U.S. patent application number 10/524329 was filed with the patent office on 2006-05-25 for impact-resistant polyoxymethylene moulding compounds, use thereof and moulding compounds produced therefrom.
This patent application is currently assigned to TICONA GmbH. Invention is credited to Nicolai Papke.
Application Number | 20060111507 10/524329 |
Document ID | / |
Family ID | 31501806 |
Filed Date | 2006-05-25 |
United States Patent
Application |
20060111507 |
Kind Code |
A1 |
Papke; Nicolai |
May 25, 2006 |
Impact-resistant polyoxymethylene moulding compounds, use thereof
and moulding compounds produced therefrom
Abstract
The present invention relates to a polyoxymethylene molding
composition comprising: (A) from 0.1 to 5.0% by weight of a
compatibilizer, (B) from 5 to 50% by weight of an impact modifier,
(C) the remainder to 100% by weight of a polyoxymethylene. The
molding compositions of the invention have substantially improved
mechanical properties, in particular impact resistance.
Inventors: |
Papke; Nicolai;
(Mainz-Kastel, DE) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ, LLP
P O BOX 2207
WILMINGTON
DE
19899
US
|
Assignee: |
TICONA GmbH
Professor-Staudinger-Strasse
Kelsterbach
DE
65451
|
Family ID: |
31501806 |
Appl. No.: |
10/524329 |
Filed: |
August 16, 2003 |
PCT Filed: |
August 16, 2003 |
PCT NO: |
PCT/EP03/09074 |
371 Date: |
April 11, 2005 |
Current U.S.
Class: |
524/593 |
Current CPC
Class: |
C08L 51/003 20130101;
C08L 59/00 20130101; C08L 59/00 20130101; C08L 59/00 20130101; C08L
83/04 20130101; C08L 59/00 20130101; C08L 59/00 20130101; C08L
75/04 20130101; C08L 2205/08 20130101; C08L 55/02 20130101; C08L
33/068 20130101; C08L 2666/02 20130101; C08L 59/00 20130101; C08L
2666/20 20130101; C08L 2666/24 20130101; C08L 83/00 20130101; C08L
2666/06 20130101 |
Class at
Publication: |
524/593 |
International
Class: |
C03C 25/26 20060101
C03C025/26 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 19, 2002 |
DE |
102 37 884.3 |
Claims
1. A polyoxymethylene molding composition comprising (A) from 0.1
to 5.0% by weight of a compatibilizer, (B) from 5 to 50% by weight
of an impact modifier, (C) the remainder to 100% by weight of a
polyoxymethylene.
2. The polyoxymethylene molding composition comprising (A) from 0.2
to 2% by weight of a compatibilizer, (B) from 5 to 40% by weight of
an impact modifier, (C) the remainder to 100% by weight of a
polyoxymethylene.
3. The polyoxymethylene molding composition comprising (A) from 0.3
to 0.6% by weight of a compatibilizer, (B) from 7 to 30% by weight
of an impact modifier, (C) the remainder to 100% by weight of a
polyoxymethylene.
4. The polyoxymethylene molding composition as claimed in claim 1,
where the compatibilizer contains many underlying units of the
following formulae: ##STR15## and, where appropriate, ##STR16##
where R and R.sub.2 are a hydrogen atom or an alkyl group having 1
or 2 carbon atoms, ##STR17## and where X is CH.sub.3 or ##STR18##
and at least one X is ##STR19## and where a is a number from 1 to
10, b is 0 or 1, c is a number from 0 to 10, l is a number from 0
to 10, R.sub.3, R.sub.5 are a hydrogen atom or a methyl group,
R.sub.4 is a hydrogen atom or an alkyl group having from 1 to 4
carbon atoms, m is 1 or 2, n is 0 or 1 or 2, x is an integer from 0
to 10, Y is H or ##STR20## where R.sub.6, R.sub.7 are identical or
different and are an alkyl group having from 1 to 4 carbon atoms,
R.sub.8 is an alkyl group having from 1 to 12 carbon atoms, phenyl,
alkylphenyl or cycloalkyl having from 3 to 12 carbon atoms
##STR21## where the underlying units of the formulae (Ia), (Iia),
(IIIa), (Iva) and (Va) may have bonding to underlying units of the
formulae (I), (II), (III), (IV), or (V), and the compatibilizer
comprises from 29 to 70% by weight of underlying unit of the
formula (I) from 0.5 to 30% by weight of underlying unit of the
formula (II) from 10 to 70% by weight of underlying unit of the
formula (III) and from 0 to 10% by weight of underlying units of
the formula (IV) and/or (V).
5. The polyoxymethylene molding composition as claimed in claim 1,
wherein the compatibilizer has a molecular weight of from 5000 to
10.sup.8.
6. The polyoxymethylene molding composition as claimed claim 1,
wherein the compatibilizer has a molecular weight of from 10.sup.4
to 10.sup.6.
7. The polyoxymethylene molding composition as claimed in claim 1,
where component (B) comprises a polyurethane or a two-phase mixture
made from polybutadiene and styrene-acrylonitrile (ABS), or
comprises modified polysiloxanes and, respectively, silicone
rubbers, or graft copolymers made from an elastomeric, single-phase
core based on polydiene and from a hard outer graft layer, with
fine distribution.
8. The polyoxymethylene molding composition as claimed in claim 1,
where component (B) comprises graft polymers made from an
elastomeric, single-phase core based on polydiene and a hard outer
graft layer, the outer layer of the particles having one or two
subshells, where in the case of particles having one subshell the
shell is composed of poly(meth)acrylate and
poly(meth)acrylonitrile, and in the case of particles having two
such shells the inner subshell is composed of crosslinked
polystyrene and the outer subshell is composed of crosslinked
polymethacrylate.
