DE19509613A1 - Moulded prods., esp. hollow tubing etc., with oxygen barrier layer - Google Patents

Abstract

Moulded prods. with an oxygen barrier layer, esp. hollow section mouldings, comprise a first layer (A) made of organosilane-grafted polyolefin and an oxygen barrier layer (B) consisting of material which can form covalent bonds with the grafted organosilane gps. in layer (A) and which is coextruded directly onto layer (A) under pressure. Also claimed is the prodn. of these mouldings, in which the melt streams for layers (A) and (B), and opt. for a base layer and another barrier layer, are fed into an extruder head and coextruded in close contact at up to 300 bar.

Description

The invention relates to a molding with an oxygen barrier layer, in particular a hollow profile molding, such as he especially as a pipeline for floor heating systems, for the drinking water supply, etc. is used.

For this type of Kunststofformkörpern are often Polyethy len body, however, due to their sour Perviousness in untreated form an oxygen DIF allow fusion through the pipe into the heating or drinking water, resulting in corrosion of the metal parts in the heating system leads. This problem has been, as for example in DE-A-39 03 436 described, thereby encountered that one after or at the Extrusion of the body a coating of the body or tube with a bonding agent and then a sour fabric barrier layer and then the finished, mehrschichti ge plastic pipe networked. As a barrier layer is a layer recommended from ethylene / vinyl alcohol (EVAL).

A disadvantage of this technology is that first a detention Mediator must be applied, as the oxygen barrier ethylene / vinyl alcohol layer not directly on the polye Thylene basic body adheres. Such a production route, the Construction of the pipes according to the prior art requires requires a production plant of considerable complexity, resulting in Cost disadvantages of such pipes reflects.

Object of the present invention is to provide a molded body of initially proposed type, in which the sour  Fabric barrier layer without the use of a primer or primer can be applied.

This object is achieved in that the Shaped body one of an organosilane-grafted polyolefin formed first layer and one under pressure with the first Layer and directly on this coextruded oxygen bar layer of one with the organosilane groups of the first Layer comprises covalently linkable material.

Due to the novel material selection for the first layer can an oxygen barrier layer, for example of ethylene / Vi nyl alcohol (EVAL), without the previous coating with a Adhesion promoters in a one-step process directly on the first layer are applied, d. H. the first layer and the oxygen barrier layer are in a coextrusion Tool formed, for example, to the tube to the two-layer tenrohr merged and deployed simultaneously.

The coextrudate is then flowed through by a hot water flow (60 ° T _W 90 °) for several hours. A hydrolysis and condensation reaction takes place in the silane-grafted polyolefin, which cross-links the main body in the solid state to a high degree (gel contents 65-85%).

This structure of the molding according to the invention allows a significant improvement and simplification in the production of the molding by the oxygen barrier layer without the Zwi circuit of a primer layer, also coupling layer or primer layer, applied and fixed with the ground tube or the first layer can be connected. As a result, not only investment costs can be saved, son Above all, they also reduce ongoing operating costs.

The product according to the invention is of undiminished quality received in a cost-optimized one-step process. Insbeson dere remains the previous property profile, for example  the dimensional stability at elevated temperature, the kink-proof in any case, and in case of doubt will be more likely improved. Furthermore, a high production reliability, a Consistently high and long-lasting product quality be targeted.

Furthermore, the structure according to the invention allows the shaped body because of the specific choice of material for the formation of he most layer, to use a crosslinking mechanism which much easier and with much lower costs too reali is than the electron beam initiated crosslinking, such as it is used in the prior art.

As polyolefins are in particular polyethylenes with medium or high density, low propylene ethylene / propylene copolymers component (10 mol% of propylene) or a polypropylene in Fra ge.

Particularly preferred as a polyolefin is a high molecular weight Ethylene-propylene copolymer with small propylene content (3-6 mol% Propylene).

For the grafting of the polyolefins vinyltri are preferably methoxysilane and / or vinyltriethoxysilane used. The ver used technology to graft the polyolefin starting material For example, in the publication by S. Ultsch and H.G. Fritz in PLASTICS 79 (1989), No. 10, page 1051 to 1056 described. The grafting of polypropylene with Organosilane groups is a bit more difficult as among the usual conditions in which polyethylene can be grafted, regular degradation of the polymer chain of polypropylene instead place. A way to graft polypropylene and the Vermei These problems may be related to the examples wrote.

As an oxygen barrier layer are different, acidic fabric impermeable materials, among which any Ma  terial, which on the one hand has a low acidity material permeation coefficients PO₂ (preferably

and with the organosilane or sila nol groups of the grafted polyolefins covalently linkable is.

