JPS5942009B2 - Method for producing polyamide resin composition containing inorganic filler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a homogeneous composite composition by mixing a high concentration of inorganic filler into a polyamide resin, and provides an extremely simple and economical method. It is.

The composition obtained by filling polyamide resin with an inorganic filler is industrially used as mineral-reinforced nylon because it improves various properties such as rigidity, hardness, heat deformation resistance, dimensional stability, and water absorption. We are looking forward to further developments.

However, industrially, polyamide resin is generally in the form of pellets or coarse chips, and it is extremely difficult to crush the pellets, so many difficult issues remain in the method of filling inorganic materials in the form of fine powder. Ta.

When using well-known mixing techniques, for example, when mixing by charging into various extruders, poor classification and biting are noticeable, and it is extremely difficult to fill in more than 40% by weight of finely powdered inorganic substances.

On the other hand, even when using a kneading device such as a Panbury mixer or kneader, polyamide resin has a high melting point and low melt viscosity, so self-heating due to friction is insufficient, making it difficult to completely melt and uniformly disperse. It is. The present inventors have surprisingly found that by mixing polyamide in the form of pellets, threads, or other shapes with a smooth surface with a finely powdered inorganic substance under special conditions at high speed, it can be turned into homogeneous flakes or powder. The inventors have discovered that it is possible to produce a useful material that is easily moldable by providing a composition, and have arrived at the present invention.

That is, the present invention comprises 60 to 15 parts by weight of polyamide resin of various shapes having an average specific surface area of 2 μm/g or more, and 40 to 85 parts by weight of inorganic filler powder having an average particle size in the range of 0.01 to 100 μm. The components are mixed at high speed in a high-speed fluid mixer with built-in rotary blades at a temperature range of 20°C above the melting point of the resin, and immediately after the rotor torque (motor load) starts to rapidly increase, the mixture is mixed with high-speed fluid mixer. The present invention relates to a method for producing an inorganic filler-containing polyamide resin composition, which comprises discharging and rapidly cooling the composition. There has already been a long-standing method to obtain a composition by mixing a thermoplastic resin such as polyolefin (PVC) whose melt viscosity has a slow temperature dependence with an inorganic substance at a temperature above its melting point using a high-speed fluid stirring device such as a pen shell mixer. Several examples are known.

For example, for PVC, a method is known in which powder is used, and fillers, stabilizers, etc. are mixed in and gelled in a wide temperature range above the melting softening temperature (Masayuki Furuya, [Vinyl Chloride Resin], p. 270, Showa Published by Nikkan Kogyo Shimbun in 1947). In addition, although it is more difficult in the case of polyolefins that have a distinct melting point compared to PVC, the present invention provides a method for obtaining useful compositions by mixing specific powder resins with inorganic substances under specific conditions. (Japanese Unexamined Patent Application Publication No. 11344/1989,
JP-A No. 48-92441). Furthermore, similar technology was subsequently reported for polyolefin (Japanese Unexamined Patent Publication No. 4
No. 9-18148). It has also been proposed that polyolefins need to be made into a porous resin belet having a smooth surface before being mixed with an inorganic substance. However, due to the various difficulties mentioned above, there have been no successful examples of polyamide resins.

However, as a result of intensive studies based on the already completed invention (Japanese Unexamined Patent Publication No. 48-92441), the inventors of the present invention discovered that it is possible to homogenize a highly concentrated inorganic substance using resin in the form of pellets, threads, or other shapes. We have now arrived at the method of the present invention, which allows to obtain a composition that is easy to mix and useful.

The present invention will be explained in more detail below.

The polyamide resin used in the present invention is a general polyamide, such as nylon-6, nylon-66, nylon-610, nylon-11, nylon-12, or a polyamide having an aromatic ring or a heterocyclic ring in the main chain. These are homopolymers and copolymers, and the type is not particularly limited.

The shape of the polyamide during mixing is preferably powdery or granular, and may be film-like or fibrous.
It may be a molded product or a crushed product thereof. In the case of films or fibers, large ones are possible as long as there is no problem with mixing (overload of mixer motor, etc.).
Preferably shredded. Molded products or their crushed products are also possible, but the wall thickness is 10 mm or less and the cross-sectional area is 1.
It is desirable to have a small piece shape of 0d or less. Overall, the average specific surface area of each shape needs to be 2d/9 or more, preferably 5cii/9 or more, and more preferably 10d/fl or more. If the surface area of the resin is smaller than this range, heat transfer will not be sufficient and heating will not be uniform, making it impossible to obtain a homogeneous mixture according to the present invention. Fillers useful in this invention include all inorganic fillers and inorganic pigments, but must be in the form of fine powder particles.

