(19)
(11)EP 0 213 673 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
12.07.1989 Bulletin 1989/28

(21)Application number: 86201431.3

(22)Date of filing:  15.08.1986
(51)International Patent Classification (IPC)4B65D 77/28

(54)

Container for drink and method of manufacturing the container

Getränkebehälter und Verfahren zu seiner Herstellung

Récipient pour boissons et procédé de fabrication


(84)Designated Contracting States:
AT BE CH DE FR GB IT LI NL SE

(30)Priority: 28.08.1985 NL 8502366

(43)Date of publication of application:
11.03.1987 Bulletin 1987/11

(73)Proprietor: KONINKLIJKE EMBALLAGE INDUSTRIE VAN LEER B.V.
1182 HL Amstelveen (NL)

(72)Inventors:
  • Koudstaal, Willem
    NL-3645 JB Vinkeveen (NL)
  • Thomas, Alan
    Horsell Park Woking GU21 4LU Surrey (GB)
  • Lewis, Jeffrey Lloyd
    Farnham Surrey (GB)

(74)Representative: van der Beek, George Frans, Ir. et al
Nederlandsch Octrooibureau P.O. Box 29720
2502 LS 's-Gravenhage
2502 LS 's-Gravenhage (NL)


(56)References cited: : 
EP-A- 0 106 648
GB-A- 723 588
US-A- 3 545 604
FR-A- 1 264 666
US-A- 2 996 239
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] The invention relates to a container for drink consisting of a bag of flexible thermoplastic material, comprising sheets of plastic material which are welded upon each other by means of longitudinal and transverse seams, which bag moreover is provided with a third sheet, welded upon the bag material in a manner such that a space is obtained into which a small straw can be inserted.

    [0002] A container of this type is known, for example, from the British Patent 723 588. In this known container the part which defines the space into which a straw can be inserted consists of a sleeve which is open at the end facing the interior of the bag and forms a valve at that point which is closed by the pressure of the liquid because the wall parts of the sleeve are pressed against each other. The sleeve is secured by welding into one of the longitudinal seams of the bag and has a section projecting outwards which can be sealed by folding. If this end is opened, then a small straw can be inserted into the sleeve, as a result of which the latter loses its valve function and opens up so that the contents can be consumed.

    [0003] This known container has the drawback that the valve is not always adequately sealed and that the manufacture is complicated. At the point where the sleeve extends through the transverse seam, the number of layers welded onto to each other is locally doubled, which often gives rise to a poor weld as a result of which leakage way occur. In addition, the small straw is a loose component which has to be supplied separately.

    [0004] The object of the invention is to provide a container in which said drawbacks no longer occur.

    [0005] This object is achieved according to the invention in the first place in that the space for the insertion therein of the straw is exclusively defined by welding seams between one of the two sheets forming the bag and the third sheet, which welding seams are situated in such a manner that the seams defining the said space leave unchanged the layer thickness of the longitudinal and transverse seams of the bag and that the outer sheet of the two sheets which define the said space is provided with an opening inside the region of the longitudinal and transverse seams which define the said space, through which opening a straw can be inserted or has been inserted. According to the invention the space for the inserting therein of the small straw therefore now has only an insertion opening in which a small straw can be placed but the space itself is closed. The valve function therefore no longer exists. If it is desired to consume the contents of the container, the wall has to be punctured by means of the small straw, an operation which is otherwise known in the case of containers with small straws supplied loose. Because the space is normally closed and has only an insertion opening, the small straw may already have been placed in the insertion opening before the container is delivered. The small straw is therefore no longer a loose component, or at least does not have to be one.

    [0006] The welding seams which define the insertion space for the small straw leave the layer thickness at the position of the longitudinal or transverse seams of the bag undisturbed, as a result of which the risk of leakage is avoided.

    [0007] According to the invention the inner sheet defining the said space and facing the interior of the bag may consist of an elastically deformable film and the small straw may be obliquely cut off at its lower end at an acute angle such that the straw after perforation of the said inner sheet elastically expands the opening formed by the perforation.

    [0008] This has the result that the film surrounds the small straw so as to form a seal. No leakage can therefore occur along the outside wall of the small straw during the consumption of the contents or if a portion of the content is still being kept.

