EP0357866B1 - Cationic sizing agent for paper - Google Patents

Abstract

The present invention relates to stable aqueous colloid-disperse solutions of the salt of copolymers built up from the monomers N,N-dimethylaminoethyl acrylate and/or methacrylate and of the methacrylate and/or acrylate of a C10- to C22-fatty alcohol, acrylic acid and/or methacrylic acid and methyl acrylate and/or methacrylate. The copolymers can be prepared by solution polymerisation initiated by free radicals. They display a strong sizing action even at a low concentration and are particularly stable towards electrolytes.

Description

The present invention relates to stable, aqueous, colloidally disperse solutions of copolymers consisting of the monomers N, N-dimethylaminoethyl acrylate and / or methacrylate, and also of the methacrylic acid and / or acrylic acid ester of a C10 to C22 fatty alcohol, acrylic and / or methacrylic acid and Methyl acrylate and / or methacrylate are constructed. The copolymers may also contain n-butyl (meth) acrylate and / or i-butyl (meth) acrylate. The invention furthermore relates to the production of these copolymers by free-radical-initiated solvent polymerization and finally the use of these copolymers as a cationic paper sizing agent.

The production and use of aqueous, cation-active polymer dispersions for sizing paper has long been known.

For example, DE-B-1 696 326 describes an aqueous cationic plastic dispersion for surface sizing which is obtained by copolymerizing water-insoluble, olefinically unsaturated compounds with N- or C -vinyl-substituted aromatic compounds or their salts, which are found in the core or in the side chains contain at least one quaternary N atom. The polymerization is carried out in the presence of cationic and, if appropriate, nonionic dispersants. A disadvantage of this sizing agent is the poor compatibility with anionic products which can be used simultaneously in paper production. So For example, the effectiveness of optical brighteners can be greatly reduced or even completely prevented by the known cationic polymers.

An improved process for the surface sizing of paper is described in DE-A-2 040 692, in which water-soluble salts of statistical copolymers are also proposed as sizing agents. Monomers which are contained in this sizing agent are: acrylic acid and / or methacrylic acid as carboxyl-containing monomers, alpha olefins and non-basic, polymerizable compounds such as methyl methacrylate or methyl acrylate, acrylamide, acrylonitrile and others. The copolymers are preferably prepared by free-radical suspension or precipitation polymerization. The sizing agents according to DE-A-2 040 692 are said to be alkali-proof and have good compatibility with fillers.

DE-A-3 401 573 discloses paper sizing agents which are said to be particularly suitable for wrapping paper, ie for paper from a recycling process. They are prepared in such a way that a water-soluble cationic, chemically uniformly structured terpolymer compound of N, N-dimethylaminoethyl acrylate and / or methacrylate, styrene and acrylonitrile is first prepared in an aqueous medium, in which the N, N-dimethylamino groups are partially quaternized and the rest are protonated and then a radical emulsion polymerization in this solution of acrylonitrile and / or methacrylonitrile with styrene and acrylic acid and / or methacrylic acid ester with 1 to 12 carbon atoms in the alcohol residue. The terpolymer compound containing N, N-dimethylaminoethyl acrylate and / or methacrylate is the cationic emulsifier in free-radical emulsion polymerization. As practice has shown, this sizing agent also has an unsatisfactory sizing effect in many cases.

US-A-3,385,839 discloses cationic copolymers consisting of hydroxyalkyl and primary amino-containing acrylates and methacrylates, as well as a process for their preparation and their use as filler retention agents in papermaking. These copolymers are obtained by radical polymerization. Monomers containing acid groups and those which initiate crosslinking should only be used to a minor extent. Apparently, it was surprising to the inventors of this patent that salts of aminoalkyl esters could be polymerized and that the polymers contained the monomers in the amount used, i.e. practically in quantitative yield. However, the fact that polymers were hydrophilic and cation-active was particularly important. This fact is due to the aminoalkyl ester component, which is present in amounts of 30 to 95% by weight. However, these compounds are not suitable as sizing agents for paper because of their strong hydrophilicity. In contrast, when gluing the paper surface should be made hydrophobic.

