SEALED EDGE DETECTABLE TAPE

Abstract: An improved detectable tape including a ductile metal foil layer (31) which is enclosed in a sheath (34) of thermoplastic coating which provides sealed edges (36, 38) along the length of the tape. The thermoplastic coating sheath protects the foil from corrosion when the detectable tape is placed underground above a non-metallic body such as plastic pipe. The sealed edge detectable tape can also include a reinforcement layer which provides additional tensile length.

Description: The detection of underground pipes and utility lines is a necessity when any construction work involving digging trenches is necessary. Many types of service lines such as telephone and telegraph cables, gas and sewer lines, electrical lines and water mains are located below the surfae. It has become increasingly popular to utilise plastic pipe or plastic wrapped cables in this service. Also, ceramic and other non-metallic material such as concrete are used in underground service. The precise location of the non-metallic lines cannot be determined by the metal detectors above ground used to locate metal pipe. It is important to have a simple method to locate these underground lines when underground construction is in the vicinity or repair of the lines is needed. This problem has been addressed in several patents. In U.S. Patent No. 3,115,861 a frangible coloured body is laid underground over the buried service line. The coloured body has a water insoluble colour and has the benefit of being visible when contacted with soil during digging operations to warn the operator of the proximity of a service line. In U.S. Patent No. 3,282,057 the use of a coloured plastic tape laid over a service line when it was installed was disclosed. The plastic tape is coloured and when it is pulled up by a digger, it provides a warning of the proximity of a buried line. Both patents have the drawback that the coloured frangible bodies or tapes are not detectable from the surface. Also, the use of excavation equipment which makes deep entrenchments may encounter the coloured body or tape and the line in one operation which would provide no warning. In U.S. Patent No. 3,504,503 a method was disclosed for locating underground lines which included using a metallic foil with a moisture and soil resistant coating and a colouring to distinguish from the soil. The coloured foil frangible body is laid over the service line. The benefit of the foil is that metal detectors can be used to locate the foil and thereby the location of the service line. In U.S. Patent 3,633,533, a method of locating underground service line is disclosed using a metal film coated with a coloured plastic. The plastic is moisture and soil resistant. In an alternative embodiment a metallic wire is provided under the plastic coating. The plastic coated foil tape is used quite extensively. These are colour codes for water, gas, electric, buried telephone and telegraph lines and other services. The tapes are printed with a cautionary message corresponding to the type of service line underlying the tape. With the proliferation of plastic piping the tapes have widespread use throughout the world. The plastic coated metallic tapes have a life of about six to seven years. The life of the tape depends upon the moisture and soil conditions which will invade the edges of the tape where the metal is exposed and cause corrosion of the metallic element. There are certain bacterial conditions which contribute to an environment which will cause corrosion of the metallic element and deterioration of the pigment. Also, many of the tapes have printed messages on the outside of the tape which will wear off with abrasion. The plastic coated tapes in use have other drawbacks. When a trench is dug for a utility line and a detectable tape is used, typically, the line is laid first. Then there is a partial backfilling of the trench and the tape is laid over the line coming off a roll on a tractor. Then in a continuous process the trench backfilling is completed. As the tape is laid there may be some tension placed on it, as the backfill process is completed, stretching the tape. During this process if too much tension is placed on the tape, it can break causing the operation to be halted until the tape can be mended. Also, the foil layer is not elastic and tension on the tape may cause the metallic foil to break while the plastic coatings are stretched. In some cases a continuous length of metallic conductive material is desirable. Also, the present plastic coated types have a tendency to curl on the edges and care must be taken when laying the tape that it does not become twisted or folded. Although the plastic coated metallic foil tapes have provided a cost efficient method to detect underground piping systems, there are some aspects which can be improved upon. The present invention is a detectable tape comprising a layer of ductile metal foil having a first surface and a second surface, and two sides, each defining an edge of said foil; a first film of thermoplastic material, directly or indirectly coating the first surface of the foil; a second film of thermoplastic material, directly or indirectly coating the second surface of the foil; characterized in that said first film of thermoplastic material extends beyond the edges of the foil; said second film of thermoplastic material extends beyond the edges of the foil; and said films of thermoplastic material are sealed