WO1996015899A1

WO1996015899A1 - Process for joining plastic moulded parts

Info

Publication number: WO1996015899A1
Application number: PCT/EP1995/004465
Authority: WO
Inventors: Michael Schätzle
Original assignee: Henkel Teroson Gmbh
Priority date: 1994-11-23
Filing date: 1995-11-14
Publication date: 1996-05-30
Also published as: DE4441681A1

Abstract

Thermoplastic moulded parts (5) may be joined by means of metal strips (3) provided with a plurality of pins (1). In order to anchor the metal plate in the plastic moulded part in a solid manner, the metal strips (3) are heated above the softening point of the plastic material and the pin-bearing side of the metal plate is then pressed into the plastic material (5). These metal strips (5) may then be at least partially embedded in an adhesive or filler layer. This process is particularly suitable to improve damaged plastic moulded parts, in particular car parts, such as fenders or projector housings. The moulded parts repaired by this process recover their original performance capabilities, in particular their dimensional stiffness, their shock-resistance and their visual appearance. When the thus repaired moulded parts are scrapped, they may be entirely recycled by the usual methods.

Description

Process for connecting molded plastic parts

The invention relates to a method for connecting thermoplastic molded parts with the aid of a metallic bridge, the connecting joint being bridged by metal strips, in particular it relates to a method for repairing damaged thermoplastic molded parts.

In a number of industries, particularly in the automotive industry, molded metal parts are increasingly being replaced by plastic parts. This use of plastic molded parts serves, on the one hand, to save weight and, on the other hand, to simplify production processes. In the automotive industry, for example, tailgates of automobiles, fender parts and in particular bumpers or lamp housings made of molded plastic parts are being used to an increasing extent. These plastic molded parts can consist of a large number of different plastics or composite materials, examples include polyethylene, polypropylene, polycarbonate, acrylonitrile butadiene styrene polymers (ABS), polyamide, polyurethane. In addition, so-called polymer blends, such as the EPDM-modified polyethylenes and polypropylene, Materials used. When operating the machines, apparatuses and in particular vehicles (automobiles) equipped with these plastic molded parts, these plastic molded parts can be damaged. In particular, the bumpers or lamp housings of automobiles are often damaged in motor vehicle accidents.

So far, the damaged molded parts have usually been replaced by new parts and not repaired.

This procedure has two decisive disadvantages for the consumer: firstly, the costs of replacing the part with a new part are considerably higher than if the plastic molded part were repaired using simple methods, and secondly the damaged plastic molded part must be disposed of. This previously necessary disposal of bulky and voluminous parts is highly undesirable for reasons of environmental protection, and the disposal costs also make a significant contribution to increasing repair costs.

There has therefore been no lack of attempts to develop repair processes for the repair of such damaged plastic molded parts, but all the processes known hitherto have shown considerable disadvantages in practice.

EP-A-186081 proposes the use of metal sheets for body repairs, which are coated with hot melt adhesives based on thermoplastic copolymers, these metal sheets coated in this way are then glued over the damaged area. However, this method can only be used for sheet metal parts and not for molded plastic parts, since here the point to be repaired must be preheated to temperatures at which the hot-melt adhesive Softened material based on thermoplastic block copolymers, that is, it must be heated to temperatures above 100 ° C. Many plastic molded parts, in particular those based on thermoplastic materials, lose their dimensional stability and their mechanical properties at these temperatures, so that the process proposed in EP-A-186081 is not suitable for the repair of plastic molded parts.

EP-A-315101 describes a method for repairing damaged articles made of composite materials. The damaged area of the composite material is repaired by gluing metal or hardened composite material pieces onto the area surrounding the damaged area. A rubber-modified vinyl ester resin composition is proposed here as the adhesive. In another embodiment, an uncured reinforcing material is impregnated with a rubber-modified vinyl ester resin composition and placed over the prepared damaged zone and cured there. Graphite fiber or glass fiber fabrics are proposed as the reinforcing material. According to EP-A-315101, the damaged zone is completely covered with the metal or composite material. No information is given as to whether this repair method is also suitable for the repair of molded plastic parts made of thermoplastic materials.

The damaged areas of plastic molded parts, in particular bumpers or lamp housings of automobiles, very often have longer cracks, which drastically reduce the mechanical strength of the molded part. Attempting to repair these points by conventional methods of the prior art by reinforcing the full area with sheet metal parts or by gluing with the aid of glass fiber fabrics, shows that the mechanical properties of the molded part repaired in this way are considerably poorer than those of the original undamaged molded part. In the case of large-area gluing with metal sheets, it is observed that, for example in the case of a pendulum impact test, the gluing flakes off extensively, when repairing with the aid of glass fiber mats, the tensile test tears at the original crack point when the molded part is twisted. The fiber tissue also tears at the original tear point during the pendulum impact test. A method has recently been specified in which plastic molded parts are connected using a 1- or 2-component adhesive, the connecting joint being bridged by metal strips.