9. The polyoxymethylene molding composition as claimed in claim 1,
where component (C), the polyoxymethylene, has been prepared using
trifluoromethanesulfonic acid or boron trifluoride as
initiator.
10. The use of the thermoplastic molding composition as claimed in
claim 1 for producing moldings or films.
11. A molding produced from a thermoplastic molding composition as
claimed in claim 1.
Description
[0001] The present invention relates to impact-modified
polyoxymethylene molding compositions suitable for production of
moldings or of extrudates. The products produced therewith have
improved mechanical properties.
[0002] Since their introduction to the market, polyoxymethylenes
have become established as extremely useful technical materials in
many applications. Polyoxymethylene is particularly widely used as
an engineering material in automotive construction, in the
electrical industry, and in medical technology. In these
applications, polyoxymethylene molding compositions are subject to
a requirement for a certain level of mechanical properties, such as
stiffness, hardness, and toughness, this level being an essential
requirement for the use of these materials for technical components
like gear wheels and levers, among many other examples. The
published values for yield stress are from 60 to 70 N/mm.sup.2. The
values found for the tensile modulus of elasticity of unmodified
copolymers are from 2400 to 3100 N/mm.sup.2. The values found for
tensile strain at break are from 10 to 30%.
[0003] However, the impact resistance of polyoxymethylenes is too
low for many potential applications. Another desirable property in
these applications is the capability of the products to retain
their good impact resistance properties even at relatively low
ambient temperatures.
[0004] It is known that polyoxymethylenes can be toughened by
adding impact modifiers. Impact modifiers used comprise organic
additives, such as crosslinked or non-crosslinked elastomers, or
graft copolymers made from an elastomeric, single-phase core and
from a hard outer graft layer. Impact-modified polyoxymethylene
molding compositions are known from the patent literature, e.g.
polyoxymethylene modified with polyurethanes (DE 1 193 240),
polyoxymethylene modified with a 2-phase mixture made from
polybutadiene and styrene-acrylonitrile (ABS) (DE 1 931 392),
polyoxymethylene modified with a graft copolymer prepared from
acrylatebutadiene (DE 1 964 156), a polyoxymethylene provided with
modified polysiloxanes and, respectively, silicone rubbers (DE 2
659 357), and finally polyoxymethylene modified with a graft
copolymer composed of an elastomeric, single-phase core based on
polydiene and of a hard, single- or multiphase outer graft layer,
e.g. made from poly(alkyl)acrylates, poly(alkyl)acrylonitriles or
polystyrene (EP 01 56285 B1).
[0005] However, the general increase in requirements placed upon
materials often includes a further improvement in impact resistance
and an improvement in mechanical properties.
[0006] The object of the present invention consists in providing
polyoxymethylene molding compositions which have further improved
impact resistance and mechanical properties. These molding
compositions may be processed to give moldings with improved
properties.
[0007] The object is achieved via a polyoxymethylene molding
composition comprising: [0008] (A) from 0.1 to 5.0% by weight of a
compatibilizer, [0009] (B) from 5 to 50% by weight of an impact
modifier, [0010] (C) the remainder to 100% by weight of a
polyoxymethylene.
[0011] Surprisingly, it has been found that the inventive
polyoxymethylene molding compositions have considerably better
impact resistance than the prior art. In particular, the present
invention gives a surprising improvement in low-temperature impact
resistance.
[0012] The inventive molding composition comprises from 0.1 to 5.0%
by weight, preferably from 0.2 to 2% by weight, particularly
preferably from 0.3 to 1% by weight, in particular from 0.3 to 0.6%
by weight, of a compatibilizer, component (A), which encompasses a
plurality of units of the formula ##STR1## and, where appropriate,
##STR2## where R and R.sub.2 are a hydrogen atom or an alkyl group
having 1 or 2 carbon atoms, ##STR3## and where X is CH.sub.3 or
##STR4## and at least one X is ##STR5## and where [0013] a is a
number from 1 to 10, [0014] b is 0 or 1, [0015] c is a number from
0 to 10, [0016] l is a number from 0 to 10, [0017] R.sub.3, R.sub.5
are a hydrogen atom or a methyl group, [0018] R.sub.4 is a hydrogen
atom or an alkyl group having from 1 to 4 carbon atoms, [0019] m is
1 or 2, [0020] n is 0 or 1 or 2, [0021] x is an integer from 0 to
10, [0022] Y is H or ##STR6## where [0023] R.sub.6, R.sub.7 are
identical or different and are an alkyl group having from 1 to 4
carbon atoms, R.sub.8 is an alkyl group having from 1 to 12 carbon
atoms, phenyl, alkylphenyl or cycloalkyl having from 3 to 12 carbon
atoms ##STR7## where the units of the formulae (Ia), (IIa), (IIIa),
(IVa) and (Va) may have bonding to of the formulae (I), (II),
(III), (IV), or (V), and the compatibilizer comprises [0024] from
29 to 70% by weight of units of the formula (I) [0025] from 0.5 to
30% by weight of units of the formula (II) [0026] from 10 to 70% by
weight of units of the formula (III) [0027] and from 0 to 10% by
weight of units of the formula (IV) and/or (V).
[0028] The inventive compatibilizer usually has a molecular weight
of from 5000 to 1.cndot.10.sup.8, and preferably from
1.cndot.10.sup.4 to 1.cndot.10.sup.6. Glycidyl acrylate monomers of
the formula ##STR8## may be mentioned as specific examples of
precursors of the units of the formula (II), where R and R.sub.1
are as defined above.
[0029] It is advantageous to use glycidyl methacrylate.
[0030] Acrylate monomers of the formula ##STR9## may be mentioned
as specific examples of precursors of units of the formula (III),
where R and x are as defined above.
