US2375403A - Process of impregnating webs - Google Patents

Description

y 1945- M. cRocE PROCESS OF IMPREGNATING A WEB Filed Sept. 14, 19.40

INVENTOR Mas 545 CIEQCE BY a ATTORNEY Patented May 8 1 945 I 2,375,403 4 rnocass or IMPREGNATING waas Michele Croce, Buffalo, N; Y,, assignor to Certain- Teed Productsv Corporation, New York, N. Y., a corporation of Maryland Application September 14, 1940, Serial No. 356,788 I I 2 Claims. (Cl. 117-68) This invention relates to. processes of and apparams for impregnating a felted web. The invention especially relates to the impregnation of felted webs withthermoplastic materials, and particularly with asphalt saturants for weather'- proof roofing.

In the practice of impregnating felted webs, such as those which are prepared in a paper malting process, impregnating materials of various kinds are used, especially those which are of such character that, after absorption in liquid form by the felted structure of the web, they fill up and more or less solidify in the pores of the fibrous material and the interstices or voids between the fibres. In the-manufacture of weatherproof roofa high melting point asphalt is less fluid and more ing of such character and of such thickness as effectively to seal the impregnated structure against further access of airand moisture. The material used as coating upon a roofing sheet is usually a so -called high melting point asphalt which melt at. a, higher temperature than that which isused for the saturating of the web. Such cohesive and, therefore, serves as a better seal for the web when applied upon the surface. of

' the impregnated web. Moreover, it resists being drawn into the felted structure more than the ing materials it is common to impregnate with a I bituminous saturan't, such as asphalt, a felted web formed on a paper-making machine from stocks of rags, paper, wood and other fibrous materials. Especially'with thermoplastic impregnating materials, such as asphalt, which for practical impregnationprocesses' require heating to produce the fluidity and reduce the viscosity of the saturant to be absorbed by the felted web,

there arises the condition that the amount of such saturant which is carried by the sheet after it is cooled to normal temperatures is limited -be-" cause the thermoplastic saturant in its expanded condition upon heating fills the felted structure .andv upon subsequent cooling thereof contracts within the felted structure of the web. In the manufacture of roofing by ordinary methods thisv problem is well recognized and it is known that not as much asphalt is contained within the cooled impregnated felted web as would bethe case if the voids or spaces formed by the contraction of the asphalt, particularly as it recedes from a the surface of the sheet toward the center of the felted structure. could be filled up with'asphalt.

"It is an object of the invention to carry out the process of impregnating the felted web, particularly a felt to be impregnated with a thermoplastic saturant such as asphalt, in such a manner that the voids or spaces formed by contraction of the cooled saturant shall be filled up with saturant to the greatest practical eitent.

It,is especially an object of the invention so to carry on the filling up of these voids or spaces that access of air or moisture-to these voids or spaces is prevented until the usual sealing coatingiaappliedtothefacesofthewebthereafter to prevent entrance of air or moisture. a

,In the manufacture of roofing it is low melting point asphalt used as saturant. On the other hand, the low melting point asphalt used for impregnation of the web makes it possible to secure the fluidity of theheated asphalt necessary for easily wetting the fibres and com plete filling of the pores and voids without increasing the temperature of the asphalt -above atmospheric temperature to such a degree as to injure the fibres by overheating and matching.

In the saturant, asphalt of low melting point it is desired to have a sufiicient, fluidity and a viscosity of such low degree that the capillary action of the fibres of the felted web will rapidly takeup the saturant. and that this absorptive action willcontinue even though the temperature of the asphalt saturant reduces during the process of impregnation.

The invention purposes to conditions for impregnating a sheet, particularly a roofing sheet, as'above outlined, while preventing entrance of air and moisture into the im-- practice to apply such a sealingcoating upon both faces of the saturatedweb, said coating bepregnated structure during the cooling of the sheet and its absorbed saturant and to continue this safeguard against entrance of air and moisture until the sheet has reached a condition, particularly a condition of reduced temperature, at

which the coating of high melting point, may

be applied to the impregnated web. Moreover, the invention securesan increased content of saturant so that the web or finished sheet of reater weather-resisting capacity is obtained.

By the practice of the invention the impreg- 'nated web becomes prepared for receiving the sealing coatings in a condition which insures a minimum of subsequent contraction of the impregnating satin-ant and with a minimum but sumcient entering of the higher melting point asphalt into the voids created by the receding 'saturantto insure that the coating is securelybonded to the impminated web. Y

It has heretofore been proposed to apply satursnts. such as, llphllt, to a web with reduction of the temperature the batman... In some mum the requisite cases the proposal has been to pass the web containing a certain amount of saturant through a cooling zone to insure the contraction of the saturant and thereafter to fill up the voids created by this contraction with subsequent applications of saturant at a cooler temperature. It also has been proposed to pass a web impregnated with a saturant and cooled to a certain degree into a bath of higher melting point saturant at a higher temperature. Thereafter the web is passed successively through successive baths of said high melting point asphalt at successively lower temperatures.

