DE3134670A1 - THERMAL RECORDING SHEETS - Google Patents

Description

CHARCOAL HARVESTED GLAESEEI

MONKS

DR, E. WIEGANDt
(1932-19B0)

DR. M. KOHLER
DIPL-ING. C. GERNHARDT

HAMBURG
DIPL.-ING. ). GLASSES

PATE N T&N WH ITG Europeon patent attorneys

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DIPL.-ING. W. NlEMANN
OF COUNSa

TELEPHONE: 089-555476 / 7
TELEGRAMS: KARPATENT TElEXl 529068 KAI (PD

D-8000 MDNCHEN2 HERZOG-WILHEIM-STR. Ii

September 2, 198I

W. 44031/81 - Ko / Ne

Fuji Photo Film Co ,, Ltd. Minami Äshigara-Shi Kanagawa ^ Japan

Thermal recording sheets

The invention relates to thermal recording sheets.

Thermal recording or thermography forms a recorded image by making use of physics or chemical change of a substance due to thermal energy and a large number of Procedures were investigated for thermal recording. Thermal recording sheets from "Wax types", in which the physical change of a substance due to "heat" is used, have been since have been known for many years and are used, for example, in electrocardiograms. Various thermal Recording sheets produced by various color-forming mechanisms taking advantage of the chemical change of a substance due to heat and thermal recording sheets of the type ■ the "two-color forming component" are typical of this type of sheet.

To a thermal recording sheet having a two-color forming component to form a fine particle dispersion of two thermally reactive compounds mixed with binder particles to form a coating solution which is based on a base in the manner is applied that the two thermally reactive compounds from each other through the binder particles are separated. This sheet forms an image by means of a color-forming reaction that occurs when the two come into contact Connections is initiated when one or both connections melt from the heat. The two connection fertilizers are commonly referred to as an electron donor compound and an electron acceptor compound. There are numerous

+) (i.e. on a carrier)

-'ϊ

known combinations of such compounds and they generally consist of those which form an image of metallic compounds and those which form a dye image. Examples of combinations which form a metal compound image use phenols and other organic reducing agents, chelating agents, sulfur compounds and amine compounds as electron donating compounds and organometallic salts as electron accepting compounds. Examples of combinations "° which form a dye image use electron-donating colorless dyes as the electron-donating compound and phenols and other acidic substances as the electron-accepting compound, as described in, for example, Japanese Patent Publications 4160/68 and 3680/69.

These thermal recording sheets with the two-color forming component have advantages when used as thermal recording sheets because they are, for example (.Ί) only from the primary color formation reaction and do not require a separate stage of development, (Z) the texture of the leaf similar to that of ordinary paper and (3) easy to use. The leaves using colorless dyes as electron donor compounds are of greater technical importance since they not only include the three above Achieve the listed benefits, but also the following two additional benefits: (4) They provide a higher Color density and (5) thermal recording sheets providing various colors can be easily obtained will. In view of these advantages, sheets of the latter type are most widely used as thermal recording materials.

Thermal recording sheets including those listed above Features were examined as image receiving papers for use in facsimile messages. The use of thermal recording sheets as recording Drawing paper for facsimile has two advantages; (1) Since no stage of development is necessary, the structure simplification of equipment and (2) the fact that the recording paper itself is the only consumable part is beneficial in terms of equipment maintenance. However, the fact that they are on already shows based on thermal recording, a serious problem, namely, a slow recording speed. This is believed to be mainly due to the slow thermal response from the recording head and sheet. Recently, there have been some thermal recording heads with rapid thermal responsiveness, but none of the currently known thermal Recording sheets have sufficiently quick responsiveness and the development of sheets with quick responsiveness is therefore very desirable.

One object of the invention is thermal recording sheets with rapid thermal response, suitable for high speed recording.

Another object of the invention is a recording paper which has a sufficient color density with heat pulses with a duration of 2 ms (milliseconds) is achieved, which is far shorter than the duration of 5 ms that is used in thermal recording by the conventional method was required.

/ T-

The objects of the invention are provided by thermal Recording sheets, one with one electron-donating colorless dye and a thermal color-forming layer containing an electron accepting compound have coated base, wherein the electron-donating colorless dye in the form of fine particles with a average volume size of 2.0 μm or less is present.

In the "drawings, FIG. 1 is a graph showing the relationship between the average volume size of the particles in the sample prepared according to Example 1 of the thermal The electron-donating colorless dye used on the recording sheet and the obtained color density shows, and

FIG. 2 is a graph showing the same relationship with the sample prepared in Example 2. FIG.

