INKING DEVICE AND PRODUCTION THEREOF

Abstract: According to the present invention, an ink delivery roller is formed of a core metal and a base material layer (11) which is formed on the peripheral surface of the core metal and is made of rubber or resin, a large number of substantially semi-spherical recesses (12) are formed on the surface of the base material layer (11) and a large number of very small hol­ low spherical members (13) are buried in the base material (11). Accordingly, even when the surface of the delivery roller is worn out, spherical recesses appear afresh and the surface condition stays unchanged, thus keeping printing quali­ ty stable. Thus the invention provides an economical inking device having a long service life and a method of producing the same. ABSTRACT According to a printing machine ink roller and a method of the invention for manufacturing the same, a surface layer (18) consisting of a synthetic resin or a rubber-like material, which has ink absorbency and which allows surface polishing, is arranged on a surface of a mandrel, a large number of substantially spherical particles are mixed in the surface layer (18), and a large number of independent projections (16) are formed by partially exposing predetermined substantial par­ ticles in a surface region (17) of the surface layer (18). The ink roller can maintain a function of trans­ ferring a predetermined amount of ink for a long period of time so that the performance of a printing machine can thus be improved, and such a printing machine can be very easily manufactured and repaired.

Description: The present invention relates to an inking unit for use in a printing machine, and also to a method of manufacturing this inking unit. Recently so-called "keyless" printing machines, which have no buttons to operate in order to control the ink-supplying rate, are used in place of conventional printing machines which have a number of ink-supply control buttons which only a skilled person can appropriately operate to control the rate of supplying ink to the ink transfer rollers such that a sheet of paper is printed in a uniform density. This is partly because the keyless printing machine is less expensive than the conventional one, and partly because no skilled labor is required to operate the keyless printing machine. The keyless printing machine will be described, with reference to Fig. 1. As is shown in Fig. 1, the keyless printing machine comprises ink pan 1 containing ink 2, and an ink fountain roller 4 with its lower part being immersed in ink 2. The machine further comprises anilox roller 5 located above ink fountain roller 4 and contacting therewith, doctor blade 6 arranged in contact with anilox roller 5, plate cylinder 7 provided above anilox roller 5, and two inking rollers 8 each arranged in contact with roller 5 and plate cylinder 7. Ink fountain roller 4 is rotated, thereby to transfer ink from ink pan 1 onto anilox roller 5. Doctor blade 6 is operated to remove an excess of ink 2 from anilox roller 5. Thus, an appropriate amount of ink is transferred from roller 5 onto both inking rollers 8 as roller 5 rotates in contact with inking rollers 8. Inking rollers 8 transfers ink 2 onto plate cylinder 7 as rollers 8 rotate in contact with plate cylinder 7. Anilox roller 5 comprises a core roller (not shown) and a matrix layer (not shown, either) formed on the periphery of the core roller. The matrix layer is made of either ceramics (e.g., alumina ceramics or tungsten carbide) or a soft metal. A number of patterned cells or depressions 5a, which are quadrangular pyramid-shaped as is shown in Fig. 2B, are made in the surface of the layer as is illustrated in Fig. 2A. Alternatively, a number of cells 5b, which are shaped like quadrangular frustrum pyramid shaped as is shown in Fig. 3B, are made in the surface of the matrix layer as is illustrated in Fig. 3A. These cells 5a or 5b are formed by applying a laser beam onto the layer when the layer is made of ceramics, or by rolling a matrix roll, which has a number of projections, on the layer when the later is made of a soft metal. This anilox roller acts as ink metering and transfer roller. The conventional keyless printing machine and anilox roller have the following drawbacks. (1) The machine is expensive when the cells of anilox roller 5 are formed by means of a special apparatus such as a laser. (2) The cells may have different sizes when formed by means of a laser, due to changes in the intensity of the laser beam emitted by the laser. The cells may have different