EP0280284B1 - Heat-sensitive recording material - Google Patents

Description

The invention relates to a heat-sensitive recording material which is suitable for optical readability in the near ultraviolet range and which can be detected locally when irradiated with UV light.

Heat-sensitive recording sheets in which a color reaction between a colorless or slightly colored chromogenic substance and a phenolic substance or an organic acid takes place due to the action of heat or heat include in Japanese Patent Publications No. 4160/1968 and 14039/1970 and in JP-OLS No. 27736/1973. They are used in many different ways in practice.

A heat-sensitive recording sheet is generally prepared by applying to the surface of a support such as paper, film, etc. a coating composition which is obtained by finely grinding and dispersing a colorless chromogenic substance and a color developing material, mixing the dispersions obtained with one another and adding a binder, filler, Sensitizer, lubricant and other aids have been obtained. When exposed to heat or heat, the coating is instantly chemically converted to form a color.

The various practical uses of these heat-sensitive recording sheets include use in medical and technical recording devices, terminal printers for computers and information systems, printers for facsimile or copying machines and electronic calculating machines, ticket machines and the like.

The heat sensitive recording sheets containing a leuco dye and a coloring agent are used as thermal labels in the field of POS systems. The color development occurs in the visible range, so that the color development cannot be read by the bar code scanner when a semiconductor laser beam is used in the near ultra-red range.

In contrast to the above heat-sensitive color development system that uses colorless dyes, a heat-sensitive color development system that uses metal compounds is also known. For example, Japanese patent publication 8787/1957 describes the combined use of iron stearate as an electron acceptor with tannic acid or gallic acid as an electron donor, and Japanese patent publication 6485/1959 describes the combined use of an electron acceptor such as silver stearate, iron stearate, gold stearate, copper stearate or mercury behenate an electron donor such as methyl gallate, ethyl gallate, propyl gallate, butyl gallate or dodecyl gallate.

• Eine mit einem Strichcode-Zettel beklebte Packung wird von einem Förderer in eine Dunkelkammer eingeführt, in dem sie mit einem UV-Strahl einer bestimmten Wellenlänge bestrahlt wird. Dabei wird das aus dem Fluoreszenzfarbstoff in dem Strichcode-Zettel entstehende Fluoreszenzlicht von einem Fluoreszenzdetektor erfaßt und die Stelle des Strichcode-Zettels auf der Packung wird beobachtet. Dann erfolgt das Sortieren automatisch durch das Lesen der Information des Strichcodes mittels eines Halbleiter-Laser-Abtasters bei einer Transmissionswellenlänge im nahen ultraroten Bereich.

Increasingly, heat-sensitive recording sheets are used as barcode labels for labeling packaged products. The products marked in this way go through many rapid automatic sorting processes in which barcode readers are switched on. In principle, such fast automatic sorting systems work as follows:

• A package stuck with a bar code note is introduced into a dark room by a conveyor, in which it is irradiated with a UV beam of a certain wavelength. The fluorescent light resulting from the fluorescent dye in the bar code slip is detected by a fluorescence detector and the position of the bar code slip on the package is observed. Then the sorting is carried out automatically by reading the information of the bar code by means of a semiconductor laser scanner at a transmission wavelength in the near ultra-red range.

The above system is one of the conceivable examples. With such sorting systems, the previous heat-sensitive recording sheets cannot be used.

The invention has for its object to provide a heat-sensitive recording material which has a superior local detectability when irradiated with UV light and good optical readability in the near ultraviolet range.

This object is achieved according to the invention in that, in the case of a heat-sensitive recording material which has a heat-sensitive recording layer of the chelating agent type on a support and which contains a fluorescent dye and / or a fluorescent pigment, the fluorescence maximum when irradiated with UV light is in the visible wavelength range of 450- 700 nm. One speaks of the "chelating agent" type here because the electron donor and electron acceptor components contained in the recording layer react with one another to form a chelate.

