EP1355004B1 - Use of optical brighteners for the manufacturing of coating mixes - Google Patents

Description

The invention relates to the use of special brighteners for the production of coating slips, coating slips per se and their use for producing brightened papers.

Optical brighteners are mainly used for whitening paper, textiles or as an additive to detergents. The whitening of uncoated papers or base paper can be done by mass application and / or surface application of optical brighteners, which are usually present in dissolved form. In the production of coated papers, the addition of optical brightener to the coating color is common, so that the optical brightener in the finished coated paper is also in the pigment layer applied to the paper. Coated papers are particularly suitable for making high quality prints. In addition to good printability properties, their quality is therefore assessed mainly for optical properties such as gloss and whiteness. There is a continuing trend towards coated papers with high whiteness and therefore the desire for most effective optical brighteners as coating components.

worin

oder

oder

und

M

für Na, K oder gegebenenfalls substituiertes Ammonium steht.

The most common and widely used paper lighteners are those of the formula (I),

wherein

or

or

and

M

is Na, K or optionally substituted ammonium.

If one compares the use of the so-called tetrasulfo type and hexasulfo type shown in formula (I) in the paper coating, a saturation behavior with respect to the CIE whiteness is shown for certain brightener addition amounts of the tetrasulfonotype. That larger amounts do not lead to further whiteness build-up and may even have a negative effect on the CIE whiteness. This saturation behavior occurs when using the Hexasulfotyps usually only at much higher levels, compared to Tetrasulfotyp on. As a result, Hexasulfoflavonate Brighteners can generally achieve higher degrees of whiteness than Tetrasulfoflavonate Brighteners. The effect of saturation is also called greening. The greening border, i. the point above which increasing brightener amounts cause virtually no increase in whiteness can e.g. are derived from the a * b * diagram, where a * and b * are the color coordinates in the CIELab system.

Since the greening in hexasulfonotypes only occurs at relatively high levels of use, the other hexasulfoflavonate brightener shown in formula (I) is particularly suitable for producing coated, off-white papers. The exact amounts at which the greening occurs in the case of tetra- or hexasulfoflavone brighteners depend on the composition of the respective coating color, inter alia on its carrier content.

When recycling coated papers, e.g. in the reuse of coated broke in the paper mill, the coated paper is re-opened, with the non-fiber-fixed brightener from the line first dissolving and partially drawing on paper fibers. In this regard, the increased solubility of the hexasulfoflavone brightener is disadvantageous because non-fiber-fixed brightener in the recirculating water of the papermaking machine acts as an anionic impurity and the effect of cationic paper chemicals such as e.g. Retention or engine sizing agents reduced, so that an excess consumption of these paper chemicals results.

There is therefore a desire for improved optical brighteners for whitening coating colors, in particular paper coating colors, which have higher whiteness than using conventional di- and tetrasulfonyphene, e.g. the one shown in formula (I), but on the other hand lead recycling of coated papers less contaminant load in the circulating water of the paper machine than Hexasulfotypen.

The main focus is on the whitening of coating colors based on synthetic cobinders. Natural cobinders, in particular starch, are poorly suited for topcoats or single strokes due to their swelling behavior on contact with aqueous liquids. The swelling reduces the quality of the printed image when printing the coated paper. Starch is therefore preferably used as a co-primer in precursors for multi-coated papers. while synthetic co-weighters are preferred for single-coated papers or toppings. Whiteness is generally higher for single-stroke or top-coat than for primer.

Surprisingly, it has now been found that a particular class of Bistriazinylflavonataufhellern with 4 sulfo groups these requirements in excellent In coating systems containing special synthetic co-binders.

EP-A 192 600 describes that certain polyethylene glycol-containing brightener formulations are particularly suitable as coating color additives. However, only latex binders are used explicitly in combination with natural coasters for coating compounds.

worin

Y

ein Rest der Formel

oder

bedeutet und

R¹

für C₁-C₆-Alkyl und

R²

für H, oder

R¹

für H und

R²

für C₁-C₆-Alkyl steht, und unabhängig davon

R³

für H, Methyl, Ethyl, CH₂CH₂OH oder CH₂CH₂OCH₃ steht,

R^1'

für C₁-C₆-Alkyl und

R^2'

für H, oder

R^1'

für H und

R^2'

für C₁-C₆-Alkyl steht, und unabhängig davon

R^3'

für H, Methyl, Ethyl, CH₂CH₂OH, CH₂CH₂OCH₃ sowie

R⁴

für C₁-C₄-Alkyl stehen

Z

H oder SO₃M bedeutet, wobei die Sulfogruppen in o-, m- oder p-Position stehen können und

