DE970084C - Process and devices for the hot welding of thermoplastic films or surfaces with coverings made of thermoplastic materials - Google Patents

Description

ISSUED AUGUST 21, 1958

B 25485 XI39a

The invention relates to a method for hot welding thermoplastics Films, in particular of surfaces with spreads or coverings made of thermoplastic material, for Production or for closing packaging bags, packaging boxes or the like, in which the foils or the surfaces with the facing coverings are heated the seam to be closed are pressed together.

In the manufacture and closing of packaging, folding bags or the like of the aforementioned Art one has so far generally proceeded that the foils or the coverings from thermoplastic material at the weld seams converted into a plastic state by heating and that then a set pressure for joining the material to the Suture was exercised. This pressure had to have a certain strength so that the ao plastic material was pushed away to the side, so that not enough material remained at the seam, in order to achieve sufficient or the same strength at the weld seam as at other parts of the collapsible bag or the like. Under certain circumstances, excessive pressure

SW 594/27

or too high a temperature, the tightness of the folding bag at the weld seam due to this process get lost. A reinforcement of the material covering on the seam parts of the surfaces 5 or foils or an increase in temperatures or prints did not lead to better, but to worse results.

To the seam connections in the production or for closing of collapsible bags or the like

ίο thermoplastic films, especially from surfaces Made of paper or the like with coverings made of thermoplastic materials, even when relatively thin foils or coverings, so that the strength at the seams is absolutely sufficient or

is the same or about the same as on the remaining parts of the packs, without the Leak tightness is adversely affected, the method according to the invention is that after Heating of the foils or the thermoplastic

Surface coverings on the surfaces to be welded at the weld seam initially only a light, that softened plastic material is not exerted pressure that would cause it to give way to the side, whereupon the pressure increases as the thermoplastic material cools down is chosen larger.

This is done by applying relatively light pressure on the areas to be welded Heating plasticized material of the foil

or the covering is not pushed away laterally, so that one can use relatively thin foils or coverings can work. Only after the actual welding zone is the pressure corresponding to the cooling and according to the resulting

the gradual reduction of the plastic state is continuously enlarged so that the connection the surface parts is maintained, but even then no lateral pushing away of the Material can take place. The thickness of the foils or the coverings is thus at the weld seams maintained so that there is a firm, intimate connection at these seams, that too cannot lead to leaks.

The device used to carry out this process is essentially identified by a transport device, e.g. B. od a transport channel. Like., With a preheating zone, a consisting of heated jaws or pressure rollers that exert a slight pressure on the weld metal Welding zone and one of several unheated pairs of rollers that gradually exert increasing pressure on the weld metal Jaw pairs existing pressing and cooling zone. The transport device can be in any In the form of a transport channel, a conveyor belt or in the form of rollers with grippers or the like. be designed, depending on whether only welds to close the filled Pack or whether during the production of the foldable bags or the like. Welded seams and additional fold lines or the like. To be produced.

The diagrams in Fig. Ι of the drawing show the temperature profile, the profile of the plastic And the pressure exerted as a function of time.

According to the diagram, the temperature rises uniformly on the curve T ₁ -X ₁ during the period AB ₁ in a first phase, which represents the preheating of the thermoplastic material. The plastic state of the thermoplastic material follows a parallel curve AY ₁ , during which time the. pressure exerted on the contacting surfaces is zero (line AB ₁ ). During the time B ₁ -B ₂ , the two contacting surfaces are gently pressed together in a pair of tongs, between a pair of jaws or between rollers. The temperature and the plasticity have risen to a maximum, which is approximately maintained over the curve parts X ₁ -X ₂ and F ₁ -F _2. When exiting the press jaws at time B ₂ , the pressure begins to rise uniformly and the temperature begins to drop uniformly on curve X ₂ -D , as does the plasticity of the thermoplastic material on curve Y ₂ -E. The pressure is growing

increases evenly during the time B ₂ -C according to the curve segment FG , only to suddenly become zero at time C (curve GC).

The plasticity of the thermoplastic material is _{negligibly small below the temperature T 0} , so that from this point on it is no longer necessary to continue with the pressing together of the contacting surfaces to be welded as soon as the temperature has dropped below this limit value.

The reasons for proceeding in the above-mentioned manner when welding result from the fact that that when a large pressure is applied at the moment when the temperature and the plasticity have reached a maximum, the plastic material outwards from the pressure zone is squeezed out and accordingly from the weld line or your sweat streak the to be connected Areas with which one takes the great risk that on this welding line or on this one There is too little or no thermoplastic material at all, so that the welding of the contacting surfaces is prevented at all, or at least one Weakening of the material occurs along the weld line or the weld strip.

On the other hand, if the pressure is released immediately after the intense heating, the Surfaces to be welded that always retain a certain elasticity and also butting be subjected to detach from each other even with slight knocks. A detachment of oneself surfaces in contact with each other is therefore inevitable, because that is still warm and So iao still has liquid thermoplastic material insufficient adhesion to keep the two touching surfaces in contact.

By contrast, the method according to the invention only leaves a thin layer or layer made of thermoplastic material is required, and any excess amount can be omitted as it is practical

there is no possibility for the material to evade while the pressure is applied. Greater pressure is only applied when the material has already regained a greater viscosity S as a result of cooling.

For each individual case it is of course necessary to have a maximum temperature and a pressure to choose the one that depends on the nature of the surfaces to be welded and on the type of

ίο depends on the thermoplastic material used. In Fig. 3 is an embodiment of a device for hot welding according to the Process according to the invention shown.

Fig. 2 shows an embodiment with a schematic vertical view of part of a is known per se machine for the production of bags. FIG. 2 shows the section of Shaping and the hot welding of the bag bottoms.

