CA1260646A

CA1260646A - Polyamide-based tubular packaging film

Info

Publication number: CA1260646A
Application number: CA000491042A
Authority: CA
Inventors: Hans Strutzel
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1984-10-05
Filing date: 1985-09-18
Publication date: 1989-09-26
Also published as: EP0176980B1; DE3436682A1; FI78378B; JPS6191252A; FI853839L; AU4827385A; US4659599A; ATE37771T1; BR8504895A; ZA857187B; EP0176980A3; FI78378C; FI853839A0; AU574031B2; EP0176980A2; DE3565448D1

Abstract

ABSTRACT OF THE DISCLOSURE

A tubular packaging film, in particular a sausage casing for scalded and cooked sausages. The polymer mix-ture of said film has, on a 100 parts polymer basis, from 30 to 90 parts by weight homopolyamide or copoly-amide, and from 70 to 10 parts polyterephthalic acid ester and/or copolyester of terephthalic and isophthalic acid units. The polyester is formed with an aliphatic or alicyclic diol. The film also optionally contains addi-tives such as silicone oils which improve slip properties.

Description

` ~

1~60646 POLYAMIDE-BASED TUBULAR PACKAGING FILM

BACKGROUND OF THE INVENTION

The present invention relates to a tubular packa-ging film, useful in particular as a sausage casing for scalded and cooked sausages, which is constructed of po-lyamide, and which has improved physical properties com-pared with known polyamide tubings. While the film canadvantageously be used for packaging purposes, it is especially suitable for use as a crease-free and defor-mation-resistant sausage casing for scalded and cooked sausages.
A great number of tubular films comprising synthetic plastic materials, for example, polyester or polyamide, are known in the art. But in sausage casings, above all, stringent requirements must met with regard particularly to their suitability from a physiological point of view, their strength, and dimensional stability.
Tubular films made of a variety of synthetic mate-rials have the drawback of reduction in strength if wa-ter is absorbed. In many cases, the packaged material contains water and gives off moisture to the adjoining packaging film, Reduction of film strength is particu-larly apparent in the course of scalding or cooking of ~; tubular casings filled with sausage meat, when the film material comes into contact with hot water or steam. The ::
strength of the film material thereby decreases sharply due to the absorption of water.

"'' ~

~L2~064~

Sausages can be treated with hot steam by being suspended by a string loop in a cooking cabinet. During this process, the lower portion of the sausage casing is heavily loaded by the weight of the filled-in sausage ~eat. If the casing material has insufficient dimen-sional stability, it then expands, such that the origi-nally cylindrical sausage turns into a deformed pear-shaped product.
To compensate for this unwelcome effect, the thick-ness of the packaging film has hitherto been increased correspondingly or, alternatively, attempts have been made to enhance the film strength by expensive process steps during tubing manufacture.
The strength of the casing material, however, which is reduced at the cooking or scalding temperature, can only be improved by these measures to a limited extent, and thus the deformation resistance of the casing mate-rial at this temperature is therefore only slightly in-creased. An excessive thickness of the casing material also involves the risk that the packaging casing becomes too rigid and inelastic. The casing can then only insuf-ficiently expand when the filling is pressed in, and after the cooking or scalding process, it does not fully conform to the shrunken contents in the cooled state, so that the product obtained is wrinkled and unattractive.

SUMMARY OR THE INVENTION

It is accordingly an object of the present inven-tion to provide a tubular packaging film, useful, for

- 2 -.

~60646 example, as a sausage casing for scalded and cooked sau-sages, which is capable of satisfying the high require-ments relating to dimensional stability upon treatment with hot water or steam.
It is another object of the invention to provide a tubular packaging film, as above, which provides for a crease-~ree appearance after high-temperature treatment and subsequent cooling of the film and of the product contained in the film.
These objects are achieved by a polymer mixture useful as a tubular packaging film, which comprises, on 100 parts polymer basis, from about 30 parts to about parts of a polyamide selected from the group consis-~ ting of homopolyamides, copolyamides, and mixtures there-: 15 of, and from about 70 parts to about ~ parts of a poly-ester having repeating units selected from the group consisting of terephthalic acid and a mixture of tereph-thalic and isophthalic acids.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

