METHOD AND PUNCH FORM FOR DIE-CUTTING OF PACKAGING MATERIAL AND THE USE THEREOF

Abstract: A punch form (1) for die-cutting of packaging material (7), comprising cutting knives and/or scoring rules, wherein the punch form at least partly is provided with sheet material provided in such a way that a crack-reducing effect is achieved in the packaging material, at least in connection to the cutting knives and/or scoring rules, wherein the sheet material is air permeable to during die-cutting evacuate air between the packaging material and the parts of the punch form which are provided with sheet material; a method for die-cutting packaging material by means of a punch form as above, in which air between the packaging material and the punch form provided with sheet material is evacuated; and the use of a punch form as above.

Description: METHOD AND PUNCH FORM FOR DIE-CUTTING OF PACKAGING MATERIAL AND THE USE THEREOF Technical field The present invention concerns a punch form, comprising cutting knives and/or scoring rules, wherein the punch form at least partly is provided with sheet material which is provided in the punch form so that a crack-reducing effect of the packaging material is achieved at least in association to the cutting knives and/or scoring rules; a method for die-cutting of packaging material by a punch form, comprising cutting knives and/or scoring rules and sheet material which is provided in the punch form so that a crack-reducing effect is achieved at least in association to the cutting knives and/or scoring rules, wherein the packaging material is brought in between said punch form and an anvil, whereby said punch form and said anvil is brought together so that the packaging material will be die-cut, and the use of a punch form as above. The expression "packaging material" shall here be considered to have a broad meaning and compile also, for example, display material. Background art Die-cutting of packaging material may be executed in different ways. Thus, a punch form may be stationary or movable. In the first case the punch material is fed in between the punch form and an anvil and in the second case the punch material is fed together with the punch form. In the punching nip, i.e. where the punching takes place, the packaging material is clamped between the cutting knives and/or scoring rules of the punch form and an anvil, and die-cutting occur rapidly. Cutting means, i.e. cutting knives, scoring rules etc, are generally mounted to a flat or cylindrical bed, a so called flat punch form and rotational punch form, respectively. For each package to be produced a specially formed punch form is required, which is mounted in the present die-cutting apparatus at the time for production. The punch anvils may have the form of a flat plate or a rotating cylinder. In the punch nip the cutting knives cut fully through the punch material while the scoring rules and other means only partly cut through or only deform the packaging material. Generally, score or foldlines are attained, which reduce the bending rigidity in the packaging material. The die-cut packaging material is usually pushed out of the punch form by means of resilient ejecting elements, usually so called rubber ejectors. Such rubber ejectors are generally in direct contact with the packaging material. After the rejection from the punch form, the die-cut packaging material is passed on and overflow material, so called die-cutting spill, is removed from the packaging blanks when they leave said punch form and said punch nip or directly afterwards. A slight denting of the packaging material often arises when it is brought upon the punch form, during the punch pressure load, during feeding throught the punch nip, during rejection and during the removal of spill, which can cause packaging blanks with wrong dimensions or wrong cutting positions or damages to the packaging blanks. The problem increases with increasing production speed. Another problem is damages to the surface of the packaging material caused by the rubber ejectors, especially when die-cutting pressure sensitive packaging materials and at high production speeds. These problems can be alleviated by providing a crack reducing sheet material between the punch form and the packaging material, as is shown in EP 454 753 Bl, which hereby is incorporated in this description. The crack reducing sheet material may be provided at parts of or over the whole punch form. Even with this solution problem may arise with damaged packaging blanks, with wrong dimensions or wrong cutting positions in relation to a graphic print or the like. These problems increase with increased production speed. Summary of the invention The object of the present invention is, in an easy and inexpensive way, to improve the known die-cutting art to reduce unwanted faults in the die-cut packaging blanks and at the same time allow higher production speed. According to the present invention