US 3252851 A
Description (OCR text may contain errors)
May 24, 1966 J. R. BENSON 3,252,851
MEMBRANE-LINER AND PROCESS OF MANUFACTURE Filed Feb. 1B, 1965 2 Sheets-Sheet l 1N VEN TOR.
Jewell R. Benson F'g 5 BY wHlTEHEAD, voGL a LowE ATTORNEYS May 24, 1966 J. R. BENSON MEMBRANELINER AND PRocEss oF MANUFACTURE Filed Feb. 18, 196:5
2 Sheets-Sheet 2 Q .um @ma E u EEEQQEE. l SEEQQEQ. W m.. cov o com @om o oom @om m nu w M m. N S R M U E n L o m. W I W A rA u. D.. m R M M mm W H H vm awww@ NN EBS f/ W n 7W Soo mm e Jyw m .mi B P QON .u w g con w n Jv V mm uvm. A
United States Patent O 3,252,85ll MEMBRANE-LINER AND PRUCESS OF MANUFACTURE Jewell R. Benson, 1035 th St., Denver 2, Colo. Filed Feb. 18, 1963, Ser. No. 260,343 8 Claims. (Cl. 161-236) This invention relates to membranes and linings and more particularly to impermeable membranes and linings for general construction purposes, a primary object of the invention being to provide a novel and improved impermeable sheet material which may be used as a water and vapor barrier membrane in certain types of constructions and also as a water retaining liner in other types of constructions. As such, the invention will be hereinafter referred to as a membrane-liner.
This application is a continuation-impart of rny -application for a membrane-liner, led June 23, 1961, Serial No. 119,098, now abandoned, to include the results of tests, di-scoveries and developments subsequent to that time which are herein disclosed to better enable the public to understand, know the limitations of, and to practice the invention. Subsequent to the filing of the application, it was discovered that the critical temperatures could be higher than those originally disclosed, that prompt cooling was an extremely importantfactor to the long life of the product, that only certain classes of vinyl chloride sheets could be used to produce a product with the components being adequately bonded together and having the toughness and ductility needed for severe field usage.
A variety of membranes and liners are commonly `available and asphalt and asphalt impregnated sheets are often used for this purpose because of the impermeability of asphalt, the ease with which they may be formed and the low cost. A very simple liner may consist of a sheet of asphalt saturated felt, however, the application of such a liner material is limited because of its low strength and brittleness, especially 'after aging a few years. More often, felt sheets are mopped or welded together with alternating layers yof asphalt and asphaltic materials to form a membrane or liner of appreciable thickness, increased strength and resistance to aging. In another, better, type of lining a ve-element composition is used, including a central core of asphalt, a mineral ller and a iibrous material such as felt, asbestos and glass libre. The core is covered with asphalt saturated lfelts which are, in turn, weather coated with asphalt.
The patent to Bramble, No. 2,771,745, issued Nov. 27, 1956, is exemplary yof a laminated asphaltic lining material. Such lining is necessarily made in thicknesses of one-fourth to one-half inch and this imparts a.severe commercial disadvantage because of the weight and shipping costs involved. This is a heavy material having low tensile strength and will break easily when not carefully handled when being shipped and installed.
Certain types of synthetic resins and especially the polyvinyl chloride polymers are available yas sheets or Webs and because of their impermeability, they are also' used as membranes in some structural applications. Also, some types of polyvinyl chloride polymers, which will be hereinafter referred to as polyvinyl chloride, are very ductile and are capable of being elongated as much as 200 to 300% of their original length. This is contrasted with other types which resist elongation and which are almost brittle. Polyvinyl chloride types of synthetic resins, hereinafter referred to as polyvinyl chloride are as yet quite expensive and thus comparatively thin sheets of the material are used for membrane purposes. This disadvantage is offset in many ways by the toughness, ductility and pliability of certain selected types of the material and it has been proposed to line ice comparatively large areas, such Ias a reservoir basin, with a thin membrane of polyvinyl chloride. The results of attempts to do so were generally unsatisfactory -because of the dilculty in handling the material and the diculty of joining the edges of individual sheets. For example, the slightest Wind action lbillows and tears the sheets as they are placed 4and before they can be protectively covered. Also, although tough, ductile and pliable, the sheets are easilyv cut or punctured by small sharp objects such as crushed rock. Moreover, expensive, toxic solvents or special electronic or other heating equipment is required to join and weld edges of adjacent sheets. Another disadvantage lies in the adverse aging eiects of the material when exposed to -air and especially to sunlight since it will become comparatively hard and brittle.
It has been proposed to combine polyvinyl chloride sheets with other materials and especially asphalt to obtain an improved product having the advantages of both the `asphalt and the synthetic resins. The patent toI Bove, No. 2,893,907, issued July 7, 1959, is exemplary of a laminated material using layers of polyvinyl chloride and asphalt. However, this lproduct and other products available which endeavor to combine the materials have been developed for special purposes and limited applications.
