Patent Description:
Resin products are broadly produced by extrusion molding and by injection molding.

According to the extrusion molding, a resin material is extruded from an extruder. The extruder includes a heating cylinder, an extrusion screw, and a screw rotating mechanism. The resin material loaded in the heating cylinder is plasticized by kneading by the rotating extrusion screw and by heat from the heating cylinder.

When it is defined that an effective screw length is L and an outer diameter (will be simply referred to as "diameter" below) is D, LID of the extrusion screw in the case of extrusion molding is made about <NUM>.

According to injection molding, a resin material is injected from an injector to a metal mold. The injector includes a heating cylinder, an injection screw, a screw rotating mechanism, and a screw moving mechanism.

The resin material loaded in the heating cylinder is plasticized by kneading by the rotating injection screw and by heat from the heating cylinder. The plasticized resin material is accumulated at the front part of the heating cylinder, and the injection screw is moved back by such an accumulation. When moved back by a certain distance, the injection screw is then moved forward to inject the resin material.

When moved forward, the injection screw receives reaction force in the axial direction. When the reaction force in the axial direction exceeds a certain value, the injection screw is collapsed. Hence, in order to avoid the occurrence of such a collapse, L/D of the injection screw in the case of injection molding is made about to <NUM>.

For example, <CIT> discloses such an injection screw.

The technology disclosed in <CIT> will be described with reference to <FIG>.

<FIG> is a side view of a conventional injection screw, and an injection screw <NUM> is located in a heating cylinder <NUM> so as to be rotatable and movable in the axial direction.

The heating cylinder <NUM> includes a nozzle <NUM> at a tip, and also includes a heater <NUM> on the outer circumference.

Some of the necessary heat for plasticization is supplied by the heater <NUM>. A plasticized resin material is injected from the nozzle <NUM> by the forward movement actuation of the injection screw <NUM>.

The injection screw <NUM> includes a flight <NUM> corresponding to a spiral thread, and a groove <NUM> corresponding to a root of the screw thread.

Providing that an effective screw length of the injection screw <NUM> is L and a diameter is D, L/D disclosed in <CIT> is set to be <NUM> to <NUM>,<NUM>.

Such an injection screw <NUM> is applied for injection of syndiotactic polymer that is a kind of resin material.

The inventors of the present disclosure attempted to inject rigid vinyl chloride using an injection screw equivalent to the injection screw <NUM>.

An injection screw <NUM> equivalent to the injection screw <NUM> is taken as a model <NUM>. <FIG> illustrates the injection screw <NUM>.

As illustrated in <FIG>, the injection screw <NUM> includes a flight <NUM> and a groove <NUM>, and a width t of the flight <NUM> and a pitch P thereof are constant. D is a diameter and L is an effective screw length.

An effective screw length L becomes the sum of a length Lf of a supply portion, a length Lc of a compression portion, and a length Lm of a measure portion.

A depth of the groove at the supply portion is hf, a depth of the groove at the compression portion is hc, and a depth of the groove at the measuring unit is hm.

TABLE <NUM> illustrates specifications of the injection screw <NUM>.

The compression ratio in the lowest row of TABLE <NUM> is the compression ratio at the compression portion.

Since the pitch P is constant and the width t of the flight <NUM> is constant, the compression ratio is <NUM>,<NUM> obtained from a calculation (the depth hf of the groove at the supply portion)/(the depth hm of the groove at the measure portion) = <NUM>,<NUM>/<NUM>,<NUM> = <NUM>,<NUM>.

Rigid vinyl chloride was injected on a trial basis using the above-described screw <NUM>. At that time, circuit pressure relating to the rotation of the screw <NUM> and the temperature of the nozzle (see <FIG>, reference numeral <NUM>) were measured.

Note that at the initial stage of shots, since there are a large number of variable factors, data and a situation at the eighth shot conceivable that such factors became substantially stabilized were checked.

Even at the eighth shot, a color change was observed in the injected rigid vinyl chloride. Hence, the result was dissatisfied according to the model <NUM>. Note that the temperature of the nozzle at the eighth shot was <NUM>,<NUM>.

