Note: Descriptions are shown in the official language in which they were submitted.
33
SPECIFICATION
INJECTION-MOLDING POLYOLEFIN COMPOSITION
Field of Technology
This invention relates to an injection-molding
polyolefin composition, and more specifically, to an
injection-m~lding polyolefin composition suitable for
obtaining injection-molded articles having excellent
abrasion resistance and impact strength and being free
from delamination.
Background Technology
Ultrahigh-molecular-weight polyolefins, for
example ultrahigh-molecular-weight polyethylene, have
higher impact strength, abrasion resistance, chemical
resistance, tensile strength, etc D than general-purpose
polyolefins such as general-purpose polyethylene, and have
found increasing applications as engineering plastics.
The ultrahigh-molecular-weight polyethylene, however, has
the defect that it is very difficult to mold by extrusion
or injection-molding because it has a much higher melt
viscosity and thus lower flowability than general-purpose
polyethylene.
At present, therefore, most articles from ultra-
high-molecular-weight polyethylene are produced by com-
pression molding, and only some articles such as rods are
produced by extrusion-molding at very low speeds.
When such ultrahigh-molecular-weight poly-
ethylene having low melt-flowability is molded by an
ordinary injection-molding method, shear broken streams of
the polymer always form during the filling of the polymer
in a mold cavity, and the resulting molded article under-
goes delamination like mica and cannot exhibit the excel-
lent properties of the ultrahigh-molecular-weight poly-
ethylene. Rather, its quality is inferior to that of a
molded article of general-purpose polyethylene.
Japanese Patent Publications Nos~ 300~7/1982 and
58010J1985 propose an injection-molding method free from
3~ 733
-- 2 --
causing delamination, in which the capacity of a mold
cavity is slightly increased before or after a resin is
filled in the cavity, and then the resin is compressed to
a predetermined volume. This method enabled production of
injection-molded articles free from delamination and
having the impact strength and abrasion resistance which
are the inherent characteristics of the ultrahigh-
molecular-weight polyethylene. To perform injection
molding by this method, however, it is necessary to use an
injection-molding machine equipped with a variable mold
cavity system, and the general injection-molding machine
for polyethylene cannot be used as it is.
On the other hand, for improving the melt-flow-
ability of ultrahigh-molecular-weight polyolefins, mixing
of an ultrahigh-molecular-weight polyolefin with a low to
a high molecular weight polyolefin was proposed.
Japanese Patent Publication No. 27,06~/1971
discloses an abrasion-resistant polyethylene resin com-
position comprising polyethylene having an average mol~
ecular weight of at least 500,000 and 20 to 50 % by weight
of polyethylene having a density of at least 0.940 and an
average molecular weight of 30,000 to 120,000.
Japanese Patent Publication No. 30,293/1972
discloses a process for producing a material for use in
that surface of agricultural machines, earth-moving
machines, etc. which comes into contact with the soil,
which comprises mixing screw-extrudable polyethylene
having a molecular weight of not more than 200,000 and
produced by the medium-pressure or the low-pressure method
with 10 to 30 % by weight of ultrahigh-molecular-weight
polyethylene having a molecular weight of about 1 million
and being incapable of screw-extrusion, melting the
mixture uniformly, and continuously molding the uniform
molten mixture by an extruder.
Japanese Patent Publication No. 41,309/1983
discloses a polyethylene composition comprising a mixture
. . .
.~
~Z~733
of 85 to 50 parts by weight of polyethylene having a
viscosity average molecular weight of 500~000 to 150,000
and 15 to 50 parts by weight of granular uitrahigh-
molecular-weight polyethylene having a viscosity average
molecular weight of at least 1 million and a particle size
smaller than 10 mesh.
Japanese Laid-Open Patent Publication No.
177,036/1982 discloses an ultrahigh-molecular-weight
polyethylene composition having improved moldability
comprising 100 part~ by weight of ultrahigh-molecular-
weight polyethylene having a molecular weight of at least
1 million and 10 to 60 parts by weight of low-molecular-
weight polyethylene having a molecular weight of 5,000 to
20,000. The specification of this patent document states
that the moldability of this ultrahigh-molecular-weight
polyethylene composition is such that in the production of
a slab having a thickness of 50 mm by a compr~ssion mold-
ing method, the molding cycle required was decreased to
-- 200 C x 2 hours while with the ult~rahigh-molecular-weight
polyethylene along a molding cycle of 200 C x 3 hours was
required; and that in a ram extrusion method, the speed of
pipe extrusion was increased from 5 cm/min. to 10 cm/min~
Japanese Laid-Open Patent Publication No.
126,446/1984 discloses an ultrahigh-molecular-weight
polyethylene resin composition comprising 9S to 50 parts
by weight of an ultrahigh-molecular-weight polyethylene
resin and 5 to 50 parts by weight of a general-purpose
polyolefin resin. The specification of this document
discloses a composition in which a silane-modified poly-
ethylene resin having a melt index of 2.5 or 5~0 g/10 min.as an actual specific example of the general-purpose
polyolefin resinO
Japanese Patent Publication No. 41,309/1983
discloses a polyethylene composition comprising a mixture
of 85 to 50 parts by weight of polyethylene having a
viscosity average molecular-weight of 500,000 to 150,000
~Z~733
-- 4 --
and 15 to 50 parts by weight of granular ultrahigh-
molecular-weight polyethylene having a visçosity average
molecular weight of at least 1 million and a particle size
smaller than 10 mesh. As stated in column 3, lines 17 28
of this document, the moldabil:ity of the ultrahigh-
molecular-weight polyethylene in this composition has not
improved, but the purpose of providing this composition is
to produce a molded article having excellent impact
strength by reducing anisotropy utilizing the granular
state of the ultrahigh-molecular-weight polyethylene.
