JP7413461B2 - hollow circular tube - Google Patents

Description

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

In recent years, pipes made of foamed resin (foamed pipes) are increasingly being used as drainage pipes in apartments or buildings. For foam pipes, the foaming ratio is appropriately selected to reduce the specific gravity of the foam in order to reduce the weight of the entire pipe. Foamed pipes also have the advantage of being able to reduce the sound of running water due to the soundproofing effect of the foam.

For example, in Patent Document 1 (Japanese Unexamined Patent Publication No. 2007-283733), a vinyl chloride resin foam layer with few open cells and homogeneous cells and a vinyl chloride resin with a substantially non-foamed structure are laminated. discloses a polyvinyl chloride resin foam tube that prevents water from entering between the two layers when joined to a joint, etc., and has excellent heat insulation effects, dew condensation prevention effects, and the like.

The vinyl chloride resin foam tube described in Patent Document 1 (Japanese Unexamined Patent Publication No. 2007-283733) is an extrusion-molded 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-foamed structure, and the outer skin layer has a thickness of 0.2 to 1.5 mm and has a substantially non-foamed structure, In addition, the cells in the foam layer are not substantially connected in the 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:

Further, Patent Document 2 (Japanese Unexamined Patent Publication No. 11-257548) discloses a sound-muffling pipe that is made for the purpose of providing a sound-muffling pipe that is excellent in workability and productivity and has a sufficient sound-damping effect. There is.

The sound-muffling pipe described in Patent Document 2 (Japanese Unexamined Patent Publication No. 11-257548) is a sound-muffling pipe that is applied to water supply pipes and drain pipes, is formed from a vinyl chloride resin composition, and has an expansion ratio of 1.2 to 1.2. It is characterized by being composed of an intermediate tube made of a 5 times larger foam, and an outer tube and an inner tube made of a soft vinyl chloride resin composition.

Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2002-234066) describes a method comprising an inner layer and an outer layer formed from a non-foamed foamed thermoplastic resin composition, and an intermediate layer formed from a foamed thermoplastic resin composition. A method for manufacturing a resin pipe with a three-layer structure is disclosed, in which the resin pipe is manufactured so that the wall thickness of the finished resin pipe is always uniform.

The method for manufacturing a resin pipe with a three-layer structure described in Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2002-234066) includes a foamed thermoplastic resin composition that forms an intermediate layer between unfoamed thermoplastic resin compositions that form an inner layer and an outer layer. A three-layered unsolidified tubular body with an object interposed therein 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 for manufacturing a three-layer resin pipe, the amount of blowing agent added to the thermoplastic resin forming the intermediate layer is determined by the amount of blowing agent added to the thermoplastic resin forming the intermediate layer to achieve the specified product dimensions when molded without restricting the radial expansion of the resin pipe. The amount added is greater than the theoretical addition amount to obtain the foaming ratio, and a resin tube is formed by sizing to the specified finished dimensions against foaming pressure using a tube for forming the outer surface of the tube and a core for forming the inner surface of the tube. It is characterized by the fact that

Patent Document 4 (Japanese Unexamined Patent Publication No. 9-222185) discloses a composite pipe that has excellent heat insulation and heat retention functions without thermal deformation of the coating layer or water absorption from the surface even when used at high temperatures, and a method for manufacturing the same. ing.

The composite pipe described in Patent Document 4 (Japanese Unexamined Patent Publication 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 a vinyl chloride resin. , the covering layer is composed of a foamed inner layer portion and a substantially non-foamed surface layer portion formed around the outer periphery of the foamed inner layer portion, and the inner layer portion and the surface layer portion are integrally formed. It is something.

Patent Document 5 (Japanese Unexamined Patent Publication No. 7-217934) discloses a drain pipe for draining water from an air conditioner that can reliably prevent dew condensation on the surface and is easy to install.

The drain pipe described in Patent Document 5 (Japanese Unexamined Patent Publication No. 7-217934) is made of closed-cell foamed vinyl chloride resin with an average expansion ratio of 2 to 7 times, and the inner peripheral surface of this foamed vinyl chloride resin A skin layer with a thickness of 0.2 to 0.5 mm is provided on the foamed vinyl chloride resin, and a skin layer with 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:

Japanese Patent Application Publication No. 2007-283733 Japanese Patent Application Publication No. 11-257548 Japanese Patent Application Publication No. 2002-234066 Japanese Patent Application Publication No. 9-222185 Japanese Patent Application Publication No. 7-217934

As mentioned above, many developments have been made regarding various foamed pipes. All foam pipes are usually manufactured with the aim of uniformizing the expansion ratio of the foam and homogenizing the bubbles from the viewpoint of dimensional stability and the like.
The expansion ratio of the foam layer in a foam pipe is set in consideration of the strength and weight of the entire pipe. For example, when the foaming ratio is increased, the mechanical properties such as bending strength and impact resistance of the pipe decrease, so it is necessary to ensure the overall strength by laminating both the inside and outside of the foam layer with non-foamed resin. . In order to ensure strength, the thickness of the non-foamed resin layer needs to be large. Therefore, the weight of the entire pipe inevitably increases, making it difficult to achieve the 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 that can satisfy multifunctionality that combines at least light weight and mechanical properties.

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

Since the hollow tube of the present invention includes a foam, it has excellent lightness. Furthermore, since the foam has a gradient structure with different porosity in the thickness direction, it has excellent mechanical properties.
In this way, the hollow tube of the present invention has multifunctionality that combines at least light weight and mechanical properties.

Note that multifunctionality refers to characteristics that combine at least lightness and mechanical properties, and in addition, depending on how the hollow tube is used, it also has properties such as sound deadening, heat retention, insulation, dew condensation prevention, and weather resistance. It can also refer to the characteristics it exhibits. Note that the mechanical properties include at least one of bending properties (flexibility), internal pressure resistance properties, and flatness (cushioning properties).

In the present invention, a gradient structure in which the porosity differs in the thickness direction refers to a structure in which the porosity shows a gradient in the thickness direction, and more specifically, a structure in which the porosity gradually changes in the thickness direction. , a mode in which the porosity changes stepwise in the thickness direction, and a mode in which these are mixed.

(2)
The graded structure may include a structure in which the porosity is higher on the side farther from the axis of the tubular foam than on the side closer to the axis.

This improves the mechanical properties (eg, internal pressure resistance) of the hollow tube.

