JP2002194033A - Method for producing thermoplastic graft polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inexpensive and high quality thermoplastic graft polymer which is obtained not only by recycling a crosslinked polyolefin but also by performing the plasticization and grafting of the polyolefin in the same step. SOLUTION: This method for producing the polymer is characterized in that the polyolefin is plasticized by melting and kneading at the temperature of at least one or more mixing zones and specific shear rate in a same-direction rotating biaxial extruder of a screw structure which has the mixing zone and at least one pressure retaining zone for damming or sending back a resin mixture, and a grafting agent is added in the flow direction of the mixture at least in the front of the last pressure retaining zone.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for easily producing a thermoplastic graft polymer from a crosslinked polyolefin.

[0002]

2. Description of the Related Art Conventionally, crosslinked polyolefins used for covering electric wires and foamed moldings have a feature that they are not melted by heating due to a network structure formed by crosslinking, making it difficult to rework and reuse. For this reason, it is presently incinerated or landfilled to recover and waste crosslinked polyolefins and loss during production. For example, when cross-linked polyolefins are used as wire coatings, the value of copper and other metals used as wire conductors is high, so the cross-linked polyolefin coatings are stripped from the conductor and then disposed of. In many cases, effective utilization methods were desired.

[0003] Methods for recycling cross-linked polyolefins include, in addition to thermal recycling used as fuel, a method of converting the oil into a petroleum feedstock by pyrolysis oil conversion, and a method of mechanically applying high shear to pulverized materials. There is a technique used as a reinforcing material or an expanding material for plastic molding. All of these are one-time recyclings, and are not material recyclings that are reused multiple times, but many issues still remain in terms of economic efficiency and environmental load.

Recently, a technique for regenerating and reusing cross-linked polyethylene has been proposed. Japanese Patent No. 3026270 proposes a method in which a crosslinked polyethylene is extruded at a certain temperature and a specific energy or more using a bidirectional twin screw extruder to obtain a regenerated product having a gel fraction of 0.1% or less. . Japanese Unexamined Patent Publication No. 11-189670 discloses that a cross-linked polyethylene is recycled by a method in which a twin-screw extruder having a screw having a plurality of thread blocks is used to machine with a specified specific energy, residence time, and shear stress. A way to do this has been proposed. However, these methods described above only plasticize and regenerate the crosslinked polyolefin,
It does not provide materials with new functions.

[0005]

SUMMARY OF THE INVENTION The present invention provides an inexpensive and high-quality thermoplastic graft polymer by not only recycling the crosslinked polyolefin but also plasticizing and grafting the crosslinked polyolefin in the same step. The purpose is to do.

[0006]

SUMMARY OF THE INVENTION To solve these problems, the present inventors have developed a structure having at least one or more kneading zones and at least one pressure holding zone for damming or reversing the resin mixture. In a co-rotating twin-screw extruder having a screw, the temperature of the kneading zone is 250 to 400 ° C., and the shear rate of the kneading zone is 200 / s or more. β-unsaturated carboxylic acids and derivatives thereof, C 3-20 hydrocarbons having a terminal double bond, aromatic compounds having a vinyl group as a substituent, and organosilane compounds represented by the formula RR′SiY ₂ (R
Means that at least one selected from the group consisting of monovalent olefinically unsaturated hydrocarbon groups or hydrocarboxyl groups) is added at least before the last pressure holding zone in the flow direction of the resin mixture. The present inventors have found that a thermoplastic graft polymer can be obtained from a crosslinked polyolefin by a method for producing a thermoplastic graft polymer, which is a feature of the present invention.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, it is possible to easily produce a thermoplastic graft polymer by carrying out plasticization of a crosslinked polyolefin and a graft reaction to the plasticized crosslinked polyolefin in the same step. Become.

