PRINTING APPARATUS FOR OFFSET PRINTING, PRINTING BELT AND PRINTING ROLLER THEREFOR, AND METHOD FOR THE MANUFACTURE OF SUCH A PRINTING BELT AND PRINTING ROLLER

Abstract: A printing apparatus comprises a printing roller (1) provided with a profile which contains raised (8) and lowered (9) parts in circumferential direction, a printing belt (3) provided at one side with a complementary profile, and an opposite roller (2) which together with the printing roller (1) determines a nip through which the printing belt (3) runs, in such a way that its profile side interacts with the printing roller, and its printing side interacts with the impression roller, which printing belt (3) is composed of an interlocked strip of plate material which is flexible as regards bending and is rigid as regards deformations in its plane, on one side of side of which a profiling of another, for instance rubber-like, material is provided. Preferably, the profiling is carried out in the form of conical projections (6) distributed at regular intervals over the plate surface in question, and the printing roller (3) is provided with complementary recesses (9) distributed in a corresponding manner over its surface.

Description: Printing apparatus for offset printing, printing belt and printing roller therefor. and method for the manufacture of such a printing- belt and printing roller. The present invention relates to a printing apparatus with a printing roller provided with a profile which comprises raised and lowered parts in circumferential direction, a printing belt provided at one side with a complementary profile, and an opposite roller which together with the printing roller determines a nip through which the printing belt runs, in such a way that its profile side interacts with the printing roller, and its printing side interacts with the opposite roller. Such a printing apparatus is known from Dutch Application 8700431. In the case of this known printing apparatus the printing belt is made of a flexible, rubber-like material on which printing plates containing the printing image are placed. The flexible belt is provided with teeth running in the crosswise direction which interact with complementary teeth provided on the printing roller. The purpose of these interacting teeth is to position the printing plates correctly with the web of paper to be printed, which must also be guided through the nip between printing roller and impression roller. This known printing apparatus has various disadvantages. The first disadvantage is that the flexible printing belt has a varying flexural rigidity, viewed in its lengthwise direction. At the position of the teeth the printing belt is thicker and therefore more rigid than at the places between the teeth. This means that the printing plates do not run in an accurate circular shape around the printing roller and through the nip, but at the position of the teeth are more flattened than at the places between the teeth. This leads to imperfections in the image printed on the web of paper. A further disadvantage of this known printing belt arises from the fact that it is made of relatively flexible material. As a result of the undercut, in other words the distance over which the impression roller presses in the printing belt, a certain displacement of the flexible material occurs at the position where it is pressed in. This displacement manifests itself in a widening of the pressed-in material, which leads to the image on the printing plates also being widened. A point in the image to be printed, for example, acquires greater dimensions as a result which adversely affects the printing obtained on the paper web. The object of the invention is to provide a printing apparatus o the above-mentioned type which does not have these disadvantages. This i achieved in that the printing belt is composed of an interlocked strip o plate material which is flexible as regards bending and is rigid a regards deformations in its plane, on one side of which a profiling o another material is provided. The printing belt according to th invention has a printing surface which consists entirely of the plat material suitable for offset printing. This means that deformation of th image in the plane of said plate material is virtually out of th question. Contrasting with the known apparatuses, in which the images t be printed were on separate plates which were interconnected by flexible printing belt, the correct relative positions of the images can be ensured in this way. It is also no longer possible for point widening to occur as a result of the undercut, as in the case of the known printing apparatus described above. As a result of the profiling present on one side of the printing belt, it can be accurately positioned relative to the paper web