FI96894C - Method and apparatus for coating paper or the like - Google Patents

Description

96894

METHOD AND APPARATUS FOR COATING PAPER OR THE LIKE

It is well known that paper, board, or other such materials can be coated with a variety of coatings to change the texture, color, or the like of the surface.

This coating material often contains clay (kaolin) or other relatively heavy materials, talc or chalk, and a binder, such as latex or modified starch, to fill the slightly porous surface of the paper or board 10 to produce a flat surface.

The coating material provides improved paper quality, e.g., gloss, brightness, translucency, evenness, surface strength, absorption properties. One or more coating layers are applied to the surface of the uncoated paper 15 to fill the irregularities on the surface of the paper and thus to smooth said surface to provide a smoother and microporous surface. Depending on the quality of the paper, different amounts of coating material and either 20 one or more times are coated on the web. An additional wet coating composition is suitably applied to the paper web by means of a dosing device through which the web is conveyed. In order to obtain a uniform thickness from the coating on the surface of the paper web, a scraper, i.e. a so-called scraper blade, is placed some distance from the dosing device. extends across the entire width of the paper web. Up to 90% of the coating material is formulated. This consumes scraping and • · · scraper maintenance, such as replacement, takes considerable time.

• · · • »• 30 • · · • · ·« "Only starch, for example, can be used as a coating material, as is done, for example, in the production of copy or letter paper, • · in which case it is referred to as surface sizing. In surface sizing, the paper web is placed after surface coating. Examples of surface sizing are given in Tappi J. August 1992, pp. 79-84 (Jarkko Tehomaa et al: A comparison of different high 2 96894 speed surface sizing techniques for fine papers) and Tappi J.

Dec. 1990 pp. 69-75 (Charles P. Class: Trends and developments in size press technology).

As is well known in the art, paper is generally made in a continuous process in which the web initially has a very high water content, after which the water content is gradually reduced until substantially water is removed from the web. Due to the nature of the method and apparatus used to coat the coating materials, it is generally very limited to select the stage of paper production at which the coating materials are added. In particular, the clay or the like is coated on the surface and scraped to the desired thickness with a scraper blade or similar mechanical means, e.g. an air scraper.

Many different types of scrapers are known and although the present text always refers to a scraper blade for simplicity, it is emphasized that the invention is not limited to the use of scrapers, but can be applied to all types of scrapers extending over the entire width of the paper web and applied after the paper coating material is applied. .

Some effort has been made on my coating spray! for paper-like materials, but the coating materials 25 have never been successfully coated by spraying techniques. A method and an apparatus for coating a web without mechanical contact with the web are disclosed in FI patent application • 912390, according to which the web is continuously moved along a web, the material to be coated on the web is formed into a slurry containing • · · f * · * * solid particulate coating material, the slurry is dispersed: * · *: material to be coated on the web into small particles • ·, * · *. to produce a mist containing solid particulate material as a gaseous suspension, a suitable gas flow is produced so as to keep the solid particulate material in suspension and to direct the solid particulate material into suspension.

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3 96894

A mist containing iin per web for attaching a solid particulate material to the web.

For several years now, it has been desired to achieve high speeds of paper-5 web in order to achieve higher production. Today, speeds of 1000 - 1500 m / min are already normal and in the future higher speeds will be possible.

In order to solve the above-mentioned problems, the invention is characterized by what is stated in the characterizing part of claim 1.

The present invention relates generally to the coating or surface sizing of paper webs or the like, and more particularly to a method and apparatus for coating a web. Another object of the invention is to provide a flat paper surface. It is a further object of the invention to provide a better paper quality so that the paper can be coated with higher coating amounts and / or previously achieved coating amounts can be achieved with fewer coating times. The pressure of the mechanical scraper can be reduced. The required scraper pressure is significantly lower than with existing equipment in the industry. The wetting of the paper web can be reduced. The production efficiency of surface gluing will be improved.

This invention includes the preparation of a slurry for use as a coating composition or adhesive composition and the generation of a mist. its. The coating composition or adhesive composition is decomposed into a mist with a pressurized gas before adhering to the paper. After spraying, the coated or surface-glued web is treated with a scraper or pressed by two rotating rollers. ** ·. or the like, smoothing the coating layer or. an adhesive layer and allowing chemicals, coating material 35 and / or adhesive to penetrate the paper.