    [0009] It is observed that from US-A 3 545 604 a container is known for a liquid drink comprising a bag from thermoplastic material with welding seams at top and bottom which bag at one side has a cover sheet of substantially the same dimensions as the side wall of the bag which cover sheet is adhered to said side wall and keeps in place a straw. After tearing away part of the cover sheet said straw can be removed and used for consumption of the drink by puncturing the wall of the bag with the sharpened outer end of the straw. This cover sheet is adhered to the bag after having filled and sealed the bag. Said cover sheet accordingly does not interfere with the welding seams of the bag, but on the other hand does not provide a sealed space within which the straw can already be present, need not to be removed for puncturing the wall and consuming the drink whereas said cover sheet does not form either a space into which liquid can penetrate without leakage.

    [0010] The container of US-A 3 545 604 has to be of a material of adequate strength. The cover sheet is not a wall of the container, it merely provides a pocket for the straw. Said straw has to pierce the outer wall of the container which wall for obvious reasons has to be puncture resistant.

    [0011] The container according to the present invention also has outer walls of adequate strength when as the third sheet which lies inside the outer walls forms the pocket for the straw can be of a material which is selected for its elastic deformability and capability of becoming pierced by the straw which material after being pierced elastically clamps around the straw so that leakage can be avoided.

    [0012] According to the invention the third sheet may be a strip welded onto one wall of the bag and having a length and width respectively which are shorter than the longitudinal and transverse seams respectively of the bag. In that case the longitudinal and transverse seams defining the space for the inser- ion of the straw are kept at a distance from the longitudinal and transverse seams which define the bag.

    [0013] According to a preferred embodiment of the invention the width and length of this third sheet may be equal to the width and the length respectively of the wall sheets of the bag so that the welding seams of the three sheets coincide. Accordingly the bag is formed out of three sheets of which two sheets define a space for receiving the liquid and one of said two sheets with the third sheet defines the space for the insertion of the straw. All welding seams are triple seams.

    [0014] Moreover if such a third sheet is used having dimensions which are equal to those of the side walls of the bag it is according to the invention further possible to provide additional welding seams between said third sheet and one of the wall sheets. Said additional seams may consist of a longitudinal seam which extends from the top transverse triple layer seam of the bag to a transverse seam and the said transverse seam extends from said longitudinal seam to a longitudinal triple layer bag wall seam, said additional seams defining the said space for the straw.

    [0015] The invention also relates to a method for making a bag according to the invention in which two sheets of thermoplastic plastic material are brought up against each other and bags are formed by means of welding seams, in which process, according to the invention, a third sheet is then brought up against one of the sheets defining the bag wall and is secured thereto by welding to form the said space before or during the welding of the bag seams, the sheet which defines the outside wall of the space is provided before welding with insertion openings at distances from each other which coincide with the pitch distance of the bags, said openings are opened after welding the sheets defining the space to each other and a small straw is inserted into each of said opened openings in step with the advance of the sheets.

    [0016] According to the invention, therefore, the third sheet is welded onto one of the two sheets before the bags are formed in order to form the insertion space, or the three sheets are welded to each other simultaneously.

    [0017] If the third sheet is applied to the outside of a bag wall, said third sheet should be provided with the insertion opening for the small straw. However, if the third sheet is applied to the inside of a sheet of film defining a bag wall, said sheet of film determining a bag wall should be provided with the insertion opening for the small straw. The opening of the insertion opening can be performed in an easy manner with nozzles, after which small straws can be inserted into the openings from the top, for example by means of a device which operates in step, which feeds the small straws and inserts them into the openings by means of a transverse stroke.

    [0018] The invention thus now provides the possibility of providing a container for drink which is already provided with a small straw, is easy to manufacture and presents no leakage problems.

    [0019] The invention will now be explained in more detail by reference to the drawings.

    Figure 1 is a front view of a container according to the invention.

    Figure 2 is a section along the lint II-II of Figure 1.

    Figure 3 is a section along the line 111-111 of Figure 1.

    Figure 4 is a front view of another embodiment of the container according to the invention.

    Figure 5 is a section along the line V-V of Figure 4.

    Figure 6 is a front view of yet another embodiment of the container according to the invention.

    Figure 7 is a section along the line VII-VII of Figure 6.