The organosilane content in the grafted polyolefin is preferably 1.5 to 3 wt .-%, which is completely sufficient for a secure connection of the oxygen barrier layer with the first layer (main body).

During production, the grafted in the same extruder head Polyolefin with the material of the oxygen barrier layer un pressure and coextruded, so that already upon extrusion, intimate contact of the oxygen barrier layer materials with the grafted polyolefin material of he most layer.

In the selection of polyolefin materials, consideration is genom on the intended use of the resulting shaped body, wherein at For example, polyethylene as a polyolefin sufficient Tempe temperature resistance for temperature applications between 40 and 70 ° C, for example, when used as Pipes for underfloor heating, supplies.

Read low-propylene ethylene-propylene copolymers may graft as well as polyethylenes, but have ge compared to the pure polyethylene homopolymer a lower Young's modulus, d. H. a reduced bending stiffness, which facilitates the laying of hot water pipes made from them tert.

Polypropylenes are particularly suitable as starting materials for shaped bodies, for example, as pipes in solar collector ren or greenhouse heaters are used, which  with significantly higher temperatures, for example 70 to 80 ° C, work. This is where the higher softening point of the poly plays propylene plays a crucial role.

In selecting the organosilane groups for the grafting of the Polyolefins will be more likely due to the vinyltriethoxysilane grab when the pipes, for example, for the transport of Drinking water or generally used in the food industry should be. The reason for this is that in the hydrolysis action of the first layer of ethanol instead of methanol is set, which is physiologically harmless.

As initiators for the chain activation of the polyolefin molecules, organic peroxides (eg dicumyl peroxide, dimethyl hexan butyl peroxide) are preferably used. These decompose under the influence of temperature (160 T _M 240 ° C)
Peroxide radicals. The latter abstract from the polyethylene or polypropylene hydrogen atoms, causing radicals to form macromolecular chains, to which the organosilanes are grafted with dissolution of the vinyl group double bond.

In the selection of the agent for accelerating the crosslinking of Silane-grafted polyolefin molecules can be applied to a variety of Networking agents are used, but be preferably as a suitable catalyst system Organotin Ver bonds, such. DBTL. The for the silanolbil The required water molecules are diffusion-controlled provided.

At the interface body / oxygen barrier layer already brings the oxygen barrier layer material that before Preferably EVAL is and which in only slightly dried Zu is used, sufficient water with the to Hydrolysis of the trimethoxy or triethoxysilane groups and thus the subsequent, as condensation reaction occurring covalen te coupling between the polyolefin and the EVAL initiate. The covalent linkage of the silanol groups with the  OH groups of the EVAL are removed during the extrusion process splitting of water.

The polymer materials to be used according to the invention are each one that of the aforementioned layers can in addition to the already beschrie Components also contain other polymer components for improvement contain special properties. In addition, the According to the invention to be used polymer materials further Addi tive, in particular pigments, fillers, dyes, Metallio end activators, flame retardants, stabilizers, processing and optionally plasticizers. The Additives or additives to other polymer materials are according to the respective intended use for the molding selected.

In the moldings described so far was on the Fe no contribution was made by the individual layers fen. In one embodiment of the invention, the first Layer of organosilane-grafted polyethylene as carrier be formed layer, d. H. as a layer that in the we sentlichen the mechanical properties of the molding firm sets.

Through the crosslinking reaction of the organosilane-grafted mate Rials of the first layer is obtained one of the degree of crosslinking dependent increase in the bending stiffness of the molding. In Cases where such an increase is less desirable, Alternatively, a part of the carrier layer of an unge grafted polyolefin are formed, on which then he ste layer as another part of the carrier layer of Organosi lan grafted polyolefin is extruded, which first Layer then, as previously described, the Oxygen barrier layer follows.

Thus, there is the possibility that, for example, the innermost Layer of a hollow profile molding in the form of a pipe Polyethylene layer is to which an organosilane-grafted  Polyethylene layer follows as the first layer, which in turn covalently with the oxygen barrier layer extruded thereon connected is. This embodiment has the advantage that lower proportions of the polyolefin of an organosilane grafting must be subjected. The innermost layer becomes later generally electron beam crosslinked. The modulus of elasticity grows less strongly than in the case of silane crosslinking. On the choice of the proportions of ungrafted polyolefin at the Carrier layer can be in a simple way, the mechanical egg property profile of the molding vary.

