DE2609528A1 - POLYMER FILMS - Google Patents

Description

IEDTKE - BüHLING - KlNNE - UnUPE Dipi.-lng.Tiedtke

Dipl.-Chem. Bühling Dipl.-Ing. Chins Dipl.-Ing. Group

8000 Munich 2, P.O. Box 20 24 Bavariaring 4

2609528 Tel .: (0 89) 53 96 53 -

Telex: 5 24845 tipat cable. Germaniapatent Munich March 8, 1976 B 7195 / case Po / Q 27657

Imperial Chemical Industries Limited London, UK

Polymer films

The invention relates to films made from polymeric materials, in particular olefin polymers are produced.

According to the invention, a film is created which consists of a copolymer of ethylene and at least one mono- «ε-olefin comonomer provided that the film has an impact resistance function (as defined below) with a Has a value of at least 750.

The impact stiffness function is understood to mean the following relationship:

Impact strength (g) X / stiffness modulus (MNm ~ ² ) -loq [film thickness (u)

609838/0966

VIII / 14

Dresdner Bank (Munich) Account 3939 844 Postscheck (Munich) Account 670-43-804

Impact strength is measured according to British Standard 2,782, Method 306 F, 1970. The modulus of stiffness is the 1% secant module ■ according to ASTM method D 882-73 using 254.0 mm by 12.7 mm test specimens and a pulling speed of 25.4 mm per minute is measured. Four measurements were made in the machine direction and four in And the geometric mean of the averages is taken as the stiffness modulus.

The impact stiffness function is preferably at least 1000, in particular at least 1250 and can be one Have a value of a few 1000, for example 5000.

The films of the invention have been found to have a combination of toughness and stiffness. Thus, the films according to the invention with a thickness of 30 µ can have an impact strength of the order of 600 g. Films 150 microns thick can have impact strengths greater than 1460 grams. The stiffness modulus of the films is

-2

typically at least 200 MNm and can be as high as 400 MNm " ² .

In contrast, it can be noted that the impact stiffness function of films formed from free radical ethylene polymers or copolymers, typically im Range from 300 to 400.

In addition to an impact stiffness function of at least 750 /, many films according to the invention also have a tear strength, (measured according to British Standard 2782, Method 3O8B), which is at least 5 g / μ and as high as 35 g / μ of the film thickness in one direction in the film is, or can be. Preferably, the tear strength is at least 5 g _> / u _/, preferably at least 7 g ^ u in both the machine and cross directions.

Furthermore, many of the films have a tensile tear strength (measured according to ISO recommendation 1184, 1970 at a tension rate of 500 mm / min .) Of at least 20 MN / m, preferably

at least 30 MN / m. The tensile strength typically exceeds

wise 50 MN / m not.

In addition, the film has a relatively high elongation at break (measured according to ISO recommendation 1184, 1970 at a pull rate of 500 mm / min.) of at least 300% and it can be as high as Be 1100%.

All of the above properties (impact strength, stiffness modulus, Tear strength, tensile strength and percentage elongation) are measured at ambient temperature on a sample of the Films for sure.

€ 09830/0966

Particularly preferred films according to the invention combine all of the above characteristics.

Accordingly, there is provided a film made of a copolymer is at of ethylene with at least one mono- (^ - 01efin comonomer is formed / wherein the film has an impact resistance function of at least; 750, a tear resistance of at least 5 g and no more than 35 g per micron film thickness in at least one direction in the film, a tensile strength

0 2

of at least 20 MN / m and not more than 50 MN / m and one Has elongation of at least 300% and not more than 1100%.

Films according to the invention have a density in the range

from 915 to 935 kg / m, preferably up to 930 kg / m, especially

3
special up to 925 kg / m.

The melt flow index of the film (measured at 190 ⁰ C with a weight of 2.16 kg using the technique of ASTM method 1238-62 T) is typically from 0.05 to about 0/7, preferably from 0.1 up to 0.3.

