JPH0357848B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a silane-crosslinked polyolefin molded product, and more particularly to a method for producing a silane-crosslinked polyolefin molded product that does not generate voids at the interface with other rubber or plastic layers co-extruded in a common head. It is. Conventionally, in general, a method for producing a silane-crosslinked molded product of polyolefin involves adding an organic silane compound and an organic peroxide to polyolefin and causing a graft reaction to form a silane-grafted polyolefin.
This is produced by extrusion molding or the like in the presence of a silanol condensation catalyst to obtain a molded product, and then exposing the molded product to an atmosphere containing moisture to crosslink it. In this case, the silanol condensation catalyst is added either after the silane grafting of the polyolefin or mixed at the same time as the silane grafting. There is a strong tendency for this method to be commonly used. In addition, when manufacturing high-voltage power cables by coating conductors with two or three layers of a silane crosslinked material and other rubber or plastic compositions, the following three methods are used: be able to. That is, (1) As shown in Figure 1, the internal conductive layer is extruded, wound up, used as a supply, extruded a silane cross-linked polyolefin layer thereon, wound up, and again used as a supply. A method of extruding an outer conductive layer onto the silane crosslinked polyolefin layer. In other words, it is a method consisting of completely separate steps. (2) As shown in Figure 2, a method in which extruders are installed sequentially in one extrusion line, and each extruder sequentially extrudes an inner conductive layer, a silane-crosslinked polyolefin layer, and an outer conductive layer. Namely, tandem extrusion method. (3) As shown in Figure 3, a method in which three extruders are installed on one extrusion line and the forming dies (crossheads) are used together to simultaneously extrude three layers at once. Namely, common extrusion method. Here, method (1) is difficult to adopt because the extrusion steps are completely separate, resulting in decreased productivity and increased costs. Next, in method (2), after extruding the internal conductive layer, it is immediately supplied to the silane crosslinked polyolefin layer forming step, but at this time, the internal conductive coating layer is not completely cooled until the molding die of the silane polyolefin molded body is pressed. In other words, the cable obtained through this process is likely to have poor electrical properties because it becomes rubbed at the nipple (the internal conductive layer lacks smoothness). Finally, method (3) allows extrusion coating on the conductor simultaneously with three layers, so the fatal problem of the internal semiconducting layer impairing the smoothness as in (2) is unlikely to occur. . However, as the concept is shown in FIGS. 4 and 5, in this method, the silane crosslinked body 1
There is a drawback that voids 4 are generated at the mutual interface 3 between the inner conductive material 2 and the outer conductive material 2, or inside the silane crosslinkable resin 1 itself, which deteriorates the electrical characteristics. In addition to high voltage polyolefin insulated power cables, silane crosslinked polyolefin 1 has excellent properties such as chemical resistance and environmental crack resistance.
Various studies are being conducted on molded products with two- or three-layer laminated structures with other rubber or plastic layers, such as pipes and sheets, but in addition to voids in the silane crosslinked layer, At present, realization of this method is hindered by a decrease in adhesion between the two layers due to the effect of voids 4 occurring at the interface with the rubber or plastic layer. As a result of intensive studies aimed at solving these drawbacks, the inventors of the present invention discovered that the silane crosslinked polyolefin crosslinked layer 1 and another rubber or plastic layer were placed in a common head in the simultaneous presence of the above-mentioned silanol condensation catalyst. In order to obtain a molded product by co-extrusion molding, the multilayer melt molded product obtained by common co-extrusion is cooled and solidified in a pressurized atmosphere of 0.2 Kg/cm ² or more and less than 3.0 Kg/cm ² . crosslinked resin layer 1,
Furthermore, it has been found that the voids 4 occurring at the interface 3 with other rubber or plastic layers can be eliminated, thereby solving the above-mentioned problems at once. That is, the method for producing a silane-crosslinked polyolefin molded article of the present invention includes a silane-crosslinked polyolefin layer 1 in which an organic silane compound, an organic peroxide, and a silanol condensation catalyst are present in a polyolefin.
