DE19842962A1 - Aqueous formulation for surface preparation and coating of paper and cardboard contained sulfoethylcellulose ether as cobinder - Google Patents

Abstract

In an aqueous formulation for surface preparation of paper and cardboard, with a cobinder based on polysaccharide, the cobinder is a water-soluble cellulose derivative etherified with sulfoethyl groups.

Description

The invention involves the use of water-soluble sulfoethyl cellulose ethers, such as e.g. B. sulfoethyl cellulose ether, carboxymethyl sulfoethyl cellulose ether, hydroxyethyl Sulfoethyl cellulose ether, methyl sulfoethyl cellulose ether, hydroxypropyl sulfoethyl cellulose ether and correspondingly hydrophobically modified sulfoethyl cellulose mixture ether ether as cobinder for aqueous formulations for the surface preparation of Paper and cardboard. Appropriate formulations are also called coating colors designated.

Water-soluble polyvinyl alcohols, polyacrylamides, polyacrylates, alginates, starches, Chitosans, starch ethers, modified starch ethers, non-ionic cellulose ethers, such as e.g. B. methyl cellulose ether, hydroxyethyl cellulose ether and hydroxypropyl cellulose ethers and hydrophobically modified cellulose ethers, ionic cellulose ethers, such as. B. Methyl, carboxymethyl cellulose ether (CMC) and carboxymethyl cellulose ether, have long been used as co-binders for pigmented coating colors for coating of paper and cardboard used (see DE 16 21 694, EP 0 399 775, US-PS 4,994,112, EP 0 382 576, U.S. Patent 5,080,717).

The products used as cobinder have the task of coating to control the required rheology of the coating color and the same guarantee moderate coating of the paper or cardboard surface. It's be knows that when using cellulose ethers, especially carboxymethyl cellulose ethers, the properties required for the coating process via the poly Degree of merization of the original cellulose and the degree of substitution of the cellulose ethers can be set.

In addition to setting the rheology dependent on the respective application unit the cobinder in pigmented coating colors also have the task of a way hitting the coating color during the coating process and preventing a ensure trouble-free processing of the colors. Improving the water  Restraint is of particular importance here because it makes it inadmissible Increases in the concentration of the coating color avoided during the coating process and thus longer runtimes or less machine downtimes with less downtime crack rates can be set. They can also be more uniform Higher quality coatings are guaranteed because of the controlled Penetrating the additives contained in the coating colors into the base paper during during the coating process or during the drying process Coating color components in the stroke can be reduced (see J. S. Malik, J. E. Kline, Tappi 1992, Coating Conference Proceedings Tappi-Press, Atlanta, pp. 105 to 113).

According to the prior art, the rheology of coating colors and. a. by the type and amount of pigment (e.g. chalk and / or kaolin) and the binder or Set the cobinder (e.g. CMC) specifically. When using CMC as cobinder you can improved values for the dynamic water release capacity of the coating color or the quality of the surface coating of the papers by increasing the quantity the share in Cobinder or by providing a CMC with a higher one Degree of substitution obtained by carboxymethyl groups of approximately 1 or above become. However, these options come with economic disadvantages for both connected to the manufacturer of the CMC as well as for the paper refiner itself, since the improved properties only by using larger amounts of raw materials (Alkali, chloroacetic acid) or longer reaction times during alkalization or Let etherification of the cellulose stop.

Improved values for the dynamic water release capacity of the coating color can also be achieved by the molecular weight or the viscosity of the used CMC increased. High molecular weight carboxymethyl cellulose ethers are all However, it can only be processed to a limited extent, since the viscosity of the coating is too high Color must be avoided, otherwise there will be processing problems in the form of Squeegee strips, web breaks and. Ä. can come. When using highly viscous carboxy As a rule, methyl cellulose ethers for coating color can therefore only be used in low concentrations CMC solutions are processed. However, this is again Ver  deterioration in the quality of the coated papers (e.g. decline the paper white u. a.). High-molecular cobinder is added in the form aqueous solutions, there is also an undesirable high entry from water to pigment coating. Lower solids content of the pigment spread Color or extended drying times of the coated paper or cardboard web and thus higher energy costs for the user with lower quantities Paper throughputs are the result.

