WO1991001349A1

WO1991001349A1 - Process for the production of a filler for pvc moulding materials, the use of the filler produced by this process and pvc moulding materials containing the filler produced by this process

Info

Publication number: WO1991001349A1
Application number: PCT/EP1990/001176
Authority: WO
Inventors: Franz Wirsching; Rolf HÜLLER; Albert W. PÜRZER; Michael Rosenthal
Original assignee: Robaco Chemie Handelsgesellschaft Mbh; Gypsum Research, S.A.
Priority date: 1989-07-19
Filing date: 1990-07-18
Publication date: 1991-02-07
Also published as: EP0483193A1

Abstract

The invention concerns a process for the production of a filler, based on an hydrous calcium sulphate II, for PVC moulding materials in which finely divided calcium sulphate dihydrate is moistened with a dilute dessicating acid and the mixture subjected to heat treatment at elevated temperatures, viz: either (a) the mixture is heated at temperatures of 50-190 °C and the acid remaining in the product obtained is neutralized with an alkali metal carbonate or alkaline earth carbonate, distilling off the water which is still present or which forms, plus the carbon dioxide which forms: or (b) the mixture is heated in a counter-current of hot gas to temperatures of over 350 °C, then cooled, separated by sieving from all particles greater than 90 νm, preferably greater than 63 νm, in diameter and, optionally, ground.

Description

Process for the production of a filler for PVC

Molding compositions, use of the filler thus produced and PVC mold mass containing the filler thus produced.

description

The present invention relates to a method for producing a filler based on

Calcium sulfate anhydrite II for PVC molding compounds

Use of a filler so produced for

PVC molding compounds and a PVC molding compound containing one produced by the process according to the invention

Filler.

In order to be suitable as a filler for PVC molding compositions, this must meet a number of requirements, both with regard to the incorporation into the PVC molding compositions and with regard to the properties of the

Molding compositions produced moldings, such as

Thermostability, brightness and electrical

Characteristics. The known fillers for both hard and soft PVC molding compounds are fine-particle

Calcium carbonate is considered well suited and wide

widely used.

DE-AS 1 18S 281 describes the use of

Calcium sulfate, which has been produced by an annealing process by prolonged heating to about 300 ° C, is known as a filler for PVC molding compositions. It will

indicated that the water-binding anhydrite stage destroyed by such an annealing process and that

Calcium sulfate is "burnt to death". However, it has

shown that one in such an annealing process

Calcium sulfate produced is still active, i.e.

contains water-binding components, so that the water or thermal stability of a PVC molding compound filled with it is deteriorated in such a way that for practice

there are unacceptable products. Furthermore, with such an annealing process, coarse and hard particles are formed, which require considerable effort have to be refined in order to be suitable as a filler for PVC molding compounds.

It is known that calcium sulfate dihydrate is first dewatered by heating in a dry form to give β-calcium sulfate hemihydrate, which loses the rest of its water of crystallization when heated further and thereby

Calcium sulfate anhydrite is transferred. With this

The first step is calcium sulfate anhydrite III

(Soluble calcium sulfate), which is largely the

Has retained the crystal structure of the calcium sulfate hemihydrate. It is therefore able to be relatively easy

rehydrate and in a known manner to

Calcium sulfate dihydrate. Calcium sulfate anhydrite

III is therefore a relatively quickly setting with water

Form of calcium sulfate. When heated further, calcium sulfate anhydrite II (insoluble calcium sulfate) is formed, which is relatively stable against water.

EP-A-0 237 802 describes a method for

Preparation of calcium sulfate anhydrite and settable calcium sulfates by reacting calcium sulfate dihydrate with a dehydrating acid at temperatures of 50 to 130 ° C and optionally subsequent

Neutralization with calcium hydroxide. It is mentioned in this publication quite generally that a product obtained by this process can be used as a filler, for example for plastics. However, studies have shown that the calcium sulfate anhydrites obtained by this process, i.e. both not

neutralized as well as those with calcium hydroxide

neutralized, are not suitable as a filler for PVC molding compounds. On the one hand, the use of non-neutralized anhydrite as a filler for PVC leads to a deterioration in the stability of the PVC molding, obviously due to an acid-catalyzed degradation of the PVC by the residual acid contained in the anhydrite.