M

H oder ein Äquivalent eines Kations bedeutet, ausgewählt aus der Gruppe Li, Na, K, Ca, Mg, Ammonium oder Ammonium, welches mono-, di-, tri- oder tetrasubstituiert ist durch die Reste C₁-C₄-Alkyl oder C₂-C₄-Hydroxyalkyl

zum Aufhellen von wässrigen Streichmassen enthaltend wenigstens einen Latex-Binder und wenigstens einen davon verschiedenen synthetischen Cobinder ausgewählt aus der Gruppe bestehend aus Polyvinylalkoholen Carboxymethylcellulosen sowie Mischungen dieser beiden Substanzen.The invention therefore relates to the use of optical brighteners of the formula (II)

wherein

Y

a remainder of the formula

or

means and

R ¹

for C ₁ -C ₆ -alkyl and

R ²

for H, or

R ¹

for H and

R ²

is C ₁ -C ₆ -alkyl, and independently thereof

R ³

is H, methyl, ethyl, CH ₂ CH ₂ OH or CH ₂ CH ₂ OCH ₃ ,

R ^{1 '}

for C ₁ -C ₆ -alkyl and

R ^{2 '}

for H, or

R ^{1 '}

for H and

R ^{2 '}

is C ₁ -C ₆ -alkyl, and independently thereof

R ^{3 '}

for H, methyl, ethyl, CH ₂ CH ₂ OH, CH ₂ CH ₂ OCH ₃ as well

R ⁴

represent C ₁ -C ₄ -alkyl

Z

H or SO ₃ M, where the sulfo groups can be in the o-, m- or p-position, and

M

H or one equivalent of a cation selected from the group consisting of Li, Na, K, Ca, Mg, ammonium or ammonium which is mono-, di-, tri- or tetrasubstituted by the radicals C ₁ -C ₄ -alkyl or C C ₂ -C ₄ hydroxyalkyl

for brightening aqueous coating compositions comprising at least one latex binder and at least one synthetic cobinder other than those selected from the group consisting of polyvinyl alcohols, carboxymethylcelluloses and mixtures of these two substances.

In a preferred embodiment, the synthetic cobinder is not a latex binder.

With regard to the brightener of the formula (II), mixtures of the abovementioned possibilities for M are also suitable.

• R¹ = H,
• R² = lineares C₁-C₆-Alkyl sowie
• R³ = H;

weiterhin die optischen Aufheller der Formel (II) mit

• R^1' = H,
• R^2' = lineares C₁-C₆-Alkyl sowie
• R^3' = H und R⁴ = H, Methyl.

Preference is given to the optical brightener of the formula (II)

• R ¹ = H,
• R ² = linear C ₁ -C ₆ -alkyl and
• R ³ = H;

furthermore the optical brightener of the formula (II)

• R ^{1 '} = H,
• R ^{2 '} = linear C ₁ -C ₆ -alkyl and
• R ^{3 '} = H and R ⁴ = H, methyl.

worin

M

die oben angegebene Bedeutung hat.

Particularly preferred is the use of the optical brightener of formula (IIa),

wherein

M

has the meaning given above.

The particularly preferred brightener of the formula (IIa) and related structures are known per se. Thus, GB-A 896 533 describes the preparation of this brightener and the use in mass and size press use for whitening paper.

The brighteners used according to the invention can be used as an aqueous solution which contains substantially dissolved brightener salts, water and optionally adjusters. Furthermore, they can be used as aqueous carrier-containing formulations containing substantially dissolved brightener salts, water and carrier substances.

Also possible is the use of the brightener according to the invention in solid form, for example as a powder or granules. It is advantageous if the brighteners go into solution before applying the coating color. The dissolving process of the brightener can be combined with the application of the coating color when using powder or granules.

