Method and production line and for producing fiber webs

Abstract

 The invention relates to a method for producing a fiber web, in which the fiber web (W) is surface sized with starch or other sizing agent in a sizer (20) and in which the fiber web (W) is calendered or correspondingly treated by contacting press-treatment. The fiber web is surface sized by applying low soluble starch, such as maize starch or wheat starch or barley starch or rice starch, or other sizing agent that is low soluble or not re-soluble in moisturizing. The invention also relates to a production line for producing fiber webs which comprises a sizer (20) for surface sizing the fiber web (W) with starch or other sizing agent in a sizer and a calender (40; 60) or corresponding treatment device for calendering or correspondingly treating by contacting press-treatment the fiber web (W). The sizer (20) is provided with application means for surface sizing the fiber web (W) by applying low soluble starch, such as maize starch or wheat starch or barley starch or rice starch, or other sizing agent that is low soluble or not re-soluble in moisturizing.

Description

[0001] The invention relates to producing fiber webs, in particular paper and board webs. Especially the invention relates to a method for producing fiber webs according to the preamble of claim 1 or 2 and to a production line for producing fiber webs according to the preamble of claim 14.

[0002] As known from the prior art in fiber web producing processes typically comprise an assembly formed by a number of apparatuses arranged consecutively in the process line and forming process steps. A typical production and treatment line comprises a head box, a wire section and a press section as well as a subsequent drying section and a reel-up. The production and treatment line can further comprise other devices and/or sections for finishing the fiber web, for example a sizer, a pre-calender, a coating section, a final-calender. The production and treatment line also comprises at least one slitter-winder for forming customer rolls as well as a roll packaging apparatus. In this description and the following claims by term fiber web are meant for example a paper and board webs.

[0003] In production of fiber webs, for example of paper or board webs, sizing is used to alter the properties of a fiber web by adding sizing agents, for example starch or other sizing agents. In surface sizing the sizing agent is added onto the surface of the fiber web at the dry end of the fiber web machine. Surface sizing is used in production of many fiber web grades, for example of uncoated fine papers and of several board grades.

[0004] Pre-calendering is typically used for creating required surface properties for further treatment for example for coating. Final-calendering is generally carried out in order to improve the properties, like smoothness and gloss, of a web-like material such as a paper or board web. In calendering the web is passed into a nip, i.e. calendering nip, formed between rolls that are pressed against each other, in which nip the web becomes deformed as by the action of temperature, moisture and nip pressure. In the calender the nips are formed often between a smooth-surfaced press roll such as a metal roll and a roll coated with resilient material such as a polymer roll or between two smooth-surfaced rolls. The nips can be formed also by using instead one of rolls a belt or a shoe as known from prior art. Many different kinds of calenders to be used as a pre-calender and/or as an final-calender are known, for example hard nip calenders, soft nip calenders, supercalenders, metal belt calenders, shoe calenders, long nip calenders, multinip calenders etc.

[0005] Further web treatment producing web smoothing effect can be done in various hot pressing contact treatment processes, like Condebelt -drying, BoostDryer -drying, metal belt drying or treatment, Yankee cylinder drying, MG-cylinder drying etc. cylinder drying.

[0006] In web treatment processes where smoothening is desired the applied heat can be used to raise the surface temperature of the fiber web to glass transition temperature, which causes the fibers to soften and conform to the surface of the roll. Moisture, for example water or steam can also be added before the nip to the surface to be treated to further lower the glass transition temperature. Thus the gradients in the temperature and moisture level tend to lower the glass transition temperature preferentially on the external surfaces of the fiber web and allow the web to achieve a desired smoothness without significant reduction in caliber.

[0007] In calendering and corresponding web treatment processes of moistened or moist fiber web, which has been sized with water soluble sizing agent like starch, a disadvantage is that the starch and associated fibers tend to pick and stick on the heated calender rolls and corresponding heated metal surfaces contacting the fiber web. This tends to be aggravated at higher nip loads and temperatures required for achieving high smoothness levels. The sticking and fiber pulling are caused by dissolving of starch or other binders that are added in to the web and may lead to runnability problems, roll contamination and calendered or treated quality reduction

[0008] In the contact drying or hot contact treatment processes the surfaces can be contamined by stickies, fiber picking and binders in the web. In the beginning of drying section the web is wet (moist) which aggravates the problem.

[0009] In US patent publications 6645349 and 6905573 it is disclosed a method to use roll surface monitoring systems, for example camera systems, to detect the roll picking and contamination and control roll cleaning operation.

[0010] In WO publication 99/25921 is disclosed a method for detecting contamination that runs through a nip or nips in a calender, in which method vibrations occurring in connection with the constructions of calender are detected and processed. The source of unusual vibrations is located, which makes it possible to start eliminating the contaminations or to replace the damaged part.

[0011] In US patent publication 6274001 is disclosed a calendering method in which lubricant is applied to both sides of the web to prevent fiber sticking/picking in the hot nip. The lubricant may be applied by the sizer, by the moisturizing showers or by separate lubricant showers.

[0012] In US patent publications 3145116, 5114999 and 6300393 are disclosed some known examples of insolubilizers for starches and coating binders and surface sizes.

[0013] In fiber web production when fiber web is surface sized with water soluble starch and dried, the dried starch film easily dissolves in connection with moisture addition and can stick to the contacting surfaces. In pilot scale test is has been detected that even a small amount of starch deposits on roll surfaces can cause quality loss of a fiber web for example due to decreased smoothness. Due to the high water solubility of the starch the moisture addition before calendering has not been possible.

