FI114231B - Procedure for coating paper or cardboard - Google Patents

Description

114231

Method for coating paper or board

The invention relates to the coating of paper and board using spray coating technology, and more particularly relates to a method of adjusting the surface tension of the coating paste used to provide a good coating result, in particular good uniformity and opacity, based on the surface energy of the paper or board being coated.

BACKGROUND OF THE INVENTION The purpose of the coating is to improve the surface properties of the paper or board, such as gloss, smoothness and printability. Various techniques have been developed for coating, of which the most commonly used is the blade coating process. However, the blade coating process requires a certain strength of the base paper to be coated. The strength requirement has set conditions for the composition of the base. The strength of the pulp fiber providing the base must be high. Suitable blade coatings are, for example, LWC base paper in which the pulp typically comprises at least 40% of the fibrous material and fine paper grade pulp *; almost 100% of the material.

; · 20. Low-cost pulp-based base papers are more expensive than wood-based: paper or board grades. For this reason, it would be advantageous to be able to coat lower strength grades of low strength pulp with a low pulp content or a high content of recycled fiber. It is economically viable to use a coating method which is less burdensome to the base paper. Spray Coatings developed in recent years • · ♦ · · '; non-contact paper web and coating dispensing surface; · Sometimes, well suited for this purpose. The method is described, for example, in U.S. Patent No. 6,106,902.

* • 30 In the spray coating process, the coating paste is led under high pressure through a plurality of nozzles positioned adjacent to the paper or board web. The nozzle row 114231 2 is positioned across the web so that the coating paste spreads evenly throughout the web in small droplets. Suitable pressure generated by the pump is used to make the pasta into small droplets.

5 Applying a uniform coating to a paper or board surface has proved difficult in spray coating. The high pressure coating paste from the nozzles spreads poorly on absorbent paper or board. To obtain the necessary coverage, the shower nozzles are positioned so that the edges of the pasta jets overlap.

10

The edges of the paste jets tend to dry during coating and to form visible stripes of thicker coating. Stripes or patches on the coating are more easily formed with higher solids pastes. Reducing the dry matter content of the pigment paste, i.e. increasing the amount of water, improves the coating's age reduction. However, it is not advantageous to bring very much water into the coating as it has to be dried off the web. Low dry solids content of the paste can also cause a large amount of water to penetrate from the paste to the bottom web, which can, for example, stretch the web to reduce its runnability and to reduce paper quality.

f »• · • ·;: · 20 Spray coating sets requirements for paper surface smoothness.

: _: In the spray coating method, the coating is applied to the entire surface of the base paper and follows the unevenness of the base, resulting in an uneven coated surface. Blade *: in coating, on the other hand, the physical treatment of the surface produces a flat surface * * ·. 'Despite variations in the surface of the paper. Coating paste compositions suitable for blade coating have proven to be unsatisfactory when using spray coating techniques; / particularly in terms of the uniformity of the coating.

♦ 114231 3 for a smooth coating. Particularly large pigment particles in the spray paste rapidly form an ethereal barrier to droplets. This effectively prevents the spread of the paste and leaves the coating uneven.

5 Summary of the Invention

In accordance with the invention, it has now been found that when coating base paper or board, the spray coating technique must be hydrophobic in nature, in particular for the uniformity of the coating, to provide either a base (i.e., paper or board) or a coating paste. Thus, the spray-coated paste on hydrophilic base paper or board must be adjusted to be hydrophobic in nature, and the spray-coated paste on hydrophobic base paper or board should preferably be adjusted to be hydrophilic in nature.

The invention thus relates to a method of coating paper or board with spray coating technology on at least one side, wherein the value of the dispersive component of the surface energy of the surface to be coated is (i) not more than 20 mN / m, preferably not more than 10 raN / m. 65 mN / m, preferably i * 20 at least 70 mN / m; (ii) above 20 mN / m, preferably from 30 to 60 mN / m, the dynamic surface tension of the coating paste is adjusted to a maximum of 60 mN / m, preferably to a value of 55 mN / m; Followed by the application of the coating paste thus obtained using a spray-coating technique.

«» ♦

The process of the invention is preferably used for coating high mechanical pulp * * * ', * or recycled fiber board or paper such as newsprint or' * LWC base paper with a pulp content of 20-40%.

I · • »• ♦ · 30 114231 4

DETAILED DESCRIPTION OF THE INVENTION Hydrophilic base 5 Hydrophilic paper or paperboard refers to paper or paperboard having a large polar component of surface energy and a nearly zero dispersion component. Thus, the polar component of hydrophilic paper or board surface energy is about 30 to 70 mN / m, preferably 40 to 60 mN / m, and the dispersive component is less than 20 mN / m, more preferably less than 10 mN / m.

