DE4316863A1 - Coextruded composite foam elements and process for their production - Google Patents

Abstract

A process for producing composite foam elements from different foam materials is provided, in which at least two polymer melts with different physical and/or chemical properties are coextruded after mechanical blowing in the extruders. This preferably involves the different foamable polymer melt streams in the extrusion die already being brought into contact a little ahead of the die outlet, without mixing them, to be precise in such a way that, after emerging from the die and after cooling, the different coextruded foam layers are strictly separate from each other, but nevertheless are fused homogeneously and firmly to one another over the entire contact surfaces.

Description

The present invention relates to coextruded foam composite body and process for its preparation.

It is known, non-foaming thermoplastics to plates, foils, bars, profiles, tubes, hoses and to extrude, such products also from two or more different thermoplastic art can be produced by coextrusion. In the Coextrusion is the tool of several extruders Melts charged, which deformed in separate channels and be brought together just before leaving the nozzle. Especially for plates and foils, but also for profiles and Tubes are often made up of multiple layers produced. It will be cheaper own achievements, cost savings or decorative effects.

It is also known from expandable thermoplastics in the Di Direct gasification processes Panels, foils, profiles and tubes to extrude. Coextrusions of different foamable Thermoplastics, however, have not been described.

However, from German Patent 28 53 626 a Method has become known in which an electrically isolated Wire is made by applying to the wire in the Co Extrusion a foamed inner layer and a non-foamed coat as outer layer applies.

Object of the present invention is therefore, foam to provide composite bodies consisting of min at least two foamable polymer melts with difference physical and / or chemical properties  be prepared, with the individual foam Schich preferably sharply separated in the final product, nevertheless homogeneous over the entire contact surfaces and should be firmly connected.

This problem was solved according to the present invention in that the ver coming from different extruders various made foamable by direct gasification Polymer melt streams coextruded.

The subject of the present invention is thus a method ren for the production of foam composite bodies from ver different foams, which is characterized that at least two polymer melts differed with physical and / or chemical properties after direct gassing in the extruders, coextruded.

Preferably, the process according to the invention is carried out the foamable polymer melt streams to be combined are not just before leaving the nozzle, but already in one Distance A from the nozzle exit together. It leads the various polymer melt streams together so that they only with their upper without substantial mixing surfaces come into contact. The distance A, the practical which forms "confluence" becomes empirical depending on the used foamable polymer streams preferably so set that the different foam layers after exiting the nozzle and after cooling sharply vonein separated, but still over the entire touch surfaces are homogeneously and firmly connected to each other. The ho Mogens and solid composite provides a kind of enamel welding connection.  

In certain cases, the distance A can be reduced to zero be diced, d. H. the different foamable polymer Melting streams are only shortly before leaving the Nozzle merged, for example, when the ver different polymer melt streams are virtually identical and differ only by the color.

On the other hand, the distance A becomes larger or the "Zu merge flow distance "the longer the more the foamable polymer melt streams in their physical Distinguish properties.

In addition, it has been found that the distance A is preferably set in relation to the outer circumference B of the melt stream 1 . Preferably, the ratio is B: A = 4 to 6. The outer circumference B is equal to dx (B = d · II), where d is the outer diameter of the melt stream 1 before the confluence distance (d = distance A).

If the distance A is too small, so have the different Foams tend to expand immediately after foaming disconnect, thereby losing the tight bond. Is the Distance A too large, so mix both melts easy and you get the finished product no clear op table separation between the different foam layers.

Furthermore, it has been found according to the present invention that particularly good foam composites are produced can when the foamable poly to be united melt in their melting temperatures during the assembly not too different from each other. virtue example, the difference between the temperatures of the individual polymer melt streams not more than 10 ° C.  

In the case of the foamable poly to be combined according to the invention Merschmelzen is preferably the polymer of the one Polymer melt stream of a low density polyethylene (LDPE) and the other polymer of the other polymer melt stream of ethyl vinyl acetate, d. H. from the combination LDPE / EVA. Further inventively preferably used polymer combinations are: LDPE / LLDPE EVA / EAA LDPE / ionomers HDPE / PP PP / PS HDPE / PS SAN / PS.

