WO1997018077A1

WO1997018077A1 - Method and device for the production of convex shells made of polystyrene foam

Info

Publication number: WO1997018077A1
Application number: PCT/EP1996/004942
Authority: WO
Inventors: Bernd Friemuth
Original assignee: Bernd Friemuth
Priority date: 1995-11-16
Filing date: 1996-11-12
Publication date: 1997-05-22
Also published as: AU7622796A; DE19542717C1

Abstract

The invention relates to a method and a device for the production of convex shells (2), in particular food shells made of polystyrene foam. The method comprises the following steps: (a) cutting a foam block into individual blanks shaped like plates or strips (1.1 ...1.n); (b) mounting and moving the blanks in a row on a horizontal plane (E); (c) producing an intermediate plate from a blank by contacting and lightly pressing both flat surfaces of the blank each with with a heated, flat pressure surface (14, 14') to achieve superficial melting; (d) shaping the intermediate plate in a mould formed from a heated top die (20) and bottom die (22') to form a food shell; (e) ejection or removal of the food shell.

Description

METHOD AND DEVICE FOR PRODUCING CURVED SHELLS FROM POLYSTYRENE FOAM

The invention relates to a method for producing domed trays, in particular sales trays, from polystyrene foam.

The above-mentioned curved shells are to be understood as plate-like and bowl-like vessels, such as are used for example for packaging purposes, fast food, covers and insulating parts. Meat products in particular are sold on such trays.

Curved shells are currently known which are mainly produced by the following manufacturing processes:

Extruded polystyrene foam trays

Shells made of extruded polystyrene foam have skin on both main surfaces. Because of the resulting good seal against water and other non-pyrolytic liquids, they are widely used. They are made from a sheet of film by deep drawing and deformation under heat and pressure. However, a foam process that uses CFC gases is used for the raw material during manufacture. This leads to considerable ecological criticism. Many retailers therefore no longer use these packaging trays. The production price for the production of the web film is also associated with a very high investment. Since the extruder should also work as continuously as possible, this leads to high capital expenditure. Molded polystyrene foam trays

Such foam trays are foamed in individual forms. They have a surface which consists of many contiguous polystyrene beads, but which is not closed-pore. In particular, moisture and secretions, such as blood, of the product to be packaged penetrate into the spaces between the beads, which gives rise to hygienic and aesthetic concerns. In addition, the production of sales trays in polystyrene single foam molds is very complex. Each shell must be manufactured individually by blowing in a multiple mold. The polystyrene beads are provided with a blowing agent, for example pentane. In the expanded form, the polystyrene becomes soft enough at a temperature of about 100 ° C. so that it expands due to the evaporation of the pentane. After the blowing process, the metal molds have to be cooled again in order to remove the polystyrene shell. This known method does result in packaging trays which are satisfactory in terms of packaging technology. However, it is energy-intensive to use and also expensive to invest.

Furthermore, it is known from US Pat. No. 4,239,727 to produce vessels from a preheated foam sheet in a form formed from a heated male and female mold.

It is also known from DE-AS 22 12 355 to smooth the surface of blanks made of polystyrene using a tool heated up to a temperature of at least 500 ° C. However, this refers to rough surfaces that result from the machining of plastics.

It is therefore the task of a process for Manufacture of packaging trays made of polystyrene foam, which does not have to be foamed in individual molds and which nevertheless results in a largely closed-pore and fused surface on the tray surface, which is much better from the point of view of packaging technology than an open-pore sales tray.

This object is achieved with a method of the type mentioned at the outset, which has the following method steps:

(a) cutting foam blocks into individual plate-shaped blanks or a blank web;

(b) placing and shifting the blanks or the blank web on a horizontal plane and, if appropriate, cutting the blank web to individual blanks;

(c) producing intermediate product plates from the blanks by exerting pressure on the two flat sides of the blank, each with a heated, flat stamp surface, the contacting regions of the blank being softened and superficially fused;

(d) shaping the intermediate product plates in a form formed from a heated male and female mold to form the shells, essentially while maintaining the volume of the intermediate product plate;

(e) ejecting or removing the shells.

