymerizable therewith. May be. A polarizing film can be produced by subjecting a film made of such a polyvinyl alcohol resin to uniaxial stretching, dyeing with a dichroic dye, and boric acid crosslinking treatment after dyeing. As the dichroic dye, iodine or a dichroic organic dye is used. Uniaxial stretching may be performed before dyeing with a dichroic dye, may be performed simultaneously with dyeing with a dichroic dye, or after dyeing with a dichroic dye, for example, during a boric acid crosslinking treatment. May be. A polarizing film made of a polyvinyl alcohol-based resin thus manufactured and having a dichroic dye adsorbed and oriented is one of the raw materials for the polarizing plate.

[Optical film]
An optical film made of a thermoplastic resin is bonded to the polarizing film to produce a polarizing plate. The optical film preferably has a refractive index in the range of 1.4 to 1.7 as measured by the D line at a temperature of 20 ° C. The refractive index of the optical film is measured according to JIS K 0062: 1992 “Method for measuring refractive index of chemical product”. If the optical film has a refractive index in this range, it will have excellent display characteristics when the produced polarizing plate is incorporated in a liquid crystal panel. For the same reason, the preferable refractive index of the optical film is in the range of 1.45 to 1.67. This optical film has a haze value in the range of about 0.001 to 10% to improve the contrast of the obtained polarizing plate, particularly when it is incorporated into a liquid crystal panel to display black, and the brightness is reduced. This is preferable because it is less likely to cause defects. The haze value is a value defined by (diffuse transmittance / total light transmittance) × 100 (%), and is measured in accordance with JIS K 7136: 2000 “How to determine haze of plastic-transparent material”. The

Examples of the thermoplastic resin constituting such an optical film include the following, and here, the refractive index measured by the D-line at a temperature of 20 ° C. is also taken as n _D (20 ° C.). indicate.

Cycloolefin-based resin [n _D (20 ° C.) = 1.51 to about 1.54],
Crystalline polyolefin resin [n _D (20 ° C.) = 1.46 to 1.50 or so]
Polyester resin (n _D (20 ° C.) = 1.57 to 1.66),
Polycarbonate resin [n _D (20 ° C.) = 1.57 to 1.59],
Acrylic resin [n _D (20 ° C.) = 1.49 to about 1.51],
Triacetyl cellulose resin [n _D (20 ° C.) = 1.48 or so].

  The cycloolefin resin is a polymer having a cycloolefin monomer such as norbornene as a main structural unit, a resin obtained by hydrogenating a ring-opening polymer of a cycloolefin monomer, a cycloolefin monomer, Examples include addition polymers with chain olefin monomers having 2 to 10 carbon atoms such as ethylene and propylene and / or aromatic vinyl monomers such as styrene.

  The crystalline polyolefin-based resin is a polymer mainly composed of a chain olefin monomer having 2 to 10 carbon atoms, and is a homopolymer of a chain olefin monomer and two or more types of chain olefin monomers. Binary or ternary or higher copolymers using are included. Specifically, a polyethylene resin, a polypropylene resin, an ethylene-propylene copolymer, a homopolymer of 4-methyl-1-pentene, a copolymer of 4-methyl-1-pentene and ethylene or propylene, etc. Is included.

  Polyester resins include aliphatic polyesters as well as aromatic polyesters such as polyethylene terephthalate and polyethylene naphthalate. The polycarbonate-based resin is typically a polymer obtained by a reaction of bisphenol A and phosgene and having a carbonate bond —O—CO—O— in the main chain. The acrylic resin is typically a polymer mainly composed of methyl methacrylate. In addition to a methyl methacrylate homopolymer, methyl methacrylate and other methacrylate esters and / or acrylic esters. And copolymers thereof are also included. Triacetyl cellulose resin is an acetate of cellulose.

  From these thermoplastic resins, a film can be formed into a film by a solvent casting method, a melt extrusion method, or the like to obtain an optical film used in the present invention. Moreover, what was extended | stretched further uniaxially or biaxially after film forming can also be made into the optical film used for this invention. Prior to bonding to the polarizing film, the optical film may be subjected to easy adhesion treatment such as saponification treatment, corona treatment, plasma treatment, primer treatment or anchor coating treatment. Moreover, you may provide various process layers like a hard-coat layer, an antireflection layer, or an anti-glare layer in the surface on the opposite side to the bonding surface to the polarizing film of an optical film.

  The optical film preferably has a thickness of usually about 5 to 200 μm. If the optical film is too thin, the handling property is lacking, and there is a high possibility that the optical film will be broken in the polarizing plate production line or cause wrinkles. On the other hand, if it is too thick, the resulting polarizing plate becomes thick and the weight increases, which may impair the commercial properties. For these reasons, a more preferable thickness is 10 to 120 μm, and further 10 to 85 μm.

[adhesive]
When bonding an optical film to the above polarizing films, an adhesive is first apply | coated to the bonding surface to the polarizing film of an optical film. The thickness of the adhesive is set to a predetermined value in the range of 0.5 to 5 μm. If the thickness is less than 0.5 μm, uneven adhesion strength may occur. On the other hand, when the thickness exceeds 5 μm, not only the manufacturing cost increases, but also the hue of the polarizing plate may be affected depending on the kind of the adhesive. If the thickness is relatively thick within this range, for example, 3.5 μm or more, especially 4 μm or more, even if the thickness varies somewhat, defects such as bubbles are less likely to appear. Since increasing the thickness may lead to an increase in cost, it is desirable to reduce the thickness as much as possible. For these reasons, the preferred thickness of the adhesive is in the range of 1 to 4 μm, more preferably 1.5 to 3.5 μm.

