DIE CUT ROLL

Abstract: A die cut roll is provided which comprises a die cutter obtained by providing on a surface of a rotary driving roll with projecting pressure cutting blades formed in accordance with the shape of a product to be cut, and an anvil roll adapted to receive the edges of the projecting pressure cutting blades of the die cutter, and which has an improved cutting performance of the edges of the projecting pressure cutting blades and a prolonged lifetime. 1. Inclined finishing surfaces are formed adjacently to a top smooth portion of an edge of each of the projecting pressure cutting blades, by grinding each of surface portions adjacent to the top smooth portion so that the surface portion has grinding flaws making an angle  of 50°-90°, and preferably 80°-90° to a relative ridgeline defining the top smooth portion. 2. A difference between the hardness of the cutting blades of the die cutter and that of the surface of the anvil roll is set different in die cut rolls of different driving systems, i.e., a two-shaft driving system and a single-shaft driving system. 3. Projecting pressure cutting blades not directly working to cut a product are provided so as to compensate for at least the discontinuous portions, which extend in the circumferential direction of the rotary driving roll, of the product cutting projecting pressure cutting blades of the die cutter. 4. Connected portions of plural product cutting projecting pressure cutting blades on the die cutter form a continuous linear cutting blade. 5. Plural projecting pressure cutting blades are provided with their end portions disposed side by side in the circumferential direction of the die cutter. A die cut roll having excellent cutting characteristics, a prolonged lifetime and a high reliability can be obtained by minimizing the occurrence of minute chippings and abnormal abrasion of the projecting pressure cutting blades and effectively reducing stress concentration on the edge of each cutting blade.

Description: This invention relates to a die cut roll used to cut sheet type products, such as paper diapers and sanitary napkins. Background of the Invention: This die cut roll comprises a combination of a die cutter formed by providing projecting pressure cutting blades, which are formed in accordance with the shape of a sheet type product to be cut, on a surface of a rotary driving roll, and an anvil roll. A sheet type work to be cut is made to run between the two rolls, and the die cutter is rotated in an anvil roll-pressing manner so as to cut the sheet type work to a predetermined shape with the projecting pressure cutting blades. Many attempts have heretofore been made to improve the cutting quality of the cutting blades and prolong the lifetime thereof. For example, Japanese Patent Registration No. 2593570 discloses that the relation between the hardness of pressing ends of cutting blades and that of a surface of an anvil roll has influence upon the lifetime of the cutting blades, and that, when a hardness difference HrA therebetween is set to more than 0.1, the lifetime of the cutting blades increases more than ten times. Japanese Patent Laid-Open No. 227798/1995 discloses the selection of specific materials for creating a proper hardness difference. Japanese Patent Laid-Open No. 71999/1996 discloses the prolonging of the lifetime of cutting blades with respect to the shape thereof, i.e., it discloses the possibility of increasing the lifetime of cutting blades by setting the cutting blade width of an axial portion thereof smaller than that of a circumferential portion thereof. Japanese Patent Laid-Open No. 72000/1996 discloses crowned die cutters provided in both a die cut roll of a two-shaft driving system in which an anvil roll is driven by two synchronously rotated shafts, and a die cut roll of a single-shaft driving system in which a die cutter alone is driven with an anvil roll driven thereby. Japanese Patent Laid-Open No. 267299/1997 discloses the techniques for improving the cutting quality of cutting blades without spoiling the strength thereof, by setting the angles α, β (apex angle becomes α +β) of two inclined surfaces of each edge of the cutting blades with respect to a radius vector to α ≠β, 0≦ α ≦60°, 25≦β≦80° and 5≦β- α ≦80°. In particular, it discloses a die cut roll according to the preamble of claim 1. The mode of abrasion of a die cut roll is complicated, and various things cause imperfect cutting of a work, chipping of projecting pressure cutting blades, early deterioration of the cutting performance of edges