OVERLAPPINGLY OVERSTRIKEABLE RIBBON AND USE THEREOF IN CONTINUOUSLY FULL CASSETTES

Abstract: An overlapping overstrikeable ribbon is described having a carrier film (2) and an ink-releasing coating (3) in the form of a plastic matrix applied thereto, which contains at least one fatty dye and/or oil-soluble dye and optional carbon black and/or other ink pigments, as well as further conventional additives. According to fig. 1 the ink-releasing coating (3) can be subdivided into differently coloured coatings (4a, 4b and 4c) representing the three primary colours and a black coating (4d) for producing colour prints. The ink-releasing coating contains no fillers and contains a polyethoxylated fatty acid ester of a polyhydric alcohol as a solvent for the dye(s). This ribbon has advantages when used in continously full cassettes, which are more particularly used in matrix printing systems.

Description: The invention relates to an overlappingly overstrikeable ink ribbon with a carrier film and an ink-releasing coating in the form of a plastic matrix applied thereto, which contains at least one oil-soluble dye and/or one fatty dye and optionally carbon black and/or other ink pigments, as well as further conventional additives, and the use thereof in continuously full cassettes. "Overlappingly overstrikeable ribbons", which are particularly intended for type wheel printers are known. The term "overlappingly overstrikeable" means that the ribbon transfer per strike which is normally somewhat more than one character width is reduced to a fraction of the character width, e.g. to 1/3 or 1/5, so that each strike only impinges on a fresh area of the ribbon with a small surface proportion, whereas the larger surface proportion of the character strike is on a ribbon area which was struck once or several times immediately beforehand. Such typewriter ribbons are also called "overstrike" ribbons. Such a ribbon, like a single-pass ribbon, only has to be moved in one direction, but is still utilized several times. Compared with repeatedly overstrikeable ribbons which have to be correspondingly moved forwards and backwards (with a full transverse stage of approximately one character width per strike), this procedure obviates the complicated and troublesome reversing mechanism required for changing the ribbon running direction. In order to obtain high overstrike figures, it has hitherto been considered necessary to incorporate into the ink-releasing coating of an overlappingly overstrikeable ribbon fillers, particularly with large inner surface and a small particle size distribution of e.g. 0.2 to 20 micrometers. The fillers fulfill a number of functions and in particular serve to increase to productivity of the ribbon. It was also hitherto considered necessary to integrate the oil-based ink paste into a plastic matrix. These requirements were made no matter whether the particular overlappingly overstrikeable ribbon for the printing process was used with a type wheel printer, as a winding spool or as a continously full cassette. Only as a result of this special construction, i.e. plastic matrix with filler, together with the colouring constituents and the oil, was it considered possible to permanently increase the ink supply for the printing process and thereby obtain the desired overstrike values. Reference is made to German patents 32 14 305 and 33 07 432 relative to the above prior art. It could be asumed that excessively thick ink coatings no longer ensured a constant ink supply. It was in particular assumed that a ribbon of this type wound up into a reel would have an "oiling out" tendency, i.e. there would be wetting of the engaging back of the winding. This wetting could lead to a sticking of the winding spool and to transfer problems in the cassette. This sticking could also occur if the ambient temperature rose greatly e.g. in excessively heated rooms. The objekt of the present invention is therefore to propose an overlappingly overstrikeable ribbon which, contrary to the requirements of the prior art does not necessarily require the incorporation of fillers into the ink paste of the ink -releasing coating of a ribbon and which should have the same overlappingly overstrikeable properties but with production and machine function advantages. According to the invention these objects are solved in that the ink-releasing coating, whilst excluding fillers, contains a polyethoxylated fatty acid ester of a polyhydric alcohol as the solvent of the dye(s). For the purpose of forming the plastic matrix of the ink ribbon according to the invention, it is possible to use the plastic binders conventionally used for such ribbons, such as polyacrylates, vinylchloride acetate copolymers, linear polyesters, polyvinylacetate, polystyrene and polyamide. The