JP2012215781A - Method for manufacturing polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of manufacturing a polarizing plate which has high durability and hardly causes discoloration of a polarizing film even under a severe condition of high temperature and high humidity when an optical film is adhered to the polarizing film via an adhesive.SOLUTION: There is provided a method for manufacturing a polarizing plate 4 by adhering an optical film 2 to a polarizing film 1 via an ultraviolet curing type adhesive containing a polymerization initiator, the method comprising each of the following steps (A) to (E): (A) a step of applying an adhesive to the optical film 2; (B) a step of overlapping and pressing the polarizing film 1 to the surface of the applied adhesive; (C) a step of irradiating ultraviolet ray from an ultraviolet irradiation device 16 to cure the adhesive; (D) a step of measuring the luminance of an ultraviolet ray irradiated by using an illuminometer 17 as a polychromator to measure an integrated value of an ultraviolet illuminance in a predetermined absorption wavelength region including an absorption peak wavelength of the polymerization initiator; and (E) a step of controlling the output of ultraviolet irradiation device 16 when the measured luminance integrated value X is different from the set luminance integrated value Y by 5% or more.

Description

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

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

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

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

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

JP 2004-245925 A JP 2009-134190 A

  In the method of manufacturing a polarizing plate by irradiating UV rays to cure UV curable adhesives, the UV illuminance gradually decreases even when the same power is applied when the lamp of the UV irradiation device deteriorates over long periods of use. In this case, there is a concern that the curing of the adhesive becomes insufficient and the performance as a polarizing plate is insufficient. Also, in the case of long-term use, the filter and reflector attached to the lamp, the ultraviolet irradiation device, the glass placed on the front surface, etc. may become dirty due to the installation environment of the ultraviolet irradiation device or structural problems of the device. In this case, the transmittance of light with a wavelength of 400 nm or less, for example, of the irradiated ultraviolet light is reduced, causing a decrease in illuminance, and the adhesive may be insufficiently cured. If the curing of the adhesive is insufficient, troubles such as insufficient adhesive strength may occur, and the polarizing film may cause decolorization in the durability test, which may adversely affect the performance as a polarizing plate. There has been a demand for a method for producing a polarizing plate in which ultraviolet illuminance is appropriately controlled.

  The illuminance of the irradiated ultraviolet rays is generally measured using an ultraviolet sensor device such as GaN or AlGaN called a power monitor. However, the power monitor has the following features: 1) The detection wavelength of the UV sensor device is limited to a specific wavelength range, and the measurement sensitivity (sensitivity of light absorption for each wavelength) differs for each wavelength. The measurement accuracy of illuminance is relatively low because the illuminance of ultraviolet light cannot be measured directly, and the reflected light of the irradiated ultraviolet light must be measured to measure the illuminance indirectly. Has the problem of low. Because of these problems, the power monitor is applied to the production of a polarizing plate using an ultraviolet curable adhesive, and the activity of the polymerization initiator contained in the ultraviolet curable adhesive greatly affects the degree of cure of the adhesive. It has been difficult to accurately detect a decrease in illuminance in the wavelength region necessary for conversion. Therefore, it has been desired to develop a technique for manufacturing a polarizing plate that can accurately detect such a decrease in illuminance in a specific wavelength region and maintains the necessary illuminance.

  Therefore, an object of the present invention is a method for producing a polarizing plate by laminating an optical film on a polarizing film via an ultraviolet curable adhesive and curing the adhesive by ultraviolet irradiation. By accurately detecting the illuminance in the wavelength region necessary for the activation of the polymerization initiator and appropriately controlling it, it is highly durable polarized light that does not easily cause decolorization of the polarizing film even under severe conditions of high temperature and humidity It is to provide a method capable of manufacturing a plate.

  The present invention is a method for producing a polarizing plate by bonding an optical film made of a thermoplastic resin to a polarizing film made of a polyvinyl alcohol resin through an ultraviolet curable adhesive containing a polymerization initiator, The manufacturing method of a polarizing plate provided with each process of (A), (B), (C), (D) and (E).

