EP2328691A1 - A method for making printing paper - Google Patents

A method for making printing paper

Info

Publication number
EP2328691A1
EP2328691A1 EP09784158A EP09784158A EP2328691A1 EP 2328691 A1 EP2328691 A1 EP 2328691A1 EP 09784158 A EP09784158 A EP 09784158A EP 09784158 A EP09784158 A EP 09784158A EP 2328691 A1 EP2328691 A1 EP 2328691A1
Authority
EP
European Patent Office
Prior art keywords
treating agent
roll
paper
surface treating
gravure
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP09784158A
Other languages
German (de)
French (fr)
Inventor
Timo Koskinen
Vilho Nissinen
Tarja Sinkko
Matti Lindeman
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
UPM Kymmene Oy
Original Assignee
UPM Kymmene Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by UPM Kymmene Oy filed Critical UPM Kymmene Oy
Publication of EP2328691A1 publication Critical patent/EP2328691A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
    • D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
    • D21H23/22—Addition to the formed paper
    • D21H23/52—Addition to the formed paper by contacting paper with a device carrying the material
    • D21H23/56—Rolls
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H25/00—After-treatment of paper not provided for in groups D21H17/00 - D21H23/00
    • D21H25/08—Rearranging applied substances, e.g. metering, smoothing; Removing excess material
    • D21H25/12—Rearranging applied substances, e.g. metering, smoothing; Removing excess material with an essentially cylindrical body, e.g. roll or rod
    • D21H25/14—Rearranging applied substances, e.g. metering, smoothing; Removing excess material with an essentially cylindrical body, e.g. roll or rod the body being a casting drum, a heated roll or a calender