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In various embodiments, the mist may be mixed with mists containing other coating agents, if desired; then the final materials to be coated on the web are directed against the web. In one embodiment, the mist and web 5 may contain static charges that aid in both contact and retention of the mist on the web, although success has been achieved without the use of static charges.

In addition, the mist can be generated in many ways, e.g. with conventional spray nozzles. The invention can utilize ultrasonic energy to produce a mist and possibly an ultrasonic nozzle of the type well known in the art.

These and other features and advantages of the present invention will become apparent from the description of the following description when taken in conjunction with the accompanying drawings, in which:

Figure 1 shows a schematic cross-sectional view of the coating nozzle.

Figure 2 shows a schematic flow diagram illustrating a dispensing device for coating paper according to the present invention.

Figures 3a and 3b show different options for smoothing a paper web coated with a paper machine or a separate coating machine.

Figures 4 and 5 show the structure of the nozzle.

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Referring now in more detail to the drawing and the present invention here • ·. ···. to the embodiments presented by means of the description, it should be noted that • · · a large number of FI patents can be included in the apparatus. features of application 911390.

• · · •• »3o • · · • · · * · · Figure 1 shows an example of a coating nozzle 24,: * · *: with a sludge channel, located around the capillary tube 26; air ducts 25. The coating sludge is introduced into the sludge «<·. in the form of a sludge duct 26. The sludge duct and the air duct taper towards the outlet. The air coming from the air ducts is directed ‘’ to break up the sludge into a mist or to disperse more if the sludge has already been broken up into a mist at an earlier stage. The coating mix

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5 96894 hits and sticks to the paper web. The distance of the cover nozzle from the paper can be adjusted as needed. The slurry is introduced in the form of a slurry into the slurry channel if it is dilute, in which case it is decomposed shortly before hitting the paper.

5 The outlet end of the nozzle is, for example, with an opening of approx. 1-5 mm in diameter and an opening of 3-5 mm. The nozzles can be arranged in a row across the width of the web to be coated, either in the same plane or in a different plane, so that the mist coming through the paper surface is arranged evenly over the entire paper surface 10 so that the air and sludge channels are arranged concentrically. The nozzle according to Figure 1 can be constructed as a single unitary nozzle, in which case the outlet of the sludge channel is constructed as a gap the entire width of the web and its size is e.g. 2-5 mm x 6 m. The air ducts are then arranged on both sides of the gap at certain distances from each other.

In a more preferred situation, only the nozzle 24 with its air and sludge ducts needs to be built in place of the conventional dosing device. Figures 4 and 5 further show different embodiments of the nozzles. In addition, the amount of coating can be easily adjusted. Penetration and remnant of the amount of coating can be optimized by finding a suitable spray stroke angle for each spray angle. The optimum angle is not critical in all situations, as the extra coating can always be collected: or scraped off, but this adds to the strain on the paper. A suitable diffuser / accelerator gas (air) pressure to be used in the nozzle is 50-2500 kPa (0.5-25 bar). Great • ·. ·; ·. the pressure usually results in a higher velocity of the coating composition after the nozzle and as a result the coating penetrates. deeper into the pores of the paper. The maximum penetration depth of 30 mm is achieved when the nozzles are installed slightly against the incoming direction of the incoming paper path. The optimum angle of the nozzles against the web plane depends as stated on: • · - the speed of the paper web, - the average droplet velocity of the dispersed coating mist produced by the nozzle depending on), - the distance of the nozzle from the track (0.02-2 m), - the diameter of the coating opening of the nozzles (0.02-10 mm) or the width of the coating gap 5 and the output speed given to the coating / adhesive by the pump or internal ejector.

When moving the mist, the pressure can be adjusted as needed to provide an acceptable coating. Naturally, a sufficient air conditioning system, not described, is placed around the device 10.

After coating, the web is conveyed along a scraper 32.

The scraper 32 is pressed against the roll 33. It should be noted that the blade pressure may be lower than that used in conventional coating techniques because the amount of coating material fed can be easily dispensed, thereby avoiding a substantially excessive amount of coating material. The main function of the scraper can be leveling. In the pilot plant experiment, a coating amount of 25 g / m 2 was achieved with one coating, while with conventional methods a coating amount of 15-16 g / m 2 was reached in one application and on one side. A mechanical (or air scraper can act as both a brush and a paste remover. The choice of the main method, between brushing or paste removal 25 depends on the running speed of the track to be coated, j .. type of paste and desired amount of coating. High formula • ·. ·· *. It should be noted that when gluing paper with a starch solution, the properties of this solution are completely different from those of a normal mineral coating, i.e. a paste.

