TWI535571B - A method of manufacturing a polarizer - Google Patents

Description

Method for manufacturing polarizing plate

The present invention relates to a method of manufacturing 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 a polarizing plate on both surfaces of a liquid crystal cell. In general, the 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-based resin via an adhesive. In many cases, the transparent resin film is bonded to the other surface of the polarizing film via an adhesive. The transparent resin film on the side is not only the protective film for the polarizing film but also the protective film. A so-called retardation film having a protective function and imparting a phase difference in the in-plane and/or thickness direction for the purpose of optical compensation or viewing angle compensation of the liquid crystal cell. In the present specification, such a protective film or a retardation film which is bonded to a polarizing film via an adhesive is referred to as an "optical film". The adhesive for bonding the optical film to the polarizing film is usually liquid, and the adhesive force is expressed between the polarizing film and the optical film by the hardening reaction of the liquid adhesive.

In recent years, the price of liquid crystal display devices, including televisions, has rapidly declined, and the demand for lowering the cost of the components constituting them has become stronger. On the other hand, the demand for quality has become stronger. In this trend, the type of the optical film that can be used in the production of the polarizing plate is limited to a water-based adhesive of a specific resin such as a cellulose resin, and the type of the optical film that can be applied is changed. A large number of active energy ray hardening type adhesives. A bonding example of a polarizing film and an optical film using an active energy ray hardening type adhesive It is proposed in Japanese Patent Laid-Open Publication No. 2004-245925.

Preparing a liquid active energy ray-curable adhesive, using a die coater for directly applying the liquid adhesive to the coated object, or carrying a liquid adhesive in a groove formed in the surface and The gravure roll transferred to the surface of the object to be coated is precoated on the bonding surface of the optical film to the polarizing film. Then, the polarizing film is superposed on the adhesive-coated surface, and an active energy ray such as an ultraviolet ray or an electron beam is irradiated to cure the adhesive to express an adhesive force. Regarding such an embodiment in which an active energy ray-curable adhesive is used, many optical films can be applied, which is a very effective method.

As a method of producing a polarizing plate using the active energy ray-curable adhesive, for example, Japanese Laid-Open Patent Publication No. 2009-134190 discloses a method of obtaining a laminate by superimposing a protective film on both surfaces of a polarizing film via an adhesive. The active energy ray is irradiated while the laminated body is in close contact with the outer surface of the convex curved surface which is formed in a meandering shape along the conveying direction of the laminated body. According to this method, it is possible to manufacture a polarizing plate which can suppress the occurrence of reverse curl and wave curl which are likely to occur in the obtained polarizing plate, and which has excellent performance.

In the method of the document, it is considered that the thickness of the adhesive layer formed on the protective film does not greatly affect the reverse curl and the waveform curl of the manufactured polarizing plate, so that it is not necessary to apply the adhesive to the adhesive. Thickness management. However, most of the defects caused by fluctuations in the thickness of the adhesive layer are not problematic, but defects such as bubbles may occur, and when the defects are large, the yield of the polarizing plate may be lowered. Further, in the case of stably producing an inexpensive and higher-performance polarizing plate, in many cases, the active energy ray-curable adhesive is applied thicker than the previous water-based adhesive, and, in addition, due to its own Since it is also desirable to reduce the thickness of the polarizing plate itself, it is desirable to manage it in such a manner as to obtain the minimum thickness required for the fluctuation range (variation).

An infrared film thickness meter is known as a machine for measuring the coating thickness after the application of the adhesive in the line, that is, after the application of the adhesive in the manufacturing line of the polarizing plate, and before the polarizing film is bonded to the optical film. However, since the resolution of the infrared film thickness meter has a limit, it is difficult to accurately measure the thickness of the coating layer (adhesive layer) formed on the film which is continuously conveyed as in the case of the polarizing plate manufacturing line by several μm. Specifically, in the polarizing plate manufacturing line, as shown in FIG. 1 described later, the polarizing film and the optical film bonded to at least one surface thereof are continuously conveyed without respective support bodies, and Fit somewhere. The film thus continuously conveyed will be slightly shaken (vibrated) in the direction of the thickness direction and the direction of the applied tension (flow direction), and if the thickness of the coating layer is to be measured by the infrared film thickness gauge in the presence of the above shaking, It is virtually impossible to manage the coating thickness based on the accuracy of about ±1 μm. Further, if the thickness of the adhesive layer formed on the optical film is to be measured by an infrared film thickness meter, there is a significant difference between the infrared absorption peak provided by the optical film and the infrared absorption peak provided by the adhesive. In some cases, depending on the type of the optical film, the peaks of the two overlap, and the measured value itself cannot be obtained. Therefore, in the manufacture of a polarizing plate using a liquid adhesive, the thickness of the liquid adhesive applied to the film cannot be checked in-line.

In view of the above, it is an object of the present invention to provide an optical film by a liquid adhesive which is a representative example of an active energy ray-curable adhesive on a polarizing film, and the thickness of the adhesive is adjusted by the thickness of the in-line management adhesive. The method of suppressing the occurrence of defects such as bubbles in the adhesive layer and suppressing the generation of the polarizing plate at a low cost.

The present inventors have intensively studied to solve the above problems, and as a result, it has been found that when a liquid adhesive is applied to an optical film and the coating layer is bonded to a polarizing film to produce a polarizing plate, The method measures the thickness of the applied adhesive, accurately determines the thickness, and based on the result, controls the coating thickness of the adhesive at the time of coating, whereby a polarizing plate having a uniform thickness of the adhesive and less defects can be produced. Thus, the present invention has been completed.

In other words, the present invention provides a method for producing a polarizing plate, which is obtained by laminating a polarizing film made of a thermoplastic resin to an optical film made of a polyvinyl alcohol-based resin, and comprising the following (A). The steps of (B), (C) and (D).

(A) a coating step of applying the above-mentioned adhesive to the bonding surface of the optical film to the polarizing film using a coating machine having a coating thickness control mechanism of an adhesive; (B) a measuring step using the spectral wavelength region The spectroscopic interference method in the range of more than 800 nm is set, the thickness of the optical film is measured before the coating step, and the total thickness of the optical film and the applied adhesive is measured after the coating step, and these are in-line by the coating step. The absolute value of the difference between the measured values is used to determine the thickness of the applied adhesive; (C) the bonding step, coating in the above coating step and passing the above measurement The adhesive surface of the step overlaps the polarizing film and is pressurized; and (D) the control step, based on the set thickness Y of the adhesive set in the range of 0.5 to 5 μm and the measured thickness X of the adhesive obtained in the measuring step, The coating thickness control mechanism of the agent is controlled.

The method for producing a polarizing plate of the present invention preferably comprises the following step (D).

(D) a control step in which the absolute value of the difference between the measured thickness X of the adhesive obtained in the above measuring step and the set thickness Y of the adhesive set in the range of 0.5 to 5 μm is a specific value or more with respect to the ratio of the above Y In the case of, for example, 5% or more, the coating thickness control means is controlled.

Further, the method of the aspect of the invention provides a method of producing a polarizing plate comprising the steps (A), (B), (C) and (D) below.

