Device, mould assembly and method for thermoforming of a product from a plastic film

Abstract

A device and method for thermoforming of a product from a plastic film includes a mould assembly which is used in such a device. The plastic film is clamped between the mould parts in primary and secondary manner. The forming process can hereby be divided into more or less independent zones. Different forming techniques, positive or negative, can be used in the different zones. This makes it possible to combine the advantages of the two techniques in one forming process.

Claims

1. A device for thermoforming of a product from a plastic film, comprising: a first mould part comprising a first forming part, said first forming part being configured to form a first part of the product; a second mould part comprising a second forming part, said second forming part being configured to form a second part of the product which is integrally connected to the first part of the product, wherein the first forming part and the second forming part co-act for a purpose of forming a secondary clamping of the film; a clamping frame disposed between the first mould part and the second mould part, the clamping frame configured to provide a primary clamping of the plastic film upon movement of the first mould part and the second mold part toward each other; a spring configured to resiliently mount the clamping frame to the bottom surface of the second mould part; a seal disposed on the bottom surface of the second mould part and above the clamping frame, the seal configured to ensure that an overpressure or an underpressure is realized inside a space bounded by the clamping frame; and a pressure system configured to apply: a first pressure difference over the plastic film situated between the primary and secondary clamping for a purpose of carrying the plastic film to the second forming part; and a second pressure difference over the plastic film situated inside the secondary clamping for a purpose of carrying the plastic film to the first forming part, wherein the first mould part comprises a first cavity in which the first forming part is placed and wherein the second mould part comprises a second cavity in which the second forming part is placed, wherein at least one of the first forming part and the second forming part is received movably in the first or second cavity, respectively, and wherein the first forming part and the second forming part are movable relative to each other for the purpose of said forming of the secondary clamping of the film, and wherein after the primary clamping of the plastic film has been achieved a first chamber is at least partially bounded by the second forming part and the plastic film situated inside the secondary clamping and after the primary and secondary clampings of the plastic film have been achieved a second chamber is at least partially bounded by the first forming part or a wall of the first cavity and the plastic film situated between the primary and secondary clampings.

2. The device recited in claim 1, wherein the pressure system is configured to apply a pressure difference between a pressure in the first and second chamber and a pressure prevailing on another side of the film at a position of the first and second chamber, respectively.

3. The device recited in claim 1, wherein the pressure system comprises one or more conduits for supplying gaseous medium under pressure to the first chamber or the second chamber.

4. The device recited in claim 3, wherein the one or more conduits for supplying the gaseous medium under pressure to the first chamber are arranged in the second forming part or a wall of the second cavity.

5. The device recited in claim 3, wherein the one or more conduits for supplying the gaseous medium under pressure to the second chamber are arranged in the first forming part or a wall of the first cavity.

6. The device recited in claim 2, wherein the pressure system comprises one or more channels for discharging gaseous medium which is enclosed on the another side of the film at a position of the first and second chamber, respectively.

7. The device recited in claim 1, wherein the first part comprises a central part of the product and wherein the second part comprises a rim part of the product which is integrally connected to the central part.

8. The device recited in claim 7, wherein the rim part wholly encloses the central part.

9. The device recited in claim 1, wherein the first forming part is configured to negatively form the first part of the product and the second forming part is configured to positively form the second part of the product.

10. The device recited in claim 9, wherein the first forming part defines a forming cavity for a negative forming of the first part of the product.

11. The device recited in claim 1, wherein the second forming part takes a substantially hollow form.

12. The device recited in claim 11, wherein a wall of the second forming part engages during said secondary clamping via the plastic film on a stop which is formed in a wall of the first cavity or engages on a stop formed in the first forming part.

13. The device recited in claim 11, wherein the second forming part has a sleeve form.

14. The device recited in claim 11, wherein the first forming part is configured to negatively form an inner part, the device further comprising a pre-stretcher which is received movably in the second forming part, which the pre-stretcher is configured to move the plastic film toward the first forming part during operation and after the primary and secondary clampings of the plastic film have been achieved.

15. The device recited in claim 14, wherein the pre-stretcher and the second forming part move independently of each other, wherein the pre-stretcher and the second forming part are disposed coaxially.

16. The device recited in claim 1, wherein the pressure system comprises one or more channels for discharging gaseous medium which is enclosed inside the secondary clamping between the film and the first forming part or which is enclosed between the primary and secondary clampings and between the second forming part and the film.

17. The device recited in claim 16, wherein the one or more channels for the discharging of the gaseous medium between the film and the first forming part are received in a wall of the first cavity or in the first forming part.

18. The device recited in claim 16, wherein the one or more channels for the discharging of the gaseous medium between the film and the second forming part are received in a wall of the second cavity or in the second forming part.

19. The device recited in claim 16, wherein the one or more channels for the discharging of the gaseous medium are connected to a vacuum system.

20. The device recited in claim 1, wherein at least one of the first mould part and the second mould part takes a stationary form.

21. The device recited in claim 1, further comprising punching knives configured to cut through the plastic film after the formation of the product.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The present invention will be elucidated in more detail hereinbelow with reference to the accompanying figures, wherein:

(2) FIG. 1 shows an example of negative forming;

(3) FIG. 2 shows an example of positive forming;

(4) FIGS. 3A-3F show an embodiment of the present invention; and

(5) FIG. 4 is an example of a punching technique which can be used in the embodiment shown in FIGS. 3A-3F.