(3)
The graded structure may include a structure in which the porosity is lower on the side farther from the axis of the tubular foam than on the side closer to the axis.

This improves the mechanical properties (eg, bending properties) of the hollow tube.

(4)
The graded structure may include a laminated structure of multiple layers having different porosity.
This allows the porosity gradient to be varied.

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

In the present invention, since the tubular foam has not only lightness but also mechanical properties, the wall thickness of the inner layer tube can be reduced in this way.

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

This allows the outer layer of the tubular foam to be covered by the covering layer.
The thickness of the coating layer may be 10% or more and 30% or less of the 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 in this way.

(7)
The tubular foam may be an inorganic foam and/or an organic foam.

In this way, the hollow tube of the present invention can be implemented with either an inorganic foam or an organic foam, or even a mixture of an inorganic foam and an organic foam.

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

In this way, the hollow tube of the present invention can be realized using 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 lamination step, at least a first foamable material containing a predetermined amount of a foaming agent and a second foamable material containing a foaming agent in an amount different from the predetermined amount are laminated in a tubular shape. A tubular laminate of foamable material is obtained that includes a foamable material and a second foamable material. In the foaming step, a tubular foam is obtained by foaming a tubular laminate of foamable material.

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

(10)
In the hollow tube manufacturing method of the present invention, the number of laminated tubular laminates of foamable materials may be three or more.
This produces hollow tubes containing tubular foams with varying porosity gradients.

(11)
In the method for manufacturing a hollow tube of the present invention, the number of laminated layers of the tubular laminate made of foamable material is 4 or more and 10 or less, and the foamable material constituting each layer is on the side farther from the axis of the tubular laminate than on the side closer to the axis of the tubular laminate. The foaming agent content may be adjusted to be higher in the layer.

This produces a hollow tube including a tubular foam having a structure in which the porosity is higher on the side farther from the axis than on the side closer to the axis.

(12)
In the method for manufacturing a hollow tube of the present invention, the number of laminated layers of the tubular laminate made of foamable material is 4 or more and 10 or less, and the foamed material constituting each layer is on the side farther from the axis of the tubular laminate than on the side closer to the axis of the tubular laminate. The foaming agent content may be adjusted to be lower in the layer.

This produces a hollow tube including a tubular foam having a structure in which the porosity is lower on the side farther from the axis than on the side closer to the axis.

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

This produces a hollow tube in which the tubular foam is laminated with the non-foamed material.
A non-foam layer may be laminated to the inside and/or outside of the tubular foam.

(14)
In the hollow tube manufacturing method of the present invention, the blowing agent may be a solid thermally decomposable blowing agent.
In this case, the amount of blowing agent can be easily adjusted.

(15)
In the hollow tube manufacturing method of the present invention, the blowing agent may be an inorganic gas.
In this case, good long-run performance can be maintained.

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

(17)
A hollow tube manufacturing apparatus according to still another aspect includes a first extruder that extrudes a first foamable material, a first gas supply unit that supplies foaming gas to the first foamable material, and a first extruder that extrudes a first foamable material. a first molding section that molds the foamable material into a tubular shape; a second extruder that extrudes the second foamable material; a second gas supply section that supplies foaming gas to the second foamable material; It includes at least a second molded part formed into a tubular shape so as to be laminated on the first foamable material. Furthermore, the first gas supply section and the second gas supply section are configured to be able to independently control the gas pressures of each other.

This makes it possible to obtain a tubular foam having a gradient structure in which the porosity differs in the thickness direction.

FIG. 1 is a schematic cross-sectional view showing an example of a hollow circular tube according to the first embodiment. It is a graph which shows the gradient structure of the foam layer of the hollow circular pipe concerning 1st Embodiment. It is a typical sectional view showing an example of a hollow circular tube concerning a 2nd embodiment. It is a graph which shows the gradient structure of the foam layer of the hollow circular pipe concerning 2nd Embodiment. It is a typical sectional view showing an example of a hollow circular tube concerning a 3rd embodiment. It is a graph which shows the gradient structure of the foam layer of the hollow circular pipe concerning 3rd Embodiment. It is a typical sectional view showing an example of a hollow circular tube concerning a 4th embodiment. It is a graph which shows the gradient structure of the foam layer of the hollow circular pipe concerning 4th Embodiment. It is a typical sectional view showing an example of a hollow circular tube concerning a 5th embodiment. It is a graph which shows the gradient structure of the foam layer of a hollow circular pipe in other examples. FIG. 1 is a schematic diagram showing an example of a hollow circular tube manufacturing apparatus. FIG. 1 is a schematic diagram showing an example of a hollow circular tube manufacturing apparatus. FIG. 2 is a schematic enlarged sectional view of a mold for a hollow circular tube. It is a schematic diagram which shows the other example of the manufacturing apparatus of a hollow circular tube. FIG. 3 is a schematic enlarged sectional view showing another example of a mold for a hollow circular tube. FIG. 3 is a schematic enlarged sectional view showing another example of a mold for a hollow circular tube. FIG. 3 is a schematic enlarged sectional view showing another example of a mold for a hollow circular tube. It is a schematic diagram which shows the other example of the manufacturing apparatus of a hollow circular tube. FIG. 3 is a schematic enlarged sectional view showing another example of a mold for a hollow circular tube. It is an X-ray CT image of a cross section of a hollow circular tube manufactured in an example.

Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same parts are given the same reference numerals. In addition, when the symbols are the same, their 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 consists of an inner layer 210, an outer layer 220, and a covering 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 non-foamed hard resin. Specifically, the hard resin may be hard vinyl chloride resin (PVC). More specifically, hard vinyl chloride resins include, in addition to homopolymers of vinyl chloride monomers, for example, chlorinated vinyl chloride resins, vinyl chloride monomers, and polymerizable monomers other than vinyl chloride monomers. copolymers with vinyl chloride monomers, and graft copolymers in which vinyl chloride monomers are grafted onto polymers other than vinyl chloride resins. The hard vinyl chloride resin may contain a rubber component in the form of ultrafine particles. In this case, impact resistance can be improved. The ultrafine particle rubber component may be physically or chemically bonded to the vinyl chloride resin.

Note that the non-foamable resin forming the inner layer 210 is not limited to the above-mentioned 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, (meth)acrylic resin, and the like. The above resins may be used alone or in combination of two or more.