    Figure 8 shows diagrammatically in perspective a device for applying the method for the manufacture of the container according to the invention.



    [0020] The container shown in the drawings consists of two films 1 and 2 respectively in the form of sheets of film which are formed by vertical welding seams 3 and 4 respectively and a horizontal bottom seam 5 into bags which are closed after filling by means of the top welding seam 6.

    [0021] Before the films 1 and 2 are welded to each other by means of the vertical seams 3 and 4 respectively, a strip 7 is attached by welding by means of the vertical welding seams 8 and 9 and the horizontal welding seams 10 and 11 to the inside surface of the film 2 or to the outside surface of said film.

    [0022] Before this an opening is punched in the film 2 at 12 for the insertion therein of a small straw 13 which is provided with a sharp point 14 and preferably consists of the type which has a pleated bent section 15 so that the end 16 can be laid flat against the side wall of the container. A bag of this type is completely closed. If it is desired to consume the contents, the small straw is thrust through the bottom section 17 of the welded-in strip 7 by means of the sharp point.

    [0023] If the strip 7 is welded onto the outside of the sheet of film 2 the strip 7 should be provided with an insertion opening and the sharp point of the small straw must be pressed through the sheet of film 2, i.e. through the wall of the container.

    [0024] If the contents are only partially consumed, the container can conceivably be sealed by pulling the small straw back, in which case the pressure of the contents will press the strip 7 against the inside wall 2. A valve action is then produced such as is known per se in the container according to the British Patent 723 588 mentioned earlier.

    [0025] It is, however, of greater benefit to take for the wall to be pierced a material which is elastically deformable such as, for example, a low-pressure polyethylene. With a sufficiently robust small straw and a point cut off obliquely, for example cut off at 45°, the point of the small straw will pierce the film material, after which the hole formed is elastically expanded and forms a seal around the small straw. Leakage along the outside wall of the small straw is not then possible, which is of benefit both during the consumption of the contents and if a portion of the contents is being kept.

    [0026] Whereas in the embodiment of the Figures 1, 2 and 3, the strip has welding seams 8 to 11 incl. which are clearly situated at a distance from the welding seams 3 to 6 incl. of the container, it is, of course, also possible to apply welding seams in a different manner without this resulting in a change of the layer thickness at the position of the welding seams 3 to 6 incl. of the container. Possibilities of this type are shown in the Figures 4 to 7 incl.

    [0027] In the embodiment of figures 4 and 5, the starting point is sheets of film of the same width. To the sheets of film 1 and 2 is added a third sheet of film 23 which defines the space 24 for the small straw 13. There are therefore now no separate welding seams, but the welding seams 3, 4, 5 and 6 comprise three layers instead of two layers. Over the entire length of each welding seam, however, the number of layers remains constant.

    [0028] In this embodiment the small straw 13 is secured to the outside wall of the container by means of an adhesive strip 25 which can be pulled off. This adhe- sive strip can be used in any embodiment.

    [0029] The embodiment according to Figures 6 and 7 differs from that according to Figures 4 and 5 in that the third film 23, in addition to being secured by welding to the sheet of film 2 at the position of the welding seams 3 to 6 incl., is secured by welding by means of a vertical seam 26 and a horizontal seam 26', as a result of which a small space 27 is isolated from the large space 24 to accommodate the small straw. The welding seams 26 and 26' comprise two layers and adjoin the welding seams 6 and 3 respectively consisting of three layers without, however, having any effect on the layer thickness.

    [0030] The method of manufacture of the containers according to Figures 1 to 7 incl. is explained by reference to Figure 8.

    [0031] This figure shows a supply reel 32 for the sheet of film 2 which passes over the deflecting rollers 33 and 34 and through a guide 35 so that the sheet of film 2 is guided accurately in a vertical plane.

    [0032] At 36 a device is located for punching the insertion openings for small straws.

    [0033] At 31 is located the supply, reel for the sheet of film 7 which is guided over the deflecting rollers 37 and 38, as a result of which the two sheets of film 1 and 2 end up alongside each other.

    [0034] At 39 and 40 are situated the welding devices for having the vertical welding seams 3 and 4.

    [0035] At 41 is situated the welding device for making the bottom transverse seam 5.

