JPH06220244A - Method for recycling crystalline polyolefin resin composition containing organic peroxide - Google Patents

Abstract

PURPOSE:To recycle an uncrosslinked crystalline polyolefin resin compsn. contg. an org. peroxide as an easily reusable crystalline polyolefin resin. CONSTITUTION:Only an org. peroxide contained as a crosslinker in an uncrosslinked crystalline polyester resin compsn. is thermally decomposed without causing the crosslinking of the compsn. by applying pressure to the compsn. to elevate the m.p. of the crystalline polyolefin resin above the thermal decomposition point of the peroxide and heating the compsn. to a temp. between the elevated m.p. and the decomposition point. Thus, the compsn. that has not been converted into a salable product can be recycled as a reusable crystalline polyolefin resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, an insulating material for a polyethylene insulated power cable, a semiconductive material, or a material for a crosslinked foamed molded article, which is an organic material which has not been commercialized after being extruded from an extruder. The present invention relates to a method of regenerating a crystalline polyolefin resin composition containing a peroxide into a reusable resin composition by decomposing and deactivating only the contained organic peroxide.

[0002]

2. Description of the Related Art Conventionally, a composition prepared by blending a crystalline polyolefin resin with an organic peroxide as a cross-linking agent has been used as a material such as an insulating material for electric cables or a protective sheath material, or a cross-linked polyolefin foam molded article. Has been done. And, usually, the organic peroxide used in the production of the crosslinked resin molded body, the one that does not decompose at the melt extrusion temperature of the resin composition, and that the crosslinking rate in the subsequent crosslinking step is not too slow is used. There is. Therefore, as the organic peroxide as the cross-linking agent, one whose thermal decomposition temperature is higher than the melting point of the crystalline polyolefin resin but which is not far from the melting point is used. In the production of a product using a crosslinkable resin composition containing such a crosslinking agent, a large amount of uncrosslinked material (so-called undecomposed organic solvent) is used for cleaning the inside of the extrusion molding machine or adjusting the dimensions of the molded product. A crystalline polyolefin composition containing an oxide, hereinafter referred to as an uncrosslinked product) is discharged from the extruder. The uncrosslinked product generated by cleaning the inside of the extrusion molding machine may be contaminated with impurities and the like. It is necessary to pelletize the crosslinked product again into the required shape.

[0003]

However, when the uncrosslinked product is remelted to pelletize it into a required shape again, the organic peroxide therein is thermally decomposed and a crosslinking reaction occurs. Repelletization of this uncrosslinked material was difficult. Further, even if the uncrosslinked product can be re-pelletized, the crosslinking of the crystalline polyolefin will proceed due to the contained crosslinking agent, and the appearance and physical properties of the extruded product molded using the regenerated pellets. Will be greatly reduced.
For this reason, it was no longer possible to reuse the regenerated crystalline polyolefin resin pellets not only as an insulating material for electric cables but also as a protective layer material or a material for a crosslinked polyolefin foamed molded article. If the structure and the physical properties of the crystalline polyolefin resin in the uncrosslinked product are treated without any change to eliminate the effect, the regenerated crystalline polyolefin resin obtained is molded. It becomes easier and the range of use is expanded. However, since an effective method for this purpose has not been found at present, an uncrosslinked product of the organic peroxide-containing crystalline polyolefin resin composition as generated through an extruder is generally buried in the soil. , Was incinerated and not reused. Such treatment is not preferable from the viewpoint of effective use of resources and the occurrence of pollution.

[0004]

[Means for Solving the Problems] In view of the above situation,
In order to expand the reusable range of the uncrosslinked material of the crystalline polyolefin resin composition containing an organic peroxide which is generated in a large amount through an extruder, intensive research was conducted on its recycling method. Crystalline polyolefin resins are often used in the production of cross-linked polyethylene insulated power cables, and dicumyl peroxide has been used as a cross-linking agent.

In the use of such an organic peroxide-containing resin composition, the inventor carried out the following experiment by assuming an uncrosslinked product of the composition which is generated through an extruder. A sheet-shaped sample was prepared from a composition in which polyethylene was mixed with dicumyl peroxide, and the melting point of polyethylene and the decomposition temperature and pressure of dicumyl peroxide when the sheet-shaped sample was heated at a heating rate of 10 ° C / min. I investigated the relationship. The obtained results are shown in FIG. As is clear from FIG. 1, under these conditions, the pressure is 5000 Kg / c.
At m ² or more, the melting point of polyethylene is higher than the thermal decomposition temperature of dicumyl peroxide. From this, the polyethylene composition containing dicumyl peroxide was treated at 10 ° C./m under a pressure of 5000 kg / cm ² or more.
It was found that when heat-treated at a temperature rising rate of in, polyethylene was not cross-linked at all and only dicumyl peroxide could be decomposed, and this polyethylene composition could be regenerated into polyethylene not containing dicumyl peroxide.

From such an experiment, the inventor newly found that the rate of increase in the melting point of the crystalline polyolefin resin due to the pressurization was higher than the rate of increase in the thermal decomposition temperature of the organic peroxide due to the pressurization. The inventors have found that by utilizing the above facts, only the organic peroxide in the uncrosslinked material of the organic peroxide-containing crystalline polyolefin resin composition can be decomposed to be ineffective, and the present invention has been completed.

That is, according to the method of the present invention, only the organic peroxide is thermally decomposed from the crystalline polyolefin resin composition containing an organic peroxide as a crosslinking agent to regenerate a crystalline polyolefin resin containing no crosslinking agent. At that time, pressure is applied to the organic peroxide-containing crystalline polyolefin resin composition to raise the melting point of the crystalline polyolefin resin to a temperature equal to or higher than the thermal decomposition temperature of the organic peroxide, and lower than the raised melting point. By heating at a temperature above the thermal decomposition temperature of the organic peroxide, the organic peroxide is thermally decomposed without crosslinking the crystalline polyolefin resin.

