DE4421016A1 - Thick slabs of carbon di:oxide-blown plastic foam - Google Patents

Abstract

The prodn. of thick, CO2-foamed plastic slabs, pref. from polystyrene (PS) and/or polyethylene (PE), comprises welding two sheets (1, 2) together at the contact surfaces to double the thickness. Pref. the process is carried out with a heating bar (13), pref. an oil-heated tube with a thickness of 1-10 mm and/or a width of 20-100 mm, rollers (5, 6) for applying the welding pressure, feed rollers (7, 8, 9, 10) and an upstream cooler (14) in front of the heater, pref. a water-cooled wedge-shaped cooler with a thickness 1-20 mm greater than that of the heater.

Description

The invention relates to a method for producing plastic foam plates by extrusion and using carbon dioxide in particular made of polystyrene (PS) and / or polyethylene (PE). The production of plastic foam sheets by extrusion has long been known. Here the plastic in granulate form together with blowing agents and Aggregates placed in an extruder. There is an intense one Mixing and heating instead, so that the plastic is plasticized and that evenly distributed blowing agents in the plastic plastic mass builds up considerable pressure. Form after leaving the extruder a variety of more or less small bubbles in the plastic. It creates the foam. Originally, gaseous agents were used as blowing agents Hydrocarbons used. However, it was soon recognized that the foaming process very easily due to fluorocarbons (CFC) can be controlled.

Unfortunately, the fluorocarbons cause a very strong environmental impact burden. They damage the ozone layer.

In order to reduce the environmental impact, partial halogens were then used Fluorocarbons used. These propellants are also called classified as environmentally harmful.

For some time now, the professional world has been trying to find a suitable new one Propellant. The CO2 is particularly high view awarded. CO2 has long been known as a blowing agent and also used in practice. It is less common exclusive use of CO2 as a blowing agent.

The exclusive use of CO2 prepares considerable Difficulties. This is mainly due to the sudden driving effect of the CO2 attributed. The result is the exclusive use of CO2 so far only successful to a limited extent. Not all common ones Plastics can be foamed with CO2. The achievable so far Thicknesses are 80 mm. In contrast, thicknesses are used for insulation materials up to 150 mm and more required.  

The invention is based, with the required thicknesses only represent CO2 foamed plastics. After Invention is made by duplicating plastic foam sheets under Welding reached on the contact surfaces.

Multi-layer plastic foam panels are in themselves z. B. from the DE-OS 43 34 453 known. However, there is not the achievement otherwise not attainable thicknesses but the joining of materials the nature of the measure. Accordingly it is provided that foam blocks are cut, treated and be glued with other material.

In a further embodiment of the invention, the welding takes place under Use of a heating sword. Plastic foam sheets from one certain thickness can not be easily welded. The problem is the necessary melting of the contact surfaces. So far Welding processes taking place on plastic foam is only one in practice Melting with hot air is common. As long as they are together welding plastic foam parts can have a small area the melting of the welding surfaces can be controlled relatively well. A simultaneous melting of large areas has not yet been achieved been. Although it is known large-area plastic foam sheets to be welded to one another or to other plastic sheets. Here but only a small part of the surface is melted with hot air, by blowing hot air into a nip between the webs is the z. B. from above and below over the rollers in the nip to run. A transfer of this welding process to plastic foam plate fails because the plates are too thick for that they are sufficiently curved without damage over rollers could. Blowing the entire surface at the same time is too difficult Alternative.

In this situation, the invention proposes using a heater swords a simple and safe to implement solution. The heating sword has a small thickness. Thicknesses from 1 to 10 are possible mm, preferably 2 to 4 mm. The heating sword can be electric or with a flowing heating medium to the necessary welding temperature to be brought. Depending on the plastic foam, this temperature is between 100 and 150 degrees Celsius. Both types of heating can be operated safely dominate.  

With the help of the heating sword, the plastic foam is touched plates melted their surface. That means the heating sword will pulled through between two plates, pulling or pushing the plates over the heating is even more advantageous sword. Again, two rollers can be used. Cheap are relatively large radius rollers that are driven and the plates pull over the sword and the welding surfaces after leaving the Bring the sword into contact with the necessary welding pressure. The Plastic foam sheets are also made with thicknesses of 50 to 80 mm sufficiently flexible to be one for the after leaving the heating sword Touch to show necessary deflection. This mechanics is through the dimensioning of a distance between the heating bar and the nip favorable. However, the distance is dimensioned so that the melted Welding surfaces on the way into the nip are not inadmissible Experience temperature drop. The right distance measure can be with the help identify less experimental settings.

The same applies to the dimensioning of the width of the heating element. In practice the heating sword depending on the intended heating sword temperature have a width of 20 to 100 mm. The right width can be by experimentally using different heating blades with determine different widths. The process can also be changed change in the temperature of the heating element within the permissible tolerance range influence. Preferably, however, the heating element temperature is only used Optimization of the welding process changed.

The length of the heating sword is dimensioned so that it extends over the extends the entire width of the plastic foam panels. Optionally leave there are also several heating blades one behind the other across the plates arrange.