10

The hydrophilic base paper may be, for example, a mechanical base paper or board made without adhesives, a paper or board glued to a pulp or surface with a starch or other hydrophilic polymer, or a paper or board pre-coated with a hydrophilic paste.

15

Mechanical base paper without adhesives is made from hydrophilic fibers. The structure of the paper consists of capillaries of various sizes and shapes. Due to its porous structure and the tendency of the fibers to absorb water, the paper is highly absorbent hydrophilic.

Γ 20, · Starch is hydrophilic due to its hydroxyl groups. Adding starch to the pulp or surface of the paper alters the surface energy of the paper beyond the polar component * 9. As a surface sizing agent, it changes the surface structure of the paper but increases its hydrophilicity.

. . The paper or board may also be coated with a hydrophilic pre-coating containing hydroxyl groups. The binder of the pre-coating may contain hydroxyl groups or pigments; / ment may be, for example, hydrophilic kaolin. In the preparation of the pre-coated paste, it may be necessary to use a high dispersant which reduces the hydrophobicity * · · '· * 30. Dispersants affect the surface energy by reducing the dispersive component of the I · * ·· * club.

114231 5

In the process of the invention, the hydrophilic base paper or board is spray-coated with a paste of hydrophobic nature. By hydrophobic paste is meant a paste having a dynamic surface tension of at least 65 mN / m, preferably at least 70 mN / m, as measured by the Bubble Pressure method at 10 5 milliseconds.

The hydrophobic spray paste is obtained by adding chemicals to the paste that increase the dispersive component of the paste's surface energy. Such chemicals include styrene acrylate-based polymers, alkenyl succinic anhydride compounds, styrene-maleic anhydride-based polymers, alkyl ketene dimer compounds, other waxes, other hydrophobising agents (eg, resin) or various combinations thereof. In addition, the binder may be selected so as to be free of reactive hydrophobic lowering hydroxyl groups. The paste pigment may also be hydrophobic.

15 In order to improve the opacity, it is also necessary to try to construct a composition which is as ethereal as possible. We have found that the best results on a hydrophilic base are provided by small, circular or needle-like pigments in the hydrophobic paste.

:. 20 In addition, the water retention of the paste should be good to retain water in the coating paste; *. as long as possible. The water retention of the paste can be improved by various water-binding chemicals. These include starch, soybean, carboxymethylcellulose, poly: *, polymeric thickeners and associative thickeners. In spray coating, the paste must not have a high viscosity due to its technical function. Therefore, the use of these chemicals · · 25 is strictly limited. Spray coating paste Haake- *. *: viscosity shear rate of 25,000 rpm should be less than 11, preferably less than 10, when using carbonate pigments, and less than 7, preferably less than 6, when using kaolin pigments.

»» ·: * · *: 30 For blade coating, the dry solids content of the paste can be as high as 65-70% when using carbonate pigment, while for spray coating 55-60% is the usual level.

114231 6

Hydrophobic sole

By hydrophobic paper or paperboard is meant paper or paperboard having a large dispersive component of surface energy and a nearly polar component. The surface energy dispersion component of hydrophobic paper or board is thus more than 20 mN / m, preferably 30-60 mN / m, and the polar component is less than 15 mN / m, more preferably less than 10 mN / m. The dispersive component is thus clearly larger than the polar one.

The hydrophobic base paper or board may be, for example, pulp or surface glued with a hydrophobic chemical or may be coated with a hydrophobic pre-coating.

Usually, the hydrophobicity of the paper is increased by adding a hydrophobic gluing compound to the pulp, thereby improving the machine runnability as the tensile strength increases. Such hydrophobizing agents include, for example, styrene acrylate-based polymers, alkenyl succinic anhydride compounds, styrene-maleic anhydride-based polymers, alkyl ketene dimer compounds, other waxes, other hydrophobising agents (e.g., resin) or the like. In the surface sizing of paper or board, similar chemicals are used in Seam -.;. 20 to give hydrophobicity.

"; The hydrophobic pre-coating contains chemicals that increase the surface area of the paper: *: energy dispersive component is much higher than the polar. Such chemicals include the hydrophobizing agents listed above. In addition, the binder is selected so that it does not have reactive hydrophobicity reducing hydroxyl groups. Also the paste *. '·: Pigment may be hydrophobic.

