FI114230B - A method for heating web-like material - Google Patents

Description

j 114230

The present invention relates to a method for heating a moving paper or board web during calendering according to the preamble of claim 1.

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The purpose of calendering is to increase the smoothness and gloss of paper or cardboard and to enhance other printing surface properties. When calendering paper and board, the web is formed in a nip formed by two opposing rolls. Variables affecting the calendering result include: the temperature and humidity of the web to be calendered, as well as the pressure and compression time applied to the web at the nip.

The temperature and humidity of the web to be calendered particularly affect the surface properties of the paper, i.e. gloss. High temperatures soften the substances on the surface of the paper, making them easier to process. In high humidity, the softening temperature of the paper 15 components decreases. If the temperature and humidity of the web entering the calender are not high enough, the temperature of the web can be increased by heated thermo rolls and the humidity by water or steam wetting devices.

Compression pressure and compression time particularly affect the smoothness and density of the paper. Ideally, the compression pressure smoothes the tops of the paper but does not over-tighten the paper structure. Compression time affects the permanence of the change. The compression pressure depends on the nip. · ·, The line load used, the roller diameters and the elasticity of the roll coating.

• Il. · ·. The pressing time depends on the length and number of nipples and the speed of the calender.

• · *. ' * '. 25 Thermal rolls used to heat the calendering web are generally manufactured

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of iron and may be heated with oil, steam, or other means, for example, • '·; duktiokuumentamalla. The heating medium circulates longitudinally in the drill bore

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: ". * In full holes. Up to half of the heat introduced into the thermo rolls may be dissipated by the roll. . \ from the diaper surface directly to the environment without participating in the calendering process. Typically. * '*. The thermal input of 30 thermal rollers is 50-70 kW / meter of width, so the heat roll has a shark,. ' high power output and high heat loss costs. In addition,

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\. The lan has a complex structure due to heating ducts, media heating and recycling devices, and is expensive to manufacture.

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In high-speed machines, the thermal rollers only heat the surface of the web, which means that larger line loads need to be applied to the calender nipples. This causes excessive compaction and bulk loss of the web.

The object of the present invention is to provide a novel method by which the web material can be heated for calendering.

The invention is based on adding capsules to the web prior to calendering which are broken by pressure, temperature or other external factors during calendering or shortly before calendering. The capsules contain the first substance or compound which, upon breaking of the capsules, enters the web material. The substance or compound contained in the capsules is reacted with another substance or compound. The substance or compound contained in the capsules and the other substance or compound are chosen such that the reaction between them releases heat energy, i.e. the reaction is exothermic. Releasing! thermal energy in turn heats the web. Capsules may be added, for example, to the coating composition and / or to the mass in the headbox.

More specifically, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1.

»» »I» • »» i ;; The invention provides considerable advantages.

I * k * • <* • f • ·.! By means of the invention, the web to be calendered is heated internally by the heat generated by the reaction of the substance or compound contained in the capsules. In this case, the heating power of the thermo rolls can be reduced, which in turn reduces the caloric loss and so on; and the cost of calendering. Possibly

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. · * \ Even some types of thermo rolls can be replaced by other types of rolls, which makes it * * * 'calenderable. ri is simpler and cheaper to manufacture. Capsules can be placed • · ». § · 30 such that their distribution changes in the thickness direction of the paper so that the heating power is • »t; # different size across the web and loss of sweat can be better managed.

The invention will now be described in more detail with reference to the accompanying drawings.

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Figure 1 is a side elevational view of a multi-roll calender.

Figure 2 is a cross-sectional view of the web entering the calender of Figure 1.

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The multi-roll calender shown in Fig. 1 comprises an upper 1 and a lower roll 2, and intermediate rolls 3 disposed therebetween. The calendering web 4 passes through the overlapping nipples N. The direction of the web is indicated by an arrow. Usually, one of the nip forming rolls is a 10 heatable roll and a second soft surface roll. The web 4 is pressed into nipples N to increase the smoothness and density of the paper. Typically, the nip pressures used in calender nipples are between 5 and 80 MPa. The line loading of the nipples can be varied by loading cylinders 5 acting on the lower 1 and / or upper roll 2.

! Prior to calendering, capsules 8 are added to the web 4 which contain a substance or compound which, when reacting with another substance or compound, generates heat. The capsules 8 are disintegrated by the nip pressure during the calendering step as the web 4 passes through the calipers N, whereby the substance or compound contained in the capsules 8 is released from the capsules 8 into the web material. The substance contained in the capsules 8 is then reacted with another substance or compound. The substance contained in the capsules 8 and the second substance are selected so that when they react with each other, heat is exothermic; by that reaction. The heat released in the reaction warms the web 4.