(A) A coating process in which the ultraviolet curable adhesive is applied to the bonding surface of the optical film to the polarizing film,
(B) A laminating process in which a polarizing film is stacked on the UV curable adhesive surface applied in the coating process and pressed.
(C) A curing step of curing the ultraviolet curable adhesive by irradiating the ultraviolet light from the ultraviolet irradiation device to the laminate in which the optical film is bonded to the polarizing film via the ultraviolet curable adhesive,
(D) Using a polychromator, the illuminance of ultraviolet rays irradiated in the curing step is measured, and based on this, a predetermined absorption wavelength range including the absorption peak wavelength of the polymerization initiator, for example, −40 nm of the absorption peak wavelength. A measurement step of measuring an integral value of ultraviolet illuminance within a wavelength range of ~ 40 nm, and (E) a measured illuminance integral value X obtained in the measurement step with respect to a set illuminance integral value (set illuminance integral value) Y and the A control step of controlling the output of the ultraviolet irradiation device when the ratio of the absolute value of the difference from Y is equal to or higher than a predetermined value, for example, 5% or higher.

  According to the present invention, when a polarizing plate is produced by bonding an optical film to a polarizing film via an ultraviolet curable adhesive and curing the adhesive by ultraviolet irradiation, an ultraviolet curable adhesive is used using a polychromator. Accurately measure the illuminance integral value in the predetermined absorption wavelength range including the absorption peak wavelength of the polymerization initiator contained in the agent, and based on the result, output the UV irradiation device so that the adhesive will not be cured sufficiently Since it is controlled, it is possible to provide a highly durable polarizing plate that has good adhesive strength and is resistant to decoloration of the polarizing film even under severe conditions of high temperature and humidity.

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

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

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

[Optical film]
An optical film made of a thermoplastic resin is bonded to the polarizing film to produce a polarizing plate. The optical film preferably has a refractive index in the range of 1.4 to 1.7 as measured by the D line at a temperature of 20 ° C. The refractive index of the optical film is measured according to JIS K 0062: 1992 “Method for measuring refractive index of chemical product”. If the optical film has a refractive index in this range, it will have excellent display characteristics when the produced polarizing plate is incorporated in a liquid crystal panel. For the same reason, the preferable refractive index of the optical film is in the range of 1.45 to 1.67. This optical film has a haze value in the range of about 0.001 to 3% to improve the contrast of the obtained polarizing plate. This is preferable because it is less likely to cause defects. The haze value is a value defined by (diffuse transmittance / total light transmittance) × 100 (%), and is measured in accordance with JIS K 7136: 2000 “How to determine haze of plastic-transparent material”. The

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

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

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

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

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

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

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

[UV curable adhesive]
In pasting the optical film on the polarizing film as described above, an ultraviolet curable adhesive is first applied to the surface of the optical film to be bonded to the polarizing film. The thickness of the adhesive is usually in the range of 0.5 to 5 μm. If the thickness is less than 0.5 μm, uneven adhesion strength may occur. On the other hand, when the thickness exceeds 5 μm, not only the manufacturing cost increases, but also the hue of the polarizing plate may be affected depending on the kind of the adhesive. If the thickness is relatively thick within this range, for example, 3.5 μm or more, especially 4 μm or more, even if the thickness varies somewhat, defects such as bubbles are less likely to appear. Since increasing the thickness may lead to an increase in cost, it is desirable to reduce the thickness as much as possible. For these reasons, the preferred thickness of the ultraviolet curable adhesive is in the range of 1 to 4 μm, and further 1.5 to 3.5 μm.

  As long as the UV curable adhesive is supplied in a liquid coatable state, it can be any of those conventionally used in the production of polarizing plates, but from the viewpoint of weather resistance, polymerizability, etc. A cationically polymerizable compound, for example, an epoxy compound, more specifically, an epoxy compound having no aromatic ring in the molecule, as described in Patent Document 1 (Japanese Patent Laid-Open No. 2004-245925), What is contained as one of the ultraviolet curable components is preferable. Such an epoxy compound is, for example, a hydrogenated epoxy obtained by nuclear hydrogenation of an aromatic polyhydroxy compound, which is a raw material of an aromatic epoxy compound represented by diglycidyl ether of bisphenol A, and converting it to glycidyl ether. The compound, an alicyclic epoxy compound having at least one epoxy group bonded to the alicyclic ring in the molecule, an aliphatic epoxy compound typified by a glycidyl ether of an aliphatic polyhydroxy compound, and the like.

  In addition to cationically polymerizable compounds such as epoxy compounds as representative examples of ultraviolet curable adhesives, polymerization initiators, particularly to generate cationic species or Lewis acids upon irradiation with ultraviolet rays, initiate polymerization of cationically polymerizable compounds. The photocationic polymerization initiator is blended. Further, a thermal cationic polymerization initiator that initiates polymerization by heating, and various other additives such as a photosensitizer may be blended.

