DE10254070A1

DE10254070A1 - Heat sensitive recording material and its use

Info

Publication number: DE10254070A1
Application number: DE2002154070
Authority: DE
Inventors: Takao Masuda; Gerhard Dr. Stork; Wolfgang Dr. Wagner
Original assignee: Mitsubishi HiTech Paper Flensburg GmbH
Current assignee: Mitsubishi HiTech Paper Flensburg GmbH
Priority date: 2002-11-19
Filing date: 2002-11-19
Publication date: 2004-06-09
Also published as: ES2295669T3; AT375258T; EP1565321A1; DE50308369D1; WO2004045862A1; EP1565321B1; AU2003288116A1

Abstract

A heat-sensitive recording material having a substrate layer and, applied thereon in this order, a pigmented intermediate layer, a heat-sensitive recording layer containing color formers and color acceptors and a protective layer is proposed, each applied layer completely covering the layer to which it is applied, the intermediate layer contains a pigment mixture of inorganic and organic pigment, the organic pigment has a particle size (D¶50¶) in a range from 0.75 mum to less than 1.5 mum and a glass transition temperature greater than or equal to 100 ° C. and the protective layer has one Contains polyvinyl alcohol and a crosslinking aid. DOLLAR A The new heat-sensitive recording material has a high resolution of the heat-induced print image and excellent printability in offset printing.

Description

The invention relates to a heat sensitive Recording material with a substrate layer on which in this Order a pigmented intermediate layer, a color former and heat-sensitive containing color acceptors Recording layer and a protective layer are applied as well the use of such a heat sensitive Recording material.
A heat-sensitive recording material of the type mentioned is for example from the DE-A-101 08 982 known. The well-known recording material had the task of guaranteeing excellent stamp validity as a ticket; there was also a demand for high environmental resistance of the known recording material against water, fats, oils and plasticizers and for good printability, inter alia in offset printing. The above-mentioned recording material was convincing in most applications, but the market requirements, particularly with regard to printability, continued to increase, which is why there was a need not only for minor modifications but for fundamental innovations.
From the EP-A-0 341 715 a heat-sensitive recording material is known with one or more intermediate layers which are arranged between the recording layer and the substrate. An intermediate layer contains particles of an oil-absorbing inorganic pigment. In another intermediate layer, fine hollow particles of a synthetic resin made of styrene, acrylic or a copolymer of styrene and acrylic are optionally arranged together with other inorganic pigment particles. A particle size range (average diameter) of 0.75 μm to 1.5 μm for the organic hollow particles is disclosed.
As suitable inorganic pigments, the intermediate layer containing the organic hollow particles are added can, are among others Calcium and magnesium carbonate, silicon oxide, titanium oxide, kaolin and called calcined kaolin. Lessons on a protective layer and the glass transition temperature the organic hollow particles are not apparent from this document.
In the EP-A-1 243 437 discloses a heat-sensitive recording material in which a dye precursor dispersion is used, the dye precursor particles of which should not be outside a range from 0.1 μm to 0.3 μm, a maximum of 1% being permitted for particles of 0.07 μm or less is. A layer arranged between the recording layer and the substrate should preferably contain hollow particles of a thermoplastic resin, with a particle size of 2 μm to 10 μm being particularly preferred. Production difficulties are expected below a particle size of 2 μm. As an example, coating compositions are proposed for the intermediate layer, which contain either calcined kaolin or organic hollow particles. This document contains no information regarding a certain glass transition temperature.
From the EP-A-1 174 278 the substrate of a recording paper for heat-sensitive or heat transfer recording with a security feature arranged in the substrate is known. An intermediate layer provided on the substrate contains an inorganic pigment with an average particle size of 0.1 μm to 5 μm or organic particles with an average particle size of 0.5 μm to 30 μm. A coating composition for an intermediate layer is disclosed by way of example, which in addition to styrene particles also contains calcined kaolin and calcium carbonate. The document contains no information on the glass transition temperature of the organic particles.
Finally, that affects US 4,929,590 a heat-sensitive recording material with an intermediate layer which contains spherical plastic particles with an average particle size of 0.2 μm to 1.5 μm and a glass transition temperature between 40 ° C. and 90 ° C. In a comparative example, plastic particles with a glass transition temperature of 110 ° C. and an average particle size of 3 μm are also disclosed, but which have a low recording quality.
The difficulties that the inventors of the new recording material faced are

