Note: Descriptions are shown in the official language in which they were submitted.
~.~768i,~)
ENLARGED POWDER PARTICLES OF CRYSTALLINE
POLYOLEFIN AND METHOD OF PRODUCING THE S~IE
The present invention relates to enlarged fine powder
particles of crystalline polyolefin prepared by suspension
polymerization or gas phase polymerization and, also,
relates to a method of enlarging fine powder particles of
crystalline polyolefin at relatively low energy.
Crystalline polyolefin is generally used in the form
of pellets due to their easy handling properties when the
crystalline polyoelfin is utilized in conventional molding
techniques such as various types o~ extrusion molding,
injection molding and th~ ~. These pellets are produced
by extruding resins through die-holes by using various type
extruders, followed by pelletizing by using a strand cut
method or an underwater cut method. However, when the
polyolefin is obtained in the form of fine powder particles
as prepared ~y suspension polymerization or gas phase
polymerization, the energy consumption required for the
pelletizing step comprises a ma~or portion of the energy
cost for the production of the polyolefin in the form of
pellets. Especially when high-molecuIar weight resins are
pelletized through melt extrusion, the energy consumption
is remarkably high. Accordingly, the energy-saving in the
pelletizing step is eargerly desired in the art due to the
recent rapid increase in the price of energy.
Known processes for pelletizing thermoplastic resin
~176810
powder particles without using an extruder include, for
example, a powder compacting process in which powder
particles are pelletized under compression. However, since
the particle strength of the pellets so obtained is not
su~ficient, there is a problem in that the pellets are
likely to be broken or crushed during transportation. In
order to obviate this problem, a binder can be used to
improve the particle strength. However, the desired resin
properties are undesirably changed by the use of a binder.
Furthermore, we proposed a preparation method of
uniformly dispersed powder particles in Japanese Laid-Open
Patent Application No. 48-11336/73 in which a mixture of
the powder particles of crystalline thermoplastic resins
obtained by suspension polymerization with inorganic
5 fil lerR is stirred at a temperature of at lea~t
crystallization temperature but less than a mutual welding
t~mperature as defined hereinbelow. Eiowever, according to
this proposed method, the powder particles are not enlarged
due to the fact that the powder particles are mixed with
one another at a temperature of less than the mutual
welding temperature~ In addition, it was believed
heretofore that powder particles readily become massive
bulk material or conglomerates when they are stirred at a
temperature higher than the mutual welding temperature.
However, we have found that the high-molecular weight
crystalline polyolefine has a large elasticity when it is
melted and does not readily cause the viscous flow under no
load.
~768~0
-- 3 --
Accordingly, an object of the present invention is to
provide enlarged powder particles of crystalline polyolefin
;prepared by suspension polymerization or gas phase
polymerization.
Another object of the present invention is to
provide a method of enlarging powder particles of
crystalline polyoelfin obtained from suspension poly-
merization or gas phase polymerization at low energy
consumption without using an extruder.
Other objects and advnatages of the present invention
will be apparent from the description set forth
hereinbelow.
In accordance with the pre8ent invention, there are
provid~d enlarged powder par'ci~l~ of crystallin0
15 polyolefin obtained from the welding of crystalline
polyolefin powder particles with one another, said
crystalline polyolefin powder particles having an
average partice size of smaller than 30 meshes and
a viscosity-average molecular weight of at least
20 50,000 and being prepared by one-step or multi-step
suspension polymerization or gas phase polymerization
and the particle size of the enlarged powder particles
being larger than that of the starting crystalline
polyolefin powder particles.
In accordance with the present invention, there is
also provided a method of enlarging powder particles of
crystalline polyolefin having an average particle size of
smaller than 30 meshes and a viscosity-average molecular
1~76t310
-- 4
weight of at least 50,000 and being prepared by one-step or
multi-step suspension polymerization or gas phase
polymerization comprising the steps of:
(i) treating said crystalline polyolefin powder
particles under a mutual welding temperature condition to
enlarge the crystalline polyolefin powder particles, while
the powder particles being subjected to the rate of mutual
travel sufficient to prevent the conglomeration of the
powder particles due to the complete mixing of the molten
powder particles and, then,
(ii) cooling the resultant crystalline olefin powder
particles.
