US2856697A - Method of loosening and conditioning a stack of sheets - Google Patents

Description

H. F. FRUTH Oct. 21, 1958 METHOD OF LOOSENING AND CONDITIONING A STACK OF SHEETS Filed June 22. 1955 2 Sheets-Sheet 1 Oct. 21, 1958 FRUTH 2,856,697

METHOD OF LOOSENING AND CONDITIONING A STACK OF SHEETS Filed June 22, 1955 2 Sheets-Sheet 2 I Jar/Q1222? A aef Freoi era'ef Fraiyz United States Patent METHOD OF LUGSENING AND CONDITIONING A STACK OF SHEETS Hal Frederick Fruth, Skokie, Ill. Application June 22, 1955, Serial No. 517,250 14 Claims. (Cl. 34-16) The present invention pertains to the conditioning of sheet materials and more particularly to vacuum treatment of stacked or bundled sheets of material.

Many types of sheet materials are stored in stacks or bundles until needed for use. After being so stored, the individual sheets in the stack or bundle tend to adhere to one another making removal of the sheets one at a time from the stack very difficult and time consuming.

It is an object of the present invention to provide a new and improved method of treating bundles or stacks of sheet material so that the individual sheets may be rapidly and effectively loosened from each other and conditioned for subsequent uses.

Another object of the present invention is to provide an improved method of positively loosening the sheets in a stack or bundle of relatively impervious sheet material so that each sheet may be readily lifted from the stack either manually or by a mechanical feeder. It is a more detailed object of the present invention to provide a method and apparatus for loosening the individual sheets in a stack of sheet material quickly and economically by treating a large quantity of such material at one time and at the same time arranging the sheet material in a neatly alined and arranged stack.

Various types of sheet materials and the uses to which they are put require control of the physical properties of the sheets, such as moisture content, temperature, surface cleanliness, and odor. it is, consequently, a further object of the present invention to provide a novel method for conditioning stacked or bundled sheet materials effectively and economically. A related object is to provide a method for equalizing and controlling the moisture content and temperature of sheet material. A more detailed object is to provide a novel method of treating stack of paper for high grade color printing so that the paper will have constant dimensions throughout the printing process making possible accurate register of the successively printed colors.

It is also an object. of the present invention to provide a method of treating sheet material subsequent to use in printing processes to condition the sheets rapidly and economically for further use.

Further objects and advantages of the invention will become apparent as the following description proceeds, taken in connection with the accompanying drawings, in which:

Figure 1 shows diagrammatically apparatus suitable for use in carrying out the present invention.

Fig. 2 is a vertical section, taken along the line 2-2 of Fig. 3 illustrating a treating tank embodying features of the present invention.

Fig. 3 is a plan view of the apparatus of Fig. 2, being a section taken along the line 3-3 of Fig. 2.

Fig. 4 is a detail view in section taken along the line 44 of Fig. 2 showing the construction of the movable guides.

While the invention is susceptible of various modifications, alternatives and variations, I have described in some detail the preferred mode of carrying out my invention, but it is to be understood that I do not thereby intend to limit the invention to the specific process or apparatus disclosed, but intend to cover all modifications and alternative methods falling within the spirit and scope of the invention as expressed in the appended claims.

It has been common practice in the past for the individual sheets of paper in a stack to be loosened from each other by laboriously jarring or bending a small quantity of bundled paper at a time. This has been done either manually or by machine and is variously termed jogging, airing or fiufling, particularly as applied to sheets of paper. The sheets are loosened in these methods by mechanically forcing individual sheets to slide laterally across the face of adjacent sheets a sufiicient number of times to break the bond between them. Bending or jarring does not assure separation throughout the entire stack, nor does it permit the treating of large stacks because of the physical manipulation required. In addition, when applied to freshly printed or coated sheets, as has been done in the past especially with printed sheets of paper, the wet ink or coating is deleteriously smeared and blurred.

With my new and improved method, large stacks of relatively thin and relatively impervious sheet material may be treated with the same facility as small stacks and positive separation of the individual sheets of material is attained throughout the entire bundle of material. Between adjacent sheets of the stacked or bundled sheets there is a small quantity of entrapped air. This entrapped air is present regardless of how long the sheets have been bundled and, within practical limits, regardless of how tightly the bundle has been pressed together. I have found that this entrapped air may be employed in a novel manner to loosen the individual sheets of material by rapidly reducing the air pressure surrounding the stack, which pressure may be equal to or different from atmospheric pressure.