The thickness (thickness) of the inner layer 210 in the stacking direction may be 10% or more and 70% or less of the thickness of the outer layer 220, which will be described later. In addition, the upper and lower limits of the thickness of the inner layer 210 in the stacking direction are set to any two percentage values of 10%, 20%, 30%, 40%, 50%, 60%, and 70% of the wall thickness of the outer layer 220. The thickness may be within a range. More specifically, it may be, for example, 0.3 mm or more and 10 mm or less. However, the thickness (thickness) of the inner layer 210 in the stacking direction may be less than 0.3 mm if it does not cause any problem in terms of strength, and may not exceed 10 mm if it does not cause any problem in the construction surface. There may be.

(outer layer and covering layer)
The outer layer 220 shown in FIG. 1 is formed by laminating the outer periphery of the inner layer 210. The outer layer 220 is made of foamed resin having many 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 that makes up the outer layer 220 may be the same as the resin that makes up the inner layer 210, except that voids are included, or it may be a different resin.

FIG. 2 is a graph schematically showing the relationship between the distance from the axis 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 a gradient structure in which the porosity gradually changes in the thickness direction. Specifically, the further away from the axis (closer to the outer periphery) the smaller the porosity (more dense), and the closer to the axis (closer to the inner periphery) the larger the porosity (more sparse). Porosity refers to the volume occupied by 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 manner in which the porosity changes in the outer layer 220 is arbitrary. For example, as shown in FIG. 2(A), the rate of change in porosity may be constant throughout the wall thickness, or as shown in FIG. 2(B) and FIG. 2(C), the porosity may vary. You may. In the case shown in FIG. 2(B), the closer to the inner periphery, the larger the variation in porosity is, and in the case shown in FIG. 2(C), the closer to the outer periphery, the larger the variation in porosity is.

The average porosity of the outer layer 220 is, for example, 50% or more and 80% or less, and is, 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, the heat insulation performance or dew condensation prevention performance is also good, for example. 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 the flatness when cracks or cracks occur in a flatness test) is easily ensured. In this way, the inclined structure can ensure excellent mechanical strength in relation to the average porosity.

The thickness of the outer layer 220 is arbitrary, and is, for example, 2 mm or more, preferably 4 mm or more. By being 2 mm or more, an inclined structure can be effectively ensured. Further, by having a wall thickness of 4 mm or more, the above-mentioned inclined structure can be provided more easily. Although the upper limit of the thickness of the outer layer 220 is not limited, an example is 15 mm from the viewpoint of light weight.

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, as for the size of the voids, it is preferable that the average cell diameter is in the range 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 cell diameters in cross sections perpendicular to the axial direction are accumulated from the smallest. Note that the cell diameters of the illustrated voids are all shown in the same size because they are schematically expressed to express the porosity, but the cell diameters are not limited to such an embodiment. For example, the structure may be such that the higher the porosity, the larger the cell diameter, and the lower the porosity, the smaller the cell diameter.

Furthermore, the foamed resin forming the outer layer 220 may further contain heat stabilizers, processing aids, lubricants, impact modifiers, fillers, antioxidants, ultraviolet absorbers, light stabilizers, pigments, etc. may be included as appropriate.

Further, in this embodiment, the thickness of the covering layer 230 may be 5% or more and 30% or less of the thickness of the outer layer 220. The thickness of the covering layer 230 is within a range whose upper and lower limits are any two of the percentage values of 5%, 10%, 15%, 20%, 25%, and 30% of the thickness of the outer layer 220. There may be. Specifically, it is preferably 0.1 mm or more and 1.5 mm or less, for example, 0.5 mm.
When the thickness of the coating 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 coating layer 230 can be formed within the wall thickness of the hollow circular tube 100. The occupied portion of the hollow cylinder 100 can be made small, the porosity can be preferably ensured, and the weight of the hollow circular tube 100 can be improved.

The covering layer 230 may be made of the same resin as the outer layer 220 except that it is non-foamed, or may be made of 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 100a mainly consists of an inner layer 210, an outer layer 220a, and a covering 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 explained.

FIG. 4 is a graph schematically showing the relationship between the distance from the axis 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 larger porosity (more sparse) as it moves away from the axis (closer to the outer periphery), and the porosity increases as it gets closer to the axis (closer to the inner periphery). It has a sloped structure in which the density is smaller (more dense).

The manner in which the porosity changes in the outer layer 220a is arbitrary. For example, as shown in FIG. 4(A), the rate of change in porosity may be constant throughout the wall thickness, or as shown in FIG. 4(B) and FIG. 4(C), the porosity may vary. You may. In the case shown in FIG. 4(B), the closer to the outer periphery, the larger the variation in porosity is, and in the case shown in FIG. 4(C), the closer to the inner periphery, the larger the variation in porosity is.

[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 100b mainly consists of an inner layer 210, an outer layer 220b, and a covering layer 230. The hollow circular tube 100b is the same as the hollow circular tube 100 of the first embodiment except that the foaming mode of the outer layer 220b is different. Hereinafter, differences from the first embodiment will be explained.

As shown in FIG. 5, the outer layer 220b has a laminated structure of foam layers 221b, 222b, and 223c each having a different porosity. The foam layers 221b, 222b, and 223c may be made of the same resin except for their foaming rates, or may be made of different resins. An example of a case where the foamed layers 221b, 222b, and 223c are each made of different resins is a mode in which the blended amounts of functional resins are different in each foamed layer. In this case, by configuring the foamed layers 221b, 222b, and 223c to increase or decrease the blending amount of the functional resin or additive that exhibits a specific function, the gradient structure (gradient function gender). The specific function is not particularly limited, but may include, for example, 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 a gradient structure in which the porosity gradually decreases from the inner periphery to the outer periphery in the order of the foamed layers 221b, 222b, and 223b.

When a plurality of foam layers with different foaming rates are laminated as in this embodiment, an example is shown in FIG. 6(A) in which the boundaries between adjacent foam layers are relatively clear due to the difference in porosity. However, it is not limited to this embodiment. The boundaries between adjacent foam layers are not necessarily clear, and as shown in Figure 6(B), while maintaining a gradient structure in which the porosity changes stepwise, the porosity changes near the boundaries between the foam layers. may be more gradual.

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

The foam layer is multi-layered (for example, the number of layers is within the range of upper and lower limits of any two of 4, 5, 6, 7, 8, 9, or 10), and the porosity decreases sequentially from the inner periphery to the outer periphery. When stacked, the boundaries of the foam layer tubes are no longer clear, so that the porosity appears to change gradually and continuously, as shown in the first embodiment, as shown in FIG. 6(C). In some cases, the structure may be a sloped 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 100c mainly consists of an inner layer 210, an outer layer 220c, and a covering 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 explained.