  As long as the adhesive is supplied in a liquid-applicable state, it can be any of those conventionally used in the production of polarizing plates, but from the viewpoint of weather resistance and polymerizability, cationic polymerization Active compounds such as an epoxy compound, more specifically, an epoxy compound having no aromatic ring in the molecule, as described in Patent Document 1 (Japanese Patent Laid-Open No. 2004-245925). An active energy ray-curable adhesive contained as one of the curable components is preferable. Such an epoxy compound is, for example, a hydrogenated epoxy obtained by nuclear hydrogenation of an aromatic polyhydroxy compound, which is a raw material of an aromatic epoxy compound represented by diglycidyl ether of bisphenol A, and converting it to glycidyl ether. The compound, an alicyclic epoxy compound having at least one epoxy group bonded to the alicyclic ring in the molecule, an aliphatic epoxy compound typified by a glycidyl ether of an aliphatic polyhydroxy compound, and the like. In addition to cationically polymerizable compounds, typically epoxy compounds, active energy ray-curable adhesives usually generate polymerization species, especially cationic species or Lewis acids upon irradiation with active energy rays. A cationic photopolymerization initiator for initiating polymerization of the active compound is blended. Further, a thermal cationic polymerization initiator that initiates polymerization by heating, and various other additives such as a photosensitizer may be blended.

  When the optical film is bonded to both sides of the polarizing film, the adhesive applied to each optical film may be the same or different, but from the viewpoint of productivity, an appropriate adhesive force is obtained. It is preferable to use the same adhesive on both surfaces on the assumption that

[Production method of polarizing plate]
In this invention, an optical film is bonded to the polarizing film which consists of a polyvinyl alcohol-type resin demonstrated above through an adhesive agent, and a polarizing plate is manufactured. At this time, the following steps (A), (B), (C) and (D) are performed.

(A) The coating process which apply | coats an adhesive agent to the bonding surface to the polarizing film of an optical film using the coating machine which has a coating thickness control means of an adhesive agent,
(B) With the radiation film thickness meter, the thickness of the optical film is measured before the coating process, and the total thickness of the optical film and the applied adhesive is measured after the coating process. A measurement process for determining in-line the thickness of the applied adhesive from the absolute value of the measured value difference,
(C) A bonding step in which the polarizing film is applied to the adhesive surface that has been applied in the coating step and passed through the measurement step, and (D) an adhesive that is set within a range of 0.5 to 5 μm. When the ratio of the absolute value of the difference between the measured thickness X of the adhesive obtained in the measuring step and the Y with respect to the set thickness Y exceeds a predetermined value, the coating thickness control means is controlled. Control process.

  FIG. 1 is a side view schematically showing an example of the arrangement of manufacturing apparatuses preferably used in the present invention, and FIG. 2 is a block diagram showing the relationship between the steps in the present invention. Hereinafter, the manufacturing method of a polarizing plate is demonstrated in detail, referring also to these figures.

  The manufacturing apparatus shown in FIG. 1 pastes the first optical film 2 on one surface of the polarizing film 1 while continuously conveying the polarizing film 1, and the second optical film 3 on the other surface. Thus, the polarizing plate 4 is manufactured and wound around the winding roll 30. As shown in this figure, typically, an optical film is bonded to both surfaces of the polarizing film 1, but a mode in which the optical film is bonded only to one surface of the polarizing film 1 is also included in the present invention. The The form in that case will be understood by a person skilled in the art to the extent that it can be easily implemented by excluding the description of the other optical film from the following description.

  First, the thickness of the first optical film 2 is measured by the first radiation film thickness meter 14, and then an adhesive is applied from the first coating machine 10 to the surface to be bonded to the polarizing film 1. After that, the total thickness of the optical film and the applied adhesive is measured by the second radiation film thickness meter 15 and applied from the absolute value of the difference between the measured values by the two radiation film thickness meters 14 and 15. The thickness of the adhesive is now required. Similarly, the thickness of the second optical film 3 is first measured by the third radiation film thickness meter 16, and then the adhesive is applied from the second coating machine 12 to the surface to be bonded to the polarizing film 1. Is applied, the total thickness of the optical film and the applied adhesive is measured by the fourth radiation film thickness meter 17, and the absolute value of the difference between the measured values by the two radiation film thickness meters 16, 17 is measured. The thickness of the applied adhesive is determined.

  In the first optical film 2 and the second optical film 3 after the thicknesses before and after the adhesive coating are measured, the respective adhesive coating surfaces are superimposed on both surfaces of the polarizing film 1, and the nip roll 20 for bonding is applied. , 21 and pressed in the thickness direction, then irradiated with active energy rays from the active energy ray irradiating device 18 and the adhesive is cured, and then obtained through nip rolls 22 and 23 before winding. The polarizing plate 4 is wound around a winding roll 30.

  In the 1st coating machine 10 and the 2nd coating machine 12, an adhesive agent is apply | coated to the 1st and 2nd optical films 2 and 3 from the gravure rolls 11 and 13 provided in each. Yes. A conveyance guide roll 24 is appropriately provided on one surface of the polarizing film 1 and the surface of the first optical film 2 and the second optical film 3 opposite to the surface to which the adhesive is applied. As described above, when the optical film is bonded only to one surface of the polarizing film 1, only one of the first optical film 2 and the second optical film 3 shown in FIG. Only one optical film 2) may be applied. The straight arrows in the figure indicate the film flow direction, and the curved arrows indicate the roll rotation direction.

