JP2006001265A - Screw for thermoplastic resin molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screw for a thermoplastic resin molding which inhibits heat generation by local shearing and improves mixing performance by the application of the mixing method by a straightening stream to a screw. <P>SOLUTION: A resin passage having the cross-sectional area reducing in the direction from the screw tip side to the rear end side is formed on a spiral flight of the screw. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermoplastic resin molding screw for an extrusion molding machine or an injection molding machine, and particularly suitable as a screw for a twin-screw extruder for molding a thermoplastic resin that is easily thermally decomposed, such as a vinyl chloride resin. It is. The thermoplastic resin molding includes thermoplastic resin foam molding.

In a molding machine with a built-in screw, it is necessary to sufficiently melt and knead the molding resin composition in order to obtain a homogeneous molded product. The kneading is carried out by applying a shearing force to the material. Further, from the viewpoint of weight reduction, cost reduction, and designability of molded products, molding as a foam has been conventionally performed. In this thermoplastic resin foam molding (hereinafter also simply referred to as “foam molding”), in order to uniformly disperse and mix the foaming agent in the resin, the gas lump is crushed and kneaded by applying a shearing force in the same manner as described above. The foamed cells are uniformly dispersed.
However, when kneading is performed by applying a shearing force, the mixing performance is improved, but the molten resin generates heat due to the shearing force, and there is a problem that the performance such as the quality of a molded product obtained by the deterioration of the molten resin is deteriorated due to the heat generation. there were.

  As a solution to the problem of heat generation of the molten resin, it is suitable for extrusion molding of resins such as vinyl chloride resin that generate a large amount of heat due to shearing between the cylinder and the screw during extrusion molding and are susceptible to resin burning due to heat. An extruder screw having a cooling function by a simple heat pipe has been proposed. For example, in a screw main body composed of a screw part and a driving part, a hollow hole extending from the vicinity of the front end of the screw main body to the rear end is provided in the axial center of the screw main body. A heat conduction layer is formed on each peripheral surface, a heat insulating layer is formed on an inner peripheral surface of a substantially central portion of the screw portion in the hollow hole, and a heat pipe having a length slightly shorter than the length of the screw portion is formed in the hollow hole. An extrusion machine, wherein an operating mechanism that is inserted and moves the heat pipe in the axial direction of the screw main body is provided at a rear end portion of the screw main body and is operable from the rear end portion. "Screw" has been proposed (see, for example, Patent Document 1).

Japanese Patent Publication No. 6-88308 (Claims, Fig. 1)

  In the screw of the extrusion machine described in Patent Document 1, if the position of the heat pipe 3 is set according to the type of resin and the amount of extrusion (the number of rotations of the screw), the heat of the metering / melting section 12 is absorbed. Since the heat is absorbed through the part 31 and is radiated through the heat radiating part 32 in the preheating part 14, the metering / melting part 12 is cooled, and the temperature of the metering / melting part 12 rises and is always kept at the optimum condition without overheating. However, since the screw structure is complicated and the manufacturing cost of the screw is high, there is a disadvantage that it is an expensive equipment. In addition, adjustment of the setting position of the heat pipe and maintenance are necessary, and there is a problem that maintenance is troublesome.

  Accordingly, an object of the present invention is to provide a thermoplastic resin molding screw that suppresses local shearing heat generation and improves mixing performance by applying a mixing method by extension flow to the screw.

The thermoplastic resin molding screw according to claim 1 has a resin passage in which a cross-sectional area is reduced from a screw front end side to a rear end side in a flight of a screw formed by forming a flight spirally. It is formed.
The thermoplastic resin molding screw according to claim 2 is the thermoplastic resin molding screw according to claim 1, wherein the resin passage having a reduced cross-sectional area has a height of a flight outer peripheral surface of the screw. The inclined surface is formed so as to be low on the front end side and high on the screw rear end side.

