Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C51/00—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
  • B29C51/04—Combined thermoforming and prestretching, e.g. biaxial stretching
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C2791/00—Shaping characteristics in general
  • B29C2791/004—Shaping under special conditions
  • B29C2791/007—Using fluid under pressure
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C51/00—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
  • B29C51/10—Forming by pressure difference, e.g. vacuum

Definitions

• the present invention relates to the manufacture of plastic pots intended to contain liquid or pasty products such as edible foodstuffs, dairy products, fruit juices, etc. or inedible foodstuffs, for example cleaning products, shampoo, detergents, etc ...
• plastic pots are usually made by the ⁇ noformage by deforming with a punch a sheet of heated plastic material and pinched between a counter mold and a mold in which is formed an imprint in hollow corresponding to the shape of the pot which must be manufactured.
• the punch descends to the bottom of the mold by taking and stretching the plastic material so as to make it take the shape of the imprint.
• the main problem which arises during the thermoforming of a pot is that of the non-uniformity of the thickness of the walls due to the fact that the material is not uniformly stretched.
• the first punches of shape and dimensions such that they almost completely fill the mold imprint, are very complex to implement because the portion of material they contact at the start of their descent is practically not stretched , while the portion of plastic material between the support means of the punch and the upper rim pinched between the mold and the counter-mold is very stretched.
• the pots thus obtained have a very thin peripheral wall and therefore very weak.
• the aforementioned patent FR 73 03314 proposes improving the thermoforming operation of the pots by providing a finger disposed axially in the punch which is moved towards the front of the punch.
• This finger is intended to prevent the material from being pressed against the end face of the punch and to keep the material its stretching capacity.
• the punch continues its stroke until it is also in contact with the background while the finger is retracted.
• the material tends to return to its initial shape, which practically cancels the stretching carried out by the movable finger.
• this type of punch does not completely solve the problem of the non-uniformity of thickness of the walls of the pot because the material slides very little on the periphery of the end face of the punch, the stretching caused by the finger retractable therefore brings very little improvement.
• Other devices have also been proposed in an attempt to improve the quality of the pots obtained by mermoforming.
• the patent FR 7438821 proposes to shape the punch so that it is radially expandable.
• the punch consists of a large number of articulated blades arranged around a central point so as to form a sort of funnel. .
• the blades pivot so as to increase the radius of the circle formed by their free ends, until they are in contact with the periphery of the background of the imprint. In doing so, the blades stretch the material initially pushed by the punch.
• This device effectively makes it possible to better stretch the plastic material and to obtain its best distribution against the walls of the imprint.
• it has the disadvantage of being very fragile and of not allowing high working rates due to the number of moving parts which it comprises. It is more expensive to manufacture.
• the material is only cooled at these extremely small surface contact points, which makes it possible to reduce the heating temperature of the plastic sheet and to obtain a more regular stretching of the material between the punch and the upper edge of the imprint, and therefore pots whose walls are less fragile.
• the object of the present invention is to provide a thermoforming process which. allows maximum use of the stretching capacity of the surface of material on which the punch acts and to obtain a container whose thickness is substantially uniform over its entire surface (peripheral walls and bottom).
• This process is further adapted to be implemented at high rates in the machines usually called "form-fill-seaT in which the pots are formed from a sheet of plastic material, filled and closed at a rate of 30 jars per minute and per thermoforming imprint.
• the method according to the invention of the type in which a sheet of preheated plastic material is pinched between a mold and a counter-mold and then stretched by a punch resting on the plastic sheet by a plurality of means of support of reduced surface defining between them a disc of material, then cooled and withdrawn from the mold after withdrawal of the punch is characterized in that the stroke of the punch is less than the depth of the mold and in that, after the arrival of the punch in limit switch, without contact with the bottom of the mold, a pressurized air blowing is carried out in the direction of the portion of material defined by the support means of the punch.
• the method according to the invention is also remarkable in that:
• the plastic forming the portion of material between the support means of the punch constitutes the bottom of the pot and the lower part of the peripheral walls of the pot to a plane disposed at a distance from the bottom of the imprint substantially equal to the height of the lowest point reached by the punch during its movement, while the plastic material constituting the crown disposed between the means for supporting the punch and the peripheral wall of the impression forms the peripheral wall of the pot located between said plane and the top of the pot,
