Cross-linked polyethylene and cross-linked polyethylene pipe and its manufacturing method

Abstract

To provide a crosslinked polyethylene pipe which is excellent in creep resistance and is also excellent in piping construction efficiency, and crosslinked polyethylene constituting the crosslinked polyethylene pipe.SOLUTION: Crosslinked polyethylene is provided which has resin density of 0.931-0.938 g / cm3, and in which a ratio (ΔH1 / ΔHm) of heat of fusion (ΔH1) in a range of 60-95°C to heat of fusion (ΔHm) in a range of 60-140°C, in heat of fusion measured by a differential scanning calorimeter is 0-0.1 A crosslinked polyethylene pipe composed of the crosslinked polyethylene is also provided.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to cross-linked polyethylene, cross-linked polyethylene pipes, and methods for producing the same. More specifically, the present invention relates to a cross-linked polyethylene pipe which has excellent mechanical properties and workability and can be suitably used as a piping for water or hot water supply, a method for producing the same, and the cross-linked polyethylene which constitutes the cross-linked polyethylene pipe. [Background technology]

[0002] In recent years, plastic piping materials with excellent corrosion resistance and ease of installation have been used for cold and hot water supply piping. Cross-linked polyethylene pipes in particular are widely used due to their excellent pressure resistance and creep resistance at high temperatures. Among them, the resin density is 0.938 g / cm 3 Cross-linked polyethylene pipes obtained by cross-linking the above polyethylenes have been proposed as having excellent pressure resistance and being suitable for piping exposed to higher water pressures (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4066114 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when high-density polyethylene is used as a raw material, as in the cross-linked polyethylene pipe of Patent Document 1, the resulting cross-linked polyethylene pipe is hard and difficult to bend, making it difficult to install as a piping pipe. On the other hand, if low-density polyethylene is used as the raw material to make construction easier, the resulting cross-linked polyethylene pipe is soft and easy to bend, but has low pressure resistance and cannot be used as piping for cold or hot water supply. Therefore, the present invention provides a cross-linked polyethylene pipe that has excellent creep resistance and excellent piping workability, a method for producing the same, and the cross-linked polyethylene that constitutes the cross-linked polyethylene pipe. [Means for solving the problem]

[0005] The present inventors have discovered that cross-linked polyethylene, which has excellent creep resistance and workability, satisfies specific resin properties, and have arrived at the present invention.

[0006] [1] Resin density is 0.931 to 0.938 g / cm 3 and wherein, in the heat of fusion measured by a differential scanning calorimeter, the ratio (ΔH1 / ΔHm) of the heat of fusion in the range of 60°C to 95°C (ΔH1) to the heat of fusion in the range of 60°C to 140°C (ΔHm) is in the range of 0 to 0.1. [2] A cross-linked polyethylene pipe, characterized by being made of the cross-linked polyethylene described in [1]. [3] A method for producing a cross-linked polyethylene pipe according to [2], characterized in that uncross-linked polyethylene is molded, cross-linked, heated at 110 to 200°C, and then cooled. [Effects of the Invention]

[0007] The cross-linked polyethylene and its manufacturing method of the present invention can produce a cross-linked polyethylene pipe that has excellent creep resistance and excellent piping workability. Furthermore, the cross-linked polyethylene pipe of the present invention has excellent creep resistance and excellent piping workability. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram of a method for calculating the heat of fusion ratio (ΔH1 / ΔHm). [Figure 2] FIG. 1 is an explanatory diagram of a test piece for a high-temperature tensile creep test. [Figure 3] FIG. 1 is an explanatory diagram of how to determine the 10-hour rupture stress in a high-temperature tensile creep test. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described in detail below. The following embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to these embodiments. The present invention can be implemented in various modifications within the scope of its gist. In this specification, the use of "to" to indicate a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0010] <Cross-linked polyethylene> The cross-linked polyethylene of this embodiment has a resin density of 0.931 to 0.938 g / cm 3 and in the heat of fusion measured by a differential scanning calorimeter (DSC), the ratio (ΔH1 / ΔHm) of the heat of fusion in the range of 60°C to 95°C (ΔH1) to the heat of fusion in the range of 60°C to 140°C (ΔHm) (hereinafter referred to as "heat of fusion ratio (ΔH1 / ΔHm)") is in the range of 0 to 0.1.

