SE544923C2 - Punch form and method for scoring laminated packaging material - Google Patents

Abstract

A punch form (1) for scoring laminated packaging material (10) having a cutting knife (4), a scoring rule (5) and rubber ejectors (6) and at least partly dressed with a sheet material (7) arranged at the rubber ejectors (6). The rubber ejectors (6) are provided symmetrically on both sides of the at least one scoring rule (5) and the rubber ejectors (6) protrude further than the scoring rule (5). The sheet material (7) is provided over the rubber ejectors (6) and the at least one scoring rule (5). The sheet material (7) has a bending stiffness and a Young's modulus between 1200 and 1450 MPa, a low adhesion of maximum 0,050 N/m and a friction coefficient of maximum 0,39. A method using the punch form (1) whereby the at least one scoring rule (5) pushes down the sheet material (7) into the packaging material (10) and when the punch form (1) retires, the sheet material (7) flexes back and thus enhance cleaning of spill, together with the rubber ejectors (6).

Description

PUNCH FORM AND l\/IETHOD FOR SCORING LAl\/IINATED PACKAGING MATERIAL Field of invention The invention relates to punch form and a method for scoring laminated paperbased pack- aging material, especially corrugated cardboard. Preferably, the punch form and method also perform die-cutting and is at least partly dressed with a sheet material so that a crack reducing effect on the laminated packaging material is achieved at least in association with the scoring rule and cutting knives. The laminated packaging material may be used in pack- aging or for display, for example. The punch form and method may be performed also on similar material. The laminated packaging material is brought in between said punch form and an anvil, whereby the punch form and the anvil are brought together so that the lami- nated packaging material will be scored and die-cut.

Technical background Die-cutting or punching of packaging material may be performed in different ways. Thus, a punch or die-cutting form may be stationary or movable. ln the first case the packaging material is fed in between the punch form and the anvil and in the second case the packag- ing material is fed together with the punch form. ln the punch nip, i.e., were the punching takes place, the packaging material is clamped between the cutting knives and the scoring or creasing rules ofthe punch form and the anvil, and the cutting and scoring occur rapidly.

Cutting means, such as cutting knives and scoring rules, are generally mounted on a flat or cylindrical bed, a so-called flat punch form and rotational punch form, respectively, for each package or display to be produced a specially designed punch form is required, which is mounted in a die-cutting apparatus at the time for production. The punch anvil may have the form of a flat plate or a rotating cylinder. ln the punch nip the cutting knives cut fully through the packaging material, while the scor- ing rules and other means only partly cut through or deform the packaging material. Gen- erally, score or fold lines are attained, which reduce the bending rigidity in the packaging material.

During die-cutting cracks easily arise in the die-cut and scored packaging material, especially in the vicinity ofthe cutting knives and scoring rules, due to the severe stress in the packag- ing material.

The die-cut packaging material is pushed out of the punch form by means of resilient ele- ments generally so-called rubber ejectors. Such rubber ejectors are conventionally in direct contact with the packaging material.

After the ejection from the punch form the die-cut packaging material is passed on and overflow material, so-called die-cutting spill, is removed from the package or display blanks, either in connections of the ejection of the blanks from the punch form and leaves the punching nip in question or at a special operation directly afterwards.

When feeding packaging material to and from the punching nip, during the punch pressure is activated or deactivated, at ejection and connected removal of spill, the packaging mate- rial sometimes is deformed in an unwanted way, for example, being bent and/or sheared. As a result, a certain percentage of the produced blanks will be damaged, incompletely cleaned from spill or obtain erroneous dimensions. The problems increase with increasing production speed and the level of problem varies for packaging material ofdifferent rigidity, moisture level, etc.

Another problem is damages in the surface of the packaging material caused by the at cer- tain points arranged rubber ejectors.

About thirty years ago these problems were in some extent alleviated with a thin and flexi- ble sheet material in the form of a foil or film provided over at least parts ofthe punch form. See WO 90/08018. At that time the die-cutting process was not so rapid, and the packaging material was made of higher quality, i.e., more paper per surface area and contained more or less no recycled fibres. lt was important to keep the packaging material fixed and still in between the punch form and the anvil. Thus, the thin and flexible film had a relatively high friction coefficient.