The present invention will be better understood from
the description set forth below with reference to th~
accompanying drawings in which:
Fig. 1 is a phase contrast photomicrograph
(magnified 30 times) of the high-density polyethylene
powder particles having a viscosity-a~erage molecular
weight of 280,000 used in Example 1 hereinbelow at room
temperature;
Fig. 2 is a phase contrast photomicrograph
(magnified 30 times) of the polyethylene powder particles
of Fig. 1 after allowing it to stand for 15 minutes at a
temperature of 150C;
Fig. 3 is a phase contrast photomicrograph
(magnified 30 times) of the high-density polyethylene
powder particles having a viscosity-average molecular
weight of 30,000 used in Comparative Example 1 hereinbelow;
117615110
-- 5 --
Fig. 4 i5 a phase contrast photomicrograph
~magnified 30 times) of the polyethylene powder particles
of Fig. 3 after allowing it to stand for 30 seconds at a
temperature of 150C;
Fig. 5 is a scanning type electron photo-
micrograph (magnified 30 times) of the enlarged powder
particles obtained in Example 1 hereinbelow;
Fig. 6 is a ccanning type electron photo-
micrograph (magnified 30 times) of the enlarged powder
particles obtained in Example 2 hereinbelow; and
Fig. 7 is a scanning type electron photo-
micrograph (magnified 30 times) of the cross-section of the
enlarged powder particles of Fig. 6.
The cry~talline polyolefins used in the present in-
vention include, for eY.ample, high-density polyethylene,
me~ium-density polyethylene, low-density polyethylene,
crystalline polypropylene, polybutene, poly(4-methyl-
pentene-l) and the like as well as crystalline ethylene-pro-
pylene copolymer, ethylene-~-olefin copolymer, pro-
pylene-~-olefin copolymer, ethylene-butadiene copolymer and
the like. These crystalline polyolefins can be prepared in
the form of powder by using an anionic coordination poly-
merization catalyst such as a Ziegler catalyst according to
a suspension polymerization process or gas phase polymeri-
zation process. These crystalline polyolefins can be usedalone or in any mixture thereof in the present invention.
The crystalline polyolefins used in the present
invention are fine powder particles having an average
117~810
-- 6 --
particle size of smaller than 30 meshes. The term "mesh"
used herein means a Tyler mesh. Since these powder
particles generally have a low bulk density, these powder
partieles have disadvantages that the transportation cost
is high, the working conditions in the molding process
become worse due to the flying of the dust particles and
- the dcrease in the productivity is caused due to the fact
that the feeding of the powder particles into an extruder
is poor and non-uniform. Therefore, these powder particles
cannot be used in the molding operation in the same way as
the pellets can be used.
The crystalline polyolefin powder particles used in
the present invention are those which have a viscosity-
-average molecular weight of 5D,000 or more, more
lS preferably lS0,000 or more. In the case where the
viscosity-average molecular weight of the crystalline
polyolefin is smaller than 50,000, the powder particles
readily cause a viscous flow to form massive bulk material
or conglomerates in the form of glutinous rice jelly. Ac-
cordingly, the desirable viscosity-average molecular weight
of the crystalline polyolefin is as high as possible and
ultra high molecular weight polyethylene powder particles
even having a viscosity-average molecular weight of
1,000,000 or more can be enlarged. However, it should be
noted that a higher temperature and a longer time are
required in the enlargement of the powder particles, as the
viscosity-average molecular weight of the powder particles
becomes high and, also, that sufficient rate or pressure
1176~3~0
-- 7 --
should be imparted to the powder particles to obtain
enlarged powder particles having a high bulk density.
The powder particles which are relatively easy to
enlarge are the powder particles of the crystalline
S polyolefin prepared by suspension polymerization or gas
phase polymerization comprising (i) 40 to lO0~ by weight of
a high molecular weight component of which individual
particles do not cause viscous flow deformation upon
melting even when they are heated, under no load, to a
temperature of at least the melting point thereof but less
than 20C higher than the melting point thereof and (ii) 0
to 60% by weight of a low molecular weight component of
which individual particles cause a viscous flow deformation
upon melting under the above ~entioned conditions.
