RU2799333C2 - Optically brightened latexes - Google Patents

Abstract

FIELD: chemical industry.

SUBSTANCE: present invention relates to a group of inventions: a method for producing an aqueous composition, an aqueous composition for optical brightening of a cellulose substrate, the use of an aqueous composition, a coating composition, a method for optically brightening a cellulose substrate, and a cellulose substrate. The method for obtaining an aqueous composition includes emulsion polymerization of at least one ethylenically unsaturated monomer in the presence of at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1):

This method includes the steps: a) preparing an aqueous solution containing or consisting of at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1) and optionally at least one dispersing agent; b) preparing a homogeneous pre-dispersion, the pre-dispersion containing or consisting of at least one ethylenically unsaturated monomer, water and at least one dispersing agent; c) preparing an aqueous solution containing or consisting of a water-soluble azo compound of formula (2) and/or formula (3); d) adding the pre-dispersion obtained in step (b) and the aqueous solution obtained in step (c) simultaneously to the aqueous solution obtained in step (a). The aqueous composition is used to optically brighten a cellulose substrate. The coating composition contains this aqueous composition. A method for optically brightening a cellulose substrate includes: applying a given aqueous composition or coating composition to a cellulose substrate and drying the cellulose substrate. A cellulose substrate treated with a given aqueous or coating composition.

EFFECT: development of water-based latex binders that are easily produced in the form of an emulsion, resistant to washout, capable of providing a higher threshold of whiteness without the use of carriers, toxicologically safe and economical to use.

17 cl, 2 tbl, 7 ex

Description

The field of technology to which the invention belongs

The present invention relates to a method for producing an aqueous composition by emulsion polymerization of at least one ethylenically unsaturated monomer in the presence of at least one water-soluble diaminostilbene-disulfone optical brightener, as well as to an aqueous composition obtained by this method, the use of this aqueous composition for optical brightening of a cellulose substrate (substrate ) and a cellulose substrate (substrate) treated with an aqueous composition.

State of the art

Surface treatment of paper or paperboard with a pigmented coating composition is used to improve surface properties such as brightness, smoothness, gloss, opacity and printability. Coating compositions are aqueous dispersions in which the total solids content is typically in the range of 50-70%, of which 80-90% contains one or more pigments such as kaolin clay or calcium carbonate. The pigment particles are fixed to the surface of the paper and to each other by a binder, which can be natural, such as starch, or synthetic, such as acrylate, styrene-acrylate, or styrene-butadiene latex. The coating composition also contains various additives such as colorants, optical brighteners, insolubilizers, plasticizers, rheology modifiers, dispersants, preservatives and defoamers.

Increasing the speed of coated paper production to 3000 m/min or more has led to a shift from natural binders to synthetic latexes capable of delivering high solids content while maintaining low viscosity.

The industry requires synthetic latex to be supplied as a water-based emulsion that can be applied directly to paper.

The consumer preference for coated paper (coated paper) for increased whiteness and brightness has led papermakers to mix optical brighteners with a pigmented coating composition (pigmented coating composition, pigmented coating composition).

Industrially preferred optical brighteners are of the water-soluble diaminostilbene-disulfone type due to their substantivity and affinity for cellulose fiber, their safety of use, and low cost of application.

However, the use of optical brighteners in coated paper is limited by a number of factors. One problem that needs to be addressed is that the optical brightener is washed out of the coated paper over time by the action of solvents, resulting in a pronounced yellowing of the paper. The second problem to be solved is that only a limited increase in whiteness is possible before the coating becomes "saturated" with optical brightener and the paper begins to take on a greenish tint. This second problem can currently only be solved by introducing high concentrations of the so-called "carrier" into the coating composition. Examples of suitable carriers include polyethylene glycol and polyvinyl alcohol.

One approach to solving the washout problem is to include a water-insoluble optical brightener in the emulsion polymerization process. Such optical brighteners are expensive, not readily available, and are not accepted for commercial use in the required quantities. In addition, they do not provide a solution to the problem of low whiteness threshold.

A second approach to solving the washout problem is to copolymerize the ethylenically unsaturated monomer with an acrylic, methacryl, or allyl substituted diaminostilbene disulfone optical brightener. Information on obtaining an emulsion that could be used in industry is not reported. Acryl-, methacryl- and allyl-substituted diaminostilbene disulfones are also expensive to manufacture and have an unexplored toxicological profile. In addition, no claim has been made of 100% optical brightener retention in the polymer.

Thus, there continues to be a need for water-based latex binders that are easy to emulsify, resistant to washout, capable of achieving a higher brightness threshold without the use of carriers, toxicologically safe, and economical to use.

Disclosure of invention

The problem is solved by a method for obtaining an aqueous composition, preferably a water-based latex binder, by emulsion polymerization of at least one ethylenically unsaturated monomer in the presence of at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1)

wherein

R ¹ and R ⁶ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN,

R ² and R ⁴ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CO ₂ M, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN ,

R ³ and R ⁵ are independently linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CO ₂ M, CH(CO ₂ M)CH ₂ CO ₂ M, CH( CO ₂ M)CH ₂ CH ₂ CO ₂ M, benzyl or

R ² and R ³ together with their neighboring nitrogen atom represent a morpholine ring and/or

R ⁴ and R ⁵ together with their neighboring nitrogen atom represent a morpholine ring,

R ⁷ and R ⁸ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl,

X and Y are independently CO ₂ M or SO ₃ M,

n and m are independently an integer selected from 0, 1, or 2, and

M is at least one cation for balancing the anionic charge of the optical brightener and is selected from the group consisting of or essentially consisting of hydrogen, an alkali metal cation, an alkaline earth metal cation, ammonium, an ammonium which is mono-, di-, tri-, or tetra-substituted linear or branched C ₁ -C ₄ alkyl radical, ammonium, which is a mono-, di -, tri - or tetrasubstituted linear or branched C ₁ -C ₄ hydroxyalkyl radical, ammonium, which is a di-, tri - or tetrasubstituted mixture of linear or branched C ₁ -C ₄ alkyl radicals, or linear or branched C ₁ -C ₄ hydroxyalkyl radicals, or a mixture of these cations.

Preferably, in the process of the invention, at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1)

R ¹ and R ⁶ are independently hydrogen, methyl, linear or branched C ₁ -C ₄ hydroxyalkyl or CH ₂ CH ₂ CONH ₂ ,

R ² and R ⁴ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN,

R ³ and R ⁵ are independently linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH(CO ₂ M)CH ₂ CO ₂ M, CH(CO ₂ M)CH ₂ CH ₂ CO ₂ M, benzyl or

R ² and R ³ together with their neighboring nitrogen atom represent a morpholine ring and/or

R ⁴ and R ⁵ together with their neighboring nitrogen atom represent a morpholine ring, and

R ⁷ and R ⁸ are independently hydrogen or methyl, and

M means at least one cation as defined above.

Preferably, in the process of the invention, at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1)

R ¹ and R ⁶ are hydrogen,

R ² and R ⁴ are independently hydrogen, linear or branched C ₁ -C ₂ alkyl, linear or branched C ₁ -C ₃ hydroxyalkyl,

R ³ and R ⁵ are independently linear or branched C ₁ -C ₂ alkyl, linear or branched C ₁ -C ₃ hydroxyalkyl, CH(CO ₂ M)CH ₂ CO ₂ M, CH(CO ₂ M)CH ₂ CH ₂ CO ₂ M, or

R ² and R ³ together with their neighboring nitrogen atom represent a morpholine ring and/or

R ⁴ and R ⁵ together with their neighboring nitrogen atom represent a morpholine ring, and

R ⁷ and R ⁸ are independently hydrogen or methyl, and

M means at least one cation, as previously defined.