Another advantage is the use of a Teflon-coated Heating swords. The Teflon layer prevents caking of plastic on the heating sword.

Optionally, the heating sword is in the direction of movement Plastic foam panels also preceded a cooling wedge. The cooling wedge has that  Task to prevent preheating of the welding surfaces. The Preheating is caused by the heating sword also in the direction heat flow emanating from the direction of plate movement. Preheating can have an unfavorably long exposure to heat effect on the surfaces of the plastic foam panels. Then it can to undesirable damage to the under the welding surface lying cells of the plastic foam come. Then there is also the risk of tearing open the welding surfaces when touching the heating sword.

The cooling wedge has a thickness that is 1 to 20 mm, preferably 5 to 8 mm, is greater than the thickness of the heating sword. The cooling wedge can be used with a suitable cooling medium are flowed through. One is cheap Water cooling, because water is cheaply available in every company and Water at elevated temperature due to evaporation in particular Way of extracting heat from the environment.

It is favorable if the cooling wedge ver in the direction of the heating sword tapers that he at the selected distance from the cooling wedge resulting wedge-shaped gap between the plastic foam sheets completes. However, there is a sufficient cooling effect also with differently shaped coolers, e.g. B. right in cross section cooler if the cooling capacity is increased accordingly. I.e. the invention is not limited to a wedge-shaped cooler shape. In this sense, the term cooling wedge also closes differently than wedge-shaped coolers.

The welding can advantageously also be carried out on plates other than CO2 foamed plastic foam sheets are used.

In the drawing, an embodiment of the invention is shown. 1 and 2 are two 80 mm thick plastic foam panels made of polystyrene with a quality weight of 40 kg per cubic meter. Panels 1 and 2 have been foamed with CO2 as the blowing agent only. A plastic foam sheet with a thickness of 160 mm is created from the two sheets 1 and 2 by welding. For this purpose, the plates to be welded together are brought up on an upper roller conveyor 11 and on a lower roller conveyor 12 and are guided in a roller gap with rollers 5 and 6 . In the drawing, the sheets shown on the rollers are labeled 3 and 4 .

The plates coming from the roller conveyors 11 and 12 first pass between insertion rollers 7 , 8 , 9 and 10 before they reach the nip. The plates are brought into contact with a heating sword 13 , which has a constant temperature of 120 degrees Celsius. The temperature is reached with the help of a liquid heating medium, here an oil. This has the advantage that the heating element can be made extremely flat. At the same time, the heating element can be made very thin-walled. The thin walls together with the oil heating have the advantage that the heat supply can be interrupted suddenly in the event of a malfunction. There are hardly any problems with subsequent heat supply.

By touching the heating element, the surface of the plates is melted, so that the subsequent pressing in the nip of the rollers 5 and 6 creates a weld.

The heating element 13 is coated with Teflon. It has a width of 50 mm and a thickness of 3 mm and consists of 1 mm thick sheet metal. This results in a free flow opening width of 1 mm.

In the exemplary embodiment, the distance between the heating bar and the nip is 100 mm, and the diameter of the rollers 5 and 6 is 150 mm.

A cooling wedge 14 is arranged at a distance of 20 mm in front of the heating element in the direction of movement of the plates. The cooling wedge has a thickness of 6 mm at the wider rear end and tapers to 4 mm. The rear end is the end in the direction opposite to the direction of movement of the plates.

In the exemplary embodiment, the cooling wedge fills the wedge-shaped gap the plates completely along its length and at the same time forms one advantageous support surface for the plates.

The cooling wedge is flooded with water and takes the opposite of the movement Direction of the plates from the heating sword from the heat, so that excessive heat load on the welding surfaces is prevented.

Claims (10)

1. A process for the production of CO2 foamed plastic foam sheets of great thickness, in particular made of polystyrene and / or polyethylene, characterized by a duplication of the sheets ( 1 , 2 ) while welding the contact surfaces. 2. The method according to claim 1, characterized by the use of a heating sword ( 14 ). 3. The method according to claim 2, characterized by the use of a heating sword ( 14 ) with a thickness of 1 to 10 mm and / or a width of 20 to 100 mm. 4. The method according to claim 2 or 3, characterized by the use of a heating bar ( 14 ) with an oil heater. 5. The method according to one or more of claims 1 to 4, characterized by the use of rollers ( 5 , 6 ) for applying the welding pressure. 6. The method according to claim 5, characterized by the use of insertion rollers ( 7 , 8 , 9 , 10 ). 7. The method according to one or more of claims 1 to 6, characterized by the use of a cooler ( 14 ) in the plate movement direction in front of the heating element ( 13 ). 8. The method according to claim 7, characterized by the use of a wedge-shaped cooler ( 14 ). 9. The method according to claim 8, characterized by the use of a heating wedge ( 14 ) with a thickness which is 1 to 20 mm larger than the thickness of the heating sword. 10. The method according to claim 8 or 9, characterized by the use of a cooler ( 14 ) with water cooling.