WO2014146938A1

WO2014146938A1 - Process for producing a container from a preform having a portion to be superheated comprising a layer of material capable of being selectively superheated

Info

Publication number: WO2014146938A1
Application number: PCT/EP2014/054787
Authority: WO
Inventors: Sébastien FEVRE
Original assignee: Sidel Participations
Priority date: 2013-03-19
Filing date: 2014-03-12
Publication date: 2014-09-25
Also published as: FR3003505B1; FR3003505A1

Abstract

The invention relates to a process for producing a container (26), made of a thermoplastic material, the process comprising a final step (E2) of forming the container (26) by blow moulding or stretch-blow moulding during which at least one portion (14) of the body (18) of the preform (10) undergoes a more rapid stretching than the rest of the body (18), characterized in that it comprises: - an initial step (E0) of manufacturing the preform (10) during which the body (18) is made using a first thermoplastic material, each portion (14) to be stretched more rapidly comprising a second layer (32) of a second thermoplastic material that has a higher coefficient for absorption of the heating radiation than that of the first material; - an intermediate step (E1) of heating via uniform exposure of the body (18) of the preform to the electromagnetic heating radiation.

Description

"Process for producing a container from a preform comprising an overheating portion comprising a layer of material that can be selectively superheated"

The invention relates to a method for producing a container, such as a bottle, made of thermoplastic material by forming, such as blowing or stretch-blow molding, the body of a preform preheated by heating radiation.

The invention more particularly relates to a method of producing a container, such as a bottle, made of thermoplastic material by blowing or stretch-blow molding the body of a preform preheated by heating radiation, the method comprising a final step of forming the container by blow molding or stretch blow molding in which the container is obtained by stretching the body of the preform, at least a portion of the body of the preform being stretched more rapidly relative to the portions forming the remainder of the body;

the process comprising:

an initial step of manufacturing a preform in which the portion of the body intended to undergo a faster drawing has a coefficient of absorption of the heating radiation greater than that of the rest of the body, the body of the preform being made at the means of a first thermoplastic material, each portion intended to undergo a faster drawing during the forming step being made by superposition of a first layer of said first material and a second layer of a second thermoplastic material having a coefficient absorbing the heating radiation greater than that of the first material;

an intermediate step of heating the body of the preform by uniformly exposing the whole body of the preform to the electromagnetic heating radiation, at the end of which the entire body of the preform is heated to a temperature above the temperature of softening materials constituting it by electromagnetic radiation heating, each portion intended to undergo a faster stretching during the forming step being superheated at a temperature still higher than that of the rest of the body because of its absorption coefficient.

Thermoplastic preforms are obtained by injection into a mold during an initial manufacturing step.

The preforms generally have a substantially cylindrical body of revolution with a thick tubular wall which is closed at one of its axial ends by a thick-walled bottom, and which is extended at its other end by a collar, also tubular. The neck is shaped according to its shape and its final dimensions while the body of the preform is called to undergo a relatively large deformation to form the final container during a final forming step.

During an intermediate heating step, the body of the preform is made malleable by heating beyond a glass transition temperature.

Then, during the final forming step, the preform thus heated is placed in a mold which has a mold cavity corresponding to the final container to obtain. A pressurized fluid, such as air, is then injected into the malleable body of the preform so as to press the wall against the cavity of the mold.

Traditionally, the body of the preform is heated homogeneously during the heating step. As a result, it undergoes expansion that is homogeneous in all radial directions.

The mold is generally maintained at a cold temperature relative to that of the preform. Thus, when the wall of the preform comes into contact with the mold, it is cooled suddenly so as to be fixed in a semi-crystalline state. This cooling phenomenon makes it difficult to produce containers, especially bottles, having a cross section that is not approximately symmetrical with respect to the axis of the neck from the preform. For example, containers of polygonal cross-section in which each approximately planar face deviates substantially from a cylindrical surface surrounding the edges, or containers with flattened bodies such as detergent bottles.

This last case is illustrated in FIGS. 1A to 1C. The body of a preform 10 which is arranged in a mold 12 is thus shown in cross-section. The body of the preform 10 is homogeneously heated.

Because of the asymmetrical shape of the final container revolution, some proximal portions 14 of the preform 10 are arranged radially near the cavity of the mold 12, while other portions 16 distal of the preform 10 are relatively more radially distant. of the mold cavity 12.

