Polyolefin pipe and its manufacturing method

Abstract

To provide a polyolefin pipe that prevents, when cut, whisker-like swarf arising from a resin layer on the peripheral face.SOLUTION: A polyolefin pipe has: a single-layer polyolefin pipe body 10; and a resin layer 11 disposed on the peripheral face of the polyolefin pipe body 10. When the Young's modulus of a resin composition constituting the resin layer 11 is defined as x (unit: MPa) and the thickness of the resin layer 11 is defined as y (unit: μm), y>-0.0453x+218.62 holds true.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a polyolefin pipe and a method for producing the same. [Background technology]

[0002] It is well known to use an electric fusion joint (hereinafter referred to as a joint) when connecting plastic pipes such as polyolefin pipes. This joint is made of plastic and has sockets at both ends, into which the ends of the plastic pipes are inserted. A heating element is embedded in the inner periphery of each socket of the joint, and when electricity is passed through the heating element via a terminal protruding from the outer periphery of the joint, the inner periphery of the joint and the outer periphery of the plastic pipe melt, and the joint and the plastic pipe are fused together.

[0003] Prior to the above electric fusion, it is necessary to scrape the outer surface of the end of the plastic pipe to be fused, i.e., the end that will be inserted into the socket of the fitting. A layer called a skin layer, which contains impurities, oxidized deterioration substances, bleed-out additives, etc., may be formed on the outer surface of the plastic pipe, and this skin layer cannot be removed even by cleaning with acetone, and prevents good fusion.

[0004] As mentioned above, removing the skin layer by scraping is essential. To prevent forgetting to scrape, it is common to mark the outer surface of the end of the plastic pipe beforehand. When the marking disappears after scraping, it can be confirmed that the scraping is complete.

[0005] Patent Document 1 proposes laminating an identification layer of a different color from the resin pipe on the intended fusion region or the entire outer surface of the resin pipe. When the intended fusion region is scraped, the identification layer is removed and the color of the resin pipe is revealed, making it possible to confirm the completion of scraping.

[0006] Patent Document 2 also proposes providing a fusion-inhibiting layer containing a fusion-inhibiting substance on the outer surface of the plastic pipe in the region to be fused or on the entire outer surface. With this configuration, if the region to be fused of the plastic pipe is not scraped before fusing the plastic pipe and the electric fusion joint, the plastic pipe and the electric fusion joint will not be fused in the adhesion region of the fusion-inhibiting layer. Therefore, when a water pressure test is performed after the fusion process is completed, water will always leak to the outside through the adhesion region of the fusion-inhibiting substance. If water leakage occurs, it is understood that there is a poor fusion between the electric fusion joint and the plastic pipe. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 6-2794 [Patent Document 2] JP 2019-158147 A Summary of the Invention [Problem to be solved by the invention]

[0008] When installing the polyolefin pipe, the polyolefin pipe is cut as necessary using a cutting machine such as a band saw, a vinyl cutter, or a rotary cutter. According to the findings of the present inventors, when cutting a polyolefin pipe having a resin layer such as a discrimination layer or a fusion-inhibiting layer on the circumferential surface, the resin layer may be stretched and torn off, generating whisker-like chips. Such chips tend to adhere to the cut surface, and may cause poor appearance, poor fusion, and the leakage of foreign matter when a fluid is passed through the polyolefin pipe. In addition, whisker-like chips are easily generated when cutting with a rotary cutter, and they often adhere to the end of the tube, which is the cut surface, rather than to the tube side, which is the surface of the tube. Therefore, even if the tube side is cut during scraping, the chips tend to remain on the tube end and not be removed together with the chips. The present invention has been made in consideration of the above circumstances, and provides a polyolefin pipe in which, when the polyolefin pipe is cut, whisker-like chips derived from the resin layer on the peripheral surface are less likely to be produced, and a method for producing the same. [Means for solving the problem]

[0009] The present invention has the following aspects. [1] A polyolefin pipe having a single-layer polyolefin pipe body and a resin layer present on the peripheral surface of the polyolefin pipe body, wherein the Young's modulus of the resin composition constituting the resin layer is x (unit: MPa) and the film thickness of the resin layer is y (unit: μm), and the following formula 1 is satisfied: y>-0.0453x+218.62...Equation 1 [2] The polyolefin pipe of [1], wherein an adhesive layer is present between the polyolefin pipe body and the resin layer. [3] A method for producing a polyolefin pipe having a single-layer polyolefin pipe body and a resin layer present on the peripheral surface of the polyolefin pipe body, comprising measuring the Young's modulus x (unit: MPa) of a resin composition constituting the resin layer, and forming the resin layer so as to satisfy the following formula 1: y>-0.0453x+218.62...Equation 1 Effect of the Invention

