TW201346352A - Manufacturing method of polarizing plate - Google Patents

Abstract

The invention provides a manufacturing method of polarizing plate, which is a method for manufacturing a polarizing plate by laminating an optical film on a polarizing film via an adhesive, the method including: (A) a coating step of coating an adhesive on the optical film by a coating machine having a control means for controlling the coating thickness of the adhesive; (B) a measurement step of measuring the film thickness before and after the coating step by a radiant ray film thickness gauge, and obtaining the thickness of the coated adhesive from the absolute value of the difference in-line; (C) a lamination step of overlapping and pressurizing the polarizing film to the adhesive surface of the optical film; and (D) a control step of controlling the coating thickness control means, when a ratio of the absolute value of the difference between the measured thickness X of the adhesive and the set thickness Y of the adhesive exceeds a predetermined value.

Description

Polarizing plate manufacturing method

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

The liquid crystal panel constituting the core of the liquid crystal display device is generally configured by providing a polarizing plate on both sides of the 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. On the other surface of the polarizing film, a transparent resin film is bonded to the surface of the polarizing film. The transparent resin film on the other side is the same as the protective film on the opposite side, except that it has only a protective function for the polarizing film. A so-called retardation film which has a protective function and imparts a phase difference in the in-plane and/or thickness direction for the purpose of optical compensation or viewing angle compensation of a liquid crystal cell. In the present specification, 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 used when the optical film is bonded to the polarizing film is generally liquid, and the adhesion between the polarizing film and the optical film is exhibited by the hardening reaction of the liquid adhesive.

In recent years, the price of a liquid crystal display device such as a television has been drastically lowered, and the price of components constituting the liquid crystal display device has been lowered. The requirements are also gradually increasing. On the other hand, the requirements for quality are further enhanced. In this trend, the adhesive used in the production of the polarizing film is also changed from a water-based adhesive which is a specific resin film such as a cellulose resin film to a suitable optical film. A variety of active energy ray-curable adhesives. For example, Japanese Laid-Open Patent Publication No. 2004-245925 (Patent Document 1) proposes a bonding of a polarizing film using an active energy ray-curable adhesive to an optical film.

The active energy ray-curable adhesive is prepared in a liquid form, and is applied by a die coating method in which the liquid adhesive is directly applied to a coated object, or is carried by the liquid adhesive on a surface. The formed groove is transferred to the surface of the object to be coated by a gravure roll method, and is applied in advance to the bonding surface of the optical film to be bonded to the polarizing film. Then, the polarizing film is superposed on the surface to which the adhesive is applied, and an active energy ray such as an ultraviolet ray or an electron beam is irradiated to harden the adhesive to exhibit an adhesive force. As a result, an active energy ray-curable adhesive is used, and a wide variety of optical films can be used, which is an extremely effective method.

In the method of producing a polarizing plate using an active energy ray-curable adhesive, for example, Japanese Laid-Open Patent Publication No. 2009-134190 (Patent Document 2) discloses a method of overlapping protective films via an adhesive, respectively. A layered body is obtained on both sides of the polarizing film, and the method of irradiating the active energy ray while the laminated body is in close contact with the outer surface of the convex curved surface formed in an arc shape along the conveying direction of the laminated body. According to this method, it is possible to suppress the reverse curl and the wave curl which are easily generated by the obtained polarizing plate, and it is possible to manufacture a polarizing plate having good performance.

In the method of Patent Document 2, it is formed on a protective film. The thickness of the adhesive layer is considered to be less necessary for managing the thickness of the adhesive layer due to the fact that the anti-curl and the wave curl of the polarizing plate to be produced are not greatly affected. However, since the thickness of the adhesive layer fluctuates, most of them do not cause problems, 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 a cheap and higher-performance polarizing plate, the active energy ray-curable adhesive is mostly coated thicker than the conventional water-based adhesive, and since the adhesive itself is expensive, It is desirable to achieve thinning of the polarizing plate itself, and it is preferable to manage the thickness of the adhesive layer in such a manner as to minimize the required thickness of the fluctuation range.

In order to manage the coating thickness in an in-line manner A machine for measuring the thickness is known as an infrared film thickness meter. However, since the decomposition of the infrared film thickness meter has a limit, it is difficult to accurately measure the coating layer (adhesive layer) formed by several μm on the film which is continuously conveyed as in the case of a polarizing plate production line. thickness. Specifically, in the polarizing plate production line, as shown in FIG. 1 described later, the polarizing film and the optical film system bonded to the at least one surface are continuously conveyed without a special support, and are somewhere In the film thus continuously conveyed, in the direction of the thickness direction and the direction in which the tension is applied (flow direction), subtle shaking occurs, and in the state of being shaken, it is determined by an infrared film thickness meter. When the thickness of the coating layer is applied, only an accuracy of about ±1 μm can be obtained, so that it is practically impossible to manage the coating thickness based on the measurement result.

In addition, when optical is to be measured by an infrared film thickness meter The thickness of the adhesive layer formed on the film must have a clear distinction between the infrared absorption peak imparted by the optical film and the infrared absorption peak imparted by the adhesive, and there may be differences in the type of the optical film. The peaks of the two overlap, so that the measured value itself cannot be obtained.

From the above-mentioned reasons, the process of inspecting the thickness of the liquid adhesive applied on the film in an in-line manner has not yet been performed in the production of a polarizing plate using a liquid adhesive.

(previous technical literature) (Patent Literature)

Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-245925

Patent Document 2: Japanese Laid-Open Patent Publication No. 2009-134190

Therefore, an object of the present invention is to provide a coating thickness for managing an adhesive in an in-line manner when an optical film is bonded to a polarizing film via a liquid adhesive represented by an active energy ray-curable adhesive. Further, it is possible to reduce the variation in the thickness, thereby suppressing generation of defects such as bubbles in the adhesive layer, and at the same time, producing a method of inexpensive polarizing plates.

The present invention has been intensively studied in order to solve the above problems, and as a result, it has been found that a specific method is used when a liquid adhesive is applied to an optical film and a polarizing film is bonded to the coating layer to produce a polarizing plate. Measuring the thickness of the adhesive after coating, thereby correctly determining the thickness and rooting According to the results, the thickness of the adhesive applied during coating is controlled, and a polarizing plate having a uniform thickness of the adhesive and few defects can be produced, and thus the present invention has been completed.

That is, the present invention encompasses the following.