shapes when formed by means of a matrix roll. In either case, the machine cannot print a sheet of paper in an uniform density. (3) As the outer layer of the anilox roller is worn by the doctor blade, the shapes of the cells will change. Hence, the lifetime of the roller is short. DE-A-2 8 56 088 discloses an inking unit which comprises an ink fountain roller having a mantle of foamed, ink accepting plastic material. The mantle is provided with uniformly distributed small pores which at the surface layer are open to the outside. The open pores are being filled with ink which is then transferred to a plate cylinder. Accordingly it is the object of the present invention to provide an inking unit which has an anilox roller always having spherical cells in its periphery even if the periphery is worn, and which is inexpensive, and which has a long lifetime, and also to provide a method of manufacturing this inking unit. According to the present invention, there is provided an inking unit comprising an ink pan (1), an ink fountain roller (4) for forming an ink layer on its periphery, at least one inking roller (8) arranged in contact to an ink transfer roller (5) for transferring the ink from the ink fountain roller (4) onto the inking roller (8) such that the inking roller (8) supplies the ink to a plate cylinder (7) and a doctor blade (6) located near the ink transfer roller (5) for removing an excess of the ink from the periphery of the ink transfer roller (5), a number of depressions (12) being provided in the surface of the ink transfer roller (5), which is characterized in that said ink transfer roller (5) comprises a core roller and a matrix layer (11) made of a mixture of an elastomer or a resin and a number of hollow microballoons (13) of predetermined diameter and formed on the periphery of the core roller, said number of hollow microballoons (13) being embedded within said matrix layer (11), said depressions (12) being substantially hemispherically and formed by opening said hollow microballoons (13) by grinding the surface of said matrix layer (11). Further, according to the present invention, there is provided a method of manufacturing an inking unit comprising an ink pan, an ink fountain roller for forming an ink layer on its periphery, at least one inking roller arranged in contact to an ink transfer roller for transferring the ink from the ink fountain roller onto the inking roller such that the inking roller supplies the ink to a plate cylinder, and a doctor blade located near the ink transfer roller, for removing an excess of the ink from the periphery of the ink transfer roller, said method being characterized in that the process of manufacturing said ink transfer roller comprises the steps of: adding a hardener and hollow microballoons of predetermined diameter to a material whose main component is a resin or elastomer, and mixing the hardener, hollow microballoons, and the material, thereby forming a mixture; pouring the mixture into a mold containing a core roller, and hardening the mixture, thereby forming a matrix layer, which contains the hollow microballoons, on the periphery of the core roller; and grinding said matrix layer such that substantially hemispherical depressions are formed in the surface of said matrix layer by opening the hollow microballons. It is desirable that the material of the matrix layer be resistant to ink and detergent. The material may be an elastomer such as acrylonitrile butadiene rubber, urethane rubber, chloroprene rubber, epichlorohydrin rubber, fluoroelastomer, silicone rubber, acrylic rubber, or chlorosulphonated polyethylene. Alternatively, it may be a synthetic resin such as polyurethane resin, epoxy resin, polyester resin, nylon resin, vinyl chloride resin, phenol resin, urea resin, diallyl phthalate resin, polyamide resin, or polyamideimide resin. The material must be one which mixes well with the hollow microballoons and does not thermally set at 10 to 80°C. Also, it should preferably have a hardness ranging from 10 to 100 as measured by the JIS.A hardness tester, or a hardness ranging from 70 to 90 as measured by the Shore D durometer. The hollow microballoons, which will form the depressions, are made of either an inorganic material or an organic material. The inorganic material may be, for example, alumina, silica, aluminosilicate, glass or ceramics. The organic material may be, for example, polyvinylidene chloride or phenol resin. The hollow microballoons should have a diameter of 5 to 100 µm, preferably 20 to 80 µm. If the diameter is