CN104736320A - Method for forming a container by stretch-blowing wherein part of the wall of the container is not moulded - Google Patents

Abstract

The invention relates to a method for forming a container (10C) from a preform (10A) by stretch-blowing, the method comprising: a first step of positioning the preform (10A) on a fixed support (26) (E1); the second step (E2) of free expansion of the preform (10A) by stretch-blowing, whereby the preform (10A) is formed into a bubble-like intermediate container (10B); the third step of forming Step (E3), in which at least a first portion (50, 52) of the deformed wall of the preform (10A) is brought into contact with at least one profile (44, 46); characterized in that the intermediate container ( The second portion (54) of the deformed wall of 10B) does not come into contact with any profile until the final container (10C) cools below its glass transition temperature (Tg).

Description

Stretch-blow molding method for container with part of container wall not molded

technical field

The invention relates to a method of forming a final container of thermoplastic material from a preform by stretch-blowing, wherein the body of the preform is heated above its glass transition temperature.

The invention more particularly relates to a method of forming a final container of thermoplastic material by stretch-blowing from a preform, wherein the body of the preform is heated above its glass transition temperature, the method comprising:

- the first step of positioning the neck of the preform on the fixed support;

- a second step of free expansion, during which a pressurized molding fluid is injected into the preform to deform the hot body of the preform and during which the stretch rod shaft introduced axially into the preform to axially stretch the body by axially separating the bottom of the preform relative to the neck, so that the preform is shaped into a bubble-like intermediate container;

- a third step of forming, during which at least a first portion of the deformed wall of the preform is brought into contact with at least one profile to give the container its final shape, the intermediate portion of the deformed wall of the container At least a second portion is not in contact with any molded surface, at least until the final container has cooled below its glass transition temperature.

Background technique

It is known that forming devices of this type allow the formation of containers, such as bottles, based on preforms made of thermoplastic material.

In the following description and claims, a container in its initial shape will be referred to as a preform, a container in its intermediate shape will be referred to as an intermediate container, and a container in its final shape will be referred to as a final container .

The body of the preform is preheated above its glass transition temperature to make its walls sufficiently malleable.

The neck of the preform already has its final shape. In this respect, the material constituting the neck is kept at a temperature below its glass transition temperature in order to avoid any deformation of the neck during the process.

The preform so heated is inserted into the cavity of the mould, the neck of the preform resting on the upper mold plate forming the support.

The cavity has profiles that form the cavity of the final container. The profile is already in the modeling position from the start of the method. Thus, the profile remains fixed relative to the support during the entire method.

The blowing nozzle then injects a molding fluid, usually air, at a first pressure into the preform so that the walls of the preform are brought close to the cavity face of the mold cavity.

This blowing operation is usually accompanied by a stretching operation, during which a stretching rod is inserted into the preform to axially stretch the extensible wall portion of the body.

These two combined operations of stretching and blowing allow simultaneous axial and circumferential stretching of the wall. This allows obtaining a final container with mechanical characteristics adapted to the container's use.

The preform is then shaped into a bubble-like intermediate container. As the blowing fluid continues to be injected, the bubble continues to expand until it touches the fixed surface.

At this point, blowing fluid is injected into the intermediate container at a second, higher pressure, so that the entire deformed wall of the main body bears strongly against the fixing profile.

Contact with the fixed profile cools the deformed wall below its glass transition temperature, thereby fixing the final shape of the final container.

This method generally has satisfactory results for obtaining final containers whose dimensions should be very precise.

However, this method is very cumbersome since it requires the formation of complex profiles.

In addition, molds are bulky parts that are difficult to handle.

In addition, the blowing fluid should be injected into the preform at extremely high pressure. This leads to high energy consumption, especially when producing large batches of containers. For example, the first injection pressure is about 20 bar and the second injection pressure is about 40 bar.

Contents of the invention

In order to solve especially the above-mentioned problems, the invention proposes a forming method of the above-mentioned type, characterized in that the third step comprises an active forming phase during which at least one profile, referred to as a "movable" profile The face moves between the following positions relative to the support:

- the waiting position, in which the movable profile is not in contact with the deformed wall of the body;

- and the extreme position of the profile, in which the movable profile presses against a part of the deformed wall of the body to reduce the volume of the intermediate container.

