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EP3765303B1 - Thermoresponsive paper coatings based on cellulose derivatives - Google Patents

Thermoresponsive paper coatings based on cellulose derivatives Download PDF

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Publication number
EP3765303B1
EP3765303B1 EP19722558.4A EP19722558A EP3765303B1 EP 3765303 B1 EP3765303 B1 EP 3765303B1 EP 19722558 A EP19722558 A EP 19722558A EP 3765303 B1 EP3765303 B1 EP 3765303B1
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EP
European Patent Office
Prior art keywords
heat
recording material
sensitive recording
material according
thermoresponsive
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP19722558.4A
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German (de)
French (fr)
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EP3765303A1 (en
Inventor
Maximilian Nau
Markus BIESALSKI
Michael Horn
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Technische Universitaet Darmstadt
Koehler Paper SE
Original Assignee
Technische Universitaet Darmstadt
Koehler Paper SE
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Publication of EP3765303A1 publication Critical patent/EP3765303A1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
    • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
    • B41M5/36—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using a polymeric layer, which may be particulate and which is deformed or structurally changed with modification of its' properties, e.g. of its' optical hydrophobic-hydrophilic, solubility or permeability properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
    • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
    • B41M5/36—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using a polymeric layer, which may be particulate and which is deformed or structurally changed with modification of its' properties, e.g. of its' optical hydrophobic-hydrophilic, solubility or permeability properties
    • B41M5/366—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using a polymeric layer, which may be particulate and which is deformed or structurally changed with modification of its' properties, e.g. of its' optical hydrophobic-hydrophilic, solubility or permeability properties using materials comprising a polymeric matrix containing a polymeric particulate material, e.g. hydrophobic heat coalescing particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M2205/00—Printing methods or features related to printing methods; Location or type of the layers
    • B41M2205/04—Direct thermal recording [DTR]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
    • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
    • B41M5/36—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using a polymeric layer, which may be particulate and which is deformed or structurally changed with modification of its' properties, e.g. of its' optical hydrophobic-hydrophilic, solubility or permeability properties
    • B41M5/361—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using a polymeric layer, which may be particulate and which is deformed or structurally changed with modification of its' properties, e.g. of its' optical hydrophobic-hydrophilic, solubility or permeability properties using a polymeric matrix with inorganic particles forming an image by orientation or agglomeration