The rapid reduction in external'pressure surrounding the stack of sheets causes the entrapped air to expand rapidly and seek a means of escape from between the sheets. In so doing the air effectively pushes the individual sheets of material apart and loosens any adherence between them. The present method is efiective even when the air or gas between adjacent sheets of material is in the form of bubbles in a layer of oil or similar material coated between the sheets of material, such as is the case in many instances in stacks of metallic sheets. A coating between the sheets of a volatile liquid, which is readily vaporized under reduced pressure, also operates to separate the individual sheets from each other.

The present method is useful withmany types of sheet materials, which are relatively thin and relatively impervious to the passage of air through the sheets. By way of example, it is useful in connection with separating stacked sheets of paper, plastics, metals, and relatively impervious textiles and organic leaf materials. The thickness of the sheets in the stack may vary widely, from the very thin metallic foil, measured in tenths of a thousandth of an inch, to sheets having a thickness in the nature of a quarter of an inch or more. For illustrative purposes, the method as applied to sheets of paper is used in the following description of the preferred embodiment of the invention.

Referring now more particularly to the drawings, Fig. 1 shows apparatus for carrying out my invention in the preferred manner with reference to atmospheric air pressure. A vacuum tank or container 10 is shown defining a treating chamber 11 for use in carrying out the present invention. A stack of untreated paper 12 is placed in the tank through an opening 14 provided for that purpose. A removable cover or lid 15, placed over the opening 14 after the paper stock has been inserted, is sealed to a flange 16 on the tank by a sealing ring or gasket 17 and clamps 18 to isolate the chamber 11 from the atmosphere. It will be apparent that an airtight door on the side of the tank may be provided in place of the top cover 15, and the stack of paper supported on skids or rollers for horizontal movement through the door. Preferably the paper occupies practically the entire volume of the chamber 11. When this is not feasible, I employ lightweight filler blocks, such as shown at 19, which serve to displace a substantial amount of the air in the unoccupied space surrounding the stack of paper 12. The filler blocks may, for example, take the form of hollow, sealed plastic bodies.

Having placed the stack of untreated paper in the tank 10 and sealed the latter, the next step or steps in performing my invention consists of rapidly reducing the air pressure surrounding the stack of paper. The latter is accomplished by employing a high speed vacuum producing device, indicated generally at 20, which communicates with the interior of the tank through a vacuum pipe or conduit 21 having a control valve 22 interposed between the vacuum device and the tank. As a vacuum source, I prefer to use an auxiliary Vacuum tank. or reservoir 23 in communication with the vacuum pipe 21 and a small vacuum pump 24. In operation, the valve 22 is normally closed and the pump 24 runs continuously, pumping the air at a moderate rate of speed from the auxiliary tank 23 to a low pressure, say about one inch of mercury or less. When it is desired to reduce the air pressure surrounding the stack of paper in the treating chamber 11, the valve 22 is opened allowing the air in the tank to flow into the previously evacuated reservoir 23. The air which occupied only the small space surrounding the paper stack 12 in the chamber 11 has now expanded into a much greater volume and consequently is greatly reduced in pressure. My observations indicate that by proportioning the volume of the reservoir 23 to the unoccupied volume surrounding the paper in the treating tank 10 in the ratio of about ten to one, a suitable vacuum apparatus for practicing my invention is provided.

It will be appreciated by one skilled in the art that a vacuum pump may be connected directly to the vacuum pipe 21 without the use of the reservoir 23. A pump suitable for this purpose should be a high speed, large capacity pump capable of reducing the pressure in the tank to less than one-tenth of an atmosphere, that is, three inches of mercury pressure, in one second or less. A pump for direct connection to the vacuum pipe 21, however, is of larger size and hence more costly than the smaller pump used in the preferred arrangement.

