WO2000069540A1

WO2000069540A1 - Method for manufacturing filter bags, and also filter bags manufactured in accordance with the method

Info

Publication number: WO2000069540A1
Application number: PCT/NL2000/000306
Authority: WO
Inventors: Roelof Pijsel
Original assignee: Roelof Pijsel
Priority date: 1999-05-12
Filing date: 2000-05-10
Publication date: 2000-11-23
Also published as: EP1194203A1; DE20080303U1; NL1012047C2

Abstract

A method for manufacturing more particularly coffee filter bags from filter material such as filter paper. In order to reduce the amount of waste paper arising during the manufacture, this method comprises joining the two longitudinal strip edges of a strip of filter material that has a continuous longitudinal joint, so that a tube of filter material is developed, flattening the tube to a flattened tube having two superposed layers of filter material with two parallel longitudinal tube edges across from each other and two, in essence, flat outside surfaces lying across from each other and forming in the transverse direction of the flattened tube two filter bags side by side, which have first filter sides along the respective tube edges lying across from each other and have second filter sides turned towards each other.

Description

WO 00/69540 PCTtNLOO/00306

METHOD FOR MANUFACTURING FILTER BAGS, AND ALSO FILTER BAGS MANUFACTURED IN ACCORDANCE WITH THE METHOD

The present invention relates to a method for manufacturing filter bags in accordance with the introductory part of claim 1, and also to a filter bag manufactured in accordance with the method and in accordance with the introductory part of the independent claims 19, 20, 21 and 22. Filter bags of the type defined above are known, for example, from the document DE 298 02 745 Ul . This type of filter bags with an open base, one folded side and a side and bottom where the layers of filter material are joined, is used in large quantities in coffee makers. The two layers of filter material are commonly joined by embossing as a result of which a connection is obtained completely without any extra connection means such as, for example, glue. This type of filter bags is manufactured in practice by implementing the general method as defined in the introductory part of claim 1. According to the method a strip of filter material is folded double, so that on one side in the longitudinal direction of the strip a fold is developed. The individual filter bags are cut out from this folded strip so that one of the sides of the final filter bag comprises part of the fold of the folded strip. This is advantageous in that only the other side and the bottom of the filter bag need to be joined. A disadvantage is that due to the arrangement of the bags to be cut out, in the longitudinal direction of the folded strip of filter material there is relatively much waste material, which is in the form of the parts of the folded strip of filter material that are not used for the filter bags. In practice, even 25 to 30% of the filter material remains as waste.

This waste material is a valuable material per se and is suitable for recycling. Therefore, it is collected, pressed to packets and transported to a company that is capable of making filter material again from waste material. Although in this manner the filter material can advantageously be reused for the manufacture or with the manufacture of new filter material, it is nevertheless highly important to maximize the reduction of the amount of waste material. The smaller the amount of waste material, the smaller the logistic efforts will be for collecting and sending back the waste material and, in consequence, the less also the environmental pollution will be. It is an object of the invention to provide a method of the type defined in the introductory paragraph in which the amount of waste material left can be reduced considerably and is characterized by the characterizing part of claim 1. By first manufacturing a tube from a strip of filter material and flattening this tube, a flat tube will arise having two layers of superposed filter material and having two longitudinal tube edges where the layers of filter material are joined. In transverse direction of this flattened tube the filter bags are arranged side by side so that both at one tube edge and at the other tube edge there is a side of the filter bag. As will further appear from the discussion of the invention with reference to the drawings, in this manner the filter bags can be arranged relative to each other so that there will be a considerably smaller amount of waste material. Tests have shown that the amount of waste material may drop to 5 to 12% and may thus be at least half the amount produced according to the state of the art mentioned above.

