DE1504109A1 - Method and device for applying film-like coatings made of thermoplastic material to sheets or bands made of metal or the like. - Google Patents

Description

"Method and device for applying film-like coatings made of thermoplastic material on sheets or binders made of metal or dl, the invention relates to a process for applying film-like coatings made of thermoplastic material Waterial od on sheets or bands of metal. Like. In which the along a predetermined Web-guided sheets and an extruded film of still hot thermoplastic material are united under pressure by a fusible link and a device to carry out this aforementioned procedure.

It is known to use film-like coatings, for example in the form of lacquer or to apply paint to sheets or strips of metal and thereby create a solution or to use dispersing agents to be able to spray the film material0 This results in increased costs and difficulties, since the solution or Dispersant must be expelled.

In order to avoid these components, the application is made of: thermoplastic Material on metal switched to heating the thermoplastic materials and roll them onto the metals. Since the rollers, which the plastic materi @ 1 in contact with the metal, only for one brief moment are effective, irregularities in the layer thickness cannot be avoided. If the thermoplastic material is not heated to its melting point, it is the connection with the metal unsatisfactory, unless caf ?, the surface of the thermoplastic material has been pretreated in this way secure intimate connection with the metal.

In order to avoid the aforementioned disadvantages, it has already been provided that To use adhesives to create the connection. The plastic needs to be there Material cannot be raised to a temperature at which a noticeable Softening occurs, but the choice of adhesive in this process is extraordinary limited. Furthermore, the additional use of glue makes the manufacturing process easier noticeably more expensive, In order to use an adhesive, be it in the form of a permanent one It continues to be to avoid substance or in the form of a removable solution became known, for the temporary joining of separate sheets or foils, at least one of which consists of a non-conductive material between the Orbits before they are brought together to create a potential difference and these orbits diinn to be pressed together in a calender, so that one improvement the adhesion and also an attracting force between the webs is achieved. The permanent connection between the balms is in this, known Verfarhen generated by the subsequent assembly in the calender. So abs is here about a process in which the organic binder between the Replaced the webs to be pressed together by an electrostatic binder will.

In contrast, the present invention is based on that described at the beginning Process in which the organic binder is therefore unnecessary, that the tracks are united with the aid of a fusion connection $, whereby the in the internal heat from the extrusion is used for the fusion connection will. In this known method, the temperature conditions and the required Pressures can be set very precisely to create an intimate connection between the two Materials to achieve. This is also known as an extrusion coating in technology called procedure is much simpler than the others described above Process, however, is more difficult to control as the work flow changes only extends over a very narrow area and is interrelated depending on the conditions, namely pressure and temperature.

The legs play a special role here, the initial contact of extruded plastic film still in the molten state and of the moving metallic sheet or belt. The pressure and the temperature are critical, but the process is also time-dependent, and both with regard to the temperature effects at the various points of the Process sequence, as well as the effects in relation to the draw ratio, the constriction, the thickness and other properties of the thermoplastic film. look at that Methods of extrusion coating as described above are practically the necessary compressive forces have been applied in that tan the brought together layers passed between pressure rollers. here exists the danger that the thermoplastic material will be heated up enough to achieve it a secure adhesion to the metal also adheres to the pressure rollers. It surface damage can occur, which occurs particularly when the Pressure roller has a rubber jacket. On the other hand, there is no excessive cooling During the pressure treatment to occur is the use of cooled rollers or a pre-cooling of the material is not expedient and undermined. aside from that the movement of the layers to be joined between the pressure rollers must be very precise be adapted to each other if a uniform coating is to be achieved.

It is the object of the present invention to provide the aforementioned and im To simplify the above described method of extrusion coating and at the same time to improve so that the hitherto in gauf to. increasing disadvantages, which is achieved through the back roller treatment and in other cases through the use of an adhesive; be avoided.

