SK278418B6 - Magnesium hydroxide, in the form of fine powder, manufacturing process and application thereof and plastic material containing its - Google Patents

Abstract

Magnesium hydroxide, in the form of fine powder, suitable as a filling agent for plastic materials having a capability to prevent ignition, containing particles or a thin coating material closed to the surface active agent, while the article size measured based on the laser rays diffraction,is less than 10 micrometers, the average size is greater than 0,8 micrometers and the content of ion type water soluble impurities is described by the following values when talking about the weight parts: Ca++ less than 1 000 ppm, Na+ less than 20 ppm, K+ less than 20 ppm, SO4- less than 1 500 ppm, Cl- less than 1000 ppm and the content of Mn, Cu and Ni closed to the values in the weight parts is as follows: MnO less than 100 ppm and CuO less than 10 ppm. The production of this material is based on that principle, that magnesium oxide gained as a result of hydropyrolysis of magnesium chloride solution, while the foreign substances are removed, is mixed with water, when a hydration is passing and the created magnesium hydroxide is removed with use of filtration, however the filter cake is being washed with the use of water containing no salts, and then this cake is dried.

Description

Technical field

The invention relates to finely powdered magnesium hydroxide, which is particularly suitable as a non-flammable filler for plastics, the particles of which are optionally provided with a thin coating of surfactant.

BACKGROUND OF THE INVENTION

Fine-powdered magnesium hydroxide is often used as a non-flammable filler in plastics, in particular based on thermoplastics. In this case, relatively large amounts of this substance are added so that the weight of the magnesium hydroxide is half to twice the weight of the conventional mass. However, finely powdered types of magnesium hydroxide may have a negative effect on the mechanical properties of said compositions. In particular, there is a tendency to water uptake, a decrease in tensile strength and a faster aging of these materials.

Often the workability of these plastics as well as the surface appearance of the products are adversely affected, in particular depending on the grain size of the magnesium hydroxide and its water content.

In German Pat. No. 2,624,065 discloses magnesium hydroxide with a particular particle structure to overcome these drawbacks. The particles should have a deformation in the direction (101) of at most 3 x 10 ^-3 , a crystal size in the same direction of more than 800A and a specific surface area of less than 20 m ² / g. According to DE 2 659 933, anionic surfactant coatings are also required to overcome the above-mentioned disadvantages.

However, it has now been shown that even the above parameters do not ensure the suitability of magnesium hydroxide for these purposes, since in practice undesirable effects occur despite adherence to this structure.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION It is an object of the present invention to provide a type of finely powdered magnesium hydroxide which is suitable as a non-flammable filler for plastics and removes the above mentioned disadvantages without affecting the chemical and physical properties, in particular insulation and chemical stability, in the presence of water and other environmental influences. Magnesium hydroxide should be easily workable by plastic as its non-flammable filler, ensuring sufficient strength and good product surface.

The method according to the invention solves this problem with finely powdered magnesium hydroxide, the particle size of which, when measured by laser beam bending, is below 10 µm, the mean particle size is higher than 0.8 µm and not more than 3 µm, of water-insoluble ion type impurities, in particular Ca ⁺⁺ . Na ⁺ , K ⁺ , SO ⁴ , and Cl 2 lie in the following weight fraction range: Ca 4 less than 1000 ppm, Na ⁴ less than 20 ppm, K ⁺ less than 20 ppm, S ⁴ less than 1500 ppm, Cl 1 less as 1000 ppm, wherein the content of Mn, Cu and Ni in magnesium hydroxide is less than (mass fractions) MnO less than 100 ppm, NiO less than 100 ppm, CuO less than 10 ppm.

By using this type of magnesium hydroxide it is possible to overcome all of the above disadvantages.