Definitions

  • the present invention relates to a method for making paper, in which method a surface treating agent layer is formed on the surface of the base paper.
  • Publication WO 03/004768 presents that paper is calendered before it is surface treated, wherein the amount of the surface treating agent is very small, 0.5 to 1.5 g/m 2 /side.
  • the surface treating agent is applied by film coating, i.e. the surface treating agent is first applied to the surface of the roll and surface treating agent is transferred from the surface of the roll to the surface of the base paper.
  • Publication Fl 990558 and corresponding international publication WO 00/55424 disclose a method for making paper, wherein a base paper made with a paper machine is coated and calendered in order to improve its printing properties. Before calendering the moisture percentage of the base paper is between 4 to 14 % of the total weight of the paper, after which the base paper web is conveyed to the multinip calender and the base paper is calendered with the multinip calender.
  • the calendered base paper is coated with at least one layer of the surface treating agent using, for example, film transfer method or spray application.
  • prior art in the manufacture of coated papers is to precalender the paper to be coated in a machine calender with a nip formed by hard rolls. Of the rolls forming the nip, one is a heated roll and the other is a variable-crown roll.
  • the purpose of the precalendering is to reduce roughness and porosity and to control the thickness.
  • the nip pressure is typically 10 to 40 kN/m, and the temperature of the water intended for heating the heated roll is 80 to 100°C. This fact is discussed e.g. in the book Papermaking Science and Technology, Papermaking Part 3, Finishing, Editor: Mikko Jokio, Fapet Oy, Helsinki, 1999, p. 58.
  • the surface roughness values achieved by machine calendering typically exceed 2.0 ⁇ m.
  • the method according to the present invention is characterized in that a roll is used for applying the surface treating agent, which roll has in its cylindrical outer jacket recesses or pores that are filled with the surface treating agent, and the surface treating agent is transferred from the recesses or pores of said roll directly to the surface of the paper in such a manner that the surface treating agent forms a layer of the surface treating agent to the surface of the paper.
  • a printing paper is attained the properties of which are better than those of conventional supercalendered paper, and the paper according to the invention can be utilized to replace known coated paper grades, such as LWC paper.
  • the printing paper according to the invention can be printed with printing inks used in connection with LWC papers.
  • the consumption of the surface treating agent is very small.
  • the need for drying the paper is very small as well.
  • the broke generated by the manufacturing process can be recycled easily.
  • the method according to the invention can be used in applications where a very small dose of agent is needed onto the surface of the paper.
  • the base paper is calendered before forming the layer of the surface treating agent, the base paper obtains such a smooth and pore-free structure that as small amount of the surface treating agent as possible is consumed, and nevertheless, a printing paper with good printing properties is obtained.
  • the calendering can also be performed after forming the layer of the surface treating agent. Furthermore, it is possible to perform calendering both before and after forming the layer of the surface treating agent.
  • the paper according to the invention can be used both as an offset paper and gravure paper.
  • Paper with surface roughness of 3 to 10 ⁇ m, typically 5.0 to 7.5 ⁇ m, when measured with the PPS-10 method is used as base paper.
  • the raw material content of the base paper can correspond to typical supercalendered (SC) printing paper.
  • the fibre content of the base paper is typically 60 to 90 weight-% of mechanical pulp, such as groundwobd or refiner groundwood, and 10 to 40 weight-% of chemical or recycled pulp, or a mixture of these.
  • the filler such as clay mineral, talc or calcium carbonate, can be present by
  • the grammage typically varies between 39 to 80 g/m 2 .
  • the base paper can also be such paper that comprises mechanical pulp and/or recycled fibre over 90 weight-%, advantageously over 95 weight-% of the total fibre content of paper.
  • the fibre content of the base paper may also consist entirely of mechanical pulp and/or recycled fibre. Because the use of chemical pulp in paper improves, for example, the strength properties of the paper, the use of fillers, in turn, weakens the paper, as the amount of chemical pulp is reduced, the amount of filler might also be smaller, for example 10 to 15 weight-% of the fibre content.
  • the moisture percentage of the base paper before transferring the surface treating agent to the paper is advantageously 3 to 9 %, more preferably 5 to 7 %.
  • the base paper can be calendered before forming the layer of the surface treating agent in such a manner that the surface roughness is at the most 2.5 ⁇ m, generally 1.0 to 1.6 ⁇ m.
  • a layer of the surface treating agent is formed to the surface of the calendered base paper, wherein the amount of the surface treating agent is at the most 0.8 g/m 2 /side.
  • the presented amounts of surface treating agent represent dry matter contents.
