WO2015181129A1

WO2015181129A1 - Mixture for producing an impregnation liquor for impregnating papers and nonwoven hybrids

Info

Publication number: WO2015181129A1
Application number: PCT/EP2015/061523
Authority: WO
Inventors: Bernd Ullmann
Original assignee: Jokiel & Ullmann Consulting Gbr
Priority date: 2014-05-27
Filing date: 2015-05-26
Publication date: 2015-12-03
Also published as: EP2949812A1

Abstract

The aim of the invention is to provide a formulation, the solution of which in water or aqueous solutions of mucilage, starches, starch derivatives, and/or polyvinyl alcohols provides paper with a high dimensional stability without having to accept the disadvantages of the prior art, such as the use of synthetic fiber materials or the use of mineral fiber materials in the form of glass fibers. Additionally, papers impregnated using the formulation according to the invention can also be produced with a hydrophobic design. This is achieved by a formulation composed of the mineral epsomite and the potassium salt of sorbic acid, which are dissolved in water or in aqueous solutions of mucilage, carob seed grain, starches, starch derivatives, and/or polyvinyl alcohols as a mixture. The solution is rendered hydrophobic by adding a copolymer of acrylic ester and styrene. The impregnation liquors are used in the production of wall paper, poster paper, affiche paper, map paper, and dimensionally stable printing paper.

Description

Mixture for producing an impregnating liquor for impregnating papers and nonwoven hybrids

Field of the invention

The present invention provides a composition whose solution in aqueous or aqueous solutions of mucilages, starches and starch derivatives and / or polyvinyl alcohols gives papers high dimensional stability without the disadvantages of the prior art, such as the use of synthetic fibers or the use of mineral Fiber materials in the form of glass fibers in purchasing. In addition, papers impregnated with the formulation according to the invention can also be produced in a hydrophobized version. In particular, the invention provides a composition comprising the mineral epsomite and the potassium salt of sorbic acid which is solubilized as a mixture in water or in aqueous solutions of plant slimes, locust bean gum, starches, starch derivatives and / or polyvinyl alcohols. Hydrophobia, the solution is adjusted by addition of a copolymer of acrylic acid ester and styrene. The impregnating fleets are used in the production of wallpaper papers, poster papers, affiche papers, map papers and dimensionally stable printing papers.

Background of the invention

When paper, which usually contains cellulosic fibers, comes into contact with water or water-containing materials, e.g. with water-based glue, wallpaper paste or poster adhesives, the cellulose fibers swell. This leads to a change in the dimensions of the paper by expansion in the wet state and vice versa by shrinkage in the dry state. The swelling of cellulose fibers thus leads to dimensional changes, also called wet transverse stretching. Such dimensional change is usually undesirable, instead requiring dimensional stability of papers in wet and dry climates.

Dimensional changes are objectionable precisely in applications in which the three-dimensional stability under air-dry and moist conditions is absolutely necessary. This applies, for example, to wallpaper, where only a minimal change in dimensions after the application of predominantly water-based Tapetenkieistern or subsequent drying on a wall is allowed. Similar problems arise with the use of water-based adhesives for use in billboards and large-area printing of paper with water-based inks. Such dimensional changes are also undesirable for other applications, eg for art papers, rotogravure papers, affiche papers and map papers.

In order to achieve improved dimensional stability, it has been proposed to blend synthetic fibers into the paper to produce so-called nonwoven papers. Since synthetic fibers have low wet transverse elongation, the paper is stabilized against wet-transverse elongation. However, a major disadvantage of nonwoven papers is the high production costs. In order to "spin" the synthetic fibers, the synthetic fibers must be heavily diluted with water, and synthetic fibers tend to form dust and are generally not biodegradable.

Other papers also sought to achieve improved dimensional stability by incorporation of synthetic fibers. Thus, WO 2008040635 A1 describes a method for producing a wallpaper substrate, which can be drawn dry and has a minimum wet transverse elongation. In this method, a multilayered substrate having a lower layer facing toward a wall and an upper layer facing toward a space is formed. A lower fiber layer consisting of a blend of cellulosic fibers and synthetic fibers is felted with an upper layer which is free of synthetic fibers. Again, the manufacturing costs are disadvantageous because the manufacturing process is complex and the wallpaper tends to curl because of the different expansibility of the various layers.

