JALLIINA, JÄRVINEN (Honkapirtinkatu 6 B, Lahti, FI-15950, FI)
NIILO, PÖYHÖNEN (Eino Leinonkatu 7 A 10, Helsinki, FI-00250, FI)
TEEMU, KARHU (Maratonmiehentie 2 C, Imatra, FI-55420, FI)
VESANTO, Heli (Opiskelijankatu 30 A, Tampere, FI-33720, FI)
JALLIINA, JÄRVINEN (Honkapirtinkatu 6 B, Lahti, FI-15950, FI)
NIILO, PÖYHÖNEN (Eino Leinonkatu 7 A 10, Helsinki, FI-00250, FI)
TEEMU, KARHU (Maratonmiehentie 2 C, Imatra, FI-55420, FI)
Claims:
1. A method for forming a package, wherein a package with the shape of a container is formed of a cardboard blank (A), the package having a bottom and side walls (7) extending upwards from the bottom, characterized in that, in the upper part of the side walls (7), a rim (8) of moulding material extending sideways at the final stage of the compression moulding when the mould is kept closed, in such a way that the mould cavity (5) corresponding to the rim is formed by moving a counter surface inside the mould backwards from a surface opposite to it, after which the moulding material is introduced into the mould cavity (5).
2. The method according to claim 1 , characterized in that the mould cavity (5) is formed by moving an annular part (4) of a holding surface, which encircles a forming recess (1 a) of the mould.
3. The method according to claim 1 or 2, characterized in that the length of the movement of the counter surface backwards is 0.4 to 2 mm.
4. The method according to any of the preceding claims, characterized in that the same moulding material is also moulded inside the side walls (7) of the package.
5. The method according to claim 4, characterized in that in compression moulding, a bend is formed in the side wall (7), which bend expands the upper part of the wall outwards to guide moulding material from the mould cavity to the inside of the side walls.
6. The method according to any of the preceding claims, characterized in that the rim (8) is moulded totally of the moulding material directly to the upper edge of the side walls (7), to extend sideways thereof.
7. The method according to any of the preceding claims, characterized in that the container-shaped package (T) is closed with a lid (L) by attaching the lid (L) to the rim (8).
8. A package, which is a container (T) formed of a cardboard blank by compression moulding, such as a tray, the container having a bottom and side walls (7) extending from the bottom upwards, characterized in that the package comprises an edge flange (8) consisting of moulding material, joining the upper edge of the side walls (7) at an angle and extending directly sideways from them. |
A METHOD FOR FORMING A PACKAGE, AND A PACKAGE
The invention relates to a method for forming a package, wherein a package with the shape of a container is formed of a cardboard blank, the package having a bottom and side walls extending upwards from the bottom. Such a package is used as a so-called tray package for keeping food, wherein it is hermetically sealed with a lid. To attach the lid to the package, the edge of the container must be equipped with a horizontal rim or flange extending from the upper end of the side walls and encircling the package. The upper surface of this flange normally comprises a suitable coating, by means of which the lid can be attached to the package tightly. For example, it is very common to use heat-sealable plastic materials to attach the lid part to the package. Examples of food packages and package materials used therein are mentioned, inter alia, in documents WO 03/033258, EP 1 289 856, WO 00/21854, and US 5 425 972.
The above-described package is normally formed of a flat blank by pressing it to shape in a mould. Thus, the coating of the cardboard, which forms the inner surface of the package, also forms the upper surface of said flange which will come into contact with the lid.
Sometimes there is a need to provide the edge flange with a material that is suitable for fixing the lid but is not necessarily required in the middle part, that is, inside the package, or that is even unsuitable as a material inside the package. Another problem may also be posed by insufficient mechanical properties, for example insufficient rigidity, of the edge flange. The choice of materials for the inner part of the package should not excessively determine the materials for the edge flange. A method is also known to form the edge flange independently of the rest of the package, as disclosed in international patent document WO 03/078012 and the corresponding US application publication 2004/0262322, presenting a method in which the rim of a tray-like package is moulded of a plastic material separately. This document discloses a solution, in which the blank is provided with the joined together at their edges with moulded plastic material, after which the plastic rim is moulded to the upper edges of said side walls, to form a flange extending outwardly from them and encircling the package. According to this publication, the packages
made by press-forming are always first equipped with the edge flange, to which the plastic material is attached by moulding, for example under the flange or at its edge, as an extension of the flange outwards, as shown, for example, in Figures 59 to 63 and 66 of the publication. Furthermore, the document mentions the possibility of forming a tray-like package "in-mold"; in other words, the press-forming and the moulding of the plastic material to the edge take place in the same mould. This is shown in more detail in Figures 70 to 76 of the publication, which illustrate the feeding of moulding material underneath the edge flange all the way to the outer surface of the side wall and as a horizontal extension to the upper surface of the flange, and in Figures 77 to 80, which illustrate a mould for implementing this. The upper surface of the edge flange of the package, that is, the surface coming against the lid, is tightly against a shutoff surface during the moulding phase. The mould may comprise several openings for supplying moulding material at the circumference of the package.
