JPS63199623A - Thermoplastic resin molding screw - Google Patents

Abstract

PURPOSE:To enable uniform kneading properties, high-speed stabilized extruding properties and low-temperature extruding properties, by a method wherein a first extrusion part having a supply part, a compression part and a measuring part in this order from a resin supply side is formed and a mixing part, a shearing part and a second extrusion part are provided further. CONSTITUTION:A first extrusion part having a supply part 11, a compression part 12 and a measuring part 13 from a resin supply side is formed and further a mixing part 14, a shearing part 15 and a second extrusion part 16 are formed in order, in a thermoplastic resin molding screw. A resin pellet is supplied to the supply part 11, and pressure feed to the compression part 12 is performed while the same is being heated. A groove depth of a screw becomes shallower gradually normally, and compression of the resin pellet is effected while the same is being melted and plasticized, in the compression part 12. A compression ratio is 2-4. The measuring part 13 has a fixed groove depth normally and in the case where melting at the compression part is incomplete, the melting and plasticization are accelerated. The mixing part 14 mixes the plasticized resin, and especially an unmolten resin layer in the case of high-speed extrusion is cut apart and destroyed. The shearing part 15 performs uniform melting of melted resin and unification of a resin temperature through shearing in a comparatively short period of time. The resin kneaded uniformly is extruded to a die by the second extrusion part 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a thermoplastic resin molding screw used in a thermoplastic resin molding apparatus for producing sheets, films, etc.

[Background technology and its problems]

Various molded products such as sheets, films, and containers are obtained from thermoplastic resins by extrusion molding, blow molding, injection molding, etc., but in all of these molding fields, it is necessary to thoroughly heat, melt, and knead the resin. In order to manufacture products with excellent uniformity with good productivity, the structure of the screw in the molding device is an important factor.

The most common conventional screw is shown in FIG. 1, for example. This is done by increasing the compression ratio, such as a full-flight metalinges screen, which has a supply section 1, a compression section 2, and a metering section 3 sequentially from the resin supply side to the resin extrusion side. The main purpose was to do. Therefore, although the resin can be kneaded relatively well, the compression ratio is large and high shear is involved, resulting in several problems. That is, the resin pressure fluctuates greatly during high-speed extrusion molding, making it impossible to stably obtain high-quality molded products with excellent thickness accuracy and the like. In addition, heat generation occurs due to high shear stress, which causes the resin to deteriorate due to an unnecessarily high rise in resin temperature, resulting in deterioration of the physical properties of the molded product, and drawbacks such as difficulty in take-up and sizing during extrusion molding.

For this reason, the compression ratio is made relatively small, and in some cases 1
A screw with a structure that suppresses the generation of shear heat as follows:
A two-stage extrusion type screw with a shearing section provided in the middle of the screw has been proposed.

However, in either case, the kneading is insufficient, resulting in uneven resin temperature and poor dispersion of various additives, making it difficult to obtain good molded products and extremely limiting the range of applications. Ta. In particular, in the case of a two-stage extrusion screw, more shear than necessary occurs in the intermediate shearing section, resulting in resin deterioration as the resin temperature increases, and difficulty in cooling and sizing due to extrusion of high temperature resin.

By the way, in order to solve these problems of the prior art, the present applicant has already proposed an extrusion device equipped with a slow pressure line section in which the compression section of the screw has a relatively small compression ratio (Japanese Patent Application No. 266398).

He also proposed a screw that was further improved (Japanese patent application No. 60-180846, Japanese patent application No. 60-180-
180847).

However, in a screw with a shearing section in the middle of the screw, in order to keep the shearing heat generation in this shearing section low, it is necessary to make the length of the supply section and compression section sufficiently long. Undesirable. Furthermore, even if the length is long, when high-speed extrusion molding is performed, sufficient kneading is not performed in the shearing section, and in some cases, a large amount of unmelted resin may flow into the shearing section, causing fluctuations in the extrusion amount. A good product cannot be obtained, and as a result, stable extrusion molding cannot be performed at high productivity and high speed.

[Purpose of the invention]

An object of the present invention is to provide a screw for thermoplastic resin extrusion molding that enables sufficient uniform kneading, high-speed stable extrusion, and low-temperature extrusion, which were conventionally difficult to achieve.

[Means and effects for solving the problems] The present invention has the following features:
A first extrusion section having a supply section, a compression section, and a metering section is formed sequentially from the resin supply side to the resin extrusion side, and a mixing section and a shearing section are sequentially formed from the first extrusion section toward the resin extrusion side. By arranging a second extrusion section, sufficient kneading is performed while suppressing excessive heat generation of the resin.
Moreover, it is intended to achieve the above object by enabling high-speed stable extrusion.

