JPS582056B2 - Thermoplastic resin molding screw - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a screw for a thermoplastic resin extruder, injection molding machine or blow molding machine.

Research is being conducted in various fields regarding the melt form of thermoplastic resins, and many theories and experimental data have been reported. A typical example is the melting model proposed by Tadmor et al. as shown in FIG.

In FIG. 1, 1 represents a solid bed (unmelted material), 2 represents a molten material, and 3 represents a melt film.

Also, 4 is a screw flight.

In the early stage of melting, the morphology as shown in this model is clearly maintained, but as melting progresses and the melting ratio increases, an unsteady phenomenon called destruction of the solid bed due to interference of the melt occurs. Phenomena occur, resulting in unfavorable results such as extrusion fluctuations, contamination of unmelted materials, or entrainment of air bubbles.

This phenomenon is especially noticeable during high-speed extrusion, and is therefore the biggest factor regulating the performance of extruders.

According to the screw proposed in Japanese Patent Publication No. 42-11505 (Fig. 6-A), the solid bed and molten material are separated by the second flight during the melting process, so the above-mentioned destruction phenomenon of the solid bed can be prevented. It is easy to peel off and can continue to operate well under certain conditions.

However, in general, there are a wide range of conditions such as the composition of materials handled by extruders, the types of physical molded products, and the required production volume, and the melting forms of the resins corresponding to each of them are also vastly different. I have to think about it.

Under such circumstances, if the solid side passage groove is blocked at its end, it lacks adaptability to various conditions, and for example, a relatively large amount of resin still in solid form may reach the vicinity of the end. It has been confirmed that under severe conditions, the resin often becomes clogged in the channel grooves, resulting in a sharp drop in extrusion performance.

Furthermore, when changing colors or resin grades, problems due to retention at the ends of the passage grooves are observed.

This is often observed even when the start of the second flight is in contact with the first flight or when there is only a very small gap.

In order to prevent the above-mentioned clogging phenomenon, it may be possible to assist the melting by external heating, but resin is generally a poor conductor of heat, and much cannot be expected due to the structural limitations of the heating system.

Also, it can be improved by preparing several types of screws with different shapes and selecting and operating the screw that suits each condition, but this is not economical.

On the other hand, special public service No. 53-145874 No. 53-136062
(Fig. 6-D), etc., in the case of a screw in which the end of the solid side passage is open, the phenomenon of resin clogging is prevented, but on the other hand, since it is an open type, the conventional screw (
Since it has characteristics similar to those of a full-flight (full-flight) screw, complete melting cannot be guaranteed under all of the various extrusion conditions described above.

That is, there is a possibility that some or a considerable amount of the unmelted material may flow out to the next step and have an undesirable effect on the extruded product.

Although it is possible to improve the degree of melting to some extent by changing the cross-sectional area of the solid side passage groove, it is fundamentally difficult to achieve both complete melting of the resin and non-occlusion, so the screw shape is complicated. No significant effect was achieved.

In addition, since the fluid flowing out from different passages to the next process naturally has different state quantities such as resin temperature, it is difficult to maintain the homogeneity of the extruded product unless there is an appropriate device to mix the two fluids. Become.

The object of the present invention is to provide a screw that can solve the basic problems of the melting process that may occur under practical operating conditions as described above with a relatively simple structure.

Hereinafter, the present invention will be explained based on the accompanying drawings showing one embodiment thereof.

FIG. 2 shows the entire screw according to the present invention, and the screw is composed of a supply section, a melting progressing section A, a mixing section B, a melting completion section C, and a measuring section in order from the material input port.

Figure 3 is an enlarged view of the two-phase distribution of the resin that is generally observed at the starting point of the melting promotion zone when the screw according to the present invention is actually operated, and the inflow of molten material into a part of the solid side passage is observed. This shows that.

FIG. 4 is an enlarged view of the state observed at the end point of the melt promotion zone A, particularly when high-speed extrusion is performed, showing that some unmelted material remains in the solid side passage.