The dimensions of the forming and moulding tool, especially the shapes of the surfaces defining the mould cavity, determine the final dimensions of the plastic part at the edge of the package, which dimensions must be taken into account already when designing the forming tool. It must be possible to keep the cardboard blank with a given holding force between the shutoff surfaces of the mould up to the end of the forming step, so that the package is formed evenly at all sides and a good-quality product is obtained. By the method presented in the publication, the plastic part can only be moulded underneath the edge flange.
It is an aim of the invention to present a method, by which the material can be moulded in a more versatile manner to the edge of the package in connection with forming of the package, without compromising the quality of the cardboard part of the package. Furthermore, it is an aim to present a package with a novel structure which can be made by such a moulding method.
The method for implementing this according to the invention is primarily characterized in that, in the upper part of the side walls, a rim of moulding material extending sideways is moulded at the final stage of the compression
moulding when the mould is kept closed, in such a way that the mould cavity corresponding to the rim is formed by moving a counter surface inside the mould backwards from a surface opposite to it, after which the moulding material is introduced into the mould cavity. In the cavity, the material is cured to form a solid flange, after which the mould is opened and the finished tray-shaped package is removed from the mould.
In the above-described manner, the whole circumference of the package can be provided with a moulded rim which has an upper surface consisting of the moulding material, which is different from the cardboard, and which can be selected by taking into account its function in conjunction with the lid that will later seal the package. The counter surface to be moved backwards may act as a retaining surface for obtaining a sufficient retaining force also at the edges of the blank at the very end of the forming stage. In principle, thanks to the invention it is possible to mould rims whose dimensions in the thickness direction are not limited to only one possible. Similarly, the method can be used for moulding a sidewardly extending rim fully of moulding material, directly at the upper edge of the cardboard side wall of the package. In this way, it is possible to make packages with novel shapes which will be described in more detail hereinbelow.
The movement can be arranged at the holding surface or shutoff surface of one of the mould halves in an area encircling the package-to-be in a ring-like fashion. This movement is in the order of a few millimetres only, advantageously from 0.4 to 2 mm, wherein the thickness of the moulded rim is in the same order. However, the invention is not limited to these dimensions only.
The package according to the invention, in turn, is characterized in that the package formed of a cardboard blank by compression moulding comprises an edge flange formed of moulding material joining the upper edge of the side walls of the package at an angle and extending directly sideways from them. The joint between the moulding material and the cardboard package may also extend to the inside of the side walls of the package.
In the following, the invention will be described with reference to the appended drawings, in which
Figs. 1 to 4 show the different steps of forming the package, starting from a flat blank,
Fig. 5 shows a detail of the mould just before the injection of the moulding material,
Fig. 6 shows the point of contact between the side wall and the flange of the package in a cross-sectional view, and
Fig. 7 shows a closed package.
Figure 1 shows a cross-sectional view of a forming and moulding tool for forming a package, starting from the forming of the package and ending in the forming of the rim. The tool is a kind of a compression and cast mould, intended for forming, in a first step, a substantially flat cardboard blank A with an even thickness into a package with the shape of a container, which can also be called a tray. The tool is also provided with an integrated moulding function for the moulding of material to the edges of the package shaped by compression.
The tool comprises a first mould half 1 or "front mould", which comprises a recess 1a, against which the flat blank A is shaped and which determines the general shape of the package (bottom, the shape of the side walls extending from the bottom, the inclination of the side walls, the roundings off, etc.), as well as a second mould half " or "rear mould", which presses the blank into said recess 1a. For this purpose, the rear mould is equipped with a so-called forming core 2a that fits into said recess 1a so that the blank is pressed between the core and the recess and obtains its final form. The mould halves, or the front mould and the rear mould, are arranged to be movable in relation to each other for closing and opening the mould by arrangements which are not described in more detail in this context. In the mould shown in the drawings, the front mould 1 is the solid part and the rear mould 2 is the moving part.