[0014] As known, the reactive part of a starch molecule is a hydroxyl group due to which one of the basic properties of starch is water solubility. Dried starch in sized fiber web is soluble in water and thus it sticks to for example calender rolls, if water is applied. This is preventing the use of water moisturizing in calendering of starch sized fiber webs even though the moisturizing before calendering would be very advantageous particularly due to enhanced moisture gradient calendering effect.

[0015] The water solubility of starch can be decreased by modifying starch or by adding chemicals that prevent solubility. It is known for example to decrease water solubility of a starch based binding agent of a coating medium by the above means in order to prevent starch dissolving due to water based printing colors in offset printing or to improve wet rub-off properties of fiber webs.

[0016] Sticking and picking problems at heated calender rolls may also occur with other sizing agents especially when moisturizing and/or high moisture content before calendering is used.

[0017] Paper and board are available in a wide variety of grades and can be divided according to basis weight in two categories: papers with a single ply and a basis weight of 25 - 300 g/ m² and boards manufactured in multiply technology and having a basis weight of 150 - 600 g/ m². It should be noted that the borderline between paper and board is flexible since board grades with lightest basis weights are lighter than the heaviest paper grades. Generally speaking, paper is used for printing and board for packaging.

[0018] The subsequent descriptions are examples of some values presently applied for fibrous webs, and there may be considerable variations from the disclosed values. The descriptions are mainly based on the source publication Papermaking Science and Technology, section Papermaking Part 3, edited by Jokio, M., published by Fapet Oy, Jyväskylä 1999, 362 pages.

[0019] Mechanical-pulp based, i.e. wood-containing printing papers include newsprint, uncoated magazine and coated magazine paper.

[0020] Newsprint is composed either completely of mechanical pulp or may contain some bleached softwood pulp (0 - 15 %) and/or recycled fiber to replace some of the mechanical pulp. General values for newsprint can be regarded as follows: basis weight 40 - 48,8 g/m², ash content (SCAN-P 5:63) 0 - 20 %, PPS s10 roughness (SCAN-P 76:95) 3,0 - 4,5 µm, Bendtsen roughness (SCAN-P 21:67) 100 - 200 ml/min, density 200 - 750 kg/m³, brightness (ISO 2470:1999) 57 - 63 %, and opacity (ISO 2470:1998) 90 - 96 %.

[0021] Uncoated magazine paper (SC=supercalendered) usually contains mechanical pulp to 50 - 70 %, bleached softwood pulp to 10 - 25 %, and fillers to 15 - 30%. Typical values for calendered SC paper (containing e.g. SC-C, SC-B. SC-A/A+) include basis weight 40 - 60 g/m², ash content (SCAN-P 5:63) 0 - 35 %, Hunter gloss (ISO/DIS 8254/1) < 20 - 50 %, PPS s10 roughness (SCAN-P 76:95) 1,2 - 2,5 µm, Bendtsen roughness (SCAN-P 21:67) 100 - 200 ml/min, density 700 - 1250 kg/m³, brightness (ISO 2470:1999) 62 - 70 %, and opacity (ISO 2470:1998) 90 - 95 %.

[0022] Coated magazine paper (LWC = lightweight coated) contains mechanical pulp to 40 - 60 %, bleached softwood pulp to 25 - 40 %, and fillers and coaters to 20 - 35 %. General values for LWC paper can be regarded as follows: basis weight 40 - 70 g/m², Hunter gloss 50 - 65 %, PPS s10 roughness 0,8 - 1,5 µm (offset), 0,6 - 1,0 µm (roto), density 1100 - 1250 kg/m³, brightness 70 - 75 %, and opacity 89 - 94 %.

[0023] General values for MFC (machine finished coated) can be regarded as follows: basis weight 50 - 70 g/m², Hunter gloss 25 - 70 %, PPS s10 roughness 2,2 - 2,8 µm, density 900 - 950 kg/m³, brightness 70 - 75 %, and opacity 91 - 95 %.

[0024] General values for FCO (film coated offset) can be regarded as follows: basis weight 40 - 70 g/m², Hunter gloss 45 - 55 %, PPS s10 roughness 1,5 - 2,0 µm, density 1000 - 1050 kg/m³, brightness 70 - 75 %, and opacity 91 - 95 %.

[0025] General values for MWC (medium weight coated) can be regarded as follows: basis weight 70 - 90 g/m², Hunter gloss 65 - 75 %, PPS s10 roughness 0,6 - 1,0 µm, density 1150 - 1250 kg/m³, brightness 70 - 75 %, and opacity 89 - 94 %.

[0026] HWC (heavy weight coated) has a basis weight of 100 - 135 g/m² and can be coated even more than twice.

[0027] Pulp-produced, wood free printing papers or fine papers include uncoated - and coated - pulp-based printing papers, in which the portion of mechanical pulp is less than 10 %.

[0028] Uncoated printing papers (WFU) contain bleached birch wood pulp to 55 - 80 %, bleached softwood pulp 0 - 30 %, and fillers to 10 - 30 %. The values with WFU have a large variation: basis weight 50 - 90 g/m², Bendtsen roughness 250 - 400 ml/min, brightness 86 - 92 %, and opacity 83 - 98 %.

[0029] In coated printing papers (WFC), the amounts of coating vary widely in accordance with requirements and intended application, the following are typical values for once- and twice-coated, pulp-based printing paper: once-coated basis weight 90 g/m², Hunter gloss 65 - 80 %, PPS s10 roughness 0,75 - 2,2 µm, brightness 80 - 88 %, and opacity 91 - 94 %, and twice-coated basis weight 130 g/m², Hunter gloss 70 - 80 %, PPS s10 roughness 0,65 - 0,95 µm, brightness 83 - 90 %, and opacity 95 - 97 %.