According to other characteristics of the method:

- During the active forming phase of the third step, at least two opposing profiles are simultaneously moved towards each other in radial direction to squeeze the body of the intermediate container, the two profiles being radial to each other in their shaping limit positions ground apart such that the extruded portions of the walls do not contact each other;

- start of the active forming phase after completion of injection of the pressurized forming fluid into the container;

- the third step includes a passive forming phase preceding the active forming phase, during which the injection of the pressurized forming fluid started at the second step continues, and during which the intermediate container A part of the deformed wall is in contact with a profile called the "fixed" profile, which is immobilized relative to the support;

- injection of molding fluid at a constant pressure of less than 20 bar;

- injection of molding fluid at a pressure of less than 10 bar, especially at 5 bar;

- During the active forming phase of the third step, the discharge flow rate of the forming fluid is controlled so that at the end of the movement of the movable profile, the pressure in the body remains high enough to cool the wall below the glass transition temperature Keep the deformed wall tightly against the movable profile for the required time, so that the wall retains the shape given by the profile;

- During the third step, the molding fluid is discharged at a defined constant flow rate.

The invention also relates to a device for applying the method implemented according to the teaching of the invention, the device comprising:

- a fixed support for receiving the neck of the preform, a blowing part for blowing the molding fluid into the neck of the preform;

- tensile rods capable of sliding axially;

- at least one radially movable mold with movable profiles,

It is characterized in that each movable mold has a temperature maintaining member for maintaining the movable molded surface at a certain temperature.

Description of drawings

Other features and advantages of the present invention will appear in the course of reading the following detailed description, and for an understanding of the description, reference is made to the following drawings, in which:

- Figure 1 is a perspective view showing a preform;

- Figure 2 is a perspective view schematically showing a device for applying the forming method according to the teaching of the present invention;

- Figure 3 is a schematic view in axial section showing the first step of positioning the preform in the device of Figure 2;

- Figure 4 is a view similar to that of Figure 3, showing the second step of stretch-blowing the preform;

- Figure 5 is a view similar to that of Figure 3, showing a third step in forming the preform;

- Figure 6 is a view similar to that of Figure 3, showing a fourth step of discharging the final container.

Detailed ways

For the following description, parts having the same structure or similar functions are denoted by the same reference numerals.

For the description below, the following orientations are adopted in a non-limiting manner:

- longitudinal orientation from rear to front as indicated by arrow "L" in the figure;

- vertical orientation from bottom to top according to the orientation of the main axis of the preform as indicated by the arrow "V" in the figure;

- Transverse orientation from left to right as indicated by the arrow "T" in the figure.

Figure 1 shows a preform 10A made of a thermoplastic material such as polyethylene terephthalate or "PET". Preform 10A has the shape of a test tube having a major vertical axis "A". The lower end of the preform is closed by a hemispherical bottom 12, while the upper end of the preform has an opening 14 radially delimited by a tubular neck 16 of axis "A".

The lower end of the neck 16 has a collar 18 that separates the upper neck 16 from the lower body 20 including the base 12 .

The body 20 of the preform 10A is intended to be formed into the final container 10C shown in FIG. 7 by using a forming method which will be described in more detail below.

Hereinafter, the terms "preform 10A", "intermediate container 10B", and "final container 10C" refer to the same container according to the shape of the container during the molding process.

The neck 16 and hoop 18 of the preform 10A already have their final shape. In this respect, the neck and hoop will not be deformed when the method is carried out.

The pre-form 10A is generally obtained by a molding method in which thermoplastic material is injected from the base 12 . The bottom 12 has irregular point-like portions at the injection positions, which will be referred to as "injection points 22" hereinafter.

The material constituting the body 20 , the neck 16 and the hoop 18 of the preform 10A thus obtained has what is known as an "amorphous" state in which the material is hard. By heating this "amorphous" material above a temperature "Tg" known as the "glass transition" temperature, the material transitions to a "glass" state in which the material has a soft and viscous texture that allows it to be stretched. Thick texture.

It is known to prepare the preform 10A prior to carrying out the method by heating the body 20 above its glass transition temperature "Tg" while keeping the neck 16 and hoop 18 at a temperature below its glass transition temperature "Tg". temperature to prevent them from deforming.

FIG. 2 shows a device 24 for applying the forming method for forming a final container 10C from a preform 10A.

