LARGE-SIZED CONTAINER

DESCRIPTION

SCOPE OF THE INVENTION

The present invention falls within the field of apparatuses for forming large-sized blown containers starting from a preform. Said containers are made from polyethylene terephthalate, hereinafter referred to as PET, and their volume is over 10 liters.

PRIOR ART

Different methods and therefore different apparatuses are known in the art for the manufacture of large PET containers having a volume of over 10 liters, generally 20 liters or 5 gallons. These are typically containers used for beverages, generally mineral water, which have the prerogative of being able to be re-used after appropriate washing with suitable detergent solutions at temperatures of about 65 degrees.

The current technology is aimed to manufacture said large- sized containers, preferably of PET, alongside or better even replacing traditional polycarbonate containers, more briefly referred to as PC. In fact, the latter have problems due to the release of BPA, i.e. an endocrine disruptor chemical thought to be carcinogenic.

Most of large 5-gallon containers are still made of PC due to its high heat resistance and high transparency properties, both advantages which allow rotations or re-fills up to 60 times.

However, due to the above problems, many manufacturers are beginning to introduce the use of PET to anticipate local regulations.

In fact, PET is now the best alternative in terms of competitiveness of PC. To date, the rotations or re-fills can arrive to up to 30 times.

Among other advantages of using PET are:

• Economic advantages:

• reduction of resin costs by about 50%

• reduction of the container weight by about 15-20%

• reduction of logistics costs.

• Performance advantages:

• Better resistance to impact

• High mechanical properties

• Improved appearance and transparency

• Good variety of shapes and geometries

• Simple forming process and better control of the distribution of materials.

• Environmental sustainability advantages

• Highly advanced facilities for PET recycling

• No presence of Bisphenol-A

• No presence of antimony

Switching from PC to PET is not so straightforward as it has the following critical points: • The containers and preforms must have large thickness while ensuring excellent transparency.

• The dimensions of the PC containers must be maintained due to logistical requirements.

• The profiles of the shoulders of the PC bottles must be maintained to ensure the automatic handling of said containers.

• The current diameters and heights of the neck must be maintained in accordance with the valves of the water dispensers.

• Meet the needs of functional requirements such as adding handles or possibility of creating ridged surfaces, especially at the base.

Said large-sized PET containers, which are also referred to as "final containers" hereinafter, are obtained by starting from a preform obtained by injection in a mold; said preform and the final container only have the neck in common. A first problem to be addressed is the fact that the inner diameter of the bottle neck determines the inner diameter of the preform.

Since the preform is injected melted into a mold and since PET is a material which has a cooling problems since it must be cooled quickly in order not to crystallize, said preforms should have a thickness of less than 9mm.

Since the inner diameter of the neck determines the inner diameter of the preform and given the constraint of the preform thickness, the diameter of the neck also determines the outer diameter of the preform and the average diameter thereof.

In order to properly stretch PET, i.e. without defects and without crystallization, parameters referred to as "stretching parameters" or "stretching ratios" must be respected. Distinction is made between "radial stretching parameters" and "axial stretching parameters."

The radial stretching parameters are given by the ratio between the diameter of the final container and the average diameter of the preform and must be contained within certain limits; likewise, the "axial stretching parameters" are given by the ratio between the length of the bottle without neck and the length of the preform without neck, and they should always remain within certain limits, as well.

For considerable bottle diameters such as those of said containers, since the diameter of the preform is limited by the diameter of the neck, these stretching ratios are not met, therefore they may exhibit defects, such as whitening and the difficulty of creating and filling complex geometries such as those in close proximity of the seats for handles.

In order to overcome such problems and optimize the "stretching parameters", solutions have been devised adapted to try to increase the diameter of the preform, thereby creating an intermediate stage. In said stage, the preform is blown up to reach a significant enlargement which increases the diameter thereof; said preform with increased diameter has the above "stretching parameters" which are correct.

