JP2024101781A - Polarized light sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for measuring a polarized light laminate with less optical distortion measured by MIL-DTL-43511D.

SOLUTION: A method for measuring optical distortion of a subject comprises the steps of: placing a subject in an optical tester having a diffraction grating; acquiring an image of a bright line of the subject passing through the diffraction grating set in the optical tester; determining a shape of one or more bright lines transmitted through the diffraction grating; and determining a degree of optical distortion of a polarized light laminate using the shape of the bright line.

SELECTED DRAWING: Figure 3

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to polarizing films and polarizing sheets that constitute polarizing lenses used in sunglasses, goggles, etc., and to a method for evaluating the optical performance of these. In particular, the present invention relates to a method for quantitatively evaluating polarizing films with extremely low optical distortion.

Well-known examples include curved polarized lenses made by laminating transparent protective sheets, via an adhesive, to both sides of a polarized film made of a resin substrate such as polyvinyl alcohol that is substantially oriented in one direction and has a dichroic dye or the like adsorbed thereon, and processing the film into a spherical or aspherical surface, or polarized lenses for sunglasses made by injection molding a transparent resin for lenses onto the concave surface of the curved polarized lens.

These transparent protective sheets are required to have small optical distortion so as not to change the polarization direction of the polarizing film. To achieve this, a manufacturing method has been proposed for the transparent protective film so as not to create surface irregularities. On the other hand, eyewear used by pilots and other people engaged in special tasks is required to have more specific optical requirements than those generally available on the market. For example, there is a standard used for procuring materials required by the US military, which is generally called the MIL standard. Regarding optical distortion in this MIL standard, the light transmitted through the polarizing lens is visually observed through a diffraction grating using the device shown in the following non-patent document, and the pass/fail of the optical distortion is judged.

MIL-DTL-43511D, DETAIL SPECIFICATION VISORS, FLYER'S HELMAT, POLUCARBONATE

One indicator of eyewear lenses with little optical distortion is the measurement method according to the MIL standard described in non-patent literature. In this measurement method, an inspector visually judges whether or not there is distortion in pass and fail products. This poses a problem of human differences depending on the level of skill of the inspector. Despite the existence of standards, no method has been proposed to objectively evaluate optical distortion. It is also desirable to be able to confirm that optical distortion has passed the standards in the pre-eyewear lens stage, such as in bent products or sheets, while conforming to such standards.

In order to solve the above problems, the inventors of the present application conducted extensive research and discovered that by capturing optical distortion to a degree that meets the MIL standard as image data and evaluating the shape of each bright line in the inspection field, it is possible to objectively evaluate the optical distortion in a polarizing sheet and to evaluate it quantitatively, which led to the present invention. Furthermore, the present invention can also be used to determine whether or not a transparent plastic sheet that constitutes a polarizing laminate meets the MIL standard.

That is, the present invention provides
placing a test object on an optical tester that includes a diffraction grating;
acquiring an image of a bright line of a test object passing through a diffraction grating set in an optical tester;
determining a shape of one or more bright lines transmitted through the diffraction grating;
determining a degree of optical distortion of the object using the shape of the bright line;
A method for measuring optical distortion of a subject, comprising:

The present invention also provides a method for measuring the optical distortion of a specimen, which can be measured when the specimen is a polarizing sheet formed by placing a transparent plastic sheet as a protective layer on a polarizing film made of a uniaxially stretched polyvinyl alcohol resin film via an adhesive layer, a punched lens formed by punching a polarizing sheet into a predetermined shape, a heat-bent lens formed by heat-bending a punched product, an injection-molded lens formed by injection-molding a molten resin onto the concave surface of a heat-bent product (these are collectively referred to as "polarizing laminate" in this specification), or a transparent plastic sheet used as a protective layer for a polarizing sheet.

The present invention also includes a method for measuring optical distortion of a subject, the step of determining the shape of the bright line further comprising a step of quantifying the shape of the bright line.

The present invention also includes a method for measuring optical distortion of a subject, the method further comprising a step of determining a minimum and a maximum value of the width of the acquired bright line image in the step of quantifying the shape of the bright line.

Another aspect of the present invention is a method for measuring optical distortion of a specimen, in which one or more bright lines in the specimen are two adjacent slits in a protective layer, and the difference between the maximum and minimum values of the bright line shape (slit spacing) is 1.05 mm or less at all measurement points.

Another aspect of the present invention is a method for measuring optical distortion of a specimen, in which the protective layer is made of aromatic polycarbonate resin, and the difference between the maximum and minimum values of the bright line shape (slit spacing) is 0.75 mm or less at all measurement points.

Another aspect of the present invention is a method for measuring the optical distortion of a test object having a protective layer thicker than 100 μm.

Another aspect of the present invention is a method for measuring optical distortion of a specimen in which the adhesive layer has a thickness of less than 40 μm.

The present invention makes it easy to objectively evaluate and standardize the optical distortion of polarizing laminates and their constituent elements to military grade levels. It also makes it possible to preselect non-defective products based on the optical distortion of the elements that make up the polarizing laminate, such as protective layers.

FIG. 1 is a schematic diagram showing the principle of an optical tester used in the present invention. FIG. 2 is a schematic diagram of an optical distortion measurement system used in the present invention. FIG. 3 shows an example of pass/fail judgment based on optical distortion measured by the present invention. FIG. 4 shows the results of measuring the slit intervals of a passed product and a failed product described in the non-patent document.

The configuration of the present invention will be described below.
(Optical tester)
The optical tester used in the present invention is based on the method introduced by V. Ronchi and M. Lenouvel. In this method, as shown in FIG. 1, when light emitted from a light source at P passes through a lens, mirror, or optical window, which is a diffraction grating with an array of equally spaced parallel slits near the focal plane, an observer P sees the light transmitted through the slits. An example of a device using this principle is the Model C Optical tester (DATA OPTICS INC.), but is not limited to this. In addition, a transmitted image of the diffraction grating can be recorded by placing a camera in front of the optical tester (for example, at the position of the observer's viewpoint).