The above polyethylesle resin compositions are
prepared by mixing ultrahigh-molecular-weight polyethylene
with polyethylene or other polyolefins having lower mol-
ecular weights.
Japanese Laid-Open Patent Publication No.
94,593/1979 (corresponding to V. S~ Patent No. 4,414,369)
discloses a process ~or producing a polyolefin having a
broad molecular weight distribution by polymerizing an
olefin in the presence of a solvent and hydrogen using a
Ziegler-type catalyst of enhanced activity supported on a
solid carrier to produce a polyolefin continuously, which
comprises continuously feeding a main olefin monomer and
at least one olefin comonomer under pressure using a
plurality of reactors in which a gaseous phase containing
an inert gas is present in the upper part of a first-stage
reactor, and copolymerizing these monomers, continuously
transferring the polymerization reaction mixture in which
high-molecular-weight polymer particles are dispersed in a
solvent to a second-stage reactor composed of a vertical
stirred vessel maintained at a lower pressure than the
first-stage reactor by differential pressures without
substantially separating part of the components in the
mixture and without using any forced transferring means,
continuously performing polymerization in the second~stage
stirred vessel in the presence of the main olefin monomer
and hydrogen while a gaseous phase exists in the upper
~2~733
part of the stirred vessel, thereby to form a polymer
having a lower molecular weight than in the first stage
polymerization, continuously withdrawing the polymeriza-
tion reaction mixture containing the resulting polymer
particles dispersed in a solvent from the second-stage
stirred vessel, and recovering the polymer.
Japanese Patent Publ;cation No. 10,724/1984
~corresponding to U. S. Patent No. 4,336,352) discloses a
process in which polyethylenes of different molecular
weights are produced by multi-stage continuous poly-
merization in at least three polymerization vessels con-
nected in series. The purpose of this process is to
produce polyethylene having excellent properties and
moldability with high productivity. With regard to
moldability, this process is for producing polyethylene by
extrusion molding, above all blow molding, with improved
die swelling. It does not relate to an improvement in an
injection-molded article. Even when a composition con-
taining not more than 10 % by weight of ultrahigh-
molecular-weight polyethylene and having an MI of 0.3 or
an intrinsic viscosity ~1 of 2.3 to 3~0 dl~g (corres-
ponding to an MI of about 0.2 to 0.8) is used in injection
molding, the content of ultrahigh-molecular-weight poly-
ethylene is as low as not more than 10 ~ by weight.
Japanese Patent Publication No. 11,349/1971
discloses a process which comprises producing 5 to 30 % by
weight of an ethylene/alpha-olefin copolymer having a
reduced specific viscosity of 30 to 5 in a first step, and
producing polyethylene or an ethylene~alpha-olefin co-
polymer having a reduced specific viscosity of 4.6 to 1.5
in a second stage to obtain a homogeneous mixture of it
with the polymer obtained in the first stage. The purpose
of this process is to improve moldability in the extrusion
molding of bottles, cables, pipes, etc. and does not
pertain to an improvement in an injection-molded article.
Japanese Laid-Open Patent Publication No.
~29~L733
-- 6 --
141,409/1982 discloses a process for producing poly-
ethylene which comprises polymerizing ethylene, or co-
polymerizing ethylene with an alpha-olefin, using a
catalyst comprising a reaction product between a magnesium
compound and a titanium halide and an organoaluminum
compound; wherein the following three polymerization
steps,
(a) a step of forming an ethylene polymer or
copolymer having an alpha-olefin content of
not more than 10 % by weight and an in-
trinsic viscosity [~] of 0O3 to 1.5,
(b) a step of forming an ethylene polymer or
copolymer having an alpha-olefin content of
not more than 30 % by weight and an in-
trinsic viscosity ~] of 1.5 to 7, and
(c) a step of forming an ethylene polymer orcopolymer having an alpha-olefin content of
not more than 30 % by weight and an in-
- trinsic viscosity ~] of 7 to 40-,-
are carried out in any desired sequence, and the poly-
merization reactions are carried out while adjusting the
ratio of the amounts of the polymers formed in step
(a):step (b~:step (c) to 1:0.1-1.5:0.01-1.2.
Japanese Laid-Open Patent Publication ~o.
8713/1983 discloses a process for producing an ethylenic
copolymer which comprises copolymerizing ethylene and an
alpha-olefin using a catalyst system obtained from ~A~ a
solid catalyst component containing at least magnesium,
halogen and titanium atoms and (B) an organoaluminum
compound in at least two steps, wherein
(1) in at least one step, 80 to 20 parts by
weight of a copolymer having a high-load
melt index o~ 0.03 to 10 g/10 min. and a
density of 0.890 g/cm3 to less than 0.905
g/cm3 is produced~
~2) in a second step, 20 to 80 parts by weight
, .
