U.S. patent application number 10/469254 was filed with the patent office on 2004-07-29 for silicon dioxide dispersion.
Invention is credited to Adam, Johannes.
Application Number | 20040147029 10/469254 |
Document ID | / |
Family ID | 8176631 |
Filed Date | 2004-07-29 |
United States Patent
Application |
20040147029 |
Kind Code |
A1 |
Adam, Johannes |
July 29, 2004 |
Silicon dioxide dispersion
Abstract
The invention relates to a silicon dioxide dispersion that
comprises a) an outer flowable phase containing a1) polymerizable
monomers, oligomers and/or prepolymers that can be converted to
polymers by non-radical reaction; and/or a2) polymers, b) a
disperse phase containing amorphous silicon dioxide. The inventive
dispersion is characterized in that the average particle size
d.sub.max of the silicon dioxide as measured by small angle neutron
scattering (SANS) is between 3 and 50 nm at a maximum half-width of
the distribution curve of 1.5 d.sub.max. Such a silicon dioxide
dispersion can be easily manufactured even at higher concentrations
of the disperse phase and can be used to produce polymer materials
that have advantageous properties, especially advantageous
mechanical properties.
Inventors: |
Adam, Johannes; (Dreseden,
DE) |
Correspondence
Address: |
Mary Ann D Brow
Medlen & Carroll
Suite 350
101 Howard Street
San Francisco
CA
94105
US
|
Family ID: |
8176631 |
Appl. No.: |
10/469254 |
Filed: |
March 15, 2004 |
PCT Filed: |
February 28, 2002 |
PCT NO: |
PCT/EP02/02198 |
Current U.S.
Class: |
436/8 |
Current CPC
Class: |
C08K 3/36 20130101; C08K
7/18 20130101; Y10T 436/10 20150115 |
Class at
Publication: |
436/008 |
International
Class: |
G01N 031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2001 |
EP |
01104919.4 |
Claims
1. A silicon dioxide dispersion comprising a) an external fluid
phase comprising a1) polymerizable monomers, oligomers and/or
prepolymers convertible to polymers by nonradical reactions; and/or
a2) polymers, b) a disperse phase comprising amorphous silicon
dioxide, characterized in that the average particle size d.sub.max
of the silicon dioxide as measured by means of small-angle neutron
scattering (SANS) is between 3 and 50 nm at a maximum half-width of
the distribution curve of 1.5 d.sub.max.
2. The dispersion of claim 1, characterized in that the average
particle size is between 6 and 40 nm, preferably 8 and 30 nm, more
preferably 10 and 25 nm.
3. The dispersion of claim 1 or 2, characterized in that the
half-width of the distribution curve is not more than 1.2
d.sub.max, preferably not more than d.sub.max, more preferably not
more than 0.75 d.sub.max.
4. The dispersion of one of claims 1 to 3, characterized in that
the fraction of the external phase as a proportion of the
dispersion is 20-90% by weight, preferably 30-80% by weight, more
preferably 40-70% by weight.
5. The dispersion of one of claims 1 to 4, characterized in that
the fraction of the disperse phase as a proportion of the
dispersion is 10-80% by weight, preferably 20-70% by weight, more
preferably 30-60% by weight.
6. The dispersion of one of claims 1 to 5, characterized in that
the silicon dioxide particles are substantially spherical.
7. The dispersion of one of claims 1 to 6, characterized in that it
further comprises auxiliaries selected from the group consisting of
solvents, plasticizers, crosslinkers, catalysts, stabilizers,
dispersants, curing agents, reaction mediators and agents for
influencing the fluidity of the dispersion.
8. The dispersion of one of claims 1 to 7, characterized in that it
is water-free.
9. The dispersion of one of claims 1 to 8, characterized in that
the external phase comprises at least one substance selected from
the group consisting of polyols, polyamines, linear or branched
polyglycol ethers, polyesters and polylactones.
10. The dispersion of one of claims 1 to 8, characterized in that
the external phase comprises at least one reactive resin.
11. The dispersion of one of claims 1 to 10, characterized in that
the polymerizable monomers, oligomers and/or prepolymers contain C,
0, N and/or S atoms in the main chain.
12. The dispersion of one of claims 1 to 11, characterized in that
the external fluid phase comprises polymerizable monomers without
radically polymerizable double bonds and/or reactive resins.
13. The dispersion of one of claims 1 to 12, characterized in that
the external fluid phase further comprises silanes.
14. The dispersion of claim 13, characterized in that the silanes
are present in an amount of 60-150 mol % based on the molar amount
of the silanol groups on the surface of the silicon dioxide
particles of the amorphous phase.
15. A process for preparing a dispersion of one of claims 1 to 14,
characterized by the following steps: a) introducing an aqueous
silicate solution, b) polycondensing the silicate to a particle
size of 3-50 nm, c) adjusting the resulting silica sol to an
alkaline pH, d) optionally concentrating the sol, e) mixing the sol
with constituents of the external fluid phase of the dispersion, f)
optionally removing water and/or other solvent constituents from
the dispersion.
16. The process of claim 15, characterized in that the aqueous
silicate solution is an alkali metal silicate solution, in
particular a sodium silicate and/or potassium silicate
solution.
17. The process of claim 16, characterized in that the
concentration of the aqueous silicate solution is 20-50% by
weight.
18. The process of one of claims 15 to 17, characterized in that
the silica sol in step c) is adjusted to a pH of between 10 and
12.
19. The process of one of claims 15 to 18, characterized in that
the silica sol in step d) is concentrated to a concentration of
30-40% by weight.
20. The process of one of claims 15 to 19, characterized in that in
step f) water is removed by means of a process selected from the
group consisting of distillation, membrane separation, extraction
and use of a molecular sieve.
21. The use of a dispersion of one of claims 1 to 14 for producing
a polymeric material.
22. The use of claim 21, characterized in that the material is
selected from the group consisting of polyurethanes, polyureas,
epoxy resins, polyester resins and polysiloxanes.
23. The use of claim 21 or 22, characterized in that the material
is a thermoset.
24. The use of claim 21 or 22, characterized in that the material
is a thermoplastic.
25. The use of claim 21 or 22, characterized in that the material
is a polymeric coating, a paint, an ink or a foam.
26. A polymeric material, characterized in that it has been
produced from a dispersion of one of claims 1 to 14.
Description
[0001] The invention relates to a silicon dioxide dispersion
comprising:
[0002] a) an external fluid phase comprising
[0003] a1) polymerizable monomers, oligomers and/or prepolymers
convertible to polymers by nonradical reactions; and/or
[0004] a2) polymers,
[0005] b) a disperse phase comprising amorphous silicon
dioxide.
