Resin pellets for manufacturing foamed layers of polyvinyl chloride resin pipes and method for manufacturing the same

Abstract

The present invention provides resin pellets and a method for producing the same, which can be used in the production of a foamed layer for polyvinyl chloride resin pipes that combines the characteristics of closed-cell and open-cell structures. [Solution] The resin pellets 90 for manufacturing the foamed layer of a polyvinyl chloride resin pipe according to the present invention have thermally expandable microcapsules 94 added to a polyvinyl chloride resin 92, and have a specific gravity of less than 1. It is preferable that the thermally expandable microcapsules are in a slightly foamed state. Furthermore, when the specific gravity of a plurality of resin pellets is measured, it is preferable that 40% or more of the resin pellets have a specific gravity of less than 1.

Description

Technical Field

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[0001] The present invention relates to resin pellets used for manufacturing a foamed layer of a vinyl chloride resin pipe and a method for manufacturing the same.

Background Art

[0002] Vinyl chloride resin pipes (hereinafter, appropriately referred to as "PVC pipes") are used as pipes for flowing fluids, such as drain pipes and air conditioner drain pipes. For example, the PVC pipe of Patent Document 1 has a structure including a foamed resin layer, a so-called foamed layer, and non-foamed inner and outer layers are formed on the inner peripheral side and the outer peripheral side of the foamed layer. The foamed layer is foamed by mixing a chemical foaming agent such as sodium bicarbonate or ADCA with the raw material during extrusion molding. Since this foamed layer contains a large number of independent bubbles, weight reduction can be achieved, and the foamed layer exhibits heat insulation and sound insulation effects, thereby reducing the flow sound, heat dissipation, and dew condensation of the fluid flowing inside the PVC pipe.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Regarding PVC pipes having a foamed layer, further weight reduction is required while maintaining heat insulation and sound insulation effects.

[0005] The foamed layer of Patent Document 1 is formed by chemical foaming, and the independent foaming rate is very high at 48% or more. That is, the foamed layer consists of bubbles that are completely independent of each other. When there are many such independent bubbles, the heat insulation, sound insulation, and vibration damping properties are inferior to those of continuous bubbles.

[0006] The present invention aims to provide resin pellets and a method for producing the same that can be used in the production of a foamed layer for polyvinyl chloride resin pipes that possesses both closed-cell and open-cell properties. [Means for solving the problem]

[0007] The resin pellets for manufacturing the foamed layer of a polyvinyl chloride resin pipe according to the present invention are The vinyl chloride resin contains heat-expandable microcapsules. The specific gravity is less than 1.

[0008] The aforementioned thermally expandable microcapsules are preferably in a slightly foamed state.

[0009] When measuring the specific gravity of multiple resin pellets, it is preferable that 40% or more of the resin pellets have a specific gravity of less than 1.

[0010] Furthermore, the method for producing resin pellets for manufacturing the foamed layer of a polyvinyl chloride resin pipe according to the present invention is as follows: This process involves mixing polyvinyl chloride resin powder with heat-expandable microcapsules and then extruding the mixture.

[0011] It is preferable that the thermally expandable microcapsules are slightly foamed after the mixing and extrusion molding described above. [Effects of the Invention]

[0012] The resin pellets for manufacturing the foamed layer of a polyvinyl chloride (PVC) resin pipe according to the present invention contain thermally expandable microcapsules. By manufacturing a PVC resin pipe using these resin pellets, the thermally expandable microcapsules foam up due to the release of pressure during discharge from the mold, forming a foamed layer. This foamed layer has a structure that combines the characteristics of closed-cell and open-cell structures. As a result, the PVC resin pipe has the characteristics of a closed-cell structure, which prevents the permeation and leakage of liquids such as water flowing inside, thus overcoming the weakness of open-cell structures in terms of water permeability, and also possesses mechanical properties (rigidity, impact strength, etc.). On the other hand, because the foamed layer has the characteristics of an open-cell structure, the PVC resin pipe also possesses thermal insulation, sound insulation, sound damping, and vibration damping properties. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a cross-sectional view of a polyvinyl chloride resin pipe showing one embodiment of the present invention. [Figure 2] Figure 2 is an enlarged schematic diagram of the foamed layer. [Figure 3] Figure 3 is an explanatory diagram showing a cross-section of the colored water immersion test apparatus. [Figure 4] Figure 4 is a photograph of the second raw material, resin pellets, taken from the side. [Figure 5] Figure 5 is a cross-sectional photograph of the second raw material, resin pellets. [Figure 6] Figure 6 is a magnified cross-sectional photograph of the resin pellets, which are the second raw material. [Figure 7] Figure 7 is an explanatory diagram showing a manufacturing apparatus for polyvinyl chloride resin pipes. [Figure 8] Figure 8 is a cross-sectional view of the mold. [Figure 9] Figure 9 is an explanatory diagram of a vacuum sizing apparatus. [Modes for carrying out the invention]

[0014] First, a vinyl chloride resin pipe 10 (hereinafter referred to as a "PVC pipe") according to an embodiment of the present invention will be described. The PVC pipe 10 of the present invention can be used for various applications as a pipe for draining pipes or air conditioning drain pipes through which fluids flow.

