JP4312168B2 - Thermal transfer sheet - Google Patents

Description

The present invention relates to a thermal transfer sheet in which an undercoat layer and a dye layer are sequentially formed on one surface of a substrate.

As a method of forming an image using thermal transfer, a thermal transfer sheet in which a thermal diffusion dye (sublimation dye) as a recording material is carried on a base sheet such as a plastic film, and another base such as paper or plastic film A thermal diffusion transfer system (sublimation thermal transfer system) is known in which a full-color image is formed by superimposing a thermal transfer image-receiving sheet provided with a dye receiving layer on a sheet. Since this method uses a thermal diffusion dye as the color material, the density and gradation can be freely adjusted in dot units, and a full-color image exactly as the original can be clearly displayed on the thermal transfer image-receiving sheet. It is applied to color image formation for computers and the like. The image is of a high quality comparable to a silver salt photograph.

However, the image formation by the sublimation transfer method has a problem that a sufficient reflection density cannot be obtained with the conventional thermal transfer sheet as the printing speed of the thermal transfer printer increases.
In the image formation by the sublimation transfer method, in order to prevent so-called abnormal transfer in which the dye layer is transferred to the thermal transfer image receiving sheet, it is required that the adhesive strength between the base material sheet and the dye layer in the thermal transfer sheet is high.
As a thermal transfer sheet having a high reflection density and improved adhesion strength between a base sheet and a dye layer, a thermal transfer sheet in which an intermediate layer is provided between the base sheet and the dye layer is known.

As a thermal transfer sheet provided with an intermediate layer, for example, an undercoat layer using a hydrophilic barrier composed of polyvinylpyrrolidone and polyvinyl alcohol, a thermal transfer sheet provided between a dye layer and a base sheet, a base film and a sublimation dye There is known a thermal transfer sheet or the like provided with an intermediate layer containing a sublimation dye having a diffusion coefficient smaller than that of the sublimation dye contained in the recording layer (for example, Patent Document 1 and Patent Document 2). However, none of the thermal transfer sheets can obtain a printed matter having a sufficiently high reflection density.

Patent Document 3 describes a thermal transfer sheet in which a layer formed by depositing a metal or metal oxide on a substrate is formed, and a dye thin film is provided on the layer. However, this thermal transfer sheet has a problem that a printed matter having a sufficiently high reflection density cannot be obtained, and a special apparatus is required for vapor deposition, resulting in an increase in production cost.

Patent Document 4 describes a thermal transfer sheet in which an easy-adhesion layer containing a homopolymer of N-vinyl pyrrolidone or a copolymer of N-vinyl pyrrolidone and other components is provided between a substrate and a dye layer. ing. The easy-adhesion layer may be formed by blending alumina or the like in addition to the above-mentioned polymers, but the inclusion of these compounds is not essential. In addition, the thermal transfer sheet of Patent Document 4 has a problem that the dye transfer efficiency is insufficient, and the release property at the time of printing is inferior, and the release property is further deteriorated when stored under high temperature and high humidity. is there.

Patent Document 5 describes an example in which trialkoxysilane is applied as an undercoat layer between a base material and a dye layer of a thermal transfer sheet, but the dye-donor element is a receiving element after printing on the thermal transfer image-receiving sheet. It has been pointed out that it has a problem of sticking and inferior in mold release.
JP-A-5-131760 JP-A-60-232996 JP 59-78897 A Japanese Patent Laid-Open No. 2003-312151 JP-A-63-135288

In view of the above situation, the object of the present invention is excellent in the adhesive strength between the dye layer and the base material even after storage under high temperature and high humidity, and good releasability from the thermal transfer image receiving sheet during printing. Another object is to provide a thermal transfer sheet having a high reflection density.

The present invention is a thermal transfer sheet in which an undercoat layer formed using aluminum alcoholate and a dye layer are sequentially laminated on one surface of a substrate.
The present invention is described in detail below.