Furthcrmore, the powder particle~ of crystalline polyolefin
comprising 30 to 100~ by weight of the high molecular
weight crystalline polyolefin powder particles having a
viscosity-average molecular welght of 150,000 or more and 0
to 70% by weight of the low molecular weight crystalline
polyolefin powder particles having a viscosity-average
molecular weight of 1000 to 100,000 can be used in the
present invention. Especially, the powder particles of
crystalline polyolefin comprising 40 to 90~ by weight of
high molecular weight crystalline polyolefin powder
particles having a viscosity-average molecular weight of
200,000 to 1,000,000 and 10 to 60% by weight of low
molecular weight crystalline polyolefin powder particles
having a viscosity-average molecular weight of 5,000 to
1~76810
-- 8 --
50,000 can be desirably used in the present invention. The
powder particles having the different viscosity-average
molecular weight portions can be present in such a state
that each particle is individually present or that many
particles are adhered to one another. In the latter case,
both particles having different viscosity-average molecular
weight portions can be adhered to each other in such a
state that both particles appears in the surfacq of the
adhered particles or that one of the particles having a
different molecular weight portion is wrapped or surrounded
with the other or vice versa.
Since the above mentioned powder particles having
different molecular weight portions contain powder
particles whose viscous flow d~form~tion occurs with
difficulty at a melting temperature range under no load and
powder particles whose viscous flow deformation easily
occur, these powder particles can be readily enlarged and,
also, enlarged powder particles having a high bulk density
can be readily obtained. In the case where the proportion
of the high molecular weight powder particles in the powder
particles is smaller than the upper limit of the
above mentioned range, the powder particles are liable to
become massive bulk material and are difficult to granulate
even when an appropriate temperature and mutual travel rate
are imparted to the powder particles to be enlarged.
The above mentioned powder particles can be prepared
during polymerization by either one step continuous
polymerization or two or more step (i.e. multi-step)
1~7681~)
g
continuous polymerization, or can be prepared by mixing two
or more types of polymer powder particles after
polymerization.
The powder particles of the crystalline polyolefin
according to the present invention can further contain the
same or different type polyolefin wax, as long as the
characteristics of the resultant powder particles are
acceptable for the intented use. The-poiyolefin wax can be
present in the state of individual particles or in the
state where the polyolefin wax is adhered to the surface or
the interior portion of the crystalline polyolefin powder
particles. The polyolefin waxes used in the present
invention are those having a viqcosity-average molecular
weight of ~rom 500 to 5,00~. .The incorporation of 0.1
to 10~ by weight of the polyolefin wax into the powder
particles facilitate the enlargement of the powder
particles and the formation of the enlarged powder
particles having a smooth surface. Especially when the
powder particles having a viscosity-average molecular
weight of 150,000 or more are to be enlarged, the use of
the polyolefin wax is effective.
Since the above mentioned polymer powder particles
generally have high melt viscosity, a large amount of power
is required when these powder particles are pelletized or
granulated by melt extruding through an extruder. Contrary
to this, according to the present invention, the enlarged
powder particles can be obtained at a low energy consumption
by mutually welding the crystalline polyolefin powder
1176810
-- 10 --
particles under a mutual welding temperature condition of
the particles, while the powder particles being subjected
to the rate of the mutual travel suf f ic ient to prevent the
conglomeration of the powder particles due to the complete
mixing of the moleten powder particles, and, then, cooling
the resultant powder particles.
The apparatus for enlarging the powder particles
according to the present invention can be any apparatus
capable of heating or maintaining the temperature of the
powder particles and fluidizing the powder particles at a
high speed. For instance, a high speed fluid mixer
provided with a heating jacket and a high speed rotary
blade can be desirably used in the practice of the present
invention. Either the continuouC t~pe or batchwise type
apparatus can be used in the present invention. The volume
fraction of the powder particles occupying the empty space
of the apparatus can be appropriately selected. This
selection can be easily made by those skilled in the art,
taking into consideration the following. That is, in the
case where the volu~e fraction of the powder particles is
too small, the productivity is decreased. Contrary to
this, in the case where the volume fraction of the powder
particles is too large, the powder particles are liable -to
conglomerate.