- On the one hand, to want to provide a heat-sensitive recording material that has a high resolution of the heat-induced print image in order to be able to display fine 1-point barcodes. The protective layer of the recording material which is necessary for environmental resistance should therefore be applied - if possible only in a small thickness, and - be as smooth as possible. Both points help to keep the distance between the heat-sensitive recording layer and the thermal head producing the printed image small. As the distance between the recording layer and the thermal head increases, the resolution becomes worse, the resolution being approximately inversely proportional to the square of the distance. At the same time, however, the protective layer must not lose its environmental resistance and should not be deposited or glued to the thermal head, which is why the protective layer should have a rather sealing character.
- On the other hand, the new heat-sensitive recording material should have excellent printability in offset printing, including in particular a sharp-edged, brilliant Printed image and a slight tendency to be deposited on the printing blanket is to be understood. While in known cases such a printing blanket can often be cleaned after 3,000 to 6,000 running meters when printing known heat-sensitive recording materials, such a cleaning process with the recording material according to the invention is often only necessary after 24,000 meters. According to popular opinion, an open-pore, voluminous printing base is advantageous, which is in contrast to a smooth, rather sealing surface.

The inventors recognized numerous Try that with a restriction of considerations the task described above does not apply to the protective layer alone solve. Rather, one comes between substrate and heat sensitive Intermediate layer to be positioned is of great importance to.
Finally, the solution provides a heat-sensitive recording material with a substrate layer, on which at least the following layers are applied in this order:

- a pigmented intermediate layer,
A heat-sensitive recording layer containing color formers and color acceptors and
- a protective layer,

- each layer applied completely covers the layer to which it is applied,
The intermediate layer contains a pigment mixture of an inorganic and an organic pigment,
The organic pigment has a particle size (D ₅₀ ) in a range from 0.75 μm to less than 1.5 μm,
- The organic pigment has a glass transition temperature greater than or equal to 100 ° C and
- The protective layer contains at least one polyvinyl alcohol and a crosslinking aid.