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With the method according to the invention, the speed of surface gluing and coating can be increased and it is estimated that it reaches a speed of 2000 m / min, which was the maximum speed of the test machine used in one test run. The limit speed of the coating can be said to depend on the mechanically achievable speed of the machine rather than on the coating event itself. The coating can be carried out several times or only once. The coated paper can be flattened instead of or with a scraper, e.g. between two rollers. An air sweep blade or air brush or even a combination of some or some may also be used.

Visually, using ultraviolet light, it was observed in coating experiments with both gravure and offset papers at paper speeds of 1000 to 1800 m / min that the method of the invention gave a smoother paper than without scraping and spraying.

In the solution of Figure 2, the sludge is removed from the tank 10 by a pump 14, the outlet of which is connected to a line 15 for supplying a nozzle 16. The nozzle 16 breaks the sludge coming from the tank 10 so that the sludge becomes a spray with a very small particle or mist size. In this application, the material refers to the mist 20 and should be understood that this term includes a number of forms from a very small particle size aerosol to a relatively small particle size spray.

Nozzle 16 may include many special hardware components. It is possible that by using a pump 14 with sufficient space. . those, the nozzle 16 may in fact be a liquid type nozzle, the nozzle dispersing the liquid substance flowing through it, producing a fine particle spray, or the nozzle,. wherein the pressurized gas disperses the liquid and mixes with it • · · • · ·; ** 30 to form a mist. It is also possible to use an ultrasonic nozzle, generally of the type disclosed in U.S. Patent 4,352,459 to Berger et al. Ultrasonic nozzles are well known in the art and will be known to those skilled in the art without further explanation.

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One additional form that can be implemented by the nozzle 16 is a transducer located at the bottom of the tank 18. It should be noted 96894 8 that the tank 18 is described as having a slurry at the bottom, and the mist at the top of the tank 18. By placing the transducer on the bottom of the tank 18, the ultrasonic energy can be dispersed into fine particles in the slurry to produce the desired mist on the liquid, the additional mist provided as a mist being removed for use.

It should be noted that the mist coming from the mist chamber 18 is directed to the mixing chamber 19, and in addition that there is a second tank 10 18A, the outlet of which is also directed to the mixing chamber 19.

If desired, there may also be two or more containers, each containing a different slurry and a different mist, so that two or more materials can be coated on the web 11 simultaneously.

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Another means of producing two different materials for coating the web 11 is to provide two or more containers, such as container 10. In the drawing, a second container 10A is shown and pump 14A transfers material from container 10A and feeds material through line 15A to container 18 nozzle 16A. Therefore, it is to be understood that two different mists are generated in the tank 18 by the nozzles 16 and 16A. The mixed sprays are then directed to the mixing chamber 19 or directly to the coating nozzle 24.

25 i ·; The present invention also provides an injection means 23 for injecting air or other gas into the mist stream. The injection means 23 are shown to be located on the walls of the coating nozzle 24. close and in this position the gas curtain settles along the walls • * · • * ‘30 preventing the droplets from sticking to the walls.

• * · · • · · *: * · [: To help the mist to adhere to the web 11, it is possible to use a static charge. *. in favor of mist and web 11. One skilled in the art will readily appreciate that web 11 may be reserved, and that mist may be provided by a grating or the like. For illustrative purposes, the charge generator is denoted by 30, as shown

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9 96894 only one charge generator. Nevertheless, it is to be understood that one charge (e.g., negative) may be generated and placed on the web 11, while the opposite charge (e.g., positive) may be placed on the mist. These 5 opposite charges cause the web 11 to attract the mist and the mist to adhere to it.

Figure 3 shows various options for smoothing the paper 10 with a paper machine or a separate coating machine. Figure 3a illustrates an example of an embodiment of a scraper 32, a cloth brush, or a combination thereof. Figure 3b illustrates a pair of rollers 34 used in a surface sizing paper web through which the paper is passed. The dashed air scraper can be added after a pair of rollers if desired.

15 The paper path can move from bottom to top or horizontally. Small amounts of pigment are sometimes added to the starch, in which case we speak of pigmentation.