This was further examined in detail. In comparison with other general-purpose resin materials, the rigid vinyl chloride has a high viscosity and has a self-heating properties by shear at the time of kneading. In addition, in comparison with other general-purpose resin materials, the rigid vinyl chloride has a high heat susceptibility, and is thermally decomposed. Hence, it becomes clear that a color change occurs because of such reasons. Such a color change is not acceptable in practice.

As for a provision against such a color change, since it is effective to decrease the temperature of a resin material, a scheme of decreasing the temperature is to increase the depth. This will be described with reference to the figure.

A technology is known in which the groove of the supply portion is deepened and the ratio of the length of the compression portion Lc to the effective screw length L is <NUM> to <NUM>, as disclosed in <CIT>. A screw equivalent to the screw disclosed in <CIT> is shown in <FIG>.

<FIG> is an enlarged view of a major section in <FIG>. As illustrated in <FIG>, it is defined that the depth of a groove <NUM> is h. Since the temperature of the heating cylinder <NUM> is high and the temperature of the injection screw <NUM> is low, heat transfers from the heating cylinder <NUM> to the injection screw <NUM>, and the resin material <NUM> is heated by the transferred heat.

When the depth h of the groove <NUM> is made shallow, the thickness of the resin material <NUM> decreases, a temperature gradient within the resin material <NUM> becomes small, and thus the temperature of the injection screw <NUM> increases. Consequently, the average temperature of the resin material <NUM> increases.

In contrast, when the depth h of the groove <NUM> is deep, the thickness of the resin material <NUM> increases, the temperature gradient within the resin material <NUM> becomes large, and thus the temperature of the injection screw <NUM> decreases. Consequently, the average temperature of the resin material <NUM> decreases.

When the groove <NUM> is made deep, it is expected that the average temperature of the resin material <NUM> decreases. A model that made a groove deeper will be referred to as a model <NUM>.

<FIG> illustrates an injection screw <NUM> that has a deeper groove than that of the injection screw <NUM>.

As illustrated in <FIG>, the injection screw <NUM> includes a flight <NUM> and a groove <NUM>, and a width t of the flight <NUM> and a pitch P thereof are constant. D is a diameter, and L is an effective screw length.

TABLE <NUM> illustrates specifications of the injection screw <NUM>. Note that those of the model <NUM> are also shown as references.

That is, the depth hf of the groove at the supply portion was changed from <NUM>,<NUM> to <NUM>,<NUM>, and the depth hm of the measure portion was changed from <NUM>,<NUM> to <NUM>,<NUM>. In order to maintain the compression ratio to be <NUM>,<NUM> or so, the length Lc of the compression portion was changed from <NUM> to <NUM>.

According to the model <NUM>, although the nozzle temperature was <NUM>,<NUM>, according to the model <NUM>, the nozzle temperature became <NUM>,<NUM>, which was a temperature drop by <NUM>,<NUM>.

Consequently, the color change level was suppressed. However, a color change was still observed, and this is still dissatisfied.

Since a color change is not acceptable in practice, a rigid vinyl chloride injection screw that is suitable for rigid vinyl chloride so as not to cause a color change is desirable.

It is an object of the present invention to provide a rigid vinyl chloride injection screw suitable for rigid vinyl chloride. This object is solved by the subject-matter of independent claim <NUM>. Preferred embodiments are subject of the dependent claims.

The inventors of the present disclosure reached a thought such that, in addition to by making a groove deep, by decreasing a compression ratio, a temperature would be reduced. This is because the smaller the compression ratio is, the more the heat generation by compression is suppressed.

<FIG> is an exemplary diagram for describing the width of a flight and the depth thereof.

<FIG> illustrates a groove <NUM> at a supply portion according to the model <NUM>, and a lengthwise area Sf of the groove is (P - t) × hf.

<FIG> illustrates a groove <NUM> at a measure portion according to the model <NUM>, and a lengthwise area Sm of the groove is (P - t) × hm.

A compression ratio is expressed by Sf/Sm.

Sf/Sm = ((P - t) × hf)/((P - t) × hm), and (P - t) is eliminated from a denominator and a numerator. Hence, this formula becomes Sf/Sm = hf/hm.

That is, when P is constant and a width t of the flight is constant, the compression ratio becomes hf/hm.