[0031] It is advantageous to use ethyl acrylate and methyl
methacrylate. Periodic units of the formulae ##STR10## may be
mentioned as specific examples of precursors of the units of the
formulae (IV) and (V), where R.sub.2, R.sub.3, R.sub.4, R.sub.5,
R.sub.6, R.sub.7, R.sub.8, m, and n are as defined above.
[0032] The inventive alloy-compatibilizer containing the units of
the formula (I), (II), and (III) may in principle be obtained by
the known high-pressure free-radical copolymerization process. The
process consists in reacting the precursors of said units at a
temperature of from 50 to 300.degree. C. and at a pressure of from
500 to 3000 bar in the presence of initiators of organic peroxide
type. The amount of the copolymerization initiators is from 0.0001
to 0.1% of the total weight of the starting monomers.
[0033] If the compatibilizer for the inventive alloy also contains
units of the formula (IV) and/or (V), it is in principle obtained
by the process which consists in: [0034] a. preparing a copolymer
which contains units of the formula (I) and (II) or (III) or a
terpolymer which contains the units (I) and (II) and (III), by the
known high-pressure free-radical polymerization process, [0035] b.
bringing the resultant polymer, in a reactor kept at a temperature
of from 60 to 85.degree. C., into contact for two or more hours
with a solution, the contents of the solution being the monomer(s)
of the formula (VI) and/or (VII), the monomer(s) of the formula
(VIII) and/or (IX), a peroxide initiating the polymerization, and a
chain transfer agent, [0036] c. subjecting the resultant product,
washed with water and then dried, to treatment in an extruder at
about 200.degree. C.
[0037] The component (B) used comprises from 5 to 50% by weight,
preferably from 5 to 40% by weight, particularly preferably from 7
to 30% by weight, of an impact modifier. Impact modifiers which may
used, individually or as a mixture, are polyurethanes, two-phase
mixtures made from polybutadiene and styrene-acrylonitrile (ABS),
modified polysiloxanes and, respectively, silicone rubbers, or
graft copolymers made from an elastomeric, single-phase core based
on polydiene and from a hard outer graft layer (core-shell
structure). In the latter case, component (B) is composed of
particles most of which, preferably more than 70% of which, have a
structure of core and outer layers. The core here is formed from an
elastomeric polymer phase onto which has been grafted the hard
outer layer, which may also be composed of two or more layers. The
core is preferably single-phase, meaning that the core is composed
mainly, preferably completely, of the elastomeric soft phase and
comprises only small amounts of, preferably no, inclusions made
from hard polymer constituents of the outer layer. The graft
copolymer is mostly composed of from 40 to 95% by weight,
advantageously from 60 to 90% by weight, particularly
advantageously from 70 to 80% by weight, of the elastomeric core.
The proportion of the outer layer (shells) is from 5 to 60% by
weight, advantageously from 10 to 40% by weight, particularly
advantageously from 20 to 30% by weight. The core is generally
composed of polydienes, e.g. polybutadiene or polyiosprene, and can
contain up to 10% by weight, advantageously up to 5% by weight, of
comonomer units. Styrene or acrylonitrile may advantageously be
used as comonomer. The core polymer may also have been crosslinked
and have a gel content, measured in toluene, generally greater than
70%, and preferably greater than 80%. An example of a crosslinker
which may be used is divinylbenzene. The outer layer of the
particles is composed of hard polymers which have been grafted onto
the core as graft substrate. The outer layer here may have a
single- or multishell structure, advantageously a dual-shell
structure. If there is more than one outer layer, it is
advantageous for the various layers to be composed of different
polymers or copolymers. It is advantageous here for the first layer
to have been crosslinked. However, where appropriate, the other
layers may also have been crosslinked. Examples of suitable
monomers which give suitable polymers for the outer layer of the
particles are unsaturated nitriles, acrylates, methacrylates, vinyl
esters, styrene derivatives, advantageous monomers being
acrylonitrile, methacrylonitrile acrylates and methacrylates having
an alcohol component which has from 1 to 6, preferably from 1 to 4,
carbon atoms, examples being methyl acrylate, ethyl acrylate,
propyl acrylate, n-butyl acrylate, methyl methacrylate, ethyl
methacrylate, propyl methacrylate, butyl methacrylate, and
tert-butyl methacrylate. Vinyl compounds which may also be used
with advantage are vinyl acetate, vinyl ethers,
N-vinyl-N-methylacetamide, and vinylpyrrolidone, and examples of
styrene derivatives which may be used with advantage are styrene,
.alpha.-methylstyrene and vinyltoluene. Copolymers made from at
least two of the abovementioned monomer groups and monomers may
also be used in the structure of the outer layer, in particular
copolymers of the specified styrene derivatives with the other
monomers. Particularly advantageous copolymers are those prepared
from a mixture comprising from 20 to 80% by weight of acrylonitrile
or methacrylonitrile with from 80 to 20% by weight of the other
specified monomers, in particular acrylates, methacrylates and
vinyl esters. Preference is also given to graft polymers which have
a dual-shell outer layer structure, the first shell being composed
of polystyrene and the second, outer, shell being composed of a
poly(meth)acrylate, which has particularly preferably been
crosslinked to some extent. The crosslinking monomers used may in
principle comprise any of the compounds suitable for this purpose,
for example multifunctional olefins, such as divinylbenzene,
ethylene glycol dimethacrylate, butylene glycol dimethacrylate, or
else triallyl cyanurate.
[0038] According to the invention, the glass transition temperature
of the component (B) described above is from -40 to -120.degree.
