JP2009297967A - Screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screw which uniforms a foaming gas in a resin and can efficiently mold a thermoplastic foam resin molded article having a high foaming magnification ratio. <P>SOLUTION: The screw 1 is housed in a cylinder barrel to compose a part of a molding machine. In the screw 1, an area (measuring part MZ) where a resin is in a molten state is composed of a flight 7 of at least one start. The flight 7 has a meandering shape, a groove 8 is formed by the flights 7 with each other, and the formed groove 8 has a meandering shape. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a screw used in an extrusion molding machine or an injection molding machine for producing a foam molded article made of a thermoplastic resin and a foaming agent.

An injection molding machine such as an in-line screw type melts and plasticizes a material such as a thermoplastic resin and molds it as a molded product. Specifically, the thermoplastic resin is melted and plasticized by the shearing energy generated by the rotation of the heater and the injection screw, and kneaded in a supply unit, a compression unit, and a metering unit formed in the axial direction of the injection screw. And the thermoplastic resin which passed through the process is inject | poured in a metal mold | die, and is shape | molded as a thermoplastic resin molded object.
The injection screw has a flight spirally wound over the entire length of the screw, and many ideas have been made so far regarding the screw.

  As one of the injection-molded products, a foam-molded product is known. The foam molded product is obtained by blending or mixing a foaming agent with a raw material resin and foaming the resin in a mold. In the prior art, the same screw as the above-described injection screw has been used even when injection molding is performed by blending such a foaming agent.

  For this reason, some problems may occur depending on the material and additive of the thermoplastic foam resin to be molded. That is, generally, the decomposition temperature of the foaming agent is lower than the melting point of the thermoplastic resin. Therefore, the foaming agent having a low decomposition temperature starts to decompose near the starting point of the screw. This decomposition generates foaming gas, but the foaming gas leaks to the outside through the hopper without being substantially impregnated with the thermoplastic resin having a high unmelted ratio near the hopper. That is, there has been a problem that the foamed gas of the foaming agent cannot be effectively used effectively and a thermoplastic foamed resin molded product having a high foaming ratio cannot be obtained.

Patent Document 1 discloses an injection molding screw that solves such a problem.
JP 2003-145597 A

In order to prevent the leakage of foaming gas, the injection molding screw described in Patent Document 1 has a groove depth on the resin supply side and a groove depth in a completely melted region of the resin (generally referred to as a metering section MZ). The ratio (compression ratio) is made low (1.5 or less).
This is intended to suppress the extrusion of gas to the front side (hopper side) by lowering the compression ratio of the metering section.
However, according to the invention of Patent Document 1, there is a problem that the kneadability is insufficient in the cylinder barrel, the foaming agent is not sufficiently dispersed in the thermoplastic foamed resin, and the foamed gas does not become uniform bubbles. Therefore, according to the measure described in Patent Document 1, the distribution and size of the bubbles in the molded body are not uniform. That is, according to the prior art, it was difficult to efficiently disperse the foaming agent in the molten resin in the injection molding apparatus, and it was difficult to mold a resin molded product having a high expansion ratio.

  Then, this invention makes it a subject to provide the screw which can shape | mold a foaming gas uniformly in resin, and can shape | mold the thermoplastic foamed resin molded product of a high foaming ratio efficiently in view of the fault mentioned above.

  In order to solve the above problems, the invention of claim 1 is a screw which is housed in a cylinder barrel and constitutes a part of a molding machine, and a region where the resin is in a molten state is composed of at least one or more flights. The region has a groove constituted by the flight, and the flight has a meandering shape, and the groove meanders by the meandering shape.

  In the screw according to the present invention, a groove through which the resin passes is formed by a flight provided in a region where the resin is in a molten state, and the flight itself constituting the groove has a meandering shape. That is, the molten resin that passes through the groove is kneaded more than in the prior art groove. In the case of thermoplastic foamed resin molding, the melted thermoplastic resin is sufficiently kneaded under the influence of the meandering shape of the grooves, and uniform fine gas can be dispersed throughout the thermoplastic resin. Therefore, it is possible to obtain a molded product having a high expansion ratio. In other words, it is possible to efficiently mold a thermoplastic foamed resin molded article having a high foaming ratio without increasing the amount of foaming agent. This leads to cost reduction.

