GB2025895A - Bags made of composite thermoplastic films for preserving transfusion blood - Google Patents

Abstract

A bag for preserving organic liquids, more particularly human blood, is formed by high-frequency welding of sheets of a composite film of polyvinyl chloride (2) and polyolefin (3), the polyolefinic layer (3) being towards the inside of the bag (1). Tubes (5) for the inlet and outlet of the liquid to be preserved are provided at the top (6) of the bag (1). <IMAGE>

Description

SPECIFICATION Bags made of composite thermoplastic films for preserving transfusion blood This invention relates to plastics bags of films of polyvinyl chloride (PVC) and polyolefins to be utilized for preserving blood, more particularly human blood, intended for transfusions.

The realization of bags to be utilized for preserving blood, plasma and physiologic liquids in general, is a rather complex problem. The bags available at present and produced according to the art are inadequate-in toxicological respects-to ensure preservation of the organic liquid (blood) over a long period.

In consequence it proved necessary to seek an alternative improval solution. For the preparation of such bags, the art has used plasticized PVC, a material that has proved to be unsuitable for meeting requirements connected with the preservation of the organic liquid, but which, nevertheless, offers the great advantages of being capable of being high-frequency welded.

The present invention provides a plastics bag for organic liquids, particularly human blood, formed by high-frequency welding a coupled or coextruded composite film comprising a polyvinyl chloride (PVC) layer and a polyolefin layer; the polyolefin layer being on the inner surface of the bag for contacting the contained liquid and the PVC layer being on the outside of the bag.

The use of such PVC/polyolefin composite film, either coupled or coextruded, essentially studied to ensure the best possible protection of the physiological liquid (blood) from a sanitary viewpoint, has unexpectedly offered considerable advantages. The most important of these is that this coupled or coextruded film while exhibiting a permeability to air (in particular to oxygen and to carbon dioxide) substantially equivalent to the permeability of PVC alone, has a permeability to water vapour significantly lower than that of PVC, which is of considerable importance.

In fact the blood being preserved must "breath", i.e. it must remain in contact with the air, particularly with regularly changing air; but at the same time the blood must not be allowed to become concentrated during the long preservation times, as may happen when the blood loses water vapour. This drawback occurs to a high degree with films made of PVC only.

It has been ascertained that a conventional film made of plasticized PVC only, having a thickness of 400 ,um, possesses an average permeability to oxygen of 650 cm3/m2.24 h. atm (at 250 C and 0% relative humidity (RH) ), and to carbon dioxide of 4200 cm3/m2 . 24 h . atm (under the same conditions). On the other hand, for PVC/polyolefin films having thicknesses preferred by the present invention, the average permeability values-under the same conditions-are 580 cm3/m2. 24 h . atm for oxygen, with peaks of 700, and 1700 cm3/m2.

24 h. atm for carbon dioxide, with peaks of 2000, which are substantially equivalent to the values of the PVC film. With regard to water vapour, the permeability of such plasticized PVC film is on average 4 g/cm2 . 24 h (at 380C and 90% of A IRH), with peaks of 5,5, while for said PVC/poiyolefin films the average value of permeability to water vapour is 2,5 g/m2. 24 h, with minima of 0,8, which are far lower than the permeability values of plasticised PVC alone as defined hereinbefore.

From a comparison between conventional PVC films and the PVC/polyolefin coupled or coextruded films it appears, therefore, that the former is: weil suited to meet the requirements of the preserved liquid as regards the permeability to air; less suited as concerns the permeability to water vapour; and unsuitable for a long preservation because of its toxicity. Conversely, the PVC/pplyolefin films are fully suitable in every respect, as they possess a permeability to air equivalent to that of PVC, a permeability to water vapour considerably lower, and they do not exhibit any drawbacks due to toxicity.

Furthermore, the use of the PVC/polyolefin coupled or coextruded film offers another considerable advantage: that of still permitting the utilization of the high-frequency welding technique and, in consequence, of allowing the present methods of production of the bags to be continued without having to resort to other less economic methods.