[0015] FIG. 1 is a cross-sectional view showing an embodiment of the PVC pipe 10 of the present invention. As shown in the figure, the PVC pipe 10 is a pipe including a foam layer indicated by reference numeral 14. In the illustration, the PVC pipe 10 is a multilayer pipe having a three-layer structure with an inner layer 12 on the inner peripheral side of the foam layer 14 and an outer layer 16 on the outer peripheral side. However, as long as it includes the foam layer 14, it may be a single-layer pipe having only the foam layer 14, or a two-layer pipe having the foam layer 14 and the inner layer 12 or the foam layer 14 and the outer layer 16, or further a multilayer pipe having a multilayer foam layer 14 or a multilayer pipe having a multilayer inner layer 12 and / or outer layer 16.

[0016] In the PVC pipe 10 of the present invention, the inner layer 12, the foam layer 14, and the outer layer 16 are all formed of a vinyl chloride resin. Examples of the vinyl chloride resin include, but are not limited to, polyvinyl chloride, copolymers of vinyl chloride monomers and ethylene, etc. The vinyl chloride resins of each layer may be the same including the average degree of polymerization described below, or may be different materials.

[0017] The average degree of polymerization of the vinyl chloride resin is preferably 400 or more and desirably 2000 or less. When the average degree of polymerization of the vinyl chloride resin is less than 400, the thermal stability and fatigue characteristics are likely to deteriorate. Also, when the average degree of polymerization exceeds 2000, molding at a general molding temperature becomes difficult and the vinyl chloride resin decomposes. A more desirable average degree of polymerization of the vinyl chloride resin has a lower limit of 600 or more and an upper limit of 1500 or less.

[0018] The vinyl chloride resin preferably has an average degree of polymerization of the foamed layer 14 smaller than those of the inner layer 12 and the outer layer 16, that is, the average degrees of polymerization of the inner layer 12 and the outer layer 16 are preferably larger than that of the foamed layer 14. The inner layer 12 is in direct contact with the fluid, so it has strength to suppress breakage and to enhance the burst pressure performance. The outer layer 16 serves as an outer shell to bear external strength. On the other hand, for promoting foaming, a vinyl chloride resin with a low degree of polymerization is desirable for the foamed layer 14. Specifically, the average degree of polymerization of the vinyl chloride resin of the inner layer 12 and the outer layer 16 is preferably 800 to 1500, and the average degree of polymerization of the vinyl chloride resin of the foamed layer 14 is preferably 400 to 800. More preferably, the average degrees of polymerization of the inner layer 12 and the outer layer 16 are 100 or more larger than that of the foamed layer 14.

[0019] As shown in the schematic diagram 2 showing a partially enlarged view of the foamed layer 14, the foamed layer 14 has a form in which the bubbles 14a and 14b are partitioned by the resin 15. In reality, the bubbles 14a and 14b are not discretely present as shown in the figure, but are in close proximity almost in contact with the thin resin 15 wall. The foamed layer 14 of the present invention has independent bubbles 14a in which individual bubbles are independent within the resin 15, and continuous bubbles 14b (open cells) that are open (released) on the surface of the resin 15. That is, if it is not open on the surface of the resin 15, even if the bubbles are connected, they are independent bubbles 14a, and if the bubbles are single or connected bubbles and are open on the surface of the resin 15, they are continuous bubbles 14b.

[0020] The foamed layer 14 preferably has a continuous cell ratio Cok, which is the proportion of continuous cells 14b within the resin 15, of 52% or more and 90% or less, and is more desirable to be 60% or more and 85% or less. Furthermore, the foamed layer 14 preferably has a closed cell ratio Cck, which is the proportion of closed cells 14a within the resin 15, of 10% or more and 48% or less, and is more desirable to be 15% or more and 40% or less. By controlling the continuous cell ratio Cok and closed cell ratio Cck of the foamed layer 14 in this way, the PVC pipe 10 containing the foamed layer 14 possesses the characteristics of closed cells, which prevent the permeation and leakage of liquids such as water flowing inside, thus overcoming the weakness of continuous cells in terms of water permeability, and also possesses mechanical properties (rigidity, impact strength, etc.). On the other hand, because the foamed layer has the characteristics of continuous cells, the PVC pipe 10 also possesses heat insulation, sound insulation, sound dampening, and vibration damping properties.

[0021] The open-cell ratio Cok and closed-cell ratio Cck of the foamed layer 14 can be measured in the following manner.

[0022] Specifically, as shown in part in Figure 2, the geometric volume of the cube 15 created by cutting the foam layer 14 is Vg, the volume of the open-cell 14b (where some of the cells open on the outer surface of the resin cube 15) is Voc, the volume of the closed-cell 14a (where the cells do not open on the outer surface of the resin cube 15) is Vcc, the volume of the plastic is Vp, and the true volume is V. The geometric volume Vg is measured by dimensional measurement or the water displacement method (JIS K7112). This geometric volume Vg corresponds to the sum of the open-cell volume Voc, the closed-cell volume Vcc, and the volume of the resin Vp (Vg = Voc + Vcc + Vp). Furthermore, the open-cell volume Voc can be measured, for example, by a Shimadzu dry densimeter, as shown below. The volume Vcc of closed cells 14a can be calculated by subtracting the volume Vp of the resin and the volume Voc of open cells 14b from the geometric volume Vg of the cube 15 (Vcc = Vg - Vp - Voc). The volume Vp of the resin can be calculated by W / D, where W is the weight of the cube and D is the density of the plastic. The true volume V can be measured using an air-comparison hydrometer (JIS K7138). The true volume V corresponds to the sum of the volume Vp of the resin and the volume Vcc of closed cells 14a.