In the oxygen barrier layers, in particular those from EVAL, which due to the material structure is a hygroscopic Behavior, it has been found that over time the oxygen diffusion increases due to the absorption of water, so that the oxygen barrier layer their effectiveness in the course the time, at least partially, loses something for some users dungsfälle is disadvantageous.

A long-term remedy can be here as a barrier Create a moisture barrier, which is the access undesirable Moisture content to the oxygen barrier layer ver prevents. A barrier layer as a moisture barrier can be in particular from an organosilane-grafted polypropylene which is preferably on the oxygen barrier layer is extruded. Again, this is preferred Coating again simultaneously with the other layers trudieren. A covalent linkage of the organosilane grafted polypropylene barrier with the EVAL material he follows as described above with respect to the first layer and the oxygen barrier layer. That also here is enough Water content of the oxygen barrier layer, which naturally 2 se in the EVAL material is off to the hydrolysis initiate the trimethoxy or triethoxy groups and thus a covalent bond between the EVAL material and the organ to start up nosilane-grafted polypropylene.  

The shaped bodies of the type described above are suitable in particular re as plastic pipes in heating systems, and that, depending on used material for the first layer or the carrier layer, for low temperature heating or high temperature heating tions. In addition, the inventively created Shaped body advantageous as pipes in drinking water networks bar.

The invention further relates to a process for the preparation a shaped body of the type described above and is distinguished characterized in that the melt streams of the materials for which he ste layer and the oxygen barrier layer or for the Carrier layer and the barrier layer in a helical distributor coextru combined under a pressure of about 10 to about 300 bar, preferably at most about 200 bar, in Close contact of the layer materials coextruded become. The pressure at the tool outlet corresponds to the environment print.

The merge temperatures for the polyethylene Ma terialien and polyethylene / propylene copolymers are present preferably about 180 to about 230 ° C, preferably 195 to 220 ° C, for the polypropylene materials is the Zusammenfüh temperature about 190 to about 240 ° C, preferably 200 to 230 ° C, and for the oxygen barrier materials of EVAL about 170 to 240 ° C, preferably about 190 to 230 ° C.

The contact time of the coextruded layers on the above Mass temperatures mentioned is a few seconds to about 1 Minute, preferably about 5 seconds to about 40 seconds. With the running of the coextrudate in a calibration device he follows a spontaneous Extrudatkkühlung, the Kondensationsreakti on comes to a halt.

The EVAL material is preferably presented in a weak dried state used so that its moisture content in the range of about 0.1 to 3 wt .-%, preferably between  0.2 and 2.5 wt .-%, based on the EVAL material. In order to is for silanol formation (→ hydrolysis reaction) in the Orga nosilane molecules sufficient reaction water ge available provides to within the in an industrial production to Available times to a sufficiently strong covalen ten linking the oxygen barrier layer with the darun terliegenden first layer or one optionally above to come extruded moisture barrier layer. At this as condensation reaction proceeding covalent coupling of EVAL and the silane-grafted polyolefin become water molecules free, which in turn are available for the hydrolysis.

For providing the grafted polyolefin materials There are two ways to go.

First, the grafted polyolefin materials can be separated grafted from the manufacturing process of the shaped bodies and be be prepared and already used as grafted material in the Extruder for the production of the shaped body to be fed.

Alternatively, the grafting of the polyolefins with organosilanes occur within the actual manufacturing process, d. H. the molding is herge in a real one-step process provides. In this case, the polyolefin components by addition of radical donors, in particular organic peroxides, and by the addition of organosilanes, especially vinyl trim thoxysilane or vinyltriethoxysilane, silane in the extruder grafted.

These and other advantages of the invention will become apparent below explained in more detail with reference to the examples and the drawings. It show in detail:

Fig. 1a is a sectional view of an inventive Shen shaped body in the form of a heating pipe;

Fig. 1b is a sectional view of an inventive Shen shaped body in the form of a heating pipe;

Fig. 2 shows another embodiment of a Hei tion tube in a sectional view;

Fig. 3 is a schematic representation of a one-stage production process for the molding according to the invention;

Figure 4 is a schematic representation of a one-stage production method for a further inventive shaped body.

Fig. 5 is a schematic representation of a one-stage manufacturing process for the molding according to the invention shown in FIG. 1; and

Fig. 6 is a schematic representation of a one-stage production method for the inventive molding body according to FIG. 2.

Fig. 1a shows a provided with the reference numeral 10 inventions to the invention moldings in the form of a hot water pipe, which consists of a first layer 12 of organosilane-grafted polyethylene Polye and an oxygen barrier layer 14 with which he most layer 12 covalently connected EVAL material.

