The invention relates to a shaped longitudinal strip of polymeric film, in tubular form and a continuous method of making such tubular form. The tube may be used as a conduit for gases and for wrapping or protecting cable, optical fibres, pipe and other materials. Background of the Invention

It is often desirable to protect elongated structures such as pipes, cables, fibres, and tree trunks and limbs, or a plurality of objects such as ball bearings, castors, tennis balls. For example, protection of wire, cable, optical fibre has been done in the past by extrusion coating such wire, cable or fibre with a rubber or plastic material and/or spiral wrapping it tightly with thin films. One of the disadvantages of such coatings or wrappings is that in order to inspect the wire, cable or fibre it is necessary to cut the coating or wrapping with the consequent danger of also cutting or nicking the wire, cable or fibre. A removable wrapping is desirable. The present invention is intended to provide a wrapping material which not only may be removed easily but may be replaced easily and retain the shape it had before being removed. Tubes have also been used to carry gases, e.g. air ducts for use in buildings. It is known to make air ducts by rolling sheets of metal into discrete lengths of tube. The ends are shaped so that there is a male and female end, thus allowing the discrete lengths of tube to be joined to form a long run of ductwork. The longitudinal edges of the pieces of metal of the duct are mated. Such ducts occupy enormous amounts of room, which is a major disadvantage for storing before installation and for transporting. The cost of transporting the ducts is relatively expensive. It would be a great step forward if the ducts could be in much longer lengths and could be in compact form. Similar savings in terms of

space and transportation costs are also desired, for example, for tubes used for forming columns of concrete. Disclosure of Invention

The present invention provides a tube which has a longitudinal axis and is made from an elongated strip of oriented crystalline thermoplastic polymer film, said strip having two longitudinal edges, said strip being memory-set into a split tubular shape.

In one embodiment the split is parallel to the longitudinal axis.

In another embodiment the split follows the shape of a helix.

In one embodiment, the strip is memory set such that the longitudinal edges are adjacent one another. In another embodiment, the strip is memory-set such that portions adjacent the longitudinal edges overlap.

In yet another embodiment the longitudinal edges are adapted to be interlocked. Preferably the interlocking edges are J-shaped in cross-section. In a further embodiment the longitudinal edges are interlocked.

In a further embodiment the cross-sectional shape of the memory-set tube is selected from the group consisting of a circle, an oval and a polygon. In yet another embodiment the polygon is selected from a triangle, a square, a rectangle, a pentagon, a hexagon and an octagon.

In a preferred embodiment the strip is memory-set in circular or oval form. In yet another embodiment the memory-set tube encases a strand-like or tubular article.

In a further embodiment the strand-like or tubular article is selected from wire, cable, optical fibre and pipe. It is to be understood that the wire or optical fibre may be single strand or multi-strand.

In another embodiment the memory-set tube encases a plurality of objects.

In a further embodiment the memory-set tube is temporarily opened into flat form.

In another embodiment the memory-set tube is temporarily opened into flat form, and the temporarily flat form is in a roll.

The polymeric film used in the present invention is an oriented, crystalline film of a thermoplastic polymer. The term "film" as used herein also encompasses what are known in the art as sheets. The term "crystalline film" also encompasses what is known in the art as semi-crystalline film. Crystalline film is distinguishable from amorphous film, by those skilled in the art. Crystallinity may be measured by methods such as differential scanning calorimetry (DSC), density determinations and X-ray diffraction (XRD) .

In one embodiment the thermoplastic polymeric film is selected from polyamide, polyester and polyimide films.

The polyesters are film forming polyesters which may be made from diols and di-acids, for example alkylene glycols and aromatic dicarboxylic acids. A preferred alkylene glycol is ethylene glycol. Preferred dicarboxylic acids are terephthalic acid, isophthalic acid and naphthalenic acid. In another embodiment the polyester is polyethylene terephthalate.

In a further embodiment the polyester is polyethylene naphthalate.