  The polarizing film 1 is supplied to the polyvinyl alcohol resin film as it is after undergoing uniaxial stretching, dyeing with a dichroic dye, and boric acid crosslinking treatment after dyeing in a polarizing film manufacturing process (not shown). Of course, it is of course possible to wind up the product manufactured in the polarizing film manufacturing process once on a roll, and then feed it out of the feeder again. On the other hand, the first optical film 2 and the second optical film 3 are each fed out from a roll (not shown) by a feeding machine. Each film is conveyed so as to have the same flow direction at the same line speed, for example, at a line speed of about 10 to 50 m / min. The first optical film 2 and the second optical film 3 are drawn out while applying a tension of about 50 to 1000 N / m in the flow direction.

  Then, the first coating machine 10 and the second coating machine 12 perform the above-described coating process (A), and the first and second radiation film thickness meters 14 and 15 and the third and fourth. The above-described measurement step (B) is performed by the radiation film thickness meters 16 and 17, and the above-described bonding step (C) is performed by the bonding nip rolls 20 and 21. The control process (D) described above is performed by turning the measurement results at 16 and 17 back to the coating machines 10 and 12. The gravure rolls 11 and 13 of the coating machines 10 and 12 are rolls having concave grooves, and the concave grooves are filled with an adhesive in advance, and by rotating on the optical films 2 and 3 in this state, An adhesive is transferred onto the optical films 2 and 3. By adjusting the rotation speed, it is possible to control the supply amount of the adhesive onto the optical films 2 and 3, and thus the coating thickness, which can be controlled by the coating thickness control means of the coating machines 10 and 12. Become.

  The relationship between these steps will be described based on the block diagram of FIG. First, in setting (0), a set thickness Y is set in advance within a range of 0.5 to 5 μm with respect to the thickness of the adhesive applied in the coating step (A). Then, as the first half of the measurement step (B), after the thicknesses of the optical films 2 and 3 are previously measured by the radiation film thickness meters 14 and 16, the initial stage of the coating thickness control means of the coating machines 10 and 12 is measured. Conditions are set and the coating process (A) is operated. Next, as a second half step of the measurement step (B), the total thickness of the optical film and the applied adhesive is measured by the radiation film thickness meters 15 and 17, and the measured value of the first half step and the measured value of the second half step are measured. The thickness of the applied adhesive is obtained from the absolute value of the difference and output as the measured thickness X. Regardless of the measured thickness X, the optical films 2 and 3 to which the adhesive has been applied are bonded to both surfaces of the polarizing film 1 at the respective adhesive application surfaces in the bonding step (C). On the other hand, in the control step (D), the measured thickness X is compared with the set thickness Y. When the absolute value of the difference between the measured thickness X and the set thickness Y is a predetermined value or more, for example, 5% or more with respect to the set thickness Y, the coating thickness control means of the coating machines 10 and 12 is used. So that the difference between the two becomes small as an absolute value, preferably the absolute value of the difference between the measured thickness X and the set thickness Y is less than 5% with respect to the set thickness Y. Control. Here, the fact that the absolute value of the difference between the measured thickness X and the set thickness Y is 5% or more with respect to the set thickness Y means that the following formula (I) is satisfied. Whether or not the condition is changed by the control means is determined depending on whether or not this equation is satisfied.

  Hereinafter, the coating process (A), the measurement process (B), the bonding process (C), and the control process (D) constituting the method of the present invention will be described in detail. In addition, when an active energy ray-curable adhesive is used, the curing step (E) is performed after each of the above steps, and this step will also be described.

(A) Coating process In the coating process (A), the bonding surface to the polarizing film 1 of the optical films 2 and 3 which passed through the first half process (process which measures the thickness of optical film itself) of a measurement process (B). An adhesive is applied to the surface. Although the coating machine used here will not be specifically limited if it has a means to control application | coating thickness, The system using the gravure rolls 11 and 13 demonstrated with reference to FIG. 1 is typical. Examples of the coating machine using a gravure roll include a direct gravure coater, a chamber doctor coater, an offset gravure coater, a kiss coater using a gravure roll, and a reverse roll coater composed of a plurality of rolls. In addition, there are a cylindrical blade, a die coater that supplies adhesive directly to the application part by applying adhesive to the application part and scraping off with the blade, applying a slot die, etc., and a liquid reservoir Various coating machines such as a knife coater that makes and applies excess liquid while scraping off with a knife can be used. Among these, direct gravure coater, chamber doctor coater, offset gravure coater, etc. are preferable among coating machines using gravure rolls, considering thin film coating and pass line freedom, etc. Then, a die coater using a slot die is also preferable. A chamber doctor coater is more preferable because it can easily cope with the widening of the polarizing plate and hardly releases the odor of the adhesive supplied in liquid.

  Here, the chamber doctor coater makes the gravure roll contact the chamber doctor that has absorbed the liquid paint (adhesive), and transfers the paint (adhesive) in the chamber doctor to the concave groove of the gravure roll. Is a coating machine of a type in which the film is transferred to the optical films 2 and 3 which are the objects to be coated. The compact design is also called a microchamber doctor coater.

  When the adhesive is applied using a gravure roll, the thickness of the adhesive layer can be adjusted by the speed ratio of the gravure roll to the line speed. The line speed of the optical films 2 and 3 is set to 10 to 50 m / min, the gravure roll is rotated in the opposite direction to the transport direction of the optical films 2 and 3, and the rotational peripheral speed of the gravure roll is set to 10 to 500 m / min. Thereby, it can adjust so that the application | coating thickness of an adhesive agent may be set to 0.5-5 micrometers. Since the coating thickness at this time is also affected by the porosity of the surface of the gravure roll, it is preferable to select a gravure roll having a surface porosity suitable for the set thickness Y in advance. In addition, the system which rotates a gravure roll in the reverse direction with respect to the conveyance direction of the optical films 2 and 3 is also called a reverse gravure.

