WO2018007948A1

WO2018007948A1 - Method for manufacturing of granular fillers using a granular nuclei, producing device and granulate obtained by this method

Info

Publication number: WO2018007948A1
Application number: PCT/IB2017/054034
Authority: WO
Inventors: Michal GORA
Original assignee: Polcalc Sp. Z O.O.
Priority date: 2016-07-04
Filing date: 2017-07-04
Publication date: 2018-01-11
Also published as: EP3478401A1

Abstract

The invention relates to a vibrating table for use in the method for manufacturing of granulate from calcium carbonate meal, magnesium carbonate meal or a mixture thereof comprising tabletop equipped with vibration means and connected to the support with shock- absorbing means, characterized in that the tabletop comprises sections parallel to each other forming a cascade over which the granular material in a form of a mixture of the meal and the microgranulate formed therefrom is moved, wherein each of the sections are independently inclined by 10-25% relative to the support and equipped with scraping means for removing the meal from section of the cascade and breaking up the granules, and a sprinkler delivering the granulation liquid in a form of droplets. Disclosed herein is also a method for manufacturing of granulate from calcium carbonate meal, magnesium carbonate meal or a mixture thereof, the granulate obtained by this method and use of this granulate as a filler for plastics.

Description

METHOD FOR MANUFACTURING OF GRANULAR FILLERS USING A GRANULAR NUCLEI PRODUCING DEVICE AND GRANULATE OBTAINED BY THIS

METHOD

FIELD OF THE INVENTION

The invention relates to a device for the manufacture of granular nuclei used in a method for manufacturing of granular fillers, a method for manufacturing of granular fillers for use in the chemical industry, in particular the plastics industry, the food, metallurgical, construction and other industries, in which the use of the obtained filler will be advantageous, as well as the granular filler obtained by this method. The device of the invention can also be used in the manufacture of granulated lime fertilizer.

STATE OF THE ART

Granulation methods in disc, agitating, drum or vibration granulators are known. Polish patent application P.410130 discloses a two-step granulation method during which the calcium carbonate starting material or its mixture with calcium sulfate is pre-granulated in an agitating granulator, wherein the material is homogenized and the granulation nuclei are formed, followed by proper granulation in a disc granulator in which the granulate achieves its final spherical shape with an appropriate diameter. In both of these steps, granulation liquid may be added which is preferably different in the first and second granulation steps.

US Pat. No. 4015973 B l discloses a method for obtaining granulate from raw material with a high content of calcium and/or magnesium and bentonite, which also acts as a binder. The raw material is continuously introduced and mixed in a pulverizer, such as a cage mill. Part of the homogeneous mixture is recycled through the cage mill and the rest is transferred to a granulator where it undergoes granulation using water as a granulating agent.

Patent PL197599 describes a method for manufacturing of magnesium and calcium containing granulated fertilizer from raw materials containing magnesium and calcium carbonates or oxides, especially dolomite, which raw materials are degraded using sulfuric acid. The resulting mass is then granulated in a drum granulator and dried, in a subsequent step the granulate is subjected to granular segregation, and the undersized grains are then directed to regranulation. Granulation processes are important in the production of mineral fertilizers. The main fertilizing agent is Jurassic or Cretaceous limestone, as well as magnesium carbonates and mixtures of magnesium carbonate and calcium carbonate, so called magnesites and dolomites. These rocks are currently processed in various ways for fertilizing purposes. Most are subjected to crushing process and subsequent grinding. There are many different grinding installations and many varieties of mills. However, the sieving parameters of the product obtained by grinding are important. Most limestone rocks are milled to a size of less than 2 mm. Due to its moisture content (less than 0.3% of water in the mass) a large part of limestone meals is not suitable for use with standard agricultural spreaders and therefore they are subjected to further treatment consisting in agglomeration of particles into fertilizing granulate with granules size from 2 mm to 10 mm. Such granulation is most often accomplished using disc granulators in a wet granulation process. The essence of such granulation is efficient production of granulate of the desired fraction and without the presence of a dusty fraction.

Frequently, to obtain a stable and suitably hard granulate, binders are added which prevent the granulate from disintegration. In the field of fertilizer granulation, normally a binder such as molasses or cellulose derivatives is used, which can optimize bulk density and particle size distribution in granulation, as well as facilitate the formation of granules. Such binders, however, increase the cost of fertilizer production and hinder the production process by extending it.