Fig. 1b shows the tube of Fig. 1a with an outer Feuch activity barrier layer 16 made of organosilane-grafted Polypropy len, which protects the underlying oxygen barrier layer 14 against moisture and so their oxygen barrier property over the life of the tube 15 is constant.

Exemplary layer thicknesses of the individual layers are like follows:

First shift 12 : 1.5-3.0 mm, preferably 1.8-2.4 mm Oxygen Barrier Layer 14 : 50-140 μm, preferably 70-100 μm Moisture barrier layer 16 : 50-150 μm, preferably 70-120 μm

The requirements placed on the heating water pipe 10 and 15, respectively, with respect to the mechanical strength and the heat resistance, are provided by the so-called base pipe or layer 12 , which forms the majority of the pipe cross-section. The layer structure, as shown in FIGS. 1a and 1b, does not correspond to the actual values in the ratios of the thicknesses of the individual layers, and the selected representation serves merely to illustrate the layer structure.

The necessary property level is of that as the base material predominantly used high-density polyethylene at correct reached reached degree of crosslinking in full measure. Insbeson It is important to ensure that, on the one hand, the degree of crosslinking high enough (gel content <65%), for example, in the Creep pressure test at elevated temperature (according to DIN 16 894 et seq.), But others on the other hand is not too high (gel content depending on the application and polyolefin type preferably 75%), since its increasing always associated with an increase in the modulus of elasticity.

The latter is undesirable insofar as then the critical Bie straight line, where the pipe bend and thus the for the Flow through available cross-section to veren starts, is increased. This means that the pipes problem los can only be laid with larger bending radii.  

The latter has the consequence that laying aids, as example be used in the soil heating area adapted or be re-dimensioned.

Furthermore, when increasing the bending radius and the maxi times to reach surface specific installation density and thus the area-specific heating density drop, which is industri view is unacceptable. When using the invent Silane-crosslinkable or crosslinked high-density poly according to the invention Ethylene base tube is a sufficient dimensional stability reachable below a temperature of about 70 ° C. The to aspiring gel content of the base pipe should be about 72 to about 74% be.

To protect the valves used in the heating circuit before Kor rosion, which is particularly important for heat transfer temperatures of up to 70 ° C, the enrichment of the heating medium with diffused oxygen is to be avoided. This is achieved by the oxygen barrier layer 14 , which is made of ethylene-vinyl alcohol (EVAL). In particular, EVAL types with VAL contents between 25 and 68 mol% are used. In order to maintain the lasting barrier effect against oxygen diffusion in the oxygen barrier layer 14 , the layer 14 must again be protected from moisture, since otherwise the barrier properties decrease very sharply with increasing moisture content. This is particularly problematic due to the hygroscopic property of the EVAL material. For this purpose, the further moisture barrier barrier layer 16 is made of organosilane-crosslinked polypropylene.

This multilayer pipe can be particularly advantageous produce with the manufacturing process of the invention, since due to the specific material choices for each Layers dispensed with the previously required primer layers can be. Besides, it can affect others, from the electrons Beam crosslinking various networking methods zurückge  with the crosslinking of the polyolefins Organosilanes via Si-O-Si bridges.

Fig. 2 shows a modified hot water pipe 17 , in which a part of the so-called base tube of ungrafted high-density poly ethylene is prepared as a partial support layer 18 , on wel che a thinner, first layer 12 is applied from organosilane-grafted high-density polyethylene , In order to achieve the same effect with respect to the effect of diffusing oxygen, the oxygen barrier layer 14 and the moisture barrier layer 16 are applied in the same way as shown in FIGS. 1a and b and described in connection therewith. Again, preferably the single-stage production process is used, which will be described in detail below.

The previously mentioned several times grafting of polypropylene with Or ganosilane molecules succeed without appreciable degradation of the poly mer chain while maintaining the following parameters:

Based on the polypropylene mass flow is in a reacti The preparation process 0.5 to 3.5 wt .-%, based on the Po polypropylene mass, vinyltremethoxysilane (VTMOS) preferably used in the range of 1.0 to 2.5 wt .-%. As initiator is a peroxide in the mass ratio VTMOS: peroxide of 5: 1 to 60: 1, preferably 10: 1 to 50: 1 used. Furthermore is in the reaction mixture monomeric styrene in Molar ratio VTMOS: Styrene added from 0.1 to 1.0. After all is still a catalyst, such. B. dibutyltin dilaurate in egg ner dosage of 0.01 to 0.05 wt .-%, based on the poly propylene mass flow, metered.