[1] A method for producing a polarizing plate, which comprises a method of producing a polarizing plate by bonding an optical film made of a thermoplastic resin to a polarizing film made of a polyvinyl alcohol-based resin via an adhesive, and the method comprises There are: (A) a coating machine using a coating thickness control means having the above-mentioned adhesive, and applying the adhesive to a coating step of the optical film adhered to the bonding surface of the polarizing film; The thickness of the optical film is measured by a radiation film thickness meter before the coating step, and after the coating step, the total thickness of the optical film and the adhesive after coating is measured, and the measured values are measured. The absolute value of the difference, the measurement step of determining the thickness of the adhesive after coating in an in-line manner; (C) superposing the polarizing film on the adhesive applied in the coating step and passing through the aforementioned measuring step And a pressure-adhesive bonding step; and (D) a measured thickness Y of the adhesive obtained in the above-mentioned measuring step with respect to the set thickness Y of the adhesive set in the range of 0.5 to 5 μm and the aforementioned Y Ratio of absolute values of difference When the rate is equal to or greater than a predetermined value, the control step of the coating thickness control means is controlled.

[2] The method for producing a polarizing plate according to [1], wherein in the controlling step (D), the measuring step with respect to the set thickness Y of the adhesive When the ratio of the measured thickness X of the adhesive obtained by the adhesive to the absolute value of the difference of the above Y is 5% or more, the coating thickness control means is controlled.

[3] The method for producing a polarizing plate according to [1], wherein the adhesive is a liquid active ray-curable adhesive.

[4] The method for producing a polarizing plate according to [3], wherein after the bonding step (C), a curing step (E) of curing the adhesive by irradiation with an active energy ray is provided.

According to the invention, when the optical film is bonded to the polarizing film via an adhesive, the film thickness before and after the coating step is measured by using a predetermined film thickness meter, and the adhesion formed on the optical film is instantaneously measured in an in-line manner. The thickness of the agent is transmitted to the coating thickness control means of the adhesive which the applicator has to control the coating thickness of the adhesive, so that a polarizing plate having a uniform thickness of the adhesive can be manufactured. As a result, defects such as bubbles which are easily generated due to variations in the thickness of the adhesive can be suppressed.

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 Radiation Film Thickness Gauge

14a‧‧‧First radiation source

14b‧‧‧First detector

15‧‧‧Second Radiation Film Thickness Gauge

15a‧‧‧Second radiation source

15b‧‧‧Second detector

16‧‧‧ Third Radiation Film Thickness Gauge

16a‧‧‧ Third radiation source

16b‧‧‧ third detector

17‧‧‧Fourth Radiation Line Thickness Gauge

17a‧‧‧Fourth source of radiation

17b‧‧‧ fourth detector

18‧‧‧Activated ray (ultraviolet) irradiation device

20, 21‧‧‧Finishing rolls (rollers)

22, 23‧‧‧ Roll before rolling

24‧‧‧guide roller

26‧‧‧Ring winding roller

30‧‧‧Winding roller

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

Figure 2 is a block diagram showing the relationship between the steps in the present invention.

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

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 via an adhesive to produce a polarizing plate. The optical film system can be bonded only to one side of the polarizing film or 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 can be applied to the bonding of one of the optical films, or the method of the present invention can be applied to the bonding of the optical films of the two.

[Polarizing film]

The polarizing film is made of a polyvinyl alcohol-based resin, and has a light that can penetrate a vibration surface having a certain direction of light incident on the film, and absorbs light having a vibration surface orthogonal to the direction. A film of a nature is typically a film in which a dichroic dye is adsorbed to a polyvinyl alcohol-based resin.

The polyvinyl alcohol-based resin constituting the polarizing film can be obtained by saponifying a polyvinyl acetate resin. The polyvinyl acetate resin as a raw material of the polyvinyl alcohol-based resin may be vinyl acetate and other monomers copolymerizable with the vinyl acetate in addition to the polyvinyl acetate of the vinyl acetate monomer. Copolymer.

A polarizing film can be obtained by subjecting a film made of a polyvinyl alcohol-based resin to a uniaxial stretching treatment, a dyeing treatment by a dichroic dye, and a boric acid crosslinking treatment after dyeing. As the dichroic dye system, iodine or a dichroic organic dye can be used. The uniaxial stretching system can be carried out before the dyeing by the dichroic dye, or simultaneously with the dyeing by the dichroic dye, or after the dyeing by the dichroic dye, for example, in the boric acid crosslinking treatment. get on.

So produced and adsorbed by a two-color pigment A polarizing film composed of a polyvinyl alcohol-based resin is one of raw materials of a polarizing plate.

[Optical film]

An optical film made of a thermoplastic resin is bonded to a polarizing film to produce a polarizing plate. The refractive index of the optical film measured by D rays at a temperature of 20 ° C is preferably in the range of 1.4 to 1.7. The refractive index of the optical film is measured in accordance with 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 manufactured polarizing plate when assembled to 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.

Although the haze value of the optical film is in the range of about 0.001 to 10%, the contrast of the obtained polarizing plate is improved, and in particular, when it is assembled on a liquid crystal panel and displayed in black, the possibility of occurrence of loss of brightness or the like is lowered, so that the possibility is lowered. More ideal. The haze value is a value defined by (diffusion transmittance/total light transmittance) × 100 (%), and is measured in accordance with JIS K 7136:2000 "Method for obtaining haze of plastic-transparent material".

The thermoplastic resin constituting the optical film may, for example, be as follows. Here, the refractive index measured by D-ray at a temperature of 20 ° C is set to n _D (20 ° C) and displayed together.

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

The cycloolefin-based resin is a polymer having a cycloolefin-based monomer such as norbornene as a main constituent unit, and includes a resin obtained by adding hydrogen to a ring-opening polymer of a cycloolefin-based monomer, and a cyclic olefin series. And an addition polymer of a chain olefin monomer having a carbon number of 2 to 10 such as ethylene or propylene and/or a styrene-like aromatic vinyl monomer.

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

The polyester-based resin contains an aliphatic polyester in addition to an aromatic polyester such as polyethylene terephthalate or polyethylene naphthalate.

The polycarbonate resin is typically a polymer obtained by a reaction of bisphenol A with carbonyl dichloride and having a carbonate bond -O-CO-O- in the main chain.

Acrylic resin, typically a polymer composed mainly of methyl methacrylate, excluding: methyl methacrylate and other methacrylic acid in addition to the methyl methacrylate monomer. Copolymers of esters and/or acrylates, and the like.

The cellulose triacetate resin is cellulose acetate.