In Figure 2, the capsules 8 are disposed in the web 4 during the coating step. Capsules 8 are added *>. · ·, 25 before the coating composition is applied to the web 4. Then

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the capsules 8 have a coated width of the web 4. Application and pouring of coating mixture:.:. The dressing may be performed by any conventional method. Capsules 8 added to the coating composition are contained in the coated surface portions 6 of the web, which causes the web 4 to become warmer than the central portion 7 as the capsules 8 are disintegrated. 4 such that the heat released by the reaction of the substance in the capsules 8 and the other material increases the temperature of the web 4 by about 10 ° to 15 ° C. The web 4 warms at least at the width where the capsules 8 are placed. 114230 4 heating to the final calendering temperature is generally accomplished by calender thermo rolls.

Alternatively, the capsules 8 may be added to the pulp 5 used to make the web 4 in the headbox of a paper or board machine. In this case, capsules are provided over the entire width of the web 4. If the headbox is so called. a multi-layered headbox, from which the pulp is fed in several layers, can be filled with the desired number of capsules in each layer 8.

In this case the capsule) and the heating power obtained from the capsules in the thickness direction of the web 4 can be varied. A similar effect is obtained if the capsules 8 are added both to the coating mixture and to the mass in the headbox. Generally, it is preferred that the surface portions of the web 4 have more capsules 8 than the central portion of the web, whereby the surface portions warm up more than the central portion.

The diameter of the capsules 8 ranges from 0.1 to 100 µm, preferably from 0.2 to 2 µm. The shell portion of the Kap-15 rib 8 has a wall thickness of 0.01 to 5 µm, preferably 0.02 to 0.05 µm. Suitable ingredients for the shell component include, for example, synthetic polymers, cellulose derivatives, gelatin, starch, resins, paraffins and silicones. Methods for making capsules 8 are described, for example, in U.S. Patents 4,157,983 and 4,020,210.

The material contained in the capsules 8 should be a sufficiently non-toxic and neutral material or compound that does not interfere with the web production process. The capsules 8 contain, for example, sodium hydroxide (NaOH) or calcium chloride (CaCl 2), which upon disintegration of the capsules 8 react with the moisture / water contained in the web 4 to release heat. Provided

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, ': The amount of sodium hydroxide or calcium chloride contained in the capsules 8 is about 1 g / m 2 of the surface area of the web 4: 25 g / m, the web having a basis weight of about 50 g / m warms with 10-15 ° C. The water reacting with sodium hydroxide or calcium chloride is generally moisture in the web 4, but may be added to the web 4 in capsules 8 similar to sodium hydroxide, if necessary; Bridged or calcium chloride.

C: 30: ·. In another embodiment of the invention, the capsules 8 to be inserted into the web 4 are filled with explosive materials.

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, *. : a substance which, upon breaking of the capsule 8, reacts with oxygen in the ambient air to generate heat. One substance of this type is the cotton ball. When using an explosive 5114230, the heat production may be up to ten times the heat production of an equivalent amount of sodium hydroxide or calcium chloride.

The shell portion of the capsules 8 is so strong that it can withstand, prior to the calendering step, the stresses exerted upon them, for example during the preparation, application and scraping of the coating composition. The capsules 8 are disintegrated during the calendering step because the compression of the calendering nipples N on the web 4 is significantly higher than the loads indicated above. Typically, capsules 8 will disintegrate at a pressure of 5 to 80 MPa.

The invention has embodiments different from those described above.

Heat may be used instead of or in addition to compressing the capsules 8, for example. The other substance or compound involved in the exothermic reaction may also be placed in capsule lenses to be added to the web 4 to be degraded during the calendering step.

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Claims (7)

114230 A method for heating a web-like material (4) during a calendering step, characterized in that: 5. adding capsules (8) containing a first substance or compound which produces heat upon reaction with the second substance or compound, to the web (4); ) in the calendering step, and - reacting the first agent with the second agent or compound. 10 Method according to Claim 1, characterized in that the capsules (8) are added to the coating composition prior to application of the coating composition to the web (4). Method according to claim 1 or 2, characterized in that the capsules 15 (8) are added to the pulp in the headbox of the paper or board machine. Process according to Claim 1, characterized in that sodium hydroxide (NaOH) or calcium chloride (CaCl 2) is used as the first substance or compound. . \ 20 The process according to claim 1 or 4, characterized in that the second. *: ·. the substance contained in the web (4) is used as the substance or compound. • ''; Method according to claim 1, characterized in that the web (4) is heated to 10-15 ° C. • ·: 1 A method according to any one of the preceding claims, characterized in that the capsules (8) are disrupted by the nip pressure present in the nip (N) of the calender. »T · * ·» * · 1 · • »» »· 114230