CHO, Hong-Youl (Donga Apt. 104-901, Jorye-dong Suncheon-si, Jeonranam-do 540-320, KR)
KIM, Dong-Young (Wolbong Ilseong Apt, Ssangyong-dong Cheonan-si, Chungcheongnam-do 330-090, 512-1405, KR)
CHO, Seong-Keun (Jinjamtown Apt. 206-104, Wonnae-dong Yuseong-gu, Daejeon 305-757, KR)
CHO, Hong-Youl (Donga Apt. 104-901, Jorye-dong Suncheon-si, Jeonranam-do 540-320, KR)
KIM, Dong-Young (Wolbong Ilseong Apt, Ssangyong-dong Cheonan-si, Chungcheongnam-do 330-090, 512-1405, KR)
Claims
[1] A flame-retardant optical filter for display panels comprising an electromagnetic interference (EMI) shielding film, an anti-reflection (AR) film, a near infrared (NIR) shielding and selective optical absorbent film, and at least one adhesive layer disposed between said films, wherein at least one of said films comprises a phosphorous-containing polyester resin.
[2] The flame-retardant optical filter of claim 1, wherein the phosphorous-containing polyester resin contains a phosphorous-containing repeating unit of formula (I) in an amount of 3 to 30 mol% and an ester repeating unit in an amount of 70 to 97 mo% in the polyester chain:
0 Il
-O-p-R-C- I Il R 1 0 ω wherein, R is C saturated alkylene or an arylene group, and R is C alkyl or an aryl group. [3] The flame-retardant optical filter of claim 1, wherein the phosphorous-containing polyester resin is used in the form of a mono or biaxially oriented polyester film comprising a flame-retardancy enhancing agent in an amount of 0.05 to 5 wt% based on the phosphorous-containing polyester resin. [4] The flame-retardant optical filter of claim 2, wherein the phosphorous-containing repeating unit is derived from a compound selected from the group consisting of
2-carboxymethylethylphosphinic acid, carboxymethylphenylphosphinic acid,
2-methyl-2,5-dioxo- 1 -oxa-2-phosphorane, carboxyphenylethylphosphinic acid and a mixture thereof. [5] The flame-retardant optical filter of claim 3, wherein the flame-retardancy enhancing agent is selected from the group consisting of polytetrafluoroethylene
(Teflone ), an epoxy- or methacrylate-grafted silicon powder, boron phosphate, aluminum oxide and a mixture thereof. [6] The flame-retardant optical filter of claim 2, wherein the phosphorous-containing polyester resin has an intrinsic viscosity of 0.4 to 0.9 dl/g. [7] The flame-retardant optical filter of claim 1, wherein the adhesive layer comprises a flame-retardancy enhancing agent. [8] The flame-retardant optical filter of claim 1, wherein the AR layer is disposed on the outer layer of the filter. [9] The flame-retardant optical filter of claim 1, wherein the AR film, and the NIR shielding and selective optical absorbent film are each formed on one transparent substrate film. [10] The flame-retardant optical filter of claim 1, wherein the NIR shielding and selective optical absorbent film is prepared by incorporating an NIR cutting agent and a selective optical absorbent in an adhesive. [11] The flame-retardant optical filter of claim 1, which has a light transmittance of
30 to 60% at a wavelength ranging 380 to 780 nm. |
Description
FLAME-RETARDANT OPTICAL FILTER FOR DISPLAY
PANELS
Technical Field
[1] The present invention relates to a flame-retardant optical filter for display panels.
[2]
Background Art
[3] A plasma display panel (PDP) is more suitable for high definition television (HDTV) having an enlarged, flat frame than other display devices such as a cathode ray tube (CRT) or a liquid crystal display (LCD), but has the problems of: emitting undesirable electromagnetic interference (EMI) / infrared (IR) emissions; high photopic reflection on its surface; and lower color purity than CRT caused by orange light emitted from injected Ne or He gas. Accordingly, an appropriate filter has been applied in front of a plasma display panel to solve the above problems, the filter having optical properties such as EMI/IR and NIR shielding ability, anti-reflection and color purity.
