MXPA98007514A - A method for optically opening the pa - Google Patents

Abstract

A simplified method for the optical brightening of the paper, or in the pulp mass, the sizing press or the dosing press, or the coating by the use of a formulation of an optical brightening agent, together with an inflatable silicate in cap

Description

A METHOD TO OPTICALLY OPPILLATE PAPER The present invention relates to a simplified method for increasing the whiteness of paper, by the application of optical brighteners, also known as fluorescent whitening agents. Optical brightening formulations, together with layered inflatable silicates, have been described in the German Patent Application, open to the public, 19538029, as additives for detergents with improved properties. Surprisingly, it has been found that such formulations can be used advantageously for the optical brightening of the paper, in the pulp mass, the size press, the measuring press or in the coating. The object of the present invention is thus a method for the optical brightening of paper, which comprises the use of a formulation, consisting essentially of an inflatable layered silicate and an optical brightener. The silicates in inflatable layers are, for example, clay minerals, natural or synthetic, or sodium silicates. A suitable natural clay mineral is, for example, montmorillonite, beidelite, saponite or hectorite; Preferred synthetic species are zeolites (type A, X or β, etc.) and bentonites modified with acid or alkali.

The formulations used in the invention may be in the form of a dry mixture or, alternatively, in the form of an aqueous dispersion. In this way, the known advantages of the silicates in swellable layers, which are, for example, clay, natural or synthetic minerals or synthetic sodium silicates, such as high opacity, high whiteness, ion exchange properties and improved properties of the retention, can be combined simply with the properties of the optical brighteners, without losing the desired fluorescence effect of the latter. Preferably, the aqueous formulation contains 0.1 to 15% by weight, preferably 1 to 10% by weight of the optical brightener, based on the weight of the inflatable layered silicate. When the formulation is in the form of an aqueous dispersion, it contains about 2 to 60% by weight of the swellable layered silicate. The preferred range of bentonites is from about 2 to 25% and more preferably from 2 to 20%, by weight, for synthetic zeolites the appropriate range is from 2 to 50% by weight. Dispersing agents may be used, such as the naphthalenesulfonic acid polycondensates and the formaldehyde or lignin sulfonates.

When the formulation is in the form of a dry mixture, it may contain from 0.1 to 90% by weight, preferably from 1 to 50% by weight, of the optical brightener, based on the weight of the inflatable layered silicate. The optical brightener used in the method of the present invention is preferably a 4,4'-bis (triazinylamino) -stilben-2,2 * -disulfonic acid derivative, a 4,4'-styryl-biphenyl derivative or a derivative of dibenzo-furanylbiphenyl. Preferably, the optical brightener of the acid 4,4 * -bis (triazinylamino) -stilben-2, 2'-disulfonic has the formula: wherein R ^ and R2, independently, are phenylamino, phenylamino mono- or disulfonated, morpholino, -N (CH2CH2? H) 2, -N (CH3) (CH2CH2OH), -NH2, -N (Cj-C ^ alkyl) , -OCH3, -Cl, NHCH2CH2S? 3H, CH2CH2OH or ethanolamino-propionic acid amide, and M is H, Na, Li, K, Ca, Mg, ammonium, mono-di-, tri- or tetrasubstituted ammonium by C1 alkyl -C4 hydroxy-C1-C4 alkyl, or a mixture thereof Preferably, the optical 4,4'-diestinyl-biphenyl brightener has the formula: wherein R3 and R4, independently, are H, SO3M, S02N (C1-C alkyl) 2.0 (CiC ^ alkyl), CN, Cl, COO (C2-C4 alkyl), CON (C1-C4 alkyl) 2 or (CH2) 3N + (CH3) 2An ~, wherein M is H, Na, Li, K, Ca, Mg, ammonium or ammonium mono-, di-, tri- or tetrasubstituted by C1-C4 alkyl, hydroxyalkyl C ± - C ^ or a mixture thereof, and An is an anion, for example a mineral acid (hydrochloric or sulfuric acid) or lower carboxylic acid (C1-C4). Preferably, the dibenzofuranyl biphenyl optical brightener has the formula: which is unsubstituted or mono- or polysubstituted by radicals, R = hydrogen, alkyl ^ -C ^, alkoxy ^ -04, halogen, preferably chloro, phenoxy and benzyloxy, R ^ is hydrogen, C1-C4 alkyl, halogen, preferably chloro , phenyl or SO3M, M is hydrogen and / or an equivalent of a non-chromophoric cation and n is zero, 1 or 2. Preferred compounds of the formula (3) are those of the formula: where M, R and Rj have the indicated meanings, R and R- ^ are preferably methyl. More preferably, the optical brightener has the formula: Rx CH2CH2OH (6a) Rx CH3 (6b).

