Multilayer pipe

Abstract

To provide a multilayer pipe having an outer layer with rigidity, and capable of suppressing diameter reduction when the pipe is cut.SOLUTION: A multilayer pipe 10 of the present invention comprises an outer layer 12 composed of a non-foamed layer made of polyvinyl chloride resin, an intermediate layer 14 formed on an inner peripheral side of the outer layer and composed of a foamed layer made of polyvinyl chloride resin, and an inner layer 16 formed on the inner peripheral side of the intermediate layer and composed of a non-foamed layer made of polyvinyl chloride resin, where the outer layer has a thickness larger than 30% of the intermediate layer. The intermediate layer desirably has an open cell rate of 50% or more. The intermediate layer desirably has a closed cell rate of 15% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a multi-layer pipe having inner and outer non-foamed layers made of a vinyl chloride resin and an intermediate foamed layer made of the same resin. [Background technology]

[0002] Multi-layer pipes made of polyvinyl chloride resins are used as piping for circulating fluids, such as water pipes and air conditioning drain pipes. Multi-layer pipes have an inner layer and an outer layer that are non-foamed, and an intermediate layer between them that is foamed. The inclusion of a foamed layer can reduce the weight of the multi-layer pipe, and the foamed layer has soundproofing and heat-insulating effects that can reduce the flow noise, heat dissipation, and condensation of the fluid flowing inside. Multi-layer pipes have a function of preventing deformation and scratches by sandwiching a low-rigidity intermediate layer between rigid outer and inner layers.

[0003] For example, Patent Document 1 discloses a multi-layer pipe in which the thickness of the outer layer relative to the thickness of the intermediate layer is set at an upper limit of 30%. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7123880 Summary of the Invention [Problem to be solved by the invention]

[0005] By forming the outer layer thin, it is possible to reduce costs and weight. However, since the intermediate layer has low rigidity, making the outer layer thin reduces the rigidity of the multi-layer pipe.

[0006] In addition, when laying multi-layer pipes, it is necessary to cut the pipes as necessary to adjust their length, but when cutting the pipes, residual strain causes the pipe ends (outer layers) to shrink in diameter. Shrinkage of the pipe ends is one of the causes of water leakage at the joints with pipe joints.

[0007] An object of the present invention is to provide a multi-layer pipe that has an outer layer with sufficient rigidity and that can suppress reduction in diameter when cut. [Means for solving the problem]

[0008] The multilayer pipe of the present invention is an outer layer made of a non-foamed layer made of a polyvinyl chloride resin; an intermediate layer formed on the inner circumferential side of the outer layer and made of a foamed layer made of a vinyl chloride resin; an inner layer formed on the inner periphery of the intermediate layer and made of a non-foamed layer made of a vinyl chloride resin; A multi-layer pipe comprising: The outer layer has a thickness that is greater than 30% of the thickness of the intermediate layer.

[0009] The intermediate layer desirably has an open cell ratio of 50% or more.

[0010] The intermediate layer preferably has a closed cell ratio of 15% or less.

[0011] The degree of polymerization of the vinyl chloride resin in the intermediate layer is desirably 400-800.

[0012] The degree of polymerization of the vinyl chloride resin in the outer layer and the inner layer may be greater than the degree of polymerization of the vinyl chloride resin in the intermediate layer.

[0013] The outer layer desirably has a thickness of 60% or less than that of the intermediate layer.

[0014] It is desirable that the outer layer has an outer diameter reduction rate of 0.3% or less when cut into a pipe by a cutter.

