DE2226287B2 - Process for the production and molding of a mixture of thermoplastics and solid fillers - Google Patents

Description

The invention relates to a method of manufacture and forming a mixture of thermoplastics and solid fillers, in which the optionally preheated thermoplastic material and heated to a temperature above the melting point of the thermoplastic heated fillers, the heat content of which melts the Plastic is sufficient to be mixed together and the hot mixture is molded.

It is known to produce artificial stones in that a mixture of a large amount of finely divided stones with the liquid prepolymer or monomer a thermosetting resin such as a saturated polyester resin, epoxy resin or melamine resin, hot pressed or a similar mixture in which finely divided stone material, for example by shaking, uniformly distributed, heated and cured, or by adding the liquid prepolymer or monomer in Gaps between finely divided stone material are poured and the mass is then hardened. It is also known, synthetic wood or chipboard by connecting wood powder or wood particles with a Manufacture phenolic resin.

In these common processes for the production of artificial stone and synthetic wood, the hardening of the thermosetting resin through polymerization a considerable time and the introduction of the to be molded Material into a metal mold and the removal of the molded products require a significant amount of work. An even more serious disadvantage of this method is that the slightest error when introducing and Hardening the mass to be molded traps air bubbles or cracks during hardening, surface defects forms, shrinks or warps, so that standardized products are very difficult to obtain.

Attempts have been made to use this method for the mass production of artificial stone and synthetic wood, by using thermoplastics instead of thermosetting resins and in a screw press processed. However, no satisfactory results have been obtained in this way.

A thermoplastic material that can be used for this purpose

^r ) 0

Plastic material is generally in the form of powder or pellets and will never mix well enough with a substantial amount of an organic or inorganic filler to provide useful products by simple hot pressing. In addition, a molding machine loaded with such a mixture often fails after a short time and in any case does not deliver a product of higher quality Filler just a mediocre product with no good structure. If a more finely divided stone material is used, the degree of mixing of the plastic with the filler is somewhat improved, but the penetration of the plastic into the interstices of the stone powder remains uneven, and a product with a fine structure and evenly distributed filler cannot be obtained. The same applies when using other types of plastics.

When such a mass to be molded is put into an ordinary screw press, its out Metal existing cylinder and mold are well heated, the machine is overloaded and eats itself in a short time Time fixed because the filler has no lubricating effect and the plastic does not melt enough. Around To solve the problem, attempts have been made to separate the plastic pellets and the filler Heat and mix the preheating vessel and then feed the mixture to the screw press. if however, in this case the preheating temperature is lower than the softening point of the plastic the screw press overloaded in the same way. However, if the preheating temperature is at the melting point of the Plastic, the pellets melt together if they are stirred a little in the preheating vessel, and it is difficult for the material to flow into the screw press. When it is pushed into this, it sticks to the Screw between the filling zone and the compression zone, which means that the machine runs empty and does not is working. Only if the preheating temperature is slightly higher than the plastic's softening point is selected, the screw press works for a certain time, but then the squeezed out Quantities gradually decrease until finally the plastic has melted onto the screw and with it the Operation of the screw press becomes completely impossible. So in none of these cases you get satisfactory results.

According to an older proposal (DE-PS 21 21 424), which, among other things, a method of the aforementioned Kind regards, the excess of the during mixing does not adhere to the grains of the inorganic Separated filler sintered plastic powder before molding the object. This is supposed to a good bond between filler and plastic and high strength of the end product can be achieved. The grains with a grain size of 5 to 10 mm, coated on all sides with plastic, are pourable and can be molded while still warm without pressure. However, through such a process, fine-grained Fillers are evenly and thinly coated with plastic and no fittings, especially those of smaller dimensions, can be obtained from masses with a high proportion of fine-grained fillers.