While the valve 22 may be of the simple, quick opening type, I prefer to use a valve in which the orifice in the open condition is adjustable by means of a control 22a. Thus the time interval required for reducing the pressure in the treating tank to the desired value may be controlled by regulating the orifice adjustment. In large size chambers, it is desirable to have as large a diameter vacuum pipe 21 and valve 22 as practical. By way of illustration, a vacuum pipe 21 having at least a three inch inside diameter, preferably a larger diameter in the range of 8 to 12 inches, and a valve 22 of corresponding size, should be provided for a treating chamber 11 having an empty volume of about 150 cubic feet. These connections should also be as short and as free of internal obstruction and bends as possible. To provide quick opening and closing of the valve 22, it is preferable to use one of the well known rapid opening hydraulically or pneumatically actuated valves.

As stated above, the initial or beginning pressure in the treating chamber may be any suitable pressure. Very often atmospheric pressure will be found most convenient to use a the initial pressure. However, for sheet material having a large weight per unit of area, and in other applications where a 'large separating force is desired, the initial pressure can be greater than atmospheric pressure. In such case, the stack of material would be sealed in the treating chamber and the latter pressurized, as by means of an ordinary gas compressor (not shown).

I have found that for stacks of sheets of paper, a pressure reduction from the initial pressure by about three or four inches of mercury pressure, around one-eighth of an atmosphere, is etfective to loosen the sheets of paper. A larger reduction in pressure may be used to advantage to increase the degree of separation between the sheets. The final pressure in the chamber is not, however, critical so long as it is sufficient to permit the air entrapped between the sheets to expand and push the sheets apart. Where an initial pressure substantially greater than atmospheric pressure is used, the final pressure after reduction may even be above atmospheric pressure. As noted above, a greater reduction in pressure is desired for heavier weight materials, and in addition, it is useful for taller stacks of material.

The rate of pressure reduction in the case of sheets of paper in the range of about one-eighth of an atmosphere reduction within one to ten seconds operates effectively to loosen the sheets. It will be found that a stack of paper will measurably increase in height when subjected to the vacuum, indicating that the spacing between the individual sheets of paper has been increased due to the differential in gas pressure between the air entrapped between the sheets of paper and the air surrounding the stack during the evacuation of the chamber. If the vacuum is applied too rapidly, the entrapped air causes the stack to explode scattering the paper about the chamber. On the other hand, reducing the pressure too slowly, say over a period of ten seconds or more, considerably reduces the separating action. The relative time to be employed will depend to some extent on the dimensions of the sheets of paper since the separating is influenced by both the area subjected to the expanding air and the resistance of the long lateral escape path of the air moving from the center portion of the sheet to its edge. Thus, a stack of large sheets of paper will ofier increased air escape resistance producing a greater separating force. With relatively small sheets, the evacuation time should approach the lower time limit, that is, one second, while larger sheets require a longer time, say around five seconds to prevent too rapid expansion of the entrapped arr.

The method has been found so effective that even sheets of paper in a stack which is tightly bound with steel bands will be loosened from each other by my method.

The foregoing reduction in pressure and rates of reduction are likewise applicable to materials other than paper. Some slight modification will be required for materials having a greater per unit weight and a surface I less resistant to the passage of air laterally across it.

The heavier materials will, generally speaking, operate more satisfactorily with pressure reductions somewhat in excess of that for paper. Those materials having less surface resistance of lateral passage of air will require a rate of reduction in pressure at the higher portion of the range specified for paper, that is at least one-eighth of an atmosphere within about one second.

An air pipe or conduit 26, having a shutoff valve 28 which is normally closed, leading from the interior of the tank 10 to the atmosphere is provided for the purpose of breaking the vacuum in the latter. Regulating the air valve 28 varies the rate at which the pressure in the tank 10 is returned to normal atmospheric pressure. If the time interval is from two to six seconds the stack will close or approach its original height. However, upon again evacuating the chamber as above described, the stack will re-open increasing in height. This opening and closing of the stack may be repeated as often as desired. However, one cycle of operation, that is, reducing the pressure in the tank and returning it to normal pressure, is suflicient in many cases to provide the desired loosening of the paper, and the paper may be removed from the tank if further conditioning. is not needed.

