EP2226257A1 - Plastic, thin-walled, heat-resistant container for hot filling with liquid contents - Google Patents

Abstract

The method involves providing a container made of a material in accordance with an extrusion/blowing process following a heat resistant treatment. The container is filled with a hot sterilized liquid and the container is closed immediately after it is filled. The container is allowed to cool below a congealing temperature, for deforming the container by a formation of depression in it. The container is heated to bring relaxation of the residual stresses for reduction and generation of internal pressurization of the container to compensate for the deformations caused by the depression effects.

Description

The present invention relates to a thin-walled, lightweight, heat-resistant plastic container for hot filling of a liquid content.

Polyethylene terephthalate, PET, is a polymer that is widely used for producing containers for liquids. Its main assets are transparency, low weight, the release of shapes allowing distinctive profiles depending on products or commercial needs, unlike metal cans, all of the same shape and dimensions. It is the same for containers made from cardboard whose forms are limited.

PET is unbreakable and with good mechanical properties of preservation, permeability, which makes it very attractive and largely explains its very strong use.

These PET bottles are used for flat liquids such as oils and mineral waters. In this case, the containers undergo only very few mechanical stresses. PET is quite suitable. Indeed, these liquids are filled cold and without pressure.

These bottles were also used in the case of carbonated drinks and therefore likely to pressurize the container.

Design tricks with grooves on the bottle body or so-called petaloid bottoms make it possible to reinforce the mechanical strength and / or the resistance to pressure, without penalizing the weight of the container.

When manufacturers need to fill a container hot, it is necessary to use different designs that require greater thicknesses, different geometries and lead to high weight with high material consumption, up to twice the weight one bottle for cold-filled liquids.

Indeed, the mechanical characteristics of the PET degrade strongly when the temperature rises.

There are so-called "Heat Resistant" methods, more commonly referred to as HR.

A first one-wheel method achieves filling temperatures of 80/88 ° C.

A second so-called two-wheel process which allows the liquids to be conditioned at temperatures of 88/95 ° C.

A hot-filled bottle undergoes many mechanical stresses during the different phases.

Thus the bottom must withstand the hydrostatic pressure of the hot liquid during filling.

The container must withstand the forces generated during the vacuum generated by the cooling of the liquid while the container has been clogged hot, to ensure the sterility of the liquid. The cooling causes a double contraction, that of the liquid and that of the air of the headspace of said bottle.

It is for this reason that the profiles are much more complex with panels and beams on the body, belts marked on the body as well as a shoulder between the neck and the body, whose shape is rather bulbous .

The advantage of the thickness necessary for the mechanical strength is also to present a greater inertia at the temperature.

The manufacture of lightweight PET bottles uses the so-called extrusion / blowing process. This method consists in producing a preform by extrusion, this preform having a tube profile with one end formed to the dimensions and the definitive shape of the neck, the other end being closed.

After reheating of this preform, especially by infrared radiation, up to 100/120 ° C, the amorphous material is softened and can be blown from the inside after it has been placed in a suitable mold.

This mold is of such dimensions that the removal of the material on cooling is taken into account so that the final container has the desired dimensions.

During this blowing phase, longitudinal stretching occurs under the action of a drawing rod and inflation by pressurized air thus introduced. More precisely, the air is first introduced at low pressure to ensure proper deformation of the material during high amplitudes and then at high pressure to ensure a plating against the walls of the finished mold and for very small amplitudes.

The mussels are also water-cooled to dissipate contact heat, which also freezes the bottle.

In fact, the bottles thus obtained are said to be bi-oriented because they have been stretched in one direction and an omni directional inflation.

The macromolecular chains thus oriented in two directions lead to excellent mechanical strength parameters at room temperature. The disadvantage of this bi-orientation is to be partly reversible and the material thus regains a certain freedom as soon as the temperature rises.

In fact, the material tends to return to its original form in which it has the least constraints.

This is the so-called memory phenomenon.

For thick bottles to be used for hot-filled beverages, extrusion blow molding is also used but with more sophisticated and complex driving parameters.

Indeed, the preform is warmed to a higher temperature than in the case of lightweight containers, close to crystallization to minimize this form of PET memory and relax the constraints due to blowing.

In the case of one-wheel manufacture, so as to increase its temperature resistance, the initially amorphous material of this container is subjected to heat treatment during and after its forming.

The material when stretched after softening, generates an induced but reversible crystallinity, the material remaining transparent.

Then, if the heating is maintained after having generated this induced crystallization, a spherulitic crystallization occurs, causing some crystallinity of the chains already organized by bi-orientation.