[0006] It is known to provide polymeric materials such as
polyurethanes, polyureas or reactive resins, as they are known,
with fillers in order to modify certain properties of the polymeric
material. By way of example it is possible in this way to improve
impact strength, flexural strength, hardness or electrical
insulation capacity.
[0007] It is already known to use silica or silicon dioxide
(SiO.sub.2) as a filler in polymers. Various processes for
preparing SiO.sub.2 fillers are known from prior public use.
[0008] Natural (mineral) SiO.sub.2 can, for example, be brought to
desired particle size by grinding and mixed with the polymer or a
polymer precursor. Ground SiO.sub.2 generally has a very broad
particle size distribution and an irregular particle structure.
Particle sizes of less than 1 .mu.m are difficult to obtain or
unobtainable by mechanical comminution of the SiO.sub.2.
[0009] It is further known to precipitate SiO.sub.2 from aqueous
alkali metal silicate solutions by acidification and then to dry
it. This precipitated SiO.sub.2 is mixed with the polymer or a
precursor. Here again, irregular particle structures with very
broad particle size distributions are obtained.
[0010] Another possibility is to prepare pyrogenic silica by flame
hydrolysis of silicon halogen compounds. This produces particles of
very complex morphology and extremely broad particle size
distribution, since the primary particles produced in the flame
hydrolysis undergo partial agglomeration and form other associated
superstructures. Pyrogenic silica, moreover, is expensive to
prepare.
[0011] It is additionally known to hydrolyze and condense organo
functional silanes (especially alkoxy silanes) in order to prepare
aqueous or aqueous-alcoholic silica sols and to mix these sols with
a polymer precursor. Water and/or alcohol can then be removed from
the mixture. This process is expensive and difficult to control on
an industrial scale.
[0012] The processes depicted have the drawback, furthermore, that
the targeted preparation of SiO.sub.2 fillers with a monomodal,
narrow particle size distribution is impossible; this drawback is
particularly pronounced in the case of the three first-mentioned
processes. The result of this is that dispersions of the filler in
polymer precursors exhibit unwanted rheological properties, in
particular a high viscosity, even at relatively low filler
concentrations, and these properties make processing more
difficult.
[0013] The present invention is based on the object of providing a
silicon dioxide dispersion of the type specified at the outset
which is easy to process even at relatively high filler
concentrations, which produces an effective improvement in
mechanical and/or electrical properties of the polymer end product,
and which can be prepared from a process, likewise in accordance
with the invention from inexpensively obtainable starting
materials.
[0014] The silicon dioxide dispersion accordingly comprises
[0015] a) an external fluid phase comprising
[0016] a1) polymerizable monomers, oligomers and/or prepolymers
convertible to polymers by nonradical reactions; and/or
[0017] a2) polymers,
[0018] b) a disperse phase comprising amorphous silicon
dioxide,
[0019] and is characterized in that the average particle size
d.sub.max of the silicon dioxide as measured by means of
small-angle neutron scattering (SANS) is between 3 and 50 nm at a
maximum half-width of the distribution curve of 1.5 d.sub.max.
[0020] The process of the invention for preparing such dispersion
is distinguished by the following steps:
[0021] a) introducing an aqueous silicate solution,
[0022] b) polycondensing the silicate to a particle size of 3-50
nm,
[0023] c) adjusting the resulting silica sol to an alkaline pH,
[0024] d) optionally concentrating the sol,
[0025] e) mixing the sol with constituents of the external fluid
phase of the dispersion,
[0026] f) optionally removing water and/or other solvent
constituents from the dispersion.
[0027] To start with, some of the terms used in the context of the
invention will be elucidated:
[0028] The so-called external phase of the silicon dioxide
dispersion of the invention is fluid. This means that at customary
processing temperatures (e.g., 18 to 300.degree. C., preferably 18
to 100.degree. C.) it is either liquid or else sufficiently fluid
or viscous to be subjected to the desired further processing, in
particular mixing with further constituents of the polymeric
material to be produced or shaping as part of processing.
[0029] This external phase comprises, in accordance with one aspect
of the invention, polymerizable monomers, oligomers and/or
prepolymers. Prepolymers are relatively small polymer units which
are able to crosslink and/or polymerize to form larger polymers.
"Polymerizable" means that in this external phase there are still
polymerizable and/or crosslinkable groups which are able to enter
into a polymerization reaction and/or crosslinking reaction in the
course of further processing of the dispersion. The external phase
comprises polymerizable constituents which are convertible to
polymers by non radical reactions. This means that the
polymerization to polymers does not proceed by way of a
free-radical mechanism. Preference is given instead of this to
polycondensations (polymerization occurring in stages with the
elimination of secondary products) or polyadditions
(polymerizations proceeding in stages without elimination of
secondary products). Likewise provided by the invention are anionic
or cationic polymerizable constituents in the external phase. Not
provided by the invention in any case are dispersions having
external phases which comprise polymerizable acrylates or
methacrylates as a substantial constituent.
[0030] Polymerizable acrylates or methacrylates are all monomeric,
oligomeric or prepolymeric acrylates or methacrylates which in the
course of the production of a material from the dispersion are
deliberately subjected to a further polymerization. One example of
the polyadditions is the synthesis of polyurethanes from diols and
isocyanates, one example of polycondensations is the reaction of
dicarboxylic acids with diols to form polyesters.
[0031] In accordance with a further aspect of the invention the
external fluid phase may comprise a polymer or two or more
polymers. Polymers in this sense are macromolecules which are no
longer reactive and which therefore do not react to form larger
polymer units.
[0032] The material in question may in particular be a melted
and/or dissolved material which can be converted to said material
again physically by cooling and/or removal of the solvent. In this
version of the invention, therefore, the dispersion of the
invention does not cure chemically to form a polymer; instead, use
is made as the external phase of a ready-produced polymer which for
the purpose of preparation of the dispersion is brought by merely
physical means (thermally and/or by solvent addition) into a liquid
or viscous aggregate state, in order to allow the mixing in of the
disperse phase. Following the preparation of the dispersion a
material comprising the disperse phase, and whose polymer
composition is substantially unchanged in comparison with the
polymeric material originally employed as external phase, can be
produced by cooling and/or by removal of the solvent.
"Substantially unchanged" means that, in the course of the
conversion of the original material into the external phase
(thermally or by solvent addition) and of the resolidification
which takes place after the disperse phase has been mixed in, to
form a material of the invention (by cooling or stripping of the
solvent), there is no deliberate further polymerization; instead,
at the most, polymer reactions occur to a slight extent as
secondary reactions. Example 21 in the experimental section is an
example of this version of the invention.