An improved model of the model <NUM> will be defined as a model <NUM>.

<FIG> illustrates a groove <NUM> at a supply portion according to the model <NUM>, and a lengthwise area Sf of the groove is (P - tf) × hf.

<FIG> illustrates a groove <NUM> at a measure portion according to the model <NUM>, and a lengthwise area Sm of the groove is (P - tm) × hm.

Hence, compression ratio = Sf/Sm = ((P- tf) × hf)/((P - tm) × hm).

In the above formula, P is a pitch. tf is the width of the flight at the supply portion. hf is the depth of the groove at the supply portion. tm is the width of the flight at the measure portion. hm is the depth of the groove at the measure portion.

In ((P - tf) ×hf)/((P -tm) ×hm), when tf increases, (P -tf) decreases, and thus the compression ratio decreases.

That is, the compression ratio can be changed by changing the width tf of the flight at the supply portion. The greater tf is, the smaller the compression ratio becomes. When the compression ratio decreases, a resin temperature decreases.

Although detailed forms and specifications of the model <NUM> will be described later, according to the model <NUM>, a color change was eliminated, and thus a preferable result was accomplished. The present disclosure that is achieved from such technical knowledges is as follows.

According to a first embodiment of the present disclosure, there is provided a rigid vinyl chloride injection screw which kneads and injects rigid vinyl chloride and which includes: a flight; and a groove, in which:.

According to the present disclosure, the rigid vinyl chloride injection screw has L/D set to be <NUM>,<NUM>, has tf/tm set to be <NUM>,<NUM>, has hf/hm set to be <NUM>,<NUM>, and has the compression ratio set to be <NUM>,<NUM>.

Conventionally, the compression ratio is usually set to be around <NUM>,<NUM>, but according to the present disclosure, such a ratio is set to be <NUM>,<NUM>. This causes the temperature of a resin to decrease, causing rigid vinyl chloride that is sensitive for temperature not to make a color change.

Moreover, rigid vinyl chloride has a higher viscosity than those of other resin materials, and thus rotation torque to rotate the injection screw increases.

According to the present disclosure, the compression ratio is reduced that is <NUM>,<NUM>, and the supply amount of the resin material is reduced by increasing the width tf of the flight at the supply portion. Consequently, the rotation torque can be reduced.

As described above, according to the present disclosure, there is provided a rigid vinyl chloride injection screw suitable for rigid vinyl chloride.

Based on the model <NUM>, when the model <NUM> and the several subsequent models were examined, the actions and advantageous effects similar to those of the present disclosure were confirmed.

According to a second embodiment of the present disclosure, there is provided a rigid vinyl chloride injection screw which kneads and injects rigid vinyl chloride and which includes: a flight; and a groove, in which:.

According to the present disclosure, the rigid vinyl chloride injection screw has L/D set to be in a range that is <NUM>,<NUM> to <NUM>,<NUM>, has tf/tm set to be in a range that is <NUM>,<NUM> to <NUM>,<NUM>, has hf/hm set to be in a range that is <NUM>,<NUM> to <NUM>,<NUM>, and has the compression ratio set to be in a range that is <NUM>,<NUM> to <NUM>,<NUM>.

Conventionally, the compression ratio is often set to be around <NUM>,<NUM>, but according to the present disclosure, such a ratio is set to be <NUM>,<NUM> to <NUM>,<NUM>. This causes the temperature of a resin to decrease, causing rigid vinyl chloride that is sensitive for temperature not to make a color change.

According to the present disclosure, the compression ratio is reduced that is <NUM>,<NUM> to <NUM>,<NUM>, and the supply amount of the resin material is reduced by increasing the width tf of the flight at the supply portion. Consequently, the rotation torque can be reduced.

Preferably, the above-described L/D is <NUM>,<NUM>.

The rotation torque is substantially proportional to the length L of the screw. Since L/D is <NUM>,<NUM>, the rotation torque is minimized.

Several preferable embodiments of the present disclosure will be described in detail with reference to the accompanying figures in which:.

Embodiments of the present disclosure will be described below with reference to the accompanying figures.

