DE1802693A1 - Method and apparatus for manufacturing cellulose-containing sheet material such as paper and cardboard - Google Patents

Description

DR. BERG DlFL.-ING. STAPF

PATENT LAWYERS B MUNICH 2, HiLBLESTRASSE 2O

Dr. Berg Dipl.-Ing. Stopf, 8 Munich 2, HilblestraBa 20 Our sign date

Gg / fr 17 722 JI October _{1, 1968}

Lawyer file no .: Λ7 722

Ransburg Electro-Ooating Corp., Indianapolis, Indiana / V.St.A.

Method and device for the production of cellulose-containing Sheet material such as paper. And cardboard

The invention relates to the production of pulp-containing Sheet material, such as paper and cardboard, in which on a feuohtes, fibrous, pulp-containing Sheet material placed on the metal cloth of a Fourdrinier paper machine, for example, fabrics be sprayed on electrostatically.

In the production of pulp-containing sheet materials

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(0811) * 5 16 20 81 telegrams, PATENTEULE Munich Banki Bayerliche Vereinsbank Munich 453 100 postal check! Munich 653 43

rial materials such as paper and cardboard, influencing their physical properties is essential for different purposes. For this reason, substances are often deposited on the pulp-containing sheet during sheet formation. In the production of printing paper, such as newsprint, for example, the so-called "pick" resistance is to be generated as the most essential property in use. This ^w Pick ^M resistance is a measure of the degree of solubility or removability of the fibers lying on the surface, so it is a measure of the surface strength of the sheet material. During printing, ink is applied to the surface of the sheet by means of a printing plate or, in the case of offset printing, by means of the rubber blanket cylinder. If the sheet is pulled off the plate or the blanket cylinder, the fibers lying on the surface tend, in the event of insufficient gluing with the core fibers, to detach from the sheet and adhere to the plate or the blanket cylinder. If a large number of such fibers have accumulated, then they impair the color distribution, and this then leads to a speckled, uneven print image. To increase the "pick" resistance of a sheet, it is

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therefore it is desirable to apply a thin layer of starch to the surface of the paper. The strenght is transferred to the surface of the paper fleece while it is still moist during sheet formation applied to the metal cloth of a Fourdrinier paper machine. Further usage properties, soften for paper refinement through the deposition of substances The strength, stiffness, smoothness, porosity, brightness, and mattness of the paper web are improved and the ability to withstand the penetration of various liquids such as water, oil, wax and paint prevent or promote.

For numerous coating processes it is desirable that the respective substance is applied to the cellulose-containing Sheet, hereinafter referred to as paper web for short, during sheet formation over the metal cloth of the Fourdrinier paper machine is applied. However, the wet paper web supported by the metal cloth is still extremely brittle, so there is a risk of tearing or damage to the surface larger drops of liquid are deposited. However, damage caused by the deposition of such larger liquid droplets in the area of the Fourdrinier metal cloth is on the end product visible, which is why they are extremely undesirable.

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In the case that the Besohiohtungsstoffβ _s not be applied electrostatically on a paper web, the materials are sprayed onto the paper web, either as a result of its gravity or by means of devices which accelerate the substances to the paper web out. The fineness of the atomizer jet depends on the air movement in the area of the Fourdrinier metal tube. Small diameter atomizer droplets have a large surface-mass ratio and can be easily moved by air currents. If the deposition is caused by gravity or by the fact that the substances are accelerated towards the paper web, penetration of the moving air in the vicinity of the paper web can only be achieved by means of relatively large droplets are charged and guided into the vicinity of the paper web, while the paper web is made to attract the atomizing jet by the fact that the Fourdrinier metal tube is grounded Hindu attracted and deposited on the surface of the paper web. An apparatus and method for charging a liquid atomizing material is disclosed in U.S. Patents 3,169,882 and US Pat

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3 169 883. Such a device is capable a liquid dispersion of finely divided solids, such as uncooked starch in water, or a Charging substances in their liquid state and spraying them onto the paper web, substances in dry powder form can be applied to the paper web by liquefying it, liquefying it Introducing powder into a moving air stream by means of an injection pump and that this air stream then leads to an atomizer device, which is provided with a charging electrode, to welohe a high voltage is applied. It is often desirable to have such an electrostatic atomizing device to be arranged above the Fourdrinier-Metalltu.ch, in order to achieve an even distribution of the substances over the paper web.

