KEYLESS PRINTING PRESS

Abstract: The known keyless printing press including an ink feeder section consisting of an ink source roller, a transfer roller, a doctor roller, an anti-hysteresis doctor disposed on the circumferential surface of the doctor roller and the like, and also provided with a wet­ ting device for a plate drum, is improved in order to realize a fresh condition of the ink source roller which is free from residual ink before printing ink having a uniform moisture content proportion is applied thereto and to thereby improve printing quality. The improvements reside in that a refresh doctor is disposed on the ink source roller at a position behind the contact portion between the ink source roller and the transfer roller for scraping out residual ink on the circumferential surface of the ink source roller.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to a keyless printing press including an ink feeder section consisting of an ink source roller, a transfer roller, a doctor roller, an anti-hysteresis doctor disposed on the circumferential surface of the doctor roller, and the like, and also provided with a wetting device. A keyless printing press means a printing press in which ink keys provided in a doctor of an ink source roller are omitted. Description of the Prior Art: One example of the above-mentioned keyless printing press in the prior art is shown in Fig. 5. In this figure, ink b within an ink reservoir 1 associated with an ink feed port 17 is sent under a pressure through a suction pipe 2 and a delivery pipe 4 to an ink delivery nozzle 5 by means of a pump 3, the ink delivery nozzle 5 is disposed in opposition to and in parallel to the circumferential surface of the ink source roller 7 with a minute gap clearance held therebetween, and it is provided with a large number of delivery holes aligned in the axial direction of the ink source roller 7. The ink delivered from the ink delivery nozzle 5 and adhered to the ink source roller 7 rotates jointly with the ink source roller 7 rotating at a low speed, and it is metered into a predetermined thickness by passing through the minute gap clearance held between the ink source roller 7 and an ink feed doctor 6 disposed in parallel to the former. Surplus ink b ₁ is returned by the ink feed doctor 6 into the ink reservoir 1, while the ink having passed through the minute gap clearance is transferred to a transfer roller 8 rotating at a high speed in contact with the ink source roller 7, and then the transferred ink is fed to a plate drum 14 by the intermediary of a doctor roller 9 having an ink film of uniform thickness formed thereon by an anti-hysteresis doctor 10, and ink application rollers 11 and 12. On the other hand, wetting water c is fed from a wetting device 13 to the plate drum 14, thus on the plate drum 14, ink adheres to a pattern portion while wetting water c adheres to a non-pattern portion, and thereby a predetermined ink film image is formed. This ink film image is transferred via a blanket drum 15 to a paper sheet a . In the above-described keyless printing press in the prior art, since ink b ₂ adhered to the doctor roller 9 and containing the wetting water c is scraped out by the anti-hysteresis doctor 10 and is made to drop into the ink reservoir 1, the ink b delivered from the ink delivery nozzle 5 to the ink source roller 7 and adhering thereto contains 10 - 30% of wetting water c , and also, a part of the wetting water c flows inversely to the ink source roller 7 via the doctor roller 9 and the transfer roller 8. Moreover, a transfer proportion of ink and water from the ink source roller 7 rotating at a low speed to the transfer roller 8 rotating at a high speed is unstable, and in the case where a moisture content proportion of ink is high, the transfer proportion would become uneven along the widthwise direction of the roller, hence the moisture content proportion of residual ink on the ink source roller after passage through a nip portion between the ink source roller 7 and the transfer roller 8 is also uneven along the widthwise direction of the ink source roller 7, and so, even if fresh ink having a uniform moisture content proportion is fed onto the residual ink, the unevenness of the moisture content proportion of the ink film on the ink source roller 7 would be mitigated only a little, but the moisture content proportion cannot be uniform. Accordingly, there exists a problem that a difference would arise in the transfer proportion or transfer amount of ink along the widthwise direction of the roller, resulting in an uneven printing depth along the widthwise direction of the roller. SUMMARY OF THE INVENTION: The present invention has been developed in order to deal with the aforementioned problem in the prior art, and it is one object of the present invention to provide a novel keyless printing press, in which ink feed performance and reliability are improved and printing quality is enhanced. According to one feature of the present invention, there is provided a keyless printing press including an ink feeder section consisting of an ink source roller, a transfer roller and a doctor roller rotating in contact with one another for making printing ink delivered from an ink delivery nozzle adhere onto their circumferential surfaces and subsequently transferring the printing ink to the next step, an anti-hysteresis doctor for scraping out surplus ink adhered onto the circumferential surface of the doctor roller, and the like, and also provided with a wetting device, in which there is provided a refresh doctor disposed on the ink source roller at a position behind the contact point