U.S. patent application number 10/856668 was filed with the patent office on 2004-12-02 for process for preparing spherical zinc oxide particles.
Invention is credited to Hynek, Bernd, Marx, Thiemo, Wege, Volker.
Application Number | 20040241085 10/856668 |
Document ID | / |
Family ID | 33441441 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040241085 |
Kind Code |
A1 |
Marx, Thiemo ; et
al. |
December 2, 2004 |
Process for preparing spherical zinc oxide particles
Abstract
The present invention provides a process for preparing
ball-shaped zinc oxide particles and their use.
Inventors: |
Marx, Thiemo; (Viersen,
DE) ; Hynek, Bernd; (Pulheim, DE) ; Wege,
Volker; (Neuss, DE) |
Correspondence
Address: |
Patent Department
Bayer Polymers LLC
100 Bayer Road
Pittsburgh
PA
15205-9741
US
|
Family ID: |
33441441 |
Appl. No.: |
10/856668 |
Filed: |
May 28, 2004 |
Current U.S.
Class: |
423/622 ;
106/425 |
Current CPC
Class: |
B82Y 30/00 20130101;
C08K 3/22 20130101; A61K 8/0241 20130101; C01P 2004/04 20130101;
C01P 2006/10 20130101; C01G 9/02 20130101; C08L 11/00 20130101;
C09J 11/04 20130101; A61K 8/27 20130101; A61K 2800/413 20130101;
C09C 1/043 20130101; C01P 2004/64 20130101; C08L 61/04 20130101;
A61Q 19/00 20130101; C08K 3/22 20130101; C08L 11/00 20130101; C08K
3/22 20130101; C08L 11/02 20130101; C08L 11/00 20130101; C08L
2666/16 20130101 |
Class at
Publication: |
423/622 ;
106/425 |
International
Class: |
C01G 009/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2003 |
DE |
10324305.4 |
Claims
What is claimed is:
1. A process for the batchwise preparation of zinc oxide particles
comprising A1) treating a methanolic solution of zinc salts
corresponding to formula (I) 6 with a concentration of zinc ions
(Zn) of 0.01 to 5 mol per kg of solution with A2) a methanolic
potassium hydroxide solution with a concentration of hydroxide ions
(OH) of 1 to 10 mol per kg of solution in a molar ratio of OH to Zn
of 1.5 to 1.8 with stirring, wherein the precipitation solution is
matured at a temperature of 40 to 65.degree. C. for a period of 5
to 50 min and is then cooled down to a temperature of
.ltoreq.25.degree. C.
2. A process for the continuous preparation of zinc oxide particles
comprising B1) mixing a methanolic solution of zinc salts
corresponding to formula (I) 7 with a concentration of zinc ions
(Zn) of 0.01 to 5 mol per kg of solution and B2) a methanolic
potassium hydroxide solution with a concentration of hydroxide ions
(OH) of 1 to 10 mol per kg of solution in a mixing unit wherein b1)
the molar ratio of OH to Zn is 1.5 to 1.8, b2) mixing is
homogeneous, and the precipitation solution formed is matured at a
temperature of 40 to 65.degree. C. for a period of 5 to 50 min and
is then cooled down to a temperature of .ltoreq.25.degree. C.
3. A process for the batchwise preparation of zinc oxide particles
comprising A1) treating a methanolic of zinc salts corresponding to
formula (I) 8 solution with a concentration of zinc ions (Zn) of
0.01 to 5 mol per kg of solution with A2) a sodium hydroxide
solution, which may optionally contain dissolved KOH, with a total
concentration of hydroxide ions (OH) of 1 to 10 mol per kg of
solution in a molar ratio of OH to Zn of 1.5 to 1.8 with stirring,
wherein, the precipitation solution obtained is matured at a
temperature of 40 to 65.degree. C. for a period of 5 to 50 min and
is then cooled down to a temperature of .ltoreq.25.degree. C.
4. A process for the continuous preparation of zinc oxide particles
comprising B 1) mixing a methanolic solution of zinc salts
corresponding to formula (I) with a concentration of zinc ions (Zn)
of 0.01 to 5 mol per kg of solution and B2) a sodium hydroxide
solution, which may optionally contain dissolved KOH, with a total
concentration of hydroxide ions (OH) of 1 to 10 mol per kg of
solution in a mixing unit wherein b1) the molar ratio of OH to Zn
is 1.5 to 1.8, b2) the mixture being formed in the mixing unit is
blended homogeneously, and, the precipitation solution formed is
matured by keeping at a temperature of 40 to 65.degree. C. for a
period of 5 to 50 min and is then cooled down to a temperature of
.ltoreq.25.degree. C.
5. A process according to claim 1, wherein the molar ratio of OH:Zn
is 1.7-1.8 and the methanolic zinc salt solution is a methanolic
solution of zinc acetate.
6. Zinc oxide particles prepared by a process according to any of
claims 1 to 5.
7. Dispersions comprising zinc oxide particles according to claim
6.
8. Dispersions according to claim 7, having azinc oxide content of
5 to 40 wt. %.
9. Dispersions according to claim 7, wherein the dispersion
comprises water mixed with ethylene glycol and/or
triethanolamine.
10. A filler and/or additive comprising zinc oxide particles
according to claim 6.
11. Vulcanization coactivator comprising zinc oxide particles
according to claim 6.
12. UV absorbers comprising zinc oxide particles according to claim
6.
13. Fungicides and/or biocides comprising zinc oxide particles
according to claim 6.
