JP5429777B2 - Polarizer - Google Patents

Description

  The present invention relates to a polarizing plate in which pressure-sensitive adhesive layers are laminated on both surfaces of a polarizing film made of a polyvinyl alcohol-based resin, and a protective film is laminated on at least one surface thereof.

  A polarizing plate is widely used as a polarized light supplying element and a polarized light detecting element in a liquid crystal display device. Conventionally, a polarizing film made of a polyvinyl alcohol resin and a transparent protective film made of triacetyl cellulose are used as such polarizing plates. In recent years, mobile devices such as notebook personal computers and mobile phones for liquid crystal display devices have been used. Thinner and lighter weights are being demanded with the development of equipment and even with large televisions. Moreover, since the place of use is wide due to portability, improvement in durability is also demanded at the same time.

  The polarizing film is generally produced by impregnating a polyvinyl alcohol resin with a dichroic dye typified by iodine and the like and uniaxially stretching at a high magnification. For this reason, when a polarizing film is exposed to a dry heat environment, a large dimensional change with shrinkage occurs. For example, when a dimensional change rate before and after heating at 100 ° C. for 2 hours is measured for a polarizing film as described in JP-A-6-109922 (Patent Document 1), a large shrinkage exceeding 10% is observed. Is done. For this reason, the dimensional change of a polarizing film is usually reduced by laminating | stacking a transparent protective film on both surfaces of a polarizing film via an adhesive layer etc., and manufacturing a polarizing plate. Patent Document 1 describes the dimensional change rate before and after heating at 100 ° C. for 2 hours for a polarizing plate in which triacetyl cellulose films are laminated on both sides of a polarizing film, but shrinkage is 2% or less. It can be seen that the contraction is suppressed.

  Japanese Patent Laid-Open No. 6-59123 (Patent Document 2) describes a dimensional change rate before and after heating a polarizing plate in which a triacetyl cellulose film is laminated on both sides of a polarizing film at 80 ° C. for 4 hours. However, shrinkage | contraction is 0.3% or less, and it turns out that shrinkage | contraction is suppressed.

  However, in recent years, there has been a demand for a polarizing plate in which a transparent protective film is laminated only on one surface of a polarizing film in order to reduce the thickness and weight. When such a polarizing plate is exposed to a dry high-temperature environment. , The shrinkage of the polarizing film could not be suppressed, and there was a tendency for defects to occur. For this reason, an adhesive layer is provided on the polarizing film surface of the polarizing plate in which the transparent protective film is laminated only on one surface of the polarizing film, and the adhesive layer is bonded to the liquid crystal cell, or the When another optical film such as a retardation film is bonded to the pressure-sensitive adhesive layer and then exposed to a dry high temperature environment with the pressure-sensitive adhesive bonded to the liquid crystal cell, the adhesive at the end of the polarizing plate peels off. In some cases, the end of the polarizing plate rises and the screen display is distorted. These defects were considered to be caused by only one surface of the polarizing film being restrained by the protective film.

Then, the present inventors examined whether a malfunction could be solved by forming an adhesive layer on both surfaces of a polarizing film. An example in which a protective film is laminated by forming an adhesive layer on both surfaces of a polarizing film is shown in, for example, Japanese Patent Application Laid-Open No. 5-212828 (Patent Document 3), but requires sufficient thermocompression bonding. There was a problem that the production was complicated. JP-A-9-105814 (Patent Document 4) discloses an optical film having an adhesive layer having a relaxation elastic modulus of 15 × 10 ⁵ dyn / cm ² or less (0.15 MPa or less) at a relaxation time of 10 ⁵ seconds. The liquid crystal cell using a polarizing plate formed by laminating such a pressure-sensitive adhesive on both sides of the polarizing film is peeled off when exposed to a heat-resistant environment. Or the polarizing film contracts and the end of the polarizing plate floats.

On the other hand, a pressure-sensitive adhesive having an increased storage elastic modulus is also known. For example, JP-A-2006-235568 (Patent Document 5) discloses a pressure-sensitive adhesive for a polarizing plate having a storage elastic modulus at 23 ° C. of 0.3 MPa or more. JP-A 2006-309114 (Patent Document 6) discloses an adhesive material containing an acrylic copolymer and an acrylic copolymer having an active energy ray polymerizable group in the side chain. A pressure-sensitive adhesive for polarizing plates is disclosed in which an active energy ray is irradiated and a storage elastic modulus at 23 ° C. is 0.3 to 10 MPa. In these documents, such a storage layer is used as an adhesive for adhering a three-layer polarizing plate in which triacetyl cellulose is bonded to both surfaces of a polyvinyl alcohol polarizing film (polarizer) to an optical component such as a liquid crystal cell. It has been proposed to use a material having a high elastic modulus.
JP-A-6-109922 JP-A-6-59123 Japanese Patent Laid-Open No. 5-212828 JP-A-9-105814 JP 2006-235568 A JP 2006-309114 A

  This invention was made in order to solve the said subject when an adhesive layer was formed on both surfaces of a polarizing film, Comprising: The objective is the case where it pastes to a liquid crystal cell and it is set as a liquid crystal panel Another object of the present invention is to provide a polarizing plate that does not cause problems such as the end of the polarizing plate floating even when exposed to various environmental conditions.

  In the polarizing plate of the present invention, a pressure-sensitive adhesive layer is laminated on both sides of a polarizing film made of a polyvinyl alcohol-based resin, and a protective film is further laminated on at least one surface of the polarizing film via the pressure-sensitive adhesive layer, and is bonded to a liquid crystal cell. Among the pressure-sensitive adhesive layers, the pressure-sensitive adhesive layer on the side close to the liquid crystal cell has a storage elastic modulus of 0.15 MPa or more and 1 MPa or less in a temperature range of 23 ° C. or more and 80 ° C. or less. And the peel strength for the polarizing film is 11 N / 25 mm or more.

  Here, the pressure-sensitive adhesive layer on the side close to the liquid crystal cell preferably has a thickness of 1 μm or more and 10 μm or less.

  Moreover, according to this invention, the liquid crystal display device formed by arrange | positioning said polarizing plate to at least one side of a liquid crystal cell is also provided.

  Since the polarizing plate of the present invention has the above-described configuration, a transparent protective film is laminated on one side of a polarizing film made of a polyvinyl alcohol resin via an adhesive layer, and an adhesive layer is provided on the other side. Compared to conventional polarizing plates, there are no problems such as the end of the polarizing plate floating even when exposed to various environmental conditions in the state of being bonded to a liquid crystal cell to form a liquid crystal panel or liquid crystal display device. It will be excellent in durability.

<Polarizing plate>
FIG. 1 is a schematic cross-sectional view showing an example of a layer structure of a polarizing plate according to the present invention. As shown in this figure, the polarizing plate 10 of the present invention has a first pressure-sensitive adhesive layer 1 and a second pressure-sensitive adhesive layer 3 laminated on both surfaces of a polarizing film 2 made of polyvinyl alcohol resin, respectively. The first protective film 5 and / or the second protective film 6 are laminated on at least one surface via the pressure-sensitive adhesive layer. As for the protective films 5 and 6, only one may be arrange | positioned and both may be arrange | positioned. Such a polarizing plate constitutes a liquid crystal display device by being bonded to a liquid crystal cell, for example. In the present invention, the first pressure-sensitive adhesive layer 1 that is close to the liquid crystal cell when bonded to the liquid crystal cell has a storage elastic modulus of 0.15 MPa to 1 MPa in a temperature range of 23 ° C. to 80 ° C. And the peel strength with respect to the polarizing film is 11 N / 25 mm or more.