EP 1914087 A1 also relates to a paper substrate for wallcoverings which comprises a nonwoven with up to 50% by weight of synthetic fibers. Again, the use of synthetic fibers is disadvantageous, as described above.

JP 20090961 08 A discloses a paper substrate comprising a layer of an expanded resin. However, papers having a surface coating with an expanded resin can be used only for limited applications and have therefore disadvantages. So coated papers are usually not suitable for the production of wallpaper.

EP 98971 A2 relates to a textured wallpaper with a visible surface, which is relief-like and can be painted over. The wallpaper consists of an embossed wallpaper base embossed on both sides, with a smooth paper, e.g. Old paper, glued on. By using a water-insoluble and water-impermeable adhesive, areas are created that can not absorb water and therefore can not swell or expand. A disadvantage of such a wallpaper is that the wallpaper base necessarily has an embossment, whereby the applicability of this base is limited to wallpaper and the possibilities for additional modifications are further limited. Also, the manufacturing process is rather tedious. WO 2005095712 A1 discloses a wallpaper that is preferably free of synthetic fibers. The wallpaper consists of a number of layers wherein a hydrophobic barrier layer is intended to separate the remaining layers of the wallpaper from a hydrophilic layer intended for adhering the wallpaper to a wall. The water absorption and wet transverse strain should be limited to the hydrophilic layer. Disadvantages of this wallpaper are the complex manufacturing process and the increased tendency of the resulting wallpaper to curl.

EP 2 682 522 A1 discloses a dimensionally stable paper comprising a base paper which has been treated on at least one surface with an impregnating liquor comprising a sugar alcohol, urea and at least one compound selected from polyalkylene glycol and glycerine. The fundamental disadvantages of the paper disclosed in EP 2 682 522 A1 are that the wallpaper papers impregnated with the liquor formulation described therein can not be rendered hydrophobic and, in addition, a loss of strength must be accepted as a result of the impregnation.

WO 20121 15626 A1 relates to a production process for papers for inkjet printers. The manufacturing method comprises dissolving epsomite in a coating solution containing at least one additive for surface sizing of papers, and coating at least one side of the paper with the paper Coating solution. The epsomite in this surface coating serves primarily to improve the adhesion and retention of the printing inks on the paper surface. However, surface sizing does not allow the epsomite to penetrate the paper structure and therefore can not contribute to dimensional stability improvement.

WO2010148156 A1 relates to paper products or paper substrates for use as reinforcing tape (also known as drywall tape or joint tape). The paper products contain a sizing agent, an antimicrobial agent, as well as other optional ingredients, including a binder. In making the paper products of WO2010148156 A1, the cellulosic fibers may be contacted with the sizing agent, antimicrobial substance and optional ingredients at any point in the papermaking process. Potassium sorbate is used as a potential antimicrobial substance in these paper products. Brief description of the invention

The invention relates to a dry mixture of epsomite and potassium sorbate and an impregnating liquor, which is prepared from this dry mixture by dissolving the mixture in water or in already existing aqueous solutions and serves for the impregnation of papers and nonwoven hybrids. As a result of this impregnation, these papers or nonwoven hybrids are given high dimensional stability. The present invention permits a paper or nonwoven hybrid production in which the impregnating liquor can be adjusted both hydrophobicizing and non-hydrophobicizing without the effect of improving the wet cross-stretching being impaired.

