DE19802662A1 - Compound laminated film material for foodstuff packaging - Google Patents

Abstract

To produce a compound film material, a plastics film (14) is bonded to another web material (16) through a corona discharge on at least one side. The layers are bonded together by heat and pressure, without any additional adhesive while the film temperature is held below its melting point. The web material is of paper, nonwovens, metal, woven fabrics or even of plastics. The web is treated on at least one side with a corona discharge in short separate pulses. The discharge pulses have a frequency of 10-30 kHz and preferably 16-20 kHz. They have a pulse width of <= 30 mu s and preferably 10-20 mu s. The discharge pulses have a rise time of <= 5 mu s and preferably <= 3.5 mu s. The corona discharge is between two rod electrodes (20,22), both in the same structure and cross section. Each has an electrically conductive core and a shrouding (24) of a dielectric material, and preferably ceramic. The corona discharge is between two unearthed electrodes (20,22) which, with the secondary circuit of a corona generator, forms a high frequency oscillation circuit. The plastics film (14) is bonded continuously to the carrier web (16) into a compound web (30) through the pressure between two rollers (10,12). The corona discharge stretch (18,28) is directly upstream of the paired pressure rollers. The rollers (10,12) apply a pressure of 50-1000 kN/m and preferably 300-400 kN/m. The plastics film (14) has a temperature in the roller gap of 50-150 deg C and preferably 100 deg C. An Independent claim is included for an apparatus with at least one corona discharge stretch (18) with a pair of rod electrodes (20,22) where the film (14) passes between them. It then passes through the gap between two pressure rollers (10,12) where the film is laminated to the carrier.

Description

The invention relates to a method for producing a Composite film made from one plastic film and another Web material.

In conventional methods of this type, the plastic foil glued to the other web material. This ver driving are relatively complex and above all have that Disadvantage that the use of an adhesive for release of solvent damaging to health and the environment fen leads. This makes the area of use such Composite films, for example as packaging in Le food industry, significantly restricted.

The object of the invention is to provide a method where the plastic film without using an adhesive be permanently connected to the other web material can.

This object is achieved with those specified in claim 1 Features resolved.  

It is known that the printability of plastic upper surfaces can be improved if this surface with Is pretreated with the help of a corona discharge. A sol che pretreatment has the main effect that the behan delte plastic surface for liquids with higher Surface tension becomes wettable. Attempts by the inventors have now shown that it is possible to use a plastic film permanently onto another without using one glue Laminate web material when the plastic film at least on the other web material facing Side is subjected to such a corona treatment and then at moderate temperature with a certain amount of pressure force is pressed against the other web material. The The temperature of the film always remains below that Melting temperature of the plastic material, so that the method according to the invention no welding actually sense takes place.

Advantageous refinements of the invention result from the subclaims.

The other web material can be, for example another plastic film or paper or a act different fabrics.

The composite film is preferably produced in a continuous process in which the plastic first lay between two rod-shaped, lying across Corona electrodes extending in the web direction and immediately afterwards together with the other web material runs through the nip between two pressure rollers. The pressure force in the nip is preferably in Range from 50 to 1000 kN / m, particularly preferably between 300 and 400 kN / m. The temperature of the plastic film is preferably between 50 ° and 150 ° C. In a preferred one Embodiment is at least one of the two pressure roller  zen heated so that a temperature of around 100 ° C.

The plastic film should be free of lubricant or release agent be because these agents reduce the adhesion of the film belittle. Unless it is the other web material this is also a plastic film for this other web material.

The intensity of the pretreatment should be one of the surfaces tension of at least 50 mN / m, preferably 70 mN / m correspond to wetting liquid.

Particularly good results are achieved if the Corona electrodes supplied high voltage from a sequence there are very short high voltage pulses, for example from approximately rectangular pulses with one pulse width of less than 30, preferably less than 20 µs and a rise time of less than 10, preferably less than 4 µs. The peak tension of each high voltage pulses should be at least 50 kV, preferably be about 100 kV. A corona generator with which one Such voltage signal can be generated is described in DE 42 35 766 C1 described.