• the process is such that the blowing of pressurized air in the direction of the material between the support means and relaxed by the movable finger, is controlled when the movable finger is retracted,
• the punch implemented comprises a movable finger which, extending towards the front of the punch during its downward stroke in the cavity, makes it possible to stretch the plastic material constituting the portion of material between the support means, the method is such that: - during the stroke of the punch towards the bottom of the impression, the movable finger is moved forward relative to the punch body and then retracted before said finger touches the bottom of imprint,
• the body of the punch continues its course in the direction of the bottom of the imprint after the blowing control so as to continue accompanying the material towards the bottom of the imprint during blowing,
• the air injection channel is a single channel located in the center of the punch
• the air injection channel consists of several channels opening at different points on the end face of the punch.
• the invention also provides a punch for implementing the method of thermoforming pots by stretching and blowing a sheet of plastic material, pinched between a mold and a counter-mold, driven by the support means of said punch during of its stroke towards the bottom of the mold, characterized in that it comprises means for drawing the portion of material included inside the support means of the punch, such that said portion of material not only forms the bottom but also the lower part of the walls of the pot
• the punch according to the invention is also remarkable in that:
• - It consists of a tail and a disc carrying fingers with rounded ends which are distributed around the circumference of the disc, and comprises an air injection channel extending axially in the tail and opening into the disc.
• - It has a peripheral skirt whose front end is cut so as to form recessed parts which do not touch the plastic sheet and parts constituting the support means of reduced surface, and an injection channel d air extending axially in the tail and emerging inside the peripheral skirt
• - It comprises a generally tabular ring whose end directed towards the material to be formed is flared in order to constitute support means in the form of a ring of small radial dimension, and whose central bore ensures the routing of the blowing air in the direction of the material entrained towards the bottom of the cavity, - it comprises a core attached to a rod and which carries fins, held in place by a ring screwed onto this core and distributed over its periphery, whose free ends project beyond the front of the core so as to form the support means with reduced surface area, said ring being traversed by vertical channels arranged between the fins and intended to ensure a circulation of pressurized air in the direction of the front end of the punch,
• the core carries several crowns of points arranged further and further from the end face of said core and distributed over circles of different radii, the radius decreasing as one moves away from the nucleus,
• the finger has a finger mounted on the punch so as to protrude from the front of the support means, - the finger has fins or points distributed over a circle of small diameter,
• the finger is movable, it is carried by a rod mounted in a bore in the core, said movable finger being positioned in the center of the end face of the punch and movable in translation relative to the core, its external surface carries a bead intended to come into contact with the stretched material between the means for supporting the punch and the upper edge of the impression in order to participate in the stretching of this material,
• the invention also relates to a pot obtained by the implementation of the method and the punch according to the invention, characterized in that it has zones of thickness slightly greater than the thickness of the rest of the peripheral wall at of a plane arranged at a distance from the bottom of the pot, said zones being constituted by the material cooled in contact with the means for supporting the punch.
• the peripheral wall has at least one slightly thicker ring of material.
• FIGS. 2 and 3 show two embodiments of the end face of the punch used in the method according to the invention
• FIG. 4 is a schematic view of another embodiment of a punch used in the method according to the invention.
• FIGS. 5a to 5f schematically show the steps of the method according to the invention when it is implemented with a plunger with a movable finger
• - Figure 6 is a sectional view of a first embodiment of a movable finger punch that can be implemented in the method according to the invention
• - Figure 7 is a schematic view of a finger punch mobile according to a second embodiment.
• Figure 1 are shown schematically the mold 1 having an imprint 10, the counter-mold 2 and the punch 3 used for the production of a pot from the plastic sheet 12 previously heated and pinched between said molds and counter mold.
• the arrows P and A respectively represent the direction of movement of the punch and the injection of air under pressure.
• the punch 3 is moved in the direction of the bottom of the cavity 10, during this step, the punch 3 comes into contact with the plastic sheet 12 by the end of its means of support, then push this leaf.
• the stroke of the punch 3 is less than the depth of the cavity 10 of the mold, this movement is thus stopped before the punch touches the bottom of the cavity 10.
• the second step of the process according to the invention is carried out, consisting of a blowing of pressurized air in direction of the material between the support means of the punch.
