DE2061831A1 - Cross-linked polyolefin mouldings prodn - by reacting polyolefin with an oxidising agent and then moulding - Google Patents

Abstract

An opt. foamed moulding of crosslinked polyolefin is mfrd. by reacting the polyolefin with an oxidising agent (e.g. O3 or a peroxide), followed by moulding. Reaction may be effected in a fluidised (cyclone sintering) bed. A foaming agent may be employed during moulding to give an expanded article. Cross-linking is uniform and reaction occurs in mild. conditions. No degradation of polymer takes place.

Description

Process for the production of non-hemmed or foamed molded articles.

The invention relates to a method for producing non-foamed or shaped bodies made of crosslinked polyolefins.

In the production of such crosslinked moldings from polyolefins it is necessary to carefully mix the polyolefin with the crosslinking agent, this ensures an even distribution of the crosslinking agent in the plastic is.

It is known that plastic is used to meet this requirement with the crosslinking agent, e.g. a peroxide, on a two-roll mill or to plasticize in a Banbury mixer and to granulate the band obtained chop up (OS 1 800 279).

It is also known that the crosslinking agent is the powdered plastic to be closed in dissolved or melted form or to be fixed with the aid of one Binders the crosslinking agent on the plastic surface.

It has also been proposed to use polyolefin granules with a crosslinking agent to stir under such conditions that local melting of the surface of the rlyolefin granulate occurs, as a result of which the crosslinking agent diffuses into it (OS 1 803 972).

During the plasticization of the plastic with the crosslinking agent on rollers or in the Banbury mixer, care must be taken to ensure that the dabet occurring temperature below the light-off temperature of the crosslinking agent to avoid premature networking.

These disadvantages are admittedly when adding the crosslinking agent in dissolved form avoided, but the substances used as solvents are often flammable and poisonous. If they have a swelling effect on the plastic, they are also very difficult to remove.

Melted crosslinking agents are easily decomposed and the handling gefälicii with melted peroxides; 8o that the incorporation of melted crosslinking agents is practically hardly through-filled into the polyolefin.

The pixellation of the crosslinking agent on the surface of the plastic by means of ßinder there is a risk that lumps will form. Besides that it is undesirable to introduce foreign substances into the polyolefin because these can make them noticeable in later use, e.g. by occurring Discoloration.

By superficial melting of polyolefin granules and allowing them to diffuse the crosslinking agent is distributed fairly well, but here too Thermal damage to the plastic cannot be ruled out and the gel ear it does not prevent the crosslinking reaction from starting too early.

Whatever the way the crosslinking agent into the polyolefin is introduced, the next I measure always follows the heating of the mixture until on the start-up temperature of the crosslinking agent, which causes the crosslinking reaction is set in motion. If you want to produce foamed, crosslinked polyolefins, so a blowing agent is added to the starting mixture, the foaming process can steer in such a way that networking and foaming take place at about the same time. at the production of moldings is done in such a way that the driftable, the mixture containing the crosslinking agent is filled into a mold which is open or closed can be and heated to the required temperature.

The previous procedure for the production of non-foamed or foamed moldings made of crosslinked polyolefins consists in the crosslinking agent to be mixed thoroughly with the plastic, if necessary with the addition of propellants and then -to deform.

It is only possible in the rarest of cases, in the most gentle way Way to incorporate the crosslinking agent into the plastic. The amount of resources required Apparatus and personnel are very expensive. Degradation reactions through intensive Mixing or kneading are inevitable.

The invention is based on these and other disadvantages the known processes for the production of non-foamed or foamed Forzkodies from cross-linked polyolefins.

This object is achieved according to the invention in that one polyolefins Reacts with oxidizing agent and deforms the implementation produle, t.