It is vital that all of the above features can be combined with each other since only the task is convincing solely through the combination of features solved can be.
The one in the heat sensitive recording layer the color-forming reaction of the color formers with the color acceptors triggering Thermal head causes the wax-like components to melt in the recording layer. To avoid sticking this wax-like components as a melt on the thermal head is on the one hand a sealing, completely covering the recording layer Protective layer provided. On the other hand, is between the substrate layer and the recording layer completely covers the substrate layer Intermediate layer positioned, the pigment mixture from a contains inorganic and an organic pigment.
The inorganic pigments of this intermediate layer absorb the melt. It is particularly advantageous if the pigment of the intermediate layer of at least 80 ^cm3 / 100 g, and more preferably of 100 cm, having an oil absorption ^3/100 g, determined according to the Japanese standard JIS K 5,101th Calcined kaolin, calcium carbonate, silicon dioxide and kaolin have proven particularly useful due to their high absorption capacity. Mixtures of several different types of inorganic pigments are also conceivable.
The inclusion of organic pigments in the intermediate layer is justified by the fact that such organic Pigments to a special degree a high heat reflectivity of the intermediate layer beneficial are. That in an intermediate layer of a heat-sensitive recording material arranged organic, so-called hollow body pigments have in their Internal air, which is a good thermal insulator. The so as a heat reflection layer optimized intermediate layer increased the response of the recording layer to heat what the resolving power of the thermosensitive Recording material increased significantly and also the printing speed can set up in the thermal printer.
The quantitative ratio between organic and inorganic pigment is a compromise of the two types of pigment effects brought about, which is particularly advantageously solved when the pigment mixture 20 to 50% by weight from organic and from 80 to 50 wt .-% of inorganic pigment consists. It is very particularly preferred if the pigment mixture 25 to 40% by weight of organic and 75 to 60% by weight of inorganic Pigment exists.
The organic pigments have one Wall made of thermoplastic resin, which preferably (meth) acrylonitrile copolymer, Polyvinyl chloride, polyvinylidene chloride, polystyrene, styrene acrylate, Polyacrylonitrile or polyacrylic acid ester includes. Pigment mixtures made from different organic pigments are conceivable. A glass transition temperature bigger or equal to 100 ° C and prefers bigger or equal to 105 ° C was recognized as essential to the invention, because below these temperatures an increased Degree of yellowing was found.
The particle size, determined as the D ₅₀ value, of the organic pigments present in the intermediate layer are in a range from 0.75 μm to less than 1.5 μm, preferably in a range from 0.9 μm to 1.2 μm. Particle sizes below 0.75 μm are prohibited due to rheological processing difficulties. Particle sizes above 1.5 μm show too coarse-grained behavior and prevent a preferred leveling effect of the intermediate layer. For the inorganic pigments A particle size of less than 2 μm, determined as a D ₅₀ value, is particularly recommended. Pigments which have a particle size distribution of 34 to 40% by weight less than 1 μm and 57 to 63% by weight less than 2 μm have proven to be advantageous. Another suitable particle size distribution is obtained when 88% by weight are less than 1 μm. In experiments, it was found to be advantageous if the ratio of the particle size of the organic pigment to the particle size of the inorganic pigment was in a range from 1: 0.38 to 1: 1.5.
The intermediate layer further comprises selected a binder from the group comprising polyvinyl alcohol, styrene-butadiene latex, Strength, Carboxy-methyl-cellulose, Cellulose derivatives, styrene-butadiene latex being particularly preferred is. In the case of binder mixtures, the proportion of binder is: the intermediate layer is preferably 69 to 76% by weight of styrene-butadiene latex.
In addition, it should be noted that a between substrate layer and heat sensitive Recording layer positioned intermediate layer a positive one Contribute to the leveling of the substrate layer surface can, with which the mass of coating color necessarily to be applied for the heat-sensitive Recording layer reduced.
The formation of the intermediate layer with a mass per unit area in a range from 5 g / m ² to 20 g / m ² and even better between 7 g / m ² and 10 g / m ^{2 has a} particularly advantageous effect.
The heat-sensitive recording layer can in principle contain all known color formers as well as matching color acceptors, in particular organic color acceptors. Color formers are particularly preferably selected from the group of the fluoran compounds, and suitable organic color acceptors selected for this purpose are selected from the group comprising

- 2,2 bis (4-hydroxyphenyl) propane,
- 4 - [(4- (1-methylethoxy) phenyl) sulfonyl) phenol,
4,4'-dihydroxy-diphenyl sulfone,
- N- (p-toluenesulphonyl) - N '- (3-p-toluenesulphonyl-oxyphenyl) urea,
2,4'-dihydroxy-diphenyl sulfone,
- N- (2-hydroxyphenyl) -2 - [(4-hydroxyphenyl) thio) acetamide,

