A process for loading porous polymer particles with solid substances is known from the European patent application EP 459 208 A. In EP 459 208 A two different process are described, in which porous polymer particles are loaded so that concentrates are formed. By means of a first process these solid substances are melted to form liquids of a low viscosity and are then absorbed into the porous polymer particle as liquids. By means of a second process the solid substances are mixed with the porous polymer particles in the presence of wetting and/or surfactant auxiliaries, for example paraffin oils and fluid ethoxylated amines, to obtain good absorption of the solid substances into the porous polymer particle.

Drawbacks of these processes are that they are laborious and time-consuming and (especially the second process) involve auxiliaries that are undesirable in the use of the concentrates obtained.

The invention's aim is to provide a process that eliminates the aforementioned drawbacks.

This aim is achieved because the solid substance and the porous polymer particle are mixed in a mixing apparatus in which a vibration field is created which has a frequency f of between 10 and 5000 Hz and an amplitude A of between 0.05 and 100 mm.

The process according to the invention presents the additional advantage that the porous polymer particle can be filled to a great extent because no auxiliaries need to be absorbed into the pores of the porous polymer particle. In addition, a concentrate of very fine particles that flows freely and is substantially free of dust can now be formed in a simple manner. A further advantage of the process of the invention is that porous particles can be obtained that are partly or substantially filled with one or more solid substances that cannot be melted at a temperature below the melting temperature of the porous polymer particle while no use is made of liquid auxiliaries.

A mixing apparatus is an apparatus in which the solid substance and the porous polymer particles can be mixed with one another. The nature of the apparatus is of minor importance, providing a sufficient degree of mixing of porous polymer particles and solid substance can occur. Examples of suitable mixing apparatuses are vibrators, stirred reactors, conical mixers, tube mixers, vibrating conveyors, vessels on roller benches and powder mixers. The mixers known in the state of the art are usually used only for drying solid substances, for mixing two solid substances to form a homogeneous mixture in which the

individual solid substances are still recognisable as two separate substances, or for mixing solid substances with liquids. Without vibration of the porous polymer particles with the solid substances, virtually no loading of the porous polymer particles with the solid substance will occur.

A vibration field is created in the mixing apparatus. This can for example be realised by causing the entire mixing apparatus to vibrate or by installing special vibrating elements for example vibrating rods, vibrating nets or vibrating grids. It is possible that the vibration field is present in only a part of the mixing apparatus.

The porous polymer particles are brought into vibration inside and due to the vibration field of the mixing apparatus. The vibration frequency of the porous polymer particles will be determined by the vibration frequency (f) of the vibration field of the mixing apparatus. For good, efficient loading of the porous polymer particle with solid substance it is important that the vibration field has a correct vibration frequency coupled to a correct amplitude. A low frequency results in very slow loading. Too high a frequency results in inefficient loading. A preferred embodiment of the process is that in which the vibration field has a frequency (f) of between 25 and 1000 Hz.

The porous polymer particles vibrate due to the vibration field at a certain amplitude. This amplitude will generally decrease as the polymer particles become further removed from the vibration

field. A large amplitude may cause mechanical decomposition of the porous polymer particles, too small an amplitude will lead to inefficient loading.

The vibration field will preferably have an amplitude (A) of between 0.1 and 50 mm. In particular, A is between 0.2 and 10 mm.

The loading process can be carried out both batchwise and in continuous mode. Preferably the solid substance and the porous polymer particle are well mixed. It may be necessary to bring about a mixing or stirring movement independently of the vibrating movement, so that any precipitated solid substance can be efficiently absorbed by the porous polymer particle.

This mixing or stirring movement can be carried out simultaneously with the vibrating movement or independently of the vibrating movement, continuously or discontinuously.

The loading will proceed efficiently if a homogeneous distribution of the porous polymer particle and the solid substance is realised in the mixing apparatus with simultaneous vibration at a suitable frequency and amplitude.

Polymers that are suitable for use as a basis for the porous polymer particle to be used in the process according to the invention can be chosen from a wide range of polymers. An example of a suitable polymer is a thermoplastic organic polymer, for example a vinyl-addition polymer or a condensation polymer. The polymers may be homopolymers or copolymers. Examples of suitable polymers are polyacetals, polyamides, polyesters, polyurethanes, polysiloxanes, polyoxiranes,

polydienes, polystyrenes, polymethacrylates, polyvinyl chloride, polyamides and polyolefins for example polyethylene and polypropylene. Preferably the polymer is a polyolefin.

The porous polymer particles to be loaded in the process of the invention usually have a porosity of between 10 and 90 volume% and have an open pore structure. Preferably the porosity is between 30 and 80 volume%. The pore diameter generally varies between 0.01 pm and 100 pm. The average pore diameter and the porosity are determined with the aid of mercury porosimetry using an Autopore II 9220 from Micrometrics (U. S. A). The pressure exerted on the Hg column is then set to be so high that even the smallest pores are filled with Hg. To fill pores of a nanometre-scale size, pressures of up to 500 MPa are usually required.