14. Coatings and molded parts comprising zinc oxide particles
according to claim 6.
Description
FIELD OF THE INVENTION
[0001] The present invention provides a process for preparing
ball-shaped zinc oxide particles and their use.
BACKGROUND OF THE INVENTION
[0002] DE-A 199 07 704 discloses a process for the preparation of
zinc oxides with a mean diameter of 5 to 30 nm and the formulation
of these as concentrated dispersions in organic solvents and/or
water by redispersion, wherein the dispersed zinc oxide is present
substantially as isolated primary particles, i.e. agglomerate-free.
Due to their fine state of division, these particles are
outstandingly suitable as inorganic UV absorbers in transparent
coatings or as coactivators for latex vulcanization.
[0003] Zinc oxides prepared in this way, as compared with those
prepared by a calcination process, have the advantage that the
primary particles are present in a non-agglomerated form or, if
agglomerated to some extent, are reversibly agglomerated so they
can be introduced and dispersed in gaseous, liquid or solid media
in a homogeneous, primary particulate manner by means of
appropriate measures. In contrast, in the case of thermally
prepared particles, the primary particles grow together to give
secondary particles or agglomerates with much higher particle
sizes, due to the effects of heat, and these cannot be broken down
into the primary particles again, either physically, mechanically
or chemically, in an economic manner. Therefore the two types
differ fundamentally, Which is why there are generally completely
different, non-overlapping, areas of use for the two types.
[0004] It has now been found that, ZnO particles with spherical,
ball-shaped surfaces can be obtained during preparation of the
particles. These novel ZnO particles have improved vulcanization
activity, as compared with zinc oxides which are prepared in
accordance with DE-A 199 07 704 and lead to improved material
properties for the vulcanizates.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to a process for the
batchwise preparation of zinc oxide particles including
[0006] A1) treating a methanolic solution for zinc salts
corresponding to formula (I) 1
[0007] wherein
[0008] R represents H or a C.sub.1-C.sub.10 residue with a
concentration of zinc ions (Zn) of 0.01 to 5 mol per kg of solution
with
[0009] A2) a methanolic potassium hydroxide solution with a
concentration of hydroxide ions of 1 to 10 mol per kg of
solution
[0010] in a ratio of OH to Zn of 1.5 to 1.8 with stirring, the
precipitation solution obtained after completion of the addition is
matured at a temperature of 40 to 65.degree. C. for a period of 5
to 50 min and is then cooled down to a temperature of
.ltoreq.25.degree. C.
[0011] The present invention also provides a process for the
continuous preparation of zinc oxide particles including
[0012] B 1) mixing a methanolic solution of zinc salts
corresponding to formula (I) 2
[0013] with a concentration of zinc ions (Zn) of 0.01 to 5 mol per
kg of solution and
[0014] B2) a methanolic potassium hydroxide solution with a
concentration of hydroxide ions (OH) of 1 to 10 mol per kg of
solution
[0015] such that
[0016] b1) the ratio of OH to Zn is 1.5 to 1.8, and
[0017] b2) the mixture being formed in the mixing unit is blended
homogeneously, i.e. to give a mixture with uniform density,
[0018] the precipitation solution formed is matured at a
temperature of 40 to 65.degree. C. for a period of 5 to 50 min and
is then cooled down to a temperature of <25.degree. C.
[0019] In addition, the present invention provides a process for
the batchwise preparation of zinc oxide particles including
[0020] A1) treating a methanolic solution of zinc salts
corresponding to formula (I) 3
[0021] with a concentration of zinc ions (Zn) of 0.01 to 5 mol per
kg of solution with
[0022] A2) an optionally methanolic sodium hydroxide solution,
which may optionally contain dissolved KOH, with a total
concentration of 1 to 10 mol of hydroxide ions (OH) per kg of
solution
[0023] in a molar ratio of OH to Zn of 1.5 to 1.8 with stirring,
the precipitation solution obtained after completion of the
addition is matured at a temperature of 40 to 65.degree. C. for a
period of 5 to 50 min and is then cooled down to a temperature of
.ltoreq.25.degree. C.
[0024] Further, the present invention also provides a process for
the continuous preparation of zinc oxide particles including
[0025] B 1) mixing a methanolic solution of zinc salts
corresponding to formula (I) 4
[0026] with a concentration of zinc ions (Zn) of 0.01 to 5 mol per
kg of solution and
[0027] B2) a optionally methanolic sodium hydroxide solution, which
may optionally contain dissolved KOH, with a total concentration of
1 to 10 mol of hydroxide ions (OH) per kg of solution
[0028] such that
[0029] b1) the ratio of OH to Zn is 1.5 to 1.8,
[0030] b2) the mixture being formed in the mixing unit is blended
homogeneously, i.e. to give a mixture with uniform density,
[0031] the precipitation solution formed is matured at a
temperature of 40 to 65.degree. C. for a period of 5 to 50 min and
is then cooled down to a temperature of <25.degree. C.
DETAILED DESCRIPTION OF THE INVENTION
[0032] Zinc oxides prepared according to the present invention
preferably have a mean primary particle size of 5 to 50 nm, more
preferably of 5 to 20 nm. The particle size can be determined by
ultracentrifuge measurements (H.G. Muller, Colloid. Polym. Sci.,
267, 1113-1116 (1989)).