The choice of the electron acceptor used according to the invention is not subject to any particular restrictions; the known electron acceptors, preferably the metal double salts of the higher fatty acids, can be used.

The metal double salts of higher fatty acids according to the invention are double salts which have at least two types of metal atoms per molecule. They therefore differ significantly in their physicochemical properties from the previous metal salts of higher fatty acids, which only contain one type of metal atom in their molecule.

These metal double salts of the higher fatty acids are prepared by reacting at least two inorganic metal salts with an alkali metal salt or ammonium salt of the selected higher fatty acid. The type and the mixing ratio of the metal atoms of the at least two inorganic metal salts can be easily adjusted and controlled in this way. For example, the zinc-iron double salt of behenic acid with iron and zinc in a ratio of 2: 1 can be prepared by reacting sodium behenate with an aqueous solution of ferrichloride and zinc chloride in a molar ratio of 2: 1.

Suitable metals for the double salt formation of the higher fatty acids are polyvalent metals, for example iron, zinc, calcium, magnesium, aluminum, barium, lead, manganese, tin, nickel, cobalt, copper, silver, mercury, etc .; preferably iron, zinc, calcium, aluminum, magnesium and silver.

Suitable fatty acids for the double salt formation are saturated and / or unsaturated aliphatic fatty acids with 16 to 35 carbon atoms.

• 1) Eisen-Zink-Doppelsalz der Stearinsäure
• 2) Eisen-Zink-Doppelsalz einer Montansäure
• 3) Eisen-Zink-Doppelsalz einer Wachssäure
• 4) Eisen-Zink-Doppelsalz der Behensäure
• 5) Eisen-Calcium-Doppelsalz der Behensäure
• 6) Eisen-Aluminium-Doppelsalz der Behensäure
• 7) Eisen-Magnesium-Doppelsalz der Behensäure
• 8) Silber-Calcium-Doppelsalz der Behensäure
• 9) Silber-Aluminium-Doppelsalz der Behensäure
• 10) Silber-Magnesium-Doppelsalz der Behensäure
• 11) Calcium-Aluminium-Dopelsalz der Behensäure

The choice of the metal double salt of a higher fatty acid according to the invention is not subject to any particular restrictions, for example the following can be used.

• 1) Iron-zinc double salt of stearic acid
• 2) Iron-zinc double salt of a montanic acid
• 3) Iron-zinc double salt of a wax acid
• 4) Iron-zinc double salt of behenic acid
• 5) Double iron-calcium salt of behenic acid
• 6) Iron-aluminum double salt of behenic acid
• 7) Iron-magnesium double salt of behenic acid
• 8) Silver-calcium double salt of behenic acid
• 9) Silver-aluminum double salt of behenic acid
• 10) Silver-magnesium double salt of behenic acid
• 11) Calcium aluminum double salt of behenic acid

Such metal double salts of higher fatty acids can be used as an electron acceptor alone or in a mixture.

in der R eine Alkylgruppe mit 18 bis 35 Kohlenstoffatomen,

(worin R₁ eine Alkylgruppe mit 18 bis 35 Kohlenstoffatomen bedeutet); n eine ganze Zahl von 2 bis 3 bedeutet; und "-X-" für

• 
  -CH₂-, -CO₂-, -CO-, -O-, -CONH-,
  
  (worin R' eine Alkylgruppe mit 5 bis 30 Kohlenstoffatomen bedeutet), - S0₂ -, - SOa - oder - S0₂NH - steht.

The electron donors according to the invention, which are used with the metal double salt of a higher fatty acid, are preferably polyvalent aromatic hydroxyl compounds, diphenylcarbazide, diphenylcarbazone, hexamethylenetetramine, spirobenzopyran and 1-formyl-4-phenylsemicarbazide; most preferred are the polyvalent aromatic hydroxyl compounds of the general formula (I):

in which R is an alkyl group with 18 to 35 carbon atoms,

(wherein R _{1 represents} an alkyl group having 18 to 35 carbon atoms); n represents an integer from 2 to 3; and "-X-" for

• 
  -CH ₂ -, -CO ₂ -, -CO-, -O-, -CONH-,
  
  (wherein R 'is an alkyl group having 5 to 30 carbon atoms), - S0 ₂ -, - SOa - or - S0 ₂ NH -.

