JPS6254648B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to an improved method for producing molded products such as pipes, tubes, and wire coating layers made of silane-crosslinked linear ethylene copolymers. Generally, when obtaining extruded products such as pipes, tubes, or wire coating layers using an extruder, there may be cases where the finished state of the pipes, etc. is unsatisfactory, or when trying to obtain these products with crosslinked products. There is a problem in that the degree of crosslinking becomes non-uniform in the length direction, making it impossible to obtain uniform properties. Polyethylene is the most widely used resin for such molded articles, and this polyethylene generally includes low-density polyethylene produced by a high-pressure method and high-density polyethylene produced by a medium-low pressure method. However, in recent years, the relative relationships of polyethylene products produced by this production method do not necessarily match, and for example, low-density polyethylene obtained by a medium-low pressure method is also well known. This low-density polyethylene is a copolymer of ethylene and higher α-olefins such as butene-1 and pentene-1, which are produced by, for example, the Phillips method, the Ziegler method, or a method using a chromium compound as a catalyst. Compared to the low-density polyethylene produced by the conventional high-pressure method mentioned above, it has a linear structure in its molecular structure that does not contain long chain branches but only short chain branches based on comonomers (because of this structure, it is generally called a linear ethylene copolymer). Hereafter, I will refer to this as L-
(also abbreviated as LDPE). The number average molecular weight (n) is about 30% larger than that obtained by the high-pressure method, and the molecular weight distribution (M/M) is also characterized by a narrow value of about ≧2.7 to ≦4.0. Due to such differences in molecular structure, etc., the above-mentioned L-
LDPE has better tensile strength, impact resistance, heat resistance and resistance than traditional high pressure low density polyethylene.
Polyolefins have been widely used in recent years because they exhibit excellent physical properties such as ESCR (environmental cracking resistance) and can provide excellent properties to wire coating materials. Furthermore, polyolefins are generally used to improve the mechanical properties of electrical wires by crosslinking them. Generally, it is molded as a crosslinked molded product because it can further increase the physical properties and heat resistance. However, on the other hand, this L-LDPE has a different molecular structure as mentioned above, for example, it does not contain long chain branches during extrusion melting, so there is less molecular entanglement, and the molecular weight distribution is narrow and sharp. High shear rate during melting (10 ^-2 ~10 ^-3 /sec)
Approximately twice the viscosity (apparent viscosity 2×
10 ^-4 Poise), and as a result, it is easy to generate heat and increase the resin pressure in the extruder, which tends to deteriorate the appearance of the molded product, ie, the finished state described above. Furthermore, during silane crosslinking, which is widely applied to crosslinking this type of resin, the reaction conditions of the silane compound etc. in the extruder tend to become non-uniform, resulting in the above-mentioned instability of the gel fraction. Moreover, the extruded product suffers from serious defects such as surface irregularities, rough skin, and foaming, which contribute to deterioration in the finish of the molded product. Therefore, various considerations have been made regarding the extrusion conditions of the extruder and the amount of silane compounds added, etc., in order to avoid the above-mentioned problems. However, at present, regarding the molding of crosslinked molded products using L-LDPE, the surface of the molded product can be maintained smooth and the desired degree of crosslinking can be achieved even by adjusting the amount of silane compounds added and controlling the extrusion conditions. It is extremely difficult to obtain a molded product with a high temperature, and each time the type of molded product, extrusion conditions, extrusion material, etc. change, it is necessary to find the interrelationships between the amount of the silane compound added and the various properties of the molded product. I was worried that having to do this would not only unnecessarily increase work costs but also become a serious obstacle to improving productivity. In view of the above circumstances, the inventors have conducted extensive studies, and as a result, they have formulated various additives such as a silane compound necessary for silane crosslinking, and have decided to form an extrusion molded product using a linear ethylene copolymer. A gear pump for transporting high-viscosity melt is placed at the tip of the extruder, and the action of this pump minimizes the back pressure flow and leakage flow of the extruded melt, thereby reducing the amount of shear mentioned above and the amount of heat generated. They discovered that the above-mentioned problems could be significantly solved by this method, and completed this invention. That is, the present invention provides linear ethylene copolymers with the general formula RR'SiY ₂ (wherein R is a monovalent olefinic unsaturated hydrocarbon group or hydrocarboxyl group, Y is a hydrolyzable organic group, R' is a monovalent hydrocarbon group other than a fatty acid unsaturated hydrocarbon group or a group Y), a free radical-generating compound, and a silanol condensation catalyst. When extruding a molded product such as a layer, a gear pump for transporting a high-viscosity melt is installed between the tip of the extruder and the crosshead, and the extruded molten material from the extruder is guided to the crosshead via the gear pump and discharged from the crosshead. This is a method for producing a silane-crosslinked linear ethylene copolymer molded product, characterized in that extrusion molding is carried out at a temperature of the molten resin above the softening point and below 213°C. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 10 denotes an extruder equipped with a screw 11, and a gear pump 13 for transporting a high-viscosity melt is installed between the tip of the extruder 10 and a forming die, or crosshead 12. This gear pump 13 has gears 14 that rotate outwardly relative to each other within the pump body, as shown in the figure.
