GB1558529A - Transparent polyamide films - Google Patents

Abstract

Transparent films based on polyhexamethyleneisophthalamide having a thickness of from 10 mu m to 1000 mu m are generally used as a covering material, for packaging foodstuffs and chemicals. Thermoformed films are employed, for example, for the production of packaging cans.

Description

(54) TRANSPARENT POLYAMIDE FILMS (71) We BAYER AKTIENGESELLSCHAFT, a body corporate organised under the laws of the Federal Republic of Germany of 509 Leverkusen, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to transparent films of polyhexamethylene isophthalamide with a thickness of from 10u to 1000cm.

Films of 6- and 6,6-polyamide are distinguished by a number of excellent properties, such as high toughness and abrasion resistance, low permeability to gases, good printing and metallising properties, and their high melting point and their high resistance to non-polar organic solvents. By virtue of these properties, polyamide films are used as a packaging material.

One disadvantage of these films is their high permeability to water vapour and the high melting point of the polyamides. Their high permeability to water vapour prevents them from being used as a long-term packaging material for foodstuffs. Because of the high melting temperature of the polyamides and their low melt viscosity the films have poor deep-drawing and heat-sealing properties.

Another disadvantage of the polyamide monofilms in particular but also of the composite films, is their pronounced tendency towards blocking which complicates processing of the films to a considerable extent.

Attempts have been made to overcome these disadvantages by using composite films of polyamides and polyolefins, such as polyethylene. Thus, polyethylene acts as a barrier to water vapour and provides the composite films with good heat-sealing properties. Unfortunately, the composite films can only be produced with considerable effort and at considerable expense.

It has now surprisingly been found that polyamide films of polyhexamethylene isophthal amide do not have the disadvantages of the 6 and 6,6-polyamide films and have a reduced water vapour permeability similar to that of the composite films.

Accordingly, the present invention provides transparent films of polyhexamethylene isophthalamide with a thickness of from 10 to 10001.1, preferably of from 20 to 500cm with excellent physical properties.

In contrast to films of 6- or 6,6-polyamide, the films remain transparent, even in increasing layer thicknesses. The permeability of the films to water vapour is considerably lower than that of conventional polyamide films. They are further distinguished by good deep drawing properties and improved heat sealing properties.

They do not show any tendency towards blocking; in other words, they do not show reduced sliding properties during processing.

The polyhexamethylene isophthalamides used for producing the films according to the invention can be obtained by conventional condensation processes for polyamides. Poly amides with a relative viscosity of at least about 2.3, preferably from 2.5 to 3.5, as measured on a 1% solution of the polyamide in m-cresol at 250C, are preferably used for the production of the films.

The films may contain the auxiliary agents known in polyamide chemistry such as pigments, colours or lubricants.

The films are produced in known manner by extruding the polyamide through flat sheeting dies on conventional machines at temperatures in the range of from 250 to 3200C and prefer ably at temperatures in the range of from 270 to 3000C, or by tubular film blowing, as de scribed for example in Vieweg/Muller, Kunststoff Handbuch, Vol. VI, polyamide, pages 326 et seq (Munich 1966).

The films according to the invention are used as a covering material and for the packaging of foodstuffs and chemicals. Deep-drawn films are used, for example, for the production of - packaging containers.

The invention is illustrated by the following examples.

EXAMPLE I A polyamide of isophthalic acid and hexamethylene diamine with a relative viscosity lirel of 2.63, as measured on a 1% solution in mcresol at 250C in an Ubbelohde viscosimeter, was extruded at 2900C through a film die having a breadth of 300mm on a Reifenhauser extruder S 30 (length of the screw = 20 x diameter of the screw). The film was run off over cooling rolls at a temperature of 950C. The films were 50,u thick. They were transparent and could readily be welded on standard film welders. The films did not show any tendency towards blocking.

Their permeability to water vapour, as measured in accordance with DIN 53122 at 85% relative humidity and at an average measuring tempera ture of 23cm, amounted to 7.6 g.m i .

By comparison, the permeability to water vapour of known polyamide films amounts to: 35 g,m-2.d-l in the case of 6-polyamide (40,u) 17 gXm~2.d-l in the case of 6,6-polyamide (40,u).

EXAMPLE 2 A 450,u thick film was produced under the extrusion conditions described in Example 1.

The film was transparent After preheating for 90 seconds, it could readily be deep-drawn to form fault-free parallelepipedic or semispherical containers approximately 6cm deep.

WHAT WE CLAIM IS: 1. A transparent film of polyhexamethylene isophthalamide having a thickness of from 10 to 1000,u.

2. A film as claimed in claim 1, substantially as herein described with reference to Example 1 or2.

3. A method of making a film as claimed in claim 1, which comprises extruding or blowing the film from polyhexamethylene isophthalamide.

4. A method as claimed in claim 3, wherein the film is extruded at a temperature in the range of from 250 to 320 C.

5. A method as claimed in claim 3, substantially as herein described with reference to Example 1 or 2.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. The invention is illustrated by the following examples. EXAMPLE I A polyamide of isophthalic acid and hexamethylene diamine with a relative viscosity lirel of 2.63, as measured on a 1% solution in mcresol at 250C in an Ubbelohde viscosimeter, was extruded at 2900C through a film die having a breadth of 300mm on a Reifenhauser extruder S 30 (length of the screw = 20 x diameter of the screw). The film was run off over cooling rolls at a temperature of 950C. The films were 50,u thick. They were transparent and could readily be welded on standard film welders. The films did not show any tendency towards blocking. Their permeability to water vapour, as measured in accordance with DIN 53122 at 85% relative humidity and at an average measuring tempera ture of 23cm, amounted to 7.6 g.m i . By comparison, the permeability to water vapour of known polyamide films amounts to: 35 g,m-2.d-l in the case of 6-polyamide (40,u) 17 gXm~2.d-l in the case of 6,6-polyamide (40,u). EXAMPLE 2 A 450,u thick film was produced under the extrusion conditions described in Example 1. The film was transparent After preheating for 90 seconds, it could readily be deep-drawn to form fault-free parallelepipedic or semispherical containers approximately 6cm deep. WHAT WE CLAIM IS:

1. A transparent film of polyhexamethylene isophthalamide having a thickness of from 10 to 1000,u.

2. A film as claimed in claim 1, substantially as herein described with reference to Example 1 or2.

3. A method of making a film as claimed in claim 1, which comprises extruding or blowing the film from polyhexamethylene isophthalamide.

4. A method as claimed in claim 3, wherein the film is extruded at a temperature in the range of from 250 to 320 C.

5. A method as claimed in claim 3, substantially as herein described with reference to Example 1 or 2.