So far, granulated fertilizing substances based on calcium carbonate or magnesium carbonate had sieving parameters in the range of less than 300 μιη, optionally less than 100 μιη. Thus, they were characterized by a rather large grain size. In the case of granulating calcium carbonate in the form of limestone meal with a grain size in the range of 120-300 μιη, during granulation of grains with such size, the grain itself is the nucleus for the forming granule. However, the commonly used meal has the disadvantage that the grain size is heterogeneous, leading to the formation of granules of heterogeneous granules size.

In the field there are also known fillers made from mineral materials such as calcium carbonate, magnesium carbonate, silicon or talc. These are dusty substances that are used in the manufacture of various products, such as plastics, glass, food products, paints and hygiene products. The use of fillers in the dusty form in the manufacturing process results in a complicated and troublesome process of dosing these substances. The main inconveniences associated with these substances are their dusty form causing dustiness, lack of uniformity in the dosing process and clogging of dosing devices, which in turn results in discontinuation of the production process. Fillers reduce production costs, but their use affects qualitive parameters of the product, so there is a need in the field for fillers characterized with a good degree of dispersion, that would be easy to transport, dosing and that have the least negative impact on the quality of the obtained product.

DISCLOSURE OF THE INVENTION

So far the methods of granulating calcium carbonate meal, magnesium carbonate meal or mixtures thereof with a grain size of less than 40 μιη have not been disclosed. Basically this type of starting material was considered unsuitable for granulation. The present invention solves the problem of granulating the calcium carbonate meal, magnesium carbonate meal or a mixture thereof, wherein the particle size is less than 40 μιη, more preferably less than 10 μιη, even more preferably less than 4 μιη and most preferably less than 2 μιη, by using 3 -step granulation in which granulate with uniform grain size distribution in the range of 2-4 mm is produced.

The invention relates to a vibrating table for use in a method of producing calcium carbonate meal, magnesium carbonate meal or a mixture thereof, comprising a tabletop equipped with vibration means connected to the support by shock-absorbing means, wherein the tabletop comprises sections parallel to each other, each of them independently inclined by 10 - 25% relative to the support, forming together a cascade upon which the granular material in the form of a mixture of the meal and the microgranulate formed therefrom is moved. The table is also equipped with overhead scraping means for removing the meal from the cascade section and breaking the granules, and a sprinkler delivering the granulation liquid in a form of droplets.

Preferably, the table according to the invention comprises a support in the form of a beam. Equally preferably, the shock- absorbing means connecting the tabletop to the support consists of springs and a motor acts as the vibrating means. In a preferred embodiment, each cascade section is inclined at the same angle to the support. Preferably, the scraping means comprise a pin or paddle scraper and are driven by a gearmotor.

The invention also provides a method for manufacturing of granulate from calcium carbonate meal, magnesium carbonate meal or a mixture thereof comprising the following steps:

(a) dosing the material in the form of meal with a grain size of less than 40 μιη by means of a screw feeder into a paddle conditioner in which it is sprayed with a granulation liquid at a pressure in the range oi l - 9 bar, preferably 8 bar, and mixed at a speed of 700 - 900 rpm, preferably 800 rpm, to produce a microgranulate,

(b) introducing the granulated material in the microgranulate form obtained in step (a) together with the remaining non-granulated meal onto the vibrating table defined in claim 1 driven by an engine running at a speed of 900 - 1600 rpm, where the granulated material is sprinkled with droplets of granulation liquid supplied from the sprinkler, and under gravity moves between individual sections of the cascade with concurrent bouncing of said material in the opposite direction resulting from table vibration and scraping of said material with scraping means operating in the spiral arrangement with simultaneous breaking of the oversized granules, resulting in the granulate mass increase and hardening, wherein the granulate nuclei of 2-4 mm are obtained;

(c) introducing the granulate nuclei obtained in step (b) together with residues of the non-granulated meal into the disc granulator, where it is wet-ground with the granulation liquid to form the target granulate with increased mechanical stability and even size of granules.

In a preferred embodiment, limestone meal, magnesite meal or a mixture thereof having a grain size of less than 40 μιη, more preferably less than 10 μιη, more preferably less than 4 μιη, most preferably less than 2 μιη, is used as the starting material for granulation.