In the production of the coating composition by dispersing this polyhydric phenol derivative in an aqueous or solvent-soluble binder, it is necessary to avoid a reaction of this phenol derivative with an electron donor and to increase the solvent and dispersion stability of this phenol. It is desirable that the substituent other than the color developing group has a large number of carbon atoms, namely 18 to 35, 2 to 3 OH groups are present, and these OH groups are close to each other.

The heat-sensitive color development layer according to the invention with the above electron acceptor and the above electron donor contains a fluorescent dye and / or a fluorescent pigment, the maximum fluorescence of which when irradiated with UV light is in the visible range of 450-700 nm wavelength.

Heat sensitive color development layers containing a fluorescent brightener are known. They convert UV light in the invisible range of 300-400 nm wavelength in sunlight into visible blue light of around 420 nm wavelength.

The structures and functions of the fluorescent dyes according to the invention differ from the previous fluorescent brighteners. The fluorescent dyes and / or pigments according to the invention are anthraquinone, indigo, azine, xanthene, acridine, diphenylmethane, triphenylmethane, thiazine, thiazole fluorescent dyes or pigments.

Preferred fluorescent dyes and / or pigments according to the invention are:

The fluorescent pigments according to the invention comprise resin powders which are colored with Rhodamine B, Rhodamine 6G, Azosol-brilliant Yellow 6G or basic fluorescent dye. Examples of this resin are melamine, toluenesulfoamide, triazone, acrylic and polyvinyl chloride resin, etc.

The fluorescent dye may be in the heat sensitive color developing layer by itself and may be contained therein as a powdered pigment. The latter is prepared from a solid solution which is obtained by dissolving the fluorescent dye in a synthetic resin, e.g. Toluene sulfonamide melamine resin, melamine resin, benzoguanamine resin, polyvinyl chloride resin, polyamide resin, polyester resin, polyurethane resin, etc. were obtained. The preferred fluorescent dye is made by the following surface treatment process:

The fluorescent dye is mixed with a polymerization initiator, an amount of vinyl monomer that can be applied to the fluorescent dye, and a solvent in which the vinyl monomer is soluble and which has a lower boiling point than the vinyl monomer, evenly mixed. Then the solvent is removed and the vinyl monomer on the surface of the fluorescent dye particles is polymerized under the action of the polymerization initiator present on the fluorescent dye, thereby obtaining a fluorescent dye coated with a polymer film. The fluorescent dye obtained is easily and uniformly dispersible.

In accordance with the present invention, a leuco dye which absorbs radiation in the near ultrarot range can be used to such an extent that the effect of this invention is not impaired. The leuco dye, which is absorbable in the near infrared, effectively absorbs the radiation in the near ultra-red range (especially in the range of 700 - 1500 nm) during color development after the heat-melting reaction with an acidic substance.

Examples of such fluorescent dyes are fluorene leuco dyes, monovinyl phthalide derivatives, divinyl phthalide derivatives, fluoran leuco dyes and so on.