In one embodiment the polyamide is of film-forming molecular weight and selected from polyamides made from i) an aliphatic aminoacid having from 6 to 12 carbon atoms, ii) from an aliphatic dicarboxylic acid and an aliphatic diamine, each having from 6 to 12 carbon atoms, and iii) mixtures of said polyamides In a further embodiment, the crystalline polyamide is selected from nylon 6, nylon 6,6, nylon 6,9, nylon 6,10, nylon 6,12, nylon 12,12, and mixtures

thereof.

In a preferred embodiment the polyamide is selected from nylon 6, nylon 6,6 or mixtures thereof.

In a further embodiment the elongated film is machine direction oriented or biaxially oriented.

In order to add a little elasticity to the finished tube a minor amount, e.g. 5-15% of an elastomer may be added to the crystalline film. For example, a polyester elastomer may be added to a crystalline polyethylene terephthalate film. One such polyester elastomer is sold under the trade mark Hytrel and avaialbe from E.I du Pont de Nemours and Company, Delaware, U.S.A. Addition of such an elastomer assists in the wind-up of a roll of tube, without materially affecting the memory-set feature of the tube.

The present invention also provides a continuous process for making a tube, said process comprising: a) feeding a continuous elongated strip of oriented crystalline thermoplastic polymer film, which has two longitudinal edges, through a tube-forming section; b) in the tube forming section, continuously forming the strip into a tube, which has a longitudinal axis, so that the longitudinal edges of the strip are adjacent one another; c) heating the so-formed strip to its memory-setting temperature and then cooling the strip, to form a continuous, memory-set, split tube.

In one embodiment the continuous strip is fed into the tube forming section in a direction parallel to the longitudinal axis so that the split is parallel to the longitudinal axis.

In another embodiment the continuous strip is fed into the tube forming section at an angle to the longitudinal axis so that the split follows the shape of a helix.

In one embodiment the continuous split tube is wound into a roll.

In a further embodiment the continuous split tube is opened out until it is temporarily flat, and the temporarily flat form is wound into a roll.

In another embodiment the continuous split tube is cut to form discrete lengths of tube.

In another embodiment, the strip is formed so that portions adjacent the longitudinal edges overlap.

In yet another embodiment the strip is formed so that the longitudinal edges of the strip are adjacent one another and are adapted to interlock with one another. In a preferred embodiment the longitudinal edges are formed into J-shapes.

In another embodiment the strip is formed so that the longitudinal edges of the strip are adjacent one another and are interlocked with one another.

In a further embodiment the strip is formed so that the cross-sectional shape of the strip is selected from the group consisting of a circle, an oval and a polygon.

In yet another embodiment the cross-sectional shape of the strip is selected from a triangle, a square, a rectangle, a pentagon, a hexagon and an octagon.

In a preferred embodiment, the strip is memory set in circular or oval form.

In a further embodiment, a continuous elongated structure is continuously fed into the tube forming section so that the structure is encased in the split tube. In preferred embodiments, the structure is selected from rope, wire, cable and optical fibre.

If desired the encased structure may further be coated or wrapped with other films or materials, e.g. for waterproofing or other purposes.

The invention is described more fully with the aid of the drawings.

Brief Description Of The Drawings Figures la and lb are three quarter views of a portion of tube with overlapping longitudinal edges. Figure 2 is a three quarter view of a portion of a tube

with interlocking longitudinal edges. Figures 3 and 4 are schematic representations of one process of the present invention, for making a tube with a split parallel to the axis of the tube, seen from the side and top respectively. Figures 5 and 6 show a variation of the process shown in Figures 3 and 4. Figure 7 is a schematic representation of a process of the invention in which the tube has a helical split. Detailed Description Of The Invention Figure la shows strip 11 which has been formed and memory-set into tubular form. The tube 10 so formed has longitudinal edges 12 and 13 placed such that a portion of the strip adjacent 13 overlaps a portion of the strip adjacent edge 12. The split in the tube is parallel to the longitudinal axis of tube 10. Figure lb shows strip 11' which has been formed and memory-set into tubular form. The tube 10' so formed has longitudinal edges 12* and 13' placed such that a portion of the strip adjacent 13' overlaps a portion of the strip adjacent edge 12'. The split in the tube follows a helical path around tube 10' .