    [0036] At 42 and 43 are located cutting knives by means of which the still open empty containers are separated from each other and are passed by means of a transfer device 44 to a filling station where the containers are opened with suction nozzles 45, are flushed with gas at 46 and then pass through the filling stations 47, after which the top transverse seam 6 is made at 48.

    [0037] Before the two sheets of film 1 and 2 are brought up against each other at the deflection roller 38, a third sheet of film 23 is brought up against the sheet of film 2 from a supply reel 49 via the deflecting rollers 50 and 51. The vertical welding seams 8 and 9 are then made between the sheets of foil 2 and 23 by means of the welding devices 52 and the horizontal welding seams 10 and 11 with the welding devices 53.

    [0038] The space is then opened with the vacuum devices 54 so that the small straws 13 can be inserted into the openings 12.

    [0039] Said small straws are fed from a stock container 55 by means of a conveyor belt 56 which carries the small straws at regular distances from each other. The small straws may be secured, for example, by friction in sheaths or clips present in the belt 56. At 57 is situated the device for cutting off the bottom end of the small straws obliquely. At 58 is situated a device which has pushing elements 59 which can perform a vertical stroke and insert the small straws 13 into an opening 12 via the guide 60.

    [0040] The small straws are then folded over by means of the device 61 and at 62, at the end of the complete operation, are provided with the adhesive strip 25 shown in Figure 4.

    [0041] The device shown in Figure 8 refers in particular to the embodiments of Figures 1 to 3 incl.

    [0042] For the embodiments of Figures 4 and 5 the welding devices 52 and 53 can be omitted. The welding then takes place exclusively by means of welding devices 39 and 41 and the means fpr opening the openings 12 and the means for inserting the small straws are situated downstream of the welding devices 39, 40 and 41.

    [0043] In the embodiments of Figures 6 and 7 the welding seams 26 and 26' are first applied with welding devices comparable to the welding devices 52 and 53 and the feed device for the small straws should be situated downstream of the welding devices 39, 40 and 41.


    Claims

    1. Container for drink consisting of a bag of flexible thermoplastic material, comprising sheets (1, 2) of plastic material which are welded upon each other by means of longitudinal and transverse seams (3, 4, 5, 6), which bag moreover is provided with a third sheet (7, 23) welded upon the bag material in a manner such that a space is obtained into which a small straw (13) can be inserted, characterized in that the space for the insertion therein of the straw (13) is exclusively defined by welding seams (3, 4, 5, 6, 8, 9, 10, 11, 2θ, 26) between one of the two sheets (1, 2) forming the bag and the third sheet (7, 23), which welding seams (3, 4, 5, 6, 8, 9, 10, 11, 26, 26') are situated in such a manner that the seams defining the said space leave unchanged the layer thickness of the longitudinal and transverse seams (3-6) of the bag and that the outer sheet of the two sheets which define the said space is provided with an opening (12) inside the region of the longitudinal and transverse seams which define the said space, through which opening (12) a straw (13) can be inserted or has been inserted.
     
    2. Container according to claim 1, characterized in that the inner sheet defining the said space and facing the interior of the bag consists of an elastically deformable film and the small straw (13) is obliquely cut off at its lower end (14) at an acute angle such that the straw after perforation of the said inner sheet (2, 7, 17) elastically expands the opening formed by the perforation.
     
    3. Container according to claim 1 or 2, characterized in that the third sheet is a strip (7) welded onto one wall (2) of the bag and having a length and width respectively which are shorter than the longitudinal and transverse seams respectively of the bag.
     
    4. Container according to claim 1 or 2, characterized in that the width and length of the third sheet (23) are equal to the width and the length respectively of the wall sheets (1, 2) of the bag such that the welding seams (3-6) of the three sheets coincide.
     
    5. Container according to claim 4, characterized in that the third sheet (23) has been welded onto a wall sheet (2) by means of additional welding seams (26, 26').
     
    6. Container according to claim 5, characterized in that said additional seams consist of a longitudinal seam (26) which extends from the top transverse triple layer seam (6) of the bag to a transverse seam (26') and the said transverse seam (26') extends from said longitudinal seam (26) to a longitudinal triple layer bag wall seam (3), said additional seams (26, 26') defining the said space for the straw (13).
     
