EP2980312A1 - Paper filler - Google Patents

Abstract

Method for producing a paper filler comprising the steps: a) providing an aqueous polymer dispersion b) mixing the aqueous polymer dispersion with a flocculant to obtain a mixture c) dispersing a pigment in solid form in the mixture.

Description

The present invention relates to a paper filler and a process for its preparation.

The manufacturers of coated and uncoated paper products try to use as large amounts of filler as possible. On the one hand, this is the cost savings, since the filler is usually much cheaper than the fiber material used. In addition, fillers can improve relevant paper properties, especially optical properties as well as printability and printability.

However, the filler reduces the strength. With increasing filler content occurs a disturbing loss of strength, since the strength arises only by the connection between the fibers. This loss of strength can be counteracted by the fact that small filler particles are aggregated, so that with increased filler content, the forces acting between the fibers - and thus the strength - are reduced less.

US 4,295,933 discloses a process for preparing an aqueous dispersion so as to continuously provide a polymer suspension. In this polymer suspension is added a filler which is pre-flocced by the polymer before the mixture is brought into contact with paper fibers. The invention more particularly relates to an improvement in the continuous provision of the polymer suspension.

US 4,272,297 discloses a composition for flocculating filler in aqueous suspension. According to the disclosure, this composition comprises cold-soluble starch and another agent which prevents an excessive increase in viscosity.

US 2012/0199304 A1 discloses the use of two flocculants to flocculate fillers wherein the addition of the first flocculant does not yet cause flocculation of the filler. Only when adding the second flocculant, the filler is flocculated, so that for this a defined size distribution and increased shear resistance is achieved.

WO 2013/107933 A1 discloses the treatment of a dispersion of at least one filler with a cationic polymeric reagent which induces flocculation of the filler.

There are a variety of fillers known. The use of known, flocculated fillers can lead to disadvantages in the further processing of the paper, e.g. with regard to ink absorption and dusting of the paper.

Typically, fillers and paper fibers are used in the ratio of about 30:70. With significantly higher amounts of filler, there is a deterioration in the paper properties, which makes the paper unsuitable for the purpose. The exact amounts of filler depend on the requirements for the mechanical properties of the paper.

Although a variety of fillers are already known, there continues to be a need for paper fillers.

The object of the present invention was to provide such fillers.

1. a) Bereitstellen einer wässrigen Polymerdispersion
2. b) Vermischen der wässrigen Polymerdispersion mit einem Flockungsmittel um eine Mischung zu erhalten
3. c) Dispergieren eines Pigments in fester Form in der Mischung.

The object is achieved by a method for producing a paper filler comprising the steps:

1. a) providing an aqueous polymer dispersion
2. b) mixing the aqueous polymer dispersion with a flocculant to obtain a mixture
3. c) dispersing a pigment in solid form in the mixture.

According to the invention, therefore, an aqueous polymer dispersion is provided. The aqueous polymer dispersion thus contains polymer. Examples of suitable polymers are polyvinyl acetates, styrene-butadienes / (meth) acrylic esters, copolymers of styrene and (meth) acrylic esters, styrene copolymers with ethylene, acrylates, acrylamides and acrylic acid and mixtures thereof.

In the aqueous polymer dispersion, the weight ratio between the water and the polymer of the polymer dispersion is typically 1: 1 to 20: 1.

Such polymer dispersions are commercially available. They often also contain other auxiliaries for stabilizing the dispersion.

According to the invention, the aqueous polymer dispersion is mixed with a flocculant. In this case, the aqueous polymer dispersion can be added to the flocculant or the flocculant into the aqueous polymer dispersion. Both can also be introduced simultaneously in a mixer or the like. Preferably, the polymer is flocculated by the added flocculant.

In a preferred process, blending the aqueous polymer dispersion with a flocculating agent achieves aggregation of the polymer. The reaction of the flocculant with the polymer is seen as a change in the turbidity of the dispersion, in particular a reduction in the turbidity of the dispersion, combined with a slight increase in viscosity.

