US 3906064 A
Process and apparatus for dry forming paper from gas-dispersed fibers. The gas-fiber mixture is circulated in a loop which incorporates a converging-diverging section and a converging choke section and a portion of the fibers is withdrawn for web formation at a point between the converging-diverging section and the choke section. The fibers in the loop are circulated in the loop at a rate which is at least twice the rate that fibers are introduced and withdrawn from the loop. The paper web is formed on the underside of a papermaking wire. Fine particulate materials may be added and the moisture content of the air and fibers may be controlled.
Description (OCR text may contain errors)
United States Patent lannazzi et al.
1 51 Sept. 16, 1975 3,550,868 12/1970 Stcphanoff........ 264/5 3,630,456 12/1971 Mark 264/121 3,675,858 7/1972 Stcphanoif 264/5 3,692,618 9/1972 Dorschncr et a1. 161/72 3,709,670 1/1973 Eriksen 264/176 F 3,734,803 5/1973 Lipscomb et a1. 425/83 3,738,894 6/1973 Lipscomb et a1. 425/83 FOREIGN PATENTS OR APPLICATIONS 268,613 3/1970 U.S.S.R 425/83 Primary Examiner-Jay H. W00 Attorney, Agent, or Firm-Bessie A. Lepper 57 ABSTRACT Process and apparatus for dry forming paper from gasdispersed fibers, The gas-fiber mixture is circulated in a loop which incorporates a converging-diverging sec-  References Cited tion and a converging choke section and a portion of UNITED STATES PATENTS the fibers is withdrawn for web formation at a point 2,057,166 10/1936 Schur 264/121 between h convergmg'fhvergmg 5 and h 223799 4/1941 stcphanoffm 241/5 choke sect1on. The fibers in the loop are circulated in 2335080 7/1943 stcphanoff 2415 the loop at a rate which is at least tw1ce the rate that 3 333 849 14 1945 D v 425 3 fibers are introduced and withdrawn from the loop. 2,590,219 3/1952 Stcphanoff... 241/5 The paper web is formed on the underside of a paper- 2,715,755 8/1955 Jones 1. 19/1563 making wire. Fine particulate materials may be added 1073.534 1/1963 Hampshire 425/80 and the moisture Content f the air and fibers may be 3.165.570 1/1965 Dcutsch 264/121 controlled 3,224,852 12/1965 Stalcgo 65/16 3.482.287 12/1969 264/121 Claims, 7 Drawing Figures 52 f 17 I2 56 57v [0/ PATENTEU E I 6 W5 3, 9 O8, 06
sum 2 OF 2 3| Fig. 3
Fig. 5 Fig 7 PROCESS FOR DRY FORMING PAPER This invention relates to papermaking and more particularly to a process and apparatus for papermaking which eliminate the formation and use of a water slurry. Because the papermaking fibers are not deposited from a water slurry, e.g., a furnish, the process and apparatus of this invention may be referred to as dry forming," a term used to indicate that the fibers are dispersed in a carrier gas. The gas-dispersed fibers may contain water or other liquid during dispersion and paper formation so long as they are capable of being borne by the dispersing gas to the point of web formation.
The standard commercial process for papermaking has long been a conventional wet forming one in which the papermaking fibers are dispersed in water, worked by various mechanical techniques to develop the desired fiber surface characteristics in contact with water, and then deposited on a moving wire from an extremely dilute slurry. The water-to-fiber ratio by weight in the slurry during the web forming conventionally ranges from about 200 to l to about 1,000 to l. The great quantity of water required to manufacture paper by this conventional technique results in a very high capital investment per ton of product, a high potential for water pollution, and severe restrictions in usable plant locations.
it has long been recognized that the major disadvantages of the conventional process could be eliminated by dispersing and forming the fiber in air rather than in water. Dry forming processes, such as those described in US Pat. Nos. 2,700,188 and 2,744,294, are commonly used for dry forming of textile type fibers into nonwoven fabrics. However, dry forming techniques suitable for nonwoven fabrics have not proven to be useful for dry forming of paper. The methods for controlling the uniformity of the web in nonwoven fabric production are not suitable for dry forming paper fibers because the uniformity requirements for paper are more stringent and because paper generally has a much lower basis weight than nonwoven fabrics. Thus processes and apparatus developed for the dry forming of nonwoven fabrics are not applicable to papermaking It would therefore be desirable to have available a process for dry forming paper which makes it possible to eliminate the necessity for supplying and handling large quantities of water and also eliminates the pollution problems attendant thereto.
