EP0000084B1 - Use of alpha-polyolefin compositions for extrusion - Google Patents

Description

The present invention relates to the use, for extrusion, of compositions based on polymers of alpha-olefins. It relates more particularly to the use, for the manufacture of objects by extrusion followed by water cooling, of compositions based on propylene polymers.

The polymers of alpha-olefins, in particular the polymers of lower alpha-monoolefins such as ethylene and propylene are thermoplastic polymers suitable for processing by extrusion. An important outlet for this transformation process lies in the production of films, sheets, tubes and filaments. In the particular case of propylene polymers, a large volume of these extruded polymers is intended for the manufacture of fibers and films. These can for example be used as such as packaging films, can be cut into strips for weaving, or can be fibrillated for various textile applications.

Very often, the actual extrusion of the polymer is followed by a sudden cooling treatment (quenching) of the extruded objects by means of water.

However, in the extrusion processes carried out continuously and involving a cooling or a time of the objects extruded by a water bath, the problem arises of the entrainment, by the extruded object, during its progression, of varying amounts of cooling water. This training often manifests itself already for low extrusion speeds. The presence of this water is particularly troublesome for the continuation of the operations which the objects to be shaped are called upon to undergo.

Thus, the films and filaments generally undergo stretching in order to increase their resistance. Furthermore, the films can be cut into strips before stretching.

The presence of water disturbs this stretching and causes frequent breaks of these filaments and strips.

Furthermore, the entrainment of the cooling water by sheets or extruded tubes generates surface defects in the former and causes an irregular withdrawal and a heterogeneous composition of the latter.

These drawbacks have, up to now, made air to be preferred to water for the quenching treatments of extruded objects (H. Hagen and H. Domininghaus, Potyathyten und andere Polyolefinen 1961, page 162 and Extrudierte Feinfolien und Verbundfolien (1976). ), VDI-Verlag, pages 18-19).

However, in order to be able to make satisfactory use of the quenching of objects extruded with water, attempts have been made to remedy the drawbacks caused by the entrainment of cooling water by the extruded object. Attempts in this direction have mainly resided in the search for additives which would have eliminated, or at least reduced, the entrainment of water by the objects extruded from compositions based on polyolefins, but they have never leads to completely satisfactory results; it has not been possible, in fact, to reduce in this way the entrainment of water by the objects extruded at high speed, without harming the other essential properties of these objects, such as the stability, the coloring and the anti-corrosion action.

On the other hand, the incorporation, in polyolefinic compositions intended to be extruded, of compounds well known for their beneficial action on the coloring and the odor of the polymer during molding and for their anti-corrosive action, such as, for example. For example, calcium stearate, described in patent GB-A-826748 (Farbwerke Hoechst), in no way contributes to reducing the entrainment of water by objects extruded at high speed.

The Applicant has now found that certain compositions based on alpha-olefin polymers make it possible to manufacture objects by extrusion followed by cooling with water, without the latter being entrained, even for high extrusion speeds, and without harming the other essential properties of the extruded objects.

• (a) au moins un anti-oxydant phénolique;
• (b) au moins un phosphite organique;
• (c) au moins un carbonate d'un métal alcalino-terreux.

The present invention therefore relates to the use, for the extrusion followed by cooling with water of the extrudate, of compositions based on alpha-olefin polymers comprising:

• (a) at least one phenolic antioxidant;
• (b) at least one organic phosphite;
• (c) at least one carbonate of an alkaline earth metal.

In this regard, it should be mentioned that we had previously described previously (patent FR-A-1296276) of SHELL INT. RES. MIJ.) Compositions containing low polyolefins (polyethylene) added with at least 10% by weight of an inorganic filler covered with a layer of a higher fatty acid or a salt or ester thereof (page 4 , ABSTRACT). This would significantly improve the resistance to cracking under tension of polyethylene without appreciable reduction in its elongation at break (page 1, col d, last paragraph on page 2, col. G. Line 13).

Patent FR-A-1345203 (from SHELL INT. RES. MIJ). mentions that the addition to polyolefins of the combination of organic sulfur and phosphorus compounds and an organic or inorganic base would give these polyolefins good heat and light stabilization (page 1, col. d, last paragraph).

The basic proportion is between 0.1 and 5% approximately, for example between 0.3 and 1% approximately (page 3, col. D, lines 4 to 7).

