JP2000207961A - Method for manufacturing cross-linked polyethylene electric wires and cables - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method for preventing occurrence of spots in the production of outdoor crosslinked polyethylene electric wires and cables. SOLUTION: A conductor is extrusion-coated with a water-crosslinkable silane-grafted polyethylene composition containing a silane-grafted polyethylene in which the amount of unreacted silane is suppressed and a silanol condensation catalyst, and then water-crosslinked. As a result, spots are prevented from occurring without deteriorating the product characteristics of the thick-insulated wires / cables.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a crosslinked polyethylene electric wire / cable which is crosslinked by a water crosslinking method. The present invention relates to a method for producing a cross-linked polyethylene electric wire / cable which is cross-linked by a water cross-linking method and is particularly suitable for outdoor cross-linked polyethylene electric wires / cables.

[0002]

2. Description of the Related Art Cross-linking methods for cross-linked polyethylene wires and cables have been industrially performed, such as electron beam irradiation cross-linking and chemical reaction cross-linking with organic peroxides. A cross-linking method comprising grafting a silyl group-containing compound represented by methoxysilane or vinyltriethoxysilane to produce a silane-grafted polyethylene, extrusion-coating a conductor with a mixture of a silane-grafted polyethylene and a silanol condensation catalyst, and then water-crosslinking. It has been developed and applied to the manufacture of various products. The water-bridge method is being rapidly developed, for example, because it does not require large capital investment and is capable of reducing energy costs, as compared with other conventional technologies. Medium voltage (6.6-22
KV) Practical application to relatively thick and thick insulator products such as cross-linked polyethylene wires and cables and outdoor cross-linked polyethylene wires and cables has been promoted.

However, in the production of such a thick insulating product, the crosslinking time must be extended to secure a sufficient degree of crosslinking (gel fraction) as compared with the case of a thin insulating product. Have to do so, but this has created new problems. That is, what should be noted as this kind of problem is a phenomenon in which white spots occur on the surface of the crosslinked polyethylene electric wire / cable. A particularly prominent example is the case of crosslinked polyethylene wires and cables for outdoor use. In this case, the carbon black is generally blended in an amount of 0.5 to 1.0% for the purpose of imparting weather resistance, so that the insulator is black, and as a result, white spots are more clearly observed. . In fact, in the production of this type of outdoor cross-linked polyethylene cable, when it is wound on a drum after extrusion and left in steam for 24 hours or more to form a water cross-link, the surface of the cross-linked wire or cable becomes white. Spots have been clearly observed, which has become an important problem which obviously leads to product defects as abnormal appearance.

[0004]

The inventors of the present invention have studied the causes and mechanisms of the occurrence of spots in outdoor water-crosslinked polyethylene electric wires and cables as described above.
The cause was found to be due to the unreacted vinylsilane compound in the silane-grafted polyethylene.

[0005] It is an object of the present invention to prevent the formation of spots on cross-linked polyethylene wires and cables cross-linked by a water cross-linking method.

An object embodied by the present invention is to prevent the occurrence of spots in a thick-insulated type crosslinked polyethylene wire / cable, particularly a crosslinked polyethylene wire / cable blended with carbon black, which is crosslinked by a water crosslinking method. An object of the present invention is to obtain electric wires and cables having a high gel fraction, a low thermal deformation rate and an excellent elongation rate.

[0007]

According to the present invention, there is provided a water-crosslinkable crosslinkable polyethylene resin composition comprising (1) a water-crosslinkable silane-grafted polyethylene and (2) a silanol condensation catalyst on a conductor, or The water-crosslinkable crosslinkable polyethylene resin composition containing (1) the silane-grafted polyethylene, (2) the silanol condensation catalyst, and (3) carbon black is extrusion-coated, and then in the presence of water or steam (under wet conditions). In the method for producing a crosslinked polyethylene wire / cable which undergoes a hydrolysis / condensation crosslinking reaction to form a water crosslink, the amount of unreacted silane in the (1) silane-grafted polyethylene is controlled to 0.3% or less. Is a method for producing a crosslinked polyethylene electric wire / cable.

