JP7085330B2 - Molded body and processing method - Google Patents

Description

The present application relates to a molded product processed with a synthetic resin and a method for processing the synthetic resin.

Conventionally, products in which a resin tubular body is bent have been widely sold.
The general method for bending a resin tubular body is as follows. First, the tubular body to be the original tube is heated to a temperature at which it can be bent and deformed, then a core material to prevent crushing is inserted into the tubular body, and a mold with a cavity that follows the desired shape is used. The tubular body is molded and deformed. After the deformation, the tubular body is cooled inside the mold, the mold is opened, and the core material is removed from the tubular body. This gives a tubular body bent to the desired bending angle.
For example, Patent Documents 1 to 3 describe a method for processing such a tubular body.

Tokushu Kohei No. 4-42974 Japanese Unexamined Patent Publication No. 5-69480 Special Fair No. 6-5430 Japanese Unexamined Patent Publication No. 7-223274 Japanese Unexamined Patent Publication No. 2008-284714

Currently, a tubular body made of a crosslinkable resin has been developed, and a method for bending the tubular body is being studied.
The characteristics of the crosslinkable resin are that the crosslinking improves and stabilizes thermal stability such as heat resistance, oil resistance, and creep resistance, as well as chemical stability and mechanical properties.
However, since the crosslinkable resin has the above-mentioned characteristics, there is a problem that processing such as bending is extremely difficult if the crosslinkable resin is crosslinked. For example, it is difficult to bend a tubular body made of a crosslinkable resin by the methods disclosed in Patent Documents 1 to 3.

Therefore, conventionally, the tubular body has been bent in a state before cross-linking or in a state where the degree of cross-linking is reduced. For example, Patent Documents 4 and 5 disclose a method for bending a tubular body made of a crosslinkable resin.
According to Patent Document 4, bending is performed in an unreacted state before cross-linking, and then a heat medium is passed through the tube to react the base material and the cross-linking material to bend a tubular body made of a cross-linking resin. It has been disclosed. Patent Document 5 discloses that the tubular body is crosslinked to a certain degree of cross-linking so as not to melt, and then the tubular body is heated and bent.
However, the methods disclosed in Patent Documents 4 and 5 require a step of cross-linking to the final degree of cross-linking after bending, so that the shape may be deformed if an extra load is applied to the tubular body in the cross-linking step. There is. Therefore, a holder and a safety device that match the shape after processing are required. It is also necessary to control the time and temperature from the bending process to the cross-linking process.
Therefore, in the methods described in Patent Documents 4 and 5, it is necessary to control the time and temperature between the processes while considering the shape change from the post-bending process to the cross-linking process.

Therefore, the present application discloses a molded body having a stable shape even after secondary processing such as bending, and a processing method that does not require post-processing after secondary processing.

One aspect of the present invention for solving the above problems is
A molded body in which the synthetic resin is secondarily processed, the temperature at which the loss tangent (tan δ) of the synthetic resin is maximized is T1 (° C.), and the temperature at T1 + 30 ° C. is T2 (° C.). The storage elastic modulus (E') of the synthetic resin in the range from T1 to T2 is within ± 10% of the storage elastic modulus (E'T1) of the synthetic resin in _T1 . A molded body in which the resin is heated to a temperature of T1 + 15 ° C. or higher and secondarily processed.

Preferably, the synthetic resin is heated and secondary processed in a temperature range in which the storage elastic modulus (E') of the synthetic resin is within ± 10% of the storage elastic modulus (E'T1) in _T1 . It is a molded body.

Further, the molded body is preferably a tubular body. The outer diameter of the tubular body is preferably 35 mm or less, and the wall thickness of the tubular body is preferably 10 mm or less.

Moreover, one aspect of the present invention for solving the above-mentioned problem is.
A processing method for secondary processing of a synthetic resin, the temperature at which the loss tangent (tan δ) of the synthetic resin is maximized is T1 (° C.), and the temperature at T1 + 30 ° C. is T2 (° C.). The storage elastic modulus (E') of the synthetic resin in the range from T1 to T2 is within ± 10% of the storage elastic modulus (E'T1) of the synthetic resin in _T1 . Is a processing method for secondary processing by heating to a temperature of T1 + 15 ° C. or higher.

