Modified nacreous luster pigments for water paint systems

Details Modified nacreous luster pigments for water paint systems Modified nacreous luster pigments for water paint systems

1998-05-22

2001-01-23

Green, Anthony (Department: 1755)

Compositions: coating or plastic

Materials or ingredients

Pigment, filler, or aggregate compositions, e.g., stone,...

C106S416000, C106S417000, C106S436000, C106S438000, C106S439000, C106S442000, C106S445000, C106S446000, C106S447000, C106S448000, C106S450000, C106S455000, C106S460000, C106S481000, C106S482000, C106S483000, C106S490000

Reexamination Certificate

active

06176918

ABSTRACT:

The invention relates to surface-modified pearl lustre pigments for waterborne coating systems.
BACKGROUND OF THE INVENTION
It is known that titanium dioxide particles present as the pigment component in a coating material cause oxidative decomposition of the polymer on exposure to ultraviolet rays and moisture, which is known as whitening. In order to suppress this effect of titanium dioxide, it has been proposed to coat or dope titanium dioxide with compounds of chromium, silicon, aluminium, zinc, phosphorus or zirconium.
EP-A-0 268 918 describes a weathering-resistant pearl lustre pigment having a hydrated zirconium oxide coating on the titanium dioxide base pigment, this coating being obtained by hydrolysis of a zirconium salt in the presence of a hypophosphite.
EP-A-0 342 533 describes a weathering-resistant pearl lustre pigment having, on the titanium dioxide base pigment, a top layer which consists of hydrated zirconium oxide, obtained by hydrolysis in the presence of a hypophosphite, and a hydrated metal oxide. The metal oxide can be cobalt oxide, manganese oxide or cerium oxide.
The modified pearl lustre pigments possess sufficient dispersibility and weathering resistance in nonaqueous coating systems. However, they are unsuitable for use in water-thinable coating systems, since they cause the formation of microfine bubbles in the coating film which significantly increase light scattering and thus have an adverse effect on lustre and colour. In addition, the distinctness of image (DOI) is severely reduced and the regeneration capacity of the coating film is impaired.
U.S. Pat. No. 5,472,491 describes a pearl lustre pigment based on a platelet-form substrate coated with metal oxides and on a top layer which is located on the metal oxide layer and consists of silicon dioxide, at least one further metal hydroxide or metal hydrate of the elements cerium, aluminium or zirconium, and at least one organic coupling reagent. This coupling reagent can be a zirconium aluminate, a metal-acid ester or an organofunctional silane. The coupling reagents must be hydrolysed before binding to the pigment surface. When two or more compounds are used, problems occur as a result of different rates of hydrolysis. Moreover, not more than 60% of the coupling reagents added can be bound to the pigment surface, as a result of which it is necessary to make a corresponding increase in the material employed. The non-coupled fractions remain in the reaction medium and impair the filterability of the pigment. For the binding of the pigment to the coating binder, however, it is necessary for different functional groups to be present on the pigment surface.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a pearl lustre pigment having an aftercoat which contains coupling reagents by means of which the disadvantages of the aftercoat described in U.S. Pat. No. 5,472,491 are avoided.
This object is achieved in accordance with the present invention by a pearl lustre pigment based on a platelet-form substrate coated with metal oxides and on a top layer which is located on the metal oxide layer and consists of at least two oxides and/or mixed oxides from the group consisting of silicon dioxide, aluminium oxide, cerium oxide, titanium oxide and zirconium oxide, and consists of a water-based oligomeric silane system.
The water-based oligomeric silane system is known from EP 0 675 128, EP 0 716 127 and EP 0 716 128. It is prepared by
Mixing water-soluble aminoalkylalkoxysilanes of the general formula I
R—Si(R
1
)
v
(OR
1*
)
3−v
  (I),