In contrast to the direct spherolitic crystallization of PET, spherolitic crystallisation posterior to a bi-orientation perfectly retains the transparency of the material.

In the case of two-wheel manufacture, the method achieves higher performance but at the cost of a succession of more complex steps.

In fact, in this case, a volume blank much larger than the volume of the final container is first made two to three times, therefore with a proportional stretching ratio.

This blank is then reheated beyond the glass transition to relax the stresses, which causes a decrease in volume and a return to the dimensions of the preform but with a high rate of spherulitic crystallinity, this in a proportional manner leading to a homothetic container. There is self-regulation with PET.

When this restricted blank is in temperature, a blowing step with a mold to the dimensions of the final container to obtain, close withdrawals, allows to manufacture the final container.

The high degree of crystallinity gives this container improved resistance to hot filling.

It is noted that such a process is much heavier to put in place.

Once these containers are manufactured, there are several filling methods and different behaviors of the liquids to be packaged.

There are light-sensitive liquids such as milk or beer, with the absorption of oxygen and therefore oxydo-sensitive such as the juice, the beer, the oil, with the return of water, with the loss of gas, the development of yeasts, molds or bacteria.

Liquids may include preservatives and are therefore not very sensitive, however certain so-called flat and sensitive liquids such as milks, juices, coffee, tea, fruit drinks, certain waters, do not include any preservatives and must nevertheless be packaged in the containers. best conditions.

To ensure such packaging, aseptic filling or hot filling is provided.

Aseptic filling is simple in theory since it involves filling and filling sterilized liquids in sterilized packages with sterilized caps in a sterile environment.

Nevertheless, it is understood that the chain is not simple to set up and leads to high costs. In such a chain, it is necessary to resort to chemical sterilizations that use chemicals with the resulting treatments, an expertise of the personnel, a low efficiency due to the low speeds of treatment, and it is moreover impossible to control on line sterility of the contents in the container.

The advantage is to require thin-walled bottles of low weight, free form since the filling is cold.

The hot filling also guarantees a quality of asepsis since the control of the temperature of the contents is simple and easy at any time.

The bottling line is simple and the treatments of the container and the stopper are limited since the sterilization is obtained by the hot liquid introduced into the container which is immediately closed. A tilting of the bottle also sterilizes the inner face of the plug in contact with the liquid.

By cons, it is necessary to use containers resistant to the filling temperature between 60 and 95 ° C, more particularly between 80 and 92 ° C depending on the products.

In addition, the bottles have high weights and substantially identical shapes and allow only a very low differentiation.

Also, it is concluded that there are two methods that have advantages and disadvantages. Nevertheless, the extra cost generated by the particular characteristics of the containers required for hot filling tends to direct the industrialists concerned towards the commissioning of filling lines by the aseptic route.

The solution would be to be able to fill hot liquids to obtain the guarantee of asepsis but in thin-walled bottles for cold filling to limit the costs of both containers and the packaging line.

This is what the method according to the present invention proposes, which is now described in detail according to a preferred, nonlimiting embodiment. The example given relates to PET bottles but could be applied to any container of polymer material of the same kind and having similar properties.

The method consists in carrying out a hot filling of a container, this container having to have suitable characteristics as described below.

This container is of cylindrical shape, possibly with grooves to stiffen the body, with a light base like that of the containers for mineral waters flat, but reinforced, the total weight of the container being substantially that of containers used for containers of mineral water , with equal capacity.

The reinforced bottom usually consists of a bulging bottom to the neck with reinforcements to prevent its reversal under slight pressure.

This container is made from either one or two wheel "HR" treatment methods, depending on the desired packaging temperatures.

The container is thus able to withstand hot and remains of reduced weight.

In addition, there is the absence of the characteristic elements of PET bottles of the prior art hot-packaged such as belt, bulb at the shoulder, panels.

The filling is carried out from the tank of a filling machine of known type, generally by gravity directly in the container, the liquid being carried and maintained at a temperature of 60 to 95 ° C depending on the intended applications.

• montée en température rapide de la paroi puisque l'épaisseur est faible et que l'inertie correspondante est limitée.
• la mise en pression liée à la pression hydrostatique due à la charge résultant de l'écoulement gravitaire, et
• la charge du volume de liquide introduit dans le contenant.

When the liquid in temperature enters the container, there are three actions:

• rapid temperature rise of the wall since the thickness is small and the corresponding inertia is limited.
• pressurization related to the hydrostatic pressure due to the load resulting from the gravity flow, and
• the charge of the volume of liquid introduced into the container.