It also appears to be advantageous if the corona Treatment between two is essentially the same rod-shaped corona electrodes, each an electrically conductive core and a sheath a dielectric, for example made of ceramic and which are both floating and one parallel to the secondary coil of the corona generator switched discharge path form, so that the two electrodes alternately positive and negative high voltage pulses are supplied.  

The use of short discharge pulses with short Rise time seems especially for the long-term stabili the composite film to be advantageous. It was observed makes sure that the adhesion between the plastic film and the other web material with increasing age of the Ver bund Folie gets better. This could be due to this be that the very short, but extreme discharge pulses in the corona path are a long way going ozone-free and therefore not oxidizing or even reducing atmosphere that creates a retrospective Networking of the composite materials at the boundary layer favors or at least prevents chemical bin oxidation can be destroyed again.

The following are exemplary embodiments of the invention explained in more detail with reference to the drawing.

Show it:

Fig. 1 is a schematic diagram of an apparatus for performing the method according to the invention and

Fig. 2 is a simplified circuit diagram of a corona generator.

In Fig. 1 to 12 recognizes two pressure rollers 10, which form with each other a roll gap, which is traversed in the direction of arrow A by a plastic film 14 and another web material 16, such as a paper web or a further plastic film. The roller 12 has a relatively hard surface, while the roller 10 has a softer surface. The two rollers are mechanically biased against each other, so that a pressure force of, for example, 350 kN / m is generated in the roller gap. Both rollers 10 , 12 are heated so that a temperature of 100 ° C is maintained in the nip.

Immediately upstream of the roll gap, the plastic film 14 runs through a corona discharge path 18 between two rod-shaped electrodes 20 , 22 which extend parallel to one another over the entire width of the film web and are arranged as close to the roll gap as is structurally possible. Each of the two electrodes 20 , 22 has a rod-shaped, electrically conductive core which is surrounded by a dielectric sheath 24 made of ceramic material. The two electrodes 20 , 22 are connected to the two floating output terminals of a corona generator 26 , the basic structure of which is shown in FIG. 2. A corona discharge is thus generated between the electrodes, by means of which both surfaces of the plastic film 14 are pretreated. The parameters of the corona treatment are selected so that the pretreated surfaces of the plastic film 14 can be wetted by a liquid which has a surface tension of 72 mN / m (water). The plastic film 14 pretreated in this way is intimately connected to the web material 16 in the nip between the pressure rollers 10 , 12 , so that a composite film 30 is obtained downstream of the nip.

If the web material 16 is also a plastic film, this plastic film can also run through a corona discharge path 28 , which is indicated by dashed lines in FIG. 1, and in principle has the same structure and mode of operation as the corona discharge path 18 Has.

The corona generator 26 shown in FIG. 2 is fed by a DC voltage source 32 , which supplies a DC voltage of, for example, 300 V. A capacitor C is charged via a charging choke L1. The primary circuit of a weakly coupled transformer T (without iron core) contains the capacitor C, an electronic switch S and a further choke L2. The secondary coil of the transformer T forms with the capacity of the electrodes 20 , 22 a high-frequency resonant circuit with a natural frequency of, for example, 150 to 200 kHz. The secondary side of the transformer T is ungrounded, while the primary side is earthed.

The electronic switch S, for example a Thyri stor, is controlled by the voltage on capacitor C. Once the capacitor voltage reaches a certain threshold value reached, the switch S closes, so that the Capacitor across the choke L2 and the primary coil of the Transformer T discharges. Doing so will in the secondary coil of the transformer induced a high voltage.

When the voltage of the capacitor C decreases, the remains Switch S until the next zero crossing of this switch flowing current closed. When opening Switch S becomes the primary circuit of the Transforma tors interrupted, and the capacitor C is on the Charging choke L1 recharged during the Hochfre quenz resonant circuit on the secondary side of the Transforma torsion dampens afterwards.

The system is designed so that the periodic charge and discharge cycles of the capacitor C run at a frequency of 20 kHz, for example. Since the capacitor is charged via the charging inductor L1, a peak voltage is reached at the capacitor, which is significantly higher than the DC voltage supplied by the voltage source 32 and can be, for example, 800 to 1000 V. The control for the electronic switch S is designed so that the switch closes shortly before this peak voltage is reached. The inductance of the inductor L2 is much smaller than that of the charging inductor L1. When the switch S is closed, the primary current of the transformer rises very steeply, so that a strong voltage pulse is generated which triggers the high-frequency oscillation on the secondary side. On the secondary side, peak voltages in the order of magnitude of well over 100 kV are reached, so that the necessary ignition voltage for the Koro na discharge is provided. The further voltage curve is largely determined by the load formed by the corona discharge path. Each time the switch S is closed, an approximately rectangular voltage pulse with a pulse width of approximately 16 microseconds and a very short rise time of only approximately 3 microseconds is obtained.