The crosslinked polyolefin used in the present invention is ethylene or propylene alone or copolymerized with α-olefin or other derivatives, or a mixture obtained by crosslinking a mixture thereof, and the gel fraction is 30 to 90%.
The degree is preferred. The method of crosslinking is not particularly limited, but generally a crosslinking method using an organic peroxide, water crosslinking using a silane graftmer, irradiation crosslinking by irradiation with ionizing radiation, and the like are generally used. Known additives such as various acrylates, methacrylate compounds, and cyanurate compounds may be blended as a crosslinking aid. Further, additives such as an antioxidant, a filler, a foaming agent, and a pigment may be added to the crosslinked polyolefin. In the production method of the present invention, it is necessary to cut or pulverize the crosslinked polyolefin to an appropriate size.
The pulverization size varies depending on the screw diameter of the extruder, but is usually preferably 20 mm or less.

In the production method of the present invention, an α, β-unsaturated carboxylic acid and its derivative, a hydrocarbon having a terminal double bond having 3 to 20 carbon atoms, an aromatic compound having a vinyl group as a substituent, and At least one selected from the group consisting of organic silane compounds represented by the formula RR′SiY ₂ (R is a monovalent olefinically unsaturated hydrocarbon group or hydrocarboxyl group) is used for grafting (hereinafter, referred to as “R”).
In the present invention, it is referred to as a grafting agent).

[0010] The function of the grafting agent is to modify the properties of the plasticized crosslinked polyolefin. As the α, β-unsaturated carboxylic acid used as the grafting agent, acrylic acid, methacrylic acid, acrylate,
Examples include methacrylic acid esters, phthalic anhydride, maleic anhydride, and itaconic acid. Examples of the hydrocarbon having a terminal double bond and having 3 to 20 carbon atoms include 1-dodecene and 1,4-hexadiene. Examples of the aromatic compound having a vinyl group as a substituent include styrene, vinylpyridine, and divinylbenzene.

In the organic silane compound represented by the formula RR'SiY ₂ (R is a monovalent olefinically unsaturated hydrocarbon group or hydrocarboxyl group), R is, for example, vinyl, allyl, butenyl, cyclohexenyl, cyclopentane It is a monovalent olefinically unsaturated hydrocarbon group such as dienyl, cyclohexadienyl or a hydrocarboxyl group. Y is, for example, an alkoxy group such as methoxy, ethoxy, butoxy group, an acyloxy group or a propoxy group such as formyloxy or acetoxy group, -NH
Alkylamino groups such as C ₂ H _5, is an organic group capable of hydrolysis of such arylamino groups such as -NH (C ₄ H _8). R 'is a compound represented by, for example, a monovalent hydrocarbon group other than an aliphatic unsaturated hydrocarbon such as methyl, ethyl, propyl, tetradecyl, octadecyl, phenyl, benzyl, and tolyl groups or the same as Y).
In particular, it is desirable to use an organic silane compound represented by RSiY _{3 in} which R ′ is the same as Y, and for example, vinyltrimethoxysilane, vinyltriethoxysilane and the like are preferable. Formula RR ′ used in the method of the invention
The amount of the organic silane compound represented by SiY ₂ is 0.1 to 15 parts by weight with respect to the crosslinked polyolefin 100 parts by weight, preferably 1 to 10 parts by weight.

Conventionally, in order to produce a thermoplastic graft polymer, it was necessary to add an organic peroxide as a graft initiator. However, in the present invention, radicals generated in the process of thermoplasticizing a crosslinked polyolefin are grafted. It acts as an initiator and can be grafted even with the addition of a vinyl compound alone. Of course, an organic peroxide may be added as needed. In the production method of the present invention, the step of plasticizing the crosslinked polyolefin and the step of grafting the grafting agent are performed in the same step using a co-rotating twin-screw extruder. The extruder screw has a screw having at least one or more kneading zones and a pressure holding zone for damping or reverse feeding at least one or more resin mixtures.

The kneading zone is mainly composed of elements called kneading disks and rotors, in which shearing stress is applied to the resin mixture. At least one kneading zone is provided on the extrusion head side with a pressure holding zone which acts to dam or reverse the material.
The pressure holding zone is composed of an element having a function of damming or reverse feeding the resin mixture, and is usually provided with a sealing disk, a reverse flight, a reverse kneading disk element and the like. The grafting agent is applied before the last pressure holding zone, relative to the flow direction of the resin mixture. What is important is that the grafting agent be added just before the pressure holding zone when there is one pressure holding zone and before the last pressure holding zone when there are a plurality of pressure holding zones.