[0023] The open-cell volume Voc of the foam layer 14 can be measured using a dry automatic densimeter in accordance with ASTM D2856 (1998). For example, the AcuPic 1330 (Shimadzu dry densimeter) manufactured by Shimadzu Corporation can be used as a dry automatic densimeter, and measurements can be taken using nitrogen gas, helium gas, etc.

[0024] In the above, the open-cell ratio Cok of the foamed layer 14 can be defined as Voc / Vg × 100 (where Voc is the volume of open-cell 14b and Vg is the geometric volume of the cube 15), and similarly, the closed-cell ratio Cck can be defined as 100-Cok (where Cok is the open-cell ratio).

[0025] By adjusting the open-cell ratio Cok and closed-cell ratio Cck of the foamed layer 14 of the PVC pipe 10 as described above, the bubbles (closed-cell 14a, open-cell 14b) have both continuity and independence. As a result, the PVC pipe 10 has the characteristics of closed-cell bubbles, which prevent the permeation and leakage of liquids such as water flowing inside, thus overcoming the weakness of open-cell bubbles in terms of water permeability, and possesses mechanical properties (rigidity, impact strength, etc.). Furthermore, because the foamed layer 14 has the characteristics of open-cell bubbles, it also possesses thermal insulation, sound insulation, sound dampening, and vibration damping properties.

[0026] Furthermore, the PVC pipe 10 having the foamed layer 14 of the present invention is characterized in that the foamed layer 14 is configured so that water does not pass through in the axial direction of the pipe. The water permeability can be measured using the colored water immersion test apparatus 80 shown in Figure 3. The colored water immersion test apparatus 80 involves closing the opening at the lower end of the PVC pipe 10 with a cap 81 and attaching the PVC pipe 10 to a hydraulic jig 83 containing colored water 82. Then, a water pressure of 4 m water head (0.04 MPa) is applied to the hydraulic jig 83 using a hose 84. After 15 minutes, the PVC pipe 10 is cut lengthwise, and the cross-section of the foamed layer 14 with the highest average foaming ratio is observed. If there is water permeability and coloring of 20 cm or more, it is determined that water is passing through.

[0027] Furthermore, the average foaming ratio of the foamed layer 14 of the PVC pipe 10 of the present invention is preferably 3 times or more and 8 times or less, and preferably 4 times or more and 7 times or less. The lower the average foaming ratio of the foamed layer 14, the more the foamed layer 14 has closed-cell characteristics, and the higher the average foaming ratio, the more the foamed layer 14 has open-cell characteristics. In the present invention, the average foaming ratio is set as described above in order to obtain a foamed layer 14 that has both open-cell and closed-cell characteristics.

[0028] The foam layer 14 is formed by mixing thermally expandable microcapsules 94 (microspheres) as a foaming agent into a vinyl chloride resin 92 and performing molding such as extrusion molding, thereby forming bubbles 14a and 14b through heating during molding. The thermally expandable microcapsules 94 are foaming agents in which a gas that acts as a foaming component is encapsulated in an outer resin shell. The diameter of the thermally expandable microcapsules 94 is, for example, 0.005 mm to 0.050 mm. Examples of outer resins include vinylidene chloride copolymers and acrylic acid copolymers, and examples of gases include hydrocarbon gases and halogen element compound gases.

[0029] The above-mentioned heat-expandable microcapsules 94 are used in the form of resin pellets 90 (hereinafter referred to as "pellets" as appropriate) that are pre-mixed with a polyvinyl chloride resin 92 powder and extruded. For example, pellets 90 can be produced by pre-mixing the polyvinyl chloride resin 92 and heat-expandable microcapsules 94 using a heating mixer and a Kuhnring mixer, and then extruding them. The expansion ratio of the heat-expandable microcapsules 94 in the pellets 90 can be adjusted by adjusting the temperature conditions, mixing time, and extrusion molding conditions during this mixing process. As a specific embodiment, examples include mixing in a heating mixer at approximately 110°C for 10 to 20 minutes, and mixing in a cold mixer at 50°C to 75°C. Of course, the mixing conditions are not limited to these.

[0030] Figures 4 and 5 are photographs of pellets 90 (referred to as the second raw material in this specification) containing thermally expandable microcapsules 94 (not visible to the naked eye). Figure 6 is a magnified cross-sectional photograph of the pellets 90. The pellets 90 are, for example, cylindrical in shape; Figure 4 is a side view, and Figure 5 is a cross-sectional view. Referring to Figure 6, which shows a magnified cross-section, it can be seen that thermally expandable microcapsules 94 are scattered within the vinyl chloride resin 92 on the surface of the pellets 90. The thermally expandable microcapsules 94 in Figure 6, which were 0.025 mm before micro-expansion, have been micro-expanded to a diameter of approximately 0.05 mm (pre-expansion ratio of approximately 8 times).

