Note: Descriptions are shown in the official language in which they were submitted.
2032 470
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The present invention relates to a finely powdery
magnesium hydroxide suitable especially as flame-retardant
filler for plastic compounds, the particles thereof being
provided optionally with a thin coating of a surfactant.
Frequently, finely powdery magnesium hydroxide is used as
flame-retardant filler for plastic compounds, especially those
on basis of thermoplastic materials. In such a use relatively
high amounts of magnesium hydroxide are added to the plastics,
the weight of the magnesium hydroxide frequently amounting to
the half up to the double weight of the plastic. Kinds of
finely powdery magnesium hydroxide often have properties which
exert a negative influence on the mechanical properties of
plastic compounds to which such a magnesium hydroxide has been
added as filler. Often e.g. a tendency of such plastic
compounds and articles produced from such plastic compounds
respectively to take up relatively high amounts of water, to a
decrease of the tensile strength and to an increased aging may
be observed.
Frequently, the flowability and formability of such
plastic compounds and the appearance of the surface of
articles formed from such plastic compounds is adversely
influenced by the properties of certain kinds of finely
powdery magnesium hydroxide, e.g. by the grain structure and
the contents of water thereof.
German patent No. DE-C3-2 624 065 issued April 30, 1980
describes a magnesium hydroxide having the special structure
of particles which should eliminate in use of said magnesium
hydroxide in plastic compounds disadvantages as mentioned
above. The particles should have a deformation in the <101>-
direction of not more than 3 x 10-3, a crystallite size in the
0
<101>-direction of more than 800 A and a specific surface,
determined according to BET, of less than 20 m2/g. According to
German patent No. DE-C3-2 659 933, issued August 5, 1981, in
addition to that structure of the particles of the magnesium
hydroxide said particles are covered with anionic surfactants
so as to eliminate the above mentioned disadvantages.
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2032470
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Now it has been found that the above mentioned structural
parameters are not suitable for the characterization of a
magnesium hydroxide to be used for the above mentioned
purpose, by which the above mentioned disadvantages can be
eliminated reliably. Despite of such a structure in the
practice the mentioned disadvantages may occur.
It is an object of the present invention to provide a
finely powdery magnesium hydroxide as defined above, which in
use as
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flame-retardant filler in plastic compounds eliminates reliably
the mentioned disadvantages and which, also after a longer period
of time, does not induce both any impairment of the chemical-
physical properties, especially of the electrical insulating
property and of the chemical resistance, and any impairment of the
mechanical properties and of the dimensional stability and does
not favor disadvantageous changes of the plastic compounds under
the influence of moisture and other environmental influences. The
finely powdery magnesium hydroxide to be prepared should allow
also a simple processing of plastic compounds, in which it serves
as flame-retardant filler, and should allow to obtain good
strength properties of articles prepared from such plastic
compounds as well as a uniformly closed surface of said articles,
which does not show any trouble by surface faults.
The finely powdery magnesium hydroxide of the present
invention is characterized by a grain size, measured by laser
diffraction, of below 10 Vim, the median value of the grain size
being greater than 0.8 wm and 3 ~m at the utmost and further
characterized in, that the magnesium hydroxide contains water-
soluble ionic impurities, viz. Ca++, Na+, K+, S04--,
Cl-, in amounts below the following limits (in parts by weight):
Ca++ < 1000 ppm, Na+ < 20 ppm, K+ < 20 ppm,
S04-- < 1500 ppm, C1- < 1000 ppm,
and that the magnesium hydroxide contains Mn, Cu and Ni in amounts
below the following limits (in parts by weight):
Mn0 < 100 ppm, Ni0 < 100 ppm, Cu0 < 10 ppm.
Magnesium hydroxide having such features allows to achieve
well the above mentioned objects.
