The invention relates to a polyolefin-based pigmented composition including an inorganic, in particular yellow-coloured pigment. It also relates to articles shaped starting from this composition, in particular pipes.
The pigment is intended to denote a pulverulent substance endowed with a colouring and/or opacifying power, generally insoluble in the substance to be coloured.
It is generally known to use white-coloured titanium dioxide as an opacifying agent in plastics and to add thereto a pigment, frequently organic, to obtain the desired colouring. In order to obtain plastics of various colours, for example yellow-colored, it has already been proposed in Patent Application JP 75/73940 to employ a mixture of titanium dioxide with a yellow pigment. In fact, in this Patent Application a masterbatch intended to colour polyethylene is prepared by mixing 1000 g of titanium dioxide, 400 g of a product called "Titan Yellow", 100 g of a dispersing agent and 700 g of polyethylene.
In order to obtain a yellow-coloured composition, this known mixture requires a relatively large quantity of brightly coloured yellow pigment (because the latter is diluted with white-coloured titanium dioxide). These commercially available yellow pigments are generally costly.
The use of a masterbatch as described above for colouring polyethylene, when mixed with virgin polyethylene to obtain a final composition - generally in an extrusion granulation process - has the additional disadvantage of rapidly causing abrasion of the parts of the equipment which are in contact with the mixture used. In particular, in an extrusion granulation line it gives rise to high abrasion of the gear pump whose function is
to feed the extruder at a high rate, as well as of the mixing zones of the extruder screw. Abrasion also takes place when the final composition thus obtained is introduced into a process for the manufacture of shaped articles, for example by extrusion, by blow-extrusion, by extrusion-thermoforming or by injection moulding. Such a phenomenon of abrasion of the equipment requires frequent refurbishing of the plant, and this is industrially unacceptable.
The invention overcomes these disadvantages by providing a new, polyolefin-based composition including an inorganic pigment which, when used, for example in an extrusion process, does not give rise to abrasion of the equipment. Another objective of the invention is to reduce as much as possible the content of bright-coloured pigment in this composition while maintaining the shade of colouring and its opacity. Furthermore, the invention is aimed at providing a pigmented composition whose colour is thermally stable and resistant to UV radiation.
To this end the invention relates to a polyole-fin-based pigmented composition characterized in that it includes, per 100 parts by weight of polyolefin, from 0.01 to 5 parts by weight of an inorganic pigment containing mixed phases of oxides of titanium, antimony and of another metal chosen from the group containing barium, nickel, chromium and manganese. Nickel and chromium are preferred among these other metals. Nickel is particularly suitable.
"Mixed phases of oxides" is intended to denote the intimate mixtures of oxides which can be obtained, for example, by heat treatment of a mixture of a number of oxides at very high temperature, but below the melting temperature of the oxides. These intimate mixtures, which are also called "mixed oxides", differ from physical mixtures of oxides, prepared, for example, by mechanical mixing of a number of oxides at ambient temperature.
The inorganic pigment of the composition according to the invention preferably has a "rutile" crystal structure.
The inorganic pigment of the composition according to the invention generally includes at least 35 % by weight of titanium, more particularly at least 42 % by weight, titanium contents of at least 47 % by weight being recommended. In most cases the titanium content does not exceed 60 % by weight, more particularly 53 % by weight, contents not exceeding 49 % by weight being the preferred ones.
The pigment usually includes at least 1 % by weight of antimony, in particular at least 2 % by weight, contents of at least 4.5 % by weight being the most advantageous ones. The antimony content is preferably not greater than 10 % by weight, in particular not greater than 8 % by weight, contents not greater than 6.5 % by weight being especially preferred.
In general, the pigment contains at least 1 % by weight of the metal other than titanium and antimony, more precisely at least 2 % by weight, values of at least 3 % by weight being the most common ones. The metal content is usually not more than 10 % by weight, more especially not more than 8 % by weight, contents of not more than 5 % by weight being the most common ones.
The titanium is generally present in the form of titanium dioxide and the antimony in the form of antimony trioxide. When the metal is nickel, it is in most cases present in the form of nickel monoxide. The inorganic pigment usually also contains traces of sodium, magnesium, phosphorus and iron, the content of each of these elements generally not exceeding 1 % by weight of the inorganic pigment.
