JP6580814B2 - Manufacturing method of hollow tube - Google Patents

Description

  The present invention relates to a hollow tube, a hollow tube manufacturing apparatus, and a hollow tube manufacturing method.

  In recent years, an example in which a pipe (foamed pipe) using a foamable resin is used as a drain pipe of an apartment or building is increasing. For the purpose of reducing the weight of the entire pipe, the foamed pipe has an appropriate foaming ratio to reduce the specific gravity of the foam. The foamed pipe also has an advantage that running water noise can be reduced by the soundproofing action of the foam.

  For example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2007-283733), a vinyl chloride resin foam layer having few open cells and homogeneous bubbles and a vinyl chloride resin having a substantially non-foam structure are laminated. In addition, a vinyl chloride resin foamed tube that is excellent in heat insulating effect, anti-condensation effect, etc., in which water does not enter between the two layers at the time of joining with a joint or the like is disclosed.

  The vinyl chloride resin foam tube described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2007-283733) is an extruded vinyl chloride resin foam tube in which a foam layer is formed between an inner skin layer and an outer skin layer. The inner skin layer has a thickness of 0.05 to 0.6 mm and has a substantially non-foaming structure, and the outer skin layer has a thickness of 0.2 to 1.5 mm and has a substantially non-foaming structure. The bubbles in the foam layer are not substantially communicated in a direction parallel to the extrusion direction, the average cell diameter in the cross section perpendicular to the extrusion direction is 30 to 150 μm, and the foaming ratio of the foam layer is 2 to 5 times. It is characterized by being.

  Further, Patent Document 2 (Japanese Patent Application Laid-Open No. 11-257548) discloses a muffler pipe that is excellent in workability and productivity and has a purpose of providing a muffler pipe having a sufficient sound muffling effect. Yes.

  The muffler pipe described in Patent Document 2 (Japanese Patent Laid-Open No. 11-257548) is a muffler pipe applied to a water supply pipe and a drain pipe, and is formed from a vinyl chloride resin composition and has an expansion ratio of 1.2 to It is characterized in that it is constituted by an intermediate tube made of a five-fold foam and an outer tube and an inner tube formed from a soft vinyl chloride resin composition.

  Patent Document 3 (Japanese Patent Application Laid-Open No. 2002-234066) includes an inner layer and an outer layer formed of a non-foamed foamed thermoplastic resin composition, and an intermediate layer formed of a foamed thermoplastic resin composition. A method of manufacturing a resin pipe having a three-layer structure is disclosed in which the resin pipe is manufactured so that the thickness of the resin pipe when finished is always uniform.

  The method for producing a resin pipe having a three-layer structure described in Patent Document 3 (Japanese Patent Application Laid-Open No. 2002-234066) is a foamed thermoplastic resin composition that serves as an intermediate layer between a non-foamed thermoplastic resin composition that serves as an inner layer and an outer layer. An unsolidified tubular body having a three-layer structure in a state where an object is interposed is coextruded from a mold, the foamed thermoplastic resin composition in the coextruded unsolidified tubular body is foamed, and the thermoplastic resin is cooled and solidified. In the method of manufacturing a three-layered resin pipe, the amount of the foaming agent added to the thermoplastic resin forming the intermediate layer is the same as the predetermined product dimensions when molded without restricting the spread of the resin pipe in the radial direction. Resin tube is formed by sizing to a predetermined finished size against the foaming pressure using the tube outer surface forming tube and the tube inner surface forming core in addition to the theoretical amount added to obtain the expansion ratio What you did It is an butterfly.

  Patent Document 4 (Japanese Patent Laid-Open No. 9-222185) discloses a composite pipe excellent in heat insulation and heat retention functions and a method for producing the same without using thermal deformation or water absorption from the surface even when used at high temperatures. ing.

  The composite pipe described in Patent Document 4 (Japanese Patent Laid-Open No. 9-222185) is a composite pipe in which a coating layer made of a vinyl chloride resin foam is provided on the outer peripheral surface of a pipe body made of vinyl chloride resin. The coating layer comprises a foamed inner layer portion and a substantially non-foamed surface layer portion formed on the outer periphery thereof, and the inner layer portion and the surface layer portion are integrally formed. Is.

  Patent Document 5 (Japanese Patent Laid-Open No. 7-217934) discloses a drain pipe for drainage of an air conditioner that can reliably prevent surface condensation and is easy to construct.

  The drainage pipe described in Patent Document 5 (Japanese Patent Laid-Open No. 7-217934) is composed of a closed-cell foamed vinyl chloride resin having an average foaming ratio of 2 to 7, and the inner peripheral surface of the foamed vinyl chloride resin. In addition, a skin layer having a thickness of 0.2 to 0.5 mm is provided, and a skin layer having a thickness of 0.2 to 1.0 mm is provided on the outer peripheral surface of the foamed vinyl chloride resin. It is characterized by.

JP 2007-283733 A Japanese Patent Laid-Open No. 11-257548 JP 2002-234066 A JP-A-9-222185 JP 7-217934 A

As described above, many developments have been made on various foamed pipes. All the foamed pipes are usually manufactured for the purpose of homogenizing the bubbles by making the foaming ratio of the foam uniform from the viewpoint of dimensional stability and the like.
The expansion ratio of the foam layer in the foam pipe is set in consideration of the strength and weight of the entire pipe. For example, when the expansion ratio is increased, the mechanical properties such as the bending strength and impact resistance of the pipe are lowered. Therefore, it is necessary to ensure the overall strength by laminating both the inner and outer surfaces of the foam layer with a non-foam resin. . In order to ensure strength, the thickness of the non-foamed resin layer needs to be large. Therefore, the weight of the whole pipe inevitably increases, and it is difficult to achieve a desired weight reduction.

  An object of the present invention is to provide a hollow tube, a hollow tube manufacturing apparatus, and a hollow tube manufacturing method capable of satisfying the multifunctionality having at least light weight and mechanical properties.

(1)
The hollow tube according to one aspect includes a tubular foam having an inclined structure with different porosity in the thickness direction.

Since the hollow tube of the present invention includes a foam, it is excellent in light weight. Furthermore, since it has the inclination structure from which the porosity differs in the thickness direction of a foam, it is excellent in mechanical physical property.
Thus, the hollow tube of the present invention has multi-functionality that combines at least light weight and mechanical properties.

  Multifunctionality refers to the characteristics that combine at least light weight and mechanical properties.In addition, depending on the use mode of the hollow tube, etc., it has silence, heat retention, heat insulation, anti-condensation, weather resistance, etc. It may also refer to the characteristics that are exhibited. The mechanical properties include at least one of bending properties (flexibility), internal pressure resistance properties, and flatness (cushion properties).

  In the present invention, the inclined structure having a different porosity in the thickness direction means a structure showing a gradient of the porosity in the thickness direction, more specifically, an aspect in which the porosity gradually changes in the thickness direction. And a mode in which the porosity changes stepwise in the thickness direction, and a mixed mode thereof.

(2)
The inclined structure may include a structure having a high porosity on the side farther from the side closer to the axial center of the tubular foam.

  As a result, the mechanical properties (for example, internal pressure resistance) of the hollow tube are more excellent.

(3)
The inclined structure may include a structure having a low porosity on the side farther from the side closer to the axis of the tubular foam.

  Thereby, the mechanical properties (for example, bending properties) of the hollow tube are more excellent.

(4)
The inclined structure may include a stacked structure of a plurality of layers having different porosity.
Thereby, the gradient of the porosity can be varied.

(5)
The hollow tube of the present invention includes a non-foamed inner layer on the inner peripheral surface of a tubular foam, and the wall thickness of the non-foamed inner layer tube is 10% to 70% of the wall thickness of the tubular foam. It's okay.

  In the present invention, since the tubular foam has light weight and mechanical properties, the thickness of the inner tube can be reduced in this way.

(6)
The hollow tube of the present invention may include a non-foamed coating layer on the outer peripheral surface of the tubular foam.

Thereby, the outer layer of the tubular foam can be covered with the covering layer.
The wall thickness of the coating layer may be 10% or more and 30% or less of the wall thickness of the tubular foam. In the present invention, since the tubular foam has light weight and mechanical properties, the thickness of the outer coating layer can be reduced as described above.

(7)
The tubular foam may be at least one of an inorganic foam and an organic foam.

  Thus, the hollow tube of the present invention can be embodied by either an inorganic foam or an organic foam, and can also be embodied by a mixture of an inorganic foam and an organic foam.

(8)
The tubular foam may be at least one of a vinyl chloride resin and an acrylonitrile-styrene resin.

