GB1583560A

GB1583560A - Propylene copolymer film and process for its manufacture

Info

Publication number: GB1583560A
Application number: GB3510577A
Authority: GB
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1976-08-24
Filing date: 1977-08-22
Publication date: 1981-01-28
Also published as: FR2362894B1; FR2362894A1; JPS5326883A; NL7709079A; DE2637991A1; BE858007A

Description

(54) PROPYLENE COPOLYMER FILM AND PROCESS FOR ITS MANUFACTURE (71) We, HOECHST AKTIENGESELLSCH AFT, a body corporate organised according to the laws of the Federal Republic of Germany, of 6230 Frankfurt (Main) 80, Postfach 80 03 20, 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 state ment The present invention relates to an unstretched or stretched plastics film composed of a terpolymer of ethylene, propylene and afurther cc-olefin, and to a process for the manufacture of the film.

It has already been proposed to produce propylene/ethylene copolymers or propylenej l-butene copolymers in the presence of mixed complexjmetalorganic catalysts. The catalyst is normally a combination of a compound of an element of main Group I, II or III of the Periodical Table with a compound of a transition element of Group IVa, Va or VIa, occasionally with a third component. The molecular weight of the polymer produced with such a catalyst in suspension, solution or in the gaseous phase may be adjusted to a chosen value within a range from approximately 50,000 to 5,000,000 units by adding suitable regulators and by influencing the reaction temperature Highly stereospecific catalyst systems have been proposed by means of which it is possible, under some conditions, to polymerise propylene in such a manner that more than 95 per cent by weight of the monomer is converted to an isotactic polymer.

The advantageous mechanical properties, for example, hardness, rigidity, and dimensional stability, of objects made from isotactic polypropylene are due to its high degree of crystallinity. Furthermore, isotactic polypropylene has the advantage that its softening point Tm is relatively high, namely, around 170"C. On the other hand, for some applications, for example, when paper or cardboard is to be coated, a lower melting point would be desirable, and this may be achieved by incorporation of a comonomer. The preparation and use of some propylene copolymers is disclosed, for example, in US Patent Specification No. 2,918,457, British Patent Specification No. 1,084,953, German Patent Specification No. 1,230,224, and German Offenlegungsschriften Nos. 1,694,694 and 2,460,597.

Furthermore, German Offenlegungsschriften Nos. 1,936,963 and 2,061,418 described biaxially stretched films in sheet form which are prepared from a propylene copolymer containing between 1 and 10 per cent by weight of ethylene.

Although it is possible to alter favourably certain properties, for example, the melting point or particular defined physical strength values, by the incorporation of comonomers, it has been found in practice that a film consisting, for example, of a copolymer of propylene and ethylene tends to be somewhat turbid, so that packaging films made of such material do not possess the desired transparency.

The incorporation of l-butene in propylene is difficult because only small proportions can be incorporated. Since only part of the 1butene reacts during polymerisation, high losses of material occur, which has an adverse effect upon the manufacturing costs because l-butene is relatively expensive. Moreover, the manufacturing temperatures are not in the desired range, that is to say, they are not below that required for polypropylene.

It is an object of the present invention to provide a stretched or unstretched film which is superior in its properties to films of copolymers of propylene and ethylene, especially as regards turbidity and resistance to scratching, and which nevertheless has good welding properties and, if stretched, preferably has a high degree of shrinkage.

The present invention provides a plastics fiim composed of a terpolymer consisting of from 93 2 to 99 0 per cent by weight of propylene units, from 0 5 to 1.9 per cent by weight of ethylene units, and from 0 5 to 4.9 per cent by weight of units of an oe-olefin having from 4 to 10 carbon atoms, in which the comonomers are substantially statistically distributed.