:'
733
of a copolymer having a melt index of L0 to 5000 g/10 min.
and a density of 0.905 to 0.940 g/cm3 is produced,
whereby a copolymer having a melt index of 0.02 to 30 g/10
min. and a density of 0.890 to 0.935 g/cm3 is produced.
This patent document discloses that the high-
load melt index was measured al: a temperature of 190 C
under a load of 21.6 kg in accordance with JIS K-6760.
Japanese Laid-Open Patent Publication No.
871~/1983 discloses a process for producing an ethylenic
copolymer using the same catalyst as described in the
above~cited Japanese Laid-Open Patent Publication NoO
8713/1983 by multisteppolymerization, wherein
(1) in at least one step, 80 to 20 parts by
weight of a copolymer of ethylene with
propylene and/or butene-l having a high-
load melt index of 0.03 to 10 g/10 min. and
a density of 0.890 to 0~935 g/cm3 is
produced, and
(2) in at least one other step, 20 to-80 parts -
by weight o~ a copolymer of ethylene and an
alpha-olefin having at most 12 carbon atoms
as a comonomer having a melt index of 10 to
5000 g/10 min. and a density of 0.89Q to
0.940 is produced, said alpha-olefin con-
taining at least 30 mole % of alpha-olefins
having 5 to 12 carbon atoms,
whereby a copolymer having a melt index of 0.02 to 30 g~l0
min. and a density of 0.890 to 0.936 g/cm3 is produced.
Japanese Laid-Open Patent Publication No.
120,605/1984 discloses a process for producing an ultra-
high-molecular-weight polyethylene resin with improved
moldability and processability, which comprises poly-
merizing monomers using a Ziegler-type catalyst comprising
a solid catalyst component containing a transition metal
ingredient and an organometallic catalyst component in at
least two steps having different monomer compositions and
~Z~733
hydroyen concentrations; wherein in at least one step,
propylene or monomers mainly comprising propylene, or
butene-l or monomers mainly comprising butene-l are poly-
merized in the presence of hydrogen to produce 2 to 60 ~
by weight, based on the entire polymer to be produced, of
a polypropylene or polybutene-l component, and in at least
one remaining step, ethylene or monomers mainly comprising
ethylene are polymeri~ed in th~e substantial absence of
hydrogen to produce 98 to 40 ~ by weight, based on the
entire polymer produced, of an ultrahigh-molecular-weight
polyethylene component.
British Patent No. 1,174,542 discloses a process
for the preparation of a homo- or co-polymer of ethylene by
a gaseous phase polymerization, or by a suspension poly-
merization in which the dispersion medium is in contactwith a gaseous phase, of ethylene or a mixture comprising
ethylene and up to 10 % by weight of an alpha-olefin that
contains from 3 to 15 carbon atoms, which process com-
prises preparing from 5 to 30 % by weight of the total
polymer in the presence of from 0 to 10 % of hydrogen,
calculated on the total volume of the gaseous phase, and
preparing from 70 to 95 % by weight of the total polymer
in the presence of from 20 to 80 ~ of hydrogen, cal-
culated on the total volume of the gaseous phase, both
stages of the polymerization being carried out at a tem-
perature within the range of from 50 to 120 C and a
pressure of up to 10 atmospheres gauge, in the presence of
a catalyst which is present in the first stage in an
amount sufficient for both stages, siad catalyst com-
prising
a) in the case of a suspension polymerization,from 0.05 to 0.3 millimol per litre of di-
spersion medium, or in the case of a poly-
merization in the gaseous phase, from O.OS to
0.3 millimol per 0.5 litre of reactor volume,
of a trivalent titanium compound that contains
chlorine, and
~Z'3~733
. g
b) from 0.1 to 3.0 millimols of aluminum per
litre of dispersion medium or reactor volume,
in the form of an aluminum trialkyl having
the general formula AlR, in which each R
represents a hydrocarbon radical that con-
tains;from 4 to 40 carbon atoms, or in the
form of the reaction product of an aluminum
trialkyl or an aluminium alkyl hydride with a
diolefin that contains fro~ 4 to 20 carbon
atoms.
Japanese Laid-Open Patent Publication No.
275,313/1986 laid-open after the priority date of the
present application discloses an ultrahigh-molecular-
weight polyethylene composition having improved
injection-moldability which has an intrinsic viscosity,
determined in decalin at 135 C, of 10 to 30 dl/g and
obtained by polymerization reaction in at least two steps
mentioned below.
(First step)
A step of forming 50 to 99.5 parts by weight o~
polyethylene having an intrinsic viscosity,
determined in decalin at 135 C, of 12 to 32
dl/g by polymerizing ethylene in the absence of
hydrogen or in a lowered hydrogen concentration
with a catalyst comprising a solid catalyst
component containing at least Mg, Ti and/or V
and an organometallic compound.
5Second step)
A step of forming 50 to 0.5 parts by weight of
polyethylene by polymerizing ethylene in a
hydrogen concentration increased over that in
the first step.
