JP2002328206A - Optical filter for display screen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical filter using a crazed film so that when the filter is attached to the front face of the display screen of a liquid crystal display, the filter prevents peeping in an oblique direction, that the filter is easily attached without requiring changes in the inner structure of the display for attaching, that the filter is easily attached and detached and that no contamination is left on the display screen after the filter is detached and this makes reuse of the screen possible. SOLUTION: The optical filter for a display screen is used to control the visible range by attaching it to the front face of the display screen of a display. The filter is prepared by laminating a self-adhesive layer made of a transparent soft polymer and having a smooth surface and both of re-peeling property and self-adhering property on a crazed film produced by forming a great number of craze lines parallel to one another on the surface of a transparent plastic film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical filter for a display screen, which is mounted on the front of a display screen of a liquid crystal display to control the field of view and prevent peeping from the side.

[0002]

2. Description of the Related Art An electronic display device such as a liquid crystal display is
OA for personal computers, word processors, copiers, facsimile machines, etc.
Cash dispenser, AT
It is used in a wide range of fields such as M, game consoles, televisions, clocks, telephones, and control devices in factories. In particular, cash dispensers and ATMs, and laptops and mobiles, peeping from the side to protect privacy. Is required to prevent the view.

In order to provide the above-mentioned visibility control function, a kind of optical filter called a viewing angle adjusting film is attached to the display screen so that the image looks bright from the front but is dark from the side and cannot be seen. Has been done. A so-called craze film in which a large number of crazes are formed on the surface of a transparent synthetic resin film in parallel with the molecular arrangement direction is known as the visible angle adjusting film (JP-A-6-82607, JP-A-7-82607). -1
46403 and JP-A-11-231108).

In order to fix the above-mentioned optical filter on a display screen, a pressure-sensitive adhesive is generally used. Although this adhesive has a practically sufficient fixing force, it has a problem that it is inferior in workability at the time of adhesion, air pockets are easily generated, and it is difficult to apply it neatly. In addition, since the adhesive force is strong and the adhesive force increases with the lapse of time, visibility control becomes unnecessary, or the optical filter becomes dirty, and it is difficult to remove it when it becomes necessary to remove it. If it is forcibly peeled off, there is a problem that the protective glass or the film of the display screen is damaged, or the adhesive is left on the surface and becomes dirty.

[0005]

SUMMARY OF THE INVENTION The present invention relates to an optical filter using the above-mentioned craze film, which can be attached to the front of the display screen of a liquid crystal display to prevent peeping from the side and is easy to attach. It is not necessary to change the internal structure of the display at the time of installation, and when it is necessary to view the display screen from other than the front, it can be easily removed, and the display screen after removal does not remain dirty, It is another object of the present invention to provide an optical filter for a display screen which can be reused thereafter.

[0006]

SUMMARY OF THE INVENTION An optical filter for a display screen according to the present invention is an optical filter for a display screen attached to a front surface of a display screen of a display to control a visible range, and is provided on a surface of a transparent plastic film. It is characterized in that a self-adhesive layer made of a transparent flexible polymer having a smooth surface and having removability and self-adhesiveness is laminated on a craze film formed by forming many parallel crazes.

[0007] The above-mentioned optical filter has a self-adhesive layer placed on the front surface of a display screen of a liquid crystal display and pressed by hand, so that no air bubbles are formed between the self-adhesive layer and the display screen, and the self-adhesive layer is self-adhesive. It can be mounted uniformly by the adhesive force, and the workability is good. And since this self-adhesive layer is formed on a smooth surface with a flexible polymer and has re-peelability together with self-adhesive force, it can be easily peeled off if necessary, The same optical filter can be fixed again on the front surface of the display screen after peeling and can be reused without any part being chipped. Therefore, even if there is a sticking error, the sticking can be performed again, and a part of the self-adhesive layer does not adhere to the trace of peeling and remains, and the display screen is not stained.

