EP1812644B1 - Aqueous paper coating slip containing pigment-polymer hybrids - Google Patents

Abstract

The invention relates to aqueous paper coating slips containing organic polymers as binding agents and inorganic pigments. The invention is characterised in that the binding agents are at least partially in the form of pigment-polymer hybrids and are chemically or physically bound to the inorganic pigments.

Description

• organische Polymere als Bindemittel und anorganische Pigmente, dadurch gekennzeichnet, dass die Bindemittel zumindest zum Teil in Form eines Pigment - Polymerhybrids vorliegen, in denen das Bindemittel chemisch oder physikalisch an die anorganische Pigmente gebunden ist und das Bindemittel zu mindestens 60 Gew. % aus Butadien oder C1 bis C20 Alkyl acrylaten oder Mischungen einer der vorgenannten Monomere mit Styrol aufgebaut ist.

The invention relates to aqueous paper coating slip containing

• organic polymers as binders and inorganic pigments, characterized in that the binders are present at least partly in the form of a pigment - polymer hybrid, in which the binder is chemically or physically bound to the inorganic pigments and the binder to at least 60 wt.% Of butadiene or C1 to C20 alkyl acrylates or mixtures of one of the aforementioned monomers with styrene is constructed.

Paper coatings consist essentially of pigment and binder. The binder should fix the pigments on the paper and ensure cohesion in the resulting coating.

When printing z. B. in an offset printing press, act because of the high viscosity of the ink strong tensile forces on the coated paper. The resistance that the coated paper provides against these forces is called pick resistance. Depending on the moisture condition, a distinction is made between dry picking strength and wet picking strength.

Aqueous paper coating slips containing composite particles of inorganic pigments and organic polymers are described in FR 1 572 674 , wherein the organic polymers each consist of only one polymer. Possible polymers mentioned are vinyl polymers, such as polyvinyl chloride and polyvinyl acetate or copolymers of these substances, cellulose derivatives, methyl acrylate, such as meth-methyl acrylate or ethyl methacrylate, and also polystyrenes. Exemplified are the use of cellulose derivatives and vinyl acetate. They are used to improve the smoothness of paper.

Composite particles of inorganic pigments and organic polymers are z. B. off WO 93/12183 known; the composite particles are used in paints.

Anhydrous paper coating slips containing composite particles of organic pigments and organic polymers in WO 01/00712 and WO 01/00713 described.

In previously known paper coating slips the binding force of the binder and thus the Rupffestigkeit is not sufficient.

Object of the present invention was therefore paper coating slips with improved pick resistance.

Accordingly, the paper coating slip described above was found.

An essential component of the paper coating slips is a binder. According to the invention, the binder is a polymer which consists of at least 60% by weight, preferably at least 80% by weight, of so-called main monomers.

The main monomers are C ₁ -C ₂₀ , preferably C ₁ -C ₁₀ -alkyl acrylates and mixtures of the alkyl acrylates with styrene, (polymers with these main monomers are collectively called polyacrylates for short) or, alternatively, butadiene, or mixtures of butadiene with styrene (US Pat. Polymers with these main monomers are collectively called polybutadienes for short).

For mixtures of butadiene with styrene, the ratio z. B. between 10:90 to 90:10, in particular 20:80 to 80:20.

In addition to the main monomers, the polymer may contain monomers having at least one acid group (short acid monomer), z. As monomers with carboxylic acid, sulfonic acid or phosphonic acid groups. Preferred are carboxylic acid groups. Called z. As acrylic acid, methacrylic acid, itaconic acid, maleic acid or fumaric acid.

Other monomers are also z. As well as hydroxyl-containing monomers, in particular C ₁ -C ₁₀ hydroxyalkyl (meth) acrylates, (meth) acrylamide.

