US 3850670 A
A hot melt method is described for forming a polymer-coated bitumen-saturated asbestos felt. The polymeric coating is composed of polyethylene, polypropylene, or 160 DEG -180 DEG F. AMP microcrystalline wax. The polymeric coating is deposited in a hot melt on the surface of the felt in a quantity sufficient to cover the felt and to penetrate into the outermost layer of the felt adjacent to the surface. After the coating is allowed to solidify at least partially, the coated felt is passed under a heated doctor blade which levels the surface, removes excessive coating material and trims the coating to the desired thickness. An interlocked, intimate bond between the saturated felt and the polymeric material results. This interlocking mechanical bond is substantially stronger than conventional laminar bonds between the polymeric material and the saturated felt. The products of this process are useful as soil slip wrappings for underground pipelines.
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Description (OCR text may contain errors)
United States Patent  Gregory et al.
1 1 Nov. 26, 1974 1 PIPELINE COVERING WITH PROTECTIVE SOIL SLIP COATINGS AND METHOD FOR MAKING SAME  Inventors: Milton Wesley Gregory, Englewood,
Colo.; Bernard John Olszyk, Somerville, N.J.; Oscar Pierce Bowles, Dallas, Tex.
 Assignee: Johns-Manville Corporation, New
. York, N.Y.
 Filed: Sept. 13, 1972  Appl. No.: 288,632
 U.S. C1. 117/64 R, 117/76 FB, 117/92, 117/102 L, 117/126 AB, 117/126 AQ, l17/140R,117/l68,138/146,138/177  Int. Cl..... B44d l/44, B32b 11/02, B32b 27/12  Field of Search... 117/126 AB, 126 AQ, 102 L,
117/92, 76 PB, 72, 64 R, 168, 32, 140 R, 111 F; 161/205, 236, 247; 138/145, 146
3,511,693 5/1970 Davidson 117/102 L FOREIGN PATENTS OR APPLICATIONS 735,301 8/1955 Great Britain 161/236 Primary ExaminerWil1iam D. Martin Assistant Examiner-William H. Schmidt Attorney, Agent, or FirmJohn A. McKinney; Robert M. Krone; James W. McClain  ABSTRACT A hot melt method is described for forming a polymer-coated bitumen-saturated asbestos felt. The polymeric coating is composed of pollyethylenefpolypro pylene, or l60180F. AMP microcrystalline wax. The polymeric coating is deposited in a hot melt on the surface of the felt in a quantity sufficient to cover the felt and to penetrate into the outermost layer of the felt adjacent to the surface. After the coating is allowed to solidify at least partially, the coated felt is passed under a heated doctor blade which levels the surface, removes excessive coating material and trims the coating to the desired thickness. An interlocked, intimate bond between the saturated felt and the polymeric material results. This interlocking mechanical bond is substantially stronger than conventional laminar bonds between the polymeric material and the saturated felt. The products of this process are useful as soil slip wrappings for underground pipelines.
3 Claims, No Drawings PIPELINE COVERING WITH PROTECTIVE SOIL SLIP COATINGS AND METHOD FOR MAKING SAME BACKGROUND OF THE INVENTION 1. Field of the Invention This application relates to processes for forming coated asbestos felt compositions and to the products of such processes, which find use as soil slip coverings or wrappings for underground pipelines.
Underground pipelines normally have a composite of coatings and wrappings covering the pipe iteself, to protect the pipe from the deteriorating effects of direct contact with the soil. A common protective treatment involves first a coating of asphalt, coal tar, or some similar material applied to the outer surface of the pipe itself to form a chemically resistant barrier to the corrosive components of the soil. A bitumen-saturated asbestos felt is then wrapped around the asphalt coating both to retain in place and to serve as physical protection for the coating.
The outer surface of this saturated asbestos felt is i normally relatively rough. If it were placed in direct contact with the soilthe frictional forces between the two would be quite high and there would be a strong tendency for the felt to be torn by any motion of the pipeline relative to the soil. Similarly, such tearing would be expected when the trench into which the pipe is laid is refilled with dirt, for during the filling process large amounts of dirt, rocks, etc., would fall upon and rub against the outer surface of the felt.
To minimize or prevent this physical damage to the felt it has been a common practice to add a third comwrapped around the outer surface of the asbestos felt.
Use of such materials, however, necessitates a second in situ wrapping step with the associated extra equipment, time and expense called for. Consequently, it
would be desirable to have a soil slip coating of a type which can be made integral with the asbestos felt at the factory where the asbestos felt is prepared. Thereafter on the jobsite only one material, the coated asbestos felt, need be handled by the wrapping equipment and the entire wrapping of the coated pipe with the asbestos felt and the soil slip coating can be accomplished in a single wrapping operation. i
Among the materials which have been found to have suitable properties to serve as such soil slip coatings are polyethylene, polypropylene, and l60-l80F.AMP microcrystalline wax. These materials are flexible enough to bewrapped around the pipe along with the saturated felt without cracking, breaking or otherwise failing as a coating. in addition, and most importantly,
they form surfaces which have quite low coefficients of friction. They are also readily available and quite inexpensive, a feature which is significant when one considers large quantities of such materials which would be used in many miles of pipeline.
