DE1228396B - Device for welding thermoplastic materials - Google Patents

Description

Device for welding thermoplastic materials. The invention relates to a device for welding or sealing thermoplastic materials using heat and pressure.

The well-known heat sealing processes fall into three categories organize. In the first category, namely the baking sealing process, two heated jaws with the foil layers between them pressed together. Through the Heat is used to melt the sheet material, while the pressure exerted on the layers are fused together.

The pressure exerted by the jaws causes something to melt Foil material squeezed out, with the result that after solidification the Foil thickness of the edge of the heat seal is reduced. A second disadvantage is that the jaws are opened while the heat seal is in place is still in the molten state so that the sealing point is damaged can experience.

A second method is what is known as impulse heat sealing which one or two heat seal tapes through cushioned, unheated jaws pressed against the film layers. A current is then passed through the heating bands so that the foil melts and brings the pressure exerted by the jaws the film layers together for fusing.

The disadvantages are the same as with the baking heat sealing method. Some molten material is squeezed out of the heat seal, causing the film is weakened and the heat seal is damaged when the sealing tapes be lifted from the still molten sealing point.

A third process is the so-called continuous heat sealing process, in which two endless belts are driven by rotating rollers. These Tapes are pressed together against the film layer by stationary heated jaws. The disadvantages are more or less the same as before. Although the tapes do not squeeze out as much liquid film material as in the other two cases, there is still some squeezing out, causing the film to become adjacent the heat seal is weakened. During the cooling period, the foil layers are with the molten heat seal deposited on the tapes. This is but not necessarily, so that a certain deformation of the heat seal the Consequence is. This deformation is greater in the case of vertical heat sealing pronounced.

The invention is based on the object of creating a device in which these shortcomings and difficulties are avoided. This is done in the The device according to the invention achieved in that not during the welding process molten material lying at the weld point in the direction of the melt is moved towards the welding point in order to reinforce the material at the welding point, without it being squeezed out.

Further objects of the invention emerge from the following Description of exemplary embodiments in conjunction with the drawings, namely Fig. 1 shows in cross section a jaw sealing device in its open position, F i g. 2 shows a cross section of a jaw sealing device in its closing or Sealing position, Figure 3 shows a section of a jaw sealing device in its open (withdrawn) position, Fig. 4 a section of a jaw sealing device with a pulse heating on the outside of the printing belts, Figure 5 is a section of a Jaw sealing device with pulse heating on the inside of the printing belts, F. i g. 6 is a longitudinal view of continuously heated jaws for a continuous heat sealing process; F i g. 7 is a sectional view of the FIG. 6 shown device according to the line 7-7, Fig. 8 is a sectional view of the FIG. 6 shown device according to the Line 8-8, Fig. 9 is a longitudinal view of continuously heated band heating elements for one continuous heat sealing process, F i g. 10 is a side view of the FIG. 9 shown device according to the line 10-10, F i g. 11 is a side view of a heat sealing device with wheel heating, FIG. 12 is a sectional view of the device shown in FIG along the line 12-12, FIG. 13 is a plan view and a sectional view of a printing tape, 14 is a plan view and a sectional view of another embodiment of the Printing tape, F i g. 15 is a plan view and two sectional views showing two types of flat print ribbons, FIG. 16 is a side view of another device when using converging tapes on each side of the sealing point, Fig. 17 a plan view of the device shown in FIG. 16 and FIG. 18 is a sectional view the in F i g. 16 shown device along the line 18-18.

The inventive device can reduce the Film thickness are brought to a standstill adjacent the heat seal point. With With the help of the invention it is possible to make the thickness at the edge of the heat seal the same the thickness of the base material or, if necessary, the thickness at the edge of the Sealing point larger or smaller than the base material to make what by the inventive regulation is achieved. In this way the strength achieved can be achieved equal to, larger or smaller than the sealing point than that of the base material.

In Fig. 1 shows a device according to the invention, wherein an apparatus for baking heat sealing is shown in its open position. the Both sides of the film layers 1 to be hot-sealed are heated by baking 2 and specially shaped pressure bands 3 pressed together. These bands are preferred made of heat-resistant steel, although other suitable materials are also suitable can be used. There are conveyor belts between the pressure belts and the film layers 4 arranged. These tapes can be made from a woven or knitted or from a Another material are made up of synthetic fibers, such as nylon, polytetrafluoroethylene or glass fibers, or made from natural fibers such as cotton.

