DE2057255A1 - Process for the production of tubular films from thermoplastics with a defined volume shrinkage using the blow molding process - Google Patents

Description

CHEMISCHE IiERKE HÜLS AG 4370 Mari, the 20. November 197O - Patent Department - 2066 / G

Our reference: 0.Z.2517

Process for the production of tubular films made of thermoplastic plastics with a defined volume sump with the aid of the blow molding process

The invention is a process for the production of Tubular films made of thermoplastics with a defined volume shrinkage at the further processing temperature Help of the blow molding process.

Tubular films are used, among other things, for packaging purposes, in which the packaged goods are to be enclosed without wrinkles. In many cases the content of the slide will shrink however, after a heat treatment, for example by boiling or sterilizing the filled packaging, so that subsequently the film encloses the contents in folds. The packaging must then be re-tied. In particular, kick these disadvantages, for example when using tubular films made of thermoplastics, in particular Polyamides, as sausage casings, because of the dwindling sausage filling during cooking and because of the shrink-free behavior of the tubular film used as artificial casing, this lies after the Cooking the sausage is not wrinkle-free.

The object of the invention is to avoid these disadvantages and to produce a tubular film, which has a defined

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Has lumen shrinkage while maintaining the caliber. In the following, volume shrinkage is not understood to mean the shrinkage of the volume of the film itself, but rather the change in the volume enclosed by the film, this volume shrinkage being intended to occur in the desired manner at the application ^{temperature, for example at about 100 °} C. during thermal sterilization. A wrinkle-free package with the film according to the invention is also obtained if one of the corresponding short-term higher temperature exposing the packaging film ¹ with the already cooled conserved filling material and thereby subjecting the film to a second shrinking process.

In the case of a monoaxially stretched film, longitudinal shrinkage is achieved, but no volume shrinkage, since it occurs at the same time the circumference of the tubular film increases according to the longitudinal shrinkage, with the result that the tubular film after its shrinking, the filling material encloses in folds.

In the case of biaxial stretching, the circumference of the tubular film is enlarged in any case, so that the shrinkage triggers the Heat treatment shrinks the film in both directions. A constant caliber is therefore according to this method not guaranteed.

It has now been found that tubular films made of thermoplastic Plastics with a defined volume shrinkage can be produced while maintaining the caliber if the film tube stretched lengthwise at temperatures well below the melting range of the thermoplastic material is, while at the same time the caliber of the film tube is kept constant within the stretching section. You can do that for Achieve example in that the caliber is specified with gaseous or liquid or solid packing, with

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at the same time the set caliber is constant via regulating elements is held. A device for carrying out the method according to the invention is described.

Suitable thermoplastic materials for the production of tubular films with a defined volume shrinkage are polyolefins such as polyethylene, which may have been prepared by the so-called low-pressure polymerization, polypropylene, poly-et- butylene or copolymers of these polyolefins, such as ethylene TDC butylene - or ethylene-propylene copolymers or copolymers in which comonomers with more than four carbon atoms are contained in the chain · Linear polyesters, for example polyethylene terephthalate or a polyester based on terephthalic acid and 1,4-bis ~ are also suitable (hydroxymethyl) ~ cyclohexane or mixed condensates from the monomers mentioned, but in particular polyamides such as polycaprolactam, especially polyaminoundecanoic acids or polylaurolactam, or polyamides made from diamines and dicarboxylic acids, such as polyamide 6,6, polyamide 6,10 or polyamide 6 , 12 and polyamides based on aromatic, cycloaliphatic or branched aliphatic diamines or dicarboxylic acids. Copolyamides made from several polyamide-forming components, for example from caprolactam and laurolactam in a weight ratio of 20 to 80, can also be used.

The method according to the invention works substantially below the melting range of thermoplastics. In particular, the process is carried below the softening point, for example when low pressure polyethylene between 70 and 100 ⁰ C, for polypropylene between 70 and 110 ⁰ C, at polylaurolactam between 70 and 120 ⁰ C. For example, the melting range of iJiederdruckpolyäthylen 124-132 ⁰ C, that of polypropylene between 158 and 164 ⁰ C and that of

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Polylaurinlactam 175-180 ⁰ C. In any case, the orientation is however carried out at a temperature that is close to the temperature of the proposed heat treatment for the shrinking process. In special cases, the stretching can therefore also take place below the specified temperature limits.

The stretching takes place solely in the monoaxial direction, i.e. in the take-off direction, with the stretching path in a corresponding manner heated channel or tunnel. The film tube is carried with a gas, in particular air, within the stretching section a liquid, especially water, filled or drawn over a solid inner mandrel. It is essential that the packing keeps the specified caliber constant within the stretching section. Care will therefore be taken that For example, a pressure drop due to escaping gas or escaping liquid or a pressure increase when the temperature rises is avoided.

To keep the internal pressure constant, a variable stretching section can advantageously be used. The variable The stretching distance can be achieved, for example, by godet stands that can be moved on one or both sides in the direction of travel of the film, whose movement sequence is linked to the desired final caliber via a controlled system. In the following a Device described as shown in Figure 1.