*, * j Physically sealed base paper or board behaves in spray coating :: like hydrophobic base paper or board. Due to the reduced pore size, the surface of 30 paper absorbs less water than untreated base paper. Such: The physically compacted base paper or board may be, for example, uncoated base paper which has been hot-calendered or pre-coated paper or board which has been calendered.

With hot calendering, the surface of uncoated paper is smoother and at the same time the pores of the paper become denser. Heating raises any adhesive from the lower layers to the surface of the paper. The adhesives may be hydrophobizing agents added to the pulp or lignins from the original wood. As a result of these, the dispersive component of surface energy becomes larger relative to the polar, i.e. the surface becomes hydrophobic.

10

In the process of the invention, the hydrophobic base paper or board is spray-coated with a hydrophilic paste. However, a hydrophobic base paper or board is not as demanding on a spray coating as a hydrophilic one. However, it has been found that the best surface for hydrophobic or physically compacted base paper is obtained by spray coating using a hydrophilic spray paste, preferably a hydrophilic paste having mostly small, circular or needle-like pigment particles. By hydrophilic paste is meant a paste having a dynamic surface tension of up to 60 mN / m, preferably up to 55 mN / m, as measured by the Bubble pressure method at 10 milliseconds.

V. 20

The hydrophilic paste is obtained, for example, by using a hydrophilic binder,. containing reactive hydroxyl groups. An example of such a hydrophilic paste component is starch. However, starch increases the viscosity, for which reason it is more advantageous to use surfactants which increase the hydrophilicity of the paste.

25 Of these, alkylphenol ethoxylates, alkylphenol sulphonates, alcohol ethoxylates, polymylenates, alkylene oxide block copolymers and other polymeric surfactants and combinations thereof.

:: Good hydration retention is also important in hydrophilic pastes. Water retention of hydrophilic paste: 30 tanks can be improved with the same water-binding chemicals mentioned above in connection with the hydrophobic paste.

114231 8

In both hydrophobic and hydrophilic pastes, theology of the paste can be adjusted by removing as much air as possible from the paste during mixing. The viscosity of the pasta decreases as the air mixed with the pasta decreases. In spray coating, spray-5 as uniformity is improved when the paste material from the nozzles is homogeneous without air bubbles. Suitable chemicals for removing the air in the pasta include organic silane compounds, hydrocarbons, vegetable or mineral oil-based fatty acid esters, or mixtures of a fatty acid and an ester.

10 The paste Theology can also be influenced by dispersants. They are used to change the viscosity of the coating paste at the shear rates available for spray coating. Commonly known dispersants include, for example, polymeric acrylic acid salts, fatty alcohol ethoxylates, propylene oxide-ethylene oxide block copolymers, polycarboxylic acid salts, and naphthalene sulfonic acid and phenolic sulfonic acid derivatives.

The active ingredients in the spread of the pasta are so-called. lubricants that do not have a chemical interaction with the pigment or binder. Stearate does not act as a lubricant for this purpose because it has chemical interactions in the paste and raises. 20 viscosities. Suitable lubricants include, for example, polyalkylene glycols, fatty; *; acid salts and wax emulsions.

The spray technology-based coating method of the invention enables a good, opaque and uniform coating result to be obtained on base papers or paperboards of different hydrophobicity / hydrophilicity. Method, · ·: Suitable for coating a variety of wood-containing paper grades, as well as for paper containing mainly pulp fiber.

• I

The invention also relates to a method of coating paper or board with a spray-coating technique on at least one side, wherein the surface to be coated is made hydrophobic and then coated with a coating paste 114231 9 by spray coating technique. The paper or board to be coated can be adjusted to be hydrophobic, for example by mass gluing the paper or board with a hydrophobic chemical.

The invention will be further illustrated by the following example.

5

The surface paper of Table 2 of hydrophobic (base paper 1) or hydrophilic (base paper 5) basis weight of 70 g / m 2 was spray coated with the pastes shown in Table 1 with a coating amount of 10 g / m 2.

10 Table 1. Properties of pastes used in spray coating

Pasta__1_10_23

Pigment__GCC PCC Kaolin Cap .__ 60.0 60.0_59.1

pH__9J1_9J__9J

Brookfield (mpas) __ 102_126_154

Haake (mpas) __ 10.2_6 ^ _9.7

Water retention (g / m2) __ 337 461 131 dyn surface. 10ms (mN / m) _68_55] _52

Table 2. Properties of base papers used in spray coating

Base paper__1_5 total surface energy (mN / m) __ 35.53 56.72: pol. (mN / m) __ 10.2 47.3 'j' disp.comp. (mN / m) __ 25.33 9.42

Roughness (nm) __ 87.2 55.6 i5 •. After drying, photographs of the spray-coated papers were taken, which are reproduced at magnification in the attached figures.