The thermoplastic resin thus obtained can be formed into a film by a solvent casting method or a melt extrusion method to form an optical film used in the present invention. Further, it is also possible to use uniaxial stretching or biaxial stretching after film formation as an optical film used in the present invention. The optical film can be adhered to the bonding surface by saponification treatment, corona treatment, plasma treatment, primer treatment or anchor coating treatment before being attached to the polarizing film. deal with. Further, various treatment layers such as a hard coat layer, an antireflection layer or an antiglare layer are provided on the opposite side of the bonding surface to which the optical film is bonded to the polarizing film.

The optical film usually has a thickness of about 5 to 200 μm. When the optical film is too thin, the handling property is lacking, and the possibility of occurrence of breakage or wrinkle generation in the polarizing plate production line is increased. On the other hand, when the thickness is too large, the obtained polarizing plate becomes thick and the weight also increases, which may impair the commercial property. For these reasons, the optical film preferably has a thickness of 10 to 120 μm, more preferably 10 to 85 μm.

[adhesive]

When the optical film is bonded to the polarizing film, first, an adhesive is applied to the bonding surface of the optical film bonded to the polarizing film. The thickness of the adhesive is set to a predetermined value in the range of 0.5 to 5 μm. When the thickness is less than 0.5 μm, the adhesion strength may be uneven. 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. Within the above range, if set in relative When the thickness is, for example, 3.5 μm or more, particularly 4 μm or more, even if the thickness is slightly changed, defects such as bubbles due to the above are not easily exhibited. On the other hand, since the increase in thickness is likely to cause an increase in cost, it is preferably Thinned to the extent possible. For these reasons, the adhesive preferably has a thickness of from 1 to 4 μm, more preferably from 1.5 to 3.5 μm.

Adhesive system as long as it can be applied in liquid form The supplier can use various types of conventional polarizing plates, and is preferably a cationically polymerizable compound such as an epoxy compound from the viewpoints of weather resistance and polymerizability, and more specifically, as in the prior patent document. An active energy ray-curable adhesive containing an epoxy compound having no aromatic ring in the molecule as one of the active energy ray-curable components, as described in JP-A-2004-245925.

The above epoxy compound may, for example, be bisphenol A The diglycidyl ether is a hydrogenated epoxy compound obtained by adding hydrogen to an aromatic polyhydroxy compound of a raw material of a representative aromatic epoxy compound, and is subjected to glycidyl etherification; having at least one bond in the molecule An alicyclic epoxy compound having an epoxy group of an alicyclic ring; and an aliphatic epoxy compound represented by a glycidyl ether of an aliphatic polyhydroxy compound.

In addition, in the active energy ray hardening type adhesive, In addition to the cationically polymerizable compound represented by an epoxy compound, a polymerization initiator is usually formulated, and in particular, a cationic species or a Lewis acid is generated by irradiation of an active energy ray to start polymerization of the cationically polymerizable compound. Cationic polymerization initiator. Further, various additives such as a thermal cationic polymerization initiator which starts polymerization by heating and other photosensitizers may be blended. Additives.

When the optical film is bonded to both surfaces of the polarizing film, the adhesives suitable for the respective optical films may be the same or different, but from the viewpoint of productivity, it is premised on the viewpoint that moderate adhesion can be obtained, preferably double The same adhesive is used for all surfaces.

[Method of Manufacturing Polarizing Plate]

In the present invention, an optical film is bonded to a polarizing film composed of the polyvinyl alcohol-based resin described above via an adhesive to produce a polarizing plate. This is via the following steps (A), (B), (C) and (D).

(A) a coating machine using a coating thickness control means having an adhesive, applying an adhesive to a coating step of an optical film attached to a bonding surface of a polarizing film; (B) by a radiation film thickness meter Before the coating step, the thickness of the optical film is measured, and after the coating step, the total thickness of the optical film and the applied adhesive is measured, and the absolute value of the difference between the measured values is determined by in-line coating. a step of measuring the thickness of the adhesive after the cloth; (C) a step of laminating the polarizing film on the adhesive surface coated in the coating step and passing through the measuring step, and pressurizing; and (D) With respect to the set thickness Y of the adhesive set in the 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 above measuring step and the aforementioned Y is a predetermined value or more, the above control is controlled. The control step of coating the thickness control means.

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

The manufacturing device shown in Fig. 1 is continuously transported The polarizing film 1 is bonded to the one surface of the first optical film 2, and the second optical film 3 is bonded to the other surface to manufacture the polarizing plate 4, and the polarizing plate 4 is taken up by the winding. The roller 30 is constructed. As shown in the figure, typically, each of the optical films is bonded to both surfaces of the polarizing film 1, but only the optical film is bonded to one surface of the polarizing film 1, and is also included in the present invention. In this case, as long as it is a related company, the description of the other optical film can be deducted from the following description, and the degree of ease of implementation can be understood.

The first optical film 2 is firstly thickened by the first radiation film The thickness was measured 14 and then applied to the surface of one of the polarizing films to apply the adhesive from the first coater 10. Then, the total thickness of the first optical film 2 and the applied adhesive is measured by the second radiation film thickness meter 15, and the absolute difference of the measured values measured by the two radiation film thickness meters 14, 15 is absolute. The value was determined to determine the thickness of the adhesive after application. Similarly, the second optical film 3 is first measured by the third radiation film thickness meter 16, and then applied to the surface of one of the polarizing films to apply the adhesive from the second coater 12. Then, the total thickness of the second optical film 3 and the applied adhesive is measured by the fourth radiation film thickness meter 17, and the difference between the measured values measured by the two radiation film thickness meters 16, 17 is measured. The absolute value was used to determine the thickness of the adhesive after application.

Measuring the first optical after the thickness of the adhesive before and after coating In the film 2 and the second optical film 3, the adhesive application surfaces are superposed on both sides of the polarizing film 1, respectively, and then sandwiched by the bonding rolls 20 and 21, whereby Pressurize in the thickness direction. Next, irradiation with an activation energy ray from the activation energy ray irradiation device 18 is received to harden the adhesive. Then, the obtained polarizing plate 4 is taken up by the take-up roll 30 via the pre-winding rolls 22 and 23.

The first coater 10 and the second coater 12 are each In the gravure rolls 11 and 13 provided, an adhesive is applied to the first and second optical films 2 and 3. The guide roller 24 for transportation is appropriately provided on the surface of one of the polarizing films 1 or the surface of the first optical film 2 and the second optical film 3 opposite to the surface on which the adhesive is applied, respectively. As described above, when only the optical film is bonded to one surface of the polarizing film 1, it can be applied to only one of the first optical film 2 and the second optical film 3 shown in Fig. 1 (for example, only the first An optical film 2). The straight arrow in the figure means the flow direction of the film, and the curved arrow means the direction of rotation of the roll.