Preferably, in the process according to the invention, at least one ethylenically unsaturated monomer is selected from (a) C ₁ -C ₁₈ -alkyl esters of (meth)acrylic acid, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl versatates, styrene and α-methylstyrene; (b) hydrophilic monomers such as (meth)acrylic acid, itaconic acid, vinylsulfonic acid, C ₁ -C ₈ -hydroxyalkyl esters of C ₁ -C ₆ -carboxylic acids, (meth) acrylamide, N-methylol (meth) acrylamide, ( meth)acrylonitrile, N-vinylformamide and N-vinylpyrrolidone; or (c) crosslinkers that have two or more ethylenically unsaturated double bonds, such as ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, divinylbenzene and trivinylbenzene; or mixtures of two or more of them.

Preferably, in the process according to the invention, at least one ethylenically unsaturated monomer is selected from (a) C ₁ -C ₆ -alkyl esters of (meth)acrylic acid, vinyl acetate, vinyl propionate and styrene; (b) hydrophilic monomers such as (meth)acrylic acid, vinylsulfonic acid, (meth)acrylamide and (meth)acrylonitrile; or mixtures of two or more of them.

Preferably, in the process according to the invention, at least one ethylenically unsaturated monomer is selected from (a) methyl methacrylate, butyl acrylate, vinyl acetate and styrene; (b) hydrophilic monomers such as (meth)acrylic acid, vinylsulfonic acid and acrylamide; or mixtures of two or more of them.

Preferably, in the process according to the invention, the emulsion polymerization is initiated with a water-soluble azo compound of formula (2) and/or formula (3)

(2)

(2)

(3)

(3)

wherein

X and Y are independently O or NH,

R and R' are independently hydrogen, or linear or branched C ₁ -C ₄ alkyl substituted with one or more hydroxyl, CO ₃ M ¹ or CO ₃ M ² groups, where M ¹ and M ² are at least one cation for balancing the anionic charge of the azo compound of formula (3) and are independently selected from the group consisting of or essentially consisting of hydrogen, an alkali metal cation, an alkaline earth metal cation, ammonium, ammonium, which is mono-, di-, tri-, or tetrasubstituted linear or branched C ₁ -C ₄ alkyl radical, ammonium, which is a mono-, di -, tri - or tetrasubstituted linear or branched C ₁ -C ₄ hydroxyalkyl radical, ammonium, which is a di-, tri - or tetrasubstituted mixture of linear or branched C ₁ - ₄ alkyl radicals, or linear or branched C ₁ -C ₄ hydroxyalkyl radicals, or a mixture of these cations.

Preferably, in the process according to the invention, the emulsion polymerization comprises at least the following four steps (a) to (d):

a) preparing an aqueous solution containing or consisting of at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1) and optionally at least one dispersing agent, and

b) preparing a homogeneous pre-dispersion, wherein the pre-dispersion contains or consists of at least one ethylenically unsaturated monomer, water and at least one dispersing agent, and

c) preparing an aqueous solution containing or consisting of a water-soluble azo compound of formula (2) and/or formula (3), and

d) adding the pre-dispersion obtained in step (b) and the aqueous solution obtained in step (c) simultaneously to the aqueous solution obtained in step (a).

The problem is also solved by an aqueous composition obtained by the method for obtaining an aqueous composition according to the invention, preferably an aqueous latex binder, by emulsion polymerization of at least one ethylenically unsaturated monomer in the presence of at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1)

wherein

R ¹ and R ⁶ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN,

R ² and R ⁴ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CO ₂ M, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN ,

R ³ and R ⁵ are independently linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CO ₂ M, CH(CO ₂ M)CH ₂ CO ₂ M, CH( CO ₂ M)CH ₂ CH ₂ CO ₂ M, benzyl or

R ² and R ³ together with their neighboring nitrogen atom represent a morpholine ring and/or

R ⁴ and R ⁵ together with their neighboring nitrogen atom represent a morpholine ring,

R ⁷ and R ⁸ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl,

X and Y are independently CO ₂ M or SO ₃ M,

n and m are independently an integer selected from 0, 1, or 2, and

M is at least one cation for balancing the anionic charge of the optical brightener and is selected from the group consisting of or essentially consisting of hydrogen, an alkali metal cation, an alkaline earth metal cation, ammonium, an ammonium which is mono-, di-, tri-, or tetra-substituted linear or branched C ₁ -C ₄ alkyl radical, ammonium, which is a mono-, di -, tri - or tetrasubstituted C ₁ -C ₄ linear or branched hydroxyalkyl radical, ammonium, which is a di-, tri - or tetrasubstituted mixture of linear or branched C ₁ -C ₄ alkyl radicals, or linear or branched C ₁ -C ₄ hydroxyalkyl radicals, or a mixture of these cations.

Preferably, at least one further additive is present in the aqueous composition according to the invention, the additive being selected from one or more biocides, one or more antifoam agents, one or more preservatives, one or more antifreeze agents, one or more thickeners, or mixtures thereof.

Preferably, in the aqueous composition according to the invention, more than 90% by weight, or more than 92% by weight, or more than 94% by weight, or more than 96% by weight, or more than 98% by weight, or more than 99% by weight of optical brightener of formula (1) were retained in the polymer, the weight % being based on the total amount of optical brightener of formula (1) present in the aqueous composition.

Another aspect of the invention relates to the use of an aqueous composition of the invention for optically brightening a cellulose substrate, preferably wherein the aqueous composition is used in the coating composition.

Another aspect of the present invention relates to a coating composition containing at least an aqueous composition according to the invention.

Another aspect of the present invention relates to a method for optically brightening a cellulose substrate, comprising the steps of i) applying an aqueous composition of the invention or a coating composition of the invention to a cellulose substrate and ii) drying the cellulose substrate.

Another aspect of the invention relates to a cellulose substrate treated with an aqueous composition of the invention or a coating composition of the invention.

Implementation of the invention

The method according to the invention has the advantage of obtaining an aqueous composition according to the invention containing at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1).

The term "aqueous composition" as used in the context of this application refers to an aqueous composition, i.e. the composition contains water. In addition, the aqueous composition of the invention is in the form of a polymer dispersion in which a non-polymerizable, water-soluble diaminostilbene-disulfone optical brightener of formula (1) is included/retained.

In this regard, we are talking about example 1, given in the section of examples of the invention, which discloses how to determine the amount of free, i. non-trapped/retained non-polymerizable, water-soluble diaminostilbene-disulfone optical brightener of formula (1).

The advantage of the aqueous composition according to the invention is that when applied to the surface of a substrate, for example the surface of a cellulose substrate, either in the form of an aqueous composition according to the invention or in the form of, for example, a coating composition (coating composition), followed by a drying step, on the surface substrate, a coating is formed in which the non-polymerizable water-soluble diaminostilbene-disulfone optical brightener of formula (1) is still retained in the polymer matrix and is not released into the environment, i.e. exhibits washout resistance. Another advantage is that the surface of the substrate thus treated has a high whiteness threshold without requiring the presence of a secondary binder or carrier.