[0030] Release papers have a basis weight within the range of 25 - 150 g/m².

[0031] Other papers include e.g. sackkraft papers and wallpaper bases.

[0032] Board making makes use of chemical pulp, mechanical pulp and/or recycled pulp. Boards can be divided e.g. in the following main groups cartonboards, containerboards and specialty boards. Cartonboards are mainly used for consumer product packaging and they comprise boxboards, used for making boxes, cases, which boxboards include e.g. liquid packaging boards; FBB = folding boxboard, WLC = white-lined chipboard, SBS = solid bleached sulfate board, SUS = solid unbleached sulfate board and LPB = liquid packaging board. Containerboards comprise f. ex. linerboard and fluting board and other corrugated boards and specialty boards comprise wallpaper base, plaster board etc. Graphic boards are used for making e.g. cards, files, folders, cases, covers, etc. and wallpaper bases. Each end use sets its own demands on the mechanical and functional properties of boards. Basically a certain mechanical strength and stiffness, especially bending stiffness is required, and in the optimum structure middle-ply is very bulky, and top and back plies have high modulus of elasticity. Often also purity and cleanliness requirements are very high and also almost all boards have defined printing properties and for example the printing requirements of folding box board are usually very high and also high bulkiness is required of folding box board.

[0033] As known temperature and moisture gradient calendering utilize the Z-directional temperature and moisture profiles in the fiber web. The fiber plasticization, and therefore the deformation of web structure in calender nip compression, is more concentrated to the surface layers due to favorably adjusted moisture and temperature profiles in Z-direction. Particularly the moisture gradient calendering can offer very high smoothness while maintaining the inner web structure less compacted and thus keeping the bulk at a reasonable level. In the moisture gradient calendering the moisture gradient is in practice obtained by first drying the paper web to sufficiently dry and then applying water on to the web surface. Water is applied usually by water showers (spray nozzles). Water can be applied also by steam boxes (or pipes) and letting the steam to condensate at web surface, giving some moistening effect. Application of external water results almost always high moisture content at the surface. Moisture gradients in web thickness direction may arise also from one-sided heating, for example in Condebelt drying, hot metal belt and hot drying cylinder contacts. Moisture is transported from the hot side towards cooler side, and possibly condensing there at the cooler surface. In this case, redistribution of internal water results high local moisture content at the surface.

[0034] Starch sizing is used in order to improve paper web properties, in particular water resistance, water absorption properties, strength, internal strength and bending stiffness. In addition, runnability as well as dusting tendency can be affected favorably.

[0035] Starch based sizes, among some other sizing agents, are known to be water soluble. This will pose a major problem in moisture gradient calendering when sized paper is first moistened and soon after that calendered. It has been observed, that moistening of starch sized webs prior to hot calendering leads to problems like sticking, starch picking and deposit building on the calender roll surfaces. It is believed, that the applied water is dissolving the dried starch film in the web surface layers. The dissolved starch can be transported, particularly with water movement, into a direct contact with roll surface. The mechanism of sticking and picking is not well known, but it can be assumed, that at hot roll surface the water is evaporated while the size (binder) remains at the surface contact. The binder is adhered to and possibly held by sticky bonds at the metal surface.

[0036] The root cause to the roll picking seems to be the water dissolving property of the binder. In order to solve the root cause in practical applications, it is important understand the binder chemistry in relation to its water dissolution.

[0037] For example, the source of starch, the ways of modifying starch, the use of various insolubilizers and way of dosing then is significantly affecting the water resistance and dissolution properties of starch. The root cause, the starch dissolution to water, can be approached in different ways. The most obvious solution is to use as small amounts of water as possible, but this is diminishing the benefits of the moisture gradient calendering. Ultimately, the starch dissolving and picking at the calender can be prevented when the process is arranged in such way that starch and water are not brought together in to a contact before calendering. If water-soluble starch needs to be used, sizing must then be done after the water-critical calendering.

[0038] An object of the invention is to create a method and a production line for producing fiber webs in which the above problems and disadvantages are eliminated or at least minimized.

[0039] A particular object is to prevent starch sticking from wet / moistened fiber web into the contacting surfaces, particularly hot drying surfaces and hot calendering surfaces.

[0040] In order to achieve the above objects the method for producing fiber webs according to the invention is mainly characterized by the features of claim 1 or 2 and the production line for producing fiber webs according to the invention is mainly characterized by the features of claim 14.

[0041] According to advantageous aspect of the invention to prevent or reduce starch dissolution chemicals (like insolubilizers) or other means, like starch modification is used. Preferably the soluble binder, like starch, is partially or fully, is replaced with other less soluble sizing agents. The sizing agent can also be a sizing agent with an insolubilizer additive for decreasing the solubility.

[0042] According to further advantageous aspects to prevent the binder from sticking to rolls, additional chemicals, like lubricants, roll surface passivation agents or cleaning chemicals, are applied either directly on the web, or mixed with moistening water or applied directly to the roll surface or mixed with sizing agent.

[0043] According to one aspect of the invention in production of fiber webs, in which the fiber web is surface sized and moisturized by water and/or by steam and calendered or correspondingly treated by pressure, the fiber web is surface sized by applying low soluble starch, such as maize starch or wheat starch or barley starch or rice starch, or other sizing agent and the fiber web is moisturized and treated by contact pressure treatment, for example by calendering or drying. The starch can be natural starch or genetic modified starch.