[0031] The presence of slightly foamed, heat-expandable microcapsules 94 in the pellets 90, and the expansion ratio, can be confirmed by referring to the specific gravity of the pellets 90. The more slightly foamed, heat-expandable microcapsules 94 there are, and the greater the expansion ratio, the lower the specific gravity of the pellets 90. It is most desirable that the specific gravity of the pellets 90 be less than 1. However, it is not necessary for all pellets 90 to have a specific gravity of less than 1; the composition may include 20% or more, preferably 30% or more, preferably 40% or more, and more preferably 60% or more, of pellets 90 with a specific gravity of less than 1. The percentage can be converted to the number of pellets 90; for example, 60% of pellets 90 with a specific gravity of less than 1 means that when 10 pellets are placed in a container of water and stirred with a stirrer for, for example, 5 seconds, 6 pellets 90 float. This measurement should be performed immediately after the pellets 90 are formed, for example, within 10 minutes, preferably within 5 minutes, after pellet production. After some time has passed since the manufacture of Pellet 90, for example, about a week, the specific gravity increases due to factors such as temperature and microcrystallization, although the reason is still under investigation.

[0032] The pellets 90 containing thermally expandable microcapsules 94 are prepared by adding 5 to 20 parts by mass of thermally expandable microcapsules 94 to 100 parts by mass of vinyl chloride resin (reference numeral 92). Preferably, 7 to 11 parts by mass of pellets 90 are added to 100 parts by mass of vinyl chloride resin. This is to adjust the average bubble ratio of the foamed layer 14 of the final product, the PVC pipe 10, as described above.

[0033] Unlike chemical foaming, which involves supplying carbon dioxide, baking soda, ADCA (azodicarbonamide), etc., during molding to expand to a free volume, thermally expandable microcapsules expand while maintaining their spherical shape. In this case, the foam layer 14 has relatively thin partitions between bubbles, but there are no large holes (voids) that cross the foam layer 14, so water does not pass through. On the other hand, because the open-cell ratio Cok is high, it also has excellent thermal insulation performance.

[0034] With respect to the foamed layer 14, the inner layer 12 and outer layer 16 can be either foamed or non-foamed. For example, by foaming the inner layer 12 and outer layer 16, the weight of the PVC pipe 10 can be reduced, and the heat insulation and sound insulation performance can be improved. Conversely, by making the inner layer 12 and outer layer 16 non-foamed, the strength of these layers is increased, thereby improving the mechanical properties of the PVC pipe 10. When the inner layer 12 and outer layer 16 are foamed, it is desirable that the foaming ratio of these layers in the final product, the PVC pipe 10, be lower than the foaming ratio of the foamed layer 14. This is to ensure the mechanical properties of the PVC pipe 10. Specifically, the foaming ratio of the inner layer 12 and outer layer 16 is preferably 2 times or less, and preferably 1.1 times or less.

[0035] Specifically, when the inner layer 12 and outer layer 16 are in a foamed form, the amount of foaming agent added is greater than 0 parts by mass and less than or equal to 0.5 parts by mass, preferably between 0.05 parts by mass and less than or equal to 0.30 parts by mass, per 100 parts by mass of vinyl chloride resin. Of course, the amount of foaming agent added to the inner layer 12 and outer layer 16 may be varied.

[0036] To improve the moldability and product characteristics of the vinyl chloride resin, in addition to the vinyl chloride resin and foaming agent, stabilizers such as heat-resistant stabilizers, weather-resistant stabilizers, and light-resistant stabilizers, as well as nucleating agents, lubricants, flame retardants, crosslinking agents, and copper damage inhibitors (neutralizing agents, anti-fogging agents, neutralizing agents) may be added to the foam layer 14, inner layer 12, and outer layer 16. Examples of stabilizers include Ca-Zn, Ba-Zn, Sn, and Pb-based stabilizers. Examples of light stabilizers include ultraviolet absorbers such as salicylic acid esters, benzophenones, benzotriazoles, and cyanoacrylates, as well as hindered amine light stabilizers. Only one type of stabilizer may be used, or two or more types may be used in combination.

[0037] Furthermore, the outer layer 16 may contain a pigment to improve its appearance. The pigment is not particularly limited and examples include organic pigments such as azo, phthalocyanine, slene, and dye lake pigments, as well as inorganic pigments such as oxide, molybdenum chromate, sulfide-selenium, and ferrocyanide pigments. Only one type of pigment may be used, or two or more types may be used in combination. Of course, pigments may also be added to the foam layer 14 and the inner layer 12.

[0038] The PVC pipe 10 can be in an annular shape as shown in Figure 1. The inner diameter, outer diameter, and thickness of the PVC pipe 10, which includes the inner layer 12, foam layer 14, and outer layer 16, can be selected as appropriate. For example, the inner diameter of the PVC pipe 10 is preferably 20 mm or more, and preferably 65 mm or less. The outer diameter of the PVC pipe 10 is preferably 32 mm or more (nominal diameter 20), and preferably 89 mm or less (nominal diameter 65). The thickness of the PVC pipe 10 is preferably 6.0 mm or more, and preferably 11.0 mm or less.

