JPS59172522A - Production of spherical thermoplastic resin particle - Google Patents

Abstract

PURPOSE:To obtain exactly spherical particles having a sharp particle size distribution and a desired particle size, by centrifugally sparging a thermoplastic resin melt into the form of liquid drops from the periphery of a rotary hollow body having a downwardly enlarging opening. CONSTITUTION:A solvent-free thermoplastic resin melt is fed along the inside wall of a rotary hollow body having a downwardly enlarging opening to be centrifugally sparged into the form of liquid drops from the periphery of the rotary body. The periphery is maintained at a temperature higher than the m.p. of the melt by heating it by supplying heating gas to the external wall of the rotary body. The sparged liquid drops are cooled and solidified by contact with a cool gas. Desirable thermoplastic resins applicable include those having an intrinsic viscosity <=1.2dl/g. A particularly desirable effect can be obtained when this process is applied to a polyolefin.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing spherical fine particles of thermoplastic resin, particularly polyolefin.

Particulate polyolefins have traditionally been used in the fields of rotary molding and powder coating, and polyolefins with relatively medium to low molecular weights, with a molecular weight of 30,000 or less, are used as pigment dispersants, processing modifiers, and polyolefins during plastic processing. It is used in a wide range of applications, including mold release agents and wax product additives. Its particle size is several 1
The size is from 00 microns to 1000 microns and the shape is irregular.

However, in recent years, when handling powder, it has become necessary to have a spherical shape and uniform particle size distribution from the viewpoint of good fluidity and uniform dispersibility in glass or wax-like materials. . Furthermore, requirements for different particle sizes are emerging depending on the application.

By the way, it is known that there are two types of conventional techniques for powderizing thermoplastic resins such as polyolefins.

The first type is mechanical comminution. For example, a method is known in which a suitable solvent is added and the material is mechanically pulverized using a ball mill or the like at 0° C. as is or while the solvent is volatilized at a low temperature.

(Japanese Patent Publication No. 37-32g77, Japanese Patent Publication No. 37-32-t3θ) In this method, the particle size distribution is wide and the shape is irregular and has an acute fracture surface, which is far from spherical.

The second type is a dissolution/precipitation method, in which a specific solvent is used to melt the material by heating, followed by cooling and precipitation after I'c, or a method in which a poor solvent is used for precipitation.

Various proposals have been made for this method depending on the solvent separation method.
jj7, Tokko Sho 3t-/70♂7, Tokko Sho ≠ -l,!
After filtration, centrifugation or evaporation separation using solvent,
During the drying process of the particle cake, agglomeration of the polymer particles is unavoidable, requiring re-grinding. Furthermore, the shape of the particles is not spherical.

The third type involves dispersing the molten polymer in a solvent under high shear agitation with the aid of various dispersants and then cooling. The dispersant is a surfactant, and the solvent is water. For example, a block copolymer of ethylene oxide and propylene oxide is used as the surfactant (4? Kosho 32=
, 23rij) This method makes it relatively easy to obtain spherical particles, but it has drawbacks such as loss of product value.

The gg method is a method of spraying a polyolefin melt into the atmosphere, and was developed in the 1970s. -/74L01t using one type of co-fluid nozzle has been proposed. This method is an excellent method in that the equipment is simple, but as stated in the specification, high pressure (/00~j001)sig) is required to inject the molten material. can be,
It also has a wide particle size distribution and has drawbacks such as easy formation of fibrous substances.

The present inventors conducted intensive studies with the aim of overcoming these drawbacks and obtaining substantially spherical particles with a sharp particle size distribution at any desired particle size, and as a result, they identified thermoplastic resins such as polyolefins. It has been found that a method of dispersing particles using a rotating body having a shape is suitable, and the present invention has been achieved.

That is, the object of the present invention is to reduce the particle size to 10. %1000μ,
The objective is to industrially advantageously obtain a substantially spherical thermoplastic resin, particularly polyolefin, fine particle aggregate with uniform particle size. The melt is distributed as droplets by centrifugal force from the edge of the dispersion section by supplying it to the inner wall surface of a rotating body having an opening that expands downward, and at this time, the edge is supplied to the outer wall surface of the dispersion section. This can be easily achieved by heating and maintaining the melt at a temperature higher than the melting point of the melt using heated gas, and then cooling and solidifying the dispersed droplets by contacting them with cold gas.