  Further, the thermoplastic resin molding screw according to claim 3 is the thermoplastic resin molding screw according to claim 2, wherein the clearance between the flight outer peripheral surface on the screw front end side and the barrel inner surface is the flight outer periphery on the screw rear end side. The clearance between the surface and the barrel is 1.5 to 3.5 times, and the clearance between the screw bottom and the barrel is 0.05 to 0.20 times.

  Further, the thermoplastic resin molding screw according to claim 4 is the thermoplastic resin molding screw according to claim 1, wherein the screw is formed at a predetermined interval in the circumferential direction of the flight of the screw from the screw front end side to the rear end side. A resin passage comprising a notch penetrating therethrough is formed, and the thermoplastic resin molding screw according to claim 5 is the thermoplastic resin molding screw according to claim 4, wherein the notch on the screw tip side of the notch is provided. The cross-sectional area is 1.5 to 3.5 times the cross-sectional area on the screw rear end side, and the total cross-sectional area on the screw front end side of the notch existing around one screw axis of the flight is the screw axis of the screw flight. The cross-sectional area per rotation is 0.05 to 0.20 times.

  The thermoplastic resin molding screw according to claim 6 is the thermoplastic resin molding screw according to any one of claims 1 to 5, wherein a resin passage having a reduced cross-sectional area is a meter of the screw. The thermoplastic resin molding screw according to any one of claims 1 to 6, wherein the thermoplastic resin molding screw according to claim 7 is provided in a flight corresponding to a ring zone or a compression zone. The screw is for a twin-screw extruder.

  In the thermoplastic resin molding screw according to claim 1 of the present invention, a resin passage having a reduced cross-sectional area from the screw front end side to the rear end side is formed in the screw flight. When the thermoplastic resin is molded by the molding machine equipped with the, the molten resin flows through the resin passage from the high resin pressure side to the low resin pressure side. That is, it flows from the screw front end side to the rear end side. Since this resin passage has a cross-sectional area that is reduced from the screw front end side to the rear end side, the molten resin that flows through the resin passage undergoes elongational flow and effective dispersion mixing is performed. The resin composition is homogeneously dispersed and a product having excellent quality performance free from burning (deterioration) due to shearing heat generation is obtained. Also in foam molding, a molded product in which foam cells are uniformly dispersed can be obtained by the same effect as described above.

  The thermoplastic resin molding screw according to claim 2, wherein the resin passage having a reduced cross-sectional area is inclined such that the height of the flight outer peripheral surface of the screw is low on the screw front end side and higher on the screw rear end side. Since it is formed as a surface, the molten resin is stretched over the circumferential direction of the outer periphery of the screw, effective dispersion mixing is performed throughout the molten resin passage, and it is excellent without homogeneous deterioration As a result, the above-mentioned effect is further ensured.

  Further, in the thermoplastic resin molding screw according to claim 3, the clearance between the flight outer peripheral surface on the screw tip side and the barrel inner surface is 1.5 to 3.5 of the clearance between the flight outer peripheral barrel on the screw rear end side. Since it is doubled and 0.05 to 0.20 times the clearance between the screw bottom and the barrel, heat generated by shearing is large and even if the resin is susceptible to resin burning due to heat, it is uniformly dispersed Thus, an excellent quality molded product without deterioration is obtained, and the above effect is further ensured.

Further, the thermoplastic resin molding screw according to claim 4 has a resin passage formed of a notch penetrating from the screw front end side to the rear end side at a predetermined interval in the circumferential direction of the flight of the screw. The molten resin that flows along the bottom surface of the screw is caused to generate an extension flow to effectively mix and disperse, and a homogeneously dispersed molded product having no deterioration can be obtained. It will be certain.

  Further, in the thermoplastic resin molding screw according to claim 5, the cross-sectional area of the notch on the screw front end side is 1.5 to 3.5 times the cross-sectional area on the screw rear end side, and the flight screw shaft The total cross-sectional area of the screw tip side of the notch existing per turn is 0.05 to 0.20 times the cross-sectional area per screw axis of the flight of the screw. Even with a resin that is susceptible to resin burning, a molded product of excellent quality that is homogeneously dispersed and has no deterioration can be obtained, and the above-described effect is further ensured.

