Heat-sensitive inked element for impactless printers of thermal type

Description

[0001] Tne present invention relates to a heat-sensitive inked element for impactless printers of thermal type, comprising a plastics material base carrier coated on one side with a coating of a mixture which is transferable to a printing carrier when it is subjected to heat and pressure, the mixture comprising a pigment and/or colouring agent, a thermoplastic resin and a wax.

[0002] Various inked elements in the form of single-use ribbons are known. In a known ribbon, 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 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.

[0003] The object of the present invention is to provide an inked element in which the resin-wax mixture 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.

[0004] The inked element according to the invention is characterised in that the resin is of thermoadhesive polymeric type and the wax is of polymeric type compatible with the resin and such as to impart to the mixture a high characteristic in respect of plasticity and softness, thereby to cause the ink to adhere to any printing carrier having a roughness of between 10 and 500 ml/min.

[0005] 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.

[0006] The ribbon comprises a thermoplastic material base carrier which is covered on one side with a thin layer of solid ink 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 a printing head to the inked ribbon to produce the effect of transfer of the ink from the ribbon to the printing carrier.

[0007] The ribbon is provided for printing with a serial thermal head comprising a vertical raw of printing elements, and with a 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.

[0008] It has been found that the best results are achieved with mixtures of polymeric waxes of the type Protektor, Lunamelt or Lunatack (Spica) and particular thennoadhesive polymeric resins compatible with the above-mentioned waxes, for example:

Piccolastic E100 (Picco), Hercolyn 1150, Hercolyn 1151, Ercolyn D, Pentalyn H (Hercules), Dertoline C.G., Dertoline G. (DRT).

[0009] Those two components, mixed in various ratios, impart to the ink thermoadhesive characteristics which are particular 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.

[0010] A colouring agent and/or pigment is added to the mixture of the two basic components, wax and resin, in order to produce a black or coloured ribbon. The colouring agent and/or pigment 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.

[0011] 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, Graftolo BP Ruby, Graftolo GXS Yellow, Graftolo WTP Ruby, Sandorin 5 BL Brilliant Red (Sandoz) and Fat Black HT (Hoeschst). The ribbon is produced by spreading over a carrier of nylon, polythene, kapton, etc, of a thickness of from 5 to 15 µ, 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 µ. 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 µ.

[0012] 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.

[0013] 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.

[0014] It was found that a ribbon produced by applying that ink to a 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.

[0015] 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.

[0016] 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

[0017] 75g of Piccolastic E 100 and 25^g of Lunamelt HS 600 are dissolved in 300g of toluene, 180g of methylisobutylketone and 60g of methylethylketone. The resulting solution is poured into a 1500 ml steel bowl with 500 ml of glass marbles.

[0018] 3g of Sandorin 2 GLS Blue (Sandoz), 8g of Graftolo BP Ruby (Sandoz), 3g of Graftolo GXS Yellow (Sandoz) and 25g of Fat Black HT (Hoechst) are added to the bowl.

[0019] The bowl is set milling for 76 hours. After the milling operation, the glass marbles are separated off and 100g of toluene and 60g 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.

[0020] 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

[0021] 75g of Hercolyn 1151, and 25g of Lunatack P are dissolved in 300g of toluene and 200g of MIK. The resulting solution is poured into a 1500 ml bowl with 500 ml of glass marbles. 25g of Fat Black HT, 3g of Sandorin 2 GLS Blue,,8g of Graftolo BP Ruby and 3g 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 100g of toluene and 80g of MIK are added, and the ink produced in that way is spread in a spreading machine over a polythene carrier which is 10,u in thickness, as in the preceding Example. The ribbon produced has substantially the same characteristics in respect of quality as the previous ribbon.

[0022] 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 for impactless printers of thermal type, comprising a plastics material base carrier coated on one side with a coating of a mixture which is transferable to a printing carrier when it is subjected to heat and pressure, the mixture comprising a pigment and/or colouring agent, a thermoplastic resin and a wax, characterised in that the resin is of thermoadhesive polymeric type and the wax is of polymeric type compatible with the resin and such as to provide a high characteristic in respect of plasticity and softness, so as to cause the ink to adhere to any printing carrier having a roughness of between 10 and 500 ml/min.

2. An element according to claim 1, characterised in that the ratio between the resin and the wax in the mixture is substantially 3 to 1.

3. An element according to claim 1 or 2, characterised in that the base carrier is between 5 and 15µ in thickness and the mixture is in a layer of thickness between 2 and 6µ.

4. An element according to claim 1,2 or 3, characterised in that the mixture comprises Piccolastic E 100 and Lunamelt HS or Hercolyn 1151 and Lunatack P.

5. An element according to claim 1,2,3 or 4, characterised in that the mixture comprises a black colouring agent, with the addition thereto of about 40% of three complementary colours.

6. An element according to claim 5 characterised in that said black comprises Fat Black HT in an amount substantially equal to tne amount of wax, and the complementary colours comprising Sandorin 2 GLS Blue, Graftolo BP Ruby and Graftolo GXS Yellow.