[0039] When the PVC pipe 10 is composed solely of a foamed layer 14, the inner diameter, outer diameter, and thickness of the PVC pipe 10 correspond to the inner diameter, outer diameter, and thickness of the foamed layer 14. When the PVC pipe 10 is a multi-layered pipe, the thickness of each layer (average: the same applies below) of the inner layer 12 is preferably 35% or more, more preferably 40% or more, and more preferably 45% or more, compared to the thickness of the foamed layer 14. Since the inner layer 12 has a lower foaming ratio and higher rigidity than the foamed layer 14, defining the thickness of the inner layer 12 as described above provides high rigidity to the inner circumference of the PVC pipe 10, preventing deformation and damage due to contact with fluids flowing inside.

[0040] On the other hand, since the inner layer 12 has a higher specific gravity than the foam layer 14, increasing the thickness of the inner layer 12 leads to an increase in the weight of the PVC pipe 10. Therefore, it is preferable that the thickness of the inner layer 12 be 85% or less of the thickness of the foam layer 14, more preferably 80% or less, and more preferably 75% or less.

[0041] Furthermore, the outer layer 16 is preferably more than 30% thicker than the foam layer 14, more preferably 35% or thicker, and more preferably 40% or thicker. Because the outer layer 16 has a lower foaming ratio and higher rigidity than the foam layer 14, specifying the thickness of the outer layer 16 as described above provides high rigidity to the outer circumference of the PVC pipe 10, thereby preventing deformation and damage.

[0042] On the other hand, since the outer layer 16 has a higher specific gravity than the foam layer 14, a thicker outer layer 16 leads to an increase in the weight of the PVC pipe 10. Therefore, it is preferable that the outer layer 16 be 55% or less in thickness of the foam layer 14, more preferably 50% or less, and even more preferably 45% or less.

[0043] Furthermore, when comparing the thickness of the inner layer 12 and the outer layer, the overall strength of the pipe can be maintained by making the outer layer 16 thicker. Specifically, the outer layer 16 is preferably more than 1.0 times thicker than the inner layer 12, more preferably 1.2 times or more, and more preferably 1.4 times or more.

[0044] Conversely, by making the inner layer 12 thicker, deformation of the inner layer 12 (fluid path) in contact with the fluid can be suppressed while allowing a certain degree of deflection of the entire pipe. Specifically, the inner layer 12 is preferably more than 1.0 times thicker than the outer layer 16, more preferably 1.2 times or more, and more preferably 1.4 times or more.

[0045] A PVC pipe 10 containing a foamed layer 14 can be manufactured using a manufacturing apparatus 20, for example, as shown in Figure 7. The manufacturing apparatus 20 includes a first extrusion molding machine 21 for extruding the inner layer 12 and the outer layer 16, a second extrusion molding machine 22 for extruding the foamed layer 14, a vacuum sizing device 24, a take-up machine 26, and a cutting machine 28, etc. In this embodiment, the manufacturing apparatus 20 uses one extrusion molding machine 21 because the inner layer 12 and the outer layer 16 are molded from the same raw material (first raw material). However, the extrusion molding machine may be divided into two, and the inner layer 12 and the outer layer 16 may be molded from different raw materials (first raw material and third raw material).

[0046] The first extruder 21 and the second extruder 22 include a first extruder 34 and a second extruder 36 that heat, melt, and extrude raw materials supplied from hoppers 30 and 32. For example, the extruders 34 and 36 can be single-screw extruders or twin-screw opposite-direction conical extruders. Molds 38 are attached to the outlets of the first extruder 34 and the second extruder 36. The hopper 30 of the first extruder 21 is supplied with first raw materials that constitute the inner layer 12 and outer layer 16 of the PVC pipe 10, and the hopper 32 of the second extruder 22 is supplied with second raw materials that constitute the foam layer 14.

[0047] The first raw material is a mixture of vinyl chloride resin powder and, if necessary, a predetermined amount of heat-expandable microcapsules. The second raw material is a pellet 90 in which a predetermined amount of heat-expandable microcapsules 94 is pre-kneaded into vinyl chloride resin 92. The first raw material may also be a pellet in which heat-expandable microcapsules are pre-kneaded into vinyl chloride resin, similar to the second raw material.

[0048] The first raw material is heated and melted in the first extruder 34 and kneaded under pressure in the first extruder 34 to become molten resin 44. Similarly, the second raw material is heated and melted in the second extruder 36 and kneaded under pressure in the second extruder 36 to become molten resin 46. Although the vinyl chloride resins of the first and second raw materials melt under high pressure, the heat-expandable microcapsules of the first raw material do not foam in the first extruder 34 (if the first raw material contains heat-expandable microcapsules), and further foaming of the heat-expandable microcapsules of the second raw material, which are already slightly foamed, is suppressed in the second extruder 36.

[0049] As shown in Figure 8, the mold 38 is a multilayer (three-layer) extrusion mold and includes a confluence section 40 and a molding section 42. Molten resins 44 and 46 discharged from the first extruder 34 and the second extruder 36 are released from pressure, causing thermally expandable microcapsules to foam. At this time, the thermally expandable microcapsules expand within the molten resins 44 and 46 while maintaining their spherical shape. The foamed molten resins 44 and 46 are then co-extruded and merged at the confluence section 40, where they are laminated near the outlet to form a laminate. The laminate containing the laminated molten resins 44 and 46 is molded into a tubular shape in the molding section 42 while remaining laminated. That is, the molten resin 44 later becomes the inner layer 12 and the outer layer 16, and the molten resin 46 becomes the foamed layer 14. The thicknesses of the inner layer 12, the foamed layer 14, and the outer layer 16 can be appropriately adjusted by adjusting the supply pressure of the molten resins 44 and 46 or the flow area.