A method for producing a silane-crosslinked polyolefin molded article by co-extruding at least one layer of the same with another rubber or plastic layer 2 in a common head, the silane-crosslinked polyolefin layer obtained by co-extrusion molding in a common head and the other rubber. Or a multilayer melt-molded body consisting of plastic layers with 0.2
It is characterized by being cooled and solidified under a pressurized atmosphere of Kg/cm ² or more and less than 3.0 Kg/cm ² . Regarding the phenomenon of generating voids 4 at the interface, etc., it has not necessarily been possible to clarify this in detail, but according to the results of multifaceted studies by the present inventors, Gas components such as unreacted silane compounds and methanol generated during the crosslinking reaction are dissolved in the polyolefin, but when it is discharged from the molding die and coated on the conductor 5, the resin pressure is released. As the resin temperature decreases, the aforementioned gas components are sequentially volatilized from the surface of the crosslinked polyolefin silane body 1. Here, in the case of common extrusion in which both sides or one side of the silane crosslinked body 1 are coated with another rubber or plastic layer 2, the gas permeability between the silane crosslinked polyolefin layer 1 and the other rubber or plastic layer 2 is determined. , and solidification of other rubber or plastic composition layers on that side of the silane-crosslinked polyolefin layer and on the conductor 5 side before all gaseous components have volatilized from the silane-crosslinked polyolefin layer due to slight differences in the crystallization rate of the polymers. It is presumed that the gas components that could not be volatilized as a result gather particularly at the mutual interface 3 between the silane-crosslinked polyolefin resin layer 1 and the other rubber or plastic layer 2, forming voids 4. In contrast, in the method of the present invention, by cooling the melt discharged from the molding die opening under a pressurized atmosphere, the saturated solubility of the gas component in the silane crosslinked polyolefin layer 1 to be solidified is increased, and as a result, the gas component is evaporated. It becomes possible to confine and solidify gas components that could not otherwise be dissolved in the silane cross-linked polyolefin layer 1, thereby eliminating the void generation phenomenon in the silane cross-linked body and at the interface with other layers. It is roughly estimated. The phenomenon of void generation is naturally correlated with the pressurized cooling atmosphere, that is, the pressure state during cooling, and the voids 4 tend to disappear as the pressure is increased. Note that if the pressing force is 0.1 Kg/cm ² or less, it will be difficult to remove all the voids 4, and the voids 4 will completely disappear in the range of 0.2 to 3 Kg/cm ² . In addition, as a specific example necessary for pressurized cooling,
It is shown in FIG. Pressure Example A structure 11 in which the extruder B side of the device body A can be directly connected to the molding die C (for example, a slide tube is provided to make the molding die C and the cooling tank body A completely sealed). do. Further, a gasket 12 having a hole approximately equal to the outer diameter of the cable is provided at the rear portion as a seal. Cooling is carried out by shearing 13, and a piston valve 14 is provided to discharge water outside the cooling device main body A, thereby blocking the pressure inside the cooling tank from leaking outside the main body A while adjusting the water level. Pressurization is performed using nitrogen gas and air from a cylinder 15 or a compressor, and the pressure is adjusted by a valve 16. Next, in the present invention, the other rubber or plastic layer 2 co-extruded at the same time as the above-mentioned silane-crosslinked polyolefin 1 is ethylene-
In addition to polyolefin resins such as vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, and ethylene-propylene copolymer, other plastic and rubber materials such as vinyl chloride, polyester, and nylon-66 are all used. There are no particular limitations, and desired fillers such as these conductive carbon black inorganic fillers may be mixed therein. Furthermore, in the present invention, simultaneous extrusion using a common head refers to, for example, a general method in which two or more extruders are installed to share a single crosshead, and two or more layers of material are simultaneously extruded and coated on a conductor. It means the method. As is clear from the above description, the present invention provides a silane-crosslinked polyolefin layer in which an organic silane compound, a peroxide, and a silanol condensation catalyst are simultaneously present in a polyolefin, at least one layer 1 is common-headed with another rubber or plastic layer 2. By cooling and solidifying the multilayer melt molded product obtained in the method for producing a silane-crosslinked polyolefin molded product co-extruded in a pressurized atmosphere of 0.2 Kg/cm ² or more and less than 30 Kg/cm ² , the above-mentioned molded product is The problem of voids can be solved, and as a result, the effect of contributing to improving the properties of the molded product, specifically, the electrical properties of the covered wire, is very large. The present invention will be described below with reference to Examples. Example 1 Extruder A (D=60φ, L/D=30) and extruder B (D=45φ, L/D=24) were installed,
