DE2347708A1 - Thermocopying compsn. with improved resistance to light - contains tris (4-hydroxy 3-branched alkyl phenol) cpd. besides colour former and acid - Google Patents

Abstract

The compsn. comprises a dispersion of a normally colourless or pale colour-former (I), an org. acid (II), permitting colour formation of (I) on heating, and a phenol of formula (III): (in which R1 is 3-8C branched alkyl; R2 and R3 are H or 1-8C alkyl; X is PO3, PO4, PO3S or a gp. of formula (IV); R4 is lower alkyl or OH; R5 and R6 are H or lower alkyl). There is practically no fading or discolouration when the material is (in) directly exposed to light and, unlike certain low-melting phenols, (III) does not have a negative effect on the thermal stability. The compsn. contains 10-500 (wt.)% (III) w.r.t. (I) and 1-100, pref. 3-50, pts. (II)/pt.(I). It is mixed with a binder (5-50, pref. 15-40% w.r.t. all solids) and coated on a substrate.

Description

Thermosensitive Recording Composition This invention relates to a heat-sensitive recording composition with improved light resistance.

In particular, the invention relates to such heat-sensitive recording compositions with improved lightfastness, which, dispersed in a binder, in layers on supports, for example on paper, can be applied, so that for the thermal information recording suitable carriers arise.

The reaction between a color former such as Crystal violet lactone and a phenol to form a colored fabric has already been used by 0. Fischer and F. Roter in * Reports of the German Chemical Society "42 (1909), 2934 - 2935 described. The application of this reaction in the field of heat-sensitive Recording papers have been disclosed, for example, in Japanese Patent Application 14039/70 described.

One by thermal reaction between a color former and a The color image obtained from organic acid is generally not visible when exposed to light stable. For example, using crystal violet lactone this way The color images produced are even extremely unstable. For the use of recording media however, on the basis of such color development reactions it is necessary to that the information thermally recorded on the carrier also lasts for a long time can be stored in gas unchanged and safely. The ones available so far heat-sensitive recording materials do not meet this requirement.

In the context of the present description, the term with means improved light resistance "that neither discoloration nor discoloration of the colored areas of the recording medium do not occur even if these are exposed directly or indirectly to light.

The use of dyed fabrics with high lightfastness is one Way on which attempts have been made for a long time to improve the light resistance of thermal To improve recording media. However, there have not yet been any on this path radical results have been achieved.

The invention is therefore based on the object of recording compositions for heat-sensitive recording media that have a high level of lightfastness exhibit.

According to the invention, a composition is used to solve this problem proposed of the type mentioned.

characterized by a dispersion of a normally colorless or only weakly colored. color-forming substance, an organic acid. which enables the coloring of the color-forming substance when heated, and a phenol of the general formula where R1 is a branched alkyl with 3 - 8 carbon atoms, R2 and R3 hydrogen or alkyl with 1 - 8 carbon atoms and X = P03, = P04a = PO3S or R4 is lower alkyl or hydroxyl and R5 and R6 are hydrogen or lower alkyl.

Typical representatives of preferred phenols are shown in the table below 1 summarized.

Table 1 The abovementioned compounds are known as stabilizing additives for the most varied types of rubber, plastics, fibers or petroleum products. The processes for producing the phenols mentioned are also known per se. However, from the known uses of phenols, it could not be foreseen that adding these phenols to the heat-sensitive recording systems based on a color former and an organic acid would, quite surprisingly, improve the light resistance of such systems. This effect must be all the more surprising, as other known plastic stabilizers such as diphenylamine, phenothiazine, phenyl-alphanaphthylamine or, N'-diphenyl-p-phenylenediamine and metal soaps such as cadmium atearate, tin stearate or lead naphthenate have a practical effect on the light resistance of the heat recording systems had no influence, but rather often gave rise to instabilities in the systems.

The phenols used in plastics technology for the same purpose on the other hand, lead to an unexpected one in the thermosensitive recording systems Improvement of the light resistance. Even when storing colored images the basis of these systems over a long period of time there is practically no discoloration of the pictures. Such image stability has not been possible in this area up to now and should give new impetus to thermal recording technology.

Among the phenols of the type mentioned are those for thermal recording systems not suitable, which have a very low melting point. Such phenols work themselves negatively affect the thermal stability of the systems.

Phenols are therefore preferably used in the context of the invention, whose melting point is above 60 ° C.