The silane-grafted polyethylene in the present invention is a water-crosslinkable silane-grafted polyethylene, and various kinds of polyethylene or a mixture thereof are polymerizable unsaturated organic groups represented by vinyltrimethoxysilane, vinyltriethoxysilane and the like. It is obtained by grafting a silane compound containing a hydrolyzable organic group to make it water-crosslinkable.

The silanol condensation catalyst of the present invention is an organometallic compound or a metal organic acid salt containing an organotin compound represented by dibutyltin dilaurate, which acts as a catalyst for hydrolysis and condensation of silane-grafted polyethylene. is there.

The carbon black of the present invention is various carbon blacks for various polyethylene wires and cables, particularly for outdoor crosslinked polyethylene wires and cables having weather resistance.

The unreacted vinyl silane in the present invention is the unreacted vinyl silane compound (monomer) used in the production of the above-mentioned silane-grafted polyethylene, which remains after the grafting and before the crosslinking. Is controlled.

The extrusion coating on the conductor according to the present invention comprises:
The extrusion process in the production of electric wires and cables can be applied.

The crosslinking by the water crosslinking reaction in the present invention is as follows:
A water cross-linking step of a cross-linked polyethylene electric wire / cable can be applied, for example, a step of leaving an uncross-linked polyethylene electric wire / cable wound in a drum-wound state by extrusion coating in saturated steam.

The amount of the unreacted silane compound to be controlled in the method of the present invention is controlled to 0.3% or less after the graft reaction of the silane-grafted polyethylene and before the water crosslinking reaction. If necessary, a drying step may be provided after the grafting reaction to completely volatilize the unreacted silane and then extrusion-coated.

The occurrence of spots in the crosslinked polyethylene wires and cables by the water crosslinking method, which is a problem to be solved by the present invention, is more likely to be caused by the reduced amount of unreacted vinylsilane contained in the insulator in thin insulator type wires and cables. Occurrence is reduced and it is not a major problem.
In addition, in the case of a general white indoor electric wire / cable having the same color as the spot, the same occurs, but the spot is hard to be found. However, in any case, it is still a fundamental problem.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The silane-grafted polyethylene in the method of the present invention is a water-crosslinkable silane-modified polyethylene as described above, and is not limited by the production steps. Are (A) polyethylene, (B) a polymerizable unsaturated organic group and a hydrolyzable organic group-containing silane compound (for example, vinyltrimethoxysilane, vinyltriethoxysilane) (C)
Organic peroxide or a mixture thereof with an antioxidant (for example, dicumyl peroxide and 2,2′thio [diethyl-bis-3 (3,5 ditert-butyl-4-hydroxyphenol) propionate]) Are mixed, heated, melted, and reacted using an extruder to obtain a silane-grafted polyethylene having an unreacted silane compound amount of 0.3% or less.

The blending of the silanol condensation catalyst or carbon black with the catalyst in the method of the present invention is not limited by the blending step, but industrially preferred steps include (A) polyethylene and (B) silanol condensation. A catalyst (eg, an organotin compound such as dibutyltin dilaurate) and an antioxidant (eg, 2,2′thio [diethyl-bis-3 (3,5 ditertiarybutyl-4-hydroxyphenol) propionate]) and (C A) a step of blending carbon black or a masterbatch thereof, and mixing, heating, melting and mixing with an extruder to obtain a polyethylene composition containing a silanol condensation catalyst.

The step of extrusion coating of the conductor in the present invention is not limited, but industrially preferred are the silane-grafted polyethylene obtained as described above and the silane-grafted polyethylene obtained as described above. The mixture containing the obtained polyethylene composition containing a silanol condensation catalyst is supplied to an extruder, and mixing, heating, melting and mixing of the components and extrusion coating on a conductor are performed in one step by an extrusion step.

Hereinafter, the examples and comparative examples of the present invention will be further described by experiments (1), (2) and (3).

