EP0121379B1

EP0121379B1 - Heat-sensitive inked element for impactless printers of thermal type

Info

Publication number: EP0121379B1
Application number: EP84301913A
Authority: EP
Inventors: Franco Knirsch; Giovanni Gianolini
Original assignee: Ing C Olivetti and C SpA
Current assignee: Telecom Italia SpA
Priority date: 1983-03-30
Filing date: 1984-03-21
Publication date: 1989-07-19
Also published as: IT8367353A0; DE3479013D1; IT1158916B; EP0121379A3; JPS59196295A; EP0121379A2

Description

The present invention relates to a heat-sensitive inked element comprising a plastics base material coated on one side with a dried adhesive coating layer of a mixture which is transferable to a printing carrier when it is subjected to heat and pressure and comprises a colouring agent, and a binder composed of a blend of at least one thermoplastic resin and at least one wax.
Various inked elements in the form of single- use ribbons are known. In a ribbon known from GB-A-1 473 870, the resin requires an elevated fusion temperature and is accordingly relatively rigid and fragile at room temperature, whereby it has a tendency to crack. In order to remedy that disadvantage, a ribbon has already been proposed in our EP-A-76044, in which the mixture comprises a plasticising agent in order to enhance adhesion to the paper. However, that ribbon is not suitable for printing in a satisfactory manner on carriers which have widely varying roughness, for example both on very smooth paper or plastic film such as the films used in educational projectors, wherein the Bendtsen roughness is between 10 and 30 ml/min, and on very rough paper, that is to say, with a degree of roughness of between 300 and 500 ml/min. This measure of roughness is defined, for example, in British Standard 4420: 1969.
There has been also proposed in the US-A-3 944 695 a heat sensitive inked element of the decalcomania type as defined above, adapted to transfer intricately shaped marks onto fabric or cloth, plastics or rigid materials, by ironing the element. This latter includes 5-40 weight % of a filler in form of talc or clay which serves to resist deformations of the printed marks. By reason of this the inked element is not adapted for printing on paper by a dot matrix printer.
The object of the present invention is to provide an inked element for an impactless dot printer in which the binder does not require any plasticising agent to reduce the fragility of the coating and is sufficiently resistant to rubbing against any type of printing carrier, and which is capable of adherence to any printing carrier having a roughness of between 10 and 500 ml/min.
The inked element according to the invention is characterised in that for impactness dot printers or thermal type the carrier has a thickness of from 5 to 15 µm, and that the coating layer has a thickness of from 2 to 6 Ilm and consists of a binder consisting of thermoadhesive polymeric resin and hot melt adhesive in a weight ratio of substantially 3 to 1, said polymeric resin being composed of a polystyrene having a softening point of about 100°C or an esterified rosin or resin, said hot melt adhesive being composed of a blend of thermoplastic resin and a hydrocarbon or paraffin wax and having a softening point between 70° and 80°C, together with the colouring agent which is present in an amount substantially equal to the weight of the hot melt adhesive.
These and other features of the invention will be more clearly apparent from the following description of some preferred embodiments, given by way of non-limiting example.
The inked element is in the form of a ribbon comprising a thermoplastic material base which is covered on one side with a thin layer of solid link thermotransferable to a printing carrier of paper or thermoplastic nature. The printing process provides for the simultaneous application of pressure and heat by means of printing head to the inked ribbon to produce the effect of transfer of the ink from the ribbon to the printing carrier.
The ribbon is provided for printing with a serial thermal head comprising a vertical row of printing elements, and with definition of 8 to 10 dots/ mm at the normal typing or automatic printing rate of from 20 to 40 characters/sec. That makes it possible to achieve a high quality in respect of print, character definition, resistance to rubbing and clean adhesion to the printing carrier (card or plastics film), whether it is of a smooth type (10 to 30 ml/min) or very rough type (300 to 500 ml/min). The inking mixture or ink, used for the ribbon has the particular feature of having a binder of polymeric type such that, when it is heated, it softens, substantially increasing adhesiveness to the printing carrier. The binders used are generally employed for formulating adhesives which are applied by a hot fusion process, known as hot melt.