The powder particles to be enlarged according to the
present invention should be heated to a mutual welding
temperature of the powder particles. The term "mutual
welding temperature" used herein means a temperature range
1176810
-- 11 --
which is at least the melting initiation temperature of the
crystalline of the polyolefin and within which the powder
particles can be mutually fused with one another. From the
point of view of (i) the decrease in the heat energy
consumed, (ii) the prevention of the heat deterioration of
the powder particles and (iii) the prevention of the
formation of particles which are too large, the use of an
extremely high temperature is not necessary. Generally,
from a temperature at which the surface of the powder
particles is melted to a temperature of 20C higher than
the meltin~ point of the powder particles can be
advantageously used in the present invention. Such
temperature can be obtained by preheating the powder
particles, or heating the pow~er particles through a
heating jacket during high speed fluidization of the powder
particles, or the heat generation due to the impingement or
friction of the powder particles during high speed
fluidiza-tion of the powder particles, or any combination
thereof.
In order to prevent the conglomeration of the powder
particles due to the complete melting of the powder
particles, a sufficient rate of mutual travel should be
imparted to the powder particles under the mutual welding
temperature conditions. In the case where the rate of
mutual travel is too low, the powder particles become
massive bulk material and finally form the conglomerates
thereof, and also the particle size distribution of the
resultant particles becomes wide. The preferable rate of
~76810
- 12 -
mutual travel of the powder particles is as high as
possible. Especially when the polyolefin powder particles
having a viscosity-average molecular weight of 200,000 or
less which have low melt viscosity are to be enlarged, the
use of high speed fluid mixing as in a Henschel mixer is
desirable. Although the use of the high speed fluid mixing
is also desirable when the polyolefin powder particles
having high melt viscosity are to be enlarged, medium or
low speed fluid mixing as in a ribbon blender or a cone
blender can slso be used.
The heated powder particles enlarged by the mutual
welding of the powder particles of the crystalline
polyolefin are then cooled. The powder particles are
desirably cooled in such a state that the powder particles
are subjected to the rate of mutual travel sufficient to
prevent the further enlargement of the heated powder
particles. During or after cooling, the enlarged powder
particles can be mechanically ground or crushed by using a
grinder or a crusher. Thus, the enlarged powder particles
2~ ha~ing too large a particle size can be crushed and the
particle size of the enlarged powder particles is desirably
adjusted. Especially when the massive large particles or
agglomerates having a size of 5 mm or more are obtained
under mutual welding temperature conditions, these large
particles or agglomerates can be readily crushed to powder
particles having a desired appropriate size, as long as the
large particles are coarsely welded and are in the porous
or sintered state. The cooling can be effectively carried
117683~
- 13 -
out by air cooling. Water cooling and the subsequent
cutting and drying steps which are usually adopted in the
granulation or pelletization by using an extruder are not
necessary in the present invention.
The average particle size (median diameter) of the
enlarged powder particles as obtained above is larger than
25 meshes. Furthermore, the enlarged powder particles
having an average particle size (median diameter) of from
25 to 7 meshes and having a particle size distribution of
such that 90% by weight or more of the total powder
particleQ is within the range of from 30 to 4 meshes can
also be obtained.
Furthermore, in accordance with the present inv~ntion,
the powder particles of the crystalline polyolefin having
an average particle size of ~maller than 25 meshes can be
effectively obtained by enlarging the fine powder
particles. For instance, it is desirable to use powder
particles having a particle size as large as possible (but
not as large as 25 meshes) when the powder particles are
used in the fields of powder molding such as co~pression
molding, sinter molding and rotational molding, or powder
coating. For instance, it is ~ell-known in the art that,
when powder particles having an average particle size of
smaller than 100 meshes are used, the workability and the
finish of the molded articles deteriorate. These problems
can be solved when the powder particles, having an average
particle size of 25 to 75 meshes, enlarged by the present
invention are used. On the other hand, since the filtering
1l768l~
characteristics and the gas-permeability of porous articles
molded by sinter molding largely depend upon the particle
size of the powder particles used, a wide range of the
characteristics and the specification of desired molded
articles can be covered by controlling the average particle
size of the powder particles in accordance with the present
invention.