EP-A-221400 describes cationic sizing agents for paper. The main components in these sizing agents are styrene (40 to 80% by weight) and acrylonitrile up to 40% by weight. In addition to a cationic emulsifier consisting of an acrylic acid or methacrylic acid ester with 1 to 12 carbon atoms, the sizing agent also contains a nonionic emulsifier.

This sizing agent contains relatively large amounts of styrene up to 80% by weight, which has the consequence that it has a poor sizing effect. However, it is relatively stable and has little tendency to foam.

The object of the present invention was to find a new cationic sizing agent for paper which has a high sizing effect even in low concentrations and which is also simple and inexpensive to produce.

It has now surprisingly been found that the object can be achieved with a cationic sizing agent in the form of a stable, aqueous, colloidally dispersed solution of the salt of a copolymer consisting of the monomers a) to f) according to claim 1. The nitrogen content of the copolymer should be 100 to 200 mmol per 100 g of the total weight of the monomers a) to f). The salt of the copolymer can be both the salt of an inorganic and an organic acid. Formic acid and acetic acid are particularly suitable for salt formation. The copolymer can be neutralized in whole or in part. According to the invention will be neutralized at least to the extent that colloidal solutions are formed when water is added.

According to a further embodiment of the invention, the salt of the copolymer is completely or partially quaternized with epichlorohydrin. The molar ratio of epichlorohydrin to the amine nitrogen of N, N-dimethylaminoethyl acrylate or N, N-dimethylaminoethyl methacrylate can be 0.5 to 2 to 1, a molar ratio of 1 to 1.5 to 1 being particularly advantageous.

The cationic sizing agents according to the invention are obtainable by a radical-initiated solvent polymerization, the solvent being a water-miscible solvent in which both the monomers and the resulting copolymer dissolve. Isopropanol is preferably used as the water-miscible solvent.

The solvent polymerization is carried out in a reaction vessel in which isopropanol and the monomers a) to f) are introduced in succession at room temperature. The proportion of monomer a) is chosen so that the nitrogen content is 100 to 200 mmol per 100 g of the total weight of components a) to f). In the examples, this mixture is stirred at a stirrer speed of 120 to 160 rpm and flushed with an inert gas, for example nitrogen, for about 10 minutes. The free radical initiator slurried in isopropanol is then added. The reaction temperature is then set to 80 degrees C within 20 minutes. The inert gas supply is then switched off. Under these Conditions starts the polymerization of the monomers and reaches the desired degree of polymerization after about 70 minutes. The neutralization takes place after the polymerization by adding acid, preferably by formic, acetic and / or hydrochloric acid. The quaternization of the nitrogen groups is carried out after the neutralization with the acid, preferably with epichlorohydrin, in such a way that the molar ratio of epichlorohydrin to amine nitrogen in the finished copolymer is 0.5-2.0: 1, preferably 1.0-1 , 5: 1.

The copolymer prepared in this way can be used as a particularly highly effective sizing agent in the surface sizing of paper and is stable against electrolytes. It also works well as a mass sizing agent.

The new sizing agent is very easy to handle due to its low viscosity and good dilutability with water. The rheology of the starch fleet remains unaffected. For this reason, the new product can also be used to advantage in high-speed paper machines. The good starch and electrolyte stability of the sizing agent according to the invention, which is highlighted here, prevents precipitation and the deposits that are caused by it on the rollers of the size press, thereby preventing disruptions in the production process.

The monomers a) to f) are commercially available compounds which do not cause any problems in their handling. The radical-initiated solvent polymerization is carried out with the aid of known initiators which disintegrate into free radicals. As initiators e.g. Azobisisobutyronitrile, dibenzoyl peroxide, dilauryl peroxide can be used. The initiators are used in amounts of 0.05-2.0% by weight, based on the total weight of the monomers.

