DE102012111719A1 - Preparation, useful in sheet-shaped substrate for producing decorative paper, decorative laminate and/or decorative coating material, comprises finely divided inorganic pigment, and microcapsules formed in the presence of inorganic pigment - Google Patents

Abstract

Preparation comprises a finely divided inorganic pigment, and microcapsules, which are formed in the presence of finely divided inorganic pigment. An independent claim is included for a sheet-shaped substrate comprising the preparation.

Description

FIELD OF THE INVENTION

The invention relates to a process for the preparation of a preparation containing an inorganic pigment and microcapsules and to sheet-like pulp-based substrates containing this preparation.

BACKGROUND OF THE INVENTION

Mineral pigments are used in a variety of applications, in particular for the production of opaque materials and for the coloring of materials. The opacity or opacity is caused by light scattering on the pigment particles. On the one hand, for high light scattering power, it is advantageous to use pigment particles having a specific size and a narrow size distribution. Furthermore, it is also advantageous if the light-scattering pigment particles are distributed as uniformly as possible in the medium to be rendered opaque. Clusters of pigment particles reduce light scattering. In particular, when introducing pigments into papermaking, however, a conglomeration of the pigment particles is usually observed with the consequence that there are microscopic areas in the paper in which a large number of pigment particles are arranged close to one another. In contrast, other areas in the leaf contain only a few pigment particles, with the result that the light passes through such areas largely unhindered and not scattered. From this unequal distribution follows a reduced opacity of the paper, which must be compensated with an increased use of the pigment. In addition to a higher use of material, this frequently also means a deterioration in the mechanical properties of the paper sheet. Various proposals have been made to improve the uniform distribution of pigment particles.

According to the US 2009/107362 A1 For example, the surface of titanium dioxide pigment particles is coated with inorganic nanoparticles, preferably zinc oxide nanoparticles, which function as spacers and prevent too dense aggregation of the titanium dioxide pigment particles, for example in paints and coatings. Because of the small size of the spacers, the effect is not sufficient in a system that is only comparatively slightly filled, such as paper.

The US 4,608,401 describes covering titanium dioxide particles with a voluminous polymer shell to increase the distance between the particles. Similarly, in the US 2006/009546 A1 describes the coating of pigments with multilayer polymer shells. Also in DE 199 61 964 A1 discloses a process for producing a stable dispersion of composite particles consisting of a finely divided inorganic solid and a polymerate. For applications in porous systems with comparatively low pigment fill levels, however, the described teachings can not be used advantageously because, on the one hand, the achievable distances between the pigment particles are too low and, on the other hand, the pore volume of the medium is reduced by the soft polymer latex components of the pigment preparation.

In the US 2008/266646 A1 the production of microencapsulated pigment particles such as carbon black and titanium dioxide for the production of electrophoretic displays is described. In the mentioned embodiment, the pigment particles are dispersed in a high-boiling oil. The aim is not to bring about a high opacity and opacity of the pigment particles by the preparation form, which is not expected due to the comparatively high refractive index of the dispersing medium oil.

The DE 103 44 660 A1 describes encapsulated pigments which consist of an outer water-soluble shell and a core of organic and / or inorganic pigments and optionally solvents and / or customary additives. The encapsulation is carried out by film formers of water-soluble resins, cellulose and cellulose derivatives, sugar, sorbitol, starch, alginates and / or chitosan, in particular polyvinyl alcohol or polyvinylpyrrolidone.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to find a formulation for a pigment whose application in a sheet-like material allows a homogeneous distribution of the pigment and thus a high hiding power or opacity.

This object is achieved by a preparation of an inorganic pigment in which pigment particles and microcapsules are present as a dispersion, wherein the microcapsules are formed in the presence of the finely divided inorganic pigment.

The invention thus also provides a pigment preparation containing a finely divided inorganic pigment and microcapsules, the pigment preparation being obtained by dispersing a finely divided inorganic pigment in the aqueous phase of a water-in-oil emulsion or in the nonaqueous phase of a Oil-in-water emulsion and formation of microcapsules in the presence of the finely divided inorganic pigment.

