JP2008292674A - Method for reducing light leakage of large display device and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a light leakage part generated in an arc shape at each edge of a TN mode liquid crystal display having ≥19 inch diameter size and to provide a method by which the existence of the light leakage part is hardly recognized even when the light leakage part is generated. <P>SOLUTION: In the method for reducing light leakage generated in the arc shape at an edge part of the large sized display by thermal contraction of an extended polarizing plate film stuck to the TN mode large sized display having ≥19 inch in full length, strength resistant to thermal contraction of the extended polarizing film is imparted to an adhesive for sticking the extended polarizing plate film so that the ratio (W/L) of the maximum value (W) of the light leakage arc generated in the edge part to the length (L) of a long side is ≤0.1 and a side chain is introduced to a hydrocarbon main chain of the adhesive so that darkened luminance (X) of the light leakage part formed in the arc shape at the edge part is ≤4 cd/m<SP>2</SP>and its ratio (X/Y) to darkened luminance (Y) of a part where light leakage is not generated is ≤20. Thus the light leakage part generated in the arc shape at the edge part of the large sized display can be made small and difference of luminance of the light leakage part and a polarizing film disposed part is made small and the light leakage part is made inconspicuous even when being darkened. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method and a display device for reducing light leakage that occurs at the edge of a display device due to contraction of a polarizing film to be attached to a TN mode large-sized display device having a passing length of 19 inches or more.

  In a display device, particularly a liquid crystal display device, a polarizing plate is arranged in a crossed Nicols position on the surface of two glass substrates forming a liquid crystal cell, and a voltage is applied to the liquid crystal component filled in the liquid crystal cell to thereby display the liquid crystal component. This is a device that reveals an electrical signal by controlling the light transmission from a light source disposed on the back side of the liquid crystal display device by changing the orientation state of the liquid crystal display device.

In such a display device, particularly a liquid crystal device, a polarizing film is adhered as described above. In this display device, a stretched film (PVA) generally provided with a non-stretched protective film (TAC) on the front and back surfaces. ) Is attached, the polarizing film stretched by heat generated when the liquid crystal device is driven for a long time or when the liquid crystal device is driven for a long time is thermally contracted and attached to the polarizing film. It has the characteristic that high internal stress occurs at the edge.

On the other hand, the pressure-sensitive adhesive that sticks to such a polarizing film is not stretched. Therefore, even if heat is applied to the pressure-sensitive adhesive, it does not shrink.
When heat is applied to the liquid crystal device, the glass substrate of the liquid crystal device does not change in particular, but the stretched polarizing film causes thermal contraction toward the center of the liquid crystal device surface as shown in FIG. ), A large internal stress is present toward the center as indicated by an arrow.

  At this time, the adhesive attached to the surface of the glass substrate of the liquid crystal device is in a state of being attached to the surface of the glass substrate that does not change due to heat, but the adhesive attached to the surface of the polarizing film is Pulled by the heat shrinkage of the polarizing film. The function of the polarizing film is lost or reduced by the internal stress generated in the polarizing film by being pulled in the center direction due to the heat shrinkage, and this portion is formed in an arc shape from the edge of the liquid crystal device even if the entire surface is displayed in black. A white part is formed. Transmission of light in an arc shape due to heat shrinkage applied to the polarizing film is called light leakage, and a portion having a high light transmittance formed in the arc shape is called a light leakage portion.

  When the size of the liquid crystal device (passing length) is small, the thermal contraction of the polarizing film is also small, and the light leakage arc generated at each edge is also small, and it is placed around the display portion of the liquid crystal device to support the liquid crystal display portion It was difficult to recognize the existence of this light leakage arc by the supporting frame.

  However, in recent liquid crystal display devices, a large-sized liquid crystal display device having a passing length exceeding 19 inches is often used, and it is difficult to cover the light leakage arc by the support frame. Furthermore, in the large liquid crystal display device, the area of the polarizing film to be attached becomes very large, and the size of the light leakage arc generated at the edge of the liquid crystal display device gradually increases. It is becoming necessary.

  When the passing length of the liquid crystal display device is less than 19 inches, in order to prevent light leakage due to heat shrinkage of the polarizing film, a pressure sensitive adhesive containing a relatively large amount of a low molecular weight substance or a pressure sensitive adhesive having a low gel fraction is used. In addition, an adhesive having a high stress relaxation property that can follow the heat shrinkage of the polarizing film is used. When the size is less than 19 inches, the polarizing film has a relatively small shrinkage. Therefore, even when an adhesive having a high stress relaxation property as described above is used, light leakage is small and there is no practical problem.

  However, in the TN mode liquid crystal display device, a large number of large liquid crystal display devices whose passing length exceeds 19 inches are already on the market, and at the present time, there are also 32 inch liquid crystal display devices in the TN mode. .