worin die Reste

• Ri, R₂, R₃, R₄, Rs, und Rs gleich oder verschieden sind und jeweils ein Wasserstoffatom, einen Alkylrest mit 1-18 C-Atomen, einen Cycloalkylrest mit 3-7 C-Atomen, eine niedere Alkoxygruppe, halogenierte Alkylgruppe mit 1-18 C-Atomen, Phenylgruppe, substituierte Phenylgruppe oder Benzylgruppe bedeuten;
• R₇, Rε und Rg gleich oder verschieden sind und jeweils ein Wasserstoffatom, ein Halogenatom, eine niedere Alkylgruppe oder niedere Alkoxygruppe bedeuten,
• X ein Kohlenstoffatom, Stickstoffatom oder Schwefelatom bedeutet, und wobei
• R₁ und R₂, oder R₃ und R₄ gegebenenfalls mit dem Stickstoffatom (der Aminogruppe) einen heterocyclischen Ring mit 4-6 Kohlenstoffatomen (der ein Sauerstoff-, Schwefel- oder ein zweites Stickstoffatom enthalten kann) bilden konnen.

Of the fluorene series leuco dyes, the near-infrared absorbing leuco dyes of the following formulas (11) or (III) are preferred.

where the residues

• Ri, R ₂ , R ₃ , R ₄ , Rs, and Rs are the same or different and each have a hydrogen atom, an alkyl radical with 1-18 C atoms, a cycloalkyl radical with 3-7 C atoms, a lower alkoxy group, halogenated alkyl group with 1-18 C atoms, phenyl group, substituted phenyl group or benzyl group;
• R ₇ , Rε and Rg are the same or different and each represents a hydrogen atom, a halogen atom, a lower alkyl group or lower alkoxy group,
• X represents a carbon atom, nitrogen atom or sulfur atom, and wherein
• R ₁ and R ₂ , or R ₃ and R _{4 can} optionally form a heterocyclic ring with 4-6 carbon atoms (which may contain an oxygen, sulfur or a second nitrogen atom) with the nitrogen atom (the amino group).

Binders according to the invention are e.g. B. fully saponified polyvinyl alcohol, degree of polymerisation: 200-1900, partly saponified polyvinyl alcohol, carboxylated polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, other modified polyvinyl alcohols, hydroxyethyl cellulose, methyl cellulose, carbohydride-polyol ethylene-copolymeric, polyhydric copolymers, Cellulose derivatives such as ethyl cellulose and acetyl cellulose, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid ester, polyvinyl butyral, polystyrene, copolymers of the above compounds, polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin and coumarone resin. These high molecular weight binders can be used after being dissolved in a solvent such as water, alcohol, ketone, ester, hydrocarbon, etc., or in water or Solvents have been emulsified or dispersed.

The type and amount of the electron acceptor, e.g. the metal salt of the higher fatty acid, the electron donor, e.g. the polyvalent phenol derivative, the fluorescent dye and / or pigment, the binder, the other additives, which are determined depending on the desired effect and suitability for recording purposes, are not particularly limited. In general, it is advantageous to use 1 to 6 parts by weight of the electron donor, 1 to 10 parts by weight of fluorescent dye and / or pigment, 2 to 15 parts by weight of filler and 0.5 to 4 parts by weight of binder to use 1 to 9 parts by weight of the electron acceptor.

The heat-sensitive material according to the invention is produced by applying the coating composition to a base material such as paper, synthetic paper, film, etc.

• Anorganische oder organische Füllstoffe, wie Siliziumdioxyd, Calciumcarbonat, Kaolin, gebrannter Kaolin, Diatomeenerde, Talk, Titaniumdioxid,, Aluminiumhydroxid usw.; Trennmittel wie Metallsalze von Fettsäuren; Gleitmittel wie Wachse; UV-Absorptionsmittel der Bezophenon- und Triazolreihe; wasserfest machende Mittel wie Glyoxal usw., Dispergiermittel; Antischaummittel und so weiter.

The above-mentioned electron acceptor, the above electron donor, optionally the basic, colorless chromogenic dye are ground to a particle size of several microns or smaller by means of a milling device such as a ball mill, attritor, sand grinder, etc., or by means of a suitable emulsifying machine. Various additives are added to this. The additives that can be used according to the invention are e.g. B. the following:

• Inorganic or organic fillers such as silicon dioxide, calcium carbonate, kaolin, baked kaolin, diatomaceous earth, talc, titanium dioxide, aluminum hydroxide, etc .; Release agents such as metal salts of fatty acids; Lubricants such as waxes; UV absorbers of the bezophenone and triazole series; waterproofing agents such as glyoxal, etc., dispersants; Antifoam and so on.

