EP1590380A1

EP1590380A1 - Aqueous dispersions containing ethylene copolymer waxes

Info

Publication number: EP1590380A1
Application number: EP04702330A
Authority: EP
Inventors: Wolfgang Gaschler; Andreas FECHTENKÖTTER
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2003-01-27
Filing date: 2004-01-15
Publication date: 2005-11-02
Anticipated expiration: 2024-01-15
Also published as: US20060063877A1; WO2004067587A1; JP2006519274A; DE502004001099D1; EP1590380B1; DE10303170A1; ATE335017T1; ES2270334T3

Abstract

Aqueous dispersion of hydrophobic, low-mol. wt. organic substances (A), contains ethylene copolymer wax(es) (B) comprising 60-99.5 wt% ethylene and 0.5-40 wt% unsaturated carboxylic acid units. Independent claims are also included for (1) a method for the production of such dispersions by mixing (A) with (B) and dispersing the mixture in water (2) paper coating materials containing such dispersions (3) paper containing oil-soluble fluorescent dyes (4) paper treated with the above coating materials.

Description

Aqueous dispersions containing ethylene copolymer waxes

description

The present invention relates to aqueous dispersions containing at least one ethylene copolymer wax which contains 60 to 99.5% by weight of ethylene and 0.5 to 40% by weight of at least one ethylenically unsaturated carboxylic acid in copolymerized form, and at least one hydrophobic low-molecular organic substance.

The production of aqueous dispersions per se of hydrophobic substances is of great technical importance. As an aid to the preparation and stabilization of the dispersion i. A. Emulsifiers. For numerous applications, for example in paper coating, one would like to dispense with the use of emulsifiers.

From EP-A 0 691 390, Progress in Organic Coatings 1995, 26, 207 and Progress in Organic Coatings 1996, 29, 201 aqueous dispersions of fluorescent dyes are known which can be obtained by radical polymerization of, for example, acrylic acid, methyl methacrylate, n-butyl acrylate and Styrene in an organic solvent, for example isobutanol, in the presence of a fluorescent dye. The copolymers obtainable in this way have a weight-average molecular weight M _w of 20,000 to 500,000 g. The solvent can be removed later, ie before or after the actual application of the dispersion. However, the use of solvents is generally disadvantageous.

From EP-A 0 691 384, aqueous dispersions of dyes are known, for the production of which two copolymers are used, which are also prepared by solution polymerization. The solvent can be removed later, i.e. before or after the actual application of the dispersion. The above applies to the use of solvents.

Fluorescent dyes are used, for example, to give objects such as plastics or fibers an improved whiteness. It is generally desirable to use fluorescent dyes, if possible, that have a high quantum yield. Oil-soluble fluorescent dyes are generally superior to polar and therefore water-soluble fluorescent dyes. It is it is difficult to use oil-soluble fluorescent dyes in processes that run in an aqueous environment. So far, it has not been possible to use oil-soluble fluorescent dyes in paper production, especially in paper coating.

The object was therefore to provide aqueous dispersions of hydrophobic substances which are simple to prepare and contain very little or no additional emulsifiers. A further object was to provide a simple process for the preparation of aqueous dispersions of hydrophobic substances. There was also the task of providing new uses for aqueous dispersions.

Accordingly, the aqueous dispersions defined at the outset were found.

The dispersions according to the invention contain at least one ethylene copolymer wax. This is at least one ethylene copolymer wax which contains 60 to 99.9% by weight, preferably 65 to 85% by weight of ethylene and 0.1 to 40% by weight, preferably 15 to 35% by weight of at least one contains copolymerized ethylenically unsaturated carboxylic acid.

Furthermore, the dispersions according to the invention contain at least one hydrophobic low-molecular organic substance. For the purposes of the present invention, hydrophobic substances are understood to mean those organic substances which have a solubility of less than 0.5 g / l of water at room temperature. Low molecular weight substances are substances with a molecular weight of up to 2000 g / mol, whereby polymer waxes are excluded. In the case of such low molecular weight substances which are present in the form of molecular weight dispersions, the so-called number average M _{n is} to be understood by the molecular weight.