In experiments carried out during the development of subject
matter of this invention is was found that by keeping the values
of water-soluble ionic impurities of the magnesium hydroxide in
the mentioned ranges the insulating resistance and the electrical
breakdown resistance of bodies or articles consisting of a plastic
compound filled with such a magnesium hydroxide are definitely
higher than in case of using other usual kinds of magnesium
hydroxide, which fact is particularly observed, if such bodies or
articles are exposed to the influence of moisture. Furthermore by
keeping the amounts of water-soluble ionic impurities of the
magnesium hydroxide in the-.mentioned ranges the swelling of
plastic compounds occurring under the influence of moisture, which
w _ 3 _ ~03Z4
swelling was observed often with use, of usual kinds of magnesium
hydroxide, a.s prevented effectively, and by using of the magnesium
hydroxide of the invention very good mechanical properties (e. g.
strength, elongation at break and dimensional stability) of the
articles produced from the plastic compounds as well. as a good
resistance thereof. against phenomena of ageing are achieved.
Keeping the amounts of contaminations by heavy metals within the
mentioned ranges contributes to these features, which fact
probably can be explained that thereby a chemically
disadvantageous influence on the plastic material (e. g. oxidative
degradation) is substantially eliminated. Observing the above
mentioned upper limit of the grain size contributes to the good
mechanical properties and the large avoidance of disadvantageous
effects of extraneous influences, especially of moisture, by
allowing to achieve a high surface quality of the bodies or
articles produced from the plastic compounds, that means a dense
and closed surface counteracting to the penetration of forein
matter. Equally, the mentioned grain size is advantageous for
obtaining a good tensile strength. Also the observation of the
above mentioned range of the median value (designated "d5o") of
the grain size of the magnesium hydroxide is advantageous for the
achievment of favourable mechanical properties of the plastic
compounds and also with respect to the flame-retardant effect. It
should be mentioned that the stated values of grain sizes are
based on a measurement of the grain size with laser diffraction. A
measurement of the grain size by other measuring methods may give
other values. The measurement with laser diffraction does not
detect an amount of up to 1 $ (by weight) of oversized particles.
Therefore, it appears to be particularly advantageous that
bodies or articles produced from plastic compounds containing the
magnesium hydroxide of the invention as a filler show several
favorable mechanical properties in combination. Thus, e.g. very
good values of tensile strength and simultaneously good values of
elongation at break may be obtained in elastomeric plastic
compounds.
A preferred embodiment of the magnesium hydroxide of the
invention for obtaining a particularly good resistance to
influences of moisture provides that the amount of Ca++, Na+,
S04--, C1- is below the following limits:
Ca++ < 500 ppm, Na+ <'10 ppm, K+ < 10 ppm,
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S04-- < 800 ppm, Cl- < 500 ppm.. ..
As to the contents of heavy metals in the magnesium hydroxide
a preferred embodiment provides that the amount of Mn, Cu and Ni
is below the following limits: Mn0 < 50 ppm, Ni0 < 50 ppm, Cu0 < 5
ppm. Thereby the catalytic promotion of phenomena of degradation
of the plastic material can be eliminated substantially
completely.
As to the flame-retardant effect of the finely powdery
magnesium hydroxide it is also advantageous if the loss at red
heat of the magnesium hydroxide is > 30,0 $.
The electrical conductivity of the magnesium hydroxide,
determined according to DIN 53208 on an aqueous suspension, is
preferably < 500 ~.S/cm, preferably < 300 wS/cm.
For obtaining favorable mechanical properties of the plastic
compounds and the articles produced therefrom and also for
achieving the flame-retardant effect of the magnesium hydroxide a
maximum value of the grain size of 7 ~m and a median value of the
grain size of 1 ~ 0,2 ~m proved to be especially advantageous.
As to the processing the magnesium hydroxide with the plastic
material to give a plastic compound and as to the dispersion of
the magnesium hydroxide in the plastic material and also as to an
influence on the E-modul of the plastic compounds filled with the
magnesium hydroxide it is advantageous if the ratio of the
diameter of the primary particles of the magnesium hydroxide to
the height of said primary particles, designated "aspect ratio",
is between 2 and 6. A ratio of the diameter of said primary
particles to the height thereof of between 3 and 4 is particularly
favorable for the dispersibility.
The optional provision of a thin coating of a surfactant on
the particles of the magnesium hydroxide is mainly advantagous for
a further improvement of the dispersibility and for a further
improvement of the mechanical properties of the plastic compounds.
