OVERLAPPINGLY OVERSTRIKABLE RIBBON FOR MATRIX PRINTING SYSTEMS AND A PROCESS FOR THE PRODUCTION THEREOF

Abstract: An overlappingly overstrikable ink ribbon for matrix or needle printing systems is described having a carrier film 3 and an ink-releasing coating 4, as well as optionally further conventional intermediate coatings. An rubber-elastic layer 2 is formed on the needle impression side. A process for producing this ribbon is also described. This ribbon has many advantages compared with known ribbons. It protects the print head, withstands the needle pressure for a longer time due to the elastic layer and improves the printing definition. It can be produced by coextrusion of the starting materials of the carrier film and the rubber-elastic layer.

Description: The invention relates to an overlappingly overstrikable ink ribbon for matrix or needle printing systems with a carrier film and at least one ink-releasing coating and optinonally further conventional intermediate coatings, as well as a process for the production thereof. Overlappingly overstrikable ribbon for matrix printing systems with a carrier film are already known. The carrier film is made from a plastic, which can e.g. be of a thermosetting or thermoplastic nature. When using such ribbons in matrix printing systems many different disadvantages are encountered. The needles rapidly lead to perforations and deformations and consequently to damage to the carrier film and make the ribbon unusable, particularly on passing through several times. These disadvantageous effects lead to unsatisfactory printing clearness or definition, which in particular applies to new matrix printing systems with a larger number of needles per surface unit and with finer needles. EP-A-o 167 932 referrs to ribbons of typewriters. Rear coatings of the ribbon is formed with binders. These binders are resins which are usually amorphus, hard to brittle and have no fixed melting point and instead have a varying melting range, in which they gradually pass into the liquid state from the softening temperature. Resins are not rubber-elastic materials. Such materials are macroporous high polymeric materials crosslink to the decomposition point, which have a steel-elastic behaviour at low temperatures and which also do not flow in viscous manner at high temperatures and instead are rubber-elastic from 20°C or a lower temperature of the decomposition point. DE-A-21 06 610 also described ribbons in particular discuss a porous resin matrix transfer coating, which contains an ink which can be squeezed out a supporting layer, which is bound to the back of the transfer coating by a thin intermediate coating on an elastomeric polymer adhesive. In connection with these ribbons also no rubber-elastic materials in connection with the back coating of the ribbon are described. The object of the invention is to propose an overlappingly overstrikable ribbon for matrix printing systems, which largely prevents performation and deformation of the ribbon through the action of the needles in use and on printing leads to a satisfactory printing definition. According to the invention is object is solved in that on the side of the needle impression is formed a layer of an rubber-elastic material. When choosing the starting material for the carrier film of the ribbon according to the invention no significant limitations are imposed. It is possible to use the conventionally employed plastics in this field, which can e.g. be of a thermosetting or thermoplastic nature. Polyester and polypropylene films have proved to be particularly advantageous in practice. Polyethylene terephthalate is of particular significance among the polyesters. The thickness of the carrier film is not decisive, but it is generally advantageous if it does not exceed a value of 30 micrometers and is in particular approximately 10 micrometers. In the case of the ribbon according to the invention there is an elastic material layer on the side where needles act in matrix printing systems during the printing process. Within the context of the invention, the term "elastic material" is to be understood in the broadest sense and covers in particular "elastomers". This is the collective term for synthetic and natural polymers with rubberlike characteristics. According to DIN 7724 and the February 1972 supplement, elastomers are "wide-meshed high polymers crosslinked up to the decomposition temperature, which behave in steel-elastic manner at low temperatures and which even at high temperatures do not flow in a viscous manner and are instead rubberlike from 20°C or a lower temperature to the decomposition temperature. The rubberlike nature is characterized by substantially temperature-independent shear modulus values between approximately 0.1 and 100 MPa and a large reversible deformability." The elastomers comprise long, tangled polymer chains, which are crosslinked in wide-mesh manner with one another. As a result of the