JP2535422B2 - Method to evenly disperse particles in polymer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for uniformly dispersing inert particles (hereinafter, simply referred to as particles) in a polymer, and more specifically, premixing the particles with a molten polymer, However, after passing through an inorganic porous body having specific continuous pores (hereinafter, simply referred to as a porous body), a plurality of particles existing in the premixture are aggregated into a secondary particle into a single particle. It relates to a method of separating and dispersing into a homogeneous mixture, which additionally gives rise to a high affinity between the polymer and the particles.

[Prior art] The most common method of melt mixing a polymer and particles is
The solid polymer and the particles are introduced into a single screw extruder or a multi-screw kneader, and a local strong shearing force is applied to overcome the cohesive force of the secondary particles in a state where the polymer is melted, thereby forming the secondary particles. This is a method of dispersing and extruding single particles.

In order to enhance the mixing and dispersing action of this extruder,
Various screw designs have been devised. For example,
BM screw of Maillefer, screw with flute groove barrier of Union Carbide, DIS screw with various pins arranged in screw groove, plug with special groove and hole at the tip, spiral angle Known is a dullage type screw or the like in which a continuous shallow groove cut into multiple screws is attached to the tip.

In addition, the barrel design has been improved to improve the kneading action. For example, a KCK kneading extruder in which a rotary blade is attached to a screw shaft and a barrel groove is a fixed blade is known.

Generally, a multi-screw kneader has a higher kneading effect, and for example, the kneading effect of a twin-screw extruder having two rotors having special blades or a kneading disk in a kneading section is generally highly evaluated. I have.

As another means for static mixing, for example, a static mixer manufactured by Kenix is known. This is one in which clockwise and counterclockwise spiral elements are alternately connected in a polymer pipe, and a mixing action occurs while the polymer passes through the pipe.

[Problems to be solved] The effect of mixing and dispersing by the extruder is as follows:
It is manifested by a shearing action. However, when a strong shearing or shearing action acts on the polymer, a part of the energy is converted into heat energy and the temperature of the polymer rises, resulting in a decrease in molecular weight and coloring due to thermal degradation. As a result, the mechanical properties of molded articles made from this polymer may be seriously affected, or the commercial value may be reduced by coloring, and there is a limit to enhancing the kneading action. Actually, a polymer extruded by a twin-screw kneader having a high kneading action also has a large number of secondary agglomerated particles, and often exceeds the permissible limit of dispersibility required for forming into a fiber or a film.

Also, in a static mixer, the polymer flow is divided, then the flow direction is reversed and the flow is re-merged repeatedly, so mixing of the polymer is promoted, but secondary particles that have agglomerated are separated and dispersed into temporary particles. Almost no effect is observed. Therefore, when mixing the particles with the molten polymer, it is difficult to produce a highly dispersed mixture up to the primary particles.

From the above situation, in order to obtain a polymer in which particles are highly dispersed, conventionally, it is general to disperse and polymerize at the stage where the viscosity of the liquid is low in the polymerization process of the polymer. For example, Japanese Patent Publication No. Sho 59-1415 proposes a method of producing a polyester in which particles are uniformly dispersed, by uniformly dispersing the particles in glycol by ultrasonic treatment, and then polymerizing the particles.

Generally, in order to stably and uniformly disperse the particles in glycol, the surface of the particles must be hydrophilic, but the polyester obtained by polymerizing the particles is lipophilic, so the affinity between the particles and the polymer is low, Therefore, the polymer is separated from the grain interface by a stretching operation during the production of a film or the like to form a void, which adversely affects the surface properties and mechanical properties of the product.

Conversely, when particles having a high lipophilicity are used, it is difficult to disperse the particles uniformly in glycol, and this is a trade-off relationship.

[Object of the Invention] An object of the present invention is to provide a method for uniformly dispersing and mixing fine particles in a molten polymer, and another object is to use for molding fibers, films, etc., in which particles are highly dispersed. It is an object of the present invention to provide a method for producing a uniform polymer without lowering the molecular weight due to heat deterioration and without causing coloring, and for producing a product having a high affinity between particles and the polymer.