  Thus, the hollow tube of the present invention can be embodied with a general-purpose resin.

(9)
A method for manufacturing a hollow tube according to another aspect includes a laminating step and a foaming step. In the laminating step, at least the first foamable material containing a predetermined amount of foaming agent and the second foamable material containing an amount of foaming agent different from the predetermined amount are laminated in a tubular shape, so that at least the first foamable material is laminated. A tubular laminate of the foamable material including the foamable material and the second foamable material is obtained. In the foaming step, a tubular foam is obtained by foaming a tubular laminate of foamable material.

  Thus, a hollow tube including a tubular foam having a different porosity in the thickness direction is manufactured.

(10)
In the method for manufacturing a hollow tube of the present invention, the number of layers of the tubular laminate of the foamable material may be 3 or more.
As a result, a hollow tube including a tubular foam having various porosity gradients is manufactured.

(11)
In the method for producing a hollow tube of the present invention, the number of layers of the tubular laminate of foamable material is 4 or more and 10 or less, and the foamable material constituting each layer is farther from the side closer to the axis of the tubular laminate. This layer may be prepared so that the content of the foaming agent is increased.

  As a result, a hollow tube including a tubular foam having a structure with a high porosity on the side farther from the side closer to the axis is manufactured.

(12)
In the method for producing a hollow tube of the present invention, the number of layers of the tubular laminate of foamable material is 4 or more and 10 or less, and the foamable material constituting each layer is farther from the side closer to the axis of the tubular laminate. This layer may be prepared so that the content of the blowing agent is reduced.

  As a result, a hollow tube including a tubular foam having a structure with a low porosity on the side farther from the side closer to the axis is manufactured.

(13)
The method for producing a hollow tube of the present invention may further include a step of laminating a non-foamable material on the tubular laminate or the tubular foam.

Thus, a hollow tube in which a tubular foam is laminated with a non-foam is manufactured.
The non-foam layer may be laminated on at least one of the inside and the outside of the tubular foam.

(14)
In the method for producing a hollow tube of the present invention, the foaming agent may be a solid pyrolyzable foaming agent.
In this case, the amount of the foaming agent can be easily adjusted.

(15)
In the method for producing a hollow tube of the present invention, the foaming agent may be an inorganic gas.
In this case, the long run property can be kept good.

(16)
A hollow tube according to another aspect has a structure obtained by the method for manufacturing a hollow tube according to any one of (9) to (15).
Therefore, the hollow tube of the present invention has multi-functionality that combines at least light weight and mechanical properties.

(17)
A hollow tube manufacturing apparatus according to still another aspect includes a first extruder for extruding a first foamable material, a first gas supply section for supplying a foaming gas to the first foamable material, and a first A first molding section that molds the foamable material into a tube; a second extruder that extrudes the second foamable material; a second gas supply section that supplies a foaming gas to the second foamable material; And a second molding part that is molded into a tubular shape so as to be laminated on the first foamable material. Furthermore, the first gas supply unit and the second gas supply unit are configured such that the gas pressures can be independently controlled.

  Thereby, a tubular foam having an inclined structure with different porosity in the thickness direction can be obtained.

It is typical sectional drawing which shows an example of the hollow circular tube concerning 1st Embodiment. It is a graph which shows the inclination structure of the foaming layer of the hollow circular tube concerning 1st Embodiment. It is typical sectional drawing which shows an example of the hollow circular tube concerning 2nd Embodiment. It is a graph which shows the inclination structure of the foaming layer of the hollow circular tube concerning 2nd Embodiment. It is typical sectional drawing which shows an example of the hollow circular tube concerning 3rd Embodiment. It is a graph which shows the inclination structure of the foaming layer of the hollow circular tube concerning 3rd Embodiment. It is typical sectional drawing which shows an example of the hollow circular tube concerning 4th Embodiment. It is a graph which shows the inclination structure of the foaming layer of the hollow circular tube concerning 4th Embodiment. It is typical sectional drawing which shows an example of the hollow circular tube concerning 5th Embodiment. It is a graph which shows the inclination structure of the foaming layer of the hollow circular pipe in another example. It is a schematic diagram which shows an example of the manufacturing apparatus of a hollow circular tube. It is a schematic diagram which shows an example of the manufacturing apparatus of a hollow circular tube. It is a typical expanded sectional view of the metal mold | die of a hollow circular tube. It is a schematic diagram which shows the other example of the manufacturing apparatus of a hollow circular tube. It is a typical expanded sectional view which shows the other example of the metal mold | die of a hollow circular tube. It is a typical expanded sectional view which shows the other example of the metal mold | die of a hollow circular tube. It is a typical expanded sectional view which shows the other example of the metal mold | die of a hollow circular tube. It is a schematic diagram which shows the other example of the manufacturing apparatus of a hollow circular tube. It is a typical expanded sectional view which shows the other example of the metal mold | die of a hollow circular tube. It is a X-ray CT image of the cross section of the hollow circular tube manufactured in the Example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Moreover, in the case of the same code | symbol, those names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[First Embodiment]
FIG. 1 is a schematic cross-sectional view (a cross-sectional view taken along a plane perpendicular to the axis) showing an example of a hollow circular tube 100 according to the first embodiment.

(Outline of hollow circular tube)
As shown in FIG. 1, the hollow circular tube 100 mainly includes an inner layer 210, an outer layer 220, and a coating layer 230. Of these, the inner layer 210 and the covering layer 230 are not essential components.

(Inner layer)
The inner layer 210 shown in FIG. 1 is made of a non-foamed hard resin. Specifically, the hard resin may be a hard vinyl chloride resin (PVC). More specifically, the hard vinyl chloride resin includes, for example, a chlorinated vinyl chloride resin, a polymerizable monomer other than a vinyl chloride monomer and a vinyl chloride monomer, in addition to a homopolymer of a vinyl chloride monomer. Examples thereof include a copolymer with a monomer, and a graft copolymer obtained by grafting a vinyl chloride monomer to a polymer other than a vinyl chloride resin. The hard vinyl chloride resin may contain an ultrafine rubber component. In this case, impact resistance can be improved. The ultrafine rubber component may be physically or chemically bonded to the vinyl chloride resin.

  The non-foamable resin forming the inner layer 210 is not limited to the above-described vinyl chloride resin, and may be any other resin. For example, polyethylene, polypropylene, polybutene, chlorinated polyethylene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, polyvinyl fluoride, polycarbonate, Examples include polyacetal, polyphenylene sulfide, polyphenylene oxide, nylon-6, nylon-6 / 6, nylon 12, polyethylene terephthalate, polybutylene terephthalate, acrylonitrile-butadiene-styrene resin, and (meth) acrylic resin. The above-mentioned resins may be used alone or in combination of two or more.

  The thickness (wall thickness) of the inner layer 210 in the stacking direction may be 10% or more and 70% or less of the wall thickness of the outer layer 220 described later. In addition, the thickness in the stacking direction of the inner layer 210 has upper and lower limits of any two ratio values of 10%, 20%, 30%, 40%, 50%, 60%, and 70% of the thickness of the outer layer 220. The thickness may occupy a range. More specifically, for example, it may be 0.3 mm or more and 10 mm or less. However, the thickness (wall thickness) in the stacking direction of the inner layer 210 may be less than 0.3 mm when no problem is caused in strength, and more than 10 mm when there is no problem in construction. There may be.

(Outer layer and coating layer)
The outer layer 220 shown in FIG. 1 is formed by being laminated on the outer periphery of the inner layer 210. The outer layer 220 is made of a foamed resin having a large number of voids (bubbles). The resin constituting the outer layer 220 can be selected from the resins exemplified as the resin constituting the inner layer 210. The resin constituting the outer layer 220 may be the same as or different from the resin constituting the inner layer 210 except that voids are included.

  FIG. 2 is a graph schematically showing the relationship between the distance from the axial center of the hollow circular tube 100 and the porosity of the outer layer 220. As shown in FIG. 2, the foamed resin constituting the outer layer 220 has an inclined structure in which the porosity gradually changes in the thickness direction. Specifically, the porosity is smaller (more dense) as it is farther from the axial center (closer to the outer periphery), and the porosity is larger (less sparser) closer to the axial center (closer to the inner periphery). The porosity refers to the volume occupied by the voids relative to the volume of the foam. Therefore, the higher the foaming rate, the higher the porosity, and the lower the foaming rate, the lower the porosity.

  The aspect of the porosity change in the outer layer 220 is arbitrary. For example, as shown in FIG. 2 (A), the change rate of the porosity may be constant over the entire thickness, and the porosity changes as shown in FIGS. 2 (B) and 2 (C). May be. In the case shown in FIG. 2B, the variation in porosity is larger as it is closer to the inner periphery, and in the case shown in FIG.

