DE2102493A1 - Vacuum packaging - in sealed thin film envelope with mouth supported by clamp allowing air escape - Google Patents

Abstract

In vacuum packaging in thin plastic film envelopes, the mouth of the envelope is held clamped at spaced points across the width, allowing air to escape when vacuum is applied and affording support throughout the operation of a pair of welding bars until after restoration of atmospheric pressure. Appts. includes a vacuum chamber and a clamping device having >=1 bar with spaced grooves for the air escape.

Description

Method and device for tightly closing a plastic casing The invention relates to a method and an apparatus for manufacturing a tight seal of a cover or a packaging with a plastic film by welding. Through the invention, the openings of sheaths or Packaging, such as bags or envelopes made of thermoplastic films or closed by heat welding foils connected by heat welding after the goods to be packaged have been inserted and after the wrapping was placed in a container from which to produce a vacuum-tight Packaging the air was evacuated.

Previous machines for vacuum packing bags or wrappings made of plastic have a lock that can be hermetically sealed and the devices for closing the bag or the envelope by means of Hot welding having.

These devices generally consist of two parallel bars, at least one of which is provided with a heating element to protect the material or to melt the thermoplastic layers. At least one of these poles is movable so that they are pressed against the other and are moved away from her can to create a free space or gap between the rods.

If the casing to be welded is made of thermoplastic material, so the heating element very often has a surface resistance that by means of an electrical current pulse is heated very quickly to the desired temperature This current pulse can be controlled depending on the intensity and / or duration is. The surface will then return to its original temperature as quickly as possible cooled down.

One or more packages previously filled with goods to be packed are placed in the lock so that the edges of the pack finings are between the welding rods while they are open or partially open. The air is then sucked out of the bell and thus also out through the opening the packaging.

After the desired dilution has been reached, the Welding rods operated by an automatic control and seal the openings of the bags or wrappings.

After the welding process has been carried out, the thermoplastic is left Material that has now melted is allowed to cool sufficiently and then sets restore atmospheric pressure in the bell. The welding rods and the lock are then opened again to remove the finished packaging.

Although these closure devices work well on bags and These devices can be used to supply casings made of special plastic materials very difficult to use for packaging made from other plastic materials exist because a large reject is created and in many cases they are not applicable at all are.

For reasons that will be described later, this limitation is related especially on the use of highly flexible foils, because these are either very are thin or because the material is not rigid. These limitations are great important for thermoplastic films with low viscosity at welding temperature.

Other characteristics of the olives used, such as some stickiness, Adhesion, degree of contraction or shrinkage at temperatures below the welding temperature can come together and the application and use of such Foils limit The low rigidity of the material used for packaging can be a disadvantage as it makes wrinkles and shrinkages more easily in the weld area which then becomes uneven and does not provide a secure, tight seal forms. Depending on the type of material used, the wrinkles can be Form passages or cracks that run, or can, through the weld Perforations in the film in the welding area near the fold. In both Falling does not result in an airtight seal and the pack due to the welding will leak after a certain time. The folds and the resulting perforations in the welding area can result from improper arrangement of the bag or the envelope appear in the suction cup, but in general almost all of the wrinkles will appear generated by stresses in the bag or wrapping during the evacuation of air develop.

In order to avoid these disadvantages, attempts have already been made the packing area according to the opening to hold on. In addition For example, spring-loaded pins were used inside the Packaging and on the outer edges of the opening were effective and the walls in the welding area put under tension. This arrangement has the disadvantage that it is rather complicated and is sensitive, the packaging speed slows down and with every change the form of packaging must be readjusted and regulated. Although the essential Causes for the formation of wrinkles can be balanced and eliminated by the Arrangement further disadvantages occur due to the other characteristic folds arise in that area of the packaging on which the pins act.

The low viscosity and mechanical strength of the thermoplastic Foil at welding temperature increases the risk of damage in the welding area, when it is exposed to tensions and other external loads. It has However, it has been shown that the in the welding area as a result of the hot welding under Vacuum tensions on the packaging inside the container do not occur are harmful. These tensions arise in the packing inside the chamber at vacuum. during different periods of time in the process.