  • the base paper can also be calendered after forming the layer of the surface treating agent.
  • the amount of the surface treating agent is at the most 0,8 g/m2/side. It is also possible to calender the base paper before and after forming the layer of the surface treating agent. As in the preceding, the amount of the surface treating agent is at the most 0.8 g/m 2 /side.
  • the base paper is advantageously first treated with a calendering treatment to reduce the surface roughness. Thereafter the base paper is coated with a surface treating agent, and the attained finished paper is calendered again so that a suitable smoothness of the surface is attained after the coating.
  • the surface treating agent may comprise a mineral substance, such as kaoline, calcium carbonate, talc, or mixtures of these, but the components of the surface treating agent are often non-mineral.
  • Suitable surface treating agents include, for example, starch and a derivative thereof, carboxymethyl cellulose (CMC), casein, protein, lignin, saccharide, hemicelluloses, wax or resin, or synthetic polymer such as polyvinyl alcohol (PVA) or latex.
  • the surface treating agent can contain a cross-linker.
  • the base paper is calendered before it is coated with the surface treating agent in a calender with more than one nip.
  • the calender comprises at least one nip that is formed between a hard-faced roll and a soft-faced roll.
  • the hard-faced roll is typically a heated metal roll.
  • the soft-faced roll may be, for example, a roll with a paper surface or a roll with an elastic surface.
  • the surface of an elastic roll is typically composed of a polymer surface.
  • the calendering can be conducted in a supercalender or a multinip calender. In connection with the calendering, it is possible to moisten the paper with steam or by spraying water.
  • the term supercalender refers to a calender with several nips, in which hard and soft rolls alternate.
  • the supercalender may also contain nips, typically only one, in which the nip is formed between two soft-faced rolls.
  • the soft roll can be a roll with a paper surface (filled roll), or an elastic roll with a polymer surface.
  • the same calender may contain both rolls with a paper surface and rolls with a polymer surface.
  • the supercalender typically comprises 9 to 12 rolls.
  • the supercalender is typically an off-line calender.
  • multinip calender refers to calenders that contain several nips and that comprise nips formed between a hard-faced heated roll and a roll with an elastic surface.
  • the roll with an elastic surface is typically a polymer coated roll.
  • the multinip calenders can be on-line or off-line calenders.
  • Such calenders include, for example, the Janus calender (Voith-Sulzer), the Prosoft calender (Kusters-Beloit), and the OptiLoad calender (Metso Paper).
  • the base paper After calendering the base paper, whose surface roughness after calendering is typically 1.0 to 1.6 ⁇ m, the base paper is coated with a surface treating agent.
  • the coating is typically two-sided.
  • the coating can be performed with a gravure roll coating.
  • the surface treating agent is brought to the gravure cells of the gravure roll, from which it is delivered to the surface of the paper.
  • the paper is in direct contact with the gravure roll.
  • the gravure roll can be, for example, of such a type gravure roll used in gravure printing.
  • the surface treating agent can be sprayed onto the surface of the gravure roll and then the surface of the roll can be wiped with a flexible means similar to a coating blade, wherein the surface treating agent is substantially only in the gravure cells.
  • the volume of the gravure cells is generally 3 to 30 cm 3 /m 2 , typically 5 to 15 cm 3 /m 2 .
  • the agent amount remaining on top of the paper is typically proportional to the speed difference between the paper and the roll. The agent amount is at its largest when the speed is the same, and it decreases when the speed difference increases.
  • the roll can be made of porous material or coated with porous material.
  • the surface treating agent is delivered to the porous material that is permeable to liquid from which material the agent is applied to the surface of the paper.
  • This kind of porous roll is advantageous because wear does not affect its function, but the porous remains constant. Furthermore, it is advantageous for the cells to be in uneven rows.
  • the roll can be, for example, a steel roll roughened with a suitably rough grinding device.
  • the roll is a roll from a hard nip calender. It is also possible to use a pair of rolls.
  • the gravure roll unit can be formed by a gravure roll and its backing roll, a pair of rolls or gravure roll without a backing roll in such a manner that the contact between the paper web and gravure roll is determined by the tension of the paper web.
  • a suction apparatus has to be in a unit without a backing roll for removing the interface forming between the roll and the paper and for ensuring a good contact.
  • the surface treating agent transfers from the gravure cells to the surface of the paper web when the paper web is in contact with the gravure roll.
  • electrical charges can be used.
  • the gravure cells are separate from each other at the surface of the roll, the surface treating agent spreads evenly to the surface of the paper web.
