JP2003253040A - Method for recycling crosslinked polyolefin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recycling a crosslinked polyolefin wherein the recycled product obtained by making the crosslinked polyolefin thermoplastic can develop markedly improved mechanical properties. <P>SOLUTION: The method for recycling the crosslinked polyolefin comprises adding 0.1-10 pts.wt. lactone antioxidant to 100 pts.wt. crosslinked polyolefin to make the crosslinked polyolefin thermoplastic. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for regenerating a crosslinked polyolefin by thermoplasticization, whereby a regenerated product having excellent mechanical properties can be obtained. [0002] Crosslinked polyolefins have excellent electrical properties and heat resistance and are therefore used in a wide range of applications such as covering materials for electric wires and cables, foam sheets, and pipes. However, cross-linked polyolefins have a three-dimensional structure due to cross-linking, so they do not melt even when heated, and are difficult to reprocess and reuse. Therefore, recovered cross-linked polyolefin products and losses generated during production are incinerated. Or, because it is landfilled as industrial waste, an effective utilization method has been desired. [0003] Conventionally, methods for recycling crosslinked polyolefins include a method of converting a crosslinked polyolefin into a petroleum raw material by converting it into a pyrolysis oil, a method of pulverizing the crosslinked polyolefin and using it as a filler for a resin, A method of reducing the molecular weight by water / subcritical water or heat / shearing force and performing thermoplasticization is known. For example, Japanese Patent No. 3026270 and Japanese Patent Application Laid-Open No. H11-189670 disclose a method in which heat and shear are applied to a crosslinked polyolefin using a twin-screw extruder or the like to continuously plasticize the crosslinked polyolefin. [0004] However, in these methods, in order to cut the molecular structure of the crosslinked polyolefin, a temperature of 200 ° C to 400 ° C is required.
Since the treatment is carried out at a high temperature of ℃, the melt flow rate (MFR) is extremely increased due to the excessive decrease in the molecular weight of the recycled product, and the quality is deteriorated such that the mechanical properties such as tensile properties are significantly reduced. Easy to cause. For this reason, when the thermoplasticized regenerated product is molded and used again, it is necessary to mix a large amount of an uncrosslinked virgin material to secure the characteristics, which is not desirable from the viewpoint of original recycling. SUMMARY OF THE INVENTION An object of the present invention is to heat a crosslinked polyolefin that does not melt even when heated so that the crosslinked polyolefin can be melt-processed, that is, to obtain a recycled product obtained by thermoplasticization. An object of the present invention is to provide a reproduction processing method capable of greatly improving mechanical characteristics. [0006] A method for regenerating a crosslinked polyolefin according to the present invention comprises the steps of:
It is characterized in that 0.1 to 10 parts by weight of a lactone-based antioxidant is added to parts by weight and is thermoplasticized. In the present invention, the thermoplasticization is performed by applying heat and shearing force to an object containing a crosslinked polyolefin using an extruder to cut the molecular structure of the crosslinked polyolefin. In the present invention, in addition to the lactone-based antioxidant, at least one selected from the group consisting of a phenol-based antioxidant, a phosphorus-based antioxidant and a sulfur-based antioxidant is added to the crosslinked polyolefin. Some antioxidants may be added. DETAILED DESCRIPTION OF THE INVENTION In the present invention, a crosslinked polyolefin is defined as an ethylene homopolymer, a copolymer of ethylene and an α-olefin or another vinyl monomer, or a mixture thereof with an organic peroxide. , A silane compound, ionizing radiation or the like. Examples of the crosslinked polyolefin include those used for coating materials of electric wires and cables, but those used for other purposes may also be used. The method and conditions for crosslinking the crosslinked polyolefin are not particularly limited. Further, for example, various acrylate compounds, methacrylate compounds, cyanurate compounds and the like may be blended in the crosslinked polyolefin as a crosslinking assistant. Further, additives such as a filler, a foaming agent, and a pigment may be blended with the crosslinked polyolefin. [0010] An electric wire using a crosslinked polyolefin as an insulator.