From GB-PS 9 19 490 a method of the type specified for the production of

Mixtures for road surfaces known, which od from 90-99% by weight of a filler such as sand. Like. And 1 to 10% by weight of a thermoplastic linear polyolefin as a binder having a softening point of at least 49 ° C, with the filler heated to 149-260 ° C and then the Polymer is added solid or melted, or vice versa, and mixed in a heavy kneader will. The filler bonded in this way can be applied while still hot as a road surface or as a road boundary be extpjdiert. This method is not suitable for the production of molded parts by extrusion in the sense of plastics technology, and it also leads due to the low proportion of binder, not to moldings with sufficient mechanical bending and Breaking strength and smooth surface.

On the basis of this prior art, a heat-moldable mixture of thermoplastic Plastic and solid fillers are produced in which the filler particles are so in the thermoplastic Plastic are involved that from the mixture, optionally in one operation, molded parts with high strength, uniform structure and smooth surface can be produced.

According to the invention, this object is achieved with a 2s The method of the type specified at the outset is achieved in that the fillers in a volume related to 0.5 to! ^ times the amount of the thermoplastic Plastic are present and the melting of the plastic under the action of the heated fillers j » done by kneading the mixture.

The mixture is preferably kneaded and shaped in one operation.

The method of the invention is low cost and with a variety of molding machines such as ^ Screw presses, injection molding machines and calendering rolls, which are connected to kneading drums and interact with them, feasible and can also operated continuously.

The molded parts obtained by the process according to the invention show high, uniform strength Structure and smooth surface and are therefore suitable for a variety of uses, especially as artificial stones and synthetic wood for building purposes, also in the form of extruded profiles.

Polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyamide, acrylic styrene can be used as plastics (AS plastics), acrylic butadiene styrene (ABS plastics) and other thermoplastics with a relatively high heat resistance and a low melt viscosity can be selected.

Examples of organic fillers are various wood chips, usually from 1 mm to in size 10 μm, like sawdust, although not limited to it. The water content of the filler should not be more than 10%, so that the development of air and Steam bubbles when kneading the filler into the plastic is avoided. Examples of inorganic Fillers are limestone, granite, andesite and other stones, all in finely divided form, as well as calcium carbonate. Silica, clay, asbestos, plaster of paris, alumina, cement and glass in granular or powder form.

In the process according to the invention, other conventional additives, such as dyes, Pigments or stabilizers, if necessary, use 1.5 will. In particular, an organic filler can be mixed with a suitable dispersing agent or lubricant such as a surfactant, wax, lead stearate or a thermosetting agent Resin, for example epoxy resin or unsaturated polyester resin, to ensure the intimate mixing of the filler to improve with the thermoplastic material.

It is essential for the method according to the invention that in a based on the volume 0.5 to 1.5 times the amount of the organic or inorganic filler present in the thermoplastic material, which is preheated to a temperature 71 before mixing. the 50 to 200 ° C above the temperature 7i of the thermoplastic material is so that the The heat content of the heated filler is sufficient to melt the plastic when mixed with the Knead plastic, causing the melting of the plastic under the action of the heated Fillers takes place

It is obvious that to carry out this process T _{2 must} not be lower than the melting point of the plastic under the process conditions and that the mixing ratio of plastic and filler, based on the real volume, must be chosen so that the heat from the filler is let out is released to the plastic at a temperature which is not significantly higher than the decomposition point of the plastic. On the other hand, when using an organic filler, e.g. B. sawdust from 1 mm to 10 μιτι size, when setting 7Ί and T> take into account that the filler carbonized at temperatures of about 200 ° C or above. It is advisable, but not always necessary, to preheat the thermoplastic material to around its softening point in order to effectively utilize the heat content of the filler.

The ratio of thermoplastic to added plastic, based on the real thing Volume should be between 1: 0.5 and 1: 1.5, since the filler volume is less than 50% of the plastic volume the properties desired from such a mixture made of artificial stones or artificial wood would not have, while with more than 150% filler volume the melted plastic with the Filler cannot be intimately mixed and the malleability of the kneaded mixture is reduced is.

To explain the invention, an embodiment using a screw press is shown below described.