  • a roll made of porous material or coated with porous material or a roughened roll can be used in a roll unit of the type described above.
  • the printing paper is dried and calendered to restore the smoothness of the surface after coating, advantageously the printing paper is treated lightly in a calender with one or two nips.
  • the calender advantageously comprises a nip that is formed between a hard-faced roll and a soft-faced roll.
  • the base paper is first calendered in a multinip calender, after which it is surface treated and after the surface treatment it is calendered with a soft calender with two nips.
  • the manufacturing line of the printing paper according to the invention can be for example the following.
  • the base paper can consist of normal supercalendered paper (SC) which has already been treated in a supercalender or in a multinip calender into a suitable surface roughness.
  • SC supercalendered paper
  • the base paper is unwound from the roll in the beginning of the coating line and is coated with the surface treating agent in the gravure roll unit.
  • the surface treating agent is dried and the printing paper is calendered in a calender with one or two nips. After this, the printing paper coated with the surface treating agent is reeled up.
  • printing paper with a maximum surface roughness of 2.0 ⁇ m is advantageously manufactured.
  • the surface roughness is less than 2.0 ⁇ m, advantageously it is 1.0 to 1.2 ⁇ m.
  • the density of printing paper is typically at least 900 kg/m 3 .
  • the aforementioned numerical values refer to the results obtained by means of the following test methods: - surface roughness SCAN-P 76:95
  • the problem in the method according to the invention can be the fact that when using certain surface treating agents, the surface treating agent adheres to the heated roll of the calender.
  • the surface treating agent can be, for example, natural polymer or a derivative thereof, such as starch, casein, protein, lignin, saccharide, hemicelluloses, carboxymethyl cellulose (CMC), wax or resin, or synthetic polymer such as polyvinyl alcohol (PVA) or latex. Often starch or a derivative thereof is used.
  • the adhering of the surface treating agent to the calender roll is prevented by cooling the calender roll to such a temperature that is in a condensation point of the surrounding air, or below it.
  • a protective water layer is formed onto the surface of the calenderer roll and the surface treating agent does not adhere to the calender roll.
  • the above-mentioned arrangement enables e.g. that the application roll of the surface treating agent can be integrated into the calender, wherein the assembly of the production line reduces the price of the assembly.
  • the above-mentioned arrangement is suitable to be used in connection with other methods than with the gravure roll application.
  • Other possible methods are spray coating, blade or bar application, roll application, brush application, foam application, electro-static wet application or electro-static dry application.
  • Fig. 1 and 2 are diagrammatic figures of possible assembly of the part of the production line.
  • Fig. 1 shows a possible assembly of a part of the production line.
  • the production line comprises a calender unit 11 , gravure roll unit 12, an evaporation unit 13 and a second calender unit 14.
  • Rolls 1 to 4 are in the first calender unit 11 , from which rolls 2 and 3 are heated.
  • Rolls 5 to 8 are in the second calender unit 14, from which rolls 5 and 8 are heated.
  • the location of the heated rolls in the first calender unit 11 can be in accordance with the second calender unit 14, wherein the location of the heated roll in the second calender unit is in accordance with the first calender unit 11.
  • the heated rolls 5 and 8 can be cooled rolls. Rolls 5, 8 are cooled to a temperature below than the condensation point, wherein a protective water layer is formed onto the surface of the roll, which layer prevents the surface treating agent from adhering to the calender roll.
  • the surface treating agent is applied in the gravure roll unit 12.
  • the gravure roll 9 can be a gravure roll 9 and its backing roll 10 in the gravure roll unit 12, or the gravure roll 9 can be without its backing roll in such a manner that the contact between the paper web and gravure roll 9 is determined by the tension of the paper web W.
  • the surface treating agent is supplied to the surface of the gravure roll 9, for example, by spraying the surface treating agent that settles in the gravure cells on the surface of the gravure roll.
  • the surface treating agent transfers from the gravure cells onto the surface of the paper web.
  • electrical charges can be used.
  • the gravure cells are separate from each other at the surface of the roll, the surface treating agent spreads evenly to the surface of the paper web W. Thus, small amounts of agent can be used and still uniform properties can be achieved. It has been observed that over 90 % of the surface treating agent is at 5 ⁇ m penetration depth at the most in the paper.
  • the assembly of the part of the production line shown in Fig. 2 differs from the assembly according to Fig. 1 in that gravure rolls 9 without backing rolls are used to apply the surface treating agent.
  • the surface treating agent is applied to the both sides of the paper web W.
  • suction boxes 15 in the production line are suction boxes 15 in the production line.