[0044] Many starch properties, like viscosity, solubility and strength building characteristics are inherited from the starch composition and chemical structure at the molecular level. For example, the proportions of the amylose and amylopectin molecules, the degree of polymerization, and molecular weight of the polymer structure affect the end use properties. As is well known, the chemical nature and therefore the end use properties vary greatly depending on the source of the starch, for example giving higher solubility to the potato starch due to the higher amylopectin proportion, more branched molecular chains and in general more loose amorphous macromolecular structure.

[0045] The chemical structure and chemical characteristics of the starch can be modified also using means of genetic modifications. In this way, using genetically improved starch, it is possible to increase desired functionality and properties, like strength, and remove the less desired features, such as water solubility.

[0046] In order to avoid or reduce sizing agent dissolving and picking to the process surfaces, it is advantageous to keep the internal moisture content in the web as low as possible during the moistening and calendering stages of the sized web. Particularly, the lower base sheet moisture is reducing the picking risk and enhancing the moisture gradient calendering effect.

[0047] According to an advantageous aspect of the invention to prevent sizing agent to dissolve and pick to the process surfaces in fiber web treatment process, in which process fiber web is sized, and dried and possibly moisturized and thereafter treated in a contact treatment process, like calendering, after the sizing the fiber web is dried to the dryness 8% or less, preferably to 5 % or less, before the web is moistened and / or treated in surface treatment process, for example calendered.

[0048] According to one aspect of the invention in production of fiber webs, a starch size with chemical additive decreasing water solubility of the dried starch size is applied into the web and the fiber web is dried in which
in at least one process step following the sizing water is added into the fiber web by water moisturizing means or by steaming means of by other corresponding moisturizing means, and/or
in at least one process step following the sizing the fiber web is treated by a hot surface contacting a side of the fiber web that is moist and sized, and/or
in at least one process step following the sizing the fiber web is dried and/or calendered by a hot surface.

[0049] According to an advantageous features in the method the calendering or treating the web by a hot surface; the surface temperature is in belt calendering 100 - 200 °C, in roll nip calendering 1 30 - 350 °C, in cylinder or belt drying 80 - 200 °C is and the sizing is internal or surface sizing.

[0050] According to advantageous features sizing amount is per side 0,1 - 5 g/m² (solids), preferably for paper webs per side 0,1 - 2 g/m² and for board webs per side 0,5 - 3 g/m², web ingoing moisture 4 - 10 %, preferably 5 - 8 %, water application (moistening) 1 - 3 g/m² for paper webs for one side of the web and 2 - 6 g/m² for board webs for one side of the web, thermo roll temperature 130 - 350 °C, preferably 17 5 - 250 °C.

[0051] According to an advantageous feature at least one of the calendering surfaces is provided by oil-heated roll, and the sizing is internal or surface sizing.

[0052] According to one aspect the hot calendering is done by surfaces, wherein at least one of the surfaces is a high surface temperature roll, preferably a hot oil heated thermo roll, which has surface temperature over 150 °C, preferably over 175 °C. According to a very adv antageous feature the hot roll is a high power shrink fitted thermo roll.

[0053] According to one aspect the calendering is done with metal belt calender, wherein the temperature of the metal belt is 100 - 200 °C.

[0054] According to one aspect the fiber web is dried and calendered in a metal belt contact zone, wherein at least one of the surfaces has surface temperature 100 - 200 °C. According to one aspect of the invention the water solubility of starch is decreased by additives provided in sizing process to create water resistant starch sizing in connection with hot calendering. In hot calendering the temperatures of calender rolls can be 130 °C - 350 °C and the rolls are advantageously heated by oil circulation. By the improved water resistance it is further possible to use water moisturizing. This provides for great quality advantages in particular in hot calendering. For example smoothness is improved, raw material can be saved and process can be designed simpler.

[0055] According to one aspect the additive decreasing water solubility of starch creates covalent or hydrogen bonds with the hydroxyl groups of the starch and/or works as a cross-linker. The additive is activated after it is applied by drying of the sized fiber web and by effect of the temperature. When activated, the additive creates bonds with the hydroxyl groups in the starch, cross-linking and passivizing the hydroxyl groups and thus preventing the adherence of water molecule bonding with them.

[0056] According to one inventive aspect a low soluble starch, for example corn starch, rice starch or wheat starch, or other sizing agent that is less soluble in moisturizing is used as sizing agent and thus sticking of the binder or sizing agent to the calender rolls or other corresponding contacting surface of a treatment device is avoided.

[0057] According to one advantageous feature the moisturizing is provided by water spray means just before calendering.

[0058] According to one aspect of the invention the sizing agent applied on the fiber web is modified by adding insolubilizers and thus the dissolving and sticking of sizing agent onto the surfaces of calender rolls and other corresponding process surfaces of fiber web production line devices is decreased. When less soluble starch or sizing agent is used it is possible to use increased moisture addition and thus for example better calendering results are achieved.

[0059] According to an advantageous feature of the invention as additives for decreasing the solubility of starch or other sizing agent insolubilizers are used, for example zirconium based salts, such as AZC (Ammonium Zirconium Carbonate) or PZC (Potassium Zirconium Carbonate) or Glyoxal resins can be used. Also formaldehyde resins or CMC, polycarboxylic acids like citric acid can be used as insolubilizers.

[0060] According to an advantageous feature of the invention the surface sizing is done with spray sizing but also other sizing methods can be used.

[0061] According to an advantageous feature of the invention the fiber web production comprises following steps: sizing with starch or sizing agent with insolubiliser additive, drying of fiber web at drying section, moisturizing and calendering or corresponding contacting press treatment.