One factor which has inhibited development of improved membranes and liners by combining these materials, other than by using rigid types of polyvinyl chloride sheets, such as disclosed by Bove, lies in the fact that a suitable weld-bonded laminate combination of coherent ductility has proven to be unattainable. This is because the softening point temperatures of the synthetic resins and especially selected types polyvinyl chloride, which have desirable properties of elongation, toughness, and ductility, is as low as, or lower than the temperatures necessary to render asphalts, suitable for the purpose at hand, sufficiently iluid, to be worked. The types of Iasphalts which melt at temperatures below the softening point temperatures of ductile polyvinyl chloride sheets are so soft at ordinary temperatures that they `are not suitable for laminated -asphaltic lining materials. When a soft, low softening-point asphalt is used in such a liner, theliner will not :adequately bond to the synthetic resin sheet, Will sag under stress rand be very difficult to handle in installation, and once installed at an exposed location and on the slightest slope the layers Will slip and the liner Will come apart the first hot day of summer,
A further problem in the development of a membraneliner using a synthetic resin between layers of asphalt lies in the existence of factors which lead to deterioration lof the resin. Many types of synthetic resins are not at all compatible with asphalt and in this regard vinyl chloride appears to be one of the best practical materials. It adheres to asphalt under appropriate temperature conditions with an excellent bond without a tendency for the plasticisers or other constituents in the polyvinyl chloride to migrate to the surface `of the resin and destroy the bond thereto. Nor do the oils or other constituents of the asphalt tend to migrate into the resin to adversely effect either the bond or the properties of the resin.
Overheating of the resin, however, is an important and critical factor. Under the influence of heat, the vinyl chloride will break down releasing chlorine and free carbon. This causes the material to turn black and also to become very brittle. Small amounts of chlorine produced in the first few seconds of heating will actually catalyze the breakdown process causing it to speed up. To counteract this, ordinary commercial polyvinyl chloride will include stabilizers such as tribasic lead stearate, epoxies and cadmium and barium soaps. These stabilizers are chlorine acceptors which hook onto the first wisps of chlorine and therefore impede the catalyst action. Such stabilizers cannot completely inhibit breakdown of the material under sustained influence of heat but they can delay breakdown for remarkable periods of time.
There is a real and denite need for an improved general purpose membrane-liner which is sufficiently rigid to be handled as comparatively large flat sheets such as the liner material disclosed by Bramble, and which has the advantages of asphalt-impregnated felt sheets and asphalt layers integrally supplementing the toughness, ductility and pliability possible only with 'selected ductile types of synthetic resins such as polyvinyl chloride. A liner material is also needed which is not thick and as heavy as the one-fourth inch to one-half inch sheets of the type disclosed by Bramble, now -in common use.
It was with such factors in View, that the present invention was conceived and developed and the invention comprises, in essence, a membrane-liner formed as a wellbonded laminate of compatible asphalt layers and a sheet of a selected ductile type of polyvinyl chloride between sheets of saturated felt. The invention includes further, unique and simplified steps in a process of manufacturing the membrane-liner to integrate the polyvinyl chloride with and between layers of selected asphalt having a working fluid temperature as great or greater than the softening or melting temperature of the synthetic resin by taking advantage of a discovery that a polyvinyl chloride type synthetic resin apparently requires a time lag to lose its strength and to soften when heated to its softening temperature, and also that heating followed by quick cool* ing, or quenching of the laminate does not adversely affect the polyvinyl chloride sheet to a degree where breakdown of the material is serious or critical.
It follows that an object of the invention is to provide Va novel and improved membrane-liner which advantageously presents a sheet of polyvinyl chloride thermally bonded to layers of a selected type of compatible asphalt as a core sandwiched between sheets of asphalt saturated felt to obtain a moderately flexible membrane-liner which is sufficiently rigid to be easily handled in shipping and in installation, to combine the toughness and ductility of the polyvinyl chloride with the compatible properties of its covering layers and with the stiffening and shape retaining effect of the asphalt saturated felt sheets and to effectively armor plate the polyvinyl chloride sheet against weathering effects with enhanced immunity from puncture or tear by sharp objects.
Another object of the invention is to provide a novel and improved membrane-liner which is especially adapted for use in a building or structure as a moisture and vapor barrier, as in a floor or wall section, and which is also well adapted to be used as a liner within an earth body surrounding a structure, as to protect the structure from the effects of moisture, and especially frost action.
Another object of the invent-ion is to provide a novel and improved membrane-liner which may be furnished as sheets which are not unduly thick and heavy, which are easy to handle, easy to join and which are especially suitable for lining reservoirs, ponds and like basins and which will require a minimum of protective covering material after the lining.
A further object of the invention is to provide a novel I and effective method for the manufacture of an improved membrane-liner having a sheet of polyvinyl chloride thermally bonded to and between layers of a selected compatible asphaltic material in a rapid efficient manner and in a manner which accommodates the use of ductile asphalts having comparatively high softening point temperatures, and workable uid temperatures.