Claim 2 relates to a first embodiment for the invention. In this embodiment the joint where the two longitudinal strip edges of the strip of filter material are joined is formed by superposing parts of the same surface of the strip of filter material on the outside of the tube. A joint of this type is easy to apply. On the outside of the tube and adjacent to the outside surface thereof a narrow strip is developed which comprises superposed parts of the filter material. With a method as claimed in claim 3 also a similar narrow strip is developed, but now on the inside of the tube. A joint according to this embodiment of the method is more difficult to make, it is true, but this embodiment offers the advantage that the narrow strip is not visible on the outside of the tube and thus is not visible on the outside of a finally formed filter bag either. In a finally formed filter bag the narrow strip which carries the joint will be present in the container space of the filter bag, which need do no harm to the working of the filter bag. In a preferred method as defined in claim 4, the joint is formed by joining parts of surfaces of the strip of superposed filter material. This causes an overlapping joint to arise which does not protrude from the surface of the tube, neither to the exterior nor to the interior. True enough, in a finally manufactured filter bag which has part of the joint in it, the joint is visible both on the outside of the filter bag and on the inside of the filter bag, but there is no strip extending from the side wall. According to the embodiment of the method as defined in claim 5, the flat tube is in such a form that the joint is located at a position between the two longitudinal tube edges. The two longitudinal tube edges are thus formed by a fold in the strip of filter material, so that the filter bags formed beside one another in the transverse direction of the flat tube have each one side formed by a fold, just like most filter bags known from the prior art, see DE 298 02 745 Ul . According to the method as defined in claim 5, the joint is additionally positioned in line with the longitudinal center line of the tube. This means that the joint is located at a symmetrical position between the two tube edges. Another possibility is the implementation of the method as defined in claim 7 according to which the joint is made just not at a central position between the longitudinal center line and the tube edge. A special embodiment for this, which in many cases will be preferred, is characterized in claim 8. In this embodiment the joint is located near a longitudinal tube edge. Advantages of the latter two embodiments will become apparent in the course of the description. The embodiment of claim 9 is suitable for efficiently manufacturing, from one tube, completely identical coffee filter bags having the general shape as known from DE 298 02 745 Ul mentioned above. The trapezoid shape of the filter bags provides that their second sides can be placed contiguously, thus in a most space-saving manner, the two sides intersecting the longitudinal center line of the flat tube. Due to the symmetrical positioning of the filter bags lying next to each other and the central position of the longitudinal center line of the flat tube, a single type of filter bags is formed from the flat tube, which bags are all completely identical. Another possibility is to utilize the method as defined in claim 10. According to this method specifically the embodiment of the invention mentioned previously is utilized in which the longitudinal center line of the flat tube is particularly not positioned centrally. The joint is then shifted so far away from the longitudinal center line that it finally runs over not more than either of the two filter bags placed side by side in transverse direction. The result is two types of filter bags which may be identical with each other as regards outward shape, but of which not more than half carry a joint in the filter material.

This joint can run through either of the side walls of the filter bag, from a filter side to the filter base or, in an embodiment of the method as defined in claim 11, be located near the first filter sides of the respective filter bags. As defined in claim 12 the joint may then be located beside a folded tube edge and on the inside of the flat tube . Placed in this manner a filter bag will arise of which the joint in question can hardly be seen, or not be seen at all from the outside of the filter bag. However, in the container space of the filter bag the narrow strip of superposed filter material mentioned previously stretches out. At this very point such a strip will probably be least undesired.

A method which most probably is to be preferred is defined in claim 13. In this embodiment the second filter side of the filter bag which has a joint again comprises a folded filter side and the joint is adjacent to the folded filter side in not more than one filter side wall. It is true, the joint can be perceived from the outside and from the inside on the side of the respective side wall of the filter bag, but is located completely inside the respective filter side wall.

The most economic use of the filter material may be achieved with an embodiment as defined in claim 14 in that the second filter sides are substantially adjacent to each other in the flat tube. When the filter bags are cut loose, no material gets lost at the position of the second filter sides.

In the embodiment as defined in claim 15 of the method according to the invention, the joint is used by letting it have different markings, such as a brand name, a type number, an instruction or something similar. The joint is highly suitable for this purpose, because it forms a separate element of the filter bag and will often be found in a filter side wall of the filter bag.