C., preferably below -60.degree. C., in particular from -80 to
-120.degree. C. The preparation of the graft copolymers which can
be used as component (B) and have a core-shell structure is known
and can use single-stage polymerization in the case of a
single-shell outer layer or multistage polymerization in the case
of a multishell outer layer, for example as described in the Patent
Specification U.S. Pat. No. 3,985,704, which is incorporated herein
by way of reference. The graft copolymerization is carried out
using water-soluble initiators or using activated initiator systems
of which one component at least is water-soluble, for example as
described in C. B. Bucknall, "Toughened Plastics", p. 98, Applied
Science Publishers Ltd. 1977 (London)). For the single- or
multistage graft copolymerization the starting material is a
polydiene, preferably in the form of an aqueous latex with defined
average particle size, particularly preferably in the range from
0.1 to 5 .mu.m, where the polydiene has particularly preferably
been partially crosslinked.
[0039] For the preparation, the monomer or the monomer mixture is
polymerized in the presence of the polydiene, whereupon the major
portion of the monomers is grafted onto the polydiene particles.
The amount of polydiene is generally from 40 to 95% by weight, and
the amount of the monomer or monomer mixture is generally from 5 to
60% by weight, based in each case on the total amount. The graft
yield achieved varies from 60 to 95%, preferably from 80 to 90%.
The graft polymerization is carried out in solution or emulsion,
preferably in aqueous dispersion. For this purpose, the
fine-particle polydiene latex forms an initial charge with addition
of the usual polymerization auxiliaries, such as emulsifying agents
or suspending agents, free-radical initiators, regulators, etc.,
and the monomer or the monomer mixture is added and polymerized at
temperatures from 30 to 95.degree. C., preferably from 50 to
80.degree. C. For a single-stage reaction the initiator is
water-soluble, and examples of initiators which may be used are
water-soluble peroxides, percarbonates or perborates. In the case
of a multicomponent initiator system (redox system) at least one
component has to be water-soluble. Examples of emulsifiers which
may be used, and are also termed dispersing agents, are aliphatic
and aromatic sulfates, sulfonates, and salts of carboxylic acids,
for example dresinates. The compounds suitable for this purpose are
well known to the skilled worker.
[0040] For a multistage reaction the graft polymerization and the
work-up generally take place as described in U.S. Pat. No.
3,985,704. To form a multishell outer layer, a monomer or a monomer
mixture, such as styrene, is first grafted onto the core polymer,
such as butadiene-styrene copolymer, and then another monomer or
monomer mixture is used, where appropriate in the presence of a
crosslinker. The average particle size of the particles is
advantageously from 0.1 to 5 .mu.m.
[0041] Other materials which can be used as graft copolymers for
component (B) are those in which the core is composed mainly or
completely of, preferably partially crosslinked, polyacrylates or
polymethacrylates, the alcohol component of which contains from 1
to 15 carbon atoms, preferably from 1 to 8 carbon atoms. Olefinic
monomers may be used as comonomers, advantageously butadiene,
cyclooctadiene, vinyl ethers and haloalkyl acrylates. The gel
content, measured in toluene, is preferably at least 50%,
particularly preferably at least 70%. For the outer graft layer use
may be made of the monomers and monomer mixtures described above.
The particle sizes, too, are in the same range. Graft polymers
based on polyacrylates and on polymethacrylates are described by
way of example in DE 1964156, DE 2116653, EP 50265, EP 60601 and EP
64207, incorporated herein by way of reference. The core of the
graft polymer may also be composed entirely or partially of a
silicone rubber and/or of non-crosslinked organopolysiloxanes. The
other monomers and/or monomer mixtures described above may be
grafted onto this core, which preferably contains functional groups
having graft activity. These materials are described by way of
example in DE 2659357, incorporated herein by way of reference.
Component (B) preferably comprises a diluent, and in particular if
the core of the graft polymer is composed of partially crosslinked
polyacrylates or polymethacrylates. The diluent is a low-melting,
advantageously polymeric substance which has good miscibility in
the melt with the graft polymers used as impact modifier. It is
particularly advantageous to use this diluent if the level of
crosslinking of the graft polymers is sufficiently high to make
them insoluble in the diluent, and a two-phase system forms, and
the surface tension leads to fine distribution of the graft
polymers in the diluent. The graft polymer is preferably present
mainly in the peripheral region of the two-phase system. As the
amount of graft polymer increases it is also increasingly present
in the core, and, with a further increase in the amount of the
graft polymer, also outside the two-phase system within the matrix
polymer, component (C). It is particularly advantageous to have
uniform distribution of the two-phase system and of the graft
polymer in component (C), in particular if the graft polymer is
mainly present at the periphery of the two-phase system. The
melting point of the diluent should be below 250.degree. C.,
preferably from 180 to 210.degree. C. The amount of the diluent is
from 10 to 95%, advantageously from 30 to 70%, particularly
preferably from 40 to 60%, based on the entirety of graft polymer
and diluent. Materials which may be used with very particular
advantage as diluents are polyurethanes and segmented copolyesters
and ethylene-vinylacetate copolymers. Other suitable diluents are
known to the skilled worker and are described by way of example in
DE 2818240 and DE 2523991, incorporated herein by way of reference.
The diluent may advantageously be mixed with the graft polymer
prior to addition to component (C).
[0042] Other impact-modifying components, component (B), which may
be used are advantageously polyurethanes, preferably thermoplastic
polyurethanes. The polyurethanes which may be used according to the
invention are known products described by way of example in DE
1193240 and DE 2051028, and in Kunststoff-Taschenbuch, [Plastics
Handbook] (Saechtling, 27th edition, Hanser Verlag 1998) on pages
523-542, incorporated herein by way of reference. They are prepared
in a known manner via polyaddition, from polyisocyanates, in
particular diisocyanates, polyesters, polyethers, polyesteramides,
polyacetals or other suitable hydroxy or amino compounds, such as
hydroxylated polybutadiene, or mixtures of the abovementioned
compounds. Where appropriate, use is also made of chain extenders,
such as low-molecular-weight polyols, in particular diols,
polyamines, in particular diamines, or water.