The air surrounding a paper machine is now heavily loaded with water vapor, the permanent evaporation of the water is formed, which is abundant in the headbox and in the wire and the press section is released. In addition, in the dryer section of the paper machine directly generates steam. This water vapor the surrounding Air now condenses on every cold surface, and the condensate gradually forms drops, which are such

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Drain surfaces. Is an electrostatic atomizing device arranged above the surface of the paper web formed on a Fourdrinier metal cloth, then water will condense on the surfaces of this device in drops on the paper web drip off, with the result that the paper web is torn or that bumps are formed on it. An electrostatic atomizer is now generally located on the ground supporting stand supported. The electrostatic The atomizing device comprises insulating bodies which carry the charging electrode. The surfaces of these insulating bodies are under high electrical stress, caused by the high voltage that is applied the charging electrode is applied. If water is deposited on such surfaces, it becomes a Current path created across the insulating surface so that between the charging electrode and the grounded Stand of the atomizer device high currents flow ) can. This can ultimately also lead to damage to the paper web. Is in the nebulizer In addition, a resistor with a high line resistance is arranged in series with the charging electrode, then that can be in the current path which is accumulated through the on the insulating surfaces Moisture is formed, current flowing to the

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Reduce the voltage applied to the charging electrode to such an extent that the atomized particles are charged is prevented.

To avoid the aforementioned disadvantages is according to the invention the electrostatic atomizer device surrounded by a Qas, and this gas is atomized out into the surrounding air to thereby an accumulation of water caused by condensation on the electrostatic atomizing device to prevent. According to a preferred embodiment, the electrostatic atomizer device is according to the invention surrounded by a porous, non-conductive housing with an opening for the front The end of the atomizer device and its charging electrode are provided. This housing is a Gas introduced under pressure, so that the housing interior has a higher pressure than the surrounding air. The gas penetrates the porous walls of the housing and its opening, which surrounds the front area of the atomizer device and its charging electrode, daduroh will the accumulation of condensed moisture on the housing and on the surrounding air Prevents exposed surfaces of the atomizer device.

The invention is based on one in the

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Zeiohnung illustrated embodiment in more detail described. It shows

1 shows the arrangement of four in a perspective view electrostatic atomizing devices according to the invention in a paper machine, and

Fig. 2 is a cross-section, on an enlarged scale,

an electrostatic atomizing device according to the invention

In Fig. 1, 10 denotes the entirety of a Fourdrinier paper machine, which «in a headbox 11 with adjustable lip 12 and register roller 13, rollers and suction roller 15 includes, over which the rotating Metal cloth or endless screen 16 is placed · If necessary, a screen roller can also be provided, which but not shown in the drawing * With 17 are common suction boxes. The paper pulp P diluted with water passes through the fabric run-up 11 on the revolving, endless wire 16 and is gradually dewatered in the wire section of the paper machine, after the leaf formation has taken place, the water is sucked off in the later stage, so that in the area of roller 15 lowered the water content to about $ 80 is. Following the Fourdrinier paper machine the paper web passes through a dryer section, which.

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from grouped press rolls 18 and steam-heated drying cylinders D, which continue to remove water from the paper web. The paper web is in this section by means of drying felts 19 » 20 and 21 moved. The heated drying cylinders D

ultimately remove so much water from the paper web that it has the desired final moisture content.