The polarizing film 1 is a step of manufacturing a polarizing film not shown in the drawing. In many cases, the polyvinyl alcohol-based resin film is supplied by a uniaxial stretching treatment, a dyeing treatment by a dichroic dye, and a boric acid cross-linking treatment after dyeing, but it is of course Alternatively, the polarizing film obtained in the polarizing film production step may be taken up by a roll and then sent out from the feeder again. On the other hand, the first optical film 2 and the second optical film 3 are respectively fed out from rollers not shown in the drawings by a feeder. Each film is conveyed at the same line speed, for example, a line speed of about 10 to 50 m/min, in the same manner as the flow direction. The first optical film 2 and the second optical film 3 are fed while applying a tension of 50 to 1000 N/m in the flow direction.

Then, by the first coater 10 and the second coater 12 Performing the coating step (A) previously described by the first and second radiation film thicknesses The steps 14, 15 and the third and fourth radiation film thickness gauges 16, 17 perform the previously described measuring step (B), and the bonding step (C) described above is performed by the bonding rolls 20, 21, The previously described control step (D) is performed by feeding back the measurement results in the radiation film thickness gauges 14, 15, 16, 17 to the coaters 10, 12. The gravure rolls 11, 13 which the coaters 10 and 12 have are rolls having grooves, by which an adhesive is previously filled in the grooves, and rotated in the state of the first and second optical films 2, 3 in this state. Thereby, the adhesive is transferred onto the first and second optical films 2, 3. By adjusting the rotation speed, the supply amount of the adhesive to the first and second optical films 2, 3, and the coating thickness can be controlled, which is the coating of the first and second coaters 10, 12. Thickness control means.

Describe the steps of these steps according to the block diagram of Figure 2. relationship. First, in the setting (0), the thickness of the adhesive applied in the above coating step (A) is set to a predetermined thickness Y in the range of 0.5 to 5 μm. Then, in the first half of the measuring step (B), the first and second coating machines are set by measuring the thicknesses of the first and second optical films 2, 3 in advance by the first and third radiation film thickness gauges 14, 16. The coating step (A) is carried out under the initial conditions of the coating thickness control means of 10 and 12.

By taking the work as the second half of the measurement step (B), The second and fourth radiation film thickness gauges 15 and 17 measure the total thickness of the optical film and the adhesive after coating, and determine the applied value 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. The thickness of the adhesive is output as the measured thickness X. Regardless of the measured thickness X, the first and second optical films 2, 3 coated with the adhesive are in the bonding step (C), respectively Each of the adhesive application faces is attached to both sides of the polarizing film 1.

On the other hand, in the control step (D), the above comparison is compared The thickness X is set to the thickness Y set as described above. 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 value Y, for example, 5% or more, the coating thickness control means of the first and second coaters 10 and 12 are operated. In order to reduce the absolute value of the difference between the two, it is preferable to control the absolute value of the difference between the measured thickness X and the set thickness Y to less than 5% with respect to the set thickness Y. 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 (1) is satisfied, and the second figure shows whether or not the formula is satisfied. Decide whether to change the conditions by means of control.

The following is a detailed description of the coating constituting the method of the present invention. Step (A), measurement step (B), bonding step (C), and control step (D). 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 this step will be described.

(A) Coating step

In the coating step (A), the first and second optical films 2, 3 are applied to the polarizing film by applying the adhesive to the first half of the measuring step (B) (the step of measuring the thickness of the optical film itself). 1 fit surface. The applicator used herein is not particularly limited as long as it has a means for controlling the coating thickness, and representative ones use the gravure rolls 11 and 13 as described with reference to FIG. The way.

The coater using the gravure rolls 11, 13 includes, for example, a direct gravure coater, a blade coater, a lithographic gravure coater, a contact coater using a gravure roll, and a reverse roll composed of a plurality of rolls. Coating machine, etc. In addition, a die coater having a cylindrical scraper, an adhesive applied to the coating portion and scraped off by a doctor blade, and a die coater for directly supplying an adhesive using a slit die or the like may be used. Or a coater such as a blade coater that forms a liquid reservoir and is coated with a blade to scrape off excess liquid. In this case, the degree of freedom of the film coating or the path line is considered, and in the coater using the gravure roll, a direct gravure coater, a blade coater, a lithographic gravure coater, etc. are preferable. Further, in addition to the gravure roll, a die coater using a slit die is preferred. It is more preferably a blade coater from the viewpoint of easily conforming to the wideness of the polarizing plate or the release of the odor of the adhesive supplied in a liquid state.

Here, the blade holder coater abuts the gravure roll against the blade holder that absorbs the liquid paint (adhesive), and moves the coating material (adhesive) in the blade holder to the groove of the gravure roll, and then This coating material is transferred to the coater of the first and second optical films 2, 3 of the object to be coated. Designed as a compact type, also known as a micro-blade coater.

When the adhesive is applied using a gravure roll, the thickness of the adhesive can be adjusted in accordance with the speed ratio of the gravure roll to the line speed. The production line speeds of the first and second optical films 2, 3 are set to 10 to 50 m/min, and the gravure roll is rotated in the opposite direction with respect to the conveyance directions of the first and second optical films 2, 3, and the gravure roll is The rotation cycle speed is set to 10 to 500 m/min, thereby 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 preselect a gravure roll having a void ratio suitable for the surface of the set thickness Y in advance. The manner in which the gravure roll is reversely rotated with respect to the conveyance direction of the first and second optical films 2, 3 is also referred to as a reverse intaglio.

(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 a radiation film thickness meter, and the measuring step performed after the coating step (A) ( In the second half of step B), the total thickness of the optical film and the applied adhesive is measured by a radiation film thickness meter. 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. As shown in Fig. 1, the first to fourth radiation line thickness gauges 14, 15, 16, 17 are detected by the first to fourth radiation sources 14a, 15a, 16a, 17a and the first to fourth detection, respectively. The devices 14b, 15b, 16b, and 17b are arranged such that they are disposed opposite to each other by the optical film measured by the spacers.

Radiation film thickness gauges 14, 15, 16, 17 are by the spokes The radiation sources 14a, 15a, 16a, 17a illuminate the optical film with radiation, and the radiation passing through the optical film is detected by the detectors 14b, 15b, 16b, 17b. The irradiated radiation is attenuated as it penetrates the optical film. The radiation film thickness gauges 14, 15, 16, and 17 determine the amount of the optical film from the amount of attenuation and convert it into a thickness. Although the attenuation amount of the radiation may be affected by the density of the optical film, the larger the film thickness of the optical film is, the larger the attenuation is.