[0033] The disperse phase comprises amorphous silicon dioxide.
Preferably it consists essentially of amorphous silicon dioxides.
The method employed for measuring the amorphous silicon dioxide
particles is that of small-angle neutron scattering (SANS). This
measurement method is familiar to the skilled worker and requires
no more detailed elucidation here. In the SANS measurement a
particle size distribution curve is contained in which the volume
fraction of particles of corresponding size (diameter) is parted
against the particle diameter. Defined as the average particle size
for the purposes of the invention is the peak of such a SANS
distribution curve, i.e., the greatest volume fraction with
particles of corresponding diameter.
[0034] The half-width of the distribution curve is the width (in
nm) of the distribution curve at half its height, i.e., at the half
of the particle volume fraction at the distribution curve peak
d.sub.max, or, expressed alternatively, the width of the
distribution curve at half the height of the Y axis (relative to
the height of the curve at d.sub.max).
[0035] The average particle size is preferably been 6 and 40 nm,
more preferably between 8 and 30 nm, with particular preference
between 10 and 25 nm. Silicon dioxide dispersions according to the
invention have good processing properties and, even where the
concentration of the disperse phase is relatively high, exhibit a
rheology which approximates to the ideal Newtonian flow behavior.
At the given particle concentration they generally have a lower
viscosity than corresponding prior art dispersions.
[0036] The half-width of the distribution curve is, in accordance
with the invention, preferably not more than 1-2 d.sub.max, more
preferably not more than d.sub.max, with particular preference not
more than 0.75 d.sub.max.
[0037] The fraction of the external phase as a proportion of the
dispersion can in the context of the invention be between 20 and
90% by weight, preferably from 30 to 80% by weight, more preferably
from 40 to 70% by weight. Accordingly the fraction of the disperse
phase can be between 10 and 80% by weight, preferably from 20 to
70% by weight, more preferably from 30 to 60% by weight. The
silicon dioxide particles of the dispersion of the invention are
preferably substantially spherical. The dispersion may further
comprise auxiliaries selected from the group consisting of
solvents, plasticizers, crosslinkers, catalysts, stabilizers,
dispersants, curing agents, reaction mediators and agents for
influencing the fluidity of the dispersion.
[0038] With particular preference the dispersion of the invention
is water-free, i.e., it contains only small traces of water which
remain even after conventional methods of removing water, described
in more detail below, have been performed.
[0039] The external phase may be one of two or more reaction
constituents for the preparation of a polymer. The polymers can be
thermoplastics or thermosets. By way of example mention may be made
of polyurethanes, polyureas, expoxy resins, polyester resins,
polysiloxanes (silicones), and, in general, reactive resins for the
production of thermosets. It can, for example, comprise a substance
selected from the group consisting of polyols, polyamines, linear
or branched polyglycol ethers, polyesters and polylactones.
[0040] A multiplicity of known compounds can be used as monomeric
polyols for the purpose of the invention. Owing to their ready
availability and advantages, particularly the excellent
compatibility and good processing properties of the resultant
products, polyols used with preference for the external phase of
the dispersion of the invention are linear or branched aliphatic
glycols, the external phase of the SiO.sub.2 dispersion featuring
with particular preference ethylene glycol, 1,2- or
1,3-propanediol, 1,2- or 1,4-butanediol, 1,6-hexanediol,
2,2,4-trimethylpentane-1,3-diol and/or neopentylglycol.
[0041] Use is further made, as aliphatic polyols, of, preferably,
glycerol, trimethylolpropane, and also sugar alcohols, especially
erythritol, xylitol, mannitol and/or sorbitol. The external phase
may further comprise, as preferred polyols, one or more alicyqlic
polyols, especially 1,4-cyclohexane-dimethanol, and/or sucrose.
[0042] Suitable polymeric polyols for the external phase include
preferably those having an average molecular weight of from 200 to
20,000, the polymeric polyol preferably being one based on akylene
glycol (polymeth)acrylates. The external phase of the dispersion of
the invention may further comprise preferably polymeric polyols
which are obtained by hydrolysis or partial hydrolysis of
vinyl-ester-containing polymers.
[0043] Suitable polyethers for the external phase include in
particular the linear or branched polyglycol ethers obtainable by
ring-opening polymerization of cyclic ethers in the presence of
polyols, e.g., the aforementioned polyols; of these polyglycol
ethers, preference is given, on account of their relatively easy
availability, to polyethylene glycol, polypropylene glycol and/or
polytetramethylene glycol or the copolymers thereof.
[0044] Suitable polyesters for the external phase of the dispersion
of the invention include those based on polyols and aliphatic,
cycloaliphatic and aromatic polyfunctional carboxylic acids (for
example, dicarboxylic acids), and specifically all corresponding
saturated polyesters which are liquid at temperatures of 18 to
300.degree. C., preferably 18 to 150.degree. C.: preferably
succinic esters, glutaric esters, adipic esters, citric esters,
phthalic esters, isophthalic esters, terephthalic esters and/or the
esters of the corresponding hydrogenation products, with the
alcohol component being composed of monomeric or polymeric polyols,
for example, of those of the above-mentioned kind.
[0045] Further polyesters which can be used in accordance with the
invention are aliphatic polylactones, preferably
.epsilon.-polycaprolacto- nes, and/or polycarbonates, which for
example are obtainable by polycondensation of diols with phosgene.
For the external phase it is preferred to use polycarbonates of
bisphenol A having an average molecular weight of from 500 to
100,000.
[0046] Instead of the aforementioned polyols, polyethers and
saturated polyesters, it is also possible for the purpose of the
invention to use mixtures of the aforementioned classes of
substance for the external phase of the dispersion of the
invention. The use of such mixtures may be an advantage, for
example, in respect of a reduction in the glass transition
temperature and/or melting temperature of the resultant products.
For the purpose of further reaction the aforementioned polyethers
and polyesters may carry functional groups, such as hydroxyl,
carboxyl, amino or isocyanato groups, for example.
[0047] For the purpose of influencing the viscosity of the external
phase, in particular the viscosity reduction or the liquefaction,
the polyols, polyethers and saturated polyesters and/or mixtures
thereof provided in accordance with the invention for the external
phase may where appropriate be admixed with further suitable
auxiliaries, particularly solvents, plasticizers, diluents and the
like.
[0048] In the context of the invention the external phase may
comprise at least one reactive resin.
