FI62116C - SAETT ATT FRAMSTAELLA TVAERBUNDNA FORMADE PRODUCT FRAON TVAERBINDBARA OLEFIN- ELLER VINYLCHLORIDEPOLYMERMATERIAL - Google Patents

Description

fBl ANNOUNCEMENT

4STa (1) UTLÄGGNINGSSKRIFT 6211 6 C (45) Patent .uyonretty 10 11 1982 Patent meddelat vyy (51) Ky.lk?/lnt.CI.3 C 08 J 7/12, 3/24 // H 01 B 13 / 06

FINLAND —FINLAND (21) Ρκ · η «Ι * .Κ. ™ ~ Ρ« «« »ι» 6ΙιηΙη | 2989 / TU

(22) Hak «ml * pllvl - AiMBknlnpdag lU .10.7¾ (23) AlkupUvt —GHcffhetsdif 1 ^ .10.7¾ (41) Tullut | ulklt« kt! - Bllvlt off * ntll | l6.0! +. 7 5

National Board of Patents and Registration (44) Nlht »vik» ip * nen | » month.Jullut «un pvm.—

Patent · och registerstyreisen Amekui utitgd eeh uti. »Krift * n pubiicurad 30.07.82 (32) (33) (31) PnrJ *« y «tuelk ·» »- tu« srd priority 15.10.73 English-England (GB) ^ 7993/73 (71) Aktieselskabet Nordiske Kabel- og Traadfabriker, La Cours Vej 7, DK-2000 K ^ benhavn F, Denmark-Danmark (DK) (72) Francesco Paolo Procida, Lyngby, Svend Sandholm Pedersen, Holbaek,

Peter Carstensen, K ^ benhavn, Denmark-Danmark (DK) (7¾) Oy Kolster Ab (5¾) A way to make crosslinked, molded products from crosslinkable olefin or vinyl chloride polymer materials - Sätt att framställa tvärbundna formade produkter elllin tvärbindbara olef

The invention relates to a method of making crosslinked molded articles having a dimension in at least one direction significantly larger than the dimension in the other or other directions from crosslinkable olefin or vinyl chloride polymeric materials, preferably HD polyethylene, the material being thermoformed into the desired product followed by heating with organic peroxide.

The process according to the invention is characterized in that the product is heated in the presence of an aqueous medium which does not contain a polymeric blowing agent and contains one or more peroxides and one surfactant, under conditions such that the peroxide or peroxides penetrate the product mainly without crosslinking, followed by heating. continued in the same medium or in an aqueous medium free of peroxide and no surfactant at an elevated temperature at which the peroxide or peroxides substantially decompose to free radicals to achieve the desired uniform degree of crosslinking of the product, at least the crosslinking step preferably performed in an aqueous medium, is approximately the same as the polymeric material. Examples of the above-mentioned molded products are pipes, cables, plates and profiles. The invention is thus not limited to products made, for example, by injection molding, compression or injection molding, but also encompasses all other production methods customary for polymeric materials, such as extrusion, calendering, lamination, casting, blowing, etc.

Molded products need not exclusively be a polymeric material. Firstly, the polymers can, of course, contain the usual fillers and other additives, but they can also contain reinforcing materials, and in particular cables in which the metal core is coated with insulating and / or semiconducting polymer layers.

Several million tons of plastic materials are used every year for various purposes and therefore it seems unnecessary to try to improve the properties of these materials. However, certain limitations in the physical properties of these substances affect it so that they are not used in certain areas where their other properties would be ideal for their use. For example, for polyethylene, the following properties can be mentioned which would lead to improvements: 1) Resistance to plastic flow at room temperature and elevated temperatures.

2) Resistance to solvents at elevated temperatures.

3) Resistance to environmental stresscracking.

4) Resistance to brittleness occurring in uncrosslinked PE pipes after prolonged pressure loads at elevated temperatures.

The emergence of low-pressure polyethylene (HD-PE) is a good step on the road to solving these problems, but crosslinking, a method similar to rubber vulcanization, further improves these properties.