The invention further provides a pulp-based sheet-like substrate containing an inorganic pigment in a preparation containing pigment particles and microcapsules formed in the presence of at least a portion of the pigment particles. The microcapsules have been formed in the presence of the finely divided inorganic pigment.

Finally, the invention relates to the use of a pigment preparation which contains an inorganic pigment in a preparation which, in addition to the pigment particles, contains microcapsules which have been formed in the presence of at least part of the pigment particles in decorative coatings, paints and varnishes.

It has surprisingly been found that the use of a preparation according to the invention of pigment particles and microcapsules, which have been formed in the presence of pigment particles, produces increased opacity in the production of sheet-like cellulose-based substrates. The resulting opacity is significantly increased compared to the use of equal amounts of pigment particles and microcapsules, which were not prepared in the presence of the pigment particles. Although the effect is not understood in detail, it is believed that the pigment particles accumulate in the capsule wall, in the interior of the microcapsules or attached to the capsule wall in the production of the microcapsules and are thus protected from aggregation in the formation of the sheet substrate.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of the invention is meant by the term pigments finely divided mineral substances, which are obtained naturally or synthetically and are suitable for coloring purposes or as a filler.

The invention can be applied particularly advantageously to mineral pigments which are used to increase the opacity in paints and coatings, in sheet-like materials such as paper or plastic film or the like.

Such pigments may be, for example, kaolins, calcium carbonate in its natural form, such as limestone, marble or dolomite, precipitated calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, talc, silica, alumina and mixtures thereof. Because of its high hiding power and opacity, titanium dioxide is preferred for many applications.

In addition to white or colorless pigments, the invention can also be advantageously applied to colored inorganic pigments, for example those based on iron oxide.

The particle size of the pigments contained in preparations according to the invention is in the range from 100 nm to 10 .mu.m, preferably in the range from 200 nm to 3 .mu.m. For the cases in which the pigment particles have a non-spherical shape, "particle size" is understood to mean the diameter of a sphere which is the same volume as the particle.

The pigment preparation according to the invention contains microcapsules in addition to the pigments. For the purposes of the invention is meant by the term microcapsules hollow body whose shell is mainly made of a solid material, preferably a synthetic resin or a high molecular weight organic material of natural origin. In a particular embodiment of the invention, however, the sheath can also consist predominantly of a mineral solid substance, for example silicon dioxide.

The numerical ratio of pigment particles and microcapsule may be on average below 500: 1, preferably below 100: 1 pigment particles per microcapsule. The mean inner diameter of the Microcapsules may be larger by a factor of 1 to 100 than the average diameter of the pigment particles contained therein. Preferably, an inner diameter of the microcapsule will be at least twice as large as the pigment particle. Internal diameters which are greater than five times the pigment particle diameter are particularly preferred. The weight ratio of capsule material to pigment is 1:10 to 10: 1, preferably 4: 1 to 1: 1.

In a particular embodiment of the invention, the residual internal volume of the microcapsules in the final product is filled with air or water.

The microcapsules may be completely closed bodies, but they may also have openings in their surface.

Preference is given to microcapsules whose surface has no openings.

The preparation of the microcapsules is carried out by per se known methods of spray drying or polymer encapsulation in the stirred tank by interfacial polymerization or crosslinking. Such methods are described, for example, in "H. Mollet and A. Grubemann: Formulation Technology ", Weinheim (2006), pages 241 to 252 ,

As shell materials, resins such as polymethyl methacrylates, polyurethanes, polyureas, polystyrene (PS), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) or polyamide (PA) are suitable. Particularly preferred melamine-formaldehyde resin is used as the shell material. The capsule formation can as in the DE 198 35 114 A1 described at a pH of 3 to 5 done. According to a further preferred embodiment of the invention, the shell materials are organic substances or mixtures obtained as natural raw materials or produced from such as starch, dextrins, gelatin, chitosan, cellulose and their derivatives such as carboxymethylcellulose (CMC), hydroxypropylcellulose (HPC) or Methylhydroxycellulose (MHC). In a particular embodiment of the invention, the shell material may also be predominantly an inorganic solid such as silica.