[0033] A substantial proportion of the particles, i.e. at least
60%, preferably at least 80%, more preferably at least 95% of the
particles, have a spherical, ball-shaped surface, wherein the %-age
data is calculated from the number of ball-shaped particles, with
reference to the total number of particles found in a volume
increment. The method used to determine this includes producing TEM
images of the methanolic zinc oxide precipitates prepared in
accordance with the present invention and evaluating the images
visually. To prepare a sample, the zinc oxide precipitate or
dispersion being investigated can be diluted about 1:1000 with a
mixture of 2 parts by weight of ethylene glycol and 1 part by
weight of water, dripped onto a TEM grid and dried.
[0034] The terms "spherical" or "ball-shaped" mean that the ratio
of the particle length to the particle width is of 3:1 to 1:1,
preferably 2:1 to 1:1, more preferably 1.5:1 to 1:1.
[0035] The proportion of secondary particles (hard, irreversibly
agglomerated primary particles), using the process according to the
present invention, is .ltoreq.20 wt. %, preferably .ltoreq.5 wt. %,
preferably 2 wt. %, with respect to the total amount of
precipitated zinc oxide. To determine this proportion, a 10 wt. %
strength ZnO dispersion can be prepared in the same way as in
working Example 6, stored for 5 days at room temperature and then
filtered through a 0.2 .mu.m cellulose membrane filter. The filter
residues can be dried and weighed. The proportion of agglomerates
can then be obtained by dividing the amount of solid determined in
that way by the amount of ZnO used for the determination.
[0036] Mixtures of methanol with organic solvents and/or water can
be used as solvents in the process according to the present
invention. Methanol/water mixtures are preferably used. The use of
methanol with less than 1 wt. %, preferably less than 0.5 wt. % of
water is preferred. The use of methanol-free solvent systems does
not lead to the formation of zinc oxide particles within the scope
of the present invention.
[0037] The zinc acetate solution of the zinc salts corresponding to
formula (I) 5
[0038] used in the process according to the present invention can
be obtained by simple dissolution of the commercially available
zinc salt, in a methanolic solvent as described above. For economic
reasons, coarsely divided zinc oxide can also be initially
introduced into a methanolic solvent and can be converted into a
zinc salt solution by simply adding the corresponding acid and
optionally water.
[0039] The residue R in formula (I) represents preferably H or an
aliphatic or cycloaliphatic residue, more preferably H, CH.sub.3,
C.sub.2H.sub.5 or C.sub.3H.sub.7.
[0040] Most preferably zinc acetate optionally in form of its
dihydrate can be used as zinc salt in the process of the present
invention.
[0041] These solutions have a zinc ion concentration of preferably
1 to 2 mol per kg of solution.
[0042] The hydroxide solutions A2) or B2) have a concentration of
hydroxide ions of preferably 3 to 6 mol per kg of solution.
[0043] Basically, a methanolic or aqueous sodium hydroxide
solution, which may optionally contain dissolved potassium
hydroxide, can also be used instead of a methanolic potassium
hydroxide solution. The use of KOH-containing precipitation media
(KOH and NaOHIKOH-containing solutions), however is advantageous as
compared with pure NaOH-containing precipitation media and is
therefore normally preferably used.
[0044] For the precipitation reaction, the zinc salt solution A1)
or B1) is kept at a constant temperature of 30 to 65.degree. C.,
preferably 50 to 65.degree. C., more preferably 55 to 58.degree.
C.
[0045] The hydroxide solutions A2) or B2) have a temperature of 10
to 65.degree. C., preferably 15 to 30.degree. C., more preferably
18 to 25.degree. C.
[0046] Preferably the molar ratio of base (OH) to Zn is 1.7-1.8,
more preferably 1.72-1.78. Basically, ratios of less than 1.7 or
more than 1.8 are also possible. Even when the ratio is <1.7,
particles with the initially described sizes, shapes and properties
can be obtained, but the amount of Zn which is not converted to ZnO
is too large (poor space-time yield) so the process becomes
unnecessarily costly and this embodiment is not preferred. When the
ratio is >1.8, preferably >1.9, precipitation can no longer
be controlled in such a way that particles with the initially
described shapes and properties are obtained. Therefore a ratio
>1.8 may not be preferred.
[0047] Basically, to control particle growth and particle
morphology (the shape and surface structure), substances can also
added before, during or after precipitation. These may be
alkoxysilanes such as tetraethyl orthosilicate, zwitterionic
compounds such as "betaine" (carboxytrimethylammonium) or
6-aminohexanoic acid or surface-active substances from colloid
chemistry which are known to a person skilled in the art. Anionic,
cationic or non-ionic surfactants, emulsifiers and/or stabilizers
with carboxylate, sulfonate, ammonium or polyether groups may be
preferred.
[0048] The process according to the present invention is normally
performed at atmospheric pressure (1013 mbar), but may also be
performed at higher or lower pressures. The process temperatures
should then be adjusted accordingly so that they are not above the
boiling point of the lowest-boiling component in the process. For
the upper limit of 65.degree. C. for the process temperature
(corresponding to the boiling point of methanol at that pressure),
this means that if the pressure is >1013 mbar the upper limit
for the process temperature, corresponding to the boiling point of
methanol, may be raised to the boiling point of methanol at the
pressure then prevailing, or in the event of a lower pressure, has
to be lowered accordingly. An upper limit of >65.degree. C. for
the temperature during the process is therefore possible.
[0049] For blending purposes, all stirring and mixing techniques
included in the prior art can be used in the batch process, the use
of radial and horizontal mixers such as cross-arm paddle mixers and
MIG stirrers with aligned blades in combination with flow spoilers
being preferred.