About ten years later the packaging material contained a larger amount of recycled fibres, which increased the cracking during production. At the same time the market required less cracks. Quicker production velocities were sought after, too. The solution of WO 90/08018 was not working any longer. A radical solution was described in WO 03/066291, where in- stead of increasing the requirement of keeping the packaging material fixed and still be- tween the sheet material in the punch form and the anvil, to let a relative sliding between the sheet material and the packaging material. The sheet material had slits for the cutting knives and scoring rules and the packaging material could slide between the cutting knives during the punching impact and in this way the punch energy was spread out over a larger area. This sheet material had not only a low friction surface but also a low adhesion, which decreased the risk of incomplete cleaning of spill. With this technology more or less all cracks disappeared. Due to these advantages, the speed of production could be risen.

Today, even more recycled fibres are used in packaging material and also less paper in weight per surface area. Thus, the packaging material of today is brittle and sensitive. A further increase of production speed is desired. The solution of WO 03/066291 is still work- ing when it comes to crack reduction. The cleaning of spill works, too. But in the industry, it is always of interest to refine the technology, and take away all the problems. This invention focusses on solving the problem with unsatisfactory score or fold lines or notches in lami- nated paperbased packaging material, such as corrugated cardboard or honeycomb card- board, of today and in the future. The fold lines will act differently depending on the varia- tion of crush resistance in the material, for example the inner flutes or holes and walls of a honeycomb and their positions. Uneven moisture levels in the laminated packaging material will also induce irregular crush resistance.

Since the crush resistance ofthe laminated paperbased packaging material differs depend- ing on the inner layer and positions of walls, voids, and flutes, the crush deformation on opposite sides of a scoring rule will be different, causing an asymmetrical score. When folding, the laminated packaging material will fold in an unwanted way. Often the fold will occur outside the centre ofthe score, sometimes on both sides, making a wiggly fold, some- times on only one side, thus changing the measurement of the finished corrugated card- board product. Problems arise also in machines for automatic raising of packaging material. ln Fig 3a and 3b two figures show the problem in the prior art with the uneven crush defor- mation with a conventional scoring rule against a piece of corrugated cardboard. ln Fig. 3a a schematic cross-sectional view is shown of a piece of corrugated cardboard 100, having an upper liner 101 and a lower liner 102 and therebetween a flute layer 103. The flute layer 103 is glued at the upper liner 101 at the tops 104 of the flutes and at the lower liner 103 at the bottoms 105 of the flutes. A scoring rule 106 hits the corrugated cardboard 100 at the top of a flute 104. This will give a symmetric crush deformation and the upper liner 101 will deform also in a symmetrical manner. ln Fig. 3b the scoring rule 106 instead hits close to the top 104 of the flute. This renders an asymmetrical crush deformation of the flute and the upper liner 101. As can be seen in Fig. 3b the upper liner 101 after the scoring punch has a longer indent between the end of the score line 107, i.e., the top of the next flute, to the bottom 108 of the indent on the side where most ofthe crushed flute 109 is present than the other side between the bottom 108 and the indent to the other end of the score line 110, i.e., the top of the next flute. The inclination of the two sides of the score line is also different. When folding a corrugated cardboard having an asymmetrical score line like in Fig. 3b the folding will tend to move out from the bottom 108 towards the next flute top One way of trying to solve the problem has been to provide the punch forms with wider scoring rules. Unfortunately, this has not solved the problem. lnstead, surprisingly, this has led to even more side dislocation during the folding. Additionally, wider scoring rules will increase the cost and the punch form makers cannot use their automatic machines for wider scoring rules, which further add costs to the punch forms.

Another way oftrying to solve the problem has been to add a slanted, porous or solid rubber wedge on both sides of a scoring rule, in flush with the rule, so that a triangle having an obtuse angle is formed where the rule forms the peak. These rubber wedges give very wide score or fold lines, up to several centimetres instead of conventional few millimetres, which is very negative for folding exactness as well as for stacking, and handling strength of boxes, why both end users of boxes, as well as die-makers, are still calling for a much better solu- tion.

Summary of the invention A solution which surprisingly delimit the problems ofthe score or fold lines is to provide the punch form with a sheet material, which has an appropriate bending stiffness, low friction coefficient and low adhesion and does not break by the punching forces. The sheet material is arranged at conventional rubber ejectors on both sides of the scoring rule and the sheet material covers the scoring rule.

