EP1987195B1 - Base paper and production thereof - Google Patents

Abstract

The invention relates to a dispersion for incorporation into a fibrous suspension for producing paper or card or for coating paper or card or other sheetlike, preferably fibrous structures; the coating dispersion contains microcellulose; the microcellulose has an average particle diameter of 1 to 100 nm; the particles have a weakly anionic surface charge.

Description

The invention relates to the use of a water-insoluble microcellulose for coating color dispersions for coating printing substrates, in particular for paper and board.

Graphic papers make up an important part of paper production and occupy a leading position in society's use: they are a medium of information, entertainment and advertising. Their development will largely depend on their ability to compete with other communication and advertising media.

In order to achieve good profitability, the value of a product must rise while at the same time reducing production costs. These partially contradictory requirements, such as increasing quality, reducing the basis weight at increasing production speeds, can be achieved with conventional finishing methods, more or only with increased costs.

To stay competitive; Paper manufacturers have to optimize the cost structure of their entire production process over and over again. The biggest cost factors are easy to identify: total energy consumption and raw material costs. While energy costs as well as raw material costs such as coating pigments, binders and other additives have required substantial cost increases over the past two years, a steady downward trend in real paper prices has been recorded since the 1980s.

These development costs call for cost savings in papermaking with specialized manufacturing technology online, if possible, without the risk of disruptions served by bespoke, high solids content coating colors.

To really reduce energy consumption, both machine technology and control and raw materials must be included in the optimization.

In the surface treatment, the trend towards less contact or surface contact has improved the overall cost-effectiveness of the process.
By making better use of the existing chemical potential, considerable savings are also possible.

While only the optical qualities of the coated and printed paper were of importance in the early days of paper coating, the running properties of the coating process are becoming increasingly important. To remain economically competitive, coated board and paperboard producers must not only reduce their input and formulation costs, but also significantly increase their productivity. The easiest way to increase production is to increase the web speed, as this step can usually be done without major technological investment. Therefore, it is understandable that the web speed for the coated mass papers (for example, LWC web offset and gravure printing) has reached 1700 m / min today, unimaginable a few years ago. The technological development to increase the machine speed continues unabated.

To accompany this technological progress, coating colors must have a very good running behavior. Not only increasing web speeds but also higher solids contents and novel pigments with rheologically problematic particle morphology (for example PCC) and higher shape factor (for example talcum) make the running behavior extremely difficult and are a real challenge in recipe optimization.

The increased demand for productivity and process capability in the production of coated papers and cartons on the one hand and quality, On the other hand, the appearance and printability of the end product have caused a large number of different additives to find their way into papermaking, but in some areas they no longer fully meet the requirements.

For example, previously proven cobinders and thickeners such as water-soluble starch and CMC show insufficient water retention at higher shear effects or web speeds and the higher temperature of the coating color due to the online driving style, which leads to considerable running and quality problems such as excessive water repellency and thus increased penetration Penetration of binders, cobinders and other additives, weakening of the fiber structure, sagging of the coating color, drastic change in rheology, bar weight fluctuations, increase in solids content in coating color cycle, increased blade pressure on blade coating, decrease in coating volume and uneven binder distribution (mottling in offset printing).

If the water retention is increased by increased amounts of CMC or synthetic thickeners, the strong viscosity increase must reduce the solids content with all its adverse consequences.

The whiteness or brightness of the papers is a key technical parameter of the final product and more than ever a very powerful marketing tool.

To achieve the highest whiteness and brightness, optical brighteners are increasingly used today.

Brighteners are known to be bound to suitable carrier materials (carriers, such as PVA, CMC), but due to a possible increase in viscosity with possible solids content reduction can be used only to a limited extent. In practice, therefore, especially at high brightener quantities - no longer the optimal brightener / carrier ratio can be set, which leads to a poorer whitening effect and to a graying, poorer light fastness and increased bleeding. With a microcellulose with a narrow particle distribution, which is produced especially for coating colors, very good water retention values and simultaneously higher solids contents of the coating color are obtained even at high web speeds and high temperatures. In addition to the intrinsic water retention of the microcellulose, microcellulose particles result in a barrier layer or rapid immobilization of the coating color on the raw paper interface, which prevents the water from being washed away too quickly and also binders, cobinders and other additives.

This means not only an improvement of the running properties but also at high Bahngeschvirihdigkeiten and at high temperatures (online mode) by a lower penetration of water, binders and other additives - due to the higher solids content and barrier effect of microcellulose and a saving of binders and other additives with simultaneous gloss and smoothness increase.

In particular, the savings in drying energy due to the higher solids content must be emphasized here.

At high brightener doses can be achieved by partial replacement of PVA by microcellulose without solids content reduction by optimizing the brightener carrier ratio better brightening effect, light fastness with excellent bleeding fastness.

Furthermore, the production of high-quality, low-cost inkjet papers with cationized microcellulose without and with pigment is described.
In contrast to the water-soluble cobinders result in the coating color recirculation or reject processing water insoluble microcellulose no circulation and sewage pollution by COD.

State of the art

For the "runabitity" of a coating color, solids content, viscosity and water retention are the most important control variables, which are regulated predominantly by cobinder and thickener. The matching of these coating color criteria to the respective application method, base paper and the working speeds is a necessary measure for achieving good running properties and optimal lines.

The main function of the co-binders and thickeners is to impart to the coating the desired viscosity and water repellency, even at higher temperatures (on-line) and higher shear stresses, i.e., higher production speeds.

Even from the first contact with the more or less absorbent surface of the paper or cardboard, the coating color loses considerable amounts of water by capillary pressure of the substrate. The release of water is further enhanced by Dnickverhältnisse that prevail both in the applicator roll and under the doctor. This must be counteracted by cobinder and thickener accordingly.

At the PTS seminar 2006 in Munich Production and evaluation of coating colors "Manuskript SK 659 2006 the production and evaluation of coating colors is described in detail. The contribution of H. Hanciogullari deals explicitly with additives for the targeted influence of running and quality properties.

You can roughly divide cobinders and thickeners into "natural" and "synthetic" products. In the so-called natural products (that is, on a natural raw material basis) one differentiates between proteins and polysaccharides.