• the blowing is carried out through the channel 30 of the punch.
• the air injection channel 30 opens into the end face of the punch so as to act in the direction of the portion of material included between the means for supporting the punch.
• this portion of material may be called a disc 121 although the support means of the punch arranged at the front of said punch may not be arranged according to a circumference but according to any other contour.
• air is injected through a single channel 30 located in the center of the punch, this channel can alternatively be replaced by several channels opening at different points on the end face of the punch.
• pressurized air makes it possible, in a manner known per se, to complete the drawing of the plastic material and to press it against the walls of the cavity.
• the blowing can be carried out on the periphery of the punch, outside of the support means thereof, it then acts on the edge of the material driven in front of the means d 'support.
• the air is sent parallel to the axis of the punch.
• the plastic forming the disc 121 of material defined by the support means of the punch forms the bottom of the pot and the lower part of the peripheral walls of the pot to a plane P disposed at a distance from the bottom of the footprint substantially equal to the height H of the lowest point reached by the punch during its movement.
• thermoforming method makes it possible to obtain a stretching of all the plastic material entrained by the punch: both that of the disc 121 and that of the crown 120.
• the thickness of the walls of the pots obtained according to the method of the invention is substantially constant, which gives said pots good mechanical strength. Furthermore, the material of the disc 121 being as much stretched as the material of the crown 120, it is possible on the one hand to reduce the amount of material used for the manufacture of each jar and on the other hand to adapt the dimension of the disc 121, and consequently the diameter d of the punch, or more exactly of the crown formed by the support means, as a function of the dimensions of the pot to be obtained.
• the diameter d of the punch can then be very much less than the diameter D of the pot to be produced.
• the pots usually used for packaging dairy products have a height of approximately 65 mm and a diameter of approximately 55 mm.
• these pots can be formed with sheets of 70 / 100th of thickness by implementing a punch whose support means are arranged on a circle of 38 millimeters in diameter including the descent stroke stops 8 millimeters from the bottom of the footprint.
• the punch allowing the implementation of the method of the invention is thus a punch comprising means for realizing a stretching of the portion of material included inside the support means of the punch, such that said portion of material forms not only the bottom but also the lower part of the walls of the pot.
• the constructive parameters of such a punch are in combination: the coefficient of stretching of the plastic material used, the depth of the pot to be manufactured, a contact by reduced surface of the means for supporting the punch on the material and a blowing in the direction of the portion of material defined by said support means
• FIGS. 2 and 3 show two embodiments of the punch. These punches are similar to those described in FR 94 11581. However, they differ from the punches described in the aforementioned document in that they comprise, for the implementation of the method according to the invention, a channel 30 air injection opening into their end face and in that their dimension is adapted to the dimensions of the pot to be formed.
• the punch consists of a tail 31 and a disc 32 carrying fingers 33 with rounded ends.
• the fingers 33 are distributed around the circumference of the disc 32 and constitute the support means with reduced surface area.
• the air injection channel 30 extends axially in the tail 31 of the punch and opens into the disc 32 so as to act on the plastic material pushed back at the front of the punch when it descends into the cavity 1 of the mold.
• the punch shown in Figure 3 has a peripheral skirt 34 whose front end is cut so as to form recessed portions 36 which do not touch the plastic sheet and portions 35 constituting the support means of reduced surface .
• the cutting of the peripheral skirt 34 can of course be carried out according to undulations as shown in the drawing, or according to any other shape such as spikes.
• the air injection channel 30 extends axially in the tail 31 and opens out inside the peripheral skirt 34.
• FIG. 4 represents another alternative embodiment of a punch implemented in the method of the invention.
• This punch has a generally tubular ring 534 whose end directed towards the material to be formed is flared in order to constitute the support means 533.
• the central bore 531 of said ring 534 ensures the supply of the blowing air in direction of the entrained material towards the bottom of the imprint.
• the support means 533 are in this form of embodiment in the form of a ring of small radial dimension. It is of course possible to propose an alternative embodiment of this punch in iacUe the front end of the ring 534 is deformed, for example by undulations, so as to form support means spaced circumferentially from each other.
• the ring 534 can be made of a synthetic material generally known under the name of Nylon, for example that sold under the name EXALRET. The use of this material, associated with the use of small surface support means, makes it possible to reduce the cooling which the material undergoes when it is pushed by the punch.
• the ring 534 of the punch carries a bead 541 intended, as will be explained later, to participate in the drawing of the material located between the punch and the edge of the imprint.