The invention proposes to apply a aturant, such as asphalt, to a felted web, preferably in the manner disclosed in the patent to Miller No. 1,6363750. In this patent a continuously moving felted web passes adjacent a series of sprays or jets' spaced apart in the direction of the movement of the web. The jets are arranged with respect to one face of the web so as to direct thereagainst'a jet or spray of the saturant heated to a temperature to secure the necessary fluidity for capillary absorption of the saturant by the felted structure of the web. The temperature of the saturant for such absorption may be between 350 to 500 -F. With the ordinary asphalt saturants commonly used in the manufacture of roofing the'temperature of the saturant preferably is between 425 to 475 .F. In the practice of the process of the Miller patent the saturant is delivered to all of the sprays or jets substantially at .the

same temperature, being pumped thereto from a still or other source of heated saturant by a common pump in excess of the amount which can be absorbed by the-felted structure in'the passage thereof from one Jet to another. As disclosed in said patent, the application of saturant atone face of the web serves to drive out the air and moisture at the other face of the web. The application of saturant at said one face may be continued until the saturant appears at the opposite face of the web so as to color the whole area of said opposite face of the web or such part'thereof as will indicate substantial approach to complete ,filling of the felted structure with the saturant at its temperature so that upon subsequent dipping of the web in the bath of asphalt the saturation of the web will be complete.

In the passage of the web as it is being saturated between Jets or sprays-particularly in-view ofthe feature of the process of the Miller patent by virtue of which the sheet travels through a distance providing asubstantial time for the absorption of the saturant, some cooling of the web and its absorbed saturant takes place. In order to insure the absorption of the asphalt received by the sheet from subsequent sprays scrapers are provided as-disclosed in the patent to remove any skin of congealed asphalt which may have developed during such travel of the web. In the further travel of the web between sprays, and

V subsequent to the last spray before dipping the sheet into a dip tank as disclosed inv the patent,

cooling of the sheet causes contraction of the asphalt and may cause the formation of voids into which air and moisture may, enter and in which they may become entrapped. This air and moisture may be sealed in the felted structure by the saturant applied to the web as the web passes through the dip tank.

It is a feature of the invention that the application of the asphalt saturant to one face of the web, as proposed in the Miller patent, in what may be called the fhot section" of the apparatus,

is carried out with such repeated applications of the hot saturant at points spaced sufiiciently close together that a continuous film or layer of the saturant is' carried upon said face of the web. This continuous film or layer of saturant upon said face} of the web acts as abarrier to prevent the access'of air and moisture at that face during the time necessary for the saturant to impregapplication of the saturant may be made to said opposite face by' sprays or jets in the same manner as to said first face of the web. 'Saidapplication of saturant at both faces is made, according to the invention, before thelsaturant and the web have cooled to such substantial degree as to draw into the felted structure so much of the saturant carried by "the web as to leave portions' without the barrier layer. It is desirable in im pregnating the web at the first face thereof that said impregnation be carried out until a substantial layer of the saturant forms uponthe opposite face of the web.. By maintaining the temperature of the applied asphalt during its application at said first face of the Web the impregnation is insured and. the air and moisture are completely driven from the web. Immediately thereafter the barrier layers of saturant which prevent the access of air or return thereof into the felted structure are applied to and are. maintained upon both faces of the web while-it cools. These barrier layers of saturant preferably are maintained upon the impregnated web until the web has cooled to the greatest possible extent, that is, until further application of saturant no longer can be made because sufilcient fluidity for absorption and for handling thereof cannot be secured. Within the scope of the invention, and utilizing the'ordinary asphalt saturants commonly used in the manufacture of roofing, the temperature of the saturant applied to both faces of the web,in this second partof the process in what may be called the "cold section of the apparatus, may gradually be reduced from that first applied to both faces, which may be of the degree of 350 to 500 F., until the temperature of the saturant so applied to both faces is of the degree of 225 to 275 F. In some cases and with some 'asphalts a lower temperature of the saturant finally applied at both faces may be used. Part of the saturant thus carried as barrier layers upon the faces of the 'be made and any excess thereof may finally be removed just priorto delivery of the fully impregnated and filled up web to the usual coating apparatus 'for applying to the faces of the web the ,high melting point asphalt forming the sealing coating.