Experiments have shown that by using magnesium hydroxide while maintaining the above-mentioned water-soluble ionic impurities, it is possible to maintain the insulating properties of plastic articles at much better levels than by using hitherto known types of magnesium hydroxide, particularly under humid conditions. . In addition, the swelling of the plastic by the action of water, which was often observed by the use of the previously known types of magnesium hydroxide, can be completely suppressed by adhering to the stated values. In addition, very good mechanical properties such as strength, elongation at break, shape stability and good aging resistance are achieved. By keeping the heavy metal impurities low, it is possible to favorably influence, for example, the oxidative degradation of the plastic, which is virtually eliminated. Also, adherence to the highest grain size value contributes to good mechanical properties and to avoiding the adverse effect of, for example, water, since a good and closed surface of the products obtained from these 20 plastics is formed. The grain size of this range also contributes to good tensile strength. Compliance with the mean d ₅₀ of the particle size of the hydroxide contributes both to the mechanical properties of the plastics and to their flame resistance. It should also be emphasized that the particle size measurement is based on the bending of the laser beams. Different results may be obtained when measuring otherwise. When measuring the laser beam bend, a proportion of particles less than 1% by weight is not included.

It is particularly advantageous that in the production of plastics, the use of said type of magnesium hydroxide as a filler results in favorable mechanical properties. For example, elastomers can achieve good tensile strength and at the same time good strength.

In a preferred embodiment, particularly good water resistance can be achieved if the Ca content of ^4-4, Na ⁴ , K ⁴ , SO ⁴ ", Cl 2 in magnesium hydroxide is maintained at the following values: Ca ⁴⁴ less than 500 ppm, Na ⁺ less than 10 ppm, K ⁴ less than 40 ppm, SO 4 - less than 800 ppm, Cl 4 less than 500 ppm.

As regards the heavy metal content, in a preferred embodiment, the content of Mn, Cu and Ni is maintained at MnO values of less than 50 ppm, NiO less than 50 ppm, 45 CuO less than 5 ppm. In this way, the catalytic degradation of plastics can be favorably influenced and virtually eliminated.

From the standpoint of flameproofing, it is further preferred that the loss on ignition for magnesium hydroxide is 50 more than 30.0%.

The electrical conductivity of magnesium hydroxide according to DIN 53208 in the aqueous suspension is preferably less than 500pS / cm, preferably less than 300pS / cm.

Due to the good mechanical properties of the plastics material and the articles thereof, and in view of the anti-flare effect, the magnesium hydroxide preferably has a largest grain size of 7 µm and the mean value is preferably 1 + 0.2 µm.

In view of the treatment of the magnesium hydroxide with the plastics material, and in particular the dispersion of the hydroxide therein, and at the same time the influence on the modulus of elasticity of the plastic material, it is preferable that the ratio of the diameters of the magnesium hydroxide particles to is particularly advantageous for the dispersibility of the hydroxide in the plastic.

Optional thin coating of the surfactant on the hydroxide particles can cause further improvement of the dispersibility of the hydroxide and further improvement of the mechanical properties of conventional masses. This is a relatively small amount of up to 2%, based on the weight of the hydroxide.

The invention also relates to a process for the production of finely powdered magnesium hydroxide, which comprises that the spray dried magnesium chloride solution previously free of contaminants to obtain the oxide containing Ca ", Na ^+, K ^+, SO ₄ ^_ below the values of: Ca 'less than 10 000 ppm, Na ⁺ less than 1000 ppm, K ⁺ less than 1000 ppm, SO / less than 3000 ppm, Cl' less than 100 000 ppm and containing Mn, Cu and Ni below the following values (parts by weight): MnO less than 150 ppm, NiO less than 150 ppm, CuO less than 15 ppm, this magnesium oxide is mixed with water and the suspension is allowed to react while stirring, the formed magnesium hydroxide is filtered off and the filter cake is washed once or several times with dehydrated water , in which case it is again freed from water and dried. For the hydration of the magnesium oxide, water which is completely free of salt is preferably used.

The suspension is preferably reacted with stirring at 55 to 100 ° C. A temperature range of 80 to 90 ° C is preferred for rapid and complete hydration and to achieve the desired values.

In this way, the desired special properties of the finely powdered magnesium hydroxide can be easily achieved. However, care should be taken that magnesium chloride is already obtained from suitable materials such as divine, serpentine, gamierite and other materials containing magnesium silicates by hydrochloric acid followed by purification.

The magnesium oxide recovery process of the present invention is accomplished by spraying the magnesium chloride solution with simultaneous drying by spraying the solution into a reactor containing the hot combustion gases. There is practically complete pyrohydrolysis of magnesium chloride, while the other components of the solution, for example the water-soluble potassium, sodium or calcium salts, remain unchanged.

