METHOD FOR PRODUCTION OF PAPER
The present invention relates to a method for the production of paper from a suspension containing cellulosic fibers comprising adding to the suspension and/or to a formed paper prepared from the cellulosic suspension i) a nitrogen-containing organic compound separately and/or in conjunction with, ii) an aqueous dispersion of an acid anhydride and iii) at least one shading dye, draining the suspension on a wire to form a paper.
Latest Akzo Nobel N.V. Patents:
The present invention refers to papermaking and more specifically to a method for the production of paper wherein a nitrogen-containing organic compound, an aqueous dispersion of an acid anhydride and at least one shading dye are added to a cellulosic suspension.
BACKGROUNDIn the papermaking art, an aqueous suspension containing cellulosic fibers, and optional fillers and additives, referred to as stock, is fed into a headbox which ejects the stock onto a forming wire. Water is drained from the stock through the forming wire so that a web of paper is formed on the wire, and the web is further dewatered and dried in the drying section of the paper machine. The obtained water, usually referred to as white water and containing fine particles such as fine fibers, fillers and additives, is usually recycled in the papermaking process. When producing paper where the aesthetic impression, including properties such as whiteness, brightness and/or the printability is important, hereinafter referred to as higher grade paper or high grade paper, the amount and number of fillers and additives are often increased compared to papers of lower quality. While the performance chemicals are added to the suspension or to the paper web to improve the runnability of the papermaking machine and/or increase the quality, they may influence the performance of each other.
Commonly, papers of higher grade, such as white fine paper, need some degree of resistance to wetting and penetration of aqueous liquids. Therefore, sizing agents, such as cellulose-reactive sizing agents, are typically added to the cellulosic suspension and/or the paper web. Cellulose-reactive sizing agents including ketene dimer based sizing agents and acid anhydrides are frequently used in neutral to slightly alkaline stocks. Acid anhydrides are often used in papermaking processes requiring fast curing of the sizing agent. Fast curing, i.e. high rate of obtaining hydrophobic properties of the paper, is often required for coated paper grades. Furthermore, paper sized with acid anhydrides achieves better runnability in printing processes e.g. with respect to reduced tendency of agglomeration of reactive sizing agent related derivatives in the printing machinery compared to e.g. paper sized with ketene dimer agents. Yet, when acid anhydrides are used in a papermaking process where performance chemicals having an impact on the aesthetic properties of the formed paper, such as color and whiteness, are present in the suspension, uneven distribution of dyes in the finished paper may occur which is perceived as color spots.
US 2003/0188393 A1 refers to a process for controlling the brightness of paper while using shading dyes.
WO 2007/073321 relates to an aqueous dispersion of cellulose-reactive sizing agent, a method for preparing the dispersion, and a process for producing paper comprising adding the dispersion to the suspension.
However, an irregular distribution of pigments (dyes), perceived by the human eye as colored spots, may be observed in white paper, such as white fine paper, when shading dyes are present in the cellulosic suspension and acid anhydrides are used as a sizing agent. The presence of colored spots in the paper may occur during initial production. However, colored spots tend to increase over time. Shading dyes are typically added to a cellulosic suspension in order to increase the whiteness. Accordingly, it is an objective with the present invention to reduce or eliminate the presence of colored spots in paper. A further object is to reduce or eliminate the presence of colored spots in paper obtained from a process for production of paper comprising adding an acid anhydride to a cellulosic suspension comprising at least one shading dye. A still further object is to reduce or eliminate irregular distribution of shading dye in paper obtained from a process for production of paper comprising adding an acid anhydride to a cellulosic suspension comprising at least one shading dye. Further objects will appear hereinafter.
THE INVENTIONThe present invention relates to a method for the production of paper, paper which may be obtained by the method, and the use of a nitrogen-containing organic compound as further defined herein.
More specifically, the present invention relates to a method for production of paper web from an aqueous suspension containing cellulosic fibers comprising adding to the suspension and/or to a paper web prepared from the suspension i) a nitrogen-containing organic compound, ii) an aqueous dispersion of an acid anhydride; and iii) at least one shading dye, draining the suspension on a wire to form a paper. The invention further pertains to the use of a nitrogen-containing organic compound being an amine or quaternary ammonium compound thereof having a molar mass less than about 180 g/mol in a method for producing paper from a suspension as an additive for improving the distribution of dyes in the paper, wherein the suspension comprises at least one shading dye. According to one embodiment of the invention the nitrogen-containing organic compound is comprised in the aqueous dispersion comprising an acid anhydride.
Also, the present invention pertains to paper obtainable from the method as disclosed herein, and paper comprising acid anhydride and/or derivatives thereof, a nitrogen-containing organic compound and at least one shading dye, wherein the paper has no visual agglomerations of pigments.
Shading dyes, are believed to be more evenly distributed in the paper when a nitrogen-containing organic compound is added to a cellulosic suspension comprising at least one shading dye and sized by the addition of an aqueous dispersion of an acid anhydride.
