JP2011242749A - Inspection method for polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspecting method capable of easily measuring the thickness of an adhesive layer, regarding a polarizing plate where a protective film is laminated on a polarizing film with the adhesive layer therebetween, and capable of easily measuring the thickness of a primer layer, regarding a polarizing plate where the primer layer is interposed between the adhesive layer and the protective film.SOLUTION: Regarding the polarizing plate comprising the polarizing film, the adhesive layer and the protective film or comprising the polarizing film, the adhesive layer, the primer layer and the protective film (it is allowable that the adhesive layer and the protective film are located in this order outside the polarizing film), a cut line is formed in a direction in-plane perpendicular to the absorption axis of the polarizing plate from the side of one protective film (with the presence of the primer layer, from the side of the protective layer contacting with the primer layer) into the thickness direction, and also, up to the vicinity of an interface between the protective film and the adhesive layer or the primer layer, then, the polarizing plate is bent and cut along the cut line with the cut line side as a mountain ridge, then, the thickness of the adhesive layer or the primer layer is measured by an optical microscope based on the cut surface.

Description

  The present invention relates to a polarizing plate in which a protective film is bonded to at least one surface of a polarizing film via an adhesive layer, a method for inspecting the thickness of the adhesive layer, and at least one surface of the polarizing film Further, the present invention relates to a method for inspecting the thickness of a primer layer of a polarizing plate in which a primer layer and a protective film are laminated in this order via an adhesive layer.

  2. Description of the Related Art In recent years, liquid crystal displays that consume less power, operate at a low voltage, and are lightweight and thin have rapidly spread as information display devices such as mobile phones, personal digital assistants, computer monitors, and televisions. Along with this, durability performance required for a polarizing plate mounted on a liquid crystal display has been increasing year by year.

  The polarizing plate usually has a configuration in which a transparent protective film is bonded to both sides or one side of a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol resin. And in order to satisfy | fill required durability, the thickness of the adhesive bond layer used in order to bond a transparent protective film to a polarizing film is a very important parameter.

  On the other hand, in order to improve durability performance, it is often used to improve the adhesion with the polarizing film by applying a primer treatment to the transparent protective film to form a primer layer. For example, in JP 2009-175222 A (Patent Document 1), an ordinary protective film is bonded to one surface of a polarizing film, and rubber particles are formed on both surfaces of a core layer made of a styrene resin on the other surface. In the polarizing plate which bonded the retardation film (it also has a function of a protective film) of the three-layer structure in which the skin layer which consists of a (meth) acrylic-type resin composition containing this was bonded, the primer on the surface of the retardation film A technique is disclosed in which a layer is formed and bonded to a polarizing film via an adhesive on the primer layer side. Thus, also when taking the structure of polarizing film / adhesive layer / primer layer / protective film, the thickness of the primer layer is an important parameter.

  As a method for inspecting the thickness of the adhesive layer or primer layer existing between the polarizing film and the transparent protective film of such a polarizing plate, conventionally, the end face of the polarizing plate is thinly scraped with a microtome etc. Observation was performed to measure the adhesive layer thickness and the primer layer thickness. However, such a method has a problem that it takes a lot of time for measurement, particularly for preparation of an observation sample, and the measurement result cannot be reflected in production in a timely manner.

  For example, when using a photocurable adhesive as disclosed in JP 2009-258226 A (Patent Document 2), the adhesive layer has a thickness of about 0.5 to 5 μm and can be inspected with an optical microscope. It becomes. When the primer layer is formed on the surface of the protective film, the thickness of the primer layer is often set to about 0.5 to 5 μm and can be inspected with an optical microscope. However, if the polarizing plate is cut with a cutter or simply broken, the adhesive layer or primer layer does not appear in the cross section due to damage to the cross section during cutting, so the thickness of the adhesive layer or primer layer It was difficult to measure accurately.

JP 2009-175222 A JP 2009-258226 A

  One of the objects of the present invention is an inspection method capable of easily measuring the thickness of an adhesive layer for a polarizing plate in which a protective film is bonded to at least one surface of the polarizing film via an adhesive layer. Is to provide. Another object of the present invention is to easily measure the thickness of the primer layer for a polarizing plate in which a primer layer and a protective film are laminated in this order via an adhesive layer on at least one surface of the polarizing film. It is to provide an inspection method that can be performed.