N HO OH or mixtures of at least two of the compounds (5) to (10). Using the method of the present invention, it has been found that it is possible to increase the whiteness of a pulp containing lignin, by a process which comprises adding to an aqueous pulp, which includes a pulp containing lignin, during the manufacture of the pulp. , before the drying stage or the paper manufacturing stage, if the pulp is not insulated, an effective amount of an optical rinse aid. While this optical brightener can be added to the slurry comprising the pulp with lignin, at any stage of the process, to minimize losses. It is advantageously added in the last stages of the manufacture of the pulp, before the final stages of dehydration and drying. Preferably, it is added before completing the bleaching stage. By "a pulp containing lignin" is meant any pulp that still contains about 5% or more of lignin by weight, on a dry basis. By definition, lignin is that portion of the pulp that is insoluble in 72 weight percent of the sulfuric acid. Suitable test procedures for the lignin content are given in TAPPI T 223 and ASTM D 1106. The process of this invention is useful in producing significant bleaching of pulps containing about 5% lignin in a dry weight basis, up to 100% of the lignin present in an equivalent amount of wood chips. Thus, the process can be employed, for example, in pulps with relatively low lignin content, such as certain bleached pulps of strong paper, up to and including larger lignin-containing pulps, such as thermomechanical pulps, thermo- chemi-mechanical bleached ("CTMP") and even de-inked bleached thermo-mechanical pulps. Preferably the pulps contain about 10% lignin by weight, on a dry weight basis; more preferably, they contain at least 15%. The bright range! which can be obtained varies from approximately 50 to 90+, depending on the brightness, the starting pulp and the type of pulp used. It is known to use chelating agents in processes to whiten the pulps of the mechanical processes that form these pulps. See V. N. Gupta ,. Pulp Paper Mag. Can. , 71 (18), T391-399 (1970). The addition of a chelating agent to an aqueous pulp paste controls the natural tendency of the yellowish color of the glucuronic, extractive and lignin acids present in the pulp, removing or minimizing iron and other heavy metals, such as copper. , zinc and manganese, which catalyze secondary reactions that form color. Iron and other heavy metals are converted into the highly soluble chelate form and are removed in large quantities in the dehydration stages. This decreases the incorporation of heavy metal ions into the pulp. Additionally, the chelating agent secretes salts of iron and other heavy metals, which remain and which, by themselves would otherwise relax the excited state of the optical brighteners and render them ineffective. Depending on the parameters of the process used in the pulp mill, this stage of metal control can be made routine in pulp formation processes, where reductive bleaching (for example by bisulfite bleach), hydrosulphite or formamidine sulphite) or oxidative bleaching (eg, bleached peroxy or peroxide) are employed. The addition of a chelating agent to an aqueous pulp slurry, if necessary, should be carried out prior to the addition of the optical brightener. The basic level of residual iron and other heavy metals and their ions in wood chips is generally about 10-25 ppm, although it is rather dependent on considerations of geography and species. The amount of iron and other heavy metals and their ions in the water used in pulp mills varies widely. Significant additional amounts of iron and other heavy metals and their ions are introduced during mechanical pulp formation of wood chips, as in recycling newspapers. Thus, the amount of iron and other heavy metals and their ions in the aqueous pulp during manufacture may be several hundred parts per million by weight, based on the dry weight of the pulp, in some stages of the manufacture of the pulp. pulp. It is often not necessary to add a chelating agent prior to the addition of the optical brightener, due to the common use of peroxy bleach, which requires the prior addition of chelating agents to be effective. However, a chelating agent is used advantageously if the aqueous pulp, which comprises the pulp with lignin, still contains 25 to 500 ppm by weight, based on the dry weight of the pulp, of iron salts and other heavy metals in the pulp. the process stage, where the optical brightener is going to be added. At the high end of this range, the polishing gain is moderated by the relaxation of the iron in the optical brightener, the tarnish of the pulp due to the natural color of the heavy metal salts, and the catalytic effect of the metals in the species of peroxy or reducing species (which, in turn, react with the cellulo-sa and the properties of the impact pulp). Initial levels of the iron salts and other heavy metal ions of 25 to 100 ppm, give the greatest improvement in polishing when the pulp slurry is treated with a chelating agent, before the combination with an optical brightener. In general, there is no practical advantage in reducing the content of iron and other heavy metals and their ions below the residual fundamental level found in wood chips. The heavy metal content can be determined by standard analytical methods, such as atomic absorption spectroscopy or inductively coupled plasma analysis. Once the type and amounts of the various heavy metals are known, the amount of the chelating agent to be used to reach 100 ppm or less, preferably 25 ppm or less, can be easily calculated or determined from the tables. It is not harmful to use a small excess. Thus, depending on the heavy metal content of the pulp slurry before the addition of the optical brightener, the selected chelating agent and the desired degree of improvement in whiteness, from 0 to about 1% by weight, based on the dry weight of the pulp, of a chelating agent, can be advantageously employed. An additional and substantial benefit of the chelate treatment is to open the matrix of the fibers to make it more accessible to the optical brightener. All types of chelating agents are suitable in the present invention, that is, those that offer the thermodynamic or kinetic control of metal ions.