This optical tester mainly consists of the following four parts: The optical tester used in the present invention is not limited to the ones specified above, as long as it can be configured by combining the following four parts.
a) Optical distortion image acquisition unit b) Lens c) Sample holder d) Mirror

a) Optical Distortion Image Acquisition Unit The optical distortion image acquisition unit in the present invention includes a light source that radiates light toward the sample, and a window through which the inspector checks the inspection image. A diffraction grating can be installed on one side of the window. A type of diffraction grating that can be used is called a Ronchi Ruling. The Ronchi Ruling has a fixed light-shielding line within a certain distance. That is, by placing the diffraction grating in this specification in front of an observer, the observer can visually recognize the light-transmitting portion and the non-light-transmitting portion on the object. The light-transmitting portion is a bright band-like portion consisting of the light-transmitting portion or slit portion of the diffraction grating and the light diffracted by hitting the light-shielding line of the diffraction grating. In this specification, this band-like portion is called a slit or a bright line, meaning that the light-shielding portion is missing. By mechanically capturing the image of the light on the object and quantifying the characteristics of the image of the light, it becomes possible to objectively evaluate the optical distortion of the object. In the optical tester of the present invention, Ronchi rulings having 50, 100, 200, etc. light-shielding lines per inch (2.54 cm) are available, but which scale is preferable can be selected by a person skilled in the art depending on the object of inspection. The light source provided in a) is a 7.5 volt filament lamp, and the window for confirming the image may be one that allows the observer to observe with the naked eye, or one that allows the test image to be electrically converted and viewed. The type of 7.5 volt filament lamp is not particularly limited, but any lamp having optical performance equivalent to that described in the above DATA OPTICS INC. can be used in the present invention.

b) Lens The lens installed in the optical tester is reflected from the mirror d) and magnifies the diffraction grating image of the sample set in c). At this time, it is preferable to adjust the distance from a) so that a predetermined number of bright lines can be confirmed in the field of view projected in the window of a). The number of measurements and the measurement location for confirming the slit interval can be appropriately changed depending on the type of specimen. In an embodiment of the present invention, in an apparatus specified by MIL-DTL-43511D, in order to ensure a field of view for confirming 13 to 14 bright lines from a plate with 60 bright lines at a predetermined position, it is preferable that the distance from a) to d) is about 200 mm. Depending on the arrangement of the apparatus, this distance can be made shorter or longer than 200 mm, but of course if it is made shorter, the distorted part will be magnified, and if it is moved farther away, the distorted part will be reduced and difficult to confirm.

c) Sample holder: A sample is set here. As an embodiment of the present invention, a polarizing sheet formed by laminating a transparent plastic sheet on at least one side of a polarizing film via an adhesive layer, a punched lens formed by punching these into a predetermined shape, a polarizing lens for sunglasses formed by heat bending such a punched product, and an injection molded product formed by injection molding a molten resin on the concave surface of a polarizing lens for sunglasses can be measured for optical distortion by appropriately selecting the shape of the sample holder with the device and method of the present invention. In addition, in the present invention, the installation direction of the subject is not particularly limited as long as the measurement conditions are the same and comparisons can be made, but for example, in the case of a polarizing lens that has been heat bent, it is preferable to face the surface with less spherical aberration toward a).

d) Mirror d) reflects the light from a) and delivers the image of the subject magnified by b) to a).

(Measurement System)
The optical system described above can be installed on an optical tester bench configured to change the distance of each of the lenses, mirrors, or optical windows on one axis to carry out the method of the present invention. An example of such an apparatus is a MODEL E DISTORTION TESTER (DATA OPTICS INC.) described in MIL-DTL-43511D, DETAIL SPECIFICATION VISORS, FLYER'S HELMAT, POLUCARBONATE.

(Measuring method)
In the method of the present invention, the image acquired by the optical system is recorded as an image, for example, by a camera. The selection of the image recording means is not particularly important in the present invention, but by recording as an image, optical distortion can be compared on the same basis. Therefore, in the present invention, when comparing the same products or using for quality control, it is preferable to leave an image record as an image of the same resolution.

(Optical distortion pass/fail judgement)
The optical distortion measured in the present invention can be measured using a Model E Destination Tester manufactured by DATA OPTICS INC. or a device having the same configuration. In a conventional optical distortion test in which the optical distortion is individually judged to be pass or fail by visual inspection, an objective evaluation becomes possible by processing an image obtained from the Model E Destination Tester based on the present invention.

For objective evaluation, it is possible to quantify the characteristics of the image seen by the optical tester. In a specimen with little optical distortion, the slits or slit intervals are seen as linear, while in a polarizing laminate with a certain degree of optical distortion, distortion is seen in the slits or slit intervals. There are several methods, including a method of taking a transmission image of a diffraction grating with only slits, setting the specimen and taking a transmission image of the diffraction grating, and taking the difference in slit intervals and area, a method of measuring the entire length of the entire length of the slits in the field of view, a method of taking the average value of the maximum-minimum difference of a specified number of slit intervals, a method of measuring one slit interval at several points and measuring only the maximum value of a specified number of slit intervals, and a method of measuring one slit interval at multiple points and taking the sum of a specified number of slit intervals. Alternatively, there is a method of calculating the undulation of the light lines as a curve, but these are not limited to these.

(Polarizing film)
In the present invention, the polarizing film is produced by swelling a resin film as a substrate in water, and then immersing the substrate in a dyeing solution containing the dichroic organic dye of the present invention while stretching the substrate in one direction, thereby dispersing the dichroic dye in an oriented state in the substrate resin, thereby obtaining a film imparted with polarizing properties and a desired color tone.

The resin used as the base material for the polarizing film used in this case is a polyvinyl alcohol, and preferred examples of this polyvinyl alcohol include polyvinyl alcohol (hereinafter referred to as PVA), PVA with a trace amount of acetate ester structure remaining, and PVA derivatives or analogs such as polyvinyl formal, polyvinyl acetal, and saponified ethylene-vinyl acetate copolymer, with PVA being particularly preferred.

The molecular weight of the PVA film is preferably a weight average molecular weight of 50,000 to 350,000 in terms of stretchability and film strength, more preferably a molecular weight of 100,000 to 300,000, and particularly preferably a molecular weight of 150,000 or more. The magnification when stretching the PVA film is preferably 2 to 8 times in terms of the dichroic ratio and film strength after stretching, particularly preferably 3 to 6.5 times, and particularly preferably 3.5 to 4.5 times. There are no particular restrictions on the thickness of the PVA film after stretching, but a thickness of 20 μm or more and 50 μm or less is preferred in terms of being able to handle it without being integrated with a protective film, etc.

A typical manufacturing process when using PVA as the base film is as follows:
(1) The PVA is swelled in water and washed with water to remove impurities,
(2) While appropriately stretching,
(3) Dyeing in a dyeing tank;
(4) crosslinking or chelation in a treatment tank containing boric acid or a metal compound;
(5) Drying,
The steps (2) and (3) (and optionally (4)) may be carried out in a different order or simultaneously.

First, the swelling and water washing process in step (1) absorbs water, softening the PVA film, which easily breaks when dry at room temperature, uniformly so that it can be stretched. This process also removes water-soluble plasticizers used in the PVA film manufacturing process, or preliminarily adsorbs additives as appropriate. At this time, the PVA film does not swell uniformly in sequence, and variations are inevitable. Even in this state, it is important to take measures to apply as small a force as possible uniformly so that there is no localized stretching or insufficient stretching, and to prevent the occurrence of wrinkles, etc. Also, in this process, it is most desirable to simply swell uniformly, and excessive stretching, etc., can cause unevenness, so it is best to avoid it.

