JPS6223643B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for granulating polycarbonate.

An object of the present invention is to provide polycarbonate granules that are particularly suitable for molding molded articles with excellent thermal stability.

Polycarbonates, particularly bisphenol-based aromatic polycarbonates, have many excellent properties and are therefore widely used in various applications. Such polycarbonates are generally bisphenol A
It is synthesized by reacting divalent phenols typified by carbonate precursors such as phosgene and diaryl carbonate.

A polycarbonate synthesis method in which phosgene or a chloroformate compound is reacted in the presence of a solvent is known as a solvent method.

According to the solvent method, polycarbonate is obtained as a solution, which is sufficiently purified by washing with water, and then isolated as a powder.

In order to make the polycarbonate powder isolated in this way easier to handle, the powder is once melt-extruded using a melt-molding machine, and the extrudate is cut into suitable particles to be used for molding as chips or pellets. .

However, when using the above conventional method, even if the drying is strengthened, the solvents used, such as methylene chloride, toluene, etc., are not sufficiently removed, resulting in a serious drawback that the thermal stability of the resulting molded product is greatly deteriorated. .

One possible method for almost completely removing the solvent is to further sufficiently pulverize the polycarbonate and then strengthen the drying process. However, if the polycarbonate powder is pulverized to such an extent that the solvent can be completely removed, the bulk density becomes small when the obtained polycarbonate powder is granulated using a melt molding machine, resulting in an extremely low extrusion rate. Pulsating flow occurs in the process, the size of the granules is not constant, and the productivity is extremely poor, so it cannot be used in practice.

As a result of intensive studies aimed at solving these problems, the inventors of the present invention discovered that the above problems could be completely solved by adopting dry compression molding as the granulation means, and thus arrived at the present invention. .

That is, the present invention is a polycarbonate granulation method characterized by granulating polycarbonate powder by dry compression molding.

In the present invention, polycarbonate refers to polycarbonate that is subjected to melt molding, such as extrusion molding, injection molding, blow molding, or compression molding.
The present invention is particularly applicable to bisphenol aromatic polycarbonates produced by a solvent method, such as bis(4-hydroxyphenyl)alkane, bis(4-hydroxyphenyl)sulfone, etc. Applying this granulation technology will have a significant improvement effect. Of course, the polycarbonate to which the present invention can be applied may have its benzene nucleus substituted with a halogen atom, an alkyl group, etc., and may also be a copolymerized polycarbonate, a mixture of two or more types of polycarbonate, or a mixture with other thermoplastic polymers. include. Furthermore, if necessary, glass fibers such as milled fibers and chopped strands, fillers such as calcium carbonate and talc, stabilizers, ultraviolet absorbers, or colorants may be contained.

In the present invention, the polycarbonate powder to be applied may be obtained by any method, but powder obtained by the method described below is particularly preferred. First, polycarbonate is isolated from a solvent solution of polycarbonate produced by a solvent method. As this isolation method, any method that does not pass through a molten state may be employed. For example, a method of removing the solvent from a polycarbonate solution using a heat medium or a non-solvent, a method of gelation using crystallization of polycarbonate (single solvent, a combination of solvent-solvent or solvent-non-solvent, etc.), etc. can be arbitrarily adopted. . Next, this polycarbonate is further pulverized by physical means such as crushing.

In order to find out the trend between the particle size of polycarbonate powder and the amount of solvent contained (methylene chloride), we crushed the easily crushed polycarbonate obtained by solidifying it by gelation method from polycarbonate solution produced by solvent method and sieved it. The following shows the solvent content when the various powders obtained were dried at 120°C for 10 hours using a hot air circulation dryer.

Sieve mesh Methylene chloride content (wt%) ~16 0.4 16~50 0.1 50~60 0.03 60~115 0.01 In the present invention, the thus pulverized and dried polycarbonate powder is dry compression molded. granulation by. The size of the powder at this time does not need to be particularly limited, but it must be fine enough that the entire amount passes through a 16-mesh sieve and 80% by weight passes through a 48-mesh sieve, and its solvent content but
The content is preferably 0.03% by weight or less. The presence of particles that are too large to pass through a 16-mesh sieve not only increases the total amount of solvent but also tends to make granulation difficult.