This sealing-coating, being. applied to the completely filled up web impregnated with the sat-.

'urant substantially at the lowest practical tern perature of. the web andf'its impregnating saturant, for practical purposes maybe at a temperature somewhat above the temperature of the impregnatedweb as it arrives at the coating apparatus. Any expansion of the saturant contained within the felted structure of the web caused by the hotter sealing coating will be counteracted and the saturant thus expanded will be reabsorbed by the felted structure of the web upon again cooling as the coated web passes from the coating apparatus. Preferably, however, the coating operation is also carried out at as low a temperature as is practical for maintenance of suflicient fluidity in the high melting point asphalt for said application thereof to the impregnated web.

From the above description it will be understood that the invention improves upon the processes of the prior art by providing a barrier layer of the impregnating saturant itself, which may be the same type of material as that contained in the hot impregnated web. layers, however, within the scope of the invention may be of such type compatible with said hot impregnation of low melting point that the barrier layers can be appliedat temperatures still lowerthan those at which the hot .impregnation can be applied and in some cases below the melting point of said hot impregnation. The invention thus provides for control of the temperature of the barrier layers of saturant so that further absorption may take place from these barrier layers as the web cools to secure a web impregnated with a homogeneous impregnating material or a web filled up with compatible saturants to the greatest practical extent. During this period of absorption with concomitant cooling of the web prevention of access of air and moisture to the web structure is accomplished by the barrier layer which makes effective the subsequent applicationof the sealing coating heretofore commonly used and used likewise in the product of the invention.

Within the scope of the invention, also, the temperature of the saturant applied at both faces of the web whether of the same type as the saturant applied in the "hot section or one of lower melting point compatible therewith, may be substantially lower than the temperature of the web fully impregnated with hot saturant" throughout the whole of said application at both faces of the web. Thus, for example, immediately after completely filling the web from one face with saturant at the relatively high temperature of 425 to 475 F., cold saturant" at a temperature of 250 to 275 F. may be applied at both faces. This cooler saturant: continuously applied will serve to cool the web and its impregnating "hot saturant. The heat thus absorbed by the cold saturant applied at both faces of the .web will These barrier- 90 F. and of'such composition as to be compatible with the hot saturant having a melting point of 150 F. is used as the cold saturant applied as barrier layers as above described, the temperature at which this cold saturant may be applied may be of the degree of 125 to-150 F. in order to obtain the requisite fluidity for such application. The temperature at which hot saturant must be applied when used as cold saturant, however, must be of the degree of at least 200 to 225F. in order to obtain th necessary fluidity for delivery of this saturant to both faces of the web to form the barrier layers. Thus a lowering of the temperature of the barrier lay ers is used to the degree of 50 to 100 F. below what would be possible by the use of the usual saturant for the barrier layers, that is, one which is the same as that used for the "hot saturant of the impregnating asphalts thus may be ac complished beforedeliveringthe web, filled up with an increased amount of saturant, to the coating apparatus for applying'the sealing coating of high melting point. The invention-includes within its scope the application of saturants of such low melting point at such low -temperatures, as compared with the melting point of the saturant which impregnates the main portion of the felted structure of the web and its temperature of application, that a substantial increase in the contraction of the saturant so impregnating the main portion of the web is secured with concomitant increase in the total'amount of the saturant which is carried by the web and the substantiall complete avoidance of voids and air pockets which otherwise would become sealed in the impregnated web by the sealing coating of higher melting point.

The difference intemperature between the'hot saturated sheet and the cold saturant secures a marked increase in the amount of saturant which will be carried by the completely impregnated and coated web. This increase may be of the degree of 8 to 13% and in some cases greater. Asthe coeflicient of the contraction of asphalt is about serve to keep it fluid and ofiset to that degree'the chilling which occurs at the outer face of the sealing film or layer of cold saturant. Moreover, further application of saturantjf need be,

may be made to' both faces of the web to main-- tain the temperature of the barrier layers at the degree of 250 to 275 F. to maintain the necessary fluidity for absorption and filling up of the voids and spaces created by the contraction .of the previously absorbed "hot saturant.

By using saturants which are compatible with the hot saturant impregnating the web applied thereto at one face thereof in order to drive out the air and moisture from the opposite face thereof but which have a melting point below and in some cases a. marked degree below that of the hot saturant, further advantages are obtained by the process of the invention. If, for

example, a saturant having a melting point of .0004 per degree F. of temperature, a reduction in the temperature of the asphalt saturant impregnating the web, for example, from 450 to 250 F., that is 200 F., corresponds to 8% increase in the amount of saturant contained in the impregnated web when filled up with saturant drawn from the barrier layers. If the temperature reduction were effected by barrier layers at F., representing. a reduction of 325 below 450 F., the increase in saturant carried by the'web would be 13%.