Oxidizing agents in the context of the invention are peroxides, preferably Organic-based peroxides. Such peroxides are, for example, diacyl peroxides, such as di-benzoyl peroxide, dialkyl peroxides such as liauroyl peroxide, diethyl peroxide, di-tertiary butyl peroxide, Diisopropyl peroxide, hydroperoxides such as hydroxymethyl hydroperoxide, tertiary butyl hydroperoxide, ethyl hydroperoxide, peracids such as acetoperacid, Benoeperic acid, phthaloperic acid, succinic monoperic acid, trimethylacetoperic acid; Perester e.g.

Esters of perbenzoic acid, such as ethyl perbenzoate or tertiary butyl perbenzoate.

Ozone is also suitable as an oxidizing agent. To produce the ozone the usual ozonizers can be used.

The polyolefin is advantageously reacted with the oxidizing agents in a fluidized bed, for which simple fluidized reactors or e.g. suitable for fluidized bed sintering Devices can be used.

The conversion of the polyolefins with the oxidizing agent takes place below mild conditions. The temperature can be between 10 and 150 ° C., preferably However, it is between 20 and 10,000.

Most reactions are carried out at room temperature.

The deformation of the reaction product takes place at temperatures between 80 and 250 ° O, whereby exceeding the temperature upwards is not very critical is. A temperature range between 100 and 2000C is preferably chosen.

According to a further development of the invention, the reaction product is used before deforming unsaturated compounds into.Such unsaturated compounds are for example organic compounds with multiple bonds such as styrene, triallyl cyanurate, Divinylbenzene or diallyl phthalate.

The unsaturated compounds can also be in polymeric form, for example as unsaturated polyester resins.

If you want to produce a foamed molding, you give the reaction product from polyolefins and oxidizing agents to a blowing agent before molding.

Gases, also in liquefied form, such as, for example, can be used as propellants Pentane, hexane. Or fluorinated hydrocarbons such as Prigen (Farbwerke Hoechst) be used.

Solid propellants are those produced by the action of heat or by chemical reaction with a second substance decompose to form gases and thereby inflate the plastic. As solid propellants e.g.

Sodium hydrogen carbonate, ammonium carbonate, ammonium nitrite, ammonium carbamate, Metal powder in the presence of solid acids or solid alkalis, organic compounds e.g.

organic nitro compounds, used The choice of propellant. for the process according to the invention depends primarily on the softening point des-plastic. The well-known solid, nitrogen-releasing compounds are particularly important for the process Suitable for connections. These are organic compounds from the group the azo compounds, sulfohydrazides, N-nitroso compounds or azides, such as azoisobutyric acid dinitrile, Azodicarbonamide, substituted thiatriazoles, benzenesulfohydrazide, diphenylsulfone-3.5'-disulfohydrazide, Bensol-1,3-disulfohydrazide, Dinitrosopentamenthylenetetramine, N.N'-Dinitroso-N, N ' dimethyl terephthalamide, terephthalazide, p-tert-butylbenzazide.

These substances are available under various company names such as Porofor (BAYER), Genitron (Whiffen & Sons), Celogen (Naugatuk), Unicel (DUPONT), Vulkacel (ici), Nitrosan (DUPONT), Wingcel (Goodyear) in stores. You will be the to be foamed plastics in amounts up to about 20 Gew.o added.

The blowing agents are the reaction product of polyolefins and Oxidizing agents added in the usual form. The admixture can also be in a fluidized bed take place. A concentrate can be produced first - and the mixture afterwards The addition of further plastic can be adjusted to the desired concentration. The propellant can also be mixed with inert solvents, for example with linear oil or acetone and then added to the plastic.

The mixture can also be dyes, pigments, Yüll, extenders or leveling agents; Lubricants, accelerators, means for increasing the non and heat resistance, vulcanizing agent or the like added will.

The foaming can be at atmospheric pressure or at a low pressure Overpressure can be carried out. If you foam it out in molds, its own weight is sufficient of the lid to ensure that it is properly attached. The height of the foamed Share can also be done by so-called limiting screws can be set. Since no pressure is required, molds made from cheap materials are sufficient. e.g. from light metals, iron, copper or zinc or from plaster of paris, wood and plastics.

