DE1938637B2 - Process for the pressureless curing of ethylene polymers - Google Patents

Description

45

The present invention relates to a process for pressureless curing of ethylene polymers for the production of pore-free moldings and cable covers, in which a homogeneous mass consists of

a) a homo- or mixed polymer of ethylene,

b) a usual hardening formula,

c) a mineral filler treated with an organosilicon compound

55

at no more than atmospheric pressure by an inert, non-aqueous, heat-transferring medium, which on finer is kept sufficiently high temperature for the hardening of the mass, is conducted, according to patent application P 18 06 194.4-43, characterized. that the mineral filler with 0.15 to 4 percent by weight Tetramet hy pretreated with ravinylcyclotctrasiloxane has been.

Thermosetting or crosslinked polyethylene compounds are known per se and have extensive uses, particularly as insulating materials for Wires liiiu cables, found, J-ur this application However, it is necessary that the hardened masses are as pore-free as possible so that the insulation provides the required Has dielectric strength.

Known processes for the production of such pore-free, hardened Äihyier.-PoJymerisate work under relatively high pressures of about 14 to 19 kg / cm ² (see. FR-PS 13 07 208 and US-PS 29 30 083). The magazine "Modern Plastics", 44, pp. 91 to 93 and 169 to 172, nothing else can be found in this regard.

This hardening at increased pressure, which is also usually done with the use of steam is carried out, however, because of the equipment and monitoring required for this on the one hand expensive and on the other hand for some conductors, such as sodium conductors, because of the water present not applicable.

The invention was therefore based on the object of providing a pressureless process for curing ethylene polymers to create that enables the production of pore-free moldings and cable covers.

On those with such a hardening under low pressure, as in a liquid bath vulcanization, associated difficulties is already in the publication of the Bayer works »Vulcanization and Vulkanisationshilfsmitlel ", in particular on pp. 7S and 79, pointed out. According to the aforementioned publication the use of a desiccant »is suggested. However, one such desiccant is not always desirable for the production of insulation materials. The invention was therefore further the task of specifying a method without the use of such a drying agent that enables pressureless curing for the production of pore-free moldings and cable insulation.

A method for pressureless curing of ethylene polymers of the type mentioned is in the earlier patent application P Γδ 06 194.4 described. In this method, as mentioned above, one treated with an organosilicon compound is used mineral filler used. In the present invention it has now been recognized that this is in the above-mentioned older German patent application can be improved by the method described, if the organosilicon compound is tetramethyltetravinylcyclotetrasiloxane used.

The compound tetramethyltetravinylcyclotetrasiloxane is known. So it is in the French Patent specification 12 70 320 their use for hydrophobing pigments and analogous materials described. This known use implies the use of this compound for the treatment of mineral Fillers in a process for pressureless curing of ethylene polymers for production pore-free molded body and cable coatings, however, not close.

To produce the mass, the polymer, filler, vinylsiloxane and other additives are intimately mixed with one another in a Banbury mixer. During this mixing process, the vinylsiloxane reacts with the filler or provides it with a coating, which is generally understood as a filler treated with siloxane. If necessary, the mineral filler can be pretreated with the vinylsiloxane in a separate process solution and then the treated filler can be mixed with the polymer and the other additives. Then there is a hardening niiuel. preferably a tertiary orcanic

Peroxide, added to the mixture, so that after hardening of wire and cables it represents a small amount

ten a complete crosslinking of the polymer in terms of apparatus and little heat transfer

is enough. The mass is required as an insulating layer over the medium

"A conductor is extruded and then through a non- The tube 20 ends in a housing 24, which

aqueous heat-transferring medium through 5 preferably via an exhaustor 28

guided that is kept at a temperature, the exhaust pipe 26 seen with the Außeniutt in connection

sufficient for the ethylene-containing polymer to stand “in situ”. In the housing 24 there is a

to harden completely. The hardened product is. Pulley 30 and the cable comes off the tube 20

as explained in more detail below via the role in an elongated cooling tube 32, the

will be distinguished by the fact that it will keep an io at a sufficiently low temperature

has a relatively high density and is therefore special to cool the insulated conductor. In all-

useful as an insulating material. mine it is enough to bring the cooling pipe to room temperature

The invention will be kept in the following on the basis of the door and with the exhaustor 28 in the countersignature explained in more detail the preferred outflow to the cable direction air through the tube implementation of the new process for producing 15 sausen. If necessary, of course of wires and cables describes in more detail. other means of cooling the cable are also used The figure shows a schematic view of a be. For example, the tube can be connected to a Apparatus for carrying out the present invention may be provided with a cooling jacket and a coolant through it in elevation. these are guided through, or the cooling pipes