In addition to having an impact stiffness function of at least 750, it is preferred that the films of the invention also have a "secondary function" (as defined below) of at least 1,800.

609833/0966

The "secondary function" is understood to mean the following relationship:

Impact strength (g) X modulus of stiffness (MNm " ² )

T film thickness (/ I) J ⁰ ' ⁵

The secondary function shows less change with the thickness of the film than the impact stiffness function.

The copolymers from which the films are formed are preferably copolymers of ethylene with a comonomer, which is at least one mono- / Ar olefin, at least 50 mol% of the mono- <X-01efin have 5 or more carbon atoms. Although in the preferred copolymer the comonomer is not more than 50 mol% of a mono - <^ - 01efins with less than Contains 5 carbon atoms, for example butene-1, it is preferred that the comonomer only mono-ul-olefins with at least Contains 5 carbon atoms. The comonomer expediently contains no more than 12 carbon atoms, preferably no more than 10 and especially not more than 8 carbon atoms. The comonomer is expediently a linear mono-cL-01efin, preferably Witches-1.

The copolymers from which the films are made typically contain the comonomer in an amount of 6.5

9833/0968

2603528

up to 30% by weight, preferably from 8.0 to 27% by weight of the copolymer. If the copolymer is a copolymer containing hexene-1, the amount is hexene-1 typically from 6.5 to 16.5% by weight, in particular from 8.0 to 15% by weight of the copolymer. If the comonomer Is pentene-1, is the amount of pentene-1 that is in the copolymer is present at 6.5 up to 20%, especially 7.2 up to 16.5% by weight; if the comonomer is 4-methylpentene-1, the amount of 4-methylpentene-1 present in the copolymer is 6.5 to 18.0%, preferably 7.2 to 16.5% by weight; and if the comonomer is decene-1, this is in the copolymer Amount of decene-1 present 7.5 up to 23%, preferably 9 up to 21.5% by weight.

A particularly suitable copolymer from which the films of Invention can be produced is a copolymer of Ethylene with a comonomer which is at least one mono- (X-01efin is, with at least 50 mol% of the mono - # - 01efins, whichjs the comonomer is has 5 or more carbon atoms, where ^ the copolymer has the following properties: a cured density (as defined below is in the range of

-j 3

918 up to 940 kg / m, preferably from 920 up to 935 kg / m, an apparent viscosity, (as defined below), measured at a temperature of 200 ° C and a shear rate

609838/0966

-1 3 3-2

from 100 seconds in the range of 0.5 χ 10 up to 3.0 χ 10 Nsm,

3 3-2

preferably 1.3 10 up to 2.4 χ 10 Nsm, and a viscosity, measured at a temperature of 200 ° C. and a force of 10 N / m, of at least 2Ae " ^x , preferably at least 3.5 Ae '' ^x and not more than 1000 Å, preferably not more than 500A, where A is the apparent viscosity at 200 ° C and a shear rate of 100 seconds " ¹ .

The expression used above "hardened density" refers to the density of which is as described in ASTM 1928/70, Method A _/, is measured using a Dichtegradientsäule, at 23 ° C and considering remaining Polymerisationskatalysatormengen _/ cured to the " Density ". The following relationship is used here:

/ V ^A P

whereby

0 is the "cured density";

P _{m is} the measured density of the total polymer product including catalyst residues;

_s the density of the catalyst support and / or the catalyst

€ 098387031) 6

sators is; and

A is the weight fraction of the catalyst support and / or the The catalyst in the polymer is as calculated from the amount of ash.

The "apparent viscosity" of the polymer is measured using a capillary viscometer and is through defines the following relationship:

8Ql

T) is the apparent viscosity in Nsm; r is the nozzle radius in mm;

P is the pressure gradient across the nozzle in Nm "²; Q is the volume flow rate in mm sec; 1 is the length of the nozzle in mm.