  When the optical film is bonded to both sides of the polarizing film, the ultraviolet curable adhesive applied to each optical film may be the same or different, but from the viewpoint of productivity, moderate adhesion It is preferable to use the same adhesive on both surfaces on the premise that force can be obtained.

[Production method of polarizing plate]
In the present invention, an optical film made of a thermoplastic resin is bonded to a polarizing film made of the polyvinyl alcohol resin described above via an ultraviolet curable adhesive to produce a polarizing plate. At this time, the following steps (A), (B), (C), (D) and (E) are performed.

(A) A coating process in which the ultraviolet curable adhesive is applied to the bonding surface of the optical film to the polarizing film,
(B) A laminating process in which a polarizing film is stacked on the UV curable adhesive surface applied in the coating process and pressed.
(C) A curing step of curing the ultraviolet curable adhesive by irradiating the ultraviolet light from the ultraviolet irradiation device to the laminate in which the optical film is bonded to the polarizing film via the ultraviolet curable adhesive,
(D) Using a polychromator, the illuminance of ultraviolet rays irradiated in the curing step is measured, and based on this, the integrated value of ultraviolet illuminance in a predetermined absorption wavelength region including the absorption peak wavelength of the polymerization initiator is measured. And (E) the ratio of the absolute value of the difference between the measured illuminance integrated value X obtained in the measuring step and the Y with respect to the set illuminance integrated value (set illuminance integrated value) Y is not less than a predetermined value. The control process which controls the output of said ultraviolet irradiation device when it becomes 5% or more, for example.

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

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

  The surface of the first optical film 2 to be bonded to the polarizing film 1 is coated with an ultraviolet curable adhesive from the first coating machine 10, while being bonded to the polarizing film 1 of the second optical film 3. The adhesive is also applied to the surfaces to be joined from the second coating machine 12. The first optical film 2 and the second optical film 3 after the UV curable adhesive is applied are overlapped on both surfaces of the polarizing film 1 with the adhesive nip rolls 20 and 21, respectively. After being sandwiched and pressurized in the thickness direction and then receiving the ultraviolet irradiation from the ultraviolet irradiation device 16, the adhesive is cured, and then the obtained polarizing plate 4 is wound through the nip rolls 22 and 23 before winding. The roll 30 is wound up. Here, in the manufacturing apparatus shown in FIG. 1, an illuminance meter 17 using a polychromator is installed between the ultraviolet irradiation device 16 and the film to be conveyed, and the optical film is attached to the polarizing film via an ultraviolet curable adhesive. The illuminance of ultraviolet rays applied to the laminated body can be measured in-line. Then, based on the illuminance measurement by the illuminance meter 17, the illuminance integrated value in a predetermined absorption wavelength region including the absorption peak wavelength of the polymerization initiator contained in the ultraviolet curable adhesive is measured.

  In addition, as FIG. 1 shows, the thickness of the ultraviolet curable adhesive apply | coated to the optical film is made into the 1st film thickness meter 14 and the 2nd film thickness meter 15 before bonding with a polarizing film. It is also preferable to control the coating thickness control means of the coating machine so that a uniform desired adhesive thickness can be maintained based on the measurement result.

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

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

  And the coating process (A) mentioned above by the 1st coating machine 10 and the 2nd coating machine 12 is performed, and the bonding process (B) mentioned above by the nip rolls 20 and 21 for bonding are performed, The aforementioned curing process (C) is performed by the ultraviolet irradiation device 16, the measurement step (D) is performed by the illuminance meter 17, and the measurement result by the illuminance meter 17 is turned back to the ultraviolet irradiation device 16, thereby controlling the above. Step (E) is performed.

  The relationship between these steps will be described based on the block diagram of FIG. First, after performing the coating process (A) and the bonding process (B), in the setting (0), the wavelength range to be subject to illuminance integration is set, and the set value of the integrated value of the ultraviolet illuminance (set illuminance) Integration value) Y is set. Of course, this setting (0) may be carried out before the bonding step (B) or before the coating step (A). The wavelength range to be subject to illuminance integration is an absorption wavelength range including the absorption peak wavelength of the polymerization initiator, and is determined according to the polymerization initiator to be used. The set illuminance integral value Y is within a range that has been proven in advance that a highly durable polarizing plate that can cure the adhesive satisfactorily and is difficult to cause decoloration of the polarizing film even under severe conditions of high temperature and humidity. Selected.