It has been observed that acid anhydride sizing of cellulosic suspensions comprising shading dyes used for the manufacturing of paper has resulted in paper containing agglomeration of pigment rendering visual spots of color, often of bluish color. Surprisingly, the addition of a nitrogen-containing organic compound counteracts the agglomeration of dyes in the formed paper. What is more, agglomeration of white pigments is also reduced by the addition of a nitrogen-containing organic compound.
As used herein, by paper is meant paper intended for printing, such as office paper and paper for graphic production, commonly simply referred to as printing paper. Usually, the paper is white, nevertheless, the term “paper” may include any kind of colored papers. The present invention is, however, advantageous for the production of white paper, including white printing paper. According to one embodiment, the paper, suitably white paper, has a grammage up to about 350 g/m2. According to one embodiment, the term “paper” does not embrace board and paper board. Yet, paper according to the present invention can be applied as the top layer of board and paper board.
As whiteness is an issue of the paper manufactured according to the present invention, cellulosic fibers, often referred to as pulp, should preferably have a κ (kappa number) of less than about 8 (ISO 302), less than about 4, less than about 3, or less than about 2. The cellulosic fibers may be obtained by any pulping processes as long as the fibers can be used for the production of paper. Pulping processes include mechanical, thermal, semi-mechanical, semi-chemical, and chemical pulping processes. Commonly chemical processes are sulfite and sulphate processes, the latter also referred to as the kraft pulping process. Cellulosic fibers obtained by chemically pulping processes, suitably fibers from the kraft process, are preferred. The cellulosic fibers are usually also bleached in order to reduce the content of lignin and to achieve a high brightness of the fibers. In order to obtain cellulosic fibers with a high brightness and low content of lignin, raw fiber material is commonly subjected to a chemical (kraft) pulping process and subsequently bleached. The bleaching sequence usually comprises several bleaching operations interrupted by washing stages and alkaline extraction. Bleaching chemicals include e.g. chlorine dioxide, peroxides such as hydrogen peroxide, oxygen, ozone, and peracetic acid. Preferred cellulosic fibers are chemically delignified fibers subsequently bleached using an elemental chlorine free (ECF) bleaching sequence or a total chlorine free (TCF) bleaching sequence.
According to one embodiment, the cellulosic fibers used in the present invention have a brightness of above about 83 (ISO 3688), above about 88, or above about 90. Cellulosic fibers may have a κ (kappa number) of less than about 4 and a brightness above about 88.
Fiber raw material used in the above pulping processes may include but are not limited to wood such as hardwood, softwood, agricultural residues e.g. straw, annual plants (hemp, jute, kenaf, bamboo, etc), recycled or secondary fibers, and any type of deinked fibers.
In order to further improve the quality of the paper with respect to e.g. whiteness, brightness, several non-fiber constituents can be added to the cellulosic suspension and/or to the dewatered paper web. The cellulosic suspension and finished paper can contain mineral fillers such as kaolin, china clay, titanium dioxide, gypsum, talc, calcium carbonate e.g. chalk, ground marble and precipitated carbonate. According to one embodiment, the cellulosic suspension contains more than about 5% by weight of mineral fillers based on dry cellulosic suspension and optional fillers, such as more than about 10% by weight.
According to the present invention at least one shading dye is present in the cellulosic suspension. Shading dyes, are compounds which further improve the whiteness of the paper. Whiteness is the sensation of those colors perceived by the human eye as being white. In physical terms a substrate is perceived as white if all visible light (to the human eye) impinging on the substrate is reflected without any loss of intensity. By visible light is meant the part of the electromagnetic spectrum which can be detected by the human eye. Very few substrates and chemical compounds reflect the entire spectrum of light without absorbing certain wavelengths of the visible electromagnetic radiation. Clouds and new fallen snow reflect most of the light, also some pigments, notably titanium dioxide, have such a property. However, usually some light is absorbed by the object, commonly light in the blue range of the spectrum, rendering a yellowish appearance. In order to improve the whiteness of paper, e.g. decrease of yellowness, shading dyes may be added in the production process. Fluorescent whitening agents (FWA), including optical brightening agents (OBA) can also be added to the cellulosic suspension, improving inter alia the brightness of the paper. OBA and FWA are fluorescent molecules improving the brightness of paper through an additive color mixing process since they emit most of the absorbed light. Shading dyes, on the other hand, are compounds typically increasing the whiteness by subtracting color mixing.
As used herein, shading dyes are the group of compounds enhancing the perceived whiteness of paper, however, without including brightening agent, i.e. compounds emitting radiation (fluorescent compounds).
Shading dyes may be selected from naturally and synthetic inorganic compounds and synthetic organic compounds. One preferred group of compounds are synthetic organic compounds. Suitably, the structure of the synthetic organic compounds comprises a system of conjugated double bonds. Said conjugate double bonds can oscillate more or less freely. Typically, the synthetic organic compounds comprise one or more of same or different chromophoric groups (electron acceptors groups) such as ethylene-, keto-, thioketo-, azo-, and carbon-nitrogen-groups.