  That is, according to the present invention, there is provided a method for inspecting the thickness of an adhesive layer of a polarizing plate in which a protective film is bonded to at least one surface of a polarizing film via an adhesive layer; A step of making a cut from the protective film side in the thickness direction in a direction substantially perpendicular to the absorption axis of the polarizing plate in the film plane and near the interface of the protective film with the adhesive layer; And bending the polarizing plate so that the cut side is convex along the line, and breaking the polarizing plate; and from the broken surface, measuring the thickness of the adhesive layer of the polarizing plate using an optical microscope A method for inspecting the thickness of the adhesive layer of the polarizing plate is provided which performs the steps in this order.

  According to the present invention, there is also provided a method for inspecting the thickness of a primer layer of a polarizing plate in which a primer layer and a protective film are laminated in this order via an adhesive layer on at least one surface of the polarizing film; A step of making a cut from the one protective film side of the plate in the thickness direction, in a direction substantially perpendicular to the absorption axis of the polarizing plate in the film plane, and near the interface of the protective film with the primer layer; Bending the polarizing plate so that the cut side is convex along the cut and breaking the polarizing plate; and measuring the thickness of the primer layer of the polarizing plate using an optical microscope from the fracture surface A method for inspecting the thickness of the primer layer of the polarizing plate is provided, in which the three steps are performed in this order.

  According to the method of the present invention, a cut is made in a direction substantially perpendicular to the absorption axis of the polarizing plate from the side of one protective film of the polarizing plate toward the thickness direction, and the cut actually enters only the protective film layer. Thus, the polarizing plate can be instantaneously broken when it is bent along the cut line. As a result, the thickness shape of the adhesive layer or the primer layer remains almost intact on the fracture surface, so that the thickness can be easily measured with an optical microscope. Therefore, the thickness of the adhesive layer or primer layer bonding the polarizing film of the polarizing plate and the transparent protective film can be determined easily and in a short time. Therefore, the measurement result can be reflected in production in a timely manner, and can be incorporated as one process of production management.

  Hereinafter, the present invention will be described in detail. A polarizing plate is usually formed by laminating a protective film made of a transparent resin via an adhesive layer on at least one surface of a polarizing film in which a dichroic dye made of iodine or a dichroic organic dye is adsorbed and oriented on a polyvinyl alcohol resin. Configured. Further, as described above, a primer layer may be interposed between the adhesive layer and the protective film.

  As described above, a protective film is directly bonded to at least one surface of a polarizing film via a photocurable adhesive, and the photocurable adhesive is cured to form a polarizing film / adhesive layer / protective film. In many cases, the adhesive layer obtained by curing the photocurable adhesive is often set to a thickness of about 0.5 to 5 μm, and the thickness of the adhesive layer is inspected by observing the cross section with an optical microscope. be able to. When bonding a protective film on both surfaces of a polarizing film, the same adhesive is often used on both surfaces.

  In addition, when a primer layer is formed on the surface of the protective film and bonded to the polarizing film via an adhesive on the primer layer side, a primer film / adhesive layer / primer layer / protective film structure is used. The thickness of the layer is often set to about 0.5 to 5 μm, and the thickness of the primer layer can also be inspected by observing the cross section with an optical microscope. In this case, if the adhesive layer is formed from the photocurable adhesive described above, the thickness will be about 0.5 to 5 μm, so the thickness of the adhesive layer can also be measured by observing the cross section with an optical microscope. . However, when interposing a primer layer, an aqueous adhesive, typically an aqueous solution of a polyvinyl alcohol resin, is often used, and an adhesive layer formed from an aqueous adhesive is hardly observed by microscopic observation of its cross section. Since the thickness is negligible, virtually only the thickness of the primer layer is observed.

  The primer layer is often formed on a protective film that does not have sufficient adhesion to the polarizing film. Therefore, a primer layer can be comprised with various materials according to the kind of transparent resin which comprises a protective film. Polyolefin resin modified with an unsaturated carboxylic acid compound and a (meth) acrylic compound disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2009-175222), specifically, Nippon Paper Chemicals Co., Ltd. The “Auroren” series sold by the company and the “Unistal” series sold by Mitsui Chemicals, Inc. are examples of the material forming the primer layer.

