WO2006016175A2

WO2006016175A2 - Creasing plastic sheet materials

Info

Publication number: WO2006016175A2
Application number: PCT/GB2005/003172
Authority: WO
Inventors: Thomas Harney; Robin Arnold Nailer
Original assignee: Field Group Plc
Priority date: 2004-08-13
Filing date: 2005-08-12
Publication date: 2006-02-16
Also published as: GB0418165D0; WO2006016175A3; GB2417010A

Abstract

A method of cold forming a crease line (12) in a sheet plastics material (14) is disclosed which comprising the steps of positioning the sheet material (14) over a planar platen surface (2), and forming the crease line by bringing a scoring rule (4) into engagement with the plastic sheet material (14) and deforming the sheet material between the end of the rule (4) and the platen surface (2), the rule having a main body portion (8) and a pointed tip portion (10).

Description

CREASING PLASTIC SHEET MATERIALS

The present invention relates to creasing plastic sheet materials and in particular to a process and apparatus for effecting the same. More particularly the invention relates to a method and apparatus which will allow sheet material to be creased to form creases with measurably consistent crease resistance values which facilitates automatic machine erection, lading and filling of product.

Traditionally cartons and similar packages have been made from paperboard or similar paper based materials. However, there is now a move towards the use of plastic sheet materials in such cartons .

Paperboard cartons typically comprise a series of crease lines which allow the sheet material to be erected into the finished shape. In traditional paperboard cartons, these fold lines are created using a rule which deforms the sheet material to form the crease line. The creased blank is then erected, either manually or by machine, into the carton. Such methods have not, however, been successfully employed on plastic sheet materials to date. It is more usual in plastic sheet materials to form a hinge line ultrasonically, or by heat creasing. However, these are expensive and complicated procedures.

Accordingly, the present invention seeks to provide a simplified method for forming crease lines in sheet plastics material.

From a first aspect, therefore, the present invention provides a method of cold forming a crease line in a sheet plastics material comprising the steps of: a) positioning the sheet material over a planar platen surface; b) forming the crease line by bringing a scoring rule into engagement with the plastic sheet material and deforming the sheet material between the end of the rule and the platen surface, the scoring rule having a main body portion and a pointed tip.

The invention also extends to creasing apparatus for creasing a plastics sheet material, comprising a planar platen surface and a scoring rule, which in use is brought into engagement with the plastic sheet material to deform the sheet material between the end of the rule and the platen surface, the rule having a main body portion and a pointed tip portion.

It has been found that by using a scoring rule, a relatively high force can be applied to the rule without it buckling or deforming while at the same time a satisfactory deforming force can be applied to the plastics material to neck out the plastics material to form a very satisfactory crease line.

Preferably the scoring rule is a 2pt scoring rule, having a main body width of 0.7 mm.

Preferably the tip has an included angle of between 60° and 110°, more preferably between 80° and 105°. Preferred included angles include 84° and 104°.

The pointed tip makes it easy to produce a crease having a relatively low crease strength, which means that the plastic sheet may be formed more easily into a desired shape.

The tip preferably tapers symmetrically from the main body portion of the rule.

Preferably the tip at least of the tool has a Rockwell C hardness of over 55, more preferably 60 or more. This assists in reducing wear on the tool and ensures that the crease depth remains constant through a prolonged production run.

Preferably the plastics material is cut at the same time as it is creased using a cutting rule. This cutting rule cuts completely through the plastics material to the underlying platen surface. The cutting rule and scoring rule are preferably mounted such that the tip of the scoring rule is set back 0.2 mm from the tip of the cutting rule. With such an arrangement, scoring rule cuts through enough of the plastic material to ensure that the processed material has a weak crease suitable for running on a carton- erecting machine. At the same time it does not give so weak a crease that the folded carton after the gluing step has no gape in it. Gape is an important property of a folded glued carton; it ensures that a carton does not collapse when pulled from a magazine by the feeding arm, but readily assumes a hollow shape. The use of a scoring rule having a smaller setback has been found to result in cartons which can be used immediately straightaway after gluing and folding, but which lose their gape after only two to three months in storage. This is not acceptable as it may be some time between a carton being creased and eventually being folded and filled.

The rule is typically pushed into the plastics sheet to a depth of between 50% and 90% of the sheet thickness, in some cases over 75% of the sheet thickness .