After neutralization and quaternization, and after addition of water, a clear to slightly cloudy, almost colorless, aqueous, colloidal solution of the cationic surface sizing agent according to the invention is obtained. The following examples demonstrate the excellent sizing effectiveness and technical superiority of the new cationic surface sizing agent.

example 1

An externally heated double-jacket flask with a capacity of 500 ml serves as the reaction vessel, which is equipped with a stirrer, reflux condenser, thermometer, gas inlet, bubble counter and dropping funnel with gas compensation. The following are initially introduced in the flask at room temperature:
20.0 g isopropanol
32.0 g methyl methacrylate (0.32 mol)
16.5 g methacrylic acid ester of a C 16-C 18 fatty alcohol (0.05 mol)
15.7 g of N, N-dimethylaminoethyl methacrylate (0.01 mol) and
2.5 g acrylic acid (0.035 mol).

The homogeneous mixture is at a stirrer speed of 150 rpm. stirred and 10 minutes with an inert gas, e.g. Nitrogen, purged.

Then 0.25 g of azodiisobutyronitrile, slurried in 5 g of isopropanol, are added. The mixture is heated to 80 ° C. within 20 minutes and the nitrogen supply is switched off when the temperature is reached. The copolymerization of the monomers begins and reaches the desired degree of polymerization after about 70 minutes; (K value = 12 in dimethylformamide, at 25 degrees C and 1.0 g per 100 ml)

It is neutralized with 10 g of 98% formic acid. The polymer salt is dispersed by adding 315 g of hot, demineralized water within 10 minutes. The water temperature is 80 degrees C.

An almost colorless, slightly opalescent colloidal solution with a solids content of 16.0% by weight is formed. The viscosity of the solution measured according to Brookfield with spindle H 1, speed 50 rpm, is 15 m Pa s. The neutralized nitrogen content is 150 mmol per 100 g of copolymer.

Example 2

The procedure is as in Example 1, but 10.25 g of 32% hydrochloric acid (0.09 mol) are used instead of formic acid for the neutralization. The result is a bright, slightly opalescent solution with a viscosity of 20 m Pa s. The pH of this sizing agent is 4.0.

Example 3

The example describes the additional quaternization of the sizing agent produced in Example 2. 250 g of the 16% solution are mixed at 30 degrees C with 5.5 g epichlorohydrin (1.25 mol per mole of amine nitrogen). The mixture is then heated to 50 degrees C and stirred for four hours at this temperature. Almost complete alkylation of the tertiary nitrogen takes place here. A sizing agent with a solids content of 17.8% and a pH of 6.4 is formed.

In the examples 4 to 6 listed below are: indicated further copolymer compositions which were prepared by the method described in Example 1. Table 1 example 4th 5 6 component Amounts used in g Isopropanol 25th 20th 20th Methyl methacrylate 25.1 28 32 C12-C14 methacrylate 57.6 - - C16-C18 methacrylate - 18.5 16.5 N, N-dimethylaminoethyl methacrylate 21.5 18th 15.7 Acrylic acid 10.8 - 2.5 Methacrylic acid - 7.0 - Azodiisobutyronitrile 0.30 0.25 0.25 Formic acid 17.0- - 4.6 Hydrochloric acid 32% - 11.8 - Water the. 585 294 325 Solids content (% by weight) 16 18th 16 mmol N / 100 g copolymer 135 160 150 Appearance slightly cloudy bright clear slightly cloudy Viscosity (mPa.s) 45 10th 20th

Examples 7 to 9 show the application advantages which can be achieved with the new sizes.

