Note: Descriptions are shown in the official language in which they were submitted.
INORGANIC PIGMENTS WITH IMPROVED GLOSS AND DISTRIBUTION
IN LACQUER BINDERS
The present invention relates to inorganic pigments
which have improved gloss and distribution in lacquer
binders as a result of treatment with organic auxil-
iaries either before or during a final micronization.
Fog-free high glo-ss coatings and good distri-
bution when incorporated in lacquer binders are im-
portant requirements of high quality pigments.
Apart from other properties, such as good resistance
to weathering and good brightening or tinting power,
the above constitute important criteria for assess-
ing quality. There has been no lack of proposals in
the past for achieving such an aim. One procedure
which characterizes many of thepatents relating to
this subject matter is the treatment of the pigment
surface with organic auxiliaries before or during a
grinding operation which operation concludes the
process of manufacturing the pigment. The grinding
of the pigment is normally carried out in a pin
mill, a ball mill or a ring roll mill such as a
Raymond mill, but exceptionally high quality pigments
may be obtained by micronizationin jet mills such
as air jet or steam jet mills. Numerous compounds
are known for use as organic auxiliaries for modify-
ing the surface of pigments. Apart from polyols,
alkylene oxides, phenols, long chain fatty alcohols
and fatty acid esters, to name but a few examples,
it has also been proposed to use organosilicon
compounds.
The use of organosilicon compounds is aimed
3 at rendering pigments or fillers hydrophobic and at
improving their dispersibility and incorporation in
synthetic materials. German Offenlegungsschrift No.
2,012,017, for example, describes the treatment of
TiO2 with sodium methyl siliconate to improve its
dispersibility in polystyrene. It is also customary
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to render pigments hydrophobic with polysiloxanes,
e.g. with octamethylcyclotetrasiloxane (British Patent
No. 959,211) to improve their incorporation in poly-
amides or to treat them with silanes, e.g. with tri-
alkoxysilanes, as described in British Patent No.825,404.
In addition, the preparation of stable dispersions
in water with the aid of polymethylsiloxanes contain-
ing Si-H groups has been disclosed in Spanish Patent
No. ~9,831.
With the surface treatments described above,
however, it is not possible to obtain pigments which
produce an excellent fog-free gloss in lacquer binders.
It is also known to treat pigments with alkanol-
amines. The use of trialkanolamines, for example, hasbeen proposed in US Patent No. 3,345,187 and the use
of diisopropanolamine in German Patent No. 2,442,678.
In the process according to German O~fenlegungsschrift
No. 1,792,022, triethanolamine is brought into contact
with the pigment surface in the course of a so-called
double steam jet milling process. US Patent No. 2,
737,460 relates to the milling of pigments with tri-
alkanolamines in the pr~sence of finely divided
B fillers such as Aerosil. It is also known to use salts
of alkanolamines with organic acids such as, for
example, lactic acid (~erman Patent No. 1,271,862) or
benzoic acid (US Patent No. 3,172,772).
The procedures mentioned above are either tech-
nically complicated or else expensive and the re-
3o sulting p~gments, although showing marked improvementscompared with titamium dioxides which have not been
organicallS treated, do not meet the highest demands
for ~uality with regard to gloss distribution and
subdivision, and this applies particularly to pigments
which have been after-treated with SiO2 and A120~.
rf~ e
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11~7'711
It has now surprisingly been found that pigments with improved gloss
and distribution in lacquer binders can be obtained easily by treatme~t with
organic auxiliaries before the final micronization if a combination of poly-
hydrogen siloxanes and alkanolamines is used.
The present invention provides inorganic pigments with improved gloss
and distribution in lacquer binders having a coating of polyhydrogen siloxanes
and alkanolamines and also a process for the preparation thereof by coating the
pigments with the above mentioned compounds before or during the final micron-
ization. White pigments based on TiO2 or titanates which have optionally been
after-treated inorganically are particularly suitable inorganic pigments. The
new pigments are suitable in particular for pigmenting polymer materials and
aqueous suspensions. It has been found to be advantageous to use about 0.1 to
3% by weight of polyhydrogen siloxane plus alkanolamine, and a ratio by weight
of polyhydrogen siloxane to alkanolamine within the range of about 2:1 to l:lO,
- preferably about 1:2 to 1:5.
