KR20150002586A

KR20150002586A - Polarizing plate fabrication method

Info

Publication number: KR20150002586A
Application number: KR1020147022427A
Authority: KR
Inventors: 히로아키 다카하타; 아즈사 히로이와
Original assignee: 스미또모 가가꾸 가부시키가이샤
Priority date: 2012-03-29
Filing date: 2013-03-07
Publication date: 2015-01-07
Also published as: TW201346352A; WO2013146162A1; JP5988649B2; KR101920107B1; JP2013205741A; TWI603121B

Abstract

A method for producing a polarizing plate by bonding an optical film to a polarizing film through an adhesive, the method comprising: (A) a coating step of applying an adhesive to an optical film using a coating machine having a coating thickness control means of an adhesive; (B) A measuring step of measuring the thickness of the film before and after the coating step by a succession of steps and obtaining the thickness of the applied adhesive in in-line from the absolute value of the difference, (C) a bonding step of superimposing and pressing a polarizing film on the adhesive surface of the optical film, And (D) controlling the coating thickness control means when the ratio of the measured thickness X of the obtained adhesive to the absolute value of the difference in Y becomes equal to or larger than a predetermined value with respect to the set thickness Y of the adhesive Method is provided.

Description

POLARIZING PLATE FABRICATION METHOD [0002]

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

A liquid crystal panel constituting the core of a liquid crystal display device is usually constituted by disposing a polarizing plate on both sides 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 side of a polarizing film made of a polyvinyl alcohol-based resin through an adhesive. In many cases, a transparent resin film is bonded to the other surface of the polarizing film through an adhesive. Like the protective film on the opposite side, the transparent resin film has not only a protective function against the polarizing film, In addition, for the purpose of optical compensation of the liquid crystal cell or compensation of the viewing angle, there is a case of a so-called phase difference film imparted with a retardation in the plane and / or in the thickness direction. In the present specification, such a protective film, a retardation film, and the like that are bonded to a polarizing film through an adhesive will be referred to as an " optical film ". The adhesive used for bonding the optical film to the polarizing film is generally liquid, and the adhesive force is developed between the polarizing film and the optical film by the curing reaction of the liquid adhesive.

In recent years, the price of a liquid crystal display device including a television is severely reduced, a demand for a reduction in the price of the member constituting it is intensified, and the demand for quality is further increased. Of these flows, the adhesives used in the production of the polarizing plate can also be obtained from water-based adhesives in which the types of optical films that can be applied are limited to specific resin films such as cellulose-based resin films, Curing type adhesive. Bonding of a polarizing film and an optical film using an active energy ray-curable adhesive is proposed, for example, in Japanese Patent Application Laid-Open No. 2004-245925 (Patent Document 1).

The active energy ray-curable adhesive is prepared in a liquid form, and is applied to a die coater which directly applies the liquid adhesive to the object to be painted, or a gravure roll which carries a liquid adhesive on a concave groove formed on the surface and transfers the liquid adhesive onto the surface of the object to be painted , And the optical film is previously coated on the bonding surface to the polarizing film. Then, a polarizing film is superimposed on the coated surface of the adhesive, and an active energy ray such as ultraviolet rays or electron rays is irradiated to cure the adhesive, whereby the adhesive force is developed. The method using such an active energy ray-curable adhesive is a very effective method because there are many optical films that can be applied.

JP-A-2009-134190 (Patent Document 2) discloses a method for producing a polarizing plate using an active energy ray-curable adhesive. For example, JP-A-2009-134190 discloses a method for producing a polarizing plate by laminating a protective film on both surfaces of a polarizing film, Discloses a method of irradiating an active energy ray while adhering the laminated body to the outer surface of a 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 opposite curl and wave curl, which are likely to occur in the obtained polarizing plate, and to produce a polarizing plate having good performance.

In the method of Patent Document 2, it is considered that the thickness of the adhesive layer formed on the protective film does not greatly affect the curl and wave curl of the polarizing plate to be produced, so that there is little need to manage the coating thickness of the adhesive . However, when the thickness of the adhesive layer is deviated, defects such as bubbles are sometimes generated at a level at which most of the problems are not a problem, and when the defects are large, the yield of the polarizing plate may be lowered. In order to stably produce an inexpensive, higher-performance polarizing plate, the active energy ray-curable adhesive is often coated thicker than conventional water-based adhesives, and is expensive in itself, and is thinned ), It is desired to control the thickness of the adhesive layer so as to be the minimum necessary thickness in consideration of the deviation width.

An infrared film thickness meter is known as a device for measuring the thickness of a coating in order to manage the coating thickness in-line. However, since the infrared film thickness meter has a limited resolution, it is difficult to accurately measure the thickness of the coating layer (adhesive layer) formed on the film continuously transported, such as a polarizing plate production line, on the order of several micrometers. Specifically, in the polarizing plate production line, as shown in FIG. 1, which will be described later, the polarizing film and the optical film bonded to at least one of the surfaces thereof are successively conveyed without any special support, However, in such a continuously transported film, subtle fluctuations occur in the thickness direction and in the direction (flow direction) in which the tension is applied. In order to measure the thickness of the coating layer by means of an IR , Accuracy of only about 1 占 퐉 was obtained, and it was practically impossible to manage the coating thickness based on this precision.

In addition, when the thickness of the adhesive layer formed on the optical film is measured by an infrared film, there is a limitation that the infrared absorption peak imparted by the optical film and the infrared absorption peak imparted by the adhesive should be clearly distinguished, The peaks of both are overlapped, and the measured value itself is sometimes not obtained.

From the above reasons, up to now, in the production of a polarizing plate using a liquid adhesive, the thickness of the liquid adhesive applied on the film has not been inspected in-line.

Patent Document 1: Japanese Patent Application Laid-Open No. 2004-245925 Patent Document 2: JP-A-2009-134190

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a polarizing film in which an optical film is adhered to a polarizing film through a liquid adhesive, which is a typical example of an active energy ray curable adhesive, by controlling the coating thickness of the adhesive inline, And a method for producing a polarizing plate at low cost while suppressing the occurrence of defects such as bubbles in the adhesive layer.

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted intensive studies in order to solve the above problems. As a result, the present inventors have found that when a polarizer is produced by applying a liquid adhesive onto an optical film and bonding a polarizing film to the coated layer, , It is found that the thickness of the adhesive can be precisely determined and that the thickness of the adhesive can be uniform and the defects can be reduced by controlling the coating thickness of the adhesive at the time of coating based on the result of the measurement. It came to the following.