In Figure 2, tube 20 has been formed and memory set with longitudinal edges 21 and 22 curled into interlocking relationship. In the embodiment shown the edges have J-shaped cross-sections.

In the process shown in Figures 3 and 4 a long strip of flat film 30, e.g. polyester terephthalate film or polyimide film, is unwound from roll 31. Roll 31 is on spindle 40 on an unwind stand (not shown). Flat film 30 is fed past controlling roller 42 and passed through a tube forming section 32, a heating section 33 and a cooling section 34 to form a memory-set tube 35. As will be seen more clearly from Figure 4, strip 30 is fed in a direction parallel to the longitudinal axis of the tube and the split 45 in the memory-set tube 35 is parallel to the longitudinal axis of the tube. The memory set tube 35 is fed past controlling rollers 44 and rolled up on a

spindle or core 37 to form a reel of tubing 36. Optionally, a strand 38, e.g. rope, can be fed from roll 39, under controlling roller 43 so that strand 38 is encased in tube 35. Strand 38 is on spindle 41 on an unwind stand (not shown). The function of such a strand is to assist in keeping the tubular shape to tube 35 while on reel 36. In place of the rope, optical fibre or wire may be fed into the tube forming section. If such were the case, then it may be desirable to overwrap or coat tube 35 before being wound onto reel 36.

In the process illustrated in Figure 5, a long strip of flat film 50, e.g. polyester terephthalate film ro polyimide film, is unwound from roll 51, which is on spindle 59. Film 50 is passed under controlling roller 60 and passed through a tube forming section 52, a heating section 53 and a cooling section 54 to form a memory-set tube 55. The memory-set tube 55 is splayed open in splaying section 56 to form temporarily flat strip 57 which is then wound up in roll 58. When the strip is later unwound from roll 58, the tube 55 automatically reforms because the strip is memory-set in tubular form.

In the process illustrated in Figure 7, a long strip of flat film 65, e.g. polyester terephthalate film, is unwound from roll 66 and passed through a tube forming section 67, a heating section 68 and a cooling section 69 to form a memory-set tube 70. During manufacture of the tube, the pitch of the helix is dependent on the angle at which the roll of flat film 65 is directed, relative to the longitudinal axis of the tube. The memory-set helically formed strip of tube 70 is unwound and rewound to form temporarily flat strip 71 which is then wound up in roll 72.

In the tube forming section of the process, there are mandrels and forming shoes (not shown) which shape the flat film into tubular form. The shapes of the mandrels and forming shoes will dictate the cross-

sectional shape of the tube, e.g whether it is circular, square, rectangular, whether there is any overlap of the longitudinal edges, as for example shown in Figure la, and whether the edges are themselves shaped, as for example shown in Figure 2. For wrapping optical fibres, wire and cable, tree trunks and the like, the preferred cross-sectional shape is circular and it is preferred that the split is parallel to the longitudinal axis of the tube and that the longitudinal edges overlap, as shown in Figure la. For air ducts and the like it is preferred that the cross-sectional shape of the tube be circular or rectangular and it is preferred that the longitudinal edges are able to be interlocked, e.g. with J-shaped edges. It may be possible, in instances wherein the strip is being wrapped around an elongated material, e.g. rope, cable, to use the elongated material in lieu of an internal forming mandrel, e.g. in the process shown in Figure 7 a cable may be used in lieu of a mandrel.

Tube forming may be aided by heating the film prior to the tube forming section, or in the tube forming section. After being constrained into tubular form in the tube forming section, the tube is passed into the heating section. The tube may be heated by infra-red heaters (shown as 61 in Figures 5 and 6, but not shown in Figures 3, 4 or 7), a hot air oven or other means. For example, the strip may be coated evenly or selectively with a microwave absorbing material and heating be accomplished with microwave energy. The temperature and residence time of the tube in the heating section is adjusted so that the film reaches its memory-setting temperature range. The temperature and residence time will affect the strength of the memory-set. Easy experimentation will determine the optimum temperature and residence time for a given polymeric film and film thickness. In the case of Mylar® polyester film the memory-setting temperature is preferably in the range of about 143-154°C (290-310°F). Memory-setting temperatures

for other memory-settable films may be determined by easy experimentation.

