Title: Cross-linkable, halogen-free flame-resistant plastic mixture, especially for cables
Abstract: The invention relates to a cross-linkable, halogen-free, flame-resistant plastic mixture which can especially be used, in a cross-linkable state, for coating cables. The inventive plastic mixture comprises the following plastic components: (a) 3 to 50 weight parts (phr) of at least one ethylene copolymer from the group comprising ethylene vinyl acetates, ethylene ethyl acrylates, ethylene methyl acrylates or ethylene butyl acrylates, (b) 30 to 96 weight parts (phr) of a high-density polyolefin, especially a HDPE (High Density Polyethylene) having a density of >0.94 g/cm3, and (c) 1 to 20 weight parts (phr) of a polyolefin which has been grafted with a derivative of an unsaturated carboxylic acid, especially HDPE-g carboxylic acid derivatives. Components (a) to (c) together produce a total of 100 weight parts (phr) of plastic. The mixture also comprises the following components: (d) 40 to 250 weight parts (phr) of a filling material, and (c) 0.1 to 15 weight parts (phr) of a stabilizer system.
Patent Number: 6,894,101 Issued on 05/17/2005 to Paul, et al.
| Inventors:
|
Paul; Heinz (Dinslaken, DE);
Herbiet; René (Eupen, BE);
Eichler; Hans Jürgen (Elsdorf-Oberembt, DE);
Jodocy; Guido (Amel, BE);
Toedt; Winifried (Köln, DE)
|
| Assignee:
|
Martinswerk GmbH (Bergheim, DE)
|
| Appl. No.:
|
333673 |
| Filed:
|
July 18, 2001 |
| PCT Filed:
|
July 18, 2001
|
| PCT NO:
|
PCTEP01/08266
|
| 371 Date:
|
May 16, 2003
|
| 102(e) Date:
|
May 16, 2003
|
| PCT PUB.NO.:
|
WO0208331 |
| PCT PUB. Date:
|
January 31, 2002 |
| Current U.S. Class: |
524/436; 524/99; 524/100; 524/349; 524/350; 524/351; 524/400; 524/437 |
| Intern'l Class: |
C08K 003/22 |
| Field of Search: |
524/99-100,349-351,400,436-437,394
|
References Cited [Referenced By]
| Foreign Patent Documents |
| 0546841 | Jun., 1993 | EP.
| |
Other References
Low-Smoke Self-Extinguishing Electrical Cable and Flame-Retardant . . . Therein
Research Disclosure, No. 407, Mar. 1, 1998, pp. 245-262.
|
Primary Examiner: Szekely; Peter
Attorney, Agent or Firm: Hoefling; Marcy M.
Parent Case Text
This application is the national phase of PCT/EP01/08266 and claims priority
of German application 100 35 647.8, filed Jul. 20, 2000.
Claims
1. Cross-linkable, halogen-free, flame-retardant plastic mixture, especially
for cables, comprising the plastic components
(a) 3-50 phr of at least one ethylene copolymer from the group comprising ethylene-vinyl
acetates, ethylene-ethyl acrylates, ethylene-methyl acrylates, or ethylene-butyl
acrylates,
(b) 30-96 phr of a high-density polyolefin, and
(c) 1-20 phr of an HDPE grafted with a maleic anhydride,
such that components (a) to (c) together add up to 100 phr of plastic, further
comprising the additional components
(d) 40-250 phr of a filler, and
(e) a stabilizer system, the components of which are present in the following
proportions:
the phenolic primary antioxidant: 0.1-6.0 phr,
the secondary antioxidant: 0-12.0 phr,
the metal deactivator: 0.1-6.0 phr,
the aminic light stabilizer: 0.1-3 phr,
the calcium stearate: 0-3 phr,
the aromatic polycarbodiimide: 0-6.0 phr.
2. Cross-linkable, halogen-free, flame-retardant plastic mixture in accordance
with claim 1, characterized by the fact that the mixture contains the following
proportions of components (a), (b), (c), (d) and (e):
(a) 10-40 phr,
(b) 87-50 phr,
(c) 3-10 phr,
(d) 60-150 phr, and
(e) 2-15 phr.
