JP5789333B2 - Polarizing plate and manufacturing method thereof - Google Patents

Description

  The present invention relates to a polarizing plate and a method for producing the same.

  In recent years, with the expansion of applications of liquid crystal display devices, there is an increasing demand for thinning and cost reduction of liquid crystal display devices. On the other hand, conventionally, a polarizing plate excellent in resistance to cracking due to moisture absorption, light heat or the like has been desired. For example, there has been proposed a polarizing plate that includes a polarizer and a pair of protective layers provided on both sides of the polarizer, and the pair of protective layers are joined at the edges of the polarizer (Patent Document 1). However, there are problems such as insufficient crack resistance depending on the material of the protective layer, and inability to cope with an inexpensive and thin polarizing plate provided with a protective layer only on one side of the polarizer.

JP-A-10-206633

  The present invention has been made to solve the above-described conventional problems, and an object thereof is to provide a polarizing plate having excellent crack resistance.

The polarizing plate of the present invention, a polarizer, and a protective layer disposed on at least one side of the polarizer, the depolarization portion along the end side at least facing is formed.
In preferable embodiment, the width | variety of the said depolarization part is 1 micrometer or more .
In a preferred embodiment, the depolarizer is formed along a direction substantially orthogonal to the absorption axis direction of the polarizer .
In a preferred embodiment, the depolarizing part is a thick part thicker than the other part .
According to another situation of this invention, the manufacturing method of the said polarizing plate is provided. In this method of manufacturing a polarizing plate, the depolarizing portion is formed by irradiating a laser beam.
In a preferred embodiment, the laser is a semiconductor laser.
In preferable embodiment, the said laser beam is irradiated with respect to the cut piece cut out from the polarizing plate sheet.

  According to this invention, the polarizing plate which has the outstanding crack resistance can be provided by forming a thick part along the edge which opposes at least.

It is a top view of the polarizing plate in preferable embodiment of this invention. FIG. 2 is an enlarged cross-sectional view in the vicinity of an end side of the polarizing plate shown in FIG. 1. It is a SEM observation photograph of a polarizing plate.

A. Polarizing Plate FIG. 1 is a plan view of a polarizing plate according to a preferred embodiment of the present invention, and FIG. 2 is an enlarged sectional view of the vicinity of the edge of the polarizing plate shown in FIG. The polarizing plate 100 includes a polarizer 10 and a protective layer 20 disposed on one side of the polarizer 10. The polarizing plate 100 has thick portions 110 and 110 formed along the left and right edges 101 and 101. By forming such a thick portion, excellent crack resistance can be imparted. Although not shown, practically, the polarizing plate 100 includes an adhesive layer provided between the polarizer 10 and the protective layer 20. In the illustrated example, the protective layer is disposed only on one side of the polarizer to form the polarizing plate, but the protective layer may be disposed on both sides.

  In the illustrated example, the cross-sectional shape of the thick part 110 is an inclined thick part formed so that the film thickness gradually increases from the thin part 120. The thickness 10b of the polarizer in the thick portion 110 is preferably 1.3 times or more, more preferably 1.4 times or more than the thickness 10a of the polarizer in the thin portion 120. By satisfying such a thickness relationship, excellent crack resistance can be obtained. On the other hand, the thickness 10b of the polarizer in the thick portion 110 is preferably 2.0 times or less, more preferably 1.8 times or less than the thickness 10a of the polarizer in the thin portion 120. If it exceeds 2.0 times, bubbles may be generated when the obtained polarizing plate is laminated on another member such as a liquid crystal cell or an optical film. In addition, the thickness of a thin part respond | corresponds to the thickness of the below-mentioned polarizing plate sheet substantially.

  The thickness of the polarizing plate can be set to any appropriate thickness depending on the configuration. Typically, it is 40 μm to 300 μm, preferably 40 μm to 250 μm.