Compounds improving the whiteness of paper may be selected from the group consisting of azo dyes, anthraquinone dyes, indigoid dyes, polymethine dyes, aryl-carbonium dyes, phtalocyanine dyes and nitro dyes.
Azo-group containing compounds usually contain the moiety A-N═N-D, where A and D often are aromatic moieties. The A-N═N-D moiety may be part of a ring system, e.g. hydrazones, or the azo-group containing compound may form metal complexes. The azo-containing compound may have up to four azo-groups.
Synthetic organic compounds comprising keto groups include compounds having a anthraquinone moiety, such as 9,10-quinone. 9,10-quinone may be substituted by electron donator groups in the free positions 1 to 4 and 5 to 8, specifically in the positions 1, 4, 5, and 8.
Indigoid compounds include the structure element —CO—CX═CY—CO—, where X, Y is selected from O, S, Se, or NH. Indigo (1) and substituted indigo compounds are examples of indigoid compounds.
Polymethine compounds comprise the general structure (2). Polymethine compounds may be cationic, neutral or anionic, depending on the character of groups A and B.
[A=CR—(X═Y)x—B]Z (2), wherein X and Y independently can be C or N, x is an integer, and z being +n, 0 or −n (n being an integer). Cyanines (Cl basic red 12) and hemicyanines (Cl basic violet 7) are examples of cationic polymethines where both X and Y are carbon atoms. Diazahemicyanines (Cl basic blue 41), azacarbocyanines (Cl basic yellow 11) and diazacarbocyanines (Cl basic yellow 28) are examples of polymethines where X and Y are nitrogen or a combination of nitrogen and carbon. Neutral polymethine compounds may be exemplified by meroxyanine and anionic polymethines by oxonol.
Aryl-carbonium compounds include a group of compounds comprising the general structure (3),
wherein m and n is 0 or 1, X is C or N, Y is O, S or NR, A and B are independently O, S or NR, and R is an alkyl- or aryl-group.
Other compounds improving the whiteness of paper may include phthalocyanine compounds and nitro containing compounds. The latter typically comprises two or more aromatic rings, usually benzene or naphthalene, containing at least one nitro-group and an electron donor group such as NH2 or OH.
Shading dyes are dyes which absorb light (electromagnetic radiation) in the visible spectrum without significantly emitting electromagnetic radiation or without emitting electromagnetic radiation in addition to the reflected radiation. Accordingly, shading dyes do not increase the intensity of the reflected radiation in the visible spectrum of the substrate, i.e. they do not emit radiation (light) or they do not significantly emit radiation. Shading dyes can, thus, be referred to as subtractive dyes. Shading dyes (subtracting dyes) absorb the complementary wavelength region to the wavelength region leading to yellowness. Shading dyes may be defined as non-fluorescent compounds (dyes) absorbing radiation in the visible spectrum in such a way that the perceived whiteness of the paper is increased. Shading dyes typically absorb light in the bluish portion of the visible spectrum (from about 380 nm to about 495 nm), and/or in the orange-reddish portion of the visible spectrum (from about 590 nm to about 750 nm). Shading dyes may be referred to as organic molecules comprising conjugated systems, i.e. conjugated organic molecules, absorbing electromagnetic radiation in the visible spectrum, i.e. from about 380 nm up to about 750 nm, preferably in the range of from about 380 nm to about 500 nm and/or in the range of from about 580 nm to about 750 nm). As used here a conjugated system denotes a delocalisation of electrons across adjacent parallel aligned p orbitals of atoms.
A preferred class of dyes is dyes under the name Viscofil®. Another preferred group of shading dyes are phthalocyanine compounds (organic compounds comprising a phthalocyanine moiety) including but not limited to metal phthalocyanine compounds optionally comprising solubilising groups such as sulphonic acid functions, e.g. salts of phthalocyanine-sulfonic acids such as sodium or ammonium salts of copper phthalocyanine. Organic amine salts of sulfonic acids may also be comprised in the phthalocyanine type compounds. Phthalocyanine type compounds are able to co-ordinate hydrogen and/or metal cations in the centre. Common coordinated metal cations are copper and cobalt. Other phthalocyanine dyes include derivatives of metal phthalocyanine and organic amines. Yet further preferred classes of dyes are triphenodioxazines commonly referred to as dioxazines. Preferred dioxazines include dihalide triphenodioxazine such as 9,10-dichlorotriphenodioxazine and triphenodioxazines comprising a acetylamino or bezoylamino group, ethoxy group, halide atom or an HNCOCH3 group. Preferred shading dyes are also selected from the group consisting of dioxazines and organic compounds comprising a phthalocyanine moiety.
Examples of shading dyes are Viscofil® dyes from Clariant® and Levanyl® dyes from Laxness®, including but not limited to Viscofil®: Orange GG, Orange S-RL, Red R 30, Red BL, Red F5RK, Bordo BB, Violet BLN, Blue B2G, Blue BLF, Levanyl® Violet 23. Further shading dyes are Cartasol® F, Cartasol® K, Cartasol® M, Carta® dyes, Carta® powder dyes, Cartazine®, Diresul® P, Cartaren®, Flexonyl®, Cartacrom®, Hostatint®.