The abbreviations have the following meaning:

LDPE = low density polyethylene
LLDPE = Linear Low Density Polyethylene
EVA = ethylene vinyl acetate
EAA = ethylene ethyl acrylate
HDPE = high density polyethylene
PP = polypropylene
PS = polystyrene
SAN = styrene acrylonitrile.

As blowing agent for direct gasification is set according to the before i invention preferably i-butane, n-butane, propane, Pentane, i-pentane, CO₂, N₂, F142b (difluoro-mono-chloro-ethane), F22 (difluoro-mono-chloro-methane), F134 (tetrafluoro-ethane) or Mixtures thereof.

In various polymer combinations, it has to be as particularly advantageous when it comes to direct fumigation the individual foamable polymer melt to be combined streams using the same blowing agents.

It should be noted that it is in accordance with the present Invention is not only possible, different foamable Polymer melt streams to tightly interconnected foam  fabric composite bodies by coextrusion, but that the method according to the invention can also be designed in such a way that and this represents a particularly important aspect of the present the invention is that one the different foamable Polymer melt streams in such compositions and with directly fumigated such amounts of propellant that each of individual interconnected in the foam composite body Foam layers Room weights below 100 kg / m³, before preferably below 30 kg / m³.

In carrying out the method according to the invention it is important that the extrusion tool, especially the extru is cooled uniformly and homogeneously. in particular special occur in the production of hollow Schaumstoffver bundkörper, such as "2- or 3-shell" foam composite pipes have additional difficulties, as in extrusion tool in addition a bolt is needed, which until the Nozzle outlet is sufficient and tempered from the inside with air must become. It is important to ensure that the air is not too cold, otherwise the extrusion nozzle freezes. In the Practice was good experience with air temperatures he that is about 50 ° C below the glass transition temperatures of used polymer melt streams are.

For foam composites whose density is less than 80 kg / m³ where a salable foam quality is particularly rig is feasible, the extrusion head size on the machines be adapted output.

Too small extrusion channels cause excessive friction, which in turn causes temperature control problems and Partial melt fracture also occurs on the foam surface.  

The following table shows the ratio in which preferably the length L and the diameter D of the extruder tool (see FIG. 1) are in relation to the total polymer foam output.

Ratio length (L) to diameter (d) Total output (kg / h) 2 50 2 100 1.8 200 1.6 300 1.4 500

With the coextrusion process according to the invention it is possible Lich, foam composite body with completely new Eigen to produce combinations of combinations.

The foam composite bodies show firmly together bonded foam layers of different colors, Bulk densities and temperature resistance. Furthermore you can by different polymers and fillers the electro static as well as the mechanical properties of the foam stoffverbundkörper be influenced.

The invention will be explained with reference to FIGS . 1 to 8 wei terhin. The details and details shown in the figures belong to the disclosure of the invention and represent preferred embodiments, so that the invention is not limited thereto.

. The USAGE in FIGS and in subsequent versions Deten reference numerals have the following meanings:

1 polymer melt stream from extruder 1
2 polymer melt stream from extruder 2
3 polymer melt stream from extruder 3
4 thorn
5 nozzle
6 centering housing
7 centering screw
8 pressure probe
9 temperature probe
10 heating tape
11 cooling air
12 mouthpiece
13 mandrel holder
A distance = confluence distance
L length of the extruder tool
D diameter of the extruder tool
d outer diameter of the melt stream 1 before the confluence section A.

Fig. 1 shows a cross section through an extruder die, which is connected to 2 extruders and in the 2 polymer melt streams, which are brought together at a distance A from the nozzle exit. The length of the extruder tool is designated with L and the diameter with D net. "d" shows the outer diameter of the polymer melt stream 1 within the extrusion die.

Fig. 2 shows a cross section through the extruder die, which is connected to 3 extruder and are extruded with the 3 polymer melt flows to a tube free in the air. At this point it is noted that one of the preferred features according to the present invention is also to be seen in the fact that the extrudates foam freely in the air without any calibration or cooling devices are used, except for the air supply to the hollow body through the outlet nozzle.

Fig. 3 shows a cross section through a coextruded foam composite tube. The inner layer is made of a more temperature-resistant polymer than the outer foam material layer. In general, it can be said that the inner layer is particularly oriented towards optimum insulation and optimum thermal protection, whereas the outer layer preferably exhibits better mechanical protection in terms of tear strength, abrasion resistance and the like.