• 1) Der Leimungsgrad wird gegen Tinte mit dem Leimungsgradprüfer Typ PLG e der Fa. Schröder, Weinheim, entsprechend der Bedienungsanleitung bestimmt.. Gemessen wird die Zeit in Sekunden , die bis zum Remissionsabfall auf 80 bzw. 50 % des Remissionswertes vom zu prüfenden Papier nach dem Kontakt mit der Prüftinte vergeht.
  Prüftinte: Papier-Prüftinte, blau, nach DIN 53126.
• 2) Cobb-Wert nach DIN 53132
  Angegeben wird hierbei die Wasseraufnahme des Papiers oder Kartons in g pro qm nach dem Kontakt mit destilliertem Wasser nach einer bestimmten Zeit (1 Minute, 5 Minuten oder 30 Minuten). Die Leimungswirkung ist umso besser, je niedriger der Cobb-Wert ist.

The following explanations are given for the measurement variables used:

• 1) The degree of sizing against ink is determined using the type PLG e from Schröder, Weinheim, in accordance with the operating instructions. The time in seconds before the remission drop to 80 or 50% of the remission value of the paper to be tested is measured contact with the test ink disappears.
  Test ink: Paper test ink, blue, according to DIN 53126.
• 2) Cobb value according to DIN 53132
  The water absorption of the paper or cardboard is given in g per square meter after contact with distilled water after a certain time (1 minute, 5 minutes or 30 minutes). The lower the Cobb value, the better the sizing effect.

Example 7

An unsized raw paper made from 100% by weight bleached softwood -Sulfate pulp, with a basis weight of 50 g / sqm, is impregnated in a laboratory glue press from Einlehner with a glue liquor which contains 5% enzymatically degraded wheat starch and 8 g of sizing agent, produced according to Examples 1 or 4, per liter of this starch solution. The paper is then dried on a type 64/60 J photo dryer from Gerster, Bruchsal) at 100 ° C. for 2 minutes. The absorption of the paper in dry matter in the size press is 4.5% by weight.
Surface sizing is carried out under the same conditions using a sizing liquor which contains a commercially available sizing agent based on a copolymer of styrene, butyl acrylate and vinylimidazole with a solids content of 20.5% by weight.

The properties measured on the paper are summarized in Table 2. Table 2 Commercial product Polymer dispersion according to the invention (16%) 20.5% Ex. 1 Ex.4 Degree of sizing (s) 154 804 1150 Cobb value water 1 min. 29 25th 21

The compilation shows the improved sizing effect of the products according to the invention. It is also worth mentioning at this point that the improved sizing effect occurs with a smaller proportion of active ingredient.

Example 8

A filter cardboard according to DIN 53106 from Macherey and Nagel / Düren with a basis weight of 270 g / sqm is impregnated with a glue liquor containing 5% enzymatically degraded wheat starch and 0.06, 0.08 or 0.1% by weight. atro on sizing agent, prepared according to Example 1 or 3, contains. The temperature of the glue liquor is 60 degrees C. The sizing agent based on a copolymer of styrene, butyl acrylate and vinylimidazole mentioned in Example 7 is used for comparison. The impregnation process takes place in the following way: The cardboard cut to A4 format is soaked in the glue bath in a 1.5 liter photo bowl for 10 seconds, then pressed between filter cardboard with a hard rubber roller and then on a photo dryer from Gerster / Bruchsal Dried at 100 degrees C for 4 minutes. The weight of the cardboard is 5.7% (starch plus sizing agent). The following values are measured on the cardboard glued in this way and are shown in Table 3: Table 3 Sizing agents Commercial product Sizing agents according to the invention Ex. 1 Ex. 3 Solids content atro 0.06 0.08 0.1 0.06 0.08 0.1 0.06 0.08 0.1 Cobb value exposure time d. Water: 30 min. 320 94 92 108 95 87 100 90 83

Example 9

This example shows the effectiveness of the products according to the invention as mass sizing agents.

A paper with the following composition is produced on a Kämmerer test machine:
40% softwood sulfate pulp
40% beech sulfite pulp
20% calcium carbonate.