How to determine pore diameters and porosities by means of mercury porosimetry is described in ASTM standard D4284-83.

Also important is the pores'accessibility.

If the pores are connected to one another by thin channels, loading porous polymer particles with solid particles will be a laborious process, or incomplete loading will take place. If the pores are accessible from one side only, the amount of time required to realise complete loading will be longer.

Whether or not a solid substance can be loaded into a porous polymer particle is partly dependent on the average diameter of the solid substance relative to the porous polymer particle's pore diameter. A solid substance with a relatively

large average diameter for example requires in general a porous polymer particle with a large pore diameter.

Solid substances may derive from several sources. Examples of solid substances are fillers, pigments and additives. Fillers'are understood to be organic and inorganic solid substances, for example mica, carbon black, silica, zeolites, talcum, nanocomposites and carbonates. Pigments'are understood to be organic and inorganic colourants for example titanium oxide, zinc oxide, chromium oxide and phthalocyanides. Additives'are understood to be stabilisers, modifiers, surface-active agents and process-improving agents. Examples of stabilisers are stearates, hydrotalcite and HALS compounds (Hindered Amine Light Stabilisers), benzophenone and benzotriazoles. Examples of modifiers and process- improving agents are peroxides, sulphur, zinc oxide, metal stearates and crystallisation nuclei. Solid substances which are temperature sensitive or instabile or shearsensitive, for example peroxides, can be used very well in the process of the invention.

The solid substances may have all kinds of shapes. Examples of shapes that can be used are beads, small plates, bars or needles, aggregates and agglomerates. Preferably suitable solid substances have a diameter that is smaller than the porous polyolefins'average pore diameter. It is also possible that the solid substances are present in the form of aggregates and agglomerates, which contain tertiairy, secundairy and primary particles. In general, the primary particles have agglomerated into clusters of

secondary particles, which may be grouped together in the form of tertiary particles. The solid substances formed from primary particles may have a diameter that is larger than the porous polymer particle's average pore diameter. During the loading process, aggregates and agglomerates will disintegrate into their primary or secondary particles. The primary or secondary particles will preferably have an average diameter that is smaller than the porous polymer particle's average pore diameter. Preferably use is made of solid particles that contain primary particles that have an average diameter of less than 5 pm. They are quickly absorbed and can fill the porous polymer particle to a higher weight percentage. Particularly preferable are solid particles that contain primary particles having an average diameter of less than 1 pm. The particles' shape is not so important per se. Preferably use is made of particles that can be well stacked, for example round particles or small plates. The solid substance can be loaded in an optimum manner if the solid substance behaves as a pseudo-liquid or as a free- flowing powder.

The average diameter of the solid substances can be determined by means of Malvern laser light scattering, centrifugal sedimentation techniques or, preferably, electron microscopy. A person skilled in the art will in a simple manner be able to determine whether a solid substance is suitable for loading with a porous polymer particle by vibrating this solid substance with the porous polymer particle under the conditions described above.

The amount of time required to fill the porous polymer particles is for example dependent on the amount of solid substance, the size and shape of the solid substance particles, the size of the pores in the porous polymer particle and the accessibility of the pores in the carrier material. The amount of time required will generally vary between a few seconds and an hour.

The temperature at which the vibration is effected is not critical, providing the porous polymer particle and the solid substance remain solid. The temperature is certainly lower than the porous polymer particle's melting or softening temperature. When a polyethylene is used as the porous polymer during the vibration, the temperature is preferably between room temperature and 80 °C.

The process of the present invention is suitable for simultaneously mixing one or more solid substances with porous polymer particles.

In addition to the solid substances, liquids can also be absorbed into the porous polymer particle. This preferably takes place before or most preferably after the absorption of the solid substances. Absorption of liquids after the absorption of solid substances gives the advantage that the solid substance may be separated from air and moisture.

Especially when the solid substance is air and/or moisture sensitive, the absorption of a low melting liquid, for example a wax, is advantageous. The mixing in of liquids can be carried out in the manner described in the state of the art, namely by simply

mixing the porous polymer particle with the liquid.

Examples of liquids that are suitable for absorption are antioxidants (for example phenols, phosphites, thioesters and thioethers), lubricants, antistatic agents (for example waxes, paraffin oils and ethoxylated amines), silicone fluids, plasticisers and blowing agents.

The process of the invention can preferably be applied for forming concentrates by loading porous polymer particles with solid substances that cannot be melted at a temperature below the melting temperature of the porous polymer particle and with the proviso that liquid auxiliaries are absent.

The invention also relates to concentrates obtainable by the process of the invention comprising a porous polymer particle and solid substances, wherein the solid substances can not be melted at a temperature below the melting temperature of the porous polymer particle and with the proviso that liquid auxiliaries are absent.