The mixture can also be processed in an extruder or by means of injection molding machines take place. In this way, unfoamed and foamed molded articles can be produced.

The foaming can, depending on the blowing agent used, between 80 and 250 ° C. In the case of those preferably used in the context of the invention solid blowing agents, the foaming temperature is between 100 and 200 ° C.

The required opening time depends on the intensity the heat source, the heat capacity of the metal molds and the foaming intensity of the propellant. After the end of the heating time, the mold is cooled down and that foamed plastic part removed from the mold.

The cooling of the foamed product can be by air or by Water can be sprayed on.

Also copolymers or mixtures of different plastics or Graft polymers of various starting components can be used, as well as plastics, containing polar groups, e.g. ionomers.

Particularly suitable for carrying out the method according to the invention are polyolefins, e.g. low-pressure, medium-pressure, or high-pressure polyethylene or Polypropylene, also IIischpolynerisate based on ethylene, propylene, butylene and Isobutylene.

According to the invention, the reaction product can be made from polyolefins and oxidizing agents pre-cross-link eyes to a certain extent before deforming, the usual radicals releasing compounds, in particular, as crosslinking agents Peroxides, are suitable. The degree of pre-crosslinking can be up to 10%. Preferred becomes a degree of crosslinking of about 2 to 6%.

The invention is explained in more detail with the aid of the following exemplary embodiments described.

Example 1 to 4 Polyethylene (I.upolen 1800; BASF) with 20 wt.% Di-tert-butyl peroxide carefully mixed in an intensive mixer, keeping the temperature of 450C is not exceeded.

The mixture is then open for 24 hours at room temperature stored so that the excess peroxide can completely evaporate. This The reaction product is precrosslinked by heating over a period of 30 minutes. The degree of crosslinking achieved as a function of the temperature is temperature 0 Example 1 Example 2 Example 9 Example 4 125 135 160 165 Degree of crosslinking o7o 2 4 4 5 For comparison, the same plastic is used under the same conditions the same oxidizing agents mixed and immediately after the mixing process in the same form under the same conditions i.e. for 30 minutes with the specified Temperatures heated. Crosslinking did not occur, i.e. the degree of crosslinking was O Vo.

The pre-crosslinked reaction product is then in each case The same form heated for 1 hour at 150 ° C under a pressure of 1 ati. After cooling down will the Degree of crosslinking in the usual way by boiling with decalin and weighing, it's right. It was Example 1 Example 2 Example 3 Example 4 Degree of crosslinking % 37 40 41 - 42 Example 5 A mixture of 100 parts by weight of high-pressure polyethylene (Density: 0.92 gZcm3, crystallinity 65%) 2 "di-tert-butyl peroxide 0.1 II Irganox 1076 (.Fa, Geigy) is immediately after mixing on an AUMA machine at a Roller temperature from 140 to 1700C and a belt temperature of approx. 15000 in plates processed.

The degree of crosslinking is 3 yf. When processing the mixture after 48 hours of standing, the degree of crosslinking of the molding increased to 80-80%. Peroxide-free Polyethylene blends also showed signs of standing for months after processing no networking.

Example 6 The mixture prepared according to Example 5, which does not had more volatile peroxide content of 0.5% (based on H 2 O 2), 2.5 parts by weight were used Azo dicarbonamide, 4.5 parts by weight sodium bicarbonate and 0.7 parts by weight zinc oxide were added. This mixture is poured evenly in powder form into a mold and at 2000C foamed practically without pressure. It became a foamed molded article with a degree of crosslinking received by 63%.

Example 7 A reaction product of oil pressure polyethylene (density 0.96 g / cm3; Crystallinity 90% and 4 0 dicumyl peroxide is heated to 1400 C, a degree of crosslinking of 2% is obtained. This pre-crosslinked reaction product is then with 4.5 wt.

Azodicarbonamide and 0.7 wt. Zinc oxide mixed and foamed in powder form at 2000C. The degree of crosslinking of the foamed molding is 45%.