In a particularly preferred method, a flocculating agent suitable for flocculating the polymer is mixed with the aqueous polymer dispersion.

For example, organic polyelectrolytes, such as polymers based on polyimines, such as polyethylenimine, have proven successful as flocculants.

As the weight ratio between the flocculant and the polymer of the polymer dispersion, a range of 1: 5 to 1:20 has been proven. In this case, the water contents of the polymer dispersion or optionally also of the flocculant are not taken into account.

Subsequently, a pigment is dispersed in solid form into this mixture. It is important that the addition of the pigment takes place in solid form. Preferred pigments in solid form are powders or granules. The addition of the pigment thus takes place after bringing the polymer provided in aqueous dispersed form together with the flocculant. Most preferably, the addition of the pigment occurs after the flocculation of the provided polymer is completed. Further preferably, a pigment in solid form is dispersed into the mixture of aqueous polymer dispersion and flocculant, wherein the pigment is not preclaked. The proportion of organic material in the pigment to be added is particularly preferably less than 15% by weight, more preferably less than 10% by weight, even more preferably less than 8% by weight.

After the addition of the pigment to the mixture, a bond between polymer and pigment preferably forms, comprising chemical and physical bonds or forces and combinations thereof, so that a polymer pigment compound is formed. Preferably, the proportion of organic material in the polymer pigment compound is more than 2% by weight, more preferably more than 4% by weight, even more preferably more than 5% by weight.

Powders within the meaning of this application are free-flowing solids with low residual moisture (≦ 1% by weight of water).

Granules for the purposes of this application are free-flowing solids with> 1 wt .-% residual moisture.

Both forms are well suited for the process of this application.

The pigment preferably has a particle size of 0.2 μm to 8 μm, measured as d50 (volume). d50 (volume) means that 50% by volume of the pigments have a particle size smaller than the d50 value and 50% by volume have a larger particle size. Such grain sizes are suitably determined by the provision Z / 27.3 / 90 of the Association of Pulp and Paper Chemists and engineers (ZellChemIng) using a Sedigraph. During the process according to the invention, no significant change in the particle sizes takes place. There is no aggregation or flocculation of the pigment. In particular, the fineness of the particles does not decrease significantly during the process according to the invention.

Fineness is defined as the weight fraction [% by weight] of the particles whose particle size is less than a specific threshold value, for example 2 μm. A decrease in fineness thus means a decrease in the proportion by weight [% by weight] of the particles whose particle size is less than said threshold value.

During a preferred process, the fineness of the particles in dispersing the pigment decreases by less than 5%, more preferably by less than 2%, most preferably by less than 1% (as judged by the 2 μm value).

As the weight ratio of the polymer in the aqueous polymer dispersion to the pigment, the range of 1: 5 to 1:50, without consideration of the water in the polymer dispersion has been proven. The smaller the particle size of the pigment, the larger the surface area and the larger must be the proportion of polymer dispersion in order to precipitate on the pigment can.

In particular, inorganic substances such as kaolin, talc, carbonates (natural or precipitated), bentonites, satin white, barium sulfate or titanium dioxide and mixtures thereof have proven suitable as the pigment. The use of kaolin is particularly preferred.

In some embodiments of the invention, a dispersing agent, for example a polyacrylate, is additionally added.

As the weight ratio of dispersant to pigment, a range of 1: 2000 to 1:50, without consideration of any water present, has been found to be suitable.

The dispersion of the pigment in the mixture of polymer dispersion and flocculant can be carried out by means known to those skilled in the art. Rotor-stator systems or toothed disc stirrers have proven to be particularly suitable.

Preferably, the dispersion is carried out at a high speed.

In an industrial production, the energy input of the dispersing leads to a heating of the solution, which accelerates the crosslinking of the polymer at the filler surface. Typically, one tonne of filler requires energy of the order of 20 kWh.