of the projecting pressure cutting blades and a decrease in the lifetime thereof to occur. Moreover, die cut rolls of different driving systems have greatly different modes of abrasion of a die cutter and an anvil roll, i.e., in a certain driving system, occurs ununiform abrasion of the rolls, or a decrease in the lifetime of the edge of the cutting blades ascribed to the chipping thereof. When the projecting pressure cutting blades on the surface of the die cutter are formed discontinuously in the rotational direction thereof, an extreme repeated stress is exerted on the pressure cutting blades, and a rate of abrasion thereof increases, so that the imperfect cutting of a work and the chipping of the pressure cutting blades occur. Even when the projecting pressure cutting blades are provided over the whole of the circumferentially continuous portion of the die cutter with the axial cutting length thereof decreasing due to the shape of the same, the concentration of stress on the blades occurs to cause an increase in the rate of abrasion thereof and the chipping thereof. Disclosure of the Invention: An object of the present invention is to provide a die cut roll having an improved cutting performance of the edges of projecting pressure cutting blades and a prolonged lifetime. Another object of the present invention is to provide a die cut roll capable of resisting the stress occurring when an edge of a projecting pressure cutting blade and an anvil roll are brought into contact with each other adjacently to a top smooth portion of the edge. Still another object of the present invention is to provide a die cut roll which has attained a long lifetime thereof with respect to greatly different modes of abrasion of a die cutter and an anvil roll occurring due to different die cut roll driving systems in use. A further object of the present invention is to provide a die cut roll which has attained the reduction of stress concentration on projecting pressure cutting blades used for cutting a work to a final shape. The invention of this application is directed to a die cut roll according to claim 1. For driving the die cut roll consisting of a die cutter and an anvil roll, two types of driving system can be adopted. One is the two-shaft driving type in which the driving force of a motor is transmitted to both shafts of the die cutter and the anvil roll by means of a gear to rotate the die cutter and the anvil roller synchronously. And the other is the single-shaft driving type in which the driving force is transmitted to the shaft of the die cutter and the anvil roller which is in contact with the die cutter and is aligned in parallel with the axis of the shaft of the die cutter and is rotated by the friction with the die cutter. The projecting pressure cutting blades for products of a die cutter may be provided so that the blades extend continuously in the circumferential direction of the die cutter, or so that end portions of the blades overlap in the circumferential direction thereof. The materials out of which the die cutter and anvil roll can be formed include hard materials, such as a sintered hard alloy inclusive of a WC based alloy, a cermet inclusive of a Ti based alloy, high speed steel, and a ceramic material of Al 2 O 3 ·ZrO 2 ·SiC·Si 3 N 4 , out of which hard materials of carbide bond, such as the WC based alloy and Ti based alloy in particular are preferably used. Brief Description of the Drawings: Fig. 1 shows an example of a die cut roll to which the present invention is applied; Fig. 2 shows the shape of an edge of a projecting pressure cutting blade provided on a surface of a die cutter of Embodiment 1; Fig. 3 shows an example of a two-shaft driving type die cut roll to which the present invention is applied; Fig. 4 shows an example of a single-shaft driving type die cut roll to which the present invention is applied; Fig. 5 shows the relation between a hardness difference and lifetime of the two-shaft driving type die cut roll; Fig. 6 shows the relation between a hardness difference and lifetime of the single-shaft driving type die cut roll; Fig. 7 shows an example of a die cutter in the present invention, provided with projecting pressure cutting blades not directly working to cut a product, so-called supporting blades in addition to proper projecting pressure cutting blades; Fig. 8 shows another example of a die cutter in the present invention, having another type of supporting blades; Fig. 9 shows still another example of a die cutter in the present invention, having parts substitutable for the supporting blades; and Fig. 10 shows a further example of a die cutter in the present invention, having another type of parts substitutable for the supporting blades. The descriptions of the reference numerals and letters shown in the drawings are as follows. 