[0050] Then, the molten resins 44 and 46 in the laminate are extruded as a continuous tube 52 consisting of three layers: an inner layer 12 on the inner side, a foamed layer 14 in the middle, and an outer layer 16 on the outer side, with the outer and inner circumferences being restricted to a somewhat appropriate size by the die ring 48 and mandrel 50 provided at the tip of the molding section 42. Reference numerals 49 and 51 indicate heaters positioned on the outer circumference of the die ring 48 and the inner circumference of the mandrel 50. Because the material systems of the inner layer 12 and the foamed layer 14, and the foamed layer 14 and the outer layer 16 are close to each other, the pressure of the resin increases due to the pressure of the thermally expandable microcapsules 94 trying to expand. As a result, the adhesion of each resin layer that merges in the mold increases, and the bonding performance improves.

[0051] The continuous tube 52, having passed between the diling ring 48 and the mandrel 50, is sent to the vacuum sizing device 24. The vacuum sizing device 24 is located downstream of the mold 38 and is used to size and cool the outer surface of the continuous tube 52 extruded from the mold 38. As shown in Figure 9, it includes a main body 54 that extends in the extrusion direction of the continuous tube 52. An inlet 56 and an outlet 58 for the tube are formed at one end and the other end of the main body 54 in the longitudinal direction. A vacuum chamber 62 connected to a vacuum pump 60 is provided on the inlet 56 side of the main body 54, and a sizing sleeve 64 is placed inside 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 spray pipe 68 is placed between the vacuum chamber 62 and the cooling chamber 66.

[0052] When the continuous pipe 52 is supplied to the vacuum sizing device 24, the negative pressure from the vacuum pump 60 causes the continuous pipe 52 to expand, and its outer surface is sized by making close contact with the inner surface of the sizing sleeve 64. The sized continuous pipe 52 is then cooled and hardened by cooling water sprayed from the watering pipe 68.

[0053] The pull-up machine 26 is for pulling up the continuous pipe 52 at a constant speed and includes pull-up rollers 70 that press against the lower and upper parts of the continuous pipe 52. A motor (not shown) is connected to at least one of the pull-up rollers 70, and the speed at which the continuous pipe 52 is pulled up is adjusted by controlling the rotational speed of the motor.

[0054] The cutting machine 28 is for cutting the continuous pipe 52 to a predetermined length and includes a sensor 71 for detecting the tip position of the continuous pipe 52 and a saw blade 72 that is driven in conjunction with the sensor 71. When the tip of the continuous pipe 52 presses against the sensor 71, the saw blade 72 is driven and the continuous pipe 52 is cut, resulting in a PVC pipe 10 including the inner layer 12, foam layer 14 (see also Figure 2), and outer layer 16 shown in Figure 1.

[0055] The above manufacturing method is just one example, and it is certainly possible to manufacture the PVC pipe 10 by other methods. For example, the PVC pipe 10 can be obtained by extruding the inner layer 12, and then molding the foamed layer 14 and outer layer 16 onto the inner layer 12 in separate processes.

[0056] The resulting PVC pipe 10 has a foamed layer 14 with the open-cell ratio Cok and closed-cell ratio Cck mentioned above, possessing the characteristics of both closed-cell and open-cell structures. As a result, the PVC pipe 10 has the closed-cell characteristic of preventing the permeation and leakage of liquids such as water flowing inside, thus overcoming the weakness of open-cell structures in terms of water permeability, and also possesses mechanical properties (rigidity, impact strength, etc.). On the other hand, because the foamed layer 14 has the characteristics of an open-cell structure, the PVC pipe also possesses thermal insulation, sound insulation, sound dampening, and vibration damping properties. [Examples]

[0057] PVC pipes 10 were manufactured according to the following procedure and various tests were conducted. The manufactured PVC pipes 10 are the inventive examples 1 to 12 and comparative examples 1 to 3. Examples 7 and 9 have a two-layer structure consisting of an inner layer 12 and a foamed layer 14, while the other examples and comparative examples have a three-layer structure consisting of an inner layer 12, a foamed layer 14, and an outer layer 16. Examples 10 to 12 are test examples in which the closed-cell ratio Cck and open-cell ratio Cok of the foamed layer 14 are higher and lower compared to Examples 1 to 9, while the comparative examples are test examples in which the bubbles of the foamed layer 14 were formed by chemical foaming (sodium bicarbonate or ADCA) during extrusion molding.

[0058] The raw materials for the inner layer 12, foam layer 14, and outer layer 16 of the examples and comparative examples are as follows. The same raw materials were used for the inner layer 12 and the outer layer 16.