Thermoplastic pellets and filler granules are among those given above Conditions preheated and lightly mixed together before being fed into the screw press will. The preheated fillers melt on the surface and the somewhat softened plastic pellets something penetrate into them so that the surface of each pellet is completely covered with filler. These Pellets are then fed to the feed area of the extruder mixed with the remaining filler and conveyed into the compression zone, only the filler contained in the mixture itself with the Comes into contact with the surfaces of the machine parts. The filler particles penetrate into the compression zone into the plastic pellets and give off their heat, making the entire mixture at once gets into the melting state and is kneaded well. This mixture then enters the melting zone of the extruder and becomes a uniform melt that is pressed out of the mouthpiece. at

With this method, the press cylinder should only be heated at the start of operation of the machine, as in further operation, the heat given off by the filler itself and that by kneading the filler with the Frictional heat given off by plastic is sufficient The -> surfaces de? Cylinder can by means of a Fan or the like are cooled. Under such conditions, the plastic can adhere to the The surface of the screw does not stick, and there can be no reduction in the extruded quantities of Enter mixed. In addition, the extruder barrel heated as required when the heat given off by the organic filler is less than that given off by an inorganic filler.

Regarding the process conditions, it should be mentioned that of the 3 temperatures, namely the screw, the Plastic and the barrel, the temperature of the screw, except in the filling area, than the highest temperature, the next lowest that of the plastic and the lowest that of the cylinder is held. The screw temperature is higher than the others because it is due to the preheated filler and the frictional heat decreases and the screw itself has little heat dissipation. It is generally said that that plastics adhere to highly heated metals, but this only applies if you use the Metal surface coming into contact with plastic is considered. In fact, the one with very heated Plastics that come into contact with metals have a low viscosity, whereas those with low-temperature plastics have a low viscosity Metals come into contact with a high Vif -cosity. So when the twisting or shearing force is effective, the surfaces of the screw have little frictional resistance and that of the cylinder has high frictional resistance, which is an ideal condition for there is sufficient propulsion of the mixture.

The method according to the invention can, however, not only be used with screw presses, but also with others shaping machines are carried out.

For example, with a kneading machine using the prescribed amounts of plastic and filler, which have been preheated to the temperature Ti or Ti , the melting point Tm of the plastic is selected to be somewhat higher than in the case of an extruder. when the kneading machine is preheated to a temperature slightly above Tm , a uniform, molten mixture is obtained in a short time.

Further, when a roller mixer was used for the same purpose, the prescribed ones became Amounts of plastic and filler after pretreatment similar to that in the above case Kneading machine mixed slightly so that each plastic pellet was coated with the filler. in this case The first stage of kneading could be done on the roller in a short time because the plastic was on the surfaces of the rollers began to adhere only after it had absorbed the heat of the filler and was mixed to a considerable extent in molten form, while the sticking that otherwise occurs of the plastic on the rollers at the beginning of the kneading could be avoided.

According to the method according to the invention from a thermoplastic and an organic Filler, such as wood powder, made molded b5 Products were as strong as ordinary wood and could be sawn like this, screwed and nailed. However, for technical reasons, the products received are right different from ordinary synthetic wood, which is made from thermoplastics due to low foaming is produced as high density foam.

According to the method according to the invention, the most varied of thermoplastic products Plastics made in conjunction with an inorganic filler instead of an organic filler will. For example, products made from the combination of polyethylene and limestone are useful as Floor panels, while those made of styrene and finely divided limestone are used as hard artificial stones for manufacturing and cladding of walls or furnishings. Another example are Polypropylene and calcium carbonate products which are designed as panels with appropriate rigidity and flexibility recommended.

The invention is further illustrated by the following examples, in which the starting mixtures and process conditions are indicated.

example 1

A. Molding Process Conditions

1. Composition of the mixture:

Plastic 1: 100 parts by weight blown high-pressure polyethylene, finely divided, with some content of pigments. Real specific weight: 0.95.

Filler I: 100 parts by weight of cedarwood seeds

flour. Real specific weight: 0.80.

(Volume ratio of plastic I to filler I

about 1: 1.2.)