In one embodiment, the granulation liquid used in the method of the invention is water. In an alternative embodiment, the granulation liquid is water with added binder. The binder is preferably selected from the group consisting of paraffin, montan, polyethylene, polypropylene waxes, fatty acids and their salts, esters and amides, and molasses and cellulose derivatives, or mixtures thereof. Also preferably dispersion facilitating substances are added to the water in the amount of 1-5% by weight. In a particular embodiment, the binder added to the granulation liquid is paraffin.

The invention further relates to the granulate having a granule size in the range of 2-4 mm from limestone meal, magnesite meal or a mixture thereof with grain size of less than 40 μιη obtained by the method of the invention and the use of said granulate as a filler, especially as a filler for plastics.

The advantage of the present invention is that it enables the granulation of limestone meal with a homogeneous grain size distribution of 40 μιη, and obtaining the desired granulate fraction with granules size in the range of 2 - 4 mm in the amount of 80 - 98% by weight of the total granulate.

Due to the fact that the resulting granulate is made of such fine meal, it is suitable for use as a filler in many industries, in particular as a filler for plastics from which thin films and foils are made, for example. The filler made from fine meal has the advantage of uniformly dispersing in the plastic providing equal qualitative properties. For use in plastics, the filler is preferably granulated in the presence of a substance facilitating its dispersion, such as an external lubricant, for example paraffin, montan, polyethylene and polypropylene waxes, and/or internal lubricant, for example fatty acids and their salts, esters and amides. More preferably, the substances facilitating dispersion are added in the amount of 5% by weight, more preferably 2% by weight, most preferably 1% by weight. Lubricants affect the improvement of processing properties of polymers, such as viscosity and adhesion of melt, limit mechanical degradation of polymers, facilitate melting of polymers, increase plasticity and gliding of articles, have antistatic properties and improve color and impact strength, so adding them to the filler in the granulate form is preferable.

BRIEF DESCRIPTION OF FIGURES

Figure 1 is a schematic diagram of a vibrating table according to the invention equipped with scraping means

Figure 2 is a schematic diagram of scraping means equipped with pins with which the vibration table cascade section is equipped.

Figure 3 is a schematic diagram of the production line where the method for manufacturing granulate according to the invention is used.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides means for granulating very fine meal of calcium carbonate, magnesium carbonate or mixtures thereof. The term "fine meal" refers to dusts which grains have size less than 40 μιη, more preferably less than 10 μιη, more preferably less than 4 μιη, most preferably less than 2 μιη. As used herein, the terms "calcium carbonate meal" and "limestone meal" and "magnesium carbonate meal" and "magnesite meal" are used interchangeably and refer to the material obtained from the milling of natural minerals, e.g. limestone. According to the invention, a vibrating table 8 for granulation of fine calcium carbonate meal, magnesium carbonate meal or mixtures thereof has been developed, incorporation of which into the granulation process including standard granulation techniques results in a stable and suitably hard granulate having homogeneous grain size distribution in the range of 2-4 mm. The vibrating table 8 is shown in Fig. 1. It comprises a tabletop 81 connected to the support 82, preferably in the form of a beam, by means of shock- absorbing means 82, which preferably consist of springs. The worktop is equipped with vibration means 84, which preferably consist of a motor that operates at a speed of 900 - 1600 rpm and it vibrates the tabletop 81. The tabletop 81 comprises sections 85 parallel to each other and forming a cascade over which the granular material in a form of a mixture of the meal and the microgranulate formed therefrom is moved, wherein each of the sections 85 is independently inclined by 10-25% relative to the support 82. Preferably, the tabletop 81 of the table according to the present invention is divided into four cascaded sections 85, each of which has a square shaped surface. Also preferably, all sections 85 are inclined at the same angle with respect to the support.

An important element of the vibrating table 8 are the scraping means 86, which preferably consist of a pin or paddle scraper mounted over each section 85 of the cascade. Scraper pins 861 or paddles are directed perpendicularly to the surface of the section 85 of the cascade. The scheme of the preferred pin scraper is shown schematically in Fig. 2. The scraper is operating in a spiral arrangement and in the preferred embodiment it is driven by the gearmotor 862. The scraping means 86 move around their own axis at a speed of 60 rpm. scraping the supplied granulate and dusty material for granulation and break up oversized granules.