crosslinking bonding (adhesion points, e.g. sulphur or ether bridges introduced by vulcanization) in the case of tensile and compressive stressing the chains are prevented from sliding past one another (flowing away). The characteristics of the elastomers can be varied by fillers, stabilizers, etc. Natural rubber of butadiene-styrene copolymers can e.g. also be vulcanized by microwaves. Important elastomers within the scope of the invention are e.g. natural rubbers (NR), synthetic rubbers, e.g. B. CR, CSM, EVA, IIR, NBR, PUE, RUC, RUI, SBR, acrylic rubber, fluorelastomers, polyolefins, polyphosphorus nitride chloride, polysulphides, silicone rubbers and polyurethane rubbers. In the widest sense, a rubber is a high polymeric, mainly plastic substance, which through vulcanization passes into a highly elastic state and thereby loses its solubility in organic solvents. These rubber materials are applied in low viscosity form, e.g. in the form of a solution to one side of the carrier film of the inventive ink ribbon and subsequently undergo the specific vulcanization. There can be additional vulcanization accelerators, e.g. xanthogenates, dithiocarbamates and tetramethylthiuram disulphide. Vulcanization e.g. takes place by heat action or by evaporating the solvent and leads to the desired elastic material. Appropriately in producing the laminate from the carrier film and the elastic layer, the starting materials of the rubberlike products are used as a basis and are applied in an appropriate form, particularly in the dissolved form, to the carrier film and are vulcanized there. It is possible to use starting materials of natural and synthetic rubbers. Within the scope of the invention, it is advantageously possible to use thermoelastic elastomers for producing the elastic layer on the ribbon carrier film. According to DIN 7724 and the February 1972 supplement, they are high polymers, which are so crosslinked in wide-meshed manner up to the decomposition temperature that the polymer molecules are no longer in a position to perform macro-Brownian movements at any temperature. However, micro-Brownian movements are possible between the glass transition temperature (in the case of amorphous polymers) or the melting point (in the case of partly crystalline polymers), both of which are by definition above 0°C, and the decomposition temperature. Typical thermoelastic elastomers are wide-meshed crosslinked polyethylene and polypropylene. Through a coextrusion of a thermoplastic carrier material and the thermoelastic material, it is in particular possible to produce the composite structure constituted by the carrier film and the elastic layer. There are no significant restrictions in choosing the elastic material for forming the elastic layer of the inventive ribbon. It is known from the prior art how the elastomer material and possibly the starting materials used have to be chosen in order to ultimately obtain the desired composite structure constituted by carrier film and elastic layer. The essence of the invention is that, as will be shown hereinafter, said composite structure provides particularly advantageous and extremely surprising results when correctly used in matrix printing systems. Thus, in the process for producing the inventive ink ribbon, it is preferable to proceed in such a way that the starting materials for the elastic layer and the carrier film, which during or after extrusion are subject to crosslinking or are thermoplastically deformable, are coextruded and subsequently the ink-releasing coating is applied in a conventional manner. It is fundamentally also possible to process finished elastic films from the aforementioned materials with a finished carrier film to give a laminate, conventional laminating adhesives appropriately being used for providing adhesive characteristics. Materials of this type are known. The adhesion-imparting coating of the laminating adhesive is preferably approximately 3 to 10 micrometers thick. A particularly advantageous procedure for forming the elastic layer of the laminate structure will now be described. It has proved advantageous to use commercially available solvent-soluble, non-reactive polyurethane rubbers or resins for producing the elastic layer, which are applied in solution to the carrier and are physically dried. These e.g. include the linear aromatic polyurethane marketed under the trade name "Desmolac 2100" by Bayer AG, Leverkusen. These materials have completely reacted, but compared with a conventional fully reacted polyurethane resin, which is crosslinked three-dimensionally and insoluble in solvents, have a mainly linear structure, optionally with branched side chains and generally also have a lower molecular weight. They can be derived from aromatic or aliphatic hyrocarbons. To obtain the desired elasticity, the solution of said polyurethane resin applied must be supplied with a frifunctional isocyanurate or a corresponding prepolymer (at least at