More specifically, a supply device such as a plunger pump or a side feeder capable of mixing a predetermined amount of a grafting agent is provided between a material supply section and a zone where the thermoplasticization of the crosslinked polyolefin is completely completed. Examples include a method of injecting a compound and a method of using a mixture of the crosslinked polyolefin and a vinyl compound in a mechanical mixer. The grafting agent may be diluted with a solvent as necessary, or a mixture of a plurality of vinyl compounds may be used. It is more preferable to mix the grafting agent in a state where the cross-linked polyolefin is not sufficiently plasticized in order to increase the grafting rate. It is preferred to use the above or to mix the grafting agent simultaneously in the kneading zone. In the pressure holding zone, by increasing the pressure in the kneading zone, the crosslinked polyolefin is plasticized in the kneading zone, and a sufficient residence time for generating radicals is secured. The pressure holding zone is
It is desirable to provide after the kneading zone with respect to the flow direction of the resin mixture, but depending on the case, it may be arranged at the middle of the kneading zone provided at several places, or may be arranged at a plurality of places such as immediately after the middle of the kneading zone You may.

[0015] In the kneading zone, the crosslinked polyolefin is plasticized in a temperature range of 250 to 400 ° C. The kneading zone temperature is the temperature of the extruder barrel, and is usually measured with a thermocouple or the like. In order to set the kneading zone in this temperature range, external heating by an extruder barrel heater or the like is generally used, but shear heat generated by kneading the crosslinked polyolefin inside the extruder may be used as a heat source. If the temperature of the kneading zone is lower than 250 ° C., the plasticization cannot be performed sufficiently. If the temperature exceeds 400 ° C., the MFR of the plasticized product is excessively increased, which causes deterioration in quality.
In particular, when using a crosslinked polyolefin having a gel fraction of about 60 to 80%, the temperature range of the kneading zone is 300 to 3%.
A temperature range of 50 ° C. is desirable.

When the crosslinked polyolefin is plasticized by the above-described extruder and screw configuration, the shear rate in the kneading zone needs to be 200 / s or more. Here, the shear rate is a numerical value obtained by dividing the peripheral speed (mm / s) of the outermost peripheral portion of the screw element by the clearance (mm) between the screw and the barrel. The higher the shear rate, the greater the shear stress applied to the material. It becomes possible. If the shear rate is less than 200 / s, the material cannot be given sufficient shearing stress, and will be discharged from the extruder without sufficient plasticization, making it difficult to re-form the plasticized product. Become. The shear rate may be 200 / s or more, but the upper limit is preferably 5000 / s in order to suppress an excessive increase in MFR and deterioration of the thermoplastic graft polymer.

In addition, conventional additives of polyolefins such as, for example, stabilizers, antistatic agents, and organic or inorganic coloring agents can be appropriately added so that they do not hinder the grafting reaction. The extrusion zone closest to the extrusion head of the extruder serves to cool the grafted polyolefin to a temperature suitable for extrusion to prevent re-crosslinking reaction and deterioration reaction after extrusion, and to extrude the plasticized product at a constant speed. Therefore, a certain length is required, and the length is preferably 5 or more in L / D. When L / D is less than 5, the plasticized material heated in the kneading zone is extruded without cooling. In some cases, burning of the plasticized product may occur after extrusion or may cause deterioration in quality such as coloring. In the extrusion zone, it is necessary to cool and extrude the grafted polymer to a predetermined temperature. Therefore, the temperature of the extrusion zone is preferably in the range of 80 to 250 ° C. If the temperature is lower than 80 ° C., the melt viscosity of the grafted polymer becomes high, so that the extrusion becomes unstable and the load on the extruder increases, which is not economical. If the temperature is higher than 250 ° C., the grafted polymer which has come into contact with the atmosphere after extrusion tends to deteriorate, and in extreme cases, burning occurs. Desirable extrusion zone temperatures are between 120C and 220C.