The rear mould 2 comprises, in a ring-like manner around the core 2a, a shutoff surface 2b that faces a corresponding surface 1b encircling the recess la in the front mould 1. When the mould is closed (the mould halves 1 , 2 come together), these surfaces come against each other. This shutoff surface 2b also acts as an ejection surface in an ejection part that can be moved in relation to the core 2a in its depth direction. The ejection part thus moves between a front position (shown in Fig. 1 ) and a rear position (shown in Figs. 3 and 4). The holding force of the shutoff surface 2b can be controlled by means of an actuator 3 driven by pressurized medium and fixed to the rear mould 2. This actuator 3 is preferably a pneumatic cylinder.
The core 2a is also encircled by a collar ring 4 which is capable of making a short reciprocating motion in relation to the shutoff surface 2b and whose front surface can be moved to be aligned with the ejection surface or to lie a very short distance backwards from it. When the front surface of the collar ring 4 is flush with the shutoff surface 2b, it is, in a way, part of the shutoff surface. This front surface of the collar ring also exerts a holding force on the cardboard blank between the shutoff surfaces. Consequently, the collar ring 4 is placed inside the ejection part, between the ejection part and the core 2a.
Figure 1 shows the situation before the closing of the mould. The blank A to be pressed into shape is brought by a robot into small holders (not shown) in the front mould 1. After this, the mould is closed, the core 2a is pressed into the recess 1a, and the blank remaining therebetween is pressed into a container with the shape of a tray. Figure 2 shows the step in which the core 2a starts to form the blank after being pressed into the recess 1a. The shutoff surface 2b, including the front surface of the collar ring 4, leans forward by the force of the actuator 3, preferably by pressurized air, and holds the blank A at its edges between the shutoff surface 2b and the corresponding shutoff surface 1 b of the front mould 1 in the pressing step. Figure 3 shows a situation, in which the mould is fully closed and the blank A is pressed to form a tray in such a way that its outermost edge (the upper edge of the side walls of the tray) is aligned with the front surface of the collar ring 4 or slightly in front of it. The last holding force on the edges of the blank was caused by the
front surface of the collar ring 4 facing the shutoff surface of the front mould that encircles the recess 1a in the front mould.
Figure 4 shows a situation, in which the mould is still closed but the collar ring 4 has moved a short distance backwards from the shutoff surface 1b of the front mould 1 , that is, towards the rear mould 2. The movement is exerted by an actuator making a precise movement, for example by pulling an ejection rod 6 by means of an ejection motor. Thus, a small mould cavity 5 is left between the surface encircling the recess 1a in the front mould 1 , the inner surface of the ejection part, the front surface of the collar ring 4, and the outer surface of the core 2a, which cavity is connected to the outer edge of the tray and encircles the tray in a ring-like manner. When molten plastic material is fed into this mould cavity, it forms a flange-like rim extending outwards from the side walls of the tray. This situation is illustrated by the detailed views of Fig. 4, which show the position of the core 2a, the ejection surface 2b, the shutoff surface 1b of the front mould, and the blank A formed to a tray, as well as the collar ring 4 at the step of injecting the moulding material. In the rear position, the collar ring 4 is tightened against the core 2a, thanks to the conical shape of these, to secure the tightness of the mould cavity 5. The channel for injection of moulding material is preferably introduced via the front mould 1 , and one channel that opens in the shutoff surface 1b of the front mould at the mould cavity 5 is illustrated with a broken line. The injection channels may be evenly distributed around the cavity 1a, for example at corners, if the tray to be shaped has the general shape of a rectangle.
The detailed views of Fig. 5 show how the side walls of the tray at their upper parts are bent outwards with a sharp bend in relation to the lower part, thanks to the corresponding design of the core 2a and the recess 1a. At this "nipping point" formed by the outer surface of the core 2a and the inner surface of the recess 1a, the blank is pressed against the inner wall of the recess 1a, wherein the moulding material has access from the cavity 5 across the outer edge of the blank, that is, the upper edge of the ready formed tray, also to the inside of the tray, wherein the surface of attachment of the rim or flange to the blank material becomes larger. Furthermore, the upper edge of the blank remains slightly underneath the shutoff surface of the front mould 1. It should
be noted that all the detailed views showing cross-sections illustrate the situation on the circumference of the whole package.