Preferred low molecular weight substances are selected from oil-soluble dyes, in particular oil-soluble fluorescent dyes, so-called optical brighteners, biocides, fragrances and flavorings. At least one low-molecular hydrophobic substance which is contained in the dispersions according to the invention is preferably an oil-soluble dye. In particular, the low molecular weight hydrophobic substance is oil-soluble dyes. Preferred oil-soluble dyes from the class of optical brighteners are, in particular, optionally substituted distyrylbiphenyls and distyrylbenzenes. Are particularly preferred

- Distyryl compounds of the general formula II a

- Benzoxazole derivatives of the general formula II b

II b where

R ³ , R ^{4 are} identical or different and are independently selected from hydrogen, cyano, methyl or ethyl; both radicals R ³ are preferably the same, and particularly preferably both radicals are cyano or methyl; n is an integer in the range from 1 to 5, in particular 1 or 2.

A very particularly preferred example of oil-soluble dyes of the general formula II b is the compound of the formula II b.1

ll b.1

The dispersions according to the invention contain 0.001 to 10% by weight, preferably up to 5% by weight and particularly preferably up to 1% by weight, of one or more of the organic low molecular weight hydrophobic substances described above.

Ethylene copolymer waxes of ethylene and ethylenically unsaturated carboxylic acids can advantageously be prepared by radical-initiated copolymerization under high pressure conditions, for example in stirred high pressure autoclaves or in high pressure tube reactors. Production in stirred high pressure autoclaves is preferred. Stirred high-pressure autoclaves are known per se; a description can be found in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, keywords: Waxes, Vol. A 28, pp. 146 ff., Verlag Chemie Weinheim, Basel, Cambridge, New York, Tokyo, 1996 For them, the ratio length / diameter is predominantly in intervals of 5: 1 to 30: 1, preferably 10: 1 to 20: 1. The equally applicable high-pressure tube reactors can also be found in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, keywords: Waxes, Vol. A 28, p. 146 ff., Verlag Chemie Weinheim, Basel, Cambridge, New York, Tokyo, 1996.

Suitable pressure conditions for the polymerization are 500 to 4000 bar, preferably 1500 to 2500 bar. The reaction temperatures are in the range from 170 to 300 ° C., preferably in the range from 200 to 280 ° C.

The polymerization can be carried out in the presence of one or more regulators. The regulator used is, for example, hydrogen or an aliphatic aldehyde or an aliphatic ketone of the general formula III

or mixtures thereof.

The radicals R ⁸ and R ^{9 are the} same or different and selected from hydrogen; - -C ₆ alkyl such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, iso-pentyl, sec-pentyl , neo-pentyl, 1, 2-dimethylpropyl, iso-amyl, n-hexyl, iso-hexyl, sec-hexyl, particularly preferably C 1 -C ₄ -alkyl such as methyl, ethyl, n-propyl, iso-propyl, n -Butyl, iso-butyl, sec-butyl and tert-butyl; C ₃ -C ₁₂ cycloalkyl such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl and cyclododecyl; cyclopentyl, cyclohexyl and cycloheptyl are preferred.

In a particular embodiment, the radicals R ⁸ and R ⁹ are covalently bonded to one another to form a 4- to 13-membered ring. For example, R ^δ and R ⁹ can be common: - (CH ₂ ) -, - (CH ₂ ) ₅ -, - (CH ₂ ) 6, - (CH ₂ ) ₇ -, -CH (CH ₃ ) - CH ₂ -CH ₂ -CH (CH ₃ ) - or -CH (CH ₃ ) -CH ₂ -CH2-CH ₂ -CH (CH ₃ ) -.

Suitable regulators are alkyl aromatic compounds, for example toluene, ethylbenzene or one or more isomers of xylene. It is preferred not to use aldehydes and ketones of the general formula III as regulators. Particularly preferably, no further regulators are metered in, with the exception of the so-called desensitizers, which can be added to organic peroxides for better handling and which can also function as a molecular weight regulator.

The usual free radical initiators such as organic peroxides, oxygen or azo compounds can be used as starters for radical polymerization. Mixtures of several radical initiators are also suitable.

