KR100592417B1 - A liquid crystal display device comprising a method for forming an alignment film of the liquid crystal display device and an alignment film formed therefrom. - Google Patents

Abstract

The present invention relates to a photoalignable polymer which can be used as an alignment film of a liquid crystal display device, an alignment film formed therefrom, and a liquid crystal display device having the alignment film, wherein the photoalignable polymer of the present invention is represented by the following Chemical Formula 1.

The photo-alignment polymer according to the present invention not only forms an alignment film having excellent alignment characteristics and high thermal stability even by a small amount of light irradiation, but the prepared liquid crystal cell has little change in alignment characteristics for a long time at high temperature and is stable.

Photoalignment, Polymer, Liquid Crystal Display, Alignment Film

Description

A manufacturing method of photoalignment film for liquid crystal display and a liquid crystal display having the alignment film formed therefrom}

1 is a polarization micrograph of a liquid crystal cell according to Example 1 of the present invention,

2 is a polarization micrograph of the liquid crystal cell according to Comparative Example 1.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoalignable polymer that can be used as an alignment film of a liquid crystal display device, an alignment film formed therefrom, and a liquid crystal display device having the alignment film. The present invention relates to a photoalignable polymer capable of producing a stable liquid crystal cell having a high alignment film as well as little change in orientation characteristics at high temperatures for a long time, an alignment film formed therefrom, and a liquid crystal display device having the alignment film.

Liquid crystal display (LCD) is attracting attention as the most competitive display that can replace the CRT because it has the advantages of light weight and low power consumption. The liquid crystal panel of the liquid crystal display device is formed by sequentially forming a transparent electrode and an alignment layer on the upper substrate and the lower substrate facing each other, and by injecting a liquid crystal between the alignment layers, in order to fulfill its role as a display, light transmissive Function as a display element such as response time, viewing angle, contrast and the like. Since the above function is determined according to the arrangement characteristics of the liquid crystal molecules of the liquid crystal display device, a technique of uniformly controlling the alignment of the liquid crystal molecules is very important.

As a method of obtaining the alignment of the liquid crystal, methods such as a rubbing method, a stretching method, a light irradiation method and the like are known. Among these, the most widely used as an alignment film to date is a rubbing alignment film that induces alignment by using a rubbing technique on a polyimide polymer. The rubbing method is a simple method of rubbing a substrate coated with a polymer with a cloth. The rubbing method is a method widely used industrially since the process is simple, large area and high speed treatment are possible.

However, the above rubbing method has some critical defects. For example, since the shape of the microgrooves formed in the alignment layer varies depending on the friction strength between the alignment cloth and the alignment layer, the arrangement of liquid crystal molecules becomes nonuniform, resulting in phase distortion and light scattering. . In addition, there is a problem that the production yield is reduced due to substrate damage and dust generated from the rubbing cloth caused by electrostatic discharge (ESD) generated by rubbing the polymer surface. In addition, the process of forming a multidomain, which is a method of aligning only locally selected regions so that each region is oriented differently, is very complicated, and thus, viewing angle improvement is fundamentally impossible. Therefore, development of an alignment film using a new structure and an alignment method has been required.

M. Schadt et al. (Jpn. J. Appl. Phys., Vol. 31, 1992, 2155), Dae S. Kang et al. (US Pat. No. 5,464,669), Yuriy, as proposed to improve the deficiencies of the aforementioned rubbing method. There is a photoalignment method published by Reznikov (Jpn. J. Appl. Phys., Vol. 34, 1995, L1000). Photo-alignment method induces photo-dimerization, photo-isomerization or photo-decomposition by irradiating linearly polarized ultraviolet rays on the substrate coated with photosensitive polymer. It is a method of providing an orientation direction to an orientation film. Since the photo-alignment method is a non-contact method, it is possible to fundamentally exclude the problems caused by the introduction of impurities and the generation of static electricity, so that the alignment process is easy to improve the yield, so that it is suitable for mass production. It is an advantageous method for improving the viewing angle because multi-domains can be formed by a relatively simple process of irradiation.