The preparation of the microcapsules according to the invention is carried out in the presence of at least a portion of the pigment particles, preferably in the presence of the total amount of the pigment particles. The pigment particles can be present, for example, as an aqueous dispersion from which a water-in-oil emulsion is prepared by means of suitable wetting agents and processes. The formation of the polymeric shell occurs at the oil-water interface by precipitation, gelation, crosslinking or polymerization reactions. However, the pigment particles may also be present in the aqueous phase of an oil-in-water emulsion in which the microcapsules are formed at the interface. In another embodiment of the invention, the pigment particles are incorporated into the non-aqueous phase of an oil-in-water or water-in-oil emulsion prior to the formation of the microcapsules. The use of the microencapsulated pigments according to the invention can be carried out in all application areas in which uniform introduction of a pigment into a matrix takes place and in which agglomeration of the pigment particles is to be avoided. Such applications include the coloring of plastic and elastic plastic compositions, coating compositions in particular for decorative coatings, paints and paints. Also advantageous is the use of the microencapsulated pigments as a filler in papermaking, as it can be achieved a significant improvement in the uniformity of the pigment distribution and thus an increase in the opacity of the paper sheet. Microencapsulated pigments of the invention are used particularly advantageously as a filler and as impregnating and coating composition for decorative base papers and decorative films.

The following embodiments serve to further explain the invention.

EXAMPLES

Preparation A (Invention): Dispersion of microcapsules prepared in the presence of aqueous dispersed titanium dioxide

Titanium dioxide dispersion: 146 g _TiO2 (Ti-Pure ^® R-796 + laminates Grade Titanium Dioxide pigment manufacturer DuPont) are mixed with water with 254 g and with a rotor-stator dispersion ULTRA-TURRAX ^® Model T25 for five minutes at 9600 revolutions per minute (RPM), the pH of the dispersion is then adjusted to 8.5 with 10 wt .-% sodium hydroxide solution. The solids content of the dispersion thus obtained is 36.5% by weight.

Precondensate: 87.8 g (corresponding to 17.6 g solid) LUPASOL ^® PA 140 (polymer based Acrylamidosulfonat, manufacturer BASF SE, Ludwigshafen, Germany) and 93.6 g (corresponding to 65.5 g solid) LURACOLL ^® SD (methoxymethylated Melamine, manufactured by BASF AG, Ludwigshafen, Germany) are made up to 500 g with water and formic acid is added at 30 ° C. with stirring to a pH of 4.1 ± 0.5. The mixture is stirred for an additional 60 minutes at 30 ° C until visible turbidity occurs.

Capsule formation: 100 g (corresponding to 36.5 g of titanium dioxide) of the titanium dioxide dispersion prepared in the first step are mixed with the entire amount of precondensate (500 g with 83.1 g of solid), and then 136 g of n-hexane are added and the mixture is stirred at 6000 rpm using a dispersing disk stirrer. Emulsified for 15 minutes. The emulsion obtained is further stirred for 60 minutes at 30 ° C. at 1000 rpm, the temperature is raised to 90 ° C. at a rate of 2 ° C./min and then further stirred for 90 minutes. This melts the melamine resin and evaporated n-hexane. After cooling to 50 ° C., the dispersion is adjusted to a pH of> 8 with sodium hydroxide solution. This gives a dispersion of microcapsules having a solids content of 20 wt .-% and a titanium dioxide content of 6 wt .-%.

Preparation B (Invention): Dispersion of microcapsules prepared in the presence of titanium dioxide dispersed in the oil phase

Titanium dioxide dispersion: There are 36.5 g hydrophobic titanium dioxide (Kronos ^® 2450, available from KRONOS TITAN GmbH, Leverkusen, Germany) are stirred in 136 g of n-heptane.