  A protective film having a primer layer can be bonded to both sides of the polarizing film via an adhesive layer to form a polarizing plate, but on one side of the polarizing film, a protective film having a primer layer is provided. In many cases, bonding is performed on the primer layer side, and a protective film having no primer layer is directly bonded to the other surface of the polarizing film via an adhesive.

  A polarizing plate having the configuration of a polarizing film / adhesive layer / protective film as described above, when the thickness of the adhesive layer is about 0.5 to 5 μm, and the polarizing film / adhesive layer / primer layer The method of the present invention is effectively applied when the polarizing plate has a protective film structure and the primer layer has a thickness of about 0.5 to 5 μm.

  In the present invention, for such a polarizing plate, a step of making a cut from the protective film side (hereinafter sometimes referred to as a “cutting step”), a step of bending along the cut and breaking the polarizing plate (hereinafter referred to as a “breaking step”). ) And the fractured cross section thereof are observed using an optical microscope and the thickness of the adhesive layer or primer layer of the polarizing plate is measured (hereinafter referred to as “thickness measurement step”). 3) are performed in this order. Each of these steps will be described step by step.

[Cutting process]
For a polarizing plate in which a protective film is bonded to at least one surface of the polarizing film via an adhesive layer, or a polarizing plate in which a primer layer is interposed between the protective film and the adhesive layer, first, the protective film side From the thickness direction to the direction of the thickness of the polarizing plate, in a direction substantially perpendicular to the absorption axis of the polarizing plate within the plane of the film, to the vicinity of the interface with the adhesive layer of the protective film, or to the vicinity of the interface with the primer layer . In this step, by virtually cutting only the protective film layer, it is possible to suppress the distortion of the cross-sectional shape that is likely to occur due to the elongation of the protective film at the time of breaking in the subsequent breaking step. Moreover, by making a cut in a direction substantially perpendicular to the absorption axis of the polarizing plate, the polarizing plate is easily broken in the direction of the cut.

  Any method can be used for cutting the protective film of the polarizing plate as long as it can be cut from the protective film side to the adhesive layer or primer layer, that is, near the interface with the adhesive layer or primer layer. Form can be used. For example, a method of cutting only the protective film with a commercially available cutter knife or the like is preferably employed.

  When the protective film is bonded only to one surface of the polarizing film, a cut is made from the protective film side. When the protective film is bonded on both surfaces of the polarizing film, a cut is made from one of the protective films. If the protective film bonded to both sides of the polarizing film has the same type and the same thickness and no primer layer is present on both sides, and if the same primer layer is present on both sides, the cut from either protective film side May be put in.

  When the protective layer bonded to both surfaces of the polarizing film is a different type of resin film and / or the thickness of the protective film bonded to both surfaces of the polarizing film is different. In this case, the effect of the present invention can be exhibited even if a cut is made from any protective film side. However, in these cases, in the next breaking step, it is possible to suppress the occurrence of distortion in the fracture surface as much as possible, and from the viewpoint of leaving the cross-sectional shape of the adhesive layer as close to the original shape as possible, if the former, It is preferable to make a cut from the protective film side having a high elastic modulus, and in the latter case, it is preferable to make a cut from the thick protective film side. When the primer layer does not intervene and the types and thicknesses of the protective films present on both sides are different, the protective film to be cut may be determined according to each difference, but generally has a high elastic modulus. It is advantageous to make a cut from the protective film side.

  Explaining the form in which the primer layer is interposed, a protective film is bonded to both sides of the polarizing film via an adhesive layer, and the primer layer is interposed only between one of the adhesive layer and the protective film. In the case, a cut is made from the protective film side on which the primer layer is formed. When the primer layer and the protective film are laminated in this order via adhesive layers on both sides of the polarizing film, respectively, and the protective films on both sides are different types of resin films, and / or When the thickness of the protective film is different, it is only necessary to determine which protective film is to be cut according to the above-described form in which the primer layer is not interposed.