The outer layer 220c has a structure in which two outer layers 220 of the first embodiment are laminated. 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 axis of the hollow circular tube 100c and the porosity of the outer layer 220c. The foam layers 221c and 222c are each configured such that the porosity gradually decreases from the inner circumferential side to the outer circumferential side. Therefore, the entire thickness of the outer layer 220c includes two inclined structures in which the porosity gradually decreases from the inner circumferential side to the outer circumferential side.

In this embodiment, an example was given in which the foam layers 221c and 222c have different average porosity (see FIG. 8(A)), but the present invention is not limited to this embodiment. The foam layers 221c and 222c may have the same average porosity (see FIG. 8(B)). 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 circumferential side to the outer circumferential side.

In this embodiment, the foam layers 221c and 222c may be made of the same resin except for having different average porosity, or may be made of different resins. An example of a case where the foam layers 221c and 222c are each made of different resins is a mode in which the blended amounts of functional resins are different in each foam layer. In this case, by configuring the foamed layers 221c and 222c to increase or decrease the blending amount of the functional resin that exhibits a specific function, the specific function is also provided with a graded structure (graded functionality). be able to.

In this embodiment, two foam layers 221c and 222c each having a porosity gradient structure are laminated, but the number of laminated layers is not limited to this, and more foam layers may be laminated. You can leave it there. The number of laminated layers may be 2 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 consists of an inner layer 210d, an outer layer 220a, and a covering 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 explained.

The hollow circular tube 100d has a relatively thin non-foamed inner layer 210d. The inner layer 210d has the same thickness as the covering layer 230 (5% or more and 30% or less of the thickness of the outer layer 220a, or any two of 5%, 10%, 15%, 20%, 25%, and 30%). It is provided within a range with upper and lower limits, specifically, for example, from 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 may be made of different resins.

The hollow circular tube 100d has an outer layer 220a between the inner layer 210d, which is a thin non-foamed layer, and the covering layer 230, and the porosity gradually increases from the inner circumference to the outer circumference, so it was cut along a plane perpendicular to the axis. The cross section of the case is similar to bamboo. Therefore, the hollow circular tube 100d has a function similar to that of bamboo in terms of having voids.

In addition to the embodiments described above, the present invention includes any aspect in which the embodiments are combined as appropriate. 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. 10(A) shows an embodiment in which the outer layer 220a of the second embodiment is arranged on the inner circumferential side and the outer layer 220 of the first embodiment is arranged on the outer circumferential side, and FIG. A mode is shown in which the outer layer 220 of the first embodiment is disposed on the circumferential side and the outer layer 220a of the second embodiment is disposed on the outer circumferential side.

[Manufacture of hollow circular tube according to the first embodiment]
(Outline of hollow circular tube manufacturing equipment)
11 and 12 are schematic diagrams showing an example of a manufacturing apparatus 500 for the hollow circular tube 100.
FIG. 11 is a plan view of the manufacturing apparatus 500 for the hollow circular tube 100 viewed from above and downward, 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, an extruder 530 for non-foaming resin compositions, an extruder 540 for foamable resin compositions, a mold 550, and a tube outer surface. It includes a regulating device 560, a cooling water tank 570, a pulling machine 580, and a cutting machine 590.

FIG. 13 is a schematic enlarged sectional view of an elliptical portion of the mold 550 in the manufacturing apparatus 500, indicated by a dotted line in the figure.

(Manufacturing method of 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-foaming resin composition extruder 530, a non-foaming 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 a foamable resin composition 220' (described later) in a mold 550, and then sent out of the mold 550 and solidified in a cooling water tank 570. This becomes the inner layer 210 (see FIG. 1).

An example of a vinyl chloride resin composition includes 100 parts by weight of vinyl chloride resin, 2.0 parts by weight of lead-based heat stabilizer, 0.5 parts by weight of polyethylene wax, 2.0 parts by weight of acrylic processing aid, Examples include resin compositions obtained by feeding 0.7 parts by weight of ester wax, 3.0 parts by weight of calcium carbonate, and 0.5 parts by weight of pigment into a Henschel mixer or the like and mixing them. Furthermore, the non-foamable resin composition may contain a rubber component in the form of ultrafine particles. The ultrafine particle rubber component may be physically or chemically bonded to the vinyl chloride resin.

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

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

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, an embodiment is shown in which carbon dioxide, which is a foaming gas, is used as a foaming agent, but the present invention is not limited to this. Examples of the foaming gas include carbon dioxide gas, inorganic gases such as nitrogen gas, and organic gases such as butane gas and fluorocarbon gases. These foaming gases may be used alone or in combination of two or more. Note that inorganic gases are preferable because they do not need to be recovered and do not generate by-decomposition products, so they have excellent long-run properties.

Further, another example of the blowing agent is a pyrolyzable blowing agent. Examples of thermally decomposable blowing agents include thermally decomposable inorganic blowing agents such as sodium bicarbonate, ammonium bicarbonate, and ammonium carbonate, and nitroso compounds such as N,N': dinitrosoterephthalamide, azodicarbonamide, and azobis. Examples include thermally decomposable organic blowing agents such as azo compounds such as isobutyronitrile, and sulfonyl hydrazide compounds such as benzenesulfonyl hydrazide and toluenesulfonyl hydrazide. These thermally decomposable foaming agents may be used alone or in combination of two or more. In this case, the resin is foamed using gas generated by the thermal decomposition reaction of the foaming agent. In addition, a solid thermally decomposable foaming agent is preferable in that the content in the resin composition can be easily adjusted.

Further, other examples of blowing agents include solvent-based blowing agents. In this case, the resin is foamed using gas generated by vaporization due to heat or pressure release. Examples of the solvent-type blowing agent include solvents with 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 blowing agent, a blowing gas, a pyrolytic blowing agent, and a solvent blowing agent can be used together in any combination. When no foaming gas is used, the manufacturing apparatus 500 does not require the carbon dioxide gas cylinder 510 and the metering pump 520.