When crosslinking plastics, it is known to use free radical generating agents, usually organic peroxides, to effect crosslinking by chemical heat treatment and / or in combination with accelerators, activators and / or auxiliaries. Most known methods for making molded, crosslinked products from crosslinkable polymeric materials require that the free radical generating agent be blended or added to the polymer prior to molding.

The addition of the free radical generating agent usually takes place with conventional mixers. For example, for low density polyethylene (LD-PE), twin rolls or Banbury mixers can be used. The agitator is heated to about 110 ° C and polyethylene, which may contain fillers, antioxidants and excipients, is added and treated for a suitable time until the material is homogeneously melted. The free radical generating agent is then added, after which an additional mixing time of 2-5 minutes is usually sufficient. As a rule, the temperature after the addition of the free radical generating agent would not exceed 120 ° C. When the mixing process is completed, the material is granulated in a known manner and is then ready to be fed to extruders or die casting machines, where the finished materials are formed at such low temperatures as to avoid premature crosslinking or blistering.

The heat treatment that is then required to effect crosslinking in the now preformed products can be performed in a number of different ways:

In principle, heat can be introduced into the extruded materials 9 by continuous processes in the form of water vapor / CCV (contact vulcanization) or CCV (catenary CV), salt baths and fluidized beds, or in the form of infrared light or microwave energy. The first four heat sources have the disadvantage that they all require that the material to be crosslinked must be supported in one way or another to avoid deformation at the high temperatures at which crosslinking occurs and where the uncrosslinked material is in the molten state. Therefore, these methods have not come into use, for example, in the manufacture of profiles or pipes from crosslinked polymeric waves, but only in the manufacture of cables in which the conductor is able to hold the material in place during vulcanization. The fifth method (microwave energy) for introducing the necessary heat into the preformed materials is limited to polymeric materials which themselves have high insulation loss coefficients (tg b) or which are combined with a filler, e.g. chimneys, which causes high insulation losses.

Compared to the very complex methods of heat transfer mentioned above, the direct method in which granules containing a free radical generating agent are extruded from a press head or special tool of an extruder, while introducing sufficient heat to effect crosslinking in the material, is that the crosslinked material easily clogs the extruder and the extruded material becomes deformed and often tears into pieces and does not obtain a smooth surface.

The above-mentioned methods for crosslinking crosslinkable polymeric materials in which a free radical generating agent has been added before molding the finished materials cannot be used, for example, with HD-PE because HD-PE requires both high processing temperatures in both the free radical generating agent mixing step and the molding step and premature crosslinking. or blistering cannot be avoided.

Another known method that can be used to make crosslinked extruded products from HD-PE basically involves mixing powdered HD-PE with peroxide and various excipients with a feed press of a hydraulic press, whereby a press under elevated pressure feeds the material to a heated tool with is the desired profile of the finished product. This method has two major disadvantages: 1) The method can only be implemented on specially designed machines; 2) the method cannot be used to prepare crosslinked materials from HD-PE containing a filler.

When molding materials from a crosslinked polymeric material according to known methods for injection molding, compression or injection molding, it is necessary to add or mix the free radical generating material according to it before the material is introduced into the molding machine. As a result, molding conditions become unfavorable because premature crosslinking or blistering can only be prevented at low processing temperatures and, in addition, the crosslinking process itself can occur in the tool in which the material is molded. As a result, the substance does not acquire optimal properties and the long residence time of the substances in the molding tool becomes a factor limiting production, which makes the process unprofitable for most products.

To avoid these disadvantages, products have been made from polymeric materials without the addition of a crosslinking agent and then ionizing radiation has been used to effect crosslinking. However, the use of such processes is limited to products with small cross-sections. Expensive hardware is still required and energy consumption is high.

U.S. Pat. No. 5,621,116 3,198,868 and the corresponding GB patent 940,876 describe a process for vulcanizing molded materials with an impregnating vulcanizing agent. In practice, the cooled material is immersed in a bath of 30-50 ° C containing organic peroxide dissolved in an organic solvent such as acetone or alcohol. After an immersion time of one hour to a few days, the substance is removed and the absorbed solvent is evaporated in vacuo at low temperature, after which the substance is heat-treated at 100-200 ° C in an autoclave and later possibly in a press to effect vulcanization.