In the first half of the measurement step (B), the output is: The radiation penetrates the optical film before the application of the adhesive and determines the film thickness value measured by the amount of attenuation. In the second half of the measuring step (B), the output is: after the radiation penetrates the coating adhesive The optical film was used to determine the total film thickness value of the adhesive layer and the optical film measured by the amount of attenuation, and the thickness of the adhesive was determined as the absolute value of the difference between the film thickness values of the two. According to the film thickness measuring method using the radiation film thickness meter as described above, the thickness of the adhesive can be accurately determined in an in-line manner.

The film thickness measurement method using a radiation film thickness meter is There is an advantage that the thickness of the adhesive can be determined regardless of whether or not there is a difference in refractive index between the optical film and the adhesive, and even if no difference is observed in the characteristic absorption of the infrared absorption spectrum. In addition, the film thickness measurement method using the radiation film thickness meter is different from the film thickness measurement method using the optical interference type film thickness meter, and is not susceptible to the optical film transparency such as transparency, alignment degree, and alignment direction. The influence of characteristics makes it possible to perform film thickness measurement stably.

Convert the attenuation of the radiation into an optical film or adhesive In the case of the thickness of the coating layer optical film, the relationship between these is measured in advance and the measured calibration curve is produced. The attenuation of the radiation is usually measured by the detector as the current value or the voltage value. Therefore, the current value or the voltage value of the optical film of the same material having different thicknesses can be measured in advance, and the current with respect to the thickness can be made. A calibration curve for values or voltage values. The optical film used in the production of the calibration curve is the same as the optical film having the same thickness as the optical film used in the actual production of the polarizing plate, and the thickness is thinner than the optical film used in the actual production of the polarizing plate. The optical film of the material can be made with higher precision The viewpoint of thickness measurement is preferable. A calibration curve was also prepared in the same manner for the adhesive layer optical film.

In addition, in order to improve the thickness of the adhesive measurement The degree of radiance attenuation of the optical film of the same material having different thicknesses and the radiation attenuation of the optical film of the adhesive layer of the same material having different thicknesses can be determined separately, and the thickness of the adhesive can be determined as adhesion. The absolute value of the difference between the thickness of the coating layer optical film and the thickness of the optical film, and a calibration curve for the amount of radiation attenuation with respect to the thickness of the adhesive is produced.

Radiation film thickness meter can be used with X-ray, β Film thickness gauge of radiation such as rays or gamma rays. In view of the thickness of the optical film and the adhesive layer optical film to be measured (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 preferred to use X-rays or Radiation film thickness meter for beta rays.

X-ray radiation film thickness meter (X-ray film thickness) In general, an X-ray source tube using a titanium target or a tungsten target or the like is applied, and a voltage is applied to the X-ray source tube to generate X-rays. A β-ray radiation film thickness meter (β-ray film thickness meter) is generally used to generate β-rays using Pm147, 氪85 or Sr90 as a radiation source. From the viewpoint of more accurately measuring the thickness of the adhesive, in the β-ray film thickness meter, a β-ray film thickness meter using Pm147 as a radiation source is preferably used.

The X-ray film thickness meter is compared with the beta ray film thickness meter. There is a tendency that the amount of radiation attenuation when the radiation penetrates the optical film is likely to depend on the type (material) of the optical film. Therefore, when the thickness of the optical film itself is determined from the above-mentioned calibration curve, it must be recreated depending on the type of the optical film. The calibration curve or the pre-production of the calibration curve for different types of optical films is higher than the beta ray thickness gauge. Therefore, in the case where the first optical film attached to one surface of the polarizing film is different from the second optical film attached to the other surface of the polarizing film, or different types are produced in the same production line In the case of a heterogeneous polarizing plate of an optical film, etc., in order to obtain a higher thickness measurement accuracy of the adhesive, it is sometimes preferable to use a beta ray film thickness meter.

From the viewpoint of measuring the thickness of the adhesive more accurately It is to be noted that the measurement point of the radiation film thickness meter (the area irradiated by the radiation irradiation area on the optical film) is preferably about 10 to 30 mm in diameter. Further, the measurement accuracy of the radiation film thickness on the inner line is preferably ±0.15 μm or less, and particularly preferably ±0.1 μm or less. In order to achieve this measurement accuracy, the radiation source of the radiation film thickness meter is preferably one having a higher energy intensity, and it is more preferable to use a radiation source that does not reach a half-life, from the viewpoint of a measurement that can be made with higher accuracy.

In addition, the stability of the measured value from the thickness of the adhesive From a viewpoint, the radiation film thickness meter preferably performs one measurement at a measurement interval of 0.005 to 1 second, particularly 0.01 to 0.5 second, and more preferably from 10 to 50000 points from the obtained data. The measured value is obtained by the moving average and is output. For example, when a moving average is obtained for a measured value exceeding 50,000 points, and the measurement interval exceeds 0.5 second, the deviation between the measured value and the actual thickness sometimes becomes large. For the same reason, it is more preferable to use a measurement interval of 0.005 to 1 second for one measurement, and to output a moving average film thickness meter from a continuous measurement value of 10 to 50000 points.

In order to improve the measurement accuracy of the thickness of the adhesive, Preferably, the position of the radiation film thickness meter for measuring the thickness of the optical film itself before the coating step (A) and the radiation of the total thickness of the measuring optical film and the adhesive after the coating step (A) are used. The position of the film thickness meter is the same in the width direction of the optical film. Further, for the same reason, it is preferable to make the thickness measurement points coincide in the longitudinal direction (transport direction) of the optical film. Further, for the same reason, the interval between the two radiation film thickness gauges is preferably set to be within 10 m along the longitudinal direction of the optical film, and more preferably 1 to 5 m.

(C) lamination step

After the coating step (A) and the measuring step (B), the polarizing film 1 is superposed on each of the first and second optical films 2 and 3, and the pressure is applied to each other. Step (C). In the pressurization of this step, it is preferable to use a pair of rolls 20 and 21 as shown in Fig. 1 from the viewpoint of being continuously pressurized while being conveyed by a generally known means. The way. In this case, it is preferable that the time points at which the first and second optical films 2 and 3 are superposed on the polarizing film 1 and the time at which the first and second optical films 2 and 20 are pressurized are preferably the same, even if they are different. The shorter the difference in time points, the better. The combination of the pair of rolls 20 and 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 pressure at the time of pressurization is a line pressure when held by a pair of rolls 20, 21, and is preferably set to be about 150 to 500 N/cm.