. A further object of the invention is to provide a novel and effective method for the manufacture of an improved membrane-liner having a sheet of polyvinyl chloride integrally combined with compatible asphaltic materials at comparatively high bonding temperatures, with immediate cooling action in a manner which advantageously A. tempers and toughens the resulting laminate sheet of polyvinyl chloride and asphalt to a desirable degree without permitting significant deterioration and breakdown of the vinyl chloride resin.
With the foregoing and other objects in view, all of which more fully hereinafter appear, my invention c0mprises certain improved constructions, combinations and arrangements of parts and elements and certain steps, sequences and operations as hereinafter described, defined in the appended claims and illustrated in preferred embodiment in the accompanying drawing, in which:
FIGURE 1 is a perspective view of a rectangular sheet of a membrane-liner constructed in accordance with the principles of the invention, and with portions of a corner being broken away to show the laminated character of the construction.
FIGURE 2 is a fragmentary sectional detail of the membrane-liner as viewed from the indicated line 2 2 at FIG. l but on a greatly enlarged scale to better illustrate the character and co-action of the materials forming the laminated construction.
FIGURE 3 is a fragmentary edge View of the corner portions of two adjacent sheets abutted together and interconnected by a joint strip.
FIGURE 4 is a fragmentary edge view of the corner portions of two adjacent sheets as being joined together with one shee-t overlapping the other.
FIGURE 5 is a diagrammatic perspective view of a roll of the membrane-liner illustrative of an alternate manner of furnishing the material, as at an installation where long unbroken lengths of the membrane-liner are desired.
FIG-URE 6 is a diagrammatic fragmentary sectional view of a portion of a struc-ture wherein the improved membrane-liner is embedded, and illustrating further, in a somewhat exaggerated manner, a shrinkage crack and offsetting movement such as will occur in many types of structures and the manner in which the unique core component of the membrane-liner will stretch and otherwise function to prevent rupture thereof and failure of the membrane-liner as a water or vapor barrier.
FIGURE 7 is a diagrammatic fragmentary sectional View of a portion of the improved membrane-liner as lying upon and covering a bed having sharp pointed rocks therein and illustrating further the manner in which the unique core component of the membrane-liner will yield to further resist puncture, as by an object which will ordinarily puncture a membrane made only of asphalt saturated felt sheets and asphaltic materials.
FIGURE 8 is a diagrammatic layout, along a longitudinal axis, of a preferred arrangement of apparatus carrying the essential webbing materials and bringing these materials together to form a uniquely cored membrane-liner in accordance with the principles of the invention.
FIGURE 9 is a graphic diagram illustrating the relationship of tensile strength and ductility of a selected type of a polyvinyl chloride sheet to temperature.
FIGURE 10 is a graphic diagram illustrating the relationship between viscosity and the temperature of compatible types of asphalts used in the practice of the mvention.
FIGURE 11 is a graphic diagram, associated with FIG. 8 illustrating the relationship of temperature to the movement of material through the apparatus and to the point where it cools to solidification.
.FIGURE 12 is a diagrammatic section detail of certain components of the apparatus as taken from the indicated line 12-12 at FIG. 8 but on an enlarged scale.
Referring more particularly to the drawing, the improved membrane liner 20 is a laminated sheet having sheets of asphalt saturated felt protectively overlying al core comprised of la central sheet 21 of polyvinyl chloride type synthetic resin heat welded to and between layers of compatible asphalt. The preferred construction of the membrane-liner, as illustrated at FIG. 2, is a symmetrical arrangement, including a core surface layer 22 of asphalt of a type hereinafter described thermally bonded to each side of the central sheet 21, a reinforcing sheet 23 of a sa-turated felt added to the outer side of each core layer 22 anda protective layer 24 of asphalt, of a type hereinafter described, 'at the outer side of each reinforcing sheet 23. In addition, other coatings, not shown, may cover the protective outer layers 24, one such cover material commonly used being With such core and layers the membrane-liner may be manufactured to vary in thickness from 1/16- inch to rvVle-inch and the thickness and character of the materials must be such that the sheets are comparatively rigid and easy t-o handle. It has been found that -a sheet 1/s-inch -thick is preferable for many commercial purposes.
For practical handling of the membrane-liner, it has been found best to provide the material as rectangular sheets 20 cut to a desirable module size suc-h as 4 x 8,
4 x 10,14 x 12 or 4 x 20 feet, as in the manner illustrated at FIG. 1. In field installations the individual sheets may be joined by abutting their adjacent edges 25 together and covering the joints with a strip 26 which is bonded to the top surfaces of the sheets as by a mastic 27, as in the manner illustrated at FIG. 3. Another mode of joining the sheets is to lap the adjacent edges 25 to join the lapped surfaces at the edges as by mastic 27', as illustrated at FIG. 4, for the sheets, in contrast with commonly used laminated asphaltic liner sheets, are sufficiently flexible for such type of joining.