It is therefore a primary object of this invention to provide an improved process for dry forming paper by conveying papermaking fibers dispersed in air and depositing them as a web. It is another object to provide a process of the character described which makes it possible to smooth out wide fluctuations in fiber concentration in the dispersion feed and to deliver the fibers to the web-forming wire at a desired uniform concentration across the web with minimum variation in fiber concentration with time. lt is still another object of this invention to provide a dry formed paper which has product uniformity comparable to wet laid paper. Yet another object is to provide a dry forming paper process which is capable of handling fibers having wide variations in length and surface characteristics and which are formed of such diverse materials as cellulose, glass, leather, asbestos, synthetic resins and watersoluble materials such as polyvinyl alcohol. An additional object is to provide a process of dry forming paper which makes possible the incorporation of nonfibrous fillers, binders and the like into the finished paper.
Another principal object of this invention is to provide improved apparatus for the .dry forming of paper using a wide range of fibers to form paper having uniform fiber distribution. Other objects of the invention will in part be obvious and will in part be apparent hereinafter.
The sequential steps in any dry forming process are (l) dispersing the fibers into the gas, normally air; (2) cleaning out and removing any undispersed fiber bundles and unwanted nonfibrous material from the dispersion; (3) conveying the gas-dispersed fibers uniformly to the web-forming section without developing concentration gradients and re-entanglement of fibers; and (4) forming the web on a screen.
The process of this invention is concernedwith steps (3) and (4) and the apparatus with the means for performing these last two steps. in the process of this invention the opened fibers dispersed in a gas (hereinafter referred to as air for convenience) are fed into an intake port of a recirculating loop which is at negative pressure. The fiber-air mixture is circulated around the recirculating loop at a rate greater than that at which the fibers are introduced into and withdrawn from the system. In drawing off a portion of the fiber-air mixture from the recirculating loop to form a web, the fibers are taken through a converging-diverging takeoff section which is connected to the loop immediately downstream of a converging-diverging section of the loop and immediately upstream of a converging choke section of the loop. The recirculating loop apparently serves as a surge capacity in the 'system to efficiently smooth out variations in the fiber feed rate.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangements of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.
For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which FIG. 1 is a side elevational view of the apparatus of this invention showing the components of the loop and the takeoff and web formation means;
FIG. 2 is a perspective view of the convergingdiverging loop section upstream of the take-off section;
FIG. 3 is a side view of the throat joining the elements making up the converging-diverging section;
FIG. 4 is a perspective view of the takeoff and web formation means;
FIG. 5 is a side view of the lower end of the takeoff and web formation means;
FIG. 6 is a perspective view of the choke section of the loop downstream of the take-off and web formation means; and
FIG. 7 is a side view of the downstream end of the choke section.
The use of a recirculating loop in dry forming has been disclosed (see for example U.S. Pat. Nos. 2,715,755 and 3,482,287) but its use has not resulted in the formation of paper webs of good formation from fibers having a wide variation in fiber lengths and fiber characteristics. Through the use of a unique form of recirculating loop and fiber takeoff and web forming means, the apparatus of this invention makes possible the dry forming of paper webs having uniform formation, irrespective of fiber length (within a fairly wide range) and of fiber material and characteristics.
FIG. 1 is a side elevational view of the apparatus of this invention. It comprises a recirculating loop generally indicated by the numeral 10, a gas-dispersed fiber intake 11, and a fiber takeoff and web formation means 12. The loop may be considered to comprise several sections beginning with a gas-dispersed fiber intake section 13 into which the fibers are introduced through a fiber feed port 14 which is at negative pressure. A number of suitable methods are known for forming fiber dispersions in a gas, e.g., air (see for example U.S. Pat. Nos. 3,252,186 and 3,268,954) and the formation of such dispersions are not part of this invention.
A blower 15, driven through suitable shafts and gears by motor 16, is incorporated into the loop. Motor 16 is preferably of the variable speed type and the blower should have the capacity to circulate the gas-dispersed fibers in the loop (as indicated by the arrows) at a rate which is at least twice the rate at which fibers are introduced into and withdrawn from the loop.