According to one embodiment of the present invention, the cellulosic suspension may also contain at least one fluorescent compound e.g. OBAs, such as fluorescent organic compounds absorbing ultraviolet light (e.g. from daylight at 300-430 nm) and emitting most of the absorbed energy as blue fluorescent light in the range of from about 400 up to about 500 nm. Examples of OBAs are those OBAs sold under the name Leucophor®.
The shading dyes and OBAs may be added to the cellulosic suspension and/or applied to the surface of a cellulosic sheet or web of paper. They may be added at any point to the cellulosic suspension starting from the mixing chest up to and including the head box and/or to the formed web of paper after the head box. The sequence of addition of the shading dye(s) and/or the OBAs, dispersion of acid anhydride, and nitrogen-containing organic compound, where appropriate, the sequence of the addition of the shading dyes and/or the OBAs and the acid anhydride dispersion comprising a nitrogen-containing organic compound may vary and may be in any order.
The total amount of added shading dye(s) is usually up to about 400 g/t based on dry cellulosic suspension and optional fillers, suitably less than about 300 g/t. The shading dye(s) may be added to the mixing chest. OBAs, if present in the formed paper, are typically added to the suspension in an amount of up to about 30 kg/t based on dry cellulosic suspension, suitably up to about 20 kg/t. Commonly, OBAs are added to the cellulose suspension up to and including the level box. If both shading dyes and OBAs are used, the shading dyes may be added prior to the addition of the OBAs. Shading dyes may e.g. be added to the mixing chest and OBAs to the level box.
The nitrogen-containing organic compound may be selected from amines such as primary, secondary and tertiary amines; and quaternary ammonium compounds thereof. Suitable nitrogen-containing organic compounds further include monoamines, diamines and polyamines and quaternary ammonium compounds thereof. Suitable quaternary ammonium compounds include protonated, alkylated, arylated and alkarylated amines of the above-mentioned types, which can be formed by reaction of the amines with, for example, acids, e.g. hydrochloric acid, and methyl chloride, dimethyl sulphate and benzyl chloride. According to one embodiment, the nitrogen-containing organic compound is an amine or quaternary ammonium thereof optionally having one or more hydroxyl groups. Preferably, one or more hydroxyl groups are present in a terminal position of one or more substituents of the nitrogen-containing compound, i.e. a hydroxyl group terminated amine or quaternary ammonium compound thereof.
Examples of suitable nitrogen-containing organic compounds include the following amines and their quaternary ammoniums: diethylene triamine, methylene tetramine, hexamethylene diamine, diethyl amine, dipropyl amine, di-isopropyl amine, cyclohexylamine, pyrrolidine, guanidine, triethanol amine, monoethanol amine, diethanol amine, 2-methoxyethyl amine, aminoethylethanol amine, alanine and lysine. Further examples of suitable nitrogen-containing organic compounds include choline hydroxide, tetramethyl ammoniumhydroxide, tetraethyl ammoniumhydroxide. Preferred nitrogen-containing organic compounds include triethanol amine and quaternary ammonium compounds thereof.
The molar mass of the nitrogen containing organic compound can vary within wide limits. As used herein, nitrogen-containing organic compounds refer to non-polymeric compounds, i.e. compounds not comprising repetitive structural units. Typically, the molar mass of the nitrogen-containing organic compound is up to about 500 g/mol, e.g. up to about 400 g/mol, or up to about 180 g/mol.
In one embodiment of the invention, the molar mass of the amine or quaternary ammonium compound thereof is less than about 180 g/mol, e.g. up to about 170 g/mol or up to about 160 g/mol. The molar mass is usually at least about 30 g/mol. As stated herein, the molar mass of a quaternary ammonium of an amine means the molar mass of the cationic part of the quaternary ammonium compound, meaning that the anionic part of the quaternary ammonium compound is not included in the molar mass given above. For nitrogen-containing organic compounds which are selected from amines and quaternary ammoniums thereof having one or more hydroxyl groups, the molar masses may be higher, e.g. less than about 500 g/mol and usually less than about 300 g/mol, although the above-mentioned molar masses are also suitable for such compounds.
The nitrogen-containing organic compound may be added separately/singly to the cellulosic suspension or in conjunction with other additives such as the acid anhydride sizing agent, e.g. comprised in the aqueous dispersion of the acid anhydride. If added singly, the nitrogen-containing organic compound can be added to the aqueous cellulosic suspension and/or to the formed paper web, typically at any point starting from the machine chest up to and including the head box and/or to the paper web after the head box. The amount of nitrogen-containing organic compound as a single addition can be from about 0.0004 up to about 0.1% by weight based on dry cellulosic suspension and optional fillers, e.g. from about 0.0008 up to about 0.01% by weight.