Casein (from cow's milk) and soy protein (from seeds of the soybean plant) belong to the proteins, while starch (oxidatively or enzymatically degraded starches of different origin), carboxymethylcellulose (= CMC) hydroxyethylcellulose (= HEC) alginates (from certain sea algae) belong to the Polysaccharides are counted. Both CMC and HEC are obtained by chemical derivatization of the cellulose. Most natural products are supplied in powder or granular form. Often, these products must first be dissolved in separate preparatory steps and only then added to the coating color.

Starch, soy protein and casein were used as binders in the early stages of paper coating. These products were characterized by the fact that, in addition to their binding power for the pigments, they also had the necessary thickening effect and water retention. Because of these properties, protein and especially starch are still used today as co-binder in addition to the more modern synthetic binders.

The synthetic products include polyvinyl alcohol (= PVOH), acrylate copolymers and associative thickeners. Polyvinyl alcohol is prepared by polymerization of vinyl acetate followed by hydrolysis. Acrylate copolymers are produced by polymerization of suitable monomers such as acrylic acid and methacrylic acid and their esters, acrylonitrile, vinyl acetate, etc. The so-called "associative thickeners" are hydrophobically modified acrylate copolymers with some pronounced properties.

The main function of these products is to give the coating color the desired viscosity and water retention capacity. Around To show these effects, a co-binder or thickener must have a strong interaction with water molecules (for water retention) and other recipe components, in particular with pigments (for thickening effect). In addition, a pronounced structural viscosity (= pseudoplatancy) in the rheological behavior is expected. Only the combination of these factors provides a good starting point for good running properties. Regardless of the form and chemical basis on which these products are available, they must meet some of the key requirements to be used as cobinder or thickener at all.

• Wechselwirkung mit Wasser: Wasserretention
  • Vermeidung übermäßiges Wegschlagen des Wassers (Penetration wasserlösliche Binder, Cobinder und Additive)
  • keine Schwächung des Fasergefüges
    Das Papiergefüge wird durch die aufgenommene Wassermenge schwächer, die Papierbahn kann dann unter Zugbeanspruchung leicht reißen.
  • Keine drastische Änderung der Rheologie zunehmender Feststoffgehalte und zunehmende Viskositäten bei niedriger Wasserretention führen zu dilatanten Fließverhalten und somit zu Rakelstreifen, Bartbildung am Blade etc.
  • Kein anstieg des Feststoffgehaltes im Streichfarbenkreislauf
    Der Feststoffgehalt der Streichfarbe im Kreislauf erhöht sich innerhalb weniger Stunden, da übermäßige Wasserabgabe an das Papier auch eine Verarmung an wasserlöslichen Polymere in der Streichfarbe bedeutet. Insbesondere bei Vorstrichen ist dieses Phänomen oft anzutreffen. Außerdem kommt es zu einer Bindemittelverarmung, was zu Verdruckbarkeitsproblemen führen kann. Mit der Erhöhung des Feststoffgehaltes der Streichfarbe wird ein konstanter Strichauftrag immer schwieriger; oft muss man den Blade-Druck erhöhen, um das Strichgewicht zu halten.
• Wechselwirkung mit Pigmenten: Verdickungswirkung

The main requirements and main functions of thickeners are:

• Interaction with water: water retention
  • Avoidance of excess water penetration (penetration of water-soluble binders, cobinders and additives)
  • no weakening of the fiber structure
    The paper structure is weaker by the amount of water absorbed, the paper web can then tear easily under tensile stress.
  • No drastic change in the rheology of increasing solids contents and increasing viscosities with low water retention lead to dilatant flow behavior and thus to doctor blade streak, blade formation on the blade, etc.
  • No increase in solids content in the coating color cycle
    The solids content of the coating in the circulation increases within a few hours, since excessive release of water to the paper also means a depletion of water-soluble polymers in the coating color. Especially with primers, this phenomenon is often encountered. In addition, there is a binder depletion, which can lead to Verdruckbarkeitsproblemen. With the increase in the solids content of the coating color, a constant coating application becomes more and more difficult; Often you have to increase the blade pressure to keep the line weight.
• Interaction with pigments: thickening effect

The interaction with water is not only essential for water retention, but also significantly affects the viscosity in the water phase. In addition to the hydrodynamic effect, there are a few other ways to limit the mobility of the water phase.

Both high molecular weight and higher structural order significantly increase the hydrodynamic volume of the dissolved polymers.

Stretched, rigid polymer chains reduce the mobility of the water phase as well as the slight crosslinking of these polymers with one another. Finally, the maximum of internal "cross-linking" is achieved by associative interactions through hydrophobic side chains. These effects have in common that they increase the viscosity in the water phase by lowering the mobility as a result of the intra- and intermolecular crosslinking and the volume increase.

• Keine Migration des Verdickers im Rohpapier
• Leichte Strukturbildung
• Prozessfähigkeit

Thickeners should preferably have the following functions:

• No migration of the thickener in the base paper
• Easy structure formation
• process capability

To develop their thickening effect, the hydrocolloids must be present in dissolved form.

While most natural products must be brought into an aqueous solution by heating and boiling, the dissolution process of the acrylate copolymers is based on the alkali ions present in the coating color.

Structural Viscous, Rheological Behavior: Low high shear viscosity.

A precisely set and sufficient water retention are still no guarantee for good running properties. The coating color must also have an overall favorable rheology. In particular, modern coating processes with high solids contents and web speeds require pronounced pseudoplasticity, that is, decreasing viscosity at higher shear rates.

• Gute Laufeigenschaften bei hohen Bahngeschwindigkeiten
• Niedriger Blade-Druck
• Leichte Kontrolle des Strichgewicht.

The following functions are to be achieved by low high-shear viscosities:

• Good running properties at high web speeds
• Low blade pressure
• Easy control of the coating weight.

At high solids levels, the least increase in solids content with inadequate water retention can result in a pronounced dilatancy in the same coating formulation.

As the warm cardboard box is very absorbent and the coating color in continuous contact with the warm cardboard is heated up to 60 ° C, you need a very high water retention to ensure a good coating quality, but CMC also meets its strength in terms of high temperatures and shear this requirement only conditionally. The influence of starch on water retention in such conditions is often overestimated and so the increase in solids content in the coating cycle during production of 5-7% is considered normal and unavoidable. The consequence of this is an increased penetration of binders and other additives (depletion of binders and additives in the coating color) Poor coating holdout, matt and glossy spots due to uneven distribution of birheum and mottling in offset printing.

With the addition of synthetic thickeners, the conditions can be improved somewhat, but they are limited because of the large increase in viscosity.