2. Preheating temperatures:
Plastic I: 90 ⁰ C
Filler I: 160 ^° C

3. Features of the extruder used:
Cylinder diameter: 70 mm

L / D of the cylinder = 20
Compression ratio: 1:22
The cylinder has vertical grooves on the inner walls in the filling area in order to increase the feed exerted by the machine on the mixture being filled.
Temperatures: Filling area: 130 ⁰ C

Compression range: 170 ° C
Melting range: 170 ^° C
Mouthpiece: 200 ⁰ C

The screw is equipped with a heater.
Extruder mouthpiece: With a rectangular outlet opening 150 mm wide and 20 mm high.

B. Performing the molding process

The starting products, plastic I and, preheated to the temperatures given above under 2. Filler I, were easily mixed in a drum and fed to the preheated feed hopper of the extruder, whereupon the extruder was switched on. After about 5 minutes, the metal mouthpiece on the The outlet of the extruder was a sheet of uniform composition, 20 mm thick and 150 mm Width, according to the dimensions of the mouthpiece, extruded. The plate was then covered with a heated calender roll is compressed and gradually

lent chilled. It was obtained continuously in this way a synthetic wood with an even structure and smooth surface.

The extruder die had a rectangular outlet opening 150 mm wide and 5 mm Height.

25th

Example 2

A. Molding Procedure Requirements

1. Composition of the mixture:

Plastic II: 100 parts by weight blown polystyrene, finely divided. True specific gravity 1.05.

Filler II: 80 parts by weight of finely divided sapwood particles. Real specific Weight 0.8.

2. Preheating temperatures:
Plastic II: 100 ° C
Filler II: 250 ° C

3. Features of the kneading drum used:
Diameter: 300 mm
Temperatures: 160 ° C on the front roller

150 ° C on the rear roller
Roll ratio of the front roller to the rear roller: 1: 1.3.

B. Performing the molding process

Plastic II and filler II were mixed gently by tumbling and fed to the roller. First the nip between the two rollers was kept at only 2 mm and the mixture fed to the roller was collected in the collecting container. After the mixture was put on the roller about 2 times, it remained completely on the rollers. The gap between the rollers was then enlarged to about 5 mm, and repeated repeating of the compound gave a plastic mixture with a uniform structure, a certain amount of which was poured into a ^{metal mold preheated to about 170 °} C. and pressed in it and cooled immediately. The product obtained was tough and of the desired shape with very attractive surfaces and a fine structure.

Example 3 _Ai

A. Molding Process Conditions

1. Composition of the starting mixture:
Plastic III: 100 parts by weight of low-pressure polyethylene pellets. Specific gravity 0.95, specific heat 0.55; Softening point 120 ° C.

Filler III: 200 parts by weight of finely divided limestones with an average Grain size of 0.5 mm; specific gravity 2.7; specific Heat 0.2.

2. Preheating temperatures:
Plastic III: 90 ⁰ C
Filler III: about 90 ° C

3. Features of the extruder used:
Cylinder diameter: 70 mm
L / D of the cylinder = 20
Compression ratio: 1: 1.7
Temperatures: Filling area: 140 ⁰ C

Compression range: 160 ⁰ C
Melting range: 170 ^° C
Mouthpiece: 180 ° C

B. Performing the molding process

The extruder was operated at 20 rpm and a melt emerged from the mouthpiece 3 minutes after the start of operation. The melt then became a uniform mixture, and stable operation of the molding machine could be continued for about 10 minutes. During operation were the temperatures of the compression zone and melting zone at 150 ⁰ C and 160 ⁰ C reduced υπJ repeated with a fan cooled. The number of revolutions of the machine was increased to 28 and the power consumption of the motor was kept at 22 A. A melt of uniform quality was obtained at a throughput of 1 kg / min., Ie 60 kg / hour. extruded. After cooling, the melt was passed through a calender roll and produced an artificial stone with smooth surfaces and the desired strength and flexibility.

Example 4
A. Molding Process Conditions

1. Composition of the starting mixture:
Plastic IV: 100 parts by weight of styrene resin GP-

Pellets; specific weight: 1.05; specific heat 0.4; Softening point 100 ⁰ C.

Filler IV: 300 parts by weight of finely divided limestone with an average Grain size of 0.5 mm; specific gravity 2.7; specific heat 0.2.