less than 5 µm, the ink will be supplied from the ink transfer roller to the inking roller in an insufficient amount, and the sheet of paper will be inevitably printed in too low a density. Conversely, if the diameter exceeds 100 µm, the ink will be supplied from the ink transfer roller to the inking roller in an excessive amount, and the sheet of paper cannot be printed in an uniform density. The matrix layer may contain copper powder, copper alloy made of brass powder, or bronze powder, so as to increase ink affinity. It is preferable that the powder be used in an amount ranging from 50 to 400 parts by weight per 100 parts by weight of the layer whose main component is an elastomer or a synthetic resin. It is preferable that hollow microballoons be used in an amount ranging from 10 to 400 parts by weight per 100 parts by weight of the layer whose main component is an elastomer or synthetic resin. If the hollow microballoons are used in an amount of less than 10 parts by weight, less depressions than necessary will be formed in the surface of the matrix layer, and the ink transfer roller will not be able to hold a sufficient amount of ink. If the hollow microballoons are used in an amount of more than 400 parts by weight, more depressions than necessary will be formed in the surface of the matrix layer, and the ink transfer roller will not be able to hold an appropriate amount of ink. Various methods can be performed to form the matrix layer on the periphery of the core roller. Among these methods are: cast molding, rotational molding, sheet-winding, reaction injection molding (RIM), and flame spraying. The cast molding method is used when the material of the matrix layer is available in the form of a liquid. In this method, the material, the hollow microballoons, and a hardener are mixed, thus forming a mixture. The mixture is degassed. An adhesive is coated on a core roller. The adhesive-coated core roller is set in place within a mold. The degassed mixture is poured into the mold and is allowed to stand until it becomes sufficiently hard, thus forming a matrix layer on the core roller. After this, the matrix layer is ground, whereby hollow hemi-spherical depressions are formed in the surface of the matrix layer. As a result, the ink transfer roller is made. The rotational molding method is also employed when the material of the matrix layer is available in the form of a liquid. In this method, a hollow cylindrical mold is used. The inner periphery of mold is polished, and the polished inner periphery of the mold is coated with a mold-releasing agent. Then, a measured amount of the mixture, which is identical to that used in the cast molding method, is poured into the cylindrical mold. The mold is spinned for a prescribed time, while the mixture is being hardened at a predetermined temperature. As a result, a matrix layer is formed on the inner periphery of the hollow cylindrical layer. The matrix layer, which is in the form of a hollow cylinder, is released from the mold, and its inner periphery is polished. A core roller is inserted into the cylinder of the matrix layer. The resultant structure is subjected to shrink fitting. Thereafter, the outer surface of the matrix layer is ground, whereby hemi-spherical depressions are formed in the surface of the matrix layer. As a result, the ink transfer roller is made. The sheet-winding method is used when the material of the matrix layer is available in the form of a solid which has been prepared by mixing the hollow microballoons, a cross-linking agent, and necessary additives such as a processing aid, with an elastomer or a synthetic resin, kneading the resultant mixture with a mixing roller, and calendering or injection-molding the kneaded mixture into a sheet. In the sheet-winding method, the sheet is wound around the core roller. The roller is heat-treated, thereby forming a matrix layer integral with the core roller. Then, the surface of the matrix layer is ground, whereby hemi-spherical depressions are formed in the surface of the matrix layer. As a result, the ink transfer roller is made. In the method of making the ink transfer roller, use is made of either a grinding stone or a grinding cloth in order to grind the outer surface of the matrix layer. The present invention has been made on the basis of the following finding of the inventors. As has been described, in a keyless printing machine, the ink fountain roller supplies ink from the ink pan to the ink transfer roller, the doctor blade removes an excess of ink from the ink transfer