The process is therefore based on the energetically favorable block foaming technique, in which first a block, for example with dimensions of 1 x 1 x 1 m, or a cylinder, for example with a length of 3 m and a diameter of 3 m, is made of polystyrene that adheres Beads are made in a mold using a blowing agent at a temperature above 80 ° C. The The block cools and is cut into individual plate-shaped blanks with a visible cut of the polystyrene beads located on the cut surface of the blank.

The cooled foam cylinder, on the other hand, is processed into one or more sheet-like blanks in the peeling process. These peeled, web-shaped blanks are then available as rolls for further continuous processing. The blank web can also be flattened into individual blanks after step c.

These cut blanks are preferably wetted on both opposite main surfaces with a release agent before the intermediate product plate is briefly heated at at least 125 ° C. by contacting and gently pressing both flat sides of the blank. A surface fusion and surface smoothing are formed in that the cut-off foam spheres form a fusion skin. This intermediate product plate, which has already been sealed on the surface, is then deformed and punched out in a form formed from a heated male and female mold.

The surface of the blanks is changed by the initially flat contact heating in contrast to the radiation heating so that the individual cut polystyrene beads fuse together and form a compacted mass on the surface of the plate. This effect can also be called "smoothing". The pores of the foams essentially close and optically form a closed surface on the surface, the cell structure present in the plate blank being homogenized. A waterproof or water-repellent surface is formed. The flat stamp surface for the plate-shaped blanks has a temperature of at least 110 ° C., preferably between 120 ^° and 160 ^° C. The contact time should be between 0.1 and 10 s, preferably between 0.5 and 1.5 s to get the highest possible production rate in the time unit.

The deformation in the form formed from a heated male and female mold into a sales tray should be carried out at a temperature between 100 ° and 300 ° C., preferably between 165 ^° and 185 ° C.

The pressure exerted on the blanks should be between 1 10 ^s and 2-10 ^s Pa.

Another important advantage is that the blanks or the blank web can be laminated on their flat side with a film web before being shaped into a shell. A thin, extruded polystyrene foam sheet is preferably suitable for this purpose, and can only be connected to the blank directly by thermal melting of the blank, without an additional adhesive layer. For this purpose, the film web should consist essentially of polystyrene and at least on its side that comes into contact with the blank.

The melted, optionally laminated blanks are formed into a shell in a shaping station at a temperature between 100 ° and 300 ^° C., preferably between 165 ° and 185 ^° C.

This packaging shell made from the laminated blank can even be watertight. A vapor-tight shell can also be produced by laminating a polystyrene aluminum foil. Also one Foil consisting essentially or purely of aluminum can be fused with a polystyrene blank or with the blank web.

Release agents are usually used in the individual molding steps, as are customary for the pressing of polystyrene sheets. This is intended to reduce adhesion forces between the metal mold surface and the polystyrene foam surface. Silicones in the form of oils and oil emulsions in water are suitable for this. Metal soaps are also suitable, the latter also being used in particular since they are harmless to food. The liquid release agent is applied to the unpressed main surfaces by spraying. A part of the release agent is transferred to the mold surface, so that multiple press passes are usually possible with one release agent spray.

The invention further relates to a device for producing curved trays, in particular sales trays, with the following individual parts:

plate-shaped foam blanks or the blank sheet can be placed and displaced on a displacement table,

a pressing station which has a heatable stamp with flat stamp surfaces,

a deformation station, each with an exchangeable, heated patrix and die, the deforming surface of which are compatible with one another, with a mold cavity remaining when the patrix and die are moved together,

- And with an ejection device.

Further features that can be found in further subclaims are explained in the description below. The description is based on the drawing, the figures of which show:

Figure la is a schematic representation of an inventive device in side view.

FIG. 1b the device according to FIG. 1a with a blank web and foil feed;

FIG. 2 shows the device according to FIG. 1b seen from above, but with a blank stacking container;

3 shows a schematic illustration of a deformation station;

4 shows a perspective view of a sales tray manufactured according to the principle of the invention;

5a and 5b the average through an intermediate product plate.

A device 100 for producing packaging trays 10 is shown in FIGS. 1 a, 1 b and 2.