  In such a large liquid crystal display device, the polarizing film to be attached naturally has a large area corresponding to the size of the liquid crystal display device. As described above, the polarizing film adhered to the liquid crystal display device is stretched, and the internal stress generated when such a large-area stretched polarizing film is thermally contracted becomes very large, and the liquid crystal display device of less than 19 inches If an adhesive having a high stress relaxation property such as that used in the above is used, the maximum width of the arc-shaped light leakage portion generated at each edge tends to increase.

In order to reduce light leakage in such a large-sized liquid crystal display device, Japanese Patent Application Laid-Open No. 2006-259664 (Patent Document 1) describes “a polarizing plate having a pressure-sensitive adhesive layer, the light of the pressure-sensitive adhesive layer”. An invention of a polarizing plate characterized by having an absolute value of an elastic modulus of 500 × 10 ⁻¹² (1 / Pa) or more ”is disclosed. Further, Patent Document 1 describes that the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive, and this acrylic pressure-sensitive adhesive copolymerizes benzyl (meth) acrylate and phenyl (meth) acrylate.

However, even when an adhesive as specifically disclosed in Patent Document 1 is used, light leakage cannot be completely prevented.
JP 2006-259664 A

  The present invention reduces the occurrence of a light leakage portion that occurs in an arc shape at each edge of a TN mode liquid crystal display device having a span length of 19 inches or more, and even if such a light leakage portion is formed, It aims at providing the method of making it difficult to recognize the presence of a light leak part.

  Furthermore, the present invention reduces the occurrence of a light leakage portion that occurs in an arc shape at each edge of a TN mode liquid crystal display device having a span length of 19 inches or more, and even if such a light leakage portion is formed. An object of the present invention is to provide a display device using a method for making it difficult to recognize the presence of the light leakage portion.

The present invention is a method for reducing light leakage that occurs in an arc shape at the edge of a large display device due to thermal contraction of a stretched polarizing film attached to a TN mode large display device having an extension length of 19 inches or more. ,
The maximum value (W) from each edge of the light leakage arc generated at each edge of the large display device is such that the ratio (W / L) to the length (L) of the long side of the large display device is 0.1 or less. The pressure-sensitive adhesive for sticking the stretched polarizing film is imparted with a strength capable of resisting thermal shrinkage of the stretched polarizing film, and the light leakage portion formed in an arc shape at the edge of the large display device The luminance (X) when the light is dark is 4 cd / m ² or less, and the ratio (X / Y) to the luminance (Y) when the light is not darkened is 20 or less. In addition, a side chain is introduced into the main hydrocarbon chain of the pressure-sensitive adhesive, and there is a method for reducing light leakage formed in an arc shape at the edge of a large display device.

Furthermore, the present invention provides a method for reducing light leakage that occurs in an arc shape at the edge of a large display device due to thermal contraction of a stretched polarizing plate film attached to a TN mode large display device having a span length of 19 inches or more. A display device used,
The maximum value (W) from each edge of the light leakage arc generated at each edge of the large display device is such that the ratio (W / L) to the length (L) of the long side of the large display device is 0.1 or less. The pressure-sensitive adhesive for sticking the stretched polarizing film is imparted with a strength capable of resisting thermal shrinkage of the stretched polarizing film, and the light leakage portion formed in an arc shape at the edge of the large display device So that the brightness (X) when dark is 4 cd / m ² or less, and the ratio (X / Y) to the brightness (Y) when dark where the light leakage does not occur is 20 or less. A display device using a method of reducing light leakage formed in an arc shape at the edge of a large display device, wherein side chains are introduced into the hydrocarbon main chain of the adhesive.

  In the present invention, the light generated at each edge due to the contraction of the stretched polarizing film using a strong adhesive having a relatively high strength despite the fact that the polarizing film is attached to a large liquid crystal display device. A leaking part is formed small. The pressure-sensitive adhesive strength of such a pressure-sensitive adhesive is often due to a cross-linked structure that mutually constrains the chain molecules forming the pressure-sensitive adhesive, and in the present invention, a tetrafunctional cross-linking agent is used and three or more of them are used. The pressure-sensitive adhesive molecules having a chain structure with a functional group are mutually restrained to give fastness to the pressure-sensitive adhesive itself.

  Even when such a robust crosslinking agent is used, arc-shaped light leakage portions are formed at the respective edges of the glass substrate forming the liquid crystal device. However, according to the present invention, the maximum width (W) of the arc-shaped light leakage portion with respect to the long side length (L) of the glass substrate can be made very narrow as described above.

Even if the polarizing film is attached with a strong adhesive in this way, in a large-screen liquid crystal display device, an arc-shaped light leakage portion is formed along each edge as described above. The brightness (X) when darkening the arc-shaped light leaking part is 4 cd / m ² or less, and the ratio ((X) with the brightness (Y) when darkening the part where the polarizing film is normally attached) If the ratio of the luminance is small when (/ (Y)) is taken, the light leaking portion is substantially difficult to be recognized as the light leaking portion. That is, although the light leakage part is formed, this light leakage part becomes difficult to be recognized as the light leakage part.

