U.S. patent application number 13/110074 was filed with the patent office on 2011-09-08 for process for preparing aqueous dispersions.
This patent application is currently assigned to EVONIK ROEHM GMBH. Invention is credited to Werner Hoess, Reiner Mueller, Hartmut Schikowsky, Klaus SCHULTES, Thomas Suefke.
Application Number | 20110218291 13/110074 |
Document ID | / |
Family ID | 32404073 |
Filed Date | 2011-09-08 |
United States Patent
Application |
20110218291 |
Kind Code |
A1 |
SCHULTES; Klaus ; et
al. |
September 8, 2011 |
PROCESS FOR PREPARING AQUEOUS DISPERSIONS
Abstract
The present invention relates to a process for preparing aqueous
dispersions. The invention also relates to the formation of
core-shell particles in aqueous dispersions. The core-shell
particles are useful as impact-modifiers for poly(meth)acrylate
moulding compositions.
Inventors: |
SCHULTES; Klaus; (Wiesbaden,
DE) ; Suefke; Thomas; (Erzhausen, DE) ;
Mueller; Reiner; (Biebesheim, DE) ; Schikowsky;
Hartmut; (Darmstadt, DE) ; Hoess; Werner;
(Griesheim, DE) |
Assignee: |
EVONIK ROEHM GMBH
Darmstadt
DE
|
Family ID: |
32404073 |
Appl. No.: |
13/110074 |
Filed: |
May 18, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10539132 |
Jun 16, 2005 |
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PCT/EP03/11543 |
Oct 18, 2003 |
|
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13110074 |
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Current U.S.
Class: |
524/521 ;
428/407; 524/523; 525/227; 525/230 |
Current CPC
Class: |
C08F 285/00 20130101;
C08L 33/10 20130101; C08L 33/12 20130101; C08L 33/12 20130101; C08L
51/003 20130101; C08L 2666/04 20130101; C08F 220/12 20130101; Y10T
428/2998 20150115; C08L 33/12 20130101; C08L 55/005 20130101; C09D
133/10 20130101; C08L 35/06 20130101; C08L 33/20 20130101; C08L
51/003 20130101; C09D 133/10 20130101; C08L 2666/02 20130101; C08F
285/00 20130101; C08L 2666/04 20130101; C08L 2666/24 20130101 |
Class at
Publication: |
524/521 ;
525/227; 525/230; 524/523; 428/407 |
International
Class: |
C08L 25/14 20060101
C08L025/14; B32B 15/02 20060101 B32B015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2002 |
DE |
10260089.9 |
Claims
1. Core-shell particles obtained by a process comprising: (1)
preparing an aqueous polymer dispersion, and (2) separating
core-shell particles therefrom, wherein (1) comprises: a) preparing
an initial charge of an aqueous emulsion of a long chain alkyl
alcohol or a seed latex by polymerization of an alkyl
(meth)acrylate in an aqueous medium comprising an emulsifier to a
seed particle radius ranging from 3.0 to 20.0 nm b) adding from
25.0 to 45.0 parts by weight of a first composition comprising: A)
from 50.0 to 99.9 parts by weight of an alkyl (meth)acrylate having
from 1 to 20 carbon atoms in the alkyl radical, B) from 0.0 to 40.0
parts by weight of an alkyl acrylate having from 1 to 20 carbon
atoms in the alkyl radical, C) from 0.1 to 10.0 parts by weight of
a crosslinking monomer, and D) from 0.0 to 8.0 parts by weight of a
styrenic monomer of the formula (I) ##STR00006## where each of the
radicals R.sup.1 to R.sup.5, independently of the others, is
hydrogen, a halogen, a C.sub.1-6-alkyl group or a C.sub.2-6-alkenyl
group, and the radical R.sup.6 is hydrogen or an alkyl group having
from 1 to 6 carbon atoms, emulsified in water with an emulsifier,
to said aqueous emulsion or seed latex, and polymerizing the added
monomers to a conversion of at least 85.0% by weight, based on the
total weight of components A), B), C) and D), c) adding from 35.0
to 55.0 parts by weight of a second composition comprising E) from
80.0 to 100.0 parts by weight of a (meth)acrylate, F) from 0.05 to
10.0 parts by weight of a crosslinking monomer, and G) from 0.0 to
20.0 parts by weight of a styrenic monomer of the formula (I),
emulsified in water with an emulsifier, to the aqueous polymer
emulsion of step (b), and polymerizing the added monomers to a
conversion of at least 85.0% by weight, based on the total weight
of components E), F) and G), d) adding from 10.0 to 30.0 parts by
weight of a third composition comprising: H) from 50.0 to 100.0
parts by weight of an alkyl (meth)acrylate having from 1 to 20
carbon atoms in the alkyl radical, I) from 0.0 to 40.0 parts by
weight of an alkyl acrylate having from 1 to 20 carbon atoms in the
alkyl radical, and J) from 0.0 to 10.0 parts by weight of a
styrenic monomer of the formula (I), emulsified in water with an
emulsifier, to the aqueous polymer emulsion of step (c), and
polymerizing to a conversion of at least 85.0% by weight, based on
the total weight of components H), I) and J), where the parts by
weight given for the compositions b), c) and d) give a total of
100.0 parts by weight, wherein e) each polymerization is carried
out at a temperature in the range from above 60 to below 90.degree.
C. and f) the relative proportions of all of the substances are
selected in such a way that the total weight of components A) to
J), based on the total weight of the aqueous dispersion, is greater
than 50.0% by weight, the product particles have a particle size
ranging from 150 to less than 250 nm, and the amount of coagulate
in the dispersion is 0.1% or less by wt, based on the total weight
of the dispersion.
2. A moulding composition comprising, based in each case on its
total weight, of A) from 1.0 to 50.0% by weight of at least one
core-shell particle according to claim 1, B) from 1.0 to 99.0% by
weight of at least one (meth)acrylic polymer, C) from 0.0 to 45% by
weight of at least one styrene-acrylonitrile polymer, and D) from
0.0 to 10.0% by weight of other additives, where the percentages by
weight give 100.0% by weight in total.
3. The moulding composition according to claim 2, wherein the
(meth)acrylic polymer encompasses, based in each case on its total
weight, of a) from 50.0 to 100.0% by weight of alkyl methacrylate
repeat units having from 1 to 20 carbon atoms in the alkyl radical,
b) from 0.0 to 40.0% by weight of alkyl acrylate repeat units
having from 1 to 20 carbon atoms in the alkyl radical and c) from
0.0 to 8.0% by weight of styrenic repeat units of the formula (I),
where the percentages by weight give 100.0 W by weight in
total.
4. The moulding composition according to claim 2, wherein the
moulding composition comprises styrene/acrylonitrile copolymers,
where the styrene/acrylonitrile copolymers are obtained by
polymerizing any mixture which comprises from 70 to 92 W by weight
of styrene, from 8 to 30% by weight of acrylonitrile, and from 0 to
22% by weight of other comonomers, based in each case on the total
weight of the monomers to be polymerized.
5. The moulding composition according to claim 2, wherein the
moulding composition comprises, based on its total weight, from 0.1
to 10.0% by weight of another polymer whose weight-average
molecular weight is higher by at least 10% than that of the
(meth)acrylic polymer.
6. A moulding obtained from a moulding composition according to
claim 2.
7. The moulding according to claim 6, wherein the moulding has a
Vicat softening point ISO 306 (B50) of at least 85.degree. C., a
notched impact strength NIS (Charpy179/1eA) to ISO 179 of at least
6.0 kJ/m.sup.2 at 23.degree. C. and of at least 2.5 kJ/m.sup.2 at
-10.degree. C., a modulus of elasticity to ISO 527-2 of at least
1500 Pa s, a haze to ASTM D 1003 (1997) of at most 2.5%, a
transmittance (D) 65/10.degree. to DIN 5033/5036 of at least
88.5%.
8. The moulding according to claim 7, wherein the moulding has a
Vicat softening point ISO 306 (B50) of at least 90.degree. C.
9. The moulding according to claim 8, wherein the moulding has a
Vicat softening point ISO 306 (B50) of at least 93.degree. C.
10. The core-shell-particles according to claim 1, wherein a seed
latex whose particle radius, measured by the Coulter method, is in
the range from 5.0 to 20.0 nm is used to form the initial
charge.
11. The core-shell-particles according to claim 1, wherein said
initial charge is an aqueous emulsion of said long chain alkyl
alcohol having from 12 to 20 carbon atoms in the alkyl radical.
12. The moulding composition according to claim 2, wherein the
(meth)acrylic polymer has a number-average molar mass of from 1000
to 100,000,000 g/mol.
13. The moulding composition according to claim 12, wherein the
number-average molar mass is from 10,000 to 1,000,000 g/mol.
14. The moulding composition according to claim 12, wherein the
number-average molar mass is from 50,000 to 500,000 g/mol.
15. The moulding composition according to claim 3, wherein the
(meth)acrylic polymer comprises from 85.0 to 100.0% by weight of
alkyl methacrylate repeat units.