  The average porosity of the outer layer 220 is, for example, 50% or more and 80% or less, for example, 75%. When the porosity of the outer layer 220 is 50% or more, the lightness is good, and when the inner layer 210 is protected as in this embodiment, for example, the heat insulation performance or the dew condensation prevention performance is also good. When the porosity of the outer layer 220 is 80% or less, the mechanical strength of the outer layer 220 (for example, it can be measured as a flatness ratio when a crack or a crack occurs in a flattening test) is easily secured. As described above, the inclined structure can ensure the mechanical strength superior to the average porosity.

  The thickness of the outer layer 220 is arbitrary, for example, 2 mm or more, preferably 4 mm or more. By being 2 mm or more, the inclined structure can be effectively secured. Moreover, the above-mentioned inclined structure can be more easily provided by being 4 mm or more thick. Although the upper limit of the thickness of the outer layer 220 is not limited, as an example, it is 15 mm from the viewpoint of lightness and the like.

  Note that the voids in the outer layer 220 are formed to be closed-cell foam cells that do not communicate with adjacent voids. Further, the size of the voids is preferably in the range of an average cell diameter of 30 μm or more and 150 μm or less. Here, the average cell diameter refers to the cell diameter when the cumulative cell diameter fraction is 50% when the cell diameter in the cross section perpendicular to the axial direction is accumulated from the smaller one. In addition, since the cell diameter of the space | gap shown in figure is typically expressed in order to express a porosity, it is displayed with the same magnitude | size all, However, It is not limited to such an aspect. For example, the cell diameter may be larger as the porosity is higher, and the cell diameter may be smaller as the porosity is lower.

  Further, the foamed resin for forming the outer layer 220 may further include a heat stabilizer, a processing aid, a lubricant, an impact modifier, a filler, an antioxidant, an ultraviolet absorber, a light stabilizer, a pigment, and the like as necessary. May be included as appropriate.

In the present embodiment, the thickness of the covering layer 230 may be not less than 5% and not more than 30% of the thickness of the outer layer 220. The thickness of the covering layer 230 is a thickness that occupies a range in which any two ratio values of 5%, 10%, 15%, 20%, 25%, and 30% of the thickness of the outer layer 220 are the upper and lower limits. There may be. Specifically, it is preferably 0.1 mm or more and 1.5 mm or less, for example, 0.5 mm as an example.
When the thickness of the covering layer 230 is 0.1 mm or more, it is easy to ensure the strength of the hollow circular tube 100 itself, and when the thickness is 1.5 mm or less, the covering layer 230 within the thickness of the hollow circular tube 100 is obtained. The occupied portion of the hollow tube 100 can be made small, the porosity is preferably ensured, and the lightness of the hollow circular tube 100 can be improved.

  The covering layer 230 may be the same resin as the outer layer 220 except that it is not foamed, or may be a different resin.

[Second Embodiment]
FIG. 3 is a schematic cross-sectional view showing an example of a hollow circular tube 100a according to the second embodiment.
As shown in FIG. 3, the hollow circular tube 100 a mainly includes an inner layer 210, an outer layer 220 a, and a coating layer 230. The hollow circular tube 100a is the same as the hollow circular tube 100 of the first embodiment except that the foaming mode of the outer layer 220a is different. Hereinafter, differences from the first embodiment will be described.

  FIG. 4 is a graph schematically showing the relationship between the distance from the axial center of the hollow circular tube 100a and the porosity of the outer layer 220a. As shown in FIG. 4, the foamed resin constituting the outer layer 220a has a higher porosity (more sparse) as it is farther from the axial center (closer to the outer periphery), and a porosity that is closer to the axial center (closer to the inner periphery). Has an inclined structure that is small (more dense).

  The aspect of the porosity change in the outer layer 220a is arbitrary. For example, as shown in FIG. 4 (A), the change rate of the porosity may be constant over the entire thickness, or the porosity varies as shown in FIGS. 4 (B) and 4 (C). May be. In the case shown in FIG. 4B, the variation in the porosity is larger as it is closer to the outer periphery, and in the case shown in FIG.

[Third Embodiment]
FIG. 5 is a schematic cross-sectional view showing an example of a hollow circular tube 100b according to the third embodiment.
As shown in FIG. 5, the hollow circular tube 100 b mainly includes an inner layer 210, an outer layer 220 b, and a coating layer 230. The hollow circular tube 100b is the same as the hollow circular tube 100 of the first embodiment except that the foaming aspect of the outer layer 220b is different. Hereinafter, differences from the first embodiment will be described.

  As shown in FIG. 5, the outer layer 220b has a laminated structure of foam layers 221b, 222b, and 223c having different porosity. The foamed layers 221b, 222b, and 223c may be the same resin except that the foaming rates are different, or may be different resins. As an example of the case where each of the foam layers 221b, 222b, and 223c is composed of different resins, there is an embodiment in which the blend amount of the functional resin is different in each foam layer. In this case, by configuring so that the blending amount of the functional resin or additive that exhibits a specific function increases or decreases in the order of the foam layers 221b, 222b, and 223c, the specific function also has an inclined structure (inclined function). Property). The specific function is not particularly limited, and examples thereof include a weather resistance function.

  FIG. 6 is a graph schematically showing the relationship between the distance from the axis of the hollow circular tube 100b and the porosity of the outer layer 220b. As shown in FIG. 6, the resin constituting the outer layer 220b has an inclined structure in which the porosity changes in a stepwise manner from the inner periphery to the outer periphery in the order of the foam layers 221b, 222b, and 223b.

  In the case of a laminated mode of a plurality of foam layers having different foam ratios as in this embodiment, as shown in FIG. 6A, an example in which the boundary between adjacent foam layers is relatively clear due to the difference in porosity. However, it is not limited to this embodiment. The boundary between adjacent foam layers is not always clear, and as shown in FIG. 6 (B), the porosity changes near the boundary between the foam layers while maintaining an inclined structure in which the porosity gradually changes. May be more gradual.

  In the present embodiment, an embodiment in which three foam layers having different porosity are laminated is described. However, the number of layers is not limited to this embodiment, and the number of layers may be two or more.

  The foam layer is multi-layered (for example, the number of layers in the range where any two of 4, 5, 6, 7, 8, 9, 10 are the upper and lower limit values), so that the porosity gradually decreases from the inner periphery to the outer periphery. When the layers are stacked, the boundary of the foam layer tube becomes unclear, and as shown in FIG. 6C, the porosity gradually changes continuously as shown in the first embodiment. In some cases, the structure may be an inclined structure.

[Fourth Embodiment]
FIG. 7 is a schematic cross-sectional view showing an example of a hollow circular tube 100c according to the fourth embodiment.
As shown in FIG. 7, the hollow circular tube 100 c mainly includes an inner layer 210, an outer layer 220 c, and a coating layer 230. The hollow circular tube 100c is the same as the hollow circular tube 100 of the first embodiment except that the foaming mode of the outer layer 220c is different. Hereinafter, differences from the first embodiment will be described.

The outer layer 220c has a structure in which two layers of the outer layer 220 of the first embodiment are stacked. As shown in FIG. 7, the foamed resin constituting the outer layer 220c has a laminated structure of foamed layers 221c and 222c having different average porosity.
FIG. 8 is a graph schematically showing the relationship between the distance from the axial center of the hollow circular tube 100c and the porosity of the outer layer 220c. Each of the foam layers 221c and 222c is configured such that the porosity gradually decreases from the inner peripheral side to the outer peripheral side. Therefore, the entire thickness of the outer layer 220c includes two inclined structures in which the porosity gradually decreases from the inner peripheral side to the outer peripheral side.

  In the present embodiment, the foam layers 221c and 222c have different average void ratios (see FIG. 8A). However, the present invention is not limited to this mode. The average porosity of the foam layers 221c and 222c may be the same (see FIG. 8B). Even in this case, the entire thickness of the outer layer 220c includes two inclined structures in which the porosity gradually decreases from the inner peripheral side to the outer peripheral side.

  In the present embodiment, the foamed layers 221c and 222c may be the same resin or different resins except that the average porosity is different. As an example of the case where each of the foam layers 221c and 222c is made of a resin different from each other, there is an embodiment in which the blend amount of the functional resin is different in each foam layer. In this case, an inclined structure (inclined functionality) is also provided for the specific function by configuring so that the blending amount of the functional resin exhibiting the specific function increases or decreases in the order of the foam layers 221c and 222c. be able to.