[0011] The resin density of cross-linked polyethylene is 0.931 to 0.938 g / cm 3 and 0.933 to 0.936 g / cm 3 It is preferable that: Resin density is 0.931g / cm 3 When the resin density is 0.938 g / cm or more, excellent creep resistance is obtained. 3 By satisfying the following, excellent piping workability can be obtained. The resin density is a value measured by the underwater displacement method specified in Method A of JIS K 7112.

[0012] The ratio of heats of fusion (ΔH1 / ΔHm) is preferably 0 to 0.1, and more preferably 0.05 to 0.1. The smaller the value of the heat of fusion ratio (ΔH1 / ΔHm), the higher the uniformity of the crystalline lamella thickness, and in particular, the fewer the components of thin crystalline lamella. When the heat of fusion ratio (ΔH1 / ΔHm) is 0.1 or less, excellent creep resistance is obtained.

[0013] The cross-linked polyethylene of this embodiment is obtained by cross-linking polyethylene. The cross-linked polyethylene may contain components other than polyethylene depending on the method for cross-linking the polyethylene. For example, a cross-linked polyethylene obtained by cross-linking raw polyethylene using a silane water cross-linking method contains a vinylsilane compound and a radical generator in addition to polyethylene. In addition, known additives may be included as necessary.

[0014] <Cross-linked polyethylene pipe> The cross-linked polyethylene pipe is a cylindrical or polygonal pipe. There are no particular limitations on the size of the cross-linked polyethylene pipe as long as it meets the specifications of commonly used hot water supply piping, etc., but in general, it is preferable that the outer diameter is 6 to 200 mm, the thickness is 1 to 30 mm, and the length is 0.3 to 200 m.

[0015] The cross-linked polyethylene pipe may be a multi-layer pipe in which at least one of the inner surface and the outer surface of the pipe is coated with a coating layer. The material of the coating layer is preferably a flexible thermoplastic resin. Examples of such thermoplastic resins include polyolefin, polyvinylidene fluoride, polyamide, etc. One type of thermoplastic resin may be used alone, or two or more types may be used in combination.

[0016] <Cross-linked polyethylene and cross-linked polyethylene pipe manufacturing method> The cross-linked polyethylene of this embodiment is obtained by cross-linking uncross-linked polyethylene, heating it, and then cooling it. The cross-linked polyethylene pipe of this embodiment is obtained by molding uncross-linked polyethylene, cross-linking it, heating it, and then cooling it.

[0017] In this specification, uncrosslinked polyethylene refers to a resin composition in which a component for crosslinking is blended with raw material polyethylene so that crosslinking can be achieved by a crosslinking treatment, or polyethylene that has been pre-modified so that crosslinking can be achieved by a crosslinking treatment, or a resin composition containing the pre-modified polyethylene.

[0018] The method for crosslinking polyethylene is not particularly limited. Examples include the peroxide crosslinking method (Engel method) described in JP-B-45-35658 and the silane crosslinking method described in JP-B-48-1711. Among these, the silane crosslinking method is preferred.

[0019] Among silane crosslinking methods, the silane-water crosslinking method is particularly preferred. The silane-water crosslinking method is a crosslinking method in which a vinylsilane compound and a radical generator are added to polyethylene as components for crosslinking the polyethylene, and the mixture is reacted to obtain uncrosslinked polyethylene grafted with the vinylsilane compound, and the uncrosslinked polyethylene is then subjected to silanol condensation in the presence of water. In the silane water crosslinking method, in order to promote the silanol condensation reaction, a silanol condensation catalyst may be used as a component for crosslinking polyethylene in addition to the vinylsilane compound and the radical generator.

[0020] In the case of the silane water crosslinking method, the uncrosslinked polyethylene may be a resin composition in which a vinylsilane compound and a radical generator are blended with raw material polyethylene, or a resin composition in which a silanol condensation catalyst is further blended, or polyethylene grafted with a vinylsilane compound, or a resin composition containing a silanol condensation catalyst in addition to polyethylene grafted with a vinylsilane compound. Below, the manufacturing method of cross-linked polyethylene and cross-linked polyethylene pipe will be described in detail, taking the case of cross-linking by the silane water cross-linking method as an example.