It has been found preferable to orient the loop so that it lies in a vertical plane as shown in FIG. 1 and locate the takeoff and web forming means on the inside of the loop. It appears that any heavy dirt particles in the feed tend to stay on the outside of the loop and the withdrawing of fibers from the inside of the loop effects a final separation of the well-dispersed fibers from any fiber bundles and heavy dirt.
The loop wall is preferably circular in cross section and if the outlet of blower is rectangular, then an adapter section 17 is required, this adapter section changing from rectangular to circular cross section. That portion of the loop which is defined by a housing wall of circular cross section of constant diameter may be formed in any suitable manner. In the embodiment of FIG. 1 it comprises vertical section 18, an elbow 19, an upper horizontal section 20 formed of one or more lengths, an elbow 21, a vertical section 22 formed of one or more lengths, an elbow 23 and a short lower horizontal section 24.
The desired control over the fibers to achieve uniform dispersion and distribution of the fibers on the papermaking screen is attained through the use of a converging-diverging section 25 upstream from takeoff and web forming means 12 and a choke section 29 downstream from the takeoff and web forming means.
The converging-diverging section is illustrated in perspective in FIG. 2 and in partial side elevational view in FIG. 3. The converging element 26 extends between a loop-joining flange 27 and a throat-defining flange 28 which has a rectangular (preferably square) cross section. The converging element 26 must therefore change from a circular to a rectangular cross section to serve as an adapter between the lower horizontal leg of the loop and the remaining part of the loop. The diverging element 30 of the converging-diverging loop section has a rectangular cross section (preferably square) and extends between the throat-defining flange 28 and a loop-joining flange 31 which connects the convergingdiverging section 25 to a fiber takeoff loop section 32 (FIG. 1).
As shown in FIG. 3 the angles of convergence, (1, is essentially equal to the angle of divergence, [3, and these angles are small acute angles, preferably ranging between about 5 and about 10. In a preferable embodiment the diameter D (FIG. 2) of the inlet 36 of the converging section 26 is about twice the width (or height) of the throat 37; and the width (or height) of the outlet 38 of the diverging section 30 is also about twice that of the corresponding dimensions of throat 37. The convergent-divergent section greatly improves the uniformity of the fiber dispersion as the fibers are withdrawn from the loop for web formation.
A portion of the dispersed fibers entering the loop takeoff section 32 are withdrawn through the takeoff and web forming means 12 to form the paper. This element of the apparatus is shown in detail in FIGS. 4 and 5. It will be seen to comprise a converging element 42, a diverging element 43, a web forming section 44 and a gas conduit 45 which is connected to a vacuum pump 46 (FIG. 1).
The converging-diverging portion of the takeoff and web forming means 12 eliminates swirling and eddying and minimizes edge and corner effects in the web forming element. The converging element 42 can be relatively short and may have an angle of convergence ()5 (FIG. 5) ranging between about 10 and 18.
The diverging element 43 may have either a square or rectangular cross section. For example, it has been found that when diverging element 43 has a square cross section with an angle of divergence 0 ranging between about 3 and 8, a uniform web is produced. Using the same diverging element, it was also possible to form a uniform web which was rectangular in shape, the length of which was four times its width. The longer dimension of the web could be oriented either parallel with or perpendicular to the direction of fiber flow in the loop. It is generally preferable to have the cross section of throat 50 smaller than the cross section of fiber feed port 14. Moreover, the cross section of throat 52 must be smaller than the area of the web formed. However, the actual configuration (square or rectangular) of the throat need not, as shown above, conform to the configuration of the web.
Web forming wire 51 is mounted in a square wireholding frame 52 which forms a seal around all of the upper edge of diverging section 43 except for narrow clearance 53 defined between the bottom side of screen 51 and a shallow cutout in the wall of diverging section 43. The paper web 56 (FIG. 1) is thus formed on the underside of the wire 51 and may be continuously withdrawn through the narrow clearance 53 and taken upon take up roll 57. By vertically orienting the fiber takeoff and web forming means, gravity effects are eliminated and contamination with heavy impurities (dirt and fiber bundles) is minimized.
Care must be exercised to distribute the vacuum uniformly across the downstream side of web forming wire 51. Therefore, it is preferable to place a suitable gas flow straightening means in the web forming element 44. In FIG. 4 a layer of honeycomb material 54 located above the forming wire is used for this purpose. The web forming element 44 terminates at a flange 55 which serves to join it with fluid conduit 45 which conveniently has a circular cross section.
ln H6. 5 it will be seen that a short horizontal section 60 joins the choke 29 with the take off section 32 through flanges 61 and 62. This choke, which is a rela tively short converging section, contributes materially to the providing of constant conditions in the fiber takeoff area defined within loop takeoff section 32. in the absence of choke 29, variations in downstream conditions and turbulence from blower cause unwanted variations in the flow pattern at the fiber takeoff. With the choke, conditions at the fiber takeoff point are not affected by fluctuations downstream of the choke.