16. The moulding composition according to claim 5, wherein said
weight-average molecular weight is higher by at least 50% than that
of the (meth)acrylic polymer.
17. The moulding composition according to claim 5, wherein said
weight-average molecular weight is higher by at least 100% than
that of the (meth)acrylic polymer.
18. The moulding composition according to claim 2, wherein the
(meth)acrylic polymer encompasses, based in each case on its total
weight, of a) from 85.0 to 99.5% by weight of alkyl methacrylate
repeat units having from 1 to 4 carbon atoms in the alkyl radical,
b) from 0.1 to 15.0% by weight of alkyl acrylate repeat units
having from 1 to 4 carbon atoms in the alkyl radical and c) from
0.0 to 8.0% by weight of styrenic repeat units of the formula (I),
where the percentages by weight give 100.0% by weight in total.
Description
[0001] This is a divisional application of U.S. application Ser.
No. 10/539,132, filed Jun. 16, 2005, which is a 371 of
PCT/EP03/11543 filed on Oct. 18, 2003.
[0002] The present invention relates to a process for preparing
aqueous dispersions. In particular, it relates to a process for
preparing, in aqueous dispersion, core-shell particles which can be
used for the impact-modification of poly(meth)acrylate moulding
compositions.
[0003] It has long been known that the impact strength of moulding
compositions, in particular of poly(meth)-acrylate moulding
compositions, can be improved by adding, to the moulding
composition, a suitable amount of what are known as impact
modifiers. The use of core-shell particles and/or core-shell-shell
particles for this purpose has become established industrially.
These generally have an elastomeric phase, and in the case of the
core-shell structure here the core is mostly the elastomeric phase,
while in the case of a core-shell-shell structure the first shell
grafted onto the core is mostly the elastomeric phase.
[0004] By way of example, U.S. Pat. No. 3,793,402 discloses
toughened moulding compositions, in particular based on
poly(meth)acrylate, which comprise from 90 to 4% by weight of a
multistage core-shell particle with a hard core, an elastomeric
first shell and a hard second shell. Typical main constituents of
the core and of the second shell are alkyl methacrylates having
from 1 to 4 carbon atoms in the alkyl radical, in particular methyl
methacrylate. The first shell is substantially composed of
butadiene, substituted butadienes and/or alkyl acrylates having
from 1 to 8 carbon atoms in the alkyl radical. However, it may also
contain from 0 to 49.9% by weight, in particular from 0.5 to 30% by
weight, of copolymerizable monomer units, such as copolymerizable,
monoethylenically unsaturated monomer units. According to U.S. Pat.
No. 3,793,402, the presence here of from 10 to 25% by weight of
copolymerizable, monoethylenically unsaturated monomer units, in
particular of styrene, is very particularly advantageous.
[0005] The overall diameter of the core-shell particles is in the
range from 100 to 300 nm.
[0006] The core-shell particles are produced by multistage emulsion
polymerization, using thermal initiators, such as persulphates or
redox initiator systems. The intention here is that the
polymerization takes place at a temperature in the range from 0 to
125.degree. C., in particular in the range from 30 to 95.degree.
C.
[0007] Similarly, the German Patent Application DE 41 21 652 A1
describes impact modifiers for thermoplastics, such as polymethyl
methacrylate, composed of an at least three-phase emulsion polymer,
comprising [0008] A) a hard core composed of a crosslinked homo- or
copolymer of ethylenically unsaturated monomers capable of
free-radical polymerization; [0009] B) an elastomer phase generated
in the presence of the core material and having a glass transition
temperature not above 10.degree. C., and composed of [0010] a) an
alkyl ester of acrylic acid having from 1 to 8 carbon atoms in the
alkyl radical; [0011] b) at least one crosslinking monomer having
two or more polymerizable double bonds in the molecule; [0012] c)
arylalkyl acrylate or arylalkyl methacrylate; [0013] d) a hard
phase generated in the presence of the elastomer phase and composed
of a homo- or copolymer of ethylenically unsaturated monomers
capable of free-radical polymerization, its glass transition
temperature being at least 50.degree. C.
[0014] A moulding composition (Example 3) cited by way of example
in that publication has an Izod notched impact strength of 6.2
kJ/m.sup.2 at room temperature, 4.7 kJ/m.sup.2 at -10.degree. C.,
and 3.7 kJ/m.sup.2 at -20.degree. C. The Vicat softening point of
that moulding composition is 97.degree. C.
[0015] The core-shell particles are likewise prepared by means of
multistage emulsion polymerization, using an alkali metal
peroxodisulphate or ammonium peroxodisulphate as initiator, and
carrying out the polymerization at a temperature in the range from
20 to 100.degree. C., for example at 50.degree. C.
[0016] The German Patent Application DE 41 36 993 A1 discloses
impact-modified moulding compositions which comprise from 10 to 96%
by weight of a polymer based on polymethyl methacrylate and from 4
to 90% by weight of a multistage core-shell-shell particle, using,
for the preparation of the core and, respectively, of the second
shell, a monomer mixture composed substantially of methyl
methacrylate. The monomer mixture for the first shell encompasses
from 60 to 89.99% by weight of alkyl acrylate having from 1 to 20
carbon atoms in the alkyl radical and/or cycloalkyl acrylates
having from 5 to 8 carbon atoms in the cycloalkyl radical and from
10 to 39.99% by weight of phenylalkyl acrylate having from 1 to 4
carbon atoms in the alkyl radical, and also, where appropriate,
other constituents. The average particle diameter of the
core-shell-shell particles is in the range from 50 to 1000 nm, in
particular in the range from 150 to 400 nm.
[0017] According to that publication, the core-shell particles are
obtained by a multistage seed latex process which uses ammonium or
alkyli [sic] peroxodisulphates, such as potassium peroxodisulphate,
or initiator combination systems as polymerization initiators, the
intended polymerization temperature being from 50 to 100.degree. C.
when use is made of the ammonium and alkyli [sic]
peroxodisulphates, which require thermal activation.
[0018] The European Patent EP 0 828 772 B1 describes the
impact-modification of poly(meth)acrylates by multi-stage
core-shell particles which are composed of a core, a first shell
and, where appropriate, a second shell, and are free from
vinylically unsaturated compounds having at least two equally
reactive double bonds. In this the case, the core comprises a first
(meth)acrylic polymer. The first shell comprises a polymer which
has a low glass transition temperature and which encompasses from 0
to 25% by weight, in particular from 5 to 26% [sic] by weight, of a
styrenic monomer and from 75 to 100% by weight of a (meth)acrylic
monomer which forms a homopolymer with a glass transition
temperature of from -75 to -5.degree. C. The second shell present
where appropriate comprises a second (meth)acrylic polymer which
may be identical with the first (meth)acrylic polymer or may differ
therefrom. The overall diameter of the core-shell particles is in
the range from 250 to 320 nm.
[0019] The core-shell particles are in turn prepared by multi-stage
emulsion polymerization at 80.degree. C., using a potassium
persulphate as initiator.
[0020] Although the processes described above are usually used when
preparing core-shell particles, they all have the disadvantage that
the polymerization have [sic] to be carried out at comparatively
low monomer concentration, generally less than 50.0% by weight, in
order to obtain the desired particle sizes with a narrow particle
size distribution. A polymerization at higher monomer
concentration, in contrast, leads in [sic] to a marked broadening
of particle size distribution and to the formation of large amounts
of coagulate, which significantly impairs the properties of the
core-shell particle.
[0021] For application, in particular for the impact-modification
of moulding compositions, the core-shell particles cannot be used
in the form of an aqueous dispersion, but instead have to be
isolated from the aqueous dispersion. The low solid content of the
aqueous dispersion therefore has a direct adverse effect on the
possible use of the abovementioned core-shell particles, because
their separation requires major cost for energy and other
resources. There is therefore a need for higher-efficiency
processes for preparing core-shell particles.
[0022] In addition to the emulsion polymers, suspension polymers
are also occasionally used for the impact-modification of moulding
compositions. The rubber here, for example grafted with polymethyl
methacrylate, has relatively fine distribution in the matrix of the
moulding composition, for example polymethyl methacrylate. The
elastomeric phase is composed of a mostly crosslinked copolymer
with a low glass transition temperature below 25.degree. C., which
usually contain [sic], as main component, alkyl acrylate units
having from 1 to 8 carbon atoms in the alkyl radical, in particular
butyl acrylate units. Use is also occasionally made of
polybutadiene or polybutadiene copolymers as tough phase.
[0023] Although it is true that use of the impact modifiers
described above can achieve a significant improvement in notch
impact strength, for a wide variety of applications this is still
not fully satisfactory. For example, impact-modification at room
temperature (23.degree. C.) in particular requires a relatively
large amount of these impact modifiers, which in turn leads to
significant impairment of the other properties important for
applications of the moulding composition, in particular of modulus
of elasticity, melt viscosity, Vicat point and by the die
swell.