Examples of the crystalline polyolefin resin in the present invention include polyethylene and ethylene-based copolymers such as ethylene-vinyl acetate copolymer and ethylene-ethyl acrylate copolymer. In setting the pressurization and heating conditions in the method of the present invention, the relationship between the pressure and the thermal decomposition temperature as shown in FIG. 1 and the melting point of the resin with respect to the organic peroxide and the resin contained in the composition are previously set. Seek a relationship with. Then, based on these relationships, the minimum value of the pressure at which the melting point of the resin exceeds the thermal decomposition temperature of the organic peroxide is determined, and a pressure higher than that pressure is set as the processing capacity in the present invention, and the resin at that pressure is set. The temperature is lower than the melting point of and is higher than the thermal decomposition temperature of the organic peroxide at that pressure as the heating temperature.

The regenerated crystalline polyolefin resin obtained by the method of the present invention contains organic peroxide decomposition residues, and depending on the purpose of reuse, it may be necessary to remove such organic peroxide decomposition residues. There is. As a method for removing the decomposition residue generated by the thermal decomposition of the organic peroxide, for example, the regenerated crystalline polyolefin resin obtained is subjected to a heat treatment to easily remove it by increasing the diffusion coefficient of the decomposition residue. it can. In this case, the crystalline polyolefin resin may deteriorate due to heat, so it is desirable to heat in a vacuum.

[0010]

[Function] By pressurizing the uncrosslinked product of the crystalline polyolefin resin composition containing an organic peroxide to a predetermined pressure, the melting point of the crystalline polyolefin resin exceeds the thermal decomposition temperature of the coexisting organic peroxide. Therefore, even if the organic peroxide is heated to a temperature at which it decomposes thermally in this state, the radicals generated from the organic peroxide do not act on the crystalline polyolefin resin at the melting point or lower, and therefore the crystalline polyolefin resin No crosslinking reaction occurs, and only the organic peroxide is decomposed and the crosslinking ability is lost.

[0011]

【Example】

Example 1 When manufacturing a crosslinked polyethylene insulated power cable using the crosslinkable polyethylene resin composition for cable insulation having the composition shown in Table 1 and the semiconductive resin composition for the inner and outer conductive layers, the insulation thickness Uncrosslinked product (crosslinkable polyethylene resin composition for insulation) discharged from the extruder to adjust
Was placed in a pressure vessel and heat-treated at a pressure of 6000 Kg / cm ² and a temperature of 200 ° C. for 30 minutes. After the heat treatment, the obtained material was extruded from an extruder set at a temperature of 190 ° C. and pelletized. The pelletized state of the material after this heat treatment and the physical properties of the obtained pellets were measured. Example 2 The uncrosslinked material of the semiconductive resin composition discharged from the extruder in Example 1 was put in a pressure vessel, and the pressure was 7,000 Kg / c.
Heat treatment was performed for 30 minutes at m ² and a temperature of 200 ° C. After the heat treatment, the obtained material was extruded from an extruder set at a temperature of 190 ° C. and pelletized. The pelletized state of the material after this heat treatment and the physical properties of the obtained pellets were measured.

Comparative Examples 1 and 2 For comparison, the insulating layer before heat treatment used in Examples 1 and 2,
The same resin composition as the semiconductive layer-forming resin composition (organic peroxide-containing uncrosslinked material) was extruded from the extruder under the same pelletizing conditions as in Examples 1 and 2 without being subjected to a predetermined heat treatment. Pelletized. Table 2 shows the state of the pelletizing and the physical properties of the obtained pellets.

[0013]

[Table 1] * ... dicumyl peroxide (DCP) ** ··· 4,4 ^'- thiobis (3-methyl -6-te
rt butylphenol)

[0014]

[Table 2]

As is clear from Table 2, in the comparative example method, the uncrosslinked product of the organic peroxide-containing crystalline polyolefin resin composition is crosslinked inside the extruder to form a powder, which is pelletized. Although it was not possible, in the method of the present invention,
It can be seen that pelletization was possible without any problem, and the pellets obtained could be regenerated to have the same physical properties as the initial crystalline polyolefin resin.

[0016]

According to the method of the present invention, in the production of a crosslinked polyolefin resin molded article, for example, an organic peroxide-containing crystalline polyolefin resin which has not been commercialized after being extruded from an extruder. The uncrosslinked product of the composition can be regenerated into a reusable crystalline polyolefin resin by decomposing and deactivating only the contained organic peroxide, and its industrial effect is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a polyethylene (P) measured by using a sheet sample of a composition in which dicumyl peroxide is mixed with polyethylene, under pressure and at a temperature rising rate of 10 ° C./min.
It is a graph which shows the melting | fusing point of E), the thermal decomposition temperature of dicumyl peroxide (DCP), and the relationship of pressure.

Claims (1)

[Claims] 1. When regenerating a crystalline polyolefin resin containing no crosslinking agent by thermally decomposing only an organic peroxide from a crystalline polyolefin resin composition containing an organic peroxide as a crosslinking agent, the organic peroxide is used. Pressure is applied to the oxide-containing crystalline polyolefin resin composition to raise the melting point of the crystalline polyolefin resin to the thermal decomposition temperature of the organic peroxide or higher, and at a temperature lower than the raised melting point, and An organic peroxide-containing crystalline polyolefin resin composition characterized by thermally decomposing the organic peroxide without crosslinking the crystalline polyolefin resin by heating the organic peroxide to a temperature not lower than the thermal decomposition temperature of the organic peroxide. How to recycle things.