The amount of phenol that is advantageously added to the system, depends on the type and proportions of the color-forming substance and the organic Acid off. The phenols are preferably obtained in amounts of 10-500% by weight on the color former added. The organic acid can be used in amounts of 1 - loo Parts by weight, preferably 3 to 50 parts by weight, are used for one part of color former will. The binder used for the composition can be used in amounts of 5 - 50 % By weight, preferably from 15 to 40% by weight, based on the total solids mass, are present.

As color former or "color-forming substance" are used in the context of the description normally colorless or only faintly tinted substances understood by reaction colored with organic acids, especially by reaction with polyhydric phenols can be. The following is a list of examples of such color formers reproduced: crystal violet lactone, malachite green lactone, 3,3-bis- (p-dimethylaminophenyl) -6-aminophthalide, 3,3-bis- (p-dimethylaminophenyl) -6- (p-toluenesulfonamide) phthalide, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7- (N-methylanilino) -fluorane, 3-diethylamino-7- (N-methyl-p-toluidine) -fluorane, 3-dimethylamino-6-methoxyfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluoran, 3-dibutylamino-6-methyl-7-chlorofluoran, 3-diethylamino-7-phenylfluoran, 3-morpholino-5, 6-benzofluorane, 6'-chloro-8'-methoxy-indoline-benzospiropyran, Benzo-ß-naphthospiropyran, 3-methyl-di-ß-naphthospiropyran.

The organic acids to be used in the context of the invention must to liquefy or to liquefy above room temperature

to be evaporated, preferably above 70 0C, so that they the Color formers can color verb through the thermal reaction. Come as acids especially aromatic carboxylic acids such as phthalic anhydride, gallic acid or salicylic acid and phenols, for example 4,4'-isopropylidene-diphenol, 4,4'-isopropylidene-bis- (2-chlorophenol), 4,4'-isopropylidene-bis- (2-tert-butylphenol), 4,4'-sec-butylidenediphenol, p, p '- (1-methyl-n-hexylidene) -diphenol, 4-phenylphenol, 4-hydroxy-diphenoxide, methyl-4-hydroxybenzoate, phenyl-4-hydroxybenzoate, 4-hydroxyacetophenone, Salicylanilide, novolaks, halogenated novolaks, alpha-naphthol or beta-naphthol. In particular, of these acids are the phenols with at least two hydroxyl groups preferred.

By using at least two different of these in combination organic acids, the color formation temperature can be reduced.

To apply the composition according to the invention to a carrier, for example a piece of paper or a film, the three components the phenol, the organic acid and the color former, dispersed in a binder.

The binder used is preferably a water-soluble one which is known per se Resin used, for example polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, Gum arabic, carboxymethyl cellulose, starch, gelatin, casein, polyvinylpyrrolidone, a copolymer of styrene and maleic anhydride, a polyacrylate or a copolymer a polyacrylate. However, if you use thin paper as a support, then they are Dispersions based on water-soluble polymer binders are not particularly suitable, as most thin papers will stretch, warp, or warp. In these Cases, a non-aqueous coating dispersion based on an in organic solvents soluble resin used, for example based on terpene resins, petroleum resins or cyclic rubbers.

The three components of the thermosensitive recording system should preferably be dispersed in the binder as finely as possible. The grain size the components should preferably be in the range from 1 to 10 μm, especially after Possibility in the range of 1 / um or just a little more. The components can with pulverization devices known per se, for example with a good Ball mill, can be ground to this grain size without difficulty.

A surfactant such as a dispersant or a suds suppressor may be added as a pulverizing aid if necessary will. Brighteners or fillers, such as, for example, can also be used Talk, Clay, or starch, may be added to prevent the layered sides of the thermally sensitive ones made from the compositions according to the invention Recording media stick to the thermal print heads during recording. To suppress the discoloration under pressure, which leads to staining of the substrate and scratches on the surface from rubbing or pressing can cause the sensitive If necessary, waxes are also added to the coating of the recording media will.

The invention is described in more detail below with the aid of examples.

Example 1 Liquid A Crystal Violet Lactone 1 g of 5% strength aqueous Solution of Hydroxyäthylce 1 lulos e (HEC BL-15 Fuji Chemical K.K.) 5 g water 4.4 g liquid B 4,4'-isopropylidenediphenol 5 g 5% aqueous solution of hydroxyethyl cellulose 2 5 g water 22 g liquid C Tris- (4-hydroxy-2,5-di-tert-butylphenol ) phosphite (Formula 1 in Table 1) lg 5% aqueous solution of hydroxyethyl cellulose 5 g Water 4.4 g The liquids A, B and C are separated from each other for two days long grind in the ball mill and then to produce a heat-sensitive Coating compound mixed together. The coating composition thus obtained is applied to normal paper with a basis weight of 50 g / m2 in such a way that that the surface weight of the coating after drying is 3 g / m2. For comparison heat-sensitive recording papers were produced in an identical manner, in which, however, the phenol component according to the invention (formula 1 of the table 1) replaced by the connections shown in Table 2 below had been. The results of quality studies of the heat-sensitive ones thus obtained Recording papers are summarized in Table 2.

