FI119742B - Procedure for preventing contamination of a roller - Google Patents

Description

A method of preventing roll contamination

Field of the Invention 5

The invention relates to a method for preventing and cleaning the surface of a paper or board machine roll and especially the surface of a central roll. 1

State of the art

A very common problem in rolls for paper and board machines, and especially for central rolls, is the rapid contamination of the roll, regardless of the surface material used in the roll. The central roll roll contamination is manifested in a paper or board machine with reduced roll operation, reduced web release from the central roll 15, and increased web breaks. Contamination of the center roller occurs over time and increases quantitatively when the first dirt layer has formed on the surface of the center roller. The center roll is in contact with the wet paper web, the process water leaving the web, the jet cleaners, and the roll mechanically cleans.

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Components that dirt the central roller enter the process water of a paper and board machine from a variety of sources, such as mechanical pulp, recycled fibers and coated wreckage. The center-roll dirt components are, depending on their origin, ¾ anionic, colloidal, or neutral hydrophobic components.

In addition to cellulose and hemicelluloses, the mechanical pulp is also rich in lignin and extracts which tend to dissolve from the fibers in colloidal form or dispersed in small droplets from the surface of the fiber to the aqueous phase during the manufacturing process.

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Chemimechanical pulps contain dirty colloidal material; since chemimechanical pulping converts lignin and extracts into more soluble form. The hemicelluloses are water soluble and may act like anionic interfering agents, lignin-derived substances are released and dissolved in a manner similar to carbohydrates, and as the pH increases, the lignin-derived substances increase in water solubility.

Extracts of woody pulps consist of triglycerides, stearyl esters, diterpenes and resin acids. The resin and fatty acids are water-stable and anionic compounds which are neutralized as the pH rises and become soluble alkaline salts upon saponification with sodium. The soaps produced are slightly soluble and may dissolve the neutral resin in small drops in water.

Recycled fibers come with sticky-type components that cannot be completely removed from the pulp during the de-inking process. The sticky components may be of synthetic origin such as latexes, adhesive adhesives, hot melt or natural materials such as extraction agents and resins. The inorganic material may also be accompanied by inorganic materials such as pigments, dissolved salts, and readily soluble organic components, such as lignin-based substances, hemicelluloses and starch, and some other soluble components such as dispersants, antifoams, and cleaning agents. When coated wreck is used as a raw material in papermaking, coatings containing binders such as anionically stabilized latex and starch, as well as various pigments to which anionic dispersants are often used, are added to process waters.

A number of prior art solutions have been used to reduce and prevent the transmission of dirt. The central rollers are continuously cleaned by scrapers, ultrasonic scrubbers, carbonated ice blasting, or oscillating scrub heads 30, or are performed during shutdown. The purpose of these methods is to mechanically remove the dirt layer already formed on the surface of the roll, but these methods have little effect on the formation of 3 new dirt layers.

From the foregoing, it can be seen that there is an obvious need for a method which prevents the adhesion and retention of dirt and distractions on a roll, such as a center roll, and keeps the surface of the roll free from dirt and distractions during the process. ?

Purpose of the Invention

It is an object of the invention to provide a method for preventing contamination of a roll of a paper or board machine, especially a central roll, and for keeping the surface of the roll clean during the process.

The features of the method for preventing roll contamination according to the invention and keeping the surface of the roll, especially the center roll clean, are set forth in the claims.

In the method of the invention, a charge space repelling dirt particles is provided on the roll surface. The surface of the roll surface is imparted to a dirt repellent by making the surface of the roll from a material having a dirt repellent charge and / or reverting the roll surface such that the roll surface is continuously restored to a dirt repellent charge.

DESCRIPTION OF THE INVENTION The above objects can be achieved and the problems of the prior art solutions can be avoided or at least substantially reduced by the method according to the invention. It has been found that the charge state of the roll and the charge state of the interfering substances mainly determine the adherence and retention of dirt and interfering substances on the surface of the roll. Thus, the problem of roll fouling can be prevented by adjusting the chemical and physical properties of the roll surface to repel 4 components that cause fouling, i.e., by adjusting the charge surface of the roll.

When the fouling components are hydrophobic and neutral, fouling can be minimized by a hydrophilic roller coating. A hydrate layer is formed on the hydrophilic surface in an aqueous environment, whereby the hydrophobic component is unable to spread or adhere to the surface.

When the dirty components are anionically charged, the roll coating 10 must also have a negative charge, whereby an electrostatic repulsion is created between the roll and the dirt components and no contamination occurs because the dirt particles cannot adhere to the roll surface.

According to the invention, a dirt-repellent roll coating is made which is both hydrophilic and of the same charge as the dirt. Most of the dirt particles are anionic in nature, such as pitch, deodorizing residue, multiple fibers and fillers. In addition to the properties of the surface, the charge behavior of the surface is affected by the environment in which the surface is located. Thus, the surface charge of a roll, especially a center roll, in a paper and board machine is also dependent on the prevailing process conditions such as the pH of the process water and the electrical conductivity.

The almost ideal roll surface is natural granite, which is highly anionic, but for practical reasons, the use of granite rolls is quite limited and so far no granite-like coating has been achieved. Ceramic surfaces of Ke-25 are often quite hydrophilic, so that when they are in an aqueous solution, they get a hydrate layer on their surface. The more hydrophilic the ceramic surface is, the thicker the surface of the hydrate layer gets. The hydrate layer prevents the hydrophobic dirt from sticking to the ceramic surface of the roll itself. Since the charge state of the roll surface is pH dependent, the surface should be negative at least within the pH range of process 30.