the ends in each case one isocyanate group). Triisocyanurates with free NCO groups are polyisocyanates, which are derived from isocyanuric acid, in that their three H-atoms are replaced by hydrocarbon radicals, which in turn carry free NCO groups. Within the scope of the invention this NCO isocyanurate is added to the solution containing the solvent-soluble, non-reactive polyurethane resin. The solvents can e.g. be methyl ethyl ketone, toluene and the like. It cannot react with the polyurethane resin, because the latter no longer contains any NCO-reactive OH-groups, but it e.g. reacts with water from the air or solvents to a three-dimensional polyurethane system, which passes through the layer of solvent-soluble, non-reactive polyurethane resin and thereby additionally strengthens the same. The NCO isocyanurate can e.g. be constituted by the products supplied by Bayer AG, Leverkusen under the name "Haftvermittler 2005". The quantity ratio of the two aforementioned reactants is not critical. As a rough guideline approximately one part by weight of NCO isocyanurate can be used for approximately 5 to 30 parts by weight of polyurethane resin. However, in the individual case, it is possible to go above or below these ranges. After evaporating the solvent, a crosslinking reaction leads to a fully elastic material, which meets in a very adequate manner the requirements of the invention. The elasticity in the sense of a better "needle pliability" can be favourably influenced in that a plasticizer, e.g. from the group of phthalic acid esters is incorporated into the solution applied. The thickness of the two layers of the laminate structure of carrier film and elastic layer is not critical. Advantageously the elastic layer thickness is approximately 20 to 30% of the total thickness of the composite film (carrier film/elastic layer). The composite film preferably has a thickness of approximately 5 to 50 micrometers, particularly 10 to 40 micrometers and in particularly preferred manner the thickness is 20 to 30 micrometers. For producing the ready-to-use ink ribbon according to the invention, the ink-releasing coating is applied to the remainig free side of the carrier film. It is possible to apply random ink pastes, optionally in solution and if a solvent is present the latter is evaporated to ultimately form the ink-releasing coating. The finished ink-releasing coating can be in the form of a plastic matrix with an oil-based ink paste dispersed therein and which contains dyes and/or ink pigments and optionally fillers and wetting agents, advantageous types being described in German patents 32 14 305 and 33 07 432. According to German patent 32 14 305 the oil base of the ink paste is a mineral oil containig 25 to 40% aromatic hydrocarbons, in which 30 to 40% of the saturated-bonded C-atoms are cycloaliphatically bonded. The advantageously used wetting agent belongs to the group of fatty amine salts. If fillers are used, they are preferably finely divided, storage-active fillers with a high inner surface. The viscosity of the ink paste contained in the ink-releasing coating is appropriately set to the range approximately 4,000 to 10,000 mPa.s (20°C). In order to obtain particularly favourable overstrike values with the ribbon according to the invention, use is advantageously made of the ink paste described in German patent 33 07 432. According to the latter the ink-releasing coating obtained after evaporating the solvent of an ink paste applied comprises a plastic matrix with an oily paste dispersed therein and containing carbon black and/or ot her ink pigments, as well as fillers with a large inner surface and with a particle size distribution of approximately 0.2 to 40, particularly 0.2 to 20 micrometers. The oil is a polyethoxylated fatty acid ester of a polyhydric alcohol and an excellent solvent for oil-soluble or fatty dyes. The polyethoxylated fatty acid ester is preferably an ester of fatty acids with approximately 12 to 25 C-atoms and alcohols with 3 to 6 OH-groups, approximately 20 to 60 ethoxy groups being contained in the molecule. Particular preference is given to a polyoxyethylene-(40)-sorbitan pentaoleate to octaoleate as the polyethoxylated fatty acid ester. Reference should be made to the aforementioned patent specification for further details. Diverging from the statements made in German patent 33 07 432 the filler proportion of the ink-releasing coating can be omitted if the ribbon is used in continuously filled cassettes and it can be placed in the cassette in a more or less loose loop form. Thus, unlike in the case of a spool there is no excessive pressing effect between the contacting ribbon surfaces. The inventive ribbons housed in continuously filled cassettes have a particularly high yield, if the ink paste is applied in a larger quantity, which is not prejudicial here, there being no sticking due to "oiling out". Prior to the formation of the ink-releasing coating, it is possible