〔Example〕

Hereinafter, the present invention will be explained in more detail based on the drawings.

First, the thermoplastic resin used in the present invention is not particularly limited, and includes, for example, high-density polyethylene, high-pressure low-density polyethylene, linear low-density polyethylene, polypropylene, ethylene or propylene and other α-olefins. Examples include copolymers, polystyrene, polyamides, polyesters, polycarbonates, polyvinyl chloride, polyacrylonitrile, polyvinylidene chloride, polyphenylene oxide, boimide, polysulfone, polyphenylene sulfide, and polyketones. Among them, polypropylene, linear low density polyethylene,
Polycarbonate, polystyrene, etc., which have double-nine shear characteristics (characteristics that exhibit relatively high melt viscosity under high shear rates) due to factors such as relatively narrow molecular weight distribution.
It is suitably used in the case of thermoplastic resins that exhibit This is because these resins have a high viscosity in the high shear region of the extruder, and extruding this high viscosity resin requires a large screw power consumption, resulting in low extrusion productivity and high manufacturing costs. It is.

Furthermore, an increase in resin temperature due to shear heat generation may cause deterioration of the resin and deterioration or decomposition of the additive.

In addition, among the resins used in the present invention, resins that need to improve the optical properties such as transparency and gloss of the extruded molten resin include polypropylene, ethylene, etc.
- Random copolymerized polypropylene copolymerized with 20% by weight or less of olefin, linear low-density polyethylene (L-L
DPE) etc. Due to the crystallinity of these resins, it is difficult to produce sheets and films with excellent transparency.

Therefore, if such a resin is extruded using the molding screw of the present invention and rapidly cooled using means such as water cooling,
Products with excellent optical properties such as transparency can be obtained.

FIG. 2 shows an example of the thermoplastic resin molding screw according to the present invention.
3 is formed, and this first extrusion
Further, from the extrusion part toward the resin extrusion side, a mixing part 14,
A shearing section 15 and a second extrusion section 16 are formed in sequence.

Resin pellets are supplied to the supply section 11 from a resin supply port of a cylinder (not shown), and are pumped to the compression section 12 by the driving force of the screw while being heated. The feed section 11 is normally of a constant groove depth with a compression ratio of 1. In addition, the compression part 12 is usually compressed while being melted and plasticized, with the groove depth of the screw becoming gradually shallower, and the compression ratio is 2 to 2.
4, preferably 2-3. If the compression ratio exceeds 4, the shear stress at the end of the compression section 12 will increase, resulting in an increase in resin temperature, accumulation of shear stress, breakup phenomenon, etc., which is not preferable. Next, the metering section 13 usually has a constant groove depth and promotes melting and plasticization when melting in the compressed section is incomplete.

The measuring section of the present invention has a relatively deeper groove depth than a normal one,
3-15III11.

The mixing section 14 mixes the plasticized resin sent from the measuring section 13, and has the function of dividing and destroying an unmelted resin layer (solid bed) particularly in the case of high-speed extrusion molding. Here, the mixing section 14 is not particularly limited, and may be a gear type, a dalmage, a reverse thread with cuts, a multi-pin type, etc., and is mainly used to divide and destroy the unmelted resin layer, and is used for kneading by high shear. is relatively small, and abnormal heating of the resin due to shearing force does not occur.

Among these, a gear-type mixing section is preferable because it has many features such as simple structure, easy processing, reliable separation and destruction of the solid bed, and low shearing action. In addition, as the gear type l11M in the gear type mixing part, a spur gear type is sufficient, but a hasp gear type etc.
There is no restriction as long as the resin is divided when it passes through 4. Next, an example in which the mixing section 14 is of a spur gear type will be described. The number and thickness of the gear ridges, the clearance between the top of the ridges and the cylinder, etc. vary depending on the type of thermoplastic resin, the type of molding in which the screw is used, molding conditions, the size of the screw (diameter = D), etc. . However, generally, the clearance between the top of the gear and the cylinder is 0.1 to 3 mm.

If it is less than 0.1 nua, the shearing action will be strong, and 3111f
If fi is exceeded, the dividing and destroying effects become weaker, which is not preferable.

Further, the tooth thickness is in the range of (0,1 to 1)D, and 0.5D or less is sufficient from the viewpoint of dividing action. Further, the number of gears may be plural.

The resin mixed in the mixing section 14 passes through a cylindrical section 17 provided as necessary, and is sent to the shearing section 15. Shearing section 15
This has the effect of uniformly melting the molten resin and making the resin temperature uniform by shearing in a relatively short time. Here, the shearing part 15 includes a torpedo, a dam ring, a Murdoch, a Trestar, etc., and a small clearance between the shearing part 15 and the cylinder may cause resin flow obstruction and increase shearing. There are no particular restrictions. However, in general, a torpedo is preferably used because of its simple structure and workability.