As is known per se, polystyrene foam blanks 1.1. ... ln cut out from a deposited foam block (not shown) in a disk-like manner. The foam disks or blanks 1.1 ... ln have a small thickness of approximately 4.0 mm and a size of 750 x 750 mm. The polystyrene foam blanks are stacked in one of the open, rectangular blank stack containers 2. The container 2 has two slots 3, 3 '. Through a slot 3, a sliding plate 4 always presses the lowest polystyrene foam blank cyclically with a piston-cylinder Arrangement 5 working horizontally through the other slot 3 'to the outside.

The polystyrene foam blank leaving the container 2 is always shifted further in the course of the manufacturing process on the shifting plane (E) of a shifting table 6 in the rhythm of the cyclically driven units. The units described below are arranged along the sliding table 6 in technological order: a spray device 7, a press station 8 and a deformation station 9.

The task of the spray device 7 is to uniformly wet the two surfaces of the polystyrene foam blanks 1.1... Ln with a release agent 11, for example with silicone oil. The spray device 7 consists of an upper and a lower spray chamber 12 and 12 ', which are each equipped with a pulse generator 13 and 13'. The two spray chambers 12, 12 'are preferably arranged one above the other in a space-saving manner, although it is also possible to keep a distance between the spray chambers 12, 12'.

The press station 8 has two smooth stamps 14,. 14 ', of which the lower 14' is provided with a perforation (not shown) for the purpose of sucking and locking the blanks. The locking is controlled by means of a vacuum pump 15. The heatable stamps 14, 14 'consist of hardened steel or brass, and are coated on the sides facing the blank (stamp surfaces 39, 39') with an anti-adhesive, e.g. PTFE, coated.

It can also be expedient to vulcanize the punches 14, 14 'with a 0.8 mm thick, heat-resistant elastomer layer 16 which has sufficient elasticity has to compensate for the slight unevenness of the stamp surfaces and the blank. In the pressing station 8, the blanks are heated on their flat sides, so that the surfaces are then homogeneously fused. The use of the elastomer significantly improves the required brilliance of the fused surfaces.

The subsequent deformation station 9 has two heatable metal molds 17, 17 ', the upper of which

- Male 17 - several troughs 18 and the lower one

- Die 37 - has bulges 19 almost compatible with the troughs 18. The deformation station 9 also has a rectangular frame 20 in which the two metal shapes, i.e. Die 17 and male 37, are attached to a piston rod 21 and correspondingly 21 'interchangeably. The shape of the male and female molds then gives the desired product shape.

Fig. Lb shows a polystyrene foam blank sheet 111, which has been peeled out of a deposited foam cylinder (not shown) in a spiral. The blank web 111 has a small thickness of approximately 3.5 mm and a width of 600 mm. It is pushed forward by means of a drive roller 113.

In the further course of the manufacturing process, the blank web is always shifted further on the shifting plane (E) of a shifting table 6 in the rhythm of the cyclically driven units. The assemblies described below are arranged along the sliding table 6 in technological order: a spray device 7, a cutting station 112, a pressing station 8 and a deformation station 9.

The spray device 7 is preceded by a film supply roll 29, which is arranged under the sliding table 6, from which a film web 27 is 1 motor 26 and a compensation device 31 is deducted. The compensating device 31 consists of deflection rollers 32, 32 'and a dance roller 33 which compensates for the tension differences of the film to be wound and always has a film supply available. In the press station 8, the polystyrene foam blank sheet is laminated on one side, over the entire area with the film sheet, ie, is melted flat without adhesive, ₁₀ if necessary with the omission of partial areas.

The task of the spray device 7 is to uniformly wet the two surfaces of the polystyrene foam blank web 111 with a release agent 11, for example with silicone oil. The spray device 7 consists of an upper and a lower spray chamber 12 and 12 ', which are each equipped with a pulse generator 13 and 13'. The spray device 7 is followed by a separation station 112, which the Rohlmgs-

20 lane 111 m individual blanks 1.1 ... l.n separates.

A press station 8, which corresponds to that in FIG. The press station 8 has two smooth stamps 14,. 14 ', of which the

25 lower 14 'is provided with a perforation (not shown) for the suction and locking of the blanks.