The processing method is a method for processing a tubular body containing at least the synthetic resin, and the tubular body is installed along the shaped mold engraved in a shaped shape covering the entire outer circumference of the tubular body. It is preferable to apply pressure from the inside of the tubular body in a state where the tubular body is placed in the shaped mold.

According to the molded product of the present invention, it is possible to provide a molded product having a stable shape even after secondary processing. Further, according to the processing method of the present invention, post-processing after the secondary processing becomes unnecessary.

It is a figure which showed the typical example of the viscoelastic behavior of a cross-linked polyethylene resin. It is a figure which showed the typical example of the viscoelastic behavior of ultra-high molecular weight polyethylene. It is a flowchart of the processing method 10. It is a figure which showed the relationship between each process and temperature in a processing method 10. It is a figure explaining the method of installing a synthetic resin pipe in a shaped form covering the whole synthetic resin pipe. It is a figure explaining the method of installing a synthetic resin pipe in a shaped form covering only the heated part of a synthetic resin pipe. It is a schematic diagram of a shaping type having a split surface in a direction perpendicular to a bent shape. It is a figure explaining the method of installing a synthetic resin pipe in a shaping type which performs bending processing at a plurality of places. It is a figure for demonstrating the change amount ε to the bending shape. It is a figure which showed the temperature behavior of the synthetic resin pipe in the internal pressure loading process S13. It is a figure explaining that the outer surface of a synthetic resin pipe is processed into a curved shape. It is a figure explaining that the outer surface of the end portion of a synthetic resin pipe is processed into a bent shape. It is a figure which showed the relationship between the heating temperature and the bending angle of a synthetic resin pipe in an Example.

Hereinafter, the molded body and the processing method of the present invention will be described, but the present invention is not limited thereto.

<Molded body>
The molded product of the present invention is a product obtained by heating a synthetic resin and performing secondary processing. The secondary processing is to further process the synthetic resin formed by extrusion molding or injection molding into a desired shape, and includes, for example, bending processing, drawing processing, burring processing, diameter expansion processing, and the like.
In the following, the effect of bending the synthetic resin may be described, but such an effect is also exhibited in other secondary processing.

The shape of the molded body is not particularly limited, and examples thereof include a tubular body, a flat plate-shaped body, and a curved plate-shaped body, and among them, the tubular body is preferable. Further, when the molded body is a tubular body, it is preferable that the synthetic resin before the secondary processing is also a tubular body.
When the molded body is a tubular body, the lower limit of the outer diameter of the tubular body is preferably 5 mm or more, more preferably 7 mm or more, and the upper limit is preferably 35 mm or less, preferably 30 mm or less. Is more preferable. Further, the wall thickness of the tubular body preferably has a lower limit of 1 mm or more, more preferably 1.5 mm or more, and an upper limit of 10 mm or less, more preferably 7 mm or less, and more preferably 5 mm. The following is more preferable.

[Synthetic resin]
The synthetic resin is a viscoelastic body and has a storage elastic modulus (E ′) and a loss elastic modulus (E ″) as physical parameters expressing its properties. Further, the ratio of the loss elastic modulus (E ″) to the storage elastic modulus (E ′) is referred to as loss tangent (tan δ = E ″ / E ′).

In the synthetic resin of the present invention, these physical parameters behave as follows. That is, when the temperature at + 15 ° C. at the maximum loss tangent (tan δ) of the synthetic resin is T1 (° C.) and the temperature at T1 + 30 ° C. is T2 (° C.), the synthetic resin in the range of T1 to T2. It shows the behavior that the storage elastic modulus (E') is within ± 10% of the storage elastic modulus (E'T1) of the synthetic resin in _T1 . This will be described in detail with reference to FIG. It should be noted that FIG. 1 is a diagram in which the viscoelastic behavior of the cross-linked polyethylene resin used in the examples described later was measured.

The vertical axis of FIG. 1 represents the storage elastic modulus (E ′), the loss elastic modulus (E ′ ′), or the loss tangent (tan δ), and the horizontal axis represents the temperature. The storage elastic modulus (E ′) is represented by a line, the loss elastic modulus (E ″) is represented by a chain line, and the loss tangent (tan δ) is represented by a two-dot chain line. When the temperature at which the loss tangent (tan δ) is maximized is T0 (120 ° C.), the temperature at T0 + 15 ° C. is T1 (135 ° C.) and the temperature at T1 + 30 ° C. is T2 (165 ° C.).

