Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Metal-, ~oxide, -phosphate, -chromate, or -molybdate
anti-corrosion pig~nents are known.
Some of these pigMents have the disadvantage that they
provide only inadequate corrosion pro-tection in paint systems
and tend to form blisters.
An-ti-corrosion agents are described in DE-PS 22 04 985 which
are intended to be used in the manufacture of coatings for
the protection of metals, in particular iron. These coatings
contain zinc- and/or lead salts of nitrophthalic acid. One
is concerned here with so-called corrosion inhibitors, which
are relatively very expensive and can only be used in
combination with other pigments. However, it is pointed out
in DE-AS 25 02 781 that such salts of the ni-trophthalic acids
still have disadvantages which can be attributed to a
deterioration of the anti-corrosion value through blister
formation. ~n place of the salts of phthalic acid, the
corresponding zinc or lead salts of nitroisopn-tilalic acici
nitroterephthalic acid are recommended. In this case one is
again concerned with so-called corrosion inhibitors which
are to be added to the paint systems in coMbination with
other pigments. The very high cost of these corrosion inhibitors
limits their scope of application.
In additionlthese corrosion inhibitors can only be used in
small quantities in order not -to affect other film characteristics
deleteriously.Furtherlnore, their effectiveness cannot
be compared with active anti-corrosion pigments.
The invention has as its ob,ject the improvement of the anti-
corrosive action of the initially mentioned anti-corrosion
pigments and in particular the thorough modification of
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these pigments, so that they significantly improve the adhesion in
paint systems and therewith the anti-corrosive action. This also
presumes a stronger bond betwe~n the pigment surfaee and the
oleophilic binding agents.
This object is satisfied by the invention in aecordanee with the
patent claim.
The pigments in accordance with the invention-possess the advantage
that the reeiprocal effect with the binding agent and the surface
is influeneed in a particularly advantageous manner which leads to
a signi.fieant improvement of the adhesion and of -the anti-corrosive
aetion of coatings obtained by using paints whieh have been form-
. ulated to use the pigments of the invention.
Aeeording to one broad aspeet, therefore, the present invention
.~ relates to metal-, -oxide, -phosphate, -ehromate or -molybdate
anti- eorrosion pigments on the basis of the metals lead, zinc,
aluminium, iron, barium, ealeium, magnesium or ehrome, individually
or in eombination, wherein said pigments are obtained by treatment
of said metal-, -oxide, -phosphate, -ehromate or -molybdate with
phthalie aeid and/or phthalie aeid anhydride at an elevated
temperature.
The pigments in accordance with the invention are preferably
obtained by treatment with phthalie aeid and/or phthalie aeid
anhydride in an amount up to 10 ~ by weight, in partieular 0.3 to
3 % by weight, rela-ted to the pigmen-ts. The treatment with phthalic
aeid and/or phthalic acid anhydride is preferably earried out in an
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aqueous medium with the concentration of the phthalic acid and/or
phthalic acid anhydride solutions preferably amounting to 5 to 8 %
by weight. The treatment is nevertheless preferably carried out at
an elevated temperature, in particular a temperature between 70
and 80 C.
In accordance with another embodiment of the invention, one ean
also mix the pigments with pulverized phthalic aeid and/or pulver-
ized phthalic acid anhydride and heat the mixture up to temperatures
of 150 C.
. .
. Another manufacturing variant consists of adding phthalie aeid
and/or phthalic aeid anhydride in the given manner to a reaetion
component and subsequently effecting the reaction with
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with the other reaction components, for example phosphoric acid.
Pigments in accordance with the invention are primarily
used in paints.
The following examples explain the invention.
Example 1
100 kg. zinc oxide are made into a slurry or suspension with
800 liters of water and are reacted with 88 kg. of an 85 %
phosphoric acid over a time-span of 2 -to 3 hours. One -thereby
obtains a product with the following composition:
0.18 ZnO 0.82/_Zn3 (P04)2 2 ~
Subsequently an almost boiling solution of 0.8 parts phthalic
acid anhydride and 10 parts water , related to pigment, is
added to the product, which is still in the aqueous slurry,
at a temperature of 70 to 80 C. over a time-span of 30
minutes. After stirring for 10 minutes, the pigments are
separated from the aqueous suspension by filtration, are
dried at 105 C. and ground.
Example 2 shows the treatment of zinc oxide. Zinc oxide ,
treated in this way, has a significan-tly better anti-corrosive
value than the initial material.
