DESCRIPTION

FIELD OF THE INVENTION

The present invention refers to the use of rigid and/or semi-rigid PVC for manufacturing containers which are apt to be terminally sterilised through ionising radiations, as well as to a PVC formulated product suited for such a use and to a film and/or to a container which may be obtained from such formulated product.

BACKGROUND OF THE INVENTION

The use of packaging for objects to be transported is extremely ancient and varied. The objects are normally transported in different kinds of containers, depending on the type of object, oN the use thereof and on the modes of transport. Therefore, non-fragile objects, to be transported arranged in an orderly manner, may be transported wrapped in a sheet of paper or little more, while fragile objects and/or objects to be transported together with many other objects are generally put into boxes of sturdy material (for example cardboard, plastic or wood), containing inside layers of soft and flexible material, such as fabric or plastic material partly blown with air or another gas which surround them, so as to dampen the impacts between the different parts contained in the wrapping or with the walls of the wrapping, making such impacts harmless for the objects to be transported.

In recent times it has become necessary also to use special packaging for the materials and equipment for medical and/or pharmaceutical use. In this case, it has also become necessary for said materials and equipment to be contained in the packaging thereof in sterile conditions until the use thereof, so as to avoid infections of any kind for the patient they are meant for. This is particularly important when these are complex tools for medical use and/or prosthesis and/or plants. The packaging for this kind of devices must exhibit some fundamental features. It must be sturdy and resistant, so as not to break upon the impacts which it will inevitably undergo during transport. Moreover, it must be able to withstand sterilisation, without changing substantially. Such requirements extend also to other kinds of objects, such as certain foods and certain electronic equipment. Sterilisation modes seriously affect the type of materials which may be employed for packaging. Sterilisation may occur thermally, chemically or through ionising radiations. Generally, the technique with ionising radiations is preferred, as it allows to sterilise materials which would soften at temperatures above 100°C, it is less expensive and does not require long waiting times to remove from the container the toxic agents by which the sterilisation has been performed. Γ rays, naturally available and effective, are normally used. Other types of radiations (such as β rays) may also be used, provided they are effective. However, a number of materials, in the presence of ionising radiations tend to deteriorate, losing a good deal of the mechanical properties and of the value thereof, even aesthetic ones. For this reason, the materials used until today in this field are very few.

In actual fact, almost the entire world market employs an amorphous polymer, based on PETG copolyester, manufactured in granules by chemical synthesis, transformed into thin films of different thickness and ther- moformed into the desired shape thereof. Such material, although effective in terms of mechanical performance and resistance to radiations, nevertheless requires to pay special attention during the manufacturing and thermal transformation steps to avoid depolymerisation thereof with resulting loss of the mechanical features. It further has extremely high costs, which meaningless add to the already high costs of the materials contained in these packaging items. It would therefore be desirable to be able to find materials suited to this type of packaging.

Among the plastic materials which withstand the terminal sterilising conditions with ionising radiations there is certainly rigid and/or semi-rigid polyvinyl chloride (in the following called PVC), widely used, among other things, for manufacturing apparatuses for medical and/or pharmaceutical use. However, rigid PVC has never been turned into film and thermoformed for applications which provide terminal sterilisation with ionising radiations. PROBLEM AND SOLUTION

The problem at the basis of the invention is to propose a packaging structure which overcomes the mentioned drawbacks and which allows a safe, non-toxic packaging with the full opportunity to terminally sterilise with ionising radiations, at lower costs than those which are faced today and through a simplified productive process. This object is achieved through the use of rigid and/or semi-rigid PVC for the manufacture of containers which may be terminally sterilised with ionising radiations. The present invention relates also to a PVC formula, characterised in that it contains polyvinyl chloride, mercapturic tin and/or derivatives thereof, tioglycolic acid and/or derivatives thereof, acrylic and metacrylic copolymers, as well as to a film and to a terminally sterilisable container with ionising radiations, manufactured starting from such formulated product.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention consists in the use of PVC for manufacturing containers which are apt to be terminally sterilised with ionising radiations.

Generally, PVC is not used as such for these containers, but as a formulated product.

Any kind of rigid and/or semi-rigid PVC formulated product which is used for manufacturing containers apt to be terminally sterilised with ionising radiations falls within the scope of the present invention. However, it has been appreciated that particularly advantageous results can be obtained by a formulated product comprising: polyvinyl chloride, mercapturic tin and/or derivatives thereof, tioglycolic acid and/or derivatives thereof, acrylic and metacrylic copolymers. More advantageous results are obtained with a formulated product containing: polyvinyl chloride, organic phosphitic esters, epoxy soy oil, mercapturic tin and/or derivatives thereof, tioglycolic acid and/or derivatives thereof, acrylic and metacrylic copolymers, fatty acid esters of mono and polyhydric alcohols, polyetylenic waxes, sterammides and/or derivatives thereof. Particularly preferred is a formula as just described, wherein the concentrations, expressed as percentages by weight, of the individual components are as follows: polyvinyl chloride 75-90%, organic phosphitic esters 0.1-1%, epoxy soy oil 1-5%, mercapturic tin and/or derivatives thereof 1-5%, tioglycolic acid and/or derivatives thereof 0.5- 5%, acrylic and metacrylic copolymers 5-20%, esters of mono and polyhydric alcohols 0.2-2.0%, polyetylenic waxes 0.01-0.2% and sterammides and/or derivatives thereof 0.1-0.5%. The formulated product can be made semirigid by optionally adding up to 7% of one or more plasticisers, known per se.