Experiment (1) (Comparative Example): A crosslinked polyethylene cable for outdoor use was experimentally manufactured, and the factors causing the occurrence of spots were examined in detail.

First, the overall outline of the experiment (1) will be described.

(A) Silane-grafted polyethylene: First, (a) a composition for forming a silane-grafted polyethylene is blended and adjusted, and then (b) the composition for forming a silane-grafted polyethylene is extruded by extrusion and grafting into an extruder. To produce a silane-grafted polyethylene.

(B) Composition for master batch of silanol condensation catalyst: Predetermined components were blended and adjusted (the components and blending are described later).

(C) Extruded cable: The above-mentioned (A) silane-grafted polyethylene and (B) a composition for a silanol condensation catalyst masterbatch are blended in a predetermined ratio, supplied to an extruder hopper, and extruded to coat a conductor to form a cable. Manufactured.

(D) Crosslinked cable: The above (C) extruded cable was hydrolyzed, condensed and crosslinked under predetermined conditions to produce a crosslinked polyethylene cable.

(E) Analysis / Evaluation: At a necessary stage,
Predetermined analysis and evaluation were performed.

Hereinafter, the detailed conditions of the experiment (1) will be described.

(A-a) Components and composition of the composition for molding silane-grafted polyethylene: polyethylene (trade name U
BEZ-514, density: 0.932, MI: 3.0) 1
00 parts by weight, 1.5 parts by weight of a vinylalkoxysilane compound (vinyltrimethoxysilane), 1 organic peroxide
(Dicumyl peroxide) 0.1 part by weight, antioxidant (2,2′thio [diethyl-bis-3 (3,5
Butyl-4-hydroxyphenol) propionate]) 0.1 parts by weight.

(Ab) Conditions for the above extrusion and grafting:
As an extruder, L / D = 28, screw outer diameter 65mm
The temperature conditions of each zone were as follows. That is, the first region: 160 ° C., the second region: 1
80 ° C., the third region: 200 ° C., the fourth region: 230 ° C., the head region: 230 ° C., and the die region: 230 ° C. Under the above conditions, the strand was extruded into a strand, water-cooled, and pelletized by a pelletizer.

(Ba) Components and composition of the composition for the master batch of silanol condensation catalyst: polyethylene (trade name: NUC9060, density: 0.922, MI: 1.0) 6
0 parts by weight, an organic tin compound catalyst (dibutyltin dilaurate) 1.0 part by weight, an antioxidant (2,2′thio [diethyl-bis-3 (3,5 ditert-butyl-4-hydroxyphenol) propionate) ]) 1.0 part by weight, carbon (carbon black masterbatch (trade name Vulcan 9)
25%)) 40 parts by weight.

(Bb) The above extrusion conditions: L / D = 28,
A screw having an outer diameter of 65 mm was used, and the temperature conditions were such that the temperature of each zone was as follows. That is, the first area:
160 ° C., second region: 180 ° C., third region: 180 ° C.,
The fourth region: 180 ° C., the head region: 180 ° C., and the die region: 180 ° C.

Under the above conditions, the strand was extruded into a strand, water-cooled, and pelletized by a pelletizer.

(C) Manufacturing conditions of the above-mentioned extruded cable: The mixing ratio of (A) the silane-grafted polyethylene and (B) the composition for the silanol condensation catalyst master batch is A / B.
= 19/1. As an extruder, L / D = 2
4. Screws having an outer diameter of 130 mm were used, and the temperature conditions were such that the temperature of each zone was as follows. That is, the first
Area: 130 ° C., second area: 150 ° C., third area: 18
0 ° C., the fourth area: 180 ° C., the head area: 180 ° C., and the nozzle area: 180 ° C. The dimensions of the extruded cable were as follows: conductor size: 60SQ (outer diameter: 9.3 mm); insulator thickness: 4.5 mm. The other extrusion conditions were a take-up speed of 20 m / min and a take-up drum of 1000 mm iron-made drum.

(D) Cross-linking reaction conditions in the production of the cross-linked cable: The cross-linking cable was left standing in saturated steam at 80 ° C. for 24 hours.