Relatively small amounts of up to 2 $, related to the weight of
the magnesium hydroxide, may be sufficient.
The present invention also relates to a process for preparing
the finely powdery magnesium hydroxide, said process comprising
adding water to magnesium oxide obtained by spray roasting from a
magnesium chloride solution from which previously foreign matter
has been removed, which magnesium oxide contains Ca++, Na+,
K+, S04--, C1-, in amounts below the following limits (in
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parts by weight):
Ca++ < 10 000 ppm, Na+ < 1000 ppm, K+ < 1000 ppm,
S04-- < 3000 ppm, Cl- < 100 000 ppm,
and Mn, Cu and Ni in amounts below the following limits (in parts
by weight): Mn0 < 150 ppm, Ni0 < 150 ppm, Cu0 < 15 ppm, allowing
to react the suspension with stirring, removing then the magnesium
hydroxide formed in suspension by filtration and subjecting the
filter cake material to one or several post-washes with completely
desalted water, dewatering the filter cake material again and
finally drying thereof. Preferably completely desalted water is
used for the hydration of the magnesium oxide.
In the process of the invention the suspension preferably is
allowed to react with stirring at a temperature of between 55 to
100°C. For a rapid and complete progress of the hydration and for
obtaining the features essential for the magnesium oxide of the
invention it is advantageous to allow react the suspension with
stirring at a temperature of between 80 and 90°C.
In the scope of the process of the invention it is possible
in a particularly simple way to achieve the special properties and
features respectively of the finely powdery magnesium hydroxide if
the magnesium chloride solution in turn is prepared by digestion
of a magnesium silicate material or magnesium hydrosilicate
material, such as olivine, serpentine, garnierite and the like
with hydrochloric acid and subsequent purification of the
digestion pulp.
The production of the magnesium oxide in the process of the
invention is effected by spray roasting of a magnesium chloride
solution. By this technique a magnesium chloride solution is
sprayed within a reactor, in which an atmosphere of hot gas
generated by burners is present. This results in the substantially
complete pyrohydrolysis of the magnesium chloride, whereas other
components of the magnesium chloride solution, e.g. watersoluble
potassium, sodium or calcium salts, are not modified.
It should be mentioned that also processes for preparing
magnesium hydroxide and magnesium oxide different from the above
mentioned spray roasting technique may be used. Thus, for the
production of magnesium hydroxide and magnesium oxide from sea
water lime milk or dolomite milk is added to the sea water,
resulting in the precipitation.of the magnesium hydroxide, the
latter being separated by sedimentation and washed subsequently,
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whereupon the formed magnesium hydroxide is converted into the
magnesium oxide by thermical treatment. Such a preparation of
magnesium hydroxide and magnesium oxide is exposed to several
disadvantageous influences by extraneous substances present in the
sea water and in the lime milk or dolomite milk, which may result
in the disadvantageous presence thereof in the end product.
Furthermore, the invention relates to the use of the finely
powdery magnesium hydroxide of the invention as flame-retardant
filler in plastic compounds. A preferred embodiment of the
invention relates to the use of the finely powdery magnesium
hydroxide of the invention as flame-retardant filler in plastic
compounds, the plastic component of which being a thermoplastic
substance.
Finally the invention relates to a plastic compound
containing a plastic material and as flame-retardant filler a
finely powdery magnesium hydroxide of the invention. A preferred
plastic compound is characterized in that the compound contains as
plastic component a thermoplastic material and as flame-retardant
filler a finely powdery magnesium hydroxide of the invention.
In the following examples the invention is illustrated in
more detail.
Example 1:
10 1 of completely desalted water are added into a reaction
vessel and heated to a temperature of 70°C. 850 g of a magnesium
oxide having the chemical analysis and grain size analysis shown
in table I, column 1, prepared by pyrohydrolysis of a magnesium
chloride solution, are introduced into the above solution and
stirred sufficiently by means of a stirrer for 3 hours. Subsequent
to the hydrothermical treatment the product is filtered and washed
with water. After drying a product is obtained, the chemical
analysis and grain size analysis of which is given in table II,
column 1. The electrical conductivity of the magnesium hydroxide
thus obtained was determined according to DIN 53208 on an aqueous
suspension with 265 ~S/cm. The primary particles have a ratio
diameter to height of 3 to 4.