  Next, the curing step (C) is performed by irradiating the ultraviolet ray from the ultraviolet ray irradiating device 16, and the integral value (measured illuminance integral value) X of the illuminance in the wavelength range set by the setting (0) of the irradiated ultraviolet ray is obtained. Measure using a polychromator illuminometer and output this (measurement step (D)). On the other hand, in the control step (E), the measured illuminance integrated value X and the set illuminance integrated value Y are compared. When the absolute value of the difference between the measured illuminance integral value X and the set illuminance integral value Y becomes a predetermined value or more, for example, 5% or more with respect to the set illuminance integral value Y, the difference between the two becomes small as an absolute value. As described above, the input power to the ultraviolet irradiation device 16 is preferably adjusted so that the absolute value of the difference between the measured illuminance integral value X and the set illuminance integral value Y is less than 5% with respect to the set illuminance integral value Y. And control the output. As described above, the illuminance in a specific wavelength region may decrease due to deterioration due to long-term use of a lamp provided in the ultraviolet irradiation device or contamination due to long-term use of a member attached to the ultraviolet irradiation device. In general, the measured illuminance integrated value X gradually becomes smaller than the set illuminance integrated value Y due to the long-term use of the ultraviolet irradiation device.

  Here, the fact that the absolute value of the difference between the measured illuminance integrated value X and the set illuminance integrated value Y is 5% or more with respect to the set illuminance integrated value Y means that the following equation (I) is satisfied. In FIG. 2, whether or not to change the output condition of the ultraviolet irradiation device is determined depending on whether or not this equation is satisfied.

  Hereinafter, the coating process (A), the bonding process (B), the curing process (C), the measurement process (D), and the control process (E) constituting the method of the present invention will be described in detail.

(A) Coating step In the coating step (A), an ultraviolet curable adhesive is applied to the bonding surface of the optical films 2 and 3 to the polarizing film 1. As a coating machine used here, the system using the gravure rolls 11 and 13 demonstrated with reference to FIG. 1 is mentioned. Examples of the coating machine using a gravure roll include a direct gravure coater, a chamber doctor coater, an offset gravure coater, a kiss coater using a gravure roll, and a reverse roll coater composed of a plurality of rolls. In addition, there are a cylindrical blade, a die coater that supplies adhesive directly to the application part by applying adhesive to the application part and scraping off with the blade, applying a slot die, etc., and a liquid reservoir Various coating machines such as a knife coater that makes and applies excess liquid while scraping off with a knife can be used. Among these, direct gravure coater, chamber doctor coater, offset gravure coater, etc. are preferable among coating machines using gravure rolls, considering thin film coating and pass line freedom, etc. Then, a die coater using a slot die is also preferable. A chamber doctor coater is more preferable because it can easily cope with the widening of the polarizing plate and hardly releases the odor of the adhesive supplied in liquid.

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

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

  As described above, the thickness of the ultraviolet curable adhesive applied to the optical film is in-line using the first film thickness meter 14 and the second film thickness meter 15 before being bonded to the polarizing film. It is also preferable to measure and control the coating thickness control means of the coating machine based on the measurement result so that a uniform desired adhesive thickness can be maintained. As a film thickness meter, for example, various types of types in which light is applied to the applied adhesive surface, the reflected light obtained as interference light is dispersed in a predetermined wavelength range, and the film thickness is obtained from the obtained spectral waveform pattern A spectral interference type film thickness meter can be used. The spectral interference type film thickness meter can directly measure the thickness of the applied adhesive (about 0.5 to 5 μm) (the first film thickness meter 14 and the second film thickness meter 15 in FIG. This is an example) and some are not. In the latter case, film thickness meters are installed upstream and downstream of the coating machine, the thickness of the optical film itself is measured with the film thickness meter on the upstream side, and the optical film is measured with the film thickness meter on the downstream side. The total thickness of the adhesive and the adhesive is measured, and the thickness of the adhesive is obtained from the difference between these measured values.

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

(C) Curing Step After the optical films 2 and 3 are bonded to the polarizing film 1, from the ultraviolet irradiation device 16 to the laminate in which the optical film is bonded to the polarizing film 1 via an ultraviolet curable adhesive. The polarizing plate 4 is manufactured by irradiating ultraviolet rays and curing the ultraviolet curable adhesive. Ultraviolet rays are irradiated through the optical film 2.