The subsequent deformation station 9 has two

30 heatable metal molds 17, 17 ', the upper of which

- Male 17 - several troughs 18 and the lower one

- Die 37 - has bulges 19 almost compatible with the troughs 18. The deformation station 9 also has a rectangular frame 20 in which the

35 two metal molds, that is to say die 17 and male 37, are fastened to a piston rod 21 and correspondingly 21 'so that they can be replaced. The shape of the male and female molds then gives the desired product shape. As shown in FIG. 3 in particular, the die 17 and the die 37 are designed as heatable metal plates 22 and 22 ', optionally made of hardened steel, which are particularly suitable for a longer production run. Both the troughs 18 and the bulges 19 are provided with a wafer-thin layer of silicone oil. However, it should not be excluded that the troughs 18 and bulges are also provided with a thin elastomer layer, it being possible for at least the trough surface to be provided with a pattern in relief, for example with the brand of the manufacturer or user.

The two metal plates 22 and 22 'are also provided with through holes 23 which are connected to compressed air supply lines 24. These bores 23 are distributed as evenly as possible on the trough and bulge surfaces in order to implement the punched-out molded parts properly with a compressed air pulse.

Furthermore, the device 100 includes a collecting grid 30 which can be shifted to the side (cf. FIG. 2) and transversely to the direction of displacement (arrows X) in the deformation station 9.

Functional description

The bottom polystyrene foam blank 1.1 ... ln is ejected from the blank stack container 2 with the help of the sliding plate 4 through the slot 3 'in the direction of the shift table 6 and passed on to the spray device 7. There, the blanks are sufficiently wetted on both sides with a silicone oil as a release agent so that they do not adhere to the heating plates in the next processing stages. A food-grade composition, for example an aqueous oil emulsion or a metal soap, can also be used as the non-stick agent.

The blank provided with release agent then passes under the metal plates 14 and 14 'of the pressing station 8. The pressing process takes approximately 0.8 s at a temperature of the metal plates of 170 ^° C. at a pressure of 1.25 10 ^* Pa. With these parameters, both surface areas 41 of the blanks are melted and homogenized uniformly in such a way that the pores and interspaces between the foam spheres are completely closed. In this way, a smooth intermediate product plate 40 or 40 '(with film) is produced, from which various shell-like products can be produced.

After the pressing process, the intermediate product plates reach the shaping station 9, where they are also briefly embossed, in this case for 0.9 s at a temperature (in the contact area with the female 17 and male 37) of approximately 180 ° C. and under pressure of about 1.4-10 ^s Pa.

In a hot stamping process, several sales trays of the size 120 • 175 mm ² are stamped out of a 750 ♦ 750 mm ² foam blank (FIG. 4).

Sales trays 10 thus produced are punched out simultaneously during the hot stamping process by circumferential cutting 25 with which the male part 37 is provided. After this operation, the contact surfaces 35, 35 'through the supply lines 24 and bores 23 are supplied with compressed air, whereby the compressed air is first supplied to the male 37, so that the upper female 17 still holds the packaging trays until Approaching a starting grid 30 which is arranged to be displaceable under the shifting plane E and moving the male part out of the preforming station. After the next compressed air pulse, the punched-out sales trays 10 fall onto the collecting grid 30.

The catch grid 30 and the male part 37 are displaced by means of transverse to the direction of displacement (arrows X)

1 0 arranged guide strips 38, 38 'and a piston-cylinder arrangement (not shown) realized (see. Fig. 2).

Should the sales trays 39,. a thin film is coated by the

Foil supply roll 29 is pulled off a foil web 27 by means of the electric motor 26 and compensating device 31 and fed to the pressing station 8 via the spraying device 7. Particularly suitable as film material are all thermoplastically deformable films, including films made of pure aluminum or laminated with aluminum, in which the film web consists at least on its side that comes into contact with the blank from polystyrene.

25

The tests carried out by the applicant with an extruded thin polystyrene foam film have proven to be promising. The polystyrene foam film is easy to deform thermally, is characterized by a silky gloss surface structure and is suitable for food.

The film section lying against the foam blank is sucked in by means of a vacuum pump 15 and thus locked. After the 5 contact surfaces of the foam blank and the film have melted together, the excess film piece is cut off in the cutting station 34. All operations described above are coordinated with each other. The parameters, such as foam blank density and thickness, pressing force, temperatures and time, can be programmed and changed, so that the process can be optimally controlled with the aid of a computer.

When using blank webs, an analogous flow diagram is provided, which can be seen from FIG. 1b.