The choke terminates at its downstream end in flange 65 which joins it to the loop inlet section 13. The dimensions (width and height) of the choke inlet 66 are preferably at least twice the corresponding dimensions of the choke outlet 67 and the angle of convergence 0: (FIG. 7) preferably ranges between about 10 and about 18.
in the practice of the process of this invention the gas-dispersed fibers are introduced into and withdrawn from the loop at essentially the same rate. It is necessary however to circulate the fibers (along with any particulate additives) around the loop at a rate which is greater than the rate at which the fiber/gas mixture is introduced into the loop and withdrawn from the loop. The loop circulation rate may be from about 2 to 10 times the fiber introduction and withdrawal rate, with a range from about 2 to 6 being preferred. The control of these rates will be effected by adjustments in pressures maintained at the discharge of blower l5 and at the discharge of web forming section 44 (FIG. 1). Flow rates around the loop may range between about 500 and 2,000 feet per minute; while intake and withdrawal rates may range between about 250 and 1,500 feet per minute.
It is, of course, desirable to maintain as low an air/fiber ratio consistent with uniform web formation. Such ratios may be as low as about 130 cubic feet of air/one pound of fiber. They may, of course, be greater and the optimum ratio for any type of fiber (length, density, material) along with any particulate additive or additives may be readily determined for any given system.
The dispersing gas may contain inert or reactive vapors, e.g., water vapor and the fibers themselves do not have to be dry. As noted in the definition ofdry forming the fibers may contain water or other liquid as long as they are capable of being borne by the dispersing gas through the system. As an example, air with 50 percent relative humidity has been used to form webs of a number of different kinds of fibers.
Fine particulate materials normally added in the wet forming of papers may be added in the process of this invention. These additives may be introduced into the air-fiber mixture prior to introduction into the loop, or they may be added directly to the loop upstream from the converging-diverging section. These particulate additives in accordance with known papermaking art include, but are not limited to, pigments, binders, inkcontrol agents, etc. illustrative of such additives are titania, clay, starch, thermoplastic and thermosetting resins and the like. The amounts of such additives used will be essentially the same which can be used in wet forming paper and the determination of such amounts are well within the skill of those knowledgeable in the art of papermaking.
Papers may be made of fibers ranging in length from 0.1 inch to greater than one inch in length, e.g., about 1.5 inches. in handling the longer fibers, e.g., A to 1V2 inches, it is necessary to use a blower of a type which will not pill or curl the fibers. In general, the optimum fiber length for dry forming paper with good formation is between about A; and about /2 inch. Crimped fibers behave in accordance with their crimped length rather than their total length.
Although hydrophilic fibers are more easily handled than hydrophobic fibers, either type may be used. Fibers with realtively high static charges may be handled by maintaining a high relative humidity to percent) in the dispersing air,'by the addition of a small amount of an antistatic additive to the air or by a combination of both of these techniques. In some cases, it may be desirable to charge the web forming wire with a charge which is opposite in polarity to that borne by the fibers being used. Fiber density has a minor effect on some operating conditions. For example, when using the higher density fibers such as nylon, glass and leather it may be necessary or desirable to increase the air to fiber ratio to establish efficient fiber circulation in the loop and to obtain good paper formation. Fiber blends (mixtures) of different kinds and lengths of fibers are readily processed. In some cases where fibers of different lengths are mixed, it may be preferable to first deposit the shorter fibers and then the longer fibers as the supply of shorter fibers is gradually decreased.
Hand sheets 5 inches X 5 inches were formed on apparatus constructed as shown in FIG. 1. An air/fiber ratio of cubic feed/pound was used, the airdispersed fibers were circulated in the loop at a rate of about 800 feet/minute air velocity, and fiber introduction and takeoff was at a rate of about 350 feet/minute air velocity. A relative humidity of 50 percent or greater was maintained in the air and the hand sheets were formed to have a basis weight of 50 pounds per ream (3000 square feet). Hand sheets having uniform formation were formed of the following fibers:
Fiber Material Length Denier rayon 1 Va in. rayon polyester polyester nylon nylon polyarylic glass (with starch) sulfite wood pulp ln addition, handsheets of uniform formation were formed of the blends of nylon and sulfite wood pulp fibers (75/25, 50/50 and 25/75) and of equal weights of nylon, polyvinyl alcohol and sulfite wood pulp.
