Composition for developing a visually discernible colour and corresponding heat-sensitive recording material

Abstract

A composition for forming a visually discernible color, the use of this composition for producing a heat-sensitive recording material, the corresponding heat-sensitive recording material includes a substrate and this composition, and a process for producing the heat-sensitive recording material.

Claims

1. A composition for forming a visually discernible color comprising: a) one, two, three or more color developers comprising in each instance one, two, three, or more than three structural units of formula (I) ##STR00010## wherein, in each of the structural units of formula (I), z means an integer greater than 1, wherein the respective meaning is independent of the meaning in further structural units of formula (I) which may be present; b) one, two, three or more dye precursors for forming the visually discernible color through reaction with the color developer or color developers; and c) one, two or more compounds selected from the group comprising zinc salts, ammonium salts and zinc oxide.

2. The composition according to claim 1, wherein the one, two or more compounds of component c) increase the maximum dynamic print density and/or the maximum static print density.

3. The composition according to claim 1, wherein the total amount of component c) is in the range of from 7 to 33 percent by weight with respect to the total mass of components a), b) and c).

4. The composition according to claim 1, wherein one, two, three, more than three, or all of the dye precursors is or are a compound selected from the group comprising 3-diethylamino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-propyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-tolyl)amino-6-methyl-7-anilinofluoran, and 3-(N-ethyl-N-tetrahydrofuryl)amino-6-methyl-7-anilinofluoran.

5. The composition according to claim 1, wherein the composition is adapted in such a way that the visually discernible color is formed when the temperature of the composition is increased.

6. The composition according to claim 1, wherein one, two, three, more than three, or all of the color developers is/are made by (I) conversion of an x-functional carboxylic acid with compounds containing structural units of formula (I), wherein z in each of the structural units of formula (I) means an integer greater than 1, wherein the respective meaning is independent of the meaning in further structural units of formula (I) which may be present; and wherein x is two, three, or more than three.

7. The composition according to claim 1, comprising two, three, or more than three color developers, wherein (I) a first color developer is made by conversion of an x-functional carboxylic acid with compounds containing structural units of formula (I), wherein z in each of the structural units of formula (I) means an integer greater than 1, wherein the respective meaning is independent of the meaning in further structural units of formula (I) which may be present; wherein x is two, three, or more than three; and wherein (II) a second color developer is made by conversion of a y-functional carboxylic acid compounds containing structural units of formula (I), wherein z in each of the structural units of formula (I) means an integer greater than 1, wherein the respective meaning is independent of the meaning in further structural units of formula (I) which may be present; wherein y is three, or more than three, with the proviso that the x-functional carboxylic acid is not identical to the y-functional carboxylic acid.

8. The composition according to claim 1, wherein all of the color developers contained in the composition contain one, two, three, or more than three structural units of formula (I).

9. The composition according to claim 1, additionally comprising one, two or more binders, wherein the one binder of the one or more than one binders is selected from the group comprising polyvinyl alcohol, ethylene vinyl alcohol copolymer and a combination of polyvinyl alcohol and ethylene vinyl alcohol copolymer.

10. A heat-sensitive recording material comprising: a substrate and a heat-sensitive recording layer; and wherein the heat-sensitive recording layer comprises a composition according to claim 1.

11. The heat-sensitive recording material according to claim 10, wherein all of the color developers contained in the heat-sensitive recording layer contain one, two, three, or more than three structural units of formula (I).

12. A process for the production of a heat-sensitive recording material comprising the following steps: providing a composition according to claim 1; providing a substrate; and coating the substrate with the composition; wherein the step of coating is preferably carried out by a coating apparatus, wherein the coating apparatus is selected from the group comprising a roll doctor coating unit, knife coating unit, curtain coater and air brush.

13. The composition according to claim 1, wherein the total amount of component c) is in the range of from 12 to 25 percent by weight with respect to the total mass of components a), b) and c).

14. The composition according to claim 1, wherein the total amount of component c) is in the range of from 14 to 20 percent by weight with respect to the total mass of components a), b) and c).

15. The composition according to claim 1, comprising two, three, or more than three color developers, wherein (I) a first color developer is made by conversion of an x-functional carboxylic acid with compounds containing structural units of formula (I), wherein z in each of the structural units of formula (I) means an integer greater than 1, wherein the respective meaning is independent of the meaning in further structural units of formula (I) which may be present; wherein x is two, three, or more than three; and wherein (II) a second color developer is made by conversion of a y-functional carboxylic acid compounds containing structural units of formula (I), wherein z in each of the structural units of formula (I) means an integer greater than 1, wherein the respective meaning is independent of the meaning in further structural units of formula (I) which may be present; wherein y is three, or more than three, with the proviso that the x-functional carboxylic acid is not identical to the y-functional carboxylic acid; and wherein y is greater than x.

16. A method of modifying the dynamic print density and/or the static print density, particularly for increasing the maximum dynamic print density and/or the maximum static print density of a mixture of one, two, three or more color developers and one, two, three or more dye precursors for forming a visually discernible color, said method comprising the step of: reacting one or more than one compound selected from the group comprising zinc salts, ammonium salts and zinc oxide with the color developer or color developers; wherein the one, two, three or more color developers, comprise in each instance one, two, three, or more than three structural units of formula (I) ##STR00011## wherein, in each of the structural units of formula (I), z means an integer greater than 1, wherein the respective meaning is independent of the meaning in further structural units of formula (I) which may be present.

17. The method according to claim 16, wherein the zinc salts and/or ammonium salts are selected from the group comprising zinc carbonate, zinc oxide, ammonium hydrogen sulfate, ammonium nitrate, ammonium hydrogen phosphate and zinc acetate.