Example 8 EiR composition product of low-pressure polyethylene (density 0.94, crystallinity 80 ffi) and 6 wt.% Di-tert. butyl peroxide are 6% by weight Azodicarbonamide and 0.7% by weight of zinc oxide mixed in.

From this mixture in 45 minutes at a temperature of 135 plates melted up to 1400C, the degree of crosslinking is 3%. The pre-networked Panels were then foamed at 2200C. It was a foamed molding with obtained a degree of pre-crosslinking of over 80%.

Example 9 Polyethylene is introduced into a fluidized bed and through a porous base plate an ozone-containing gas, generated with a commercially available taborozonizer passed through at 80 ° C '. The whirled up polyethylene is thereby ozonated.

The ozonated product is turned into plates in a press at 2000C produced, whose degree of crosslinking is 30 wt., ó.

The advantages achieved with the connection are in particular: that it is possible to produce homogeneous, i.e. continuously crosslinked, molded bodies made of polyolefins to manufacture. Parts with different degrees of crosslinking, e.g. heavily crosslinked outer ones jeile, next to weakly cross-linked internal parts, practically do not occur. That has As a result, even relatively thick-walled molded bodies from the outside inwards as a result their uniform degree of crosslinking always the same chemical and physical Have properties.

The reaction products according to the invention of polyolefins with oxidizing agents have an unlimited shelf life and do not have to, such as mixtures of polyolefins with peroxides, can be processed immediately.

The conversion of the PolyoleSinen with the oxidizing agents does not require any special apparatus and it is not necessary to use, for example, the peroxide Using kneaders to incorporate them into the plastic. For subsequent deformation and simultaneous crosslinking, no high pressures and no high temperatures are required.

The conversion of the polyolefins with the oxidizing agents takes place below mild conditions, i.e. only with low pressure and relatively low temperatures, so that otherwise common degradation phenomena of the polymers do not occur. Under under these conditions, no crosslinking or oxidation of the polymer occurs. The reaction product differs in the starting product in the IR spectrogram newly emerging, not clearly separated bands at 1700 to 1740 cm 3. Surprisingly the reaction product is less sensitive to temperature, so that the subsequent Deformation the deformation temperature can be exceeded without affecting the end product Damage suffers, which is important in the production of framed plastic bodies is. If the conversion product is pre-crosslinked before tracking, another comes Added the advantage that higher foaming ratios are obtained without the Older products tend to shrink.

Claims (12)

Claims X Process for the production of non-foamed or foamed Moldings made from crosslinked polyolefins, characterized in that polyolefins reacts with oxidizing agent and deforms the reaction product. 2) Method according to claim 1, characterized in that as Oxidizing agents peroxides, preferably organic peroxides used. 3) Method according to claims 1 and 2, characterized in that that ozone is used as the oxidizing agent. 4) Method according to claims 1 to 3, characterized in that that one carries out the conversion in a fluidized bed. 5) Method according to claims 1 to 3, characterized in that that the polyolefin with the oxidizing agent at temperatures between 10 and i500C, preferably 20 to 1000C. 6) Method according to one or more of claims 1 to 4, characterized characterized in that the reaction product at temperatures between 80 and 2500C, preferably 100 to 2000C deformed. 7) Method according to one or more of claims 1 to 6, characterized characterized in that unsaturated compounds are added to the reaction product; 8) Method according to one or more of claims 1 to, characterized in that that blowing agent is added to the reaction product. 9) Method according to one or more of claims 1 to g, characterized characterized in that the polyolefins are polyethylene and / or copolymers of the Polyethylene used. 10) Method according to one or more of claims 1 to 8, characterized characterized in that the polyolefins used are polypropylene and / or copolymers of the Polypropylene used. ii) The method according to one or more of claims 1 to 19, characterized characterized in that the reaction product is precrosslinked. 12) non-foamed or foamed molded body made of crosslinked polyolefin, produced according to one or more of the preceding claims 1 to 10