JPH021650B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an intermeshing type co-rotating extruder, and more particularly to an extrusion method for removing air contained in a fine powder raw material supplied into a barrel from a raw material supply port of the extruder. Fully intermeshing co-rotating twin-screw extruders have been widely used in the past because they can mix and disperse many raw materials well and deliver stable extrusion amounts.
However, conventionally, when extruding a fine powder resin with a small apparent specific gravity or a plastic material containing a large amount of similar inorganic fine powder, the amount of raw material fed into the feed section of the extruder often limits the amount of extrusion. It is well known to use, for example, forced feeding devices (compactors) as a means of solving this problem. However, even if a compactor is used, the effect is not perfect for powders that are very fine, have a low apparent specific gravity, and are easily fluidized, and it is difficult to obtain the desired amount of extrusion when operating under a limited range of extrusion conditions. I had no choice but to do it.

The biggest factor that prevents the fine powder from being fed into the supply section is the large amount of air that the fine powder contains due to its small apparent specific gravity.The material containing a large amount of air is compressed in the extruder and the air is released. This is because the separated air flows toward the hopper, that is, in the opposite direction to the direction of movement of the material, and as a result, the fine powder becomes fluid in the barrel. As a result, the apparent coefficient of friction of the material becomes smaller, making it difficult for the powder to be compressed by the screw, and as a result, the amount of mass transfer inherent to the screw decreases. Of course, in this case as well, the material is heated and softened by the heating from the barrel, and combined with the shearing force from the screw, the compression melting progresses, so the extrusion action is not lost, but the original function of the extruder is to compress the material. However, the extrusion capacity is much lower than that obtained by melting mainly by mechanical shear heat generation.

The present invention is a method for solving problems in extruding fine powder raw materials or materials containing a large amount of fine powder in such a fully intermeshing twin-screw extruder, without causing the air contained in the fine powder to flow back into the supply port of the extruder. By releasing these trapped air through a discharge port provided downstream of the supply port, the relative velocity of the powder and air is reduced, and the powder and air are extruded without being fluidized. This is a new extrusion method that aims to improve the problem and increase the throughput.

Next, one embodiment of the present invention will be described with reference to FIG. 1. Reference numeral 1 is a twin-screw extruder in which screws 3 are disposed within a barrel 2 over the entire length, have the same diameter, mesh with each other, and rotate in the same direction. 4 is a raw material supply port, and 5 is an air vent opening provided downstream of the raw material supply port. 6 is a vent hole. A kneading element 7 for dissolving and kneading the supplied raw material is provided in the screw 3 between the raw material supply port 4 and the air vent opening 5. The materials handled can be broadly classified into the following two types: (1) When the fine powder material is plastic or other organic matter.

(2) When the fine powder material is an inorganic substance and is kneaded with the plastic material.

In the former case, when the fine powder material reaches the air vent opening in an unmolten state, it is compressed to some extent, and the fluidized fine powder and heated air suddenly become open at the air vent opening. It is easier to blow up than the other parts.

In the latter case, when the plastic material reaches the opening of the air vent hole while being unmelted and not sufficiently mixed with the inorganic material, a phenomenon similar to venting occurs at the opening of the unmelted plastic material, and the inorganic fine powder is removed from the former. The same thing will blow up from the opening.

In either case, even if the plastic material in the barrel is in an unmelted state, even if an air vent opening is provided in the area where the plastic material in the barrel is in an unmelted state, it is not possible to separate and exhaust only the air.

In order to separate and discharge only the air, the plastic material must be in a molten state to some extent before reaching the air vent opening. Therefore, as mentioned above, when the fine powder is a plastic material, a kneading element 7 for melting the fine powder is required between the raw material supply port 4 and the air vent opening 5. As the kneading element 7, a screw with a small pitch as shown in FIG. 1 or a kneading block as described in the literature PLASTICS VOL 29 No. 12 P54 is generally used. Of course, the combination of kneading blocks must be such that the feeding action is such that this area is not completely filled with material.
If the fine powder is an inorganic material, the kneading element 7 for melting the plastic material and mixing it to some extent with the inorganic fine powder is similarly required between the raw material supply port 4 and the air vent opening 5. However, what is important here is that the screw 3 is provided with an element 7 for melting or kneading, and that there is a zone in which the plastic material completely fills the cross section of the barrel 2 with this element 7, or that the material is On the other hand, melting or kneading must be carried out without providing a pressure increase area that would give strong compression. Otherwise, the air will not reach the opening and will flow back into the raw material supply port.

In the present invention, the compressed part refers to a part where the inside of the screw is completely filled with material, and even if there is no compression by the screw 3, the material partially expands due to heating, for example, and closes the groove of the screw 3. If the area is filled with water, such a part is considered to be a compressed area.