Another mode of handling the membrane-liner is to roll substantial lengths 20 of thematerial as upon a reel 28 having a diameter sufficient as to not unduly bend the membrane-liner. This arrangement, using rolls 20' of the material, is especially effective for installa tion of the membrane-liner over comparatively large The liner-membrane 20 may be encased in a structure S as a membrane where there is the possibility of shrinkage cracks, settlement cracks or fracture for the like occurring, as in the manner illustrated at FIG. 6. The separation of the parts of the structures is often sufficient t-o pull .an ordinary membrane apart. As would be anticipated, the felt sheets 23 and the protective outer layers 24 of asphalt will rupture; however, the central sheet core component 21 is stretched and the core surface layers 22 bonded to it are likewise stretched and necked out to conform w-ith the ductility of the central sheet 21. core surface layers 22 will thus protect the central sheet from sharp corners which might otherwise cut the sheet. Before the membrane-liner 20 will be completely ruptured the fracture will ordinarily be widened to such an extent that other ystructural problems will also exist which are even more serious than the breaking down of an effective moisture-holding membrane. When the membraneliner 20 is` laid as a mat upon a flat surface B and may -be exposed without cover, as in a basin, there is always the danger yof the liner being punctured by an o bject being dropped upon it. FIG. 7 illustrates such a situation as where a branch stub of a log L is actually pushed into the liner. This, of course, will tend to push a hole through the protective outer layer and through the felt sheets. However, the ductile central sheet core component 21, protected by the cushioning effect of the felt and the i integrated core layers 22, will be stretched with the latter areas, as in the lining of a basin, since transverse joints are eliminated; however, shipping and handling costs are increased somewhat because of the need for increased space and the possible need of a reel 28 within each roll. A reel having a diameter in excess of eighteen inches is desirable to properly roll a membrane layer 1a-inch thick.
The central core sheet `21 of a selected synthetic resin may be any one of several types of polyvinyl chloride and polyvinyl-chloride-acetate materials now commercially available -as thin ductile, tough sheets, and the physical properties of the several different types are substantially the same insofar as their action in connection with the present invention is concerned. It is to be noted that polyvinyl-chloride sheets are also available as comparatively rigid, hard sheets, but such are not desired for the purpose at hand, as will be hereinafter explained.
The thickness of the central sheet may vary as desired, according to sheet material, and is commonly available in thickness as from 2 mils -to 30 mils. The preferred thickness is 4 to 10 mils, and it would appear that the thicker sheets are unnecessary for most applications.
The ductile types of polyvinyl chloride sheets are expecially suitable for this purpose because good thermal bonding with compatible asphalt is possi-ble, as with the manner hereinafter explained, and the synthetic resin is not adversely affected by the constituents of asphalt. Also, the desired types of tough, ductile sheets will stretch to a lconsiderable extent before they will rupture or tear. This in combination with a suitable asphalt imparts to the membrane-liner 20 a property that does not exist in other types of asphaltic liner sheets, since the proportions of the asphalt forming the core surface layers 22 and the physical properties of such asphalt, hereinafter set forth, cooperate with the polyvinyl chloride sheet 21 to supplement its toughne-ss by incorporating it in a yieldable, plastic medium. This also very effectively protects the sheet 21 from deterioration by sunlight and air.
to a substantial degree before rupturing or tearing. It is to be noted that fragments of the felt will effectively blunt the point of a puncturing object; moreover, the asphalt core surface layers 22 will parallel to a considerable degree the ductility of the sheet 21 and such will further tend to cover and blunt sharp edges of the object, such as a branch stub of a log. The felt and core surface layers will thereby act to prevent an actual cutting action through the core component sheet 21. Also, it is to be noted that the liner will not ordinarily be pierced by `sharp pointed rocks such as r, illustrated at FIG. 7.
It was discovered that, for a membrane-liner suitable for the uses above mentioned, the type of asphalt appropriate for use in the core surface layers 22 was critical. Too soft an asphalt will cause the liner material to sag so badly at ordinary temperatures that it cannot be handled. Moreover, in field use, when a membrane-liner is exposed to the sun, it will easily heat up to temperatures as high as and 165 F. and to a point where the component layers of a lsoft asphalt will slip apart for lack of adequate interbond. At the other extreme, too hard an asphalt core will -be brittle, will crack the protective felt sheets and will not effectively bond to the ductile polyvinyl chloride sheets.
The best asphalts were found to be unfilled, air-blown asphalts, or their equivalents such as might be produced with fillers, having an effective 20G-235 F. softening point as measured by Ring and Ball Test Method A.S.T.M. E28 and a 25-42 penetration at 77 F. as measured -by A.S.T.M. Test Method D-5. The preferred material was found to be an air-blown asphalt having a 210-220D F softening point and a 30-40 penetration at 77 F. Such asphalts are comparatively stiff but not brittle at ordinary temperatures. The softest asphalt that can :be conveniently used has a softening point of not less than F. and a penetration of not more than 40 at l 77 F., although a sheet made with such asphalt is too l'imber for most pur-poses. It was .also found that as an upper limit, asphalts having a softening point greater than 245 F. and a penetration of less than 20` at 77 F. were too hard and brittle and would not effectively bond to the polyvinyl chloride sheets.