Likewise~ European Laid-Open Patent Publication
No. 0186995 laid-open after the priority date of the
present application discloses a process for producing
ultrahigh-mo:Lecular-weight polyethylene having an
~LZ9~3~3
-- 10
intrinsic viscosity, determined in decalin at 135 C, of
10 to 30 dl/g by polymerization in at least two steps,
which comprises
(a) a first step of forming 70 to 99.5 parts by
weight of polyethylene having an intrinsic
viscosity~ determineld in decalin at 135 C, of
12 to 32 dl/g by polymerizing ethylene monomer
in the absence of hydrogen or in the presence of
hydrogen in a low concentration using a combina-
tion catalyst comprising a solid component
containing at least ;magnesium, titanium and/or
vanadium and an organometallic compounc~, and
~b) a second step of forming 30 to 0.5 parts by
weight of polyethylene having an intrinsic
viscosity, determined in decalin at 135 C, of
0.1 to S dl/g by polymerizing a freshly fed
ethylene monomer in the presence of hydrogen in
a high concentration.
--- It is an object of this invention to provide an
injection-molding polyolefin composition comprising an
ultrahigh-molecular-w~ight polyolefin component and having
very good injection-moldability.
Another object of this invention is to provide
an injec~ion-molding polyolefin composition which is
suitable for obtaining an injection-molded article free
from delamination without impairing the inherent excellent
mechanical properties, such as high abrasion resistance,
of the ultrahigh-molecular-weight polyolefin.
Other objects of the invention along with its
advantage will become apparent from the following descrip-
tion.
In the present invention, the ultrahigh-mol-
ecular-weight polyolefin has an intrinsic viscosity [~]u'
measured in decalin at 135 C, of 10 to 40 dl/g, prefer-
ably 15 to 35 dl/g.
The other low-molecular-weight or high-molecular-
129~733
-- 11 --
weight polyolefin, as referred to in this invention, has
an intrinsic viscosity 17]h, measured in decalin solvent
at 135 C, of less than 10 dl/g, preferably 0.1 to 5 dl/g,
more preferably 0.5 to 3 dl/g.
The polyolefin in this invention is a homo-
polymer or copolymer of an alpha-olefin such as ethylene,
propylene, l-butene, l-pentene, l-hexene, 1-octene, 1-
decene, l-dodecene, 4-methyl-1-pentene and 3-methyl-1-
pentene. The homopolymer of ethylene or a copolymer
comprising ethylene as a main component and another alpha-
olefin of the type exemplified above is desirable.
The quantitative proportions of the ultrahigh-
molecular-weight polyolefin and the low-molecular-weight
or high-molecular-weight polyolefin are such that the
ultrahigh-molecular-weight polyolefin accounts Eor 15 to
40 % by weight of the total weight of the two polymer or
the low-molecular-weight or high-molecular-weight poly-
olefin accounts for 85 to 60 ~ by weight of the total
weight of the two polyolefins. The preferred quantitative
proportions are such that the proportion of the ultra-
high-molecular-weight polyolefin is 20 to 35 % by weight
based on the total weight of the two polyolefins.
The injection-molding polyolefin composition of
this invention comprises the ultrahigh-molecular-weight
polyolefin and the low-molecular-weight or high-mol-
ecular-weight polyolefin in the above quantitative pro-
portions~ The injection-molding polyolefin composition of
this invention has an intrinsic viscosity [~]c' measured
in decalin solvent at 135 C, of 4.0 to 10 dl/g and a
melting torque T ~kg-cm) of not more than 4.5 kg-cm. The
melting torque T is measured by using a JSR curelastometer
(made by Imanaka Machine Industry K. K.) under conditions
involving a temperature of 240 C, a pressure of 5 kg/cm2,
an amplitude of 135 and a frequency number of 6 CPM.
The injection-molding polyolefin composition of
this invention preferably has an l~Jc of 4 to 9 dl/g.
1~473~
- 12 -
The injection-molding polyolefin composition of
this invention may be prepared by blending the ultrahigh-
molecular-weight polyolefin and the low-molecular-weight
or high-molecular-weight polyolefin in the proportions
mentioned above. It has been found, however, that it can
be advantageously prepared by a multistep polymerization
method to be described below which comprises polymerizing
olefins in the presence of a catalyst formed from a
specific highly active solid titanium catalyst component
and an organoaluminum compound catalyst component. The
multistep polymerization method is carried out by poly-
merizing olefins in a multiplicity of stages in the pre-
sence of a Ziegler-type catalyst formed from (A~ a highly
active titanium catalyst component containing magnesium,
titanium and halogen as essential ingredients and (B) an
organoaluminum compound catalyst component. Specifically,
in at least one polymerization step, an ultrahigh-mol-
ecular-weight polyolefin having an intrinsic vi~cosity
t~]u f 10 to 40 dlJg is formed, and in-another poly-
merization, an olefin is polymerized in the presence ofhydrogen to give a low-molecular-weight or high-molecular-
weight polyolefin having an intrinsic viscosity t~]h of
0.1 to 5 dl/g is formed.