<Polarizing film>
The polarizing film used in the present invention is made of a polyvinyl alcohol-based resin. Specifically, the film made of such a polyvinyl alcohol-based resin (also simply referred to as a polyvinyl alcohol-based resin film) is uniaxially stretched and a dichroic dye. The dichroic dye is dyed and adsorbed and oriented.

  The polyvinyl alcohol-based resin constituting such a polarizing film is usually obtained by saponifying a polyvinyl acetate-based resin. The saponification degree of the polyvinyl alcohol-based resin is usually 85 mol% or more, preferably 90 mol% or more, and more preferably 99 to 100 mol%. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymers. Etc. Examples of other monomers copolymerizable with vinyl acetate include olefins including ethylene, unsaturated carboxylic acids, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol-based resin is usually in the range of 1000 to 10000, preferably in the range of 1500 to 5000.

  These polyvinyl alcohol resins may be modified. For example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like modified with aldehydes may be used. Usually, as a starting material for producing a polarizing film, an unstretched film of a polyvinyl alcohol-based resin film having a thickness of 20 to 100 μm, preferably 30 to 80 μm is used. Industrially, the practical width of the film is 1500 to 4000 mm. A polarizing film can be obtained by treating this unstretched film in the order of swelling treatment, dyeing treatment, boric acid treatment, and water washing treatment, uniaxially stretching in the steps up to boric acid treatment, and finally drying. Thus, the thickness of the polarizing film obtained is 5-50 micrometers, for example.

  There are roughly two methods for producing a polarizing film. In the first method, a polyvinyl alcohol-based resin film is uniaxially stretched in air or an inert gas, followed by solution treatment in the order of a swelling treatment step, a dyeing treatment step, a boric acid treatment step and a water washing treatment step, and finally drying. How to do it. In the second method, the unstretched polyvinyl alcohol resin film is subjected to a swelling treatment with an aqueous solution, followed by a solution treatment in the order of a dyeing treatment step, a boric acid treatment step, and a water washing treatment step. In this process, wet uniaxial stretching is performed, and finally drying is performed.

  In any method, the uniaxial stretching may be performed in one step or in two or more steps, but is preferably performed in a plurality of steps. As a stretching method, a known method can be adopted. For example, a stretch between rolls in which stretching is performed with a peripheral speed difference between two nip rolls that transport a film, a hot roll stretching method (for example, described in Japanese Patent No. 2731813). And the tenter stretching method. The order of the steps is basically as described above, but there are no restrictions on the number of treatment baths, treatment conditions, and the like. Moreover, you may add the process which is not described in the said 1st and 2nd method for another objective. Examples of such processes include immersion treatment with an aqueous iodide solution not containing boric acid (iodide treatment) or immersion treatment with an aqueous solution containing zinc chloride not containing boric acid (zinc treatment) after boric acid treatment. Can be mentioned.

  The swelling treatment step is performed for the purpose of removing foreign matter from the film surface, removing the plasticizer in the film, imparting easy dyeability in the next step, and plasticizing the film. The processing conditions are determined within a range in which these objects can be achieved, and in a range in which problems such as extreme dissolution and devitrification of the base film do not occur. When the film previously stretched in the gas is swollen, the film is immersed in an aqueous solution at 20 to 70 ° C., preferably 30 to 60 ° C., for example. The immersion time of the film is 30 to 300 seconds, preferably 60 to 240 seconds. In order to swell the unstretched raw film from the beginning, the film is immersed in an aqueous solution of 10 to 50 ° C., preferably 20 to 40 ° C., for example. The immersion time of the film is 30 to 300 seconds, preferably 60 to 240 seconds.

  In the swelling process, since the film is likely to swell in the width direction and wrinkles into the film, a known wide roll (expander roll), spiral roll, crown roll, cross guider, bend bar, tenter clip, etc. It is preferable to convey the film while removing the wrinkles of the film with a widening device. For the purpose of stabilizing the film transport in the bath, the water flow in the swelling bath is controlled by an underwater shower, the EPC (Edge Position Control device: a device that detects the edge of the film and prevents the film from meandering), etc. It is also useful to use together. In this step, since the film swells and expands in the film transport direction, it is preferable to take measures such as controlling the speed of the transport roll before and after the treatment tank in order to eliminate the sag of the film in the transport direction. In addition to pure water, the swelling treatment bath used is boric acid (for example, described in JP-A-10-153709), chloride (for example, described in JP-A-06-281816), inorganic acid, inorganic salt, An aqueous solution to which a water-soluble organic solvent, alcohols and the like are added in the range of 0.01 to 0.1% by mass can also be used.

  The dyeing process with the dichroic dye is performed for the purpose of adsorbing and orienting the dichroic dye on the film. The processing conditions are determined within a range in which these objects can be achieved, and in a range in which problems such as extreme dissolution and devitrification of the base film do not occur. When iodine is used as the dichroic dye, for example, iodine / potassium iodide / water = 0.003 to 0.2 / 0.1 in a mass ratio under a temperature condition of 10 to 45 ° C., preferably 20 to 35 ° C. An immersion treatment is performed for 30 to 600 seconds, preferably 60 to 300 seconds, using an aqueous solution having a concentration of 10/100. Instead of potassium iodide, other iodides such as zinc iodide may be used. Other iodides may be used in combination with potassium iodide. Furthermore, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc. may coexist. When boric acid is added, it is distinguished from the following boric acid treatment in that it contains iodine. Any dye containing 0.003 parts by mass or more of iodine with respect to 100 parts by mass of water can be regarded as a dyeing tank.

  When a water-soluble dichroic dye is used as the dichroic dye, for example, dichroic dye / water = 0.001 to 0.1 / by mass ratio under a temperature condition of 20 to 80 ° C., preferably 30 to 70 ° C. A 100-concentration aqueous solution is used for immersion treatment for 30 to 600 seconds, preferably 60 to 300 seconds. The aqueous solution of the dichroic dye to be used may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant or the like. The dichroic dye may be used alone, or two or more dichroic dyes may be used in combination.

  As described above, the film may be stretched in a dyeing tank. Stretching is performed by a method of giving a peripheral speed difference between the nip rolls before and after the dyeing tank. Similarly to the swelling treatment step, a widening roll (expander roll), a spiral roll, a crown roll, a cross guider, a bend bar and the like can be installed in the dyeing bath and / or at the bath entrance / exit.

  The boric acid treatment is performed by immersing a polyvinyl alcohol resin film dyed with a dichroic dye in an aqueous solution containing 1 to 10 parts by mass of boric acid with respect to 100 parts by mass of water. When the dichroic dye is iodine, it is preferable to contain 1 to 30 parts by mass of iodide. Examples of iodide include potassium iodide and zinc iodide. Further, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may coexist.

  The boric acid treatment is carried out for water resistance by crosslinking or hue adjustment (for example, to prevent bluish tint). When boric acid treatment is performed for water resistance by cross-linking, a cross-linking agent such as glyoxal or glutaraldehyde other than boric acid or together with boric acid can be used as necessary. In addition, the boric acid treatment for water resistance may be referred to by names such as water resistance treatment, crosslinking treatment, and immobilization treatment. In addition, boric acid treatment for hue adjustment may be referred to by a name such as complementary color treatment or re-dyeing treatment.

  This boric acid treatment is performed by appropriately changing the concentrations of boric acid and iodide and the temperature of the treatment bath according to the purpose. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment are not particularly distinguished, but can be carried out under the following conditions. When the raw film is subjected to swelling treatment, dyeing treatment, boric acid treatment, and boric acid treatment is aimed at water resistance by crosslinking, boric acid is added in an amount of 3 to 10 parts by mass with respect to 100 parts by mass of water. A boric acid treatment bath containing 1 to 20 parts by mass of iodide is used, and it is usually carried out at a temperature of 50 to 70 ° C, preferably 55 to 65 ° C. The immersion time is 90 to 300 seconds. In addition, when performing the dyeing | staining process and a boric-acid process for the film extended | stretched previously, the temperature of a boric-acid processing bath is 50-85 degreeC normally, Preferably it is 55-80 degreeC.