    7. Method for manufacturing the container according to one or more of the preceding claims 1 to 6 incl. in which two sheets (1, 2) of thermoplastic material are brought up against each other and bags are formed by means of welding seams, characterized in that a third sheet (23) is brought up against one of the sheets defining the bag and is attached thereto by welding to form the said spaces before or during the welding of the bag seams, the sheet which defines the outside wall of the space is provided prior to welding with insertion openings at distances from each other which coincide with the pitch distance of the bags, said openings are opened and small straws are inserted into each of the said openings in step with the advance of the sheets.
     


    Ansprüche

    1. Getränkebehälter bestehend aus einem Beutel aus flexiblem thermoplastischen Material aus Kunststoffolien (1, 2), die miteinander durch Längs- und Quemähte (3, 4, 5, 6) verschweißt sind, wobei der Beutel darüber hinaus mit einer dritten Folie (7, 23) versehen ist, die so auf das Beutelmaterial geschweißt ist, daß ein Zwischenraum erhalten wird, in den ein kleiner Strohhalm (13) eingesetzt werden kann, dadurch gekennzeichnet, daß der Raum für das Einsetzen des Strohhalms (13) durch die Schweißnähte (3, 4, 5, 6, 8, 9, 10, 11, 26, 26'), die ausschließlich zwischen einer der beiden den Beutel bildenden Folien und der dritten Folie ausgebildet sind, bestimmt ist, wobei die Schweißnähte (3, 4, 5, 6, 8, 9, 10, 11, 26, 26'), die den besagten Raum bestimmen, so gelegen sind, daß sie die Schichtdicke der Längs- und Quemähte (3 bis 6) des Beutels unverändert lassen, und daß die äußere Folie der beiden Folien, die den Raum bilden, mit einer Öffnung (12) innerhalb des Bereiches der diesen Raum begrenzenden Längs- und Quemähte versehen ist, durch die ein Strohhalm (13) eingesetzt werden kann oder worden ist.
     
    2. Behälter nach Anspruch 1, dadurch gekennzeichnet, daß die innenliegende Folie, die den Raum bestimmt und dem Beutelinneren zugewandt ist, aus einer elastisch verformbaren Folie besteht, und daß der kleine Strohhalm (13) an seinem unteren Ende (14) im spitzen Winkel schräg abgeschnitten ist, so daß der Strohhalm nach der Perforation dieser innenliegenden Folie (2, 7, 17) die durch Perforation gebildete Öffnung elastisch ausweitet.
     
    3. Behälter nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die dritte Folie ein Streifen (7) ist, der auf eine Wandung (2) des Beutels aufgeschweiBt ist, und eine Länge und eine Breite aufweist, die jeweils kürzer als die jeweilige Längs- und Quemaht des Beutels ist.
     
    4. Behälter nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Breite und Länge der dritten Folie (23) gleich der Breite und Länge der jeweiligen Wandungsfolien (1, 2) des Beutels ist, so daß die Schweißnähte der drei Folien zusammenfallen.
     
    5. Behälter nach Anspruch 4, dadurch gekennzeichnet, daß die dritte Folie (23) mittels zusätzlicher Schweißnähte (26, 26') mit einer Wandungsfolie (2) verbunden ist.
     
    6. Behälter nach Anspruch 5, dadurch gekennzeichnet, daß die zusätzlichen Schweißnähte aus einer Längsnaht (26), die sich von der oberen querliegenden, drei Lagen verbindenden Naht (6) des Beutels bis zu einer Quemaht (26') erstreckt, und der Quemaht (26') bestehen, die sich von der Längsnaht (26) bis zu einer in Längsrichtung verlaufenden drei Lagen verbindenden Beutelnaht (3) erstreckt, wobei die zusätzlichen Nähte (26, 26') den Raum für den Strohhalm (13) bestimmen.
     