This process is complicated in that it comprises several processing steps and further has the disadvantage that it is limited to elastomeric materials such as rubber, styrene rubber, butyl rubber and silicone rubber, but in particular to straight amorphous ethylene copolymers with α-olefins, especially propylene. The process is less useful for the treatment of olefin homopolymers, in particular polyethylene, in particular because it is not possible to absorb the peroxide vulcanizing agent. If it is desired to make materials from polyethylene and highly crystalline polypropylene, it is necessary to blend homopolymers with linear ethylene-propylene copolymers to ensure absorption of the peroxide crosslinker.

German Offenlegungsschrift DE 1 056 822 describes a method for surface-treating low-pressure polyethylene by spraying a crosslinking agent, in particular organic peroxides, in the form of a finely divided solution onto a thermoplastic material. The immersion of high pressure polyethylene materials in a solution containing a crosslinking agent or a liquid crosslinking agent is known in the art. The method according to the publication often achieves surface crosslinking and Absorption requires surface swelling.

German patent DE 1 072 803 discloses a process for crosslinking polyethylene moldings by treatment with dicarboxylic acid dichlorides, optionally in the presence of blowing agents such as carbohydrates. However, the use of these acid chlorides requires working in completely anhydrous conditions and, in addition, acid chlorides are difficult to obtain and difficult to handle.

French patent FR 2 068 882 deals with the crosslinking of certain vinyl chloride copolymer materials by the addition of certain silanes to polymer chains. Crosslinking is achieved by treatment under acidic conditions at 0-150 ° C, and this method is particularly applicable to films and fibers formed under acidic conditions, which crosslink when drawn out. German application DE 2 204 655 describes a method for producing electrical cables coated and / or insulated with crosslinked polyethylene, in which uncrosslinked polyethylene containing peroxide is extruded together with a cable core which supports the polyethylene during heat treatment crosslinking. The process is limited to polyethylene having a density of 0.935 or less and requires, as stated above, that the crosslinking agent be added prior to extrusion.

German application DE 2 204 658 describes a similar method using polyethylene having a density of 0.935 or more. Here, too, the crosslinking agent is preferably added to the polyethylene during extrusion, but the addition can also be carried out by treating the formed material with peroxide in the gas phase and then heat-treating at 250 ° C in a salt bath. The method requires a cable core to support the polyethylene during crosslinking.

U.S. Patent 3,705,257 describes cables consisting of multiple layers with one or more layers crosslinked. The inner insulating layer is preferably crosslinked PE, which together with the crosslinking agent is extruded and then crosslinked in a vulcanization chamber. After extrusion of the outer semiconducting layer, the surface is crosslinked, preferably by spraying the outer part of this layer with dicumyl peroxide dissolved in acetone or in molten form. After coating, the cable coated with the crosslinking agent is placed in a special curing chamber where the crosslinking is effected by heating. This method is also limited to the manufacture of cables. German application 2 214 628 describes a process for preparing foamed, crosslinked polymer particles, in which the polymer particles (granulate) are suspended in an aqueous emulsion containing a crosslinking agent and heated until crosslinking has taken place. Only then is flotation and molding performed. The blowing agent can be added to the particles either after or simultaneously with crosslinking. The particles state in the publication that they can be of any shape and have a dimension of 1 to 10 mm, and more generally state that there are no restrictions on the shape and size of the particles, which, however, must be suitable for the intended use. However, when the particles are subsequently foamed to 5-30 times the particle size, the restrictions on particle shape and size are quite strict, so that products with a dimension in at least one direction significantly larger than in another or other directions (eg pipes and cables) are not immediately possible. In the process of the present invention, an insoluble, inorganic metal salt should be used as a particle dispersant to prevent the particles from sticking together, and a surfactant should also be added to dissolve or disperse the crosslinking agent homogeneously and to facilitate absorption into the polymer particle. Numerous polymers are listed with respect to the polymeric materials used, but all examples are based on the high-pressure (LD) polyethylene "Miroson-9", which is not further characterized and which invariably has a particle size of 3-4 mm. About 10-70% is mentioned as the desired gel percentage and it is found that a higher gel percentage interferes with foaming. However, there is nothing in the specification to indicate that higher "undesired" higher gel percentages are achievable at all (up to 72% in the examples).