The film of the invention may be either unstretched or stretched. Surprisingly, an unstretched film according to the present invention has been found to combine a low turbidity with a high resistance to scratching and good welding properties. A film with such properties may be used with considerable advantage in applications, for example, the packaging industry, where a low turbidity is of the greatest importance. Since it has the advantage of being highly resistant to scratching, the film according to the present invention is especially suitable for packaging hard goods, because virtually no loss of transparency due to scratching during packaging and/or shipping occurs. The goods are thus offered to the customer in an optically clear package.

The melting temperature of the terpolymer used is lower by at least 10 C than that of polypropylene. Its RSV value (reduced specific viscosity) is preferably within the range from 1 5 to 15 dl/g, more preferably from 2-0 to l0dlJg, resulting in favourable processing temperatures.

The film of the invention may be manufactured by, for example, any method suitable for the manufacture of polypropylene films, either in the form of sheets or in tubular form.

Apart from the fact that dosing devices for the comonomers will additionally be neceessary, the terpolymer to be used according to the present invention may be prepared using the same polymerisation facilities as are used for preparing isotactic propylene homopolymers.

Stereospecific catalyst may be used for the preparation of the terpolymer. Thus for example, the terpolymers may be produced using a catalyst suitable for the production of isotatic polypropylene. An example of a catalyst suitable or use in the preparation of the terpolymer is a catalyst comprising a TiCI3 component, for example a combination of aluminium diethyl monochloride, as the activator, with a TiCl3-containing component obtained by reducing TiCI4 with aluminium, aluminium diethyl chloride, or aluminium ethyl sesquichloride, and then subjected to a thermal after-treatment. Alternatively, a TiCI3 component may be used which has been aftertreated with a complex forming compound (a compound that forms a complex with the TiCI3), and/or the stereo specific effect of the catalyst system may be increased by the addition of a so-called "third component" to the polymerisation mixture (see German Offenlegungsschriften Nos. 1,495,629, 2,409,726 and 2,413,261).

Other TiCI3 components, for example, a commerically available catalyst of the composition TiC1, 1/3 AICI3, may also be used, either alone or in combination with complex formers, to increase the stereospecific effect, provided that in combination with the abovementioned activator they form a highly stereospecific catalyst system.

The terpolymer may be prepared in an inert diluent or in the gaseous phase. Preferred diluents include aliphatic or cycloaliphatic hydrocarbons, for example, pentane, hexane and heptane (including isomers of these compounds), cyclohexane, or methyl cyclohexane. Further, aromatic hydrocarbons may be used, for example, benzene or xylene, petroleum fractions or hydrogenated diesel oil fractions carefully freed from oxygen, sulphur compounds, and moisture.

The concentration of the catalyst and the temperature and pressure conditions are preferably substantially the same as those normally selected for the homopolymerisation of propylene with the same catalyst.

Preferably, a pressure within the range of from 0 5 to 40 kp/cm2 and a temperature within the range of from 40 to 900C are used.

Advantageously, the film according to the present invention contains l-butene or 1hexene as the cr-olefin component of the terpolymer, because these monomers lend themselves very readily to a statistical incorporation in the terpolymer chain.

Although the film according to the invention may be used as an unstretched film, it is possible to modify the film by subjecting it to at least one stretching (orienting) operation; biaxial stretching by the sheet stretching process or the tubular stretching process, preferably at a stretching ratio ranging from 3 to 12 (that is, the unstretched film is preferably stretched to 3 to 12 times its original length), is preferred. In this manner, a shrinkable film of very low turbidity is produced which has a high resistance to scratching and to piercing, but which may be welded, for example, by means of hot-wire welding, if it is to be used for packaging purposes.

If a film of reduced shrinkage is desired, the stretching film may be subjected to a heatsetting process, which has already been proposed in connexion with polypropylene or propylene/ethylene copolymers, for example, in German Offenlegungsschriften Nos.

1,779,585 and 1,936,963. The stretched films have the good strength values desirable for some applications.

The thickness of the film is not limited, but thicknesses within the range of from 8 to 100 ,am, preferably from 20 to 60 Fm, are preferred.

