FI62380C - FOER FARING FOR FRAME STOPPING WITH PAPER OF HOUSE TORRHAOLLFASTHET OCH LAOG VAOTHAOLLFASTHET - Google Patents

Description

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Federal Republic of Germany-Förbundsrepubliken

Uyskland (DE) P 27 ^ 1753 Λ (71) Basf Aktiengesellschaft, 6700 Ludwigshafen, Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) (72) Joachim Stedefeder, Lampertheim, Wolf Guender, Neustadt, Sigberg Pfohl, Speyer, Federal Republic of Germany DE) (7 * 0 Oy Kolster Ab (5U) Method for producing high dry strength and low wet strength paper - Förfarande for framställning av papper med hög torrhällfasthet och läg väthällfasthet

The invention relates to a process for the production of paper with high dry strength and low wet strength by treating the surface of the paper with water-soluble salts of polymers based on ethylenically unsaturated carboxylic acids.

Improvement of the strength properties of the paper, e.g. breaking load, splitting pressure and tensile strength, can be achieved both by adding excipients to the fiber suspension before sheet formation and by impregnating the formed paper with a suitable product by surface coating, e.g. in an adhesive press. Starch and starch derivatives, as well as synthetic products, mostly based on no-lyacrylamide, are used in the bulk addition. Starches and starch derivatives are used almost exclusively as surface coatings for this purpose.

It is known that wet strength-increasing resins, e.g. with a bulk formaldehyde base or melamine formaldehyde, which are added as a surface coating to give the paper wet strength, also lead to an increase in the dry strength of the foam; however, such products are not normally used as agents to increase the dry strength of paper, due to the great difficulty in redistributing wet-finished paper, especially in the case of waste from paper mills.

According to U.S. Pat. No. 2,999,038, it is known to prepare high wet strength paper by applying to the surface of the paper 2-8% by weight, based on the weight of dry paper, of an aqueous solution of ammonium salts of high molecular weight polymers containing acrylic acid, methacrylic acid as typical monomers. or itaconic acid.

The object of the invention is to propose compounds for the method already described, which, when used as paper impregnating agents, lead to an increase in the dry strength of the paper, without, however, affecting the wet strength at all or only to a negligible extent.

The object is achieved according to the invention by using as water salts of the polymers the water-soluble alkali and / or alkaline earth metal salts of the following copolymers: a) 90-30% by weight of acrylic acid and / or methacrylic acid, b) 10-70% by weight of acrylonitrile, methacrylonitrile and acrylamide or methacrylamide and optionally c) up to 30% by weight of an ester of acrylic acid or methacrylic acid having a viscosity in a 2% aqueous solution at 20 ° C of 5-100 mPas (with a Brookfield viscometer, 20 rpm).

Copolymers are prepared by known methods by oligomerization of monomers, cf. U.S. Patents 2,819,189 and 2,999,038. The monomer mixture is then polymerized continuously or discontinuously by means of radical polymerization initiators, in particular water.

When alkali or naa-alkali salts of acrylic acid or methacrylic acid are added already during the polymerization of the monomers, the copolymer salt solutions used according to the invention are obtained directly. Acrylic acid and / or methacrylic acid can be polymerized with the corresponding amides or nitriles in the same way as precipitation polymerization. In this case, the precipitating copolymers can be neutralized directly with alkali or alkaline earth metal hydroxides.

However, it is also possible to polymerize 10-40% *

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3 62380 with ammonium, alkali or naa-alkali ions, polymerize the neutralized acrylic acids or methacrylic acids in aqueous solution and finally neutralize the completely obtained aqueous polymer solution with alkali or alkaline earth metal salts. One process for the preparation of cooolerates to which acrylic acids or methacrylic acids partially neutralized with ammonium ions are added is known from German patent publication DT-AS 20 04 676.

However, copolymers obtained in water by precipitation polymerization can also be isolated, dried and mixed with one or more dry, powdered alkali hydroxides or alkaline earth hydroxides or oxides. These powder mixtures can then be easily soaked in water to give a clear solution.

The copolymers of components a), b) and possibly c) can also be prepared by the reverse suspension polymerization known from German patent publication DT-PS 1 081 228 and by the reverse emulsion polymerization process according to DT-PS 1 089 173.

To the extent that alkali or alkaline earth salts of acrylic acid or methacrylic acid are not added already during the polymerization, the copolymers are finally neutralized with alkali hydroxides or alkaline earth hydroxides or alkaline earth oxides at the end of the polymerization. Of particular interest are the sodium and potassium, calcium and magnesium salts of the above copolymers. However, the alkali metal salts of the invention do not comprise the ammonium salts of the copolymers. The copolymers contain 90-30%, preferably 90-60% by weight of acrylonitrile, methacrylonitrile, acrylamide or methacrylamide and optionally up to 30% by weight of acrylic ester or methacrylic acid ester. The esters are preferably derived from primary alcohols having 1 to 4 carbon atoms.