inventively essential solvent of the fatty dye in the form of a polyethoxylated fatty acid ester of a polyhydric alcohol is sufficiently incompatible with said binders to form a type of sponge layer on the ribbons. Certain polymeric materials are of particular advantage, e.g. cellulose-acetate-butyrate or -propionate (e.g. CAB 0.4 sec and MW of Eastman Chem.) The effects are further improved, if additionally to the cellulose derivative materials poly (lower) alkylmethacrylate or - acrylate materials are used, e.g. polymethylmethacrylate (e.g. Elvacite of Du Pont). For the purposes of the invention, particular suitability has been revealed in the case of those polyethoxylated fatty acid esters which are derived from fatty acids with approximately 12 to 25 carbon atoms and from alcohols with approximately 3 to 6 hydroxy groups and which contain approximately 20 to 60 ethoxy groups per molecule. Particularly preferred examples are polyoxyethylene (40)-sorbitan pentaoleate to octaoleate, polyoxyethylene-glycerol triricinolate and the corresponding compounds of other fatty acids with on average approximately 40 ethoxy groups. As a result of the higher solvency of the aformentioned specific polyethoxylated fatty acid esters for fatty dyes compared with conventional solvents, there is no need for the entire oil base of the ink-releasing coating of the ribbon to comprise said fatty acid esters. In fact they can readily be extended with up to 50% of the oils conventionally used hitherto for overstrike ribbons, including mineral oils, without this leading to an inadequate dye concentration of the ink paste. It can also be appropriate to add cationic wetting agents to the ink-releasing coating, because they prevent an excessively intense wetting of the inner surfaces of the sponge structure of the plastic matrix with the normally acid colouring agent particles and therefore aid the mobility thereof. Preferably the wetting agents are constituted by fatty amine salt, i.e. salts of long-chain alkyl amines or diamines obtained from natural or synthetic fatty acids, particularly with long-chain or short-chain fatty acids. The overlapping overstrikeably ribbons according to the invention can also have juxtaposed or successively arranged, differing ink-releasing coatings, instead of a single colour range, in order to permit multicolour printing. In order to provide high fidelity multicolour prints, it is therefor appropriate to choose the three primary colours yellow, blue-green and purple-red. Particularly in the case of a matrix or needle printing system, this can lead to colour pictures, which are very similar to a colour original, reproduced on a copy sheet or film through producing images corresponding to the particular colour signals produced by colour separation of the original with separation filters, i.e. blue, green and red three-colour filters. According to the invention the different colour-releasing coatings are formed by applying the differently coloured ink pastes, which in each case contain dyes and optionally ink pigments with a yellow, purple-red or blue-green colour and a solvent to be evaporated, apart from the binder and further appropriate additives. All oil-soluble dyes, such as e.g. Sudan deep black (C.I. 26150) or fat-soluble black HB (C.I. 26150) are suitable as oil-soluble or fatty dyes. It is obviously possible to produce other colours or fluorescent characters by using corresponding oil-soluble dyes. If use is made of a black fatty dye in order that the typing system gives black printing, it is appropriate for obtaining a better lightfastness of the black printing to incorporate carbon black into the ink-releasing coating, in addition to the fatty dye. If it is a differently coloured oil-soluble dye or fatty dye, it is advantageously possible to use additionally ink pigments of the same colour. Thus, advantageously the ribbon according to the invention contains both a (fatty) dye(s) and an ink pigment. Within the sense of the invention "dyes" in solvents and/or binders are understood to means soluble colouring agents, as opposed to insoluble ink pigments (cf. Römpps Chemie-Lexikon, 8th edition, vol. 2, p. 1239 ff.). As a result mixtures of different dyes can be used, e.g. to reduce the tendency of fading and to improve the colour tone or shade. With regards to the proportions in which the constituents of the ink-releasing coating of the ribbon according to the invention are to be used, the following framework formulation (in parts by weight) has proved appropriate : approximately 10 to 25 parts by weight of polyethoxylated fatty acid ester with up to approximately 60 ethoxy groups, particularly approximately 20 to 60 ethoxy groups in the molecule, approximately 4 to 15 parts by weight of the