The trend towards ever higher machine speeds as well as the tendency in to use calcium carbonate a pigment, the use of which without kaolin, which has so far often been used, becomes a much worse one Water retention of the coating color leads to the need for qualitatively improved products with lower dynamic water release capacity to provide. The addition of such an improved cobinder to the pigment coating In addition, paint should not be used with inadmissible increases in viscosity of the paint accompanied. Furthermore, the quality of the coated paper will not deteriorate.

Surprisingly, it was found that the use of sulfoethyl cellulose derivatives, especially sulfoethyl cellulose ethers (SEC), carboxymethyl sulfoethyl cellulose ethers, methyl sulfoethyl cellulose ethers, methyl hydroxyethyl sulfoethyl cellulose ethers, methyl hydroxypropyl sulfoethyl cellulose ethers. Ethyl sulfoethyl cellulose ethers, hydroxyethyl sulfoethyl cellulose ethers and hydroxypropyl sulfo ethyl cellulose ethers as cobinder improves the quality of coating colors. It was found that coating colors containing cobinder based on sulfoethyl cellulose in same solids content and same viscosity lower values for the dynamic Water release capacity with simultaneously improved rheology show as a prank colors with CMC as Cobinder. In addition, the use of hydrophobic modified sulfoethyl cellulose mixed ethers, such as in particular hydroxypropyl sulfo ethyl cellulose ether, to improve the quality of the paper when printing.  

When using cellulose-based cobinder as an additive for pigment-containing Coating colors are preferably to be used in cellulose ethers which, if possible possess high quality solutions. Gel particles, fibers and specks can ver blockages of filters and sieves. If coarser, water-insoluble Cellulose particles stuck under the coating unit, it can form doctor strips or Web breaks come. It is therefore necessary to use cellulose ethers that are soluble in water without gels, fibers and specks. The water solubility of Cellulose ethers are usually based on the level of substitution of etherification components set.

In the claimed according to the invention and further described below by way of example Cellulose ethers are the "DS" (degree of substitution) the average number the hydroxyl groups substituted in the cellulose per anhydroglucose unit. According to the invention, it is advantageous if, in the cellulose ethers used, the DS by sulfoethyl groups is less than 1.2. It is known to the person skilled in the art that provision of a water-soluble CMC a degree of substitution of approx position of a water-soluble, unsubstituted SEC the amount of the substitu tion must be at least about 0.2-0.3. For aqueous form according to the invention rations with SEC without further substituents is preferably the DS of the SEC 0.2 to 0.9, in particular 0.3 to 0.75. For the production of fiber-free solutions is the Degree of substitution generally significantly higher (see EP 0 319 867). With mixed starters, containing sulfoethyl groups, is necessary to achieve water solubility The degree of substitution by sulfoethyl groups is significantly lower. For in Mixed ethers used in the formulations according to the invention is the substitution degree DS by sulfoethyl groups, preferably 0.05 to 0.9, in particular 0.01 to 0.7 and particularly preferably 0.1 to 0.7.

The aqueous formulation according to the invention can be one or more auxiliaries the prior art, preferably from the group of dispersing aids (ins special polyphosphates, polyacrylates), binders (especially starch and Starch ether, casein, polymer dispersions based on butadiene styrene, acrylic acid ester Styrene, acrylic acid ester vinyl acetate, vinyl acetate-ethylene and copolymers  above products with acrylonitrile), anti-foaming agents (especially Emul sions of animal or vegetable fats, silicone emulsions or higher alcohols and their esters), optical brighteners and acceptors therefor (in particular Polyvinyl alcohols, casein, CMC), shading dyes (especially pigment dyes substances, substantive and basic dyes) for setting the color location, products to increase water resistance (especially melamine and urea resins, Glyoxal, epoxy resins) and / or auxiliaries for the final equipment of the coated paper are required (especially calcium, sodium or Ammonium stearate, wax dispersions, polyglycols and polyethylene dispersions) contain. Those skilled in the art come as pigments in pigmented coating colors common raw materials, such as preferably kaolin, natural calcium carbonate, talc, Satin white, precipitated calcium carbonate, titanium dioxide, aluminum hydroxide, plaster, Barium sulfate, plastic or plastic pigments alone or as a mixture in dry or in an already predispersed form (so-called slurry form).