As illustrated in <FIG>, an injection screw <NUM> for rigid vinyl chloride (will be referred to as an "injection screw" <NUM> below) includes a flight <NUM> corresponding to a spiral screw thread, and a spiral groove <NUM>. The width of the flight <NUM> differs portion by portion.

When a width of the flight <NUM> at a supply portion, a width of the flight <NUM> at a compression portion, and a width of the flight <NUM> at a measure portion are defined as tf, tc and tm, respectively, the width of the flight <NUM> at the supply portion is set to be twice to three times to the width tm of the flight <NUM> at the measure portion. The width tc of the flight <NUM> at the compression portion gradually changes from the width tf of the flight <NUM> at the supply portion to the width tm of the flight <NUM> at the measure portion.

In addition, a diameter of the injection screw is defined as D, a pitch is defined as P, and an effective screw length is defined as L.

The effective screw length L is the sum of a length Lf of the supply portion, a length Lc of the compression portion, and a length Lm of the measure portion.

A depth of the groove at the supply portion, a depth of the groove at the compression portion, and a depth of the groove at the measure portion are defined as hf, hc, and hm, respectively.

TABLE <NUM> shows the specifications of the injection screw <NUM> according to the model <NUM>. Note that those of the model <NUM> are also shown as references.

According to the model <NUM>, the width tf of the flight at the supply portion was increased that was <NUM>, and the width tm of the flight at the measure portion was maintained as <NUM>.

Moreover, while the effective screw length L was maintained at <NUM>, the length Lf of the supply portion was increased that was <NUM>, the length Lc of the compression portion was reduced that was <NUM>, and the length Lm of the measure portion was set to <NUM>.

Moreover, the depth hf of the groove at the supply portion was made slightly shallow that was <NUM>,<NUM>, and the depth hm of the groove at the measure portion was made slightly shallow that was <NUM>,<NUM>.

The compression ratio is calculated from ((P - tf) × hf)/((P - tm) ×hm). From the calculation that is ((<NUM> - <NUM>) × <NUM>,<NUM>)/((<NUM> - <NUM>) × <NUM>,<NUM>) = <NUM>,<NUM>, the compression ratio is thus <NUM>,<NUM>. In comparison with the model <NUM>, the compression ratio of the model <NUM> was reduced.

Rigid vinyl chloride was injected on a trial basis using the above-described injection screw <NUM>. At this time, circuit pressure relating to the rotation of the injection screw <NUM> and the temperature of the nozzle (see <FIG>, reference numeral <NUM>) were measured.

Note that at the initial stage of shots, since there are many variable factors, a state at the eighth shot conceivable as substantially stable was examined.

TABLE <NUM> shows the results. Note that those of the model <NUM> are also shown as references.

According to the model <NUM>, although the compression ratio was <NUM>,<NUM>, according to the model <NUM>, since the compression ratio decreased to <NUM>,<NUM>, the following advantageous effects to be described below are accomplished from the model <NUM>.

First, the circuit pressure changed from <NUM>,<NUM> MPa to <NUM>,<NUM> MPa.

Next, no color change was observed. That is, a disadvantage that is a color change is addressed. The temperature of the nozzle changed from <NUM>,<NUM> to <NUM>,<NUM>. It is thought that such a disadvantage is addressed because the temperature of the nozzle decreased.

That is, according to the model <NUM>, the width tc of the flight at the measure portion was kept unchanged at <NUM>, but the width tf of the flight at the supply portion was set to <NUM>, and thus the compression ratio decreased. Hence, a disadvantage that is a color change is addressed. In addition, the plasticization was excellent, and the rotation torque was reduced.

Consequently, a rigid vinyl chloride injection screw that is suitable for rigid vinyl chloride is provided by the model <NUM>.

That is, according to the model <NUM>, the injection screw <NUM> that employs the structure to be described below is provided.

The injection screw <NUM> which kneads and injects rigid vinyl chloride includes the flight <NUM> and the groove <NUM>. In the rigid vinyl chloride injection screw <NUM>, the effective screw length L is divided into the supply portion, the compression portion, and the measure portion. The width tf of the flight at the supply portion is set to be wider than the width tm of the flight at the measure portion. The depth hf of the groove at the supply portion is set to be larger than the depth hm of the groove at the measure portion.