These examples illustrate that by the process and apparatus of this invention it is possible to dry form paper from a wide variety of fiber types and mixtures thereof. The process and apparatus of this invention can be used for manufacture of commodity-type paper products, such as newsprint, corrugating medium, tissue, and others. The process and apparatus are particularly suitable for manufacturing products which are now difficult or costly to manufacture by the conventional wet forming process. As shown by the examples, noncellulosic fibers and mixtures of cellulosic and noncellulosic fibers can readily be formed into webs by this process. Inasmuch the noncellulosic fibers are difficult to form with a wet process, the dry forming process of this invention is particularly useful for products made from nylon, glass, leather, asbestos, polyacrylics, polyesters, polyvinyl alcohol, and other noncellulosic products, as well as mixtures of these fibers with cellulosic fibers. Moreover, the process of this invention can readily produce webs which are lofty" (i.e., low density), with a high proportion of fibers oriented in the direction perpendicular to the plane of the web. This combination of properties makes this process especially useful for filter papers, gasket stock, vibration insulation papers, and battery separators. The ability also to admix large quantities of nonfibrous filler or binder to the fibrous materials also makes this process useful for these products, as well as highly-loaded stocks such as shoe counter, interlinings, waterproof papers, and gummed stocks. Finally, the process of this invention, as shown in the examples, can form high-quality webs from water-soluble fibers, such as polyvinyl alcohol. These fibers are, of course, extremely difficult and costly to handle by the wet slurry method. The resulting watersoluble products are suitable for such uses as security paper, water-activated adhesive webs and the like.
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above process and in the constructions set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
1. A process for dry forming paper from gasdispersed fibers, comprising the steps of a. introducing gas-dispersed paper forming fibers, ranging in length from about 0.1 to about 1.5 inches, into a circulating loop having a convergingdiverging section and a converging choke section, there being at least 130 cubic feet of said gas to one pound of said fibers;
b. circulating said gas-dispersed fibers in said loop, the gas flow rate within said loop ranging between about 500 and about 2000 feet per minute;
c. withdrawing downstream from said convergingdiverging section and upstream from said choke section a portion of the circulating fibers; and
d. directing the fibers withdrawn from said loop against a papermaking wire to deposit them thereon to form paper; the rate at which said gasdispersed fibers are circulated in said loop being at least twice the rate at which they are introduced into and withdrawn from said loop.
2. A process in accordance with claim 1 wherein said loop is in a vertically oriented plane.
3. A process in accordance with claim 1 wherein said gas is air.
4. A process in accordance with claim 1 including the step of adding finely divided particulate material to said gas-dispersed fibers.
5. A process in accordance with claim 1 including the step of adjusting the relative humidity of said gas to a desired level.
6. A process in accordance with claim 1 wherein the gas flow rate within said loop is from 2 to 10 greater than the rate at which said gas-dispersed fibers are introduced into and withdrawn from said loop.
7. A process in accordance with claim 1 wherein said portion of said circulating fibers in step (c) are withdrawn through converging-diverging zones upstream of said papermaking wire.
8. A process in accordance with claim 1 including the step of directing the flow of gas immediately downstream from said papermaking wire straight upwardly thereby to ensure uniform distribution of said fibers on said wire.
9. A process in accordance with claim 1 wherein said withdrawing of said portion of said fibers is done from the inside of said loop.
10. A process in accordance with claim 1 including the step of electrically charging said papermaking wire with a charge of opposite polarity to charges borne by said fibers.
11. A process in accordance with claim 1 wherein said fibers are blends of fibers formed of different materials.
12. A process in accordance with claim 1 wherein said fibers are blends of fibers of shorter and longer lengths.
13. A process in accordance with claim 12 wherein at least a portion of said shorter length fibers are deposited on said papermaking wire before any appreciable quantity of said longer length fibers are deposited.
14. A process in accordance with claim 1 wherein said fibers are blends of fibers formed of different materials and fibers of different lengths.
15. A process in accordance with claim 1 wherein at least a fraction of said fibers are formed of a watersoluble material.