  In the present invention, by using an adhesive with high cohesive force, the internal stress of the polarizing film is concentrated at the end as much as possible, so that the area of the light leakage part is very small, and the temperature sensitive to the adhesive polymer side chain. Introducing a functional group that lowers the elastic modulus of the adhesive polymer at high temperatures reduces the brightness of the light leaking part. It is difficult to recognize as a light leakage part.

  According to the present invention, in a TN mode large-sized liquid crystal display device having a handing length of 19 inches or more, an arc-shaped light leakage portion generated at each edge portion of the display device can be reduced, and the light leakage portion becomes inconspicuous.

Next, a method and a display device for reducing light leakage formed in an arc shape at the edge of the large display device of the present invention will be described in detail.
The light leakage reduction method of the present invention can be suitably applied to a large TN mode display device having a display device handing length (S) of 19 inches or more in FIG. In the light leakage reducing method of the present invention, the longer the passing length S of the liquid crystal device is, the higher the usefulness is. However, there is a driving limit of the liquid crystal display device itself, and the upper limit value corresponds to the driving limit of the TN mode display device. It is a size.

  In FIG. 1 (A), reference numeral 10 indicates the front surface of the liquid crystal display device, and this liquid crystal display device has a large number of cells filled with a liquid crystal substance, and an alignment is formed on the surface of the large number of cells. A glass substrate 15 is disposed via a film, an ITO electrode, or the like.

A polarizing film 19 is attached to the surface of the glass substrate 15 with an adhesive layer 17.
The polarizing film 19 is formed of a stretched synthetic resin film, and an unstretched protective film (TAC) is usually disposed on the front and back surfaces of the polarizing film. Two polarizing films 19 having such a configuration are usually arranged on the front and back glass substrates 15 constituting the liquid crystal device so as to be in a crossed Nicols position of 45 ° and 135 °.

The polarizing film 19 is stuck and fixed to the glass substrate 15 by the adhesive layer 17.
Since the polarizing film 19 is a stretched film as described above, when heat is applied to the polarizing film 19, thermal contraction occurs in the central direction of the liquid crystal display device 10 as shown in FIG. Since the film is an unstretched film, heat shrinkage does not occur and internal stress occurs.

  In particular, in the part where the direction of heat shrinkage (direction where internal stress is applied) and the direction of the polarization axis are different (the center part of each side of the display device), linearly polarized light becomes elliptically polarized light due to birefringence, and light is transmitted. Since the polarization axis and the contraction direction are approximated at the corner, birefringence hardly occurs and light does not leak easily, so that an arc-shaped light leakage portion is generated on each side of the display device.

In the arc-shaped portion 20 where a strong internal stress is inherent in the TAC film, the function of the polarizing film is impaired, and light leakage occurs in an arc shape. In FIG. 2 (B), the part where the polarization function is impaired by the internal stress is indicated by reference numeral 19a, and the direction and strength of heat shrinkage are indicated by arrows.

Such light leakage is a portion having a high internal stress generated when the stretched polarizing film 19 is thermally contracted as shown in FIG. 2B.
Thus, in the arc-shaped part in which a large stress is inherent, the characteristics of the polarizing film change due to the stress, and in this part, the polarizing film does not act as the polarizing film, and the light that should be shielded by the polarizing film 19 is transmitted to the liquid crystal display device. It will be transparent.

  In the method for reducing light leakage of the display device of the present invention, first, in order to reduce the light leakage area, the light leakage portion 20 formed in an arc shape using a strong adhesive is used as an end portion (corner portion). Concentrate. The arc-shaped light leakage portion 20 has the largest distance (W) from the edge portion 21 at the center of the long side (L) of the liquid crystal display device.

  In the present invention, the maximum value of the ratio (W / L) of the maximum value W from each side of the light leakage arc to the long side L of the liquid crystal display device is usually 0.1 or less, preferably 0.06 or less. In addition, a polarizing film is attached to a glass substrate using a strong adhesive.

  The pressure-sensitive adhesive used here is a polymer whose main chain is a hydrocarbon chain formed by (co) polymerization of a monomer having an ethylenic double bond. Among them, a polymer obtained by (co) polymerizing a monomer having a double bond derived from an acryloyl group is excellent in transparency.

  The main chain of the (co) polymer which is the main component of such an adhesive includes, for example, a polar group-containing side chain such as a hydroxyl group, a carboxyl group (a salt thereof), an amino group, an alkylamino group, an alkoxyl group, and an amide group. Derived from, for example, a linear or branched alkyl group, a saturated cyclic hydrocarbon group such as a cycloalkyl group that may have a substituent, or a cyclic compound such as a phenyl group that may have a substituent A side chain such as a nonpolar group-containing side chain such as a group derived from a cyclic compound such as a benzyl group is introduced.