In a further embodiment of the invention, the aqueous formulation is a So-called sizing agent, which the Cobinder in a pigment-free Formulation, optionally together with one or more of the above Tools, contains. It is preferably an aqueous solution which the sulfoethyl cellulose ether in a concentration of 0.1 to 30%, in particular 0.1 to 15%.

The cobinders used in the examples were found to be highly concentrated, aqueous Solutions of the pigment slurry are added. The aqueous solutions of the Invention According to the sulfoethyl cellulose derivatives claimed, all have high transmissions values of T <95% (2% by weight aqueous solution, wavelengths of the used Light λ = 550 mm, optical path length of the cuvette = 10 mm) [Hitachi spectral photometer, model 101, Hitachi Ltd. Tokyo-Japan). The setting low fiber this guaranteed levels of <1%.  

For the determination of dynamic water release, rheology and immobilization The coating colors used a dynamic measurement method, as described in the literature is described (see Das Papier 50 (1996), No. 3, 97 ff).

For the experiments described below, those designated in Table 1 were used Cellulose ether used. The production of those claimed in the invention Sulfoethyl cellulose derivatives are known from the literature (see US Pat. No. 2,811,519; US Pat 4,972,007; EP 0 319 865 A2).

Table 1

Characteristics of the products used to determine water retention

The products listed in Table 1 were coated with kaolin and Chalk as pigment according to the standard formulation listed in Table 2 is working. The rheological behavior and the initial water release after one dynamic measurement method were examined. The standard formulation was first the recipe listed in table 2 is used. A limitation to the However, the recipe components described here are not connected to this.

Table 2

Standard coating color formulation for investigations of the water release ability

The results of the studies on rheology and initial water release under dynamic measuring conditions, each with 0.3 part of Cobinder Table 3 shows 100 parts of pigment.  

Table 3

Comparison of rheology and initial water release (WAV) of coating colors

Basically there is a tendency to use coating colors with as little water as possible content, i.e. high solids content. Energy savings when drying, higher throughputs and more voluminous coating layers can be achieved in this way. Around To ensure the flowability of such a paint, the viscosity and the Water release, especially the initial water release of a coating color, low his. This eliminates the risk of a sudden increase in viscosity and thus minimize the solids content of the coating color during the coating process. Lies the water retention of the paint in a critical area, the under the Coating unit effective pressure pulses of about 2-4 bar cause, conditionally due to the water penetrating too quickly into the paper, the solids content below the squeegee soaring. Then there is the so-called scraper boiling over or Beard formation, i.e. deposits of the coating color on the coating unit, squeegee strips or tearing off the paper web.

After the coating process, the immobilization of the Coating color, so that all transport processes from existed in the formulation recipe components are prevented. If this takes too long, can migrate both to paper and to the paper surface are triggered, which may lead to a loss of quality when printing (e.g. Mottling) can lead.

In the experiments carried out here to investigate the water retention of Coating colors became a dynamic measuring method, as they are in the literature (see D. W. Jones et al. in: Das Papier, 50 (3) (1996) pp. 97-106) used. The procedure is such that the coating color to be examined in the the aforementioned measuring cell is entered and sheared under defined conditions. The amount of water delivered is a function of the current color present solids content added. The value for the water delivered quantity at time t = 0 is called the initial water release. The he Results in Table 3 show that those formulated with sulfoethyl cellulose ethers Coating colors (serial no. 3-6) compared to the standard (Walocel CRT 5 G (= Stand the technology)) have improved dynamic water discharge capacity at 5 bar.  

