JP2004268505A - Method for manufacturing resin pellets - Google Patents

Abstract

An object of the present invention is to provide a method for producing resin pellets for producing resin pellets that do not generate deformed objects based on the generation of snake skin or the like.
A method for producing resin pellets by extruding a molten polyolefin from an extruder and cutting the same is characterized in that the obtained resin pellets are cut so as to exhibit the following property (A). Method for producing pellets.
Characteristics (A): The average weight per cut resin pellet is 6 to 18 mg in the case of an ethylene polymer pellet, and 6 to 23 mg in the case of a propylene polymer pellet.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a method for producing resin pellets by cutting polyolefin extruded from an extruder, more specifically, producing resin pellets free from foreign matter generation based on powdering of particles or snake skin, streamer, etc. About the method.
[0002]
[Prior art]
In the production of a polyolefin resin on a commercial production scale, a polyolefin resin is produced, and then, various kinds of additives are blended using a melt kneader, and then the molten resin is extruded by an extruder and cut while cooling. Thus, it is used as pellet particles.
[0003]
The pellet particles are transferred and facilitated in handling at the time of molding.The pellet particles thus produced are usually pneumatically transported through pipes and stored in storage silos, and stored in packing bags or containers at the time of shipping. It is sent to the dispensing silo by air to fill the pellets.
[0004]
However, non-standard products in shape may be mixed into the manufactured pellet particles due to cutting mistakes, and if non-standard pellets are mixed in product pellets, it will adversely affect the operating equipment etc. of the secondary processing user. In addition, it is necessary to separate and remove the variant.
[0005]
Vibrating sieves are usually used for removing irregular objects, and the vibrating sieve is installed immediately after the cutting mechanism and used in combination with the pneumatic transportation system.The pneumatic transportation system is simple and advantageous. This method has the following drawbacks.
[0006]
In other words, pneumatic transportation using pipes has a large contact friction on the inner wall of the transport pipe and a large pressure loss, resulting in an increase in energy cost, and a powdering of the pellet particles due to contact friction between the pellet particles or with the inner wall of the transport pipe. Fine powder due to welding / peeling to the inner wall, or snake skin, streamer or floss is generated, which causes foreign matter to be generated after separating and removing the deformed object.
[0007]
The generation of snake skin and the like is called the Skotonicky effect. When a plastic pellet is transported at a high speed by air, the collision of the pellet becomes strong, and the impulse at the time of the collision causes a decrease in melting point of the plastic pellet. It is generated when a part of the pellet is fused to the pipe wall (Non-Patent Document 1).
[0008]
In recent years, with the progress of automation of secondary processing, quality control requirements from processing companies have become more and more strict, and measures to remove foreign substances or prevent their generation have become a major issue. In order to avoid this problem, a method of performing pneumatic transportation at a low speed has been proposed (Non-Patent Document 1), but the equipment becomes complicated, the equipment cost increases, and the pressure loss of the transportation piping increases. There are inconveniences.
[0009]
In addition, a method has been proposed in which water is added during pneumatic transport to form a water film on the particle surface to reduce frictional resistance between the pellets and between the pellets and the tube wall (Patent Document 1). As long as the effect is not satisfactory. Further, no attempt has been made to solve the above-mentioned problem by manipulating the cutting conditions.
[0010]
[Patent Document 1] Japanese Patent Application Laid-Open No. 10-147433 [Non-Patent Document 1] Chemical Apparatus February 2000, pp. 46-70
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION The present invention provides a method for producing resin pellets for producing resin pellets without the generation of deformed products based on the formation of snake skin and the like.
[0012]
[Means for Solving the Problems]
The present inventors have conducted intensive studies focusing on the above problems, and as a result, have found that it is possible to prevent the occurrence of a deformed object by cutting under specific conditions, and have accomplished the present invention. .
[0013]
Specifically, the present invention relates to a method for producing a resin pellet by melting and extruding a polyolefin comprising an ethylene-based polymer or a propylene-based polymer using an extruder, and cutting the same to obtain a resin pellet. It is intended to provide a method for producing a resin pellet, characterized in that the pellet is cut so as to exhibit the following property (A).