[0050] The energy input for the stirrers is generally 0.1 to 3
Watts per liter, preferably 0.2 to 0.8 Watts per liter.
[0051] Solution A2) is preferably added to A1) within less than 6
minutes, preferably within less than 4 minutes, more preferably
within less than 3 minutes.
[0052] The temperature during the precipitation process is
preferably, .ltoreq.65.degree. C., more preferably,
.ltoreq.60.degree. C., most preferably 55 to 60.degree. C.
[0053] The subsequent maturation process can be performed by
continuing to stir the precipitation solution at preferably 50 to
65.degree. C., more preferably 55 to 60.degree. C. for preferably
20 to 40 min, more preferably 30 to 35 min.
[0054] The lower limit of 40.degree. C. cited as the lower limit
for the maturation temperature in all the process variants is the
temperature above which maturation proceeds satisfactorily and
above which therefore the maturation process is also normally
performed. However, this does not exclude the use of maturation
temperatures of .ltoreq.40.degree. C.
[0055] Subsequent cooling down is achieved by the use of external
cooling with a suitable medium such as cold water or brine, wherein
the final temperature is preferably 10 to 25.degree. C., more
preferably 15 to 20.degree. C., which means that further growth of
the particles to give primary particles >50 nm, the formation of
particles with e.g. rod-shaped morphology and/or agglomeration to
give secondary particles, is prevented. The cooling process for the
entire precipitation solution preferably takes less than 60
min.
[0056] In the continuous process, the two solutions B1) and B2) can
be continuously brought together in a mixing unit of the static
mixer type, or a T- or Y-junction piece, optionally with a
downstream mixing section, and blended. The mixing units and the
rates of flow of the reactant solutions or the precipitation
solution are designed in such a way that homogeneous blending is
achieved within preferably less than 6, preferably less than 4,
more preferably less than 3 seconds. The time refers to a volume
increment which is formed at time t =0 during the combination of a)
and b) having a uniform density after preferably t <6, more
preferably <4, most preferably <3 seconds.
[0057] The amount delivered of solutions B1) and B2) is adjusted in
the process according to the present invention in such a way that,
with the given starting temperatures of B 1) and B2), the
temperature of the precipitation solution is preferably,
.ltoreq.65.degree. C., more preferably, .ltoreq.60.degree. C. and
more preferably 55 to 60.degree. C. and the criterion for mixing
time given above is complied with.
[0058] Subsequent particle maturation can be performed by passing
the precipitation solution through a residence time section which
is kept at a constant temperature of 50 to 65.degree. C.,
preferably 55 to 60.degree. C., wherein the latter is designed in
such a way that the residence time for a volume increment of
precipitation solution is preferably 20 to 40 min, more preferably
30 to 35 min. Subsequent cooling down to preferably 10 to
25.degree. C., more preferably 15 to 20.degree. C. can be performed
by e.g. collecting the precipitation solution emerging from the
residence time section in a tank with adequate jacket cooling or
via heat exchangers from the prior art which are known per se to a
person skilled in the art. Alternatively, a residence time section
is not used, wherein the entire precipitation solution being
produced after the blending procedure is collected in a stirred
tank cooled to .ltoreq.20.degree. C., preferably,
.ltoreq.10.degree. C. (effective internal temperature) and, after a
desired time, this is heated with stirring to preferably 50 to
65.degree. C., more preferably 55 to 60.degree. C., without the
further addition of any precipitation solution, and is matured for
preferably 20 to 40 min, more preferably 30 to 35 min
(semi-continuous process).
[0059] Also possible is precipitation in a stirred-tank under the
conditions given for the batch process, wherein, however, the
precipitate being formed is continuously withdrawn and either
collected in a second tank at a temperature of .ltoreq.20.degree.
C., preferably .ltoreq.10.degree. C. (effective internal
temperature) and then matured (see semi-continuous process) or is
continuously matured in a suitably designed stirred tank
cascade.
[0060] Subsequent cooling down is achieved by external cooling with
a suitable medium such as cold water or brine, wherein the final
temperature is preferably 15 to 25.degree. C., more preferably 15
to 20.degree. C. The cooling process for the entire precipitation
solution preferably takes less than 60 min.
[0061] According to the present invention, dissolved substances can
be removed from the zinc oxide precipitates prepared and matured in
accordance with the present invention and the precipitates are
concentrated down by sedimentation in a centrifuge or under the
effects of gravity or by cross-flow membrane filtration
(nanofiltration or ultrafiltration using ceramic membranes having
an average pore diameter of 5 nm build in multi-channel
elements).
[0062] From the zinc oxides or their precipitates prepared by the
process according to the present invention can be prepared
dispersions in a variety of organic or aqueous solvents or
mixtures, optionally with the aid of mechanical or chemical
dispersers such as ionic or non-ionic surfactants, and/or
surface-modifying compounds such as alkanoic acids and alkanoates
with preferably 3 to 25 carbon atoms such as e.g. oleic acid,
amines, aminoalcohols, alkoxysilanes or the products of hydrolysis
of one or more alkoxysilanes by aqueous acids.
[0063] The dispersions mentioned above are prepared by stirring the
methanolic zinc oxide precipitates obtainable in accordance with
the present invention into organic and/or aqueous solvents or
mixtures of these, optionally with the aid of surface-modifying
substances.
