Dampening water feed roller for planographic printing press

Abstract: A dampening water feed roller, characterized by a process of manufacture which comprises forming a flame sprayed layer of a ceramic material composed of 100 to 0% by weight of Al₂O₃ and 0 to 100% by weight of TiO₂ on the peripheral surface of a metallic roller, subjecting the flame sprayed ceramic layer to a pore-occluding treatment with a hydrophilic SiO₂ type inorganic pore-occluding agent, and grinding the treated layer to surface roughness of not more than 1.6 S, and which permits supply of the dampening water without using the additives such as isopropyl alcohol in the dampening water.

Description: This invention relates to such dampening water feed rollers as a master water roller and a water spreading roller which are used in a continuous water feed device in a planographic printing press. The planographic printing is a process of printing which utilizes the nature of an oily ink to repel water and uses a printing plate having an oleophilic picture formed on a hydrophilic base. The printing is effected by indirect printing of the so-called offset printing technique which comprises alternately feeding water and ink to the plate surface, causing the ink selectively adhering to the picture portion of the plate surface to be transferred tentatively to a blanket, and transferring the ink from the blanket to an object of printing. The printing press to be used for the planographic printing, therefore, is inherently provided with a dampening mechanism for feeding water to the non-picture portion of the printing plate and an inking mechanism for feeding ink to the picture portion. A notable example of the existing dampening mechanism is configured as follows. This dampening mechanism is provided with a metallic master water roller rotated as partly dipped in a water supply pan disposed underneath, a metering roller of rubber and a water applying roller of rubber severally held in contact with the master water roller. In this mechanism, the water adhering to the surface of the master water roller and consequently ascending with the rotation of this roller is deprived of an excess portion thereof in consequence of its contact with the metering roller. The remaining, owing to the contact of the master water roller and the water applying roller, transferred to the water applying roller. The water applying roller, on contact with the plate cylinder, passes the water to the non-picture portion of the surface of plate cylinder. The water which remains after failure to adhere to the surface of the plate cylinder is returned from the plate cylinder back to the water supply pan through the medium of the interveing rollers. Another dampening mechanism comprises a metallic water discharging roller rotated as partly dipped in a water supply pan installed underneath, a water transferring roller of rubber held in contact with the water discharging roller, a metalic water spreading roller held in contact with the water transferring roller, and a water applying roller of rubber held in contact with the water spreading roller. In this dampening water mechanism, the water adhering to the surface of the water discharging roller and consequently ascending from the water supply pan with the rotation of the water discharging roller is deprived of an excess portion thereof during the course of transfer through the medium of the water discharging roller and the water spreading roller, then guided to the water applying roller, and passed from the water applying roller to the non-picture portion of the surfaces of the plate cylinder with which the water applying roller comes into contact. The water which remains after failure to reach the picture portion of the surface of the plate cylinder is returned from the plate cylinder back to the water supply pan through the medium of the intervening rollers. As described above, the dampening mechanism, owing to the alternate arrangement of rubber rollers and metallic rollers, is enabled to feed the water in the water supply pan to the non-picture portion of the plate cylinder and return the water remaining after failure to reach the picture portion back to the water supply pan through the medium of the intervening rollers. It has been heretofore customary for the metallic rollers used in the dampening mechanism of the planographic printing press to have their surfaces coated with a hard chromium plating to acquire improved proofness against corrosion and abrasion and enhanced affinity for water. In spite of the hard chromium plating of the nature described above, such metallic rollers as the master water roller and the water spreading roller which are used in the dampening mechanism are still deficient in hydrophilicity and water-retaining property and, therefore, entails the following difficulties in printing. The water film on these rollers draws into drops or loss uniformity and impairs the uniformity of density of the ink film on the plate cylinder; the uniformity of supply of the dampening water is disrupted and, as the result, the so-called halftone of the picture portion is deprived of definition; and the dampening water is not fed sufficiently to the non-picture portion of the plate and, as the result, the ink is suffered to adhere to the non-picture portion and smear the plate