The solution described in the introduction is used to solve the above problem Method according to the invention in that first on the film in a per se known Way electrostatic charges are generated and the film with the on a predetermined Potential held arc only below that of an electric field between the two pressure generated are pressed together, simultaneously and for one certain duration after the union of the film on one enabling the fusion connection Maintained temperature and then before contacting solid surfaces to below Solidification temperature is turned away.

The invention uses the knowledge that it is possible those necessary to create intimate contact between the layers Generate pressures exclusively by electrosationic charges. The practice has demonstrated that it succeeds in creating very solid connections these Way between the heated thermoplastic material and a heated metal to obtain. This new formation of the fusion bonding process avoids -simple Avoid any mechanical contact of the layer materials with any foreign surfaces, until the thermoplastic material solidifies sufficiently and thus against damage is secured.

Purely the electrostatic charge it is necessary that one of the used layers or components of the material to be combined in layers is sufficiently electrically non-conductive to ensure that the electrical Charges also applied and retained in the critical ~ phases of the process can be. In particular, it is necessary to choose a material that too retains its non-conductive property in the molten or considered state. Materials that are suitable for this are those that are also softened or melted State have a volume resistance of about at least 105 ohm-cm. It has it has been found that most common thermoplastics, including synthetic resins can be used.

Polyethylenes of low, medium or high, for example, are suitable Density, polypropylenes and other polyolefins including copolymers of olefins and other monomers, vinyl chloride Copolymers, polystyrene, polyethylene glycol terephthalate ud copolymers of these substances, cellulose acetates, various halogenated polymers including polytetrafluoroethylene, polyvinylformaldehyde, polyacetates and polycrbonarte. As a layer material made of metal, such materials come into consideration, which exhibit a volume resistivity of Ao 6 ohm-cm or less. With these materials the method according to the invention can be carried out without difficulty. Everyone meet common metals in the form of foils or sheets or sheets or tape wraps this requirement.

It could be established that with the new process layered materials with a plastic film thickness of 1.2 x 10-3 to 1.2 x 10-2 mm and thicker are to be established.

It is useful if, in further development of the new procedure, intermediate d'em made of metal or the like. Conductive material sheet or tape and one Fixed electrode arrangement, an electric field is generated and the film immediately after-its exit from the extrusion nozzle contact-free through this field Bow or ribbon is fed. By this measure one achieves a special one favorable utilization of the heat generated by extrusion and the resulting heat given high adaptability of the filmmaking. substance at the Association with the metallic material.

In a further development of the invention, the bow or the tape can be used a speed significantly exceeding the extrusion speed move the union zone if you want a particularly thin film coating, which can no longer be produced by extrusion alone ..

An improvement in adhesiveness and bonding of the thermoplastic According to the invention, the material with the metallic sheet or band can be thereby achieve that the bow or ribbon is up before reaching the junction evaluate a temperature supporting the fusion bond, which after the Fused metal and thermoplastic joints produced in a new process Material are particularly suitable for the production of containers for food, which have to be exposed to a temperature for pasting without being the layers detach from each other or show signs of perforation. For such Uses are linear polyethylenes at 8 mg / 6.25 mm2 to be satisfactory found. Tin sheets iporm of wrapping strips, which on both sides with Low density polyethylene-coated could be manufactured to manufacture cans, it got excellent adhesion self found on previously uncleaned metal strips which still had traces of rolling oil. These cans made from the aforementioned strips went through a pasteurization process without showing any reduction in the adhesion between the two layers of plastic.

The invention relates to a device for the implementation of the method with a device for feeding a sheet or strip of metal or the like. to a union zone with one in the hot state of one immediately in front the unification zone arranged extrusion molding device fed film of thermoplastic Material as well as a facility in the union zone for pressing together Film and sheet or tape under pressure and a subsequent cooling zone for the layer material. This device described is characterized according to the invention in that the Union zone means a device for generating an electric field between is assigned to the sheet or tape and the film and that sheet or tape and film in the union zone and up to a noticeable section in the cooling zone opposite fixed surfaces are guided without contact.

