DE3310294C1 - Process for producing a pipe or tube from a crosslinked polyolefin - Google Patents

Abstract

In a process for producing a pipe or tube from a crosslinked polyolefin, a moisture-crosslinkable graft polymer is added to the polyolefin containing a peroxide in order to prevent the undesired collapse or deformations of cross section during the crosslinking heat treatment. The polymer mixture is then extruded and the pipe exposed to moisture to attain a precrosslinking, before the heat treatment for peroxidic full crosslinking takes place. By means of the precrosslinking, the pipe or the tube attains an intrinsic strength and dimensional stability which is retained even during the heat treatment for peroxidic full crosslinking.

Description

The invention is based on the object of providing a method in which the undesired collapse or cross-sectional deformations avoided without the need to apply a Internal mandrel or one Requires internal pressure with previous attachment of an outer jacket.

The task at hand is based on the method of the introduction designated genus solved by the characterizing measures of claim 1.

According to the basic idea of the present invention, there is a two-stage Crosslinking, in which between the extrusion process and the full peroxidic crosslinking, that is, the second crosslinking stage, a moisture crosslinking as the first crosslinking stage is interposed, which increases the inherent strength of the extruded Pipe or hose.

This intrinsic strength then goes to the subsequent peroxidic Networking is not lost, which makes the pipe or hose dimensionally stable and remains true to size.

It has been found that by admixing one with moisture crosslinkable graft polymers to the peroxidic starting material, such as polyethylene or copolymer-ethylene-propylene can produce a pipe or hose which Subjected to pre-crosslinking even at room temperature and normal room humidity which the dimensional stability and dimensional stability of the extrudate in the following guaranteed peroxidic crosslinking.

Such a graft polymer can be obtained by grafting on a vinyl silane, such as B. trimethoxyvinylsilane, on the polyolefin used, such as. B. polyethylene or polyethylene copolymers.

When exposed to moisture, the crosslinking takes place as follows: Here "R" is the radical, in the selected example the vinyl.

The graft polymer has the property that with the addition of a Catalyst such as an organic tin compound, e.g. B. dibutyltin dilaurate, under Exposure to water or water moisture removes the thread molecules of hydrocarbons networked. This cross-linking already occurs at room temperature and normal humidity a. It is thus possible to extrude a graft polymer into a pipe and subsequently to a certain extent to crosslink by exposure to moisture, whereby the extrudate for the subsequent hot peroxidic crosslinking remains dimensionally stable and dimensionally stable.

When producing a flexible hose, an elastomer is made from the graft polymer mixed with a copolymer of ethylene-propylene.

A peroxide is added to the success of the inventive idea Polyolefin, e.g. B. polyethylene or polyethylene copolymer with the catalyst offset graft polymer is admixed in a proportion of 5 to 45% by weight and the Mixture extruded into a pipe or hose. Then the extruded Pipe or hose pre-crosslinked at a temperature below 1000C and then fully crosslinked at a temperature between 130 and 2500 C. For pre-networking the pipe or hose filled with water after the extrusion research and during stored for a period of 1 to 5 days at room temperature. This is a normal one Humidity sufficient. During this aging process, the moisture diffuses from the inside as well as from the outside into the pipe wall and causes the desired pre-crosslinking. The "cold" pre-crosslinking achieved in this way causes a degree of crosslinking in the pipe wall from 20 to 50%, based on the total polymer mass. During the pre-networking can the tube or hose must also be placed in a water bath. An acceleration The pre-crosslinking can be achieved if water is in the pipe or in the hose a temperature of 60 to 1000C is initiated, followed by a Temperature between 130 and 2500 C is fully crosslinked.

With full peroxidic crosslinking in the temperature range between 130 and 2500C, a degree of crosslinking of 80 to 95%, based on the total polymer mass, achieved without affecting the dimensional accuracy of the extruded tube or hose get lost. With peroxidic crosslinking, the heat comes from the outside of the pipe or hose into the wall and brings it within a few Minutes to fully network. The pipe produced in this way or the hose produced in this way has all the advantages of the extrudate crosslinked exclusively by peroxide.

Further details of the invention are given below with reference to two Embodiments explained in more detail.