The thermoplastic graft polymer produced by the method of the present invention has a gel fraction of 0.3 to 30%, and has a state in which minute crosslinked portions are present. This minute crosslinked portion is not only a problem in ordinary applications of a thermoplastic graft polymer, but also forces a gel fraction of 0.1.
If the plasticization is lower than 3%, an excessive increase in MFR and deterioration of the thermoplastic graft polymer are caused, which is not preferable. The gel fraction of the thermoplastic graft polymer is
Although it varies depending on the application, it is preferably about 1 to 20% in the case of extrusion molding, and preferably about 0.3 to 2% for high flow applications such as injection molding.

Hereinafter, the present invention will be described in detail with reference to the following examples. Examples 1 to 5 Organic peroxide crosslinked polyethylene obtained from power CV cable coating waste material (peroxide crosslinked, gel fraction 80%) was pulverized to a size of 10 mm or less, and the feed zone length in order from the hopper side. L / D = 16, kneading zone length L / D
= 10.5, pressure holding zone length L / D = 1, feed zone length L / D = 11, pressure holding zone length L / D =
0.5, co-rotating twin screw extrusion (L / D = 48, 4) having a screw having an extrusion zone length L / D = 9.
0 mmφ), and vinyltrimethoxysilane as a grafting agent having the composition shown in Table 1 was added by a plunger pump installed in a kneading zone. At this time, the temperature and shear rate of the kneading zone were set to the conditions shown in Table 1. The gel fraction of the obtained graft polymer was measured.
Next, the catalyst MB was mixed with the graft polymer, kneaded, and then immersed in hot water of 80 ° C. for 24 hours to crosslink. Then, the gel fraction and the melt flow rate of the obtained crosslinked polyethylene were measured.

Examples 6 and 7 Organic peroxide-crosslinked polyethylene obtained from waste CV cable coating waste (peroxide crosslinked, gel fraction: 80%) was crushed to a size of 10 mm or less and fed in order from the hopper side. Zone length L / D = 16, kneading zone length L / D
= 10.5, pressure holding zone length L / D = 1, feed zone length L / D = 11, pressure holding zone length L / D =
0.5, co-rotating twin screw extrusion (L / D = 48, 4) having a screw having an extrusion zone length L / D = 9.
0 mmφ), and a styrene monomer as a grafting agent having the composition shown in Table 2 was added by a plunger pump installed in a kneading zone. At this time, the temperature and shear rate of the kneading zone were set to the conditions shown in Table 2, and the gel fraction of the obtained graft polymer was measured.

Examples 8, 9 CV for power milled to a size of 10 mm or less according to the formulation shown in Table 2 using maleic anhydride as a grafting agent
Dry blend with organic peroxide crosslinked polyethylene obtained from cable coating waste material (peroxide crosslinked, gel fraction 80%) and feed zone length L / D in order from hopper side
= 16, kneading zone length L / D = 10.5, pressure holding zone length L / D = 1, feed zone length L / D = 1
1. It was charged into a co-engaging twin-screw extruder (L / D = 48, 40 mmφ) having a screw with a pressure holding zone length L / D = 0.5 and an extrusion zone length L / D = 9. At this time, the temperature and shear rate of the kneading zone were set to the conditions shown in Table 2, and the gel fraction of the obtained graft polymer was measured.

Example 10 Organic peroxide-crosslinked polyethylene obtained from waste materials (peroxide-crosslinked, gel fraction: 80%) coated with power CV cables was ground to a size of 10 mm or less, and the feed zone length was set in order from the hopper side. L / D = 16, kneading zone length L / D
= 10.5, pressure holding zone length L / D = 1, feed zone length L / D = 11, pressure holding zone length L / D =
0.5, co-rotating twin screw extrusion (L / D = 48, 4) having a screw having an extrusion zone length L / D = 9.
0 mmφ), and a compound obtained by dissolving dicumyl peroxide (hereinafter abbreviated as DCP) as a radical generator in a ratio shown in Table 2 in a weight ratio of 100: 3.2 to vinyl kneading zone. It was added by an installed plunger pump. At this time, the temperature and shear rate of the kneading zone were set to the conditions shown in Table 2, and the gel fraction of the obtained graft polymer was measured. Next, the obtained graft polymer was mixed with the catalyst MB and kneaded.
The polymer was immersed in warm water at 24 ° C. for 24 hours for crosslinking.