[0024] Industry therefore demands impact modifiers which permit
sufficient improvement in the notched impact strength of a moulding
composition, in particular at room temperature, using minimum
amounts of impact modifier, without any noticeable associated
impairment in the other important properties of the moulding
composition, in particular modulus of elasticity, melt viscosity,
Vicat point and die swell. The moulding composition here is
intended to have a Charpy notched impact strength (ISO 179) which
is preferably at least 6.0 kJ/m.sup.2 at 23.degree. C. and is
preferably at least 2.5 kJ/m.sup.2 at -10.degree. C., a modulus of
elasticity (ISO 527-2) which is preferably greater than 1500 MPa, a
haze to ASTM D 1003 (1997) which is preferably at most 2.5%, a melt
viscosity which is preferably greater than 2000 Pa s and more
advantageously below 4500 Pa s, a Vicat softening point which is
preferably at least 85.degree. C., more advantageously at least
90.degree. C., in particular at least 93.degree. C., a
transmittance (D) 65/10.degree. to DIN 5033/5036 which is
preferably at least 88.5%, and a die swell which is preferably in
the range from 0 to 20%.
[0025] In light of the prior art, it was then a object of the
present invention to provide, for moulding compositions, in
particular for poly(meth)acrylate moulding compositions, impact
modifiers which permit improvement of the notched impact strength
of moulding compositions, in particular at room temperature, with
no noticeable associated impairment of the other moulding
composition properties important for applications, in particular
modulus of elasticity, melt viscosity, Vicat point and die swell.
The moulding compositions are intended to have a Charpy notched
impact strength (ISO 179) which is preferably at least 6.0
kJ/m.sup.2 at 23.degree. C. and preferably at least 2.5 kJ/m.sup.2
at -10.degree. C., a modulus of elasticity (ISO 527-2) which is
preferably greater than 1500 MPa, a haze to ASTM D 1003 (1997)
which is preferably at most 2.5%, a melt viscosity which is
preferably greater than 2000 Pa s and more advantageously below
4500 Pa s, a Vicat softening point which is preferably at least
85.degree. C., more advantageously at least 90.degree. C., in
particular at least 93.degree. C., a transmittance (D)
65/10.degree. to DIN 5033/5036 which is preferably at least 88.5%,
and a die swell which is preferably in the range from 0 to 20%.
[0026] Another object of the present invention was to provide a
more efficient process which can prepare core-shell particles which
in particular permits less complicated isolation of the core-shell
particles.
[0027] Another object of the present invention was to be found in
the provision of a process which can prepare core-shell particles
and which can be carried out simply, on an industrial scale, and at
low cost.
[0028] A further object underlying the present invention was to
provide a process for preparing core-shell particles with maximum
narrowness of particle size distribution, preferably with a
P.sub.80 value below 0.22.
[0029] Another object of the present invention was to provide a
process which can prepare core-shell particles and which minimizes
coagulate formation, preferably to less than 5.0% by weight.
[0030] Furthermore, another object of the present invention was to
provide a process for preparing core-shell particles with a
particle radius, measured by the Coulter method, in the range from
150.0 to below 250.0 nm, because these core-shell particles are
very particularly suitable for the impact-modification of moulding
compositions, in particular of polyalkyl (meth)acrylate moulding
composition.
[0031] A process for preparing an aqueous dispersion with all of
the features of claim 1 of the present patent achieves these
objects, and also achieves other objects which, although not
explicitly mentioned, are readily derivable or producible from the
circumstances discussed in the above introduction. Advantageous
modifications of the procedure of the invention are protected in
the subclaims dependent on claim 1. The product claim 11, protects
the core-shell particles obtainable by the process. Impact-modified
poly(meth)acrylic moulding compositions which comprise core-shell
particles of the invention are also claimed, as are preferred
application sectors for these moulding compositions.
[0032] A process for preparing an aqueous dispersion, by [0033] a)
using water and emulsifier to form an initial charge, [0034] b)
adding from 25.0 to 45.0 parts by weight of a first composition
comprising [0035] A) from 50.0 to 99.9 parts by weight of alkyl
methacrylates other than C) having from 1 to 20 carbon atoms in the
alkyl radical, [0036] B) from 0.0 to 40.0 parts by weight of alkyl
acrylates other than C) having from 1 to 20 carbon atoms in the
alkyl radical, [0037] C) from 0.1 to 10.0 parts by weight of
crosslinking monomers and [0038] D) from 0.0 to 8.0 parts by weight
of styrenic monomers of the general formula (I)
[0038] ##STR00001## where each of the radicals R.sup.1 to R.sup.5,
independently of the others, is hydrogen, a halogen, a
C.sub.1-6-alkyl group or a C.sub.2-6-alkenyl group, and the radical
R.sup.6 is hydrogen or an alkyl group having from 1 to 6 carbon
atoms, and polymerizing to a conversion of at least 85.0% by
weight, based on the total weight of components A), B), C) and D),
[0039] c) adding from 35.0 to 55.0 parts by weight of a second
composition comprising [0040] E) from 80.0 to 100.0 parts by weight
of (meth)acrylates [0041] F) from 0.05 to 10.0 parts by weight of
cross-linking monomers and [0042] G) from 0.0 to 20.0 parts by
weight of styrenic monomers of the general formula (I), and
polymerizing to a conversion of at least 85.0% by weight, based on
the total weight of components E), F) and G), [0043] d) adding from
10.0 to 30.0 parts by weight of a third composition comprising
[0044] H) from 50.0 to 100.0 parts by weight of alkyl methacrylates
having from 1 to 20 carbon atoms in the alkyl radical, [0045] I)
from 0.0 to 40.0 parts by weight of alkyl acrylates having from 1
to 20 carbon atoms in the alkyl radical and [0046] J) from 0.0 to
10.0 parts by weight of styrenic monomers of the general formula
(I) and polymerizing to a conversion of at least 85.0% by weight,
based on the total weight of components H), I) and J), where the
parts by weight given for the compositions b), c) and d) give a
total of 100.0 parts by weight, a feature of the process being that
[0047] e) carrying out each polymerization at a temperature in the
range from above 60 to below 90.degree. C. and [0048] f) selecting
the relative proportions of all of the substances in such a way
that the total weight of components A) to J), based on the total
weight of the aqueous dispersion, is greater than 50.0% by weight,
provides an unforeseeable route to a process which permits the
efficient preparation of core-shell particles in aqueous
dispersion. The high solids content of this aqueous dispersion
makes the separation of the core-shell particles substantially
easier than in the conventional processes.
[0049] A series of other advantages can moreover be achieved
through the procedure of the invention. These include: [0050] The
process of the invention can be carried out simply on industrial
scale and at low cost. [0051] The core-shell particles obtainable
by the process of the invention have narrow particle size
distribution, preferably a P.sub.80 value below 0.22. [0052] The
process of the invention almost completely suppresses the formation
of coagulate. [0053] The process of the invention is particularly
suitable for preparing core-shell particles with a particle radius,
measured by the Coulter method, in the range from 150.0 to below
250.0 nm. [0054] The process of the invention provides, for
moulding compositions, in particular for poly-(meth)acrylate
moulding compositions, impact modifiers which permit improvement of
the notched impact strength of moulding compositions, in particular
at room temperature, with no noticeable associated impairment of
the other moulding composition properties important for
applications, in particular modulus of elasticity, melt viscosity,
Vicat point and die swell. Moulding compositions which are
particularly suitable according to the invention has a Charpy
notched impact strength (ISO 179) which is preferably at least 6.0
kJ/m.sup.2 at 23.degree. C. and preferably at least 2.5 kJ/m.sup.2
at -10.degree. C., a modulus of elasticity (ISO 527-2) which is
preferably greater than 1500 MPa, a haze to ASTM D 1003 (1997)
which is preferably at most 2.5%, a melt viscosity which is
preferably greater than 2000 Pa s and more advantageously below
4500 Pa s, a Vicat softening point which is preferably at least
85.degree. C., more advantageously at least 90.degree. C., in
particular at least 93.degree. C., a transmittance (D)
65/10.degree. to DIN 5033/5036 which is preferably at least 88.5%,
and a die swell which is preferably in the range from 0 to 20%.
[0055] Use of the core-shell particles provides access to moulding
compositions with significantly improved notched impact strength
values, in particular at low temperatures below 0.degree. C.,
advantageously moulding compositions with an Izod notched impact
strength to ISO 180 of at least 3.5 kJ/m.sup.2 at -10.degree. C.
[0056] A comparison is made with conventional impact modifiers,
significantly smaller amounts of the core-shell particles of the
invention are sufficient to give moulding compositions with
comparable notched impact strength at room temperature, in
particular at 23.degree. C. [0057] The moulding compositions
impact-modified in the manner of the invention feature a
significantly improved property profile at room temperature, in
particular at 23.degree. C. This makes them useful for applications
these [sic] temperatures, in particular at temperatures in the
range from 0.degree. C. to 50.degree. C.
[0058] According to the present invention, an aqueous dispersion is
prepared by a process in which water and emulsifier are used to
form an initial charge. This initial charge preferably comprises
from 90.00 to 99.9 parts by weight of water and from 0.01 to 10.00
parts by weight of emulsifier, where the stated parts by weight
advantageously give a total of 100.00 parts by weight.