DETAILED DESCRIPTION

(6) FIG. 3A shows an embodiment according to the present invention. This embodiment comprises a first mould part, embodied here as lower mould 13, and a second mould part 12, embodied here as upper mould 12. Lower and upper moulds 13, 12 are movable relative to each other. This makes it possible to clamp film 1 as shown in FIG. 3B. This clamping is referred to as the primary clamping.

(7) Lower mould 13 comprises a first cavity in which a first forming part 15 is fixedly disposed. Upper mould 12 comprises a second cavity in which a second forming part 20 is movably disposed. Second forming part 20 is formed here as a hollow sleeve-like element which defines on the upper side an opening in which a pre-stretcher 14 is movably received.

(8) Discharge channels 21 and compressed air supply conduits 16 are received in the body of upper mould 12, more particularly in a wall of the second cavity. Compressed air supply conduits 22 are received in the body of lower mould 13, more particularly in a wall of the first cavity. Discharge conduits 17 are further received in first forming part 15 itself.

(9) After first mould part 13 and second mould part 12 have been moved toward each other as shown in FIG. 3B, second forming part 20 and pre-stretcher 14 will then move toward first forming part 15, see FIG. 3C. An end part 30 of second forming part 20 will come to lie here against a stop 31 formed in the first forming part and the wall of the first cavity, whereby film 1 is clamped once again, see FIG. 3D. This clamping is referred to as the secondary clamping. Pre-stretcher 14 carries film 1 into first forming part 15.

(10) The primary clamping results in the formation of a first chamber 23 which is bounded by film 1 and second forming part 20, see FIG. 3C. The secondary clamping results in the formation of a second chamber 24 by first forming part 15, the wall of the first cavity and film 1 which is situated between the primary and secondary clamping, see FIG. 3D.

(11) In the next step compressed air is supplied by means of conduits 16, 22. An overpressure will hereby be created in first chamber 23 and second chamber 24. Film 1 will hereby be pressed further into first forming part 15 and film 1 will also come to lie against second forming part 20, see FIGS. 3E and 3F. The forming close to first chamber 23 is based here on negative forming and the forming close to second chamber 24 is based on positive forming.

(12) Because film 1 is pressed against first forming part 15 and second forming part 20, the air has to be discharged at this position. This can be done by means of discharge conduits 21, 23. In another embodiment these conduits are connected to a vacuum pump. The compressed air can optionally be dispensed with since the vacuum pump generates sufficient overpressure in the first and second chamber, by means of evacuating the space on the other side of the film, for forming the product.

(13) After forming and cooling of the product, second forming part 20 and pre-stretcher 14 are moved back and lower mould 13 and upper mould 12 are moved apart. The overpressure built up in first chamber 23 and second chamber 24 can be reduced here by means of ventilation, optionally using conduits 16, 22.

(14) The product is generally knocked out after forming. This can for instance be done by providing first forming part 15 with a movable forming base on the underside. By moving this forming base upward the product is knocked out and can be processed further. The use of movable forming bases is known from the prior art.

(15) In order to separate products from each other film 1 with the products formed therein can be subjected to a punching or cutting operation. This operation preferably takes place immediately after the forming, while the formed product is still present in first forming part 15. Use can be made for this purpose of known techniques, as shown in FIG. 4. For the sake of clarity this figure only shows the punching principle, and further details of first cavity 50 and second cavity 51 are omitted. It will be apparent to the skilled person that this technique can be combined with the embodiments shown in FIGS. 3A-3F.

(16) FIG. 4 shows how upper mould 12 comprises punching knives 40. Further shown is a resiliently arranged clamping frame 41 which is situated between upper mould 12 and lower mould 13. The primary clamping is in this case achieved in that film 1 is clamped by clamping frame 41 as a result of the relative movement between lower mould 13 and upper mould 12. This clamping frame is pressed by upper mould 12. Clamping frame 41 is resiliently mounted by means of a spring 42. When upper mould 12 and lower mould 13 are moved toward each other spring 42 will be compressed and will exert a spring force on clamping frame 41, whereby film 1 is clamped. Also provided is a seal 43 which ensures that an overpressure or underpressure can be realized inside the space bounded by clamping frame 41 for the purpose of forming the product from film 1.

(17) After forming of the product the upper mould 12 and lower mould 13 will perform a small cutting stroke by moving toward each other. Spring 42 will hereby be compressed further still and punching knives 40 will cut through film 1. As a result, the products are separated from each other. It is noted that lower mould 13 can be provided with a punch plate which serves as stop for punching knives 40.

(18) In another embodiment (not shown) use is made of a cutting nipple in the lower mould and a cutting plate in the upper mould, or vice versa. The first or second forming part is placed in the cutting nipple here. The products can be separated in that the upper mould and lower mould perform a cutting stroke after the forming. During this movement the cutting plate will move along the cutting nipple, whereby the film present between these elements is cut. This technique is also known from the prior art and can also be combined with the embodiments of FIGS. 3A-3F.

(19) The terms lower mould and upper mould are used in the foregoing. It will be apparent to the skilled person that these terms serve only for the purpose of illustration. This is likewise the case for the movements made by these mould parts. It is possible to reverse the roles of the lower mould and upper mould. It is likewise possible to give one of these mould parts a stationary form, or to make them both movable. Further modifications are possible for the skilled person without departing from the scope of protection of the present invention, which is defined in the following claims.