HK1137385B - Improved plastic preform - Google Patents

Description

Improved plastic preform

Technical Field

The present invention relates to an improved preform for the manufacture of hollow bodies, in particular bottles of any kind and size, by a blow-moulding process.

Background

As is well known to those skilled in the art, the manufacture of bottles or cans of plastic material is currently almost exclusively carried out by a 2-step process, which 2-step process comprises the manufacture and use of hollow, semi-shaped products, precisely preforms or parisons, having a substantially cylindrical shape. The manufacture of the hollow preform of the first step of the process is carried out in a highly concentrated manner by a few specialist manufacturers, said preform having a greater thickness and an aspect ratio of about 1: 2 to 1: 4 with respect to the finally shaped bottle. In the second step of the process, which is not normally carried out in the same factory as the liquid-filled package, the hollow preform is introduced into a mold, heated to a temperature sufficient to accomplish the desired softening, stretched to the final length of the bottle by introducing a stretch rod into the preform, and thus blow-molded in the heated and stretched preform by introducing one or more streams of compressed air.

This manufacturing system allows significant and numerous advantages to be present in the entire manufacturing chain, which are well known to the skilled person and therefore do not have to be reiterated here, which advantages, as mentioned previously, result in the almost global adoption of this manufacturing system in order to obtain hollow bodies, in particular bottles of any type, shape and size.

In particular, it was found that the above-described process is particularly suitable for application to transparent plastic materials, such as PET (polyethylene terephthalate), which, during the blow-moulding process, undergo such an orientation of the crystalline structure to give the bottle particular safe mechanical properties, even if the material has particularly small final thickness values.

Precisely, for such bottles, the search is constantly being made for optimum manufacturing methods aimed at reducing the quantity of plastic material, the final bottle volume being constant, and therefore the final cost of the bottle. The main aim of this search up to now consists on the one hand in the shape change of the finished bottle (in order to produce better shape stability) and on the other hand in the adjustment of the different moulding parameters (stretch ratio of the preform, heating temperature, blowing air pressure, etc.).

The shape of the preform, which remains substantially unchanged for many years, is formed as described above by a hollow cylinder, with constant or variable thickness, the open end of which is already the final shape of the neck region, thus also providing the necessary thread for connection with the screw cap, and the closed end of which is in most cases hemispherical.

In order to reduce the amount of plastic material that remains in the central area of the bottom of the finished bottle and is therefore not used directly, preforms with non-spherical heads, in particular heads with conical, elliptical or parabolic shape, have been proposed and are used in part. However, while this type of preform has in fact some advantages during the preform shaping, due to the increased streamlines of the flow path of the molten plastic material, there is also a modest reduction in the shaping time (which is in fact injected at the vertex of the respective preform closed end), and since the material distribution of the finished bottle does not finally behave significantly differently from that obtained with preforms having a hemispherical head, no appreciable result is obtained in terms of reduction in the preform weight.

Disclosure of Invention

The object of the present invention is therefore to provide an improved preform which results in bottles having the same dimensions and mechanical characteristics, but with a significantly reduced weight compared to the known types of preforms currently used.

Another object of the present invention is to provide an improved preform by means of which it is possible to concentrate the reduction in weight of the bottle in the central area of the respective bottom.

According to the invention, an injection-moulded preform of plastic material for the manufacture of a hollow body by a blow-moulding process, wherein the preform comprises a substantially cylindrical central body having an open end and a closed end, characterized in that the closed end has a hollow appendage projecting towards the outside of the preform in its central region, the closed end adjacent to the central appendage having a spherical, conical, elliptical or parabolic shape.

According to the invention, the hollow body is a bottle or a can and the open end forms the base of the neck and the cap of the finished bottle or can.

According to the invention, said appendage extends radially with respect to the adjacent portion of said closed end of the preform.

According to the invention, the central appendage has an internal shape at least sufficient to house the free end of the stretch rod of the preform.

Drawings

The figures show a schematic side view of an improved cylindrical preform according to the present invention.

Detailed Description

Further structures and advantages of the present invention will become more apparent in the ensuing description of the preferred embodiments and the accompanying drawings, which show a schematic side view of an improved cylindrical preform according to the present invention.

As clearly seen in the figures, the preform 1 according to the invention has a completely conventional structure due to the shape of the open end 2, to the known manner of having a screw cap and ribs for receiving and abutting the bottle, and to the elongated cylindrical shape of the body 3 of the preform.

In fact, the innovation of the preform of the invention relies entirely on the shape of the closed end or head 4 of the preform, whose corresponding central zone forms an axial appendage 5 adapted to extend radially with the remaining side of the head 4. The remaining side of the head 4 may have any of the known shapes described above and preferably has a hemispherical shape.