L/D is set to be <NUM>,<NUM> that is obtained from a calculation that is <NUM>/<NUM> = <NUM>,<NUM> where L is the effective screw length and D is the diameter of the injection screw.

The rigid vinyl chloride injection screw is provided which has a compression ratio that is that is calculated from ((P - tf) ×hf)/((P - tm) × hm) is set to be <NUM>,<NUM> (the detailed calculation has been described above, thus omitted) where P is the pitch of the injection screw.

Next, on the basis of the model <NUM>, extension of the model is attempted. For such a purpose, a model <NUM> and subsequent models were examined. TABLE <NUM> shows the results.

According to the model <NUM>, the width tf of the flight at the supply portion was narrowed to <NUM>. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, although the compression ratio slightly increased that was <NUM>,<NUM>, no color change occurred. Since the plasticization was excellent, the evaluation is thus concluded as "good".

According to a model <NUM>, the width tf of the flight at the supply portion was further narrowed to <NUM>. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, the compression ratio increased to <NUM>,<NUM>. Hence, a color change was observed. Consequently, the result and evaluation are "no good".

According to a model <NUM>, the width tf of the flight at the supply portion was elongated to <NUM>. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, the compression ratio was <NUM>,<NUM>. Since the compression ratio decreased, no color change occurred. Since the plasticization was excellent, the evaluation is thus concluded as "good".

According to a model <NUM>, the width tf of the flight at the supply portion was further elongated to <NUM>. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, the compression ratio was <NUM>,<NUM>. The compression ratio decreased and no color change occurred. However, the plasticization was inadequate. This may be because of the insufficient compression. The result and evaluation are thus concluded as "no good".

According to a model <NUM>, the depth hf of the groove at the supply portion was made deep that was <NUM>,<NUM>. The other specifications were the same as those of the model <NUM>.

According to a model <NUM>, the compression ratio was <NUM>,<NUM>. Although the compression ratio slightly increased, no color change occurred. Since the plasticization was excellent, the evaluation is thus concluded as "good".

According to a model <NUM>, the depth hf of the groove at the supply portion was made further deep that was <NUM>,<NUM>. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, a color change was observed. This may be because of the increase in compression ratio increased to <NUM>,<NUM>. The result and evaluation are thus concluded as "no good".

According to a model <NUM>, the depth hf of the groove at the supply portion was made shallow that was <NUM>,<NUM>. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, since the compression ratio decreased to <NUM>,<NUM>, no color change occurred. Since the plasticization was excellent, the evaluation is thus concluded as "good".

According to a model <NUM>, the depth hf of the groove at the supply portion was made further shallow that was <NUM>,<NUM>. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, the compression ratio was <NUM>,<NUM>. Since the compression ratio decreased, no color change occurred. However, the plasticization was improper. This may be because of the insufficient compression. The result and evaluation are thus concluded as "no good".

The following points became clear from the model <NUM> to the model <NUM>.

It is recommended that the ratio of the width of the flight (tf/tm) should be <NUM>,<NUM> to <NUM>,<NUM>.

It is recommended that the ratio of the depth of the groove (hf/hm) should be <NUM>,<NUM> to <NUM>,<NUM>.

It is recommended that the compression ratio should be <NUM>,<NUM> to <NUM>,<NUM>.

Next, the recommended range of the ratio (L/D) will be examined. In order to do so, a model <NUM> and subsequent models were examined. TABLE <NUM> shows the results.

According to the model <NUM>, the effective screw length L was <NUM> which was extended by <NUM>. L/D became <NUM>,<NUM>. Lf, Lc, and Lm were also changed in accordance with a change in such a length. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, since the effective screw length L increased, the circuit pressure slightly increased that was <NUM>,<NUM> MPa, but no color change occurred. The plasticization was excellent. It is defined that an expected value of the circuit pressure is equal to or smaller than <NUM>,<NUM> MPa. Since the circuit pressure was <NUM>,<NUM> MPa, the evaluation is thus concluded as "good".