It is advantageous if at the level of the extrusion inlet one the Arch or the band at a predetermined distance from this exit leading role is arranged, which is connected to a predetermined potential (earth) is, while on the opposite side of the austetenden from the extruder Film are arranged at a small distance from this charging electrodes. By this configuration results in a particularly simple structure of the device, which can be further developed in that between the union zone and a heating zone is arranged in the cooling zone, which the materials with safety brings or maintains the temperature required for the fusion bond.

The invention is based on schematic drawings an exemplary embodiment explained in more detail.

Am winding 10 of a metal strip, e.g. B. tinned sheet metal supplies the strip 11, which is deflected over an idle roller 12 and from there moved past a Vorerwärmungsein direction 13, the illustration is shown as a gas burner. The strip rings in contact with a ground rod 14 over and then receives a film 15 of thermoplastic material, namely shortly after the film exits from an extruder 16. The extrusion tool is arranged so that it is the film at an acute angle to the moving Strip 11 can be pulled out. An electrostatic charger 17 is like that shown, that it has several rods 18 which face each other at a high potential the grounding rod 14 and the machine frame or the earth. This device generates electrical charges on the surface of the passing plastic Films. These charges are of opposite polarity to those induced Charges on the strip 11 so that they are effective through the plastic film are to keep this in firm and permanent bond with the surface of the strip bring to. The laminated material 20, which consists of the metal strip 11 and the electrostatically adhering plastic film 15 is given a firm bond at its interfaces when the metal and the plastic material are on the exit temperature of the thermoplastic material. There is a time dependency here plays a role, the temperature can be maintained by suitable means, for example by appropriate coats or the like, which prevent heat loss. However, a special device 21 can also be used for further heating be reproduced in the example shown in the form of a group of infrared lamps is. The plastic material and the metal only get together but otherwise not brought into contact with any solid body, so that heat losses only through Radiation and air convection can occur during 'physical contact with one third I (drper does not present a print on the layers. The composite laminate passes through a cooling device 22, e.g. a water tank, which is fed with cooling water through a pipe 24 and the heated water through a pipe 25 can drain. In this way it is achieved that a touch of the Laminate with another solid body is avoided as long as the plastic material in a state that is softened by heat and easily deformable is located.

After the water has cooled down, the now dimensionally stable Layer material run around a deflection roller 23 and from there over a drive roller 26, which rubber-covered rollers 27 are connected downstream, the speed control to serve. Thereafter, the layered material can be wound onto a roll 30.

The invention has also been carried out with success in the cases in which a cooling roller in an open air stream is used for cooling, which in at a distance from the point where the metal strip and the molten one thermoplastic material touching each other for the first time, this distance being like this it is chosen that the thermoplastic material has previously been sufficiently attached to the support strip can adapt and the molecules of the thermoplastic material on the contact surface align to ensure the required bond.

Preferably, a device for determining the temperature of the preheated metal strip provided. A thermocouple, for example, is used for this purpose 35 is provided, the conductors 36 of which lead to a measuring device 37. With this help you can the metal strips are brought to a temperature at which the thermoplastic Material is soft and can adapt to the metal. The temperature is like this high that quenching does not take place at the point of contact and yet so low that the material cannot deform or otherwise change, e.g. by melting the pewter train of a tin sheet. The same must of course Temperature can be chosen so that the temperature refinement of aluminum part. Connections will not be reversed or the thermoplastic iciterial not decomposed when touched. The grounding rod 14 also has a guiding function for the metal strip 11 and can be designed in the form of an idle roller be. The charges on the plastic film 15 cause the film 15 to move in Moved towards the metal strip 11. The distance between the metal strip should be 11 are maintained by the extruder outlet lips. Consequently it is preferred to place the ground rod in the angle between the film 15 and the Arrange strip 11 so that this rod at the same time mechanically serves to determine the exact position of the strip in relation to the extrusion tool as well to maintain the mechanical stresses that act on this strip.