In particular, the invention provides a mixture of the mineral epsomite and the potassium salt of sorbic acid in the ratio of their dry weights of from 20: 1 to 5: 1, preferably from 12: 1 to 8: 1. In a preferred embodiment, the invention provides a mixture of the mineral

Epsomit and the potassium salt of sorbic acid to improve the dimensional stability of papers or nonwoven hybrids ready, and their solution in water or in aqueous solutions of locust bean gum, mucilages, starches and derivatives and / or polyvinyl alcohol. The mixture comprises 15.5 to 30 wt% epsomite and 1.3 to 4% by weight potassium sorbate. Copolymers may additionally be added to the aqueous solution of the mixture. The copolymers are preferably selected from a copolymer consisting of the monomers acrylic acid and acrylamide and a copolymer consisting of the monomers acrylic ester and styrene. In a particularly preferred embodiment, the aqueous solution of the mixture 1 0 to 20 wt.% Of a copolymer consisting of the monomers acrylic acid and acrylamide and / or 3.2 to 5.4 wt.% Of a copolymer consisting of the monomers acrylic acid ester and styrene added , The mixture of epsomite and potassium sorbate has a dry matter content of 85 to 90% by weight in the mixture. The copolymer of acrylic acid and acrylamide is preferably present in a concentration of 20% and the copolymer of acrylic acid ester and styrene is preferably present in a concentration of 50%. The values given for the dry matter content or the concentrations relate to the starting materials which are used to prepare the impregnating liquor according to the invention.

In the overall formulation, i. in the aqueous solution of the impregnating liquor the erfindungsmäße mixture of epsomite and potassium sorbate in a concentration of 10 to 38% is included.

The invention further provides a process for producing an impregnating liquor which comprises the mixture according to the invention of epsomite and potassium sorbate and optionally further components.

In a further embodiment, the invention provides a process for the impregnation of papers with the mixture of epsomite and potassium sorbate according to the invention or the impregnation liquors prepared therefrom. The invention further relates to the inventive mixture of epsomite and

Potassium sorbate or the impregnation liquors impregnated therefrom. The papers are preferably selected from wallpaper papers, poster papers, affiche papers, map papers, and dimensionally stable printing papers. Nonwoven hybrids in the sense of the present invention are wallpaper substrates produced on long-screen paper machines, which consist of 80% by weight of native fibrous materials and 20% by weight of polyester fiber short-cut. If less than 20% by weight of polyester fiber short cut is used, the dimension stability also increasingly suffers from nonwoven hybrids. In particular, the native fibers swell in thickness upon contact with moisture and shrink again when they dry again. The associated changes in the dimensions of the papers and nonwoven hybrids are known as disturbing. In papers or nonwoven hybrids made on a fourdrinier paper machine, the fibers preferably orientate longitudinally and thus the dimensional change is concentrated on the transverse direction of the paper and nonwoven hybrid webs. The change in the dimensions of map paper, poster paper and affiche paper is particularly disturbing. Poor print retention and poor dimensional stability in the processing of the printed products are in the foreground. Detailed description of the invention

In particular, the native fibers swell in thickness upon contact with moisture and shrink again when they dry again. The associated changes in the dimensions of the papers and nonwoven hybrids containing less than 20 wt.% Polyester fiber short cut are known to be disturbing. In papers or nonwoven hybrids made on a fourdrinier paper machine, the fibers preferably orientate longitudinally and thus the dimensional change is concentrated on the transverse direction of the paper and nonwoven hybrid webs. The change in the dimensions of map paper, poster paper and affiche paper is particularly disturbing. There are bad Passerhaltigkeit the pressure and bad

Dimensional accuracy in the processing of printed products in the foreground.

The object of the invention is to provide a means for improving the dimensional stability of papers and nonwoven hybrids while overcoming the disadvantages of the means known from the prior art. Since nonwoven hybrids already have a high dimensional stability, the object of the invention in this case is to be able to significantly lower the generally recognized in the art polyester fiber content of 20%. The dimensional stability is defined as the dimensional change of a paper between standard climate (22 ° C / 50% relative humidity) and complete swelling of the fibers after storage in the water.