The enlarged powder particles of the present invention
can be classified by using an appropriate classificator to
adjust the desired partcle size of the enlarged powder
particles. The coarse powder particles having a particle
size larger than the desired size classified by a
classificator can be recovered by mechanic~l grinding or
crushing, whereas the fine powder particles having a
particle size smaller than the desired size classified by a
classificator can be reused in the enlargement step of the
present invention.
Especially when 1 to 100 parts by weight, more
preferably 1 to 50 parts by weight, of the fine powder
particles classified by a classificator, or ground or
crushed by a grinder or crusher is added to 100 parts by
weight of the powder particles of the crystalline
polyolefin prepared by suspension polymerization or gas
phase polymerization, the enlargement of the powder
particles is facilitated and the bulk density of the
enlarged powder particles is desirably improved. However,
in the case where the addition amount of the above-
-mentioned fine powder particles is increased beyond the
- 15 - ~7681~
above mentioned range, the overall productivity is
disadvantageously decreased. It is believed that the
above mentioned effects obtained from the addition of the
classified or crushed fine powder particles are due to the
facts that, since the enlarged powder particles and the
mechanically crushed powder particles have a large surface
area and contain whisker type particles or particles having
projecting portions, heat transfer is rapidly effected and,
as a result, the welding of the powder particles is rapidly
and effectively caused.
The specific embodiments of the present invention are
further clearly illustrated by the accompanying
photomicrographs. It is clearly understood from the
comparison of Figs. 1 to 4 that th~ powder particl~s of the
high-molecular ~leight crystalline polyolefin are difficult
to cause a viscous flow at a temperature of not less than
~.
the melting point.
Fig. 1 is a phase contrast photomicrograph (magnified
30 times) of the high-density polyethylene powder particles
haying a viscosity-average molecular weight of 280,000 used
in Example 1 hereinbelow at room temperature, and Fig. 2 is
a phase contrast photomicrograph ~magnified 30 times) of
the polyethylene powder particles of Fig. 1 after allowing
it to stand for 15 minutes at a temperature of 150C.
Although a portion of the powder particles appears to be
transparent due to the melting thereof in Fig. 2, the
original shapes of the powder particles at room temperature
are substantially sustained. Contrary to this, Fig. 3 is a
1~7681~
- 16 -
phase contrast photomicrograph (magnified 30 times) of the
high-density polyethylene powder particles having a
vi.scosity-average molecular weight of 30,000 used in
Comparati~e Example 1 hereinbelow, and Fig. 4 is a phase
contrast photomicrograph (magnified 30 times) of the
polyethylene powder particles of Fig. 3 after allowing it
to stand fGr 30 seconds at a temperature of 150C. As is
clear from Fig. 4, the powder particles are changed to
spherical shapes and cause fluidization due to the melting
thereof.
Fig. 5, is a scanning type electron photomicrograph
(magnified 30 times) of the enlarged powder particles
obtained in Example 1 hereinbelow and clearly shows the
conditions that the individual fine powder particles are
sintered with one another to form enlarged powder particles.
Fig. 6 shows the enlarged powder particles obtained in
Example 2 hereinbelow. The sintering conditions of the
fine powder particles are coarse and a lot of pores are
present in the interior portions of the powder particles,
20 as is clear from Fig. 6. Fig. 7 shows the cross section of
the enlarged powder particles of Fig. 6. It is clearly
understood from Fig. 7 that complicated and irregular open
pores are contained in the interior of the enlarged powder
particles of Fig. 7.