to apply an adhesive coating to the carrier film, particularly if extreme overstrikes are required. Particularly suitable materials for forming an adhesive coating are described in detail in German patent 28 25 344, to which reference is made. If the laminate structure is provided with such a coating giving adhesion and static characteristics is wound up, then a thin antistatic coating can also be formed on the elastic layer surface through the contact setting between the front and back of the laminate structure. This can be advantageous in certain cases. Such an antistatic coating can be separately applied to the elastic layer by conventional methods. It preferably has a thickness of approximately 1 to 10 micrometers, the range 2 to 7 micrometers being especially preferred. Different ink-releasing coatings of different colours can be applied in juxtaposed and successive manner on the ribbon according to the invention, so that the latter can be used for multicolour printing or typing. These can e.g. be the primary colours yellow, blue-green and purple-red making high-fidelity colour printing possible. It is also possible to provide a black strip, so that simultaneously normal characters can be printed. In order to supply high-fidelity multicolour prints, it is consequently appropriate to choose the three primary colours yellow, blue-green and purple-red. Therefore colour pictures, which are very similar to a colour original can be reproduced on a copy sheet or page by producing images corresponding to the particular colour signals produced by the colour separation of the original with separation filters, i.e. blue, green and red three-colour filters. The invention is described in greater detail hereinafter relative to the drawings, wherein show: Fig. 1 An inventive ink ribbon for multicolour printing. Fig. 2 A detail of the ribbon according to fig. 1. According to fig. 1 the ink ribbon 1 has an elastic layer 2 formed from a crosslinked synthetic rubber (polyurethane), a carrier film 3 and an ink-releasing coating 4. The latter is subdivided into strips 5a, 5b, 5c and 5d, strips 5a, 5b and 5c having the three primary colours, yellow, purple-red and blue-green, whilst the final colour strip 5d is black. Fig. 2 is a detail enlargement of colour strip 5a, which comprises a plastic matrix 7, which contains a homogeneous ink paste 5′ and incorporated carbon black particles 5 and is applied to a polyester (polyethylene terephthalate) carrier film 2. Ink paste 5′ contains the fatty dye Sudan deep black (C.I. 26150) dissolved in polyoxyethylene sorbitan septaoleate with approximately 40 ethoxy groups per molecule. The inventive ribbon has numerous advantages. Compared with the known products of the same film thickness, it is able to longer withstand the needle pressure of the needle printing sytem, because the needles do not directly strike the carrier film and are instead cushioned by the elastic layer. Therefore perforations and deformations are largely prevented. As a result of the elastic coating the ribbon is better and moe reliably passed in a cassette for continuous drive purposes. As a result of the aforementioned damping of the needle action, the needles are subject to reduced wear and the print head of the matrix printing system is given a longer life. There is a further advantage compared with a cloth ribbon that the needles no longer pass into the ribbon and therefore do not carry ink with them on retraction. As a result of the better ductility obtained, better defined printing and higher marginal definitions are obtained. This also leads to a better "dot definition", because the elastic layer material is directly adapted to the surfaces of the needles of the matrix printing system. The inventive ribbon can be used for black prints and colour prints with equally advantageous results. The hitherto known systems employing a cloth ribbon as the carrier can be constructed as follows. The ink strips in the cloth ribbon can be juxtaposed, but also successively arranged in order to produce high fidelity colour copies. To permit a better explanation reference is made to the last mentioned embodiment of the known cloth ribbon. This cloth ribbon is generally partly wound onto a first reel and partly onto a second reel, where there are three ink-releasing coatings with the particular primary colours following one another. In the case of a colour cloth ribbon a special linking of the strips is necessary. If the ribbon is e.g. made from Nylon, bonding is necessary at the connecting points and an intermediate portion must be provided so that the colours do not pass into one another. This bonding or welding is labour-intensive and the intermediate portion can be prejudicial during colour printing. The other aforementioned deficiencies of cloth ribbons also occur here. An advantageous use of the inventive ribbon is based on the finding that a single unitary carrier film with the three differently coloured and