[0059] The following sequence of steps is now applied to this
initial charge [0060] b) adding from 25.0 to 45.0 parts by weight
of a first composition and polymerizing to a conversion of at least
85.0% by weight, preferably at least 90.0% by weight,
advantageously at least 95.0% by weight, in particular at least 99%
by weight, based in each case on the total weight of components A),
B), C) and D), [0061] c) adding from 35.0 to 55.0 parts by weight
of a second composition and polymerizing to a conversion of at
least 85.0% by weight, preferably at least 90.0% by weight,
advantageously at least 95.0% by weight, in particular at least 99%
by weight, based in each case on the total weight of components E),
F) and G), [0062] d) adding from 10.0 to 30.0 parts by weight of a
third composition and polymerizing to a conversion of at least
85.0% by weight, preferably at least 90.0% by weight,
advantageously at least 95.0% by weight, in particular at least 99%
by weight, based in each case on the total weight of components H),
I) and J), where the stated parts by weight give a total of 100.0
parts by weight.
[0063] For the purposes of the present invention, polymers here are
compounds whose molecular weight is at least ten times that of the
respective starting compounds A) to J), known as the monomer.
[0064] The progress of the polymerization reaction into each step
may be followed in a known manner, for example gravimetrically or
by means of gas chromatography.
[0065] The first composition comprises [0066] A) from 50.0 to 99.9
parts by weight, advantageously from 60.0 to 99.9 parts by weight,
preferably from 75.0 to 99.9 parts by weight, in particular from
85.0 to 99.5 parts by weight, of alkyl methacrylates having from 1
to 20, preferably from 1 to 12, in particular from 1 to 8, carbon
atoms in the alkyl radical, [0067] B) from 0.0 to 40.0 parts by
weight, preferably from 0.0 to 24.9 parts by weight, in particular
from 0.1 to 14.9 parts by weight, of alkyl acrylates having from 1
to 20, preferably from 1 to 12, in particular from 1 to 8, carbon
atoms in the alkyl radical, [0068] C) from 0.1 to 10.0 parts by
weight, preferably from 0.1 to 5.0 parts by weight, in particular
from 0.1 to 2.0 parts by weight, of crosslinking monomers and
[0069] D) from 0.0 to 8.0 parts by weight of styrenic monomers of
the general formula (I)
[0069] ##STR00002## where the stated parts by weight preferably
give a total of 100.0 parts by weight.
[0070] These compounds A), B), C) and D) are naturally different
from one another, and in particular the compounds A) and B)
encompass no crosslinking monomers C).
[0071] Each of the radicals R.sup.1 To R.sup.5, independently of
the others, is hydrogen, a halogen, in particular fluorine,
chlorine or bromine, or an alkyl group having from 1 to 6 carbon
atoms, preferably hydrogen. The radical R.sup.6 is hydrogen or an
alkyl group having from 1 to 6 carbon atoms, preferably hydrogen.
Particularly suitable alkyl groups having from 1 to 6 carbon atoms
are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl,
tert-butyl, n-pentyl, n-hexyl groups, and cyclopentyl and
cyclohexyl groups.
[0072] Styrenic monomers of the general formula (I) therefore
encompass styrene, substituted styrenes having an alkyl substituent
in the side chain, for example .alpha.-methyl-styrene and
.alpha.-ethylstyrene, substituted styrenes having an alkyl
substituent on the ring, for example vinyl-toluene and
p-methylstyrene, halogenated styrenes. [sic] for example
monochlorostyrenes, dichlorostyrenes, tribromostyrenes and
tetrabromostyrenes.
[0073] The abovementioned alkyl methacrylates (A) are esters of
methacrylic acid, for example methyl methacrylate, ethyl
methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl
methacrylate, sec-butyl methacrylate, tert-butyl methacrylate,
pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl
methacrylate, 2-octyl methacrylate, ethylhexyl methacrylate, nonyl
methacrylate, 2-methyloctyl methacrylate, 2-tert-butylheptyl
methacrylate, 3-isopropylheptyl methacrylate, decyl methacrylate,
undecyl methacrylate, 5-methylundecyl methacrylate, dodecyl
methacrylate, 2-methyldodecyl methacrylate, tridecyl methacrylate,
5-methyltridecyl methacrylate, tetradecyl methacrylate, pentadecyl
methacrylate, hexadecyl methacrylate, 2-methylhexadecyl
methacrylate, heptadecyl methacrylate, 5-isopropylheptadecyl
methacrylate, 5-ethyloctadecyl methacrylate, octadecyl
methacrylate, nonadecyl methacrylate, eicosyl methacrylate,
cycloalkyl methacrylates, for example cyclopentyl methacrylate,
cyclohexyl methacrylate, 3-vinyl-2-butylcyclohexyl methacrylate,
cycloheptyl methacrylate, cyclooctyl methacrylate, bornyl
methacrylate and isobornyl methacrylate.
[0074] In one particularly preferred embodiment of the present
invention, the first composition comprises, based on the total
weight of components A) to D), at least 50% by weight,
advantageously at least 60% by weight, preferably at least 75% by
weight, in particular at least 85% by weight, of methyl
methacrylate.
[0075] The abovementioned alkyl acrylates (B) are esters of acrylic
acid, for example methyl acrylate, ethyl acrylate, propyl acrylate,
isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate,
tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl
acrylate, octyl acrylate, 2-octyl acrylate, ethylhexyl acrylate,
nonyl acrylate, 2-methyloctyl acrylate, 2-tert-butylheptyl
acrylate, 3-isopropylheptyl acrylate, decyl acrylate, undecyl
acrylate, 5-methylundecyl acrylate, dodecyl acrylate,
2-methyldodecyl acrylate, tridecyl acrylate, 5-methyltridecyl
acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl
acrylate, 2-methylhexadecyl acrylate, heptadecyl acrylate,
5-isopropylheptadecyl acrylate, 5-ethyloctadecyl acrylate,
octadecyl acrylate, nonadecyl acrylate, eicosyl acrylate,
cycloalkyl acrylates, for example cyclopentyl acrylate, cyclohexyl
acrylate, 3-vinyl-2-butylcyclohexyl acrylate, cycloheptyl acrylate,
cyclooctyl acrylate, bornyl acrylate and isobornyl acrylate.
[0076] Crosslinking monomers (C) encompass all of the compounds
which are capable, under the present polymerization conditions, of
bringing about crosslinking. These include in particular [0077] (a)
Difunctional (meth)acrylates, preferably compounds of the general
formula:
[0077] ##STR00003## [0078] where R is hydrogen or methyl and n is a
positive whole number greater than or equal to 2, preferably from 3
to 20, in particular di(meth)acrylates of propanediol, of
butanediol, of hexanediol, of octanediol, of nonanediol, of
decanediol, and of eicosanediol;
[0079] Compounds of the general formula:
##STR00004## [0080] where R is hydrogen or methyl and n is a
positive whole number from 1 to 14, in particular di(meth)acrylate
of ethylene glycol, of diethylene glycol, of triethylene glycol, of
tetraethylene glycol, of dodecaethylene glycol, of
tetradecaethylene glycol, of propylene glycol, of dipropyl glycol
and of tetradecapropylene glycol.
[0081] Glycerol di(meth)acrylate,
2,2'-bis[p-(.gamma.-methacryloxy-(.beta.-hydroxypropoxy)phenylpropane]
or bis-GMA, biphenol [sic] A dimethacrylate, neopentyl glycol
di(meth)acrylate, 2,2'-di(4-methacryloxypolyethoxyphenyl)propane
having from 2 to 10 ethoxy groups per molecule and
1,2-bis(3-methacryloxy-2-hydroxypropoxy)butane. [0082] (b) Tri- or
polyfunctional (meth)acrylates, in particular trimethylolpropane
tri(meth)acrylate and pentaerythritol tetra(meth)acrylate. [0083]
(c) Graft crosslinking agents having at least two C--C double bonds
of differing reactivity, in particular allyl methacrylate and allyl
acrylate; [0084] (d) aromatic crosslinking agents, in particular
1,2-divinylbenzene, 1,3-divinylbenzene and 1,4-divinylbenzene.
[0085] The manner of monomer selection or, respectively, of
selection of the proportions by weight of the monomers A) to D) of
the first composition is preferably such that the polymer
obtainable by polymerization of the first monomer mixture has a
glass transition temperature Tg of at least 10.degree. C.,
preferably of at least 30.degree. C. The glass transition
temperature Tg of the polymer here can be determined in a known
manner by differential scanning calorimetry (DSC). The glass
transition temperature Tg may also be approximated by means of the
Fox equation. According to Fox T. G., Bull. Am. Physics Soc. 1, 3,
p. 123 (1956):
1 Tg = x 1 Tg 1 + x 2 Tg 2 + + x n Tg n ##EQU00001##
where x.sub.n is the proportion by weight (% by weight/100) of the
monomer n and Tg.sub.n is the glass transition temperature in
Kelvin of the homopolymer of the monomer n. The person skilled in
the art may obtain further useful information from Polymer Handbook
2.sup.nd Edition, J. Wiley & Sons, New York (1975), which gives
Tg values for the homopolymers most commonly encountered.
