Multi-layer laminated preform and method of its manufacture

Details Multi-layer laminated preform and method of its manufacture Multi-layer laminated preform and method of its manufacture

1999-01-14

2001-07-03

Silbaugh, Jan H. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Direct application of electrical or wave energy to work

Limited to treatment of surface or coated surface

C264S454000, C264S457000, C264S458000, C264S478000, C264S513000, C264S516000, C264S274000, C264S455000, C264S532000

Reexamination Certificate

active

06254820

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The invention concerns a multi-layer laminated preform and a method of its manufacture, as well as a method of manufacturing a container, and an accordingly manufactured container.
Multi-layer preforms as a start product for the manufacture of hollow containers such as bottles are known in various embodiments. Containers manufactured from preforms comprising several layers of differing materials will have different advantages. A combination of physical properties can be attained, for example, that cannot be achieved with a single material. Thus, materials with high heat resistance, for example, are combined with materials possessing good gas tightness or high mechanical loading capacity. Another possibility is the use of different layers of the same material, such as layers of recycled material and layers of virgin material.
The problem in the case of multi-layer containers concerns separation of wall layers, in other words delamination. For example, in the case of inhibiting the gas leakage or permeation between two layers of a container such as PET, if a gas barrier material is applied, then there will be a subsequent risk of separation of these layers during processing of the preform or storage of the container. In order to prevent such delamination, the layers can be joined together by means of an adhesive layer. Such as when copolymers containing maleic anhydride are used to adhere EVOH to polyolefins or polyesters. This requires a further layer, however, and will result in an unnecessary complication of the manufacturing process.
U.S. Pat. No. 4,980,100 discloses a multi-layer container with which delamination is prevented through the application of small perforations to the outer layer. These perforations, which approximately extend into the main delamination zone, permit the escape of gas that has collected between two layers of different gas permeability. In this way, delamination should be prevented. This method has the disadvantage that a further process step is required after completed manufacture of the container, in order to apply such apertures to the outer layer of the container.
SUMMARY OF THE INVENTION
The object of the invention is to avoid the disadvantages of the state of the art and to create a method for the manufacture of a multi-layer laminated container or preform that can be economically and simply carried out, wherein a delamination of the different layers of the said container is reliably prevented.
It is a further object of the invention to create a preform from which a container can be manufactured, wherein no delamination of the different layers will arise.
It is a further object of the invention to create a method of manufacturing a container and an accordingly manufactured multi-layer laminated container which can be manufactured in a simple way and wherein delamination of the different layers is reliably avoided. According to the invention, these objects are particularly fulfilled in accordance with the characteristics of the independent patent claims.
A single-layer blank is formed as a first step in a method for manufacturing a multi-layer laminated preform. For the manufacture of hollow bodies, the blank itself is preferably a hollow body and has an inner and outer surface. With the manufacturing process, however, multi-layer laminated planar blanks can also be manufactured.
The blank for the manufacture of hollow bodies is provided with protrusions on its inner and/or its outer surface.
In a subsequent working step, the blank is subjected to heating in such a way that the protrusions reach a temperature in which they assume a plasticized or melted state. Since the protrusions possess less mass in comparison to the body of the blank, on the application of heat they will be heated more rapidly than the rest of the body, and thus become plasticized or melted. The amount of heat required for melting the protrusions is less than that required for melting the entire blank.
In a further working step, the blank is covered with a layer of plasticized or liquid material such as a molten polymer on the surface that possesses the protrusions. With that, the blank will form one layer of a laminated preform, and the covering layer will form a further layer of the preform.
Because the protrusions are partially plasticized or in a softened state, and because the covering layer is likewise applied in the form of plasticized material, a connection, in the form of local weld positions in the area of the protrusions on the blank, will arise between the two layers. The two layers will become connected by means of these microweld positions. In a final process step, the multi-layer preform thus formed is cooled. In this configuration, the preform can be stored or transported, and is also suited to further processing, for example for the application of one or more further layers.
In a preferred method according to the invention, a blank in the form of a hollow body is manufactured by means of injection molding. In an initial procedural step, plasticized material is injected into a mold cavity. The core of the tool possesses a smooth surface, and the mold is gently conical in shape so that the blank can be removed from the core axially. In order to manufacture the protrusions on the outer surface of the blank, the surface of the injection molding tool forming the outer wall of the preform, is provided with irregularities, preferably with regularly arranged indentations or tectural pattern. In order to be able to remove a blank that has been injection molded in this way from the injection molding tool, the tool is opened radially and the size of the projections is small enough to avoid tool removal obstruction.
Subsequently, the blank, the protrusions of which have been previously brought to a plasticized condition, is introduced into an injection molding tool that possesses a greater inside diameter than the outside diameter of the blank. In this step, the blank assumes the role of the core of an injection molding tool. Plasticized material is injected into the cavity between the wall of the tool and the outer wall of the blank. Because the protrusions of the blank are in a softened state or will be by virtue of the heat energy of the covering layer melt and the thinness of the protrusions in a softened state connections will arise between the covering layer and the blank, in the region of the protrusions. The covering layer material will be pressed, in a plasticized state, onto the surface of the blank and will become connected with the said surface at spots or in zones. After cooling of the preform formed in this way, a multitude of microweld spots and microweld positions will arise between the two layers.
In an alternative embodiment, a blank for the manufacture of a hollow body is provided with protrusions on its inner surface. To that end, a conventional injection molding tool with a smooth casing surface is used, and a core which, on its surface, possesses regular recesses. For removal from the mold, the core of the tool must be collapsible, so that the protrusions manufactured by the injection molding process on the inner side of the blank are released from the surface of said core.
The protrusions on the inner side of the blank are, after removal of the blank from the tool, heated and plasticized.
In a subsequent procedural step, a second tool core that possesses a smaller outer diameter than the first core is introduced into the blank. Plasticized plastic is injected into the cavity formed by this second core and the inner surface of the blank. Since the protrusions of the blank and the injected inner layer are in a plasticized state, the blank will become connected to the inner layer in the region of the protrusions. The second core is removed from the preform thus formed, and the preform is cooled. After cooling, the inner layer will be connected with the blank by microweld positions in the form of spots or zones.
The manufacture of a preform that comprises more than one layer is also conceivable. Wit

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