(B) Measurement process In the first half of the measurement process (B) performed before the coating process (A), the thickness of the optical film itself is measured after the coating process (A) (B In the latter half of the process, the total thickness of the optical film and the applied adhesive was measured with a radiation film thickness meter, and applied from the absolute value of the difference between the measured value in the first half process and the measured value in the second half process. The thickness of the adhesive is required. As shown in FIG. 1, the first to fourth radiation film thickness meters 14, 15, 16, and 17 are respectively connected to the first to fourth radiation sources 14 a, 15 a, 16 a, and 17 a and the first to fourth radiation sources. It consists of detectors 14b, 15b, 16b, and 17b, and these are arranged so as to face each other through the optical film to be measured.

  The radiation film thickness meters 14, 15, 16, and 17 irradiate the optical film with radiation sources 14a, 15a, 16a, and 17a, and the radiation transmitted through the optical film is detected by the detectors 14b, 15b, 16b, and 17b. Detect by. The irradiated radiation attenuates when passing through the optical film. The radiation film thickness meters 14, 15, 16, and 17 obtain the weight of the optical film from the attenuation amount and convert it to the thickness. The amount of radiation attenuation can be affected by the density of the optical film, but generally increases as the film thickness of the optical film increases.

  In the first half of the measurement process (B), radiation is transmitted through the optical film before the adhesive is applied, and the film thickness value measured by obtaining the attenuation is output, and the second half of the measurement process (B). In the process, radiation is transmitted through the optical film coated with the adhesive, and the attenuation value is obtained to output the film thickness value of the adhesive layer and the optical film, and the difference between the film thickness values of the two. The thickness of the adhesive is obtained as an absolute value of. According to the film thickness measuring method using such a radiation film thickness meter, the thickness of the adhesive can be accurately obtained in-line.

  The film thickness measurement method using a radiation film thickness meter can be used regardless of whether there is a difference in refractive index between the optical film and the adhesive, or when there is no difference in the characteristic absorption of the infrared absorption spectrum. There is also an advantage that the thickness of can be obtained. Furthermore, unlike the film thickness measurement method using an optical interference type film thickness meter, the film thickness is not easily affected by the optical properties of the optical film, such as the transparency of the optical film, the degree of orientation, and the orientation direction. It becomes possible.

  In converting the radiation attenuation to the thickness of the optical film or the optical film with the adhesive layer, these relationships are measured in advance and a calibration curve is prepared. The amount of radiation attenuation is usually obtained as a current value or voltage value by a detector. In such a case, the current value or voltage value is measured for optical films of the same material having different thicknesses, and the thickness changes. A calibration curve of current value or voltage value for is created. The optical film used when creating the calibration curve is made of the same material that is thicker than the optical film that is actually used to manufacture the polarizing plate and the same material that is thinner than the optical film that is actually used to manufacture the polarizing plate. It is preferable that an optical film is included in that the thickness can be measured with higher accuracy. A calibration curve is prepared in the same manner for the optical film with an adhesive layer. In addition, in order to improve the measurement accuracy of adhesive thickness, radiation attenuation for optical films of the same material with different thicknesses and radiation attenuation for optical films with adhesive layers of the same material with different thicknesses May be measured, and a calibration curve for radiation attenuation with respect to changes in the thickness of the adhesive obtained as an absolute value of the difference between the thickness of the optical film with the adhesive layer and the thickness of the optical film may be created.

  As the radiation film thickness meter, a film thickness meter using radiation such as X-rays, β rays, or γ rays can be used. In view of the thickness of the optical film to be measured and the optical film with the adhesive layer (as described above, the thickness of the optical film is usually 5 to 200 μm and the thickness of the adhesive is 0.5 to 5 μm. It is preferable to use a radiation film thickness meter using X-rays or β-rays.

  A radiation film thickness meter (X-ray film thickness meter) using X-rays usually has an X-ray source tube using a titanium target, a tungsten target or the like, and generates X-rays by applying a voltage to the tube. . A radiation film thickness meter (β-ray film thickness meter) using β-rays usually generates β-rays using Pm147, krypton 85 or Sr90 as a radiation source. From the viewpoint of measuring the thickness of the adhesive more accurately, it is preferable to use a β-ray film thickness meter using Pm147 as a radiation source among the β-ray film thickness meters.

  Compared with a β-ray film thickness meter, the X-ray film thickness meter tends to depend on the type (material) of the optical film for the amount of radiation attenuation when the radiation is transmitted through the optical film. Therefore, when the thickness of the optical film itself is obtained from the calibration curve, it is necessary to create a new calibration curve depending on the type of the optical film or to create a calibration curve for each of the different types of optical films. The case is higher than the β-ray film thickness meter. Therefore, when the type of the first optical film to be bonded to one surface of the polarizing film and the second optical film to be bonded to the other surface are different, or different types having different types of optical films in the same production line In the case of manufacturing a polarizing plate, a β-ray film thickness meter may be preferable in order to obtain a higher thickness measurement accuracy of the adhesive.

  From the viewpoint of measuring the thickness of the adhesive with higher accuracy, the measurement spot (area of the radiation irradiation area on the optical film) by the radiation film thickness meter is preferably about 10 to 30 mm in diameter. The in-line measurement accuracy of the radiation film thickness meter is preferably ± 0.15 μm or less, and more preferably ± 0.1 μm or less. In order to achieve such measurement accuracy, it is preferable to use a radiation source that does not reach the half-life because the radiation intensity of the radiation film thickness meter is high in energy intensity and can be measured with higher accuracy.

