Opening device, method for manufacturing such opening device and packaging material for use in said method

Abstract

The present invention relates to an opening device comprising a first portion on one side of a fibre based packaging laminate and a second portion on an opposite side of the fibre based packaging laminate, the first and second portion being formed in one and the same piece and joined by at least one material bridge extending through the packaging laminate. The present invention also relates to a method for manufacturing the opening device and to a packaging material to be used is such a method.

Claims

1. A method of manufacturing an opening device, comprising: arranging a first mold half comprising a first mold cavity on a first side of a fibre based packaging laminate, arranging a second mold half comprising a second mold cavity having a continuous channel on an opposing side of the fibre based packaging laminate, wherein the first mold cavity partly overlaps the second mold cavity in one or more overlapping areas, and injecting a melt into at least said first mold cavity, wherein the melt, due to pressure being built up in said cavity, penetrates through a part of the fibre based packaging laminate that is not weakened in any way in an overlapping area and fills also at least said second mold cavity for generation of an opening device extending through the packaging laminate, wherein, a first portion on one side of a fibre based packaging laminate and a second portion on an opposite side of the fibre based packaging laminate, the first and second portion being formed in one and the same piece and joined by at least one material bridge extending through the packaging laminate.

2. Method according to claim 1, wherein the overlap between the first and second mold cavity is positioned in accordance to a mark on the fibre based packaging laminate.

3. The method of claim 1, wherein the first side of the fibre-based packaging laminate is to face that an interior of a package formed from the packaging laminate and the opposing side of the fibre-based packaging laminate is to face an exterior of the package formed from the packaging laminate, and the injecting of the melt is arranged such that penetration of the fibre-based packaging laminate by the melt is directed from the first side of the fibre based packaging laminate towards the opposing side of the fibre-based packaging laminate.

4. The method of claim 3, wherein melt is injected into the first mold cavity arranged on the first side of the fibre-based packaging material.

5. The method of claim 1, wherein the injected melt is directed directly towards one of the overlapping areas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described in more detail with reference to the appended schematic drawings, which shows an example of a presently preferred embodiment of the invention.

(2) FIG. 1 is a plan view of an opening device according to a first embodiment of the present invention, illustrating the portion of the opening device arranged on an outside of the packaging container.

(3) FIG. 2 is a view of the opening device of FIG. 1, illustrating the portion of the opening device arranged on the inside of the packaging container.

(4) FIG. 3a is a view combining the view of FIG. 1 and FIG. 2.

(5) FIG. 3b is a cross section along the line V-V of FIG. 3a.

(6) FIG. 3c is a graph over the scissors action.

(7) FIG. 4 is a plan view of the opening device shown in FIGS. 1-3a-c after it has been opened.

(8) FIG. 5 is a plan view of an opening device in accordance with a second embodiment of the present invention.

(9) FIG. 6 is a cross section along the line VI-VI of FIG. 5.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(10) FIG. 1 illustrates an opening device 101 in accordance with a first embodiment of the present invention. The view shows the opening device 101 in a plan view, as seen from a first side of the packaging container (packaging material 102). For all foreseeable purposes this first side corresponds to an outer side of the packaging container 102 onto which the opening device may be arranged. The packaging container 102 is made of a packaging material laminate. The material has a base layer for stiffness and strength, which comprises a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material; and a number of lamination layers of heat-seal plastic material, e.g. polyethylene films, covering both sides of the base layer. In the case of aseptic packages for long-storage products the packaging material may also comprise a layer of gas-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product. Such layers may also operate as light barriers.

(11) The base layer is a paper having a thickness around 50-200 μm and a weight of around 40-180 gram per m.sup.2. Thickness can also go up to 400 μm for specific containers.

(12) A first portion 104 of the opening device, the portion visible in FIG. 1, has a tab section 106 and a frame section 108, which at a first glance appears to be formed from separate parts. It will be shown, however, that this does not have to be the case, and for the present embodiment it is certainly not. A user may use the tab section 106 in order to obtain a firm grip of the opening device 101, and a specific function of the frame section 108 is described below. The skilled person realizes that for the material combinations preferably used for the materials of the opening device and an outer layer of the packaging material on which the opening device is arranged, the tab section 106 will adhere and even weld to the outer layer. An advantage of this effect is that there will be no crevices between the tab section and the outer layer, which facilitates sterilization.