Focusing on the storage elastic modulus (E ′) and the loss elastic modulus (E ″), the storage elastic modulus (E ′) and the loss elastic modulus (E ″) gradually decrease from the low temperature side toward the vicinity of T0. There is a tendency to go, and it decreases sharply around T0. Then, in the vicinity of T1, the storage elastic modulus (E ′) and the loss elastic modulus (E ″) are stable in a very low state. This stability continues at least in the range T1 to T2. That is, in the synthetic resin having the viscoelastic behavior of FIG. 1, the storage elastic modulus (E') of the synthetic resin in the range of T1 to T2 is within ± 10% of the storage elastic modulus (E'T1) of the synthetic resin in _T1 . It shows the behavior of. Furthermore, the storage elastic modulus (E') of the synthetic resin in the range of T1 to T2 is within ± 1% of the storage elastic modulus (E'T1) of the synthetic resin in _T1 .

In a synthetic resin having such viscoelastic behavior, the effect of bending on the temperature of the synthetic resin is as follows.
First, the synthetic resin has a high storage elastic modulus (E ′) and a loss elastic modulus (E ″) at T1 or less, and has a large bending difficulty and a large bending back amount during bending. In addition, it is unstable near T1 and the amount of bending back is large. Therefore, from the viewpoint of reliable bending, it is important to heat the synthetic resin to T + 15 ° C. or higher. By heating the synthetic resin to a temperature of T1 + 15 ° C. or higher, the storage elastic modulus (E ′) and the loss elastic modulus (E ″) are sufficiently lowered, and the storage elastic modulus (E ′) and the loss elastic modulus are sufficiently reduced. Since (E ″) is in a stable state, the amount of return after bending is small, and a stable bending product can be obtained. In addition, the amount of return due to subsequent changes over time is also stable.

On the other hand, as shown in FIG. 1, the synthetic resin begins to deteriorate when the temperature becomes too high, and the storage elastic modulus (E') increases. As a result of the study by the present inventors, when the synthetic resin is heated until the storage elastic modulus (E') exceeds ± 10% of the storage elastic modulus ( _E'T1 ), the synthetic resin deteriorates too much and the quality of the molded product is obtained. Was found to decrease significantly.
Therefore, the more preferable heating temperature of the synthetic resin is T1 + 15 ° C. or higher, and the storage elastic modulus (E ′) of the synthetic resin is within ± 10% of the storage elastic modulus (E ′ _T1 ). More preferably, the temperature range is T1 + 15 ° C. or higher, and the storage elastic modulus (E') of the synthetic resin is within ± 5% of the storage elastic modulus (E'T1), and particularly preferably _T1 + 15 ° C. or higher and T1 + 15 ° C. or higher. The storage elastic modulus (E') of the synthetic resin is within ± 1% of the storage elastic modulus ( _E'T1 ) (150 ° C to 310 ° C). By heating the synthetic resin pipe in the above temperature range, a stable secondary processed product can be obtained with a small return amount after the secondary processing.
However, even within the above temperature range, if there is an influence on the appearance and quality such as discoloration due to heating, it is preferable to set the temperature range excluding the temperature range.

Examples of the synthetic resin having such viscoelastic behavior include ultra-high molecular weight polyethylene in addition to the above-mentioned cross-linked polyethylene.

FIG. 2 shows a representative example of the viscoelastic behavior of ultra-high molecular weight polyethylene.
As is clear from FIG. 2, the storage elastic modulus (E') of the synthetic resin in the range of T1 to T2 of the ultra-high molecular weight polyethylene is within ± 10% of the storage elastic modulus (E'T1) of the synthetic resin in _T1 . It shows the behavior that there is. Furthermore, the storage elastic modulus (E') of the synthetic resin in the range of T1 to T2 is within ± 1% of the storage elastic modulus (E'T1) of the synthetic resin in _T1 .
Here, the specific numerical values of T0, T1 and T2 in FIG. 2 are as follows.
T0 = 125 ° C
T1 = 140 ° C
T2 = 165 ° C
Further, the temperature range of T1 + 15 ° C. or higher and the storage elastic modulus (E ′) of the synthetic resin within ± 1% of the storage elastic modulus (E ′ _T1 ) is 155 ° C. to 175 ° C.