  The width of the thick part is preferably 1 μm or more, more preferably 5 μm or more. On the other hand, the width of the thick part is preferably 500 μm or less, more preferably 100 μm or less. Depolarization described later can be suppressed.

  Polarization of the polarizer can be canceled in the thick part. However, even if the polarization is eliminated at the end portion of the polarizing plate, the polarization elimination unit is accommodated in, for example, the outer frame of the liquid crystal display device, and there is no substantial adverse effect on the display characteristics. Note that the depolarization property can be confirmed, for example, by superimposing two polarizing plates so that the absorption axes thereof are orthogonal to each other and observing whether or not color loss has occurred from the end portion with an optical microscope. Can do.

  Preferably, as shown in the example, the thick portions 110 and 110 are formed along a direction substantially orthogonal to the absorption axis direction A of the polarizer 10. With such a configuration, the formation of the thick portion can be reduced while maintaining excellent crack resistance. As a result, the influence on the display characteristics can be further suppressed.

  The formation site of the thick portion is not particularly limited as long as it is formed along at least the opposite end sides. For example, the thick portion may be formed along the periphery of the polarizing plate.

  On the outer peripheral end face of the polarizing plate, the polarizer may be exposed, or may be covered with, for example, a protective layer.

A-1. Polarizer Any appropriate polarizer may be employed as the polarizer depending on the purpose. For example, dichroic substances such as iodine and dichroic dyes are adsorbed on hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films. And polyene-based oriented films such as a uniaxially stretched product, a polyvinyl alcohol dehydrated product and a polyvinyl chloride dehydrochlorinated product. Among these, a polarizer obtained by adsorbing a dichroic substance such as iodine on a polyvinyl alcohol film and uniaxially stretching is particularly preferable because of its high polarization dichroic ratio.

  A polarizer uniaxially stretched by adsorbing iodine to a polyvinyl alcohol film can be produced by, for example, dyeing polyvinyl alcohol in an aqueous solution of iodine and stretching it 3 to 7 times the original length. . If necessary, it may contain boric acid, zinc sulfate, zinc chloride or the like, or may be immersed in an aqueous solution such as potassium iodide. Further, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing.

  By washing the polyvinyl alcohol film with water, not only can the surface of the polyvinyl alcohol film be cleaned and the anti-blocking agent can be washed, but also the effect of preventing unevenness such as uneven dyeing can be obtained by swelling the polyvinyl alcohol film. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. The film can be stretched in an aqueous solution of boric acid or potassium iodide or in a water bath.

  The thickness of the polarizer is preferably 1 μm to 50 μm, more preferably 5 μm to 30 μm.

A-2. Protective layer The protective layer is typically formed of any suitable film that can be used as a protective layer for a polarizing plate. Specific examples of the material as the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based materials. And transparent resins such as polystyrene, polynorbornene, polyolefin, (meth) acryl, and acetate. Further, thermosetting resins such as (meth) acrylic, urethane-based, (meth) acrylurethane-based, epoxy-based, and silicone-based or ultraviolet curable resins are also included. In addition to this, for example, a glassy polymer such as a siloxane polymer is also included. Moreover, the polymer film as described in Unexamined-Japanese-Patent No. 2001-343529 (WO01 / 37007) can also be used. As a material for this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in the side chain For example, a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer can be mentioned. The polymer film can be, for example, an extruded product of the resin composition.

  The thickness of the protective layer is preferably 10 μm to 150 μm, more preferably 20 μm to 100 μm.

A-3. Adhesive Layer Any appropriate adhesive is used as the adhesive forming the adhesive layer. The adhesive layer is preferably formed from an adhesive composition containing a polyvinyl alcohol-based resin. The polyvinyl alcohol-based resin preferably contains an acetoacetyl group. This is because the adhesion between the polarizer and the protective layer is excellent and the durability can be excellent.

  The thickness of the adhesive layer is preferably 10 nm to 300 nm, more preferably 10 nm to 200 nm, and particularly preferably 20 nm to 150 nm.