Each section 85 of the tabletop 81 of the table 8 is additionally equipped with an overhead sprinkler 87 which supplies the granulation liquid to the surface of the section in a form of droplets. Thanks to the granulation liquid droplets provided by the sprinkler 87, the granulation process is initiated. In one embodiment, the granulation liquid is water. In an alternative embodiment, the granulation liquid is water with addition of binder, preferably paraffin. More preferably, the granulation liquid is a dispersion of a binder, preferably paraffin, in water. Other binders such as external lubricant, for example, paraffin, montan, polyethylene and polypropylene waxes, and/or internal lubricant, for example fatty acids and their salts, esters and amides, may also be used. Preferably, the binder is added in the amount of 5% by weight, more preferably 2% by weight, most preferably 1% by weight. According to the invention, the process for the manufacturing of granulate from calcium carbonate meal, magnesium carbonate meal or a mixture thereof comprises the following three steps: (1) producing microgranulate in a paddle conditioner 6, (2) treating the granulate on a vibrating table 8 to form granulate nuclei; and (3) treating the granulate nuclei obtained in the second step in disc granulator 10 to form the target granulate.

In the first step of the method according to the invention, the material in the meal form, having a grain size of less than 40 μιη, more preferably less than 10 μιη, more preferably less than 4 μιη, most preferably less than 2 μιη, is fed with a screw feeder 5 into a paddle conditioner 6 in which it is sprayed with a granulation liquid at a pressure in the range of 7 - 9 bar, preferably 8 bar, and mixed at 700 - 900 rpm, preferably 800 rpm, to produce microgranulate that is transferred to the vibrating table 8.

In the second step, the microgranulate and residues of the non-granulated meal are treated on a vibrating table 8 described above, which is set into vibration with a motor working at a speed in the range of 900 - 1600 rpm, preferably at a speed in the range of 1000 - 1500 rpm, more preferably at a speed in the range of 1100 - 1200 rpm. The treated material is sprayed with droplets of granulation liquid supplied from the sprinkler 87. In a preferred embodiment, the granulation liquid is water. In an alternative embodiment, the granulation liquid is water with addition of binder, preferably paraffin. The microgranulate moves under gravity between individual sections 85 of the cascade of the vibrating table 8. As a result of vibrations it is bounced and moved in the opposite direction. At the same time the treated material is scraped with scraping means 86, preferably a pin or paddle scraper, operating in a spiral arrangement. Scraping removes the excess of unbound meal and the oversized granules are broken down. As a result of the treatment on the vibrating table 8, the granulate mass increases and hardens to produce granulate nuclei with a size of 2-4 mm which are fed to the disc granulator.

In the final step of the method according to the invention, the granulate nuclei material obtained by treatment on a vibrating table with the residues of the non-granulated meal are transferred to a disc granulator 10 where it is wet-ground with a granulation liquid, preferably water or alternatively with water with an addition of a binder, more preferably paraffin, to form target granulate with increased mechanical stability and an even size of granules. The method according to the invention is carried out as part of the process carried out on the installation shown in Fig. 3. In this process, limestone meal, magnesite meal or a mixture thereof with sieving parameters of less than 40 μιη, more preferably 10 μιη, more preferably less than 4 μιη, most preferably less than 2 μιη, is pneumatically loaded to a silo 1 with capacity of 100 tons. Then, with the aid of a screw feeder 2, the meal enters a buffer 3 of an exemplary capacity of 3 tons where by means of gravity and with a cell sluice 4 it is fed to a screw feeder 5 wherein stretching of the material to ensure uniform dosing takes place.

Subsequently, the material is transferred to a paddle conditioner 6 operating at 800 rpm, where it is sprayed with granulation liquid fed at 8 bar by sprinklers 7 and mixed. In this phase, the microgranulate is formed, which, along with the dusty fraction, goes to the cascading vibrating table 8, where the granulation process is initiated.