The heat-sensitive recording material according to the invention contains at least one polyvinyl alcohol and a crosslinking aid in its protective layer. It is preferred that the polyvinyl alcohol coexists with the protective layer Carboxyl or silanol groups is modified. Such a protective layer has a high affinity across from the one used in the offset printing process, preferably UV-crosslinking Printing ink, which helps decisively, the demand for a to meet improved printability within offset printing. It is still conceivable to mix different carboxyl groups or use silanol-modified polyvinyl alcohols.
As a networking aid in the Protective layers are particularly suitable for those that are selected from the group comprising: boric acid, polyamine, Epoxy resin, dialdehyde, formaldehyde oligomers, epiochlorohydrin resin, Dimethyl urea, melamine formaldehyde. Mixtures of different cross-linking aids are possible.
It is preferred if the ratio of the modified polyvinyl alcohol to the crosslinking aid 100 Parts by volume is 15 to 30 parts by volume.
Particularly good results have been achieved if the protective layer also contains an inorganic pigment contains. It is particularly recommended if the inorganic pigment selected is from the group comprising silicon dioxide, aluminum hydroxide, Calcium carbonate, kaolin or a mixture of the aforementioned inorganic Pigments.
It is preferred to apply the protective layer, which is to be formed as one layer for economic reasons, with a mass per unit area in a range from 1.5 g / m ² to 6 g / m ² and in particular between 1.8 g / m ² and 3 g / m ² . A smoothness of the protective layer in the range from 1000 Bekk-seconds (sec) to less than 3000 Bekk-sec has proven to be advantageous. Values from 1200 Bekk-sec to less than 2500 Bekk-sec are particularly suitable.
The gloss of the protective layer lies preferably in a range from 30 to 50, very particularly preferably at a value of 40 to 48, measured according to Tappi 450 or ISO 2813 at a reflection angle of 75 °.
Paper and especially a non-surface treated one Coating base paper preferred, without the invention on such Limited substrate layer is. Under a non-surface treated Coating base paper is not in a size press or coating device to understand treated coating base paper. The same applies to the invention Dimensions of foils for example made of polyolefin and papers coated with polyolefin possible as substrate layer, without such an execution exclusive Has character.
In a particular embodiment, the recording material according to the invention has a backside coating which is applied to the substrate layer side and which the layer sequence comprising at least an intermediate layer warms sensitive recording layer and protective layer side is opposite. Such a back coating is for example in the DE-A-197 48 258 proposed and then serves an improved printability on the back of the recording sheet in the offset and flexographic printing process and an improved blocking effect of the reverse side against plasticizers, oils and greases. For the basis weight of the backcoat to order quantities have proved advantageous in a range of 1 g / m ^z to 3 g / m ² and particularly between 1.5 g / m ² and 2.5 g / m ^2.
The invention claims the use to the same extent of the recording material according to the invention in all of its disclosed embodiments as a label.
The in the description and in the claims information on the area-related mass and% by weight (% by weight) each refer to the "atro" weight, i.e. absolutely dry parts by weight.
For the information given in the description and in the claims on the particle size of the organic and inorganic pigments and the color former, D ₅₀ measurements based on the principle of laser diffraction were used, measured with the HELOS device from Sympatec GmbH D-38678 Clausthal-Zellerfeld ,
The invention is based on the following For example closer explained become:
On a Fourdrinier paper machine, a paper web is produced as a substrate layer from a mixture of bleached and ground softwood sulphate pulp and eucalyptus pulp with a mass per unit area of 63 g / m ² with the addition of conventional admixtures in customary amounts. On-line within the paper machine, the substrate layer is provided on the front by means of a blade applicator with an intermediate layer of 9 g / m ² , which completely covers the substrate layer. The intermediate layer comprises a pigment mixture of 30% by weight (atro) organic pigment with a particle size (D ₅₀ ) of 1 μm and 70% by weight (atro) calcined kaolin with a particle size (D ₅₀ ) of 0.9 μm and an oil absorption of 110 cm ³ / 100g. The organic pigment has a glass transition value of 105 ° C. The intermediate layer further comprises a binder mixture of 75% by weight styrene-butadiene latex and 25% by weight starch.
Using a doctor blade applicator in a separate coating machine is on the intermediate layer a heat sensitive Recording layer applied with a fluoran color former and 4 - [(4- (1-methylethoxy) phenyl) sulfonyl) phenol as a color acceptor, both with a particle size of 0.9 μm.
In the same operation, after drying the recording layer using an air brush, a protective layer of 2 g / m ² completely covering the recording layer is applied with a silanol-modified polyvinyl alcohol and a mixture of an epichlorohydrin resin and a dialdehyde as crosslinking aid. The ratio of the silanol-modified polyvinyl alcohol to the mixture of the crosslinking aids is 100 parts by volume to 23 parts by volume. The protective layer further comprises aluminum hydroxide as a pigment.
The heat sensitive so produced Recording material has a smoothness of after calendering 1800 Bekk seconds and a gloss value of 40, measured according to the Tappi standard 450 or ISO 2813 at a reflection angle of 75 °.
The recording material according to the invention thus produced exhibits high environmental resistance and an outstanding one Offset printability.