Despite the advantageous features which recommend the use of these three materials, in practice it has been found that it is extremely difficult to produce satisfactory coated felt material. Attempts to laminate sheets of polyethylene or the other two resinous materials onto saturated asbestos felt have been largely unsatisfactory. The polymeric sheets do not adhere well to the saturated felt and thus the laminate tends to separate, particularly during the rapid bending and twisting that occur during the actual wrapping of the pipe. Further, the laminate bonding between the polymeric layer and the saturated felt often becomes distorted by temperature changes. This is particularly true of wrappings on pipelines carrying high temperature fluids and wrappings applied over hot asphaltic or other hot bituminous pipe coatings. In many such cases, the laminate not only separates but also forms [heat blisters. In the polymeric layer such blisters are usually broken by friction with the soil, thus exposing the underlying felt to abrasive contact with the soil.
Consequently, it would be desirable to provide a process for forming a satisfactory bond between a polymeric coating and an underlying saturated asbestos felt, which bond would be sufficiently strong to permit use of the coated felt as a pipeline wrapping or covering.
BRIEF SUMMARY OF THEv INVENTION It has now been discovered that the process described herein will produce a superior quality coated asbestos felt composition which is highly satisfactory as a covering for buried pipelines. The composition comprises an outer (or soil slip") layer of a polymeric resin selected from the group consisting'of polyethylene, polyproplyene, and l-l80 F.AMP microcrystalline wax and an inner layer of bitumen saturated asbestos felt. Between the two layers is a strong intimate physical bond composed solely of material of the layers themselves. This bond is quite resistant to either physical or thermal separation forces. In the compositions produced by the process of this invention there is thus no laminar bond to be easily separated, for the layers themselves are interwoven and interlocked.
The process of this invention involves a hot melt application of the polymeric resin onto the saturated asness of the coating resin on the surface by passing the DETAILED DESCRlPTlON OF THE INVENTION The invention herein is a process for forming a coated asbestos felt composition which is useful as a pipeline covering or wrapping. By the process of this invention polyethylene, polypropylene and 160- 180 F. AMP microcrystalline wax, al of which are materials with good frictional characteristics, can be securely bonded to bitumen saturated asbestos felt. This process thus overcomes the inability of the prior art to form reliable bonds between such polymeric materials and the saturated asbestos felts.
The process of this invention comprises forming an asbestos felt saturated with bituminous material; heating a polymeric resin selected from the group consisting of polyethylene, polypropylene and 160l80 F. AMP microcrystalline wax to a temperature above the melting point of the resin and in the range of 200450F; depositing the melted resin on one surface of the felt in a quantity sufficient to cover the surface and to penetrate into at least a portion ofthe outermost layer of the felt adjacent to that surface; controlling the thickness of the coating of resin on the surface by passing the coated felt under and in contact with a doctor blade heated to a temperature above the melting point of the resin and not exceeding 500F; and cooling and solidifying the resin to form a solid flexible coating on the surface, the underside of the coating being interlocked with the outermost portion of the felt adjacent to the surface.
The invention herein also includes a coated composition comprising an asbestos felt substrate saturated with bituminous material; a polymeric resinous coating selected from the group consisting of polyethylerg, polypropylene and l60l8()F.AMP microcrystalline wax; with the coating and the substrate being bonded together solely by the physical interlocking of adjacent portions ofthe polymeric resinous coating and the saturated felt substrate.
' The saturated asbestos felt is produced in a conventional matter. The felt production normally involves a two step process in which a felt of asbestos fibers is first formed in a manner similar to paper making, and then the felt is submerged in a liquid bituminous material which penetrates the felt and saturates it.
To form the felt. an aqueous slurry of asbestos is first produced by adding fibers of asbestos to water and beating the slurry until it is free of large fiber bundles. Dispersing agents, flocculating agents, and the like may also be added to the water to aid in formation of the felt. Beating ofthe slurry will be continued fora period of time sufficient to break up all large lumps of fibers; normally this can be accomplished in no more than about minutes. During the beating one may also add materials such as fillers. sizing agents or strengthening agents to enhance the finished properties of the asbestos felt. Thereafter the slurry is passed to a conventional paper making machine where the water is drained from the slurry and the suspended fibers are matted together and dried to form a felt.
Following formation and drying of the felt, it is submerged and passed through a saturation tank or vat of hot liquid bituminous material. As the felt passes through the tank the bituminous material penetrates into and thoroughly saturates it. The bituminous material also adheres to the felt as the felt is withdrawn from the tank. Thereafter any excess bituminous material on the surface of the felt is removed and the felt is dried (often by heating) to solidify the bitumen.