  In the present embodiment, an example in which two foam layers 221c and 222c each having a sloped structure of porosity are stacked is described. However, the number of layers is not limited to this mode, and more foam layers are stacked. It may be. The number of stacks may be two or more, and may be 3, 4, or 5, for example.

[Fifth Embodiment]
FIG. 9 is a schematic cross-sectional view showing an example of a hollow circular tube 100d according to the fifth embodiment.
As shown in FIG. 9, the hollow circular tube 100d mainly includes an inner layer 210d, an outer layer 220a, and a coating layer 230. The hollow circular tube 100d is the same as the hollow circular tube 100a of the second embodiment except that it has an inner layer 210d instead of the inner layer 210. Hereinafter, differences from the second embodiment will be described.

  The hollow circular tube 100d has a relatively thin non-foamed inner layer 210d. The inner layer 210d has the same thickness as the coating layer 230 (5% or more and 30% or less of the thickness of the outer layer 220a, or any two ratios of 5%, 10%, 15%, 20%, 25%, and 30%) It is provided in a range in which the value is an upper and lower limit, specifically, for example, 0.1 mm to 1.5 mm, for example, 0.5 mm. The inner layer 210d and the covering layer 230 may be made of the same resin or different resins.

  The hollow circular tube 100d has an outer layer 220a in which the porosity gradually increases from the inner periphery to the outer periphery between the inner layer 210d, which is a thin non-foamed layer, and the coating layer 230, and thus is cut along a plane perpendicular to the axis. The cross section is similar to bamboo. Therefore, the hollow circular tube 100d has a function similar to that of bamboo with respect to having a gap.

  In addition to the above-described embodiments, the present invention includes any aspect in which the embodiments are appropriately combined. For example, FIG. 10 is a graph schematically showing the relationship between the distance from the axis of the hollow circular tube and the porosity when the outer layer 220 of the first embodiment and the outer layer 220a of the second embodiment are combined. It is. FIG. 10A shows an aspect in which the outer layer 220a of the second embodiment is arranged on the inner peripheral side and the outer layer 220 of the first embodiment is arranged on the outer peripheral side, and FIG. The aspect laminated | stacked so that the outer layer 220 of 1st Embodiment may be arrange | positioned at the peripheral side and the outer layer 220a of 2nd Embodiment may be arrange | positioned at an outer peripheral side is shown.

[Manufacture of hollow circular tube according to the first embodiment]
(Outline of manufacturing equipment for hollow circular tubes)
FIG. 11 and FIG. 12 are schematic views showing an example of a manufacturing apparatus 500 for the hollow circular tube 100.
FIG. 11 is a plan view when the manufacturing apparatus 500 for the hollow circular tube 100 is viewed from above, and FIG. 12 is a side view of the manufacturing apparatus 500 for the hollow circular tube 100.

  As shown in FIGS. 11 and 12, the manufacturing apparatus 500 includes a carbon dioxide gas cylinder 510, a metering pump 520, a non-foamable resin composition extruder 530, a foamable resin composition extruder 540, a mold 550, and a pipe outer surface. An adjustment device 560, a cooling water tank 570, a take-up machine 580 and a cutting machine 590 are included.

  FIG. 13 is a schematic enlarged cross-sectional view of an ellipse portion indicated by a dotted line in the mold 550 in the manufacturing apparatus 500.

(Method for producing hollow circular tube)
An example of a method for manufacturing the hollow circular tube 100 will be described. As shown in FIGS. 11 and 12, in the non-foamable resin composition extruder 530, the non-foamable resin composition 210 ′ (see FIG. 13) is melt-kneaded and extruded into a tubular shape through a straight die. . The non-foaming resin composition 210 ′ is specifically a non-foaming thermoplastic resin composition, for example, a vinyl chloride resin composition. As will be described later, the non-foamable resin composition 210 ′ is laminated together with the foamable resin composition 220 ′ described later in the mold 550, then sent out of the mold 550 and solidified in the cooling water tank 570. The inner layer 210 (see FIG. 1).

  As an example of the vinyl chloride resin composition, vinyl chloride resin 100 parts by weight, lead thermal stabilizer 2.0 parts by weight, polyethylene wax 0.5 parts by weight, acrylic processing aid 2.0 parts by weight, A resin composition obtained by supplying 0.7 parts by weight of an ester wax, 3.0 parts by weight of calcium carbonate, and 0.5 parts by weight of a pigment to a Henschel mixer or the like and mixing them. Further, the non-foamable resin composition may contain an ultrafine rubber component. The ultrafine rubber component may be physically or chemically bonded to the vinyl chloride resin.

  In addition to the above-described vinyl chloride resin composition, any resin composition is appropriately selected by those skilled in the art to form a non-foamed resin to be formed.

  On the other hand, carbon dioxide gas as a foaming agent is supplied from the carbon dioxide gas cylinder 510 into the foamable resin composition extruder 540 through the vent hole through the metering pump 520. In the foamable resin composition extruder 540, the thermoplastic resin composition and the carbon dioxide gas press-fitted into the thermoplastic resin composition are melt-kneaded to prepare a foamable resin composition 220 ′ (see FIG. 13). Is done. The foamable resin composition 220 ′ is laminated together with the non-foamable resin composition 210 ′ in the mold 550 and then sent out of the mold 550 to be foamed and solidified in the cooling water tank 570 as will be described later. Thus, the outer layer 220 (see FIG. 1) is formed.

  The foamable resin composition 220 'can be prepared by further adding a foaming agent to the non-foamable resin composition 210' that can be used to form the inner layer 210 described above. The resin contained in the foamable resin composition 220 'may be the same as or different from the resin contained in the non-foamable resin composition 210'.

  In this embodiment, although the aspect which uses the carbon dioxide gas which is a gas for foaming as a foaming agent was shown, it is not limited to this. Examples of the foaming gas include carbon dioxide, inorganic gas such as nitrogen gas, and organic gas such as butane gas and chlorofluorocarbon gas. These foaming gases may be used alone or in combination of two or more. Inorganic gas is preferable in that it does not need to be recovered and does not generate by-products, and is excellent in long-running properties.

  Another example of the foaming agent is a pyrolytic foaming agent. Examples of the thermal decomposition type foaming agent include thermal decomposition type inorganic foaming agents such as sodium bicarbonate, ammonium bicarbonate, and ammonium carbonate, and nitroso compounds such as N, N ′: dinitrosotephthalamide, azodicarbonamide, and azobis. Examples include azo compounds such as isobutyronitrile, and pyrolytic organic blowing agents such as sulfonyl hydrazide compounds such as benzenesulfonyl hydrazide and toluenesulfonyl hydrazide. These pyrolytic foaming agents may be used alone or in combination of two or more. In this case, the resin is foamed using a gas generated by the thermal decomposition reaction of the foaming agent. In addition, a solid thermal decomposition type foaming agent is preferable at the point that adjustment of content in a resin composition is easy.

  Furthermore, a solvent-type foaming agent is also mentioned as another example of a foaming agent. In this case, the resin is foamed using a gas generated by vaporization by heat or pressure release. Examples of the solvent-type blowing agent include solvents having a low boiling point such as lower alcohols such as methanol and ethanol and lower alkanes such as pentane and hexane. These solvent type blowing agents may be used alone or in combination of two or more.

  As the foaming agent, a foaming gas, a pyrolytic foaming agent, and a solvent-type foaming agent can be used in any combination. When the foaming gas is not used, the manufacturing apparatus 500 does not require the carbon dioxide gas cylinder 510 and the metering pump 520.

  The amount of the foaming agent can be adjusted according to the desired expansion ratio. When obtaining a foam having a higher expansion ratio or porosity, a larger amount of the foaming agent can be used, and when obtaining a foam having a lower expansion ratio or porosity, a lower amount of the foaming agent is used. be able to.

  As shown in FIG. 13, the mold 550 includes a straight die 551 and a crosshead die 552. A vacuum slit VS2 is formed in the cross head die 552. In the mold 550, the non-foamable resin composition 210 ′ melt-kneaded by the non-foamable resin composition extruder 530 is formed into a tubular shape via a straight die 551, and the foamable resin composition extruder 540 is used. The melt-kneaded foamable resin composition 220 ′ is formed into a tubular shape so as to be laminated on the outer periphery of the tubular non-foamable resin composition 210 ′ via the crosshead die 552. In this manner, a laminated tube including the non-foamable resin composition 210 'and the foamable resin composition 220' is prepared in the mold 550.

  A non-foaming resin composition (not shown) is further laminated on the laminated tube to form a coating layer 230 (see FIG. 1). Lamination of the non-foamable resin composition for forming the coating layer 230 may be performed in the mold 550 or may be performed after foaming of the foamable resin composition 220 ′ described later is performed. Good.