[0010] According to the present invention, it is possible to provide a polyolefin pipe in which whisker-like chips originating from the resin layer on the peripheral surface are hardly generated when the polyolefin pipe is cut, and a method for producing the same. [Brief description of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing one embodiment of a polyolefin pipe according to the present invention. [Diagram 2] 1 is a photograph showing an example of a result of a cutting test. [Diagram 3] 13 is a photograph showing another example of the results of the cutting test. [Figure 4] 1 is a graph showing the measurement results of an example and a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 1 is a cross-sectional view of a polyolefin pipe of the present embodiment. The polyolefin pipe of the present embodiment has a polyolefin pipe body (hereinafter also simply referred to as a “pipe body”) 10 and a resin layer 11 present on the circumferential surface of the pipe body 10. The polyolefin pipe of the present embodiment may be a pressure resistant pipe such as a gas pipe or a water distribution pipe, or may be an electric fusion polyolefin pipe that can be connected using an electric fusion joint.

[0013] [Tube body] The pipe body 10 is made of a single layer, that is, made of a homogeneous resin composition. The resin composition constituting the pipe body 10 contains polyolefin and, if necessary, additives. Examples of polyolefins include polyethylene, polypropylene, and polybutene. Polyethylene is preferred, and high density polyethylene (HDPE) is more preferred. There is no particular limitation on the size of the pipe body 10. For example, the nominal diameter is 20 to 300 (outer diameter 27 to 355 mm, thickness 3.4 to 32.2 mm).

[0014] The Young's modulus of the resin composition constituting the pipe body 10 is preferably 300 to 1500 MPa, more preferably 900 to 1100 MPa. If it is below the upper limit of the above range, deformation is likely to occur when cutting, and chips extending from the resin layer 11 are likely to be generated, so that the application of the present invention is highly effective. If it is above the lower limit, the pipe has sufficient strength and pressure resistance.

[0015] [Resin layer] The resin composition constituting the resin layer 11 contains one or more resins and additives as required, which may include coloring components such as pigments. When the Young's modulus of the resin composition constituting the resin layer 11 is x (unit: MPa) and the film thickness of the resin layer 11 is y (unit: μm), the following formula 1 is satisfied. y>-0.0453x+218.62...Equation 1 If the above formula 1 is satisfied, whisker-like chips originating from the resin layer 11 are unlikely to be generated when the polyolefin pipe is cut.

[0016] The thickness y of the resin layer 11 is greater than 0 and may be any thickness that can be formed. For example, it is preferably 10 μm or more, and more preferably 18 μm or more. There is no particular upper limit. In terms of ease of scraping, it is preferably 300 μm or less, more preferably 250 μm or less, and even more preferably 200 μm or less. Furthermore, if the resin layer 11 is 300 μm or less, it is also preferable in that when a mechanical joint (watertight packing, cap nut tightening, etc.) is used for connection, the watertight function of the packing or the like is not impaired. The film thickness y of the resin layer 11 is obtained by measuring the thickness of the resin layer 11 in the radial direction of the pipe body 10 in a cross section perpendicular to the pipe axis direction of the pipe body 10. If the thickness of the resin layer 11 is not uniform in the circumferential direction of the pipe body 10, the minimum value is taken as the film thickness y of the resin layer 11.

[0017] The Young's modulus x of the resin composition constituting the resin layer 11 is preferably 1500 to 5000 MPa, and more preferably 2000 to 4500 MPa. If it is equal to or greater than the lower limit of the above range, chips extending from the resin layer 11 are unlikely to be generated when the pipe is cut, and if it is equal to or less than the upper limit, the blade can easily enter the pipe when scraping, making it possible to cut the pipe. The Young's modulus x can be adjusted by blending the resin composition. For example, a method of selecting and using a resin having a desired Young's modulus, a method of adjusting the Young's modulus of the resin composition by blending resins with different Young's moduli, and a method of increasing the Young's modulus of the resin composition by mixing an inorganic reinforcing material such as talc, calcium carbonate, or glass fiber can be exemplified.

[0018] In the case of a polyolefin pipe for electric fusion, it is preferable that the resin layer 11 is a fusion-inhibiting layer that inhibits fusion with the electric fusion joint. The adhesion-preventing layer preferably contains at least one selected from the group consisting of polycarbonate (PC), polyethylene terephthalate (PET), nylon, polyvinyl chloride (PVC), ethylene-vinyl alcohol copolymer (EVOH), and homopolypropylene. Examples of nylon include nylon 6 and nylon 66.