In the practice of the enlargement of the powder
particles according to the present invention, it is
recommendable that the enlargement operation is carried out
in, for example, a nitrogen atmosphere to prevent the heat
1~76~1~
- 17 -
cleterioration of the polyolefin. Furthermore, various
conventional additives such as antioxidants, ultraviolet
absorbing agents, lubricants, antistatic agents, coloring
agents, fire retardants and the like can be blended during
the enlargement step so long as the desired enlargement is
not impaired.
The enlarged powder particles obtained above can be
directly used as molding materials suitable for use in
various molding machines to form various molded articles as
in the case of conventional pellets. In addition, the
enlarged powder particles prepared by the present invention
can also be directly used as molding materials suitable for
use in various powder molding processes such as sinter
molding, compression molding, ~otational molding and the
li~e.
The present invention will now be specifically
illustrated by, but is by no means limited to, the Examples
set forth below.
The properties defining the powder particles of the
present invention were determined according to the
followins methods.
Bulk Density : ASTM D 1895
Particle Size Distribution : JIS K 0069
Viscosity-Average ~olecular ~7eight (MW): Mw was
25 determined from the relationship set forth in Journal of
Polymer Science 36, p91 (1957),
6 1 ~4 0.67
in which the intrinsic viscosity ~ of the polymer powder
1~761~10
- 18 -
particle was measured in the decaline solution at a
temperature of 135C.
Example l
High-density polyethylene powder particles obtained by
suspension polymerization and having powder properties of
an average particle size (i.e. median diameter) of
100 meshes, a particle size distribution of such that more
than 90% by weight of the total powder particles.had a
particle size within the range of from 40 to 280 meshes and
a bulk density of 0.37 and having a density of 0.955 and a
viscosity-average molecular weight of 280,000 were used as
a starting material. According to microscopic observation,
100% by weight of these polymer powder particles did not
remarkably change their individual powder particle shapes
even in the case where these powder particles were heated,
under no load, to a temperature 20C higher than the
melting point thereof (refer to Fig. 2).
15 kg of these powder particles was preheated to a
temperature of 80C by using an air dryer and, then,
charged into a 150 liter Henschel mixer manufactured by
Mitsui Miike Seisakusho and enlarged under the following
conditions.
Enlarging Conditions:
Jacket condition 120C steam
Revolution number of blades 1460 rpm
Type of blade P-type blade
Stirring time 7 mins.
The heated powder particles thus enlarged by mutually
117681~)
-- 19 --
welding with one another were withdrawn and charged into a
150 liter cooling mixer and cooled with stirring under the
following conditions.
Jacket condition 20C water
Revolution speed of blades 730 rpm
Type of blade Cooling blade
Stirring time 5 mins.
The enlarged powder particles thus prepared had an
average particle size (median diameter) of 14 meshes, a
particle size distribution of such that more than 90% by
weight of the total powder particles had a particle size
within the range of from 25 to 6 meshes and a bulk density
of 0.42.
Energy required for granulating these powder particles
was about one third when compared with the case where an
extruder was use~.
Example 2
A mixture of (ii 50% by weight of high molecular
weight high-density polyethylene powder particles obtained
by suspension polymerization and having powder properties
of an average particle size of 80 meshes, a particle size
distribution of such that more than 90~ by weight of the
total powder particles had a particle size within the range
of from 40 to 280 meshes and a bulk density of 0.35 and
having a density OL 0.954 and a viscosity-average molecular
weight of 800,000 and (ii) 50% by weight of low molecular
weight polyethylene powder particles obtained by suspension
polymeriæation and having the same properties as those of
1~76810
- 20 -
the above mentioned component (i) except that the
iscosity-average molecular weight was 20,000 was used.
According to microscopic observation, about half of these
powder particles did not remarkably change their individual
powder particle shapes even in the case where these powder
particles were heated, under no load, to a temperature 20C
higher than the melting point thereof.
These powder particles were enlarged in the same
manner as described in Example 1 except that the stirring
time was 4 minutes. The enlarged powder particles thus
obtained had an average particle size of 16 meshes, a
particle size distribution of such that more than 90% by
weight of the total powder particles had a particle size
within the range of from 25 tQ 8 meshes and a bulk density
of 0.36.