  Although the coating layer 230 (refer FIG. 1) can be formed by lamination | stacking of a non-foaming resin composition as mentioned above, it is not limited to this method. For example, when the surface where the crosshead die 552 is in contact with the foamable resin composition 220 ′ is configured as the cooling surface S2, the outer peripheral surface of the foamable resin composition 220 ′ is cooled by the cooling surface S2. It may be formed by solidifying the vicinity of the surface prior to foaming.

  When the laminated tube containing the non-foamable resin composition 210 'and the foamable resin composition 220' is sent out of the mold 550, the pressure is reduced, and the foamable resin composition 220 'is foamed. The foamed laminated tube is sized by applying an appropriate pressure to the outer layer surface by a tube outer surface adjusting device 560 attached to the cooling water tank 570. The tube outer surface adjustment device 560 includes a tube for forming in contact with the outer surface of the tube.

  When foaming, the temperature adjusting part (not shown) of the tube outer surface adjusting device 560 cools the layer surface of the foamable resin composition 220 ′ so that the outer peripheral side becomes lower temperature and the inner peripheral side becomes higher temperature. A temperature gradient is generated in the layer of the resin composition 220 ′. Thereby, the inclination structure (refer FIG. 2) of the porosity in the outer layer 220 (refer FIG. 1) after foaming can be adjusted.

The laminated tube sent out from the tube outer surface adjustment device 560 is sufficiently cooled and solidified in the cooling water tank 570 to become the hollow circular tube 100. In the present embodiment, the coolant used in the cooling water tank 570 is water. However, as the coolant, liquid and gas can be used as long as they are not corrosive to the product and have good fluidity and heat exchange. It doesn't matter. For example, air, oil, polyethylene glycol, etc. are also mentioned.
The hollow circular tube 100 is taken up by a take-up machine 580 and cut into an appropriate length by a cutting machine 590.

  In the above description, the example in which the inclined structure of the outer layer 220 in the hollow circular tube 100 is formed by the method of varying the expansion ratio in the thickness direction by temperature control is described. However, the method of forming the outer layer 220 is limited to this method. It is not a thing. In addition to the method based on temperature control, it can also be formed by a method in which a large number of layers having different amounts of the foaming agent are stacked to vary the expansion ratio in the thickness direction. The number of layers may vary depending on the thickness of the outer layer 220 to be formed, but is the number of layers in a range in which any two of 4, 5, 6, 7, 8, 9, 10 are the upper and lower limits. It means to be laminated.

  A method for differentiating the expansion ratio in the thickness direction by stacking a large number of layers having different amounts of the foaming agent will be described in detail in the manufacture of the hollow circular tube according to the second embodiment to be described later. In the case of forming the layer, the amount of the foaming agent contained in each of the laminated layers is controlled so that the layers farther away than the layers closer to the axial center are smaller. As a result, foaming is performed in a state where each layer is laminated so that the amount of the foaming agent gradually decreases from the side closer to the axis toward the far side, and the overall appearance is gradually continuous from the inner peripheral side to the outer peripheral side. This is an aspect in which the porosity is reduced.

[Manufacture of hollow circular tube according to the second embodiment]
FIG. 14 is a schematic diagram showing an example of a manufacturing apparatus 500a for the hollow circular tube 100a (schematic view in plan view when the manufacturing apparatus 500a is viewed from the top down). FIG. 15 is a schematic enlarged cross-sectional view of an oval portion indicated by a dotted line in the mold 550a in the manufacturing apparatus 500a. In the following, differences from the manufacture of the hollow circular tube according to the first embodiment will be mainly described, and description of the same points will be omitted.

  As shown in FIG. 14, the manufacturing apparatus 500a of the hollow circular tube 100a melts and kneads the non-foamable resin composition extruder 530 for melt-kneading the non-foamable resin composition 210 ′ and the foamable resin composition. A plurality of extruders are included. In FIG. 14, only two of the first extruder 540a1 and the second extruder 540a2 are displayed among the plurality of extruders for melt-kneading the foamable resin composition, and the other extruders are not shown. A carbon dioxide gas cylinder 510 and a metering pump 520 are connected to each of the plurality of extruders for melt-kneading the foamable resin composition, and different amounts of carbon dioxide gas are supplied to each of the plurality of extruders 540 for the foamable resin composition. The gas pressure is configured to be independently controllable so as to be dispersible.

  In the non-foamable resin composition extruder 530, the non-foamable resin composition 210 '(see FIG. 15) is melt-kneaded. In the first extruder 540a1, the foamable resin composition 221a 'is melt-kneaded, and in the second extruder 540a2, the foamable resin composition 222a' is melt-kneaded. Similarly, the foamable resin composition 223a 'is melt-kneaded in an extruder (not shown). The foamable resin compositions 221a ', 222a', and 223a 'are prepared so that the foaming gas content gradually increases in this order. In another extruder (not shown), the foamable resin composition is similarly melt-kneaded so that the content of the foaming gas is gradually different.

  As shown in FIG. 15, the mold 550 a includes a straight die 551 and crosshead dies 552, 553, and 554. The cross head dies 552, 553, and 554 are provided with vacuum slits VS2, VS3, and VS4, respectively. The mold 550a also has other similar crosshead dies not shown.

  The extruded non-expandable resin composition 210 ′ and expandable resin compositions 221a ′, 222a ′, 223a ′,... Are placed in a mold 550a, respectively, with a straight die 551 and crosshead dies 552, 553, 554,. .. Are formed into a tubular shape and guided from the inside so as to be laminated in the order of the non-foamable resin composition 210 ′, the foamable resin compositions 221a ′, 222a ′, 223a ′,. In this manner, a multilayer tube having a multilayer structure including the non-foamable resin composition 210 'and the foamable resin compositions 221a', 222a ', 223a', ... is prepared in the mold 550a. The number of layers may vary depending on the thickness of the outer layer 220a to be formed, etc., but for example, the number of layers in a range in which any two of 4, 5, 6, 7, 8, 9, 10 are upper and lower limits. It means to be laminated.

  A coating layer 230 (see FIG. 3) is formed on the laminated tube by further laminating a non-foamable resin composition (not shown). Lamination of the non-foamable resin composition for forming the coating layer 230 may be performed in a mold 550, or foaming of foamable resin compositions 221a ', 222a', 223a ', which will be described later. Lamination may be performed after the above.

  Although the coating layer 230 (refer FIG. 3) can be formed by lamination | stacking of a non-foaming resin composition as mentioned above, it is not limited to this method. For example, when the crosshead die for forming the outermost layer of the foamable resin composition is configured as a cooling surface on the surface contacting the outermost foamable resin composition, the outermost foamable resin composition on the cooling surface You may form by cooling the outer peripheral surface of a thing, and solidifying the outer peripheral surface vicinity prior to foaming.

The laminated tube including the non-foamable resin composition 210 ′ and the foamable resin compositions 221a ′, 222a ′, 223a ′,... Is sent out of the mold 550a, and the pressure is reduced. The objects 221a ′, 222a ′, 223a ′, etc. are foamed.
Since foaming occurs in a state in which a large number of foamable resin compositions are laminated in this way, the porosity gradually increases continuously from the inner peripheral side to the outer peripheral side in terms of the overall appearance because each layer becomes familiar with each other near the boundary. It becomes the aspect which becomes large.

  Thereby, the inclination structure (refer FIG. 4) of the porosity in the outer layer 220a (refer FIG. 3) after foaming can be formed. By setting the layer thickness of each layer in consideration of the expansion ratio expected from the amount of the foaming agent, the inclined structures shown in FIGS. 4 (A), 4 (b) and 4 (c) are formed. Can be divided.

[Manufacture of hollow circular tube according to the third embodiment]
FIG. 16 is a schematic enlarged cross-sectional view of a mold 550b in the manufacturing apparatus for the hollow circular tube 100b. An example of the manufacturing apparatus of the hollow circular tube 100b is based on the manufacturing apparatus 500a shown in FIG. 15, and the number of extruders for melt-kneading the foamable resin composition is three, and the three extruders Are similar to the manufacturing apparatus 500a except that the crosshead dies 552, 553, and 554 are connected to each other.

  In three extruders for melt-kneading the foamable resin composition, foamable resin compositions 221b ', 222b' and 223b 'having different amounts of foaming gas are prepared. The foamable resin compositions 221b ', 222b', and 223b 'are prepared in this order so that the content of the foaming gas gradually decreases.