However, preference is given to chelating agents that offer thermodynamic control, i.e. chelating agents that form a stable complex, which can be isolated, with a heavy metal ion. Within this group, it is particularly preferred to use the acid chelates to non-carboxylates. Well known and commercially available members of this class include ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), hydroxyethylenediaminetriacetic acid (HEDTA) and nitrilotriacetic acid (NTA). Mixtures of thermodynamic and kinetic chelating agents (eg, citrates, keto-acids, gluconates, heptagluconates, phosphates and phosphonates) also work well at reducing the content of heavy metal ions in the pulp to acceptable levels. A number of these kinetic control chelating agents are also commercially available. Kinetic control chelating agents are those that do not form stable, insulable complexes with a heavy metal ion. When used for fluorescent bleaching of paper, the formulations according to the present invention can also be applied to the paper substrate in the form of a paper coating composition or directly on the size press.

In a second aspect, the present invention provides a method for fluorescent bleaching of a paper surface, comprising contacting the surface of the paper with a coating composition comprising a white pigment; a binder dispersion; optionally, a co-binder, soluble in water; and a sufficient amount of a formulation according to the invention, to ensure that the treated paper contains 0.01 to 2% by weight, preferably 0.01 to 1% by weight, based on the white pigment, of the optical brightener (parts of the optical brightener for 100 parts of the pigment). As the white pigment component of the paper coating composition, used according to the method of the present invention, there are preferred inorganic pigments, for example aluminum or magnesium silicates, such as Chinese clay and kaolin and, in addition, barium sulfate, satin white, titanium dioxide, calcium carbonate (chalk) or talc; as well as white organic pigments. The used paper coating compositions, according to the method of the present invention, may contain, as a binder, among others, the dispersions of plastics based on copolymers of butadiene / styrene, acrylonitrile / butadiene / styrene, esters of acrylic acid, acrylic acid / styrene / acrylonitrile, ethylene / vinyl chloride and ethylene / vinyl acetate steres; or homopolymers, such as polyvinyl chloride, polyvinylidene chloride, polyethylene and polyvinyl acetate or polyurethanes. A preferred binder consists of copolymers of styrene / butyl acrylate or styrene / butadiene / acrylic acid or styrene / butadiene rubbers. Other polymer latexes are described, for example, in Patent Specifications of U.A.A., Nos. 3,265,654, 3,657,174, 3,547,899 and 3,240,740. The optional water-soluble protective colloid may be, for example, soy, protein, casein, carboxymethylcellulose, natural or modified starch, chitosan or a derivative thereof or, especially, polyvinyl alcohol. The preferred protective colloid component of polyvinyl alcohol can have a wide range of saponification and molecular weight levels; for example a level of saponification ranging from 40 to 100; and an average molecular weight that varies from 10,000 to 100,000. Formulations for coating compositions for paper are described, for example, in J. P. Casey "Pulp and Paper"; Chemistry and Chemical Technology, 2nd edition, Volume III, pages 1684-1649 and in "Pulp and Paper Manufacture" (2nd Edition), Volume II, page 497 (McGraw-Hill). The paper coating compositions used, according to the method of the present invention, contain from 10 to 70% by weight of a white pigment. The binder is preferably used in an amount which is sufficient to obtain the dry content of the polymer component, up to 1 to 30% by weight, preferably 5 to 25% by weight, of the white pigment. The amount of the preparation of the optical brightener used according to the invention is calculated so that this optical brightener is preferably present in amounts of 0.01 to 1% by weight, more preferably 0.05 to 1% by weight and especially 0.05 to 0.6. % by weight, based on the white pigment. The paper coating composition, used in the method according to the invention, can be prepared by mixing the components in any desired sequence, at a temperature of 10 to 