CH650520A5 - ETHYLENE TERPOLYMERS, A PROCESS FOR THEIR MANUFACTURE AND THEIR USE IN THE MANUFACTURE OF FILMS. - Google Patents

Description

The present invention relates to polymers of ethylene comprising units derived from maleic anhydride and their use in the manufacture of films.

French Patent No. 1323379 describes terpolymers of ethylene, alkyl acrylate and maleic anhydride, of low crystallinity, used as modifiers of petroleum waxes at a rate of 5 to 10% by weight in said waxes , for coating on paper.

The present invention relates to improved polymers comprising on the one hand ethylene as the main monomer, and on the other hand at least two comonomers including a (meth) acrylic ester and maleic anhydride. Optionally, they can comprise a fourth monomer copolymerizable with the first three and they are then qualified as tetrapolymers.

The polymers according to the invention comprise:

- from 88 to 98.7% by moles of units derived from ethylene,

From 1 to 10 mol% of units derived from at least one ester chosen from alkyl acrylates and methacrylates, said alkyl group having from 1 to 6 carbon atoms,

- from 0.3 to 3 mol% of units derived from maleic anhydride.

They are characterized by a fluidity index (measured according to standard ASTM D 1238-73) of between 1 and 500 dg / min, a polydispersity index Mw / Mn greater than 6 and a Vicat temperature of between 30 C (high contents comonomers) and 85 C (low contents).

When the polymers according to the invention comprise a fourth comonomer, this can be chosen from α-olefins having from 3 to 8 carbon atoms, alkyl monomaleates and dialkyl maleates whose alkyl groups have from 1 to 6 carbon atoms, vinyl acetate, carbon monoxide, and may be present at a rate of up to 5 mol%, the proportion of ethylene in the tetrapolymer then being reduced by as much compared to the range indicated above.

The process for manufacturing the polymers according to the invention consists in copolymerizing, in the presence of at least one free radical initiator, a mixture composed of 94 to 99% by weight of ethylene, from 0.7 to 5% by weight of '(meth) acrylic ester and from 0.2 to 0.9% by weight of maleic anhydride in a reactor maintained under a pressure of 1000 to 3000 bar and at a temperature of 170 ° to 280 ° C, to relax then to separate the mixture of monomer and polymer formed in the reactor, and finally to recycle to the reactor the mixture of ethylene and monomers previously separated, the recycled stream comprising from 99 to 99.8% of ethylene and from 0.2 to 1% (meth) -acrylic ester. In the process according to the invention, it is possible to provide for a separate supply of fresh ethylene on the one hand, of the comonomers and of recycled ethylene on the other hand. The introduction of the comonomers into the reactor is preferably done by pumping under pressure a solution of maleic hydride in the (meth) acrylic ester, mixing this solution with the ethylene flow and homogenizing said mixture before its entry into the reactor. By way of nonlimiting example, mixing and homogenization can be carried out simultaneously in a Venturi type device. Of course, it can be envisaged to separate the recycled ethylene and (meth) -acrylic ester, but such an operation does not provide advantages which make it possible to compensate for the corresponding increase in the manufacturing cost.

As free radical initiators which can be used in the context of the present invention, mention may, for example, be made of 2-ethylhexyl peroxydicarbonate, ditertiobutyl peroxide, tert-butyl perbenzoate, 2-ethylbuthexanoate terbutyl. In a perfectly known manner, it is also possible to use, in the process according to the invention, one or more chain transfer agents, such as for example hydrogen, to adjust and control the characteristics of the polymer and in particular its melt index.

The method according to the invention is implemented continuously either in a stirred autoclave reactor comprising one or more zones, or in a tubular reactor as for example described in the East German patent No. 58.387. Downstream of the reactor are located an expansion valve then a separator operating under a pressure of 200 to 500 bar. The method according to the invention can implement cooling of the mixture of polymer and monomers between the expansion valve and the separator, for example in accordance with French patent No. 2313399 by injecting ethylene at a pressure lower than that of separator, said ethylene being able to be collected downstream of an exchanger of the recycling circuit.