The thermal transfer sheet of the present invention is obtained by sequentially laminating an undercoat layer and a dye layer on one surface of a substrate.
Although it does not specifically limit as said base material, What consists of resin which has the heat resistance and intensity | strength of the grade which does not deteriorate at the time of thermal transfer is preferable.
Examples of the resin constituting the substrate include polyethylene terephthalate, 1,4-polycyclohexylenedimethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, polystyrene, polypropylene, polysulfone, polyamide (aramid), polycarbonate, polyvinyl alcohol, Examples thereof include cellulose derivatives such as cellophane and cellulose acetate, polyethylene, polyvinyl chloride, nylon, polyimide, ionomer and the like. As the resin, polyethylene terephthalate is preferable.
The base material may be composed of only one kind of the above-described resin, or may be composed of two or more kinds of resins.

The base material has a thickness of usually about 0.5 to 50 μm, preferably about 1 to 10 μm.

As will be described later, the thermal transfer sheet of the present invention is formed by using an aluminum alcoholate as the undercoat layer, and thus has excellent adhesion between the substrate and the undercoat layer. In order to improve further, it is preferable to perform an adhesion treatment on the surface on which the undercoat layer and the dye layer are formed.
Examples of the above-mentioned adhesion treatment include corona discharge treatment, flame treatment, ozone treatment, ultraviolet treatment, radiation treatment, surface roughening treatment, chemical treatment, plasma treatment, low temperature plasma treatment, primer treatment, grafting treatment, etc. Modification techniques can be applied. Only one kind of the above-mentioned adhesion treatment may be performed, or two or more kinds may be performed.
In the present invention, among the above-mentioned adhesion treatments, corona discharge treatment or plasma treatment is preferable in that the adhesion between the substrate and the undercoat layer can be enhanced without increasing the cost.

The undercoat layer in the thermal transfer sheet of the present invention is formed using aluminum alcoholate.
The aluminum alcoholate generally has the following formula:

(In the formula, R ¹ represents an alkyl group having 1 to 10 carbon atoms. R ² and R ³ are the same or different, and are an alkyl group having 1 to 10 carbon atoms, an alkoxyl group having 1 to 10 carbon atoms, phenyl, A group or a phenoxy group, wherein the alkyl group and the alkoxyl group may each be a straight chain or a branched chain when the number of carbon atoms is 3 or more.
Examples of the aluminum alcoholate include aluminum ethylate (Al (OCH ₂ CH ₃ ) ₃ ), aluminum isopropylate [AIPD] represented by the following formulas (I) to (III), and aluminum isopropylate monosecondary butyrate. [AMD], aluminum secondary butyrate [ASBD] and the like.

The aluminum alcoholate may be various products such as a product manufactured by Kawaken Fine Chemical Co., Ltd.
In the present specification, the undercoat layer may be formed using only one kind of the above-described aluminum alcoholate, or may be formed using two or more kinds.

The thermal transfer sheet of the present invention is excellent in the adhesive strength between the dye layer and the substrate, but this characteristic is considered to be due to the fact that the undercoat layer is formed using aluminum alcoholate. Although the mechanism is not clear, for example, (1) -Al-OH groups generated by hydrolysis of the alkoxyl group of the aluminum alcoholate form -Al-O-Al- bonds by dehydration condensation. (2) Hydrogen bond between the -Al-OH groups, and (3) -Al-OH group generated by hydrolysis of the alkoxyl group of the aluminum alcoholate, and the substrate surface And (4) a hydrogen bond between the -Al-OH group generated by hydrolysis of the alkoxyl group of the aluminum alcoholate and the polar group of the binder in the dye layer, etc. Can be considered.
In the thermal transfer sheet of the present invention, it is considered that strong adhesiveness can be obtained particularly when the hydrogen bond of (3) above occurs. It is thought that the hydrogen bond of said (3) accelerates | stimulates formation by using the base material which performed the corona treatment as a base material.

The thermal transfer sheet of the present invention is provided with a dye layer through the undercoat layer described above. In general, the dye layer is formed on the same surface of the base material in a surface sequential manner in a plurality of regions via the undercoat layer described above.
The thermal transfer sheet of the present invention may have only one kind of layer containing a desired dye as the dye layer, or may have two or more layers containing a desired dye. .

The dye layer is formed by supporting a dye with a binder.
The above dye is not particularly limited as long as it is a dye that can be used for a conventionally known sublimation transfer type thermal transfer sheet and can be melted, diffused, or sublimated by heat. Hue, print sensitivity, light resistance, storage stability The solubility can be appropriately selected in consideration of the solubility in the binder.