It has been shown that during the suction of the air from the bell an overpressure is created inside the packaging, which inflates the container and that Material settles. This expansion leads to tension in the walls of the packaging, even after closing the welding rods to carry out hot welding are still present and thus affect the heated area of the film.

If the atmospheric pressure is restored in the bell, so the walls of the bag or the envelope are pressed down and lie thereby firmly attached to the packaged goods. These movements press the plastic material against the packaged goods and have a tendency to close the film from the sealing bar solve while the plastic material is still hot and therefore sensitive to mechanical Deformation is. This effect is tangential to the contact surface of Welding rod and foil, i.e. in an unfavorable direction to overcome the adhesive forces between the welding rod and the foil after welding the stickiness of the film. In most cases, these forces do not lead either to loosen the foil from the welding rod, but they damage both the welding area the foil as well as the heated area in the immediate vicinity of the welding element.

If the air chamber is raised, the operator which removes the packaging, another mechanical effect on the welding area.

Removal is generally relatively quick Movements and because the ventilation forces between the film and welding rods are overcome must be, this results in tensions and deformations in the film, which depend on the skill of the operator.

An attempt to overcome the stresses caused by the foregoing The disadvantages incurred limited the damage caused by the removal of the film can occur from the welding rod. In particular, the tendency of the film to to stick to the welding rod, by making a strip non-sticky Materials (in this context are thin films made of polytetrafluoroethylene or Polytetrafluoroethylene known applied to glass fiber fabric) between was and that the thermoplastic material before the restoration of the atmospheric Pressure in the vacuum bell and before removal of the bag from the sealing rod was cooled, Both measures are used in practice, however, in difficult pollen they cannot eliminate the problems of certain materials lose their crystalline structure when heated and acquire it after cooling back very slowly. In the amorphous state, these materials have low strength that the welding area is still very sensitive even after cooling down. It is obviously impossible and also uneconomical, the work process up to the occurrence interrupt the crystallization.

Another difficulty with welding certain thermoplastic Plastics consists in achieving good heat transfer and those to be welded To join layers together, for which a certain pressure on the welding rods must be exercised.

This pressure is generally also applied during cooling to the Material exercised. For material that has a low viscosity at the welding temperature this can lead to a reduction in the thickness of the film, which is the result at the welding point has a low strength. With certain substances that contract when exposed to heat it is possible to improve the strength when welding by the The film shrinks in one direction or in the longitudinal and transverse directions to thereby reduce the To increase the film thickness in and next to the welding area. Previous attempts on this were based on the shape of the heating element and how it worked and contained all of them the risk of overheating and the generation of undesirable shrinkage stresses, the led to unusable perforations in the film.

The invention overcomes these disadvantages and in particular avoids them the formation of folds in the opening area of the bag or the Wrapping during the suction of the air from the inside of the bag, so that undesirable Stresses in the weld area during suction and recovery the atmospheric pressure inside the bell can be avoided.

Furthermore, with the invention in the welding area during the Removing the packaging from the sealing rod reduces the stresses that occur and the cooling of the film can be accelerated during this process. About that In addition, by means of the invention, the thickness of the film in the welding area should be achieved through utilization of surface tension and shrinkage forces that occur when the material shrinks occur, are enlarged.

According to the invention there is a device for sealing plastic casings by means of vacuum welding used, which a vacuum chamber, arranged in this Welding rods for closing and welding the edges of the opening of the packaging envelope, at least one pair of clamping rods arranged parallel to the welding rods for Clamping the cladding opening before, during and after welding, one or more clamping rods having grooves for partial separation Clamped the edges of the cladding opening to allow the wipe of the rods is so that air can be sucked out of the interior of the envelope while the Clamp bars hold the edges in place before and after vacuuming.

The invention also relates to an airtight sealing device of plastic envelopes by means of vacuum welds, which have a vacuum chamber, in this attached welding rods for closing and welding the edges the opening of the envelope and at least one nozzle which has an air jet over the surface of one of the welding rods between the welding rod and the welded packaging opening conducts, wn the weld seam to cool and the loosening of the welding area from the welding rod.