The amount of blowing agent can be adjusted depending on the desired expansion ratio. To obtain a foam with a larger expansion ratio or porosity, a larger amount of blowing agent can be used, and to obtain a foam with a lower expansion ratio or porosity, a lower amount of blowing agent can be 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 crosshead die 552. In the mold 550, the non-foamable resin composition 210' melt-kneaded by the extruder 530 for non-foamable resin compositions is molded into a tubular shape through a straight die 551, and is then molded into a tube shape by the extruder 540 for foamable resin compositions. The melt-kneaded foamable resin composition 220' is formed into a tubular shape through a crosshead die 552 so as to be laminated on the outer periphery of the tubular non-foamable resin composition 210'. In this way, a laminated tube containing the non-foamable resin composition 210' and the foamable resin composition 220' is prepared within the mold 550.

A coating layer 230 (see FIG. 1) is formed on the laminated tube by further laminating a non-foaming resin composition (not shown). Lamination of the non-foamable resin composition for forming the coating layer 230 may be performed within the mold 550, or may be laminated after the foamable resin composition 220' described below is foamed. good.

The covering layer 230 (see FIG. 1) can be formed by laminating non-foaming resin compositions as described above, but is not limited to this method. For example, when the surface of the crosshead die 552 in contact with the foamable resin composition 220' is configured as the cooling surface S2, by cooling the outer peripheral surface of the foamable resin composition 220' with the cooling surface S2, the outer peripheral surface of the foamable resin composition 220' is cooled. It may be formed by solidifying the area near the surface prior to foaming.

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

During foaming, the temperature control unit (not shown) included in the tube outer surface adjusting device 560 cools the layer surface of the foamable resin composition 220', so that the foaming property is adjusted such that the outer circumference side is lower temperature and the inner circumference side is higher temperature. A temperature gradient is created in the layer of resin composition 220'. Thereby, the porosity gradient structure (see FIG. 2) in the outer layer 220 (see FIG. 1) after foaming can be adjusted.

The laminated tube sent out from the tube outer surface conditioning device 560 is sufficiently cooled and solidified in the cooling water tank 570 to become the hollow circular tube 100. In this embodiment, the refrigerant used in the cooling water tank 570 is water, but liquids and gases may be used as long as the refrigerant is not corrosive to the product and has good fluidity and heat exchangeability. No question. Examples include air, oil, polyethylene glycol, and the like.
The hollow circular tube 100 is taken up by a taking machine 580 and cut into a suitable length by a cutting machine 590.

In the above, an example was given in which the sloped structure of the outer layer 220 in the hollow circular tube 100 is formed by a method of varying the expansion ratio in the wall thickness direction by temperature control, but the method of forming the outer layer 220 is limited to this method. It's not a thing. In addition to a method using temperature control, it can also be formed by a method in which the foaming ratio is varied in the thickness direction by laminating a large number of layers containing different amounts of foaming agents. The term "multilayer" may vary depending on the thickness of the outer layer 220 to be formed, but for example, the number of layers is within a range of 4, 5, 6, 7, 8, 9, or 10, with the upper and lower limits being any two of the number of layers. It means to be layered.

The method of varying the foaming ratio in the wall thickness direction by laminating a large number of layers containing different amounts of foaming agents will be described in detail in the production of the hollow circular tube according to the second embodiment, which will be described later. , the amount of blowing agent contained in each laminated layer is controlled so that the amount of blowing agent contained in each layer is smaller in the layer farther from the axis than in the layer closer to the axis. As a result, each layer is laminated and foamed so that the amount of foaming agent gradually decreases from the side closer to the axis to the side farther from the axis, and the overall appearance appears to be gradually continuous from the inner circumference to the outer circumference. The porosity becomes smaller.

[Manufacture of hollow circular tube according to second embodiment]
FIG. 14 is a schematic diagram illustrating an example of a manufacturing apparatus 500a for the hollow circular tube 100a (a schematic diagram in a plan view when viewing the manufacturing apparatus 500a from above downward). FIG. 15 is a schematic enlarged sectional view of an elliptical portion of a mold 550a in the manufacturing apparatus 500a, indicated by a dotted line in the figure. In addition, below, the different points from the manufacture of the hollow circular tube according to the first embodiment will be mainly explained, and the explanation of the same points will be omitted.

As shown in FIG. 14, the apparatus 500a for manufacturing the hollow circular tube 100a includes a non-foaming resin composition extruder 530 for melt-kneading the non-foaming resin composition 210', and a non-foaming resin composition extruder 530 for melt-kneading the foamable resin composition. Contains multiple extruders. In FIG. 14, only two extruders, the first extruder 540a1 and the second extruder 540a2, are shown among the plurality of extruders that melt and knead the foamable resin composition, and the other extruders are omitted. 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 foamable resin composition extruders 540. The gas pressure is configured to be independently controllable so that it can be dispersed.

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

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

The extruded non-foamable resin composition 210' and the foamable resin compositions 221a', 222a', 223a', . ... is formed into a tubular shape, and guided so that the non-foamable resin composition 210', the foamable resin compositions 221a', 222a', 223a', etc. are laminated in this order from the inside. In this way, a laminated tube with a multilayer structure containing the non-foamable resin composition 210', the foamable resin compositions 221a', 222a', 223a', . . . is prepared in the mold 550a. The term "multilayer" may vary depending on the thickness of the outer layer 220a to be formed, but for example, the number of layers is within a range of 4, 5, 6, 7, 8, 9, or 10, with the upper and lower limits being any two of the number of layers. It means to be layered.

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

The covering layer 230 (see FIG. 3) can be formed by laminating non-foaming resin compositions as described above, but is not limited to this method. For example, when a crosshead die for molding the outermost layer of a foamable resin composition has a surface that contacts the outermost layer of the foamable resin composition as a cooling surface, the outermost layer of the foamable resin composition is formed on the cooling surface. It may be formed by cooling the outer circumferential surface of the object and solidifying the vicinity of the outer circumferential surface prior to foaming.

The laminated tube containing the non-foamable resin composition 210' and the foamable resin compositions 221a', 222a', 223a'... is fed out of the mold 550a, so that the pressure is reduced and the foamable resin composition The objects 221a', 222a', 223a', . . . foam.
In this way, since many foamable resin compositions are laminated and foamed, each layer blends into each other near the boundary, and the porosity increases gradually and continuously from the inner circumferential side to the outer circumferential side in the overall appearance. It will become larger.

This makes it possible to form a porosity gradient structure (see FIG. 4) in the foamed outer layer 220a (see FIG. 3). Note that by setting the layer thickness of each layer in consideration of the foaming ratio expected from the amount of foaming agent, the sloped structures shown in FIGS. 4(A), 4(b), and 4(c) can be formed. Can be divided.