The superior optical readability of the heat-sensitive recording sheet of the present invention in the near-red range may have the following cause. In the color formation by the heat-melting reaction between the metal double salt of higher fatty acid than the electron acceptor and the electron donor, e.g. B. the polyvalent phenol derivative, etc., the color development area results in a visible in the visible and in the near ultra-red range (wavelength range 700 to 1000 nm) readable recording image.

The superior local detectability when irradiated with UV light can be attributed to the fact that the heat-sensitive color development layer contains a fluorescent dye and / or pigment, the maximum fluorescence of which is UV radiation in the visible wavelength range of 450-700 nm. For example, a package pasted with a bar code is inserted by a conveyor into a dark room where it is irradiated with UV radiation of a certain wavelength. The fluorescence of the fluorescent dye and / or pigment in the bar code slip is detected by a fluorescence detector, and the position of the bar code slip on the package can be easily observed and tracked.

(Examples)

The invention is illustrated by the following examples.

As an abbreviation for parts by weight, "parts" is used.

(Synthesis example)

1000 parts of thioflavin as fluorescent dye (dye designation C), 350 parts of ethyl ether, 70 parts of styrene monomer, 2 parts of 2,2'-azobis (2,4-dimethylvaleronitrile), 5 parts of dialkylsulfosuccinic acid ester salt were kneaded by means of the ball mill for 2 hours, one time to obtain uniform dispersion. The resulting dispersion was kept in the thermostat at 65 ° C and polymerized for 1 hour. The dispersion was then heated up to 90 ° C. and the remaining monomer was removed. In this way, fine particles of styrene resin colored with thioflavine were obtained.

The fluorescent dyes used in the following examples are those in which the surface has been coated with high molecular weight polymers according to the above synthesis example.

(Example 1 (Test No. 1-4))

Lösung B (Elektronendonatordispersion)

Lösung C (Fluoreszenzfarbstoffdispersion)

Solution A (electron acceptor dispersion):

Solution B (electron donor dispersion)

Solution C (fluorescent dye dispersion)

The solutions of the above compositions were individually milled to a particle size of 3 microns in an attritor.

Kaolinton (5%ige wäßrige Dispersion) 12,0 TeileThe solutions were then mixed together in the following ratio to obtain a heat sensitive coating composition.

Kaolin clay (5% aqueous dispersion) 12.0 parts

The above coating composition was applied in a coating amount of 6.0 g / m ² on a base paper with a weight of 50 g / m ² , dried and supercalendered to adjust a smoothness of 200-600 seconds. A heat sensitive recording sheet was obtained.

Example 2 (Test No. 5-12)

A heat-sensitive recording sheet was obtained in the same manner as in Example 1, except that Solution D was used instead of Solution C.

Solution D

Fluoreszenzfarbstoff (40%ige Dispersion von Sinloihi Co. hergestellt, Sinloihi Color Base SP-X Series, X= 13 bis 17, 27, 37 und 47) 12,5 Teile (Vergleichsbeispiele (Test-Nr. 13-16)) Lösung A (Elektronenakzeptordispersion)

Fluorescent dye (40% dispersion manufactured by Sinloihi Co., Sinloihi Color Base SP-X Series, X = 13 to 17, 27, 37 and 47) 12.5 parts (Comparative Examples (Test No. 13-16)) Solution A (Electron acceptor dispersion)

Solution B

The solutions of the above compositions were individually milled in a attritor to a particle size of 3 microns.

Man erhielt in der gleichen Weise wie im Beispiel 1 ein wärmeempfindliches Aufzeichnungsblatt.The solutions were then mixed together in the following ratio to obtain a heat sensitive coating mass.