Fig. 1 also shows at 22 an electrostatic atomizer device, by means of which dry, piiyer-shaped coating materials are applied to the surface of the paper pulp P. This device comprises a plurality of electrostatic atomizing devices 23, which are arranged at a distance from one another and bring the powder uniformly onto the surface of the paper pulp for distribution. Since all atomizing devices 23 are constructed in the same way, the following description can be restricted to the embodiment of one device. The powdery coating material is introduced into an air stream by means of a special pump and then fed to the atomizing device 23 via a hose Zk, the coating material is distributed at the front end of the device by a rotating distributor. A high voltage DC power source 25 is across

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a cable Z6 and a series resistor arranged in each atomizing device are connected to a conductive charging electrode of the rotating distributor of this device, so that an electrostatic field is formed between the charging electrode and the paper pulp to be coated. The applied voltage is preferably negative »The powder particles are electrically charged, then introduced into the electrostatic field and are finally attracted by the paper pulp or the paper web and deposited on it.

The powder particles are liquefied in a bed of liquid by introducing them in batches into a housing 27 through which air under pressure is passed. A collector of the regulating device for the supply of air is designated by 28, the source of which is not shown. With a control valve 29 is designated, which is assigned to the liquid bed. For each atomizer device 23, an injection pump (not shown) is provided, which is arranged in the liquid bed and to which a pressure regulating valve 31 and a pressure indicator 32 are assigned. The outlet line of this pump is connected to the atomizing device via the hose 2k. Through the valve 31 can be the pressure

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control the air to the injection pump and thus also the flow resistance of the powder particles Air pressure brawn by display device 32 for display can thus be used as a control variable in a simple manner can be used for the flow rates of the powdery coating material. One Individual control of the individual atomizer devices is for the purpose of uniform distribution of the coating material desired on the paper web.

The electrostatic atomizer device 22 is now surrounded in the area above the paper web P by a housing made of porous polyethylene, which was produced by sintering and is sold under the trade name ^M VYON ^W. The porous housing is pressurized with a gas, such as Luftι, which penetrates the porous housing to the outside and thereby prevents the deposition of condensed water on the surfaces of the electrostatic atomizing device.

Fig. 2 shows an atomizer device according to the invention 23 in cross section. The distributor 33 is rotated by an air-driven motor 3 ^ · to provide a distribution to effect the powder particles. The engine 3 ^ is via a hose, a pressure regulating valve and a shut-off valve connected to a compressed air source,

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none of these parts are shown. A change in the air pressure causes a change in the speed of the motor Jk and thus the speed of the distributor 33. In order to bring about a uniform distribution of the powder particles, the speed should be of the order of at least 400 rpm of insulating material surrounding insulating body referred to, which extends from a conductive housing 36 to the front. The hollow shaft 37 is rotatably mounted in the insulating body 35, specifically by means of a bearing arranged in the housing 36 and a guide for the insulating body designed as a bearing surface. A gear wheel is seated on the hollow shaft 37, which meshes with a gear wheel set in rotation by the motor 3k, the hollow shaft 37 is thereby set in rotation. The charging electrode 38 includes a resist coating on the rear surface of the manifold 33,. one such coating is through the US patent

\ 3,021,077 known. The insulating body 35 and the hollow shaft 37 create an insulating support for the Charging electrode 38 at a distance from the conductive housing 36. This allows the conductive rear part the atomizing device 23 are grounded, while a hollow voltage with respect to the charging electrode 38 of the ground is created. The insulator carries

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also a resistor 39 with a high resistance value of a few hundred megohms. The cable 26 is fed via the rear part of the atomizing device 23 and connected to the resistor 39 within the insulating body 35. A brush is designated by kO , which is held by the front end of the insulating body 35 and creates an electrical connection between the front end of the resistor 39 and the charging electrode 38.