[Manufacture of hollow circular tube according to third embodiment]
FIG. 16 is a schematic enlarged sectional view of a mold 550b in the apparatus for manufacturing the hollow circular tube 100b. An example of the manufacturing apparatus for 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 The manufacturing apparatus 500a is the same as the manufacturing apparatus 500a except that crosshead dies 552, 553, and 554 are respectively provided in series.

In the three extruders that melt and knead the foamable resin compositions, foamable resin compositions 221b', 222b', and 223b' each containing a different amount 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-foamable resin composition 210' and foamable resin compositions 221b', 222b', and 223b' are formed into a tubular shape by a straight die 551 and a crosshead die 552, 553, and 554, respectively, in a mold 550b. The non-foamable resin composition 210', the foamable resin compositions 221b', 222b', and 223b' are laminated in this order from the inside. In this way, a laminated tube containing the non-foamable resin composition 210' and the foamable resin compositions 221b', 222b', and 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-foaming resin composition (not shown). Lamination of the non-foamable resin composition for forming the coating layer 230 may be performed within the mold 550, or foaming of the foamable resin compositions 221b', 222b', and 223b', which will be described later, may be performed. It may also be laminated after it has been removed.

The covering layer 230 (see FIG. 5) can be formed by laminating non-foaming resin compositions as described above, but is not limited to this method. For example, when the crosshead die 554 for molding the foamable resin composition 223b' has a surface in contact with the foamable resin composition 223b' as the cooling surface S4, the outermost layer of the foamable resin is formed on the cooling surface S4. It may be formed by cooling the outer circumferential surface of the composition 223b' and solidifying the vicinity of the outer circumferential surface prior to foaming.

The laminated tube containing the non-foamable resin composition 210' and the foamable resin compositions 221b', 222b', and 223b' is fed out of the mold 550b, whereby the pressure is reduced and the foamable resin composition 221b ', 222b', and 223b' foam.
By foaming the foamable resin composition in a state in which three layers are laminated in this manner, the porosity becomes gradually smaller from the inner circumferential side to the outer circumferential side.
This makes it possible to form a porosity gradient structure (see FIG. 6) in the foamed outer layer 220b (FIG. 5).

[Manufacture of hollow circular tube according to fourth embodiment]
FIG. 17 is a schematic enlarged sectional view of a mold 550c in the apparatus for manufacturing the hollow circular tube 100c. An example of the manufacturing apparatus for the hollow circular tube 100c is based on the manufacturing apparatus 500a shown in FIG. 14, and the number of extruders for melt-kneading the foamable resin composition is two, and The crosshead dies 552 and 553 are respectively arranged in series, and the surfaces of the crosshead die 552 and the crosshead die 553 that contact 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 that

In the two extruders that melt and knead the foamable resin compositions, foamable resin compositions 221c' and 222c' are prepared using different amounts of foaming gas, respectively. Specifically, the foamable resin composition 221c' is prepared to have a smaller foaming gas content 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 a crosshead die 552 and 553, respectively, in a mold 550c, and are non-foamed from the inside. The foamable resin composition 210', the foamable resin compositions 221c', and 222c' are guided to be laminated in this order. In this way, a laminated tube containing the non-foamable resin composition 210' and the foamable resin compositions 221c' and 222c' is prepared in the mold 550c.

Furthermore, in the mold 550c, the surface where the crosshead die 552 contacts the foamable resin composition 221c' and the surface where the crosshead die 553 contacts the foamable resin composition 222c' serve as a cooling surface S2 and a cooling surface S3, respectively. It is configured. By cooling the foamable resin compositions 221c' and 222c' on the cooling surfaces S2 and S3, respectively, the outer peripheral side becomes lower temperature and the inner peripheral side becomes higher temperature in each layer of the foamable resin compositions 221c' and 222c'. Creates a temperature gradient. Further, the outer peripheral surface of the foamable resin composition 222c' cooled on 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 fed out of the mold 550c, whereby the pressure is reduced and the foamable resin composition 221c' , 222c' foam. This makes it possible to form a porosity gradient structure (see FIG. 8) in the foamed outer layer 220b (FIG. 7).

[Manufacture of hollow circular tube according to the 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 of a mold 550d in a manufacturing apparatus 500d, indicated by a dotted line in the figure.

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

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

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

In the mold 550d, the extruded foamable resin composition 221d' is passed through a straight die 551d1, and the foamable resin compositions 222d', 223d', 224d'... are passed through a crosshead die 552d, 553d, 554d..., respectively. The foamed resin compositions 221d', 222d', 223d', 224d', . . . are laminated in this order from the inside. In this way, laminated tubes containing the foamable resin compositions 221d', 222d', 223d', 224d', . . . are prepared in the mold 550d.

An inner layer 210d and a covering layer 230 (see FIG. 9) are formed on the laminated tube by further laminating a non-foaming resin composition (not shown). Lamination of the non-foamable resin composition for forming the inner layer 210d may be performed within the mold 550, or lamination of the foamable resin compositions 221d', 222d', 223d', 224d', etc., which will be described later, may be carried out in the mold 550. Lamination may be performed after foaming is completed. Lamination of the non-foamable resin composition for forming the coating layer 230 may also be performed within the mold 550, or lamination of the foamable resin compositions 221d', 222d', 223d', 224d', etc. to be described later.・Lamination may be performed after foaming is completed. When lamination of the non-foamable resin composition for forming the inner layer 210d and/or the covering layer 230 is performed within the mold 550, the manufacturing device 500d further performs extrusion for extruding the non-foamable resin composition. It further includes a die for forming into a tubular shape so as to laminate foamable resin compositions 221d', 222d', 223d', 224d', . . . described later.

The inner layer 210d and the covering layer 230 (see FIG. 9) can be formed by laminating non-foaming resin compositions 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 cooling and solidifying the foamable resin compositions 221d', 222d', 223d', 224d'... before foaming. good. Specifically, when the surface of the inner surface regulating portion 551d2 provided in the mold 550a that is in contact with the inner circumferential 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 circumferential surface with the cooling surface S1 to solidify the vicinity of the inner circumferential surface prior to foaming. In addition, when the crosshead die that molds the outermost layer of the foamable resin composition has a surface in contact with the outermost layer of the foamable resin composition as a cooling surface, the outermost layer of the foamable resin composition can be formed on the cooling surface. The coating layer 230 may be formed by cooling the outer circumferential surface of the object and solidifying the vicinity of the outer circumferential surface prior to foaming.