As illustrated in FIG. 1B, the injection of the fluid under pressure into the body of the homogeneously heated preform 10 causes a homogeneous expansion of the body in all radial directions. However, the proximal portions 14 contact the mold 12 before the distal portions 16. The proximal portions 14 are thus frozen in a state of stretch much less important than the distal portions 16.

Since the homogeneous heating gives the material the same stretching characteristics regardless of the portions 14, 16 of the body of the preform 10, the upper stretch of the distal portions 16 of the body of the preform 10 is accompanied by a increased thinning of this portion 16 of the wall. As shown in FIG. 1C, there is finally obtained a container with a wall of non-constant thickness, which is thinner in the portions 16 distal to the body of the preform 10 starting and thicker in the proximal portions 14 of the preform 10 starting.

This entails many drawbacks which are cited in the document FR-A1-2.703.944.

A method has already been proposed, in particular in said document FR-A1 -2,703,944, to obtain a container of non-symmetrical section of revolution with a wall of homogeneous thickness obtained by blow molding or stretch-blow molding.

This document proposes, in particular, to heat the portions

14 proximal to the body of the preform 10 at a temperature above the glass transition temperature, without however reaching the crystallization temperature of the material. Subsequently, the proximal portions 14 will be referred to as "portions 14 to be overheated" or "portions 14 superheated".

As illustrated in FIGS. 2A to 2C, such a method, commonly known as the "preferential heating method", makes it possible to give the superheated portions 14 mechanical characteristics that make drawing, in particular circumferential, more rapid compared to the distal portions 16. For example, the superheated portions 14 have greater elasticity than the distal portions 16.

The shape and distribution of superheated portions 14 and distal portions define a heating profile of the preform. The heating profile is adapted according to the shape of the final container to obtain.

As illustrated in FIG. 2B, when the pressurized fluid is injected into the body of the preform 10, the superheated portions 14 are stretched more rapidly than the distal portions 16 under the effect of the fluid pressure. Thus, at the instant when the superheated portions 14 come into contact with the mold 12, they have a thickness less than that of the distal portions 16. The superheated portions 14 are then cooled and fixed in their state, making it possible to progressively stretch the rest of the body of the preform 10 to match the mold cavity 12. By adjusting the temperature of each portion 14, 16, this allows to obtain a final container wall homogeneous thickness, as shown in Figure 2C.

Of course, to obtain a satisfactory final container, it is necessary to index the angular position around its main axis relative to the mold in order to correctly orient the superheated portions to the corresponding proximal portions of the mold cavity.

However, the implementation of the method disclosed in this document requires an oven provided with means for restricting the heating of the distal portions. This is for example shield to protect the distal portions of a heating radiation, or means to temporarily disengage the preform revolution. Such means are very expensive to manufacture.

In addition, it is very difficult to adjust the oven to obtain accurate heating profiles depending on the shape of the container to obtain.

To solve these problems in particular, the present invention provides a method of the type described above, characterized in that the first layer of each portion to be heated has a thickness less than the rest of the body of the preform.

According to other features of the invention:

the second layer of each portion to be superheated has a thickness proportional to the heating temperature to be obtained in the portion to be superheated;

the preform has a wall of uniform thickness, including in the portion to be overheated;

the first layer of each portion to be overheated is made integrally with the rest of the body; the second layer is produced by injection molding;

the first layer is produced by overmoulding on the second layer previously obtained by injection molding;

the second material has the same composition as the first material to which an additive is added which promotes the absorption of the heating radiation;

the second thermoplastic material has a composition different from the first thermoplastic material;

the second layer of at least one portion to be superheated is arranged outside the preform;

the second layer of at least one portion to be overheated is arranged inside the preform.

Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings, among which:

FIGS. 1A, 1B and 1C show different state of expansion of a preform during a forming step belonging to a process carried out according to the state of the art without preferential heating;

FIGS. 2A, 2B and 2C are views similar to those of FIGS. 1A, 1B, 1C which represent different states of expansion of a preform during a forming step belonging to a process carried out according to the teachings of FIG. invention;

- Figure 3 is a front view which shows a preform made at the end of a first step of manufacturing the process carried out according to the teachings of the invention;

FIG. 4 is a front view showing the final container obtained from the preform of FIG. 3 after implementation of the method produced according to the teachings of the invention; - Figure 5 is a top view which shows the container of Figure 4;

- Figure 6 is an axial sectional view which shows the preform of Figure 3 obtained according to a first embodiment of the invention;

FIG. 7 is a perspective view showing a preform at the end of a first phase of the initial manufacturing step carried out according to a second embodiment of the invention;

- Figure 8 shows the preform of Figure 7 at the end of the initial step of manufacturing.

In the description and in the claims, the portions 14 of the body of the preform which are heated to a temperature greater than that of the distal portions 16 during the heating step will be indifferently called:

- "superheated portions 14" after the heating step, or

- "portion 14 to overheat" before the heating step.

FIG. 3 shows a preform 10 made of thermoplastic material made according to the teachings of the invention. Conventionally, the preform 10 comprises a substantially cylindrical body 18 of revolution with thick tubular wall 20 which is closed at one of its axial ends by a thick walled bottom 22. The body 18 is extended at its open end by a neck 24, also tubular. The axis "A" of the neck 18 also forms the axis of the body 18 of the preform 10.

The neck 24 is shaped in its shape and its final dimensions while the body 18 of the preform 10 is called to undergo a relatively large deformation to form a final container 26 during a forming step.

FIGS. 4 and 5 show the final container 26 that must be obtained from said preform 10. It can be seen that this container 26 is asymmetrical with respect to the "A" axis of the neck 24. Thus, a distal portion 16 of the body 18 of the container 26 arranged on the left in Figures 4 and 5 is substantially eccentric with respect to the portion of the body 12 arranged on the right. A proximal portion 14 of the body 18 of the container shown on the right in FIGS. 4 and 5 is arranged near the axis "A" with respect to the distal portion 16. Such a container 26 is for example intended to contain a household product such as a detergent product.

As explained in the preamble of the description, the distal portion 16 of the container 26 corresponds to the distal portion 16 of the preform 10 which has been arranged at a distance from the cavity of the mold 12 during the forming operation, while the portion 14 proximal of the container 26 corresponds to the superheated portion 14 which has been arranged near the cavity of the mold 12.

In FIGS. 3 to 5, the superheated portion 14 is delimited with respect to the distal portion 16 by a boundary 28.

It can be seen in FIGS. 3 to 5 that the bottom 22 of the preform 10 is considered as an integral part of the superheated portion 14. Indeed, it is known that obtaining the bottom of the container 26 requires stretching greater than that of the distal portions 16, especially when the preform is stretched axially by an elongation rod during the forming step, thus conferring proximity between the bottom 22 of the preform and the cavity of the mold 12.

In the example shown in the figures, the body 18 of the preform 10 and the container 26 has only one portion 14 to overheat and a single distal portion 16. It will be understood, however, that the invention is applicable to preforms and containers having a plurality of unrelated superheating and / or distal portions.

The invention proposes a method for producing an asymmetrical container made of thermoplastic material, such as the container 26 shown in FIGS. 4 and 5.

The method comprises an initial step "E0" for manufacturing the preform 10 in which the portion 14 of the body 18 for faster drawing has a higher heating radiation absorption coefficient than that of the rest of the body 18.

More particularly, during the step "E0" of manufacture, the body 18 of the preform 10 is made by means of a first thermoplastic material and a second thermoplastic material, the second thermoplastic material having an absorption coefficient heating radiation greater than that of the first thermoplastic material.

Each portion 14 to be overheated, that is to say destined to undergo a faster drawing during the forming step, is made by superposition of a first layer 30 of said first material and a second layer 32 of said second material .

The second material does not enter the constitution of the distal portions 16. In other words, only the portions 14 to be overheated comprise the second more absorbent thermoplastic material. In the example shown in the figures, the distal portion 16 consists of a single layer of the first thermoplastic material.

The neck 24 of the preform 10 is made of the same material as the distal portion 16.

Thus, the first layer 30 of each portion 14 to be overheated is formed integrally with the rest of the body 18 and with the neck 24.