The previously known methods are not or only insufficiently suitable for connecting very non-polar materials such as Polyethylene, polypropylene, EPDM and poly fade from these thermoplastic polymers. In particular, the latter methods also require complex surface pretreatments, such as mechanical roughening, plasma or corona pre-treatments or the use of primer primers, which usually contain solvents. There was therefore a need to develop a method which enables the repair of damaged plastic molded parts, in particular those used in the automotive industry, with simple means. This process should also ensure that the repaired part not only looks optically perfect, but is also equivalent in mechanical properties to that of the new part.

It has now been found that specially shaped metal strips enable the connection of thermoplastic molded parts, in particular in the case of repairs, in such a way that the molded parts regain their original mechanical properties, with fillers or adhesives / sealants only still for sealing the connection point and to improve the visual appearance, but not to establish the non-positive connection between the parts.

The invention thus relates to a method for connecting thermoplastic molded parts with the aid of specially shaped metal strips with which the connecting joint is bridged. The metal strips are provided with a large number of pins which protrude 0.1 to 15 mm from the metal strip. In a further embodiment, the metal strips are provided with openings which protrude like a grater.

The protruding pins or the projecting openings ensure a firm, permanent, force-locking connection of the bridging metal strip with the thermoplastic molded part.

Another object of the invention is a composite of thermoplastic molded parts, the connecting joint being bridged by at least one metal strip with protruding pins or projecting openings. To seal the connection joint and to restore an optically appealing smooth surface of the connection joint during repairs, the connection joint can be coated with a filler known per se and / or an adhesive / sealant known per se, the metal strips at least partially in the layer of the filler or the adhesive / sealant are embedded.

All molded parts made of thermoplastic materials, such as those used in automobile construction, are suitable for this repair process: polyolefins, such as Polyethylene, polypropylene, rubber-modified polyolefins, in particular EPDM-modified polyethylene and / or polypropylene, polycarbonate, ABS, polyamide, thermoplastic polyurethane, which can also be designed as fiber-reinforced plastics.

All one- or two-component materials are suitable as adhesives / sealants or fillers for the repair processes according to the invention, provided that they cure at a sufficient speed in a temperature range from room temperature to about a maximum of 90 ° C. Examples of such adhesives are one or two-component epoxy adhesives, unsaturated polyesters in combination with styrene and / or methacrylates, (meth) acrylate adhesives or two-component polyurethane adhesives.

Spring steel, aluminum and very particularly electrolytically galvanized steel sheet, such as is used, for example, in body construction, are suitable as reinforcing metal strips. The metal strips can be surface-pretreated in addition to the galvanizing or instead of the galvanizing by other common methods. These include e.g. Coating with so-called primers, electro-dip painting, phosphating and / or painting.

According to the invention, the metal strips are provided with a multiplicity of pins which protrude 0.1 to 15 mm from the metal strip either on one side or on both sides. The pins are preferably arranged in rows and the lateral distance between two pins is 3 to 15 mm. The pins protrude from the surface of the metal strip in a manner similar to a "nail board". The free end of the pins is preferably barb-like or has a thickening. The non-positive connection to the connecting thermoplastic molded parts takes place in that the metal strips according to the invention are heated to a temperature above the softening point of the thermoplastic and in the warm state are pressed into the plastic molded parts to be connected with the protruding pins, so that the plastic initially melts around the hot pins. After the subsequent solidification of the thermoplastic, the metal strips are firmly anchored in the plastic by the pins protruding into the solidified plastic. This positive connection is particularly reliable and resilient if thickenings at the upper ends of the pins are designed in the manner of a nail head, mushroom head or spherical. The metal strips can be heated with all common heat sources, for example a hair dryer, electrically or gas-heated hot air blowers, open flames, soldering irons, induction ovens or normal heating cabinets.

A reactive adhesive / sealant or filler can be applied to the metal strips anchored in this way in the molded plastic part in order to seal the connecting joint or to restore the pleasing optical appearance. Since in this method the largest part of the surface to be wetted by the adhesive or by the filler is formed by the metal strips, this method can also be used to directly and non-positively bond plastics with one another, which have hitherto been very difficult to bond. These thermoplastic plastics, which have hitherto been very difficult to bond, include, for example, pure polyethylene, pure polypropylene and soft PVC or fluorinated polyolefins such as Teflon. This repair method is particularly economical because, compared to other methods, the positive connection of the molded parts is particularly quick he follows. In a preferred embodiment, the surface of the metal strips facing away from the plastic molded part is used for the further operations as an easily bondable surface with which all conventional one- and two-component adhesives or fillers or hot melt adhesives form a permanent bond.