The present invention also provides a process for the manufacture of the film of the invention, where a melt comprising a sub stantially statistical terpolymer consisting of from 93 2 to 99 0 per cent by weight of propylene units, from 0 5 to 1 9 per cent by weight of ethylene units, and from 0-5 to 4 9 per cent by weight of units of an -olefin having from 4 to 10 carbon atoms, is extruded from a die, preferably at a temperature within the range of from 190 to 280 C, and cooled to form a film.

After extrusion, the melt is generally allowed to solidify on a cooled support to form the film.

After extrusion and cooling the film may if desired be heated to a temperature at which it is capable of being stretched, and is stretched monoaxially or biaxially. Advantageously, the film is produced in sheet form and is stretched first longitudinally and then transversely.

The film of the invention may if desired contain additives, provided they do not significantly detract from the desired good properties of the film. Preferred additives include antistatic agents, slip promoters, dyestuffs, and anti-oxidants.

The invention also provides a process for packaging goods, wherein the goods are packaged in a plastics film according to the invention. Advantageously, the film package is closed by welding.

The following Examples illustrate the invention.

Example 1 A terpolymer composed of 97 0 per cent by weight of propylene units, 1 0 per cent by weight of ethylene units, and 2 0 per cent by weight of 1-butene unts was extruded from a slot die at 250"C. The melt was cooled on a casting drum maintained at 300 C.

The resulting film had a thickness of 30 fim.

Example 2 The procedure described in Example 1 was repeated, except that the terpolymer was composed of 95.3 per cent by weight of propylene units, 1-7 per cent by weight of ethylene units, and 3 0 per cent by weight of 1butene units.

Example 3 The procedure was the same as in Example 1, except that the terpolymer was composed of 95 1 per cent by weight of propylene units, 1-8 per cent by weight of ethylene units, and 3-1 per cent by weight of 1-butene units.

Example 4 The procedure was the same as in Example 1, except that the terpolymer was composed of 93.9 per cent by weight of propylene units, 1-8 per cent by weight of ethylene units, and 4.4 per cent by weight of 1-butene units.

Example 5 The procedure was the same as in Example 1, except that the terpolymer was composed of 93.7 per cent by weight of propylene units, 1-8 per cent by weight of ethylene units, and 4.5 per cent by weight of 1-hexene units.

Examples 6 and 7 The polymers used were those used in Examples 1 and 5 respectively, but a tubular die was employed. In each case, the extruded melt was drawn over a cooling mandrel provided with an additional cooling water jacket; the extrusion temperature was 210 C. In each case a 20 ,um thick tube was produced.

The unstretched films produced in Examples 1 to 7 possessed very low tubidity, that is to say, good transparency, and also displayed good resistance to scratching and good weldability. They were very suitable for use as packaging films.

Examples 8 and 9 The terpolymers described respectively in Examples 1 and 5 were extruded at 250qC from a slot die and the melts were cooled on a casting drum maintained at 30 C. The cooled preliminary films were heated to a temperature of 125 C and conveyed to a stretching roller maintained at 130"C. The stretching gap between rollers rotating at different speeds was 28 mm wide. The longitudinal stretching ratio was adjusted to S 6. The films were cooled to 30"C and then passed into a heated tenter-frame clamped in clips, an4 stretched at a temperature of 150"C. The transverse stretching ratio was adjusted to 8 0. The finished films were 30 Cam thick.

Application of the hot-wire process showed that the films had good welding qualities; furthermore, they were distinguished by a low degree of turbidity, very high resistance to scratching, high shrinkage, good resistance to piercing, and good strength in the longitudinal and transverse direction, according to their orientation.

Examples 10 and ii Examples 8 and 9 were repated, except that the films were heat-set after the biaxial stretching process.

The resulting films had the same good qualities as the films according to Examples 8 and 9, but their shrinkage was only 1/5 of that of the corresponding films produced in those Examples.