Preferably, calcium and magnesium salts of copolymers of acrylic acid and acrylamide, acrylic acid and acrylonitrile, acrylic acid, methacrylic acid and acrylamide are used, as well as alkaline earth and alkali metal salts and copolymers of acrylamide and acrylamide. At least 30% of the carboxyl groups of the copolymers have been neutralized with alkaline earth ions. The degree of neutralization is usually 70-100%.

The viscosity of a 2% aqueous solution of alkali or alkaline earth salts used according to the invention at 20 ° C at 4 62380 (Brookfield 20 / min) is 5-100, preferably 10-30 mPas. The pH of the copolymer salt solution is in the range of 4.0-10.0.

The water-soluble alkali and alkaline earth metal salts of the copolymers in question are applied to the paper in the form of a 1-10% aqueous solution. The paper can be impregnated with an alkali or alkaline earth solution of the copolymer paths, e.g. in an adhesive press, or a solution of the copolymer salt can be sprayed onto the paper. The absorption of the preparation solution depends on the absorbency of the paper used. Depending on the amount of solids, for a good increase in the dry strength of the paper, it is sufficient to impregnate the paper with the alkali or alkaline earth salts of the copolymers described by 1 to 4% by weight.

The increase in paper strength is achieved immediately after drying the paper under conventional conditions, e.g. at a temperature of 80-110 ° C. Maturation of impregnated paper is not necessary. It is also particularly advantageous that the alkali and alkaline earth metal salts of the copolymers used according to the invention can also be used in combination with starches which are often added in practice. In this case, mixtures of starch solutions and copolymer solutions containing 2-10% by weight, preferably 2-6% by weight of starch and 1-3% by weight of alkali and alkaline earth salts of the copolymers to be added according to the invention can be used.

All known paper grades, e.g. writing, printing packaging papers can be impregnated with the products used according to the invention. The paper can then be made of several different fibrous materials, such as sulphite or sulphate pulp (bleached or unbleached), wood chips or waste paper. The use of alkaline earth metal salts of copolymers of acrylic acid and / or methacrylic acid and the use of the comonomers mentioned in b) as surface coatings on paper results in an unexpected increase in the dry strength of the paper without significantly increasing the wet strength of the paper. The dry strength properties of the paper, which are significantly improved, are, for example, the tear length, the splitting pressure, the buckling strength and the CMT value.

The invention will be described in more detail with reference to the following examples. The parts given in the examples are parts by weight, percentages are by weight. The viscosities given were measured at 20 ° C on a Brookfield viscometer at 20 rpm. The dry crack length * 5 62380 was determined in accordance with DIN 53112, sheet 1 and the wet crack length in accordance with DIN 53112, sheet 2. Paper twist strength was determined according to the Dennison-Wachs experiment.

Example 1

A copolymer of 65% acrylic acid and 35% acrylonitrile (prepared by polymerizing partially neutralized acrylic acid with ammonia in aqueous solution as potassium peroxide sulfate as a catalyst at pH 3.5) is converted with calcium hydroxide to pH 7.0 (pH 7). Paper-free wood-free, non-adhesive offset paper with a grinding liquid of 25 ° SR, ash 14% (Kaolin) and alum 1% is impregnated with the above-mentioned calcium salt of a copolymer of acrylic acid and acrylonitrile, and finally dried at 100 ° C. Table 1 shows the viscosity of the preparation solution, the amount of pure copolymer salt applied to the paper based on the weight of the paper, and some properties of the obtained paper in aggregate. Comparative Example Sat.

The ammonium salt of the copolymer of 65% acrylic acid and 35% acrylonitrile described in Example 1 is adjusted to pH 7.0 and used for the impregnation of paper described in Example 1. The results are summarized in Table 1.

Comparative Example Ib

For comparison, the paper described in Example 1 is impregnated with water and finally dried at 100 ° C.

table 1

Example 1 Comparative Example (calcium salt), la ib

Ammonium- Water _salt_ Viscosity (mPa.s) of a 2% aqueous solution 8 25 5

Substance uptake (%) (solids calculated on a dry basis).

paper weight) ’1.85 1.92 -

Dry head length (m) 3700 3500 2400

Dennison 14 11 3 Wet tear length (m) 150 665 0 Φ 6 62380

Example 2 The ammonium salt of a copolymer comprising 65% acrylic acid and 35% acrylonitrile, described in Example 1, is neutralized with sodium hydroxide. The pH of an aqueous 2% solution of the alkali salt is 7.5. The paper described in Example 1 was impregnated with this solution and dried at 100 ° C.

Comparative Example 2a A copolymer comprising 65% acrylic acid and 35% acrylonitrile is used in the form of a neutralized 2% aqueous solution having a pH of 3.5 to impregnate the paper described in Example 1. The paper was dried at the same temperature as in Example 2. The results are given in Table 2. For comparison, Table 2 also gives the values obtained when the paper described in Example 2 is impregnated with water and dried at 100 ° C.