(D) Control steps

In the present invention, a control step (D) for controlling the coating thickness of the adhesive in the coating step (A) is provided in accordance with the result of the measuring step (B) described above. That is, the thickness of the adhesive applied in the coating step (A), There are some variations in the temperature of the adhesive or the ambient temperature, the surface tension of the first and second optical films 2, 3, or the tension applied thereto, and sometimes there are some variations. The desired coating thickness (set thickness Y) causes a deviation. In order to correct the deviation of the coating thickness, the coating thickness control means of the coater can be controlled according to the coating thickness (measured thickness X) measured by the radiation film thickness meter in the measuring step (B). .

For example, when the coater is a die coater, the thickness is measured. When the degree X is larger than the set thickness Y, the ability to feed the liquid from the pump or the like to the mold is lowered. Conversely, when the measured thickness X is smaller than the set thickness Y, the ability to feed the liquid from the pump or the like to the mold is improved. This controls the coating thickness. Further, when the coater is a doctor blade coater using a gravure roll, when the measured thickness X is larger than the set thickness Y, the number of revolutions of the reverse gravure is increased and the rotation peripheral speed is increased to reduce the transfer amount of the adhesive. Conversely, when the measured thickness X is smaller than the set thickness Y, the number of revolutions of the inverted intaglio plate is lowered and the rotation peripheral speed is lowered to increase the amount of transfer of the adhesive, whereby the coating thickness can be controlled.

The degree of film thickness control can be experimentally adapted to different times The environmental factors, the viscosity of the adhesive, the surface shape of the optical film, and the like are arbitrarily set. The actual control system can be carried out using a computer or manually.

(E) hardening step

As described above, after the first and second optical films 2, 3 are attached to the polarizing film 1, when the adhesive is an active energy ray-curable type, it is subjected to a hardening step of hardening the adhesive by irradiation of an active energy ray. After (E), the polarizing plate 4 was produced. In the example shown in Fig. 1, the hardening step (E) is performed by activation energy. The radiation irradiating device 18 irradiates the active energy ray to the laminated body in which the first and second optical films 2 and 3 are bonded to the polarizing film 1. In this step, the energy required to harden the active energy ray-curable adhesive is irradiated over the first optical film 2.

Specifically, the active energy ray system can use an electron beam or Ultraviolet rays are selected in response to the hardening reaction mechanism of the adhesive. Since the electron beam irradiation device is shielded so that the generated electron beam does not leak to the outside, the size or weight of the device increases. On the other hand, since the ultraviolet irradiation device has a relatively delicate structure, it is preferably cured by irradiation with ultraviolet rays.

In the example shown in Figure 1, the activation energy ray pair is via The adhesive is applied to the laminate of the polarizing film 1 and the first and second optical films 2, 3, and is applied to the rolls 20 and 21 before and after the activation of the energy ray irradiation device 18 and the rolls 22 and 23 before the winding. The tension is applied to the laminate. The present invention is not limited to this, and it is preferable to support a convex curved surface which is formed in an arc shape along the conveying direction, and is typically a peripheral of a roller, as disclosed in the prior patent document 2 (JP-A-2009-134190). In the state of the surface, the active energy ray is irradiated. In particular, when heat is generated by the irradiation of the active energy ray, and the product can be adversely affected, it is preferable to irradiate the active energy ray in a state where the laminated body is supported on the outer peripheral surface of the roll as in the latter, and at this time, the laminated body is supported. The rolls are preferably temperature-adjustable in the range of 10 to 60 °C. Further, the activation energy ray irradiation apparatus can be provided only by one at the irradiation site or two or more along the flow direction of the laminate, and is also irradiated from a plurality of light sources, and is also effective for effectively increasing the integrated light amount.

When the ultraviolet ray is used to harden the adhesive, it is used. Although the ultraviolet light source is not particularly limited, a light-emitting distribution having a wavelength of 400 nm or less can be used. 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, a black lamp, and a microwave-excited mercury lamp can be used. , metal halide lamps, etc. When an epoxy compound is used as an adhesive for an active energy ray-curable component, the absorption wavelength exhibited by a general photopolymerization initiator is considered, and a high-pressure mercury lamp or metal having a light of more than 400 nm is preferably used. The halide lamp is used as an ultraviolet light source.

When ultraviolet rays are irradiated to an adhesive having an epoxy compound as a curable component and cured, the production line speed of the laminate is not particularly limited, but generally the coating step (A) or the bonding step (C) can be maintained. Production line speed. In addition, it is preferable to apply an amount of light to the irradiation amount in the wavelength region in which the activation of the polymerization initiator is effective while applying a tension of 100 to 1000 N/m in the longitudinal direction (transport direction) of the laminate (irradiation in the laminate) The total energy of the body is irradiated with ultraviolet rays in such a manner as to be 100 to 1500 mJ/cm ² . When the amount of integrated ultraviolet light irradiated 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, when the integrated light amount is excessively large, the heat radiated from the light source and The heat generated during the polymerization of the adhesive may cause yellowing of the active energy ray-curable adhesive or deterioration of the polarizing film.

In addition, when it is desired to achieve the necessary integrated light amount by one-time ultraviolet irradiation, the film may reach a high temperature exceeding 150 ° C due to heat generation, and deterioration of the polarizing film may occur at this time. In order to avoid this, it is also effective to provide a plurality of ultraviolet irradiation devices along the transport direction of the film as described above and to divide into a plurality of irradiations. In the standard, it is preferable that the irradiation amount of the ultraviolet irradiation device from one place is 600 mJ/cm ² or less in terms of the integrated light amount, and finally, the integrated light amount of 100 to 1500 mJ/cm ² as described above can be obtained.

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

Example

The present invention will be more specifically described below by showing examples and comparative examples, but the present invention is not limited thereto. The experiment shown below is carried out to confirm the effect of the present invention. For example, the thickness of the adhesive which is applied to the polarizing film and applied to the opposite side to the thickness of the adhesive after the thickness measurement is described. In such a way that no defects are generated there, the optimum value used in the actual operation is set to be thicker.

Fig. 3 is a schematic side view showing the manufacturing apparatus used in the following examples and comparative examples. The manufacturing apparatus shown in Fig. 3 differs from the first one described above in that only the following two points are different, and the parts other than the different points are denoted by the same reference numerals as in the first drawing, so the details of these parts are For instructions, please refer to the description of Figure 1.