[4] Also, an optical filter for use on a PDP has recently prepared using a transparent polyethyleneterephthalate (PET) substrate for laminating predesigned optical layers thereon, instead of a glass plate, to impart an improved impact strength and lightweight to the filter. However, such a filter prepared using such a PET transparent film substrate has poor heat stability and its properties deteriorate with use.
[5] Accordingly, the present inventors have endeavored to develop an optical filter having flame-retardancy.
[6]
Disclosure of Invention Technical Problem
[7] It is, therefore, an object of the present invention to provide an optical filter having flame-retardancy as well as good optical properties.
[8]
Technical Solution
[9] In accordance with the present invention, there is provided a flame-retardant optical filter for display panels comprising an electromagnetic interference (EMI) shielding film, an anti-reflection (AR) film, a near infrared (NIR) shielding and selective optical absorbent film, and at least one adhesive layer disposed between said films, wherein at least one of said films comprises a phosphorous-containing polyester resin.
Brief Description of the Drawings
[11] The above and other objects and features of the present invention will become apparent from the following description, when taken in conjunction with the accompanying drawings which respectively show:
[12] FlGs. 1 and 2: schematic diagrams of exemplary optical filters for display panels of the present invention; and
[13] FlG. 3: the light transmittance characteristics of the optical filter for display panels prepared in Example 1 of the present invention.
[14]
Mode for the Invention
[15] The optical filter for display panels according to the present invention is characterized in that at least one of the functional films comprises a flame-retardant, more specifically, a phosphorous-containing polyester resin.
[16] The phosphorous-containing polyester resin suitable for use in the present invention contains a phosphorous-containing repeating unit of formula (I) in an amount of 3 to 30 mol%, preferably 5 to 20 mol%, and an ester repeating unit in an amount of 70 to 97 mo%, preferably 80 to 95 mol% in the polyester chain:
[17]
-O
[18] wherein, R is C saturated or an arylene group, and R is C alkyl or an aryl group.
[19] Examples of the phosphorous-containing repeat unit of formula (I) are derived using a phosphorous compound selected from the group consisting of 2-carboxymethylethylphosphinic acid, carboxymethylphenylphosphinic acid, 2-methyl-2,5-dioxo-l-oxa-2-phosphorane, carboxyphenylethylphosphinic acid and a mixture thereof.
[20] The phosphorous-containing polyester resin may be used as a component in a mono or biaxially oriented flame-retardant polyester film which may comprise a flame- retardancy enhancing agent in an amount of 0.05 to 5 wt% based on the phosphorous- containing polyester resin.
[21] Examples of the flame-retardancy enhancing agent include polytetrafluoroethylene
(Teflone ), an epoxy- or methacrylate-grafted silicon powder, boron phosphate, aluminum oxide and a mixture thereof.
[22] The phosphorous-containing polyester resin mentioned above may be prepared by the method disclosed in Korean Application Patent Publication Nos. 1999-81266 and 2005-37854, and it preferably has an intrinsic viscosity of 0.4 to 0.9 dl/g, more
preferably 0.5 to 0.8 dl/g (measured at 35°C using a 0.3g sample dissolved in 25D of ortho-chlorophenol). When its intrinsic viscosity is less than 0.4 dl/g, frequent breakages occur during drawing and the final film product's mechanical strength becomes poor. When it is greater than 0.9 dl/g, the shear stress increases to cause poor processibility.
[23] Furthermore, in order to enhance of the flame-retardancy of the inventive optical filter, the phosphorous compound and the flame-retardancy enhancing agent mentioned above may also be incorporated in at least one adhesive layer that coats a transparent press-sensitive adhesive (PSA) of an acryl or a thermoplastic elastomer such as styrene-butadiene-styrene (SBS) and styrene-ethylene-butadiene-styrene (SEBS), which is used in laminating each of the functional films.