In the context of the description of the invention in detail, for the formation of a thermal recording sheet, which is suitable for high speed recording, applied the following procedures:

(1) The color formation temperature is determined by adding a low-melting thermally fusible substance or a low-melting electron-accepting compound, hereinafter referred to as "developing agent", is reduced,

(2) The heat transfer efficiency is increased by improving the smoothness of the recording surface and

(3) more color forming component is used.

However, sheets made by these methods suffer from increased background fogging during storage, their surface properties are worse than that of ordinary paper, and the manufacturing cost is high. To solve these problems, made extensive studies of the color formation mechanisms of thermal recording sheets. Included It has now been found that in practically all thermal recording sheets of the color type, the color passes through the order of (1) melting the developing agent and / or the low-melting thermally fusible substance, (2) mutual dissolution of the molten one Developing agent and the low-melting compound, (3) dissolution of the electron-donating colorless dye in the molten eutectic mixture of the developing agent and the low-melting compound, the dye being referred to hereinafter as "chromogen", and (4) the color development reaction between development Resistant agent and chromogen is formed. It was found, that the speed of dissolution in the third stage controls the speed of the color formation reaction. On the basis of these results, thermal recording sheets using fine particles of the Chromogens made of different sizes and that The following found: The particle size has little effect on the recording properties when the average Volume size is between about 3 and TO μΐη, while, if the average volume size is 2.0 μΐη or is less, there is a dramatic increase in color density and the difference from the case of applying one Chromogen with a larger particle size is particularly large in the high-speed recording embodiment is. Even better results are obtained if

the chromogen has an average volume particle size of 1 μπι or less.

The volume particle size (ic) according to the invention used particle is represented by the following equation:

- _, _4_. Total volume of particles . 1/3 3π total number of particles

So far, no suitable measures were known to to produce fine particles of the chromogen and the minimum size of the chromogen particles in the dispersion, which was previously possible could be achieved, was about 3 or 4 μΐη. As above discussed, if the particle size in the dispersion is 3 μm or more, the effect of the particle size is on the color formation property is relatively low, so that up to now the advantage according to the invention, which by Reduction of the particle size in the dispersion to 2 μm or less is achieved, was previously unknown. The average particle size of the chromogen to 2 μΐη or less was successfully reduced, partly by special measures in the dispersing machine and partly some water-soluble polymers as protective colloids of the dispersion were mixed to increase the viscosity of the dispersion to lower.

The recording sheets according to the invention have a quick response to thermal impulses of very short duration and achieve a sufficient color density by means of a small amount of thermal energy.

The following is the method of manufacturing the thermal recording blades according to the invention explained. The particles of the chromogen and the developing agent are separated in a solution of a dispersed water-soluble polymers in a ball mill or other suitable dispersing device, 'where for example the fine chromogen particles according to Invention by dispersing the same during a sufficient period of time (about 16 to 24 hours) using balls of different sizes, which in

mixed in a given proportion _r can be produced. The use of a sand mill (Dyno mill, product of Wiely A. Bachofen AG Maschinenfabrik; Switzerland) can also be "effective.
15th

For example, if the dispersion is molded using a ball mill to prepare the chromogen of fine particles with an average volume size of 2.0 μΐη or less, it is: cheap, balls of fine size, for example about 1 to 5 mm in diameter, in combination with the usual Dispersion balls, for example about 2 to .4 cm in diameter, to be used in the appropriate proportion. The suitable one

The proportion of fine balls is about 10 to 100% by volume,

preferably 20 to 50% by volume per volume of the ordinary Bullets. The preferred examples of the fine ball material include hard glass, alumina, zircon and the like.

Palis also made the dispersion, according to a process which the introduction of the sub- punch into the vessel, such as a sand mill and the like, in which the medium is filled, and vigorously stir the resulting Comprising mixture, a dispersion particle size of 2 µm or below can be more easily obtained. In the-

/ 11

In this case it is also necessary to use media with a diameter from about 1 to 5 mm, preferably 1 to 3 mm, for example made of hard glass, aluminum oxide, zircon, Ottawa sand and the like., apply. However, the dispersion methods are not particularly limited to the methods set forth above.

The thermal recording materials used according to the invention are in solutions of water-soluble polymers, such as polyvinyl alcohol, hydroxyethyl cellulose,

1Q polyacrylamide, starches and the like., Dispersed. If sodium caseinate is added at the same time as the dispersion, there will be an increase in viscosity during the dispersion and the resulting increase in temperature is preferably prevented, and consequently a suitable redispersion solution can can be obtained. The amount of sodium caseinate used is 0.1 to 5% by weight, preferably 0.5 to 2% by weight, based on the weight of the dispersion solution.