[0064] According to the present invention, the methanol present in
the dispersions can be removed by distillation in order to improve
the dispersion status of the particles.
[0065] According to the present invention, water, monoalcohols,
diols, aminoalcohols, alkanes, ethers, esters and also mixtures
thereof can be used as solvents.
[0066] The use of halogenoalkanes and halogenoalkane/alcohol
mixtures, such as dichloromethane/methanol and chloroform/methanol
mixtures, are also preferred.
[0067] The use of alkanoic acids and alkanoates with preferably 3
to 25 carbon atoms, such as e.g. oleic acid, amines, preferably
alkyl-, dialkyl- or trialkylamines, as stabilizers enables the zinc
oxide particles prepared in accordance with the present invention
also to be provided as a stable finely divided dispersion in
non-polar solvents such as oils, alkanes and/or aromatic
compounds.
[0068] Preferably, 10 wt. % of water, with respect to the ZnO
present (dry weight), is added, with stirring, to a zinc oxide
precipitate prepared in accordance with the invention and then a
mixture of a monoalcohol, preferably n-butanol, and at most 5 wt. %
of triethanolamine is added and after stirring for 30 minutes the
methanol present is removed by distillation.
[0069] The solids concentration of the zinc oxide precipitates used
to formulate dispersions is typically 5 to 80 wt. %, preferably 15
to 40 wt. %. The conductivity of the methanolic phase in these
precipitates is less than 200 mS/cm, preferably less than 15 mS/cm,
more preferably 0.005 to 5 mS/cm.
[0070] To improve the degree of dispersion of the particles,
mechanical homogenization processes from the prior art can be used,
with instruments such as high-speed stirrers (e.g.
IKA-Ultra-Turrax.RTM. T25 basic, IKA-Werke GmbH & Co KG,
D-79219 Staufen), ultrasonic dispersers (e.g. UP200S, UP400S, Dr.
Hielscher GmbH, D-14513 Berlin) and/or jet dispersers (Chem. Ing.
Tech. (69), 6/97, p. 793-798; EP-A 0 766 7997) being used.
[0071] The present invention also provides zinc oxides obtainable
by the process according to the present invention and also
dispersions prepared from same.
[0072] The use of these dispersions of primary particulate
redispersed zinc oxides includes the preparation of molded items
and/or coatings, for example those with UV-absorbing and/or a
biocidal effect. Coatings are understood to be either polymeric
systems for the coating of or adhesion of materials such as metals,
plastics or glass or else cremes, salves, gels or similar solid or
free-flowing formulations for use in the cosmetic or pharmaceutical
area. Zinc oxides according to the present invention can also be
used in plastics, rubbers, sealant compositions or adhesive
compositions as fillers and/or additives with e.g. an acid-binding
or catalytic effect.
[0073] The use of zinc oxides according to the present invention as
vulcanization coactivators in rubbers and/or latex molded items is
preferred.
[0074] The redispersible nanoparticulate zinc oxides according to
the present invention can, as mentioned, be used as vulcanization
coactivators during the preparation of latices based on natural and
synthetic rubbers of all kinds.
[0075] Suitable rubbers which can be used to prepare latices
include, apart from the wide variety of different natural latex
formulations, synthetic rubbers such as natural latex and synthetic
polyisoprenes, acrylonitrile/butadiene copolymers optionally
containing carboxylated and/or self cross-linking groups,
styrene/butadiene copolymers optionally containing carboxylated
and/or self cross-linking groups, acrylonitrile/butadiene/styrene
copolymers optionally containing carboxylated and/or self
cross-linking groups, and optionally carboxylated chlorobutadiene
latices. However, natural latex, carboxylated
acrylonitrile/butadiene copolymers and chlorobutadiene latices as
well as carboxylated chlorobutadiene latices are preferred.
[0076] During the vulcanization of different rubber latices, zinc
oxide dispersions according to the invention are used in amounts of
2.0 to 0.01, preferably 0.5 to 0.05 parts by weight, with respect
to 100 parts by weight of a latex mixture (dry wt./dry wt.) during
vulcanization.
[0077] The zinc oxide dispersions used have a ZnO content of
typically 5 to 40 wt. %, preferably 15 to 25 wt. %, wherein any
aqueous medium, preferably mixtures of ethylene glycol/water,
triethanolamine/water or ethylene glycol/water/triethanolamine, are
suitable as the dispersion medium. The ratio by weight of ethylene
glycol to water is preferably 5:1 to 1:1, more preferably 2.5:1 to
1.5 1. The ratio by weight of triethanolamine amine to water is
preferably 1:5 to 1:1, more preferably 1:2.5 to 1:1.5. The ratio by
weight of ethylene glycol to water to triethanolamine is preferably
10:5:5 to 10:5 0.1, more preferably 10:5:2 to 10:5:0.5.
EXAMPLES
[0078] The concentration of zinc oxide was determined in a similar
way to that described in DE-A 199 07 704, by UV spectroscopic
absorption measurements or, after dissolving the zinc oxide with
glacial acetic acid or ammonia, by a volumetric titration with
EDTA, using indicator buffer tablets.
Example 1
Preparation of Nano-ZnO from Zinc Oxide
[0079] 240.35 g of zinc oxide (tech. grade 99.8 wt. %) were
initially introduced into 1320 g of methanol (tech. grade 99.9 wt.