FIG. 5 is an enlarged view showing the process in which the remaining unmelted material is completely melted in the mixing section B and melting completion section C of the screw according to the present invention.

In order to maintain an appropriate viscosity without applying excessive shear to the resin flow that has already been melted in the mixing section B, the resin flows flowing out from different passages are mixed as uniformly as possible, so that the melted resin flow in the melting completed section C is maintained. The grooves are deep so that the grooves are equally divided, and to allow time for heat exchange between the molten and unmelted particles, and a beat as shown in the figure or an auxiliary mixing device with a similar function may be installed. .

The screw according to the present invention has the above-mentioned structure, and its operation will be explained next.

The room-temperature or slightly preheated resin supplied from the material input port is heated by an external heater as it passes through the supply section, and its temperature rises due to frictional heat generated between it and the inner surface of the barrel. Figure 2 a~
It starts to melt between b and the first part is in contact with the inner surface of the barrel.
A melt film as shown in the figure is produced.

These are scraped off by the top of the flight to form a melt pool as shown in FIG. 1 on the front side of the flight, and the melt pool gradually increases in volume and advances until it reaches the starting point of the melt promotion zone A.

That is, a predetermined amount of melting has already progressed at the starting point of part A.

In order to satisfy this condition, the starting point of part A must be at least upstream of the point where the solid bed breaks down and downstream of the expected slowest melting start point.

In fact, it is preferable to study various assumed operating conditions by theory, empirical rules, or experiments using a small test extruder, and to set the volume melting ratio at a position that reaches approximately 13 to 18%.

Also, the opening degree at the starting point position of the molten material side passage (Fig. 3 wm
/w×100%), it is assumed that the ratio is slightly lower than the melting ratio, that is, 10 to 15%.

However, even if a situation occurs in which the melting pattern is quite different from the initially designed value due to unexpected operating conditions, for example, the melting ratio is lower than the opening of the melt gutter at the starting point of part A, 1.
Even if some solid particles enter the molten material side passage, the basic function of the screw is not impaired, and it is possible to continue operating at least better than a conventional screw.

Now, the solid-side passage of the melt-promoting section A is divided internally into the melt passage groove, which is approximately 85 to 90% at the starting point position and approximately 30 to 80% at the end point position, which is a relatively large ratio. It has a barrel contact area, and the resin is moderately compressed, and its melting is promoted by the frictional action with the barrel inner surface and heat transfer from the outside.

In this part, the resin (melt film) in the part that is in contact with the inner surface of the barrel, which has been completely melted, gradually passes over the second flight mountain part, which has an outer diameter smaller than that of the first flight, and flows into the passage groove of the melt, so that A good steady state can be maintained without causing any destruction of the solid bed.

The purpose of the screw according to the present invention is to prevent the phenomenon of destruction of the solid bed under all various operating conditions in the melting promotion section A, and also to prevent the phenomenon of material clogging in the solid side passage. It does not require complete separation of solid and melt.

Therefore, as a general rule, the cross-sectional area of the solid-side passage, especially the passage width, should be designed to be slightly larger than the actual expected width of the remaining solid.

For exactly the same reason, the solid side passage is open at the end point of the melting promotion section A, and the groove depth at this point is made somewhat larger than the grain size of the material passing through, and the opening degree (solid section groove width / total Width x 100%) is usually set to a large value of 30 to 80%.

For this reason, during high-speed extrusion, it is natural that the melting of the resin is incomplete at the end of the melting promotion zone.
Although about 5 inches of unmelted particles remain, the screw according to the present invention does not prevent these portions from flowing out to the next process.

However, these unmelted portions are 100% in the next mixing section B and melting completion section C specified by the screw according to the present invention.
% melting and at the same time make the resin temperature uniform.

Next, this operation will be explained in detail with reference to FIGS. 3 and 5.

In the melting zone A, the solid bed is not destroyed and is sufficiently heated under normal action, and the unmelted particles, which have a temperature at least above the secondary dislocation point and just below the melting point, and have undergone considerable softening, are As shown in Figure 3, they are unevenly distributed on the back side of the flight in the solid side passage.