The hose 2k, which carries the powder enclosed in air, opens into a channel 41 in the rear housing J6 of the atomizer device.This channel ^ I is sealed off from the hollow shaft 37 by a rotating sealing washer, and the air flowing through it with enclosed powder continues to flow through the cavity of the hollow shaft 37 to the distributor 33. The distributor 33 surrounds the hollow shaft 37 with a hub.In the hollow space of the shaft 37, a cover kZ is inserted in such a way that a lateral outlet opening k3 is formed, through which the powder cells flow out in a direction essentially perpendicular to the axis of the shaft 37 . The cover k2 and the distributor 33 are preferably made of non-conductive material, with the rear surface of the distributor

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is provided with a conductive coating, which has a high resistance value and thus as Charge electrode 38 can serve.

The distributor bell 33 is slightly inclined towards the front with respect to a plane perpendicular to the axis of the hollow shaft 37. The outlet opening 43 is located in the immediate vicinity of the front, concave surface
the bell jar, in the vicinity of its
Axis of rotation so that the powder particles flowing out
of the coating material can be passed to the outside via this area. The rotation of the bell jar while the powder particles flow out causes them to be uniformly distributed over the surface of the paper web. The front surface of the cover 42 is preferably held at a small distance behind the front edge of the manifold 33. The electrostatic field for charging and distributing the powder particles preferably extends from the front edge of the bell jar
Powder particles are greatest when the gradient of the electrostatic field is greatest at the edge of the junction box.

The distribution device 23 is supported by a carrier 44 supported, by means of cap screws 45, which

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are screwed into the conductive housing 36. The carrier kk extends horizontally above the Fourdrinier metal cloth over its width and serves to hold all atomizing devices. This carrier hk can be supported against the Brdboden by a suitable frame construction «

The atomizer devices 23 and the carrier * »Λ are surrounded by a porous housing k6 · The side walls 47 and the top wall k8 of this housing are made of sintered polyethylene, which is sold under the trade name" VYON "» The walls have a dioke of about 5 mm on the bottom wall 4 ° of this housing, which is also made of sintered polyethylene, however, has a thickness of about 3 mm in order to obtain a suitable air flow in the area of the distributor 33. The aforementioned starting material for the housing k6 can be deformed under heat in order to make a desired adaptation to the shapes of the atomizing devices, the material can be welded along the abutting edges in order to make the housing airtight along these edges. The opening between the rotating distributor 33 and the housing k6 is kept relatively small, for example an annular opening with a diameter of approximately 1.6 mm is provided. One

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Amount of about 14,000 dm / min of gas under one pressure from about 50 mm water column reloht usually for the supply of the entire device, if this consists of four housings corresponding to the housing 46, which are fixed opposite the carrier 44 «The interior of the housing 46 is below a pressure higher than the pressure of the surrounding air, so that the gas penetrates the porous walls the housing 46 penetrates close to the outside and thereby ^ keeps the surrounding air away from the electrostatic atomizing devices 23 and the carrier 44,

The porosity of the side walls and the top wall a housing is chosen so that at a pressure difference of about 50 mm water column in the housing introduced compressed air in an amount of about 370 dnrymin per area in the order of magnitude

2 Approximately 9.3 dm near the outside penetrates these walls

have, as already mentioned, a thickness of about 5 mm f on. So the air is in an amount of about 680

dm / min per unit area in the order of magnitude of βίο wa 9.3 dm emerge from the housing when it is in the Housing is held under a pressure of about 100 mm water column. The porosity of the bottom wall of the housing is chosen so that about 85Ο dm / min per area

unit in the order of about 9 »3 dm

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flow at a pressure difference of about 50 mm water column with a dioke of the bottom wall of about 3 mm. Albeit the aforementioned porosity of the housing in practical testing the best efficiency in terms of preventing an accumulation of condensed water vapor on the outer surface of the housing other values for the porosity of the housing can produce the same results. It In any case, it is only necessary to prevent the outside air charged with water vapor from exposing it Reached surfaces of the electrostatic atomizing device. More porous walls of the case bring larger ones Flow rates of the air, but this has the disadvantage of increased operating costs of the device,

Heated air can also be used, whereby practical testing has shown that heating the air to around 60 ° C. is a favorable degree of efficiency results. The heating of the air is particularly advantageous when part of the outer surface of the housing for the electrostatic atomizing device cannot be made of a porous material can. As the heated gas penetrates to the outside via the porous part of the housing, it can continuously enter the inside of the housing can be fed so that the non-porous part of the housing on a solo tem-

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temperature can be maintained so that water vapor cannot condense on this part. Advantageous the hot air available in the dryer section of the paper machine is used for charging of the housing.