The vertical movement of the paper upon opening and closing of the stack tends to cause the sheets of paper to scatter and assume a haphazard arrangement in the stack. .To retain the sheets in a neat pile, especially when a very sudden reduction of pressure is applied causing the stack to rise vigorously or explode, and upon settling of the sheets, a set of vertical guide bars or strips 27 are mounted at spaced points about the inner walls of the tank 10. The guide bars 27 may be adjustably mounted to permit them to be positioned close to the sides of stacks of various sizes of sheets to restrain the individual sheets against relative lateral or edgeWise movement, and also to allow withdrawal of the bars to prevent interference upon removing the paper from the chamber.

It has been found that the tendency of the sheets in the stack to shift laterally upon opening and closing the stack may be utilized to straighten a stack of sheets, initially disarranged when put into the treating chamber. For this purpose means are provided for resiliently biasing the guide bars or strips in a direction to press them against the sides of the stack of sheet material. In the embodiment of the invention shown in Figs. 2 and 3 of the drawings, the biasing force applied to the guide bars is provided by means of weights, although it will be understood that resilient spring, hydraulic or pneumatic mechanisms may also be used.

Shown in Figs. 2 and 3 is a treating tank 40 of rectangular outline defining a treating chamber formed by straight side walls 4-1, end walls 42 and top and bottom walls 43, 44, which walls may have suitable openings for communicating the interior of the tank with a vacuum producing device 20 and the atmosphere, as shown in Fig. 1. One of the side walls 41 has a rectangular opening which is closed by a door 46 of corresponding shape suitably mounted as by hinges 47 for swinging between open and closed positions. To limit the inward closing movement of the door, its edges and the mating edges of the side wall 41 are inclined or beveled outwardly. The door 46 is fastened in close-d position by a hasp or fastener 48 and is sealed against leakage of air by a gasket 49 positioned about the edges of the door opening.

A stack of paper 50 is shown in treating position in the tank 46 and is supported on a skid or platform 52 for insertion or removal on a dolly or other load moving device. The guide means for the stack of paper comprises two sets of stationary guides 55, 56 and two sets of movable guides 57, 58. The stationary guides 55, 56 are mounted on the walls of the tank in a vertical, fixed position. Each of the two sets of stationarygurdes is arranged in a spaced series beginning at an interior corner of the tank 4i) and extending outwardly along the res ective side and end walls 41, 42 forming the corner of the tank. The stack of paper 50 is positioned in the interior corner of the tank which has the stationary guides 55, 56 with two sides of the stack pressed against the respective sets of the stationary guides.

The movable guides 57, 53 are mounted on the walls of the tank in vertical, spaced relation for movement toward and from corresponding ones of the stationary uides. To accomplish this, the exemplary embodiment 3f the invention is provided with trolley rails 60, 61 fixed tothe top wall 43 of the tank. Two such trolley rails are provided for each of the sets of movable guides, and extend perpendicularly to the side and end walls 41, 42 having the stationary guides 55, 56. The trolley rails 6t 61 may convenient be of I-shaped cross section to receive trolley wheels 63 running between the upper and lower flanges of the rails. The upper end portions of each set of movable guides 57, 58 are interconnected for movement as a unit by means of upper and lower horizontal frame members 65, 66. The frame members in turn are interconnected by a series of vertical backing members 67. Mounted on the top of the frame members are two pairs of inverted triangularly shaped suspension plates 69. The front and rear upper corners of each triangular plate 69 carry a trolley wheel 63 to permit movement of the movable guides 57, 58 toward and from the sides of the stack of paper 50. By virtue of the upper and lower flanges on the trolley rails cooperating with the front and rear trolley wheels on each triangular plate, the movable guides are maintained in a substantially vertical position and held from swinging.

Resilient force is applied to the movable guides by means of cables '71, 72 attached to the central portion of the upper horizontal frame member 65 of each set of guides 57, 53. Each at the cables 71, 72 extends perpendicularly away from the horizontal frame member 65, across the top of the stack of paper 50, and through suitable pulleys 73, 74 affixed to the walls of the tank. In this manner, the cables '71, 72 are directed such that their free ends hang downwardly, adjacent the wall of the tank, away from and out of interference with the movable guides 57, 58 and stack of paper 50. To the free ends of the cables are connected weights '76 which tend to pull the movable guides into contact with the sides of the stack of paper and toward a corresponding set of the stationary guides. With the resiliently loaded guide bars pressing against the sides of the stack, the sheets are not only restrained from scattering about the chamber, but are guided into a neatly arranged stack upon repeated opening and closing of the stack.

