Stock material or miscellaneous articles – Sheet including cover or casing – Including elements cooperating to form cells
Reexamination Certificate
1999-01-15
2003-04-01
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Sheet including cover or casing
Including elements cooperating to form cells
C428S035200, C428S035700, C428S158000, C428S166000, C428S178000, C428S180000, C428S198000
Reexamination Certificate
active
06541095
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to a flattened tubular film and to a process for its production.
Plastic pouches or bags for medical use are conventionally made by extruding the plastic in the molten state through a tubular die in order to form a cylindrical film, blowing using a pressurized gas and flattening of this film without welding or gluing of its inner faces. The bags themselves are subsequently made from this film by cutting it up, inserting various accessories (connecting tubes, etc.) between the two walls and welding them together, usually at their ends or their periphery.
Most of the plastics used in this application have the drawback of creating blocking between the two inner faces of the flattened film. The consequence of this blocking is, in particular, that it makes it more difficult subsequently to separate the two faces of the film, in order to introduce the various accessories between them. The rate of production of such articles is reduced thereby, which leads to a certain economic disadvantage.
A second consequence of this blocking is that the two inner faces are in almost continuous mutual contact over the entire surface of the flattened film. During the subsequent step of welding the two inner faces together, there is thus no free volume, between these two faces and along the welded zone, to allow the formation of a welding bead, which guarantees good-quality welding. This phenomenon thus leads to welded articles whose weld strength may not be uniform, or may possibly even be deficient.
One attempt to solve this problem of blocking has been, for example, to create caulking on at least one of the inner faces of the flattened tubular film. For example, patent application EP-A-0,445,793 describes the creation of caulking on a tubular film over a part of its circumference by means of a specific temperature conditioning of the core of the annular die used.
However, this process is expensive and complex to implement and leads to articles whose overall transparency is reduced, which is a result to be avoided in the case of medical applications.
Consequently, the subject of the present invention is a flattened tubular film in which the subsequent separation of the two inner faces is easy, in which the welding together of the two inner faces leads to good-quality welding, and whose walls are highly transparent.
Consequently, the invention relates to a flattened tubular film made of thermoplastic material, of which the two inner faces are not welded or glued, which is characterized in that the said inner faces are in mutual contact only over a part of their surface, thus forming a plurality of cells of determined shape, essentially hermetic, containing a gas.
SUMMARY OF INVENTION
In the context of the present invention, the term “tubular film” is intended to refer to any hollow body of indefinite length whose average wall thickness is markedly less than a half-diameter of its transverse section. The thickness of the wall is generally between 0.01 and 2 mm, usually between 0.1 and 0.5 mm. The width of the flattened film is generally between 10 and 1000 mm.
The tubular film can quite equally be multilayer or monolayer, and oriented or non-oriented.
The term “flattened tubular film” is intended to denote any tubular film whose wall has been deformed so as to make two half-circumferences of the tubular film parallel and to bring them into mutual contact over a part of their inner face. This bringing in contact takes place under conditions, in particular of temperature and pressure, such that the two inner faces of the film remain distinct and separable later, i.e. they are not mutually welded or glued, i.e. there is no intentional bonding. This absence of intentional welding or gluing, in particular, distinguishes the films in accordance with the invention from the bubble films mainly used in packaging for protecting fragile articles.
The mutual bringing in contact of the said inner faces of the tubular film is partial, i.e. they are in mutual contact only over a part of their surface, the places in which there is no mutual contact thus forming a plurality of cells described below.
Hereinbelow, the flattened tubular film in accordance with the invention will thus be considered as comprising two walls, the width of which corresponds approximately to a half-circumference of the tubular film and an interface between the two inner faces of these walls. The said walls are in mutual contact only in certain regions of the interface, the other regions being occupied by the gas cells.
For the purpose of clarity hereinbelow, it will be assumed that the flattened tubular film has an essentially plane interface, but it can, quite obviously, be in any other configuration, for example rolled up or folded.
The term “thermoplastic material” denotes any thermoplastic polymer, including thermoplastic elastomers, as well as mixtures thereof. The term “polymer” denotes both homopolymers and copolymers (in particular binary or ternary polymers), for example randomly-distributed copolymers, sequenced copolymers, block copolymers, grafted copolymers, etc.
Preferably, the thermoplastic material consists essentially of one or more polymers chosen from plasticized vinyl chloride polymers, polyolefins, polyesters and polyamides.
The term “plasticized vinyl chloride polymer” is intended to denote any vinyl chloride homopolymer, any vinyl chloride copolymer and mixtures of these homo- and/or copolymers. The polymer is said to be plasticized when it comprises a substantial amount of plasticizer, in particular at least 20 parts of plasticizer per 100 parts of polymer (by weight). Any type of plasticizer can be used, the amount present obviously being adapted in consequence. For example, alkyl phthalates, citrates, trimellitates and phosphates are widely used. The plasticizer used can also be polymeric, which has the advantage of reducing its exudation.
The term “polyolefin” is intended to denote any olefin homopolymer, any copolymer containing at least two different olefins and any copolymer comprising at least 50% by weight of olefin-derived units. In the latter case, the comonomer can be of any other nature. It can be, in particular, a vinyl ester, for example vinyl acetate.
In the case of a polyolefin, this material can advantageously be mixed with at least one elastomer, for example such as a styrene/ethylene butylene/styrene (SEBS) or styrene/ethylene propylene/styrene (SEPS) three-block copolymer. In this case, the content of the elastomer mixture can be up to 80% by weight.
The term “polyester” is intended to denote any thermoplastic homopolymer or copolymer comprising repeating units linked by ester-type functions integrated into the polymer backbone.
The term “polyamide” is intended to denote any thermoplastic homopolymer or copolymer comprising repeating units linked by amide-type functions integrated into the polymer backbone.
More preferably, the thermoplastic material consists essentially of a plasticized vinyl chloride polymer (PVC).
Advantageous results have also been obtained with a thermoplastic material essentially consisting of a random copolymer of ethylene and vinyl acetate (EVA).
One or more standard, polymeric or non-polymeric additives, such as organic or inorganic fillers, reinforcing materials, plasticizers, stabilizers, lubricants, etc., can be added to the thermoplastic material.
The gas filling the cells located between the two inner faces of the flattened film can be of any nature or can be a mixture of different gases. This gas may be, in particular, air, nitrogen or carbon dioxide. Preferably, and in particular for economic reasons, the gas is essentially air.
In order to prevent any contamination, the gas is preferably free of foreign bodies such as dust or bacteria.
In the context of the present invention, the gas cells of determined shape are located between the two inner faces of the flattened film. This means that the two faces of the film are not in mutual contact over their entire surface and that the zones in which they are not in cont
Miggins Michael C.
Pyon Harold
Schneller Marina V.
Solvay ( Societe Anonyme)
Venable LLP
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