GB1592642A

GB1592642A - Manufacture of biaxially oriented films by blowing polyolefin moulding compositions

Info

Publication number: GB1592642A
Application number: GB12478A
Authority: GB
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1977-01-05
Filing date: 1978-01-04
Publication date: 1981-07-08
Also published as: FR2376736A1; DE2700235B2; ES465762A1; DE2700235C3; AT370122B; FR2376736B1; DE2700235A1; BE862668A; IT1088744B; ATA6878A; NL7800105A

Description

(54) MANUFACTURE OF BIAXIALLY ORIENTED FILMS BY BLOWING POLYOLEFIN MOLDING COMPOSITIONS (71) We, BASF AKTIENGESELL SCHAFT, a German Joint Stock Company of 6700 Ludwigshafen, Federal Republic of 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 the use of a polyolefin molding composition for the manufacture of biaxially oriented films, which are from 10 to 500, especially from 10 to 80, and above all from 10 to 30, ,um thick, by blowing, using a blow-up ratio of up to 1:10 and especially of from 1:2 to 1:7.

In general, films of this type, including thin and very thin films (such as are used conventionally for, for example, wrapping or bag-making) can be manufactured in satisfactory quality by blowing, without any particular difficulty, if polyolefin molding compositions based on a Ziegler polyethylene, i.e. a polythylene manufactured using a titanium-containing catalyst, are used, whilst in the case of molding compositions based on a Phillips polyethylene, i.e. a polyethylene manufactured using a chromium-containing catalyst, increasing difficulties are encountered as the thickness of the film is decreased. These difficulties have hitherto made it impossible to manufacture sufficiently thin films of satisfactory quality (such as paper-like films) by blowing if molding compositions containing a Phillips polyethylene as the polyolefin are used.

On the other hand, it would be desirable to be able to use such polyethylenes for the purpose in question, since Ziegler polyethylenes in other respects present great problems. for example in respect of the requisite stabilization to deterioration by UV light or oxygen.

The present invention seeks to enable a Phillips polyethylene to be used for the manufacture of films, including thin and very thin films, of satisfactory quality, by blowing.

According to the present invention, there is provided a process for the manufacture of a biaxially oriented film which is from 10 to 500 ,am thick by blowing, using a blow-up ratio of up to 1:10, a molding composition com rising:- (1 100 parts by weight of a polyethylene which has been manufactured using a chromium-containing catalyst, has a density greater than 0.945 g/cm3, preferably from 0.950 to 0.960 g/cm3, has a melt index (measured in accordance with DIN 53,735 at 190"C/2.16 kg) of less than 1.0 g/10-min and has a solution viscosity (measured according to DIN 53,728/page 4) of from 1 to 5 cm3/g, and (2) from 0.05 to 1, preferably from 0.1 to 0.5, part by weight of a tris-(2,4dialkylphenyl) phosphite in which the alkyl groups are identical or different and each is of 1 to 9 carbon atoms.

A preferred film thickness is from 10 to 80 ,um, and a preferred blow-up ratio is from 1:2 to 1:7.

The following should be noted with respect to the materials used in the composition.

(1) The polyethylenes to be employed may be the conventional commercial materials, and do not require further comment. However, it may be noted that the following two observations have been made: (a) Polyethylenes which have a melt index (measured according to DIN 53,735 at 1900C/2.16 kg) of from 0.1 to 0.6 g/10 min and a solution viscosity (measured according to DIN 53,728/page 4) of from 1.8 to 2.6 cm3/g are particularly suitable. For example, such polyethylenes can be used preferentially for the manufacture of wrapping films.

(b) Polyethylenes which have a melt index (measured according to DIN 53,735 at 190"C/21.6 kg) of from 6 to 20 g/10 min and a solution viscosity (measured according to DIN 53,728/page 4) of from 2.7 to 4.0 cm3/g are also particularly suitable. For example, such polyethylenes can be used preferentially for the manufacture of films for bags, carrier bags, sacks, tapes for weaving and adhesive tapes, as well as for the manufacture of laminating films; the films possess a high tensile strength and high impact strength; they can also be used as shrink films.

(2) Suitable tris-(2,4-dialkylphenyl) phosphites are in particular those in which the alkyl groups are branched; preferred alkyl groups are branched groups of 3 to 5 carbon atoms. Tris-(2,4-di-tert.butylphenyl) phosphite is particularly suitable.

If desired, the compositions may contain one or more other additives, i.e. auxiliaries and adjuvants, which may be the convention additives added in the conventional amounts. Examples of such additives are processing assistants, such as metal stearates, e.g. calcium stearate zinc stearate or potassium stearate, in amounts of from 0.02 to 0.5 part by weight per 100 parts by weight of polyethylene; antioxidants, such as phenolic compounds, t.g. pentaerythrityl tetrakis - [3 - (3,5 - di tert. - butyl - 4 - hydroxyphenyl) propionate] or octadecyl 3 - (3,5 - di tert. - butyl - 4 - hydroxyphenyl) propionate, in amounts of from 0.01 to 0.2 part by weight per 100 parts by weight of polyethylene; anti-blocking agents, e.g.

silica, in amounts of from 0.05 to 0.5 part by weight per 100 parts by weight of polyethylene; and antistatic agents, pigments, fillers and nucleating agents.