[Structure / Effect of Invention] According to the present invention, the average particle diameter is 0.7 to
0.005 to 4% by weight of inorganic or organic particles (with respect to the polymer) having a particle diameter of 5 μm and a contact angle with water of 10 ° or more are premixed with a molten polymer, and then the obtained premix is averaged. The pore size is 10 times or more the average particle size (X) of the above particles, It is achieved by a method of uniformly dispersing particles in a polymer, which is characterized by passing the particles through an inorganic porous material having continuous pores to uniformly disperse the particles.

The polymer to be used in the present invention is a thermoplastic polymer, and examples thereof include olefin polymers such as polyethylene, polypropylene and polystyrene, amide polymers such as polyhexamethylene adipamide and poly-ε caprolactam, and polybutylene terephthalate. Examples thereof include ester-based polymers such as polyethylene terephthalate and polyethylene naphthalene dicarboxylate, and polycarbonate, polyacetal, polyphenylene ether, and polyphenylene sulfide. Of these, medium ester polymers, particularly aromatic polyesters are preferable.

In the present invention, as the fine particles to be dispersed in the polymer, for example, a single or a combination of two or more kinds of inorganic fine particles such as torque, clay, kaolin, silica, alumina, titania, zirconia, calcium phosphate, calcium carbonate, etc. It is made of. Examples of the organic fine particles include fine particles of high melting point organic substances such as silicone resin and polyarylate. Here, the high melting point means that the fine particles do not melt during melt mixing. The organic fine particles can be used together with the inorganic fine particles.

The average particle size of such particles is 0.7 to 5 μm. If the average particle size is less than 0.7 μm, especially less than 0.01 μm, the effect when dispersed in the polymer is not sufficient, and for example, when imparting slipperiness by forming fine irregularities on the surface of the film The effect is not sufficient, which is not preferable. On the other hand, those having an average particle size of more than 5 μm are not preferable because when they are dispersed in a polymer, they have an adverse effect, and for example, the fine irregularities are too large and the film surface is too rough.

The particles used in the present invention must have a contact angle with water of 10 ° or more, preferably 15 ° or more, particularly preferably 20 ° or more. When this "contact angle with water" is less than 10 °, a sufficient dispersion effect cannot be obtained, voids are easily formed around the particles, and sometimes the porous body is clogged to cause a void before and after the porous body. Can cause large pressure differences,
Not preferred.

Here, the contact angle with water means that the particle aggregate is formed into a smooth film, a water drop is placed on the surface of the obtained formed body, and when the state of equilibrium is reached, water and the surface of the formed body around the water drop are formed. Expressed as an angle.

Generally, the higher the lipophilicity of the particles, the larger this contact angle. However, if this contact angle is too large, the adhesion between the particles and the polymer decreases, so this contact angle is 170 ° or less.
More preferably, it is 160 ° or less.

Silicone particles are originally lipophilic and have a high "contact angle with water."
However, many particles of metal oxides such as alumina and silica are hydrophilic. To make these hydrophilic particles lipophilic so that the "contact angle with water" is 10 ° or more, for example, known surfactants and coupling agents such as fatty acid salts, silanes, titanates, and aluminum It can be easily applied to the present invention by the surface treatment with.

Also, the amount of particles to be dispersed is based on the polymer,
It is in the range of 0.005 to 4% by weight. If this amount exceeds 4% by weight, the porous material may be clogged, which is not suitable.

In order to preliminarily melt-mix such fine particles with a polymer, an ordinary single-screw extruder and a multi-screw kneader (multi-screw extruder) can be used. However, it is a matter of course that conditions that do not generate excessive heat should be selected.