Embodiment

Using a conventionally designed paper machine, For example, as described with reference to FIG. 1, an electrostatically charged, finely divided starch powder can be applied. There are four electrostatic atomizers provided for this purpose at a distance of about 180 mm above a about 1380 mm wide paper web are arranged. Each atomizer is equipped with a bell-shaped manifold of the type shown in Fig. 2 which is rotated at a speed of about 700 rpm. the individual distribution devices are arranged offset from one another at a distance of approx. 350 mm, in order to achieve a uniform distribution of the starch over the paper web. The distribution facilities and their support are surrounded by a porous housing. In this porous housing, air is under pressure

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Clay about 50 mm water column introduced continuously. The paper machine produces newsprint ($ 65 wood pulp, $ 35 sulfite) with a final weight of about 17 kg per line (635 x 965.2 tnm-500 sheets) (30 657 dm ² ).

The paper machine is operated at a speed of about 35 dm / min and uncooked, powdery starch, which has previously been treated with oxyethylene to reduce its initial gelation temperature to about 60 to 63 C, is applied to the felt side of the paper by applying the Atomizer units can be electrically negatively charged with about 65 to 75 kV. The starch particles are entrapped in air and are fed to each atomizer at a rate of about 3.8 kg / h. The atomizing device for applying the starch to the upper surface of the paper web is located near the squeegee cylinder where the moisture content of the paper web is about 85 % . Then the paper web arrives in the dryer section of the paper machine, in which it is continuously dried by means of steam-heated dryer cylinders. The dried paper web then passes through a calender

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of the paper fiber or about 0.038 kg per area

2 surface units in the order of about 9290 dm.

The finished sheet has a much improved "pick" resistance on the side of the paper, despite a slight loss of absorbency, it shows no damage as a result of possibly Drops fallen on the paper web.

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Claims (1)

Claims 1, paper machine for the continuous production of an endless paper web with a headbox for the paper pulp, a continuous, endless one Sieve or Fourdrinier metal cloth for its dewatering, one above the sieve at a distance electrostatic atomizing device with an atomizing device, which is provided with a storage container for connected to the Sfeoff to be sprayed onto the paper web and comprises a charging electrode, to which a high voltage to form an electrostatic Field and for charging and depositing the particles of matter coming to be sprayed, and with a dryer section for drying the paper web, characterized in that the electrostatic atomizing device is of a porous, non conductive housing is surrounded, which is in an opening of the atomizer and its charging electrode is penetrated, and that a gaseous medium is continuously introduced under pressure into the interior of the housing is which is higher than the pressure of the atmosphere surrounding the nebulizer device, - 22 - 909821 / Ö75Ö 802693 2, paper machine according to claim 1, characterized in that with an opening for the atomizer and the wall of the housing provided with the charging electrode has a larger one at least in the vicinity of this opening Has porosity than the other housing parts. 3. Paper machine according to claim 1, characterized in that that at least part of the housing is made of sintered polyethylene, k, A method for producing paper by continuously applying a paper fiber material with uniform distribution on a rotating, endless screen, subsequent dewatering of the paper fiber material and electrostatic coating of the paper web before its final drying, characterized in that the device for applying a coating material when coating the paper web this is shielded from the surrounding atmosphere by a gaseous medium, 5. Apparatus according to claim k, dadui-ch characterized ,, that the gaseous medium is previously heated. - 23 - 9098 2 1/0758 6. The method according to claim k or 5 »characterized in that available compressed air is used as a gaseous, heated medium via the dryer section of the paper machine. 909821/0758 ORIGIMAL INSPECTED