An important feature of the present invention is the coating of the mist-containing coating material 20 on the web 11 at low pressure and without mechanical or similar treatment. This allows the system of the present invention to be utilized for coating paper in any paper production line, from the first dewatering step until the paper is completely dried. If desired, the paper can * *. can be made and wound, and the rolls can be transported to another location, unwound, and then coated using the system of the present invention.

Therefore, it should be noted that the present invention provides in particular:; ,.

its simple method and apparatus for coating paper webs and: * ·]: the like. Since the r * '* slurry to be coated on the web has been converted to a mist and the mist is coated at a very low pressure, it should be noted that the web is never damaged, even when the web contains a lot of water. Furthermore, in view of the coating technique, it will be appreciated that any conventional Drying Technique 10 96894 is suitable so that infrared lamps or the like can be utilized to dry the coating material on paper or paperboard.

5 The excess coating material that accumulates on the scraper can be collected in a conventional manner so that it can be used later.

The invention has been described above with reference to only one preferred embodiment thereof, but it is clear that the invention can also be implemented in other possible ways within the limits set forth in the claims without changing the scope of the invention. It is possible to use different coating methods or equipment. Significant improvements have been made to the prior art.

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Claims (10)

Method for coating the paper web, cardboard web or the like, in which the coating butter is dispersed into fog which is spread under pressure in the paper web (11) through nozzles (24) located at a distance from the web, characterized in that it The paper web (11) coated with the fog is smoothed after coating with an evening agent (32, 34). 20 Method according to claim 1, characterized in that the paper web (11) coated with the starch mist is pressed with two pii on the sides of the paper web placed rollers (34), e.g. di it is free of a surface sizing unit. 25 3. A method according to claim 1, characterized in that the paper web (11) is leveled with a creator (32) known in the industry in and in which the blade pressure of the creator (32) is lower. than when leveling with the conventional method, or evening the paper web (11) with an air knife or airbrush. • «·« • 4. A method according to any preceding claim, characterized in that the paper web (11) is leveled with a combination of air knife and / or air brush and creates 35 or with rollers or a combination of some of them. 96894 5. Method of coating paper, cardboard or equivalent paper web or equivalent, in which the paper web (11) moves continuously along a web, a suspension is produced containing the coating material, the suspension is dispersed to 5 forging particles in the web (11), the fog containing the coating agent is produced, the fog is directed toward the paper web (11) to be attached to the web (11), in the alignment of the fog, the coating nozzle is placed near the web (11) and a positive force is produced to force the fog against the web (11) and a plurality thereof is produced. suspensions for coating the web (11), the mist is produced from each of these suspensions, all the produced mist is mixed and the resulting mist mixture is directed to the coating nozzle (24), fed to the web (11), characterized in that the web coated with the mist is leveled after coating with the leveling agent (32, 34). A paper coating apparatus for coating a continuously moving paper web (11) or the like, which apparatus comprises a dosing apparatus for the coating agent, a maker or equivalent of the coated web, the apparatus having a coating nozzle (24) p in distance from the paper web for feeding the suspension or the mist to the paper web, wherein the suspension has been dispersed to fog with pressurized gas before being fixed to the ...: web, characterized in that the additional ·· ·: V comprises an equalizer (32, 34) for the coated web: J: (11). ; ; '| 0 A paper coating apparatus for coating a ··· «continuous moving paper web or equivalent (11), which apparatus comprises a means for making a suspension containing the solid material in the coating web (11), an agent (16) for dispersing the suspension in compressed gas to fine particles to replace the mist containing the solid material in the coating material of the paper web (11), a coating agent (24) for coating the mist to the web (11), wherein the coating means (24) is near the web and spaced from the web (11) / and a means (23) for producing the gas flow to pass with the mist and transporting the mist through the coating means (24), characterized in that the paper web coated with the mist (11) has been leveled with an equalizer. 8. Apparatus according to claims 6 or 7, characterized in that the paper web coated with the starch suspension fog has been leveled with cupboard (32), or with two rollers placed on both sides of the paper web, e.g. then it is a matter of a surface sizing unit. 9. Apparatus according to claim 8, characterized in that the paper web has been leveled with a sheathing (32), or air knife or air brush. Apparatus according to claim 6, characterized in that, for feeding the suspension or fog, the coating nozzle is provided with a suspension duct (26) for controlling the suspension or fog, next to which is placed an air duct or air duct (25) or there are several suspension channels (26) or only one width of the paper web (11). • ··· • · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·