US3461032A - Apparatus for applying dry powdered additives to paper on the forming wire using electrostatic attraction - Google Patents

Description

Aug. 12.- 1969 J. A. LICHTENBERGER E AL 3,461,032 APPARATUS FOR APPLYING DRY POWDERED ADD'ITIVES TO PAPER v ON THE FORMING Filed July 21. 1967 WIRE USING ELECTROSTATIC ATTRACTION 2 Sheets-Sheet IIIIW 6 r WWW W mmm m U M m mm. m

M Wm v n n m-mmmm IIIIIIN United States Patent O M 3,461,032 APPARATUS FOR APPLYING DRY POWDERED ADDITIVES TO PAPER ON THE FORMING WIRE USING ELECTROSTATIC ATTRACTION Joseph A. Lichtenberger and Theodorus G. Brandts,

GrandMere, Quebec, Canada, assignors to Consolidated Paper (Bahamas) Limited, Nassau, Bahamas Continuation-impart of application Ser. No. 509,588, Nov. 24, 1965. This application July 21, 1967, Ser. No. 655,035

Int. Cl. D21h 3/28; D21d 3/00 US. Cl. 162-266 4 Claims ABSTRACT OF THE DISCLOSURE An additive material, such as a filler, size, binder or coloring agent, is applied in dry, finely powdered form to a wet paper web during its formation on a paper machine wire at a point where there is sutficient water present in the web for the material to distribute itself throughout the web but where only a minor portion of the material drains off with the water, or at a point where most of the water has drained away and effective retention of the material in the web takes place. Application of the powdered materials is facilitated by use of electrostatic attraction.

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of application Scr. No. 509,588, filed Nov. 24, 1965.

BACKGROUND OF THEINVENTION Field of the invention This invention relates to the application of fillers, sizes, binders and coloring materials to paper.

Description of the prior art The incorporation of materials of this type in paper is a well known and widely practiced procedure in the manufacture of various kinds of paper. Thfse materials have been added to and thoroughly mixed with the fibrous pulp stock at various locations during its progress to the paper machine wire, such as in the heater, at the jordan, in the heater or machine chest, in the regulating box, at the fan pump, or in the headbox. Of course, when the excess water drains away from the stock while the paper web is being formed on the wire, it carries with it a substantial portion of the added material, and this problem of additive retention in the web is well recognized.

SUMMARY OF THE INVENTION The invention resides in a method and apparatus for applying dry, finely powdered materials to a wet paper web at a location where desired and satisfactory retention and distribution of the material occurs. Because of the finely powdered nature of the material, electrostatic means are employed to direct more positively the material onto the web.

While the invention is directed generally to the application of fillers, sizes, binders and coloringagents to the paper .web, one of the specific aspects of the invention relates to the provision of a lint-bonding additive in a paper web.

The presence of loose or loosely-bound fibers or lint on the surface of printing papers, such as newsprint and the groundwood grades of papers, has long been a source of trouble to printers. For instance, in the offset printing process, lint shed by the papers employed frequently accumulates on the offset printing blanket to such an extent that time-consuming cleaning operations are often necessary.

It has heretofore been proposed to apply various additives in the form of aqueous slurries to the wet paper web as it is being formed on the Fourdrinier wire or subsequently in the wet press or drying sections of a paper machine. While a lint-bonding additive may be added in this manner, there are certain attendant disadvantages. For instance, time and equipment are involved in making up the slurry. Suspension aids are required. The extra water added to the wet web may interfere with eflicient drainage, pressing and drying of the web.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is an end elevation, partly in section, of an apparatus in accordance with the invention,

FIGURE 2 is a side elevation of the apparatus shown in FIGURE 1,

FIGURE 3 is an elevation, partly in section, of a modified form of apparatus, and

FIGURE 4 is a side elevation of the apparatus shown in FIGURE 3.

Referring to the drawing, the apparatus shown is electrically insulated and mounted on a suitable frame for suspension over a travelling wet paper web indicated at 10. The web may be supported on a conventional wire 11.

A hopper 12 is adapted to be continuously fed with a supply of the powdered material to be applied to the web.