The invention also provides a paper filler which is obtainable by the process according to the invention and the use of the paper filler according to the invention as a filler in papermaking.

In this case, the filler according to the invention can be used alone or in combination with other fillers, for example untreated calcium carbonate. The proportion of fillers according to the invention to the total fillers used in papermaking should preferably be 10% by weight or more.

• Figur 1 zeigt Eigenschaften von mit erfindungsgemäßen Füllstoffen hergestelltem Papier.
• Figur 2 zeigt das Resultat des Zusammengebens von Polymer und Pigment bei erfindungsgemäßer Ausführung.
• Figur 3 zeigt Resultate des Zusammengebens von Polymer und Pigmenten bei gegenüber dem erfindungsgemäßen Verfahren geänderter Reihenfolge der Schritte gemäß Vergleichsbeispiel 2.

Description of the figures:

• FIG. 1 shows properties of paper produced with fillers according to the invention.
• FIG. 2 shows the result of the combination of polymer and pigment in the inventive design.
• FIG. 3 shows results of the combination of polymer and pigments with respect to the inventive method changed order of the steps according to Comparative Example 2.

The invention is explained in more detail by the following examples.

Example 1 - Preparation of the filler

Makrovil SE 348 (styrene and acrylic ester) of Indulor chemistry was mixed with water in various proportions. With stirring, 10% by weight of Polymin HM from BASF was added as flocculant. The quantities are based on the polymer and the flocculant without including the water.

Kaolin of a d50 grain size of 1.5 μm was then dispersed in these mixtures. Based on the mixture of 10 kg of aqueous dispersion with flocculant, 14.3 kg of kaolin (absolutely dry) were dispersed in and dispersed by means of a rotor-stator system. For dispersion, 0.03 kg of sodium polyacrylic resin was added as a dispersant. A B C Dilution with water 1: 3 1: 4 1: 5.8 10 liters of aqueous dispersion then contain on polymer: 1.25 kg 1.00 kg 0.75 kg flocculants 0.125 kg 0.1 kg 0.075 kg Weight ratio polymer / kaolin 1:11 1:14 1:19

To control the efficiency of the reaction, a sample was taken from the dispersion, diluted with 5 parts by weight of water and centrifuged. The supernatant proved to be clear, indicating fixation of the polymer on the filler surface (see FIG. 2 ). After decanting the supernatant, the loss on ignition of the dried sediment was determined. From the change in the loss on ignition compared to the untreated pigment can be concluded that the amount of bound polymer.

Depending on the dilution of the polymer, various amounts of polymers could be bound to the surface. A B C Dilution with water 1: 3 1: 4 1: 5.8 Supernatant after centrifuge clear clear clear Change in the loss of ignition + 10.8% + 4.6% + 5.4%

Comparative Example 2 - Preparation of the filler with modified, ie not inventive sequences of the method steps

If the sequence of the method steps according to the invention is changed, no fixation of the polymer takes place on the pigment surface.

For sample D, 14.3 kg of kaolin (absolutely dry) having a d50 particle size of 1.5 μm were dispersed in 9.2 kg of water, whereupon 10% by weight of Polymin HM from BASF was added as a flocculating agent with stirring (based on the hereinafter added polymer without including the water). There were then added 1.6 kg of the dispersion Makrovil SE 348 (styrene and acrylic acid ester) with stirring. For dispersion, 0.03 kg of sodium polyacrylic resin was added as a dispersant.

For sample E, 10% by weight of Polymin HM from BASF as flocculant (based on the polymer added hereinafter) was mixed with 9.2 kg of water. There were then 14.3 kg of kaolin (absolutely dry) a d50 grain size of 1.5 microns dispersed before 1.6 kg of the dispersion Makrovil SE 348 (styrene and acrylic acid ester) were added with stirring. For dispersion, 0.03 kg of sodium polyacrylic resin was added as a dispersant.