3 2

The viscosity at a force of 10 N / m becomes appropriate measured using the Konusurid plate technique.

6C3S33 / 0S66

The films according to the invention have a combination of properties which make them particularly useful for heavily used films ^ such as bags for Makes fertilizers, protective covers, carrier bags and liners suitable for waste bins.

The films of the invention can be produced by any film-making technique, for example, extrusion can be formed by a slot shape or by a layered film technique. One particularly suitable technique for making the films of the invention takes place by extruding a polymer through an annular die and expanding the extrudate.

In particular, a film is obtained by adding a copolymer of ethylene with at least one mono-i \ -olefin comonomer extruded through an annular nozzle maintained at a temperature in the range of 170 to 300 ° C, the Extrudate expands 1.2 to 10.0 fold circumferential expansion and elongation (as defined below) by the 2.5 up to 50 times.

"Stretch" shows the ratio / nozzle gap

Understand final film thickness.

609838/0966

The nozzle temperature is preferably in the range from 200 to 250 ° C., the circumferential expansion is expedient up to 5/0 times, in particular 1.3 up to 3.0 times, and the Stretching is preferably 5 to 30 times.

The film-making process will now be described with reference to the accompanying drawing which is a graphic Representation of a suitable system for the production of a layered film is.

In the drawing, an extrusion device 1 with an upwardly formed annular nozzle 2 is provided. An air line 3 goes through the nozzle 2. A cooling ring 4, which is equipped with a number of air inlets 5, is placed above the nozzle used, the cooling ring 4 and the nozzle 2 being separated by an insulating plate 6.

Some pairs of guide rollers 7 are arranged above the cooling ring and directly above the guide rollers 7 is a pair of holding rollers 8 arranged. A number of guide rollers IO are arranged between the holding rollers 8 and a winding roller 9.

When forming a film, an ethylene copolymer is through the extrusion device! and the nozzle 2, which at a suitable temperature of, for example, 210 ° C kept

is sent.

A tubular extrudate 11 is formed and this is in a linear direction as a result of the relative extrusion and winding speeds, and the extrudate is further circumferentially stretched by air flowing into the Extrudate flowing in through the air line 3, expanded. The extrudate is cooled by air from the cooling ring 4 and forms a bubble 12. The bubble 12 is leveled or pressed flat by the guide roller 7 by the nip rollers 8 peeled off and wound onto the take-up roller 9.

The position of the cooling ring 4 can be varied from the position shown, and the cooling ring 4 can in particular be separated be arranged by the nozzle 2. In this case, the circumferential expansion of the extrudate 11 to give the bubble 12, take place entirely or partially within the cooling ring 4.

In another variation, the guide rollers are defined by a pair of upwardly tapered bubble guide plates replaced. Other changes in the apparatus and the technology are possible in a manner known per se.

609838/0966

In order to be able to more easily understand the invention, various embodiments thereof are / are in the following examples which illustrate the invention.

Example 1 to 10

Four ethylene-hexene copolymers with different Properties and an ethylene-butene-1 copolymer were to a film using an upwardly extruding 'test device, a tubular film extrusion unit common air cooling devices for the bladder, among the following Conditions processed.

The extruder had a screw diameter of 38.1 mm with a length to diameter ratio of 18: 1 and was operated at a melt and nozzle temperature of 230 C. The nozzle was 76.2 mm in diameter and had an annular nozzle gap of 1 mm. The film was inflated to provide a 2.5: 1 circumferential expansion and films of 30, 90, 100 and 150 microns thick were made. The unit was operated at a rate of 10 kg / hour. operated. The properties of the polymers used are summarized in Table 1 and in Table 2 the properties of the films produced are summarized

609838/09156

listed with properties from filming similarly using a free radical polyethylene with a Melt flow index of 0.3 and a cured density of 924 kg / m 2 were formed.