The preparation of the brighteners used in the invention is carried out by known methods, such as e.g. in GB-A 896 533 or in EP-A 860 437 are described, for example, from about 2 moles of cyanuric chloride, about 1 mole of 4,4'-diaminostilbene-2,2'-disulfonic acid or a corresponding salt, approx 2 mol of aniline, sulphanilic acid or a corresponding salt and about 2 to 2.5 mol of the amines corresponding to the substituent Y. After completion of the reaction, the crude solution of the corresponding brightener may be e.g. desalted and concentrated by suitable membrane separation techniques, e.g. in EP-A-992,547. Preferred membrane separation processes are ultrafiltration, diffusion dialysis and electrodialysis. However, it is also possible to isolate the resulting brightener as a solid, e.g. by salting out or addition of acid and precipitation as a colored acid. The resulting solid may then be e.g. isolated on a filter press and optionally further purified by washing.

For the preparation of the brightener preparation according to the invention, the brightener can also be prepared from solution, e.g. be isolated by spray drying in the form of a powder, wherein optionally before drying further additives such as dispersants, dedusting agents, etc. are added.

Aqueous preparations can be prepared from crude solutions, on concentrated and desalted solutions, or from aqueous presscakes. For particularly good whiteness build-up, it is advantageous to incorporate so-called carrier substances into the aqueous whitener preparations.

• a) 10 bis 40 Gew.-% wenigstens eines Aufhellers der Formel (II),
• b) 0 bis 30 Gew.-% Stellmittel
• c) 0 bis 2 Gew.-% anorganische Salze und
• d) 23 bis 90 Gew.-% Wasser,

wobei die Summe der Komponenten a) bis d) 95 bis 100 Gew.-%, bezogen auf die Präparation, beträgt.Preferably, the aqueous brightener preparations contain

• a) from 10 to 40% by weight of at least one brightener of the formula (II),
• b) 0 to 30 wt .-% adjusting agent
• c) 0 to 2 wt .-% of inorganic salts and
• d) from 23 to 90% by weight of water,

wherein the sum of components a) to d) is 95 to 100 wt .-%, based on the preparation.

Usual adjusting means are e.g. Urea, diethylene glycol, triethylene glycol, propanediol, glycerol, ε-caprolactam, ethanolamine, diethanolamine and triethanolamine. Preference is given to each adjusting agent-free preparations.

• a) 5 bis 40 Gew.-% wenigstens eines Aufhellers der Formel (II)
• b) 1 bis 50 % Gew.-% wenigstens einer Carriersubstanz
• c) 0 bis 2 Gew.-% anorganische Salze und
• d) 3 bis 94 Gew.-% Wasser

wobei die Summe der Komponenten a) bis d) 95 bis 100 Gew.-%, bezogen auf die Präparation, beträgt.Also preferably, the aqueous brightener preparations contain:

• a) 5 to 40% by weight of at least one brightener of the formula (II)
• b) 1 to 50% by weight of at least one carrier substance
• c) 0 to 2 wt .-% of inorganic salts and
• d) 3 to 94% by weight of water

wherein the sum of components a) to d) is 95 to 100 wt .-%, based on the preparation.

Suitable carrier substances are generally hydrophilic polymers capable of forming hydrogen bonds. Preferred carrier substances are polyvinyl alcohols, carboxymethylcelluloses and polyethylene glycols having a number-average molecular weight of from 200 to 8000 g / mol, as well as any desired mixtures of these substances, these polymers optionally being able to be modified. Preferred polyvinyl alcohols are those with a degree of hydrolysis> 85%, preferred carboxymethylcelluloses are those with a degree of substitution DS of> 0.5. Particularly preferred are polyethylene glycols having a number average molecular weight Mn of 200 to 8000 g / mol.

Also suitable are, for example, native, derivatized or degraded starches, alginates, casein, proteins, polyacrylamides, polyacrylic acids, hydroxyalkylcellulose and also polyvinylpyrrolidone.

Irrespective of the carrier content in the coating color, formulations of this kind can generally be used to achieve more favorable whiteness build-up curves than with carrier-free brightener preparations.

In addition, in the carrier-less as well as carrier-containing preparations in smaller amounts, usually in amounts below 5 wt .-%, other adjuvants such. Dispersants, thickeners, antifreeze, preservatives, complexing agents, etc., or organic by-products from the brightener synthesis, which were not completely removed in the work-up, be included.

In the carrier-containing preparations can also be added adjusting agents to increase the solubility and storage stability.