The Ziegler-type catalyst used is basically a
catalyst having specific properties formed from a solid
titanium catalyst component and an organoaluminum compound
catalyst component. Preferably, the solid titanium cata-
lyst component is, for example, a highly active fine
powdery catalyst component which has a narrow particle
size distribution and an average particle diameter of
about 0.01 to 5 micrometers and in which several fine
spherical particles adhere firmly to one another. The
highly active fine powdery titanium catalyst component can
be prepared, for example, by the method of preparing the
solid titanium catalyst component disclosed in Japanese
Laid-Open Patent Publication No. 811/1981 in which at a
12~1~733
time of precipita~ing a solid product by contacting a
magnesium compound in solution with a titanium compound in
solution, the precipitating conditions are strictly ad-
justed. For example, in the method disclosed in the
above-cited Japanese Laid-Open Patent Publication which
involves mixing a hydrocarbon solution of magnesium
chloride and a higher alcohol with titanium tetrachloride
at low temperatures, and heating the mixture to about 50
to 100 C to precipitate the solid product, the pre-
cipitation is carried out in the presence of a slightamount, for example about 0.01 to 002 mole, per mole of
ma~nesium chloride, of a monocarboxylic acid ester with
strong stirring. If required, the product is washed with
titanium tetrachloride. Thus, a solid catalyst component
having satisfactory activity and particle form can be
obtained. This catalyst component contains about 1 to
about 6 % by weight of titanium, and has a halogen/-
titanium atomic ratio of abo~t 5 to about 90 and a
magnesium/titanium tatomic ratio3 of about 4 to about 50.
Fine spherical particles having a narrow par-
ticle size distribution and an average particle diameter
of usually 0.01 to 5 micrometers r preferably 0.05 to 3
micrometers, which are obtained by subjecting a slurry of
the solid titanium ca~alyst component prepared as above to
high-speed shear treatment are also preferably used. For
high-speed shear treatment, a method is employed in which
the slurry of the solid titanium catalyst component is
treated with a commercial homomixer in an inert gaseous
atmosphere for a suitable period of time. To prevent a
reduction in catalyst performance at this time, there may
also be employed a method in which an organoaluminum
compound is added in a proportion equimolar to titanium.
The treated slurry may be filtered through a sieve to
remove coarse particles. By these methods, highly active
fine powdery titanium catalyst components can be obtained.
~2~9~7~3
-- lDL -- J
The injection-molding polyolefin composition of
this invention may be produced by slurry polymerization of
olefins in at least two steps at a temperature of usually
0 to 100 C in a hydrocarbon medium such as pentane,
hexane, heptane or kerosene using the highly active fine
powdeey titanium catalyst component and an organoaluminum
compound catalyst component optionally in combination with
an electron donor. Examples of the organoaluminum com-
pound catalyst component are trialkyl aluminums such as
triethyl aluminum or triisobutyl aluminum, dialkyl
aluminum chlorides such as diethyl aluminum chloride or
diisobutyl aluminum chloride, alkyl aluminum sesqui-
chlorides such as ethyl aluminum sesquichloride, or
mixtures of theser
A multistep polymerization apparatus consisting
of at least two polymerization vessel usually connected in
series is used in the multistep polymerization process of
olefins, and the polymerization is carried out in two
steps, three steps, ... or n steps. The multistep poly-
merization may also be carried out batchwise in a single
polymerization vessel. It is necessary, in at least one
polymerization vessel in the multistep polymerization
process, to form a specific amount of an ultrahigh-
molecular-weight polyolefin. The step in which to form
the ultrahigh-molecular-weight polyolefin may be a first
polymerization step or an intermediate polymerization step
or may comprise two or more stages. From the viewpoint of
the polymerization treatment operations and the control of
the properties of the resulting polyolefin r it is pre-
ferred that the ultrahigh-molecular-weight polyolefin be
formed in the first polymerization step. Preferably, in
the above polymerization step, 15 to 40 % of olefins to be
polymerized in all steps are polymerized to give an ultra-
high-molecular-weight polyolefin having an intrinsic
viscosity ~]u ~measured in decalin solvent at 135 C) of
10 to 40 dl/g; and further, by polymerizing 18 to 37 % by
~z~a733
- 15 -
weight, especially 21 to 35 % by weight, of oléfins to be
polymerized in the entire polymerization steps, an ultra-
high-molecular-weight polyolefin having an intrinsic
viscosity [~]u f 15 to 35 dl/g, especially 18 to 30 dl/g,
is formed.
In the multistep polymerization process, the
polymerization in the step of forming the ultrahigh-mol-
ecular-weight polyolefin may be carried out in the pre-
sence of a catalyst composed o~E the highly active titanium
catalyst component ~A) and the organoaluminum compound
catalyst component (B). The polymerization may be carried
out by a vapor-phase polymerization method or a liquid-
phase polymerization method. In any case, in the step of
forming the ultrahigh-molecular-weight polyolefin, the
polymerization reaction can be carried out in the presence
of an inert medium as required. For e~ample, the vapor-
phase polymerization method may be carried out in the
presence of a diluent composed of an inert medium if
required. The liquid-phase polymerization method may be
carried out in the presence of a solvent composed of an
inert medium as required.