That is, the present invention includes the following.

[1] 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 through an adhesive,

(A) a coating step of applying the adhesive to the bonding surface of the optical film to the polarizing film using a coating machine having coating thickness control means for the adhesive,

(B) measuring a thickness of the optical film before the coating process by a radiation film thickness meter, measuring a total thickness of the adhesive applied to the optical film after the coating process, A measurement step of obtaining the thickness of the applied adhesive in in-line,

(C) a bonding step of covering the polarizing film on the adhesive surface which has been applied in the coating step and has been subjected to the measuring step, and

(D) when the ratio of the measured thickness X of the adhesive obtained in the measuring step to the absolute value of the difference between Y and the set thickness Y of the adhesive set within the range of 0.5 m to 5 m is equal to or larger than a predetermined value, A control step of controlling the coating thickness control means

And a polarizing plate.

[2] In the control step (D), when the ratio of the measured thickness X of the adhesive obtained in the measuring step to the absolute value of the difference between Y and the set thickness Y of the adhesive becomes 5% or more, And controlling the thickness control means.

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

[4] The method for producing a polarizing plate according to [3], further comprising a curing step (E) of curing the adhesive by irradiating an active energy ray after the bonding step (C).

According to the present invention, when an optical film is bonded to a polarizing film through an adhesive, the thickness of the film before and after the coating process is measured by using a predetermined film thickness meter, and the thickness of the adhesive formed on the optical film is measured in an in- , And the result is transmitted to the coating thickness control means of the adhesive contained in the coating machine to control the coating thickness of the adhesive. Thus, a polarizing plate having a uniform adhesive thickness can be produced. As a result, it is possible to suppress defects such as bubbles which are likely to occur due to the fluctuation of the thickness of the adhesive.

1 is a schematic side view showing an example of a manufacturing apparatus suitably used in the present invention.
Fig. 2 is a block diagram showing the relationship among steps in the present invention. Fig.
3 is a schematic side view showing a 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 through an adhesive to produce a polarizing plate. The optical film may be bonded to only one side of the polarizing film, or may be bonded to both sides of the polarizing film. When bonding an optical film to both surfaces of a polarizing film, the method of the present invention may be applied to bonding of one optical film, and the method of the present invention may be applied to bonding of both optical films.

[Polarizing Film]

The polarizing film is a film made of a polyvinyl alcohol-based resin, having a property of transmitting light having a vibration surface in a certain direction among the light incident on the film, and absorbing light having a vibration surface perpendicular to the film, Is a film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin.

The polyvinyl alcohol resin constituting the polarizing film is obtained by saponifying a polyvinyl acetate resin. The polyvinyl acetate resin to be a raw material of the polyvinyl alcohol resin may be a copolymer of vinyl acetate and other monomers copolymerizable therewith, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate.

By applying a uniaxial stretching treatment, a dyeing treatment with a dichroic dye, and a boric acid crosslinking treatment after dyeing to a film made of a polyvinyl alcohol resin, a polarizing film can be obtained. As the dichroic dye, iodine or a dichroic organic dye is used. The uniaxial stretching may be performed before dyeing with a dichroic dye, or may be performed simultaneously with dyeing with a dichroic dye, or may be performed after dyeing with a dichroic dye, for example, during boric acid crosslinking treatment.

A polarizing film made of a polyvinyl alcohol-based resin, which is produced in this way and in which a dichroic dye is adsorbed and oriented, becomes one of the raw materials for the polarizing plate.

[Optical film]

An optical film made of a thermoplastic resin is bonded to the polarizing film to produce a polarizing plate. The refractive index of the optical film measured by D-line at a temperature of 20 캜 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 of measuring refractive index of chemical product ". When the optical film has a refractive index within this range, the display characteristics when the polarizing plate to be produced is incorporated into the liquid crystal panel are excellent. For the same reason, the refractive index of the optical film is preferably in the range of 1.45 to 1.67.

The haze value of the optical film in the range of about 0.001% to 10% improves the contrast of the obtained polarizing plate, and in particular, when it is incorporated in a liquid crystal panel to obtain a black display, Is preferable. The haze value is a value defined by (diffusion transmittance / total light transmittance) x 100 (%), which is measured in accordance with JIS K 7136: 2000 " Method of determining haze of plastic-transparent material ".

As the thermoplastic resin constituting the optical film, for example, the following can be cited. Here, the refractive index measured by the D line at a temperature of 20 캜 is denoted as n _D (20 캜).

A cycloolefin-based resin [n _D (20 ° C) = about 1.51 to 1.54]

Crystalline polyolefin-based 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]

Triacetylcellulose resin [n _D (20 캜) = around 1.48], and the like.

The cycloolefin-based resin is a polymer having a cycloolefin-based monomer such as norbornene as a main constituent unit, and is a resin obtained by hydrogenating a ring-opening polymer of a cycloolefin-based monomer, a cycloolefin- Chain olefin-based monomers having 2 to 10 carbon atoms such as styrene and / or styrene; and addition polymers with aromatic vinyl monomers such as styrene.

The crystalline polyolefin-based resin is a polymer mainly comprising a chain olefin-based monomer having 2 to 10 carbon atoms, and includes a homopolymer of a chain olefin-based monomer and a copolymer of two or more homopolymers using two or more chain olefin-based monomers do. Specific examples include a homopolymer of a polyethylene-based resin, a polypropylene-based resin, an ethylene-propylene copolymer, a 4-methyl-1-pentene or a copolymer of 4-methyl-1-pentene and ethylene or propylene .

The polyester-based resin includes not only aromatic polyesters such as polyethylene terephthalate-based resins and polyethylene naphthalate-based resins, but also aliphatic polyesters.

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 (main chain).

The acrylic resin is typically a polymer having methyl methacrylate as a main constituent unit and includes a homopolymer of methyl methacrylate as well as a copolymer of methyl methacrylate and other methacrylic ester and / or acrylic ester do.

The triacetylcellulose resin is an acetate ester of cellulose.

From these thermoplastic resins, a film may be formed on a film by a solvent casting method or a melt extrusion method to obtain an optical film to be used in the present invention. It is also possible to use an optical film to be used in the present invention, which is obtained by stretching a film uniaxially or biaxially after film formation. Prior to bonding to the polarizing film, the optical film may be subjected to an easy adhesion treatment such as saponification treatment, corona treatment, plasma treatment, primer treatment or anchor coating treatment. Various treatment layers such as a hard coat layer, an antireflection layer, or an antiglare layer may be formed on the surface of the optical film opposite to the bonding surface to the polarizing film.