In principle, other processes for recovering magnesium oxide could also be used. To recover magnesium hydroxide and magnesium oxide from seawater, this water is mixed with a suspension of dolomite or lime to precipitate magnesium hydroxide, which is separated by sedimentation and then washed, then the hydroxide can be converted to magnesium oxide by heat treatment. However, this process is burdened with the presence of foreign matter from the seawater as well as from the suspension of dolomite or lime, resulting in an unsatisfactory end product.

The invention also relates to the use of the fine-powdered magnesium hydroxide according to the invention as a flame-resistant filler in plastics, in particular in thermoplastics.

The invention also relates to plastics which are formed of a thermoplastic material and contain, as a flame-resistant filler, magnesium hydroxide according to the invention.

The following examples illustrate the invention.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

The reaction vessel was charged with 10 liters of completely de-salted water and heated to 70 ° C. 850 g of magnesium oxide, whose chemical analysis and the particle diameter are given in Table I, column 1, are then added. This magnesium oxide was obtained by pyrohydrolysis of the magnesium chloride solution, brought into solution and stirred for 3 hours. The product was then filtered off and washed with water. After drying, the resulting product was obtained with a chemical analysis and particle size as shown in Table II, column 1. The electrical conductivity of this material according to DIN 53208 was in an aqueous suspension of 265pS / cm. The ratio of particle diameter to height was 3 to 4.

EXAMPLE 2 liters of completely de-salted water are placed in a vessel and heated to 85 ° C. Then 2 kg of magnesium oxide with chemical analysis values and particle size from Table I, column 2 were added. This material was obtained by pyrohydrolysis of the magnesium chloride solution and then stirred for 5 hours with water. The product was filtered at 85 ° C and washed with water. After drying, the product was obtained, the chemical analysis and particle size of which is given in Table II, column 2. The electrical conductivity, which was determined according to DIN 53208 in an aqueous suspension, was 382 pS / cm. The particles had a diameter to height ratio of 5 and 6.

Example 3

The 1500 g of magnesium hydroxide obtained according to Example 1 is vigorously stirred for 15 minutes in a blender with 15 g of alkoxysilane, thereby coating the particles with this material.

Example 4

To obtain plastic, 100 parts by weight of ethylene, propylene polymer and diene as elastomers in powder form are mixed with 220 parts by weight of calcium hydroxide of Example 1 and the resulting material is injection molded to test samples according to DIN 53670. The test results are listed in column A of Table III.

Example 5

The procedure of Example 4 is followed but the magnesium hydroxide obtained according to Example 3 is used. The results of tests on samples produced in the same manner are given in column B of Table III.

Comparative Example 1

The procedure of Example 4 is followed, but the plastic mass is produced using magnesium hydroxide obtained from seawater. The results obtained are shown in column C of Table III.

Comparative Example 2

The procedure of Example 4 is followed, but the surfactant-modified magnesium hydroxide according to DE 2 659 933 is used. Samples are made from the material in the same way, the test results are given in column D of Table III.

It can be seen from Table III that the samples made of plastic using the magnesium hydroxide according to the invention (columns A and B) have high tensile strength and at the same time good ductility, furthermore they swell only slightly when stored in water.

For samples containing normal seawater magnesium hydroxide as fillers (Table III, column

C) significantly reduced tensile strength and increased swelling are observed. Using another known

A small swelling but a strong decrease in tensile strength can be observed in the type of surfactant-modified magnesium hydroxide (Table III, column D).

Example 6 5

100 parts by weight of PP 8400 polypropylene (Hiils-Chemie) and 150 parts by weight of magnesium hydroxide of Example 1 were used in the production of plastic. After thorough mixing, test pieces 10 were tested for tensile strength and ductility according to standard. DIN 53455, for impact strength according to DIN 53453 and for flash properties according to ASTM D 2863-77 and UL 94 / V (3 mm). In addition, the melt flow rate at 240 ° C 15 was investigated as an indicator of processability in injection molding. The results are shown in Table IV, column A. Because the substance is used as a non-flammable additive, the LOI (Liming Oxygen Index) has also been determined for the material, which shows what the 20% minimum molecular oxygen content must be in percent in ambient atmosphere. to keep burning. UL 94 / V (3 mm) lays down rules (Underwrites Laboratory) for conducting tests for flame retardancy of 3 mm samples in a vertical position. The following evaluation is used: V-O = best result, V-1 = medium result, H.B. = substance is flammable.