roller, an appropriate amount of ink is thus transferred from the inking rollers, and the ink is supplied from the inking rollers onto the plate cylinder. To transfer an appropriate amount of ink to the inking rollers, the ink transfer roller must have depressions in its surface. In addition, in order to transfer the ink to the inking roller in an uniform distribution all over the periphery of either inking roller, the depressions must be evenly distributed on the surface of the ink transfer roller. Therefore, the inventors worked together to find the best possible method of forming depressions in an uniform distribution all over the surface of the ink transfer roller. The first method they proposed is to add a blowing agent to the main component of the material of the matrix layer, i.e., an elastomer or a synthetic resin, then to heat the material to a temperature above the decomposition point of the blowing agent, thus causing the elastomer or resin to generate nitrogen gas and forming micropores in the matrix layer, and finally to grind the surface of the matrix layer, thus forming depressions in the surface of the layer. However, this method has several problems. First, it is difficult to harden and foam the material at appropriate speeds. If the material is hardened faster than it is foamed, the resultant micropores are too small. Conversely, if the material is foamed faster than it is hardened, the resultant micropores are too large. Secondly, if the foaming proceeds excessively, micropores will aggregate, inevitably forming elongated pores, into which ink will remain adversely. Thirdly, it is difficult to control the foaming of the material such that depressions having a desired size are formed. The inventors at last invented a new method which solves the problems inherent in the method explained above. In this new method, hollow microballoons having a predetermined diameter are embedded in the matrix layer, and the surface of the layer is ground until depressions are formed in the surface of the layer. Fig. 1 is a schematic representation of a conventional inking unit; Figs. 2A and 2B are diagrams showing the depressions formed in the periphery of the anilox roller used in a conventional keyless printing machine; Figs. 3A and 3B are diagrams showing the depressions formed in the periphery of the anilox roller used in another prior art keyless printing machine; Fig. 4 is a diagram schematically showing a printing machine in which an inking unit according to the invention is used; Fig. 5 is a sectional view of the ink transfer roller of the inking unit according to the present invention; and Fig. 6 is a diagram schematically showing a printing machine in which another type of an inking unit according to the invention is incorporated. Embodiments of the present invention will now be described. Example 1 One hundred parts by weight of an epoxy resin (tradename: Araldite AY103 manufactured by Ciba-Geigy) and 5 parts by weight of silica used as nonsagging agent (tradename: Carplex #80 manufactured by Shionogi Seiyaku) were mixed for 5 minutes by means of a paint mill, thus forming a mixture. Then, this mixture and 30 parts by weight of hollow microballoons made of aluminosilicate (tradename: Fillite manufactured by Fillite, Inc.) and having an average diameter of 45 µm were mixed and stirred. A steel core roller, which had been scaled by means of sand blasting or a similar method, was degreased with trichloroethylene and inserted into a hollow cylinder having an inside diameter 20 mm greater than the diameter of the core roller. The core roller was placed concentric to the hollow cylinder, by means of jigs. The lower end of the cylinder was closed with a cover. Then, 17 parts by weight of a hardener (tradename: Hardener HY956 manufactured by Ciba-Geigy) was added to the mixture containing the hollow microballoons. The hardener and the mixture were stirred together. After taking off the foam of the mixture, the mixture was poured into the gap between the core roller and the cylinder. The upper end of the cylinder was closed with a cover, and the mixture within the cylinder was allowed to stand for 24 hours, whereby the mixture was hardened, thus forming a resin layer on the periphery of the core roller. The core roller, with the resin layer formed on its periphery, was released from the cylinder. The resin layer was ground by the known method, thus forming an anilox-like roller 5 having a matrix layer whose thickness was 8 mm and which had a cross section illustrated in Fig. 5. As is shown in Fig. 