The average particle diameter of the filler is in the range of 0.01 to 100μ, particularly preferably in the range of 0.04 to 40μ, and more preferably in the range of 0.4 to 20μ. If the powder particles are too small, powder scattering and other operational difficulties occur; if the powder particles are too large, it is difficult to obtain a homogeneous mixture with the resin. Examples of fillers include carbonates such as calcium carbonate, magnesium carbonate, and barium carbonate, hydroxides such as magnesium hydroxide and aluminum hydroxide, magnesium oxide, zinc oxide,
Oxides such as titanium oxide, sulfates such as calcium sulfate and calcium sulfite, white carbon, glass fiber powder,
These include asbestos, kaolin, talc, silica such as mica, and silicates. Two or more kinds of such inorganic fillers may be mixed, and the filler surface may be subjected to various surface treatments. The amount of inorganic filler mixed into polyamide resin is usually 10% in total of polyamide resin and filler.
With respect to 0% by weight, the filler concentration is 40-85% by weight, more preferably 50-70% by weight.

If the filler concentration is lower than the above range, the anti-adhesion effect of the filler at high temperatures will not be sufficient, and the resins will adhere to each other to form giant agglomerated secondary particles, inhibiting homogeneous mixing. If the filler concentration is higher than the above range, the filler particles cannot be embedded and dispersed in the polyamide resin, and the free filler powder makes workability extremely poor. The apparatus used in carrying out the present invention is:
This is a high-speed fluid mixer with built-in rotary blades that can heat up to a temperature of 20°C above the melting point of polyamide resin, and includes a thermometer and rotary blade torque meter (motor load meter) as additional equipment.

For example, a high-speed fluid mixer with a heating jacket, such as a pen shell mixer, is preferably used. In order to obtain the effects of the present invention, the most important thing is to bring about a sudden increase in rotor torque in a temperature range of 2' C1 preferably at or above the melting point of the resin and 10°C above the melting point, followed by rapid cooling immediately after that. That's true.

Therefore, in order to satisfy these conditions, conditions such as the rotational speed of the rotor, the shape of the rotor, and the jacket heating conditions should be selected. In the present invention, it is necessary to mix the polyamide with the filler at high speed when melting starts, and the effects of the present invention cannot be obtained below the melting point.

When the mixing temperature exceeds the above range, the melt viscosity of the polyamide rapidly decreases as the temperature rises, which is undesirable because the resins mutually fuse to form giant agglomerated secondary particles. The time for high-speed fluid mixing is affected by the degree of preheating of the resin and filler, but a range of 30 seconds to 10 minutes is usually sufficient if both have been heated to the melting point of the resin.

As mentioned above, the mixing end time is immediately after the rotor torque (motor load) starts to rapidly increase, but it is usually 1 to 60 seconds later, and more preferably 5 to 20 seconds later. Excessive mixing time is undesirable because the resin composition progresses to become giant agglomerated secondary particles and causes abnormal heat generation. Therefore, in the case of polyamide resin, it is necessary to discharge the resin composition from the heated mixing tank after the mixing time and rapidly cool it to below the melting point of the resin while stirring to pulverize the resin composition.

Although heating fluid mixing, stirring and cooling can be carried out in the atmosphere, it is preferable to carry out the process in an atmosphere of nitrogen or other inert gas to avoid decomposition or deterioration of the polyamide resin or filler.

The resin composition obtained above is in the form of powder or flakes, and most of them have a size of 0.2 to 5 m77! within the range of

Furthermore, since the filler powder is embedded and dispersed in the polyamide resin, there is no need to worry about classification. This uniform dispersion is then fed to a granulating device or a molding device equipped with a degassing mechanism and granulated or molded to obtain a complete polyamide resin composition.

In the case of polyamide, it is more likely to decompose on contact with inorganic substances at temperatures above its melting point than vinyl chloride resins and polyolefins, and it is hygroscopic, so it cannot be granulated or processed using equipment with a degassing mechanism. It is necessary to mold it. As for the degassing mechanism, the compression ratio is 2 in the screw extruder.
．． It is preferable that it is 5 or more, or it is preferable that it is a vent type extruder. In the case of compression molding, it is preferable to repeat the compression-degassing operation several times, and in the case of injection molding, this is possible by selecting conditions such as the back pressure per screw, the number of revolutions of the screw, and the temperature. Generally speaking, in the case of polyamide, it is preferable in terms of quality to granulate the uniform dispersion in a vented extruder and then supply it to various molding machines for molding. The polyamide resin composition of the present invention obtained by the above method may contain stabilizers, lubricants, crosslinking agents, fibrous reinforcing materials, dyes, flame retardants, antistatic agents, and other additives in addition to the above composition. good.

The present invention will be specifically explained below using examples.