Example 7

The procedure of Example 6 is followed, using the same propylene but magnesium hydroxide of Example 3. The results obtained on the resulting material by injection molding are given in column B of Table IV.

Comparative Example 3

The procedure of Example 6 was carried out using the same polypropylene but using conventional seawater magnesium hydroxide as in Comparative Example 1. The material obtained was processed into test specimens by injection molding. The test results are given in column C of Table IV.

Comparative Example 4

Following the procedure of Example 6, using 45 of the same polypropylene, the magnesium hydroxide of Comparative Example 2, modified with a surfactant, was used. The results are shown in column D of Table IV.

Comparative Example 5

The polypropylene of Examples 6 and 7 and Comparative Examples 3 and 4 were used without the addition of magnesium hydroxide. The results are shown in column E of Table IV.

T a b u r k a l

Magnesium oside 1 wt.

Table II

Magnesium hydroxide

2 wt. % wt.

Loss on ignition 2 hours at 1000 ’C 30.5 30.52 Si0 ₂ 0.012 0.021 f « ₂ o ₃ 0.005 0.002 al ₂ o ₃ 0.003 0.002 CaO 0.006 0.001 Hg (0H) ₂ (from difference) 99.9 99.9 Na ₂ O <0.001 <0.001 K ₂ o <Q, 001 <0.001 Sat ₄ - 0.025 0,017 Cl 0.014 0.082 CuO <5 <S ppm WNO 4 20 ppm NiO 20 14 ppm specific BET surface area 11 14.5 ² / g mean djQ (particle size) 1.19 1.41 pm particle surface 6.0 5,0 μιη

Table Tests that have been performed on III plastic B C D an exam A hardness Shore A DIN 53505 85 86 81 79.5

tensile strength NmnT ²

DtN 53504 glamorous value 7.0 10.0 4.4 2.8 7 days 135 ° C, ^L> 10.2 12.8 6.3 2.8 2d science days 50 • c 6.6 7.8 4.U 3.1 elongation% DIN 53504 original value * 22 185 212 534 7 days 135 ’C 179 1 <5 178 479 25 days in water 50 • c « 247 230 422 464 swelling in ft in < j water ² > 1 day 0.9 0.4 1.5 0.4 Day 3 1.5 0.8 3.8 0.7 Day 7 2.0 1.3 8.2 0.9 Day 14 2.5 1.7 9.8 1.4 Day 21 2.7 1.8 10.5 1.8 Day 28 2.8 2.0 11.8 1.9 vulcanization lowest twisting a moment 10.0 9.8 5.4 2.5 highest twisting i a moment 64.1 63.2 57.8 37.3

Explanatory notes to Table III:

1) Hot air aging tests were performed according to DIN 53508 by storage for 7 days at 135 ° C.

2) Storage in water was carried out according to DIN 53521, so that test samples were stored in water at 50 ° C for 28 days.

T a b u 1 k and IV

NgO (s ro)

SiO ₂

CO ai ₂ o ₃

Pu ₂ O ₃

MnO

NiO

Nu _z O

K ₂ O

GOV / '

Cl

Rpa-fluffy surface BCT utradndi hinlnot · ^ 30 (size of area) test plastic

A B C D E tensile strength Nmm ² 25.0 20.8 18.2 18.0 23.0 ductility (m / e) 0.035 12:34 0026 12:22 > 1 impact resistance (KJ / n ^Z >) 10.0 about. Br. 3.0 O.Br. cj. Br. LOI (0 * ₂₎ 27.0 N.B. n. b. 23.8 17.1 UL 94 / V (3mm) V-0 In-Q V-L H.B. H.B. material flow during casting vstrekovunim. 240 'C (cm) 13.5 14.0 6.0 15.0 15.0

9a

003

OZ

SO

S2

010

002 □ 07

004

003

U0 2

01 '