The insulating compound is z. B. in one labeled 10 can contain a liquid which is mixed together on the desired Banbury mixer and kept at a low temperature. Then it is required in a grinder 11, in order to be able to roll out a tub or a processing for the further course. The mass will take the place of the cooling tube 32 in the tank. A collecting container 34 which is then attached from a container to an extruder tube 32 is used to feed and for this purpose at 12 usually roughly 25 any liquids that have been ground or pelletized from the cable, in order to then stir as output and out of the tube 20 were transported with the material to be used for the extruder. How to drain. The product obtained will then be explained in detail below, wound on the reel 36, which is provided with a guide mechanism for the mineral filler with the vinyl siloxane mus 38, so that it can be pretreated in the same way by ensuring that the vinyl siloxane is rolled up moderately will.
As has already been explained above, the filler treated is subjected to the mixing process in the Banbury - the cable emerging from the extruder is subjected to a mixer. The filler and the heat transfer medium passed through, the vinylsiloxane can also be added to the Banbury mixer, kept at a sufficiently high temperature, by adding the filler and the 35 so that a complete curing of the poly-vinylsiloxane then reacts with one another. The mass inerisats is guaranteed. It should be noted that a conventional extruder is then fed to the heat-transferring medium opposite the wire sheathing 14. A metallic polymer must be completely inert. For this purpose, conductor 16 can pass from a wire roll 18 through one of the numerous heat-transferring materials extruder, where the polymeric mass is extruded 40 such as organic liquids, gases, molten and forms an insulating coating on the conductor. Salts, salt solutions and molten metal alloys

After exiting the extruder, the isogen is used. According to a preferred Auslierte conductor 19 through an elongated tube 20, guide form of the present invention, a heat-transferring medium 22, for example polyolefin glycol, is used, which either water-soluble as an organic liquid and furthermore 45 or water-insoluble and a viscosity with suitable valves or Abfiußvorrichtungen 23 may be provided 50-90000 Saybolt Universal seconds at 38 ⁰ C. Has the heat transfer medium. Other organic fluids that can be used for this purpose are kept at an elevated temperature; the fluids are glycerine and its esters, and propylene is sufficient to completely harden the glycol and its esters "in situ". To effect gaseous, heat-transferring polymers. The required temperature 50 lowing materials are air, carbon dioxide and stick depends primarily on such factors as the material, the type of polymer mass completely free at the curing temperature, the heat-transferring water vapor and the polymer medium and the curing agent used. are completely inert. The gaseous, heat over-The length of the tube 20 and the flow rate medium, which can be preheated, will flow through this tube, preferably a sufficient dwell time of the product 19 through the hardening tube or chamber, preferably in the heat over-flow The insulated conductor guided and the supporting medium allow to bring about a complete hardening of the polymer and its correct execution is practically at atmospheric pressure.

According to the invention, the hardenable composition contains a dimension that is suitable for the skilled person left. The tube 20 is, for example, 60 ethylenhaltiges polymer, a curing agent and an electrical heating coil, not shown, or a mineral filler that penetrates with telramethyl other suitable devices heated. Self-letravinylcyclotetrasiloxane is treated. Farther Understandably, other devices for getting the polymer mixture can usually also be used serve the hardening bath, z. B. can also add certain additives. These mix additives a tub or tank in place of the tube 20 65 may contain antioxidants such as polymeric trimethyldihenu7t will. However, it has been shown to be a hydroquinoline, a lubricant such as calcium stearate tubular device convenient and practical to prevent the mixture from sticking Means for use in manufacture rend processing, a non-flammable additive

such as antimony oxide and a halogenated compound to increase flame resistance, a coagents such as polybutadiene to facilitate crosslinking and a small amount of pigment or dye. The required mixing additives can be considerable vary, and it can also still depending on the properties desired in the end product other than the aforementioned means are used.

Optionally, polyethylene can be used alone or in combination with one or more other polymers be used. However, this largely depends on the requirements placed on the end product away. The ethylene-containing component can be that with other polymers and polyethylene Copolymers of ethylene and other polymerizable materials is blended. Suitable copolymers of ethylene are ethylene-propylene copolymer, ethylene-propylene-diene terpolymer and Ethylene vinyl acetate. The amount of ethylene used in the copolymer changes the properties of the end product and can therefore be varied to obtain the desired results. A typical copolymer of ethylene and propylene contains 50 mole percent of each component and one Ethylene vinyl acetate copolymer contains 72 to 95 percent by weight ethylene and the remainder is vinyl acetate.