As described above, the molded product of the present invention is obtained by secondary processing of a synthetic resin having viscoelastic behavior as described above by heating it to T1 + 15 ° C. or higher. In the prior art, when such a synthetic resin is used, a cross-linking step of cross-linking to the final cross-linking degree in the used state after bending is required, but in the present invention, the cross-linking is performed to the final cross-linking degree in the used state. Since it can be processed from the crosslinked resin that has been crosslinked, it is not necessary to consider measures for collapsing the processed shape or maintaining the shape in the crosslinking step. Therefore, according to the present invention, it is possible to provide a molded product having a stable shape even after secondary processing.

The molded product of the present invention is obtained by heating a synthetic resin to T1 + 15 ° C. or higher and secondary processing as described above. That is, it is produced by heating a synthetic resin that has been crosslinked to the final degree of cross-linking to soften the resin by breaking the crystal structure of the synthetic resin once, and then performing secondary processing. On the other hand, the conventional molded product is manufactured by processing the shape of the resin before cross-linking to the final degree of cross-linking and then cross-linking to the final degree of cross-linking after processing.
Therefore, it is considered that there may be a difference in the crystal structure between the molded body of the present invention and the molded body of the prior art. It requires a great deal of trial and error and can be said to be impractical.

<Processing method>
Next, the processing method will be described.
The processing method of the present invention is a processing method for secondary processing of a synthetic resin having viscoelastic behavior described above.
Hereinafter, a processing method 10 for bending a tubular synthetic resin (synthetic resin pipe), which is a preferred embodiment of the present invention, will be described. However, the present invention is not limited to this.

[Processing method 10]
The processing method 10 is a method of heating and bending a synthetic resin pipe. In detail, it has the following steps.
In the processing method 10, the heating step S11 for heating the synthetic resin tube to a temperature of T ₁ + 15 ° C. or higher and the synthetic resin tube heated from the heating step S11 are engraved into a shaped shape covering the entire outer periphery of the synthetic resin tube. In the mold installation step S12 installed along the shaped mold and the synthetic resin pipe installed in the shaped mold by the mold installation step S12, the internal pressure loading step S13 in which pressure is applied from the inside of the synthetic resin pipe. A cooling step S14 for ventilating gas from the inner diameter side of the pipe to the shape holding temperature of the synthetic resin pipe to cool the synthetic resin pipe, and a taking-out step S15 for taking out from the shaping mold after the completion of the cooling step are provided.
Here, FIG. 3 shows a flowchart of the processing method 10, and FIG. 4 shows the relationship between the temperature (surface temperature) of the synthetic resin pipe and the process in the processing method 10.
It is preferable that the synthetic resin pipe used in the processing method 10 has a size increased in thickness in consideration of thinning in the bent portion in advance.

[Heating step S11]
In the heating step S11, the synthetic resin pipe having the viscoelastic behavior described above is heated to a temperature of T ₁ + 15 ° C. or higher.
By heating the synthetic resin tube to a temperature of T1 + 15 ° C. or higher, the storage elastic modulus (E ′) and the loss elastic modulus (E ″) are sufficiently lowered, and the storage elastic modulus (E ′) and the loss elasticity are sufficiently reduced. Since the modulus (E ″) is stable, the amount of return after bending is small, and a stable bending product can be obtained. In addition, the amount of return due to subsequent changes over time is also stable.
The heating temperature is preferably T1 + 15 ° C. or higher, and the storage elastic modulus (E') of the synthetic resin tube is within ± 10% of the storage elastic modulus (E'T1), and more preferably _T1 + 15 ° C. or higher. The storage elastic modulus (E') of the synthetic resin is within ± 5% of the storage elastic modulus (E'T1), more preferably _T1 + 15 ° C. or higher, and the storage elastic modulus of the synthetic resin (E'T1). E') is within ± 1% of the storage elastic modulus ( _E'T1 ). By heating the synthetic resin pipe in the above temperature range, it is possible to obtain a stable bent product with a small return amount after bending.
However, even within the above temperature range, if there is an influence on the appearance and quality such as discoloration due to heating, it is preferable to set the temperature range excluding the temperature range.

As a method for heating the synthetic resin pipe, the synthetic resin pipe may be put into a heating tank such as a heating oven and heated, or may be pressed against a contact heater to heat the synthetic resin pipe. Further, the synthetic resin pipe may be heated as a whole, or only the portion to be bent may be heated.