Example 1 A commercial, filler-free high-pressure polyethylene granulate with a melt index of 0.4 to 0.6, a density of 0.93 and an average Grain size of 3 mm was placed in a high speed mixer in an amount of 20 kg and mixed with 400 g of 2,5-dimethyl-2,5-di (t-butylperoxy) -hexane and mixed intensively, until the peroxide was evenly distributed on the surface of the granulate. This mixture was then prepared in an amount of 7 kg of commercially available graft polymer from the above-mentioned high-pressure polyethylene granules and 2% by weight of trimethoxyvinylsilane and 0.1% by weight of 2,5-dimethyl,2,5-di (t-butyl peroxy) hexane as an auxiliary for the addition of the vinyl compound to the polyethylene molecule in the high-speed mixer added and mixed intensively. The total mixture was then dibutyltin dilaurate in an amount of 0.05% by weight, based on the graft polymer; as a catalyst added and mixed in in a high-speed mixer. The mixture produced in this way was a heatable extruder with an L / D ratio with the exclusion of moisture of 24: 1 supplied, melted at a melt temperature of 1300 C, to one Tube of 11 mm inside and 16 mm outside diameter extruded and after cooling wound on a drum. The tube was then filled with water at 200.degree and in a room with a relative humidity of> 60% at 200 C for Stored for 48 h. Here, a pre-crosslinking occurred up to a crosslinking degree of 45%, added to the total mass. After that the tube was after Removal of the water and still on the drum in an oven at one Temperature of 140 "C and a treatment time of 12 hours for the peroxidic crosslinking subject. The pre-crosslinked pipe proved to be so dimensionally stable that despite No cross-sectional changes or deformations occurred due to the high temperature. The pre-crosslinking also prevented sticking or welding between the individual windings of the pipe on the drum. The pipe possessed after cooling a total degree of crosslinking> 95%.

Example 2 A commercially available filler-free ethylene-propylene copolymer with an ethylene content of 60% by weight, a melt index of 6, a density of 0.92 and an average grain size of 3 mm was used in an amount of 20kg placed in a high-speed mixer and with 400 g of 2,5-dimethyl-2,5-di (t-butylperoxy) -hexane added and mixed intensively until the peroxide is evenly on the surface of the granulate was distributed. 9 kg of a graft polymer were then added to this mixture. This was made from an ethylene-propylene copolymer of the aforementioned composition and 2% by weight trimethoxyvinylsilane and 0.2% by weight 2,5-dimethyl-2,5-di (t-butylperoxy) hexane as an aid for the attachment of the vinyl compound to the copolymer molecule. The entire mixture was intensively #mixed in the high-speed mixer. Subsequently was of the total mixture dibutyltin octoate in an amount of% by weight, based on the Graft polymers, added as a catalyst and mixed in in the high-speed mixer.

This mixture was prepared under the conditions given in Example 1 Melted in the extruder and formed into a tube with an inner diameter of 10 mm and an outer diameter of 16 mm extruded, which was wound on a drum after cooling. The hose was filled with water by placing it in a water bath of 400C, whereby the storage time in the water bath was 24 hours.

Here, a degree of pre-crosslinking of 40%, based on the total mass, achieved. The hose was freed from the water after removal from the water bath and unwinding from the drum on an endless conveyor belt through a heating pipe section 40 m long, 50 x 20 mm clear cross-section and an inner wall temperature of 1800C at a belt speed of 1.6 m / min. Because of the pre-networking There were no deformations or changes in the cross-section of the hose on. During the passage through the heating pipe section, the peroxide took place Crosslinking up to a degree of crosslinking of 85%. It became a flexible hose obtained whose smallest bending radius r = 4d (d = outer diameter), the one had very good chemical resistance also to solvents and a possessed good aging resistance.

