US2939760A - Vapor treatment of a moving web - Google Patents

Description

FIPBZJDQ X5 299599760 June 7, 1960 F. B. BJARNOW ETAL ,93 ,7

VAPOR TREATMENT OF A MOVING was Filed 001- 26, 1955 4 Sheets-Sheet 1 v aha}; I co FIG. l

IN VEN TORS Non G. Hamilfim A TTORNEY June 7, 1960 F. B. BJARNOW ETAL 2,939,760

VAPOR TREATMENT OF A MOVING WEB Filed Oct. 26, 1955 4 Shee1is-Sheet 2 FIG. 2

INVENTORS Fred 5. bjav-now Mario T. clchelli Alan G HQmH' H ab-2m A 779K NE) June 1960 F. B. BJARNOW ETAL 2,939,750

VAPOR TREATMENT OF" A MOVING WEB Filed Oct. 26, 1955 4 Sheets-Sheet 3 Fma. 5

. INVENTORS F ed B. Bjcxr' now ZAW . ATTORNEY June 7,1960 F. B. BJARNOW ETAL. 2,939,760

} VAPOR TREATMENT OF A MOVING was Filed Oct. 26, 1955 4 Sheets-Sheet 4 IN VEN TORS Fred b. Bjarnow Maria T ClchQll Alan G. HanmH-on ATTORNEY,

to bleach the paper.

United States Patent VAPOR TREATMENT OF A MOVING WEB Fred B. Bjarnow, Niagara Falls, N.Y., Mario T. Cichelli, Wilmington, Del., and Alan G. Hamilton, Niagara Falls, N.Y., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Oct. 26, 1955, Ser. No. 542,813

3 Claims. (Cl. 8149.2)

This invention relates to the art of treating a moving web with a gas or vapor and more particularly, to the application of hydrogen peroxide vapor to a moving web of paper to bleach the same.

A new method for bleaching paper disclosed in the pending US. patent applications, Young, S.N. 358,503, filed May 29, 1953, now U. S. Patent 2,777,749, and Hawkinson et al., S.N. 497,432, filed March 28, 1955, now Patent No. 2,859,087, employs as one step the application of hydrogen peroxide vapor to a paper web which previously has been treated with a suitable alkaline solution. The paper web, containing a requisite amount of moisture, absorbs the hydrogen peroxide which then acts While this process can be carried out to bleach preformed paper which is moistened with an alkaline aqueous solution and then treated with hydrogen peroxide vapor, the greatest economic advantages of the process are realized by applying the alkaline solution and the peroxide vapor to the moist paper web passing through a conventional paper-making machine. This eliminates a separate operation for bleaching the pulp furnished to the machine, thus saving considerable time and expense in the over-all paper making process.

To realize this economic advantage, however, the equipment utilized to treat the paper during its passage through the paper machine must be sufficiently small and compact so that it can be located on the machine without any substantial modification of the machine construction. Most types of paper-making machines are large, complicated and exceedingly expensive; and any substantial modification of the machine construction to provide means for applying peroxide vapor would unduly add to the cost of the bleaching process.

Various methods have been utilized heretofore to treat paper webs with chemical vapors, for example chlorine,

wherein the paper, usually festooned, is passed through a chamber filled with the reagent gas. Any such method or device for applying vapor is diflicult if not impossible to apply to a conventional paper machine without extensive and costly modification of the machine construction. Many paper machines operate at paper speeds of 1000 to 1800 feet per minute and such speeds would require relatively large vapor-treating chambers of the conventional type to treat the paper in the short time available, i.e., not more than 0.06 second per linear foot of paper. To avoid chemical loss, the treating vapor must be applied in the drier part of the machine, rather than at the wet en where water is removed from the paper web by suction and pressing. But in most machines, after the paper leaves the last press rolls and begins to be dried, there is very little room available to construct a vapor applicator. There is the additional problem of uniform distribution across the paper web, which is generally from 6 to 12 feet wide. These problems are particularly acute in machines which make paper over 20 feet wide and operate at paper speeds in the neighborhood of 2000 feet per minute.