Definitions

  • the present invention relates to a heat-sensitive recording material, a process for its production and a heat-sensitive recording material obtainable by this process.
  • Heat-sensitive recording materials comprising a carrier substrate which is black or colored on at least one side, in particular paper, synthetic paper and/or a plastic film and which is coated with an opaque material on this black or colored side, are known.
  • a carrier substrate which is black or colored on at least one side, in particular paper, synthetic paper and/or a plastic film and which is coated with an opaque material on this black or colored side.
  • the black or colored carrier substrate appears white on the outside.
  • the opaque coating loses opacity at these points and becomes transparent, so that the black or colored carrier substrate becomes visible.
  • EP 2 345 678 A1 a heat-sensitive recording material comprising a coating of nanoparticles, a shell and a core each having different polymers with different glass transition temperatures.
  • the U.S. 8,054,323 B2 discloses a heat-sensitive recording material comprising a coating containing an opaque polymer, for example a styrene/acrylate copolymer.
  • the EP 2 678 167 B1 discloses a heat-sensitive recording material comprising a thermoresponsive layer with particles of a thermoplastic polymer based on ethylenically unsaturated monomers, these particles having an outer diameter of 200 nm to 1500 nm.
  • the heat-sensitive recording materials known from the prior art have the disadvantage that the structure of the heat-sensitive layer is often quite complex. For example, nanoparticles that are made up of different layers of different polymers have to be provided, which are complex to produce and therefore often expensive. In addition, many of the polymers used are questionable in terms of their sustainability and toxicity. Many heat-sensitive recording materials known from the prior art are also in need of improvement with regard to the sharpness and contrast of the printed image. In addition, many known heat-sensitive recording materials have deficiencies in storage stability.
  • the object of the present invention is to eliminate the aforementioned disadvantages of the prior art.
  • the object of the present invention is to provide a heat-sensitive recording material that comprises a thermoresponsive layer that is made up of sustainable, ie as natural and/or renewable raw materials as possible, and has as little toxicity as possible or no toxicity at all.
  • the material of the thermoresponsive layer should be able to be provided as simply and easily as possible.
  • the heat-sensitive recording material should enable a sharp and high-contrast printed image and, moreover, should not be impaired even after prolonged storage.
  • the heat-sensitive recording material should be able to be produced by a process that is as simple and inexpensive as possible.
  • the melting point of the substances used in the thermoresponsive layer should preferably be above 90°C, so that the process temperatures of up to 90°C that are common during production do not have a negative effect on the product.
  • a heat-sensitive recording material which has a carrier substrate which is black or colored on at least one side and a thermoresponsive layer on the at least one black or colored side of the carrier substrate, wherein the thermoresponsive layer comprises nanoparticles of at least one cellulose ester.
  • thermoresponsive layer comprises nanoparticles of modified cellulose, i.e. at least one cellulose ester, since the cellulose ester is non-toxic and therefore essentially harmless to health.
  • this cellulose ester is available relatively inexpensively in large quantities.
  • the cellulose ester also has high opacity and a favorable melting point and glass transition temperature for thermal printing applications.
  • a heat-sensitive recording material comprising a thermoresponsive layer comprising nanoparticles of at least one cellulose ester can also be produced relatively easily and inexpensively. In addition, it has a high storage stability and an excellent print image.
  • the cellulose ester has a relatively high melting point, so that the process temperatures of up to 90° C. that are customary in the production of the heat-sensitive recording material can be tolerated.
  • the carrier substrate of the heat-sensitive recording material according to the invention comprises at least one black or colored side.
  • the term "colored page" means that the page is a color other than white or black.
  • the heat-sensitive recording material includes at least one side that is not white.
  • Embodiments are also possible in which the at least one black or colored side has several different colors, also in combination with the color black.
  • thermoresponsive layer comprising nanoparticles of at least one cellulose ester, is applied to this at least one side of the carrier substrate that is not white, but rather colored or black.
  • thermoresponsive layer comprising the nanoparticles of at least one cellulose ester is preferably substantially white.
  • Nanoparticles of cellulose esters and production processes therefor are generally known.
  • the alcohol groups of the cellulose are usually esterified first.
  • cellulose esterifications are preferably carried out using the respective acid anhydrides and a catalyst, typically sulfuric acid.
  • a catalyst typically sulfuric acid.
  • the cellulose is initially suspended in the reaction mixture, but as the acetylation progresses, the cellulose becomes more and more soluble in the glacial acetic acid, which causes the reaction mixture to be homogenized.
  • the viscosity of the solution varies parallel to the optical change and provides information about the degree of substitution (DS).
  • DS degree of substitution
  • cellulose esters are cellulose acetate propionate, cellulose butyrate and cellulose acetate butyrate, which are prepared analogously to the process described above, preferably using the respective acid anhydrides.
  • the cellulose ester is typically dissolved in a solvent, eg THF, acetone, etc., so that the concentration of the cellulose ester is around 1 to 10 mg/mL.
  • a solvent eg THF, acetone, etc.
  • This solution is then precipitated in a non-solvent, such as a mixture of isopropanol and distilled water.
  • the non-solvent can be added to the solution of the cellulose ester.
  • the resulting suspension is typically stirred for 12 to 24 hours to enable solvent exchange between the still swollen particles and the precipitant.
  • the particles settled into the lower quarter of the precipitation mixture and about 4/5 of the solvent mixture are separated off.
  • the resulting suspension is centrifuged and the resulting particle sludge is flushed with water to then be incorporated into coating formulations.
  • the usual yields are between 70 and 80%.
  • the heat-sensitive recording material according to the invention is preferably characterized in that the nanoparticles of the at least one cellulose ester have number-average particle sizes of 50 to 400 nm, preferably 160-200 nm (+/- 40 nm), measured by means of dynamic light scattering (or “dynamic light scattering", DLS).
  • Dynamic light scattering is a method in which the scattered light from a laser is analyzed on a dissolved or suspended sample. It is often used with polymers and biopolymers or nanoparticles of these polymers and biopolymers to determine their average particle size.
  • the number-average particle size was determined in detail as follows: A "Nanophox" from the manufacturer Sympatec was used.
  • This particle size analyzer uses photon cross-correlation spectroscopy (a statistical analysis method based on DLS) to determine particle sizes and distributions.
  • the temperature was kept constant during the measurement with a thermostat, typically at 20 °C. Distilled water is usually used as the fluid medium.
  • a large number of scatter events are detected (typically set at around 300,000 per second over several minutes).
  • the measured values obtained in this way provide information about the Brownian molecular movement of the particles and their diffusion coefficients.
  • the particle diameter is calculated on the basis of this by using the Stokes-Einstein relationship.
  • thermoresponsive layer has a transparency, measured according to DIN 53147:1993-01, of less than 35%, preferably less than 30%, particularly preferably less than 25% and very particularly preferably less than 20%, in particular less than 15% or even less than 10%.
  • Transparency means the ability of matter to let electromagnetic waves through (transmission).
  • Opacity describes the opposite of transparency, i.e. lack of transparency or lack of permeability. Opacity is the reciprocal of transmission.
  • the low transparency preferred according to the invention has the advantage that the black or colored side of the carrier substrate is essentially completely covered and appears at least essentially white to the outside.
  • the heat-sensitive recording material according to the invention is preferably characterized in that the at least one cellulose ester comprises cellulose acetate, cellulose acetate propionate, cellulose butyrate and/or cellulose acetate butyrate, preferably cellulose acetate butyrate.
  • cellulose esters are particularly preferred because they have glass transition temperatures (Tg) and melting temperatures (Tm) which are particularly preferred for use in a heat-sensitive recording material.
  • nanoparticles of cellulose acetate butyrate are particularly preferred. These degrees of substitution (DS) are preferably 0.12 ⁇ 0.1 for acetyl groups and 2.62 ⁇ 0.13 for butyryl groups, the number-average molar mass (Mn) is preferably 30,000 g/mol and the Tm is approximately 141°C
  • the heat-sensitive recording material according to the invention is preferably characterized in that the at least one cellulose ester has a Tg of 45°C to 150°C and/or a Tm of 100°C to 185°C.
  • Tg and Tm are determined according to DIN 53765:1994-03 by means of differential scanning calorimetry (DDK or "differential scanning calorimetry” (DSC)).
  • the heat-sensitive recording material according to the invention is characterized in that the at least one cellulose ester is contained in the thermoresponsive layer in an amount of 35 to 70% by weight, based on the total weight of the thermoresponsive layer.
  • thermosensitive recording material is preferably characterized in that the thermoresponsive layer further comprises polyvinyl alcohol (PVA).
  • PVA polyvinyl alcohol
  • the polyvinyl alcohol is preferably contained in the thermoresponsive layer in an amount of 5 to 50% by weight based on the total weight of the thermoresponsive layer.
  • Polyvinyl alcohol reduces sample viscosity and results in a more homogeneous coating.
  • polyvinyl alcohol it is also preferred that a small amount, preferably 0.01 to 1% by weight, particularly preferably 0.05 to 0.5% by weight and very particularly preferably about 0 1% by weight of polyvinyl alcohol is added. This has the advantage that the polyvinyl alcohol can already attach to the nanoparticles of cellulose esters as a protective colloid during the precipitation process.
  • thermoresponsive layer also comprises at least one kaolin, alkali metal and/or alkaline earth metal salt.
  • the alkali metal and/or alkaline earth metal salt preferably comprises NaCl, CaCO 3 and/or CaCl 2 .
  • the at least one kaolin, alkali metal and/or alkaline earth metal salt is preferably contained in the thermoresponsive layer in an amount of 0.05 to 10% by weight, based on the total weight of the thermoresponsive layer.
  • the addition of salt is advantageous because the salt can compensate for the surface charges.
  • thermosensitive recording material is preferably characterized in that the thermoresponsive layer further comprises at least one high-molecular polyelectrolyte.
  • the at least one high molecular weight polyelectrolyte preferably comprises a poly(vinylamine-vinylformamide) copolymer, such as is available, for example, under the trade names Lupamin 9010 or Lupamin 4500 from BASF, and/or a cationic polyacrylamide, such as is available, for example, under the trade name Percol 47 from BASF is available.
  • a poly(vinylamine-vinylformamide) copolymer such as is available, for example, under the trade names Lupamin 9010 or Lupamin 4500 from BASF
  • a cationic polyacrylamide such as is available, for example, under the trade name Percol 47 from BASF is available.
  • the at least one high molecular weight polyelectrolyte is preferably present in the thermoresponsive layer in an amount of 5 to 35% by weight based on the total weight of the thermoresponsive layer.
  • thermoresponsive layer comprises at least one kaolin, alkali metal and/or alkaline earth metal salt as defined above and at least one high molecular weight polyelectrolyte as defined above.
  • the heat-sensitive recording material according to the invention is also preferably characterized in that the carrier substrate comprises paper, synthetic paper and/or a plastic film.
  • thermosensitive recording material is preferably characterized in that the thermoresponsive layer comprises at least one silicone oil defoamer, preferably in an amount of 0.05 to 5% by weight based on the total weight of the thermoresponsive layer.
  • thermoresponsive layer contains at least one binder, preferably an acrylate binder, which is available, for example, under the trade name Acronal S 360 D from BASF, preferably in an amount of 0.05 to 5% by weight, based on the total weight of the thermoresponsive layer.
  • binder preferably an acrylate binder, which is available, for example, under the trade name Acronal S 360 D from BASF, preferably in an amount of 0.05 to 5% by weight, based on the total weight of the thermoresponsive layer.
  • thermosensitive recording material of the present invention is preferably characterized in that the pH of the thermoresponsive layer is 6-9.
  • the pH is preferably adjusted by adding HCl or NaOH.
  • the heat-sensitive recording material according to the invention is preferably characterized in that the heat-sensitive color-forming layer contains customary additives, such as stabilizers, release agents, pigments and/or brighteners.
  • the heat-sensitive recording material according to the invention is preferably characterized in that the thermoresponsive layer comprises polyvinyl alcohol, preferably in an amount of 30 to 60 parts by weight, and 100 parts by weight of nanoparticles of cellulose acetate butyrate, these nanoparticles of cellulose acetate butyrate being obtainable by dissolving cellulose acetate butyrate in an organic solvent, preferably in tetrahydrofuran, and precipitating the nanoparticles of cellulose acetate butyrate by adding this solution of cellulose acetate butyrate to a non-solvent, preferably to a mixture of water and isopropanol, preferably in a mixing ratio of 1 to 4, most preferably 1 .2 to 2.8, the non-solvent preferably additionally containing polyvinyl alcohol, preferably in an amount of 0.01 to 1% by weight, particularly preferably about 0.1% by weight, based on the total amount of the non-solvent , includes.
  • the non-solvent preferably additionally containing polyvinyl
  • this heat-sensitive recording material further contains 2 to 10 parts by weight of a binder, 10 to 20 parts by weight of a viscosity regulator and 1 to 5 parts by weight of NaOH.
  • the coating weight of the (dry) heat-sensitive layer is preferably about 1 to about 10 g/m 2 , preferably about 3 to about 6 g/m 2 .
  • the nanoparticles of at least one cellulose ester can be produced by known methods.
  • the method is preferably characterized in that the cellulose ester comprises cellulose acetate, cellulose acetate propionate and/or cellulose acetate butyrate, preferably cellulose acetate butyrate.
  • the method is further preferably characterized in that the non-solvent is water or a mixture of water and at least one organic solvent, preferably in a mixing ratio of 1 to 4, particularly preferably 1.2 to 2.8, the at least one organic solvent is preferably isopropanol thereof.
  • the method is also preferably characterized in that the non-solvent additionally contains polyvinyl alcohol, preferably in an amount of 0.01 to 1% by weight, preferably about 0.1% by weight, based on the total amount of the non-solvent includes.
  • the nanoparticles of at least one cellulose ester obtained in this way usually have an average particle diameter of about 160 to 200 nm with a standard deviation of about 40 nm (measured using DLS, as described above).
  • the heat-sensitive recording material of the present invention can be produced by the usual methods.
  • the heat-sensitive recording material according to the invention is preferably produced by a method in which an aqueous suspension containing the starting materials of the thermoresponsive layer and having a solids content of from about 15 to about 60% by weight is applied to at least one black or colored side of the carrier substrate, and the aqueous suspension is applied and dried by coating processes which produce a contour coating (curtain coater) or a leveling coating (blade coater, squeegee).
  • This method is particularly advantageous from an economic point of view.
  • the heat-sensitive recording material according to the invention by means of a process in which the aqueous application suspension is applied using the curtain coating method, preferably at an operating speed of the coater of at least about 400 m/min.
  • the so-called curtain coating process is known to those skilled in the art and is characterized by the following criteria: In the curtain coating process, a freely falling curtain of a coating dispersion is formed. The coating dispersion, in the form of a thin film (curtain), is "poured" onto a substrate by free fall to apply the coating dispersion to the substrate.
  • the DE 10196052 T1 discloses the use of the curtain coating process in the production of information recording materials, including heat-sensitive recording materials.
  • Adjusting the operating speed of the coater to at least about 400 m/min has both economic and technical advantages. More preferably, the line speed is at least about 750 m/min, more preferably at least about 1000 m/min, and most preferably at least about 1500 m/min. It was particularly surprising that even at the latter speed, the heat-sensitive recording material obtained is in no way impaired and that the operation is optimal even at this high speed.
  • the aqueous, deaerated application suspension has a viscosity of about 150 to about 800 mPas (Brookfield, 100 rpm, 20° C.). If the value falls below about 150 mPas or the value of about 800 mPas is exceeded, this leads to to poor runnability of the coating material on the coating unit.
  • the viscosity of the aqueous, deaerated application suspension is particularly preferably about 200 to about 500 mPas.
  • the surface tension of the aqueous application suspension can be increased to 25 to 60 mN/m, preferably to about 35 to about 50 mN/m (measured according to the static ring method according to Du Noüy, DIN 53914, 1997-07), to be set.
  • the dried thermoresponsive layer is subjected to a smoothing operation. It is advantageous here to adjust the Bekk smoothness, measured according to DIN 53107 (2000), to about 100 to about 1200 seconds, preferably to about 300 to about 700 seconds. Bekk smoothness of 100 to 300 seconds are measured according to method A of DIN 53107 (2000) and Bekk smoothness of more than 300 according to method B of DIN 53107 (2000).
  • the present invention also relates to a heat-sensitive recording material obtainable by the above process.
  • figure 1 shows optical micrographs of a printed heat-sensitive recording material according to the invention.
  • figure 2 shows an illustration of the opacities. These are the gray values of a horizontal line. The laser power was 70%.
  • the gray value is a value between 0 and 255, where 255 represents an all-black pixel and 0 represents an all-white pixel.
  • An aqueous application suspension was prepared by mixing 100 parts of cellulose acetate butyrate nanoparticles with an average particle diameter of about 170 nm ( ⁇ 40 nm) in the presence of 0.1% polyvinyl alcohol, THF as solvent and a water/isopropanol mixture in a ratio of 1, 2 to 2.8 precipitated as non-solvent as described above, mixed with 40 parts polyvinyl alcohol, 5 parts Styronal D 517 as binder, 15 parts Sterocoll as viscosity regulator and 3 parts 1M NaOH.
  • a ratio of 11.75% by weight solids/liquid was chosen for the coating formulation. This value was chosen because the particles are in the form of ⁇ 15% by weight suspension after manufacture.
  • the solids content of the additives and coatings were determined using a dry balance.
  • the polyvinyl alcohol used is 84% saponified polyvinyl acetate (Mn 100,000 g/mol).
  • the sample vials were filled with 100 mg nanoparticles of cellulose acetate butyrate, the respective additives were added and the solids content (FS) was adjusted to 11.75% by weight with distilled water.
  • the formulation is then homogenized using a vortex shaker and an ultrasonic bath.
  • the coating was applied using an automatic film applicator from BYK Additives & Instruments to a Hostaphan film type RNK 50.0 2600 that had been precoated for line application.
  • the feed rate selected was 100 mm min -1 and the doctor blade gap 90 ⁇ m.
  • Heat-sensitive recording materials were prepared with the coating amount of the thermoresponsive layer being 2.5, 4 and 6 g/m 2 .
  • the coated substrates were cut in half with scissors. Half of a substrate was heated in a drying cabinet at 70 °C for 30 min to simulate simple drying conditions. Both samples were then "printed" with a 30-watt CO 2 laser (parameters in Table 1).
  • a light microscope in transmitted light mode was used to analyze the prints.
  • the paper coatings of formulation 1 showed promising results, which are shown in figure 1 are shown.
  • the patterns are macroscopically very homogeneous. With a laser power of 70%, sharp line profiles could already be seen. Increasing the laser power to 80% reduces the distance between the individual lines.
  • figure 2 serves to illustrate the opacities. These are the gray values of a horizontal line. The relative opacity of the PVA coatings reached a maximum of 95%. The thermal treatment showed no negative influence.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Heat Sensitive Colour Forming Recording (AREA)
  • Paper (AREA)
  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Thermal Transfer Or Thermal Recording In General (AREA)