The residual density results from a color density between 1.1 and 1,2 by the following expression: color density after exposure, color density before Exposure × 100 The color density was measured with a MACBETH densitometer.

A daylight fluorescent lamp was used as the fluorescent lamp.

Table 2 Kr. Compounds residual density residual density remarks according to Exposure after exposure with tunq with Son fluorescent lamps (24 h) (l h) L - 32 (%) 16 (%) comparison 2 formula 1 85 65 according to Erin table 1 finding 3 phenyl-alpha 31 18 Comparison naphthylamine 4 cadmium 28 15 stearate 5 zinc diethyl 22 10 dithiocarbamate 6 Mercaptobenzo- 20 10 thiazole 7 A low temperature 23 13 temperature reaction product of Diphenylamine and acetone (Sumirizer-AM by Sumitomo Kagaku K.K.) The Data in Table 2 can be clearly seen that in contrast to the comparative additives by adding the phenolic component according to the invention, the light resistance the colored recording is significantly improved.

In the same way, the long-term behavior of the recordings is improved.

Example 2 3-Diethylamino-7-chlorofluorane is used instead of that in the example 1 used crystal violet lactones and 1,3,5-trimethyl-2,4,6-tris- (3,5-di-tert-butyl-4-hydroxybenzyl} -benzene (Formula 8 of Table 1) used instead of compound 1 of Table 1. With this system becomes heat-sensitive in the manner described in Example 1 Record carrier produced. The residual density is under the light of a fluorescent lamp measured. Without the addition of compound 8 in Table 1, the residual density was 43 %, while it was 73% when compound 8 of Table 1 was added. Corresponding almost doubling the lightfastness of the record.

Example 3 Liquid A 3-diethylamino-7-dibenzylaminofluoran lg 10% aqueous solution of polyvinyl alcohol (Gosenol NH-33 from Nihon Gosei Kagaku K.K.) 2 g water 3g Liquid B p, p '- (1-methyl-n-hexylidene) -diphenol 5 g 10% aqueous solution of polyvinyl alcohol 10 g water 15 g liquid C tris (4-hydroxy-2,6-di-tert-butylphenol) phosphate (Formula 4 in Table 1) 1.5 g of 10% strength aqueous solution of polyvinyl alcohol and 3 g of water 4.5 g Liquids A, B and C were kept separately for two days in ground in the manner described in Example 1 in a ball mill and then mixed together. To this mixture were 20 g of a 50% wheat starch dispersion, 5 g of a 20% strength wax emulsion Repol No. 50 from Daikyo Kagaku K.K. and 20 g eir.ar Given 10% aqueous solution of polyvinyl alcohol. By mixing and homogenizing a heat-sensitive coating composition was obtained. This crowd was on a normal paper with a basis weight of 50 g / m2 applied in such a way, that the dried layer had a basis weight of 5 g / m2. That on this Well-prepared thermosensitive recording paper has been subjected to various Subject to quality tests. It showed both excellent lightfastness as well as excellent long-term stability.

Claims (5)

Claims 1. Heat-sensitive recording composition with improved light resistance, characterized by a dispersion of a normally colorless or only slightly colored, color-forming substance, an organic acid which, when heated, enables the color-forming substance to be colored, and a phenol of the general formula where R1 is a branched alkyl with 3 - 8 carbon atoms, R2 and R3 hydrogen or alkyl with 1 - 8 carbon atoms and X = - P03, = P04, PO P03S or R4 is lower alkyl or hydroxyl and R5 and R6 are hydrogen or lower alkyl. 2. Composition according to claim 1, characterized by one of the following phenols: 3. Composition according to one of claims 1 or 2, characterized characterized that the phenol in an amount of 10-500 wt., Based on the color-forming substance, and the organic acid in an amount of 1 - 100 parts by weight, preferably in an amount of 3 - 50 parts by weight per 1 part of the color-forming substance, are present. 4. Use of the composition according to any one of claims 1 to 3 for the production of heat-sensitive recording media by incorporating the composition into a binder and coating a corresponding carrier. 5. Use according to claim 4, characterized in that the Binder in an amount of 5 - 50 wt .-%, preferably in an amount of 15 to 40 wt.> X based on the weight of all solids. used.