The (co) polymer as the main component of the pressure-sensitive adhesive having such a side chain is usually 1,000,000 to 25.
It has a weight average molecular weight of 100,000, preferably 1.2 million to 2 million. Moreover, the narrower the molecular weight distribution of such a (co) polymer is, the more easily the structure of the pressure-sensitive adhesive layer becomes more robust, and the pressure-sensitive adhesive layer is less likely to vary in the pressure-sensitive adhesive layer. Further, the molecular weight distribution (Mn / Mw) of the (co) polymer which is the main component of such an adhesive is usually in the range of 2 to 20, preferably 4 to 10, and the adhesive having such a molecular weight distribution. By using the main component (co) polymer, it is easy to form a robust pressure-sensitive adhesive layer structure.

In addition, the (co) polymer that is the main component of this pressure-sensitive adhesive usually needs to maintain good adhesiveness in an environment where a polarizing film is attached, and the glass transition temperature ( Tg) is usually in the range of −70 to −10 ° C., preferably −50 to −30 ° C. The glass transition temperature (Tg) of such a (co) polymer can be measured from the produced (co) polymer, and can also be used for (co) polymerization. It can also be derived from the monomer found using the Fox equation.

Such a polar side chain or nonpolar side chain implanted in the main chain of the (co) polymer may be directly bonded to the hydrocarbon main chain of the (co) polymer constituting the pressure-sensitive adhesive. Is a divalent group similar to an ester bond such as —O—CO— group or —CO—O— group, or a divalent group similar to an ether bond such as —O— or —S—, —O— _They may be bonded via a group derived from phosphoric acid such as PO ₂ —O— or —OSO ₂ —O— or sulfonic acid.

  The (co) polymer having such a side chain can introduce a desired group into the main chain after (co) polymerizing a compound having an ethylenic double bond. It can be produced by (co) polymerizing a monomer having an ethylenic double bond having a group introduced therein. It is also possible to produce a (co) polymer having a desired group by implanting a desired group in the (co) polymer produced as described above.

  Polar side chains such as hydroxyl groups and carboxyl groups implanted in the (co) polymer that is the main component of the pressure-sensitive adhesive forming the pressure-sensitive adhesive as described above contribute to adhesion between the glass substrate and the polarizing film. Of course, when a cross-linking agent is blended with the (co) polymer which is the main component of this pressure-sensitive adhesive, it becomes an active point of reaction with this cross-linking agent, and the cross-linking between the (co) polymers which are the main component of the pressure-sensitive adhesive A structure is formed, and a (co) polymer that is the main component of the pressure-sensitive adhesive is combined to form a robust three-dimensional structure. The repeating unit having such a polar group is usually 0.5 to 10% by weight in 100% by weight of the monomer used to produce the (co) polymer which is the main component of the pressure-sensitive adhesive. Preferably, it is contained in an amount in the range of 1 to 6% by weight.

  The crosslinking agent that reacts with the polar group as described above to form a crosslinked structure is a compound having a plurality of groups that can react with the polar group, and examples of such reactive groups include an epoxy group, An isocyanate group, a metal chelate group, etc. can be mentioned. The crosslinking agent used in the present invention has a plurality of groups capable of reacting as described above. In the present invention, four or more active polar groups contributing to the crosslinking reaction are present in one molecule of the crosslinking agent. It is preferable to use a cross-linking agent.

In particular, in the present invention, the active polar group contributing to the crosslinking reaction of the compound serving as the crosslinking agent is an epoxy group, and a compound containing 4 or more epoxy groups in one molecule is preferably used as the crosslinking agent. . The epoxy group possessed by such a cross-linking agent reacts with, for example, a hydroxyl group or a carboxyl group implanted in the main chain of the pressure-sensitive adhesive to form an intermolecular cross-linked structure to form a robust pressure-sensitive adhesive structure. It is extremely rare that all groups that can contribute to the cross-linked structure introduced into the agent are bonded. In the present invention, the use of a cross-linking agent containing four or more epoxy groups is based on the reaction efficiency of such an epoxy group. For example, even if a cross-linking agent having four epoxy groups is used, At most, the reaction rate of this epoxy group is usually 6
About 9 to 77% react, and all the introduced epoxy groups do not react. When a cross-linking agent having four epoxy groups is used, an average of three epoxy groups out of the four epoxy groups are bonded to polar groups implanted in the main chain of the pressure-sensitive adhesive. One plane is determined by this connection point. In this way, the pressure-sensitive adhesive bonded at three points imagines a number of rigid surfaces determined by the three bonded points, and the free movement of the main chain of the pressure-sensitive adhesive is significantly restricted to form a robust pressure-sensitive adhesive layer. The And in order to obtain the intensity | strength which can resist the heat shrink of the extending | stretching polarizing film of this invention, the crosslinking agent which forms the robust adhesive layer with a high crosslinking density as mentioned above is used with respect to 100 weight part of adhesive polymers. It is preferable to use 0.05 to 0.20 parts by weight and make the gel fraction 85 to 95%.