In practice, the charger It may be positive or have negative polarity with respect to the ground rod 14.

The position of the charger 17 with respect to the plastic film allows control of the electrostatic forces between the metal strip and the plastic film for a given potential difference between the discharge electrodes 14 and 18. Contact of the electrodes 18 with the film is not necessary. A distance of 0, - 5 cm is sufficient, the electrodes 18 can in Forqp one or more electrically connected pointed metal tips be formed or rods, which, for example, a diameter of 1.5 mm. They run perpendicular to the film. But it can also be one or more fine wires are arranged at a distance from the film, which run transversely to the direction, in which the film is moved. In the latter case there are wake-up wires with a Diameter of 2.5 x 10 12.5 x 10-3 cm, which at a distance of at least a multiple of the diameter are arranged.

The voltage applied to rods or electrodes 14 and 18 is present in a typical embodiment in the range of 4-15 kV. There are both AC as well as DC potentials have been used, with DC potentials are preferred because of the greater and more uniform forces that are caused thereby.

The processes are preferably under such tension and spacing relationships kept that no visible corona or discharge and no discharge noise appear. The current requirements are small and are around 1 milliampere or less for webs which have a width of approximately 90 mm and with a Can be moved at a speed of about 6 minutes. The electrostatic forces are not only a function of voltage, but also the shape and size of the charging bars 18, the distance from the plastic film, the distance from the conductive element, the The thickness of the plastic film, its ohmic resistance and dielectric constant the process temperature, depending on the moisture content and the relative atmospheric humidity and other factors. Forces in the order of magnitude of about 1.2 kg / cm2, which act perpendicularly to the surface, were deemed to be present between a polyethylene film 2.5 x 10-3 cm thick and a smooth metal surface noted, a potential of 8300 volts and an electrode gap of about 0.8 cm have been used. The measurements were made at 50% relative humidity and 22.80 C temperature. It was swept between the opposite faces of the polyethylene measured a potential above 1000 volts.

Both sides of the conductive element, such as the tinplate strip 11, can be coated sequentially or simultaneously in the manner described will. So aluminum or other metal foils, tin sheets or the like can be used conductive materials are coated on one or both surfaces. The procedure can also be used to create a pre-formed layered material, which consists of a plurality of metal strips or layers which pass through conductive or non-conductive intermediate layers are to be coated separately.

If alternating current is used, it can run along the length of the The charge polarity of the moving material is opposite to one another in successive areas have on the plastic layer.

Example 1 Using a device in which the metal strip is fed from a supply roll and the one extruder and one Charging device like iii the Drawing shown, has, a strip of a commercially available 100 g sheet metal sheet of about 10 cm width, moving vertically downwards at a speed of 6 minutes and preheated to a temperature of about 218 ° C. The extruder was fed with an extrusion molding compound made of polyethylene with a density of 0.923 and a melt index of 3.7 (this resin composition is commercially available under the trademark name AL @ THON-16 available). This cup was extruded as a molten film of about 0.5 mm thickness in the area of the lips of the extruder. The extrusion temperatures were around 293 ° C.

The distance between the lips of the extrusion die and the surface of the metal strip passing by, measured in the opposite direction, was about 11 mm. The lips of the tool were about 23 cm away from a cooling roller, which was used here instead of a cooling tank 22. The loading device 17 had three wires about 10 cm long running across the width of the Film and which were about an inch from the metal strip.

The wires were made of platinum about 76/1000 mm in diameter.

When working without an electrostatic potential between the electrodes the film took a straight line from the lips of the tool to the cooling roller as indicated by the dashed line 11x in the drawing.

The liability was low. The plastic material could easily be removed from Metal can be peeled off.

If, on the other hand, a hoof charge potential of 12 kV was used, cause the charges the plastic molten film with the metal strip about 25 mm to come into contact below the horizontal plane of the extrusion lips. Bs excellent adhesion resulted.