The polyethylene or the copolymer of ethylene can be mixed with a chlorine-containing polymer such as chlorinated polyethylene, chlorosulioiiienem roiyäthylen and polyvinyl chloride may be blended in order to increase the flame resistance of the composition "Ec is ur. known that the flame retardant properties of the polyethylene compositions by using a chlorine-containing Polymers can be increased. These materials can contain up to 15 percent by weight of chlorine based on the total weight of all polymers present. A higher level of chlorine can cause the Adversely affect mass by forming a porous product. The chlorine-containing polymer is relative more expensive than polyethylene and it is therefore advisable to use the lowest chlorine content, the just guaranteed sufficient flame resistance, so that the hardened mass, which is attached to the End product fulfills strict requirements with regard to flame resistance. The tensile strength of the end product is generally due to an increased proportion of the unchlorinated polymer or copolymer elevated. However, there will be at least a chlorine content of about 2 percent by weight based on all Polymer components, used to give the product the desired flame resistance. the Proportions of the individual components can thus be varied within the specified limits to meet the mechanical properties and performance characteristics required for an insulating mass.

A suitable mineral filler is added to the insulating compound, which the compound needs Gives strength that is necessary for the processing of the cable, so that it is during processing maintains its structure. Used in bulk at dcii mineral fillers are those commonly used in polymer compositions Fillers such as aluminum silicate, aluminum oxide, calcium ciumcilicate. Silicon dioxide, magnesium silicate, titanium dioxide and their mixtures. The filler can contain certain inert impurities such as metal oxides, up to about 5 percent by weight of the filler can make up. Such fillers are well known and easy on the market available. The type of filler used depends largely on the desired properties of the End product and can easily be determined by a person skilled in the art. Titanium dioxide is used as a filler characteristically a particle size of

ίο about 0.2 to 0.4 μΐη (mean diameter) and a specific weight of about 3.9 to 4.1. The other fillers are typically calcined to reduce the moisture content to less than 0.5 percent by weight and generally have a particle size on the order of 2 x meters in diameter and a specific gravity of about 2.5 to 2.8. However, magnesium silicate with a platelet structure, a particle size of not more than 6 μm and expediently a specific surface area of 18 to 20 m ² / g, which was determined by the BET gas adsorption method and which has a specific weight of about 2, can also be used as a filler. 7 to 2.8.

The task of these fillers in polymeric insulation compounds is well known, and the amount of in the mass incorporated fillers can depending on the desired properties of the End product can be varied. The filler content is 25 to 60 percent by weight of the composition and preferably 30 to 50 percent by weight. The filler is 0.15 to 4 percent by weight, preferably 0.5 to 3 percent by weight telramethyltetravinylcyclo-

lU b ¹ ^ "

siloxane obviously acts as a plasticizer that enhances tensile strength and electrical properties of the hardened mass and continues to lead to a porous product and therefore avoided should be.

The mixing process is carried out in a temperature range that is high enough. to the To keep the mixture plastic for processing, but below the reaction temperature or the Decomposition temperature of the curing agent is so that the curing agent is during normal Mixing process does not decompose and thereby a partial or initial hardening of the polyethylene causes. The hardening agent used is suitably an organic peroxide such as a tertiary one Peroxide, which by at least one structural unit

C C

C-C-O-O-C-C

and which decomposes at a temperature above about 135 ^{° C.} The use of such peroxides as curing agents for crosslinking polymers such as polyethylene compounds is described in U.S. Patents 3,079,370, 2,888,424,3086,966 and 3,214,422. The peroxide most frequently used and preferred as a hardening agent is di-alpha-cumylproxide. Others need

^fi 5 bare hardening means! are the tertiary diperoxides such as 2.5-dimethyl-2.5- (t-butylpcroxy) -hxane and 2.5-dimethyl-2,5- (t-biitylperoxy) -hxane and similar di peroxy compounds.

The proportion of the Pcroxidhürumgsmiuels used depends largely on the desired mechanical properties, for example the warm / ugfesligkcit of the hardened product. A range of 0.5 to 10 parts by weight of peroxide per hundred parts of polymer satisfies most requirements and the common proportion is on the order of 2 to 4 parts peroxide. In a typical procedure, at a tertiary peroxide is used as a hardening agent, the mixing is carried out at one Temperature from about 93 to 135 ° C. If the mixing is done at a temperature much higher than the specified maximum, the peroxide decomposes and thereby at least partially causes a premature Curing the polymer. As a result, the mass is difficult to work with, and so is the end product has an irregular or rough surface.