this is accomplished by a method and a punch form, according to the preamble, which have the features shown in the appended claims. The invention implies that the crack reducing sheet material is provided with openings and holes, especially perforations. Alternatively a porous, air permeable sheet material may be used. The invention is based on the insight that air permeability solves the problem during die- cutting. The invention has proved to give the effect that stable contact rapidly occurs and that the packaging material rapidly flattens when brought upon the punch form. During use of the invention the air evacuates effectively between the packaging material and the punch form when the packaging material is brought upon the punch form. The same applies to when the punch form and the anvil rapidly are brought into the punch nip. It has shown that the die-cutting processes operates well even with high punching speeds, although increased punching speed increases the requirement on air permeability of the sheet material. In order to try to strengthen the above mentioned effect, negative pressure may be provided either to voids in the intervening space between the bottom of the punch form and the opening provided or air permeable sheet material, which voids preferably are defined by rubber ejectors, or directly to the openings. The punch form is preferably divided into a plurality of separate voids. Therefore, negative pressure may be provided selectively, both spatially and according to time, at different openings and voids, respectively, which, for example, enables retaining of the die-cut packaging blanks in the punch form while the die-cut spill is removed. Preferably, positive pressure may in a corresponding way selectively be provided to different openings and voids, respectively, which, for example, facilitates the removal of die-cut spill when the packaging blanks is retained by negative pressure. Of course the negative and positive pressures, respectively, be provided vice versa, for example, so that the die-cut spill is retained while the package blank is removed. Of course only some of the voids can be provided with openings. The provision of negative pressure also gives the advantage that no sliding of the punch material occurs in relation to the punch form during the die-cutting process. Negative pressure may be provided before the punch form and the packaging material is brought into the punch nip to be selectively disconnected after the punch nip and then totally disconnected after the removal of the spill. Those skilled in the art realize that negative pressure may also be applied to selective parts of the air permeable sheet material. Preferably the sheet material is mounted at substantially the same level above the different parts of the punch form, for example, on rubber ejectors of the same height, so that the punch material is prevented from denting. The sheet material ought to have such a high bending resistant so that the packaging material will not be dented into the punch form during the die- cutting process. The sheet material may preferably cover all of the punch surfaces of the punch form, including the areas of spill and a bit further outside the outer cutting knives. Thereby, the contact between the punch form and the punch material in the different parts of the punch form will be synchronized and become uniform, which reduces the emergence of disturbing acceleration or retardation forces in the punch material during the die-cutting process. The sheet material according to the present invention reassures that the rejecting of the packaging material occurs synchronically in different parts of the punch form and prevents effectively that parts of the packaging material get stuck in the punch form and disturb the subsequent production. It has been found that it is suitable with an air permeability of at least around 1.5 m per m and second measured over the surface of the punch form, preferably at least 2 m 3 per m 2 and second and more preferably at least 3 m 3 per m 2 and second at normal production speeds, typically 2-3 m/s. At higher production speeds the requirement on the air permeability of the sheet material increases. It has shown that the invention to a high degree prevent from problems that are connected to the packaging material sliding in relation to the punch form. The present invention that gives a possibility to increase the production speed and an improved die-cutting result, even for very light and floppy packaging materials. Further advantages is that the sheet material, especially when it is mounted at a level above the sharp edges of the cutting knives, protects the user from hurting himself on said cutting knives, and especially when the punch form is fully covered by sheet material the punch forms are more easily stacked and easier to clean from dust and paper material. One aspect of the present invention is that it can be seen as