Preferably, in the method according to the invention, the embodiment of the method as defined in claim 16 will be utilized for making the joint. In the known coffee filter bags the layers of filter paper are known to be connected to each other at the bottom and one of the sides only by embossing with a ribbed pattern. This is extremely advantageous in that no extra connection means are needed, so that the coffee filter contains no material other than the filter material. In this embodiment of the invention also the joint is advantageously formed in the same manner by embossing only. Since a flat tube of filter material is used in the method according to the invention, an interesting embodiment of the method is possible which is described in claim 17. In this embodiment the filter bags and also the parts of waste material between the filter bags continue to be connected to each other in the flat tube. Part of the flat tube with filter bags lying side by side seen in the longitudinal and transverse directions is packed and supplied to the client. The final user removes the filter bags he/she needs by tearing them loose from the delivered flat tube along the partial sections and also removes the pieces of waste material which are still present locally. The disadvantage that the recycling of the pieces of waste paper will become more difficult as a result is considerably reduced by the fact that the amount of waste paper is considerably reduced when the method according to the invention is implemented. This disadvantage could optionally be avoided completely by removing the pieces of waste paper from the flat tube of filter material already during the production of the filter bags.

Elaborating on the latter method according to the embodiment, a following embodiment as defined in claim 18 may be used in which the flat tube is rolled up prior to being packed. Since the roller forms a coherent part, it can be supplied to the consumer by using only very little packing material, for example, consisting of a simple paper tube or wrapping. As is known, considerations with respect to the environment have led to the trend of using the least possible packing material. This embodiment can very well be attuned to this trend.

The invention likewise relates to filter bags which are manufactured according to a method in accordance with the invention. A first embodiment of a suchlike filter bag is characterized in claim 19. In the filter bag according to this embodiment the joint runs through one of the filter side walls and connects to a filter side. In the embodiment as defined in claim 20 the joint is located near a filter side between the filter base and the filter bottom and next to the two filter side walls, just like a strip of layers of superposed filter material which has already been discussed above. The filter bag as defined in claim 21 also has a joint in the form of a strip, but this strip runs inside the container space of the filter bag. In the filter bag as defined in claim 22 there is no strip-like joint, but the joint runs along a filter side in either of the two filter walls.

As defined in claim 23 the joint at least partly has a distinctive marking. It should be observed that it is known, for example from EP 0 829 219 A2, to form a strip of filter material into a tube and form filter bags from the tube. However, this is a different sort of filter bags and no filter bags are formed side by side in a flat tube to minimize the amount of waste material.

The invention will now be explained by means of the appended drawings with reference to a number of non-limiting examples of embodiment, in which:

Fig. 1 is a plan view of part of a strip of filter paper for manufacturing coffee filter bags in an embodiment known from the state of the art;

Fig. 2 is a schematic cross section through the folded strip of Fig. 1 along the arrows II-II;

Fig. 3 is a side view of a state-of-the-art filter bag made from a folded strip as shown in Fig. 1;

Fig. 4 is a schematic plan view of the coffee filter bag shown in Fig. 3;

Fig. 5 is a schematic perspective view of the formation of a tube from filter material, the joint being formed with superposed parts of the surfaces of the strip of filter material lying across from each other;

Fig. 6 is also a perspective view of the manufacture of a tube, but now with a joint that is formed with superposed parts of the same surface of the strip of filter material and lying on the outside of the tube;

Fig. 7 is a schematic perspective view of a tube of filter material, the tube being provided with a joint formed from superposed parts of the same surface of the strip of filter material and lying on the inside of the tube;

Fig. 8 is a plan view of a flattened tube in which in accordance with the invention coffee filter bags are formed lying side by side in transverse direction;

Fig. 9 is a section through the flat tube of Fig. 8 along the arrows IX- IX;

Fig. 10 is a similar view to that of Fig. 8, but having a joint of a different form and at a different position;

Fig. 11 is a section through the flat tube of Fig. 10 along the arrows XI-XI;

Fig. 12 is a similar plan view to those of Figs. 8 and 10 of a flat tube of filter paper, now provided with a joint along one of the tube edges and on only one of the tube surfaces; Fig. 13 is a cross section through the flat tube of

Fig. 12 along the arrows XIII-XIII;

Fig. 14 is a similar plan view to those of Figs. 8, 10 and 12 of a flat tube of filter paper, now provided with a joint that runs like a strip along the outside of the flat tube near one of the tube edges;

Fig. 15 is a section through the flat tube of Fig. 14 along the arrows XV-XV;

Fig. 16 is a similar plan view to those of Figs. 8, 10 and 12 of a flat tube, now provided with a joint that runs like a narrow strip on the inside of the flat tube near one of the tube edges ;