Compared to coating colors formulated with CMC, it comes as a surprise with the addition of the sulfoethyl cellulose ether to the coating color to a significantly lower Thickening performance or a liquefying effect of the coating color. It falls on that the viscosities determined are still significantly below those of the undickened Coating color lie (see current No. 1 and current No. 7). This leads u. a. to the above Advantages mentioned, especially with highly pigmented, particularly critical Formulations as described under No. 7-9. This is also here Water release capacity of the coating color formulated with sulfoethyl cellulose clearly below that of the standard (see serial numbers 8 and 9). Despite a similar viscose levels of the aqueous SEC solutions (see Table 4) is the viscosity of the SEC thickened coating color significantly below the level of the reference sample and the unthickened color.

In contrast to the reference sample (Walocel CRT 5 G [serial numbers 2 and 8]) it happens moreover when using the coating formulated with sulfoethyl cellulose ethers colors for faster immobilization of the color. This eliminates the risk of Migration processes from e.g. B. Binder proportions minimized on the surface of the coating.

With the products described in Table 4, machine tests were carried out on a Coating system carried out.  

Table 4

Characteristics of the Cobinder used for machine tests

The products Walocel CRT 5 G and Walocel CRT 3 G were used as standards (both carboxymethyl cellulose ether) used. These were compared to Sulfoethyl cellulose ethers (SEC 1 and 6) or hydroxypropyl sulfoethyl cellulose ether (HPSEC) examined. The cobinders were identified in Table 5 Standard formulation in a pre-dispersed pigment slurry with the below designated additives incorporated.

A wood-containing LWC paper (36 g / m ² ) was used as the base paper. At Ge speeds of the coating machine of about 1,600 m / min, about 9 g / m ^{2 of} coating color were applied to the paper surface. The application was carried out on both sides (first screen top, then screen side) with a doctor system (stiff blade). However, this is not restricted to such application systems.

Other application units, such as. B. are roller, jet or spray units can be used in principle.

The coated papers were then dried and satined and in the Printed roller offset process. The results on rheology, immobilization and Table 6 shows the dynamic water release capacity.  

Table 5

Machine tests / recipe ¹⁾

Unlike in the preliminary tests to determine the water discharge capacity under dynamic measurement conditions were pursued with the practical tests, Adjust coating colors with as high a solids content as possible so that the running ver keep judging during the coating process under realistic conditions can. It was first attempted to apply the coating colors with a solids content of 69.0% to be applied to the paper surface. In the first carried out The solids content had to be coated on the top of the sieve during the test be withdrawn as there are rheological problems caused by scrapers cook and came. For the assessment of the patterns among themselves are therefore the Er results for coating the sieve side (Table 6).  

Table 6

The rheology and dynamic water release results (WAV) of the coating colors used for machine tests

Obtain all information on the solids content (FSG), pH value and viscosity the final value (∼ screen side) on the application unit.

The results of the preliminary experiments, according to which lower with sulfoethyl cellulose derivatives Thickening performance or more liquefying effects are connected approved. The results of those performed with SEC # 1, SEC # 6 and HPSEC  Experiments (see Table 6, serial numbers 2, 4, 5) show that everywhere there is higher solid Have the fabric content adjusted to approx. 1.5-2%. It will be compared to each some reference samples (see Table 6, serial numbers 1 and 3) are practically identical Preserve color viscosities. While the dynamic water discharge capacity at 3 bar provides similar values everywhere is the use of with sulfoethyl cellulose derivatives thickened coating colors associated with significantly shorter immobilization times. On the related advantages in drying or the subsequent loading stratification has already been mentioned above.