The dimensional change of a paper can be measured by wet transverse strain, which can be tested by the following method:

a) Sampling

From the rolled-up paper web or nonwoven hybrid web, patterns are taken from the two edge regions and from the center of the web. From these samples, 5 strips each are cut transversely in the dimensions 210 x 50 mm.

b) The specimens are marked in the track in their position.

c) Storage of the specimens for at least two hours in standard atmosphere of 22 ^< Ό ± 1 'Ό and 50% ± 2% relative humidity.

d) Thereafter, a precise marking in the form of punctures over a distance of 180 mm is carried out on the air-conditioned samples.

e) The specimens are then stored for 10 min in water at 20 ° C ± 2 ^< Ό.

f) taking the samples from the water and measuring the change in distance of the two punctures with an accuracy of ± 0.05 mm. g) calculation of the percentage change of the dimension.

h) logging the average value of the measurement results for each of the three sample positions as wet transverse strain.

According to the invention, the object is achieved by providing a dry mixture from which an impregnating liquor can be prepared by dissolving in water or in aqueous solutions comprising starches, polyvinyl alcohols, galactomannans, locust bean gum or mixtures thereof, containing one or more inorganic salts and / or or organic salts.

This impregnating liquor may additionally be added:

An anionic dry strength agent in the form of a copolymer, and

- Optionally a copolymer as a hydrophobing agent. The anionic dry strength agent is preferably a copolymer which is composed of the monomers acrylic acid and acrylamide. It is further preferred if the anionic dry strength agent has a viscosity of 50 to 700 mPas, preferably 150 to 500 mPas, particularly preferably 200 to 400 mPas (as measured for example with a Brookfield RVT Viscometer at 20 rpm and 20 ^< €).

The hydrophobizing agent is preferably a copolymer based on acrylic acid ester and styrene. In a particularly preferred embodiment, the acrylic ester is methyl, ethyl or butyl acid ester. The minimum film-forming temperature of this copolymer is in the range from 0 'Ό to 80 ^< €, preferably between 10 ° C and 40 ° C.

The water-soluble inorganic salts are preferably selected from epsomite (magnesium sulfate heptahydrate), sodium chloride and mixtures thereof. The water-soluble organic salt is preferably potassium sorbate.

The polyvinyl alcohol preferably has an average viscosity and a high degree of saponification. The polyvinyl alcohol according to the invention preferably has a viscosity in the range from 10 to 40 mPas, more preferably in the range from 15 to 35 mPas. The degree of saponification of the polyvinyl alcohol according to the invention is preferably 88 mol%, particularly preferably 98 mol%, very particularly preferably or 99 mol%.

Starches of any type and origin are basically suitable for use in the impregnating liquor according to the invention. Potato starch, corn starch, wheat starch, rice starch or peanut starch is preferably used. Particularly preferred is the use of potato starch or wheat starch. Further suitable for use in the impregnating liquor according to the invention are starch esters. The starch esters according to the invention are preferably selected from starch phosphates such as monostarch phosphate, distarch phosphate, phosphated distarch phosphate and acetylated distarch phosphate; and esters of starch with organic acids, such as acetylated starch or starch acetate, esters of starch with C ₆ -C ₂ 6 fatty acids, succinic acid, adipic acid and citric acid or salts thereof. The use of the inorganic salts, such as epsomite and / or sodium chloride, and the organic salts, such as preferably potassium sorbate, contributes in particular to improving the dimensional stability of papers and nonwoven hybrids. Potassium sorbate additionally causes rapid wetting and rapid penetration of the impregnating liquor into the raw papers or raw nonwoven hybrids. The use of locust bean gum ensures a good water retention capacity of the impregnating liquor when the impregnating liquor comprises a hydrophobizing agent, such as, for example, the copolymer of monomers of acrylic ester and styrene. The anionic dry strength agent, such as the copolymer of monomers of acrylic acid and acrylamide, or the starches or the galactomannans or polyvinyl alcohol, contribute to maintaining the strength of the impregnated papers and nonwoven hybrids.

Surprisingly, it has been found that the dissolution of the dry mixture works only in a mixture, while the solution of the components fails individually in order. It is mandatory to dissolve this dry mixture in cold or at most 40 'C warm water. The dry mixture is thus dissolved in water, which preferably has a temperature of 0 'C to 40' C, particularly preferably 15 ° C to 40 ^. A preferred composition of the impregnating liquor according to the invention is shown in Table 1. Table 1 also indicates a preferred metering sequence in column 1.