dye(s) (approximately 30 to 60% solution in a polyethoxylated fatty acid ester with up to approximately 60 ethoxy groups in the molecule), approximatly 16 to 50 parts by weight of binder and optionally approximately 6 to 25 parts by weight of carbon black and/or other ink pigments and approximately 1 to 6 parts by weight of cationic wetting agent. These constituents are dispersed in a suitable solvent and this dispersion is applied to the carrier film in the manner to be described hereinafter. In the said framework formulation use is made of approximately 45 to 90 parts by weight of solvent. It is obviously possible to pass above or below the indicated ranges of the framework formulation and this is a function of the requirements of the particular typing systems chosen. The most favourable values can be established by simple routine tests. In order to obtain the desired results importance is attached to the incorporation of the binder, which should not be in particle form and has originally completely dissolved and subsequently forms the said plastic matrix. The binder also has a "corset function" or a support function. The solvents used in producing the ribbon according to the invention are conventional solvents or solvent mixtures, such as e.g. methyl ethyl ketone, toluene and isopropyl alcohol. The "dry" ink paste obtained therewith (after evaporating the solvent in the form of e.g. toluene) is applied in a quantity of approximately 5 to 50 g per m² of carrier film and more especially 10 to 40 g per m² of carrier film. A minimum application quantity is approximately 5 to 15 g per m² of carrier film. The carrier film is made from conventional polymers, such as polyester, polyethylene, polypropylene or polyamide. The carrier film thickness is not decisive, but it is advantageously approximately 6 to 20 micrometers, especially approximately 15 micrometers, whilst it does not exceed approximately 40 micrometers. It can also be advantageous in certain cases to place an approximately 2 to 6 micrometer thick antistatic intermediate coating between the ink-releasing coating and the carrier film. Reference is made in this connection e.g. to DE-OS 28 15 344. This intermediate coating is simultaneously an adhesive agent between the carrier film and the ink-releasing coating. The indicated ink paste, which preferably dissolves the fatty dye to saturation and partly contains it in suspended form in the case of supersaturation, is applied by conventional coating methods to the ribbon carrier film, e.g. with a doctor blade or roll coater. This is followed by drying. After drying the applied coating, the easily evaporatable solvent, e.g. toluene is either not present, or is only present in insignificant quantities in the finished product. The advantages attainable with the inventive overlappingly overstrikeably ribbon appear more particularly if the ribbon is used in a continously full cassette, being located in the latter more or less loosely in loop form. Thus, unlike in the case of a winding spool, there is no longer any excessive pressure act ion between the contacting ribbon faces. Ribbons according to the invention housed in continously full cassettes have a particularly good productivity, if the ink paste is applied in a larger quantity. In the described systems, these larger quantities are not prejudicial and in particular do not lead to the aforementioned, disadvantageous "oiling out". The advantages of the inventive ribbon become particularly apparent when used in matrix printing systems, for which it was hitherto considered necessary to use ribbons with cloth supports for obtaining satisfactory printing effects. Compared with the conventional cloth typewriter ribbon, according to the invention a much lower ribbon feed speed can be set. Whereas a conventional cloth ribbon requires a certain regeneration time at overstrike, this is not the case with the ribbons according to the invention. The ink paste quantity applied leads to an extremely high overstrike value. On using solely dyes, then even a 300 times overstrike can be obtained. The additional presence of an ink pigment increases the lightfastness of the print, but reduces the overstrike value to approximatly 200. However, the prior art only discloses ribbons for matrix printing systems with an approximately 40 times overstrike. It was hitherto considered that in the case of matrix printing systems having a ribbon with a carrier film, it was not possible to achieve the productivity of a corresponding cloth ribbon. This prejudice has been overcome by the present invention. If the invention ribbon is used on more recent matrix printing systems operating with a lower pressure action, even higher overstrike values than hitherto can be achieved. In the case of a matrix printing