The inorganic pigment of the composition according to the invention is advantageously in the form of a powder of particles whose particle size distribution is characterized by a mean diameter D measured by laser particle size measurement by means of a Malvern®Msizer 20 instrument and defined by the following relationship:
where n; denotes the weight frequency of the particles of diameter Di. The diameter D is generally at least 0.1 µm, preferably at least 0.5 µm, values of at least 0.9 µm being the most common ones, for example approximately 2 µm. Generally the diameter D does not exceed 10 µm, in particular 5 µm, values of not more than 3.5 1m being recommended. The particle size distribution can be characterized by the diameter D90, which is defined by the fact that 90 % of the particles of the inorganic pigment have a diameter smaller than the diameter D90. This diameter D90 is advantageously at least 1 µm, more precisely at least 5 µm; values of at least 8 µm being preferred, for example equal to approximately 10 µm. In most cases the diameter D90 does not exceed 20 µm, more particularly 15 µm, values of not more than 12 µm being the most advantageous ones. The particle size distribution can also be defined by the diameter D10, which is characterized by the fact that 10 % of the particles of the inorganic pigment have a diameter smaller than the diameter D10. This diameter D10 is usually at least 0.05 µm, in particular at least 0.1 µm, preferably at least 0.5 µm, for example equal to approximately 0.75 µm. In most cases the diameter D10 does not exceed 5 µm, more especially 0.1 µm, preferably 1 µm. The diameters D90 and D10 as defined above are measured by laser particle size measurement by means of a Malvern®Msizer 20 instrument.
In most cases the inorganic pigment of the composition according to the invention has a density, measured according to DIN standard 53193 (1979) of at least 1 g/cm3, preferably at least 2 g/cm3, values of at least 3 g/cm3 being the most common ones. The density is generally not higher than 10 g/cm3, in particular not higher than 8 g/cm3, values not higher than 6 g/cm3 being recommended. A density of approximately 4.5 g/cm3 is particularly suitable.
Furthermore, the inorganic pigment of the composition according to the invention is generally characterized by the fact that a dispersion of 50 g of
the pigment in 1 1 of water, prepared according to DIN standard 53200 (1978) has a pH of at least 6, preferably of at least 7; the pH thus measured usually does not exceed 10, in particular does not exceed 9. Values of approximately 8 are found to be the most advantageous ones.
The inorganic pigment is preferably yellow-coloured.
The inorganic pigments most particularly advantageous in the composition according to the invention are those chosen from commercial Sicotan® yellow pigments.
The inorganic pigments usable in the composition according to the invention can, for example, be obtained by the processes described in Patent Applications DE-A1-2936746, DE-A1-3019172 and DE-A1-3401347, and in the publication "Nickeltitangelb", Farbe und Lack, vol. 68, No. 3, pages 174-175 (1962).
According to the invention the composition includes an inorganic pigment in a quantity of at least 0.01 part by weight per 100 parts by weight of polyolefin. Particularly satisfactory results are obtained with contents of at least 0.03 parts by weight, contents of at least 0.05 parts by weight being the most advantageous ones. The quantity of inorganic pigment is generally not greater than 5 parts by weight per 100 parts by weight of polyolefin. Quantities of not more than 2 parts by weight are preferred, values of not more than 0.5 being the most recommended ones. Quantities of 0.07 to 0.3 are particularly suitable.
The composition according to the invention also includes at least one polyolefin. A polyolefin is intended to denote olefin homopolymers and olefin copolymers with one or more comonomers, well known to a person skilled in the art, and mixtures thereof. The olefins may, for example, be chosen from linear olefins containing 2 to 8 carbon atoms, such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene and 1-octene. The preferred olefins are ethylene and propylene. The comonomers may be chosen from the linear olefins
described above, from branched olefins such as 4-methyl-pentene and from diolefins containing from 4 to 18 carbon atoms, such as 4-vinylcyclohexene, dicyclopentadiene, methylene- and ethylidenenorbornene, 1,3-butadiene, isoprene and 1,3-pentadiene. The preferred comonomers of ethylene are butene and hexene; the preferred comonomers of propylene are ethylene and butene.