After the molten plastic material has solidified in the cavity 5, the mould can be opened to the open position again. The ejection part is then still in the rear position. When the ejection part is pushed by the ejection bar 6 to the front position, it removes the finished container T from the rear mould 2, and simultaneously the collar ring 4 can be moved again to the front position, that is, the position shown in Fig. 1 is reassumed. Then, the robot takes out the finished container and brings a new blank A in its place, after which the work stages are repeated as described above.
To make edge flanges with varying thicknesses, it is possible to make dimensionally different collar rings 4 for one mould, which collar rings produce mould cavities of different dimensions when in the rear position.
Figure 6 shows a cross-sectional view of the edge of a finished container T made by compression moulding and casting, having an outwards substantially horizontally extending flange formed according to the invention and fixed to the upper edge of the side wall 7 of the container T as well as to the inner surface of the tray a short distance from the upper edge. The moulding material supplied into the cavity 5 and forming the flange 8 may extend inside the tray all the way to the sharp bend 9 producedin the compression moulding step. The cross-section of the upper part of the container shown in Fig. 6 is also substantially similar to that in Fig. 6 in its whole circumference, taking into account the fact that in a container having the horizontal cross-sectional shape of a rectangle with rounded edges, the flange may extend farther from the upper edge of the side walls in the corners than along the straight sides.
Figure 7 shows the finished closed package. The tray-like finished container T is closed with a lid L so that the lid is sealed at its lower surface to the upper surface of the plastic rim 8, resulting in a package sealed on all sides.
As raw materials in the manufacture, it is possible to use materials commonly known for tray packages and plastic moulding. As the blanks A, of which the
cardboard part of the tray is made, it is possible to use coated (for example coated with plastic on one or both sides) or uncoated cardboards. The method for coating the cardboard may be dispersion coating or extrusion coating. Cardboard refers to a fibre-based product which may have variable grammage, is suitable for packaging purposes, and can be formed by pressing. The coating of the cardboard, which forms the inner and/or outer surface of the container T, may, especially in view of use for food, consist of a known barrier material which prevents the leaking out of substances from the food to the outside or the entry of substances into the food from the outside of the package. It should be noted that as the flange 8 can be made of a material different from the coating of the cardboard, the coating can be selected without taking into account its functioning as a tight sealing material and/or a material facilitating the reclosing in conjunction with the lid L of the package, or the package may also be uncoated.
Suitable moulding materials include various thermoplastics which are melt processable; in other words, they can be supplied in molten state into the mould cavity, in which they solidify and attach directly to the cardboard or the plastic coating of the cardboard, forming simultaneously a rigid edge flange. Suitable polymers, on which these plastics are based, include polyolefins, polyesters and polyamides. Environmentally friendly moulding materials include biodegradable plastics, such as any of the following: polylactide (PLA), biodegradable polyester, starch-based plastics or polyhydroxy alkanoate, particularly PHB. In this way, the recyclability of the package can be improved as a whole, even though it has been made partly by injection moulding. The above-mentioned biodegradable plastics may also be used as materials for coating the cardboard blank A.
The lid L may be made of any material. The lid is preferably made of cardboard whose lower surface has been coated with a material that is compatible with the material of the flange L, for example for sealing the lid tightly and/or for allowing reclosability. The lid may also be a plastic film comprising one or more layers and sealed to the upper surface of the flange
8. Such a film may be transparent so that the content of the package can be viewed without opening the package. It is also possible that the lid L, irrespective of its material, is attached to the flange 8 mechanically only.
Even if the above-described package is particularly well suited for packaging of food in a tight manner, it is also suitable for products other than food, in which case it is possible to select the material for moulding the flange 8 by taking into account factors other than the air-tight closure required for food.
The shape of the container T may also be different from that described above; what is important is that it can be shaped by compression moulding to achieve a shape whose upper edge can be provided by moulding with a rim that is approximately in the same plane therewith. For example, there may be compartment shapes in the bottom part of the container. The horizontal cross-section of the container does not need to be polygonal, but it may be oval or even circular.
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