are placed opposite each other, and a compression section (space) is provided around the periphery, and the material pressurization in this section strengthens the action of drawing and extracting the molten material, making it especially suitable for transporting molten material with high melt viscosity. be. In the figure, numeral 15 is an extrusion molded product such as a pipe or tube. Here, the flow of molten resin inside a normal extruder will be explained with reference to FIG. Groove 11 continuous in the extrusion direction on screw 11
In a, the molten material receives a large shearing force at the part in contact with the inner wall of the cylinder, and on the other hand, a back pressure flow is generated near the bottom of the groove, resulting in a negative velocity and flowing along with the groove in that direction while taking a flow velocity distribution as shown by the solid line a. It circulates to. However, the movement of the molten resin also changes in a complicated manner as, for example, leakage flow occurs. The above-mentioned increase in back pressure flow and leakage flow not only increases the resin temperature in the extruder, but also increases the so-called resin shear amount (shear rate x residence time), and as a result, for example, silane, which is a crosslinking additive, This locally increases the reaction rate of the compound, etc., impairing uniformity of crosslinking, and causes deterioration of properties due to unnecessary side reactions and the like. On the other hand, in the method of the present invention, the above-mentioned gear pump is placed at the tip of the extruder, so that
The flow velocity distribution a in Fig. 2 due to the back pressure flow and leakage flow described above pushes back the flow of the resin in the direction of rotation of the gear.
is changed to distribution b as shown by the broken line, which results in a significant reduction in the amount of shearing of the resin and heat generation, making it possible to specify reaction conditions suitable for silane grafting. In particular, such effects are noticeable when L-LDPE, which is a high viscosity melt, is used as the extrusion resin as described above. The action of this gear pump is such that the resin pressure at the inlet of the gear pump is approximately 40% due to the interaction with the amount of resin extruded.
It is desirable to set the rotation speed etc. so that it is about Kg/cm ² . If the resin pressure is lower than necessary, the extrusion rate will not be stabilized and the object of the invention will not be achieved, which is not preferable. Specifically, as shown in Examples below, the upper limit of the temperature of the molten resin discharged from the crosshead is set at 213° C., and the lower limit is, of course, above its softening point. The gear pump for transporting high-viscosity molten material used in this invention is, for example, Kawasaki Heavy Industries KHP/BaS, which is suitable for transporting molten material with a viscosity of 10,000 poise or more.