[Mold installation process S12]
In the mold setting step S12, the synthetic resin pipe heated from the heating step S11 is installed along the shaped mold engraved in the shaped shape covering the entire outer circumference of the synthetic resin pipe. Since the synthetic resin pipe heated in the heating step S11 is in a state where the elastic modulus is lowered, it is easy to maintain the shape by forming a shaped type that covers the entire circumference of the pipe.

Further, in the heating step S11, when the entire synthetic resin pipe is heated, it is preferable to install it in a shaping mold covering the entire synthetic resin pipe and close the mold, and when only the portion to be bent is heated, it is preferable. It is preferable to install the mold in a pre-designed mold with dimensions such that the boundary between the heated portion and the non-heated portion that is not heated fits in the mold, and close the mold.
Hereinafter, the mold installation step S12 when the entire synthetic resin pipe is heated and the mold installation step S12 when only the bending portion is heated will be described separately.

FIG. 5 shows an example of a schematic diagram of the mold installation step S12 when the entire synthetic resin pipe is heated. FIG. 5A shows a state before the synthetic resin pipe 1 is installed, and FIG. 5B shows a state after the synthetic resin pipe 1 is installed and the mold is closed. The shaping mold shown in FIG. 5 is for processing one curved shape, but the present invention is not limited to this, and a shaping mold for processing two or more curved shapes may be used.
Further, as shown in FIG. 5, the shaping mold 2 has a shaping shape that covers the entire outer circumference of the synthetic resin pipe 1, and is divided into split mold shapes for installing the heating pipe (FIG. 5 is horizontal with respect to bending). It is a split shape.) It is preferable to set it. In the following, one of the split types of the shaped type 2 will be referred to as a shaped type 2a, and the other will be referred to as a shaped type 2b.

When the entire synthetic resin pipe 1 is heated in the heating step S11, it is preferable that the shaped mold 2 has a size and a structure such that the end portion 1a of the synthetic resin pipe fits inside the shaped mold 2. As a result, in the internal pressure loading step S13, which is the next step, the internal pressure is applied from the inner diameter side of the synthetic resin pipe 1 so that the entire outer circumference of the synthetic resin pipe is in close contact with the shaped shape covering the entire circumference. It becomes possible to shape.
The distance x from the tube end 1a to the outside of the shaped mold is preferably a distance x that is at least twice the outer diameter of the synthetic resin tube. This is to prevent the end portion 1a of the synthetic resin pipe 1 from squeezing out from the shaping mold.

Next, FIG. 6 shows an example of a schematic diagram of the mold installation step S12 in which only the portion to be bent is heated. FIG. 6A shows a state before the synthetic resin pipe 1 is installed, and FIG. 6B shows a state after the synthetic resin pipe 1 is installed and the mold is closed. The shaping mold 2 in FIG. 6 is a shaping mold for processing a curved shape at one place, but the present invention is not limited to this, and a shaping mold for processing two or more curved shapes can be used. You may use it.
Further, as shown in FIG. 6, the shaping mold 2 has a shaping shape that covers the entire circumference of the heating range 1b of the synthetic resin pipe 1, and is divided into split mold shapes for installing the heating pipe (FIG. 6 shows the bending shape). It is preferable to have a horizontal split shape.)

The non-heated portion that is not heated is not deformed by the internal pressure applied in the internal pressure loading step S13 of the next step. Therefore, when only the portion to be bent is heated in the heating step S11, it is not necessary to cover the portion to be heated with the shaping mold 2, so that the shaping mold can be made smaller. However, since the boundary portion 1c between the heated portion and the non-heated portion is easily deformed by the influence of heating, the distance x from the end portion of the heating range 1b to the outside of the shaped mold is the outer diameter of the synthetic resin pipe. It is preferably twice or more, and more preferably three times or more.

The direction of the split surface of the shaped type shown in FIGS. 5 and 6 is horizontal with respect to bending, but may be horizontal or perpendicular to the bending direction as long as the structure covers the entire circumference of the pipe. .. FIG. 7 shows a shaped mold having a split surface in the direction perpendicular to the bending.

Further, although the shaping mold 2 shown in FIGS. 5 and 6 is a shaping mold that bends at one place, a shaping mold that bends at a plurality of places may be used. FIG. 8 shows an example of a shaped structure in which bending is performed at a plurality of locations. At this time, the structure and shape of the shaping mold 2 may be appropriately set according to the shape to be bent.