After flowing into the mixing section B, these are divided into relatively deep grooves by an auxiliary stirring mixer such as a beat or pin as shown in the attached Figure 5, and are uniformly dispersed and mixed within a large amount of melt while supplying heat from the surroundings. As the temperature rises, although slightly, a portion of the surface layer melts and enters each inlet groove of the melting completed section C.

The flow path in this section is formed by alternately arranging grooves with one side closed so that they do not penetrate between the mixing part B and the measuring part.
The resin flow that has flowed into the flow path passes through a relatively narrow gap δ and reaches the adjacent flow path f.

In this process, a momentary but very effective shear stress is generated only in the unmolten material, which is still quite viscous (elastic), so the particles are deformed and stretched thin, and at the same time frictional heat is added, so that the melting point is quickly exceeded. Melting is complete.

According to the screw according to the present invention, as mentioned above, the shear in the melted part acts more strongly on the unmelted material side, so the temperature of the already melted part does not increase much, and there is an excellent crosstalk effect, so the resin The temperature is uniform throughout, making it possible to perform extremely good extrusion.

Such ideal melting is achieved by the Special Publication Act of 4
This can only be achieved with a screw such as No. 3-24493, in which 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 a plunger is provided with a small gap between it and the cylinder. This is not guaranteed with other kneading devices such as a dalmage or ring valve as shown in the attached Figure 7.

Moreover, it cannot be expected that the melted part C alone can sufficiently exhibit its function.

That is, it is clear that this method is not effective against destruction or blockage phenomena of the solid bed, and that its performance deteriorates when unmelted particles concentrate in some grooves.

In other words, the ideal effect of the present invention is that the melting promotion part A mixing part B
This can only be achieved through the comprehensive combination function of the three people in the melting completion section C.

A typical example of the screw according to the present invention, which was carried out using an extruder of 65 mm L/D=28, is shown below.

In the above experiment, no unmelted matter or bubbles were observed in the extruded product.

Further, none of the above embodiments indicates an upper limit of performance.

As described above, with the screw according to the present invention, it is possible to expect performance improvement of at least 150% or more than 200% over conventional screws.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is an explanatory diagram showing the state of the resin at the initial stage of melting, FIG. 2 is a side view of an embodiment of the present invention, and FIGS. 3 and 4 are melting promotion in the present invention, respectively. 5 is an enlarged view of the vicinity of section C in FIG. 2, FIGS. 6 A to E are explanatory diagrams of the conventional example, and FIG. 7 is a partial view of the conventional example. Side view, FIG. 8 is a side view of only the screw in one embodiment of the present invention.

Claims (1)

[Scope of Claims] 1. In a thermoplastic resin melt extruder screw, melting promotion specified by the following a, b, and c is performed sequentially from the supply part side between the supply part starting from the material input port and the final measuring part. Part A
, an extruder screw having a part consisting of a mixing part B and a melting completion part C. a. The volumetric melting ratio near the end of the supply section is approximately 13 to 1.
It has a second flight having a smaller outer diameter than the first flight, which starts from a position where the mixing area B is about 8% and extends to near the starting point of the mixing section B, and the resin passage groove is formed in the front mainly in the solid section by the second flight. The proportion of internal division between the passage groove and the rear melt passage groove is approximately 85 to 90% (
Solid part groove width/total width x 100% (same below) Melting promotion part A characterized in that it is approximately 30 to 80% open at the end point position and clearly open in any part. b. A relatively deep groove is located in the downstream region adjacent to the melting promotion section and is used to uniformly mix a large amount of molten resin flowing out from the previous process and a relatively small amount of unmelted material, and then send the mixture to the next process. - A mixing section B having auxiliary mixing functions such as a beat area or a pin. C. In order to instantly completely melt the resin flow containing unmelted material flowing from the mixing section and at the same time equalize the resin temperature, the grooves that do not penetrate the outer circumferential surface are arranged alternately in opposite directions so as not to communicate with each other. A melting completion part C is provided with a plunger having a small gap between it and the cylinder.