3. Cross-linkable, halogen-free, flame-retardant plastic mixture in accordance
with claim 1, wherein component (d) is a filler selected from the group consisting
of magnesium-hydroxides and aluminum hydroxides.
4. Cross-linkable, halogen-free, flame-retardant plastic mixture in accordance
with claim 1, wherein component (d) comprises coated magnesium hydroxides or coated
aluminum hydroxides, or coated magnesium hydroxides and coated aluminum hydroxides.
5. Cross-linkable, halogen-free, flame-retardant plastic mixture in accordance
with claim 3, wherein the magnesium hydroxide is synthetic [MDH] magnesium dihydroxide.
6. Cross-linkable, halogen-free, flame-retardant plastic mixture in accordance
with claim 3, wherein the magnesium hydroxides and/or the aluminum hydroxides have
a mean particle diameter (d
50 value) of 0.1-5 μm.
7. Cross-linkable, halogen-free, flame-retardant plastic mixture in accordance
with claim 3, wherein the magnesium hydroxides and/or the aluminum hydroxides have
a BET specific surface of <30 m
2/g.
8. Cross-linkable, halogen-free, flame-retardant plastic mixture in accordance
with claim 1, wherein components of the stabilizer system (e) are present in the
following proportions:
the phenolic primary antioxidant: 0.1-3.0 phr,
the secondary antioxidant: 0-3.0 phr,
the metal deactivator: 0.1-3.0 phr,
the aminic light stabilizer: 0.1-3.0 phr,
the calcium stearate: 0-3 phr.
9. Cross-linkable, halogen-free, flame-retardant plastic mixture in accordance
with claim 1, wherein the mixture contains an additional component (f) in proportions
of 1-20 phr, such that component (f) consists of an ethylene-octene copolymer or
an ethylene-hexene copolymer or an ethylene-butene copolymer.
10. The cross-linkable, halogen-free, flame-retardant plastic mixture according
to claim 1, wherein the components of the stabilizer system are present in the
following proportions:
the phenolic primary antioxidant: 0.3-3 phr,
the secondary antioxidant: 0.3-6 phr,
the metal deactivator: 0.6-3.0 phr,
the aminic light stabilizer: 0.6-1.5 phr,
the calcium stearate: 0.1-0.5 phr,
the aromatic polycarbodiimide: 2-4 phr.
11. The cross-linkable, halogen-free, flame-retardant plastic mixture in accordance
with claim 3, wherein component (d) is a filler selected from the group consisting
of magnesium dihydroxide and aluminum trihydroxide.
12. The cross-linkable, halogen-free, flame-retardant plastic mixture in accordance
with claim
8, wherein the components of the stabilizer system (e) are present
in the following proportions:
the phenolic primary antioxidant: 0.3-1.5 phr,
the secondary antioxidant: 0.3-1.5 phr,
the metal deactivator: 0.3-1.5 phr,
the aminic light stabilizer: 0.6-1.5 phr,
the calcium stearate: 0.1-0.5 phr.
13. The cross-linkable, halogen-free, flame-retardant plastic mixture in accordance
with claim 9, wherein the mixture contains the additional component (f) in proportions
of 3-12 phr.
14. Cross-linkable, halogen-free, flame-retardant plastic mixture in accordance
with claim 3, wherein the magnesium hydroxides and/or the aluminum hydroxides have
a BET specific surface of <15 m
2/g.
Description
The invention concerns a crosslinkable, halogen-free, flame-retardant plastic
mixture, especially for use in automobile cables.
Mainly PVC cable insulation or halogenated polyolefin compounds that are rendered
flame-retardant, usually with organic bromine compounds, have been used in the
past in automobile cables. In the environmental debate relating to both PVC and
halogenated flame retardants, these types of insulation materials are coming under
increasing pressure. For example, the EU guideline on scrap vehicles provides that,
starting on Jan. 1, 2006, 80% of a scrap vehicle must be recycled. Therefore, in
regard to automobile cable, it is advantageous, e.g., in the case of thermal utilization,
for the cable insulation not to contain any toxic and/or corrosive components,
such as halogen compounds.