The device 24 has a support 26 , which is used below as a fixed reference. The support 26 is intended to receive the neck 16 of the preform 10A. The preform 10A is shown in dashed lines.

More specifically, in the embodiment shown in the figures, the support 26 is a horizontal plate having a circular hole 28 into which the body 20 of the preform 10A is inserted. The diameter of the hole 28 is smaller than the outer diameter of the hoop 18 , so that the hoop 18 rests on the upper surface of the support 26 , while the body 20 of the preform extends freely below the support 26 .

The support 26 is divided into two parts which can be separated laterally from each other. A seam line between these two parts divides the aperture 28 into two equal halves. This allows to guarantee the discharge of the final container 10C at the end of the method, since the final shape of the body 20 does not allow it to pass through the hole 28 when the two parts are assembled together.

As a variant, the support is formed by clamps or any other means that make it possible to keep the neck fixed during the implementation of the method, while leaving the body of the preform to extend freely.

The apparatus 24 also has a blowing unit 30 which blows pressurized molding fluid into the neck 16 of the preform 10A.

The blowing part 30 is thus equipped with a nozzle 32 having a front section 34 arranged coaxially with the axis "A" of the preform 10A when the preform is in position on the support 26 . The nozzle 32 is slidably mounted between the rest upper position shown in FIG. 2 and the blowing lower position shown in FIG. Front section 34 of neck 16 sealingly connects with opening 14 of neck 16 .

Here, the front section 34 has the shape of a bell for enclosing the neck 16 . The lower edge of the bell is intended to bear sealingly against the upper surface of the support 26 .

As a variant, the front section is intended to be plug-tightly inserted into the neck.

Spout 32 is connected to a controlled source 36 of pressurized fluid. The pressurized fluid is formed, for example, by compressed air at 5 bar.

A vertical stretch rod 38 is vertically slidably mounted in the spout 34 and is coaxial with the axis "A" of the preform 10A when the preform is positioned on the support 26 . The stretch rod 38 has a free lower end 40 intended to be inserted through the neck 16 into the preform 10A, as will be explained in more detail below. Therefore, the sliding of the stretch rod 38 is controlled between the retracted upper position and the extreme extended lower position.

The controlled components for moving the stretch rod 38 are known and will therefore not be described again. The controlled component is, for example, a piston or a linear motor.

The device 24 additionally has two transversely movable molds 42 mounted below the support 26 at the level of the body 20 of the preform 10A positioned on the support 26 . Each mold has a movable profile 44 extending substantially in a vertical longitudinal plane. The movable profiles 44 are arranged transversely opposite each other on either side of the axis "A".

The mold 42 is controlled to translate laterally between the following positions:

- waiting position, in which the two molds are separated from each other;

- and the molding limit position, in which the two molds are laterally close to each other, yet a transverse gap remains between the two profiles 44, so that neither of the molds is in contact with the stretch rod 38 in the stretched position touch.

For example, the movement of the mold 42 is controlled by a piston, wherein only one piston push rod is shown in the figure.

As a variant, the piston is replaced by a linear motor.

The device 24 also has a profile 46 arranged below the support 26 on the axis of the hole 28 . Here, the profile 46 has the shape of a longitudinal edge. This profile is carried by a triangular prism-shaped wedge 48 whose axis extends longitudinally.

Wedge 48 is vertically translatable between an upper use position such as that shown in FIG. 3 and a lower rest position (not shown). This allows in particular to facilitate the ejection of the final container 10C at the end of the forming process by separating the wedge 48 from the final container 10C.

As will be explained hereinafter, the wedge 48 is intended to be in its position of use during the forming step of the forming method. In this respect, the profile 46 carried by the wedge 48 will be referred to hereinafter and in the claims as the fixed profile 46, since it is the deformed wall portion of the intermediate container 10B that is used to move in relation to the fixed The profiles 46 are in contact.

Now, referring to FIGS. 3 to 6 , a molding method of forming a final container 10C made of a thermoplastic material using a preform 10A by stretch-blow molding will be described. The forming method is carried out by means of the device 24 described above.

As already stated, before the first step of the forming process, the body 20 of the preform 10A has been heated above its glass transition temperature "Tg", while the temperature of the neck remains below said glass transition temperature "Tg".