In the above-mentioned craze film, since the transmitted light is scattered at the craze portion, the light transmittance changes depending on the incident angle of the light on the film surface. In a plane perpendicular to the craze, light is transmitted in the direction normal to the film surface, and scattering is small, so the light transmittance is maximized and the field of view is brightest, and the direction of emission is horizontal to the direction normal to the film surface. As the angle increases, the scattering increases, the light transmittance decreases, and the visual field becomes dark. In other words, visibility control is exhibited. Therefore, when the optical filter is fixed so that the craze direction of the craze film coincides with the vertical direction of the screen, the visibility of the image on the side is reduced, and an effect of preventing peeping is exhibited. Also,
By inclining the direction of the craze by 45 degrees with respect to the vertical direction of the screen, the visibility can be reduced in all directions, that is, left, right, and up and down.

The material of the above-mentioned craze film is not limited as long as it is a plastic film capable of forming craze. Polyester such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyolefin such as polyethylene or polypropylene, polystyrene, polystyrene, etc. Mention may be made of methyl methacrylate, polyvinylidene fluoride and modifications thereof.

The craze film of the present invention is produced by using the above-mentioned plastic film and forming a large number of crazes on its surface in parallel with each other, but the production method is arbitrary. For example, a method in which a straight blade is pressed against a film surface to bend the film, and the film is moved in a direction perpendicular to the straight blade to intermittently generate craze on the outer surface of the bent portion (Japanese Patent Laid-Open No. 6-82607; Kaihei 7
-146403 and JP-A-11-231108
And the like, and a method of cold stretching a film at a temperature equal to or lower than the glass transition point.

The craze film may be a single layer or a multilayer. The polymer constituting the multilayer body may be any of different types or the same type, and the multilayer body is
Either one in which crazing is generated in one layer or one in which crazing is generated in both layers may be used. Further, the thickness of the craze film is also arbitrary, but is 10 to 500 μm,
In particular, it is preferably from 20 to 400 μm, and if it is less than 10 μm, visibility controllability becomes insufficient and handleability deteriorates.
Even if the thickness exceeds 00 μm, the handleability deteriorates. The depth of the craze is arbitrary, may be the depth reaching from the front surface to the back surface, and the pitch is also arbitrary, and is set according to the required performance of the market.

In the above-mentioned craze film, the inner wall of the craze can be colored with a dye and / or a pigment by infiltrating the craze with a dye or a pigment. The color is arbitrary, but particularly when colored black, the visibility of the image from the front is improved, and the visibility controllability is also improved. In addition, by adding a dye or a pigment to the self-adhesive layer or the base film described below in addition to the above-mentioned craze film, the effect is inferior to the coloring of the craze inner wall, but visibility controllability can be improved. . The dye or pigment in this case is not particularly limited, but a phthalocyanine-based dye is preferable from the viewpoint of weather resistance.

The flexible polymer constituting the self-adhesive layer is made of rubber, elastomer or plastomer, and includes natural rubber, silicone rubber,
Ethylene propylene rubber, acrylonitrile butadiene rubber, styrene butadiene rubber, chloroprene rubber, acrylic rubber, fluororubber, urethane rubber, etc., as elastomers, polyester-based, polyamide-based and polyolefin-based thermoplastic elastomers, and as plastomer, polyolefin-based Plastomers are respectively exemplified. These flexible polymers may be used alone or in combination of two or more.

The above-mentioned flexible polymer can contain various functionalizing agents, stabilizers and the like as long as the transparency is not impaired. Since the optical filter of the present invention is attached to the front surface of the display screen by using the self-adhesive force of the self-adhesive layer made of the above flexible polymer, it is not necessary to add an adhesion aid. The adhesion can be increased by blending an adhesion aid within a range not to impair the object of the present invention.

The self-adhesive strength of the self-adhesive layer is generated by forming a smooth surface of the self-adhesive layer made of a flexible polymer. In this case, the preferable average surface roughness (R
a) is 0.12 μm or less. Particularly preferred is 0.
08 μm or less, and most preferably 0.05 μm or less. When the average surface roughness (Ra) exceeds 0.12 μm, no self-adhesive force is generated, and it becomes impossible to fix the optical filter of the present invention by the self-adhesive force of the self-adhesive layer.