  Further, in the thermoplastic resin molding screw according to claim 6, since the resin passage having a reduced cross-sectional area is provided in a flight corresponding to the metering zone or the compression zone of the screw, Effective stretch flow is generated, effective dispersion mixing is performed, and the obtained molded product is a homogeneous product with a uniform resin composition, and excellent quality performance without burning (deterioration) due to shear heat generation Can be obtained, and the above-described effect is further ensured.

  Moreover, the thermoplastic resin molding screw according to claim 7 is used for a twin screw extruder, and causes deterioration due to heat generation of a thermoplastic resin such as vinyl chloride resin which is easily thermally decomposed. Therefore, a molded product having excellent quality performance can be obtained, and the above effect can be further ensured.

Next, the best mode for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a partial plan view showing, in a partial cross section, an example of a thermoplastic resin molding screw of the present invention.
In the figure, reference numeral 1 denotes a thermoplastic resin molding screw, in which a flight 2 is formed in a spiral shape, and a screw groove 3 is formed between the flights 2 and 2. 6 is a barrel of the molding machine.
The outer peripheral surface 4 of the flight 2 is provided with an inclined surface in which the height of the flight outer peripheral surface 41 on the screw front side is low and the height of the flight outer peripheral surface 42 on the rear end side is increased. In the state of being mounted on, the resin passage 5 is formed between the outer peripheral surface 4 of the flight 2 of the screw 1 and the inner surface of the barrel 6 and the cross-sectional area is reduced from the screw front end side to the rear end side. Yes. In the drawing, the arrow indicates the extrusion direction (screw tip direction).

  The resin passage 5 only needs to be provided in the metering zone or compression zone of the molding machine. Even if the resin passage 5 is provided continuously over the entire length of the metering zone and compression zone of the screw 1, it is provided partially. May be. In the case where it is partially provided, if it is provided over at least 1.5 circumferences of the outer peripheral surface of the screw 1, it is possible to effect the dispersion and mixing of the molten resin by extension flow on the entire extruded molten resin. When the resin passage 5 having a reduced cross-sectional area is partially provided, it is effective to provide the resin flight 5 at the screw flight portion at the tip portion of the extruder.

  In addition, the specific dimensions of the resin passage 5 having a reduced cross-sectional area need to be considered in a state where the screw 1 is mounted on the barrel 6, and the resin characteristics such as viscosity, the extrusion amount, the flight width, The clearance 43 between the flight outer peripheral surface 41 on the screw tip side of the flight 2 and the inner surface of the barrel 6 is one of the clearances 44 between the flight outer peripheral surface 42 on the screw rear end side and the inner surface of the barrel 6. It is preferable to be in the range of 0.5 to 3.5 times and in the range of 0.05 to 0.20 times the clearance 45 between the screw bottom surface and the barrel 6 inner surface.

If the clearance 43 is smaller than 1.5 times the clearance 44, the effect of dispersion mixing due to the extension flow of the molten resin is reduced, and there is a risk that the molten resin generates heat and the resin is burnt. On the other hand, when the ratio is larger than 3.5 times, the effect of dispersion and mixing due to the extension flow of the molten resin becomes partial, and the whole cannot be mixed uniformly.
Also, if the clearance 43 is smaller than 0.5 times the clearance 45, the effect of dispersion mixing due to the extension flow of the molten resin becomes partial, and the whole cannot be mixed uniformly, and more than 0.20 times This is because the amount of extrusion of the molten resin by the rotation of the screw 1 decreases as the value increases.

  In FIG. 1, the relationship between the screw 1 and the barrel 6 is described, but this relationship is the same in both a single screw extruder and a twin screw extruder.

2 and 3 show another embodiment of the thermoplastic resin molding screw according to the present invention. FIG. 2 is a cross-sectional view of the plane perpendicular to the screw shaft viewed from the screw tip side. FIG. 3 is a partial plane of the flight. FIG.
A spiral flight 2a is formed in the thermoplastic resin molding screw 1a, and a notch 5a penetrating from the front end side to the rear end side of the screw 1a at a predetermined interval in the circumferential direction is formed in the flight 2a. . 3a is a screw groove formed between the flights 2a and 2a, and 31a is a bottom surface of the screw groove 3a.