[0059] <Examples 1-9 (Examples of Inventions)> Inner layer 12 (first raw material): Polyvinyl chloride powder (degree of polymerization 1000, manufactured by Taiyo Vinyl Chloride Co., Ltd., product name: TH-1000), thermally expandable microcapsules 94 (manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd., product name: Matsumoto Microsphere F series, acrylic shell type) Foam layer 14 (second raw material): Forms pellets from polyvinyl chloride (manufactured by Kaneka Corporation, product name: S1007) and thermally expandable microcapsules (manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd., product name: Matsumoto Microsphere F series, acrylic shell type). Outer layer 16: Same as inner layer 12 (first raw material)

[0060] For the inner layer 12 (and the outer layer 16), in Examples 1 to 7, 100 parts by mass of powdered polyvinyl chloride, 2.0 parts by mass of a Pb-based stabilizer (manufactured by NI Chemitech Co., Ltd., consisting of tribasic lead sulfate and lead stearate), and parts by mass (phr) of thermally expandable microcapsules (microspheres) shown in Table 1 were mixed to obtain the first raw materials for the inner layer 12 and outer layer 16. In Examples 8 and 9, no thermally expandable microcapsules were added to the inner layer 12 (and the outer layer 16).

[0061] For the foamed layer 14, 100 parts by weight of polyvinyl chloride, 2.7 parts by weight of a Pb-based stabilizer (same as above), and parts by mass (phr) of thermally expandable microcapsules shown in Table 1 were mixed and kneaded using a heating mixer and a cold mixer to form pellets 90 (Figures 4 to 6), which were used as the second raw material. The pellets 90 of the foamed layer 14 had the thermally expandable microcapsules 94 pre-foamed during the kneading process. By adjusting the content of these pre-foamed thermally expandable microcapsules 94 and the foaming ratio, the proportion of pellets 90 with a specific gravity of less than 1 was 50% to 90%, as shown in Table 1. The specific gravity of the pellets 90 was measured 10 minutes after manufacturing.

[0062] [Table 1]

[0063] These raw materials were supplied to the hoppers 30 and 32 of the manufacturing apparatus 20 shown in Figures 7 to 9, and multi-layer pipes with a nominal diameter of 30 were extruded to obtain the PVC pipe 10 used as a test example. 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 inside the mold 38 was 10 to 20 MPa.

[0064] <Examples 10-12 (Examples of Inventions)> Examples 10 to 12 produced PVC pipes 10 with a three-layer structure consisting of an inner layer 12, a foamed layer 14, and an outer layer 16, using the same raw materials and manufacturing method as in the above examples. However, in the case of the foamed layer 14 in Examples 10 and 11, thermally expandable microcapsules 94 were pre-foamed, but the proportion of pellets 90 with a specific gravity of less than 1 was 20% to 30%, which is lower than in Examples 1 to 9. In addition, no thermally expandable microcapsules were added to the inner layer 12 and outer layer 16 of Example 12.

[0065] <Comparative Example> The comparative example does not use thermally expandable microcapsules, but instead uses chemical foaming (sodium bicarbonate or ADCA) as a foaming agent during extrusion molding.

[0066] For the comparative examples, the inner layer 12 and outer layer 16 were made from a mixture of 100 parts by mass of powdered polyvinyl chloride and 2.0 parts by mass of a Pb-based stabilizer (manufactured by NI Chemitech Co., Ltd., consisting of tribasic lead sulfate and lead stearate), while the foamed layer 14 was made from a mixture of 100 parts by mass of powdered polyvinyl chloride and 2.7 parts by mass of a Pb-based stabilizer (same as above). Then, a chemical blowing agent was mixed into the molten resins 44 and 46 in the first extruder 34 and the second extruder 36, and foaming was performed. Specifically, the chemical blowing agent was azodicarbonamide (Vinihole AC, manufactured by Eiwa Kasei Kogyo Co., Ltd.) for comparative examples 1 and 2, and baking soda (Celbon SC-855, manufactured by Eiwa Kasei Kogyo Co., Ltd.) for comparative example 3.

[0067] <Measurement and measurement results> For the PVC pipes 10 of the obtained examples and comparative examples, the presence or absence of micro-foaming in the inner layer 12 and outer layer 16, the average foaming ratio (times), the thickness of each layer (mm), the thickness of the inner layer 12 and outer layer 16 relative to the thickness of the foamed layer 14, the ratio (%) of the total thickness of the inner layer 12 and outer layer 16, the tensile yield strength (MPa) of the inner layer 12, the short-term pressure resistance (MPa), the surface roughness Ra (μm) of the inner layer 12, the closed-cell ratio Cck and open-cell ratio Cok of the foamed layer 14 (measurement method is shown above), the presence or absence of water flow (colored water immersion test: shown above and in Figure 3), the sound insulation effect, the heat insulation effect, and for the examples, the percentage (%) of pellets with a specific gravity of less than 1 were measured, and the measurement results are shown in Table 1.

[0068] Furthermore, the inner layer tensile yield strength is evaluated as follows: over 42 MPa is rated "A", 40 MPa to 42 MPa is rated "B", and less than 40 MPa is rated "C". In addition, the short-term pressure resistance performance is evaluated as follows: over 8.5 MPa is rated "A", 8 MPa to 8.5 MPa is rated "B", and less than 8 MPa is rated "C". The inner layer surface roughness Ra is evaluated as follows: less than 1.8 μm is rated "A", 1.8 μm to 2.0 μm is rated "B", and greater than 2.0 μm is rated "C".