  In addition, from the viewpoint of the stability of the thickness measurement value of the adhesive, the radiation film thickness meter can measure once at a measurement interval of 0.005 to 1 second, particularly 0.01 to 0.5 second. It is preferable that a moving average can be obtained and output from 10 to 50000 measurement values continuous from the obtained data. For example, when the number of moving averages exceeds 50000 points and the measurement interval exceeds 0.5 seconds, the difference between the measured value and the actual thickness may increase. For the same reason, a film thickness meter that performs a single measurement at a measurement interval of 0.005 to 1 second, and outputs a moving average with respect to continuous measurement values of 100 to 50000 points from the obtained data. It is even more preferable to use it.

  In order to improve the measurement accuracy of the adhesive thickness, the installation position of the radiation film thickness meter for measuring the thickness of the optical film itself before the coating process (A) and the optical film after the coating process (A) It is preferable that the installation position of the radiation film thickness meter for measuring the total thickness of the adhesive and the adhesive coincides with the width direction of the optical film. For the same reason, it is preferable to match the thickness measurement points with respect to the longitudinal direction (conveying direction) of the optical film. Furthermore, for the same reason, the installation interval between the two radiation film thickness meters is preferably 10 m or less, more preferably 1 to 5 m along the longitudinal direction of the optical film.

(C) Bonding process After passing through the above coating process (A) and measurement process (B), the polarizing film 1 is applied to the adhesive application surfaces of the optical films 2 and 3, and the bonding process of pressing the polarizing film 1 ( C) is performed. Although known means can be used for pressurization in this step, from the viewpoint that pressurization while continuous conveyance is possible, as shown in FIG. 1, a method of sandwiching between a pair of nip rolls 20 and 21 Is preferred. In this case, it is desirable that the timing at which the optical films 2 and 3 are superimposed on the polarizing film 1 and the timing at which the optical films 2 and 3 are pressed by the pair of nip rolls 20 and 21 are the same. preferable. The combination of the pair of nip rolls 20 and 21 may be any of metal roll / metal roll, metal roll / rubber roll, rubber roll / rubber roll, and the like. The pressure at the time of pressurization is preferably about 150 to 500 N / cm as a linear pressure when sandwiched between the pair of nip rolls 20 and 21.

(D) Control process In this invention, based on the result of the measurement process (B) demonstrated above, the control process (D) which controls the application | coating thickness of the adhesive agent in a coating process (A) is provided. That is, the thickness of the adhesive applied in the coating step (A) may slightly vary depending on the temperature of the adhesive, the ambient temperature, the surface tension of the optical films 2 and 3, and the tension applied thereto. There may be a deviation from a desired coating thickness (set thickness Y). In order to correct such a deviation in coating thickness, the coating thickness control of the coating machine is based on the coating thickness (total thickness X) measured by the radiation film thickness meter in the measurement step (B). Control means.

  For example, if the coating machine is a die coater, when the measured thickness X is larger than the set thickness Y, the ability to feed liquid from a pump or the like to the die is reduced, and conversely the measured thickness X is greater than the set thickness Y. When it is small, the coating thickness can be controlled by increasing the ability to feed liquid to the die. Also, if the coating machine is a chamber doctor coater using a gravure roll, when the measured thickness X is larger than the set thickness Y, the transfer of adhesive can be performed by increasing the rotational speed of the reverse gravure and increasing the rotational peripheral speed. On the contrary, when the measured thickness X is smaller than the set thickness Y, the coating thickness is increased by increasing the transfer amount of the adhesive by decreasing the rotation speed of the reverse gravure and decreasing the rotational peripheral speed. Can be controlled. The degree of film thickness control is arbitrarily set experimentally depending on the environmental factors at that time, the viscosity of the adhesive, the surface shape of the optical film, and the like. Actual control may be performed using a computer or manually.

(E) Curing Step After the optical films 2 and 3 are bonded to the polarizing film 1 as described above, if the adhesive is an active energy ray curable type, the adhesive is cured by irradiation with active energy rays. The polarizing plate 4 is manufactured through the curing step (E). In the example shown in FIG. 1, this curing step (E) is performed by irradiating the laminated body in which the optical films 2 and 3 are bonded to the polarizing film 1 from the active energy ray irradiation device 18. . In this step, energy necessary for curing the active energy ray-curable adhesive is irradiated through the optical film 2. Specifically, an electron beam or an ultraviolet ray is used as the active energy ray and is selected according to the curing reaction mechanism of the adhesive. Since the electron beam irradiation device needs to shield the generated electron beam from leaking outside, the size and weight of the device increase. On the other hand, since the ultraviolet irradiation device has a relatively compact structure, curing by ultraviolet irradiation is preferably used.

  In the example shown in FIG. 1, the nip roll 20 in which the active energy ray is irradiated on the laminate in which the polarizing film 1 and the optical films 2 and 3 are bonded via an adhesive is disposed before and after the active energy ray irradiation device 18. , 21 and the pre-winding nip rolls 22, 23 in a state where tension is applied to the laminate. Not limited to this, for example, a convex curved surface formed in an arc shape along the conveying direction as disclosed in the above-mentioned Patent Document 2 (Japanese Patent Laid-Open No. 2009-134190), typically on the outer peripheral surface of the roll. It is also preferable to irradiate active energy rays in a supported state. In particular, when heat is generated by irradiation of active energy rays and there is a possibility that the product may be adversely affected, the active energy rays are irradiated to the laminated body supported by the outer peripheral surface of the roll as in the latter case. In this case, it is preferable that the temperature of the roll supporting the laminate can be adjusted within a range of about 10 to 60 ° C. Moreover, although only one active energy ray irradiation apparatus may be provided at the irradiation site, two or more active energy ray irradiation apparatuses may be provided along the flow direction of the laminated body, and irradiation from a plurality of light sources can be effectively performed. It is effective in raising.