[0043] Examples of suitable diisocyanates are diisocyanates of the
formula (X) OCN--R.sub.9--NCO (X) where R.sub.9 is a divalent,
straight-chain or branched aliphatic radical having from 1 to 20,
preferably from 2 to 12, carbon atoms, or a divalent cycloaliphatic
radical having from 4 to 20, preferably from 6 to 15, carbon atoms,
or a divalent, substituted or unsubstituted aromatic radical having
from 6 to 25, preferably from 6 to 15, carbon atoms. If
appropriate, the radical R.sub.9 may also be an aromatic radical,
examples being tolylene 2,4-diisocyanate, tolylene
2,6-diisocyanate, or mixtures of these, naphthylene
1,5-diisocyanate, diphenylmethane 4,4'-diisocyanates (MDI or PMDI),
individually or in the form of a mixture.
[0044] An example of a divalent, aliphatic radical is the
alkylidene radical --(CH2).sub.n--, where n=2 to 12, e.g.
ethylidene, propylidene, pentamethylene, or hexamethylene radical,
or the like, or the 2-methylpentamethylene,
2,2,4-trimethylhexamethylene or 2,4,4-trimethylhexamethylene
radical. Diisocyanates of this type which are particularly
preferred are hexamethylene diisocyanate, and 2,2,4- and
2,4,4-trimethylhexamethylene diisocyanate.
[0045] If R.sub.9 in formula I above is a cycloaliphatic radical,
this is preferably the unsubstituted or substituted cyclohexane
radical. Examples of diisocyanates of this type are 1,2- or
1,4-di(isocyanatomethyl)cyclohexane or isophorone diisocyanate.
[0046] R.sub.9 in formula I above may also be a combination of
divalent, open-chain aliphatic or cycloaliphatic radicals, for
example ##STR11## where R.sub.10 is a saturated, straight-chain or
branched aliphatic radical having from 1 to 8, preferably from 1 to
3, carbon atoms. The two rings here are preferably unsubstituted
cyclohexane, while R.sub.10 is preferably the methylene, ethylene,
methylmethylene, or dimethylmethylene group.
[0047] If R.sub.9 is an open-chain, divalent radical, it is
preferably an unbranched alkylidene radical --(CH.sub.2)n--, where
n=from 2 to 12. Examples of these are the ethylidene, propylidene,
pentamethylene and hexamethylene radicals, and also the
2-methylpentamethylene, 2,2,4-trimethylhexamethylene or
2,4,4-trimethylhexamethylene radicals. Diisocyanates of this type
which are particularly preferred are hexamethylene diisocyanate and
also 2,2,4- and 2,4,4-trimethylhexamethylene diisocyanate.
[0048] If R.sub.9 in formula (X) above is a divalent aromatic
radical, it is preferably the toluene, diphenylmethane, phenylene
or naphthalene radical. Examples of corresponding diisocyanates are
toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, diphenylmethane
4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane 4,4'-diisocyanate,
3,3'-dimethyldiphenylene
4,4'-diisocyanate(3,3'-bitoluene-4,4'-diisocyanate), m-phenylene
diisocyanate, p-phenylene diisocyanate, o-phenylene diisocyanate,
chlorophenylene 2,4-(toluene diisocyanate), 3,3'-dichlorodiphenyl
4,4'-diisocyanate 4-chlorophenylene 1,3-diisocyanate, naphthalene
1,5-diisocyanate, and naphthalene 1,4-diisocyanate.
[0049] If R.sub.9 in formula (X) above is a cycloaliphatic radical,
it is preferably the unsubstituted or substituted cyclohexane
radical. Examples of diisocyanates of this type are 1,2- or
1,4-di-(isocyanatomethyl)cyclohexane or isophorone
diisocyanate.
[0050] The diisocyanates of formula (X) may also be used in
oligomeric form, for example in dimeric or trimeric form. Instead
of the polyisocyanates, use may also be made in a known manner of
blocked polyisocyanates, these being obtained from the isocyanates
mentioned by reaction with phenol or caprolactam, for example.
[0051] Aliphatic polyhydroxy compounds which may be used are
polyethers, such as polyethylene glycol ethers, polypropylene
glycol ethers, and polybutylene glycol ethers, poly-1,4-butanediol
ethers or mixed polyethers made from ethylene oxide and propylene
oxide. Other compounds which may be used for this purpose are
polyesteramides, polyacetals, and preferably aliphatic polyesters,
all of these compounds having free OH end groups.
[0052] The aliphatic polyesters preferably used are mainly
non-crosslinked polyesters with molecular weights of from 500 to
10000, preferably from 500 to 5000. The acid components derive from
unbranched and/or branched aliphatic dicarboxylic acids, e.g.
dicarboxylic acids of the formula HOOC--(CH.sub.2).sub.p--COOH,
where p=from 0 to 20, preferably from 4 to 10, in particular adipic
acid and sebacic acid. Use may also be made here of cycloaliphatic
dicarboxylic acids, such as cyclohexanedicarboxylic acids, or of
mixtures with the abovementioned aliphatic dicarboxylic acids.
[0053] The alcohol component used for these polyesters is in
particular an unbranched or branched aliphatic primary diol, e.g. a
diol of the formula HO--(CH.sub.2).sub.q--OH, where q=from 2 to 12,
preferably from 2 to 6. Mention may in particular be made here of
1,4-butanediol, 1,6-hexanediol and 2,2-dimethylpropanediol-1,3 and
also diethylene glycol. Cycloaliphatic diols, such as
bishydroxymethylcyclohexane, are also suitable here, as are
mixtures with the aliphatic diols.