Capsule formation: The capsule formation takes place in the same manner as in Example B, except that no aqueous titanium dioxide dispersion is prescribed and instead of the n-heptane, the titanium dioxide dispersion produced in the previous step is emulsified in n-heptane at the start of capsule formation. This gives a dispersion of microcapsules having a solids content of 20 wt .-% and a titanium dioxide content of 6 wt .-%.

Preparation C (comparative): Mixture of a microcapsule dispersion which is not prepared in the presence of titanium dioxide pigment with a titanium dioxide dispersion.

An aqueous titanium dioxide dispersion is prepared in the same way as described in Example A.

Separately, a capsule dispersion is prepared in the same manner as in Example A, but without adding a titania dispersion prior to capsule formation.

The finished capsule dispersion is mixed after cooling with the aqueous titanium dioxide dispersion. This gives a dispersion of microcapsules and titanium dioxide having a solids content of 20 wt .-% and a titanium dioxide content of 6 wt .-%.

Production of a decorative paper sheet

50 g of eucalyptus pulp (Jacarei from Fibria) are filled in a 3 liter dispersion vessel with 1.5 liters of water, so that a consistency of about 3 sets. Using a laboratory dissolver and a dispersing disc (diameter 50 mm), the pulp is beaten at 3700 rpm for 30 minutes. Subsequently, the resulting pulp is filled in a distributor and filled with water to 8 liters total, so that sets a consistency of about 1. In the distributor 25 g of a 1.5 wt .-% solution of a is additionally Adipinsäurediethylentriaminepichlorhydrin copolymer (Giluton XP ^® 14, available from BK Giulini GmbH) as a wet strength agent and the suspension with 10% sulfuric acid to a pH-value set by 6.

From the pulp suspension produced in this way individual formulations are produced in the following manner to produce decorative base paper sheets on the sheet former (manufacturer ERNST HAAGE Apparatebau).

21.3 g of the titanium dioxide preparation A, B or C corresponding to 1.6 g of TiO _{2 are} added to 300 g of the pulp suspension and the suspension is mixed with a paddle stirrer for 15 seconds. Thereafter, another 0.95 g of the 1.5% by weight adipic acid diethylenetriaminepichlorohydrin copolymer solution is added and the mixture is mixed for a further 45 seconds.

The single batch thus prepared is added to the filling chamber of the sheet former to 2 l of water, made up to 4 l total volume and the sheet forming process is started.

Using the titanium dioxide preparation A according to the invention, the individual sheets A1 to A12 were thus produced, using the inventive titanium dioxide preparation B, the individual sheets B1 to B12 prepared from the comparative titanium dioxide dispersion C, the individual sheets C1 to C12.

Impregnation and compression of the decorative paper sheets

For the impregnation of the single sheets, a solution having 52 wt .-% of melamine-formaldehyde resin (Kauramin ^® 773 from BASF SE) are used in water, of 1.6 wt .-% of wetting agent (Hypersal ^® VXT 3797 of Surface Specialties Germany) and 0, 8 is added wt .-% Madurit ^® hardener MH 835 / 70W, available from Ineos Melamines, Germany.

The decorative paper sheets are placed on the resin solution until fully soaked for at least 60 seconds and then completely immersed in the resin bath. Excess resin is then doctored off and the sheet dried at 130 ° C for 25 seconds. Thereafter, the sheet is again completely immersed in the resin solution, excess resin is again doctored off and dried at 130 ° C to a residual moisture content of 6 wt .-%.

The impregnated decor paper sheets are pressed by the high-pressure process (HPL) at a temperature of 140 ° C and a pressure of 234 bar with a 40 × 40 cm size plate for 4 minutes and cooled in the press to 60 ° C. Under the sheet to be tested, a much smaller black and a white decor paper sheet for measuring the opacity are pressed in at two different places.