  The extruded non-expandable resin composition 210 ′ and expandable resin compositions 221b ′, 222b ′, and 223b ′ are molded into a tubular shape by a straight die 551 and crosshead dies 552, 553, and 554, respectively, in a mold 550b. Then, the non-foamable resin composition 210 ′ and the foamable resin compositions 221b ′, 222b ′, and 223b ′ are guided in that order from the inside. In this way, a laminated tube including the non-foamable resin composition 210 'and the foamable resin compositions 221b', 222b ', 223b' is prepared in the mold 550b.

  A coating layer 230 (see FIG. 5) is formed on the laminated tube by further laminating a non-foamable resin composition (not shown). Lamination of the non-foamable resin composition for forming the coating layer 230 may be performed in the mold 550 or foaming of the foamable resin compositions 221b ′, 222b ′, and 223b ′ described later is performed. You may laminate after.

  Although the coating layer 230 (refer FIG. 5) can be formed by lamination | stacking of a non-foamable resin composition as mentioned above, it is not limited to this method. For example, when the cross head die 554 for molding the foamable resin composition 223b ′ has a surface contacting the foamable resin composition 223b ′ as the cooling surface S4, the outermost foamable resin on the cooling surface S4. The outer peripheral surface of the composition 223b ′ may be cooled to solidify the vicinity of the outer peripheral surface prior to foaming.

The laminated tube containing the non-foamable resin composition 210 ′ and the foamable resin compositions 221b ′, 222b ′, and 223b ′ is sent out of the mold 550b, whereby the pressure decreases, and the foamable resin composition 221b. ', 222b' and 223b 'foam.
Thus, by foaming in a state where three layers of the foamable resin composition are laminated, the porosity decreases gradually from the inner peripheral side to the outer peripheral side.
Thereby, the gradient structure (refer FIG. 6) of the porosity in the outer layer 220b (FIG. 5) after foaming can be formed.

[Manufacture of hollow circular tube according to the fourth embodiment]
FIG. 17 is a schematic enlarged cross-sectional view of a mold 550c in the manufacturing apparatus for the hollow circular tube 100c. An example of the manufacturing apparatus of the hollow circular tube 100c is based on the manufacturing apparatus 500a shown in FIG. 14, and there are two extruders for melting and kneading the foamable resin composition, and the two extruders. The crosshead dies 552 and 553 are connected to each other, and the surfaces where the crosshead die 552 and the crosshead die 553 are in contact with the outer peripheral surface of the foamable resin composition are both configured as cooling surfaces S2 and S3. The manufacturing apparatus 500a is the same as the manufacturing apparatus 500a except for the above.

  In two extruders for melt-kneading the foamable resin composition, foamable resin compositions 221c 'and 222c' having different amounts of foaming gas are prepared. Specifically, the foamable resin composition 221c 'is prepared such that the foaming gas content is less than the foamable resin composition 222c'.

  The extruded non-foamable resin composition 210 ′ and the foamable resin compositions 221c ′ and 222c ′ are formed into a tubular shape by a straight die 551 and crosshead dies 552 and 553, respectively, in the mold 550c, and non-foamed from the inside. The foamable resin composition 210 ′ and the foamable resin compositions 221c ′ and 222c ′ are guided to be laminated in this order. Thus, a laminated tube including the non-foamable resin composition 210 'and the foamable resin compositions 221c' and 222c 'is prepared in the mold 550c.

  Further, in the mold 550c, the surface where the crosshead die 552 is in contact with the foamable resin composition 221c ′ and the surface where the crosshead die 553 is in contact with the foamable resin composition 222c ′ are the cooling surface S2 and the cooling surface S3, respectively. It is configured. When the foamable resin compositions 221c ′ and 222c ′ are cooled by the cooling surfaces S2 and S3, respectively, the layers of the foamable resin compositions 221c ′ and 222c ′ have lower temperatures on the outer peripheral side and higher temperatures on the inner peripheral side. Creates a temperature gradient. Furthermore, the outer peripheral surface of the foamable resin composition 222c ′ cooled by the cooling surface S3 is solidified prior to foaming, thereby forming a coating layer 230 (see FIG. 7).

  The laminated tube containing the non-foamable resin composition 210 ′ and the foamable resin compositions 221c ′ and 222c ′ is sent out of the mold 550c, so that the pressure decreases, and the foamable resin composition 221c ′. , 222c ′ is foamed. Thereby, the gradient structure (refer FIG. 8) of the porosity in the outer layer 220b (FIG. 7) after foaming can be formed.

[Manufacture of hollow circular tube according to fifth embodiment]
FIG. 18 is a schematic diagram showing an example of a manufacturing apparatus 500d for the hollow circular tube 100d. FIG. 19 is a schematic enlarged cross-sectional view of an elliptical portion indicated by a dotted line in the mold 550d in the manufacturing apparatus 500d.

  As shown in FIG. 18, the manufacturing apparatus 500d for the hollow circular tube 100d includes a plurality of extruders for melt-kneading the foamable resin composition. In FIG. 18, among the plurality of extruders, only three of the first extruder 540d1, the second extruder 540d2, and the third extruder 540d3 are displayed, and the display of the other extruders is omitted.

  In the first extruder 540d1, the foamable resin composition 221d ′ is melt-kneaded, in the second extruder 540d2, the foamable resin composition 222d ′ is melt-kneaded, and in the third extruder 540d3, the foamable resin composition 223d ′ is melt-kneaded. The Similarly, the foamable resin composition 224d 'is melt-kneaded in an extruder (not shown). The foamable resin compositions 221d ', 222d', 223d ', and 224d' are prepared so that the foaming gas content gradually increases in this order. Further, in another extruder not shown, the foamable resin composition is similarly melt-kneaded so that the content of the foaming gas is gradually different.

  As shown in FIG. 19, the mold 550d includes a straight die 551d1 and crosshead dies 552d, 553d, and 554d. The cross head dies 552d, 553d, and 554d are provided with vacuum slits VS2, VS3, and VS4, respectively. The mold 550d also has other similar crosshead dies not shown.

  In the mold 550d, the extruded foamable resin composition 221d ′ is fed by the straight die 551d1, and the foamable resin compositions 222d ′, 223d ′, 224d ′,... Are cross-head dies 552d, 553d, 554d,. And is guided in such a manner that the foamable resin compositions 221d ′, 222d ′, 223d ′, 224d ′,... In this way, a laminated tube containing the foamable resin compositions 221d ', 222d', 223d ', 224d', ... is prepared in the mold 550d.

  The laminated tube is further laminated with a non-foamable resin composition (not shown) to form an inner layer 210d and a covering layer 230 (see FIG. 9). Lamination of the non-foamable resin composition for forming the inner layer 210d may be performed in the mold 550, or foamable resin compositions 221d ′, 222d ′, 223d ′, 224d ′, which will be described later. Lamination may be performed after the foaming is completed. Lamination of the non-foamable resin composition for forming the coating layer 230 may also be performed in the mold 550, and the foamable resin compositions 221d ′, 222d ′, 223d ′, 224d ′, which will be described later,. It may be laminated after foaming is completed. When lamination of the non-foamable resin composition for forming the inner layer 210d and / or the coating layer 230 is performed in the mold 550, the manufacturing apparatus 500d further performs extrusion for extruding the non-foamable resin composition. And a die which is formed into a tubular shape so as to be laminated with foamable resin compositions 221d ′, 222d ′, 223d ′, 224d ′,.

  The inner layer 210d and the covering layer 230 (see FIG. 9) can be formed by laminating the non-foamable resin composition as described above, but are not limited to this method. For example, at least one of the inner layer 210d and the covering layer 230 may be formed by being solidified by being cooled before foaming of the foamable resin compositions 221d ′, 222d ′, 223d ′, 224d ′,. Good. Specifically, when the surface of the inner surface regulating portion 551d2 provided in the mold 550a that is in contact with the inner peripheral surface of the foamable resin composition 221d ′ is configured as the cooling surface S1, the foamable resin composition 221d ′. The inner layer 210d may be formed by cooling the inner peripheral surface of the inner surface with the cooling surface S1 and solidifying the vicinity of the inner peripheral surface prior to foaming. Further, when the crosshead die for forming the outermost layer of the foamable resin composition is configured as a cooling surface on the surface contacting the outermost foamable resin composition, the outermost foamable resin composition on the cooling surface The coating layer 230 may be formed by cooling the outer peripheral surface of an object and solidifying the vicinity of the outer peripheral surface prior to foaming.