In addition, although there exists an example which uses a trifunctional polyisocyanate compound as a crosslinking agent mix | blended with an adhesive layer, in the case of such a trifunctional polyisocyanate compound, two isocyanate groups are comparatively easy to react. The reactivity of the remaining one isocyanate group is lowered, and as a result, the reaction rate of the trifunctional polyisocyanate compound generally does not reach 65%. For this reason, when a trifunctional polyisocyanate compound is used, the two main chains of the (co) polymer forming the pressure-sensitive adhesive are connected by two isocyanate groups in the trifunctional polyisocyanate compound. The movement of the adhesive (co) polymer in the pressure-sensitive adhesive layer within the adhesive layer cannot be suppressed, and the pressure-sensitive adhesive layer becomes soft and the center of the liquid crystal is accompanied by the thermal contraction of the polarizing film. Therefore, the value of W / L, which is the size of the light leakage portion shown in FIG. 2, is increased.

Even in the method of reducing light leakage of the present invention, a stretched polarizing film is used, so that even if the pressure-sensitive adhesive layer is made quite robust, arc-shaped light is formed on the edge of the display device due to heat shrinkage of the polarizing film. It is impossible to prevent the leakage portion 20 from being formed. However, by forming a robust pressure-sensitive adhesive layer according to the present invention, the light leakage portion 2 with respect to the length L of the display device.
The ratio (W / L) of 0 to the maximum width W is 0.1 or less, preferably 0.06 or less, and the area of the light leakage portion 20 itself uses, for example, a trifunctional polyisocyanate compound. Compared to time, it is much smaller.

  Furthermore, in the method for reducing light leakage of the present invention, a group having an aromatic ring is implanted in the main chain of the (co) polymer constituting the pressure-sensitive adhesive. By introducing the group having an aromatic ring into the main chain constituting the pressure-sensitive adhesive, the polarizing film 19 is stretched by thermal contraction, and the side chain having the cyclic structure of the component constituting the pressure-sensitive adhesive is oriented by the stress. As a result, it was found that the light transmittance in the light leakage portion 20 is reduced.

  In addition, a monomer that introduces an aromatic ring into the side chain has high temperature sensitivity and lowers the elastic modulus of the adhesive polymer at high temperatures, so that stress due to thermal contraction of the polarizing plate can be relieved. Thus, in order to lower the elastic modulus of the adhesive at high temperatures and to become a hard and highly cohesive adhesive at room temperature or normal use temperature range, an aromatic ring is introduced into the side chain. The monomer preferably has a glass transition temperature of the homopolymer of −25 ° C. to 10 ° C., and the side chain having an aromatic ring is usually 20% in 100% by weight of the pressure-sensitive adhesive polymer excluding the main chain. When it is in the range of ˜60 wt%, preferably 30 to 40 wt%, light leakage can be made inconspicuous.

Further, in the pressure-sensitive adhesive layer thus oriented, about one functional group in the tetrafunctional cross-linking agent remains without reacting, and the pressure-sensitive adhesive layer is stretched by heat shrinkage of the polarizing film 19. A part of the remaining functional group is bonded to a part of the unreacted functional group among the functional groups implanted in the adhesive resin forming the adhesive layer, and stress is applied. It is believed that the layer 17 (a) is made more rigid to fix a group having an aromatic ring in the pressure-sensitive adhesive layer 17 (a) to which this stress is applied.

Accordingly, in FIG. 2A, when the arbitrary point (X) in the light leakage portion 20 and the arbitrary point (Y) of the portion where the polarizing film 19 is arranged are determined, the display device is darkened. The ratio (X / Y) between the luminance (X) when the light leakage portion is darkened and the luminance (Y) when the light leakage portion is dark is 20 or less, preferably 10 or less. This is because the group having an aromatic ring present in the pressure-sensitive adhesive layer 17 (a) relieves stress due to thermal contraction of the polarizing film and shields at least part of light that is gradually oriented and transmitted. Therefore, the difference between the luminance X and the luminance Y becomes extremely small, and it becomes difficult to visually observe the existence of the light leakage portion caused by the thermal contraction of the polarizing film 19.