[0086] The second monomer mixture comprises [0087] E) from 80.0 to
100.0 parts by weight, preferably from 92.0 to 98.0 parts by
weight, of (meth)acrylates other than F) [0088] F) from 0.05 to
10.0% parts by weight, preferably from 0.1 to 2.0% by weight, of
crosslinking monomers and [0089] G) 0.0 to 20.0 parts by weight,
preferably from 8.0 to 20.0 parts by weight, of styrenic monomers
of the general formula (I), where the stated parts by weight
preferably give a total of 100.0 parts by weight.
[0090] These compounds E), F) and G) are naturally different from
one another, and in particular the compounds E) encompass no
crosslinking monomers F).
[0091] For the purposes of the present invention, (meth)acrylates
are acrylates, methacrylates and mixtures of the two. They
therefore encompass compounds which have at least one group of the
following formula
##STR00005##
where R is hydrogen or a methyl radical. They include in particular
the abovementioned alkyl acrylates and alkyl methacrylates. Other
compounds which have proven particularly useful for the purposes of
the present invention are arylalkyl acrylates, in particular
benzyl, phenylethyl, phenylpropyl, phenylpentyl and/or phenylhexyl
acrylate. The amount preferably used of these is in the range from
0.1 to 40.0% by weight, based on the total weight of components E)
and F).
[0092] According to the invention, the crosslinking monomers F)
encompass the abovementioned crosslinking monomers C).
[0093] For the purposes of one particularly preferred embodiment of
the present invention, the second monomer mixture encompasses
[0094] E) from 90.0 to 97.9 parts by weight of alkyl acrylates
having from 3 to 8 carbon atoms in the alkyl radical and/or alkyl
methacrylates having from 7 to 14 carbon atoms in the alkyl
radical, in particular butyl acrylate and/or dodecyl methacrylate,
[0095] F) from 0.1 to 2.0% by weight of crosslinking monomers and
[0096] G) from 0.0 to 20.0 parts by weight, preferably from 8.0 to
20.0 parts by weight of styrenic monomers of the general formula
(I), where the parts by weight preferably give a total of 100.0
parts by weight.
[0097] The manner of monomer selection or, respectively, of
selection of the proportions by weight of the monomers E), F) and
G) of the second composition is advantageously such that the
polymer obtainable by polymerization of the second composition has
a glass transition temperature Tg of below 30.degree. C.,
preferably below 10.degree. C., in particular in the range from 0
to -75.degree. C. The glass transition temperature Tg of the
polymer here can be determined as mentioned above by differential
scanning calorimetry (DSC) and/or approximated by the Fox
equation.
[0098] The third composition comprises [0099] H) from 50.0 to 100.0
parts by weight, advantageously from 60.0 to 100.0 parts by weight,
particularly preferably from 75.0 to 100.0 parts by weight, in
particular from 85.0 to 99.5 parts by weight, of alkyl
methacrylates having from 1 to 20, preferably from 1 to 12, in
particular from 1 to 8, carbon atoms in the alkyl radical, [0100]
I) from 0.0 to 40.0 parts by weight, preferably from 0.0 to 25.0
parts by weight and in particular from 0.1 to 15.0 parts by weight,
of alkyl acrylates having from 1 to 20, preferably from 1 to 12, in
particular from 1 to 8, carbon atoms in the alkyl radical, [0101]
J) from 0.0 to 10.0 parts by weight, preferably from 0.0 to 8.0%
[sic] by weight, of styrenic monomers of the general formula (I),
where the stated parts by weight preferably give 100.0 parts by
weight in total.
[0102] In one particularly preferred embodiment of the present
invention, the third composition comprises, based on the total
weight of components H) to J), at least 50% by weight,
advantageously at least 60% by weight, preferably at least 75% by
weight, in particular at least 85% by weight, of methyl
methacrylate.
[0103] The manner of monomer selection or, respectively, of
selection of the proportions by weight of the monomers H), I) and
J) of the third composition is advantageously such that the polymer
obtainable by polymerization of the third composition has a glass
transition temperature Tg of at least 10.degree. C., preferably at
least 30.degree. C. The glass transition temperature Tg of the
polymer here can be determined as mentioned above by differential
scanning calorimetry (DSC) and/or approximated by the Fox
equation.
[0104] In the process of the invention, the polymerization in steps
b) to d) takes place at a temperature in the range from above 60 to
below 90.degree. C., advantageously in the range from above 70 to
below 85.degree. C., preferably in the range from above 75 to below
85.degree. C.
[0105] The initiation takes place using the initiators commonly
used for emulsion polymerization. Examples of suitable organic
initiators are hydroperoxides, such as tert-butyl hydroperoxide or
cumene hydroperoxide. Suitable inorganic initiators are hydrogen
peroxide and the alkali metal and ammonium salts of
peroxodisulphuric acid, in particular sodium peroxodisulphate and
potassium peroxodisulphate. The initiators mentioned may be used
either alone or else mixed. The amount preferably used of these is
from 0.05 to 3.0% by weight, based on the total weight of the
monomers of the respective stage.
[0106] The reaction mixture is stabilized by means of emulsifiers
and/or protective colloids. Preference is given to stabilization by
emulsifiers, in order to obtain low dispersion viscosity. The total
amount of emulsifier is preferably from 0.1 to 5% by weight, in
particular from 0.5 to 3% by weight, based on the total weight of
the monomers A) to J). Particularly suitable emulsifiers are
anionic or non-ionic emulsifiers or mixtures of these, in
particular: [0107] alkyl sulphates, preferably those having from 8
to 18 carbon atoms in the alkyl radical, alkyl and alkyl-aryl ether
sulphates having from 8 to 18 carbon atoms in the alkyl radical and
from 1 to 50 ethylene oxide units; [0108] sulphonates, preferably
alkylsulphonates having from 8 to 18 carbon atoms in the alkyl
radical, alkylarylsulphonates having from 8 to 18 carbon atoms in
the alkyl radical, esters and half-esters of sulphosuccinic acid
with monohydric alcohols or alkylphenols having from 4 to 15 carbon
atoms in the alkyl radical; where appropriate, these alcohols or
alkylphenols may also have been ethoxylated with from 1 to 40
ethylene oxide units; [0109] partial esters of phosphoric acid and
the alkali metal and ammonium salts of these, preferably alkyl and
alkyl-aryl phosphates having from 8 to 20 carbon atoms in the alkyl
and, respectively, alkyl-aryl radical and from 1 to 5 ethylene
oxide units; [0110] alkyl polyglycol ethers, preferably having from
8 to 20 carbon atoms in the alkyl radical and from 8 to 40 ethylene
oxide units; [0111] alkyl-aryl polyglycol ethers, preferably having
from 8 to 20 carbon atoms in the alkyl and, respectively,
alkyl-aryl radical and from 8 to 40 ethylene oxide units; [0112]
ethylene oxide-propylene oxide copolymers, preferably block
copolymers, advantageously having from 8 to 40 ethylene oxide and,
respectively, propylene oxide units.
[0113] According to the invention, preference is given to mixtures
composed of anionic emulsifier and of non-ionic emulsifier.
Mixtures which have proven very particularly successful here are
those composed of an ester or half-ester of sulphosuccinic acid
with monohydric alcohols or alkylphenols having from 4 to 15 carbon
atoms in the alkyl radical, as anionic emulsifier, and of an alkyl
polyglycol ether, preferably having from 8 to 20 carbon atoms in
the alkyl radical and from 8 to 40 ethylene oxide units, as
non-ionic emulsifier, in a ratio of from 8:1 to 1:8 by weight.
[0114] Where appropriate, the emulsifiers may also be used in a
mixture with protective colloids. Suitable protective colloids
encompass, inter alia, partially hydrolyzed polyvinyl acetates,
polyvinylpyrrolidones, carboxymethyl-, methyl-, hydroxyethyl-,
hydroxypropyl-cellulose, starches, proteins, poly(meth)acrylic
acid, poly(meth)acrylamide, polyvinylsulphonic acids,
melamine-formaldehydesulphonates,
naphthalene-formaldehydesulphonates, styrene-maleic acid copolymers
and vinyl ether-maleic acid copolymers. If use is made of
protective colloids, the amount preferably used of these is from
0.01 to 1.0% by weight, based on the total amount of the monomers
A) to I). The protective colloids may be used to form an initial
charge prior to the start of the polymerization, or may be metered
in.
[0115] The initiator may be used to form an initial charge or may
be metered in. Another possibility, furthermore, is use of a
portion of the initiator to form an initial charge and metering-in
of the remainder.