Since the principle of preparing the bag body from a PVC/polyolefin coupled film having its polyolefin surface turned inwards and in contact with the preserved physiologic liquid has been followed, it would seem advisable to follow an analogous principle for the small liquid inlet and outlet tubes constituting the essential outfit of this type of bag.

However, it is impossible to use tubes made from PVC/polyolefin coupled films, and so it would seem to be consistent with the inventive principle of the present invention to have recourse to small tubes exclusively made of polyolefins.

It has been found, however, that it is not possible, on the basis of the known art, to join tubes so constituted to a bag body made of a PVC/polyolefin coupled fitm by means of highfrequency welding, since the PVC/polyolefin ratio in the jointing points of the tubes is too disadvantageous.

Furthermore, the polyolefin tubes possess too high a rigidity, which renders problematic the regulation of blood flow during transfusion operations; which regulation is usually achieved by means of common sanitary clips (tongs or pins).

An optimum solution has therefore been adopted, which consists in preparing the bag body from a PVC/polyolefin coupled film and the tubes from PVC, bearing in mind that the organic liquid flowing through said small tubes will remain in contact with the PVC only during the very short transist steps (both when introducing the liquid into the bag and during the operations of transfusion or of separation of erythrocytes, plasma, plates, or during other similar operations).

Thanks to the brevity of the operations, the risk of pollution or poisoning of the liquid is minimized.

This optimum solution still permits the conventional high-frequency welding technique, not only for producing the bad body, but also for connecting said body with the relevant adduction tubes.

Thus, the present invention provides a bag in plastic materials for the preservation of organic liquids, more particularly of human blood, possessing characterisitics such as preserving capacity and non-toxicity which are significantly better than those of bags produced at present according to the known art.

The bags, though endowed with the abovecited improved characteristics, may be produced by using the same high-frequency welding technique which at present is the most economic method of join to each other sheets of thermoplastic materials and cut down sizes thereof, so avoiding more expensive and timerequiring welding techniques.

Preferably, the material of the inlet and outlet tubes is consistent with the requirements of the high frequency welding technique, and its flexibility characteristic are such as to allow still to the usual hospital techniques for stopping the flow of the liquid preserved in the bag to be used.

More particularly, the polyolefinic film or layer of said coupled or coextruded film may be made-at choic-from low density polyethylene (I.d. PE) polypropylene (PP), the composite PVC/PE films being preferably produced according to the coupling technique, while the composite PVC/PP films are preferably prepared according to the coextrusion technique.

The bag in plastic materials for the preservation of organic liquids, more particularly of human blood, forming- the object of this invention, will be now described more in detail hereinafter with reference to the attached drawings, which are given for merely indicative and illustrative, but not limitative, purposes.

Figure 1 shows a bag according to the invention, cutaway in elevation according to a vertical plane, the path of which is indicated by dash line b-b of Figure 2; Figure 2 shows the same bag in a plan sectional view according to a horizontal plane, the path of which is indicated by dash line a-a of Figure 1.

With reference to such figures, bag 1 in plastic materials for preserving organic liquids, more particularly human blood, is made by highfrequency welding of two sheets of a coupled PVC/PEfilm (or of a coextruded PVC/PP film). In these sheets the PE film has a width less than that of the PVC film, so that the resulting coupled article possesses an edge or selvedge made of PVC only. The selvedges of the two sheets of the coupled article form, after being welded with each other, head 6 of the bag, in which two small tubes 5 made of PVC and intended for inlet and outlet are inserted and welded by high-frequency welding.

The body of the bag (unlike the head, which is made only of the PVC selvedge and which does not come into contact with the preserved liquid) has walls of PVC/PE. The respective positions, both of the PE layer 3 on the film side permanently in contact with the preserved organic liquid, and of the PVC layer 2 on the film side toward the outside, i.e. toward the atmosphere, are indicated in the figures.

Reference 4 indicates the welding of the two coupled articles with each other and of the two selvedges with each other, such welding extending continuously all around the bag and along all its whole perimeter, head 6 including.