The laminated tube containing the foamable resin compositions 221d', 222d', 223d', 224d'... is fed out of the mold 550d, and the pressure is reduced, and the foamable resin compositions 221d', 222d', 222d', etc. 223d', 224d'... are foamed.
In this way, since many foamable resin compositions are laminated and foamed, each layer blends into each other near the boundaries, and the overall apparent porosity increases gradually and continuously from the inner circumferential side to the outer circumferential side. It becomes a mode.
This makes it possible to form a porosity gradient structure (see FIG. 4) in the foamed outer layer 220a (see FIG. 9).

[Other examples]
As already mentioned, the present invention includes any aspect in which the respective embodiments are combined as appropriate, for example as shown in FIG. 10. The hollow tube of this embodiment can be manufactured by a person skilled in the art by appropriately combining the above-mentioned manufacturing methods.

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

As described above, the present invention provides a manufacturing 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 a method for foaming a foamable resin composition extruded into a tubular shape. Hollow tubes may be manufactured by either one of the manufacturing methods in which multiple foamable resin compositions with different agent contents are laminated into a tubular shape and then foamed, or by a combination of both methods. Hollow tubes may also be manufactured by

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

The present invention is not limited to the above 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, which is a foam 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 one example is a foam containing cement. In either case, if the hollow tube includes a non-foamed layer, the material of the non-foamed layer may be the same as the foamed layer except that it is non-foamed, or it may be different. good.

[Effects produced by the embodiment and other examples]
Since the hollow circular tubes 100, 100a, to 100d include outer layers 220, 220a, 220b, and 220c having a gradient structure with different porosity in the wall thickness direction, they are multifunctional and have at least light weight and mechanical properties. has.

The hollow circular tubes 100a, 100c, 100d include a sloped structure in which the porosity is higher on the side far from the axis of the outer layer 220a, 220c than on the side closer to the axis, so that they are more lightweight.
The hollow circular tubes 100, 100b, 100c include a sloped structure in which the porosity is lower on the side far from the axis of the outer layer 220, 220b, 220c than on the side closer to the axis, and therefore has better mechanical properties.

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

The outer layers 220, 220a, 220b, 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 be manufactured in such a manner that the porosity differs in the thickness direction.

The hollow circular tubes 100, 100a, 100b, 100d of the present invention can be manufactured by laminating three or more types of foamable resin compositions containing different amounts of blowing agents, so that the outer layers 220, 220a, 200b, etc. In addition, the porosity gradient is diverse.

The hollow circular tube 100 is made by laminating resin compositions with different amounts of blowing agents in a number of layers of 4 or more and 10 or less so that the foaming agent content is lower in the layers on the side farther from the axis than on the side closer to the axis. By foaming, the outer layer 220 can be formed in such a manner that the porosity gradually decreases from the side closer to the axis to the side farther from the axis.
The hollow spaces 100a and 100d are formed by laminating resin compositions with different amounts of blowing agents in a number of layers of 4 or more and 10 or less so that the foaming agent content is higher in the layer on the side farther from the axis than on the side closer to the axis. By laminating and foaming, the outer layer 220 can be formed in such a manner that the porosity gradually increases from the side closer to the axis to the side farther from the axis.

The method for manufacturing hollow circular tubes using the manufacturing apparatuses 500, 500a, and 500d uses carbon dioxide gas as the foaming agent, so there is no need to recover the foaming agent, and no by-products are generated due to foaming, so long-run performance is achieved. Can be kept in good condition.

The manufacturing apparatus 500a has a first extruder 540a1 that extrudes the foamable resin compositions 221a', 221b', and 221c', and a second extruder 540a2 that extrudes the foamable resin compositions 222a', 222b', and 222c', respectively. Since they are separately connected to the carbon dioxide gas cylinder 510 and metering pump 520, the carbon dioxide content of the foamable resin compositions 221a', 221b', 221c' and the foamable resin compositions 222a', 222b', 222c' can be controlled. The outer layers 220a, 220b, and 220c can have a gradient structure with different porosity in the thickness direction.

The manufacturing apparatus 500d includes a first extruder 540d1 that extrudes a foamable resin composition 221d', a second extruder 540d2 that extrudes a foamable resin composition 222d', and a third extruder 540d3 that extrudes a foamable resin composition 223d'. , are respectively connected to the carbon dioxide gas cylinder 510 and the metering pump 520, so that the carbon dioxide contents of the foamable resin composition 221d', the foamable resin composition 222d', and the foamable resin composition 223d' can be made different. It is possible to form the outer layer 220d having a gradient structure in which the porosity differs in the thickness direction.

[Example 1]
In this example, a hollow circular tube was manufactured, which is composed of an inner layer made of a hard non-foamed resin, an outer layer made of a foamed resin laminated on the inner layer, and a covering layer made of a hard non-foamed resin laminated on the outer layer. did. Baking soda was used as the foaming agent, and the outer layer was formed by coextruding and laminating four types of resin compositions containing different amounts of sodium bicarbonate such that the content of sodium bicarbonate increased as the distance from the axis increased.

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

(Creation of hollow circular tube)
A resin composition for double foaming (i) containing 0.88 parts by weight of baking soda per 100 parts by weight of polyvinyl chloride resin, a resin composition for triple foaming (ii) containing 1.32 parts by weight of baking soda, and a resin composition for foaming three times containing baking soda. A resin composition for 4 times foaming (iii) containing 1.76 parts by weight, a resin composition for 5 times foaming (iv) containing 2.20 parts by weight of baking soda, and a resin composition for 7 times foaming containing 3.08 parts by weight of baking soda. Products (v) were prepared and pelletized using a 40 mmφ extrusion molding machine. Furthermore, a polyvinyl chloride resin composition (I) containing no baking soda was also prepared.

A separate 40 mmφ extruder was used for each resin composition, and the rotation speed and cylinder temperature of the extruder were set the same to form the resin compositions (I), (i), (ii), and (iii) from the axis. , (iv), (v), and (I) were coextruded into a mold so that they were layered in this order, and then foaming was performed outside the mold. FIG. 20 shows an X-ray CT image of a cross section of the obtained hollow circular tube wall taken 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 was obtained in such a manner that the lamination boundary of the plurality of resin compositions was not clear, and the foamed layer sandwiched between the non-foamed resin layers was They were formed so that the farther away, the higher the porosity.