With this type of grafting of polypropylene, the Po functionalize the polypropylene, the nonpolar polypropylene by grafting reactive monomeric substances which contain polar groups, is modified so that its poten substantial field of application is considerably expanded, as in  lying case for the use of tube layers, which directly and covalently coupled with EVAL material. Derar graft polymers can be due to their changed physicochemical property profile also as blend components or as so-called compatibilizers in the production of Po lymer alloys and as matrix materials with the ability a more intensive filling or reinforcing material integration put. In many cases, the grafted monomer components lead across their polar groups to increased adhesion forces between Graft polymer and metallic surfaces or decor layers.

In another context than the present, a polypro pylene grafting with maleic anhydride, hereinafter MAH for short called, be beneficial. The MAH represents for the radical initiated functionalization of polypropylene an extraordinary Lich efficient coupling molecule. In conjunction with the Grafting reaction, the following changes are observed:

With increasing MAH and Peroxidzugabemengen the resul MFI value (melt flow index) disproportionately high the effective MAH graft rate (g-MAH) with about 50 mole% of the used MAH remains approximately constant (To determine the MAH graft rate cf. Macromol. Symp. 83, 93-113 (1994)).

The radical attack initiated chain scission (so-called β-Scission) causes a pronounced decrease in Nullviskosi over two orders of magnitude, which directly reduces the molar mass is assignable. With this goes with such degradation processes accompanied by a narrowing of the molecular weight distribution. GPC measurements confirm this. It is observed that in particular the number of long-chain molecules is reduced, while in niedermo the molecular range hardly changes. The mechanical Basic properties of such graft polymers deteriorate as a result of continued fractions.  

A repression of these adverse effects can be through achieve the introduction of charge-transfer complexes (CTCs). Maleic anhydride as a pronounced electron acceptor can with a corresponding electron donor such charge-trans form fer complexes. By an increased electron density near the MAH double bond becomes their radical reactivity increased while the presence of the electron donor at the same time reduces the polypropylene macroradical formation. The addition of monomeric styrene as a formulation component and Elek tronendonator allows significantly higher MAH graft rates below simultaneous reduction of polypropylene chain degradation. A however, complete polypropylene degradation is not un terbindbar. Increasing the peroxide content increases the ef natively coupled MAH amount, but at the same time also the MFI value on.

The presence of the styrene increases the initiator efficiency and simultaneously promotes the grafting reaction of the MAH. maleic but acid anhydride and styrene can now but under radical Einwir kung also alternating copolymer sequences with MAH end groups which side-chain on the polypropylene grafted onto the main chain. In such side branches fi xed MAH molecules may be due to steric hindrance or Inhibition and / or electron interactions with the styrene molecules do not function equivalently as coupling members Accordingly, the determined MAH graft rates do not allow in the give a clear statement about the potential of the generated Graft polymers.

In contrast to the MAH grafting reaction of the polypropylene can be the first described grafting with organosilanes in polypropylene homopolymers and copolymers with the pre Perform the recipe without a significant mol mass reduction occurs. This also leaves the property obtained profile of the polypropylene as far as possible.  

For the hydrolytic degradation of the silicon functional groups to silanols water molecules are needed, which diffusion can be provided in a controlled manner. Since polypropylene ge has outstanding barrier properties over water, Occurs superficially an interlinking of surface layers, which further reduce water diffusion rates. In the Formulated introduced water molecule donors help this Reduce problem. This type of polypropylene functionali tion can be done in conjunction with the as a two-step process polypropylene foam film extrusion Gain meaning. The graft polymerization described above of polypropylene homo- and copolymers has compared to the underlying invention, dealing with multilayer moldings busy, independent quality, even if organosilane grafted polypropylene in the present invention multiple times as a preferred organosilane-grafted polymer material for Use comes.

In the following, the production method of the various multilayer molded bodies will be explained in more detail with reference to the block diagrams of FIGS. 3 to 6.

Fig. 3 shows schematically an arrangement of the individual components of a production plant of a shaped body according to the invention ge according to FIG. 1a, in which a twin-screw kneader 20 is used with a large process part length as a central unit. High-density polyethylene is introduced into the two-screw kneader and plasticized by means of a gravimetric solids metering device 22 . Subsequently, by means of a gravimetric liquid metering device 24, the organosilane required for the organosilane grafting, a grafting reaction initiated by the peroxide and a catalyst for this reaction (preferably DBTL) are metered into the twin-screw kneader.