  When the adhesive is cured by irradiating ultraviolet rays, the ultraviolet light source to be used is not particularly limited, but has a light emission distribution at a wavelength of 400 nm or less, for example, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a chemical lamp, black A light lamp, a microwave excitation mercury lamp, a metal halide lamp, etc. can be used. In the case of using an adhesive having an epoxy compound as an active energy ray-curable component, a high-pressure mercury lamp or a metal halide lamp having a lot of light of 400 nm or less is preferably used as an ultraviolet light source in consideration of an absorption wavelength exhibited by a general polymerization initiator. It is done.

When the adhesive having an epoxy compound as a curable component is cured by irradiating with ultraviolet rays, the line speed of the laminate is not particularly limited, but in general, the line speed in the coating process (A) or the bonding process (C). Is maintained almost as it is. In addition, while applying a tension of 100 to 1000 N / m in the longitudinal direction (conveying direction) of the laminate, the irradiation amount in the wavelength region effective for activating the polymerization initiator is the integrated light amount (total energy irradiated to the laminate). ) Is preferably 100 to 1500 mJ / cm ² . If the accumulated light amount to the adhesive is too small, the curing reaction of the active energy ray-curable adhesive is insufficient, and sufficient adhesive strength is difficult to be expressed. On the other hand, if the accumulated light amount is too large, the light source radiates. Heat and heat generated when the adhesive is polymerized may cause yellowing of the active energy ray-curable adhesive and deterioration of the polarizing film.

Further, if it is attempted to achieve the necessary integrated light quantity by one ultraviolet irradiation, the film may be heated to a high temperature exceeding 150 ° C. due to heat generation. In this case, the polarizing film may be deteriorated. In order to avoid such a situation, as described above, it is effective to provide a plurality of ultraviolet irradiation devices along the film conveyance direction and to irradiate a plurality of times. As a guide, the dose of the ultraviolet irradiation apparatus of one point is set to 600 mJ / cm ² or less integrated quantity of light, eventually if it is preferable that the integrated quantity of light 100~1500mJ / cm ² as described above can be obtained is there.

  The polarizing plate manufactured as described above is controlled within the range in which the thickness of the adhesive is set, variation in the adhesive strength between the films constituting the polarizing plate is small, and bubble defects in the adhesive layer are also present. The quality stability as a product is excellent.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples. The experiment shown below was performed to confirm the effect of the present invention. For example, an adhesive applied on the opposite side of the adhesive whose thickness is measured with a polarizing film interposed therebetween. It should be noted that the thickness of is set to be thicker than the optimum value adopted in actual operation so that no defect is generated there.

  FIG. 3 is a side view schematically showing the arrangement of apparatuses used in the following examples and comparative examples. The arrangement shown in FIG. 3 is different from the previously described FIG. 1 only in the following two points, and parts other than the differences are given the same reference numerals as those in FIG. For the description, refer to the description of FIG.

3 differs from FIG. 3 in FIG.
(1) When irradiating active energy rays (ultraviolet rays) to the laminate after bonding the first optical film 2 and the second optical film 3 to both surfaces of the polarizing film 1 respectively, the second of the laminate From the active energy ray (ultraviolet ray) irradiation device 18 arranged on the opposite side of the winding roll 26 with the laminated body sandwiched between the optical film 3 side and the outer peripheral surface of the winding roll 26 for irradiation, The point where the first optical film 2 was irradiated with ultraviolet rays, and
(2) Since only one set (2 units) of radiation film thickness meter is provided, the thickness of the adhesive applied to the first optical film 2 is measured by the radiation film thickness meters 14 and 15, and the second The thickness of the adhesive applied to the optical film 3 was not measured.

  Further, as the radiation film thickness meters 14 and 15, a β-ray film thickness meter “SB-1100” (β-ray source: Pm-147), which is an authentication device with a display manufactured by Nano Gray Co., Ltd., was used. This β-ray film thickness meter measures the film thickness from the attenuation when the radiation is transmitted through the optical film, and the in-line film thickness measurement accuracy is about ± 0.1 μm. Then, the film thickness of the object to be measured is measured at each preset measurement interval, and the individual film thickness values measured above are also moved and averaged at each preset measurement count, and the average film thickness therebetween And the data determined to be abnormal values out of the preset number of measurement values are automatically excluded and the average film thickness is output.

[Example 1]
(0) Material used in the experiment In this example, the first optical film 2 has a thickness of 40 μm, a width of 1330 mm, and a biaxially oriented retardation film “KC4FR-” made of triacetyl cellulose supplied from a roll. 1 ”[obtained from Konica Minolta Opto Co., Ltd., refractive index 1.48], the second optical film 3 has a thickness of 80 μm, a width of 1330 mm, and is also supplied from a roll“ triacetyl cellulose film “ KC8UX2MW ”(obtained from Konica Minolta Opto, Inc., refractive index 1.48) was used. The adhesive used for bonding the polarizing film 1 and the first optical film 2 and the adhesive used for bonding the polarizing film 1 and the second optical film 3 are both an epoxy compound and a photopolymerization initiator. It is an epoxy-based photocurable adhesive that contains substantially no solvent.