In step (2), the film is usually stretched 2 to 8 times. Since it is important that the polarizing film of the present invention has good processability after the stretching, it is preferable to select the stretching ratio from 3 to 6.5 times, particularly 3.5 to 4.5 times, and to maintain the orientation even in this state. Since the orientation relaxation progresses if the film is left in water for a long time in the stretched and oriented state, and furthermore if the time until drying is long, from the viewpoint of maintaining higher performance, the stretching process is set to a short time, and after stretching, the moisture is removed as soon as possible, that is, it is preferable to immediately proceed to the drying process and dry the film while avoiding excessive heat load. The stretching ratio is based on the original roll of polyvinyl alcohol resin film.

The dyeing in step (3) is performed by adsorbing or depositing the dye onto the polymer chains of the oriented polyvinyl alcohol resin film. This step can be performed before, during, or after uniaxial stretching without any significant changes, but the highly regulated surface, the interface, is the most susceptible to orientation, and it is preferable to select conditions that make the most of this. Due to the demand for high productivity, the temperature is usually selected from a high temperature of 40 to 80°C, but in the present invention it is usually selected from 25 to 45°C, preferably 30 to 40°C, and especially 30 to 35°C.

Step (4) is carried out to improve heat resistance, water resistance, and organic solvent resistance. The treatment with boric acid improves heat resistance by crosslinking between PVA chains, but it can be carried out before, during, or after the uniaxial stretching of the polyvinyl alcohol resin film, and does not result in a significant change. In addition, the metal compound mainly forms a chelate compound with the dye molecules to stabilize them, and is usually carried out after or simultaneously with dyeing.

There are metal compounds that have been confirmed to have the above-mentioned heat resistance and solvent resistance effects, regardless of whether the metal is a transition metal belonging to the 4th, 5th, or 6th period, but from the perspective of cost, metal salts such as acetates, nitrates, and sulfates of 4th period transition metals such as chromium, manganese, cobalt, nickel, copper, and zinc are preferred. Among these, compounds of nickel, manganese, cobalt, zinc, and copper are more preferred because they are inexpensive and have excellent effects, and nickel is particularly suitable.

More specific examples include manganese(II) acetate tetrahydrate, manganese(III) acetate dihydrate, manganese(II) nitrate hexahydrate, manganese(II) sulfate pentahydrate, cobalt(II) acetate tetrahydrate, cobalt(II) nitrate hexahydrate, cobalt(II) sulfate heptahydrate, nickel(II) acetate tetrahydrate, nickel(II) nitrate hexahydrate, nickel(II) sulfate hexahydrate, zinc(II) acetate, zinc(II) sulfate, chromium(III) nitrate nonahydrate, copper(II) acetate monohydrate, copper(II) nitrate trihydrate, and copper(II) sulfate pentahydrate. Any one of these metal compounds may be used alone, or multiple types may be used in combination.

The content of the metal compound and boric acid in the polarizing film is preferably 0.2 to 20 mg of metal in the metal compound per 1 g of polarizing film, more preferably 0.2 to 2 mg, in order to provide the polarizing film with heat resistance and solvent resistance. More specifically, the concentration of the metal compound impregnated in the polarizing film is 200 ppm to 2500 ppm, more preferably 200 ppm to 2000 ppm, even more preferably 400 ppm to 1800 ppm, even more preferably 800 ppm to 2300 ppm, and even more preferably 600 ppm to 1600 ppm. If the concentration of the metal compound is less than 200 ppm, color unevenness tends to occur, and if it exceeds 2500 ppm, problems with moist heat resistance occur.

As mentioned above, when a metal compound is impregnated into a polarizing film in a treatment tank, a chelate is formed between the dye molecules and the polarizing film, which is thought to suppress changes in the orientation of the dye. If a large amount of metal compound is added, the excess metal compound not used in the chelate will react with the dye molecules, making it difficult to adjust the color tone, but if no metal compound is added at all, the dichroic ratio will decrease, and it will be necessary to add a high dichroic ratio dye to compensate for the dichroic ratio. As a result, the polarizing film will become highly oriented in a humid and hot environment, and the humid and hot color change will be significant. Therefore, an appropriate amount of metal compound necessary for chelate formation is added to manufacture polarizing film.

In the present invention, the content of boric acid is preferably 0.3 to 30 mg of boron, and more preferably 0.5 to 10 mg. The composition of the treatment solution used in the treatment is set to satisfy the above contents, and generally, it is preferable that the concentration of the metal compound is 0.5 to 30 g/L and the concentration of boric acid is 2 to 20 g/L.

The metal and boron content in polarizing film can be analyzed by atomic absorption spectrometry.

The temperature is usually the same as that for dyeing, but is usually selected from 20 to 70°C, preferably 25 to 45°C, more preferably 30 to 40°C, and particularly preferably 30 to 35°C. The time is usually selected from 0.5 to 15 minutes.

In step (5), the dyed uniaxially stretched PVA film that has been stretched, dyed, and optionally treated with boric acid or a metal compound is dried. PVA films exhibit heat resistance that corresponds to the amount of water they contain, and when the film contains a large amount of water and the temperature rises, the film becomes distorted from the uniaxially stretched state in a shorter time, causing a decrease in the dichroic ratio.

The film is dried from the surface, and it is preferable to dry from both surfaces, and it is preferable to do so while removing water vapor by blowing dry air. As is well known, in order to avoid excessive heating, a method that immediately removes evaporated water and promotes evaporation is preferable because it allows drying with reduced temperature rise, and the temperature of the dry air is set to a range below the temperature at which the polarizing film in a dry state does not substantially discolor, usually 70°C or higher, preferably 90 to 120°C, and the film is blown dry for 1 to 120 minutes, preferably 3 to 40 minutes.

At this stage, it is preferable that the moisture content of the polarizing film be 5% or less. In the drying process, it is difficult to achieve a moisture content below 2%, and this is also undesirable from the standpoint of the strength of the polarizing film. The preferred moisture content is 2.5% to 5.0%.

In the present invention, the dye is not particularly limited as long as it can be adsorbed and aligned on the PVA polarizing film. For example, when dyeing is performed using a dichroic organic dye composition and a coloring organic dye composition, it is possible to select a wide range of transmittance, with the transmittance of the PVA polarizing film dyed with the dichroic organic dye composition as the upper limit and the transmittance of the PVA polarizing film dyed with the coloring organic dye composition as the lower limit.
Furthermore, the color tone is adjusted mainly by the organic dye composition for coloring, and a wide range of color tones can be obtained by changing the ratio of the amounts used without substantially considering the change in the degree of polarization.