Shortly before the screw ends, a vacuum pump for melt degassing is coupled via a degassing shaft 26 . The twin-screw kneader 20 feeds the melt on the outgoing side into a coextrusion die 28 , which has a feed opening 30 for a single-screw extruder or for the barrier layer material. The single-screw extruder with preferably a grooved A zugszone 32 receives via a hopper 34, the EVAL material supplied, which is melted within the extruder and the coextrusion tool 28 via the feed opening 30 to.

The coextrusion tool 28 , which may be equipped with Wendelverteilersyste men, forms an integral tube of a he most layer, which consists of organosilane-grafted high density poly ethylene and a directly applied thereto oxygen barrier layer of EVAL material. The tube produced is brought within a calibration device 36 with simultaneous cooling to the nominal dimensions.

The first layer 12 , which forms the base tube, is thus made of silane-crosslinkable polyethylene (high-density type). The main advantage of the present technology is the ability to perform grafting and crosslinking in two separate steps. In the first step, the grafting molecule is applied to the polymer to be crosslinked. After the coextrusion process, the crosslinking is completed in a second, not necessarily directly subsequent step. The properties of the already grafted but not yet crosslinked polyolefin occupy a key position in the actual coating process, which will be described in more detail later.

In the primary treatment step, 20 organosilane molecules are grafted onto the polyethylene chains in the twin-screw kneader in order to be able to carry out downstream crosslinking via precisely these molecular groups. For this purpose, a grafting solution of vinyltrimethoxysilane (VTMOS), a peroxide and a catalyst in the plasticized PE melt at the inlet 24 is injected. In this case, preference is given to using the DHBP peroxide:
2,5-dimethylhexane-2,5-di-t-butyl peroxide (DHBP)

The actual grafting step starts with the thermally in itiierten Peroxid decay. The resulting radicals over carry the radical function on the polymer chains.

Thermally initiated decay

chain activation

In the concrete case of the DHBP sees the decay reaction follow so out:

The limited process part length of the treatment unit, ie the twin-screw joint 20 , requires a high reactivity of the components used. The vinyltrimethoxysilane shown below fulfills these requirements (Vinyltriethoxysilane can likewise be used in a similar manner).

The grafting step is as follows:

Subsequent to the grafting step, the grafted Pla stifikat a equipped with spiral distribution systems coextrusion tool 28 is supplied, in which shaping and Beschich tion with the oxygen barrier layer of EVAL done in one step.

Separated in time and thus only in the fixed state takes place in tion of the crosslinking and the crosslinking reaction (→ Kon This is usually the be already pulled on drums pipe in a warm water cycle switched and flushed constantly. Here is his networking stimulated by the hydrolyzation of the methoxy or ethoxy groups:

By the final condensation of adjacent silanol groups form main valent Si-O-Si bridges, creating a three-dimensional network structure arises. The released In turn, water does not catalyze the hydrolysis reaction reacted trimethoxy or triethoxy groups.

As mentioned above, the material properties profile becomes of crosslinked polyethylene mainly through the Vernet degree of concentration or the gel content of the first layer. the This can be adjusted very precisely by qualified formulation be presented.

The essential difference of the method according to the invention or the structure according to the invention of the molded body relative to the The prior art is in the Be described below coating concept. The usual coating with funk tional layers was made with the help of so-called Primer or primer systems performed which the Task, the intimate connection of the individual layers of intrinsically incompatible polymer materials together guarantee. An incompatibility between two layers is often gege by their different molecular structure ben. Due to the incompatibility of the nonpolar polyethylene with the polar EVAL, permanent coextrudates were not without Adhesive layers can be produced.

The inventive concept now uses the by the Pfrop implementation of the polyethylene macromolecules grafted with polar and reactive organosilane groups Organosilane groups. Such a modified high-density poly ethylene offers an opportunity for an EVAL macromolecule Construction of a major valent bond to the polyethylene macromolecule.

This covalent coupling of the two layers, d. H. the first Layer and the oxygen barrier layer of EVAL, takes place in a condensation reaction. The reaction mechanism provides is as follows:

Although the resulting Si-O-C crosslinks are due to the asymmetry does not affect the stability of the later leading polyethylene crosslinking of the base material Si-O-Si bonds on, but they are sufficient to the intimate Connecting the first layer to the oxygen barrier layer to ensure.

Main influencing parameters are in the formation of this covalent compound the moisture content of the EVAL, which at the  Silane grafting catalyst used, the mass feed temperatures of the melts in the coextrusion tool as well the contact time from the confluence of the single layers to the Entry of the multi-layer extrudate into the calibrator and the da associated reaction abort by the rapid cooling of the thin-walled functional layers.