Description

Die vorliegende Erfindung betrifft ein wärmeempfindliches Aufzeichnungsmaterial, ein Verfahren zu dessen Herstellung und ein wärmeempfindliches Aufzeichnungsmaterial erhältlich nach diesem Verfahren.The present invention relates to a heat-sensitive recording material, a process for its production and a heat-sensitive recording material obtainable by this process.

Wärmeempfindliche Aufzeichnungsmaterialien, umfassend ein auf mindestens einer Seite schwarzes oder farbiges Trägersubstrat, insbesondere Papier, synthetisches Papier und/oder eine Kunststofffolie, das auf dieser schwarzen oder farbigen Seite mit einem opaken Material beschichtet ist, sind bekannt. Dadurch erscheint das schwarze oder farbige Trägersubstrat nach außen hin weiß. Bei Einwirkung von Wärme, beispielsweise lokaler Wärmeeinwirkung durch einen Thermodrucker, verliert die opake Beschichtung an diesen Stellen an Opazität und wird transparent, sodass das schwarze oder farbige Trägersubstrat sichtbar wird.Heat-sensitive recording materials comprising a carrier substrate which is black or colored on at least one side, in particular paper, synthetic paper and/or a plastic film and which is coated with an opaque material on this black or colored side, are known. As a result, the black or colored carrier substrate appears white on the outside. When exposed to heat, for example local exposure to heat from a thermal printer, the opaque coating loses opacity at these points and becomes transparent, so that the black or colored carrier substrate becomes visible.

So offenbart die EP 2 345 678 A1 ein wärmeempfindliches Aufzeichnungsmaterial, umfassend eine Beschichtung aus Nanopartikeln, die eine Hülle und einen Kern aus jeweils verschiedenen Polymeren mit unterschiedlichen Glasübergangstemperaturen aufweisen.So reveals the EP 2 345 678 A1 a heat-sensitive recording material comprising a coating of nanoparticles, a shell and a core each having different polymers with different glass transition temperatures.

Die US 8 054 323 B2 offenbart ein wärmeempfindliches Aufzeichnungsmaterial, umfassend eine Beschichtung, die ein opakes Polymer, beispielsweise ein Styrol-/ Acrylat-Copolymer, enthält.The U.S. 8,054,323 B2 discloses a heat-sensitive recording material comprising a coating containing an opaque polymer, for example a styrene/acrylate copolymer.

Die EP 2 678 167 B1 offenbart ein wärmeempfindliches Aufzeichnungsmaterial, welches eine thermoresponsive Schicht mit Partikeln aus einem thermoplastischen Polymer umfasst, welches auf ethylenisch ungesättigten Monomeren basiert, wobei diese Partikel einen äusseren Durchmesser von 200 nm bis 1500 nm aufweisen.The EP 2 678 167 B1 discloses a heat-sensitive recording material comprising a thermoresponsive layer with particles of a thermoplastic polymer based on ethylenically unsaturated monomers, these particles having an outer diameter of 200 nm to 1500 nm.

Die aus dem Stand der Technik bekannten wärmeempfindlichen Aufzeichnungsmaterialien haben den Nachteil, dass der Aufbau der wärmeempfindlichen Schicht oft recht komplex ist. So müssen Nanopartikel, die aus verschiedenen Schichten verschiedener Polymere aufgebaut sind, bereitgestellt werden, die komplex herzustellen und deshalb oft teuer sind. Zudem sind viele der verwendeten Polymere im Hinblick auf deren Nachhaltigkeit und Toxizität bedenklich. Viele aus dem Stand der Technik bekannten wärmeempfindlichen Aufzeichnungsmaterialien sind zudem im Hinblick auf die Schärfe und den Kontrast des Druckbildes verbesserungswürdig. Außerdem weisen viele bekannte wärmeempfindliche Aufzeichnungsmaterialien Unzulänglichkeiten bei der Lagerungsbeständigkeit auf.The heat-sensitive recording materials known from the prior art have the disadvantage that the structure of the heat-sensitive layer is often quite complex. For example, nanoparticles that are made up of different layers of different polymers have to be provided, which are complex to produce and therefore often expensive. In addition, many of the polymers used are questionable in terms of their sustainability and toxicity. Many heat-sensitive recording materials known from the prior art are also in need of improvement with regard to the sharpness and contrast of the printed image. In addition, many known heat-sensitive recording materials have deficiencies in storage stability.

Die Aufgabe der vorliegenden Erfindung besteht darin, vorstehend genannte Nachteile des Standes der Technik zu beheben. Insbesondere besteht die Aufgabe der vorliegenden Erfindung darin, ein wärmeempfindliches Aufzeichnungsmaterial bereitzustellen, dass eine thermoresponsive Schicht umfasst, die zum einen aus nachhaltigen, d.h. möglichst natürlichen und/oder nachwachsenden Rohstoffen, aufgebaut ist, und zum anderen eine möglichst geringe bis gar keine Toxizität aufweist. Zudem soll das Material der thermoresponsiven Schicht möglichst einfach und leicht bereitgestellt werden können. Das wärmeempfindliche Aufzeichnungsmaterial soll zudem ein scharfes und kontrastreiches Druckbild ermöglichen und außerdem auch bei längerer Lagerungszeit nicht beeinträchtigt werden. Schließlich soll das wärmeempfindliche Aufzeichnungsmaterial durch ein möglichst einfaches und kostengünstiges Verfahren herstellbar sein. Insbesondere soll der Schmelzpunkt der in der thermoresponsiven Schicht verwendete Substanzen vorzugsweise über 90°C liegen, sodass die bei der Herstellung übliche Prozesstemperaturen von bis zu 90°C keinen negativen Einfluss auf das Produkt nehmen. Obige Aufgabe wird gemäß den Merkmalen des Anspruchs 1 gelöst, d.h. mit einem wärmeempfindlichem Aufzeichnungsmaterial, das ein auf mindestens einer Seite schwarzes oder farbiges Trägersubstrat und eine thermoresponsive Schicht auf der mindestens einen schwarzen oder farbigen Seite des Trägersubstrats umfasst, wobei die thermoresponsive Schicht Nanopartikel mindestens eines Celluloseesters umfasst.The object of the present invention is to eliminate the aforementioned disadvantages of the prior art. In particular, the object of the present invention is to provide a heat-sensitive recording material that comprises a thermoresponsive layer that is made up of sustainable, ie as natural and/or renewable raw materials as possible, and has as little toxicity as possible or no toxicity at all. In addition, the material of the thermoresponsive layer should be able to be provided as simply and easily as possible. In addition, the heat-sensitive recording material should enable a sharp and high-contrast printed image and, moreover, should not be impaired even after prolonged storage. Finally, the heat-sensitive recording material should be able to be produced by a process that is as simple and inexpensive as possible. In particular, the melting point of the substances used in the thermoresponsive layer should preferably be above 90°C, so that the process temperatures of up to 90°C that are common during production do not have a negative effect on the product. The above object is achieved according to the features of claim 1, ie with a heat-sensitive recording material which has a carrier substrate which is black or colored on at least one side and a thermoresponsive layer on the at least one black or colored side of the carrier substrate, wherein the thermoresponsive layer comprises nanoparticles of at least one cellulose ester.