  In the example shown in FIG. 1, the laminated body is irradiated with ultraviolet rays while tension is applied to the laminated body between the nip rolls 20 and 21 before and after the ultraviolet irradiation device 16 and the nip rolls 22 and 23 before winding. It is supposed to be done. Not limited to this, for example, a convex curved surface formed in an arc shape along the conveying direction as disclosed in the above-mentioned Patent Document 2 (Japanese Patent Laid-Open No. 2009-134190), typically on the outer peripheral surface of the roll. It is also preferable to irradiate with ultraviolet rays while being supported. In particular, when heat is generated by irradiation of ultraviolet rays and there is a possibility of adversely affecting the product, it is preferable to irradiate ultraviolet rays there in a state where the laminate is supported on the outer peripheral surface of the roll as in the latter case, In this case, it is preferable that the roll supporting the laminated body can be adjusted in temperature in the range of about 10 to 60 ° C. In addition, although only one ultraviolet irradiation device may be provided at the irradiation site, two or more ultraviolet irradiation devices along the flow direction of the laminated body and irradiation from a plurality of light sources can effectively increase the integrated light amount. It is effective in.

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

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

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

(D) Measurement step In the measurement step, the illuminance meter 17 is used to measure the illuminance of the ultraviolet rays irradiated in the curing step (C), and based on this, a predetermined absorption wavelength region including the absorption peak wavelength of the polymerization initiator Measure the integrated value of the UV illuminance at (the measured illuminance integrated value X). The illuminometer 17 may be an illuminometer that performs spectroscopy for each wavelength in a wavelength region of 220 to 800 nm by a polychromator and measures the illuminance for each wavelength. Spectroscopy can be performed with a diffraction grating or a prism. Illuminance measurement using an illuminometer with a polychromator 1) The illuminance can be measured over a wide wavelength range, and the measurement sensitivity for each wavelength is the same, so the type of polymerization initiator used in the UV curable adhesive is changed. Even if it does, it does not involve the change of the illuminance meter. 2) Since the illuminance of the irradiated ultraviolet light can be directly measured and the measurement sensitivity for each wavelength is the same, the predetermined absorption wavelength range This is advantageous in that the integrated value of the ultraviolet illuminance at can be accurately measured.

  The wavelength range subject to illuminance integration may be any wavelength range as long as it includes the absorption peak wavelength of the polymerization initiator, but light in the wavelength range with low absorbance contributes to the curing reaction. Therefore, it is preferable to integrate the illuminance within the wavelength range of −40 nm to +40 nm of the absorption peak wavelength of the polymerization initiator, and to integrate the illuminance within the wavelength range of −30 nm to +30 nm of the absorption peak wavelength of the polymerization initiator. More preferably.

  The measured illuminance integrated value X may be obtained from one illuminance measurement with the number of measurements taken once. However, for example, when the variation is expected to increase after one measurement, a plurality of illuminance measurements may be performed. The measured illuminance integrated value X may be obtained by performing dispersion reduction processing such as Fourier transform processing using these measurement values.

(E) Control process In this invention, based on the result of the measurement process (D) demonstrated above, the control process (E) which controls the output of the ultraviolet irradiation device 16 in a hardening process (C) is provided. That is, the integrated value of the illuminance measured in the measurement step (D) is gradually lowered due to deterioration due to long-term use of the lamp provided in the ultraviolet irradiation device and contamination due to long-term use of the members attached to the ultraviolet irradiation device. Tend to. In general, the illuminance of ultraviolet rays from the lamp becomes stable for a few tens of minutes from the start of ultraviolet irradiation, but may gradually decrease due to changes in the lamp environment caused by lighting of the lamp, such as heat generation of the lamp. Such a decrease in illuminance causes a deviation from a desired illuminance integrated value (set illuminance integrated value Y). In particular, in the initial stage of ultraviolet irradiation, the voltage of the ultraviolet irradiation device is not stable, and the measured illuminance integrated value X may be higher or lower than the desired illuminance integrated value (set illuminance integrated value Y). In order to correct such a shift, the output of the ultraviolet irradiation device 16 is controlled based on the measured illuminance integrated value X measured in the measuring step (D).

  For example, when the absolute value of the difference between the set illuminance integrated value Y and the measured illuminance integrated value X is 5% or more with respect to the set illuminance integrated value Y, preferably the difference between the two is reduced as an absolute value. The input power to the ultraviolet irradiation device 16 is adjusted so that the absolute value of the difference between the set illuminance integral value Y and the measured illuminance integral value X is less than 5% of the set illuminance integral value Y, and the output is adjusted. Increase or decrease. Such control may be performed using a computer or may be performed manually.