The polymer used as the liquid crystal photoalignment film includes a cinnamate-based polymer for aligning the liquid crystal through a photodimerization reaction, a polymer including an azobenzene group for aligning the liquid crystal through a photoisomerization reaction, and a poly for aligning the liquid crystal through a photolysis reaction. A mid series polymer and the like. Since the cinnamate-based polymer has a fast photoreaction, excellent liquid crystal alignment can be obtained by light irradiation for a relatively short time. However, the linear inclination angle is less than 1 degree, and the thermal stability is weak. The photoisomerization method using a polymer containing an azobenzene group also has an advantage that the alignment is simple, but there is a problem in stability because the weak alignment property and the alignment characteristics of the oriented liquid crystals change over time.

On the other hand, various photodegradable polymers may be used in the method by photolysis, but little is known so far except cyclobutane-based polyimide, and this polymer also has excellent stability of the alignment layer and Therefore, there is an advantage that the adjustment of the pretilt angle is easy, but there is a problem that the light irradiation time is long because the light reaction is slow.

Accordingly, the technical problem to be achieved by the present invention is to solve the above problems, and not only to form an alignment film having excellent alignment characteristics and high thermal stability even by a small amount of light irradiation, but also to change the alignment characteristics at a high temperature for a long time. The present invention provides a photo-alignment polymer, an alignment film formed therefrom, and a liquid crystal display device including the alignment film, which can produce a stable liquid crystal cell.

In order to achieve the above technical problem, the present invention provides a photoalignable polymer represented by the following Chemical Formula 1.

<Formula 1>

In Formula 1, l and m are each an integer of 1 to 100, n is an integer of 0 to 100, m / (l + m + n) is 0.1 to 0.95, n / (l + m + n) Is 0 to 0.9 and R ₁ is

Any one selected from the group consisting of (R ₂ and R ₃ ) is (-H, -CH ₂ Cl), (-CH ₂ Cl, -H), (-CH ₂ Cl, -CH ₂ Cl) Any one selected from the group, X and Y are each independently selected from the group consisting of -OOC-, -NH-, -O-, p, q are each an integer of 0 to 4, A ₁ and A ₂ independently of one another is -CF _2- , -CH _2- , -CH〓, -O-, -COO-, -OOC-, -NHCO-, -CONH-, any one selected from the group B ₁ and B ₂ independently of one another is hydrogen, a halogen group, a cyano group, a nitro group, an amino group, an alkyl group having 1 to 100 carbon atoms, a haloalkyl group, a cyanoalkyl group, a nitroalkyl group, a hydroxyalkyl group, a cyanohaloalkyl group, a nitrohaloalkyl group , Cyanonitroalkyl group, hydroxyhaloalkyl group, cyanohydroxyalkyl group, hydroxynitroalkyl group, aryl group having 6 to 100 carbon atoms, alkylaryl group, haloaryl group, haloalkyl Aryl group, nitroaryl group, nitroalkylaryl group, cyanoaryl group, cyanoalkylaryl group, nitroaryl group, nitroalkylaryl group, hydroxyaryl group, hydroxyalkylaryl group, cyanohaloaryl group, cya It is any one selected from the group consisting of nohaloalkylaryl groups.

In addition, the present invention provides an alignment layer including the above-described photoalignable polymer and a liquid crystal display device having the same.

Hereinafter, looking at the synthesis method of the optical orientation polymer of the present invention as an example.

The photo-oriented polymer containing the soluble aromatic chloromethylated polyimide according to the present invention can be synthesized through the following method.

First, a soluble aromatic polyimide represented by the formula (2) is prepared. The soluble aromatic polyimide synthesizes a soluble aromatic polyimide from an aromatic dihydric acid having a fluorine substituted or cardo type and an aromatic diamine having a fluorine substituted or cardo type or a general aromatic diamine. Such soluble aromatic polyimides can be subjected to various polymerization methods including conventional general polyimide synthesis techniques, for example, by polycondensation of dihydric acid and diamine at room temperature using purified NMP solvent to form a polyamic acid, followed by chemical imidization. You can prepare it in a way.

In Formula 2, x is an integer of 1 to 300, R ₁ is

 Any one selected from the group consisting of.

Then, a chloromethyl group is introduced into the side chain of the soluble aromatic polyimide to obtain the compound of formula 3.