[0062] According to an advantageous feature of the invention the fiber web production comprises following steps: sizing with starch with additives decreasing water solubility, drying, water moisturizing and hot calendering.

[0063] According to an advantageous feature of the invention the fiber web production comprises applying starch or other sizing agent with additive insolubilizer on the fiber web before moisturizing at calender or before calendering.

[0064] According to an advantageous feature of the invention the fiber web production comprises following steps: sizing with starch or sizing agent with insolubilizer additive, contactless drying, contact drying or metal belt treatment or calendering.

[0065] According to one aspect of the invention the surface sizing with starch or other sizing agent is performed after calendering. Thus the sticking problems are avoided. Even though the sizing may increase the surface roughness, this can be compensated by calendering the fiber web to higher smoothness level than desired and thereafter by sizing reach the desired smoothness level. Particularly, a high solids content starch can be used to minimize the added water amount, thus reducing re-swelling and roughening of the fiber web.

[0066] According to an advantageous feature of the invention the fiber web production comprises following steps: internal (stock) sizing of the base fiber web with starch or other sizing agent, drying, calendering or corresponding contacting press treatment and surface sizing.

[0067] According to an advantageous feature of the invention the fiber web production comprises following steps: internal (stock) sizing of the base fiber web with starch or other sizing agent, drying, calendering or corresponding contacting press treatment, surface sizing, coating and final-calendering.

[0068] According to an advantageous feature as surface sizing method for example a film size-press, a spray-sizer or a pond-sizer can be used.

[0069] According to an advantageous feature as calender for example a hard nip calender, a soft calender, a multinip calender, a wet stack calender or a metal belt calender or a shoe calender can be used.

[0070] According to an advantageous feature moist fiber web is dried by contact drying and/or by belt drying.

[0071] According to an advantageous feature the surface sizing is performed in high dry solids content so that less water is applied on the surface of the fiber web. The solids content level is during sizing preferably 10 - 25 %. Thus the roughness increase after sizing is less. The sizing can even have a smoothness increasing effect if sizing is combined with a wet stack calender or with a hard nip calender.

[0072] According to some further aspects of the invention sticking problems can be decreased by using passivation and/or lubrication chemicals applied on the surface of the calender roll or the corresponding surface with sticking problems or by adding the passivation and/or lubrication chemical into the moisturizing agent at calender or before calender or by adjusting temperature and moisture amount. Lubricants or passivation chemicals can be: directly applied to the web before calendering, mixed with surface sizing agent, mixed with moisturizing water or directly applied to the calendering surface.

[0073] According to an advantageous feature of the invention as passivation and/or lubrication chemicals mineral oil or stearates can be used.

[0074] According to an advantageous feature of the invention the temperature of the web at ingoing to the calendering is 20 - 80°C, preferably 30 - 50 °C.

[0075] According to an advantageous feature of the invention drying temperature of the sized web is over 60 °C, preferably over 80 °C, which ensures rapid curing of insolubilizers, added to the web.

[0076] According to an advantageous feature of the invention the size treated web is arranged to stay under drying conditions where the temperature is over 60 °C at least for 2 seconds.

[0077] According to an advantageous feature the size treated web is dried with high temperature impingement drying or in contactless airborne drying, preferably flotation dryer.

[0078] According to one example of the invention less soluble starch, for example corn starch, and minimized moisture amount, for example less than 2 g/m², and high roll temperatures, for example over 175 °C, advantageously over 200 °C, and optionally passivation and /or lubrication chemicals are used in combination to eliminate sticking problems.

[0079] The different advantageous aspects and features described above and in the claims can be combined in various ways to achieve further advantages.

[0080] By the invention many advantages are achieved for example sticking problems are eliminated, dust problems are minimized, increased cleanliness and better runnability is achieved. Also the lifetime of treatment device roll or belt, or their coatings is increased, since wearing and damaging pick due to sticking is decreased. The invention also makes it possible to use water moisturizing in increased amounts, and particularly enhanced moisture gradient calendering in hot calendering in production of starch sized fiber webs. Various kinds of calender types are utilizable, for example long nip calendering. The possibility of moisturizing also makes the calendering more efficient and thus quality results and production capacity improve. Further, the water resistance and strength properties (like surface strength and bending stiffness) of the fiber web are improved without reduction of water absorption or plasticization properties of the fiber web. Since by the passivation treatement of the starch, only the water solubility of the starch is reduced but the water absorption and hygroscopic nature of the fiber web is retained. The invention also provides the possibility of replacing more expensive sizing agents by starch in production lines comprising water moisturizing. Further important benefit is the possibility of controlling curl, controlling one-sidedness and/or web profiling by water moisturizing of starch sized fiber webs.

[0081] In the following the invention is described in more detail with reference to the accompanying drawing

in which in table 1 are listed some properties of dried starch films, and in which

in figure 1 is schematically comparison of starch picking test with two sheet base moistures, 5 and 10% respectively, before moisturizing and test result shows that higher base moisture indicates much higher picking,

in figure 2 is schematically shown test results of picking at various sizing amounts, using potato starch 0, 2.5, 3.5 g/m2 (dry solids) on each side, in the test sheet moisture was 10 % before moisturizing and test results show that higher starch amount results much higher picking,

in figure 3 is schematically shown comparison of starch source test: potato vs. corn starch in the test surface sizing amount was 2 g/m2, sheet base moisture was 8 % before moisturizing and moisturizing levels were 0 and 3 g/m2 and calendering was done at 150 °C,

in figure 4 is schematically shown test results indicating the insolubilizer effect on calender roll picking, in the test sheets were sized with potato starch 2.1 g/m² with and without glyoxal insolubilizer and the sheet moisture was 8 % before moisturizing,