The hopper 12 has an elongated outlet 13 below which is positioned a metering roll 14 rotatably mounted in frame members 15 and driven in any suitable manner. The cylindrical surface of the roll 14 is scored or grooved for reception of a quantity of powder from the outlet 13. Amount of powder to be delivered is determined by the rotational speed of the metering roll.

The hopper outlet 13 is defined by inclined bottom walls 16 and 17 which direct the powdered material through the outlet. A flexible strip 18 fixed to each wall 16 and 17 rides upon the surface of roll 14 to direct the flow of material onto such surface.

Vibration may be imparted to wall 17 in order to ensure smooth flow of the powdered material through the outlet. To this end, wall 17 is hinged to the hopper at-19 and a roller carried thereby is engaged at fixed intervals by lugs 20 mounted on the roll 14.

A brush roll 21 is also rotatably mounted in frame members 15. The brush surface of roll 21 engages a lower travelling portion of roll 14 in order to brush off the powder thereon and fling or direct it downwardly onto the top surface of web 10.

Roll 21 is driven in a direction opposite to that of roll 14 and is driven at considerably greater speed.

It will be apparent that the axes of rolls 14 and 21 are parallel to each other and to the surface of the web. Moreover, it will be understood that the axial extent of rolls 14 and 21, as well as the transverse extent of outlet 13, are approximately the same, and that the ends of these rolls and the outlet are disposed approximately in the planes of the longitudinal edges of the web.

It will be apparent that the application of powder of the fineness set forth will normally result in rising clouds of particles suspended in the surrounding air. To overcome this disadvantage, it is desirable to provide electrostatic means to cause attraction of the suspended "Aura particles by the wet web. Such an electrostatic means may be combined with an air curtain or the like.

One embodiment of means for controlling the movement of the air-suspended particles is illustrated in the drawing and comprises a manifold 22 supplied with air under pressure by means of pipe 23 and having an elongated outlet 24 positioned closely adjacent the upturning side of brush roll 21 to provide a downwardly directed air curtain.

Electrostatic means comprises a plurality of pairs of electrode holders 25 carried by a common holder 26 and having a power supply connection 27. Each pair of electrode holders has a wire electrode 28 extending transversely above the web 10. The wire electrodes are arranged in a selected pattern in order to achieve satisfactory results. The wet web constitutes the ground connection of the circuit.

The modification of FIGURES 3 and 4 is quite similar to that of FIGURES 1 and 2 except that, instead of the air curtain means, a protective baffle 30 is provided closely adjacent the upper portions of rolls 14 and 21 to prevent air from being sucked into the nip between these rolls. Furthermore, a self-cleaning deflector roll 31 is provided in engagement with brush roll 21. Baffie 30 and 'roll 31 assist in controlling air currents which may be set up by the brush roll and which may cause drifting of dust.

ADDITIVES FOR-SURFACE TREATMENTS As previously indicated, the material to be applied to the web is in dry, finely divided form. If it is to be used for reducing linting tendency, it is preferably selected from the group consisting of starches, modified starches, proteins, modified proteins and synthetic resins. Examples of such materials are raw, cooked and otherwise modified starches, casein derivatives, isolated soy bean derivatives and polyvinyl alcohol.

Raw and modified starches are preferred for technical as well as economic reasons. Raw starches have a. suitable particulate size range. Various starches with their granule size ranges are listed below Micron range Potato -100 Sago 15-70 Arrowroot 15-50 Tapioca 15-35 Amioca 10-25 Corn 10-25 Wheat 2-45 Rice -3" 3-8 The short contact time of the starch particles with the web on the paper machine makes it necessary that they develop their adhesive properties very rapidly. On slow paper machines, wheat and rice starches perform satisfactorily, while on faster machines potato and tapioca starch, which are subject to rapid hydration, are particcularly satisfactory for the purpose of reducing linting tendency.

Of the modified starches, the pre-gelatinized products perform outstanding well. Pre-gelatinized starch products, ground to the proper particle size, swell instantly when brought into contact with the wet sheet and develop their adhesive properties under paper machine conditions in a matter of seconds.

