GB2267046A - Filter bag - Google Patents

Abstract

A filter bag comprises two impervious plastic sheets (2, 3) sealed to each other along three sides to form a pocket, and a filtering sheet (4) which is fixed to at least one of the two sheets (2, 3) so as to divide the interior of the pocket into at least two volumes. The bag is used in the preparation of a filtrate from a solid, fibrous, non-homogenous or insoluble sample in order to carry out a microbiological analysis. In Fig. 1 the sheets 2, 3, 4 are of equal area and sealed together along three edges. In Fig. 2 the filter sheet 4 is smaller and is sealed to only one of sheets 2, 3 along three edges of sheet 4. In Fig. 3 the bag of Fig. 1 is further divided by vertical seams connecting the filter sheet to each plastic sheet alternately, creating a series of chambers through which liquid flows in series being thereby filtered several times. The bag is made by unwinding sections of the sheets from respective rolls and heat sealing them together, while making transverse perforations which allow resulting bags to be separated as required. <IMAGE>

Description

DEFORMABLE FILTER BAG AND ITS MANUFACTURING TECHNIOUE The present invention relates to a filter bag for use in various applications and in particular, but not exclusively, for the preparation of a filtrate from a solid, fibrous, non-homogenous or insoluble sample, in order to carry out a microbiological analysis.

In general, when a contaminated, or supposedly contaminated, sample contains solid or insoluble parts, it is not possible to obtain directly an analysable filtrate Traditionally, therefore, the sample solution has been prepared by first adding a physiological liquid to a specimen, shaking the resulting mixture to wash the specimen, removing the solid material therefrom and, if necessary, further diluting it.

The most currently used methods for separating the solid specimen from the solution are either a method of collecting a supernatant liquid once the solid part has precipitated, or a method of filtering the mixture with a fixture paper.

In order to facilitate the separation method, different solutions have been developed.

One solution consists of using a rectangular bag, made of two plastic sheets sealed to each other along three sides.

The inner volume is then separated, lengthwise, into two compartments by a filtering strip which extends lengthwise from the bottom of the bag right up to the bag inlet. This filtering strip is sealed to both of the plastic sheets at the bottom, by one of its longitudinal edges to one of the plastic sheets, and by the other longitudinal edge to the other sheet.

This solution presents the following disadvantages - the manufacture of this type of bag is difficult because the filtering strip has to be put in place practically "blind", - the filtering surface is small, which means that this bag cannot be used with viscous samples, - it is very difficult to seal the bag in a leak-tight way because of the presence of the filtering strip along a fraction of the width of the bag.

Another solution consists of placing two bags, one inside the other : an outer bag made of a water-tight plastic material and an inner bag made of a filtering material.

These two bags may be sealed together along three of their sides.

It is clear that such a solution is more costly, and is not adapted to automated production. Furthermore, taking out the filtrate after preparation is not easy, mainly because of the difficulty to introduce an instrument, such as a pipette, due to lack of space resulting from the presence of two inner filtering walls.

The aim of the present invention is therefore more particularly to resolve all these problems.

The invention proposes to this end a filter bag of the said type, i.e. comprising at least two sheets of plastic material sealed to each other along part of their outer edge so as to form a pocket, and a filtering element extending inside the pocket so as to define two volumes separated by the said element.

According to the invention, this filter bag is characterised by the filtering element consisting of a permeable film of which at least part of its outer edge is fixed to one of the two sheets so as to define with the said sheet a separation which is open on the same side as the said pocket.

To great advantage, the permeable film could be of the same shape and size as the two sheets making up the bag.

In this case, the film could be sealed at the same time as the two sheets, along a common line of fixation.

Moreover, in a structure of this kind made of a porous film placed between two water-tight films of heat-sealable plastic material, it is possible, by adjusting the temperature, the processing time and the application pressure of the sealing tool, to seal the film either to one of the sheets, or to the other sheet, or even to both the sheets.

The aim of the invention is therefore to make good use of this possibility to improve even more the previously described filter bag by ensuring multiple filtering.

To this end, the invention proposes a series of sealing lines offset in relation to each other and linking the porous film alternately to one film and then to the other so as to create several chambers successively communicating with each other via the porous film.

The invention relates, of course, to the manufacturing technique of the filter bags previously described.

The methods of producing the invention are described below, as non-limited examples, with reference to the drawings in annex in which - Figure 1 is a schematic view in perspective of a first example of production of the invention; - Figure 2 is an elevated view showing the sealing lines of a bag made according to the second production method of the invention; - Figure 3 is a schematic transversal section showing the principle of a double-filtration bag; - Figures 4 and 5 are schematic representations of two installations for the production of bags according to the invention.

In the example shown in figure 1, the filter bag 1 consists of two sheets of impermeable plastic material 2 and 3, of rectangular shape, between which is placed a sheet of filtering material 4 of the same dimensions.

These three sheets, 2, 3, and 4 are sealed to each other by a sealing strip 5 which extends continuously along three edges: the sides C1 and C2, and along the bottom edge C3. Therefore this structure represents a water-tight bag, open in its upper part, and the inner volume of which is divided into two compartments, V1 and V2, by the sheet of filtering material 4.

