FR2489751A1 - THERMOGRAPHIC RECORD SHEET - Google Patents

Abstract

THE INVENTION RELATES TO THERMOGRAPHIC RECORDING. THE THERMOGRAPHIC RECORDING SHEET CONTAINS A SUPPORT ON WHICH IS APPLIED A COLOR FORMATTING LAYER CONTAINING AN ELECTRON ACCEPTING COMPOUND AND A COLORLESS ELECTRON-DONOR DYE IN THE FORM OF FINE PARTICLES OF LESS THAN 2.0 OR MIDDLE SIZE OF PARTICLES . APPLICATION TO HIGH SPEED THERMOGRAPHIC RECORDING.

Description

The present invention relates to thermal recording and more particularly

  firstly a thermographic recording sheet.

  Thermal recording, or thermography, makes it possible to reproduce a recorded image by using the physical or chemical transformation of a substance under the action of thermal energy, and a large number of processes related to the principle of thermal recording have been developed. For many years we have known thermographic sheets of the "wax" type which use the physical change of a

  substance under the action of heat, and such sheets of record-

  particularly for electrocardiography.

  grams. Several thermographic recording sheets have been proposed

  which use various mechanisms of color formation in use

  reading the chemical change of a substance under the action of heat, and for example thermographic recording sheets with component

  forming two colors belong to this type of sheet.

  In order to manufacture a two-color component thermographic recording sheet, a dispersion of particles of two thermally reactive compounds is mixed with the particles of a binder to form a coating solution which is applied to a support so that that the two thermally reactive compounds are separated from each other by the binder particles. This sheet forms an image by the chromogenic reaction which is initiated by the contact of the two compounds when one or both compounds are melted by heat. The two compounds are usually an electron donor for one, and an electron acceptor for the other. Numerous combinations of such compounds are known which generally consist of those providing an image of metal compounds and those providing a dye image. Examples of combinations providing an image of a metal compound are phenols, and other organic reducers, chelating agents, sulfur compounds and amino compounds as electron donors, and salts thereof.

  organometallic as electron acceptors. Examples of combinations

  providing a dye image o colorless dyes

  Electron donors play the role of the electron donor compound, while phenols and other acidic substances constitute the electron accepting compound, are described in patent publications.

Japanese 4160/68 and 3680/69.

  These two-color form-forming thermographic recording sheets are advantageous in use and in particular, they depend solely on the primary chromogenic reaction and do not require a separate development step, 2 / the texture of the sheet is similar to that of ordinary paper, and 30 / they are

easy handling.

  Leaves using colorless dyes as electron donors have a greater commercial value because they provide not only the three advantages above but also: 40 / they provide a density

  of greater color, and 50 / thermo-recording sheets

  graphic providing various colors can be obtained easily.

  Because of these advantages, leaves of this type are used more

  commonly for thermographic recording.

  The above thermographic recording sheets have been studied as image-receiving papers in facsimile communications because their use has two advantages: 1 / no step of

  development is required, the construction of the equipment is

  and 2 / the fact that the registration paper is the only

  consumable element is advantageous in terms of maintenance.

  However, the fact that they depend on the principle of thermographic recording implies a serious disadvantage because of the low

  recording speed. This is mainly due to the thermal response

  Slow motion of the head and the recording sheet. Recently, thermographic recording heads having a fast response have been developed, but no thermographic recording sheet provides a satisfactory rapid response and, therefore,

  point of such a quick response sheet is particularly desirable.

table in this technique.

  The present invention relates to a thermal recording sheet

  fast thermal response graph that can be used to

  high speed recording.

  The invention also relates to a recording sheet providing an appropriate color density with thermal pulses lasting about 2 ms (milliseconds), that is to say, a clearly

  less than that (5ms) that is required for thermo-

  graphic by the traditional method.

  These results can be achieved by the thermographic recording sheet according to the invention comprising a support coated with a

  chromogenic thermal layer containing a colorless dye-donor

  trons and an electron-accepting compound, the colorless dye is

  both in the form of fine particles of average volume less than or equal to

2.0 p m.

  Fig. 1 is a graph showing the relationship between the average particle volume of the colorless electron donating dye used in the thermographic recording sheet sample of Example 1,

  and the resulting color density.

  Figure 2 is a graph showing the same relationship for the sample

of Example 2.

  To obtain a thermographic recording sheet suitable for recording at high speed, the following methods were used: 1 / the color formation temperature is lowered by the addition of a hot-melt substance of low melting point, or 'a compound

  electron acceptor with a low melting point (hereinafter referred to as "

  2) the efficiency of heat transfer is increased by improving the smoothing of the recording surface, and

  30 / a chromogenic compound is used in greater quantity.

