JPS6227652B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for melt extruding styrenic polymers in a single screw extruder. polyethylene, polypropylene, nylon 6,
66, 12, regarding the melt extrusion of crystalline polymers such as polyethylene phthalate, the applicant previously published JP-A-56
The use of an extrusion screw as shown in Publication No. 92039 has been confirmed to be extremely effective in increasing processing capacity, improving quality, and reducing processing energy. The above-mentioned extrusion screw is a screw for a thermoplastic resin extruder as shown in FIG. The volume melting ratio near the end of the section is approximately 13
It has a second flight 5 having a smaller outer diameter than the first flight 4, which starts from a position of about 18% and extends to the vicinity of the starting point of the mixing section B. The proportion of the solid part passage groove in the front and the melt passage groove in the rear is approximately 85 to 90% at the starting point of the part.
(Solid part groove width/total width x 100% or less) The melting promotion part A, b is characterized in that it is approximately 30 to 80% open at the end point position and is clearly open in any part. In the adjacent downstream area, a large amount of molten resin flowing out from the previous process and a relatively small amount of unmelted material are mixed uniformly and then sent to the next process using a beat or pin etc. in a relatively deep groove. Mixing section B, which has the auxiliary mixing function of c. A first-stop groove that does not penetrate the outer circumferential surface to completely melt the resin flow containing unmelted material flowing from the mixing section and at the same time equalize the resin temperature. This extruder screw is composed of a melting completion section C, which is arranged alternately in opposite directions so as not to communicate with each other, and is provided with a plunger having a small gap between it and the cylinder. However, when it comes to amorphous polymers, especially polystyrene polymers, there is no significant functional difference compared to conventional full-flight screws. The degree of tightening of the screw in the price of an extruder is large, and it is uneconomical to install a screw exclusively for each resin depending on the type of resin, and it is more convenient to be able to mold various resins with one screw. is obvious. Therefore, it is desirable that a screw that is effective for crystalline polymers as described above can also be used to mold amorphous polymers, and the present invention was made in view of the above circumstances. An object of the present invention is to provide an extrusion method capable of melt extruding a styrenic polymer using the screw. That is,
This is an extrusion method for melt extrusion of styrenic polymers that uses low power, allows for good kneading and mixing of materials, and has a large discharge rate. Generally, based on the solid wheel feeding theory of DARNELL and SQUIRES, the friction coefficient μ _B between the polymer and the barrel inner surface is large, and the friction coefficient μ _S between the polymer and the screw surface is large.
It is known that the smaller the amount of polymer transported, the larger the amount of polymer transported, and increasing the amount of transported leads to an increase in the amount of discharge. For the former _μB , it is known to add grooves to the barrel, but for extruders for molten plastic, if there are grooves in the barrel, it tends to cause retention, seizure, etc., and a special extruder is required. However, in the present invention, we have considered the latter, that is, the direction of reducing _μS . The coefficient of friction between polystyrene and steel is shown in the graph shown in Figure 2. In order to reduce μ _S , the temperature of polystyrene must be around 150〓 (66℃) or lower, and the temperature of steel must also be around 200〓 (93℃). ) It turns out that the following is good. As a result of various tests conducted by the inventor, the relationship between the amount of raw material supplied and the temperature of the supplied raw material was as shown in the graph shown in FIG. 3, and good results were obtained at approximately 45°C to 70°C. However, the increase in transport amount alone is due to the fact that when the material is transferred to the compression section, which is the next step after the material supply section in the screw, the surface pressure increases, the friction between the material and the barrel increases, and the power for driving the screw increases. This not only causes an increase in the number of particles, but also causes uneven melting of the material, which impairs the stability of discharge. Therefore, from the viewpoint of power and discharge stability, it is necessary that the material is delivered to the compression section in a state on the verge of melting. Therefore, it was concluded that the material was supplied at a temperature of 45°C to 70°C, and that it was necessary to bring the melting temperature of polystyrene to about 143.3°C before entering the compression section. In addition, in order to reduce the μ _S , the temperature of the steel, that is, the screw, must be 93°C or less immediately after the raw material is supplied, as mentioned above, and approximately 140°C near the compression section, so it is necessary to cool the screw in the first half of the raw material supply section. I came to the conclusion that there is. Then, in order to determine the length of screw cooling, we examine the relationship among the discharge amount Q, rotational speed N, power Z, and the difference ΔP between the upper and lower limits of extrusion pressure, and the result is Q/N as shown in Figure 4 A, B, and C. In other words, it was found that a stable extrusion method with the highest discharge amount per screw rotation, a small Z/Q, that is, a small specific power, and a small ΔP can be achieved by setting the screw cooling length to 2 to 5 D. Next, a comparison between the method of the present invention and the conventional method at the same screw rotation speed will be shown below.

[Table] As can be understood from the above comparison, the raw materials are 10
It can be seen that the discharge performance is better when preheated to 60°C as in the present invention than when supplied at 60°C. As shown in Fig. 5, if the screw of the conventional method shown in Fig. 1 is cooled by 2D or more and 5D or less from the screw base and adjusted to keep the input material at a temperature of 45°C or more and 70°C or less, polystyrene can be produced. Melt extrusion of polymers in the system is possible.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a conventional screw, and Figure 2 is a graph showing the coefficient of friction between polystyrene and steel. Third
The figure is a diagram showing the relationship between the amount of raw material supplied and the temperature of the supplied raw material. Figure 4 is a graph showing extrusion characteristics, and A is Q/N.
B is a diagram showing the relationship between Z/Q and screw cooling length, C is a diagram showing the relationship between ΔP and screw cooling length. FIG. 5 is a schematic diagram of a screw for implementing the method of the present invention, 1...raw material input port, 2...supply section, 3...measuring section, 4...first flight, 5...second flight ,
6... Screw cooling section, A... Melting promotion section, B...
...mixing section, C...melting completion section.

Claims (1)

[Scope of Claims] 1. Sequentially from the supply section side between the supply section starting from the raw material input port and the final metering a Volume melting ratio near the end of the supply section is approximately 13
It has a second flight with a smaller outer diameter than the first flight, which starts from a position where the temperature is about 18% and extends to near the starting point of mixing section B, and the second flight allows the resin passage groove to extend forward. The ratio mainly divided into the solid part passage groove and the rear melt passage groove is approximately 85 to 90% at the starting point position (same below solid part groove width/total width x 100%) and approximately 30 to 30% at the end point position. 80%, and is characterized by being clearly open in any part. b. A downstream area adjacent to the melting promoting part, where a large amount of resin melt flows out from the previous process. After uniformly mixing a relatively small amount of unmelted material, the unmelted material flowing from the mixing section B, c has a relatively deep groove with an auxiliary mixing function such as a beat or pin for sending it to the next process. In order to instantaneously completely melt the resin flow containing resin and at the same time equalize the resin temperature, first-stop grooves that do not penetrate the outer circumferential surface are arranged alternately in opposite directions so as not to communicate with each other, and small grooves are placed between them and the cylinder. If a melting completion part C is provided with a plunger having a gap, and the screw diameter is D provided on the base side of the supply part.
A method for melt extrusion of polyethylene polymer, characterized by providing a temperature adjustment mechanism by screw cooling of 2D or more and 5D or less, and maintaining the input raw material at a temperature of 45°C or more and 70°C or less.