Suitable peroxides, selected from the commercially available substances, are didekanoyl peroxide, 2,5-dimethyl-2,5-di (2-ethylhexanoylperoxy) hexane, tert-amylperoxy-2-ethylhexanoate, dibenzoyl peroxide, tert-butylperoxy-2-ethylhexa- noate, tert.-butylperoxydiethyl acetate, tert.-butylperoxydiethylisobutyrate, 1, 4-di (tert-butylperoxycarbonyl) cyclohexane as a mixture of isomers, tert-butyl perisononanoate 1, 1 -di (tert-butylperoxy) -3,3,5-trimethylcyclohexane, 1, 1-di- ( tert-butyl peroxy) cyclohexane, methyl isobutyl ketone peroxide, tert-butyl peroxyisopropyl carbonate, 2,2-di-tert-butyl perox) butane or tert-butyl perox acetate;

tert-butyl peroxybenzoate, di-tert-amyl peroxide, dicumyl peroxide, the isomeric di- (tert-butylperoxyisopropyl) benzenes, 2,5-dimethyl-2,5-di-tert-butyl peroxyhexane, tert-butyl cumyl peroxide, 2, 5-dimethyl-2,5-di (tert-butylperoxy) hex-3-yne, di-tert-butyl peroxide, 1,3-diisopropylbenzene monohydroperoxide, cumene hydroperoxide or tert-butyl hydroperoxide; or dimeric or trimeric ketone peroxides of the general formula IV a to IV c.

IVa IV b IV c

The radicals R ¹⁰ to R ^{15 are the} same or different and selected from - Ci-Cs-alkyl such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl, tert.- Butyl, n-pentyl, sec-pentyl, isopentyl, n-hexyl, n-heptyl, n-octyl; preferably linear dC ₆ -alkyl such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, particularly preferably linear CC-alkyl such as methyl, ethyl, n-propyl or n-butyl, is very particularly preferred ethyl; - C ₆ -Cι ₄ -aryl such as phenyl, 1-naphthyl, 2-Naρhthyl, 1-anthryl, 2-anthryl, 9-anthryl, 1-phenanthryl, 2-phenanthryl, 3-phenanthryl, 4-phenanthryl and 9-phenanthryl , preferably phenyl, 1-naphthyl and 2-naphthyl, particularly preferably phenyl.

Peroxides of the general formulas IV a to IV c and processes for their preparation are known from EP-A 0 813 550. Di-tert-butyl peroxide, tert-butyl peroxypivalate, tert-butyl peroxyisononanoate or dibenzoyl peroxide or mixtures thereof are particularly suitable as peroxides. Azobisisobutyronitrile (“AIBN”) may be mentioned as an example as an azo compound. Free radical initiators are metered in amounts customary for polymerizations.

So-called desensitizers are added to numerous commercially available organic peroxides before they are sold in order to make them more manageable. White oil or hydrocarbons such as isododecane in particular are suitable as desensitizers. Under the conditions of radical high-pressure polymerization, such desensitizers can have a regulating effect on molecular weight. For the purposes of the present invention, the use of molecular weight regulators is understood to mean the additional use of further molecular weight regulators beyond the use of the desensitizers.

Ethylene and at least one ethylenically unsaturated carboxylic acid are used as monomers. At least one ethylenically unsaturated carboxylic acid is preferably a carboxylic acid of the general formula I.

The residues in formula I are defined as follows:

R ¹ selected from hydrogen,

Ci-Cio-alkyl, such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, iso-pentyl, sec-pentyl, neo-pentyl, 1,2-dimethylpropyl, iso-amyl, n-hexyl, iso-hexyl, sec.-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl; particularly preferably CC ₄ alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl;

R ² selected from hydrogen, - d-Cio-alkyl, such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, iso- Pentyl, sec.-pentyl, neo-pentyl, 1, 2-dimethylpropyl, iso- Amyl, n-hexyl, iso-hexyl, sec.-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl; particularly preferably dC ₄ -alkyl such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl; COOH, COOCH ₃ , COOC2H5.

R ¹ is very particularly preferably hydrogen or methyl and R ^{2 is} hydrogen.

The quantitative ratio of the monomers at metering usually does not correspond exactly to the ratio of the units in the ethylene copolymer waxes used according to the invention, because ethylenically unsaturated carboxylic acids are generally more easily incorporated into ethylene copolymer waxes than ethylene.

The monomers are usually metered in together or separately.

The monomers can be compressed to the polymerization pressure in a compressor. In another embodiment of the process according to the invention, the monomers are first brought to an increased pressure of, for example, 150 to 400 bar, preferably 200 to 300 bar and in particular 250 bar with the aid of a pump and then to the actual polymerization pressure using a compressor.

The polymerization can optionally be carried out in the absence and in the presence of solvents, mineral oils, white oil and other solvents which are present in the reactor during the polymerization and which were used for the desensitization of the radical initiator or radicals, are not considered solvents in the context of the present invention.

In one embodiment, the polymerization is carried out in the absence of solvents.