The invention also relates to a method for vacuum packaging in plastic sheaths, in which the opening of the filled plastic sheath is clamped at their edges at a distance from each other, the #our the envelope is subjected to a vacuum so that the inside of the envelope Existing air is sucked out, the opening by means of a pair of movable welding rods is closed, the welding rods are separated from each other, the outside of the welded envelope is in turn exposed to a pressure and in which finally the clamps are removed from the envelope opening.

The invention also relates to a method for vacuum packaging in Kunatatoffumhüllungsn, in which the opening of the filled Xlaststoffumhüllungsn is held in a vacuum chamber between welding rods, at least one of the Welding rods are heated, the welding rods are separated from each other and Air from a DUse is passed over at least one welding rod and the welding area is used to accelerate the cooling of the welding area and the loosening of the welding area from the welding rod to make it easier.

Finally, the invention relates to a package s L i by means of of the above devices or the above procedure The unheated welding rod is preferably withdrawn from the two welding rods or open, as this has the lower temperature during the welding process and therefore the film can be removed more easily without damage. The slide can only from the heated one.

Welding rod can be removed when it has cooled down.

By this welding rod movement, the operation of the device be accelerated by moving one of the welding rods a certain time before recovery is moved by atmospheric pressure in the bell jar.

The invention is explained in more detail below with reference to the figures.

Fig. 1 - shows schematically a section through a vacuum packaging device according to the invention along the strand I-I from FIG. 2.

Fig. 2 - shows a partial section along the line II-II from Fig. 1.

Fig. 3 - shows a further Aus £ dhrungsbeispiel the invention in a similar way View like Fig. 1.

FIGS. 4 to 8 show the various working steps schematically of the device for closing an envelope made from shrinking when exposed to heat Material.

The device shown in Figs. 1 and 2 includes a table 10, on which the goods to be packaged are placed after they have been wrapped in an H Appropriate form of heat-weldable plastic has been introduced.

The filled envelope H is placed on the table 10 in such a way that that the edges H1 and H2 of the order of the envelope H are between the welding rods A, of which a welding rod 12 is fixed and a welding rod 14 is movable is, wherein an elastic pad 15 and an electrode 16 are provided. the Rods 12 and 14 press the edges H1 and H2 together in the desired manner. the Electrode 16 is connected to a corresponding electrical voltage source. It can be coated with a layer of polytetrafluoroethylene for adhesion between the rod and the plastic material.

The movable welding rod 14 is by means of the piston rod l8 of the Piston 20 held, the intpinem cylinder 22 is movable. On a piston surface acts a compression spring 24, which the rod 14 from the fixed welding rod 12 pushes away. The upper chamber 26 of the cylinder 22 is with a connection 29 one Three-way valve 28 connected, its other connections 30 and 32 with the ambient air and an air chamber L, which encloses the package? i, K. These Chamber is formed by a bell 54 which is freely movable in the vertical direction is and on which the piston-cylinder device 20, 22 with the movable welding rod 14 and other elements described later are attached together with the welding rods 14 and 16 are at least a pair of clamping bars B for holding the edges H1 'H2 of the Opening of the envelope H is provided. Preferably, at least one is provided. these rods rubberized to increase the friction between the rods and the plastic film.

In the Ausrührungsbeispiel shown in Figs. 1 and 2 runs a crosspiece 36 formed integrally with the cylinder 22 parallel to the welding rods 12 and 14 and contains a series of holes, each of which receives a tenon 38, which by means of a spring 40 be operated and at the free ends Each have a stamp 42 with a plastic or rubber pad 44.

The pads 44 of the pin 38 are fixed in the upper surface 46 of the lying rod of the pair of Klommstangen ß. In the one shown in Figs Device, the fixed clamping rod is formed by an upwardly directed wall 50, which is arranged near the fixed welding rod 12 and rivets running vertically 48 has. The grooves 48 are shaped and dimensioned so that they can be used later fulfill the task to be described. In particular, the cross-section of each groove increases 118 in the direction from the wall 50 to the welding rod 12.