According to a model <NUM>, the effective screw length L was further increased that was <NUM>. L/D became <NUM>,<NUM>. Lf, Lc, and Lm were also changed in accordance with a change in such a length. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, since the effective screw length L was further increased, the circuit pressure increased that was <NUM>,<NUM> MPa, but no color change occurred. The plasticization was excellent. However, since the circuit pressure became <NUM>,<NUM> MPa that exceeds the expected value of the circuit pressure that is <NUM>,<NUM> MPa, the evaluation is thus concluded as "no good".

According to a model <NUM>, the effective screw length L was shortened that was <NUM>. L/D became <NUM>,<NUM>. Lf, Lc, and Lm were also changed in accordance with a change in such a length. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, since the effective screw length L was decreased, the circuit pressure decreased that was <NUM>,<NUM> MPa, and no color change occurred. The evaluation is thus concluded as "good".

According to a model <NUM>, the effective screw length L was further shortened that was <NUM>. L/D became <NUM>,<NUM>. Lf, Lc, and Lm were also changed in accordance with a change in such a length. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, since the effective screw length L was further decreased, the circuit pressure decreased that was <NUM>,<NUM> MPa, and no color change occurred. The evaluation is thus concluded as "good".

According to the model <NUM>, since the effective screw length L was further decreased, the circuit pressure decreased that was <NUM>,<NUM> MPa. The inadequate plasticization was observed although no color change occurred. This may be because of the insufficient effective screw length L. The result and evaluation are thus concluded as "no good".

It is recommended that the ratio of the length of the screw (L/D) should be <NUM>,<NUM> to <NUM>,<NUM> in view of L/D in the lowest row of TABLE <NUM>, and the evaluation thereabove.

The following points became clear when the models <NUM> to <NUM> and the models <NUM> to <NUM> are comprehensively considered.

(Matters which became clear from Model <NUM> to Model <NUM>)
It is recommended that the ratio of the length of the screw (L/D) should be <NUM>,<NUM> to <NUM>,<NUM>.

It is recommended that the ratio of the depth of the groove (hf/hm) should be <NUM>,<NUM>-<NUM>,<NUM>.

Note that the model <NUM> shown in TABLE <NUM> has (tf/tm) that is <NUM>,<NUM>, which is out of the above-described range (<NUM>,<NUM> to <NUM>,<NUM>).

The model <NUM> shown in TABLE <NUM> has (tf/tm) that is <NUM>,<NUM>, which is out of the above-described range (<NUM>,<NUM> to <NUM>,<NUM>).

The model <NUM> shown in TABLE <NUM> has (hf/hm) that is <NUM>,<NUM>, which is out of the above-described range (<NUM>,<NUM> to <NUM>,<NUM>).

According to the model <NUM> shown in TABLE <NUM>, (L/D) is <NUM>,<NUM>, which is out of the above-described range (<NUM>,<NUM>-<NUM>,<NUM>).

Regarding the model <NUM>, the model <NUM>, the model <NUM>, the model <NUM>, the model <NUM>, the model <NUM>, and the model <NUM>, the specific values fall within the above-described range group.

That is, according to the model <NUM>, the model <NUM>, the model <NUM>, the model <NUM>, the model <NUM>, the model <NUM>, and the model <NUM>, the injection screw <NUM> that employs the following structure is provided.

The injection screw <NUM> which kneads and injects rigid vinyl chloride includes the flight <NUM> and the groove <NUM>. In the rigid vinyl chloride injection screw <NUM>, the effective screw length L is divided into the supply portion, the compression portion, and the measure portion, the width of the flight hf at the supply portion is set to be wider than the width tm of the flight at the measure portion, and the depth tf of the groove at the supply portion is set to be larger than the depth tm of the groove at the measure portion.

L/D is set to be in a range that is <NUM>,<NUM> to <NUM>,<NUM> where L is the effective screw length and D is the diameter of the injection screw.

The compression ratio calculated by ((P - tf) × hf)/((P - tm) × hm) is set to be in a range that is <NUM>,<NUM> to <NUM>,<NUM> where P is the pitch of the injection screw.

Experientially, the inventors of the present disclosure have already obtained a technical knowledge such that when the measure portion is long and the compression portion is long, the temperature of a resin material increases, and thus a defect occurs.