[0014]
Characteristics (A): The average weight per cut resin pellet is 6 to 18 mg in the case of an ethylene polymer pellet, and 6 to 23 mg in the case of a propylene polymer pellet.
[0015]
The present invention also provides a method for producing the above resin pellets in which a polyolefin is melted, extruded from a nozzle into cooling water, and cut. The resin pellets have a density of 0.86 to 0.97 g / cm ³ and an MFR of 0.01. A method for producing the above resin pellets, which is an ethylene polymer having a density of 0.86 to 0.91 g / cm ³ and an MFR of 0.01 to 1000 g / 10 min. An object of the present invention is to provide a method for producing the resin pellets as a polymer.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The resin used in the production of the pellet of the present invention is a polyolefin obtained by polymerizing or copolymerizing an olefin, and specifically, an ethylene polymer or a propylene polymer is used.
[0017]
As the ethylene polymer, high-pressure low-density polyethylene, linear low-density polyethylene, or high-density polyethylene can be used. The high-pressure low-density polyethylene is obtained by copolymerizing ethylene or ethylene with a small amount of unsaturated carboxylic acid or unsaturated carboxylic acid ester by high-pressure radical polymerization. In addition, linear low-density polyethylene or high-density polyethylene is homopolymerized with ethylene, or ethylene and a small amount of α-olefin by coordinating anionic polymerization using a Ziegler-Natta catalyst, a metallocene catalyst, or a so-called single-site catalyst. It is obtained by copolymerization.
[0018]
As high-density polyethylene, the density is 0.94 to 0.97 (g / cm ³ ), MFR is 0.01 to 1000 (g / 10 min), and as high-pressure low-density polyethylene, the density is 0.86 to 0.96. Those having an MFR in the range of 0.94 (g / cm ³ ) and 0.01 to 1000 (g / 10 minutes) are desirable.
[0019]
As the propylene-based polymer, a propylene homopolymer (a so-called homopolymer), a random copolymer of propylene and another α-olefin (including ethylene), or a so-called propylene block copolymer is applied. The method for producing these propylene-based polymers is not particularly limited, and known stereoregular catalysts and production methods can be used. In particular, density 0.86~0.91 (g / ^cm 3), further preferably has in the range of ^{0.89~0.91 (g / cm 3),} MFR is 0.01 to 1000 (g / 10 minutes), and more preferably in the range of 0.1 to 100 (g / 10 minutes).
[0020]
Various additives can be added to these polyolefins as required. Examples thereof include phenol-based, organic phosphite-based, organic phosphorus-based antioxidants such as phosphite, thioether-based antioxidants; and hindered amine-based light-emitting agents. Stabilizers; UV absorbers such as benzophenones, benzotriazoles, and benzoates; antistatic agents such as nonionic, cationic, and anionic; dispersants such as bisamides, waxes, and organic metal salts; alkaline earths Chlorine scavengers such as metal carboxylate; Lubricants such as amide, wax, organic metal salt, and ester; Metal deactivators such as hydrazine and amine acid; Brominated organic, phosphoric, Flame retardants such as antimony oxide, magnesium hydroxide, red phosphorus, etc .; organic pigments; inorganic pigments; foaming agents; fillers; It may be added an antibacterial agent or the like.
[0021]
The polyolefin is melt-kneaded using an extruder, extruded from a nozzle and cut. As the polyolefin cutting mechanism itself, a known cutting device can be adopted.
[0022]
FIG. 1 shows a flow of an apparatus for in-line pelletizing by connecting to a so-called olefin polymerization post-treatment step.
[0023]
Referring to an example of the pelletizing process with reference to FIG. 1, olefins such as ethylene and propylene are polymerized in the polymerization reactor 1. Although the polymerization system is not limited, as shown in the figure, when polymerization and pelletization are performed in-line, a gas phase polymerization or a polymerization system using a monomer as a medium is preferable. The figure shows a case in which the raw material gas is connected to a high-pressure radical polymerization process, and unreacted raw material gas is separated from a polymer discharged from a polymerization reactor 1 by a high-pressure separator 2 and a low-pressure separator 3. Next, the mixture is melt-kneaded with a predetermined additive in a kneading extruder 4, and a molten polyolefin is extruded.