(Adhesive Layer)
In order to laminate a polarizing film and a transparent protective sheet to form a polarizing sheet, an adhesive layer is interposed between the polarizing film and the transparent protective sheet. Materials for the adhesive layer typically used in polarizing sheets include polyvinyl alcohol resin-based materials, acrylic resin-based materials, urethane resin-based materials, polyester resin-based materials, melamine resin-based materials, epoxy resin-based materials, silicone-based materials, and the like.
In the present application, when stability during heat bending and injection molding processes is taken into consideration, a thermosetting material is preferred, and in particular, a two-component thermosetting urethane resin consisting of a polyurethane prepolymer, which is a urethane resin material, and a curing agent is preferred.

The polyurethane prepolymer is a compound obtained by reacting a diisocyanate compound with a polyoxyalkylene diol in a certain ratio, and has isocyanate groups at both ends. As the diisocyanate compound used in the polyurethane prepolymer, diphenylmethane-4,4'-diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, lysine isocyanate, and hydrogenated xylylene diisocyanate can be used, with diphenylmethane-4,4'-diisocyanate being preferred. As the polyoxyalkylene diol, polypropylene glycol, polyethylene glycol, and polyoxytetramethylene glycol can be used, with polypropylene glycol having a degree of polymerization of 5 to 30 being preferred. The molecular weight of the polyurethane prepolymer is not particularly limited, but is usually a number average molecular weight of 500 to 5000, preferably 1500 to 4000, and more preferably 2000 to 3000.

On the other hand, the curing agent is not particularly limited as long as it is a compound having two or more hydroxyl groups, and examples thereof include polyurethane polyol, polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol, polycarbonate polyol, etc., among which polyurethane polyol having hydroxyl groups at the terminals obtained from a specific isocyanate and a specific polyol is preferred. In particular, polyurethane polyol having hydroxyl groups at at least both terminals derived from a diisocyanate compound and a polyol is preferred. As the diisocyanate compound, diphenylmethane-4,4'-diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, lysine isocyanate, and hydrogenated xylylene diisocyanate can be used, but tolylene diisocyanate is preferred. As for the polyol, a product obtained by reacting trimethylolpropane or the like with ethylene oxide or propylene oxide can be used, and it is preferable to use a polypropylene glycol derivative with a degree of polymerization of 5 to 30. There are no particular restrictions on the molecular weight of this curing agent, but it is usually a number average molecular weight of 500 to 5000, preferably 1500 to 4000, and more preferably 2000 to 3000.

These polyurethane prepolymers and curing agents can be used with solvents such as ethyl acetate and tetrahydrofuran to adjust the viscosity. In addition, when imparting a photochromic function to the adhesive layer, the use of a solvent is an effective method for uniformly dispersing the photochromic compound in the urethane resin.

(Protective Layer)
Next, the transparent plastic sheet which is the protective layer in the polarizing sheet of the present invention usually has a thickness of 0.1 to 1 mm and may be a single-layer or multi-layer sheet produced by a coextrusion method, such as an aromatic polycarbonate/polyacrylate coextrusion sheet. Furthermore, the polarizing sheet of the present invention is suitable for producing an injection-molded polarizing lens which is usually punched out into individual lens shapes with protective films attached to both surfaces, then subjected to a heat bending process, the surface protective films are peeled off, and the sheet is mounted in an injection molding die and integrated with a molten resin.

Resins for the above-mentioned transparent plastic sheets include transparent resins consisting of aromatic polycarbonates, amorphous polyolefins, polyacrylates, polysulfones, acetyl cellulose, polystyrene, polyesters, polyamides, and mixtures of these. Among these, there is acetyl cellulose, which is essential in the manufacture of the most general-purpose polarizing films. From the viewpoints of mechanical strength and impact resistance, aromatic polycarbonate-based resins are preferred, while from the viewpoints of chemical resistance, polyolefins, polyacrylates, and polyamides are preferred, and from the viewpoints of dyeability after lens molding, polyacrylates and polyamides are preferred.

From the viewpoints of film strength, heat resistance, durability, and bending workability, the aromatic polycarbonate sheet is preferably a polymer produced by a well-known method from a bisphenol compound represented by 2,2-bis(4-hydroxyphenyl)alkane or 2,2-(4-hydroxy-3,5-dihalogenophenyl)alkane, and the polymer skeleton may contain structural units derived from fatty acid diols or structural units having ester bonds. In particular, aromatic polycarbonates derived from 2,2-bis(4-hydroxyphenyl)propane are preferred. The molecular weight of the aromatic polycarbonate is preferably 12,000 to 40,000 in viscosity average molecular weight, and more preferably 20,000 to 35,000. In addition, aromatic polycarbonates have a large photoelastic constant, and are prone to colored interference fringes due to birefringence caused by stress or orientation.

The alicyclic polyester resin of the present invention, which is used as a sheet or film for a protective layer as a composition with an aromatic polycarbonate, is obtained by a known method in which, for example, a dicarboxylic acid component represented by 1,4-cyclohexanedicarboxylic acid and a diol component represented by 1,4-cyclohexanedimethanol are subjected to an esterification or ester exchange reaction, and then a polymerization catalyst is added as appropriate, and the pressure inside the reaction tank is gradually reduced to cause a polycondensation reaction.

Specific examples of alicyclic dicarboxylic acids or their ester-forming derivatives include 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,4-decahydronaphthalenedicarboxylic acid, 1,5-decahydronaphthalenedicarboxylic acid, 2,6-decahydronaphthalenedicarboxylic acid, 2,7-decahydronaphthalenedicarboxylic acid, and their ester-forming derivatives.

From the viewpoint of transparency and moldability, the polyamide resin used in the transparent plastic sheet of the present invention is preferably what is called an amorphous polyamide or a microcrystalline polyamide, and is preferably capable of injection molding as described below. In other words, any polyamide that is thermoplastic, exhibits melt fluidity that allows molding at or below its thermal decomposition temperature, and has an appropriate Tg (glass transition temperature) can be suitably used.

When amorphousness is the condition, the amount of repeating units that become crystalline is limited, and examples of molecular structures that inhibit crystallinity include structures that impart steric hindrance, and branched structures, introduction of substituents, and bulky molecular structures such as cycloalkanes are used. When moderate heat resistance is required, structures with large enthalpy in the repeating units (unit molecular chain length) and structures that limit molecular motion within and between repeating units are essential. A typical example of the former is aromatic, and examples of the latter are cycloalkanes and cycloalkenes in which the unsaturated bonds of aromatic nuclei are hydrogenated in synthetic products. In addition, as mentioned above, those with alicyclic structures have heat resistance and a molecular structure that inhibits crystallinity, and therefore can be said to be useful materials for making functional sheets for sunglasses with a protective layer of polyamide that is subjected to heat bending processing, etc.