In the arrangement described, the edges H1, H2, as become clear can be seen in Fig. 2, at points located at a distance from one another by means of Pad 44 firmly clamped and held. The distance between the plsters 44 is essentially occupied by the grooves 48, the maximum width of which depends on the properties depends on the plastic material from which the envelope H is made.

The block formed by the wall 50, which in the illustrated embodiment forms a unit with the welding rod 12, contains channels 52, the nozzles 54 with connect to a compressed air source. The nozzles are arranged 80 that their openings in line with the trailing edge of electrode 16 and the beveled ends of the grooves 48 are so that one or more Luftatrahlen on the edge H and the Electrode be steered.

The movable parts of the welding and clamping rods, A, B, are made by carried by the bell 54 and therefore move during the operation and during of welding the edges HX and H2 together with this, which will be explained later.

Fig. 3 shows a modification of the inventive device with a pair of additional clamp bars C parallel to and behind bars A are arranged.

In this illustration, parts that correspond to FIGS. 1 and 2 are identical denoted by the same reference numerals.

The fixed rod of the rod pair C forms a unit with the rest Welding rod 12a and the fixed clamping rod 50a. The other hand is the movable Rod 60 of the pair of additional clamping rods C via one or more cylinder-piston devices, for example pneumatic motors connected to the Qlocke 34a, the cylinder-piston devices being independent of the rods 14a and 42a actuating piston-cylinder device (not shown) according to the device 20, 22 from FIGS. 1 and 2 can be actuated. The moving parts of these cylinder-piston devices are connected to the rod 60, which has an elastic pad 62 at its end, which rests on the edges H1, H2 and these continuously against the fixed clamping bar 50a stuck. In this case, the rod 60 is during or immediately before Welding of the edges H1, H2 operated while the rod 42a during the suction process is actuated The characteristic steps of the closing and sealing process the packaging H, K will now be described with reference to FIGS. 4 to 8, namely first with reference to the device according to FIGS. 1 and 2 and then with reference to the device according to FIG. 3.

The packaging H, K with the Out K therein is described in Way placed on the table 10, with the edges} 112 of the opening of the envelope on the upper surface of the rod 12, 50 rest. Then the bell 34 is lowered, so that its edge is opposite the surface of the Seals table 10, so that the vacuum canister is closed. During the lowering of the bell 34 are the movable rods 14 and 36 close to the corresponding fixed rods 12, 50 brought so that the elastic pad 44 (Fig. 1) resiliently against the rest. Clamp bar 50 are pressed to hold the edges H H2 of the envelope H. Meanwhile, the movable welding rod 16 by the compression spring 24 of the associated test welding rod 12 kept revealed. Thus, the edges Separate H1 and H2 from one another by means of the grooves 48, UM corresponding to these grooves 48 To form openings through which the air can escape from the envelope H, if the chamber L is evacuated.

After the edges HX and 11a are partially clamped, will the chamber L by actuating a shut-off valve (not shown) in the line M (Fig. 6) is connected to a vacuum source and the air is drawn from the L chamber and the envelope H and dAmit also sucked out of the chamber 26 above the piston 20, since the three-way valve 28 connects the chamber 26 and the space L. In this way the required vacuum is created in the envelope.

During this process, the air can easily escape from the envelope H because between the chamber L and the inside of the Cladding creates a pressure difference through which the areas of the edges Hl and Hz, which correspond to the grooves 48, have been pulled apart, whereby the Evacuation of the envelope is facilitated.

Once the desired vacuum has been built up in the envelope H, it will be Valve 28 actuated to interrupt the communication between chambers L and 26 and the chamber 26 via the connection 30 to connect to the atmosphere. The thereby resulting pressure difference across the piston 2G causes the lowering of the movable Welding rod 14 which is pressed against the fixed welding rod 12. The electrode 16 is then connected to the electrical voltage source for welding. To After welding, the valve 28 is actuated again and into the position shown in FIG brought so that the chamber and 26 are connected to each other and the spring 24 the Welding rod 14 withdraws. Finally, before opening the bell 34, the Communication re-established between the interior of the chamber L and the atmosphere.