B. Manufacturing Method The thick part is preferably formed by irradiating a laser beam. In one embodiment, a thick piece is formed by irradiating a cut piece cut out to a predetermined size from a polarizing plate sheet with a laser beam to produce a polarizing plate. Here, any appropriate method can be adopted as a method of cutting the polarizing plate sheet. For example, the method of cut | disconnecting using a cutter is mentioned. In another embodiment, a polarizing plate is produced by irradiating a polarizing plate sheet with laser light, and cutting and forming a thick portion substantially simultaneously.

The polarizing plate sheet has any appropriate shape. Typically, it is long (raw material). The irradiation direction of the laser beam can be selected from any appropriate direction depending on the type of laser, the configuration of the polarizing plate (polarizing plate sheet), and the like. When the polarizing plate is configured with a protective layer disposed only on one side of the polarizer as in the illustrated example, irradiation may be performed from the polarizer side or from the protective layer side. For example, when a CO ₂ laser described later is used, the laser beam is preferably irradiated from the protective layer side. This is because the protective layer melted by the laser beam covers the end face of the polarizer and the crack resistance can be further improved.

Any appropriate laser can be adopted as the laser as long as the thick part can be formed. Preferably, a laser that emits light having a wavelength in the range of at least 200 nm to 11 μm is used. It is because a thick part can be formed favorably. Specific examples include a gas laser such as a CO ₂ laser; a solid laser such as a YAG laser; and a semiconductor laser. In one embodiment, a semiconductor laser is preferably used. This is because the polarizer can be selectively bulged to satisfactorily satisfy the above preferable thickness relationship. Moreover, the generation of foreign matter due to irradiation is prevented, and the cost is also excellent. In another embodiment, preferably, CO ₂ laser is used. This is because the polarizing plate sheet can be cut and the thick portion can be formed substantially simultaneously.

  Arbitrary appropriate conditions can be employ | adopted for the irradiation conditions (output condition, moving speed) of a laser beam according to the laser to be used, for example. When the semiconductor laser is used, the output condition is preferably 40W to 100W, more preferably 40W to 80W. The moving speed is typically 10 mm / second to 1000 mm / second, preferably 20 mm / second to 500 mm / second.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples.

[Example 1]
(Preparation of polarizing plate sheet)
As a polarizer, a uniaxially stretched film (thickness: 22 μm) containing a dichroic dye in a long polyvinyl alcohol film was used. A long TAC film (thickness: 80 μm) is bonded to one side of the polarizer via a polyvinyl alcohol adhesive (thickness after drying: 130 nm) to produce a polarizing plate sheet (original film of polarizing plate). did.

A cut piece was cut out from the obtained polarizing plate sheet into a size of 83.7 mm × 83.7 mm using a cutter (product name: A-300, manufactured by NT Corporation). Next, a polarizing plate was obtained by irradiating laser light with a semiconductor laser (semiconductor crystal: Ga · As, manufactured by JPSU) on the four sides of the cut piece (along the periphery) from the TAC film side. The irradiation conditions of the semiconductor laser are as follows.
(Irradiation conditions)
Wavelength: 940nm
Laser power: 50W

[Example 2]
A polarizing plate was obtained in the same manner as in Example 1 except that the laser output was changed to 40W.

[Example 3]
From the polarizing plate sheet obtained in the same manner as in Example 1, a cut piece was cut out to a size of 83.7 mm × 83.7 mm using a CO ₂ laser (manufactured by Comnet Corporation, product name: Laser Pro-SPIRIT). A polarizing plate was obtained. The CO ₂ laser was irradiated from the TAC film side. The irradiation conditions of the CO ₂ laser are as follows.
(Irradiation conditions)
Wavelength: 10.6 μm
Laser power: 30W
Oscillation mode: Pulse oscillation Laser beam diameter: 70 μm

[Example 4]
A polarizing plate was obtained in the same manner as in Example 1 except that the cut piece was irradiated with laser light only on two sides along the direction substantially orthogonal to the absorption axis direction of the polarizer.