Table 2

Example 2 Comparative Example (sodium salt) ~ 1a (poly- (aqueous) acid) Viscosity of a 2% aqueous solution (mPa.s) 30 20 5

Substance uptake (%) (solids based on dry paper weight)

Dry head length (m) 4200 4100 2400

Dennison 14 14 3 Wet tear length (m) 290 780 0

Example 3

The copolymer obtained by copolymerizing 80% acrylic acid and 20% acrylamide in aqueous solution with potassium peroxide sulfate as a catalyst is neutralized with magnesium hydroxide. A 2-centimeter solution of the magnesium salt of the copolymer having a pH of 5.5 is prepared. This solution is applied to a wood-free, alum-free, non-glued offset napper with a grinding degree of 7,62380 at 25 ° SR and an ash content of 10%. The impregnated paper is dried at 100 ° C. Further information on the preparation solution and the properties of the impregnated paper is given in Table 3. Comparative Example 3a

The copolymer described in Example 3 is used in unneutralized form as a 2% aqueous solution having a pH of 2.6 as an impregnating agent for the offset paper given in Example 3. Table 3 shows the properties of the obtained paper together with the corresponding properties of the paper measured after the paper was treated with water and dried (Comparative Example 2b).

Table 3

Example 3 Comparative Example (magnesium - salt)? A 3b (poly (aqueous) acid) Viscosity (mPa.s) of a 2% aqueous solution 11 9 5

Substance uptake (%) (solids based on dry paper weight)

Dry penetration strength (m) 4700 4400 2900

Dennison 18 16 6 Wet crack length (m) 0 250 0

Example 4 The calcium salt of a copolymer comprising 80% acrylic acid, 10% acrylamide and 10% methacrylamide is applied as a 3% aqueous solution (pH 9.0) as a surface impregnating agent on the paper described in Example 3. The results are summarized in Table 4.

Comparative Example 4a

The unneutralized copolymer of Example 4 is applied as a 3% aqueous preparation solution to the paper described in Example 3. The results are shown in Table 4 compared to paper (Comparative Example 4b) impregnated with water only and dried.

s 62380

Table 4

Example 4 Comparative Example (calcium salt) (polyhaopo (water) viscosity of a 2% aqueous solution (mPa.s) 26 48 5

Substance uptake (%) (solids based on dry paper weight) 2.96 2.88

Dry head length (m) 5100 4800 2900

Dennison 16 14 6 Wet tear length (m) 100 400 0

Example 5 A 1% aqueous solution of the calcium salt of a copolymer of 65% acrylic acid and 35% acrylonitrile, which practically contains ordinary oxidatively decomposed starches in solution, is applied to the paper described in Example 3. The results are summarized in Table 5.

Comparative Example 5a A 1% aqueous solution of the annonium salt of a copolymer comprising 65% acrylic acid and 35% acrylonitrile, which contains practically common oxidatively decomposed starches in solution, is used as a preparation solution for impregnating the paper described in Fig. 3. Table 5 summarizes the results. They are compared to an experiment in which the paper described in Example 3 is impregnated with water only and finally dried.

Table 5

Example 5 Comparative Example (calcium salt 5a 5b + starch) (ammonium (water) salt + _starch) __ Viscosity of a 2% aqueous solution (mPa.s) 10 18 5

Substance uptake (%) (solids based on dry paper weight) 4.58 4.77

Claims (3)

62380 9 Table 5 (continued) Dry crack length (m) 4800 4600 2900 Dennison 16 14 6 Wet crack strength (m) 0 250 0 The examples and comparative examples show that the copolymer salts used according to the invention lead to an increase in the dry strength of the paper compared to the corresponding ammonium or polysalt wet strength to a non-detrimental extent. A process for producing paper with high dry strength and low wet strength by treating the surface of the paper with water-soluble salts of polymers based on ethylenically unsaturated carboxylic acids, characterized in that a) 90-30% by weight of acrylic acid is used as the salts of the polymers and / or methacrylic acid, b) from 10 to 70% by weight of acrylonitrile, methacrylonitrile, acrylamide and / or methacrylamide, and optionally c) up to 30% by weight of acrylic acid or methacrylic acid ester copolymers comprising the solution at 20 ° C is 5-100 mPas (Brookfield viscometer, 20 rpm). Process according to Claim 1, characterized in that a) 90-30% by weight of acrylic acid and / or methacrylic acid, b) 10-70% by weight of acrylonitrile, methacrylonitrile, acrylamide and / or methacrylamide are used, and optionally c) 30% by weight up to water-soluble calcium and / or magnesium salts of copolymers of acrylic acid or methacrylic acid ester with a viscosity of 5-100 mPas as a 2% aqueous solution at 20 ° C (Brookfield viscometer, 20 rpm). Process according to Claim 1, characterized in that mixtures of alkali and alkaline earth metal conditions of the copolymers are used.