FIG. 3 shows a first step "E1" of positioning the thus heated preform 10A. At the beginning of this step, the spout 32 and wedge 48 are each in their rest position, and the die 42 is in its waiting position. Thus, the holes 28 of the support 26 are accessible for receiving the preform 10A. The two parts of the support 26 are separated to receive the preform 10A, and then the two parts are closed.

Then, as shown in Figure 3, the spout 32 is lowered towards its lower blowing position and the wedge is raised towards its use position.

As shown in Figure 4, at the end of the first step "E1", a second step "E2" of free expansion of the body 20 of the preform 10A is initiated.

During the blow molding operation, pressurized molding fluid is then injected at a constant pressure into the preform 10A through the nozzle 32 . The pressure inside the body 20 of the preform 10A thus becomes greater than the pressure outside the body 20 . Since the material constituting the walls of the body 20 is in a "glass" state, the pressure differential causes the body 20 to expand by deformation of its walls, the body thus stretching into a bubble shape. The neck 16 and hoop 18 of the preform 10A remain rigid, which allows them to be kept in a fixed position on the support 26 .

During the entire blowing operation, the molding fluid is injected at a pressure of less than 20 bar, more advantageously less than 10 bar, especially at a pressure of 5 bar.

In the embodiment shown in the figures, the pressure of the molding fluid is constant throughout the blowing operation.

As a variant of the invention that is not shown, the pressure of the blowing fluid is varied over time in order to improve the repeatability of the molding.

Simultaneously with the blowing operation, the preform 10A is also subjected to a stretching operation. During this stretching operation, a stretching rod 38 is introduced axially into the preform 10A through its neck 16 to push the preform axially downwards relative to the neck 16 which remains stationary. The bottom 12 of the molded part 10A stretches the body axially. This allows vertical stretching of the material constituting the wall, especially in the area immediately below the hoop 18 .

This stretching operation, carried out simultaneously with the blowing operation, thus allows to achieve a stretching of the walls of the body 20 known as "bidirectional" stretching.

The preform 10A is now shaped into an intermediate container 10B, wherein the main body 20 of the intermediate container forms an air bubble.

This second step " E2 " of free expansion continues as long as the outer surface of the wall of the body 20 of the intermediate container 10B is not in contact with any profile. Thus, during the entire second step "E2" of expansion, the walls of the body 20 are free to deform, ie deform without coming into contact with the profiled surfaces.

At the end of the second step " E2 ", the preform 10A is thus formed into a bubble-shaped intermediate container 10B as shown in FIG. 4 .

It will be appreciated that the start of the stretching operation may be slightly prior to or slightly after the start of the blowing operation, it is important that the two operations partially overlap to achieve simultaneous stretching of the material in both directions.

The third step "E3" of shaping is thus started. During the third step "E3", at least a first portion 50, 52 of the deformed wall portion of the body 20 comes into contact with at least one profile 44, 46 to give the container 10C its final shape.

At the third step "E3" and until the end of the method, at least a second portion 54 of the deformed wall portion of the body 20 of the intermediate container 10B is not in contact with any profile until the final container 10C cools below its glass Transition temperature "Tg".

Here, the third step "E3" is decomposed into a first stage "E3-1" of passive forming as shown in FIG. 5 and a second stage "E3-2" of active forming as shown in FIG.

During the first stage "E3-1" of passive forming, the blowing operation continues, so that the main body 20 continues to expand. The lower part 50 of the bottom of the deformed wall of the intermediate container 10B is now in contact with the fixing profile 46 . During the second step "E2" and the third step "E3", the fixed profile 46 is immobilized relative to the support 26, as shown by the arrow in Fig. 5, it is the expanding wall that moves and contacts the fixed profile 46.

The portion 50 of the bottom corresponds to the bottom 12 of the preform 10A and thus has the injection point 22 . The portion 50 of the bottom is in contact with the fixing profile 46 , while the rest of the body 20 continues its free expansion on both sides of the wedge 48 . The portion 50 of the bottom that touches the fixing profile 46 cools below its glass transition temperature "Tg", thereby fixing the shape of the indentation of said fixing profile 46 .

Thus, the presence of the wedge 48 allows to obtain a precise vertical dimension between the portion 50 of the bottom of the final container 10C and the neck 16 . Thus, all containers 10C produced by this method have substantially the same vertical dimensions.