According to a first aspect of the present invention a punch form for die-cutting and scoring laminated paperbased packaging material, such as corrugated cardboard, is provided hav- ing at least one cutting knife, at least one scoring rule and rubber ejectors, all arranged on a first side of the punch form. The punch form is at least partly dressed with a sheet material arranged at the rubber ejectors, a slit is provided for each cutting knife in the sheet material. The rubber ejectors are provided symmetrically on both sides of the at least one scoring rule and the rubber ejectors protrude further, out of the first side of the punch form, than the scoring rule. The sheet material is provided over the rubber ejectors and the at least one scoring rule. The sheet material has an appropriate bending stiffness and a Young's modulus between 1200 and 1450 I\/|Pa, a low adhesion of maximum 0,050 N/m and a fric- tion coefficient of maximum 0, According to some embodiments the sheet material has a thickness in the range of 0,8-1,5 mm. According to some embodiments each rubber ejector is positioned with a distance to the scoring rule between 2-5 mm, preferably about 3 mm.

According to some embodiments the rubber ejectors protrude 2-4 mm further out from the first side of the punch form than the scoring rule.

According to some embodiments the width of the rubber ejectors is 9-15 mm, preferably 10-11 mm.

According to some embodiments the sheet material is detachably arranged or fixedly ar- ranged at the rubber ejectors.

According to some embodiments the scoring rule has a width of 0,75-1,0 mm.

According to some embodiments the sheet material is of a hydrophobic material or pro- vided with a surface of hydrophobic material, preferably on both sides.

According to some embodiments the adhesion ofthe sheet material is less than 0,043 N/m. According to some embodiments the friction coefficient of the sheet material is maximum 0, According to some embodiments the Young's modulus of the sheet material is between 1300 and 1350 l\/lPa.

According to a second aspect of the invention a method of die-cutting and scoring a lami- nated paperbased packaging material using a punch form according to any one of the de- scribed above is provided. An anvil is disposed a spaced distance from the punch form and facing the at least one cutting knife and the at least one scoring rule of the punch form. The sheet material comes into planar contact with the packaging material. The method com- prises feeding the packaging material between the punch form and the anvil and bringing the punch form and the anvil together so that the packaging material is die-cut and scored. The at least one scoring rule pushes down the sheet material into the packaging material providing a score orfold line, without breaking the sheet material and then, when the punch form retires, the sheet material flexes back to its unloaded shape and thus enhance cleaning of spill, in combination with the rubber ejectors ofthe punch form.

Punching with this inventive punch form provides a stable, deep middle point in the score or fold line causing a reliable folding along the score lines. Tests have been carried out with very good and reliable results. lt is conceivable that a part of the solution, when trying to understand the results, is that the packaging material may slide much easier against the sheet material at the position of the scoring rule than against the scoring rule without any sheet material therebetween. The sliding will spread surface forces even better and thus the risk of cracking and punching through a liner of the laminated packaging material is largely decreased. Due to this de- creased risk of crushing the liner, the new inventive scoring tool, i.e., the combination of the scoring rule and the sheet material, will be punched deeper into the laminated packag- ing material, roughly a distance deeper corresponding to the thickness of the sheet mate- rial. This possibility to punch deeper will crush any walls/flutes present inside the laminated packaging material more evenly. Because of the more evenly crushed inner material of the laminated packaging material, the folding will not be influenced as much and thus can fol- low the score or fold line in the planned manner.

To provide as good scoring line as possible the new inventive scoring tool, i.e., the combi- nation of the scoring rule and the sheet material, be punched so deep into the laminated packaging material so a darker line is slightly visible on the opposite side of the laminated packaging material, but not so deep that any cracking occurs.

As acknowledged above, the sheet material flexes back to its unloaded shape when the punch form retires and thus this will enhance the cleaning of spill, in combination with the rubber ejectors of the punch form. After some time, the sheet material possibly will not flex back totally, i.e., a permanent deformation may occur, providing another unloaded shape. This will not affect the cleaning of spill particularly much, but obviously a less flexing back ofthe sheet material will contribute less, but the sheet material will still contribute and thus help the rubber ejectors with the cleaning of spill. ln some embodiments the sheet material is fixedly arranged at the rubber ejectors and dur- ing the punching the rubber ejectors will be elastically sheared towards the scoring rule, which will further contribute to the cleaning of spill during the elastic springing back to the initial shape of the rubber ejectors.