Fig. 4 shows in cross section a packaging profile with soft inner core to improve the shock absorption and a harder outer core to improve the static load availability. These differences can be distinguished by room weight differences z. B. 25 kg / m³ inside and 60 kg / m³ outside or by various polymers.

Fig. 5 shows a packaging profile with electrostatic properties egg. The core consists of a LDPE foam and the outer layer of a foam with electrically conductive properties.

Fig. 6 shows a protective profile, wherein the inner layer of a hard tear-resistant polymer foam and the outer layer of a foam with good shock absorption properties consists. The inner layer is so aligned that edges and corners of the goods to be packaged can hardly injure the inner layer.

Fig. 7 shows in cross section a round solid profile in which the core consists of a "recycled" polymer and the outer layer of a pure polymer.

Fig. 8 shows in cross-section a Schaumstoffisolierrohr with 3 different foam layers, which are homogeneously and firmly connected to each other to the composite foam body.

In carrying out the method according to the invention must the technical extrusion parameters throughout Working hours are kept constant, d. H. that you have a homo gene temperature distribution over the entire channel cross section achieved by optimal temperature control. The tempera The temperature control may not deviate by more than +/- 0.5 ° C. The gas dosage must always be kept constant, so that no space weight fluctuations can arise. These would become on the layer thickness and thus on the total cross section of Affect profiles. In addition, the throughput of the individual Polymer melt flows must be exactly matched, so that the Layer thicknesses remain constant.

An example is given below, according to which one of 2 foam Fabric layers existing pipe made according to the invention becomes.

example

By means of the extruders A and B, the following are indicated Polymer melt streams passed into the coextrusion tool:

Extruder A Extruder B 100 kg / h (Outside) 70 kg / h (Inside) EVA (14% VAcetat) 90 T LDPE 90 T   MFI = 5 MFI = 2 Talc 3 T Talc 3 T Propellant gas (n-butane) 10 T Propellant gas (n-butane) 10 T Cell Stabilizer 1 T Cell Stabilizer 1 T Carbon black 1 T

The result is a tube of high flexibility (EVA) and high Tempe Resistance to corrosion (LDPE). The T ° resistance of EVA alone would be only at 80 ° C instead of 100 ° C at LDPE. LDPE alone would result in a more inflexible pipe.

Claims (10)

1. Process for producing foam composite bodies various foams, characterized in that at least 2 polymer melts with different physi kalischen and / or chemical properties after Direktbe Gasification coextruded in the extruders. 2. The method according to claim 1, characterized in that one the various foamable polymer melt streams in the Extruder tool already at a distance A before the nozzle exit without mixing in contact with each other leads. 3. The method according to claim 1 and 2, characterized in that one the distance A, d. H. the confluence route, empirical depending on the used foamable polymer melt streams so determined that the various foam layers after Exit from the nozzle and after cooling sharply from each other separated, but still over the entire contact surfaces are homogeneously and firmly melt-welded together. 4. The method according to claim 1 to 3, characterized in that the distance A is greater or the confluence distance all the more is longer, the more the foamable polymer melt differ in their physical properties. 5. The method according to claim 1 to 4, characterized in that the ratio B: A = 4 to 6, where B is for the eyes circumference of the melt stream 1, which is calculated from d. II net. 6. The method according to claim 1 to 5, characterized in that the foamable polymer melt streams to be combined in their melting temperatures by not more than 10 ° C vonein different.   7. The method according to claim 1 to 6, characterized in that one uses as polymer melt streams to be combined such the combinations of LDPE / LLDPE; EVA / EAA; LDPE / ionomers; HDPE / PP; PP / PS; HDPE / PS; SAN / PS are. 8. The method according to claim 1 to 7, characterized in that for direct gasification as propellant i-butane, n-butane, Propane, pentane, i-pentane, CO₂, N₂, F142b, F22, F134 or mixtures thereof. 9. The method according to claim 1 to 8, characterized in that to the direct fumigation of the individual foaming to be united Baren polymer melt streams uses the same blowing agent. 10. The method according to claim 1 to 9, characterized in that the different foamable polymer melt streams in such composition and with such amounts of propellant directly fumigated that each of the individual in the foam composite body interconnected foam layers Volume weights below 100 kg / m³, preferably below 30 kg / m³.