Ein solches wärmeempfindliches Aufzeichnungsmaterial hat den Vorteil, dass die thermoresponsive Schicht Nanopartikel von modifizierter Cellulose, d.h. von mindestens einem Celluloseester, umfasst, da der Celluloseester nicht toxisch und daher gesundheitlich im Wesentlichen unbedenklich ist. Zudem ist dieser Celluloseester relativ günstig in großen Mengen erhältlich. Der Celluloseester weist auch eine hohe Opazität und für Thermodruckanwendungen einen günstigen Schmelzpunkt und eine günstige Glasübergangstemperatur auf. Auch ist ein wärmeempfindliches Aufzeichnungsmaterial, umfassend eine thermoresponsive Schicht, die Nanopartikel mindestens eines Celluloseesters umfasst, relativ einfach und kostengünstig herzustellen. Zudem weist es eine hohe Lagerstabilität und ein ausgezeichnetes Druckbild auf. Schließlich besitzt der Celluloseester einen relativ hohen Schmelzpunkt, sodass die bei der Herstellung des wärmeempfindlichen Aufzeichnungsmaterials übliche Prozesstemperaturen von bis zu 90°C toleriert werden können.Such a heat-sensitive recording material has the advantage that the thermoresponsive layer comprises nanoparticles of modified cellulose, i.e. at least one cellulose ester, since the cellulose ester is non-toxic and therefore essentially harmless to health. In addition, this cellulose ester is available relatively inexpensively in large quantities. The cellulose ester also has high opacity and a favorable melting point and glass transition temperature for thermal printing applications. A heat-sensitive recording material comprising a thermoresponsive layer comprising nanoparticles of at least one cellulose ester can also be produced relatively easily and inexpensively. In addition, it has a high storage stability and an excellent print image. Finally, the cellulose ester has a relatively high melting point, so that the process temperatures of up to 90° C. that are customary in the production of the heat-sensitive recording material can be tolerated.

Das Trägersubstrat des erfindungsgemäßen wärmeempfindlichen Aufzeichnungsmaterials umfasst mindestens eine schwarze oder farbige Seite. Unter dem Begriff "farbige Seite" wird verstanden, das die Seite eine andere Farbe als Weiß oder Schwarz aufweist. Mit anderen Worten umfasst das wärmeempfindliche Aufzeichnungsmaterial mindestens eine Seite, die nicht weiß ist. Es sind auch Ausführungsformen möglich, bei denen die mindestens eine schwarze oder farbige Seite mehrere unterschiedliche Farben auch in Kombination mit der Farbe Schwarz aufweist.The carrier substrate of the heat-sensitive recording material according to the invention comprises at least one black or colored side. The term "colored page" means that the page is a color other than white or black. In other words, the heat-sensitive recording material includes at least one side that is not white. Embodiments are also possible in which the at least one black or colored side has several different colors, also in combination with the color black.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist ferner dadurch gekennzeichnet, dass auf dieser mindestens einen nicht weißen, sondern farbigen oder schwarzen Seite, des Trägersubstrats die thermoresponsive Schicht, umfassend Nanopartikel mindestens eines Celluloseesters, aufgebracht ist.The heat-sensitive recording material according to the invention is further characterized in that the thermoresponsive layer, comprising nanoparticles of at least one cellulose ester, is applied to this at least one side of the carrier substrate that is not white, but rather colored or black.

Diese thermoresponsive Schicht, umfassend die Nanopartikel mindestens eines Celluloseesters, ist vorzugsweise im Wesentlichen weiß.This thermoresponsive layer comprising the nanoparticles of at least one cellulose ester is preferably substantially white.

Nanopartikel von Celluloseestern und Herstellungsverfahren dafür sind im Allgemeinen bekannt.Nanoparticles of cellulose esters and production processes therefor are generally known.

Üblicherweise werden zunächst die Alkoholgruppen der Cellulose verestert. Technisch werden Veresterungen von Cellulose vorzugsweise unter Verwendung der jeweiligen Säureanhydride und einem Katalysator, typischerweise Schwefelsäure, durchgeführt. Bei der Synthese von beispielsweise Celluloseacetat liegt die Cellulose zunächst suspendiert im Reaktionsgemisch vor, mit Fortschreiten der Acetylierung wird die Cellulose allerdings immer besser im Eisessig löslich, was die Homogenisierung der Reaktionsmischung hervorruft. Parallel zu der optischen Veränderung variiert die Viskosität der Lösung und gibt Aufschluss über den Substitutionsgrad (DS). Zu Beginn führt die zunehmende Lösung der Polymerketten zu einem Anstieg der Viskosität, welche durch Abbaureaktionen an dem Celluloserückgrat und damit der Verminderung der Kettenlänge später wieder abnimmt. Somit können der DS und die Kettenlänge durch Beobachtung der Viskosität online kontrolliert werden.The alcohol groups of the cellulose are usually esterified first. Industrially, cellulose esterifications are preferably carried out using the respective acid anhydrides and a catalyst, typically sulfuric acid. In the synthesis of cellulose acetate, for example, the cellulose is initially suspended in the reaction mixture, but as the acetylation progresses, the cellulose becomes more and more soluble in the glacial acetic acid, which causes the reaction mixture to be homogenized. The viscosity of the solution varies parallel to the optical change and provides information about the degree of substitution (DS). At the beginning, the increasing dissolution of the polymer chains leads to an increase in viscosity, which later decreases again due to degradation reactions on the cellulose backbone and thus the reduction in chain length. Thus, the DS and the chain length can be checked online by observing the viscosity.

Weitere bekannte Celluloseester sind Celluloseacetatpropionat, Cellulosebutyrat und Celluloseacetatbutyrat, die analog zu dem oben beschriebenen Verfahren, vorzugsweise unter Einsatz der jeweiligen Säureanydride hergestellt werden.Other known cellulose esters are cellulose acetate propionate, cellulose butyrate and cellulose acetate butyrate, which are prepared analogously to the process described above, preferably using the respective acid anhydrides.

Zur Herstellung der Nanopartikel aus den Celluloseestern werden diese in einem Nicht-Lösungsmittel präzipitiert. Dabei wird vorzugsweise wie folgt vorgegangen.To produce the nanoparticles from the cellulose esters, these are precipitated in a non-solvent. The procedure is preferably as follows.

Zur Herstellung von Nanopartikeln wird typischerweise der Celluloseester in einem Lösungsmittel, z.B. THF, Aceton etc. gelöst, sodass die Konzentration des Celluloseesters etwa 1 bis 10 mg/mL beträgt. Diese Lösung wird anschließend in einem Nicht-Lösungsmittel, z.B. einem Gemisch Isopropanol und destilliertem Wasser, gefällt. Dabei kann entweder der gelöste Celluloseester zu dem Nicht-Lösungsmittel oder umgekehrt das Nicht-Lösungsmittel zu der Lösung des Celluloseesters gegeben werden. Die resultierende Suspension wird typischerweise 12 bis 24 Stunden gerührt, um einen Lösemittelaustausch zwischen den noch gequollenen Partikeln und dem Fällungsmittel zu ermöglich. Nach Ende der Reifung sedimentierten die Partikel in das untere Viertel der Fällungsmischung und etwa 4/5 des Lösemittelgemisches werden abgetrennt. Die resultierende Suspension wird zentrifugiert und der resultierende Partikelschlamm wird auf Wasser umgespült, um anschließend in Beschichtungsformulierungen eingebracht zu werden. Übliche die Ausbeuten liegen zwischen 70 und 80 %.To produce nanoparticles, the cellulose ester is typically dissolved in a solvent, eg THF, acetone, etc., so that the concentration of the cellulose ester is around 1 to 10 mg/mL. This solution is then precipitated in a non-solvent, such as a mixture of isopropanol and distilled water. Either the dissolved cellulose ester can be added to the non-solvent or, conversely, the non-solvent can be added to the solution of the cellulose ester. The resulting suspension is typically stirred for 12 to 24 hours to enable solvent exchange between the still swollen particles and the precipitant. After the end of the maturation, the particles settled into the lower quarter of the precipitation mixture and about 4/5 of the solvent mixture are separated off. The resulting suspension is centrifuged and the resulting particle sludge is flushed with water to then be incorporated into coating formulations. The usual yields are between 70 and 80%.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass die Nanopartikel des mindestens einen Celluloseesters zahlengemittelte Partikelgrößen von 50 bis 400 nm, bevorzugt von 160-200 nm (+/- 40 nm), gemessen mittels dynamischer Lichtstreuung (oder "dynamic light scattering", DLS) aufweisen. Bei der dynamischen Lichtstreuung (DLS) handelt es sich um ein Verfahren, bei der das Streulicht eines Lasers an einer gelösten bzw. suspendierten Probe analysiert wird. Sie wird häufig bei Polymeren und Biopolymeren bzw. Nanopartikeln dieser Polymeren und Biopolymeren angewandt, um deren mittlere Partikelgröße zu bestimmen. Die zahlengemittelte Partikelgröße wurde im Detail wie folgt bestimmt: Es wurde ein "Nanophox" vom Hersteller Sympatec verwendet. Dieser Partikelgrößenanalysator verwendet Photonenkreuzkorrelationsspektroskopie (ein statistisches Analyseverfahren, basierend auf DLS) zur Bestimmung von Partikelgrößen und -verteilungen. Die Temperatur während der Messung mit einem Thermostat konstant gehalten, typischerweise auf 20 °C. Als fluides Medium wird üblicherweise destilliertes Wasser verwendet. Bei diesem Verfahren wird eine große Anzahl an Streuereignissen detektiert (typischerweise eingestellt um 300.000 pro Sekunde über mehrere Minuten hinweg). Die so erhaltenen Messwerte geben Aufschluss über die brownsche Molekularbewegung der Partikel und ihren Diffusionskoeffizienten. Durch Anwendung der Stokes-Einstein-Beziehung wird auf Basis von diesem der Partikeldurchmesser berechnet.The heat-sensitive recording material according to the invention is preferably characterized in that the nanoparticles of the at least one cellulose ester have number-average particle sizes of 50 to 400 nm, preferably 160-200 nm (+/- 40 nm), measured by means of dynamic light scattering (or "dynamic light scattering", DLS). Dynamic light scattering (DLS) is a method in which the scattered light from a laser is analyzed on a dissolved or suspended sample. It is often used with polymers and biopolymers or nanoparticles of these polymers and biopolymers to determine their average particle size. The number-average particle size was determined in detail as follows: A "Nanophox" from the manufacturer Sympatec was used. This particle size analyzer uses photon cross-correlation spectroscopy (a statistical analysis method based on DLS) to determine particle sizes and distributions. The temperature was kept constant during the measurement with a thermostat, typically at 20 °C. Distilled water is usually used as the fluid medium. In this method, a large number of scatter events are detected (typically set at around 300,000 per second over several minutes). The measured values obtained in this way provide information about the Brownian molecular movement of the particles and their diffusion coefficients. The particle diameter is calculated on the basis of this by using the Stokes-Einstein relationship.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass die thermoresponsive Schicht eine Transparenz, gemessen nach DIN 53147:1993-01, von weniger als 35%, bevorzugt von weniger als 30%, besonders bevorzugt von weniger als 25% und ganz besonders bevorzugt von weniger als 20%, insbesondere von weniger als 15% oder sogar von weniger als 10% aufweist.The heat-sensitive recording material according to the invention is preferably characterized in that the thermoresponsive layer has a transparency, measured according to DIN 53147:1993-01, of less than 35%, preferably less than 30%, particularly preferably less than 25% and very particularly preferably less than 20%, in particular less than 15% or even less than 10%.