Previous experience has shown that CMC improves runability at low sweeping speeds and low temperatures (strong static water retention) but with increasing shear and temperature, which today is often the technology of the on-line driving with the film press, loses effectiveness and multiple can even lead to problems.

The poor dynamic water retention as well as the colloidal interactions of CMC with the pigments leads to the described problems in coating.

In addition, larger amounts of CMC result in addition to the water retention too strong increase in viscosity which may require solid content reduction.

Of the various coating color additives, those for the targeted improvement of the surface properties of the coated products occupy a special position, as they have an exact influence on the characteristics of the papers and cardboards, which play a very important role in the value date at the printers and, ultimately, the final consumers. Whiteness, brightness, smoothness and gloss belong to optical properties that are perceived by the human directly through sense organs.
The trend towards very white paper continues unabated, especially in Europe and increasingly also in Southeast Asia.

In order to achieve the highest degrees of whiteness and brightness with a shift in color hue reliably and economically, optical brighteners have become indispensable today.

The whiteness-increasing effect of the mostly used derivatives of Diaminöstilbendisulfonsäuren based on their ability to absorb light from the non-visible ultraviolet range of daylight (350nm) and at higher wavelengths (440 nm) to emit or fluoresce.

The whiteness is also increased by the shift in hue from yellow to bluish. In addition, the brightness of the paper is also increased.

However, the lightening effect only occurs when the optical brightener is fixed on a suitable carrier material or carrier or can "wind up".

The most important co-binders which, among other properties before attem, perform a "carrier" function are polyvinyl alcohol, carboxymethyl cellulose (CMC), polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP) starch, casein, MF resins and styrene-acrylate copolymers.

There are some factors that can seriously affect the optical brighteners in their effect. On the one hand, these water-soluble products can migrate into the raw paper with the water, where they can hardly be reached by the UV rays. On the other hand, the molecules of the optical brightener can attach to each other and "quench" each other, that is to make ineffective. These brightener agglomerates can even shift the color locus to green (graying / greening).

In the current trend of the increased high added amounts of optical brighteners without corresponding necessary Carrier shares - due to viscosity increase or solids content reduction - it comes to graying and greening phenomena, reduced light fastness and increasing bleeding behavior.

From the EP 0 499 578 B1 For example, a microcrystalline cellutose having an average particle size of 1 to 100 μm has been proposed for whitening improvement of optical brighteners.

This proposal failed in practice mainly on the coarse fiber parts, which led to processing problems.

Furthermore, in the literature and patents Mehrzweckschrift- and printing papers are described which are used for copying and / or printed by offset and inkjet printing process.

The demand for inkjet printing papers is expected to increase. Accordingly, this is also expected for the use of laser printers and photocopiers

The quality requirements for inkjet paper continue to increase, but at the same time cost reductions are expected.

Out EP 0 710 742 A2 is a coating ink for a print carrier by the ink-jet printing method, which is characterized essentially in that a three-layer silicate is modified by acid activation of an alkali or Erdalkalismektits or by incorporation of metal oxide bridges in its layered structure and about 10 -. Parts, preferably 20 to 25 parts by weight of binder and other additives.

From the US-A-4792487 A coating ink for a printing substrate is known by the ink-jet printing method consisting essentially of a montmorillonite having a high swelling power and optionally containing a high-surface-area pigment such as synthetic silicic acid or calcium carbonate and a water-insoluble binder. The high microcapillarity or specific surface area of the pigment particles results in excellent inkjet printability in the case of color printouts with good color brilliance, optical density of the colors and dot sharpness. These papers are also characterized by a fast color drying and higher water resistance.

The acid anionic, water-soluble inks are anchored by inkjet preferably at cationic interfaces by rapid adsorption. In addition, the high capillarity of the pigments facilitates the separation of dyes and liquid by chromatographic effect. The larger dye molecules remain on the pigment surface, while smaller molecules, especially water and additives, are drawn into the interior of the pigments by the capillary forces. This requires a high microcapillarity with a defined pore radius and / or improved water resistance.
Due to their high specific surface area of the very expensive silicates used today, their binder requirement is very high (up to 30 - 40 parts binder). In turn, binders are also expensive and, in turn, occupy a large portion of the surface, thus reducing the active surface area.

The production of cationic coating colors is in EP 0 307 795 A2 described.

task

It is an object of the present invention to provide a coating color dispersion for the coating of paper and cardboard, which improves the running properties especially at high machine speeds and high temperatures in addition to cost advantages such as binder and energy savings and qualitative improvements in terms of gloss development and Printability improved.
Furthermore, cost-effective inkjet papers with high quality requirements are described with cationized microcellulose with and without pigments without binders.

According to the invention, a coating dispersion for coating paper and board contains a microcellulose with a narrow particle distribution and an average particle diameter (d 50%) of approx. And a weakly anionic interfacial charge (zeta potentials of -17 to -20 mV) specially developed for the coating process.

Due to the physical properties of the water-insoluble globular water-based "organic coating pigment" with narrow particle size distribution, the high retention of water, even with shearing action and increasing temperatures, counteracts the described penetration processes in the base paper and the migration process during drying with the described disadvantages, while water-soluble co-binders such as starch, CMC, PVA etc. penetrated with the water in the base paper or cardboard.

In addition to the high intrinsic water retention of the microcellulose, the water-affluent microcellulose particles result in a barrier layer or rapid immobilization of the coating color on the base paper interface, which prevents the water from being washed away too quickly and also binders and other additives. Like all hydrocolloids, microcellulose binds significant amounts of water molecules to their interface, increasing their diameter and volume and occupying more space in the aqueous phase of the coating.

The processes described also explain the tendency of low water retention values in laboratory methods (static water retention).

The investigations show that both the viscosity at low shear rates and at higher shear rates (high shear) with microcellulose decreases compared to starch and CMC in the coating color. The investigations also show a lower dynamic viscosity than in formulations with starch and CMC.

The oscillatory measurement makes it possible to distinguish between elastic and plastic flow behavior. The stress on the coating color is increased by the above-mentioned increase of the deflection amplitude. As a result, the particles are moved against each other.

The generated, sinusoidal specification of the shear stress causes a phase-shifted response signal. A fully elastic system shows a shift angle of 0 °; a fully plastic system with a phase shift of 90 °.