The optical film preferably has a thickness of usually about 5 to 200 mu m. If the optical film is too thin, the handling property is insufficient, and there is a high possibility that the optical film is broken in the polarizing plate production line or causes the occurrence of wrinkles. On the other hand, if the thickness is excessively large, the obtained polarizing plate becomes thick and the weight becomes large, which may impair the merchantability. For these reasons, the more preferable thickness of the optical film is 10 탆 to 120 탆, and the more preferable thickness is 10 탆 to 85 탆.

[glue]

When bonding an optical film to a polarizing film, first, an adhesive is applied to the bonding surface of the optical film to the polarizing film. The thickness of the adhesive is set to a predetermined value in the range of 0.5 탆 to 5 탆. When the thickness is less than 0.5 탆, unevenness may occur in the bonding strength. On the other hand, if the thickness exceeds 5 m, not only the production cost increases but also the color of the polarizer may be influenced depending on the kind of the adhesive. If the thickness is relatively large within the above-mentioned range, for example, not less than 3.5 占 퐉, especially not less than 4 占 퐉, defects such as bubbles caused by the fluctuation of the thickness are hard to appear. On the other hand, , It is desirable to make it as thin as possible. For these reasons, the preferable thickness of the adhesive is in the range of 1 mu m to 4 mu m, and furthermore, 1.5 mu m to 3.5 mu m.

The adhesive may be of various types conventionally used in the production of a polarizing plate as long as it is supplied in a liquid-formable state, but from the viewpoint of weatherability and polymerizability, a cationic polymerizable compound such as an epoxy compound, , 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 Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-245925) desirable.

Examples of the epoxy compound include a hydrogenated epoxy compound obtained by nuclear hydrogen addition of an aromatic polyhydroxy compound as a raw material of an aromatic epoxy compound represented by diglycidyl ether of bisphenol A and glycidyl etherification thereof, An alicyclic epoxy compound having at least one epoxy group bonded to the ring, and an aliphatic epoxy compound represented by glycidyl ether of an aliphatic polyhydroxy compound.

In addition to the cationic polymerizable compound represented by the epoxy compound as the typical example, the active energy ray-curable adhesive may be a polymeric initiator, typically a cationic polymer or a Lewis acid generated by irradiation of an active energy ray, A photocationic polymerization initiator for initiating polymerization is added. Further, a thermal cationic polymerization initiator which initiates polymerization by heating, and various additives such as photosensitizer may be blended.

When an optical film is bonded to both surfaces of a polarizing film, the adhesive applied to each optical film may be the same or different, but from the viewpoint of productivity, it is preferable to use the same adhesive on both surfaces, desirable.

[Polarizing plate production method]

In the present invention, an optical film is bonded to a polarizing film made of the above-described polyvinyl alcohol-based resin through an adhesive to produce a polarizing plate. At this time, the following steps (A), (B), (C), and (D) are performed.

(A) Coating of Adhesive A coating process for applying an adhesive to the bonding surface of the optical film to the polarizing film using a coating machine having thickness control means,

(B) The thickness of the optical film is measured before the coating process by a radiation film thickness meter, the total thickness of the optical film and the adhesive applied after the coating process is measured, and the thickness of the applied adhesive In-line measurement step,

(C) a bonding step of applying a polarizing film onto the adhesive surface which has been applied in the coating step and has undergone the measuring step,

(D) when the ratio of the measured thickness X of the adhesive obtained in the measuring step to the absolute value of the difference between Y and the set thickness Y of the adhesive set within the range of 0.5 m to 5 m is equal to or larger than a predetermined value, And controlling the coating thickness control means.

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

1, the first optical film 2 is bonded to one side of the polarizing film 1 while the polarizing film 1 is continuously conveyed, and the second optical film 3 is bonded to the other side of the polarizing film 1, , And the polarizing plate 4 is produced and wound around the winding roll 30. As shown in this figure, an optical film is typically bonded to both surfaces of the polarizing film 1, but a mode in which the optical film is bonded to only one surface of the polarizing film 1 is also included in the present invention . The form of such a case can be understood by those skilled in the art to such an extent that it can be easily carried out by omitting the description of the other optical film from the following description.

The thickness of the first optical film 2 is first measured by the first film deposition apparatus 14 and then the adhesive is applied to the surface of the first optical film 2 bonded to the polarizing film 1 from the first coating machine 10 . Thereafter, the total thickness of the adhesive applied to the first optical film 2 is measured by the second film deposition apparatus 15, and the absolute value of the difference between the measured values by the two film deposition apparatuses 14 and 15 The thickness of the applied adhesive is determined from the value. Likewise, the thickness of the second optical film 3 is first measured by the third film deposition apparatus 16, and then the surface of the second optical film 3 bonded to the polarizing film 1 is irradiated with an adhesive from the second coating machine 12 . Thereafter, the total thickness of the second optical film 3 and the adhesive applied thereto is measured by the fourth radiation film thickness meter 17, and the absolute value of the difference between the measured values by the two radiation film thickness gauges 16, The thickness of the applied adhesive is determined from the value.

The first optical film 2 and the second optical film 3 after the thickness measurement before and after the application of the adhesive are laminated on both sides of the polarizing film 1 and the bonding nip rolls 20 and 21 And is pressed in the thickness direction. Next, the active energy rays from the active energy ray irradiating device 18 are irradiated to cure the adhesive. Thereafter, the obtained polarizing plate 4 is wound on the winding roll 30 via the nip rolls 22, 23 before winding.

The first coating machine 10 and the second coating machine 12 are configured to apply an adhesive to the first and second optical films 2 and 3 from the gravure rolls 11 and 13 provided in the first coating machine 10 and the second coating machine 12, respectively. A guide roll 24 for conveyance is appropriately provided on one surface of the polarizing film 1 or on the opposite surface of the first optical film 2 and the second optical film 3 opposite to the surface to which the adhesive is applied Respectively. As described above, when the optical film is bonded to only one side of the polarizing film 1, only one of the first optical film 2 and the second optical film 3 shown in Fig. 1 (for example, Only the first optical film 2] may be applied. In the figure, the straight arrows indicate the flow direction of the film, and the curved arrows indicate the rotation direction of the roll.