[The difference between Figure 3 and Figure 1]

(1) When an active energy ray (ultraviolet light) is applied to a laminated body in which the first optical film 2 and the second optical film 3 are bonded to both surfaces of the polarizing film 1, respectively, the second layer of the laminated body is made The optical film 3 side is in close contact with the winding roller for irradiation The outer peripheral surface of the outer peripheral surface of the laminated body is sandwiched by the active energy ray (ultraviolet) irradiation device 18 disposed on the opposite side of the irradiation winding roller 26, and the ultraviolet ray is irradiated onto the first optical film 2 side of the laminated body. ;as well as

(2) Since only one (two) radiation film thickness gauges are provided, the thicknesses of the adhesive applied to the first optical film 2 are measured by the first and second radiation film thickness gauges 14, 15. The thickness of the adhesive applied to the second optical film 3 was not measured.

First and second radiation film thickness gauges 14, 15 are used A beta-ray film thickness meter "SB-1100" (beta source: Pm-147) manufactured by Nanogray Co., Ltd. with a display device. In the β-ray film thickness meter, the film thickness is determined by the amount of attenuation when the radiation penetrates the optical film, and the measurement accuracy of the film thickness in the line is set to about ±0.1 μm. The film thickness of the object to be measured is measured at each predetermined measurement interval, and when the number of times of measurement is also set in advance, the individual film thickness values measured above are subjected to moving average, and the average film thickness during the period is output. Further, in the measured value of the preset number of times, the data determined to be the abnormal value is automatically excluded to output the average film thickness.

[Example 1]

(0) Materials used in the experiment

In this example, the first optical film 2 is a biaxially oriented retardation film "KC4FR-1" composed of cellulose triacetate supplied from a roll, having a thickness of 40 μm and a width of 1,330 mm [from Konica Minolta Opto Co., Ltd. The company obtained a refractive index of 1.48], and the second optical film 3 was made of a thickness of 80 μm and a width of 1,330 mm, and was still supplied from a roll of a cellulose triacetate film "KC8UX2MW" [taken from Konica Minolta Opto Co., Ltd. Yes, refractive index 1.48]. The adhesive used in the adhesion of the polarizing film 1 to the first optical film 2 and the adhesive used in the adhesion of the polarizing film 1 and the second optical film 3 contain an epoxy compound and a photopolymerization initiator. An epoxy-based photocurable adhesive which does not substantially contain a solvent.

(A) Coating step

The polarizing film 1 having a thickness of 25 μm with iodine adsorbed on polyvinyl alcohol, the retardation film as the first optical film 2, and the cellulose triacetate film as the second optical film 3 were respectively 15 m/min. The line speed is supplied and the flow direction is the same. The epoxy-based photocurable adhesive is applied to the first half of the measurement step (B) to be described later by using the first coater 10 (the "micro-blade holder" manufactured by Fuji Machinery Co., Ltd.) having the gravure roll 11 The retardation film 2 of the step (the step of measuring the thickness of the optical film itself) is bonded to the bonding surface of the polarizing film 1. In addition, the above-mentioned epoxy-based photocurable adhesive is also applied to cellulose triacetate by using a second coater 12 (also referred to as "micro-scraper" manufactured by Fuji Machinery Co., Ltd.) having a gravure roll 13 The film 3 is bonded to the bonding surface of the polarizing film 1.

Gravure roll disposed on the first and second coaters 10, 12 11, 13 is rotated in the opposite direction with respect to the transport direction of the film. Further, in the second coater 12 on the side of the cellulose triacetate film 3, the circumferential speed of the gravure roll 13 provided in the coater 12 was set to 15 m/min, and was set to a thickness of about 4.5 μm. The adhesive is applied to the film. Since the thickness of the adhesive is not measured in the second coater 12, the film thickness control is not performed, and the adhesive is applied to a thickness where the defect is hardly exhibited. On the side of the retardation film 2, the rotational peripheral speed of the gravure roll 11 provided in the first coater 10 The initial stage was set to 21 m/min, and the adhesive was applied to a thickness of about 2.5 μm.

(B) Measurement steps

The first radiation film thickness gauge 14 is disposed on the upstream side of the first coater 10, and the second radiation film thickness gauge 15 is disposed on the downstream side of the first coater 10. The interval between the two coaters along the film flow direction was set to 1.67 μm. The thickness of the retardation film 2 was measured by the first radiation film thickness meter 14 at intervals of 0.2 seconds, and was set to a continuous measurement value for each {(2 ² ) ² } ² = 2 ⁶ = 256 times (about 51.2 seconds), the moving average is output in order (first half step).

In addition, by being configured after the above coating step The second radiation film thickness meter 15 measures the total film thickness of the retardation film 2 and the adhesive from the adhesive application surface side of the retardation film 2 at intervals of 0.2 seconds, and sets it to 256 times for each time. The continuous measurement (about 51.2 seconds) sequentially outputs the moving average (1 of the second half). Therefore, after about 51.2 seconds from the start to the 256-times measurement, the moving average of the thickness of the retardation film 2 is output from the first radiation film thickness gauge 14 every 0.2 seconds, and from the second radiation The film thickness meter 15 outputs the moving average value of the total film thickness of the retardation film 2 and the adhesive, but the value is selected every 1 second, and the value of the former in the time point (the thickness of the retardation film 2) The difference between the measured value = A) and the latter value (measured value of the retardation film 2 and the total film thickness of the adhesive = B) is sequentially recorded as the measured thickness X (2 of the second half step). Therefore, the control step (D) described later is provided, and the measurement thickness X is controlled for about 150 minutes to obtain the measured thickness X obtained during the period (the number of data is about 150 minutes × 60 pieces / minute). 9000) average Value and standard deviation, the results are shown in Table 1.

(C) lamination step

The adhesive bonding surface of the retardation film 2 and the cellulose triacetate film 3 coated with the adhesive was superposed on the polarizing film 1 and sandwiched by the bonding rolls 20 and 21 at a line pressure of 240 N/cm. hold. The laminated body of the retardation film 2 / the polarizing film 1 / the cellulose triacetate film 3 after passing through the rolls 20 and 21 is attached to the irradiation winding roll 26 set at 20 ° C in the side of the cellulose triacetate film 3 side. In the outer peripheral surface, the tension of 600 N was applied in the longitudinal direction, and the ultraviolet rays from the ultraviolet irradiation device 18 were irradiated to the retardation film 2 side while being irradiated at the same line speed of 15 m/min. The ultraviolet irradiation device 18 is made of GS Yuasa Co., Ltd., and irradiates ultraviolet rays from two lamps of the "EHAN1700NAL high-pressure mercury lamp" of the ultraviolet lamp provided in the device. The amount of light accumulated by the ultraviolet light is a total of 330 mJ/cm ² for both lamps. The adhesive layer is cured in this manner, and a polarizing plate 4 in which the retardation film 2 is bonded to one surface of the polarizing film 1 and the cellulose triacetate film 3 is bonded to the other surface is produced and wound up on the take-up roll 30. .