Unter Transparenz wird die Fähigkeit von Materie, elektromagnetische Wellen hindurchzulassen (Transmission) verstanden.Transparency means the ability of matter to let electromagnetic waves through (transmission).

Opazität bezeichnet das Gegenteil von Transparenz, also mangelnde Durchsichtigkeit bzw. mangelnde Durchlässigkeit. Die Opazität ist der Kehrwert der Transmission.Opacity describes the opposite of transparency, i.e. lack of transparency or lack of permeability. Opacity is the reciprocal of transmission.

Die erfindungsgemäß bevorzugte niedrige Transparenz hat den Vorteil, dass die schwarze oder farbige Seite des Trägersubstrats im Wesentlichen vollständig abgedeckt ist und nach außen mindestens im Wesentlichen weiß erscheint.The low transparency preferred according to the invention has the advantage that the black or colored side of the carrier substrate is essentially completely covered and appears at least essentially white to the outside.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass der mindestens eine Celluloseester Celluloseacetat, Celluloseacetatpropionat, Cellulosebutyrat und/oder Celluloseacetatbutyrat, vorzugsweise Celluloseacetatbutyrat, umfasst.The heat-sensitive recording material according to the invention is preferably characterized in that the at least one cellulose ester comprises cellulose acetate, cellulose acetate propionate, cellulose butyrate and/or cellulose acetate butyrate, preferably cellulose acetate butyrate.

Diese Celluloseester sind besonders bevorzugt, da sie Glasübergangstemperaturen (Tg) und Schmelztemperaturen (Tm) aufweisen, die für die Anwendung in einem wärmeempfindlichen Aufzeichnungsmaterial besonders bevorzugt sind.These cellulose esters are particularly preferred because they have glass transition temperatures (Tg) and melting temperatures (Tm) which are particularly preferred for use in a heat-sensitive recording material.

Besonders bevorzugt ist der Einsatz von Nanopartikeln von Celluloseacetatbutyrat. Vorzugsweise weisen diese Substitutionsgrade (DS) von 0,12±0,1 für Acetyl- und 2,62±0,13 für Butyryl-Gruppen auf, die zahlenmittlere Molmasse (Mn) liegt vorzugsweise bei 30.000 g/mol und die Tm bei etwa 141 °C.The use of nanoparticles of cellulose acetate butyrate is particularly preferred. These degrees of substitution (DS) are preferably 0.12±0.1 for acetyl groups and 2.62±0.13 for butyryl groups, the number-average molar mass (Mn) is preferably 30,000 g/mol and the Tm is approximately 141°C

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass der mindestens eine Celluloseester eine Tg von 45°C bis 150°C und/oder eine Tm von 100°C bis 185°C aufweist.The heat-sensitive recording material according to the invention is preferably characterized in that the at least one cellulose ester has a Tg of 45°C to 150°C and/or a Tm of 100°C to 185°C.

Die Werte für die Tg und die Tm werden gemäß DIN 53765:1994-03 mittels Dynamische Differenzkalorimetrie (DDK oder auch "differential scanning calorimetry" (DSC)) bestimmt.The values for the Tg and the Tm are determined according to DIN 53765:1994-03 by means of differential scanning calorimetry (DDK or "differential scanning calorimetry" (DSC)).

In einer weiteren bevorzugten Ausführungsform ist das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial dadurch gekennzeichnet, dass der mindestens eine Celluloseester in einer Menge von 35 bis 70 Gew.-%, bezogen auf das Gesamtgewicht der die thermoresponsiven Schicht, in der thermoresponsiven Schicht enthalten ist.In a further preferred embodiment, the heat-sensitive recording material according to the invention is characterized in that the at least one cellulose ester is contained in the thermoresponsive layer in an amount of 35 to 70% by weight, based on the total weight of the thermoresponsive layer.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass die thermoresponsiven Schicht außerdem Polyvinylalkohol (PVA) umfasst.The thermosensitive recording material according to the present invention is preferably characterized in that the thermoresponsive layer further comprises polyvinyl alcohol (PVA).

Der Polyvinylalkohol ist vorzugsweise in einer Menge von 5 bis 50 Gew.-%, bezogen auf das Gesamtgewicht der die thermoresponsiven Schicht, in der thermoresponsiven Schicht enthalten.The polyvinyl alcohol is preferably contained in the thermoresponsive layer in an amount of 5 to 50% by weight based on the total weight of the thermoresponsive layer.

Polyvinylalkohol setzt die Probenviskosität herab und führt zu einer homogeneren Beschichtung.Polyvinyl alcohol reduces sample viscosity and results in a more homogeneous coating.

Es ist ferner bevorzugt, dass bereits dem Fällungsmittel bei der Herstellung der Nanopartikel von Celluloseestern eine kleine Menge, vorzugsweise 0,01 bis 1 Gew.-%, besonders bevorzugt 0,05 bis 0,5 Gew.-% und ganz besonders bevorzugt etwa 0,1 Gew.-% an Polyvinylalkohol zugesetzt wird. Dies hat den Vorteil, dass sich der Polyvinylalkohol bereits im Fällungsprozess als Schutzkolloid an die Nanopartikel von Celluloseestern anlagern kann.It is also preferred that a small amount, preferably 0.01 to 1% by weight, particularly preferably 0.05 to 0.5% by weight and very particularly preferably about 0 1% by weight of polyvinyl alcohol is added. This has the advantage that the polyvinyl alcohol can already attach to the nanoparticles of cellulose esters as a protective colloid during the precipitation process.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass die thermoresponsive Schicht außerdem mindestens ein Kaolin, Alkali- und/oder Erdalkalisalz umfasst.The heat-sensitive recording material according to the invention is preferably characterized in that the thermoresponsive layer also comprises at least one kaolin, alkali metal and/or alkaline earth metal salt.

Vorzugsweise umfasst das Alkali- und/oder Erdalkalisalz NaCl, CaCO3 und/oder CaCl2.The alkali metal and/or alkaline earth metal salt preferably comprises NaCl, CaCO 3 and/or CaCl 2 .

Das mindestens eine Kaolin, Alkali- und/oder Erdalkalisalz ist vorzugsweise in einer Menge von 0,05 bis 10 Gew.-%, bezogen auf das Gesamtgewicht der die thermoresponsiven Schicht, in der thermoresponsiven Schicht enthalten.The at least one kaolin, alkali metal and/or alkaline earth metal salt is preferably contained in the thermoresponsive layer in an amount of 0.05 to 10% by weight, based on the total weight of the thermoresponsive layer.

Die Salzzugabe ist von Vorteil, da das Salz die Oberflächenladungen kompensieren kann.The addition of salt is advantageous because the salt can compensate for the surface charges.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass die thermoresponsive Schicht außerdem mindestens einen hochmolekularen Polyelektrolyten umfasst.The thermosensitive recording material according to the present invention is preferably characterized in that the thermoresponsive layer further comprises at least one high-molecular polyelectrolyte.

Der mindestens eine hochmolekulare Polyelektrolyt umfasst vorzugsweise ein Poly(vinylamin-vinylformamid)copolymer, wie es beispielsweise unter den Handelsnamen Lupamin 9010 bzw. Lupamin 4500 von BASF erhältlich ist, und/oder ein kationisches Polyacrylamid, wie es beispielsweise unter dem Handelsnamen Percol 47 von BASF erhältlich ist.The at least one high molecular weight polyelectrolyte preferably comprises a poly(vinylamine-vinylformamide) copolymer, such as is available, for example, under the trade names Lupamin 9010 or Lupamin 4500 from BASF, and/or a cationic polyacrylamide, such as is available, for example, under the trade name Percol 47 from BASF is available.