[0015] It is preferable that the nominal diameter is 20 to 65. Effect of the Invention

[0016] In the multi-layer pipe of the present invention, the thickness of the outer layer relative to the intermediate layer is specified as above, so that the outer layer has rigidity and is prevented from being deformed or scratched. In addition, the thickness of the outer layer relative to the intermediate layer is specified in the multi-layer pipe of the present invention, so that the reduction in diameter of the pipe end during pipe cutting can be reduced, and water leakage from the joint with the pipe joint can be reduced. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view of a multi-layer pipe of the present invention. [Diagram 2] FIG. 2 is an explanatory diagram showing a cross section of the open cell rate measuring device. [Diagram 3] FIG. 3 is an explanatory diagram showing a manufacturing apparatus for a multi-layer pipe. [Figure 4] FIG. 4 is a cross-sectional view of the mold. [Diagram 5] FIG. 5 is an explanatory diagram of a vacuum sizing device. [Figure 6] FIG. 6 is a graph showing the relationship between the outer layer ratio and the outer diameter reduction rate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The multi-layer pipe 10 according to one embodiment of the present invention can be used for various purposes such as a water distribution pipe or an air conditioning drain pipe for circulating a fluid.

[0019] Fig. 1 is a cross-sectional view showing one embodiment of a multi-layer pipe 10 of the present invention. As shown in the figure, the multi-layer pipe 10 includes an outer layer 12 provided on the outermost circumference, an intermediate layer 14 formed on the inner circumference side thereof, and an inner layer 16 formed on the inner circumference side thereof. Although the outer layer 12, intermediate layer 14, and inner layer 16 are each shown as a single layer in the figure, each may be a multiple layer structure.

[0020] <Material> The multi-layer pipe 10 of the present invention is constructed such that the outer layer 12 and the inner layer 16 are non-foamed layers made of vinyl chloride resin, and the intermediate layer 14 is a foamed layer made of vinyl chloride resin.

[0021] The outer layer 12, the intermediate layer 14, and the inner layer 16 may be made of a vinyl chloride resin. Examples of vinyl chloride resins include, but are not limited to, polyvinyl chloride and copolymers of vinyl chloride monomer and ethylene. The vinyl chloride resins of the outer layer 12, the intermediate layer 14, and the inner layer 16 may be the same or different materials.

[0022] The average degree of polymerization of the vinyl chloride resin is preferably 400 or more, and desirably 2000 or less. If the average degree of polymerization of the vinyl chloride resin is less than 400, the thermal stability and fatigue properties are likely to decrease, and if the average degree of polymerization exceeds 2000, molding at a general molding temperature becomes difficult, and the vinyl chloride resin decomposes. More desirably, the average degree of polymerization of the vinyl chloride resin is 600 or more at the lower limit and 1500 or less at the upper limit.

[0023] Regarding the average degree of polymerization of the vinyl chloride resin, it is preferable that the average degree of polymerization of the outer layer 12 and the inner layer 16, which are non-foamed layers, is greater than that of the intermediate layer 14, which is a foamed layer. The reason for this is that the resin of the outer layer 12 and the inner layer 16, which are responsible for strength, is preferably a vinyl chloride resin with a higher degree of polymerization and higher strength, and the polymerization degree of the vinyl chloride of the intermediate layer 14 is preferably a vinyl chloride resin with a lower degree of polymerization, which is easier to foam. The average degree of polymerization of the outer layer 12 and the inner layer 16 is preferably 800 to 1500, and the average degree of polymerization of the intermediate layer 14 is preferably 400 to 800. It is more preferable that the average degree of polymerization of the outer layer 12 and the inner layer 16 is 100 or more greater than that of the intermediate layer 14.

[0024] In order to foam the intermediate layer 14, which is a foaming layer, a foaming agent is added to the vinyl chloride resin during molding. The foaming agent may be a volatile one, a decomposition type one, or a thermally expandable microcapsule. Examples of volatile foaming agents include, but are not limited to, aliphatic hydrocarbons, alicyclic hydrocarbons, halogenated hydrocarbons, ethers, ketones, etc. Examples of decomposition type foaming agents include, but are not limited to, sodium hydrogen carbonate, sodium carbonate, ammonium bicarbonate, ammonium nitrite, etc. Note that the foaming agent may be used alone or in combination of multiple types. The foaming agent may also be a gas such as carbon dioxide gas, air, or nitrogen gas.

[0025] It is desirable for vinyl chloride resins to contain stabilizers to improve moldability and product properties. Examples of stabilizers include Ca-Zn, Ba-Zn, Sn, and Pb-based stabilizers.