[0021] [Raw material polyethylene] The density of the raw material polyethylene is not particularly limited, but is preferably 0.920 to 0.955 g / cm 3is preferable, and 0.938 to 0.950 g / cm 3 When the density of the raw material polyethylene is within the above range, it is easy to adjust the density of the resulting crosslinked polyethylene to fall within the range specified in the present invention. If the density of the raw polyethylene is equal to or greater than the lower limit, the water pressure resistance of the cross-linked polyethylene pipe is improved. If the density is equal to or less than the upper limit, the cross-linked polyethylene pipe is less likely to be excessively rigid, making it easier to bend and handle during construction. The density of the raw polyethylene is a value measured by the density gradient tube method specified in Method D of JIS K 7112.

[0022] The melt flow rate (MFR) of the polyethylene raw material is not particularly limited, but is preferably 0.01 to 10 g / 10 min. If the MFR is equal to or higher than the lower limit, the flowability is improved and moldability is good. If the MFR is equal to or lower than the upper limit, the long-term durability of the cross-linked polyethylene pipe is improved. The MFR of the raw material polyethylene is a value measured in accordance with JIS K 7210-1 under conditions of a temperature of 190°C and a load of 2.16 kg.

[0023] [Vinylsilane compounds] Examples of vinylsilane compounds include vinyltrisalkoxysilanes, and specific examples include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(methoxyethoxy)silane, etc. Among these, vinyltrimethoxysilane or vinyltriethoxysilane is preferred. In addition to the above, other vinylsilane compounds may also be used, such as vinylmethyldiethoxysilane and vinylphenyldimethoxysilane. The vinylsilane compounds may be used alone or in combination of two or more.

[0024] The amount of vinylsilane compound added is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, per 100 parts by mass of raw material polyethylene. When the amount of vinylsilane compound added is equal to or greater than the lower limit, the crosslinking reaction proceeds sufficiently. When the amount of vinylsilane compound added is equal to or less than the upper limit, the crosslinking treatment is carried out sufficiently in a short time and with a small amount of water in the crosslinking step, thereby preventing an increase in costs.

[0025] [Radical generator] Examples of radical generators include organic peroxides and organic peresters, specifically benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(peroxybenzoate)hexyne-3,1,4-bis(tert-butylperoxyisopropyl)benzene, lauroyl peroxide, tert-butyl peracetate, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butyl perbenzoate, tert-butyl perphenyl acetate, tert-butyl perisobutyrate, tert-butyl per-sec-octoate, tert-butyl perpivalate, cumyl perpivalate, and tert-butyl perdiethyl acetate. Among these, benzoyl peroxide is preferred. In addition to the above, other azo compounds such as azobisisobutylnitrile and dimethylazoisobutyrate may also be used as the radical generator. The radical generator may be used alone or in combination of two or more kinds.

[0026] The amount of radical generator added is preferably 0.005 to 1 part by mass, more preferably 0.01 to 0.5 parts by mass, per 100 parts by mass of raw polyethylene. When the amount of radical generator added is equal to or greater than the lower limit, the crosslinking reaction proceeds sufficiently. When the amount of radical generator added is equal to or less than the upper limit, deterioration of the polyethylene resin and increased costs due to excessive radical generation can be prevented.

[0027] [Silanol condensation catalyst] The silanol condensation catalyst is not particularly limited as long as it is any compound commonly used as a catalyst for promoting dehydration condensation between silanols, and examples thereof include compounds such as dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dilauryltin laurate, dibutyltin dioctoate, stannous acetate, cobalt naphthenate, lead naphthenate, ethylamine, dibutylamine, hexylamine, and pyridine; inorganic acids such as sulfuric acid and hydrochloric acid; and organic acids such as toluenesulfonic acid, acetic acid, stearic acid, and maleic acid. Among these, dibutyltin dilaurate and dioctyltin dilaurate dilauryltin laurate are preferred. The silanol condensation catalyst may be used alone or in combination of two or more kinds.

