U.S. patent application number 08/867412 was filed with the patent office on 2002-02-14 for grafted and crosslinkable pulverulent thermoplastic polyolefin composition which has elasticity and flexibility properties.
Invention is credited to MARCINIAK, TONY, VALLIGY, DOMINIQUE.
Application Number | 20020019487 08/867412 |
Document ID | / |
Family ID | 27252775 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020019487 |
Kind Code |
A1 |
VALLIGY, DOMINIQUE ; et
al. |
February 14, 2002 |
GRAFTED AND CROSSLINKABLE PULVERULENT THERMOPLASTIC POLYOLEFIN
COMPOSITION WHICH HAS ELASTICITY AND FLEXIBILITY PROPERTIES
Abstract
A bulk polymerized grafted and crosslinkable thermoplastic
polyolefin powder composition having elasticity and flexibility
properties, which is in the form of a powder intended for the
production of flexible coatings by free flow over a hot mold,
characterized in that it contains: a) from 100 to 5 % by weight and
preferably from 80 to 20 % by weight of at least one homopolymer of
ethylene and/or at least one copolymer containing at least 50 molar
% of ethylene; b) from 0 to 95 % by weight and preferably from 20
to 80 % by weight of at least one thermoplastic elastomer; c) from
0.1 to 15 parts by weight and preferably from 0.5 to 10 parts by
weight of a grafting agent, per 100 parts by weight of the
accumulated components "a" and "b". This powder composition is
suitable for the production of flexible coatings by its free flow
over a hot mold.
Inventors: |
VALLIGY, DOMINIQUE; (LILLE,
FR) ; MARCINIAK, TONY; (SEQUEDIN, FR) |
Correspondence
Address: |
MILLEN WHITE ZELANO & BRANIGAN
SUITE 1400
2200 CLARENDON BLVD
ARLINGTON
VA
22201
|
Family ID: |
27252775 |
Appl. No.: |
08/867412 |
Filed: |
June 2, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
08867412 |
Jun 2, 1997 |
|
|
|
08658624 |
Jun 5, 1996 |
|
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Current U.S.
Class: |
525/232 ;
428/402; 428/403; 525/193; 525/240; 525/324; 525/64 |
Current CPC
Class: |
B29K 2021/003 20130101;
B29C 41/18 20130101; B29C 41/04 20130101; Y10T 428/2982 20150115;
Y10T 428/2991 20150115; H01R 4/183 20130101; B29C 41/003 20130101;
B29K 2023/06 20130101; B29K 2023/08 20130101; B29K 2105/251
20130101 |
Class at
Publication: |
525/232 ;
525/240; 525/64; 525/324; 525/193; 428/402; 428/403 |
International
Class: |
C08L 023/08; C08K
005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 1993 |
FR |
93/08,934 |
Claims
1. A bulk polymerized grafted and crosslinkable thermoplastic
polyolefin powder composition having elasticity and flexibility
properties, which is in the form of a powder intended for the
production of flexible coatings by free flow over a hot mold,
characterized in that it contains: a) from 100 to 5% by weight and
preferably from 80 to 20% by weight of at least one homopolymer of
ethylene and/or at least one copolymer containing at least 50 molar
% of ethylene; b) from 0 to 95% by weight and preferably from 20 to
80% by weight of at least one thermoplastic elastomer; c) from 0.1
to 15 parts by weight and preferably from 0.5 to 10 parts by weight
of a grafting agent, per 100 parts by weight of the accumulated
components "a" and "b".
2. Thermoplastic composition according to claim 1, characterized in
that the thermoplastic polymer based on an ethylenic monomer
involved in the component "a " is chosen within the group
consisting of low density polyethylene (LDPE), linear low density
polyethylene (LLDPE), intermediate density polyethylene (IDPE) or
else a mixture of at least two of these polyethylenes, or else the
mixture of at least one of these polyethylenes with a high density
polyethylene (HDPE), the latter mixture containing at most 50% of
HDPE.
3. Thermoplastic composition according to claim 1, characterized in
that the thermoplastic copolymer based on an ethylenic monomer
involved in the component "a " is chosen within the group
consisting of copolymers of ethylene and of at least one alkylene
in which the alkylene may be a C.sub.4-C.sub.12 and preferably
C.sub.5-C.sub.10 monomer.
4. Thermoplastic composition according to claim 3, characterized in
that the alkylene is chosen within the group consisting of butene,
pentene, isobutene, diisobutene, hexene, methylpentene,
ethylbutene, heptene, octene, nonene, 2,5-dimethyl-4-heptene,
2-methyl-2-octene, decene, 2,2-dimethyl-4-octene,
5-methyl-5-nonene, trimethylheptene, undecenes (1, 4 or 5),
2,4,7-trimethyl-4-octene or dodecene.
5. Thermoplastic composition according to claim 1, characterized in
that the thermoplastic copolymer based on an ethylenic monomer
involved in the component "a " is chosen within the group
consisting of copolymers of ethylene and of at least one acrylic
monomer, in which the acrylic monomer is chosen within the group
consisting of acrylic, methacrylic, itaconic, crotonic or fumaric
acid, maleic anhydride or, again, isocrotonic, aconitic, mesaconic,
sinapic, undecylenic, angelic or hydroxyacrylic acid, neutralized
or otherwise, acrolein, acrylamide, acrylonitrile, esters of
acrylic and methacrylic acids and in particular methyl or ethyl
acrylate or methacrylate, imidazoles, styrene or
alpha-methylstyrene.
6. Thermoplastic composition according to claim 1, characterized in
that the thermoplastic copolymer based on an ethylenic monomer
involved in the component "a " is chosen within the group
consisting of copolymers of ethylene and of at least one vinyl
monomer which may be vinyl acetate, methyl vinyl ketone,
vinylpyrrolidone, vinylcaprolactam or vinyl ethers, in particular
methyl, ethyl or isobutyl ethers.
7. Thermoplastic composition according to any one of claims 3 to 6,
characterized in that the copolymers are formed from ethylene and
from at least two other monomers.
8. Thermoplastic composition according to any one of claims 1 to 7,
characterized in that the copolymers involved in the component "a "
contain quantities of ethylene which are generally between 60% and
98% and preferably between 70% and 90%, expressed by weight.
9. Composition according to any one of claims 1 to 8, characterized
in that the component "a " has a "melt flow index" (MFI, defined by
ASTM standard D 1238L: 190.degree. C. and 2.16 kg) of between 15
and 300 g in 10 minutes and preferably between 20 and 50 g in 10
minutes, and a flexural elasticity modulus (FEM, defined by ASTM
Standard D70) at most equal to 500 MPa and preferably at most equal
to 50 MPa.