  However, sheets prepared by these methods show an increased veil in the funds during storage, their surface is of a lower quality than ordinary paper, and their manufacturing cost is high. To solve these problems, extensive studies have been conducted on the mechanism of color formation of thermographic recording sheets. It was then found that for almost all the dye type thermographic recording sheets, the color is formed as a result of the steps of: melting the developer and / or the low melting point hot melt; mutual dissolving of the molten developer and the low melting compound; 30 / dissolving an electron donor colorless dye ("chromogenic dye") in a molten eutectic mixture of the developer and the low melting point compound; and

  chromogenic reaction of the developer and the dye.

  It has also been found that the dissolution rate in the third step above made it possible to control the degree of progress of the chromogenic reaction. On the basis of these results we could then prepare

  thermographic recording sheets using fine

  chromogenic dye, of various sizes, and it has been found that the particle size has little effect on the recording when the average volume is between 3 and 10 pm approximately, whereas if it is less than or equal to 2, Oim, a significant increase in

  density of color appears and the difference with the case of the use of

  The use of a larger particle sized color dye is particularly important in the case of high speed recording. Even better results are obtained when particles

  of chromogenic dye have an average volume less than or equal to 1.0 μm.

  The average volume (x) of the particles used in the invention can be represented by the following relationship: - = 4 total particle volume l / 3 X% 37 X total number of particles Jusqu'à Until now, no known means suitable for preparing fine particles of chromogenic dye, and the minimum dimension of

  chromogenic disperse dye particles that could be reached

  dre was about 3 to 4 pm. As indicated above, if the size of the particles in dispersion is greater than or equal to 3 μm, the effect of the particle size on the color formation is relatively limited, and therefore it can not be assumed until now than a larger decrease in particle size, up to

  dimension less than or equal to 2 pm, would provide the characteristic advantages

  of the invention. The average size of the chromogenic dye particles, less than or equal to 2k m, has been obtained in part by suitably adapting the dispersing device, and partly by mixing several water-soluble polymers to form a

  protective colloid of the dispersion and reduce its viscosity.

  The recording sheet according to the present invention has a rapid response to thermal pulses of very short duration, and provides

  appropriate color density for a small amount of thermal energy

  nomic. A method of manufacturing a thermographic recording sheet according to the invention is described below. The chromogenic dye and developer particles are dispersed separately in a solution of a water-soluble polymer, in a ball mill or other suitable dispersing device, and for example the fine coloring dye particles of the invention. can be prepared by dispersion for a sufficient period (16 to 24h) using beads of different sizes in a determined proportion. The use of a sand mill, for example a Dyno grinder (Wiely A. Bachofen AG

  Maschinenfabrik, Switzerland), can also be effective.

  For example, when the dispersion is carried out in a ball mill to prepare the color dye in the form of fine particles of average volume less than or equal to 2.0 μm, it is preferable to use beads of small diameter, for example 1 to 5 mm, in combination with the ordinary balls, that is to say from 2 to 4 cm in diameter, in proportion

  appropriate. The fine balls can represent 10 to 100, O and preferably

  20 to 50% of the volume of ordinary balls. The constituent material

  fine beads is preferably hard glass, alumina, zirconium

  cone, etc. In addition, when the dispersion is carried out by the method of incorporating the substance to be dispersed into the container where the grinding medium such as sand is loaded, and stirring the resulting mixture, it is

  It is possible to easily obtain a dispersion of particles of

  less than or equal to 2i m. In this case, it is also necessary

  to use a grinding means with a diameter of between 1 and 5 mm and preferably between 1 and 3 mm, for example glass, alumina, zirconia, Ottawa sand, etc. However, no particular restriction

  is necessary with regard to the dispersion method.

  The thermal recording material used in the invention is dispersed in a solution of water-soluble polymer such as polyvinyl alcohol, hydroxyethyl cellulose, polyacrylamide, starch, etc. When sodium caseinate is added simultaneously with the dispersion, an increase in the viscosity during dispersion is avoided.

  the resulting increase in temperature, and consequently the solu-

  The dispersion dispersion obtained is satisfactory. The amount of sodium caseinate used represents 0.1 to 5% and preferably 0.5 to 2% of the weight of

the dispersion solution.