Polyamides generally have structural units derived from monomers such as diamines, dicarboxylic acids, and aminocarboxylic acids. In principle, aromatic polyamides and alicyclic polyamides are produced by making structural units derived from at least one monomer that constitutes a fully aliphatic polyamide aromatic or alicyclic. All or part of these monomers can be aromatic or alicyclic, and partially aromatic polyamides, partially aromatic partially alicyclic polyamides, partially aromatic alicyclic polyamides, partially alicyclic polyamides, partially alicyclic polyamides, etc., or combinations thereof, can be used in the present invention. As a typical example of an amorphous polyamide having amorphousness and moderate heat resistance, polyamides having an alicyclic structure can be preferably used. In addition, when considering optical properties such as retardation, which will be described later, it is desirable to include an aromatic portion.

Naturally, additives such as lubricants and antioxidants are appropriately used in the polyamide resin used in the present invention to deal with oxidative degradation of polyamide and processing defects. Examples of transparent polyamide resins for lenses include those known in the art, which have a heat distortion temperature, which is an index of heat resistance, in the range of 100 to 170°C, and include aromatic polyamide resins, alicyclic polyamide resins, aliphatic polyamide resins, and copolymers thereof. Alicyclic polyamide resins are preferred in terms of the balance of mechanical strength, chemical resistance, transparency, etc., but two or more types of polyamide resins may be combined. Examples of such polyamide resins include GLILAMID TR FE5577, XE 3805 (manufactured by EMS), NOVAMID X21 (manufactured by Mitsubishi Engineering Plastics), and Toyobo Nylon T-714E (manufactured by Toyobo).

The (meth)acrylic resin is a homopolymer of various (meth)acrylic acid esters such as polymethyl methacrylate (PMMA) and methyl methacrylate (MMA), or a copolymer of PMMA or MMA with one or more other monomers, or may be a mixture of two or more of these resins. Among these, (meth)acrylates containing a cyclic alkyl structure, which have low birefringence, low moisture absorption, and excellent heat resistance, are preferred. Examples of such (meth)acrylic resins include Acrypet (manufactured by Mitsubishi Rayon), Delpet (manufactured by Asahi Kasei Chemicals), and Parapet (manufactured by Kuraray).

In the polarizing laminate of the present invention, it is desirable to dispose a protective layer exhibiting a retardation value that does not impair the function of the polarizing film layer provided as an inner layer at least in a position that will become a convex surface after lens processing.
When such a low retardation is desired, a film produced by a casting method, which is less likely to promote molecular orientation, can be suitably used as the protective layer. However, even in the case of a casting method, care must be taken to avoid unnecessary stresses occurring during removal, which would result in an unnecessarily large retardation value.

Alternatively, in a method other than keeping the retardation value small, a protective layer with an extremely large retardation value, for example, 1300 nm or more, preferably 2000 nm or more, more preferably 3000 nm or more, more preferably 4000 nm or more, is placed on the convex surface after processing into a lens, so that the phenomena of "color unevenness" and "polarized light leakage" are difficult to see to the naked eye. In this way, when the retardation value is extremely high, it is necessary to stretch the protective layer made of a transparent resin. In that case, it is desirable to stretch a sheet molded to a certain thickness, for example, 100 μm or more, preferably 150 μm or more, more preferably 200 μm or more, and even more preferably 300 μm or more, by a melt extrusion method or the like, to form a protective film having the desired retardation value and thickness. In the present invention, the retardation value is an in-plane retardation value. It is within the knowledge of a person skilled in the art that the in-plane retardation value can be derived from the refractive index in the slow axis direction, the refractive index in the fast axis direction, and the thickness of the film when the incident linearly polarized light is decomposed into the slow axis and the fast axis. In this disclosure, the retardation value is a value measured at 590 nm. Measurement devices include the Otsuka Electronics retardation measurement device: RETS-100.

To increase the retardation value by stretching a film molded by melt extrusion, there are a draw stretching method in which the film is stretched while being taken up, and an offline stretching method in which the film is taken up once after molding and then stretched separately. In the melt extrusion molding method, for example, the polyamide resin or the resin constituting the protective layer is melt mixed in an extruder or the like, extruded from a die (e.g., a T-die, etc.), and cooled to produce a transparent plastic sheet to be used for the protective layer. The resin temperature when melting and molding the resin constituting the protective layer (melt molding) varies depending on the resin, but can usually be selected from a temperature range of about 120°C to 350°C, for example, about 130 to 300°C, preferably 150 to 280°C, and more preferably about 160 to 250°C. In this case, the stretching process can be performed by making the take-up speed faster than the cooling roll speed.

The specific method of stretching is not particularly limited. In order to suppress stretching unevenness, it is preferable to keep the resin temperature constant while heating the roll of the stretching part with a mold temperature regulator or the like. In general, stretching while maintaining the suitable appearance as a sheet for sunglasses is possible near the Tg of the resin that constitutes the protective layer. If the resin temperature is stretched at a temperature range lower than the Tg of the resin used, it is easy to cause stretching unevenness that is not uniform, and uneven patterns are generated between stretched and unstretched parts. In addition, if the resin is stretched at a temperature range higher than the Tg, it causes the transparent plastic film to be welded to the roll, which leads to problems such as leaving marks when the film is peeled off from the roll. It is necessary to select the conditions of the roll and other temperature regulators appropriately, taking into consideration the relationship with the retardation described later. In addition, Tg in this invention indicates the midpoint temperature among the start point, midpoint, and end point temperatures in the Tg curve when measured by DSC.

The resin temperature of the protective layer during stretching is also related to the retardation. If the resin temperature of the film during stretching is in a temperature range lower than the Tg of the resin used, it is easier to impart a higher retardation, and the higher the temperature, the less likely the retardation is to be expressed. Furthermore, after stretching, it is preferable to cool as quickly as possible, which allows the retardation and the angle between the slow axis and the fast axis to be fixed. In addition, if stretching is performed in a temperature range lower than the Tg, it may affect problems such as shrinkage after sheet molding, so it is essential to select the stretching temperature conditions taking this into consideration. Conversely, if stretching is performed at a resin temperature higher than the Tg, the effect of the neck-in of the sheet during stretching becomes greater, affecting the thickness distribution and increasing the variation in the retardation and fast axis angle, so care must be taken not to increase the stretching ratio too much.