Another disadvantage of PVC insulation is that increasingly compact engine-compartment
construction is leading to greater and greater demands on heat stability. For example,
an operating temperature class of 125° C. or even 150° C. is now being
demanded, which cannot be realized with PVC sheaths. Crosslinked PE compounds are
now being used at temperatures up to 125° C. Of course, these compounds have
the disadvantage that they contain halogenated, usually brominated, compounds in
order to meet the flame-retardant specifications of the automobile manufacturers.
To be sure, halogen-free solutions to this problem are already available. For example,
U.S. Pat. No. 5,561,185 describes a flame-retardant plastic mixture that contains
20-60 wt. % of a polypropylene, 1-20 wt. % of a polyethylene modified by an unsaturated
carboxylic acid or by derivatives of an unsaturated carboxylic acid, 25-65 wt.
% of a metal hydrate, and an ethylene copolymer component.
These types of plastic mixtures are already well known. For example, EP 0 871
181 A1 describes a plastic mixture that consists of 5-85 wt. % (all percentages
based on the plastic component) ethylene with a copolymer, in which the fraction
of copolymer is 10-30 wt. %, 5-85 wt. % LLDPE, 5-85 wt. % of a polyolefin from
the group HDPE or PP, and 5-85 wt. % of an unsaturated carboxylic acid or of an
olefin modified by a derivative of an unsaturated carboxylic acid. The sum of the
fractions of the specified mixture should be 100 wt. %. The mixture described in
this document should also contain 40-150 wt. % of a metal hydroxide as filler.
In addition, BP 0 546 841 A1 describes an abrasion-resistant plastic mixture,
which, based on 100 parts by weight of the polymer component, contains 50-90 wt.
% of a polyolefinic resin, especially a high-density polyethylene (HDPE), and 10-50
wt. % of a polyethylenic resin, especially an ethylene-vinyl ester copolymer. To
improve the flame-retardant properties of the mixture without the use of halogenated
compounds, 30-200 parts by weight of an inorganic flame retardant are added, especially
a modified form of red phosphorus. In addition, agents may be added to prevent
external defects of the product without adversely affecting the physical properties
of the composition. Cited examples of such agents include antioxidants, although
nothing is said about their stabilizer effect.
The research disclosure "Low-smoke self-extinguishing electrical cable and flame-retardant
composition used therein", Kenneth Mason Publications, Hampshire, GB, No. 407,
March 1, 1998, pages 245-262, XP 000773863; ISSN: 0374-4353, describes a flame-retardant,
halogen-free plastic mixture for cables, which consists, for example, of 60-70%
of an ethylene or ethylene-vinyl acetate copolymer and contains 10-20% of a polyolefin
and 20% of a low-density polyethylene. To improve the mechanical properties and
flame resistance, the differences between natural magnesium hydroxide and synthetic
magnesium hydroxide are investigated. Antioxidants are used in these plastic mixtures
in the amount of 0.6 wt. % per 100 parts by weight of the plastic mixture. This
low porportion by weight of the antioxidant component is unchanged in all of the
examples that are given. The effect of this component is not explored.
The previously known halogen-free plastic mixtures for cables have so far achieved
only very low abrasion resistance values in the finished compounded state, which
do not meet the specifications especially of internal standards of various well-known
car manufacturers. Moreover, the problem of inadequate fire resistance of these
plastic mixtures persists.
Therefore, the goal of the invention is to make available a plastic mixture
that is suitable for the manufacture of electrical and/or optical cables and lines
and that has abrasion resistance and fire resistance values that meet the desired specifications.
In accordance with the invention, this goal is achieved by the crosslinkable,
halogen-free, flame-retardant plastic mixture specified in Claim
1, which
is suitable for the manufacture of electrical and/or optical cables and lines and
comprises the following components:
(a) 3-50 parts by weight (phr) of one or more ethylene copolymers from the group
comprising ethylene-vinyl acetates, ethylene-ethyl acrylates, ethylene-methyl acrylates,
or ethylene-butyl acrylates,
(b) 30-96 parts by weight (phr) of a high-density polyolefin, especially an HDPE
(high-density polyethylene) with a density >0.94 g/cm
3,
(c) 1-20 parts by weight (phr) of a polyolefin grafted with a derivative of an
unsaturated carboxylic acid, especially HDPE-g-carboxylic acid derivative,
(d) 40-250 parts by weight (phr) of a filler,
(e) 0.1-15 parts by weight (phr) of a stabilizer system.