Thus, when a person skilled in the art who is aware of the drawbacks of the prior art and wants to provide a method for producing homogeneously crosslinked molded articles with a dimension significantly larger in at least one direction than in another or other directions and higher gel percentages without risk of deformation, applicability of the method according to the chip application purpose, he notes that the prior art cannot be directly applied when HD-PE is to be used. It appears from the application that particles with a size of 3-4 mm crosslink to a gel percentage of up to 70% without adhesion if heated in an aqueous medium in which peroxide is dispersed with a surfactant and in addition has an insoluble inorganic metal salt. The publication makes no mention of shape stability during the process or of the possibility of achieving a higher gel percentage, especially in the case of products with a thickness of a few millimeters. U.S. Patent 3,198,868, which relates to the vulcanization of molded articles such as cables, pipes, and the like from elastomeric materials, emphasizes that it is impossible to crosslink an ethylene homopolymer without adding an EP copolymer. Although DE-A-2 214 628 shows another in the case of 8 62116 small-dimensional LD-PE particles, which have not been further characterized, the notion set out in the US patent must nevertheless be considered relevant in the case of the substances now mentioned. type, and especially in the case of HD polyethylene, the molecular structure of which in no way shows better absorption than LD-PE.

The present invention provides a process which is not limited by the known methods with respect to the substances to be produced or the materials used, and which is particularly suitable for the production of HD polyethylene products without deformation. This is to be considered surprising in the light of the prior art and in particular of the DE application. In particular, the process could be considered impossible without the addition of an insoluble, inorganic metal salt, unless it is accepted that the substances adhere to each other and cross-link irregularly, but as the examples show the metal salt in contrast to polyvinyl alcohol is insufficient in DE 2.

The process according to the invention prepares the substances in a conventional manner from customary starting materials without the addition of crosslinking agents, such as free radical generating agents, but the starting materials may contain fillers and / or antioxidants and / or possible auxiliaries for crosslinking. The choice of olefin or vinyl chloride polymer materials is limited by only two factors, namely. the characteristics of the finished product and the processing equipment used. Thus, if no unstressed material has been obtained in the treatment, which may be due to an extruder or other treatment device, the material may suitably be de-stressed according to the invention by treatment with a crosslinking agent, for example by heating the material. In addition, if the substance is to be, for example, HD-PE, the type of HD-PE that achieves optimal processing conditions should be chosen so that the production of the substances is easily smooth and error-free and the products have optimal properties. The process according to the invention is not limited to materials prepared by extrusion and injection molding, but can be used in connection with all processes used in the manufacture of products from polymeric materials.

62116

Once the material is molded, by one of the known methods, one or more conventional crosslinking agents or free radical generating compounds are added to the polymeric material. Examples are organic peroxides, such as di-tert-butyl peroxide and dicumyl peroxide, or organic hydrogen peroxides, such as tert-butyl hydrogen peroxide. A particularly preferred peroxide is 1,1-bis- (tert-butylperoxy) -3,3,5-trimethylcyclohexane, which causes a particularly small amount of deformation during crosslinking, in that it forms crosslinks at a fairly low temperature (about 100 ° C). ) temperatures. The choice of crosslinking agent for a particular system depends, among other things, on the olefin or vinyl chloride polymer material to be crosslinked. In principle, all crosslinkable olefin or vinyl chloride polymer materials can be used in the process, provided that the crosslinking agent or agents are soluble in the polymeric materials.

Finally, the process according to the invention can meet the following requirements, which are particularly relevant for the preparation of substances for specific purposes, either alone or in combination: 1) The process can be controlled to achieve the desired degree of crosslinking, e.g. HD-PE crosslinking so strong that there is such a decrease in density that it is no longer HD-PE.