It was established that the asphalt surface layers 22 of the core should be comparatively thick to effectively hold and protect the central sheet 21 and should be much thicker than the adhesive layers ordinarily used to hold felt `sheets together. It was found that the thickness of The the combined core surface layers 22 and central sheet 21 could be from one-third to two-thirds, and preferably about one-half, the thickness of the final laminated material to effectively form a body which will functionally protect the central sheet 21. In actual dimensions, a thickness of the core comprised of the layers 22 and a central sheet 21 may vary from 1/0 to 1/lo-inch and in a finished laminated membrane-liner which is 1s-inch thick, a core 1/lG-inch thick is preferred.
With such thickness, the core surface layers 22 of a selected asphalt having a 2l0-220 F. softening point and a penetration of -40 at 77 F. are sufficiently ductile to permit plastic deformation and flow of asphalt under sustained pressure but at the same time provide a sheet sufficiently rigid to be easily handled.
Conventional -asphalt saturated felt sheets or webbin are satisfactory for the reinforcing sheets 23. Commercial asphalt saturated felts are measured according to their weight and will ordinarily be available as light as seven pounds per square or as heavy as thirty pounds per square. The thickness of such felts will Vary from approximately one-sixty-fourth inch to one-sixteenth inch and in a finished membrane-liner 20 having a nominal thickness of one-eighth inch a fifteen pound asphalt saturated felt having a thickness of approximately one-thirtysecond inch is preferred.
The asphalt used to saturate these felts is not critical although it should be somewhat softer than the asphalt forming the core surface layers 22 to provide a better take-up and saturation action. A preferred asphalt is a blown asphalt having a 13S-170 F. softening point and a 30-50 pentration at 77 F. This type of asphalt will effectively saturate the felt and at the same time the softening point is at a temperature high enough to avoid trouble in field installations. While the felt layers impart strength to the final product and adhere to the central core surface layers to rigidify the membrane liner, it is to be recognized that the tensile strength and ductility of ordinary felt is comparatively low and such felts may be otherwise reinforced, if desired, by stronger fibrous materials.
The protective outer layers 24 of the membrane-liner are primarily for resisting weathering action and a third type of asphalt may be used for this purpose. It is desired to have a much harder asphalt and a selected type commonly used for weather protection has a 22S-245 F. softening point and a 14-21 penetration at 77 F. This is not a critical limitation however. The thickness of this protective layer is likewise not critical and the layer may be comparatively thin varying from 1/100 to 1/gg-inch and it is contemplated in the manufacture of the membrane-liner 20 that this protective layer will be applied and thinly spread onto the outer surfaces of the felt sheets 23.
Several problems exist in the manufacture of a membrane-liner 20 constructed according to the invention, with the primary problem being that the temperature necessary to melt the core surface layers 22 to permit them to be sufficiently fluid to be properly applied and bo-nded to the central resin sheet and to the felt sheets is as great as, or greater than, the softening point temperature of a ductile type of polyvinyl chloride suitable for the central core sheet 21. The types of polyvinyl chloride sheets having desirable properties of ductility and softness will have a comparatively low softening point temperature, which may be as low as 205 F. and which will not exceed approximately 300 F. The temperatures required to melt the suitable types of asphalts, having softening point temperatures ranging from 170 F. to 245 F., to a point where they will be sufficiently fluid to be worked, will vary from approximately 320 F. toA 375 F.
It would seem that a polyvinyl chloride sheet having a softening point temperature above the asphalt melting temperature would be preferable. Such materials exist and a membrane-liner was made with a high-softeningoccur between the resin core sheet 21 and the asphaltc Cit surface layers 22 if they were brought together with the asphalt temperature being greater than the softening point temperature of the resin.
A good, flexible, ductile polyvinyl chloride sheet, having a softening point, that is the point where the material loses its tensile strength, of between 275 F. and 300 F. and which is suitable for the purpose at hand, can be furnished by a number of suppliers.
Asphalts which melt below such temperatures, 275 F. to 300 F., to a degree of fluidity which permits them to be easily worked and spread on the polyvinyl chloride sheets are too soft to be used for the core surface layers 22. While the suitable materials to provide a proper core layer could be applied to the central sheet 21 by use of volatile thinners, such a method was not practical.
The preferred asphalt, being a 210220 F. softening point must be heated to approximately 350 F. to be sufciently fiuid to be easily handled. To apply this asphalt to a preferred type polyvinyl chloride sheet having a softening point temperature of approximately 300 F. it can be cooled slightly but not enough to prevent it from softening or melting the sheet. However, it was discovered that there was an apparent time delay in the breakdown and softening action of a polyvinyl chloride sheet in this range of temperatures which would avail if the manufacture of the membrane-liner could proceed at a sufficiently fast rate. For a very short time interval, the polyvinyl chloride sheet would not soften and sever at the point of first contact between the resin and the asphalt. Moreover, subsequent deterioration of the polyvinyl chloride sheet would not be significant if the hot membrane could be promptly cooled off. With such restrictions, the hot asphalt could be applied to the cengr'laslopxlyvinyl chloride sheet at temperatures as high as This phenomena is indicated by the graph at FIG. 9. The curve shows the relationship of tensile strength to temperature for a typical polyvinyl chloride material. It is to be noted that as the temperature increases, the tensile strength of the polyvinyl chloride will decrease only gradually until a critical temperature slightly lower than 300 F. is reached. At that point, there is a sudden drop in tensile strength and the polyvinyl chloride is in a range where the material may be drawn or otherwise Worked and where the material will normally Vshrink as from a plastic memory action. With a slight further increase of temperature, the strength of the material drops to zero, the apparent melting or softening point. The discovery herein taken advantage of lies in the fact that the strength-temperature relationship for the polyvinyl chloride is different for short initial time intervals than it is after a heating effect has set in. For a short time interval, for example, less than one second, the polyvinyl chloride will apparently retain tensile strength, and can be worked even at temperatures above the apparent melting or softening point of the material, as shown by the broken line curve 30. While this phenomena is not fully understood, it is easily demonstrated when manufacturing a membrane-liner according to the invention, for whenever there is any slowdown of the operation, at the necessarily high temperatures, as hereinafter described, the polyvinyl chloride sheet will melt and break where it contacts the asphalt.