The bag is completed with the proper valves, generally made of PVC too, for the inlet and the outlet of air, which are associated with head 6. For simplicity, said valves are not shown in the drawings.

For realizing the bag according to the present invention, tests on different types of coupled articles have been carried out. For example, use was made of: a film made of coupled PVC and PE having a total thickness of 300 m, resulting from the overlaying of 1 OOym of PVC over 200 ym of PE; and a film made of coupled PVC and PE having a total thickness of 330 ym, resulting from the overlaying of 200 ym of PVC over 130 ,um of PE.

For welding together two sheets of the same type of coupled film to form the bag and for attaching the tubes to the bag, use was made of high-frequency welding machines of two different powers, i.e. 1 kW and 4 kW; such machines had been equipped with electrodes theremostated (i.e.

thermoregulated) at 800C in order to facilitate the welding process. The welding of the PVC/PE coupled film of thickness 300 ,um (100 ,um of PVC +200 m of PE) has proved to be feasible by means of the welding machine of higher power (4 kW).

However, the use of preheated electrodes did not show appreciable process differences; the welding times remaining practically unchanged.

The welding together of two PVC/PE coupled films of 330 ym thickness (200 ym of PVC + 130 ,um of PE) in order to form a bag according to the present invention had been carried out by means of both the welding machine of higher power and the welding machine of lower power (1 kW).

Weldings with cold electrodes have been carried out in times of 8 seconds, while shorter times, of precisely 6 sec, with preheated electrodes were employed.

It must be noticed that, for more convenient welding on an industrial scale, the welding shall not be carried out in successive operations but conversely in a single step using an electrode shaped according to the whole bag perimeter to be welded.

The PVC/PE or PVC/PP ratio is of considerable Importance for the production of such bags; its optimum value ensues from the conciliation of contrasting requirements. In fact, for welding in a short time a higher PVC thickness is required, as this layer is subjected first to heating and then yields a great part of its heat to the PE- or PP layer. On the other hand, for a good resistance and strength of the weld a high PE- or PP-thickness is required.

Furthermore, considerations of the permeability requirements (of which mention has been made at the beginning of the present description) also contribute to determining the optimum value of said PVC/PE or PVC/PP ratio.

The PVE/polyolefin coupled or coextruded films for the production of the physiological bags for transfusion blood may have thicknesses in the following range: for the PVC/PE coupled article (in particular PVC/1 .d.PE, i.e. with low density polyethylene) the PVC film may have thicknesses ranging from 350 to 100 um, while the l.d. PE film has thicknesses ranging from 50 to 200 ,um; for the PVC/PP coextruded film the PVC layer has thicknesses comprised between 350 and 200 ,um, while the PP layer has thicknesses comprised between 50 and 100 ,um.

It is important that the welding of the two sheets of coupled or coextruded film with each other should be carried out with the utmost accuracy, as the faces of the coupled (or coextruded) films which are directly welded with each other are those made of Pre (or of PP), i.e. those towards the inside of the bag. This means that-as already explained-the heating of PE (or of PP) occurs by conduction through the external PVC, which is directly in contact with the electrodes. In consequence, if the welding is not accurate, its toughness is rather low-which could be a drawback when such weld is subjected to peeling stresses occurring during the usual utilization of the bag.In normal use the bag is frequently subjected to handling, to squashing with consequent hydrostatic stress exerted by the liquid on the walls and chiefly to centrifugation, during which such hydrostatic stress is far more intense, and causes a more significant moving of the opposite bag walls from each other, from which action the stripping stress of the weld arises. This latter is what has just been defined as peeling stress.

Besides the good execution of the welding the.

resistance to such kind of stress depends, also on the coupling degree between PVC and PE, and is of course higher, the better such coupling degree is. Easy separation of the two materials must not in any case be allowed. Anyhow, techniques for coupling films known at present are so advanced, as to always ensure a good coupling degree.

Also in case of use of composite films obtained by coextrusion (PVC/PP), the relevant production techniques ensure an excellent degree of adhesion.