The opacity of the decorative paper sheet to be tested is determined by measuring the reflection density of the plate, measured with a Color Eye 3000 Macbeth colorimeter, over the white sheet partially laminated under the sheet to be measured through the black sheet laminated over the sheet partially under the sheet to be measured divided density is divided and the result is multiplied by 100.

The basis weight of the resulting leaves, their ash content and the achieved opacity are summarized in the table below, the ash content ( DIN 54370 ) can be equated with the amount of titanium dioxide contained in terms of leaf weight or leaf area. Table 1: Test results leaf Leaf weight [g / m2] Ash content [%] Ash content [g / m ² ] Opacity [%] A1 73.9 6.1 4.5 64.6 A2 82.6 10.2 8.4 77.8 A3 94.7 13.3 12.6 83.3 A4 102.5 15.5 15.9 86.8 A5 112.1 17.0 19.1 89.3 B1 77.6 6.5 5.0 63.1 B2 82.6 10.5 8.7 76.2 B3 93.2 13.4 12.5 83.3 B4 104.0 16.3 17.0 88.4 B5 111.2 18.1 20.1 90.1 C1 72.7 8.8 6.4 63.3 C2 77.3 12.5 9.7 74.1 C3 82.3 14.6 12.0 79.4 C4 88.2 15.8 13.9 81.7 C5 91.0 17.4 15.8 83.8

If the achieved opacity is plotted against the area-related titanium dioxide content ( ), it can be seen that the titanium dioxide preparations A and B according to the invention, which contain microcapsules, which were prepared in the presence of titanium dioxide, a significantly higher opacity than when using the comparative preparation C is achieved at a comparable titanium dioxide content. Conversely, in order to achieve a given opacity by utilizing the invention, a saving of titanium dioxide of at least 20% of the amount can be made.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2009/107362 A1 [0003]
• US 4608401 [0004]
• US 2006/009546 A1 [0004]
• DE 19961964 A1 [0004]
• US 2008/266646 A1 [0005]
• DE 10344660 A1 [0006]
• DE 19835114 A1 [0024]

Cited non-patent literature

• "H. Mollet and A. Grubemann: Formulation Technology ", Weinheim (2006), pages 241 to 252 [0023]
• DIN 54370 [0044]

Claims (14)

Preparation containing a finely divided inorganic pigment and microcapsules, characterized in that the microcapsules are formed in the presence of the finely divided inorganic pigment. Preparation according to claim 1, characterized in that the inorganic pigment is a white pigment. A preparation according to claim 2, characterized in that the inorganic pigment is titanium dioxide, barium sulfate, calcium carbonate or a mixture thereof. Preparation according to claim 1, characterized in that the microcapsules are prepared by interfacial reaction in an emulsion of an aqueous and a non-aqueous phase. Preparation according to claim 1, characterized in that the microcapsules consist of a crosslinked polymer. A preparation according to claim 5, characterized in that the weight ratio of capsule polymer to pigment is 10: 1 to 1:10. A preparation according to claim 5, characterized in that the weight ratio of capsule polymer to pigment is 4: 1 to 1: 1. Preparation according to claim 5, characterized in that the capsule polymer is a crosslinked formaldehyde-melamine resin. A preparation according to claim 1, characterized in that the finely divided inorganic pigment is dispersed in the formation of microcapsules in the aqueous phase. A preparation according to claim 4, characterized in that the finely divided inorganic pigment is dispersed in the formation of the microcapsules in the nonaqueous phase. A sheet-shaped substrate containing a preparation of a finely divided inorganic pigment and microcapsules according to any one of claims 1 to 9. Leaf-shaped substrate according to claim 8, characterized in that the sheet is formed with pulp fibers. Use of a sheet-shaped substrate according to claim 11 or 12 for the production of a decorative paper. Use of a sheet-form substrate according to claim 11 or 12 for the production of a decorative laminate or decorative coating material.

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