[0116] The polymerization is preferably initiated by heating the
reaction mixture to the polymerization temperature and by
metering-in of the initiator, preferably in aqueous solution. The
feeds of emulsifier and monomers may be separate or take the form
of a mixture. If mixtures composed of emulsifier and monomer are
metered in, the procedure comprises premixing emulsifer and monomer
in a mixer installed upstream of the polymerization reactor. It is
preferable for the remainder of emulsifier and the remainder of
monomer which are not used to form an initial charge to be metered
in separately from one another after the start of the
polymerization. The feed is preferably begun from 15 to 35 minutes
after the start of the polymerization.
[0117] For the purposes of the present invention, furthermore, it
is particularly advantageous for the initial charge to comprise
what is known as a "seed latex", which is preferably obtainable by
polymerization of alkyl (meth)acrylates and moreover advantageously
has a particle radius in the range from 3.0 to 20.0 nm,
advantageously [sic] in the range from 5.0 to 20.0 nm. These small
radii may be calculated after a defined polymerization onto the
seed latex, during which a shell is built up around the seed latex,
and measuring the radii of the resultant particles by the Coulter
method. This method of particle size determination, known from the
literature, is based on measurement of the electrical resistance,
which changes in a characteristic manner when particles pass
through a narrow measuring aperture. Further details may be found
in Nachr. Chem. Tech. Lab. 43, 553-566 (1995), for example.
[0118] The monomer constituents of the actual core, i.e. the first
composition, are added to the seed latex, preferably under
conditions such that the formation of new particles is avoided. The
result of this is that the polymer formed in the first stage of the
process is deposited in the form of a shell around the seed latex.
Similarly, the monomer constituents of the first shell material
(second composition) are added to the emulsion polymer under
conditions such that the formation of new particles is avoided. The
result of this is that the polymer formed in the second stage is
deposited in the form of a shell around the existing core. This
procedure is to be repeated appropriately for each further
shell.
[0119] In another preferred embodiment of the present invention,
the core-shell particles of the invention are obtained by an
emulsion polymerization process in which, instead of the seed
latex, a long-chain aliphatic alcohol, preferably having from 12 to
20 carbon atoms, emulsified, is used to form an initial charge. In
one preferred embodiment of this process, the long-chain aliphatic
alcohol used comprises stearyl alcohol. Similarly to the procedure
described above, the core-shell structure is obtained by stepwise
addition and polymerization of the corresponding monomers, avoiding
the formation of new particles. The person skilled in the art can
find further details on the polymerization process in the patent
Specifications DE 3343766, DE 3210891, DE 2850105, DE 2742178 and
DE 3701579.
[0120] However, for the purposes of the present invention,
irrespective of the specific procedure, it has proven very
particularly advantageous for the second and the third monomer
mixture to be metered in as required by consumption.
[0121] The chain length, in particular of the (co)polymers of the
second shell (third composition) may be adjusted via polymerization
of the monomer or of the monomer mixture in the presence of
molecular weight regulators, in particular of the mercaptans known
for this purpose, for example n-butyl mercaptan, n-dodecyl
mercaptan, 2-mercaptoethanol or 2-ethylhexyl thioglycolate,
pentaerythritol tetrathioglycolate; the amounts used of the
molecular weight regulators generally being from 0.05 to 5% by
weight, based on the monomer mixture, preferably from 0.1 to 2% by
weight and particularly preferably from 0.2 to 1% by weight, based
on the monomer mixture (cf., for example, H. Rauch-Puntigam, Th.
Volker, "Acryl- and Methacrylverbindungen" [Acrylic and methacrylic
compounds], Springer, Heidelberg, 1967; Houben-Weyl, Methoden der
organischem Chemie [Methods of organic chemistry], Vol. XIV/1. p.
66, Georg Thieme, Heidelberg, 1961 or Kirk-Othmer, Encyclopedia of
Chemical Technology, Vol. 1, pp. 296 et seq., J. Wiley, New York,
1978). The molecular weight regulator used preferably comprises
n-dodecyl mercaptan.
[0122] After conclusion of the polymerization, post-polymerization
may be carried out for residual monomer removal, using known
methods, for example using initiated post-polymerization.
[0123] Since the process of the invention is particularly suitable
for preparing aqueous dispersions with high solids content above
50% by weight, based on the total weight of the aqueous dispersion,
the manner of selection of the relative proportions of all of the
substances is such that the total weight of components A) to J),
based on the total weight of the aqueous dispersion, is above 50.0%
by weight, advantageously above 51.0% by weight, preferably above
52.0% by weight. The substances to be taken into account in this
connection also include, besides the monomers A) to J), all of the
other substances used, for example water, emulsifier, initiator,
where appropriate regulators and protective colloids, etc.
[0124] For the purposes of the present invention it is moreover
particularly advantageous for the selection of the relative
proportions of all of the components to be such as to give
core-shell particles with an overall radius, measured by the
Coulter method, in a range from 150.0 to below 250.0 nm, preferably
in the range from 170.0 to 220.0 nm.
[0125] The aqueous dispersions obtainable by the process of the
invention feature a low coagulate content which, based on the total
weight of the aqueous dispersion, is preferably less than 5.0% by
weight, advantageously less than 3.0% by weight, in particular less
than 1.5% by weight. In one particularly preferred embodiment of
the present invention, the aqueous dispersion comprises, based on
its total weight, less than 1.0% by weight, preferably less than
0.5% by weight, advantageously less than 0.25% by weight, in
particular 0.10% by weight or less, of coagulate.
[0126] The term "coagulate" in this connection means
water-insoluble constituents, which may preferably be filtered off
by filtering the dispersion advantageously through a filter ruffle
in which a No. 0.90 DIN 4188 filter fabric has been fixed.
[0127] The core-shell particle of the invention may be obtained
from the dispersion for example by spray drying, freeze
coagulation, precipitation by electrolyte addition or by exposure
to mechanical or thermal stress, where the latter can be carried
out by means of a vented extruder according to DE 27 50 682 A1 or
U.S. Pat. No. 4,110,843. The process of spray drying is the most
commonly used, but the other processes mentioned have the advantage
that they provide at least some separation of the water-soluble
polymerization auxiliaries from the polymer.
[0128] The core-shell particle of the invention serves to improve
the notched impact strength of rigid thermoplastics which are
compatible with the hard phase, preferably of poly(meth)acrylate
moulding compositions, in particular of polymethyl
methacrylate.
[0129] The poly(meth)acrylate moulding compositions preferably
comprise other polymers for suitable modification of properties.
These include in particular polyacrylonitriles, polystyrenes,
polyethers, polyesters, polycarbonates and polyvinyl chlorides.
These polymers may be used individually or as a mixture, and for
the purposes of one very particularly preferred embodiment of the
present invention here, copolymers which are derivable from the
abovementioned polymers are added to the moulding compositions.
These include in particular styrene-acrylonitrile copolymers (SAN),
which are preferably added to the moulding compositions in an
amount of up to 45% by weight.
[0130] Particularly preferred styrene-acrylonitrile copolymers may
be obtained by polymerizing mixtures which are composed of
from 70.0 to 92.0% by weight of styrene from 8.0 to 30.0% by weight
of acrylonitrile and from 0.0 to 22.0% by weight of other
comonomers, based in each case on the total weight of the monomers
to be polymerized.
[0131] From 10 to 60 parts of the impact-modifying agent are
generally admixed with 100 parts of the moulding composition to be
modified.
[0132] According to the invention, particularly preferred moulding
composition [sic] comprise, based in each case on its total weight:
[0133] A) from 1.0 to 50.0% by weight of at least one core-shell
particle according to at least one of claims 1 to 9; [0134] B) from
1.0 to 99.0% by weight of at least one (meth)acrylic polymer,
[0135] C) from 0.0 to 45.0% by weight, preferably from 1.0 to 45%
by weight, of styrene-acrylonitrile copolymers and [0136] D) from
0.0 to 10.0% by weight of other additives where the percentages by
weight give 100.0% by weight in total.
[0137] The (meth)acrylic polymer here preferably encompasses, based
in each case on its total weight, [0138] a) from 50.0 to 100.0% by
weight, advantageously from 60.0 to 100.0% by weight, particularly
preferably from 75.0 to 100.0% by weight, in particular from 85.0
to 99.5% by weight, of alkyl methacrylate repeat units having from
1 to 20, preferably from 1 to 12, advantageously from 1 to 8, in
particular from 1 to 4, carbon atoms in the alkyl radical, [0139]
b) from 0.0 to 40.0% by weight, preferably from 0.0 to 25.0% by
weight, in particular from 0.1 to 15.0% by weight, of alkyl
acrylate repeat units having from 1 to 20, preferably from 1 to 12,
advantageously from 1 to 8, in particular from 1 to 4, carbon atoms
in the alkyl radical and [0140] c) from 0.0 to 8.0% by weight of
styrenic repeat units of the general formula (I), where the
percentages by weight give a total of 100.0% by weight.
[0141] According to one particularly preferred embodiment of the
present invention, the (meth)acrylic polymer comprises, based on
its total weight, at least 50.0% by weight, advantageously at least
60.0% by weight, preferably at least 75.0% by weight, in particular
at least 85.0% by weight of methyl methacrylate repeat units.