The term "retained/trapped" as used in the context of this application refers to the optical brightener molecules of formula (1) which are distributed within the polymer or polymer dispersion and therefore are not detected by the method described in Example 1. In contrast, the amount of free optical the bleach of formula (1) present in the aqueous composition according to the invention can be determined by the method described in Example 1.

Preferably, the amount of free optical brightener of formula (1) present in the aqueous composition of the invention is less than 10% by weight, or less than 8% by weight, or less than 6% by weight, or less than 4% by weight, or less than 2% by weight. mass, or below the detection limit of the method described in Example 1, ie. below 1% by weight, with the weight % based on the total amount of optical brightener of formula (1) present in the aqueous composition of the invention. On the other hand, more than 90% by mass, or more than 92% by mass, or more than 94% by mass, or more than 96% by mass, or more than 98% by mass, or more than 99% by mass of the optical brightener of formula (1) are retained, the weight % being based on the total amount of optical brightener of formula (1) present in the aqueous composition of the invention.

Preferably, the aqueous composition of the invention is in the form of an aqueous latex binder.

The term "optical brightener" in the context of the present application can be used interchangeably with the terms OOA, or optical brightening agent, or brightening agent, or fluorescent brightening agent, or FHA, or fluorescent brightening agent, and refers to a compound of general formula (1) having diaminostilbene-disulfone fragment:

wherein

R ¹ and R ⁶ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN,

R ² and R ⁴ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CO ₂ M, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN ,

R ³ and R ⁵ are independently linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CO ₂ M, CH(CO ₂ M)CH ₂ CO ₂ M, CH( CO ₂ M)CH ₂ CH ₂ CO ₂ M, benzyl or

R ² and R ³ together with their neighboring nitrogen atom represent a morpholine ring and/or

R ⁴ and R ⁵ together with their neighboring nitrogen atom represent a morpholine ring,

R ⁷ and R ⁸ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl,

X and Y are independently CO ₂ M or SO ₃ M,

n and m are independently an integer selected from 0, 1, or 2, and

M is at least one cation for balancing the anionic charge of the optical brightener and is selected from the group consisting of or essentially consisting of hydrogen, an alkali metal cation, an alkaline earth metal cation, ammonium, an ammonium which is mono-, di-, tri-, or tetra-substituted linear or branched C ₁ -C ₄ alkyl radical, ammonium, which is a mono-, di -, tri - or tetrasubstituted linear or branched C ₁ -C ₄ hydroxyalkyl radical, ammonium, which is a di-, tri - or tetrasubstituted mixture of linear or branched alkyl C ₁ -C ₄ radicals, or linear or branched C ₁ -C ₄ hydroxyalkyl radicals, or a mixture of these cations.

An advantage of the optical brightener of formula (1) used in the aqueous composition of the invention is that it is readily and substantially completely soluble in water, thereby forming an aqueous solution. Therefore, the optical brightener of formula (1) used in the aqueous composition according to the invention should be considered as "water-soluble.

In addition, the optical brightener of formula (1) used in the aqueous composition according to the invention should be considered as an anionic optical brightener due to the presence of anionic groups, in particular SO ₃ ^- and/or CO ₂ ^- groups, which introduce an anionic charge into the optical brightener molecule. The optical brightener of formula (1) is water soluble due to the presence of anionic groups, in particular SO ₃ ^- and/or CO ₂ ^- groups.

The optical brightener of formula (1) should be distinguished from cationic optical brightening agents or neutral optical brightening agents. Unlike the optical brightener of formula (1) used in the aqueous composition of the invention, cationic optical brighteners or neutral optical brighteners exhibit low solubility or even insolubility in water. The term "cationic OOA" should be understood as OOA, in which a cationic charge is located on the molecule. The term "neutral OOA" should be understood as OOA, in which there is no charge in the molecule. Examples of such OOA are stilbenes, benzoxazoles, coumarins, pyrenes and naphthalenes.

Preferably, the presence of one or more cationic and/or neutral OOA is excluded from the aqueous composition of the invention.

In addition, the optical brightener of formula (1) used in the aqueous composition of the invention is non-polymerizable, i. does not contain any ethylenically unsaturated residues. In this regard, we are talking about the definitions given here for the residues R ¹ -R ⁸ , X and Y present in the optical brightener of formula (1).

Preferably, the presence of one or more optical brighteners containing ethylenically unsaturated residues is excluded from the aqueous composition of the invention.

In addition, in a preferred embodiment of the invention, the presence of one or more optical brighteners containing ethylenically unsaturated residues and the presence of one or more cationic and/or neutral optical brighteners are excluded from the aqueous composition of the invention.

Preferred water-soluble diaminostilbene-disulfone optical brighteners of formula (1) are those wherein

R ¹ and R ⁶ are independently hydrogen, methyl, linear or branched C ₁ -C ₄ hydroxyalkyl or CH ₂ CH ₂ CONH ₂ ,

R ² and R ⁴ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN,

R ³ and R ⁵ are independently linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH(CO ₂ M)CH ₂ CO ₂ M, CH(CO ₂ M)CH ₂ CH ₂ CO ₂ M, benzyl or

R ² and R ³ together with their neighboring nitrogen atom represent a morpholine ring and/or

R ⁴ and R ⁵ together with their neighboring nitrogen atom represent a morpholine ring, and

R ⁷ and R ⁸ are independently hydrogen or methyl, and M is at least one cation for balancing the anionic charge of the optical brightener and is selected from the group consisting of or essentially consisting of hydrogen, an alkali metal cation, an alkaline earth metal cation, ammonium , ammonium which is a mono-, di-, tri- or tetra-substituted linear or branched C ₁ -C ₄ alkyl radical, ammonium which is a mono-, di-, tri- or tetra-substituted linear or branched C ₁ -C ₄ hydroxyalkyl radical , ammonium, which is di-, tri - or tetrasubstituted by a mixture of linear or branched C ₁ -C ₄ alkyl radicals, or linear or branched C ₁ -C ₄ hydroxyalkyl radicals, or a mixture of these cations.

The most preferred water-soluble diaminostilbene-disulfone optical brighteners of formula (1) are those wherein

R ¹ and R ⁶ are hydrogen,

R ² and R ⁴ are independently hydrogen, linear or branched C ₁ -C ₂ alkyl, linear or branched C ₁ -C ₃ hydroxyalkyl,

R ³ and R ⁵ are independently linear or branched C ₁ -C ₂ alkyl, linear or branched C ₁ -C ₃ hydroxyalkyl, CH(CO ₂ M)CH ₂ CO ₂ M, CH(CO ₂ M)CH ₂ CH ₂ CO ₂ M, or

R ² and R ³ together with their neighboring nitrogen atom represent a morpholine ring and/or

R ⁴ and R ⁵ together with their neighboring nitrogen atom represent a morpholine ring, and

R ⁷ and R ⁸ are independently hydrogen or methyl, and M is at least one cation for balancing the anionic charge of the optical brightener and is selected from the group consisting of or essentially consisting of hydrogen, an alkali metal cation, an alkaline earth metal cation, ammonium , ammonium which is a mono-, di-, tri- or tetra-substituted linear or branched C ₁ -C ₄ alkyl radical, ammonium which is a mono-, di-, tri- or tetra-substituted linear or branched C ₁ -C ₄ hydroxyalkyl radical , ammonium, which is di-, tri - or tetrasubstituted by a mixture of linear or branched C ₁ -C ₄ alkyl radicals, or linear or branched C ₁ -C ₄ hydroxyalkyl radicals, or a mixture of these cations.