• 10 bis 90 Gew. %, vorzugsweise 20 bis 70 Gew. %. Butadien
• 10 bis 90 Gew. %, vorzugsweise 30 bis 80 Gew. %, Styrol
• 0 bis 20 Gew. %, vorzugsweise 0 bis 10 Gew. % Säure-Monomer
• 0 bis 20 Gew. %, vorzugsweise 0 bis 10 Gew. % weitere Monomere

oder alternativ im Falle der Polyacrylate aus

• 10 bis 95 Gew. %, vorzugsweise 30 bis 95 Gew. %, C1 bis C 10 Alkyrlacrylate
• 0 bis 60 Gew. %, vorzugsweise 0 bis 50 Gew. %, Styrol und
• 0 bis 20 Gew. %, vorzugsweise 0 bis 10 Gew. % Säure-Monomer
• 0 bis 20 Gew. %, vorzugsweise 0 bis 10 Gew. % weitere Monomere

Accordingly, particularly preferred polymers are synthesized in the case of polybutadienes

• 10 to 90% by weight, preferably 20 to 70% by weight. butadiene
• 10 to 90% by weight, preferably 30 to 80% by weight, of styrene
• 0 to 20% by weight, preferably 0 to 10% by weight of acid monomer
• 0 to 20 wt.%, Preferably 0 to 10 wt.% Other monomers

or alternatively in the case of the polyacrylates

• 10 to 95 wt.%, Preferably 30 to 95 wt.%, C1 to C 10 Alkyrlacrylate
• 0 to 60 wt.%, Preferably 0 to 50 wt.%, Styrene and
• 0 to 20% by weight, preferably 0 to 10% by weight of acid monomer
• 0 to 20 wt.%, Preferably 0 to 10 wt.% Other monomers

Both the polybutadienes and the polyacrylates preferably contain acid monomers as comonomers, preferably in an amount of from 1 to 5% by weight. The maximum amount of the above aliphatic hydrocarbons in the polybuadienes and the alkyl acrylates in the polyacrylates is reduced accordingly by the minimum amount of the acid monomers.

The polymers are prepared in a preferred embodiment by emulsion polymerization, it is therefore an emulsion polymer.

However, the production can z. B. also be carried out by solution polymerization and subsequent dispersion in water.

In the emulsion polymerization, ionic and / or nonionic emulsifiers and / or protective colloids or stabilizers are used as surface-active compounds.

The surfactant is usually used in amounts of from 0.1 to 10% by weight, based on the monomers to be polymerized.

Water-soluble initiators for the emulsion polymerization are z. For example, ammonium and alkali metal salts of peroxodisulfuric, z. For example, sodium peroxodisulfate, hydrogen peroxide or organic peroxides, z. B. tert-butyl hydroperoxide.

Also suitable are so-called reduction-oxidation (red-ox) initiator systems.

The amount of initiators is generally 0.1 to 10 wt.%, Preferably 0.5 to 5 wt.%, Based on the monomers to be polymerized. It is also possible to use a plurality of different initiators in the emulsion polymerization.

In the polymerization regulators can be used, for. B. in amounts of 0 to 0.8 parts by weight, based on 100 parts by weight of the monomers to be polymerized, by which the molecular weight is reduced. Suitable z. B. Compounds with a thiol group such as tert-butylmercaptan, thioglycolic acid ethylacrylic ester, mercaptoethynol, mercaptopropyltrimethoxysilane or tert-dodecylmercaptan.

The emulsion polymerization is generally carried out at 30 to 130, preferably 50 to 90 ° C. The polymerization medium may consist of water only, as well as of mixtures of water and thus miscible liquids such as methanol. Preferably, only water is used. The emulsion polymerization can be carried out both as a batch process and in the form of a feed process, including staged or Gradientenfahrweise be performed. Preferably, the feed process in which one submits a portion of the polymerization, heated to the polymerization temperature, anepymerisiert and then the rest of the polymerization, usually upper several spatially separate feeds, one or more of which monomers in pure or in emulsified form, continuously , gradually or with the addition of a concentration gradient while maintaining the polymerization of the polymerization zone supplies. In the polymerization can also z. B. be presented for better adjustment of the particle size of a polymer seed.

The manner in which the initiator is added to the polymerization vessel in the course of the free radical aqueous emulsion polymerization is known to one of ordinary skill in the art. It can be introduced both completely into the polymerization vessel, or used continuously or in stages according to its consumption in the course of the free radical aqueous emulsion polymerization. Specifically, this depends on the chemical nature of the initiator system as well as on the polymerization temperature. Preferably, a part is initially charged and the remainder supplied according to the consumption of the polymerization.