[0054] Each of the polyesters may be prepared from one dicarboxylic
acid and one diol, or else, as mentioned, from a mixture of two or
more dicarboxylic acids and/or two or more diols.
[0055] Chain extenders which may be used in preparing the
polyurethanes are mainly low-molecular-weight polyols, in
particular diols, or else polyamines, in particular diamines, or
else water.
[0056] The polyurethanes used according to the invention are
preferably thermoplastic and therefore preferably substantially
non-crosslinked, i.e. capable of melting repeatedly without any
significant signs of decomposition. Their reduced specific
viscosities, measured at 30.degree. C. in dimethylformamide, are
generally from 0.5 to 3 dl/g, preferably from 1 to 2 dl/g. The
values for the tensile strains at break are advantageously from 300
to 1500%, preferably from more than 400 to 1500%, while the Shore
hardness A is not more than 100, advantageously not more than 85,
preferably from 60 to 90, particularly preferably from 70 to 89, in
particular from 75 to 85, and the glass transition temperatures are
mostly not above 0.degree. C., advantageously not above -10.degree.
C., particularly advantageously not above -20.degree. C.
[0057] The base material used for the molding compositions of the
invention, polyoxymethylenes (C), may be homopolyoxymethylenes or
copolyoxymethylenes. Polymers of this type are known to the skilled
worker and are described in the literature. The homopolymers are
generally obtained by polymerizing formaldehyde or trioxane, and
the polymerization here may be initiated cationically or
anionically. However, preference is given to copolyoxymethylenes
which contain not only oxymethylene units but also oxyalkylene
units, where the alkylene groups may contain from 2 to 8 carbon
units, linear or branched. The polyoxymethylenes (POMs) described
by way of example in DE-A 29 47 490 are generally unbranched linear
polymers and generally contain at least 80%, preferably at least
90%, of oxymethylene units (--CH.sub.2O--). The term
polyoxymethylenes here encompasses homopolymers of formaldehyde or
of its cyclic oligomers, such as trioxane or tetroxane, and also
corresponding copolymers.
[0058] Homopolymers of formaldehyde or of trioxane are polymers of
this type whose hydroxyl end groups have been chemically stabilized
in a known manner to resist degradation, e.g. by esterification or
etherification. Copolymers are polymers made from formaldehyde or
from its cyclic oligomers, in particular trioxane, and from cyclic
ethers, cyclic acetals, and/or linear polyacetals.
[0059] These homopolyoxymethylenes or copolyoxymethylenes are known
per se to the skilled worker and are described in the literature.
These polymers very generally have at least 50 mol % of
--CH.sub.2O-- repeat units in the main polymer chain. The
homopolymers are generally prepared by polymerizing formaldehyde or
trioxane, preferably in the presence of suitable catalysts.
Examples of particularly suitable catalysts are boron trifluoride
and trifluoromethanesulfonic acid.
[0060] For the purposes of the invention, preference is given to
copolyoxymethylenes as component (C), in particular those which
also contain, alongside the --CH.sub.2O-- repeat units, up to 50
mol %, preferably from 0.1 to 20 mol %, and in particular from 0.5
to 10 mol %, of repeat units of the following formula ##STR12##
where R.sub.11 to R.sub.14 independently of one another, are a
hydrogen atom, a C.sub.1- C4-alkyl group, or a halo-substituted
alkyl group having from 1 to 4 carbon atoms, and R.sub.15 is
--CH.sub.2--, --CH.sub.2O--, or a C.sub.1-C.sub.4-alkyl- or
C1-C4-haloalkyl-substituted methylene group, or a corresponding
oxymethylene group, and n is from 0 to 3. These groups may
advantageously be introduced into the copolymers by the
ring-opening of cyclic ethers. Preferred cyclic ethers are those of
the formula ##STR13## where R.sub.11 to R.sub.15 and r are as
defined above. Cyclic ethers which may be mentioned as examples are
ethylene oxide, propylene 1,2-oxide, butylene 1,2-oxide, butylene
1,3-oxide, 1,3-dioxane, 1,3-dioxolane and 1,3-dioxepan, and
comonomers which may be mentioned as examples are linear oligo- or
polyformals, such as polydioxolane or polydioxepan.
[0061] Particularly advantageous copolymers are those made from
99.5-95 mol % of trioxane and 0.5-5 mol % of one of the above of
the abovementioned comonomers.
[0062] Also suitable as component (C) are oxymethyleneterpolymers,
for example those prepared by reacting trioxane with one of the
abovementioned cyclic ethers and with a third monomer, preferably a
bifunctional compound of the formula ##STR14## where Z is a
chemical bond, --O--, or --ORO-- (R=C.sub.1-C.sub.8-alkylene or
C.sub.2-C.sub.8-cycloalkylene).
[0063] Preferred monomers of this type are ethylene diglycide,
diglycidyl ether, and diethers made from glycidyl compounds and
formaldehyde, dioxane or trioxane in a molar ratio of 2:1, and also
diethers made from 2 mol of glycidyl compound and 1 mol of an
aliphatic diol having from 2 to 8 carbon atoms, for example the
diglycidyl ether of ethylene glycol, 1,4-butanediol,
1,3-butanediol, 1,3-cyclobutanediol, 1,2-propanediol or
1,4-cyclohexanediol, to mention just a few examples.
[0064] Processes for preparing the above-described polyoxymethylene
homo- and copolymers are known to the skilled worker and are
described in the literature.
[0065] The preferred copolyoxymethylenes have melting points of
140.degree. C. or above and molecular weights (weight average) Mw
in the range from 2000 to 1000000, preferably from 7000 to 150000.
Particular preference is given to end-group-stabilized
polyoxymethylenes whose chain ends have carbon-carbon bonds. The
melt index (MVR 190/2.16) of the polyoxymethylenes used is
generally from 0.3 to 100 cm.sup.3/10 min (ISO 1133).