2) The process can be controlled so that the dimensional change in the materials is acceptably small.

3) The process can be controlled so that the substances do not contain detectable amounts of peroxide residues.

The addition of the peroxide crosslinking agent or agents can take place, for example, by immersing the agents in an aqueous dispersion containing the surfactant and one or more peroxides, in the form of an emulsion and prepared either by mechanical treatment, e.g. in a high-pressure homogenizer, or by emulsifiers, protective colloids or the like.

Surprisingly, it has been found that the peroxide at the temperature used is relatively evenly distributed in the material, so that after the crosslinking process a crosslink with a very good penetration depth is observed.

The crosslinking of the substance itself is achieved by a suitable treatment, e.g. a heat treatment, either in connection with the molding step and / or the addition of peroxide or peroxides or in a separate treatment step. In the former case, the heat 10 621 1 6 required for the molding itself may be transferred in whole or in part to the crosslinking process after molding.

According to a particularly preferred variant of the process of the invention, the addition of the peroxide or peroxides and the crosslinking process are carried out in one and the same aqueous medium in a closed or pressurized system. The density of the aqueous medium is preferably approximately the same as that of the material to be prepared, ensuring that the material does not deform during the heat treatment. If desired, the density of the medium can be corrected for this purpose by adding one or more salts.

In order to obtain a particularly reliable control of the degree of crosslinking, it may be expedient to change the peroxide-containing medium to an aqueous medium which does not contain peroxide after the heating step during which the crosslinking agent penetrates the substance, so that no more peroxide penetrates during heating.

Especially in the manufacture of cables, in order to prevent cross-linking when the cable is cross-unwound, the cable can be wrapped after the cross-linking agent has penetrated, but before the final treatment to effect cross-linking.

Surprisingly, it has been found that the process according to the invention gives crosslinking with an excellent depth of penetration and uniformity without deforming the substances. To determine the extent of crosslinking, the standard is to determine the insoluble portion of the crosslinked polymeric material upon extraction in a boiling stabilized solvent. For HD-PE, extraction in boiling stabilized decalin has been found to be 80-100% insoluble after crosslinking by the process of the invention.

The treatment time, both in terms of the crosslinking agent (s) addition step and the crosslinking process itself, depends on, among other things, the treatment temperature, the olefin or vinyl chloride polymer material used, the thickness of the material, the quality of the crosslinking agent or agents and the desired degree of crosslinking.

With regard to the processing pressure, it is possible to work at both atmospheric pressure and high or low overpressure. In general, the parameters temperature, processing time and pressure can vary within quite wide limits. Crucial to the selection are, in particular, the desired properties of the final product, e.g. the degree of crosslinking, the stability of the dimensions and the permissible concentration of peroxide residues. These properties 621 1 6 11 as well as the course of the process are usually also determined by the chosen peroxide, if the properties themselves in turn set wider or narrower limits on temperature, time and pressure.

It should be mentioned in particular that the blistering caused, for example, by volatile constituents coming from possible fillers or decomposition products of crosslinking agents, which is known, for example, as described above, is avoided by the method according to the invention. This is achieved by appropriately selecting the above-mentioned parameters, whereby, for example, a sufficiently long treatment time allows the decomposition product to diffuse away, while also, for example, by increasing the pressure in whole or in part, such blistering can be prevented.

Excipients may also be used in the process according to the invention, as mentioned above. These may be added during the molding step of the material or may be contained in a peroxide-containing liquid medium. Useful excipients include polyunsaturated organic compounds such as triallyl cyanurate, sorbic acid and ethylene glycol dimethacrylate.

Crosslinking of the substance per se after the addition of the crosslinking agent or agents can be achieved instead of heat treatment by treating the substance at a lower temperature with activating agents or accelerators for crosslinking agents.

The method according to the invention is described in more detail by the following examples.