surface. Further, when the water which remains after failure to reach the picture portion of the plate cylinder is returned to the water supply pan through the medium of the intervening rollers as described above, the ink on the picture portion of the plate cylinder is partly entrained by the water applying roller and passed in the form of emulsified ink to the surfaces of the rollers. Since these metallic rollers are deficient in hydrophilicity, they do not manifest the action of repelling the emulsified ink sufficiently and consequently suffer from fast deposition of the emulsified ink. Once the ink is deposited fast, the supply of the dampening water to the non-picture portion of the plate can no longer be continued. Thus, the non-picture portion of the plate is smeared with the adhering ink. For the plate cylinder to provide fine printing at all times, therefore, the printing press must be stopped periodically to permit cleaning of the defiled plate surface. From this point of view, the idea of incorporating isopropyl alcohol or other similar alcohol and a surfactant in the dampening water thereby lowering the waters ′ surface tension and enhancing the waters' ability to wet the metallic rollers has found acceptance. The incorporation of such substances as alcohol and surfactant in the dampening water, however, adds to cost and jeopardizes the hygienic condition of the workshop environment and causes the undesirable phenomenon of swelling in the rubber rollers which are exposed to the dampening water. Japanese Utility Model Publication SHO 55(1980)-14,518 discloses a water spreading roller having a porous layer formed on the surface of a steel pipe or stainless steel pipe by the flame spraying of ceramic and Japanese Utility Model Unexamined Publication SHO 62(1987)-116,869 discloses a master water roller having a layer of an oxide type ceramic formed by plasma flame spraying. These rollers merely have layers formed on metallic pipes by the flame spraying of ceramic. These layers are claimed to possess a porous surface. As recited in Japanese Utility Model Publication SHO 55(1980)-14,518, the porosity of surface is aimed at enhancing the rollers' water-retaining property. The enhancement of the water-retaining property due to the porous ceramic coating, however, is excessive for the master water roller or the water spreading roller. The water is suffered to ascend overly to the plate cylinder and the ink is renfered susceptible to emulsification. Since the master water roller and the water spreading roller are rotated as held in contact with the water applying roller, the ink adhering to the surface of the water applying roller permeates into the pores of the ceramic coating on the rollers and manifests an action of repelling water and impairs the hydrophilicity required of these rollers. Thus, the stable supply of the dampening water can be no longer be attained unless the dampening water incorporates therein an alcohol. Japanese Utility Model Unexamined Publicaiton SHO 62(1987)-116,868 discloses a dampening roller provided with a coating layer of an oxide type ceramic composed of 40 to 80% by weight of Cr₂O₃, 10 to 30% by weight of Al₂O₃ , and 10 to 30% by weight of SiO₂ and Japanese Utility Model Unexamined Publication SHO 62(1987)-136,353 discloses a dampening roller having a layer of an oxide type ceramic formed by plasma flame spraying and having the porous part of the flame sprayed layer occluded with an oxide type ceramic coating agent composed of 40 to 80% by weight of Cr₂O₃, 10 to 30% by weight of Al₂O₃ , and 10 to 30% by weight of SiO₂. These dampening rollers have a surface layer formed of a compact oxide complex ceramic material using Cr₂O₃ as a matrix or a surface layer formed of an oxide ceramic material by flame spraying and additionally have the pores in the surface layer occluded with a coating agent, so as to acquire enhanced hydrophilicity owing to the use of a ceramic layer on the surface. The Cr₂O₃ ceramic substance has no conspicuous effect in improving the rollers wettability with water. Even by the use of rollers of such a structure, the dampening mechanism cannot be operated satisfactorily when the dampening water incorporates absolutely no alcohol therein. Moreover, the oxide composite ceramic layer of compact texture using Cr₂O₃ as a matrix is expensive because the production thereof requires the immersion in the Cr₂O₃ slurry and the heating to 400° to 500°C to be alterantely repeated several to ten-odd times. Metals Handbook, Ninth Edition, Volume 5, American Society for Metals, Metals Part, Ohio (1982), "Ceramic Coating", page 532 to 547 discloses that ceramic coatings can be deposited by flame spraying a refractory oxide whose melting point is below 2760°C. These include materials such as aluminium oxide and titanium oxide. An object of this invention, therefore, is to provide a novel dampening water feed roller. Another object of this invention is to provide an inexpensive dampening water feed roller excellent in wettability with water and incapable of entraining the ink. A further object of this invention is to provide a dampening water feed roller which has no use for the incorporation of alcohol in the dampening water, permits stable supply of tile dampening water, and ensures production of prints of high quality. Yet another object of this invention is