The molding compositions may be prepared from their components in conventional mixing equipment, in a conventional manner; no special features are involved and more detailed discussion is therefore superfluous.

Similar remarks apply to the manufacture of the films from the molding compositions, since film blowing is a conventional industrial process extensively described in the literature, for example in the articles by G. Prall in "Modern Plastics", 47 (1970), No. 5, 90-92 or by S. Heimlich in "Industrieanzeiger", 94 (1972), No. 97, 2332-2336, or in the book "Extrudieren von Schlauchfolien", VDI-Verlag GmbH, 1973, especially pages 193-230.

EXAMPLE 1 The molding composition used comprises:- (1) 100 parts by weight of a polyethylene which is manufactured using a chromiumcontaining catalyst, has a density of 0.954 g/cm3, has a melt index (measured according to DIN 53,735 at 190"C/21.6 kg) of 9.1 g/10 min and has a solution viscosity (measured according to DIN 53728/page 4) of 3.4 c m'3/g, (2) 0.2 part by weight of tris - (2,4 - di tert. - butyl - phenyl) phosphite and (3) 0.15 part by weight of calcium stearate.A tube is extruded from this molding composition, and blown up in the ratio of 1:5, using conventional film-blowing equipment (diameter of the annular die: 100 mm; die gap: 0.8 mm) at a material temperature of about 250"C. The take-off speed is selected to give a 20 ssm thick biaxially oriented film, which is very suitable for the manufacture of bags and carrier bags.

EXAMPLE 2 The molding composition used comprises:- (1) 100 parts by weight of a polyethylene which is manufactured using a chromiumcontaining catalyst, has a density of 0.960 g/cm3, has a melt index (measured according to DIN 53,735 at 190"C/2.16 kg) of 0.25 g/10 min and has a solution viscosity (measured according to DIN 53,728/page 4) of 2.6 cm3/g and (2) 0.15 part by weight of tris - (2,4 - di tert.butylphenyl) phosphite.

A tube is extruded from this molding composition, and blown up in the ratio of 1:3.5, using conventional film-blowing equipment (diameter of the annular die: 100 mm; die gap: 0.8 mm) at a material temperature of about 230"C. The take-off speed is selected to give a 10 ,am thick biaxially oriented film, which is very suitable for wrapping purposes.

WHAT WE CLAIM IS: 1. A process for the manufacture of a biaxially oriented film which is from 10 to 500,um by blowing, using a blow-up ratio of up to 1:10, a molding composition comprising (1) 100 parts by weight of a polyethylene which has been manufactured using a chromium-containing catalyst, has a density greater than 0.945 g/cm3, has a melt index (measured in accordance with DIN 53,735 at 1900C/2.16 kg) of less than 1.0g/10 min, and has a solution viscosity (measured according to DIN 53,728/page 4) of from 1 to 5 cm3/g, and (2) from 0.05 to 1 part by weight of a tris (2,4 - dialkylphenyl) phosphite in which the alkyl groups are identical or different and each is of 1 to 9 carbon atoms.

2. A process as claimed in claim 1 wherein the polyethylene has a density of from 0.950 to 0.960 g/cm3, a melt index of from 0.1 to 0.6 g/10 min and a solution viscosity of from 1.8 to 2.6 cm3/g, measured as specified in

Claims

claim 1.

3. A process as claimed in claim 1 wherein the polyethylene has a density of from 0.950 to 0.960 g/cm3, a melt index of from 6 to 20 g/10 min (measured in accordance with DIN 53,735 at 1900C/21.6 kg) and a solution viscosity of from 2.7 to 4.0 (measured as specified in claim 1).

4. A process as claimed in any of claims 1 to 3 wherein the tris - (2,4 - dialkylphenyl) phosphite contains two branched alkyl radicals, each of 3 to 5 carbon atoms.

5. A process as claimed in claim 4 wherein tris - (2,4 - di - tert. - butylphenyl) phosphite is used.

6. A process as claimed in any of claims I to 5 wherein from 0.1 to 0.5 part by weight of tris - (2,4 - dialkylphenyl) phosphite per 100 parts by weight of polyethylene is used.

7. A process as claimed in any of claims 1 to 6 wherein the molding composition also contains, per 100 parts by weight of polyethylene, from 0.02 to 0.5 part by weight of a processing assistant, from 0.01 to 0.2 part by weight of an antioxidant, and/or from 0.05 to 0.5 part by weight of an antiblocking agent.

8. A process as claimed in any of claims 1 to 7 wherein the blow-up ratio is from 1:2 to 1:7 and the biaxially oriented film is from 10 to 80 ,am thick.

9. A process for the manufacture of a biaxially oriented film carried out substantially as described in either of the foregoing Examples.

10. Biaxially oriented film when manufactured by a process as claimed in any of claims 1 to 9.