With the help of the corona generator 26 , a corona discharge is obtained which consists of very short, high-energy pulses. This form of discharge has proven to be favorable for sustainable adhesion of the plastic film 14 to the sheet material 16 .

The parameters of the charge profile and the discharge distance (electrode geometry and distance), the type of Dielectric, the transport speed of the pressure roll, the pressure force and the roll temperature are in In individual cases the quality of the mate to be joined rialien adapt.

Particularly good results have been described with the above system when laminating a polyethylene film a polyamide film and when laminating a poly achieved ethylene film on paper. Immediately after leaving The nip has already become a relatively good haven tion of the two composite layers to each other. After a few days of storage, liability was still there once significantly improved.

Claims (15)

1. A method for producing a composite film from a plastic film ( 14 ) and another Bahnmate rial ( 16 ), characterized in that the plastic film ( 14 ) is pretreated by means of corona discharge on at least one side and then without using an adhesive by applying pressure and heat to the other web material ( 16 ), the temperature of the film always remaining below the melting temperature. 2. The method according to claim 1, characterized in that that the web material made of paper, fleece, metal, tissue be or also made of plastic. 3. The method according to claim 2, characterized in that that the web material on at least one side is pretreated by means of corona discharge. 4. The method according to any one of the preceding claims, characterized in that the corona discharge in takes the form of short individual pulses.   5. The method according to claim 4, characterized in that the discharge pulses have a frequency of 10 to 30 kHz, preferably 16 to 20 kHz. 6. The method according to claim 4 or 5, characterized records that the discharge pulses have a pulse width less than 30 µs, preferably about 10 to 20 µs to have. 7. The method according to any one of claims 4 to 6, characterized characterized in that the discharge pulses an on rise time of less than 5 µs, preferably less than 3.5 µs. 8. The method according to any one of the preceding claims, characterized in that the corona discharge between two rod-shaped electrodes ( 20 , 22 ) it follows, which have essentially the same structure and cross section and each have an electrically conductive core and a sheath ( 24th ) of dielectric material, preferably ceramic. 9. The method according to any one of the preceding claims, characterized in that the corona discharge takes place between two floating electrodes ( 20 , 22 ) which form a high-frequency resonant circuit with the secondary side of a corona generator ( 26 ). 10. The method according to any one of the preceding claims, characterized in that the connection of the plastic film ( 14 ) with the further web material ( 16 ) to the composite film ( 30 ) takes place continuously in a roll gap between two pressure rollers ( 10 , 12 ) and that the plastic film ( 14 ) and optionally also the further web material ( 16 ) passes through a corona discharge path ( 18 ; 28 ) arranged directly upstream of the roll gap. 11. The method according to claim 11, characterized in that the pressure force of the pressure rollers ( 10 , 12 ) is 50 to 1000 kN / m, preferably 300 to 400 kN / m. 12. The method according to claim 11 or 12, characterized in that the plastic film ( 14 ) in the nip has a temperature of 50 to 150 ° C, preferably about 100 ° C. 13. System for carrying out the method according to one of claims 1 to 12, characterized in that it comprises at least one corona discharge path ( 18 ) with a pair of rod-shaped electrodes ( 20 , 22 ) extending parallel to one another and extending transversely to the web-shaped plastic film, between which the web-shaped plastic film ( 14 ) can be passed through and to which a pair of rollers ( 10 , 12 ) is connected, in the roll gap of which the Kunststoffo lie ( 14 ) can be doubled with another web material ( 16 ). 14. Plant according to claim 13, characterized in that a further corona discharge path ( 28 ) is provided for the further web material ( 16 ). 15. Plant according to claim 13 or 14, characterized in that the corona discharge paths ( 18 , 28 ) are arranged close to the pair of rollers ( 10 , 12 ).