[Example 2]
The resin compositions of the 7-fold foaming resin composition (v), the 5-fold foaming resin composition (iv), and the 3-fold foaming resin composition (ii) are stacked in this order from the axis. Each product was co-extruded into a common mold using separate extrusion molding machines while adjusting the temperature conditions so that the resin temperatures were the same.

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

The hollow circular tube manufactured in this example was obtained in such a manner that 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 created by laminating three layers of the resin composition (iv) for 5 times foaming.
The weight per unit length of the obtained hollow circular tube was 0.10 kg/m.

<Bending pipe test>
Example 2 The hollow circular tube obtained in Comparative Example 1 was subjected to the following bending pipe test, and the strain at which bending pipe construction was possible was measured. In the bending pipe test, a 4 m long sample pipe was fixed using three pipe fittings at a position 50 cm from one end of the sample pipe (position A), at the axial midpoint of the sample pipe (position B), and at a position 50 cm from one end of the sample pipe (position B). Stop at three points 50 cm from the other end surface (position C), fix positions A and C on the reference line, and move position B away from the reference line in 5 cm increments to complete the piping construction. The limit of possible separation distance from the reference line was confirmed. In the bending pipe test, it was assumed that cracks would occur if the distance from the reference line exceeded a limit. Table 1 shows the test results (average value of three tests) of measuring the limit of the separation distance. Note that in Table 1, the movability ratio is a relative amount with the limit of the separation distance in Comparative Example 1 as a reference (100%).

As shown in Table 1, the results of the bending pipe test were good for the sample tube of Example 2, which had a foaming rate gradient in which the axial center side was sparse and the outer peripheral surface side was dense.

[Example 3]
From the axis, polyvinyl chloride resin composition (I) not containing baking soda, resin composition for 2 times foaming (i), resin composition for 3 times foaming (ii), resin composition for 5 times foaming (iv) Separate extrusion molding machines are used for each resin composition, and the temperature conditions are adjusted so that the resin temperatures are the same, so that the polyvinyl chloride resin composition (I) and polyvinyl chloride resin composition (I) that do not contain baking soda are laminated in this order. Coextruded into a common mold with adjustments.

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

The hollow circular tube manufactured in this example was obtained in such a manner that 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]
The lamination order from the axis is: polyvinyl chloride resin composition not containing baking soda (I), resin composition for 3 times foaming (ii), resin composition for 3 times foaming (ii), resin composition for 3 times foaming A hollow tube was prepared in the same manner as in Example 3, except that the material (ii) and the polyvinyl chloride resin composition (I) containing no baking soda were used, and the extrusion amount ratio of the resin composition for 3-fold foaming (ii) was the same. A circular tube was manufactured.

The overall wall thickness after foaming was 6.5 mm, and the hard layer on the axial center side and the hard layer on the outer peripheral side, which were formed from the polyvinyl chloride resin composition (I) not containing baking soda, were 2 mm and 0.5 mm, respectively. It was 5 mm. Furthermore, the weight per unit length was 0.46 kg/m.

<Evaluation of various physical properties>
As described above, the thickness of the foam layer of the sample tubes of Example 3 and Comparative Example 2 is 4 mm. In this case, calculation results showed that the thermal conductivity was about the same (0.09 W/(m K)). Furthermore, as a result of subjecting each sample tube to a dew condensation performance test, it was confirmed that the dew condensation performance was also the same.

Furthermore, an internal pressure test was conducted on each sample tube. In the internal pressure test, one end of the sample tube was sealed, water pressure was applied inside, and the internal pressure (water pressure resistance) at which the sample tube was destroyed was measured.
The results of the internal pressure test (conducted three times) are shown in Table 2 below.

As shown in Table 2, although the weight and dew condensation performance of the sample tubes are almost the same, the water pressure resistance of Example 3, in which the foam layer has a foaming rate gradient that is denser on the axial center side and sparser on the outer peripheral side, is lower than that of Example 3. The sample tube was in good condition.

[Correspondence between each part in the embodiment and other examples and each component of the claims]
Hollow circular tubes 100, 100a, ~, 100d correspond to "hollow tubes", outer layers 220, 220a, 220b, 220c correspond to "tubular foam", inner layers 210, 210d correspond to "inner layer", The coating layer 230 corresponds to a "coating layer," the manufacturing devices 500a and 500d correspond to a "hollow tube manufacturing device," and the foamable resin compositions 221a', 221b', 221c', and 221d' correspond to a "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", and the carbon dioxide cylinder 510 and metering pump 520 correspond to the "first gas supply section" and "second gas supply section". The crosshead die 552 and the straight die 551d1 correspond to a "first forming section", and the crosshead dies 553 and 552d correspond to a "second forming section".

Although some embodiments of the invention are described above, various other embodiments can be made without departing from the spirit of the invention. Therefore, these embodiments are merely illustrative in every respect, and should not be interpreted in a limiting manner. Furthermore, all changes that come within the range of equivalents of the claims are intended to be within the scope of the invention.

100, 100a, ~, 100d Hollow circular tube 210, 210d Inner layer 220, 220a, 220b, 220c Outer layer 230 Covering layer 500a, 500d Hollow circular tube manufacturing device 221a', 221b', 221c', 221d' Expandable resin composition 222a', 222b', 222c', 222d' Foamable 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 (5)

A hollow circular tube having a circular cross section and configured by coextruding and laminating an inner layer and an outer layer,
The outer layer is a foam layer containing a vinyl chloride resin, having a wall thickness of 4 mm or more and 15 mm or less, and containing closed-cell foam cells,
The inner layer includes a hard vinyl chloride resin different from the outer layer, and is a non-foamed layer laminated on the inner peripheral side of the outer layer,
The thickness of the inner layer is 40% or more and 70% or less of the thickness of the foam layer,
A hollow circular tube in which the outer layer has a smaller porosity on the outer peripheral side than on the axial center side . a covering layer is laminated on the outside of the outer layer,
The hollow circular tube according to claim 1, wherein the covering layer has a thinner wall thickness than the inner layer. The hollow circular tube according to claim 2, wherein the coating layer has a wall thickness of 0.1 mm or more and 1.5 mm or less. a covering layer is laminated on the outside of the outer layer,
The hollow circular tube according to any one of claims 1 to 3, wherein the coating layer and the outer layer are made of the same vinyl chloride resin. The hollow circular tube according to any one of claims 1 to 4 , wherein the inner layer contains a rubber component.

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