[0026] The outer layer 12, which is a non-foamed layer, may contain a pigment. By containing a pigment, the appearance of the multi-layer pipe 10 may be improved or coloring may be provided according to the needs of the user.

[0027] <shape> The multi-layer pipe 10 may be in the form of a circular ring as shown in Fig. 1. The inner diameter, outer diameter and wall thickness of the multi-layer pipe 10, which is the combination of the outer layer 12, the intermediate layer 14 and the inner layer 16, may be appropriately selected. For example, the inner diameter of the multi-layer pipe 10 is preferably 20 mm or more and preferably 65 mm or less. The outer diameter of the multi-layer pipe 10 is preferably 32 mm or more (nominal diameter 20) and preferably 89 mm or less (nominal diameter 65). The wall thickness of the multi-layer pipe is preferably 6.0 mm or more and preferably 11.0 mm or less.

[0028] With regard to the thickness of each layer, the outer layer 12 is preferably more than 30% thick, more preferably 35% or more thick, and more preferably 40% or more thick, of the intermediate layer 14. Since the outer layer 12, which is a non-foamed layer, has higher rigidity than the intermediate layer 14, which is a foamed layer, by defining the thickness of the outer layer 12 as above, it is possible to provide high rigidity to the outer periphery of the multi-layer pipe 10 and prevent deformation and damage.

[0029] On the other hand, the outer layer 12, which is a non-foamed layer, has a higher specific gravity than the intermediate layer 14, which is a foamed layer, so that a thicker outer layer 12 leads to an increase in the weight of the multi-layer pipe 10. In addition, the intermediate layer 14 has high soundproofing and heat-insulating effects because it is porous, but these effects decrease when the intermediate layer 14 becomes thinner. Therefore, the outer layer 12 is preferably 60% or less of the thickness of the intermediate layer 14, desirably 50% or less, and more desirably 45% or less.

[0030] Moreover, the inner layer 16 is preferably at least 35% thick, more preferably at least 40%, and even more preferably at least 45% thick, of the intermediate layer 14. Since the inner layer 16, which is a non-foamed layer, has higher rigidity than the intermediate layer 14, which is a foamed layer, by defining the thickness of the inner layer 16 as described above, it is possible to provide high rigidity to the inner periphery of the multi-layer pipe 10 and prevent deformation and damage due to contact with the fluid flowing inside.

[0031] On the other hand, as in the case of the outer layer 12, the inner layer 16, which is a non-foamed layer, has a higher specific gravity than the intermediate layer 14, which is a foamed layer, so that a thicker inner layer 16 leads to an increase in the weight of the multi-layer pipe 10. Furthermore, the intermediate layer 14, which is a foamed layer, has high soundproofing and heat-insulating effects because it is porous, but these effects decrease when the intermediate layer 14 becomes thinner. Therefore, the inner layer 16 is preferably 70% or less of the thickness of the intermediate layer 14, desirably 65% ​​or less, and more desirably 60% or less.

[0032] When comparing the thickness of the outer layer 12 and the inner layer 16, making the outer layer 12 thicker allows the inner layer 16 in contact with the fluid to absorb the effects of the temperature of the fluid while maintaining the strength of the entire pipe. Specifically, the outer layer 12 is preferably more than 1.0 times the thickness of the inner layer 16, desirably 1.2 times or more, and more desirably 1.4 times or more.

[0033] Conversely, by making the inner layer 16 thicker, it is possible to suppress deformation of the inner layer 16 (fluid path) that comes into contact with the fluid while allowing some degree of deflection of the entire pipe. Specifically, the inner layer 16 is preferably more than 1.0 times the thickness of the outer layer 12, desirably 1.2 times or more, and more desirably 1.4 times or more.