The cascading vibrating table 8 of the invention is a rectangular 250 x 60 cm table comprising a tabletop 81 which comprises four cascaded sections 85 parallel to each other. The tabletop 81 is connected to the support 82 by the shock-absorbing means 83 in the form of springs. Each section 85 is inclined by 25% relative to the support 82. The tabletop 8 is equipped with vibration means 84, preferably consisting of a vibration motor operating at 900 - 1600 rpm. Table 8 is equipped with scraping means 86 consisting of a pin scraper operating in a spiral arrangement and driven by a gearmotor 862. The scraping means 86 in the form of a pin scraper are provided with pins, wherein over each cascade section 85 a pin scraper is mounted with pins 861 directed perpendicularly to the surface of the cascade section 85 over which it is located. The scraper moves around its own axis at a speed of 60 rpm, and with the pins it scrapes the material on the cascade sections 85 in the form of a mixture of microgranulate and granulation meal, while breaking oversized granules at the same time.

The granulation on the vibrating table is initiated by droplets of the granulation liquid supplied from sprinklers 87 located in equal distances over the cascade sections 85. Under the influence of vibration that acts in the opposite direction to gravity, and water, the granulate mass increases, hardens, and gains quite even sizes of granules, most of which have a size of 2-4 mm. These granules serve as the granulation nuclei in the next step of the process.

Meal residues and the obtained granulate nuclei are then transferred by means of a belt conveyor 9 to a disc granulator 10 in which they are subjected to a wet grinding process, which significantly increases their mechanical strength, leveling the granules leading to obtaining the target granulate. This step allows also to get rid of dust.

The next steps of the process are standard steps. The material from the disc granulator 10 is introduced into a fluid bed dryer 11 and then to a cooler 12. At this step of the process, a dust collector 13 which removes residual dust is used. The granulate then goes to a separator where the target fraction of 2-4 mm, which is as much as 85 to 98% by weight of the total granulate obtained in the present process, is separated from the oversized and undersized grain by using 5 mm and 3 mm sieves (14, 15). The remaining fractions are grinded in the mill 16 and recycled to the disc granulator for regranulation. The target fraction goes to the bucket conveyor 17, which transfers it to the feed hopper 18 where it is packaged for transport using the big-bag loading station 19.

EXAMPLE 2

In this example, the granulation process was carried out as described in Example 1 using water as a granulation liquid. Limestone meal with sieving parameters below 40 μιη (sample A), below 10 μιη (sample B), below 4 μιη (sample C) and below 2 μιη (sample D) was used as starting material.

As a result of this process, granules of appropriate hardness were obtained, with the desired fraction having a granule size in the range of 2-4 mm, constituting 85-98% by weight of the total granulate obtained in the present embodiment.

The table below shows the percentage content of the desired fraction of the pellets for each of the samples:

Sample Content of granules fraction

having the size of 2-4 mm

A 98% by weight

B 95% by weight

C 88% by weight

D 85% by weight EXAMPLE 3

In this example, the granulation process was carried out as in Example 2, however, a mixture of limestone and magnesite meal with sieving parameters of less than 10 μιη was used as the starting material.

As a result of this process granules of appropriate hardness were obtained, the desired fraction having a granule size in the range of 2 - 4 mm constituted as much as 87% by weight of the total granulate obtained in the present embodiment.

EXAMPLE 4

In this example, the granulation process was carried out as in Example 2, however, water with addition of paraffin in the amount of 1% by weight (sample A), 2% by weight (sample B) and 5% by weight (sample C) was used as the granulation liquid.

As a result of this process, granules of appropriate hardness were obtained, with the desired fraction having a granule size in the range of 2-4 mm, constituting 93-97% by weight of the total granulate obtained in the present embodiment.

The table below shows the percentage content of the desired granule fraction for each of the samples:

COMPARATIVE EXAMPLE

In this example, the granulation process was carried out as described in Example 1, except that the microgranulate from the conditioner was placed directly in the disc granulator (i.e., the step of treating the material on the vibrating table was omitted). Water was used as the granulation liquid and limestone meal with sieving parameters of less than 40 μιη (sample A), less than 10 μιη (sample B), less than 4 μιη (sample C) and less than 2 μιη (sample D) was used as the starting material. As a result of this process, granulate was obtained in which the desired fraction of granules in the range of 2-4 mm was only 25-45% by weight of the total granulate obtained in the present embodiment.