In addition, 0.3% by weight of a cationic starch and 0.04% by weight of cationic polyacrylamide as a retention agent were continuously metered into the thin material during paper production. The pH in the headbox is 7.8 and the machine speed is 2.5 m / min. The highest temperature in the dryer section was 105 degrees C. The product produced in Example 3 was used as the sizing agent, and the commercial product mentioned in Examples 7 and 8 was used in the comparative experiment.

The sizing agent is dosed between cationic starch and retention agent. The basis weight of the paper produced is 80 g / m2 in each case. The sizing values achieved with the sizing agents used are summarized in Table 4. The test was carried out immediately after the papers had been produced. Table 4 Sizing agents Commercial product Sizing agents according to Ex. 3 % Atro 0.5 0.4 0.5 0.4 Cobb value water 60 sec 28 35 21 23

Claims (13)

1. A cationic paper-sizing agent in the form of a stable, aqueous, colloid-disperse solution of the salt of a copolymer, characterized in that the copolymer consists of the following components:

   a) 10 to 30 wt.% of N,N-dimethylaminoethylacrylate and/or -methacrylate

   b) 5 to 30 wt.% of methacrylic acid ester and/or acrylic acid ester of a C10 to C22 fatty alcohol

   c) 10 to 60 wt.% of a methyl acrylate and/or methacrylate

   d) 0 to 60 wt.% of n-butylacrylate and/or methacrylate

   e) 0 to 60 wt.% of i-butylacrylate and/or methacrylate

   f) 3 to 15 wt.% of methacrylic acid and/or acrylic acid,
   whereby the sum of the components a) to f) is always 100%.
2. A cationic paper-sizing agent according to claim 1, characterised in that the nitrogen content of the copolymer is 100 to 200 mMol to 200 mMol per 100 gram of the sum by weight of the components a) to f).
3. A cationic paper-sizing agent according to claims 1 to 2, characterised in that the salt of the copolymer is the salt of an inorganic acid, more particularly hydrochloric acid.
4. A cationic paper-sizing agent according to claims 1 to 3, characterised in that the salt of the copolymer is the salt of an organic acid, more particularly of a formic acid or acetic acid.
5. A cationic paper-sizing agent according to claims 1 to 4, characterised in that the salt of the copolymer is quarternized, either completely or partly, with epichlorohydrin.
6. A cationic paper-sizing agent according to claims 1 to 5, characterised in that the molar ratio of epichlorohydrin to amine nitrogen of component a) is 0.5 - 2 to 1, preferably 1 - 1.5 to 1.
7. A cationic paper-sizing agent according to claims 1 to 6, characterised in that the solid content in the aqueous colloid-disperse solution is 5 to 30 wt.%, preferably 15 to 25 wt.%.
8. A cationic paper-sizing agent according to claims 1 to 7, characterised in that the aqueous colloid-disperse solution contains up to 10 wt.% of an organic solvent miscible with water, more particularly isopropanol.
9. A process for preparing a cationic paper-sizing agent according to claims 1 to 8, characterised in that the components a) to f) are radically polymerised in a solvent miscible with water, the copolymer formed is neutralized, either completely or partly, with an acid and dispersed colloidally with water.
10. A process for preparing a cationic paper-sizing agent according to claim 9, characterised in that isopropanol is used as a solvent miscible with water.
11. A process for preparing a cationic paper-sizing agent according to claim 9, characterised in that the copolymer is neutralized with formic acid, acetic acid or hydrochloric acid.
12. A process for preparing a cationic paper-sizing agent according to claim 9, characterised in that the components a) to f) are radically polymerised in a solvent miscible with water, the copolymer is neutralized, either completely or partly, with an acid and quarternized with epichlorohydrin, and the quarternized copolymer is dispersed colloidally with water.
13. A process for preparing a cationic paper-sizing agent according to claim 9, characterised in that the components a) to f) are radically polymerised with a solvent miscible with water, the copolymer is neutralised, either completely or partly, with an acid, is first dispersed colloidally with water and then quarternized with epichlorohydrin.