The shaped type is not particularly limited as long as it is not a material that causes an abnormality in shape and dimensions such as deformation due to contact with a heated synthetic resin pipe. However, in the case of a material with good heat conduction such as a metal material, the temperature of the heated pipe tends to drop from the time the heated pipe is installed and the mold is closed until the internal pressure load is applied, so the material with good heat conduction is used. In that case, it is desirable to heat the shaped mold in advance or select a material that does not easily conduct heat.

[Internal pressure load step S13]
In the internal pressure loading step S13, pressure is applied from the inside of the synthetic resin pipe in a state of being installed in the shaping mold by the mold setting step S12.
Specifically, jigs for sealing are attached to both ends of the synthetic resin pipe so that the internal pressure can be applied from the inner diameter side of the synthetic resin pipe, and the pressure medium is sent from one end, and the outer diameter of the pipe is shaped. Load the internal pressure so that it adheres to the mold. The pressure medium is not particularly limited, but is preferably compressed air. In the following, the case where the pressure medium is compressed air will be described.
Further, it is preferable that the internal pressure loading step S13 is performed until the temperature of the synthetic resin pipe is at _least lower than the temperature T1. Further, the jig for sealing at both ends may be attached in advance at the time of the heating step S11.

The internal pressure of the compressed air can be appropriately set depending on the elastic modulus of the heated synthetic resin pipe, the outer diameter / wall thickness of the pipe, and the bending angle. For example, in the case of the synthetic resin pipe having the viscoelastic behavior shown in FIG. 1, when the outer diameter of the pipe is 14.6 mm and the wall thickness is 2.4 mm, 0.05 MPa to 0.2 MPa is desirable. ..

As a method of setting the internal pressure of the synthetic resin pipe 1, it is preferable to actually process and determine the transfer state to the shaping mold and set it, but as an example of a simple method, set it based on the following calculation formula. You can also do it.
Minimum required stress to deform the pipe and form a bending shape: σ
Deformation to bending shape: ε
Elastic modulus during bending (elastic modulus of material at the time of shaping mold installation): E
Outer diameter of tube: D
Tube wall thickness: t
Minimum required internal pressure: P
Then
σ ＝ εE ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (1)
P ≧ 2σt / (Dt) ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (2)
From equations (1) and (2), ∴P ≧ 2εEt / (Dt)
Here, the amount of deformation ε into the bent shape is the amount of change in the outer portion of the synthetic resin pipe contained inside the shaped mold when observed from the direction perpendicular to the bending direction. .. Specifically, it will be described with reference to FIG. FIG. 9 is a view of a synthetic resin pipe contained inside the shaping mold, which is observed through the shaping mold from a direction perpendicular to the bending direction. The amount of deformation ε into the bent shape at this time is (l2-l1) / when the length of the outer part of the synthetic resin pipe before the internal pressure load is l1 and the length of the part after the internal pressure load is l2. It becomes l1.

Further, in the internal pressure loading step S13, both ends may be completely sealed and the internal pressure load may be performed, or the pressure medium may be discharged from the other end while maintaining a predetermined internal pressure and passed through the pressure medium (internal pressure loading step S13). When compressed air is used, it is ventilated.) As a method of discharging the compressed air from the other end while maintaining a predetermined internal pressure, there is a method of discharging the compressed air at the same time as the close contact shaping to the shaping mold from the inner diameter side by the internal pressure. This is desirable because the cooling effect due to ventilation from the inner diameter side can be exhibited and the time until the end of the cooling process in the mold can be shortened. Details will be described with reference to FIG.

FIG. 10 shows the results of examination using the synthetic resin pipe having the viscoelastic behavior of FIG. 1. When the temperature of the synthetic resin pipe after the mold installation step S12 is 200 ° C., the synthetic resin pipe is formed in the internal pressure loading step S13. This is a comparison between the result when both ends of the above are completely sealed and the result when compressed air is ventilated from one end of the synthetic resin pipe at a predetermined pressure in the internal pressure loading step S13.
As is clear from FIG. 10, in the internal pressure loading step S13, it can be seen that the cooling effect is higher when the compressed air is ventilated. Further, when compressed air is ventilated, the higher the internal pressure of the synthetic resin pipe, the better the cooling effect.