10. Composition according to any one of claims 1 to 9,
characterized in that the polyolefinic elastomer forming part of
the component "b " is chosen within the group consisting of
ethylene-propylene rubber (EPR), ethylene-propylene-diene monomer
(EPDM), styrene-butadiene-styrene (SBS),
styrene-ethylene-butadiene-styrene (SEBS), styrene-butadiene rubber
(SBR), optionally partially or completely crosslinked,
styrene-isoprene-styrene (SIS), butyl rubber (BR), nitrile-butyl
rubber (NBR), hydrogeno-nitrile-butyl rubber (HNBR), thermoplastic
polyurethanes (TPU) and polyvinyl acetate.
11. Composition according to any one of claims 1 to 9,
characterized in that the polyolefinic elastomer forming part of
the component "b " is a mixture of polyethylene with at least one
of the elastomers: polyethylene/ethylene-propylene rubber (PE/EPR)
and/or polyethylene/ethylene-propylene-diene monomer (PE/EPDM).
12. Composition according to any one of claims 1 to 11,
characterized in that the grafting agent constituting the component
"c" is chosen within the group consisting of the silanes of general
formula XYSiZ.sub.2, in which: the radical X is chosen from the
vinyl, alkyl, butenyl, cyclohexenyl, cyclopentadienyl and
cyclo-hexadienyl radicals, but is preferably a vinyl radical; the
hydrolysable radical Z is chosen from the following radicals: x
alkoxy, such as methoxy, ethoxy, butoxy; x acyloxy, such as
formyloxy, acetoxy, propionoxy; x oxime, such as
--ON.dbd.C--(CH.sub.3).sub.2,
--ON.dbd.C--CH.sub.2--C.sub.2H.sub.5--ON.db- d.C
(C.sub.6H.sub.5).sub.2; xamino substituted ones such as alkylamino
or arylamino, including --NHCH.sub.3, --NHC.sub.2H.sub.5 and
NH(C.sub.6H.sub.5).sub.2, the radical Y is one of the two radicals
X or Z.
13. Composition according to claim 12, characterized in that the
grafting agent is preferably chosen from the group consisting of
vinyltrimethoxysilane, vinyltri-ethoxysilane,
vinyltrimethoxyothoxysilane- , 3-methacryloxypropyltrimethoxysilane
or else a silicone-modified silane.
14. Composition according to any one of claims 1 to 13,
characterized in that it also contains from 0.1 to 8 parts by
weight per 100 parts by weight of the grafting agent, of an agent
generating free radicals, chosen within the group consisting of
organic peroxides and peresters.
15. Composition according to claim 14, characterized in that the
agent generating free radicals is preferably chosen within the
group consisting of: dicumyl peroxide, tert-butyl cumyl peroxide,
di-tert-amyl peroxide, di-tert-butyl peroxide and
2,5-dimethyl-2,5-di-tert-butyl-peroxy-3-hexyne- .
16. Composition according to any one of claims 1 to 15,
characterized in that it contains an internal mold release agent
chosen within the group including the class of montanic derivatives
and montanic esters, stearate salts, their amines, their amides,
hydrogenated hydro-carbon resins, polyethylene, polypropylene and
ethylene/vinyl acetate (EVA) copolymer waxes, resins from
copolymerization of aliphatic and/or aromatic monomers, silicone
oils and silicone-modified ethylene oxide and/or propylene oxide
oils.
17. Composition according to claim 16, characterized in that the
internal mold release agent is preferably chosen within the group
made up of alkaline-earth stearates, including calcium and
magnesium stearate, silicone oils and silicone-modified ethylene
oxide and/or propylene oxide oils.
18. Composition according to either of claims 16 and 17,
characterized in that the internal mold release agent is introduced
into the composition in a proportion of 0.1 to 6 parts by weight
and preferably in a proportion of 0.5 to 3 parts by weight per 100
parts by weight of the components "a " and "b ".
19. Composition according to any one of claims 1 to 18,
characterized in that it comprises a flow aid which is chosen
within the group consisting of precipitated silicas, modified or
grafted preferably with a silicone or with a silicone oil.
20. Composition according to claim 19, characterized in that the
quantity of flow aid involved is between 0.1 and 5 parts and
preferably between 0.1 and 1 part by weight of the components "a "
and "b ".
21. Composition according to any one of claims 1 to 20,
characterized in that it contains adjuvants which are heat or
photochemical stabilizers, antioxidants, lubricants, antistatic
agents or flame retardants.
22. Composition according to any one of claims 1 to 21,
characterized in that it contains powdered inorganic materials
chosen from inorganic salts and/or oxides belonging to the group
consisting of calcium, magnesium and zinc carbonates, dolomite,
lime, magnesia, aluminium trihydroxide, alumina, clays and other
silico-aluminous substances, preferably talc, kaolin, mica,
bentonite, wollastonite and glass beads.
23. Composition according to any one of claims 1 to 21,
characterized in that it contains powdered organic materials chosen
within the group of colorants and carbon black.
24. Composition according to either of claims 22 and 23,
characterized in that the powdered materials are used by themselves
or mixed.
25. Composition according to any one of claims 22 to 24,
characterized in that the dimensions of the powdered materials are
between 0.01 and 300 mm and preferably between 0.1 and 100 mm.
26. Composition according to any one of claims 22 to 25,
characterized in that the powdered materials are introduced in a
proportion of 0.1 to 5 parts and preferably of 0.1 to 2 parts by
weight per 100 parts by weight of the components "a " and "b ".
27. Composition according to any one of claims 1 to 26,
characterized in that it comprises a hydrolysis catalyst chosen
within the group consisting of dibutyltin dilaurate, stannous
acetate, tin octoate, dibutyltin dioctoate, iron 2-ethylhexoate,
tetrabutyl titanate, tetranonyl titanate, diisopropyl
bis(acetylacetonyl)titanate, ethylamine, hexylamine, dibutylamine
and piperidine and inorganic acids and fatty acids and, preferably,
chosen from organic tin compounds and more particularly dibutyltin
dilaurate, tin octoate and dialkyltin mercaptide and fatty
acids.
28. Composition according to claim 27, characterized in that the
hydrolysis catalyst is introduced into the grafted composition in a
proportion of 0.001 to 0.5 parts by weight and preferably in a
proportion of 0.001 to 0.3 parts by weight per 100 parts by weight
of the accumulated components "a" and "b ".
29. A bulk polymerization process for the manufacture of a
composition according to any one of claims 1 to 28, characterized
in that: the mixing of the constituents of the composition is
performed in a molten extrusion zone; a cryogenic grinding of the
granules of the mixture is performed in conditions such that a
maximum particle size of powder of the order of 700 mm and medium
size of approximately 500 mm, preferably of approximately 300 mm,
are obtained.
30. Process for the manufacture of a composition according to any
one of claims 1 to 28, characterized in that a microgranulation is
performed by extrusion through a microdie and flat cutting in an
aqueous medium resulting in a powder which has a maximum particle
size of the order of 700 mm and a medium size of approximately 500
mm, preferably of approximately 300 mm.