As shown in the drawings, the stationary and movable guides comprise elongated semicylindrical members which may be conveniently formed of half sections of cylindrical tubing. 0 permit the movable guides 57, 58 to accommodate skids or platforms of various heights, the movable guides are made in two sections 79, 80, the lower section nesting within the upper section. In this manner the lower section of the guide may be ad justed up or down to move over the top surface of the skid 52 with only a small clearance and hence contact substantially all of the sheets of paper in the stack. Means for retaining the guides in adjusted position comprise a wing nut 81 and bolt 82 projecting through a longitudinal slot 83 in one section and a hole 84 in the other section of the guides.

In order to provide clearance for insertion of a stack of sheet material into the chamber, the front set of movable guides 58 may, if desired, be hingedly mounted at their upper ends to the triangular suspension plates 69. When so mounted the guides 58 may be swung outwardly and upwardly to a horizontal position out of the path of a stack of material being moved into or out of the chamber. Suitable latches or locks can be used in connection with the hinges to hold the guides 53 in vertical position during the treating operation. In the construction shown in the drawings, the entire movable guide assembly including the guides 58 and trolleys 63 may be pulled forwardly off the ends of the trolley rails 61 and either placed on top of the tank or to one side of the opening to make room for inserting or removing a stack of material.

With the illustrative apparatus shown diagrammatically in Fig. l, the following quick and economical method of opening and closing the stack of sheets may be used. The auxiliary vacuum tank 23 is evacuated and the control valve 22 is quickly opened as previously described. Before opening the vacuum chamber to the atmosphere to close the stack, the control valve 22 is closed. This retains the residual vacuum in the auxiliary tank 23. After the vacuum in the treating chamber 11 is broken by opening atmospheric valve 28, the latter is closed, and the control valve 22 again opened, permitting the air in the vacuum chamber to expand a second time into the auxiliary tank, reducing the pressure surrounding the stack of sheet material. This second reduction in pressure will not be as great as the initial reduction since the residual vacuum in the auxiliary tank 23 after the first treatment is somewhat lower than its original vaccum. The reduction in pressure is sufficient, however, to cause the stack of sheets to open, and the same procedure may be repeated effectively several times. Continuous pumping of the auxiliary vacuum tank 23 with the vacuum pump 24 is helpful to reduce the residual pressure (increase the vacuum) in the auxiliary tank 23 and thereby to increase the effectiveness of the successive vacuum treatments of the stack of sheets.

It might be expected that the above method would be unworkable and that the stack of paper would be more tightly compressed after the air between the sheets of paper has been allowed to escape under vacuum and the surrounding pressure again increased. 1 have found the contrary to be true. As the atmospheric air is introduced into the chamber to break the vacuum, the air flows into the space created by the expansion of the entrapped air between the sheets of paper and forms an air film separating them. In practicing the invention I break the vacuum in the treating tank with steam or air having a high moisture content. Each sheet of paper is thus in intimate over-all contact with the moisture laden gas and quickly attains an increased moisture content. To accomplish this step in my method, a gas humidifier 29 in communication with the chamber 11 through a pipe or conduit 30 and valve 31 is provided. The humidifier 29 may be of any Well known type, but is preferably either a vaporizer supplying air saturated with water vapor or an atomizer producing a water aerosol, that is a colloidal suspension of droplets of water in air.

The use of a water aerosol makes it possible to bring many times as much moisture into contact with the paper as with water vapor. A suitable aerosol may be formed of droplets of water having a size of about ten microns or less. The addition of a detergent or wetting agent to the Water reduces the surface tension of the water, permitting smaller, more effective droplets to be formed. The effective moisture content of the air introduced may also be increased by loading the air with dust or finely divided materials having a high capacity for carrying and giving up water under a reduced pressure. Such materials as finely powdered and pre-moistened diatomaceous earth, silica gel, or a hydrated alum are particularly effective for this purpose. The dust, which may, for example, be introduced into the chamber by a dust aspirator of Well known type mounted within the humidifier 29, is carried into intimate contact with the individual sheets of paper and releases its moisture to the paper.