[0034] <Middle Class 14> The expansion ratio of the intermediate layer 14, which is a foamed layer, is preferably 3.0 times or more, and more preferably 4.0 times or more. The upper limit is preferably 7.0 times or less, and more preferably 6.0 times or less. A high expansion ratio reduces the weight of the intermediate layer 14, and therefore the weight of the multi-layer pipe 10, and provides soundproofing and heat insulation effects. However, a high expansion ratio reduces the rigidity and strength, so it is preferable to keep the expansion ratio within the above range. The expansion ratio can be calculated by cutting out the intermediate layer 14 and measuring the density according to JIS K 7112:1999.

[0035] The intermediate layer 14 preferably has an open cell ratio, in which the cells contained in the foamed layer are connected to each other, of 50% or more, and preferably 70% or more. The upper limit of the open cell ratio is preferably 90% or less, and preferably 85% or less. The open cell ratio can be measured in accordance with JIS K 7138:2006. Conversely, the closed cell ratio is preferably 15% or less, and preferably 10% or less.

[0036] It is desirable to set the lower limit of the open cell ratio and the upper limit of the closed cell ratio as above, because the higher the open cell ratio and the lower the closed cell ratio, the higher the expansion ratio, the lighter the intermediate layer 14 becomes, and the better the heat insulating performance becomes. On the other hand, if the open cell ratio becomes too high, the strength and water impermeability of the intermediate layer 14 decrease, so it is desirable to set the upper limit as above.

[0037] Also, for example, the open cell ratio can be measured using an open cell ratio measuring device 80 shown in FIG. 2. The open cell ratio measuring device 80 includes a pair of upper and lower caps 81, 82 and a pump 83 connected to the lower cap 82. The multi-layer pipe 10 is cut to a length of 400 mm, and the flow path 17 inside the inner layer 16 is airtightly blocked by an air packer 84. At both ends of the multi-layer pipe 10, a seal ring 85 is attached between the outer layer 12 and the inner surface of the caps 81, 82, and the caps 81, 82 are attached leaving a gap of 1 mm from the end face of the outer layer 12. Then, water is pumped from the pump 83 at a pressure of 10 kPa and the pipe is left for 15 minutes. After 15 minutes, the multi-layer pipe 10 is cut vertically, and the cross section of the foamed intermediate layer 14 is observed. The open cell ratio can be quantified based on the height of the intermediate layer 14 to which the water has penetrated.

[0038] <Method of manufacturing multi-layer pipe 10> The multi-layer pipe 10 can be manufactured, for example, by using a manufacturing apparatus 18 as shown in Fig. 3. The manufacturing apparatus 18 includes a first extrusion molding machine 20, a second extrusion molding machine 22, a vacuum sizing machine 24, a take-up machine 26, a cutting machine 28, and the like.

[0039] The first extruder 20 and the second extruder 22 include a first extruder 34 and a second extruder 36 that heat, melt and extrude the resin raw material supplied from hoppers 30, 32, and a die 38 is attached to the outlet of the first extruder 34 and the second extruder 36. The raw materials for the outer layer 12 and the inner layer 16 of the multi-layer pipe 10 are supplied to the hopper 30 of the first extruder 20, and the raw materials for the intermediate layer 14 are supplied to the hopper 32 of the second extruder 22. Since the intermediate layer 14 is a foamed layer, a foaming agent is mixed into the resin raw material of the intermediate layer 14. Even if the foaming agent is mixed, the molten resin 46 does not foam in the second extruder 36 under high pressure.

[0040] As shown in FIG. 4, the mold 38 is a mold for multi-layer (three-layer) extrusion, and includes a confluence section 40 and a molding section 42. In the confluence section 40, the molten resins 44 and 46 introduced from the first extruder 34 and the second extruder 36 are merged and laminated near the outlet. The laminated molten resins 44 and 46 are expanded in diameter while being laminated in the molding section 42 to be tubular. That is, the molten resin 44 becomes the outer layer 12 and the inner layer 16, and the molten resin 46 becomes the intermediate layer 14. At this time, the pressure of the molten resin 46 is released, and the foaming agent foams. The thicknesses of the outer layer 12, the intermediate layer 14, and the inner layer 16 can be appropriately adjusted by adjusting the supply pressure of the molten resins 44 and 46 or the flow path area thereof.

