CA1176810A - Enlarged powder particles of crystalline polyolefin and method of producing the same - Google Patents
Enlarged powder particles of crystalline polyolefin and method of producing the sameInfo
- Publication number
- CA1176810A CA1176810A CA000375629A CA375629A CA1176810A CA 1176810 A CA1176810 A CA 1176810A CA 000375629 A CA000375629 A CA 000375629A CA 375629 A CA375629 A CA 375629A CA 1176810 A CA1176810 A CA 1176810A
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- Prior art keywords
- powder particles
- enlarged
- particle size
- molecular weight
- particles
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Classifications
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/12—Powdering or granulating
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B9/00—Making granules
- B29B9/16—Auxiliary treatment of granules
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
Abstract
ENLARGED POWDER PARTICLES OF CRYSTALLINE
POLYOLEFIN AND METHOD OF PRODUCING THE SAME
ABSTRACT OF THE DISCLOSURE
Enlarged powder particles of crystalline polyolefin and a method of producing the same are disclosed. These enlarged powder particles are obtained from the welding of crystalline polyolefin powder particles with one another at a mutual welding temperature, while the powder particles are subjected to the rate of mutual travel which is sufficient to prevent the conglomeration. These crystalline polyolefin powder particles to be enlarged have an average particle size of smaller than 30 meshes and a viscosity-average molecular weight of at least 50,000 and are prepared by one-step or multi-step suspension polymerization or gas phase polymerization.
POLYOLEFIN AND METHOD OF PRODUCING THE SAME
ABSTRACT OF THE DISCLOSURE
Enlarged powder particles of crystalline polyolefin and a method of producing the same are disclosed. These enlarged powder particles are obtained from the welding of crystalline polyolefin powder particles with one another at a mutual welding temperature, while the powder particles are subjected to the rate of mutual travel which is sufficient to prevent the conglomeration. These crystalline polyolefin powder particles to be enlarged have an average particle size of smaller than 30 meshes and a viscosity-average molecular weight of at least 50,000 and are prepared by one-step or multi-step suspension polymerization or gas phase polymerization.
Description
~.~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 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 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;
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 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 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 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 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 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 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
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 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 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;
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 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 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 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 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 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 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~
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~
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~
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 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~) 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 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 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
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 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.
1~76810 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 117681a~
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.
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
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~
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~
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 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~) 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 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 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
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 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.
1~76810 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 117681a~
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.
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 11768:10 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.
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 11768:10 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.
Claims (11)
1. Enlarged powder particles of crystalline polyolefin obtained from the welding of crystalline polyolefin powder particles with one another, said crystalline polyolefin powder particles having an average particle size of smaller than 30 meshes and a viscosity--average molecular weight of at least 50,000 and being prepared by one-step or multi-step suspension polymerization or gas phase polymerization and the particle size of said enlarged powder particles being larger than that of the starting crystalline polyolefin powder particles.
2. Enlarged powder particles as claimed in claim 1, wherein the average particle size of the enlarged powder particles is larger than 25 meshes.
3. Enlarged powder particles as claimed in claim 1, wherein the enlarged powder particles are porous particles having irregular open-pores therein.
4. Enlarged powder particles as claimed in claim 1, 2 or 3, wherein the viscosity-average molecular weight of the crystalline polyolefin powder is within the range of from 150,000 to 1,000,000.
5. Enlarged powder particles as claimed in claim 1, wherein said crystalline polyolefin comprises (i) 40 to 90% 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 a temperature 20°C higher than the melting point thereof and (ii) 10 to 60% by weight of a low molecular weight component of which individual particles cause viscous flow deformation upon melting under the above mentioned conditions, both the components being present in such a state that each particle is individually present or that plural particles are adhered to each other and a total viscosity-average molecular weight being at least 50,000.
6. Enlarged powder particles as claimed in claim 5, wherein the viscosity-average molecular weight of the high molecular weight component is within the range of from 200,000 to 1,000,000 and that of the low molecular weight component is within the range of from 5,000 to 50,000.
7. Enlarged powder particles as claimed in claim 1, 2 or 3, wherein said crystalline polyolefin powder contains from 0.1 to 10% by weight of polyolefin wax having a viscosity-average molecular weight of from 500 to 5,000 therein as the low molecular weight component in such a state that each particle of the polyolefin wax is individually present or that the particles of the polyolefin wax are adhered to the crystalline polyolefin powder particles.