As described above, the set illuminance integral value Y has been proved in advance to obtain a highly durable polarizing plate that can cure the adhesive satisfactorily and is difficult to cause decoloration of the polarizing film even under severe conditions of high temperature and high humidity. Within a range of 50 to 6000 mW / cm ² . The higher the integrated value of illuminance within this range, the easier it is to manufacture a polarizing plate having good performance even when the line speed is increased. When the set illuminance integrated value Y is less than 50 mW / cm ² , it is necessary to increase the size of the ultraviolet irradiation device (e.g., lengthen the production line) or increase the number of the ultraviolet irradiation devices in order to satisfy the above integrated light quantity. Arise. That is, the above-described integrated light amount of ultraviolet rays is determined by the line speed management and the illuminance of ultraviolet rays. Therefore, setting the set illuminance integrated value Y within the above range is important in achieving the above-described preferable integrated light amount.

  The polarizing plate produced as described above has a sufficiently high curing reaction of the UV curable adhesive, and its reaction amount is stable, so that it has good adhesive strength and is subjected to severe conditions of high temperature and high humidity. In this case, the polarizing film is less likely to be discolored, and the product has excellent quality stability.

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

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

3 differs from FIG. 3 in FIG.
(1) When irradiating a laminated body after bonding the first optical film 2 and the second optical film 3 on both surfaces of the polarizing film 1 respectively, the second optical film 3 side of the laminated body While closely contacting the outer circumferential surface of the winding roll 26 for irradiation, ultraviolet rays are applied to the first optical film 2 side of the laminate from the ultraviolet irradiation device 16 disposed on the opposite side of the winding roll 26 with the laminate interposed therebetween. The point to be irradiated.

  As the illuminance meter 17, a UV curable lamp monitor system manufactured by Otsuka Electronics Co., Ltd. was used. This illuminance meter performs spectroscopy using the polychromator described above and measures the illuminance at each wavelength. Then, the illuminance of ultraviolet rays irradiated from the ultraviolet irradiation device 16 is measured at a preset measurement time at every preset measurement interval, and the illuminance of each wavelength in a preset wavelength region is integrated to measure illuminance. An integral value X is output.

[Example 1]
(0) Material used in the experiment In this example, the first optical film 2 has a thickness of 60 μm, a width of 1490 mm, and a biaxially oriented retardation film “Zeonor” made of a cycloolefin resin supplied from a roll. [Obtained from Nippon Zeon Co., Ltd.]. The second optical film 3 is melt-kneaded with a propylene-based resin (melting point = 164 ° C.) having a thickness of 75 μm, a width of 1490 mm, and an extrusion temperature of 275 ° C. by a single screw extruder so as to form a roll. Then, after extruding into a film form from a T-die, and solidifying by cooling with a cooling roll set at 20 ° C., a propylene-based resin film obtained by removing both ends with a cutter blade was used. The adhesive used for bonding the polarizing film 1 and the first optical film 2 and the adhesive used for bonding the polarizing film 1 and the second optical film 3 are both an epoxy compound and a photopolymerization initiator. It is an epoxy ultraviolet curable adhesive containing (absorption peak wavelength = 290 nm) and substantially free of solvent.

(A) Coating process Polarizing film 1 having a thickness of 25 μm in which iodine is adsorbed and oriented on polyvinyl alcohol, the cycloolefin resin film as the first optical film 2, and the propylene as the second optical film 3 The system resin films were supplied so that the flow directions were the same at a line speed of 15 m / min. On the surface to be bonded to the polarizing film 1 of the cycloolefin-based resin film 2, using a first coating machine 10 equipped with a gravure roll 11 [“Microchamber Doctor” manufactured by Fuji Machine Co., Ltd.] The above epoxy UV curable adhesive was applied. Moreover, the 2nd coating machine 12 [A "micro chamber doctor" also made by Fuji Machine Co., Ltd.] provided with the gravure roll 13 is used also for the surface bonded to the polarizing film 1 of the said propylene-type resin film 3. Then, the above-mentioned epoxy UV curable adhesive was applied.

  The gravure rolls 11 and 13 provided in the coating machines 10 and 12 were rotated in the opposite direction with respect to the film transport direction. On the cycloolefin resin film 2 side, the rotational peripheral speed of the gravure roll 11 provided in the first coating machine 10 is 21 m / min, and the adhesive is applied with a thickness of about 2.6 μm. . In the second coating machine 12 on the propylene-based resin film 3 side, the rotational peripheral speed of the gravure roll 13 included in the second coating machine 12 is 19.5 m / min, and the adhesive is applied on the film at a thickness of about 3.0 μm. Was set to

(B) Bonding process The cycloolefin resin film 2 and the propylene resin film 3 to which the adhesive is applied are overlapped on the polarizing film 1 with each adhesive application surface, and 240 N / O by the nip rolls 20 and 21 for bonding. Clamped with a linear pressure of cm.