(A) applying an adhesive to an optical film made of a thermoplastic resin using a coater having a control portion having a coating thickness of an adhesive; (B) using a spectroscopic light having a spectral wavelength region set in a range exceeding 800 nm Interferometry, measuring the optical thickness of the optical film before application of the adhesive, and the optical thickness of the optical film coated with the adhesive, and based on the optical thickness of the optical film before application of the adhesive and the optical agent coated with the adhesive The difference in optical thickness of the film is used to determine the thickness of the applied adhesive; (C) the polarizing film made of a polyvinyl alcohol-based resin is superposed on the adhesive-coated surface of the measured optical film, and the optical film is polarized with respect to the polarizing film. Pressurizing the film to bond the polarizing film and the optical film via the adhesive; and (D) setting the thickness Y of the adhesive set in the range of 0.5 to 5 μm and the thickness X obtained by the adhesive, The control unit performs control.

The method of other aspects of the invention preferably comprises the steps of (D) below.

(D) When the ratio of the absolute value of the difference between the thickness X obtained by the above-mentioned adhesive agent and the set thickness Y of the adhesive agent to the set thickness Y of the adhesive set in the range of 0.5 to 5 μm is a specific value or more For example, when it is 5% or more, the control unit is controlled.

According to the invention, when the optical film is bonded to the polarizing film via the adhesive, the film thickness before and after the coating step is measured using a specific film thickness meter, thereby instantaneously measuring the thickness of the adhesive formed on the optical film in the line, The result is transmitted to a mechanism for controlling the coating thickness of the adhesive which the coater has, and the coating thickness is controlled, so that a polarizing plate having a uniform thickness of the adhesive can be manufactured. As a result, it is possible to suppress defects such as bubbles which are likely to occur due to uneven thickness of the adhesive.

In the present invention, a polarizing plate is produced by laminating an optical film made of a thermoplastic resin to a polarizing film made of a polyvinyl alcohol-based resin via an adhesive. The optical film may be attached 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 sides of the polarizing film, the method of the present invention can be applied to the bonding of an optical film, and the method of the present invention can be applied to the bonding of the optical films on both sides.

[Polarizing film]

The polarizing film is made of a polyvinyl alcohol-based resin and is a film having a property of penetrating light having a vibration surface of a certain direction into the light incident on the film, and absorbing the vibration surface orthogonal thereto. Light, typically, poly A dichroic dye is adsorbed and aligned on the enol resin. The polyvinyl alcohol-based resin constituting the polarizing film is obtained by saponifying a polyvinyl acetate-based resin. The polyvinyl acetate-based resin which is a raw material of the polyvinyl alcohol-based resin may be a copolymer of vinyl acetate and another monomer copolymerizable therewith, in addition to the polyvinyl acetate which is a homopolymer of vinyl acetate. The polarizing film can be produced by subjecting the film made of the above polyvinyl alcohol-based resin to uniaxial stretching, dyeing with a dichroic dye, and boric acid crosslinking treatment after dyeing. As the dichroic dye, an iodine or a dichroic organic dye can be used. The uniaxial stretching can be carried out before dyeing with a dichroic dye, simultaneously with dyeing with a dichroic dye, or after dyeing with a dichroic dye, for example, a boric acid cross-linking treatment. The polarizing film made of the polyvinyl alcohol-based resin which is produced and adsorbed and has a dichroic dye is one of the raw materials of the polarizing plate.

[Optical film]

A polarizing plate was produced by laminating an optical film made of a thermoplastic resin on the polarizing film. The optical film preferably has a refractive index in the range of 1.4 to 1.7 as measured by a D line at a temperature of 20 °C. The refractive index of the optical film is measured based on JIS K 0062:1992 "Method for Measuring Refractive Index of Chemical Products". When the optical film has a refractive index in this range, the display characteristics of the produced polarizing plate when incorporated in a liquid crystal panel are excellent. For the same reason, the preferred refractive index of the optical film is in the range of 1.45 to 1.67. The optical film preferably has a haze value in terms of improving the contrast of the obtained polarizing plate, particularly when it is incorporated into the liquid crystal panel and is set to black, and the possibility of occurrence of a defect such as a decrease in brightness is reduced. 0.001~3% range. Haze value is (diffusion transmittance / The total light transmittance is a value defined by ×100 (%), and is measured based on JIS K 7136:2000 "Method for Calculating Haze of Plastic-Transparent Material".

The thermoplastic resin constituting the optical film is exemplified by the following resin. Here, the refractive index measured by a D line at a temperature of 20 ° C is n _D (20 ° C) and is shown together.

Cycloolefin resin [n _D (20 ° C) = 1.51 to 1.54], crystalline polyolefin resin [n _D (20 ° C) = 1.46 to 1.50 or so], polyester resin [n _D (20 ° C) = 1.57~1.66], polycarbonate resin [n _D (20 ° C) = 1.57~1.59], acrylic resin [n _D (20 ° C) = 1.49~1.51], triethylenesulfonyl cellulose resin [n _D (20 ° C) = 1.48 or so] and so on.

Cycloolefin resin A cycloolefin-based monomer such as an olefin is a polymer of a main constituent unit, and includes a resin obtained by hydrogenating a ring-opening polymer of a cycloolefin monomer, a cycloolefin monomer, and a carbon such as ethylene or propylene. A chain olefin monomer having 2 to 10 and/or an addition polymer of an aromatic vinyl monomer such as styrene.

The crystalline polyolefin-based resin is a polymer having a chain olefin monomer having 2 to 10 carbon atoms as a main constituent unit, and includes a homopolymer of a chain olefin monomer and two or more kinds of chain olefins. It is a binary or ternary copolymer of a monomer. Specifically, it includes a polyethylene resin, a polypropylene resin, an ethylene-propylene copolymer, a homopolymer of 4-methyl-1-pentene, or 4-methyl-1-pentene and ethylene or propylene. Copolymers, etc.

The polyester resin also contains an aliphatic polyester in addition to an aromatic polyester resin such as polyethylene terephthalate or polyethylene naphthalate. Resin. The polycarbonate resin is typically a polymer obtained by the reaction of bisphenol A with phosgene and having a carbonate bond -O-CO-O- in the main chain. The acrylic resin is typically a polymer having methyl methacrylate as a main constituent unit, and includes methyl methacrylate and other methacrylates in addition to a homopolymer containing methyl methacrylate. Acrylate copolymer and the like. The triethylenesulfonyl cellulose resin is cellulose acetate.

The film formed from these thermoplastic resins by a solvent casting method, a melt extrusion method, or the like can be used to form an optical film used in the present embodiment. Further, the optical film used in the present embodiment may be formed by further uniaxial or biaxial stretching after film formation. The optical film may be subjected to an easy subsequent treatment such as saponification treatment, corona treatment, plasma treatment, primer treatment or anchor coating treatment on the bonding surface before bonding to the polarizing film. Further, various treatment layers such as a hard coat layer, an antireflection layer or an antiglare layer may be provided on the surface of the optical film opposite to the bonding surface of the polarizing film.

The optical film usually has a thickness of about 5 to 200 μm. If the optical film is too thin, the operability is lacking, and the possibility of occurrence of breakage or occurrence of wrinkles in the polarizing plate manufacturing line becomes high. On the other hand, if it is too thick, the obtained polarizing plate becomes thick and the weight also becomes large, and there exists a case where the commercial property is impaired. For these reasons, the thickness is preferably from 10 to 120 μm, more preferably from 10 to 85 μm.