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Abstract

The invention relates to a method for making paper, in which method a layer of surface treating agent is formed onto the surface of the base paper. A roll is used for applying the surface treating agent, which roll has in its cylindrical outer jacket recesses or pores that are filled with the surface treating agent, and the surface treating agent is transferred from the recesses or pores of said roll directly onto the surface of the paper in such a manner that the surface treating agent forms a layer of the surface treating agent onto the surface of the paper.

Description

A method for making printing paper
The present invention relates to a method for making paper, in which method a surface treating agent layer is formed on the surface of the base paper.
Publication WO 03/004768 presents that paper is calendered before it is surface treated, wherein the amount of the surface treating agent is very small, 0.5 to 1.5 g/m2/side. The surface treating agent is applied by film coating, i.e. the surface treating agent is first applied to the surface of the roll and surface treating agent is transferred from the surface of the roll to the surface of the base paper.
Publication Fl 990558 and corresponding international publication WO 00/55424 disclose a method for making paper, wherein a base paper made with a paper machine is coated and calendered in order to improve its printing properties. Before calendering the moisture percentage of the base paper is between 4 to 14 % of the total weight of the paper, after which the base paper web is conveyed to the multinip calender and the base paper is calendered with the multinip calender. The calendered base paper is coated with at least one layer of the surface treating agent using, for example, film transfer method or spray application.
As prior art, it can still be mentioned that prior art in the manufacture of coated papers is to precalender the paper to be coated in a machine calender with a nip formed by hard rolls. Of the rolls forming the nip, one is a heated roll and the other is a variable-crown roll. The purpose of the precalendering is to reduce roughness and porosity and to control the thickness. The nip pressure is typically 10 to 40 kN/m, and the temperature of the water intended for heating the heated roll is 80 to 100°C. This fact is discussed e.g. in the book Papermaking Science and Technology, Papermaking Part 3, Finishing, Editor: Mikko Jokio, Fapet Oy, Helsinki, 1999, p. 58. The surface roughness values achieved by machine calendering typically exceed 2.0 μm.
It is a problem of known coated printing papers such as LWC papers that the raw material base is expensive because of large amount of chemical pulp that is necessary and the large amount of coating material. In addition, treating the broke is complex because of the mineral coating. The use of printing papers with less expensive raw material base is, in turn, restricted by the fact that the print does not have the desired quality. When supercalendered paper (SC) is used as printing paper the screen dots in the areas between the fibres are not repeated in a sufficiently intact state. This can be affected by calendering the paper more efficiently, but this can result in blackening by calendering and/or clusters of screen dots, i.e. so-called galvanized print.
By means of the method according to the invention it is possible to avoid the above-mentioned problems. The method according to the present invention is characterized in that a roll is used for applying the surface treating agent, which roll has in its cylindrical outer jacket recesses or pores that are filled with the surface treating agent, and the surface treating agent is transferred from the recesses or pores of said roll directly to the surface of the paper in such a manner that the surface treating agent forms a layer of the surface treating agent to the surface of the paper.
By means of the method according to the invention a printing paper is attained the properties of which are better than those of conventional supercalendered paper, and the paper according to the invention can be utilized to replace known coated paper grades, such as LWC paper. The printing paper according to the invention can be printed with printing inks used in connection with LWC papers. When compared to other coated papers, the consumption of the surface treating agent is very small. As a result of the aforementioned fact the need for drying the paper is very small as well. In addition, the broke generated by the manufacturing process can be recycled easily. Furthermore, in general the method according to the invention can be used in applications where a very small dose of agent is needed onto the surface of the paper.
If the base paper is calendered before forming the layer of the surface treating agent, the base paper obtains such a smooth and pore-free structure that as small amount of the surface treating agent as possible is consumed, and nevertheless, a printing paper with good printing properties is obtained. The calendering can also be performed after forming the layer of the surface treating agent. Furthermore, it is possible to perform calendering both before and after forming the layer of the surface treating agent. The paper according to the invention can be used both as an offset paper and gravure paper.
Paper with surface roughness of 3 to 10 μm, typically 5.0 to 7.5 μm, when measured with the PPS-10 method is used as base paper. The raw material content of the base paper can correspond to typical supercalendered (SC) printing paper. The fibre content of the base paper is typically 60 to 90 weight-% of mechanical pulp, such as groundwobd or refiner groundwood, and 10 to 40 weight-% of chemical or recycled pulp, or a mixture of these. The filler, such as clay mineral, talc or calcium carbonate, can be present by
15 to 40 weight-%. The grammage typically varies between 39 to 80 g/m2.