Thermoplastic resins used in the present invention include polyolefin resins such as polyethylene and polypropylene, polycarbonate resins, fluorocarbon resins, polyester resins, styrene resins, acrylic resins, polyacetal resins, vinyl acetate resins, polyamide resins, vinyl chloride resins, etc. Intrinsic viscosity 1
．． -[dA/7) or less are preferably used.

Particularly favorable results are obtained when the present invention is applied to polyolefins. Polyolefins are polymers such as polyethylene, polypropylene, polybutene, poly≠methylpentene-1, etc., or those modified by oxidation or with a compound having a polar group. It may also be a copolymer with

In the case of polyethylene/intrinsic viscosity of tetralin solution at 30°C: o, oμ～ノ, 2eLl/g, density O1: O～θ, ri:
g, ycc-, for polypropylene 13j'c intrinsic viscosity of tetralin solution 0.0/-o, s d1/9,
A material having a density of O1 6 to 0.9/g/cc is preferably used. Substantially solvent-free polymers are used in the method of the present invention. Use of a polymer containing a solvent, that is, a polymer in the form of a solution dissolved in a solvent, is undesirable because the product powder becomes porous particles, resulting in poor surface hardness and transparency, and sometimes a decrease in bulk density.

In the present invention, a hollow rotating body having a downwardly expanding opening is used as a means for dispersing and granulating the polymer, but the downwardly expanding opening does not necessarily have to cover the entire inner wall surface.

The rotating body can take various shapes such as a conical shape, a cup shape, and a hemispherical shape. The magnitude of the rotation μ varies depending on the polymer throughput and the desired particle size, but the diameter of its lower edge is usually between 30 m* and r o o mm. The larger the processing amount and the smaller the particle size, the larger the diameter needs to be, but if it is too large, high-speed rotation will be difficult.
0θm11L is preferably used.

The number of rotations of the disk is 100 to 100,000, which is a suitable condition for a rotary furnace. The particle size can be controlled by the rotation speed. The root nodule size becomes smaller when the rotation speed is high. Usually, the rotation speed is controlled by a combination of an electric motor and a speed increaser, and a compressed air drive motor is used to obtain the desired particle size.

The molten polyolefin is introduced into the inner wall surface of the rotating body,
A thin film is formed on the inner wall, and from the edge it becomes droplets and disperses into the cooling gas stream. The cooling gas stream removes the heat of crystallization of the molten polyolefin that has been cooled in advance and becomes droplets, and solidifies it. In the case of polyolefin, the heat of crystallization is usually as high as 0 Kcal per gram of polyolefin, so it is appropriate for the amount of polyolefin to be processed. Sufficient cold airflow must be provided. However, the cold air flow often cools the rotating body, especially the edges and the surrounding space. For this reason, irregularly shaped particles and fibers are generated, making it difficult to obtain truly spherical particles. This tendency becomes more pronounced as the scale of the facility increases, and conventional methods such as strengthening heat retention in the surrounding area are completely insufficient. The reason for this is presumed to be that the high-speed rotation of the rotating disk draws in a cold air flow.

In order to solve the above problem, the inventors of the present invention (1) heated the molten resin to a sufficiently high temperature, and (2) introduced heated gas to the outside of the rotating plate (the side opposite to the surface on which the liquid film of the resin was formed). , found that it is important to spray the edges. For example, in the case of molten polyolefin, it is lower than the melting point (20℃,
Preferably, it is necessary to heat the heated gas to a temperature higher than SO°C, and the temperature of the heated gas is at least higher than the melting point, preferably at least /Q°C higher than the melting point, so that the area to be sprayed is melted. The space several tens of millimeters outside the edge and periphery of the rotating body, where the resin liquid film leaves as droplets, is the flying surface of the droplets. Since the droplets fly in a direction perpendicular to the rotational axis due to centrifugal force, the heated gas is blown against the edge of the rotating body and at the same time, it is blown parallel to the rotational axis so as to cut the droplet flying surface at right angles. This can be easily achieved, for example, by providing a fixed outer cylinder on the outside of a rotating body that rotates at high speed, introducing a molten polyolefin into the inner surface of the rotating body, and introducing heated gas into the gap between the outer surface of the rotating body and the outer cylinder. Vine.