in figure 5 is schematically shown an example of a production line for producing fiber webs, which is an on-line paper or board making line for producing uncoated web,

in figure 6 is schematically shown an example of a production line for producing fiber webs, which is an on-line paper or board making line for producing coated web,

in figure 7 is schematically shown an example of a production line for producing fiber webs, which is an on-line paper or board making line with sizing for producing uncoated web,

in figure 8 is schematically shown an example of a production line for producing fiber webs, which is an on-line paper or board making line with sizing, for producing coated web,

in figure 9 is schematically shown an example of a production line for producing fiber webs, which is an off-line paper or board making line with sizing and coating,

in figure 10 is schematically shown an example of a production line for producing fiber webs, which is an off-line paper or board making line with sizing,

in figure 11 is schematically shown an example of a production line for producing fiber webs, which is an on-line paper or board making line with sizing,

in figure 12 is schematically shown an example of a production line for producing fiber webs, in which is an on-line paper or board making line with sizing and coating,

in figure 13 is schematically shown an example of a production line for producing fiber webs, in which is an on-line paper or board making line with integrated sizing, smoothening contact treatment, coating and calendering

in figure 14 is shown table 1.

[0082] In table 1 are listed some properties of dried starch films obtained from various cooked native starches and there are differences in solubility of different starch types, as can be seen from Table 1. For example potato starch and tapioca starch have high solubility but for example maize starch and wheat starch have lower solubility. In addition it is noted that rice starch is of low solubility. The applicant has noted in trial tests that potato starch that has high solubility in water tends to stick after moisture addition to calender rolls more easily than maize starch that has lower solubility. The potato starch has been found to stick after 1 - 2 g/m² or more moisture addition but the maize starch only after 2 - 4 g/m² or more moisture addition in hot calendering contact. As previously explained in fiber web production where the fiber web is surface sized and thereafter moisturized at calendering or before calendering the starch types having high solubility in water proved in applicant's trial test to increase sticking problems and the starch types having low solubility in water solution proved to have decreased sticking problems.

[0083] Applicant has performed some trial tests and in figures 1 - 4 are schematically presented some results.

[0084] Starch dissolving and roll picking in a moisture gradient calendering was simulated using laboratory scale calendering equipment. The tests aimed to estimate the starch dissolving and picking in a quantitative way as water was applied on web surface prior a hot calender nip. Test material was typical surface sized board (250 g/m² folding boxboard). Sheets were cut from surface sized web containing 2 - 3.5 g/m² (dry amount) starch on both sides. Test sheets were conditioned into equilibrium moisture contents 5 %, 8 % and 10 %. Calendering was done at 150 °C temperature and water was applied by spray nozzles just before sheet entered calender nip. Water amount used was generally 0 - 5 g/m². Calendering test was started using clean surface in each condition. Test sheets were run using a single nip pass principle and the contact surface was then inspected immediately. Each condition was repeated 5 times with fresh sheets, without cleaning the surface. Starch and deposit picking at the contact surface was evaluated by inspecting the surface visually and by photography. The degree of picking was rated by several persons giving picking intensity values between 0...5, as follows: 0= picking free, 1= very small, 2= some, 3= medium, 4= severe, 5= very high picking. Observations were reported as averaged values. Based on research team's understanding and experience, the acceptable picking intensity in practical calendering situations should be < 0.5. Results are conservative, since they include deposit and starch picking and accumulation only from five (5) nip contacts, which is much less than picking and accumulation of repeated continuous nip rolling in real calender.

[0085] The figure 1 explains sheet base moisture effect on starch picking. In the figure 1, the bottom axis indicates used water amount and vertical axis indicates evaluated picking intensity value. As can be seen, higher basis moisture (10 %) gives higher picking compared to lower basis moisture (5%) at all moisturizing levels. Running without water (no moisturizing) is practically picking free in both cases. Calendering temperature was 150 °C. An acceptable picking level defined being < 0.5 , one can see that picking free situation is obtained with < 1 g/m² moisturizing water in the case of 10 % base moisture and with < 2 g/m² moisturizing water with 5 % base moisture, respectively. Therefore sheet basis moisture before calendering is greatly affecting the picking at calendering.

[0086] In the figure 2 it can be seen further, that increase in sizing starch amount increase the picking intensity clearly. The more starch is available to be solved into the water, more picking will take place.

[0087] In the figure 3 is presented further results, now comparing two starch sources at two moisturizing level. Sizing amount is 2 g/m² (dry starch) and base moisture 8%. As can be seen, potato starch, being more soluble to water, is giving clearly higher picking than corn starch.

[0088] In the figure 4 is presented further set of results, indicating the effect of insolubilizer. Sheets were sized using 2.1 g/m² potato starch, with and without insolubilizer. Insolubilizer used was glyoxal, mixed to starch after cooking and dilution. As can be seen, starch with glyoxal additive yield clearly less picking with all moisturizing levels. It can be concluded that the use of insolubilizer enables using more moisturizing, at least 2 g/m² or even more.

[0089] In figures 5 - 13 are schematically shown examples of production lines for producing fiber webs. In figure 5 is an on-line paper or board making line for producing uncoated web, in figure 6 is an on-line paper or board making line for producing coated web, in figure 7 is an on-line paper or board making line with sizing for producing uncoated web, in figure 8 is an on-line paper or board making line with sizing, for producing coated web, in figure 9 is an off-tine paper or board making line with sizing and coating, in figure 10 is an off-line paper or board making line with sizing, in figure 11 is an on-line paper or board making line with calendering and sizing, in figure 12 is an on-line paper or board making line with pre-calendering, sizing, coating and final calendering and in figure 13 is an on-line paper or board making line with integrated sizing, smoothening contact treatment, coating and calendering. In the figures 5 - 13 same reference signs are used for corresponding parts and sections of the fiber web production line, unless otherwise mentioned.