The polymers according to the invention can be used in numerous applications, either alone or as a mixture with other materials or polymers. Like the ethylene / (meth) acrylic ester copolymers whose properties they improve, their applications depend on the melt index obtained by the use of the chain transfer agent. They also depend on the content of units derived from maleic anhydride. Thus, a significant application of the polymers according to the invention having a melt index of between 1 and 10 dg / min and comprising from 0.3 to 1 mol% of units derived from maleic anhydride consists in the manufacture of films. These films can have a thickness of between 10 and 500 jtm (microns) when they are obtained through a flat die and

5

10

15

20

25

30

35

40

45

50

55

60

65

3

650 520

from 25 to 200 µm (microns) when obtained by extrusion-blow molding. They are used for the manufacture of sachets, food packaging. the packaging of heavy loads, and as agricultural films. The extrusion-blowing of these films is carried out using conventional machines, and with an inflation rate of between 1 and 3 and a pulling rate that can reach a few tens of meters per minute.

The following examples are given by way of illustration and without limitation of the present invention.

Examples 1 to 4

We consider a cylindrical autoclave reactor comprising three zones with a volume of 1 liter each and equipped with a paddle stirrer. The zones are separated by valve screens. Fresh ethylene compressed by a first compressor feeds the first zone. The second zone is supplied with a homogeneous mixture of ethylene, maleic anhydride (AM) and ethyl acrylate (AE). Finally, a solution of 2-ethyl terbutyl perhexanoate in a cut of hydrocarbons is injected into the third zone. This therefore constitutes the only reaction zone since it brings together the three comonomers and a free radical initiator. Table 1 below shows the proportions by weight of maleic anhydride and ethyl acrylate relative to ethylene in the reaction zone and on the other hand the temperature in said zone. The reactor is maintained under a pressure of 1600 bar. At the bottom of the third zone of the reactor is placed an expansion valve allowing the pressure to be reduced to 300 bar. The mixture of the molten polymer on the one hand and the gaseous monomers on the other hand, after passing through the expansion valve, passes into a separating hopper. While the polymer is collected at the bottom of the hopper, the monomers are conveyed, after passing through a degreasing hopper, to a second compressor. On the other hand, a solution of maleic anhydride in ethyl acrylate is pumped under pressure and conveyed to the inlet of a Venturi type homogenizer where it is mixed with the stream of recycled monomers coming from the second compressor. At the outlet of this Venturi device, the mixture of the three monomers is conveyed to a spiral homogenizer and then transferred to the second zone of the reactor.

At the outlet of the separating hopper, the terpolymer produced is analyzed by infrared spectrophotometry and the proportions by moles of ethyl acrylate units and of maleic anhydride units are determined and indicated in Table I below. Furthermore, the melt index of the polymer is determined according to standard ASTM D 1238-73 and expressed in dg / min.

Then the following characteristics of the polymer are measured:

- density p, expressed in g / cm3 and determined according to standard ASTM D 2839,

- number average molecular mass Mn, determined by gel permeation chromatography,

- polydispersity index, determined according to the same method and equal to the ratio Mw / Mn, Mw being the average molecular mass by weight,

- Vicat temperature, expressed in degrees Celsius and determined according to standard NF T 51-012 (1).

The results of these measurements are collated in Table II below.

Example 5

The device of the previous examples is used to copolymerize ethylene, maleic anhydride and ethyl acrylate under the following conditions:

reactor pressure: 1200 bar;

temperature of the reaction zone: 180 "C. The composition by weight of the mixture of monomers in the reaction zone, the composition in moles of the terpolymer obtained and its melt index are indicated in Table I below. The polymer is then analyzed and characterized by its density, its molecular mass Mn and its polydispersity index, measured as described above and the values of which appear in Table II below.

Example 6

The device of the preceding examples is used to copolymerize ethylene, maleic anhydride and butyl methacrylate (MAB) under the following conditions:

reactor pressure: 1800 bar;

temperature of the reaction zone: 180 ° C.

The proportions by weight of the comonomers in the reaction zone are as follows:

4.8% MAB, 0.38% AM.

The polymer obtained has a melt index of 30 dg / min (measured according to standard ASTM D 1238-73).

Example 7

The device of the previous examples is used to copolymerize ethylene, maleic anhydride and butyl acrylate (AB) under the following conditions:

reactor pressure: 2300 bar;

temperature of the reaction zone: 260 ° C.

The proportions by weight of the comonomers in the reaction zone are as follows:

1.3% AB, 0.23 AM.