• the punch shown in FIG. 4 also includes a finger 538 carried by a rod 536 mounted in a bore 537 of the ring 534.
• This finger 538 placed in the center of the ring pushes the disc of material defined by the support means so that it does not tend to enter the internal space of said ring.
• the finger 538 is shown in the drawing with its end in the plane of the support means. As a variant, it is possible to position the finger so that its end extends in front of said support means
• the method according to the invention is implemented with a punch comprising a movable finger which, extending towards the front of the punch, makes it possible to further improve the drawing of the plastic material constituting the disc 121 defined by the support means.
• FIGS. 5a to 5f Such a punch 4 with support means 43 of reduced surface and movable finger 41 is shown diagrammatically in FIGS. 5a to 5f which show the different stages of the thermoforming process.
• the arrows PI and P2 respectively represent the displacements of the support means 43 and of the movable finger 41.
• end 42 of the movable finger 41 is, in the example shown in the drawing, in the same plane as the ends of the support means 43 so as to come into contact with the plastic sheet at the same when said support means 43.
• said finger may have its end 42 disposed at the front of the support means 43 of the punch so as to come into contact with the plastic before said means 43 and thus ensure a first stretching of the disc 121 of material defined by said support means.
• the punch 4 continues to run towards the bottom of the cavity while the movable finger 42 is moved forward relative to the body of the punch.
• This forward movement of the movable finger 42 makes it possible to stretch the disc 121 of material driven at the front of the punch 4 by the support means of reduced surface area 43 by transforming it into a cone 123.
• the direction of movement P2 of the movable finger is inverted so that it returns to its initial rest position inside the body of the punch 4.
• the blowing of pressurized air A towards the material defined by the means d support 43 and relaxed in cone 123 by the movable finger 42 is controlled when the direction of movement of the movable finger is reversed.
• the injected air pushing the material towards the bottom of the imprint at the time of the inversion of the direction of movement of the movable finger, makes it possible to prevent it being entrained by the movable finger at the time of its withdrawal.
• the body of the punch 4 continues its course in the direction of the bottom of the cavity until reaching the distance H above said bottom.
• This step makes it possible to continue accompanying the material towards the bottom of the imprint during the blowing, which improves the effects of the blowing and makes it possible to ensure a finish of the stretching of the peripheral walls.
• the punch thus reached at the end of the stroke is then returned to its initial position (FIG. 5f).
• the method according to the invention consists in controlling the movable finger so that U carries out a backward and forward stroke of the support means during the stroke of the punch, the injection of air being controlled at the time of the reversal of the stroke of the movable finger, the strokes of the movable finger and of the support means being stopped at a distance from the bottom of the cavity.
• the movable finger 41 is disposed in its position for laqueUe it is at the end of the output travel at the front of the punch before the punch is brought into the cavity. The material is then stretched in front of the support means of the punch before the latter come into contact with the plastic sheet.
• the punch is lowered into the cavity and the movable finger is (as before) retracted before it touches the bottom of the cavity while the blowing of air is controlled.
• the thickness of the walls of the pots obtained by this process has variations of less than 2/100 th of a millimeter.
• the thickness of the plastic sheet used is precisely adapted to the containers to be formed.
• the pots obtained are also more mechanically resistant to compression due to the uniformity of the thickness of their walls, which makes it possible to have an additional layer of pots on the transport pallets. It is then possible to carry more pots during a trip which generates significant savings.
• FIG. 6 shows an example of the use of a movable finger punch particularly suitable for implementing the method according to the invention.
• the counter-mold of the mermoforming device is produced in two parts 210 and 211.
• the lower part 210 of this counter-mold is crossed by a bore 213 while the upper part 211 is crossed by a bore 212.
• the punch is positioned in the counter-mold, with its rod 431 in the bore 212 and its head in the bore 213.
• the rod 431 of the punch is adapted to couUsser in the bore 212 under the action of control means not shown in the drawing.
• the punch shown is a punch of the fin type, that is to say a punch carrying support means of reduced surface formed by the ends of tongues arranged at the end of the punch.
• This punch comprises a core 432 which is attached for example by screwing on the rod 431 and which carries fins 433 distributed over its periphery.
• these fins are planar, positioned in the grooves of the core 432 and held in place by a ring 434 screwed onto this core 432.
• the ends of the fins 433 protrude from the front of the core 432 so to form the support means with reduced surface.
• the ends of the fins are, in the example shown, terminated by points 435 so that the contact of the end of each fin with the plastic sheet is punctual.
• the fins are metalhques and are preferably made of spring stainless steel so as to limit their wear so that the tips 435 do not dull.