The manufacture of the membrane-liner is illustrated in a diagrammatic manner at FIG. 8. The polyvinyl chloride material for the central sheet 21 is furnished as a continuous web in a roll 31. This central sheet moves from the roll under a small tension and along a substantially horizontal path through the `apparatus as illustrated. The felt sheets 23 at the upper side and the under surface of the central sheet 21 are also provided as continuous webs upon supply rolls 33. These sheets, also under tension, are unwound and move in unison with the movement of the central sheet 21. The aphaltic core surface layers 22 are first applied to the under side of the upper felt sheet and the upper side of the lower felt sheet as from upper and lower applicator rollers 32; The protective outer layers 24 of the upper surface and under surface of the sheet are applied subsequently, after the other sheets and layers are bonded together as hereinafter described. The protective layers 24 are conventionally applied as by a roller applicator 34 at the under side of the newly-formed sheet 20 and a flow application 34a at the upper side of the sheet.
In further detail the rolls 31 and 33 are mounted upon suitable shafts 35 aud are braked in any conventional manner to apply a desired tension upon the webs 21 and 23 extending therefrom. The applicator rolls 32 are mounted in suitable reserv-oirs 36 which contain asphalt adapted to be carried upon the roller for transfer to the webs of the layer material 22, the asphalt being supplied to the reservoirs 36 by a conventional means.
The webs converge toward and move between a pair of driving-sizing rolls 37 which function to compress the felt sheets, core layers and central sheets together and to hold the thickness of the moving web to a selected value,
lfor example 1A; -inch.
As the combined webs move through the sizing rolls 37, they pass the applicators 34 and 34a which apply a protective outer layer 24 of asphalt. sheets move between wiping blades 38 which control the thickness of the protective outer layers 24. Next, the membrane-liner, preferably, moves past a mica applicator 39 which spreads a thin layer of mica on the top surface of the membrane-liner while the asphalt is still hot and in a tacky condition.
The next step is to move the membrane-liner through a cooling tank 40 where it may be submerged in cooling water or cooled by sprays 41 as indicated. As the cooled membrane-liner 20 emerges from Vthe cooling tank, it is then moved past edging rolls 42 which establish the proper width of the membrane-liner and remove rough edges formed during the operation. Finally, the finished membrane-liner moves upon a table 43 and past a transverse cutter 44 which cuts the membrane liner into finished lengths as illustrated.
As hereinbefore set forth, the asphalt core cover layers 22 are abnormally thick when compared with the normal applications of asphalt lon-felt sheets and to maintain such thickness, the temperature of the asphalt must be such that it is reasonably viscous. With the preferred ZIO-220 F. softening point asphalt, the temperature at the applicator rolls 32 will be approximately 350 F. to permit a layer 1/,2inch thick to be applied to the felt webbing 23. However, -it is to be recognized that the best operating temperature will vary with different batches of asphalt, but that in continuous operation the operator can quickly establish a proper temperature so that the selected thickness of the core layers 22 will be applied to each felt web 23.
As the central sheet or web 21'moves toward the sizing rolls 37, it passes underneath a spreading bar 45 which helps eliminate wrinkles that may form in the polyvinyl chloride sheet. This bar pushes the central web against the'lower felt sheet 23 and against the hot asphalt core layer 22 on that web. To facilitate guiding and holding the lower felt sheet 23, a support plate 46 may be located underneath it and directly underneath the spreader bar 45.
Next, the laminated v Not only does the spreading action of the bar 45 tend to smooth lout longitudinally disposed wrinkles which naturally occur in the web of polyvinyl chloride, but also the pressing of the polyvinyl chloride against the hot asphalt holds it in place and causes a slight transverse shrinkage of the synthetic resin. This also assists inpermitting the synthetic resin sheet to move between the sizing rolls 37 lin substantially a wrinkle-free condition.