Finally, US Pat. No. 2,985,617 (MONSANTO CHEMICAL CO) mentions that the polyvinyl chloride stabilizers are suitable for stabilizing the polyolefins produced using Ziegler catalysts (column 4, lines 49 to 54). Certain broad classes of stabilizers are preferred; organotins, organo lead, salts of alkaline earth metals and long chain fatty carboxylic acids, and epoxidized compounds (column 4, lines 60 to 72).

These documents make no mention of the problem of water entrainment by extrudates made up of the compositions they describe and therefore cannot suggest its solution. The addition of carbonates according to these documents is carried out for purposes fundamentally different from those pursued by the present invention. These carbonates, as well as the multitude of other compounds which meet the definitions appearing in these documents, exert functions completely different from that exerted by the alkaline-earth carbonate according to the invention.

The alpha-olefin polymers used in the compositions which can be used according to the invention are polymers containing at least 50 mol% and preferably at least 75 mol% of terminal unsaturated olefins the molecule of which contains from 2 to 18 and preferably from 2 to 6 carbon atoms such as ethylene, propylene, butene-1, pentene-1, methylbutenes-1, hexene-1, 3- and 4-methylpentenes-1 and vinylcyclohexane. They are more particularly polymers containing tertiary carbon atoms such as highly isotactic crystalline polymers of butene-1, 4-methylpentene-1, and very particularly, propylene.

They may also be copolymers of these alpha-olefins with each other and / or with diolefins comprising from 4 to 18 carbon atoms, such as non-conjugated aliphatic diolefins such as, for example, 1,4-hexadiene or such that alicyclic diolefins having an endocyclic bridge such as dicyclopentadiene for example.

Finally, these may be block copolymers which consist of successions of chain segments of variable lengths, each segment consisting of a homopolymer of an alpha-olefin or of a random copolymer comprising an alpha-olefin and at least one comonomer chosen from alphaolefins and diolefins.

The best results are obtained with polymers containing at least 50% by weight and preferably at least 75% by weight of propylene.

The compositions which can be used according to the invention can also be based on mixtures of two or more polymers as described above.

The polymers which can be used can be prepared according to known methods of polymerization of alpha-olefins at low pressure. In particular, highly isotactic crystalline homopolymers of propylene can be prepared in the presence of stereospecific catalytic systems based on organometallic compounds and titanium chlorides being at a valence lower than its maximum valence.

The compositions which can be used according to the invention comprise at least one constituent (a) which is any phenolic antioxidant. This antioxidant can be advantageously chosen from the group of alkylated mono-, poly- and thiobis-phenols.

As examples of alkylated monophenols, mention may be made of 2,6-di-tert-butyl-p-cresol and (3,5-di-tert-butyl-4-hydroxyphenyl) propionate n-octa-decyl .

As examples of alkylated polyphenols, mention may be made of methylene tetrakis (3,5-di-tert-butyl-4-hydroxy) methane dihydrocinnamate, 2,2'-methylene bis (4-methyl-6- terephthalate) tert-butylphenol), 2,6-bis- (2'-hydroxy-3-tert-butyl-5'-methylbenzyl) -4-methylphenol and tris- (3,5-di-tert-butyl isocyanurate) -4-hydroxy) benzyl.

The compositions which can be used according to the invention can also comprise a mixture of the phenolic antioxidants listed above.

The compositions which can be used according to the invention comprise at least one component (b) which is an organic phosphite. The main result of incorporating component (b) is to increase the effectiveness of the above-mentioned phenolic antioxidants. This organic phosphite is advantageously chosen from the phosphites and thiophosphites of general formula (RO) ₃ P and (RS) ₃ P in which the radicals R, which are identical or different, represent an alkyl, aryl, alkylaryl, cycloalkyl or alkoxyalkyl radical and among the cyclic phosphites derived from pentaerythritol.

Examples of organic phosphites meeting these definitions are found in United States Patent 3,039,993 in the name of Weston Chemical.

Preferred phosphites as constituents (b) are, on the one hand, the trialkylphosphites such as the triethyl-, tributyl- and trinonylphosphites for example and, on the other hand, the dialkylpentaerythritol diphosphites, such as the distearylpentaerythritol diphosphite for example. Mixtures of these phosphites can also be advantageously used.