to provide a dampening water feed roller excellent in proofness against corrosion and abrasion. The objects mentioned above are accomplished by a method for the production of a dampening water feed roller which comprises forming a flame sprayed layer of a ceramic material on the peripheral surface of a metallic roller, the ceramic material comprising Al₂O₃ or TiO₂ or a mixture of the two in any proportion, characterised by subjecting the flame sprayed ceramic layer to a pore-occluding treatment agent, and grinding the treated layer to surface roughness of not more than 1.6 S. The inventors have examined various flame sprayed ceramic coatings with respect to wettability with water (incorporating absolutely no isopropyl alcohol) as described specifically herein below, to find that as compared with the hard chromium coating produced by plating, the ceramic coatings as a whole possess high wettability, particularly the Al₂O₃-TiO₂ type ceramic coatings such as Al₂O₃-40% TiO₂, Al₂O₃-13% TiO₂, Al₂O₃-2.7% TiO₂, Al₂O₃, and TiO₂ coatings among other ceramic coatings exhibit the most satisfactory wettability, and the Cr₂O₃ component type coatings such as the coating produced by flame spraying Cr₂O₃, and the coating produced by the pore-sealing treatment with a Cr₂O₃ sealing agent as disclosed in Japanese Utility Model Unexamined Publication SHO 62(1987)-136,353 manifest no appreciably improved wettability. They have further examined the coatings as to the adhesiveness of ink to their surfaces by wetting their surfaces with water and subsequently allowing the ink to spread on the surfaces, to find that the hard chromium coating of poor wettability with water permits adhesion of the largest amount of ink and the flame sprayed coatings exhibiting a desirable water-retaining property and yet containing pores of a large diameter admit the ink in their pores and consequently sacrifice the hydrophilicity and suffer adhesion of the ink. For the ceramic coating produced by flame spraying to prevent the ink from permeating into the pores, therefore, it must be subjected to the pore-occluding treatment. Various organic and inorganic sealing agents are available for the purpose of the occlusion of pores. Some of these sealing agents such as the aforementioned Cr₂O₃ type agent are not incapable of seriously impairing the wettability of the coating produced by flame spraying. The inventors have continued a diligent study to find that a SiO₂ type inorganic pore-occluding agent is suitable as an agent which displays a remarkable ability to permeate micropores during the course of application to a porous surface and, on being dried and cured, gives rise to a coating of high hydrophilicity. The coating of this pore-occluding agent itself possesses lower hydrophilicity than the flame sprayed coating of Al₂O₃-TiO₂ ceramic material and offers no sufficient proofness against abrasion. It is, therefore, essential that the roll which has undergone the pore-occluding treatment should be ground to an extent of removing the SiO₂ coating and allowing the cured SiO₂ agent to remain only in the pores. It has been found that when this grinding is carried out to a surface roughness of not more than 1.6 S, the ground surface acquires uniform wettability with water and perfectly precludes the entrainment of ink by the ceramic coating. This invention has been accomplished as the result. The term "surface roughness" as used in the present specification refers to the definition given in Japanese Industrial Standard (JIS) B 0601. The dampening water feed roller of the present invention enjoys much better proofness against abrasion than the roller provided with a hard chromium plating because it possesses an Al₂O₃-TiO₂ surface coating formed by flame spraying. Fig. 1 is a perspective view illustrating as a model the structure of a dampening water feed roller of this invention, with a cross section formed in the central part thereof. Fig. 2 is a magnified cross section illustrating as a model the microfine structure of the surface portion of a dampening water feed roller of this invention. Fig. 3 and Fig. 4 are schematic diagrams illustrating as models typical examples of the dampening mechanism in the planographic printing press. Now, the present invention will be described in detail below with reference to embodiments thereof. As illustrated in Fig. 1 and Fig. 2, in the dampening water feed roller of this invention, an Al₂O₃-TiO₂ type flame sprayed coating 2 is formed on the peripheral surface of a metallic roller 1 and pores 3 opening on the surface of the flame sprayed coating 2 are filled with a SiO₂ type inorganic pore occluding agent 4. On the surface of the flame sprayed coating 2, however, there also exist minute pores 5 which have been opened in consequence of the secondary grinding to be performed as described specifically herein below and have been left unfilled with the pore-occluding agent 4. To facilitate the comprehension of this invention, the Al₂O₃-TiO₂ type flame sprayed coating 2 and the metal flame sprayed layer 7 to be mentioned herein below are illustrated with exaggerated thickness in Fig. 1 and the open pores 3, 5 and the closed pores 6 in the Al₂O₃-TiO₂ type flame sprayed coating 2 are illustrated in exaggerated sizes relative to the thickness of the coating in Fig. 2. A metallic roller 1 destined to serve