The preparation of the carrier-free aqueous brightener preparations takes place i.A. by setting a brightener solution (crude or membrane-filtered) with a base to a neutral to slightly alkaline pH, optionally adding and dissolving one or more adjusting agents and optionally diluting with water to the desired final concentration. If the brightener is used in the form of a water-moist press cake, a certain amount of press cake is completely dissolved in water with addition of base, stirring and optionally elevated temperatures and optionally adjusted to the desired concentration by adding further water.

Preferred bases for this are alkali hydroxides, for dilution demineralized water is preferred. The adjusted pH is in the range of 7 to 11, preferably from 8 to 10. For dissolving temperatures of 25 to 80 ° C are common.

The preparation of the carrier-containing preparations is generally carried out in an analogous manner, wherein additionally the carrier substance is added at any point in the production process. If the carrier substance is added in solid form, it is generally completely dissolved with stirring and optionally elevated temperatures. so that a homogeneous liquid preparation is formed. Preferably, the viscosity of the carrrierhaltigen preparations at room temperature <3000 mPas. The usual dissolution temperature is in the range of 25 to 100 ° C.

Concentrated, aqueous brightener preparations are usually characterized by the so-called E1 / 1 value. For this purpose, the extinction of a highly diluted solution of the preparation is determined by the usual and known to the expert methods of UV / Vis spectroscopy in a 1 cm cuvette at a certain wavelength. This wavelength corresponds to the long-wavelength absorption maximum of the respective brightener molecule. For flavonate brighteners it is about 350 nm. The E1 / 1 value then corresponds to the fictitious extinction value extrapolated to a 1% solution.

The E1 / 1 values of the brightener preparations used according to the invention are preferably between 50 and 180, more preferably between 70 and 140.

The coating compositions to be brightened according to the invention comprise, for example, latices based on styrene-butadiene, styrene-acrylate or vinyl acetate as latex binder. These polymers may optionally be modified by further monomers such as acrylonitrile, acrylamide, α, β-unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid or maleic acid, acrylates, vinyl esters, ethylene, vinyl chloride, vinylidene chloride, etc. In general, however, all cyanogenic latex binders which are used for the production of paper coating slips come into question.

Preferred latex binders are those based on styrene-butadiene. Preferred synthetic co-binders are polyvinyl alcohols having a degree of hydrolysis of> 85%, and in particular a Brookfield viscosity of 2-80 mPas (measured on a 4% aqueous solution at 20 ° C.), carboxymethylcelluloses, with a degree of substitution of> 0.5, and in particular a Brookfield viscosity of 5-5000 mPas (measured on a 2% aqueous solution at 25 ° C) and mixtures of these two substances.

The coating compositions to be lightened according to the invention preferably also contain white pigments.

As white pigments usually calcium carbonate in natural or precipitated form, kaolin, talc, titanium dioxide, satin white, aluminum hydroxide and barium sulfate are used, often in the form of mixtures.

As further optional ingredients of the coating compositions to be brightened according to the invention, first of all dispersing agents are to be mentioned. Usual here are polyacrylates, polyphosphates or Na citrate. In principle, polyaspartic acid is also suitable. Other possible additives are crosslinkers. Examples of these are urea-formaldehyde resins, melamine-formaldehyde resins, glyoxal or ammonium zirconium carbonate. In principle, wet strength agents based on polyamidoamine-epichlorohydrin resins, glyoxalated polyacrylamides or hydrophilicized polyisocyanates, such as, for example, are also suitable. in EP-A-825 181, as crosslinkers in question. Finally, other possible additives are defoamers, biocides, complexing agents, bases for pH adjustment, Ca stearate, optical brighteners other than those of the formula (II) and shading dyes. Sometimes surface sizing agents are also added to hydrophobize the coating color. Examples of these are polymer solutions based on styrene-acrylic acid, styrene-maleic anhydride or oligourethanes, and polymer dispersions based on acrylonitrile-acrylate or styrene-acrylate. The latter are e.g. in WO-A-99/42490.

The coating compositions to be brightened according to the invention preferably contain the latex binder in an amount of from 3 to 20% by weight and the synthetic cobinder in an amount of 0.1 to 3 wt .-%, each based on the white pigment of the coating.

• wenigstens ein Weißpigment
• wenigstens einen Latex-Binder
• wenigstens einen davon verschiedenen synthetischen Cobinder und
• wenigstens einen Aufheller der Formel (II).

