The present invention relates to a method for

manufacturing a screw cap, wherein the screw cap having a blind hole with inner threads. The invention further relates to an arrangement for manufacturing a screw cap in accordance with the method.

The invention finally relates to a screw cap having a blind hole with inner threads.

Cardboard packages for liquid or semi-liquid food stuff such as milk, water, juice, yoghurt etc. are well known. A major benefit with these cardboard packages is that the packages are biodegradable to much more extent than plastic packages. Recent years it has been more common, that the cardboard packages are equipped with an opening comprising a screw cap, wherein the opening is made of a plastic such as polyethylene. The major benefit with the screw cap is that the opening can be resealed, which is in favour for keeping the food stuff fresh. A drawback with polyethylene screw caps is that the amount of plastics in the package in increased. Such polyethylene screw caps are normally manufactured by injection

moulding .

In the following description of the invention the term microfibrillated cellulose (MFC) will be used. MFC is also known as nanocellulose . It is a material typically made from wood cellulose fibres, both from hardwood or softwood fibres. It can also be made from microbial sources, agricultural fibres such as wheat straw pulp, bamboo or other non-wood fibre sources. In

microfibrillated cellulose the individual microfibrils have been partly or totally detached from each other. A microfibrillated cellulose nanofiber is normally very thin (~20 ran) and the length is often between 100 ran to 10 μπι. However, the microfibrils may also be longer, for example between 10-200 μπι, but lengths even 2000 μπι can be found due to wide length distribution. Fibres that has been fibrillated and which have microfibrils on the surface and microfibrils that are separated and located in a water phase of slurry are included in the definition MFC. Furthermore, whiskers are also included in the definition MFC.

It is an object of the present invention, to provide a method of manufacturing a screw cap made of

microfibrillated cellulose, which eliminates or

alleviates at least some of the above mentioned

disadvantages of the prior art with plastic screw caps.

The method according to the invention is characterized in that the method comprising the steps of:

a) placing a piece of pre-preg MFC with a dryness of

40-90%, of a suitable size for forming the screw cap, between

a first tool comprising a protruded part with outer threads for forming the inner threads of the blind hole, and

a second tool comprising a section with an inner lateral surface for forming an outer lateral surface of the screw cap,

b) moving the protruded part of the first tool into the section of the second tool, such that the first and the second tool forms the screw cap,

c) drying the piece of pre-preg MFC, such that it is

shrinks onto the first tool and thereby forms the screw cap, and

d) unscrewing the formed screw cap from the threads of the protruded part of the first tool. The arrangement according to the invention is

characterized in that the arrangement comprising:

- a first tool comprising a cylindrical part which part having outer threads for forming the blind hole and the threads of the screw cap, and

- a second tool comprising an inner lateral surface for forming an outer lateral surface of the screw cap.

The screw cap according to the invention is characterized in that it is manufactured in accordance with the method above .

In the following, the invention will be described further with reference to the drawings, wherein:

Figure 1 shows a first tool and a second tool for

manufacturing a screw cap of MFC, wherein the first and the second tool is in a first position. Figure 2 shows the first tool and the second tool in a second position.

Figure 3 shows a screw cap manufactured by the inventive method .

Figure 1 and 2 shows a preferred embodiment of an

arrangement for manufacturing a substantially cylinder- shaped screw cap 12 of a piece of pre-preg MFC 11. I.e. a piece of MFC which has been pre-impregnated or mixed, with a compatibilizer (optional), and a ground polymer or a polymer Latex such as PLA Latex. The piece of pre-preg MFC 11 has a dryness between 40-90%, preferably 60-80%. The piece of pre-preg MFC 11 has preferably at least one barrier film. The barrier film is either arranged on one side or on each sides of the piece of pre-preg MFC 11. The arrangement comprising a first tool 1 and a second tool 20, which tools 1, 20 are linear movable in respect to each other, such that, the first tool 1 can be moved into the second tool 20. The screw cap 12 to be

manufactured, see fig. 3, comprises a circular blind hole 14, which is limited by a circular bottom surface 15 and a cylindrical, inner lateral surface 16, which inner lateral surface 16 is provided with threads 17 for screwing the screw cap 12 onto a package (not shown) . The screw cap 12 further comprises a cylindrical, outer lateral surface 18 which faces away from the inner lateral surface 16 and a circular, top surface 19 which faces away from the bottom surface 15. The outer lateral surface 18 having a suitable grip pattern 13, such as grooves 13 in the axial direction of the screw cap 12 for facilitate a user to screw and/or unscrew the screw cap from a package.

The first tool 1 comprising a lower, cylindrical, first part 2; a middle, cylindrical, second part 6 and an upper, cylindrical, third part 8.

The first part 2, of the first tool 1, having a first diameter Al and comprises a cylindrical, first lateral surface 3 for forming the inner lateral surface 16 of the screw cap 12. The first part 2 further comprises a circular end surface 5 for forming the bottom surface 15 of the screw cap 12, which end surface 5 facing

downwards. The first lateral surface 3 having outer threads 4 for forming the inner threads 17 of the inner lateral surface 16 of the screw cap 12.