The films produced in accordance with Examples 8 to 11 were excellently suited for use in the packaging field.

WHAT WE CLAIM IS 1. A plastics film composed of a terpolymer consisting of from 93 2 to 99 0 per cent by weight of propylene units, from 0 5 to 1-9 per cent by weight of ethylene units, and from 0 5 to 4.9 per.cent by weight of units of an o:-olefin having from 4 to 10 carbon atoms, in which the comonomers are substantially statistically distributed.

2. A film as claimed in claim 1, wherein the oc-olefin comonomer of the terpolymer is 1-butene or 1-hexene.

3. A film as claimed in claim 1 or claim 2, wherein the terpolymer has a reduced specific viscosity value within the range of from 1-5 to 15-0 dlfg.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. from 0-5 to 4 9 per cent by weight of units of an -olefin having from 4 to 10 carbon atoms, is extruded from a die, preferably at a temperature within the range of from 190 to 280 C, and cooled to form a film. After extrusion, the melt is generally allowed to solidify on a cooled support to form the film. After extrusion and cooling the film may if desired be heated to a temperature at which it is capable of being stretched, and is stretched monoaxially or biaxially. Advantageously, the film is produced in sheet form and is stretched first longitudinally and then transversely. The film of the invention may if desired contain additives, provided they do not significantly detract from the desired good properties of the film. Preferred additives include antistatic agents, slip promoters, dyestuffs, and anti-oxidants. The invention also provides a process for packaging goods, wherein the goods are packaged in a plastics film according to the invention. Advantageously, the film package is closed by welding. The following Examples illustrate the invention. Example 1 A terpolymer composed of 97 0 per cent by weight of propylene units, 1 0 per cent by weight of ethylene units, and 2 0 per cent by weight of 1-butene unts was extruded from a slot die at 250"C. The melt was cooled on a casting drum maintained at 300 C. The resulting film had a thickness of 30 fim. Example 2 The procedure described in Example 1 was repeated, except that the terpolymer was composed of 95.3 per cent by weight of propylene units, 1-7 per cent by weight of ethylene units, and 3 0 per cent by weight of 1butene units. Example 3 The procedure was the same as in Example 1, except that the terpolymer was composed of 95 1 per cent by weight of propylene units, 1-8 per cent by weight of ethylene units, and 3-1 per cent by weight of 1-butene units. Example 4 The procedure was the same as in Example 1, except that the terpolymer was composed of 93.9 per cent by weight of propylene units, 1-8 per cent by weight of ethylene units, and 4.4 per cent by weight of 1-butene units. Example 5 The procedure was the same as in Example 1, except that the terpolymer was composed of 93.7 per cent by weight of propylene units, 1-8 per cent by weight of ethylene units, and 4.5 per cent by weight of 1-hexene units. Examples 6 and 7 The polymers used were those used in Examples 1 and 5 respectively, but a tubular die was employed. In each case, the extruded melt was drawn over a cooling mandrel provided with an additional cooling water jacket; the extrusion temperature was 210 C. In each case a 20 ,um thick tube was produced. The unstretched films produced in Examples 1 to 7 possessed very low tubidity, that is to say, good transparency, and also displayed good resistance to scratching and good weldability. They were very suitable for use as packaging films. Examples 8 and 9 The terpolymers described respectively in Examples 1 and 5 were extruded at 250qC from a slot die and the melts were cooled on a casting drum maintained at 30 C. The cooled preliminary films were heated to a temperature of 125 C and conveyed to a stretching roller maintained at 130"C. The stretching gap between rollers rotating at different speeds was 28 mm wide. The longitudinal stretching ratio was adjusted to S 6. The films were cooled to 30"C and then passed into a heated tenter-frame clamped in clips, an4 stretched at a temperature of 150"C. The transverse stretching ratio was adjusted to 8 0. The finished films were 30 Cam thick. Application of the hot-wire process showed that the films had good welding qualities; furthermore, they were distinguished by a low degree of turbidity, very high resistance to scratching, high shrinkage, good resistance to piercing, and good strength in the longitudinal and transverse direction, according to their orientation. Examples 10 and ii Examples 8 and 9 were repated, except that the films were heat-set after the biaxial stretching process. The resulting films had the same good qualities as the films according to Examples 8 and 9, but their shrinkage was only 1/5 of that of the corresponding films produced in those Examples. The films produced in accordance with Examples 8 to 11 were excellently suited for use in the packaging field. WHAT WE CLAIM IS