2. Preheating conditions:
Plastic IV: U0 ° C
Filler IV: about 193 ° C

3. There was used a kneader which was equipped with a ölheizmantel and heated to 170 ⁰ C.

B. Performing the molding process

Plastic IV and filler IV were preheated in separate vessels, then removed from these and placed in a metal vessel. After they had been mixed somewhat by tumbling in the vessel with the lid on, the entire mixture was fed to the kneader. A melt with a uniform structure was obtained in about 2 minutes. Part of the melt was then placed in a ^{metal vessel preheated to 150 °} C. and immediately cooled under pressure, resulting in a very beautiful artificial stone with high hardness

Example 5

This example shows the influence of the two comparisons {, 5 under otherwise identical conditions Temperature to which the filler is heated before being mixed in, in order to achieve optimal properties of the molded product.

A. Molding Process Conditions

1. Composition of the starting mixture:
Plastic V: 100 parts by weight blow-molded high-pressure polyethylene, ground to a grain size of about 4 mm; specific gravity 0.92; specific heat 0.55; Melting point (Tm) 110 ⁰ C.

Filler V: 200 parts by weight of fine granite powder with an average Grain size of 0.5 mm; specific gravity 2.7; specific heat 0.19.

2. Preheating conditions: r, plastic V: "23 ° C

Filler V: as indicated in the following table.

3. Features of the extruder used:
Cylinder diameter: 70 mm L / D of the cylinder: 20
Compression ratio: 1: 2.2
Temperatures: Filling area: 130 ⁰ C

Compression range: 170 ⁰ C
Melting range: 170 ^° C

Mouthpiece: 200 ° C

The extruder die had a rectangular outlet opening 150 mm wide and 10 mm Height.

B. Performing the molding process

The plastic and the filler, which had the temperatures given in the following table, were gently mixed with one another by tumbling in a vessel, and the mixture obtained was then mixed with one another was fed to the inlet hopper of the extruder.

Table I.

attempt

Preheating temperatures ( ¹¹ C)

Plastic filler V fabric V

Result

45

23 50 no technical extrusion

possible because the extruder
immediately after the start of the
Extrusion seizes

Attempt pre-worm temperature result
No. ratures (C)

Plastic filler V fabric V

21 23 150 insufficient mixing;

the extruded product
has a rough surface

23 23 250 good mixing;

the extruded product
has an even, smooth surface

It turns out that if the filler is insufficiently preheated (test no. 19), extrusion is impossible. and experiment 21 does not yet provide a fully satisfactory product, since only the filler, but not the Plastic has been preheated and thereby the heat content of the filler for good melting was not enough when kneading. Experiment no. 23 gave an optimal product, since the preheating temperature of the Filler was sufficient to heat the plastic above its melting point when kneading.

The surprising improvements in the product properties obtained by the process according to the invention result even more clearly from the mechanical values given in Table II below Test values.

Table II

Attempt no.
19 21

Compressive strength, N / mm ²
Tensile strength, N / mm ²
Strain, %

Flexural strength, N / mm ²
Bend, mm
Charpy impact resistance,
Rev / m ²

SLO 19-20 39 S7 10-12 19th <0.4 0.6-0.9 1.5 S9 15-20 32 S0.4 1.0-1.5 3.55 S0.8 1.6-2.1 4.10

50 comments:

1. The test results for specimens nos. 19 and 21 are scattered considerable.

2. The numerical values of product 23 are the mean values from tests on 5 samples.

Claims (2)

Patent claims: 1. A process for the manufacture and molding of a mixture of thermoplastics and solid fillers, in which the optionally preheated thermoplastic and the fillers heated to a temperature above the melting point of the thermoplastic material, whose heat content is sufficient to melt the plastic are mixed together and the hot mixture is molded, characterized in that the fillers in one on the volume based on 0.5 to 1.5 times the amount of thermoplastic material and that Melting of the plastic under the action of the heated fillers by kneading the mixture he follows. 2. The method according to claim 1, characterized in that the mixture in one operation is kneaded and shaped.