31. Process for making use of the composition according to any one
of claims 1 to 30, characterized in that a flexible coating is
produced by free flow of the powder composition, in the presence of
the flow aid, over a heated mold, and crosslinking is carried out
at a temperature of at least 50.degree. C., in moist environment,
in the presence of a hydrolysis catalyst.
32. Process according to claim 31, characterized in that, when the
hydrolysis catalyst is in the solid state, it is used in the form
of a powder optionally coated with a fusible thermoplastic
jacket.
33. Process according to claim 31, characterized in that, when the
catalyst is liquid, it is used: in the form of a powder serving as
support, like silica, or a thermoplastic compound corresponding to
the component "a ", impregnated with the said catalyst; through the
intermediacy of a gaseous support, in particular by injection into
water vapour.
34. Molded articles characterized in that they are obtained by the
implementation of any one of claims 1 to 33.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a CIP of application Serial No.
08/658,624, filed Jun. 5, 1996.
FIELD OF THE INVENTION
[0002] The invention relates to a grafted and cross-linkable
thermoplastic polyolefin composition which has elasticity and
flexibility properties.
[0003] The invention relates more especially to a grafted and
crosslinkable thermoplastic polyolefin composition which has
elasticity and flexibility properties, which is in the form of a
powder, for the production of flexible coatings by free flow of the
powder over a heated mold, according to either of the molding
processes of slush molding or rotational molding.
[0004] The invention also relates to the process for the
preparation of the said composition.
[0005] The invention also relates to the process for making use of
the said composition.
[0006] Finally, the invention relates to the molded articles
produced by making use of the composition.
TECHNICAL BACKGROUND OF THE INVENTION
[0007] Numerous parts which are made of polymeric materials are
increasingly involved in motor vehicle construction, such as
dashboards, door panels, consoles, and the like. Some of them are
involved in a highly visible manner in the internal architecture of
the vehicle, with the result that they must offer, on the visible
surface, a pleasant aesthetic appearance giving, for example, the
appearance of leather. This visible surface constitutes the skin of
the component. This skin, coloured in bulk, must also have other
properties, which are a good resistance to scratching and to
chemical agents such as solvents, and a good resistance to.
temperature variations, ranging from severe cold to prolonged
exposure to the sun in an enclosed atmosphere.
[0008] The skin thus referred to may relate to any components,
(also called inserts) made of polymeric materials, particularly
those forming part of the internal architecture of the vehicle,
starting with the rigid inserts, generally confined to bottom-range
vehicles, as far as foamed inserts fitted to more elaborate
vehicles.
[0009] In the case of rigid inserts the skin or, at least its
appearance, is obtained by virtue of engraving of the mold, either
from the material of which the insert consists or else, for
example, using a dual injection of. two different materials, one
for the insert the other for the skin.
[0010] In the case of foamed inserts the skin is generally produced
independently of the insert itself, in a material which is
compatible, on the one hand, with the foam subsequently developed
between the said skin and the insert and, on the other hand, with
the finishing lacquers such as the polyurethane lacquers deposited
on the visible surface of the said skin in order, if need be, to
make them conform to the specifications of the motor vehicle
manufacturers.
[0011] To produce the skin of inserts such as, for example, the
dashboard, various processes are proposed, in which one of the
concerns is to produce a skin with the least possible residual
stress.
[0012] In a first type of process which makes use of a
prefabricated polypropylene-based sheet, the dashboard skins are
produced by means of the positive or negative thermoforming
process. However, the thermoforming practiced, whether positive
(the surface appearance of the skin exists on the sheet before the
thermoforming) or negative (the surface appearance is given to the
sheet by the mold at thermoforming) generally makes use of
(preheated) sheets which are preferably thin, for both technical
and economic reasons.
[0013] As a result, the forms of skins which are obtained are very
limited because they give rise to very thin skins and to residual
stresses which, when they are released by aging, generate
aesthetically unsightly small cracks.
[0014] In another type of process the dashboard skins are produced
according to the slush molding process (referred to above), which
allows them to be obtained generally free from residual stresses.
In itself the slush molding process is a molding process employing
conventional hardware (mold made of electroformed nickel heated,
for example, by a hot air system) which allows the desired skins to
be produced by making use of a polymer powder based on polyvinyl
chloride (PVC) using the free flow technique. The skins thus
produced, even if no longer containing any, or hardly any residual
stresses, and even though they essentially meet the specifications
of the motor vehicle manufacturers, exhibit immediate or potential
disadvantages, even in the short term.
[0015] One of the real and immediate disadvantages is that, owing
to their composition, PVC-based skins are fairly highly laden with
volatile materials (in particular plasticizers for PVC). In use and
under the effect of the temperature variations in the vehicle's
interior, these materials are volatilized and migrate onto the cold
regions, to condense thereon; this is the well-known phenomenon of
the slow opacifying of vehicle windshields, particularly awkward
for the driver's visibility and control of the vehicle.
[0016] Among the potential disadvantages, the use of PVC, in the
present state of the recycling at the end of the life of materials
introduced into the manufacture of motor vehicles, appears to be
doomed to a more or less short term, for better protection of the
environment. This is because the polymeric materials resulting from
the dissembling of scrap vehicles are at present employed (wholly
or partly) as fuel in some types of furnaces, such as, for example,
cement works' kilns. Now, when it is burnt, PVC converted into fuel
gives off acidic gaseous effluents which are harmful to the
environment.
[0017] This is why, in order to respond to a dual concern of the
motor vehicle manufacturers and of the public authorities, which is
firstly that for the protection of the environment (eliminating the
harmful gaseous effluents generated by the burning of waste made of
polymeric materials and limiting their dumping) and, next, that for
the most complete recycling of the waste (made up of polymeric
materials) resulting from the destruction of scrap vehicles, motor
vehicle manufacturers seriously envisage limiting the number of
polymers present in each vehicle but, at the same time increasing
their relative quantities, and in particular replacing PVC with
polyolef ins, to permit easier recycling. Thus, motor vehicles
would be fitted with components, such as foamed dashboards, in
which the skin, the foam and the rigid insert would be made of
polyolef ins which can be recycled at the end of the vehicles'
life. To do this, thermoplastic polyolef in compositions have
already been proposed.
[0018] In this context document EP0482778 describes a polyolefin
composition which has elastic properties, made up of an extruded
mixture of polypropylene and of a polyolefin elastomer
[ethylene-propylene rubber (EPR) and ethylene-propylene-diene
monomer (EPDM)], which can be employed according to the slush
molding process.