(A) Coating process Polarizing film 1 having a thickness of 25 μm in which iodine is adsorbed and oriented on polyvinyl alcohol, the retardation film as the first optical film 2, and the triacetyl cellulose as the second optical film 3 The films were fed in the same flow direction at a line speed of 15 m / min each. A first coating provided with a gravure roll 11 on the surface to be bonded to the polarizing film 1 of the retardation film 2 that has undergone the first half of the measurement step (B) described later (step of measuring the thickness of the optical film itself). The above epoxy photo-curing adhesive was applied using an industrial machine 10 (“Microchamber Doctor” manufactured by Fuji Machine Co., Ltd.). Moreover, the surface of the triacetyl cellulose film 3 to be bonded to the polarizing film 1 is also used by using a second coating machine 12 equipped with a gravure roll 13 [also a “micro chamber doctor” manufactured by Fuji Machine Co., Ltd.]. The above epoxy photo-curing adhesive was applied.

  The gravure rolls 11 and 13 provided in the coating machines 10 and 12 were rotated in the opposite direction with respect to the film transport direction. Then, in the second coating machine 12 on the triacetyl cellulose film 3 side, the rotational peripheral speed of the gravure roll 13 provided in the second coating machine 12 is 15 m / min, and the adhesive is applied on the film with a thickness of about 4.5 μm. Was set to This is because the thickness of the adhesive applied by the second coating machine 12 is not measured, and therefore the film thickness is not controlled, so that the adhesive is applied with a thickness that does not cause any defects. It is a thing. On the other hand, on the phase difference film 2 side, the rotational peripheral speed of the gravure roll 11 provided in the first coating machine 10 is set to an initial setting of 21 m / min so that the adhesive is applied with a thickness of about 2.5 μm. did.

(B) Measuring step The first radiation film thickness meter 14 is disposed on the upstream side of the first coating machine 10, and the second radiation film thickness meter 15 is disposed on the downstream side of the first coating machine 10. And the space | interval along the film flow direction of both coating machines was 1.67 m. Then, the thickness of the retardation film 2 is measured at intervals of 0.2 seconds by the first radiation film thickness meter 14, and {(2 ² ) ² } ² = 2 ⁶ = 256 consecutive measurement values ( The moving average value was set so as to be sequentially output every approximately 51.2 seconds) (first half step). Further, the total thickness of the retardation film 2 and the adhesive is set to 0. 0 from the adhesive coating surface side of the retardation film 2 by the second radiation film thickness meter 15 disposed after the above coating process. Measurement was performed at intervals of 2 seconds, and the moving average value was sequentially output every 256 consecutive measurement values (about 51.2 seconds) (1 in the second half step). Therefore, after about 51.2 seconds from which the measurement value for 256 times is obtained from the start, the moving average of the thickness of the retardation film 2 from the first radiation film thickness meter 14 is obtained every 0.2 seconds. The value is output, and the moving average value of the total thickness of the retardation film 2 and the adhesive is output from the second radiation film thickness meter 15, and the value is extracted every 1 second, and the former at that time The difference (B−A) between the value (measured value of the thickness of the retardation film 2 = A) and the latter value (measured value of the total thickness of the retardation film 2 and the adhesive = B) is The measurement thickness X was set so as to be sequentially recorded (second half process 2). In addition, a control step (D) described later is provided to operate for about 150 minutes while controlling the measured thickness X, and the measured thickness X obtained during that time (the number of data is about 150 minutes × 60 pieces / The average value and standard deviation of about 9000 pieces per minute were determined, and the results are shown in Table 1.

(C) Bonding process Each adhesive application surface of the phase difference film 2 and the triacetyl cellulose film 3 to which the adhesive is applied is superposed on the polarizing film 1, and a 240 N / cm line is applied by the nip rolls 20 and 21 for bonding. I pinched it with pressure. The laminate of the retardation film 2 / polarizing film 1 / triacetyl cellulose film 3 after passing through the nip rolls 20 and 21 has an outer periphery of the winding roll 26 for irradiation in which the triacetyl cellulose film 3 side is set to 20 ° C. A tension of 600 N was applied in the longitudinal direction so as to be in close contact with the surface, and the film was conveyed while irradiating ultraviolet rays from the ultraviolet irradiation device 18 to the phase difference film 2 side at the same line speed 15 m / min as before bonding. The ultraviolet irradiation device 18 was manufactured by GS Yuasa Co., Ltd. and irradiated with ultraviolet rays from two “EHAN1700NAL high-pressure mercury lamps” which are ultraviolet lamps included in the device. The cumulative amount of ultraviolet light was 330 mJ / cm ² for the two lamps. In this way, the adhesive layer was cured, and a polarizing plate 4 in which the retardation film 2 was bonded to one side of the polarizing film 1 and the triacetyl cellulose film 3 was bonded to the other side was prepared and wound around a winding roll 30.

(D) Control process In the control process, when the measurement thickness X obtained in the above measurement process (B) is more than 5% apart from the set thickness Y = 2.5 μm, that is, | X−Y | When ≧ 0.125 μm, the coating thickness of the adhesive was controlled while increasing / decreasing the rotational peripheral speed of the gravure roll 11 provided in the first coating machine 10 in units of 0.5 m / min. .

[Comparative Example 1]
In Example 1, without providing the control process (D), that is, even if the measurement thickness X obtained in the measurement process (B) changes, the rotation speed of the gravure roll 11 provided in the first coating machine 10 is adjusted. Without changing, a laminate was manufactured, and subsequently, ultraviolet rays were similarly irradiated to produce a polarizing plate. Table 1 shows the average value and standard deviation of the measured thickness X when operated for about 150 minutes.