This connection is achieved by a valve (not made of paste) in which the channel 52 supplying the nozzle or nozzles 54 is actuated. The Lurt flows prior to entering the chamber through the nozzles 54 over the welded edge H1, 112 so that these are cooled and released from the fixed welding rod 12. During cooling, the welded edges H1, H2 can freely contract and deform according to the welding so that the edges increase their strength can and freely swell without stresses being transferred to the envelope H, since the edges Hi, H2 of the opening are still held between the clamping rods B. will. When atmospheric pressure is restored in the chamber L, so are the welded edges Hl, H2 sufficiently cooled and strengthened.

Eventually the bell 34 is raised, causing the clamping rods B can be pulled up and the packaging H, K can be removed from the table 10. The device can then be used to close a next envelope.

The operation of the device according to FIG. 3 is identical to that described above, however, the movement of the welding rod 14a becomes simultaneous transferred to the glue bar 60. The fastening of the welded edges H1, H2 is reached in this impact by the additional rod 60, which against the entire surface 46a of the part 50a of the cross piece 12a, 50a is pressed. Is in the Chamber L atmospheric pressure is restored, the additional bar raised and the packaging removed from the table OK.

In a modification of the method for welding the edges H1, H2 it is also possible, from the movable welding rod 14 to the corresponding fixed rod to control applied pressure. The two welding rods 12 and 14 are initially brought close together so that the edges Hl, H2 held between them where the welding takes place. Immediately after welding, the pressure exerted by the movable welding rod 14 is reduced, and this rod If possible, a short distance is removed from the weld seam. This is it is possible that from the welding rods A onto the welded plastic material to counteract the pressure exerted and to switch it off. So they are welded Edges H1, H2 that are still hot are able to shrink and their strength to enlarge.

The nozzles 54a are then actuated to cool the weld seam and the The work process proceeds as described above, with the welded edges can still be held by the clamping rods B or the additional rods C.

E8 it is clear that the nozzles 54 the air jet over the entire width The weld line is conducted over the packaging, creating a controlled and gradual increasing tension is generated, which is used to overcome the adhesive forces between welded Material and welding rod is used. This creates stress concentrations and point-like Tensions at any point in the weld seam are avoided, and the packaging can can be easily removed from the welding rod without tearing, without the operator Can make mistakes. Another advantage of the Lurt beam is that the The cooling rate in the welding area is increased. The air jet will end up the cooling process after welding and after opening the two welding rods 12 and 14 actuated. This air jet is preferably generated by the fact that Outside air that is used to produce the atmospheric pressure at the end of the welding process is introduced into the lock, through which the. directs.

The above-described and illustrated device can be in any Machine or arrangement for vacuum packaging can be installed.

The specific structure of the device described can be a function be changed by the respective circumstances, in particular depending on the the goods to be packaged and the type of film used. The device can also Have facilities or equipment for the automatic implementation of the welding type.

Claims (20)