It has been found that best results are achieved with a mixture of a hot melt adhesive and particular thermoadhesive polymeric resins compatible with the hot melt adhesive. The latter is formed of refined hydrocarbon or paraffin wax mixed with a thermoplastic resin, as for example the commercially known hot melt adhesives Protektor, Lunamelt or Lunatack (trademarks of the Lueneburger Wachsbleiche fuer Moderne Wachs-Chemik), and more especially Lunamelt HS 600 and Lunatack P. These materials have a softening point at a temperature of 70° to 80°C.
The thermoadhesive polymeric resins may be of the polystyrene type having a softening point of 100°C (Piccolastic E100-trade mark of Pennsylvania Industrial Co.). Alternatively the thermoadhesive polymeric resin could be formed of an esterified rosin or resin, as for example the commercially known Hercolyn 1150 (the glycol ester of selected stabilized resin acids), Hercolyn 1151 (the ester of selectively stabilized rosin acids and blended di- and triols), Hercolyn D (the hydrogenated methyl ester of rosin), and Pertalyn H (Hercules), Dertoline CG (colophony esterified with glycerol) and Dertoline G (modified colophony esterified with glycerol) (trademarks of Derives Resiniques et Terpeniques).
Those two components, mixed in various ratios, impart to the ink thermoadhesive characteristics which are particularly suited to thermal printing. Having regard to the particular nature of the basic components of the ink, there is no need to add particular additives (plasticising agents, softening agents, etc.) insofar as the characteristics of plasticity and softness of the ink are imparted by the above-mentioned basic components.
A colouring agent is added to the mixture of the two basic components hot melt adhesive and resin, in order to produce a black or coloured ribbon. The colouring agent is suitably selected so as to be compatible with the basic components, not alter with time, and thus be stable with respect to temperature and the ambient air.
Selection of the colour used must also take account of the shade of the colour required to produce clear single-colour or three-colour printing. The more significant colours are: Sandorin 2 GLS Blue (Pigment Blue 15, C.I. 74160) Graftolo BP Ruby (Pigment Red 57, C.I. 15850:1), Graftolo GXS Yellow (Pigment Yellow 14, C.I. 21095), Graftolo WTP Ruby (Pigment Red 48:2, C.I. 15865:2), Sandorin 5 BL Brilliant Red (C.I. Pigment Red 192) (Sandoz) and a modified nigrosine soluble in fat compounds such as that commercially known as Fat Black HT (Solvent Black 3, C.I. 26150) (Hoechst).
The ribbon is produced by spreading over a carrier of nylon, polythene, kapton, etc., of a thickness of from 5 to 15 pm, an ink in a continuous-mode spreading machine. In the spreading station, the carrier, receives the mixture in the form of a thin liquid film of a thickness of about 15 to 30 pm. Subsequently, in an evaporator, the liquid mixture is dried, leaving the solid ink adhering to the substrate, in a layer of a thickness of 2 to 6 pm.
Such a type of ribbon, when prepared in black or coloured form (red, green, blue, brown, cyan, magenta or yellow) is primarily used in printing machines of thermal type.
The possibility of producing high-quality printing, that is to say, with a high level of character definition, uniformity of covering of the dot without gaps, high level of adhesion of the character to the printing carrier, and the absence of any possibility of blotting due to friction, also depends on the substrate on which the inking mixture is coated, besides the characteristics of the ink and the binder.
It was found that a ribbon produced by applying that ink to polythene carrier of 10 p in thickness makes it possible to achieve a high level of character definition over a wide range of papers, by virtue of the particular characteristic of polythene of deforming due to the effect of heat and pressure, adapting itself perfectly to the roughness of the paper. The possibility of adaptation to varying degrees of roughness of the paper is not entirely a secondary aspect for that type of impactness printing, but even becomes a factor of primary importance when the quality of printing produced is to attain high levels over all office papers.
For that reason, the roughness of a wide range of office papers available on the market was measured with an instrument from Bendtsen & Wattre (Stockholm), using the Scan-Test Standard Method Scan-P 21:67 process. The results obtained fall in a range of values of 10 to 500 ml/ min.
Set out below are two examples of ink formulations which are not to be interpreted as limiting the invention but rather as being broadly representative thereof, whenever the pigments and/or colouring agents used are replaced by pigments and/or colouring agents selected in accordance with the above-specified criteria, and in respect of the percentages set forth in the example.