  You may make it perform the boric-acid process for hue adjustment after the boric-acid process for water resistance. For example, when the dichroic dye is iodine, a boric acid treatment bath containing 1 to 5 parts by weight of boric acid and 3 to 30 parts by weight of iodide for 100 parts by weight of water is used for this purpose. Usually, it is carried out at a temperature of 10 to 45 ° C. The immersion time is usually 3 to 300 seconds, preferably 10 to 240 seconds. The subsequent boric acid treatment for adjusting the hue is usually performed at a lower boric acid concentration, a higher iodide concentration, and a lower temperature than the boric acid treatment for water resistance.

  When the dichroic dye is iodine, a treatment with an iodide solution may be further performed to adjust the hue. For example, the treatment bath which has 0.5-5 mass parts of potassium iodide with respect to 100 mass parts of water is used, and it is normally performed at the temperature of 5-40 degreeC. The immersion time is usually 3 to 300 seconds, preferably 5 to 120 seconds.

  These boric acid treatments may consist of a plurality of steps and are usually carried out in 2 to 5 steps. In this case, the aqueous solution composition and temperature of each boric acid treatment tank to be used may be the same or different within the above-described range. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment may be performed in a plurality of steps, respectively.

  In the boric acid treatment step, the film may be stretched as in the dyeing treatment step. The final cumulative draw ratio is, for example, about 4 to 7 times, preferably 4.5 to 6.5 times. The cumulative stretching ratio here means how long the reference length in the length direction of the original film is in all the films after the completion of the stretching process. For example, it is 1 m in the original film. If the portion is 5 m in all the films after the stretching treatment, the cumulative stretching ratio at that time is 5 times. The cumulative draw ratio can also be expressed as a ratio of (length of polarizing film after manufacture) / (length of original film).

  After the boric acid treatment, a water washing treatment is performed. The water washing treatment is performed by, for example, immersing a boric acid-treated polyvinyl alcohol resin film for water resistance and / or hue adjustment in water, spraying water as a shower, or using both immersion and spraying. Done. The water temperature in the water washing treatment is usually 2 to 40 ° C., and the immersion time is 2 to 120 seconds.

  Here, in each step after the stretching treatment, tension control may be performed so that the tension of the film becomes substantially constant. Specifically, when stretching is completed in the dyeing process, tension control is performed in the subsequent boric acid treatment process and the water washing process. When stretching is completed in the previous process of the dyeing process, tension control is performed in subsequent processes including the dyeing process and the boric acid process. When the boric acid treatment step is composed of a plurality of boric acid treatment steps, the film is stretched in the boric acid treatment step from the first or the first to the second stage, and the next boric acid treatment step after the boric acid treatment step in which the stretching treatment has been performed. Tension control is performed in each step from the acid treatment step to the water washing step, or the film is stretched in the boric acid treatment step from the first to the third stage, and the boric acid next to the boric acid treatment step in which the stretching treatment is performed. Although it is preferable to perform tension control in each process from the treatment process to the water washing process, industrially, the film was stretched in the boric acid treatment process from the first or first to the second stage, and the stretching process was performed. It is more preferable to perform tension control in each step from the boric acid treatment step next to the boric acid treatment step to the water washing step. In addition, when performing the above-described iodide treatment or zinc treatment after the boric acid treatment, tension control can also be performed for these steps.

  The tension in each step from the swelling treatment to the water washing treatment may be the same or different. The tension on the film in the tension control is not particularly limited, and is 150 to 2000 N per unit width. / M, preferably within the range of 600 to 1500 N / m. If the tension is less than 150 N / m, the film tends to be wrinkled. On the other hand, when the tension exceeds 2000 N / m, problems such as film breakage and life reduction due to bearing wear occur. The tension per unit width is calculated from the film width near the entrance of the process and the tension value of the tension detector. In addition, when tension control is performed, it may be inevitably slightly stretched or shrunk, but in the present invention, this is not included in the stretching process.

  At the end of the polarizing film manufacturing process, a drying process is performed. The drying process is preferably performed in a large number of stages by changing the tension little by little, but is usually performed in two or three stages due to restrictions on equipment. When performed in two stages, the tension in the front stage is preferably set in the range of 600 to 1500 N / m, and the tension in the rear stage is preferably set in the range of 250 to 1200 N / m. When the tension becomes too large, the film breaks more, and when it becomes too small, the generation of wrinkles increases, which is not preferable. Moreover, it is preferable to set the drying temperature of a front | former stage from the range of 30-90 degreeC, and the drying temperature of a back | latter stage from the range of 50-100 degreeC. If the temperature is too high, the film will be ruptured and the optical properties will be deteriorated. If the temperature is too low, streaks will increase, which is not preferable. The drying treatment temperature can be 60 to 600 seconds, for example, and the drying time in each stage may be the same or different. If the time is too long, it is not preferable in terms of productivity, and if the time is too short, drying is insufficient, which is not preferable.

  The dimensional change rate of the polarizing film thus obtained is 2.7% or less, preferably 1.5% or less, more preferably 1.0% or less. In addition, the dimensional change rate of the polarizing film is a direction (TD direction) perpendicular to the stretching axis direction of the test piece having a size of 100 mm × 100 mm so that one side of the test piece is parallel to the stretching axis direction of the polarizing film. ) And the dimension B in the TD direction after the test piece is held for 96 hours in a dry heat environment at 85 ° C.

Dimensional change rate (%) = (A−B) / A × 100
A polarizing film having a dimensional change rate within the preferred range described above can be obtained, for example, by controlling the drying temperature and / or drying time of the polarizing film.

  Further, the polarizing film obtained through the polarizing film preparation step is not particularly limited with respect to the moisture content, but is preferably in the range of 3 to 14% by mass, more preferably in the range of 3 to 10% by mass, in particular. Preferably it exists in the range of 3-8 mass%. When the moisture content of the polarizing film is less than 3% by mass, handling is difficult because the polarizing film is brittle and easily tears along the stretching direction, and when the moisture content of the polarizing film exceeds 14% by mass. May cause the polarizing film to easily shrink in a dry heat environment. In addition, the moisture content of a polarizing film can be computed from the mass change before and behind hold | maintaining, for example at 105 degreeC dry heat for 1 hour. A polarizing film having a moisture content within the above-described preferred range can be obtained, for example, by controlling the drying temperature and / or drying time of the polarizing film.

  In this way, the polyvinyl alcohol resin film is subjected to uniaxial stretching, dyeing treatment with a dichroic dye, and boric acid treatment to obtain a polarizing film made of the polyvinyl alcohol resin. The thickness of this polarizing film is usually in the range of 5 μm or more and 50 μm or less.

<Adhesive layer>
In the present invention, the pressure-sensitive adhesive layers (first pressure-sensitive adhesive layer 1 and second pressure-sensitive adhesive layer 3) are laminated and formed on both surfaces of the polarizing film 2 made of the polyvinyl alcohol resin manufactured by the above-described method. And the 1st adhesive layer 1 which becomes the side close | similar to the liquid crystal cell 20 when bonding to the liquid crystal cell 20 has a storage elastic modulus of 0.15 MPa or more and 1 MPa or less in the temperature range of 23 degreeC or more and 80 degrees C or less. It is characterized by that. If this storage elastic modulus is less than 0.15 MPa, the pressure-sensitive adhesive layer is too soft, and it becomes difficult to suppress the shrinkage of the polarizing film that occurs when the polarizing film is exposed to a heat-resistant environment. On the other hand, when the pressure exceeds 1 MPa, a polarizing plate (with a pressure-sensitive adhesive layer laminated on both sides of the polarizing film and a protective film laminated on at least one side of the polarizing film via the pressure-sensitive adhesive layer) is attached to the liquid crystal cell. When exposed to a heat-resistant environment, a deformed state that rises at the end of the polarizing plate tends to be easily observed. When the pressure-sensitive adhesive layer having such characteristics is used as the first pressure-sensitive adhesive layer 1 on the side close to the liquid crystal cell when bonded to the liquid crystal cell, the shrinkage of the polarizing film is suppressed, and the polarizing plate edge It is also possible to effectively suppress the swell phenomenon of the part.