: The tubular packaging film of the invention is formed of a single layer and substantially comprises a polymer mixture having two principal components, viz., polyamide and polyester constituents.
The polyamide comprises a saturated, linear alipha-tic polyamide customary in the production of tubular packaging films, which has the general formula ~NH-CO-Rl -CO-NH-R2~, in which R1 and R2 are the same or different and are selected from -(CH2)n- wherein n is 2 60~a~6 to 7, for example, polyhexamethylene adipic acid amide (Rl = (CH2)4, R = (CH2)6). Alternatively, the polyamide can have the general formula ~NH-R -CO~, wherein R is -(CH2)n- and n is an integer from 2 to 7, for example, polycaprolactam (R = (CH2)5). The polyamide can also comprise random copolyamides prepared from units of the above polymers and using adipic acid, azelaic acid, sebacic acid as well as terephthalic acid and diamines, such as hexamethylene dia-mine or trimethyl hexamethylene diamine. A preferred copolyamide is prepared from caprolactam, hexamethylene diamine and adipic acid.
The polyamide constituent can also be present in the form of a mix-ture of various polyamides. Of the above-mentioned polyamides, polycaprolactam (polyamide 6) is particularly praferred. For the purposes of blow extrusion, polyamides having a relative viscosity in the range from about 2.5 to 4.5, particularly from 2.8 to 4.2, measured in sulfuric acid (96% strength / 20C) are used.
The polyester which is present in the polymer mixture of the casing material is a condensation product of diols with tereph-thalic acid and optionally additionally isophthalic acid. The amount of the isophthalic acid can be up to 20 mol% of the polyester.
The diols particularly comprise aliphatic compounds corresponding to the formula HO-(CH2)n-OH (n = 2 to 6), such as ethylene glycol, 1,4-butylene glycol, 1,3-propylene glycol or hexamethylene glycol, and alicyclic compounds such as 1,4-cyclohexane dimethanol. Polybutylene terephthalate is particularly preferably used in the polymer mix-ture, the polymer having a mean melt viscosity customary for film extrusion.

~. ~

1~6~646 The polyterephthalate or polyisophthalate added can be modified to a small extent with aliphatic dicarboxy-lic acids.
Although it is possible to have a proportion of polyester from 70 to 10% by weight in the polymer mix-ture, it has nevertheless been found that, in this range, a deterioration of film properties occurs at va-lues less than 50% and greater than 25% by weight for the polyester proportion. In particular, film in this range of compositions, when extruded into tubing, tends to split before and during the stretching operation.
This disadvantageous effect is not encountered at the remaining values of the concentration range. Thus, poly-ester proportions between 70% and 50% by weight, and between 25% and 10% by weight are advantageous. In addi-tion, polyester proportions between 65% and 50% by weight and between 25% and 10% by weight in the polymer mixture are particularly advantageous.
At the very low proportions of polyester, between 25% and 10% by weight, particularly crease-free sausage casings are obtained which show good slip properties without the addition of an anti-blocking agent.
The polymer mixture can contain further additives, for example, dyes, pigments, and processing auxiliaries, which ensure a trouble-free production process.
Silicone oils, in particular polydialkyl siloxanes (Cl-C4), have proved to be particularly advantageous ad-ditives, which are used in a quantity from 0.05% to 1.2%
by weight, particularly from 0~1% to 0.6% by weight, based on the polymer mixture. Polydimethyl siloxane ....

~26~)6~6 having a viscosity from 10 to 100,000 mm2/s, particular-ly from 500 to 30,000 mm2/s (23C) is a suitable poly-dialkyl siloxane. This additive has the unexpected effect of improving the slip properties of the film during the production thereof, without causing a disad-vantageous acceleration of crystallization of the poly-mers be~ore the stretching process.
The packaging film has a wall thickness ranging between 10 and 50 /um. It is preferably used in a bi-axially oriented form. In the production of the film, the process steps known from the manufacture of poly-amide films are used.
In a first step, the individual components are mixed. It is, however, also possible to carry out the mixing operation in the extrusion apparatus. The tubu-lar pre-film which is extruded according to the film blowing process, is simultaneously biaxially stretched by inflating and drawing off. To obtain a thermally stable film, the film is heat-set in the usual manner after stretching. The film obtained has a thickness from 10 to 50 /um, particularly from 25 to 45 /um.
For packaging pasty foodstuffs, the tubular film is used in the form of sections, in a shirred form or in a curved form, as a so-called "ring". Shirring is effected ; 25 by means of the customary shirring devices. In the course of pressing in the pasty fillings, the shirred tubing is deshirred. During the following preservation of the filling under the action of hot water, the uniform cross section of the packaging casing is maintained and after cooling, tightly filled, crease-free packages are obtai-1~6(3 64~

ned. The packaging casing thus shows an excellent resis-tance to deforma~ion under the action of hot water and also an elastic recovery which is sufficient for the casing to fit closely to the cooled filling. Unexpected-ly, these properties are even present at relatively large tubing diameters from 90 to 120 mm, such that the packa-ging casing is also suitable for use as a sausage casing for particularly big and heavy sausages.
The invention is explained in detail with reference to the following example.