(E) The results of the above analysis and evaluation were as follows.

(E-1) The physical properties of the obtained crosslinked polyethylene cable were as follows: gel fraction: 70%, tensile strength: 19.5
(MPA), elongation: 390 (%).

(E-2) The results of the appearance inspection of the obtained crosslinked polyethylene cable were as follows. : The outer appearance of the cable was observed by rewinding the winding drum of the crosslinked polyethylene cable.
No abnormal appearance was found on the step surface, but the drum surface 3
Below the stage (inner layer), white spots were observed on the cable surface.

(E-3) Analysis of the above-mentioned white spots: As a result of infrared absorption spectrum analysis of the above-mentioned white spots, the hydrolyzate of vinyltrimethoxysilane was condensed and cross-linked and solidified and adhered to the cross-linked polyethylene surface. It turned out to be. Therefore, it was confirmed that the white spots (products) were insoluble in solvents such as toluene and methyl ethyl ketone, and it was extremely difficult to remove them once they were formed.

It is apparent that the above-mentioned white spots are caused by unreacted vinyltrimethoxysilane remaining in the cable insulator before the crosslinking reaction, as described above. Surface 1-2
The difference in the occurrence status between the stage and the inner layer 3 or less is considered as follows. That is, the surface 1-2 of the winding drum
The reason why white spots do not appear on the step is that unreacted vinyltrimethoxysilane remaining inside the insulator is washed away by steam at the stage of thermal diffusion, volatilization or surface transfer in the process, and the winding drum The white spots are generated in the inner layer part because the cable is tightly wound in the inner layer part, so that unreacted vinyltrimethoxysilane is not washed away by steam, and the process of hydrolysis-condensation-solidification-adhesion It is thought that it is easy to proceed.

As a result of various studies conducted by the present inventors to solve the above-mentioned problem of the occurrence of white spots, (1) lowering the crosslinking temperature to prevent the transfer of the vinylsilane compound to the surface; (2) It was confirmed that none of the methods was industrially effective, including stopping multi-step winding of the cross-linked cable in anticipation of the effect of washing with steam, and it was not possible to carry out the post-grafting stage before cross-linking. It was confirmed that the object could be achieved only by reducing the amount of the reactive vinyl silane below a certain limit, and the present invention was completed.

Experiment (2) (Examples and Comparative Examples): A vinylalkoxysilane compound (vinyltrimethoxysilane) and an organic peroxide (dicumyl peroxide) as an initiator in a composition for forming a silane-grafted polyethylene. Of the silane-grafted polyethylene (A, B, C, D, and E) having different proportions of the unreacted vinylalkoxysilane compound (vinyltrimethoxysilane) Five kinds of outdoor cross-linked polyethylene cables were trial-produced from five kinds of compositions whose amounts varied in the range of 0.21 to 0.42%, and unreacted vinylalkoxysilane compounds (vinyl trimethoxysilane) in the cables after the graft reaction. 0.3 residue
% Or less (Example), the occurrence of spots is prevented, and when the residual amount exceeds 0.3% (Comparative Example), not only the occurrence of spots occurs but also the physical properties of the crosslinked cable are inferior. Indicates that

Hereinafter, the experiment (2) will be described in detail.

(A) Silane-grafted polyethylene: Table 1
The compositions (A to E) for forming the silane-grafted polyethylene shown in the above are blended and prepared, and the same extrusion and molding as in the experiment (1) are performed.
Grafting was performed under grafting conditions to produce five types of silane-grafted polyethylene. That is, polyethylene (density: 0.
932, MI: 3.0) 100 parts by weight (common), vinylalkoxysilane compound (vinyltrimethoxysilane)
1.5 parts by weight (common), organic peroxide (dicumyl peroxide) composition A: 0.08 parts by weight, composition B:
0.1 parts by weight, composition C: 0.12 parts by weight, composition D:
0.15 parts by weight, Composition E: 0.2 parts by weight, antioxidant (2,2′thio [diethyl-bis-3 (3,5 ditert-butyl-4-hydroxyphenol) propionate]): 0.1 parts by weight (common) were blended, and extruded under the same temperature conditions using the same extruder as in Experiment (1) to obtain silane-grafted polyethylene (5 types).