The laminated tube containing the expandable resin compositions 221d ′, 222d ′, 223d ′, 224d ′,... Is sent out of the mold 550d, and the pressure is reduced, and the expandable resin compositions 221d ′, 222d ′, 223d ', 224d' ... foam.
Since foaming occurs in a state in which a large number of foamable resin compositions are laminated in this way, the layers become familiar with each other near the boundary, and the void ratio gradually increases from the inner peripheral side to the outer peripheral side in appearance. It becomes an aspect.
Thereby, the inclination structure (refer FIG. 4) of the porosity in the outer layer 220a (refer FIG. 9) after foaming can be formed.

[Other examples]
As described above, the present invention includes arbitrary modes obtained by appropriately combining the embodiments as shown in FIG. The hollow tube of this aspect can be manufactured by a person skilled in the art by appropriately combining the above-described manufacturing methods.

  The present invention includes a hollow tube having an arbitrary cross-sectional shape such as an ellipse, a rectangle, and other polygons in addition to the hollow circular tube having the circular cross-sectional shape described above. The hollow tube can be manufactured using a forming die having a shape that can be formed into a desired cross-sectional shape instead of the straight die and the crosshead die described above.

  As described above, the present invention provides a production method for foaming a foamable resin composition extruded into a tubular shape at the same time as or after creating a temperature gradient in the thickness direction, and foaming. A hollow tube may be produced by one of the production methods in which a plurality of foamable resin compositions having different agent contents are extruded and laminated so as to be laminated in a tubular shape, or a combination of both methods. A hollow tube may be manufactured.

  The present invention is not limited to the hollow tube composed of the three layers of the inner layers 210 and 210d and the outer layers 220, 220a, 220b, and 220c as described above. The hollow tube of the present invention may not have the inner layers 210 and 210d and the covering layer 230, and may be provided with other layers.

  The present invention is not limited to the above-described embodiment in which the outer layers 220, 220a, 220b, and 220c are made of a foamable resin that is an organic foam. The outer layer 220 that is a foamed layer may be an inorganic foam or a mixture of an organic foam and an inorganic foam. The inorganic foam may be appropriately selected by those skilled in the art, and examples thereof include a foam containing cement. In any case, when the hollow tube includes a non-foamed layer, the material of the non-foamed layer may be the same as or different from the foamed layer except that it is non-foamed. Good.

[Effects produced by the embodiment and other examples]
The hollow circular tubes 100, 100a,..., 100d include the outer layers 220, 220a, 220b, and 220c having inclined structures with different porosity in the thickness direction, so that they have at least light weight and mechanical properties. Have

Since the hollow circular tubes 100a, 100c, and 100d include an inclined structure having a high porosity on the side farther from the side closer to the axis of the outer layers 220a and 220c, the hollow circular tubes 100a, 100c, and 100d are more excellent in lightness.
Since the hollow circular tubes 100, 100b, 100c include an inclined structure having a low porosity on the side farther from the side closer to the axis of the outer layer 220, 220b, 220c, the mechanical properties are more excellent.

  The hollow circular tubes 100, 100a, ..., 100d include non-foamed inner layers 210, 210d on the inner peripheral surface of the outer layers 220, 220a, 220b, 220c, but the outer layers 220, 220a, 220b, 220c are lightweight and mechanical. Since it also has specific physical properties, the inner layer can be made as thin as the inner layer 210d.

  Since the outer layers 220, 220a, 220b, and 220c of the hollow circular tubes 100, 100a, ..., 100d can be formed by laminating a plurality of foamable resin compositions containing different amounts of foaming agents and then foaming them, It can manufacture in the aspect from which a porosity differs in the thickness direction.

  Since the hollow circular pipes 100, 100a, 100b, and 100d of the present invention can be manufactured by laminating three or more kinds of foamable resin compositions containing different amounts of foaming agents, like the outer layers 220, 220a, and 200b. Moreover, the gradient of porosity is various.

The hollow circular tube 100 is formed by laminating resin compositions having different amounts of the foaming agent in the number of layers of 4 or more and 10 or less so that the content of the foaming agent is less in the layer farther from the side closer to the axial center. Thus, the outer layer 220 can be formed in such a manner that the porosity gradually decreases toward the side farther from the side closer to the axial center.
The hollow spaces 100a, 100d are resin compositions having different amounts of the foaming agent, and the number of layers is 4 or more and 10 or less so that the content of the foaming agent is greater in the layer farther than the side closer to the axial center. By laminating and foaming, the outer layer 220 can be formed in such a manner that the porosity gradually increases toward the side farther from the side closer to the axial center.

  The manufacturing method of the hollow circular tube using the manufacturing apparatus 500, 500a, 500d has a long-run property because the foaming agent is carbon dioxide, and therefore, recovery of the foaming agent is unnecessary, and no by-product accompanying foaming is generated. Can keep good.

  The production apparatus 500a includes a first extruder 540a1 for extruding the foamable resin compositions 221a ′, 221b ′, and 221c ′ and a second extruder 540a2 for extruding the foamable resin compositions 222a ′, 222b ′, and 222c ′, respectively. Since it is separately connected to the carbon dioxide gas cylinder 510 and the metering pump 520, the carbon dioxide gas content of the foamable resin compositions 221a ′, 221b ′, 221c ′ and the foamable resin compositions 222a ′, 222b ′, 222c ′ is adjusted. The outer layers 220a, 220b, and 220c having an inclined structure with different porosity in the thickness direction can be formed.

  The manufacturing apparatus 500d includes a first extruder 540d1 that extrudes the expandable resin composition 221d ′, a second extruder 540d2 that extrudes the expandable resin composition 222d ′, and a third extruder 540d3 that extrudes the expandable resin composition 223d ′. Since the carbon dioxide gas cylinder 510 and the metering pump 520 are separately connected, the carbon dioxide gas contents of the foamable resin composition 221d ′, the foamable resin composition 222d ′, and the foamable resin composition 223d ′ are different from each other. The outer layer 220d having an inclined structure with a different porosity in the thickness direction can be formed.

[Example 1]
In this embodiment, a hollow circular tube composed of an inner layer made of hard non-foamed resin, an outer layer made of foamed resin laminated on the inner layer, and a coating layer made of hard non-foamed resin laminated on the outer layer is manufactured. did. Baking soda was used as the foaming agent, and the outer layer was formed by co-extrusion and laminating four types of resin compositions with different amounts of baking soda so as to increase the baking soda content as the distance from the axis was increased.

(Determining the amount of baking soda)
A resin composition containing 2.20 parts by weight of sodium bicarbonate with respect to 100 parts by weight of the polyvinyl chloride resin was prepared in advance. The foaming ratio of the foam obtained by foaming this resin composition was 5 times. Furthermore, the foaming efficiency of the resin composition calculated from the density of the obtained foam based on the amount of sodium bicarbonate used and the density of the polyvinyl chloride resin (1.44 g / cm ³ ) was 53% (volume basis). It was.
By proportional calculation based on the above results, the amount of baking soda for achieving the expansion ratio of 2 times is 0.88 parts by weight, the amount of baking soda for achieving the expansion ratio of 3 times is 1.32 parts by weight, and the expansion ratio is 4 times. The amount of baking soda to achieve 1.76 parts by weight, the amount of baking soda to achieve 5 times the expansion ratio is 2.20 parts by weight, and the amount of sodium bicarbonate to achieve the expansion ratio of 7 times is 3.08 parts by weight. It was done.

(Creating a hollow tube)
A resin composition for double foaming (i) containing 0.88 parts by weight of baking soda, a resin composition for double foaming (ii) containing 1.32 parts by weight of sodium bicarbonate, and 100% by weight of 100% by weight of polyvinyl chloride resin. 4.76 parts by weight foaming resin composition (iii), 5 times foaming resin composition (iv) containing 2.20 parts by weight baking soda and 7 times foaming resin composition containing 3.08 parts by weight baking soda The product (v) was prepared and pelletized using a 40 mmφ extruder. Furthermore, a polyvinyl chloride resin composition (I) containing no sodium bicarbonate was also prepared.

  Using an individual 40 mmφ extruder for each resin composition, setting the rotational speed of the extruder and the cylinder temperature to the same setting, resin compositions (I), (i), (ii), (iii) from the shaft center , (Iv), (v), and (I) were co-extruded into the mold so as to be laminated in this order, and then foamed outside the mold. FIG. 20 shows an X-ray CT image of a cross section of the obtained hollow circular tube wall cut along a plane including the axis. In FIG. 20, the portion displayed in white is resin. As shown in FIG. 20, the hollow circular tube manufactured in this example is obtained in a mode in which the lamination boundaries of the plurality of resin compositions are not clear, and the foam layer sandwiched between the non-foamed resin layers is from the axial center. The far side was formed so that the porosity was high.