  The colorant and developer dyes are mixed together and then mixed with an inorganic pigment, a wax, a higher aliphatic acid amide, a metal soap, and optionally a UV absorber, an antioxidant, and a binder. latex, to form a coating solution. These additives can be incorporated during the preparation of the dispersions. The coating solution is applied to a carrier in an amount such that the weight of coated chromogenic dye is about 0.1 to 0.6 g / m 2. The support is usually a paper but it can also be plastic. The lower limit of the weight of the coating depends on the desired color density, and the upper limit of the cost of manufacture. The amount of chromogenic dye is

  preferably between 0.2 and 0.4 g / m 2.

  No special limitation is required with respect to the color dye of the invention which may be of the type commonly used in pressure-sensitive recording sheets or in thermographic recording sheets. Examples include:

  triarylmethanes such as 3,3-bis (p-dimethylaminophenyl) -6-di-

  methylaminophthalide (crystal violet lactone), 3- (p-dimethylamino)

  phenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3,3-bis (9-ethylcarbamate)

  zol-3-yl) -5-dimethylaminophthalide, and 3,3-bis (2-phenylindol-3-yl) -5-di-

méthylaminophtalide;

  2 / diphenylmethanes such as 4,4'-bis (dimethylamino) ether

  benzidrinebenzyl), N-halophenyl leucoauramine, and N-2,4,5-tri-

chlorophenyl leucoauramine;

  3 / xanthenes such as rhodamine B-anilinolaetam, 3-diethyl-

  amino-7-dibenzylaminofluorane, 3-diethylamino-7-butylaminofluorane,

  3-diethylamino-7- (2-chloroanilino) fluoran, 3-diethylamino-6-methyl-

  7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane,

  3-ethyltolylamino-6-methyl-7-anilinofluorane, 3-cyclohexylmethylamino-

  6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7- (B-ethoxyethyl) -

  aminofluorane, and 3-diethylamino-6-chloro-7- (γ-chloropropyl) amino-

  fluoran; 4 / Thiazines such as benzoyl leucomethylene blue and p-nitrobenzoyl leucomethylene blue; and 5 / spiro compounds such as 3-methylspiro-dinaphthopyran, 3-ethylspiro-dinaphthopyran, 3-methylnaphtho (3-methoxybenzo) spiropyran,

as well as their mixtures.

  The appropriate chromogenic dye is chosen according to the use

and desired properties.

  The developer used in the invention is preferably a derivative

  phenol or an aromatic carboxylic acid derivative, and any

  first a bisphenol. The bisphenols which can be used in the invention as developers are represented by the formula: R 1 HO! in which R1 and R2 represent a hydrogen atom or a group

  alkyl of 1 to 12 carbon atoms, or combine to form a carbon

  cycle; their derivatives can also be used.

  Specific examples of developers are: 1) phenols such as p-octylphenol, p-t-butylphenol,

  p-phenylphenol, 1,1-bis (p-hydroxyphenyl) propane, 2,2-bis (p-hydroxy)

  phenyl) propane, 1,1-bis (p-hydroxyphenyl) pentane, 1,1-bis (p-hydroxy)

  phenyl) hexane, 2,2-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxy)

  phenyl) -2-ethylhexane, and 2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane; and 2 / aromatic carboxylic acid derivatives such as phydroxybenzoic acid, ethyl p-hydroxybenzoate, p-hydroxybenzoate of

  butyl, 3,5-di-t-butylsalicylic acid, 3,5-di-α-methylbenzyl

  salicylic acid, and the polyvalent metal salts of these acids.

  To cause fusion and the chromogenic reaction at the desired temperature, these developers are preferably added as an eutectic mixture with a hot-melt substance with a low melting point, or as fine particles on the surface of which the polymer is melted.

compound at low melting point.

  Examples of low melting point hot melt compounds are paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, and acid amides.

  higher aliphatics and for example a stearoylamide and an ethylenebis-

  stearamide, as well as higher aliphatic acid esters.

  Examples of metal soaps are polyvalent metal salts and higher aliphatic acids such as zinc stearate, stearate

  of aluminum, calcium stearate, and zinc oleate.

  Examples of inorganic pigments are kaolin, carbonized kaolin, talc, pyrophyllite, diatomaceous earth, calcium carbonate,

  aluminum hydroxide, magnesium hydroxide, magnesium carbonate

  sium, titanium oxide, and barium carbonate.