According to one embodiment, the nitrogen-containing organic compound is added in conjunction with the sizing agent.
According to one embodiment, the nitrogen-containing organic compound is comprised in an aqueous dispersion comprising the acid anhydride.
According to yet a further embodiment of the invention the aqueous dispersion comprising an acid anhydride and a nitrogen-containing organic compound additionally comprises an anionic polyelectrolyte.
The anionic polyelectrolyte according to the invention can be selected from organic and inorganic compounds and it can be derived from natural or synthetic sources. The anionic polyelectrolyte has two or more anionic groups which can be of the same or different types. Examples of suitable anionic groups, i.e. groups that are anionic or rendered anionic in an aqueous phase, include silanol, aluminosilicate, phosphate, phosphonate, sulphate, sulphonate, sulphonic and carboxylic acid groups as well as salts thereof, usually ammonium or alkali metal (generally sodium) salts. The anionic polyelectrolytes may be water-soluble, e.g. linear and branched anionic polyelectrolytes, or water-dispersable, e.g. cross-linked and/or particulate anionic polyelectrolytes. According to one embodiment, the water-dispersable and particulate anionic polyelectrolytes are colloidal, i.e. in the colloidal range of particle size. The colloidal particles suitably have a particle size from 1 to 100, e.g. from 2 to 70 or from 2 to 40 nm. The water-dispersable and particulate anionic polyelectrolytes may contain aggregated and/or non-aggregated particles.
Examples of suitable organic anionic polyelectrolytes include anionic polysaccharides like starches, guar gums, celluloses, chitins, chitosans, glycans, galactans, glucans, xanthan gums, mannans, and dextrins. Further examples of suitable organic anionic polyelectrolytes include synthetic anionic polymers such as condensation polymers, e.g. polyurethanes and naphthalene-based and melamine-based polymers, e.g. condensated formaldehyde naphthalene sulfonates and polymers based on melamine-sulfonic acid, and vinyl addition polymers prepared from ethylenically unsaturated monomers including anionic or potentially anionic monomers, e.g. acrylic acid, methacylic acid, maleic acid, itaconic acid, crotonic acid, vinylsulfonic acid, sulfonated styrene and phosphates of hydroxyalkyl acrylates and methacrylates, optionally copolymerized with non-ionic ethylenically unsaturated monomers, e.g. acrylamide, alkyl acrylates, styrene and acrylonitrile as well as derivatives of such monomers, vinyl esters, and the like.
Examples of further suitable organic anionic polyelectrolytes include water-soluble branched polymers and water-dispersible crosslinked polymers obtained by polymerization of a monomer mixture comprising one or more ethylenically unsaturated anionic or potentially anionic monomers and, optionally, one or more other ethylenically unsaturated monomers, in the presence of one or more polyfunctional crosslinking agents. The presence of a polyfunctional crosslinking agent in the monomer mixture renders possible preparation of branched polymers, slightly crosslinked polymers and highly crosslinked polymers that are water-dispersible. Examples of suitable polyfunctional crosslinking agents include compounds having at least two ethylenically unsaturated bonds, e.g. N,N-methylene-bis-(meth)acrylamide, polyethyleneglycol di(meth)acrylate, N-vinyl (meth)acrylamide, divinyl-benzene, triallylammonium salts and N-methylallyl(meth)acrylamide; compounds having an ethylenically unsaturated bond and a reactive group, e.g. glycidyl (meth)acrylate, acrolein and methylol(meth)acrylamide; and compounds having at least two reactive groups, e.g. dialdehydes like glyoxal, diepoxy compounds and epichlorohydrin.
The organic anionic polyelectrolyte usually has a degree of anionic substitution (DSA) from 0.01 to 1.4, e.g. from 0.1 to 1.2 or from 0.2 to 1.0. The anionic polyelectrolyte may contain one or more cationic groups as long as it has an overall anionic charge. The molar mass of the anionic polyelectrolyte can vary within wide ranges; usually the molar mass is above 200 such as above 500, whereas the upper limit is usually 10 million such as 2 million g/mol.
Examples of suitable inorganic anionic polyelectrolytes include anionic siliceous materials, e.g. anionic silica-based materials prepared from silicic acid and clays of the smectite type. Usually, these anionic polyelectrolytes have negative silanol, aluminosilicate or hydroxyl groups. Examples of suitable inorganic anionic polyelectrolytes include polysilicic acid, polysilicates, polyaluminiumsilicates, colloidal silica-based particles, e.g. particles of silica, aluminated (aluminium-modified) silica and aluminiumsilicate, polysilicate microgels, polyaluminiumsilicate microgels, silica gels and precipitated silica, smectite clays, e.g. montmorillonite, bentonite, hectorite, beidelite, nontronite and saponite. Preferred anionic polyelectrolytes include silica-based materials, e.g. colloidal silica-based particles.