[0024]
A die plate 5 having a large number of nozzles 5a is mounted at the tip of the kneading extruder 4, and the nozzles 5a are provided in a cooling chamber in which cooling water supplied from a cooling water tank 9 by a cooling water pump 8 circulates. 6 is communicated. The molten polyolefin extruded from the nozzle 5a is cut by the cutter 7 while being cooled and solidified by cooling water. The cutter 7 is provided with a rotary blade, and is configured such that the interval of the cutting time can be arbitrarily controlled by the number of rotations of the cutter 7. The cut and solidified resin pellets are separated from the cooling water by a pellet dryer 10, particles having a nonstandard size are removed by a vibrating sieve 11, and then transported to a product silo 13 by a pellet transport blower 12. Will be stored. Thus, pellet particles are prepared.
[0025]
Therefore, physical properties such as the shape and size of the pellet particles are determined by the amount of extrusion per unit time, the temperature in the extruder, the diameter of the nozzle, the number of nozzles, the number of rotations of the cutter, the number of cutter blades, and cooling conditions. In addition, the physical properties (density, MFR, swell value, etc.) of the molten resin may also have an effect.
[0026]
The present invention is characterized in that the cut pellet particles are cut so as to have the following property (A).
[0027]
Characteristics (A): The average weight per cut resin pellet is 6 to 18 mg in the case of an ethylene polymer pellet, and 6 to 23 mg in the case of a propylene polymer pellet.
[0028]
As described above, the weight per pellet is determined by the amount of the molten resin extruded from the extrusion hole, the rotation speed of the cutter, and the like.
[0029]
In a typical commercial production scale operation, the extruder output is 2 to 40 (tons / hr), the nozzle diameter is 1.5 to 3.5 (mm), and the rotation speed of the cutter blade is 100 to 2000 ( rev / min), 0.86 to 0.97 density of the polyolefin is an ethylene-based polymer (g / ^cm 3), a propylene-based polymer .86-.91 (g / cm ^3), in general Unless special conditions are adopted, the average weight per particle often exceeds 18 mg for an ethylene polymer and 23 mg for a propylene polymer.
[0030]
However, according to studies by the present inventors, when the weight per pellet exceeds 18 mg / particle (in the case of an ethylene-based polymer) or 23 mg / particle (in the case of a propylene-based polymer), the Scotnikky effect is reduced. Easier to trigger. This is probably because the kinetic energy of the particles during pneumatic transportation becomes too large, and the energy when colliding with the wall surface becomes large.
[0031]
Conversely, when the amount is less than 6 mg / particle, the particle becomes small like a powder, and there is a disadvantage that handling becomes difficult. In order to further exert the effects of the present invention, it is desirable that the upper limit of the average weight be 15 mg / particle for an ethylene polymer and 18 mg / particle for a propylene polymer. The preferred lower limit is 8 mg / particle, more preferably 10 mg / particle, for both the ethylene-based polymer and the propylene-based polymer.
[0032]
The difference in the upper limit between the ethylene-based polymer and the propylene-based polymer as described above may be attributed to the difference in the melting point of the polymer. Generally, a propylene-based polymer has high crystallinity and a higher melting point than an ethylene-based polymer. Therefore, it is considered that the material has heat resistance, and even if the weight of the particles to be cut is larger than that of the ethylene-based polymer, foreign matters are hardly generated.
[0033]
In order to keep the weight of the resin pellets within the range of the present invention, for example, a method of reducing the extrusion amount, increasing the number of nozzles 5a, and increasing the rotation speed of the cutter 7 can be mentioned. Among these methods, increasing the rotation speed of the cutter 7 is a preferable method because it is simple and economical. On the other hand, if the number of revolutions of the cutter 7 is excessively increased, wear of the die plate 5 and the blades of the cutter 7 tends to progress, and this is not a method that a person skilled in the art prefers. Therefore, in normal operation, the number of revolutions is set to be as low as possible, but by increasing the number of revolutions, the generation of foreign substances can be suppressed. A person skilled in the art can adjust the above conditions as appropriate to keep the average weight per pellet within the scope of the present invention.
[0034]
Here, the average weight is represented by measuring the weight of 50 arbitrarily selected pellet particles and calculating the average weight of one particle. The weighing is preferably performed using a unit capable of measuring up to the unit of 0.1 mg, for example, an analytical balance.
