DE1238651B - Process for sealing biaxially oriented films made of polyolefins - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

Int. Cl .:

B 29 c

GERMAN # 1 # PATENT OFFICE

EXPLORATION PAPER German class: 39 a2 -19/00

Number: 1 238 651

File number: K 53193 X / 39 a2

1 238 651 filing date: June 11, 1964

Opened on: April 13, 1967

Films made of isotactic polypropylene or of propylene copolymers, which in one or more Oriented directions gain due to their good mechanical and optical properties increasingly important for the packaging industry. Here, however, is a prerequisite that this Films can be welded or sealed together under the action of heat and pressure. While it is easily possible to weld polypropylene films that have not been oriented, causes the heat to act at the welding point in the case of stretched (oriented) films severe shrinkage, so that no usable bag or wrap-around packaging is created.

To eliminate these deficiencies, it has already been proposed, in particular, the stretched polyolefin films Polypropylene foils to be coated with substances that soften at lower temperatures than the carrier film. These coated foils can then be sealed in a temperature range in which the carrier film does not yet show any appreciable shrinkage. In all known processes this Art, however, means the additional operation is economically disadvantageous. Plus it is in many In cases it is difficult to achieve good adhesion between the base film and the coating, so that often the application of an intermediate layer is also required.

Attempts have also been made to reduce the sealing temperature of stretched films by the films were subjected to a surface treatment by means of electrical discharges in an air atmosphere. However, only minor improvements were achieved under extreme conditions will.

Furthermore, a chlorination of flexible films under the influence of UV light is described, in which the film absorbs 0.1% chlorine and which is intended to improve printability and sealability, although a relatively long dwell time is necessary for the chlorination. ^{It is at least 1} second, even when using UV radiation. However, such methods are unsuitable for film production machines, for subsequent coating or for high-speed packaging machines.

It has now been found that biaxially stretched films made of polyolefins, in particular those made of isotactic polypropylene and propylene copolymers, can be sealed in a temperature range in which the stretched films made of the materials mentioned do not yet have any significant process for sealing biaxially
stretched films made from polyolefins

Applicant:

Kalle Aktiengesellschaft,
Wiesbaden-Biebrich, Rheingaustr. 190-196

Named as inventor:
Dr. Gerhard Buchheister,
Wiesbaden-Biebrich;
Dr. Markus Seibel, Mainz

Suffer from heat shrinkage if the film, possibly immediately after it has been stretched, in the presence of halogens or halogen-containing gas mixtures, preferably in the presence of Chlorine or gas mixtures containing chlorine, exposed to a corona discharge and the foils treated in this way within 10 days, but preferably immediately after the electrical treatment, Sealed in a manner known per se at 120 to 130 ° C.

The electrical discharge in a chlorine atmosphere only requires periods of about one- quarter of a second to achieve the desired effect. In this case, a chlorination corresponding to the chlorination in the presence of UV light does not take place, since the amount of chlorine absorbed is still below the detection limit by infrared analysis.
The treatment of the stretched polyolefin films by electrical discharges in the presence of halogen or halogen-containing gases can be carried out in apparatuses known per se for the corona treatment of films, these also having to be provided with gas supply devices.

A special apparatus in which the film is passed through a vacuum chamber or a chamber with reduced The pressure in which the corona discharge takes place is not required. Advantage-like this The gases used are introduced under slight excess pressure so that they cover the film surface displace surrounding air.

709 549/399

To carry out the process, the film to be welded is placed over a grounded metal roller out, which carries an insulation on its surface. Above the roller are parallel to the roller surface Arranged electrodes, the shape of which can be any, as long as an unimpeded access of the halogen or halogen-gas mixture to the discharge path is not hindered by the shape of the electrodes. For example, the electrodes can consist of a wire mesh or narrow metal strips. Copper wires with a diameter of about 1 mm have proven particularly useful. The distance between the electrodes of the foil surface depends on the type and power of the generator used and amounts to for example when using 5 to 8 kHz generators with an electrode voltage of around 8 kV and an output of 2 to 4 kVA, preferably 0.5 to 2 mm. The entire electrical system is in one Box made of non-conductive material housed, which is closed at the bottom by the insulated roller is, the lower edge of the box is expediently provided with a sealing material so that an escape of the halogen-gas mixture is largely prevented. Possibly for removal However, escaping halogen can be fitted with a hood with a suction fan over the entire system will.

ίο The comparison tests shown in the diagram below were carried out under sealing conditions that are usually set on packaging machines. The diagram shows that the sealing strength achieved with a film pretreated according to the invention is still higher than that of a film coated in the usual way, while without chlorine gas a slight sealability can only be observed under extreme conditions.

