WO1995021734A1

WO1995021734A1 - Gluable plastic moulded part and process for producing the same

Info

Publication number: WO1995021734A1
Application number: PCT/CH1995/000028
Authority: WO
Inventors: Elmar Mock
Original assignee: Tetra Laval Holdings & Finance S.A.
Priority date: 1994-02-09
Filing date: 1995-02-07
Publication date: 1995-08-17
Also published as: AU1530895A; EP0693023A1; JPH08508951A

Abstract

A gluable moulded part has an integrated gluing part (3) made of a hot-melt-type glue and a moulded part (4). The gluing part (3) is produced in a separate injection moulding step, for example in a first injection moulding step, and the moulded part (4) is then cast on the gluing part (3), forming a joint line. When required, at least the surface to be glued of the gluing part (3) is activated, for example by heat irradiation, for example before the actual gluing process, and the gluable moulded part is then pressed on an object (5) to which it must be glued.

Description

ADHESIVE MOLDED PART FROM PLASTIC AND METHOD FOR PRODUCING THIS MOLDED PART

The invention is in the field of injection molding technology and relates to an injection-moldable molded part made of plastic according to the independent patent claim and a manufacturing process for producing the bondable molded part.

Molded parts made of plastic for injection molding are often glued onto other objects made of plastic or other materials. For this purpose, an adhesive is placed between the two surfaces provided for the adhesive connection, one of which is a region of the surface of the molded part, and the two surfaces are then usually pressed together. The adhesive is often sprayed, for example in liquid form, onto one of the surfaces to be bonded, or else it is positioned in the form of an adhesive film between the two surfaces to be bonded and activated, for example, by heat. In any case, the adhesive must be selected in such a way that it adheres sufficiently to the respective application by adhesion or cohesion on both surfaces after the adhesive process, which is particularly important when bonding very different surfaces (e.g. different materials) can lead to difficulties.

Furthermore, the exact positioning and metering of the adhesive is often not easy. Particularly in the case of moldings with highly structured surfaces, of which only individual areas are to be glued with complicated shapes, there is also the difficulty of applying the adhesive precisely and correctly in dosed form only to the surface parts to be glued, so that in the worst case after gluing Excess adhesive must be removed in a further step.

A lot of such difficulties have been shown in the concrete use of molded parts as closure units on beverage containers, for example made of paper, cardboard or plastic-coated materials of the type described in European application EP-Al-546999, for example, if these closure units consist of any one Basically cannot be welded to the container and must therefore be glued. Such a reason can be that the container material cannot be welded or that such or a similar closure unit is only attached to the already filled container (over a correspondingly weakened point) and the container contents could be damaged by welding.

The object of the invention is now to create a gluable molded part produced by injection molding, the gluing of which to another object can be carried out significantly more simply and precisely. Furthermore, it is the object of the invention to show a production method for such a bondable molded part. This object is achieved by the adhesive part as defined in the claims.

The adhesive part which can be glued according to the invention already has the adhesive as an integrated partial form (adhesive part). The adhesive part is connected to the effective molded part by a flow seam and the two parts together form the gluable molded part. The flow seam is created by casting together in two successive injection molding steps of the two materials (adhesive and material of the molded part) with appropriately selected injection molding parameters. The bondable molded part with the integrated adhesive is produced by a multi-material injection molding process, for example by first casting the adhesive part from the adhesive, then changing the mold and the molded part being cast from at least one thermoplastic material in at least one further injection molding step , wherein the adhesive part partially limits the casting cavity when casting the molded part.

The following conditions must be placed on the adhesive: it must be solid at ambient temperature; it must be injection moldable; it must be able to form a stable flow seam with the material of the molded part under injection molding conditions; if necessary after appropriate activation (at least on the surface), it must be able to form an adhesive or cohesive connection (adhesive connection) with the surface to be bonded to the molded part. These conditions can be met with a hot melt adhesive selected for a specific application. Hot-melt adhesives become sticky by heating to a specific activation temperature which is characteristic of an individual hot-melt adhesive and, in this state, form adhesive bonds with other surfaces which are then stable below the activation temperature. Hot melt adhesives are usually composed of a base polymer and an adhesive material and can also contain plasticizers, antioxidants and / or fillers. The base polymer essentially determines the activation temperature of the hot melt adhesive. Commercially available hotmelt adhesives often contain, as base polymer, ethyl vinyl acetate copolymers (activation temperatures in the range from 90 to 140 ° C.), polyamides (activation temperatures in the range from 120 to 180 ° C.) or polyester (activation temperatures in the range from 150 to 210 ° C). A surface made of a different material that is involved in an adhesive connection with a hot-melt adhesive usually shows no structural changes with respect to the same surface that is not involved in an adhesive connection.