[0035]
It is preferable that the cut resin pellets have a shape that minimizes the impact upon collision with a wall surface or collision between particles. Specifically, a round rice cake shape having no irregularities is preferable, and it is desirable to employ a so-called hot cut method of cutting before cooling sufficiently. Generally, it is desirable to employ an underwater cutting method. The cylindrical shape has a portion similar to a corner, and is disadvantageous when a large impact force is applied. In addition, due to the swell property of the resin, it may be deformed into a mushroom shape after cutting. The portion often has a large impact force and is not a desirable shape. However, depending on the purpose, a cold cut method in which cutting is performed after cooling sufficiently can be adopted, and this is not excluded.
[0036]
The grade index of the resin pellet can be measured by the following method.
[0037]
MFR (flowability of polyolefin): According to JIS K7210, a test load of 2.16 kg and a test temperature of 190 ° C. for an ethylene polymer and a test load of 2.16 kg and a test temperature of 230 for a propylene polymer Measure under conditions of ° C.
[0038]
Density (density of non-foamed polyolefin): Measured by a density gradient tube method for both ethylene-based polymers and propylene-based polymers according to JIS K7112.
[0039]
【Example】
Example 1
High-pressure low-density polyethylene was produced by a high-pressure radical polymerization method using an autoclave at a reaction temperature of 240 ° C., a reaction pressure of 1500 kg / cm ² , and a gas amount of 24 tons / hour. Production was 4 tonnes / hour. When a sampling test of the polymer physical properties was performed, the obtained high-pressure low-density polyethylene had an MFR of 6.7 (g / 10 minutes), a density of 0.92 (g / cm ³ ), and a memory effect (ME) of 2.01.
[0040]
The polymerized polymer is separated into an unreacted gas and a produced polymer by high and low pressure separators and sent to an extruder (screw diameter 305 mm, L / D = 9, 852 nozzles, nozzle diameter 2.4 mm). Was done. Resin pellets were produced by cutting the molten resin extruded from the nozzle while solidifying it with cooling water. The extrusion rate was 3.5 tons / hour, the resin temperature was 150 ° C., the cooling water (PCW) temperature was 49 ° C., and the flow rate was 108 tons / hour. The operating conditions of the cutter were 10 blades and 890 rpm.
[0041]
The resin pellets thus obtained were in a round cake shape. The weight per 50 randomly selected pellets was 660 mg, and the average pellet weight per pellet was 13.2 mg.
[0042]
The resin pellets thus obtained were stored in a silo for temporary storage. The following conditions were used when the product was delivered from this silo to the product delivery silo by air. That is, the drying was performed using a 10-inch diameter pipe using dry air at a transport rate of 40 tons / hour and an air flow rate of 100 m ³ / min. Foreign particles such as fine powder and snake skin generated by air transport were 16 ppm (corresponding to 56 g / hour) in total.
[0043]
Comparative Example 1
Resin pellets were produced under the same conditions as in Example 1 except that the rotation speed of the cutter was changed to 620 rpm and PCW was set to 39 ° C. The obtained resin pellet had a mushroom shape. The weight per 50 randomly selected pellets was 930 mg, and therefore the average pellet weight per pellet was 18.6 mg.
[0044]
The resin pellets thus obtained were transported by air through the pipe under the same conditions as in Example 1, and were transferred to a dispensing silo. Foreign matter such as fine powder and snake skin generated by air transport was 24 ppm (corresponding to 84 g / hour) in total, and the foreign matter increased about 1.5 times as compared with Example 1. Such an increase in the fine powder impairs the work efficiency of the product user.
[0045]
Example 2
Resin pellets were produced under the same conditions as in Example 1 except that the number of revolutions of the cutter was changed to 650 rpm. The obtained resin pellets were round cake-like. The weight per 50 randomly selected pellets was 889 mg, and the average pellet weight per pellet was 17.8 mg. The resin pellets thus obtained were sent to the dispensing silo by air under the same conditions as in Example 1. Foreign particles such as fine powder and snake skin generated by air transport were 18 ppm (corresponding to 63 g / hour) of the whole. Although there was a little fine powder, it did not hinder the work of the product user.