609838/0968

- 14 Table 1

! Polymer ι density
j Reference symbol j (Kgm / rn ³ )

- j MFI

ι (a)

content (wt .-%)

(b)

Apparent viscosity at 100 see '

(Nsm-2)

(d)

-1

Viscosity elongation

at 10 ³ N / m ² ! (%) (Nsm-2)

(f)

Methyl groups

per 1C00 carbon atoms

(G)

Vinyl groups per 1000 carbon atoms

(H)

CD!

a> j

A.
B.
C.
D.
E.

| 924.1
J926.9

■ 929.9
1926.8

| 926.7

12.9 10.8

12.1 10.2

0.23 j 0.23 I 0.17! 0.16! 0.18

1.61 χ
1.39 χ 10 ³ 1.49 χ 10 ³ 1.63 χ 10 ³ 1.72 χ 10 ³

2.3 χ 1θ5

p ', 5 χ 10 ⁴

, 1.28 χ 10 ⁵
H, 38 Χ.10 ⁵

J5,4 χ 1ο ⁴

920 880 680 940 660

22.6 21.5 20.1 20.7 27.2

0.21 0.3o 0.27 0 _f 27 0.23

! Z

■ C

CD O (JD

Comments on Table 1

(a) The cured density is measured according to ASTM 1 928/70, Method A, at 23 ° C and it contains a correction for the Presence of catalyst residues.

(b) "Measured using infrared ^{techniques. Using a mathematical comparison of the absorption curve at 1310-1430 cm" 1} with two standard polyethylenes of known methyl number. A correction was then made for those methyl groups which are molecular ends by subtracting the methyl number of a linear ethylene homopolymer made using the same catalyst system and having essentially the same molecular weight distribution and MFI. In polymer E, the comonomer is butene-1.

(c) Measured at 190 ⁰ C with a weight of 2.16 kg using the technique of ASTM-1238-62T method.

(d) Measured at 200 ⁰ C using a Kajj-ll arviskosimeters with a nozzle length of 32 mm and 2 mm diameter and a Viskosimeterrohrdurchmesser of 22 mm 2 _/ using the following relationship:

8Q3838 / 096S

8Ql

(e) Measured at 200 ° C using a cone and Plate technique with a cone of 5 cm diameter with a cone angle of 4 on a Weissenberg rheogoniometer (Type R Γ8).

(f). Measured using the technique of ASTM method D2289 at a pull rate of 50.8 cm / sec. with a test sample according to British Standard 903 Part A2, but with an effective gauge length of 19.04 mm (instead of 25.4 mm) with the test sample being immersed in water cured at 100 ° C for one hour and then allowed the water and sample to cool to ambient temperature could.

(g) Determined / As stated under note (d); However no correction was made for the methyl groups, which are the ends of the molecule.

(h) The optical density per cm of a molded sample with an approximate thickness of 0.5 mm is determined at 910 cm ". The sample is brominated by immersion in liquid bromine at room temperature for 20 minutes and the sample is dried overnight optical density per cm of the sample is again determined at 910 cm, the difference

609838/0966

26Ü9528

between the two optical densities is a consequence of the unsaturated Bond and this difference χ 0/126 gives the vinyl groups pro 1000 carbon atoms.

609830/0966

Table 2

j ■ "