Here, the difference between the internal pressure loading process 13 of the present invention and the conventional internal pressure loading process will be described.
In the internal pressure loading process of the conventional bending method, a method of inserting a soft solid core material and a method of inserting compressed air into a tubular rubber core material have been adopted. However, with these methods, it is difficult to pass through the bent portion when removing the core material after bending, so the diameter of the core material should be smaller than the inner diameter of the resin pipe, or the core material should be used. Since it is necessary to reduce the hardness, there is a limit to the prevention of crushing. In particular, it is more difficult to take out the core material in the case of complicated bending at a plurality of locations in different directions.
On the other hand, the internal pressure loading step S13 of the present invention is performed using a pressure medium as described above. That is, since the pressure medium is loaded from the inner diameter side of the pipe, there is no need to take out the core material, etc. It's easy to do.
Further, the synthetic resin pipe heated in the above-mentioned heating step S11 is in a state where the elastic modulus is lowered, so that it is easily damaged. However, by using a pressure medium such as compressed air as in the present invention, it is possible to use it. Reliable shape formation and crush prevention can be performed without damaging. Further, since the elastic modulus of the heated synthetic resin pipe is lowered, the pressure inside the pipe loaded by the pressure medium does not need to be high.

[Cooling step S14]
In the cooling step S14, gas is ventilated from the inner diameter side of the pipe to the shape holding temperature of the synthetic resin pipe and cooled. Specifically, a gas such as compressed air is sent from one end of the synthetic resin pipe, and the other end is released to allow ventilation and cooling from the inner diameter side of the pipe. At that time, the shaped mold may be further cooled.
Here, the "shape retention temperature" is a temperature at which the synthetic resin is not easily deformed when a load is applied to it by taking it out from the shaping mold, handling it, or the like, and the loss elastic modulus (E') of the synthetic resin. ´) is the temperature at which it begins to decrease. For example, the shape stabilizing temperature of the synthetic resin shown in FIGS. 1 and 2 is about 50 ° C.

[Extraction process S15]
In the take-out step S15, after the cooling step S14 is completed, the bent and shaped pipe is taken out from the shaping mold.

From the above, the bending method which is one embodiment of the processing method 10 has been described. As a method for processing a synthetic resin having a viscoelastic behavior described above, conventionally, a cross-linking step of cross-linking to the final degree of cross-linking in the used state after bending is required, but in the present invention, the final cross-linking in the used state is required. Since it can be processed from a crosslinkable resin that has been crosslinked to the degree of cross-linking, it is not necessary to control the time and temperature between the processes in consideration of the shape change between the bending process and the cross-linking process.

The above-mentioned processing method 10 is a bending processing method for changing the direction of a pipe, but the present invention is not limited to this, and for example, a processing in which the shape of the outer surface of a synthetic resin pipe is bent (processing to increase the diameter) is performed. It may be a processing method to be performed. In that case, instead of the above-mentioned shaping type, for example, the shaping type shown in FIGS. 11a, 11b, and 12 is used.
11a and 11b are examples of processing a curved shape on the outer surface of a synthetic resin pipe.
FIG. 12 is an example of processing a curved shape into the outer surface shape of the end portion of the synthetic resin pipe.
It should be noted that the bending process for changing the direction of the pipe and the processing in which the shape of the outer surface of the pipe is bent may be combined.

Further, the molded product of the present invention described above can be produced from a synthetic resin by performing the processing method of the present invention.

Examples will be described below, but the present invention is not limited thereto.

Using a commercially available crosslinkable resin material (crosslinked polyethylene resin material) synthetic resin pipe having the viscoelastic behavior of FIG. 1, the following experiment was carried out according to the processing method 10.
The synthetic resin pipe used had an outer diameter of 14.6 mm and a wall thickness of 2.4 mm.

[experimental method]
First, in the heating step, the synthetic resin pipes of each example were heated to the heating temperatures shown in Table 1.
Then, in the mold installation process, the synthetic resin pipe was installed along the shaping mold. At this time, the shaped mold had the shapes shown in FIGS. 5a and 5b, and the bending angle was 90 °.
Next, in the internal pressure loading step, the internal pressure was applied to the synthetic resin pipe using compressed air until the temperature of the synthetic resin pipe reached 100 ° C.
Then, in the cooling step, compressed air was blown from one end of the synthetic resin pipe to cool it until the temperature of the synthetic resin pipe reached 50 ° C.
Subsequently, in the extraction step, the synthetic resin pipe was taken out from the shaping mold.
Finally, as an evaluation for promoting the bending angle after processing and the subsequent change with time, the mixture was placed in a heating furnace at 100 ° C. for 3 hours and annealed.
The above operation was performed three times for each example.