1...Projecting pressure cutting blades, 2...Die cutter, 3...Anvil roll, 2a...Die cutter gear, 3a...Anvil roll gear, 4...Top smooth portion, 5...Inclined grinding surface, 6...Sintered ground, 7...Inclined finishing surface, 8...Grinding flaws, 9...Motor, 10...Supporting blades, 11...Guide flanges, 12...Continuous portion of a projecting pressure cutting blade, d...Width of a top smooth portion of a blade,  ...Apex angle of an edge, A...Product cutting regions, P...Work (object to be processed), X...Circumferential discontinuous portions of projecting pressure cutting blades, Y...Concentrated portion with respect to the axial direction of a projecting pressure cutting blade, Z...Range including circumferential end portions of a plurality of projecting pressure cutting blades. Best Mode for Carrying Out the Invention: Embodiment 1: A die cut roll shown in Fig. 1 has a die cutter 2 formed by providing a surface of a rotary driving roll with a projecting pressure cutting blade 1 formed in accordance with the shape of products to be cut, and an anvil roll 3 disposed under the die cutter and adapted to receive an edge of the projecting pressure cutting blade, and a sheet type work P to be cut is made to run between the two rolls and cut to a predetermined shape with the projecting pressure cutting blade 1 by rotating under pressure the die cutter 2 against the anvil roll 3. The projecting pressure cutting blade 1 shown in Fig. 1 is provided as shown in Fig. 2 with a top smooth portion 4, and inclined finishing surfaces 7 ground at right angles to the longitudinal direction of the top smooth portion 4. Each inclined finishing surface 7 is formed so that an angle  thereof with respect to a relative ridgeline forming the top smooth portion 4 is in the range of 50°-90°, preferably 80°-90°, and it has grinding flaws 8. The inclined finishing surfaces 7 are finished to a surface roughness Ra of less than 0.3 µm. An apex angle  made by the top smooth portion 4 having an edge width d at an edge of the projecting pressure cutting blade 1, and inclined finishing surfaces 7 which are symmetrical about the top smooth portion 4 is set so as to satisfy the following specific conditions. Moreover, the edge width d of the top smooth portion 4 and the apex angle  made by the symmetrical, inclined finishing surfaces 7 in the axial direction of the die cutter 2 and those in the circumferential direction thereof which is perpendicular to the axial direction are preferably set to different values. The specific conditions are as follows. 5µm≦Axial edge width d≦10µm 60°≦ Axial apex angle ≦120° 10µm≦Circumferential edge width d≦30µm 80°≦ Circumferential apex angle  ≦140° Axial apex angle  ≦Circumferential apex angle  Out of these conditions, the axial blade width d in the axial direction of the die cutter has to be set small so as to obtain a required contact surface pressure. However, when this axial blade width is smaller than 5µm, the chipping of the projecting pressure cutting blade occurs, so that it is preferably in the above-mentioned range. Since the contact surface pressure is high in the circumferential direction of die cutter, there is a possibility of occurrence of the chipping of the projecting pressure cutting blade. Therefore, the circumferential blade width d has to be set large. The axial edge apex angle  is set to 120° or a lower level so that the edge width does not greatly increase due to the abrasion of the edge. However, when this apex angle is not more than 60°, the chipping of the edge becomes liable to occur. Since the contact surface pressure in the circumferential direction of the die cutter is high, there is a possibility of occurrence of the chipping of the edge, so that the circumferential edge apex angle  has to be set large. An about 1 mm thick polyethylene film as a work for obtaining sanitary napkins was cut by using the die cut roll according to the present invention. The edge widths d in the axial direction and in the circumferential direction perpendicular thereto were set to 10 µm and 20 µm respectively, and the axial and circumferential apex angles,  100° and 110° respectively. A similar film was cut to a predetermined shape by using a conventional edge having the same axial and circumferential edge widths d of 20 µm and apex angles  of 