  Such an adhesive layer is formed using various adhesives conventionally used for liquid crystal display devices, such as acrylic, rubber, urethane, silicone, and polyvinyl ether adhesives. Can do. In addition, energy ray curable adhesives and thermosetting adhesives may be used. Among them, adhesives based on acrylic resins having excellent transparency, weather resistance, heat resistance, etc. (hereinafter referred to as “acrylic adhesives”). (Referred to as “agent”). The pressure-sensitive adhesive is also called a pressure-sensitive adhesive, and it adheres to the surface of other substances simply by pressing it, and when it is peeled off from the adherend surface, it leaves almost no trace as long as it has strength. It is a viscoelastic body that can be removed without any problems.

  Acrylic adhesive is not particularly limited, but (meth) acrylic such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate. An acid ester base polymer or a copolymer base polymer using two or more of these (meth) acrylic acid esters is preferably used. Furthermore, polar monomers are copolymerized in these base polymers. Examples of polar monomers include (meth) acrylic acid, 2-hydroxypropyl (meth) acrylate, hydroxyethyl (meth) acrylate, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, glycidyl (meth) And monomers having a functional group such as a carboxyl group, a hydroxyl group, an amide group, an amino group, and an epoxy group, such as acrylate.

  These acrylic pressure-sensitive adhesives can of course be used alone, but usually a crosslinking agent is used in combination. Crosslinking agents include divalent or polyvalent metal salts that form carboxylic acid metal salts with carboxyl groups, polyamine compounds that form amide bonds with carboxyl groups Examples thereof include polyepoxy compounds and polyol compounds that form an ester bond with a carboxyl group, and polyisocyanate compounds that form an amide bond with a carboxyl group. Of these, polyisocyanate compounds are widely used as organic crosslinking agents.

  The energy ray curable adhesive has the property of being cured by irradiation with energy rays such as ultraviolet rays and electron beams, and has adhesiveness even before irradiation with energy rays to adhere to an adherend such as a film. It is a pressure-sensitive adhesive that has the property of being adhered and cured by irradiation with energy rays to adjust the adhesion. As the energy ray curable adhesive, it is particularly preferable to use an ultraviolet curable adhesive. The energy beam curable pressure-sensitive adhesive generally comprises an acrylic pressure-sensitive adhesive and an energy beam polymerizable compound as main components. Usually, a crosslinking agent is further blended, and if necessary, a photopolymerization initiator and a photosensitizer can be blended.

The pressure-sensitive adhesive layer used in a normal image display device or an optical film therefor has a storage elastic modulus of about 0.1 MPa at most, and compared with that, the storage of the first pressure-sensitive adhesive layer used in the present invention. The elastic modulus is a remarkably high value of 0.15 MPa to 1 MPa. Here, the storage elastic modulus “0.15 MPa or more and 1 MPa or less in a temperature range of 23 ° C. or higher and 80 ° C. or lower” means that the storage elastic modulus takes a value in the above range at any temperature within this range. . Since the storage elastic modulus usually decreases gradually as the temperature rises, if both the storage elastic modulus at 23 ° C. and 80 ° C. are within the above range, the storage elastic modulus in the above range is exhibited at the temperature in this range. You can see. When the storage elastic modulus at 80 ° C. is below 0.15 MPa, after polarization-board processing, and it stuck to the liquid crystal cell, when exposed to heat environment, the amount of shrinkage of the polarizing film is increased. On the other hand, when the storage elastic modulus at 23 ° C. exceeds 1 MPa, after forming into a polarizing plate, it is bonded to a liquid crystal cell and exposed to a heat resistant environment, or between the polarizing film and the protective film, or between the polarizing plate and the liquid crystal cell. May cause problems such as peeling or generation of bubbles.

  In order to obtain a pressure-sensitive adhesive layer having a storage elastic modulus of 0.15 MPa or higher and 1 MPa or lower in a temperature range of 23 ° C. or higher and 80 ° C. or lower, for example, an ordinary pressure-sensitive adhesive as described above, particularly an acrylic pressure-sensitive adhesive, Specifically, an energy ray-curable pressure-sensitive adhesive that is cured by irradiating energy rays after blending a urethane acrylate oligomer may be used. As the energy ray, ultraviolet rays are preferable. The sheet-like pressure-sensitive adhesive whose storage elastic modulus is increased, that is, hardened by blending an ultraviolet curing component is known per se and can be obtained from a pressure-sensitive adhesive manufacturer (for example, see also Patent Documents 5 and 6 above).

  Here, the storage elastic modulus (G ′) can be measured using a commercially available viscoelasticity measuring device. For example, a numerical value obtained by a torsional shear method using the following device is adopted.

Test piece: 8 mmΦ × 1 mm thick measuring instrument: DYNAMIC ANALYZER RDA II (manufactured by REOMETRIC)
Frequency: 1Hz
Distortion amount: 1%
In addition to the base polymer and the cross-linking agent described above, the pressure-sensitive adhesive layer defined in the present invention adjusts the pressure-sensitive adhesive force, cohesive force, viscosity, elastic modulus, glass transition temperature, and the like as necessary. For example, natural additives and synthetic resins, tackifying resins, antioxidants, ultraviolet absorbers, dyes, pigments, antifoaming agents, corrosion inhibitors, photopolymerization initiators, and other appropriate additives are blended. You can also. Further, a pressure-sensitive adhesive layer exhibiting light scattering properties can be formed by containing fine particles.

  In the present invention, the thickness of the first pressure-sensitive adhesive layer 1 on the side close to the liquid crystal cell is preferably 1 μm or more and 10 μm or less. When the thickness exceeds 10 μm, a polarizing plate (with a pressure-sensitive adhesive layer laminated on both sides of the polarizing film and a protective film laminated on at least one side of the polarizing film via the pressure-sensitive adhesive layer) is bonded to the liquid crystal cell. When exposed to a heat-resistant environment, problems such as appearance problems such as deformation of the polarizing plate surface in the form of insulator skin tend to occur. On the other hand, when the thickness is less than 1 μm, problems such as a decrease in adhesiveness and the occurrence of bubbles when the polarizing plate is bonded to the liquid crystal cell are likely to occur.

  The storage elastic modulus of the second pressure-sensitive adhesive layer 3 on the side far from the liquid crystal cell is not particularly limited, but this also shows a storage elastic modulus of 0.15 MPa or more in a temperature range of 23 ° C. or more and 80 ° C. or less. It is preferable. The second pressure-sensitive adhesive layer 3 may exhibit a higher storage elastic modulus than that of the first pressure-sensitive adhesive layer 1, for example, a storage elastic modulus of about 5 MPa. The thickness of the second pressure-sensitive adhesive layer 3 is not particularly limited, but it is preferable that the second pressure-sensitive adhesive layer 3 is thin as long as it exhibits a suitable pressure-sensitive adhesive force because it can suppress shrinkage of the polarizing film when exposed to a heat-resistant environment. The thickness is preferably 1 μm or more and 30 μm or less, and more preferably 1 μm or more and 20 μm or less.