as a matrix for the dampening water feed roller of this invention is not specifically restricted. Suitably, it is a roller made of steel pipe or a stainless steel pipe. The metallic roller 1, prior to the formation of the Al₂O₃-TiO₂ type flame sprayed coating 2 on the peripheral surface thereof, is subjected to a blasting treatment and optionally a treatment for thermal spraying of such a corrosionproofing metal as Ni, Ni-Cr, or Ni-Al for the purpose of improving the corrosionproofness of the matrix and enhancing the adhesiveness of the matrix to the ceramic substance. When the flame spraying is carried out at all, the flame sprayed metal layer 7 to be formed suitably has a thickness approximately in the range of 50 to 100 µm. Then, on the peripheral surface of this metallic roller 1, the Al₂O₃-TiO₂ type flame sprayed coating 2 is formed by any of various flame spraying methods represented by the plasma flame spraying method. The ratio of the Al₂O₃ and TiO₂ contents in the Al₂O₃-TiO₂ type flame sprayed coating 2 need not be specifically defined because this coating acquires sufficient hydrophilicity when the Al₂O₃ content falls in the range of 100 to 0% by weight and the TiO₂ content falls accordingly in the range of 0 to 100% by weight. In consideration of the impartation of more thorough hydrophilicity and the economy, the Al₂O₃-TiO₂ type composition is desired to have an Al₂O₃ content in the range of 97.3 to 60% by weight and a TiO₂ content in the range of 2.7 to 40% by weight. The surface roughness of the roller, as described above, constitutes itself an important factor for determining the uniform wettability of the roller with water and the adhesiveness of ink to the roller surface. The Al₂O₃-TiO₂ type flame sprayed coating 2 formed by the flame spraying method is desired to undergo primary grinding and acquire surface roughness of not more than 6.3 S, preferably not more than 3.2 S. For the Al₂O₃-TiO₂ type flame sprayed coating 2 to possess sufficient layer strength and abrasionproofness, it is desired to possess a thickness approximately in the range of 100 to 300 µm, preferably 100 to 200 µm, after the primary grinding. After the Al₂O₃-TiO₂ type flame sprayed coating 2 of a smooth surface has been formed on the peripheral surface of the metallic roller 1 as described above, it is subjected to a pore-occluding treatment with a SiO₂ type inorganic pore-occluding agent 4 to occlude the pores 3 opening on the surface of the Al₂O₃-TiO₂ type flame sprayed coating 2. The SiO₂ type inorganic pore-occluding agent 4 to be used in the present invention is only required to be such that it will form, on being dried or fired, a coating of SiO₂ as a main component thereof, desirably containing not less than 55% by weight, preferably not less than 80% by weight of SiO₂ and assume the form of a varying silicon compound at the time of use. The SiO₂ type inorganic pore-occluding agents which are usable herein include the product of Okuno Chemical Industries Co. LTD. marketed under product code of "CRM-100," the product of SUNRUKU K.K. marketed under product code of "HS-2," the product of SUNRAKU K.K. marketed under product code of "HS-K," the product of Nippan Kenkyujyo marketed under trademark designation of Gulasuka 101," and the product of Nippan Kenkyujyo marketed under trademark designation of "Gulasuka 101A," for example, which are offered in the form of a solution diluted with a suitable solvent such as, for example, water or an alcohol. These are desirable because they are easily handled for the treatment. When the pore-occluding agent in the form of a solution as mentioned above is used, the pore-occluding treatment is carried out by immersing the Al₂O₃-TiO₂ type flame sprayed coating 2 in the pore-occluding agent thereby allowing the pore-occluding agent to permeate into the pores 2 of the coating 2 and then drying or firing the pore-occluding agent at suitable temperature. Besides the commercial products enumerated above, the alkali metal-silicate type, silica sol type, and metal alkoxide type agents may be cited as examples of the SiO₂ type inorganic pore-occluding agent 4. The SiO₂ type inorganic pore-occluding agent 4 manifests a notable ability to permeate into the micropores. By the surface of the Al₂O₃-TiO₂ type flame sprayed coating 2 are occluded intimately to a great depth. The coating of the SiO₂ type inorganic pore-occluding agent 4 formed on the surface of the roller in consequence of the pore-occluding treatment has lower hydrophilicity than the Al₂O₃-TiO₂ type flame sprayed coating 2 and exhibits no sufficient proofness against abrasion. If this coating is allowed to remain intact, the roller is prevented from manifesting the highly desirable hydrophilicity due to the Al₂O₃-TiO₂ type flame sprayed coating 2 and the roller is compelled to suffer from serious impairment of service life due to coarseness of the roller surface. The roller which has undergone the pore-occluding treatment, therefore, is subjected to second grinding so that the coating of the SiO₂ type inorganic pore-occluding agent 4 will be removed from the roller surface and the SiO₂ type inorganic pore-occluding agent 4 will be allowed to remain only in the pores 3 of the Al₂O₃-TiO₂ type flame sprayed coating 2. As concerns the extent to which the secondary grinding is performed, since the SiO type