An object of the present invention is to provide a new 2,939,760 Patented June 7, 1960 and improved apparatus and process for applying a vapor or gas to a moving web. A further object is to apply hydrogen peroxide vapor to a moving web, particularly in a conventional paper-making machine at a point where the drying operation has not been completed. A further object is to provide such apparatus and process which is adapted to be placed in operation on a conventional paper machine substantially without modification of the machine construction except for the provision of supports for the vapor applicator. Still further objects of the invention will be apparent from the ensuing description.

The appended drawings illustrate the apparatus of this invention. Figure 1 is a vertical section of one form of the vapor applicator. Figure 2 is in part an elevation and in part a vertical section through plane IIII of Figure 1. Figure 3 is a diagrammatic representation illustrating the location of the vapor applicator at different positions in a conventional paper-making machine. Figures 4, 5, 6, 7 and 8 are diagrammatic representations in vertical cross-section showing alternative forms of one portion of the vapor applicator.

We have discovered a means of applying hydrogen peroxide vapor to a moist paper web whereby the peroxide is absorbed by the paper in an amount adequate for bleaching in an exceedingly short period of time. This is accomplished by flowing a stream of peroxide vapor concurrently, substantially parallel to, and in contact with, a moving paper web and preferably at a velocity about equal to the web speed. Also, in the preferred mode of operation, the amount of air or other noncondensable gas in the vapor in the zone of vapor application is kept as small as possible. This results in a very rapid rate of absorption, requiring only a very small section of paper to be exposed to the vapor at any given instant, making possible the construction of a small and compact vapor applicator, which can be inserted at almost any desired point in a conventional paper-making machine without material modification of the machine construction. The new applicator may thus be applied to machines in which the paper web is moved at speeds of from 1,000 to 2,000 feet per minute. Means are also provided for obtaining uniform vapor distribution across the paper, regardless of paper width.

A suitable form of the invention is illustrated by Figures 1 and 2 of the appended drawings, which show the vaporizer positioned to apply vapor to one side of a moving paper web 1, illustrated in Figure 1 as moving from left to right as indicated by the arrows. Hereinafter the parts of the vaporizer on the left hand or upstream side of the paper will be referred to as the leading side or edge of the device while the right hand side of the vaporizer will be referred to as the trailing side or edge. A cylindrical vapor manifold 2 located above and transverse to the motion of the paper web is provided with a slot 3 almost its entire length. Depending from the edges of slot 3nare two transverse walls 4 and 5, extending toward the paper, forming channel 8 for vapor passing through slot 3. The leading edge of the channel thus formed by channel wall 4, terminating in foot 23, extends down and into contact with the moving web. Wall 5, forming the trailing edge of the channel, extends to a point spaced a short distance from the paper web and is provided with a trailing extension 6 the lower edge of which is substantially parallel to the paper web. There is thus formed the vapor treating zone or chamber 7 transverse of the paper sheet which chamber is enclosed on three sides by the foot 23 of partition 4, the paper web and extension 6. The ends of channel 8 and vapor chamber 7 are closed by end walls 18. The side edges of moving web 1 suitably over-lap the bottom edges of end walls 18. The vapor manifold 2 is likewise provided with end walls 9.

An extension 10 of element 6 extending toward the leading edge forms a bafile in the channel 8. Likewise, throttle plate 11, extending through wall 4 and mounted in slots cut in end walls 18, forms another baflle in the channel. Two screws 12, journaled in brackets 13 which are connected to throttle plate 11, are threaded into stationary brackets 14 so that the rotation of screws 12 imparts reciprocal motion to throttle plate 11, to regulate flow of vapor through channel 8.