  The wax, the metallic soap and the inorganic pigment are dispersed in a binder and mixed with the colorant and developer dispersions. Alternatively, they may be dispersed together with the color former and developer particles. The binder is generally a high molecular weight compound soluble in water and for example polyvinyl alcohol, hydroxyethylcellulose, hydroxypropylcellulose, an ethylene-maleic anhydride copolymer, a

  styrene-maleic anhydride copolymer, an isobutylene-anhy-

  Maleic acid, polyacrylic acid, casein, and gelatin. In order to be impervious, these binders are mixed with an agent

  waterproofing agent such as a gelling agent or a cross-linking agent

  lation, or with emulsions of hydrophobic polymer such as an emulsion

  styrene - butadiene rubber latex and acrylic resin.

  The following examples illustrate the invention without limiting its scope.

  Unless otherwise indicated, all parts are by weight.

EXAMPLE 1

  g of chromogenic dye, 3-diethylamino-6-methyl-7-anilinofluorane,

  are dispersed in 2.5% by weight of polyvinyl alcohol (degree of poly-

  merit: 500; saponification: 99%) using a ball mill. The ball mill is constituted by a porcelain container with a capacity of 71 containing 1.5 kg of alumina balls of 20 mm diameter and 500 g of zirconia balls of 3 mm diameter. The dispersion is sampled after 6, 12, 24, 48, and 72 hours of grinding. The average volume dimension of the chromogenic dye particles dispersed in the samples is

  5.4, 3.6, 2.0, 1.4, and 1.0 pim, respectively.

  2 g of the developer, 2,2'-bis (p-hydroxyphenyl) propane, and 120 g of stearoylamide are dispersed in 5% polyvinyl alcohol using a ball mill to provide a particle size dispersion.

average 3.5 p m.

  A portion of the chromogenic dye dispersion is mixed with 5 parts of the developer dispersion, 2 parts of 40% kaolin, 1 part of 20% zinc stearate and 5 parts of% polyvinyl alcohol to prepare a solution. coating. The solution is applied to a paper without coating at a rate of 50g / m2 until the coating of

  chromogenic dye is 0.4g / m2; a calendering is carried out at a pres-

  20kg / cm and passed through Pana facsimile

  fax-7000 (Matsushita Electric Industrial Co Ltd) o pulses of different widths are applied to develop color on any

the recording sheet.

  The color density for pulse durations of 1.5ms and 2.7ms as a function of the size of the disperse colorant dye particles is represented by curves 1 and 2 respectively in FIG.

  relationship between particle size and the color density obtained

  nude by keeping the thermographic recording sheet in contact with a hotplate at 150 C for 5s is also shown in Figure 1 by curve 3. The particle size is measured using a Model TA-II (Coulter Counter Corp.). The color density is measured using a Macbeth Model Reflector Densitometer

  RD-514, equipped with a visual filter.

EXAMPLE 2

  Chromogenic dye dispersions are prepared as in the example

  1 but using chromogenic dye as 3-diethylamino-6-chloro

  -7-3-ethoxyethylamino) fluoran. The average size of the colorant dye particles in the five dispersions is 4.6, 3.1, 1.9, 1.2, and 0.8 μm, respectively. The dispersions are then treated as in

  Example 1 for preparing thermographic recording sheets.

  The relationship between the color density and the average size of the

  Chromogenic dye is shown in Figure 2.

  Figures 1 and 2 show that the reduction in the size of the

  chromogenic dye to a value as defined in the present

  This invention makes it possible to provide a significant increase in

  color density for high speed recording.

11'n 2 489751

Claims (7)

  1. Thermographic recording sheet comprising a support coated with a thermographic color-forming layer containing a dye   colorless electron donor and an electron-accepting compound,   characterized in that the electron donor colorless dye is in the form of fine particles of average size less than or equal to 2.01 m. Thermographic recording sheet according to claim 1, characterized in that the average size of the dye particles   colorless electron donor is less than or equal to 1.0 pim.   3. Thermographic record sheet according to any one of   Claims 1 and 2, characterized in that the amount of dye   colorless coated electron donor is between 0.1 and 0.6g / m2.   Thermographic recording sheet according to claim 3,   characterized in that the amount of colorless donor dye is   trons coated is between 0.2 and 0.4g / m2.   5. Thermographic record sheet according to any one of   preceding claims, characterized in that the colorless dye   electron donor is a triaryl methane, a diphenyl methane, a xan-   thene, a thiazine, or a spiro compound.   Thermographic recording sheet according to claim 1, characterized in that the electron-accepting compound is a derivative   phenolic or an aromatic carboxylic acid derivative.   Thermographic recording sheet according to claim 1, characterized in that the electron-accepting compound is a bisphenol of formula: HO / C / H \ 'I R2 -   wherein R1 and R2 represent a hydrogen atom or a group   alkyl of 1 to 12 carbon atoms, or combine to form a carbon cycle; or one of its derivatives.