Preferably the plastics sheet material is 300 to 800 microns thick, more preferably 350 to 650 microns thick, and the thickness of the material is typically reduced to between 100 and 250 microns, more preferably to between 100 and 200 microns, more preferably still to between 100 and 150 microns, in the crease.

The crease formed in the sheet material may not extend completely to the edge of the sheet . Indeed in certain embodiments, it is preferred to offset the end of the crease from the edge so as to prevent, or at least reduce the likelihood of, the crease tearing. Offsets in the range 0.5 to 2 mm, e.g. 0.5, 1.0. 1.5 and 2.0 mm, have been used. Larger offsets are used where the crease is in a highly stressed area where tearing is more likely to occur. The plasties material is preferably creased in traditional paperboard creasing machinery. This machinery comprises a platen against which is pressed a die board. The die board mounts cutting blades and creasing rules such that when the board is pressed against the platen, the blades cut through the material in the desired pattern and the creasing rule presses into the material by a predetermined amount to form the creases. The back surface of die board is acted on by a press to effect the cutting and creasing.

In accordance with this invention, preferably a force compensation member is applied to the back surface of the die board so that the cutting and creasing force is properly distributed across the board, thereby achieving the desired depth of cut or crease. This member is applied to selected areas of the die board behind the scoring rule.

The force compensation member is typically less that 100 microns thick, more typically under 70 microns thick.

Typical thicknesses used are 36, 54 and 68 microns.

It has been found, however, that when creasing plastic sheet material, the depth of crease is much more critical than in paper creasing, and greater control of the creasing force applied may be needed. Accordingly, a force compensation member of less than 25 microns, for example 20 microns or less may be used.

The force compensation member may be in the form of a tape, such as a non metallised plastics foil material . Preferably the material is in the form of a tape. In a typical creasing operation more than one crease will be formed, and the force compensation material may be applied in a suitable pattern and with suitable thicknesses under the crease locations to achieve the appropriate creasing force distribution. It has been found that relatively soft plastic material such as polypropylene can be creased very effectively using a process as discussed above. By using the invention, a creased sheet is produced whose crease have a relatively low, and consistent, crease strength, typically in the range 400-900 πiN. This makes such sheets particularly suitable for use in automatic erection apparatus which requires blanks with relatively low crease strengths to ensure well defined corners and flat panels.

From a further aspect, therefore, the invention extends to a method of erecting, preferably machine erecting, a carton from a plastics sheet material wherein the blank for forming the carton is creased in accordance with the invention.

The invention also extends to a plastics sheet creased in accordance with the invention and a carton erected from such a sheet.

Some embodiments of the invention will now be described by way of example only, with reference to the examining drawings in which:

Figure 1 shows apparatus for creasing plastic sheet material in accordance with the first embodiment of the invention;

Figure 2 shows, schematically the profile of the crease formed by the apparatus of Figure 1; Figure 3 shows, schematically, apparatus for forming plastic sheet in accordance with the invention; Figure 4 shows a detail of the apparatus of Figure 3; and

Figure 5 shows a further detail of the apparatus of Figure 3.

With reference to Figure 1, creasing apparatus comprises a platen 2 and a steel scoring rule 4. The platen 2 has a planar upper surface 6 while the rule 4 has a main body portion 8 and a sharply pointed tip portion 10. The lower edge of the tip portion 10 runs in a continuous manner along the lower end of the rule 4.

In this particular embodiment, the main body- portion 8 of the rule has a width of 0.7 mm and the overall length of the rule 4 is 23.60 mm.

The rule 2 is used to form a crease line 12 in a sheet 14 of a plastics material such as polypropylene. Typically the thickness of the plastic sheet 14 is 350 to 650 microns. In order to produce the crease 12, the scoring rule 4 is pressed downwardly into the sheet material 14. As shown in Figures 3 and 4, one or more scoring rules 4 are mounted in a die board 16 together with one or more cutting blades 18 which project slightly below the rules 4. In this particular embodiment, the cutting blade has a length of 23.80 mm, meaning that the tip 10 of the scoring rule 4 is set back 0.2 mm from the tip of the cutting blade. A creasing and cutting force is applied to the die board by a press 20.

The force with which the rule is applied is chosen so as to give a desired crease strength in the crease 14. Typically the material in the crease is compressed so as to leave a depth D of material between 100 and 150 microns.

In order to correctly distribute the creasing force over the creasing rule, it may be necessary to apply a force correction tape or the like to the back surface 22 of the die board 16. As shown in Figure 5, the back surface 22 of the die board 16 is marked up to show the outline 24 and creases 26 in the blank being cut and creased. Typically this is done by marking the outline 24 and creases 26 on a sheet of paper which is stuck to the back surface 22, aligned with the respective cutting blades 18 and creasing rules 4.