Der mindestens eine hochmolekulare Polyelektrolyt liegt vorzugsweise in einer Menge von 5 bis 35 Gew.-%, bezogen auf das Gesamtgewicht der thermoresponsiven Schicht, in der thermoresponsiven Schicht vor.The at least one high molecular weight polyelectrolyte is preferably present in the thermoresponsive layer in an amount of 5 to 35% by weight based on the total weight of the thermoresponsive layer.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass die thermoresponsive Schicht mindesten ein Kaolin, Alkali- und/oder Erdalkalisalz wie oben definiert und mindestens einen hochmolekularen Polyelektrolyten wie oben definiert umfasst.The heat-sensitive recording material according to the invention is preferably characterized in that the thermoresponsive layer comprises at least one kaolin, alkali metal and/or alkaline earth metal salt as defined above and at least one high molecular weight polyelectrolyte as defined above.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist ferner vorzugsweise dadurch gekennzeichnet, dass das Trägersubstrat Papier, synthetisches Papier und/oder eine Kunststofffolie umfasst.The heat-sensitive recording material according to the invention is also preferably characterized in that the carrier substrate comprises paper, synthetic paper and/or a plastic film.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass die thermoresponsive Schicht mindestens einen Silikonölentschäumer, vorzugsweise in einer Menge von 0,05 bis 5 Gew.-%, bezogen auf das Gesamtgewicht der thermoresponsiven Schicht, umfasst.The thermosensitive recording material according to the invention is preferably characterized in that the thermoresponsive layer comprises at least one silicone oil defoamer, preferably in an amount of 0.05 to 5% by weight based on the total weight of the thermoresponsive layer.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass die thermoresponsive Schicht mindestens einen Binder, vorzugsweise einen Acrylatbinder, der beispielsweise unter dem Handelsnamen Acronal S 360 D von BASF erhältlich ist, vorzugsweise in einer Menge von 0,05 bis 5 Gew.-%, bezogen auf das Gesamtgewicht der thermoresponsiven Schicht, umfasst.The heat-sensitive recording material according to the invention is preferably characterized in that the thermoresponsive layer contains at least one binder, preferably an acrylate binder, which is available, for example, under the trade name Acronal S 360 D from BASF, preferably in an amount of 0.05 to 5% by weight, based on the total weight of the thermoresponsive layer.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass der pH-Wert der thermoresponsiven Schicht 6 bis 9 beträgt. Der pH wird vorzugsweise durch Zugabe von HCl bzw. NaOH eingestellt.The thermosensitive recording material of the present invention is preferably characterized in that the pH of the thermoresponsive layer is 6-9. The pH is preferably adjusted by adding HCl or NaOH.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass die wärmeempfindliche farbbildende Schicht übliche Additive, wie beispielsweise Stabilisatoren, Trennmittel, Pigmente und/ oder Aufheller, enthält.The heat-sensitive recording material according to the invention is preferably characterized in that the heat-sensitive color-forming layer contains customary additives, such as stabilizers, release agents, pigments and/or brighteners.

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial ist vorzugsweise dadurch gekennzeichnet, dass die thermoresponsive Schicht Polyvinylalkohol, vorzugsweise in einer Menge von 30 bis 60 Gew.-Teilen, und 100 Gew.-Teile Nanopartikel von Celluloseacetatbutyrat umfasst, wobei diese Nanopartikel von Celluloseacetatbutyrat erhältlich sind durch Lösen von Celluloseacetatbutyrat in einem organischen Lösungsmittel, vorzugsweise in Tetrahydrofuran, und Ausfällen der Nanopartikel von Celluloseacetatbutyrat durch Zugabe dieser Lösung von Celluloseacetatbutyrat zu einem Nicht-Lösungsmittel, vorzugsweise zu einer Mischung aus Wasser und Isopropanol, bevorzugt in einem Mischungsverhältnis von 1 zu 4, ganz besonders bevorzugt von 1,2 zu 2,8, wobei das Nicht-Lösungsmittel vorzugsweise zusätzlich Polyvinylalkohol, vorzugsweise in einer Menge von 0,01 bis 1 Gew.-%, besonders bevorzugt etwa 0,1 Gew.-%, bezogen auf die Gesamtmenge des Nicht-Lösungsmittels, umfasst.The heat-sensitive recording material according to the invention is preferably characterized in that the thermoresponsive layer comprises polyvinyl alcohol, preferably in an amount of 30 to 60 parts by weight, and 100 parts by weight of nanoparticles of cellulose acetate butyrate, these nanoparticles of cellulose acetate butyrate being obtainable by dissolving cellulose acetate butyrate in an organic solvent, preferably in tetrahydrofuran, and precipitating the nanoparticles of cellulose acetate butyrate by adding this solution of cellulose acetate butyrate to a non-solvent, preferably to a mixture of water and isopropanol, preferably in a mixing ratio of 1 to 4, most preferably 1 .2 to 2.8, the non-solvent preferably additionally containing polyvinyl alcohol, preferably in an amount of 0.01 to 1% by weight, particularly preferably about 0.1% by weight, based on the total amount of the non-solvent , includes.

Vorzugsweise enthält dieses wärmeempfindliche Aufzeichnungsmaterial zudem 2 bis 10 Gew.-Teile eines Binders, 10 bis 20 Gew.-Teile eines Viskositätsreglers und 1 bis 5 Gew.-Teile NaOH.Preferably, this heat-sensitive recording material further contains 2 to 10 parts by weight of a binder, 10 to 20 parts by weight of a viscosity regulator and 1 to 5 parts by weight of NaOH.

Das Flächenauftragsgewicht der (trocknen) wärmeempfindlichen Schicht beträgt vorzugsweise etwa 1 bis etwa 10 g/m2, bevorzugt etwa 3 bis etwa 6 g/m2.The coating weight of the (dry) heat-sensitive layer is preferably about 1 to about 10 g/m 2 , preferably about 3 to about 6 g/m 2 .

Wie vorstehend ausgeführt, können die Nanopartikel mindestens eines Cellulose ester durch bekannt Verfahren hergestellt werden.As stated above, the nanoparticles of at least one cellulose ester can be produced by known methods.

Bevorzugt werden die Nanopartikel mindestens eines Celluloseesters durch ein Verfahren, umfassend die Schritte

  1. (a) Lösen eines Celluloseesters in einem organischen Lösungsmittel, vorzugsweise in Tetrahydrofuran, und
  2. (b) Ausfällen der Nanopartikeln mindestens eines Celluloseesters durch Zugabe der Lösung des Celluloseesters (a) zu einem Nicht-Lösungsmittel, hergestellt.
The nanoparticles of at least one cellulose ester are preferably produced by a method comprising the steps
  1. (a) dissolving a cellulose ester in an organic solvent, preferably tetrahydrofuran, and
  2. (b) precipitating the nanoparticles of at least one cellulose ester by adding the solution of the cellulose ester (a) to a non-solvent.

Das Verfahren ist bevorzugt dadurch gekennzeichnet, dass der Celluloseester Celluloseacetat, Celluloseacetatpropionat und/oder Celluloseacetatbutyrat, vorzugsweise Celluloseacetatbutyrat, umfasst.The method is preferably characterized in that the cellulose ester comprises cellulose acetate, cellulose acetate propionate and/or cellulose acetate butyrate, preferably cellulose acetate butyrate.

Das Verfahren ist ferner bevorzugt dadurch gekennzeichnet, dass das Nicht-Lösungsmittel Wasser oder ein Gemisch von Wasser und mindestens einem organischen Lösungsmittel, vorzugsweise in einem Mischungsverhältnis von 1 zu 4, besonders bevorzugt von 1,2 zu 2,8 ist, wobei das mindestens eine organische Lösungsmittel vorzugsweise Isopropanol davon ist.The method is further preferably characterized in that the non-solvent is water or a mixture of water and at least one organic solvent, preferably in a mixing ratio of 1 to 4, particularly preferably 1.2 to 2.8, the at least one organic solvent is preferably isopropanol thereof.

Das Verfahren ist außerdem bevorzugt dadurch gekennzeichnet, dass das Nicht-Lösungsmittel zusätzlich Polyvinylalkohol, vorzugsweise in einer Menge von 0,01 bis 1 Gew.-%, bevorzugt etwa 0,1 Gew.-%, bezogen auf die Gesamtmenge des Nicht-Lösungsmittels, umfasst.The method is also preferably characterized in that the non-solvent additionally contains polyvinyl alcohol, preferably in an amount of 0.01 to 1% by weight, preferably about 0.1% by weight, based on the total amount of the non-solvent includes.

Die so erhaltenen Nanopartikel mindestens eines Celluloseesters, insbesondere die Nanopartikel von Celluloseacetatbutyrat, weisen üblicherweise einen mittleren Partikeldurchmesser von etwa 160 bis 200 nm bei einer Standardabweichung von etwa 40 nm auf (gemessen mit DLS, wie oben beschrieben).The nanoparticles of at least one cellulose ester obtained in this way, in particular the nanoparticles of cellulose acetate butyrate, usually have an average particle diameter of about 160 to 200 nm with a standard deviation of about 40 nm (measured using DLS, as described above).

Das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial kann nach üblichen Verfahren hergestellt werden. Vorzugsweise wird das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial durch ein Verfahren hergestellt, wobei auf der mindestens einer schwarzen oder farbigen Seite des Trägersubstrats eine die Ausgangsmaterialien der thermoresponsiven Schicht enthaltende wässrige Suspension, die einen Feststoffgehalt von etwa 15 bis etwa 60 Gew.-% aufweist, und wobei die wässrige Suspension nach Beschichtungsverfahren, welche eine Konturbeschichtung (Curtain Coater) oder eine nivellierende Beschichtung (Blade Coater, Rakel) erzeugen, aufgetragen und getrocknet wird.The heat-sensitive recording material of the present invention can be produced by the usual methods. The heat-sensitive recording material according to the invention is preferably produced by a method in which an aqueous suspension containing the starting materials of the thermoresponsive layer and having a solids content of from about 15 to about 60% by weight is applied to at least one black or colored side of the carrier substrate, and the aqueous suspension is applied and dried by coating processes which produce a contour coating (curtain coater) or a leveling coating (blade coater, squeegee).