  A second aspect of the present invention is the screw according to the first aspect of the present invention, wherein the top of the flight has a constant angle gradient.

  The screw of claim 2 applies a large shearing force to the resin or the like that passes over the flight and passes between it and the inner wall of the barrel because the flight has a gradient of a constant angle. Specifically, the top with the flight gradient generates a shearing force when rotating with the groove. Therefore, the kneadability is further increased, the foaming agent and the foaming gas are uniformly dispersed in the resin, and the foaming ratio of the resin is increased.

  A third aspect of the present invention is the injection molding screw according to the first or second aspect of the present invention, wherein the groove formed by the flight has a wider width on the opening side than the bottom.

  The screw according to claim 3 has a configuration in which the width of the opening is widened compared to the bottom of the groove, so that the resin can easily enter the groove. For this reason, even in a region having a groove configuration narrower than the groove on the side to which resin or the like is supplied, the resin or the like easily enters the narrowed groove. For this reason, the resin is easily affected by expansion and contraction of the groove. That is, the molten resin is easily kneaded, and the foaming agent and the foaming gas can be dispersed throughout the resin.

  A fourth aspect of the present invention is the screw according to any one of the first to third aspects, wherein the groove has a concave shape having a substantially arc shape at the bottom.

  In the screw according to the fourth aspect, the bottom of the groove has a substantially arc-shaped concave shape, so that the molten resin or the like is not caught in the middle and easily passes. Therefore, it is possible to prevent the molten resin from staying in the flight groove for a long time. That is, it is possible to prevent the resin from burning due to the rotational energy of the screw or the foaming agent from starting to foam and ending the foaming action.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the screw rotation speed is 100 rpm or more, and the shear rate is 500 (1 / s) or more in the region. It is a featured screw.

  Conventionally, the shear rate of a general injection screw or the like has been about 30 (1 / s) to 100 (1 / s). However, when the shear rate is low in the region where the resin is in a molten state, sufficient kneading is not performed, and a thermoplastic foamed resin molded product having a uniform foaming gas and a high foaming ratio cannot be obtained. On the other hand, the screw according to claim 5 has a foaming ratio of a uniform foaming gas having a uniform foaming gas when the rotational speed is 100 rpm or more, the shear rate of the measuring section is 500 (1 / s) or more, and the resin is sufficiently kneaded. A high thermoplastic foamed resin molded product can be obtained. That is, it is not necessary to increase the amount of the foaming agent in order to increase the expansion ratio of the resin, leading to cost reduction.

  The screw of the present invention provides a meandering flight in a region where the resin is in a molten state, a meandering groove is formed by the flight, and gives a high shearing force to the resin passing through the groove, The kneadability is increased, and a thermoplastic foamed resin molded article having a high expansion ratio and having a uniform foaming gas can be obtained.

Next, an injection molding screw 1 (also referred to as an injection screw 1) according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing an injection molding machine 11 including an injection molding screw 1 according to an embodiment of the present invention. The injection molding machine 11 includes an injection molding screw 1, a cylinder barrel 2, a heater 3, a hopper 5, and an injection cylinder (not shown).
The injection molding machine 11 is supplied with raw materials such as resin and foaming agent from the hopper 5, and the injection screw 1 is rotated at a rotational speed set by a motor or a hydraulic pump (not shown), kneaded, plasticized and melted. The molded resin composition is injected from the tip of the cylinder barrel 2 into the mold 4 so that a molded product can be molded.