By adjusting the speed of the metal strip opposite that of the film coming out of the extruder becomes a pull-out of the film from 20 to 1 received. So if the lips of the extrusion die one Had a gap of about 0.5 mm, had the plastic layer on the complete Arrangement a thickness of about 25/100 mm.

Therefore, when the extruder is under optimal temperature and Pressure conditions were operated in order to obtain the desired extrusion mass, d. H. that is, about 0.5mm thick, may be the final thickness of the resin coating regulated on the metal strip by the speed of the metal strip be, for example, by the fact that the metal strip is 20 times as fast as the exiting extrusion material moves The optimal position of the Extrusion device through which the angle between the exiting extrusion relative to the path of the metal strip is determined, depends on the location of the on charger 17, the voltage used, the speed of the metal strip and the angle of the strip against the attack of gravity. If, As shown, the charge wires 18 located near the strip may have a lower one Voltage can be applied as if the distance is greater.

In further practical use with the device according to the example 1, the ground rod 14 had a diameter of about 8 mm and a spacing of such that its lower side is about 20 mm above the level of the lips of the Extruder lay; Two horizontal wires 18 were applied, spaced parallel to one another to the path of the metal strip were arranged at a distance of about 36 mm. The wires were about 75/10 mm in diameter and made of platinum. They were about 32 mm apart. The top wire was approximately 15 mm below the extrusion lips. The extruder was like that arranged that the film is down at an angle of about 550 from the The path of the metal strip emerged, the film exiting parallel to the walls.

The process ensures that the plastic material is firmly in continuous, ubiquitous contact with the metal is maintained while it is still in the molten state. This takes a while. This makes it unnecessary to use squeezing or other rollers for contact, as long as they are the plastic film is still at the melting temperature - around the metal and the melt film to connect with each other. The method can also be carried out without the effect These forces are interrupted, creating the required touch and connection be generated.

Example 2 Here an apparatus has been applied with a Feeding device for a metal strip, an extrusion device and a charging device, as shown in the figures. A stripe Made of commercially available tinplate about 15 cm wide and about 0.25 thick mm was moved vertically downwards at a speed of 6 m / minute and warmed to about 19300. The extruder was made of polypropylene with a Melt index of about 160 supplied (which is available under the trade name ESCON CD 112 is) which as a molten film about 0.5 mm thick from the extrusion lips resigned. The extrusion temperatures were about 299 °. The exit lips the Extruder had in a perpendicular direction from the surface of the passing Metal strip a distance of about 11 mm. The lips were at a distance of the cooling tank 22 of about 75 cm. The hoof charger 17 had three wires of about 16 mm in length extending across the width of the film and about 25 mm removed from the metal strip. The metal wires had a diameter of about 75/1000 mm and made of platinum.

Example 3Bs became an apparatus with a feeder for the metal strip, an extruder and a charger gladly. the drawing used.

A strip of conventional drawing sheet with a width of about 15 cm and a thickness of about 0.25 mm was taken in the perpendicular direction at a speed moved downwards from about 6m / minute and preheated to about 204 ° C. The strand pressing device was made with a granulated copolymer of 15% ethylene glycol isophthalate and 85 % Ethylene glycol terephthalate (a resin sold under the trademark VITEL 409 is in use) t fed, which measures as a molten film of about 0.5 mm thick emerged from the extrusion lips. The extrusion temperatures were about 182 ° C. The extrusion lips got off the surface of the passing Metal strip in the vertical direction distance of about 11 mm. The extrusion lips were about 75 cm from the cooling tank 22. The charger 17 had three wires about 16 mm long running across the width of the Film extended and about 25 mm from the metal strip. The diameter the wires were about 75/1000 mm, while the wires themselves were made of platinum.

The laminated tapes of Examples 2 and 3 showed excellent results Liability.

