PROCESS FOR MAKING A BOTTLE OF A POLYMERIC MATERIAL

Abstract

A process for making a bottle of a polymeric material suitable for being used with carbonated drinks, comprising the steps of: positioning a preform in a mould; and blowing the preform. The process is characterized in that a total draw ratio greater than 16 is used.

Claims

1. A process for making a bottle in a polymeric material suitable for being used with carbonated drinks, comprising the steps of: a) positioning a preform in a mould; b) blowing of the preform to form a bottle with a non-petaloid bottom convex towards the outside, characterized in that in step b) a total draw ratio greater than 15 or greater than 16 is applied.

2. The process according to claim 1, characterized in that the total draw ratio is comprised between 16 and 23.

3. The process according to claim 1, characterized in that the intrinsic viscosity is comprised between 0.78 and 0.84 dL/g.

4. The process according to claim 1, characterized in that the temperature of the preform provided for the blowing is comprised between 90 C. and 115 C.

5. The process according to claim 1, characterized in that the blowing pressure is comprised between 2 and 15 bar.

6. The process according to claim 5, characterized in that the blowing pressure is lower than 10 bar.

7. The process according to claim 1, characterized in that the obtained bottle has a bottom consisting of a substantially hemispherical surface.

8. The process according to claim 1, wherein the axial draw ratio is comprised between 3.5 and 4.5 and the radial draw ratio is comprised between 4 and 5.5.

9. The process according to claim 1, wherein the ratio between the thickness of the preform and that of the bottom of the bottle which will be obtained therefrom, in the sprue area, is comprised between 8 and 14.

10. A bottle in a polymeric material having a non-petaloid bottom convex towards the outside, characterized by having: average bottom thickness comprised between 0.1 and 0.4 mm; ratio between the average thickness of the bottle bottom and the average thickness of the bottle body R.sub.bottom/body comprised between 0.5 and 2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 shows a lateral sectional view of a typical thermoplastic preform usable for blowing bottles;

[0038] FIG. 2 shows a lateral sectional view of a traditional bottle with petaloid bottom obtainable from the preform in FIG. 1;

[0039] FIG. 3 shows a lateral sectional view of a bottle with convex bottom obtainable from the preform in FIG. 1 by the process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0040] In particular, a process has been devised for making a bottle of a polymeric material suitable for being used with carbonated drinks, comprising the steps of:

[0041] a) positioning a preform in a mold;

[0042] b) blowing of the preform to form a bottle with a non-petaloid bottom convex towards the outside,

[0043] characterized in that in step b) a total draw ratio greater than 15 is applied.

[0044] The advantages and the features of the present invention will appear clearly from the following detailed description of some embodiment examples, made by way of non-limiting explanation.

[0045] The process for making a bottle of a polymeric material suitable for being used with carbonated drinks, according to the present invention, therefore comprises the steps of:

[0046] a) positioning a preform in a mold; and

[0047] b) blowing of the preform to form a bottle with a non-petaloid bottom convex towards the outside.

[0048] Step (b) is carried out by means of a blowing gas. In certain embodiments, the blowing gas has a pressure not greater than 15 bar, or lower than 10 bar. In other embodiments, if logos or parts of the bottle with different embossments or debossments are required, the blowing pressure can be increased.

[0049] The process is characterized in that a total draw ratio greater than 15, preferably greater than 16 is used.

[0050] More preferably, the total draw ratio is from 16 to 23.

[0051] Moreover, it has been seen that it is particularly advantageous to use an axial draw ratio from 3.5 to 4.5 with a radial draw ratio from 4 to 5.5.

[0052] According to a possible embodiment, the intrinsic viscosity can be from 0.78 to 0.84 Dl/g, preferably about 0.8 Ng.

[0053] The intrinsic viscosity is determined according to the ASTM D4603 and ISO 1628-5 standards. This determination is carried out with a capillary viscometer, e.g. Ubbelohde Type 1B, and provides for the dissolution of the polymer in a suitable solvent (60% phenol/40% tetrachloroethane) at a concentration of about 0.5 g/Dl and at a constant temperature of about 30.00.1 C., until the thermal equilibrium is achieved. The solution is passed in the capillary viscometer and the flow time is recorded.

[0054] The temperature of the preform prepared for blowing may be from 90 C. to 115 C.

[0055] In a possible embodiment of the present invention, the mold may be preheated.

[0056] In one embodiment of the present invention, the mold used in the process of the present invention is adapted to obtain a bottle with a bottom consisting of a substantially hemispherical surface.

[0057] With the process features just described, a blowing pressure from 2 to 15 bar and preferably lower than 10 bar may be used.

[0058] In order to obtain a bottle with a bottom convex towards the outside, in particular a bottle with a hemispheric bottom, it is also important to use a preform with predefined features specially designed for this purpose.

[0059] In particular, the ratio of the thickness of the preform to that of the bottom of the bottle which will be obtained therefrom, in the sprue area, is from 8 to 14. It will be useful to note herein that, for traditional bottles, this ratio is from 1.5 to 3.

[0060] By applying a total draw ratio greater than 15, preferably than 16, to a preform so designed, a bottle can be obtained which has the required tensile strength of the bottom, reduced stress cracking, higher bursting strength in case of overpressure and so on.