[0142] The (meth)acrylic polymer moreover preferably has a
number-average molar mass in the range from 1000 to 100 000 000
g/mol, preferably in the range from 10 000 to 1 000 000 g/mol, in
particular in the range from 50 000 to 500 000 g/mol. This molar
mass may be determined by gel permeation chromatography, for
example, with calibration based on polystyrene.
[0143] Mixtures of this type may be prepared in various ways. For
example, the dispersion of the core-shell particle may be mixed
with an aqueous dispersion of the blend component, and the mixture
may be coagulated, the aqueous phase separated off, and the
coagulate melted to give a moulding composition. This process can
achieve particularly homogeneous mixing of the two materials. The
components may also be prepared separately and isolated and, in the
form of their melts or in the form of powders or pellets, mixed and
homogenized in a multiscrew extruder or on a roll mill.
[0144] Conventional additives may be admixed at any processing
stage suitable for this purpose. These include dyes, pigments,
fillers, reinforcing fibres, lubricants, UV stabilizers, etc.
[0145] For the purposes of one very particularly preferred
embodiment of the present invention, the moulding composition
comprises, based in each case on its total weight, from 0.1 to 10%
by weight, preferably from 0.5 to 5.0% by weight, in particular
from 1.0 to 4.0% by weight, of another polymer (AP) whose
weight-average molecular weight is higher than that of the
(meth)acrylic polymer by at least 10%, preferably at least 50%, in
particular at least 100%. The molecular weight here may be
determined by gel permeation chromatography, for example, with
calibration based on polystyrene.
[0146] According to the invention, particularly suitable polymers
(AP) preferably encompass, based in each case on their total
weight, [0147] a) from 50.0 to 100.0% by weight, advantageously
from 60.0 to 100.0% by weight, particularly preferably from 75.0 to
100.0% by weight, in particular from 85.0 to 99.5% by weight, of
alkyl methacrylate repeat units having from 1 to 20, preferably
from 1 to 12, advantageously from 1 to 8, in particular from 1 to
4, carbon atoms in the alkyl radical, [0148] b) from 0.0 to 40.0%
by weight, preferably from 0.0 to 25.0% by weight, in particular
from 0.1 to 15.0% by weight, of alkyl acrylate repeat units having
from 1 to 20, preferably from 1 to 12, advantageously from 1 to 8,
in particular from 1 to 4, carbon atoms in the alkyl radical and
[0149] c) from 0.0 to 8.0% by weight of styrenic repeat units of
the general formula (I), where the percentages by weight give a
total of 100.0% by weight.
[0150] In one particularly preferred embodiment of the present
invention, the polymer (AP) comprises, based on its total weight,
at least 50.0% by weight, advantageously at least 60.0% by weight,
preferably at least 75.0% by weight, in particular at least 85.0%
by weight of methyl methacrylate repeat units.
[0151] The polymer (AP) moreover preferably has a weight-average
molar mass in the range from 10 000 to 100 000 000 g/mol,
preferably in the range from 50 000 to 5 000 000 g/mol,
advantageously in the range from 100 000 to 1 000 000 g/mol, in
particular in the range from 250 000 to 600 000 g/mol. This
molecular weight may be determined for example by gel permeation
chromatography with calibration based on polystyrene.
[0152] Blends of the core-shell particles, in particular with
polymethyl methacrylate, are particularly suitable for producing
mouldings, advantageously with a wall thickness above 1 mm, for
example extruded webs of thickness of from 1 to 10 mm which give
good results in a stamping process and can be used, for example, to
produce printable panels for electrical devices, or for producing
high-quality injection mouldings, e.g. motor vehicle windscreens.
They can also be used to produce relatively thin films, for example
of thickness 50 .mu.m.
[0153] The mouldings obtainable according to the invention
preferably feature [0154] a Vicat softening point ISO 306 (B50) of
at least 85.degree. C., preferably of at least 90.degree. C. and
particularly preferably of at least 93.degree. C., [0155] the
Charpy notched impact strength (ISO 179) of at least 6.0 kJ/m.sup.2
at 23.degree. C., and preferably of at least 2.5 kJ/m.sup.2, in
particular of at least 2.5 [sic] kJ/m.sup.2, at -10.degree. C. and
[0156] a modulus of elasticity to ISO 527-2 of at least 1500 MPa
[0157] a haze to ASTM D 1003 (1997) which is preferably at most
2.5%, [0158] a melt viscosity to DIN 54811 (1984) above 2000 Pa s
and advantageously below 4500 Pa s, [0159] a transmittance (D
65/10.degree.) to DIN 5033/5036 of at least 88.5% and [0160] a die
swell to DIN 54811 (1984) in the range from 0 to 20%.
[0161] For the purposes of one particularly preferred embodiment of
the present invention, the mouldings of the invention are used as a
mirror housing or a spoiler on a motor vehicle, as a pipe, or as a
protective covering or as a component of a refrigerator.
[0162] The following inventive examples and comparative examples
serve for illustration of the present invention, but there is no
intention that there be any resultant restriction of the concept of
the invention.
I. Core-Shell Particles
A. Preparation of Seed Latex
[0163] A seed latex was prepared by emulsion polymerization of a
monomer composition comprising 98% by weight of ethyl acrylate and
2% by weight of allyl methacrylate. The content of these particles
in water was about 10% by weight, their diameter being about 20
nm.
B. Preparation of Core-Shell Particles
[0164] The synthesis of the core-shell particles described below
took place according to preparation process A (inventive examples
B1 and B2), B (comparative examples VB1 and VB2), C (comparative
examples VB3 and VB4 according to U.S. Pat. No. 3,793,402) or D
(comparative examples VB5, VB6 and VB7 according to DE 41 36 993).
Use was made here of the emulsions I to III given in table 1.
B.1 Preparation Process A (Inventive Examples)
[0165] 19.416 kg of water were used to form an initial charge by
stirring at 83.degree. C. (internal vessel temperature) in a
polymerization vessel. 16.2 g of sodium carbonate and 73 g of seed
latex were added. Emulsion I was then metered in over a period of 1
h. 10 min after the end of the input of emulsion I, emulsion II was
metered in over a period of about 2 h. Then, about 90 min after the
end of input of emulsion II, emulsion III was metered in over a
period of about 1 h. 30 min after the end of input of emulsion III,
the mixture was cooled to 30.degree. C.
[0166] To separate the core-shell particles, the dispersion was
frozen at 20.degree. C. for 2 d, then thawed again, and the
coagulated dispersion was separated by way of a filter fabric. The
solid was dried at 50.degree. C. in a drying cabinet (duration:
about 3 d). Further details can be found in table 1.
[0167] The particle size of the core-shell particles (see table 2)
was determined with the aid of a Coulter N4 device, these
measurements being made on the particles in dispersion.
B.2 Preparation Process B (Comparative Examples VB1 and VB2)
[0168] 20.129 kg of water were used to form an initial charge by
stirring at 52.degree. C. (internal vessel temperature) in a
polymerization vessel, and 1.18 g of acetic acid, 0.04 g of ferrous
(II) sulphate, 12.9 g of sodium disulphite and 121.5 g of seed
latex were added. Emulsion I was then metered in over a period of
1.5 h. 10 min after the end of input of emulsion I, 38.8 g of
sodium disulphite dissolved in 1176 g of water were added, and
emulsion II was metered in over a period of about 2.5 h. Then,
about 30 min after the end of input of emulsion II, 12.9 g of
sodium disulphite dissolved in 588.2 g of water were added and
emulsion III was added over a period of about 1.5 h. 30 min after
the end of input of emulsion III, the mixture was cooled to
30.degree. C. and adjusted to pH=8, using sodium carbonate. Any
attempt to achieve a solids content higher than 48% by weight for
the resultant dispersion resulted in observation of an increased
amount of coagulate (>1% by weight of the dispersion).
[0169] To separate the core-shell particles, the dispersion was
frozen at -20.degree. C. for 2 d, then thawed again, and the
coagulated dispersion was separated off by way of a filter fabric.
The solid was dried at 50.degree. C. in a drying cabinet (duration:
about 3 d). Further details are found in table 1.
[0170] The particle size of the core-shell particles (see table 2)
was determined with the aid of a Coulter N4 device, the
measurements being made on the particles in dispersion.
B.3 Preparation Process C (Comparative Examples According to U.S.
Pat. No. 3,793,402)
[0171] The preparation for comparative examples VB3 and VB4 took
place in a manner substantially similar to that for Example 1 of
U.S. Pat. No. 3,793,402. Only the monomer ratio for the first shell
was adapted to that of the inventive examples, and the dispersions
were prepared with the aid of a "triple-batch", i.e. the monomers
for the core, the first and the second shell were respectively
added all at once and then polymerized to completion. Further
details of the synthesis can be found in tables 3 to 6. The
resultant solids contents and coagulate contents are given in table
7. To determine coagulate content here, the entire dispersion was
filtered through a VA filter sleeve in which a No. 0.90 DIN 4188
screen fabric has been fixed. The resultant residue is rinsed with
water until the aqueous run-off was clear. To the extent that
coagulate resulted, this was pressed dry with a spatula, placed in
a previously tared glass beaker, and weighed on a laboratory
balance to an accuracy of 0.1 g. The filtrate was likewise weighed
on the laboratory balance to an accuracy of 1 g. The weight of the
entire dispersion is calculated from weight of coagulate and weight
of filtrate.