Short description of the drawings The present invention will be described in more detail under referral to the enclosed draw- ings, in which Fig. 1 shows a part of an embodiment of a punch form according to the invention before punching in a cross-sectional view.

Fig. 2 shows a part of an embodiment of a punch form according to the invention during punching in a cross-sectional view and an enlarged detail of the deepest position of the scoring rule in a cross-sectional view.

Figs. 3a and 3b shows prior art.

Detailed description of embodiments of the invention ln Fig. 1 partial, cross-sectional view is shown of an embodiment of the inventive punch form 1 is shown, when in an unloaded position. The punch form 1 has a first side 2 and a second side 3. On the first side 2 at least one cutting knife 4, at least one scoring rule 5 and rubber ejectors 6 mounted in a conventional way. The punch form 1 is at least partly dressed with a sheet material 7 arranged at the top of the rubber ejectors 6. The sheet material 7 may be loosely arranged, detachably arranged or fixedly arranged. For example, the sheet material 7 could be brought into the nip at the time for punching, preferably arranged in a frame (not shown), or attached by means of an adhesive, which could be of the type where it is possible to attach and detach or of the type which fixedly attach the sheet material 7 to the rubber ejectors 6. The sheet material 7 is provided over the rubber ejectors 6 and the at least one scoring rule 5. A slit 8 is provided for each cutting knife 4 in the sheet material The rubber ejectors 6 are provided symmetrically on both sides of the at least one scoring rule 5, positioned with a distance to the scoring rule 5 between 2-5 mm, preferably about 3 mm. The rubber ejectors 6 protrude further, out of the first side of the punch form 2, than the scoring rule 5. Preferably, the rubber ejectors 6 protrude 2-4 mm further out from the first side 2 of the punch form 1 than the scoring rule 5. The width of the rubber ejectors 6 may be 9-15 mm, preferably 10-11 mm, and the hardness are of conventional type. The scoring rule 5 is blunt and of a conventional type and may have a width of 0,75-1,0 mm.

The sheet material 7 has an appropriate bending stiffness and a Young's modulus between 1200 and 1450 I\/|Pa, preferably between 1300 and 1350 I\/|Pa. The sheet material 7 cannot be flexible as a film or foil but must have a bending stiffness. The sheet material 7 further has a low adhesion of maximum 0,050 N/m, preferably maximum 0,033 N/m. The friction coefficient of the sheet material 7 is maximum 0,39, preferably maximum 0,33. The sheet material 7 may be of a hydrophobic material or provided with a surface of hydrophobic material, preferably on both sides. The sheet material 7 may have a thickness in the range of 0,8-1,5 mm. Preferably, the sheet material is made of a polymer.

An anvil 9 is provided opposite the first side 2 of the punch form 1. Therebetween laminated packaging material 10 to be die-cut is provided. The laminated packaging material 10 has an upper liner 11, a lower liner 12 and a middle layer 13, in the shown case a fluting layer of corrugated cardboard. lt could be walls of a honeycomb cardboard, too, for example. The shown packaging material 10 is a conventional corrugated cardboard with today's quality having a thickness of normally 3-4 mm. ln Fig. 2 the embodiment of a punch form 1 is shown during the punching of a laminated paperbased packaging material 10. The punch form 1 is in its deepest position, i. e., when the scoring rule 5 reaches deepest into the packaging material The scoring rule 5 reaches as deep as in the prior art shown in Figs. 3a and b during the punching in the deepest position before the punch form 1 is retracted. But in the present invention the sheet material 7 is present on top ofthe scoring rule 4 so that the upper liner 11 will be pushed down further, about the same distance as the thickness of the sheet ma- terial 7. Due to the low friction coefficient of the sheet material 7 forces and stress will be spread along the surface of the upper liner 11 so that it will not crack or become crushed.

Also, the scoring rule 5 may slide on the opposite side of the sheet material 7 if needed.

The middle layer 13 will be crushed more than in the prior art, as can be seen in the detailed view of Fig 2. Thus, the score line will be more symmetrical. The crushing ofthe middle layer 13 gradually increases along the depth of the score line. The score line will have a width of about 5-10 mm at the upper liner 11, with a distinct lowest point in the middle, running along the score line.