[0019] However, according to this document:
[0020] to promote the melting, in contact with the mold, of the
composition which is in the form of a powder, oils such as
paraffinic oils are introduced therein in a relatively high
proportion in relation to the polyolef in elastomer. These oils
constitute a potential risk of giving off volatile substances that
pollute the environment and opacify vehicle windshields, as well as
a risk of the appearance of the skin deteriorating as it ages;
[0021] to impart good heat resistance to the skin which is, by
definition, thin, and to limit the presence of interfering volatile
materials, crosslinking agents, including organic peroxides in
particular, are introduced into the composition;
[0022] finally, to permit easy demolding of the skin, mold release
agents which are external (for example dimethylsiloxane) deposited
on the mold, or internal to the composition (for example
methylpolysiloxane), are used; they also constitute a risk of
direct pollution of the environment of the manufacturing workshops,
but, above all, create greater difficulty in the subsequent
operation of lacquering the skins which is at present necessary to
make them conform to the motor vehicle manufacturers'
specifications (appearance, degree of mattness/gloss and resistance
to scratching, abrasion and to chemical agents, including
solvents).
[0023] Another document, Canadian Patent 2,129,326, also describes
a thermoplastic polyolefin composition which has elastic properties
that can be employed in the motor vehicle sector, and is in
pulverulent form. This composition includes three components:
[0024] the first (10 to 40 parts by weight) being polypropylene or
a copolymer of propylene and ethylene and/or of alpha-olefin of the
CH.sub.2.dbd.CHR type where R is an alkyl radical containing 2 to 8
carbons (I), which has an isotacticity value higher than 86;
[0025] the second (0 to 20 parts by weight) being a copolymer
containing ethylene, propylene and/or the abovementioned
alpha-olefin monomer of the CH.sub.2 .dbd.CH--R type (insoluble in
xylene at ambient temperature);
[0026] the third (50 to 80 parts by weight) being a fraction of an
ethylene copolymer with propylene and/or the abovementioned
alpha-olefin monomer of the CH.sub.2.dbd.CH--R type (soluble in
xylene at ambient temperature).
[0027] However, such a composition appears to be incapable of being
easily used in the slush molding process for the production of
skins without being modified to some extent by the addition of flow
agents for the powder composition, used in proportions such that
the melting and/or the demolding run the risk of being
jeopardized.
[0028] Another document, Japanese Patent Application J03286811,
describes a thermoplastic polyolefin composition with elastic
properties, which has the appearance of a powder that can be
employed according to the slush molding process.
[0029] This thermoplastic elastomeric composition comprises:
[0030] a polymer material made up of crystalline and noncrystalline
polyolef ins with a mean particle size of at least 10 micrometers
and an apparent density of at least 0.2 g/ml, this material being,
for example, made from ethylene, propylene and butene;
[0031] and a crosslinking agent such as, for example, an organic
peroxide.
[0032] However, this composition exhibits major disadvantages when
it is used as such in the slush molding process, in particular for
molding. Furthermore, the skins thus obtained cannot meet the
functional specifications of the motor vehicle industry and, more
precisely, do not stand up well to the thermal behaviour tests,
because it is found that the crosslinking remains incomplete.
[0033] Another document, EP0409992, describes a process for the
preparation of particles of crosslinkable thermoplastic polyolefin
polymers according to which said particles are brought into
contact, in the solid state, with the crosslinking agent, in
particular by means of a mineral oil; the crosslinking reaction
taking place at a temperature where the polymers particles are not
melted and do not stick to one another. When the contact between
the polymers particles and the crosslinking agent is established,
without mineral oil, the crosslinking action essentially takes
place on the surface of all the polymers particles. This
crosslinking is therefore heterogeneous and leads to all the
disadvantages resulting therefrom when making use of the particles
of those polymers. When the contact between the polymers particles
and the crosslinking agent takes place in the presence of mineral
oil, said oil, which migrates onto the material, constitutes a
disadvantage which is exhibited later by a poor adhesion of this
composition on the polyurethane foams or a poor bonding or
lacquering.
[0034] Finally, a last document, JP58-001724, describes a process
for the preparation of grafted and crosslinkable polyolefin
particles, consisting of bringing into contact, in the solid state,
said particles with the grafting and crosslinking agents, the
crosslinking taking place at a temperature where the polyolefin
particles are not melted and thus do not stick to one another.
[0035] This process leads to polyolefin particles which are grafted
essentially on their surface, that is to say heterogeneously and
which, once they have been crosslinked, and also crosslinked
heterogeneously, thus leading to polymers zones that are poorly
grafted and therefore, in the case of the production of molded
articles, tend to migrate onto the outside of said articles during
the thermal ageing.
[0036] Consequently, the problem of using the polyolefin
compositions to replace polyvinyl chloride in the production of
skins for the foamed or unfoamed covering of inserts remains
practically untouched.
SUMMARY OF THE INVENTION
[0037] Thus, the objectives at which the invention is aimed are to
provide a polyolefinic composition, based essentially on an
ethylenic monomer, having elastic properties, for the manufacture
of flexible coatings, which:
[0038] has the form of a powder with good flow properties, in order
to be used either in the slush molding or rotational molding
process;
[0039] when used, provides the flexible coatings with all the
characteristics required by the motor vehicle manufacturers'
functional specifications, in particular good thermal behaviour in
the most severe tests (130.degree. C.), good resistance to
scratching, abrasion and chemical agents including, in particular,
organic solvents, and good retention of flexibility with time (in
comparison, for example, with a skin based on polypropylene or
PVC);
[0040] makes it possible to produce flexible coatings of uniform
thickness and free from porosity;
[0041] makes it possible to obtain flexible coatings which are free
from residual stresses;
[0042] is compatible with the subsequent foaming and lacquering
operations;
[0043] is free from agents which have high vapour pressures;
[0044] does not exhibit counterskin whitening phenomena, when
compared with a polypropylene based skin;
[0045] does not exhibit any phenomena of exudation of the low
molecular masses of the polyolefinic elastomers ensuring the
absence of lump formation and good powder flow;
[0046] permits excellent demolding of the component produced;
[0047] is entirely recyclable after use, in the motor vehicle
industry, in order to meet the requirements of environmental
protection; and
[0048] meets the present and future technical and economic
requirements.
[0049] Moreover, it also relates to a process for the preparation
of this composition, to a process for making use of the said
composition and to the articles molded by making use of the said
composition.
[0050] Upon further study of the specification and appended claims,
further objects and advantages of this invention will become
apparent to those skilled in the art.
SUMMARY OF THE INVENTION
[0051] Because of the abovementioned disadvantages, the inventors
have pursued, through its investigations, the development of a
grafted and crosslinkable polyolefin powder composition which is
grafted in bulk, in the melted state, and meeting the above
objectives.
[0052] The thermoplastic polyolef in powder composition according
to the invention, which has elasticity and flexibility properties,
intended for the production of flexible crosslinkable articles by
free flow over a hot mold, is characterized in that it
contains:
[0053] a) from 100 to 5% by weight and preferably from 80 to 20% by
weight of at least one ethylenic polymer and/or at least one
copolymer containing at least 50% in moles of ethylene;
[0054] b) from 0 to 95% by weight and preferably from 20 to 80% by
weight of at least one thermoplastic elastomer;
[0055] c) from 0.1 to 15 parts by weight and preferably from 0.5 to
10 parts by weight of a grafting agent, per 100 parts by weight of
the accumulated components "a" and "b".