[0049] For the purposes of the present invention reactive resins
are precursors or prepolymers which before and during the
processing and/or shaping operation are liquid or plastic and give
rise after the processing operation, which is normally a shaping
operation, to thermosets as a result of polymerization
(polycondensation, polyaddition). The polymerization produces a
three-dimensionally crosslinked, hard, nonmeltable resin, the
thermoset, which thus differs fundamentally from thermoplastics,
which, as is known, can always be liquefied again or plastified by
renewed heating.
[0050] As a result of the usually very high crosslinking density
the crosslinked reactive resins exhibit a range of valuable
properties, which are the reason why together with the
thermoplastics they are among the most used of polymers. These
valuable properties include, in particular, hardness, strength,
chemical resistance and temperature stability. On the basis of
these properties these reactive resins are employed in a very wide
variety of fields: for example for the production of fibre
reinforced plastics, for insulating materials in electrical
engineering, for the production of construction adhesives,
laminates, baking varnishes and the like.
[0051] Suitable reactive resins in accordance with the invention
are all polymeric or oligomeric organic compounds which are
provided with suitable reactive groups in sufficient number for a
curing reaction. For the purpose of the invention it is irrelevant
which crosslinking mechanism or curing mechanism operates in a
specific case. Consequently, suitable starting products for the
preparation of the inventively modified reactive resins include, in
general, all reactive resins which can be processed to thermosets,
irrespective of the particular crosslinking mechanism which
proceeds in the course of the curing of the particular reactive
resin. Not provided by the invention are reactive resins having
free-radically polymerizable double bonds, which on account of
their particular reactivity are less suitable for the process of
the invention. They may be present, if at all, as an optionally
additional constituent in the external phase.
[0052] The reactive resins which can be used in accordance with the
invention as starting products can be divided fundamentally into
two groups in accordance with the nature of their crosslinking by
addition or condensation.
[0053] From the first group of the reactive resins, crosslinked by
polyaddition, it is preferred to select one or more epoxy resins,
urethane resins and/or air-drying alkyd resins as starting
material. Epoxy resins and urethane resins are generally
crosslinked by the addition of stoichiometric amounts of a curing
agent containing hydroxyl, amino, carboxyl or carboxylic anhydride
groups, the curing reaction taking place by addition reaction of
the oxirane and/or isocyanate groups of the resin with the
corresponding groups of the curing agent. In the case of epoxy
resins a further possibility is that of the so-called catalytic
curing by polyaddition of the oxirane groups themselves. Air-drying
alkyd resins crosslink by autooxidation with atmospheric
oxygen.
[0054] Examples of the second group of reactive resins, crosslinked
by polycondensation, are condensation products of aldehydes, e.g.,
formaldehyde, with aliphatic or aromatic compounds containing amine
groups, e.g., urea or melamine, or with aromatic compounds such as
phenol, resorcinol, cresol, xylene, etc., and also furan resins,
saturated polyester resins and silicone resins. Curing in this case
generally takes place by an increase in temperature accompanied by
elimination of water, low molecular mass alcohols or other low
molecular mass compounds. As starting material for the inventively
modified reactive resins it is preferred to select one or more
phenolic resins, resorcinol resins and/or cresol resins,
specifically both resoles and novolaks, and also urea-formaldehyde
precondensates and melamine-formaldehyde preconden-sates, furan
resins, and saturated polyester resins and/or silicone resins.
[0055] Not only the abovementioned reactive resins but also all
others suitable for producing thermosets can be modified in the
manner proposed in accordance with the invention and, after
crosslinking and curing, give rise to thermosets having
considerably improved fracture toughness and impact strength, which
other essential properties characteristic of the thermosets, such
as strength, heat distortion resistance and chemical resistance,
remain substantially unaffected. In this case the reactive resins
or reactive resin mixtures used in accordance with the invention
are liquid at temperatures in the range from 18 to 100.degree. C.
Further, the reactive resins or reactive resin mixtures used have
an average molecular weight in the range from 200 to 500,000,
preferably from 300 to 20,000. As external phase, furthermore, it
is also possible in accordance with the invention to use monomers
and oligomers. These include in particular those monomeric or
oligomeric compounds which can be reacted to form polymers by
polyaddition or polycondensation.
[0056] The invention possesses considerable advantages in
particular when employed in the context of reactive resins. Prior
art reactive resins are brittle owing to their highly crosslinked
state and have a low impact strength, particularly at relatively
low temperatures.
[0057] The fracture toughness and impact strength of such thermoset
polymer can be considerably improved in accordance with the
invention without adversely affecting hardness, strength and
softening temperature.
[0058] In accordance with the invention it is therefore possible to
prepare reactive resins and, from them, thermosets in which on the
one hand the liquid reactive resin is still easy to process despite
a high fraction of filler and on the other hand, by virtue of the
filling addition of monomodal particles of low diameter, a
considerable improvement occurs in the mechanical properties
(especially tensile strength, elongation at break or fracture
toughness) of the cured thermoset polymer.
[0059] In one preferred embodiment of the invention the
polymerizable monomers, oligomers and/or prepolymers contain
carbon, oxygen, nitrogen and/or sulfur atoms in the main chain. The
polymers in question are therefore organic hydrocarbon polymers
(with or without heteroatoms); polysiloxanes do not come under this
preferred embodiment.
[0060] The external fluid phase may with preference comprise
polymerizable monomers without radically polymerizable double bonds
and also reactive resins.
[0061] The external fluid phase may further comprise silanes.
[0062] The silanes may have hydrolyzable and nonhydrolyzable,
optionally functional groups. Examples of hydrolyzable groups are
halogen, alkoxy, alkenoxy, acyloxy, oximino and aminoxy groups.
Examples of functional, nonhydrolyzable groups are vinyl,
aminopropyl, chloropropyl, aminoethylamino propyl,
glycidyloxypropyl, mercaptopropyl or methacryloyloxypropyl groups.
Examples of nonhydrolyzable nonfunctional groups are monovalent
C.sub.1 to C.sub.8 hydrocarbon radicals. Examples of silanes which
can be used in accordance with the invention are:
.gamma.-aminopropyltrimethoxysilane,
.gamma.-aminopropylmethyldiethoxysil- ane,
.gamma.-aminopropyldimethylmethoxysilane,
glycidyloxypropyltrimethoxy- silane,
glycidyloxypropyldimethylmethoxysilane, methacryloyloxypropyltrime-
thoxysilane, chloropropyltrimethoxysilane,
vinylmethyldimethoxysilane, vinyltrispropenoxysilane,
vinyldimethylbutanone oxime silane, vinyltrisbutanone oxime silane,
trimethylchlorosilane, vinyldimethylchlorosilane,
dimethylchlorosilane, vinylmethylchlorosilane.