Starting from the basic structure of a manufacturing plant according to FIG. 3, which simultaneously provides the basic structure for the inventive Shen shaped body, namely the first layer of a ganosilane grafted-organic polyolefin with an oxygen barrier layer with covalent bonding of the layers together, can now to achieve further advantages be varied.

Fig. 4 shows, in this connection, a structure in which a single-screw extruder 40 is fed with high-density polyethylene via a hopper 42nd The high-density polyethylene melt is the outlet side of a coextrusion tool 44 leads supplied, in which then from the high-density polyethylene, a partial carrier layer is formed for the tube to be produced.

In a twin-screw kneader 46 , the device via a Feststoffdosier 48 high-density polyethylene is supplied and subsequently receives via a liquid metering device 50 the Si lan grafting required organosilane, peroxide and catalyst added, an organosilane-grafted polyethylene is produced, which a degassing port 52 of the two screw kneader degassed and is supplied to the three-layer coextrusion die 44 in the molten state.

The organosilane-grafted high-density polyethylene formed in the twin-screw kneader 46 serves to form the first layer as a further partial carrier layer of the ungrafted high-density polyethylene.

As an oxygen barrier layer is in a further single screw extruder 54 , which is supplied via a hopper 56 EVAL material, an EVAL melt produced and the three-layer coextrusion die 44 as the outermost layer, ie as an oxygen barrier layer supplied.

The extrusion of the pipe and the further processing is not different in principle from the procedure shown in FIG. 3. In the present case, however, a tube is obtained in which the typi cal increase the modulus of elasticity is prevented due to the silane crosslinking in the carrier layer of the pipe , The three-layer diverter head as coextrusion die 44 forms a layer of high-density polyethylene which remains unchanged in its properties on which a layer of grafted polyethylene is extruded as a first layer. This first layer is in turn surrounded by an EVAL layer as oxygen barrier layer. Subsequently, this tube can be subjected to an electron beam treatment, whereby the ungrafted part of the carrier layer is crosslinked. The PE layers are inherently compatible. The coupling of the Po lyethylenmittelschicht (first layer) and the Sauerstoffbar riereschicht takes place, as described above, already in the factory tool.

The tube thus produced aufwei a lower modulus sen than the tube described above.

The single-screw extruder 54 again preferably has a grooved te feed zone. The same applies to the single-screw extruder 40 .

From the demand for long-term constant oxygen tightness results in a further modification of the Herstellungsverfah rens or the molding according to the invention, which will be described in connexion with Fig. 5 in the following.

This modification constitutes a modification on the basis of the arrangement described in FIG. 3, for which reason the same reference symbols are used as in FIG. 3, as far as the same system components are concerned. On the basic structure of the two screw kneaders 20 and the single screw extruder 32 for the EVAL material is omitted at this point to avoid repetition. The difference with respect to the system of FIG. 3 is that instead of the two-layer coextrusion tool 28, a three-layer coextrusion tool 58 is used, to which the silane-grafted polyethylene melt from the extruder 20 to form a first layer and the EVAL material in a molten state from the Extruder 32 are fed to form the oxygen barrier layer.

Via a third inlet opening of the coextrusion die 58 he follows the addition of molten, silane grafted polypropylene. This is done plant technology in ähnli cher manner as the production of organosilane grafted Po lyethylen, namely by means of a two-screw kneader 60 , in which via a Feststoffdosiervorrichtung 62 polypropylene is fed and subsequently via a liquid metering device 64 to be grafted organosilane, a peroxide and a Kataly sator and the moderator styrene are injected. The silane-grafted PP plasticizer is still degassed ( 66 ) and then fed to the three-layer coextrusion die 58 to form an outer layer having the function of a moisture barrier layer.

Finally, it should be noted on the process variant of FIG. 6, which is a modification of the system of FIG. 4, so that the reference numbers in turn, as far as it is identical parts, are taken over and to this extent on a separate description of the parts is omitted.

Instead of the three-layer coextrusion tool 44 , a four-layer coextrusion tool (spiral distributor type) 68 is used in the system of FIG. 6, the melt streams from the extruder 40 to form the ungrafted Polyethylenträ gerschicht, the melt stream of the extruder 46 to form the first organosilane grafted polyethylene layer, from which extruder 54 EVAL material for forming the oxygen barrier layer and organosilane-grafted polypropylene material for an outermost liquid barrier layer are fed, for the production of a two-shaft kneader 70 is used, wherein, as in connection with FIG. 5, polypropylene is supplied via a solids metering device 72 . In a Flüssigdosiervorrichtung 74 , the organosilane, a peroxide, a catalyst and the moderator styrene is fed and the melt ent entgas finally via a vacuum port 76 before the melt is fed to the four-layer coextrusion die 68 .