The polarizing film 1 is produced in a polarizing film production process (not shown) in the state of being produced in the state of being produced through a uniaxial stretching treatment, a dyeing treatment with a dichroic dye, and a boric acid crosslinking treatment after dyeing However, the polarizing film produced in the polarizing film manufacturing process may, of course, be once wound on a roll and then unwound from the feeding device again. On the other hand, the first optical film 2 and the second optical film 3 are each unrolled from a roll (not shown) by a feeder. Each film is transported at the same line speed, for example, at a line speed of about 10 m / min to 50 m / min, so that the flow directions become the same. The first optical film (2) and the second optical film (3) are released while applying a tensile force of about 50 N / m to 1000 N / m in the flow direction.

The coating process A described above is performed by the first coating machine 10 and the second coating machine 12 and the first and second radiation film coating systems 14 and 15, Described bonding process C is carried out by the bonding nip rolls 20 and 21 and the radiation film thickness meter 14, 15, and 15 is performed by the film thickness meter 16 and 17, 16 and 17 to the coating machines 10 and 12, the control step (D) described above is carried out. The gravure rolls 11 and 13 of the coating machines 10 and 12 are rolls having concave grooves and the concave grooves are filled with an adhesive in advance and the first and second optical films 2 and 3, And the adhesive is transferred onto the first and second optical films 2 and 3 by rotating the image. The supply amount of the adhesive on the first and second optical films 2 and 3 and the coating thickness can be controlled by adjusting the rotation speed of the first and second optical films 2 and 3, The coating thickness control means for controlling the coating thickness.

The relationship among these processes will be described based on the block diagram of Fig. First, at the setting (0), the setting thickness Y is previously set within the range of 0.5 탆 to 5 탆 with respect to the thickness of the adhesive applied in the above coating process (A). The thickness of the first and second optical films 2 and 3 is measured in advance by the first and third radiation film thickness gauges 14 and 16 as the first half of the measuring process B , The initial conditions of the coating thickness control means of the first and second coaters 10 and 12 are set, and the coating process (A) is started.

Next, as the second half of the measuring step (B), the total thickness of the optical film and the adhesive applied by the second and fourth radiation film followers 15 and 17 is measured, and the measured values of the first half step and the second half step The thickness of the applied adhesive is obtained from the absolute value of the difference between the values and output as the measurement thickness X. The first and second optical films 2 and 3 to which the adhesive is applied are bonded to both surfaces of the polarizing film 1 on the respective adhesive application surfaces in the bonding step C regardless of the measurement thickness X .

On the other hand, in the control step (D), the measured thickness X is compared with the set thickness Y described above. When the absolute value of the difference between the measured thickness X and the set thickness Y is equal to or larger than a predetermined value, for example, 5% or more, with respect to the set thickness Y, the coating thickness control means 10 of the first and second coaters 10, The absolute value of the difference between the measured thickness X and the set thickness Y is preferably controlled to be less than 5% with respect to the set thickness Y so that the difference between the measured thickness X and the set thickness Y becomes smaller as an absolute value. Here, when 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, it means that it satisfies the following formula (I), and in FIG. 2, , It is indicated that the control means determines whether or not to change the condition.

Hereinafter, the coating process (A), the measuring process (B), the bonding process (C) and the control process (D) constituting the method of the present invention will be described in detail. When the active energy ray-curable adhesive is used, since the curing step (E) is carried out after each of the above steps, this step will also be described.

(A) Coating process

In the coating process (A), the first and second optical films (2, 3) passed through the first step (the step of measuring the thickness of the optical film itself) of the measuring step (B) The adhesive is applied. The coating machine used here is not particularly limited as long as it has a means for controlling the coating thickness, but a method using the gravure rolls 11 and 13 described with reference to Fig. 1 is representative.

Examples of the applicator using a gravure roll include a direct gravure coater, a chamber doctor coater, an offset gravure coater, a kiss coater using a gravure roll, and a reverse roll coater composed of a plurality of rolls. In addition, a die coater and a liquid reservoir for supplying a direct adhesive by applying a comma coater, a slot die or the like having a cylindrical blade and applying an adhesive to the application portion and scraping the same with a blade are made, And a knife coater for scraping and applying the coating agent. Of these, a direct gravure coater, a chamber doctor coater, an offset gravure coater and the like are preferable among the cooperators using a gravure roll in consideration of the thin film coating and the degree of freedom of the pass line. In addition to the gravure roll, Is preferably used. A chamber doctor coater is more preferable because it is easy to cope with widening of a polarizing plate and it is difficult to release odor of an adhesive supplied in liquid.

Here, the chamber doctor cotter is a system in which a gravure roll is brought into contact with a chamber doctor which absorbs a liquid coating material (adhesive), and the coating material (adhesive) in the chamber doctor is transferred to the concave groove of the gravure roll, 1 and the second optical film (2, 3). The compact design is also referred to as a microchamber doctor coater.

When an adhesive is applied using a gravure roll, the thickness of the adhesive layer can be adjusted by the speed ratio of the gravure roll to the line speed. The line speed of the first and second optical films 2 and 3 is set to 10 m / min to 50 m / min, and the gravure roll is moved in the direction opposite to the conveying direction of the first and second optical films 2 and 3 , And the rotational speed of the gravure roll is set to 10 m / min to 500 m / min, so that the coating thickness of the adhesive can be adjusted to 0.5 탆 to 5 탆. Since the coating thickness at this time is also influenced by the porosity of the surface of the gravure roll, it is preferable to select a gravure roll having a surface porosity suitable for the preset thickness Y in advance. On the other hand, a method of rotating the gravure roll in the opposite direction with respect to the transport direction of the first and second optical films 2 and 3 is also called reverse gravure.

(B) Measurement process

In the first half of the measuring step (B) carried out before the coating step (A), the thickness of the optical film itself is measured in the second half of the measuring step (B) performed after the coating step (A) The total thickness is measured by a radiation film thickness gauge. The thickness of the applied adhesive is obtained from the absolute value of the difference between the measured value of the first half process and the measured value of the second half process. As shown in FIG. 1, the first to fourth radiation film gauges 14, 15, 16 and 17 are respectively connected to the first to fourth radiation sources 14a, 15a, 16a and 17a, (14b, 15b, 16b, 17b), which are arranged to face each other through the optical film to be measured.