to be printed. In view of the constant flexural rigidity of the plate material in the lengthwise direction of the strip, it can be guided around the printing roller with a constant radius of curvature. No flattening or sharper curves occur as in the case of the known apparatus. This uniform curvature, arising from a uniform flexural rigidity in the lengthwise direction of the printing belt, can be beneficially influenced further by carrying out the profiling in a more flexible material than the plate material. According to the invention, this is achieved in that the profiling consists of a flexible, rubber-like material which is bonded to the plate material. In this way the profiling can be carried out* in the form of projections distributed at regular intervals over the plate surface in question, while the printing roller can be provided with complementary recesses distributed in a corresponding manner over its surface. The effect of these projections on the flexural rigidity of the printing belt is negligible, which means that a further improvement of the uniform running thereof through the nip can be ensured. The strip of plate material is also held in the crosswise direction with regard to the printing roller by the projections interacting with the recesses therein, as a result of which the correct position of the printing belt with regard to the paper web to be printed is also ensured in that direction. The projections preferably form parallel rows which form an angle with the generating line of the printing roller. The advantage of this design is that a vibration-free run of the printing belt over the pressure roller is thereby obtained. In order to ensure good interaction between projections and recesses, they are in the form of a truncated cone. This conical shape also ensures that the projections can be accommodated in a more or less self-centring manner in the recesses. The printing belt can also have transverse grooves at regular intervals in the lengthwise direction at the printing side, the depth of which is greater than the undercut. Such a design is advantageous when several printing apparatuses according to the invention are being used in series, and through which one and the same paper web is being guided. The transverse grooves in the printing belt mean that it can be ensured that no undesirable vibrations occur in the section of the paper web between two printing apparatuses. Tensile stresses are built up in the paper web during the printing. Once the gap now arrives at the paper web, these tensile stresses can be released, which benefits the run of the paper web. The invention also relates to an image carrying belt composed of an interlocked strip of plate material which is flexible as regards bending and which is rigid as regards deformations in its plane, on one side of which a profiling of another material is provided. Such belt is suitable i c ~ - use in a printing apparatus as described above. However, it may also be used in a photographic image developing apparatus as will be discussed below. Furthermore, the invention is related to a printing roller for a printing apparatus described above. The invention also relates to a method for the manufacture of a printing belt comprising an interlocked strip of plate material with projections of a flexible material on the printing side. According to the invention, the projections are to this end cut, punched or the like out of a strip of rubber material in such a way that they are still connected to said strip by a bridge which is simple to break, and are then bonded to the strip of plate material, following which the strip of rubber-like material is removed in such a way that the bridges between the projections and said strip of rubber-like material are broken. The projections in this case adhere so strongly to the strip o plate material that they remain on it when the remainder of the strip i pulled away. For this, an adhesive layer is preferably applied to eac projection. Finally, the transverse grooves in the printing belt can be forme by cutting to a greater depth than the undercut. If the printing belt is made of a material to which the printin image can be applied photographically, the printing belt is exposed onl after fixing of the projections. The advantage of this method is that th printing belt can also be positioned accurately relative to the exposur device by means of the projections already applied. The invention also relates to a method for the manufacture of printing roller with complementary recesses formed for the projections o the printing belt. For this, a strip of rubber-like material is applie to the periphery of the printing roller, of a length corresponding to th size of said periphery, in which strip recesses are provided by removin