[adhesive agent]

When the optical film is bonded to the polarizing film as described above, first, an adhesive is applied to the bonding surface of the optical film to the polarizing film. The thickness of the subsequent agent is set to a specific value within a range of 0.5 to 5 μm. If the thickness is less than 0.5 μm, sometimes Then the intensity is uneven. On the other hand, if 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 type of the adhesive. If it is relatively thick in this range, for example, 3.5 μm or more, especially 4 μm or more, even if the thickness thereof is slightly changed, defects such as bubbles due to it are less likely to occur, but on the other hand, this is increased. Thickness is likely to result in an increase in cost, so it is desirable to reduce it to the extent possible. For these reasons, the preferred thickness of the adhesive is from 1 to 4 μm, and more preferably from 1.5 to 3.5 μm.

The following may be used in the production of a polarizing plate as long as it is supplied in a liquid form, but it is preferable to contain cationic polymerizability from the viewpoints of weather resistance, polymerizability, and the like. The active energy ray of the compound, for example, an epoxy compound, more specifically, an epoxy compound having no aromatic ring in the molecule as described in Japanese Patent Laid-Open Publication No. 2004-245925, as one of active energy ray hardening components. Hardened adhesive. Such an epoxy compound can be obtained by subjecting an aromatic polyhydroxy compound which is a raw material of an aromatic epoxy compound represented by bisphenol G diglycidyl ether to hydrogenation, and glycidyl etherification. The hydrogenated epoxy compound; an alicyclic epoxy compound having at least one epoxy group bonded to an aliphatic ring in the molecule; an aliphatic epoxy compound represented by a glycidyl ether of an aliphatic polyhydroxy compound. Further, in the active energy ray-curable adhesive, in addition to the cationically polymerizable compound represented by an epoxy compound, a polymerization initiator may be usually blended, particularly for generating a cationic species by irradiation with an active energy ray or A photocationic polymerization initiator which starts polymerization of a cationically polymerizable compound by a Lewis acid. Enter Further, a thermal cationic polymerization initiator which starts polymerization by heating, and various additives such as a photosensitizer can be blended.

In the case where the optical film is bonded to both surfaces of the polarizing film, the adhesive applied to each of the optical films may be the same or different, but from the viewpoint of productivity, it is preferably provided before obtaining a moderate adhesive force, preferably two sides. All are the same adhesive.

[Method of Manufacturing Polarizing Plate]

In the present embodiment, a polarizing plate is produced by laminating an optical film on a polarizing film made of a polyvinyl alcohol-based resin described above via an adhesive. At this time, the following steps (A), (B), (C), and (D) are performed.

(A) a coating step of applying an adhesive to a bonding surface of the optical film to the polarizing film using a coating machine having a coating thickness control mechanism of an adhesive; (B) a measuring step of setting a spectral wavelength region For the spectroscopic interference method in the range of more than 800 nm, the thickness of the optical film is measured before the coating step, and the total thickness of the optical film and the applied adhesive is measured after the coating step, and the measurement is performed in the line. The absolute value of the difference between the values is used to determine the thickness of the applied adhesive; (C) the bonding step, the adhesive film coated in the above-mentioned coating step and passing through the measuring step is superimposed on the polarizing film and pressurized; D) a control step in which the absolute value of the difference between the measured thickness X of the adhesive obtained in the above measuring step and the set thickness Y of the adhesive set in the range of 0.5 to 5 μm is a specific value or more with respect to the ratio of the above Y At this time, the above coating thickness control mechanism is controlled.

Figure 1 is a schematic view showing a manufacturing apparatus preferably used in the present invention. A side view of a configuration example, and Fig. 2 is a block diagram showing an example of the relationship between the steps of the present invention. Hereinafter, the method of manufacturing the polarizing plate will be described in detail with reference to the drawings.

In the manufacturing apparatus shown in FIG. 1, the polarizing film 1 is continuously conveyed, the first optical film 2 is bonded to one surface, and the second optical film 3 is bonded to the other surface, and the polarizing plate 4 is manufactured and wound up. On the take-up roll 30. As shown in the figure, an optical film is usually bonded to both surfaces of the polarizing film 1, but the form in which the optical film is bonded only to one surface of the polarizing film 1 is of course included in the present embodiment. The form of this case can be easily carried out by removing the description relating to another optical film from the following description, to the extent that it is well understood by those skilled in the art.

Regarding the first optical film 2, first, the thickness is measured by the first spectral interference type film thickness meter 14, and then the first coating machine 10 applies the second component after applying the adhesive to the surface to which the polarizing film 1 is bonded. The interferometric film thickness meter 15 measures the total thickness of the optical film and the applied adhesive, and determines the applied value from the absolute value of the difference between the measured values obtained by the two spectral interferometric film thickness gauges 14, 15. The thickness of the agent. Similarly, regarding the second optical film 3, first, the thickness is measured by the third spectral interference type film thickness meter 16, and then the second coating machine 12 applies the adhesive to the surface to which the polarizing film 1 is bonded, and then The quarter-light interference type film thickness meter 17 measures the total thickness of the optical film and the applied adhesive, and is determined by the absolute value of the difference between the measured values obtained by the two spectral interference type film thickness meters 16, 17. The thickness of the adhesive.

The adhesive coating surface of each of the first optical film 2 and the second optical film 3 after measuring the thickness before and after the application of the adhesive is superposed on both sides of the polarizing film 1 to The nip rollers 20 and 21 are sandwiched and pressed in the thickness direction, and then subjected to irradiation with active energy rays from the active energy ray irradiation device 18 to harden the adhesive, and then pass through the nip rollers 22 and 23 before winding. The obtained polarizing plate 4 is taken up on the take-up roll 30.

In the first coater 10 and the second coater 12, an adhesive is applied to the first and second optical films 2, 3 from the respective gravure rolls 11, 13. The guide roller 24 for conveyance 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 on which the adhesive is applied. As described above, when only one surface of the polarizing film 1 is bonded to the optical film, only one of the first optical film 2 and the second optical film 3 (for example, the first optical film 2) shown in FIG. 1 is used. can. The straight arrow in the figure refers to the flow direction of the film, and the curved arrow refers to the direction of rotation of the roller.

The polarizing film 1 is usually produced in a polarizing film manufacturing step (not shown), and after the polyvinyl alcohol resin film is uniaxially stretched, dyed with a dichroic dye, and dyed with a boric acid cross-linking treatment, In this state, the supply is performed without being wound up on the roll. Of course, the polarizing film produced in the polarizing film production step may be temporarily wound up on the roll and then taken out by the extractor. On the other hand, the first optical film 2 and the second optical film 3 are respectively drawn out from a roll (not shown) by an extractor. Each film is conveyed at the same linear velocity, for example, at a linear velocity of about 10 to 50 m/min in the same flow direction. The first optical film 2 and the second optical film 3 are extracted while applying a tension of, for example, about 50 to 1000 N/m in the flow direction.

Further, the coating step (A) is carried out by the first coater 10 and the second coater 12, and the first and second spectral interference film thickness gauges 14, 15 and 3. The fourth spectral interference type film thickness gauges 16 and 17 perform the above-described measurement step (B), and the bonding step (C) is performed by the bonding nip rollers 20 and 21 by using the spectral interference type film thickness meter 14, The measurement results of 15, 16, and 17 are returned to the coaters 10 and 12, and the above control step (D) is carried out. The gravure rolls 11, 13 of the coaters 10, 12 are rolls having grooves in which the adhesive is pre-filled, and the optical films 2, 3 are rotated in this state, thereby making the adhesive Transfer to the optical films 2, 3. By adjusting the rotation speed, the amount of the adhesive applied to the optical films 2, 3 and the coating thickness can be controlled. In this case, the adjustment mechanism of the rotational speed of the gravure roll, particularly the gravure roll, serves as a mechanism for controlling the coating thickness of the coaters 10 and 12 (coating thickness control means or control portion for coating thickness).