successive ink coatings, i.e. with the three primary colours is provided, without the aforementioned disadvantageous connecting measures being necessary. When producing this colour film for colour printing, it is also possible to proceed in such a way that three different "Jumbo" ribbons are permanently bonded with a single adhesive using the inventive principle. The time taken for bonding is roughly 1/10 of that necessary for welding the colour strips of the known Nylon cloth ribbon. The advantages of the inventive ribbon are apparent even when it is not in the form of an elongated ribbon or tape, but also in the form of a sheet or blanket. It might be assumed that there is no need for the actual carrier film and that e.g.a hard rubberlike layer could be suitable as the carrier. However, it has been found that this does not lead to the desired results, because such carriers are too soft to fulfil the necessary functions in the cassette. Admittedly the thickness of the elastic layer could be increased, but this would have to take place to such an extent that there would no longer be the desired elasticity with respect to the needle action. There would also be a deterioration to the printing definition. A purely rubber layer would also lead to the difficulty of adequately firmly binding the ink-releasing material, even when using an adhesion-imparting layer. In addition, the oil of the ink-releasing coating would partly migrate into the elastic layer. The invention is further illustrated hereinafter by means of a pr oduction example. Example 20 parts by weight of a polyurethane resin (trade name "Desmolac 2100") were mixed with 80 parts by weight of methyl ethyl ketone, to which was added 1 part by weight of a NCO-isocyanurate (marketed by Bayer AG, Leverkusen under the name "Haftvermittler 2005"). This solution was applied to a 10 micrometers thick polyethylene terphthalate carrier in a quantity such that after evaporating the methyl ethyl ketone, the elastic layer was formed in a thickness of 10 micrometers, so that the composite film had a total thickness of 20 micrometers. The following mixture was then applied to the carrier film for forming the ink-releasing coating: mixture of 18.1 parts by weight of polyoxyethylene sorbitan septaoleate (with on average 40 ethoxy groups per molecule), 9.6 parts by weight of oil-soluble black (C.I. 26150) (30% in the above polyoxyethylene sorbitan septaoleate), 2.3 parts by weight of tallow oil diaminooleate, 2.1 parts by weight of blue pigment (C.I. 42765-1), 7.0 parts by weight of carbon black, 45.3 parts by weight of polyvinyl chloride/acetate (25% in methyl ethyl ketone), 8.8 parts by weight of filler (diatomaceous earth), 15 parts by weight of methyl ethyl ketone and 21.6 parts by weight of toluene. By applying this mixture and by evaporating the solvent (methyl ethyl ketone or toluene) an ink-releasing coating approximately 16 micrometers thick was formed on the above laminate film. When used in matrix printing systems the ribbon produced in the above manner does not cause perforations and deformations even when used for a long time, whilst giving excellent printing definitions.

Claims: Overlappingly overstrikable ink ribbon for matrix or needle printing systems with a carrier film and at least one ink-releasing coating, as well as optionally further conventional intermediate coatings, characterized in that a layer (2) of an rubber-elastic material is formed on the side of the needle impression. Ribbon according to claim 1, characterized in that different coloured, ink-releasing coatings (5a, 5b, 5c, 5d) are arranged in juxtaposed or succeeding manner. Ribbon according to claims 1 or 2, characterized in that the elastic layer (2) constitutes approximately 20 to 30% of the total thickness of the composite film (carrier film / elastic layer). Ribbon according to claim 3, characterized in that it is approximately 15 to 60 micrometers thick. Ribbon according to one of the preceding claims, characterized in that the elastic layer comprises a crosslinked rubber or a thermoelastic elastomer. Ribbon according to one of the claims 1 to 5, characterized in that a laminating adhesive coating is placed between the carrier film and the elastic layer (2). Ribbon according to claim 6, characterized in that the laminating adhesive coating has a thickness of approximately 3 to 10 micrometers. Process for producing an overlappingly overstrikable ribbon according to one of the claims 1 to 7, characterized in that the starting materials for the elastic layer (2) and the carrier film (3), which during or after extrusion are subject to crosslinking or are thermoplastically deformable, are coextruded and subsequently the ink-releasing coating is applied in a conventional manner.

Inventors: HOGARTH, IAN, MACKINTOSH, CHRISTINE, PAFFHAUSEN, HANS, SCOTT, ANDREW
Applicants: CARIBONUM LIMITED
Application year: 1987
Main classification: B41J31
IPC codes: B41J31, B41M5, B32B7, B32B25