First, the thermoplastic resin and foaming agent used as raw materials will be described.
The thermoplastic resin material applied in the foam molding is a resin that can be injected by a general injection screw 1 such as injection molding, injection compression molding, injection foam molding, etc., and is not particularly limited, but polypropylene, polyethylene, polystyrene, propylene / Examples thereof include polyolefin resins such as ethylene copolymers.
The chemical foaming agent is not particularly limited, and examples thereof include azodicarbonamide (organic compound) and bicarbonates (inorganic compounds) such as sodium bicarbonate.
In addition to the chemical foaming agent, if necessary, the foamable molten resin may be a known foaming aid, foam nucleating agent, foam molding stabilizer, stabilizer, ultraviolet absorber, antioxidant, antistatic agent, Lubricants, colorants, flame retardants, crosslinking agents and / or fillers can be blended. Incidentally, as the foaming aid, for example, stearates such as sodium stearate, calcium stearate, magnesium stearate, potassium stearate, zinc stearate, montanic acid (which is octacosanoic acid) calcium, zinc montanate, etc. Higher fatty acid metal salts such as montanate, urea or urea compounds, paraffin, and other stearamides.
Examples of the foam nucleating agent include inorganic fillers such as talc, silica, calcium carbonate, and calcium silicate.

Next, each member in the injection molding machine 11 will be described.
As shown in FIG. 1, the cylinder barrel 2 accommodates an injection molding screw 1 to be described later, and an injection hole 22 through which molten resin is injected on the front end side and a raw material such as resin on the rear end side. A loading port 23 to be loaded is provided.
Further, a hopper 5 for supplying a material such as a resin or a foaming agent is provided at the inlet 23 of the cylinder barrel 2.

The heater 3 is provided so as to cover the periphery of the cylinder barrel 2 described above. This heater 3 promotes the melting of the resin or the like.
The mold 4 has various shapes depending on the type of molding. A concave receiving port 25 provided with a filling flow path 24 is formed at a position where the molten resin is filled from the tip of the cylinder barrel 2. Yes. Note that the receiving port 25 has a shape into which the tip of the cylinder barrel 2 is fitted.

  The injection screw 1 includes a main body 12 and a check ring 13. Inside the main body 12, a substantially cylindrical shape having a spline shaft (not shown) at the substantially center, and a male screw (not shown) is formed at the tip of the main body 12. A check ring 13 having a substantially conical shape is fitted to the male screw at the one end.

On the other hand, the rear end side of the injection screw 1 which is the other end is connected to the injection cylinder, and the injection screw 1 can be moved back and forth in the axial direction of the spline shaft. The injection cylinder is operated by driving a motor or a hydraulic pump (not shown).
Here, the spline shaft (not shown) has a configuration in which the rotation of the injection molding screw 1 is restrained but is movable in the axial direction.

As shown in FIG. 1, a flight 21 is provided in a spiral shape on the main body 12 of the injection screw 1. Resin or the like passes through the groove 16 sandwiched between the flights 21. This flight 21 is formed by cutting.
In the injection screw 1 of the present embodiment, a supply unit FZ, a compression unit CZ, and a metering unit MZ are formed in the axial direction, and a region where the resin is completely melted is mainly used as the metering unit MZ.

  Further, the injection screw 1 of the present embodiment has a configuration in which the decomposed foam gas hardly leaks in the supply unit FZ and the compression unit CZ. More specifically, a gas leak prevention unit (not shown) having a certain length is provided at an arbitrary location at a position where the resin starts to melt in the supply unit FZ. The gas leak prevention unit is ΔL / D <1, where D is the combined diameter of the main body 12 and the flight 21, and ΔL (lead) is the length that the spiral flight 21 travels when it makes one revolution. This is the part where the flight 21 is provided. In other parts of the supply unit FZ, ΔL / D = 1. That is, with such a configuration, the filling rate of the foaming gas is increased between the injection screw 1 and the cylinder barrel 2, and the gas is impregnated and sealed with the semi-molten resin, so that the leakage preventing action is strengthened. And when resin is further knead | mixed and will be in a perfect molten state, a foaming agent and foaming gas will be further disperse | distributed in resin in the measurement part MZ.

  The injection screw 1 of the present embodiment is characterized by the structure of the injection screw 1 in the region where the resin is in a completely molten state, that is, in the measuring unit MZ. Next, this will be described in detail. In addition, since the flight 7 and the groove | channel 8 in the measurement part MZ differ from the above-mentioned flight 21 and the groove | channel 16, the number is changed for convenience.

In the measuring portion MZ, there are three flights 7 as shown in the development view of the injection screw 1 in FIG. 2, and the grooves 8 shown by the shaded portions in FIG. Yes. The spiral angle of the flight 7 (an angle that is counterclockwise from the angle perpendicular to the main body 12 of the injection screw 1) is 30 to 75 degrees, and preferably 45 to 60 degrees.
Each flight 7 itself has a meandering shape, and a groove 8 formed by the flight 7 also meanders.