The relationship between the steps will be described based on the block diagram of FIG. First, in the setting (0), the set thickness Y is set in advance in the range of 0.5 to 5 μm with respect to the thickness of the adhesive applied in the coating step (A). For the above reasons, the set thickness Y is preferably set to 1 to 4 μm, more preferably set to 1.5 to 3.5 μm. Then, as the first half of the measuring step (B), the initial conditions of the mechanism for controlling the coating thickness of the coaters 10 and 12 after the thicknesses of the optical films 2 and 3 are measured in advance by the spectral interference type film thickness gauges 14, 16 The setting is carried out, and the coating step (A) is carried out. Then, as the second half of the measuring step (B), the total thickness of the optical film and the applied adhesive is measured by the spectral interference type film thickness gauges 15, 17, from the measured values of the first half step and the measured values of the second half step. The absolute value of the difference is used to determine the thickness of the applied adhesive, and is output as the measured thickness X. Regardless of the measured thickness X, the optical films 2 and 3 coated with the adhesive are each in the bonding step (C). The adhesive coated surface is bonded to both sides of the polarizing film 1. On the other hand, in the control step (D), the measured thickness X is compared with the above-described set thickness Y. Then, for example, when the absolute value of the difference between the measured thickness X and the set thickness Y is equal to or greater than a predetermined threshold value, for example, 5% or more, the coating thickness control mechanisms of the coaters 10 and 12 are operated, Preferably, the absolute value of the difference is small, and the coating thickness is controlled such that the absolute value of the difference between the measured thickness X and the set thickness Y is less than a predetermined threshold value, for example, less than 5%. Here, 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, which means that the following formula (I) is satisfied, and in FIG. 2, it is indicated whether or not the change is made depending on whether or not the formula is satisfied. The conditions of the control agency. Further, the method of comparing the measured thickness X with the set thickness Y in the present embodiment is not limited to the above method in the description of Fig. 2 . That is, the comparison between the measured thickness X and the set thickness Y may not be based on the difference between the measured thickness X and the set thickness Y, or may not be based on the absolute value. For example, it may be compared according to whether the ratio of the difference between the measured thickness X and the set thickness Y to the set thickness Y is below a certain threshold or above a certain threshold, for example, -5% or less, or +5% or more, or may be based on the measured thickness X. The comparison is made with respect to whether the ratio of the set thickness Y is below a certain threshold or above a certain threshold, for example, 95% or less or 105% or more. The above threshold is not limited to 5% (or -5%, 95%, etc.), may be a lower value, such as 1% or 3%, and may be a higher value, such as 7% or 10%. Further, the upper threshold and the lower threshold may be different values (for example, -3% or less or 7% or more).

[Number 1]

Hereinafter, the coating step (A), the measuring step (B), the bonding step (C), and the controlling step (D) constituting the method of the present invention will be described in detail. Further, in the case of using an active energy ray-curable adhesive, the hardening step (E) is carried out after the above respective steps, and therefore the step will be described.

(A) Coating step

In the coating step (A), an adhesive is applied to the bonding surface of the optical films 2, 3 to the polarizing film 1 which is subjected to the first half of the measuring step (B) (the step of measuring the thickness of the optical film itself). The coater used herein is not particularly limited as long as it has a mechanism for controlling the coating thickness, and the gravure rolls 11 and 13 described with reference to Fig. 1 are typically used. In the coater using the gravure roll, there are, for example, a direct gravure coater, a chamber doctor coater, an indirect gravure coater, a kiss coater using a gravure roll, and a plurality of rolls. Reverse roll coater, etc. In addition, a dot coater that applies a cylindrical scraper and applies an adhesive to the coating section while scraping off the blade, and a die coater that directly supplies the adhesive by using a slit die or the like can be used. The liquid tank is a variety of coaters such as a knife coater coated with a knife while scraping off the remaining liquid. In consideration of the film coating, the degree of freedom of the trace, and the like, in the coater using the gravure roll, a direct gravure coater, a closed blade coater, an indirect gravure coater, etc. are preferable. In addition to the gravure roll, a die coater using a slit die is also preferred. It is easy to cope with the widening of the polarizing plate and the difficulty in releasing the odor of the adhesive supplied by the liquid, and further preferably a closed blade coater.

Here, the closed blade coater refers to a closed blade that abuts a gravure roll against a liquid-absorbent liquid paint (adhesive), and transfers the paint (adhesive) in the closed blade to the groove of the gravure roll. And transferring it to the coating machine of the optical film 2, 3 which is a coating object. Designed to be small is also known as a micro-closed blade coater.

In the case where the adhesive is applied using a gravure roll, the thickness of the adhesive layer can be adjusted by the ratio of the speed of the gravure roll to the linear velocity. The linear velocity of the optical films 2 and 3 is set to 10 to 50 m/min, and the gravure roll is reversely rotated with respect to the conveying direction of the optical films 2 and 3, and the circumferential speed of the gravure roll is set to 10 to 500 m/ In minutes, the coating thickness of the adhesive can be adjusted to 0.5 to 5 μm. Since the coating thickness at this time is also affected by the void ratio of the surface of the gravure roll, it is preferable to previously select a gravure roll having a void ratio suitable for setting the surface of the thickness Y. Further, the manner in which the gravure roll is reversely rotated with respect to the conveyance direction of the optical films 2, 3 is also referred to as a reverse gravure.

(B) Measurement steps

In the first half of the measuring step (B) performed before the coating step (A), the thickness of the optical film itself is measured by the spectroscopic interference method, and the half step after the measuring step (B) performed after the coating step (A) The total thickness of the optical film and the applied adhesive was measured by a spectroscopic interference method, and the thickness of the applied adhesive was determined from the absolute value of the difference between the measured value of the first half step and the measured value of the second half step. Here, the spectroscopic interference method is a method of obtaining a film thickness by using interference between reflected light from the front surface of the object to be measured and reflected light from the back surface.

In other words, when the optical film itself before the application of the adhesive is irradiated with light, reflected light from the front surface of the film and reflected light from the back surface of the film are generated. The reflected lights are mutually enhanced if they have the same phase, and become weaker if they are opposite in phase. The interference light is split in a wavelength region (for example, a wavelength region of 810 to 830 nm) included in a range exceeding 800 nm, and the obtained spectral waveform pattern is subjected to Fourier transform, thereby obtaining an optical film thickness. When the film thickness of the optical film itself is necessary, the film of the optical film can be obtained by considering the refractive index of the optical film (for example, by dividing the optical film thickness of the optical film by the refractive index of the optical film) thick. On the other hand, when light is irradiated from the adhesive layer side of the optical film coated with the adhesive, the reflected light from the surface of the adhesive layer and the reflected light from the back surface of the film are generated, and the same is generated as described above. Since the interference light is split in the same manner as described above and subjected to Fourier transform, the optical film thickness is obtained. When the total thickness of the adhesive layer and the optical film itself is necessary, it is necessary to consider the average refractive index of the laminate of the adhesive layer and the optical film, but the thickness of the adhesive layer is unknown, so the volume is unknown. Therefore, it is difficult to use the average refractive index in time.