[0041] The laminated molten resins 44 and 46 are then restricted in outer and inner circumference to a more or less appropriate size by a die ring 48 and a mandrel 50 provided at the tip of the molding section 42, and are extruded as a continuous tube 52 made up of multiple layers.

[0042] The vacuum sizing device 24, which is disposed downstream of the die 38, is for sizing the outer surface of the continuous pipe 52 extruded from the die 38 and cooling it, and includes a main body 54 extending in the extrusion direction of the continuous pipe 52, as shown in Fig. 5. A pipe inlet 56 and an outlet 58 are formed at one and the other longitudinal ends of the main body 54. A vacuum chamber 62 to which a vacuum pump 60 is connected is provided on the inlet 56 side of the main body 54, and a sizing sleeve 64 is disposed within the vacuum chamber 62, with one end of the sizing sleeve 64 connected to the inlet 56. A cooling chamber 66 is provided between the vacuum chamber 62 and the outlet 58, and a water sprinkling pipe 68 is disposed over the entire length of the vacuum chamber 62 and the cooling chamber 66.

[0043] When the continuous pipe 52 is fed to the vacuum sizing device 24, the continuous pipe 52 is expanded by the negative pressure of the vacuum pump 60, and the outer surface of the continuous pipe 52 is brought into close contact with the inner surface of the sizing sleeve 64, thereby being sized. The sized continuous pipe 52 is then cooled and hardened by the cooling water sprayed from the water spray pipe 68.

[0044] The take-up machine 26 is for taking up the continuous tube 52 at a constant speed, and includes take-up rollers 70 pressed against the lower and upper parts of the continuous tube 52. At least one of the take-up rollers 70 is connected to a motor (not shown), and the take-up speed of the continuous tube 52 is adjusted by controlling the number of rotations of the motor.

[0045] The cutter 28 is used to cut the continuous tube 52 to a predetermined length, and includes a sensor 71 that detects the position of the tip of the continuous tube 52, and saw blades 72 that are driven in conjunction with the sensor 71. When the tip of the continuous tube 52 presses the sensor 71, the saw blades 72 are driven to cut the continuous tube 52, and a multi-layer tube 10 including an outer layer 12, an intermediate layer 14, and an inner layer 16 as shown in FIG.

[0046] The above manufacturing method is merely an example, and it is of course possible to manufacture the multi-layer pipe 10 by other methods. EXAMPLES

[0047] A multi-layer pipe 10 was produced in the following manner, and the amount and rate of diameter reduction before and after cutting were measured.

[0048] The materials of the outer layer 12, the intermediate layer 14 and the inner layer 16 are as follows.

[0049] Outer layer 12: Polyvinyl chloride (degree of polymerization 1000, manufactured by Taiyo Vinyl Co., Ltd., product name: TH-1000) Intermediate layer 14: polyvinyl chloride (degree of polymerization 700, manufactured by Taiyo Vinyl Co., Ltd., product name: TH-700), foaming agent: thermally expandable microcapsule (manufactured by Matsumoto Yushi Seiyaku Co., Ltd., product name: Matsumoto Microsphere F Series, acrylic shell type) Inner layer 16: same as outer layer 12

[0050] A resin raw material for the non-foamed layer was prepared by mixing 100 parts by weight of polyvinyl chloride for the outer layer 12 and the inner layer 16 with a total of 2.0 parts by weight of a Pb-based stabilizer (tribasic lead sulfate and lead stearate, manufactured by Mizusawa Industrial Chemicals Co., Ltd.). Similarly, a resin raw material for the foamed layer was prepared by mixing 100 parts by weight of polyvinyl chloride for the intermediate layer 14 with 1.6 parts by weight of a Pb-based stabilizer (same as above) and 5.0 parts by weight of a foaming agent.