100 ° C, preferably 20 to 80 ° C. The components herein also include the customary auxiliaries that can be added to regulate the reologic properties, such as the viscosity or water retention capacity, of the coating compositions. Such auxiliaries are, for example, natural binders, such as starch, casein, protein or gelatin, cellulose ethers, such as carboxyalkylcellulose or hydroxyalkylcellulose, alginic acid, alginates, polyethylene oxide, alkyl ethers of polyethylene oxide, copolymers of ethylene oxide and propylene oxide, polyvinyl alcohol, water-soluble condensation products of formaldehyde with urea or melamine, polyphosphates or salts of polyacrylic acid. The coating composition used, according to the method of the present invention, is preferably used to produce printed or coated writing paper or special papers, such as cardboard or photo papers. The coating composition, used in accordance with the method of the invention, can be applied to the substrate by any conventional process, for example with an air sheet, a cover sheet, a roller, a dosing sheet or a bar, or in sizing presses, after the coatings are dried at the surface temperatures of the paper in the range of 70 to 2002C, preferably 90 to 12302c, at a residual moisture content of 3 to 8%, for example, with dryers infrared or hot air dryers. Comparatively, high degrees of whiteness are achieved even at low drying temperatures. By the use of the method according to the invention, the coatings obtained are distinguished by the optimal distribution of the optical brightener over the entire surface and by an increase in the level of whiteness thus achieved, by a high firmness to light and temperatures high (for example, a stability for 24 hours at 60-1002C) and an excellent firmness of water bleeding. In a third aspect, the present invention provides a method for optical brightening a paper surface, comprising contacting the paper in the sizing press or the dosing press, with an aqueous preparation containing a size, optionally an inorganic pigment. or organic and 0.1 to 20 g / 1 of an optical brightener. Preferably, the sizing is starch, a starch derivative or a synthetic sizing agent, especially a water soluble copolymer. The layered silicates consist of natural or synthetic clay minerals, whereby the clay mineral is preferably montmorillonite, beidelite, saponite or hectorite. Montmorillonite can be used in the form of sodium or calcium, or, respectively, in the form of a calcium montmorillonite that has been exchanged for ions with soda. Clay minerals, prepared synthetically, from the groups mentioned above, can also be used. Alternatively, the synthetic layer-type sodium silicates (for example the commercial product SKS 5 from Hoechst AG) can also be used. These layered silicates have the property, by means of internal crystalline swelling, of being able to intercalate polar agents between the silicate laminates, which results, at higher concentrations, in an increase in the distance between the layers. Since naturally occurring layered silicate agglomerates can have a beige, gray or yellow appearance, the agglomerate particles of the formulation are preferably wrapped with a synthetic zeolite or a layer-type sodium silicate (preferably a 3 to 10% strength). 15% by weight) in order to increase its whiteness. Further preferred alternatives for distinguishing the coloration of the formulation with any of the addition of "bluish" dyes or pigments, for example Unidisperse® ™ Blue BE (commercial product of Ciba Specialty Chemicals Inc.), preferably in amounts of 0.3 to 5% by weight or the addition of color active substances, such as the photo-bleach agent Tinolux® ™ BB (commercial product of Ciba Specialty Chemicals Inc.), preferably in amounts of 0.3 to 5% by weight. The process for the preparation of the formulations used in the method of the present invention is described in detail in the German Patent Application, open to the public, 19538029. These formulations provide an improved distribution of the optical brightener within the paper, a more accurate addition and simplified of the polishing agent to the paper and better protection of the polish against the influences of light and oxygen. The following examples further illustrate the invention. The parts and percentages are by weight, unless indicated otherwise.