The dye is not particularly limited, and examples thereof include diarylmethane dyes; triarylmethane dyes; thiazole dyes; merocyanine dyes; methine dyes such as pyrazolone methine; indoaniline dyes; acetophenone azomethine and pyrazoloazomethine. Azomethine dyes such as imidazole azomethine, imidazoazomethine and pyridone azomethine; xanthene dyes; oxazine dyes; cyanomethylene dyes such as dicyanostyrene and tricyanostyrene; thiazine dyes; azine dyes; acridine dyes; Dyes; azo dyes such as pyridone azo, thiophenazo, isothiazole azo, pyrrole azo, pyral azo, imidazole azo, thiadiazole azo, triazole azo, diazo; spiropyran dyes; Spiropyran dyes; fluoran dyes; rhodamine lactam-based dyes; naphthoquinone dyes; anthraquinone dyes; quinophthalone dyes.

It does not specifically limit as a binder in the said dye layer, A conventionally well-known resin binder can be used.
Examples of the resin binder include cellulose resins such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, hydroxypropyl cellulose, cellulose acetate, and cellulose butyrate; polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl pyrrolidone, Vinyl resins such as polyacrylamide; polyester resins; phenoxy resins;
As the resin binder, a resin having high adhesiveness is more preferable in that the adhesiveness between the undercoat layer and the dye layer can be maintained even after being left under high temperature and high humidity.
Examples of the resin having high adhesiveness include resins having a hydroxyl group, a carboxyl group, and the like, such as polyvinyl butyral, polyvinyl acetal, polyvinyl acetate, polyester resin, and cellulose resin.

Examples of the resin binder in the dye layer further include a releasable graft copolymer. The releasable graft copolymer can be blended with the resin binder as a release agent.
The releasable graft copolymer is composed of at least one releasable segment selected from a polysiloxane segment, a fluorocarbon segment, a fluorinated hydrocarbon segment, and a long-chain alkyl segment. It is obtained by graft polymerization on the chain.
Among these, the releasable graft copolymer is preferably a graft copolymer obtained by grafting a polysiloxane segment to a main chain composed of polyvinyl acetal.

The dye layer may be formed by blending a silane coupling agent in addition to the dye and the binder.
When a silane coupling agent is added to the dye layer, a silanol group generated by hydrolysis of the silane coupling agent and a hydroxyl group generated by hydrolysis of the aluminum alcoholate in the undercoat layer are polycondensed. It is considered that the adhesion between the dye layer and the undercoat layer is further improved. In addition, when the silane coupling agent has an epoxy group, an amino group, etc., it reacts with a hydroxyl group or a carboxyl group of the resin binder and chemically bonds to improve the strength of the dye layer itself, and the dye layer during thermal transfer, etc. Can prevent cohesive failure.

Examples of the silane coupling agent include isocyanate group-containing compounds such as γ-isocyanatopropyltrimethoxysilane and γ-isocyanatopropyltriethoxysilane; γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and N-β. -Amino group-containing compounds such as aminoethyl-γ-aminopropyltriethoxysilane, γ-phenylaminopropyltrimethoxysilane; γ-glycidoxypropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyl And epoxy group-containing compounds such as trimethoxysilane;
In the dye layer, only one silane coupling agent may be blended, or two or more may be blended.

In addition to the dye, the binder, and a silane coupling agent that is optionally added, the dye layer may further include various conventionally known additives.
Examples of the additive include organic fine particles, inorganic fine particles, and the like, such as polyethylene wax added to improve the releasability from the thermal transfer image-receiving sheet and the ink coating suitability.

The thermal transfer sheet of the present invention may further be provided with a heat-resistant slipping layer on the base material surface opposite to the surface on which the undercoat layer or the like is formed.
The heat resistant slipping layer is provided to prevent problems caused by heat of the thermal head during thermal transfer, such as sticking and printing wrinkles.