Although FIG. 1 shows an example in which the rotating body is conical, FIG. 2 shows an example in a cup shape, and FIG. 3 shows an example in a hemispherical shape, the present invention is not limited to FIGS. 7 to 3. In either case, the structure is such that the molten resin is introduced into the inner wall surface of the rotating body and the heated gas is introduced into the outer wall surface to heat the edge and its vicinity. In the figure, l is a rotating body, λ is an outer cylinder, 3 is a hot gas inlet, and G is a molten resin injection port.

Note that it is necessary to heat the rotating body in advance before introducing the molten resin, and the above heating gas introduction method and the above rotating body structure are also useful for that purpose.

The heating gas is an inert gas such as N2, He, Ar, water vapor,
Although CO, air, etc. are used, N2 is preferably used from the viewpoint of preventing dust explosions and being economical. The thermoplastic resin particles thus obtained are perfectly spherical and have a narrow particle size distribution (with a smooth particle surface and a high bulk density (e.g. 0.3~Q, l).
, g/cc] degree of fluidity. Furthermore, by controlling the rotation speed of the surrounding plate, the average particle size can be reduced from lOμ to 100μ.
It is possible to control the particle size to any size down to 0μ.

As for the width of the particle size distribution, Rosin Ramler (RO8i
n, the value of n in the Ramm1f3rJO formula is 2 or more.

Next, examples will be shown.

In the Examples, the intrinsic viscosity, density, melting point, particle size distribution, and bulk density were each measured by the following methods.

Intrinsic viscosity ° It was determined by the one-point method using an Utsbelohde viscometer.

Polyethylene 730°C Tetralin solution polypropylene / 3 J °C // tt @ degree: J engineering 8
Melting point at 67tO: PerkinElmer differential scanning thermometer DSC-
/B type was determined from the peak of the endothermic thermogram.

Particle size: @ 'l'' if the average particle size is 10μ or more
1Vji (J Engineering S-z Doni Q/) was measured using a rotary tube sieve shaker.

Light transmission if the average particle size is less than goμ Use a type particle size distribution analyzer (the dispersion medium is n-hexane).

The average grain size is 8 tons! ; Expressed as 0% particle size, particle size distribution is Ros in-Rammler distribution function R=/Q
The n value of Qe"" is calculated by Rosin=Rammler and C1og
(J-40gR): n is determined from the slope of IOgX -4-'b'].

Bulk density [:, due to Tl5- &7.2/.

Example 1 According to the flow shown in Figure t, the intrinsic viscosity t), t t ll/9
Approximately / o kg of polyethylene with a density of O, ゜A g/cc and a melting point of 20℃ is charged into a melting pot with a volume≠001, and the above resin is heated and melted by passing a heating medium of JjO℃ through the jacket of the melting pot. did. This is a double pipe transfer pipe■
The resin was controlled to have a temperature of /9.0° C., and introduced into the top of a granulation can (2) with a diameter of /7F1 and a height of J. A conical rotating body (shown in Fig. 1) with a diameter of 50 degrees and a cone angle of 60 degrees and a protection tube are attached to the top of the inside of the granulation can, which have been preheated with iso℃ N2 gas ■. It is rotated at 1,000 revolutions per minute. The molten polyethylene is inside the rotating plate at a rate of 1 Okl/hour. was introduced at a flow rate of The heated N2 gas used during preheating continues to be heated at yN per hour.
d, and the granulation can has a temperature of about 3j-℃.
7j N2 gas was introduced at a rate of 7N7.1 per minute.

The particles generated in the granulation can were extracted from the bottom of the can, collected by a bag filter (■), and then extracted from the bottom as a product.