Many cables have a semiconductive layer on the inner and outer layers of the insulator. As the semiconductive layer, for example, a material obtained by blending a conductive carbon or the like with an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, a chlorinated polyethylene, or the like is used. The semiconductive layer preferably has a gel fraction of about 30 to 70% and accounts for about 3 to 50% of the entire coating. According to the method of the present invention, the desired effect can be obtained even when such a special wire waste material is mixed into the crosslinked polyolefin. Specific examples of the lactone antioxidant used in the present invention include the following. 3- (2-acetoxyethoxy) phenyl-5,7
-Di-tert-butyl-benzofurano-2-one,
5,7-di-tert-butyl-3- (4- (2-stearoyloxyethoxy) phenyl) benzofurano-2
-One, 5,7-di-tert-butyl-3- (4-ethoxyphenyl) benzofurano-2-one, 3- (4-
(Acetoxy-3,5-dimethylphenyl) -5,7-di-tert-butylbenzofurano-2-one, 3-
(3,5-dimethyl-4-pivaloyloxyphenyl)
-5,7-di-tert-butylbenzofurano-2-one, 5,7-di-tert-butyl-3-phenylbenzofurano-2-one, 5,7-di-tert-butyl-
3- (3,4-dimethylphenyl) benzofurano-2-
On, 5,7-di-tert-butyl-3- (2,3-
Dimethylphenyl) benzofurano-2-one. Particularly preferred lactone antioxidants include at least one selected from compounds represented by the following chemical formulas (I) and (II). ## STR1 ## The lactone-based antioxidant captures an alkyl radical generated by cutting the molecular structure of the crosslinked polyolefin when the crosslinked polyolefin is subjected to heat and shearing force according to the method of the present invention to be thermoplasticized. To react with oxygen and couple some alkyl radicals. For this reason,
A reclaimed product obtained by thermoplasticization (regeneration treatment) is characterized not only by having an appropriate melt flow rate, but also by having extremely good mechanical properties. The lactone-based antioxidant is added in an amount of 0.1 to 10 parts by weight, preferably 1 to 5 parts by weight, per 100 parts by weight of the crosslinked polyolefin. If the amount of the lactone-based antioxidant is less than 0.1 part by weight, there is little effect on improving the physical properties of the regenerated product, and if it is more than 10 parts by weight, problems such as a decrease in the melt flow rate occur. Therefore, it is not very preferable. In the present invention, the lactone-based antioxidant may be used alone, or a phenol-based antioxidant may be used.
You may use together with other antioxidants, such as a phosphorus antioxidant and a sulfur antioxidant. In particular, phenolic antioxidants, phosphorus antioxidants and lactone antioxidants
It is more preferable to use an antioxidant composed of a combination of types, since a more excellent antioxidant function is exhibited due to a synergistic effect. In the present invention, when a product obtained by adding a lactone-based antioxidant to a crosslinked polyolefin is thermoplasticized and regenerated, for example, a co-rotating twin-screw extruder is used. This twin screw extruder has an extrusion zone, a kneading zone, and a pressure holding zone. The pressure holding zone is provided with an element having a function to reversely feed the object to be processed (resin mixture). Elements that have this effect are usually
Seal disks, reverse flights, reverse kneading disk elements, etc. are used. Kneading zone temperature is 250
The temperature is set in a temperature range from ℃ to 400 ℃. When the kneading zone temperature is 250 ° C. or lower, the resin mixture is not sufficiently plasticized. When the temperature exceeds 400 ° C., the melt flow rate of the regenerated product is excessively increased, and at the same time, the coloring and the deterioration of mechanical properties are caused. Hereinafter, the present invention will be described in detail with reference to examples. The cross-linked polyolefin used in these examples,
Antioxidants and extruders are as follows. [Crosslinked polyolefin] Crosslinked polyethylene obtained from waste power CV cable insulator (peroxide crosslinked, gel fraction 80%) crushed to a size of 10 mm or less [Antioxidant] Lactone antioxidant Agent: IRGANOX HP 2225 / FF manufactured by Ciba Specialty Chemicals Co., Ltd.
(Mixed with phenol and phosphorus) Phenolic antioxidant: AO-7 manufactured by Asahi Denka Kogyo KK
0, AO-330 Phosphorus antioxidant: Asahi Denka Kogyo Co., Ltd. 260 Sulfur antioxidant: Asahi Denka Kogyo Co., Ltd. AO-23 [Twin screw extruder] Same-direction meshing twin screw extruder ( L / D =
48, 40 mmφ). The color, gel fraction, melt flow rate, tensile yield strength and tensile elongation at break of the recycled product were measured and evaluated by the following methods. [Coloring] Colorimeter (Minolta Co., Ltd.)