The radiation film thickness gauges 14, 15, 16 and 17 irradiate the optical film with the radiation sources 14a, 15a, 16a and 17a and transmit the radiation transmitted through the optical film to the detectors 14b, 15b and 16b , 17b. The irradiated radiation attenuates when passing through the optical film. The weighed amounts of the optical films are obtained from the attenuation amounts of the radiation film thickness gauges 14, 15, 16, and 17, and converted into thickness. The amount of attenuation of radiation can be influenced by the density of the optical film, but becomes larger as the film thickness of the optical film becomes larger.

In the first half of the measuring process (B), the film thickness value measured by transmitting the radiation through the optical film before the adhesive is applied and the amount of attenuation is outputted. In the latter half of the measuring process (B) The thickness of the adhesive is obtained as the absolute value of the difference between the film thickness values of both the adhesive layer and the optical film by calculating the attenuation amount by transmitting the radiation through the optical film. According to the film thickness measuring method using such a radiation film thickness meter, the thickness of the adhesive can be obtained with high accuracy in in-line.

The film thickness measuring method using a radiation film thickness meter is advantageous in that the thickness of the adhesive can be obtained even when there is no difference in the characteristic absorption of the infrared absorption spectrum irrespective of the refractive index difference between the optical film and the adhesive I have. Further, according to the film thickness measuring method using the radiation film thickness meter, unlike the film thickness measuring method using the optical interferometer film thickness meter, the influence of the optical properties of the optical film such as the transparency of the optical film, the degree of orientation, It is possible to measure the film thickness which is difficult and stable.

When the amount of attenuation of radiation is converted into the thickness of the optical film or the optical film having the adhesive layer attached thereto, the relationship between them is measured in advance and a calibration curve is prepared. Since the amount of attenuation of radiation is usually obtained as a current value or a voltage value by a detector, in this case, a current value or a voltage value is measured for an optical film of the same material having a different thickness, Alternatively, a calibration curve of the voltage value is created. The optical film used for preparing the calibration curve includes an optical film of the same material thicker than the optical film actually used for producing the polarizing plate and an optical film of the same material thinner than the optical film actually used for producing the polarizing plate , And thickness measurement with higher precision is possible. A calibration curve is prepared in the same manner for the optical film having the adhesive layer.

In order to further improve the measurement accuracy of the thickness of the adhesive, the radiation attenuation amount for the optical film of the same material having different thicknesses and the radiation attenuation amount for the optical film to which the adhesive layer of the same material having different thicknesses are attached are respectively measured, A calibration curve of a radiation attenuation amount with respect to a change in the thickness of the adhesive obtained as the absolute value of the difference between the thickness of the optical film having the layer and the thickness of the optical film may be prepared.

As the radiation film deposition system, a film deposition system using radiation such as X-ray,? -Ray or? -Ray can be used. Considering the thickness of the optical film to be measured and the optical film to which the adhesive layer is attached (the thickness of the optical film is usually 5 to 200 占 퐉 and the thickness of the adhesive is 0.5 to 5 占 퐉 as described above) Or a? -Ray film is preferably used.

[0003] A radiation film deposition system (X-ray film deposition system) using an X-ray usually has an X-ray source tube using a titanium target or a tungsten target, and generates X-rays by applying a voltage thereto. ray tube (β-ray film removers) using β-rays usually generate β-rays by using Pm 147, Krypton 85, or Sr 90 as a source. From the viewpoint of measuring the thickness of the adhesive more precisely, it is preferable to use a? Ray film thickness meter using Pm 147 as a source in the? Ray film thickness meter.

The X-ray film thickness tends to be more dependent on the type (material) of the optical film when the radiation is transmitted through the optical film than the? -Film film thickness. Therefore, when the thickness of the optical film itself is determined from the calibration curve, it is necessary to prepare a calibration curve for each type of optical film or to create a calibration curve for each of different types of optical films. Higher than successors. Therefore, when the types of the first optical film bonded to one surface of the polarizing film and the second optical film bonded to the other surface are different, or when different types of polarizing plates having different types of optical films are used in the same production line In the case of manufacturing, for example, it is preferable to use a? Ray film thickness meter in order to obtain a higher accuracy of thickness measurement of the adhesive.

From the viewpoint of measuring the thickness of the adhesive more precisely, it is preferable that the measurement spot (the area of the irradiation area on the optical film) by the radiation film thickness meter is about 10 mm to 30 mm in diameter. In addition, the in-line measurement precision of the radiation film thickness meter is preferably ± 0.15 μm or less, more preferably ± 0.1 μm or less. In order to achieve such a measurement accuracy, it is preferable to use a radiation having a high energy intensity as the radiation source of the radiation film deposition system, and it is more preferable to use a radiation source that does not reach a half-life, because more precise measurement becomes possible.

From the viewpoint of stability of the thickness measurement value of the adhesive, it is preferable that the radiation film thickness meter is capable of performing measurement once at a measurement interval of 0.005 second to 1 second, particularly 0.01 second to 0.5 second, It is more preferable that the moving average can be obtained and output with respect to the measurement value of 50000 points. For example, if a moving average is obtained for measurement values exceeding 50000 points and the measurement interval exceeds 0.5 seconds, the deviation between the measured value and the actual thickness may increase. For the same reason, it is more preferable to use a film thickness meter that performs one measurement at a measurement interval of 0.005 second to 1 second and outputs a moving average for the measured values of 100 points to 50,000 points successive from the obtained data .

In order to improve the accuracy of measurement of the thickness of the adhesive, it is preferable that the installation position of the radiation film sub-system for measuring the thickness of the optical film itself before the coating process (A) and the irradiation position of the radiation film measuring the total thickness of the optical film and the adhesive after the coating process It is preferable that the installation position of the film deposition system coincides with the width direction of the optical film. For the same reason, it is preferable to match the thickness measurement points with respect to the longitudinal direction (transport direction) of the optical film. For the same reason, it is preferable that the interval between two radial film thickness gauges is set within 10 m along the longitudinal direction of the optical film, more preferably 1 m to 5 m.

(C) Bonding process

After the above-described coating step (A) and the measuring step (B), a bonding step (C) for superimposing and pressing the polarizing film (1) onto the respective adhesive application surfaces of the first and second optical films Is done. A known means can be used to pressurize the process. However, from the viewpoint of pressurization while continuously conveying, a method of sandwiching by the pair of nip rolls 20, 21 is preferable as shown in Fig. In this case, it is preferable that the timing of superimposing the first and second optical films 2 and 3 on the polarizing film 1 and the timing of pressing by the pair of nip rolls 20 and 21 are the same, , It is preferable that the difference between the timings is short. The combination of the pair of nip rolls 20 and 21 may be any of metal roll / metal roll, metal roll / rubber roll, rubber roll / rubber roll and the like. The pressure at the time of pressurization is preferably set to 150 N / cm to 500 N / cm at a linear pressure when sandwiched by the pair of nip rolls 20 and 21.