In this process variant, a tube is obtained whose Main characteristics correspond to the polyethylene, in which the Oxygen barrier layer over a first layer of Organosi lan-grafted polyethylene is applied and finally the oxygen barrier layer made of EVAL material through a Organosilane-grafted polypropylene layer with the latter covalently connected again before taking too much Moisture is protected in the long-term area.

About the variation of the thicknesses of the carrier layer and the first layer can be in a simple way the properties set the heating water pipe to be generated.

Claims (20)

1. molded body having an oxygen barrier layer, in particular hollow profile molded article, characterized by a formed from an organosilane-grafted polyolefin first layer and a coextruded under pressure with the first layer and directly on this oxygen barrier layer of a grafted over the organosilane molecules first layer covalently linkable material. 2. Shaped body according to claim 1, characterized in that the Polyolefin a medium or high density polyethylene, a Ethylene / propylene copolymer with small propylene content or a polypropylene. 3. Shaped body according to claim 2, characterized in that the Ethylene / propylene copolymers a high molecular weight copolymer is. 4. Shaped body according to one of claims 1 to 3, characterized ge indicates that the Organo used for the grafting silane molecules vinyltrimethoxysilane and / or vinyl triethoxysilane. 5. Shaped body according to one of claims 1 to 4, characterized ge indicates that the oxygen barrier layer of ethylene len / vinyl alcohol is formed. 6. Shaped body according to one of claims 1 to 5, characterized ge indicates that the organosilane addition amount to the grafting polyolefin 1.5 to 3 wt .-%, based on the grafting polyolefin.   7. Shaped body according to one of claims 1 to 6, characterized ge indicates that the shaped body is a carrier layer of egg a non-grafted polyolefin which is based on the Oxygen barrier layer opposite surface of the first layer and coextruded with it. 8. Shaped body according to claim 7, characterized in that the Carrier layer of an ungrafted polyethylene Herge is is. 9. Shaped body according to one of claims 1 to 8, characterized ge indicates that on the first layer gegenüberlie ing surface of the oxygen barrier layer a barrier layer as a moisture barrier from an organosilane grafted polypropylene is extruded. 10. Shaped body according to one of the preceding claims, characterized characterized in that the shaped body as a plastic pipe, ins special for use in underfloor heating, trained is. 11. Shaped body according to one of claims 1 to 9, characterized ge indicates that the molded body out as a drinking water pipe is forming. 12. Shaped body according to one of claims 1 to 9, characterized ge indicates that the shaped body by a Extrusi Onsprozeß blow-molded container or a film element is. 13. A process for producing a shaped article according to one of Claims 1 to 12, characterized in that the melt streams of materials for the first layer and the sow erstoffbarriere layer and optionally for the Trä gerschicht and the barrier layer in an extruder head to merged and under pressure up to about 300 bar in en according to contact of the individual coextru layers  be diert. 14. The method according to claim 13, characterized in that the Melt flows of the materials for the respective layers after passing through spiral distribution systems within of the coextrusion tool. 15. The method according to any one of claims 13 or 14, characterized ge indicates that the temperature at the merge materials for polyethylene materials and polyethy len / propylene copolymer materials about 180 to about 230 ° C, for polypropylene materials about 190 to about 240 ° C and for Ethylene / vinyl alcohol materials about 190 to about 240 ° C is. 16. The method according to any one of claims 13 to 15, characterized ge indicates that the time interval between the lead the individual layers and the entry of the extrudate into a calibration device for a few seconds to about 1 min nute, preferably 5 seconds to 40 seconds. 17. The method according to any one of claims 13 to 16, characterized ge indicates that the material for the oxygen barrier layer used with a moisture content of about 5 wt .-% becomes. 18. The method according to claim 17, characterized in that as Oxygen barrier layer material ethylene / vinyl alcohol material used in only slightly pre-dried condition becomes. 19. The method according to any one of claims 13 to 18, characterized ge indicates that the polyolefin materials during a integrated preparation step with organosilane moles grafted.   20. The method according to any one of claims 13 to 18, characterized ge indicates that the polyolefin materials are prior to use in the present process in a separate Aufberei grafted with organosilane molecules.