The dimensions and the number of metal strips to be used per repair bond can vary within wide limits and depend on the size of the point to be repaired and on the strengths which the bond must achieve. The thickness of the metal strips can vary between 0.2 and 1.5 mm, preferably between 0.2 and 1.0 mm, the sheet thicknesses of 0.6 to 0.9 mm used in automobile construction are very particularly preferred. The length and width of the metal strips depend on the adhesive joint to be bridged, the length can vary between 30 and 200 mm, the width between 5 and 20 mm. In a very special embodiment, the metal strips are between 60 and 90 mm long and 10 mm wide. When repairing long, crack-like damage, at least one metal strip is anchored at the beginning of the crack, but metal strips on the back of the damaged molded part are preferably pressed into the plastic layer at largely uniform intervals over the entire length of the crack. A further possibility of the adhesive bonding according to the invention is a combination of metal strips and fiber mats as reinforcing agents, at least one metal strip being to be glued in at the beginning of the crack. Although the metal strips can also be adapted to the shape of the plastic part to be repaired, the use of glass fiber mats or textile fabrics can be expedient if the damaged area to be bonded has a complicated shape or if parts of the repair points to be reinforced are in the visible area , so that a very smooth gluing is necessary. The curing of the adhesive bond may where appropriate by heating the splice to temperatures up to 90 ° C, preferably accelerated to about 70 ^β C so that the sealed part can be further processed after a very short time, sanded, for example, and can be kiert LAK . The heating can be carried out by all known heat sources, in particular by using hot air blowers or IR radiators.

The connection of the molded parts according to the invention is also very advantageous for reasons of environmental protection, since the glued molded parts of this type made of thermoplastic plastics remain fully recyclable: Shredder and subsequent granulation do not interfere with the hardened adhesive residues or spatula residues in the reuse of the plastic granulate; the metal parts, especially steel parts, can be separated by common separation methods such as e.g. electromagnetic separation or air separation are removed from the granulate.

The invention is explained in more detail below with reference to the description of FIGS. 1 to 4 and an exemplary embodiment:

Figure 1 shows a section of the metal strip according to the invention in side view. The pins 1 protrude from the metal sheet 3. These pins have a thickening 2 at their free end. This thickening can be designed in various ways: cylindrical, similar to a nail head, spherical or mushroom-shaped.

Figure 2 shows a section of the metal strip according to the invention in plan view, here it is clear that the pins are arranged in several rows. The number of rows of pins depends on the width of the Metal strip.

FIG. 3 shows a further embodiment of the metal strips in side view, in which pins 4 also protrude from the underside of the metal strip. The pins 4 are designed in the same way as the pins 1.

FIG. 4 shows the connection of two plastic parts 5 by means of a metal strip 3 according to the invention. The pins 1 with their heads 2 are completely embedded in the plastic matrix of the plastic molded part 5 by the melting process and thus ensure a load-bearing connection of the metal strip with the plastic molded parts 5. The joint 6 remaining in the connection can then be filled with a conventional, suitable filler or an adhesive / sealant and smoothed.

Design example:

Two EPDM plastic strips measuring 25 x 100 x 10 mm were butted together on a flat surface at their short edges. A sheet steel strip according to FIG. 1 with the dimensions 20 mm × 60 mm, from which pins 5 mm protruded, was heated to approximately 150 ° C. with a hot air blower. With the help of pliers, this steel strip was pressed with its pins into the prepared plastic strips, as shown in FIG. Immediately after cooling, the composite test specimen was clamped in a tractor and subjected to the tensile test. There followed a breakage of material within the plastic test piece not reinforced with the metal strip.

Comparative Example:

According to the state of the art, the EPDM plastic strips roughened with the help of a grinding wheel, coated with a commercially available plastic primer. Then the joint was glued with a commercially available two-component polyurethane adhesive using a glass fiber fabric. In the tensile test, the bond broke at the joint between the two plastic strips, tearing through the glass fiber fabric.

Claims

Patent claims

1.) Method for connecting thermoplastic molded parts, characterized in that the connecting joint is bridged by at least one metal strip.

2.) Method according to claim 1, characterized in that at least a part of the metal strip is provided with a plurality of pins which protrude 0.1 to 15 mm from the metal strip.

3.) Method according to at least one of the preceding claims, characterized in that the metal strips are provided with grating-like projecting openings.

4.) Method according to at least one of the preceding claims, characterized in that the individual metal strips are 30 to 200 mm long, 5 to 20 mm wide and 0.2 to 1.0 mm thick

5.) Method according to at least one of the preceding claims, characterized in that the pins are widened at their upper end.

6.) Method according to at least one of the preceding claims, characterized in that the pins are arranged in rows and the lateral distance between two pins is 3 to 15 mm.

7.) Method according to at least one of the preceding claims, characterized in that the metal strips are heated to a temperature above the softening point of the molded plastic part to be connected and in the hot state in the molded plastic parts to be connected are pressed in.

8.) Method according to at least one of the preceding claims, characterized in that the Metall¬ strips are heated to 90 ° C to 180 ° C and are pressed in the hot state in the molded plastic parts to be connected.

9.) Procedure according to at least one of the preceding claims, characterized in that the connection point are additionally sealed with one- or multi-component fillers and / or adhesives / sealants.

10.) Composite of thermoplastic molded parts, produced according to at least one of the preceding claims.