[0069] The soundproofing effect was evaluated by placing a pipe with a nominal diameter of 100 x 2000 mm in a simple noise measurement chamber, flowing 3 liters / second of water through it, and measuring the noise level using a standard sound level meter, Rion NA-29, at a point 500 mm away from the pipe. A noise level of 47 dB(A) or less was marked with "○", and anything above that was marked with "△". The thermal insulation effect was evaluated by sending 7°C water at a flow rate of 9 L / hr into a PVC pipe 10 under conditions of relative humidity of 63%, pipe gradient of 1 / 50, and ambient temperature of 35°C. No condensation was marked with "○", and condensation was marked with "△".

[0070] Referring to Table 1, all of the examples and comparative examples have inner layer tensile yield strength and short-term pressure resistance performance of "A" or "B", thus possessing the desired performance. The reason why the inner layer tensile yield strength of Example 6 is "B" is because the foaming ratio of the inner layer was high, and the reason why the short-term pressure resistance performance of Examples 4, 5, and 12 is "B" is because the inner layer was relatively thin.

[0071] Regarding the inner layer surface roughness Ra, only Example 6 was "C," while all others were "A" or "B," thus meeting the desired performance. The reason for the rough inner layer surface roughness Ra in Example 6 is that a large amount of foaming agent was added to the inner layer, resulting in a high average foaming ratio and the appearance of numerous bubbles on the inner layer surface.

[0072] The continuous cell ratio Cok of the foamed layer was 52% or higher for all of Examples 1 to 9, more specifically 71% or higher, while it was 46% to 49% for Examples 10 to 12, and 30% to 42% for the comparative examples.

[0073] Furthermore, the closed-cell ratio (Cck) of the foamed layer was 48% or less in all Examples 1 to 9, more specifically 29% or less, while it was 51% to 54% in Examples 10 to 12, and 58% to 70% in the comparative examples.

[0074] It is generally believed that a higher percentage of open cells and a lower percentage of closed cells in a foamed layer would allow water to pass through more easily, while also reducing sound insulation and heat insulation effects. However, as shown in Table 1 and below, the results differed from expectations.

[0075] First, regarding the presence or absence of water flow, Examples 1-11 had "no" water flow, while Examples 12 and Comparative Examples 1-3 had "yes" water flow. Regarding water flow, it was expected that Examples 1-9, with a high open-cell ratio Cok in the foamed layer, would have "yes" water flow, while Examples 10-12 and the Comparative Examples, with a low open-cell ratio Cok, would have "no" water flow. However, referring to Table 1, Examples 1-11 had "no" water flow, while Examples 12 and the Comparative Examples had "yes" water flow. Considering the examples, this is because the foamed layers of Examples 1-11 exhibited open-cell characteristics when measured with nitrogen gas, while exhibiting closed-cell characteristics when measured with water. This characteristic is thought to be due to the use of thermally expandable microcapsules 94 as a foaming agent. Unlike chemical foaming, which involves supplying carbon dioxide, sodium bicarbonate, ADCA (azodicarbonamide), etc., during molding to expand to a free volume, thermally expandable microcapsules 94 expand while maintaining their spherical shape. In this case, the foam layer 14 is thought to have relatively thin partitions between bubbles, but without large holes (voids) that traverse the foam layer vertically. On the other hand, in the comparative example, although the continuous foaming rate Cok of the foam layer measured with nitrogen gas was low, water permeability was observed when measured with water, suggesting that water permeability occurred locally.

[0076] Regarding soundproofing and heat insulation effects, Examples 1-9 all received a "○" rating, while Examples 10-12 and the comparative example all received a "△" rating. The reason Examples 1-9 all received a "○" rating is thought to be due to the high proportion of open cells. On the other hand, the reason Examples 10-12 and the comparative example received a "△" rating is thought to be due to the high proportion of closed cells.

[0077] The above description of the embodiments is for the purpose of explaining the present invention and should not be interpreted as limiting or narrowing the scope of the invention described in the claims. Furthermore, the configuration of each part of the present invention is not limited to the above embodiments, and various modifications are possible within the technical scope described in the claims. [Explanation of Symbols]

[0078] 10. Polyvinyl chloride resin pipes (PVC pipes) 12 Inner Layer 14 Foam layer 14a Air bubbles 14b Air bubbles 15. Resin (foamed layer) 16 Outer layer 90 pellets 92 Vinyl chloride resin 94 Thermally expandable microcapsules

Claims

1. Resin pellets for manufacturing the foamed layer of polyvinyl chloride resin pipes, The vinyl chloride resin contains heat-expandable microcapsules. The specific gravity is less than 1. Resin pellets for manufacturing the foamed layer of polyvinyl chloride resin pipes.

2. The aforementioned thermally expandable microcapsules are in a slightly foamed state. Resin pellets for manufacturing a foamed layer of a polyvinyl chloride resin pipe as described in claim 1.

3. When the specific gravity of multiple resin pellets is measured, more than 40% of the resin pellets have a specific gravity of less than 1. Resin pellets for manufacturing a foamed layer of a polyvinyl chloride resin pipe as described in claim 2.

4. A method for manufacturing resin pellets for producing a foamed layer of a polyvinyl chloride resin pipe, A polyvinyl chloride resin powder and heat-expandable microcapsules are mixed and then extruded. A method for manufacturing resin pellets for producing a foamed layer in polyvinyl chloride resin pipes.

5. As a result of the mixing and extrusion molding, the thermally expandable microcapsules are slightly foamed. A method for producing resin pellets for manufacturing a foamed layer of a polyvinyl chloride resin pipe, as described in claim 4.

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