Any similar flexible material can be used per se, that can withstand the operating temperatures of the heat sealing process.

F i g. Figure 2 shows the heat sealing device in the closed or sealed position. To form a heat seal, the heated jaws 2 are pressed against each other, as shown by the arrows, wherein the curved pressure bands 3 are flattened and the edges of the belts slide outward on the conveyor belts 4. The heat of fusion for heat sealing becomes through the pressure belts and the transport belts to both Sides of the film layers. The heat causes the film material to melt brought, and through the Pressure exerted by the jaws will bond the layers together merged. After the melting period, the jaws are opened again, as in F i g. 3 shown.

During the opening period, the pressure of the jaws 2, through the The pressure bands have been flattened out, leaving the pressure bands back take their original shape. This has an inward movement of the edges of the Result in pressure bands. The layers of film are still between the edges of the Pressure tapes 3 are pressed together, and by the inward movement, the unmelted Foil material at the edge of the heat-sealing point displaced into the liquid basin of the same. This leads to swelling of the film layers adjacent to the heat seal point and to an increase in the thickness at the melt line between the molten and the solid film material. Furthermore, the loosely woven or knitted structure allows the conveyor belts that the molten film material on the conveyor belts sticks. In this way, the liquid pelvis is passed through the top and bottom Conveyor belts held while it was pressed together by the unmelted film layers that are moved inward by the edges of the print bands.

After the heating jaws have opened, the foil layers can be moved away by the Trånsportbands. The heat seal is always in place still in a molten state but cannot be mechanically Movement stressed or deformed as they are deposited on the conveyor belts is. In fact, the conveyor belts adhere to the heat seal, but they can after the sealing point has solidified, can be easily peeled off.

By using the device according to the invention can therefore the thickness and thus the strength of the seal can be regulated. Furthermore, through the use of the conveyor belts does not seal by gravity or influenced by mechanical handling during the cooling period. Because the slide need only be between the heat-sealing jaws during the fusion time and can be taken out for cooling is the total time for heat sealing decreased.

The device according to the invention can be used in conjunction with pulse heating elements be applied. Fig. 4 shows an arrangement in which the heating elements 7 are located on the outside of the printing belts 3, while F i g. 5 the heating elements 7 on the inside of the printing tapes 3 shows.

The way it works is similar to the previous case. If the When the jaws are closed, the pressure and heating tapes are against both sides of the film layers pressed. A current pulse is passed through the heating bands, which whose temperature is increased rapidly. The heat is conducted to the film so that a seal is made.

During the opening period of the jaws, the heat seal is through the pressure belts compressed and moved through the conveyor belts.

When the pulse heating elements are placed on the inside of the printing belts the heating elements are normally covered by an insulating material, for example covered with a glass fiber material impregnated with polytetrafluoroethylene.

The device according to the invention can also be used in conjunction with continuous and wheels-heat seal work can be applied. These use cases are below described.

The application of constantly heated baking at a continuous one The heat sealing process is shown in FIG. 6 shown.

In the case of the in FIG. 6 are the fixed heated jaws 5 kept pressed together and the pressure bands 3 as well as the Conveyor belts 4 with the film 1 between them constantly in the gap between the Jaw 5 moved. At the entry point between the jaws are the pressure bands flattened out, as in FIG. 7, and if the material is melted by the heat, so that a merger occurs. After the ligaments with the molten Once the heat seal has left the bakken, the printing tapes return to their original state curved shape back and press the heat seal in the in F i g. 8 shown Way together. The heat seal is cooled as it moves, and so does the film is stripped from the conveyor belts when these belts over their return the reels 6 begin.

F i g. Figure 9 shows the use of continuously heated heat seal tapes. This mode of operation is continuous and there are two endless heating bands 8 and Printing tapes 3 used, which are driven by rollers 9 and freely rotating rollers 10 are placed. The endless conveyor belts4 are on separately driven rollers 11 and freely rotatable rollers 12 are placed.