Example A granular mixture composed of 78 parts by weight of polyamide 6 and 22 parts by weight of polybutylene terephthalate was plastified together with 0.3 part by weight of polydimethylsiloxane (viscosity 1,000 mm2/s 23C), in an extruder at a temperature of about 240~C
and was then extruded through an annular die to form a tubing having a diameter of 30 mm. The tubing, which was kept amorphous by chilling with a cooling mandrel, was immediately afterwards heated to the stretching tempera-ture by means of infrared lamps. With the aid of a gas filling in the interior of the tubing, the tubing was stretched in both directions, thereby reducing its thick-ness and increasing its surface area and was heat set in this state. After laying flat, the tubing, having a flat width of 145 mm and a thickness of 36 /mm, was wound up.
In order to test the resistance to deformation, a strip having a width of 1 cm was cut from the tubing in -~26064~

the transverse direction and was extended at 20C and also in water at 80C, under a load of Kl. The load K
was calculated as follows:

Kl = E~ = 18N

wherein:
p = internal pressure = 0.04 N/mm2 r = half of diameter = 45 mm d = thickness = 0.036 mm A = cross section = 0.36 mm2 The following applies to the change of circumference, if lo = length of the test strip prior to extension 1l = length after loading with Kl at 20 C
12 = length after loading with Kl at 80 ~C

0.8 < 1l ~ < 1.2 When the test s~rip was unloaded after the two extension procedures, the new length 13 had values from 0.95.1l to 0.98.ll.-: 25 ____________

Claims

IN THE CLAIMS

What is claimed is:

1. A tubular packaging film suitable for use as a sausage casing, wherein said tubular film comprises a polymer mixture consisting on a 100 parts polymer basis of from about 30 parts to about 95 parts of a poly-amide selected from the group consisting of homopoly-amides, copolyamides, and mixtures thereof; and from about 70 parts to about 5 parts of a poly-ester having repeating units selected from the group consisting of terephthalic acid and a mixture of tereph-thalic and isophthalic acids.

2. A packaging film as claimed in claim 1, wherein the amount of isophthalic repeating units in said mixture of terephthalic and isophthalic acids is up to 20 mol%.

3. A packaging film as claimed in claim 1, wherein said polyester is produced from a diol of the formula HO-R-OH, wherein R is selected from the group consisting of (CH2)n and and wherein n is from 2 to 6.

4. A packaging film as claimed in claim 3, wherein R is (CH2)4.

5. A packaging film as claimed in claim 1, wherein said polyamide comprises units selected from the group consisting of (A) ?NH-CO-(CH2)x-CO-NH-(CH2)y? and (B) ?NH-CO-(CH2)z?
wherein x, y and z are integers from 2 to 7.

6. A packaging film as claimed in claim 5, wherein said polyamide contains units of ?NH-CO-(CH2)5?.

7. A packaging film as claimed in claim 1, wherein said mixture further contains from about 0.05 to about 1.2 parts per 100 parts polymer of a polysiloxane.

8. A packaging film as claimed in claim 7, wherein said polysiloxane is present in an amount of from about 0.1 to about 0.6 parts per 100 parts polymer.

9. A packaging film as claimed in claim 7, wherein said polysiloxane is polydimethyl siloxane having a vis-cosity of from about 10 to about 100,000 mm2/s (23°C).

10. A packaging film as claimed in claim 9, wherein the viscosity of said dimethyl siloxane is from about 500 to about 30,000 mm2/s (23°C).

11. A packaging film as claimed in claim 1, wherein the amount of said polyamide is from about 95 to about 75 parts and the amount of said polyester is from about 5 to about 25 parts.

12. A packaging film as claimed in claim 1, wherein the amount of said polyamide is from about 90 to about 75 parts and the amount of said polyester is from about 10 to about 25 parts.

13. A packaging film as claimed in claim 1, wherein the amount of said polyamide is from about 50 to about 30 parts, and the amount of said polyester is from about 50 to about 70 parts.

14. A packaging film as claimed in claim 1, wherein the amount of said polyamide is from about 35 parts to about 50 parts, and the amount of said polyester is from about 65 parts to about 50 parts.

15. A packaging film as claimed in claim 1, wherein said casing increases in circumference when filled with material at 20°C and thereafter further increases in cir-cumference when treated with water at 80°C, such that the ratio of circumference increase due to said filling to the increase due to said water treatment is from about 0.8 to about 1.2.

16. A packaging film as claimed in claim 1, wherein said film is shirred.