The ethylene copolymer preferably has a comonomer content of 8-30% and contains
one or more oxygen atoms.
Preferred ethylene copolymers are:
EVA (ethylene-vinyl acetate), EEA (ethylene-ethyl acrylate), EMA (ethylene-methyl
acrylate), EBA (ethylene-butyl acrylate), or mixtures thereof.
The high-density polyolefin is an HDPE with a density >0.945 and especially
≧0.945 g/cm
3. Good results were obtained, for example, with an
HDPE with a density of 0.958 g/cm
3. An HDPE of this type is characterized
by its special polymer structure (crystallinity, etc.).
The use of an LLDPE as a substitute for the HDPE component is out of the question,
even if the density of an LLDPE approaches the density of an HDPE. This non-interchangeability
is due to the special polymer structure referred to above.
The polyolefin grafted with a derivative of an unsaturated carboxylic acid serves
to improve the polymer compatibility or the polymer-filler compatibility. The derivative
of the unsaturated carboxylic acid is preferably a maleic anhydride.
The crosslinkable, halogen-free, flame-retardant plastic mixture is mixed in
such proportions that components (a) to (c) together add up to 100 parts by weight.
40-250 parts by weight of the filler, which is a metal hydroxide or a mixture of
metal hydroxides with CaCO
3, and a balanced stabilizer system are added
to these mixtures of plastics standardized to 100 parts by weight. In regard to
the stabilizer system, it should be noted that amounts greater or less than the
specified values of 0.1-15 parts by weight may be used in the future as a result
of further development and variations of the substances that are available. For
example, stabilizer systems with a weight fraction of up to 20 phr were used in
more recently developed mixtures.
The term "halogen-free" as used in connection with the present invention means
that the plastic mixture contains no halogens beyond any impurities that may be present.
In accordance with Claim
2, the plastic mixture of the invention may contain
10-40 parts by weight of the ethylene copolymer, 87 to 50 parts by weight of a
high-density polyolefin, especially an HDPE, 3-10 parts by weight of a polyolefin
grafted with a derivative of an unsaturated carboxylic acid, 60-150 parts by weight
of a filler, and 0.3-15 (20) parts by weight of a stabilizer system.
The carboxylic acid derivative is preferably maleic anhydride, which ensures
intense bonding between the matrix and filler, on the one hand, and among the various
polymers, on the other hand.
The filler used as component (d) is preferably selected from the group comprising
magnesium hydroxides and/or aluminum hydroxides, especially MDH and/or ATH. In
addition to the specified metal hydroxides, the filler may contain calcium carbonate (CaCO
3).
The specified metal hydroxides may also be coated, e.g., with silanes, zirconates,
titanates, or special coatings of the types described in PCT/EP99/06,809, PCT/EP96/00,743
or EP0426196B1.
If a magnesium hydroxide is used, it is preferably a synthetic magnesium hydroxide.
Naturally, this does not exclude the possibility of using natural magnesium hydroxide
and/or synthetic aluminum hydroxide.
Good results with respect to fire resistance and abrasion resistance were obtained
with metal hydroxides, e.g., magnesium hydroxides and/or aluminum hydroxides, with
amean particle diameter (d
50 value) of 0.1-5 μm. The magnesium
hydroxides and/or aluminum hydroxides that are used preferably have a BET specific
surface of <30 m
2/g, and especially <15 m
2/g.