• the core 432 can carry several crowns of points disposed increasingly farther from the end face of said core and distributed over circles of different radii, the radius decreasing as the we move away from the core 432.
• a pipe 215 allows the introduction of pressurized air into the bore 213 of the counter mold to press the plastic against the walls of the cavity.
• the external surface of the ring 434 carries a bead 441 and a ferrule 442 whose external diameters are suitable for sealing the bore 213.
• the ring 434 is crossed by vertical channels 443 disposed between the fins
• the punch comprises a movable finger 438 carried by a rod 436 slidably mounted in a bore 437 of the core 432.
• the rod 436 is longer than the core 432 and extends partly in the internal bore 439 of the rod 431 of the punch.
• the finger 438 is mounted on the punch so as to be in the same plane as the end tips of the fins.
• the finger 438 is positioned in the center of the end face of the punch and is movable in translation relative to the core 432, and therefore to the tips 435 which it carries.
• Means not shown in the drawing ensure the displacement of the rod 436 carrying the finger 438 relative to the core 432. They may extend partly in the bore 439 of the punch rod in order to control the enlarged end of said rod 436.
• a spring 404 recalls said rod 436 and the finger 438 upwards
• the means for controlling the displacement of the rod 436 have not been shown so as not to overload the drawing and can be of any type. They are preferably such that they use the movement of the punch in order to control the movement of the rod 436 to the movement of the punch.
• the movable finger 438 may not be a single point as shown in the drawing but have fins or points distributed over a circle of small diameter.
• the method according to the invention makes it possible to reduce the external diameter of the punch by the fact that all the material is suitably drawn, both from the central disc 121 and from that of the crown 120.
• Reducing the diameter of the punch is particularly advantageous during the manufacture of decorated pots for which the decorated support is placed in the mold cavity before the formation of the pot because it makes it possible to avoid entrainment of said support by the punch during of his descent.
• pots the height of which is twice that currently used for packaging dairy products, ie around 130 mm, the remaining diameter of 55 mm.
• These pots were formed from a sheet of plastic material 140 / 100th thick, with a punch whose fins are distributed over a diameter of 28 mm, the stroke of the movable finger in front of the fins is 20 mm and the descent of the punch is stopped at 15 mm from the bottom of the impression.
• the bead 441 of the ring 434 has a second role which is particularly useful during the production of deep draws which consists in coming into contact with the drawn material between the means for supporting the punch and the upper edge of the impression in order to participate the stretching of this material.
• the entrainment of the material by the bead 441 makes it possible to reduce the support pressure of the fins and to avoid tearing of the material.
• the material is cooled when it comes into contact with the bead 441 which creates on the peripheral wall of the pot a ring in which the material is a little thicker.
• This ring then constitutes a belt for stiffening the pot, giving it good mechanical strength.
• the punch shown schematically in Figure 7 is a variant of réaUsation of the punch of Figure 6 particularly intended for very deep drawing.
• Its ring 434 does not carry a bead 441 but three beads 441, 451 and 461 distributed on its wall
• These three beads have different diameters, the diameters being increasing from the bead 441 located closest to the fins 433 towards the bead 461 located farthest from said fins.
• the bead 441 is placed approximately 15 mm above the fins 433, then the other beads are placed above the bead 441, the space between two consecutive beads being approximately 15 to 20 mm.
• this punch to achieve a deep stretch allows to uniformly stretch the material by distributing the forces on the fins and on the beads as the descent of the punch. Thanks to the method according to the invention, the applicant plans to form refills with thin walls, for example about 140 mm high and 35 mm in diameter, intended to be positioned in a support and surmounted by a stopper carrying a teat for market ready-to-use children's drinks or a pouring cap to market cleaning products. As can be seen in FIG. 7, the ends of the fins 433 can be chamfered on their outer edge so as to be less aggressive with regard to the plastic.
• the punches that can be implemented according to the invention can of course have other alternative embodiments than those described by way of example above. It is for example possible to modify the punches shown in FIGS. 2 and 3 by adding a fixed or mobile finger and or peripheral beads to adapt them for their implementation for very deep drawing, or to make the finger disposed in the punch in Figure 4.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)

Applications Claiming Priority (3)

Publications (1)

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ID=9503845

Family Applications (1)

Country Status (4)

Family Cites Families (5)

• 1997
  • 1997-02-18 FR FR9701873A patent/FR2759623B1/fr not_active Expired - Fee Related
• 1998
  • 1998-02-17 AU AU64048/98A patent/AU6404898A/en not_active Abandoned
  • 1998-02-17 WO PCT/FR1998/000297 patent/WO1998036895A1/fr not_active Application Discontinuation
  • 1998-02-17 EP EP98909548A patent/EP0961681A1/de not_active Withdrawn

Non-Patent Citations (1)

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