A treatment with heat, infrared, ultrasound, flame, discharge or plasma is conceivable as activation (heating to the activation temperature) of the adhesive part surface before the effective bonding process, with activation depending on the application before bringing the surfaces to be bonded together or afterwards can be carried out. This activation is only relevant with regard to the gluing of the adhesive part to the surface of the object to be glued. In contrast, the connection between the adhesive part and the molded part is already created during the production by injection molding in such a way that it survives the activation and the gluing process and is therefore largely independent of the activation process. Compared to the state of the art, this eliminates in particular the condition to be placed on the adhesive material, according to which an adhesive applied according to known methods must be capable of being adhesively or cohesively bonded to the materials of both surfaces to be bonded, with the same activation.

A further advantage of the moldable part according to the invention with an integrated adhesive part, in particular compared to an application of adhesive by spraying a molded part, is that the adhesive layer can be made thicker and in particular with a varying thickness. In this way, the adhesive layer can be designed to be adaptable, for example, to only locally rough or otherwise uneven surfaces, or actual adhesive bodies can be provided instead of only layer-shaped adhesive parts, which are deformed in a predetermined manner when the surfaces to be bonded are brought together.

In a manner known per se, a series of quasi-endless cords connecting similar molded parts can also be cast between the adhesive part and the molded part, which cords are then either removed or cut off during gluing. The adhesive part can also, for a defined connection of a plurality of molded parts, be cast onto a siliconized paper strip, for example, the individual molded parts then being detached from the paper strip by peeling off before being glued. Of course, the molded part can also be cast onto a paper strip in the same way. Exemplary embodiments of the moldable part according to the invention with integrated adhesive part are to be described in detail with reference to the following figures. Show:

Figures la to ld a scheme for the production and bonding of a schematized, gluable molded part;

FIG. 2 shows a plan view from the side of the adhesive part of a moldable part which is designed as a closure unit for a container for flowable material;

FIG. 3 shows a cross section through the adhesive part according to FIG. 2;

Figures 4 to 6 variants of adhesive parts and their application.

Figures la to ld show very schematically the production of an exemplary adhesive part according to the invention and its bonding to another object.

Figure la shows a section through the casting cavity 1, the two-part injection mold 10, 11 for the first injection molding step, in which the adhesive part is cast from a hot melt adhesive A. So that the sprayed hot-melt adhesive A does not adhere to the injection mold when it cools down, injection molds 10 and 11 made of nikekei coated with polytetrafluoroethylene (PTFE), made of polytetrafluoroethylene (PTFE), made of chrome or of a titanium-nickel alloy are used. FIG. 1b again shows, in section through the casting cavity 2, the two-part injection mold 10, 12 for the second injection molding step, in which the molded part is cast with a material B on the adhesive 3.

For the two injection molding steps, the parameters (injection temperature, length of cooling time, etc.) must be selected such that a durable flow seam is created between the adhesive part and the molded part.

One method variant consists in that the molded part is first cast in at least one injection molding step and the adhesive part is cast in a further injection molding step on the already existing molded part.

Figure lc shows schematically the activation step in which the surface of the adhesive part 3 to be glued is activated for the gluing process and Figure ld shows the glued product in which the glue part 3 is arranged between the molded part 4 and the glued object 5, only between glue - Part 3 and glued object 5 there is a real adhesive connection (without changing the structure of the glued surface).

FIGS. 2 and 3 show, as an exemplary embodiment of a moldable part according to the invention, a closure unit, as already mentioned at the beginning (EP-Al-546999). Figure 2 shows the closure unit as a top view and Figure 3 cut. The closure unit consists of an essentially tubular pouring part 6 and a closure part 7 which closes an opening of the pouring part. In the region of the other opening of the pouring part, a flange-shaped connecting piece 8 is formed on which the adhesive part 9 adheres. In FIGS. 2 and 3, two cords 20.1 and 20.2 are also shown by way of example, which connect a number of further identical closure units (not shown). The cords are arranged in the border area of the flow seam between the molded part and the adhesive part in such a way that they can easily be removed from the side (arrows C). Cords that are further arranged against the middle area of the flow seam must be cut to separate the closure units.