    7. Verfahren zur Herstellung des Behälters nach einem oder mehreren der vorstehenden Ansprüche 1 bis 6, wobei zwei Folien (1, 2) aus thermoplastischem Material aufeinandergelegt werden und die Beutel durch Schweißnähte gebildet werden, dadurch gekennzeichnet, daß vor oder während dem Schweißen der Beutelnähte an eine der den Beutel bildenden Folien eine dritte Folie (23) angelegt wird und an dieser mittels Schweißen befestigt wird, um die Räume zu bilden, wobei die Folie, welche die Außenwand des Raumes bildet, vor dem Schweißen mit Einsetzöffnungen versehen wird, die in Abständen zueinander angeordnet sind, welche mit dem Teilungsabstand der Beutel zusammenfallen, wobei im Verlauf mit dem Vorschub der Folien diese Öffnungen geöffnet und kleine Strohhalme in jede dieser Öffnungen eingesetzt werden.
     


    Revendications

    1. Récipient pour boisson consistant en un sac en matériau thermoplastique flexible, comprenant des feuilles (1, 2) en matériau plastique qui sont soudées l'une sur l'autre au moyen de lignes longitudinales et transversales (3, 4, 5, 6), sac qui de plus comporte une troisième feuille (7, 23) soudée sur le matériau du sac de manière à ménager une espace dans lequel peut être insérée un petite paille (13) caractérisé en ce que l'espace destiné à l'insertion de la paille (13) est exclusivement défini par des lignes de soudure (3, 4, 5, 6, 8, 9, 10, 11, 26, 26') qui sont situées d'une manière telle que les lignes définissant ledit espace laissent inchangée l'épaisseur de couche des lignes longitudinales et transversales (3 à 6) du sac et que celle des deux feuilles définissant ledit espace qui est située à l'extérieur comporte une ouverture (12) à l'intérieur de la zone des lignes longitudinales et transversales qui définissent ledit espace, ouverture (12) à travers laquelle peut être insérée ou a été insérée une paille (13).
     
    2. Récipient selon la revendication 1, caractérisé en ce que la feuille intérieure définissant ledit espace et faisant face à l'intérieur du sac consiste en une pellicule déformable élastiquement et en ce que la petite paille (13) est coupée en oblique à sa partie inférieure (14) sous un angle aigu de façon que la paille après perforation de ladite feuille intérieure (2, 7, 17) écarte élastiquement l'ouverture formée par la perforation.
     
    3. Récipient selon la revendication 1 ou 2, caractérisé en ce que la troisième feuille est une bande (7) soudée sur une paroi (2) du sac et possédant une longueur et une largeur qui sont respectivement plus courtes que les lignes respectivement longitudinales et transversales du sac.
     
    4. Récipient selon la revendication 1 ou 2, caractérisé en ce que la largeur et la longueur de la troisième feuille (23) sont respectivement égales à la largeur et à la longueur des feuilles (1, 2) de paroi du sac de sorte que les lignes de soudure (3 à 6) des trois feuilles coïncident.
     
    5. Récipient selon la revendication 4, caractérisé en ce que la troisième feuille (23) a été soudée sur une feuille (2) de paroi au moyen de lignes de soudure additionnelles (26, 26').
     
    6. Récipient selon la revendication 5, caractérisé en ce que lesdites soudures additionnelles consistent en une soudure longitudinale (26) qui s'étend depuis la ligne (6) supérieure transversale à triple couche du sac jusqu'à une soudure (26') transversale et que ladite soudure transversale (26') s'étend de ladite ligne longitudinale (26) jusqu'à une soudure longitudinale (3) de paroi de sac à triple couche, lesdites soudures additionnelles (26, 26') définissant ledit espace pour la paille (13).
     
    7. Procédé pour fabriquer le récipient selon l'une ou plusieurs des revendications précédentes 1 à 6 comprise dans lequel deux feuilles (1, 2) en matériau thermoplastique sont amenées l'une contre l'autre et les sacs sont formés au moyen de lignes de soudure, caractérisé en ce que une troisième feuille (23) est amenée contre l'une des deux feuilles définissant le sac et y est attachée par soudure pour former lesdits espaces avant ou pendant la soudure des lignes de sac, en ce que l'on pratique avant soudure dans la feuille qui définit la paroi extérieure de l'espace des ouvertures d'insertion situées à des distances l'une de l'autre qui coïncident avec la distance de pas des sacs, en ce que lesdites ouvertures sont ouvertes et en ce que de petites pailles sont insérées dans chacune des ouvertures en synchronisme avec l'avance des feuilles.
     




    Drawing