The shape of the appendage 5 and its dimensions are not particularly limited, since the internal diameter of such an appendage at the beginning of the moulding step need only be large enough to be able to accommodate the tip portion of the stretch rod of the preform located therein (not shown). In this embodiment, the illustrated appendage 5 also has a hemispherical shape with a radius R, and preferably, the appendage 5 extends radially from the side of the closed end 4 by means of an outwardly curved concave surface with the same radius R.

The radius R of the appendix 5 and its overall height h, with respect to the tangential plane of the top end of the theoretically perfectly hemispherical head (represented in the figure by a dotted line), determine the conformation of the preform of the invention. Minimum value of R, R ═ R_{Minimum size}Corresponding to the internal diameter of appendix 5, as described above, so as to be suitable for allowing the introduction of a tight fit of the preform stretch rod; maximum value of R, R ═ R_{Maximum of}Corresponding to D/2, where D is the diameter of the cylindrical central region 3 of the preform. The total height H of the preforms is equal, where R ═ R_{Minimum size}The effect of weight reduction of the preform is greatest, but when R ═ R_{Maximum of}The effect is minimal or, more exactly, zero, i.e. the effect of the weight reduction of the preform is minimal or, more exactly, zero when the shape of the head of the preform of the invention matches the shape of a conventional mould.

The height H of the appendage 5 is similarly observed, since it is clear that-again the overall height H of the preform is the same, starting from the value hmin-0, the higher the height H the most the reduction in weight of the preform, wherein the preform of the invention has the shape of the head 4 of a perfectly hemispherical head so as to match a conventional mould.

Within the above-mentioned variable limits, the size and shape of the appendix 5 can be varied at will according to the desired result, for example in order to concentrate the weight loss of the preform in correspondence of the central zone of the bottom of the bottle formed by the same, or for other purposes which can sometimes become useful or to facilitate different, individual uses.

Due to the specific shape of the preform of the invention described above, a particular effect is obtained of a preform having a lower weight than a preform of the known type having the same thickness and height, due to the fact that the overall surface of the preform of the invention has a significantly smaller extension than a corresponding, conventional preform having a perfectly hemispherical head and an equivalent height. A reduction of 3-5% by weight of the preform can thus be achieved and, moreover, this remarkable result is achieved without any change in other characteristics of the preform, in particular the same axial elongation. The stretching rod may have its terminal end modified so as to adapt to the internal shape of the appendage 5, be able to be inserted in the appendage 5 and determine the elongation of the preform of the invention, similar to what happens in conventional preforms with hemispherical heads having the same overall height H. The stretching action is moreover more smooth and uniform, due to the fact that the appendix 5 already exhibits a certain inclination for the shape of the deformed preform.

The preform of the invention therefore replaces the conventional preform without having to carry out new criteria of the blow-moulding process, thus allowing, in a simple and straightforward manner, a significant reduction in the weight of the preform and, consequently, of the finished bottle, thus achieving the first object of the invention. By suitably adjusting the dimensional parameters of the appendix 5, it is moreover possible to concentrate the weight reduction in the central zone of the respective bottom of the bottle obtained by blow-moulding said preform, thus also achieving the second object of the invention. This aim is particularly important since it improves the mechanical resistance to impacts of the bottle, eliminating, or significantly reducing, the area of weakness which, in conventional bottles, consists of an annular band of the bottom of the bottle, with a transition zone between a peripheral zone of small thickness and a central zone of large thickness.

The present invention has been described in terms of the same preferred embodiment, but it should be understood that other embodiments using the principles of the present invention can vary from the described embodiment. Accordingly, the present invention is not limited by the features of the described embodiments, which are defined only in the appended claims.

Claims (5)

1. An injection-moulded preform (1) of plastic material for the manufacture of a hollow body by a blow-moulding process, wherein the preform (1) comprises a substantially cylindrical central body (3), the substantially cylindrical central body (3) having an open end (2) and a closed end (4), characterized in that the closed end (4) has a hollow appendage (5) projecting towards the outside of the preform (1) in its central region, the preform having the same overall height as a conventional preform without the hollow appendage, the closed end (4) adjacent to the central hollow appendage (5) having a spherical, conical, elliptical or parabolic shape.

2. The injection moulding preform according to claim 1, wherein the hollow body is a bottle or a can and the open end (2) forms the base of the neck and the cap of the finished bottle or can.

3. Injection moulded preform according to claim 1 or 2, wherein the hollow appendage (5) extends radially with respect to an adjacent portion of the closed end (4) of the preform (1).

4. The injection moulded preform of claim 1 or 2, wherein the central hollow appendage (5) has an internal shape at least sufficient to accommodate the free end of a stretch rod of the preform.

5. The injection moulded preform of claim 3, wherein the central hollow appendage (5) has an internal shape at least sufficient to accommodate the free end of the stretch rod of the preform.