(D) Control steps

In the control step, when the measured thickness X obtained in the above measuring step (B) is more than 5% or more than the set thickness Y=2.5 μm, that is, when |XY|≧0.125 μm, the side is 0.5 m/min. The unit increases and decreases the rotational peripheral speed of the gravure roll 11 provided in the first coater 10, and controls the application thickness of the adhesive.

[Comparative Example 1]

In the first embodiment, the control step (D) is not set, that is, even if the test is in progress The measured thickness X obtained in the step (B) is changed, and the rotational speed of the gravure roll 11 provided in the first coater 10 is not changed to produce a laminated body, and then ultraviolet irradiation is performed in the same manner to produce polarized light. board. The average value and standard deviation of the thickness X after the operation for about 150 minutes were performed as shown in Table 1.

[Comparative Example 2]

In the first embodiment, the first radiation film thickness meter 14 is not provided, and the reflection beam splitting film "FE-2900CCD" having a spectral wavelength region of 230 to 800 nm manufactured by Otsuka Electronics Co., Ltd. is used instead of the second radiation. In the line thickness gauge 15, 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 composed of cellulose triacetate 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 cannot be The coating thickness control of the adhesive is performed.

[Embodiment 2]

In Example 1, a biaxially stretched polyethylene terephthalate film having a thickness of 38 μm and a width of 1330 mm [obtained from Mitsubishi Plastics Co., Ltd., in-plane retardation value of 1000 nm] was used as the first optical film 2 A polarizing plate was produced in the same manner as in Example 1 except that the biaxially oriented retardation film "KC4FR-1" composed of cellulose triacetate was replaced. The average value and standard deviation of the thickness X after the operation for about 150 minutes were performed as shown in Table 1.

[Comparative Example 3]

In the second 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 gravure roll provided in the first coater 10 is not changed. A laminate was produced at a rotational speed of 11, and then ultraviolet irradiation was performed in the same manner to prepare a polarizing plate. The average value and standard deviation of the thickness X after the operation for about 150 minutes were performed as 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 40 mm width portions at both ends are respectively subtracted, and the central portion of the width of 1250 mm is the effective width, and the surface covering the length of the flow direction of 3300 mm in the effective width is used. (1.25m × 3.3m ≒ 4m ² ), mark as a bright spot by visual observation, and then observe the mark at a magnifying glass with a magnification of 100 times and confirm whether there is a bubble. If it is a bubble, the following method is used. Find the size. That is, if the observed bubble is a virtual ellipse (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. Calculating a size of 100 m or more number of bubbles, when the number per 1m ² when less than 0.3, i.e. in the observation area of 4m ² is 0 or 1 when determined as "OK", in the number of or higher per 1m ² of 0.3, i.e., when viewed in the area of 4m ² as two or more, it is determined as "NG", the main variables and the results are summarized in table 1 together with the.

In the table, the "TAC" in the column of the optical film is triacetic acid. Cellulose, "PET" is polyethylene terephthalate. The bubble of a size of 100 μm or more observed by a magnifying glass is in a manner of containing the bubble When the film was cut into a size of 40 mm × 40 mm and observed by a microscope, it was confirmed that the adhesive layer was interposed between the polarizing film 1 and the first optical film 2.

As shown in the first table, it can be known that the control step (D) is not set. In Comparative Example 1 and Comparative Example 3, the measured thickness of the adhesive fluctuated, and as a result, bubble defects were observed in the obtained polarizing plate, whereas the control step (D) was provided, and in the adhesive In the first and second embodiments in which the coating thickness was changed by measuring the thickness X by more than 5% from the set thickness Y, the measured thickness was suppressed to be within approximately 5% as compared with the set thickness Y, and the bubble defects were also small. On the other hand, as in the case of Comparative Example 2, when the spectral range of the reflection and the spectral thickness of the relatively wide range of the spectral wavelength region of 800 nm or less is used, when there is almost no difference between the refractive index of the adhesive and the refractive index of the optical film, The coating thickness of the adhesive was measured.

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 Radiation Film Thickness Gauge

14a‧‧‧First radiation source

14b‧‧‧First detector

15‧‧‧Second Radiation Film Thickness Gauge

15a‧‧‧Second radiation source

15b‧‧‧Second detector

16‧‧‧ Third Radiation Film Thickness Gauge

16a‧‧‧ Third radiation source

16b‧‧‧ third detector

17‧‧‧Fourth Radiation Line Thickness Gauge

17a‧‧‧Fourth source of radiation

17b‧‧‧ fourth detector

18‧‧‧Activated ray (ultraviolet) irradiation device

20, 21‧‧‧Finishing rolls (rollers)

22, 23‧‧‧ Roll before rolling

24‧‧‧guide roller

30‧‧‧Winding roller

Claims (4)

A method for producing a polarizing plate 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-based resin via an adhesive, and the method comprises: (A) a coating machine using a coating thickness control means having the above-mentioned adhesive, applying the adhesive to a coating step of the optical film attached to the bonding surface of the polarizing film; (B) by a radiation film Thickness, before the coating step, measuring the thickness of the optical film, and after the coating step, measuring the total thickness of the optical film and the adhesive after coating, thereby determining the absolute difference between the measured values a value measuring step of determining the thickness of the adhesive after coating in an in-line manner; (C) superposing the polarizing film on the adhesive surface coated in the coating step and passing through the measuring step and performing a press-fit step; and (D) a set thickness Y of the adhesive set in the range of 0.5 to 5 μm, the absolute difference between the measured thickness X of the adhesive obtained in the aforementioned measuring step and the aforementioned Y Ratio of values When it is more than a predetermined value, the control step of the coating thickness control means is controlled. The method for producing a polarizing plate according to claim 1, wherein in the controlling step (D), the measured thickness X of the adhesive obtained in the measuring step is compared with the set thickness Y of the adhesive. When the ratio of the absolute value of the difference of Y is 5% or more, the coating thickness control means is controlled. The method for producing a polarizing plate according to claim 1, wherein the adhesive is a liquid active energy ray-curable adhesive. The method for producing a polarizing plate according to claim 3, wherein after the bonding step (C), a curing step (E) of curing the adhesive by irradiation with an active energy ray is provided.