JP3497284B2 - Polyolefin pipe - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin pipe. 2. Description of the Related Art Pipes made of polyolefin resins such as polyethylene, polypropylene and polybutene are used as hot water supply pipes. These polyolefin pipes are supplied with hot water of 100 ° C. or less for a long time. No change is found from the outer periphery, but the inner surface is thermally oxidized and the mechanical strength is reduced, which causes damage to the pipe. For this reason, various heat stabilizers and antioxidants have been added to polyolefin resins to produce pipes. Examples of piping such as a hot water supply pipe in which the above antioxidant is added to a polyolefin resin include, for example, Japanese Patent Publication No. Sho 6
As described in JP-A-3-42932.
(A) General formula, with respect to 100 parts by weight of 1-butene: Wherein R is an alkyl group having 1 to 18 carbon atoms or an arylalkyl group, wherein 0.05 to 1.0 parts by weight of
And (B) 0.1 to 1.0 part by weight of at least one compound selected from the group consisting of the following hindered phenols: (a) 1,3,5-trimethyl-2,4,6-tris ( 3,5-di-tert-butyl-4-hydroxybenzyl)
Benzene (b) 1,3,5-tris (4-tert-butyl-3-hydroxy-2,6-dimethylphenyl) isocyanurate (c) tris (3,5-di-tert-butyl-4-hydroxyphenyl ) Isocyanurate (d) n-octadecyl-3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionate (e) bis (3,5-di-tert-butyl-4-hydroxybenzoylphosphonic acid) Nickel salt of monoethyl ester (f) 2,2-dihydroxy-3,3′-di (α-methylcyclohexyl) -5,5′-dimethyl-dimethylmethane (g) 4,4-thio-bis (3- (H) 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butyl-phenyl) butane (i) tetrakis [methylene-3 (3 5-di - tert-butyl-4-hydroxyphenyl) propionate) for methane by blending water supply and hot water supply pipe poly-1-butene resin composition is disclosed. However, in any of the formulations disclosed in JP-B-63-42932, the compounds (A) and (B) migrate mainly to the inner surface of a polyolefin resin tube such as a poly-1-butene resin. It elutes out of the system in a relatively short period of time together with the fluid and the like flowing in the inside thereof, making it difficult to use the piping system requiring heat resistance for a long period of time. [0007] These antioxidants depend on the kind and combination, but generally, in a hot water supply pipe, when the concentration in the compounded resin becomes 0.001% by weight or less, the oxidation of the resin starts and the mechanical strength is reduced. It has been clarified in the investigation of the present inventors. Oxidation degradation of the polyolefin pipe inner layer, when dissolved oxygen in the hot water diffuses into the polyolefin layer, antagonizes the antioxidant, and when the concentration of the antioxidant drops below the certain concentration by consumption or elution of the antioxidant. Oxidation occurs. In water and hot water pipes, the lowest concentration of antioxidant is on the inner surface of the pipe,
A carbonyl group is first found in this part. The diffusion rate of the antioxidant in the polyolefin layer depends on its molecular weight, and the diffusion coefficient corresponding to a molecular weight of 500 of a normal average antioxidant is 200.
It is 6 times or more the diffusion coefficient corresponding to 0. On the other hand, the transfer rate of the antioxidant from the polyolefin layer also depends on the molecular weight of the antioxidants of the same system, and the lower the molecular weight, the higher the transfer rate. The compatibility of the antioxidant with the polyolefin also depends on the molecular weight of the same type of antioxidant, and the compatibility decreases as the molecular weight increases. As described above, the current technology for imparting antioxidant properties to polyolefin pipes is not yet sufficient, and there is no pipe made of a polyolefin resin alone that can withstand long-term use in the fields of hot water supply, air conditioning, and chemical plants. There is a strong demand for improved heat resistance. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has as its object to provide a polyolefin pipe which can withstand long-term use in the fields of hot water supply, air conditioning, and chemical plants. And According to the first aspect of the present invention, there is provided a resin composition comprising a polyolefin resin having 100 parts by weight of 0.3 to 3 parts by weight of an antioxidant having a molecular weight of 2,000 to 5,000. A gist of the present invention is a polyolefin pipe characterized in that an inner layer made of a polyolefin resin composition having a thickness of 1 to 2 mm is formed. In the present invention, the molecular weight is from 2,000 to 5,000.
When the molecular weight of the antioxidant is less than 2,000, migration from the polyolefin-based resin layer is large, and when the molecular weight exceeds 5,000, the compatibility with the polyolefin-based resin is reduced, In any case, it is difficult to impart long-term heat resistance to the polyolefin pipe. The above antioxidant has a molecular weight of 2,000.