At the end of the first phase "E3-1", the blowing operation ends and the second phase of active forming "E3-2" begins immediately. In other words, the active forming stage "E3-2" is started after the injection of the pressurized forming fluid into the container 10B is completed.

As shown in FIG. 5 , at the beginning of the second stage “ E3 - 2 ” of active forming, the mold 42 is always in its waiting position in which the movable profile 44 is not in contact with the deformed wall of the body 20 .

The mold 42 is then simultaneously controlled to move towards its profile limit position, in which the movable profile 44 presses transversely against the deformed wall of the body 20 to reduce the volume of the air bubbles. Thus, the movable profile 44 is in contact with the opposite lateral portion 52 of the deformed wall of the body 20 .

At the profiling extremes of the movable profiles, the transverse gap remaining between the two movable profiles 44 allows avoiding that the pressed opposite lateral portions 52 of the walls come into contact with each other.

The movement of the mold 42 is fast enough that the material making up the lateral portion 52 is stretched without being torn.

After the blowing operation is finished, the pressurized molding fluid contained in the container 10B is discharged at a determined flow rate controlled, for example, by a discharge valve (not shown). The molding fluid is discharged through nozzle 32 .

The discharge flow of molding fluid is controlled so that the pressure within the body remains high enough to hold the deformed wall tightly against the profile for the required time so that the wall retains the shape imparted by the profile. In other words, the pressure in the preform drops slowly, even increasing before the drop, to allow the portions 50, 52 of the walls that are in contact with the profiles 44, 46 to securely hold the impressions of the profiles. Thus, the portions 50, 52 of the walls are held against the profiles 44, 46 for the time required for the walls to cool below the glass transition temperature "Tg".

Here, the discharge flow rate is fixed at a constant value, for example by a valve or by passage constriction, so that it is less than the rate of change of the volume of the container when the body 20 is squeezed between the two dies 42 .

Contact of the lateral portion 52 of the body 20 with the movable profile 44 causes said lateral portion 52 to cool below the glass transition temperature "Tg".

At least a second portion 54 of the deformed wall portion of the final container 10C, referred to as the "free" portion, does not come into contact with any profile, at least until the temperature of the body drops below its glass transition temperature "Tg". Here, the free second portion 54 is never in contact with the profile.

The final container as shown in FIG. 7 is thus formed. The final container has two flattened sides 52 corresponding to the lateral portions 52 in contact with the movable profile 44 of the mould. The lower bottom 50 of the final container has the shape of an upwardly convex corrugation, wherein the edges of the corrugations correspond to the portion 50 of the bottom that is in contact with the fixing profile 46 . During the process, the vertical dimension between the bottom 50 and the neck 16 is manipulated by the presence of the wedge 48 .

A vertical side 54 of the container corresponding to the second portion 54 remaining free connects the two sides 52 to each other. These sides 54 are the parts of the wall that are not in contact with the profile. As the final container 10C cools below its glass transition temperature "Tg," the material making up these sides 54 contracts to form corrugations similar to those of the bottom 50 of the final container 10C.

The thermoplastic material making up the final container 10C is sufficiently elastic to allow the corrugations of the sides 54 and bottom 50 to form folds that allow the two sides 52 to separate laterally relative to each other when the container 10C is filled with liquid.

Thus, such a container 10C forms a flexible bag in which the neck 16 of the flexible bag is integrally formed with the main body 20 . The pouch is intended to receive liquid or viscous products, which can be expelled by squeezing the sides 52 against each other. Advantageously, the neck 16 is provided with a thread that allows the container 10C to be capped with a stopper (not shown), thus allowing it to be closed.

Thus, the method according to the teaching of the present invention allows forming the container 10C in a very simple manner, since it is not necessary to provide a mold with a complete cavity of the final container 10C.

Additionally, the molding fluid is injected into the preform 10A at extremely low pressures compared to the pressures typically required to form containers by blow molding.

As a variant of the invention not shown, each movable mold 42 has temperature maintaining means for maintaining the movable profile 44 at a determined temperature. The temperature maintaining means is, for example, a circulation circuit for a heat transfer fluid. Wedge 48 may also be equipped with similar temperature maintaining components. Thus, said temperature maintaining means allow maintaining the profiles 44, 48 at a temperature suitable for container forming, especially when containers are formed in batches with a high frequency.