It is desirable that the polymer and the particles are mixed beforehand when the raw materials are charged into the extruder. However, for example, in the case of a multi-screw extruder having a high kneading action, the polymer and the particles can be separately charged. That is, the polymer and the particles can be supplied from the same inlet, or the polymer can be supplied first, and the particles can be supplied in the melting process or the kneading process. In an extruder equipped with a vent port, the liquid can be separated and removed at the vent port, so that the particles can be dispersed in the liquid and supplied.

In the present invention, the premix thus obtained is passed through the porous body. This porous body is, for example, a porous sheet having continuous pores in which particles such as spherical or irregularly shaped metal or ceramic having protrusions are aggregated and their contact points are fixed. For example, a porous sheet-shaped molded article obtained by sintering spherical bronze particles or irregularly shaped stainless particles is convenient.

According to the experimental findings, the dispersion effect of particles by the evaluation method described below has a correlation between the average particle diameter of the particles and the average pore diameter of the porous body. Although it depends on the particle shape and particle size distribution, in the case of the same particles, generally, the smaller the pore size of the porous body, the higher the separation and dispersion action of the aggregated particles. However, if the average pore size is less than 10 times the average particle size of the particles, the effect of trapping the particles in the porous body becomes remarkable, and the pressure loss when the polymer passes through the porous body may increase rapidly. . On the other hand, the average pore size is the average particle size (X) of the particles. If it exceeds, the effect of separating and dispersing the aggregated particles of the present invention is often poor.

Therefore, the particles premixed with the molten polymer in the extruder are
In order to highly separate and disperse by passing through the porous body, the average pore size of the porous body is 10 times or more of the average particle size of the particles, Must be below, but preferably 15 times or more Or less, more preferably 20 times or more It is the following. It is desirable to select a porous body with an optimal pore size according to the shape of the particles, particle size distribution, etc.

Although it depends on the particle size distribution of the particles or the average pore diameter of the porous body, it is unavoidable that some of the coarse particles are trapped by the porous body to cause clogging of the porous body. As a result, the pressure loss when the polymer passes through the porous body increases with time. In order to alleviate this pressure rising tendency and enable continuous operation for a long time, it is necessary to reduce the flow rate of the polymer when passing through the porous body, or to increase the pressure resistance of the porous body. As a concrete measure, a porous body which is generally used as a polymer filter is preferably processed into a cylindrical shape or a disk shape.

In carrying out the method of the present invention, a method of premixing particles and molten polymer with an extruder and then passing through a porous body, or extruding the premix, cooling once,
For example, a method may be used in which the material is molded into chips, and then the preliminary mixture is melted again by an extruder, melt-mixed with other polymer if necessary, and then extruded through a porous body. Then, using the obtained polymer (a polymer in which the particles are highly dispersed in the polymer), for example, a film or the like having excellent particle dispersibility can be formed. In addition, the particles used are lipophilic with a “contact angle with water” of 10 ° or more. As a result, they generally have a high affinity with polymers and greatly suppress the voids that often occur at the particle interface due to operations such as stretching. You can do it.

The various physical properties and properties in the present invention are measured and defined as follows.

1) Average particle size (X) The particles are scattered on the electron microscope sample stand so that the individual particles do not overlap as much as possible, and a gold thin film deposition layer (layer thickness 200-300Å) is formed on the surface by a gold sputtering device. Then, observe with a scanning electron microscope at a magnification of 10,000 to 30,000 times, and use Luzex 500 manufactured by Nippon Regulator Co., Ltd.
The area-equivalent diameter of at least 100 particles is determined, and the number average value thereof is used to express the average particle diameter.

2) Average pore size of porous material A measurement method with ASTM-E-128-61 as a reference standard. One end of the pipe reaches the air supply source and the other end is a trumpet-shaped open end with this open port facing up. Using a device fixed to the bottom of the container, attach a porous plate of the DUT to the opening so that there is no gap. Fill the container so that the liquid level of isopropyl alcohol is 15 mm above the porous plate, and adjust to 25 ° C.