Low values of G 'correspond to high mobility with significantly reduced forces between the particles. The lower the value of G ', the higher the wet-pack density and the faster the formation of the initial sediment layer which prevents the penetration of binder and fines into the substrate.

The low storage modulus G 'corresponds to previous experience, that is to say a rapid immobilization and barrier action of the water-insoluble microcellulose at the paper and cardboard interface prevents the coating ink from sagging due to steric hindrance as well as increased penetration of binders and other additives. The lower the value of G ', the higher the microcellulose packing density and the faster the formation of the sediment or barrier layer preventing the said negative penetration processes.

The remaining coating color over the barrier layer, however, remains mobile, d. H. it is easy to level.

When painting at high speed (blade stroking), high pressure gradients are created in front of the blade edge. The barrier geometry of the blade must therefore be adjusted to minimize the hydraulic impact of the coating in the base paper and avoid excessive vortex formation.

While polymeric additives, including starch-based binders, have a detrimental effect, microcellulose has a positive effect on the process described by the action mechanism described, even in the case of extremely short effects of pressure pulses.

For the future development of high-speed blade coating, this inevitably leads to the use of formulations with corresponding pigments and pigment combinations or products such as microcellulose, which are able to withstand dewatering under pressure.

• Verringerung des Schaberdruckes (geringes Absacken beziehungsweise Eindrücken der Streichfarbe in die Unebenheiten des Rohpapiers, Verringerung des Durchschlagens der Streichfarbe, geringere Strichgewichtsschwankungen und des Blade-Verschleißes)
• Verringerung der Wasserabgabe an das Streichrohpapier (geringere Schwächung des Fasergefüges beziehungsweise der Festigkeit, Faserquellung und Fibre Liftung)
• Vermeidung von starken Viskositätserhöhungen beziehungsweise Feststoffgehaltszunahmen durch Wasserverlust bei der Rezirkulation der Streichfarbe (Dilatanzneigung, Rakelstreifen, Bartbildung beziehungsweise Schaberüberkochen.

This results in the following advantages of the running properties:

• Reduction of the scraper pressure (slight sagging or indentation of the coating color in the unevenness of the base paper, reduction of the strike-through of the coating color, lower coating weight fluctuations and the blade wear)
• Reduction of water output to the base paper (less weakening of fiber structure or strength, fiber swelling and fiber lifting)
• Avoidance of strong increases in viscosity or solids content increases due to water loss during the recirculation of the coating color (dilatancy tendency, doctor blade strip, beard formation or scraper overcooking).

In addition, by reducing the penetration processes, a reduction in binder and other additives is achieved.

As mentioned earlier, both low shear viscosity and high shear microcellulose viscosity decrease as compared to CMC, starch and PVA.

The above-mentioned penetration processes are additionally reduced in replacement or partial replacement of starch, CMC and PVA by microcellulose by the resulting higher solids contents accordingly.

The ability to increase the solids content with microcellulose, resulting in qualitative and economic benefits such as binder savings, improving the effect of additives such as cobhers, crosslinkers, optical brighteners or their savings, smoothness and gloss increase, improving the Wegschlagvefialtens the ink, lower Mottlingneigung and especially Saving of drying energy.

It is known that starch products are preferably used for surface sizing. With additional additives, certain effects are sought. Thus, by combining with microcellulose, the film-forming effect of the starch can be effectively improved by reducing the penetration depth or a saving of the strength can be achieved.

Compared to CMC, which has hitherto been used as a regulator for the penetration depth of starch size press formulations, the microcellulose exhibits good water retention even at relatively high temperatures and, in addition, causes a barrier at the paper interface due to steric hindrance of the water-insoluble particles, which leads to increased penetration of the starch into the base paper prevents or controls accordingly.

Due to the high efficiency, the two-sided "online" Filmoressen coating has prevailed at new production facilities. It was found that at higher speeds increased process problems such as excessive doctor blade pressure, spraying and beard formation on the doctor blade, Color splashes, mists or "Misting" and orange peel effect depending on the raw paper texture, coating color.neigenschaften and order conditions can occur more or less strongly
With microcellulose at 1700 m / min without any problems, that means without piloting or spraying pilot tests.

In addition, microcellulose has a very high substantivity for optical brightener (carrier effect), very good water resistance and an improvement in abrasion resistance (abrasion resistance).

PVA is one of the most widely used carriers in the paper industry because of its excellent carrier effect for optical brighteners, used alone or in combination with CMC. However, an optimal ratio between whitener and carrier material (carrier) is a prerequisite for the efficient use of optical brighteners. Due to the increasing trend towards higher paper whiteness levels, more and more added amounts of optical brighteners are associated with high carrier application rates, which leads to very high viscosity increases in the coating color. This is currently counteracted by dilution with water (solids content reduction) or often too small amounts of carrier added in relation to the optical brightener to avoid the viscosity increases, but this leads to insufficient utilization of the brightener potential, lack of light fastness and bleeding fastness.

Although the microcellulose is not a completely equivalent substitute for PVA, very high carrier amounts and brightener amounts without Viskosefiöhung or dilution of the coating color by the combined use of PVA and microcellulose with the advantages of high lightfastness, a high brightening effect and above all a high bleed fastness can be implemented because the water-insoluble microcellulose for steric reasons, the penetration and migration processes that lead to bleeding can not join.

As is known, the free optical brighteners which are not bound to a carrier achieve the worst light fastnesses. If the CMC is replaced by microcellulose in a combination of PVA and CMC carriers, the brightener effect is improved due to the lower penetration of the brightener into the base paper (barrier effect, higher solids content). In coated digital printing papers (for example color laser printing papers), there is often a lack of toner transfer or toner adhesion. With microcellulose, a significant improvement in toner adhesion was observed with appropriate calendering conditions.

With offset papers, microcellulose achieves a more open line structure or a faster and more uniform ink strike away from CMC or starch. The more uniform and lower binder migration to the coating surface results in a smoother printed image or less mottling. In gravure printing, no impairment of printability was observed, while starch and CMC in the form of missing dots had a negative effect.

The invention further provides a process for the preparation of a cationic microcellulose dispersion which is preferably used for specialty papers, such as inkjet papers.