[Breaking process]
Next, along the cut line of the protective film put in the upper cutting step, the bent side is bent so that the cut side is convex, and the polarizing plate is broken. In the upper cutting process, by placing a cut in the direction substantially perpendicular to the absorption axis of the polarizing plate in the film plane and effectively only in the protective film layer, both ends sandwiching the cut in the subsequent breaking process. When a force is applied, the polarizing plate can be broken instantly, usually within 1 second. In this way, when a force is applied to the polarizing plate, it can be instantly broken, so that it is possible to suppress the polarizing plate from being deformed at the fracture surface at the time of breaking. When it takes more than 1 second to break after applying force, deformation due to distortion of each layer constituting the polarizing plate is large, and the thickness of the adhesive layer or primer layer can be measured accurately. It becomes difficult.

  As the method for breaking the polarizing plate, any method can be adopted as long as the polarizing plate can be bent and broken. For example, hold the both ends of the polarizing plate with your fingers across the cut, fold and break the polarizing plate as it is, fix one end of the polarizing plate to the tip of a pliers, and fold and break the polarizing plate as it is A method or the like is preferably employed.

  In this way, by rupturing the polarizing plate instantaneously after applying force, the cross-sectional shape of the adhesive layer or primer layer remains almost as it is, and a cross-sectional observation sample that can observe the cross-section of the polarizing plate is produced. it can.

[Thickness measurement process]
The polarizing plate thus broken is then subjected to a step of observing the broken surface using an optical microscope and measuring the thickness of the adhesive layer of the polarizing plate. The thickness of the adhesive layer or the primer layer is measured using an optical microscope from the sample for observing the cross section of the polarizing plate produced in the previous steps. What is necessary is just to use what is generally marketed for an optical microscope.

  When observing the fracture surface of the polarizing plate with an optical microscope, the inspection light is incident on the fracture surface of the polarizing plate from above and observed with reflected light. At this time, since the adhesive layer or the primer layer looks brighter than other members, the adhesive layer or the primer layer can be easily specified, and the thickness of the adhesive layer or the primer layer can be accurately measured. become able to.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples, the thickness measurement of the whole film and the time measurement from when a force was applied to the polarizing plate until the film was broken were performed by the following methods.

(1) Measurement of film thickness The thickness of the film was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

(2) Time measurement until the polarizing plate breaks The time from when force was applied to the polarizing plate until the polarizing plate broke was measured using a stopwatch “Timekeeper SSBJ018” manufactured by Seiko Sports Life Co., Ltd.

[Example 1]
Using a photocurable adhesive on one side of a polarizing film in which iodine is adsorbed and oriented on polyvinyl alcohol, a 80 μm thick triacetyl cellulose film [trade name “Fujitac”, manufactured by Fuji Film Co., Ltd.] (hereinafter “TAC”) The film is abbreviated as “film”, and the opposite surface of the polarizing film is bonded with a 43 μm thick biaxially stretched polyethylene terephthalate film (hereinafter abbreviated as “PET film”) using the same photo-curing adhesive. Produced.

(A) Cutting process From the TAC film side of the polarizing plate prepared above, a line is drawn in a direction perpendicular to the absorption axis of the polarizing plate using a cutter blade “BB10K” manufactured by Olfa Co., Ltd. Cut only the film.

(B) Breaking Step The both ends of the polarizing plate were held with fingers, and the polarizing plate was broken along the cut so that the cut side became convex. The time required for breaking was 0.3 seconds.

(C) Thickness measurement process From the fracture surface of this polarizing plate, the thickness of the adhesive layer was determined using an optical microscope “Microscope VHX-500” manufactured by Keyence Corporation. As a result, the thickness of the adhesive layer between the TAC film and the polarizing film was measured to be 3.94 μm, and the thickness of the adhesive layer between the PET film and the polarizing film was measured to be 4.12 μm.

[Comparative Example 1]
From the polarizing plate produced in Example 1, a sample for cross-sectional observation was produced using a microtome [“Ultra Microtome EM UC6rt” manufactured by Hitachi High-Technologies Corporation]. The obtained sample for cross-sectional observation was observed with a scanning electron microscope [JSM-5510 type, manufactured by JEOL Datum Co., Ltd.] to determine the thickness of the adhesive layer. As a result, the thickness of the adhesive layer between the TAC film and the polarizing film was measured to be 3.66 μm, and the thickness of the adhesive layer between the PET film and the polarizing film was measured to be 4.23 μm.