Vapor manifold 2 is provided with a concentrically arranged interior cylinder 15 which is provided with a series of openings 16 arranged in a row diametrically opposite slot 3. Pipe 17 is provided to lead vapors into the interior cylinder 15 from whence the vapors pass through openings 16 and thence around the annular passageway between cylinder 15 and the interior wall of manifold 2, to pass out through slot 3. This arrangement provides uniform distribution of vapor across the width of the paper web.

the vaporizer, including its steam jacket, is covered with suitable heat insulation to the extent indicated by dotted line 22. A suitable method of insulation is to provide a sheet metal jacket filled with mineral wool or other conventional insulating material. In some cases, insulation alone may be satisfactory.

To obtain uniform distribution of vapor across the paper width (along the length of the applicator), there must be a source of back pressure on the vapor fed to the applicator. This is provided by holes 16 in cylinder 15 and by throttle plate 11, the amount of back pressure depending on the size of holes 16 or on the space between the edge of throttle plate 11 and channel wall 5. This arrangement assures uniform distribution at greatly varying rates of flow through the applicator. At moderate to high rates, sufficient back pressure is afiorded by holes 16. At lower rates of flow, the required back pressure is provided by throttle plate 11, which then is moved close to channel wall 5. When the applicator is used with little or no variation of vapor through-put, cylinder 15 may be eliminated and the required back pressure may be provided by throttle plate 11 or by making slot 3 or channel 8 sufliciently narrow with respect to the size of manifold 2. In such case, inlet pipe 17 should be made about as large as the manifold or the manifold extended lengthwise, so as to avoid high lateral vapor velocity in the manifold.

The cylindrical shape of manifold 2 shown in Figure 1 is not essential to the practice of this invention, but any desired shape for this element may be utilized, compatible with the space available for the applicator location. If desired, a plurality of contiguously arranged manifolds may be arranged along the length of the applicator, fed by a common pipe or manifold of suitable size.

Uniformity of vapor distribution over the width of the web also may be improved in some cases by providing a series of vanes or bafiles in the vapor treatment zone or chamber 7 attached, for example, to element 6, arranged parallel to the direction of web motion and. extending close to, or touching, the web.

Throttle plate 11 and the. leading projection of element 6 form two bafiles arranged in staggered relationship in channel 8. These, together with element 6, aid in directing the flow of vapor in chamber 7 parallel to the paper web and aid in the action of the terminal or channel wall 5. Bafile 10 causes a change in direction of flow, preventing the jet of vapor from striking the paper web. Without bafide 10, there is a tendency, par-.

ticularly at higher rates of flow, for the vapor stream to push the paper away from the terminal or foot 23 of wall 4, thus decreasing the skimming action of the latter. Also by the baflle action, vapor passing around the edge of battle 10 is reduced in velocity. With the preferred construction, utilizing the foot 23, curved on its trailing side as shown in Figure 1, together with a curved edge on baffle 10, the vapor is smoothly directed in flow parallel to the web.

Another function of the curved shape of foot 23 is to prevent adherence of paper fibers. When channel wall 4 terminates inside channel 8 at a right angle to the paper, as shown in Figure 4, there is some tendency for loose paper fibers to stick to the trailing edge of wall 4. By curving this trailing edge as illustrated by foot 23 of Figure 1, so as to form a sharp edge this tendency is greatly reduced. This is still further reduced by forming foot 23 of a smooth, plastic material, such as those mentioned below.

The vapor applicator should be constructed of material which, insofar as possible, is chemically inert to hydrogen peroxide and does not induce decomposition of the latter. Such materials are well-known, for example, aluminum or stainless steel. If desired, the foot 23 of wall 4, which comes in contact with the surface of the paper web and serves to skim off surface air therefrom, may be made of a suitable plastic material resistant to the chemicals involved, for example, polytetrafluorethylene, polyethylene, a phenolformaldehyde condensation product, or the like.

The vapor applicator is fastened by means of suitable brackets (not shown) to the frame of a paper-making machine in such manner that the end of partition 4 (foot 23) is in contact with the paper web, as illustrated by Figure 1. Figure 3 is a diagrammatic representation of certain parts of a conventional paper-making machine, showing the location of the vapor applicator at different positions 24, 25, 26 and 27.