  Thus, the light leakage reduction method of the present invention reduces the area of the light leaking portion by forming a robust adhesive layer, and the luminance at the light leaking portion during darkness and the luminance at the portion where the polarizing film is disposed. By reducing the difference between the light leakage portion and the light leakage portion due to the stress caused by the thermal contraction of the polarizing film, the area of the light leakage portion can be remarkably reduced. Since the difference between the luminance of the portion and the luminance of the portion where the polarizing film is attached is extremely small, there is a specific effect that a substantially arc-shaped light leakage portion can hardly be recognized.

Next, the light leakage reduction method of the present invention will be described with reference to examples, but the method of the present invention is not limited to these examples.
The measurement conditions for gel permeation chromatography (GPC) in the present invention are as follows.
Equipment manufactured by Tosoh Corporation, HLC-8120
column
G7000HXL x 1
GMHXL x 2
G2500HXL × 1 sample concentration; 1.5mg / ml (diluted with tetrahydrofuran)
Mobile phase solvent; THF
Flow rate: 1.0ml / min
Temperature; 40 ° C
[Example 1]
According to a conventional method, a copolymer (A) having a weight average molecular weight of 1.4 million measured by gel permeation chromatography was produced by solution polymerization using ethyl acetate as a reaction solvent. The molecular weight distribution (Mn / Mw) of this copolymer was 5.

The main chain composed of the hydrocarbon of the copolymer (A) contains 67.5% by weight of a monomer having —CH ₂ CH ₂ CH ₂ CH ₃ via —CO—O— and —CH ₂ —CH. ₂ % by weight of monomer having _2- OH is bonded, and 0.5% by weight of monomer having —COOH group, —CH ₂ —C ₆ H ₅ via —CO—O—. Is copolymerized in an amount of 30% by weight.

The glass transition temperature (Tg) measured for this copolymer (A) was -34 ° C.
After adjusting the concentration of the obtained copolymer (A) in an ethyl acetate solvent to 15% by weight, an epoxy-based tetrafunctional crosslinking agent (compound name: N, N) is added to 100 parts by weight of the solid content of this solution. , N, N-tetraglycidyl-m-xylenediamine, trade name: Tetrad X; manufactured by Mitsubishi Gas Chemical Co., Ltd.) 0.1 parts by weight was added and mixed uniformly to prepare an adhesive coating solution.

The obtained adhesive coating solution was applied to an easily peelable PET film so that the dry thickness was 25 μm, and after removing the solvent, it was transferred to a polarizing film and cured for 7 days at 23 ° C. A polarizing film was produced.

Prepare a glass substrate of 390 mm x 315 mm x 1.1 mm ^t , and apply the polarizing film with the adhesive layer prepared as described above to the crossed Nicols position (45 °, 135 °) on both sides of the glass substrate. The easy-peelable PET was affixed while being peeled, and further thermocompression bonded to a glass substrate under the conditions of a temperature of 50 ° C. and a linear pressure of 5 kg / cm, and left at room temperature for 1 hour.

The polarizing plate thus obtained was replaced with a polarizing plate of a display monitor BENQ PF91G and mounted. When a display monitor is connected to a PC, the screen is displayed in black on the entire screen, and the brightness of the display monitor is measured using a luminance meter RISA-COLOOR-PF91G (manufactured by Highland) in the dark room, the edge of the glass substrate No arc-shaped light leakage portion was formed.

The pressure-sensitive adhesive layer was scraped from the glass substrate with the polarizing film produced in this way, and the gel fraction of this pressure-sensitive adhesive layer was measured and found to be 91%.
Further, since the reaction rate of the epoxy group is 69 to 77%, from the viewpoint of probability, three of the four active epoxy groups capable of forming a crosslinked structure existing in the crosslinking agent are copolymers. A strong adhesive layer is formed by bonding with the functional group in the side chain of (A), but about one of the four epoxy groups does not react and is in the state of the epoxy group It remains in the cross-linking agent.

Next, the display monitor was left in an environment of 60 ° C. and humidity of 95% for 72 hours to perform a thermal deformation acceleration test of the polarizing film. Then, after allowing to cool at room temperature for 1 hour, it was connected to a personal computer in a dark room and displayed in full screen black. As shown in Fig. 2, the arc-shaped light leaking part from each edge of the glass substrate was measured using a luminance meter RISE-COLOR-CD8 (manufactured by Highland) with a full-screen black display monitor. The widest light leakage part is defined as a light leakage part up to ² cd / m ^2, which is a luminance that allows slight light leakage to be visually recognized with respect to the long side (L) of 380 mm of the glass substrate. In this case, the width (W) of the light leakage portion was 20.5 mm.