The aqueous composition of the invention may contain one or more water-soluble diaminostilbene-disulfone optical brighteners of formula (1).

The aqueous composition of the invention further comprises a polymer dispersion. The polymer dispersion results from the polymerization of at least one ethylenically unsaturated monomer, which occurs during the process according to the invention. The term "polymer dispersion" refers to a dispersion of at least one polymer in an aqueous medium, preferably water, in which, when visually inspecting the dispersion with the naked eye, only one single phase is visible. Therefore, a polymer dispersion can also be considered as an emulsion.

The polymer dispersion can be made as a homopolymer dispersion, which means that only one kind of ethylenically unsaturated monomer is used in the emulsion polymerization according to the method according to the invention. A polymer dispersion may also be defined as a copolymer dispersion. The term "copolymer" means a polymer in which at least two ethylenically unsaturated monomers are used in its polymerization, at least two monomers being different from each other. For example, monomers have different molecular formulas.

At least one ethylenically unsaturated monomer is selected from (a) C ₁ -C ₁₈ -alkyl esters of (meth)acrylic acid, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl versatates, styrene and α-methylstyrene; (b) hydrophilic monomers such as (meth)acrylic acid, itaconic acid, vinylsulfonic acid, C ₁ -C ₈ -hydroxyalkyl esters of C ₁ -C ₆ -carboxylic acids, (meth) acrylamide, N-methylol (meth) acrylamide, ( meth)acrylonitrile, N-vinylformamide and N-vinylpyrrolidone.

Preferred ethylenically unsaturated monomers are selected from C ₁ -C ₆ -alkyl esters of (meth)acrylic acid, vinyl acetate, vinyl propionate and styrene; b) hydrophilic monomers such as (meth)acrylic acid, vinylsulfonic acid, (meth)acrylamide and (meth)acrylonitrile.

The most preferred ethylenically unsaturated monomers are selected from (a) methyl methacrylate, butyl acrylate, vinyl acetate and styrene; (b) hydrophilic monomers such as (meth)acrylic acid, vinylsulfonic acid and acrylamide.

Other suitable monomers that may be included are crosslinkers (c) which have two or more ethylenically unsaturated double bonds, such as ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, divinylbenzene and trivinylbenzene.

As used herein, the term "(meth)acrylate" refers to both "acrylate" and "methacrylate", and the term "(meth)acrylic" refers to both "acrylic" and "methacrylic".

The aqueous composition of the invention contains a product obtained by emulsion polymerization of at least one ethylenically unsaturated monomer in the presence of at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1). In addition, the aqueous composition according to the invention may contain at least one dispersing agent and/or residues of a water-soluble azo compound of formula (2) and/or formula (3).

A water-soluble azo compound of formula (2) and/or formula (3) is used as a radical initiator in the method of the invention:

(2)

(2)

(3)

(3)

Where

X and Y, independently of one another, O or NH, R and R' are independently hydrogen, or linear or branched C ₁ -C ₄ alkyl substituted with one or more hydroxyl, CO ₂ M ¹ or SO ₃ M ² groups, where M ¹ and M ² denote at least one cation for balancing the anionic charge of the azo compound of formula (3) and are independently selected from the group consisting of or essentially consisting of hydrogen, an alkali metal cation, an alkaline earth metal cation, ammonium, ammonium, which is a mono-, di-, tri- or tetra-substituted linear or branched C ₁ -C ₄ alkyl radical, ammonium, which is a mono-, di-, tri- or tetra-substituted linear or branched C ₁ -C ₄ hydroxyalkyl radical, ammonium, which is di-, tri- or tetra-substituted with a mixture of linear or branched C ₁ -C ₄ alkyl radicals, or linear or branched C ₁ -C ₄ hydroxyalkyl radicals, or a mixture of these cations.

The use of water-soluble azo compounds of formula (2) and formula (3) in the method of the invention, i.e. for initiating emulsion polymerization, is advantageous for obtaining an aqueous composition according to the invention. Another advantage of using the water-soluble azo compounds of formula (2) and formula (3) in the process of the invention is that the amount of reaction mass after emulsion polymerization, which is present in the form of grits and therefore unusable, is less than 10 mass. %, or less than 8 wt. %, or less than 6 wt. %, or less than 4 wt. %, or less than 2 wt. %, or less than 1 wt. %, and mass. % is based on the total weight of the reaction mixture.

The azo compounds of formula (2) and formula (3) are well known radical initiators and can be obtained, for example, from Wako Chemicals.

The term "dispersing agent", used in the context of this application, should be understood as an agent that facilitates the dispersion of one or more components in a dispersion medium. The process of the invention uses at least one dispersing agent, i.e. used to form a pre-dispersion of water and at least one ethylenically unsaturated monomer. Anionic and nonionic dispersants are preferred.

Suitable anionic dispersing agents include, for example, alkaline fatty alcohol sulfates such as sodium lauryl sulfate; arylalkyl sultanates such as potassium isopropylbenzenesultanate; alkaline alkyl sulfosuccinates such as sodium octyl sulfosuccinate; and alkaline arylalkylpolyethoxyethanol sulfates or sultanates such as sodium t-octylphenoxypolyethoxyethyl sulfate having from 1 to 30 oxyethylene units.

Suitable non-ionic dispersing agents include, for example, alkylphenoxypolyethoxyethanols having alkyl groups from 7 to 18 carbon atoms and from 6 to 60 oxyethylene units, such as, for example, heptylphenoxypolyethoxyethanols; ethylene oxide derivatives of long chain carboxylic acids such as lauric acid, myristic acid, palmitic acid, oleic acid or mixtures of acids such as those found in tall oil containing 6 to 60 oxyethylene units; ethylene oxide condensates of long chain alcohols such as octyl, decyl, lauryl or cetyl alcohols containing from 6 to 60 oxyethylene units; ethylene oxide condensates of long chain or branched amines such as dodecylamine, hexadecylamine and octadecylamine containing from 6 to 60 oxyethylene units; and block copolymers of ethylene oxide moieties combined with one or more hydrophobic propylene oxide moieties.

High molecular weight polymers such as starch, hydroxyethylcellulose, methylcellulose, polyacrylic acid, polyvinyl alcohol can be used as dispersion stabilizers and protective colloids.

The term "pre-dispersion" refers to a dispersion of at least one ethylenically unsaturated monomer in an aqueous medium, preferably water, in which only one single phase is visible upon visual inspection of the dispersion with the naked eye. Thus, at least one ethylenically unsaturated monomer is homogeneously dispersed in the aqueous medium. Homogeneous dispersion of at least one ethylenically unsaturated monomer is preferably achieved using at least one dispersing agent.

The aqueous composition according to the invention may further comprise at least one additive selected from one or more biocides, one or more antifoam agents, one or more preservatives, one or more antifreeze agents, one or more thickeners, or mixtures thereof.

Examples of suitable biocides that can be used in the composition according to the invention are available under the trade names Acticide ^® and Nipacide ^® .