  In the polarizing plate of the present invention, the first pressure-sensitive adhesive layer 1 on the side close to the liquid crystal cell 20 needs to have a peel strength with respect to the polarizing film 2 of 11 N / 25 mm or more. This peel strength is an index indicating the adhesion between the polarizing film 2 and the first pressure-sensitive adhesive layer 1. When the peel strength is less than 11 N / 25 mm, a polarizing plate (a pressure-sensitive adhesive layer is laminated on both surfaces of the polarizing film, and at least one surface thereof is used. When a protective film is laminated on the liquid crystal cell) and then exposed to a heat-resistant environment, the film peels off between the polarizing film and the pressure-sensitive adhesive layer, and bubbles are generated. Problems occur. If the peel strength is too high, rework (operation to re-apply the polarizing plate due to a bonding error or the like when the polarizing plate is attached to the liquid crystal cell) tends to be difficult, usually at 60 N / 25 mm or less. is there. The peel strength can be adjusted by the amount of the crosslinking agent blended in the pressure-sensitive adhesive. Specifically, the peel strength can be increased by increasing the blending amount of the crosslinking agent, and the peel strength can be decreased by decreasing the blending amount of the crosslinking agent.

  In the present invention, the peel strength is measured by laminating a pressure-sensitive adhesive layer on both sides of a polarizing film, cutting out a 25 mm wide test piece without using a protective film, and using an autograph manufactured by Shimadzu Corporation at a temperature of 23 ° C. In a 50% relative humidity environment, the peeling rate is 300 mm / min and the peeling angle is 180 °. Here, since it is difficult to maintain the shape of the pressure-sensitive adhesive layer alone, the pressure-sensitive adhesive layer is measured in a state where another film is laminated on the pressure-sensitive adhesive layer for which peel strength is to be obtained. To give a specific example, in a state where the pressure-sensitive adhesive layer is laminated on the polarizing film, a plastic film is attached to the pressure-sensitive adhesive layer for which peel strength is to be obtained, and the other pressure-sensitive adhesive layer is attached to the glass. The strength when peeling the plastic film together with the pressure-sensitive adhesive layer is measured from the polarizing film as a test piece.

  In the method for producing a polarizing plate of the present invention, the method for laminating (forming) the pressure-sensitive adhesive layer on the polarizing film is not particularly limited. For example, each component described above is toluene or ethyl acetate. A pressure-sensitive adhesive composition dissolved or dispersed in an organic solvent is directly applied to the surface of the polarizing film and dried to form a pressure-sensitive adhesive layer, and then a separator that has been subjected to a release treatment such as silicone is laminated. Or after forming an adhesive layer on the separator, it may be transferred to a polarizing film and laminated. When using an energy ray curable pressure sensitive adhesive, apply a pressure sensitive adhesive composition containing an energy ray curable component such as urethane acrylate oligomer, and after drying, cure the cured component by irradiating energy rays. Let Moreover, when forming an adhesive layer in a polarizing film, you may perform an adhesion | attachment process, for example, a corona treatment, etc. to at least one of a polarizing film and an adhesive layer as needed. In addition, the surface of the formed pressure-sensitive adhesive layer is usually protected by a separator film that has been subjected to a release treatment, and the separator film is not laminated before a protective film described later or when the protective film is not laminated. It is peeled off before the polarizing plate is bonded to a liquid crystal cell or an optical film.

<Protective film>
As described above, the polarizing film provided with the pressure-sensitive adhesive layer on both sides has a protective film laminated on at least one side of the polarizing film via the pressure-sensitive adhesive layer. The protective film may be a non-oriented film of resin, or may be a film that is oriented to develop a retardation. For example, cycloolefin resin film, cellulose acetate resin film, polyethylene terephthalate, polyethylene naphthalate, polyester resin film such as polybutylene terephthalate, polycarbonate resin film, acrylic resin film, polypropylene film, etc. Mention may be made of more widely used films.

  The cycloolefin resin that can be used for the protective film in the polarizing plate of the present invention is, for example, a thermoplastic resin having a monomer unit composed of a cyclic olefin (cycloolefin) such as norbornene or a polycyclic norbornene monomer (heat It is also called a plastic cycloolefin resin. In the present invention, the cycloolefin resin may be a hydrogenated product of the above ring-opening polymer of cycloolefin or a ring-opening copolymer using two or more kinds of cycloolefin, and cycloolefin and chain olefin, It may be an addition polymer with an aromatic compound having a vinyl group. Those having a polar group introduced are also effective.

  When using a copolymer of a cycloolefin and a chain olefin or / and an aromatic compound having a vinyl group, examples of the chain olefin include ethylene and propylene, and examples of the aromatic compound having a vinyl group include Examples include styrene, α-methylstyrene, and nuclear alkyl-substituted styrene. In such a copolymer, the monomer unit composed of cycloolefin may be 50 mol% or less (preferably 15 to 50 mol%). In particular, when a terpolymer of a cycloolefin, a chain olefin, and an aromatic compound having a vinyl group is used, the amount of the monomer unit composed of cycloolefin can be made relatively small as described above. In such a terpolymer, the monomer unit composed of a chain olefin is usually 5 to 80 mol%, and the monomer unit composed of an aromatic compound having a vinyl group is usually 5 to 80 mol%.

  Cycloolefin resins are commercially available products such as Topas (manufactured by Ticona), Arton (manufactured by JSR), ZEONOR (manufactured by Nippon Zeon), ZEONEX (manufactured by Nippon Zeon Co., Ltd.). ) And Apel (Mitsui Chemicals) can be preferably used. When such a cycloolefin-based resin is formed into a film, a known method such as a solvent casting method or a melt extrusion method is appropriately used. In addition, for example, commercially available cycloolefin resin films such as Essina (manufactured by Sekisui Chemical Co., Ltd.), SCA40 (manufactured by Sekisui Chemical Co., Ltd.), Zeonoa Film (manufactured by Optes Co., Ltd.), etc. You may use goods.

  The cycloolefin resin film may be uniaxially stretched or biaxially stretched. By stretching, an arbitrary retardation value can be given to the cycloolefin-based resin film. Stretching is usually carried out continuously while unwinding the film roll, and is stretched in the heating furnace in the roll traveling direction, the direction perpendicular to the traveling direction, or both. As the temperature of the heating furnace, a range from the vicinity of the glass transition temperature of the cycloolefin resin to the glass transition temperature + 100 ° C. is usually employed. The draw ratio is usually 1.1 to 6 times, preferably 1.1 to 3.5 times.

  When the cycloolefin-based resin film is in a roll state, the films tend to adhere to each other and easily cause blocking. Therefore, the protective film is usually bonded to roll. In addition, since the cycloolefin resin film generally has poor surface activity, the surface to be bonded to the polarizing film is subjected to surface treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, and saponification treatment. Is preferred. Among these, plasma treatment and corona treatment that can be performed relatively easily are preferable.

  The cellulose acetate-based resin that can be used for the protective film is a cellulose acetate part or a complete acetate ester, and examples thereof include triacetyl cellulose, diacetyl cellulose, and cellulose acetate propionate. As such a cellulose ester resin film, an appropriate commercially available product, for example, Fujitac TD40UZ (manufactured by Fuji Film Co., Ltd.), KC4UY (manufactured by Konica Minolta Opto Co., Ltd.) or the like can be suitably used.

  Moreover, in the polarizing plate of this invention, the cellulose acetate type-resin film which provided the phase-difference characteristic as a protective film is also used suitably, WV BZ438 (made by FUJIFILM Corporation), KC4FR-1 (Konica Minolta Opt ( Etc.). Cellulose acetate is also called acetyl cellulose or cellulose acetate.