together to form a protective barrier along the respective edges of the foil. The present invention thus enables the provision of an improved detectable tape which is reinforced and has a sealed edge along the length of the tape. A foil layer of the tape is completely surrounded by a sheath of thermoplastic coating which protects the foil from corrosion. The main factor in determining the life of a detectable tape is the length of time that the metal foil can withstand corrosion. In the present known types of tape, the edges are exposed and water and soil can invade at the edge and cause eventual corrosion of the tape. The corrosion starts immediately as the tape is laid. With a continuous protective coating, the moisture and other corrosive elements would have to penetrate the thermoplastic sheath first to get to the foil. It is anticipated that the improved sealed edge detectable tape will have a useful life of at least 25 years. In addition to the sealed edge, embodiments of the improved tape can be reinforced by the thermoplastic coating or a reinforcing material incorporated into the tape. The thermoplastic coating sheath can be of a high tensile strength material such as polyester. Another layer can be included in the tape such as a polyester layer or a reinforcing fabric. The reinforcing material imparts strength to the tape such that the foil is protected from tearing. The sheath coating in this embodiment does not have to have a high tensile strength and can be a polyethylene or any other thermoplastic film. A reinforcing material which imparts particularly improved properties to the sealed edge tape in addition to those described above is a non-woven high density polyethylene fabric. The reinforcing polyethylene fabric is laminated to the foil layer and a thermoplastic coating sheath encloses the tape so that the edges are sealed from exposure. The reinforced tape exhibits very high tensile strength. Another property is that the tape does not have a tendency to curl at the edges or twist. The tape lies flat. These properties are beneficial from the installation viewpoint, because as the reinforced tape comes off the roll into the trench, there is less likelihood to tear because of the high tensile strength and the tendency of the tape not to curl will make it easier to lay the tape out in the trench. Thus the tape of the invention may be used over an element of construction beneath the earth's surface. The sealed edge tape may have all the other benefits of earlier tapes such as carrying a printed message and colour coding to designate the type of underground service and provide visibility in the soil. The tape can have a layer of colour coating as part of the tape construction. The colour coating layer will also be enclosed in the sheath of thermoplastic and the extend that environment factors and bacteria tend to degrade certain pigments the colour is protected by the sealed edge. The sealed edge tape has the same practical, economical advantages of the earlier detectable tape models. The metal detection equipment can locate the utility or other underground service in the same manner. The life of the tape will have a markedly longer lifetime with the metal foil layer protected from corrosion and the colour pigment similarly protected when necessary. The reinforced embodiments provide high tensile strength and physical properties which facilitate installation. In another aspect, the invention provides a method for manufacturing a reinforced tape comprising the following steps; slitting a foil roll lengthwise at preselected points into a plurality of tapes, rolling the tapes on a shaft with spacers between each roll, coating one side of the spaced tapes so that a continuous film is laid down in between and on top of the spaced tapes, coating the side of the spaced tapes not coated in the previous step so that a continuous film is laid down on the surface of and in between the spaced tapes whereby the two film coating layers form a continuous seal between the tapes and forming a roll of spaced tapes between two continuous layers, and slitting a roll formed by said coating steps and between the tapes lengthwise on the roll where the two film layers form a seal of film between the tapes yielding multiple tapes with a continuous sheath of film. In one embodiment the method comprises the preliminary steps of laminating a colour coating resin and a substantially transparent flexible reinforcing material to a foil roll so that the colour coating resin is next to the foil and the colour shows through the backing, and printing a message on the coloured side of said laminated roll in multiple parallel lines along the length of the roll in a pre-selected spacing on the width of the roll, said slitting step being effected to slit the roll between the lines of the printed message. In order that the invention may be readily understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: FIGURE 1 is a view of a sealed edge detectable tape as placed in service over a pipe; FIGURE 2 is a cross-section view of a non-woven fabric reinforced sealed edge detectable tape embodying the invention; and FIGURE 3 is a transverse cross-section through another sealed edge detectable tape embodying the invention. Figure 1 is a view of a roll 10 of sealed edge detectable tape 12 being laid over a pipe 14. The tape is most useful when the pipe 14 is a non-metallic construction such as ceramic or plastic. The tape can be laid over