(D) Control process

In the present invention, 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 measuring step (B) described above. That is, the thickness of the adhesive applied in the coating process (A) varies slightly depending on the temperature of the adhesive, the ambient environmental temperature, the surface tension of the first and second optical films (2, 3) And there is a case where deviation from the desired coating thickness (setting thickness Y) is accompanied. In order to correct such coating thickness deviation, the coating thickness control means of the coating machine is controlled based on the coating thickness (measurement thickness X) measured by the radiation film thickness meter in the measuring step (B).

For example, when the coating machine is a die coater, when the measurement thickness X is larger than the set thickness Y, the ability to feed the wafer from the pump or the like is lowered. Conversely, when the measurement thickness X is smaller than the set thickness Y, , The coating thickness can be controlled. When the coating doctor is a chamber doctor coater using a gravure roll, when the measurement thickness X is larger than the preset thickness Y, the number of revolutions of the reverse gravure is increased to increase the rotation speed, thereby reducing the transfer amount of the adhesive, Is smaller than the set thickness Y, by reducing the number of rotations of the reverse gravure and lowering the rotation main speed, the transfer amount of the adhesive can be increased to control the coating thickness.

The degree of film thickness control is arbitrarily set experimentally depending on the environmental factors, the viscosity of the adhesive, the surface shape of the optical film, and the like. The actual control may be performed using a computer or manually.

(E) Curing process

After the first and second optical films 2 and 3 are bonded to the polarizing film 1 as described above, if the adhesive is of the active energy ray curing type, the curing step of curing the adhesive by irradiation of active energy rays E) to produce a polarizing plate 4. In the example shown in Fig. 1, the curing step (E) is a step of curing the laminated body in which the first and second optical films 2 and 3 are bonded to the polarizing film 1, Is performed by irradiating an active energy ray. In this step, the energy required for curing the active energy ray-curable adhesive is irradiated over the first optical film 2.

Specific examples of the active energy ray include electron beams and ultraviolet rays, which are selected according to the curing reaction mechanism of the adhesive. The size and weight of the electron beam irradiating apparatus are increased due to the necessity of shielding the generated electron beam so that it does not leak to the outside. On the other hand, since the ultraviolet irradiation device has a relatively compact structure, curing by ultraviolet irradiation is preferably used.

In the example shown in Fig. 1, the active energy rays are irradiated to the laminated body in which the polarizing film 1 and the first and second optical films 2 and 3 are bonded to each other through the adhesive, In the state in which tension is applied to the laminate between the nip rolls 20, 21 before and after the nip rolls 22, 23 before winding. The present invention is not limited to this. For example, as described in the aforementioned Patent Document 2 (Japanese Patent Laid-Open Publication No. 2009-134190), convex curved surfaces formed in an arc shape along the conveying direction, typically in a state of being supported on the outer peripheral surface of the roll , It is also preferable to irradiate an active energy ray. Particularly, when heat is generated by irradiation of an active energy ray and there is a possibility of adversely affecting the product, it is preferable to irradiate the active energy ray with the laminated body being supported on the outer peripheral surface of the roll as in the latter case, , It is preferable that the roll supporting the laminate is capable of adjusting the temperature within a range of about 10 캜 to 60 캜. The active energy ray irradiating device may be provided at only one irradiation site. However, it is also effective to increase the accumulated light quantity effectively by providing two or more active energy ray irradiation devices along the flow direction of the laminate and irradiating them from a plurality of light sources.

In the case of curing the adhesive by irradiating ultraviolet rays, the ultraviolet light source to be used is not particularly limited. However, the ultraviolet light source to be used is not particularly limited, but may be a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, A microwave excitation mercury lamp, a metal halide lamp, and the like. When an adhesive containing an epoxy compound as an active energy ray-curable component is used, a high-pressure mercury lamp or a metal halide lamp having a lot of light of 400 nm or less is preferably used as an ultraviolet light source, considering the absorption wavelength indicated by a general polymerization initiator .

The line speed of the laminate when irradiated with ultraviolet rays to an adhesive containing an epoxy compound as a curing component is not particularly limited, but generally, the line speed in the coating process (A) or the bonding process (C) . Further, while the tensile force of 100 N / m to 1000 N / m is applied in the longitudinal direction (conveyance direction) of the laminate, the amount of irradiation of the wavelength region effective for activating the polymerization initiator is controlled by the accumulated amount of light (total energy irradiated on the laminate) To 100 mJ / cm < 2 > to 1,500 mJ / cm < 2 > If the amount of ultraviolet light to be irradiated on the adhesive is too small, the curing reaction of the active energy ray-curable adhesive is insufficient and the adhesive strength is not sufficiently developed. On the other hand, if the integrated amount of light is too large, There is a possibility of causing deterioration of the yellowing of the active energy ray-curable adhesive or the polarizing film due to the heat generated when polymerization occurs.

Further, in order to achieve the total amount of light necessary for one ultraviolet irradiation, the film may be heated to a high temperature exceeding 150 캜 by heat generation, and in this case, there is a possibility of causing deterioration of the polarizing film. In order to avoid such a situation, it is effective to provide a plurality of ultraviolet irradiators along the film transport direction as described above, and irradiate the ultraviolet irradiators in a plurality of divided ways. As a standard, it is preferable that the irradiation amount from one ultraviolet ray irradiating device is 600 mJ / cm 2 or less in total light amount and finally the total light amount of 100 mJ / cm 2 to 1500 mJ / cm 2 is obtained .

The polarizing plate thus produced is controlled in the thickness of the adhesive within a predetermined range and the fluctuation of the adhesive strength between the films constituting the polarizing plate is small and the bubble defects and the like in the adhesive layer are also small and the quality stability It is also excellent.

Example

EXAMPLES The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. On the other hand, the experiments shown below were carried out in order to confirm the effect of the present invention. For example, the thickness of the adhesive applied on the side opposite to the adhesive whose thickness is measured with a polarizing film interposed therebetween, It is to be noted that it is set to be thicker than the optimum value employed in the actual operation so as not to be performed.

3 is a side view schematically showing a manufacturing apparatus used in the following examples and comparative examples. The manufacturing apparatus shown in Fig. 3 is different from the above-described Fig. 1 only in the following two points, and the parts other than the upper part are denoted by the same reference numerals as those in Fig. 1, Please refer to the explanation.