The second thermoplastic material is selected to have a greater heating radiation absorption coefficient than that of the first thermoplastic material. In other words, during exposure to identical heating radiation, a wall made with the second thermoplastic material will increase its temperature faster than a wall made with the first thermoplastic material. To do this, the second material is for example made according to the same formula as the first thermoplastic material, to which is added an additive that promotes the absorption of heating radiation. This is for example an additive that is not transparent in the wavelength of the heating radiation.

In a variant, the second thermoplastic material is a thermoplastic material which has a composition totally different from the first thermoplastic material,

Whatever the chosen solution, the second thermoplastic material advantageously has mechanical characteristics substantially similar to those of the first material, at least at room temperature.

A first embodiment of the preform 10 is illustrated in FIG.

In this first embodiment, the first layer 30 which is arranged outside the preform 10 while the second layer 32 is arranged on the inside of the wall of the preform 10.

The wall of the portion 14 to be superheated has a thickness identical to that of the distal portion 16 equal to the axis "A". In this example, the body 18 of the preform has a wall of uniform thickness along the axis "A".

Thus, the first layer 30 of each portion 14 to be superheated has a thickness less than that of the wall of the distal portions 16.

In the portion 14 to be overheated, the thickness of the first layer 30 is equal to that of the second layer 32.

In variant not shown, the second layer of each portion to be heated has a thickness greater than that of the first layer. According to another variant not shown, the second layer of each superheating portion has a thickness less than that of the first layer.

According to yet another variant not shown of the invention, the second layer of each portion to be overheated has a variable thickness depending on the heating temperature gradient to be obtained in the portion to be superheated itself. For example, the thickness of the second layer is proportional to the final temperature to be obtained at the end of the heating step. Thus, even within the portion to be overheated, an area to be moderately overheated will have a second thin layer relative to an area to be overheated more intensely.

This first embodiment of the preform 10 can be obtained by an overmoulding process. Such a method is well known to those skilled in the art, and reference can be made to EP-2.159.031 which describes an example of implementation of such a method. The process described in this document is a so-called "bi-injection" process comprising:

a first phase during which the second layer 32 is firstly produced by injection molding of the second thermoplastic material,

- Then, a second phase during which the first layer 30 and the remainder of the body 18 and the neck 24 of the preform 10 are overmoulded by injection of the first thermoplastic material around this second layer 32.

For a more detailed explanation of this "bi-injection" process, reference will be made directly to the document cited.

FIGS. 7 and 8 show a second embodiment of the preform 10. In this example, the portion 14 to be overheated is essentially formed by the bottom 22 of the preform 10. The difference with respect to the first embodiment lies in the fact that the second layer 32 of the portion 14 to be overheated is here arranged outside the preform 10 while the first layer 30 is arranged towards the inside of the preform 10.

To produce such a preform, the first layer 30, the distal portion 16 and the neck 24 are first produced by injection molding of the first plastic material. An incomplete preform is thus obtained, as shown in FIG. 7, in which a recess has been formed in the thickness of the portion 14 to be superheated in order to allow the second layer 32 to be overmoulded on the outside of the first layer. By injection of the second thermoplastic material, as shown in FIG.

In the following embodiment of the process, the preform 10 thus manufactured according to any one of the embodiments undergoes a step "E1" intermediate heating.

During this heating step "E1", the body 18 of the preform 10 is heated by uniform exposure of the entire body 18 of the preform 10 to electromagnetic heating radiation. This is for example infrared radiation or microwave radiation.

According to a nonlimiting example of implementation, the heating is performed by scrolling the preforms 10 in a furnace (not shown) having at least one heating side wall, for example constituted by heating tubes attached to the wall of the furnace, with simultaneous rotation of the preforms on themselves to homogenize the exposure time of all the portions 14, 16 of the body 18 of the preform 10. Protection means provide thermal protection of the neck 18. A reflective panel can preferably be arranged opposite the tubes to reflect towards the bodies 18 of the preforms 10 the fraction of the passing heating radiation between two successive 18 bodies. Such an implementation device is particularly suitable for mass production of containers 26.

Thus, the portion 14 to be overheated and the distal portion 16 are exposed to identical heating radiation, both in terms of exposure time and power of the radiation.

At the end of this step "E1" of heating, the entire body 18 of the preform is heated to a temperature above the softening temperature, or glass transition temperature, of the material by the electromagnetic radiation heating.