The invention further relates to an aqueous coating slip, ie an aqueous pigment preparation containing

• at least one white pigment
• at least one latex binder
• at least one of them different synthetic cobinder and
• at least one brightener of the formula (II).

The amount of latex binder (calculated as dry substance) is preferably 3 to 20% by weight, in particular 5 to 15% by weight, regardless of the amount of cobinder 0.1 to 3% by weight, in particular 0.5 to 1.5 wt .-% and also independently of the amount of brightener of the formula (II) 0.025 to 1 wt .-%, each based on the amount of white pigment.

The preferred embodiments for white pigment, latex binder, cobinder, brightener and other additives, as described above, apply.

The coating composition preferably additionally contains at least one dispersing agent, in particular in an amount of from 0.05 to 1% by weight, based on the white pigment in the coating composition. As a dispersant is preferably polyacrylic acid or corresponding salts in question. The water content of the coating composition is preferably from 30 to 50% by weight, based on the total amount of coating composition.

The invention further relates to the use of the coating compositions according to the invention for the production of coated papers.

The coating compositions can preferably be applied to the paper simply or multiply by means of all suitable application methods, such as, for example In various embodiments, air knife, blade, roll coater, film press, cast coating, etc. The immobilization and drying of the coating color usually takes place first by contactless hot air and / or IR drying, which is usually followed by a contact drying by heated rollers , Thereafter, a calendering is usually carried out for densification, smoothing or gloss influence of the coated paper, for example with a calender.

As uncoated base papers or base papers, cardboard and cardboard are in principle made of bleached or unbleached, wood-containing or wood-free, waste paper-containing and deinked fibers produced papers, cardboard and cardboard. These may also contain mineral fillers such as natural or precipitated chalk, kaolin, talc or annaline. The uncoated papers, boards and cardboards may be sized in the mass and / or surface which, among other things, affect the penetration and adhesion of the coating color. Conventional engine sizing agents are alkyl ketene dimerene (AKD), alkenylsuccinic anhydride (ASA) or a combination of rosin size and alum, customary surface sizing agents the above-mentioned polymer solutions based on styrene-acrylic acid, styrene-maleic anhydride or oligourethanes, and polymer dispersions based on acrylonitrile acrylate or Styrene acrylate. To control the desired whiteness properties of the resulting coated paper, the base papers may be lightened in bulk and / or surface using, for example, flavonate brighteners.

Examples example 1

77.6 g of a membrane-filtered aqueous concentrate having an E1 / 1 value of 161 and a pH of 8.5, which contains the brightener of the formula (IIa) as Na salt are demineralisiertem with stirring at room temperature with 22 g Added water and adjusted to pH 9.0 with about 10% sodium hydroxide solution. This gives a carrier-free brightener preparation with an E1 / 1 value of 125 in the form of a yellow-brownish, homogeneous liquid. This corresponds to a content of (IIa) of about 23 wt .-%.

Example 2

65.2 g of a membrane-filtered aqueous concentrate having an E1 / 1 value of 161 and a pH of 8.5, which contains the brightener of the formula (IIa) as sodium salt, are stirred at room temperature with 31 g of polyethylene glycol 1550 (average molecular weight Mn 1550 g / mol). To this end, the polyethylene glycol 1550 waxy at room temperature is heated to about 60 ° C. before the addition, while being melted, and added as hot liquid at about 60 ° C. It continues to use 3.5 g of demineralized water and the pH is adjusted to 9.0 with about 10% sodium hydroxide solution. The preparation is then heated with stirring to 50 ° C and stirred for 30 min at this temperature. After cooling to room temperature, a carrier-containing whitener preparation having an E1 / 1 value of 105 in the form of a yellow-brownish, fluorescent, homogeneous liquid is obtained. This corresponds to a content of (IIa) of about 19 wt .-%.

Example 3 (not according to the invention)

• 64,8 g eines membranfiltrierten wässrigen Konzentrats mit einem E1/1-Wert von 162 und einem pH-Wert von 8,6, das den Tetrasulfotyp-Aufheller der Formel (I) als Na-Salz enthält
• 31 g Polyethylenglykol 1550
• 4 g demineralisiertes Wasser.

The procedure is as in Example 2, but using a different brightener type and using the following quantities:

• 64.8 g of a membrane-filtered aqueous concentrate having an E1 / 1 value of 162 and a pH of 8.6, which contains the Tetrasulfotyp-brightener of the formula (I) as Na salt
• 31 g of polyethylene glycol 1550
• 4 g demineralized water.