The polyolefin is preferably chosen from the homopolymers and copolymers of ethylene containing one or more comonomers. Among the ethylene copolymers preference is given to those containing butene or hexene as comonomer. The quantity of butene or hexene in the copolymer is generally not more than 0.01 mol%, in particular at least 0.05 mol%, quantities of at least 0.1 mol% being the most advantageous ones. The quantity of butene or of hexene is usually not more than 10 mol%, more precisely not more than 5 mol%, quantities of not more than 3 mol% being recommended. Particularly effective results are obtained with quantities of butene or hexene of 0.4 to 1 mol%.
The polyolefin generally has a standard density, measured according to ISO Standard 1183 (1987) of at least 920 kg/m3, in most cases of at least 930 kg/m3, values of at least 935 kg/m3 being the most advantageous ones. The standard density is commonly not higher than 960 kg/m3, more especially not higher than 955 kg/m3, values not exceeding 950 kg/m3 being recommended.
In most cases the polyolefin is further characterized by a melt index, measured at 190°C under a 5 kg load according to ISO standard 1133 (1991) of at least 0.05 g/10 min, in particular of at least 0.1 g/10 min, values of at least 0.2 being the most common ones. The melt index generally does not exceed 10 g/10 min, preferably 5 g/10 min, values of not more than 2 g/10 min being recommended.
When it is desired to obtain a composition of a predetermined colour, it may be found necessary to incorporate in the composition according to the invention an additional organic pigment, generally containing
aromatic radicals. This may be chosen from organic azo pigments containing at least one -N=N- group in their chemical structure, from metal salts of azo compounds containing, for example -COOH or -SO3H groups, in particular the barium or calcium salts, from pigments of quinophthalone type, from phthalocyanines, from pigments of quinacridine type, from anthraquinone derivatives, perylene derivatives and pigments of thio-indigo type. Organic pigments which may be mentioned as examples are benzimidazolone of monoazo type and diarylides, pyrazolones and dianisidine of diazo type. Pigments of quinophthalone type are preferred. The yellow organic pigment of quinophthalone type which corresponds to the formula
(Formula Removed)
is particular suitable.
The quantity of organic pigment which is incorporated depends on the desired colour; it is generally at least 0.01 part by weight per 100 parts by weight of polyolefin, preferably at leat 0.03 parts by weight, values of at least 0.05 parts by weight being the most advantageous ones. The quantity of organic pigment is usually not more than 5 parts by weight per 100 parts by weight of polyolefin, preferably not more than 2 parts by weight, more particularly not more than 0.5 parts by weight.
The incorporation of an organic pigment in the composition according to the invention has the advantage of making it possible to obtain different predetermined shades in a wide range without this requiring a large quantity of organic pigment, which is a costly product.
Besides the polyolefin and the inorganic pigment and optionally the organic pigment, the composition according to the invention may also contain usual
additives such as stabilizers (for example antiacids, antioxidants and/or UV stabilizers), antistatic agents and processing aids. The content of each of the additives is generally lower than 10 parts by weight per 100 parts by weight of polyolefin.
Additives which are suitable are, for example, pentaerythrityl tetrakis(3,5-di-t-butyl-4-hydroxyphenyl propionate) (antioxidant), tris(2,4-di-t-butylphenyl) phosphite (antioxidant), polyesters of succinic acid with n-beta-hydroxyethyl-2,2,6,6-tetramethyl-4 - hydroxy-piperidine (UV stabilizers), 2-(2'-hydroxy,3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole (UV stabilizer), 4,4'-thiobis(2-t-butyl-5-methylphenol) (antioxidant), calcium stearate (antiacid), bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (UV stabilizer) and 2-hydroxy-4-octoxybenzophenone (UV stabilizer).
The composition according to the invention may be obtained by any suitable known means. For example, one method for preparing the composition according to the invention consists in introducing the inorganic pigment and optionally the organic pigment and/or the usual additives as defined above, in the form of a powder mixture into the polyolefin. A preferred alternative method consists in mixing the polyolefin with the inorganic pigment and optionally the organic pigment and/or the usual additives as defined above, at ambient temperature and then mixing them at a temperature above the melting temperature of the polymer, for example in a mechanical mixer or in an extruder.