Co-extrusion molding was carried out on the conductor using the following coating material and extrusion conditions to form a two-layer extrusion molded product in which the coating material of extruder B was coated on the conductor side and the coating material of extruder A was coated on the upper layer of layer B. Obtained. (Extruder A) Low density polyethylene 100 parts by weight Vinyltrimethoxysilane 2.0 〃 Dicumyl peroxide 0.16 〃 Irganox 1010 (anti-aging agent) 0.4 〃 Dibutyltin dilaurylate 0.2 〃 Extrusion conditions Extrusion temperature 190℃ Screw rotation speed 60rpm (Extruder B) Ethylene ethyl acrylate copolymer 50 parts by weight Conductive carbon black 50 〃 Extrusion conditions Extrusion temperature 180℃ Screw rotation speed 35rpm The two-layer extrusion melt discharged from the forming die was
The wire was cooled with water under a pressurized atmosphere of Kg/cm ² to obtain a silane crosslinked polyethylene insulated wire with an inner conductor. Comparative Example 1 A two-layer extrusion melt obtained in the same manner as in Example 1 was cooled by passing through water under normal pressure to obtain a silane-crosslinked polyethylene insulated wire with an inner conductor. Example 2 An insulated wire of the same structure was obtained in exactly the same manner as in Example 1 except that the conditions of extruder B were changed as follows. (Extruder B) Thermoplastic elastomer (TPR5965 manufactured by Uniroyal) 100 parts by weight Extrusion conditions Extrusion temperature 170℃ Screw rotation speed 38prm, Example 2 A two-layer extruded melt obtained in the same manner as Example 2 was placed in water under normal pressure. The insulated wire had the same structure as that of Example 2. Example 3 The conditions of extruder B in Example 1 were carried out as follows, and a two-layer extrusion molded product was produced in which the coating material of extruder A was on the conductor side and the upper layer of layer A was coated with the coating material of extruder B. I got it. (Extruder B) Nylon 66 100 parts by weight Carbon black 2 Extrusion conditions Extrusion temperature 240℃ Screw rotation speed 33rpm The two-layer extrusion melt discharged from the forming die was 0.5
The wire was cooled with water under a pressurized atmosphere of Kg/cm ² to obtain a silane-crosslinked polyethylene insulated wire with a nylon coating. Comparative Example 3 A two-layer extruded melt obtained in the same manner as in Example 3 was cooled by passing through water under normal pressure to obtain an insulated wire having the same structure. When the characteristics of each insulated wire obtained in the above Examples and Comparative Examples were investigated, the characteristics are shown in the following table, and it was clear that the Example products were superior in all cases.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a process explanatory diagram showing an example of the conventional separate tandem method of manufacturing a high-voltage power cable containing a silane crosslinked material, and FIG. 2 is a process diagram showing an example of the conventional three-layer tandem method. FIG. 3 is a process explanatory diagram showing an example of the conventional three-layer common extrusion method, and FIG. 4 is a cross-sectional explanatory diagram conceptually showing the generation of voids in an example of the conventional method. Similarly, FIG. 5 is a cross-sectional explanatory diagram conceptually showing the generation of voids in another example of the conventional method, and FIG. 6 is a schematic explanatory diagram showing the pressurized cooling process in an embodiment of the present invention. It is. 1... Silane crosslinked resin layer, 2... Other resin layer (inner conductive material and outer conductive material), 3... Interface,
4... Void, 5... Conductor, 11... Structure in one embodiment of the present invention, 12... Packing, 13
...Shear ring, 14...Piston valve, 15
...Cylinder, 16...Pressure control valve, A...Pressure cooling device body, B...Extruder, C...Forming die.

Claims (1)

[Scope of Claims] 1 At least one layer of a silane crosslinked polyolefin in which an organic silane compound, an organic peroxide, and a silanol condensation catalyst are present in a polyolefin is coextruded with another rubber or plastic layer in a common head to obtain a silane product. In a method for producing a cross-linked polyolefin molded article, a multilayer melt-molded article consisting of a silane cross-linked polyolefin layer obtained by co-extrusion molding at a common head and another rubber or plastic layer is weighed at 0.2 kg/kg.
A method for producing a silane-crosslinked polyolefin molded article, which comprises cooling and solidifying under a pressurized atmosphere of ^{2 cm2} or more and less than 3.0 Kg/cm2.