Example 2:
10 1 of completely desalted water are added into a reaction
vessel and heated to a temperature of 85°C. 2 kg of a magnesium
_ ~ _ ~ ~0~~~
oxide having the chemical analysis and.grain size analysis shown
in table I, column 2, prepared by pyrohydrolysis of a magnesium
chloride solution, are stirred into the solution and subjected to
a hydrothermical treatment for 5 hours. Then the product is
filtered at 85°C and washed with water. After drying a product is
obtained, the chemical analysis and grain size analysis of which
is given in table II, column 2. The electrical conductivity,
determined according to DIN 53208 on an aqueous suspension, was
382 ~,S/cm. The primary particles showed a ratio of diameter to
height of 5 to 6.
Example 3:
1500 g of a magnesium hydroxide prepared according to Example
1 were mixed intensively with 15 g of an alkoxysilane in a rapid
mixer for 15 minutes and thereby modified in the surface.
Example 4:
For preparing a plastic compound 100 parts by weight of an
elastomeric ethylene-propylene-diene-polymer (EPDM) in form of a
powder were mixed intimately with 200 parts by weight of a
magnesium hydroxide prepared according to Example 1. Then
specimens were prepared from this plastic compound by injection
molding and said specimens were examined according to DIN 53670.
The results of the examination are mentioned in column A of table
III.
Example 5:
Example 4 is repeated using the same polymer with the
exception that a magnesium hydroxide obtained by Example 3 is
employed. The results of the examination of the specimens prepared
from the plastic compound are mentioned in column B of table III.
Comparative Example l:
Example 4 is repeated using the same polymer with the
exception that a commercial magnesium hydroxide prepared from sea
water is employed. The results of the examination of the specimens
prepared from the plastic compound are mentioned in column C of
table III.
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Comparative Example 2:
Example 4 is repeated using the same polymer with the
exception that a magnesium hydroxide modified on the surface, as
described in DE-C3-2 659 933, is employed. The results of the
examination of the specimens prepared from the plastic compound
are mentioned in column C of table III.
From table III it is immediately evident that the specimens
prepared from plastic compounds containing magnesium hydroxide of
the invention as a filler (columns A and B) show a high tensile
strength and simultaneously a good elongation at break as well as
a low swelling at storage in water.
Speciments prepared from plastic compounds containing a
commercial magnesium hydroxide prepared from sea water (table III,
column C) show a distinctly lower tensile strength and an
increased swelling at storage in water compared with the values of
columns A and B of table III. The use of another known magnesium
hydroxide being modified on its surface (comparative example 2,
table III, column D) results in a lower swelling, but decreases
highly the tensile strength.
Example 6:
For the production of a plastic compound 100 parts by weight
of a polypropylene of Type PP 8400 (Hiils-Chemie) were mixed
intimately with 150 parts by weight of a magnesium hydroxide
obtained by Example 1. Then specimens were prepared from said
plastic compound by injection molding and examined then with
respect to tensile strength and elongation at break according to
DIN 53455, to impact resistance according to DIN 53453, to
combustion properties according to ASTM D 2863-77 and to flame
resistance according to UL 94/V (3 mm). Furthermore the flow
length of the plastic compound at injection molding at 240°C was
determined according to an internal comparative method as measure
of processability. The obtained values are mentioned in table IV,
column A. With respect to the combustion properties the LOI
(limiting oxygen index) value was determined, which corresponds to
the minimum amount of oxygen (~ 02) of the environmental
atmosphere necessary to maintain the burning down. UL 94/V (3 mm)
are guidelines of Underwriters. Laboratory for conducting
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examinations of flame-resistance of specimens having a thickness
of 3 mm in vertical position; V-0... means the best result, V-1
... a moderate result, H.B. ... high burning.
Example 7:
Example 6 is repeated using the same polyproplene such as in
Example 6 with the exception that a magnesium hydroxide obtained
by Example 3 is employed. The results of the examination of the
specimens prepared from the plastic compound by injection molding
are mentioned in column B of table IV.