This gives a carrier-containing whitener preparation with an E1 / 1 value of 105 and a pH of 9.0 in the form of a yellow-brownish, fluorescent, homogeneous liquid. This corresponds to a content of the Tetrasulfotyp brightener of about 18 wt .-%.

Example 4 (not according to the invention)

The procedure is as in Example 1, but uses as a brightener the Tetrasulfotyp of the formula (I) as Na salt.

The brightener preparation has an E 1/1 value of 125. This corresponds to a content of the brightener of about 21 wt .-%.

Application Example 1

• 100 Teile Weißpigment (Kreide-Kaolin-Mischung)
• 6,5 Teile Baystal P7110 als Binder, gerechnet als Trockensubstanz (Styrol-Butadien-Latex der Polymerlatex GmbH)
• 1,5 Teile Finnfix 10 als synthetischen Cobinder (Carboxymethylcellulose der Firma Noviant)
• 0,25 Teile Polysalz® S als Dispergiermittel auf Basis von Polyacrylsäure (BASF AG) Wasser
• 10-%ige Natronlauge.

A paper coating slip is made from the following components:

• 100 parts white pigment (chalk-kaolin mixture)
• 6.5 parts of Baystal P7110 as binder, calculated as dry substance (styrene-butadiene latex from Polymerlatex GmbH)
• 1.5 parts of Finnfix 10 as a synthetic cobinder (carboxymethyl cellulose from Noviant)
• 0.25 parts of Polysalz® S as dispersant based on polyacrylic acid (BASF AG) water
• 10% sodium hydroxide solution.

The used CMC Finnfix 10 has an active content of 98%. The Brookfield viscosity of a 4% solution measured at 25 ° C is 50-200 mPas.

The amount of water and soda lye is chosen so that a solids content of 57%. and a pH of 9.0 results.

The coating composition is divided into 10 parts and one part each with 0.4%, 0.8%, 1.2%, 1.6% and 1.8% of the brightener preparation from Example 1 and then stirred for 10 min. The added amounts are based on the solids content of the coating. For comparison, each part of the coating composition is mixed in the same manner with equal amounts of the brightener preparation from Example 4.

The resulting, lightened coating slips are applied to wood-free base papers having a basis weight of about 80 g / m ² using a laboratory doctor blade (Erichsen, K-Control Coater, model K 202). The coated papers are dried for 1 min at 95 ° C on a drying cylinder and then stored for 3 h at 23 ° C and 50% relative humidity. The measurement of the parameters L *, a *, b * and the determination of the CIE whiteness is then carried out with a whiteness measuring device (Datacolor Elrepho 2000).

The values obtained are listed in Tables 1 and 2. <b> Table 1: </ b> Brightener Preparation from Example 1 (E1 / 1 = 125) Amount (%) CIE whiteness L * a * b * 0.4 101.80 94.12 0.81 -3.60 0.8 108.00 94.24 1.11 -4.89 1.2 111.50 94.34 1.26 -5.63 1.6 114.50 94.42 1.34 -6.25 1.8 116.10 94.46 1.37 -6.62 Amount (%) CIE whiteness L * a * b * 0.4 102.10 94.11 0.74 -3.69 0.8 107.70 94.33 0.97 -4.81 1.2 110.04 94.43 0.98 -5.36 1.6 113.30 94.55 0.97 -5.96 1.8 113.50 94.60 0.90 -6.04

It can be seen that in each E1 / 1-like use of the brightener used in the invention in the carboxymethylcellulose-containing coating color leads to better CIE whiteness values than that of Example 4. From the a * -b * values can be further seen that in not according to the invention Tetratyp from 1.6%, the greening sets, while this is not apparent when using the inventive brightener from Example 1 to 1.8%.

Application Example 2 :

The procedure is as in Application Example 1, but uses a polyvinyl alcohol-containing coating composition of other composition and uses the carrier-containing Brightener preparations from Examples 2 and 3 with respective aggregate amounts of 0.8%, 1.6%, 2.4% and 3.2%, based on the solids content of the coating.