In Formula 3, l and m are integers, l + m is an integer of 1 to 300, R ₁ is

Any one selected from the group consisting of (R ₂ and R ₃ ) is (-H, -CH ₂ Cl), (-CH ₂ Cl, -H), (-CH ₂ Cl, -CH ₂ Cl) Any one selected from the group.

Introduction of the chloromethyl group is performed by dissolving the soluble aromatic polyimide of Chemical Formula 2 in an organic solvent such as chloroform, tetrahydrofuran, and then using chloromethyl methyl ether, formaldehyde, or paraformaldehyde and methylene group donating reagent and hydrochloric acid. And chloromethylation by reacting with a chlorine group donating reagent such as chlorosulfonic acid in the presence of a zinc chloride or Friedel-Craft metal catalyst such as aluminum trichloride or tin chloride. In this case, chloromethylated polyimide having a chloromethyl group content of 1 to 200% per polyimide repeating unit may be prepared by controlling the amount of the reactant, the reaction time, and the reaction temperature.

The polymer compound of Formula 3 may be used as the photo-alignment polymer as exemplified in the present invention, and in order to easily control the inclination angle, a functional group known to be useful for increasing the inclination angle of the liquid crystal is introduced into the polymer of Formula 3 above. Finally, a polymer of Chemical Formula 1 is obtained.

The introduction of a functional group for increasing the inclination angle is possible by selecting one or more compounds among the compounds represented by Formula 4 to the polymer of Formula 3 and reacting under neutral or basic conditions.

In Formula 4, X is any one selected from the group consisting of -COOH, -NH ₂ , -OH, r is an integer of 0 to 4, A is -CF _2- , -CH _2- , -CH〓, Any one selected from the group consisting of -O-, -COO-, -OOC-, -NHCO- and -CONH-, B is hydrogen, a halogen group, a cyano group, a nitro group, an amino group, an alkyl group having 1 to 100 carbon atoms, Haloalkyl group, cyanoalkyl group, nitroalkyl group, hydroxyalkyl group, cyanohaloalkyl group, nitrohaloalkyl group, cyanonitroalkyl group, hydroxyhaloalkyl group, cyanohydroxyalkyl group, hydroxynitroalkyl group, carbon number 6 100 to aryl group, alkylaryl group, haloaryl group, haloalkylaryl group, nitroaryl group, nitroalkylaryl group, cyanoaryl group, cyanoalkylaryl group, nitroaryl group, nitroalkylaryl group, hydroxyaryl Group consisting of a group, a hydroxyalkylaryl group, a cyanohaloaryl group, and a cyanohaloalkylaryl group One from the one selected.

Hereinafter, the manufacturing method of the photo-orientation polyimide of the present invention will be described in more detail.

As described above, the soluble aromatic polyimide of Chemical Formula 2 may be synthesized according to a known method for preparing a soluble aromatic polyimide. In particular, in order to prepare an soluble aromatic polyimide, 4,4 ′-(hexafluoro Fluorine dianhydrides such as lysopropylidene) diphthalic anhydride [4,4 '-(hexafluoroisopropylidene) diphathalic anhydride, (6FDA)] or 9H-fluorene-9,9-yliden Cardo-type dianhydrides having substituents such as fluorine-based diamines or 9H-fluorenes such as 2,3,5,6-tetrafluoro-1,4-benzenediamine Cardio-type diamines having substituents such as -9,9-yliden, or aromatic diamines such as commonly used 4,4'-oxydianiline (ODA), etc., alone or in combination It is possible to use.

Examples of the solvent include halogenated solvents such as chloroform, 1,2-dichloroethane and 1,2-dichloropropane, or organic compounds such as tetrahydrofuran, cyclohexanone, pyridine, dimethyl sulfoxide, dimethylformamide, and N-methylpyrrolidone. Solvents are used alone or in combination.