Strips of force correcting tape 28 are selectively placed over the crease lines 26, where needed, in order that the creasing force and depth is consistent over the blank. Generally it has been found that the majority or all of the creases will need tape applying to the die board. In areas where the tape 28 is applied, a greater force will be produced.

The correction tape 28 is typically a dense but tearable paper or a non-metallised plastics foil. Typical thicknesses of foil are 20, 36, 54 and 68 microns .

Using the above described techniques, it has been found that plastics sheets can be produced to have crease strengths of 400 to 900 inN compared to 1500 or more mN of earlier creased plastics products. For the purposes of this application, the crease strength is that measured in a Messmer crease tester when the crease in a standard 38 mm wide segment is folded through an angle of 60° with the force applied at a distance of 10 mm from the crease. Such equipment and measurements are standard in the industry and need not be explained in detail here.

A sheet creased in accordance with the invention can be erected into a suitably shaped carton or merely just a folded component. Due to the relatively low crease strengths obtained using the method and apparatus of the present invention, the creased sheet is particularly suitable for erection into cartons using automatic machinery, producing cartons with crisp corners and flat panels.

Claims

1. A method, of cold forming a crease line in a sheet plastics material comprising the steps of:

a) positioning the sheet material over a platen surface; b) forming the crease line by bringing a rule into engagement with the plastic sheet material and deforming the sheet material between the end of the rule and the platen surface, the rule having a main body portion and a pointed tip portion.

2. Apparatus for creasing a plastics sheet material, comprising a planar platen surface and a rule, which in use is brought into engagement with the plastic sheet material to deform the sheet material between the end of the rule and the platen surface, the rule having a main body portion and a pointed tip portion.

3. A method or apparatus as claimed in claim 1 or 2 wherein the scoring rule is a 2pt rule

4. A method or apparatus as claimed in claim 1, 2 or 3 wherein the tip portion has an included angle of between 80° and 105°.

5. A method or apparatus as claimed in any preceding claim wherein the tip tapers symmetrically from the main body portion of the rule.

6. A method or apparatus as claimed in any preceding claim wherein the tip has a Rockwell C hardness of 55 or more .

7. A method or apparatus as claimed in any preceding claim wherein the rule is pushed into the plastics sheet to a depth of between 50% and 90% of the sheet thickness .

8. A method or apparatus as claimed in any preceding claim wherein the plastics sheet material is 300 to

800 microns thick.

9. A method or apparatus as claimed in any preceding claim wherein the plastics sheet material is 350 to 650 microns thick.

10. A method or apparatus as claimed in any preceding claim wherein the thickness of the material is reduced to between 100 and 250 microns, more preferably to between 100 and 200 microns, more preferably still to between 100 and 150 microns in the crease.

11. A method or apparatus as claimed in any preceding claim wherein the scoring rule is used in conjunction with a cutting rule and the tip of the scoring rule is set back 0.2 mm from the tip of the cutting rule.

12. A method or apparatus as claimed in any preceding claim wherein the creasing apparatus includes a platen, a die board, and a press acting on the die board, the die board mounting the scoring rule, wherein a force compensation member is applied between the die board and the press in the region of the scoring creasing rule.

13. A method as claimed in claim 12 wherein the force compensation member is less than 100 microns thick.

14. A method as claimed in claim 12 or 13 wherein the force compensation member is in the form of a tape.

15. A method as claimed in claim 12, 13 or 14 wherein the force compensation member is in the form of a non metallised plastics foil material.

16. A method or apparatus as claimed in any preceding claim wherein the sheet material is polypropylene, polyethylene or another relatively soft plastics material .

17. A method or apparatus as claimed in any preceding claim wherein the plastics sheet material in creased in an apparatus comprising a platen, a die board, and a press acting on the die board, the die board mounting the rule, wherein a force compensation member is applied between the die board and the press in the region of the creasing rule.

18. A method of erecting, preferably machine erecting, a carton from a plastics sheet material wherein the blank for forming the carton is creased in accordance with any preceding claim.

19. A plastics sheet creased in accordance with any preceding claim.

20. A plastics sheet as claimed in claim 19 wherein the crease terminates at a spacing from the edge of the sheet .

21. A carton erected from a sheet as claimed in claim 19 or 20.