Fig. 17 is a section of the flat tube of Fig. 16 along the arrows XVII-XVII;

Fig. 18 is a perspective view of a roller formed by the rolling up of part of a flat tube as shown in Fig. 8; Fig. 19 is a front view of a coffee filter bag according to an embodiment of the invention;

Fig. 20 is a schematic plan view of the coffee filter bag shown in Fig. 19; Fig. 21 is a similar front view to that of Fig. 19 of a coffee filter bag according to another embodiment of the invention;

Fig. 22 is a schematic plan view of the coffee filter bag shown in Fig. 21; Fig. 23 is a front view in accordance with Fig. 19 and Fig. 21 of a coffee filter bag according to another embodiment of the invention;

Fig. 24 is a schematic plan view of the coffee filter bag shown in Fig. 23; Fig. 25 is a front view in accordance with the Figs.

19, 21 and 23 of a coffee filter bag according to another embodiment of the invention;

Fig. 26 is a schematic plan view of the coffee filter bag shown in Fig. 25; Fig. 27 is a front view in accordance with the Figs.

19, 21, 23 and 25 of a coffee filter bag according to another embodiment of the invention;

Fig. 28 is a schematic plan view of the coffee filter bag shown in Fig. 27. With respect to the Figures there is observed that they have not all been drawn to the same scale. The Figs. 2, 4, 9, 11, 13, 15, 17, 20, 22, 24, 26 and 28 show highly schematic sections. The layers of filter material are drawn away from each other for clarity and the folded edges are drawn with exaggeratingly large rounding radii.

To clarify the invention, first a state-of-the-art method for manufacturing coffee filter bags from filter paper will be explained with reference to Figs 1 to 4.

According to this known method a strip 1 of fiber- like filter material is provided in the form of filter paper, see Fig. 2, having two substantially parallel longitudinal strip edges 3A and 3B and having a first surface 5A on one side of the filter material and the second surface 5B on the other. In the longitudinal direction of the strip 1, a fold is provided at 7 and the fold-carrying strip is flattened out, so that two layers of filter material 1A and IB are superposed. From the thus folded strip of filter material are formed coffee filter bags 9. Each one of these coffee filter bags is supplied in a flat state, see also Figs. 3 and 4, and has a form with a filter base 11 where the two layers of filter paper are unconnected, a filter bottom 13 lying across from the filter base and substantially parallel therewith, where the two layers of filter paper are joined, two filter sides 15A, 15B where the two layers of filter material are joined together, and two filter walls 17A, 17B extending between the filter sides, the filter bottom and the filter base, which walls are unconnected, so that a coffee filter bag open at the base 11 is formed having a filter container space 20, see Fig. 4, between the filter walls 17A, 17B, the filter sides 15A, 15B and the filter bottom 13.

The filter bags 9 in the strip 1 are formed according to the pattern that is shown in Fig. 1. An embossing roller joins the two layers 1A, IB of the strip of filter material at the filter bottom 13 and the filter side 15B and the filter bags are finally cut out from the strip along the boundary lines which are indicated. Between the boundary lines are left redundant pieces of filter material 19 and 21, which form waste material. As observed earlier, this waste material forms 25 to 30% of all the material of the strip 1. The joints 23 and 25 at the filter bottom and the filter side 15B respectively, form narrow strips consisting of the superposed parts of the layers 1A and IB of the strip of filter paper 1. These strips extend beyond the filter bag and do not contribute to the volume of the container space 20 of the coffee filter bag. In order to let the coffee filter bag 9 have a proper fitting in an associated filter holder of a coffee maker, these strips 23 and 25 are to be folded double in accordance with their inside boundary edges which in Fig. 3 run along the indicated axes 27 and 29 respectively. After being folded double, the said strips rest against an outside wall of the coffee filter.

Below you will find a discussion of the method according to the invention and of coffee filters made in accordance with the method according to the invention with reference to the Figs. 5 to 28. After the discussion of the manufacture of the filter bags according to the state of the art with reference to the Figs. 1 to 4 , the structure of the coffee filter bags or the filter bags in general to which the invention relates, as well as their manufacture, will also be clarified with the aid of a description which is more concise for clarity.