projections from them during the production of the printing belt. In thi method it is ensured that the recesses in the strip of rubber-lik material on the printing roller are always accurately complementar relative to the projections on the printing belt. Said strip of rubber • like material, together with the projections therein fixed to the stri of plate material, also provides a flexible layer under said strip o plate material with a constant thickness. This strip of rubber-lik material, together with the projections in the recesses thereof, ca accommodate the undercut, the rubber-like material being pressed in little. According to a preferred method, the projections are punched ou whereby during the printing operation at least at the location of th material to be punched out, the strip of rubber-like material is gradull stretched in its plane in a generally circular-symmetrical fashion, i such a way that a conical hole is formed. To this end, furthermore an apparatus for carrying out this method is provided, comprising support and clamping means for clamping the strip of rubber-like material at the circumference of at least one location for punching a recess, mandrel means for pushing the strip of rubber-like material out of its plane of clamping so as to stretch it, and punching means opposite the mandrel means, which punching means are operable for punching a recess after or during operation of the mandrel means. Preferably, the apparatus is provided with a support plate, a pressure plate with at least " one circular opening for pressing a strip of rubber- like material onto the support plate, which support plate is provided with a hole containing a mandrel which is movable in the hole, and a hollow punch opposite the mandrel whereby mandrel and punch are displaceable between a first position at a relatively large distance from each other in which a strip of rubber like material is being placed on the support plate, and a position at a small distance or in contact with each other. As already mentioned above, in view of the relatively greatof its plane of clamping so as to stretch it, and punching means opposite rigidity of the plate material with regard to deformations in its plane,the mandrel means, which punching means are operable for punching a this does not, however, have any adverse effect at all on the accuracy ofrecess after or during operation of the mandrel means. the printing image. The strip of rubber-like material with the corresponding rubber- like projections in its recesses also behaves as a single continuous layer, which favourably influences the gentle, vibration-free running of the printing apparatus. The projections can be cut in various ways out of the strip of rubber-like material. The projections are, however, preferably cut out by cutting with a high-pressure water jet. The invention will be explained in greater detail below with reference to an example of an embodiment. Figure 1 shows a side view of a printing roller with printing belt according to the invention. Figure 2 shows a bottom view of a part of the printing belt according to the invention. Figure 3 shows a view along III of Figure 2 of the printing belt. Figure 4 shows a part of a covering to be applied around the printing roller, with recesses for the projections. Figure 5 shows an enlarged detail of the printing belt. Figure 6 shows a second detail of the printing belt. Figure 7~10 show a punching apparatus at various stages in the process of punching. Figure 1 shows the printing roller 1, the impression roller 2 and the printing belt 3- The printing belt 3 runs together with the paper web through the nip between printing roller 1 and impression roller 2. Printing belt 3 is composed of an interlocked strip of plate material 5t on which projections are provided on the side facing the printing roller 1. The plate material 5 can be a material suitable for offset printin to which the printing image can be applied photographically. Thi material is relatively rigid to deformations in its plane, but i flexible enough to be guided around the printing roller 1. When th printing belt 3 and the paper web 4 are moving together through the ni the image on the printing belt is printed on the web. The parts of th printing apparatus by means of which ink is applied to the printing sid of the printing belt 3 are generally known, and are therefore no described in the present application. As shown further in Figure 1, the printing roller 1 comprises metal cylinder 7 to which a covering 8 is applied. Holes 9 > whic correspond as regards shape and positioning to the projections 6 on th printing belt 3. are made in this covering 8. This covering 8 i preferably of the same material as the projections 6. Both are therefor preferably made of a rubber-like material. At