1. A plastics film composed of a terpolymer consisting of from 93 2 to 99 0 per cent by weight of propylene units, from 0 5 to 1-9 per cent by weight of ethylene units, and from 0 5 to 4.9 per.cent by weight of units of an o:-olefin having from 4 to 10 carbon atoms, in which the comonomers are substantially statistically distributed.

4. A film as claimed in claim 3, wherein

the terpolymer has a reduced specifici viscosity value within the range of from 2 0 to 10 0 dl/g.

5. A film as claimed in any one of claims 1 to 4, wherein the terpolymer has been produced using a stereospecific catalyst.

6. A film as claimed in claim 5, wherein the terpolymer has been produced using a catalyst suitable for the production of isotactic polypropylene.

7. A film as claimed in claim 5 or claim 6, wherein the catalyst comprises a TiCl3 component.

8. A film as claimed in any one of claims 5 to 7, wherein the terpolymer has been produced at a pressure within the range of from 0 5 to 40 kp/cm

9. A film as claimed in any one of claims 5 to 8, wherein the terpolymer has been produced at a temperature within the range of from 40 to 90"C.

10. A film as claimed in any one of claims 1 to 9, which has been stretched in at least one direction.

11. A film as claimed in claim 10, which has been biaxially stretched at a stretching ratio within the range of from 3 to 12.

12. A film as claimed in any one of claim 10 to 12, which has been heat-set.

13. A film as claimed in any one ofclaims 1 to 12, which is in sheet form.

14. A film as claimed in any one of claims 1 to 13, having a thickness within the range of from 8 to 100 ium.

15. A film as claimed in claim 14, having a thickness within the range of from 20 to 60 ,um.

16. A film as claimed in any one of claims 1 to 15, which contains at least one antistatic agent andjor at least one slip promotor andjor at least one dystuff and/or at least one antioxidant.

17. A plastics film substantially as described in any one of the Examples herein.

18. A process for the manufacture of a plastics film, wherein a melt comprising a substantially statistical terpolymer consisting of from 93 2 to 99 0 per cent by wight of propylene units, from 0 5 to 1 9 per cent by weight of ethylene units, and from 0 5 to 4 9 per cent by weight of units of an o:-olefin having from 4 to 10 carbon atoms, is extruded from a die and cooled to form a film.

19. A process as claimed in claim 18, wherein the melt is extruded at a temperature within the range of from 190 to 2800C.

20. A process as claimed in claim 18 or claim 19, wherein, after extrusion and cooling, the film is heated to a temperatue at which it is capable of being stretched, and is stretched monoaxially or biaxially.

21. A process as claimed in claim 20, wherein the film is produced in sheet form and is stretched first longitudinally and then transversely.

22. A process as claimed in claim 20 or claim 21, wherein subsequent to the stretching operation the film is heat-set.

23. A process for the manufacture of a plastics film, carried out substantially as described in any one of the Examples herein.

24. A terpolymer film whenever produced by a process as claimed in any one of claims 18 to 23.

25. A process for packaging goods, wherein the goods are packaged in a plastics film as claimed in any one of claims 1 to 17 and 24.

26. A process as claimed in claim 25, wherein the film package is closed by welding.

27. Packaged goods whenever produced by a process as claimed in claim 25 or claim 26.