The dispersions according to the invention preferably contain 0.05 to 40% by weight, preferably 10 to 35% by weight, of one or more ethylene copolymer waxes. It is advantageous that the proportion by weight of the ethylene copolymer wax or waxes in the dispersions according to the invention corresponds to that of the hydrophobic or low molecular weight organic niche substances. The weight fraction of the ethylene copolymer wax or waxes in the dispersions according to the invention is advantageously more than twice as large as the weight fraction of the hydrophobic or low molecular weight organic substances, particularly advantageously more than ten times as large. In the event that the hydrophobic low molecular weight organic substances are oil-soluble fluorescent dyes, the weight fraction of the ethylene copolymer wax or waxes in the dispersions according to the invention is more than a hundred times as large as the weight fraction of the hydrophobic low molecular weight organic substances more than two hundred times larger.

The dispersions according to the invention usually contain one or more basic substances, for example hydroxides and / or carbonates and / or hydrogen carbonates of alkali metals, ammonia, organic amines such as, for example, triethylamine, diethylamine, ethylamine, trimethylamine, dimethylamine, methylamine, ethanolamine, diethanolamine, triethanolamine, methyldiethanolamine , n-butyldiethanolamine, N, N-dimethylethanolamine. The dispersions according to the invention preferably contain so much basic substance or substances that at least half, preferably at least three quarters of the carboxyl groups of the ethylene copolymer wax or waxes are neutralized.

In one embodiment of the present invention, the dispersions according to the invention contain so much basic substance or substances that the carboxyl groups of the ethylene copolymer wax or waxes are quantitatively neutralized.

The dispersions according to the invention usually have a basic pH, preferably pH values from 7.5 to 14, particularly preferably from 8 or higher and very particularly preferably from 8.5 or higher.

The dispersions according to the invention preferably contain no emulsifiers or protective colloids. The dispersions according to the invention are stable even without such surface-active auxiliaries, ie at a shear stress of 100 cm ^-1 , the light transmittance does not change by more than 2%, measured in the case of a dispersion having a solids content of 0.1% by weight with pure water Reference. According to their good application properties, modern dispersions have numerous uses.

Another object of the present invention is a method for producing the aqueous dispersions according to the invention. The process according to the invention is characterized in that one or more ethylene copolymer waxes are first mixed with at least one hydrophobic low-molecular organic substance and then dispersed in water.

To carry out the process according to the invention, one or more of the ethylene copolymer waxes described above are used. This is placed in a vessel, for example a flask, an autoclave or a kettle. In one variant, one or more hydrophobic low-molecular organic substances are added and the ethylene copolymer wax or waxes are heated to a temperature above their melting point. Advantageously, the mixture is heated to a temperature which is at least 10 ° C., particularly advantageously to a temperature which is at least 30 ° C. above the melting point of the ethylene copolymer wax or waxes.

If several different ethylene copolymer waxes are used, the mixture is heated to a temperature which is above the melting point of the ethylene copolymer wax which melts at the highest temperature. In the event that several different ethylene copolymer waxes are used, it is advantageously heated to a temperature which is at least 10 ° C. above the melting point of the ethylene copolymer wax melting at the highest temperature. In the event that several different ethylene copolymer waxes are used, it is particularly advantageously heated to a temperature which is at least 30 ° C. above the melting point of the ethylene copolymer wax melting at the highest temperature.

The dispersion of the hydrophobic or low molecular weight organic substances can be supported by further measures, for example by mechanical or pneumatic stirring or by shaking.

In a variant of the process according to the invention, the ethylene copolymer wax or waxes are first heated and the hydrophobic or low molecular weight is added organic matter to the melted ethylene copolymer (s). A portionwise addition of the hydrophobic or low molecular weight organic substances during the heating process is also conceivable.

Then water and one or more basic substances and optionally further constituents such as ethylene glycol are added, the order of addition of water and the addition of basic or basic substances and further constituents being arbitrary. If the temperature is above 100 ° C, it is advantageous to work under increased pressure and to select the vessel accordingly. The resulting emulsion is homogenized, for example by mechanical or pneumatic stirring or by shaking. The aqueous dispersion thus prepared can then be cooled.

Another aspect of the present invention is the use of the aqueous dispersions according to the invention in paper coating.

Another aspect of the present invention is paper coating slips containing the dispersions according to the invention and a process for producing the paper coating slips according to the invention using the dispersions according to the invention.