Example 1 5.0 g of Bentonite (Bentonit EX 0242®, Südchemie AG), were dispersed in 15 ml of deionized water containing 0.75 g of the compound of the formula (5) under rapid stirring, so that the resulting aqueous paste (dispersion) have a solids content of 25%. 0.27 g of this dispersion (0.068 g of bentonite and 0.01 g of the optical brightener) were added to 5 g of dry bleached CTMP short fibers (pulp), suspended in 150 ml of water (100 ppm CaO hardness). The mixture was stirred for 15 minutes, then 0.03% of a cationic retention aid (Percol 292®) was added and finally a sheet was formed using the Rapid Koethen system. The dried paper had an area weight of 160 g / m2.

The determination of the fluorescence was made with a Datacolor Spectralash 500 device. The ISO brightness was determined with and without a filter fraction at 420 nm and the difference between these two measurements is fluorescence. The ISO brightness rose from 79.9 to 87.1, which results in a fluorescence value of 7.2 Example 2 Example 1 was repeated, but using an aqueous paste prepared from 5.0 g of the bentonite and 0.25 g of the compound of the formula (8). The ISO brightness of the resulting paper increased from its initial value of 79.9 to 87.3, which results in a fluorescence value of 7.4.

Example 3 2.5 g of bentonite (Bentonit EX 0242®, Südchemie AG (or zeolite (Wessalith P80.6®, Degussa AG) were dispersed in 7.5 g of a 0.1 g aqueous solution of an optical brightener, 1 g of this suspension ( = 0.25 g of bentonite or zeolite and 0.01 g of the optical brightener) were added to 5 g of dry bleached CTMP fibers (pulp), suspended in 150 ml of water (100 ppm CaO hardness). 15 minutes, then 0.03% of the cationic retention aid (Percol 292®) was added and finally a sheet was formed using the Rapid Koethen system.The dry paper had an area weight of 160 g / m2.The following table gives the values of fluorescence that were determined as in the previous examples. 1 difference between the resulting value and the initial value (without an optical brightener) Analogous results are obtained when using the optical brighteners of formulas (9) or (10).

Claims (14)

1. A method for optically brightening paper, which comprises the use of a formulation consisting essentially of a layered inflatable silicate and an optical brightener.