DETAILED DESCRIPTION OF THE INVENTION
[0056] The invention relates to a grafted and crosslinkable
polyolefin powder composition which is grafted in the melted state
and is crosslinkable after demolding the part made from said
composition. This composition has:
[0057] elasticity and flexibility properties, used according to the
process of free flow of the powder over a heated mold, for the
manufacture of flexible coatings also known by the name of
skins;
[0058] other essential properties like those referred to above and,
in particular, ease of processing, the absence of whitening on
impact and on bending of the produced parts, ease of demolding in
the case of counterskin articles and very good thermal behaviour in
the most severe tests.
[0059] In order to obtain such properties, although the polymers
and/or copolymers used are sensitive to temperatures and contain at
least 50% in moles of ethylene, the composition is grafted in the
melted state, that is to say in bulk, contrary to the state of the
art that suggests a grafting of the polyolefin particles in the
solid state, that is to say an heterogeneous grafting that
essentially takes place on the surface. Thus, the composition is
grafted in its core and made potentially crosslinkable but is only
completely crosslinked after its transformation, by molding and
demolding, into flexible articles, in order to improve its capacity
of resistance to thermal aging.
[0060] According to the invention the thermoplastic polyolefin
composition which has elasticity and flexibility properties
comprises at least one homopolymer of ethylene polymer and/or at
least one copolymer containing at least 50%, by moles, of ethylene,
constituting the component "a" of the composition.
[0061] The thermoplastic polymer based on ethylenic monomer which
can be involved in the component "a" may be chosen, for example,
within the group consisting of low density polyethylene (LDPE),
linear low density polyethylene (LLDPE), intermediate density
polyethylene (IDPE) or else a mixture of at least two of these
polyethylenes, or else the mixture of at least one of these
polyethylenes with a high density polyethylene (HDPE), the latter
mixture containing at most 50% of HDPE.
[0062] The thermoplastic copolymer containing at least 50%, by
moles, of ethylene which can be involved in the component "a" may
be chosen within the group consisting of:
[0063] copolymers of ethylene and of at least one alkylene, in
which the alkylene may be a C.sub.4--C.sub.12 and preferably
C.sub.5--C.sub.10 monomer, such as, for example, butene, pentene,
isobutene, diisobutene, hexene, methylpentene, ethylbutene,
heptene, octene, nonene, 2,5-dimethyl-4-heptene, 2-methyl-2-octene,
decene, 2,2-dimethyl-4-octene, 5-methyl-5-nonene, trimethylheptene,
undecenes (1, 4 or 5), 2,4,7-trimethyl-4-octene or dodecene;
[0064] copolymers of ethylene and of at least one acrylic monomer
in which the acrylic monomer may be acrylic, methacrylic, itaconic,
crotonic or fumaric acid, maleic anhydride or else, isocrotonic,
aconitic, mesaconic, sinapic, undecylenic, angelic or
hydroxyacrylic acid, acrolein, acrylamide, acrylonitrile, esters of
acrylic and methacrylic acids and in particular methyl or ethyl
acrylate or methacrylate, imidazoles, styrene or
alpha-methylstyrene; the acidic functional groups thus referred to
may be in the acidic form or in a form which is at least partially
converted into salt by agents based on monovalent metals or the
like, such as sodium, potassium or ammonium, or polyvalent metals
such as calcium, magnesium or zinc, or else neutralized with
amines;
[0065] copolymers of ethylene and of at least one vinyl monomer,
such as, for example, vinyl acetate, methylvinyl ketone,
vinylpyrrolidone, vinylcaprolactam or vinyl ethers, in particular
methyl, ethyl, isobutyl or other ethers;
[0066] copolymers of ethylene and of at least two other monomers
taken within the abovementioned groups.
[0067] These polymers and/or copolymers are obtained by methods
which are well known to a person skilled in the art and also
include those making use of a catalyst of the metallocene type.
[0068] The copolymers involved in the component "a" of the
composition according to the invention contain quantities of
ethylene which are generally between 60% and 98% and preferably
between 70% and 90%, expressed by weight.
[0069] According to the invention the component "a" preferably has
a "melt flow index" (MFI) defined by ASTM standard D 1238L
(190.degree. C. and 2.16 kg) of between 15 and 300 g in 10 minutes
and preferably between 20 and 50 g in 10 minutes, and a flexural
elasticity modulus (FEM) defined by ASTM standard D70, at most
equal to 500 MPa and more preferably at most equal to 50 MPa.
[0070] According to the invention the thermoplastic polyolefin
composition which has elasticity and flexibility properties may
comprise at least one elastomer constituting the component "b".
[0071] This component "b" may be chosen from the thermoplastic
elastomers:
[0072] used alone, such as: ethylene-propylene rubber (EPR),
ethylene-propylene-diene monomer (EPDM), styrene-butadiene-styrene
(SBS), styrene-ethylene-butadiene-styrene (SEBS), styrene-butadiene
rubber (SBR), optionally partially or completely crosslinked,
styrene-isoprene-styrene (SIS), butyl rubber (BR), nitrile-butyl
rubber (NBR), hydrogeno-nitrile-butyl rubber (HNBR), and polyvinyl
acetate;
[0073] or used in accordance with a mixture, either in reactor or
by extrusion, of polyethylene and/or semi-crystalline polypropylene
with at least one abovementioned elastomer, such as, for example,
polyethylene/ethylene-propylene rubber (PE/EPR),
polyethylene/ethylene-pr- opylene-diene monomer (PE/EPDM), it being
possible for the elastomeric fraction to be optionally partially or
completely crosslinked.
[0074] or belonging to the group of polypropylenes (homopolymers)
with amorphous and semi-crystalline blocks and copolymers of
propylene-ethylene or alpha-olefin with amorphous and
semi-crystalline blocks.
[0075] The polyolefin elastomer used in the composition preferably
has a solubility of 100% to 70% in xylene at 20.degree. C.
[0076] According to the invention the thermoplastic polyolef in
composition which comprises polyolefin polymers and/or copolymers
of low heat resistance is reinforced by the presence of at least
one grafting agent constituting the component "c" permitting the
subsequent crosslinking of the grafted composition, after it has
been used in a molding-demolding operation of a flexible
article.
[0077] The component "c" is chosen within the group consisting of
the silanes which have the general formula XYSiZ.sub.2 in
which:
[0078] X is an olefinically unsaturated monovalent hydrocarbon
radical or else a hydroxycarbonoxy radical which is reactive
towards the free-radical sites which are created;
[0079] Y is a radical X or a radical Z;
[0080] Z is a hydrolyzable organic radical.
[0081] The radical X may thus be one of the vinyl, alkyl, butenyl,
cyclohexenyl, cyclopentadienyl, or cyclo-hexadienyl radicals but is
preferably a vinyl radical.