(C) Curing step, (D) Measuring step and Control step (E)
The laminated body of cycloolefin resin film 2 / polarizing film 1 / propylene resin film 3 after passing through the nip rolls 20 and 21, the winding roll 26 for irradiation in which the propylene resin film 3 side is set to 20 ° C. The film was transported at the same line speed of 15 m / min as before bonding and applied to the irradiation winding roll 26 while applying a tension of 600 N in the longitudinal direction (conveying direction) so as to be in close contact with the outer peripheral surface of the film. The body was irradiated with ultraviolet rays using the ultraviolet irradiation device 16 from the cycloolefin resin film 2 side (curing step (C)). At this time, using the illuminometer 17 by a polychromator set so as to integrate the illuminance over the wavelength range of −30 nm to +40 nm of the absorption peak wavelength 290 nm of the polymerization initiator contained in the ultraviolet curable adhesive, the ultraviolet illuminance The ultraviolet ray was irradiated while measuring the integral value of (measurement step (D)). In the curing step (C), an ultraviolet irradiation device 16 manufactured by GS Yuasa Co., Ltd. is used, and ultraviolet rays are emitted from two “EHAN1700NAL high-pressure mercury lamps”, which are ultraviolet lamps included in the ultraviolet irradiation device 16. Irradiation was performed so that the integrated illuminance at 55 mW / cm ² . The cumulative amount of ultraviolet light was 77 mJ / cm ² for the two lamps. In this way, the adhesive layer is cured, and a polarizing plate 4 in which a cycloolefin-based resin film 2 is bonded to one side of the polarizing film 1 and a propylene-based resin film 3 is bonded to the other side is wound on a winding roll 30. It was.

  In the measurement step (D), the illuminance measurement condition by the illuminometer 17 is set in advance to the number of times of measurement in one measurement, the measurement interval of 3 seconds, and the measurement time of 25 milliseconds. The instantaneous value of the integrated illuminance value was output about every minute, and this instantaneous value was taken as the measured integrated illuminance value X.

In the control step (E), when the measured illuminance integrated value X is reduced by 5% or more compared to the set illuminance integrated value Y = 55 mW / cm ² , that is, (Y−X) ≧ 2.75 mW / cm. ^In the case of ² , the ultraviolet irradiation device 16 was controlled and the output was adjusted to increase the output in units of 5 W per lamp. Deviation from the set illuminance integrated value Y of the average measured illuminance integrated value X when operated for 300 minutes, that is, (Y−X average value) / Y (%) is referred to as “illuminance deviation”. It was shown in 1.

[Comparative Example 1]
In Example 1, even if the control step (E) is not provided, that is, even if the measured illuminance integrated value X measured in the measuring step (D) is lower than the set illuminance integrated value Y by 5% or more, ultraviolet irradiation is performed. A polarizing plate was produced by performing ultraviolet irradiation without controlling the output of the device 16. “Illuminance deviation” when operated for 300 minutes is shown in Table 1.

[Example 2]
A biaxially oriented retardation film “ZEONOR” made of a cycloolefin resin having a thickness of 38 μm and a width of 1330 mm as the first optical film 2 and a thickness of 60 μm and a width of 1330 mm Was used as the second optical film 3, and an epoxy-based ultraviolet curable adhesive containing an epoxy compound and a photopolymerization initiator (absorption peak wavelength = 320 nm) was used as the ultraviolet curable adhesive. And except for the following points, in the same manner as Example 1, (A) coating process, (B) bonding process, (C) curing process, (D) measuring process and control process (E), A polarizing plate was produced.

(1) In the curing step (C), ultraviolet rays are applied so that the integrated illuminance value in the wavelength range shown in (2) below per lamp is 200 mW / cm ² (the integrated light intensity of the two lamps is 280 mJ / cm ² ). Irradiated (set illuminance integrated value Y = 200 mW / cm ² ),
(2) In the measurement step (D), the illuminometer 17 was set so as to integrate the illuminance over the wavelength range of −30 nm to +30 nm of the absorption peak wavelength of 320 nm of the polymerization initiator, and (3) in the control step (E) When the measured illuminance integrated value X is lower than the set illuminance integrated value Y by 5% or more, that is, when (Y−X) ≧ 10 mW / cm ² , the ultraviolet irradiation device 16 is controlled. The output was adjusted to increase the output in units of 5 W per lamp.