• 100 Teile Weißpigment (Kreide-Kaolin-Mischung)
• 7,5 Teile Baystal P 7110 als Binder, gerechnet als Trockensubstanz (Styrol-Butadien-Latex der Polymerlatex GmbH)
• 1 Teil Polyvinylalkohol als synthetischen Cobinder, gerechnet als Trockensubstanz
• 0,25 Teile Polysalz® S als Dispergiermittel (BASF AG)
• Feststoffgehalt: 65 %, pH-Wert: 8,8.

Composition of the coating:

• 100 parts white pigment (chalk-kaolin mixture)
• 7.5 parts of Baystal P 7110 as binder, calculated as dry substance (styrene-butadiene latex from Polymerlatex GmbH)
• 1 part polyvinyl alcohol as synthetic cobinder, calculated as dry substance
• 0.25 part of Polysalz® S as dispersing agent (BASF AG)
• Solids content: 65%, pH: 8.8.

As polyvinyl alcohol Polyviol LL 603 (Wacker chemistry) was used. It is a 20% aqueous solution of a polyvinyl alcohol with degree of hydrolysis 88%, which has a Brookfield viscosity of about 900 mPas at 20 ° C.

The coating is divided into 8 parts and one part each with the above amounts of brightener preparations from Examples 2 and 3 added.

The whiteness parameters of the resulting papers are shown in Tables 3 and 4. <b> Table 3: </ b> Brightener Preparation from Example 2 (E1 / 1 = 105) Amount (%) CIE whiteness L * a * b * 0.8 97.90 94,30 1.15 -2.68 1.6 107.10 94.52 1.59 -4.59 2.4 111.50 94.62 1.83 -5.53 3.2 114.60 94.73 2.02 -6.16 Amount (%) CIE whiteness L * a * b * 0.8 98.70 94.41 1.13 -2.79 1.6 104.50 94.55 1.27 -4.00 2.4 107.00 94.61 1.31 -4.52 3.2 109.70 94.73 1.42 -5.07

It can be seen that the whitener preparation according to the invention from Example 2 in the polyvinyl alcohol-containing coating color shows a significantly improved build-up behavior with respect to the CIE whiteness, compared to the preparation of Example 3 which is not according to the invention.

Application Example 3

The procedure is as in Application Example 1, but uses a polyvinyl alcohol-containing coating composition of other composition and uses the brightener preparations of Example 1 in concentrations of 1%, 4.5% and 8%, based on the pigment content in the coating. Polyvinyl alcohol used was Polyviol® LL 603 (Wacker Chemie).

Composition of the coating:

100 Parts kaolin 24 Parts Acronal® S 320 D (BASF AG) 8th Parts of polyvinyl alcohol, calculated as dry substance 0.3 Parts of polysalt® s (BASF AG) 0.1 Part of NaOH water

The water content is chosen so that a solids content of 50% results.

The coating composition is mixed in 3 parts and one part each with the above amounts of brightener preparation of Example 1.

The whiteness parameters of the resulting papers are shown in Table 5.

Application Example 4:

The procedure is as in Application Example 3, but uses 8 parts of the carboxymethylcellulose Finnfix® 10 (Noviant) in the coating instead of 8 parts of polyvinyl alcohol.

The whiteness parameters of the resulting papers are shown in Table 5.

Comparative Example (analogous to Example C 1 of EP 192 600):

1 part, 4.5 parts and 8 parts (based on pigment) of the brightener preparation from Example 1 are incorporated into an aqueous coating slip. the coating had the following composition: 100 Parts kaolin 24 Parts Acronal® S 320 (BASF AG) 8th Parts of starch, calculated as dry substance 0.3 Parts Polysalt® S (BASF AG) 0.1 Part of NaOH water

The water content is chosen so that a solids content of 50% results.

With the coating compositions thus obtained, papers are equipped and their whiteness parameters determined according to the procedure described in Application Example 1. The results are shown in Table 5. <b> Table 5: </ b> brightener preparation from example 1 (E1 / 1 = 125) Amount (% related to pigment) CIE whiteness L * a * b * Application Example 3 (polyvinyl alcohol-containing coating color): 1.0 106.10 94,10 1.29 -4.53 4.5 117.0 94.35 1.85 -6.81 8.0 120.6 94.43 1.97 -7.59 Application Example 4 (CMC-containing coating color): 1.0 101.7 93.98 0.85 -3.60 4.5 109.2 94.16 1.17 -5.17 8.0 114.6 94.23 1.26 -6.34 Comparative Example (Starch-containing coating color): 1.0 98.3 93.93 0.67 -2.89 4.5 103.8 94.18 0.71 -3.98 8.0 107.4 94.45 0.38 -4.63

It can be seen that the whitener preparation from Example 1 in a coating color which contains polyvinyl alcohol or carboxymethyl cellulose as cobinder leads to significantly higher whiteness values than in a starch-containing coating color with the same cobinder content.