The bag tubes made in another part of the machine with the flaps folded inward arrive flat at 1 and pass between reels 2, 3 and 4 where they be aligned. Then they run past rotating knives S and 6, which form the folding lines mark the bottom and fold the end before forming the bottom.

The entrainment takes place on the cylinder 7, which can be heated if necessary in order to achieve preheating. The end of the bag is grasped by heated pliers 8 of the cylinder 9 and gently compressed. After an ⁸ A revolution of the cylinder 9, which takes about 1 to 1V2 seconds, the bag is gripped by the tongs 11, which are arranged on the cylinder 10, where the part of the bag that has been heated by the tongs 8 is now being strongly compressed. A simple and known arrangement takes the end of the bag when it is removed from the pliers 8, folds it and compresses it strongly. The tongs 11 work together with the rotating knife 10 'in order to ensure the production of the bottom fold of the bag.

The bags, the bottoms of which are completely welded together, are then stacked at 12, where they are held by a stop 13.

3 shows in a schematic perspective the

Device for sealing bags filled with any content.

The filled bags arrive in the transport channel 14, in which they are due to their own weight sliding by a ram or by a roller conveyor or a conveyor belt. Included the upper locking folds are pressed down by several thumbs, whereby one Instead of the thumb, a similarly acting device can be used, and both of them too Welding surfaces 15 and 15 'are directly to each other, in such a way that the thermoplastic documents are facing each other.

The zone 16 indicated by dashed lines now contains any desired device for heating,

z. B. electrical resistors, infrared emitters od. Like. Which are arranged in such a way that a there is a positive temperature gradient in the direction of the forward movement of the bag, d. H. the temperature rises evenly from the entry into this to the exit from this preheating zone at. In front of the exit end of this zone there is a pair of heated jaws 17, 17 'which B. be heated by an electrical resistor. The heating of these pliers can also be on any other kind, e.g. B. by Hochfreqenzstrom are carried out. The jaws 17, 17 ' lead alternately a movement towards and away from each other according to the drawn Arrow 18 out, and this movement is brought into synchronism with the forward movement of the bags.

The shape and dimensions of the effective surfaces 19 of the jaws 17 and 17 'are of the shape and adapted to the dimensions of the welding line or the welding strip.

The pressure of the jaws 17 and 17 'can be adjusted against one another by means of springs 20. Thus, as stated above, it is possible to select the pressure applied by the jaws just so great that the inner surfaces of the two surfaces to be welded together are brought into perfect contact with one another. The heat generated by the tongs or the jaws plus the heat already exerted by the preheating in zone 16 is sufficient to completely soften the thermoplastic material and to make it well plastic at the point where the welding is to take place. Immediately after heating and after application of the slight pressure by the jaws 17, 17 ', the bag ends 15, 15' on the upper closure side between the rollers 21, 21 'and 22, 22' and 23, 23 'etc. are pressed together. These rollers, which can rotate freely about their vertical axis, are not heated, but the first rollers 21, 21 'in the immediate vicinity of the warm press jaws 17, 17', while the rollers 22, 22 ', which are already further from the jaws are removed, are less warm, so that the temperature of the rollers with increasing distance from the jaws drops very quickly to the surrounding temperature.

Each roller is provided with a device, through which the amount of pressure that is applied to the welding surfaces is applied, can be adjusted.

In the schematic embodiment, press the springs 31 and 31 ', 32 and 32', 33 and 33 'etc. the roller 21 against the roller 21', the roller 22 against the roller 22 ', the roller 23 against the roller iao 23 'etc. A system of adjusting screws allows a very simple adjustment of the pressure level to, and according to the invention, this pressure head should be uniform from one to the other The pair of rollers grow in the sense of the forward movement of the 125th bag.

grow, as explained above, with the course of cooling. The exercised Compression pressure through the rollers reaches its maximum in the last pair of rollers, and in this one At this point, the temperature of the surfaces to be welded has decreased to a level at which the plasticity of the thermoplastic material is negligibly small.

After leaving the last pair of roles, the

ίο The bag is completely sealed. The location the roles can also be adjustable in height, so that the pressure in the course of all Rolling is applied to an area corresponding to the heated zone of the bag, creating a complete sealing over the entire closure surface is achieved.

Any suitable modifications can be made within the scope of the invention, namely with regard to the type of preheating,

ao the heating and the device for progressively increasing the pressing pressure.

Claims (3)

PATENT CLAIMS: i. Process for the hot welding of as thermoplastic films, in particular of Surfaces with spreads or coverings of thermoplastic material for manufacture Or for closing packaging bags, packaging boxes or the like which the foils or the surfaces with facing coverings under heating on the to sealing seam are pressed together, characterized in that after heating the foils or the surfaces with the coverings on the surfaces to be welded the weld seam is initially only a light, the softened plastic material not to the side Dodge bringing pressure is exerted, whereupon the pressure with advancing Cooling of the thermoplastic material is chosen progressively larger. 2. Device for producing and / or closing collapsible bags according to the method of claim i, characterized by a transport device, e.g. a transport chute (14) or the like, with a preheating zone (16), one from a slight pressure on the weld metal exercising, heated jaws (17, 17 ') or pressure rollers existing welding zone and a of several progressively increasing pressure on the weld metal, unheated Pairs of rollers (21, 22, 23) or pairs of jaws existing pressing and cooling zone. 3. Device according to claim 2, characterized in that the pressure of the roller or Backenpa & re or the like can be adjusted in the welding zone as well as behind the welding zone. 1 sheet of drawings O 509 704/349 4.56 (80 »594/27». 5 »)