As will be clear, diameters of tubes, having the split parallel to the axis of the tube, will be limited by the available widths of flat film, e.g. 30 in Figure

3. Larger tubes may be formed using the helical process.

If the tube is to retain its tubular form in the roll, it may be desirable in some instances to help the tube retain its shape by encasing a disposable material, such as rope, inside the split tube. In other instances it may be of little consequence that there is no rope or other material inside the tube, because even if the tube is flattened out somewhat in the roll form, the tube will spring back to its original shape on being unwound from the roll.

In some processes, e.g. cable, optical fibre, or wire making processes, it may be desirable to incorporate the present process, so that the cable, optical fibre or wire is continuously encased in the split tube and wound up into a roll. It may also be desirable to overwrap the split tube with other materials, e.g. for waterproofing or other purposes.

It will be understood that the thickness of the oriented film will depend on the intended use for the tube. For example, a tube that is intended for wrapping wire, cable or optical fibre may be from 75-250 μ (3-10 mil) thick, whereas a tube intended for an air duct may be from 300-625 μm (12-25 mil) thick or a tube for concrete applications may be 750-1000 μm (30-40 mil) thick.

The crystalline thermoplastic film is an oriented film, and is a resiliently flexible crystalline or semi- crystalline film which is capable of being thermally treated to have a permanent memory set. The film has advantages in that it is flexible, and has strength and stability in a wide range of environments, e.g. hot, cold, wet or damp environments. It has been found that

in most environments, polyethylene terephthalate film is suitable. In certain environments, e.g. where temperatures are in excess of about 120°C (248°F), polyethylene naphthalate or polyi ide film may be desirable.

As indicated the preferred films are selected from polyester, polyamide or polyimide films. Although oriented nylon (polyamide) or polyimide films, e.g. Kapton® polyimide film may be used, the preferred film is an oriented polyester film, which is capable of being prestressed with a substantially permanent curvature of a small radius and relatively long duration memory. A particularly preferred film is an oriented polyethylene terephthalate film. One such oriented polyethylene terephthalate film is sold by E.I. du Pont de Nemours and Company under the trade mark "Mylar" . For convenience in this disclosure, reference may be made to Mylar® polyester film as the oriented thermoplastic polymeric film. It is to be understood, however, that this is for exemplification and clarity of description and is not to be considered limiting.

Commercially available polyester film suitable for use in the present invention, e.g. Mylar® polyester film, is usually biaxially oriented, flat and heat set in an annealing step. Homopoly er polyethylene terephthalate has a glass transition temperature (T _g ) of about 70°C (158°F)and a crystalline melting temperature of about 255°C (491°F). During annealing of the film, crystallinities of about 40% are achieved. In the case of polyethylene terephthalate, even though the T _g is about 70°C (158°F), it will not crystallize easily at temperatures below about 110°C (230°F), even if left for an hour or more between these temperatures. Although not wishing to be bound by any theory, it is thought that thermoplastic polymers having a glass transition temperature at about or above ambient temperature are suitable for use in the present invention.

Under some circumstances it may be desirable to impart longitudinal elasticity to the film by adding a small amount of elastomer to the crystalline film. Oriented polyethylene terephthalate film, for example, does not stretch even though it is flexible, and it may be advantageous to add small quantities of elastomer, e.g. polyester elastomer to the film.

The crystalline polyamide may be made from acid-forming and amine-forming derivatives of said acids and amines, e.g. esters, amine salts and the like.

Examples of such acids include adipic acid, azelaic acid, sebacic acid, and dodecanoic acid. Examples of such amines include hexamethylene diamine and octamethylene diamine. An especially preferred crystalline polyamide is nylon 6,6. The crystalline polyamide may be a blend of different polyamides, e.g. nylon 6 and nylon 66 or a copolymer of nylon 6 and nylon 66.