After opening the valve 31 to the chamber and admitting the moist air or Water aerosol to break the vacuum, the moistening agent is permitted to remain in contact with the paper for a sufficient length of time to increase the moisture content of the paper to a desired value. This value has been found to affect greatly the quality of printing obtainable. Sheets of paper stored in stacks or bundles tend to dry out during storage and to reabsorb moisture from the air as they pass through the printing press. Moreover, the drying of the paper, or the moistening thereof in damp locations, is more rapid on the outside portions of the stacked paper than in the center portions. Consequently, the sheets of paper generally not only have an inadequate moisture content but also have a varying moisture content from point to point on the sheet. The subsequent absorption of moisture causes expansion in the size of individual sheets of paper as Well as curling or buckling caused by uneven expan sion or contraction. This in turn contributes to improper alinement or register of the printed matter and to wrinkling and creasing of the paper. It is therefore desirable to have the humidity of the sheets of paper prior to printing such that the moisture content of the paper is equalized over the entire sheet and is maintained at a relatively constant value during the printing operations. Increasing the moisture of the paper by one or two percent to a total content of about six percent moisture by Weight is suitable for the atmospheric conditions existing in the average printing press room.

The length of time for which the paper is in contact with the moistening agent should be generally in pro portion to the atmospheric conditions in the press room, primarily the relative humidity and the characteristics of the paper itself. I have found that good results are obtained if the moisture conditioning is continued for from three to ten minutes for common types of paper. Although reducing the pressure surrounding the stack of paper, as carried out in the initial steps of my invention, tends to dry the paper due to the increased rate of evaporation of water or other volatile substances in a vacuum, such drying of the paper will be slight because of the short time the pressure is reduced. The moist air or Water aerosol may be used to break the vacuum in the chamber on each cycle if the chamber is evacuated more than once, or may be used only in the last cycle with the atmospheric air being used in the intermediate cycles.

The present method of conditioning sheets of material is also useful in connection with equalizing the temperature of the sheets of material in a stack or bundle. Very often stacks or bundles of sheet material are delivered to the place at which they are to be used or processed at a temperature differing considerably from the temperature of the place of use. Where a stack of paper or similar non-conducting material has been stored in an unheated warehouse in the wintertime, a relatively long time, often a matter of days is required to allow the heat to penetrate the stack. The present method heretofore described is useful to bring the stack of material to room temperature quickly and to equalize the temperature throughout the stack. The stack need only be placed in the vacuum chamber and opened and closed repeatedly as previously described, for a short period of time such as about fifteen minutes, to bring about the desired change and equalization in temperature.

In accordance with one of the aspects of the present invention, the so-called cockled paper may be quickly produced. This type of paper is often used for carbon copies of typewritten material. It is usually of the weight of commercial tissue for typevwiting use, having small, irregular, dome-like buckles or dimples. In carrying out this aspect of the invention, sheets of tissue weight paper are increased in moisture content to as high a value as possible without damaging the paper, in the neighborhood of eight to twelve percent moisture. This increased moisture content may be produced by the method previously described or in any other suitable manner. The sheets of paper are then placed in the vacuum chamber 11. A sudden vacuum is produced in the chamber and dry air, preferably heated, is then introduced into the chamber. This cycle is repeated continuously until the sheets of paper are substantially dry. After drying is completed the vacuum is broken and the paper in cockled form is removed from the vacuum chamber ready for use.

While my invention has been described in detail above for the conditioning of paper, it will be apparent that it is equally applicable to other sheet materials, not only to loosen individual sheets as pointed out hereinbefore, but also to condition them. Manufacturing operations involving the use of such materials often require that the individual layers of sheets of material be loosened from adjacent layers and have an increased, uniformly distributed moisture content. By placing a bundle or stack of such material in the chamber 11 and carrying out the above described steps of my method, economical and rapid conditioning of the material is provided preparatory to subsequent processing. The final moisture content desired depends, of course, on the characteristics of the particular material and its intended use. The described method in another of its applications may also be used to produce perfumed sheet materials by breaking the vacuum with a perfume-laden gas or aerosol.