The container deforms little under the effect of the rise in temperature and under the effect of the filling because the container is manufactured to meet this rise in temperature, at most a very slight barrel-shaped formation at the time of filling .

It is known that the crystallinity can be improved as indicated in the preamble of the present application, which greatly improves the mechanical strength. It is also known that if the container is used immediately after its manufacture, the moisture uptake is very limited and the initial resistance to temperature is kept almost completely.

The bottom having been designed with improved mechanical strength and its "HR" treatment, avoids the overturning of the crown of this bottom under the effect of the load and the increase in pressure once said container closed. Indeed, the increase in temperature causes a rapid shrinkage of the volume of the container while the contained liquid, it retains its volume which generates a pressure of the interior of the container.

In fact, the bottom designed to resist retains its shape while the body of the container has a significant deformation during the cooling of the liquid and the head space. It should be noted that this deformation is not irreversible since if the container is open, the body returns to its original shape. It is known that the deformation is localized in the most favorable zone for mechanical deformation such as the walls for example in the case of known containers and for which no particular modification has been made.

It is also noted that in the case of a less mechanically resistant zone, the deformation is reproducible on all the identical containers filled under the same conditions.

It is therefore possible to voluntarily create a suitable zone in any container so as to bring the deformation on this specific and determined area in a reproducible manner.

We know that a square or cylindrical container is resistant to pressure but resists poor vacuum except to provide tricks such as flutes or folds. According to the method of the invention, there is thus obtained a container with a bottom and a connecting belt of the bottom and said body undeformed by the strength of the fold formed at this junction. The container is stable on its bottom but with a deformed body, collapsed according to the word of the trade, which makes it unsuitable for marketing.

The method according to the present invention consists in reducing the volume of the container by causing a reduction in the volume of the container after partial or total cooling of the liquid.

It has been found that the bottle, even if it receives a "heat resistance" HR treatment, makes it possible to minimize the shape memory effect of the PET without, however, removing it.

The method consists of releasing the frozen constraints so that the container tends to return to its original shape, that of the preform and therefore tends to find a reduced volume.

For this purpose, once the liquid is introduced hot, then once the closed container and partial or total cooling operated, the container is subjected to a temperature rise of at least a portion of said container so as to relax the constraints and to irreversibly deform the container on all or part of its surface.

The rise in temperature must be rapid so as not to cause the rise in temperature of the liquid, which would cancel the differential necessary to compensate for the depression.

Nevertheless, the choice of means remains very wide because the ratio of the masses involved is very important. The few grams of PET in a container in front of the hundreds of grams of the content necessarily lead to a faster temperature rise of the envelope than the content. Moreover, in case of radiant heating in particular, the envelope is the first subjected to infrared radiation and absorbs primarily calories.

It is only necessary to avoid the means of heating by transmission like the bain-marie or the pasteurization. In this case, there is another parameter that is no longer suitable, it is the time needed, much too long with this type of technique.

Another prejudice to overcome is the amount of compensation needed. In view of the container after cooling, the deformation suggests that it is necessary to generate a significant reduction in volume.

For a 500 ml bottle, the volume reduction after cooling is only 3.5% of the liquid volume, so 17 ml.

In fact on such a bottle, generally about 60 mm in diameter to give an idea, it is possible to provide the shrinkage on the so-called labeling height, that is to say on the area of affixing a label.

The belt between the labeling zone and the bottom and the shoulder zone being dimensionally stable, it suffices to provide a retraction of 1 to 2 mm from the diameter. It is even possible to provide a slight overpressure to compensate for any additional shrinkage when placing in a refrigerator such a container.

It should also be noted that during hot filling, there is always a head space filled with air.

Also, it is possible to set the bottle so as to systematically conduct this air following a generatrix of said bottle at the top. In fact the method can implement hot air heating because the transmission of calories between the wall and the air is very difficult, the air being very insulating. The calories are concentrated in the wall of said bottle on the area concerned and very quickly causes the desired shrinkage.

In order not to have to make a total rise in temperature, it is also possible to achieve this heating of the envelope as soon as the internal liquid has passed below the transition temperature of the order of 40 to 50 ° C. . It may also be noted that the method according to the present invention makes it possible to produce containers of square section, the shrink then causing a deformation response of the container by triangulation which is also compensated during the relaxation of the stresses and during the shrinkage of the container.