To remove the residual monomers is usually after the end of the actual emulsion polymerization, d. H. after a conversion of the monomers of at least 95%, initiator added.

The individual components can be added to the reactor in the feed process from above, in the side or from below through the Reatctorboden.

In the emulsion polymerization, aqueous dispersions of the polymer are generally obtained with solids contents of from 15 to 75% by weight, preferably from 40 to 75% by weight.

Suitable binders are in particular mixtures of various binders, eg. As well as mixtures of synthetic and natural polymers.

The paper coating slip according to the invention contains inorganic pigments as an essential constituent. In particular, it is white pigments. To name a few are z. As barium sulfate, calcium carbonate, calcium sulfoaluminate, kaolin, talc, titanium dioxide, zinc oxide, chalk or coating Clay.

Particularly preferred is titanium dioxide or calcium carbonate.

In addition to inorganic pigments and organic pigments, as z. In WO 01/00712 and WO 01/00713 are described, be used. However, such organic pigments are no longer within the scope of the present invention mandatory. The proportion of organic pigments is preferably less than 20 parts by weight, in particular less than 10 parts by weight, more preferably less than 5 parts by weight, based on 100 parts by weight of inorganic pigment.

With particular preference, no organic pigments are used.

According to the invention, the binder and the inorganic pigment are present at least partly in the form of pigment-polymer hybrids. In these hybrids, the organic polymer or binder is chemically or physically bound to the inorganic pigment. In particular, the binder is adsorbed to the pigment surface.

The pigment-polymer hybrids are an independent particle species with a uniform density. When measuring the density of the pigment-polymer hybrids with an ultracentrifuge by the static density gradient method (at 21 ° C and 1 bar), only one density, ie one type of particle, is determined. The measuring method of the static density gradient is z. In W. Mächtle, MD Lechner, Progr. Colloid Polym. Sci (2002) 119,1 described.

To study a sample in the static density gradient (Stat DG), a mixture of light solvent and heavy solvent or additive (i.d.R Metrizamid / H2O, metrizamide / D2O) is centrifuged at moderate rotor speeds for at least 22 hours. The different sedimentation and diffusion behavior of heavy and light agents leads to the formation of a concentration and thus a density gradient across the cell. Each radial position of the measuring cell therefore has a different density of solvent. Within this density gradient, the sample or the chemically different components of the sample sediment or float precisely at the radial position at which there is a mixing ratio of light and heavy agent corresponding to their particle density. This allows a highly accurate fractionation of samples according to the density and thus the chemical composition.

Since in the system under investigation polymer (about 1 g / cm.sup.3), calcium carbonate (2.6 to 2.95 g / cm.sup.3, depending on the modification) and polymer / carbonate hybrid differ significantly in the densities of the particles, measurements of the particles can be made Hybrid in suitable static density gradients carried out the detection of free polymer or the exclusion of free polymer.

A pigment-polymer hybrid is z. B. already obtainable by mixing pigment and binder and subsequent drying or preferably by grinding the pigment in the presence of the binder.

The pigment-polymer hybrids may contain other ingredients in addition to binder and inorganic pigment, eg. B. dispersants such as polycarboxylic acid or its salts, in particular polyacrylic acid or polyphosphoric acid.

The content of the organic polymers and binders in the pigment-polymer hybrids is in particular less than 40 parts by weight, preferably less than 20 parts by weight, more preferably less than 15 parts by weight of organic polymers per 100 parts by weight of those present in the hybrids pigments.

The content of organic polymers and binders in the pigment-polymer hybrids is preferably at least 1 part by weight, more preferably at least 3 parts by weight and most preferably at least 5 parts by weight, per 100 parts by weight of the pigments present in the hybrids.

In the paper coating slips according to the invention, organic polymers, in particular binders and inorganic pigments, are particularly preferably used in the form of the pigment-polymer hybrids. In addition to the pigment-polymer hybrids, it is also possible to use organic binders and inorganic pigments which are not present in the form of the pigment-polymer hybrids.