preferably aminopropyltriethoxysilane, aminopropylmethyldiethoxysilane, aminopropyltrimethoxysilane or aminopropylmethyldimethoxysilane,
with water-insoluble alkyltrialkoxysilanes of the general formula IIa
R
2
—Si(OR
1**
)
3
  (IIa),
preferably propyltrimethoxysilane, propyltriethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, isobutyltrimethoxysilane or isobutyltriethoxysilane,
and/or water-insoluble dialkyldialkoxysilanes of the general formula III
AA′—Si(OR
1***
)
2
  (III),
preferably dimethyldimethoxysilane, dimethyldiethoxysilane, methylpropyldimethoxysilane or methylpropyldiethoxysilane,
and/or mixtures of water-insoluble alkyltrialkoxysilanes and dialkyldialkoxysilanes of the general formulae II and III,
where R is an amino-functional organic group,
R
1
, R
1*
, R
1**
and R
1***
are a methyl or ethyl radical,
R
2
is a linear or cyclic or branched alkyl radical having 1 to 8 carbon atoms,
A is an unbranched or branched alkyl radical having 1 to 3 carbon atoms and
A′ is an unbranched or branched alkyl radical having 1 to 3 carbon atoms, and
0≦v≦1,
adding water to the mixture and
adjusting the pH of the reaction mixture to between 1 and 8, and
removing the alcohol which is already present and/or has been produced in the reaction.
The oligomeric silane system can also be prepared by
mixing Q moles of water-soluble aminoalkylalkoxysilanes of the general formula I
R—Si(R
1
)
v
(OR
1*
)
3−v
  (I),
preferably aminopropyltriethoxysilane, aminopropylmethyldiethoxysilane, aminopropyltrimethoxysilane or aminopropylmethyldimethoxysilane,
with M moles of water-insoluble alkylalkoxysilanes of the general formula IIb
R
3
—Si(OR
1**
)
3
  (IIb),
where R is an amino-functional organic group,
R
1
, R
1*
and R
1**
are a methyl or ethyl radical and
R
3
is a linear or cyclic or branched alkyl radical having 1 to 6 carbon atoms or a ureido alkyl group of the general formula IV
NH
2
—CO—NH—(CH
2
)
b
—, where 1
≦b≦
6,  (IV)
preferably b=3,
and
0≦y≦1,
in the molar ratio 0<M/Q≦2,
adding water to the mixture,
adjusting the pH of the reaction mixture to between 1 and 8, and
removing the alcohol which is already present and/or has been produced in the reaction.
Furthermore, the oligomeric silane system is obtainable by
mixing water-soluble organosilanes of the general formula V
H
2
N(CH
2
)
f
(NH)
g
(CH
2
)
i
—Si(CH
3
)
h
(OR
0
)
3−h
  (V),
in which 0≦f≦6, g=0 if f=0, g=1 if f>1, 0≦i≦6, 0≦h≦1 and R
0
is a methyl, ethyl, propyl or isopropyl group,
preferably aminopropyltriethoxysilane,
with water-soluble organosilanes, which are nevertheless unstable in the aqueous medium, of the general formula VI
in which 0≦h≦1 and R
0
is a methyl, ethyl, propyl or isopropyl radical,
preferably glycidyloxypropyltrimethoxysilane,
and/or of the general formula VII
H
2
C═CR′—COO(CH
2
)
3
—Si(CH
3
)
h
(OR
0
)
3−h
  (VII),
in which 0≦h≦1, R
0
is a methyl, ethyl, propyl or isopropyl radical and R′ is a methyl radical or hydrogen,
preferably methacryloxypropyltrimethoxysilane,
and a water-insoluble organosilane of the general formula VIII
R″—Si(CH
3
)
h
(OR
0
)
3−h
  (VIII),
in which 0≦h≦1, R
0
is a methyl, ethyl, propyl or isopropyl radical and R″ is a linear, branched or cyclic hydrocarbon radical having 1 to 8 carbon atoms,
preferably propyltrimethoxysilane,
in the molar ratio M=a/(b+c+d),
where a is the sum of the mole fractions of the organosilanes according to formula V, b is the sum of the mole fractions of the organosilanes according to formula VI and c is the sum of the mole fractions of the organosilanes according to formula VII and d is the sum of the mole fractions of the organosilanes according to formula VIII, with 0≦M≦3, especially for M=0 with a=0 and/or c=d=0 and b≧1 and also, preferably 0.5≦M≦3,
adding a water/acid mixture to the mixture,
adjusting the pH of the reaction mixture to between 1 and 8, and
removing the alcohol which is already present and/or has been produced in the reaction.
During the distillative removal of the alcohol it is preferred to add water at the rate at which alcohol or alcohol/water mixture is removed from the reaction medium. For adjusting the pH, monobasic acids are pa

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