The polyhydrogen siloxanes used may have a straight chain, a branched
chain or a cyclic structure containing for example the following units, option-
ally in alternating arrangement:
[R2R'-SiOlt2] [RH-SiO] [R'-SiO3/2] and [SiO2]
wherein R and R' are the same or different and each may denote a hydrogen atom
or an alkyl, cycloalkyl, aryl and/or alkenyl group, and the number of silicon
atoms is greater than 5.
Polyhydrogen siloxanes which conform to the above definition include,
for example, [SiMe3] end blocked linear polyhydrogen methyl siloxanes, prefer-
ably having chain lengths with an average of lO, 30 or 50 [SiMe2O] units.
Partially hydrogenated polysiloxanes of the
.
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type described are also suitable, particularly those
having 5 [SiHMeO~ or 5 CSiMe2~ units. Polyvinyl
hydrogen methyl siloxanes which are ~SiHMe~ end
blocked are particularly preferred, especially those
with 5 [SiHMeO~ units and 3 ~i(CH=CH2)MeO3 units.
Another preferred class of compounds is polyhydrogen
siloxanes, an example of which is a LSiHMe2~ end
blocked, simply branched permethylated polysiloxane
having 9 [SiMe20~ units.
The a~nol~nes used may be tria~nolamunes, d~ nclamines
a ~ or m~no~no1a~nes, e.g. amlnes carrying a~yl an~or hy~xKy-
aIkyl groups of 1 to 4 ~ bon atoms. Trie~olamune, triisopr ~ nol-
amune, 2-~no-2-methyl-p~nol-1 and 2-amuno-2-hyd~methyl-pnq~r
diol-(1,3) are p~ti ~ arly suitable.
The organic auxiliaries are brought into contact
with the pigment in known manner either before or
during a final milling operation. It is immaterial
whether they are added to the moist filter cake, paste
or sludge obtained in the course of preparation of the
pigment before it is dried or whether they are added
to the dry substance before the final milling operation
in some suitable manner, for example by spraying or
even whether as in the case of milling in a steam jet
mill, they are directly added to the steam before this
is fed into the mill. Also, the effectiveness of the
compounds to be used according to the present invention
does not depend upon the sequence in which they are
added. Regardless of whether mixtures of alkanolamines
and polyhydrogensiloxanes are added or whether the
alkanolamine is added first and the polyhydrogensiloxane
later, or vice versa, the pigments obtained are superior
in their gloss, fog and granularity after micronization
than products which have been treated with alkanolamines
alone or with polyhydrogensiloxanes alone. This clearly
indicates a synergistic effect.
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All inorganic white andcolored pigments are
suitable for the process according to the present inven-
tion. Particularly advantageous results are obtained
with white pi~ments based on TiO2 or titanates or with
colored pigments such as iron oxides. Pigments which
have previously been subjected to an inorganic after-
treatment may also be used.
The process according to the present invention
for improving gloss and fog is independent of the
process used for producing the pigments. Thus a TiO2
pigment may be improved by the process according to the
present invention regardless of whether the pigment
has been prepared by the sulphate process or the TiC14
combustion process and also regardless of whether the
pigment is in the rutile or the anatase form.
To test the pigment ~or gloss and distribution
in lacquer binders, it is dispersed in a la~quer binder
by means of a dissolver. Dispersion is carried out in
a highly viscous binder/solvent mi~ture containing 600/o
of alkyd resin (ricinene-modified alkyd resin, oil
length 35; Bayer Product A~dalOE~35) in xylene under the
following conditions:
Pigment-volume concentration (PVK) of
grinding stock 37 . 6~b
25 Diameter of dissolver disc 3.5 cm = D
Diameter of container 5 . 5 cm =1. 57 D
Distance of dissolver disc ~rom bottom 1. 75 cm =0.5 D
Height to which grinding stock fills
container 3.5 cm = D
3 Peripheral speed of dissolver disc 11 m/s
Dispersion time 5 minutes.