Preferably, at least 30% by weight, in particular at least 60% by weight and very particularly preferably at least 95% by weight and in particular 100% by weight, of the total inorganic pigments present in the paper coating slip are present in the form of the pigment-polymer hybrids.

Preferably at least 30% by weight, in particular at least 60% by weight and very particularly preferably at least 95% by weight and in particular 100% by weight of the organic polymers contained in the paper coating slip, or binders in the form of the pigment-polymer hybrids.

The paper coating slips can be further additives z. B. dispersants. Suitable dispersants are polyanions, for example of polyphosphoric acids or of polyacrylic acids (polysalts), which are usually present in amounts of from 0.1 to 3% by weight, based on the amount of pigment.

In addition, the paper coating slips may contain rheology additives. There are z. As starch, casein, gelatin, alginates and soy proteins, mentioned as modified natural products hydroxyethyl cellulose, ethyl cellulose and carboxymethyl cellulose and cationically modified starch. But it can also be common synthetic additives, eg. B. on vinyl acetate or acrylate, are used, the latter usually have a content of acid monomers greater than 5, especially greater than 10 wt.%.

The rheology additives may, for. B. in amounts of 0.1 to 2 wt.%, Based on the Pigmentrnenge be included.

To prepare the paper coating composition, the ingredients are mixed in a known manner.

The paper coating composition is preferably at least 40% by weight, more preferably at least 60% by weight, most preferably at least 80% by weight or 90% by weight of pigment-polymer hybrids, water and other organic solvents having a boiling point being smaller 200 ° C at 1 bar are not counted as a component; in particular, it may also consist of at least 95 or 100% by weight of pigment-polymer hybrids.

The paper coating slip according to the invention preferably contains at least 30 parts by weight, in particular at least 40 parts by weight, of water per 100 parts by weight of inorganic pigment.

The content of water in the paper coating slip is usually adjusted to 25 to 75% by weight, particularly preferably 25 to 50% by weight, based on the total paper coating slip (including water).

The paper coating slip can be applied by conventional methods to the papers to be coated (cf. Ullmann's Encyclopadie der Technischen Chemie, 4th Edition, Vol. 17, p. 603 ff ).

The papers coated with the paper coating slips according to the invention have a high dry and wet pick resistance (adhesion of the paper coating slip). This makes them particularly suitable for offset printing, in which due to the high viscosity of the ink, the coated paper is stressed by high tensile forces.

The papers coated with the paper coating slips according to the invention show good printability. The papers are particularly suitable for offset printing.

Examples A) Preparation of pigment-polymer hybrids

The preparation was carried out according to the method described in Fr 04 07 806 Omya.

To produce the hybrid 1 calcium carbonate slurries (Hydrocarb 2 GU from Omya AG) in a Dispermat SN was - C milled 12 mill in the presence of an aqueous dispersion of a carboxylated styrene-butadiene copolymers (Styronal ^® D536 from BASF AG) as a binder.

• Umdrehungsgeschwindigkeit der Mühle 5500 r/min
• Mahldauer 30 min
• Slurrykonzentration 66 %
• Kugelgröße 33 mm Durchmesser
• Kugelmaterial Glas

Grinding conditions were:

• Rotation speed of the mill 5500 r / min
• Grinding time 30 min
• Slurry concentration 66%
• Ball size 33 mm diameter
• Ball material glass

For Hybrid H1, 10 parts of binder (solid), 0.3 part of Polysalt ^® S (dispersant) were used per 100 parts of CaCO3 and after grinding 0.4 parts of Polysalt S was added. B) Detection of the physical and / or chemical bonding of the polymer to the Pigment:

Polymer hybrid H1 and the polymer used Styronal ^® D536 were measured according to the method described above in the static density gradient of the ultracentrifuge. By using four different density gradients, a density range of 0.95 g / cm ³ to 1.30 g / cm ^{3 was} covered.

When measuring the polymer used, a sharp peak is observed at a density of 0.99 g / cm ³ .

In the measurement of the polymer hybrid H1 no peaks are observed in the entire accessible density range, in particular at the density of the pure polymer.

The polymer / pigment hybrid thus contains no unbound polymer.