As a methylene group donating reagent for preparing Chemical Formula 3 containing a chloromethyl group from the polymer of Chemical Formula 2, a reagent such as chloromethylmethyl ether, bischloromethyl ether, 1-chloro-4-chloromethoxybutane, or the like may be used alone. Methylene group donating reagents such as chloromethylmethyl ether, bischloromethyl ether, 1-chloro-4-chloromethoxybutane, formaldehyde, or paraformaldehyde are used together with chlorine donating reagents such as hydrochloric acid, chlorosulfonic acid, and the like. . At this time, the degree of chloromethylation of the chloromethylated polyimide obtained can be controlled to 1 to 200% according to the amount of reagent used. In addition, zinc dichloride, aluminum trichloride, tin dichloride, and the like are used as the catalyst, but other Friedel-Craft catalysts may be used. The amount of catalyst used may be 0.5 to 2 times the amount of methylene donating reagent used, preferably 0.5 to 1.2 times. The reaction temperature is suitable 10 ℃ to 150 ℃, preferably between 50 ℃ to 90 ℃, the degree of chloromethylation of the prepared chloromethylated polyimide can be adjusted according to the reaction temperature. The reaction time is 10 minutes to 48 hours, preferably 2 hours to 24 hours, and the degree of chloromethylation of the produced chloromethylated polyimide can be controlled according to the reaction time.

The prepared polymer of Formula 3 may be used as a photo-oriented polyimide as it is, but may be used as a photo-oriented polyimide by finally reacting with a compound such as Formula 4 to control the tilt angle to prepare a polymer of Formula 1. For example, the perfluorohexanoic acid is used at 0.01 to 2 times with respect to the chloromethyl group of formula 3 and the base catalyst such as K ₂ CO ₃ is used at room temperature by using 0.1 to 1.2 times with respect to the perfluorohexanoic acid. By reacting for a reaction time between minutes and 48 hours, introduction of functional groups for tilt angle control is possible. It is also possible to select and react one or more structures of the compound of formula 4 in place of the perfluorohexanoic acid. The base catalyst used may be an inorganic base such as Na, NaOH, K, KOH, or an organic base such as pyridine or alkylamine.

The photodegradable polymer prepared by the above-described method is represented by Chemical Formula 1, which is mixed with an appropriate solvent and coated on two glass substrates, and then dried, and the solvent has excellent orientation characteristics and thermal stability even by light irradiation. A high alignment film is formed. Subsequently, photoreaction is performed by irradiating polarized ultraviolet rays, and then, two substrates are bonded to each other in a state where a constant gap is maintained by using a spacer to complete a blank cell. Then, when the liquid crystal is injected into the empty cell, there is almost no change in the orientation characteristic at a high temperature for a long time, thereby producing a stable liquid crystal display device.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example 1

Purified 0.1 M 4,4 '-(hexafluoroisopropylidene) diphthalic anhydride [4,4'-(hexafluoroisopropylidene) diphathalic anhydride, (6FDA)] and purified 0.1 M 4,4 ' -Oxidianiline (ODA) was dissolved in 200 ml of dried N-methylpyrrolidone and stirred for 24 hours in a nitrogen atmosphere at room temperature, which was poured into methanol, and recovered the precipitate, followed by drying in a vacuum oven for 24 hours. A white soluble polyimide of formula (2) was obtained.

In a three-necked round flask equipped with a cooling tube equipped with a drying tube and a nitrogen inlet, 10 g of a soluble aromatic polyimide prepared by the above-described method was added and dissolved in 500 ml of chloroform. To the solution was slowly added 7 ml of chloromethylmethyl ether and 6 ml of tin dichloride (tin (IV) chloride) with a syringe under a nitrogen atmosphere, followed by stirring at 60 캜 for a predetermined time. After the reaction was completed, the reaction mixture was poured into 1000 ml of methanol to precipitate. The obtained precipitate was reprecipitated again with water and methanol, respectively, to obtain a soluble aromatic chloromethylated polyimide of the formula (3).

이고, R₂ 및/또는 R₃에 클로로메틸기가 치환되고, m/(l+m)은 0.5이고, n이 0인 화학식 1의 광배향성 고분자를 합성하였다. 합성한 고분자를 시클로헥사논에 1% 녹인 후, ITO가 증착된 유리기판에 스핀코팅하여 500Å의 두께로 만든 다음, 섭씨 180℃에서 1시간 열처리한 상기 기판들을 나노테크사(Nanotech Co.)의 1KW 자외선 램프 를 사용하여 0.5 J/㎠의 편광된 자외선을 45o 각도로 조사하여 배향시켰다. 그리고, 표면에 4. 5㎛의 스페이서를 산포하고 이를 동일한 물질로 코팅 광배향된 ITO와 접착하여 셀을 형성하였다. 그 후 머크사(Merck Co.)의 MLC951160 액정을 상온에서 주입하고 80℃에서 5분간 열처리하였다.By the same method as above, the molecular weight is about 30000 and R ₁ is