The particle size of the product particles is /go micron, and the particle size distribution is Rosi
n value in n-Rammler distribution function! , θte was there.

This is the cumulative fraction, 2j% particle size and 7! Expressed in terms of the ratio of particle sizes, it is 1. ≠(,2)θμ7isoμ=ノ,弘'', which is an extremely sharp distribution.

Bulk density is 0. j Og/cc, perfectly spherical in shape, transparent particles and friends.

Examples λ to Example 1 In Example 1, the shape of the rotating disk was changed to a cup shape (as shown in FIG. 2), and the operation conditions shown in Table 7 were used to obtain transparent, perfectly spherical fine particles. Measurement results of particle size, particle size distribution, and high density? It is shown in Figure 1.

Example j-10 Shown in Table 7-f Raw material polyolefin, resin temperature, extrusion amount,
Transparent θ) true spherical fine particles were obtained by performing the same operation as in Example 1 under rotating disk operating conditions, and the particle size, particle size distribution, and bulk density are shown in Table 1.

Example 1 No. 2 Maleic anhydride 1001000pp grafted with intrinsic viscosity 0. / / dl/jj, density 0.7 O, melting point /, 2
The procedure was carried out in the same manner as in Example 1 using modified polyethylene at 0° C. under the conditions of 7r' shown in Table 1 to obtain transparent true spherical fine particles. Table 7 shows the particle size, particle size distribution, and bulk density.

Example 13, /44 Intrinsic viscosity 0. / 2 d6/g, m degrees θ, 70, melting point l
The same operation as in Example 1 was carried out using polypropylene at 0.degree. C. under the conditions shown in Table 1 to obtain transparent true spherical fine particles. Table 7 shows the particle size, particle size distribution, and bulk density.

[Brief explanation of drawings]

7 to 3 show an example of the shape of the rotating body used in the present invention. is the heating gas inlet, and g is the molten resin injection port. Figure ≠ is an example of the flow when producing thermoplastic resin fine particles according to the present invention, where ■ is a melting pot, ■ is a transfer pipe, ■ is a granulation mill, ■ is a nitrogen gas introduction pipe, ■ is a rotating body, and ■ is a granulation mill. 2 is a nitrogen gas introduction pipe for cooling, and 2 is a bag filter. Applicant Mitsubishi Chemical Industries, Ltd. Agent Patent attorney For long diameter - 1 other person Procedural amendment (voluntary) 2 Name of the invention Method for manufacturing thermoplastic resin spherical particles 3 Person making the amendment Applicant (JRIB) Mitsubishi Chemical Industries, Ltd. Co., Ltd. 4 Agent 〒100 (and 1 other person) 5 Subject of amendment The "Detailed Description of the Invention" column of the specification is corrected to [Evening~A Ocab J. (3) On page 1Q, line 1j of the same page, it says “mouth plate body”.
Correct it to "rotating body." (4) On the same page 1/page No. 1 Hiroki, the text "1 Utsperohde type viscometer" has been corrected to read "Ubbelohde type viscometer."that's all

Claims (4)

[Claims] (1) A thermoplastic resin melt containing substantially no solvent is supplied to the inner wall surface of a hollow rotating body having a downwardly expanding opening, and the melt is dispersed into droplets from the edge of the rotating body by centrifugal force. At that time, the edge is heated and maintained at a temperature higher than the melting point of the melt by hot gas at the cutting edge supplied to the outer wall surface of the rotating body, and the dispersed droplets are brought into contact with cold gas. A method for producing thermoplastic resin spherical particles characterized by cooling and solidifying them. (2) Special ilF where the intrinsic viscosity of the thermoplastic resin is /, codl/j;l or less! l-The method according to claim (1). (3) The method according to claim (2), wherein the thermoplastic resin is a polyolefin. (4) Claim (1) in which a fixed outer cylinder is provided outside the rotating body, and the temperature of the edge of the rotating body is maintained by introducing heated gas into the gap between the outer surface of the rotating body and the outer cylinder. The method described in section.