[0066] Particular preference is given to polyoxymethylenes
substantially having oxymethylene units and oxyethylene units in
the polymer chain. The proportion of the oxyethylene units, based
on structural units in the polymer chain, is from 0.1 to 15 mol %,
preferably from 0.2 to 10 mol %. The melt index MFI, measured to
ISO 1133 at 190.degree. C. with an applied weight of 2.16 kg is
from 0.5 to 75 g/10 min, preferably from 2 to 60 g/10 min, and
particularly preferably from 5 to 35 g/10 min. The number-average
molar mass is at least 5000 g/mol and at most 100000 g/mol,
determined by GPC in dimethylacetamide at from 150 to 160.degree.
C. It is also possible to use a mixture of different
copolyoxymethylenes of differing compositions instead of a single
copolyoxymethylene. Well known preparation processes can be used to
prepare the copolyoxymethylenes. An example of a possible process
is the copolymerization of trioxane with dioxolane in the presence
of generally conventional amounts of BF.sub.3 and methylal.
Preference is given to polyoxymethylenes whose preparation uses
trifluoromethanesulfonic acid or boron trifluoride as
initiator.
[0067] The molding composition of the invention may comprise other
conventional additives, individually or as a mixture, at up to 40%
by weight, examples being carbon blacks, e.g. conductivity blacks,
acid scavengers, antioxidants, UV stabilizers, coupling agents,
mold-release aids, substances to improve electrical conductivity,
antistats, nucleating agents, such as polyoxymethylene terpolymers
or talc, colorants, such as inorganic pigments, e.g. titanium
dioxide, ultramarine blue, cobalt blue, or organic pigments and
colors, such as phthalocyanines, anthrachinones, fillers, such as
glass beads, wollastonite, chalk, loam, molybdenum sulfide, or
graphite, inorganic or organic fibers, such as glass fibers, carbon
fibers or aramide fibers, lubricants, such as soaps and esters,
stearyl stearate, montanic esters, partially hydrolyzed montanic
esters, stearic acids, polar and/or non-polar polyethylene waxes,
poly-.alpha.-olefin oligomers, silicone oils, polyalkylene glycols
and perfluoroalkyl ethers, polytetrafluoroethylene,
ultrahigh-molecular-weight polyethylene, paraffins, solid and
liquid, stearic acids, and thermoplastic or thermoset polymer
additives, elastomers, and other polymers, such as EPDM
(ethylene-propylene-diene rubber), EPM (ethylene-propylene
rubbers), polyester elastomers, copolymers of ethylene with
(meth)acrylates and with (meth)acrylamides, polymethyl
methacrylate, polyethylene, polystyrene.
[0068] Another additive which may be present is a cyclic stabilizer
which contains at least one nitrogen atom in a ring. Examples of
pyrrolidine, piperidine, pyrrole, pyridine, purine, indole,
carbazole, tryptophan, oxazole, imidazole, thiazole, picoline,
lutidine, collidine, quinoline, pyridazine, pyrimidine, pyrazine,
and their derivatives. Advantageous compounds are heterocyclic
compounds having at least one nitrogen atom as heteroatom which is
either adjacent to an amino-substituted carbon atom or adjacent to
a carbonyl group, examples being pyridazine, pyrimidine, pyrazine,
pyrrolidone, aminopyridine, and compounds derived therefrom.
Advantageous compounds of this general type are aminopyridine and
compounds derived therefrom. In principle, all of the
aminopyridines are suitable, examples being melamine,
2,6-diaminopyridine, substituted and dimeric aminopyridines, and
also pyrrolidone and compounds derived therefrom, and mixtures
prepared from these compounds. Examples of suitable pyrrolidones
are imidazolidinone and compounds derived therefrom, e.g.
hydantoin, the derivatives of which are particularly advantageous,
and particularly advantageous compounds among these are allantoin
and its derivatives. Other particularly advantageous compounds are
triamino-1,3,5-triazine (melamine) and its derivatives, e.g.
melamineformaldehyde condensates and methylolmelamine. Very
particular preference is given to melamine, methylolmelamine,
melamineformaldehyde condensates, and allantoin. The cyclic
stabilizers which contain at least one nitrogen atom in the ring
may be used individually or in combinations.
[0069] Use may also advantageously be made of from 0.001-0.5% by
weight of a metal salt of a carboxylic acid. Advantageous compounds
are salts of fatty acids, in particular salts of higher fatty acids
having from 10 to 32 carbon atoms, preferably from 14 to 32 carbon
atoms, and particular preference is given to salts of montanic
acids and stearic acid. Preferred metals are those which occur in
the form of mono- or divalent ions, e.g. alkali metals and alkaline
earth metals, in particular alkaline earth metals. Magnesium and
calcium are particularly preferred, an example being calcium
stearate. Magnesium stearate is very particularly preferred.
[0070] Other compounds which may be used advantageously are
sterically hindered phenol compounds, the amounts of these which
may be used being from 0.0 to 2% by weight, preferably from 0.1 to
1.0% by weight, particularly preferably from 0.2 to 1.0% by weight.
Examples of these compounds are pentaerythrityl
tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox
1010, Ciba Specialty Chemicals), triethylene glycol
bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate] (Irganox
245, Ciba Specialty Chemicals),
3,3'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionohydrazide]
(Irganox MD 1024, Ciba Specialty Chemicals), hexamethylene glycol
bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 259,
Ciba Specialty Chemicals), 3,5-di-tert-butyl-4-hydroxytoluene
(Lowinox BHT, Great Lakes). Preference is given to Irganox 1010 and
especially Irganox 245.