The resulting dispersions of the chromogen and the developing agent are mixed and further with an inorganic pigment, wax, higher aliphatic acid amides, metal soaps and, if necessary, UV absorbers, Antioxidants and latex binders mixed to form the coating solution. These additives can also be incorporated when the dispersions are made. The coating solution is based in such an amount applied so that the coating weight of the chromogen is generally

• 2 2

my is 0.1 to 0.6 g / m (g / m). The basis is there in the most typical case made of paper, but plastics can also be used be used. The lower limit of the coating weight is determined by the desired color density and

the upper limit is determined by the manufacturing cost. A particularly preferred range is 0.2

up to 0.4 g chromogen per no. . _rr

There are no particular restrictions with regard to the chromogen used according to the invention. _f if of the type commonly used in pressure sensitive recording sheets and thermal recording sheets. Specific examples include (1) triarylmethane compounds such as 3,3-bis- (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3- (p-dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) - phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindol-3-yl) -phthalide, 3,3-bis- (9-ethylcarbazol-3-yl) -5-dimethylaminophthalide and 3,3-bis- (2-phenylindol-3-yl) -5-dimethylamine-qphthalide,

(2) diphenylmethane compounds, such as. B. 4,4'-Bisdimethylaminobenzhydrinbenzyläther, N-halophenylleucoauramine and N-2,4,5-trxchlorophenylleucoauramine, (3) xanthene compounds, such as B. Rhodamine B-anilinolactam., J3-diethylamino-7-dibenzylaminofluoran, 3-diethylamine-p-7-butylaminofluoran, 3-diethylamino-7- (2-chloroanilino) -f luorane ,. 3-diethylamino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-ethyltolylamine p-6-methyl-7-a.nilinofluorSn, 3-cyclohexylmethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-chloro-T-Cß-f9; hydroxyethyl) amine pf luorane and 3-diethylamino-6-chloro-7- (γ-chloropropyl) aminofluorane, (4) thiazine compounds such as benzoyl leucomethylene blue and p-nitrobenzoyl leucomethylene blue and (5) spiro compounds such as 3-methy1-spirodinaphthopyran, 3-jithylspirodinaphthopyran, 3-benzyl- spirodinaphthopyran, 3-methylnaphtho- (3-methxybenzo) -spiropyran and mixtures thereof. The specific chromogen will depend on the specific use and selected the desired properties.

The developing agent used in the present invention is preferably a phenol derivative or an aromatic carboxylic acid derivative, bisphenols being particularly preferred will. The bisphenol compounds useful as developing agents in the invention are represented by the formula

in which R ₁ and R_ each represent a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, or R- and R "are combined to form a carbocyclic ring, or derivatives thereof. Specific examples include (1) phenols such as p-Octy.1 phenol, p-tert-butylphenol, p-phenylphenol, 1,1-bis- (p-hydroxyphenyl) -propane, 2,2-bis- (p- hydroxyphenyl) propane, 1,1-bis (p-hydroxyphenyl) pentane, 1,1-bis (p-hydroxyphenyl) hexane, 2,2-bis (p-hydroxyphenyl) hexane, 1,1 -Bis- (p-hydroxyphenyl) -2-ethylhexane, and 2,2-bis- (4-hydroxy-3,5-dichlorophenyl) propane and (2) aromatic carboxylic acid derivatives such as p-hydroxybenzoic acid, ethyl p-hydroxybenzoate , Butyl hydroxybenzoate. 3, S-di-tert-butylsalicalic acid, 3,5-di-amethylbenzylsalicylic acid and polyvalent metal salts of such carboxylic acids. In order to melt and to cause the color formation reaction at the desired temperature, these developing agents are preferably in the form of a eutectic mixture with a low-melting thermally fusible substance or fine particles, on the surface of which

the area where the low-melting point has melted is added.

Examples of low-melting thermally fusible Compounds include paraffin wax, carnauba wax, microcrystalline wax and polyethylene wax and higher aliphatic acid amides, such as stearoylamide and Ethylenebisstearamide, and higher aliphatic acid esters.

Examples of metal soaps include polyvalent metal salts of higher aliphatic acids such as zinc stearate, Aluminum stearate, calcium stearate and zinc oleate.

Examples of inorganic pigments are kaolin, burnt kaolin, talc, pyrophyllite, diatomaceous earth, Calcium carb ^ onate, aluminum hydroxide, magnesium hydroxide, magnesium carbonate, titanium oxide and barium carbonate

Wax, metal soap and inorganic pigment are dispersed in a binder and mixed with the dispersions of Chromogen and developing agent mixed. Alternatively, they are used together with the particles of Chromogen and Dispersing agent. The binder is generally water soluble and examples consist of polyvinyl alcohol, Hydroxyethyl cellulose, hydroxypropyl cellulose, ethylene-maleic anhydride copolymers, styrene-maleic anhydride copolymers, Isobutylene maleic anhydride copolymers, polyacrylic acid, starch derivatives, casein and ' Gelatin. To make these binders waterproof, they can be mixed with a waterproofing agent such as a gelling agent or crosslinking agents, or hydrophobic polymer emulsions such as styrene-butadiene rubber latex and acrylic resin emulsions ^ mixed will.