Example 3
A mixture of (i) 60~ by weight of high-molecular
weight crystalline polypropylene powder particles obtained
by suspension polymerization having powder properties of
an average particle size of 100 meshes, a particle size
distribution of such that more than 90~ by weight of the
total powder particles had a particle size within the range
of from 4Q to 280 meshes and a ~ulk density of 0.34 and
having a density of 0.91 and a viscosity-average molecular
weight of 700,000 and (ii) 40% by weight of low molecular
weight crystalline polypropylene powder particles obtained
by suspension polymerization having the same properties as
those of the above mentioned component (i) except that a
1176810
- 21 -
component having a viscosity-average molecular weight of
50,000 was used.
These powder particles were preheated to a temperature
of 120C and, then, enlarged in a Henschel mixer under the
mixer jacket condition of 150C steam ar.d a stirring time
of 6 minutes in the same manner as described in Example 1.
After cooling, enlarged polypropylene powder particles were
obtained.
The enlarged powder particles had an average particle
size of 16 meshes, a particle distribution of such that
more than 90% by weight of the total powder particles had a
particle size within the range of from 25 to 8 meshes and a
bulk density of 0.36.
Example 4 -
2 parts by weight of polyethylene wax having a
viscosity-average molecular weight of 2000 and a density of
0.953 were added to 100 parts by weight of the high-density
polyethylene powder particles used in Example 2. The mixed
powder particles were able to be enlarged for a stirring
time of 3 minutes in the same manner as described in
Example 2.
The enlarged powder particles thus obtained had an
average particle size of 16 meshes, a particle distribution
of such that more than 90% by weight of the total powder
particles had a particle size within the range of from 25
to 8 meshes and a bulk density of 0.40.
Example 5
After classifying powder particles having a particle
~1768~V
- 22 -
size of 8 meshes or above from the enlarged powder
particles obtained in Example 2, the crushed powder
particles having an average particle size of 20 meshes and
a particle size distribution of such that more than 90% by
weight of the total powder particle had a particle size
within the range of from 35 to 10 meshes were obtained by
using a turbo-type crushing machine.
10 parts by weight of the crushed powder particles
thus obtained was mixed with 90 parts by weight of the
high density polyethylene obtained by suspension
polymerization used in Example 2. The mixed powder
particles were able to be enlarged during a stirring time
of 3 minutes when they were enlarged in the same manner as
described in Example 2.
The enlarged powder particles thus obtained had an
average particle size of 14 meshes, a particle size
distribution of such that more than`90~ by weight of the
total powder particles had a particle size within the range
of from 25 to 8 meshes and a bulk density of 0.40.
Example 6
After classifying powder particles having a particle
si2e of fin~r than 40 meshes from the enlarged powder
particles obtained in Example 2, 10 parts by weight of the
powder particles thus classified was mixed with 90 parts by
weight of the high density polyethylene powder particles
obtained by suspension polymerization used in Example 2.
The powder particle mixture was able to be enlarged during
a stirring time of 3 minutes when the mixture was enlarged
~76810
- 23 -
in the same manner as described in Example 2.
The enlarged powder particles thus obtained had an
average particle size of 16 meshes, a particle size
distribution of such that more than 90% by weight of the
total powder particles had a particle size within the range
of from 25 to 8 meshes and a bulk density of 0.41.
Example 7
2 kg of medium--density polyethylene powder particles
obtained by suspension polymerization having powder
properties of an average particle size of ~0 meshes, a
particle size distribution of such that more than 9o% by
weight of the total powder particles had a particle size
within the range of from 40 to 200 meshes and a bulk
density of 0.37 and having a ~ensity of 0.938 and a
vi8cosity-averase molecular weight of 80,000 was charged
into a 20 liter ~enschel mixer manufactured by Mitsui Miike
Seisakusho and was enlarged under the following conditions.
Enlarging Conditions
Enlarging Conditions
Jacket temperature 90C
Revolution number of blades 2300 rpm
Type of blades P-type blade
Stirring time 14 mins.
*1: Although the jacket temperature was less than the
25 melting point of the powder particles, the temperature of
the surface of the powder particles became higher than the
melting point due to the occurrence of the frictional heat
and the like.