While at the beginning of the coating tests the solids content by adding Water had to be reduced to avoid problems during application Deposits on the application unit (e.g. scraper boiling over, stalagmite bil to avoid dung etc.) was the color application of the screen side with a more uniform Running behavior of the paper web connected. The solids content for the coating attempts on the sieve side were practically constant throughout the experiment (see table 7, comparison of start and end).  

Table 7

Machine tests ³⁾ / results on sieve page ¹⁾ (∼ end of test)

The results of the paper tests on uncalendered and calendered paper are listed in Tables 8 and 9.  

Table 8

Results of paper tests on uncalendered paper / VESTRA (screen side) (∼ end of test) ¹⁾

Table 9

Results of the paper tests on calendered paper / VESTRA (screen side) (∼ end of test) ¹⁾

The differences between the patterns are all within those for the paper tests applicable standard deviations.

The coating colors formulated with different co-binders or coated with them Papers were then printed in roll offset. The results of the Be Printability tests are shown in Table 10.  

Table 10

Results of the offset prints

With regard to the gloss, values of at least 23% and received a maximum of 26%. The optical density values range from 1.39  up to 1.45 and show only slight differences. The standard color no.408002 leads to the breakout of individual line particles on all papers. In contrast, the plucks no softer color with the number 408001. The pick resistance of the papers is everywhere in the critical area. However, there is no differentiation between the patterns possible, because their quality is on a uniform level. All Papers show a quick throw away behavior that has a positive effect on the Color drying affects.

When assessing the pressure drop, the Ver. Designated with V2 and V6 looking particularly positive. Especially those with hydroxypropyl sulfo Ethyl cellulose formulated ink (V3) shows advantages when printing.

Conditions defined for the tests (120-150 ° C rail temperature tur) did not result in the sudden termination known as blistering in any of the experiments occurrence of water vapor from the surface of the line or the base paper is observed.

Claims (7)

1. Aqueous formulation for the surface preparation of paper and cardboard with a cobinder based on polysaccharide, characterized in that the formulation contains as cobinder a water-soluble, etherified with sulfoethyl groups cellulose derivative. 2. Aqueous formulation for the surface coating of paper and cardboard according to claim 1, characterized in that it is the cobinder a sulfoethyl cellulose ether with a degree of substitution by sulfoethyl groups of less than 1.2, preferably in the case of sulfoethyl cellulose 0.2 to 0.9 or 0.005 to 0.9 for mixed ethers. 3. Aqueous formulation for the surface coating of paper and cardboard according to one of claims 1 or 2, characterized in that it is the cellulose derivative etherified with sulfoethyl groups by carboxymethyl Sulfoethyl cellulose, methyl sulfoethyl cellulose, methyl hydroxyalkyl sulfo ethyl cellulose, methyl hydroxypropyl sulfoethyl cellulose, hydroxyethyl Sulfoethyl cellulose or hydroxypropyl sulfoethyl cellulose. 4. Aqueous formulations for the surface coating of paper and cardboard according to one of claims 1 to 3, characterized in that it is the cobinder for sulfoethyl cellulose with a degree of substitution Sulphoethyl groups from 0.3 to 0.75 or carboxymethyl, methyl, methyl hydroxyethyl, methylhydroxypropyl, hydroxyethyl or hydroxypropyl Sulfoethyl cellulose with a degree of substitution by sulfoethyl groups of 0.01-0.7, in particular 0.1-0.7. 5. Aqueous formulation for the surface coating of paper and cardboard according to one of claims 1 to 4, characterized in that the Formulation of at least one pigment, in particular calcium carbonate, kaolin, Contains gypsum, titanium dioxide or mixtures thereof.   6. Aqueous formulations for the surface coating of paper and cardboard according to one of claims 1 to 4, characterized in that the form pigmentation and the cobinder alone or together with others Contains aids. 7. Aqueous formulation for surface coating of paper and cardboard according to claim 6, characterized in that the used as a cobinder Sulfoethyl cellulose ether in an aqueous solution with a concentration of 0.1-30%, in particular 0.1-15%, is used.