C) Preparation of the paper coating slips

The paper coating slips were prepared by stirring the ingredients according to the following table: Table 1 Formulations formulation 1 2 CaCO ₃ 100 pigment hybrid 100 Styronal D 536 10 Polysalt S * 0.3 Sterocoll FD ** 0.13 0.13 Solids content 65.7 65.3 Viscosity (CPS) 100 rpm 515 670 pH 8.5 8.5 Water retention 121 127 * Polyacrylic acid salt
** Polyacrylate-based rheology additive

D) Technical testing

The base paper used was a wood-free base paper with a basis weight of 70 g / m ² . The paper coating slip was applied on one side with 10 g / m ² on a laboratory coater. The drying took place with an IR emitter.

The papers passed a laboratory calender four times before the performance tests (one roller pair, line pressure: 2000 N / cm).

Dry picking strength (IGT-dry)

From the papers to be tested strips were cut in the size 33 x 3 cm in the longitudinal direction and these strips stored for 15 hours at 27 ° C with a relative humidity of 50% in the climatic chamber.

The strips were subsequently printed in a printing unit (IGT printability tester AC2 / AlC2) with a standard color (printing ink 3808 from Lorilleux-Lefranc).

The test strips are fed through the printing unit at a continuously increasing speed (maximum speed 200 cm / sec). As a measure of the Trockenrupffestigkeit the speed in cm / sec is specified, in which after the start of printing 10 tears from the paper coating (Rupfpunkte) are done.

offset test Paper:

From the papers to be tested, samples having a size of 240 x 46 mm are cut out in the longitudinal direction.

Carrying out the test:

On the inking roller, an appropriate amount of the ink is added and allowed to run for 1 min. Then a pressure washer is used and colored for 30 s.

The printing speed is 1 m / s. A strip of paper is returned to a print sample carrier with the printed paper strip in the starting position. After a specified period of time, the printing process is restarted without replacing the pressure disk. This process is repeated several times.

After each pass, the plucking on the printed side of the paper strip is visually inspected. The number of passes is indicated until the first time a pluck occurs. For very strong plucking, the last pass is indicated as half (eg, strong plucking after the 3rd pass is indicated as 2.5).

Specification of the result:

Number of prints until the first picking occurs.

The results are summarized in Table 2 below. Table 2 example 1 2 IGT dry (cm / s) 115 100 PB off-set 5 3

The results show that in the case of the pigment hybrid significantly increased binding forces were established in comparison to Example 2, with otherwise good paper properties

Claims (10)

1. An aqueous paper coating slip comprising

   - organic polymers as binders and inorganic pigments, wherein the binders are present at least partly in the form of a pigment-polymer hybrid in which the binder is chemically or physically bound to the inorganic pigments and the binder is composed of at least 60% by weight of butadiene or C₁- to C₂₀-alkylacrylates or mixtures of one of the aforementioned monomers with styrene.
2. The aqueous paper coating slip according to claim 1, wherein the binder is an emulsion polymer.
3. The aqueous paper coating slip according to either of claims 1 and 2, wherein the inorganic pigments are white pigments, e.g. titanium dioxide or calcium carbonate.
4. The aqueous paper coating slip according to any of claims 1 to 3, wherein the binder content is from 5 to 30 parts by weight per 100 parts by weight of inorganic pigments.
5. The aqueous paper coating slip according to any of claims 1 to 3, wherein the water content is at least 30 parts by weight per 100 parts by weight of inorganic pigments.
6. The aqueous paper coating slip according to any of claims 1 to 4, wherein at least 50% by weight of the binders are present in the form of the pigment-polymer hybrid.
7. The aqueous paper coating slip according to any of claims 1 to 5, wherein the pigment-polymer hybrid is obtainable by first preparing a mixture of inorganic pigment, the binder and optionally further assistants and then removing any concomitantly used water or solvent down to a residual content of less than 20 parts by weight per 100 parts by weight of inorganic pigment.
8. The aqueous paper coating slip according to any of claims 1 to 7, wherein the pigment-polymer hybrid is obtainable by milking the inorganic pigment in the presence of the binder.
9. The use of an aqueous paper coating slip according to any of claims 1 to 8 for coating paper or cardboard.
10. A paper or cardboard obtainable by the use according to claim 9.