[0046]
Example 3
Using an autoclave reactor 100 m ^3, it was subjected to continuous bulk polymerization of propylene. As the catalyst, a commercially available Ziegler-Natta catalyst was used, and the polymerization was performed at a polymerization pressure of 3.00 MPa and a polymerization temperature of 70 ° C. The output was 8.5 tons / hour. Regarding the physical properties of the sampled polypropylene, the MFR was 3.0 (g / 10 minutes) and the density was 0.90 (g / cm ³ ).
[0047]
The polymerized polymer was separated into an unreacted gas and a produced polymer by a separator, and sent to an extruder (screw diameter: 305 mm, L / D = 34, 256 nozzles, nozzle diameter: 2.4 mm). Using a neutralizing agent (0.05% by weight of calcium stearate) and an antioxidant (0.15% by weight of IR1010, 0.10% by weight of IF168) as additives, they are uniformly dispersed by melt-kneading in an extruder. After that, it was extruded and cut. The extrusion rate was 3.8 tons / hour, the resin temperature was 265 ° C., the cooling water (PCW) temperature was 55 ° C., and the flow rate was 102 tons / hour. The operating conditions of the cutter were 14 blades and a rotation speed of 720 rpm.
[0048]
The resin pellets thus obtained were in a round cake shape. The weight per 50 randomly selected pellets was 1145 mg, and therefore the average pellet weight per pellet was 22.9 mg.
[0049]
The resin pellets thus obtained were transported to the product dispensing silo by dry air in the piping with dry air. The air transport conditions were such that a pipe having a diameter of 9 inches was used, the pellet transport rate was 40 tons / hour, and the air flow rate was 100 m ³ / min. Foreign substances such as fine powder and snake skin generated by air transport were zero.
[0050]
Example 4
In Example 3, resin pellets were produced under the same conditions except that the extrusion rate was changed to 2.1 tons / hour and the number of revolutions of the cutter was changed to 1500 rpm. The obtained resin pellets were round cake-like. The weight per 50 randomly selected pellets was 295 mg, and the average pellet weight per pellet was 6.0 mg. The resin pellets thus obtained were transferred in a pipe under the same conditions as in Example 3. Foreign substances such as fine powder and snake skin generated by air transport were zero.
[0051]
Comparative Example 2
Resin pellets were produced under the same conditions as in Example 3 except that the number of revolutions of the cutter was changed to 670 rpm. The weight per 50 randomly selected pellets was 1197 mg, and the average pellet weight per pellet was 23.9 mg. The resin pellets thus obtained were transferred in a pipe under the same conditions as in Example 3. The amount of foreign matter of the mustache fine powder generated by the air transport was 0.05 ppm (corresponding to 200 mg / hour). Even if the presence of such mustache fines is small as described above, a user who is strict in quality control closes the filter (mesh) for removing foreign substances installed in the molding machine. In the case of this comparative example, in the molding machine of the product user, the mustache fine powder was solidified in a pill shape, clogged the filter, and had to be stopped.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an apparatus for implementing the present invention.
1: polymerization reactor 2: high-pressure separation tank 3: low-pressure separation tank 4: kneading extruder 5: die plate 5a: nozzle 6: cooling water chamber 7: cutter 8: cooling water pump 9: cooling water tank 10: pellet drying Machine 11: vibrating sieve 12: pellet blower 13: product silo

Claims (4)

In a method for producing a resin pellet by melting and extruding a polyolefin comprising an ethylene-based polymer or a propylene-based polymer using an extruder and cutting the same, the obtained resin pellet has the following property (A). A method for producing resin pellets, comprising cutting as shown.
Characteristics (A): The average weight per cut resin pellet is 6 to 18 mg in the case of an ethylene polymer pellet, and 6 to 23 mg in the case of a propylene polymer pellet. The method for producing resin pellets according to claim 1, wherein the polyolefin is melted, extruded from a nozzle into cooling water, and cut. The method according to claim 1, wherein the resin pellet is an ethylene polymer having a density of 0.86 to 0.97 g / cm ³ and an MFR of 0.01 to 1000 g / 10 min. The method for producing a resin pellet according to claim 1, wherein the resin pellet is a propylene-based polymer having a density of 0.86 to 0.91 g / cm ³ and an MFR of 0.01 to 1000 g / 10 min.

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