It is also possible to prepare, in a first step, a masterbatch including a first fraction of the polyolefin, the inorganic pigment and optionally an organic pigment and/or the usual additives as defined above, this masterbatch being rich in inorganic pigment. The inorganic pigment content in this masterbatch is generally from 0.05 to 50 % by weight, preferably from 0.5 to 40 % by weight, more particularly from 1 to 30 % by weight of the mixture. Mixtures containing from 2 to 25 % by weight of inorganic pigment are especially
preferred. This masterbatch is subsequently mixed with the remaining fraction of the polyolefin during the manufacture of granules of the composition.
These methods enable the composition to be obtained in the form of a powder which may optionally be subsequently subjected to granulation to obtain the composition in the form of granules. Granules are obtained in a known manner by extrusion of the composition, the lace leaving the extruder being cut into granules. The granulation process may be performed by feeding an extruder with a previously prepared mixture of a polyolefin with an inorganic pigment (and optionally an organic pigment and/or the usual additives) and by collecting the granules at the exit of the equipment. An alternative form of the granulation process consists in introducing a masterbatch as described above and a second portion of the polyolefin into the extruder.
Preference is given to compositions which are in the form of extruded granules.
The composition according to the invention advantageously has a standard density, measured according to ISO Standard 1183 (1987), of at least 925 kg/m3, in most cases of at least 935 kg/m3, values of at least 938 kg/m3 being the most common ones. The standard density is usually not higher than 965 kg/m3, more especially not higher than 960 kg/m3, values of not more than 955 kg/m3 being recommended.
Furthermore, the composition according to the invention usually has a melt index, measured at 190°C under a 5 kg load according to ISO Standard 1133 (1991) of at least 0.05 g/10 min, in particular of at least 0.1 g/10 min, values of at least 0.2 g/10 min being the most common ones. The melt index generally does not exceed 10 g/10 min, preferably 5 g/10 min, values of not more than 2 g/10 min being recommended.
The composition according to the invention has the advantage that it can be obtained in an extrusion granulation process or can be processed in the form of powder or in the form of granules in a process for
melt-forming articles without giving rise to an abrasion phenomenon as described above. Another advantage of the composition according to the invention lies in its stable colouring, which is not sensitive to thermal degradation or to degradation by UV radiation. In addition, the composition according to the invention requires only a small quantity of organic pigment in order to modulate the colour shade in a precise manner.
The composition according to the invention is suited for being processed by any of the conventional processes for the manufacture of shaped articles made of polyolefin and more particularly by the extrusion, blow-extrusion, extrusion-thermoforming and injection moulding processes. It is suitable for the manufacture of shaped articles such as pipes, films, sheets, receptacles, sacks or sachets. It is particularly suitable for the manufacture of pipes, especially pipes for conveying fluids, for example gases under pressure.
Consequently, the present invention also relates to a process for the manufacture of shaped articles starting from the composition according to the invention, in particular a process using extrusion, especially of pipes for conveying fluids, for example gases under pressure.
The invention also relates to the articles shaped starting from the composition according to the invention, in particular pipes, especially for conveying fluids, for example gases under pressure.
The examples whose description follows are used to illustrate the invention. The meaning of the symbols employed in these examples, the units expressing the quantities measured and the methods for measuring these quantities are detailed below. MI = melt index of the polyolefin or of the
composition, expressed in g/10 min, measured at
190°C under a 5 kg load according to ISO Standard
1133 (1991). SD = Standard density of the polyolefin or of the
composition, expressed in kg/m3, measured
according to ISO Standard 1183 (1987). CI = Colour ("Colour Index") number of a pigment according to the classification developed by the UK Society of Dyers and Colorists (SDC) in collaboration with the US American Association of Textile Chemists and Colourists" (AATCC). D = Mean diameter of the particles of inorganic pigment, expressed in µm, as defined above and measured by laser particle size measurement by means of a Malvern®Msizer 20 instrument. D90 = diameter expressed in µm, characterizing the particles of inorganic pigment so that 90 % of these particles have a diameter smaller than the diameter D90, measured by laser particle size measurement by means of a Malvern®Msizer 20 instrument. D10 = Diameter expressed in µm, characterizing the particles of inorganic pigment so that 10 % of these particles have a diameter smaller than the diameter D10, measured by laser particle size measurement by means of a Malver®Msizer 20 instrument. Example 1(reference)
In this example a polyolefin-based composition was prepared, including titanium dioxide instead of an inorganic compound containing mixed phases. The composition also included an organic pigment and the usual additives.