As hereinbefore set forth, while applying the core surface layers 22, the temperature of the asphalt is greater than the temperature at which the polyvinyl cholride sheet will soften or melt. For example, as illustrated at FIG. 10, a curve representative of a core asphalt 22 having a softening point temperature of 210-220" F. shows that a temperature range of 320 F. to 350 F. is necessary for the selected asphal-t material to be reduced in viscosity to a point where it is sufficiently fluid to be worked. At lower temperatures, the asphalt increases in viscosity to the point where adequate bonding and control of thickness of the application are limpossible. The higher softening point asphalts heretofore mentioned, which can be used for core material and which .may be bonded to the polyvinyl chloride sheet 21, as the upper limit, must be heated to even higher temperatures with the upper operable limit being approximately 375 F.
Nevertheless, it was found that'the polyvinyl chloride sheet 21 will retain its strength at high temperatures for short periods of time and it was merely necessary to move the webs through the apparatus at comparatively high rates of speed. The time interval between the rst contact of the synthetic resin with hot asphalt, at the spreader 45, and the movement of the webs past the spreader bar must be in a matter of fractions of a second, and the time interval between the rst contact of the synthetic resin with hot asphalt at the spreader 45 and the movement of the webs through the sizing rolls 37 must be in a matter of a second or two at the most.
In operation of the process, it was demonstrated that there is a critical speed and timing for any given thickness of polyvinyl chloride and any selected temperature of asphalt contacted by the polyvinyl chloride. If the process were slowed down, the central web 21 would melt and sever and would have to be rethreaded into the sizing roll. When this condition occurred, the point where the resin softened was at or `adjacent to the spreader bar 45,
close to the first point of contact between the two materi- Y als, suggesting an extremelyv short time period during which the sheet retained strength at the elevated temperatures. After contacting the hot asphalt, the tension on the polyvinyl chloride sheet was released by its movement in unison with the asphalt coated lower sheet to which 'it had joined. Aside from transverse shrinkage, it was observed that no further distortion or deterioration of the polyvinyl sheet occurred during the short time interval when the polyvinyl chloride sheet lay upon the asphalt coated lower sheet 23 and before it was enclosed by the upper asphalt coated sheet 23 and bonded between these sheets. Although it was in a softened condition, it was held in place by the asphalt. The subsequent placing of the upper layer of felt and hot 'asphalt did not further dis- -turb the polyvinyl sheet, even in its softened condition.
The temperature-material-movement curve 47 at FIG. 1l demonstrates the operation of the process. At the first point, namely, point a a hot core asphalt is applied to the lower felt sheet 23. This asphalt cools slightly in its movement from the point of 'application to the contact point b of the spreader bar. The temperature of the polyvinyl chloride sheet 21 at this Contact point is almost instantaneously brought up to the temperature of the hot asphalt because of its comparative thinness. At the same time, the hot core asphalt 22 is applied to the upper felt sheet as at c and the materials move to their ultimate contact at the sizing rolls, at which time there is a slight increase in temperature as at point d. This effects a bonding and welding together of the components forming the core structure and felt cover and this bonded material moves through and past the sizing rolls to next receive the application of the muc-h hotter protective outer layer 24 of asphalt which is applied at a temperature indicated at point e. The hot protective layer at the outside of the membrane-liner gradually increases the temperature at the center of the liner to a small degree as indicated at g. Thence, as the membrane-liner moves through the cooling tank 40, the temperature at the core is rapidly dropped to normal room temperature as indicated by the curve 47.
This severe treatment of the polyvinyl chloride resin central sheet 21, by embracing it between layers of hot asphalt followed by a sudden cooling, effects changes in the characteristics of the material. As above noted, some transverse shrinkage of the material was observed. However, the physical deterioration, as by chlorine release which might be expected from overheating when the asphalt and the polyvinyl chloride sheets were effectively bonded together did not occur, and it was apperent that 4the comparatively short time during which the polyvinyl chloride was exposed to the elevated temperatures above its softening point was not sufficient to cause deterioration of the polyvinyl chloride sheets used.
Distinctive in concept and unique in advantageous practicality, the weld-bonded laminate core comprised from the polyvinyl chloride resin sheet 21 and the asphaltic surface layers 22 in accordance with the techniques and criteria hereinbefore discussed is significantly novel in respect of properties qualifying it to function with superior merit as the essential feature of a membrane-liner. The selection and use of suitable ductile asphalt material for the surface layers 22 and the application thereof to the resin sheet 21 at briefly-effective temperatures higher than that normally disruptive of the resin sheet material, as herein taught, results in an interbonding of the consequently-softened resin sheet surfaces with the hot fluid of the asphalt layers to establish, when cooled, a welded and integrated composite web characterized throughout by strength and ductility equivalent to the original, such properties evidenced by lthe resin sheet prior to treatment and by a thermal union of its component layers inhibitive of layer separation or relative displacement under any and all non-destructive inuences of intended use.
To study the effect upon short-period elevated temperatures of the polyvinyl chloride sheets, a membrane-liner was manufactured with, and tests were made wit-h a polyvinyl chloride sheet material manufactured by the Union Carbide Plastics Company which carried a proprietory label KDA 2265. It was recommended that this material be used at a maximum temperature of 175 F. and that it could be worked at an elevated temperature of 205 F. for short periods of not more than thirty minutes. However, the application of much higher temperatures did not appear to have adverse effect on the polyvinyl chloride sheet material.