(Comparative Example 1)
A polarizing plate was obtained in the same manner as in Example 1 except that the semiconductor laser beam was not irradiated.

(Comparative Example 2)
A polarizing plate was obtained in the same manner as in Example 1 except that the laser output was changed to 30 W.

(Comparative Example 3)
A polarizing plate was obtained in the same manner as in Example 1 except that the laser output was changed to 35W.

(Comparative Example 4)
A polarizing plate was obtained in the same manner as in Example 1 except that the cut piece was irradiated with laser light only on one side along the direction substantially orthogonal to the absorption axis direction of the polarizer.

(Comparative Example 5)
A polarizing plate was obtained in the same manner as in Example 3 except that a femtosecond laser was used instead of the CO ₂ laser. The irradiation conditions of the femtosecond laser irradiation conditions are as follows.
(Irradiation conditions)
Wavelength: 780nm
Laser power: 70W
Oscillation mode: Pulse oscillation Oscillation pulse width: 150 fs
Movement speed of irradiation position: 0m / min to 1m / min

(Comparative Example 6)
A polarizing plate was obtained in the same manner as in Comparative Example 1 except that a super cutter (manufactured by Hadano Seiki Seisakusho) was used instead of the cutter.

The following evaluation was performed with respect to the polarizing plate obtained by each Example and the comparative example. The evaluation method is as follows, and the evaluation results are summarized in Table 1.
(1) Thickness The obtained polarizing plate was cut perpendicularly to the vertical direction, and the cut surface was observed using a scanning electron microscope (SEM, manufactured by JEOL Ltd.). As shown in the SEM photograph of FIG. 3, the thickness (b) of the thickest part and the thickness (a) of the thinnest part of the polarizer were measured, and the ratio (b / a) was calculated.
(2) Heat cycle (HS) test The obtained polarizing plate was allowed to stand in an atmosphere at -40 ° C for 30 minutes, and then left in an atmosphere at 85 ° C for 30 minutes. This operation was set as one cycle, and after repeating 100 cycles, the polarizing plate was observed, and when the crack had generate | occur | produced, the length was measured.
(3) Depolarization property Two polarizing plates were overlapped so that the absorption axes thereof were orthogonal to each other and the polarizers faced each other, and the end portions were observed with an optical microscope. When color loss occurred from the end portion, the length of the portion where color loss occurred was measured. When this length was 1 μm or more, it was determined that depolarization was “present”.

  In each example, excellent crack resistance was confirmed. In addition, when the obtained polarizing plate was bonded together to the glass substrate, the bubble was produced between the polarizing plate and the glass substrate only in Example 3 (15 pieces).

  As described above, since the polarizing plate of the present invention has excellent crack resistance, when used in a liquid crystal display device, it is very useful in that the deterioration of display quality due to the occurrence of cracks can be suppressed. is there.

10 Polarizer 20 Protective layer 100 Polarizing plate 110 Thick part

Claims (5)

A method for producing a polarizing plate, comprising: a polarizer ; and a protective layer disposed on at least one side of the polarizer , wherein a depolarization unit that has lost the polarization function is formed along at least opposite ends. And
The manufacturing method of a polarizing plate which forms the said depolarization part by irradiating a laser beam with respect to the cut piece cut out from the polarizing plate sheet . The manufacturing method of the polarizing plate of Claim 1 whose width | variety of the said depolarization part is 1 micrometer or more. The manufacturing method of the polarizing plate of Claim 1 or 2 with which the said depolarization part is formed along the direction substantially orthogonal to the absorption-axis direction of the said polarizer. The manufacturing method of the polarizing plate in any one of Claim 1 to 3 whose said depolarization part is a thick part thicker than another part. The manufacturing method of the polarizing plate in any one of Claim 1 to 4 whose said laser is a semiconductor laser.