In addition, it is difficult to reduce the solvent content to 0.03% by weight or less for powders with a particle size in which more than 20% by weight of the total cannot pass through the 48 mesh. It tends to be difficult to suppress the decline in sexual performance. Especially if the total amount is 20
Passes through the mesh sieve and more than 80% by weight is 60%
Powder that passes through a mesh sieve is preferred because it can contain very little solvent.

The molding machine used for dry compression molding is
Any format can be adopted. For example, a tablet machine such as a tablet machine may be used, but from the viewpoint of granulation cost and productivity, it is preferable to use a type that compresses the tablet into a plate shape using a pair of rolls and then cuts or crushes it into an appropriate shape. Furthermore, it is also preferable to provide a concave portion of an appropriate shape in one or both of a pair of rolls, and to press the material into the concave portion to perform granulation at the same time as compression. The compression pressure at this time is not particularly limited, but
If this pressure is too small, the resulting granules will be easily crushed, so it is preferably 2 Kg/cm ² or more (same as 2 Kg/cm or less in the case of roll load/roll width).
Particularly preferred is 8 kg/cm ² (Kg/cm) or more. The temperature during compression molding may be any temperature as long as it is below the melting point of polycarbonate, but if the temperature is too high, solidification or thermal deterioration of the powder tends to occur during granulation.
There is no need to take the trouble to cool the granulated product; on the contrary, if the temperature is too low, the resulting granulated product will easily break, so a temperature in the range of room temperature to 180°C is preferable, especially when drying polycarbonate powder.
Since a temperature in the range of 120°C to 160°C is used, it is preferable to use compression molding directly after drying without cooling. In addition, as a conventional method for granulating polycarbonate, only the melt extrusion method as described above has been adopted, and the dry compression molding method as in the present invention has not been considered at all. This is thought to be because the addition of wetting agents and binders, such as those used in conventional dry compression molding of powder, to polycarbonate has been neglected because it impairs its quality.

According to the present invention, polycarbonate granules with low solvent content and low thermal history can be produced extremely easily, and the resulting granules have extremely good thermal stability. By using this method, molded products with high commercial value can be obtained.

The present invention will be further explained below with reference to Examples.

It is expressed by the color tone of the molded test piece as a measure of thermal stability. Color tone is indicated by L value and b value; the higher the L value, the higher the brightness, and the higher the b value is on the plus (+) side, the stronger the yellowness, and the higher it is on the minus (-) side, the more blue. indicates that it is strong.

The higher the (Lb) value, the better the color tone.

Example 1 A purified methylene chloride solution containing about 10% by weight of polycarbonate having an average molecular weight of 22,500 obtained by phosgenating bisphenol A by a conventional method.
After stirring and coarsely crushing it for about 4 hours while keeping the internal temperature at 40℃ with stirring in a No. 100 kneader,
Grind in a hammer mill with a screen of
The powder was placed in a tray to a thickness of about 2 cm and dried at 120° C. for 12 hours in a hot air circulation dryer.

The total amount of this powder passed through a 20 mesh sieve, 90% by weight of it passed through a 60 mesh sieve, and the methylene chloride content was 0.005% by weight.

This powder was molded using two unheated rolls with a diameter of 25 cm and a length of 10 cm, at a molding temperature of 25°C and a molding pressure of the rolls.
A plate-shaped product was formed at 1500 Kg/cm ² (Kg/cm) and a roll rotation speed of 14 rpm, and the resulting granules were pulverized with a screen opening of 8 m/m, and the resulting granules were referred to as granules A.

Granules A were molded into test pieces (50 m/m x 50 m/m x 5 m/m) at 320°C for 10 minutes with a residence time of virtually 0 minutes using a 3-ounce screw-type injection molding machine. are shown in Table 1.