The following constituents were mixed in a fast mechanical mixer at ambient temperature:
100 parts by weight of the ethylene copolymer
employed in Example 1,
0.15 parts by weight of a UV stabilizer [2-(2'-
hydroxy-3 ' -t-butyl-5 ' -methylphenyl) -5-chlorobenzo-
triazole],
0.15 parts by weight of a UV stabilizer
[bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate],
0.25 parts by weight of an antioxidant stabilizer
[consisting of 50 % of pentaerythrityl tetrakis(3,5-
di-t-butyl-4-hydroxyphenyl propionate) and 50 % of
tris (2,4-di-t-butylphenyl)phosphite],
0.16 parts by weight of an antiacid stabilizer
[calcium stearate],
0.27 parts by weight of an organic pigment which has
a CI "yellow 138", and
0.018 parts by weight of titanium dioxide.
This mixture was extrusion-granulated in a single-screw extruder of Axon BX-18 type containing a hopper and 4 zones, at a temperature of 165, 210, 210, 205 and 185°C respectively. The speed of rotation of the extruder screw was 125 revoiutions/min. The granulation conditions were such that approximately 2 kg of granules per hour were produced. Example 2 (in accordance with the invention)
In this example a polyolefin-based composition was prepared, including an inorganic yellow pigment containing mixed phases of titanium, nickel and antimony oxides, as well as an organic pigment and the usual additives.
The operations of Example 1 were repeated, by mixing:
100 parts by weight of an ethylene copolymer
containing 0.8 mol% of butene and exhibiting an MI
of 0.8 g/10 min and an SD of 943 kg/m3,
0.25 parts by weight of a UV stabilizer [2-hydroxy-
2-4-octoxybenzophenone],
0.15 parts by weight of an antioxidant stabilizer
[4,4'-thiobis(2-t-butyl-5-methylphenol)],
0.16 parts by weight of an antiacid stabilizer
[calcium stearate],
0.10 parts by weight of an organic pigment which has
a CI "yellow 138", and
0.25 parts by weight of a Sicotan® K1011 inorganic
yellow pigment powder containing mixed phases of
titanium, nickel and antimony oxides, containing
47.9 % by weight of titanium, 5.4 % by weight of
antimony and 3.9 % by weight of nickel.
The granules obtained had an MI of 0.85 g/10 min
and an SD of 945 kg/m3.
No abrasion phenomenon was found. Example 3 (reference)
In this example a polyolefin-based composition was prepared, including titanium dioxide instead of an inorganic pigment containing mixed phases. The composition also included an organic pigment and the usual additives.
The operations of Example 1 were repeated by-mixing:
100 parts by weight of ethylene copolymer employed in Example 3,
0.20 parts by weight of a UV stabilizer [2-(2'-hydroxy-3' -t-butyl-5' -methylphenyl) -5-chlorobenzo-triazole],
0.15 parts by weight of a UV stabilizer [bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate], 0.25 parts by weight of an antioxidant [consisting of 50 % of pentaerythrityl tetrakis(3,5-di-t-butyl-4-hydroxyphenyl propionate) and 50 % of tris(2,4-di-t-butylphenyl) phosphite],
0.10 parts by weight of an antiacid stabilizer [calcium stearate],
0.3 0 parts by weight of an organic pigment which has a CI "yellow 183", and
0.03 0 parts by weight of titanium dioxide. Example 4 (in accordance with the invention)
In this example a polyolefin-based composition was prepared, including an inorganic yellow pigment containing mixed phases of titanium, chromium and antimony oxides, as well as an organic pigment and the usual additives.