a further development of the invention in EP 454 753 Bl, which content is incorporated, as mentioned above, in this application. Brief description of the drawings Mentioned embodiments of the invention will now be illustrated as examples referring to the appended drawings, in which: Fig. 1 illustrates the invention in a process with a flat punch form and a flat anvil. Fig. 2 illustrates the invention in a process with a flat punch form and a rotating cylinder as an anvil. Fig. 3 illustrates the invention in a process with a rotational punch form and a rotating cylinder as an anvil. Fig. 4 illustrates schematically in detail a punch form provided with sheet material comprising holes. Fig. 5 illustrates schematically in detail a punch form provided with a porous, air permeable sheet material. Fig. 6a, 6b and 6c illustrates flat punch forms from above with examples of positions of openings, slits and perforations, respectively, in the sheet material. Fig. 7 illustrates two packages of a die-cut packaging material. Fig. 8 illustrates the packages in fig. 7 after the removal of spill. Fig. 9 laterally illustrates sucking of the packages in fig. 7 while the spill is removed. Fig. 10 laterally illustrates sucking of the spill while the packages of fig. 7 is removed. Description of preferred embodiments Referring to fig. 1 an embodiment of the present invention shall be described in a die-cutting process in which a flat punch form 1, a flat anvil 2 and means (not shown) to push the punch form 1 against the anvil 2 is used. The flat punch form 1 is provided with a sheet material 3, which is provided, for example attached by adhesive, on resilient elements 4, so called rubber ejectors 4. The sheet material 3 is provided with openings 5, for exampel circular with a typical diameter of around 4 mm or of slit form with a typical width of around 3 mm. The length of the slitlike openings vary according to the form of the packaging blanks. The openings 5 are preferably positioned in the vicinity of the rubber ejectors 4 in order not to weaken the rigidity of the sheet material 3 too much but neither too close to these in order not to disturb their function. In the figs. 6a, 6b and 6c, three different ways of positioning the openings in the sheet material is illustrated. Fig. 6a shows holes, fig. 6b shows slits and fig. 6b shows perforations. Along cutting knives 6 and scoring rules 6 there are slits 16 provided in the sheet material. These slits is not comparable witht the air evacuating openings 5 in the sheet material since the sheet material tightly fits the die-cutting means 6 and since the rubber ejectors 4 are provided close up to the die-cutting means, i.e. there is nearly no space into which air could be evacuated. The sheet material 3 is preferably mounted at a level above the sharp edges of the cutting knives 6 so that the sheet material 3 comes into contact with the packaging material 7 that shall be die-cut before the die-cutting means 6 in the punch nip 8. The packaging material 7 is fed onto the anvil 2, the punch form 1 is pushed against the anvil 2 and the packaging material 7 so that a packaging blank 9 is die-cut. When the punch form 1 is pushed against the anvil 2 there are in normal cases a risk that an air cushion occurs between the packaging material 7 and the sheet material provided parts of the punch form 1. The problems increase with increased speed. The push speed is of an order of magnitude of ten times larger than the feeding speed of the punch material into the punch nip 8. Since the sheet material 3 according to the invention is air permeable the air between the packaging material 7 and the sheet material 3 will be evacuated, whereby the previously shown problems lapse. After the die-cutting the packaging material 7 is fed out of the punch nip 8 and the die-cut packaging blank 9 is cleaned from the die-cutting spill 10 in a conventional manner. The sheet material 3 may, for example, be of plastic, preferably of polypropylene plastic, and of a typical thickness of 1 - 1 Vi mm. Those skilled in the art, realize that instead of distinct openings a perforated, i.e. provided with a larger amount of smaller holes, or in itself porous, air permeable sheet material may be used. This applies of course to all of the illustrated embodiments. An example of a porous air permeable sheet material is a web of plastic, preferably polypropylene plastic. The web may preferably be mounted in double layers. Fig. 2 shows another embodiment of the present invention. The punch form 1 is in this die- cutting process flat and movable and the anvil 2 is a rotating cylinder. The punch nip occurs where the cylinder 2 is pressed against the punch form 1 during the die-cutting procedure. The packaging material 7 is positioned onto the punch form 1 provided with sheet material, whereby air present between the packaging material 7 and the sheet material 3 is evacuated through said air evacuating