For comparison, a powder was obtained by performing pulverization, solvent removal, dehydration, and drying in the same manner as in the above example except that the opening of the screen of the hammer mill in the above example was changed to 5 m/m. The total amount of this powder passed through a 16 mesh sieve, but 50% by weight did not pass through a 48 mesh sieve, and the methylene chloride content was
It was 0.035% by weight.

The powder was granulated using a vented extruder with a diameter of 30 mm at a vent pressure of 10 Torr, a screw screw of 40 rpm, and a cylinder temperature of 280°C. Its speed is 8.6Kg/Hr
It was hot. The obtained granules were referred to as B, and the granules B were injection molded in the same manner as in Example 1, and the color tone of the obtained test pieces is also listed in Table 1 as Comparative Example 1.

As is clear from the table, the color tone of the test piece of Comparative Example 1 was significantly inferior to that of the test piece of Example 1, indicating poor thermal stability.

Furthermore, for comparison, an attempt was made to directly extrude and granulate the powder obtained in Example 1 in the same manner as in Comparative Example 1 (Comparative Example 2), but pulsation occurred and the powder could not be granulated into the desired shape. It is difficult to granulate, and the granulation speed is 4.2
Productivity was extremely low at Kg/Hr.

Table 1 L value b value (L-b) value Example 1 83.1 6.7 76.4 Comparative example 1 81.5 11.7 69.8 Example 2 Except for the average molecular weight of 24,500 obtained by phosgenating bisphenol A by a conventional method. All of the materials were pulverized, solvent removed, dehydrated, and dried using a hammer mill equipped with a screen with an opening of 1.5 m/m in the same manner as in Example 1. The total amount of this powder passed through a 20 mesh sieve, and the methylene chloride content was 0.008% by weight.
It was hot.

This powder was molded using two heating rolls with a diameter of 25 cm and a length of 10 cm at a temperature of 180°C and a roll compression force of 2 kg/
cm ² (Kg/cm) The granulated product obtained in the same manner as in Example 1 is designated as C.

Table 2 shows the color tone of granulated product C molded into test pieces using a 3-ounce injection molding machine in the same manner as in Example 1.

For comparison, grinding, solvent removal, dehydration, and
I did drying. The total amount of the powder obtained passed through a 16 mesh sieve, but 50% by weight did not pass through a 48 mesh sieve, and the methylene chloride content was 0.04% by weight. This powder was granulated using an extruder in the same manner as in Comparative Example 1 above. The speed was 9.0Kg/Hr. This granulated product was designated as granulated product D, and this granulated product was injection molded in the same manner as in Example 2, and the color tone of the obtained test piece is also listed in Table 2 as Comparative Example 3.

As is clear from Table 2, the color tone of the test piece obtained from Granule D was significantly inferior to that of the test piece of Example 2, indicating poor thermal stability.

Furthermore, for comparison, an attempt was made to extrude and granulate the powder obtained in Example 2 above in the same manner as in Comparative Example 2, but pulsation occurred during melt extrusion, making granulation difficult, and the speed was 5.6. It was as low as Kg/Hr.

Table 2 L value b value (L-b) value Example 2 83.0 7.0 76.0 Comparative example 3 81.3 12.0 69.3

Claims (1)

[Scope of Claims] 1. A method for granulating polycarbonate, which comprises granulating polycarbonate powder using a dry compression molding machine. 2 The molding temperature in dry compression molding is room temperature or
The method for granulating polycarbonate according to claim 1, wherein the temperature is 180° C. and the molding pressure is 2 Kg/cm ² or more. 3. The method for granulating polycarbonate according to claim 1 or 2, wherein the entire amount of the polycarbonate powder passes through a 16-mesh sieve and the solvent content is 0.03% by weight or less. 4. The method for granulating polycarbonate according to any one of claims 1 to 3, wherein the polycarbonate powder is a polycarbonate powder mainly composed of bisphenol-based aromatic polycarbonate produced by a solvent method.