the position of the ni between the strip of plate material 5 containing the image to be printe and the cylinder 7 there is thus a compressible layer which can easil accommodate the undercut. Despite the possibility of pressing in the strip of plate material 5 and the covering 8, the strip of plate material 5 will not deform in its plane, since it is rigid there. Figure 2 shows the side of the printing belt 3 facing the printing roller 1. As can be seen clearly, there are a large number of projections on that side which are all preferably fixed thereto by gluing. A very good positioning of the printing belt 3 both in the peripheral direction of the printing roller 1 and in the axial direction of the printing roller 1 is thus obtained. As can also be seen in Figure 2, the projections run in rows across the printing belt. These rows do not, however, form a right angle with the sides of the printing belt. They run at an angle which is less than 90°. The advantage of this is that when the printing belt runs onto the printing roller only very small vibrations or none at all are produced. Figure 3 shows the view along the line III in Figure 2. The displaced position of the projections in one row can be seen clearly. Projections 10 and 11 are shown in both Figure 2 and Figure 3- It can also be seen in Figure 3 that the projections taper towards their free end. Corresponding tapering holes 9 are provided in the covering layer 8. In Figure 4 this layer 8, which must be applied to the cylinder 7 of the printing roller 1, is shown in a flattened-out state. This strip of covering material 8 is preferably made by cutting the projections 6 out of it. A strip of covering material 8 in which the projections provided on the printing belt 3 fi accurately is thus obtained. As already mentioned above, this can be achieved in a simple way by gluing the projections 6, adhering first of all by means of small bridges to the strip 8, on the cylinder 7, and then pulling away the strip 8. The projections remain adhering to the strip of plate material 5- If the covering layer is then shortened in such a way that it fits closely around the cylinder 1 , an excellent interaction between the printing belt 3 and the printing roller 8 can be achieved in this way. Figure 5 shows an enlarged detail of the view of Figure 3- In the surface facing the paper web, which thus bears the printing image of the strip of plate material 5. provision is made for a recess 12 extending crosswise to the printing belt, and the depth of which recess is greater than the undercut. This recess has the advantage already described above that it suppresses the occurrence of vibrations and tensile stresses in the paper web if the paper web is being printed in succession by two printing belts according to the invention. Finally, Figure 6 shows how the strip of plate material 5 is interlocked. The ends of the strip facing each other are to this end hollowed out a little (see the recesses 13). A layer of film of approximately the same thickness as the depth of the recess is glued into these recesses 13- Figures 7~10 show a schematic representation of an apparatus for punching a conical hole in covering 8. Said apparatus comprises a support ' table 15, onto which the covering 8 is applied. A clamping ring 16 firmly clamps covering 8 onto support table 15. Said clamping ring 16 is held by a control mechanism which is not shown in the figures. Furthermore, a mandrel 17 is provided, as well as a hollow punch 18. As shown in figure 7. initially the covering 8 is laying flat on top of the punch 17 and the support table 1 . Once the covering 8 has been clamped properly by clamping rings 16, both mandrel 17 and hollow punch 18 are moved upwardly. However, as shown by the arrows in figure 8 mandrel 17 is being moved upwardly more rapidly than hollow punch 18. The covering 8 is drawn out of its plane by the movement of mandrel 17, and due to the lower speed of displacement of hollow punch 18 the distance between punch 18 and covering 8 gradually becomes smaller. This means that the hollow punch 18 gradually cuts deeper an deeper into the covering 8 and that simultaneously, due to the fact tha mandrel 17 is constantly moving in an upward direction, the part 19 to b cut out is being stretched more and more. Once the position of mandrel 17 and hollow punch 18 as shown i figure 9 has been reached, the upward movements are stopped. At tha point in the cutting cycle, part 19 has been cut out of the covering 8. Subsequently, mandrel 17 and hollow punch 18 are being moved to th initial position, as shown in figure • Due to the simultaneous stretching and cutting operation, a conical hole 9 has been formed, as shown in figure 10. Furthermore, the part 19* cut out of the covering 8 has corresponding conical form.