[0019] As preferred embodiments of the resin composition constituting the resin layer 11, for example, the following embodiments 1 and 2 can be mentioned. (Mode 1) Talc-containing nylon obtained by mixing nylon and talc. Other additives other than talc may be contained as necessary. If the talc content is a% by mass and the nylon content is (100-a)% by mass, relative to the total mass excluding other additives, a is preferably 10 to 30% by mass, more preferably 15 to 25% by mass. If the talc content a is equal to or greater than the lower limit of the above range, the tube can be cut cleanly without generating whisker-like chips, and if it is equal to or less than the upper limit, sufficient scratch resistance is exhibited as a tube. (Aspect 2) A mixture of nylon, polypropylene and talc. Other additives besides talc may be included as necessary. If the content of talc is b% by mass and the total content of nylon and polypropylene is (100-b)% by mass relative to the total mass excluding other additives, b is preferably 10-30% by mass, more preferably 15-25% by mass. If the content of talc is equal to or greater than the lower limit of the above range, the cutting can be performed cleanly without generating whisker-like chips, and if it is equal to or less than the upper limit, sufficient scratch resistance as a pipe is exhibited. If the content of nylon is c% by mass and the content of polypropylene is (100-c)% by mass relative to the total content of nylon and polypropylene, c is preferably 4-13% by mass, more preferably 6-11% by mass.

[0020] The polyolefin pipe of this embodiment can be produced by measuring the Young's modulus x (unit: MPa) of the resin composition constituting the resin layer 11, and forming the resin layer 11 so as to satisfy the above formula 1. For example, the film thickness y of the resin layer 11 may be adjusted in accordance with a predetermined Young's modulus x so as to satisfy the above formula 1, or the Young's modulus x of the resin layer 11 may be adjusted in accordance with a predetermined film thickness y so as to satisfy the above formula 1.

[0021] The resin layer 11 can be formed by applying a coating liquid, in which the resin composition constituting the resin layer 11 is dissolved in an organic solvent, to the peripheral surface of the pipe body 10, and then drying to remove the organic solvent. Examples of the coating method include a method using a deposition roller, a spray method, and an inkjet method. The drying method is not particularly limited, but heat drying is preferable from the viewpoint of manufacturing efficiency. Alternatively, the pipe body 10 and the resin layer 11 may be molded simultaneously by co-extruding the resin composition constituting the pipe body 10 and the resin composition constituting the resin layer 11 .

[0022] The area on the circumferential surface of the pipe body 10 where the resin layer 11 is present can be appropriately set depending on the purpose. When the polyolefin pipe is cut to a desired length for use, it is preferable that the resin layer 11 is present over the entire length of the pipe body 10 .

[0023] 1, the resin layer 11 is present over the entire circumferential direction of the pipe body 10, but a strip-shaped resin layer 11 may be present over a portion of the circumferential direction. The strip-shaped resin layer 11 may be one piece, or multiple pieces spaced apart from each other in the circumferential direction of the pipe body 10.

[0024] In the example of FIG. 1, the polyolefin pipe is made up of two layers, the pipe body 10 and the resin layer 11, but an adhesive layer (not shown) may be present between the pipe body 10 and the resin layer 11. The thickness of the adhesive layer is, for example, preferably from 10 to 200 μm, and more preferably from 50 to 150 μm. The adhesive composition constituting the adhesive layer may be any composition that contains a component that enhances the adhesion between the pipe body 10 and the resin layer 11, and any known composition may be used. An example of a component that enhances the adhesion between the pipe body 10 and the resin layer 11 is modified polyolefin.

[0025] The polyolefin pipe of the present embodiment can be cut as necessary. The cutter is not particularly limited, and a known cutter can be used. For example, a band saw, a PVC cutter, a rotary cutter, etc. are included. A rotary cutter is often used for small and medium diameter pipes with a nominal diameter of about 20 to 75.

[0026] The mechanism by which whisker-like chips are generated when polyolefin pipes are cut is believed to be as follows. For example, if the sharpness of the blade of a cutting machine becomes dull and the blade cannot smoothly penetrate the surface of the polyolefin pipe, the blade will press against the surface of the pipe while cutting, causing deformation of the polyolefin pipe. In particular, since a single-layer pipe body is easily deformed by compression, when the blade penetrates the surface of the polyolefin pipe, it is compressed in the direction of the blade's advancement, and is cut in a deformed state. If a resin layer is present on the peripheral surface of the pipe body, the resin layer will stretch in response to the deformation of the pipe body, and it is thought that whisker-like chips will be generated when the resin layer breaks off in a stretched state.