Although it is not particularly limited as long as it is an antioxidant of 5,000 to 5,000, for example, dimethyl succinate-1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-
Tetramethylpiperidine polycondensate, poly [｛6- (1,
1,3,3-tetramethylbutyl) amino-1,3,5
-Triazine-2,4-diyl} (2,2,6,6-
Tetramethyl-4-piperidyl) imino {hexamethylene} (2,2,6,6-tetramethyl-4-piperidyl) imino}], N, N'-bis (3-aminopropyl) ethylenediamine-2,4- Bis [N-butyl-N
Hindered amine-based high molecular weight type antioxidants such as-(1,2,2,6,6-pentamethyl-4piperidyl) amino] -6-chloro-1,3,5-triazine condensate are preferably used. . The polyolefin resin is not particularly restricted but includes, for example, polyethylene (crosslinked polyethylene), polypropylene and poly (1-butene). The amount of the antioxidant to be added is 0.3 to 3 parts by weight based on 100 parts by weight of the polyolefin resin, but if the amount is less than 0.3 part by weight, the oxidation of the polyolefin resin may be inhibited. When the addition amount exceeds 3 parts by weight, the effect of suppressing the oxidation of the polyolefin-based resin saturates, and even if it is added more, not only a new effect is not obtained, but also an obtained effect is obtained. Decreases the mechanical strength of the polyolefin pipe. In the polyolefin pipe of the present invention, an inner layer having a thickness of 1 to 2 mm made of a polyolefin resin to which the above-mentioned antioxidant is added is formed. If the concentration of the antioxidant that can withstand use cannot be maintained and the thickness of the inner layer exceeds 2 mm, the effect of suppressing the oxidation of the polyolefin-based resin for a long time is saturated. Not only does not provide a good effect, but also lowers the mechanical strength of the resulting polyolefin pipe. The polyolefin pipe of the present invention comprises a pipe body consisting of a tubular elongated body and various cheeses, elbows, sockets, bends, bent pipes, flanges, valves and the like used for piping the pipe body for various uses. It also includes a piping member. Means for forming an inner layer having a thickness of 1 to 2 mm made of a polyolefin resin to which the above-mentioned antioxidant has been added is not particularly limited. A polyolefin-based resin containing a normal polyolefin pipe on the outside so that the thickness of the polyolefin-based resin to which the above-mentioned antioxidant is added becomes a thickness determined for each caliber within a range of 1 to 2 mm. A two-layer extrusion method of a pipe is preferably used in which the thickness is adjusted to a standard value determined for each diameter by adding the inner layer. For the piping member, the two-layer injection molding method is suitably used similarly to the above. In addition, the polyolefin-based resin layer to which the above-mentioned antioxidant is added may be provided with a concentration gradient as required to form two or more layers, and the antioxidant concentration on the inner surface of the polyolefin pipe may be averaged over time. . The polyolefin pipe of the present invention has a molecular weight of 2000 to 50 per 100 parts by weight of the polyolefin resin.
Thickness of 1 to which 0.3 to 3 parts by weight of an antioxidant is added
Since the inner layer made of the polyolefin resin composition of ~ 2 mm is formed, the concentration of the antioxidant on the inner surface of the polyolefin pipe is gradually reduced, and is maintained at a concentration that suppresses oxidation of the polyolefin resin for a long time. It can be made, and most of the thickness of the polyolefin pipe forms an outer shell composed of a mixture of ordinary polyolefin pipe with high mechanical strength, so it can be used with hot fluids such as hot water supply, air conditioning, chemical plant fields, etc. It can be used as a piping material for long-term contact. The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Example 1 Linear low density polyethylene (manufactured by Mitsubishi Chemical Corporation, density 0.936 g / cm ³ , MFR5.
0) with a silane cross-linked polyethylene resin (MFR0.
8) Hindered amine high molecular weight type antioxidant (Ciba Geigy Co., trade name: CHIMASSORB 944, molecular weight 2500) for 100 parts by weight for the inner layer
0.5 parts by weight and 0.1 parts by weight of a phosphorus-based antioxidant are added, and 0.1 parts by weight of the above-mentioned hindered amine-based high molecular weight type antioxidant and a phosphorus-based antioxidant (manufactured by Ciba Geigy Co., Ltd. Name: IRGAFOS168) Polyethylene having a thickness of 4.5 mm and an inner diameter of 50 mm was added to 0.1 part by weight of a two-layer extruder having a caliber of 75 mm at a molding temperature of 200 ° C. and an inner layer having a thickness of 1.0 mm. A pipe was made. Example 2 Polyethylene was prepared in the same manner as in Example 1 except that the amount of the hindered amine high molecular weight antioxidant of Example 1 was changed from 0.5 parts by weight to 2.0 parts by weight. A pipe was made. Comparative Example 1 A phenolic antioxidant (trade name: IRGANOX1076, molecular weight 531, manufactured by Ciba-Geigy Co., Ltd.) was added to 100 parts by weight of the silane-crosslinked linear low-density polyethylene of Example 1
0.35 parts by weight and 0.2 parts by weight of a sulfur-based antioxidant (trade name: Nocrac 400, manufactured by Ouchi Shinko Chemical Co., Ltd.) were added, and a molding temperature of 200 ° C. was added using an extruder having a diameter of 75 mm.
Thus, a polyethylene pipe having a thickness of 4.5 mm and an inner diameter of 50 mm was produced. (Comparative Example 2) Instead of the antioxidant of Comparative Example 1, 0.2 parts by weight of the hindered amine high molecular weight type antioxidant used in Example 1 and the phosphorus-based antioxidant 0.1% were used.