Deposition of relatively small amounts of discrete particles of a powdered binder material on the wet web surface results in spot-gluing of loose or loosely-bound fibers or lint to the main body of the web without, however, affecting the inherent printing quality of the resulting paper. The binder particles absorb moisture from the web to take on glue-like properties sufficient to bind the lint to the web. For maximum effect, short of coating the web, it is important not only to deposit the material uniformly but to use very fine particles. Particle sizes of 100 microns or less are, therefore, preferred.

As previously indicated, some starches and starch products are preferred materials because of their low cost, granule shape, and particle size properties, but especially because of their rapid hydration and/or gelatinization which is advantageous because of the short time available for the treatment on the paper machine and thus development of required adhesive properties is assured.

As has been mentioned, application of a powder in dry, rather than slurry, form to the wet web has several advantages. Slurry making equipment and suspension aids are not required. The efiiciency of the drying sections of the paper machine are not adversely affected by the use of extra water. When the powder is added before the wet presses and after the couch roll, pressing efficiency is unaffected. Moreover, dry powder may be delivered at higher rates to the web than would be possible if it were in slurry form. The retention of powder on the topside of the web is greater than with use of a slurry and de position is more uniform.

The powdered material is applied to the wet web during the formation thereof. Generally speaking, in a conventional paper making machine, the powder is applied between the first row of suction boxes on the Fourdrinier wire and the beginning of the dryer section. Examples of satisfactory locations are (1) between the first and second presses, (2) between the wet line and the couch roll, and (3) between the dandy roll and the last row of suction boxes. If a powder capable of rapid hydration is used, it may be added between the last press and the driers.

From the description it is evident that the powder is deposited on the web by means of the centrifugal action of the rotating brush, the deflecting means, and the electrostatic forces. Since gravitational forces do not play a critical role, the top side as well as the bottom side may be treated in this manner. It will also be understood that the powder may be applied to one or both sides of a vertical run of the web.

The following examples are illustrative of the invention:

EXAMPLE I proximately 5% inches from the wet paper web. The

closest rounded part of the machine was 7 inches away from the dispensing apparatus. The patterned or grooved metering roll was rotated at about 15 r.p.m. and the brush roll at about 500 rpm. Raw wheat starch was used as a lint binder material.

Average results of 20 to 30 tests for two separate starch applications are given in Table I. The lint resis fargce factor was determined in accordance with the following procedure.

On a Vandercock proof press two samples are printed simultaneously by rolling them side by side over a steel printing block covered with a 0.6 mil thick layer of ink. The printing conditions, such as printing pressure, speed, temperature and humidity, as well as the ink characterstics (viscosity, tack and the like) are carefully standardized.

Lint removed from the paper by the tacky ink layer will show up on the printed samples as small unprinted spots on a solid background. The surface areas of these white spots on a given sample are determined and sum-' mated visually or by electronic means. The ratio of the sums of the white surface areas of the two samples is called the lint resistance factor.

EXAMPLE II same as those in Example I. The analytical results are shown in Table I for three starch concentrations:

A 30 inch wide experimental dispensing apparatus constructed in accordance with the present description, was installed just ahead of the wet line of the paper machine. Operating conditions were similar to those described in Example I. Raw potato starch was applied at a rate of 200 grams per 3000 square feet of paper. The treated top side of this paper was compared with the untreated top side of the web run at the same time on the paper machine. A lint resistance factor of 0.3 was obtained.

In subsequent printing trials on a commercial scale, four-colour web offset printing press, approximately four rolls of treated offset paper could be printed against one roll of untreated offset before a definite reduction in print quality became noticeable.

While the above examples refer primarily to the bonding effect of starch, it is to be noted that the starch also has a sizing effect (i.e. it tends to make the paper more or less water resistant). Thus, it is obvious that many other surface effects can be achieved by the proper choice of additive and its application at the proper point along the paper machine wire. Pigments, for example, may be added to improve the opacity, colour and printability of the paper; Examples of such materials will be given hereinafter in the case where the object is to achieve certain effects by dispersing the additives throughout the web rather than primarily on its surface.

