METHOD FOR PRODUCING MULTI-LAYERED ARTICLES IN AN INJECTION-MOULDING PROCESS

Abstract

An injection-molding process for injecting a shoe soling including at least two adjacent injection-molding layers onto a shoe upper drawn over a shoe last, uses a mold cavity including a frame, the cavity being covered at the top by the upper also serving as a mold cover, with plastic material being injected into the cavity below the upper. To produce two adjacent injection-molding layers of plastic materials having different properties and reaction times in one operation, i.e. without needing an interim mold opening, before covering the cavity a film is clamped over it by a clamp mounted on the frame. When filling the cavity, the space below the film is first filled with plastic material to produce the first injection-molding layer and then, to produce the adjacent second injection-molding layer, the space above the film is filled with plastic material. Plastic materials are used that inseparably attach to the film.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to an injection molding process for injecting a shoe soling comprising at least two adjacent injection molding layers onto a shoe upper drawn over a shoe last, using a mold cavity comprising a frame, said cavity being covered at the top end by the shoe upper also serving as a mold cover, with plastic material being injected into the mold cavity below the shoe upper.

Description of the Related Art

An injection molding process of this type has been disclosed via EP 2 103 420 A2, for example. By means of this known method, the shoe upper used as a mold cover for the mold cavity has been provided in a preceding injection molding process with an injection molding layer serving as sole of the shoe upper, with an outsole having been inserted into the mold cavity, resulting in a three-layer shoe soling consisting of outsole, midsole and upper sole. However, at least two injection molding steps with an intermediate mold opening are required to produce this three-layer shoe soling.

For the manufacturer of shoes or shoe soling, optimized cycle times of the machines and injection equipment are of prime importance to achieve the largest possible number of items to be produced. However, if, to attain the desired physical or optical properties such as the strength or color of the material, for example, a shoe soling of two adjoining injection molding layers has to be produced, each injection molding layer increases the cycle time many times over because of the material used and the chemical reaction times that have to be observed between the individual injection processes in order to manufacture a shoe or shoe soling of good quality.

SUMMARY OF THE INVENTION

It is thus the objective of the present invention to further develop the injection molding method of the kind first mentioned above, in such a way that two adjacent injection molding layers of the shoe soling can be produced in a single operation, i.e. without an interim mold opening being required, from plastic materials having different properties and reaction times.

In order to achieve this objective, the invention proposed, based on the injection molding process of the kind first mentioned above, that prior to covering the mold cavity a film be clamped over the mold cavity by means of a clamping device mounted on the frame of the mold cavity and that, when filling the mold cavity, the space below the film is first filled with plastic material to produce the first injection molding layer and then, for the production of the adjacent second injection molding layer, the space above the film is filled with plastic material, wherein plastic materials being used that inseparably attach to the film.

In the method proposed by the invention, the film separates the adjacent molding layers during curing, resulting in the different reaction times of the plastic materials used to be irrelevant. On the other hand, the film connects the two adjacent injection molding layers inseparably with each other. As a result, the invention makes it possible to produce two adjacent injection molding layers, i.e. in the case of the embodiment example elucidated below, the midsole and the upper sole of a multilayer shoe soling can be produced in one operation, i.e. without having the mold to be opened intermittently.

Moreover, the invention also provides the use of a flow aid underneath the mold cover to keep the space for the production of the second injection molding layer open. During operation, this flow aid keeps the space above the film open, which is required for the production of the second injection molding layer, until this space is to be filled to produce the second injection molding layer.

Alternatively, for the creation of such a space and before filling the mold cavity, the invention provides that the mold cover is immersed by a short stroke into the mold cavity thereby tensioning the film downwards, following which the plastic material of the first injection molding layer is injected and attaches to the film, and afterwards by lifting the mold cover to its normal position, the space for injecting the plastic material of the adjacent second injection molding layer above the film is cleared.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is elucidated in sufficient detail by way of the following figures, where

FIG. 1: is a longitudinal section of an injection mold on which a clamping device is mounted;

FIG. 2: is a cross-sectional view of an injection mold with mounted clamping device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an injection mold with a frame 1 consisting of two lateral mold segments, which are moved against each other to form a mold cavity, and a base die 2. The figure shows a three-layer buildup of a shoe soling, consisting of an outsole 3 with an activated surface previously placed into the mold cavity, a midsole 4 (first injection molding layer) and an upper sole 5 (second injection molding layer). A clamping device 7 is placed on the frame 1, holding a film 6 which is spanned above the mold cavity. The plastic material of the midsole 4 (first injection molding layer) is injected into the mold cavity via a lower injection duct 10 above the outsole 3 and below the film 6. The plastic material of the upper sole 5 (second injection molding layer) is injected into the mold cavity via an upper injection duct 9 above film 6 and below a mold cover 8, which is formed by a shoe upper 11 mounted on a last.

In FIG. 2 it is illustrated how the mold cover 8 carries out a short downward stroke in such a way that it is in lowered position between the lateral mold segments of frame 1 with clamping device 7 fitted. This causes the last 8 (i.e. the mold cover) covered with the shoe upper 11 to push down the film 6 to a slight extent. When the plastic material of the midsole 4 (first injection molding layer) is injected between the film 6 and the outsole 3, said film 6 adheres to the plastic material of midsole 4 (first injection molding layer), so that after raising the mold cover 8 by the amount of the short stroke into its initial position, space 12 is created between the mold cover 8 and film 6. The plastic material forming the upper sole 5 (second injection molding layer) is injected into the space 12 thus created above the film 6, said plastic material produces the bond between film 6 and the mold cover 8 (i.e. the shoe upper 11 drawn over the last).

Claims

1. Injection molding method for injecting a shoe soling comprising at least two adjacent injection molding layers onto a shoe upper drawn over a shoe last, using a mold cavity comprising a frame (1), said cavity being covered at the top end by the shoe upper also serving as a mold cover, wherein plastic material is injected into the mold cavity below the shoe upper,wherein prior to covering the mold cavity a film (6) is clamped over the mold cavity by a clamping device mounted on the frame of the mold cavity,wherein, when filling the mold cavity, the space below the film is first filled with plastic material to produce the first injection molding layer (4) and then, for the production of the adjacent second injection molding layer (5), the space above the film is filled with plastic material,wherein plastic materials are used that inseparably attach to the film.

2-4. (canceled)

5. Injection molding method according to claim 1, wherein a space for the production of the second injection molding layer (5) is kept open by means of a flow aid arranged underneath the mold cover (8) and above the film (6).

6. Injection molding method according to claim 1, wherein, before filling the mold cavity, the mold cover (8) is immersed by a short stroke into the mold cavity thereby tensioning the film (6) downwards, following which the plastic material of the first injection molding layer (4) is injected and attaches to the film (6), and afterwards by raising the mold cover to its normal position, a space (12) is created above the film (6) for injecting the plastic material of the adjacent second injection molding layer (5).

7-15. (canceled)