[Differences in Fig. 3 for Fig. 1]

(1) When an active energy ray (ultraviolet ray) is irradiated to a laminate after bonding the first optical film 2 and the second optical film 3 to both surfaces of the polarizing film 1, (Ultraviolet) irradiating device 18 disposed on the opposite side of the winding roll 26 with the laminated body sandwiched between the optical film 3 side and the outer peripheral surface of the conditioning winding roll 26 , The point where the ultraviolet light is irradiated to the first optical film (2) side of the laminate, and

(2) Since there is only one set (two) of radial film thickness gauges, the thickness of the adhesive applied to the first optical film 2 is measured by the first and second film thickness gauges 14 and 15, The thickness of the adhesive applied to the second optical film (3) is not measured.

As the first and second radiation film guiding systems 14 and 15, a β ray film deposition apparatus "SB-1100" (β ray source: Pm-147), which is an authentication apparatus having a mark manufactured by Nano Gray Co., was used. This? -Ray film sub-system measures the film thickness from the attenuation amount when the radiation is transmitted through the optical film, and the measurement accuracy of the film thickness in the in-line is about ± 0.1 μm. Then, the film thickness of the object to be measured is measured at every predetermined measurement interval, and similarly, the individual film thickness values measured at the above-mentioned measurement times are subjected to moving average, and the average film thickness during that time is outputted. Among the measurement values of the preset number of times, the data determined to be an abnormal value are automatically excluded to output the average film thickness.

[Example 1]

(0) Material used in the experiment

In this example, as the first optical film 2, a biaxial oriented retardation film "KC4FR-1" (manufactured by Konica Minolta Opto, Inc.) having a thickness of 40 μm and a width of 1330 mm and comprising triacetyl cellulose supplied from a roll And a triacetyl cellulose film "KC8UX2MW" (manufactured by Konica Minolta Opto, Inc.), which had a thickness of 80 μm and a width of 1330 mm and which was also supplied from a roll, was used as the second optical film 3 , Refractive index 1.48] was used. The adhesive used for bonding the polarizing film 1 and the first optical film 2 and the adhesive used for bonding the polarizing film 1 and the second optical film 3 both contain an epoxy compound and a photopolymerization initiator , And an epoxy-based light-curing adhesive substantially free of a solvent.

(A) Coating process

The polarizing film (1) having a thickness of 25 占 퐉 and the retardation film as the first optical film (2) and the triacetyl cellulose film as the second optical film (3), in which iodine was adsorbed and oriented on polyvinyl alcohol, m / min. (1) provided with a gravure roll (11) is provided on the surface of the phase difference film (2) which has undergone the first step (measurement step of the optical film itself) of the measurement step (B) The epoxy-based photo-curable adhesive described above was applied using the coating machine 10 ("Micro Chamber Doctor" manufactured by Fuji Kai Co., Ltd.). The surface of the triacetyl cellulose film 3 bonded to the polarizing film 1 was coated with a second coating machine 12 having a gravure roll 13 (also referred to as " micro chamber doctor "Quot;, the aforementioned epoxy-based photo-curable adhesive was applied.

The gravure rolls 11 and 13 provided on the first and second coaters 10 and 12 were rotated in the opposite direction to the transport direction of the film. In the second coating machine 12 on the side of the triacetyl cellulose film 3, the rotational speed of the gravure roll 13 provided thereon was set at 15 m / min, and an adhesive agent . This is because the thickness of the adhesive applied by the second coating machine 12 is not measured, and therefore the film thickness is not controlled, so that the adhesive is applied so as to have a thickness substantially free from defects. On the other hand, on the side of the retardation film 2, the rotating main velocity of the gravure roll 11 provided in the first coater 10 was set to an initial setting of 21 m / min, and the adhesive was applied to a thickness of about 2.5 탆 .

(B) Measurement process

A first radiation film deposition system 14 is disposed on the upstream side of the first coating machine 10 and a second radiation film deposition system 15 is disposed on the downstream side of the first coating machine 10. The spacing along the film flow direction of the coater was 1.67 m. The first radiation film by the thickness meter 14, measuring the thickness of the retardation film 2 in the 0.2-second intervals, and {(2 ²⁾ ^2} ² = 2 ⁶ = 256 consecutive measurement values (about 51.2 seconds (The first half process).

The total thickness of the retardation film 2 and the adhesive is also measured at an interval of 0.2 second from the coated surface side of the adhesive of the retardation film 2 by the second film deposition apparatus 15 disposed after the above coating process , And set so that the moving average value is sequentially output every 256 measurement values (about 51.2 seconds) (1 in the second half of the process). Therefore, after about 51.2 seconds elapsing from the start of measurement to 256 times of measurement, a moving average value of the thickness of the retardation film 2 is outputted from the first radiation film thickness meter 14 every 0.2 seconds, A moving average value of the total thickness of the retardation film 2 and the adhesive is output from the film thickness meter 15, and values are extracted every 1 sec., And the values of the electrons at that time (measured value of the thickness of the retardation film 2 = A) and the latter value (referred to as the measured value of the total thickness of the retardation film 2 and the adhesive = B) were recorded successively as the measurement thickness X (second half of the second step) . In addition, a control step (D) to be described later is provided to perform the operation for about 150 minutes while controlling the measurement thickness X, and the obtained measurement thickness X (the number of data is about 9000 The results are shown in Table 1. The results are shown in Table 1. < tb > < TABLE >

(C) Bonding process

The adhesive application side of each of the retardation film 2 and the triacetyl cellulose film 3 to which the adhesive was applied was superimposed on the polarizing film 1 and sandwiched by the bonding nip rolls 20 and 21 at a linear pressure of 240 N / . The laminate of the retardation film 2, the polarizing film 1 and the triacetyl cellulose film 3 after passing through the nip rolls 20 and 21 has a triacetylcellulose film A tension of 600 N was applied in the longitudinal direction so as to be in close contact with the outer circumferential surface of the used winding roll 26 and ultraviolet rays from the ultraviolet irradiating device 18 were applied to the retardation film 2 side at a line speed of 15 m / And returned. The ultraviolet ray irradiator 18 was manufactured by GS Yuasa Co., Ltd. and irradiated ultraviolet rays from a second lamp "EHAN1700NAL high-pressure mercury lamp" which is an ultraviolet lamp included therein. The total amount of ultraviolet light was 330 mJ / cm < 2 > Thus, the adhesive layer is cured to prepare a polarizing plate 4 having a polarizing film 1 and a triacetyl cellulose film 3 bonded to one side of the retardation film 2 and the other side of the polarizing film 1, .