Example 1 14 kg (70% by weight) of heavy calcium carbonate fine powder with an average particle diameter of 1.8 μm and a number average molecular weight of 2300
After preheating 6 kg of No. 0 nylon-66 (4φ x 3mm pellets) to 250°C, a 1501 pen shell mixer (manufactured by Mitsui Miike Seisakusho, stirring blade rotation speed 1460rPII1) was heated to 250°C.
When fluid mixing was carried out for 4 minutes using a jacket temperature of 27°C, the temperature inside the mixing tank reached 258°C, and the rotor torque (motor load) began to rise rapidly.

Then, mixing was continued for another 10 seconds, and the mixture was discharged into a cooling mixer 1501 (manufactured by Mitsui Miike Seisakusho, blade rotation speed: 360 rpm, jacket temperature: 15° C.), and cooled while stirring for 10 minutes. The obtained resin composition was in the form of powder particles with an average particle size of 10 to 35 mesh, and there were no giant particles with a diameter of 6 mm or more.

This powdery resin composition was processed using a vent type extruder (D5Omml).
L/D=28, compression ratio=3.0), resin temperature 290℃
It was extruded and pelletized.

After drying this pellet, the resin temperature was 285°C and the mold temperature was 8°C.
When injection molded at 0°C, a molded product with a beautiful surface could be obtained. Reference Example 1 When the same composition as in Example 1 was mixed at room temperature using a pen shell mixer and then fed to an extruder in the same manner as in Example 1, the mixture did not feed into the extruder and production was impossible. Ta.

When the composition of the mixture was changed to lower the filler concentration, stable production using an extruder became possible only when the filler concentration was 35% by weight.

When this pellet was injection molded in the same manner as in Example 1, a small amount of filler aggregates and flow marks were observed on the surface of the molded product. Reference Example 2 When the same composition as in Example 1 was fluidized and mixed for about 4 minutes in the same manner as in Example 1, the temperature inside the mixing tank reached 258°C.

However, just before the rotor torque (motor load) started to rise rapidly, it was discharged into the cooling mixer and cooled in the same manner as in Example 1. The obtained mixture was mixed at room temperature in Reference Example 1.
The mixture was almost the same. Reference Example 3 When the same composition as in Example 1 was fluidized and mixed for about 4 minutes in the same manner as in Example 1, the mixing tank temperature reached 258° C. and the rotor torque (motor load) began to rise rapidly.

Then, when the mixing was continued for another 40 seconds, the resin composition progressed to become gigantic agglomerated secondary particles in the mixing tank and solidified into a lump. Example 2 12 kg (60% by weight) of magnesium hydroxide fine powder with an average particle size of 0.7 μ and 8 kg of the nylon-66 pellets used in Example 1 were heated at 250°C.
After preheating to
The temperature reached 61° C. and the rotor torque (motor load) started to rise rapidly, so mixing was continued for an additional 5 seconds, then discharged to a cooling mixer and cooled for 10 minutes while stirring.

The obtained resin composition was in the form of powder particles with an average particle size of 20 to 60 mesh, and a diameter of 6 m77! There were no larger particles.

When this powdery resin composition was pelletized in the same manner as in Example 1 and injection molded, a molded product with a beautiful surface could be obtained.

Example 3 10 kg of kaolin clay fine powder with an average particle size of 2.5 μm (
50% by weight) and nylon with a number average molecular weight of 20,000.
After preheating 10 kg of lint (lint) to 2000 C, fluid mixing was carried out for 5 minutes using the same pen shell mixer as in Example 1. The temperature inside the mixing tank reached 212 C, and the rotor torque (motor load) increased. Since the mixture started to rise rapidly, mixing was continued for an additional 5 seconds, then the mixture was discharged into a cooling mixer and cooled for 10 minutes while stirring.

The obtained resin composition was in the form of powder particles with an average particle size of 20 to 60 mesh, and there were no giant particles with a diameter of 6 mm or more.

This powdery resin composition was extruded into pellets at a resin temperature of 250°C in the same manner as in Example 1, and injection molded at a resin temperature of 250°C, resulting in a molded product with a beautiful surface.

According to the present invention, it is possible to easily mix an inorganic filler into a polyamide resin to a high concentration, which was conventionally considered difficult.

Claims (1)

[Claims] 1 60 to 15 parts by weight of polyamide resin of various shapes with an average specific surface area of 2 cm^2/g or more and an average particle size of 0
．． Inorganic filler powder in the range of 01-100μ 40-8
5 parts by weight were mixed at high speed in a high-speed fluid mixer with a built-in rotary blade at a temperature range of 20°C above the melting point of the resin, and immediately after the rotor torque (motor load) started to increase rapidly, the high-speed fluid mixer 1. A method for producing a polyamide resin composition containing an inorganic filler, which comprises discharging the composition from a container and rapidly cooling the composition.