Claims (9)

1. Use of optical brighteners of the formula (II)

   

   in which

   Y signifies a residue of the formula

   

   or

   

   and

   R¹ stands for C₁-C₆ alkyl and

   R² for H, or

   R¹ for H and

   R² for C₁-C₆ alkyl, and independently thereof

   R³ stands for H, methyl, ethyl, CH₂CH₂OH or CH₂CH₂OCH₃,

   R^1' for C₁-C₆ alkyl and

   R^2' for H, or

   R^1' for H and

   R^2' for C₁-C₆ alkyl, and independently thereof

   R^3' stands for H, methyl, ethyl, CH₂CH₂OH or CH₂CH₂OCH₃ and

   R⁴ for C₁-C₄ alkyl,

   Z signifies SO₃M, wherein the sulpho groups can stand in o-, m- or p-position, and

   M signifies H or an equivalent of a cation, selected from the group Li, Na, K, Ca, Mg, ammonium or ammonium which is mono-, di-, tri- or tetrasubstituted by the residues C₁-C₄ alkyl or C₂-C₄ hydroxyalkyl,

   for the brightening of aqueous coating compounds containing at least one latex binder and at least one synthetic cobinder differing therefrom and selected from the group comprising polyvinyl alcohols, carboxymethylcelluloses and mixtures of these two substances.
2. Use according to claim 1, characterised in that the brightener corresponds to the formula (IIa)

   

   in which
   M has the meaning indicated in claim 1.
3. Use according to claim 1, characterised in that at least one latex based on styrene butadiene, styrene acrylate or vinyl acetate is used as a latex binder.
4. Use according to claim 1, characterised in that at least one latex based on styrene butadiene is used as a latex binder and at least carboxymethylcellulose and/or polyvinyl alcohol is used as a synthetic cobinder.
5. Use according to claim 1, characterised in that the coating compound contains at least one white pigment.
6. Use according to claim 1, characterised in that the coating compound contains the latex binder in an amount of 3 to 20 wt.%, especially 5 to 15 wt.%, and the cobinder in an amount of 0.1 to 3 wt.%, especially 0.5 to 1.5 wt.%, in each case based on the amount of white pigment.
7. A coating compound containing

   - at least one white pigment

   - at least one latex binder

   - at least one synthetic cobinder differing therefrom and selected from the group comprising polyvinyl alcohols, carboxymethylcelluloses and mixtures of these two substances and

   - at least one brightener of the formula (II)

   

   in which

   Y signifies a residue of the formula

   

   or

   

   and

   R¹ stands for C₁-C₆ alkyl and

   R2 for H, or

   R¹ for H and

   R² for C₁-C₆ alkyl, and independently thereof

   R³ stands for H, methyl, ethyl, CH₂CH₂OH or CH₂CH₂OCH₃,

   R^1' for C₁-C₆ alkyl and

   R^2' for H, or

   R^1' for H and

   R^2' for C₁-C₆ alkyl, and independently thereof

   R^3' stands for H, methyl, ethyl, CH₂CH₂OH or CH₂CH₂OCH₃ and

   R⁴ for C₁-C₄ alkyl,

   Z signifies SO₃M, wherein the sulpho groups can stand in o-, m- or p-position, and

   M signifies H or an equivalent of a cation, selected from the group Li, Na, K, Ca, Mg, ammonium or ammonium which is mono-, di-, tri- or tetrasubstituted by the residues C₁-C₄ alkyl or C₂-C₄ hydroxyalkyl.
8. A coating compound according to claim 7, containing
   3 to 20 wt.%, especially 5 to 15 wt.% of a latex binder
   0.1 to 3 wt.%, especially 0.5 to 1.5 wt.% of a cobinder
   0.025 to 1 wt.% of a brightener of the formula (II)
   in each case based on the amount of white pigment.
9. Use of the coating compound according to claim 7 for the manufacture of coated papers.