(D) Control process

In the control process, when the measurement thickness X obtained in the measurement step (B) is more than 5% or more than the set thickness Y = 2.5 占 퐉, that is, when | XY |? 0.125 占 퐉, The rotational speed of the gravure roll 11 provided on the base 10 was increased / decreased by 0.5 m / minute, and the coating thickness of the adhesive was controlled.

[Comparative Example 1]

The rotation speed of the gravure roll 11 provided in the first coating machine 10 even if the measurement thickness X obtained in the measuring step B changes even if the control step (D) is not provided in the first embodiment, The laminate was prepared, and then the same ultraviolet irradiation was carried out to prepare a polarizing plate. Table 1 shows the average values and standard deviations of the measured thickness X when operating for about 150 minutes.

[Comparative Example 2]

The spectral transmittance of the first radiation film subgraph 15 was measured in the same manner as in Example 1 except that the first radiation film subgraph 14 was not provided and the spectral wavelength region was 230 nm to 800 nm The same procedure as in Example 1 was carried out except that an attempt was made to directly measure the coating thickness of the adhesive by the reflection spectroscopic film subset in the measurement step (B), with the reflection spectroscopic film sub-system "FE-2900CCD" Respectively. However, since the refractive index (1.48) of the retardation film made of triacetyl cellulose used as the first optical film (2) was close to the refractive index (1.49) of the adhesive, the thickness of the adhesive could not be measured, Could not.

[Example 2]

Except that a biaxially stretched polyethylene terephthalate film having a thickness of 38 占 퐉 and a width of 1330 mm (available from Mitsubishi Jushi Co., Ltd.) was used instead of the biaxially oriented retardation film "KC4FR-1" made of triacetyl cellulose in Example 1 Retardation value: 1000 nm) was used as the first optical film (2), a polarizing plate was produced in the same manner as in Example 1. Table 1 shows the average values and standard deviations of the measured thickness X when operating for about 150 minutes.

[Comparative Example 3]

The rotation speed of the gravure roll 11 provided in the first coater 10 is not changed even if the control process (D) is not provided, that is, the measurement thickness X obtained in the measuring process (B) The laminate was prepared, and then the same ultraviolet irradiation was carried out to prepare a polarizing plate. Table 1 shows the average values and standard deviations of the measured thickness X when operating for about 150 minutes.

[Defect evaluation test of polarizer]

In the examples and comparative examples described above, a 1250 mm wide portion at the center excluding the 40 mm wide portions at both ends of the polarizing plate obtained with a width of 1330 mm was used as the effective width, and a plane extending along the length of 3300 mm (1.25 m × 3.3 m≈4 m 2) was marked with a naked eye as a bright spot. The mark was observed with a magnifying glass having an enlargement magnification of 100 times to confirm whether or not it was air bubbles , And the size of the bubbles was obtained by the following method. That is, if the observed bubble is pseudo-elliptical (including a circle), the longest diameter is the size of the bubble, and if the bubble is linear, the length of the bubble is the size of the bubble. When the number of bubbles having a size of 100 탆 or more is counted and the number is less than 0.3 per 1 m 2, that is, when the number of bubbles is 0 or 1 in an area of 4 ㎡ observed is "OK" (NG), and the results are summarized in Table 1 together with the main parameters.

In the table, " TAC " in the egg yolk of the optical film means triacetyl cellulose and " PET " means polyethylene terephthalate. On the other hand, the film was cut into a size of 40 mm x 40 mm and observed with a microscope so that the bubbles having a size of 100 mu m or more observed with a magnifying glass were all inserted between the polarizing film 1 and the first optical film 2 In the adhesive layer interposed therebetween.

As shown in Table 1, in Comparative Examples 1 and 3 in which the control step (D) was not provided, the measurement thickness of the adhesive was varied, and thus, the bubble defect was observed in the obtained polarizing plate. In Examples 1 and 2 in which the coating thickness was changed when the measured thickness X of the adhesive deviated by 5% or more from the preset thickness Y, the measured thickness was suppressed to a variation within about 5% And the bubble defect is small. On the other hand, as in Comparative Example 2, when a reflective spectroscopic measuring device having a comparatively wide range of spectral wavelength range of 800 nm or less is used, when the difference between the refractive index of the adhesive and the refractive index of the optical film is small, I can not.

1: polarizing film 2: first optical film
3: Second optical film 4: Polarizing plate
10: first coating machine 11: gravure roll
12: Second coating machine 13: Gravure roll
14: first radiation film deposition system 14a: first radiation source
14b: first detector 15: second radiation film deposition system
15a: second radiation source 15b: second detector
16: Third Radiation Film Subtotal 16a: Third Radiation Source
16b: third detector 17: fourth radiation film deposition system
17a: fourth radiation source 17b: fourth detector
18: active energy ray (ultraviolet) irradiation device 20, 21: nip for bonding
22, 23: Nip roll before winding 24: Guide roll
26: used winding roll 30: winding roll

Claims

As 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 through an adhesive,
(A) a coating step of applying the adhesive to the bonding surface of the optical film to the polarizing film using a coating machine having coating thickness control means for the adhesive,
(B) measuring a thickness of the optical film before the coating process by a radiation film thickness meter, measuring a total thickness of the adhesive applied to the optical film after the coating process, A measurement step of obtaining the thickness of the applied adhesive in in-line,
(C) a bonding step of covering the polarizing film on the adhesive surface which has been applied in the coating step and has been subjected to the measuring step, and
(D) when the ratio of the measured thickness X of the adhesive obtained in the measuring step to the absolute value of the difference between Y and the set thickness Y of the adhesive set within the range of 0.5 m to 5 m is equal to or larger than a predetermined value, A control step of controlling the coating thickness control means
And a polarizing plate.

The method according to claim 1, wherein in the control step (D), when the ratio of the measured thickness X of the adhesive obtained in the measuring step to the absolute value of the difference between Y and the set thickness Y of the adhesive is 5% And controlling the coating thickness control means.

The method of producing a polarizing plate according to claim 1, wherein the adhesive is a liquid active energy ray-curable adhesive.

The method of manufacturing a polarizing plate according to claim 3, further comprising a curing step (E) of curing the adhesive by irradiating an active energy ray after the bonding step (C).