A heat-sensitive recording sheet was obtained in the same manner as in Example 1.

The quality of the recording sheets obtained in the examples and comparative examples was checked and the results are summarized in Tables 1 and 2.

Remarks

• (1) Image density: A heat-sensitive recording sheet is applied at an applied voltage of 18.03 V and a pulse width of 3.2 milliseconds using a facsimile machine (from TOSHIBA CORPORATION) with a record. The image density is determined using a Macbeth density meter (RD-514, using the amber filter; the measurements described below are carried out under the same conditions).
• (2) Reflectance for Ultra Red Light: The reflectance of the recording mentioned in Note (1) above is measured with a spectrometer at a wavelength of 800 nm.
• (3) Fluorescent light: In the dark room, a UV beam (of the long main wavelength of 365 nm) is directed onto a heat-sensitive recording material. The resulting fluorescent light is observed with the eyes.

(Effects of the Invention)

• (1) überlegene lokale optische Erfaßbarkeit bei Bestrahlung mit UV-Licht.
• (2) Gute optische Lesbarkeit im nahen ultraroten Bereich.

The recording material according to the invention has the following advantages:

• (1) superior local optical detectability when irradiated with UV light.
• (2) Good optical legibility in the near ultra-red range.

Claims (9)

1. Heat sensitive recording material with a heat sensitive colour developing layer on a carrier which contains an electron acceptor and an electron donor which react with one another with chelate formation and customary additives as desired, characterised in that the heat sensitive colour developing layer contains a fluorescence dyestuff and/or a fluorescence pigment, the fluorescence maximum of which, on irradiation with UV-light, lies in the visible wavelength range of 450-700 nm.

2. Heat sensitive recording material according to Claim 1, characterised in that the electron acceptor is a metal double salt of a higher fatty acid with 16 to 35 carbon atoms.

3. Heat sensitive recording material according to Claim 2, characterised in that the metal double salt of a higher fatty acid contains at least two metals from the group iron, zinc, calcium, magnesium, aluminium, barium, lead, manganese, tin, nickel, cobalt, copper, silver and mercury.

4. Heat sensitive recording material according to one of the preceding Claims, characterised in that the electron donor is at least one substance selected from polyvalent aromatic hydroxy compounds, diphenyl carbazide, diphenyl carbazone, hexamethylenetetramine, spirobenzopyran and 1-formyl-4-phenyl semicarbazide.

5. Heat sensitive recording material according to one of the preceding Claims, characterised in that the electron donor is at least one polyvalent aromatic hydroxy compound of the general formula (I)

in which R is an alkyl group with 18 to 35 carbon atoms,

(wherein R₁ represents an alkyl group with 18 to 35 carbon atoms); n represents a whole number from 2 to 3; and "-X-" stands for
-CH₂-, -C0₂-, -CO-, -O-, -CONH-,

(wherein R' represents an alkyl group with 5 to 30 carbon atoms), -S0₂-, -S0₃- or -S0₂NH-.

6. Heat sensitive recording material according to one of the preceding Claims, characterised in that the fluorescence dyestuff per se or in a pigment is at least one dyestuff selected from the series of anthraquinone, indigo, azine, xanthene, acridine, diphenylmethane, triphenylmethane, thiazine and thiazol fluorescence dyestuffs.

7. Heat sensitive recording material according to one of the preceding Claims, characterised in that the colour developing layer contains 1 to 6 parts by weight electron donor, 1 to 10 parts by weight fluorescence dyestuff and/or pigment, 2 to 15 parts by weight filler and 0.5 to 4 parts by weight binding agent taken on 1 to 9 parts by weight of the electron acceptor.

8. Heat sensitive recording material according to one of the preceding Claims, characterised in that the colour developing layer lies on a base material.

9. Heat sensitive recording material according to one of the preceding Claims, characterised in that the base material is a paper, synthetic paper or a film.