(B) Composition for master batch of silanol condensation catalyst: The composition for master batch of silanol condensation catalyst of experiment (1) was used. That is, polyethylene (density:
0.922, MI: 1.0) 60 parts by weight, an organic tin compound (dibutyltin dilaurate) 1.0 part by weight, an antioxidant (2,2′thio [diethyl-bis-3 (3,5 Butyl-4-hydroxyphenol) propionate]) and 40 parts by weight of carbon (carbon black masterbatch (containing 25% of Vulcan 9A32)).

(C) Manufacturing conditions of the extruded cable: The manufacturing conditions of the extruded cable were the same as in the experiment (1). That is, A / B of the composition for the master batch (A) silane-grafted polyethylene and (B) the silanol condensation catalyst was 19 /
One proportion of the formulation was extrusion coated under the same conditions with the extruder of experiment (1) to give cables of similar dimensions.

(D) Crosslinking conditions: The crosslinking conditions were the same as in Experiment (1). That is, the extruded cable obtained above was heated to 80 ° C.
In saturated steam for 24 hours to effect crosslinking.

(E) Analysis / Evaluation: About the obtained outdoor crosslinked polyethylene cable, (1) gel fraction% after crosslinking, (2) heat deformation rate (%) (JIS method, 120 ° C.
2.5 kg), (3) Elongation (%) and (4) Spot occurrence status (x: many occurrences, Δ: slight occurrence, ○: no occurrence)
Was analyzed and evaluated. The amount (%) of unreacted vinylsilane compound (vinyltrimethoxysilane) in the silane-grafted polyethylene (after grafting and before crosslinking) (80 ° C,
Table 1 shows the results of the above analysis and evaluation.
Shown inside.

The results in Table 1 show that although the amount of unreacted vinylsilane compound in the silane-grafted polyethylene (after grafting and before crosslinking) (volatility reducing agent) is 0.33%, spots are slightly generated, although the amount is small. On the other hand, at 0.25%, no occurrence occurs. In addition, as the amount of unreacted vinyl silane was reduced, the gel fraction and the heat deformation rate tended to be reduced, which is due to the improved grafting efficiency of vinyl silane.

Experiment (3) (Examples and Comparative Examples): Among the compositions (A to E) for forming a silane-grafted polyethylene in Experiment (2), C in which spots were observed and none of spots were observed. Four types of crosslinked polyethylene cables for outdoor use were experimentally manufactured by using two types of D and changing the graft reaction temperature, respectively, and the relationship between the grafting conditions, the occurrence of spots, and the physical properties of the cable were investigated. That is, the compositions C and D for forming the silane-grafted polyethylene were grafted under the extrusion conditions as shown in Table 2, and the four kinds of the obtained silane-grafted polyethylenes and the composition for the master batch of the silanol condensation catalyst of the experiment (1) were used. Was blended in the same ratio as in Experiment (1), an extruded cable was manufactured in the same manner as in Experiment (1), and then crosslinked in the same manner as in Experiment (1) to prototype four types of outdoor crosslinked polyethylene cables. The analysis and evaluation according to the experiment (2) were performed. The results are shown in Table 2. From this result, it can be seen that the presence or absence of spots depends on the composition and the reaction temperature, but ultimately depends on the amount of unreacted vinyl. Silane graft polyethylene (after grafting and before cross-linking) due to efficient progress of the grafting reaction
When the amount of the unreacted vinyl silane compound (vinyl trimethoxy silane) in the solution was controlled to 0.3% or less (Example), the occurrence of spots was suppressed, and the gel fraction after crosslinking and the decrease in heat deformation rate were reduced. The effect is recognized. When the amount of the unreacted vinylsilane compound (vinyltrimethoxysilane) exceeds 0.3% (Comparative Example), the occurrence of spots cannot be suppressed, and the cable properties tend to decrease accordingly.