[0063] The silanes are used preferably in a concentration of from
40 to 200 mol % and with particular preference from 60 to 150 mol %
based on the molar amount of silanol groups on the surface.
[0064] In the performance of the process of the invention first of
all an aqueous silicate solution is introduced. It can be an alkali
metal silicate solution, in particular a sodium silicate and or
potassium silicate solution. The concentration of this aqueous
silicate solution is preferably in the range between 20 and 50% by
weight. The preferred ratio of SiO.sub.2 to Na.sub.2O is between 2
and 3.
[0065] In the next step the silicate is polycondensed to a particle
size of from 3 to 50 nm. This can take place, for example, by
treating the alkali metal silicate solution with acidic ion
exchangers which replace the alkali metal ions with H.sup.+ ions
and so initiate the desired polycondensation.
[0066] The silica sol obtained is adjusted to an alkaline pH
(pH>8, preferably >9, more preferably >10, with particular
preference between 10 and 12) and in this way is stabilized against
further polycondensation or agglomeration of existing
particles.
[0067] Optionally the sol can be concentrated, for example, by
distillation, preferably to an SiO.sub.2 concentration of from 30
to 40% by weight.
[0068] In the next step the sol is mixed with constituents of the
external fluid phase of the dispersion. In this case the
constituents of the external fluid phase can be added or mixed in
either simultaneously or in two or more substeps in succession.
[0069] Thereafter, with particular preference, water and/or other
solvent constituents are removed from the dispersion, since the
intention is to use the dispersions of the invention to prepare,
with particular preference water-free plastics (referred to as
water-free nanocomposites). Use may be made of all of the customary
separation techniques familiar to the skilled worker, such as, for
example, distillation, preferably in vacuo, membrane separation,
sedimentation where appropriate, solvent extraction, use of a
molecular sieve, etc. In the case of distillation it is possible
where appropriate to add solvents which form an azeotrope with
water and so act as an azeotropic entrainer. When different solvent
constituents require removal, this can also be carried out
simultaneously or by means of two or more sequential substeps.
[0070] In the context of the invention it is also possible for
substeps of the process steps e) and f) of claim 16 to be mixed
with one another, so to speak. It is possible, therefore, following
the addition of one or more constituents in step e), first to
remove one or more solvent constituents in step f) and then to
carry out further substeps (addition of material) in step e), again
remove other solvent constituents in step f), and so on.
Consequently, substeps of the process steps e) and f) of claim 16
can be mixed with one another and swapped with one another.
[0071] It is preferred if the silicon dioxide component of a
dispersion of the invention is prepared exclusively and hence in
its entirety by the stated process. Within the context of the
invention it is also possible, however, to prepare some of the
silicon dioxide of the dispersion by prior art processes, as long
as the disperse phase overall meets the criteria of claim 1. In
particular it is possible in the context of the invention to
prepare part of the disperse phase by the process of hydrolysis and
condensation of organofunctional silanes (especially alkoxy
silanes) that was outlined in the introductory part of the
description. The silanes in question can be mono-, di-, tri- or
tetraalkoxy silanes; there must be a sufficient fraction present of
silanes having three or four hydrolyzable groups. Preference is
given in particular to mono-, di- or trimethoxy or -ethoxy silanes
in which one of the non hydrolyzable radicals is an aliphatic
(preferably having 1 to 18 carbon atoms) or aromatic hydrocarbon
radical which may additionally contain a functional group, for
example, a vinyl, allyl, (meth)acryloyl, glycidyl, halogen,
hydroxyl or mercapto group. Any further non hydrolyzable radicals
present are preferably methyl or ethyl.
[0072] Where part of the disperse phase is prepared in the manner
stated by silane hydrolysis, it is possible where appropriate for
additional solvents to be added which may serve as solubilizers
between silane and external phase of the dispersion. Suitable
examples include water-miscible alcohols of low molecular mass
(preferably C.sub.1 to C.sub.4 alcohols), ketones, amines, amides
or heterocyclic compounds such as THF or pyridine, for example.
[0073] The invention further provides for the use of a dispersion
defined above for producing a polymeric material. The polymeric
material can be a thermoplastic or thermoset polymer. By way of
example mention may be made of polyurethanes, polyureas, epoxy
resins, polyester resins, polysiloxanes, and all thermoset polymers
that can be prepared from reactive resins.
[0074] The polymeric material can on the one hand be a
thermoplastic or on the other hand a chemically crosslinked,
thermoset or elastomeric polymer. As examples of thermoset and/or
elastomeric polymers mention may be made of: polyurethanes,
polyureas, epoxy resins, polyester resins, polyimide resins,
polysiloxanes, alkyd resins, styrene-butadiene rubber,
acrylonitrile-butadiene rubber, polybutadiene rubber.
[0075] As examples of thermoplastic polymers which can be used in
accordance with the invention in the external phase mention may be
made of the following: polyolefins, polystyrene,
styrene-acrylonitrile copolymers, polyamides, polyvinyl chloride
and its copolymers, polyvinyl alcohols, and polyvinyl acetates and
polyvinyl ethers and also copolymers of these substances,
polycarbonate, polymethyl acrylates and polymethyl methacrylates,
including their copolymers, polyurethanes, polysulfones, polyether
ketones, polyesters.
[0076] The polymeric materials for the purposes of this invention
are not only compact materials; instead, the dispersions of the
invention can also be used with advantage as part of the binder in
paints, inks and coatings. In these applications it is particularly
advantageous that, through the amount of silicon dioxide on the one
hand the abrasion resistance, the scratch resistance and also the
barrier effect to the penetration of the coating by gases and
moisture are increased, but on the other hand, through the narrow
particle size distribution, the viscosity is increased to much less
of an extent than in the case of silicon dioxide fillers in
accordance with the conventional state of the art. This is a
considerable advantage particularly in the case of surface
coatings.
[0077] Furthermore, the polymeric materials modified in accordance
with the invention may also be closed-cell or open-cell foams,
based for example on polyurethanes, polysiloxanes, polyolefins or
polystyrene. The particular advantage of the dispersion of the
invention arises in this case from the fact that, owing to the low
particle size and the narrow particle distribution, the particles
can be present in the thin lamellae of the foam without disrupting
the foam structure per se. As a result it becomes possible, for
example, to raise the hardness and compressive strength of the foam
with its density unchanged or to maintain said properties despite a
decrease in density.