openings 5, perforations or porous, air permeable sheet material 3. Thereafter the punch form 1 is fed into and through the punch nip 8, whereafter the die-cut package blanks 9 are cleaned from spill 10 in a conventional way. In order to further decrease sliding movements of the packaging material 7 during positioning of the packaging material, the transport into the punch nip 8 and in the punch nip 8 itself, a negative pressure may be applied to the sheet material 3 provided with openings, from the inside of the punch form 1 by negative pressure forming means (not shown in fig. 2). This is illustrated more in detail in figs. 4 and 5, where fig. 4 shows an embodiment with openings in the sheet material 3 and fig. 5 shows an embodiment with a perforated or porous, in itself air permeable sheet material 3. In fig. 5 a variant is shown where all of the sheet material covering the punch form is perforated or porous. Of course only a few parts of the sheet material may be perforated, porous or provided with openings. The bottom 12 of the punch form 1, the sheet material 3 and, for example, rubber ejectors 4 forms voids 13. Air channels, preferably conduits 11 in the form of tubes mounted in grooves or channels, are provided in the bottom 12 of the punch form 1, between the negative pressure forming means 15 and those voids 13 to be provided with negative pressure. The punch form 1 is preferably provided with a number of separate voids 13. When a negative pressure is applied to the voids 13 in fig. 4 a suction will occur in the openings 5 of the sheet material 3. The openings 5 in the sheet material 3 may be provided with negative pressure one by one by letting a tube 11 be mounted all the way up to respective opening 5, see fig. 4. In such a way different parts of the punch form 1 may selectively be provided with negative pressure at different times. If you go back to the die-cutting process which is illustrated in fig. 2 the sucking function is used in the following way. When the packaging material 7 is positioned onto the punch form 1 a negative pressure is also applied to the sheet material 3 so that the packaging material 7 remains fixed to the punch form 1. This negative pressure is maintained during the transport and into the punch nip 8. Thereafter, preferably those openings 5 or voids 13 corresponding to the spill 10 successively are disconnected, whereby the spill 10 is removed from the die-cut package blanks 9 while the package blanks 9 still remain fixed by means of the negative pressure. This can be seen in figs. 7, 8, 9 and 10, where fig. 7 show two package blanks 9 in a die-cut packaging material 7. The dashed area shows the spill 10. The packaging blanks 9 have obtained score lines 14. Fig. 8 shows the two package blanks 9 with the spill 10 removed. In fig. 9 it is illustrated how the package blanks 9 are sucked onto the sheet material 3 while the spill 10 is removed. Of course the other way around may be the case, see fig. 10, where instead the spill 10 are sucked onto the sheet material 13 and the package blanks 9 is removed. After the cleaning operation the negative pressure is disconnected totally and the package blanks 9 are passed on, whereby the punch form 1 returns to the start position. If the die-cut assembly shown in fig. 1 is formed so that the punch form 1 and the anvil 2 have swopped places, i.e. the packaging material 7 is fed onto the punch form 1 and the anvil 2 is pushed against the punch form 1 , a sucking function according to above may be provided in the punch form 1 , of course. Fig. 3 further shows an embodiment of the present invention, where the sheet material 3 with openings is mounted on a rotational punch form 1, i.e. a cylindrical punch form 1. Also the anvil 2 is cylindrical and both the punch form 1 and the anvil 2 rotates but in opposite directions. The packaging material 7 is fed into the punch nip 8 between the punch form 1 and the anvil 2 and the air between the packaging material 7 and the punch form 1 is evacuated through the openings 5 in the air permeable sheet material 3. After the punch nip 8, the spill 10 is removed in a conventional way, also spill 10 that get stuck in the punch form 1. Also this embodiment may be provided with a sucking function, as described above. In this case the openings 5 and the voids 13, respectively, in the punch form 1 are connected to a negative pressure forming means via transmission means (not shown), which is provided at one of the axle mountings of the rotational punch form 1. Additionally, control means (not shown) for controlling the negative pressure are provided so that the negative pressure successively with the rotation of the punch form 1 is provided before the punch nip 8 to either selectively be disconnected after the punch nip 8 and totally after the cleaning or be totally disconnected after the punch nip 8. Of course the rotational punch form 1 may be used together with a flat anvil 2, too.