The operations of Example 1 were repeated by mixing:
100 parts by weight of an ethylene copolymer containing 0.4 mol% of butene and exhibiting an MI of 0.45 g/10 min and an SD of 949 kg/m3, 0.20 parts by weight of a UV stabilizer [a polyester of succinic acid with n-beta-hydroxyethyl-2,2 , 6 , 6-
tetramethyl- 4 -hydroxypiperidine],
0.15 parts by weight of a UV stabilizer [2-(2'-
hydroxy-31 -t-butyl-51 -methylphenyl) -5-chlorobenzo-
triazole],
0.25 parts by weight of an antioxidant [consisting
of 50 % of pentaerythrityl tetrakis(3,5-di-t-butyl-
4-hydroxyphenyl propionate) and 50 % of tris(2,4-di-
t-butylphenyl)phosphite],
0.10 parts by weight of an antiacid stabilizer
[calcium stearate],
0.20 parts by weight of an organic pigment which has
a CI "Yellow 183", and
0.076 parts by weight of a Sicotan® K2011 inorganic
yellow pigment containing mixed phases of titanium,
chromium and antimony oxides, whose particle size
distribution is defined by a mean diameter D of
0.75 µm, a D90 diameter of 9.76 µm and a D10 diameter
of 0.75 µm.
The granules thus obtained had an MI of 0.47 g/10 min and an SD of 953 kg/m3.
No abrasion phenomenon was found. Example 5 (in accordance with the invention)
In this example a polyolefin-based composition was prepared, including an inorganic yellow pigment containing mixed phases of titanium, nickel and antimony oxides, as well as an organic pigment and the usual additives.
The operations of Example 1 were repeated by mixing:
100 parts by weight of an ethylene copolymer
containing 1 mol% of hexene and exhibiting an MI of
1 g/10 min and an SD of 939 kg/m3,
0.25 parts by weight of a UV stabilizer [2-hydroxy-
4-octyloxybenzophenone],
0.15 parts by weight of an antioxidant [4,4'-
thiobis(2-t-butyl-5-methylphenol)],
0.10 parts by weight of an organic pigment which has
a CI "Yellow 138", and
0.25 parts by weight of a Sicotan® K1011 inorganic
yellow pigment containing mixed phases of titanium, nickel and antimony oxides.
The granules obtained had an MI of 0.85 g/10 min and an SD of 943 kg/m3.
No abrasion phenomenon was found.

We Claims:
1. Polyolefin-based pigmented composition wherein it includes, per 100 parts by
weight of polyolefin, from 0.01 to 5 parts by weight of
an inorganic pigment containing mixed phases of oxides of
titanium, antimony and of another metal chosen from the
group containing barium, nickel, chromium and manganese.
2. Composition according to Claim 1,wherein
the other metal is nickel.
3. Composition according to Claim 1 or 2,
wherein the inorganic pigment has a
"rutile" crystal structure.
4. Composition according to any one of Claims 1 to 3,Wherein the inorganic pigment contaxns
from 35 to 60 % by weight of titanium, from 1 to 10 % by weight of antimony and from 1 to 10 % by weight of another metal.
5. Composition according to any one of Claims 1 to
4 ,Wherein the inorganic pigment is yeiiow-
coloured.
6. Composition according to Claim 5,wherein in that the inorganic pigment is chosen from Sicotan commercial yellow pigments.
7. Composition according to any one of Claims 1 to 6, Wherein it additionally includes from 0.01 to 5 parts by weight of an organic pigment per 100 parts by weight of polyolefin.
8. Composition according to any one of Claims 1 to
7,Wherein the polyolefin is chosen from
homopolymers and copolymers of ethylene containing one or
more comonomers exhibiting a standard density (ISO
Standard 1183-1987) of 920 to 960 kg/m3 and a melt index
measured at 190°C under a 5 kg load (ISO Standard
1133 - 1991) of 0.05 to 10 g/10 min.
9.Composition according to Claim 8, wherein
the polyolefin is an ethylene copolymer
containing irom 0.01 to 10 mol% oi comonomer chosen from butene and hexene.
10. Composition according to any one of Claims 1 to

9.Wherein in that it is in the form of extruded
granules.
11. Process for the manufacture of shaped articles
starting from the composition in accordance with any one
of Claims 1 to 10.
12- Process according to Claim 11 wherein
it is applied to the extrusion of pipes intended for conveying gases under pressure.
13, Polyolefin-based pigmented composition substantially
as herein described uith reference to the foregoing examples,
14, Process for the manufacture of shaped articles
substantially as herein described uith reference to the
foregoing examples.