When stretching a resin molded by melt extrusion to form a protective layer, it is preferable to use a resin with a high intrinsic birefringence value. This makes it easier to develop high retardation with lower stress, and also makes it easier to maintain retardation even when stretched at a resin temperature higher than the Tg. Since the intrinsic birefringence value varies depending on the composition or type of resin, and also depends on the desired retardation value, it is necessary to appropriately adjust the stretching ratio in the stretching process. Generally, a minimum of 1.1 times, preferably 1.2 times, and more preferably 1.3 times or more is required. The higher the stretching ratio, the more necking is promoted, or there is a risk of breakage, so the upper limit is determined from the viewpoint of production efficiency. It is usually about 2.2 times, and preferably about 2.0 times or less.

In order to prevent colored interference fringes due to stretching of the transparent plastic sheet that is the protective layer, it is preferable that the retardation (Re, hereinafter, when simply referred to as retardation, it means in-plane retardation) be 1500 to 10000 nm. In this case, the preferred lower limit of the retardation is 2000 nm, the next preferred lower limit is 2500 nm, the more preferred lower limit is 3000 nm, the even more preferred lower limit is 3500 nm, and the even more preferred lower limit is 4000 nm. Depending on the type of backlight light source, if the retardation is too low, rainbow spots may appear. The preferred upper limit is 8000 nm, the more preferred upper limit is 7000 nm, the even more preferred upper limit is 6000 nm, the particularly preferred upper limit is 5500 nm, and the most preferred upper limit is 5000 nm. Transparent plastic sheets with retardation greater than this are thick and are not suitable for use in the present invention.

The transparent plastic sheet in this polarizing sheet preferably has a small deviation in in-plane retardation. In the present invention, the deviation in in-plane retardation can be determined by dividing a molded or stretched transparent plastic sheet into three parallel parts in the length direction and measuring the retardation in the central area and both end areas, based on the measured value.

(Preparation of Polarizing Sheet)
The polarizing film is used as a functional layer, and the adhesive layer is applied using a gravure coater or a die coater, and the protective layer is laminated on both sides, and the laminate is cut to a desired length to obtain the polarizing laminate of the present invention. There is no particular limitation on the lamination method, but a sufficient discharge amount is maintained in order to avoid air bubble entrapment due to insufficient coating liquid when applying the adhesive. In addition, it is desirable to appropriately adjust the tension during lamination and the nip pressure of the lamination roll, taking into consideration the warping state of the sheets after lamination, etc.

(Production of polarized lenses for sunglasses)
Next, the polarizing sheet is processed into the shape of each lens by punching or the like, and then subjected to bending. Processing into individual lens-shaped products is usually performed by punching a plurality of lens-shaped products using a punching blade made of a Thomson blade, taking into account productivity and the like. The shape of the individual lens-shaped products is appropriately selected depending on the shape of the final product (sunglasses, goggles, etc.). A standard lens-shaped product for two-eye use is a disk with a diameter of 80 mm or a slit shape in which both ends are cut to the same width in a direction perpendicular to the polarization axis. In addition, as mentioned in the selection of the type of transparent plastic sheet for the protective layer used in the polarizing sheet above, the bending process is determined under the condition that the layer that exhibits the functionality of the polarizing sheet including the colored polarizing film of the present invention does not substantially deteriorate.

When used as an injection polarized lens, the film is bent so as to follow the surface of the mold used for injection molding. When a protective layer of a high retardation sheet is used, the polarized film is prone to cracks along the stretching direction during bending, so conditions must be selected that suppress these occurrences. The mold temperature during bending of the polarized sheet is preferably equal to or lower than the glass transition temperature of the resin used, and in addition, it is preferable that the temperature of the polarized sheet immediately before bending is at least 50°C lower than the glass transition point of the resin used by preheating, but lower than the glass transition point, and in particular, it is preferable that the temperature is at least 40°C lower than the glass transition point and lower than 5°C lower than the glass transition point.

The molten resin is then injected to produce an injection polarized lens. It is essential that the processing conditions for injection molding are such that lenses with excellent appearance can be produced. From this point of view, injection conditions that produce a lens molded product with a high filling rate without producing burrs, such as injection pressure, holding pressure, metering, molding cycle, etc., are selected, and the resin temperature is the melting temperature of the resin used, and is appropriately selected from 260 to 320°C. The mold temperature is selected from temperatures 100°C lower than the glass transition temperature of the aromatic polycarbonate resin and lower than the glass transition point, preferably 80°C lower than the glass transition temperature and lower than 15°C lower than the glass transition point, and particularly preferably 70°C lower than the glass transition temperature and lower than 25°C lower than the glass transition point.

One embodiment of the present invention also includes the curved polarized lens and the injected polarized lens described above. When an injected polarized lens is manufactured through the above-mentioned processing steps, it is easily assumed that a certain degree of optical distortion occurs because the polarized laminate is subjected to physical stress. However, the measurement method of the present invention makes it possible to easily and accurately standardize optical distortion that fully meets the MIL standard, and to easily distinguish between acceptable and unacceptable products. In particular, by setting the difference between the maximum and minimum values of the width of the gap between two adjacent slits to 1.05 mm or less in the optical distortion measured based on MIL-DTL-43511D measured by the method described in this specification, it is possible to easily measure whether a binocular polarized sunglasses meets the MIL standard.

The polarizing laminate of the present invention can then be subjected to a hard coat treatment. There are no particular limitations on the material or processing conditions of the hard coat, but it is necessary that it has excellent appearance and adhesion to the resin used, or to inorganic layers such as a mirror coat or anti-reflection coat that are subsequently applied. In addition, the baking temperature is preferably a temperature that is 50°C lower than the glass transition temperature of the resin used in the polarizing sheet and lower than the glass transition point, and in particular, a temperature of around 120°C, which is 40°C lower than the glass transition point and lower than a temperature that is 15°C lower than the glass transition point, and the time required for baking the hard coat is generally between 30 minutes and 2 hours.

The following describes the details of the present invention based on examples.

Example 1
a) Preparation of Polarizing Film Polyvinyl alcohol (product name: VF-PS#7500, manufactured by Kuraray Co., Ltd.) was stretched to 2 times its original size while being swollen in water at 35° C. for 270 seconds.
Subsequently, the fabric was dyed in an aqueous solution containing 0.41 g/L of the dichroic dye Eisen Premium Blue 6GLH (C.I. Blue 202), 0.09 g/L of Sumilite Red 4B (C.I. Red 81), 0.03 g/L of Chrysophenine (C.I. Yellow 12), and 10 g/L of anhydrous sodium sulfate at 35°C.
This dyed film was stretched 4 times while being immersed in an aqueous solution containing 2.3 g/L of nickel acetate and 4.4 g/L of boric acid at 35° C. for 120 seconds. The film was dried at room temperature for 3 minutes while being kept in a tensed state, and then heat-treated at 110° C. for 3 minutes to obtain a polarizing film.