On the other hand, when using a with

Calcium hydroxide neutralized anhydrite in the

PVC moldings observed undesirable discoloration, which cannot be tolerated in particular in the case of hard PVC moldings, for example for window profiles.

Completely surprisingly, however, it has now been shown that these disadvantages can be overcome and are ideal

suitable filler based on calcium sulfate anhydrite II for PVC molding compositions can be obtained by a process in which finely divided calcium sulfate dihydrate is moistened with a dehydrating, dilute acid and the mixture is subjected to a heat treatment at elevated temperatures

Undergoes temperature, whereby one

ent neither

(a) the mixture of heat treatment at temperatures

from 50 to 190 ° C. and the acid remaining in the product obtained is neutralized with an alkali and / or alkaline earth metal carbonate by subtracting the water which is still present or being formed and the carbon dioxide which is formed or

(b) the mixture in countercurrent with hot gas

Heated above 350 ° C, then cooled, sieved from all particles with a diameter of over 90 microns, preferably over 63 microns, and optionally milled.

By means of the method according to the invention, a filler for PVC molding compositions with high purity and with high

Preserve whiteness. If in embodiment (a) in the after

When the product obtained is heated, the remaining acid is not neutralized with an alkali and / or alkaline earth carbonate and water still present or formed is not removed from the mixture, the product obtained

Filler does not have the required whiteness. This can be explained by the fact that in the mixture

varying amounts of coloring ions, in particular

Iron ions. If a neutral to alkaline medium is now formed during the neutralization, the iron present hydrolyzes to stable iron oxyahydrates, which are colored yellowish or red-brown. So colored

However, fillers are unsuitable for use in PVC molding compounds. By means of the method according to the invention, however, fillers with excellent brightness values are obtained which are comparable and in some cases better than the brightness values of the calcium carbonates usually used as fillers. This can result in considerable savings in pigmentation of the

PVC molding compounds, for example in the case of soft PVC for the production of light-colored cables, can be achieved.

Studies have shown that in the process according to the invention, even with a quantity of acid below 0.5% by weight, a very slow drainage to anhydrite II

takes place, but the conversion is very slow. It is therefore preferable to work with a minimum concentration of 1% by weight of acid. Furthermore, it has been shown that amounts of acid of more than 7 wt .-% due to

necessary separation or neutralization question the economics of the process.

Amounts of acid are therefore preferred. up to 3 wt .-% used. Preferably the

Total liquid content of the mixture less than 20 % By weight, particularly preferably between 7 and 14% by weight. Higher fluid levels can increase

lead to undesired sticking and clumping.

Humidity levels lower than 5% by weight are technically less suitable for the process.

Particularly suitable as a dehydrating acid

Sulfuric acid, phosphoric acid or a mixture thereof. In particular when using sulfuric acid, a fine, crystalline and stable anhydrite II is obtained which is excellent as a filler for PVC molding compositions

Has properties.

The heating in the method according to the invention in embodiment (a) is advantageously carried out by direct firing or by rapid heating by means of indirect heat exchangers with a relatively high level

Wall temperatures, whereby the calcium sulfate dihydrate heats up to temperatures of 80 to 190 ° C and thereby releases both the adhering water from the dilute acid and 2 moles of water of crystallization. That through direct

Firing or rapid heating received

Calcium sulfate anhydrite II, however, tends to

Rehydration. However, this undesirable reactivity can be completely eliminated if the product is annealed for 0.3 to 24 hours at temperatures of 80 to 190 ° C before neutralization, whereby an extremely stable, water-insensitive calcium sulfate anhydrite II is obtained. Preferably, the annealing

continuously in a container that can be filled from above, from which the tempered end product is at the bottom

is removed. The product is filled into this container while it is still hot. Here is the

Stabilization process depending on the time

Temperature and acidity. Will at low Temperatures, e.g. 80 to 110 ° C annealed, require longer annealing times, preferably 2.5 to 24 hours. If the temperature is between 150 and 190 ° C, times between 0.3 and 0.8 hours are sufficient.