[0090] The production and treatment line according to the examples of figure 5 - 13 comprises paper or board machine 10, which has a head box, a wire section and a press section as well as a subsequent drying section.

[0091] In the example of figure 5 the fiber web W is guided from stock sizing S to the paper or board machine 10 with drying. The drying is followed by moistening by a moistening device 35 of the fiber web W before calendering in a calender 40 and finally reeled in a reel-up 80 to a parent roll.

[0092] In the example of figure 6 the fiber web W is guided from stock sizing S to the paper or board machine 10 with drying. The drying is followed by moistening by a moistening device 35 before precalendering in a calender 40. There after the fiber web W is coated in a coating section 40 which comprises a coating device and drying section. The coating section 50 is followed by final calendering in the end calender 60 and finally the fiber web W is reeled in a reel-up 80 to a parent roll.

[0093] In the example of figure 7 the fiber web W is guided from stock sizing S to the paper or board machine 10 with drying. The drying is followed by sizing in a sizer 20 and dried thereafter by a drying device 25. Then the fiber web is moistened by moistening devices 35 before calendering in a calender 40 and finally the fiber web W is reeled in a reel-up 80 to a parent roll.

[0094] In the example of figure 8 the fiber web W is guided from stock sizing S to the paper or board machine 10 with drying. The drying is followed by sizing in a sizer 20 and dried thereafter by a drying device 25 and moistened by moistening devices 35 before precalendering in a calender 40. There after the fiber web W is coated in a coating section 40 which comprises a coating device and drying section. The coating section 50 is followed by final calendering in the end calender 60 and finally the fiber web W is reeled in a reel-up 80 to a parent roll.

[0095] In the example of figure 9 the fiber web W is guided from stock sizing S to the paper or board machine 10 with drying. The drying is followed by sizing in a sizer 20 and dried thereafter by a drying device 25 and reeled in a reel-up 80 to a parent roll. In the off-line finishing section the parent roll is unwound in an unwinder 85 and moistened by moistening devices 35 before calendering in a calender 40. There after the fiber web W is coated in a coating section 50 which comprises a coating device and drying section and at the end of the off-line part the fiber web W is reeled in a reel-up 80 to a parent roll.

[0096] In the example of the figure 10 the fiber web W is guided from stock sizing S to the paper or board machine 10 with drying. The drying is followed by sizing in a sizer 20 and dried thereafter by a drying device 25 and reeled in a reel-up 80 to a parent roll. In the off-line finishing section the parent roll is unwound in an unwinder 85 and moistened by moistening devices 35 before calendering in a calender 40 and at the end of the off-line part the fiber web W is reeled in a reel-up 80 to a parent roll.

[0097] In the example of the figure 11 the fiber web W is guided from stock sizing S to the paper or board machine 10 with drying. The drying is followed by moistening by a moistening device 35 before precalendering in a precalender 40. Then the fiber web W is sized in a sizer 20 and dried thereafter by a drying device 25. The sizer 20 and its drying device 25 are followed by optional final calendering in the end calender 60 and finally the fiber web W is reeled in a reel-up 80 to a parent roll.

[0098] In the example of the figure 12 the fiber web W is guided from stock sizing S to the paper or board machine 10 with drying. The drying is followed and moistening by a moistening device 35 before precalendering in a calender 40. There after the fiber web W is sized in a sizer 20 and dried thereafter by a drying device 25. Then the fiber web W is coated in a coating section 50 which comprises a coating device and drying section. The coating section 50 is followed by final calendering in the end calender 60 and finally the fiber web W is reeled in a reel-up 80 to a parent roll.

[0099] In the example of the figure 13 the fiber web W is guided from stock sizing S to the paper or board machine 10 with integrated sizing and smoothening contact drying and/or treatment with initial drying 15, which is followed by a sizer 20 and dried thereafter by a drying device 25 for predrying and curing. There after the fiber web is moistened by moistening devices 35 for control of water profile before drying in a drying section 45 comprising contact drying and/or smoothening metal belt treatment and curing. Then the fiber web W is coated in a coating section 50 which comprises a coating device and drying section. The coating section 50 is followed by final calendering in the end calender 60 and finally the fiber web W is reeled in a reel-up 80 to a parent roll.

[0100] The examples the fiber web the sizer 20 provided with application means by which low soluble starch or corresponding sizing agent is applied onto the fiber web. After the surface sizer 20 in some examples the fiber web is moisturized by at least one moisturizing device 35, for example by water moisturizing by sprays or by steam moisturizing with moisture amount of 1 - 10 g/m², preferably 1 - 5 g/m². The calenders 40, 60 of the examples can be for example a soft calenders or a hard nip calenders or a metal belt calenders or multinip calender. Preferably in the examples the possible insolubilizer is added as last step in size preparation, just before the application onto the web. The chemical additive amount is for example 1 - 8% of the dry solids content of the starch. The chemical is activated at drying section as water is removed and/or elevated temperature is enhancing the chemical additive curing. Due to the chemical the water solubility of the starch is lowered, which provides for the possibility of water moisturizing with greater water amounts without contamination of calender rolls. The water moisturizing with greater water amounts together with hot calendering improves the calendering results and the surface of the web when entering the coating is smoother. Thus the smoothness of the end product is better in relation to bulk and the amount of coating medium used can be decreased. The chemical additive has also strength improving effect and thus the amount of starch used can be decreased. The smoothing effect by the calender is improved and thus for example the Yankee cylinder can be removed from the production line without negative effect to the quality of the fiber web as the smoothening effect of the Yankee cylinder is no more so significant. By removing the Yankee cylinder the production speed of the production line can be increased for example by increasing the capacity (the length) of the drying section. The better smoothness and increased strength gives advantage in many ways. Increase in strength enables reduction of fiber raw materials, replacing some fiber material by cheaper filler material or by cheaper recycled fibers. Better calendering result (smoothness) enable reduction of calendering line load which means bulk savings. Bulk saving means more thickness and more bending stiffness. The better smoothness thus provides for bulk and raw material savings.