(13) FIG. 2 illustrates the portion 110 of the opening device arranged on the inside of the packaging material. The view of the portion 110 is not from the inside of the packaging container, but from the same direction as the view of FIG. 1, but with all components but portion 110 removed. The reason is to better illustrate the relationship between the portion arranged on the outside and the portion arranged on the inside, which is even more apparent from the view of FIG. 3.

(14) As the user pulls the tab section 106 the pull force will be transferred to the portion 110 on the inside of the packaging container, via a first material bridge connecting the two portions 103 and 110. The location of the first material bridge is indicated by reference numeral 112. The inside portion 110 will thanks to this arrangement push the superimposed layers of packaging laminate 102 in order to accomplish opening of the packaging container. At the end of the inside portion remote to the first material bridge 112 a second material bridge 114 is arranged, connecting the inside portion 110 and the frame section 108. In practice the frame portion 108 may be manufactured from a separate part, yet forming the entire opening device in one piece may be advantageous. The frame section 108 may not be necessary for all embodiments, yet in the present embodiment an inner perimeter of the frame section 108 will cooperate with an outer perimeter of the inside portion 110 in order to accomplish a scissor action. This scissor action enables and facilitates a clean cut of e.g. any tough polymer layer comprised in the packaging laminate 102. Further, the scissors action facilitates opening in that the force needed from the consumer is lowered, as well as it makes it possible to keep the polymer material needed in the opening device a minimum.

(15) To provide a highly effective scissors action it is known that the distance d between the “scissors blades”, which “scissors blades” in this embodiment are the inside portion 110 and the frame section 108, plays an important role as well as the thickness t of the packaging material to be cut, see FIG. 3b. The graph in FIG. 3c shows the relationship between the opening force F, the distance d between the edges of the inside portion 110 and the frame section 108 and the thickness t of the packaging material. Through simulations it has been found that, at a distance d=0 between the edges of the inside portion 110 and the frame section 108, the packaging material is exerted to a high compression force during opening. No shearing forces are present acting perpendicular to the packaging material. The result is that the opening device cannot be opened easily. The force F that the consumer needs to overcome is considered too high. Further, a distance d=0.75 t, which means a distance being 75% of the packaging material thickness, is the lower limit used in the crease tools when making crease lines in the packaging material. The force F is here also considered to be high for a consumer, but not too high if the base layer of paper in the packaging material is thin (paper thickness less than about 200 μm). The reason that the distance d is chosen to be at least 0.75 t when creasing packaging material is that cracks in the surface layers may be avoided. At distances d below 0.75 t cracks will easily arise, first in the surface layers and then sequentially in the rest of the layers.

(16) Hence, an ideal distance d, giving a minimum force F for the consumer to overcome, has been found to be within the interval 0.1 t-0.75 t, preferably 0.1 t-0.5 t. In these intervals the packaging material will fail due to shearing, i.e. when the material starts breaking merely shearing forces are present. The reason for the low forces needed is as well, as mentioned above, that the layers of the packaging material are here substantially sequentially cracking and breaking.

(17) If the distance d increases to a value of more than 50% of the thickness t of the packaging material (d>0.5 t), the force F which the consumer has to overcome will start to increase rapidly.

(18) At a distance d larger than t (t>d), the force F during breakage will be a mere tension force in the plane of the packaging material. Such may normally only be overcome by a consumer if the base layer of paper in the packaging material is thin (paper thickness less than about 200 μm).

(19) By letting the distance d stay within the interval of 0.1 t-0.75 t the force needed for opening is minimised, and that in turn makes it possible to use a weaker opening device, i.e. the amount of polymer material needed may be kept very low. In this embodiment the amount is as low as a few grams.

(20) It should however be pointed out that the present invention is not limited to a distance d=0.1 t-0.75 t. If the opening device is applied on a thin packaging material, e.g. if the base layer of paper in the packaging material is thin (paper thickness less than about 200 μm), the openability will still be satisfactory for distances d above 0.75 t. However, in order to withstand the higher force F, the opening device may have to be made of more polymer material.