ExaMple 2
500 kg. of zinc oxide are heated in 2500 liters of water to
a temperature of 70`to 90 C. An almost boiling solution of
5 parts by weight of phthalic acid anhydride and 60 parts by
weight of water rela-ted to pigment is added while stirring
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over a time-span of 60 rninutes. At the end of the reaction
the product is at once filtered off, dried and ground.
Products obtained by annealing processes, for example metallic
mixed oxide or pigments from metallic oxide and oxygenic acids
of phosporus, chroMe and molybdenum may also be treated in
the manner described in Example 2.
Example 3
Zinc molybdate with the general formula
x ZnO y ZnMoO~
is suspended in water, heated to 70 to 90 C. and an almost
boiling solution of phthalic acid added while stirring. Then
the procedure described in Example 1 and Example 2 is carried
out.
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Example 4
500 kg. ZnO are heated in 2500 liters of water to a temperature
of 70 to 80 C. An almost boiling solution of 2.5 parts phthalic
acid anhydride in 30 parts by weight of water is added while
stirring over a time-span of 30 minutes. The conversion to
basic ~inc phosphate is subsequently completed within
approximately 2 hours with 375 Kg. of 75 % phosphoric acid.
A product with the following mole formula results:
0.6 ZnO 0.4 LZn3 (P04)2. 1-8 H20J
The anti-corrosive action of the anti-corrosion pigments of
the invention were tested in the following paint systerns in
comparison wi-th corresponding pigments which had not been
treated with phthalic acid anhydride:
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1. Priming coat on the basis of epoxide ester with PVK
values of 40 % to 45 %, proportion of free binding agent
20 %, Q = 0.8.
2. Priming coat on a basis of alkyd resin modified with wood
oil/tallol, PVK values of 33 to 39 %, proportion of free
binding agent 30 %, Q = 0.7.
3. Single-layer paint on a basis of alkyd ~melamlne resin,
PVK values of 30 to 34 %, proportion of free binding agent
40 %, Q = 0.6.
The pigment-filler combinations were composed as follows:
40 Vol. -% anti-corrosion pigment
25 Vol. -% EWO*-Schwerspat (barium sulphate)
25 Vol. -% magnesium silicate
10 Vol. -% titanium dioxide
With fixed free binding agent proportions ~Q-values) the respec-
tive KVPK were ascertained via the oil number and the free PVK
determined mathematically.
_ PVK
Q KPVK
The paint ingredients were dispersed with the help of the pearl
mill, fineness of grinding c. 15 ~m and then spray-coated onto
sand-blasted deep-drawing sheet metal, sheet thickness approx-
imately 50 + 50 ~um.
The anti-corrosion examination was carried out in a salt
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spray test in accordance wi-th DIN (German Ind~s-trial Standard)
50021 and in the Kesternich test appara-tus in accordance
:: ~ith DIN (German Indws-trial S-tandard) S0018.
The criteria for evaluating the corrosion in terms of:
blister formation of the coating in accordance with
DIN 53209
loss of adhesion of ths coating in accordance with
DIN 531 S1
infiltration at poin-ts of damage in accordance with
DIN 53l67
were summarized by way of so-called evaluation numerals (BWZ):
BWZ 100 = very good
BWZ 90 - 80 = good
BWZ 70 - 60 = good to fair
BWZ 50 - Lo = fair
BWZ 30 - 20 = poor
BWZ 10 - 0 = very poor
The results obtained are summarized in the following table:
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: TABLE
Binding agent: Epoxide ester Q = 0.8
Anti-corrosion pigment PVK Evaluation numerals (BWZ)
in % SS DIN 50021 SFW DIN 50018 1.0S
300 h 10 cycles
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1 zink oxide 45 20 50
2 zink oxide -~ 3 % PSA 44.2 80 60
3 zinc chroma-te 42.3 80 20
4 zinc chromate + 0.5 % 42.0 90 50
PSA
5 zinc phosphate 45.1 20 60
6 zink oxide phosphate
+ 0.3 % PSA 41.0 90 80
7 zinc molybdate 42.8 30 40
8 zinc molybda~e-~ 0.5 %
., PS 41 50 70
PSA = phthalic acid anhydride
PS = phthalic acid
Corresponding improvements of the anti-corrosion value were
also confirmed in the above-mentioned alkyd resin based
on wood oil/tallol at a Q~value of 0.7 and in an oven-dried
single-layer paint based on alkyd /melamine resin, Q = 0.6.
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