Example 1

515 g of polyethylene ("Hostalen ^) GN 5010", melt index MFI

O

0.3 g / 10 min. density 0.955 g / cm, containing 2.5-3.0% carbon black) in the form of a tube with an outer diameter of 17.0 mm and a wall thickness of 3.0 mm and a plate measuring 600 x 65 x 11.3 mm is placed in a tube autoclave with a diameter of 80 mm and a length of 680 mm.

Prepare an emulsion containing 20 g of di-tert-butyl peroxide ("Trigonox B" Noury van der Lande) 0,1 g of polyvinyl alcohol ("Elvanol 7260", du Pont) 2.6 g of oleic acid

0.3 g NaOH

20 g of anhydrous NajSOj.

The autoclave was filled with distilled water and the above emulsion. The liquid is then circulated in the autoclave by means of a piston pump which at the same time acts as a homogenizer.

62116 12 For 2.5 hours, the liquid temperature is raised to 120 ° C and held for 4 hours, after which it is raised to 133 ° C and kept for 14 hours.

After the crosslinking thus obtained, the outer diameter of the tubes has increased from 17.0 to 17.2 mm, while their density 3 has decreased from 0.955 to 0.925 g / cm 3.

In the decalin extract, a gel content of 97% is observed for the tubes. When removed from the autoclave, the tubes did not tend to stick together.

For 113 mm thick plates, the percentage of gel in 92 material up to 1 mm from the surface is measured. In a substance located 3-4 mm from the surface, the gel content is measured to be 80%.

Example 2

495 g of polyethylene comprising 7 pieces are placed in the tube autoclave shown in Example 1. polyethylene pipes ("Hostalen © GM 5010", MFI 0.3 g / 10 min. density 0.955 g / cm 2, containing 2.5-3.0% carbon black) with a length of 60-65 cm, outer diameter 17.0 mm and a wall thickness of 2.8 mm.

An emulsion having the composition mentioned in Example 1 is prepared.

The autoclave was filled with distilled water and the above medium. The liquid then circulates in the autoclave using a gear pump at a speed of 6 1 / min.

During 2 hours, the liquid temperature is raised to 115 ° C and maintained for 3 hours, then raised to 158 ° C over the next 5 hours and maintained at this temperature for a further 7 hours.

After the crosslinking thus obtained, the outer diameter of the pipes has increased from 17.0 to 17.1 mm, in the sauna when the density has decreased from 0.955 to 0.918 g / cm 2.

In the decalin extract, a gel percentage of 99-100 is obtained.

When removed from the autoclave, the tubes do not tend to stick together.

Example 3

The tube autoclave shown in Example 1 is loaded with 475 g of polyethylene comprising a pressed polyethylene sheet measuring 100 x 70 x 12.5 mm and free of fillers ("Hostalen © GM

3 6050, MFI 0.3 g / 10 min., Density 0.946 g / cm), and an extruded polyethylene sheet, 600 x 60 x 11.3 mm ("Hostalen © GM 5010"),

An emulsion having the composition mentioned in Example 1 is prepared.

After the autoclave is filled with the above-mentioned emulsion oil and distilled water, the polyethylene is crosslinked under the same conditions as in Example 2.

After the crosslinking thus obtained, the gel percentage 77.4 in the polyethylene sheet "GM 6050" is measured at a distance of about 6 mm from the surface.

In the polyethylene sheet "GM 5010", the gel percentage is 99.7 at a maximum distance of 2.5 mm from the surface. The material has a gel percentage of 86.2 at a distance of 5-6 mm from the surface.

Example 4

Crosslinking of an unplasticized PVC profile with a thickness of about 1.5 mm.

An emulsion having the same composition as in Example 1 is prepared. It is metered in an amount corresponding to 10% by weight of peroxide relative to the weight of the PVC material, and then placed in a 2-liter stainless steel autoclave together with the PVC material. The temperature in the autoclave was slowly raised to 125 ° C (about 2 hours), which was maintained for 48 hours. After this treatment, the following changes could be observed in the PVC material: a) In the Soxhlet extract with tetrahydrofuran, a 25% insoluble residue was detected (against 0% in the untreated control).

b) In the thermal effect test (EMKO (10) 5 102/71 § 15, a), but after 1 hour at 95 ° C an effect of 2.25 mm was observed (against 4.00 mm in the untreated control sample).

c) In the mechanical measurement, a Young's modulus of 70 bar /% was measured in an Instron tensile tester (against about 140 bar /% in an untreated control).