The process is preferably carried out in the range from 130 to 150 ° C, with an annealing time of about 0.5 to 2 hours being sufficient.

The tempering can also take place in the same apparatus in which the conversion of the

Calcium sulfate dihydrate was made in anhydrite.

This is particularly useful in rotary kilns, which can then be designed accordingly for this purpose.

The method according to the invention can be carried out directly

Firing, for example in a rotary kiln, a flash dryer, a spin dryer or one

Cyclone firing unit. Direct firing can take place, for example, by burning natural gas, light heating oil, heavy heating oil or heavy oil.

When carrying out the process with indirect heat supply, for example plate or floor dryers,

indirectly heated rotary kilns, cookers or indirectly heated trough dryers with spiral guides can be used. Indirect heating can be done with hot gases, steam or

Heat transfer oils are carried out.

In embodiment (b), the heating takes place

also advantageously in a directly or indirectly fired countercurrent rotary kiln, for example by burning natural gas or heating oil. Heavy heating oil or heavy oil can also be used, since at the high temperatures of the hot gases there is no fear that soot or unburned organic residues will get into the End product.

A particular advantage of the process according to the invention is that the moist, finely divided that is obtained in large quantities as the starting material

Calcium sulfate dihydrate from flue gas desulfurization (flue gas gypsum) can be used. The process according to the invention can thus also be carried out in such a way that parts of the hot gases of an incineration plant with flue gas desulfurization plant are used for heating the calcium sulfate dihydrate and the exhaust gases are subsequently used in the desulfurization plant (in the case of

Use of sulfuric acid as dehydrating acid) can be supplied. It is therefore possible that

To carry out the method according to the invention in a particularly economical manner directly where flue gas gypsum is obtained. Form from the flue gas gypsum

Process according to the invention according to embodiment (a) loose anhydrite agglomerates made from very fine crystalline

Primary particles that can be distributed with only a small grinding effort, particle sizes of less than 5 μm, preferably less than 2 μm, of the upper grain size being available.

In embodiment (a) of the process according to the invention, the neutralization takes place by intimately mixing the still hot mixture obtained after the heating and optionally after the tempering with finely divided,

dry alkali and / or alkaline earth carbonate. Yet

Existing or forming water must be used

be subtracted, which can be carried out in an advantageous manner by applying a slight negative pressure. Carbonic acid that forms during the neutralization reaction is also removed at the same time.

Calcium carbonate is preferably used for the neutralization used because there may be excess

Calcium carbonate when used as a filler for

PVC molding compounds have no disruptive influences.

In embodiment (b) of the invention

The process not only evaporates the adhering water and water of crystallization, but also all of the diluted acid and removes it from the product. It is therefore generally no longer necessary to wash out or neutralize the remaining acid. Instead, it is removed from the product with the cooled hot gases. It is therefore expedient to use these exhaust gases,

especially in the case of using sulfuric acid as a dehydrating acid, in a

Control flue gas desulfurization plant in which the

Sulfuric acid can be converted into flue gas gypsum.

If traces of acid still interfere with the use of the filler, it is possible in embodiment (b) after heating, but before cooling, up to about 1% by weight of alkali and / or alkaline earth carbonate, preferably calcium carbonate or Limestone flour to be added. A homogeneous mixing and neutralization of the traces of acid then takes place in the subsequent process steps of sieving and optionally grinding.

In embodiment (b) it is essential to heat the mixture to temperatures above 350 ° C because this is the only way to ensure that practically all of the dilute acid is removed from the mixture. Furthermore, in this embodiment it is important to cool the product thus obtained, using heat if possible

Heat exchangers can be recovered and recycled. With the recovered heat, for example Combustion air preheated and thus the amount of heat is largely returned to the process.

Another essential step in embodiment (b) is sieving, in which all particles over 90 µm, preferably over 63 µm, are removed. Such screening is possible because all the acid and adhering water have already been removed and the product is therefore not sticky and moist. Sieving makes it possible to remove disturbing and coloring impurities from the end product. While the crystals are made of pure

Flue gas gypsum in embodiment (b) merge into a fine, crystalline, rhombic anhydrite II, which disintegrates into particles smaller than 63 .mu.m even with low mechanical stress, the grain size of coloring and disruptive impurities remains unchanged.