5, hemi-spherical depressions 12 were formed in resin layer 11, and hollow microballoons 13 were formed within resin layer 11. The surface hardness of this anilox roller-like was measured by the Shore D durometer; it was 80. Another identical anilox-like roller was also manufactured in the same way. This ink transfer roller was incorporated into the keyless printing machine shown in Fig. 4. The printing machine was operated to print sheets of papers. The prints were clearer than those made by the keyless printing machine provided with the conventional anilox rollers. Example 2 First, the following components were thoroughly kneaded by means of a mixing roll: a. Acrylontrile butadiene rubber (tradename: JSRN230 S, Nippon Gosei Gomu Co., Ltd.) 100 parts by weight Zinc oxide 5 parts by weight Sulfur 2 parts by weight Organic accelerator (tradename: Nocceler CZ, Ohuchi Shinko Kagaku) 1 parts by weight Organic accelerator (tradename: Nocceler D, Ohuchi Shinko Kagaku) 0.5 parts by weight Stearic acid 0.5 parts by weight Antioxidant (tradename: Nocrac 224S, Ohuchi Shinko Kagaku) 1 parts by weight Silica (tradename: Carplex #80, Shionogi Seiyaku, Co., Ltd.) 5 parts by weight HAF carbon black (tradename: Asahi #70, Asahi Carbon Co., Ltd.) 50 parts by weight Factice (tradename: Black Sub, Tokyo Sub Co., Ltd.) 5 parts by weight D.O.P. (tradename: Vinysyzer #80, Kao Co., Ltd.) 10 parts by weight Total: 180 parts by weight Then, 30 parts by weight of hollow microballoons which have an average diameter of 40 µm, were mixed with the kneaded mixture, by means of the mixing-roll apparatus. The microballoons were made of foamable polyvinylidene chloride (tradename: Expancel DE, manufactured by Expancel, Inc.). Care was taken not to reduce the gap between the rolls of the apparatus too much, lest the microballoons should be crushed. The resultant mixture was extruded by means of an extruder, thus forming a tube having an inside diameter of 130 mm and an outside diameter of 155 mm. Core roller was descaled and degreased. The tube, was mounted on a core roller coated with a phenol-based coating. Cotton tape was wound around the roller to prevent the tube from flowing when it is softened while being vulcanized. The roller was placed in a vulcanizer. In this vulcanizer, the tube was vulcanized by the known method. The roller was removed from the vulcanizer, and then cooled. The cooled roller was ground until its outside diameter decreased to 150 mm. As a result, an ink transfer roller 5 was manufactured which had spherical depressions 12 formed in its surface and hollow microballoons 13 embedded in it, as is illustrated in Fig. 5. The kneaded mixture prepared before mixing the hollow microballoons exhibited a hardness of 40 as was measured by a JIS.A hardness tester. Another identical ink transfer roller 5 was also manufactured in the same way. This ink transfer roller was installed into the keyless printing machine shown in Fig. 6. The printing machine was operated to print sheets of papers. The prints were clearer than those made by the keyless printing machine provided with the conventional anilox rollers. It was thus ascertained that rollers 5 transferred a proper amount of ink to the inking rollers, just as did the ink transfer rollers of Example 1. Ink transfer roller 5 of either inking unit according to the invention comprises a core roller and matrix layer 11 made of an elastomer or a resin and having a number of hemi-spherical depressions 12 formed in its surface and a number of hollow microballoons 13 embedded in it. As the matrix layer 11 is gradually worn as roller 5 is used, hollow microballoons 13 open in the surface of layer 11, thus forming new hemi-spherical depressions. Hence, spherical depressions 12 are always distributed uniformly in the surface of matrix layer 11 and hold a prescribed amount of ink. Ink transfer roller 5 therefore transfers ink in a desired amount onto the inking rollers of a keyless printing machines, in a uniform distribution all over the peripheries of the inking rollers, thereby serving to achieve high-quality printing. As has been described, the present invention provides an inking unit and a method of manufacturing the same. The inking unit comprises an ink transfer roller whose surface condition remains unchanged even if its surface is worn, since new spherical depressors are formed in the surface as the surface is worn gradually. The inking unit is therefore suitable for use in various types of printing machines, such as flexographic, offset, and relief printing machines.