Description

EXAMPLES

1. Compositions

(1) To determine the maximum dynamic print density or maximum static print density of selected compositions according to the invention or of heat-sensitive recording materials according to the invention produced therefrom, two comparison compositions (reference compositions R1 and R2) and four additional compositions according to the invention (Z1 to Z4) were produced in a first work step. The constituents of each individual composition are listed in Table 1. The amounts specified therein are dry weight parts based on 1 dry weight part of the dye precursor 3-dibutylamino-6-methyl-7-anilinofluoran. The amounts of zinc oxide, zinc acetate, zinc carbonate and ammonium hydrogen sulfate correspond to approximately equimolar amounts of zinc compounds.

(2) TABLE-US-00001 TABLE 1 Dry Weight Parts (Bone Dry Weight Parts) Constituent R1 R2 Z1 Z2 Z3 Z4 Compound of component a) 3 3 3 3 3 3 Polyvinyl alcohol 1 1 1 1 1 1 3-Dibutylamino-6-methyl-7- 1 1 1 1 1 1 anilinofluoran N-hydroxymethyloctadecanamide 1 Zinc oxide 1 Zinc acetate 2.70 Zinc carbonate 1.54 Ammonium hydrogen sulfate 1

2. Heat-Sensitive Recording Materials

(3) In a second work step, the compositions indicated above were processed to form a coating composition and subsequently applied in each instance to a paper (substrate) by laboratory roller coating so that six different heat-sensitive recording materials resulted. A pre-coated 75 g/m.sup.2 base paper was used as substrate. The pre-coating was made up chiefly of natural kaolin. Paper that was coated with compositions R1 and R2 resulted in two reference recording materials (Example 1 and Example 2); compositions Z1 to Z4 resulted in an additional four heat-sensitive recording materials according to the invention (Example 3 to Example 6). Every composition was applied such that an identical amount of dye precursor (i.e., 3-dibutylamino-6-methyl-7-anilinofluoran) was applied per m.sup.2 of substrate in each instance.

3. Determination of the Maximum Print Densities

(4) In order to determine the maximum print densities of Examples 1 to 6, (i) dynamic and (ii) static print density curves were prepared and evaluated.

(5) 3.1 Maximum Dynamic Print Density:

(6) In order to determine the maximum dynamic print density for each of the Examples 1 to 6, black-and-white checkerboard thermal test prints were prepared with an Atlantek 400 by Printex (USA), and the heat-sensitive recording materials (Example 1 to Example 6) were printed at an energy setting in the range of from 3 to 16 mJ/mm.sup.2.

(7) Each thermal test print was subsequently analyzed by means of a Gretag MacBeth D19C NB/U densitometer. The measurements (i.e., print density data in ODU) obtained by means of the densitometer were plotted against the corresponding energy inputs and resulted in a dynamic print density curve. The maximum dynamic print density Dmax (dynamic) determined for each example (i.e., the highest value reached on the Y-axis in the dynamic print density curve) is shown in Table 2.

(8) TABLE-US-00002 TABLE 2 Exam- Exam- Exam- Exam- Example 1 Example 2 ple 3 ple 4 ple 5 ple 6 (R1) (R2) (Z1) (Z2) (Z3) (Z4) D.sub.max 0.42 0.33 0.60 0.81 0.53 0.46 (dynamic)

(9) The results listed in Table 2 show that the maximum dynamic print density of heat-sensitive recording materials according to the invention (i.e., of Examples 3 to 6) is increased compared to the reference recording materials (Example 1 and Example 2). A comparison of the maximum dynamic print densities of the recording materials in Examples 1 to 4, for example, shows an increase in the maximum dynamic print density in the recording material of Example 4 (containing zinc acetate) by a factor of approximately 2 compared to the reference material (Example 1) which does not contain a compound of component c).

(10) (Remark: Results of similar quality were obtained for a large number of preferred compounds of component a); only one exemplary result is shown above for the sake of simplicity).

(11) 3.2 Maximum Static Print Density:

(12) In order to determine the maximum static print density for each of the Examples 1 to 6, thermal test prints were prepared with a heat gradient type device by Toyoseiki (Japan). The thermal test prints were prepared at temperatures in the range of from 65 to 140 C. Every thermal test print was prepared with a contact time of 2 seconds and at a pressing pressure of 0.3 mPa.

(13) Each thermal test print was subsequently analyzed by a densitometer of the type described above (3.1). The measurements (i.e., print density data in ODU) obtained were plotted against the corresponding temperatures and resulted in a static print density curve. The maximum static print density Dmax (static) determined for each example (i.e., the highest value reached on the Y-axis in the static print density curve) is shown in Table 3.

(14) TABLE-US-00003 TABLE 3 Exam- Exam- Exam- Example 1 Example 2 Example 3 ple 4 ple 5 ple 6 (R1) (R2) (Z1) (Z2) (Z3) (Z4) D.sub.max 0.15 0.20 0.61 0.85 0.53 0.70 (static)

(15) The results listed in Table 3 likewise show that the maximum static print density of heat-sensitive recording materials according to the invention (i.e., of Examples 3 to 6) is increased compared to the reference recording materials (Example 1 and Example 2). A comparison of the maximum static print densities of the recording materials in Examples 1 to 4, for example, shows an even more than five-fold increase in the maximum static print density in the recording material of Example 4.

(16) (Remark: Results of similar quality were obtained for a large number of preferred compounds of component a); only one exemplary result is shown above for the sake of simplicity).

(17) Further, the heat-sensitive recording materials according to the invention (Examples 3 to 6) show that both the maximum dynamic print density and the maximum static print density are increased compared with the reference material (Example 1).

(18) Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.