In the polymerization step of forming the ultra-
high-molecular-weight polyolefin, it is preferred to use
the highly-active titanium catalyst component (A) in an
~mount of about 0.001 to about 20 milligram atoms, es-
pecially about 0.005 to about 10 milligram-atoms, as
~itanium atoms per liter of the medium, and the organo-
aluminum compound catalyst component ~B~ in an amount
~orresponding to an Al/Ti atomic ratio of from about 0.1
to about 1,000, especially from a~out 1 to about 500. The
temperature of the polymerization step of forming the
ultrahigh-molecular-weight polyolefin is usually about -20
to about 120 C, preferably about 0 to about 100 C,
especially preferably from about 5 to about 95 C. The
pressure used in the polymerization reaction is within a
range of pressures under which the liquid-phase
4~
polymerization or the vapor-phase polymeri 2 ation is pos-
sible at the above temperatures. For example, it is
atmospheric pressure to about 100 kg/cm2, preferably from
atmospheric pressure to about 50 g/cm2. The polymeriza-
tion time in the polymerization step is set such that theamount of the pre-polymerized polyolefin formed is at
least about 1000 g, preferably at least about 2000 g, per
milligram of Ti in the highly active titanium catalyst
component. To form the ultrahigh-molecular-weight poly-
olefin in the above polymerization step, the polymeriza-
tion reaction is preferably carried out in the absence of
hydrogen. After the polymerization reaction, the polymer
may be isolated in an atmosphere of an inert medium and
stored.
Examples of the inert medium that can be used in
the polymerization step of forming the ultrahigh-molecular-
weight polyolefin include aliphatic hydrocarbons such as
propane, butane, pentane, hexane, heptane, octane, decane
and kerosene, alicyclic hydrocarbons such as cyclopentane
and cyclohexane, aromatic hydrocarbons such as ~enzene,
toluene and xylene, halogenated hydrocarbons such as
dichloroethane, methylene chloride and chlorobenzene r and
mixtures of these. Use of the aliphatic hydrocarbons is
especially preferred.
In the polymerization step of forming a poly-
olefin having an intrinsic viscosity of less than 10 dl~g
in the process used in this invention, the remaining
olefins are polymerized in the presence of hydrogen. If
this polymerization step is the first polymerization step,
the aforesaid catalyst composed of the highly active
titanium catalyst compnent ~A) and the organoaluminum
compound catalyst component ~B) is fed. If this poly-
merization step is the second or subequent step, the
catalyst contained in the polymerization product solution
formed in the preceding step may be used directly. Or as
required, the highly active titanium catalyst component
~.;2 9~7~3
(A) and/or the organoaluminum compound catalyst (B) may be
additionally supplied. The proportion of the starting
olefin polymerized i~ this polymerization step is 5 to
70 ~ by weight, preferably 20 to 60 % by weight, es-
pecially preferably 25 to 55 % by weight, based on theentire olefin components polymerized in the entire poly-
merization steps.
The proportion of hydrogen fed in this poly-
merization step is usually 0.01 to 50 moles, preferably
O.OS to 30 moles, per mole of the olefin ~ed in this step.
Preferably, the concentration of the catalyst
components in the polymerization product solution in the
polymerization vessel in this polymerization step is
adjusted to about 0.001 to about 0.1 milligram atom,
preferably about 0.05 to about 0.1 milligram-atom, cal- ;
culated as titanium atoms in the above treated catalyst,
and the Al/Ti atomic ratio in the polymerization system is
adjusted to from about 1 to about 1000, preferably from
about 2 to about 500. For this purpose, the organo-
aluminum compound catalyst component ~B) may, as required,
be additionally used. Hydrogen, electron donors, halo-
genated hydeocarbons, etc. may be caused to be present in
the polymerization system in order to adjust the molecular
weight, molecular weight distribution, etc.
The polymerization temperature is preferably
within temperatures at which slurry polymerization or
vapor-phase polymerization is possible~ and is at least
about 40 C, especially about 50 to about 100 C. The
polymerization pressure that can be recommended is atmos-
pheric pressure to about 100 kg/cm2, especially pre~erably
atmospheric pressure to about 50 kg/cm2. The polymeriza-
tion time may desirably be such that the amount of the
polymer formed is at least about 1000 g, especially pre-
ferably at least about 5000 g, per milligram-atom of
titanium in the titanium catalyst component.
This step may be carried out by a vapor-phase
.
~ l z~733
- 18 -
polymerization method or by a liquid-phase polymerization
method. Of course different polymerization conditions may
be employed in different polymerization steps. As the
liquid-phase polymerization method, a slurry suspension-
polymerization method is preferably employed. In anycase, the polymeri~ation reaction in the above polymeriza-
tion step is carried out in the presence of an inert
medium solvent. For example, t:he vapor phase polymeriza-
tion may be carried out in the presence of a diluent
composed of an inert medium ancl the liquid-phase slurry
polymerization may be carried out in the presence of an
inert solvent. Examples of the inert medium may be the
same as the inert media exemplified with regard to the
step of forming the ultrahigh-molecular-weight polyolefin.
The polymerization reaction is carried out so
that the polyolefin composition obtained in the final
polymerization step has an l~]c of usually 4.0 to 10 dl/g,
preferably 4 to 9 dl/g, and a melting torque of not more
than 4.5 kg-cm.
The multistep polymerization method may be
carried out batchwise, semicontinuously or continuously.
Olefins to which the multistep polymerization
method can be applied may be alpha-olefins such as
ethylene, propylene, l-butene, l-pentene, l-hexene, 1-
octene, 1 decene, l-dodecene, 4~methyl-1-pentene and
3-methyl-1-pentene. It may be applied to the production
of homopolymers of these alpha-olefins, or the production
of copolymers of at least two of theseO Preferably, the
method of this invention is applied to the production of
an ethylenic polymer such as an ethylene homopolymer or a
copolymer of ethylene as a major component and other
alpha-olefin.