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When the surface-charged solid is in the electrolyte solution, an electric bilayer is formed. On the surface of the solid, a stationary layer is formed of ions that are opposite to the surface. A second layer is formed on the surface of the stationary layer which contains both oppositely charged and similarly charged ions, so that the concentration of ions decreases as the surface moves and is able to move in the direction of the surface plane. This layer is called the diffusion layer. The interface between the stationary layer and the diffusion layer is called the slip plane. It is not possible to measure the value of the absolute surface charge of a solid, but instead the surface charge of a slip is measurable and is called the zeta potential.

The isoelectric point (IEP) is a pH value at which the surface has a zeta potential of zero.

At pH values higher than the isoelectric point, the zeta potential is negative and at lower pH values, the zeta potential is positive. Thus, j

The isoelectric point of a roll of 15 negatively charged rolls should be less than 3, so that the surface can be considered suitable for the roll and, in particular, for the center roll, in order to prevent contamination. In addition to the isoelectric point, the value of the zeta potential is also L

to the right level. In this case, the roll must have a negative surface charge, and the zeta potential values of the roll must be of the same order as the interfering agent zeta potential to achieve electrostatic repulsion.

According to the invention, the charge level of the roll surface can be adjusted as desired by the following methods or combinations thereof: 1) Making the surface of the roll initially desired 2) Revitalizing the surface 3) Externally providing the desired charge space to the surface.

Preferably, the surface coloration of the roll surface can be made using the following methods. According to the charge condition, a roller coating of the desired type is suitably prepared on a cast iron body made of ceramic, plastic or combinations thereof.

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The roll coating may also be a polymer-sealed ceramic, a polymer reinforced with ceramic particles, a ceramic-metal alloy to which a polymer or a diamond-like coating has been added. In this procedure, the surface material is selected according to the desired charge state.

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Alternatively, a porous ceramic material and a suitable sealant are selected to provide the desired total charge space to the surface. The porosity of the ceramic surface can also be influenced by selecting suitable ceramic injection parameters.

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As a third alternative, the adhesive layer of the ceramic surface is selected from its charge state so that the charge state of the ceramic surface is desired, wherein the charge state of the adhesive layer affects the charge state of the roll surface through the porous ceramic.

The surface of the roll can be revitalized to the desired surface charge, preferably by the following methods.

New material is introduced into the roll surface by means of the scraping material, whereby the charge state of the surface can be changed by selecting the scraping material appropriately with respect to the roll surface material. Ϊ

The charge surface of the roll surface is continuously changed by spraying a chemical onto the roll surface. The chemical to be injected is selected to be a compound or mixture of compounds that adheres poorly to the surface of the roll but strongly to the dirt. When the dirt contains enough chemical, the aggregates that form the dirt fall off the roll.

The desired charge space can be externally applied to the roll surface by means of an external voltage source. Voltage is applied, for example, between the electrolytes of the center roll and the counter roll, such as a groove roll, or a nearby paper guide roll or jet, which may also optionally contain the 7 chemicals mentioned above, but the bearing housings and fasteners must be carefully insulated.

Combinations of the above methods can also be used to provide a dirt repellent 5 on the roll surface.

Advantages of the Invention

Advantages of the inventive method of adjusting the surface condition of the roll, and preferably of the center roll, to prevent roll contamination are that the process removes dirt before large amounts have been deposited on the roll surface. The dirt is continuously discharged in small quantities and the dirty roller does not require downtime.

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Claims (7)

1. A method for preventing, in advance, contamination of a center roller in a papermaking or cardboard machine, and for keeping the center roller clean, characterized in that a charge state which repels dirt particles is obtained, the state of charge being made repellent surface. the middle roll is made of a material having a dirt repellent loading condition and according to the loading condition, a roll coating on a cast iron body is made of the middle roll of a ceramic, a plastic, a ceramic sealed ceramic, a mixture of a ceramic and a metal, a ceramic particles reinforced polymer or a diamond-like coating. 2. A method according to claim 1, characterized in that the surface of the center roller is regenerated in such a way that the dirt repellent state is continuously restored to the surface of the center roller and / or the dirt repellent state is applied to the surface of the middle roller. 3. A method according to claim 1 or 2, characterized in that a porous sealing material for a ceramic material is selected for the surface of the center roller in such a way that a dirt-repellent sealing charge condition is obtained on the surface. Method according to any one of claims 1-3, characterized in that the charging state of an adhesive layer of the ceramic surface is chosen in such a way that the charging state of the upper ceramic surface is made dirt repellent. A method according to any one of claims 2-4, characterized in that a dirt-repellent material is continuously applied to the surface of the center roller by means of a scraper material. Method according to any one of claims 2-5, characterized in that a spray material is continuously sprayed on the surface 30 of the center roller in such a way that the spray material reacts strongly with dirt, but weakly with the surface of the middle roller and releases together with the dirt from the surface of the roller. middle roll. 7. A method according to any of claims 2-6, characterized in that a dirt-repellent charging condition is achieved from the outside of the middle roll by means of an external voltage source. Method according to any of claims 1-7, characterized in that the surface of the center roller is hydrophilic, the charge state is anionic and the isoelectric point of the center roller is at most 3.