Additives for loading, sizing, coloring and the like If the material added to the paper web is for filling or loading purposes, it may be selected from a wide range of conventional materials including, clay, talc, agalite, silica, gypsum, chalk, precipitated calcium carbonate, calcium sulphite, titanium dioxide, and zinc sulphide. The amount of filler added to the web will depend on its retention in the web, and the use requirements of the finished paper. The retention will depend on the point along the paper wire that the materials are added, the basic weight of the web, and whether or not other materials are also used, such as sizes and binders.

If sizes are to be used, they too can be selected from a range of conventional materials together with precipitating agents which increase the efliciency of the sizing action. The amount of size or the like added depends on a large number of factors, such as the type of fibers in the web, temperature of the stock, hardness of the water, degree of acidity or alkalinity of the stock, nature of the sizing and precipitating agent,. type and quantity of filler used, the effect desired, and so forth.

Similarly, colouring agents can be selected from a wide range of conventional materials such as dyestuffs and pigments; however, the range of dyestuffs suitable for this purpose is narrower than for beater dyeing because of the necessity of selecting colours possessing good solubility, and also because combinations of basic and acid or basic dyestuffs cannot be employed in the formula.

As previously indicated, it will be apparent that these materials are added to the wet web at a position on the paper machine wire where the water content is such that only a minor portion of the additive will be separated from the web (through subsequent action of drainage and pressing devices) but yet where the water content is high enough for the additives to penetrate the surface of the web, not necessarily uniformly in a cross-sectional direction (thickness), but at least uniformly in the plane of the web.

The choice of location of additive application will generally be restricted to the section extending from the position on the wire where the table rolls or foils appear to be removing a small amount of white water to that where the wet line begins to disappear.

If the additive particles tend to concentrate on the surface of the web, a change in particle size may be made in order that the surface of the dried web or sheet will have the desired properties. For a smooth surface or finish the particle size should be smaller than it would be for conventional loading procedures.

We claim:

1. In combination with a papermaking machine having a moving wire and a wet web on said wire in course of formation into a paper sheet, apparatus for applying a dry powdered material to said wet web which comprises a feed hopper for said material having an outlet extending transversely of said moving web, a rotatably driven metering roll having a surface in communication with said outlet for reception of material therefrom, a rotatably driven brush roll in friction engagement with said metering roll for brushing said material therefrom, said rolls being in spaced, substantially parallel relation to said web, means for deflecting said material onto said web, and means for controlling rising clouds of said material comprising a plurality of wire electrodes, means supporting said electrodes in spaced, substantially parallel relation to said web and in a selected pattern with respect to said web, means for supplying electrical power to said electrodes, said rolls and deflecting means and said electrodes having successive confronting relationship with moving surface areas of said web.

2. Apparatus for applying a dry powdered material to a wet web as defined in claim 1, wherein said deflecting means includes a deflector roll having a surface in parallel frictional engagement with said brush roll, said deflector roll being positioned between said brush roll and said electrodes and having a direction of rotation opposite to that of said brush roll.

3. Apparatus for applying a dry powdered material to a wet web as defined in claim 2, including a battle extending from said hopper and overlying portions of said metering and brush rolls.

4. Apparatus for applying a dry powdered material to a wet web as defined in claim 1, said brush roll being located closer to said web than said metering roll.

References Cited UNITED STATES PATENTS a 1,870,041 8/1932 Dike 118-308 X 2,030,483 2/1936 Uong 162-184 2,057,548 10/1936 Wallach et a1. 118-308 X 2,276,486 3/ 1942 Harshberger 118-308 X 2,394,657 2/1946 Beregh 118-636 3,114,482 12/1963 Dunaway 118-621 X 3,210,240 10/1965 Read et al. 162-175 FOREIGN PATENTS 378,014 7/1932 Great Britain.

OTHER REFERENCES Reif, An Electrostatic Process for Applying Dry Coatings on Paper, TAPPI, October 1955, vol. 38, No. 10, pp. 607, 608 and 609.

S. LEON BASHORE, Primary Examiner US. Cl. X.R. 118-308, 325, 625, 636; 162-175, 186, 192

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