Fig. 5 shows how a strip 31 of filter paper, by joining the longitudinal strip edges 33A and 33B by a continuous longitudinal joint 35, is formed into a tube 37 of filter paper. Since the further description refers to the manufacture of coffee filter bags, in the rest of the description only filter paper will be referred to when filter material is mentioned. By way of example the joint 35 can be realized by means of two schematically indicated embossing rollers 39A and 39B. In the embodiment shown in Fig. 5 the joint is formed by superposing parts of the surfaces of the strip of filter material 31 lying across from each other. In consequence, the one embossing roller 39A is positioned on the outside of the tube and the other embossing roller 39B is positioned on the inside of the tube, across from the embossing roller 39A.

In Fig. 6 a tube 45 is formed from a strip of filter paper 41 having strip edges 43A, 43B by means of a longitudinal joint 47. Here too the joint 47 is formed by two embossing rollers 49A and 49B. Since in this case the joint is formed with parts of the same surface of the strip 41 of superposed filter paper and with the joint 47 on the outside of the tube 45, the two embossing rollers 49A, 49B are positioned on the outside of the tube 45. The joint 47 can therefore be realized in a very simple manner, if so desired the strip of filter paper 41 may even be folded together first and flattened and, subsequently, the joint 47 can be realized from the superposed strip edges 43A, 43B.

In Fig. 7 a strip 51 of filter paper having strip edges 53A, 53B is formed into a tube 55 with a joint 57. In this embodiment the joint 57 is formed by superposed parts of the same surface of the strip of filter paper 51, which are also on the inside of the tube 55. Also in this case two embossing rollers 59A and 59B respectively, which are both positioned on the inside of the tube 55, are used for forming the joint.

Figs . 8 and 9 show a tube manufactured in the way that is shown in Fig. 5 and which tube is thereafter flattened. The joint 35 in the flat tube 37 is located at a position between the two longitudinal tube edges 61A and 61B on a position along the longitudinal center line 63 of the tube. Coffee filters 65 having the same form as the coffee filters 9 from the Figs. 1 and 3 are formed from the flattened tube. As shown more particularly by the Figs. 19 and 20, the coffee filters 65 have a form with a base 67, a bottom 69 and filter sides 71A and 71B, the filter side 71A being formed by part of one of the folded tube edges 61A or 61B. The coffee filter has filter walls 73A and 73B with a joint 35 exclusively in the filter wall 73A and running at an angle from the filter side 71B to the filter base 67. The joint 35 is then contiguous to the filter side 71B, so that the filter wall 73A is completely closed. Just like the coffee filter of Fig. 3, strips 75 and 77 respectively are present at the filter bottom 69 and the filter side 71B on the outside of the filter container space 79, which strips are to be folded double along the folding lines 81 and 83 to let the coffee filter fit well into a filter holder.

As shown in Fig. 8 there remain in the flattened tube outside the peripheries of the coffee filters 65 pieces of filter paper 85 and 87 which form waste material. As will immediately be apparent from a comparison with Fig. 1, this amount of waste material as a percentage of the total amount of filter paper in the strip is considerably smaller than in the case of Fig. 1.

The flattened tube 89 from the Figs. 10 and 11 strongly resembles the flattened tube 37 from the Figs. 8 and 9, but the joint 91 is in this case positioned clearly eccentrically relative to the longitudinal center line 93 of the flattened tube 89 in the direction of the tube edge 95B.