Accordingly, as for the length Lf of the supply portion, the length Lc of the compression portion, and the length Lm of the measure portion, a model <NUM> and subsequent models were examined.

According to the model <NUM>, Lf was shortened that was <NUM>, Lc was shortened that was <NUM>, and Lm was elongated that was <NUM>. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, since the length Lm of the measure portion largely increased, a minor color change was observed. This may be because of an increase in temperature of the resin material due to the increase of Lm. However, a color change is slight, which is within an acceptable range, and thus the evaluation is concluded as "good".

According to a model <NUM>, Lf was remarkably elongated that was <NUM>, Lc was shortened that was <NUM>, and Lm was remarkably shortened that was <NUM>. The other specifications were the same as those of the model <NUM>.

According to the model <NUM>, since the length Lm of the measure portion remarkably decreased, a color change did not occur at all. This may be because of a decrease in temperature of the resin material due to the remarkable decrease of Lm. Consequently, the evaluation is concluded as "better" that is more than "good".

According to a model <NUM>, Lf was slightly elongated that was <NUM>, Lc was slightly elongated that was <NUM>, and Lm was remarkably shortened that was <NUM>. The other specifications were the same as those of the model <NUM>.

According to a model <NUM>, Lf was elongated that was <NUM>, Lc was slightly elongated that was <NUM>, and Lm was remarkably shortened that was <NUM>. The other specifications were the same as those of the model <NUM>.

According to model <NUM>, a slight plasticization defect was observed. This may be because of the decrease of Lm. However, the plasticization defect is little and within an allowable range, and thus the evaluation is concluded as "good".

Since the model <NUM> has the same evaluation result as those of the models <NUM> and <NUM>, and has the better evaluation result than those of the models <NUM> and <NUM>, the evaluation is indicated as "better" in TABLE <NUM>.

Since the model <NUM> and the model <NUM> to the model <NUM> have the evaluations that are concluded as "good" or "better", all of such models are adoptable. However, the model <NUM>, the model <NUM>, and the model <NUM> have the better evaluations than those of the models <NUM> and <NUM>. The following points became clear from such model <NUM>, model <NUM>, and model <NUM>.

It is desirable that the length Lf of the supply portion should be (<NUM>,<NUM> to <NUM>,<NUM>) times as much as the effective screw length L, i.e., (<NUM> % to <NUM> %) thereof.

Moreover, it is desirable that the length Lc of the compression portion should be (<NUM>,<NUM> to <NUM>,<NUM>) times as much as the effective screw length L, i.e., (<NUM> % to <NUM> %) thereof.

Furthermore, it is desirable that the length Lm of the measure portion should be (<NUM>,<NUM> to <NUM>,<NUM>) times as much as the effective screw length L, i.e., (<NUM> % to <NUM> %) thereof.

Claim 1:
A rigid vinyl chloride injection screw (<NUM>) which kneads and injects rigid vinyl chloride comprising: a flight (<NUM>); and a groove (<NUM>),
wherein an effective screw length (L) is divided into a supply portion, a compression portion, and a measure portion, a width (tf) of the flight (<NUM>) at the supply portion is set to be wider than a width (tm) of the flight (<NUM>) at the measure portion, and a depth (hf) of the groove (<NUM>) at the supply portion is set to be larger than a depth (hm) of the groove (<NUM>) at the measure portion,
wherein L/D is set to be in a range that is <NUM>,<NUM> to <NUM>,<NUM> where L is the effective screw length and D is a diameter of the injection screw (<NUM>),
wherein tf/tm is set to be in a range that is <NUM>,<NUM> to <NUM>,<NUM> where tf is the width of the flight (<NUM>) at the supply portion and tm is the width of the flight (<NUM>) at the measure portion,
hf/hm is set to be in a range that is <NUM>,<NUM> to <NUM>,<NUM> where hf is the depth of the groove (<NUM>) at the supply portion and hm is the depth of the groove (<NUM>) at the measure portion, and
wherein a compression ratio that is calculated from ((P - tf) × hf)/((P - tm) × hm) is set to be in a range that is <NUM>,<NUM> to <NUM>,<NUM> where P is a pitch of the injection screw (<NUM>).