The invention is explained in detail below with reference to the following examples, which are merely illustrative serve without limiting the invention. In the examples, all parts are by weight. 5

example 1

200 g of the chromogen. S-diethylamino-e-methyl-V-ariilinofluoran, were in 2.5 wt.% polyvinyl alcohol (degree of polymerization 500, saponification number 99%) with a ball mill. The ball mill consisted of a porcelain pot with 7 1 content, which is 1.5 kg of aluminum oxide balls of 20 mm in size and 500 g of zirconium balls of 3 mm in size contained. The dispersion became samples after 6, 12, 24, 48 and 72 hours of ball milling taken. The average volume size of the chromogenic particles dispersed in the respective samples was 5.4 / 3.6; 2.0, - 1.4 or 1.0 μm.

80 g of the developing agent, 2,2'-bis (p-hydroxyphenyl) propane, and 120 g of stearoylamide were ground in 5% polyvinyl alcohol with a ball mill, wherein a dispersion with particles with an average size of 3.5 μm was obtained.

.

One part of the dispersion of the chromogen was mixed with 5 parts of the dispersion of the developing agent, 2 parts 40% kaolin, 1 part 20% zinc stearate and 5 parts 10% polyvinyl alcohol for the preparation of the coating solution mixed. The solution was applied to an uncoated paper

2 pier with a basic weight of 50 g / m drawn up until

2 the coating weight of the chromogen was 0.4 g / m 2

a pressure of 20 kgw / cm and passed through a facsimile (PANAFAX-7000 from Matsushita Electric Industrial Co., Ltd.) where pulses of varying widths were applied to develop the color on the recording sheet. The color density at pulse times of 1.5 ms and 2.7 ms compared to the size of the dispersed chromogenic particles is shown in curves (1) and (2) in FIG. The relationship between the particle size and the color density obtained when the thermal recording sheet was held in contact with a heating stamp "at 150 ° C. for 5 seconds is also shown in FIG. 1 by the line (3). The particle size became was measured using a Model TA-II Particle _{Size Distribution Meter from Coulter Counter Corp.}} The color density was measured with a visual filter on a Macbeth reflection densitometer, Model RD-514.

Example 2

Chromogen dispersions were prepared as in Example 1, but using 3-diethylamino-6-chloro-7- (ß-ethoxyethylamino) fluorane as the chromogen was used. The average size of the chromogenic particles in the respective dispersion was 4.6 / 3.1; 1.9, '1.2 and 0.8 μm. The dispersions were then as in example 1 treated for the production of thermal recording sheets. The relationship between the color density and the The average size of the chromogenic particles is shown in FIG. 2.

From Figs. 1 and 2 it can be seen that by

tr

Reduction of the size of the chromogenic particles to that according to the invention defined value, the color density can be significantly increased in high-speed recording can.

The invention has been preferred by way of above Embodiments described without affecting the invention is limited to this.

Claims (7)

Claims 1. Thermal recording sheets consisting of a carrier coated with a thermally color-forming layer, which is an electron-donating colorless Contains dye and an electron acceptor compound, characterized in that the electron-donating colorless dye is in the form of fine particles with a average volume size of 2 μτη od§ £ less is present. 2. Thermal recording sheets according to claim 1, characterized in that the fine particles of the electron donating colorless dye have an average Have a volume size of 1.0 pm or less » 3. Thermal recording sheets according to claim 1 or 2, characterized in that the electron-donating colorless dye in an amount of 0.1 to 0.6 g / m ² on. 20 is drawn. 4. Thermal recording sheets according to claim 3 " characterized in that the electron-supplying coloring loose dye in an amount of. 0.2 to 0.4 g / m ^{2 is} drawn up. 5. Thermal recording sheets according to claim 1 to 4, characterized in that the electron-donating colorless dye from the group of (1) triarylmethane compounds, (2) diphenylmethane compounds, (3) xanthene compounds, (4) thiazine compounds and / or (5) Spiro connections exist.
- 6. Thermal recording sheets according to claim to 5, characterized in that the electron acceptor compound consists of a phenol derivative or an aromatic Carboxylic acid derivative consists. 7. Thermal recording sheets according to claim 1 to 5, characterized in that the electron acceptor compound from a bisphenol compound corresponding to formula R ₇
- 2 where R ₁ and R 1 denote a hydrogen atom or an alkyl group having 1 to 12 carbon atoms or R ₁ and R 2 are combined to form a carbocyclic ring, or consists of derivatives thereof.