[0082] The hydrolyzable organic radical Z may be an alkoxy radical
such as the methoxy, ethoxy and butoxy radicals or else an acyloxy
radical such as the formyloxy, acetoxy, or propionoxy radicals,
radicals derived from oxime such as, for example:
--ON.dbd.C--(CH.sub.3).sub.2,
--ON.dbd.C--CH.sub.2--C.sub.2H.sub.5--ON.dbd.C(C.sub.6H.sub.5).sub.2
or else aminosubstituted radicals such as alkylamino or arylamino
radicals including, for example, --NHCH3, --NHC.sub.2H.sub.5 and
NH(C.sub.6H.sub.5).sub.2.
[0083] The silane is preferably chosen within the group consisting
of vinyltrimethoxysilane, vinyltriethoxy-silane,
vinyltrimethoxyothoxysilane- ,
3-methacryloxy-propyltrimethoxysilane or else a silicone-modified
silane.
[0084] Contrary to the state of the art in which the grafting is
carried out in the solid state of fine polymers particles, leading
to a partial grafting, essentially on their surface, and thus
heterogeneous and therefore to an heterogeneous crosslinking that
leaves some polymers zones poorly grafted, the operation of
grafting the component "c" onto the mixture of components "a" and
"b" or preferably onto component "a" alone, is performed in the
melted state, that is to say in bulk and preferably under
mechanical shearing of the components, according to processes which
are known to a person skilled in the art. This operation consists
in reacting the polyolefin compound, in the melted state, with a
silane, preferably in the presence of an agent generating free
radicals, creating free radical sites in the polyolefin
compound.
[0085] The grafting operation in the melted state is generally
performed at a temperature of at least 140.degree. C., in an
appropriate technology, for example a twin-screw extruder, the
screws rotating in opposite directions, in which the polyolefin
compound and the grafting agent are brought into contact at the
appropriate temperature; the grafting agent may be introduced into
the equipment used in a form dispersed at the surface of the
polyolefin compound, or else introduced directly, for example by
injection, into the reaction mixture.
[0086] The agent generating free radicals, referred to above, may
be introduced in a form dispersed at the surface of the polyolef in
compound or else may be introduced by injection simultaneously with
the grafting agent, optionally in the presence of an appropriate
solvent, in a portion of 0.1 to 8 parts by weight per 100 parts by
weight of the grafting agent (component "c").
[0087] The agent generating free radicals which is capable of
creating free-radical sites in the polyolef in compound is an
organic peroxide or a perester such as, for example,
tert-butylperoxy 3,5,5-trimethylhexanoat- e,
2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butyl-peroxy
2-ethylhexyl carbonate, tert-butylperoxy acetate, tert-amylperoxy
benzoate, tert-butylperoxy benzoate,
2,2-di(tert-butylperoxy)butane, n-butyl
4,4-di(tert-butyl-peroxy)valerate, ethyl 3,3-di(tert-butylperoxy)-
butyrate, dicumyl peroxide, tert-butyl cumyl peroxide, di-tert-amyl
peroxide, di(2-tert-butylperoxyisopropyl)benzene,
2,5-dimethyl-2,6-di(ter- t-butylperoxy)hexane, di-tert-butyl
peroxide, 2,5-dimethyl-2,5-di-tert-but- ylperoxy-3-hexyne,
3,3,6,6,9,9-hexamethyl-1,2,4,5-tetraoxacyclononane, tert-butyl
hydroperoxide, 3,4-dimethyl-3,4-diphenylhexane,
2,3-dimethyl-2,3-diphenylbutane and tert-butyl perbenzoate and azo
compounds, for example azobisisobutyronitrile and dimethyl
azodiisobutyrate; the said agent is preferably chosen within the
group consisting of dicumyl peroxide, tert-butyl cumyl peroxide,
di-tert-amyl peroxide, di-tert-butyl peroxide and
2,5-dimethyl-2,5-di(tertbutylperoxy)- -3-hexyne.
[0088] The thermomechanical characteristics of the grafted
thermoplastic polyolefin composition according to the invention are
preferably the following:
1 melt flow index (ASTM Standard 1238L: 190.degree. C. and 2.16 kg)
20 to 30 g/10 min density (ASTM Standard 1505): approximately 0.87
to 0.91 g/cm.sup.3 flexural modulus (ASTM Standard D 790):
preferably <50 MPa yield point stress (ASTM Standard D 638):
approximately 4 to 5 MPa elongation at break (ASTM Standard D 638):
>400 % notched bar impact strength (ASTM Standard D 256) at
23.degree. C. >500 J/m at 0.degree. C. >500 J/m heat
deflection temperature (HDT) >40.degree. C. (ASTM Standard D
648)
[0089] According to the invention the thermoplastic polyolefin
composition which has elasticity and flexibilty properties may
contain at least one internal mold release agent.
[0090] The internal mold release agent may be chosen from one of
the conventionally known agents belonging to the group including
the class of the montanic derivatives and montanic esters, stearate
salts, their amines, their amides, such as ethylene bis stearamide,
hydrogenated hydrocarbon resins, polyethylene, polypropylene. and
ethylene/vinyl acetate (EVA) copolymer waxes, resins from
copolymerization of aliphatic and/or aromatic monomers, silicone
oils or else silicone-modified ethylene oxide and/or propylene
oxide oils.
[0091] The internal mold release agent may be preferably chosen
within the group made up of alkaline-earth stearates such as
calcium and magnesium stearate, the most widely employed of which
is magnesium stearate, silicone oils or else silicone-modified
ethylene oxide and/or propylene oxide oils.
[0092] The internal mold release agent which, finally, is
preferably used in the composition according to the invention is
magnesium stearate, in the case of which it has been ascertained by
experiment, the absence of the. phenomenon of migration of the core
towards the surface of the skin containing it, a phenomenon which
is generally manifested at the surface of the said skin by the
appearance of a slight whitish deposit whose presence is
unacceptable in view of the qualification standards of some motor
vehicle manufacturers.
[0093] The magnesium stearate used as internal mold release agent
offers many advantages, the most notable of which are listed
below:
[0094] it ensures, by its presence, excellent demolding of the
skin; and
[0095] it allows the skin to be lacquered with good adhesion of the
lacquer following a special preparation, such as flaming or the use
of an adhesion primer.
[0096] The internal mold release agent may be introduced into the
composition of the invention on the occasion of a mixing operation,
for example at the time of the grafting operation, or else at the
time when the mixing of the grafted composition with a crosslinking
catalyst is performed.
[0097] The internal mold release agent is introduced into the
composition in a proportion of 0.1 to 6 parts by weight and
preferably in a proportion of 0.5 to 3 parts by weight per 100
parts by weight of the components "a" and "b".
[0098] However, the mold release agent may also be external and, in
this case, it is deposited directly on the surface of the mold. In
this case this agent may be chosen within the group consisting of
the class of silicones, aliphatic and aromatic naphthas and
polyphosphatides or oils which are well known to a person skilled
in the art. However, in addition, the mold release agent, whether
internal or external, may be replaced by a surface treatment of the
mold, making it non-adhesive.