Wherein a chloromethyl group is substituted for R ₂ and / or R ₃ , m / (l + m) is 0.5, and n is 0. After dissolving the synthesized polymer in cyclohexanone 1%, spin-coated to ITO-deposited glass substrate to a thickness of 500Å, the substrates were heat-treated at 180 ° C. for 1 hour to obtain nanotechnologies. The polarized ultraviolet light of 0.5 J / cm <2> was irradiated at 45 degree angle using the 1KW ultraviolet lamp, and orientated. And, the surface was sprayed with a spacer of 4.5㎛ and bonded to the coating photo-aligned ITO with the same material to form a cell. Thereafter, Merck Co., Ltd. MLC951160 liquid crystal was injected at room temperature and heat treated at 80 ° C. for 5 minutes.

Thus, the pre-tilt angle was measured using the crystal rotation method of the completed cell, and the results are shown in Table 1 below.

Example 2

 The alignment film prepared by using the same polymer and method as in Example 1 was heat-treated at 210 ° C. for 90 minutes, and then, the same method spreads a spacer of 4.5 μm on the surface and coated it with the same material. To form a cell. Thereafter, Merck Co., Ltd. MLC951160 liquid crystal was injected at room temperature and heat treated at 80 ° C. for 5 minutes. Thus, the pre-tilt angle was measured using the crystal rotation method of the completed cell, and the results are shown in Table 1 below.

Example 3

 The liquid crystal cell prepared by using the same polymer and method as in Example 1 and Example 1 was left in an 85 ° C. oven for 7 days, and then the pre-tilt angle was measured using the crystal rotation method. It is shown in Table 1 below.

Comparative Example 1

In order to compare the optical orientation of the photo-oriented polyimide polymer and the general polyimide polymer of the present invention, the soluble polyimide polymer of Formula 2 prepared as an intermediate in Example 1 was coated and irradiated in the same manner as in Example 1 And liquid crystal cell were manufactured.

Example 4

이고, R₂ 및/또는 R₃에 클로로메틸기가 치환되고, m/(l+m+n)이 0.5이고, n/(l+m+n)이 0.1이고, X가 -OCO-이고, A₁, A₂ 가 각각 -CF₂-이고, B₁, B₂가 각각 -C₄F₉인 화학식 1의 고분자를 분자량 30000 정도로 얻어서 사용한 것을 제외하고는 실시예 1과 동일한 방법으로 액정셀을 제조하였다. 이와 같이 완성된 셀을 크리스탈 로테이션방법을 이용하여 프리틸트각을 측정하였고, 그 결과는 하기 표 1에 나타내었다.Example 1 was dissolved in 10g of polymer in 500ml of tetrahydrofuran was added to hexa noik acid and triethylamine 0.2g perfluoroalkyl 0.2g were reacted for 24 hours at room temperature, precipitated in methanol, and the R ₁

R ₂ and / or R ₃ is substituted with a chloromethyl group, m / (l + m + n) is 0.5, n / (l + m + n) is 0.1, X is -OCO-, A A liquid crystal cell was manufactured in the same manner as in Example 1, except that ₁ and A ₂ were each -CF _2- , and B ₁ and B ₂ were each -C ₄ F ₉ to obtain a polymer having a molecular weight of about 30000. It was. Thus, the pretilt angle was measured using the crystal rotation method of the completed cell, and the results are shown in Table 1 below.

Example 5

A polymer of Chemical Formula 1 having n / (l + m + n) of 0.2 was synthesized in the same manner as in Example 4 except that 0.4 g of perfluorohexaoic acid and 0.4 g of triethylamine were used. A liquid crystal cell was manufactured in the same manner as in Example 1 except for using the same. Thus, the pretilt angle was measured using the crystal rotation method of the completed cell, and the results are shown in Table 1 below.