  The protective film provided with such retardation characteristics has both the characteristics as a protective film and the characteristics as a retardation film. However, in the case of using a film mainly having only an action as a retardation film, the protective film of the present invention is formed by laminating a film showing characteristics as a protective film and a film showing characteristics as a retardation film. You can also. As described above, the protective film of the present invention can be composed of only one film and can be a laminate of two or more films.

  On the other hand, in order to provide a phase difference, a cellulose acetate-based resin film may be stretched. Further, this cellulose acetate-based resin film is usually subjected to saponification treatment in order to improve the adhesiveness with the polarizing film. As the saponification treatment, a method of immersing in an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide can be employed.

  In addition, a reflective polarizing film that transmits certain types of polarized light and reflects polarized light that exhibits the opposite properties can be used as a protective film. Specifically, for example, a reflective polarizing film in which multiple layers of at least two kinds of polymer thin films are alternately laminated and the reflectance anisotropy due to the refractive index anisotropy is used can be mentioned. As such a reflective linearly polarizing film, for example, DBEF series sold by 3M Corporation (Sumitomo 3M Co., Ltd. in Japan) can be cited.

  The surface of the protective film may be subjected to a surface treatment such as a hard coat treatment, an antiglare treatment, an antireflection treatment, or an antistatic treatment depending on the application. Further, an optical layer such as a liquid crystal layer may be formed in order to improve the viewing angle characteristics. The method of performing these surface treatments and the method of forming the optical layer are not particularly limited, and known methods can be employed.

  When such a protective film is in a roll state, the films tend to adhere to each other and easily cause blocking. Therefore, the roll end portion is subjected to uneven processing, a ribbon is inserted into the end portion, or the protective film is attached. It is pasted and rolled.

  In the present invention, the thickness of the protective film is preferably thin, but if it is too thin, the strength is lowered and the processability is poor. On the other hand, when it is too thick, problems such as a decrease in transparency and a longer curing time after lamination occur. Accordingly, the appropriate thickness of the protective film used in the present invention is, for example, from 5 μm to 200 μm, preferably from 10 μm to 150 μm, more preferably from 20 μm to 100 μm.

<Production method and usage of polarizing plate>
The method of bonding the protective film or the retardation film to the pressure-sensitive adhesive layer formed on both surfaces of the polarizing film is not particularly limited, and the films may be stacked and bonded by a roll or the like. The roll used for bonding is preferably a combination of a rubber roll and a rubber roll or a combination of a rubber roll and a metal roll. Examples of the rubber type of the rubber roll include silicone rubber, butyl rubber, EPDM rubber, and nitrile rubber. Of these, silicone rubber is preferred from the viewpoint of durability. The rubber hardness of the rubber roll is a value measured in the A type of a spring type hardness test specified in JIS K 6301, and usually has a range of 20 to 90 degrees.

  A polarizing plate laminated with a protective film or a polarizing plate laminated with a retardation film can be attached to a liquid crystal cell to form a liquid crystal panel or a liquid crystal display device. For sticking to the liquid crystal cell, it is preferable to use an adhesive from the viewpoint of simplicity and prevention of optical distortion. The pressure-sensitive adhesive is not particularly limited, and for example, an acrylic polymer, a silicone polymer, polyester, polyurethane, polyether, or the like as a base polymer can be used. Among them, like acrylic adhesives, it has excellent optical transparency, retains appropriate wettability and cohesion, has excellent adhesion to substrates, and has weather resistance and heat resistance. However, it is preferable to select and use a material that does not cause peeling problems such as floating and peeling under the conditions of heating and humidification. The second pressure-sensitive adhesive layer 3 and the second protective film 6 are laminated in this order on one surface of the polarizing film 2, and the other surface of the polarizing film 2 is 0.15 MPa in a temperature range of 23 ° C. or higher and 80 ° C. or lower. When the polarizing plate of the present invention in which only the first pressure-sensitive adhesive layer 1 showing a storage elastic modulus of 1 MPa or less is laminated is bonded to the liquid crystal cell on the first pressure-sensitive adhesive layer 1 side, The adhesive layer 1 may be bonded to the liquid crystal cell as it is.

  The pressure-sensitive adhesive layer used for sticking to the liquid crystal cell is prepared by, for example, preparing a 10 to 40% by mass solution by dissolving or dispersing the pressure-sensitive adhesive composition in an organic solvent such as toluene or ethyl acetate. A method of coating directly on a protective film or retardation film of a plate, or a separator that has been subjected to a release treatment such as a silicone system in advance, and forming it on a protective film of a polarizing plate or a retardation film It can be formed by a method of transferring to the top. Although the thickness of an adhesive layer is determined according to the adhesive force etc., it is the range of 1 micrometer or more and 50 micrometers or less normally. In addition, when the formed adhesive layer is exposed on the surface, it is better to arrange a separator in order to prevent contamination. The same separator as described above is used as the separator.

  Moreover, the pressure-sensitive adhesive layer used for sticking to the liquid crystal cell may contain fine particles for imparting light scattering properties, if necessary, glass fiber, glass beads, resin beads, metal powder, and others. A filler made of an inorganic powder or the like, a pigment or a colorant, an antioxidant, an ultraviolet absorber, or the like may be contained. Examples of ultraviolet absorbers include salicylic acid ester compounds, benzophenone compounds, benzotriazole compounds, cyanoacrylate compounds, and nickel complex compounds.

  In addition, you may laminate | stack an optical film on the surface of the polarizing plate of this invention. As an example of the laminated optical film, a liquid crystal compound is coated on the surface of the base material, an oriented optical compensation film, a reflection that transmits a certain kind of polarized light and reflects a polarized light having the opposite property. Type polarizing film, retardation film made of polycarbonate-based resin, retardation film made of cyclic polyolefin-based resin, film with anti-glare function having a concavo-convex shape on the surface, film with anti-reflection function on the surface, reflective film having a reflection function on the surface And a transflective film having both a reflection function and a transmission function. Commercially available products corresponding to the optical compensation film in which a liquid crystal compound is coated on the substrate surface and oriented include WV film (manufactured by FUJIFILM Corporation), NH film (manufactured by Nippon Oil Corporation), NR Examples include films (manufactured by Nippon Oil Corporation). As a commercially available product corresponding to a reflective polarizing film that transmits certain types of polarized light and reflects polarized light that exhibits the opposite properties, for example, the DBEF series (manufactured by 3M, available in Japan from Sumitomo 3M Ltd.) ) And the like. Moreover, as a commercial item corresponding to the phase difference film which consists of cyclic polyolefin resin, for example, Arton Film (made by JSR Corporation), Essina (made by Sekisui Chemical Co., Ltd.), Zeonore Film (made by Optes Co., Ltd.) Etc.

  The polarizing plate produced according to the present invention usually has a form of a large roll material or sheet material, and in order to obtain a polarizing plate having a desired shape and transmission axis, it is cut with a sharp blade. It is cut (chip cut) with a tool. For this reason, in the polarizing plate chip obtained by cutting, since the polarizing film is exposed to the outside at the outer peripheral end, it is preferable to continuously cut the outer peripheral end surface by a fly-cut method or the like.

