The present invention relates to a preform suitable for being used in the production of bottles made of polymeric material.

In particular, the present invention relates, albeit not exclusively, to preforms made of PET (polyethylene terephthalate). The principles of the present invention may, however, be advantageously applied also to preforms made of other types of materials such as PLA (polylactate), OPP (oriented polypropylene), PEN (polyethylene naphthalate), etc.

It is known to produce a bottle of polymeric material using a preform obtained by means of injection-moulding inside a first injection mould. The preform generally has a cylindrical form and has an open end (mouth) which has the dimensions and the definitive form of the neck of the bottle.

Then the preform is heated and introduced into a second mould in order to undergo in succession stretching and blowing steps.

During the stretching step the preform is stretched longitudinally by means of the introduction through the mouth of a stretching rod, while during the blowing step pressurised air is introduced inside the stretched preform so as to cause the polymeric material to adhere to the walls of the blowing mould.

The dimensions and the weight of the preform have a direct influence on the final characteristics of the bottle since thicknesses and lengths which are not suitably defined may give rise to bottles which have non-uniform or insufficient distribution of polymeric material.

Recently, in the international beverages market and in particular mineral water market, the format of 5-litres bottle is assuming increasingly greater importance.

5-litres bottles in fact, in certain countries, already represent a not insignificant percentage of the bottles sold, owing to an advantageous price/litre product ratio.

It must be emphasized how, with reference to the final liquid container, usually comprising, in addition to the bottle, a handle, a cap and a label, the bottle per se represents the most expensive item.

The cost of the bottle is directly associated with its weight and, consequently, the quantity of polymeric material used for the manufacture thereof.

In standard international production 5-litres bottles have a size which is dependent upon palletization or the existing filling lines, with a bottle neck having a nominal diameter of 48 mm and an empty weight which is usually greater than 75 grammes.

Recently, in order to reduce the weights and the associated costs of the bottles, bottles which have a bottle neck with a nominal diameter of 38 mm have been introduced, this type of neck being already used in the beverages or milk sector. However, in the light of that indicated above, the variation in the dimensions of the bottle neck, and consequently the variation in the dimensions of the initial preform, has given rise to problems during the preform blowing and stretching steps.

The reduction in the diameter of the neck of the preform from the initial 48 mm to 38 mm was in fact initially accompanied, in order to optimize the process for moulding thereof, by a proportional reduction in the diameters of the known preforms. The various diameters were, in other words, substantially reduced compared to the preforms used previously.

However, using preforms with smaller diameters, for the same bottle design, has increased the radial stretching ratios and this results, at the end of the blowing step, in qualitative defects along the profile of the finished bottle, with a consequent deterioration in the mechanical characteristics of the bottle itself.

The object of the present invention is therefore to solve the drawbacks of the prior art, providing a preform of reduced weight which can be used to obtain a 5-litres bottle having a neck with a nominal neck diameter of 38 mm able to ensure a superior mechanical performance.

A second task of the present invention is to provide a preform for a 5-litres bottle with a nominal neck diameter of 38 mm, which allows 5-litres bottles to be produced easily by means of normal blow-moulding.

A further task of the present invention is to provide a preform for a 5-litres bottle with a nominal neck diameter of 38 mm, which allows to be achieved a significant reduction in the cost of the final bottle.

The object and the tasks are achieved with a preform according to claim 1.

The characteristic features and advantages of a preform provided in accordance with the principles of the invention will emerge more clearly from the description below of a number of examples of embodiment provided by way of a non-limiting example with reference to the accompanying drawings in which:

Figure 1 shows a perspective view of a known 5-litres bottle with a bottle neck of 48 mm;

Figure 2 shows a side view of the bottle according to Figure 1 ;

Figure 3 shows a perspective view of a 5-litres bottle with a 38 mm bottle neck made using a preform according to the present invention;

Figure 4 shows a side view of the bottle according to Figure 3;

Figure 5 shows a cross-sectional view of a preform according to the invention;

Figure 6 shows a cross-sectional view, similar to that of Figure 5, of a second embodiment of the preform according to the invention.

The bottles shown in Figures 1-4 have a body with a rectangular cross-section, but may also have a round or square cross-section.

Figures 1 and 2 show a known bottle 1A with a capacity of 5 litres and a bottle neck with a nominal diameter B of about 48 mm. This bottle 1A is made from a preform of polymeric material.

Figures 3 and 4 show a bottle 1 suitable for containing about 5 litres of liquid and with a bottle neck 2 having a nominal diameter C of about 38 mm. Said bottle 1 is made from a preform 10 of polymeric material according to the invention (shown in Figures 5 and 6).

The reference numbers 4, 6 and 8 indicate, respectively, the shoulder part, the body and the base of the bottle.

With reference to Figures 3 and 4, "longitudinal axis 3 of the bottle 1 " refers to the axis which substantially coincides with the direction of extension of the bottle 1, whereby the direction of extension of the bottle is understood as meaning the direction which joins the mouth 5 to the base of the bottle. In a similar manner, "transverse plane of the bottle 1" refers to any plane perpendicular to the longitudinal axis thereof.