A film tube is placed over a conventional blown film line (1) (2) extruded, which after laying flat (3) and passing some deflection rollers (4) and a dancer roller (5) either after the pair of draw-off rollers (6) in a known manner the roll (7) is wound up or inserted directly into the stretching stand (8). In the first case, the stretching takes place from the

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Roll (7) off, i.e. in a two-stage process, in the second In this case, the operation is continuous.

The rolled up with a given lying width or immediately To carry out the stretching process, extruded film is fed to the godets (9) of the stretching stand (8) and passed through then a stretching tunnel (10) heated with circulating air and finally, after passing through the gallettes (11), it becomes the stretching stand (12) wound up again at the roll (13). Through the different speeds of the gallette groups (9) and (11), the hose is stretched in the longitudinal direction by an amount that is determined by the stretching ratio. To prevent the hose from constricting in the transverse direction, becomes the same at the same time with a support medium, for example air, a liquid or a thorn on the Original caliber kept. The air or liquid is injected into area A using an injection needle. To the The stretching stand is used to take account of air expansion during heating and the loss of air through the roller gap of the gallettes (12) movable, for example arranged on rails and via the motor (14) for example via a spindle (15) moved from C to B or C to D. One the lying width mechanically or optically scanning device controls it the sequence of movements. To ensure that the hose is guided and laid flat, the guide plates (1.6) intended.

The stretching ratio can usually be achieved by different speeds of the take-off rollers. It can be 1 · 3.1 to 1: 6, but is in particular between 1: 2 and 1: 4. The desired volume shrinkage is generally from 5 to 25 %, in particular from 8 to 15%.

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Tubular films are obtained by the process according to the invention their specified caliber in the shrinking process at the processing temperature is practically preserved.

In the following, the method is illustrated using the example of a polylaurolactam tubular film are described using the device shown in the accompanying drawing.

t example 1

Polylaurolactam having a melting range of 175 to 180 ^0C is formed by means of a film die into a film tube. The tubular film exiting the extruder with a diameter at the die of 50 mm and a finally desired diameter of 100 mm is laid flat in a known manner. The lay-flat tubular film to be used as a sausage casing is fed between the conveyor rollers (9) to the ⁰ to 100 C, heated to 80 channel (10) and the discharged-with-off rollers (11) thereof. The hose section is inflated with air between the conveyor rollers and the take-off rollers, for example via the injection point (A). The pressure within the film tube section is kept constant by the roller arrangement (12) being displaced from the point marked by the line (C) in the direction of the point marked by the line (B) when the pressure is reduced. When the pressure increases, a corresponding movement in the opposite direction takes place. The roller arrangement (12) is controlled accordingly with the aid of a caliber scanning, for example mechanically or optically. The stretching ratio is 1 s 2.5. The folded tubular film guided over the take-off arrangement (12) is then rolled up over the roll (13) in the usual manner. The tubular film has a volume shrinkage of 10 %. When used as a sausage casing ura-

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the film closes the sausage filling without wrinkles after cooking.

Example 2

According to the method described in Example 1 was treated polyethylene having a melting range of 128 ⁰ C at a temperature of 115-120 ⁰ C in the heating channel "The stretch ratio is 1; 4.0. The volume shrinkage of the tubular film is IO %. A sterilized and cooled massecuite was surrounded with the tubular film and then heated to 100 ⁰ C. The tubular film then encloses the packaging wrinkle-free.

ic-

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Claims (10)

- 8 - QZ 2517 2ο.11.1970 Pate n tansprüche j IJ Process for the production of tubular films from therrao- ^ -plastic plastics with a defined volume shrinks in the Further processing temperature with the help of the blowing process characterized by that the film tube at temperatures well below the melting range of the thermoplastic material Is stretched lengthwise, while at the same time keeping the caliber of the film tube constant within the stretching stretch will. 2. The method according to claim 1, characterized in that the tubular film is stretched at temperatures which are close to the temperature of the heat treatment envisaged for the shrinking process. 3. The method according to claim 1 and 2, characterized in that stretching ratios between 1: 1.1 and 1: 6, preferably between 1: 2 and 1: 4, are used. 4. The method according to claims 1 to 3, characterized in that the caliber of the film tube is adjusted with the aid of air and kept constant. 5. The method according to claim 4, characterized in that the caliber of the film tube is adjusted with the help of water and keeps it constant. 6. The method according to claims 4 and 5, dadu r-c'it ^ ' ⁴ ^ marked, önß 209822/0805 BATH 9 - OZ 2517 11/20/1970 the caliber of the film tube with the help of a mandrel adjusts and keeps constant .. 7. The method according to claims 1 to 6, characterized in that the thermoplastic plastic is linear polyethylene / polypropylene, Polybutene-1, a linear polyester based of terephthalic acid and 1,4-bis (hydroxymethyl) cyclohexane or polylaurolactam are used. ' 8. Device for performing the method according to the claims 1 to 7 consisting of the godet stand · (8) with the godets (9) and the godet stand (12) with the godets (11) and the heating channel (10) characterized in that the godet stand (12) from position (C) in direction (B) or (D) is arranged to be displaceable in a controlled manner and its movement over the caliber of the tubular film (2) with the aid of the Motor (14) and the spindle (15) is controlled. 9. Use of the tubular film obtained according to claims 1 to 8 for packaging food. 10. Use of the obtained according to claims 1 to 9 Tubular film as a sausage casing. BAD ORfGINAL 209822/0805 Blank page