Referring to Figure 3, the paper web 1, supported by wet felt 28, passes through the press rolls 29, the last of a series of press rolls which squeeze out water from the wet paper web. Leaving the press rolls, the paper passes over idler rolls 30 and thence into contact with the first drier roll 31. Leaving drier roll 31, the paper is passed in contact with drier roll 32 and succeeding drier rolls in conventional arrangement, not shown. Drier felt 33, passing over idler roll 34, embraces drier roll 31 and serves to hold the paper in contact therewith. Another drier felt 35, passing over idler roll 36, holds the paper in contact with drier roll 32. As shown by locations 24 and 25, the vapor applicator may be adapted to apply the vapor to either side of the paper or to both sides by utilizing two applicators in staggered relationship. Location 26 illustrates how the applicator may be mounted in the relatively small space between drier rolls at practically any desired point in the entire drier roll train.

If desired, the applicator can also be located ahead of the press rolls, for example, at location 27. Such location, however, is less desirable since some of the peroxide thus applied would be squeezed out of the paper as aqueous solution by the action of the press rolls, whereas peroxide absorbed by the paper after leaving the press rolls will substantially all remain thereon to complete the bleaching action.

If desired, the applicator may be shorter than the paper width, so that a portion only of the moving web is treated with vapor. In this way, it is possible to bleach only a portion of the output of a single paper machine, the sheet produced being cut at the boundary between the bleached and unbleached product.

Figures 4, 5, 6, 7 and 8 diagrammatically illustrate some alternate forms of the vapor treating zone or chamber 7, formed by the leading edge 4 of the vapor channel 8 and the trailing edge 6 on two sides and by the moving paper web 1 on the third side. The alternate forms represented by Figures 7 and 8 are the least eflicient, as

they cause induction of air under trailing edge 6 into the vapor stream issuing from channel 8, thus diluting the vapor with non-condensable gas and thereby decreasing the efiiciency of the vapor application to the paper. Also the designs of Figures 7 and 8 permit the possibility of some hydrogen perioxide vapor passing directly from channel 8 into the opening between the paper and trailing edge 6 whereas in the forms illustrated by Figures 4, 5, and 6 there is a definite parallel tflow of all of the vapor along the surface of the paper. In all cases illustrated by Figures 4-8, however, the leading edge 4 makes contact with the paper thereby skimming ofi surface air, thus preventing the drag-in of air into the chamber 7 by the motion of the paper. The design of Figure 6 insures that the velocity of the vapor in cham her or zone 7 will be substantially constant from one side to the other. It is evident that in the construction of Figures 4 and 5 the velocity will tend to decrease from the leading side of chamber 7 to the trailing side as vapor is absorbed by the paper. In Figure 6, the cross-sectional area of chamber 7 constantly decreases in the direction of flow to compensate for vapor absorption, thereby maintaining a relatively constant velocity of vapor throughout the chamber, which velocity preferably is equal to the paper speed. In constructing an applicator according to Figures 4, 5, and 6, the best results are obtained by rounding corners and stream-lining insofar as possible, as indicated by Figure 1, so as to achieve vapor flow parallel to, and in contact with the paper with a minimum of turbulence. In utilizing the principle of design illustrated by Figure 6, the trailing edge 6 may be made to contact the paper web. In such case for best results the flow of vapor should be controlled and properly correlated with paper speed and rate of absorption of vapor by the paper, to maintain the pressure in chamber 7 reasonably close to ambient air pressure.

In operating the applicator, the rate of flow of hydrogen peroxide vapor into pipe 17 together with the adjustment of throttle plate 11 determines the rate of flow or velocity of the peroxide vapor passing out of channel 8 and hence in chamber 7. The optimum results generally are secured when the average velocity of the vapor in chamber 7 is equal to the speed of the moving paper web.