(21) Further, to increase the efficiency of the scissors action the opening device should preferably be shaped with sharp edges towards the packaging material. The material of the opening device is also a parameter. The scissors action may be “sharpened” by choosing material having a high crystallinity or a material being under its glass transition temperature T.sub.g. Examples of materials can be found in the group of polyamides, polypropylenes, polystyrenes, polyesters, liquid crystal polymers, polyethylenes (linear low density polyethylene, low density polyethylene, high density polyethylene).

(22) The portion of the frame section 108 which is not contributing to the scissor action, i.e. the portion of the frame section 108 radially outside of the tab section 106, generally does not contribute to the function of the opening device 101 in relation to the act of opening, yet it may serve a purpose of protecting the tab section 106 from being inadvertently actuated. Also it may ensure that delamination of the outermost plastic layer, which may occur during opening, is confined within the constraints of the frame section 108. It may also contribute to the visual appearance of the opening device 101, and facilitate for a user to grasp the function of the opening device.

(23) FIG. 4 illustrates the opening device 101 in an opened state. The user has lifted the tab section and pulled it upwards (away from the packaging laminate) and to the right, thus accomplishing opening of the packaging container. At this point the user may continue pulling, remove and dispose of the loose part of the opening device. The user may also use the partially loosened section in order to partially reclose the opening. In cases where removal of the tab section and the associated opened portion of the opening device is not desired, the opening device may be reinforced at the “hinged” end of the first portion, remote to the tab section, which may be affected in accordance with the embodiment illustrated in FIG. 4 where the hinged end is connected to an inside of the packaging container, thus providing an anchor function. For the present embodiment full liquid tight closure is not to be expected in the reclosed state, yet within the scope of the present invention reclosable opening devices may be designed.

(24) The opening device may be manufactured using two mold cavities only. A first mold half has a mold cavity shaped as the first portion of the opening device, and a second mold half has a mold cavity shaped as the second portion of the opening device. The mold halves are arranged in register on opposite sides of a packaging laminate, and a melt is injected in at least one position into the second mold cavity. The melt will rapidly fill the mold cavity and in places where the first and second mold cavity overlaps, the lack of support will cause the packaging material to rupture such that the melt may fill the second mold cavity too, thus completing the manufacture of the opening device. If desired, or needed for a specific design, more than two mold cavities may be used.

(25) During the injection process the flow rate will be essentially constant and the amount of plastic being injected will correspond to the volume of the mold cavity. The pressure in the melt, however, will vary significantly during the short injection process. Before the cavity into which the melt is injected is filled, there will be no significant pressure increase. When the said cavity has been filled there will be a rapid pressure build-up until the rupture of the packaging material. The pressure will peak moments before the rupture, and the rate at which it is reduced will depend on e.g. the dimensions of the opening generated. It is reasonable to state that if the injection flow rate is high the rupture will be more violent than if the injection flow rate is lower, and that the higher flow rate will result in a larger opening. A larger opening may result in that the full mold cavity is filled more rapidly, which may be beneficial. The optimum flow rate may vary with design of the opening device, properties of the packaging material, properties of the plastic used, etc. yet in a presently operational embodiment the cycle time is less than about 300 ms, i.e., about three opening devices per second may be manufactured by a single mold using the inventive technique.

(26) The dimensions of the opening device may be optimized to achieve an adequate opening of the packaging container only and any surplus use of material may be avoided. In this way only a relatively small amount of plastic is needed (compared to known opening devices). This as the beneficial effect that the time needed for injection is small, yet it also has the effect that the mold does not have to be closed for very long since the plastic will start to freeze (or solidify) immediately. The small amount of plastic vouches for that even if only a surface layer has started to freeze, this will be enough to retain the shape of the opening device until it has fully frozen, which in turn implies that the mold will be opened basically as soon as the injection is finalized. An outermost skin layer of the plastic melt will freeze as soon as it contacts the walls of a mold cavity, or the outermost layer of the packaging material. For non-complex designs this vouches for that the mold may be opened as soon as it is filled. For more complex designs, e.g. designs incorporating steep edges or distinct ridges more time may have to be allocated for the plastic to freeze, such that the plastic is allowed to solidify from the skin and inwards before opening the mold. In this context it should be understood that the plastic will shrink (from the outside and inwards) as it freezes, and in a conventional injection molding process it is known to continue to inject plastic during the freezing, such that the finished detail is an exact replica of the mold cavity. It may also be important to realize that the longer the mold remains closed, the more heat will be transferred from the melt to the mold. This results in a need for installing a cooling arrangement, such as channels for leading cooling fluid through the mold halves. For the present invention such arrangements may not be necessary due to the inherently low cycle times.