The injection-molding polyolefin composition of
this invention may contain additives normally used for
addition to polyolefins, such as thermal stabilizers,
weatherability stabilizers, pigments~ dyes, lubricants,
~ ~94733
-- 19 --
inorganic fillers or reinforcing agents such as carbon
black, talc or glass fibers, fire retardants and neutron
shielding agents within the range which does not impair
the objects of this invention.
E~fects of the Invention
The injection-molding polyolefin composition of
this invention can be injection-molded without substan-
tially impairing the inherent excellent mechanical pro-
perties (such as abrasion resistance), chemical resist-
ance, lubricity and non-water-absorption of ultrahigh-
molecular-weight and without molding failure and delami-
nation in a molded article which are the defects of
ultrahigh-molecular-weight polyolefin in the case of using
a general-purpose injection-molding machine. Accordingly
it can be conveniently used in various applications in-
cluding not only bearings, gears and cams but also sliding
members in household electrical appliances, and office
automation machines in which conventional general-purpose
polyolefins cannot ~ind use because of poor abrasion
resistance~
The following examples illust-rate the present
invention in more detail. The invention, however, should
not be restricted to these examples unless it departs from
its scope.
The intrinsic viscosity [~h f the low-mol-
ecular-weight or high-molecular-weight polyethylene in the
polyethylene compositions in the following examples was
calculated by the following procedure.
~1) The density du of the ultrahigh-molecular-
~eight polyethylene and the density dc of the final poly-
e~hylene composition were measured, and the density dh of
the low-molecular-weight or high-molecular-weight poly-
ethylene is calculated in accordance with the following
e~uation.
dc - (du x a)
dh =
~25~4~33
- 20 -
wherein dh, dc and du are as defined above, a is
the proportion of the ultrahigh-molecular-weight
polyethylene in the final polyethylene composi-
tion, and b is the proportion of the low-mol-
ecular-weight or high-molecular-weight poly-
ethylene in the final polyethylene composition.
(2) Low-molecular-weight or high-molecular-
weight polyethylenes having various intrinsic viscosities
were produced under substantially the same polymerization
conditions (including the monomer composition and cata-
lyst) as the conditions for producing the low-molecular-
weight or high-molecular-weight polyethylene of which
density d was calculated as above except that the partial
hydrogen pressure was varied~ The relation between the
densities and the intrinsic viscosities [~] of the result-
ing polyethylenes was determined.
The density d determined in (1) above of the
low-molecular-weight or high-molecular-weight polyethylene
- in the polyethylene composition of this invention is taken
as the density in the above relation, and the intrinsic
viscosity [~]h is determined from the above relation.
- ~3~ The density of each of the samples was
determined by the following procedure. Two sets of a
stacked structure composed of an aluminum plate 13 x 300 x
300), an asbestos plate (5 x 250 x 250), a stainless plate
(3 x 220 x 220) and a polyester film stacked in this order
were prepared. One set was placed on the heating plate of
a compression molding machine so that the polyester film
was directed upward. A molding frame (2 x 200 x 200) was
placed on it and the other set was superimposed on the
frame so that the polyester film faced downward.
The sample was put in the frame and melted at
190 C+2 C without pressure, and then molded under-a
pressure of 300 kg/cm2 for 5 minutes. Thereafter, the
sample was cooled to 60 C at a cooling rate of 15+2 C/
min., and taken out. The sample was maintained for 1 hour
- ~25~L733
in a constant-temperature oil vessel at 120-~0.2 C and
cooled to room temperature at a cooling rate of 1.5 C/
min~ over the course of 1 hour. After cooling, the sample
was taken out, and left to stand at room temperature for 1
hour. Then, the density of the sample was measured by a
density gradient method (ASTM D-1505~.
Example 1
Preparation of a catalyst sample
Anhydrous magnesium chloride (47.6 g; 0.5 mol),
0.25 liter of decane and 0.23 liter (1.5 mol) of 2-ethyl-
hexyl alcohol were heated at 130 C for 2 hours to form a
uniform solution, and then 7.4 ml (50 mmol) of ethyl
benzoate was added. The uniform solution was added drop-
wise with stirring over 1 hour to 1.5 liters of TiC14
maintained at -5 C. The reactor used was a 3-liter
separable glass flask, and the stirring speed was adjusted
to 950 rpmO After the addition, the temperature was
raised to 90 C, and the reaction was carried out at 90 C
for 2 hours-. After the reactioni-the solid portion was
collected by filtration, and washed fully with hexane to
give a highly active fine powdery titanium catalyst com-
ponent containing 3.8 % by weight of titaniu~ atoms.
Polymerization
Continuous polymerization was carried out by
using a continuous two-step polymerization apparatus
consisting of two 220-liter polymerization vessel con-
nected to each other in series. To the first-step poly-
merization vessel (to be abbreviated as the polymerization
- vessel 1) in the continuous two-step polymerization ap-
paratus 130 liters of n-hexane was added, and the tem-
perature was raised to 60 C. n-Hexane t35 liters/hr),
triethyl aluminum t45 mM/hr), the titanium catalyst com-
ponent tl.0 milligram-atom/hr as titanium atoms~ and
ethylene gas t4.3 Nm3/hr) were continuously introduced
into the polymerization vessel 1. By using a pump, the
resulting polymerization reaction mixture slurry in the
;~294733
- 22 -
polymerization vessel 1 was fed to the second-step poly-
merization vessel ~to be referred to as the polymerization
vessel 2), and the level of the polymerization vessel 1
was maintained at 130 liters. The polymerization pressure
in the polymerization vessel 1 at this time was 4.7 kg/
cm2_G .