[0028] The amount of silanol condensation catalyst added is preferably 0.0005 to 1 part by mass, more preferably 0.01 to 0.5 parts by mass, per 100 parts by mass of raw material polyethylene. When the amount of silanol condensation catalyst added is equal to or greater than the above-mentioned lower limit, the crosslinking reaction proceeds sufficiently. When the amount of silanol condensation catalyst added is equal to or less than the above-mentioned upper limit, the generation of foreign matter caused by the catalyst being locally present in the extruder during extrusion and crosslinking proceeding locally can be suppressed.

[0029] [Other ingredients] Furthermore, the uncrosslinked polyethylene may contain optional components such as antioxidants, ultraviolet absorbers, organic fillers, inorganic fillers, pigments, dyes, and processing aids, if necessary. The optional components may be used alone or in combination of two or more.

[0030] [Molding and cross-linking treatment] In the silane water crosslinking method, polyethylene, a vinylsilane compound, a radical generator, and, if necessary, a silanol condensation catalyst and optional components are fed into an extruder, and the uncrosslinked polyethylene grafted with the vinylsilane compound is extruded into a tubular shape to obtain a molded tube.

[0031] The crosslinking treatment is carried out by heating the obtained molded tube in the presence of water (water vapor). The temperature during the crosslinking treatment is preferably 80 to 125°C, more preferably 95 to 115°C. When the temperature during the crosslinking treatment is equal to or higher than the above lower limit, the crosslinking reaction proceeds efficiently and the crosslinking time is shortened. When the temperature is equal to or lower than the above upper limit, the molded tube can be prevented from softening and deforming during the crosslinking reaction. In addition, when a multi-layer pipe having a coating layer is to be produced, the material for the coating layer may be subjected to multi-layer extrusion molding together with the material for the coating layer.

[0032] [Heating and cooling treatment] In order for the crosslinked formed tube to satisfy the predetermined density and heat of fusion ratio (ΔH1 / ΔHm) in the present invention, it is necessary to further carry out heating and cooling treatments.

[0033] The heating temperature after the crosslinking treatment is preferably 110 to 200°C, more preferably 120 to 180°C, and even more preferably 130 to 160°C. By heating the material at a temperature of 110°C or higher after cross-linking, some of the crystals that melt below the heating temperature recrystallize and grow during heating, changing into crystals with a higher melting temperature, improving creep resistance. Furthermore, when the temperature is lowered and recrystallization occurs, the cross-linking points inhibit crystallization, reducing the density of the cross-linked polyethylene pipe and improving flexibility. When the heating temperature is below the melting point, the higher the heating temperature after crosslinking, the smaller the heat of fusion ratio (ΔH1 / ΔHm). Also, when the heating temperature is above the melting point, the density and heat of fusion ratio (ΔH1 / ΔHm) do not depend on the heating temperature but on the cooling rate.

[0034] Furthermore, by setting the heating temperature after the crosslinking treatment to 200° C. or less, it is possible to suppress oxidative degradation of the resin. The heating time after the crosslinking treatment is not particularly limited, but is preferably 0.5 to 12 hours, and more preferably 0.5 to 3 hours. When the heating time after the crosslinking treatment is equal to or greater than the lower limit, crystal melting proceeds sufficiently. When the heating time is equal to or less than the upper limit, oxidation degradation of the resin during heating can be suppressed.

[0035] After the crosslinked molded tube is heated, it is cooled. The cooling temperature is preferably 0 to 80°C, more preferably 10 to 40°C. When the cooling temperature is equal to or higher than the lower limit, time for the melted crystals to recrystallize during cooling can be ensured. When the cooling temperature is equal to or lower than the upper limit, the cooling time is shortened, allowing for efficient cooling treatment. The lower the temperature during the cooling treatment and the faster the cooling, the lower the density of the resulting crosslinked polyethylene tends to be. Furthermore, water cooling has a faster cooling rate than air cooling, and the density tends to be lower than that of air cooling. [Example]

[0036] Next, in order to specifically explain the present invention, examples of the present invention and some comparative examples for comparison with the examples will be given.