Preferably, the aqueous composition of the invention is essentially free, preferably completely free, of any precipitated and/or coagulated polymer particles or optical brightener particles.

Another advantage of the aqueous composition according to the invention is that it is stable, for example, with respect to electrolytes, temperature effects or tangential forces.

The aqueous composition of the invention is obtained by the process of the invention by emulsion polymerization of at least one ethylenically unsaturated polymer in the presence of at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1).

The term "emulsion polymerization" as used in the context of this application refers to a polymerization in which water-insoluble monomers are dispersed in water with the help of dispersing agents such as lauryl sulfate and the polymerization is initiated using radical initiators, preferably water-soluble azo compounds of formulas (2) and (3).

The advantage of using emulsion polymerization in the process according to the invention is that the aqueous composition according to the invention thus obtained can be used immediately, i.e. the aqueous composition thus obtained can be packaged for sale or storage with or without a preceding purification step, or directly used. , for example, in a coating composition with or without a previous cleaning step.

Emulsion polymerization in the process of the invention comprises at least the following four steps: (a) preparing an aqueous solution containing or consisting of at least one water-soluble diaminostilbene optical brightener of formula (1) and optionally at least one dispersing agent, and (b) preparing a homogeneous pre-dispersion, the pre-dispersion comprising or consisting of at least one ethylenically unsaturated monomer, water and at least one dispersing agent, and (c) preparing an aqueous solution containing or consisting of a water-soluble azo compound of formula (2) and/or formula (3), and (d) adding the pre-dispersion obtained in step (b) and the aqueous solution obtained in step (c) simultaneously to the aqueous solution obtained in step (a).

The term "aqueous solution", as used in the context of this application, refers to a liquid medium, which is water, in which one or more components, for example, an optical brightener according to formula (1) or azo compounds according to formula (2) or formula (3), essentially completely dissolved in the liquid, that is, particles of one or more components are absent in the aqueous solution.

In the method according to the invention, steps (a) to (c) can be performed in any order. In addition, steps (a) to (c) can be performed simultaneously.

In step (d) in the process according to the invention, the pre-dispersion obtained in step (b) and the aqueous solution obtained in step (c) are added to the aqueous solution obtained in step (a), mixing at a speed of 50 to 200 rpm /min The pre-dispersion obtained in step (b) and the aqueous solution obtained in step (c) are added simultaneously over a period of 1 to 10 hours, preferably over a period of 2 to 6 hours.

The emulsion polymerization is preferably started with heating. The heating temperature must be high enough so that the radical initiator, ie the azo compound of formula (2) and/or formula (3), separates nitrogen, thus forming an organic radical. A suitable temperature range is 55 to 95°C, preferably 75 to 95°C. Preferably, the aqueous solution obtained in step (a) is heated to the desired temperature before adding the pre-dispersion obtained in step (b) and the aqueous solution obtained in step (c). The temperature must be maintained during the addition of the pre-dispersion obtained in step (b) and the aqueous solution obtained in step (c).

After adding the pre-dispersion obtained in step (b) and the aqueous solution prepared in step (c) to the aqueous solution prepared in step (a), the reaction mixture thus obtained can either be further maintained at the desired temperature for a certain additional period of time, or the reaction mixture can be allowed to cool, for example, to room temperature.

The method of the invention may further comprise one or more purification steps after the emulsion polymerization. For example, one purification step can be carried out after completion of the emulsion polymerization by removing solid particles, such as large aggregates (grits) of the reaction mass, by filtering the reaction mixture.

The optical brightener of formula (1) is prepared by methods known to those skilled in the art and described in the prior art. The following production method is one example of a production method for an optical brightener of formula (1).

The method for producing an optical brightener of formula (1) includes reaction A followed by reaction B followed by reaction C. The following production method can be applied to each optical brightener that falls under the general formula (1).

In reaction A, a compound of formula (10) reacts with a compound of formula (11) to form a compound of formula (12)

In reaction B, the compound of formula (12) obtained in reaction A reacts with the compound of formula (13) to form a compound of formula (14)

Alternatively, a compound of formula (14) is prepared by reacting a compound of formula (10) first with a compound of formula (13) and then reacting with a compound of formula (11).

In reaction C, the compound of formula (14) obtained in reaction B is reacted with a compound of formula (15) and a compound of formula (16) to form an aqueous composition containing a compound of formula (I) and diethanolamine.

In formulas (10) - (16) R ¹ and R ⁶ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN, R ² and R ⁴ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CO ₂ M, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN, R ³ and R ⁵ are independently linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CO ₂ M, CH(CO ₂ M)CH ₂ CO ₂ M, CH(CO ₂ M)CH ₂ CH ₂ CO ₂ M, benzyl, or R ² and R ³ together with their neighboring nitrogen atom represent a morpholine ring and/or R ⁴ and R ⁵ together with their neighboring nitrogen atom represent a morpholine ring , R ⁷ and R ⁸ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, X and Y are independently CO ₂ M or SO ₃ M, n and m are 0, 1 or 2, and M is a cation for balancing the anionic charge of the optical brightener and is selected from the group consisting of or essentially consisting of hydrogen, alkali metal cation, alkaline earth metal cation, ammonium, ammonium, which is mono-, di-, tri- or tetra-substituted linear or branched C ₁ -C ₄ alkyl radical, ammonium, which is a mono-, di -, tri - or tetrasubstituted linear or branched C ₁ -C ₄ hydroxyalkyl radical, ammonium, which is a di-, tri - or tetrasubstituted mixture of linear or branched C ₁ - C ₄ alkyl radicals, or linear or branched C ₁ -C ₄ hydroxyalkyl radicals, or a mixture of these cations.

Each reaction A, B and C is preferably carried out in water or in a mixture of water and a non-aqueous organic solvent. Preferably the compound of formula (10) is suspended in water or the compound of formula (10) is dissolved in a solvent such as acetone. Preferably the compound of formula (10) is used as a suspension in water.

Each compound of formula (10), (13), (15) or (16) may be used with or without dilution; in the case of dilution, the compounds of formula (10), (13), (15) or (16) are preferably used in the form of an aqueous solution or suspension.

Preferably, the compound of formula (10) reacts in an excess of 0 to 10 mol. % relative to the compound of formula (11). One mol equivalent of a compound of formula (13) is reacted with two mol equivalents of a compound of formula (12), preferably in an excess of 0 to 10 mol. % relative to the compound of formula (12). The compound of formula (15) and the compound of formula (16) are reacted with one mol equivalent of the compound of formula (14), preferably the compounds of formulas (15) and (16) are co-reacted with an excess of 0 to 30 mol. % relative to the compound of formula (14).

Preferably any reaction A, B and C is carried out under pressure in the range from atmospheric to 10 bar, more preferably at atmospheric pressure.

In reaction A, the reaction temperature is preferably -10 to 20°C. In reaction B, the reaction temperature is preferably 20 to 80°C. In Reaction C, the reaction temperature is preferably 60 to 102°C.

Reaction A is preferably carried out under acidic or neutral pH conditions, more preferably the pH is between 2 and 7. Reaction B is preferably carried out under slightly acidic or slightly alkaline conditions, more preferably the pH is between 4 and 8. Reaction C is preferably carried out under slightly acidic or alkaline conditions, more preferably the pH is from 5 to 11.