These are especially silicate

Impurities that also interfere with the subsequent grinding due to their mechanical hardness, but also contribute to a poorer degree of whiteness. The degree of whiteness is further increased by the fact that among the

Process conditions according to embodiment (b), all organic substances and flue gas coke present in the flue gas are oxidized and thus removed from the end product.

If necessary, the cooled and sieved product obtained in embodiment (b) can be dry-milled in order to obtain a high-quality filler of a desired grain size.

The embodiment (b) of the method according to the invention offers the advantage that flue gas gypsum of various qualities and purity levels can be used as the starting material, since it is possible to use the disruptive ones Remove contaminants, such as fly coke or fly ash. This was certainly not foreseeable, since it is known that such contaminants are built into the flue gas plaster and can normally only be removed from it again by recrystallization. In the method according to the invention, these impurities are burned, oxidized or mechanically by sieving from the

End product removed.

In a preferred embodiment of the method according to the invention, a masking agent or precipitant for egg ions is added. In embodiment (a), the addition is preferably carried out at the time of neutralization. Suitable masking agents are the agents typically used for this purpose, for example

Phosphates such as alkali and / or

E rdalkali-Hexametaphospate. The addition of such masking agents reliably prevents unwanted discoloration due to the presence of iron ions.

In a further preferred embodiment of the

the filler obtained is coated. The coating is preferably as

Dry coating is carried out, for example directly after the neutralization and / or during the

Grinding of the filler formed. For example, fatty acids and are suitable as coating agents

Fatty acid metal salts, for example calcium stearates. With such a coating the stability of the

obtained filler increased and the

Spreadability of the filler in the PVC molding compounds improved.

The invention is illustrated by the examples below explained in more detail.

Example 1 and Comparative Example 1

An uncoated filler produced according to the invention and, for comparison purposes, one for PVC in the trade

available CaCO ₃ filler were in a

PVC pipe formulation used in the composition shown in Table 1 below.

Table 1

Components Example 1 Comp. Ex. 1

(Parts by weight) (parts by weight)

S-PVC-K 68 ¹ ) 100.0 100.0

Bäropan SMS 305 2) 1.7 1.7 invention. acc. produced filler 5.0 -

Omyalite 95 T3) - 5.0

1)

Made by suspension polymerization,

medium-molecular, powdery vinyl chloride homopolymer; K value 68

2)

Stabilizer / lubricant compound (more basic

Pb complex stabilizer) for pipe extrusion;

Manufacturer: Bärlocher GmbH

3)

Microcrystalline calcium carbonate (champagne chalk, surface-treated, of natural origin; sales: Omya GmbH

Furs were made from the above recipes on a laboratory rolling mill. The roller temperature was 190 ° Rolling time 5 min. The rolled skins were subjected to a thermal stability test in accordance with DIN VDE 0472, part 614, at 200 ° C. It has been shown that both test specimens with a thermal stability of 12 min. have identical thermal stability.

The static thermal stability, tested in an oven at 180 ° C, sample ejection every 15 min., Gave identical color behavior and a thermal break after approx. 80 min in both test specimens. (Brown / black discoloration).

The theological behavior of the invention

prepared filler and the comparative filler were mixed with the processing formulations mentioned above in a kneading chamber with a chamber volume of 30 cm,

Sample weight 37 g, kneader temperature 180ºC and a speed of 60 rpm tested (Brabender Plasti-Corder). The sample with the filler produced according to the invention showed an approx. 25%. Longer gel time compared to the comparison sample with calcium carbonate. At the

Example according to the invention, the force recordings, measured after 3, 6 and 10 min., were approximately 4-6% lower than in the comparative example. The mass temperatures were about 1 ° C lower in the example according to the invention.

These results show that when using the

filler produced according to the invention in

H a rt -PVC -M i nc h e n ts the processing masses are less stressed and continue to be less

Machine wear is expected. In other words, this means that in this case a longer service life for screws and cylinders of the processing machines is achieved. Example 2 and Comparative Examples 2 and 3

A filler made according to the invention and, for comparison purposes, commercially available for PVC

CaCO ₃ fillers were used in a PVC cable jacket recipe in the composition shown in Table 2 below.