[0027] The present inventors have found that, as shown in the examples described later, when a polyolefin pipe is produced so that the Young's modulus x of the resin composition constituting the resin layer and the film thickness y of the resin layer satisfy the above-mentioned formula 1, whisker-like chips originating from the resin layer are less likely to be generated. When the Young's modulus x and film thickness y are within the range satisfying the formula 1, the resin layer is less likely to stretch, and the pressure when the blade penetrates the surface of the polyolefin pipe is less likely to be transmitted to the pipe body. As a result, the resin layer can be cut before the pipe body deforms, and whisker-like chips derived from the resin layer are less likely to be generated. EXAMPLES

[0028] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0029] (Examples 1 to 26) Examples 9, 15, 16, 18, and 20 to 26 are working examples, and Examples 1 to 8, 10 to 14, 17, and 19 are comparative examples.

[0030] The pipe body 10 used was a polyethylene water pipe (nominal diameter 50, outer diameter 60 mm, thickness 5.5 mm, length 2 m) made of a resin composition (Young's modulus 1000 MPa) containing HDPE and an additive. The following resin compositions A to F were used to compose the resin layer 11. The Young's modulus of the resin compositions A to F is shown in Table 1. In the following, the content of the components contained in the resin composition is the content relative to the total mass excluding additives other than talc. Resin composition A: Mitsui Chemicals product name ADMER (registered trademark), imine-modified polyolefin. Resin composition B: a mixture of nylon and talc-containing polypropylene, talc content 20 mass %, nylon content 71 mass %, polypropylene content 9 mass %. Resin composition C: nylon. Resin composition D: talc-containing nylon, talc content: 5% by mass. Resin composition E: talc-containing nylon, talc content: 10% by mass. Resin composition F: ethylene vinyl alcohol copolymer (EVOH). Polyolefin resin composition: high density polyethylene (HDPE).

[0031] Using the resin composition shown in Table 1, a resin layer 11 was formed so as to cover the entire peripheral surface of the pipe body 10, to produce a polyolefin pipe having the structure shown in Fig. 1. In Examples 1 to 26, the resin layer 11 was provided on the peripheral surface of the pipe body 10 via an adhesive layer (modified polyolefin, thickness 80 µm). The thickness of the resin layer 11 in each example is as shown in Table 1.

[0032] [Cutting test] The polyolefin pipes produced in each example were cut using a cutter, and the cut surfaces were visually inspected to evaluate the cuttability. Of the commonly used cutters, a band saw, a vinyl cutter, and a rotary cutter, the rotary cutter was used for the evaluation, as it was the one that was most likely to produce chips. 2 and 3, when whisker-like chips 11a formed by breaking off the stretched resin layer were present on the cut surface of the pipe body 10, the test was evaluated as × (fail), and when no chips were present, the test was evaluated as ○ (pass). The results are shown in Table 1.

[0033] [Table 1]

[0034] 4 is a graph plotting the results of Examples 1 to 26, with the vertical axis representing the film thickness y (unit: μm) of the resin layer and the horizontal axis representing the Young's modulus x (unit: MPa) of Resin Compositions A to F. ◯ indicates that the evaluation of cutting suitability was passed, and × indicates that it was failed. Based on the results in Table 1 and FIG. 1, it was found that good cutting suitability was obtained when y>-0.0453x+218.62 was satisfied. [Industrial Applicability]

[0035] The present invention can be applied to a plastic pipe that is fused to an electric fusion joint. [Explanation of symbols]

[0036] 10 Polyolefin pipe body (pipe body) 11 Resin layer 11a Chips

Claims

1. A single-layer polyolefin pipe body; a resin layer present on the peripheral surface of the polyolefin pipe body, A polyolefin pipe (excluding a resin pipe having a bellows portion in which a plurality of resin materials are simultaneously extruded to form a passage for fluid and in which peaks and valleys are arranged in succession), which satisfies the following formula 1, where x (unit: MPa) is the Young's modulus of the resin composition constituting the resin layer, and y (unit: μm) is the film thickness of the resin layer. y>-0.0453x+218.62...Formula 1

2. A polyolefin pipe as described in claim 1, wherein the resin layer is the outermost layer on the circumferential surface of the polyolefin pipe body.

3. 3. The polyolefin pipe according to claim 1 or 2, wherein an adhesive layer is present between the polyolefin pipe body and the resin layer.

4. A method for producing a polyolefin pipe having a single-layer polyolefin pipe body and a resin layer present on the peripheral surface of the polyolefin pipe body (excluding a resin pipe having a bellows portion in which a plurality of resin materials are simultaneously extruded to form a passage for a fluid and in which peaks and valleys are continuously arranged), comprising the steps of: A method for producing a polyolefin pipe, comprising: measuring a Young's modulus x (unit: MPa) of a resin composition constituting the resin layer; and forming the resin layer so as to satisfy the following formula 1, where y (unit: μm) is a film thickness of the resin layer: y>-0.0453x+218.62...Formula 1

5. A method for manufacturing a polyolefin pipe as described in claim 4, wherein the resin layer is the outermost layer on the peripheral surface of the polyolefin pipe body.

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