In general, the process of cationization is carried out by initially introducing the anionic microcellulose in an aqueous medium and adding one or more cationic additives to this medium while stirring, depending on the desired charge density. Depending on the polymer used and the amount added, a zeta potential of + 5 mV to + 90 mV results. The cationic or cationized water-soluble polymers are generally characterized by containing quaternary nitrogen atoms in the main chain and / or in the side chains. Examples of such compounds are polymeric diallyl compounds, melamine-formaldehyde resins, epichlorohydrin resins, dicyandiamide resins, quaternary acrylates and inorganic polymers such as Polyaluminum hydroxychloride (PAC), cationically modified polyacrylamides (PAA), polyamidoamines (PAAM), polyamines (PA) and polyethylenimine (PEI). In particular, poly (diallyldimethylammonium chloride) (poly-DADMAC), which preferably has a molecular weight of 60.00 to 120,000, has proved to be particularly suitable.

The cationic microcellulose thus prepared may be applied to the base paper in the present form or may be applied in admixture with various pigments without binder addition such as, for example, kaolin, GCC, PCC, precipitated silicates, bentonites or other pigments. Based on the pigment 0.05 to 3 parts, preferably between 0.1 to 1.0 parts of microcellulose dry in dry (otro) calculated to the coating color are added in the preparation of conventional anionic coating colors according to the investigations. For cationic formulations, up to 100 parts of the cationic microcellulose can be used. The active ingredient content can be set individually according to customer requirements and is 10% dry matter in the application examples. The coating pigments used are commercial pigments and mixtures thereof, such as, for example, kaolin, ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), talc, precipitated silicates, titanium dioxide and aluminum hydroxides. Both the basic binder and the Spezialbirider are polymer dispersions (manufacturers for example BASF AG or Dow Chemical), which are found on the market with a wide variety of product properties. Combinations and copolymers are found which have been prepared with very different starting materials (monomers) (for example butadiene styrene, acrylic acid ester styrene, acrylic acid ester vinyl acetate, etc.). As Cobinder the products described in the patent can be used. Suitable optical brighteners are derivatives of diaminostilbenesulfonic acids, which are preferably used in the paper industry. There are both disulfo-, tetrasutfo- or Hexasulfoaufheller used (manufacturer Clariant AG, Bayer or Ciba Geigy). As crosslinkers are preferably modified glyoxal products, epoxy resins, urea and melamine-formaldehyde resins and zirconium derivatives used. The classical leveling agents (lubricants) are predominantly dispersions of calcium stearates, ammonium stearates, wax emulsions and PEG.

The base paper is wood-free, wood-containing and up to 100% recycled paper containing base paper or paperboard. The print carrier has a basis weight between 30 g / m ² otro and 350 g / m ² otro. The application of the coating color dispersion takes place according to the present invention within (online) and / or outside (offline) the paper machine. As applicators known from the prior art applicators are used, which, for example. Film presses, curtain coater, spray coating, roller coating, bar coating, blade coater, speed coater, Massey process, flooded nip, and the like. The coating speed of the coating color dispersion takes place at a speed between 150 m / min and 2000 m / min. The coated papers lend themselves to a variety of printing processes as known in the art. These may be, for example, the offset printing method, the gravure printing method, inkjet method, flexographic printing method, heat set method, cold set method, laser printing method and the like. Another aspect of the invention is that the coated paper according to the invention has an excellent recycling behavior.

Embodiment 1

Production of a coated offset paper with water-soluble co-binder (hydrocolloids) and a development product according to the invention of a microcellulose. In these first investigations, it was to be determined to what extent the water-insoluble microcellulose can successfully and advantageously replace commercially available, water-soluble co-binders in their function.

As a base paper 46 g / m ² wood-containing base paper and a 42g / m ² base paper, which was prepared with 100% recycled fibers was used.

A high performance disperser was used to prepare the coating. Binder (BASF), cobinder, microcellulose and other additives were added successively to the GCC slurry (Omya) with stirring, the pH was adjusted with NaOH, and the viscosity was adjusted with residual water.
The microcellulose products are described in the company publication J. Rettenmaier u. Sons, Rosenberg described in detail.

Carrying out the experiment

Solids content according to DIN ISO 787 part 2, pH value according to DIN ISO 787 part 9, low shear viscosity according to Brookfield at 100 rpm according to DIN ISO 2555.
The coating colors were applied by means of a motorized hand doctor blade (Erich K Control Coater) to hot-containing or AP-containing coating raw materials with an application rate of 10 g / m ² . The thus-coated paper is calendered in a laboratory calender under the following conditions. Walzenobertlächentemperatur: 95 ° C Line force: 200 N / mm Speed: 10 m / min number of passes 4 V1 V2 V3 Pigment: CaCO ₃ (GCC-slurry) 100 100 100 Binder / co-binders additives Synthetic binders (Styrene-acrylate) 11 11 11 PVA (4-98) 0.6 0.6 0.6 CMC 0.5 - 0.2 Strength 3 3 1 optical brightener 0.5 0.5 0.5 nitrocellulose - 0.4 0.6 (Trial product) Solids content 68.0 69.8 69.2 pH 8.9 8.8 8.9 viscosity 1130 1050 1080 (Brooks 100 rpm)

The investigations showed that the microcellulose in terms of viscosity behavior, brightener development, coating hold-out but above all the possibility of solids content increase compared to commercial cobinder such as starch or CMC advantages The coated, satin-finished papers with microcellulose (test product), however, showed doctor strips after corresponding studies of larger microcellulose particles touched. The further experiments were therefore concerned with an optimization of the grinding of the microcellulose (narrower combination, no coarse fibers, etc.)
Repetition of the experiments with a microcellulose optimized by appropriate grinding conditions showed no line markings or doctor blade strips.