<Liquid crystal display device>
The liquid crystal display device of the present invention is obtained by disposing the polarizing plate produced as described above on at least one side of the liquid crystal cell via the pressure-sensitive adhesive layer as described above. FIG. 2 is a schematic cross-sectional view showing an example in which the polarizing plate of the present invention is applied to a liquid crystal cell, and FIG. 3 is a schematic cross-sectional view showing another example in that case. As shown in FIG. 2, the second pressure-sensitive adhesive layer 3 and the second protective film 6 are laminated in this order on one surface of the polarizing film 2, and the other surface of the polarizing film 2 has a temperature of 23 ° C. or higher and 80 ° C. or lower. A polarizing plate in which only the first pressure-sensitive adhesive layer 1 exhibiting a storage elastic modulus of 0.15 MPa or more and 1 MPa or less in the range can be bonded to the liquid crystal cell 20 on the first pressure-sensitive adhesive layer 1 side. . Moreover, as shown in FIG. 3, the 1st adhesive layer 1 and the 1st protective film 5 which show the storage elastic modulus of 0.15 MPa or more and 1 MPa or less in the temperature range of 23 degreeC or more and 80 degrees C or less on the single side | surface of the polarizing film 2 are shown. (For example, retardation film) are laminated in this order, and a polarizing plate in which the second adhesive layer 3 and the second protective film 6 are laminated in this order on the other surface of the polarizing film 2 It can also be laminated on the liquid crystal cell 20 on the protective film 5 side. In the case of the example shown in FIG. 3, the third pressure-sensitive adhesive layer 7 can be usually used for bonding the first protective film 5 and the liquid crystal cell 20. In any example, it is customary to arrange a polarizing plate on the other side of the liquid crystal cell 20, and the polarizing plate on the other side may be the same as or different from the above. Also good. The bonding method between the polarizing plate and the liquid crystal cell is not particularly limited, and may be generally known. For example, the method of bonding a polarizing plate to a liquid crystal cell using one rubber roll, the method of passing a liquid crystal cell and a polarizing plate between two rubber rolls, etc. can be mentioned.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these examples. In the examples, “%” and “part” representing the content or amount used are based on mass unless otherwise specified.

<Example 1>
(A) Polarized film A film made of polyvinyl alcohol having an average degree of polymerization of about 2400 and a saponification degree of 99.9 mol% or more and a thickness of 75 μm was uniaxially stretched about 4.2 times in a dry manner and further kept in a tension state. The sample was immersed in pure water at 60 ° C. for 1 minute, and then immersed in an aqueous solution having a mass ratio of iodine / potassium iodide / water of 0.1 / 5/100 at 28 ° C. for 60 seconds. Then, it was immersed in an aqueous solution having a mass ratio of potassium iodide / boric acid / water of 10.5 / 7.5 / 100 at 72 ° C. for 300 seconds. Subsequently, the film was washed with pure water at 10 ° C. for 5 seconds, and then dried at 90 ° C. for 180 seconds to obtain a polarizing film in which iodine was adsorbed and oriented on polyvinyl alcohol (a polarizing film made of the polyvinyl alcohol resin referred to in the present invention). . The thickness of this polarizing film was 25 μm.

(B) High elastic modulus pressure-sensitive adhesive Polyethylene terephthalate film (separator) in which a pressure-sensitive adhesive layer obtained by adding a urethane acrylate oligomer and an isocyanate-based crosslinking agent to a copolymer of butyl acrylate and acrylic acid is subjected to a release treatment. The sheet-like pressure-sensitive adhesive formed with a thickness of 5 μm was used on the release treatment surface. In addition, when the storage elastic modulus of this adhesive layer was measured by the above-mentioned method, it was 0.6 MPa at 23 ° C. and 0.19 MPa at 80 ° C.

(C) Protective film A film having a thickness of 43 μm ([40CHC], manufactured by Toppan Printing Co., Ltd.) having a hard coat treatment applied to one side of a film made of triacetyl cellulose is subjected to a saponification treatment, and a surface treatment ( The protective film was subjected to a hard coat treatment.

(D) Retardation film Retardation film consisting of a stretched film of norbornene-based resin, having an in-plane retardation of 140 nm that is λ / 4 with respect to the wavelength λ of light, and a retardation film (Essina film, Sekisui A sheet-like acrylic pressure-sensitive adhesive was bonded to one side of Chemical Industries Co., Ltd. to obtain a retardation film with a pressure-sensitive adhesive layer. The storage elastic modulus of this pressure-sensitive adhesive layer was 0.05 MPa at 23 ° C. and 0.04 MPa at 80 ° C.

(E) Preparation of polarizing plate The sheet-like adhesive shown in (B) was bonded to both surfaces of the polarizing film shown in (A) above to form an adhesive layer. Next, the separator was peeled off from one of the pressure-sensitive adhesive layers, and the protective film shown in (C) was attached to the exposed surface of the pressure-sensitive adhesive layer on the surface not subjected to the hard coat treatment. Next, the separator was peeled off from the pressure-sensitive adhesive layer on the other surface of the polarizing film, and the surface of the pressure-sensitive adhesive layer exposed surface on which the pressure-sensitive adhesive layer of the retardation film shown in (D) was not provided was attached. . In this way, a polarizing plate with a pressure-sensitive adhesive layer provided with a retardation function was obtained.

  Separately, in the state where the pressure-sensitive adhesive layer is formed on both surfaces of the polarizing film as described above, the same retardation film as shown in (D) above (Essina without the pressure-sensitive adhesive layer) is formed on the one-side pressure-sensitive adhesive layer. Film), a 25 mm wide test piece was cut out, the other adhesive layer was attached to glass, and the peel strength between the polarizing film and the adhesive layer was measured to be 16.2 N / 25 mm. there were. Peel strength is an autograph manufactured by Shimadzu Corporation. In an environment of a temperature of 23 ° C. and a relative humidity of 50%, a peel rate of 300 mm / min, a peel angle of 180 °, and the above retardation film is an adhesive layer. At the same time, it was measured so as to peel off from the polarizing film.

<Example 2>
A sheet-like pressure-sensitive adhesive different from that shown in Example 1 (B) was used, and the others were the same as in Example 1 to obtain a polarizing plate with a pressure-sensitive adhesive layer provided with a retardation function. About the sheet-like adhesive used here, when the storage elastic modulus of the adhesive layer was measured by the above-mentioned method, it was 0.25 MPa at 23 degreeC and 0.15 MPa at 80 degreeC. Moreover, the peeling strength between this adhesive layer and a polarizing film was 20.0 N / 25mm.

<Example 3>
Here, different types of pressure-sensitive adhesive layers were formed on both surfaces of the polarizing film to produce a polarizing plate. The pressure-sensitive adhesives used are as follows. A first pressure-sensitive adhesive layer was formed with the first pressure-sensitive adhesive, and a second pressure-sensitive adhesive layer was formed with the second pressure-sensitive adhesive.

  First pressure-sensitive adhesive: Same as shown in Example 1 (B), a pressure-sensitive adhesive layer having a storage elastic modulus of 0.6 MPa at 23 ° C. and a storage elastic modulus of 0.19 MPa at 80 ° C. was 5 μm on the separator. A thick adhesive sheet. The peel strength for the polarizing film is 16.2 N / 25 mm.

  Second pressure-sensitive adhesive: A pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive layer having a storage elastic modulus of 0.55 MPa at 23 ° C. and a storage elastic modulus of 0.27 MPa at 80 ° C. is formed on the separator with a thickness of 5 μm. The peel strength for the polarizing film was 1.7 N / 25 mm.

  The first pressure-sensitive adhesive (sheet) was bonded to one side of the same polarizing film as used in Example 1, and the second pressure-sensitive adhesive (sheet) was bonded to the other side to form a pressure-sensitive adhesive layer. . The peel strength of the second pressure-sensitive adhesive layer with respect to the polarizing film is such that the same retardation film as used in Example 1 is attached to the second pressure-sensitive adhesive layer side in this state, and the first pressure-sensitive adhesive layer side is made of glass. And measured by the same method as in Example 1. Then, instead of the protective film with a hard coat layer in Example 1, a reflective polarizing film (DBEF-P2, manufactured by 3M Co.) made of a polyester-based resin multi-layered film was used, which was subjected to a hard coat treatment. The surface not subjected to the hard coat treatment was bonded to the second pressure-sensitive adhesive layer, and the others were the same as in Example 1 to produce a pressure-sensitive adhesive layer-attached polarizing plate having a retardation function.