Claims: An inking unit comprising an ink pan (1), an ink fountain roller (4) for forming an ink layer on its periphery, at least one inking roller (8) arranged in contact to an ink transfer roller (5) for transferring the ink from the ink fountain roller (4) onto the inking roller (8) such that the inking roller (8) supplies the ink to a plate cylinder (7) and a doctor blade (6) located near the ink transfer roller (5) for removing an excess of the ink from the periphery of the ink transfer roller (5), a number of depressions (12) being provided in the surface of the ink transfer roller (5), characterized in that said ink transfer roller (5) comprises a core roller and a matrix layer (11) made of a mixture of an elastomer or a resin and a number of hollow microballoons (13) of predetermined diameter and formed on the periphery of the core roller, said number of hollow microballoons (13) being embedded within said matrix layer (11), said depressions (12) being substantially hemispherically and formed by opening said hollow microballoons (13) by grinding the surface of said matrix layer (11). The inking unit according to claim 1, wherein said matrix layer (11) is made of a material selected from the group consisting of acrylonitrile butadiene rubber, urethane rubber, chloroprene rubber, epichlorohydrin rubber, fluoroelastomer, silicone rubber, acrylic rubber, chlorosulphonated polyethylene, polyurethane resin, epoxy resin, polyester resin, nylon resin, vinyl chloride resin, phenol resin, urea resin, diallyl phthalate resin, polyamide resin, and polyamide-imide resin. The inking unit according to claim 1, wherein said substantially hemi-spherical depressions (12) and said hollow microballoons (13) have a diameter ranging from 5 to 100 µm. The inking unit according to claim 1, wherein said hollow microballoons (13) are made of a material selected from the group consisting of alumina (Aℓ₂O₃), silica (SiO₂), aluminosilicate, glass, and ceramics. The inking unit according to claim 4, wherein said hollow microballoons are made of polyvinylidene chloride or phenol resin. The inking unit according to claim 1, wherein the surface region of said matrix layer contains copper powder, copper alloy made of brass powder, or bronze powder. The inking unit according to claim 1, wherein said hollow microballoons are embedded in said matrix layer at a depth of at least 2.5 µm from the surface of said matrix layer. A method of manufacturing an inking unit comprising an ink pan, an ink fountain roller for forming an ink layer on its periphery, at least one inking roller arranged in contact to an ink transfer roller for transferring the ink from the ink fountain roller onto the inking roller such that the inking roller supplies the ink to a plate cylinder, and a doctor blade located near the ink transfer roller, for removing an excess of the ink from the periphery of the ink transfer roller, said method being characterized in that the process of manufacturing said ink transfer roller comprises the steps of: adding a hardener and hollow microballoons of predetermined diameter to a material whose main component is a resin or elastomer, and mixing the hardener, hollow microballoons, and the material, thereby forming a mixture; pouring the mixture into a mold containing a core roller, and hardening the mixture, thereby forming a matrix layer, which contains the hollow microballoons, on the periphery of the core roller; and grinding said matrix layer such that substantially hemi-spherical depressions are formed in the surface of said matrix layer by opening the hollow microballons. The method according to claim 8, wherein said matrix layer is made of a material selected from the group consisting of acrylonitrile butadiene rubber, urethane rubber, chloroprene rubber, epichlorohydrin rubber, fluoroelastomer, silicone rubber, acrylic rubber, chlorosulphonated polyethylene, polyurethane resin, epoxy resin, polyester resin, nylon resin, vinyl chloride resin, phenol resin, urea resin, diallyl phthalate resin, polyamide resin, and polyamide-imide resin. The method according to claim 8, wherein said substantially hemi-spherical depressions and said hollow microballoons have a diameter ranging from 5 to 100 µm. The method according to claim 8, wherein said hollow microballoons are made of a material selected from the group consisting of alumina (Aℓ₂O₃), silica (SiO₂), aluminosilicate, glass, and ceramics. The method according to claim 8, wherein said hollow microballoons are made of polyvinylidene chloride or phenol resin. The method according to claim 8, wherein the surface region of said matrix layer contains copper powder, copper alloy made of brass powder, or bronze powder. The method according to claim 13, wherein said copper powder, copper alloy made of brass powder or bronze powder is used in an amount of 50 to 400 parts by weight per 100 parts by weight of the resin or elastomer which is the main component of said matrix layer. The method according to claim 8, wherein said hollow microballoons are used in an amount of 10 to 400 parts by weight per 100 parts by weight of the resin or elastomer which is the main component of said matrix layer.

Inventors: ISHIBASHI NOBUYUKI, SONOBE SABURO, ISHIBASHI, NOBUYUKI, SONOBE, SABURO
Applicants: KINYOSHA KK, KINYOSHA CO. LTD.
Application year: 1988
Main classification: B41N7
IPC codes: B41N7