The stabilizer system (e) that is used preferably comprises one or more of the
following additives: primary antioxidants, secondary antioxidants, metal deactivators,
aminic light stabilizers, hydrolysis stabilizers, UV absorbers, and calcium or
zinc stearate. These stabilizer components are needed especially for thermal stabilization
during the compounding step, during extrusion, and during irradiation crosslinking,
and for the aging in air and resistance to chemical media of the crosslinked cable
insulation. Resistance to chemical media means the mechanical stability of a cable
sample after storage in various fuels, oils, acids, alkalies, and, in general,
the types of liquids typically used in automobiles. In addition it was found that
the stabilizer system also has an effect on cable abrasion properties. In addition
to the stabilizer system described above, a crosslinking agent, e.g., triallyl
cyanurate, may be added to the plastic mixture. The crosslinking agent acts as
an activator for the crosslinking process, which occurs either by means of high-energy
radiation or by means of additional peroxide crosslinking agents, e.g., dicumyl peroxide.
The plastic mixture may also contain a synergistically acting additive that contains
especially a silicon and/or boron compound. This additive is intended to have a
synergistic effect especially on the flame-retardant filler. The plastic mixture
may also contain agents that enhance its workability (especially extrudability),
e.g., a fatty acid or polyethylene wax. In one formulation of the plastic mixture,
the stabilizer system contains a primary phenolic antioxidant, a secondary antioxidant
with a phosphorus or sulfur compound, a metal deactivator, a hindered aminic light
stabilizer (HALS), and calcium stearate.
The proportions of these components in the stabilizer system are as follows:
phenolic primary antioxidant 0.1-6.0 parts by weight, and especially 0.3-3.0
parts by weight,
secondary antioxidant 0-12.0 parts by weight, and especially 0.3-6 parts
by weight,
metal deactivator 0.1-6.0 parts by weight, and especially 0.6-3.0 parts by weight,
aminic light stabilizer 0.1-3.0 parts by weight and especially 0.6-1.5 parts
by weight,
calcium stearate 0-3.0 parts by weight, and especially 0.1-0.5 parts by weight, and
aromatic polycarbodiimide 0-6.0 parts by weight, and especially 2-4 parts
by weight.
In this connection, it should be noted that suitable selection of the aminic
light
stabilizer may make it possible to eliminate the primary antioxidant wholly or
partially from the stabilizer system. In this case, a higher proportion of the
aminic light stabilizer would possibly be used.
The addition of a component (f), which consists of an ethylene-octene copolymer
or an ethylene-hexene copolymer or an ethylene-butene copolymer, in proportions
of 1-20 phr, and especially 3-12 phr, results in increased flexibility of the cable
extruded from the compound.
The plastic mixtures of the invention can be produced by mixing the individual
components by methods that are already well known. The plastic mixture is preferably
produced by mixing the components in a Buss Ko-kneader, a twin-screw kneader, or
an internal mixer. After the plastic mixture has been produced, a granulated material
is removed from the kneaders, which is used to produce the electrical and/or optical
cables and lines that are to be manufactured from the plastic mixture in accordance
with the invention. This is accomplished by extrusion methods, in which the optically
or electrically active metal or glass-fiber core of a cable is directly covered
with a cable sheath made of the plastic mixture of the invention.
Cables and lines that are covered with the crosslinked plastic mixture of
the invention as sheathing material are highly flame-retardant and have excellent
abrasion resistance, even with extremely small cable diameters and insulation thicknesses.
In addition to their good abrasion properties and fire resistance, the crosslinked
plastic mixtures of the invention have very good mechanical properties, as we were
able to determine by the cold coiling test and the test for percent elongation
at break.
The invention is illustrated by the following examples.
EXAMPLE 1
A plastic mixture was produced from 30 parts by weight EVA (with 12 wt. % VA),
65 parts by weight HDPE (density 0.945), 5 parts by weight HDPE-g-MAH (HDPE grafted
with maleic anhydride), 100 parts by weight MDH (a coated MDH produced by the company
Alusuisse Martinswerk GmbH), 0.3 part by weight of a metal deactivator, 0.15 part
by weight of a phenolic primary antioxidant, 0.15 part by weight of a secondary
antioxidant, and 2.0 parts by weight of a crosslinking activator. The plastic components
are first premixed by standard methods with the stabilizer system and the crosslinking
activator, and the finished mixture, together with 50% of the filler, is then fed
into a Buss Ko-kneader through the first feed worm by means of two gravimetric
metering batchers. The second portion of filler (50% of 100 parts by weight) was
added through the second feed worm with another metering batcher, and pellets were
produced in the usual way by discharge through a discharge extruder with front
granulation. The dried pellets were used to extrude a cable with a total diameter
of 1.2 mm, which contained a copper conductor with a cross-sectional area of 0.35
mm
2. The cable produced in this way was then crosslinked by high-energy
radiation and subjected to the following tests:
1. Abrasion Test
This test was performed with an apparatus in which a piece of cable about 140
mm long can be clamped by means of suitable mounting devices in such a way that
about 70 mm of the middle region of the piece of cable rests flat on a support.