[0099] The composition according to the invention is prepared
according to a number of manufacturing processes.
[0100] According to a first process the various constituents of the
composition according to the invention are introduced, mixed and
then grafted, in a mixing and/or extrusion zone, heated at least to
the melting temperature of said mixture. Then the materials
originating from the mixing and/or extrusion zone, transformed into
granulates or another form, are subjected to cryogenic grinding in
such a way that this produces a grafted crosslinkable thermoplastic
polyolefin powder which is grafted in bulk and has the required
elasticity and flexibility properties.
[0101] According to another process the composition according to
the invention may be prepared by microgranulation, which consists
of an extrusion of the composition in the melted state through a
microdie and flat cutting in aqueous medium, which results in a
grafted crosslinkable thermoplastic polyolefin powder which is
grafted in bulk which has elasticity and flexibility
properties.
[0102] The thermoplastic polyolef in powder according to the
invention, obtained according to a suitable process such as, for
example, those mentioned above, has. a maximum particle size of
approximately 700 mm and a medium size of approximately 500 mm, but
preferably of approximately 300 mm.
[0103] This is why, in order to ensure the best flow over the mold
of the powder resulting from one or other of the abovementioned
processes for preparation of the composition according to the
invention, to avoid local overloading of this composition, whatever
the shape of the mold, and to decrease the thickness of the skins
to be produced, it is desirable to associate, with the composition
according to the invention, a flow aid for the powders, by dry
mixing.
[0104] This flow aid is desirably a precipitated silica, of
spherical form and preferably surface-grafted with a silane or a
silicone oil.
[0105] The quantity of flow aid introduced into the composition
according to the invention is between 0.1 and 5 parts and
preferably between 0.1 and 1 part by weight per 100 parts by weight
of the components "a" and "b".
[0106] The precipitated and grafted silica used as flow aid in the
composition according to the invention has the following
characteristics:
[0107] hydrophobic or hydrophilic, loose white powder
[0108] BET specific surface (DIN standard 66131): <300
m.sup.2g.sup.-1
[0109] mean diameter of the primary particles: <50
nanometres
[0110] packing density (DIN-ISO Standard 787/XI): <200
g/l.sup.1
[0111] Various adjuvants of a known type may also be introduced
into the composition according to the invention during the
preparation of the mixture of the constituents, tuents, or even
subsequently, during the preparation of the composition according
to the invention, by the use of its various constituents "a",
"b"and "ct". These various adjuvants are, for example, heat or
photochemical stabilizers, antioxidants, lubricants, antistatic
agents, flame retardants or still others.
[0112] In addition, some powdered inorganic materials may also be
introduced into the composition according to the invention; they
may be chosen from inorganic salts and/or oxides which have or have
not undergone a surface treatment, such as calcium, magnesium or
zinc carbonates, dolomite, lime, magnesia, aluminium trihydroxide,
alumina, clays and other silicoaluminous substances, preferably
talc, kaolin, mica, bentonite, wollastonite and glass beads.
[0113] Finally, other organic powdered materials of natural or
synthetic origin may also be introduced, such as, for example,
colorants or carbon black.
[0114] All these powdered materials may be used by themselves or in
combination.
[0115] The dimensions of these inorganic materials are generally
between 0.01 and 300 mm and preferably between 0.1 and 100 mm.
[0116] These powdered inorganic materials may be introduced into
the compositions according to the invention in a proportion of 0.1
to 5 parts and preferably of 0.1 to 2 parts by weight per 100 parts
by weight of the components "a" and "b".
[0117] Since the grafted and crosslinkable thermoplastic polyolefin
composition is prepared by an appropriate means, it is liable to be
used for the production of crosslinkable flexible articles by
either the slush molding or the rotational molding process
eventually, in the presence of a hydrolysis catalyst.
[0118] The hydrolysis catalyst thus referred to is generally
incorporated into the thermoplastic polyolef in composition
according to the invention immediately before it is used according
to either the slush molding or the rotational molding process.
[0119] According to one embodiment the grafted and crosslinkable
polyolefin composition is delivered according to two separate
components, one of the components comprising the polyolef in
composition to be crosslinked, the other component contributing the
hydrolysis catalyst in an appropriate form.
[0120] These two components may then be mixed according to the
desirable proportions to allow the crosslinking of the composition
according to the invention, in the presence of water.
[0121] The hydrolysis catalyst may be chosen from various compounds
which are well known to a person skilled in the art, which are
generally in a liquid form, but, in the case of some, also in a
solid form. These various compounds form the group consisting of
metal carboxylates such as dibutyltin dilaurate (DBDL), tin
dibutyltrilaurate (DBTL), tin acetate, stannous acetate, tin
octoate, tin oxalate, tin dibutyltriacetate (DBTA), dibutyltin
maleate (DBTM), tin butyltricaprylate (BTTO), iron 2-ethylhexoate,
organometallic compounds such as titanium esters and chelates, for
example tetrabutyl titanate, tetranonyl titanate, diisopropyl
bis(acetylacetonyl)titanate, organic bases such as ethylamine,
hexylamine, dibutylamine and piperidine and acids such as inorganic
acids and fatty acids. The hydrolysis catalyst is preferably chosen
from organic tin compounds, for example dibutyltin dilaurate, tin
dibutyltrilaurate, tin butyltricaprylate, tin oxalate, tin
dibutyltriacetate, dibutyltin maleate, tin octoate.
[0122] The hydrolysis catalyst when implemented is introduced into
the grafted crosslinkable composition according to the invention in
a proportion of 0.001 to 0.5 parts by weight and preferably in a
proportion of 0.001 to 0.3 parts by weight relative to 100 parts by
weight of the components "a" and "b" of the said composition.
[0123] When the hydrolysis catalyst is in a solid form it may be
introduced in the form of a fine powder (from 0.1 mm to 10 mm)
optionally coated with a meltable thermoplastic jacket giving it,
when used according to either the slush molding or the rotational
molding process, a delay effect which is particularly favourable
for controlling the start of the crosslinking which is thus started
after the operation of hot forming and demolding. But the solid
catalyst may also be in the form of a fine powder component,
obtained, for example, by extrusion, followed by a grinding, of a
mixture made of said catalyst, with
[0124] a polypropylene wax (MFI superior to 100 g/10 min. at
190.degree. C. under 2,16 kg), grafted or not, by means of a
component such as maleic anhydride ;
[0125] a thermoplastic polyurethane (TPU)
[0126] a thermoplastic polyester.
[0127] This fine powder component may be microencapsulated in order
to give it the same retarding effect already mentioned.
[0128] When the hydrolysis catalyst is in a liquid form it may be
used through the intermediacy of a finely divided, powdered
inorganic solid support such as precipitated silica referred to
earlier in the role of flow aid or else through the intermediacy of
a thermoplastic compound corresponding to the component "a" or
microencapsulated in a thermoplastic meltable envelope to give it a
retarding effect or else again introduced through the intermediacy
of a gaseous carrier, for example steam injected into an
appropriate vessel.