Substituent Pretilt angle (degrees) Example 1 -CH ₂ Cl 0.7 Example 2 -CH ₂ Cl 0.65 Example 3 -CH ₂ Cl 0.65 Comparative example - Not measurable Example 4 -CH ₂ Cl, -OC (O) C ₅ H ₁₁ 2.3 Example 5 -CH ₂ Cl, -OC (O) -C ₅ F ₁₁ 3.9

Referring to Table 1, the liquid crystal cell manufactured using the photoalignable polymer of the present invention not only has excellent pretilt angle characteristics, but also can adjust the pretilt angle according to the molar ratio of the copolymer and the type of the substituent. Able to know. In addition, as shown in Examples 2 and 3, the alignment film prepared using the photo-alignment polymer of the present invention is excellent in heat resistance and does not change the orientation characteristic even when heat treated at high temperature.

On the other hand, Figure 1 is a polarizing microscope picture of the liquid crystal cell according to the first embodiment of the present invention, Figure 2 is a polarizing microscope picture of the liquid crystal cell according to Comparative Example 1. 1 and 2, the liquid crystal cell prepared using the photo-alignment polymer according to the present invention can be confirmed that the photo-alignment is well by polarized ultraviolet irradiation, while the liquid crystal prepared using a conventional polymer It can be seen that the cell is not photoaligned at all under the same conditions. In addition, the irradiation amount of the photo-alignment is also significantly lower than the exposure amount (> 1 J / cm ² ) required for general photo-alignment can save a lot of time for light irradiation, it can be seen that the production yield is improved and suitable for mass production.

The present invention is not limited to the above-described embodiments, and various modifications and changes may be made by those skilled in the art without departing from the spirit of the present invention and the equivalent scope of the claims to be described below. Of course it is possible.

As described above, the photoalignable polymer according to the present invention forms a liquid crystal alignment layer having excellent alignment characteristics and high thermal stability. In addition, the amount of radiation for photo-alignment is also much lower than that for general photo-alignment, which can save a lot of time for light irradiation, thus improving the production yield, which is suitable for mass production.

Claims (3)

(S1) preparing a photo-alignment polymer represented by Formula 1; (S2) dissolving the photo-alignment polymer in a solvent and then applying and drying the photo-alignment polymer film on a substrate on which a transparent electrode is formed; And (S2) irradiating polarized ultraviolet rays to the photoalignable polymer film to photoalignment; forming an alignment layer of the liquid crystal display device. <Formula 1>

In Formula 1, l and m are each an integer of 1 to 100, n is an integer of 0 to 100, m / (l + m + n) is 0.1 to 0.95, n / (l + m + n) Is 0 to 0.9 and R ₁ is

Any one selected from the group consisting of (R ₂ and R ₃ ) is (-H, -CH ₂ Cl), (-CH ₂ Cl, -H), (-CH ₂ Cl, -CH ₂ Cl) Any one selected from the group, X and Y are each independently selected from the group consisting of -OOC-, -NH-, -O-, p, q are each an integer of 0 to 4, A ₁ and A ₂ independently of one another is -CF _2- , -CH _2- , -CH〓, -O-, -COO-, -OOC-, -NHCO-, -CONH-, any one selected from the group B ₁ and B ₂ independently of one another is hydrogen, a halogen group, a cyano group, a nitro group, an amino group, an alkyl group having 1 to 100 carbon atoms, a haloalkyl group, a cyanoalkyl group, a nitroalkyl group, a hydroxyalkyl group, a cyanohaloalkyl group, a nitrohaloalkyl group , Cyanonitroalkyl group, hydroxyhaloalkyl group, cyanohydroxyalkyl group, hydroxynitroalkyl group, aryl group having 6 to 100 carbon atoms, alkylaryl group, haloaryl group, haloalkyl Aryl group, nitroaryl group, nitroalkylaryl group, cyanoaryl group, cyanoalkylaryl group, nitroaryl group, nitroalkylaryl group, hydroxyaryl group, hydroxyalkylaryl group, cyanohaloaryl group, cya It is any one selected from the group consisting of nohaloalkylaryl groups. delete An upper substrate and a lower substrate facing each other; Transparent electrodes formed on the upper substrate and the lower substrate, respectively; Alignment layers formed on the transparent electrodes, respectively; And a liquid crystal layer formed between the alignment layers, wherein the alignment layer comprises an alignment layer formed according to claim 1.

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