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The heated powder particles thus enlarged by the
mutual welding were withdrawn and charged into a 20 liter
cooling mixer and cooled with stirring under the following
conditions.
Jacket condition 20C water
Revolution speed of blades 2300 rpm
Type of blades Cooling blade
Stirring time 5 mins.
The enlarged powder particles thus obtained had an
average particle size of 28 meshes, a particle size
distribution of such that more than 90% by weight of the
total powder particles had a particle size within the
range of from 8 to lO0 meshes and a bulk density of 0.39.
Example 8
15 High-density polyethylene powder particles prepared by
two-step continuous suspension polymerization
comprising (i) 50~ by weight of low molecular weight
polyethylene having a viscosity-average molecular weight of
15,000 obtained in the first step polymerization and (ii)
50% by weight of high molecular weight polyethylene having
a viscosity-average molecular weight of 800,000 obtained in
the second step polymerization were used. These powder
particles had powder properties of an averag~ particle size
of lO0 meshes, a particle size distribution of such that
more than 90~ by weight of the total powder particles had a
particle size within the range of from 50 to 280 meshes and
a bulk density of 0.35 and had a density of 0.955.
According to microscopic observation, almost all of these
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- 25 -
polymer powder particles did not remarkably change their
polymer powder particle shape even in the case where these
polymer powder particles were heated, under no load, to a
t:emperature 20C higher than the melting point thereof.
These powder particles were enlarged during a stirring
time of 3 minutes and 40 seconds, followed by cooling in a
cooling mixer, in the same manner as described in
Example 1. Thus, the enlarged powder particles were
obtained.
The enlarged powder particles thus obtained had an
average particle size of 16 meshes, a particle size
distribution of such that more than 90~ by weight of the
total powder particles had a particle size within the range
of from 25 to 8 meshes and a bulk density of 0.39.
Examples 9
High density polyethylene powder particles obtained by
gas phase polymerization and having powder properties of an
average particle size of 60 meshes, a particle size
distribution of such that more than 90~ by weight of the
total powder particles had a particle size within the range
of 25 to 150 meshes and a bulk density of 0.36 ~nd having a
density of 0.945 and a viscosity-average molecular weight
of 180,000 were used.
These powder particles were enlarged during a stirring
time of 5 minutes and 30 seconds, followed by cooling in a
cooling mixer, in the same manner as described in
Example l. Thus, the enlarged powder particles were
obtained.
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The enlarged powder particles thus obtained had an
average particle size of lO meshes, a particle distribution
of such that more than 90% by weight of the total powder
particles had a particle size within the range of from 25
to 6 meshes and a bulk density of 0.40.
Example 10
The polyethylene powder particles used in Example 1
were enlarged under the same conditions as described in
Example 1 except that the stirring time was 5 minutes.
After cooling, the enlarged powder particles were obtained.
The powder particles thus enlarged had an average
particle size of 35 meshes, a particle size distribution of
such that more than 90% by weight of the total powder
particles had a particle size within the range of from 80
to 20 meshe5 and a bulk density of 0.39.
Cylindrical molded filters having a wall thickness of
3.2 mm, an outer diameter of 36 mm and a length of 178 mm
were sinter molded from the enlarged powder particles
obtained above. The cylindrical filters thus obtained had
a filtering characteristics of 120 microns.
Comparative Example 1
~ igh-density polyethylene powder particles obtained by
suspension polymerization and having powder properties of
an average particle size of 70 meshes, a particle size
distribution of such that more than 90~ by weight of the
total powder particles had a particle size within the range
of from 40 to 280 meshes and a bulk density of 0.35 and
having a density of 0.953 and a viscosity-average molecular
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- 27 -
weight of 30,000 was used. According to microscopic
observation, the particle shapes of 100~ by weight of the
powder particles first changed to spherical shapes, and
then fluidized to form mutually welded massive particles
(see Fi.g. 4).
Although these particles were enlarged in the manner
as described in Example 7, the particles became
conglomerates during a stirring time of less than 4 minutes
and enlarged particles were not obtained.