  This notch 5a has a wide width on the front end side 51a of the screw 1a, a narrow width on the rear end side 52a, and a bottom surface 53a formed slightly above the bottom surface 31a of the screw groove 3a. The cross-sectional area is reduced from the cross-sectional area S1 on the front end side 51a toward the cross-sectional area S2 on the rear end side 52a.

  In order for this notch 5a to balance the transfer function of the molten resin and the dispersion and mixing function by extension flow, the cross-sectional area S1 of the screw front end 51a of the notch 5a is 1.5 to 1.5 of the cross-sectional area S2 of the screw rear end 52a. The total cross-sectional area S1 of the screw tip 51a of the notch 5a existing around the screw shaft of the flight 2a is 3.5 times the cross-sectional area of the screw 2a of the flight 2a of the screw 1a. .20 times is preferable.

The dimensions of the notch 5a are such that the lateral width of the tip side 51a of the screw 1a is narrower than the height of the flight 2a, the bottom surface 53a is close to the bottom surface 31a of the screw groove, and the total cross-sectional area S1 of the screw tip side 51a is The cross-sectional area per rotation of the screw shaft of 2a is preferably 0.05 to 0.20 times. That is, the circumferential interval of the notches 5a may be determined according to the dimensions of the notches 5a.
When such a notch 5a is provided, an extended flow is generated in the entire molten resin transported by the rotation of the screw, and effective dispersion mixing can be performed.

  The thermoplastic resin molding screw according to the present invention is configured as described above, so that only a little processing is applied to the flight of the screw to generate an extension flow in the molten resin transported by the screw, thereby causing local shearing. While suppressing heat generation and preventing resin burn, a foaming agent and the like can be uniformly dispersed and mixed, and a molded product in which foamed cells are uniformly dispersed can be produced.

Hereinafter, the present invention will be described more specifically by showing Examples and Comparative Examples.
In addition, this invention is not limited only to the following Example.
Example 1
The test result in the biaxial different direction rotation screw extruder using the screw 1 shown in FIG. 1 is demonstrated.
The biaxial counter-rotating screw extruder has an outer diameter of screw 1 of 50 mm, a ratio L / D of the length L of the extruder to the outer diameter D of screw 1 of 17, the height of flight 2 is 7.6 mm, and the flight width The inclined surface of the outer peripheral surface 4 of the flight 2 has a clearance 43 of 2.5 mm, a clearance 44 of 1 mm, and a clearance 45 of 7.7 mm. The flight 2 with the inclined surface was formed in a range of 80 mm at the tip of the screw 1 in the screw axial direction.

Using the above biaxial different direction rotating screw extruder, a cylindrical body was extruded at a set resin temperature of 180 ° C., an extrusion rate of 30 kg / h, and a screw rotation speed of 20 rpm. A foamed cylindrical body was extruded in the same manner as described above except that nitrogen gas was introduced into the extruder barrel from a cylinder at a pressure of 4 MPa.
The obtained cylindrical body is a homogeneous one in which the resin composition is uniformly melt-dispersed, and the foamed cylindrical body is one in which the foamed cells are uniformly dispersed, both of which are free from burning (deterioration) due to shearing heat generation. It was excellent in performance.

(Comparative Example 1)
A cylindrical body and a foamed cylindrical body were extruded in the same manner as in Example 1 except that a conventional extruder in which the outer peripheral surface of the flight 2 was a cylindrical surface having no inclined surface was used.

(Comparative Example 2)
A cylindrical body and a foamed cylindrical body were extrusion molded in the same manner as in Comparative Example 1 except that the screw rotation speed was 30 rpm.