It is known to manufacture an intermediate bottle, i.e. going from the preform to an actual bottle that has a size greater than the final container while ensuring correct "stretching ratios" in the axial direction. An example, in particular, is that described in document EP2517862B1, which describes a method for manufacturing said large PET containers which provides for starting from a preform having a greater length of the longitudinal axis than the final container; an intermediate molding step for blowing the preform and forming a product molded by primary blowing having a size larger than that of the final container; a heating step of the product molded by primary blowing causing it to shrink to a smaller size than the final container, to form an intermediate molded product; a final molding step in which the intermediate molded product is blown within a heated mold to obtain the final container having predetermined shape. Since said method contemplates different intermediate steps, it is burdensome in terms of productivity and time. Moreover, commercial preforms cannot be used since preforms that are longer than the final container are used in order to reach the weight of the material required (from 550 g to 800 g) distributed on a thickness of about 6-7 mm.

Document WO2014167408 instead describes a process which starting from a preform of injection-molded material having a large thickness, comprises a first area for the thermal pre-treatment of the preform, an area for pre-blowing the preform, said pre-blowing area comprising a pre-blowing mold, and an area for the final blowing of the pre-treated preform.

The pre-blowing and the final blowing steps are carried out in two separate presses/molds; this causes a change in the geometry of the preform in the path from the first to the second press, in fact, during said path, the preform cools down and it gets deformed since the material naturally tends to shrink. The preform that enters the second mold is not the same preform that comes out of the first mold but it is smaller since the PET preform always tends to shrink and return to its original shape.

DESCRIPTION AND ADVANTAGES OF THE INVENTION

One object of the present invention is to provide an improved apparatus within a high-productivity solution, at a quite low cost and which ensures the best features of heat resistance and transparency of the final product.

These and other objects are achieved with the features of the invention described in the independent claim 1. The dependent claims describe preferred and/or particularly advantageous aspects of the invention.

In particular, an embodiment of the present invention provides a method and relevant apparatus which involves manufacturing not an intermediate bottle but an intermediate preform, i.e. an intermediate preform having with a slight increase in diameter compared to the initial preform, without changing the dimensions in length thereof; said intermediate preform is then blown permanently to achieve the dimensional and geometric features of the final container. Said method is carried out in a single press which comprises two stages: the diameter of the preform is increased in the first stage, which is also called pre-blowing, and the final blowing is carried out in the second stage, which is also called blowing.

Large-sized PET bottles are obtained with this solution having optimal transparency features, high heat resistance and good capacity of manufacturing complex geometries, such as for making handles.

Compared to the existing methods, with this solution it is possible to obtain the above results using commercial preforms with large thickness, at most equal to 10 mm, but shorter than the container, without having to use elongated preforms as it happens with other methods, which use non-standard, i.e. longer preforms, in order to ensure the basis weight from 550 g to 800 g required for the finished bottle.

Another aspect of the invention is to implement a container forming cycle divided into four steps, A-B-C-D, in which starting from the empty apparatus condition corresponding to the beginning of production, the steps are as follows:

• step A, in which the press opens and the preform enters the first mold, then the press closes and blowing into the mold takes place; • step B, in which the press opens and the intermediate preform comes out of the first mold to enter the second mold, at the same time another preform enters the first mold;

• step C, in which the press closes and the final blowing of the intermediate preform takes place, at the same time the pre-blowing of the preform into the first mold takes place;

• step D, in which the press opens and the finished container comes out of the mold; at the same time, the intermediate preform moves from the first mold to the second mold, while a new preform enters the first mold.

With this cyclic solution, once ready the intermediate preform immediately goes in the second mold without stand-by cycle times, preventing the preform from cooling down and/or become deformed during the possible path, with the consequence that the preforms entering the second mold is not the same preform that came out of the first mold.

Another aspect of the invention provides for blowing the intermediate preform formed in the previous pre-blowing cycle at the same time as the pre-blowing of the preform.

Therefore, having both the pre-blowing and the blowing the same duration of time, the production time of said apparatus is optimized.

Another aspect of the invention is a press having two integrated molds of which the first mold used for pre-blowing the preform; the second mold for blowing the intermediate preform. The advantage of having the pre-blowing and the blowing in the same piece, the manufacturing costs are definitely more contained in addition to a logistic optimization of the production area.

Said objects and advantages are all achieved by the apparatus object of the present invention, which is characterized by the following claims.

BRIEF DESCRIPTION OF THE FIGURES

This and other features will become more apparent from the following description of some of the configurations, illustrated purely by way of example in the accompanying drawings.

- Figure 1 : shows an example of a large-sized container which can be manufactured by the two-mold press object of the present invention.

- Figure 2: shows a section of the monobloc press in which the two molds are highlighted,

- Figure 3 : shows a sequence of the steps which make up the manufacturing process of a large container starting from a PET preform obtained by injection in a mold.