As described above, it is necessary to consider not only the refractive index of the adhesive but also the refractive index of the optical film. However, in the present invention, the thickness of the adhesive can be determined from the difference in film thickness before and after the application of the adhesive. The refractive index of the optical film can be ignored. That is, in the first half of the measuring step (B), the optical film thickness obtained by irradiating the optical film before the application of the adhesive agent is considered as the optical film in consideration of the refractive index of the adhesive. The film thickness in the state of the adhesive (the thickness of the optical film before the application of the adhesive) is output, and in the second half of the measuring step (B), the optical film is also coated with the adhesive. The optical film obtained by irradiating light on the side of the agent layer Thickness considers the refractive index of the adhesive, and the obtained thickness can be regarded as the film thickness of the state in which the optical film is replaced with the adhesive (the state in which the original adhesive is carried) (the thickness of the optical film coated with the adhesive) The output is performed, and if so, the thickness of the adhesive which is the absolute value of the difference between the two can be obtained. Furthermore, when the difference between the two is not negative, it is not necessary to use an absolute value, and the simple difference between the two may be obtained as the thickness of the adhesive. Further, the thickness of the adhesive may be obtained by dividing the difference between the optical thickness of the optical film before the application of the adhesive and the optical thickness of the optical film coated with the adhesive, by dividing the difference by the refractive index of the adhesive. Find out.

According to the film thickness meter based on the above-described spectroscopic interference method, the thickness of the applied film can be accurately determined without affecting the thickness of the applied adhesive, and the thickness of the optical film itself before the coating step can be accurately obtained. The thickness of the adhesive of the difference between the total thickness of the optical film and the adhesive after the coating step. Further, the method of the present embodiment in which the thickness of the adhesive is determined from the difference in film thickness before and after the application of the adhesive has the advantage that the adhesive can be obtained regardless of the difference in refractive index between the optical film and the adhesive. The thickness.

The film thickness meter based on the spectroscopic interference method as described above can be selected from commercially available products. Commercially available spectroscopic interferometric film thickness gauges are often used in a film thickness meter to automatically perform a series of operations based on the above principle, and average the measured values or the measured values in a specific time, and output them as measured values. By. The film thickness which can be measured by the spectral interference type film thickness meter used in the present embodiment is usually 10 μm or more depending on the limitation of the wavelength of the wavelength to be used. As a light source for light irradiation, it is preferable to have a wavelength region included in a range exceeding 800 nm (for example, 810 to 830 nm) In the light source of the wavelength region, an SLD (Super Luminescent Diode) or the like can be used. In the present embodiment, it is preferable to select a film thickness gauge having a resolution of a thickness of 1 to 10 nm in a state where the film is left standing while being off-line.

Further, from the viewpoint of the stability of the thickness measurement value, the spectral interference type film thickness meter used in the present invention is preferably one capable of measuring once at a measurement interval of 0.00001 to 1 second, particularly 0.00001 to 0.5 second, more preferably From the obtained data, the moving average is obtained for the continuous measurement value of 10 to 100,000 points and can be output. For example, when the number of moving averages exceeds 100,000 points and the measurement interval exceeds 0.5 seconds, the deviation between the measured value and the actual thickness may become large. For the same reason, it is further preferred to use a measurement at a measurement interval of 0.0001 to 0.2 second, and the obtained data is output to a moving average film thickness meter for a continuous measurement value of 10 to 70,000 points.

In order to improve the measurement accuracy of the thickness of the adhesive, the position of the spectroscopic interferometer film thickness measuring the thickness of the optical film itself before the coating step, and the spectroscopic interference of the total thickness of the optical film and the adhesive after the coating step are measured. The arrangement position of the film thickness meter is preferably uniform with respect to the width direction of the optical film. Moreover, for the same reason, it is preferable to make the thickness measurement points coincide with respect to the longitudinal direction (transport direction) of an optical film. Further, for the same reason, the interval between the two spectral interference type film thickness gauges is preferably 10 m or less in the longitudinal direction of the optical film, and more preferably 1 to 5 m.

In the film thickness meter based on the spectroscopic interference method as described above, light emitted from a light source (for example, SLD or the like) may be polarized, and the degree of the polarized light may be different depending on the thickness of each film, or the polarized light may be plural. Mixed wave of species. herein In some cases, especially when the optical film has an in-plane retardation value of 300 nm or more, even if the same optical film is measured, a difference of measured values of 0.5 μm or more may occur. In the present embodiment, as described above, the thickness of the optical film itself is measured in the first half of the measuring step (B), and the optical film and the adhesive applied thereto are measured in the second half of the measuring step (B). When the total thickness is equal, the direction of vibration of the polarized light emitted from the light source equal to the film thickness meter used in the first half step and the second half step is the same as the vibration direction of the strongest polarized light in the case of a mixed wave of a plurality of polarized lights. The measurement error based on the polarization described above can sometimes be suppressed to some extent. Further, in particular, when the optical film has an in-plane retardation value of 300 nm or more, it is preferable to provide a near-infrared polarizing filter between the spectral interference type film thickness meter and the optical film. When the near-infrared polarizing filter is disposed, the transmission axis or the absorption axis of the near-infrared polarizing filter is usually at an angle of 45 degrees with respect to the length direction of the optical film (for the transport direction, usually the fast axis or the slow axis). The way to configure. If the direction of the polarized light emitted from the light source of the film thickness (the direction of the strongest polarized light in the case of a complex wave of a plurality of polarized lights) is overlapped with the transmission axis of the near-infrared polarizing filter, Increase the amount of reflected interference light used for film thickness measurement.

(C) lamination step

After the coating step (A) and the measuring step (B) described above, the bonding step (C) in which the polarizing film 1 is superposed on each of the adhesive coating surfaces of the optical films 2 and 3 and pressurized is applied. A known method can be used for the pressurization in this step. However, from the viewpoint of pressurization while continuously transporting, it is preferable to hold the pair of nip rolls 20 and 21 as shown in Fig. 1 . In this case, the polarizing film 1 is heavy The timing of stacking the optical films 2, 3 and the timing of pressurizing the optical films 2, 3 with respect to the polarizing film 1 by the pair of nip rolls 20, 21 are preferably the same, and even if they are different, the difference between the timings of the two is Shorter is appropriate. The combination of the pair of nip rolls 20, 21 may be any one of a metal roll/metal roll, a metal roll/rubber roll, a rubber roll/rubber roll, and the like. The line pressure gauge when the pressure at the time of pressurization is sandwiched by the pair of nip rolls 20, 21 is preferably set to about 150 to 500 N/cm.

(D) Control steps

In the present embodiment, a control step (D) for controlling the coating thickness of the adhesive in the coating step (A) is provided based on the result of the measurement step (B) described above. That is, the thickness of the adhesive applied in the coating step (A) may vary depending on the temperature of the adhesive or the ambient temperature, or the surface tension of the optical films 2, 3 or the tension applied thereto. There is a case where there is a deviation from the desired coating thickness (set thickness Y). In order to correct the deviation of the above coating thickness, the coating thickness control mechanism of the coater is controlled based on the coating thickness (measured thickness X) measured by the spectroscopic interference method in the measuring step (B). Specifically, when the measured thickness X is larger than the set thickness Y, the coating thickness control mechanism is controlled to reduce the coating thickness, and when the measured thickness X is smaller than the set thickness Y, the coating thickness is increased. The coating thickness control mechanism controls.