The polymer obtained has a melt index of 2 dg / min (measured according to standard ASTM D 1238-73), a Vicat temperature of 65 '' C and a density of 0.935 g / cm3. Its analysis by infrared spectrophotometry makes it possible to highlight the presence of:

- 2.0 mole% of units derived from butyl acrylate,

- 0.8% by moles of units derived from maleic anhydride.

Example 8

The terpolymer obtained in Example 2 is transformed by extrusion-blow molding at a temperature of 140 ° C. into a film with a thickness of 100 μm (microns), the drawing rate being equal to 2.5 m / min and the inflation rate being equal to 2. On the film obtained, the following properties are measured:

- elastic resistance RE expressed in kg / cm2 and determined according to standard NF T 51-034,

- RR breaking strength (expressed in kg / cm2) and AR elongation (expressed as a percentage) determined according to ASTM D 882-67.

The following values are found, perfectly balanced in the longitudinal and transverse directions:

RE- 51 kg / cm2;

RR = 112 kg / cm2;

AR = 540%.

Example 9

The terpolymer obtained in Example 1 is transformed into a film with a thickness of 100 m, under the same conditions as in Example 8. The properties measured on this film are as follows:

RE = 59 kg / cm2 RR = 100 kg / cm2 AR = 450%.

(Tables on next page)

5

10

15

20

25

30

35

40

45

50

55

60

650 520

4

Table I

Example

T C

Reactor

Polymer

I.F.

% AM

% AE

% AM

% AE

1

230

0.25

0.85

0.4

1.3

3.8

2

200

0.31

1.16

0.8

2.1

4.8

3

180

0.30

3.5

1.0

4.7

8.2

4

175

0.84

4.4

2.1

7.7

50

5

180

0.36

3.6

1.0

6.7

200

Table II

Example

1

2

3

4

5

P

0.930

0.936

0.942

0.960

0.944

Mn

17,500

17000

15,500

9500

7850

Mw / Mn

10.0

7.2

9.0

8.4

73.5

T Vicat

81

77

51

Claims (10)

650520 1. Ethylene terpolymer with a melt index of between 1 and 500 dg / min, comprising: - from 88 to 98.7% by moles of units derived from ethylene, From 1 to 10 mol% of units derived from at least one ester chosen from alkyl acrylates and methacrylates, said alkyl group having from 1 to 6 carbon atoms, and - from 0.3 to 3 mol% of units derived from maleic anhydride, characterized in that its polydispersity index is greater than 6. 2. Terpolymer according to claim 1, characterized in that its Vicat temperature is between 30 C and 85 C. 2 3. Terpolymer according to one of claims 1 and 2, characterized in that it comprises up to 5 mol% of units derived from a fourth comonomer chosen from a-olefins having from 3 to 4. Terpolymer according to one of claims 1 to 3, characterized in that it comprises from 0.3 to 1% by moles of units derived from maleic anhydride and in that its melt index is between 1 and 10 dg / min. 5. Terpolymer according to one of claims 1 to 4, characterized in that the ester is butyl methacrylate. 6. Terpolymer according to one of claims 1 to 4, characterized in that the ester is butyl acrylate. 7. Terpolymer according to one of claims 1 to 4, characterized in that the ester is ethyl acrylate. 8. A method of manufacturing a terpolymer according to claim 1, comprising copolymerizing, in the presence of at least one free radical initiator, a mixture composed of 94 to 99% by weight of ethylene, from 0.7 to 5% by weight of at least one (meth) acrylic ester and from 0.2 to 0.9% by weight of maleic anhydride in a reactor maintained under a pressure of 1000 to 3000 bar and at a temperature of 170 to 280 C, to relax and then to separate the mixture of monomer and of the terpolymer formed in the reactor, and finally to recycle to the reactor the mixture of ethylene and of monomers previously separated, characterized in that the mixture recycled to the reactor comprises from 99 99.8% ethylene and 0.2-1% (meth) -acrylic ester. 8 carbon atoms, alkyl monomaleates and dialkyl maleates whose alkyl groups have from 1 to 6 carbon atoms, vinyl acetate and carbon monoxide. 9. Method according to claim 8, characterized in that the free radical initiator is chosen from 2-ethylhexyl peroxydicarbonate, ditertiobutyl peroxide, tert-butyl perbenzoate and 2-ethylbuthexanoate terbutyl. 10. Use of a terpolymer according to claim 6 for the manufacture of films of thickness between 10 and 500 µm (microns).