The dynamic hardness of the surface layer of the pressure-sensitive adhesive layer is as follows:
The type, structure, and formulation of the flexible polymer (eg, filler,
It is controlled by the amount of the crosslinking assistant, the adhesion assistant, the pressure-sensitive adhesive, etc.) and the degree of crosslinking (particularly, the degree of crosslinking of the surface layer), but the size is preferably 0.01 to 20 mN / 25 μm ^2. . Particularly, 0.02 to 10 mN / 25 μm ² is preferable, and 0.04 to 5 mN / 25 μm ² is most preferable. This dynamic hardness is 0.01 mN / 25 μm
^When it is less than ² , peeling becomes difficult, and the repairability including the reattachment described above decreases, and when it exceeds 20 mN / 25 μm ² , the fixing force becomes insufficient.

The initial adhesive strength of the surface of the self-adhesive layer is determined by the type of the flexible polymer constituting the self-adhesive layer, the type of the adhesive aid and the pressure-sensitive adhesive added to the self-adhesive layer in the same manner as the dynamic hardness described above. Can be controlled by quantity etc.
Generally, it is inversely proportional to the dynamic hardness, but the preferred size is 29 to 1960 mN / 25 mm. If the initial adhesive strength is less than 29 mN / 25 mm, the optical filter is likely to fall off the display screen, and conversely 1960
If it exceeds mN / 25 mm, the above-mentioned repairability is reduced.

The self-adhesive layer made of the above-mentioned flexible polymer can be formed by any method such as laminating the flexible polymer on one of the front and back surfaces of the craze film by an extrusion method or a coating method. Its thickness is generally 5 to 2
00 μm is preferred. This self-adhesive layer may be laminated directly to the craze film, or by interposing a transparent base film between the craze film and the laminate to reinforce the optical filter and improve its dimensional stability. It can be easily handled. The material of the substrate film is arbitrary, but polyethylene terephthalate is preferred in terms of transparency, dimensional stability, economy, and the like.
The thickness of the base film is generally 50 to 250 μm.
m is preferred.

In order to interpose a base film between the craze film and the self-adhesive layer, (a) a method of laminating the base film having the self-adhesive layer laminated thereon and the craze film with a double-sided adhesive tape, (b) A method in which a self-adhesive layer is laminated on one side of a base film and a craze film is laminated on the other side via a pressure-sensitive adhesive layer, (c) a craze film in which the pressure-sensitive adhesive is laminated, and a self-adhesive layer. A method of laminating the laminated base film with the above-mentioned pressure-sensitive adhesive, a method of (d) laminating a craze film on one side of the base film and laminating a self-adhesive layer on the other side, and the like can be used. it can.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1 A uniaxially stretched film made of a plastic such as polyester, polyolefin, polystyrene, polymethyl methacrylate, polyvinylidene fluoride or the like having a thickness of 10 to 500 μm, preferably 20 to 400 μm, is parallel to the orientation direction. By applying tension to the film and applying a local bending stress by applying a crazing edge parallel to the orientation direction, the above film is slid vertically to the direction of the edge, so that craze parallel to the orientation direction is achieved. Are formed into vertical stripes to obtain a craze film.

A base film of polyethylene terephthalate having a thickness of 50 to 250 μm is laminated on one side with a crosslinkable flexible polymer made of rubber, preferably silicone rubber, and an easy-peelable cover made of an arbitrary plastic is formed thereon. The film is laminated and the smooth surface of the cover film is transferred to the surface of the flexible polymer layer. Next, a flexible polymer layer is crosslinked by performing a crosslinking treatment, and is integrated with the base film. The thickness of the flexible film is 5 to 200 μm on one surface of the base film, and the average surface roughness (Ra
) 0.12 μm or less, dynamic hardness of surface layer 0.0
1 to 20 mN / 25 μm ² , initial adhesive strength 29 to 1960
A self-adhesive layer of mN / 25 mm is formed. Then, any one side of the craze film is bonded to the opposite surface of the base film with a pressure-sensitive adhesive.