b) Preparation of protective layer and retardation measurement b-1) Polycarbonate protective layer A polycarbonate film having a thickness of 275 μm was obtained by melt extrusion manufacturing method in which aromatic polycarbonate resin was heated and melted, extruded from a T-die with a short-axis extruder, cooled with a cooling roll, and then wound up with a winder. Next, the polycarbonate sheet obtained above was cut into 40 cm squares, fixed with clamps on all four sides, and held at Tg (midpoint in DSC measurement) temperature for 20 minutes, then stretched in only one axial direction at a stretching ratio of 1.5 times and a stretching speed of 2 m/min, and cooled at room temperature for 30 minutes while maintaining the tension after stretching, to obtain a polycarbonate protective film having a thickness of 200 μm. After stretching, the film was cut about 25 mm from both left and right ends in the width direction, and retardation measurements were performed and used for manufacturing a polarizing laminate sheet.
b-2) Retardation Measurement The retardation was measured using a WPA-200-L manufactured by Photonics Lattice Corporation. A polycarbonate protective film having a length of 300 mm and a width of 295 mm was divided into three parts (L, C, R) in the width direction, and an average retardation value was calculated by measuring an area of 70 mm on each side.

c) Preparation of polarizing sheet A thermosetting polyurethane adhesive was applied to the polarizing film obtained above, and the polycarbonate protective film obtained above with a thickness of 200 μm was laminated thereon. A polycarbonate protective film with a thickness of 200 μm was laminated on the remaining side of the polarizing film in the same manner. After lamination, the laminate was left in a thermostatic chamber at 70° C. to harden the adhesive, and a polarizing sheet with an adhesive layer of 10 μm was obtained.

d) Preparation of polarized lenses A disk with a diameter of 80 mm was cut in parallel on both sides of a straight line passing through its center to produce a punched piece for a twin-lens lens with a width of 55 mm, a slit shape or a longitudinal cross-sectional shape of a capsule or a bale, and small projections for positioning on the arcuate portions on both sides that were not cut out. The punched piece was punched in the longitudinal direction along the absorption axis of the polarizing film. The punched piece was then subjected to a heat bending process.
The hot bending was performed using a continuous hot bending device, which preheated the punched piece in a preheater, placed it on a partially spherical female mold of a predetermined temperature and curvature, and pressed it with a male mold made of silicone rubber while simultaneously starting the pressure reduction to adhere it to the female mold. The male mold was then pulled up, and the punched piece adhered to the female mold was kept in a hot air atmosphere of a predetermined temperature for a predetermined time and then removed.
In the above, when aromatic polycarbonate was used as a protective layer, the punched piece was preheated to an atmospheric temperature of 136°C, the female mold had a partial spherical surface equivalent to 8R (radius approximately 65.6 mm) with a surface temperature of 139°C, the pressing time with the silicone rubber male mold was 4 seconds, and the adsorption to the female mold was performed for 5 minutes in an atmosphere where the temperature of the blown hot air was 170°C.
The protective film of the heat-bent punched piece produced above was peeled off, and the piece was mounted in the mold cavity of an injection molding machine, and injection molding was performed using molten aromatic polycarbonate (blended with ultraviolet absorber, product name: Mitsubishi Engineering Plastics Corporation, IUPILON, CLS-3400). The injection molding conditions were resin temperature 290°C, injection filling speed 30 mm/s, holding pressure 30 MPa, mold temperature 90°C, cooling time 30 seconds, and injection cycle 70 seconds, and injection was performed to obtain an injected lens with a thickness of 2.2 mm.

d) Optical Distortion Measurement d-1) Visual Optical Distortion Measurement Method In accordance with Sections 3.5.5 and 4.3.5 of MIL-DTL-43511D, a military standard established by the US Department of Defense, the optical distortion of the test specimen was measured in accordance with the measurement method described in the standard using a Model E Distortion Tester manufactured by DATA OPTICS INC., and the test specimen was visually judged to be pass or fail based on the optical distortion tolerance criteria described in the standard.
d-2) Optical distortion measurement method using an image discrimination device Using a Model E distortion tester from DATA OPTICS INC., a sample was set in accordance with the description of MIL-DTL-43511D, Section 4.4.5 and Figure 4, and the observed optical distortion was photographed with a digital still camera (Panasonic LUMIX, DMC-TZ10) (exposure: 1/5, ISO sensitivity: 100, F value: 6.3).
The Model E Destination Tester is comprised of the following four components as described above, which can be moved in a straight line on a 24 inch (approximately 60 cm) rail.
a) Optical distortion image acquisition unit b) Lens c) Sample holder d) Mirror In this embodiment, the distance between a) and b) was 199 mm. This distance can be determined from the focal length of the sample. At this time, 14 bright lines were visible in a). In this embodiment, b), c) and d) were measured in a connected state. The subject was oriented so that the side with less spherical aberration was facing a).

a) The image captured by the optical distortion image acquisition unit is quantified by an image discrimination device to objectively evaluate the optical distortion. In this embodiment, first, the passed and failed products described in MIL-DTL-43511D were measured. Specifically, the image was read using Keyence Corporation's image discrimination software IV3-CP50, and the widths of adjacent bright lines (slit spacing) in the image were measured at three points at the top, middle, and bottom of each spacing. The difference between the maximum and minimum widths for each measured spacing was quantified as the optical distortion in this embodiment, and in the case of a polarizing laminate, a slit spacing of less than 1.05 mm was considered to be passed. The results are shown in Figure 4.

In Figure 4, the difference between the maximum and minimum values for each slit spacing (white lines) was calculated, and the value in the table was the largest difference. Note that since the slit spacing could not be measured in the areas where the light lines were stuck together (part of the first and third failed sheets), the slit spacing was calculated in the other areas.

In addition, it was confirmed from the polarizing laminates that passed the above method that it is preferable to judge the pass/fail status of the polycarbonate protective layer when the slit spacing is 0.75 mm or less. Note that the measurements were taken at 12 intervals for the specimens used for the polarizing laminates and protective layers of the present invention.

e) Polarization Leakage A curved polarizing plate obtained by heat bending a polarizing laminate was stacked on a plane polarizing plate arranged so that their polarization axes were perpendicular to each other. When fluorescent light was shone on the plane polarizing plate side, the film was visually observed to see whether any light was transmitted.

Example 2
The same procedure as in Example 1 was carried out except that the protective layer on one side was changed to a polycarbonate protective film having a thickness of 200 μm, and the stretching process was omitted.

Example 3
The same procedure as in Example 1 was repeated, except that the protective layers on both sides were made of a polycarbonate protective film having a thickness of 320 μm, which was produced at a stretch ratio of 1.7 times using an apparatus capable of continuously performing processes from melt extrusion to stretching of polycarbonate resin.