telephone cables and buried electrical lines in addition to the piping system shown in Figure 1. Any type of underground service which needs to be located to be protected from digging equipment operating in the vicinity or located for repairs can be covered with the detectable tape. The tape can be laid directly on the pipe, cable or other underground construction. More typically, the pipe, cable or underground construction is laid first in the prepared trench. The trench is then partially backfilled and the detectable tape 12 is laid with the underground system approximately directly below the tape 12. The roll 10 is placed on a tractor or other piece of equipment used in the field. The backfilling and tape laying is often an almost simultaneous process and backfill dirt can place stress or tension on the tape during the procedure. The tape generally carries a printed message of caution that a pipe or cable is buried as shown in Figure 1. The printed message can include the type of service or any other cautionary message desired. Also, the tapes are colour coded according to the service lying under the tape with a particular colour generally associated with water, gas, electrical and buried phone lines. The colour generally contrasts to the soil so that the tape is visible when digging operations occur to locate the line. Figure 2 shows one embodiment of a section of a sealed edge tape 20 with a non-woven fabric reinforcement material. The section of seal edge tape has the layers separated in Figure 2 to show the relationship of the materials used to make this embodiment. A foil layer 22 can be any desired thickness depending on the service of the product with typical range of between about 0.1(0.25 mm) and about 3 mils (0.76mm). The foil can be any ductile metal or alloy such as aluminium, copper, steel, silver and iron. The foil typically used commercially is aluminium because of the cost and ease of handling. The foil is laminated with a coloured coating layer 24 over which a layer 26 of reinforcement fabric is placed. The coloured coating can be any type of colour impregnated film. The typical colour coating is a coating grade low density polyethylene with a stable pigment. The coating can be other thermoplastic polymers or blends which will carry a pigment. The colour pigment chosen relates to the colour code corresponding to the buried service line or any other colour desired by the user. The reinforcing non-woven material can be any type of flexible material which wilt provide the tensile strength desired for the tape. The reinforcement layer can be chosen from the high performance engineering polymers which have the desired strength characteristics. These polymers can include polypropylene, nylon and polyester. The reinforcing material can also include polyamide and carbon fibres. If the reinforcing material is laid over the colour coating, it should be substantially transparent so that he colour layer 24 underneath will be visible. The reinforcing layer 26 shown in Figure 2 is a non-woven fabric of high density polyethylene which imparts a texture of the fabric to the finished product. A reinforcement fabric which was used in the preferred embodiment is Conwed Product No. CC1001 which is a high density polyethylene non-woven fabric. The Conwed products come in various weights and can be chosen depending on the strength desired. Other reinforcing materials with similar characteristics can be used also. With Conwed No. CC1001 the colour coating underneath clearly shows through in the finished product. During the lamination process the colour coating migrates through the interstices of the fabric and since the fabric is essentially clear the colour shows through a layer of the fabric as well. After the foil 22, colour coating 24 and reinforcing material 26 are laminated together, the tape can be printed with a cautionary message on either side of the laminate and then coated with the outer thermoplastic sheath. The lettering would be protected from moisture, soil conditions, bacteria and abrasion. Outer coating layers 27 and 28 which form the sheath around the laminate can be of any type of thermoplastic. If a reinforcing layer 26 has been used, it is not necessary to have a high tensile strength resin for the coating. Any low density polyethylene coating resin or other thermoplastic can be used. It is necessary that the coating resin extend beyond the laminate and seal together to form sealed edges 29 and 30 which run lengthwise on either edge of the tape. If for any reason a colour coating is not desired, the colour coating can be omitted from the manufacturing to give a plain metallic tape. The colour coating is generally applied to one side of the tape. However, if desired, colour coating could be applied to one or both sides of the tape. Also, printing a cautionary or informative message is optional depending on the use. The printed message may be applied to outer sheath coating if desired. It is apparent that to practice the invention many variations of colour, printing and reinforcement are available depending on the needs of the user. A sealed edge detectable tape of the construction shown in Figure 2 was prepared from aluminium foil 0.35 mils (0.89mm), coating resin Gulf P E 1017 with 5% blue colour concentrate extrusion coating grade low density polyethylene laminated with Conwed CC1001 high density polyethylene non-woven fabric. The laminate was coated with a sealed edge by a low density