In consequence, from the flattened tube 89 there are developed two types of coffee filter bags, that is, a first type of coffee filter bags 97 which are completely identical with the coffee filter bags 9 of Fig. 3, and a second type of coffee filter bags referenced 99 and more specifically shown in the Figs. 21 and 22. The tube 89 of filter paper is shaped in the same manner as the tube 37 in Fig. 5, but now with the aid of embossing rollers (not shown in the drawing) which have a slightly meandering pattern, so that the joint 91 is formed from sections 91A and 91B which are situated in a direction transverse to the center line 93, slightly staggered relative to each other. If so desired, other patterns too may be used for forming the joint. The shape of the filters 99, see more particularly Figs. 21 and 22, is largely equal to that of the filter 65 of Fig. 19 and has a base 101, a bottom 103 and filter sides 105A and 105B. Filter side 105A is formed by part of the folded tube edge 95B. At the filter bottom 103 and the filter side 105B there are joints which are formed by strips 107 and 109 which are to be folded double in accordance with folding lines 111 and 113 respectively. The joint 91 is positioned exclusively in one of the two filter walls 115 and 117, in filter wall 117 that is, and runs at an angle between the filter base 101 and the filter side 105B and is contiguous thereto, so that the filter wall 117 is completely closed. In Figs. 12 and 13 the tube formed in accordance with the method shown in Fig. 5 is started from again. The flattened tube 37 has tube edges 119A and 119B, which are both formed by folds in the filter paper. But the joint 35 is now positioned strongly eccentrically relative to the longitudinal center line 121 of the flattened tube, that is, adjacent to the tube edge 119B. The tube of Fig. 12 has the same width as the tube of Figs. 8 and 10 and may, in principle, be manufactured from a strip 31 which has the same width as is the case of the tube of Figs. 8 and 10. Two different types of coffee filter bags are made in this way, that is, coffee filter bags 123 which are completely identical with the coffee filter bags 9 of Fig. 3, and a second coffee filter bag 125 of a type that is shown in more detail in Figs. 23 and 24. The coffee filter bag 125 has a shape with a base 127, a bottom 129, filter sides 131A and 131B, filter walls 134 and 136 and a container space 137. At the filter bottom 129 or the filter side 131B respectively, strips 133, 135 respectively are present, which are to be folded double along the folding lines 137 and 139 respectively. At the joint 35 which runs along the filter side 131A and extends from the filter bottom 129 to the filter base 127, however, such folding double is not necessary, so that in practice the filter of Fig. 23 permits to be handled as the filter 9 of Fig. 3.

Figs. 14 and 15 show a flattened tube 45 that is equal to the tube 45 of Fig. 6. The flattened tube 45 is bounded on both sides by tube edgesl41A and 141B, while the joint 47 is positioned eccentrically relative to the center line 143 of the flattened tube and adjacent to the tube edge 141B. The flattened tube of Fig. 14 has near the tube edge a narrow strip 142 of two layers of superposed filter paper. The width of the flattened tube of Figs. 14 and 15 is therefore larger than that of the flattened tubes of Figs. 8, 10 and 12. The strip of filter paper 41 of which the flattened tube 45 is made therefore has a larger width than the strip 31 which is used in Fig. 5. The amount of extra material that is thus needed is equal to one time the width of the joint 47.

Again two different types of coffee filters are made in this way, that is, coffee filters 145 which are completely identical with the coffee filters 9 of Fig. 3 and coffee filters 147 whose shape is shown in Figs. 25 and 26. The coffee filters 147 have a base 149, a bottom 151, filter sides 153A and 153B, filter walls 155A and 155B and a container space 157. The strips 143, 159 and 161 respectively, are present at the filter side 153A, the filter bottom 151 and the filter side 153B and all three of them are to be folded double along the respective folding lines 163, 165 and 167.

Figs. 16 and 17 show the tube 55 which is formed according to Fig. 7 in a flattened state with the joint near the tube edge 169B. The joint 57 is thus on the inside of the flattened tube 55. The result is that the filter bags 173 and 175 which are formed on both sides of the center line 171 are externally completely or substantially completely identical, and equal to the filter bag 9 of Fig. 3. In essence, however, the filter bags 173 and 175 are not identical, since the filter bags 175 have the inside joint 57. The width of the strip 51 is to be equal to the width of the strip of filter paper 41 of Fig. 6.

The shape of the coffee filters 175 is shown in more detail in Figs. 27 and 28. The filters have a shape with a base 177, a bottom 179, filter sides 181A and 181B, filter walls 183, 185 and a container space 187 therebetween. The strips 189 and 191 at the bottom 179 and at the filter side 181B respectively are to be folded double along the respective folding lines 193 and 195. At the filter side 181A no strip need be folded double. On the inside of the respective side of the coffee filter bag, however, in the container space 187, there runs a strip on which the joint 57 is to be found, that is, from the bottom 179 to the filter base 177.