Claims (6)

Claims: 1. Method for producing a pipe or hose from a crosslinked polyolefin, the polyolefin with a peroxide to form a Extrusion mixture is mixed, the extrusion mixture into a pipe preform or tube parison is extruded and then the extruded tube parison or hose preform crosslinked to form the pipe or hose by heat treatment is, characterized in that the extrusion mixture is also due to water moisture crosslinkable graft polymer is admixed and that the pipe preform or the Tube preform exposed to moisture in the water to achieve pre-crosslinking will. 2. The method according to claim 1, characterized in that a through Grafting a vinylsilane onto the polyolefin used graft polymer is admixed. 3. The method according to claim 1 or 2, characterized in that for the production of a flexible hose from an elastomer made from a copolymer Ethylene-propylene is admixed with the graft polymer. 4. The method according to any one of claims 1 to 3, characterized in that that the polyolefin mixed with a peroxide, the graft polymer in one portion from 5 to 45% by weight is admixed. 5. The method according to any one of claims 1 to 4, characterized in, that the pipe preform or the hose preform after extrusion molding filled with water and kept at room temperature for 1 to 5 days is stored for pre-crosslinking. 6. The method according to any one of claims 1 to 5, characterized in, that the pipe preform or the hose preform for pre-crosslinking in a water bath is inserted. Method according to one of Claims 1 to 4, characterized in that that for pre-crosslinking in the pipe preform or in the hose preform water a temperature of 60 to 1000C is initiated, followed by a Temperature between 130 and 250 C is fully crosslinked. The invention relates to a method for producing a pipe or hose made of a crosslinked polyolefin according to the preamble of the claim 1. The production of peroxide cross-linked polyethylene pipes or hoses encounters the known problem that the polymer mixed with the peroxide can be extruded with an extruder to a pipe or hose, which resp. which, however, in the subsequent heat treatment serving for crosslinking His reaching the crosslinking temperature when passing through the melting range Loses its own strength and collapses. In the production of hoses from elastomeric polymers speaks from the “green strength” of the polymer emerging from the hose tool having. The disadvantage of the low intrinsic strength becomes particularly clear here illustrated. The material emerging from the hose tool has a so low intrinsic strength that it is despite the use of all available means not drawn off and wound up with the desired dimensional stability and dimensional accuracy can be. The hose inevitably collapses. Steps even more clearly this disadvantage manifests itself when trying to vulcanize such a hose or subject to peroxidic crosslinking. This process, which is a connection or bridging between causes the long, thread-like molecular chains of the pipe material, only takes place under the action of the required crosslinking reaction temperature. Depending on the duration This reaction proceeds faster when the required temperatures are applied or slower. However, this heat treatment causes an additional one in each case Reduction in the inherent strength of the hose. According to the state of the art, this disadvantage is eliminated by that you put the hose in a cross-molding tool on a round mandrel or support, which by the tool on a round mandrel or carrier, which by the Tool is moved, applies. The hose is thus made on a round profile Metal applied. This process is also carried out in the manufacture of cables and in itself does not present any difficulties. During the subsequent vulcanization or In the cross-linking process, the mandrel in the hose prevents it from collapsing of the hose. Then the crosslinked or vulcanized hose is removed Mandrel withdrawn. If necessary, the hose attached to the mandrel before crosslinking or vulcanization with a flexible tape made of a textile Tissues are bound to avoid any deformation during crosslinking or vulcanization to prevent. The tape is then unwound again and the mandrel is pulled out. This procedure is very cumbersome and it has no attempts there is a lack of avoiding this costly, discontinuous production method. So is z. B. a method known, which the polyolefin mixture by intermittent Piston pressure is pressed into a heated tubular tool, in which the crosslinking takes place. During the subsequent piston thrust, uncrosslinked material gets into the tool pressed, at the same time the cross-linked pipe is pressed out of the pipe tool will. This process requires the use of high-density pipe materials that are correspondingly expensive. In addition, the intermittent procedure is time consuming because the crosslinking must take place in the rest of the material. In a generic, known method (DE-PS 243435) one of a crosslinkable polyethylene or a crosslinkable polyethylene copolymer Ren existing pipe extruded and after extrusion molding with an outer jacket provided, whereupon the resulting composite pipe of a crosslinking effect Heat treatment is subjected, in which at least in the first phase the Crosslinking reaction in the inner tube an overpressure is maintained. With this. Although dimensionally stable and dimensionally stable polyolefin pipes are achieved, however the process requires the application of an outer jacket and temporary maintenance an internal pressure.