Example 4
The same procedure as in Example 1 was repeated, except that the protective layer on one side was a 320 μm thick polycarbonate protective film produced at a stretching ratio of 1.7 times using an apparatus capable of continuously performing processes from melt extrusion to stretching of polycarbonate resin, and the other protective layer was changed to a 280 μm thick polycarbonate protective film without the stretching process.

Example 5
The same procedure as in Example 1 was repeated except that the protective layer on one side was a 200 μm thick polycarbonate protective film, excluding the stretching step, and the thickness of the cured adhesive layer was changed to 5 μm.

Example 6
The same procedure as in Example 1 was repeated, except that the protective layer on one side was a 700 μm thick polycarbonate protective film produced at a stretching ratio of 1.3 times using an apparatus capable of continuously performing processes from melt extrusion to stretching of polycarbonate resin, and the other protective layer was changed to a 700 μm thick polycarbonate protective film without the stretching process.

(Example 7)
The protective layer on one side was a polyamide protective film having a thickness of 275 μm, which was prepared by a melt extrusion method in which an amorphous transparent polyamide resin consisting of an aliphatic and an alicyclic group was melt extruded, cooled by a cooling roll, and then wound up by a winding machine. The other protective layer was a polyamide protective film having a thickness of 200 μm, which was prepared by cutting the polyamide protective film obtained above into a 40 cm square, fixing the four sides with clamps, holding it at Tg (midpoint in DSC measurement) temperature for 20 minutes, stretching it in only one axial direction at a stretch ratio of 1.5 times and a stretching speed of 2 m/min, and cooling it at room temperature for 30 minutes while maintaining the tension after stretching. A polarizing laminate was prepared in the same manner as in Example 1, except that the other protective layer was a polyamide protective film having a thickness of 200 μm.
The punching process was the same as in Example 1, and the hot bending process also used a continuous hot bending device in the same manner as in Example 1. When a transparent plastic sheet made of polyamide resin was used as the protective layer, the ambient temperature was 136°C, the female mold had a partial spherical surface equivalent to 8R (radius of approximately 65.6 mm) with a surface temperature of 135°C, the pressing time with the silicone rubber male mold was 4 seconds, and the adsorption to the female mold was performed for 5 minutes in an atmosphere with a blown hot air temperature of 166°C.
The protective film of the heat-bent punched piece produced above was peeled off, and the piece was mounted in a mold cavity of an injection molding machine, and injection molding was performed using molten polyamide resin (product name: Grilamid, TR90, manufactured by EMS-CHEMIE). The injection molding conditions were a resin temperature of 280°C, injection filling speed of 30 mm/s, holding pressure of 30 MPa, mold temperature of 80°C, cooling time of 30 seconds, and injection cycle of 70 seconds, and injection was performed to obtain an injected lens having a thickness of 2.2 mm.

(Comparative Example 1)
The same procedure as in Example 1 was repeated, except that the protective layers on both sides were made of a polycarbonate protective film having a thickness of 320 μm, which was produced at a stretch ratio of 2 times using an apparatus capable of continuously performing processes from melt extrusion to stretching of polycarbonate resin.

(Comparative Example 2)
The same procedure as in Example 1 was repeated, except that the protective layer on one side was a 400 μm thick polycarbonate protective film produced at a stretching ratio of 1.8 times using an apparatus capable of continuously performing processes from melt extrusion to stretching of polycarbonate resin, and the other protective layer was changed to a 300 μm thick polycarbonate protective film without the stretching process.

(Comparative Example 3)
The same procedure as in Example 1 was repeated, except that the protective layers on both sides were changed to polycarbonate protective films having a thickness of 700 μm, which were produced at a stretch ratio of 1.5 times using an apparatus capable of continuously performing processes from melt extrusion to stretching of polycarbonate resin.

(Comparative Example 4)
The same procedure as in Example 1 was repeated, except that the thickness of the cured adhesive layer was changed to 40 μm.

(Comparative Example 5)
The same procedure as in Example 1 was repeated, except that the protective layer on one side was a 320 μm thick polycarbonate protective film produced at a stretching ratio of 1.7 times using an apparatus capable of continuously performing processes from melt extrusion to stretching of polycarbonate resin, and the other protective layer was changed to a 100 μm thick polycarbonate protective film without the stretching process.

(Comparative Example 6)
The same procedure as in Example 1 was repeated, except that the protective layers on both sides were changed to polycarbonate protective films having a thickness of 200 μm, and the stretching process was omitted.

(Comparative Example 7)
The same procedure as in Example 7 was repeated except that the stretching speed was 4 m/min and the protective layers on both sides were changed to polyamide protective films having a thickness of 320 μm.

The evaluation results of each of the Examples and Comparative Examples prepared as described above are shown in Table 1 below.

Table 1

As shown in Table 1, it has become clear that the optical distortion of the protective layer affects the optical distortion of the polarizing laminate. Specifically, it has become clear that in a polarizing laminate that is judged to be an acceptable product by the method of the present invention, when the slit spacing of the protective layer is greater than 0.75 mm, the slit spacing of the polarizing laminate is greater than 1.05 mm, and the visual optical distortion is also equivalent to a failure. It has become clear that the optical distortion of this protective layer tends to worsen when the retardation variation is large.

In addition to the optical distortion of the protective layer, it was also found that the optical distortion of the polarizing laminate worsened when the thickness of the adhesive layer was increased to 40 μm or more in Comparative Example 4, and when the thickness of the protective layer was decreased to 100 μm or less in Comparative Example 6.

According to the present invention, it is possible to efficiently select a polarizing laminate having a uniform slit width, and therefore it is possible to easily and accurately provide a polarizing sheet having extremely little optical distortion equivalent to a so-called military grade.

Claims (4)

placing a test object on an optical tester that includes a diffraction grating;
acquiring an image of a bright line of a test object passing through a diffraction grating set in an optical tester;
determining a shape of one or more bright lines transmitted through the diffraction grating;
determining a degree of optical distortion of the object using the shape of the bright line;
16. A method for measuring optical distortion of a subject, comprising: The method for measuring the optical distortion of a specimen according to claim 1, wherein the specimen is any one of a polarizing sheet formed by placing a transparent plastic sheet as a protective layer on a polarizing film made of a uniaxially stretched polyvinyl alcohol resin film via an adhesive layer, a punched lens formed by punching a polarizing sheet into a predetermined shape, a heat-bent lens formed by heat-bending a punched product, an injection-molded lens formed by injection-molding a molten resin onto the concave surface of a heat-bent product, and a transparent plastic sheet used as a protective layer for a polarizing sheet. The method for measuring optical distortion of a subject according to claim 1, further comprising a step of quantifying the shape of the bright line in the step of determining the shape of the bright line. The method for measuring optical distortion of an object according to claim 3 , further comprising the step of determining a minimum value and a maximum value of a width of the acquired bright line image in the step of quantifying the shape of the bright line.

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