For the purpose of applyin the barrier films or layers of saturant to both faces of the web any suitable apparatus may be used. Preferably, however, in addition to the hot section such as is shown in the Miller patent a similar set of rolls is provided in the cold section.affording a substantial length of travel of the web, with sprays or jets placed at both sides of each stretch of the It is an important advantage of this arrangement that the cooling of the web and its contained saturant is rapidly effected in the air where the heat may be readily dissipated.

The drawing shows a diagrammatic elevationof the apparatus of the invention.

In the drawing the web of dry felt of the character commonly used in asphalt roofing is delivered to the apparatus over tension rolls 3 from which, in the manner illustrated in the Miller jward again to the next roll 5. In the particular embodiment illustrated, adjacent each stretch of I the web as it leaves a roll and travels toward a roll I a spray or jet pipe 9 is arranged for directing a jet or spray or stream of asphalt against the j web. It will be noted that the spray or jet pipes 9 all are arranged so that the jet or stream will be directed against the same face of the web I as means of the first spray or sprays II may be subit travels upon rolls 5 and I. As many rolls and spray pipes are utilized as will secure the application of the asphalt at said first face of the web in sufiicient amount and at surhciently rejpeated intervals to provide the asphalt which will be absorbed by the web and to drive the air and moisture out at the opposite face of the web I and, as well, to form and maintain the barrier layer of iasphalt upon said face of the web. If desired, on

I :said first face thereof so that the asphalt appears at the opposite face of the web and preferably colors the whole of said opposite face of th web with a substantial or a complete wetting of the opposite face, the web is delivered to the second or cold section of the apparatus where asphalt is applied at both faces of the web .as above described. In Fig. l the rolls 5 and 1 and the jets 9 are assumed to provide sufflcient application of asphalt to produce the wetted condition just deiscribed witl'ra given structure of the felted web and a given character of the saturant utilized. Thereafter the web passes downwardly from the last roll I to and under a roll I3 and upwardly and over roll I5 and thereafter downwardly and :under rolls I3 and upwardly and over rolls I5. In this portion of the apparatus to which the invention particularly relates asphalt is applied at both faces of the web by means of spray pipes H which fapply and maintain the barrier layers of asphalt on said faces. After passing the last roll I3 the ;web I with its barrier layer of asphalt on both faces thereof may be passed between control or doctor rolls I9 or other device for removal of any asphalt in said barrier layers which is in excess 1 of that which is required just to fill the sheet as it reaches the apparatus for the application of the fsealing coating. r A sufficient number of rolls I 3 and] 5 and of jets 3 I1 is used to secure the application of the saturant of low melting point at both faces of the web I at sufllciently close intervals and in suil'icient amount to maintain the barrier layer upon each face of the, web during the coolin'gof the web in its passage from the last roll I to the apparatus for applying the sealin coating of high melting jpoint asphalt. As has been explained-during this cooling saturant from the barrier layers will be drawn into the structure of the web as the saturant previously absorbed at the higher temperature recedes because of its contraction. The barrier layers are maintained upon the web on both ifaces thereof in sufllcient thickness and uniformity over the faces of the web to insure that l ientrance of air and moisture into the web follow- The temperature of the saturant applied by stantially that of the saturant applied by sprays 8. The temperature maybe gradually reduced from that which is applied by the first pair of sprays II to that whichis applied by the last pair of sprays II past which the web I moves. As this gradual reduction, however, may involve the use of numerous pumps to deliver the saturant to the sprays or jets II in the several steps of reduced temperature, it is preferable to apply the saturant to the web I by means of the first sprays or jets H at as low a temperature as is practical and saturant of such'low temperature, that is, "cold saturant, may be applied by all sprays I]. The low melting point saturant at lower temperature than that in the hot section of the apparatus, however, may be applied in two steps or a limited number of steps of temperature to prevent undue immediate congealing of the hot saturant whichhas been absorbed by the web in passage thereof over the rolls 5 and I of said firstsection. In any case it is the aim of the invention to apply the saturant by means of the jets I! so that the barrier layers carried thereby will be at as low a temperature as is practical just prior to delivery of the web to the apparatus for applying the sealing coating. 'Such a temperature will be that which will insure that the saturant is fluid enough to be pumpedand sprayed and absorbed by the voids left by the receding hot saturant but low enough to produce before it sets in any of the usual finishing processes commonly used in the roofing industry. v I