Example 1

75 g of Piccolastic E 100 and 25 g of Lunamelt HS 600 are dissolved in 300 g of toluene, 180 g of methylisobutylketone and 60 g of methylethylketone. The resulting solution is poured into a 1500 ml steel bowl with 500 ml of glass marbles.
3 g of Sandorin 2 GLS Blue (Sandoz), 8 g of Graftolo BP Ruby (Sandoz), 3 g of Graftolo GXS Yellow (Sandoz) and 25 g of Fat Black HT (Hoechst) are added to the bowl.
The bowl is set milling for 76 hours. After the milling operation, the glass marbles are separated off and 100 g of toluene and 60 g of MIK are added and the ink produced in that way is then spread in a spreading machine over a polythene carrier which is 10 p in thickness.
The ribbon produced with the polythene carrier makes it possible to print with a high quality of printing over a wide range of office papers, at a rate of 20 characters/sec. The quality of printing is satisfactory even at printing rates of up to 40 characters/sec.

Example 2

75 g of Hercolyn 1151, and 25 g of Lunatack P are dissolved in 300 g of toluene and 200 g of MIK. The resulting solution is poured into a 1500 ml bowl with 500 ml of glass marbles. 25 g of Fat Black HT, 3 g of Sandorin 2 GLS Blue, 8 g of Graftolo BP Ruby and 3 g of Graftolo GXS Yellow are added to the bowl. The bowl is set milling for 76 hours. After the milling operation, the glass balls are separated and 100 g of toluene and 80 g of MIK are added, and the ink produced in that way is spread in a spreading machine over a polythene carrier which is 10 µ in thickness, as in the preceding Example. The ribbon produced has substantially the same characteristics in respect of quality as the previous ribbon.
In the two Examples set out above, the addition to black of the three colours cyan, magenta and yellow, which are complementary with respect to the three primary colours red, green and violet, serve to impart a more intense shade to the black, inasmuch as synthesis of the three complementary colours gives black. The three colours are added to the black in a percentage of about 40% of the amount of black.

Claims

1. A heat sensitive inked element comprising a plastics carrier material coated on one side with a dried adherent coating layer of a mixture which is transferable to the printing substrate when it is subjected to heat and pressure and comprises a colouring agent and a binder composed of a blend of at least one thermoplastic resin and at least one wax characterized in that for impactless dot printers of thermal type the carrier has a thickness of from 5 to 15 pm, and that the coating layer has a thickness of from 2 to 6 pm and consists of a binder consisting of thermoadhesive polymeric resin and hot melt adhesive in a weight ratio of substantially 3 to 1, said polymeric resin being composed of a polystyrene having a softening point of about 100°C or an esterified rosin or resin, said hot melt adhesive being composed of a blend of thermoplastic resin and a hydrocarbon or paraffin wax and having a softening point between 70° and 80°C, together with the colouring agent which is present in an amount substantially equal to the weight of the hot melt adhesive.

2. An element according to claim 1, characterized in that said colouring agent is black, and that the mixture additionally comprises complementary colours in a total of 56% by weight of the said colouring agent to impart a more intense shade to the black.

3. An element according to claim 2 characterized in that the colouring agent is formed of Solvent Black 3 (C.I. 26150) and the mixture additionally includes cyan, magenta and yellow colours.

4. An element according to claim 3, characterized in that the complementary colours comprise, in percentage by weight of said colouring agent, 12% of Pigment Blue 15 (C.I. 74160), 32% of Pigment Red 57 (C.I. 15850:1) and 12% of Pigment Yellow (C.I. 21095).