90°. These two film cutting operations were compared with each other by using a die cut roll comprising a combination of a die cutter and an anvil roll, both of which were formed out of a WC-Co sintered hard alloy. According to this embodiment, the anvil roll pressing cycle in the present invention was lengthened as compared with that in the conventional die cut roll, and a long lifetime, which was about 1.5 times as large as that of the conventional die cut roll, could be attained. This effect was, for one thing, ascribed to the inclined finishing surfaces 7 of a surface roughness Ra of less than 0.3 µm formed between the top smooth portion 4 and inclined grinding surfaces 5 of the edge of the projecting pressure cutting blade 1 of the die cutter so that the inclined finishing surfaces 7 were ground to form grinding flaws extending at 50°-90°, and preferably 80°-90° with respect to the top smooth surface portion 4. This effect was also ascribed to the compounded specific conditions for the width and apex angle of the edge. It was also ascertained that, even when the respective conditions were utilized independently, different effects were obtained, though the levels thereof were various. When the direction in which the inclined finishing surfaces are ground is not perpendicular to the ridgelines of the top smooth portion 4, the same effect can also be obtained by setting the surface roughness Ra to less than 0.1 µm. The reason resides in that setting the surface roughness Ra of the inclined finishing surface to less than 0.1 µm serves to eliminate the microscopic notches which cause the minute chippings of the projecting pressure cutting blade to occur. Embodiment 2: In this embodiment, die cutters 2 and anvil rolls 3 all of which were formed out of a WC-Co sintered hard alloy were used, in which compounding ratios of WC were varied to set the hardness of at least the top side portions of projecting pressure cutting blades 1 on the die cutter rolls 2 and that of at least the roll surfaces of the anvil rolls 3 to different levels, whereby die cutters and anvil rolls which had different hardness differences were provided for different driving systems employed. Referring to Fig. 3 showing an example of die cut roll of a two-shaft driving system, a driving shaft of a motor 9 directly drives a die cutter 2, and a die cutter gear 2a drives an anvil roll gear 3a, a driving shaft connected to the anvil roll gear 3a driving an anvil roll 3 synchronously, whereby a sheet type work P passing between the die cutter 2 and anvil roll 3 is cut to a shape in accordance with that of a projecting pressure cutting blade 1. The die cutter 2 and anvil roll 3 were formed so that the relational expression 0<H 2 -H 1 <5 wherein 82≦(H 1 , H 2 )≦96(H R A) is established, wherein H 1 represents the hardness (H R A) of at least the top side portion of the projecting pressure cutting blade 1, and H 2 the hardness (H R A) of at least the surface of the anvil roll. The relation between a difference (H 2 -H 1 ) between the hardness (H R A)H 1 of the top side portion of the edge of the die cutter 2 in the two-shaft driving system of Fig. 3 and that (H R A)H 2 of the anvil roll 3, and the lifetime of the test machines manufactured with the hardness differences (H R A) set to various levels is shown in the form of a lifetime curve of die cut rolls in Fig. 5. The ideal die cutter lifetime curve and ideal anvil roll lifetime curve are lifetime curves obtained when the die cut rolls are operated without encountering the abrasion of the anvil rolls and die cutters. The reason for attaining the relational expression 0<H 2 -H 1 resides in the following. When the projecting pressure cutting blade 1 of the die cutter 2 is harder than the anvil roll 3, the pressing force is concentrated on the surface of the anvil roll 3 to wear the same. Especially, when the die cutter and anvil roll are rotated synchronously, abrasion occurs in a concentrated manner on the portions of the surface of the anvil roll 3 which the cutting blade 1 of the die cutter 2 contacts, so that the lifetime of the die cut roll decreases to such a level that gives rise to practical problems. Furthermore, the tenacity of the edge of the die cutter 2 relatively decreases as compared with that of the anvil roll 3, and this causes the chipping of the edge of the die cutter 2 to occur. The reason why the difference H 2 -H 1 was set to H 2 -H 1 <5 resides in the following. When H 2 -H 1 is set larger than 5, the hardness of the die cutter 2 becomes too low as compared with that of