The film layers 1 enter on the left side and are through the conveyor belts 4 between the heating belts 8 and the pressure belts 3 (which are move at the same speed as the conveyor belts) into the gap between brought the stationary unheated jaws 2. Electricity is passed through the heating cables Brushes 13 supplied.

At the point of entry to the jaws, the pressure tapes, like shown in Fig. 10, flattened and the heating tapes against the foil layers pressed.

The heat sealing is effected by the application of heat and pressure. At the exit end of the fixed jaws, the pressure on the pressure belts is released, so that they take up their original curved shape again, which has the consequence that the heat seal is compressed as previously described.

The use of a wheel heat sealer is shown in Figs 12 shown. As shown in the schematic is a set of heating tapes 8 and print tapes 3 wrapped around the circumference of each of two rotating wheels 14.

There is one between the pressure belt and the hub of each wheel Layer 15 made of a soft, pliable material such as silicone rubber. This cover is flattened on contact with the opposite wheel, reducing the time the contact and thus the sealing time is extended.

The heating tapes are continuously supplied with electric current by brushes 13 supplied to generate the required heat. The two sealing wheels 14 are supported between two sets of driven rollers 9 and freely rotatable rollers 10. The film layers to be hot-sealed are brought into the clamping point by the conveyor belts brought the sealing wheels between the heating bands 8 and the pressure bands 3, so that the pressure bands are flattened The heating tapes therefore press against the film, with the result that the film layers melt and fuse together. At The pressure belts can regain their original shape on the exit side of the wheels ingestion, compressing the still molten sealing point. at This unit can be of sufficiently short dimensioning for the production of curved seals be used.

Figures 13, 14 and 15 show three main types of printing tapes for use for the applications described above.

F i g. 13 shows a double curvature embodiment for use, when thin films or medium-thick films are to be heat sealed.

F i g. 14 shows an embodiment for medium and coarse films and when multi-layer heat seals are required.

F i g. Figure 15 shows an embodiment for use in conjunction with straight heat-sealing jaws.

Two cross sections are shown, around those with light and heavy foils the tapes used.

The in F i g. 13 and 14 shown printing tapes have slotted Margins. The reason for this is twofold. First, the slots prevent one mechanical overstressing of the tape edges when they are wound around a roll, and second, the slots minimize the thermal stresses in the tape down. Since the heat is supplied at the middle part, the thermal expansion is at the middle larger than at the edges where the temperature is lower.

Fig. 16 shows another embodiment of the invention. Also in In this case again the principle is applied to the material on each side of the Move seal site to the seal's molten basin to prevent that the material is squeezed outwards at the sealing point and thereby the obtained Seal is weakened.

The device shown works continuously.

The material to be sealed 1 is from the left side of the in F i g. 16 is fed between endless flat belts 23. These tapes are placed around driven rollers 21 and around freely rotatable rollers 20. How out given the plan view given in Fig. 17, the bands converge so that they have a smaller distance from one another at the exit end of the sealing device than at the entry end. Motors 27 drive the rollers 21.

The converging flat belts 23 convey the material 1 into the Device in which they are heated and sealed by being with the Sealing tapes 24 are brought into contact or in close proximity thereof. The sealing tapes are heated by electric current supplied by means of brushes 26. A number flexible pressure rollers 22 provided with a cover press the flat ones Bands 23 and the sealing bands 24 against the material to be sealed. It was determined, that it is not necessary to drive the pressure rollers 22 when passing through them a movement is imparted to the flat tapes, which in turn applies to the sealing tapes 24 transferred. Tension rollers 25 are intended to ensure that the correct tension is applied all ligaments are maintained.

The time it takes to seal depends on a number of factors, such as the properties and thickness of the film. The exact time, however, can be easy determine by experiment. This required sealing time, together with the desired linear working speed the length of the sealing zone.

As can be seen, is during the time during which the material is in the device, this is constantly exposed to a side force, which by the converging course of the moving, flat converging bands 23 is caused, which have the tendency to remove the material on each side of the Seal point in the molten basin of the seal to move to a reinforced To obtain the sealing point which is very similar to the one obtained by using it is achieved by spring-like bands.