Dieses Verfahren ist insbesondere unter wirtschaftlichen Gesichtspunkten vorteilhaft.This method is particularly advantageous from an economic point of view.

Wird der Wert des Feststoffgehaltes von etwa 15 Gew.-% unterschritten, dann verschlechtert sich die Wirtschaftlichkeit, da eine große Menge Wasser aus der Beschichtung durch schonende Trocknung in kurzer Zeit entfernt werden muss, was sich nachteilig auf die Streichgeschwindingkeit auswirkt. Wird auf der anderen Seite der Wert von 60 Gew.-% überschritten, dann führt dies lediglich zu einem erhöhten technischen Aufwand, um die Stabilität des Streichfarben-Vorhangs während des Beschichtungsprozesses zu gewährleisten.If the value of the solids content of about 15 wt .-% falls below, then the economy deteriorates because a large amount of water from the Coating must be removed by gentle drying in a short time, which has a negative effect on the coating speed. On the other hand, if the value of 60% by weight is exceeded, then this only leads to increased technical effort to ensure the stability of the coating color curtain during the coating process.

Wie vorstehend erwähnt, ist es von Vorteil das erfindungsgemäße wärmeempfindliche Aufzeichnungsmaterial mittels eines Verfahrens herzustellen, bei dem die wässrige Auftragsuspension mit dem Curtain-Coating-Beschichtungsverfahren vorzugsweise bei einer Betriebsgeschwindigkeit der Streichanlage von mindestens etwa 400 m/min aufgetragen wird. Das sogenannte Curtain-Coating-Verfahren ist dem Fachmann bekannt und zeichnet sich durch folgende Kriterien aus:
Beim Curtain-Coating-Beschichtungsverfahren (Vorhangbeschichtungsverfahren) wird ein frei fallender Vorhang einer Beschichtungsdispersion gebildet. Durch freien Fall wird die in Form eines dünnen Filmes (Vorhangs) vorliegende Beschichtungsdispersion auf ein Substrat "gegossen", um die Beschichtungsdispersion auf das Substrat aufzubringen. Die DE 10196052 T1 offenbart den Einsatz des Curtain-Coating-Beschichtungsverfahrens bei der Herstellung von Informationsaufzeichnungsmaterialien u.a. auch von wärmeempfindlichen Aufzeichnungsmaterialien.As mentioned above, it is advantageous to produce the heat-sensitive recording material according to the invention by means of a process in which the aqueous application suspension is applied using the curtain coating method, preferably at an operating speed of the coater of at least about 400 m/min. The so-called curtain coating process is known to those skilled in the art and is characterized by the following criteria:
In the curtain coating process, a freely falling curtain of a coating dispersion is formed. The coating dispersion, in the form of a thin film (curtain), is "poured" onto a substrate by free fall to apply the coating dispersion to the substrate. The DE 10196052 T1 discloses the use of the curtain coating process in the production of information recording materials, including heat-sensitive recording materials.

Die Einstellung der Betriebsgeschwindigkeit der Streichanlage auf mindestens etwa 400 m/min hat sowohl betriebswirtschaftliche als auch technische Vorteile. Besonders bevorzugt beträgt die Betriebsgeschwindigkeit mindestens etwa 750 m/min, ganz besonders bevorzugt mindestens etwa 1000 m/min und ganz besonders bevorzugt mindestens etwa 1500 m/min. Es war insbesondere überraschend, dass selbst bei letztgenannter Geschwindigkeit das erhaltene wärmeempfindliche Aufzeichnungsmaterial in keiner Weise beeinträchtigt ist und dass die Betriebsdurchführung selbst bei dieser hohen Geschwindigkeit optimal abläuft.Adjusting the operating speed of the coater to at least about 400 m/min has both economic and technical advantages. More preferably, the line speed is at least about 750 m/min, more preferably at least about 1000 m/min, and most preferably at least about 1500 m/min. It was particularly surprising that even at the latter speed, the heat-sensitive recording material obtained is in no way impaired and that the operation is optimal even at this high speed.

In einer bevorzugten Ausführungsform des erfindungsgemäßen Verfahrens weist die wässrige entlüftete Auftragssuspension eine Viskosität von etwa 150 bis etwa 800 mPas (Brookfield, 100 U/min, 20 °C) auf. Wird der Wert von etwa 150 mPas unterschritten bzw. der Wert von etwa 800 mPas überschritten, dann führt dies zu einer mangelhaften Lauffähigkeit der Streichmasse am Streichaggregat. Besonders bevorzugt beträgt die Viskosität der wässrigen entlüfteten Auftragssuspension etwa 200 bis etwa 500 mPas.In a preferred embodiment of the method according to the invention, the aqueous, deaerated application suspension has a viscosity of about 150 to about 800 mPas (Brookfield, 100 rpm, 20° C.). If the value falls below about 150 mPas or the value of about 800 mPas is exceeded, this leads to to poor runnability of the coating material on the coating unit. The viscosity of the aqueous, deaerated application suspension is particularly preferably about 200 to about 500 mPas.

In einer bevorzugten Ausführungsform kann zur Optimierung des Verfahrens die Oberflächenspannung der wässrigen Auftragssuspension auf 25 bis 60 mN/m, bevorzugt auf etwa 35 bis etwa 50 mN/m (gemessen entsprechend der statischen Ringmethode nach Du Noüy, DIN 53914, 1997-07), eingestellt werden.In a preferred embodiment, to optimize the process, the surface tension of the aqueous application suspension can be increased to 25 to 60 mN/m, preferably to about 35 to about 50 mN/m (measured according to the static ring method according to Du Noüy, DIN 53914, 1997-07), to be set.

Es ist vorteilhaft, wenn die getrocknete thermoresponsive Schicht einer Glätt-Maßnahme unterzogen wird. Hierbei ist es vorteilhaft, die Bekk-Glätte, gemessen nach DIN 53107 (2000), auf etwa 100 bis etwa 1200 sec, vorzugsweise auf etwa 300 bis etwa 700 sec, einzustellen. Bekk-Glätten von 100 bis 300 sec werden nach Methode A der DIN 53107 (2000) und Bekk-Glätten von über 300 nach Methode B der DIN 53107 (2000) gemessen.It is advantageous if the dried thermoresponsive layer is subjected to a smoothing operation. It is advantageous here to adjust the Bekk smoothness, measured according to DIN 53107 (2000), to about 100 to about 1200 seconds, preferably to about 300 to about 700 seconds. Bekk smoothness of 100 to 300 seconds are measured according to method A of DIN 53107 (2000) and Bekk smoothness of more than 300 according to method B of DIN 53107 (2000).

Die im Zusammenhang mit dem wärmeempfindlichen Aufzeichnungsmaterial aufgeführten bevorzugten Ausführungsformen gelten ebenfalls für das erfindungsgemäße Verfahren.The preferred embodiments listed in connection with the heat-sensitive recording material also apply to the process according to the invention.

Die vorliegende Erfindung betrifft auch ein wärmeempfindliches Aufzeichnungsmaterial erhältlich nach dem obenstehenden Verfahren.The present invention also relates to a heat-sensitive recording material obtainable by the above process.

Beschreibung der FigurenDescription of the figures


Figur 1 zeigt Lichtmikroskopaufnahmen eines bedruckten erfindungsgemäßen wärmeempfindlichen Aufzeichnungsmaterials. Oben: Laserleistung 80% Unten: Laserleistung 70% Links: Ohne thermische Behandlung Rechts: Mit thermischer Behandlung (30 min bei 70°C)
Figur 2 zeigt eine Illustration der Opazitäten. Es handelt sich um die Grauwerte einer horizontalen Linie. Die Laserleistung betrug 70%. Der Grauwert ist ein Wert zwischen 0 und 255, wobei 255 ein komplett schwarzes Pixel und 0 ein komplett weißes Pixel widerspiegelt.
figure 1 shows optical micrographs of a printed heat-sensitive recording material according to the invention. Above: Laser power 80% Below: laser power 70% Left: Without thermal treatment To the right: With thermal treatment (30 min at 70°C)
figure 2 shows an illustration of the opacities. These are the gray values of a horizontal line. The laser power was 70%. The gray value is a value between 0 and 255, where 255 represents an all-black pixel and 0 represents an all-white pixel.

Die Erfindung wird nachfolgend anhand von nicht beschränkten Beispielen im Detail erläutert.The invention is explained in detail below using non-restricted examples.

Beispieleexamples Rezeptur 1recipe 1

Eine wässrige Auftragssuspension wurde hergestellt, indem 100 Teile Nanopartikel von Celluloseacetatbutyrat mit einem mittleren Partikeldurchmesser von etwa 170 nm (±40 nm), die in Gegenwart von 0,1 % Polyvinylalkohol, THF als Lösungsmittel und einem Wasser/Isopropanol-Gemisch im Verhältnis 1,2 zu 2,8 als Nicht-Lösungsmittel wie oben beschrieben gefällt wurden, mit 40 Teilen Polyvinylalkohol, 5 Teilen Styronal D 517 als Binder, 15 Teilen Sterocoll als Viskositätsregler und 3 Teilen 1M NaOH gemischt wurden.An aqueous application suspension was prepared by mixing 100 parts of cellulose acetate butyrate nanoparticles with an average particle diameter of about 170 nm (±40 nm) in the presence of 0.1% polyvinyl alcohol, THF as solvent and a water/isopropanol mixture in a ratio of 1, 2 to 2.8 precipitated as non-solvent as described above, mixed with 40 parts polyvinyl alcohol, 5 parts Styronal D 517 as binder, 15 parts Sterocoll as viscosity regulator and 3 parts 1M NaOH.