[0071] A stabilizer from the group of the benzotriazole derivatives
or benzophenone derivatives or aromatic benzoate derivatives may
also be present, its amount being from 0.0-1.0% by weight,
preferably from 0.0-0.8% by weight. Preference is given to
2-[2'-hydroxy-3',5'-bis(1,1-dimethylbenzyl)-phenyl]benzotriazole,
which is commercially available as Tinuvin 234 (Ciba Specialty
Chemicals).
[0072] Another additive which may be used advantageously in the
inventive molding composition is from 0.01-0.8% by weight,
preferably from 0.01-0.5% by weight, very particularly preferably
0.4% by weight, of a sterically hindered amine as light stabilizer
(HALS). Preference is given to 2,2,6,6-tetramethyl-4-piperidiyl
compounds, e.g. bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate
(Tinuvin 770, Ciba Specialty Chemicals) or the polymer composed of
dimethyl succinate and
1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethyl-4-piperidine
(Tinuvin 622, Ciba Specialty Chemicals).
[0073] The polyoxymethylene molding compositions of the invention
may be prepared using the conventional and known mixing methods,
such as pelletizing, extrusion, kneading, etc. The molding
compositions of the invention are preferably prepared by mixing
polyoxymethylene polymer with additives and stabilizers and then
pelletizing the mixture.
[0074] The polyoxymethylene molding compositions of the invention
have substantially improved mechanical properties and low
formaldehyde emission. The reduction in the amount of formaldehyde
released can be observed even during preparation of the molding
composition, e.g. during pelletizing, and also during processing.
The polyoxymethylene molding composition of the invention therefore
contributes to health and safety at work.
[0075] The mechanical properties of the inventive molding
compositions exceed most of the usual requirements placed upon
polyoxymethylene products, thus permitting unrestricted utilization
of the processing techniques and application sectors usual for
polyoxymethylene. There is a substantial improvement in impact
resistance. The invention in particular gives a surprising
improvement in low-temperature impact resistance.
[0076] Particular application sectors for the molding compositions
of the invention are internal fittings and cladding for means of
transport, such as automobiles, aircraft, etc. Other application
sectors being household goods, toys, baby items, and also devices
and components for electronics and for electrical engineering. The
molding compositions of the invention are particularly suitable for
producing apparatus and instruments, or parts thereof, for medical
applications. The molding compositions prepared according to the
invention have the lowest formaldehyde emission of any currently
commercially available products, have defect-free surfaces, and
have high colorfastness when the moldings are exposed for a long
time to light or heat.
[0077] All of the references mentioned in this patent application
are expressly incorporated herein by way of reference. Those
references are therefore part of the disclosure of this patent
application.
EXAMPLES
[0078] The examples below are intended to illustrate the invention
for the person skilled in the art and to disclose further
advantageous embodiments, but without restricting the scope of
protection.
[0079] The base material used comprised Hostaform C 9021
polyoxymethylene copolymer from Ticona. Other auxiliaries used
comprised 0.4% by weight of a mixture comprising wax and
antioxidants.
[0080] Experiment 1 is a comparative example. Experiments 2 to 4
are the examples according to the invention. Experiment 1 used no
adhesion promoter. Experiments 2 and 3 used an ethylene-glycidyl
methacrylatemethyl acrylate terpolymer (E-GMA-MA, Lotader AX 8900,
Atofina). Experiment 4 used an ethylene-glycidyl methacrylate
copolymer (E-GMA, Lotader AX 8840, Atofina). The amounts stated in
the table are in % by weight, tensile strength and tensile modulus
of elasticity are in MPa, tensile strain at break is in %, impact
resistance is in kJ/m.sup.2, and fracture energy is in J.
[0081] The constituents were mixed and then extruded (ZSK 25MC
twin-screw extruder from Werner & Pfleiderer, Germany) at
190.degree. C. barrel temperature, and pelletized.
[0082] Test specimen production: The polyacetal granulates were
injection molded to give standard test specimens and characterized
in accordance with the methods listed below: tensile strength,
tensile strain at break, tensile modulus of elasticity were
determined in the tensile test to ISO 527. Charpy impact resistance
was determined to ISO 179-1/eU for test specimens without notch and
to ISO 176-1/eA for notched test specimens, in the tensile impact
strength test. The fracture energies were determined on plaques
(80.times.80.times.2 mm) to ISO 6603 (part 2).
[0083] Table 1 contains the formulations of the molding
compositions and the corresponding test results.
[0084] Use of the reactive adhesion promoters improved mechanical
impact properties, such as Charpy notched impact strength and, even
more significantly, fracture energy in the automated penetration
test (biaxial impact), in particular even at low temperatures
(-30.degree. C.). An additional feature of the molding compositions
prepared was that there was only a minimal reduction in static
mechanical properties (tensile strength, modulus). There is
likewise an improvement in the ductilities (tensile strain at
break) achievable. TABLE-US-00001 TABLE 1 Constituent/properties
Unit 1 2 3 4 Polyoxymethylene copolymer % by wt. 89.5500 89.5500
89.5500 89.5500 Additives % by wt. 0.45 0.45 0.45 0.45 TPU % by wt.
10 9.5 9 9.5 E-GMA copolymer % by wt. 0.5 E-GMA-MA terpolymer % by
wt. 0.5 1 MVR 190/2.16 ml/10 min 7.2 7.3 7.4 7.3 Tensile modulus of
elasticity MPa 2272 2135 2103 2094 Tensile strength MPa 55 53 52 52
Tensile strain at break % 36 41 40 38 Notched impact strength
(Charpy, 23.degree. C.) kJ/m.sup.2 12.8 15.5 15.3 14.4 Fracture
energy WS (2 mm, 23.degree. C.) J 9.0 14.4 10.7 10.7 Fracture
energy WS (2 mm, -30.degree. C.) J 3.9 5.2 4.2 5.5
* * * * *