[0101] Overall the invention provides for the possibility of simple and cost effective line concept, for example hard calender and water moisturizing in conjunction of efficient production line. This example is suitable for example in production of boards (FBB, liners etc.) and of uncoated or coated printing papers (WFU, LWC, MWC etc.).

[0102] In one example the starch sized fiber web is moisturized and end calendered. This example is suitable for example in production of wood-free sized paper grades, for example copy papers. The starch is used to improve strength properties and increasing surface strength, decreasing dusting etc. In particular wood containing or wood-free uncoated printing paper grades are sized or pigmented with insolubilized starch before moistening and calendering.

[0103] In one example the starch sized fiber web is contact dried. The sizing by water resistant starch is followed by contact drying, either cylinder drying or drying-treatment by hot metal belt. The lower solubility of starch enables picking and contamination free operation

[0104] Above the invention has been described with reference to only some examples to which the invention is not to be narrowly limited and features of different examples can be combined in various ways.

Claims

1. Method for producing a fiber web, in which the fiber web (W) is surface sized with starch or other sizing agent in a sizer (20) and in which the fiber web (W) is calendered or correspondingly treated by contacting treatment, characterized in that the fiber web is surface sized by applying low soluble starch, such as maize starch or wheat starch or barley starch or rice starch, or other sizing agent that is low soluble or not re-soluble in moisturizing.

2. Method for producing a fiber web, in which the fiber web (W) is sized with starch or other sizing agent and in which the fiber web (W) is calendered or contact dried or correspondingly treated by contacting treatment, characterized in that the fiber web is sized by applying starch with chemical additive decreasing water solubility of the dried starch size and the fiber web is then dried.

3. Method according to claim 1 or 2, characterized in that the fiber web is surface sized by applying starch or other sizing agent, which is modified by using additives that decrease solubility in calendering.

4. Method according to claim 1 or 2, characterized in that passivation and/or lubrication chemicals are applied on the surface of the calender roll or the corresponding process surface and/or the passivation and/or lubrication chemicals are provided with the moisturizing agent at calender or before calender or that the passivation and/or lubrication chemicals are added directly to the fiber web or passivation/lubrication chemicals are provided in mixed with the sizing agent.

5. Method according to claim 1 or 2, characterized in that fiber web is moisturized by water mist and/or by steam in a moisturizing device (35) after the sizing but before the calendering or the corresponding contacting treatment and the moisturizing is provided by water spray means or by steam-box means.

6. Method according to claim 1 or 2, characterized in that as additives for decreasing solubility of starch or other sizing agent insolubilizers are used, for example zirconium based salts, such as AZC (Ammonium Zirconium Carbonate), PZC (Potassium Zirconium Carbonate), Glyoxal, CMC, Citric acid, Polycarboxylic acid are used.

7. Method according to any of claims 1 - 6, characterized in that the sizing is by performed by spray sizing or by film sizing or by pond sizing.

8. Method according to claim 1 or 2, characterized in that the fiber web production comprises at least following steps: sizing with starch or sizing agent with insolubiliser additive, drying of fiber web, moisturizing and calendering or corresponding contacting press treatment.

9. Method according to claim 1 or 2, characterized in that the fiber web production comprises at least following steps: sizing with starch or sizing agent with insolubilizer additive, treatment in hot contact zone, drying and calendering.

10. Method according to claim 1 or 2, characterized in that the fiber web production comprises at least applying starch or other sizing agent with additive insolubilizer on the fiber web before moisturizing at calender or before calendering.

11. Method according to claim 1 or 2, characterized in that the fiber web production comprises at least following steps:

sizing with starch or sizing agent with insolubilizer additive, contactless drying, drying or metal belt treatment or calendering or

internal sizing of the base fiber web with starch or sizing agent, drying, calendering or corresponding contacting press treatment and surface sizing or

sizing of the base fiber web with starch or sizing agent, drying, calendering or corresponding contacting press treatment, surface sizing, coating and final-calendering or

sizing by starch with additives decreasing water solubility and water moisturizing and hot calendering.

12. Method according to claim 1 or 2, characterized in that the surface sizing is performed in high dry solids content, preferably the solids content level during sizing is 10 - 25% so that less water is applied on the surface of the fiber web.

13. Method according to claim 2, characterized in that the chemical additive dosing is 1- 10 % from the dry solids content of the starch.

14. Production line for producing fiber webs which comprises a sizer (20) for surface sizing the fiber web (W) with starch or other sizing agent in a sizer and a calender (40; 60) or corresponding treatment device for calendering or correspondingly treating by contacting press-treatment the fiber web (W), characterized in that the sizer (20) is provided with application means for surface sizing the fiber web (W) by applying low soluble starch, such as maize starch or wheat starch or barley starch or rice starch, or other sizing agent that is low soluble or not re-soluble in moisturizing.

15. Production line according to claim 14, characterized in that the production line further comprises a moisturizing device (35).

Drawing