Here, the length of the torpedo is 0.05 to 2 times, preferably 0.1 to 1 time, the screw diameter (D), and the clearance between the torpedo and the cylinder is 0.
3 to 6 mm, preferably 0.5 to 4 mm. However, these values are not necessarily limited to these values, as they may be optimally selected depending on the size of the screw, the combination of torpedo length and clearance, the type of resin, etc. In addition to serving as a structural link between the mixing section 14 and the shearing section 15, the cylindrical section 17 also serves as a structural link between the mixing section 14 and the shearing section 15. Since the passage of the resin is likely to be difficult, providing a release part such as the cylindrical part 17 has the role of making it easier for the resin to pass through the shearing part 15.

The thermoplastic resin molding screw of the present invention, as described in detail above, is provided with a low-shear mixing section 14 in particular in front of the shearing section 15, and by dividing and breaking the solid bed, a large amount of unmelted material is transferred to the shearing section 15. A major feature is that the resin is prevented from being transferred. Therefore, supply section 1
1. Compression section 12) The length of the measuring section 13 may be arbitrarily determined in consideration of the type of resin, etc. However, in the present invention, by providing the mixing section 14, high-speed molding can be performed with good extrusion stability without making the screw length up to the measuring section 13 relatively long.

Next, the resin uniformly kneaded in the shearing section 15 is transferred to the second
The extrusion section 16 extrudes it into a die (not shown). Here, the extrusion section 16 may be any type of normal extrusion screw, and most commonly, a screw with a metering effect is used. In the illustrated example, a release part with a deep groove is formed adjacent to the shearing part 15, and a metering part with a constant groove depth shallower than this is provided on the downstream side of this release part.

Here, the resin is quantitatively extruded while being cooled if necessary. The screw has a compression ratio of 3 to 0.5, preferably 2.5 to 1. In particular, in order to produce a sheet with good transparency from a crystalline resin such as polypropylene by rapid cooling, a compression ratio of 1. It is preferable to use a slow compression type screw of 5 or less to relieve residual stress in the molten resin. In other words, in normal cases, no additional kneading is required in this extrusion section 16, but in order to uniformly disperse additives, colorants, etc., a mixing section may be provided at the tip of the second extrusion section 16. I don't mind.

In addition, in this specification, the most common single thread screw and constant pitch screw have been described, but multiple thread threads, partial multi thread threads, pitch variable screws, etc. may also be used, as long as they have the effects of the present invention. It is not limited to these. Moreover, the term compression ratio means "(groove depth at the resin inflow end)/(groove depth at the resin extrusion end)" in each structural part.

[Specific Examples and Comparative Examples]

Polypropylene (Idemitsu Polypro, F-2005, M I (melt index) 2g/10 minutes, manufactured by Idemitsu Petrochemical ■] at cylinder temperature,
Extrusion molding was performed at a die temperature of 250''C, and moldability and extrudates were evaluated.

The results are shown in Table 2.

Table 2 As is clear from Table 2, when compared at the same rotation speed, the examples of the present invention are superior in pressure fluctuation at the gouer part and resin temperature at the goulet outlet.

In addition, the extrusion rate that can be stably extruded has been significantly improved.

〔Effect of the invention〕

According to the present invention, it has been difficult to achieve both
Improved kneading properties, low-temperature extrusion molding, and even high-speed stable extrusion molding are now possible. Therefore, sheets, films, etc. with excellent uniformity can be manufactured with good productivity and at low cost. This is a molding screw that is particularly suitable for molding polypropylene sheets that develop transparency through rapid cooling.

[Brief explanation of the drawing]

Figure 1 is a side view of a conventional general screw;
The figure is a side view showing a thermoplastic resin molding screw according to the present invention. DESCRIPTION OF SYMBOLS 11... Supply part, 12... Compression part, 13... Measuring part, 14... Mixing part, 15... Shearing part, 16...
Second extrusion section.

Claims (3)

[Claims] (1) A first extrusion section having a supply section, a compression section, and a metering section is formed sequentially from the resin supply side toward the resin extrusion side, and a mixing section is formed sequentially from the first extrusion section toward the resin extrusion side. A screw for molding a thermoplastic resin, characterized in that a shearing section and a second extrusion section are formed. (2) The screw for thermoplastic resin molding according to claim 1, characterized in that the mixing part is gear-shaped. (3) A screw for thermoplastic resin molding according to claim 1 or 2, characterized in that the shearing portion is torpedo-shaped.