Claims: CLAIMS 1. A punch form for die-cutting of packaging material, comprising cutting knives and or scoring rules, wherein the punch form at least partly is provided with sheet material, which is provided in such a way in the punch form that a crack-reducing effect in the packaging material is achieved at least in connection with the cutting knives and/or scoring rules, wherein the sheet material is air permeable to be able to, during punching, evacuate air between the packaging material and the portions of the punch form, which are provided with sheet material. 2. The punch form according to claim 1 , wherein the sheet material is provided with air evacuating openings. 3. The punch form according to claim 1 or 2, wherein the sheet material is perforated to accomplish desired air permeability. 4. The punch form according to claim 1 , 2 or 3, wherein the sheet material is porous to accomplish the desired air permeability. 5. The punch form according to claim 1, 2, 3 or 4, wherein the air permeability at least is 1.5 m 3 per m 2 and second taken over the surface of the punch form, preferably at least 2 m 3 per m 2 and second and most preferably at least 3 m 3 per m 2 and second. 6. The punch form according to claim 1 , 2, 3, 4 or 5, wherein the punch form has the provision for application of a negative pressure from the side of the sheet material, which is not facing the packaging material to be die-cut, through the air permeable sheet material so that the packaging material to be die-cut is sucked against the sheet material of the punch form. 7. The punch form according to claim 6, wherein conduits are directly applied to at least one opening in the sheet material of the punch form for connection to negative pressure forming means. 8. The punch form according to claim 6, wherein conduits are connected to at least a defined void where openings are provided in said sheet material, for connection to negative pressure forming means. 9. The punch form according to claim 6, 7 or 8, wherein the punch form is divided into more than one defined void. 10. The punch form according to any of the previous claims, wherein the punch form is fully covered by said sheet material. 11. A method for die-cutting punch material by means of a punch form, comprising cutting knives and/or scoring rules and sheet material, which is provided in such a way in the punch form that a crack-reducing effect is achieved in the packaging material, at least in connection to the cutting knives and/or scoring rules, where the packaging material is fed into said punch form and an anvil, wherein the punch form and the anvil is brought together so that the packaging material is die-cut, in which an air permeable sheet material is used, through which air between the punch material and the at least partly with sheet material covered punch form is evacuated. 12. The method according to claim 11 , in which a sheet material with openings or a porous perforated sheet material is used. 13. The method according to claim 11 or 12, in which air is actively evacuated through the sheet material by sucking. 14) The method according to any of claims 11-13 )in which a negative pressure is applied to ^ the punch form so that the packaging material Islϊucked against the air permeable sheet material of the punch form. 15. The method according to claim 14, in which negative pressure selectively is connected and disconnected to the different sheet material covered parts of the punch form. 16. The method according to claim 14 or 15, in which negative pressure is applied before feeding into the area where the punch form and the anvil cooperates to die-cut and selectively is disconnected after said area. 17. The method according to claim 14, 15 or 16, in which the negative pressure is disconnected after the superflous die-cutting spill has been removed after the die-cutting. 18. The method according to claim 13, 14, 15, 16 or 17, in which one or many from the packaging material die-cut packages are sucked onto the punch form and the negative pressure for the die-cutting spill is disconnected while the die-cutting spill is removed. 19. Use of a punch form, die-cutting packaging material, comprising cutting knives and/or scoring rules and an air permeable sheet material which at least partly covers the punch form and which is provided in the punch form for contact with said packaging material during die- cutting of packaging material so that air between the packaging material and the parts of the punch form which is provided with sheet material is evacuated through the air permeable sheet material during die-cutting of the packaging material.

Inventors: CAVLIN SOEREN, CAVLIN, SOEREN
Applicants: CAVLIN SOEREN, SOBI HB, CAVLIN, SOEREN
Application year: 2000
Main classification: B31B1
IPC codes: B26D7, B26F1, B31B1