"Radial direction of the bottle" will be used to indicate any direction which lies in a transverse plane and which intersects the longitudinal axis thereof.

Figures 5 and 6 show a preform 10 of polymeric material according to the invention.

Preferably, the preform is made of PET (polyethylene terephthalate). The principles of the following invention may, however, be advantageously applied also to preforms made of other types of polymeric material such as PLA (polylactate), OPP (oriented polypropylene), PEN (polyethylene naphthalate), etc.

The preform 10, in a known manner, comprises four elements: preform neck 12, preform transition zone 14, preform body 16 and preform base 18.

The zone of the preform 10 substantially comprised between its open end 11 and the plane 13 of the collar is defined as the neck 12 of the preform 10. The neck 12 of the preform 10 is characterized in that it has the same form and the same dimensions as the neck 2 of the final bottle 1.

"Transition zone 14 of the preform 10" refers to the zone of the preform 10 designed to obtain, once moulding has been completed, part of the shoulder 4 of the bottle 1.

The transition zone 14 of the preform has a tapered form determined essentially by a variation in thickness. The thicknesses of the transition zone 14 of the preform 10 in fact increase gradually with an increase in the distance calculated along the longitudinal direction, from the plane 13 of the collar.

The preform 10 also comprises a body 16 and a base 18 which are ideally separated by a transverse plane 17 defined below as being the plane of attachment of the base of the preform.

With reference again to Figures 5 and 6, said preform 10 may be characterized by means of the following dimensional parameters:

A: inner diameter of the neck 12 of the preform 10; H: distance between the plane 13 of the collar of the preform 10 and a plane transverse to the longitudinal axis 21 of the preform 10 passing through the point of the transition zone 14 of the preform 10 having maximum thickness; said point generally forms part of the transverse plane

15 which separates ideally the transition zone 14 of the preform 10 from the body portion 16 of the preform;

G: distance between the plane 13 of the collar of the preform 10 and the plane 17 of attachment of the base of the preform 10;

E: generic intermediate thickness of the cross-section of the preform in the body portion

16 of the preform.

Studies carried out by the Applicant have shown that the dimensional parameters H, G, E may be advantageously defined separately, during the design stage, once the inner diameter A of the neck 12 of the preform 10 has been set.

In a particular manner - this forming the subject of the present invention - analyses carried out by the Applicant have shown how it is possible to define ratios of proportionality between said dimensional parameters H, G, E and the inner diameter A of the neck 12 of the preform 10.

In detail, it was observed that, if the proportionality ratio between said dimensional parameters H, G, E and the inner diameter A of the neck 12 of the preform 10 is kept within given values, it is possible to obtain a preform 10 having a lower weight than the known preforms, without however adversely affecting the mechanical characteristics thereof.

An effective reduction in the weight of the preform 10 may be obtained, in accordance with the invention, by concentrating the variation in the thicknesses and dimensions of the preform in specific zones of its profile. Moreover, it has been shown by the Applicant how it is not necessary for the thicknesses and the dimensions of these specific zones of the profile of the preform to be varied proportionately all by the same value.

In detail, the Applicant has determined that the following numerical coefficients of proportionality exist between the value of the inner diameter A of the neck 12 of the preform 10 and the dimensional parameters H, G and E defined above:

δ: first coefficient of proportionality equal to H/A;

φ: second coefficient of proportionality equal to G/A; and

a: third coefficient of proportionality equal to A/E.

The preform 10 according to the present invention is characterized in that, once the value of the inner diameter A of the neck 12 of the preform 10 has been fixed within a range comprised between 31.8 mm and 34 mm (limit values included) so as to obtain a neck 12 of the preform 10, and consequently a neck 2 of the bottle 1, compatible with the caps of 38 mm diameter currently present on the market, the first, second and third coefficient of proportionality are comprised in the following ranges (limit values included): 0.4 < δ < 0.9;

2.9 < φ < 3.7;

8 < α < 11.

With these values of the first, second and third coefficient of proportionality it is possible to obtain bottles with a lower weight and a correct distribution of the weights and the thicknesses as well as optimum mechanical characteristics. There is no longer the risk that, following the subsequent processing stages, the bottles obtained from this type of preform may have anomalous shrinkage zones or other defects.

With specific reference to a preform made of PET, the Applicant has found that a preform 10 of PET, in which the dimensional parameters H, G and E fall within the aforementioned proportionality ratios with the inner diameter A, has a weight not greater than 68 grammes, while the known preforms used to obtain bottles with a capacity of 5 litres and neck diameter B of 48 mm weigh not less than 75 grammes. Therefore, with the preform 10 according to the present invention, it is possible to obtain in a novel and innovative manner, a considerable saving in material, with a consequent significant reduction in the production costs, without adversely affecting in any way the mechanical strength characteristics required for the final bottle.