The compositions used according to the invention finally comprise at least one component (c) which is a carbonate of an alkaline earth metal. All the alkaline earth metal carbonates are suitable as constituents (c). Mention may be made, for example, of magnesium, calcium, strontium and barium carbonates. However, it is preferred to use calcium carbonate, and in particular calcium carbonates which are in the form of particles with an average diameter of less than 10 microns. The so-called "aforementioned" calcium carbonates, that is to say the calcium carbonates obtained by carbonation of a lime milk, are very suitable.

The Applicant has indeed found with surprise that the incorporation of these carbonates in the compositions used in accordance with the invention most effectively reduces the entrainment of water by the objects extruded from these compositions.

It is also possible to incorporate into the compositions mixtures of the carbonates defined above.

Components (a) and (b) are incorporated into the compositions used in accordance with the invention in the usual stabilizing amounts. These amounts are generally between 0.005 and 10% by weight of the polymer entering into the composition and preferably between 0.01 and 5%. More particularly, these quantities are of the order of 0.05 to 0.5%.

Component (c) is incorporated into the compositions in an amount of 0.1 to 50% (per thousand) by weight of the polymer approximately, preferably in an amount of 0.1 to 10%.

The best results are obtained with amounts of component (c) of approximately 0.2 to 0.3%.

In order to be able to easily and homogeneously incorporate the latter constituent in the compositions which can be used according to the invention, it is preferred that the mean diameter of its particles is a fraction of a micron. More particularly, the particles have an average diameter of between 0.05 and 0.8 microns. It has been found in fact that if the size of the particles of component (c) is greater, this results, in the case of the extrusion of films cut into strips, of rapid wear of the cutting blades.

In addition to the polymer and the constituents (a), (b) and (c), the compositions which can be used according to the invention can contain other usual additives such as, for example, other antioxidants such as thioesters generally derived thiodipropionic acid, other polymers, agents that facilitate processing, reinforcing agents, pigments, fillers, lubricants, anti-static agents, etc.

Components (a), (b) and (c) can be incorporated into the polymer in any manner known per se, for example by dry mixing or by impregnating the polymer in powder or granules by means of a solution of the components in a suitable solvent, alone or as a standard charge with other ingredients, or by mixing a solution or a suspension of the polymer with a solution of the constituents.

The incorporation can be carried out for example, either in a mixer or a grinder where the solvent is evaporated, or by kneading on heated cylinders or by extrusion of a mixture of the polymer and the other constituents.

The extrusion of the compositions which can be used according to the invention can be carried out according to all the conventional techniques known to those skilled in the art.

The characteristics of the apparatus will obviously be chosen as a function of the transformation which it is desired to subject to the composition to be extruded and of the type of object which it is intended to shape. As for the cooling or quenching treatment by means of water, it is carried out at a temperature which depends on the nature of the extruded object and on the properties which it is intended to confer on the latter.

For example, in the case of the extrusion, from compositions based on propylene polymers, of films intended to be cut into strips, the temperature of the quench bath of the primary film is generally between approximately 20 and approximately 50 ° vs.

The use for the extrusion of the compositions according to the invention therefore provides an elegant solution to the problem of the entrainment of water, by these compositions, when they are cooled with water. In addition, the use, which is the subject of the invention, of the compositions described above, makes it possible, surprisingly, to ensure an excellent compromise between the elimination of the entrainment of water even at extrusion speed. high, the initial coloring and the anti-corrosion efficiency, a compromise which is not achieved with the compositions of the prior art. In addition, the preferred compositions which can be used according to the invention contain “aforementioned” calcium carbonate in particles of average diameter of the order of a fraction of a micron, do not soil the extruder die; during the extrusion of films which are cut into strips, they do not cause premature wear of cutting knives.

The invention is illustrated by the following illustrative and nonlimiting examples.

Example 1

• -1000 parties en poids d'un homopolymère cristallin du propylène;
• -0,3 parties en poids de téréphtalate de 2,2'-méthylène-bis(4-méthyl-6-tert-butylphénol) vendu sous la dénomination HPM 12 par Organosynthèse;
• -0.2 parties en poids de diphosphite de distéarylpentaérythritol vendu sous la marque WESTON 618 par Borg-Warner;
• -1 partie en poids de trinonylphosphite vendu par Rhône-Poulenc;
• -0,3 partie en poids de carbonate de calcium "précipité" vendu sous la marque SOCAL U1 par Solvay.