In practice this was converging in the use of these bands on fairly light materials, for example less than 0.1 mm (0.004 "), found that this material is not sufficiently stiff to withstand the converging ligaments caused side forces to resist. Through this wrinkles developed and the reinforcing effect could therefore not be fully utilized will. A fairly stiff conveyor belt was used to overcome this problem used behind the sealing tape and around the flexible pressure rollers.

In addition, a thin coating of silicone oil is usually applied applied to the surface of the sealing tapes in order to prevent them from adhering to the Sealing adhere. In this case, the power supply brushes on the inside of the tape are arranged.

The pressure-heat sealing has been very successful not only for Heat sealing of two layers of film, but also for heat sealing of several layers of film applied. The physical properties of each layer are determined by the heat seal in contrast to the conventional heat sealing process, it is not affected.

For example, an eight-ply sample of a 0.2 mm (0.008 ") each low pressure polyethylene film heat sealed that none of the layers of the bundle could be separated and none of the layers were weakened by the heat seal.

A very difficult sealing problem exists when materials are dusty need to be sealed.

This is particularly true in the bag filling industry.

After a sack has been filled with a dusty granular good is, the closure sealing is extremely difficult to perform. It was however, it was found that under such conditions seals of very high strength can be prepared using the methods described herein.

The pressure-heat sealing process can also be used without conveyor belts will. In this case, the pressure bands are covered by an insulating material, for example made of polytetrafluoroethylene, glass fibers, nylon or another suitable Material to facilitate removal of the seal adhering to the pressure tape.

In the foregoing description, foils were in the simple Examples are used, but this is not in any way limiting the invention Meaning, since this applies equally well to thermoplastics in general and to thermoplastics coated materials is applicable. There are therefore under thermo- plastic materials also to understand thermoplastic coated materials.

The following is an example of a compilation of thermoplastic Given materials that can be used in the context of the invention: polyethylene with a density of 0.9125-0.975, polyvinyl chloride, polypropylene, nylon, polyester, Polyolefins, polystyrene, rubber hydrochloride, mixtures of polyethylene with polypropylene, Polyvinyl chloride, elastomers such as polyisobutylene, chlorinated polyethylene, ethylene-propylene compounds, Polyvinyl acetate, ethylene-vinyl acetate copolymers and copolymers from Ethylene with vinyl acetate, propylene and octene-1.

Claims (10)

Claims: 1. Device for welding thermoplastic Materials using heat and pressure, characterized in that the Welding process the unmelted material lying on the welding point in the direction of the melt at the welding point is moved to the material to reinforce at the welding point without it being squeezed out. 2. Apparatus according to claim 1 with jaws, of which at least one is heated, characterized by at least one curved, between the jaws arranged, spring-like band which is supported on at least one of the jaws. 3. Apparatus according to claim 2, characterized by a cloth-like, between the spring-like band and the material to be sealed. 4. Apparatus according to claim 2, characterized in that the tape is movable between the jaws by means of a drive. 5. Apparatus according to claim 3, characterized in that the cloth-like Tape between the spring-like tape and the material to be sealed by means of a Drive is movable. 6. Apparatus according to claim 4 and 5, characterized in that at least one heating band and at least one spring-like band between the jaws are movably arranged. 7. Apparatus according to claim 6, characterized in that between the jaws at least one heating band, at least one spring-like band and one cloth-like band Tape are moved between the spring-like tape and the material to be sealed. s. Device according to claim 4 and 5, characterized in that the aforementioned Jaws consist of one or more rotating wheels, at least one of which is heated. 9. Apparatus according to claim 6 and 7, characterized in that the jaws consist of one or more rotatable wheels or rollers. 10. The device according to claim 1, characterized in that at least a pair of conveyor belts is arranged around driven and freely rotating rollers so that that the distance between these Ribbons, measured in the to that to be sealed material parallel plane, is larger at the entry end than at the discharge end and that between the driven and the free rotatable rollers a series of flexible pressure rollers and around these pressure rollers arranged at least one sealing tape is. Considered publications: German utility model no. 1 823 832> 1807696.