(27) The area in which the rupture of the packaging material occurs is not pre-treated in any way. “Pre-treated” in this context meaning perforated, creased or weakened in any other way. The absence of a weakening is an advantage since it increases the tolerances acceptable when arranging the mold halves in register with the packaging material, since no alignment with a weakening has to be performed. A result from the absence of the weakening may be that the unguided rupture of the packaging laminate may generate an uneven edge of the thus formed opening. In such a situation there is an advantage in injection of the melt into the second mold cavity. The advantage is that opening and any resulting projection edge section will be directed outwards, such that the fibre based core material is prevented from being exposed on the inside of the packaging container. Also, as the opening is funnel shaped there is ample surface area on the inside of the packaging material where the plastic of the opening device may adhere or weld to the innermost laminate layer of the packaging material. In this way the risk of contamination of the inside of the packaging container is minimized. An additional effect of an inventive method and thus a feature of the inventive device may be found on the outside of the packaging material. This effect is that the exposed edge of the fibre based core will be caught inside the mold cavity and thus it may be covered by molten material during the injection process. This will eliminate or alleviate the risk of the fibre-based core absorbing moisture and it also improves the visual appearance since the uneven edges may be hidden inside the plastic of the opening device.

(28) Further embodiments may provide a solution where more than two mold parts are used, and where injection of melt is performed in two or more of the mold parts.

(29) In the sections of the opening device where there is no overlap between the mold cavities the opening device will adhere to the surface layer of the packaging laminate. If the temperature and chemical composition allows for it, it may weld to the surface layer, and in other instance it may adhere by a weaker bonding effect. The bond between the packaging laminate will thus generally not be stronger than the adhesive force between the surface layer of the packaging laminate and any adjacent layers. This may be a problem for an opening device relying on this adhesion only, since delamination may result in that the packaging material is not fully penetrated during opening. Since the present invention provides a direct mechanical connection in the form of the first material bridge the pulling force will instead be transformed to a pushing force, enabling reliable opening of a packaging container.

(30) FIGS. 5 and 6 show an opening device 201 in accordance with a second embodiment of the present invention. Having described the first embodiment in some detail the second embodiment needs less description. The opening device of the second embodiment is less complex than the first in that opening is effected by a pull-strip function. By pulling a tab 206 of the first portion 204 the second portion 210 will penetrate the packaging material 202 in a zipper-like fashion. Again, the first portion 204 may comprise a frame section 208 that may be arranged to accomplish a scissor action together with the second portion 210 like the one described in accordance with the first embodiment. However, opening device 201 may be made without the frame 208 if one would like to manufacture a very simple opening device where one would not take advantage of the scissors action. In thin packaging material it may function very well, and such opening device can be manufactured using a very small amount of polymer material, for instance less than 0.5 gram. Such may be realized by for example making the second portion 210 short and the pull-tab 206 small. When opening the opening device only a small hole, such as straw hole or a small pouring hole, will be made in the package. For a consumer the only visible part of such opening device will be the pull-tab 206.

(31) Though there is no drawing of a mold or mold cavity the skilled person realizes that the shape of the mold cavity will correlate to the shape of the manufactured opening device (or rather—vice versa), and since the present invention is not directed to the shaping of mold cavities this will not be described any further. Also, injection molding is a well-established technique not the least for some of the suggested materials: PE, PP and PET. Therefore a disclosure of an injection molding process or features thereof is not considered essential for the skilled person to apply the present invention, and it is therefore omitted.