For sample F, 1.6 kg of the dispersion Makrovil SE 348 (styrene and acrylic ester) were mixed with 9.2 kg of water. Then, 14.3 kg of kaolin (absolutely dry) of a d50 particle size of 1.5 μm were dispersed in with stirring, before 10% by weight of Polymin HM from BASF were added as flocculant (based on the polymer). For dispersion, 0.03 kg of sodium polyacrylic resin was added as a dispersant.

After centrifugation of the dispersion, the supernatant of all samples D, E and F remains turbid (see FIG. 3 ). Thus, non-bound polymer is still in the aqueous phase. After decanting the supernatant, the loss on ignition was determined in comparison to the untreated system. The results summarized in the table below show that far less polymer is bound to the pigment surface than expected based on the kaolin / polymer weight ratio used. D e F sequence Water pigment flocculant polymer Water flocculant pigment polymer Water polymer pigment flocculant Got over cloudy cloudy cloudy Expected change in the loss of ignition + 8% + 8% + 8% Measured change in the loss of ignition <+ 2% <+ 2% <+ 2%

Example 3 - Raw paper production

From the filler prepared in Example 1, laboratory sheets were produced on a Rapid-Köthen sheet former. As a measure of the strength development of the breaking length was used and compared with a filler that did not undergo the treatment according to the invention, ie untreated kaolin. The results are in FIG. 1 shown. It turns out that with the same tear length (measured according to ISO 1924-1, Part-1) the filler content can be increased from 31% to 35% compared to the control.

Claims (15)

Method for producing a paper filler comprising the steps: a) providing an aqueous polymer dispersion b) mixing the aqueous polymer dispersion with a flocculant to obtain a mixture c) dispersing a pigment in solid form in the mixture. The method of claim 1, wherein mixing the aqueous polymer dispersion with a flocculant flocculates a polymer in the aqueous polymer dispersion. Process according to claim 1 or 2, wherein polymers of the aqueous polymer dispersion are selected from the group consisting of polyvinyl acetates, styrene-butadienes / (meth) acrylic esters, copolymers of styrene and (meth) acrylic esters, styrene copolymers with ethylene, acrylates, acrylamides and acrylic acids and mixtures thereof. Process according to any one of claims 1 to 3, wherein the weight ratio between water and polymer of the polymer dispersion is in the range 1: 1 to 20: 1. A process according to any one of claims 1 to 4, wherein the flocculating agent is an organic polyelectrolyte, in particular polymers based on polyimines, such as polyethyleneimine. Method according to one of claims 1 to 5, wherein the weight ratio between flocculant and polymer of the polymer dispersion without consideration of the water content in the range of 1: 5 to 1:20. Method according to one of claims 1 to 6, wherein the pigment has a particle size in the range of 0.2 microns to 8 microns, measured as d50 by Sedigraph, according to the Zellcheming regulation Z / 27.3 / 90, having. The method of any one of claims 1 to 7, wherein the weight ratio of polymer in the aqueous polymer dispersion to the pigment is in the range of 1: 5 to 1:50, without regard to the water. The method of claims 1 to 8, wherein the pigment is selected from kaolin, talc, carbonates, bentonites, satin whites, barium sulfate or titanium dioxide, and mixtures thereof. A method according to any one of claims 1 to 9, wherein additionally a dispersing agent is added, said dispersing agent preferably being a polyacrylate. The process of claim 10, wherein the weight ratio of dispersant to pigment is in the range of 1: 2000 to 1:50, without regard to the water. Method according to one of claims 1 to 11, wherein the dispersion is carried out with rotor-stator systems or Zahnscheibenrührern. Paper filler obtainable by a process according to any one of claims 1 to 12. Use of a paper filler according to claim 13 as a filler in papermaking. Use according to claim 14, wherein the filler used is a mixture of the paper filler according to claim 13 with other fillers.

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