INDEX

(1) Silo

(2) Screw feeder

(3) Buffer

(4) Cell sluice

(5) Paddle conditioner

(6) Sprinklers

(7) Vibrating table

(81) Tabletop

(82) Support

(83) Shock- absorbing means

(84) Vibration means

(85) Sections

(86) Scraping means

(861) A pin or a paddle of the scraper

(862) Gearmotor

(87) Sprinkler

(8) Belt conveyor

(9) Disc granulator

(10) Fluid bed dryer

(11) Cooler

(12) Dust collector (14, 15) Sieves

(16) Mill

(17) Bucket feeder

(18) Feed hopper

(19) Big-bag loading station

Claims

PATENT CLAIMS

1. A vibrating table (8) for use in the method for manufacturing of granulate from calcium carbonate meal, magnesium carbonate meal or a mixture thereof, comprising a tabletop (81) equipped with vibration means (84) and connected to the support (82) with shock-absorbing means (83), characterized in that the tabletop (81) comprises sections (85) parallel to each other, forming a cascade over which the granular material in a form of a mixture of the meal and the microgranulate formed therefrom is moved, wherein each of the sections (85) is independently inclined by 10-25% relative to the support (82) and equipped with scraping means (86) for removing the meal from the section (85) of the cascade and breaking up the granules, and a sprinkler (87) delivering the granulation liquid in a form of droplets.

2. The table according to claim 1, characterized in that the support (82) consist of a beam.

3. The table according to claim 1 or 2, characterized in that the shock-absorbing means (83) consists of springs.

4. The table according to any of claims 1-3, characterized in that the vibration means (84) consist of a motor.

5. The table according to any of claims 1-4, characterized in that each of the sections (85) of the cascade are inclined at the same angle with respect to the support (82).

6. The table according to any of claims 1-5, characterized in that the scraping means (86) consist of a pin or paddle scraper.

7. The table according to any of claims 1-6, characterized in that the scraping means (86) are driven with a gearmotor (88).

8. A method for manufacturing of granulate from calcium carbonate meal, magnesium carbonate meal or a mixture thereof comprising the following steps:

(a) dosing the material in the form of meal with a grain size of less than 40 μιη by means of a screw feeder (5) into a paddle conditioner (6), in which it is sprayed with a granulation liquid at a pressure in the range of 7 - 9 bar and mixed at a speed of 700 - 900 rpm to produce a microgranulate,

(b) introducing the granulated material in the microgranulate form obtained in step (a) together with the remaining non-granulated meal onto the vibrating table (8) defined in claim 1 driven by an engine running at a speed of 900 - 1600 rpm, where the granulated material is sprinkled with droplets of granulation liquid supplied from the sprinkler (87), and under gravity moves between individual sections (85) of the cascade, with concurrent bouncing of said material in the opposite direction resulting from table (8) vibration and scraping of said material with scraping means (86) operating in the spiral arrangement with simultaneous breaking of the oversized granules, resulting in the granulate mass increase and hardening, wherein the granulate nuclei of 1-4 mm are obtained;

(c) introducing the granulate nuclei obtained in step (b) together with residues of the non-granulated meal into the disc granulator (10), where it is wet-ground with the granulation liquid to form the target granulate with increased mechanical stability and even size of granules.

9. The method according to claim 8, characterized in that limestone meal, magnesite meal or a mixture thereof having a grain size of less than 10 μιη, more preferably less than 4 μιη, most preferably less than 2 μιη, is used for granulation.

10. The method according to claim 8 or 9, characterized in that the granulation liquid in step (a) is fed at the pressure of 8 bar.

11. The method according to any of claims 8-10, characterized in that the material in step (a) is mixed at the speed of 800 rpm.

12. The method according to any of claims 8-11, characterized in that the granulation liquid is water.

13. The method according to any of claims 8-11, characterized in that the granulation liquid is water with the addition of a binder.

14. The method according to claim 13, characterized in that the binder is preferably selected from the group consisting of paraffin, montan, polyethylene, polypropylene waxes, fatty acids and their salts, esters and amides, and molasses and cellulose derivatives, or mixtures thereof.

15. The method according to claim 14, characterized in that the binder is molasses.

16. The method according to claim 13-15, characterized in that the binder is added to the granulation liquid in the amount of 1 - 5% by weight.

17. The granulate manufactured from limestone meal, magnesite meal or a mixture thereof with the grain size of less than 40 μιη obtained by the method defined in claims 8-16.

18. Use of the granulate defined in claim 17 as a filler for plastics.