Fig. 18 shows how the flattened tube 37 of Fig. 5, after partial intersections at the bottoms 69 and the filter sides 71B, can be rolled up to a roll 199. A roll of this type can be used for delivery to a client and in the end to an end user who can easily tear away the individual coffee filter bags 65 along the edges and can throw away the redundant pieces of waste material 85 and 87. Such a roll can also be made based on the flattened tubes as shown in Figs. 10, 12, 14 and 16.

In two cases, that is, with the filter bags according to Fig. 19 and Fig. 21 respectively, there is shown that on or in the immediate vicinity of the joint 35, 91 respectively, a distinguishing mark 201, 203 respectively may be provided. Such a mark may be applied, for example, by embossing or by another way, for example, by printing, for example, inkjet printing with a type of ink that is suitable for the intended purpose and, obviously, should not be poisonous, but should not cause a change of aroma either. Apart from such marks, other marks and/or prints can be applied to the manufactured filters, if desired. Although the invention has been explained with reference only to a limited number of examples of embodiment, the invention is not restricted at all to these examples of embodiment, but, on the contrary, extends to all embodiments that are possible within the scope of the independent claims 1, 19, 20, 21 and 22. In this context it is also important to note that a strip of filter material is formed into a tube by means of a joint which joins the edges of the strip, and that filter bags are formed on both sides of the center line of the flattened tube which is the result of the flattening of the manufactured tube. By arranging the filter bags over the surface of the flattened tube, so that for each filter bag one filter side coincides with a tube edge, a considerable saving can be achieved on the use of the relatively costly filter paper or the respective other filter material .

Claims

1. A method for manufacturing filter bags, more particularly for manufacturing coffee filter bags, with which method filter bags are manufactured which comprise a folded piece of fiber-like filter material and is supplied in a flat state with two superposed layers and in the flat state have a filter base where the two layers of filter material are free, a filter bottom lying across from the filter base and at least substantially parallel thereto where the two layers of filter material are joined, two filter sides where the two layers of filter material are joined and one of which is formed by a fold in the filter material, as well as two filter walls extending between the filter sides, the filter bottom and the filter base, which filter walls are unconnected so that filter bags are formed open at the base and having a filter container space between the filter walls, the filter sides and the filter bottom, the method comprising:

- providing a strip of fibrous filter material having two mainly parallel longitudinal strip edges and a first surface on one side of the filter material and a second surface on the other side of the filter material,

- introducing a fold in the longitudinal direction of the strip and causing the strip having a fold to adopt a flat shape,

- superposing the two layers of filter material folded over each other at the said filter bottom and at one of the said two filter sides, and

- cutting the filter material and forming separate filter bags thereby, characterized in that the method further includes :

- joining the two longitudinal strip edges of the strip by a continuous longitudinal joint, so that a tube of filter material arises, - flattening the tube to a flattened tube having two superposed layers of filter material with two parallel longitudinal tube edges lying across from each other and with two substantially flat outside surfaces lying across from each other, - forming two filter bags beside one another in the width of the flattened tube, with first filter sides along the respective opposite tube edges and with second filter sides turned towards each other.

2. A method as claimed in claim 1, characterized

- in that the joint is formed by superposed parts of the same surface of the strip of filter material and on the outside of the tube.

3. A method as claimed in claim 1, characterized - in that the joint is formed by superposed parts of the same surface of the strip of filter material and on the inside of the tube.

4. A method as claimed in claim 1, characterized

- in that the joint is formed by superposed parts of the surfaces of the strip of filter material which lie across from each other.

5. A method as claimed in claim 1, characterized

- in that the joint in the flattened tube is located at a position between the two longitudinal tube edges.

6. A method as claimed in claim 5, characterized in that

- the joint in the flattened tube is located at a position along the longitudinal center line of the tube .

7. A method as claimed in claim 5, characterized

- in that the joint in the flattened tube is located at a position along the longitudinal center line and a tube edge.

8. A method as claimed in claim 1, characterized - in that the joint in the flattened tube is located near the longitudinal tube edge .

9. A method as claimed in claim 6, characterized

- in that the second filter sides run at an angle relative to the longitudinal center line of the flattened tube and

- in that the joint intersects the second sides of all the filter bags at corresponding spots.

10. A method as claimed in claim 6, characterized - in that the second filter sides run at an angle relative to the longitudinal center line of the flattened tube and

- in that the joint intersects only the second filter sides of the filter bags whose first filter sides are adjacent to the same tube edge .