The obtained laminate has a five-layer structure of a cover film, a self-adhesive layer, a substrate film, a pressure-sensitive adhesive layer, and a craze film, and the cover film protects the self-adhesive layer. Then, since the cover film is easily peelable from the self-adhesive layer, the cover film is peeled off to reveal the self-adhesive layer, and the self-adhesive layer is applied to the display screen of the liquid crystal display to hold down the craze film on the surface. Thereby, the optical filter for a display screen composed of the four layers of the self-adhesive layer, the base film, the pressure-sensitive adhesive layer, and the craze film is fixed to the display screen, and the display screen has visibility controllability.

Embodiment 2 In Embodiment 1 described above, a black dyeing solution is applied to the surface of the craze film, penetrated into craze, and dried.
Otherwise, a display screen optical filter colored black is obtained in the same manner as in the first embodiment. This optical filter is
Although it can be used similarly to the first embodiment, the visibility controllability is improved as compared with the first embodiment.

Embodiment 3 In Embodiment 1, at least one of the base film and the self-adhesive layer is colored with a dye or a pigment, preferably with a phthalocyanine pigment, and the others are colored in the same manner as in Embodiment 1. To obtain an optical filter for a display screen.
This optical filter can be used in the same manner as in the first embodiment. However, compared to the first embodiment, the visibility control is improved and the fashionability is improved.

Embodiment 4 In Embodiment 1 described above, a non-crosslinkable flexible polymer such as a thermoplastic elastomer is used in place of the crosslinkable flexible polymer, and the crosslinking treatment of Embodiment 1 is omitted. An optical filter for a display screen is obtained in the same manner as in the first embodiment. The surface of the base film that is in contact with the self-adhesive layer can be previously subjected to a treatment for improving adhesiveness, for example, an actinic radiation treatment or an undercoat. The obtained optical filter of Embodiment 4 can be used similarly to Embodiment 1. Also in this case, the second embodiment
In the same manner as in Embodiment 3 or Embodiment 3, the craze film, the base film, or the self-adhesive layer can be colored to improve the visibility control.

[0026]

EXAMPLES Various optical filters for display screens were prototyped,
Their performance was compared. The initial adhesive strength of the self-adhesive layer,
Surface dynamic hardness and average surface roughness (Ra)
It was measured by the following. 1. Initial adhesive strength According to JIS-Z-0237, adhere to a stainless steel plate, and after 20 minutes, peel angle 180 °, pulling speed 3
It was measured at 00 mm / min. 2. Surface dynamic hardness Shimadzu Dynamic Ultra Micro Hardness Tester DUH2 manufactured by Shimadzu Corporation
Test mode: mode 3 (soft material test), type of indenter: 115, test load: 1.97 mN,
The measurement was performed under the conditions of a load speed: 0.0142 mN / sec and a retention time: 5 seconds. The sample was fixed on a slide glass with an epoxy adhesive and set on a measuring table. As for the dynamic hardness evaluated by the present measurement method, different measured values are obtained depending on the depth from the surface of the sample. In this invention, 3 μm from the surface
The measured value of the depth m was defined as the surface hardness. 3. Average surface roughness (Ra) Using a Kosaka Laboratory SE200 type surface roughness meter, longitudinal magnification:
The measurement was performed under the conditions of 1000, lateral magnification: 20, cutoff: 0.08 mm, measurement length: 8 mm, and measurement speed: 0.1 mm / min.

Example 1 A tension was applied to a longitudinally uniaxially stretched polypropylene-based film (thickness: 25 μm) in the longitudinal direction, and a crazing blade was applied to the film in the longitudinal direction to apply local bending stress. By sliding the film in the horizontal direction, crazes in the vertical direction were formed on the film in the form of vertical stripes and at a depth extending over both the front and back surfaces of the film, thereby producing a craze film.