Next, when the air pressure in the pipe is gradually increased and air bubbles start to emerge from the medium and the air amount is further increased, the rate of change in the air flow rate becomes substantially constant. The value when the air pressure at this time is extrapolated to zero flow rate is taken as the bubble point pressure P (mmH ₂ O) at the intersection, and the average pore diameter D (μm) of the porous body is obtained by the following formula.

D = 3700 / P 3) Dispersion effect A mixture obtained by mixing particles with a molten polymer is extruded from a die by a conventional method and rapidly cooled to form an amorphous film having a thickness of 15μ. This film was observed under a microscope under transmitted light, and 2
Secondary particles in which more than one primary particles are aggregated and single particles are all regarded as one particle, and 100 particles are randomly selected and expressed by the number of single particles in them.

4) Contact angle 1g of particles is mixed with an appropriate amount of 0.5-1.0ml of ethyl alcohol (determined by the density of particles, etc.) to form a paste, and applied on a smooth glass plate to form a smooth film with a thickness of about 0.2mm. To form. The surface of this coating is held horizontally, and water droplets are placed on it. The equilibrium state is represented by the angle formed by water and the coating formed of aggregates of particles.

[Examples] Hereinafter, the present invention will be specifically described with reference to Examples.

Examples 1 to 3 Spherical silica particles having an average particle size of 0.7 μm and a contact angle with water of 60 ° were uniformly solid-phase mixed with 500 times the weight of polyethylene terephthalate chips, and then charged into a single-screw extruder and melt-mixed. Then, the shaped stainless steel particles were separately passed through three different porous bodies formed by sintering, extruded in a sheet form from a die and rapidly cooled to obtain a film having a thickness of 15 μm.

The average pore size of the porous body used here and the particle dispersion effect of the film obtained by passing through the porous body are as shown in Table 1, and the dispersion effect is significantly improved as compared with Comparative Examples described later.

Comparative Example 1 The same procedure as in Example 1 was repeated except that the molten mixture was not directly passed through the porous body but was directly extruded. The results are shown in Table 2.

Comparative Examples 2-3 In Example 1, except that the porous body had the configuration described in Table 2, the same film formation and evaluation were performed. The results are shown in Table 2.

Example 4 A spherical silicone resin particle having an average particle size of 1.0 μm and a contact angle with water of 110 ° was uniformly mixed in a solid phase with a 700-fold weight polyethylene terephthalate chip, and a twin-screw extruder (made by Nippon Steel, TEX-44) was used. ) Is melt-mixed and passed through a two-layer structure porous body (molded into a leaf disk structure) having the structure shown in Table 3,
A 15 μm-thick amorphous film was formed into a film, and the dispersion effect was evaluated. The results are shown in Table 3, and the film has excellent dispersibility of particles.

Example 5 An amorphous film having a thickness of 210 μm was prepared by using the same particles, a film forming apparatus and a porous body as in Example 1, and the film was vertically oriented at 85 ° C.
The film was stretched 3.6 times and 3.9 times in the transverse direction at 100 ° C. and then heat treated at 220 ° C. to form a biaxially stretched film having a thickness of 15 μm.

As a result of microscopic observation of the film with transmitted light, the same stretched film containing the same particles as in Example 1 except that the contact angle with water was 0 ° (water droplets penetrated into the film formed by the particles). Although a large number of agglomerated particles were found and voids were found around the particles, no voids were found in the film of this example, and the adhesion between the particles and the polymer was excellent.

Claims (1)

(57) [Claims] 1. Extrusion of 0.005 to 4% by weight (based on the polymer) of inorganic or organic particles except carbon black having an average particle size of 0.7 to 5 μm and a contact angle with water of 10 ° or more and a molten polymer. Pre-mixing in a machine and then the resulting pre-mixture was mixed with an average pore size of 10 times the average particle size (X) of the above particles.
More than double, A method for uniformly dispersing particles in a polymer, which is characterized in that the particles are uniformly dispersed by allowing the particles to pass through an inorganic porous body having the following continuous pores.