Embodiment 2

Brightening development with microcellulose by substitution of commercially available co-binders. In addition to water retention, viscosity and solids content development, this series of experiments was designed primarily to determine the carrier function of microcellulose for optical brighteners in comparison with commercially available carriers. For this purpose, 2 different addition amounts of a Tetrasulfo Aufheliers were used with different carrier amounts. To prepare the coating colors and measurement of the rheological properties, application by hand wringer and calendering the methods mentioned in Example 1 were used. The measurements were carried out at 40 ° C. Whiteness measurement (reflection factor R 457). The measurement of bleeding fastness was carried out according to DIN EN 648. A rapid test (10 min) with the medium of water was carried out and evaluated.
Formulations, characteristics of the coating colors and measurement results of the coated papers. V1 V2 V3 V4 V5 V6 V7 Pigment: CaCO ₃ (GCC) 100 100 100 100 100 100 100 Binder / co-binder Additive synth. binder 9.5 9.5 9.5 9.5 9.5 9.5 9.5 PVA (4-98) 0.6 0.6 - 1.0 1.0 - 1.0 CMC 0.45 - - 0.45 - 0.45 - Strength 2 1.5 0.8 2 1.5 2.0 0.8 nitrocellulose - 0.45 0.75 - 0.45 0.75 0.75 stearate 0.3 0.3 0.3 0.3 0.3 0.3 0.3 optical brightener 0.3 0.3 0.3 0.6 0.6 0.6 0.6 Solids content (%) 68.6 70.2 72.1 67.2 68.8 69.1 69.5 pH 8.8 8.6 8.7 8.8 8.7 8.7 8.8 Viscosity (mPas) 1240 1120 1180 1220 1140 1220 1130 Brookf. 100U / min water retention (Rheolab) 34 36 25 39 37 40 38 Shine Tappi 75 26.5 27.5 30.0 22 25 24 26 Whiteness R 457 (with UV) 95.5 95.8 94.8 98.7 99.2 97.0 98.8 to bleeding - - - Good very well Good very well

From the experiments V1 - V3 it is clear that by replacing or partially replacing co-binders such as starch, CMC and PVA with the microcellulose higher solids contents can be achieved without changes in viscosity and Water retention losses. At the low brightener levels, no loss of whiteness can be seen, apart from the low whiteness loss, with complete replacement of PVA. PVA is the scale of the optical brightener as a carrier. The increase in solids content and the replacement of low-gloss agents such as starch, CMC and PVA by microcellulose also result in a gloss improvement. In tests V4-V / 7 with higher brightener and PVA contents, the same tendencies with respect to solids content, viscosity behavior, water retention and gloss development as in V1-V3 result. However, the complete replacement of PVA (with a higher proportion of brightener) showed even greater losses in brightener development (whiteness).

The measurement results of the optical properties of the glass fiber pads used to determine bleed fastness showed the best results with microcellulose in combination with PVA. It can be assumed that with even higher brightener proportions with the water-insoluble microcellulose than the water-soluble carriers such as starch, CMC, PVA, PEG, etc., even greater differentiations occur.

Embodiment 3

Substitution of commercial cobindems by microcellulose
Offset recipes with
a pigment mixture of calcium carbonate and kaolin.

In the investigations, it was to be determined to what extent the microcellulose according to the invention, by increasing the solids content in comparison with other commercially available cobinders, saves binder without impairing the
other
Functions of Cobindem permits.
The base paper used was a 46 g / m2 wood-containing base paper. to
Production of the
Coating colors as well as measurement of the rheological properties, order with the
manual knife
and Satinage and optical paper tests, the methods mentioned in Example 1 and 2 were used.

The coating is 12 g / m ² .
The smoothness of Bekk sec. Was in accordance with DIN 53107. The assessment of the printability was carried out with the test printing device Fa. Prüfbau (multi-purpose trial printing device).

Impact test color 520068 M. Huber Munich, pluck test color 408001 colors Huber Munich print speed 1.5 m / s (1.0m / s is standard)

Offset Strichfarbenreptur with and without microcellulose. V1 V2 V3 V4 V5 Pigment: calcium carbonate 70 70 70 70 70 (GCC) coating kaolin 30 30 30 30 30 Binder / co-binders additives: (Styrene-acylate) 10 10 9 10 9.5 PVA (4-98) 2.0 2.0 2.0 2.0 1.5 Ca stearate 0.15 0.15 0.15 0.15 0.15 CMC 0.4 - - - - Strength - - - 3.0 1.0 optical brightener 0.6 0.6 0.6 0.6 0.6. nitrocellulose - 0.3 0.4 - 0.6 Solids content (%) 66.2 67.9 67.7 65.6 67.2 pH 8.7 8.8 8.7 8.8 8.9 Viscosity (mPas) 1420 1350 1420 1310 1580 Brookf. 10U / min UV whiteness R 457% 84.5 84.9 85.1 83.8 84.2 Shine Tappi 575 72.1 73.8 74.2 71.4 73.2 Smoothness Bekk sec. 1290 1385 1420 1310 1380

The results of the investigation confirm the possibilities of setting higher solids contents with microcellulose, which were determined in Example 2, even with pigment mixtures without sacrificing the other functions of Cobindem. Rather, a slight improvement in whiteness and smoothness, but above all a gloss increase is found.
In the printability evaluation, there was a slightly faster ink bleed performance with the microcellulose formulations versus the CMC and starch formulations. From the impact process Printing ink substrates are influenced, among other things, such as ink acceptance, picking behavior, mottling and abrasion resistance. Despite a binder savings in formulations V3 and V5 showed no plucking with microcellulose. Plucking means the damage to the paper surface by the tensile forces exerted by the printing ink during the separation process.
Different types of plucking can be observed, such as occasional bar breakage, fiber breakage, tearing of the paper or detachment of the celluloid blanket in the case of cardboard.

The binder savings, which can be up to more than 2 parts binder depending on the formulation and solids content increase, is made possible by the lower penetration of the binder by the higher solids content and by the barrier action of the microcellulose at the paper's interface.

Embodiment 4 Microcellulose in gravure formulation

From ULWC paper (Ultra Light Weight Coated FG 35 - 48 g / m ² ) and LWC (Light Weight Coated FG 51 - 72g / m ² ) are due to the low coating order and the high job speeds particularly high standards posed the rheological behavior. The achievable solids contents are therefore only at ULWC at about 46 - 49% and at LWC at 56 - 60%. Here, too, there is an intensified trend towards so-called upgraded LWC papers, that is primarily coated papers with a higher whiteness. In some cases, this can only be achieved by means of optical brighteners, so that LWC optical brighteners have also recently been used in gravure printing.

Since carriers for optical brighteners such as CMC and gravure printing can not be used due to the impairment of printability (missing dots) and PVA additionally leads to increases in viscosity, alternative carriers or cobinders, for example microcellulose, are sought. The coating tests were carried out with a 36 g / m ² wood-containing base paper.

To prepare the coating colors and the rheological properties, application by hand wringer and calendering the methods mentioned in Example 1 were used. At the same time measurements were carried out with the Haake viscometer in the higher shear range. The rotational viscometer with a coaxial cylinder system enables measurements in the defined shear gap. By choosing the speed of the rotating body and the dimensions of the shear gap can be the shear rate in the wide range up. Max. 4 10 ⁴ s ^-1 vary.