In addition to the polymerization mixture in
slurry sent from the polymerization vessel 1, n-hexane and
ethylene gas were continuously introduced into the poly-
merization vessel 2 at a rate of 25 liters/hr and 11.2Nm3/hr, respectively. A moder,ate amount of hydrogen gas
was added to adjust the composition of the vapor phase of
the vessel 2 to an ethylene/hydrogen mole ratio of 1000:30O
The slurry formed by the polymerization reaction was
intermittently withdrawn Erom the bottom of the poly-
merization vessel 2 by using a timer valve, and the level
of the polymerization vessel 2 was maintained at 120
liters. In the polymerization vessel 2, the polymeriza-
tion temperature was 85 C and the polymerization pressure
was 7.2 kg/cm . The resulting polymer was separated from`
the solvent by a centrifuge, and dried in a stream of N2.
The 17] and contents of the components of the
resulting polyolefin composition, the [~1 of the com-
position and its melting torque T were measured by the
following methods.
t~]: intrinsic viscosity measured in decalin
solvent at 135 C
Melting torque (T): The stress torque of the
sample in the molten state which ~as measured~by using a
JSR curelastometer (made by Imagawa Machine Industry
R. K.~ under conditions involving a temperature of 240 C,
a pressure of 5 kg/cm , an amplitude of +3 and a frequency
of 6 CPM.
Injection mold_ng
One hundred parts by weight of the polyolefin
composition was mixed with 0.1 part by weight of tetra-
733
kistmethylene(3,5-di-tert-butyl~4-hydroxy3hydrocinnamate]-
methane (IRGANOX 1010, a tr ~ for a product of Japan
Ciba-Geigy Co.), 0.1 part by weight of tetrakislmethylene-
(2,4-di-tert-butylphenyl)-4,4-biphenylenediphosphite~
(Sandostab P-EPQ, a- ~ ~ for a product of Sandoz AG)
and 0.12 part by weight of calcium stearate (a product of
Nippon Oils and Fats Co., Ltd.) by a Henschel mixer.
Then, the mixture was molded into a rectangular plate ~130
x 120 x 2 mm) and cut to prepare test samples~
Injection-molding conditions
Cylinder temperature (C): 200/230/270/270
Injection pressure (kg/cm2): primary/secondary
= 1000/~00
Cycle (seconds): primary/secondary/cooling
= 5/3/25
Injecting speed (-): 2/10
Screw rotating speed (rpm): 97
Mold temperature (C): water cooled ~32 C)
- - The properties of the samples were evaluated by
the following methods.
Tensile test
The tensile test was conducted in accordance
with ASTM D-638 except that a test specimen having the
shape of ASTM No. 4 was used and the tensile speed was set
at 50 mm/min. The stress at yield (YS: kg/cm2), tensile
strength at break (TS: kg/cm2) and elongation at break
(EL: %) of the test sample was determined.
Izo impact strength (kg-cm/cm?
Measured in accordance with ASTM D256 on a
notched test sample.
Olsen rigidity (kg/cm2?
Measured in accordance with ASTM D747.
Friction-abrasion test
The test was conducted by using a Matsubara-type
friction-abrasion tester (made by Toyo Baldwin Company)
under a compression load of 3.4 kg/cm2 at a friction speed
~2~ 3
- 24 -
of 30 m/min. for 24 hours, and the amount of loss by
abrasion and the coefficient of friction were determined.
Appearance
The surface condition of a molded rectangular
plate was visually observed and rated on the scale of the
following four grades.
(A): No flowmark existed.
~B): Slight flowmarks were observed~
~C): Flowmarks were! observed.
~D): Flowmarks exis;ted throughout.
Delamination
The end of a molded sample was ~haven by a
knife, and delamination was evaluated on the scale of the
following four grades.
lD): The surface was easily peeled.
tC): The surface was slightly peeled.
~B): The surface was hardly peeled.
(A): The surface was not peeled at all.
Examples 2-6
In each run, Example 1 was repeated except that
the polymerization conditions were changed as indicated in
Table 1, and the molecular weights of the ultrahigh-
molecular-weight polyethylene and the low-molecular-weight
or high-molecular-weight polyethylene and the ratio
between the amounts of the ultrahigh-molecular-weight
polyethylene and the low-molecular-weight or high-mol-
ecular-weight polyethylene were changed. The results are
shown in Table 2.
Referential Examples 1-2
Commercial ultrahigh-molecular-weight poly-
ethylene tHizex MillionR240M, a ~ e-for a product of
~ Mitsui Petrochemical Industries, Co., Ltd.) was injection-
molded by the same method as in Comparative Example 3
using an injection-molding machine having a screw of the
three-stage compression type.
Furthermore, commercial injection-molding high-
~2~4~3
5 - ~ rqden~A~
density polyethylene (Hize*~ 2208J, a ~de~ for a
product of Mitsui Petrochemical Industries, Ltd.) was
injection-molded by the same method as in Example 1.
The results are also shown in Table 2.
~L294733
-- 26 --
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