Since, in the manufacture of the membrane-liner, as above described, the temperatures far exceeded the recommended maximums, a group of indicative tests were made at higher temperatures. Strips of the polyvinyl chloride sheet were heated in an oven to temperatures which were as high as 375 F. for various periods of time. The strips \were then cooled to room temperature and changes in the tensile strength and percent elongation noted. While these tests cannot be comparable with folding the polyvinyl chloride sheets between layers of hot asphalt, the indications were that if the polyvinyl chloride sheets were exposed to high temperatures for short periods only, no deterioration would occur.
At a temperature of 315 F. exposures up to three minutes did not appear to damage the material, but actually tempered and improved it slightly by increasing the elongation approximately six percent. Longer exposures at the temperature of 315 F. showed an effect of deterioration for then the tensile strength and elongation were less. When the material was exposed to a temperature of 375 F., an exposure of 25 seconds increased the tensile strength approximately ten percent and the elongation approximately three percent, while longer exposures severely reduced both tensile strength and the elongation.
Aging effects upon the polyvinyl chloride were considered, and a specimen of a membrane-liner were exposed to the weather for more than a year. The polyvinyl chloride in this material did harden, increased its strength and decreased its elasticity but not to a degree which was considered as being serious.
While I have now described my invention in considerable detail, it is obvious that others skilled in the art can devise and build alternate and equivalent constructions which are nevertheless within the spirit and scope of my invention. Hence, I desire that my protection be limited, not by the illustrations and constructions herein described, but only by the proper scope of the appended claims.
1. A process for the manufacture of a laminated membrane-liner web, characterized by having a central sheet of a ductile vinyl chloride polymer having a softening point of 205 F. to 300 F. enveloped between and thermally bonded to asphaltic layers of asphalt having a softening point between 170 F. and 245 F. and which is fluid at a temperature betweenl 300 F. and 375 F. which asphaltic layers combine with the central sheet to form a core and an asphalt saturated reinforcing sheet at each side of the core, including the steps of moving a web of the vinyl chloride polymer between webs of the reinforcing sheets in unison from spread-apart positions along converging paths to interlaminating contact, coating the inner surface of each reinforcing sheet with a layer of liquid asphalt of sufficient thickness to form a portion of the core with the asphalt temperature being, at the time of contact, significantly above the softening point temperature of the vinyl chloride polymer, compressing the converging webs as they ycome together to a predetermined thickness to form the membrane-liner while moving the webs together with a rapidity sufficient to envelope the vinyl chloride polymer before it loses sufficient tensile strength by heat softening to break where it contacts the asphalt, and cooling the membrane-liner before the heat of the asphalt layers initiates significant deterioration of the tensile strength of the vinyl chloride polymer sheet.
2. In the process defined in claim 1, wherein the softening point temperature of the polymer is less than approximately 300 F. and the softening point temperature of the asphalt is between 170 F. and 245 F.
3. In the process defined in claim 1, wherein the asphalt temperature, at the time of contact with the polymer, is at least 20 F. above the softening point temperature of the polymer.
4. In the process set forth in claim 1, the further steps of applying a protective coating of asphalt, having a softening point of at least 225 F., after the combined sheets alrle sized for thickness and promptly cooling the finished s eet.
5. In the method set forth in claim 1, the further step of pressing the vinyl chloride polymer web against the asphalt coated surface of one reinforcing sheet immediately before the web and the reinforcing sheet converges with the opposing reinforcing sheet.
6. In the process set forth in claim 5, wherein the time interval of contacting the synthetic resin web with one asphalt coated surface and converging the same to convergence with the opposing coated surface is less than two seconds and the total time interval from first contact of the synthetic resin web with the hot asphalt and initiation of cooling the same is less than five seconds.
' 7. In the process set forth in claim 1, wherein the asphalt forming the core is heated to a temperature not exceeding approximately 375 F. and the time interval between first contacting the synthetic resin web with the hot asphalt and cooling the finished liner below F. is less than 25 seconds.
8. As an article of manufacture, an asphalt-vinyl chlo ride polymer core sandwiched between asphalt saturated reinforcing sheets at each side of the core wherein the core is one-third to two-thirds of the total thickness of said article of manufacture, said core comprising a central sheet 2 to 30 mils thick of ductile, stretchable vinyl chlov ride polymer having a softening point of 205 F. to 300 F. thermally bonded between layers of asphalt softening between 170 F. and 245 F. and having a uid temperature between 320 F. and 375 F., the central sheet of vinyl chloride polymer having a softening point temperature significantly less than the fluid temperature of the asphalt of the core, each layer of asphalt of the core being 100 to 200 mils thick, said asphalt being sufficiently ductile to permit plastic deformation and How thereof under sustained pressure while at the same time providing a core suiciently rigid to be easily handled.
References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS 6/ 1953 France.
15' EARL M. BERGERT, Primary Examiner.
I. I. BURNS, C. B. COSBY, Assistant Examiners.