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 the liquid from the pump or the like is reduced, and when the measured thickness X is smaller than the set thickness Y, the mold is increased. The ability to deliver liquid, whereby the coating thickness can be controlled. Moreover, if the coater is a closed blade coater using a gravure roll, when the measured thickness X is larger than the set thickness Y, by increasing the inverse To the rotational speed of the intaglio plate, the rotational speed of the rotation is increased, and the transfer amount of the adhesive is reduced. Conversely, when the measured thickness X is smaller than the set thickness Y, the rotational speed is reduced by reducing the rotational speed of the reverse gravure, and the adhesive is increased. The amount of transfer, whereby the coating thickness can be controlled. The degree of film thickness control can be arbitrarily set experimentally based on the environmental factors at the time, the viscosity of the adhesive, the surface shape of the optical film, and the like. The control of the actual coating thickness control mechanism based on the measured thickness X and the set thickness Y can be performed using a computer or manually.

(E) hardening step

As described above, after the optical films 2 and 3 are bonded to the polarizing film 1, when the adhesive is an active energy ray-curable type, the adhesive is cured by the hardening step (E) of curing the adhesive by irradiation of active energy rays. Polarizing plate 4. In the example shown in FIG. 1, the hardening step (E) is performed by irradiating the laminated body of the optical films 2 and 3 on the polarizing film 1 with the active energy ray by the active energy ray irradiation device 18. In this step, the energy required to harden the active energy ray-curable adhesive is irradiated over the optical film 2. Specifically, as the active energy ray, an electron beam or an ultraviolet ray is used, and it can be selected according to the hardening reaction mechanism of the adhesive. Regarding the electron beam irradiation device, since the generated electron beam is not shielded from the outside, the size or weight of the device is increased. On the other hand, since the ultraviolet irradiation device has a relatively small structure, it is preferable to use hardening by ultraviolet irradiation.

In the example shown in FIG. 1 , the irradiation of the active energy ray to the laminate of the polarizing film 1 and the optical films 2 and 3 via the adhesive is applied to the irradiation device. The nip rollers 20 and 21 for bonding before and after the 18 are placed between the nip rollers 22 and 23 before the winding, and tension is applied to the laminated body. The present invention is not limited to this, and it is preferable to irradiate the active energy in a state in which a convex curved surface formed in an arc shape along the conveying direction, typically a peripheral surface of the roller, is supported, as disclosed in Japanese Laid-Open Patent Publication No. 2009-134190. Rays. In particular, when heat is generated by irradiation of active energy rays, which may adversely affect the product, it is preferred that the laminate is irradiated with active energy rays in a state where the laminate is supported by the outer peripheral surface of the roller as in the latter case, in which case Preferably, the roller supporting the laminate is capable of adjusting the temperature within a range of about 10 to 60 °C. Further, the active energy ray irradiation device may be provided in only one irradiation site or two or more in the flow direction of the laminate, and it is effective to increase the amount of accumulated light by irradiation from the complex light source.

When the ultraviolet ray is used to cure the adhesive, the ultraviolet light source to be used is not particularly limited, and can be used for, for example, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a chemical lamp having a light-emitting distribution at a wavelength of 400 nm or less. Black light, microwave excited mercury lamp, metal halide lamp, etc. When an epoxy compound is used as an adhesive for an active energy ray-curable component, a high-pressure mercury lamp or metal halide having a large amount of light of 400 nm or less is preferably used in consideration of an absorption wavelength exhibited by a usual polymerization initiator. The object light acts as an ultraviolet light source.

When the ultraviolet ray is cured by irradiating ultraviolet rays with an adhesive having an epoxy compound as a curable component, the linear velocity of the laminate is not particularly limited, and the line in the coating step (A) and the bonding step (C) is usually maintained almost as it is. speed. In addition, it is preferable to apply an amount of light to the wavelength region in which the activation of the polymerization initiator is effective by applying a tension of 100 to 1000 N/m to the longitudinal direction (transport direction) of the laminate (the irradiation of the laminate) The total energy) is calculated to be 100 to 1500 mJ/cm ² . When the amount of accumulated light to the adhesive is too small, the hardening reaction of the active energy ray-curable adhesive is insufficient, and it is difficult to exhibit sufficient adhesive strength. On the other hand, if the accumulated light amount is too large, the heat radiated from the light source and then The heat generated during the polymerization of the agent may cause yellowing of the active energy ray-curable adhesive or deterioration of the polarizing film.

In addition, if the desired amount of accumulated light is to be irradiated with ultraviolet rays once, the film may be heated to a temperature higher than 150 ° C by heat, and in this case, deterioration of the polarizing film may occur. In order to avoid the above-described state of affairs, it is also effective to provide a plurality of ultraviolet irradiation devices in the direction in which the film is transported as described above, and to perform irradiation in plural times.

In some cases, it is preferable to set the irradiation amount of the ultraviolet irradiation device from one place to 600 mJ/cm ² or less in terms of the cumulative light amount, and finally obtain the cumulative light amount of 100 to 1500 mJ/cm ² described above.

The polarizing plate manufactured in the above manner can control the thickness of the adhesive within a set range, and the variation in the bonding strength between the films constituting the polarizing plate is small, and the bubble defects in the adhesive layer are also small, and the quality of the product is small. The stability is also excellent.

[Examples]

The invention is further illustrated by the following examples and comparative examples, but the invention is not limited by the examples. In addition, the experiment shown below is carried out for confirming the effect of this invention, for example, the following is the case where it apply|coated on the opposite side with the adhesive agent of thickness measurement with the polarizing film. The thickness of the subsequent agent is set to be thicker than the optimum value used in the actual operation so that it does not cause defects.

Fig. 3 is a side view schematically showing the arrangement of the apparatus used in the following examples and comparative examples. The arrangement shown in FIG. 3 differs from FIG. 1 described above in only the following two points, and the same reference numerals are attached to the parts other than the different points. Therefore, the detailed description of the parts will be described with reference to FIG.

3 is different from FIG. 1 : (1) When the laminated body after bonding the first optical film 2 and the second optical film 3 to both surfaces of the polarizing film 1 is irradiated with active energy rays (ultraviolet rays), the layer is laminated. The second optical film 3 side of the body is in close contact with the outer peripheral surface of the coating roll 26, and the active energy ray (ultraviolet) irradiation device 18 is disposed on the opposite side of the winding roller 26 from the laminated body. The first optical film 2 side is irradiated with ultraviolet rays; and (2) since only one type (two sets) of the spectral interference type film thickness meter is used, the measurement is applied to the first optical film by the spectral interference type film thickness gauges 14, 15 The thickness of the adhesive of 2 is not measured by the thickness of the adhesive applied to the second optical film 3.

Further, as the spectral interference type film thickness gauges 14 and 15, a spectral interference type film thickness meter "SI-F80" manufactured by Keyence Co., Ltd. was used. The spectroscopic interference type film thickness meter is a film thickness measured by the spectroscopic interference method described above, and the light source is an SLD having a spectral wavelength region of 810 to 830 nm and a resolution of 1 nm. Then, the film thickness of the object to be measured is measured every predetermined measurement interval, and the individual film thickness values measured in the above are moved and averaged every similar measurement times, and the average film thickness is outputted therebetween, and automatically Excluding data that is determined to be an abnormal value among the measured values of the preset number of times, And output the average film thickness.