Example 5

The tube autoclave used in Example 1 is charged with 569 g of polyethylene comprising 7 polyethylene tubes, 17 mm x 2.5 mm (diameter x wall thickness). Used pipes made of plastics "HostA len GM-5010" or "Lupolen 5261Z" (density 0.950, melt index according to DIN 53 735) of 21.6 kg load: 1.7-2.3). Some of the following by-products had been used in some of the tubes and two of the tubes were tension balanced.

An emulsion is prepared containing: 10 g of 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane 30 g of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane 32.6 g of oleic acid

4.7 g NaOH

621 1 6 liters 1.3 g polyvinyl alcohol 50 g Na2SC> 2 5 1 distilled water.

The emulsion was added to the autoclave and recycled by a centrifugal pump. The temperature is maintained at 82 ° C for 7 hours, after which the emulsion is changed to distilled water containing 50 g of λ 2803.

During 12 hours, the temperature is raised from 105 ° C to 150 ° C at a rate of 3-5 ° C / h so that the temperature rise is smallest at the lowest temperatures.

After crosslinking, the following densities, gel percentages and shrinkages in the longitudinal direction of the tubes are measured.

Ingredients Gel% Density Shrinkage% H0stalen® <3! 5010 76 0.947 3.9

Hostalen ® (¾ 5010 + 2% ethylene glycol dimethacrylate 87 0.946 4.0

Hostalen ^ (34 5010 + 2% sorbic acid 83 0.946 4.0

Hostalen® (31 5010 + 2% triallyl 1 cyanurate 85 0.945 2.8

Hostalen® (31 5010 heat treated to remove internal stresses 80 0.946 2.3

Lupolen ®5261 Z 99 0.931 4.2

Lupolen ®5261 Z heat-treated 99 0.931 2.7

Example 6

420 g of polyethylene comprising 8 polyethylene tubes, 17 mm x 2.5 mm, are placed in the tube autoclave of Example 1. The tubes were partly made of "Lupolen®5261Z" plastic and partly of "Rigi-dex ® H 02054P" plastic (density 0.954, melt index (DIN53735) with a load of 21.6 kg: 2.0).

An emulsion according to Example 5 is prepared, however, containing 20 g of 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane as the sole peroxide.

The emulsion is added to the autoclave and circulated by a centrifugal pump.

The temperature is maintained at 94 ° C for 6.5 hours, after which it is raised to 150 ° C over 9 hours so that the temperature rise to 110 ° C is limited to 2-4 ° C / h.

The temperature is maintained at 150 ° C for 2 hours.

After crosslinking, the following values were measured:

Substances Gel percentage Density Shrinkage%

Lupolen® 5261 Z 97 0.930 3.1

Rigidex®H02054P 82 0.933 5.8 1 - »y m ...." 'I „

Claims (2)

15 A method of making crosslinked molded articles having a dimension in at least one direction significantly larger than the dimension in the other or other directions (e.g. pipes, cables, sheets and profiles) from crosslinkable olefin or vinyl chloride polymeric materials, preferably HD polyethylene, wherein the material thermoforming into the desired product, which is then treated with organic peroxide under heating, characterized in that the product is heated in the presence of an aqueous medium free of polymeric blowing agent and containing one or more peroxides and one surfactant under conditions such that the peroxide or peroxides penetrate the product essentially without causing crosslinking, followed by heating in either the same medium or an aqueous medium containing no peroxide or surfactant at an elevated temperature at which the peroxide or peroxides decompose substantially; open to free radicals, to achieve the desired uniform degree of crosslinking of the product, wherein at least the crosslinking step is performed with the product contained in an aqueous medium, preferably having a density approximately equal to that of the polymeric material. Method according to Claim 1, characterized in that the product is released from the stresses before heating in the presence of peroxide.