The pH of each reaction A, B and C is usually controlled by the addition of a suitable base, the choice of base being dictated by the desired composition of the product. Preferred bases are selected from the group consisting of aliphatic tertiary amines and alkali and/or alkaline earth metal hydroxides, carbonates and bicarbonates and mixtures thereof. Preferred alkali and alkaline earth metals are selected from the group consisting of lithium, sodium, potassium, calcium and magnesium. Preferred aliphatic tertiary amines are 2-[2-hydroxyethyl(methyl)amino]ethanol, 2-(dimethylamino)ethanol, triethanolamine and triisopropanolamine. If a combination of two or more different bases is used, the bases may be added in any order or at the same time. Preferred bases are NaOH, LiOH and KOH.

In cases where it is necessary to adjust the pH of the reaction with an acid, preferred acids are selected from the group consisting of hydrochloric acid, sulfuric acid, formic acid and acetic acid.

The resulting compositions containing an optical brightener of formula (1) may optionally be desalted by membrane filtration. The membrane filtration process is preferably an ultrafiltration process. It is preferable to use thin film membranes. Preferably the membrane is made from polysulfone, polyvinylidene fluoride or cellulose acetate.

The present application also relates to the use of the aqueous composition of the invention for the optical brightening of a cellulose substrate. Preferably, the aqueous composition of the invention is used in the coating composition of the invention to optically brighten a cellulose substrate.

The term "cellulose substrate" in the context of this application refers to a substrate/substrate that contains or consists essentially of cellulose. The cellulose substrate can be selected from paper, cardboard or cotton.

Preferably, the cellulosic substrate comprises a web/web of cellulosic fibers, which may be synthetic or derived from any fibrous plant, including woody and non-woody sources. Preferably, the cellulosic fibers are derived from hardwood and/or softwood. These fibers can be either natural fibers or recycled fibers or any combination of natural and recycled fibers.

The cellulose fibers contained in the cellulose substrate can be modified by physical and/or chemical methods, as described, for example, in chapters 13 and 15, respectively, in the Handbook for Pulp & Paper Technologists by GA Smook, ^2nd Edition Angus Wilde Publications, 1992 One example of chemical modification of cellulose fiber is the addition of an optical brightener, as described, for example, in EP 0 884 312 A1, EP 0 899 373 A1, WO 02/055646 A1, WO 2006/061399 A2, WO 2007/017336 A1, WO 2007/143182 A2, US 2006/0185808 and US 2007/0193707.

The aqueous composition according to the invention can be applied to a cellulosic substrate in a coating composition, in particular in a pigmented coating composition. The amount of aqueous composition present in the coating composition is in the range from 1 to 40 wt. %, and mass. % based on dry weight of white pigment.

The coating composition for optically brightening a cellulose substrate contains or consists of an aqueous composition according to the invention and may additionally contain or consist of at least one pigment and/or at least one binder.

However, the use of the aqueous composition according to the invention has the advantage that no additional binder is required in the coating composition.

Preferably, the amount of free optical brightener of formula (1) present in the coating composition of the invention is less than 10% by weight, or less than 8% by weight, or less than 6% by weight, or less than 4% by weight, or less than 2% by weight. mass, or below the detection limit of the method described in Example 1, ie. below 1% by weight, with the weight % based on the total amount of optical brightener of formula (1) present in the coating composition of the invention. On the other hand, more than 90% by mass, or more than 92% by mass, or more than 94% by mass, or more than 96% by mass, or more than 98% by mass, or more than 99% by mass of the optical brightener of formula (1) are retained, the weight % being based on the total amount of optical brightener of formula (1) present in the coating composition of the invention.

If the coating composition according to the invention is made in the form of a pigmented coating composition, then the composition contains from 10 to 70 wt. %, preferably from 40 to 60 wt. % white pigment(s), and wt. % is based on the total weight of the pigmented coating composition. Although it is possible to obtain coating compositions that do not contain white pigment(s), the best white substrates for printing are made using opaque coating compositions containing white pigments in the above amounts.

The white pigment is selected from inorganic pigments, preferably from the group consisting of, for example, aluminum silicates (kaolin, otherwise known as China clay), calcium carbonate (chalk), titanium dioxide, aluminum hydroxide, barium carbonate, barium sulfate or calcium sulfate (gypsum ) or mixtures thereof. Preferably, a mixture of 10 to 20% by weight of clay and 30 to 40% by weight of chalk is used as the white pigment, the weight percentages being based on the total weight of the pigmented coating composition. The term "pigment" in the context of this application refers to a water-insoluble compound.

Where an additional binder is used in the coating composition of the invention, the binder may be any of those commonly used in the paper industry for the production of coating compositions and may consist of a single binder or a mixture of primary and secondary (additional) binders. The binder is selected from the main binder containing one or more synthetic latexes, polymers of styrene-butadiene, vinyl acetate, styrene-acrylate, vinyl acrylate or ethylene vinyl acetate, and optionally from an auxiliary binder containing one or more starches, carboxymethyl cellulose, casein, soy polymer, polyvinyl alcohol.

The sole or primary binder is preferably a synthetic latex, typically a styrene-butadiene polymer, a vinyl acetate polymer, a styrene-acrylic polymer, a vinyl acrylic polymer, or an ethylene vinyl acetate polymer. The preferred base binder is a latex binder.

The amount of binder and aqueous composition according to the invention is typically in the range of 2 to 25% by weight, preferably 4 to 20% by weight, with the % by weight based on the total weight of white pigment present in the pigmented coating composition.

Preferably, however, no additional binder is used in the coating composition of the invention. Thus, the amount of the aqueous composition of the invention used in the coating composition of the invention is typically in the range of 2 to 25% by weight, preferably 4 to 20% by weight, with the % by weight based on the total weight of the white pigment present in the pigmented coating composition.

The auxiliary binder, which may optionally be used, may be, for example, starch, carboxymethyl cellulose, casein, soy polymers, polyvinyl alcohol, or a mixture thereof. A preferred auxiliary binder, which may optionally be used, is a polyvinyl alcohol binder.

Polyvinyl alcohol, which may optionally be used as an auxiliary binder in the pigmented coating composition, preferably has a degree of hydrolysis greater than or equal to 60% and a Brookfield viscosity in the range of 2 to 80 MPa.s (4% aqueous solution at a temperature of 20 °C). More preferably, the polyvinyl alcohol has a degree of hydrolysis greater than or equal to 80% and a Brookfield viscosity of 2 to 40 MPa.s (4% aqueous solution at 20°C).

When optionally used, the auxiliary binder is used in an amount typically in the range of 0.1 to 20% by weight, preferably 0.2 to 8% by weight, more preferably 0.3 to 6% by weight, the weight percentages being based on the total weight of white pigment present in the pigmented coating composition.

The pH value of the coating composition according to the invention is usually in the range of 5 to 13, preferably 6 to 11, more preferably 7 to 10. In cases where it is necessary to adjust the pH of the coating composition, acids or bases can be used. Examples of acids that can be used include, without limitation, hydrochloric acid, sulfuric acid, formic acid, and acetic acid. Examples of bases that can be used include, without limitation, alkali metal and alkaline earth metal hydroxide or carbonates, ammonia or amines.