The coat application weight is 10 g / m ² .

LWC rotogravure formulation

V1 V2 V3 V4 Pigment: coating kaolin 70 70 70 70 (high aspect ratio) Calcium carbonate (GCC) 15 15 15 15 Talcum (50% <μm) 15 15 15 15 Binder / co-binders additives Synthetic binders 4.5 4.5 4.5 4.5 PVA - - 0.8 0.5 nitrocellulose - 0.2 - 0.3 Synthetic thickener 0.5 0.3 0.35 0.2 Ca stearate 0.8 0.8 0.8 0.8 optical brightener - - 0.5 0.5 Solids content% 57.5 58.8 56.2 57.8 Brookfield viscosity 100 rpm (mPas) 950 890 1050 1020 Whiteness R 457 with UV 76.1 75.9 82.6 82.0

The results of the investigation show that even with gravure inks with microcellulose solid content increases - with the already described advantages - without increase in viscosity or other adverse effects is possible.

The Haake viscosity of the individual formulations correlates with the Brookfield viscosity, with the formulations with the microcellulose tending to be slightly lower.

When painting at high speed, high pressure gradients are created in front of the blade edge. Due to the physical properties of the microcellulose such as good water retention at high shear, rheological behavior and the barrier effect on the paper interface or function as an "organic coating pigment" a reduction of the scraper pressure and a reduction of the water delivery to the base paper (less weakening of the fiber structure) is achieved, as well Counteracts a hydraulic injection of the coating color in the base paper.

Embodiment 5 Improvement of the inkjet

Due to the high cationic interfacial charge (zeta potential) and microcapillarity of the microcellulose, the anionic, water-soluble ink ink inks are anchored to the surface by rapid adsorption.
In addition, the capillarity of the microcellulose promotes the separation of dyes and liquid by the chromatographic effect. Cationic microcellulose has an excellent water retention capacity, which has a correspondingly positive effect on the quality properties, especially of pigmented cationic streaks.

For the preparation of the cationic coating colors and measurement of the rheological properties, application by doctor blade and calendering the methods mentioned in Example 1 were used. The charge measurement (zeta potential) was carried out with a zeta meter based on the principle of microelectrophoresis.

Line formulations for cationic coating colors:

V1 V2 V3 V4 V5 Coating pigments: coating kaolin - - 100 mod. CaCO3 - - - 100 100 Binder / co-binders additives Synth. Binder (cat.) - - - 18 18 nitrocellulose 85 70 35 - 2 cationic agents 15 30 15 9 9 crosslinkers 0.2 0.2 0.2 0.5 0.5 Coating color properties Solids content (%) 10.5 10.0 15.6 26.0 27.2 Viscosity Brookf. 940 640 620 540 450 (MPas) Zeta potential (MV) +64 +90 +93 +82 +85 PH value 7.3 8.2 5.9 8.6 8.7

The test results showed that the microcellulose cationic coating colors provide excellent inkjet printability in both HP CP 1160, HP 895 Cxi, HP 950, Epson C 80, and Canon J750 inkjet prints that are significantly superior to conventionally coated and surface sized papers on color brilliance, optical density of Distinguish colors, point sharpness, bleeding and mottling. The coating colors are also characterized by rapid color drying (increase in smudge resistance) and higher water resistance. Due to the excellent water retention capacity of cationic microcellulose, even with pigmented, cationic coating colors with high inkjet quality characteristics with 1-2 parts of cationized microcellulose, further quality improvements can be achieved in all printers in terms of color brilliance, bleeding and mottling.

Embodiment 6 Pilot experiment with offset formulations for coated digital printing papers (laser printing).

• Streichfarbenaufbereitung mit 3 Rotor-Stator-Systemen (GAW VST "Variable Shear Technology)
• Batch- und Jet-Kocher zur Stärkeaufbereitung
• Streichmaschine (Breite 59 cm) mit Walzen- und Düsenauftragssystem mit Stiff oder Bent Blade oder Rollrakel sowie mit Filmpresse mit allen gängigen Vordosiersystemen für Streichgeschwindigkeiten zwischen 50 m/min und 2500 m/min.

These studies aimed to improve the runnability of coated papers in digital printing lines (laser printing). Coated papers often still have residual charges in the tray or when passing through the post-processing machines and thereby generate paper jams and storage errors.
In a pilot experiment microcellulose was used in experiments. To adjust the passage and surface resistance, the loading and unloading processes, NaCl was also used. As a base paper, a wood-free paper with a basis weight of 138 g / m ^{2 was} used. The following machines and equipment are available for carrying out the tests:

• Coating color preparation with 3 rotor-stator-systems (GAW VST "Variable Shear Technology)
• Batch and jet cooker for starch preparation
• Coater (width 59 cm) with roller and nozzle application system with Stiff or Bent Blade or roller blade as well as with film press with all common pre-metering systems for coating speeds between 50 m / min and 2500 m / min.

Technical description:

Off, reeling Jagenberg drive Siemens Master Drives quality control system Measurex process Control System GAW / M + R Draft measurement ABB, both sides Web guide Erhardt & Leimer desiccation Warrior INFRA-AIR-Dryer CB-AIR-Dryer

The application unit Jetflow F with Stiff Blade was used as the application unit.

Coating application weight 12 g / m ² .

• Arbeitsgeschwindigkeit:    400 m/min
• Walzentemperatur H1/H2:    60°C, 60 °C
• Linienkraft:    180N/mm
• Nip:    2

The coated paper rolls were then calendered on the 12-roll supercalender (Voith Sulzer). The parameters set for the calendering of the paper samples V1, V2 and V3 were:

• Working speed: 400 m / min
• Roll temperature H1 / H2: 60 ° C, 60 ° C
• Line force: 180N / mm
• Nip: 2

To study the influence of the calendering conditions on the running properties of the paper samples on a digital printing line, one-third of the paper sample V4 was calendered (setting 1) and calendered with two different calendering settings (settings 2 and 3).

The following settings have been made altogether: attitude 1 2 3 Working speed - 300 m / min 500 m / min Roll temperature H1 / H2 - 90 ° C / 90 ° C 90 ° C / 90 ° C line force - 110 N / mm 300 N / mm nip - 3 11

The calendering according to setting 2 corresponded to the calendering conditions of an offset paper and the setting 3 to the calendering conditions of a rotogravure paper. The non-calendered paper pattern (setting 1) was changed to V4, the setting 2 calendered paper samples to V4! as well as the calendered with the setting 3 Papiermusten marked V4II.