The heat resistant slipping layer is usually made of a heat resistant resin.
The heat-resistant resin is not particularly limited. For example, polyvinyl butyral resin, polyvinyl acetoacetal resin, polyester resin, vinyl chloride-vinyl acetate copolymer resin, polyether resin, polybutadiene resin, styrene-butadiene copolymer resin. , Acrylic polyol, polyurethane acrylate, polyester acrylate, polyether acrylate, epoxy acrylate, urethane or epoxy prepolymer, nitrocellulose resin, cellulose nitrate resin, cellulose acetate propionate resin, cellulose acetate butyrate resin, cellulose acetate hydrogen Phthalate resin, cellulose acetate resin, aromatic polyamide resin, polyimide resin, polyamideimide resin, polycarbonate resin, salt Polyolefin resins.

The heat resistant slipping layer is usually formed by blending a slipperiness imparting agent in addition to the heat resistant resin in order to improve the slipperiness of the thermal head.
Examples of the slipperiness-imparting agent include phosphate polymers, metal soaps, silicone oils, graphite powders, fluorine-based graft polymers, silicone-based graft polymers, acrylic silicone graft polymers, silicone polymers such as acrylic siloxanes and arylsiloxanes. Can be mentioned.
In the heat resistant slipping layer, only one kind of slipperiness-imparting agent may be blended, or two or more kinds may be blended.
In addition, it replaces with mix | blending with the said heat resistant slipping layer, and you may coat the said slipperiness | lubricity imparting agent on the said heat resistant slipping layer.

The heat-resistant slipping layer may be formed by blending additives such as a crosslinking agent, a release agent, an organic powder, and an inorganic powder in addition to the heat-resistant resin and the slipperiness-imparting agent that is optionally blended. .
For example, when a crosslinking agent such as polyisocyanate is blended in the heat resistant slipping layer, the heat resistance, the mechanical strength of the film, the adhesion to the substrate, and the like can be improved. In addition, when a release agent, organic powder, inorganic powder, or the like is blended in the heat resistant slipping layer, the running performance of the thermal head can be improved. Examples of the release agent include waxes, higher fatty acid amides, esters, and surfactants. Examples of the organic powder include a fluororesin. Examples of the inorganic powder include silica, clay, talc, mica, and calcium carbonate.

The thermal transfer sheet of the present invention can be prepared, for example, by sequentially forming an undercoat layer and a dye layer on one surface of a substrate using an undercoat layer coating solution and a dye layer coating solution. Among them, as shown in FIG. 1, (1) on one surface of the substrate 1, a heat-resistant slip layer coating solution is applied and dried to form the heat-resistant slip layer 4, (2) For the base material 1 having the obtained heat resistant slipping layer 4, an undercoat layer coating solution and a dye layer coating solution are used on the surface opposite to the heat resistant slipping layer 4. It is preferable to prepare the layer 2 and the dye layer 3 by sequentially forming them.

The heat-resistant slipping layer is usually prepared by adding the above-mentioned heat-resistant resin, and optionally adding the slipperiness-imparting agent and the additive to an appropriate solvent, and dissolving or dispersing each component. A coating solution can be prepared, and then the heat resistant slipping layer coating solution can be applied on a substrate and dried.
Examples of the application method of the heat resistant slipping layer coating liquid include a gravure printing method, a screen printing method, a reverse roll coating method using a gravure plate, and the like, and gravure coating is particularly preferable.
The heat-resistant slip layer coating solution, dry coating amount is preferably 0.1 to 3 g / ^{m 2,} more preferably may be applied so as to be 1.5 g / ^{m 2} or less.

The undercoat layer coating solution is composed of the aluminum alcoholate, and can be prepared by mixing or dissolving aluminum alcoholate in a suitable solvent or dispersion medium.
It does not specifically limit as a solvent or a dispersion medium in the said undercoat layer coating liquid, For example, water; Alcohols, such as ethanol, propanol, isopropyl alcohol;
The pH of the undercoat layer coating solution is not particularly limited.

Examples of the application method of the undercoat layer coating liquid include the methods exemplified in the application of the heat resistant slipping layer described above, and gravure coating is particularly preferable.
The undercoat layer coating solution may be applied so that the dry coating amount is preferably about 0.02 to 1 g / m ² , more preferably about 0.03 to 0.3 g / m ² .
The undercoat layer coating liquid can be dried, for example, while heating.