Since it is possible to continue to use conventional high-frequency welding techniques even with bags having the inside walls made of PE or PP formed of coupled or coextruded articles of the type and thicknesses specified hereinbefore, an attempt was made to achieve the same aim for the joining of the tubes to the body of the bag.

Tests with PE tubes gave negative results with both the 1 kW and the 4 kW welding machines, because, as already explained, the ratio of the PVC thickness to the PE thickness is too disadvantageous to lead to satisfactory joining.

In consequence, in order to maintain the possibility of utilizing the high-frequency welding technique, it was decided to use PVC tubes, on the basis of the consideration, already explained, of the very short contact times between blood and PVC; such times corresponding to the very short duration required by operations such as transfusions, or separation of the plates or of other blood components, or the like, during which operations the liquid must pass through such tubes.

In conclusion, the plastic material bag for preserving organic liquids, more particularly human blood, according to the present invention, can be advantageously produced by means of the high-frequency welding technique, by assembling with each other PVC/PE coupled films, having a PVC selvedge constituting the head thereof, and by assembling inlet and outlet PVC tubes with said head.

Of course, to the invention as described, exemplified and illustrated various modifications and variants may be made.

For example, the bag may be prepared by folding and welding (on only three sides, the bag bottom-which is opposite to the head-being obtained simply by folding, instead of by welding) or a single sheet of PVC/PE coupled film (or of PVC/PP coextruded film) in which the polyolefinic film has a width less than that of the PVC film, but in such manner that the resulting coupled (or coextruded) film may have two edges or selvedges of PVC only, so that the two selvedges may still be welded to each other to form head 6 of the bag; said selvedges, however, being the selvedges of a single sheet of composite film.

In this case, as explained hereinbefore, the welding of the bag need be carried out only on three sides (the head and the two longer sides, excluding the short bottom side). But there is hothing to prevent--should it be more profitable for the production on an industrial scale--the use of the electrode shaped as an entire bag, as previously employed, to weld the bottom edge of the bag, even if it did not require it.

Claims (9)

1. A plastic bag for organic liquids, particularly human blood, formed by high-frequency welding a coupled or coextruded composite film comprising a polyvinyl chloride (PVC) layer and a polyolefin layer; the polyolefin layer being on the inner surface of the bag for contacting the contained liquid and the PVC layer being on the outside of the bag.

2. A bag according to claim 1, wherein the polyolefinic layer consists of low density polyethylene (I.d. PE) or of polypropylene (PP); the composite PVC/PE film being produced according to a coupling process, while the composite PVC/PP film is produced according to a coextrusion process.

3. A bag according to any preceding claim, wherein the composite film is a coupled film of polyvinyl chloride (PVC) and low density polyethylene (I.d. PE); the thicknesses being between 100 and 350 ,um for the polyvinyl chloride layer, and between 200 and 50 ,um for the low density polyethylene layer.

4. A bag according to claim 3, wherein the thickness of the PVC layer is between 1 50 and 300 ym, and the thickness of the low density polyethylene layer is between 200 and 130 ,um.

5. A bag according to claim 1 or 2 wherein the composite film is a coextruded film of polyvinyl chloride (PVC) and of polypropylene (PP); the thickness of which-range from 200 to 350 Mm for the PVC layer, and from 100 to 50 ym for the PP layer.

6. A bag according to any preceding claim wherein the polyolefinic layer is less wide than the PVC layer; the ovedapping part'of the PVC layer forming at least a selvedge welded to form a PVC head edge of said bag.

7. A bag according to claim 6 wherein thepolyolefinic layer is less wide than the PVC layer along both edges, the overlapping parts of the PVC layer forming two selvedges welded together to form the PVC head edge; the bag being formed of a single sheet of composite film, folded so that the fold forms the bottom edge of said bag.

8. A bag according to claim 6 or 7, provided with inlet and outlet tubes of polyvinyl chloride (PVC) high-frequency welded into said PVC head edge.

9. A plastics bag for organic liquids, particularly human blood, substantially as described with reference to and as shown in the drawings.