In addition, the coating composition may contain by-products resulting from the preparation of the optical brightener of formula (1), as well as other conventional additives. Examples of such additives are, for example, antifreeze agents, dispersing agents, synthetic or natural thickeners, carriers, defoamers, wax emulsions, colorants, inorganic salts, solubilizers, preservatives, complexing agents, biocides, crosslinkers, pigments, specialty resins, etc.

The present application also relates to a method for optically brightening a cellulose substrate, comprising the steps of i) applying an aqueous composition of the invention or a coating composition of the invention to a cellulose substrate and ii) drying the cellulose substrate.

The present application also relates to a cellulose substrate treated with an aqueous composition according to the invention or a coating composition according to the invention.

EXAMPLES

The examples are to be understood as illustrating the method and composition of the invention. However, the examples given do not limit the scope of the invention. Unless otherwise indicated, "parts" means "parts by weight".

Example 1 Determination of Free Optical Brightener Content in Aqueous Compositions

The following description generally describes the method for determining the amount of free, i. unretained optical brightener, either in conventional aqueous compositions (also referred to as latex) or in aqueous compositions of the invention.

0.50 parts of the aqueous composition is added with stirring to 40 ml of 1% of the mass. aqueous solution of aluminum sulfate. After coagulation, the dispersion is centrifuged at 4000 rpm for 15 minutes. 1.5 parts of serum is diluted with 3 parts of water and the optical density is measured with a spectrophotometer, comparing with an aqueous reference solution. The concentration of free optical brightener in the aqueous composition is then calculated from the calibration curve.

Example 2: Preparation of an aqueous composition according to the invention

290 parts of demineralized water and 5 parts of an optical brightener of formula (5) were introduced into a 1 liter reactor. The stirred solution was heated to 80°C.

In a second vessel, by mixing 160 parts of demineralized water, 3 parts of sodium lauryl sulfate, 248 parts of butyl acrylate, 226 parts of styrene and 10 parts of acrylic acid, a pre-dispersion was prepared.

In a third vessel, 3 parts of the radical initiator of formula (6) were dissolved in 30 parts of demineralized water.

(6)

(6)

The pre-dispersion and the initiator solution were then added to the optical brightener solution simultaneously at a stirring speed of 100 rpm for four hours while maintaining the internal temperature at 80°C.

After four hours, any remaining pre-dispersion and monomer were placed in the reactor with another 20 parts of demineralized water, and the internal temperature was maintained at 80° C. for another two hours.

The aqueous composition thus formed was allowed to cool to room temperature and the pH was adjusted to about 7 with 5 parts of a 25% ammonia solution to give 1000 parts of an aqueous composition of optically brightened styrene-acrylate latex containing 49% dry solids and about 0.5% optical brightener by weight, and mass. % is based on the weight of the total aqueous composition. Less than 1% by weight of the resulting latex was in the form of grits (removed by filtration) and was unusable (wt.% based on the weight of the total aqueous composition).

The content of free optical brightener, measured according to example 1, was below the detection limit. By mass balance, >99% of the optical brightener (5) was retained in the latex.

Example 3: Preparation of an aqueous composition according to the invention

Example 2 was repeated using an optical brightener of formula (7) instead of an optical brightener of formula (5) to obtain 1000 parts of an aqueous composition of optically brightened styrene-acrylate latex containing 48% dry solids and approximately 0.5% optical brightener by weight, and wt. . % is based on the weight of the total aqueous composition. Less than 1% by weight of the resulting latex was in the form of grits (removed by filtration) and was unusable (wt.% based on the weight of the total aqueous composition).

The content of free optical brightener, measured according to example 1, was below the detection limit. By mass balance, >99% of the optical brightener (7) was retained in the latex.

Example 4 Preparation of Comparative Aqueous Composition

Example 2 was repeated using 5 parts of optical brightener monomer of formula (8) instead of optical brightener of formula (5) to obtain 1000 parts of optically brightened styrene-acrylate latex containing 49.7% dry solids and approximately 0.25% optical brightener by weight . Less than 1% by weight of the resulting latex was in the form of grits (removed by filtration) and was unusable (wt.% based on the weight of the total aqueous composition).

The content of free optical brightener, measured according to example 1, was 42%.

Example 5: Comparative preparation of an aqueous formulation using AIBN

Example 2 was repeated using a solution of 3 parts of AIBN (azobisisobutyric acid dinitrile), a radical initiator of formula (9), in 10 parts of acetone, instead of an aqueous solution of a radical initiator of formula (6).

(9)

(9)

Only 750 parts of optically brightened styrene-acrylate latex were obtained containing 40% dry solids (approx. 60% yield). More than 20% by weight of the resulting latex was in the form of large aggregates (removable by filtration) and was unusable (wt.% based on the weight of the total aqueous composition).

The content of free optical brightener, measured according to example 1, was 82%.

Example 6: Application example

A coating composition was prepared containing 70 parts of chalk (commercially available under the tradename Hydrocarb 55 from OMYA), 30 parts of clay (commercially available under the tradename Polygloss 90 from KaMin), 49.5 parts of water, 0.6 parts of a dispersing agent (commercially available under the trade name Topsperse GX-N from Coatex) and 20 parts of 50% latex (a styrene-acrylate copolymer commercially available under the trade name Cartacoat B631 from Archroma). The solids content of the coating composition was adjusted to approx. 65% by adding water, and the pH was adjusted to 8-9 with sodium hydroxide.

The coating composition was then applied to a 75 g/m2 commercial neutral paper base sheet using an automatic wire rod applicator with standard speed setting and standard rod loading. The coated paper was then dried for 5 minutes in a hot air stream. The paper was then aged and measured for CIE whiteness and ISO brightness on a calibrated Autoelrepho spectrophotometer.

The procedure was repeated to further obtain coated paper using coating compositions in which the commercial latex was gradually replaced with 25% by weight, 50% by weight, 75% by weight and 100% by weight of the aqueous composition of the invention obtained in Example 2, while wt% were based on the total weight of the coating composition.

The results are shown in Table 1 and clearly show that the aqueous composition of the invention provides high levels of CIE whiteness and ISO brightness without saturation.

Table 1 commercial latex latex example 2 CIE whiteness ISO Brightness 100% 0% 74.8 85.4 75% 25% 84.7 88.7 50% 50% 88.3 90.1 25% 75% 91.5 91.2 0% 100% 93.4 91.9

Example 7: Application example

Example 7 was repeated with the only difference that the aqueous composition according to the invention obtained in Example 3 was used.