On one side of a base film made of polyethylene terephthalate and having a thickness of 188 μm, a pressure-sensitive strongly-adhesive type adhesive made of an acrylic polymer is laminated to a thickness of 25 μm, and the laminated surface of this adhesive is made of polyethylene terephthalate. Then, the easy-adhesion-treated surfaces of the cover film A having a thickness of 25 μm which had been subjected to the easy-adhesion treatment in advance were laminated. A commercially available high transparency type low hardness (hardness: 10 degrees) silicone rubber compound is applied to a thickness of 100 μm on the surface of the base film of the obtained base film / pressure-sensitive adhesive layer / cover film A laminate, and is peeled off again. A self-adhesive layer having adhesiveness and self-adhesiveness was formed to obtain a self-adhesive layer / substrate film / adhesive layer / cover film A laminate.

The above laminate is made of polyethylene terephthalate and has a thickness of 3
A cover film B having a thickness of 0 μm was laminated so that the easily-adhesive treated surface was in contact with the self-adhesive layer of the laminate. Obtained cover film B, self-adhesive layer, base film,
The adhesive layer / cover film A laminate is introduced into an electron beam irradiation device, and the self-adhesive layer made of silicone rubber is crosslinked.
And it was integrated with the base film.

In the obtained laminate having a five-layer structure, both the cover film A and the cover film B can be easily peeled off. When the cover film B on the side of the self-adhesive layer was peeled off and the characteristics of the self-adhesive layer were evaluated, the average surface roughness (Ra) was 0.04 μm, the surface dynamic hardness was 0.09 mN / μm ² , and the initial adhesive force was 240 mN. / 25
mm.

Next, the adhesive film on the pressure-sensitive adhesive layer side of the laminate was peeled off, and the above-mentioned craze film was overlaid on the pressure-sensitive adhesive layer and adhered to obtain the optical filter for a display screen of Example 1. . This display screen optical filter was cut into a rectangle corresponding to the shape of the liquid crystal display screen. At that time, the craze direction of the craze film was set at an angle of 90 degrees with respect to the side of the liquid crystal display screen. Then, the above-mentioned optical filter was attached to the display screen by the self-adhesive force of the self-adhesive layer while peeling off the self-adhesive layer side cover film B on the back surface.

This optical filter has high visibility of an image when the screen is viewed from the front, but has low visibility when viewed from the side, and the viewing direction is substantially horizontal to the normal direction of the display screen. When the angle exceeds 60 degrees, the above-mentioned image becomes difficult to see. In other words, it had a visibility control function that made it possible to prevent peeping. In addition, since the optical filter is formed of a craze film, the reflection of external light is reduced, and a function of preventing reflection is provided.

Further, since the optical filter has a self-adhesive layer made of a flexible polymer on the back surface, it can be attached to a display screen without using an adhesive or an adhesive. Moreover, since the cover film B is provided on the surface of the self-adhesive layer, the self-adhesion proceeds only by bringing the self-adhesive layer into contact with the display screen while peeling off the cover film B, and the sticking is easily performed. In addition, air interposed between the optical filter and the surface of the display screen is pushed out by self-adhesive force, so that air does not bite.

The optical filter of the first embodiment is
Since the initial adhesive strength of the self-adhesive layer satisfies the requirement of claim 4, the self-adhesive layer has excellent fixing force, and can be easily peeled off after being attached to a display screen or the like, and can be peeled off with a weak force. Unlike the adhesion caused by the above, there was no surface dirt on the display screen after peeling. Then, in the optical filter after peeling, the initial adhesive strength of the self-adhesive layer was not different from that before sticking, and the same was obtained even after sticking and peeling were repeated 20 times, and the repairability was excellent.

Comparative Example 1 An optical filter for a display screen was manufactured in the same manner as in Example 1 except that a uniaxially stretched polypropylene film was used in place of the craze film of Example 1 described above. The obtained optical filter of Comparative Example 1 did not have visibility controllability and could not prevent peeping.

COMPARATIVE EXAMPLE 2 In Example 1, the self-adhesive layer was laminated on one side of the base film and the acrylic adhesive layer was laminated on the other side. An acrylic pressure-sensitive adhesive layer was laminated on both sides, and the other steps were the same as in Example 1 to produce an optical filter for a display screen of Comparative Example 2. The obtained optical filter of Comparative Example 2 was inferior in workability when sticking to a display screen, and could not be stuck neatly without introducing air into the interface. In addition, since the pressure-sensitive adhesive layer had a strong adhesive force, it was difficult to peel off the adhesive layer after application, and the handleability as an optical filter for a display screen was poor.