<Example 4>
The second pressure-sensitive adhesive was changed to the following, and others were the same as in Example 3 to prepare a polarizing plate with a pressure-sensitive adhesive layer to which a retardation function was imparted.

  Second pressure-sensitive adhesive: Light-diffusible by mixing fine particles, and a pressure-sensitive adhesive layer having a storage elastic modulus of 3.97 MPa at 23 ° C. and a storage elastic modulus of 1.67 MPa at 80 ° C. is formed on the separator with a thickness of 15 μm. Adhesive sheet. The peel strength for the polarizing film was 3.6 N / 25 mm.

<Comparative Examples 1-4>
As shown in Table 1, the pressure-sensitive adhesive layer was formed using sheet-like pressure-sensitive adhesives having different “storage modulus”, “peeling strength” and “thickness” with respect to the surface of Example 1, respectively. Except for the above, a polarizing plate with an adhesive layer to which the same retardation function as in Example 1 was applied was obtained.

<Evaluation>
Thus, the produced polarizing plate of Examples 1-4 and Comparative Examples 1-4 was cut into the size of 40 mm x 40 mm, and it bonded to glass with the adhesive layer on retardation film, and was set as the evaluation sample. . The evaluation sample produced here is the same as the layer configuration shown in FIG. 3 except that the liquid crystal cell 20 is changed to glass. About the evaluation sample immediately after production, after confirming that there are no defects in appearance, peeling, shrinkage, and edge bulging as shown below, each evaluation sample is held for 96 hours in a dry heat environment at 85 ° C. The state after the dry heat test was evaluated. The results are shown in Table 1.

  “Appearance” as an evaluation item is a result of visual observation as to whether or not the surface state of the evaluation sample is a mirror surface. From the results in Table 1, it can be seen that when the thickness of the first pressure-sensitive adhesive layer is thin, it tends to be favorable. In addition, the thing with a bad external appearance was described as "coconut skin."

  The evaluation item “peeling” is a result of visual observation using a 10 × magnifying glass to determine whether there is a film peeling that tends to occur mainly at the end of the evaluation sample or bubbles that are likely to occur in the adhesive layer. It is. From the results in Table 1, it can be seen that if the peel strength of the first pressure-sensitive adhesive layer is 11 N / 25 mm or more, peeling tends not to occur.

  “Shrinkage” of the evaluation item indicates the shrinkage amount of the polarizing film generated at the end of the evaluation sample. The larger the shrinkage amount, the more the polarizing film sandwiched between the protective film and the retardation film or the reflective polarizing film is located on the inner side. And the large gap is generated between the end of the polarizing film and each end of the protective film and the retardation film or the reflective polarizing film. Such shrinkage is also called “open mouth” because the end of the polarizing film appears to be depressed and the mouth is opened. The larger the gap, the easier it is for the protective film to peel off due to external stress, or the effect of moisture (a phenomenon in which the polarizing film loses iodine and the polarizing performance is not exhibited).

  The amount of shrinkage, that is, the gap generated between the polarizing film and the protective film and retardation film or reflective polarizing film sandwiching it from both sides, is the MD direction (stretching axis direction of the polarizing film) and the TD direction (with respect to the stretching axis). In contrast, the measurement was performed using a Nikon Corporation two-dimensional measuring instrument (NEXIV VMR-12072). In Table 1, “contraction (MD direction)” and “contraction ( TD direction) ". In the measurement, the edge of the evaluation sample attached to the glass is observed from above, and the outermost edge (which becomes the edge of the protective film, retardation film or reflective polarizing film) is detected. The part which became the edge part of a polarizing film inside was detected, and it displayed by the maximum value of both difference (distance). In addition, the part used as the edge part of a polarizing film can be identified by the color peculiar to a polarizing film. From the results of Table 1, the higher the storage elastic modulus of the first pressure-sensitive adhesive layer is within the upper limit of 1 MPa, and in the case of the same storage elastic modulus, the thinner the first pressure-sensitive adhesive layer, the smaller the shrinkage. There is a tendency to be able to suppress.

  “Elevation of end” of the evaluation item indicates a deformed state in which the polarizing plate generated at the end of the evaluation sample rises, and the height at the highest peak at the end of the evaluation sample and the horizontal plane at the center of the evaluation sample. It is the result of measuring the difference (μm) from the height. The measurement was performed using a confocal interference microscope “PL-μ2300” manufactured by SENSOFAR. This measurement was performed in two directions of the MD direction and the TD direction, which were respectively “end rising (MD direction)” and “end rising (TD direction)”. From the results of Table 1, it can be seen that the lower the storage elastic modulus of the first pressure-sensitive adhesive layer, the more the rise can be reduced. Note that when the height of the end portion exceeds about 1 μm, it becomes easy to visually recognize by visual observation, and when it becomes about 4 μm, distortion of reflected light is strongly recognized by visual observation, which is not preferable in terms of appearance. This means that as the edge bulge becomes larger than 1 μm, when the polarizing plate is bonded to a liquid crystal cell to form a liquid crystal panel, the end of the polarizing plate is more likely to float.

  In Table 1, “first pressure-sensitive adhesive layer” refers to a pressure-sensitive adhesive layer on the side close to the liquid crystal cell, and “second pressure-sensitive adhesive layer” refers to a pressure-sensitive adhesive on the side different from the first pressure-sensitive adhesive layer. Layers are shown (however, in Examples 1 and 2, both are the same). The “first protective film” is a protective film bonded to the “first adhesive layer” side, and the “second protective film” is applied to the “second adhesive layer” side. It is a protective film to be combined. Moreover, regarding these protective films, “TAC” indicates the triacetylcellulose film with a hard coat layer used above, “DBEF” indicates the reflective polarizing film used above, and “RF” indicates the above The retardation film used in is shown.

  As is clear from Table 1, the polarizing plate of the example of the present invention shows an excellent effect as compared with the polarizing plate of the comparative example, and the configuration of the polarizing plate of the present invention (in particular, has a specific storage elastic modulus, The configuration in which the pressure-sensitive adhesive layer having excellent peel strength with the polarizing film is laminated on the side close to the liquid crystal cell of the polarizing film is excellent.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a cross-sectional schematic diagram which shows the example of the laminated constitution of the polarizing plate which concerns on this invention. It is a cross-sectional schematic diagram which shows the example in the case of applying the polarizing plate of this invention to a liquid crystal cell. It is a cross-sectional schematic diagram which shows another example in the case of applying the polarizing plate of this invention to a liquid crystal cell.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 1st adhesive layer (adhesive layer used as the side close | similar to a liquid crystal cell), 2 polarizing film, 3 2nd adhesive layer (adhesive layer used as the opposite side to a liquid crystal cell), 5 1st protection Film, 6 second protective film, 7 third pressure-sensitive adhesive layer, 10 polarizing plate, 20 liquid crystal cell (glass).

Claims (2)

A pressure-sensitive adhesive layer is directly laminated on both surfaces of a polarizing film made of a polyvinyl alcohol-based resin, and a protective film is further laminated on at least one surface of the polarizing film via the pressure-sensitive adhesive layer. A polarizing plate,
Among the pressure-sensitive adhesive layers, the pressure-sensitive adhesive layer on the side close to the liquid crystal cell is
The thickness is 1 μm or more and 10 μm or less,
The storage elastic modulus is 0.15 MPa or more and 1 MPa or less in a temperature range of 23 ° C. or more and 80 ° C. or less, and
A polarizing plate having a peel strength with respect to a polarizing film of 11 N / 25 mm or more. A liquid crystal display device comprising the polarizing plate according to claim 1 disposed on at least one side of a liquid crystal cell.

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