DESCRIPTION OF THE INVENTION

With particular reference to figure 10, it shows an example of a large-sized PET container 1. Said containers have a volume greater than 10 liters and are typically made with volumes equal to 5 gallons or about 20 liters and have a diameter of between 250 and 300mm. They are made starting from a preform 11 having an outer diameter equal to about 60mm obtained by injection in a mold. Said preform 11 and the final container 10 have in common only the neck.

The inner diameter of the neck of container 10 determines the inner diameter of preform 11 ; said preforms 11 must have a basis weight of material equivalent to that of the final container 10 and cannot have a larger thickness than 9 mm because of the crystallization problems and subsequent whitening of the PET during the cooling step, if this does not take place quickly.

Since the inner diameter of the neck of container 10 determines the inner diameter of preform 11 and since its thickness cannot be more than 8mm, the diameter of the neck also determines the outer diameter of preform 11 and the average diameter thereof.

For significant bottle diameters such as those of said containers 10, the "stretching ratios" are not met, in particular the ratio of the diameter of the final container 10 to the average diameter of preform 11, which may lead to defects, such as crystallization and difficulty of making and filling complex geometries.

In order to overcome said problems and optimize the "stretching parameters", said containers 10 are manufactured by carrying out an intermediate stage adapted to increase the diameter of preform 11. In said stage, the preform is blown up to reaching a slight enlargement which increases the diameter thereof from about 60mm to about 90mm; said preform, which is referred to as intermediate preform 12, and the final container 10 have the above "stretching parameters" that are correct.

The method and relevant apparatus object of the present patent therefore provides for producing the large-sized container 10 starting from a PET preform 11 and manufacturing, through a pre-blowing, an intermediate preform 12 bearing a slight increase in diameter with respect to the initial preform 11, preferably without changing the size in length thereof; said intermediate preform 12 is then definitively blown to achieve the dimensional and geometric features of the final container 10.

Said method is carried out within a single apparatus which comprises two stages, as shown in figure 2:

• first stage where the diameter of preform 11 is increased, also known as pre-blowing

• second stage, where the final blowing is carried out, also known as blowing of the intermediate preform 12.

The intermediate preform 12 in the first stage undergoes an increase of at least one dimension with respect to preform 11. The pre-blowing and blowing take place simultaneously on two molds 2 and 3, part of the same press 1. The first stage is carried out in the first heated mold 2 where the pre-blowing is carried out; the second stage is carried out in the second cold mold 3, where the blowing is carried out.

The two molds 2 and 3, in addition to being different in geometry, also have two different temperatures since mold 2 is heated and mold 3 is cold to ensure the correct formation of container 10 and the correct definition of all its details.

The manufacturing cycle can be divided into four steps A-B-C-D, shown in figure 3. The description of the steps starts from the empty apparatus condition, i.e. beginning of the production :

• step A: press 1 opens and preform 11 enters the first mold 2, then press 1 closes and blowing into mold 2 takes place;

• step B: press 1 opens and the intermediate preform 12 comes out of the first mold 2 to enter the second mold 3, at the same time another preform 11 enters the first mold 2;

• step C: press 1 closes and the final blowing of the intermediate preform 12 takes place, at the same time the pre-blowing of preform 11 into the first mold 2 takes place;

• step D: press 1 opens and the finished container 10 comes out of mold 3; at the same time, the intermediate preform 12 moves from the first mold 2 to the second mold 3, while a new preform 11 enters the first mold 2.

The cycle time is calculated from when press 1 opens to let preform 11 into mold 2 and at the same time the intermediate preform 12 into mold 3 up to when, at the end of the pre- blowing/blowing, the press opens again.

The pre-blowing and blowing cycle time are equal and therefore the pre-blowing of preform 11 and the blowing of the intermed iate preform 12 take place simulta neously, avoid ing the need to create storage areas of intermed iate preforms 12 between the two stages which may affect the stability of the material in contact with the air.

It is understood, however, that the a bove description is a non-limiting example, therefore possible variants of detail that may be necessary for technica l and/or functional reasons are deemed as falling within the same protection scope defined by the following claims. For example, the intermed iate preform 12 may d iffer from preform 11 , in add ition to a larger d iameter, also for a d ifferent heig ht.