Beneath the sets of rolls 6 and 'I' and I3- and I5 is arranged a pan III which serves to catch and drain towards one end thereof, the righthand end in the embodiment illustrated in Fig. 1, the excess of asphalt which may drip from the web I and the rolls over which it passes. If the saturant which is applied to the-web I by means of the spray I1 is substantially the same as that which is applied by means of the sprays 9, these excesses may be collected in the common collecting pan III as shown and returned to the still for reheating for delivery to jets or sprays l or the collected excesses, especially if cooled, may be supplied directly to the jets II or may be mixed with saturant of lower temperature which is to be applied by the jets II. Removal of the excess caught by the pan I0 may be effected through a pipe I2. If desired, however, separate collect- 1 ing pans maybe provided for the hot" or cold,

sections and the excessesthereby kept separate to be returned to their respective supplies. Saturants of different character but compatible 'with each other thus may be used in the two sections.

The process of the invention may be practiced by other apparatus which will insure the application of the saturating asphalt at one face of the web until the web is completelyfilled with asphalt at the high temperature of the hot'section and which apparatus also will insure the subsequent application at both faces of the web of saturating asphalt of the same or such compatible composition and capillary properties as to be absorbed by the felted structure to complete the impregnation in a manner comparable to and compatible with the asphalt which is used to impregnate the web in the hot section. The web thus becomes completely filled up by the process of the invention with saturant which is of substantially homogeneous character or with saturant of substantially the same effectiveness. The

web may then receive its sealing coating of high.

melting point which will remain, as it is intended, upon the surfaces of the web while suitably gripping the saturated web without being unduly drawn thereinto tofollow the receding saturant as is the case with roofing sheets in the present practice.

It should be noted, however, that the preferred method and apparatus which utilizes a set of rolls l3 and I5 and jets I! for applying the saturant to both faces of the web in jets or sprays makes it possible to pass the web through the air for a long distance while maintaining thereon the barrier and cooling layers. This cooling is more effective than that which can be secured by passing the web through a bath of the saturant at lower temperature because the heat removed from the web may be dissipated more easily in the air.

Moreover, the temperature as well as the amount delivered and thickness of the barrier layers to efiect the filling up of the web may be controlled so that the proper condition of the web as it is' delivered to the coating apparatus 2|, 23, is insured,

For the purpose of full understanding of the invention, note is made that the melting points of low melting point asphalts commonly used as saturants for impregnation of roofing materials are gener' lly in the range between 90 and 150? F. The m ting points of the high melting point asphalts which are commonly used for sealing coatings applied to the impregnated sheet are generally in the range between 200 F. and 235- F. For the purposes of the invention the melting point of the cold saturant however, be as low as about 75 for carrying out that phase of the invention described above which utilizes a saturant of lower melting point than the commonly 'used low melting point asphalts. For the purposes of the invention the melting point of the hot saturant" may be as high as 175' F. Y 1

Having thus described my invention, It now asphalt may, F. particularly web and in an amount to maintain substantially a continuous fluid layer of the saturant upon said face of the web preventing entrance of air and moisture at said face of the web, continuing said application to said face of the web to drive out air and moisture at the opposite face of the web until the impregnating saturant appears at said opposite face of the web, thereafter before substantial contraction of saidimpregnating saturant occurs applying a thermoplastic saturant to both faces of said web so as to maintain a substantially continuous fluid layer of said saturant upon both faces of the web preventing entrance of air and moisture at said faces, and gradually cooling said web during the application of said saturaiit to both faces with concomitant contraction of the impregnating saturant. carried thereby, said structure of said web and in an amount to main- 1. Process of impregnating a felted web with a saturant which comprises applying atone face of the web a thermoplastic saturant heated to a condition of fluidity readily to impregnate said thermoplastic saturant applied to both faces of the web being in a condition of-fiuidity and impregnating capacity similar to that applied at said first face so'as to flow into and iii] up the'voids left by the contraction of the impregnating saturant.

2. Process of impregnating a felted web with a saturant which comprises applying at one face of the web a thermoplastic saturant heated to a condition of fluidity to be absorbed by the felted pregnating capacity so as to form barrier layers of liquid saturant preventing access of air and moisture to said webat said faces, continuing the application of the saturant simultaneously at both said faces of the web to'maintain a'ibarrier layer upon each face of the web, gradually cooling said web during the application of saturant to both faces with concomitant absorption of the saturant therefrom, the amount of saturant in said barrier layers being suflicient to supply that absorbed by the impregnated web' upon such cooling and as well 'to maintain said barrier layersthroughout the coollngof said web to a temperature suitable for application of a sealingcoating.

and applyinglsaid sealing coating to the cooled web permanently to prevent access of air to the impregnated structure of the web.

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