HYDROXYDE D'ALUMINIUM CRISTALLIN

CRYSTALLINE ALUMINIUM HYDROXIDE

Abrégé anglais

Described is a new crystalline aluminium hydroxide which, because of its high-level purity and its outstanding electrical properties
along with good viscosity characteristics, is especially well-suited for flarne-proofing of thermosetting plastics dlat are used in electrical
applications.

Revendications

- 5 -


Claims

1. Crystalline aluminium hydroxide, characterized by
a particle size in the 50% range d50 of 15 - 50 µm, an
Na2O content of 0.1%, a content of soluble Na2O of
0.005% and a specific surface area according to BET of
0.4 m2/g to 1.2 m2/g.
2. Crystalline aluminium hydroxide according to
Patent Claim 1, characterized by a particle size in the
10% range d10 of 2 - 6 µm and in the 90% range d90 of 35
- 100 µm.
3. Crystalline aluminium hydroxide according to one
of Patent Claims 1 to 2, characterized by the electrical
conductivity of a 10% suspension of the crystalline
aluminium hydroxide in deionized water of 5 25 µS/cm.
4. Process for preparing a crystalline aluminium
hydroxide having tke properties according to one of
Patent Claims 1 to 3, characterized by washing an
aluminium hydroxide having a particle size in the 50%
range d50 of 25 - 95 µm, an Na2O content of 0.15% and a
content of soluhle Na2O of 0.02% with hot water and
subsequent deagglomeration of the aluminium hydroxide
obtained.
5. Crystalline aluminium hydroxide, obtainable by
the process according to Patent Claim 4.
6. Use of a crystalline aluminium hydroxide
according to one of Claims 1 to 3 or 5 as filler for the
flameproof finishing of thermosetting plastics.
7. Flameproofed thermosetting plastics, containing
a crystalline aluminium hydroxide according to one of
Claims 1 to 3 or 5.

Description

21573~9
W0 94/21559 - 1 - PCT/EP94/00798
Cry~talline aluminium hydroxide
The invention relates to a crystalline aluminium
hydroxide which is suitable for the flameproofing of
thermosetting plastics.
In particular for thermosetting plastics which
are used in the electronics field, there are official
requirements to replace the toxic halogenated flameproof
finishes by non-halogenated finishes.
Aluminium hydroxide would be an obvious choice,
provided that, with respect to its properties, it can
readily be processed with the thermosetting plastic and,
in view of the electrical properties demanded, has a very
high purity. An aluminium hydroxide which shows both the
properties mentioned ha not been known hitherto.
It was therefore the object to develop an alumi-
nium hydroxide which has the d~n~ed property profile,
high purity, outst~n~; ng electrical properties and good
viscosity behaviour.
It was possible to achieve the object by means of
a cry~talline aluminium hydroxide according to Patent
Claim 1.
The percentage data below relating to the par-
ticle size distribution are given in % by weight (percent
by weight).
According to the invention, this crystalline
aluminium hydroxide has a particle size in the 50% range
d50 of 15 - 50 ~m, preferably of 20 - 35 ~m.
The particle size in the 10% range dlo i8 ex-
pediently between 2 and 6 ~m, preferably between 4 and
6 ~m. The particle size in the 90% range dgo is ex-
pediently between 35 and 100 ~m, preferably between 40
and 95 ~m. The essential points for the electrical
properties of the crystalline aluminium hydroxide are the
Na20 content which, according to the invention, is ~ 0.1%
and the content of soluble Na20 which, according to the
invention, is 5 0.005%. Preferably, the content of
soluble Na20 is s O.004%.
The measure of the purity of the crystalline
aluminium hydroxide is the electrical conductivity of a