Für die Beschichtungsformulierung wurde ein Verhältnis von 11,75 Gew.-% Feststoff/Flüssigkeit gewählt. Dieser Wert wurde gewählt, da die Partikel nach der Herstellung als ~15 Gew.%ige Suspension vorliegen. Die Feststoffgehalte der Additive und Beschichtungen wurden mit einer Trockenwaage bestimmt. Bei dem verwendeten Polyvinylalkohol handelt es sich um zu 84 % verseiftes Polyvinylacetat (Mn 100.000 g/mol). Bei einer typischen Testformulierung wurden die Probengefäße mit 100 mg Nanopartikeln von Celluloseacetatbutyrat befüllt, die jeweiligen Additive hinzugefügt und der Feststoffgehalt (FG) mit destilliertem Wasser auf 11,75 Gew.% eingestellt. Anschließend wird die Formulierung mittels Vortex-Rüttler und Ultraschallbad homogenisiert. Es erfolgte die Applikation der Beschichtung mit Hilfe eines automatischen Filmapplikators von BYK Additives & Instruments auf eine für Strichauftragung vorbeschichtete Hostaphan Folie Typ RNK 50.0 2600. Als Vorschubgeschwindigkeit wurden 100 mm min-1 gewählt und als Rakelspalt 90 µm.A ratio of 11.75% by weight solids/liquid was chosen for the coating formulation. This value was chosen because the particles are in the form of ~15% by weight suspension after manufacture. The solids content of the additives and coatings were determined using a dry balance. The polyvinyl alcohol used is 84% saponified polyvinyl acetate (Mn 100,000 g/mol). In a typical test formulation, the sample vials were filled with 100 mg nanoparticles of cellulose acetate butyrate, the respective additives were added and the solids content (FS) was adjusted to 11.75% by weight with distilled water. The formulation is then homogenized using a vortex shaker and an ultrasonic bath. The coating was applied using an automatic film applicator from BYK Additives & Instruments to a Hostaphan film type RNK 50.0 2600 that had been precoated for line application. The feed rate selected was 100 mm min -1 and the doctor blade gap 90 μm.

Es wurden wärmeempfindliche Aufzeichnungsmaterialien hergestellt, wobei die Auftragsmenge der thermoresponsiven Schicht 2,5 4 und 6 g/m2 betrug.Heat-sensitive recording materials were prepared with the coating amount of the thermoresponsive layer being 2.5, 4 and 6 g/m 2 .

Nachdem die Papierstriche angefertigt und bei Raumtemperatur getrocknet waren, wurden die beschichteten Substrate mit einer Schere halbiert. Eine Hälfte eines Substrats wurde für 30 min im Trockenschrank bei 70 °C temperiert, um einfache Trocknungsbedingungen zu simulieren. Anschließend wurden beide Proben mit einem 30-Watt-CO2-Laser "bedruckt" (Parameter in Tab. 1).After the paper coatings were made and dried at room temperature, the coated substrates were cut in half with scissors. Half of a substrate was heated in a drying cabinet at 70 °C for 30 min to simulate simple drying conditions. Both samples were then "printed" with a 30-watt CO 2 laser (parameters in Table 1).

Hierbei wurden jeweils 10 unterschiedliche Energiemengen (0,43 - 4,3 mJ/mm2) deponiert und mit jeder Energiemenge 12 Linien in die Beschichtung eingeschrieben ("gedruckt").In each case 10 different amounts of energy (0.43-4.3 mJ/mm 2 ) were deposited and 12 lines were written ("printed") into the coating with each amount of energy.

Diese zwei Proben wurden an einem Lichtmikroskop eingehender untersucht.These two samples were examined more closely on a light microscope.

Zur Analyse der Drucke wurde ein Lichtmikroskop im Durchlichtmodus eingesetzt.A light microscope in transmitted light mode was used to analyze the prints.

Die Auswertung erfolgte mit dem Open Source Bildanalyseprogramm ImageJ. Die Helligkeit wurde so eingestellt, dass die hellsten Bereiche den Sensor gerade nicht auslasten. Basierend auf den Gauwerten konnten so relative Opazitäten zwischen den eingeschmolzenen und den nicht behandelten Stellen berechnet werden. Tabelle 1: Parameter CO2-Laserdruck Parameter Lasereinstellungen Linienabstand [mm] 0,35 Höhe [mm] 4,2 Breite [mm] 10,33 Leistung [%] 10-100 Deponierte Energie [mJ/mm2] 0,43-4,3 Frequenz [Hz] 100 Geschwindigkeit [mm/s] 20.000 Druckzeit [ms] 803 The evaluation was carried out with the open source image analysis program ImageJ. The brightness was set in such a way that the brightest areas just don't load the sensor. Based on the gauge values, relative opacities between the melted and untreated areas could be calculated. Table 1: CO 2 laser printing parameters parameter laser settings line spacing [mm] 0.35 Height [mm] 4.2 Width (mm] 10:33 Perfomance [%] 10-100 Deposited energy [mJ/mm 2 ] 0.43-4.3 Frequency [Hz] 100 Speed [mm/s] 20,000 Print time [ms] 803

Unter dem Lichtmikroskop zeigten die Papierstriche der Rezeptur 1 vielversprechende Ergebnisse, die in Figur 1 dargestellt sind. Wie bereits in der Beschichtungsformulierung festgestellt wurde, sind die Muster makroskopisch sehr homogen. Mit einer Laserleistung von 70 % waren bereits scharfe Linienprofile zu erkennen. Durch eine Erhöhung der Laserleistung auf 80 % reduziert sich der Abstand zwischen den einzelnen Linien.Under the light microscope, the paper coatings of formulation 1 showed promising results, which are shown in figure 1 are shown. As already noted in the coating formulation, the patterns are macroscopically very homogeneous. With a laser power of 70%, sharp line profiles could already be seen. Increasing the laser power to 80% reduces the distance between the individual lines.

Figur 2 dient der Illustration der Opazitäten. Es handelt sich um die Grauwerte einer horizontalen Linie. Die relative Opazität erreichte bei den PVA-Beschichtungen Höchstwerte von bis zu 95 %. Die thermische Behandlung zeigte keinen negativen Einfluss. figure 2 serves to illustrate the opacities. These are the gray values of a horizontal line. The relative opacity of the PVA coatings reached a maximum of 95%. The thermal treatment showed no negative influence.

Claims (11)

  1. Heat-sensitive recording material comprising a carrier substrate which is black or coloured on at least one side, and a thermoresponsive layer on the at least one black or coloured side of the carrier substrate, wherein the thermoresponsive layer comprises nanoparticles of at least one cellulose ester.
  2. Heat-sensitive recording material according to claim 1, characterised in that the nanoparticles of the at least one cellulose ester have a number-averaged particle size of 50 to 400, measured by means of dynamic light scattering (DLS).
  3. Heat-sensitive recording material according to any one of the preceding claims, characterised in that the thermoresponsive layer has a transparency, measured according to DIN 53147:1993-01, of less than 35%.
  4. Heat-sensitive recording material according to any one of the preceding claims, characterised in that the at least one cellulose ester comprises cellulose acetate, cellulose acetate propionate, cellulose butyrate and/or cellulose acetate butyrate, preferably cellulose acetate butyrate.
  5. Heat-sensitive recording material according to any one of the preceding claims, characterised in that the at least one cellulose ester has a glass transition temperature Tg of 45°C to 150°C and/or a melting temperature Tm of 100°C to 185°C in each case determined according to DIN 53765:1994-03.
  6. Heat-sensitive recording material according to any one of the preceding claims, characterised in that the at least one cellulose ester is contained in the thermoresponsive layer in an amount of 35 to 70% by weight in relation to the total weight of the thermoresponsive layer.
  7. Heat-sensitive recording material according to any one of the preceding claims, characterised in that the thermoresponsive layer additionally comprises polyvinyl alcohol, preferably in an amount of 5 to 50% by weight in relation to the total weight of the thermoresponsive layer.
  8. Heat-sensitive recording material according to any one of the preceding claims, characterised in that the thermoresponsive layer additionally comprises at least one kaolin, an alkali and/or alkaline earth salt, especially NaCl, CaCO3 and/or CaCl2, preferably in an amount of 0.05 to 10% by weight in relation to the total weight of the thermoresponsive layer.
  9. Heat-sensitive recording material according to any one of the preceding claims, characterised in that the thermoresponsive layer additionally comprises at least one high-molecular polyelectrolyte, especially a poly(vinylamine-vinylformamide) copolymer, preferably in an amount of 5 to 35% by weight in relation to the total weight of the thermoresponsive layer.
  10. Heat-sensitive recording material according to any one of the preceding claims, characterised in that the carrier substrate comprises paper, synthetic paper and/or a plastics film.
  11. Method for producing a heat-sensitive recording material according to any of the preceding claims, characterised in that an aqueous suspension containing the starting materials of the thermoresponsive layer and having a solids content of 15 to 65 % by weight is applied to the at least one black or coloured side of the support substrate, the aqueous suspension being applied and dried according to coating methods which produce a contour coating with a curtain coater or a levelling coating with a blade coater or with a squeegee.
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DE102013002297A1 (en) 2013-02-08 2014-08-14 Papierfabrik August Koehler Se Heat-sensitive recording material
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RU2677706C1 (en) 2014-12-23 2019-01-21 Мицубиси Хайтек Пэйпер Юроп Гмбх Heat sensitive recording material for offset printing

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ES2954503T3 (en) 2023-11-22
FI3765303T3 (en) 2023-09-12
DE102018111495A1 (en) 2019-11-14
DE102018111495B4 (en) 2020-04-09
CN112004687B (en) 2023-04-28
CN112004687A (en) 2020-11-27
US20210213769A1 (en) 2021-07-15
WO2019219391A1 (en) 2019-11-21
EP3765303A1 (en) 2021-01-20
US11975553B2 (en) 2024-05-07

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