An extrudable composition is prepared by dry mixing of the following constituents:

• 1000 parts by weight of a crystalline propylene homopolymer;
• -0.3 parts by weight of 2,2'-methylene-bis (4-methyl-6-tert-butylphenol) terephthalate sold under the name HPM 12 by Organosynthesis;
• -0.2 parts by weight of distearylpentaerythritol diphosphite sold under the brand Weston 618 by Borg-Warner;
• -1 part by weight of trinonylphosphite sold by Rhône-Poulenc;
• -0.3 part by weight of "precipitated" calcium carbonate sold under the brand SOCAL U1 by Solvay.

This granulated composition is then extruded in the form of a film approximately 100 microns thick. This film is cooled by passing through a water bath at room temperature (25 ° C) and then cut into strips which are stretched, at a stretching rate of about 1/6 in a stretching oven brought to a temperature 150,180 ° C. .

It can be seen that these strips do not carry water, even when the extrusion speed of the primary film reaches 40 m / min. In addition, their cutting does not cause premature wear of the knives. Finally, it can be seen that the extruded compositions do not corrode the implementation pairing.

Example 2

• - 1 partie en poids de (3,5-di-tert-butyl-4-hydroxyphényl)propionate de n-octa-décyle vendu sous la dénomination Irganox 1076 par Ciba-Ceigy, au lieu de HPM 12;
• - 0,2 partie en poids de SOCAL U1.

An extrudable composition is prepared as in Example 1, except that one uses:

• - 1 part by weight of (3,5-di-tert-butyl-4-hydroxyphenyl) n-octa-decyl propionate sold under the name Irganox 1076 by Ciba-Ceigy, instead of HPM 12;
• - 0.2 parts by weight of SOCAL U1.

This composition is transformed into strips as indicated in Example 1. These strips show the same properties as those found for the strips of Example 1.

Example 3

• - 0,25 partie en poids de tétrakis[méthylène (3,5-di-tert-butyl-4-hydroxy) dihydrocinnamate]méthane vendu sous la dénomination Irganox 1010 par Ciba-Geigy;
• - 0,75 partie en poids d'Irganox 1076; .
• - 1,5 partie en poids de trinonylphosphite;
• - 0,2 partie en poids de SOCAL U1.

An extrudable composition is prepared as in Example 1, except that in addition to the propylene polymer:

• - 0.25 part by weight of tetrakis [methylene (3,5-di-tert-butyl-4-hydroxy) dihydrocinnamate] methane sold under the name Irganox 1010 by Ciba-Geigy;
• - 0.75 part by weight of Irganox 1076; .
• - 1.5 parts by weight of trinonylphosphite;
• - 0.2 parts by weight of SOCAL U1.

Once again, the same advantageous properties are observed on the strips obtained in the manner described in Example 1.

Example 4

This example is given for comparison.

An extrudable composition is prepared as in Example 3, except that SOCAL U1 is replaced by 0.5 part by weight of calcium stearate. When strips are produced, as described in Example 1, from these compositions, the phenomenon of water entrainment already occurs for extrusion speeds as low as 12 m / min.

Claims (10)

1. Use, for extrusion followed by water-cooling of the extrudate, of compositions which are based on alpha-olefine polymers and contain:

(a) at least one phenolic antioxdant,

(b) at least one organic phosphite and

(c) at least one alkaline earth metal carbonate.

2. Use according to Claim 1, characterised in that the alpha-olefine polymer is a propylene polymer.

3. Use according to Claim 1 or 2, characterised in that the phenolic antioxidant is chosen from among alkylated monophenols, polyphenols and thiobisphenols.

4. Use according to any one of Claims 1 to 3, characterised in that the organic phosphite is chosen from among trialkyl phosphites and dialkylpentaerythritol diphosphites.

5. Use according to any one of Claims 1 to 4, characterised in that the alkaline earth metal carbonate is calcium carbonate.

6. Use according to Claim 5, characterised in that the calcium carbonate is in the form of particles of mean diameter less than 10 microns.

7. Use according to any one of Claims 1 to 6, characterised in that the alkaline earth metal carbonate in incorporated into the compositions in an amount of 0.1 to 10 parts per thousand, by weight of the polymer.

8. Use according to any one of Claims 1 to 7, characterised in that the alkaline earth metal carbonate is in the form of particles of mean diameter between 0.05 and 0.8 micron.

9. Use according to any one of Claims 1 to 8, characterised in that it is applied to the manufacture of films.

10. Use according to Claim 9, characterised in that the films are cut into tapes.