Seal strength (g / cm)

150

100

50

■ C - ^ 5— ( )
I. /
/
/ / -
/
O
C. [ ]

1 2

0 = electrical discharge with chlorine, □ = electrical discharge in air,

1 = film coated with polyvinylidene chloride.

Sealing time (seconds)

The drawing shows the exemplary embodiment of a device with the aid of which the pretreatment according to the invention of the stretched films can be carried out. It consists of a grounded metal roller 1, which is insulated with about ten layers of a polyethylene terephthalate film with a thickness of 125 μ! is wrapped. Above this roller is a box 5 made of non-conductive material, which has gas supply pipes 7 and the lower edge of which is adapted to the shape of the roller, with sealing strips 8, for example made of polytetrafluoroethylene, being attached between roller 1 and box 5. In the box 5 there are copper wires 6 , which run parallel to the roll surface, serve as electrodes and are conductively connected to a generator 4. The film 3 is now guided over the roller 1 and exposed to an electrical discharge when it passes between the electrodes 6 and the roller 1 , whereby the supply lines? Chlorine gas or bromine vapor alone or in a mixture with other gases can be introduced into the discharge space. The dwell time can be ¹ Ao to Vioo second.

The method according to the invention is distinguished from the usual coating by its simplicity and is recommended for technical implementation due to its economic efficiency. The following Application examples explain the method according to the invention.

example 1

A 20 μm thick, 1 m wide, biaxially stretched polypropylene film was passed at a speed of 40 m / min over the insulated roller under the electrode box. The electrode consisted of an approximately 2 cm wide brass mesh at a distance of 0.8 mm The required voltage was supplied by a 450 kHz generator, and chlorine gas was introduced into the electrode box at a rate of 800 l / hour.
The film was first wound up and then sealed on a sealing device which allows the sealing temperature, time and pressure to be set precisely. Sealing of the samples took place within 3 days after the treatment. The seal strength of the sealed samples was determined on 1 cm wide cut-out strips. At a sealing temperature of 125 ° C, a sealing pressure of 1.3 Kp / cm ² and a sealing time of 2 seconds, the force required to seal the

Claims (1)

tearing apart the th strip, determined to be 180g / cm. The sealed sample of an untreated film or a corona-treated film without a chlorine feed line showed no liability under the same sealing conditions. washing bottle filled with liquid bromine. The treated film samples attached to a laboratory sealing apparatus were sealed at about 130 ° C, had a tear strength of about 40 g / cm, while 5 comparison samples which were treated without bromine showed no sealability whatsoever. Example 2 Example 4 A 20 μ thick, biaxially oriented polypropylene, a 20 μ thick biaxially stretched film made of poly film was at a rate of 60 m / min io ethylene the density of 0.95 was performed under the in Example 3 through the discharge zone. Arrangement and conditions mentioned, treated as described in Example 1 in the chlorine feed. A 5 kHz -6 kV generator served as the electrode box with a quantity of 200 liters of chlorine gas per power source. The hour was initiated. The sealing values for the film were also treated in a second pass on the side second to 120 ° C. and a sealing pressure of 1.3 Kp / cm ² and then rolled up. 15 th were 200 to 260 g / cm. Exclusion wedge lent the cutting to the required width by means of electrical discharge treated film, the film was not sealable on a bag packaging machine,
used. Between the surface treatment and the use on the packaging machine lay claim to:
4 days. The sealing jaws were fluted and on a 20 Temperature set from 120 to 130 ° C. The ar- method for sealing biaxially ver operating speed was 20 bags per minute. stretched films made of polyolefins by exposure The bags, which are filled with 50 g and 100 g contents, use pressure and heat, thereby showed seal strengths at the seams indicating that such films are 130 to 220 g / cm. 25 applies that in a known manner only Beisoiei 3 by corona discharge in the presence of halo ^ genes or gases containing halogens A 25 μ thick, biaxially oriented polypropylene have been wherein the sealing within film was passed through at a speed of Γ0 m / min 10 days after the corona treatment led through the discharge space. The electrode 30 leads. consisted of three taut copper wires of about 30 cm long and 0.8 mm in diameter. Publications considered as electricity: source was a 10 kHz generator using an electrical system. British Patent Nos. 882 008, 921276; delivers a current of 70 mA. Belgian patent documents laid out in the electrodes Nitrogen was introduced into the box, which was replaced by a with 35 No. 635 729. 1 sheet of drawings