[0051] These raw materials were supplied to hoppers 30, 32 of the manufacturing apparatus 18 shown in Figures 3 to 5, and extrusion molding was performed to form a multi-layer pipe 10. The heating and melting temperature of the resin raw materials in the first extruder 34 and the second extruder 36 was 180°C, and the pressure in the mold 38 was 10 to 20 MPa. The expansion ratio of the intermediate layer 14 was about 5.0 times.

[0052] The multi-layer pipes 10 produced as described above were of three different nominal diameters, one for the invention and one for the comparison. The thickness of each layer of the multi-layer pipe 10, the ratio of the thickness of the inner layer 16 and the outer layer 12 to the thickness of the middle layer 14, and the outer diameter of the multi-layer pipe 10 before cutting are shown in Table 1.

[0053] [Table 1]

[0054] Each multi-layer pipe 10 was cut using a PVC pipe cutter. The dimensions of the end of the cut pipe were measured, and the amount and rate of diameter reduction relative to the dimensions before cutting were calculated. The results are shown in Table 1. The rate of diameter reduction of the outer diameter is plotted in the graph of FIG. 6.

[0055] Referring to Table 1 and Figure 6, comparing the invention examples with the comparative examples for each nominal size, it can be seen that the invention examples have a smaller amount and rate of diameter reduction than the comparative examples. Specifically, the squareness ratio could be suppressed to 0.3% or less. This is because the thickness of the outer layer 12 is more than 30% of the intermediate layer 14, which provides high rigidity to the outer periphery of the multi-layer pipe 10 and reduces residual strain when the pipe is cut. Since the amount and rate of diameter reduction are small, it can be seen that the multi-layer pipe 10 of the invention examples can reduce water leakage at the joint with the pipe joint.

[0056] Impact resistance can also be improved by making the outer layer 12 thicker. For example, comparing a multi-layer pipe in which the ratio of the outer layer 12 to the intermediate layer 14 is 27% with a multi-layer pipe in which the ratio is 48%, the strength can be improved by approximately 16%. The strength comparison was performed by dropping a 3 kg cylindrical weight onto the circumference of the multi-layer pipe, and calculating from the minimum height at which cracks occurred.

[0057] In addition, the regression approximation equation was calculated from the plot in Figure 6, and the equation was y = 2.1858e -0.06x This approximation formula is illustrated in Figure 6, which shows that the larger the outer layer ratio, the smaller the outer diameter shrinkage rate.

[0058] The above description of the embodiment is for the purpose of explaining the present invention, and should not be interpreted as limiting the invention described in the claims or narrowing its scope. Furthermore, the configuration of each part of the present invention is not limited to the above embodiment, and various modifications are possible within the technical scope described in the claims. [Explanation of symbols]

[0059] 10 Multilayer pipe 12 Outer layer 14 Middle Class 16 Inner layer

Claims

1. an outer layer made of a non-foamed layer made of a polyvinyl chloride resin; an intermediate layer formed on the inner circumferential side of the outer layer and made of a foamed layer made of a vinyl chloride resin; an inner layer formed on the inner periphery of the intermediate layer and made of a non-foamed layer made of a vinyl chloride resin; A multi-layer pipe comprising: The outer layer has a thickness greater than 30% of the intermediate layer. Multilayer tube.

2. The intermediate layer has an open cell ratio of 50% or more. The multi-layer pipe according to claim 1.

3. The intermediate layer has a closed cell ratio of 15% or less. The multi-layer pipe according to claim 2.

4. The degree of polymerization of the vinyl chloride resin of the intermediate layer is 400 to 800. The multi-layer pipe according to claim 3.

5. the degree of polymerization of the vinyl chloride resin in the outer layer and the inner layer is greater than the degree of polymerization of the vinyl chloride resin in the intermediate layer; The multi-layer pipe according to claim 4.

6. The outer layer has a thickness of 60% or less of the intermediate layer. The multi-layer pipe according to claim 5.

7. The outer layer has an outer diameter reduction rate of 0.3% or less when cut into a tube by a cutting machine. The multi-layer pipe according to claim 5.

8. The nominal diameter is 20 to 65. The multi-layer pipe according to claim 5.

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