In this region, a metal needle (material as specified in ISO 8458-2) with a diameter
of 0.45 mm is set vertically on the piece of cable. A force of 7±0.05 N is
applied to the needle, which is then drawn along the cable specimen by means of
a guide device. The travel of the needle is 20 mm. The frequency of this needle
movement is 55±5 cycles per min. One complete back-and-forth movement of the
needle along the piece of cable constitutes one cycle. The test is automatically
terminated when the needle makes contact with the conductor inside the piece of
cable. The measurement is carried out four times at room temperature, and the mean
value is given as the result.
2. Fire Resistance Test
In this test, a piece of cable with insulation at least 600 mm long was fastened
to a mounting device at an angle of 45°. A gas-operated Bunsen burner with
an inside diameter of 9 mm was adjusted in such a way that the total length of
the flame was 100 mm, and the blue flame cone inside the flame was 50 mm long.
The Bunsen burner is brought up to the cable specimen from below in such a way
that it forms an angle of 90° with the cable, and in such a way that the tip
of the blue flame cone touches the cable. The point of contact of the flame with
the cable is 500 mm from the upper end of the insulation. The cable is exposed
to the flame for 5 s, and at most until the conductor becomes visible.
3. Cold Coiling Test
The test was conducted using the standard test with which the expert is familiar,
i.e., the test specified in DIN 72551, Part 5.3.6.3, at -40° C.
4. Test of Percent Elongation at Break
The test was carried out on specimens taken from the cable insulation with the
standard test with which the expert is familiar, i.e., the test specified in DIN-VDE
0472, Part 602.
The test results are compiled in Table 1.
| TABLE 1 |
| Abrasion |
Fire |
|
|
| Target: |
Resistance, s |
Cold Coiling |
Elongation at |
| >200 cycles |
Target: <30 s |
Test: at -40° C. |
Break, % |
| 336 |
13 |
passed |
165 |
EXAMPLE 2
A plastic mixture was produced from 30 parts by weight EVA (with 12 wt. % VA),
65 parts by weight HDPE, 5 parts by weight HDPE-g-MAH, 100 parts by weight MDH
(a coated MDH produced by the company Alusuisse Martinswerk GmbH), 0.5 part by
weight of a phenolic primary antioxidant, 0.6 part by weight of an aminic light
stabilizer, 0.6 part by weight of a metal deactivator, 0.2 part by weight calcium
stearate, and 2.0 parts by weight of a crosslinking activator. The plastic mixture
was processed into pellets by the method described in Example 1. The pellets were
used to produce a cable, which was then crosslinked by high-energy radiation. The
cable was 1.2 mm in diameter and had a copper conductor core with a cross-sectional
area of 0.35 mm
2. The cable was subjected to the tests described above.
The test results are compiled in Table 2.
| TABLE 2 |
| Abrasion |
Fire |
|
|
| Target: |
Resistance, s |
Cold Coiling |
Elongation at |
| >200 cycles |
Target: <30 s |
Test: at -40° C. |
Break, % |
| 717 |
14 |
passed |
130 |
As the examples show, the cables produced with the plastic mixture of the invention
have abrasion values that far exceed the stipulated minimum number of cycles of
200. Moreover, the fire resistance values are well below the stipulated minimum
requirement of 30 s. The mechanical properties of the plastic mixture compounded
in accordance with the invention are also very good.
A comparison of Example 1 with Example 2 clearly shows the effect of a balanced
stabilizer system in accordance with Claim 11 on abrasion resistance, which
increased from 336 cycles in Example 1 to 717 cycles in Example 2.
*