inorganic pore-occluding agent 4 possesses a notable ability as described above and the pores 3 opening in the surface of the Al₂O₃-TiO₂ type flame sprayed coating 2 are occluded therewith to a great depth, the posibility of the occluded pores being reopened by secondary grinding is very remote even when the grinding is made to a fairly large depth such as, for example, 30 µm. In due consideration of the possibility that the fine pores existing in the Al₂O₃-TiO₂ type flame sprayed coating 2 will be opened anew by the grinding, it is desirable that the secondary grinding should be limited to the extent of not more than 2 µm in depth. By the second grinding, the roller is desired to acquire surface roughness of not more than 1.6 S, preferably not more than 0.8 S. Even when the roller has the surface thereof covered with a compact ceramic coating of very high hydrophilicity, any insufficiency of surface smoothness entails the possibility that this roller will scrape the ink off the water applying roller, give rise to a suspension of ink in the water supply pan, pass the scraped ink onto the metering roller, with the result that the master water roller fails to manifest uniform wettability with water and the produced printed picture is smeared with the astray ink. On the greater part of the surface of the dampening water feed roller of this invention, the Al₂O₃-TiO₂ type flame sprayed coating of very high hydrophilicity is formed. The small remaining part of the surface which is occupied by the open pores in the Al₂O₃-TiO₂ type flame sprayed coating is filled with the SiO₂ type inorganic pore-occluding agent of high hydrophilicity. As the result, the surface of the roller is formed of a compact ceramic coating of very high hydrophilicity and high surface smoothness. The roller of this surface, therefore, permits stable and uniform supply of the dampening water even through no additive such as isopropyl alcohol was added to the dampening water, and has no possibility of entraining the ink. There is no doubt that the roller also permits stable and uniform supply of the dampening water with using the additive in the dampening water. In this case, it is desirable that the amount of isopropyl alcohol incorporating to the dampening water is not more than 5 % by weight, more particularly not more than 3 % by weight. The dampening water feed roller of this invention, accordingly, is suitable for use as a dampening water feed roller of a varying dampening mechanism in the planographic printing press. Typical structures of the dampening water feed roller are illustrated in Fig. 3 and Fig. 4, for example. Of course, the dampening water feed roller of this invention need not be limited to the structures illustrated herein below but may be applied similarly to a varying dampening water feed mechanisms adapted for the planographic printing press. The dampening mechanism illustrated in Fig. 3 comprises a master water roller 12 rotated as partly dipped in the water in a water supply pan 11 disposed underneath and a metering roller 13 of rubber and a water applying roller 14 of rubber both held in contact with the master water roller 12. The water adhering to the surface of the master water roller and consequently ascending with the rotation of the master water roller 13 is passed to the water applying roller 14 in consequence of the contact of the master water roller 12 with the water applying roller 14 and then is passed from the water applying roller 14 to the picture portion of a plate cylinder 15 on contact of the water applying roller 14 with the plate cylinder 15. The water which remains after failing to reach the picture portion of the plate cylinder 15 is returned from the plate cylinder 15 back to the water supply pan 11 through the medium of the intervening rollers. As the master water roller 12 in the dampening mechanism configured as illustrated in Fig. 3, the dampening water feed roller of this invention can be advantageously utilized in the place of the conventional metallic roller. The other dampening mechanism illustrated in Fig. 4 comprises a water discharging roller 22 rotated as partly dipped in the water of a water supply pan 21, a water transferring roller of rubber held in contact with the water discharging roller 22, a water spreading roller 27 held in contact with the water transferring roller 26, and a water applying roller 14 of rubber held in contact with the water spreading roller 27. In this dampening mechanism, the water adhering to the surface of the water discharging roller 12 and consequently ascending from the water supply pan 21 with the rotation of the water discharging roller 22 is deprived of an excess amount thereof during the passage thereof through the medium of the water transferring roller 26 and the water spreading roller 27, then guided to the water applying roller 24, and passed on from the water applying roller 24 to the plate cylinder 25 by virtue of the contact of the water applying roller 24 with the plate cylinder. The water which remains after failing to reach the picture portion of the plate cylinder 25 is returned from the plate cylinder 25 back to the water supply pan 21 through the medium of the intervening rollers. As the water discharging roller 22 and the water spreading roller 27, particularly as the water spreading roller 27, the dampening