Therefore, the W / L of this glass substrate is 0.054, and it can be seen that this W / L is very small as compared with the arc-shaped light leakage portion in a general liquid crystal substrate.
The luminance (X) of the portion where light leakage occurred was measured, and the luminance (Y) when the portion where light leakage did not occur was measured, and it was 4 cd / mm ² at the brightest portion of the light leakage portion. The brightness (X) of the lightly bright part is 2 cd / mm ² and the brightness (X) of the part where no light leakage occurs is 0.2 cd / mm ² , so the value of (X / Y) is in the range of 20-10. Become. Since the brightest part is almost covered by the frame of the display device, the actual (X / Y) value of this display device is 10. The closer this value is to 1, the more difficult it is to determine the presence of a light leakage part, and the value 10 of (X / Y) represents that there is much less light leakage than a conventional display device.

Although the light leakage portion is formed in this way, the brightness at the light leakage portion during darkness is low because the internal stress is concentrated at the end as much as possible by forming a robust adhesive layer. In addition, when the polarizing film is heated in a thermostatic chamber as described above to cause thermal contraction, the adhesive at the portion denoted by reference numeral 17a in FIG. 2 (B) is accompanied by thermal contraction of the polarizing film. While being pulled in the center direction of the liquid crystal display device, —CH ₂ —C ₆ H ₅ is oriented through —CO—O— in the copolymer (A) constituting the pressure-sensitive adhesive, and in this state, in the crosslinking agent A pressure-sensitive adhesive in which at least a part of the epoxy group remaining in the reaction reacts to form a new crosslinked structure with the polar group remaining in the copolymer (A) and pastes the part indicated by the number 19a Oriented —CH ₂ —C ₆ H ₅ is fixed.

Since this oriented —CH ₂ —C ₆ H ₅ exhibits orientation, a part of the light that is about to pass through this light leakage portion is a —CH ₂ —C ₆ H ₅ group fixed with this adhesive. Therefore, the transmission of light is blocked, and according to the method of the present invention, the luminance at the light leakage portion is lowered.

In order to compare this point, the polarizing film was prepared as follows and the state of the light leakage part was compared and examined.
In a 1000 cc reactor equipped with a gas introduction tube, a stirring device, and a heating / cooling device, 68.5 parts by weight of n-butyl acrylate (BA) and 1 part by weight of acrylic acid (AA). 2-hydroxyethyl methacrylate (2HEMA) 0.5 part by weight, benzyl methacrylate (BZMA)
30 parts by weight and 100 parts by weight of ethyl acetate (EA) as a reaction solvent were added, nitrogen gas was introduced into the reactor, the air in the reactor was replaced with nitrogen gas, and the temperature of the reaction liquid was 65 ° C. Maintained.

Next, 0.1 part by weight of azobisisobutyronitrile (AIBN), which is a reaction initiator, was dissolved in ethyl acetate to prepare a 50% by weight solution of the polymerization initiator.
A 50% by weight solution of the polymerization initiator prepared as described above was added dropwise to the reaction liquid introduced with the raw material components and heated to 65 ° C., and the reaction was continued for 10 hours.

  After 10 hours, the solid content concentration of the obtained pressure-sensitive adhesive solution was adjusted to 15% by weight, and trimethylolpropane tolylene diisocyanate adduct having trifunctionality with respect to 100 parts by weight of the solid content of this solution was 1 A diluted solution obtained by diluting 2 parts by weight with 50 parts by weight of ethyl acetate was prepared and added to the reaction solution to prepare a coating solution.

In the same manner as described above, this coating solution was applied to an easily peelable PET film so as to have a dry thickness of 25 μm, and after removing the solvent, the polarizing film was transferred and the easily peelable PET was placed on the coated surface. It was cured at 23 ° C for 7 days.

Prepare a glass substrate of 390 mm x 315 mm x 1.1 mm ^{t and} apply the polarizing film with the adhesive layer prepared as described above to the crossed Nicols position (45 °, 135 °) on both sides of the glass substrate. The easy-peelable PET was affixed while being peeled, and further thermocompression bonded to a glass substrate under the conditions of a temperature of 50 ° C. and a linear pressure of 5 kg / cm, and left at room temperature for 1 hour.

The polarizing plate thus obtained was replaced with a polarizing plate of a display monitor BENQ PF91G and mounted. When a display monitor is connected to a computer, the screen is displayed in black and the brightness of the display monitor is measured in a dark room using a luminance meter RISA-COLOR-CD (manufactured by Highland).
An arc-shaped light leakage portion was not formed at the edge of the glass substrate.

When the gel fraction of this pressure-sensitive adhesive layer was measured, it was 83%, indicating that this pressure-sensitive adhesive layer was soft.
In addition, since the reaction rate of the isocyanate does not normally reach 63%, from a stochastic point of view, two of the three active isocyanate groups capable of forming a crosslinked structure present in the crosslinking agent are on the side of the copolymer. Bonded with the functional group in the chain to form an adhesive layer, but about one of the three isocyanate groups does not react and remains in the crosslinking agent. . Therefore, two points of the copolymer are bonded by the polyisocyanate compound as the cross-linking agent, and such a copolymer has a low binding force due to the cross-linking agent and the pressure-sensitive adhesive is soft.