In the present embodiment, the relationship between the width t of the flight 7 and the width w of the groove 8 is such that the flight width t is 1 to 5 times the groove width w, but preferably 3 to 4 times. Each said width maintains a constant value.
Further, as shown in FIG. 3, the top portion 14 of the flight 7 has a constant angle gradient α. The gradient α of the present embodiment is configured to have an upward gradient α toward the tip of the injection screw 1 in the width direction of the flight 7, and the gradient α is 3% to 12%, preferably 4% to 8%. To do. Here, the gradient α is (displaced height Δh) / (flight 7 width t). In calculating the gradient α, the gradient of the angle θ described later is ignored.

In addition to the above-described configuration, the side surface of the flight 7 forming the groove 8 has a gradient of a constant angle θ as shown in FIG. The angle θ is 7 degrees to 12 degrees, preferably about 10 degrees. Further, the bottom of the groove 8 is a substantially arc-shaped concave shape.
Since it has such a configuration, the resin or the like that passes through the measuring unit MZ easily enters the groove 8 even if the groove width is narrower than that of the supply unit FZ and the compression unit CZ. Therefore, it is easy to be affected by expansion / contraction of the groove 8, and the foaming gas is easily impregnated in the molten resin. Further, since the bottom has a substantially arc shape, it is possible to prevent the resin and the like from passing smoothly and prevent the resin and the like from staying in the groove 8 for a long time. That is, it is possible to prevent the resin from being burnt by the shearing energy of the injection screw 1 and the foaming agent from starting to foam and ending foaming.

Thus, by setting the injection screw 1 as described above, as shown in Table 1, the shear rate in the measuring unit MZ is greatly increased in proportion to the rotational speed of the screw. Specifically, when the rotation speed of the screw is 100 rpm or more, the shear rate is 500 (1 / s) or more. Furthermore, the most preferable foamed molded product can be obtained when the rotational speed of the screw is 200 rpm or more. Specifically, the shear rate at the measuring unit MZ is 1000 (1 / s) or more, and the foaming gas having a fine and stable bubble diameter is uniformly dispersed in the resin. That is, if the injection screw 1 of the present embodiment is used, the resin can be sufficiently kneaded even if the rotational speed of the screw is increased to 100 rpm or more. And as a result, the molded foamed thermoplastic foamed resin product can have a high foaming ratio because the foamed gas made fine by kneading is uniformly dispersed in the resin.
As shown in the following table, the specific expansion ratio is 2.0 or more. In addition, the expansion ratio said here is (apparent volume of a molded article) / (raw material resin weight).

  On the other hand, as a comparative example, a screw having the same conditions as in the example except for the weighing unit MZ is used. Therefore, the injection screw 1 under the following conditions, which is a conventional technique, is used as the screw. The comparative examples include a general-purpose screw (Comparative Example 1) that is generally used, a screw that uses a dull mage type for a part of the weighing unit MZ (Comparative Example 2), and a barrier type for a part of the weighing unit MZ. The screw used (Comparative Example 3).

  As shown in Table 1, in each comparative example, the shear rate in the measuring unit MZ is about 135 to 670 (1 / s). Specifically, as in the embodiment, when the screw rotation speed is increased to 100 rpm or more, the value of the shear rate gradually increases in proportion thereto. However, the expansion ratio is reduced so as to be approximately inversely proportional to them.

  Many conventional screws have a large groove width formed by the flights 21 and a small ratio of the width of the flight 21 to the groove width. For this reason, when the number of rotations is increased, the amount of resin extruded per time is increased in proportion to the number of rotations. In short, with the conventional screw, even when the rotation speed is high speed of 100 rpm or more, the molten resin is not sufficiently kneaded in the measuring unit MZ. Therefore, the foaming gas is not uniformly dispersed in the resin and is pushed out in front of the screw. Therefore, in the screw of the prior art, when the number of rotations is increased, the shear rate slightly increases, but the foaming gas cannot be uniformly dispersed, and the foaming ratio of the foamed molded product cannot be increased. Specifically, the expansion ratio is about 1.02 to 1.80, and cannot be 2.0 or more.