water feed roller of this invention can be advantageously utilized in the place of the conventional metallic roller. EXAMPLES Now, the present invention will be described more specifically below with reference to working examples. These examples are cited solely for the purpose of illustration of this invention. The scope of this invention is not limited in any way by the procedure of manufacture and the compositions specifically mentioned in the examples. Preliminary Experiment 1 First to test various flame sprayed ceramic layers for wettability with water (containing absolutely no isopropyl alcohol), test pieces were prepared by flame spraying various ceramic substances indicated in Table 1 on substrates of steel plate 5 x 5 cm and the test pieces were dipped in water to find their angles of contact with water by the use of a contact angle meter (produced by Kyowa Kagaku K.K. and marketed under trademark designation of "Kyowa Contactanglemeter CA-A"). The same flame sprayed ceramic layers were subjected severally to a pore-occluding treatment using a SiO₂ type inorganic pore-occluding agent, an epoxy type organic pore-occluding agent, or a Cr₂O₃ type pore-occluding agent and then tested similarly to angle of contact. As a control, a test piece prepared by forming a hard chromium plating 30 µm in thickness on the surface of a similar steel plate and tested for wettability with water. The test piece of the hard chromium plating was additionally tested for wettability with water incorporating therein 10% of isopropyl alcohol. The results wee as shown in Table 1. The flame sprayed ceramic layers were formed after the steel plates had been blasted to a surface roughness of Ra 40 µm and then coated with a flame sprayed Ni-Cr layer 50 µm in thickness. Preliminary Experiment 2 To test for adhesiveness of ink, test pieces were prepared by flame spraying Al₂O₃-40% TiO₂ on a substrate of steel plate 5 x 5 cm, flame spraying Al₂O₃-40% TiO₂ on a similar substrate and subjecting the flame sprayed layer to a pore-occluding treatment with a SiO₂ type inorganic pore-occluding agent (in conformity with the present invention), flame spraying Al₂O₃ on a similar substrate and subjecting the flame sprayed layer to a pore-occluding treatment with a Cr₂O₃ type pore-occluding agent, and coating a similar substrate with a hard chromium plating. These test pieces were wetted with water and ink was placed on the wetted surfaces and left spreading to determine the degrees of adhesion of ink to the test pieces. The results were as shown in Table 2. The flame sprayed ceramic layers and the hard chromium plating were formed under the same conditions as in Preliminary Experiment 1, with necessary modifications. Coating Wettability with by angle of contact (%) TiO₂ 50 Al₂O₃ - 40%TiO₂ 60 Al₂O₃ - 13%TiO₂ 66 Al₂O₃ - 2.7%TiO₂ 70 Al₂O₃ 80 Cr₂O₃ 70 WC - 25%Co 80 Al₂O₃ - 40%TiO₂ + pore-occluding treatment with SiO₂ type inorganic pore-occluding agent 43 Al₂O₃ - 40% TiO₂ + pore-occluding treatment with epoxy type organic pore-occluding agent 83 Al₂O₃ + Cr₂O₃ type pore-occluding treatment 70 hard chromium plating 84 hard chromium plating (water incorporating 10% of isopropyl alcohol) 55 Coating Adhesiveness of ink Al₂O₃ - 40%TiO₂ + SiO₂ type pore-occluding treatment o ○ Al₂O₃ - 40%TiO₂ (no pore-occluding treatment) ▵ Al₂O₃ + Cr₂O₃ type pore-occluding treatment ○ hard Cr plating X It is clearly noted from the results shown in Table 1 that the Al₂O₃-TiO₂ type ceramic substances, i.e. Al₂O₃-40% TiO₂, Al₂O₃-13% TiO₂, Al₂O₃-2.7% TiO₂, Al₂O₃, and TiO₂ which are fit for use in the dampening water feed roller of the present invention invariably exhibited better wettability than not only the hard chromium plating but also other ceramic substances. When the Al₂O₃-TiO₂ type ceramic layers were subjected to the pore-occluding treatment, the SiO₂ type inorganic pore-occluding agent 4 for use with the dampening water feed roller of this invention, unlike other pore-occluding agents, brought about no hindrance what ever to the satisfactory wettability of the Al₂O₃-TiO₂ type ceramic layers. It is clearly noted from the results shown in Table 2 that the adhesiveness of ink to the surface hinged heavily on the pore-occluding treatment. Example 1 On the peripheral surface of a master water roller of steel pipe which had been blasted to surface roughness of Rz 40 µm, Ni-Cr was flame sprayed in a thickness of 50 µm. On the flame sprayed Ni-Cr layer, Al₂O₃-40% TiO₂ was flame sprayed in a thickness of 250 µm by the plasma flame spraying technique. The Al₂O₃-40% TiO₂ ceramic layer thus formed was ground with a diamond grinding stone, #1000, to a depth of 150 µm and surface roughness of 0.8 S. Then, a SiO₂ type inorganic pore-occluding agent (produced by Okuno Chemical Industries Co. LTD. and marketed under product code of "CRM-100") was applied on the flame sprayed Al₂O₃-40% TiO₂ ceramic layer by the immersion technique to occlude the pores and this layer was fired at 230°C to complete a pore-occluding treatment. Subsequently, the coated roller was ground with a diamond grindstone, #4000, until the outside diameter thereof produced a decrease of 2 µm from that before the pore-occluding treatment so as to remove the coating of the SiO₂ type inorganic pore-occluding agent formed on the roller surface. In consequence of this grinding, the roller