The second part 6, of the first tool 1, is arranged axially with, and located above, the first part 2. The second part 6 having a second diameter A2 and comprises a cylindrical, second lateral surface 7 of the first tool 1 for cutting the piece of pre-preg MFC to a desirable size, which is explained more in detail below.

The third part 8, of the first tool 1, is arranged axially with both the first part 2 and second part 6. The third part 8 is located on top of the second part 6.

Hence, the second part 6 is located between the first part 6 and the third part 8. The third part 8 having a third diameter A3 and comprises a third lateral surface 9 for steering the first tool 1 into the second tool 20.

The third diameter A3 is greater than the second diameter A2 and the second diameter A2 is greater than the first diameter Al . The transition between the first part 2 and the second part 6 forms a first cutting edge 10 of the device at the first tool 1. In use the first part ^' s 2 outer lateral surface 3, with threads 4, forms the inner surface 16 and the threads 17 of the screw cap 12. The end surface 6 of the first tool 1 forms the bottom surface 15 of the screw cap 12.

The second tool 20 comprises an opening 28 of a blind hole 21, which blind hole comprises a lower, cylindrical, first section 22; a middle, cylindrical, second section 23 and an upper, conical, third section 24.

The first section 22 is formed by a cylindrical,

circumferential, first inner lateral surface 25 for forming the outer lateral surface 18 of the screw cap 12. The first inner lateral surface 25 having protrusions 30 for forming the grooves 13 on the outer lateral surface 18 of the screw cap 12. The first section 22 having a first inner diameter Bl .

The second section 23 is formed by a cylindrical, second inner lateral surface 26 for steering the first tool 1 through the second tool 20. The second section 23 having a second inner diameter B2. The third section 24 is formed by a conical, third inner lateral surface 27 for folding the outer ends of the piece of pre-preg MFC 11 upwards. The third section 24 having a third inner diameter B3. The third diameter B3 increases continuously upwards towards the opening 28 of the blind hole 21. The third diameter B3 is equal to the second diameter B2 in the transition between the third section 24 and the second section 23. The second diameter B2 is greater than the first diameter Bl, such that, the transition between the first section 22 and the second part 6 forms a second cutting edge 29 of the device at the second tool 20. For producing a screw cap 12 the method comprising the steps of placing the first tool 1 and the second tool 20 in a first position, which is shown in fig. 1. In the first position, the first tool 1 is positioned at a predetermined distance away from second tool 20, wherein the end surface 5 of the first tool 1 facing against the opening of the second tool 20.

A piece of pre-preg MFC 11 of a suitable size for forming the screw cap 12 is placed over the opening 28.

The first tool 1 is then axially moved against the upper side of the piece of pre-preg MFC 11 and into the opening 28 of the second tool 20. Hence, the piece of pre-preg MFC 11 is pushed by the end surface 5 of the first tool 1 and into the third section 24 of the blind hole 21.

The conical, third inner lateral surface 27 brings the outer parts of the piece of pre-preg MFC 11 to be folded upwards and behind that part of the piece of pre-preg MFC 11 that is in contact with the end surface 5. The piece of pre-preg MFC 11 is continuously pushed by the end surface 5, through the second section 23 of the blind hole 21, towards the first section 22 of the second tool 20.

When the end surface 5 has reached the first section, the outer portions of the piece of pre-preg MFC is folded upwards by the first inner lateral surface 25, such that, the cylindrical walls of the screw cap 12 is formed.

When the first cutting edge 10 at the first tool reaches the second cutting edge 29 at the second tool, the outer parts of the piece of pre-preg MFC 11 are cut off between the two cutting edges 10, 29.

The first and second tool 1, 20 have now finally reached the second position, which is shown in figure 2.

The piece of pre-preg MFC 11 is drying by the first 1 and second tools 20, which tools 1, 20 have been heated to a suitable temperature for drying pre-preg MFC. A suitable temperature of the tools is typically 50-200°C,

preferably 100-170°C. The drying brings the piece of pre-preg MFC to shrink, such that, the screw cap 12 is formed by the surrounding tools 1, 20. The threads 4 of the first part 2 forms the inner threads 17 of the screw cap 12 and the protrusions 30 of the first inner lateral surface 25 forms the grip pattern 13 of the outer lateral surface 18 of the screw cap 12.

After completed drying, the screw cap 12 is unscrewed from the threads 4 of the first part 2.

In the foregoing, the invention has been described on the basis of a specific preferred embodiment. It is

appreciated, however, that other embodiments and variants are possible within the scope of the following claims. For instance instead of moving the first tool, it is obvious that it also would be possible to move the second tool upwards, or even both tools simultaneously.

Moreover, the second tool could be in the form of

rotating rollers, wherein the circumferential surface of the rollers forms an inner lateral surface for forming the outer lateral surface 18 of the screw cap and wherein the pre-preg MFC is fed against the first tool by the rotating rollers. Other possibilities of drying are also possible, for example drying with external heaters, such as infrared heating/drying. It is also possible to manufacture a screw cap with other grip pattern than grooves or even a screw cap without a grip pattern.

Moreover, the inner lateral surface of the first section, for forming the outer lateral surface of the screw cap, does not necessarily need to be cylindrical.