%) and heated to a steady 50.degree. C. The solid was dissolved by
adding 355.74 g of glacial acetic acid (tech. grade 99.9 wt. %) and
51.15 g of fully deionized water and the mixture was then heated to
a steady 55.degree. C. In order to remove any undissolved ZnO, a
total of 34.36 g of KOH (tech. grade 90.22 wt. %) were added in 3
portions. Stirring was continued for 40 minutes and then a solution
of 290.00 g of KOH (tech. grade 90.22 wt. %) in 660.00 g of
methanol were added over the course of 2 minutes. The reaction
temperature was 60.degree. C. during the entire precipitation
process. After a maturation time of 35 min, the reaction mixture
was cooled to room temperature within 10 minutes by means of
external cooling with ice.
Example 2
Preparation of Nano-ZnO from Zinc Acetate Dihydrate
[0080] 19800 g of methanol were initially introduced into a tank,
under an atmosphere of nitrogen, and 9626 g of KOH were added
carefully in portions with external water cooling. After stirring
for a further 60 min, the dissolution process was terminated. In a
second tank, 19338 g of zinc acetate dihydrate in 39600 g of
methanol were initially introduced, at room temperature and under
inert conditions. Then, under intensive stirring (MIG stirrer, 0.5
W/I), the mixture was heated to 50.degree. C. and stirred for 30
min. After 60 min, the internal temperature had risen to 55.degree.
C. and 3130 g of the KOH/MeOH solution already made up was added to
the vigorously stirred zinc acetate solution. The mixture than
became largely clear. After a total of 30 min after adding the KOH,
the actual precipitation process was initiated by transferring the
major amount of the methanolic KOH solution over the course of 5
min. The temperature then rose to 58.degree. C. After completion of
the transfer process, the mixture was heated to 60.degree. C. and
the temperature was held for 35.degree. C. Then the mixture was
cooled to 20.degree. C. by means of external water-cooling.
Example 3
Purification and Concentration of a ZnO Precipitation Prepared
According to Example 1
[0081] The particles were compacted by sedimentation of the ZnO
particles in the precipitate prepared according to example 1 for a
period of 12 hours under the effects of gravity, then the clear
methanolic supernatant liquid was removed from above via a lance
using an attached pump, 550 g of fresh methanol were added with
stirring and then the particles were allowed to settle out for a
further 12 hours. The procedure was repeated a further 4 times,
until the conductivity of the methanol removed from above was 1.9
mS/cm. The compacted zinc oxide precipitate had a ZnO content of
37.0 wt. %.
Example 4
Preparation of a 6-Aminohexanoic Acid-Stabilized Hydrosol
[0082] 54.1 g (ZnO content: 37.0 wt. %, corresponding to 20 g of
ZnO) of the washed precipitate from example 3 were dispersed with a
solution of 1 g of 6-aminohexanoic acid in 200 g of water. Then the
total amount of dispersion was concentrated down to 200 g using a
rotary evaporator at 45.degree. C. bath temperature and 100 mbar
pressure, wherein a translucent long-term stable dispersion of
primary particulate redispersed particles was obtained.
Example 5
Preparation of a Sol in Triethanolamine/Water
[0083] 54.1 g (ZnO content: 37.0 wt. %, corresponding to 20 g of
ZnO) of the washed precipitate from example 3 were dispersed in 180
g of a mixture of triethanolamine and distilled water. Then the
total amount of dispersion was concentrated down to 200 g using a
rotary evaporator at 45.degree. C. bath temperature and 100 mbar
pressure, wherein a translucent long-term stable dispersion of
primary particulate redispersed particles was obtained.
Example 6
Preparation of a Sol in Ethylene Glycol/Water/Triethanolamine
[0084] 62.5 g (ZnO content: 37.0 wt. %, corresponding to 20 g of
ZnO) of a ZnO precipitate according to example 3 were dispersed in
180 g of a mixture of ethylene glycol/water/triethanolamine (ratio
10:5:1). Then the total amount of dispersion was concentrated down
to 200 g using a rotary evaporator at 45.degree. C. bath
temperature and 100 mbar pressure, wherein a translucent long-term
stable dispersion of primary particulate redispersed particles was
obtained.
Example 7
Preparation of a Sol in Ethylene 2Glycol/Water
[0085] 62.5 g (ZnO content: 32.0 wt. %, corresponding to 20 g of
ZnO) of a washed precipitate according to example 3 were dispersed
in 180 g of a 2:1 mixture of ethylene glycol/water. Then the total
amount of dispersion was concentrated down to 200 g using a rotary
evaporator at 45.degree. C. bath temperature and 100 mbar pressure,
wherein a translucent long-term stable dispersion of primary
particulate redispersed particles was obtained.
Example 8
Preparation of an Organosol in CH.sub.2Cl.sub.2
[0086] A ZnO precipitate prepared according to example 1 was
allowed to settle out for 4 hours. The supernatant liquid (2043 g,
conductivity 24.3 mS) was removed from above and the residue was
stirred for 30 min with 600 g of methanol. The dispersion of
primary particulate redispersible particles was then centrifuged
for 30 min at 5500 rpm in a laboratory centrifuge (Haraeus
Variofuge RF, rotor radius 20.4 cm). The transparent supernatant
liquid (837 g, conductivity 15.7 mS) was decanted off. The solid
residue (263.1 g) was redispersed with 263.1 g of dichloro-methane.
The dispersion of primary particulate redispersed ZnO particles
made up had a weight of 508.3 g. After settling out for 72 h, this
mixture was centrifuged for 30 min at 5500 rpm and pressure
filtered through a 1 Am filter. A translucent, long-term stable
dispersion of primary particulate redispersed particles was
produced.