Due to this the folding will be more reliable, as previously discussed. Since there are only slits 8 for the cutting knives 4 the risk of spill getting caught in slits is delimited. The cleaning ofthe spill is also enhanced due to the flexing back of the sheet material 7 when the punch form 1 is retracted.

The invention also covers a method ofdie-cutting and scoring a laminated paperbased pack- aging material using such a punch form 1. An anvil 9 is disposed a spaced distance from the punch form 1 and facing the at least one cutting knife 4 and the at least one scoring rule 5 of the punch form 1, see Fig 1. The sheet material 7 comes into planar contact with the packaging material 10. The method comprises feeding the packaging material 10 between the punch form 1 and the anvil 9 and bringing the punch form 1 and the anvil 9 together so that the packaging material 10 is die-cut and scored. The at least one scoring rule 5 pushes down the sheet material 10 into the packaging material providing a score or fold line, with- out breaking the sheet material 7 and then, when the punch form 1 retires, the sheet ma- terial 7 flexes back to its unloaded shape and thus enhance cleaning of spill, in combination with the rubber ejectors of the punch form.

The skilled person will be able to reach the result with a more reliable score or fold line by fine tuning of rubber ejectors, height of cutting knifes and scoring rules, sheet material and so on for each type of laminated packaging material using the information in the present description. By using the sheet material cracks along the cutting knives will also be delim- ited, as well as the contact wear of the ejection rubbers against the liner surfaces due to friction and adhesion forces.

Claims (10)

1. A punch form (1) for die-cutting and scoring laminated paperbased packaging mate- rial (10), such as corrugated cardboard, having at least one cutting knife (4), at least one scoring rule (5) and rubber ejectors (6), all arranged on a first side (2) of the punch form (1), the punch form (1) is at least partly dressed with a sheet material (7) arranged at the rubber ejectors (6), a slit (8) is provided for each cutting knife (4) in the sheet material (7), characterised in that rubber ejectors (6) are provided sym- metrically on both sides of the at least one scoring rule (5), the rubber ejectors (6) protrude further, out of the first side (2) of the punch form (1), than the scoring rule (5) and the sheet material (7) is provided over the rubber ejectors (6) and the at least one scoring rule (5), wherein the sheet material (7) has an appropriate bending stiff- ness and a Young's modulus between 1200 and 1450 I\/|Pa, a low adhesion of maxi- mum 0,050 N/m and a friction coefficient of maximum 0, A punch form according to claim 1, wherein the sheet material (7) has a thickness in the range of 0,8-1,5 mm. A punch form according to claim 1, wherein each rubber ejector (6) is positioned with a distance to the scoring rule (5) between 2-5 mm. A punch form according to claim 1, wherein the width of the rubber ejectors (6) is 9-15 mm, preferably 10-11 mm. A punch form according to claim 1, wherein the sheet material (7) is of a hydropho- bic material or provided with a surface of hydrophobic material, preferably on both sides. A punch form according to claim 1, wherein the adhesion of the sheet material (7) is less than 0,043 N/m. A punch form according to claim 1, wherein the friction coefficient of the sheet ma- terial (7) is maximum 0, A punch form according to claim 1, wherein the Young's modulus of the sheet ma- terial (7) is between 1300 and 1350 I\/|Pa. A punch form according to claim 1, wherein the sheet material (7) is detachably ar- ranged or fixedly arranged at the rubber ejectors (6).10. A method ofdie-cutting and scoring a laminated paperbased packaging material us- ing a punch form (1) according to any one ofthe preceding claims, wherein an anvil (9) is disposed a spaced distance from the punch form (1) and facing the at least one cutting knife (4) and the at least one scoring rule (5) of the punch form (1), the sheet material (7) coming into planar contact with the laminated packaging material (10), the method comprising feeding the packaging material (10) between the punch form (1) and the anvil (9) and bringing the punch form and the anvil together so that the laminated packaging material (10) is die-cut and scored, whereby the at least one scoring rule (5) pushes down the sheet material (7) into the laminated packaging material (10) providing a score or fold line, without breaking the sheet material (7) and then, when the punch form (1) retires, the sheet material (7) flexes back to its unloaded shape and thus enhance cleaning of spill, in combination with the rubber ejectors (6) of the punch form (1).