Expectations 1. Device for airtight sealing of plastic casings by means of vacuum welding, with a vacuum chamber, in the welding rods for closing and welding the edges of the opening of a plastic envelope are characterized by at least one pair parallel to the welding rods (A) arranged clamping rods (B) for Pegtklermen the envelope opening before, during and after welding, one or more of which the clamping rods t50) grooves (48) for the partial separation of the clamped edges of the opening (H1, H2> the Enclosure (H) has, so that air can be sucked out of the interior of the envelope can, while the clamping rods firmly hold the edges in their before and after suction Hold position. 2. Apparatus according to claim 1, characterized in that the Grooves (48) extend across the clamping rods and that their cross-section in the direction decreases on the welding rods. 3. Apparatus according to claim 1 or 2, characterized in that one of a pair of clamp bars is movable and the other clamp bar (50> test is, and that the movable clamping rod (56) has clamping areas (92), to exert a controllable clamping pressure on the opening edges of the envelope are elastically attached between the test and movable clamping rod (36, 50). ii. Device according to one of Claims 1 to 3, characterized in that that two cooperating clamping rods have mutually matching grooves. 5. Apparatus according to claim 3, characterized in that the movable Clamping rod has a number of pins (38), each of which is elastic with respect to the movable clamping rod are attached and each with an elastic pad (44) are provided to rest on the opening (H1, H2) of the envelope (H). 6. Device according to one of claims l to 5, characterized by a pair of additional clamping rods tC) between the welding rods (A) and the clamping rods (B), wherein one of the additional clamping rods (60) is movable and in accordance with the Actuation of the other movable rods (42a, 14a) can be driven. 7. Apparatus according to claim 6, characterized in that the remainder Rods of the pairs of welding rods, clamping rods and additional Klewtangen for Forming a single component (12a) are interconnected. 8. Device according to one of claims 1 to 7, characterized in that that one of the welding rods (12) rest and the other welding rod (14) is movable and is actuatable by a pneumatic motor (20, 22) which controls the movable welding rod (depending on pressure changes in the vacuum quay (L> against the fixed Welding rod (12) presses. 9. Apparatus according to claim 8, characterized in that the pneumatic Motor consists of a piston (20) and a cylinder (22), which is the movable welding rod retracts under spring force and a pneumatic connection on one side of the piston with the interior of the vacuum chamber (L) and the other side of the piston optionally is connectable to the interior of the vacuum chamber and the outside air. 10. Apparatus according to claim 9, characterized in that the other Piston side is connected to an opening (29) of a three-way valve (28), the other openings (30-32) each with the surrounding Lurt and the interior of the chamber (L) is connected, and that the three-way valve from one to that of the vacuum chamber prevailing pressure responsive device is controllable. 11. The device according to claim 3 and one of claims 8 to 10, characterized in that the movable welding rod (14) from a movable Support (3X) is held and the pneumatic motor (20, 22) opposite the welding rod this support moves, and that the movable clamping rod at least one elastic with a further support (36> connected clamping element (42), wherein the further support can be moved together with the movable support of the welding rod is. 12t device according to one of claims 1 to 11, characterized through at least one nozzle (54) connectable to a compressed air source, the outlet of which is arranged near one or both welding rods (1, 6) and a jet of air over the edges of the welded envelope opening (H1, H2) so that the cooling process speeds up and makes it easier to remove the welded edges from the welding rods will. 13. Device according to claims 7 and 12, characterized in that that each of the nozzles (54> at least partially through the fixed welding rod (12) is limited, and that the nozzles in line with a first side of the rest Welding rod placed near the pair of clamping rods (B) and over the welding surface the fixed welding rod (12) to the opposite side of the remaining welding rod are directed. 14. Apparatus according to claim 12 or 13, characterized in that that the opening of the nozzle or each nozzle (54) near the end regions of the grooves (48) lies. 15. Device according to one of claims 12 to 14, characterized through another three-way valve between a compressed air source, the vacuum chamber (L) and the nozzles (54), which by the movement of at least one of the welding and Clamping rods (A, B) is controllable to the nozzles at least part of the ones To supply air necessary for the production of the atmospheric pressure in the vacuum chamber is forwarded. 16. Process for vacuum packaging in plastic envelopes, in which the xussere of the filled envelope is subjected to a vacuum to remove the air suction the inside of the envelope, whereupon the opening by contact with a Pair of mutually movable welding rods is closed and the ambient pressure around the envelope is restored, characterized in that the opening the envelope at spaced locations along the opening edge is clamped before the end of the evacuation, and that the bond after the restoration the ambient pressure is canceled. 17. The method according to claim 16, characterized in that the weld seam by means of a stirred after separation of the welding rods over the opening of the envelope Air jet is cooled. 18. The method according to claim 17, characterized in that the air jet consists at least in part of the same lurt that corresponds to the exterior of the envelope is supplied to restore atmospheric pressure. 19. The method according to any one of claims 16 to 18, characterized in, that the contact pressure of the welding rods is controlled so that this first merged with the required contact pressure and then with an electrical Voltage source are connected, whereupon the touch pressure is reduced, so the welded edges contract completely and increase their strength can. 20. The method according to claim 19, characterized in that the welding rods completely separated from each other while the contact pressure is being released. L e r s e i t e