Claims: C L A I M S 1. Printing apparatus with a printing roller provided with a profile which comprises raised and lowered parts in circumferential direction, a printing belt provided at one side with a complementary profile, and an opposite roller which together with the printing roller determines a nip through which the printing belt runs, in such a way that its profile side interacts with the printing roller, and its printing side interacts with the impression roller, characterised in that the printing belt is composed of an interlocked strip of plate material which is flexible as regards bending and is rigid as regards deformations in its plane, on one side of which a profiling of another material is provided. 2. Printing apparatus according to Claim 1, in which the profiling is a flexible rubber-like material which is bonded to the plate material. 3. Printing apparatus according to Claim 2, in which the profiling is carried out in the form of projections distributed at regular intervals over the plate surface in question, and the printing roller is provided with complementary recesses distributed in a corresponding manner over its surface. 4. Printing apparatus according to Claim 3_ in which the projections form rows parallel to each other which form an angle with the generating lines of the printing roller. 5. Printing apparatus according to Claim 3 ° r 4, in which the projections are the shape of a truncated cone. 6. Printing apparatus according to Claim 3 . 4 or 5 . n which the printing roller is covered with a corresponding layer of flexible, rubber-like material in which the recesses are provided. 7. Printing apparatus according to any of the preceding claims, in which the printing belt has transverse grooves at regular intervals in the lengthwise direction at the printing side, of which the depth is greater than the undercut. 8. Printing apparatus according to one of the preceding claims, in which the opposite roller is an impression roller. 9. Printing apparatus according to one of the claims 1-7, in which a second printing belt with second printing roller is provided, the first and the second printing roller determing a nip through which the first and the second printing belt run. 10. Image carrying belt composed of an interlocked strip of plate material which is flexible as regards bending and which is rigid as regards deformations in its plane, on one side of which a profiling of another material is provided. 11. Belt according to claim 10 for a printing apparatus according to one of the preceding claims. 12. Belt according to claim 10 for a photographic image developing apparatus. 13. Printing roller for a printing apparatus according to any of the preceding Claims 3 to 6. 14. Method for the manufacture of a printing belt according to Claims 3 to 5, in which the projections are cut, punched or the like out of a strip of rubber-like material and are then bonded to the strip of plate material. 15. Method according to claim 14, in which the projections are cut out in such a way that they are still connected to said strip by a bridge which is simple to break and whereby after bonding of the projections the strip of rubber-like material is removed in such a way that the bridges between the projections and said strip of rubber-like material are broken. 16. Method according to Claim 14 or 15, in which a layer of adhesive is .applied to each projection. 17. Method according to Claim 14, 15 or 16 for the manufacture of a printing belt for the apparatus according to Claim 7. in which the transverse grooves are formed by cutting to a greater depth than the undercut. 18. Method according to Claim 14, 15, 16 or 17, for the manufacture of a belt according to claim 10 to which the printing image can be applied photographically, the printing belt being exposed after fixing of the projections. 19. Method for the manufacture of a printing roller according to Claim 6, in which a strip of rubber-like material is applied to the periphery of the printing roller, of a length corresponding to the size of said periphery, in which strip recesses are provided by removing projections from them according to the method of one of Claims 14 - 18. 20. Method according to Claim 14-19, in which the projections are cut out of the strip of rubber-like material by means of cutting with a high- pressure water jet. 21. Method according to one of the claims 14-19, in which the projections are punched out and whereby during the punching operation at least at the location of the material to be punched out, the strip of rubber-like material is gradually stretched in its plane in a generally circular-symmetrical fashion, in such a way that a conical hole is formed. 22. Method according to claim 21, whereby, around the punching location the material is held against movements in and perpendicular with reference to its plane, and the stretching is obtained by forcing the material upwardly in the middle of the fixed part. 23. Apparatus for carrying out the process according to claim 22, comprising support and clamping means for clamping the strip of rubber- like material at the circumference of at least one location for punching a recess, mandrel means for pushing the strip of rubber-like material out of its plane of clamping so as to stretch it, and punching means opposite the mandrel means, which punching means are operable for punching a recess after or during operation of the mandrel means. 24. Apparatus according to claim 23, provided with a support plate, a pressure plate with at least one circular opening for pressing a strip of rubber-like material onto the support plate, which support plate is provided with a hole containing a mandrel which is movable in the hole, and a hollow punch opposite the mandrel whereby mandrel and punch are displaceable between a first position at a relatively large distance from each other in which a strip of rubber like material is being placed on the support plate, and a position at a small distance or in contact with each other. 25. Apparatus according to claim 24, in which in the first position the mandrel is flush with the support plate, and in the second position the mandrel projects with respect to the support plate. 26. Apparatus according to claim 25, in which the mandrel and the punch are operable in such a way that upon moving the mandrel towards its second position the punch moves in the same direction as the mandrel, but at a lower speed.

Inventors: SCHOEN DAVID, SCHOEN, DAVID
Applicants: DRUKBAND BV, DRUKBAND B.V.
Application year: 1991
Main classification: B41F7
IPC codes: B41F1, B41F17