acquired surface roughness of 0.8 S. Example 2 A dampening water feed roller was produced by following the procedure of Example 1, excepting Al₂O₃-13% TiO₂ was used in the place of Al₂O₃-40% TiO₂. Example 3 A dampening water feed roller was produced by following the procedure of Example 1, excepting Al₂O₃-2.7% TiO₂ was used in the place of Al₂O₃-40% TiO₂. Control 1 A flame sprayed Al₂O₃-40% TiO₂ ceramic layer having surface roughness of 2.2 S was formed on the same matrix as used in Example 1 by performing the same pretreatment, flame spraying A l 2O₃-40% TiO₂, and grinding the coated matrix. The coated roller thus obtained was not subjected to the pore-occluding treatment but was used immediately as a dampening water feed roller. Control 2 A dampening water feed roller was produced by following the procedure of Control 1, excepting Al₂O₃-13% TiO₂ was used in the place of Al₂O₃-40% TiO₂. Control 3 A chromium-plated roller in popular use of the kind was produced by applying a hard chromium plating on the peripheral surface of a master water roller of steel and grinding the plating by buffing to surface roughness of 0.2 S. -Actual printing test- The dampening water feed rollers of examples 1 to 3 and Controls 1 to 3 produced as described above were each set in place in a commercial offset printing press provided with a dampening water feed mechanism using an array of rollers illustrated in Fig. 3 and subjected to a printing test under the conditions shown in Table 3, using water containing absolutely no isopropyl alcohol, water containing 3% by weight of isopropyl alcohol, and water containing 7% by weight of the alcohol respectively as the dampening water. Conditions for actual printing test Machine used Bestech 640 (I type inking) Materials used Plate Akiyama test plate, 80% halftone (135 lines) Umpire photographic plate (4 colors) Ink Dainippon Ink Process Paper Double-face coated 76.5 Kg Conditions for test Dampening water temperature 13°C±2°C pH 5.5 (using H liquid (made by Toho)) Amount of isopropyl alcohol added 7%, 3%, 0% Operating speed of printing press 8,000 sheet/hour The chromium-plated roller of Control 3 produced uneven ascent of the dampening water containing no ispropyl alcohol and imparted the phenomenon of so-called rainfall to the print. The master water roller, therefore, entrained ink and prevented normal printing. Even by the use of the dampening water containing no isopropyl alcohol, the rollers of examples 1 to 3 could produce prints equal to or better than the print produced by the chromium-plated roller of Control 3 with the dampening water containing 7% by weight of isopropyl alcohol. The pictures printed were very sharp and glossy. The master water roller and the metering roller entrained virtually no ink. The printing press using these rollers could continue very stable printing for a very long time since immediately after the start of paperfeeding. In the case of the rollers of Controls 1 and 2 which were not subjected to the pore-occluding treatment, they exhibited a high initial water-retaining property and brought about excessive ascent of water so that the ink was emulsified and was entrained by the master water roller to the metering roller or the ink was suspended in the water supply pan. They prevented the printing operation from being continued stably for a long time. When the use of the rollers was continued for a while, the ink permeated into the pores of the ceramic coatings. Since the ink repelled the ink repelled the water, the rollers brought about uneven ascent of water and smeared the prints and, at the same time, encouraged the entrainment of the ink by the rollers. As described above, the dampening water feed roller of this invention possess high hydrophilicity, exhibits uniform wettability with water, and produces very uniform ascent of water. Thus, it allows a generous saving in the dampening water and permits production of fine prints of sharp and glossy pictures without use of any alcohol or other additive in the dampening water. It not merely reduces the cost owing to the omission of the use of such additives but also brings about a marketed advance in the improvement of the working environment. Further, since the use of the dampening water feed roller of this invention allows stable production of fine prints from the beginning, the effect brought about in the reduction of cost is remarkable even from the standpoint of the prevention of waste of paper and the enhancement of productivity. Moreover, since the dampening water feed roller of this invention exhibits outstanding proofness against abrasion and corrosion and enjoys a long service life and can be produced by a relatively simple procedure, the cost of its production is significantly low as compared with the dampening water feed roller configured as disclosed in Japanese Utility Model Unexamined Publication SHO 62(1987)-116,868 or Japanese Utility Model Unexamined Publication SHO 62(1987)-136,353. Thus, the present invention has a very large economic effect. It should also be understood that the foregoing relates to only the scope of the invention as defined by the apended claims rather than by the description preceding them, and all changes that fall within meets and bounds of the claims, or equivalence of such meets and bounds are therefore intended to embraced by the claims.