While theoretically, substantially pure hydrogen peroxide vapor containing little or no water vapor might be utilized, for practical reasons the vapor fed into the applicator will be a mixture of hydrogen peroxide and water vapors containing less than 50% by weight of H and preferably in the range of 3 to 15% H 0 We have found that when such mixed vapors are brought in contact with a paper web containing or more of moisture, the hydrogen peroxide is preferentially absorbed by the paper. The amount of water vapor absorbed by the paper will depend upon the water content of the paper and the paper temperature. Depending upon such factors and on the amount of mixed vapor fed into the application chamber 7 it is possible to so operate that some water vapor but little or no hydrogen peroxide vapor emerges from the open end of chamber 7, or to so operate that substantially all of both the water vapor and hydrogen peroxide vapor are absorbed by the paper as it passes along. At a given paper speed the amount of hydrogen peroxide absorbed by the paper may be varied and controlled as desired (a) by the concentration of peroxide in the vapor fed into applicator (b) by the size (particularly the width, i.e., the dimension in the direction of web movement) of vapor chamber 7 where the vapor contacts the paper and (c) the rate of flow of the vapors into chamber 7. Having a given installation and operating so that the vapor velocity in chamber 7 is substantially equal to the paper web speed, the amount of peroxide absorbed on the paper may be controlled quite accurately, for example, by varying the concentration of hydrogen peroxide in the vapor.

As an example, utilizing an applicator constructed according to Figure 1 located on a Fourdrinier machine at location 25 (Figure 3) and maintaining a paper speed of 175 feet per minute, the paper absorbed 1% of the dry fiber weight of hydrogen peroxide. In this operation, substantially no steam or water vapor issued from application chamber 7, indicating substantially complete absorption of both water and hydrogen peroxide vapors.

For optimum results, it is important that air or other noncondensable gases, i.e., gases which will not be readily absorbed by the moist paper web, should be absent in the vapor applied to the paper. This is accomplished first by providing hydrogen peroxide vapors which are substantially free of air or other noncondensable gases (which can be formed, for example, by evaporating an aqueous hydrogen peroxide solution) and secondly by insuring that the rapid motion of the paper-web entering the zone of contact with the vapor does not carry in air which is on the surface of the web. To keep the vapor in the application chamber 7 free of air, close contact is maintained between the moving paper web and the lead ing edge 4 (or foot 23 thereof) of the vaporizer channel, so as to skim surface air from the surface of the web that is to be treated. It was found that unless this precaution is taken to skim the air from the surface of the paper, it is impossible to obtain the high rate of absorption of hydrogen peroxide by the paper, whereby a relatively large amount of peroxide may be absorbed on paper moving at high speed, as in a paper-making machine. It is, of course, doubtful that the skimming effect of the leading edge of the vapor channel removes absolutely all the air from the paper since some air may be included in the interior of the paper but the air adhering to the surface of the paper is removed. By thus skimming the air from the surface of the paper, supplying peroxide vapor free from noncondensable gas containing about 10% by weight of H 0 passing the vapor in contact with the paper at a velocity of about the paper speed and having the moisture content of the paper at 50 to by weight (a paper consistency of 20 to 50% it is possible to apply to the paper an amount of hydrogen peroxide equal to 1% of the dry weight of the paper, using a single applicator in which the width of chamber 7 is not more than about 12 inches for paper speeds of up to 1200 ft./min. Using two applicators to apply vapor to both sides of the paper at such paper speeds, the applicator chamber width need not be more than about 3 inches. Paper machines have been designed to operate at speeds as high as 2500 ft./min. and these being larger, afford room for applying applicators of the present invention having application chambers of 20 to 30 inches in width, which is ample to absorb any desired amount of hydrogen peroxide for bleaching purposes.

In the foregoing, the width of the application chamber of vapor treatment zone 7 refers to the, dimension in the direction of movement of the paper web, as illustrated by the cross-sectional view of chamber 7 in Figure 1.