Nevertheless, the second layer 32 of the portion 14 to be overheated will have absorbed more energy than the distal portion 16. This results in a faster increase of the temperature of the second layer 32 of the portion 14 to overheat relative to the distal portion 16. Due to the large contact surface between the first layer 30 and the second layer 32, the heat stored in the second layer 32 is transmitted by conduction to the first layer 30. Thus, the temperature of the portion 14 to be superheated is homogeneous in its entire thickness and is greater than the glass transition temperature reached by the distal portion 16.

Thus, at the end of the heating step "E1", each portion 14 to be heated is heated to a temperature even higher than that of the remainder of the body 18 because of the absorption coefficient of the second layer 32.

As explained in the preamble of the description, this disparity in temperature between the portion 14 to be heated and the distal portion 16 makes it possible, after a final step "E2" forming, for example by blowing or by stretching blowing, to an asymmetrical container 26 having a homogeneous wall thickness, as illustrated in Figures 2A, 2B and 2C.

The process carried out according to the teachings of the invention advantageously makes it possible to simplify the heating furnaces for the implementation of the intermediate "E1" heating stage.

Furnaces with fewer parts are thus less expensive to manufacture.

In addition, it is possible to produce containers of different shapes without losing time in setting the oven, All preforms can be uniformly exposed to the heating radiation regardless of the shape of the final container, including a symmetrical shape of revolution. The heating profile of the preforms is in fact now determined by the structure of the preform itself, in particular by the distribution of the second absorbent thermoplastic material, and not by its exposure time to the heating radiation.

In addition, it is possible to achieve very precise heating profiles because the portions 14 to be overheated are now determined structurally.

Claims

1. A method of producing a container (26), such as a bottle, of thermoplastic material by blow molding or stretch blow molding of the body (18) of a preform (10) preheated by heating radiation, the method comprising a final step (E2) for forming the container (26) by blow molding or stretch-blow molding during which the container (26) is obtained by stretching the body (18) of the preform (10), at least a portion (14) ) the body (18) of the preform (10) being stretched more rapidly relative to the portions (16) forming the remainder of the body (18);

the process comprising:

an initial step (E0) of manufacture of a preform (10) in which the portion (14) of the body (18) intended to undergo a faster drawing has a coefficient of absorption of the heating radiation greater than that of the remainder of the body, the body (18) of the preform being made by means of a first thermoplastic material, each portion (14) intended to undergo a more rapid drawing during the forming step (E2) being carried out by superposition of a first layer (30) of said first material and a second layer (32) of a second thermoplastic material having a greater heating radiation absorption coefficient than that of the first material;

an intermediate step (E1) for heating the body (18) of the preform by uniform exposure of the entire body (18) of the preform to the electromagnetic heating radiation, at the end of which the entire body (18) of the preform (10) is heated to a temperature above the softening temperature of the materials constituting it by the electromagnetic heating radiation, each portion (14) intended to undergo a faster stretching during the forming step (E2) being superheated to a temperature still higher than that of the rest of the body (18) due to its absorption coefficient;

characterized in that the first layer (30) of each portion (14) to be superheated has a thickness less than the rest of the body (18) of the preform (10).

2. Method according to the preceding claim, characterized in that the second layer (32) of each portion (14) to superheat has a thickness proportional to the heating temperature to be obtained in the portion (14) to overheat.

3. Method according to any one of the preceding claims, characterized in that the preform (10) has a wall of uniform thickness, including the portion (14) to overheat.

4. Method according to any one of the preceding claims, characterized in that the first layer (30) of each portion to be overheated is made integral with the rest of the body (18).

5. Method according to the preceding claim, characterized in that the second layer (32) is produced by injection molding.

6. Method according to the preceding claim, characterized in that the first layer (30) is formed by overmoulding on the second layer (32) previously obtained by injection molding.

7. Method according to any one of the preceding claims, characterized in that the second material has the same composition as the first material to which is added an additive that promotes the absorption of the heating radiation.

8. Method according to any one of claims 1 to 6, characterized in that the second thermoplastic material has a different composition of the first thermoplastic material.

9. Method according to any one of the preceding claims, characterized in that the second layer (32) of at least one portion (14) to be heated is arranged outside the preform (10).

10. Process according to any one of claims 1 to 8, characterized in that the second layer (32) of at least one superheating portion is arranged inside the preform (10).