. ·: 20 Figure 1 illustrates a situation where hydrophobic base paper 1 is spray-coated with hydrophobic paste 1, in which the pigment particles were mostly small and circular (GCC or ground calcium carbonate).

• ♦ · 114231 10

Figure 2 illustrates a situation where the hydrophobic base paper 1 is spray-coated with hydrophilic paste 10 in which the pigment particles were mostly small and needle-like (PCC or Precipitated calcium carbonate).

Figure 3 illustrates a situation where the hydrophobic base paper 1 is spray-coated with a hydrophilic paste 23 in which the pigment particles were mostly large and flat (kaolin).

Figure 4 illustrates a situation where the hydrophilic base paper 5 is spray-coated with a hydrophobic paste 1 in which the pigment particles were mostly small and round (GCC).

Figure 5 illustrates a situation where the hydrophilic base paper 5 is spray-coated with a hydrophilic paste 10 in which the pigment particles were mostly small and needle-like (PCC).

Figure 6 illustrates a situation where the hydrophilic base paper 5 is spray-coated with a hydrophilic paste 23 in which the pigment particles were mostly large and flat (kaolin).

20, i From Figures 1-3, it can be concluded that spray coating of a hydrophobic base paper achieves the best result with respect to coating uniformity by using a hydrophilic paste in which the pigment particles are mostly small and needle-like.

Figures 4-6 show that the hydrophilic base paper spray coating has an overcoat; it is essential for the consistency of the slurry that the pasta is hydrophobic. Large and tile • ·, earthy pigment is clearly a worse choice than small and needle-like or round.

Based on the results, it appears that spray coating is less critical to hydrophobic surface than hydrophilic base paper or board in terms of coating uniformity.

Claims (13)