[Example 2]
Each resin composition is laminated so that the resin composition for 7-fold foaming (v), the resin composition for 5-fold foaming (iv), and the resin composition for 3-fold foaming (ii) are laminated in this order from the axis. Each product was coextruded into a common mold while adjusting the temperature conditions so that the resin temperatures were the same using individual extruders.

  In addition, the extrusion amount ratio of each foaming resin composition is the reciprocal ratio of the foaming ratio (that is, 7-fold foaming resin composition (v): 5-fold foaming resin composition (iv): 3-fold foaming resin) The composition (ii) = 1/7: 1/3: 1/5 (volume basis)), and the take-up speed so that the overall thickness after foaming outside the mold is 6.5 mm. Adjusted.

The hollow circular tube manufactured in this example was obtained in a mode in which the lamination boundaries of the plurality of resin compositions were not clear.
Moreover, the weight per unit length was 0.15 kg / m.

[Comparative Example 1]
A hollow circular tube was prepared by laminating three layers of the 5-fold foaming resin composition (iv).
The weight of the obtained hollow circular tube per unit length was 0.10 kg / m.

<Bending piping test>
Example 2 The hollow circular pipe obtained in Comparative Example 1 was subjected to the following bending pipe test, and the strain capable of bending pipe construction was measured. In the bending pipe test, a 4 m sample tube is positioned by 50 cm from one end face of the sample tube (position A), the position of the midpoint in the axial direction of the sample tube (position B), and the sample tube by three pipe clamps. Stop at three points of 50cm from the other end face (position C), fix the positions A and C on the reference line and move the position B so that the distance from the reference line is 5cm increments. The limit of possible separation from the reference line was confirmed. In the bending pipe test, cracks occurred when the distance from the reference line exceeded the limit. Table 1 shows the test results (average value of three times) of measuring the limit of the separation distance. In Table 1, the mobility is a relative amount based on the limit (100%) of the separation distance in Comparative Example 1.

  As shown in Table 1, the result of the bending pipe test was good in the sample tube of Example 2 having an expansion rate gradient in which the axial center side is sparse and the outer peripheral surface side is dense.

[Example 3]
Polyvinyl chloride resin composition not containing sodium bicarbonate (I), resin composition for 2-fold foaming (i), resin composition for 3-fold foaming (ii), resin composition for 5-fold foaming (iv) In order for the polyvinyl chloride resin composition (I) not containing sodium bicarbonate to be laminated in this order, use individual extruders for each resin composition, and set the temperature conditions so that the resin temperatures are equal to each other. Co-extruded into a common mold while adjusting.

  In addition, the extrusion amount ratio of each foaming resin composition is the reciprocal ratio of the foaming ratio (that is, the resin composition for 2 times foaming (i): the resin composition for 3 times foaming (ii): the resin for 5 times foaming. The composition (iv) = 1/2: 1/3: 1/5 (volume basis)), and the take-up speed so that the overall thickness after foaming outside the mold is 6.5 mm. Adjusted. The hard layer on the axial center side and the hard layer on the outer peripheral side produced from the polyvinyl chloride resin composition (I) not containing sodium bicarbonate were 2 mm and 0.5 mm, respectively.

The hollow circular tube manufactured in this example was obtained in a mode in which the lamination boundaries of the plurality of resin compositions were not clear.
Moreover, the weight per unit length was 0.45 kg / m.

[Comparative Example 2]
Polyvinyl chloride resin composition not containing baking soda (I), 3 times foaming resin composition (ii), 3 times foaming resin composition (ii), 3 times foaming resin composition Except that the product (ii) and the polyvinyl chloride resin composition (I) containing no baking soda were used, the hollow ratio was the same as in Example 3 except that the extrusion rate ratio of the three-fold foaming resin composition (ii) was the same. A circular tube was manufactured.

  The total thickness after foaming is 6.5 mm, and the hard layer on the axial center side and the hard layer on the outer peripheral side produced from the polyvinyl chloride resin composition (I) not containing sodium bicarbonate are 2 mm and 0.00 mm, respectively. It was 5 mm. Furthermore, the weight per unit length was 0.46 kg / m.

<Various physical property evaluation>
As described above, the thicknesses of the foam layers of the sample tubes of Example 3 and Comparative Example 2 are both 4 mm. In this case, a calculation result indicating that the thermal conductivity is comparable (0.09 W / (m K)) was obtained. Furthermore, as a result of subjecting each sample tube to a dew condensation performance test, it was confirmed that the dew condensation performance was equivalent.

Further, an internal pressure test was performed on each sample tube. In the internal pressure test, one end face of the sample tube was sealed, water pressure was applied to the inside, and the internal pressure (water pressure resistance) at which the sample tube was broken was measured.
The results of the internal pressure test (implemented 3 times) are shown in Table 2 below.

  As shown in Table 2, even though the weight and the dew condensation performance of the sample tube are almost the same, the water pressure resistance is that of the foaming layer of Example 3 in which the foamed layer has a foaming rate gradient in which the axis side is dense and the outer peripheral side is sparse. The sample tube was good.

[Correspondence Relationship Between Each Part in Embodiment and Other Examples and Each Component in Claim]
The hollow circular tubes 100, 100a, ..., 100d correspond to "hollow tubes", the outer layers 220, 220a, 220b, 220c correspond to "tubular foams", the inner layers 210, 210d correspond to "inner layers", The coating layer 230 corresponds to the “coating layer”, the production apparatuses 500a and 500d correspond to the “hollow tube production apparatus”, and the foamable resin compositions 221a ′, 221b ′, 221c ′, and 221d ′ correspond to “first”. The foamable resin compositions 222a ′, 222b ′, 222c ′, and 222d ′ correspond to the “second foamable material”, and the first extruders 540a1 and 540d1 correspond to the “first extrusion material”. The second extruders 540a2 and 540d2 correspond to the “second extruder”, the carbon dioxide gas cylinder 510 and the metering pump 520 correspond to the “first gas supply unit” and the “second gas supply unit”, Crosshead die 552, Toretodai 551d1 corresponds to the "first formation part", crosshead die 553,552d corresponds to the "second forming unit".

  Although some embodiments of the present invention are as described above, various other embodiments can be made without departing from the spirit of the present invention. Therefore, these embodiments are merely examples in all respects and should not be interpreted in a limited manner. Further, all modifications belonging to the equivalent scope of the claims are within the scope of the present invention.

100, 100a, ..., 100d Hollow circular tube 210, 210d Inner layer 220, 220a, 220b, 220c Outer layer 230 Coating layer 500a, 500d Manufacturing apparatus for hollow circular tube 221a ', 221b', 221c ', 221d' Expandable resin composition 222a ', 222b', 222c ', 222d' Expandable resin composition 540a1, 540d1 First extruder 540a2, 540d2 Second extruder 510 Carbon dioxide cylinder 520 Metering pump 552, 553, 552d Crosshead die 551d1 Straight die

Claims (7)

By laminating at least the first foamable material containing a predetermined amount of foaming agent and the second foamable material containing an amount of foaming agent different from the predetermined amount in a tubular shape, at least the first foamable material. And a laminating step of obtaining a tubular laminate of foamable material comprising the second foamable material;
A foaming step of obtaining a foamed layer by foaming the tubular laminate of the foamable material,
The foam layer has an inclined structure in which the porosity gradually varies in the thickness direction, and the inclined structure has a structure having a higher porosity on the side farther from the side closer to the axis of the foam layer, or A method for producing a hollow tube, which has a structure having a low porosity on a side farther from the side closer to the axis of the foam layer.   The method for producing a hollow tube according to claim 1, wherein the number of layers of the tubular laminate of the foamable material is 3 or more.   The number of layers of the tubular laminate of the foamable material is 4 or more and 10 or less, and the foamable material constituting each layer is more in the layer farther from the side closer to the axis of the tubular laminate. The manufacturing method of the hollow tube of Claim 1 or 2 prepared so that content may increase.   The number of layers of the tubular laminate of the foamable material is 4 or more and 10 or less, and the foamable material constituting each layer is more in the layer farther from the side closer to the axis of the tubular laminate. The manufacturing method of the hollow tube of Claim 1 or 2 prepared so that content may become small.   The manufacturing method of the hollow tube of any one of Claim 1 to 4 which further includes the process of laminating | stacking a non-foamable material on the said tubular laminated body.   The manufacturing method of the hollow tube of any one of Claim 1 to 5 whose said foaming agent is a solid thermal decomposable foaming agent. The manufacturing method of the hollow tube of any one of Claim 1 to 5 whose said foaming agent is inorganic gas.