Claims: A method for the production of a dampening water feed roller which comprises forming a flame sprayed layer of a ceramic material on the peripheral surface of a metallic roller, the ceramic material comprising Al₂O₃ or TiO₂ or a mixture of the two in any proportion, characterised by subjecting the flame sprayed ceramic layer to a pore-occluding treatment agent, and grinding the treated layer to surface roughness of not more than 1.6 S. A method as claimed in Claim 1, wherein a roller made of a steel pipe or a stainless steel pipe is used as the matrix. A method as claimed in Claim 1 or Claim 2, wherein the peripheral surface of the metallic roller is subjected to a blasting treatment and then flame sprayed with a corrosionproofing metal comprising Ni, Ni-Cr or Ni-Al prior to the application of the flame sprayed Al₂O₃-TiO₂ type coating. A method as claimed in any preceding Claim, wherein the flame sprayed ceramic layer is subjected to primary grinding to a surface roughness of not more than 6.3 S before the pore-occluding treatment, and the treated layer is subjected to a secondary grinding to a surface roughness of not more than 1.6 S. A method as claimed in Claim 4, wherein the primary grinding produces a surface roughness of not more than 3.2 and the secondary grinding produces a surface roughness of not more than 0.8 S. A method as claimed in any preceding Claim, wherein the amount ground from the surface of the ceramic layer, or from the primary ground surface of the ceramic layer, in the grinding step following the pore-occluding treatment is not more than 2 µm. A dampening water feed roller obtainable by a process as claimed in any preceding Claim. A roller as claimed in Claim 7, characterised in that the surface roughness is not more than 0.8 S. A roller as claimed in Claim 7 or Claim 8, characterised in that the SiO₂ type inorganic pore-occluding agent, on being dried or fire, forms a coating having a SiO₂ content of not less than 55% by weight. A roller as claimed in any of Claims 7 to 9, characterised in that the flame sprayed ceramic layer is composed of 97.3 to 60% by weight of Al₂O₃ and 2.7 to 40% by weight of TiO₂. A dampening water feed roller produced by a method as claimed in any of Claims 1 to 6 or as claimed in any of Claims 7 to 10, characterised in that it is used for feeding a dampening water incorporating no alcohol or a dampening water incorporating not more than 5% by weight of isopropyl alcohol.

Inventors: AKIYAMA MASAMI C O NIPPON STEE, ANDO TEIICHI C O NIPPON STEEL, KOJIMA YASUTAKA AKIYAMA PRINTI, YOKOYAMA KAZUHIRO C O NIPPON S, AKIYAMA, MASAMI, ANDO, TEIICHI, KOJIMA, YASUTAKA, AKIYAMA PRINTING MACHINERY, YOKOYAMA, KAZUHIRO, Akiyama, Masami, c/o Nippon Steel Corp., Ando, Teiichi, c/o Nippon Steel Corp., Yokoyama, Kazuhiro, c/o Nippon Steel Corp.
Applicants: AKYAMA INSATSUKI SEIZO KK, NIPPON STEEL CORP, AKIYAMA PRINTING MACHINERY MANUFACTURING CORP., NIPPON STEEL CORPORATION
Application year: 1989
Main classification: C23C4
IPC codes: C23C4, B41N7