[Comparative Example 2]
The polarizing plate produced in Example 1 is in the same direction as Example 1 using the same cutter blade used in Example 1, but the whole is cut from the TAC film side to the PET film side, and its cross section Thus, the measurement of the adhesive layer thickness was attempted using the same optical microscope used in Example 1. However, the adhesive layer could not be specified from the cross section of the polarizing plate, and the thickness of the adhesive layer could not be measured.

[Comparative Example 3]
(A) Cutting process A line is drawn from the TAC film side of the polarizing plate produced in Example 1 in the direction parallel to the absorption axis of the polarizing film using the same cutter blade used in Example 1, and the TAC film. Only cut it.

(B) Breaking Step The both ends of the polarizing plate were held with fingers, and the polarizing plate was broken along the cut so that the cut side became convex. The time required for breaking was 3.6 seconds.

(C) Thickness measurement process From the fracture surface of this polarizing plate, the same optical microscope as used in Example 1 was used to measure the adhesive layer thickness. However, the adhesive layer could not be specified from the cross section of the polarizing plate, and the thickness of the adhesive layer could not be measured.

  As shown in the above Examples and Comparative Examples, in order to measure the thickness of the adhesive layer by cutting the polarizing plate in which the protective film is bonded to the polarizing film via the adhesive layer in the thickness direction. The following points are important.

(1) Make a cut from one protective film side of the polarizing plate, and make the cut into only the protective film layer (does not cut into the adhesive layer), and (2) the cut The in-plane direction of the film shall be a direction substantially orthogonal to the absorption axis of the polarizing plate.

  After making a cut in this way, if the polarizing plate is bent so that the cut side is convex along the cut, the polarizing plate can be broken instantaneously (within 1 second), and the adhesive Since the shape in the thickness direction of the layer remains almost intact on the fracture surface, the thickness of the adhesive layer can be accurately measured by observing the fracture surface with an optical microscope.

  On the other hand, when the sample for cross-sectional observation is prepared from the end face of the polarizing plate using a microtome as in Comparative Example 1, the thickness of the adhesive layer can be accurately measured, but it takes time to prepare the sample for cross-sectional observation. It is difficult to incorporate it into production process management.

  On the other hand, when the whole is cut from one protective film side to the opposite surface of the polarizing plate using a cutter as in Comparative Example 2, or only one protective film layer is cut as in Comparative Example 3, When the in-plane direction of the cut film is parallel to the absorption axis of the polarizing plate, the cut surfaces of the protective film, the adhesive layer, and the polarizing film are distorted at the time of cutting or breaking. Therefore, even if the cross section is observed with an optical microscope, the adhesive layer cannot be specified, and the thickness of the adhesive layer cannot be measured from the cross section.

Claims (2)

A method for inspecting the thickness of an adhesive layer of a polarizing plate in which a protective film is bonded to at least one surface of a polarizing film via an adhesive layer;
In the thickness direction from one protective film side of the polarizing plate, in a direction substantially perpendicular to the absorption axis of the polarizing plate in the film plane, and near the interface with the adhesive layer of the protective film The step of adding
Bending the polarizing plate so that the cut side is convex along the cut and breaking the polarizing plate; and measuring the thickness of the adhesive layer of the polarizing plate using an optical microscope from the broken surface One process is performed in this order, The inspection method of the adhesive layer thickness of a polarizing plate characterized by the above-mentioned. A method for inspecting the thickness of a primer layer of a polarizing plate in which a primer layer and a protective film are laminated in this order via an adhesive layer on at least one surface of a polarizing film;
In the thickness direction from one protective film side of the polarizing plate, in a direction substantially perpendicular to the absorption axis of the polarizing plate in the film plane, and near the interface with the primer layer of the protective film Adding step;
Bending the polarizing plate so that the cut side is convex along the cut and breaking the polarizing plate; and measuring the thickness of the primer layer of the polarizing plate using an optical microscope from the broken surface A method for inspecting a primer layer thickness of a polarizing plate, wherein the steps are performed in this order.