SUBSEQUENT

[Example poly- ^u meri-
sat,
Loading
sugs-
synibol Pilin '?
dik4
ke j
(μ) Ι Impact resistant
speed
(g) (i) 500 Edge • Tear
strength
^(j) (g / p) ) TD (k) tensile strenght TD (k) __— 2 "'' TD (k) ¹ Zerreii? -: lel -! -
nimgeii _; TD (k) Stiff·
health
(MN / m ^: I. Blow
stiff-
(P) Secondary
function
(G) pder ver
equal
at- A. 30; front G50 575 M) (k 21.5 Load capacity 11.5 fracture 36.2 VD (k) 730 3Ξ5 j ιεο * 3 » 3A COO ispiel A. 90 575 100 ΐ 5 « 1100 "12.6 M) (k) 11.6 VD (k) 36.2 "to 785 j 170 SiO 3-Ί OC-J j 1 A. 150 11 * 150 [69-0 1 * 60 5/2 11.8 • », 6 11.4 ^ fO _f 2
i 30.7
f 575 7CO 2 * 1 > 1570 > 2S 7C..1 i 2 B. 100 > 1 * S0 6JO ^ß . ⁵ 12.7 11.0 13.5 39.0 32.8 6fiO 890 2S9 1190 18, 2OJ ! 3 B. 150 630 1000 5.7 11.8 10.3 12.3 31.1 3 * _r 6 705 & 00 255 1020 S3 GCM i 4 C. «00 650 7.7 11.1 11.9 VuS '3 ^ 1 35.1 970 860 315 1500 27 (»0 i 5
ί D. 150 ί «50 270 7.3 19.1 V, 9 15.2 25.6
I. 835 825 326 ΓΟόΟ 22 7OJ 6th D. 30: X ₀₀ 1 * 00 3.2 12.8 12.8 13.3 37.0 39 _? 8th 390 S15 204 > 1597 > 31 400 7th E. 150 17 * 8.1 18.8 10.9 11.6 45.9 26.2 765 865 310 21 ^ 0 17,000 8th E. 30th 6O0 2.0 8.0 11.7 12.1 33.5 31.2 A10 675 £ 50 17 500 9
I. X * 150 5.6 S ⁶ 9.8 lOjA VS, 1 655 620 kos. 9,000 I ίο X * to 2 _r S 5.0 11.1 -W, 7 Ti Q 530 7ü0 9 6x> 3.7 10.6 .33.9 595 ß 10.2 P6 _; 6th

CD CD CTI NJ OO

26Ü9528

Comments on Table 2

This polymer is a commercially available free radical polyethylene polymer with a melt flow index of 0.3 and a cured density of 924 kg / m.

i) Impact strength was measured according to British Standard 2782, 1970, Method 306F.

j) Determined in accordance with British Standard 2782; 1970 Method 3O8B.

k) MD means machine direction. TD means cross direction.

1) The tensile measurements on the film were made on 10 mm wide samples and using the method described in ISO Recommendation 1184, 1970 m) is described / at a tension or pull rate of 500 mm performed per minute.

n) The stated film stiffness values are the 1% secant modules, measured according to ASTM method D882-73. Four test samples, 10.4 inches by 1.27 cm, are placed in both Querais - also used in machine direction. A pulling speed of one inch per minute is used. The listed Number is the geometric mean of the measured mean values in the cross and machine directions.

609838/0968

ρ) The relationship:

Front impact strength (g) χ / stiffness modulus (MNm " ² ) - lOcTJ film thickness (μ)

q) The relation: front impact (film thickness (u) j ° ' ⁵

Front impact strength (g) X stiffness modulus (MNm)

Example 11

The polymer A became a film having a thickness of 150 µ at a rate of 23 kg / hour. processed using a larger extruder than in Examples 1-10. The extruder had a screw diameter of 63 mm with a ratio of amount to diameter of 25: 1 and a compression ratio of 3: 1. The melt and die temperatures were both 200 ⁰ C and the film was inflated to a peripheral expansion of 2.0: to give first All other conditions were as described in Examples 1-10. The obtained film had the following properties;

Θ09830 / 0966

Repartee (i) 1460 g tear strength (j) MD (k) 8.1 g / μ

TD (k) 11.9 g / μ tensile strength (1) MD (k) 33.3 MNm " ²

TD (k) 32.9 MNm " ² Elongation at break (m) MD (k) 670%

TD (k) 760%

Modulus of stiffness 240 MNm " ²

Impact stiffness function (p) 1365 Secondary function (q) 27700

(i) to (q) are as in the comments in Table 2 Are defined.