The base paper can also be such paper that comprises mechanical pulp and/or recycled fibre over 90 weight-%, advantageously over 95 weight-% of the total fibre content of paper. The fibre content of the base paper may also consist entirely of mechanical pulp and/or recycled fibre. Because the use of chemical pulp in paper improves, for example, the strength properties of the paper, the use of fillers, in turn, weakens the paper, as the amount of chemical pulp is reduced, the amount of filler might also be smaller, for example 10 to 15 weight-% of the fibre content.
The moisture percentage of the base paper before transferring the surface treating agent to the paper is advantageously 3 to 9 %, more preferably 5 to 7 %.
The base paper can be calendered before forming the layer of the surface treating agent in such a manner that the surface roughness is at the most 2.5 μm, generally 1.0 to 1.6 μm. A layer of the surface treating agent is formed to the surface of the calendered base paper, wherein the amount of the surface treating agent is at the most 0.8 g/m2/side. The presented amounts of surface treating agent represent dry matter contents.
The base paper can also be calendered after forming the layer of the surface treating agent. In the preceding formation of the layer of the surface treating agent the amount of the surface treating agent is at the most 0,8 g/m2/side. It is also possible to calender the base paper before and after forming the layer of the surface treating agent. As in the preceding, the amount of the surface treating agent is at the most 0.8 g/m2/side.
In the method according to the invention the base paper is advantageously first treated with a calendering treatment to reduce the surface roughness. Thereafter the base paper is coated with a surface treating agent, and the attained finished paper is calendered again so that a suitable smoothness of the surface is attained after the coating. The surface treating agent may comprise a mineral substance, such as kaoline, calcium carbonate, talc, or mixtures of these, but the components of the surface treating agent are often non-mineral. Suitable surface treating agents include, for example, starch and a derivative thereof, carboxymethyl cellulose (CMC), casein, protein, lignin, saccharide, hemicelluloses, wax or resin, or synthetic polymer such as polyvinyl alcohol (PVA) or latex. The surface treating agent can contain a cross-linker.
The base paper is calendered before it is coated with the surface treating agent in a calender with more than one nip. The calender comprises at least one nip that is formed between a hard-faced roll and a soft-faced roll. The hard-faced roll is typically a heated metal roll. The soft-faced roll may be, for example, a roll with a paper surface or a roll with an elastic surface. The surface of an elastic roll is typically composed of a polymer surface.
The calendering can be conducted in a supercalender or a multinip calender. In connection with the calendering, it is possible to moisten the paper with steam or by spraying water. The term supercalender refers to a calender with several nips, in which hard and soft rolls alternate. The supercalender may also contain nips, typically only one, in which the nip is formed between two soft-faced rolls. The soft roll can be a roll with a paper surface (filled roll), or an elastic roll with a polymer surface. The same calender may contain both rolls with a paper surface and rolls with a polymer surface. The supercalender typically comprises 9 to 12 rolls. The supercalender is typically an off-line calender.
The term multinip calender refers to calenders that contain several nips and that comprise nips formed between a hard-faced heated roll and a roll with an elastic surface. The roll with an elastic surface is typically a polymer coated roll. The multinip calenders can be on-line or off-line calenders. Such calenders include, for example, the Janus calender (Voith-Sulzer), the Prosoft calender (Kusters-Beloit), and the OptiLoad calender (Metso Paper).
After calendering the base paper, whose surface roughness after calendering is typically 1.0 to 1.6 μm, the base paper is coated with a surface treating agent. The coating is typically two-sided. The coating can be performed with a gravure roll coating. The surface treating agent is brought to the gravure cells of the gravure roll, from which it is delivered to the surface of the paper. The paper is in direct contact with the gravure roll. The gravure roll can be, for example, of such a type gravure roll used in gravure printing. The surface treating agent can be sprayed onto the surface of the gravure roll and then the surface of the roll can be wiped with a flexible means similar to a coating blade, wherein the surface treating agent is substantially only in the gravure cells. The volume of the gravure cells is generally 3 to 30 cm3/m2, typically 5 to 15 cm3/m2. The agent amount remaining on top of the paper is typically proportional to the speed difference between the paper and the roll. The agent amount is at its largest when the speed is the same, and it decreases when the speed difference increases.
The roll can be made of porous material or coated with porous material. The surface treating agent is delivered to the porous material that is permeable to liquid from which material the agent is applied to the surface of the paper. This kind of porous roll is advantageous because wear does not affect its function, but the porous remains constant. Furthermore, it is advantageous for the cells to be in uneven rows.
The roll can be, for example, a steel roll roughened with a suitably rough grinding device. Advantageously, the roll is a roll from a hard nip calender. It is also possible to use a pair of rolls.
The gravure roll unit can be formed by a gravure roll and its backing roll, a pair of rolls or gravure roll without a backing roll in such a manner that the contact between the paper web and gravure roll is determined by the tension of the paper web. Generally a suction apparatus has to be in a unit without a backing roll for removing the interface forming between the roll and the paper and for ensuring a good contact. The surface treating agent transfers from the gravure cells to the surface of the paper web when the paper web is in contact with the gravure roll. For facilitating the emptying of the gravure cells electrical charges can be used. Although the gravure cells are separate from each other at the surface of the roll, the surface treating agent spreads evenly to the surface of the paper web.