The results are shown in table 2.

table 2 commercial latex latex example 3 CIE whiteness ISO Brightness 100% 0% 74.8 85.4 75% 25% 83.8 88.4 50% 50% 87.4 89.8 25% 75% 90.2 90.7 0% 100% 91.5 91.3

Claims (52)

1. A method of obtaining an aqueous composition by emulsion polymerization of at least one ethylenically unsaturated monomer in the presence of at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1)

in which R ¹ and R ⁶ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN, R ² and R ⁴ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CO ₂ M, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN , R ³ and R ⁵ are independently linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CO ₂ M, CH(CO ₂ M)CH ₂ CO ₂ M, CH( CO ₂ M)CH ₂ CH ₂ CO ₂ M, benzyl or R ² and R ³ together with their neighboring nitrogen atom represent a morpholine ring and/or R ⁴ and R ⁵ together with their neighboring nitrogen atom represent a morpholine ring, R ⁷ and R ⁸ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, X and Y are independently CO ₂ M or SO ₃ M, n and m are independently an integer selected from 0, 1, or 2, and M is at least one cation for balancing the anionic charge of the optical brightener and is selected from the group consisting of or essentially consisting of hydrogen, an alkali metal cation, an alkaline earth metal cation, ammonium, an ammonium which is mono-, di-, tri-, or tetra-substituted linear or branched C ₁ -C ₄ alkyl radical, ammonium, which is a mono-, di -, tri - or tetrasubstituted linear or branched C ₁ -C ₄ hydroxyalkyl radical, ammonium, which is a di-, tri - or tetrasubstituted mixture of linear or branched C ₁ -C ₄ alkyl radicals, or linear or branched C ₁ -C ₄ hydroxyalkyl radicals, or a mixture of these cations, wherein the emulsion polymerization comprises at least the following four steps (a) to (d): a) preparing an aqueous solution containing or consisting of at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1) and optionally at least one dispersing agent, and b) preparing a homogeneous pre-dispersion, wherein the pre-dispersion contains or consists of at least one ethylenically unsaturated monomer, water and at least one dispersing agent, and c) preparing an aqueous solution containing or consisting of an emulsion polymerization initiator, and d) adding the pre-dispersion obtained in step (b) and the aqueous solution obtained in step (c) simultaneously to the aqueous solution obtained in step (a). 2. The method of claim 1 wherein the aqueous composition is an aqueous latex binder. 3. The method according to p. 1 or 2, in which at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1) R ¹ and R ⁶ are independently hydrogen, methyl, linear or branched C ₁ -C ₄ hydroxyalkyl or CH ₂ CH ₂ CONH ₂ , R ² and R ⁴ are independently hydrogen, linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH ₂ CH ₂ CONH ₂ or CH ₂ CH ₂ CN, R ³ and R ⁵ are independently linear or branched C ₁ -C ₄ alkyl, linear or branched C ₁ -C ₄ hydroxyalkyl, CH(CO ₂ M)CH ₂ CO ₂ M, CH(CO ₂ M)CH ₂ CH ₂ CO ₂ M, benzyl or R ² and R ³ together with their neighboring nitrogen atom represent a morpholine ring and/or R ⁴ and R ⁵ together with their neighboring nitrogen atom represent a morpholine ring, and R ⁷ and R ⁸ are independently hydrogen or methyl, and M means at least one cation, as defined in paragraph 1 of the claims. 4. The method according to p. 1, in which at least one water-soluble diaminostilbene-disulfone optical brightener of formula (1) R ¹ and R ⁶ are hydrogen, R ² and R ⁴ are independently hydrogen, linear or branched C ₁ -C ₂ alkyl, linear or branched C ₁ -C ₃ hydroxyalkyl, R ³ and R ⁵ are independently linear or branched C ₁ -C ₂ alkyl, linear or branched C ₁ -C ₃ hydroxyalkyl, CH(CO ₂ M)CH ₂ CO ₂ M, CH(CO ₂ M)CH ₂ CH ₂ CO ₂ M, or R ² and R ³ together with their neighboring nitrogen atom represent a morpholine ring and/or R ⁴ and R ⁵ together with their neighboring nitrogen atom represent a morpholine ring, and R ⁷ and R ⁸ are independently hydrogen or methyl, and M denotes at least one cation, as defined in paragraph 1 of the claims. 5. The method according to p. 1, in which at least one ethylenically unsaturated monomer is selected from (a) C ₁ -C ₁₈ -alkyl esters of (meth)acrylic acid, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl versatates, styrene and α-methylstyrene; (b) hydrophilic monomers such as (meth)acrylic acid, itaconic acid, vinylsulfonic acid, C ₁ -C ₈ -hydroxyalkyl esters of C ₁ -C ₆ -carboxylic acids, (meth) acrylamide, N-methylol (meth) acrylamide, ( meth)acrylonitrile, N-vinylformamide and N-vinylpyrrolidone; or (c) crosslinkers that have two or more ethylenically unsaturated double bonds, such as ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, divinylbenzene and trivinylbenzene; or mixtures of two or more of them. 6. The method according to p. 1, in which at least one ethylenically unsaturated monomer is selected from (a) C ₁ -C ₆ -alkyl esters of (meth)acrylic acid, vinyl acetate, vinyl propionate and styrene; (b) hydrophilic monomers such as (meth)acrylic acid, vinylsulfonic acid, (meth)acrylamide and (meth)acrylonitrile; or mixtures of two or more of them. 7. The method according to p. 1, in which at least one ethylenically unsaturated monomer is selected from (a) methyl methacrylate, butyl acrylate, vinyl acetate and styrene; (b) hydrophilic monomers such as (meth)acrylic acid, vinylsulfonic acid and acrylamide; or mixtures of two or more of them. 8. The method according to p. 1, in which the emulsion polymerization is initiated with a water-soluble azo compound of formula (2) and/or formula (3)

(2)

(3) in which X and Y are independently O or NH, R and R' are independently hydrogen or linear or branched C ₁ -C ₄ alkyl substituted with one or more hydroxyl, CO ₃ M ¹ or CO ₃ M ² groups, where M ¹ and M ² represent at least one cation to balance the anionic charge of the azo compound of formula (3) and are independently selected from the group consisting of or essentially consisting of hydrogen, an alkali metal cation, an alkaline earth metal cation, ammonium, an ammonium which is mono-, di-, tri-, or tetra-substituted linear or branched C ₁ -C ₄ alkyl radical, ammonium, which is a mono-, di -, tri - or tetrasubstituted linear or branched C ₁ -C ₄ hydroxyalkyl radical, ammonium, which is a di-, tri - or tetrasubstituted mixture of linear or branched C ₁ -C ₄ alkyl radicals, or linear or branched C ₁ -C ₄ hydroxyalkyl radicals, or a mixture of these cations. 9. Aqueous composition for optical brightening of the cellulose substrate, obtained by the method according to p. 1. 10. An aqueous composition according to claim 9, which is a water-based latex binder. 11. An aqueous composition according to claim 9, wherein at least one other additive is present, wherein the additive is selected from one or more biocides, one or more antifoam agents, one or more preservatives, one or more antifreeze additives, one or more thickeners, or mixtures thereof. 12. An aqueous composition according to claim 9, in which more than 90% by weight, or more than 92% by weight, or more than 94% by weight, or more than 96% by weight, or more than 98% by weight, or more than 99% by weight by weight of formula (1) optical brightener were retained in the polymer, with the weight % based on the total amount of formula (1) optical brightener present in the aqueous composition. 13. The use of an aqueous composition according to at least one of paragraphs. 9-12 for optical brightening of the cellulose substrate. 14. Use according to claim 13, wherein the aqueous composition is used in the coating composition. 15. Coating composition containing at least an aqueous composition in accordance with at least one of paragraphs. 9-12. 16. A method for optically brightening a cellulose substrate, comprising steps i) applying an aqueous composition according to at least one of paragraphs. 9-12 or the coating composition of claim 15 on a cellulose substrate; and ii) drying the cellulose substrate. 17. Cellulose substrate treated with an aqueous composition, as stated in at least one of paragraphs. 9-12 or the coating composition according to claim 15.