[0061] The bottle obtained with this process has a high uniformity of thicknesses of the bottom, as shown in FIG. 3, where a slight thickening is visible only at the area of the sprue. In contrast, the traditional bottle with petaloid bottom, shown in FIG. 2, obtained starting from a same preform (FIG. 1) has a remarkable variability of thickness, which results in the disadvantageous properties listed above.

[0062] In particular, the convex bottom of the bottle according to the invention will be preferably characterized by average thicknesses from 0.1 to 0.4 mm, while in a bottle with hemispheric bottom of the traditional type, with the same weight of 18 g, the thickness of the bottom normally ranges from 0.18 to 2.5 mm.

[0063] The high homogeneity of thicknesses in the bottom area allows the bottle according to the invention to maximize the mechanical features, avoiding over-draw areas or accumulation of material. Also gas impermeability is improved, due to the absence of over-drawn areas.

[0064] A further feature of the bottle of the invention which testifies to the high homogeneity of thicknesses obtainable with the process described above is the ratio of the average thickness of the bottle bottom to the average thickness of the bottle body. This parameter (R.sub.bottom/body) is preferably from 0.5 to 2. Conversely, in a traditional bottle with a hemispheric bottom, such R.sub.bottom/body is from 7 to 12.

[0065] This advantageous feature of the bottle according to the present invention allows to reduce the material used, thus the cost of the bottle, whilst improving its mechanical and physical performance.

[0066] The bottle according to the invention is further characterized by a greater bursting strength than traditional bottles of equal weight. The greater the drawing, the better the mechanical properties of the bi-oriented PET film and therefore the greater the bursting strength.

[0067] With the draw ratios shown above, very high bi-orientation values can be obtained throughout the resulting bottle. High bi-orientation values allow to obtain high mechanical features, while maintaining the ability to retain carbon dioxide inside the bottle. This is because the greater levels of bi-orientation allow to reduce the expansion of the bottle under pressure and allow to increase the crystallinity values of the bi-oriented film and thus the barrier to CO.sub.2.

[0068] If a bottle with traditional petaloid base were produced with total draw ratio values from 17 to 23 using polymers with intrinsic viscosity from 0.78 to 0.84 Dl/g, a bottle with extremely uneven thicknesses and difficulty to form the bottom would be obtained.

[0069] In bottles with traditional bottom, be it spherical or petaloid, total draw ratios from 8 to 14 are in fact obtained, with the same weight of the preform and intrinsic viscosity.

[0070] The process of the present invention allows a simpler design of the preform and the container, since the complexities of the petaloid bottoms are eliminated.

[0071] In addition, a reduced complexity of the process is ensured, eliminating the structural complexity due for example to the use of high pressures.

[0072] Although bottles with a round bottom were made in the past, they were not made with a total draw ratio like that of the present invention, since there was no need to reduce the weights of the material used for the preform.

[0073] The bottles obtained according to the present invention have also shown a remarkable thermal stability. In particular, in a thermal stability test (24 hours at 38 C. with 4.2 GV) on samples of the bottle of the invention, the following values were obtained: [0074] Average height percent variation [0075] Average value 1% [0076] Minimum value 0.88% [0077] Maximum value 1.1% [0078] Percentage variation of the average shoulder diameter [0079] Average value 2.63% [0080] Minimum value 2.45% [0081] Maximum value 2.85%.

[0082] It is noted that the normally accepted percentage variation of the dimensions is from 2.5% to 3.5%.

[0083] The advantages attainable using draw ratios like those shown above primarily relate to the mechanical features of the bottom which can be obtained, due to the maximum bi-orientation values which can be obtained at the bottom of the bottle.

[0084] Moreover, the bursting strength is maximized and it is therefore possible to use polymers with lower features in terms, for example, of intrinsic viscosity.

[0085] A further advantage with respect to the petaloid bottom is the elimination of the transition areas between drawn amorphous area and non-drawn amorphous area, and as a result of the areas where the phenomenon of stress cracking, breakage by bursting during the filling and/or storage step or extroversion of the bottom could occur.

[0086] In fact, in the gate area, i.e. in the central area of the bottom of the bottle, in bottles with petaloid, the thickness is reduced by about one third with respect to the thickness in the corresponding point of the preform, and sometimes the thickness of the bottle at that point is almost the same as that of the preform due to process limits of the plant or due to an unsuitable design of the preform or bottle, in particular of the bottom. In the bottle obtained with the present invention, the thickness is reduced at least seven times, but it is possible to reach even values of twenty, ensuring highly satisfactory mechanical features.

[0087] Moreover, an advantage is also obtained with respect to traditional bottles with round bottom, because using such high total draw ratios, the accumulation of material around the gate, i.e. around the central part of the bottom of the bottle is eliminated.

[0088] Although the bottle according to the invention requires the use of a base for keeping it in a vertical position, the additional cost of such a base is substantially low, a particular material and processing not being required, and it is greatly outweighed by the advantage of cost and performance obtained according to the invention.

[0089] Those skilled in the art may make several changes to the embodiments described above and/or replace the elements described with equivalents in order to meet specific needs, without departing from the scope of the appended claims.