[0078] A further embodiment of the polymeric materials modified in
accordance with the invention are liquid, curable casting and
impregnating compounds for the production, for example, of
electrical insulating resins or fiber composites. In many
applications of electrical insulating resins, e.g., in the casting
of coils or transformers, the critical factor is the ability of the
impregnating resin to flow as far as possible easily and without
defect through the spacings of the coil windings, which are often
just a few .mu.m, a task virtually impossible for resins filled
with prior art fillers owing to their particle size and irregular
distribution. In principle the same applies to the application of
impregnating resins in fiber composites, where particularly in the
case of highly stressed parts the individual reinforcing fibers are
so tightly packed that in the prior art no filled systems at all
can be used. In both applications the impregnating resins prepared
with the dispersions of the invention are readily able to penetrate
the intestacies of the windings or fibers, respectively, owing to
the extremely small particle size and the narrow diameter
distribution of the silicon dioxide. Accordingly, the advantageous
mechanical and thermal properties of the silicon-dioxide-filled
resin can be manifested throughout the component.
[0079] A further advantageous quality of the polymeric materials
modified with the dispersions of the invention is their optical
clarity, which is again a result of the extremely low particle size
and narrow diameter distribution for silicon dioxide. Especially in
the case of plastics which are naturally optically clear, the prior
art does not provide any possibility for adding more than just a
very small fraction of inorganic fillers to the polymer without
detriment to its optical properties. Consequently, in the case of
polymer applications where optical clarity is important, it is
virtually impossible to improve properties such as hardness or
modulus of elasticity, scratch resistance, fracture strength,
thermal conductivity, expansion coefficient, diffusion barrier
effect, and so on, which in the case of non transparent systems
would normally be effected by adding inorganic fillers. In
principle this relates to a very large number of polymeric
materials and their applications, e.g., polymethyl methacrylate,
polycarbonate, polyalkylene terephthalates, a variety of clearcoat
systems, for example, for top coats of vehicles, furniture,
flooring, printed matter, etc.
[0080] By way of example the dispersion of the invention can
comprise polyols or polyamines of the type described in more detail
above from which polyurethanes and/or polyureas can be produced.
The dispersion is then mixed conventionally with polyisocyanates
and reacted in order to prepare the desired polymeric materials
whose properties have been modified accordingly by the disperse
SiO.sub.2 phase. In a manner familiar to the skilled worker the
polymerization reaction can be implemented in one or more stages,
where appropriate at elevated temperature.
[0081] Where the dispersion of the invention includes a reactive
resin, it can be subjected in a known manner to further processing,
by the known single-stage or multistage processes of reactive resin
engineering, to give a polymer, preferably a thermoset polymer.
[0082] Preferably with the addition of catalysts, curing agents or
crosslinkers, a three-dimensional polymeric network is developed.
Further additives and adjuvants can be added to the reactive resin
prior to crosslinking, examples being organic or inorganic fillers,
fibres, pigments, flow assistants, reaction accelerants or
retardants, plasticizers or the like.
[0083] Examples of the invention are illustrated below. All
percentages in the examples are by weight, with the indication
"parts" referring to parts by mass. The size distribution of the
SiO.sub.2 particles (also called diameter distribution) is
specified in the examples as x.+-.y nm. X here is the peak
d.sub.max of the distribution curve, y half the half-width of the
distribution curve. Accordingly, the half-width of the distribution
curve amounts to 2 y.
EXAMPLE 1
[0084] A commercial aqueous alkali silicate solution having a water
content of 47% and a ratio of SiO.sub.2 to Na.sub.2O of 2.4 was
diluted with demineralized water to a water content of 97%. 100
parts of this diluted solution were passed at a rate of 20 parts
per hour through a column packed with a commercially acidic ion
exchanger and subsequently was supplied to a distillation receiver
in which the incoming deionized silicate solution was held at
boiling temperature and the water distilling off was removed from
the solution. After the end of the introduction the silica sol
formed was concentrated by further heating to 10 parts. The pH was
adjusted to 10.5 to 11.
EXAMPLES 2 TO 4
[0085] Batches of 100 parts of the sol prepared in example 1 were
mixed with 2000 parts of isopropanol and the water was removed by
atmospheric distillation down to a level, determined by the
Karl-Fischer method, of less than 0.1%. Thereafter 80 parts of one
of the following polyethers were added with stirring:
[0086] Example 2: polypropylenediol (PPG), molar mass (MM) 1000
[0087] Example 3: PPG end capped with 15% polyethylene glycol (PEG)
MM 4000
[0088] Example 4: Polypropylenetriol, MM 6000
[0089] Subsequently the volatile constituents were removed by
distillation at 50.degree. C. and a vacuum of up to 85 mbar.
[0090] The three samples obtained were water-clear. The particle
size distribution was measured by means of SANS and for all three
samples gave a diameter distribution which matched within the
bounds of measurement accuracy and was 47.+-.11 nm.
EXAMPLE 5
[0091] Example 1 was repeated with the difference that the water
content of the diluted alkali metal silicate solution was adjusted
to 98% and the rate of introduction to the distillation receiver
was 15 parts per hour. Following concentration, 9 parts of silica
sol were obtained. The pH was adjusted to 10.5 to 11.
EXAMPLES 6 TO 10
[0092] Batches of 100 parts of the sol prepared in example 5 were
admixed with 2.5 parts of trimethylmethoxysilane and stirred. Added
to these mixtures were 2000 parts of isopropanol and the water was
removed by atmospheric distillation down to a level, determined by
the Karl-Fischer method, of less than 0.1%. Thereafter 80 parts of
the following polyethers were added with stirring:
[0093] Example 6: PPG MM 12000
[0094] Example 7: PPG with 10% ethylene oxide randomly
copolymerized, MM 3000
[0095] Example 8: Polypropylenetriol, MM 550
[0096] Example 9: Polypropylenetriol end capped with 20% PEG, MM
2000
[0097] Example 10: Polytetramethylene glycol, MM 650
[0098] Subsequently the volatile constituents were removed by
distillation at 50.degree. C. and a vacuum of up to 85 mbar.
[0099] The five samples obtained were water-clear. The particle
size distribution was measured by means of SANS and for all samples
gave a diameter distribution which matched within the bounds of
measurement accuracy and was 30.+-.7 nm.
EXAMPLE 11
[0100] Example 1 was repeated with the difference that the rate of
introduction to the distillation receiver was 30 parts per hour.
Following concentration, 15 parts of silica sol were obtained. The
pH was adjusted to 10.5 to 11.
EXAMPLE 12
[0101] 100 parts of the sol prepared in Example 11 were admixed
with stirring with 3.9 parts of n-propyl-trimethoxysilane, which
was stirred in. Thereafter this mixture was stirred into 620 parts
of isopropanol and at 40.degree. C. and 85 mbar was concentrated to
113 parts.