Further reductions in the weight of the preform 10 according to the invention may be obtained, subject to the conditions stated above, by adjusting in a suitable manner other dimensional parameters of the preform 10.

In a particular manner, studies carried out by the Applicant have shown how there exists a relation of proportionality also between the inner diameter A of the preform 10 and the maximum outer diameter I of the preform 10.

In detail a fourth numerical coefficient of proportionality Θ equal to I/A may in fact be advantageously defined.

In a particular manner, studies carried out by the Applicant have shown how, in order to obtain preforms with optimum mechanical strength characteristics together with an optimum weight, the fourth coefficient of proportionality Θ must be preferably comprised between 1.08 and 1.3 (limit values included).

With reference to the embodiment in Figure 5, in which a preform 10 having a neck with a standard geometry is shown, the fourth coefficient of proportionality Θ may be preferably comprised between 1.15 and 1.3 (limit values included).

With reference to the embodiment in Figure 6, which shows a preform 10 having a neck with a "Swerve shape" geometry, i.e. neck reinforced in the zone of the plane 13 of the collar and forming the subject of Italian patent 1392541 filed in the name of the same Applicant, the fourth coefficient of proportionality Θ may be preferably comprised between 1.08 and 1.15 (limit values included). Studies carried out by the Applicant have also shown that there exists a coefficient of proportionality between the value of the generic intermediate thickness E of the cross-section of the body portion 16 of the preform 10 and the value of the thickness D of the cross-section of the preform 10, at the transverse plane 15 which separates ideally the transition zone 14 from the body portion 16 of the preform 10. In particular, the Applicant has determined that the value of the thickness D is equal to the value of the generic intermediate thickness E multiplied by a fifth numerical coefficient of proportionality 1 +λ. In order to obtain bottles with a lower weight and an optimum distribution of the weights and thicknesses, the value λ is preferably comprised between - 0.1 and 0.5 (limit values included).

Moreover, studies carried out by the Applicant have also shown that a further dimensional parameter of the preform 10, i.e. the thickness F of the cross-section of the preform 10 at the plane of attachment 17 of the base may be advantageously determined in function of the value defined for the generic intermediate thickness E of the cross-section of the body portion 16 of the preform 10. In fact, the value of the thickness F may be advantageously determined by multiplying the value of the thickness E by a sixth numerical coefficient of proportionality l +σ. In particular, studies carried out by the Applicant have shown that, in order to obtain bottles with a lower weight or optimum mechanical strength characteristics it is preferable that the value σ should be comprised between -0.1 and 0.5 (limit values included).

Finally, the Applicant has determined that a further dimensional parameter, i.e. the thickness d' of the cross-section of the preform 10 at a generic point located at a distance h' from the plane 13 of the collar and lying between the plane 13 of the annular lip and the transverse plane 15, may be advantageously expressed in function of the thickness D. In particular, the thickness d' is equal to the thickness D multiplied by a seventh numerical coefficient of proportionality γ.

Preferably, in order to obtain bottles with a lower weight and an optimum distribution of the material, the seventh coefficient of proportionality varies between 0.35 and 1 (bottom limit included).

Studies carried out by the Applicant have shown how, by defining the fourth coefficient of proportionality (Θ), the fifth coefficient of proportionality (l +λ), the sixth coefficient of proportionality (1 +σ) and the seventh coefficient of proportionality (γ) within the value ranges indicated above, it is possible to obtain preforms 10 with a weight of about 62-66 grammes, with a further reduction in weight and costs compared to that indicated above.

Two tables summarising the parameters and values indicated above are shown below, Table 1 refers to the preform shown in Figure 5 (standard neck), while Table 2 refers to the preform shown in Figure 6 (neck with "Swerve shape" geometry). Table 1 : Geometric characteristics for preform with standard neck (Figure 5)

Table 2: Geometric characteristics for preform with "Swerve shape" neck (Figure 6)

It should be noted how advantageously the profile and the dimensions of the preform 10 according to the invention are independent of the design of the base 18 of the preform 10. Therefore the preform 10 according to the present invention may be advantageously provided with a traditional base of the spherical type or an ogival base.

Similarly, the preform 10 according to the present invention may advantageously be provided with a conical base or with a flat base.

It must also be emphasized how the innovative preform 10 according to the present invention has a profile and dimensions such as not to hinder injection-moulding of the said preform. Moreover, it must be pointed out how the innovative profile of the preform 10 according to the invention does not affect the structure of the mould in which the stretching and blowing operations are performed, so that the reduction in the costs of production of the 5-litres bottles with a neck diameter C equal to 38 mm, associated with the reduction in weight of the preforms, is achieved without an increase in the equipment and processing costs.

To conclude, the preform 10 according to the invention has a weight which is surprisingly lower and mechanical performance characteristics at least the same as those of the preforms described with reference to the prior art.

With regard to the embodiments of the preform 10, the person skilled in the art may, in order to satisfy specific requirements, make modifications to and/or replace elements described with equivalent elements, without thereby departing from the scope of the accompanying claims.