012

065

2:43

24.6

2.43 μι

24.6 impact strength: o. Br. = break point LOI: n. b. = not determined

Claims (17)

PATENT CLAIMS Fine powdered magnesium hydroxide, particularly suitable as a filler, flame retardant for use in plastics, with particles, optionally coated with a thin coating, of a surfactant, characterized in that its particle size, measured by laser beam bending, is below 10 µm, medium size The content of water-soluble impurities of the ionic type, namely Ca ⁺⁺ , Na ⁺ , K ⁺ , SO 4 -, Cl 2 has the following values in parts by weight: Ca "less than 1000 ppm, Na ⁺ less than 20 ppm, K ⁺ less than 20 ppm, SO ₄ less than 1500 ppm, Cl 2 less than 1000 ppm, and the content of Mn, Cu and Ni in magnesium hydroxide has values by weight: MnO less than 100 ppm, NiO less 100 ppm, CuO less than 10 ppm. Fine powdered magnesium hydroxide according to claim 1, characterized in that the content of Ca ", Na ⁺ , K ⁺ , SO ₄ -, Cl 'has values of: Ca" less than 500 ppm, Na ⁺ less than 10 ppm, K ⁺ less 10 ppm, SO 4 - less than 800 ppm, C 1 - less than 500 ppm. Fine powdered magnesium hydroxide according to claim 1 or 2, characterized in that the Mn, Cu and Ni contents have: MnO less than 50 ppm, NiO less than 50 ppm, CuO less than 5 ppm. Fine powdered magnesium hydroxide according to claims 1 to 3, characterized in that the annealing losses are higher than 30.0%. Fine powdered magnesium hydroxide according to claims 1 to 4, characterized in that the electrical conductivity of the magnesium hydroxide is less than 500 pS / cm. Fine powdered magnesium hydroxide according to claim 5, characterized in that the electrical conductivity is less than 300pS / cm. Fine powdered magnesium hydroxide according to claims 1 to 6, characterized in that the mean particle diameter is 1 + 0.2 µm. Fine powdered magnesium hydroxide according to claims 1 to 7, characterized in that the upper limit of its particle size is below 7 µm. 9. The finely divided magnesium hydroxide of claims 1 to 7, wherein the ratio of the particle diameter to the height thereof is in the range of 2 to 6. The finely powdered magnesium hydroxide of claim 9, wherein the ratio of the diameter of the primary particles to their height is in the range of 3 to 4. Process for the production of finely-powdered magnesium hydroxide according to claims 1 to 10, characterized in that the magnesium oxide, previously obtained by pyrohydrolysis of a foreign matter-free magnesium chloride solution containing Ca ", Na ⁺ , K ⁺ , SO 4", Cl 2 Values in mass fractions: Ca ⁺⁺ less than 10000 ppm, Na ⁺ less than 1000 ppm, K ⁺ less than 1000 ppm, SO4 less than 3000 ppm, Cl + less than 100000 ppm, Mn, Cu and Ni contents in mass fractions : MnO less than 150 ppm, NiO less than 150 ppm, CuO less than 15 ppm, mixed with water, the suspension is allowed to react while stirring, the formed magnesium hydroxide is filtered off, the filter cake is washed once or repeatedly with water, completely free of salts, in this case, it is again freed from water and dried. 12. The method of claim 11, wherein the hydration of the magnesium oxide is carried out in water, completely free of salts. Process according to claims 11 and 12, characterized in that the suspension is reacted with stirring at a temperature of 55 to 100 ° C. 14. The process according to claim 13, wherein the suspension is reacted with stirring at a temperature of 80 to 90 [deg.] C. Process according to claims 1 to 14, characterized in that a magnesium chloride solution obtained by treating a material containing magnesium silicate or magnesium silicate, such as olivine, serpentine, gamierite and the like, is treated with hydrochloric acid, followed by purification of the suspension obtained. Use of the finely powdered magnesium hydroxide according to claims 1 to 10 as a flame retardant filler in plastics, in particular containing thermoplastics. 17. A plastics material, characterized in that it comprises a thermoplastic material as a plastic material and a magnesium hydroxide according to claims 1 to 10 as a flame retardant filler.