~. ~ 215738~
-- 2
10% su~pension in deionized water. The crystalline
aluminium hydroxide according to the invention shows a
value of advantageously 5 25 ~S/cm.
The specific surface area, meas-~red according to
BET, of the crystalline aluminium hydroxide is expedient-
ly within the range from 0.4 m2/g to 1.2 m2 /g
The production of the crystalline aluminium
hydroxide according to the invention ~tarts from an
especially crystallized aluminium hydroxide having a
10particle size in the 50% range d50 of 25 - 90 m, prefer-
ably of 35 - 75 ~m, an Na20 conte~t o~ ~ 0.15% and a
content of soluble Na20 of < 0.02%. The particle size of
the starting al~ nium hydroxide in the 10% range d1o i8
expediently 10 ~m to 30 ~m and in the 90% range dgo
15expediently 45 ~m to 150 ~m. The electrical conducti~ity
of a 10% suspension of the starting aluminium hydroxide
is expediently between 25 ~S/cm and 55 ~S/cm. The
specific surface area according to BET of the starting
aluminium hydroxide is in the range between c 0.1 m2/g
and 1.0 m2/g.
The said starting aluminium hydroxide is first
wa3hed with hot water (temperatures of expediently ~0C
to 95C), in order to lower the Na20 content. The pro-
cedure at this point is expediently such that the
alumi~ium hydroxide is treated, for example on a belt
filter with a ~uantity of w~h;ng water from 1.5 m3/tonne
to 2 m'/tonne of aluminium hydroxide.
The resulting aluminium hydroxide is then
expediently dried. The Na20 content of thi~ alumini
hydroxide is within the range of 5 0 .1%, and the content
of soluble Na20 is in the range of 5 0.005%.
The subsequent deagglomeration is expediently
carried out in a suitable mill, preferably in an impact
mill.
35Ad~antageously, the deagglomeration is carried
out continuously.
As regards the product properties according to
the invention, it is important to set the mill parameters
of speed of rotation of the separator (speed of rotatio~

~_ 3 21573~9

of the rotor body) of the impact mill and the % feed of
the product (fraction of the continuously di~charged
product, the difference from 100% is recycled into the
mill) to appropriate ~alues.
S It has been found that the speed of rotation of
the separator i8 expediently set in the range from 650 to
950 revolutions/minute. The % feed can ~ary in the range
of 35% to 75%.
According to the in~ention, the resulting alumi-
nium hydroxides can be used for the flameproofing of
~h~rmogetting plastics such as, for example, unsaturated
polyester resins, acrylic resins or epoxy resins.
The degree of filling ranges here within the
usual order of magnitude necessary for achie~ing a flame
resi~tance in accordance with U~-94 (Underwriter
Laboratories).
The flameproof thermosetting plastics are distin-
guished by an excellent viscosity behaviour with at the
same time out8t~n~; ng electrical properties.
ExamPles:
Ex~le 1:
Preparation of a crystalline deagglomerated aluminium
hydroxide
The aluminium hydroxide specially crystallized
from the Bayer process and ha~ing the following
properties:
- dlo (~m) : 20.4
- d50 (~m) : 40.9
- dgo (~m) : 66.7
- Solu~le Na2O (%) : 0.005
- Na2O (%) : 0.054
- Csn~cti~ity (~S/cm, : 26
10% suspension in deionized water)
- Specific surface area
according to BET : 0.3 m2/g
was treated on a belt filter with a quantity of w~h; ng
water (95C) of 1.8 m'/tonne and dried ~ia a ~low dryer
to a moisture content of 0.15%.
The aluminium hydroxide treated in this way was

` _ 4 _ 21S738~

then deagglomerated in an impact mill (ACM mill) by means
of the special impact technique thereof with a feed of
about 70%, a separator speed of 850 rpm and without the
use of impact bodies.
The aluminium hydroxide resulting from the above
process showed the following properties: ~
- dlo (~m) : 3-~
- d50 (~m) :23.0
- dgo (~m~ :42.9
- Soluble Na2O (%) :0.003
- - Na2O (%) :0.049
- Conductivity (~S/cm, : 15
10% suspension in deionized water)
- Specific surface area
according to BET : 0.44 m2/g
To measure the viscosity behaviour, 150 parts by
weight of the aluminium hydroxide obtained were mixed
into 100 parts of the unsaturated polyester resin
(Synolite 0020 N-2; DSM Resins BV). The processing
viscosity was measured at 23C, using a Brookfield ~BT
viscometer with a No. 3 spindle.
- starting hydroxide: 165 Pas
- deagglomerated hydroxide: 52 Pas
Example 2:
Correspon~;ng to Example 1, an aluminium hydrox-
ide having the following properties:
dlo (~m) 5.9
d50 (~m)
dgo (~m) 93
Soluble Na2O (%) 0.0034
Na2O (%) 0.093
Conductivity (~S/cm, 22
10% suspension in deionized water)
Specific surface area
35 according to BET (m2/g) 0.44
was obtained from an aluminium hydroxide having the
following properties:

~ _ 5 _ 2157389
dlo (~m) 26
d50 (~m) 70
dgo (~m) 100
Soluble Na20 (%) 0.015
Na2O (%) 0.121
Conductivity (~S/cm, - 50
10% suspension in deionized water)
Speci~ic surface area
according to BET (m2/g) c 0.1.
To measure the viscosity behaviour, 150 parts by
weight of the aluminium hydroxide obtained were mixed
into 100 parts of the unsaturated polyester resin
(Synoiite 0020 N-2; DSM Resins BV). The processing
viscosity was measured at 23C, using a Brookfield HBT
viscometer with a No. 3 spindle.
- Starting hydroxide: 368 Pas
- deagglomerated hydroxide: 38 Pas
Example 3:
Viscosity behaviour of further crystalline,
deagglomerated aluminium hydroxides in ~P resins
(Synolite 0020 N-2).
A8 compared with the specially crystallized
starting product, the deagglomerated aluminium hydroxide
~hows a falling processing viscosity (here in Synolite
0020 N-2) dep~n~ing on the degree of deagglomeration.
Example:
Starting hydrate: dlo (~m) : 15.9
dso (~m) 36.3
dgo (~m) : 62.0
Viscosity at
150 phr~: 150 Pas

Deagglomerated hydrate No. 1: dlo ( m) : 5.1
dso (~m) 24.6
dgo (~m) : 46.0
Viscosity at
150 phr~: 57 Pas

21~3~
-- 6
Deagglomerated hydrate No. 2: dlo (~m) : 3.5
dso (~m) : 18.3
dgo (~m) : 39.6
Viscosity at
150 phr*: 41 Pas

* Measurement conditions: Brookfield HBT; No. 3 spindle; 23C

Example 4:
The Al(OH)3 obtained in Example 2 was tested for
comparison with commercially obt~;n~hle aluminium hydrox-
ides with respect to the viscosity behaviour and elec-
- trical properties.

Comparison aluminium hydroxides:
Apyral 2 (VAW) Higilite H 320 I
(Showa Denko)
d50 (~m) 20 - 25 10
Soluble Na20 (%) 0.05 0.001
Na20 (%) 0.25 0.06
Specific surface area
according to BET (m2/g) 0.2 3.5
~ 50 ~m (%) 10 - 20 0
5 ~m (%) 5 - 15 25 - 35

120 parts by weight of the aluminium hydroxides
concerned were wor~ed into 100 parts of the epoxy resin
Rutapox 0167 (Bakelite AG, Duisburg). The viscosity
measurements were carried out in accordance with the
conditions in Examples 1 to 3.
For one measurement series, 1~ by weight, rela-
tive to the aluminium hydroxide, of the visco~ity depres-
sant BYR -W 995 (BY~ Chemie) was added to the resin
30 mixture.
Results in Pas without BYR-W 995 with BYR-W 995
Al(OH)3 according to
Example 2 87 54
Apyral 2 73 53
Higilite H 320 I 138 65

21573g9
-- 7
For measurement of the electrical properties
(dielectric strength), a cast moulding according to I~C
St~n~rd 243 (3 mm, 20 seconds at 22C) was stored in a
steam pressure vessel at 1.2 to 1.5 bar and 121C for 1,
2 and 3 days.
Results in kV/mm after 0 1 2 3 (days)
Al(O~)3 according to
Example 2 27 24 22 22
Apyral 2 29 7 6 5
Higilite H 320 I 28 17 16 16
For the measurement of the flame resistance
according to UL-94 st~n~rd, the said epoxy resin had a
degree of filling of 60% by weight. This resulted in a
VO classification.