A roll made of aluminum alloy with a thickness of about 0.35 mm was made by applying electrostatic forces in the manner previously described coated with a low density polyethylene, which mass under the trade name ALATHON-1540 is available. The pilm thickness was 37/1000, 75/1000 and 150/1000 Millimeters, with the coating on one side only. At film thickness from 37/1000 and 57/1000, or 75/1000 and 75/1000, or 50/1000 and 100/1000 mm when used on both sides. It became satisfactory from a commercial point of view Establish liability.

The same aluminum material was made in a similar manner with a polyethylene high density (a resin that is commercially syllable under the trademark SL'LA! PHON-7250 is known) coated, with a thickness of about 75/1000 mm on one or both times Again, there was a satisfactory adhesion achieved.

Corresponding commercially available tin sheets for cans (known than 107-MCT6-0.25 lb. sheet) were lower, medium and higher with polyethylene Dense coated and molded into beer can lids. The metal was at around 21,600 + 50 preheated. When the temperature of the extruded film using a Needle point thermometer was measured when the film emerged from the mold, a measured value of 190 ° C. was obtained. In this case, the adhesion was insufficient and the film could be peeled off easily. If the extrusion 2emrepatur, however Was 224 ° C, peeling was difficult. At 2380C the adhesion was very high. at During this work, the metal strip was moved at a speed of 5 - 6 m / minute emotional.

Low or medium density polyethylene has been used for extrusion coating used, the electrostatic charge to achieve one over all areas going contact it is applied between the metal strip and the plastic film with film covers of about 12/1000, 18/1000 and 25/1000 Millimeter. There was also a high density polyethylene of the same thickness, as well a thickness of 50/1000 mm is used. The adhesion was satisfactory.

Claims (7)

Claims 1. Method for applying film-like coatings of thermoplastic material on sheets or bands of metal od. Like. In which the sheet guided along a predetermined path and an extruded film made of hot thermoplastic material under pressure through a fusion bond be united, d u r c h e k e n n n z e i c h n e t, which is initially based on the Film in a known manner, electrostatic charges are generated and the Film with the arc held at a predetermined potential alone under the pressed together by an electric field created between the two pressure being taken simultaneously and for a predetermined duration after the union the film is kept at a temperature permitting the fusion bond and then cooled to below solidification temperature before contact with solid surfaces will. 2. The method according to claim 1, d a d u r c h g e k e n n -z e i zu without that between the metal or the like. Existing conductive material Arc or ribbon and a fixed electrode arrangement generates an electric field becomes and the film is free of irrigation immediately after its exit from the extrusion nozzle is fed through this field to the Bo bow or tape. 3. The method according to claim 1 or 2, d a d u r c h g e -k e n n z E i c h n e t that sheet or band with one the extrusion speed considerably exceeding speed can be moved through the merging zone. 40 The method according to claims 1 to 3, d a d u r c h g e -k e n n z e i c h n e t that sheet or ribbon on a die before reaching the union point Melt joint supporting temperature are heated. 5. Device for carrying out the method according to claim 1 to 4, with a device for feeding a sheet or strip of metal tod. like to a union zone with one in the hot state of one immediately in front of it thermoplastic film fed to the extrusion molding device arranged in the merging zone Material as well as a facility in the union zone for compressing Film and sheet or tape under pressure and a subsequent cooling zone for the layer material, d a d u r oh g e k e n n z e i c h-n e t that the unification zone is a facility (14,17,18) to create an electric field between the bow or ribbon (and and associated with the filii (15), and that sheet or ribbon and film in the merging zone and up to a noticeable section in the cooling zone (22) with respect to solid surfaces (23) are guided without contact. 6. Apparatus according to claim 5, d a d u r c h g e k e n n z e i c h n e t that at the level of the extrusion inlet (16) one of the arches or the band (11) arranged at a predetermined distance from this exit leading roller (14) which is connected to a predetermined potential (earth) while on the remote side of the film emerging from the extrusion device (16) in a small amount Distance from this charging electrodes (18) are arranged 7. Device according to Claim 6, d a d u r o h g e k e n n -z e i c h n e t that between the union zone and a heating zone (213 is arranged in the cooling zone.