11. A method as claimed in claims 2 and 8, characterized

- in that the joint forms the first filter sides of the filter bags which are adjacent to the respective tube edge where the joint is.

12. A method as claimed in claims 3 and 8, characterized

- in that the said joint is adjacent to a folded tube edge and on the inside of the flattened tube.

13. A method as claimed in claims 4 and 8, characterized

- in that the joint is adjacent to a folded tube edge and only on an outside surface of the flattened tube.

14. A method as claimed in claim 1, characterized

- in that for cutting the second filter sides loose they are at least substantially parallel with each other and at least substantially contiguous in the flattened tube of filter material.

15. A method as claimed in claim 1, characterized

- in that the joint has distinguishing marks.

16. A method as claimed in claims 2 - 4, characterized

- in that the said joint is made by superposing the parts of the surfaces of the strip of filter material and subsequently joining the said parts exclusively by means of embossing.

17. A method as claimed in claim 1, characterized

- in that the flattened tube is provided with partial intersections and, as a result, is formed into a flattened tube from which individual filter bags can be severed by hand, and

- in that after the partial intersections have been provided, part of the flattened tube, having such a length that there are, seen in longitudinal direction, a plurality of filter bags side by side, is packed in essence without severance of individual parts for supply to a user.

18. A method as claimed in claim 1, characterized

- in that the flattened tube is rolled up prior to being packed.

19. A filter bag manufactured according to a method as claimed in claim 1, the filter bag in the flat state approximately having the shape of an isosceles trapezium with a filter base where the two layers of filter material are unconnected, a filter bottom located across from the filter base and being substantially parallel and shorter where the two layers of filter material are joined, two filter sides where the two layers of filter material are joined, as well as two filter walls extending between the filter sides, the filter bottom and the filter base, which walls are unconnected, so that a filter bag is formed open at the base having a filter container space between the filter walls, the filter sides and the filter bottom, characterized

- in that one of the two filter walls is crossed by a joint which crosses one of the filter sides at an angle, and

- in that the respective filter side and the joint are contiguous.

20. A filter bag manufactured according to a method as claimed in claim 1, the filter bag in the flat state approximately having the shape of an isosceles trapezium with a filter base where the two layers of filter material are unconnected, a filter bottom located across from the filter base and being substantially parallel and shorter where the two layers of filter material are joined, two filter sides where the two layers of filter material are joined, as well as two filter walls extending between the filter sides, the filter bottom and the filter base, which walls are unconnected, so that a filter bag is formed open at the base having a filter container space between the filter walls, the filter sides and the filter bottom, characterized

- in that the two layers of filter material are crossed by a joint which runs along a filter side between the filter base and the filter bottom and on the outside of the two filter walls on the outside of the filter bag.

21. ^'A filter bag manufactured according to a method as claimed in claim 1, the filter bag in the flat state approximately having the shape of an isosceles trapezium with a filter base where the two layers of filter material are unconnected, a filter bottom located across from the filter base and being substantially parallel and shorter where the two layers of filter material are joined, two filter sides where the two layers of filter material are joined, as well as two filter walls extending between the filter sides, the filter bottom and the filter base, which walls are unconnected, so that a filter bag is formed open at the base having a filter container space between the filter walls, the filter sides and the filter bottom, characterized

- in that the two layers of filter material are crossed by a joint which runs along a filter side between the filter base and the filter bottom and between the two filter walls within the filter container space of the filter bag.

22. A filter bag manufactured according to a method as claimed in claim 1, the filter bag in the flat state approximately having the shape of an isosceles trapezium with a filter base where the two layers of filter material are unconnected, a filter bottom located across from the filter base and being substantially parallel and shorter where the two layers of filter material are joined, two filter sides where the two layers of filter material are joined, as well as two filter walls extending between the filter sides, the filter bottom and the filter base, which walls are unconnected, so that a filter bag is formed open at the base having a filter container space between the filter walls, the filter sides and the filter bottom, characterized

- in that one of the two filter walls is crossed by a joint which runs along a filter side between the filter base and the filter bottom.

23. A filter bag as claimed in claim 19-2, characterized in that the joint at least over a portion has a distinguishing mark.