the anvil roll 3, and the abrasion of the edge of the die cutter 2 becomes liable to occur with the lifetime thereof decreasing to such a level that gives rise to practical problems. Referring to Fig. 4 showing an example of a die cut roll of a single-shaft driving system to which the present invention is applied, a die cutter and an anvil roll were formed so that the relational expression -5<H 2 -H 1 <1 wherein 82≦(H 1 , H 2 )≦96(H R A) is established, wherein H 1 represents the hardness (H R A) of at least a top side portion of a projecting pressure cutting blade 1 of the die cutter, and H 2 the hardness (H R A) of at least the surface of the anvil roll. The relation between a difference (H 2 -H 1 ) between the hardness (H R A)H 1 of the top side portion of the edge of the die cutter 2 in the single-shaft driving system of Fig. 4 and that (H R A)H 2 of the anvil roll 3, and the lifetime of the test machines manufactured with the hardness differences (H R A) set to various levels is shown in Fig. 6. As compared with the case of the die cut roll of a two-shaft driving system, a load is imparted to the projecting pressure cutting blade 1 while the die cutter frictionally drives the anvil roll 3 via the work P, so that the lifetime of the die cut rolls of a single-shaft driving system generally decreases. The lifetime of the anvil rolls 3 generally increases since the abrasion spreads over the whole surface of each thereof to cause an abrasion rate to decrease. When the hardness difference is set in the range of -5<H 2 -H 1 , the lifetime of the die cut roll reaches a maximum level. The reason why the hardness difference was set to -5<H 2 ≦H 1 resides in the following. When the hardness difference H 2 -H 1 is set smaller than -5, the abrasion rate of the anvil roll 3 becomes markedly high as compared with that of the die cutter 2 to cause the lifetime thereof to decrease, and the tenacity of the projecting pressure cutting blade 1 of the die cutter 2 decreases as compared with that of the anvil roll 3 to cause the edge of the projecting pressure cutting blade 1 to be chipped. The hardness difference was set to H 2 -H 1 <1 because, when H 2 -H 1 is set larger than 1, the hardness of the die cutter 2 becomes excessively low as compared with that of the anvil roll 3, and the wear on the edge of the cutting blade of the die cutter 2 becomes liable to occur. Embodiment 3: This embodiment was provided with supporting blades, which did not directly serve to cut products, in addition to the projecting pressure cutting blades provided on the above embodiments. The provision of the supporting blades enables the concentration of excessively large repeated stress on the edge of the projecting pressure cutting blades to be lessened. Referring to Fig. 7, a die cutter 2 having guide flanges 11 on circumferential portions of both ends thereof is provided with projecting pressure cutting blades 1 formed in accordance with the shape of paper products to define product cutting regions A on the inner sides thereof. 10 denotes projecting pressure cutting blades not directly working to cut products of the present invention, i.e. so-called supporting blades provided besides the product-obtaining projecting pressure cutting blades 1. The supporting blades 10 are provided so as to compensate for a circumferentially discontinuous portion shown by X of the rotary driving roll body so as to extend in the circumferential direction thereof. The supporting blades 10 are formed of the same material as the projecting pressure cutting blades 1 so that the shape and height of the edges become the same as those thereof since stable cutting characteristics can be obtained by setting the abrasion rate of the waste blades substantially equal to that of the projecting pressure cutting blades 1. When a distance between the supporting blades is within the range of levels lower than that of the width of work paper P with the length of the former within the range of levels higher than that of the circumferential size of the discontinuous portion X of the die cutter 2, the excessively large repeated stress can be lessened, and the abrasion rates of the projecting pressure cutting blades 1 and supporting blades 10 can be set substantially equal, so that this die cut roll is advantageous in cutting performance and economical efficiency. The supporting blades 10 may be provided in more than two axial rows or formed to an arcuate shape. Embodiment 4: Fig. 8 shows a modified example of the supporting blades 10 of Fig. 7, which are provided on a die cutter 