Claims

Heat-sensitive recording material with a substrate layer, on which the following layers are applied in this order: - a pigmented intermediate layer, - a heat-sensitive recording layer containing color formers and color acceptors and - a protective layer, characterized by the combination of the following features - each applied layer covers the layer on which it is applied completely, - the intermediate layer contains a pigment mixture of inorganic and organic pigment, - the organic pigment has a particle size (D ₅₀ ) in a range from 0.75 μm to less than 1.5 μm, - the organic pigment has a glass transition temperature greater than or equal to 100 ° C and - the protective layer contains a polyvinyl alcohol and a crosslinking aid.
thermosensitive Recording material according to claim 1, characterized in that the organic pigment has a glass transition temperature greater than or equal to 105 ° C Has.
Heat-sensitive recording material according to one of claims 1 or 2, characterized in that the organic pigment of the intermediate layer has a particle size (D ₅₀ ) in a range from 0.9 μm to 1.2 μm.
A heat-sensitive recording material according to any one of claims 1 to 3, characterized in that the inorganic pigment of the intermediate layer g an oil absorption of at least 80 ^cm3 / 100 is determined according to the Japanese standard JIS K 5101, has.
Heat-sensitive recording material according to one of claims 1 to 4, characterized characterized in that the inorganic pigment of the intermediate layer has an oil absorption of at least 100 ^cm3 / 100 g, determined according to the Japanese standard JIS K 5,101th
thermosensitive Recording material according to one of claims 1 to 5, characterized in that that the inorganic pigment of the intermediate layer is selected one or more of the pigments listed below: calcined Kaolin, calcium carbonate, silicon dioxide and kaolin.
Heat-sensitive recording material according to one of claims 1 to 6, characterized in that the inorganic pigment of the intermediate layer has a particle size (D ₅₀ ) less than 2 microns.
thermosensitive Recording material according to one of claims 1 to 7, characterized in that that the relationship the particle size of the organic Pigments for the particle size of the inorganic Pigments is in a range from 1: 0.38 to 1: 1.5.
thermosensitive Recording material according to one of claims 1 to 8, characterized in that that the pigment mixture consists of 20 to 50% by weight of organic and consists of 80 to 50 wt .-% of inorganic pigment.
thermosensitive Recording material according to one of claims 1 to 9, characterized in that that the intermediate layer one or more of the binders listed below contains: polyvinyl alcohol, Styrene-butadiene latex, Strength, Carboxy-methyl cellulose, cellulose derivatives.
thermosensitive Recording material according to claim 10, characterized in that the binder consists of 69 to 76 wt .-% of styrene-butadiene latex.
thermosensitive Recording material according to one of claims 1 to 11, characterized in that that the polyvinyl alcohol of the protective layer with carboxyl or silanol groups is modified.
thermosensitive Recording material according to one of claims 1 to 12, characterized in that that the crosslinking aid of the protective layer is selected from the group comprising boric acid, Polyamine, epoxy resin, dialdehyde, formaldehyde oligomers, epiochlorohydrin resin, Dimethyl urea, melamine formaldehyde.
thermosensitive Recording material according to one of claims 12 to 13, characterized in that that the relationship of the modified polyvinyl alcohol to the crosslinking aid 100 volumes to 15 to 30 volumes.
thermosensitive Recording material according to one of claims 1 to 14, characterized in that that the protective layer contains an inorganic pigment.
thermosensitive Recording material according to claim 15, characterized in that the inorganic pigment of the protective layer is selected from the group comprising silicon dioxide, aluminum hydroxide, calcium carbonate, Kaolin.
thermosensitive Recording material according to one of claims 1 to 16, characterized in that that the substrate layer is made of paper.
thermosensitive Recording material according to claim 17, characterized in that the paper is a non-surface treated Coating base paper is.
thermosensitive Recording material according to one of claims 1 to 18, characterized in that that the protective layer is smooth in a range of equal to or greater than 1000 Bekk seconds to less than 3000 Bekk seconds.
thermosensitive Recording material according to one of claims 1 to 19, characterized in that that the protective layer has a gloss value in a range from 30 to 50 measured according to Tappi 450 or ISO 2813 (reflection angle 75 °).
Use of a heat-sensitive recording material according to one of the claims 1 to 20 as a ticket.