“Illuminance deviation” when operated for 300 minutes is shown in Table 1.
[Comparative Example 2]
In Example 2, even if the control step (E) is not provided, that is, even when the measured illuminance integrated value X measured in the measuring step (D) is lower than the set illuminance integrated value Y by 5% or more, the ultraviolet irradiation is performed. A polarizing plate was produced by performing ultraviolet irradiation without controlling the output of the device 16. “Illuminance deviation” when operated for 300 minutes is shown in Table 1.

[Decoloration evaluation test of polarizing plate]
Each of the obtained polarizing plates is cut into a strip of 80 mm (flow direction) × full width, and a plurality of small pieces obtained by further cutting the strip into a width of 300 to 400 mm are used as one sample. The small pieces were suspended in a thermostat / humidifier adjusted to 60 ° C. × 90% RH so as not to contact each other and held for 500 hours. While transmitting light on the light box, it was visually compared with a polarizing plate not placed in a constant temperature / humidity chamber, and the presence or absence of light leakage was evaluated. Such a decoloration evaluation test is performed on four samples cut out at an arbitrary position of the polarizing plate, and when no light leakage occurs in all four samples, “OK” is obtained, and light leakage occurs in one or more of the four samples. The result is shown in the column of “Decoloration evaluation result” in Table 1. The numerical value in parentheses in this column indicates the number of samples in which light leakage occurred among the four samples.

  As shown in Table 1, in Comparative Examples 1 and 2 in which the control step (E) was not provided, the illuminance integrated value of the ultraviolet rays was greatly reduced, and along with this, decoloration was observed in the harsh environment of the obtained polarizing plate. On the other hand, in the first embodiment, the control step (E) is provided and the ultraviolet irradiation output is changed when the measured illuminance integrated value X in the predetermined wavelength region is reduced by 5% or more compared to the set illuminance integrated value Y. No. 2 shows that the average of the measured illuminance integrated value X (deviation of illuminance) is suppressed to a fluctuation within 5% as compared with the set illuminance integrated value Y, and a polarizing plate that cannot be decolored in a harsh environment can be manufactured.

  DESCRIPTION OF SYMBOLS 1 Polarizing film, 2 1st optical film, 3 2nd optical film, 4 Polarizing plate, 10 1st coating machine, 11 Gravure roll, 12 2nd coating machine, 13 Gravure roll, 14 1st Film thickness meter, 15 Second film thickness meter, 16 UV irradiation device, 17 Illuminance meter, 20, 21 Nip roll for bonding, 22, 23 Nip roll before winding, 24 Guide roll, 26 Winding roll for irradiation, 30 rolls Take roll.

Claims (3)

A method for producing a polarizing plate by laminating an optical film made of a thermoplastic resin through an ultraviolet curable adhesive containing a polymerization initiator to a polarizing film made of a polyvinyl alcohol resin,
(A) A coating step of applying the ultraviolet curable adhesive to the bonding surface of the optical film to the polarizing film,
(B) A laminating step in which the polarizing film is stacked and pressed on the ultraviolet curable adhesive surface applied in the coating step,
(C) The ultraviolet curable adhesive is cured by irradiating ultraviolet rays from an ultraviolet irradiation device to the laminate in which the optical film is bonded to the polarizing film via the ultraviolet curable adhesive. Curing process,
(D) Using a polychromator, the illuminance of ultraviolet rays irradiated in the curing step is measured, and based on this, the integrated value of the ultraviolet illuminance in a predetermined absorption wavelength region including the absorption peak wavelength of the polymerization initiator is measured. And (E) when the ratio of the absolute value of the difference between the measured illuminance integrated value X obtained in the measuring step and the Y with respect to the set illuminance integrated value Y is equal to or greater than a predetermined value, A control step of controlling the output of the ultraviolet irradiation device;
The manufacturing method of a polarizing plate provided with.   In the control step (E), when the ratio of the absolute value of the difference between the measured illuminance integral value X obtained in the measurement step and the Y with respect to the set illuminance integral value Y is 5% or more, The manufacturing method of the polarizing plate of Claim 1 which controls the output of the said ultraviolet irradiation device.   The production of the polarizing plate according to claim 1 or 2, wherein a predetermined absorption wavelength range including an absorption peak wavelength of the polymerization initiator in the measurement step (D) is within a wavelength range of -40 nm to +40 nm of the absorption peak wavelength. Method.

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