114231 A method for coating paper or cardboard by spray coating technology on at least one side, characterized in that the surface energy of the surface to be coated has a dynamic surface tension of at least 65 mN / m when the dispersive component of the surface energy is (i) 20 mN / m or less; (ii) greater than 20 mN / m, adjusting the dynamic surface tension of the coating paste to a maximum of 60 mN / m; Followed by coating the resulting surface with a spray coating technique. Method according to Claim 1, characterized in that, when the value of the dispersive component of the surface energy of the surface to be coated is 15 (i) up to 10 mN / m, the dynamic surface tension of the coating paste is adjusted to at least 70 mN / m; (ii) 30 to 60 mN / m, the dynamic surface tension of the coating paste is adjusted to a maximum of 55 mN / m. :. A method according to claim 1 or 2, characterized in that in step (i); '; the dynamic surface tension of the coating paste is adjusted to the desired value by adding chemicals that increase the dispersive component of the surface energy to the paste by selecting '. ί binder without reactive hydrophobic lowering hydroxyl groups. And / or by selecting a hydrophobic pigment for the pasta pigment. The process according to claim 3, characterized in that the surface-raising chemicals of the coating paste '' are selected from the group consisting of styrene acrylate-based polymers, alkenyl succinic anhydride compounds, styrene maleic anhydride polymers, , waxes, resins and various combinations thereof. »· · H4231 3. Förfarande enligt patentkravet 1 eller 2, kännetecknat därav, att beläggningspas-tans dynamic yamming point (i) regleras account det self-image colors genomic paste full chemical, som Höjer ytenergins dispersing component, genom att field bindemedel. innehäller reactive hydroxylgrupper, som nedsätter 5 hydrofobiteten och / eller genome att hygro pigment till pastans Pigment. 4. Förfarande enligt patent kravet 3, kangnetecknat därav, att chemikaliema som Höjer beläggningspastans ytenergi expression ur Gruppen, som bestär av styrenacrylate-baserade polymerer, alkenylbiststensyran anhydride, polymeric, styrenmaleinanhydrid 10, 5. Förfarande enligt patentkravet 1 eller 2, kännetecknat därav, att beläggningspastans dynamic yuspänning i point (ii) regleras account self-image colors genom att 15 paste full active, som ecar hydrofileten, och / ellervän anan last. , som innehäller reactive hydroxylgrupper. • t 6. Förfarande enligt patentkravet 5, kännetecknat därav, att de hydrofiliteten ekan-:. de ytaktiva medlen urs Group, som bestar av alkylphenolethoxylat, alkylphenol- »'. 20 sulfonates, alcohol ethoxylates, polymaleins, alkylenoxide block copolymer and and polymeric medication and oleaginous combinations. »»: 7. Förfarande enligt patentkravet 1, kännetecknat därav, att beläggningspastans pigmentpartiklar and account formen Runda eller starvig. * 25 '· ·>' 8. Förfarande enligt nägot av de foregäende patentkraven, kännetecknat därav, att • '. papperet eller kartonen, som ska beläggas, har förbelagts. ; ':': 9. Förfarande enligt patentkravet 1, kännetecknat därav, att i point (i) papperet: \ i 30 eller cardboard, som ska beläggas, business mechanism, after adhesive filler frame from baspapper eller cardboard, med stärkelse eller annan hydrophilic polymer i pulp 114231 eller ρέ ytan warmest papper eller carton eller med en hydrophilic förpasta förbelagt papper eller carton. Process according to claim 1 or 2, characterized in that in step (ii) the dynamic surface tension of the coating paste is adjusted to the desired value by adding hydrophilic surfactants to the paste and / or by using a hydrophilic binder containing reactive hydroxyl groups in the paste. 5 6. A process according to claim 5, characterized in that the hydrophilicity enhancing surfactants are selected from the group consisting of alkylphenol ethoxylates, alkylphenolsulfonates, alcohol ethoxylates, polymaleinates, alkylene oxide block copolymers and other polymeric surfactants and various combinations thereof. A method according to claim 1, characterized in that the pigment particles of the coating paste are spherical or needle-shaped. Method according to one of the preceding claims, characterized in that the paper or paperboard to be coated is pre-coated. Method according to Claim 1, characterized in that the paper or paperboard to be coated in (i) is mechanical without the use of adhesives. 20 t base paper or paperboard, with starch or other hydrophilic polymer; ': Paper or paperboard adhered to a pulp or surface, or paper or paperboard pre-coated with a hydrophilic paste. The process according to claim 1, characterized in that the paper or paperboard to be coated in (ii) 25 is pulp or surface glued with a hydrophobic chemical. 1 l paper or board pre-coated with a hydrophobic paste or physically * · sealed base paper or board. Use of a process according to any one of the preceding claims, which is rich in mechanical pulp or recycled fiber or cardboard, such as newsprint 114231, or LWC base paper having a pulp content of 20-40%. , for coating. A method for coating paper or board with spray coating technique 5 on at least one side, characterized in that the surface to be coated is adjusted to be hydrophobic (the dispersive component of surface energy is greater than 20 mN / m), followed by coating with a hydrophilic coating paste. A method according to claim 12, characterized in that the surface to be coated is made hydrophobic by gluing a paper or board with a hydrophobic chemical. 15 1. Förfarande för beläggning av papper eller cardboard med spraybeläggningsteknik naphtminstone ena sidan; *, (i) högst 20 mN / m, regleras beläggningspastans dynamic ytspänning account:. of which 65 mN / m; 20 (ii) Över 20 mN / m, regleras beläggningspastans dynamic ypin ping account: högst 60 mN / m; ; varefter ifrägavarande yta beläggs med den sä erhällna beläggningspastan genom att: använda spraybeläggningsteknik. : 25 2. Förfarande enligt patentkravet 1, kännetecknat därav, närenergins dispersiva '* component hos ytan som ska beläggas är • · (i) högst 10 mN / m, regleras beläggningspastans dynamic ypin ping account',: minst 70 mN / m; (H) 30-60 mN / m, regleras beläggningspastans dynamic ypin ping account 30 högst 55mN / m. 114231 10. Förfarande enligt patentkravet 1, kännetecknat därav, att papperet eller karton, som ska beläggas i) (ii) and pulp eller med en hydrofob chemical, that med en hydro fob förpasta förbelagt papper eller carton, eller that physical-condenser baspapper eller cardboard. 11. Användning av et förfarande enligt face av de föregäende patentkraven för 10 beläggning av papper eller carton, som innehäller rikligt med mechanisk pulp eller returfiber, sommelididingspapper eller LWC-baspapper, color and cellulosan hem 20 - 40%. 12. Förfarande för beläggning av papper eller carton med spraybeläggningsteknik 15 déminstone en sida, rotation därav, att ytan, som ska beläggas, regleras account hydrophob (ytenergins dispersing component å 20 mN / m), varefter den beläggs med en hydrofil belts . > · *:. 13. Förfarande enligt patentkravet 12, kännetecknat därav, att ytan som ska beläggas regleras account hydro phob genom massalimning av papperet eller cardboard med en hydrophob chemical. «'I» «t a · • a •» • i a • • a ♦ i · • * »· a> t»> i a * «•»