Example 9
Preparation of an Organosol in Butanol/triethanolamine
[0087] 28.4 g of a 4 wt. % strength solution of triethanolamine in
n-butanol were added, with stirring, to 71.6 g of a precipitate
prepared according to example 1 and washed according to example 3
(34.8 wt. % ZnO, conductivity of the liquid phase 3 mS/cm). To
improve the degree of dispersion of the primary particles, the
dispersion obtained was homogenized by a single treatment with a
nozzle jet disperser at 400 bar. A translucent, long-term stable
dispersion of primary particulate redispersed particles was
produced.
Example 10
Redispersible Zinc Oxides in Latex Molded Parts
[0088] Use of the dispersion obtained from example 6 to produce
latex molded parts.
[0089] 167 g of a natural latex of the-HA type (according to the
ISO 2004 specification) was mixed, at room temperature with
stirring, with 5.0 parts by weight of a 10 wt. % strength aqueous
potassium hydroxide solution and with 0.70 parts by weight of a 20
wt. % strength potassium laurate solution as stabilizer. Then 20.6
parts by weight of a vulcanization paste, consisting of 1.5 parts
by wt. of colloidal sulfur, 0.6 parts by wt. of zinc
dithiocarbamate (ZDBC), 1.5 parts by wt. of zinc
mercaptobenzothiazole (ZMBT), 1.5 parts by wt. of an anti-ageing
agent based on phenol and 15.5 parts by wt. of a 5 wt. % strength
solution of a disperser consisting of an Na salt of a condensation
product of naphthalinesulfonic acid and formaldehyde, were added.
In addition, 0.25 parts by wt. of a commercially available
colophonium wax emulsion (Michemlube.RTM. 124, (Michelman, Inc.,
9080 Shell Road, Cincinnati, Ohio 45236-1299 USA)) were added.
[0090] The solids content of this latex compound was 56 wt. %.
[0091] The data relating to parts by wt. (parts by weight) refer to
100 parts by weight of dry rubber substance, which corresponds to
167 parts by weight of wet natural latex.
[0092] The vulcanization activator ZnO was then added in two
different ways:
[0093] a) the corresponding amount of zinc oxide was added directly
following the previous steps or
[0094] b) this was only added 2 hours after the previous steps,
with stirring.
[0095] Amount of Zinc Oxide Added:
[0096] Trial series 10-A with 0.05 parts by wt. of zinc oxide,
prepared as in example 6 (according to the invention)
[0097] Trial series 10-B with 2.0 parts by wt. of zinc oxide, white
sealer (surface area 10 m.sup.2/g; manufactured by Grillo Zinkoxid
GmbH, Germany; powdered form) (comparison)
[0098] Trial series 10-C with 1.0 parts by wt. of active zinc oxide
(surface area at least 45 m.sup.2/g; manufactured by Bayer AG,
Germany; powdered form) (comparison)
[0099] Following this, maturation was performed for 48 hours in
each case with constant stirring at 50 rpm and a temperature of
40.degree. C. This matured compound was then filtered through a 100
.mu.m filter in order to remove any coagulated material. After
allowing the filtered latex to stand for 10 minutes, dip molding
was performed to prepare specimen molded parts. Here, lightly
sand-blasted glass plates (dimensions 100.times.180.times.4 mm)
were dipped into a 15 wt. % strength calcium nitrate solution, as
coagulant solution, for 10 seconds and dried. A film deposition of
about 0.30 mm was achieved in this way. The films prepared in this
way were then dried at 80.degree. C. in hot air for a period of 30
min and then vulcanized at 120.degree. C. for 15 min.
[0100] After a conditioning phase of 24 hours in a normal
atmosphere, the non-aged specimen molded parts obtained were
subjected to materials testing, wherein the modulus (M300: modulus
at 300% extension), the strength (F-max) and the extension at break
(Break ext.: extension up to the break point) were determined
(Zwick test equipment measured in accordance with DIN 53 504,
specimen molded part S2, and ISO 37).
1TABLE 1 Strength values without thermal ageing M300 F-max Break
ext. Example [MPa] [MPa] [%] 10-A a) 1.7 21.9 774 10-A b) 1.5 24.9
832 10-B a) 2.0 18.3 619 10-B b) 1.5 21.6 774 10-C a) 2.3 15.7 569
10-C b) 2.4 14.1 552
[0101] The results show that the zinc oxide prepared according to
the present invention provides comparable strength values, despite
a lower amount being used, to those obtained with the use of 2.0
parts by wt. of white sealer zinc oxide or 1.0 parts by wt. of a
zinc oxide with a high surface area. The modulus at 300% extension
is much lower when using the zinc oxide prepared according to the
present invention than when using comparison samples with zinc
oxides which are not according to the present invention. This
effect leads to greater wearer comfort which is of importance, for
example, when producing latex gloves. The extension up to the break
point in the case of trial series 10-A according to the invention
also gives higher values than the comparison tests 10-B and
10-C.
[0102] To assess the resistance to ageing, the specimen molded
parts were then stored for 8 and 16 h in hot air at 100.degree. C.
and the strength values mentioned above were determined again.
2TABLE 2 Strength values after thermal ageing, 8 h at 100.degree.
C. M300 F-max Break ext. Example [MPa] [MPa] [%] 10-A a) 1.7 18.6
745 10-A b) 1.5 23.2 816 10-B a) 2.5 15.4 566 10-B b) 1.4 20.5 798
10-C a) 2.8 11.8 510 10-C b) 2.8 12.1 495
[0103]
3TABLE 3 Strength values after thermal ageing, 16 h at 100.degree.