Example 12 to 16

Copolymers of ethylene with 1-pentene, 1-decene or 4-methylpentene-1 was made into a film by the method of Example 1 to 10 processed, with the exceptions that the Melt and die temperatures were 225 ° C and the circumferential expansion when making a film 30 µm thick 3.0: 1 was.

The properties of the polymers used are summarized in Table 3 and in Table 4 are the properties of the polymers produced Movies listed.

609838/0986

• - 22 -

Tabel

'ί

polymer density CcxtDncHTeres lot MFI Apparent Vis viscosity strain Methyl groups Vinyl groups i (kg / m3) Type Wt% viscosity at 100 at 10 ³ (%) per 1000 per 1000 ί (r) (b) sec. ~ ¹ (Nsnf ² ) Csi / sm " ² ) C atoms C atoms I. (a) 10.1 (C) (d) (e) (f) (G) (H) I.
1
j
!
F. 927.1 P. 11.3 0.20 1.54 χ 10 ³ 2.2 χ 10 ⁵ 650 21.3 0.51; i G 927.2 D. 13.1 0.11 1.60 χ 10 ³ 2.4 χ 1ο ⁵ 650 16.0 0.30 : ^H 928.1 MP 0.19 1.60 χ 1o ³ 1.9 χ 10 ⁵ 610 30.4 0.24

Comments on Table 3

(a) to (h) are all as defined in the comments on Table 1,

(r) P is pentene-1 D is decene-1 MP is 4-methylpentene-1

CD O CD cn

OO

- 23 table

co ca ο »

Polymeri
sat, loading
Zugssym-
bol Movie-
thickness
(U)] Impact resistance
g) (i)
"" rant edge; 240 Tear-resistant
j) ig / p)
W (k) TD (k) 18.6 I. AFTER G-KS! CHTJ MN / m ² 14.5 52.4 41.0 Rupture
nations
MD (k) TD (k) 650 Stiff-
ieits-
module
(μ) ₇
(MN / m ² ) Impact
stiff-
neatly
function
(P) Secondary
function
(q) example
or
equal
example F. 30th 320 890 2.3 10.0 Tensile strength (1) Breaking load capacity
MD (k) TD (k) MD (k) TD (k) 13.5 31.5 31.6 44o 795 320 2350 18700 12th F. 150 '1170 260 6.9 18.2 15.2 17.0 56.6 45.1 780 700 270 1330 25800 13th G 30th 270 1010 1.1 13.6 13.0 14.2 35.9 32.8 400 745 38o 2500 18700 14th G 150 1170 1060 8.5 10.1 15.2 13.5 35.6 33.8 680 790 270 1330 25800 15th H 150 1290 9.4 13, -4 760 300
-; -, 1720 31600 16 12.7
J

Comments on Table 4

(i) to (q) are all as defined in the comments on Table 1,

N3 CD CD CD Cn hO CX)

Claims (1)