The acid anhydride can be any acid anhydride-based sizing agent known in the art. Suitably, the sizing agent is a hydrophobic acid anhydride. Suitable hydrophobic acid anhydrides can be characterized by the general formula (I) below, wherein R1 and R2 are independently selected from saturated or unsaturated hydrocarbon groups which suitably contain from 8 to 30 carbon atoms, or R1 and R2 together with the —C—O—C— moiety can form a 5 to 6 membered ring, optionally being further substituted with hydrocarbon groups containing up to 30 carbon atoms.
R1—(C═O)—O—(C═O)—R2
Examples of suitable acid anhydrides include alkyl and alkenyl succinic anhydrides, e.g. iso-octadecenyl succinic anhydride, iso-octadecyl succinic anhydride, n-hexadecenyl succinic anhydride, dodecenyl succinic anhydride, decenyl succinic anhydride, octenyl succinic anhydride, tri-isobutenyl succinic anhydride, 1-octyl-2-decenyl-succinic anhydride and 1-hexyl-2-octenyl-succinic anhydride. Examples of suitable acid anhydrides further include the compounds disclosed in U.S. Pat. Nos. 3,102,064; 3,821,069; 3,968,005; 4,040,900; 4,522,686; and Re. 29,960, which are hereby incorporated herein by reference.
The cellulose-reactive sizing agent may contain one or more acid anhydrides, e.g. one or more alkyl and/or alkenyl succinic anhydrides. Usually, the acid anhydride of this invention is liquid at room temperature.
The dispersion suitably contains a dispersant, or dispersant system, comprising an anionic polyelectrolyte and a nitrogen-containing organic compound. When used in combination, these compounds are effective as a dispersant for the acid anhydride sizing agent although the anionic polyelectrolyte and nitrogen-containing organic compound may not be effective as a dispersant when used singly. Preferably, the dispersion is anionic, i.e. the dispersant, or dispersant system, has an overall anionic charge.
With respect to the embodiment where the nitrogen-containing organic compound is comprised in the dispersion of the acid anhydride, the acid anhydride may be present in an amount of from about 0.1 to about 50, e.g. from 0.1 to about 30, or from about 1 to about 20% by weight, based on the weight of the aqueous dispersion. The optional anionic polyelectrolyte is usually present in an amount of up to about 100% by weight, usually from 0.1 to 15% by weight, suitably from 0.5 to 10, e.g. from 1 to 7% by weight, based on the weight of the acid anhydride. The nitrogen containing organic compound can be present in an amount of up to 20% by weight, usually from 0.1 to 15, such as from 0.5 to 10, or from 1 to 7% by weight, based on the weight of the acid anhydride. In addition to the acid anhydride, anionic polyelectrolyte and nitrogen containing organic compound, optional additional compounds may be present in the dispersion. Examples of such compounds include mono-, di- and poly-anionic and non-ionic surfactants and dispersing agents, stabilizers, extenders and preservative agents such as, for example, hydrolyzed acid anhydrides, e.g. hydrolyzed alkyl and alkenyl acid anhydrides as mentioned above, preferably hydrolyzed alkenyl succinic anhydrides, e.g. hydrolyzed acid anhydrides in the form of carboxylic acid and/or carboxylic acid ester derivatives, anionic surfactants like phosphate esters, such as ethoxylated phosphate esters, alkyl sulphates, sulphonates and phosphates, alkylaryl sulphates, sulphonates and phosphates, e.g. sodium lauryl sulphonate and ethoxylated, phosphated isotridecylalcohol. If present, the content of such additional compounds in the dispersion can be from 0.1 to 15, e.g. from 1 to 10, or from 2 to 7% by weight, based on the weight of the acid anhydride. Water is also present in the dispersion and may constitute the remainder of the dispersion up to 100% by weight.
The aqueous dispersion comprising the nitrogen-containing organic compound, the acid anhydride and optionally an anionic polyelectrolyte can be produced by forming a mixture containing the acid anhydride, anionic polyelectrolyte and nitrogen-containing organic compound as defined above and dispersing the mixture in the presence of water. The components of the dispersion may be admixed in any order but preferably the anionic polyelectrolyte and the nitrogen-containing organic compound are mixed and diluted with water to appropriate concentration, and then the acid anhydride is dispersed therein. According to an embodiment the dispersion containing the anionic polyelectrolyte, nitrogen-containing organic compound and acid anhydride is mixed with starch prior to the addition to the cellulosic suspension and/or to the paper web. The starch which is premixed with the acid anhydride dispersion may form part of the retention system. The mixture may be dispersed by using suitable dispersing equipment providing sufficient degree of dispersing, e.g. a static mixer providing relatively low shear forces. The obtained dispersion contains droplets of acid anhydride usually having a droplet size of from 0.1 to 10 μm in diameter.
The aqueous dispersion of acid anhydride comprising the nitrogen-containing organic compound may be added to the cellulosic suspension, i.e. anywhere between and including the machine chest and head box, or alternatively to the cellulosic web or sheet, e.g. at the size press. According to one embodiment, the aqueous acid anhydride dispersion is added to the cellulosic suspension prior to the head box.