The dye layer is usually prepared by adding the dye and binder and, if necessary, an additive in an appropriate solvent to dissolve or disperse each component to prepare a dye layer coating solution. A layer coating solution can be applied on the undercoat layer and dried.
Examples of the method for applying the dye layer include the methods exemplified in the application of the heat-resistant slip layer described above, and gravure coating is particularly preferable.
The dye layer coating solution may be applied so that the dry coating amount is preferably about 0.2 to 6 g / m ² , more preferably about 0.3 to 3 g / m ² .

The thermal transfer sheet of the present invention is excellent in the adhesive strength between the dye layer and the substrate as described above, and can maintain the adhesive strength even after being stored for a long time under high temperature and high humidity.
The thermal transfer sheet of the present invention exhibits excellent releasability with respect to the thermal transfer image-receiving sheet even when it is used for printing after being stored for several days in an environment of 40 ° C. and 90% RH. High reflection density.

Since the thermal transfer sheet of the present invention has the above-described configuration, it has excellent adhesive strength between the dye layer and the substrate even after being stored under high temperature and high humidity, and has a releasability from the thermal transfer image receiving sheet during printing. Good and high reflection density.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited only to these Examples and Comparative Examples.
In the text, “part” or “%” is based on mass unless otherwise specified.

Example 1
As a base material, an undercoat layer coating solution 1 having the following composition was applied on a polyethylene terephthalate [PET] film having a thickness of 4.5 μm by gravure coating so that the dry coating amount was 0.1 g / m ^2. And dried to form an undercoat layer.
On the undercoat layer, a dye layer coating solution having the following composition was applied by gravure coating so that the dry coating amount was 0.7 g / m ² and dried to form a dye layer. Example 1 A thermal transfer sheet is prepared.
In addition, a heat-resistant slipping layer coating solution having the following composition was applied to the surface of the substrate opposite to the dye layer in advance by gravure coating so that the dry coating amount was 1.0 g / m ² and dried. Thus, a heat-resistant slip layer was formed.

<Undercoat layer coating solution 1>
Mono sec-butoxyaluminum diisopropylate (AMD, manufactured by Kawaken Fine Chemical Co., Ltd.)
1 part Isopropyl alcohol 10 parts

<Dye layer coating solution>
C. I. Solvent Blue 63 6.0 parts Polyvinyl butyral resin (S-REC BX-1 manufactured by Sekisui Chemical Co., Ltd.) 3.0 parts Methyl ethyl ketone 45.5 parts Toluene 45.5 parts

<Heat resistant slipping layer coating solution>
Polyvinyl butyral resin (ESREC BX-1, manufactured by Sekisui Chemical Co., Ltd.) 13.6 parts polyisocyanate curing agent (Takenate D218, manufactured by Takeda Pharmaceutical Co., Ltd.) 0.6 parts Phosphate ester (Plysurf A208S, Daiichi Kogyo Seiyaku Co., Ltd.) 0.8 parts Methyl ethyl ketone 42.5 parts Toluene 42.5 parts

Example 2
A thermal transfer sheet was produced in the same manner as in Example 1 except that the undercoat layer coating solution 2 was used instead of the undercoat layer coating solution 1 to form the undercoat layer.
<Undercoat layer coating solution 2>
Aluminum sec-butylate (ASBD, manufactured by Kawaken Fine Chemical Co., Ltd.) 1 part Isopropyl alcohol 10 parts

Comparative Example 1
A thermal transfer sheet was produced in the same manner as in Example 1 except that the undercoat layer coating solution 3 was used instead of the undercoat layer coating solution 1 to form the undercoat layer.
<Undercoat layer coating solution 3>
Alumina sol (Alumina sol 200, manufactured by Nissan Chemical Industries, solid content 10%) 30 parts Water 21.5 parts Isopropyl alcohol 48.5 parts

Comparative Example 2
A thermal transfer sheet was prepared in the same manner as in Example 1 except that the undercoat layer coating solution 4 was used instead of the undercoat layer coating solution 1 to form the undercoat layer.
<Undercoat layer coating solution 4>
Polyvinylpyrrolidone resin (K-90, made by ISP) 3 parts Water 48.5 parts Isopropyl alcohol 48.5 parts

Comparative Example 3
A thermal transfer sheet was produced in the same manner as in Example 1 except that the undercoat layer was not formed.