Claims

> 5 PATENT CLAIMS

1. Process for the production of curved trays, in particular sales trays, from polystyrene foam, with the following process steps:

(a) cutting foam blocks or cylinders into sheet-like blanks or into a blank web;

(b) Placing and moving the blanks or the blank web on a horizontal plane, and, if necessary, cutting the blank web to individual blanks

(d) deforming the intermediate product plates into the shells in a form formed by a heated male and female die, essentially while maintaining the volume of the intermediate product plate;

(e) ejecting or removing the shells.

2. The method according to claim 1, characterized gekenn¬ characterized in that the flat stamp surface has a temperature of at least 110 ° C, preferably between 110 ° and 160 ^° C.

3. The method according to claim 1 or 2, characterized characterized in that the contact time of the stamp surface with the blank flat sides is between 0.1 and 10 s, preferably between 0.5 and 1.5 s.

4. The method according to any one of the preceding Ansprü¬ che, characterized in that the pressure exerted on the blanks is between about 10 ^s and 2 »10 ^s Pa.

5. The method according to any one of the preceding Ansprü¬ surface, characterized in that the deformation in the form formed from a heated male and female mold into a shell at a temperature between 100 ° and 300 ^° C, preferably between 165 ^° and 185 ° C. becomes.

6. The method according to any one of the preceding Ansprü¬ surface, characterized in that the blanks or the blank web are laminated at least on one of their flat sides with a film web (27).

7. The method according to claim 6, characterized gekenn¬ characterized in that the film web (27) consists of extruded poly styrene foam.

8. The method according to claim 6 or 7, characterized gekenn¬ characterized in that the laminated film web is connected to the blank surface over the entire surface or only in the area of partial surfaces, preferably fused.

9. The method according to claim 1, 6 to 8, characterized in that the deformation in the form formed from a heated male and female mold into a shell in a time of 0.2 s to 10 s, preferably between 0.8 s and 1 , 5 s, is carried out.

10. Device for performing the method according to claims 1 to 9 with the following individual parts: - a sliding table (6), on the sliding plane (E) of which plate or sheet-shaped foam blanks (1.1 ... ln) or a corresponding blank sheet (111) can be placed and moved,

- a press station (8) which has a heatable stamp with flat stamp surfaces (39; 39 '),

- A deformation station (9), each with an interchangeable, heated male (37) and female (17), the deforming surface of which are compatible with one another, with a mold cavity remaining in the collapsed state of male and female,

- And with an ejection device (36).

11. The device according to claim 10, characterized in that the pressing station (8) is preceded by a film supply roll (29) from which a film web (27), optionally via a compensating device (31), to the displacement plane (E) is removable.

12. The apparatus of claim 10 or 11, characterized in that the pressing station (8) is followed by a cutting station (34).

13. The apparatus according to claim 10, characterized gekenn¬ characterized in that the compensating device (31) has at least two deflection rollers (32, 32 ') and a dancer roller (33).

14. Device according to one of the preceding claims 10 to 12, characterized in that the pressing station (8) is connected to a vacuum pump (15) with which a vacuum is located below the displacement plane (E) in the region of the stamp surface (39, 39 ') can be generated.

15. Device according to one of the preceding claims 10 to 14, characterized in that the deforming surface (35 ') of the male part (37) is provided with at least one peripheral cutting edge (25) which corresponds to the circumference of the shell to be manufactured.

16. Device according to one of the preceding claims 10 to 15, characterized in that the stamp surfaces (39) of the pressing station (8) and / or the deforming surfaces (35; 35 ') of the male (37) or female (17) with are provided with a thin, heat-resistant elastomer layer or a non-stick layer.

17. Device according to one of the preceding claims 10 to 16, characterized in that the deforming surfaces (35; 35 ') of the male (37) and / or the female (17) are in relief.

18. The apparatus according to claim 10, characterized gekenn¬ characterized in that the ejection device (36) comprises at least one in the male (37) and female (17) incorporated bore (23) to which a compressed air supply line is connected.

19. Device according to one of the preceding claims 10 to 18, characterized in that the deformation station (9) is provided with a collecting grid (30) which can be moved laterally towards it and that the male part (37) is also laterally displaceable in the deformation station .