The amount of acid anhydride sizing agent added to the cellulosic suspension or applied to the cellulosic sheet or web can be from about 0.01 up to about 1% by weight based on dry cellulosic suspension and optional fillers, such as from about 0.05 up to about 0.5% by weight.
The method and the use of the nitrogen-containing compound, and the aqueous sizing dispersions are also useful in the manufacture of paper from an aqueous cellulosic suspension having a high conductivity. The conductivity of the suspension that is dewatered on the wire can be within the range of from 0.3 mS/cm to 10 mS/cm. According to this invention, good results can be achieved when the conductivity is at least 2.0, e.g. at least 3.5 or at least 5.0, such as at least 7.5 ms/cm. Conductivity can be measured by standard equipment such as, for example, a WTW LF 330 instrument supplied by Christian Berner. The values referred to above are suitably determined by measuring the conductivity of the cellulosic suspension that is fed into or present in the headbox of the paper machine or, alternatively, by measuring the conductivity of white water obtained by dewatering the suspension. High conductivity levels mean high contents of salts (electrolytes) which can be derived from the materials used to form the stock, from various additives introduced into the stock, from the fresh water supplied to the process, etc. Further, the content of salts is usually higher in processes where white water is extensively recirculated, which may lead to considerable accumulation of salts in the water circulating in the process.
The invention also relates to a paper obtainable from the method as defined herein and to a paper comprising acid anhydride and/or derivatives thereof, a nitrogen-containing organic compound and at least one shading dye; and optionally at least one optical brightening agent, wherein the paper has no visual agglomerations of pigments.
The paper may be used in any conventional application. However, the paper can typically be used as printing paper or copying paper or any other use involving good printability properties of the paper.
The invention is further illustrated by the following examples, which, however, are not intended to limit the same. Parts and % relate to parts by weight and % by weight, respectively, unless otherwise stated.
EXAMPLE 1Aqueous dispersions of alkenyl succinic anhydride (ASA) were prepared by dispersing 10 g ASA based on an olefin fraction comprising iso-hexadecenyl and iso octadecenyl succinic anhydride in 190 g water containing 200 mg/l calcium chloride. All dispersion were prepared by using an Osterizer laboratory mixer. The aqueous phase was first added to the mixer. After addition of the ASA and optional amine containing silica sol (dispersion no. 2), the compositions were dispersed at high speed for 2 minutes.
ASA dispersion no. 1 was prepared by dispersing 10 g ASA (EKA SA 420) in the presence of 190 g water containing 200 mg/l calcium chloride at a temperature of 0° C. (ASA content of 5% by weight).
ASA dispersion no. 2 was prepared by dispersing 10 g ASA (EKA SA 820 SF) in 190 g water containing 200 mg/l calcium chloride at a temperature of 12° C. in the presence of 5 g of a silica sol having a content of SiO2 of 8.0% by weight and containing 50 (42.5% as active) % by weight of triethanol amine (TEA) based on SiO2 (ASA content of 5% by weight, triethanol amine content of 0.1% by weight, as active 0.085% by weight).
ASA dispersion no. 3 was prepared by dispersing 10 g of 100% hydrolysed ASA in 190 g water containing 200 mg/l calcium chloride at a temperature of 12° C. (ASA content of 5% by weight).
To all of the above prepared ASA dispersions were added 3.3 g of blue shading dye (undiluted Viscofil® blue BLF, Clariant®) and 28.6 g of violet shading dye (undiluted Levanyl® Violet BN-LF, Lanxess®). If the ASA dispersions (5%) correspond to an addition of 30 kg ASA/t dry fiber then the addition of shading dyes correspond to an addition of 100 g/t (blue) and 860 g/t (red/violet), respectively. After mixing the shading dye containing dispersions were allowed to rest for 20 minutes.
EXAMPLE 2Paper sheets were prepared according to a process in which the shading dye containing ASA dispersions of example 1 were added to an aqueous cellulosic suspension comprising 80% of softwood fibers and 20% of hardwood fibers (based on total fibers) having a fiber concentration of 5 g/l, 7% of ground calcium carbonate (GCC), a conductivity of 2 mS/cm (by the addition of calcium chloride), a pH of 7.9, and 1.75 kg/t optical brightener agent (OBA) (Leuchophore, UKO). The dispersions were added in an amount of 30 kg/t calculated as ASA based on dry cellulosic suspension. A retention system was used comprising 5 kg/t of cationic starch having a D.S. of 0.047 (Perlbond 970) and 7 kg/t polyaluminium chloride (PAC). After addition of the ASA dispersion to the aqueous cellulosic suspension the so formed cellulosic suspension was mixed during 10 sec. prior to the formation of a sheet using a KCL sheet former. The sheets were subsequently pressed during 8 minutes at 3.5 bar and thereafter dried. In this example, all amounts are based on dry cellulosic suspension if not otherwise indicated. Evaluation of the paper sheets with respect to color spots. Each paper was divided into four equal parts, each measuring 8×8 cm, which were labelled 1 through 4. Seven individuals (people) were given the task to count the number of blue and white spots in each paper section and record the total. The average number of spots recorded for each sheet is displayed in table 1 below.