Table 2

Components Example 2 Comp. Ex. 2 Comp. Ex. 3

(Parts by weight) (parts by weight) (parts by weight)

S-PVC-K 70 ¹ ) 100.0 100.0 100.0

DIDP Chairman /

0.2% Bisp.A ² ) 55.0 55.0 55.0

Bäropan TX 770 ³ ) 3.0 3.0 3.0

Filler 80.0 - -

Omya EXH 1 ⁴⁾ - 80.0 - M icromya ⁵⁾ - - 80.0

1) prepared by suspension polymerization

medium molecular, powdery

Vinyl chloride homopolymer; K value 70 2)

Plasticizer, di-iso-decyl phthalate, pre-stabilized, Hexaplas MDS; Manufacturer: ICI

3)

Stabilizer / lubricant compound (basic Pb complex stabilizer or for cable extrusion;

Manufacturer: Bärlocher GmbH

4)

Microcrystalline calcium carbonate, surface treated, of natural origin; Distribution:

Omya GmbH

5) Microcrystalline calcium carbonate, not

surface-treated, of natural origin;

Sales: Omya GmbH Furs were produced from the above recipes on a laboratory rolling mill. The roll temperature was 180 ° C, the rolling time 5 minutes. The rolled skins were subjected to a thermal stability test in accordance with DIN VDE 0472, part 614

Subjected to 200 ° C. It has been shown here that the sample with the uncoated according to the invention

Filler a thermal stability of 90 min. compared to 89 min. for the non-surface treated and 98 min. for the surface treated calcium carbonate.

The static thermal stability, tested in an oven at 200ºC and one. Sampling every 10 minutes gave a significantly lighter and whiter initial color for the example according to the invention. The old 3 test specimens thermally stopped after approx. 90 min. Due to the lighter initial color that when using the invention

produced filler can be achieved, significant pigment savings for the large

Achieve the use of light cables. Examples 3 and 4 and Comparative Examples 4 and 5

An uncoated filler prepared according to the invention and, for comparison purposes, a CaCO ₃ filler available for PVC in the trade were used in a PVC window profile formulation of the composition shown in Table 3 below. T a b le 3

Components Example 3 Comp. Ex. 4 Example 4 Comp. Ex. 5

(Parts by weight) (parts by weight) (parts by weight) (parts by weight)

S-PVC-K 68 ¹⁾ 93.0 93.0 93.0 93.0 Bärodur EST 3 ²⁾ 7.0 7.0 7.0 7.0

Kronoε CL 220 ³⁾ 4.0 4.0 4.0 4.0

Bärorapid 10 F ⁴⁾ 0.5 0.5 1.0 1.0

Bεropan VPF 893 ⁵⁾ 3.4 3.4 - -

Bäropan MC 5060 FP ⁶⁾ - - 4.3 4.3

Bar CWM 201 ⁷⁾ 0.2 0.2 - - manufactured

Filler 6.0 - 6.0 -

Hydrocarb 95T ⁸ ) - 6.0 - 6.0

¹⁾ See explanation for Table 1 2 ⁾ Impact toughener for PVC based on multiple phases

Polyacrylate; Sales: Bärlocher GmbH 3 ⁾ white pigment, titanium dioxide, post-treated rutile pigment;

Manufacturer: Kronos Titan GmbH 4 ⁾ Processing aids based on poly methacrylate with high molecular weight;

Sales: Bärlocher GmbH Ca-Zn stabilizer-lubricant compound: Manufacturer:

Bärlocher GmbH

6) stabilizer / lubricant compound based on Pb-Ea-Cd; Manufacturer: Bärlocher GmbH

7) organic phosphite to improve the

Thermostability and color rendering;

Manufacturer: Bärlocher GmbH

8) surface-treated calcium carbonate,

Uronic limestone; Sales: Omya GmbH

Furs were made from the above recipes on a laboratory rolling mill. The roll temperature was 180 ° C, the rolling time 5 minutes. The rolled skins were subjected to an oven test at 200 ° C. to test the static thermal stability,

Samples are ejected every 5 minutes.