[Example 1]

(0) Materials used in the experiment

In this example, as the first optical film 2, a biaxial aligning retardation film "KC4FR-1" made of triethyl fluorene cellulose having a thickness of 40 μm and a width of 1330 mm is supplied from a roll [from Konica Minolta Opto The company obtained] as the second optical film 3, a triacetonitrile cellulose film "KC8UX2MW" (available from Konica Minolta Opto Co., Ltd., having a refractive index of 1.48) having a thickness of 80 μm and a width of 1330 mm and supplied from a roll. The adhesive for the polarizing film 1 and the first optical film 2, and the adhesive for the polarizing film 1 and the second optical film 3 are both an epoxy compound and a photopolymerization initiator, and substantially A solvent-free epoxy-based photocurable adhesive.

(A) Coating step

The polarizing film 1 having a thickness of 25 μm having iodine adsorbed on the polyvinyl alcohol, the retardation film as the first optical film 2, and the above-mentioned triacetyl cellulose film as the second optical film 3 were respectively 15 m. The line speed of /min is supplied in the same manner as the flow direction. The first coater 10 having the gravure roll 11 is used for the surface of the retardation film 2 which is subjected to the first half of the measuring step (B) (the step of measuring the thickness of the optical film itself) to be applied to the polarizing film 1 [ "Micro-closed doctor blade" manufactured by Fuji Machinery Co., Ltd.] is coated with the epoxy-based photocurable adhesive. Further, a second coater 12 having a gravure roll 13 is also used on the surface of the triacetonitrile cellulose film 3 to be bonded to the polarizing film 1, [the same is a "micro-closed blade" manufactured by Fuji Machinery Co., Ltd.] The above epoxy-based photocurable adhesive is applied.

The gravure rolls 11 and 13 provided in the coaters 10 and 12 are rotated in the reverse direction with respect to the conveyance direction of the film. Then, the second coater 12 on the side of the triacetone cellulose film 3 was set to have a gravure roll 13 having a rotational peripheral speed of 15 m/min and coated on the film at a thickness of about 4.5 μm. Follow-up agent. Since the thickness of the adhesive applied by the second coater 12 is not measured, and thus the film thickness control is not performed, the adhesive is applied in a thickness where almost no defects occur. On the other hand, on the side of the retardation film 2, the circumferential speed of the rotation of the gravure roll 11 provided in the first coater 10 was initially set to 21 m/min, and the adhesive was applied at a thickness of about 2.6 μm.

(B) Measurement steps

The first spectral interference type film thickness meter 14 is disposed on the upstream side of the first coater 10, and the second spectral interference type film thickness meter 15 is disposed on the downstream side of the first coater 10, and the flow of the two coaters along the film The spacing between the directions is 1.67 m. Further, it is set to measure the thickness of the retardation film 2 at intervals of 0.0002 second by the first spectral interference type film thickness meter 14, and the continuous measurement value of [{(2 ² ) ² } ² ] ² = 2 ¹⁶ = 65536 times. Each of the (about 13.1 seconds) outputs a moving average (first half of the steps). Further, after the coating step is performed, the retardation film 2 is measured at intervals of 0.0002 seconds from the adhesive-coated surface side of the retardation film 2 by the second spectral interference type film thickness meter 15 disposed. The total thickness of the subsequent agents was sequentially output as a moving average (one of the latter half steps) for each of 65536 consecutive measurements (about 13.1 seconds). Therefore, after the start, after about 13.1 seconds of obtaining the measurement of 65,536 times, the moving average of the thickness of the retardation film 2 is output from the first spectral interferometric film thickness gauge 14 every 0.0002 seconds, and is set to be the second. The spectral interferometric film thickness meter 15 outputs a moving average of the total thickness of the retardation film 2 and the adhesive, and extracts the value in each second, respectively, and the value before the time point (the measured value of the thickness of the retardation film 2) =A) The difference (BA) from the value of the latter (the measured value of the total thickness of the retardation film 2 and the adhesive = B) is recorded as the measured thickness X in sequence (second in the second half). Thereafter, a control step (D) to be described later is provided, and while the measurement thickness X is controlled, the operation is performed for about 150 minutes, and the measured thickness X obtained therebetween is obtained (the number of data is about 150 minutes × 60 cells/minute, which is about The average value and standard deviation of 9000) are shown in Table 1.

(C) lamination step

The retardation film 2 and the triacetyl cellulose film 3 to which the adhesive is applied are superposed on each of the adhesive application surfaces and the polarizing film 1, and the bonding nip rollers 20 and 21 are used as 240 N/. The line pressure of cm is clamped. The laminated system of the retardation film 2 / the polarizing film 1 / triacetyl cellulose film 3 after the nip rolls 20 and 21 is adhered to the side of the triethylene cellulose film 3 to the irradiation roll 26 set at 20 ° C. The outer peripheral surface was conveyed by applying a tension of 600 N/m in the longitudinal direction, and irradiating the retardation film 2 side from the ultraviolet irradiation device 18 at the same linear velocity of 15 m/min as before the bonding. The ultraviolet light is transported. The ultraviolet irradiation device 18 is manufactured by GS Yuasa Co., Ltd., and is irradiated with ultraviolet rays from the ultraviolet light "EHAN1700NAL high pressure mercury lamp" which is provided in the factory. Regarding the cumulative amount of ultraviolet light, the total of 2 lamps is 330 mJ/cm ² . In this manner, the adhesive layer is cured, and the polarizing plate 4 on which the retardation film 2 is bonded to the other surface of the polarizing film 1 and the triacetyl cellulose film 3 is bonded to the other surface is wound up on the winding roller 30.

(D) Control steps

In the control step, when the measured thickness X obtained in the above measuring step differs from the set thickness Y=2.6 μm by more than 5%, that is, |XY| In the case of 0.13 μm, the coating circumferential thickness of the gravure roll 11 provided in the first coater 10 is increased and decreased in units of 0.5 m/min, and the coating thickness of the adhesive is controlled to be close to the set thickness Y.

[Comparative Example 1]

In the first embodiment, the control step (D) is not provided, that is, even if the measured thickness X obtained in the measuring step (B) is changed, the rotation speed of the gravure roll 11 provided in the first coater 10 is not changed, Then, a laminate was produced, and then ultraviolet irradiation was performed to prepare a polarizing plate. The average value and standard deviation of the measured thickness X when the operation was performed for about 150 minutes are shown in Table 1.

[Comparative Example 2]

In the first embodiment, it is attempted that the first spectral interference type film thickness meter 14 is not provided, and as the second spectral interference type film thickness meter 15, a reflection light-splitting film having a wavelength range of 230 to 800 nm manufactured by Otsuka Electronics Co., Ltd. is provided. In the measurement step (B), a polarizing plate was produced in the same manner as in Example 1 except that the coating thickness of the adhesive was directly measured by the reflection spectroscopic film thickness meter. However, since the refractive index (1.48) of the retardation film made of triacetyl cellulose used as the first optical film 2 is close to the refractive index (1.49) of the adhesive, the thickness of the adhesive cannot be measured, and thus it is impossible to control the subsequent The coating thickness of the agent.