polyethylene coating resin Gulf P E 1017. The finished tape was 6 inches (15.2 cm) wide with about a 1/4 (0.64 mm) seal edge extending from the laminate. The finished tape laid very flat without a tendency to curl. The following physical properties were shown as compared to TerraTape (Registered Trade Mark) Detectable by Reef Industries, Inc. which is a tape now used for underground detection of non-metallic lines. Figure 3 is an embodiment of a sealed edge detectable tape that does not use a separate reinforcing material to give the tensile strength. Figure 3 is an enlarged cross-section view showing the metal foil layer 31 which has been laminated to a colour coating layer 32. The colour coating can be any type of pigment carrying film or optional as the user desires, as previously discussed. The outer sheath 34 is made of a polymer or blend that has sufficient tensile strength to serve as a reinforcing material as well as a continuous coating. The outer sheath 34 can be made of polyester, oriented polypropylene and nylon as well as other resins with similar tensile characteristics chosen from the high performance engineering polymers that can be used for the sheathing. The outer sheath 34 terminates on either side of the laminated layers 32 and 30 to form sealed edges 36 and 38. The sealed edges form the protective barrier previously discussed. This embodiment does not have the characteristic of not tending to curl although all the other benefits are present. Printed messages may be placed on the laminate before coating or on the tape after coating. The steps in the method for manufacturing the sealed edge detectable tape can be varied depending on the coloured coating desired, the type of reinforcement in the placement of printing on the tape. The following is a description of the manufacturing process which can be varied according to the desired end product. In the first step, a roll of the selected ductile metal foil is laminated with one or both of a colour coating and reinforcing material. The materials used in this process have been more fully described previously. The materials selected are laminated by a typical extrusion coating method and the coated foil laminate is taken up on a roll. The colour coating is preselected for the end user and can be virtually any colour. The reinforcing material is likewise chosen for strength desired in the finished tape. The roll is then printed with a message in multiple parallel lines on the length of the roll with a pre-selected spacing between the messages on the width of the roll. The width of the printing depends in some part on the desired width of the finished tape. The printed message must be sized to fit the width of the finished tape. The tape can be cut to any width and typically the width of the tapes are from 3 inches (7.6 cms) and larger depending on the use. Printing can be done on either side of the laminate. The usual tape has the printing over a colour coating. After printing, the laminate is placed on a take up roll. This step is omitted if no printing is desired under the thermoplastic coating. The next step is to slit the roll into the desired widths. If the roll is printed the slits are made between the printed messages. This step yields a number of laminated foil tapes. Then the laminated foil tapes are placed on a roll with spacers in between each rolled tape. The tapes are run parallel according to the spacers on the roll through a coating machine to apply a continuous thermoplastic film to one side and in between the tapes. This roll is taken up and run through the same coating process to lay down a thermoplastic film on the other side of the roll. With the second coating, a seal is made with the first film layer and the second film layer in between each tape. The films can be laid down by a number of processes however, the usual extrusion method where a hot coating or film contacts the first film layer and causes the seal by heat adhesion is the most common method. The roll coming off this step has parallel lines of coated tapes with bands of sealed film in between each tape. The roll of heat sealed tapes is taken up and slit a second time through the sealed film bands between the tapes. The extension of the sealed edge on either side of the tape depends on the size of spacer used in the roll on which the coated foil tapes were placed. A sealed edge of 1/4 inch (0.64cm) or more can be achieved by using spacers of 1/2 inch (1.28cm) or more and slitting in the middle of the sealed film band. The laminated foil is enclosed in a sheath of thermoplastic film with sealed edges and is protected from moisture or other environmental elements. The sealed edge detectable tapes are now ready for use. In some cases, printing may be desired on the thermoplastic coating on the outside. In manufacturing the sealed edge detectable tape that does not have a separate reinforcing fabric or layer, the foil layer is not laminated to a reinforcing material in the first step. The other steps are followed. The thermoplastic film coating is of a resin with high tensile strength which provides a sheath for the foil, but also reinforces the tape so it will not stretch and cause the foil to tear. Printing and colour coating steps are the same as the reinforced version. The features disclosed in the foregoing description, in the following claims and/or in the accompanying drawings may be matter for realising the invention in forms within the definitions of the claims.