It has been shown here that in Comparative Example 4 and Example 3 according to the invention no significant

Differences in thermal stability behavior occurred. The stability drop was about 35 min.

Also in the comparison example was 5 and the

Example 4 according to the invention shows no significant difference in the thermal stability. The

Stability loss was about 55 minutes.

Press plates were also used for the purpose of color measurement

manufactured. For this purpose, the rolled skins, as described above, were folded twice while still hot and placed in a press preheated to 190.degree. The total press time was 60 seconds. The color measurement on the press plates produced in this way, based on the CIE-LAB DIN 6174 method, gave the following evaluations: Example 3 according to the invention showed that

Comparative example 4 in the color difference measurement

(Standard illuminant D 65/10) the following values:

Total color difference Delta E * 0.78

Brightness difference Delta L ⁺ - 0.58 darker

Red / basic difference delta a * 0.32 redder

Yellow / blue difference Delta b * 0.4 yellow

The results show that there are no significant color differences.

The comparison of the inventive example 4 with the comparative example 5 resulted in the following measured values:

Total color difference Delta E * 1.25

Frequency difference Delta L * - 0.48 darker

Red / green difference Delta a * 0.19 redder

B tau / getdifference delta b * - 1.14 bluer

The results show that although the brightness of the case according to the invention is somewhat lower, a much more blue coloring is achieved. However, a bluish tint is usually desirable for window profits, which is why, in addition, for optical protection

Blueing agents are used. Thus, at

Use of the filler produced according to the invention

Achieve savings on bluing agent.

Claims

Patent claims

1. Process for the production of a filler for

PVC molding compounds based on calcium sulfate anhydrite II, in which, finely divided calcium sulfate dihydrate is moistened with a dehydrating, dilute, acid and the mixture is subjected to heat treatment at an elevated temperature, either

(a) subjecting the mixture to heat treatment at temperatures of 50 to 190 ° C and the acid remaining in the product obtained with an alkali and / or Heating takes place by means of indirect heat exchangers with relatively high wall temperatures.

7. The method according to any one of claims 1 to 6,

characterized in that in embodiment (a) an annealing is carried out at temperatures of 80 to 190 ° C for 0.3 to 24 hours before neutralization.

8. The method according to any one of claims 1 to 7,

characterized in that in the embodiment

(a) Calcium carbonate used for neutralization.

9. The method according to any one of claims 1 to 5,

characterized in that in the embodiment

(b) the power is carried out in a directly or indirectly fired countercurrent rotary kiln.

10. The method according to any one of claims 1 to 9,

characterized in that the waste gases resulting from the heat treatment are passed into a flue gas desulfurization plant.

11. The method according to any one of claims 1 to 10,

characterized in that the filler obtained

is coated.

12. The method according to claim 11, characterized in that fatty acids and / or as coating agents

Fatty acid metal salts used.

13. Use of the filler for PVC molding compositions produced by the process according to claims 1 to 12.

14. PVC molding composition containing a filler prepared by the process according to claims 1 to 12. Alkaline earth carbonate neutralized by pulling off the still existing or bilge water as well as the carbonic acid that forms

(b) heating the mixture in countercurrent with heating gas to temperatures above 350 ° C, then cooling, by sieving old particles with a. Diameter over 90 microns, preferably over 63 microns, freed and optionally milled.

2. Procedure na er. Claim 1, characterized in that the dehydrating dilute acid is used in an amount of less than 20% by weight, preferably 7 to 17% by weight, the acid content being 0.5 to 7% by weight, preferably 1 to 3% by weight, based on the total mixture.

3. The method according to claim 1 and / or 2, characterized

characterized in that as a dehydrating acid

Sulfuric acid, phosphoric acid or a mixture thereof is used.

4. The method according to any one of claims 1 to 3,

characterized in that smoke gypsum plaster is used as calcium sulfate dihydrate.

5. Method according to one of claims 1 to 4,

characterized in that during the process, a fogging or precipitation for iron ions is carried out

adds.

6. The method according to one of claims 1 to 5,

characterized in that in the embodiment

(a) warming by direct heating or by rapid