Therefore, the material is not completely filled in the barrel 2 but is melted to some extent by the kneading element, the air contained inside the material is separated, and the gas flows to the outside from the air vent opening 5. The screw shape for effectively accomplishing this is well known to those skilled in the art. In a co-rotating intermeshing twin-screw extruder, generally the screw groove depth h is approximately constant over the entire length as shown in Figure 2, and the compression due to the screw configuration is caused by screws 3a and 7 in Figure 1. This is done by changing the pitch P as shown. Regarding the transport capacity of such things, for example, refer to the document An Analysis
of the Coveying Characteristics of Twin−
Screw Co−Rotating Extruders.SPE37th
ANTEC, Technical Paper P181 (May1979)
As shown in FIG. 14, the feed amount increases in proportion to the filling rate ε of the material in the screw chamber, and at the same time, it increases in proportion to cos ² φ as the helix angle φ of the screw. Here, in order to prevent the gas flow from being substantially sealed between the opening 5 and the supply port 4 in the screw, it is necessary to It is sufficient to select φ or pitch P such that the filling rate ε described above is 1 or less. Furthermore, even when the groove depth h changes, it is sufficient to set the filling rate ε<1 for the wheel feed amount determined in the same manner. Note that although the conveyance amount in the above-mentioned document refers to a molten body, the filling rate of a solid can be treated in the same manner.

In the above explanation, it should be noted that plastics are generally fed into an extruder and
In the process of progressing in the order of raw material supply port 4 → screw 3a → kneading element 7 in the figure, the temperature rises due to heating from barrel 2 or frictional heat generation due to shearing force from screw 3, and as a result, porous powder In the case of powders and granules that contain moisture or other gases in their internal pores, the bulk increases, so the volumetric transport rate increases, and with the same screw size, the filling rate becomes ε1, which can lead to a blockage state. obtain. In order to prevent blockage between the air vent opening 5 and the supply port 4 even in such a state, it is up to the manufacturer to select the groove depth h and pitch P of the screw so that ε<1 in the relevant part. This is something that can be done easily. Literature Plastic Age 77-2,
Co-rotating twin screw extruder (TEM) for kneading on page 87
As described in the structure and characteristics of the extruder, which is constructed by assembling screw elements with different screw pitches, it is necessary to replace the screw element in the part that actually closes with one with a larger pitch. This can also be achieved by In any case, in a twin-screw extruder, selection of a screw shape or operating conditions such that the gas flow is not blocked by plastic material at the opening 5 and the supply port 4 in the section, or such operating conditions, is required in the extruder. Selection can be made without difficulty without significantly deviating from the kneading conditions and other extrusion conditions.

The difference between the generally used vent for deaeration and the air vent opening in the present invention is whether or not a pressurizing region (compression section) is provided in front of the opening.
If the air vent opening were to be depressurized to the same level as a vent, there would be no pressure increase area, and the fine powder would be sucked in through the raw material supply port, making normal venting impossible.

In the present invention, the air inside the barrel can be naturally discharged by selecting the type of plastic material and configuring a screw suitable for that material, and then providing an opening at an appropriate position.

Next, examples according to the present invention will be shown below.

Example 1 Extruder: Toshiba Machine intermeshing co-rotating twin screw extruder, model TEM-50 Screw diameter 53φ Raw materials: Polymer (75% by weight) + inorganic fine powder (15% by weight) (apparent specific gravity 0.05) Extrusion The polymer and the inorganic fine powder were simultaneously dropped into the feed port of the machine using separate quantitative feeding devices.

Results: (a) If there is no air vent opening, the maximum extrusion amount is 90Kg/H (b) If the air vent opening is provided, the maximum extrusion amount is
175Kg/H Screw rotation speed 600r.pm in either case Example 2 Extruder: Toshiba Machine Co-rotating co-rotating twin screw extruder, model TEM-100 Screw diameter 94φ Raw material: Styrene fine powder (50% by weight) ) + inorganic fine powder (50% by weight) Both have passed 200 meshes and are pre-blended products (apparent specific gravity 0.5).

Result: (a) No air vent opening Maximum extrusion amount 300
Kg/H (b) With air vent opening Maximum extrusion amount 750Kg/
As is clear from the results that the H screw rotation speed is 300 rpm or higher, the amount of extrusion of the fine powder raw material is significantly increased compared to the conventional method, and the amount of extrusion is about twice that of the conventional method.

Further, depending on the raw material, even greater effects can be expected.

[Brief explanation of drawings]

FIG. 1 is a diagram showing one embodiment of the present invention. Figure 2 is an explanatory diagram of the screw. 2... Barrel, 3... Skrill, 4... Raw material supply port, 5... Air vent opening.

Claims (1)

[Claims] 1. In an extrusion method using a fully intermeshing type co-rotating twin screw extruder in which the raw material is fine powder or a material containing a large amount of fine powder, an opening for discharging air contained in the material is provided in the barrel downstream from the material supply port. A fully intermeshing type screw having a flight diameter constant over the entire barrel is provided, and a kneading element is provided between the material supply port and the opening to melt or knead the material without compressing the material. 1. A method for extruding a fine powder material for air removal, characterized in that air contained in the material is removed from the opening between the two openings.