It is obvious that a roll made of porous material or coated with porous material or a roughened roll can be used in a roll unit of the type described above.
After coating, the printing paper is dried and calendered to restore the smoothness of the surface after coating, advantageously the printing paper is treated lightly in a calender with one or two nips. The calender advantageously comprises a nip that is formed between a hard-faced roll and a soft-faced roll.
According to an advantageous embodiment the base paper is first calendered in a multinip calender, after which it is surface treated and after the surface treatment it is calendered with a soft calender with two nips.
The manufacturing line of the printing paper according to the invention can be for example the following. The base paper can consist of normal supercalendered paper (SC) which has already been treated in a supercalender or in a multinip calender into a suitable surface roughness. The base paper is unwound from the roll in the beginning of the coating line and is coated with the surface treating agent in the gravure roll unit. The surface treating agent is dried and the printing paper is calendered in a calender with one or two nips. After this, the printing paper coated with the surface treating agent is reeled up.
By means of the method according to the invention printing paper with a maximum surface roughness of 2.0 μm is advantageously manufactured. Typically, the surface roughness is less than 2.0 μm, advantageously it is 1.0 to 1.2 μm. The density of printing paper is typically at least 900 kg/m3. The aforementioned numerical values refer to the results obtained by means of the following test methods: - surface roughness SCAN-P 76:95
- density SCAN-P 7:96
The problem in the method according to the invention can be the fact that when using certain surface treating agents, the surface treating agent adheres to the heated roll of the calender. The surface treating agent can be, for example, natural polymer or a derivative thereof, such as starch, casein, protein, lignin, saccharide, hemicelluloses, carboxymethyl cellulose (CMC), wax or resin, or synthetic polymer such as polyvinyl alcohol (PVA) or latex. Often starch or a derivative thereof is used.
The adhering of the surface treating agent to the calender roll is prevented by cooling the calender roll to such a temperature that is in a condensation point of the surrounding air, or below it. Thus, a protective water layer is formed onto the surface of the calenderer roll and the surface treating agent does not adhere to the calender roll.
The above-mentioned arrangement enables e.g. that the application roll of the surface treating agent can be integrated into the calender, wherein the assembly of the production line reduces the price of the assembly.
The above-mentioned arrangement is suitable to be used in connection with other methods than with the gravure roll application. Other possible methods are spray coating, blade or bar application, roll application, brush application, foam application, electro-static wet application or electro-static dry application.
In the following, the invention will be described by using, as an example, Fig. 1 and 2. Fig. 1 and 2 are diagrammatic figures of possible assembly of the part of the production line.
Example.
Fig. 1 shows a possible assembly of a part of the production line. The production line comprises a calender unit 11 , gravure roll unit 12, an evaporation unit 13 and a second calender unit 14. Rolls 1 to 4 are in the first calender unit 11 , from which rolls 2 and 3 are heated. Rolls 5 to 8 are in the second calender unit 14, from which rolls 5 and 8 are heated. The location of the heated rolls in the first calender unit 11 can be in accordance with the second calender unit 14, wherein the location of the heated roll in the second calender unit is in accordance with the first calender unit 11.
Alternatively the heated rolls 5 and 8 can be cooled rolls. Rolls 5, 8 are cooled to a temperature below than the condensation point, wherein a protective water layer is formed onto the surface of the roll, which layer prevents the surface treating agent from adhering to the calender roll.
The surface treating agent is applied in the gravure roll unit 12. There can be a gravure roll 9 and its backing roll 10 in the gravure roll unit 12, or the gravure roll 9 can be without its backing roll in such a manner that the contact between the paper web and gravure roll 9 is determined by the tension of the paper web W. The surface treating agent is supplied to the surface of the gravure roll 9, for example, by spraying the surface treating agent that settles in the gravure cells on the surface of the gravure roll. The surface treating agent transfers from the gravure cells onto the surface of the paper web. For facilitating the emptying of the gravure cells electrical charges can be used. Although the gravure cells are separate from each other at the surface of the roll, the surface treating agent spreads evenly to the surface of the paper web W. Thus, small amounts of agent can be used and still uniform properties can be achieved. It has been observed that over 90 % of the surface treating agent is at 5 μm penetration depth at the most in the paper.
The assembly of the part of the production line shown in Fig. 2 differs from the assembly according to Fig. 1 in that gravure rolls 9 without backing rolls are used to apply the surface treating agent. In the situation according to the Fig. 2, the surface treating agent is applied to the both sides of the paper web W. For removing the air interface there are suction boxes 15 in the production line.