The following evaluation was performed about the obtained cylindrical body or foamed cylindrical body.
(Degree of gelation)
The degree of gelation evaluated how uniformly the obtained cylindrical body was kneaded. The degree of gelation was measured with a capillary rheometer.
When the extrusion pressure when extruding a powdered vinyl chloride resin is P0, the extrusion pressure when extruding a completely gelatinized vinyl chloride resin is P100, and the extrusion pressure when extruding a vinyl chloride resin raw material is PS,
Gelation degree (%) = (PS−P0) / (P100−P0) × 100
Is calculated by

(Average cell diameter and variation in diameter)
The cross section of the obtained foamed cylindrical body was observed with a secondary electron reflection electron microscope. The cross-section photograph observed and photographed was binarized into a white portion (resin portion) and a black portion (foamed cell portion) by image analysis. The area of the black portion was defined as a pseudo circular surface area, and the foamed cell diameter was calculated therefrom, and the average value and the standard deviation of the cell diameter were calculated. The standard deviation of the calculated cell diameter was taken as the variation in diameter.

  The molding conditions and evaluation results in the above are shown in Table 1. The melt resin temperature in Table 1 is obtained by measuring the temperature of the melt resin at the exit of the extruder using a thermocouple.

  As is clear from Table 1, in the examples of the present invention, it was confirmed that a good gelation degree was obtained and the mixing performance was improved while suppressing the melt resin temperature due to the shear heat generation. . Moreover, also in foam manufacture, it has confirmed that a foaming cell could be disperse | distributed uniformly by mixing performance improving.

It is a partial top view which shows an example of the thermoplastic resin molding screw of this invention in a partial cross section. It is sectional drawing which showed the other Example of the thermoplastic resin molding screw of this invention, and was seen from the screw front end side in a surface perpendicular | vertical to a screw axis | shaft. It is a partial top view of the flight in the AA line of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a Thermoplastic resin molding screw 2, 2a Flight 3, 3a Screw groove 31a Bottom surface of screw groove 3a 4 Flight outer peripheral surface 41 Flight outer peripheral surface 42 on the screw front end side Flight outer peripheral surface 5 on the screw rear end side Resin passage 5a Notch 51a Tip side 52a of screw 1a in notch 5a Rear end side 53a of screw 1a in notch 5a Bottom surface 6 of notch 5a Barrel S1 Cross sectional area S2 of tip side 51a of screw 1a in notch 5a Rear end side of screw 1a in notch 5a 52a cross-sectional area

Claims (7)

  A thermoplastic resin molding characterized in that a resin passage having a cross-sectional area reduced from a screw front end side to a rear end side is formed in a screw flight formed by forming a flight in a spiral shape. screw.   2. The thermoplastic resin according to claim 1, wherein the resin passage having a reduced cross-sectional area is formed as an inclined surface in which a height of a flight outer peripheral surface of the screw is low on a screw front end side and is increased on a screw rear end side. Molding screw.   The clearance between the flight outer peripheral surface on the screw front end side and the inner surface of the barrel is 1.5 to 3.5 times the clearance between the flight outer peripheral surface on the screw rear end side and the barrel, and is 0. 0 of the clearance between the screw bottom surface and the barrel. The thermoplastic resin molding screw according to claim 2, wherein the screw is 0.5 to 0.20 times.   The thermoplastic resin molding screw according to claim 1, wherein a resin passage formed of a notch penetrating from the screw front end side to the rear end side is formed at a predetermined interval in the circumferential direction of the screw flight.   The cross-sectional area on the screw front end side of the notch is 1.5 to 3.5 times the cross-sectional area on the screw rear end side, and the total cross-sectional area on the screw front end side of the notch existing around one screw axis of the flight is The thermoplastic resin molding screw according to claim 4, wherein the screw cross section is 0.05 to 0.20 times per screw axis of the flight of the screw.   The thermoplastic resin molding screw according to any one of claims 1 to 5, wherein a resin passage having a reduced cross-sectional area is provided in a flight corresponding to a metering zone or a compression zone of the screw.   The screw for thermoplastic resin molding according to any one of claims 1 to 6, wherein the screw is for a twin screw extruder.

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