between the ink source roller and the transfer roller for scraping out residual ink on the circumferential surface of the ink source roller, whereby the ink adhering to the ink source roller, rotating and transferring can be made to consist of only new fresh ink by scraping out the residual ink at the position behind the contact portion between the ink source roller and the transfer roller by means of the refresh doctor disposed on the ink source roller, and thus the unevenness of a moisture content proportion of ink along the widthwise direction of the roller, that is, the difference in a transfer proportion or a transfer amount of the ink can be effectively eliminated. In operation of the ink feeder section in the keyless printing press according to the present invention, residual ink on the circumferential surface of the ink source roller is scraped out by the refresh doctor disposed on the ink source roller at a position behind the contact portion between the ink source roller and the transfer roller, hence the ink adhering to the ink source roller, rotating and transferring is only new fresh ink delivered from the ink delivery nozzle, thus unevenness of a moisture content proportion along the widthwise direction of the roller is eliminated, a difference in an ink transfer proportion or an ink transfer amount in the widthwise direction disappears, and a printing depth can be equalized. The above-mentioned and other objects, features and advantages of the present invention will become more apparent by reference to the following description of preferred embodiments of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS: In the accompanying drawings: Fig. 1 is a schematic side view showing a first preferred embodiment of the present invention; Fig. 2 is a partial enlarged view of an essential part of the construction in Fig. 1; Fig. 3 is a schematic side view showing a second preferred embodiment of the present invention; Fig. 4 is a partial enlarged view of an essential part of a keyless printing press showing a third preferred embodiment of the present invention; and Fig. 5 is a schematic side view of a keyless printing press in the prior art. DESCRIPTION OF THE PREFERRED EMBODIMENTS: Now description will be made on a first preferred embodiment of the present invention illustrated in Figs. 1 and 2. In these figures, printing ink b within an ink reservoir 1 provided with an ink feed port 17 is sent under a pressure to an ink delivery nozzle 5 through a suction pipe 2 and a delivery pipe 4 by means of a pump 3. The printing ink is delivered to an ink source roller 7 through an ink delivery nozzle 5, which is disposed in parallel to and in opposition to a circumferential surface of the ink source roller 7 with a minute gap clearance held therebetween, and which is provided with a large number of delivery holes disposed along the axial direction of the ink source roller 7, then the ink adheres to the roller and rotates jointly with the roller, and the ink adhered to the ink source roller 7 is metered into a predetermined thickness by an ink feed doctor 6 which is disposed in parallel to the ink source roller with a minute gap clearance held therebetween, while surplus ink b ₁ is returned into the ink reservoir 1. In addition, surplus ink b ₂ containing wetting water on a doctor roller 9 is scraped out by an anti-hysteresis doctor 10 and drops into the ink reservoir 1. The above-mentioned component elements constitute an ink circulation system 18 encircled by a dash-dot line frame. In addition, the illustrated keyless printing press comprises an ink feeder section consisting of the ink source roller 7, a transfer roller 8 and the doctor roller 9 rotating in contact with one another for making printing ink delivered from the ink delivery nozzle 5 adhere onto their circumferential surfaces and sequentially transferring the printing ink to the next step, an anti-hysteresis doctor 10 for scraping out surplus ink b ₂ adhered onto the circumferential surface of the doctor roller 9, furthermore ink application rollers 11 and 12, a plate drum 14 and a blancket drum 15 are provided in succession to the doctor roller 9, and further, a wetting device 13 is provided. Still further, in the illustrated keyless printing press embodying the present invention, there is provided a refresh doctor 20 which is disposed so as to held in contact with the ink source roller 7 at a position behind the contact portion between the ink source roller 7 and the transfer roller 8 for scraping out residual ink b ₃ on the circumferential surface of the ink source roller 7. Next, the operation of the keyless printing press according to the first preferred embodiment of the present invention which has the above-described construction as shown in Fig. 1, will be described in detail. In the ink feeder section, since the residual ink on the ink source roller 7 after passage through a nip portion, that is, the contact portion between the ink source roller 7 and the transfer roller 8 has a high moisture content proportion and the moisture content proportion is not uniform along the widthwise direction of the ink source roller 7 due to the fact that a part of the wetting water c fed from the wetting device would flow inversely via the doctor roller 9 and the transfer roller 8, even if fresh ink having a constant and uniform moisture content proportion is fed from the ink delivery nozzle 5 onto the residual ink, the moisture content proportion of the resultant ink film would not become uniform along the widthwise direction of the ink source roller 7, and a difference would arise in an ink transfer proportion or an