Claims: A detectable tape (20) comprising a layer of ductile metal foil (22) having a first surface and a second surface, and two sides, each defining an edge of said foil; a first film of thermoplastic material (27), directly or indirectly coating the first surface of the foil (22); a second film of thermoplastic material (28), directly or indirectly coating the second surface of the foil (22); characterized in that said first film of thermoplastic material (27) extends beyond the edges of the foil (22); said second film of thermoplastic material (28) extends beyond the edges of the foil (22) and said films of thermoplastic material (27,28) are sealed together to form a protective barrier (29,30) along the respective edges of the foil (22). A detectable tape (20) according to Claim 1, wherein said film of thermoplastic material (27) is a resin with tensile strength which provides reinforcement to the tape. A detectable tape (20) according to Claim 2, wherein said resin is selected from the group consisting essentially of polyester, oriented polypropylene, nylon and high performance engineering polymers and mixtures thereof. A detectable tape (20) according to any one of Claims 1 to 3, wherein said ductile metal foil (22) is colour coated. A detectable tape (20) according to Claim 1 and comprising a layer of flexible reinforcing material (26) laminated to said ductile metal layer. A detectable tape (20) according to Claim 5, wherein said reinforcing material (26) is selected from the group consisting of polypropylene non-woven fabric, polyester film, oriented polypropylene, nylon, high performance engineering polymers, polyamide fibres and carbon fibres. A detectable tape (20) according to Claim 5, wherein said film of thermoplastic material (27,28) is low density polyethylene. A detectable tape (20) according to any one of Claims 5 to 7, wherein said layer of foil (22) is laminated with a layer of colour coating (24) between the foil layer (22) and the reinforcing material (26). A detectable tape (20) according to Claim 8, wherein said layer of colour coating (24) is a low density polyethylene film impregnated with colour stable pigment. A detectable tape (20) according to any preceding Claim, wherein the tape bears a printed message on at least one side. A detectable tape (20) according to any preceding Claim, wherein said ductile metal foil (22) is chosen from the group consisting essentially of aluminium, copper, steel, iron and silver. A detectable tape (20) according to any one of the preceding Claims, wherever used over an element (14) of construction beneath the earth's surface. A method of manufacturing a reinforced tape (20) characterized in that the method comprises the following steps; slitting a foil roll lengthwise at pre-selected points into a plurality of tapes, rolling the tapes on a shaft with spacers between each roll, coating one side of the spaced tapes so that a continuous film is laid down in between and on the top of the spaced tapes, coating the side of the spaced tapes not coated in the previous step so that a continuous film is laid down on the surface of and in between the spaced tapes whereby the two film coating layers form a continuous seal between the tapes and forming a roll of spaced tapes between two continuous layers, and slitting the roll formed by said coating steps between the tapes lengthwise on the roll where the two film layers form a seal of film between the tapes yielding multiple tapes with a continuous sheath of film. A method according to Claim 13 comprising the preliminary steps of laminating a colour coating resin and a substantially transparent flexible reinforcing material to a foil roll so that the colour coating resin is next to the foil and the colour shows through the backing, and printing a message on the coloured side of said laminated roll in multiple parallel lines along the length of the roll in a pre-selected spacing on the width of the roll, said slitting step being effected to slit the roll between the lines of printed message.

Inventors: GILBERT, RONALD EDWARD
Applicants: REEF INDUSTRIES, INC.
Application year: 1986
Main classification: H02G9
IPC codes: H02G9, F16L1, B32B15, G01V15