The absorption of peroxide by the paper, and hence the efficiency of the applicator, varies with the moisture content of the paper, higher moisture content (lower consistencies) favoring absorption. In most instances, where it is desired to apply relatively large amounts of peroxide to the paper, we prefer a paper consistency of around 20 to 50%. However, appreciable quantities of peroxide are absorbed when our applicator is used at higher paper consistencies, up to or even higher.

While the invention has been described with reference to the application of hydrogen peroxide vapor to paper, the principles disclosed may also be applied to the treatment of moving webs of other materials, e.g., textile fab rics, and to the application of vapors or gases other than hydrogen peroxide vapor. Obviously, the invention may be used either to treat unbleached fiber, or to further whiten fiber that has been partially bleached by other methods. The gist of the invention is to bring the moving web into a zone of treatment where a gas or vapor absorbable by the web flows concurrently therewith, preferably at a mean velocity in said zone not more than about 20% faster or slower than the web speed (80 to 120% of the web speed). The best results are obtained when the vapor velocity approximates the web speed and means are employed to exclude noncondensable gas (i.e., gas which is not readily absorbed by the web) from the treatment zone. If the vapor velocity is much faster than that of the web speed, there is an undue loss of unab sorbed vapor, unless the length of the zone of treatment is sufiiciently extended and also there is a tendency to draw noncondensable gas (e.g., air) into the treatment zone. If the vapor velocity is much less than the web speed, there is a tendency for back mixing of air with the treating vapor by entrance through the opening at the trailing edge.

We claim:

1. The process for applying hydrogen peroxide to a moist fibrous web which comprises continuously moving the moist fibrous web past a peroxide application zone so that the moving web constitutes one of the confining sides of said zone, and continuously flowing with a minimum of turbulence a stream of hydrogen peroxide vapor substantially free from non-condensible gas into contact in said zone with said moving web and substantially parallel thereto while removing air from the surface of the web entering said zone, and while confining said vapor in said zone on all sides except the downstream side of said zone, the flow of said vapor in said zone being in the same direction as the direction of travel of said moving 8 web and at a vapor velocity approximating the web speed. 1,

2. The process of claim 1 wherein said web is paper having a consistency of about 20 to and said peroxide-containing vapor is a mixture of hydrogen peroxide and water vapors containing about 1 to 20% by weight of hydrogen peroxide.

3. The process of claim 2 wherein the paper consistency is about 20 to 50% and the peroxide-containing vapor contains about 3 to 15% by weight of hydrogen peroxide.

References Cited in the file of this patent UNITED STATES PATENTS 92,210 Richardson July 6, 1869 545,674 Burns Sept. 3, 1895 602,799 Burns Apr. 19, 1898 1,095,796 Brandwood May 5, 1914 1,403,126 Lyth Jan. 10, 1922 1,759,341 Baum May 20, 1930 2,037,119 Comey Apr. 14, 1936 2,225,505 OfiEen Dec. 17, 1940 2,496,797 Kenyon et al. Feb. 7, 1950 2,627,667 Gillis Feb. 10, 1953 FOREIGN PATENTS 427,028 Great Britain Apr. 15, 1935 609,728 Great Britain Oct. 6, 1948 OTHER REFERENCES Textile Manufacturer, October 1949, top left drawing, p. 465.

Claims (1)

1. THE PROCESS FOR APPLYING HYDROGEN PEROXIDE TO A MOIST FIBROUS WEB WHICH COMPRISES CONTINUOUSLY MOVING THE MOIST FIBROUS WEB PAST A PEROIXDE APPLICATION ZONE SO THAT THE MOVING WEB CONSTITUTES ONE OF THE CONFINING SIDES OF SAID ZONE, AND CONTINUOUSLY FLOWING WITH A MINIMUM OF TURBULENCE A STREAM OF HYDROGEN PEROXIDE VAPOR SUBSTANTIALLY FREE FROM NON-CONDENSIBLE GAS INTO CONTACT IN SAID ZONE WITH SAID MOVING WEB AND SUBSTANTIALLY

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