Claims

Claims:
1. A method for making paper, in which method a layer of surface treating agent is applied onto the surface of a base paper, characterized in that
- a roll is used to apply the surface treating agent, which roll has in its cylindrical outer jacket recesses or pores that are filled with the surface treating agent, and
- the surface treating agent is transferred directly onto the surface of the paper from the recesses or pores of said roll in such a manner that the surface treating agent forms a layer of the surface treating agent onto the surface of the paper.
2. The method according to claim 1 , characterized in that the dry matter content of the surface treating agent transferred to the surface of the paper is at the most 0.8 g/m2/side of the paper.
3. The method according to claim 1 or 2, characterized in that the moisture percentage of the paper before transferring the surface treating agent onto the above-mentioned paper is 3 to 9 %.
4. The method according to claim 3, characterized in that the moisture percentage of the paper before transferring the surface treating agent onto the paper is 5 to 7 %.
5. The method according to any of the preceding claims 1 to 4, characterized in that
- a gravure roll (9) having gravure cells that are filled with surface treating agent, is used to apply the surface treating agent, and
- the gravure cells of the gravure roll are emptied in such a manner that the paper is in direct contact with the gravure roll, and the surface treating agent forms a layer of the surface treating agent onto the surface of the paper.
6. The method according to claim 5, characterized in that the gravure cells of the gravure roll are emptied utilizing an electric field.
7. The method according to claim 5 or 6, characterized in that the volume of the gravure cells is 3 to 30 cm3/m2, typically 5 to 15 cm3/m2.
8. The method according to any of the claims 1 to 4, characterized in that said roll is made of porous material or is a roll coated with porous material.
9. The method according to any of the claims 1 to 4, characterized in that the surface of the hard-faced roll is roughened in such a manner that the recesses have formed on it.
10. A roll according to claim 9, characterized in that said hard-faced roll is a roll from the hard-nip calender.
11. The method according to any of the preceding claims, characterized in that the base paper is calendered before forming the layer of the surface treating agent.
12. The method according to claim 11 , characterized in that the surface roughness of the base paper before forming the layer of the surface treating agent is 10 μm at the most, more preferably 7.5 μm at the most and more preferably 2.5 μm at the most.
13. The method according to claim 11 or 12, characterized in that the calendering is performed in a multinip calender or supercalender.
14. The method according to any of the preceding claims, characterized in that the base paper is calendered after forming the layer of the surface treating agent.
15. The method according to claim 14, characterized in that the application roll of the surface treating agent is integrated in connection with the calender.
16. The method according to claim 14 or 15, characterized in that at least some of the heat adjusted rolls (5, 8) is adjusted to a temperature corresponding a condensation point or below.
17. The method according to any claim 14 to 16, characterized in that the calendering is performed in a calender with one or two nips.
18. The method according to any claim 14 to 17, characterized in that the surface roughness of the final product is 2 μm at the most, advantageously
1.2 μm at the most.
19. The method according to any of the preceding claims, characterized in that the surface treating agent used in the coating is one of the following: starch and a derivative thereof, carboxymethyl cellulose (CMC), casein, protein, lignin, saccharide, hemicellulose, wax or resin, or some synthetic polymer such as polyvinyl alcohol (PVA) or latex.
EP09784158A 2008-08-11 2009-08-06 A method for making printing paper Withdrawn EP2328691A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20085765A FI20085765A0 (en) 2008-08-11 2008-08-11 Process for producing printing paper
PCT/FI2009/050649 WO2010018302A1 (en) 2008-08-11 2009-08-06 A method for making printing paper

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EP2328691A1 true EP2328691A1 (en) 2011-06-08

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Publication number Priority date Publication date Assignee Title
SE535270C2 (en) 2010-08-12 2012-06-12 Stora Enso Oyj A method for coating paper or cardboard

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EP0089616B1 (en) * 1982-03-22 1988-06-08 Foamink Company Printing and coating processes employing pigmented water based foamed compositions
JPH027663Y2 (en) * 1985-09-06 1990-02-23
EP0235425A1 (en) * 1986-02-28 1987-09-09 Acumeter Laboratories Inc. Porous roll fluid coating applicator and method
US4770909A (en) * 1986-02-28 1988-09-13 Acumeter Laboratories, Inc. Porous roll fluid coating applicator and method
EP0286755B1 (en) * 1987-04-16 1995-03-15 Yasui Seiki Co., Ltd. Coating feeder system
CA2228566A1 (en) * 1995-08-31 1997-03-06 Minnesota Mining And Manufacturing Company Reverse gravure kiss coating system with output roller
DE19714645A1 (en) * 1997-04-09 1998-10-15 Jagenberg Papiertech Gmbh Web coating station roller
WO2000032870A1 (en) * 1998-11-30 2000-06-08 Blandin Paper Company Method for producing coated calendered paper
FI111476B (en) 1999-03-12 2003-07-31 Metso Paper Inc Method and apparatus for making coated paper and coated paper
FI20011429A0 (en) 2001-07-02 2001-07-02 Upm Kymmene Corp Printing paper and process for its manufacture
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FI20085765A0 (en) 2008-08-11

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