Table 1: Composition of the impregnating liquor according to the invention

Parts by weight of the starting materials in the impregnating liquor,

² concentration / dry content of the components in the starting material,

3 Component 5 is optionally added if a paper is to be impregnated which is said to be hydrophobic in nature.

Surprisingly, the dimensional stability of the impregnated papers and nonwoven hybrids does not deteriorate due to the addition of the hydrophobic copolymer of acrylate and styrene, although this would have been expected as a result of the indirectly effective reduction in the quantity of epsomite / potassium sorbate. In contrast, the use of the well-known hydrophobicizing agent alkyl ketene dimer (AKD), while also providing the desired hydrophobicity, degrades dimensional stability. The impregnating liquor according to the invention (including component 5) according to Table 1 has the following chemical-physical parameters:

Concentration of dry mix solution: 34 to 38%

pH value: 7.0 to 7.2

Charge: anionic

Flow behavior: aqueous; Newtonian fluid

Penetration time in unsized base paper: 0.5 sec. At 35 ° C

The stated concentration of the dry mixture according to the invention in the aqueous impregnating liquor is 10 to 38%, preferably 15 to 38%, particularly preferably 30 to 38%. In particular, other additives, such as solutions of starches, polyvinyl alcohols can lead to concentrations below 38%.

The base papers to be impregnated with the impregnating liquor according to the invention are preferably hydrophilic, ie unsized. Mass-glued base papers absorb too little substance during the impregnation process and thus the desired effect of dimensional stabilization can not develop. Preferred according to the invention are base papers having a basis weight in the range of 40 to 130 g / m ² , particularly preferably in the range of 50 g / m ² to 1 10 g / m ² . Favorable and the object of the invention corresponding improvements in dimensional stability are achieved at a substance entry of at least 10%, but preferably 12 to 30%, particularly preferably 14 to 20 wt.% Based on the dry mass of the non-impregnated paper. The substance entry also applies as dry matter.

The formulation according to the invention can be introduced into the respective base papers both inside and outside of conventional paper machines in off-line coating systems by means of size press, film press, blade coaters or blade coaters. Especially to be preferred are the Equipment size press and film press, because here the liquor is introduced into the base paper with pressure.

Table 2 shows various embodiments of the impregnating liquors according to the invention.

Table 2: Variants of the impregnating liquors according to the invention

Concentration / dry content of the components in the starting material,

² parts by mass of the starting materials in the impregnating liquor.

The invention further provides a method of making an impregnating liquor comprising dissolving the dry mixture of epsomite and potassium sorbate in water. The concentration of the mixture in the solution after dissolution is 8 to 38%, preferably 15 to 30%.

In a further process step, from 0 to 0.6% by weight of locust bean gum, preferably from 0.1 to 0.3% by weight, based on the dry matter of the impregnating liquor, of the solution thus prepared can be added. In a further process step, 10 to 20% by weight, preferably 10.5 to 19% by weight of solid substance of the dry strength acrylic acid-acrylamide copolymer can be added to the impregnating liquor. In a preferred embodiment of the process according to the invention, the dry strength acrylic acid-acrylamide copolymer is added in the form of a solution of the dry strength agent in water.

In a particularly preferred embodiment of the process according to the invention, the solution is dissolved in aqueous solutions which already comprise starches, degraded starches, starch esters, polyvinyl alcohols and / or galactomannans or mixtures thereof.

Optionally, 2.9 to 5.4 wt .-%, preferably 3.2 to 5.4 wt .-% solids of the hydrophobing agent acrylic acid ester-styrene copolymer, based on the solids of the impregnating liquor, can be added to the impregnating liquor. In a preferred embodiment of the process according to the invention, the hydrophobizing agent is admixed with acrylic acid ester-styrene copolymer of the impregnating liquor in the form of a dispersion in water. The invention will be further elucidated by way of examples, the examples not intended to limit the scope of the invention.