Thus, according to the present invention, the method consists in using a container able to resist mechanically without deformation when hot filling a liquid in a temperature range of a sterilized liquid, generally from 80 to 95 ° C., for example a polyethylene container, said container being made by extrusion / blowing and having a shape memory before blowing, to fill said container with said hot liquid, to close the filled container and to cool at least below a freezing temperature of the container, then causing a deformation by forming a vacuum inside the container, then heating the container to cause relaxation of the stresses and a return to the shape before blowing generating a shrinkage and an internal pressure of the container leading at least to compensate for the deformations suffered by the effects of depression.

Thus, according to the present invention, a container filled with a pasteurized content, which can be guaranteed pasteurization by a simple measurement of filling temperature. The cost of the container for the implementation of the process is no longer detrimental since it is completely comparable to that of containers capable of undergoing aseptic filling.

The advantage is to be able to meet the needs of industrial filling rates, need for aseptic guarantee without requiring expensive bottling lines investment, also expensive and complex in operation.

Thus, thanks to the method according to the present invention, not only is the cost of raw material for producing a hot-filled container reduced, but this smaller quantity of raw material leads to reduced recycling costs for the same bottled volume.

According to the present invention, it should be noted that a suitable device can be provided for carrying out the method.

One solution is to make shells comprising at least two parts so as to come wrapping the container, said shells being heated by any suitable means to emit the necessary calories.

The shells have a substantially conjugated profile of that of the container to emit the calories closer to the walls, or even in a localized area of this wall, these shells being oriented horizontally if the heating is performed on a generator with the air in the upper part. . In this case, it is then possible to cause more intense heating in a particular area.

Claims (15)

Thin-walled, lightweight, heat-resistant plastic container for hot filling of liquid contents, comprising: a neck to allow filling of the contents with the liquid contents, a plug configured to close the neck, a base comprising a bottom curved towards the neck, the base comprising a structural reinforcement configured to withstand the hydrostatic pressure due to the charge resulting from the hot-introduced liquid and configured to prevent significant deformation of the base during the cooling of the hot liquid , a side wall extending upwards from the bottom to the neck, the side wall comprising a deformation zone, characterized in that the deformation zone of the side wall is configured to withstand initial deformation generated by the cooling of the contents and to substantially recover its initial shape upon release of residual stresses. Container as claimed in claim 1, characterized in that the container comprises polyethylene terephthalate, PET. Container according to claim 1, characterized in that the container is cylindrical. Container according to claim 1, characterized in that the structural reinforcement avoids the overturning of the bottom when said container is under slight pressure. Container according to claim 1, characterized in that the side wall has splines. Container according to claim 1, characterized in that the deformation zone is mechanically less resistant to pressure than another part of the side wall. Container according to claim 1, characterized in that the deformation zone is reproducible on identical containers under similar conditions. Container according to claim 1, characterized in that , under the effect of releasing residual stresses, the content has an internal pressure at least equal to the external atmospheric pressure. Container according to claim 1, characterized in that the weight of the container is equivalent to that of a container of equal volume which is configured for cold filling by the aseptic route. Container according to claim 1, characterized in that the internal pressure of the container increases, and simultaneously, the internal volume of the container and the head space decrease when the deformation zone returns to its original shape. Container according to claim 1, characterized in that it comprises a shoulder zone between the side wall and the neck. Container according to claim 11, characterized in that the shoulder region is configured to resist deformation. Container according to claim 1, characterized in that the relaxation of the residual stresses consists of an application of heat in the deformation zone. Thin-walled, lightweight, heat-resistant plastic container for hot filling of liquid contents, comprising: a neck to allow filling of the container with the liquid contents, a plug configured to close the neck, a base comprising a bottom curved towards the neck, the base comprising a structural reinforcement configured to withstand the hydrostatic pressure due to the charge resulting from the hot-introduced liquid and configured to prevent significant deformation of the base during the cooling of the hot liquid , a side wall extending upwards from the bottom to the neck, a deformation zone which is configured to withstand an initial deformation generated by the cooling of the contents and to substantially recover its initial shape when releasing residual stresses Thin-walled, lightweight, heat-resistant plastic container for hot filling of liquid contents, comprising: a neck to allow filling of the contents with the liquid contents, a base comprising a bottom curved towards the neck, the base comprising a structural reinforcement configured to withstand the hydrostatic pressure due to the charge resulting from the hot-introduced liquid and configured to prevent significant deformation of the base during the cooling of the hot liquid , a side wall extending upward from the bottom to the neck, and a deformation zone which is configured to withstand initial deformation caused by the cooling of the hot-filled liquid content, after the closure, the deformation zone being configured to substantially return to its original shape when the residual stresses that manifest themselves are released; during cooling after sealing when cooling hot-filled liquid contents.

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