Next, the display monitor was left in an environment of 60 ° C. and 95% humidity for 72 hours to perform a thermal deformation acceleration test of the polarizing film. Then, after allowing to cool at room temperature for 1 hour, connect it to a personal computer in a dark room and display a full screen black display monitor with a luminance meter RIS-
When measured using COLOR-CD8 (manufactured by Highland), arc-shaped light leaking portions having a large area and high luminance were confirmed from the respective edge portions of the glass substrate, as shown in FIG. The widest light leakage portion with respect to the long side L380 mm of the glass substrate has a light leakage portion width W of 56.5 mm when a portion having a brightness higher than ² cd / m ² is used as the light leakage portion.

  Therefore, the W / L of this glass substrate is 0.149, and this W / L is remarkably large as compared with the arc-shaped light leakage portion in the liquid crystal substrate prepared as described above. Recognize.

  In addition, the luminance (X) at the same position (20.5 mm from the end) as the light leakage position determined in the example is measured, and the luminance (Y) when the portion where light leakage does not occur is measured. The ratio (X / Y) between the two was measured and found to be 15. The closer this value is to 1, the more difficult it is to identify the presence of the light leakage part, and it can be seen that light leakage is stronger than in the example.

  In this way, the brightness at the time of darkening of the light leakage part is high because the group derived from benzyl acrylate in the part of the adhesive indicated by number 17a in FIG. 2 (B) is not fixed and is derived from benzyl acrylate. The reason for this is that it does not become an obstacle to the light transmitted through the number 17a in FIG.

  Thus, the polarizing plate specifically described in Patent Document 2 is not employed at all in the technique of the light leakage prevention method in the present invention.

  According to the present invention, it is possible to reduce a light leakage portion generated in an arc shape at the edge of a large display device, and a large internal stress is applied to the luminance of the light leakage portion and the polarizing film even during darkness. The difference from the brightness of the lighted portion becomes small, and the light leakage portion becomes hardly noticeable. In a large display device, it is necessary to use an extremely robust adhesive to attach a polarizing film so as not to form an arc-shaped light leakage portion at the edge of the screen. Even if a strong adhesive is used, it is extremely difficult to completely prevent the occurrence of an arc-shaped light leakage portion over a long period of use, and this tendency increases as the screen of the display device becomes larger.

  In the present invention, the light leakage portion can be made inconspicuous by adjusting the adhesive to adjust the luminance of the light leakage portion that has been formed while preventing the light leakage portion from being generated as much as possible.

FIG. 1 is a plan view and an end sectional view of a display device. FIG. 2 is a plan view and an end cross-sectional view of a display device in which an arc-shaped light passage portion is formed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Front surface of liquid crystal display device 11 ... Four corners 15 of liquid crystal display device ... Glass substrate 17 ... Adhesive layer 17 (a) ... Stress-sensitive adhesive layer 19 ... Polarizing film 19a ... (of light leaking part) Polarizing film 20 ... light leaking part 21 ... edge

Claims (2)

A method of reducing light leakage generated in an arc shape at an edge of the large display device by heat shrinkage of a stretched polarizing film attached to a TN mode large display device having a passing length of 19 inches or more,
The maximum value (W) from each edge of the light leakage arc generated at each edge of the large display device is such that the ratio (W / L) to the length (L) of the long side of the large display device is 0.1 or less. The pressure-sensitive adhesive for sticking the stretched polarizing film is imparted with a strength capable of resisting thermal shrinkage of the stretched polarizing film, and the light leakage portion formed in an arc shape at the edge of the large display device So that the brightness (X) when dark is 4 cd / m ² or less, and the ratio (X / Y) to the brightness (Y) when dark where the light leakage does not occur is 20 or less. A method for reducing light leakage formed in an arc shape at the edge of a large display device, wherein a side chain is introduced into the hydrocarbon main chain of the adhesive. This is a display device using a method of reducing light leakage generated in an arc shape at the edge of the large display device by thermal contraction of the stretched polarizing film attached to a TN mode large display device having a passing length of 19 inches or more. And
The maximum value (W) from each edge of the light leakage arc generated at each edge of the large display device is such that the ratio (W / L) to the length (L) of the long side of the large display device is 0.1 or less. The pressure-sensitive adhesive for sticking the stretched polarizing film is imparted with a strength capable of resisting thermal shrinkage of the stretched polarizing film, and the light leakage portion formed in an arc shape at the edge of the large display device The luminance (X) when the light is dark is 4 cd / m ² or less, and the ratio (X / Y) to the luminance (Y) when the light is not leaked is 20 or less. Further, a display device using a method for reducing light leakage formed in an arc shape at the edge of a large display device, wherein a side chain is introduced into the hydrocarbon main chain of the adhesive.

Images