When the paper or other material has attained the desired moisture content, the lid 15 of the tank is easily removed since introducing the moist air or water aerosol returns the pressure in the tank to atmospheric pressure. The stack or bundle is then removed from the treating chamber 11 and is ready for feeding into a printing press or other operation fully conditioned for accurate and consistent production.

The present method of loosening individual sheets of paper is also very beneficial when applied to freshly printed paper. It is known that certain inks, especially inks used in lithography, set or dry by various chemical processes, such as oxidation, polymerization and condensation, rather than by evaporation of solvents. The reaction rate of these setting processes may be greatly increased by treating stacks of freshly printed paper as described above for loosening sheets of paper. The moisture conditioning steps,-of course, need not be used for this purpose since there will be very little drying of the paper, as previously noted. In addition to breaking the vacuum with air, other oxidizing or catalytic agents in the form of gases, dust or aerosols, well known to one skilled in the art, may be brought into intimate contact with the ink on each sheet of paper in the same manner as described in detail for the moistening materials.

I claim as my invention:

1. A method of conditioning a stack of thin, relatively light weight and relatively impervious sheet material, comprising placing a stack of such material in an airtight chamber, reducing the air pressure in said chamber by at least about one-eighth of an atmosphere of pressure Within from one to ten seconds to cause said sheets of material to separate bodily from each other, returning the air pressure in said chamber to atmospheric pressure, and restraining said sheets of material against lateral movement relative to each other during said separating movement of the sheets of material.

2. A method of conditioning a stack of thin, relatively light weight, and relatively impervious sheet material, comprising the steps of placing a stack of such material in a gastight chamber, rapidly reducing the gas pressure in said chamber by at least about one-eighth of an atmosphere of pressure at a rate equivalent to about oneeighth of an atmosphere of pressure within from one to ten seconds, and introducing a gaseous medium into the vacuated space created thereby to return the gas pressure therein to atmospheric pressure so that the sheets of material are loosened from one another.

3. A method of conditioning a stack of thin, relatively light weight, and relatively impervious sheet material, comprising placing a stack of such sheets in a sealed chamber, producing an initial air pressure in said chamber and reducing the air pressure in said chamber by at least about one-eighth of an atmosphere of pressure within from one to ten seconds to increase the spacing between adjacent sheets of material, restoring the pressure in said chamber so that said sheets are loosened one from another, and restraining said sheets from lateral movement relative to the stack and to each other, and subsequently repeating said vacuum and pressure restoring cycles.

4. The method of conditioning a stack of thin, relatively light weight, and relatively impervious sheet material, comprising the steps of placing a stack of such sheet material in an airtight chamber, reducing the air pressure in said chamber by at least about one-eighth of an atmosphere of pressure within from one to ten seconds, and introducing into the evacuated space created thereby a humidifying gaseous medium, said gaseous me-,

dium being maintained in contact with said stack for a length of time such that said sheets are increased in moisture content.

5. The method defined in claim 4 in which the humidifying gaseous medium includes an aerosol of water.

6. The method defined in claim 4 in which the humidifying gaseous medium includes a dust comprised of material capable of giving off moisture under reduced pressure.

7. A method of conditioning printed sheet material comprising placing a stack of sheets of freshly printed material having Wet ink thereon in an airtight chamber, reducing the air pressure in said chamber by about at least one-eighth of an atmosphere of pressure at a rate equivalent to about one-eighth of an atmosphere of pressure within from one to ten seconds to bodily separate individual ones of said sheets from adjacent sheets, and breaking the vacuum created thereby with a gaseous medium containing an ink drying agent.

8. A method of conditioning a stack of thin, relatively light Weight and relatively impervious sheet material, comprising placing a stack of sheets in an airtight chamber, communicating said chamber to an auxiliary tank having an air pressure substantially lower than the pressure in said chamber and of a volume of about at least ten times the unoccupied space surrounding said stack of paper, allowing the pressures in said chamber and said tank to become equalized, closing the communication between said chamber and said tank, opening said chamber tothe atmosphere to increase the pressure therein, isolating said chamber from the atmosphere, and repeating the foregoing cycle of alternating communicating said chamber to said auxiliary tank and to the atmosphere until the pressure in said auxiliary tank is substantially the same as the original pressure in said chamber, so that said sheets are loosened from each other and equalized in moisture content and temperature.