ink transfer amount along the widthwise direction of the roller. However, in the illustrated embodiment, since the above-mentioned residual ink is completely scraped out and caused to drop into the ink reservoir 1 by means of the refresh doctor 20 disposed on the ink source roller 7, the ink newly made to adhere onto the ink source 7 is only that delivered from the ink delivery nozzle 5, hence even if the surplus ink b ₁ containing the wetting water c which is sent from the feed doctor 6, the surplus ink b ₂ sent from the anti-hysteresis doctor 10 and the residual ink b ₃ sent from the refresh doctor 20 are added to the ink within the ink reservoir 1, as a result of mixing within the ink reservoir 1, conveyance under a pressure through the suction pipe 2 and the delivery pipe 4 by the pump 3 and delivery by the ink delivery nozzle 5, the ink delivered from the ink delivery nozzle 5 would be newly fed and would adhere onto the ink source roller 7 as fresh ink having a constant and uniform moisture content proportion, thus the moisture content proportion of the ink film adhering onto the ink source roller 7 becomes uniform along the widthwise direction of the roller. Accordingly a difference in a transfer proportion or a transfer amount of the ink is eliminated, a printing depth is equalized, and a printing performance and a reliability are remarkably improved. A second preferred embodiment of the present invention is illustrated in Fig. 3. As compared to the first preferred embodiment described above, this second preferred embodiment is characteristic in that a refresh doctor 21 is disposed on the underside of the ink delivery nozzle 5 as viewed in Fig. 3, that is, at the upstream side portion of the ink delivery nozzle 5 with respect to the direction of rotation of the ink source roller 7, and with regard to the other construction, the second preferred embodiment is similar to the first preferred embodiment and hence like functions and effects are provided. Or else, in a third preferred embodiment of the present invention illustrated in Fig. 4, a refresh doctor 22 is disposed on a main body 5a of an ink delivery nozzle 5 so that the refresh doctor 22 may be held in contact with the ink source roller, an ink delivery port 5c is formed by a cap 5b on the main body 5a, thus the refresh doctor is disposed at the upstream side portion of the ink delivery port 5c with respect to the direction of rotation of the ink source roller 7 (at the bottom of the ink delivery port 5c), and new ink is delivered from the ink delivery port 5c so as to adhere into the ink source roller 7. In such a modified embodiment also, basically the same functions and effects can be provided. As described in detail above, since the keyless printing press is constructed in the above-described manner, in the ink feeder section of the keyless printing press, residual ink having non-uniform moisture content proportion on the ink source roller after passage through the gap clearance between the ink source roller and the transfer roller, is scraped out by the refresh doctor, hence the ink adhering onto the ink source roller, rotating jointly with the roller and being transferred, consists of only the ink having a uniform moisture content proportion which is delivered from the ink delivery nozzle, thus a difference in an ink transfer proportion or an ink transfer amount is eliminated, a printing depth is equalized, and jointly with an ink feeding performance and a reliability, printing quality is remarkably improved. While a principle of the present invention has been described above in connection to preferred embodiments of the invention, it is a matter of course that many apparently widely different embodiments of the present invention can be made.

Claims: A keyless printing press including an ink feeder section consisting of an ink source roller, a transfer roller and a doctor roller rotating in contact with one another for making printing ink delivered from an ink delivery nozzle adhere onto their circumferential surfaces and sequentially transferring the printing ink to the next step, an anti-hysteresis doctor for scraping out surplus ink adhered onto the circumferential surface of said doctor roller, and the like, and also provided with a wetting device; characterized in that said keyless printing press comprises a refresh doctor disposed on said ink source roller at a position behind the contact portion between said ink source roller and said transfer roller for scraping out residual ink on the circumferential surface of said ink source roller. A keyless printing press as claimed in Claim 1, further characterized in that said refresh doctor is disposed at a position behind the contact portion between the ink source roller and the transfer roller and also between said contact portion and an ink delivery nozzle. A keyless printing press as claimed in Claim 1, further characterized in that said refresh doctor is disposed at an upstream side portion of an ink delivery nozzle with respect to the direction of rotation of said ink source roller. A keyless printing press as claimed in Claim 1, further characterized in that said refresh doctor is disposed at an upstream side portion of a delivery port in an ink delivery nozzle with respect to the direction of rotation of said ink source roller.

Inventors: HIROTA, MASATAKA C/O RYOMEI ENG. CO.LTD, NAKANO, TAKAFUMI C/O MIHARA MACHINERY WORKS, SEO,AKIKAZU C/O MIHARA MACHINERY WORKS, SOEDA, HIROMITSU C/O HIROSHIMA TECH INST
Applicants: MITSUBISHI JUKOGYO KABUSHIKI KAISHA, RYOMEI ENGINEERING CO., LTD.
Application year: 1989
Main classification: B41F31
IPC codes: B41F31