Furthermore, this method allows to obtain a pouch-like container which, together with its neck, forms a single part.

It will be appreciated that the method may be used to form containers having shapes other than bags. Thus, the method can use more than two movable profiles, which are not necessarily arranged opposite each other.

In addition, this method allows saving material compared to known forming methods. In fact, conventional containers formed according to the methods of the prior art must be rigid and therefore have relatively thick walls. The flexible bag obtained by the method according to the invention can be formed with thinner walls than those of conventional containers, which allows saving a considerable amount of material.

Claims (9)

1. A method of forming a final container (10C) made of thermoplastic material by stretch-blowing from a preform (10A), the body (20) of which is heated above its glass transition temperature (Tg), The methods include: - a first step (E1) of positioning the neck (16) of the preform (10A) on the fixed support (26); - a second step (E2) of free expansion, during which a pressurized molding fluid is injected into the preform (10A) to deform the hot body (20) of the preform, and during the second step In a two-step process, a stretch rod (38) is introduced axially into the preform (10A) to separate the base (12) of the preform (10A) axially relative to the neck (16). while axially stretching the main body (20), so that the preform (10A) is formed into a bubble-like intermediate container (10B); - a third step (E3) of forming, during which at least a first portion (50, 52) of the deformed wall portion of the preform (10A) comes into contact with at least one profile (44, 46) , to give the final container (10C) the final shape, at least a second portion (54) of the deformed wall of the intermediate container (10B) is not in contact with any profile, at least until the final container (10C) cools below its Glass transition temperature (Tg), It is characterized in that the third step (E3) comprises an active forming phase (E3-2), during which at least one profile (44), called "movable" profile, is positioned relative to the fixed support (26) Move between: - a waiting position, in which the movable profile is not in contact with the deformed wall of the body (20); - and the shape limit position, in which the movable profile squeezes a part (52) of the deformed wall portion of the main body (20) to reduce the volume of the intermediate container (10B). 2. The method according to claim 1, characterized in that, during the active forming phase (E3-2) of the third step (E3), at least two opposite movable profiles (44) simultaneously moving towards each other in order to squeeze the main body (20) of the intermediate container (10B), the two movable profiles (44) are radially separated from each other in their shape limit position, so that the squeezed part of the wall (52) Not touching each other. 3. A method according to any one of the preceding claims, characterized in that the active forming phase (E3-2) is started after the injection of the pressurized forming fluid into the intermediate container (10B) has ended. 4. Method according to any one of the preceding claims, characterized in that the third step (E3) comprises a passive forming phase (E3-1) preceding the active forming phase (E3-2), in which During the process, the injection of the pressurized forming fluid started at the second step (E2) continues, and during the passive forming phase, a portion (50) of the deformed wall portion of the intermediate container (10B) is aligned with the fixed The support ( 26 ) is in contact with a profile ( 46 ), called the "fixed" profile, which does not move. 5. Method according to any one of the preceding claims, characterized in that the pressurized forming fluid is injected at a constant pressure of less than 20 bar. 6. Method according to claim 5, characterized in that the pressurized forming fluid is injected at a pressure of less than 10 bar, in particular at 5 bar. 7. The method according to any one of the preceding claims, characterized in that, during the active forming stage (E3-2) of the third step (E3), the discharge flow rate of the pressurized forming fluid is controlled so that the movable At the end of the movement of the profile (44), the pressure in the body remains high enough to hold the deformed wall against the movable profile for the time required for the wall to cool below the glass transition temperature (Tg) (44), so that the wall retains the shape imparted by the profile. 8. The method according to claim 7, characterized in that, in the third step, the pressurized molding fluid is discharged at a determined constant flow rate. 9. An apparatus (24) for applying the method according to any one of the preceding claims, said apparatus (24) comprising: - a fixed support (26) for receiving the neck (16) of the pre-form (10A), a blowing part for blowing pressurized molding fluid into the neck (16) of the pre-form (10A) ( 32); - stretch rod (38) able to slide axially; - at least one radially movable die (42) with a movable profile (44), It is characterized in that each radially movable mold (42) has a temperature maintaining member for maintaining the movable profile (44) at a determined temperature.