Apart from the fact that the curing can be carried out more cost-effectively by avoiding high pressure, there is a further essential advantage that, according to the invention, cables can be produced with a sodium cable insulated by a chemically crosslinked polyolefin. A cable of this type and the manufacturing process are described and claimed in our own FR-PS 15 61 864. It is readily apparent that such a cable cannot be cured under steam pressure, since working with sodium in an aqueous and / or steam-containing atmosphere is extraneous. In addition, sodium is at the temperatures required for manufacture and curing of the cable, liquid and since the insulation layer is in the plastic state when it exits the extruder and enters the curing oven, the high pressure used in the curing oven would compress the walls of the cable and thereby squeeze the sodium out of its insulating jacket . It should be noted that in the method of the present invention an aqueous environment is avoided and curing is accomplished in the absence of increased pressure, and thereby an insulated sodium cable can be made.
According to a further embodiment of the present invention, the hardenable composition can be subjected to a vacuum treatment before the hardening process. For example, the extruder can be vented and attached to the cylinder barrel of the extruder

ίο a vacuum can be applied when the mass liquefies or plasticized by the cylinder screw is pressed through the cylinder liner. Possibly the mixture can also be fed to the extruder from a storage container kept under vacuum will. The execution of this operation under vacuum has proven to be particularly advantageous, to obtain a relatively dense product.

The invention is described in more detail below with reference to the examples:

20th

Examples 1 to 5

In Examples 1 to 5, the Iviassen na <.! I conventional mixing process according to the recipes listed in the table. The filling

^ 5 fabric and the vinylsiloxane were used during the Mixing process added separately. Example 1 was a control sample in which the mineral filler was not treated with vinylsiloxane. The amount given in the table for each component are essential parts. The masses were then to plates of 29 cm 'with a thickness of about 0.19 cm deformed. The rluUcu »iuuc; · then through Immerse for two minutes in polyolefin glyeol, which has a viscosity of 300 Saybolt universal seconds had and was kept at 200 C, cured. The hardened products were examined for their degree of hardening by toluene extraction. Therefor a 2-gram sample was prepared according to test specification ASTM D-297 for 16 hours by means of a boiling

4 "toluene extracted.

Recipes and toluene extractc

Examples

1

Polyethylene

Ethylene vinyl acetate copolymer
(6 percent by weight vinyl acetate)

Ethylene propylene copolymer
(50 mole percent ethylene)

Aluminum silical

Precipitated SiO ₂ aq
Magncsiumsi Heat
Vinyl siloxane
Di-alpha-cumyl-pcroxide

Toluene extracts

(",, on the connection)

100

100

50

50

100

100

100

120

1.5 50 1.5 1.5 3.5 1.5 3.5 3.5 3.5 9. (> 3.5 10.5 7.3 1.6 11. «

The toluene extracts show the polymer to give 65 15 "". All samples were visually checked for porosity compared to conventional steam curing methods. Example 1, the control, was cured to a relatively high degree, which was porous and therefore used as insulation unusable for wires and kcnnzeichncnderwcisc a Toluolcxtrakt of (1 to cable. The remaining examples showed

509 524,397

ίο

little or no porosity and are therefore suitable and a relatively dense product is obtained

for use as insulation.

As can be seen from the above description and the examples, there are those with the term Achieved advantages in particular in that the use of a high pressure hardening system avoided is particularly suitable for insulating wires and cables. I: s it is expressly pointed out that the disclosure contained in the entire description is to be regarded as essential is.

1 sheet of drawings

Claims (3)

Patent claims: 1. Process for the pressureless curing of ethylene polymers for the production of pore-free moldings and cable covers, in which from a) customary ethylene homopolymers or copolymers or mixtures of these polymers with other polymers that give the mass flame resistance, if necessary, b) 0.5 to 10 parts by weight, based on 100 parts by weight of polymer, of conventional peroxides and c) 25 to 60 percent by weight, based on the Mass of a mineral treated with 0.15 to 4 percent by weight of an organosilane Filler a homogeneous mass is produced and this mass by at most atmospheric pressure a substantially inert, non-aqueous, heat transfer medium passed therethrough that is kept at a sufficiently high temperature for the hardening of the mass, according to patent application P 18 06 194, characterized in that the mineral filler with 0.15 to 4 percent by weight tetramethyltetravinylcyclotetrasiloxane has been pretreated. 2. The method according to claim 1, characterized in that the mineral filler aluminum silicate, Calcium silicate, magnesium silicate, silicon dioxide, aluminum oxide or titanium dioxide is. 3. Application of the method according to claim 1 or 2 for the production of an isolated electrical Cable, characterized in that the hardenable mass is applied around an electrical conductor and is cured. 40