A polyethylene pipe was produced in the same manner as in Comparative Example 1, except that 1 part by weight was added. Comparative Example 3 In place of the antioxidant of Comparative Example 1, 5.0 parts by weight of the hindered amine-based high molecular weight type antioxidant and phosphorus-based antioxidant used in Example 1 were used.
A polyethylene pipe was produced in the same manner as in Comparative Example 1, except that 1 part by weight was added. Example 3 Hindered amine high molecular weight type antioxidant (manufactured by Ciba Geigy Co., trade name: TINUVIN 622, molecular weight 3) for 100 parts by weight of polypropylene (MFR1.5, manufactured by Tokuyama Corporation)
000) 0.5 parts by weight and sulfur-based antioxidant (see above)
0.2 parts by weight, and 0.1 part by weight of the above-mentioned hindered amine-based high molecular weight type antioxidant and 0.1 part by weight of a sulfur-based antioxidant (described above) for the outer layer are added.
using a two-layer extruder having a thickness of 4.5 mm and an inner diameter of 50 mm at a molding temperature of 230 ° C. and an inner layer thickness of 1.0 mm.
Was produced. Example 4 Polypropylene was prepared in the same manner as in Example 3 except that the amount of the hindered amine high molecular weight type antioxidant of Example 1 was changed from 0.5 parts by weight to 2.0 parts by weight. A pipe was made. Comparative Example 4 A hindered phenol-based antioxidant (trade name: IRGANOX1 manufactured by Ciba-Geigy Co., Ltd.) was added to 100 parts by weight of the polypropylene resin of Example 3.
010, molecular weight 1178) 0.35 parts by weight and a sulfur-based antioxidant 0.2 parts by weight were added, and using an extruder having a diameter of 75 mm, a molding temperature of 230 ° C., a thickness of 4.5 mm, and an inner diameter of 5 were used.
A 0 mm polypropylene pipe was produced. Comparative Example 5 Instead of the antioxidant of Comparative Example 4, 0.2 parts by weight of the hindered amine high molecular weight type antioxidant and 0.2 parts by weight of sulfur type antioxidant used in Example 3 were used. A polypropylene pipe was produced in the same manner as in Comparative Example 4 except that the addition was performed. Comparative Example 6 In place of the antioxidant of Comparative Example 4, 5.0 parts by weight of the hindered amine high molecular weight type antioxidant and 0.2 part by weight of sulfur type antioxidant used in Example 3 were used. A polypropylene pipe was produced in the same manner as in Comparative Example 4 except that the addition was performed. Hot water at 95 ° C. was passed through the polyethylene pipes and polypropylene pipes obtained in the above Examples and Comparative Examples at a hot water pressure of 2 kg / cm ² to perform a hot water aging resistance test. Sampling was performed at regular intervals, the test sample was cut open, and the state of embrittlement on the inner surface was observed. The results are shown in Table 1. [Table 1] In the table, the arrow means the same in the left column, and the cross-linked polyethylene pipe of the example takes 33,000 hours (about 4 years).
Although no change was found after the lapse of time, the polypropylene pipe of the example showed that the sample after 33000 hours (about 4 years) had an oxidized state in which the surface was whitish and diffusely reflected light, and the surface was powdered. there were. On the other hand, the crosslinked polyethylene pipe of the comparative example has 8760 although the absolute amount per unit weight of the compounding amount is much larger than that of the example.
From time (1 year) to 25000 hours (approximately 3 years), cracks of a degree that can be visually confirmed from the above-mentioned surface powder state appeared, and the oxidation state was represented by fine cracks in the table. The polypropylene pipe of the comparative example is shorter than the crosslinked polyethylene pipe of the above-mentioned comparative example for 8760 hours (one year).
In about 17500 hours (about 2 years), the surface had been oxidized in the state of powdering to fine cracks. Since the polyolefin pipe of the present invention is constructed as described above, the concentration of the antioxidant on the inner surface of the polyolefin pipe is reduced gradually, and the concentration of the polyolefin resin for suppressing oxidation of the polyolefin resin is reduced. For a long period of time, and most of the thickness of the polyolefin pipe forms an outer shell made of a mixture of ordinary polyolefin pipe with high mechanical strength. It can be used as a piping material for long-term contact with high-temperature fluid.

Continuation of the front page (56) References JP-A-9-3266 (JP, A) JP-A-7-166000 (JP, A) JP-A-6-1000074 (JP, A) JP-A-62-262845 (JP) JP-A-4-107381 (JP, A) JP-A-63-39940 (JP, A) JP-A-7-133389 (JP, A) JP-A-5-170932 (JP, A) 2-153955 (JP, A) JP-A-3-259938 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08L 23/00 F16L 9/12

Claims (1)

(57) [Claim 1] 0.3 to 3 of an antioxidant having a molecular weight of 2000 to 5000 per 100 parts by weight of a polyolefin resin.
A polyolefin pipe comprising an inner layer made of a polyolefin-based resin composition having a thickness of 1 to 2 mm to which parts by weight are added.