[0102] Subsequently 110 parts of a hydroxyl-containing polyacrylate
("Desmophen A 870 BA", Bayer AG) were added. The volatile
constituents were subsequently removed by distillation at
40.degree. C. and 58 mbar in a manner sufficiently gentle that the
higher-boiling butyl acetate present in the polyacrylate remained
in the dispersion. This gave a water-clear dispersion having a
SANS-determined diameter distribution of 8.+-.2.5 nm.
EXAMPLE 13
[0103] 100 parts of the sol prepared in Example 11 were admixed
with 5.9 parts of .gamma.-glycidyloxypropyldiethoxymethylsilane,
with stirring, and then introduced into a solution of 60 parts of a
cycloaliphatic epoxy resin ("ERL 4221", Union Carbide) in 620 parts
of isopropanol. The volatile constituents were subsequently removed
by distillation at 50.degree. C. and 85 mbar. This gave a
water-clear dispersion having a SANS-determined diameter
distribution of 8.+-.2.5 nm
EXAMPLE 14
[0104] 100 parts of the sol prepared in Example 11 were admixed
with stirring with 588 parts of isopropanol.
[0105] The mixture was then concentrated at 40.degree. C. and 85
mbar to 147 parts. Thereafter 5.7 parts of
.gamma.-glycidyloxypropyltrimethoxysil- ane were added with
stirring and the mixture was subsequently introduced into a
solution of 60 parts of a cycloaliphatic epoxy resin ("ERL 4221",
Union Carbide) in 168 parts of isopropanol. The volatile
constituents were subsequently removed by distillation at
50.degree. C. and 3 mbar. This gave a water-clear dispersion having
a SANS-determined diameter distribution of 8.+-.2 nm.
EXAMPLE 15
[0106] Example 1 was repeated with the difference that the rate of
introduction to the distillation receiver was 43 parts per hour.
Following concentration, 8 parts of silica sol were obtained. The
pH is adjusted to 10.5 to 11.
EXAMPLE 16
[0107] 100 parts of the sol prepared in example 15 were admixed
with 5.6 parts of trimethoxyphenylsilane and stirred. Thereafter
this mixture was stirred in 610 parts of isopropanol and
concentrated at 40.degree. C. and 85 mbar to 118 parts.
Subsequently 225 parts of isopropyl acetate were added and the
mixture was concentrated again by distillation at 40.degree. C. and
85 mbar to 134 parts.
[0108] This mixture was then introduced into 125 parts of a 50%
strength solution of bisphenol A epoxy resin ("Epilox A 17-01",
Leuna Harze GmbH) in isopropyl acetate and subsequently the
volatile constituents were removed by distillation at 50.degree. C.
and 3 mbar. This gave a slightly opaque dispersion having a
SANS-determined diameter distribution of 16.+-.5 nm.
EXAMPLE 17
[0109] 100 parts of the sol prepared in example 15 were admixed
with 2.8 parts of methoxytrimethylsilane and stirred. Thereafter
this mixture was stirred in 820 parts of isopropanol and
concentrated at 40.degree. C. and 85 mbar to 118 parts. This
mixture was then stirred with 423 parts of a 15% strength solution
of bisphenol F epoxy resin ("Epilox F 16-01", Leuna Harze GmbH) in
isopropyl acetate and subsequently the volatile constituents were
removed by distillation at 50.degree. C. and 3 mbar. This gave a
slightly opaque dispersion having a SANS-determined diameter
distribution of 17.+-.5 nm.
EXAMPLE 18
[0110] Batches of 100 parts of the sol prepared in Example 15 were
admixed with 5.3 parts of phenyltrimethoxysilane and stirred. 1000
parts of isopropanol were added to these mixtures which were then
concentrated at 40.degree. C. and 85 mbar to 120 parts in each
case. Subsequently 220 parts of isopropyl acetate were added to
each of the mixtures, which were again concentrated by distillation
at 40.degree. C. and 85 mbar to 120 parts. Thereafter 135 parts of
a 50% strength isopropyl acetate solution of the following
polyester polyols were added in each case:
[0111] Example a: Branched polyester polyol ("Desmophen 1100",
Bayer AG)
[0112] Example b: Polycarbonate-polyester polyol ("Desmophen C
200", Bayer AG)
[0113] Example c: Polycaprolactonpolyol ("TONE 2241", Dow
Chemical)
[0114] Subsequently the volatile constituents were removed by
distillation at 50.degree. C. and a vacuum of up to 85 mbar. The
three samples obtained were water-clear. The particle size
distribution was measured by means of SANS and on all three samples
gave a diameter distribution which was the same within the bounds
of measurement accuracy and was 17.+-.5 nm.
EXAMPLE 19
[0115] 100 parts of the sol prepared in Example 15 were admixed
with 4.5 parts of n-propyltrimethoxysilane and stirred. Thereafter
this mixture was stirred into a solution of 80 parts of
E-caprolactam in 520 parts of n-propanol. The volatile constituents
were subsequently removed by distillation at 60.degree. C. and a
vacuum of up to 85 mbar. This gave a water-clear dispersion which
at room temperature solidifies to a colorless solid.
[0116] Melting at 70.degree. C. again gives a water-clear
dispersion having a SANS-determined diameter distribution of
16.+-.7 nm.
EXAMPLE 20
[0117] 100 parts of the sol prepared in Example 15 were admixed
with stirring with 4.5 parts of propyltrimethoxysilane with
stirring and subsequently introduced into a solution of 38 parts of
an adipate-based plasticizer ("Plasticiser 109", hanse chemie GmbH)
in 522 parts of isopropanol. The volatile constituents were removed
by distillation at 50.degree. C. and 3 mbar. This gave a yellow,
water-clear dispersion having a SANS-determined diameter
distribution of 18.+-.5 nm.
EXAMPLE 21
[0118] 100 parts of the sol prepared in Example 15 were admixed
with 5.8 parts of phenyltrimethoxysilane and stirred. 1000 parts of
isopropanol were added to this mixture, which was then concentrated
at 40.degree. C. and 85 mbar to 122 parts. Subsequently 225 parts
of isopropyl acetate were added and the mixture was again
concentrated by distillation at 40.degree. C. and 85 mbar to 110
parts. 100 parts of PMMA molding compound pellets ("Plexiglas 6N",
Rohm GmbH) were melted in a twin-screw devolatilizing extruder
("ZSK 25", Werner & Pfleiderer). Under a pressure of 42 bar 100
parts of the above-prepared isopropyl acetate sol were fed in from
the side, the components were mixed homogeneously and then the
volatile constituents, in a two-stage devolatilizing operation,
were blown off and degassed under vacuum. By means of a downstream
pelletizer water-clear colorless pellets were obtained with a
SANS-determined diameter distribution of 17.+-.7 nm.