The concentrates obtainable by the process according to the invention are particularly suitable for being mixed with another polymer. The mixing results in a polymer composition in which the solid substances and any liquids are very homogeneously and uniformly distributed. Suitable processes for mixing in concentrates are known to a person skilled in the art.

Concentrates are very suitable for use especially in an extruder.

The invention will be explained with reference to the following examples, without being

limited thereto.

In the examples use was made of a shaking tube consisting of two glass tubes with a diameter of 2.5 cm which were connected to one another by means of a screwed coupling ring. The ends of the glass tubes were sealed and had round bases. The shaking tube was caused to vibrate with the aid of a vibrator from Chemie Apparatenbau Zurich at a frequency of 100 Hz.

The vibration amplitude was set by means of a control transformer; it amounted to 5 mm.

During the loadingprocess, a small portion of the solid substances ends up on the surface of the porous polymer particle. This solid substance was not loaded into the porous polymer particle and could easily be removed from the polymer. After the loading experiment, the porous polymer particles were therefore sieved through a sieve with a meshwidth of 0.2 mm. The sieve was mounted in a shaking machine (Fritsch). An amplitude of 0.5 mm was used in all the sieving tests, for sieving for 5 minutes. The sieving analyses indicated, apart from the loose particles present at the surface of the concentrate, no loss of these particles from the porous structure.

Example I Approx. % of a vertically arranged first glass tube was filled with 9.3 grams of porous low- density polyethylene (LDPE), Stamypor@, with a particle size distribution of 0.4-1.2 mm and an average pore radius of lym, onto which was introduced a weighed amount of Printex P (carbon black, with a bulk density

of 450 kg/m3, the carbon black consisting of primary particles with a diameter of approx. 0,2 pm which had agglomerated into larger units). After a second glass tube had been coupled to the first by means of the screwed coupling ring, vibration was realised for 15 minutes. After these 15 minutes the carbon black had precipitated to the bottom of the first shaking tube, as a result of which the carbon black and the porous polymer particle were no longer mixed with one another, so no more loading could take place. After a first mixing had taken place, the shaking tube was rotated 180°, so that porous polymer particle and solid substance were again mixed, and vibration was once again effected for 15 minutes. The rotation or inversion of the shaking tube followed by further vibration was carried out three times in total. After sieving, 12.3 grams of concentrate was obtained. This concentrate contained 25 mass% carbon black.

Example II Example I was repeated, using as the porous polymer particle 10.1 grams of Stamypor with a particle size distribution of 0.2-0.4 mm. During the vibration process the carbon black took 1 hour to reach the bottom of the tube. The shaking tube was inverted three times during the vibration, after which the total sample was sieved. 12.7 grams of concentrate was obtained. The product obtained contained 21 mass% carbon black.

Example III Example I was repeated, using 11 grams of Stamypor as the porous polymer particle and zinc oxide (ZnO, NanoX consisting of small plates with an average diameter of 40-70 nm) as the solid substance. It took 7 minutes for the ZnO to precipitate through the porous LDPE during the vibration process.

The shaking tube was inverted, after which vibration was effected for another 7 minutes. This procedure was repeated 3 more times, a new amount of ZnO being added each time. After sieving, 24.6 grams of concentrate was obtained that contained 55 mass% ZnO.

Example IV Example III was repeated, the porous Stamypor being replaced by 7.3 grams of porous Accurel PE granules. The sample was inverted 20 times and each time vibrated for 30 seconds. After sieving, 11 grams of concentrate containing 32.6 mass% ZnO was obtained.

Example V Example III was repeated, the porous Stamypor being replaced by 6 grams of porous Accurel (EP 100, a porous polypropylene). The sample was inverted 3 times and was each time vibrated for 30 seconds. The shrunken volume of solid substance was after each vibration time replenished with fresh ZnO.

This was repeated until the total volume of the solid substance (ZnO) no longer decreased. The sieved sample weighed 21.6 grams and contained 72 mass% ZnO.

Example VI Example I was repeated, using 10.2 grams of Stamypor and Tioxide TC 30 (average particle size 0.19 ) as a filler. The sample was inverted 3 times and each time vibrated for 30 seconds. The shrunken volume was after each vibration session replenished with Tioxide until the total volume no longer decreased.

After sieving, a 22.9 grams concentrate was obtained that contained 55.4 mass% Tioxide.

Example VII Example I was repeated, using 9.9 grams of Stamypor and uncoated calcium carbonate (Hydrocarb, average particle size 0.8 J. m) as a filler. The sample was inverted 3 times and was each time vibrated for 1 minute. The shrunken volume was after each vibration session replenished. After sieving, 19.7 grams of concentrate was obtained that contained 49.8 mass% CaC03.

Example VIII Example I was repeated, using 9.6 grams of Stamypor and coated calcium carbonate (Superflex 200, average particle size 0.8 pm) as a filler. After sieving, 14.2 grams of concentrate was obtained that contained 32.8 mass% CaC03.