As already mentioned, a paper or plastic strip 21 (only shown in FIG. 3) can also be used as a variant for a connection of a plurality of closure units. The material of the strip 21 must be selected such that the adhesion between the adhesive part 3 and the strip 21 is sufficient for the transport of the connected closure units, but that it can be released for the gluing without damaging the adhesive part.

FIGS. 4, 5 and 6 show two exemplary applications of, in contrast to essentially flat adhesive layers, three-dimensional adhesive bodies which can perform a wide variety of functions.

FIG. 4 shows in section a part of a moldable part that can be glued, for example the adhesive edge of a closure unit, to the left before gluing and glued to an object 5 on the right. The adhesive part consists of an adhesive layer 3.1, which is pressed together during gluing (3.1 '), and an adhesive body 3.2, which is deformed during gluing (3.2'). The adhesive layer 3.1 'has, for example, the function of a mechanical one Adhesion while the adhesive body 3.2 'takes over the function of the seal.

FIG. 4 also shows that the adhesive part can consist of different, separate areas (3.1, 3.2), the flow seams of the areas being arranged, for example, in one plane.

FIG. 5 shows (partially) a further adhesive part that can be glued (again left before gluing, right after gluing), which has an adhesive body 3.3. The adhesive body 3.3 'deformed during the bonding can, as shown, adapt, for example, to non-planar locations on the object 5 to be bonded, it can fill cavities or cracks or perform other functions.

FIG. 6 shows a further application of an adhesive body, again on the left in front of the adhesive and right in the bonded state. This is a molded part that is to be glued, for example, over a seam 6 of a container made of paper or cardboard, the paper or cardboard edges overlapping in the seam 6 and thereby resulting in a thickening of the material. If the adhesive body 3.4 has already matched the shape of the seam 6 to be covered, a significantly more precise bonding is possible.

Claims

PATENT CLAIMS

1. Injection molded molded part made of at least two thermoplastic materials, characterized in that it has an adhesive part (3) and a molded part (4), the adhesive part

(3) consists of a hot melt adhesive (A) and is connected to the molded part (4) by a flow seam.

2. Adhesive molded part according to claim 1, characterized in that the flow seam consists of several, separate seam areas.

3. Adhesive molded part according to one of claims 1 or 2, characterized ge indicates that the adhesive part (3.3) perpendicular to the flow seam has different thicknesses at different points.

4. Adhesive molded part according to one of claims 1 to 3, characterized ge indicates that it is provided as a closure unit (6/7) on a container made of paper, cardboard or polyethylene-coated paper or cardboard that the molded part at least in the Flow seam with the adhesive part consists of polyethylene or polypropylene and that the adhesive part consists of a hot melt adhesive which contains an ethylene-vinyl acetate copolymer or a polyamide as the base polymer.

5. Adhesive molded part according to one of claims 1 to 4, characterized ge indicates that between the adhesive part and molded part a plurality of cords (20.1, 20.2) which connect a plurality of at least similar, gluable molded parts.

6. Adhesive molded part according to one of claims 1 to 5, characterized ge indicates that it adheres to a strip (21) together with a plurality of at least similar, bondable molded parts, with at least part of the adhesive part (9) between Strip and molded part is angeord¬ net.

7. Manufacturing process for the adhesive molded part according to one of claims 1 to 6 by a multi-material injection molding process with at least two injection molding steps, characterized in that in one of the injection molding steps, a hot melt adhesive is cast into an adhesive part and that the parameters of the injection molding steps are such be set up so that a flow seam is formed between the adhesive part (3) and the molded part (4).

8. Manufacturing method according to claim 7, characterized in that - first the adhesive part (3) is cast, then the injection mold is changed and then the molded part (4) is cast in at least one further injection molding step.

9. Manufacturing method according to claim 7 or 8, characterized in that at least for the production of the adhesive part (2) injection molds (10, 11) or parts of injection molds coated with polytetrafluoroethylene. nickel, polytetrafluoroethylene, chrome or a rivet

Kel titanium alloy can be used.

10. Manufacturing method according to one of claims 7 to 9, characterized ge indicates that between the adhesive part and molded part almost endless cords (20.1, 20.2) are introduced.

11. Manufacturing method according to one of claims 7 to 9, characterized in that the adhesive part is poured onto a quasi endless strip (21).