[Experimental result]
Table 1 shows the heating temperature of each example, the bending angle and appearance (color) after processing, and the storage elastic modulus at the heating temperature of each example when the storage elastic modulus (E'T1) at _T1 is 100%. The rate of change of E') is shown. Further, FIGS. 13 (a) and 13 (b) show graphs of the measurement results with the heating temperature on the horizontal axis and the bending angle on the vertical axis. Note that FIG. 13 (b) is an enlarged graph of FIG. 13 (a).
The evaluation of the bending angle in Table 1 is "◎" when the average bending angle is 75 ° or more and 3σ (variation) is 2.0 or less, and the average bending angle is 75 ° or more. If there is, and 3σ is 3.0 or less, it is regarded as "○", and in other cases, it is regarded as "×". For the comprehensive evaluation of the bending state, the one with the worse evaluation was adopted from the evaluation after the bending process and the evaluation after annealing at 100 ° C. for 3 hours.

From FIG. 1, T1 of the synthetic resin pipe is around 135 ° C., and at a temperature lower than T1, the storage elastic modulus (E ′) and the loss elastic modulus (E ″) are high, and the bending back becomes large and reliable shaping cannot be performed. Is expected.
Looking at Table 1 and FIGS. 13 (a) and 13 (b), it is true that the bending angle is small in Comparative Example 1 in which the heating temperature is 130 ° C. or lower, and in Comparative Example 2, the bending angle after 100-hour annealing. Was small and the variation was large.

From FIG. 1, at T1 (135 ° C.) or higher, the bending back after processing should be stable. However, in Comparative Example 3 in which T1 = 135 ° C., it can be seen that the variation after 3 hours of charging into a heating furnace at 100 ° C. and annealing is large, and the variation with time thereafter is large.

On the other hand, in Examples 1 to 5 heated to 150 ° C. or higher, the bending angle after processing is stable, and even after processing at 100 ° C. for 3 hours of charging as an evaluation for promoting the subsequent change with time, after processing. In comparison, the bending angle was stable, although there was bending back.
However, in Example 5 heated to a temperature exceeding 300 ° C., although the bending angle after processing was almost stable, the variation tended to be large after 100 ° C. for 3 hours injection annealing as an accelerated evaluation. .. This is because, in FIG. 1, the storage elastic modulus (E') at a temperature exceeding 300 ° C. exceeds ± 1% of the storage elastic modulus (E'T1) at _T1 , and the storage elastic modulus increases again and is unstable. Is consistent with that.

From the above, it was found that in the bending process in this experiment, processing at a heating temperature of 150 ° C. or higher and 300 ° C. or lower is preferable in order to obtain a bent product having a stable bending angle. Further, it was found that 200 ° C. to 250 ° C. is more preferable in consideration of the variation in the processing process.

1 Synthetic resin pipe 2 Shaped type

Claims (4)

This is a processing method for secondary processing of cross-linked polyethylene .
When the temperature at + 15 ° C. at the maximum loss tangent (tan δ) of the cross-linked polyethylene is T1 (° C.) and the temperature at T1 + 30 ° C. is T2 (° C.).
The storage elastic modulus (E') of the cross-linked polyethylene in the range from T1 to T2 is within ± 10% of the storage elastic modulus (E'T1) of the cross-linked polyethylene in the T1.
A processing method for secondary processing by heating the cross-linked polyethylene to a temperature of T1 + 15 ° C. or higher. The processing method according to claim 1, wherein the cross-linked polyethylene is heated to a temperature of T1 + 15 ° C. or higher and T1 + 16 ° C. or lower for secondary processing. The processing method according to claim 1, wherein the cross-linked polyethylene is heated to a temperature of T1 + 65 ° C. or higher and T1 + 115 ° C. or lower for secondary processing. A method for processing a tubular body containing at least the cross-linked polyethylene .
The tubular body is placed along the shaped mold engraved in a shaped shape that covers the entire outer circumference of the tubular body.
The processing method according to any one of claims 1 to 3 , wherein pressure is applied from the inside of the tubular body in a state where the tubular body is placed in the shaped mold.

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