[0037] <Measurement method> [density] The density of the cross-linked polyethylene constituting the cross-linked polyethylene pipe obtained in each example was measured by cutting a 50 mm long pipe from the obtained cross-linked polyethylene pipe and using it as a test piece. The density of this test piece was determined by measuring it by the water displacement method specified in Method A of JIS K 7112.

[0038] [Heat of fusion ratio] The heat of fusion ratio (ΔH1 / ΔHm) of the cross-linked polyethylene constituting the cross-linked polyethylene pipe obtained in each example was measured using a DSC (trade name: DSC7020, manufactured by Seiko Instruments Inc.) A sample of 10±0.5 mg was cut out from the cross-linked polyethylene pipe obtained in each example, inserted into an aluminum pan, and placed in the DSC.

[0039] While purging with nitrogen at a flow rate of 50 mL / min, the sample of each example was heated from 20°C to 210°C at a rate of 10°C / min, and the heat of fusion was measured. In the obtained endothermic curve, a straight line was drawn between 60°C and 140°C as a baseline, as shown in Figure 1, and the heat of fusion in the range of 60°C to 95°C (ΔH1) and the heat of fusion in the range of 60°C to 140°C (ΔHm) were determined, and the ratio of heats of fusion (ΔH1 / ΔHm) was calculated.

[0040] [Flexural modulus] The flexural modulus of the cross-linked polyethylene constituting the cross-linked polyethylene pipe obtained in each example was measured using an autograph manufactured by Shimadzu Corporation. A rough piece 35 mm long x 5 mm wide was cut out from the cross-linked polyethylene pipe obtained in each example, and the arcs on the inner and outer surfaces of this rough piece were polished to make it smooth, to prepare a test piece 35 mm long x 5 mm wide x 1.6 to 1.8 mm thick.

[0041] The flexural modulus was measured in accordance with JIS K 7171. The test speed was 2 mm / min, and the distance between supports L was adjusted to be [L = 16 × thickness of test piece h]. The smaller the flexural modulus, the more flexible the pipe and the easier it is to install. Flexural modulus of 700 MPa or less was evaluated as good (◯), and that of more than 700 MPa was evaluated as poor (×).

[0042] [High temperature tensile creep test] The cross-linked polyethylene constituting the cross-linked polyethylene pipe obtained in each example was subjected to a high temperature tensile creep test at 80°C, and the 10-hour breaking stress was measured. The test specimens for the high-temperature tensile creep tests were prepared by punching out a cross-linked polyethylene pipe into a No. 2 dumbbell shape as specified in JIS K7115:2015, and then cutting a U-shaped notch with a diameter of 4 mm on both sides of the parallel part in the width direction, as shown in Figure 2. The values ​​in Figure 2 are in mm.

[0043] As shown in Figure 3, the 10-hour rupture stress was determined by applying three to six levels of stress to each sample at 80°C, measuring the time until the test piece ruptured at each level, plotting the measurement results with rupture time on the X axis and stress on the Y axis, and calculating an approximate straight line of the plot to obtain a creep diagram, and then calculating the stress value when the rupture time was 10 hours. The higher the 10-hour rupture stress value in the high-temperature tensile creep test, the higher the creep resistance at high temperatures. If the 10-hour rupture stress value was 8.0 MPa or higher, it was evaluated as good (◯), and if it was less than 8.0 MPa, it was evaluated as poor (×).

[0044] <Raw materials used> The raw materials used in each example are as follows: PE1: Creolex (registered trademark) K4750 (manufactured by Asahi Kasei Corporation), polyethylene density 0.947 g / cm 3 . PE2: Creolex K4125 (manufactured by Asahi Kasei Corporation), polyethylene density 0.941 g / cm 3 . PE3: Evolue® SP4030 (Prime Polymer Co., Ltd.), polyethylene density 0.938 g / cm 3 . Vinylsilane compound: trimethoxyvinylsilane (manufactured by Tokyo Chemical Industry Co., Ltd.). Organic peroxide: Perhexa 25B (manufactured by NOF Corporation). Silanol condensation catalyst: dilauryl tin dilaurate (Tokyo Chemical Industry Co., Ltd.).