[Comparative Example 2]
In Example 1, the first radiation film thickness meter 14 was not installed, and instead of the second radiation film thickness meter 15, a reflection made by Otsuka Electronics Co., Ltd. with a spectral wavelength range of 230 to 800 nm was used. A spectral film thickness meter “FE-2900CCD” was installed, and the same procedure as in Example 1 was performed except that in the measurement step (B), an attempt was made to directly measure the coating thickness of the adhesive with this reflective spectral film thickness meter. A polarizing plate was produced. However, since the refractive index (1.48) of the retardation film made of triacetyl cellulose used as the first optical film 2 was close to the refractive index (1.49) of the adhesive, the thickness of the adhesive can be measured. Therefore, the application thickness of the adhesive could not be controlled.

[Example 2]
In Example 1, instead of the biaxially oriented retardation film “KC4FR-1” made of triacetylcellulose, a biaxially stretched polyethylene terephthalate film having a thickness of 38 μm and a width of 1330 mm [obtained from Mitsubishi Plastics, Ltd., A polarizing plate was produced in the same manner as in Example 1 except that the in-plane retardation value 1000 nm was used as the first optical film 2. Table 1 shows the average value and standard deviation of the measured thickness X when operated for about 150 minutes.

[Comparative Example 3]
In Example 2, the rotational speed of the gravure roll 11 provided in the first coating machine 10 is changed without providing the control step (D), that is, even when the measurement thickness X obtained in the measurement step (B) changes. Without changing, a laminate was manufactured, and subsequently, ultraviolet rays were similarly irradiated to produce a polarizing plate. Table 1 shows the average value and standard deviation of the measured thickness X when operated for about 150 minutes.

[Defect evaluation test of polarizing plate]
Of the polarizing plates obtained with a width of 1330 mm in the above examples and comparative examples, the surface extending over a length of 3300 mm in the flow direction within the effective width, with the central 1250 mm width portion excluding the 40 mm width portions at both ends as the effective width. With respect to (1.25 m × 3.3 m≈4 m ² ), a place that is a bright spot is visually observed, and the marked place is further observed with a magnifying glass having a magnification of 100 times to confirm whether it is a bubble or not. In addition, if it was a bubble, its size was determined as follows. That is, if the observed bubble is a pseudo-elliptical shape (including a circle), the longest diameter is the size of the bubble, and if the bubble is linear, the length of the line is the size of the bubble. Then, the number of bubbles having a size of 100 μm or more is counted, and when the number is less than 0.3 per 1 m ² , that is, when the observed area of 4 m ² is 0 or 1, “OK”, When the number is 0.3 or more per 1 m ² , that is, when the number is ² or more in the observed area of 4 m ² , the result is summarized in Table 1 together with main variables. In the table, “TAC” in the column of optical film means triacetyl cellulose, and “PET” means polyethylene terephthalate. In addition, as for the bubble of the magnitude | size of 100 micrometers or more observed with the loupe, when the film was cut out to the size of 40 mm x 40 mm so that it might enter, and both were observed with the microscope, both were the polarizing film 1 and the 1st optical film. 2 was confirmed to be in the adhesive layer interposed between the two.

  As shown in Table 1, in Comparative Examples 1 and 3 in which the control step (D) was not provided, the measured thickness of the adhesive varied, and along with this, bubble defects were seen in the obtained polarizing plate. On the other hand, in the first and second embodiments in which the coating thickness is changed when the control step (D) is provided and the measured thickness X of the adhesive is 5% or more away from the set thickness Y, the set thickness Y It can be seen that the measured thickness is suppressed to a fluctuation of approximately 5% or less and that there are few bubble defects. On the other hand, when a reflection spectral film thickness meter having a spectral wavelength range of 800 nm or less is used as in Comparative Example 2, there is almost no difference between the refractive index of the adhesive and the refractive index of the optical film. Furthermore, the application thickness of the adhesive cannot be measured.

  DESCRIPTION OF SYMBOLS 1 Polarizing film, 2 1st optical film, 3 2nd optical film, 4 Polarizing plate, 10 1st coating machine, 11 Gravure roll, 12 2nd coating machine, 13 Gravure roll, 14 1st Radiation thickness meter, 14a first radiation source, 14b first detector, 15 second radiation thickness meter, 15a second radiation source, 15b second detector, 16 third radiation thickness meter , 16a Third radiation source, 16b Third detector, 17 Fourth radiation film thickness meter, 17a Fourth radiation source, 17b Fourth detector, 18 Active energy ray (ultraviolet) irradiation device, 20, 21 Nip roll for bonding, 22, 23 Nip roll before winding, 24 guide roll, 26 winding roll for irradiation, 30 winding roll.

Claims (2)

A method for producing a polarizing plate by bonding an optical film made of a thermoplastic resin to a polarizing film made of a polyvinyl alcohol resin through an adhesive,
(A) The coating process which apply | coats the said adhesive agent to the bonding surface to the polarizing film of the said optical film using the coating machine which has a coating thickness control means of the said adhesive agent,
(B) The thickness of the optical film is measured before the coating step by a radiation film thickness meter, and the total of the optical film and the applied adhesive before curing is applied after the coating step. A measurement step of measuring the thickness and determining in-line the thickness of the adhesive before curing applied from the absolute value of the difference between those measurements,
(C) a bonding step in which the polarizing film is applied to the adhesive surface that has been applied in the coating step and passed through the measurement step, and (D) an adhesive set within a range of 0.5 to 5 μm. When the ratio of the absolute value of the difference between the measured thickness X of the adhesive obtained in the measuring step and the Y with respect to the set thickness Y is equal to or greater than a predetermined value, the coating thickness control means is controlled. Control process,
The manufacturing method of a polarizing plate provided with.   In the control step (D), when the ratio of the absolute value of the difference between the measured thickness X of the adhesive obtained in the measuring step and the Y with respect to the set thickness Y of the adhesive is 5% or more The manufacturing method of the polarizing plate of Claim 1 which controls the said coating thickness control means.

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