Comparative Example 3:
. Example 6 is repeated using the same polyproplene such as in
Example 6 with the exception that a commercial magnesium hydroxide
prepared from sea water and used in comparative example 1 is
employed. The results of the examination of the specimens prepared
from the plastic compound by injection molding are mentioned in
column C of table IV.
Comparative Example 4:
Example 6 is repeated using the same polyproplene such as in
Example 6 with the exception that a magnesium hydroxide modified
on its surface and used in comparative example 2 is employed. The
results of the examination of the specimens prepared from the
plastic compound by injection molding are mentioned in column D of
table IV.
Comparative Example 5:
Specimens were prepared from the polypropylene used in
examples 6 and 7 and the comparative examples 3 and 4 by injection
molding without addition of magnesium hydroxide and subjected to
the examinations mentioned in these examples and comparative
examples. The results given in column E of table IV were obtained.
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T A B L E I
Magnesium oxide
1 2
Chemical analysis
Mg0 (from the difference) ~ by weight 98.2 94.1
Si02 " 0.005 0.02
Ca0 " 0.50 0.52
A1203 " 0.010 0.002
Fe203 " 0.007 0.004
Mn0 " 0.0005 0.003
Ni0 " 0.003 0.002
Na20 " 0.02 0.018
K20 " 0.02 0.012
S04-- " 0.04 0.065
C1- " 1.2 5.28
jspecific surface BET m2/g 5.0 4.7
Grain analysis:
Median value d5o ~m 2.43 2.68
er rain limit m 24.6 24.6
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T A B L E II.
Magnesium hydroxide
1 2
Chemical analysis
loss at red heat at 1000C/
2 hours $ by weight 30.5 30.52
Si02 " 0.012 0.021
e203 " 0.005 0.002
1203 " 0.003 0.002
a0 " 0.006 0.001
g(OH)2 (from the difference) " 99.9 99.9
a20 " <0.001 <0.001
20 " <0.001 <0.001
04-- " 0.028 0.017
1- " 0.014 0.082
u0 ppm < 5 < 5
n0 " 4 20
i0 " 20 14
pecific surface BET m2/g 11 14.5
rain anal sis:
edian value d5o ~.m 1.19 1.41
er rain limit m 6.0 5.0
T A B L E III
Determinations of specimens
Plastic compound A B C D
Kind of
xamination
Shore A-hardness 85 86 81 79.5
IN 53505
ensile strength/Nmm-2
IN 53504
riginal 7.0 10.0 4.4 2.8
7 days at 135C 1) 10.2 12.8 6.3 2.8
28 da s stora a in water 50C 6.6 7.8 4.0 3.1
2)
Elongation at break/$
IN 53504
riginal 224 185 212 534
7 days at 135C 1) _ 179 145 178 479
8 da s stora a in water 50C 2) 247 230 422 464
_ 12 _ ~U~~4 ~C
Continuation: Table III
Swelling at storage
in water/$ 2)
Day 1 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
Da 28 2.8 2.0 11.8 1.9
ulcanization
inimum of torque ML 10.0 9.8 5.4 2.5
aximum of for ue M 64.1 63.2 57.8 37.3
1) Ageing by hot air was carried out in accordance with DIN
53508 by storage at 135°C for 7 days.
2) The storage in water was carried out in accordance with
DIN 53521 by subjecting the specimens to the contacting
medium water for a period of 28 days at 50°C.
T A B L E IV
Plastic compound
ind of A B C D E
examination
Tensile strength (N/mm2) 25.0 20.8 18.2 18.0 23.0
Elongation at break (m/m) 0.035 0.34 0.026 0.22 > 1
impact resistance (KJ/m2) 10.0 w.f. 3.0 w.f. w.f.
LOI ($ 02) 27.0 n.d. n.d. 23.8 17.1
UL 94/V (3 mm) V-0 V-0 V-1 H.B. H.B.
flowing length at injection
moldin 240C (cm) 13.5 14.0 6.0 15.0 15.0
impact resistance w.f. - without fracture
LOI n.d. - not determined