system, in conjunction with the desired overstrike value, it must be borne in mind that the basis for the consideration is the needle width. Thus, during an advance, e.g. with a 200 times overstrike, 1/200 of the needle width is covered, which means that the ribbon, without overstrike, would have to revolve 200 times, whereas in the case of overstrike a single revolution takes place. The single revolution leads to further important advantages in that the slower the ribbon is advanced, the better the needles can be retracted. Obviously the ribbon can also be moved rapidly, so that it can be used on conventional typewriters of the corresponding system. Thus, this also covers the possibility of use in matrix printing systems originally designed for cloth typewriter ribbons. In the case of the invention, the overstrike system also leads to reduced mechanical effort in the typewriter and to a more uniform utilization of the ribbon with a better and more uniform character pattern. The intensity gradient in the dot can no longer be perceived, which does not apply in old type wheel systems, where the basis is the width of the letter. Thus, it is possible by means of the invention in the case of a set slower ribbon transfer to obtain very high productivity levels, without the start being too black and the end too pale. In fact, the whole cassette types with a uniform, set average intensity. The advantages of the inventive ribbon also become apparent when it is not understood to mean solely an elongated ribbon, but also a sheet or a blanket, the invention also extending to such cases. Advantages developments of the invention can be gathered from the attached drawings, wherein show: Fig 1, a mulitcolour ribbon according to the invention. Fig 2, a larger-scale detail of the ribbon. Fig 1 shows the ink ribbon 1 with a carrier film 2 an ink-releasing coating 3, which is subdivided into different colour coatings 4a, 4b, 4c and 4d. Colour coatings, 4a, 4b and 4c represent the three primary colours yellow, purple-red and blue-green necessary for high-fidelity colour printing, whilst coating 4d is black and is used for normal typing. Fig. 2 shows a detail of colour coating 4a. The lat ter comprises a plastic matrix 6, which contains a homogeneous ink paste 4′ and incorporated carbon black particles 5 and is applied to the carrier film 2. The ink paste 4′ contains the oil-soluble, black fatty dye, e.g. Sudan deep black (CI 26150), dissolved in polyoxyethylene-sorbitan septaoleate with approximately 40 ethoxy groups per molecule. The following examples illustrate the invention, the abbreviation PSSO standing in each case for polyoxyethylene-sorbitan septaoleate with on average 40 ethoxy groups per molecule. Note to the proceeding examples 6 to 9: "Neopen" is the trade name for a BASF range of solvent dyes. These examples include combination of dyestuffs.

Claims: 1. Overlappingly overstrikeable ribbon with a carrier film and a colour-releasing coating in the form of a plastic matrix applied thereto, which contains at least one oil-soluble dye and/or one fatty dye and optionally carbon black and/or other ink pigments, as well as further conventional additives, characterized in that the ink-releasing coating, whilst excluding fillers, contains a polyethoxylated fatty acid ester of a polyhydric alcohol as the solvent for the dye(s). 2. Ribbon according to claim 1, characterized in that the polyethoxylated fatty acid ester is an ester of fatty acids with approximately 12 to 25 C-atoms and alcohols with 3 to 6 OH-groups, which contains approximately 20 to 60 ethoxy groups in the molecule. 3. Ribbon according to claim 2, characterized in that the polyethoxylated fatty acid ester is a polyoxyethylene-(40)-sorbitan pentaoleate to octaoleate. 4. Ribbon according to one of the claims 1 to 3, characterized in that the polyethoxylated fatty acid ester is extended by up to 50% with a natural and/or synthetic oil. 5. Ribbon according to one of claims 1 to 4, characterized in that the ink-releasing coating additionally contains a cationic wetting agent. 6. Ribbon according to one of claims 1 to 5, characterized in that it contains different colour coatings for multicolour printing arranged in juxtaposed or successive manner. Ribbon according to claim 6, characterized in that there are four different colour coatings with the colours yellow, blue-green, purple-red and black. 8. Use of the ribbon according to at least one of the claims 1 to 7, in continously full cassettes. 9. Use of the ribbon according to at least one of the claims 1 to 8, in matrix printing systems.

Inventors: HOGARTH, IAN, MACKINTOSH, CHRISTINE, PAFFHAUSEN, HANS, SCOTT, ANDREW
Applicants: CARIBONUM LIMITED
Application year: 1987
Main classification: B41J31
IPC codes: B41J31, C09D11, B41M5