[0119] These pellets were used with a commercial injection molding
machine to produce specimens whose mechanical and thermal
characteristics were determined and compared with unmodified
"Plexiglas 6N". The resulting values were as follows:
1 Measurement value Characteristic Unit Standard Unmodified
Modified Tensile elasticity MPa ISO 527 3,200 4,900 modulus
Breaking stress MPa ISO 527 67 103 Elongation at break % ISO 527 3
3 Softening .degree. C. ISO 306 96 115 temperature Linear expansion
10.sup.-6K.sup.-1 ASTM E 831 80 60 coefficient Optical % DIN 5036
92 90 transmittance
[0120] The example demonstrates the considerably improved
mechanical and thermal characteristics of the Plexiglas, without
marked detriment to its optical properties from the addition of the
silicon dioxide.
EXAMPLE 22
[0121] 100 parts of the sol prepared in Example 15 were admixed
with stirring with 588 parts of isopropanol.
[0122] The mixture was then concentrated at 40.degree. C. and 85
mbar to 147 parts. Thereafter 5.7 parts of
.gamma.-glycidyloxypropyltrimethoxysil- ane were added with
stirring and the mixture was subsequently introduced into a
solution of 60 parts of a cycloaliphatic epoxy resin ("ERL 4221",
Union Carbide) in 168 parts of isopropanol. The volatile
constituents were subsequently removed by distillation at
50.degree. C. and 2 mbar. This gave a water-clear dispersion having
a SANS-determined diameter distribution of 15.+-.4 nm.
EXAMPLE 23
[0123] In this example the Theological properties of resins and
polyether polyols filled on the one hand with pyrogenic silica of
the prior art and on the other hand with SiO.sub.2 dispersions of
the invention are compared. AEROSIL.RTM. R8200 is a pyrogenic
silica prepared by flame hydrolysis from silicon tetrachloride,
obtainable from Degussa.
2TABLE 1 Viscosities of SiO.sub.2-filled resins and polyether
polyols SiO.sub.2 Resin/polyether polyol content Type of SiO.sub.2
.eta. (25.degree. C.) (Manufacturer) [%] particles [mPa .multidot.
s] ERL 4221 (Union Carbide) 0 -- 381 ERL 4221 (Union Carbide) 23
Ex. 22 422 ERL 4221 (Union Carbide) 40 Ex. 22 25810 ERL 4221 (Union
Carbide) 5 AEROSIL .RTM. R8200 491 ERL 4221 (Union Carbide) 23
AEROSIL .RTM. R8200 paste Baycoll BT 1380 (Bayer) 0 -- 595 Baycoll
BT 1380 (Bayer) 20 Ex. 8 1030 Baycoll BT 1380 (Bayer) 50 Ex. 8
19800 Baycoll BT 1380 (Bayer) 5 AEROSIL .RTM. R8200 815 Baycoll BT
1380 (Bayer) 10 AEROSIL .RTM. R8200 1487 Baycoll BT 1380 (Bayer) 20
AEROSIL .RTM. R8200 paste BisGMA/TEDMA 0 -- 1194 BisGMA/TEDMA 16
Ex. 12 2001 BisGMA/TEDMA 45 Ex. 12 42900 BisGMA/TEDMA 5 AEROSIL
.RTM. R8200 1864 BisGMA/TEDMA 10 AEROSIL .RTM. R8200 3899
BisGMA/TEDMA 20 AEROSIL .RTM. R8200 paste
[0124] It is seen that in accordance with the invention it is
possible to realize high SiO.sub.2 contents without an excessive
increase in viscosity and hence without processing being made more
difficult or impossible. In contrast, an AEROSIL content of
approximately 20% by weight already regularly leads to a pastelike
consistency of the resin or polyether polyol.
EXAMPLE 24
[0125] The beneficial effect of SiO.sub.2 dispersions of the
invention on the mechanical properties of polymers is elucidated
using epoxy resins as example. In this example the epoxy resin ERL
4221 is mixed with the SiO.sub.2 dispersion of Example 22 to give
the SiO.sub.2 contents indicated in Tab. 2. For UV curing (c to e)
the samples were admixed with 1% of UV initiator ("CYRACURE.RTM.
UVI-6974", from Union Carbide), placed in aluminum trays and
degassed at 60.degree. C. and 1 mbar for 15 minutes.
[0126] Subsequently these samples were irradiated for 10 minutes
with a UV lamp (UVASPOT 400H, from Dr. K. Honle GmbH) from a
distance of 20 cm and heated at 160.degree. C. for 1 hour. For
thermal curing (a and b) the epoxy equivalent weight was determined
in accordance with the standard DIN 16 945 and one equivalent of a
cycloaliphatic anhydride ("ALBIDUR HE 600", hanse chemie GmbH) was
added. The samples are placed in aluminum trays and degassed at
60.degree. C. and 1 mbar for 15 minutes. Curing takes place in 4
stages: 90 minutes at 90.degree. C., 120 minutes at 120.degree. C.,
120 minutes at 140.degree. C. and 60 minutes at 160.degree. C.
[0127] For the subsequent fracture-mechanical investigations to
determine the fracture toughness K.sub.IC, the fracture energy
G.sub.IC and the elasticity modulus E, CT standard test specimens
with an edge length of 33 mm were milled from the compact material
and were tested in accordance with the standard ASTM E 399-83 under
quasistatic load. Flexural tests were carried out in three-point
bending tests in accordance with the standard DIN 53 452.
3TABLE 2 Results of fracture-mechanical investigation SiO.sub.2
content K.sub.IC [%] Curing [MPa .multidot. m.sup.1/2] G.sub.rc
[J/m.sup.2] E [MPa] a 0 HE600 0.47 .+-. 0.05 77.2 .+-. 22.0 3053
.+-. 276 b 23 HE600 0.78 .+-. 0.02 147.7 .+-. 7.9 4146 .+-. 122 c 0
UV 0.28 .+-. 0.05 26.2 .+-. 8.4 3156 .+-. 81 d 23 UV 0.43 .+-. 0.04
47.0 .+-. 6.1 3893 .+-. 191 e 40 UV 0.51 .+-. 0.04 45.7 .+-. 7.6
5795 .+-. 276
[0128] The results of the experiment show that by means of the
SiO.sub.2 dispersion of the invention fracture toughness, fracture
energy and elasticity modulus of the polymeric material can be
substantially improved.
* * * * *