Filter bags of this kind can be produced totally automatically by the installation illustrated in figure 4 which uses three bobbins B1, B2 and B3, on parallel axes two bobbins B1 and B3 around which are wound two strips made of impermeable plastic material, 6 and 7 respectively, and a bobbin B2 around which is wound a strip 8 made of porous material, the three strips being of the same width. On leaving the bobbins B1 to B3, the three strips 6, 7, and 8 are guided in such a way that they are superposed, the porous strip 8 being between the two others, 6 and 7. This ensemble then passes through a heatsealing unit P1 before reaching the receiving bobbin B4, driven by a synchronous stepping motor.With each advance of the bobbin, the heat-sealing unit simultaneously seals the three sheets 6, 7 and 8 so as to create a bag, with a transversal perforation, allowing the detachment of each bag.

In the example shown in figure 2, the filter bag 9 consists of two rectangular sheets 10 and 11, made of an impermeable plastic material placed one against the other and sealed to each other by an outer seal 12 along three sides. To one of the two sheets, a third sheet 14, made of a porous material, is also sealed along a part of its outer edge by a sealing strip 13. This sheet 14 constitutes an inner pocket housed inside the outer pocket formed by sheets 10 and 11, and is open on the same side.

It is from this inner pocket that the filtrate can be taken out.

This filter bag 9 is produced using an installation shown in figure 5 using three bobbins B5, B6 and B7, laid out as in the previous example, figure 4. However, in this case, the strip of porous material 15 is guided so that it comes to be superposed on the strip 16 coming from the bobbin B7. This ensemble 15 and 16 passes through an initial sealing unit P2, which creates the inner pocket. Strip 17, coming from bobbin B5, then comes to be superposed on the sealed ensemble 15 and 16. This new ensemble passes through a second sealing unit P3 where the outer, watertight pocket is created. As in the previous example, the successive bags, which are linked to one another by a perforation line, are wound around a receiving bobbin B8, driven by a synchronous stepping motor.

Figure 3 shows a method of producing a triple-filtration filter bag using a structure similar to that in figure 1 but in which the film of porous material 21 is also fixed to the sheet 22 by a vertical seal 23, then to sheet 24 by a second vertical seal 25. These two seals 23 and 25 extend the whole length of the bag and define two successive compartments which communicate with each other and with the bag compartment through the two successive zones Z1 and Z2 and distinct from the porous film 21.

So if the sample to be filtered is placed in compartment V3, three filtrations are obtained successively through zone Z3 of film 21 separating compartments V3 and V4, through zone Z1 of film 21 separating compartments V4 and V5, and through zone Z2 of film 21 separating compartments V5 and V6. The filtrate is then obtained in compartment V6.

Of course, the number of filtrations possible is not limited to three. By adding successive vertical seals, similar to 23 and 25, as indicated by dotted lines in figure 3, the number of filtrations is increased by an equal number.

The material used for the two outer sidewalls of the bag could be, for example, polyethylene, polypropylene, polyester, a sandwich or a complex of different materials.

The material used for the filter could consist of a material permeable to liquids but impermeable to solids above a certain size. For example, such materials could be a non-woven synthetic material, or perforated sheets of plastic In the previously described filter bags, the filtering wall could even be fixed to one of the two outer sheets, for example sheet 3 on a small portion of surface 27, possibly parallel to the bottom so that one of the two compartments V1 is more open than the other, V2.

This portion 27 could be positioned vertically at a distance from the top edge, preferably in the top third of the filtering wall and, horizontally, in the middle.

Claims (6)

1. A filter bag of the type consisting of at least two outer sheets of plastic material fixed to each other along part of their outer edge so as to form a pocket, and a filtering element in the form of a sheet extending inside the pocket so as to define two volumes separated by the said element, being characterised by this filtering element consisting of a permeable film of which at least a part of its outer edge is fixed to one of the two sheets so as to define, together with the said sheet, a volume open on the same side as the said pocket.

2. A filter bag according to Claim 1, characterised by the permeable film being of the same shape and size as the two sheets making up the bag, and by the film being fixed, at the same time as the ,ty extending along three sides of the bag.

3. A filter bag-according to Claims 1 and 2, characterised by the filtering element being furthermore fixed to one of the two outer sheets at a distance from the upper edge of the bag.

4. A filter bag according to Claims 1, 2 and 3, characterised by its having several sealing lines offset in relation to each other and linking the permeable film alternately to one outer sheet and to the other so as to form several chambers communicating successively with the others via the permeable film

5. Manufacturing technique of a filter bag according to one of the previous Claims, characterised by consisting of unwinding three superposed strips : two outer strips of impermeable material and a central strip of porous material and of carrying out, at each advance of the strips, a sealing operation which simultaneously executes all the seals of the bag.

6. Manufacturing technique of a filter bag according to Claims 1 to 4, characterised by unwinding step by step an outer strip of impermeable material on which is superposed a strip of porous material, of executing an initial sealing operation of these two strips to form a pocket, of superposing on this pocket a second strip of impermeable material and of executing a second sealing operation so as to obtain a second pocket housing the first.