Another component of the paper coating slips according to the invention are commonly used pigments, in particular white pigments, for example barium sulfate, calcium carbonate, calcium sulfoaluminate, kaolin, talc, titanium dioxide, chalk or coating clay. Powdered plastics, for example polystyrene, are also suitable.

The paper coating slips according to the invention contain at least one pigment. The other constituents of the paper coating slips according to the invention are typically standardized to the proportion of pigment.

In one embodiment of the present invention, the paper coating slips according to the invention contain one or more dispersions according to the invention in a proportion of 0.5 to 95% by weight, based on the pigment or pigments, 1 to 50% by weight being preferred. The paper coating slips according to the invention can contain further dispersants which can serve to disperse the pigment or pigments. For example, aqueous polymer solutions are suitable. The aqueous polymer solutions include, for example: aqueous solutions of polyalkali metal salts of poly (meth) acrylic acid, copolymers of (meth) acrylic acid and (meth) acrylic acid-C C ₀ -alkyl esters, the copolymers being completely or partially neutralized with basic alkali metal salts could be.

The concentrations of the aqueous polymer solutions are usually in the range from 10 to 50% by weight. If it is desired to use dispersants, amounts of, for example, 0.01 to 5% by weight, based on the pigment or pigments, are suitable.

The paper coating slips according to the invention can furthermore contain one or more binders. For example, aqueous polymer dispersions of polymers or copolymers composed of one or more of the following monomers are suitable: butadiene, styrene, acrylonitrile, vinyl acetate, (meth) acrylic acid-C ₁₀ alkyl ester, (meth) acrylic acid-hydroxy-CrC ₁₀ alkyl ester, Acrylamide and N-methylolacrylamide. The solids content is usually in the range from 30 to 70, preferably 40 to 60,% by weight. Examples of polymer dispersions which can be added as binders to the paper coating slips according to the invention are described in US 3,404,116 and US 3,990,080. If it is desired to add a binder, typical proportions are in the range from 0.1 to 50% by weight, preferably 2 to 20% by weight, particularly preferably 8 to 14% by weight, of aqueous polymer dispersion, based on the or the Pigments as a binder.

If it is desired to use larger amounts of dispersions according to the invention, for example in the range from 60 to 95% by weight, based on the pigment or pigments, it is possible to add smaller proportions of binder, for example in the range from 0.1 to 14% by weight. -%, based on the pigment or pigments, or omit the binder or binders entirely.

The paper coating slips according to the invention can also contain co-binders. Examples of so-called natural co-binders are starch, casein, gelatin, Al- called ginate and soy protein. Examples of modified natural co-binders are hydroxyethyl cellulose, methyl cellulose and carboxymethyl cellulose and cationically modified starch. Examples of synthetic co-binders are the customary synthetic co-binders, for example co-binders based on polyvinyl acetate or polyacrylate.

Co-binders can be contained in a proportion of 0.1 to 10 wt .-%, based on the proportion of pigment.

Another component of the paper coating slips according to the invention is water. The water content is usually set to 25 to 75% by weight, based on the total mass of the paper coating slip according to the invention.

For the production according to the invention of a paper coating slip according to the invention, one can work according to methods known per se.

The paper coating slips according to the invention can then be applied to various materials, in particular to paper. The devices usually used, for example doctor blades, are used for the application.

Another aspect of the present invention is paper containing oil-soluble fluorescent dyes. It is characterized by particularly advantageous whiteness and can be produced with small amounts of fluorescent dyes with a high quantum yield. Overall, it has advantageous application properties. The content of oil-soluble fluorescent dyes in the paper according to the invention is generally 0.0001 to 5% by weight, preferably 0.001 to 3% by weight, particularly preferably 0.002 to 1% by weight, in each case based on paper.

A special aspect of the present invention is paper treated with the paper coating slips according to the invention. Paper according to the invention is distinguished by particularly advantageous whiteness and can be produced with small amounts of fluorescent dyes with a high quantum yield. Overall, it has advantageous application properties. The content of the paper coated according to the invention Oil-soluble fluorescent dyes are in particular 0.0001 to 5% by weight, preferably 0.001 to 3% by weight, particularly preferably 0.002 to 1% by weight.