Claims \\ y polymer film, formed from a copolymer of ethylene with at least one mono-ÄL-olefin comonomer, characterized in that the film has an impact strength and a stiffness modulus, with the proviso that an impact stiffness function ,, which is given by the relationship: Impact strength (in g) x stiffness modulus (in MNm " ² ) - locj film thickness (in μτη) is defined, has a value of at least 70. 2. Film according to claim 1, characterized in that it has an impact stiffness function with a value of at least 1000 has. 3. Film according to claim 1 or 2, characterized in that _2 that its modulus of stiffness has a value of 200 MNm up to 400 MNm " ² . 803818/0966 4. Film according to one of claims 1 to 3, characterized in that that it has a tear resistance of at least 5 g / p film thickness in one direction in the film. 5. A film according to claim 4, characterized in that it has a tear strength of at least 5 g // U «i _f in particular at least 7 g / pm film thickness both in the machine and in the transverse direction in the film. 6. Film according to one of claims 1 to 5, characterized in that it has a tensile strength, measured at a Pulling speed of 500 mm / minute, of at least 20 MN / m 2 in particular from 30Ls to 50 MN / m. 7. A film according to any one of claims 1 to 6, characterized in that it has an elongation at break, measured at a pulling speed from 500 mm / minute from 300 up to 1100%. 8. A film according to any one of claims 1 to 7, characterized in that it has a density in the range of 915 up to 935 kg / m ³ . 9. Film according to one of claims I to 8, characterized in that that its melt flow index, measured at 190 ° C using a 2.16 kg weight, is in the range S0983S / 096S from 0.05 up to 0.7. 10. Film according to one of claims 1 to 9 _r, characterized in that the impact strength and the stiffness modulus of the film are such that the relationship: Impact strength (in g) χ modulus of stiffness (in MNm) [Film thickness (in ^ om)] ⁰ ' ^{5 has} a value of at least 18,000. 11. Film according to one of claims 1 to 10, characterized in that the film is formed from a copolymer of ethylene and a comonomer, which at least one
mono-ct-oiefin, with at least 50 mole percent of the mono-ct-olefin having 5 or more carbon atoms. 12. Film according to claim 11, characterized in that
the film is formed from a copolymer in which the comonomer contains only mono-ot-olefins with at least 5 carbon atoms. 809838/0986 - 27 - '26U9528 13. Film according to one of claims 11 or 12, characterized in that the film consists of a copolymer with a content of 6.5 up to 30 wt .-% comonomers, based on the copolymer. is produced. 14. Film according to claim 13, characterized in that the film consists of a copolymer with a content of 6.5 to 16.5% by weight of 1-hexene, based on the copolymer / produced is. 15. Film according to one of claims 1 to 14, characterized in that the film is made from .einem copolymer of ethylene with a comonomer which is at least one mono-ol-olefin, with at least 50 mol% of the mono- ^ -oiefins, which is the comonomer, has 5 or more carbon atoms, and the copolymer has the following properties: a cured density (as defined above) in the range from 918 to 940 kg / m ³ , in particular 920 to 935 kg / m 3, an apparent viscosity (as defined above), measured at a temperature of 200 ° C. and a shear rate of 100 sec. "in the range from 0.5 x 10 ³ up to 3> 0 χ 10 ³ Nsm" ² , in particular 1, 3 χ 10 up to 2.4 χ 10 ³ Nsm " ² and a viscosity, measured at a temperature of 200 ° C and a force of 10 N / m, of at least 2 Ae ⁽¹ ' ^{6A X 10} K in particular 609838/0966 at least 3.5 Ae ^{(1 '6A χ 10} and not more than lOOOA, preferably not more than 5OOA, where A is the apparent viscosity at 200 ⁰ C and a shear rate of 100 sec. ^"1. 17. Use of the films according to one of claims 1 to 16 as a fertilizer sack, protective cover, carrier bag or insert for a waste bin. 18. A process for preparing a polymer film, characterized in that a copolymer of ethylene with at least one mono - ^ - extruded olefin comonomers through an annular die maintained at a temperature in the range from 170 ⁰ C to 300 ° C, the extrudate at inflates 1.2 to 10.0 times the circumferential expansion, and then stretches 2.5 to 50 times. 19. The method according to claim 18, characterized in that a copolymer of ethylene with a comonomer, which at least one mono-C-oiefin with at least 5 carbon atoms is used. 20. The method according to claim 18, characterized in that a copolymer according to claim 15 is extruded. 609838/0966 21. The method according to any one of claims 18 to 20, characterized in that the copolymer through an annular nozzle that is extruded at a temperature in the range from 200 to 25O ° C is maintained. 22. The method according to any one of claims 18 to 21, characterized in that the extrudate to a 5-fold, in particular inflated 3.1 to 3.5 times the circumferential expansion will. 23. The method according to any one of claims 18 to 22, characterized in that the extrudate to 5 times to 30 times is stretched. 609838/0966 so Blank page