Example 1: Background Art, Map Paper A base paper having a basis weight of 86 g / m ² and a filler content of 15% was produced on a fourdrinier paper machine with integrated size press by the generally accepted state of the art. The pulp composition consisted of 28% elementary chlorine-free bleached pine sulphate pulp, 68% elemental chlorine-free bleached aspen pulp and 4% own pulp. The fibrous materials were ground in an upstream grinding mill to 25 to 28 ° SR. Under ° SR understands the

Professional the degree of milling treatment of the pulps, indicated in the Schopper Riegler degree. The fiber mixture dispersed in water was added with calcium carbonate as a filler, cationic epichlorohydrin resin as a wet strength agent, succinic anhydride dispersed in cationic starch, as a water repellent, and polyaluminum chloride as a precipitant.

The total mixture was then fed continuously in a concentration of 0.9 to 1, 0% over a headbox on the wire, which moved at a speed of about 600 m / min. With simultaneous dehydration to a dry content of about 16 to 20%, the paper web formed, which was later mechanically pressed and thermally dried.

Dried to a dry content of 92 to 98%, the base paper web reached the size press, where it received a surface treatment with a 7% solution composed of 93 parts water, 4 parts enzymatically degraded wheat starch and 3 parts potato starch ester. The coating weight was 3.5 g / m ^{2 of} oven-dry coating spread on both sides of the paper. After drying the paper in the so-called after-dryer section of the paper machine to 93 to 94% final dry content, the paper, which now had a final surface weight of 89 to 91 g / m ² , was smoothed in a machine calender.

The resulting map paper is wet-strength, hydrophobed, off-set method printable and has a wet transverse elongation of 2.3%, wherein in both edge regions of the paper web even 2.5 to 2.9% were determined. Example 2: Map paper according to the invention

There was an industrially manufactured base paper with a basis weight of 50 g / m ^{2 available} . The base paper was wet strength with epichlorohydrin resin and filled with 1 8% titanium dioxide, based on the dry weight of the base paper. In contrast to Example 1, no hydrophobizing agent was added in the preparation of the raw paper. The pulp mixture consisted of 23% elementary chlorine-free bleached pine sulphate pulp, 73% elementary chlorine-free bleached eucalyptus sulphate pulp and 4% own pulp. The pulp mixture was ground to 36 ⁰ SR.

A4 sheets prepared from the base paper were impregnated with the liquor of the invention, which consisted of 150 g of water, 0.05 g of locust bean gum, 39 g of dry mixture consisting of 35 g epsomite and 4 g of potassium sorbate, 15 g of anionic 20% copolymer from the monomers acrylic acid and acrylamide and 5 g of 50% copolymer consisting of the monomers acrylic ester and styrene. The individual components were dissolved in the order mentioned at a temperature in the range of 20 to 35 ° C. Following the impregnation process, the sheets were dried on a photodryer at 75 to 80 'Ό.

The drying process did not hinder the shrinkage of the paper due to the removal of water, so that no Meßwertverfälschungen for the Naßquidehnung can arise.

After two hours of air conditioning, the following measured values were determined:

(1) wet transverse elongation

Base paper: 2.7%

Impregnated paper: 1, 4%

(2) basis weight

Base paper: 50.5 g / m ²

Impregnated paper: 59 g / m ²

The impregnated paper is hydrophobic and printable in offset printing. The improvement in wet transverse strain amounts to 1, 3% absolute, compared to

Base paper.

Example 3 Inventive Simplextapetenpapier There was an industrially produced Simplextapetenpapier as untreated base paper with a comparable composition of Example 1 including the grinding treatment of the fibers, the filler content and the wet consolidation with cationic epichlorohydrin resin.

In contrast to Example 1, however, no sizing agent and no water repellent had been added to the Simplextapetenpapier in the preparation of the raw paper.

The base paper had a basis weight of 72 g / m ² .

It was impregnated with the liquor according to the invention as described in Example 2, and also dried on a photothermal dryer without shrinkage at a temperature in the range from 75 to 80 ° C. After two hours of conditioning of the impregnated A4 sheet, the following measured values were determined:

(1) wet transverse elongation

Base paper: 2.5%

Impregnated paper: 1, 0%

(2) basis weight

Base paper: 72 g / m ²

Impregnated paper: 86 g / m ²

As a result of the impregnation with the liquor according to the invention, an improvement of the wet transverse elongation of 1.5% absolute or 60% based on the value of the raw paper occurred.