Experiment (4) (Example and Comparative Example): In the same manner as in Experiment (3), four types of uncrosslinked outdoor crosslinked polyethylene cables were produced. That is, the same cables as the cables in the uncrosslinked stage of the experiment (3) are used in the first to third experiments (4), and the cables in the second unbridged stage in the second experiment (3) are used in the experiments (4). The same cable as the cable of the experiment (4) was used for the same cable as the cable of the uncrosslinked stage of the experiment (3).
For Nos. To 12, the same cable as the cable in the uncrosslinked stage of 4 in the above experiment (3) was used.

Next, the crosslinking conditions shown in Table 3, ie, 80
12 hours, 24 hours and 36 hours in saturated steam at ℃ C. Prototype 12 kinds of outdoor cross-linked polyethylene cables for trial use, spot generation, gel fraction after cross-linking (%) and heat deformation (%) The relationship between the amount of the unreacted vinyl silane compound (vinyl trimethoxy silane) after grafting and the crosslinking time was examined. Table 3 shows the results. That is, when the residual amount of the unreacted vinylsilane compound (vinyltrimethoxysilane) after grafting and before crosslinking is 0.3% or less (Example)
When the amount of unreacted vinylsilane compound (vinyltrimethoxysilane) after grafting exceeds 0.3% (comparative example), it is apparent that the crosslinking time is shortened. However, it can be seen that the characteristics and physical properties of the cable are clearly reduced to unsatisfactory levels, and that the formation of spots is inevitable if the crosslinking time is prolonged. From the above results, the amount of unreacted silane before water crosslinking in the silane-grafted polyethylene was 0.3
% Is important in preventing spots and efficiently producing a stable product.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

[Table 3]

[0055]

As described above, in summary, according to the present invention, it is possible to prevent the occurrence of spots in the production of crosslinked polyethylene wires and cables by the water crosslinking method. Further, according to the present invention, it is possible to not only prevent the occurrence of spots, but also to efficiently produce a stable product, particularly in the production of a crosslinked polyethylene wire / cable by a thick insulator type water crosslinking method. .

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoshi Hashimoto 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Prefecture Inside the Hidaka Plant, Hitachi Cable Co., Ltd. (72) Inventor Kenichi Furusawa 5 Hidaka-cho, Hitachi City, Ibaraki Prefecture No. 1-1, Hitachi Cable Co., Ltd. H-Taka Plant F term (reference) 5G305 AA02 AB40 BA12 CA01 CA26 CA53 CA54 CB26 CD05 DA23 5G325 GA18 GC05 GD06

Claims (2)

[Claims] 1. A crosslinkable resin composition comprising (1) a silane-grafted polyethylene and (2) a silanol condensation catalyst on a conductor, or (1) a silane-grafted polyethylene, (2) a silanol condensation catalyst, and (3) carbon black. In the method for producing a crosslinked polyethylene wire / cable by extrusion-coating a crosslinkable resin composition containing the following, followed by crosslinking in the presence of water or steam, the amount of unreacted silane in the (1) silane-grafted polyethylene is 0.3 %
A method for producing a crosslinked polyethylene electric wire / cable, characterized in that the method is controlled as follows. 2. (1) A silane compound having a polymerizable unsaturated organic group and a hydrolyzable organic group is subjected to a graft reaction to polyethylene in the presence of an organic peroxide, so that the amount of the unreacted silane compound is 0.3%. (2) a step of producing a silanol condensation catalyst-containing polyethylene composition (B) containing polyethylene, a silanol condensation catalyst, an organic peroxide and carbon black, A) blending the silane-grafted polyethylene (A) and the silanol condensation catalyst-containing polyethylene composition (B) and extrusion-coating on a conductor; and (4) subjecting the extrusion-coated product obtained in step (3) to steam coating. A method for producing a crosslinked polyethylene electric wire / cable, comprising a step of water crosslinking in the presence.