After 5 minutes' dispersion time, samples are
removed and lacquered to a PVK of 15o~b with the alkyd
resin and a melamine resin (trade product Maprenal MF
800, registered Trade Mark of Hoechst AG) so that the
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ratio of alkv~ resin to melamine resin is 77:23. The
degree of fineness of dispersion is determined in the
usual manner with a grindometer (DIN 53 203). The
lac~uers prepared in this way are t,hen applied to
glass plates to form films 120 ~m thic~ when wet, and
the films are hardened at 120C for 30 minutes. The
gloss is measured with a Gonio photometer at an angle
of 25. The height of the peak obtained in the re-
flection maximum is a measure of the gloss and the
height of the scatter curve 1 next to the reflection
maximum is a measure of the gloss fog value.
A high gloss lacquer is distinguished by high
- gloss values and low gloss fog values.
The preparation of the pigments according to the
present invention is described below:
Example 1
A TiO2 pigment having a rutile structure and
prepared by the sulphate process was after-treated
inorganically with 3.8~o SiO2 and 4% A1203 and was then
dried after the usual washing and filtration. The
pigment was sprayed with 0.12~ by weight (based on
the dry pigment) of the polymethyl hydrogen siloxane
having a structure corresponding to the following
average formula
CH3 1 3 /~ 3
CH3 - Si - O - Si ~0~-- Si - CH3
CH3 H 40
and 0.36~ of triethanolamine and was then micronized
in a jet mill operated on superheated steam.
The fineness of the dispersion, tl-e gloss values
and gloss fog values are set forth in Table 1.
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_ 7 ~ 7
Comparison Example ~A)
This comparison example shows that the use of
triethanolamine solely results in a qualitatively
inferior pigment. The rutile pigment used in Example
l`is sprayed with 0.48~ triethanolamine a~ter it has
been dried, and it is then micronized in a jet mill
as described in Example 1. The dispersion properties
are entered in Table l_
Comparison Example (B)
This comparison example shows that the use of -
polymethylhydrogen siloxane solely also results in a
qualitative]y inferior pigment.
The rutile pigment used in Exa~nple 1 is dried
and then sprayed with 0.48~ of the polymethylhydrogen
siloxane described in Example 1 and then micronized;
see Table 1.
Example 2
0.15~ by,weight (based on the dry pigment) of
the polymethylhydrogen siloxane used in Example 1 is
added to the washed filter cake of the rutile pigment
as used in Example 1 before it is,dried. After drying,
the pigment is sprayed with 0. 45% triisopropanolamine
and micronized as described in Example l; see
Table 1.
Example 3
The rutile pigment used in Example 1 is dried
and then sprayed with 0.12~ of the polymethylhydrogen
siloxane described in Example 1 and 0.58~ of 2-amino-2
methyl-l-propanol and then milled in a steam jet mill
as described in Example l; see Table 1,
Example 4
~5 The rutile,pigment used in Example 1 is not organ-
ically after-treated; see ~able 1.
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'`71~
Table 1
Example Organic treatmentGloss Fog Grind- Hegman
(%) (%)ometer value
value
(h)
0.12% o(,~bis(tri- 88 24 12 7
methylsilyl)polyme-
thylhydrogenosilox-
ane
0.36% triethanol-
amine
A 0.48% triethanol- 77 37 20 6.4
amine
B 0.48% O~ -bis(tri- 76 35 16 6.7
methylsilyl) poly-
methylhydrogen-
siloxane
2 0.15% OC,~-bis(tri- 89 22 10 7.2
methylsilyl)poly-
methylhydrogen-
siloxane
0.45% triisoprop-
anolamine
3 0.12% O~,~-bis(tri- 86 26 14 6.9
methylallyl) poly-
methylhydrogen-
siloxane
0.58% 2-amino-2-
methyl-l-propanol
4 None 49~ 10038 4.9
Samples 1, A and B show that a glven weight of mixture is better
than the same weight of the individual components.
,,~.,,~
~,
- 9 -
It will be appreciated that the instant specification
and examples are set forth by way of illustration and not
limitation, and that various modifications and changes may
be made without departing from the spirit and scope of
the present invention.
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