Comparative Examples 1 to 3 Organic peroxide-crosslinked polyethylene obtained from waste materials coated with power CV cables (peroxide crosslinked, gel fraction: 80%) was crushed to a size of 10 mm or less and fed in order from the hopper side. Zone length L / D = 16, kneading zone length L / D
= 10.5, pressure holding zone length L / D = 1, feed zone length L / D = 11, pressure holding zone length L / D =
0.5, co-rotating twin screw extrusion (L / D = 48, 4) having a screw having an extrusion zone length L / D = 9.
0 mmφ), and vinyltrimethoxysilane as a grafting agent having the composition shown in Table 1 was added by a plunger pump installed in a kneading zone. At this time, the temperature and shear rate of the kneading zone were set to the conditions shown in Table 3, and the gel fraction of the obtained graft polymer was measured.
Next, the catalyst MB was mixed with the obtained graft polymer,
The mixture was kneaded and then immersed in warm water of 80 ° C. for 24 hours for crosslinking. For Comparative Examples 1 and 2, the gel fraction and the melt flow rate were not measured because the molding process was impossible, and the gel fraction and the melt flow rate of the crosslinked polyethylene obtained only in Comparative Example 3 were measured. .

The gel fraction and melt flow rate of the above Examples and Comparative Examples were measured as follows, and the results are also shown in Tables 1 to 3. (Gel Fraction) 0.3 g or more of a sample was wrapped with a 400-mesh wire net, and measured in accordance with JIS K6769 Appendix 2 “Gel Fraction Measurement Method for Crosslinked Polyethylene Pipe”. (Melt flow rate) 1 according to JIS K7210
It was measured at 90 ° C. × 2.16 kg.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

As is apparent from Tables 1 to 3, a graft polymer having a graft ratio of 1 to 80% can be obtained by the production method of the present invention. Grafting was performed not only in the case of using vinyltrimethoxysilane as a grafting agent, but also in Examples 6 and 7 using a styrene monomer and Examples 8 and 9 using maleic anhydride. In Comparative Example 1, the temperature range of the kneading zone is out of the range of the present invention, and in Comparative Example 2, the shear rate is out of the range of the present invention, so that only a graft polymer that cannot be molded can be obtained. In Comparative Example 3, since the temperature range of the kneading zone was out of the range of the present invention, the melt flow rate was excessively high even after plasticization, and coloring due to deterioration became remarkable, so that a good graft polymer could not be obtained. .

[0029]

According to the present invention, a crosslinked olefin is extruded at a specific temperature and a shear rate using a co-rotating twin-screw extruder, and a thermoplastic graft polymer is produced by adding a grafting agent. Becomes possible. Even a crosslinked polyethylene having a high gel fraction, which has been difficult to plasticize with the conventional processing methods, can be plasticized to a practically no problem level, and can be grafted to obtain a high-quality regenerated material. The obtained graft polymer can be processed by an ordinary molding machine, and material recycling in the true sense can be achieved.

Claims (1)

[Claims] 1. A co-rotating twin-screw extruder having at least one or more kneading zones and a screw having at least one pressure holding zone for damming or back-feeding the resin mixture, wherein At a temperature of 250 to 400 ° C., the kneading zone has a shear rate of 200 / s or more, melt-kneads and plasticizes the crosslinked polyolefin, and has an α, β-unsaturated carboxylic acid and its derivative, and a terminal double bond. A hydrocarbon having 3 to 20 carbon atoms, an aromatic compound having a vinyl group as a substituent, and an organic silane compound represented by the formula RR′SiY ₂ (R is a monovalent olefinically unsaturated hydrocarbon group or a hydrocarboxyl group) At least one selected from the group consisting of at least before the last pressure holding zone with respect to the flow direction of the resin mixture. Method for producing a thermoplastic graft polymers, characterized in that the pressure.