Test Example The thermal transfer sheet obtained from each example and each comparative example was evaluated by the following method.
1. Reflection density (1) Using the thermal transfer sheet of each example and each comparative example and a thermal transfer image-receiving sheet (manufactured by OLYMPUS) dedicated to the P-400 printer, using a P-400 printer (manufactured by OLYMPUS) under the following conditions: Printed.
・ Printing condition thermal head: KGT-217-12MPL20 (manufactured by Kyocera Corporation)
Heating element average resistance value: 2994 (Ω)
Print density in the main scanning direction; 300 dpi
Sub-scanning direction print density; 300 dpi
Applied power: 0.10 (w / dot)
1 line cycle: 5 (msec.)
Printing start temperature; 40 (° C)
・ Applied pulse (gradation control method); using a multi-pulse test printer that can vary the number of divided pulses with a pulse length that equally divides one line period into 256, and using a multi-pulse test printer, the duty ratio of each divided pulse Was fixed at 70%, and 0 to 255 pulses per line period were divided into 15 parts. Thereby, different energy can be given to 15 steps.
(2) About each obtained printed matter, the reflection density of the density | concentration max (255th gradation) was measured by the Macbeth reflection densitometer RD-918 (made by Macbeth).

2. Adhesive strength of dye layer Using the thermal transfer sheet obtained from each example and each comparative example, a cellophane (registered trademark) of 200 mm in length and 12 mm in width was rubbed twice with the thumb on the dye layer, and then peeled off immediately. The presence or absence of adhesion of the dye layer on the tape side was examined visually and evaluated according to the following criteria. The same test was performed after each thermal transfer sheet was stored for 100 hours in an environment of 40 ° C. and 90% RH.
(Evaluation criteria)
○: Adhesion of the dye layer is not recognized.
Δ: Slight adhesion of the dye layer is observed.
X: Adhesion of the dye layer is observed on the entire surface.

3. Evaluation of releasability after storage The thermal transfer sheets obtained from the respective examples and comparative examples were stored for 100 hours in an environment of 40 ° C. and 90% RH, and then subjected to the same printing conditions as those for the above-mentioned reflection density measurement. The entire surface of the printed material is printed with a solid printing pattern (gradation value 255/255: density max), and the dye layer of the thermal transfer sheet and the thermal transfer image-receiving sheet are thermally fused, or the thermal transfer image is received together with the dye layer. Whether or not so-called abnormal transfer to be transferred to the sheet was visually examined and evaluated according to the following criteria.

(Evaluation criteria)
○: Abnormal transcription did not occur.
Δ: Slightly abnormal transfer occurred.
X: The entire stamp screen was abnormally transferred.

Table 1 shows the measurement results.

From the measurement results, it was found that the thermal transfer sheets of the respective examples were all excellent in adhesive strength, releasability and reflection density. Moreover, compared with each Example, (1) The thermal transfer sheet of the comparative example 1 which mix | blended the alumina sol in the undercoat layer is a little inferior in the adhesive strength after storage, releasability, etc., (2) In the undercoat layer The thermal transfer sheet of Comparative Example 2 containing a polyvinylpyrrolidone resin is slightly inferior in reflection density and releasability, inferior in adhesive strength after storage, and (3) The thermal transfer sheet of Comparative Example 3 having no undercoat layer Was found to be inferior in adhesive strength, releasability and reflection density.

Since the thermal transfer sheet of the present invention has the above-described configuration, it has excellent adhesive strength between the dye layer and the substrate even after being stored under high temperature and high humidity, and has a releasability from the thermal transfer image receiving sheet during printing. Good and high reflection density.

It is an example of sectional drawing of the thermal transfer sheet of this invention.

Explanation of symbols

1. Base material 2. 2. Undercoat layer 3. Dye layer Heat-resistant slip layer

Claims (2)

A thermal transfer sheet, wherein an undercoat layer formed by using aluminum alcoholate and a dye layer are sequentially laminated on one surface of a substrate. The thermal transfer sheet according to claim 1, further comprising a heat-resistant slip layer provided on the other surface of the substrate.

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