or Zenith Pump HLB type are suitable. Next, L-LDPE in this invention is a copolymer of ethylene and higher α-olefins such as butene-1 and pentene-1, which are obtained by the Phillips method, Ziegler method, etc., and include long chain branches. It is a straight chain with only short chain branches, and the number average molecular weight (n) is approximately 30% larger than the molecular weight distribution (M
)/M) is approximately ≧2.7 to ≦4.0. Specifically, these include Neozex (Mitsui Petrochemicals), Urtozex (the same company), Linirex (Nisseki Chemical), and Sklare (DuPont, Canada). Further, as the silane crosslinking method, the method disclosed in Japanese Patent Publication No. 1711/1983 is most suitable. That is, with respect to 100 parts by weight of the above-mentioned L-LDPE, the general formula RR'SiY ₂ (wherein R is a monovalent olefinic unsaturated hydrocarbon group or hydrocarboxyl group, Y is a hydrolyzable organic group, and R' is 1 to 10 parts by weight of a silane compound represented by a monovalent hydrocarbon group other than a fatty acid unsaturated hydrocarbon group or group Y, 0.054 to 0.54 parts by weight of a free radical-forming compound such as dicumyl peroxide, dibutyltin dilaurylate. 0.05 to 0.5 parts by weight of a silanol condensation catalyst, such as silanol condensation catalyst, and other desired antioxidants are added and extrusion molded. The present invention uses a simple configuration in which the above-mentioned gear pump is disposed at the tip of the extruder, thereby optimizing the extrusion flow distribution of resins exhibiting high viscosity, such as L-LDPE, as explained above. As described above, it is possible to significantly improve various problems during extrusion molding that are likely to occur with this resin, and the effect of improving various properties of the obtained molded product is truly significant from an industrial perspective. The present invention will be specifically explained below with reference to Examples. Comparative Examples 1 to 9 Using an extruder with L/D=30 and D=40φ, the following Table 1
Add the material according to the composition and increase the screw rotation speed.
Extrusion coating was performed on a 2 square conductor at 50 rpm. The nipple diameter was 1.83 mm and the die diameter was 3.4 mm. The amount of methanol generated during extrusion, appearance, gel fraction of the coating layer, gel fraction after 48 hours at 80°C, tensile properties, and heat aging properties were evaluated and the results are shown in Table 2. Examples 1 to 9 A gear pump for transporting high-viscosity melts, HLB5548-10 manufactured by Zenith Pump Co., Ltd., was installed at the tip of the extruder used in Comparative Example 1, and the extruder screw rotation speed was adjusted.
Set the resin pressure at the inlet of the gear pump to 40 rpm at 50 rpm.
Comparative example 1 except extruding the composition material in Table 1 below while adjusting the gear pump rotation speed to set it to Kg/cm ²
9 to 9, respectively, and the results were similarly displayed.

【table】

[Table] However, in Table 2 above: Resin pressure: The resin pressure at the tip of the extruder was set to be the same as the inlet of the gear pump. Extrusion appearance: 〇...Good, △...Good, ×...Not good, ××...Not good at all Gel fraction: Measured after xylene extraction at 120℃ x 24 hours Resin temperature: Temperature of molten resin discharged from the crosshead According to the results in the table above It is clear that: (i) Crosslinking by silane grafting can originally be controlled and stabilized by adjusting the amount of additives, but as shown in Comparative Examples 1 to 3, this has not been done appropriately with L-LDPE. In the embodiment this is suitably stabilized. (ii) In general, in silane crosslinking, CH ₃ OH is generated due to a condensation reaction during extrusion of vinyltrimethoxysilane, which causes foaming. In the comparative example, 3~
Foaming was observed as high as 10 ppm, but this was hardly observed in the Examples. (iii) Occurrence of a side reaction (ethylene condensation reaction) is required depending on the gel fraction immediately after extrusion, but this was not observed at all in the examples. (iv) Due to the good results of the Examples according to the above items, the tensile properties and heat aging properties were improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of an extruder used in the method of the present invention, and FIG. 2 is an enlarged view of the main parts thereof. DESCRIPTION OF SYMBOLS 10... Extruder, 12... Crosshead, 13... Gear pump, 14... Gear, 15... Molded object, 16...
Metering pump.

Claims (1)

[Claims] 1 The linear ethylene copolymer has the general formula RR′SiY ₂
(In the formula, R is a monovalent olefinic unsaturated hydrocarbon group or a hydrocarboxyl group, Y is a hydrolyzable organic group, and R' is a monovalent hydrocarbon group or group Y other than an aliphatic unsaturated hydrocarbon group. When extruding molded products such as pipes, tubes, and wire coating layers using a composition prepared by mixing a silane compound represented by A gear pump for transporting a viscous melt is installed, the extruded molten material from the extruder is guided to a crosshead via the gear pump, and extrusion molding is carried out at a temperature of the molten resin discharged from the crosshead above the softening point and below 213°C. A method for producing a silane crosslinked ethylene copolymer molded article.