[Embodiment 2]

In the first embodiment, a biaxially oriented retardation film "KC4FR-1" made of triacetyl cellulose was used, and a double shaft having a thickness of 38 μm and a width of 1330 mm was used. A polarizing plate was produced in the same manner as in Example 1 except that the polyethylene terephthalate film (the in-plane retardation value of 1000 nm was obtained from Mitsubishi Plastics Co., Ltd.) was used as the first optical film 2. The average value and standard deviation of the measured thickness X when the operation was performed for about 150 minutes are shown in Table 1.

[Example 3]

In the second embodiment, for the spectral interference type film thickness gauges 14 and 15, respectively, between the spectral interference type film thickness meter and the biaxially oriented polyethylene terephthalate film, the absorption axis of the polarization filter is relative to A polarizing filter is provided in such a manner that the flow direction of the biaxially-oriented polyethylene terephthalate film is rotated by 45 degrees to the right [Ndmund Optics Co., Ltd., a near-infrared polarizing filter obtained from Edmund Optics Japan Co., Ltd., A laminate was produced in the same manner as in Example 2 except that the functional wavelength region was 750 to 800 nm. Then, ultraviolet irradiation was performed in the same manner to prepare a polarizing plate. The average value and standard deviation of the measured thickness X when the operation was performed for about 150 minutes are shown in Table 1.

[Comparative Example 3]

In the third embodiment, the control step (D) is not provided, that is, even if the measured thickness X obtained in the measuring step (B) is changed, the rotation speed of the gravure roll 11 provided in the first coater 10 is not changed, A laminate was produced, and then ultraviolet irradiation was performed in the same manner to prepare a polarizing plate. The average value and standard deviation of the measured thickness X when the operation was performed for about 150 minutes are shown in Table 1.

[Polarization evaluation test of polarizing plate]

In the above embodiments and comparative examples, in the polarizing plate obtained by the width of 1330 mm, the 1250 mm width portion at the center of each of the 40 mm width portions is taken as the effective width, and the effective width span and the flow direction are 3300. The surface of the mm length (1.25 m × 3.3 m ≒ 4 m ² ), the portion of the bright spot is marked by visual observation, and the marked portion is observed with a magnifying glass having a magnification of 100 times to confirm whether it is a bubble, and if it is a bubble, Find the size according to the following methods. That is, if the observed bubble is approximately elliptical (including a circle), the longest diameter is set to the size of the bubble, and if the bubble is linear, the line length is set to the size of the bubble. Then, the number of bubbles having a size of 100 μm or more is counted when the number is less than 0.3 per 1 m ² , that is, when 0 or 1 of the observed 4 m ² area is set, "OK", when the number is 0.3 or more per 1 m ² , that is, when the observed 4 m ² area is two or more, it is set to "NG", and the result is summarized together with the main variable. In Table 1. In the table, "TAC" in the optical film column refers to triacetyl cellulose, and "PET" refers to polyethylene terephthalate. Further, regarding the bubble of a size of 100 μm or more observed by a magnifying glass, the film was cut into a size of 40 mm × 40 mm in such a manner that the bubble entered, and observed by a microscope, and it was confirmed that both were sandwiched by polarized light. In the adhesive layer between the film 1 and the first optical film 2.

Note) OK: The number of bubbles having a size of 100 μm or more is less than 0.3 per 1 m ² . NG: The number of bubbles having a size of 100 μm or more is 0.3 or more per 1 m ² .

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 was changed, and as a result, a bubble defect was observed in the obtained polarizing plate, and the bubble defect was set. In the first and second embodiments in which the coating thickness is changed when the measured thickness (X) of the adhesive is changed by 5% or more compared with the set thickness Y, the measured thickness is suppressed to be substantially smaller than the set thickness Y. Within 5% of the change, there are fewer bubble defects. Further, in the third embodiment in which a specific polarization filter is provided between the spectral interference type film thickness meter and the optical film 2, the thickness is further increased and the fluctuation can be suppressed. On the other hand, when the reflection spectroscopic film thickness meter having a relatively wide range of the spectral wavelength region of 800 nm or less is used as in Comparative Example 2, the difference between the refractive index of the adhesive agent and the refractive index of the optical film is hard. When it is not possible to measure the coating thickness of the adhesive.

1‧‧‧ polarizing film

2‧‧‧First optical film

3‧‧‧Second optical film

4‧‧‧Polar plate

10‧‧‧First coater

11‧‧‧ gravure roll

12‧‧‧Second coating machine

13‧‧‧ gravure roll

14‧‧‧First Spectroscopic Interferometric Film Thickness Gauge

15‧‧‧Second Spectral Interferometer Thickness Gauge

16‧‧‧ Third Spectral Interferometer Thickness Gauge

17‧‧‧Fourth optical interferometric film thickness meter

18‧‧‧Active energy ray (ultraviolet) irradiation device

20, 21‧‧‧ nip rollers for lamination

22, 23‧‧‧ Rolling front nip rollers

24‧‧‧guide roller

26‧‧‧Feed roll for irradiation

30‧‧‧Winding roller

Fig. 1 is a schematic side view showing an arrangement example of a manufacturing apparatus preferably used in the present invention.

Fig. 2 is a block diagram showing an example of the relationship between the steps of the present invention.

Fig. 3 is a schematic side view showing the configuration of a manufacturing apparatus used in the embodiment.

1‧‧‧ polarizing film

2‧‧‧First optical film

3‧‧‧Second optical film

4‧‧‧Polar plate

10‧‧‧First coater

11‧‧‧ gravure roll

12‧‧‧Second coating machine

13‧‧‧ gravure roll

14‧‧‧First Spectroscopic Interferometric Film Thickness Gauge

15‧‧‧Second Spectral Interferometer Thickness Gauge

16‧‧‧ Third Spectral Interferometer Thickness Gauge

17‧‧‧Fourth optical interferometric film thickness meter

18‧‧‧Active energy ray (ultraviolet) irradiation device

20, 21‧‧‧ nip rollers for lamination

22, 23‧‧‧ Rolling front nip rollers

24‧‧‧guide roller

Claims (3)

A method for producing a polarizing plate, which comprises the steps of: (A) applying a coating machine having a coating thickness of an adhesive to a film made of a thermoplastic resin; (B) using a spectroscopic interference type film thickness meter, a state in which a near-infrared polarizing filter is provided between the spectral interference type film thickness meter and the optical film, and a spectral range in which the spectral wavelength region is set to be more than 800 nm is used. An interferometry method for measuring an optical thickness of the optical film before applying the adhesive and an optical thickness of an optical film coated with the adhesive, based on an optical thickness of the optical film before applying the adhesive, and coating the above The difference in optical thickness of the optical film of the agent is determined as the thickness of the applied adhesive; (C) the polarizing film made of a polyvinyl alcohol-based resin is superposed on the adhesive-coated surface of the optical film subjected to the above measurement, The optical film is pressed against the polarizing film to bond the polarizing film and the optical film via the adhesive; and (D) is set based on the range of 0.5 to 5 μm. The control portion is controlled by the set thickness Y of the agent and the thickness X obtained by the above-mentioned adhesive. The method of claim 1, wherein when the ratio of the absolute value of the difference between the thickness X obtained by the adhesive agent and the set thickness Y of the adhesive agent to the set thickness Y of the adhesive is a specific value or more, The control unit performs control. The method of claim 1, wherein the thickness X obtained by the above adhesive is The control unit is controlled when the ratio of the absolute value of the difference between the set thickness Y of the adhesive agent to the set thickness Y of the adhesive is 5% or more.