CR-300) by measuring the L ^* a ^* b ^* color specification mode, the Comparative Example 1 and color difference reference _{^{color, (L 0 *, a 0}} *, b 0 *)
And the color ΔE ^* ab was determined by the following equation. ΔE ^* ab = ((L ₁ −L ₀ ^* ) ² + (a ₁ −a ₀ ^* ) ² + (b ₁
−b ₀ ^* ) ² ) ^1/2 [Gel fraction] 0.095 to 0.10 collected from recycled product
Wrap the 5 g sample in a 400 mesh wire mesh,
It was measured according to JIS K6769 Appendix 2 "Method for measuring gel fraction of crosslinked polyethylene pipe". [Melt flow rate] JIS K720
According to No. 1, the measurement was performed at 190 ° C. × 2.16 kg. [Tensile test] Measured at a tensile speed of 200 mm / min according to JIS K7113. (Examples 1 and 2) Crosslinked polyolefin 10
0 parts by weight of a lactone antioxidant (IRGANO
X HP 2215 / FF) was added in an amount of 0.5 part by weight or 3 parts by weight, and the mixture was extruded using a twin-screw extruder while setting the temperature of the kneading zone at about 300 ° C. to obtain a regenerated product. (Comparative Examples 1 and 2) An unsuitable amount (0.05 parts by weight) of a lactone-based antioxidant was added to 100 parts by weight of crosslinked polyolefin alone or crosslinked polyethylene.
Extrusion was performed using the twin-screw extruder under the same conditions as in the example,
A refurbished product was obtained. (Comparative Examples 3, 4, 5) To 100 parts by weight of a crosslinked polyolefin, only an antioxidant other than a lactone-based antioxidant was added, and extruded using a twin-screw extruder under the same conditions as in the example. And a regenerated product was obtained. Table 1 below summarizes the amount of the antioxidant added to the crosslinked polyolefin and the coloring, gel fraction, melt flow rate, tensile yield strength, and tensile elongation at break. [Table 1] Table 1 shows the following. In Comparative Example 1, since the crosslinked polyolefin alone was extruded without adding the lactone-based antioxidant, the alkyl radical generated during the regeneration treatment could not be captured. Therefore, the recycled product has a high melt flow rate and a small tensile elongation at break. In Comparative Example 2, since only 0.05 part by weight of the lactone-based antioxidant was added to 100 parts by weight of the crosslinked polyolefin, the obtained regenerated product showed almost the same physical properties as Comparative Example 1, and the lactone-based antioxidant was obtained. No effect was observed due to the addition of the agent. Comparative Examples 3, 4 and 5 are crosslinked polyolefin 1
Since 100 parts by weight of an antioxidant other than the lactone-based antioxidant are blended and extruded, the obtained regenerated product has no particular problem in terms of gel fraction and melt flow rate, and has a good tensile property. It can be seen that although the coloration was partially improved, the progress of the coloring presumably due to burning of the antioxidant was severe. As described above, when a phenol-based, phosphorus-based, or sulfur-based antioxidant is used instead of a lactone-based antioxidant, coloring due to decomposition proceeds when heated to a temperature of about 300 ° C. I do. On the other hand, in Examples 1 and 2, 0.5 parts by weight or 3 parts by weight of a lactone-based antioxidant were added to 100 parts by weight of the cross-linked polyolefin and extruded. Shows little progress of coloring as compared with that of Comparative Example 1. The regenerated products obtained in Examples 1 and 2 had gel fractions and MFR values particularly suitable for recycling, and a tensile elongation at break of 170.
% Or 340%. As described in detail above, according to the present invention, the addition of a lactone-based antioxidant to a crosslinked polyolefin suppresses an increase in the MFR of a recycled product, and increases mechanical strength such as tensile elongation at break. Characteristics can be greatly improved, and a recycled product having characteristics preferable for recycling can be obtained.

Claims (1)

Claims: 1 to 10 parts by weight of a lactone antioxidant is added to 100 parts by weight of a crosslinked polyolefin,
A method for regenerating a crosslinked polyolefin, which comprises thermoplasticizing.