[0045] <Example> [Example 1] PE1, a vinylsilane compound, an organic peroxide, and a silanol condensation catalyst were mixed and extrusion-molded to obtain a molded tube with an inner diameter of 12.8 mm and a thickness of 2.1 mm. The resulting molded tube was crosslinked by passing steam at 105°C through the tube. After crosslinking, the molded tube was heated in an oven at 130°C for 3 hours and then quenched in cold water at 10°C to produce the crosslinked polyethylene pipe of Example 1.

[0046] [Example 2] Except for using PE2 instead of PE1, extrusion molding and crosslinking treatment were carried out in the same manner as in Example 1 to obtain a molded tube. The obtained molded tube was heated in an oven at 130°C for 3 hours and then cooled by radiation in air at 25°C to produce a crosslinked polyethylene pipe of Example 2.

[0047] [Comparative Example 1] Except for using PE2 instead of PE1, a molded pipe was obtained by extrusion molding and crosslinking treatment in the same manner as in Example 1. The obtained molded pipe was used as it was, without being heated or cooled, as the crosslinked polyethylene pipe of Comparative Example 1.

[0048] Comparative Example 2 PE1 was used and subjected to extrusion molding and crosslinking treatment to obtain a molded pipe in the same manner as in Example 1. The obtained molded pipe was used as it was, without being heated or cooled, as a crosslinked polyethylene pipe of Comparative Example 2.

[0049] Comparative Example 3 Except for using PE3 instead of PE1, a molded pipe was obtained by extrusion molding and crosslinking treatment in the same manner as in Example 1. The obtained molded pipe was used as it was, without being heated or cooled, as a crosslinked polyethylene pipe of Comparative Example 3.

[0050] Comparative Example 4 Except for using PE2 instead of PE1, a molded pipe was obtained by extrusion molding and crosslinking treatment in the same manner as in Example 1. The obtained molded pipe was heated in an oven at 130°C for 3 hours and then quenched in cold water at 10°C to produce a crosslinked polyethylene pipe of Comparative Example 4.

[0051] Comparative Example 5 Except for using PE2 instead of PE1, a molded tube was obtained by extrusion molding and crosslinking treatment in the same manner as in Example 1. The obtained molded tube was heated in an oven at 120°C for 3 hours and then cooled by radiation in air at 25°C to produce a crosslinked polyethylene pipe of Comparative Example 5.

[0052] <Evaluation results> Table 1 shows the flexural modulus and high-temperature tensile creep test results for the cross-linked polyethylene pipes of each example.

[0053] [Table 1]

[0054] As shown in Table 1, the cross-linked polyethylene pipes of Examples 1 and 2 had a sufficiently low flexural modulus and good workability. They also had a high 10-hour breaking stress and good high-temperature tensile creep performance. In contrast, the cross-linked polyethylene pipes of Comparative Examples 1 and 2, which had too high a density, had good high-temperature creep performance, but had a high flexural modulus and were poor in workability. Furthermore, the cross-linked polyethylene pipe of Comparative Example 3, in which the ratio (ΔH1 / ΔHm) was too large, had a good flexural modulus, but a low 10-hour breaking stress and poor high-temperature tensile creep performance. Furthermore, the cross-linked polyethylene pipe of Comparative Example 4, which had too low a density, had a good flexural modulus, but a low 10-hour breaking stress and poor high-temperature tensile creep performance. Furthermore, the cross-linked polyethylene pipe of Comparative Example 5, which had too high a density, had good high-temperature creep performance, but had a high flexural modulus and was therefore poor in workability.

Claims

1. Cross-linked polyethylene cross-linked with a vinylsilane compound, having a resin density of 0.931 to 0.938 g / cm ３ and wherein, in the heat of fusion measured by a differential scanning calorimeter, the ratio (ΔH1 / ΔHm) of the heat of fusion in the range of 60°C to 95°C (ΔH1) to the heat of fusion in the range of 60°C to 140°C (ΔHm) is in the range of 0 to 0.

1.

2. A cross-linked polyethylene pipe, characterized in that it is made of the cross-linked polyethylene according to claim 1.

3. 3. A method for producing a cross-linked polyethylene pipe according to claim 2, characterized in that uncross-linked polyethylene is molded, cross-linked with a vinylsilane compound, heated at 110 to 200°C, and then cooled.

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