As far as polyvinyl chloride is concerned, a PVC is preferred with a monomer content below 1 ppm and having Kw ranging between 56 and 62, produced in slurry or in mass.

As far as ^phosphitic esters are concerned substituted esters of organic phosphites are preferably used.

In order to improve the appeal of the packages obtained, epoxy soy oil is deodorised before employing it for the preparation of the formula.

Among the possible derivatives of mercapturic tin, those chosen among methyl, ethyl, butyl, hexyl, octyl (mono-, di-, o tri-substituted) are preferred.

Among the possible derivatives of tioglycolic acid, single or double derivatives are preferred, preferably with linear and branched hydrocarbon chains, from C to C ₈ .

Acrylic and metacrylic copolymers will be apt to contain or not sty- rene, butadiene and/or butylacrilate.

As far as fatty acid esters with mono and polyhydric alcohols are concerned, they can be partial or total and the ones with high molecular weight among them are preferred, with glycerols and calcium soaps.

Finally, polyetylenic waxes will preferably have a high molecular weight and can be oxidised or non oxidised. The optional addition of one or more plasticisers up to 7% by weight of the total composition is admissible according to the present invention. By "plasticiser" any additive is meant which imparts flexibility, elasticity and manageability to the plastic material.

The composition according to the present invention can be obtained in pellets or in powder (for example as so-called dry-blend), according to the standard procedures of organic chemistry.

The formulated product according to the present invention is generally manufactured through a dry blending. That is, the components of the formulated product are blended through heating. The temperature may vary between 80 and 150°C, preferably between 100 and 130°C. A particularly preferred temperature for blending is 110°C. Thereby, expansion of the res- ins takes place, which resins can thus absorb the liquid additives and homogenise with the solid ones. Once this step has ended, the cooling of the obtained powder occurs.

The obtained powder may possibly be pelletised. In this case it is first proceded to gelification of the dry blend obtained; such gelification is preferably obtained thermally in an extruder, but can be obtained through any prior art procedure. Compacting of the molten material then occurs, followed by the cutting thereof into pellets, at the exit of a drawing machine.

In turn, for the use according to the present invention, the pellets are used, in a way known per se, for manufacturing a rigid film, possibly apt to be combined to form multiple layers.

The film can be prepared, starting from the pellets, according to some processes, known per se in the art.

A suitable process is calendering: the plastic material, in the paste state, is caused to pass through a series of pairs of rotary cylinders which obtain sheets or plates thereof of the desired thickness, which depends on the distance between the cylinders. Another suitable process is planar-head extrusion : the material is plastically deformed, using an outlet, said linear head and suitable cooling cylinders as well as dimensional abutment cylinders, so as to obtain a constant-thickness film or plate. Finally, bubble extrusion can be resorted to: here too a head is used, which allows to produce a constant-thickness film through a forced flow of cooling and stretching air, resorting also to a dimensional abutment frame.

The film then undergoes thermoforming, still in a known manner, in order to obtain containers.

A particularly preferred use is for manufacturing containers for equipment and devices for medical and/or pharmaceutical use. As a matter of fact, rigid or semi-rigid PVC, used according to the present invention, can undergo terminal sterilisation, both chemically and by irradiation with ionising radiations and is fully stable in both cases.

The features of the final container can be widely modulated, depending on the packaging requirements and on the process for the manufacture thereof. There is no depolymerisation risk during film manufacture, which process, as seen previously, can occur preferably by extrusion or by calendering, with no need to first dry the formulated product.

As regards thermoforming, the same procedures employed for PETG may be used, preferably using lower work temperatures. The film preferably undergoes a softening process; that is generally obtained by heating the film and deforming it inside moulds or predesigned cavities. Of course, any technique which obtains the desired container can be used in the scope of the present invention.

Once filled, the container manufactured according to the present invention may be advantageously sealed with paper or with high-density polyethylene fibers, laminated with a suitable adhesive.

Compared to current containers made of PETG which can be terminally sterilised through ionising radiations, the rigid or semirigid PVC, used according to the present invention, has, in addition to a lower cost of raw materials, the following advantages: A) it is more resistant to possible depoly- merisation during the transformation step; B) it is more easily processable, since the PVC formulated product does not require a drying step before forming the film and/or thermoforming the same; C) it requires lower processing temperatures, so as to be able to be manufactured with a discrete energy saving; and D) being used as formulated product, it is more easily adaptable to the end consumer's requirements.

Subsequent table 1 reports the results of a comparison between a formulated product of the present invention and the PETG commonly used for these purposes.

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Table 1 - Comparison between PETG and PVC

However, it is understood that the invention must not be considered limited to what has been illustrated in detail above, which represents only an exemplifying embodiment thereof, but that a number of variants are possible, all within the reach of a person skilled in the field, without departing from the scope of protection of the invention, as defined in the following claims.