Line formulas for the pilot trial.

V1 V2 V3 V4 Pigment: Calcium carbonate (GCC) 70 70 70 70 coating kaolin 30 30 30 30 Binder / co-binder additives: Synth. Binder 1 12.0 12.0 - - (Styrene-acrylate) Synth. Binder 2 - - 9.0 9.0 (Styrofoam-acrylate) PVA 4-98 - - 2.5 2.5 CMC 0.4 0.4 - - optical brightener 0.5 0.5 0.5 0.5 NaCl - 2.0 - 2.0 nitrocellulose - - 0.5 0.5

The most important characteristics from the coating tests are shown in the following table:

(Coating color viscosity, solids content, pH see Example 1) Characteristics of the coating colors V1 - V4

V1 V2 V3 V4 Coating speed (m / min) 900 1400 1400 1400 Coating order weight (g / m2) 12.2 12.0 12.0 12.4 Coating color viscosity Brookfield 100 (mPas) 1550 2980 740 2420 Solids content (%) 68 62 66.6 65.0 PH value 8.8 8.8 8.9 8.8

Methods of determination for paper testing and printability evaluation:

• Determination of basis weight (DIN EN ISO 536)
• Determination of absolute humidity (DIN EN 20287)
• Measurement of the reflection factor R 457 (whiteness measurement)
• Measurement of the gloss according to ZM V / 22/72
• Printability test with the offset proofing device

• Wegschlagtest (Wegschlagverhalten von Farben)
• Rupftest (Ermittlung der Rupffestigkeit)
• Nassrupftest (Berücksichtigung der Feuchtung von Offsetdruckpapieren)
• Bestimmung des elektrostatischen Auf- und Entladeverhalten (Static Charge Analyser Fa. Monroe Elektronics)

The following printability tests are carried out (see "Test Methods in the Offset for Printing Inks and Substrates Michael Huber Munich 2 Edition):

• Impact test (color impact behavior)
• Plucking test (determination of pick resistance)
• Wet picking test (consideration of the dampening of offset printing papers)
• Determination of electrostatic charging and discharging behavior (Static Charge Analyzer from Monroe Elektronics)

Physical paper testing of coated and calendered papers V1-V4

V1 V2 V3 V4 V4I V4II Areal mass (g / m ² ) 95.1 93.2 92.9 93.2 93.6 94.5 Thickness (μm) 81 81 81 95 86 73 absolute humidity (%) 4.3 4.5 4.3 4.8 4.8 4.6 Smoothness (PPS m) 1.4 / 1.8 2.0 / 2.1 2.4 / 2.3 4.8 / 4.9 2.9 / 3.0 1.4 / 1.4 Whiteness R 457 (%) OS 97.1 97.5 100.3 100.5 100.3 99.4 US 97.5 98.5 100.3 100.7 100.6 99.6 Gloss 75 ° (%) OS 61.3 49.3 46.3 24.0 38.0 70.9 US 58.4 45.7 44.0 21.4 35.1 68.9

Testing the dry picking strength with the Prüfbau
Multipurpose proof printing machine MZ II was made according to the specifications printing ink Plucking test color 40 8002, normal tack speed 3 m / s thrust 150 N / cm inking 200 mg (= approx. 1.5 g / m2) distribution time 30 s Coloring time pressure roller 30 s printing form rubber

Dry and wet picking strength V1-V4

paper pattern dry pick wet pick resistance V1 OS perfect strong building V1-SS perfect strong building V2 OS perfect strong building V2-SS perfect strong building V3 OS perfect no to easy repulsion V3-SS perfect no to easy repulsion V4 OS perfect no to easy repulsion V4-SS perfect no to easy repulsion V4I-OS perfect easy repulsion V4I-SS perfect easy repulsion V4II-OS perfect strong repulsion V4II-SS perfect strong repulsion

Repel:

The applied dampening solution is not sufficiently adsorbed by the coating surface, as a result of which the printing ink is not completely accepted by the paper surface in this zone and remains on the printing form.

Build up:

The paper coating is dissolved by the dampening agent applied or reduced in its surface strength and accumulates in the printing process due to the tensile force in its zone on the printing plate.

The color density values and the ink-rebound behavior are to be regarded as normal, with V2 and V4I and V4II having a slower ink-rebound behavior. V3 with microcellulose shows the fastest color pathway behavior.

The results of the investigation show that microcellulose, in addition to the good running properties, results in no printability problems with regard to plucking despite the somewhat lower binder content.

Rather, microcellulose gives rise to advantages in terms of offset in terms of repelling the printing ink. Only with strong gravure inking (V4 II), which are not common in offset, it comes to repel the ink.
Despite the stronger thickening effect or stronger
Viscosity increase of PVA
compared to the synthetic binders there are advantages with solid content development. It can also be deduced from the investigations that the combination PVA / microcellulose has a good degree of whiteness or a good carrier effect for optical brighteners.
The printing and processing experiments with the test papers V1-V4 were carried out with a digital printing line of Océ. It can come at 1000 pages per minute with double-sided printing at the offset formulation V1 because of the high static charge to running problems. In particular, the coated papers produced with microcellulose are characterized in terms of toner adhesion.

Claims (8)

1. A coating dispersion,

   1.1 the dispersion containing microcellulose;

   1.2 the microcellulose having a mean particle diameter of 10 to 1000 nm and an anionic interfacial charge.
2. A dispersion according to claim 1, characterized in that the mean particle diameter lies between 10 and 500 nm.
3. A dispersion according to claim 1, characterized in that the mean particle diameter lies between 10 and 200 nm.
4. A dispersion according to one of the claims 1 to 3, characterized in that the particles have a zeta potential of -17 to -20 mV.
5. A method for the cationization of the dispersion according to claim 1, characterized in that the anionic microcellulose is presented in an aqueous medium and one or several cationic additives are added to said medium under stirring.
6. A method according to claim 5, characterized in that the particles have a zeta potential of 5 to 90 mV.
7. A method for the cationization of the dispersion according to claim 6, characterized in that the cationic additives are water-soluble polymers.
8. A method for the cationization of the dispersion according to claim 7, characterized in that the water-soluble polymers contain quaternary nitrogen atoms in the main chain and/or in the side chains.