With respect to Mylar polyester film, the heat deformation point is well below the melting point. There is a relatively narrow temperature range over which the film may be memory-set for use in the present invention. For example, below about 120°C (248°F), the film is difficult to memory-set properly and above about 160°C (320°F) the film tends to become embrittled. A suitable memory-setting temperature for Mylar polyester film is around 143-154°C (290-310°F). For other oriented memory- settable films, the preferred temperatures can be determined by easy experimentation. When the tube is intended to be used as a protective device, e.g. when wrapping wire, cable, optical fibre, tree trunks and the like, it may be desirable for the memory-settable film to be laminated to another material. For example to prevent puncturing the film, it may be desirable for the oriented crystalline thermoplastic polymer film to be laminated to an aramid fabric, e.g. a fabric of Kevlar® aramid fibre. For insulation purposes,

e.g. for lagging pipes, it may be desirable for the oriented crystalline thermoplastic polymeric film to be laminated to an insulating material, e.g. polyurethane foam. An advantage of the invention for the protection of trees is that it can expand at the same rate that the diameter of the tree trunk grows.

The split tube has a large number of uses. For example, such a memory-set tube may be used to hold heat tracing cables in place around a pipe. Thermal insulation wrap may then be placed around the memory-set tube. Indeed, the thermal insulation may be held in place with the memory-set tube. In order to wrap insulation in the memory set tube, the insulation is held in place on the pipe, temporarily. With a memory-set tube having the split parallel to the longitudinal axis, the longitudinal edges of the memory-set split tube are pried apart so that the edges are wider apart than the diameter of the insulation, and the tube is slipped over the insulation. The edges of the tube are released and the tube returns to its memory-set form. Although not necessary, the memory-set tube may be additionally secured with securing bands or tape. The split tube is applied in a similar manner when wrapping materials like wire, cable or optical fibre. The split tube may be encased in other materials, or sealed with, e.g. waterproofing materials.

If materials, e.g. optical fibre, wire, need to be examined after they have been wrapped, it is an easy matter to pry open the split tube by grasping the longitudinal edges and pulling them apart, thus exposing the wire of fibre inside. A section of the wire or fibre can even be removed from the split tube so that closer examination or repair may take place before reinserting the wire of fibre back inside the split tube. The split tube will return to its memory-set configuration, e.g. with overlapped edge portions.

In the case of memory-set tube (with the split parallel to the longitudinal axis), which has been splayed and wound up in flat form, e.g. in a roll, such as for an air duct, a workperson takes the roll to the building site, unrolls an appropriate length and cuts to length. As the person unrolls the strip, the memory-set feature causes the strip to reform into a tube. It is preferred that the longitudinal edges have interlocking edges in order to allow the person to interlock the edges after unrolling the tube. If desired the edges, after interlocking, can be further secured with tape, or if the edge surfaces are coated with an adhesive or thermoplastic coating, the edges can be joined more permanently. The tube can then be put in place in the building. If necessary, such duct work can be inspected by prying the tube apart at its longitudinal edges, inspecting the tube or removing the debris and then re- closing the tube merely by releasing the pried-apart edges. As describe hereinbefore, helically-set tube may also have been wound up in flat form on a roll. Obviously, in order to make a tube with helical windings, the length of strip needed to make a given length of tube is longer than the tube itself and depends on the pitch of the helix. The steeper the pitch the more windings per metre of tube are required. For example, at a pitch of only 5° or so, the tube may only have a few turns per metre, whereas for a 30° pitch the tube would have a larger number of turns per meter. Accordingly, a tube with a helix of 30° pitch would require a longer strip to make than would a tube with a helix of 5° pitch.

A tube with interlocked longitudinal edges can also be used, in discrete lengths, to encase objects as diverse as ball bearings, documents, tennis balls, castors or to provide formers for concrete pouring and curing, and the like.