Coagulate (% by weight)=100.times.[weight of resultant coagulate
(g)]/[weight of entire dispersion (g)]
[0172] The radii of the resultant core-shell particles and their
particle size distribution are given in table 8. In this case the
particle size was characterized both by means of a Coulter N4
device and by means of an analytical ultracentrifuge. The particle
size distribution (PSD) is also determined by means of the
analytical ultracentrifuge. The sizes given in table 8 are defined
as: [0173] R10, R50, R90: radius greater than that of 10, 50 and,
respectively, 90% by weight of the core-shell particles in the
dispersion
[0173] P80:=(R90-R10)/R50 (measure of PSD uniformity-covers 80% by
weight of the core-shell particles)
B.4 Preparation Process D (Comparative Examples According to DE 41
36 993)
[0174] The preparation for comparative examples VB5, VB6 and VB7
was substantially in accordance with Example 1 of DE 41 36 993.
However, the amount of emulsion used to form an initial charge was
reduced from 30 to 20% by weight, in order to adjust the particle
size of the dispersions to those of the inventive examples. In
addition, an aqueous initiator solution was metered in in the final
stage. Further details of the synthesis are found in tables 3 to 6,
and the characteristic parameters are given in tables 7 and 8 and
are compared with polymer B1.
C. Preparation of a Blended Dispersion
[0175] The blended dispersion (solids content about 50% by weight)
is prepared by way of an emulsion polymerization, and its monomer
composition is 95% by weight of methyl methacrylate and 5% by
weight of ethyl acrylate. The particle size of the particles is 260
nm in diameter (measured in the Coulter N4 tester), and the J value
of the polymer (measure of molecular weight) is 203 mL/g (measured
in chloroform at a temperature of 25.degree. C., DIN ISO
1628-6)
II. Moulding Compositions
A. Blending of Moulding Compositions
[0176] A moulding composition based on polymethyl methacrylate,
PLEXIGLAS.RTM. 7 N (Rohm GmbH & Co. KG, Darmstadt) was blended
with the respective core-shell particles by means of an extruder.
The compositions for the individual inventive examples and
comparative examples are documented in table 9.
B. Testing of Moulding Compositions
[0177] Test specimens were produced from the blended moulding
compositions. The moulding compositions and, respectively, the
corresponding test specimens were tested according to the following
measuring methods: [0178] melt viscosity .eta.s (220.degree. C./5
MPa): DIN 54811 (1984) [0179] die swell B: DIN 54811 (1984) [0180]
Vicat softening point (16 h/80.degree. C.): DIN ISO [sic] 306
(August 1994) [0181] Izod notched impact strength: ISO 180 (1993)
[0182] Charpy notched impact strength: ISO 179 (1993) [0183]
modulus of elasticity: ISO 527-2 [0184] transmittance (D
65/10.degree.): DIN 5033/5036 [0185] haze (BYK Gardner
Hazegard-plus haze meter): ASTM D 1003 (1997)
[0186] The results of the tests are likewise shown in table 2.
[0187] The advantages of the blends A, B, C and D of the invention
over the conventionally impact-modified moulding compositions (VB A
and VB B) are clearly seen:
[0188] At comparable content of the core-shell particles (<400
by weight), the Charpy notched impact strength of the moulding
compositions of the invention at 23.degree. C. is significantly
higher than that of the comparative moulding compositions, and is
at a comparable level at -10.degree. C. The optical properties
(haze, transmission), the rheological properties (viscosity of the
melt, widening of the melt flow) and the mechanical properties
(module of elasticity) are on a comparable level.
TABLE-US-00001 TABLE 1 Composition of individual emulsions (all
amounts in [g]) VB1 VB2 B1 B2 Emulsion I Water 8823.5 8823.5
8109.65 8109.65 Sodium persulphate 8.24 8.24 Potassium persulphate
9.4 9.4 Aerosol OT 75 82.4 82.4 65.88 65.88 Methyl methacrylate
8622.0 8276.1 14216.72 14216.72 Ethyl acrylate 345.9 593.60 593.60
Allyl methacrylate 25.9 25.9 29.68 29.68 Emulsion II Water 7140
7140 7081.18 7081.18 Sodium persulphate 18.59 18.59 Potassium
persulphate 28.2 28.2 Aerosol OT 75 82.4 82.4 84.71 84.71 Butyl
acrylate 14438 14438 15454.8 15454.8 Styrene 3004.2 3004.2 3453.48
3453.48 Allyl methacrylate 229.74 229.74 171.72 171.72 Emulsion III
Water 4542.4 4542.4 2992.59 2992.59 Sodium persulphate 8.24 8.24
Potassium persulphate 8.8 8.8 Aerosol OT 75 15.3 15.3 10.59 10.59
Methyl methacrylate 10828.8 10828.8 7632 7632 Ethyl acrylate 451.2
451.2 848 848 Dodecyl mercaptan 39.5 39.5
TABLE-US-00002 TABLE 2 Test results from impact-modified moulding
compositions Blend VB A VB B A B C D Core-shell particles VB1 VB2
B1 B1 B2 B2 Particle radius [nm] 188 188 164 164 Content of
core-shell 39.3 39.3 38.4 35.7 38.4 38.4 particles in Plexiglas
.RTM. 7N [% by weight] Viscosity .eta.s [Pa s] 2120 2780 3210 3060
3210 3600 Die swell B [%] 21.4 11.0 3.8 6.9 5.6 12.6 Vicat
softening point [.degree. C.] 99.8 95.5 95.6 96.2 94.9 95 Izod
notched impact strength 23.degree. C.: [kJ/m.sup.2] 6.2 6.1 6.4 6.0
-10.degree. C.: [kJ/m.sup.2] 4.1 3.5 3.6 3.7 Charpy notched impact
strength 23.degree. C.: [kJ/m.sup.2] 5.2 6.0 7.4 6.7 -10.degree.
C.: [kJ/m.sup.2] 2.0 2.9 3.9 2.7 Modulus of elasticity [MPa] 2180
1805 1660 1900 Transmittance [%] 89.1 88.7 90.5 90.7 90.9 Haze
23.degree. C.: [%] 1.2 1.3 2.3 2.0 1.8 1.6 40.degree. C.: [%] 5.43
5.39 5.8 5.8 4.7 4.7 *with blended dispersion (3% by weight of the
solid in the blended dispersion based on the solid in the
dispersion)
TABLE-US-00003 TABLE 3 Structure of core-shell particles VB3 VB4
VB5 VB6 VB7 B1 Core 25.05 25.05 20 20 20 35 1.sup.st shell 50.5
50.5 50 50 50 45 2.sup.nd shell 25 25 30 30 30 20
TABLE-US-00004 TABLE 4 Composition of core VB3 VB4 VB5 VB6 VB7 B1
Methyl methacrylate 99.8 99.8 98.6 98.6 98.6 95.8 Methyl acrylate
0.87 0.87 0.87 Ethyl acrylate 4.0 Allyl methacrylate 0.2 0.2 0.52
0.52 0.52 0.2
TABLE-US-00005 TABLE 5 Composition of 1.sup.st shell VB3 VB4 VB5
VB6 VB7 B1 Butyl acrylate 81.1 81.1 80.1 80.1 80.1 81.0 Styrene
17.9 17.9 18.9 18.9 18.9 18.1 Allyl methacrylate 1.0 1.0 1.0 1.0
1.0 0.9
TABLE-US-00006 TABLE 6 Composition of 2.sup.nd shell VB3 VB4 VB5
VB6 VB7 B1 Methyl methacrylate 96.0 96.0 96 96 96 90 Ethyl acrylate
4.0 4.0 4 4 4 10 Dodecyl mercaptan
TABLE-US-00007 TABLE 7 Solids content and coagulate content VB3 VB4
VB5 VB6 VB7 B1 Solids content.sup.+ [% by wt.] 46.3 53 50.2 50.2 53
53 Coagulate content.sup.+ 0.2 >25 0.12 0.16 20 0.1 [% by wt.]
.sup.+based in each case on the total weight of the dispersion
TABLE-US-00008 TABLE 8 Particle radii VB3 VB4 VB5 VB6 VB7 B1
R10.sup.1 [nm] 172 113 133 165 R50.sup.1 [nm] 163 123 145 180
R90.sup.1 [nm] 166 145 168 202 P80.sup.1 0.08 0.26 0.25 0.21
Particle radius.sup.2 [nm] 191 128 162 188 Particle radius.sup.2 of
59 64 10 seed latices and, respectively, fully polymerized initial-
charge emulsion [nm] .sup.1ultracentrifuge .sup.2measured using
Coulter N4
* * * * *