In this example, all amounts are based on dry cellulosic suspension if not otherwise indicated. In a full scale trial printing and writing paper with a basis weight of 100-280 gram/m2 was manufactured using a papermaking process comprising a Fourdrinier Bruderhaus with a multi-cylinder drying process. The furnish suspension contained 50% virgin fibers, 15-20% dry broke, 17% dry broke, and 3-12% GCC or precipitated calcium carbonate (PCC) filler. The pH range of the furnish composition was between 6.8 and 7.4. To the wet end of the process the following components were added:
The acid anhydride sizing dispersion (Eka ASA 420) was fed into a starch stream prior to addition to the suspension. A nitrogen-containing organic compound was not present in the dispersion nor in the cellulosic suspension
b) According to InventionThe acid anhydride sizing agent EKA SA 820SF was emulsified into a stream of silica sol having a content of SiO2 of 8.0% by weight and containing 50% (42.5% as active) by weight of triethanol amine (TEA) based on SiO2 with a weight ratio of 2:1 prior to feeding the obtained dispersion into a cationic starch stream prior to addition to the suspension.
While using the EKA ASA 420 sizing dispersion, blue spots visually appeared in the paper after less than 5 days.
When using a sizing dispersion comprising Eka SA 820 SF and silica sol having a content of SiO2 of 8.0% by weight and containing 50% (42.5% as active) by weight of triethanol amine (TEA) based on SiO2 the paper had no visual blue spots after 125 day of continuous running.
Claims
1. A method for production of paper from an aqueous suspension containing cellulosic fibers comprising adding to the suspension and/or to a paper web prepared from the suspension i) a nitrogen-containing organic compound, ii) an aqueous dispersion of an acid anhydride; and iii) at least one shading dye, draining the suspension on a wire to form a paper.
2. The method according to claim 1, wherein the shading dye absorbs electromagnetic radiation in the visible spectrum without significantly emitting electromagnetic radiation or without emitting electromagnetic radiation.
3. The method according to claim 2, wherein electromagnetic radiation is absorbed in the spectrum from about 380 nm up to about 750 nm.
4. The method according to claim 2 or 3, wherein electromagnetic radiation is absorbed in the spectrum from about 380 nm up to about 495 nm and/or from about 590 nm up to about 750 nm.
5. The method according to any of the preceding claims, wherein the dye is selected from the group consisting of dioxazines and organic compounds comprising at least a phthalocyanine moiety.
6. The method according to any of the preceding claims, wherein the nitrogen-containing organic compound has a molar mass of up to about 500 g/mol.
7. The method according to any of the preceding claims, wherein the nitrogen-containing organic compound is an amine or a quaternary ammonium compound thereof.
8. The method according to any of the preceding claims, wherein the nitrogen-containing organic compound is an amine or quaternary ammonium compound thereof having a molar mass up to about 180 g/mol.
9. The method according to any of the preceding claims, wherein the nitrogen-containing organic compound is comprised in the aqueous dispersion comprising an acid anhydride.
10. The method according to claim 9, wherein the aqueous dispersion comprising an acid anhydride further comprises an anionic polyelectrolyte.
11. The method according to claim 10, wherein the anionic polyelectrolyte comprises colloidal silica-based particles.
12. The method according to claim 11, wherein the colloidal particles have a particle size from about 1 to about 100 nm.
13. The method according to any of the preceding claims, wherein the cellulosic fibers have a kappa number of less than about 8.
14. The method according to any of the preceding claims, wherein the cellulosic fibers have a brightness of more than about 83.
15. The method according to any of the preceding claims, wherein the conductivity of the cellulosic suspension is at least about 2.0 mS/cm.
16. The method according to any of the preceding claims, wherein the suspension further comprises at least one optical brightening agent.
17. Paper obtainable according to the method as defined by any of the preceding claims.
18. Paper comprising acid anhydride and/or derivatives thereof, a nitrogen-containing organic compound and at least one shading dye, wherein the paper has no visual agglomerations of pigments.
19. The paper according to claim 18, wherein the pigments are bluish.
20. Use of a nitrogen-containing organic compound being an amine or quaternary ammonium compound thereof having a molar mass less than about 180 g/mol in a method for producing paper from a suspension as an additive for improving the distribution of dyes in the paper, wherein the suspension comprises at least one shading dye.
21. The use according to claim 20, wherein the nitrogen-containing organic compound is comprised in an aqueous dispersion comprising an acid anhydride.
Type: Application
Filed: Jan 26, 2009
Publication Date: Jun 2, 2011
Applicant: Akzo Nobel N.V. (Arnhem)
Inventors: Marie Turunen (Spekerod), Jonas Liesén (Jorlanda), Hubert Igel (Gauriac)
Application Number: 12/864,986
International Classification: D21H 21/28 (20060101); D21H 23/04 (20060101);