[24] The inventive optical filter for display panels may comprise conventional functional films which are well known in the art, an EMI shielding film, an AR film, and an NIR shielding film and selective optical absorbent film. For example, as shown in FIGs. 1 and 2, the inventive optical filter comprises an AR film (1, a) having a substrate (2, b) formed on the outer layer so as to prevent reflection by external light; an NIR shielding/selective optical absorbent film (3, d) containing an NIR cutting agent and a selective optical absorbent, which may have a substrate (e) and an EMI shielding film (5, g) having a substrate (6, h) laminated by an adhesive layer (4, c, f); and an adhesive layer (7, i) for attaching to a display module and a release film (not shown). The adhesive layer (7, i) is used to join the inventive filter to a display module, through the removal of the releasable film. If necessary, the EMI shielding film and NIR shielding film may be laminated in turn.
[25] The EMI shielding film is preferably in the form of a conductive mesh made of a metal fiber or a metal-coated fiber, and may be also formed in at least two layers by laminating repeatedly a metal layer and a dielectric layer using a dry coating method such as sputtering.
[26] The NIR shielding/selective optical absorbent film may be prepared by mixing an
NIR cutting agent, a selective optical absorbent and a plastic transparent resin in a solvent and applying the resulting solution on a transparent substrate to a thickness of 1 to 20 D. Examples of the NIR cutting agent include a mixture of a Ni complex and a diammoniumcompound, an organic pigment and a pigment containing Cu or Zn ion. Examples of the selective optical absorbent include derivative pigments in which a metal atom located in the center of octaphenyl tetraazaporphyrin and tetraazaporphyrin is coordinated with one ligand selected from the group consisting of NH , H O and halogen. Examples of the plastic transparent resin include poly(methyl methacylate) (PMMA), polyvinylalcohol (PVA), polycarbonate (PC), ethylenevinyl acetate (EVA), poly(vinylbutylal) (PVB) or polyethylene terephthalate (PET). Examples of the solvent
which may be used include toluene, xylene, acetone, methyl ethyl ketone (MEK), propylalcohol, isopropyl alcohol, methyl cellulose, ethyl cellulose and dimethyl- formamide (DMF).
[27] The AR film may be formed by first hard-coating a scratch-resistant acryl resin on one surface of the substrate film, and then forming a low refractive index layer or forming thereon transparent layers having alternate high and low refractive indexes. The coating of the AR film may be carried out by vacuum-coating, or wet-coating, e.g., roll-coating, or die-coating.
[28] The AR film and the NIR shielding/selective optical absorbent film may be formed on the surfaces of separate transparent substrates, or on both sides of one transparent substrate. The NIR shielding/selective optical transmission film may be formed by incorporating an NIR cutting agent and selective optical absorbent in an adhesive.
[29] The inventive optical filter thus obtained has a light transmittance of 30 to 60% at a wavelength ranging 380 to 780 nm.
[30] Thus, the optical filter for display panels according to the present invention has flame-retardancy as well as good optical properties, and may be attached by any of the conventional means to the front glass of a display.
[31]
[32] The present invention is further described and illustrated in Examples provided below, which are, however, not intended to limit the scope of the present invention.
[33]
[34] Preparation 1
[35] A flame-retardant phosphorous-containing polyester film was prepared by the method according to Example 1 of Korean Application Patent Publication No. 2005-37854, as follows.
[36] Dimethyl terephthalate and ethylene glycol were mixed in an equivalent ratio of 1 :2, and calcium acetate monohydrate was added thereto in an amount of 0.05% by weight based on the weight of dimethyl terephthalate to produce bis-2-hydroxyethyl terephthalate. 2-Carboxyethylmethylphosphinic acid was added to the reaction mixture in an amount of 0.2 equivalent based on the amount of dimethyl terephthalalte, and then, trimethylphosphate (a stabilizer) and antimonytrioxide (a polymerization catalyst) were added thereto in amounts of 0.05% and 0.04% by weight, respectively, based on the weight of dimethyl terephthalate, to obtain a polyester resin having an intrinsic viscosity of 0.640 dl/g.
[37] 5 parts by weight of polytetrafluoroethylene (a flame-retardancy enhancing agent) was added to 100 parts by weight of the polyester resin, and mixed at 285°C using a compounder screw at a rotation rate of 300 rpm, to obtain a high-concentration master chip.