C. M300 F-max Break ext. Example [MPa] [MPa] [%] 10-A a) 1.7 17.3
728 10-A b) 1.6 21.4 789 10-B a) 2.6 13.2 526 10-B b) 1.4 18.7 785
10-C a) 2.9 10.1 478 10-C b) 2.8 6.2 453
[0104] Assessment after ageing showed clear improvements in
stability after 8 and 16 hours storage in hot air at 100.degree. C.
in the case of trial series 10-A a) and b) (better resistance to
ageing).
Example 11
[0105] 167 g of a natural latex of the HA type (according to the
ISO 2004 specification) were mixed with 5.0 parts by wt. of a 10
wt. % strength aqueous potassium hydroxide solution and with 1.25
parts by weight of a 20 wt. % strength potassium laurate solution
as stabilizer, at room temperature and with stirring. Then 7.8
parts by weight of a vulcanization paste consisting of 1.0 parts by
wt. of colloidal sulfur, 0.6 parts by wt. of zinc dithiocarbamate
(ZDBC), 0.3 parts by weight of zinc mercaptobenzothiazole (ZMBT),
1.0 parts by wt. of an anti-ageing agent based on phenol were added
and 4.9 parts by wt. of a 5 wt. % strength aqueous solution of a
disperser consisting of the Na salt of a condensation product of
naphthalinesulfonic acid and formaldehyde were also added.
[0106] Then the stated amounts of zinc oxide were added, with
stirring.
[0107] 11-A: 0.05 parts by wt. of a zinc oxide prepared according
to example 6 and
[0108] 11-B: 0.05 parts by wt. of a zinc oxide prepared according
to DE-A 199 07 704
[0109] 11-C: 1.0 parts by wt. of zinc oxide WS (surface area 10
m.sup.2/g, manufactured by Grillo Zinkoxid GmbH, Germany; powdered
form), used as a 50 wt. % strength aqueous paste
[0110] 11-D:0.5 parts by wt. of active zinc oxide (surface area at
least 45 m.sup.2/g;
[0111] Bayer AG, Germany; powdered form) used as a 5 wt. % strength
aqueous paste.
[0112] These mixtures were then adjusted to a solids content of 45
wt. % by adding water. Following this, the maturation process was
performed in each case for 48 hours with constant stirring at 50
rpm and at a temperature of 40.degree. C. This matured compound was
then filtered through a 100 .mu.m filter in order to remove any
coagulated material. After allowing the filtered latex to stand for
10 minutes, dip molding was performed to prepare specimen molded
parts. Here, glass plates (as described in example 10) were dipped
into a 15 wt. % strength calcium nitrate solution, as coagulant
solution, for 10 seconds and dried. A film deposition of about 0.30
mm was achieved in this way. The films prepared in this way were
then dried at 80.degree. C. in hot air for a period of 30 min and
then vulcanized at 120.degree. C. for 15 min.
[0113] After a conditioning phase of 24 hours in a normal
atmosphere, the non-aged specimen molded parts obtained were
subjected to materials testing, wherein the moduli (M300 and M700:
modulus at 300 and 700% extension respectively), the strength
(F-max) and the extension at break (Break ext.: extension in % up
to the break point) were determined (Zwick test equipment measured
in accordance with DIN 53 504, specimen molded part S2, and ISO
37).
4TABLE 4 Strength values without thermal ageing M300 M700 F-max
Break ext. Example [MPa] [MPa] [MPa] [%] 11A 1.1 7.1 23.6 934 11B
1.4 8.6 22.1 857 11C 1.5 13.4 26.2 829 11D 1.6 19.1 21.7 725
[0114] The nanoparticulate zinc oxide according to example 6,
according to the invention, exhibits a higher strength, a lower
modulus and a higher extension at break in comparison to the
nanoparticulate zinc oxide already described but also as compared
with the types of zinc oxide used in practice.
[0115] To assess the resistance to ageing, the specimen molded
parts were then stored in hot air at 100.degree. C. for 8 h and 16
h and the strength values mentioned above were determined
again:
5TABLE 5 Strength values after thermal ageing, 8 h at 100.degree.
C. M300 M700 F-max Break ext. Example [MPa] [MPa] [MPa] [%] 11A 1.2
6.7 23/6 923 11B 1.5 12.1 18.7 764 11C 1.5 12.1 22.7 797 11D 1.7
17.2 21.2 735
[0116]
6TABLE 6 Strength values after thermal ageing, 16 h at 100.degree.
C. M300 M700 F-max Break ext. Example [MPa] [MPa] [MPa] [%] 11A 1.1
5.9 21.4 921 11B 1.5 10.7 17.3 770 11C 1.6 17.2 21.8 734 11D 1.8
18.8 669
[0117] The improved resistance to ageing was also exhibited after
the ageing process. This was expressed in particular by the virtual
absence of losses in strength as compared with all the other types
of zinc oxide and especially in that no increases in the modulus
values were noted. The extension at break determined was virtually
unaltered, whereas the extension at break decreased clearly, by up
to 100%, with the types of zinc oxide used for comparison
purposes.
[0118] Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood
that such detail is solely for that purpose and that variations can
be made therein by those skilled in the art without departing from
the spirit and scope of the invention except as it may be limited
by the claims.
* * * * *