Alternatively, an aqueous emulsion of bituminous material may be added to the slurry of asbestos fibers in the beater. The emulsion is then broken physically or chemically and the emulsified bitumen particles coat the individual asbestos fibers. The coated fibers are then formed into a felt in the manner described above. Since the cost of the emulsified bituminous material is usually considerably higher than the cost of liquid bitumen, this latter procedure is generally less economically attractive than the saturation tank process although it does require less equipmenf. It is also consid ered less attractive technically, for it requires the additional step of breaking the bituminous emulsion in the presence of the asbestos, a step which on occasion is difficult to accomplish.
The saturated asbestos felt is then coated with the polymeric resin by a hot melt technique. A supply source of molten polymer is prepared. The felt is continuously passed under a dispensing device through which the molten polymer pours (ordinarily by gravity) onto the surface of the felt. Normally such a dispensing device is a reservoir with a long narrow opening at the bottom extending laterally across and above the passing felt. The polymer pours through in a thin continuous sheet and completely coats the upper surface of the passing felt. The dispensing device is usually equipped with conventional regulating means to control the quantity of molten polymer which passes therethrough.
A portion of the molten polymer which deposits on the surface of the felt penetrates into the various pores and openings in the upper surface of the saturated felt. The remaining portion ofthe polymer completely coats the surface of the felt. The result of this penetration is to form a interlocked, intimate bond between the saturated felt and the polymeric layer. This interlocking mechanical bond is substantially stronger than conventional laminar bonds between the polymeric material and the saturated felt which rely on simple adhesion of the surfaces of the two materials or on a separate adhe sive composition binding the two materials together.
The molten polymer will be held in the dispensing device at a temperature above its melting point and in the range of 200F to 450F. The higher temperatures of the melt within this range may aid the material to penetrate and interlock with the surface of the saturated felt but conversely require longer times in which to cool and solidify. At temperatures much above 450F the polymer will often be degraded if the high temperature is maintained for an appreciable period.
Following coating of the felt with the polymeric resin, the coated felt is passed under and in contact with a doctor blade which levels and smooths the polymeric coating and removes any excess coating material. The doctor blade is positioned downstream from the dispensing device at a distance sufficiently far that the polymeric coating is at least partially, and usually completely, solidified at the time it reaches the doctor blade. The doctor blade is positioned such that its trimming edge is at the height required to trim the polymeric surface coating to the desired thickness. The blade is heated to a temperature above the melting point of the resin but not greater than 500F. It thus operates by melting the surface layer of the resin and removing the excess material as a melt. Simultaneously the remaining molten resin acquires a level, smooth, low-friction surface. The technology of doctor blade operation is wellknown, and need not be further described here. The excess coating removed as a melt may be collected, and returned for reuse as coating.
The materials used for producing the saturated asbestos felt are asbestos and a bituminous material. The as bestos may be any desired fibrous grade or mixture of fibrous grades. In common practice, the longer fibers are generally used for felting of asbestos. The bituminous material may be any common asphalt, coal tar, pitch, or other heavy bituminous material. The material will normally have a softening point (Ring-and-Ball; ASTM D36) of at least 100F, and a liquifying point of at least 140F. It will, of course, be maintained in the saturation tank at a temperature considerably above its liquification point so that initial contact with the cooler asbestos felt does not cause local solidification of the bitumen in the vicinity of the belt, thus preventing the hot molten bitumen from saturating the felt.
The polymeric coating material will be selected from the group consisting of polyethylene, polypropylene, and l60l80F.AMP microcrystalline wax. These three materials all are easily melted, readily available and have the good low friction characteristics required for the process of this invention. Polyethylene normally has a melting point in the range of about 185F to 2l2F while polypropylene (isotactic) generally has a melting point in the range of about 334F to about 340F; the wax will, of course, have a melting point of from l57F to 177F.
What we claim is:
l. A process for the production of a coated asbestos felt composition which comprises:
a. forming an asbestos felt saturated with bituminous material,
b. heating a polymeric resin selected from the group consisting of polyethylene, polypropylene and l60-l80F. AMP microcrystalline wax to a temperature above the melting point of the resin and in the rangeof 200F.to 450F,
c. depositing the melted resin on one surface of said felt in a quantity sufficient to cover said surface and to penetrate into at least a portion of the outer most layer of said felt adjacent to said surface,
cooling the deposited resin to form an at least partially solidified coating on said. felt,
e. controlling the thickness of the coating of said resin on the said surface by passing the coated felt under and in contact with a doctor blade heated to a temperature above the melting point of said resin and not exceeding 500F to melt at least a portion of the surface layer of said coating, remove excess resin, and level the surface of said coating, and
f. cooling and solidifying said resin to form a solid flexible coating on said surface, the underside of said coating being interlocked with the outermost portion of said felt adjacent to said surface.
2. The process of claim 1 wherein said polymeric resin is polyethylene.
3. The process of claim 1 wherein said polymeric resin is polypropylene and said temperature in step (b) is in the range of 334F to 450F.