2. A method, according to claim 1, wherein the formulation is in the form of a dry mixture or an aqueous dispersion.

3. A method, according to claim 2, in which the dry mix contains from 0.1 to 90% by weight of the optical brightener, based on the weight of the layered inflatable silicate.

4. A method, according to claim 2, in which the aqueous dispersion contains from 0.1 to 15% by weight of the optical brightener, based on the amount of the layered inflatable silicate.

5. A method, according to claim 4, in which the aqueous dispersion contains from 1 to 10% by weight of the optical brightener, based on the amount of the layered inflatable silicate.

6. A method, according to any of claims 2, 4 and 5, wherein the aqueous dispersion contains from 2 to 60% by weight of the layered inflatable silicate.

7. A method, according to claim 6, wherein the aqueous dispersion contains from 2 to 60%, preferably from 2 to 25%, by weight of a synthetic bentonite.

8. A method, according to claim 6, wherein the aqueous dispersion contains from 2 to 60%, preferably from 2 to 50%, by weight of a synthetic zeolite.

9. A method, according to any of claims 1 to 8, wherein the optical brightener is a derivative of 4,4'-bis- (triazinylamino) -stilben-2,2'-disulfonic acid or a derivative of 4.4 '-styryril-biphenyl.

10. A method, according to any of claims 1 to 8, wherein the optical brightener is a derivative of a dibenzofuranylbiphenyl.

11. A method, according to claim 9, wherein the optical brightener of 4,4'-bis- (triazinylamino) -stilben-2, 2'-disulfonic acid has the formula: wherein R ^ and R2, independently, are phenylamino, phenylamino mono- or disulfonated, morpholino, -N (CH2CH2? H) 2, -N (CH3) (CH2CH2OH), -NH2, -N (alkyo ^ -04) 2, -OCH 3, -Cl, NHCH 2 CH 2 SO 3 H, CH 2 CH 2 OH or ethanolamino-propionic acid amide; and M is H, Na, Li, K, Ca, Mg, ammonium, mono-di-, tri- or tetrasubstituted ammonium by C 1 -C 4 alkyl hydroxy (C 1 -C 4) alkyl, or a mixture thereof.

12. A method, according to claim 9, wherein the 4,4 '-distyryl-biphenyl optical brightener has the formula: wherein R3 and R4, independently, are H, SO3M, S02N (alkyl ^ -04) 2, O (C1-C4 alkyl), CN, Cl, COO (C2-C4 alkyl), CON (alk? C ^ C ^ or (CH2) 3N + (CH3) 2An-, wherein M is H, Na, Li, K, Ca, Mg, ammonium or ammonium mono-, di-, tri- or tetrasubstituted by alkyl 02-04, hydroxyalkyl C; j_-C4 or a mixture thereof, and An is an anion, for example a mineral acid (hydrochloric or sulfuric acid) or lower carboxylic acid (C1-C4).

13. A method, according to claim 9, wherein the optical brightener has the formula: Rx CH2CH2OH (6a) Rx CH3 (6b) or mixtures of at least two compounds of the formulas (5) to (8).

14. A method, according to claim 10, wherein the optical brightener has the formula: which is unsubstituted or mono- or poly-substituted by radicals R = hydrogen, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, halogen, preferably chlorine, phenoxy and benzyloxy, R 4 is hydrogen, C 1 -C 4 alkyl, halogen, preferably chloro, phenyl, or SO3M, M is hydrogen and / or an equivalent of a non-chromophoric cation and n is zero, 1 or 2; and preferably of the formula: where M, R and R ^ have the indicated meanings, R and ^ are preferably methyl.

15. A method, according to any of claims 1 to 14, wherein the formulation is added to the pulp mass.

16. A method, according to any of claims 1 to 14, wherein the formulation is added to the paper coating.

18. A method, according to any of claims 1 to 14, wherein the formulation is added to the sizing press or the dosing press.

19. Paper, which has been optically brightened by the method according to any of claims 1 to 18.