8. Enlarged powder particles of crystalline polyolefin obtained from the welding of the crystalline polyolefin powder particles with each other said crystalline polyolefin powder particles comprising (i) 100 parts by weight of crystalline polyolefin powder having a viscosity-average molecular weight of at least 50,000 and an average particle size of less than 30 meshes and being prepared by one-step or multi-step suspension polymerization or gas phase polymerization and (ii) 1 to 100 parts by weight of mechanically crushed polyolefin powder particles having an average particle size of smaller than 30 meshes, the particle size of said enlarged powder particles being larger than those of the starting crystalline polyolefin powder particles.
9. Enlarged powder particles obtained from the welding of (i) 100 parts by weight of crystalline polyolefin powder particles having an average particle size of smaller than 30 meshes and a viscosity-average molecular weight of at least 50,000 and being prepared by one-step or multi-step suspension polymerization or gas phase polymerization and (ii) 1 to 30 parts by weight of the enlarged powder particles as set forth in claim 1 having a particle size of less than 30 meshes, the particle size of said enlarged powder particles thus obtained being larger than those of the starting powder particles.
10. A method of enlarging powder particles of crystalline polyolefin having an average particle size of smaller than 30 meshes and a viscosity-average molecular 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 olefin powder particles under a mutual welding temperature condition to enlarge the crystalline olefin particles by the use of high speed mixing, while the powder particles have sufficient relative motion to 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.
(i) treating said crystalline olefin powder particles under a mutual welding temperature condition to enlarge the crystalline olefin particles by the use of high speed mixing, while the powder particles have sufficient relative motion to 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.
11. A method as claimed in claim 10, wherein the mutually welded enlarged powder particles are mechanically ground or crushed during or after cooling.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6226280A JPS56159116A (en) | 1980-05-13 | 1980-05-13 | Method of coarse granulation of crystalline polyolefin powder and coarse granules |
| JP62262/80 | 1980-05-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1176810A true CA1176810A (en) | 1984-10-30 |
Family
ID=13195051
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000375629A Expired CA1176810A (en) | 1980-05-13 | 1981-04-16 | Enlarged powder particles of crystalline polyolefin and method of producing the same |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS56159116A (en) |
| CA (1) | CA1176810A (en) |
| DE (1) | DE3118499C2 (en) |
| GB (1) | GB2077272B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6262710A (en) * | 1985-09-13 | 1987-03-19 | Achilles Corp | Manufacture of synthetic resin granule |
| US9386803B2 (en) | 2010-01-06 | 2016-07-12 | Celanese Acetate Llc | Tobacco smoke filter for smoking device with porous mass of active particulate |
| BR112012028077A2 (en) * | 2010-05-03 | 2016-08-02 | Ticona Llc | polyethylene powders and porous articles thereof |
| CA2814074C (en) | 2010-10-15 | 2017-01-17 | Celanese Acetate Llc | Apparatuses, systems, and associated methods for forming porous masses for smoke filter |
| CN111094466B (en) * | 2017-08-17 | 2022-02-22 | 塞拉尼斯销售德国有限公司 | Polymer composition for producing gel extruded articles and polymer articles made therefrom |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1426438A (en) * | 1964-01-18 | 1966-01-28 | Hoechst Ag | Process for conditioning olefin polymers in powder form for the preparation of shaped articles |
| US3527845A (en) * | 1967-06-28 | 1970-09-08 | Avisun Corp | Method of reducing fines in alphaolefin polymer powder |
-
1980
- 1980-05-13 JP JP6226280A patent/JPS56159116A/en active Pending
-
1981
- 1981-04-16 CA CA000375629A patent/CA1176810A/en not_active Expired
- 1981-04-24 GB GB8112731A patent/GB2077272B/en not_active Expired
- 1981-05-09 DE DE19813118499 patent/DE3118499C2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE3118499A1 (en) | 1982-03-25 |
| GB2077272A (en) | 1981-12-16 |
| DE3118499C2 (en) | 1984-07-26 |
| JPS56159116A (en) | 1981-12-08 |
| GB2077272B (en) | 1983-11-23 |
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