The molding machines, molds, and molding conditions used in the examples and comparative examples are as follows.
Used injection molding machine: EC-160 (manufactured by Toshiba Machine Co., Ltd.)
Screw diameter φ36 L / D = 22 (L is the effective length of the screw)
Cylinder barrel set temperature
Supply unit FZ 180 ° C (180 degrees Celsius)
Compression section CZ 200 ° C (200 degrees Celsius)
Weighing section MZ 190 ° C (190 degrees Celsius)
Thermoplastic resin: 100 parts by weight of polypropylene Chemical foaming agent: 3 parts by weight of sodium bicarbonate Mold used: 330 mm × 116 mm × 1.5 mm

It is the table | surface which showed the experimental result of above-described Example and Comparative Examples 1-3.

  From this, the injection screw 1 of the present embodiment is configured to be able to efficiently take in the foaming gas in the measuring unit MZ even if the same amount of foaming agent is used due to a dramatic improvement in the shear rate. In other words, even if the gas leakage prevention unit is provided in the supply unit FZ and the gas leakage is prevented, if the foaming gas cannot be impregnated or sealed in the resin by the metering unit MZ, as in the present embodiment. A molded product with a high expansion ratio cannot be obtained. In other words, even if the amount of the foaming agent is increased, the raw material may be wasted if it cannot be efficiently taken into and dispersed in the resin by the measuring unit MZ.

  From the above, with the injection screw 1 of the present embodiment, the foaming gas secured by the gas leak prevention unit can be efficiently taken into the resin in the measuring unit MZ, and the gas bubbles are uniform and highly foamed. A thermoplastic foamed resin molded article having a magnification can be obtained.

Although the screw 1 for injection molding of the said embodiment showed the structure which the supply part FZ in the main-body part 12, the compression part CZ, and the measurement part MZ integrated, this invention is not necessarily limited to this.
For example, the supply unit FZ, the compression unit CZ, and the measurement unit MZ are connected in segments, or ΔL (the length that travels in the axial direction when the flight 21 makes one rotation) / D (the main unit 12 and the flight are aligned. (Diameter) may be connected in segments. Even in that case, it is necessary to provide the gas leak prevention unit in the supply unit FZ and provide the above-described configuration in the measuring unit MZ, as in the above embodiment.

Although the screw 1 for injection molding of the said embodiment showed the measurement part MZ comprised by the three flights 7, the present invention is not necessarily limited to this.
For example, the measuring section MZ may be composed of two or four flights 7. However, in order to obtain the above effect, when the number of flights 7 is less than 3, it is necessary to increase the width of the flight 7 or to decrease the length ΔL that the flight 7 travels when it makes one revolution. If 7 is greater than 3, it is necessary to reduce the width of flight 7 or increase ΔL.

  The injection molding screw 1 of the above embodiment may be formed by forming grooves and grooves as shown in the above embodiment by cutting a cylindrical iron-based material or the like.

It is the schematic which shows an injection molding machine. It is an expanded view in the measurement part of the screw for injection molding. It is AA sectional drawing of the measurement part shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Screw for injection molding 2 Cylinder barrel 3 Heater 4 Mold 5 Hopper 7 Flight 8 Groove 11 Injection molding machine 12 Main body part 13 Check ring 14 Top part 16 Groove α Gradient θ Angle

Claims (5)

A screw that is housed in a cylinder barrel and constitutes a part of a molding machine, and a region in which the resin is in a molten state is composed of at least one or more flights,
The region has a groove constituted by the flight,
The flight has a meandering shape, and the groove meanders by the meandering shape.   The screw according to claim 1, wherein a top portion of the flight has a slope of a constant angle.   The screw according to claim 1 or 2, wherein the groove formed by the flight has an opening width wider than that of a bottom portion.   The screw according to any one of claims 1 to 3, wherein the groove has a concave shape having a substantially arc shape at the bottom. The rotational speed of the screw is 100 rpm or more,
The screw according to any one of claims 1 to 4, wherein a shear rate is 500 (1 / s) or more in the region.

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