In the same way, further industrially produced base papers were impregnated, dried and evaluated by measurement with the following results:

a) rotogravure paper; 70 g / m ² ; Raw material base 100% recovered paper

(1) wet transverse elongation

Base paper: 3.2%

Impregnated paper: 2.3%

(2) basis weight Raw paper: 70 g / m ²

Impregnated paper: 79 g / m ² b) Gravure paper; Pulp composition 35% elemental chlorine-free bleached pine sulfate pulp and 65% thermomechanical pulp, known to those skilled in the art as TMP, from spruce wood; Basis weight: 80 g / m ²

(1) wet transverse elongation

Base paper:

Impregnated paper:

(2) basis weight

Base paper: 80 g / m ²

Impregnated paper: 96 g / m ²

Depending on the dimensional stability requirements of the respective impregnated paper grades according to the invention, the air-dry substance entries based on the liquor composition according to Table 1 are introduced by at least 10% based on the air-dry base paper, but preferably 12 to 30% by weight and particularly preferably 14 to 20% by weight ,

The amount of substance input is determined by the liquor concentration, using a concentration of at most 38%.

Claims

claims

1 . Mixture of the mineral epsomite and the potassium salt of sorbic acid in the ratio of their dry weights from 20: 1 to 5: 1, preferably from 12: 1 to 8: 1.

2. Mixture according to claim 1, characterized in that the mixture is air-dry.

3. A process for producing an impregnating liquor comprising dissolving the mixture according to claim 1 or 2 in water.

4. The method according to claim 3, characterized in that the concentration of the mixture in the solution is 8 to 38%, preferably 15 to 30%.

5. The method according to claim 2 or 3, characterized in that the solution 0 to 0.6 wt .-% locust bean gum, preferably 0.1 to 0.3 wt .-%, based on the dry matter of the impregnating liquor, are added.

6. The method according to at least one of claims 2 to 4, characterized in that the impregnating liquor 10 to 20 wt .-%, preferably 10.5 to 19 wt .-% solids of the dry strength acrylic acid-acrylamide copolymer are added.

7. The method according to claim 6, characterized in that the addition of the dry strength acrylic acid-acrylamide copolymer takes place in the form of a solution of the dry strength in water.

8. The method according to at least one of claims claims 2 to 7, characterized in that the solution of the mixture is carried out in aqueous solutions comprising starches, degraded starches, starch esters, polyvinyl alcohols and / or galactomannans or mixtures thereof.

9. The method according to at least one of claims 2 to 8, characterized in that the impregnating liquor 2.9 to 5.4 wt .-%, preferably 3.2 to 5.4 wt .-% solid of the hydrophobing agent acrylic ester-styrene copolymer , based on the solids of the impregnating liquor, are admixed.

10. The method according to claim 9, characterized in that the water repellent acrylic acid ester-styrene copolymer is added to the impregnating liquor in the form of a dispersion in water.

1 1. Impregnating liquor, prepared by the process according to at least one of claims 2 to 10.

12. Impregnating liquor comprising the constituents:

o water: 40 to 70% by weight,

o potassium sorbate: 1, 3 to 4.0% by weight,

o Epsomit: 15.5 to 30% by weight

o and / or 10 to 20 wt.% Copolymer of acrylic acid and acrylamide, o and / or 0 to 0.6 wt.% Locust bean gum.

13. impregnating liquor according to claim 12, further comprising 3.2 to 5.4 wt.% Copolymer of acrylic acid ester and styrene.

14. A process for the impregnation of papers, characterized in that the papers are impregnated with the impregnating liquor according to at least one of claims 2 to 13, wherein the proportion of dry mass of the impregnating liquor at least 10 wt .-% based on the weight of the dry base paper, preferably 12th to 30 wt .-%, particularly preferably 14 to 20 wt%.

15. Impregnated paper produced by the process according to claim 14.