2, to which the present invention is applied, having two projecting pressure cutting blades 1 crossing each other to form continuous blades. Referring to Fig. 8, the supporting blades 10 are formed so as to compensate for an axially concentrated portion shown by Y of the projecting pressure cutting blades 1. The provision of these supporting blades 10 enables stress occurring due to a difference between the peripheral speed of the die cutter and that of the anvil roll and the feeding of a work to be lessened. Embodiment 5: Fig. 9 shows an example provided with a continuous portion 12 formed on a die cutter 2 having two projecting pressure cutting blades 1 crossing each other, instead of providing such an independent supporting blades 10 as shown in Fig. 8, so as not to form a stress concentrated portion. This continuous portion 12 comprises not a one-point cross of the projecting pressure cutting blades 1 having product cutting regions A but a linear continuous cross thereof elongated in the axial direction of the cutter roll. This continuous portion 12 extending in the axial direction of the die cutter 2 may also be formed so as to include circumferentially extending sections, or so as to extend in the circumferential direction, for the purpose of preventing the formation of a stress concentrated portion. This enables the concentrtation of an excessively large repeated stress on the two projecting pressure cutting blades 1 to be lessened. Embodiment 6: Fig. 10 shows another example which is not provided with supporting blades either just as Embodiment 5, and which is provided with projecting pressure cutting blades l so as to extend in the direction of the whole circumference of the die cutter for the purpose of preventing the formation of a stress concentrated portion. In the example of Fig. 10, plural projecting pressure cutting blades l formed in accordance with the shape of products to be cut are arranged side by side in the circumferential direction of a die cutter. These projecting pressure cutting blades 1 are disposed side by side circumferentially in a range Z including at least their respective circumferential end portions, so that stress concentration on the circumferential end portions of the cutting blades can be avoided. In Embodiments 5 and 6, supporting blades 10, which were provided in Embodiments 3 and 4 besides the projecting pressure cutting blades l, can, of course, be used additionally. Industrial Applicability: A die cut roll of a long lifetime can be provided which is capable of preventing the occurrence of minute chippings of the edges of the axially extending projecting pressure cutting blades, and maintaining a cutting performance even when the width of the edges increases due to the abrasion of the top smooth portions. A die cut roll of a long lifetime which has a long pressing cycle, especially, in an initial operating period can be provided. A die cut roll having a lasting cutting quality without encountering abnormal abrasion of the edges of the cutting blades, can be provided. The prevention of the chipping of edges of the cutting blades and the prolongation of the lifetime of a die cut roll, which are necessary to maintain a required shape of edges on contact surfaces of the cutting blades, can be attained by reducing the width of the edges of the projecting pressure cutting blades extending in the axial direction of a cutter.

Claims: A die cut roll comprising a die cutter (2) obtained by providing on a surface of a rotary driving roll with projecting pressure cutting blades (1), which are formed in accordance with the shape of a product to cut, and an anvil roll (3) adapted to receive an edge of each of said projecting pressure cutting blades of said die cutter, wherein inclined finishing surfaces (7) are formed adjacently to a top smooth portion (4) of an edge of each of said projecting pressure cutting blades by a grinding process, characterized in that said inclined finishing surfaces (7) have grinding flaws (8) which make an angle  of 50°-90°, and preferably 80°-90° to ridgelines defining said top smooth portion. A die cut roll according to claim 1, wherein a surface roughness Ra of said inclined finishing surfaces (7) is less that 0.3 µm.

Inventors: EGUCHI SHOUJI, IBUSUKI KOICHI, KITAHARA KOHEI, NAKAHARA KENJI, SAKAGUCHI SHIGEYA, TOKUMOTO KEI, EGUCHI, SHOUJI, IBUSUKI, KOICHI, KITAHARA, KOHEI, NAKAHARA, KENJI, SAKAGUCHI, SHIGEYA, TOKUMOTO, KEI
Applicants: NIPPON TUNGSTEN, NIPPON TUNGSTEN CO., LTD.
Application year: 1998
Main classification: B26F1
IPC codes: B26F1