Example 2 A black dye was applied to the craze film of Example 1 while applying a tension in a direction perpendicular to the craze, and the dye was permeated into the craze by pressing with a roll and dried. A colored type craze film was produced. Further, the optical filter for a display screen of Example 2 was manufactured in the same manner as in Example 1 except that the thicknesses of the base film and the silicone rubber compound of Example 1 were changed to 50 μm.

Since the obtained optical filter for a display screen of Example 2 used a colored type craze film,
The visibility control function was superior to that of the first embodiment. When the viewing direction exceeded approximately 45 degrees horizontally with respect to the normal direction of the display screen, the image became difficult to see. The total thickness is 150μ.
Because of its small thickness of m, it was practical as an optical filter for a display screen for pen touch input of a mobile device or the like.

Example 3 The display screen of Example 3 was prepared in the same manner as in Example 1 except that the phthalocyanine-based blue pigment and carbon black were blended with the silicone rubber compound for a self-adhesive layer of Example 1 and colored blue. An optical filter was obtained. This optical filter had a better visibility control function than the optical filter of Example 1, and when the viewing direction exceeded approximately 45 degrees horizontally with respect to the normal direction of the display screen, the image became difficult to see. In addition, since it was colored blue, the fashionability was also good.

Examples 4 to 6 In Example 2, three kinds of flexible polymers of a high elongation type urethane rubber, an olefin thermoplastic elastomer and a 50 degree silicone rubber were used instead of the silicone rubber compound for the self-adhesive layer. And Example 2
In the same manner as in Example 1, optical filters for display screens of Examples 4 to 6 were obtained. However, the crosslinking treatment was omitted for the high elongation type urethane rubber and the olefin-based thermoplastic elastomer. The characteristics of the self-adhesive layer in the obtained optical filter were the same as those of Example 2 as shown in Table 1 below, and the optical filter was highly practical for preventing peeping.

[0041]

[Table 1]

[0042]

As described above, since the optical filter for a display screen of the present invention uses a craze film,
By being attached to the front of the display screen of the liquid crystal display, peeping from the side can be prevented, and reflectivity of external light is reduced, so that reflection can be prevented. And since it is mounted on the front of the display screen, there is no need to change the internal structure of the display, and since it is mounted with the self-adhesive force of the self-adhesive layer, workability is good and easy to attach and detach The display screen can be viewed not only from the front but also from an oblique direction so that a plurality of persons can view the display screen at the same time.

In particular, in the invention according to claim 2, since the base film is interposed between the craze film and the self-adhesive layer, the rigidity and dimensional stability of the optical filter are improved, and the handling and workability thereof are improved. Become good. In the invention according to claim 3, since the craze is colored, the visibility control function is improved. The invention according to claim 4 limits the surface dynamic hardness, the average surface roughness (Ra), and the initial adhesive strength of the self-adhesive layer.
Handling and workability are further improved.

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Claims (4)

[Claims] An optical filter for a display screen attached to a front surface of a display screen of a display to control a visible range, and formed on a transparent plastic film by forming a plurality of parallel crazes on a surface of a plastic film. An optical filter for a display screen, comprising a self-adhesive layer having a smooth surface and a removability and a self-adhesive property made of a transparent flexible polymer. 2. The optical filter for a display screen according to claim 1, wherein a base film is interposed between the craze film and the self-adhesive layer. 3. The craze film according to claim 1, wherein the craze inner wall of the craze film is colored with a dye and / or a pigment.
An optical filter for a display screen according to item 1. 4. The self-adhesive layer has a surface dynamic hardness of 0.01 to 20 mN / 25 μm ² , an average surface roughness (Ra) of 0.12 μm or less on the surface of the self-adhesive layer, and an initial adhesive force of 29 on the self-adhesive layer surface. The optical filter for a display screen according to any one of claims 1 to 3, wherein the optical filter has a thickness of 1960 mN / 25 mm.