9. A method of conditioning a stack of sheets of tissue weight paper for use as cockled paper, comprising in combination increasing the moisture content of the sheets to within the range of eight to twelve per cent moisture content, sealing the stack of sheets in an airtight chamber, rapidly reducing the pressure in said chamber by at least one-eighth of an atmosphere of pressure within one to ten seconds, introducing a drying gas into said chamber, and subsequently repeating said reduction of pressure and introduction of drying gas cycle until said sheets are substantially dry so that said sheets are cockled.

10. A method of treating a stack of thin, relatively light weight and relatively impervious sheet material comprising placing a stack of sheets in an airtight chamber, rapidly reducing the pressure in said chamber by at least one-eighth of an atmosphere of pressure within one to ten seconds to cause said stack to expand upwardly, restoring the pressure in said chamber to the original pressure, repeating the above said pressure reducing and storing cycle, and resiliently pressing guide means against the sides of said stack during said cycles so that the sheets in said stack are loosened from each other and are forced into alinement to form a neatly arranged stack of sheets.

11. A method of conditioning a stack of thin, relatively light weight and relatively impervious sheet material, comprising the steps of placing a stack of such material in a gastight chamber, rapidly reducing the gas pressure in said chamber by at least about one-eighth of an atmosphere of pressure at a rate equivalent to about one-eighth of an atmosphere of pressure Within from one to ten seconds, and introducing a heated gas into said chamber to raise the reduced pressure therein, so that the sheets are loosened from each other and the temperature thereof is increased and equalized.

12. In an apparatus for conditioning a stack of sheet material comprising, in combination, a tank defining a conditioning chamber and having an opening for receiving a stack of material to be treated,said tank having an airtight closure for sealing said opening, means for producing a vacuum in said chamber, a series of vertical guides in said tank, said guides being positionable in contact with the sides of a stack of material in said chamber, means for mounting at least certain of said guides for bodily movement in a horizontal direction into and out of contact with the sides of said stack, and means for continuously urging said guides into contact with the sides of said stack for alining individual sheets of material in said stack upon alternately producing and relieving a vacuum in said chamber.

13. in an apparatus for conditioning a stack of sheet material, the combination comprising a tank defining a conditioning chamber and having an opening for receiving a stack of material to be treated, said tank having at least two straight vertical walls defining a corner of said tank, said tank also having an airtight closure for sealing said opening, means for producing a vacuum in said chamher, a set of vertical guides fixed in stationary position at spaced intervals along said two Walls, means supporting one of said movable guides for movement toward one of said walls, means supporting the other of said movable guides for movement toward the other of said walls, each of said means including a horizontal rail adjacent the top of said tank extending toward the respective one of said walls for supporting said guide in depending relation, a Weight and a cable interconnecting said weight and the top of said guide, said cable having a horizontal run and a vertical. run arranged to urge said guide toward the respective wall for pressing said guides into contact with the sides of a stack of sheet material 1.2 placed in the corner defined by said two walls and alining individual sheets of material in said stack upon alternately producing and relieving a vacuum in said chamber.

14. An apparatus for conditioning a stack of thin, relatively light weight and relatively impervious sheet material comprising, in combination, a gastight tank defining a treating chamber and having an opening for loading a stack of sheet material into the tank, rack means disposed within the tank for receiving the stack of sheet material, said rack means having sides which are movably adjustable relative to each other to engage the edges of the sheets and prevent lateral movement of the sheets with respect to one another, a vacuum. producing means having a capacity relative to the volume of said chamber such that the pressure in said chamber may be reduced by at least about one-eighth of an atmosphere of pressure and at a rate at least as fast as about one-eighth of an atmosphere of pressure within one second, means for communicating said vacuum producing means with said chamber and including a variable control valve to vary the rate of pressure reduction in said chamber between the rates of pressure reduction of one-eighth of an atmosphere in one second and one-eighth of an atmosphere in ten seconds, and means for admitting gas to said chamber to break a vacuum in said chamber produced by said vacuum producing device.

References Cited in the file of this patent UNITED STATES PATENTS

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