The invention is illustrated by working examples.

working examples

1. Production of ethylene copolymer wax

Ethylene and methacrylic acid were copolymerized in a high-pressure autoclave as described in the literature (M. Buback er a /., Chem. Ing. Tech. 1994, 66, 510). For this purpose, ethylene (12.3 kg / h) was fed into the autoclave under the reaction pressure of 1700 bar. Separately, 1.04 l / h of methacrylic acid were first compressed to an intermediate pressure of 250 bar and then fed in under the reaction pressure of 1700 bar. Separately, 2 l / h of an initiator solution consisting of tert-butyl peroxypivalate (0.13 molT ¹ in isododecane) was fed into the autoclave under the reaction pressure of 1700 bar. The reaction temperature was 220 ° C. 3.4 kg / h of ethylene copolymer wax were obtained with the following properties: 26% by weight of methacrylic acid, 76% by weight of ethylene, melting range 70-80 ° C., dynamic melt viscosity η 68,000 mPas, measured at 120 ° C. according to DIN 51562, Acid number 172 mg KOH / g (determined according to DIN 53402).

The ethylene and methacrylic acid content in the ethylene copolymer wax was determined by NMR spectroscopy or by titration (acid number). The acid number of the ethylene copolymer wax was determined titrimetrically in accordance with DIN 53402. The KOH consumption corresponds to the methacrylic acid content in the ethylene copolymer wax.

2. Preparation of a dispersion according to the invention

200 g of ethylene copolymer wax according to Example 1 were placed in a 2 liter stirred kettle with anchor stirrer and reflux condenser. 1 g of the fluorescent dye of the formula II a.1 was added

ll a.1 and heated to 160 ° C with stirring. The mixture was stirred for an hour. The fluorescent dye dissolved completely. The mixture was cooled to 140 ° C., Λ /. / V-dimethylethanolamine was adjusted to a pH of 8 and the mixture was made up to a total volume of 1 liter with water. The solids content was 19.7% by weight.

3. Production and use of paper coating slips

The following were mixed with one another in a flask with stirring: 253 g of a dispersion according to the invention from Example 2, 100 g of calcium carbonate (90% by weight of the particles with a diameter of less than 2 μm, commercially available as Hydrocarb 90® from Omya), 0 , 3 g sodium polyacrylate with M _w 4000 g, completely neutralized, 0.2 ml of a 25% by weight aqueous solution of NaOH and 0.75 g of an aqueous dispersion of an acrylic acid-acrylic ester copolymer, which is characterized as follows: acrylic acid 44 % By weight, ethyl acrylate 56% by weight, Brookfield viscosity at 100 s ^{"1 of} a 1% by weight solution at a pH of 9.5: 15 mPa's solids content of the dispersion: 39.7% by weight The mixture thus obtained was adjusted to a solids content of 39.5% by weight with water, giving a paper coating slip with a pH of 9.1. The paper coating slip obtained in this way was applied to Scheufelen raw paper (coat weight 12 g / m ² ) applied and dried.

The whiteness (R457) was determined with the aid of a spectrometer of the brand Elrepho G-50-660 according to DIN 53 145 with UV light to 91.5% at 457 nm, without UV light to 83.5% at 457 nm there was a difference of 8.0%.

Claims

claims

1. Aqueous dispersion containing at least one ethylene copolymer wax which contains 60 to 99.5% by weight of ethylene and 0.5 to 40% by weight of at least one ethylenically unsaturated carboxylic acid, and at least one hydrophobic low-molecular organic substance.

2. Dispersion according to claim 1, characterized in that at least one ethylenically unsaturated carboxylic acid is a carboxylic acid of the general formula I.

the residues are defined as follows:

R ¹ selected from hydrogen, unbranched or branched CrC ₁₀ alkyl, R ² selected from hydrogen, unbranched or branched C Cι ₀ alkyl or COOH, COOCH ₃ , COOC ₂ H ₅ .

3. Dispersion according to claim 1 or 2, characterized in that at least one low molecular weight hydrophobic substance is an oil-soluble dye.

4. Dispersion according to claim 1 to 3, characterized in that the low molecular weight hydrophobic substance is selected from distyryl compounds and benzoxazole derivatives.

5. A process for the preparation of aqueous dispersions according to one of claims 1 to 4, characterized in that first one or more

Ethylene copolymer waxes mixed with at least one hydrophobic low molecular weight organic substance and then dispersed in water.

6. Use of dispersions according to one of the preceding claims in paper coating. Paper coating slips containing dispersions according to one of the preceding claims.

Paper containing oil-soluble fluorescent dyes.

Paper treated with paper coating slips according to claim 7.