[38] The polyester resin and the master chip thus obtained were mixed in a weight ratio of
4:1. The mixture was dried and melt-extruded by a conventional film preparation procedure to obtain a sheet. The sheet was drawn at a draw ratio of 3.5 in both the longitudinal and transverse directions, followed by heat-setting at 220°C, to obtain a flame-retardant polyester film of IOOD thick.
[39]
[40] Example 1
[41]
[42] Step 1: Preparation of AR film
[43] On the flame-retardant polyester film obtained in Preparation 1, a hard-coating layer was formed, on which a zirconium-based layer and a fluorosiloxane-based layer were successively formed by a wet-coating process, to obtain an AR film.
[44]
[45] Step 2: Preparation of NIR shielding/selective optical absorbent film
[46] 300g of poly(methyl methacrylate) was dissolved in IOOOD of MEK, to which IOOD of octaphenyl tetraazaporphyrin and 150D of IRG022 (Nippon Chemical pharmaceutical Co.) were added. To the resulting solution, a solution of 120D of Acridine Orange (Aldrich Chemical Co.) in 50D of isopropyl alcohol was slowly added. The resultant was applied on a biaxially drawn PET film, a substrate film, through a wet-coating process and dried, to obtain an NIR shielding/selective optical absorbent film having a thickness of about 5D.
[47]
[48] Step 3: Preparation of transparent adhesive layer
[49] An acrylate-based transparent adhesive was applied on a silicon release layer by a comma coating method and dried, on which another release film was laminated, to obtain a transparent adhesive layer having release films on both sides thereof in the form of a roll.
[50]
[51] Step 4: Preparation of EMI shielding film
[52] A transparent adhesive was applied on a copper mesh film having a specific mesh pattern (line width: 10 m, line pitch: 300 m, open area ratio: 93%) and dried, on which a release film was laminated, to obtain an EMI shielding film.
[53]
[54] Step 5: Preparation of optical filter assembly
[55] As schematically shown in FIG. 2, the AR film and the NIR shielding/selective optical absorbent film obtained in Steps 1 and 2 were laminated by disposing therebetween the transparent adhesive layer obtained in Step 3, both of the release films were removed, followed by applying a constant pressure of 3kgf/m . On the NIR
film, the EMI shielding film obtained in Step 4 was laminated using the transparent adhesive layer and applying a constant pressure of 3kgf/m 2 , to obtain an optical filter assembly for display panel.
[56]
[57] Example 2
[58] The procedure of Example 1 was repeated except that the flame-retardant polyester film obtained in Preparation 1 was used instead of a biaxially drawn PET film as a substrate film in Step 2, to obtain an optical filter assembly for display panel.
[59]
[60] Comparative Example 1
[61] The procedure of Example 1 was repeated except that a biaxially drawn PET film was used instead of the flame-retardant polyester film in Step 1, to obtain an optical filter assembly for display panel.
[62]
[63] Performance Test
[64] The optical filters prepared in Examples 1-2 and Comparative Example 1 were each measured for its flame-retardancy, light tranmittance and color coordinate using the methods described below. The results are shown in Table 1 and FIG. 3.
[65]
[66] (1) Flame-retardancy
[67] A filter specimen was subjected to UL 94 Vertical flame Test, and the flame- retardancy thereof was determined according to UL 94 rating of: V-O superior; V-I good; and V-2 poor.
[68]
[69] (2) Light transmittance (%) : measured with a spectrophotometer (U-4100 manufactured by Hitachi, Ltd.)
[70] The transmittance means a luminous transmittance at 380 to 780 nm according to
CIE (Commission Internationale d'Eclairage) requirements.
[71]
[72] (3) Color coordinate : measured with a spectrophotometer (U-4100 manufactured by
Hitachi, Ltd.)
[73] The color coordinate was determined according to CIE color coordinate system.
[74] Table 1
[Table 1] [Table ]
[75] As can be seen in Table 1, the inventive optical filter applying a flame retardant to at least one functional film has flame-retardancy without adversely affecting optical properties such as light transmittance and color characteristic.
[76] [77] While the present invention has been described and illustrated with respect to the preferred embodiments only, various changes and modifications may be made therein without departing from the inventive concept of the present invention which should be limited only by the scope of the appended claims.