[0129] The crosslinking of the grafted and crosslinkable
thermoplastic polyolefin composition is performed after hot forming
in the presence of the hydrolysis catalyst, according to either the
slush molding or the rotational molding process, by exposing the
molded article to moisture.
[0130] Atmospheric moisture is usually sufficient to permit this
crosslinking. However, the crosslinking may be accelerated either
by the use of a controlled artificial moist atmosphere or by
immersion of the article in water, or else by raising the
temperature of the treatment medium, whether it is gaseous or
liquid.
[0131] By way of example, the crosslinking of the molded article
may be performed in a hot environment at a temperature of at least
50.degree. C. in the presence of water vapour.
[0132] However, the crosslinking of the thermoplastic composition
according to the invention may be performed:
[0133] either by simple impregnation of the flexible coating with
the pure hydrolysis catalyst when it is liquid or dissolved in
water or a solvent;
[0134] or by immersion in a liquid or gaseous medium containing the
hydrolysis catalyst.
[0135] Thus, the composition according to the invention is used for
the production of skins by the method of the flow of powder over a
hot mold. These skins are intended to be fitted to inserts, foamed
or otherwise, such as, for example, dashboards which, on being
tested, meet the highest requirements of the motor vehicle
manufacturers.
[0136] The invention will be understood better by virtue of the
illustrative and non-limiting examples described below.
EXAMPLE 1
[0137] This example illustrates a composition according to the
invention, subsequently used in the manufacture of foamed
dashboards.
[0138] The various components constituting the composition
according to the invention were the following:
[0139] component "a": 100 parts by weight of ethyleneoctene
(marketed by Dow under the reference Engage 8400);
[0140] component "c": 2 parts by weight of the mixture of the
grafting agent, which is vinyltrimethoxy-silane, associated with a
radical generator, which is dicumyl peroxide, the latter being
present in the master mix thus formed in a proportion of 8.5% by
weight relative to the grafting agent.
[0141] To these two components there are added, in parts by weight,
per 100 parts by weight of the cumulative total of the components
"a" and "b":
[0142] 2 parts by weight of carbon black;
[0143] 0.5 part by weight of the mold release agent, which is
magnesium stearate;
[0144] 0.1 part by weight of a flow aid, which is precipitated
silica (marketed by Degussa under reference Sipernat 22S), of
spherical form.
[0145] All the aforementioned components with the exception of the
flow aid were introduced into a twin-screw extruder brought to a
temperature of 220.degree. C. The polyolefin component "a" has been
introduced first in the extruder in order to be melted, and the
other components (grafting agents, generator of free radicals,
carbon black and demolding agent) have been introduced in a mixing
zone, downstream of the melting zone. Grafted and crosslinkable
granulates have then been produced from the mixture (melted) of the
various components.
[0146] The granules thus prepared were subjected to cryogenic
grinding, (in the presence of liquid nitrogen at a temperature of
between -100.degree. C. and -70.degree.C.).
[0147] On leaving the grinding the grafted and crosslinkable
thermoplastic polyolefin composition was collected in the form of
fine powder whose median particle size was approximately 400 mm and
the maximum particle size approximately 700 mm.
[0148] The grafted and crosslinkable polyolefin powder was then
introduced into a fast mixer (Henschel) together with the
abovementioned flow aid.
[0149] The hydrolysis catalyst dibutyl tin dilaurate (DBTL) was
introduced into this mixer on a support consisting of precipitated
silica, in a proportion of 0.1 part by weight per 100 parts by
weight of component "a".
[0150] Tests of the powder flow and of the production of skins by
means of this powder were performed on a nickel mold heated to a
temperature of between 200.degree. C. and 240.degree. C. and made
it possible to obtain skins of good quality for a dashboard to be
foamed, of uniform thickness (1 mm).
[0151] The skins thus obtained were subjected to crosslinking in an
appropriate vessel, into which water vapour was injected and whose
ambient temperature was 60.degree. C.
[0152] Foamed, unlacquered dashboards were then produced, which
were subjected to qualification tests for the motor vehicle
manufacturers; they were found to be very close to
specification.
EXAMPLE 2
[0153] This example illustrates another composition according to
the invention, subsequently used in the manufacture of foamed
dashboards. The various components constituting this composition
were the following:
[0154] component "a": 100 parts by weight of a mixture including 90
parts by weight of an ethylene-octene copolymer (marketed by Dow
under the reference Engage SM 8400) and 10 parts by weight of
linear low density polyethylene (LLDPE) (marketed by Neste under
reference NCPE 8030);
[0155] component "c": 2 parts by weight of the grafting agent,
which is vinyltrimethoxysilane associated with a radical generator,
which is dicumyl peroxide (the latter being present in the master
mix thus formed in a proportion of 8.5% by weight relative to the
grafting agent).
[0156] To these two components there is added, in parts by weight,
per 100 parts by weight of the cumulative total of the components
"a":
[0157] 0.1 part by weight of a flow aid which is a precipitated
silica of hydrophobic nature (marketed by Degussa under reference
Sipernat D10) of spherical form, onto which a silicone oil is
grafted.
[0158] All the components with the exception of the flow aid were
introduced into a twin-screw extruder brought to a temperature of
180.degree. C., the component "a" being introduced first in order
to be melted and the other components (grafting agent, generator of
free radicals) in a mixing zone down the melting zone. Thus,
microgranulates were produced from the melted mixture of the
various components.
[0159] On leaving the microgranulation the grafted and
crosslinkable thermoplastic polyolefin composition was collected in
the form of a fine powder whose median particle size was
approximately 400 mm and the maximum particle size approximately
500 mm.
[0160] Tests of powder flow and of the production of skins by means
of this powder were performed on a nickel mold treated with a mold
release agent, which is a mixture of aliphatic naphthas and heated
to a temperature of between 200.degree. C. and 240.degree. C. The
tests made it possible to obtain skins of good quality for a
dashboard to be foamed, of uniform thickness (1 mm).
[0161] The skins thus obtained were subjected to crosslinking in an
appropriate vessel, into which water vapour containing 5% by weight
of dibutyltin dilaurate (DBTL) was injected and the ambient
temperature of which was 60.degree. C. (duration of the treatment:
1 h 30 min). Foamed, unlacquered, dashboards were then made, which
were subjected to qualification tests for the motor vehicle
manufacturers: they were found to be very close to
specification.
[0162] The entire disclosure of all applications, patents and
publications, cited above and below, and of corresponding French
application No. 9604296, filed Apr. 1, 1996, are hereby
incorporated by reference.
[0163] The preceding examples can be repeated with similar success
by substituting the generically or specifically described reactants
and/or operating conditions of this invention for those used in the
preceding examples.
[0164] From the foregoing description, one skilled in the art can
easily ascertain the essential characteristics of the invention
and, without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions.
* * * * *