Aqueous emulsion of a sizing agent

Abstract

A method of preparing an aqueous emulsion of a sizing agent for use in a papermaking process comprising, emulsifying the sizing agent into an aqueous liquid, in which an aqueous dispersion of a water-soluble polymer of N-vinylformamide and/or N-vinylacetamide units is added to either the sizing agent or the aqueous liquid before, during or after emulsification, wherein the dispersion contains, based on 100 parts by weight of water, (A) from 0.1 to 80 parts by weight of a water-soluble polymer containing N-vinylformamide units and/or N-vinylacetamide units, and (B) from 0.02 to 50 parts by weight of at least one polymeric dispersant.

Claims

1. A method of preparing an aqueous emulsion of a sizing agent for use in a papermaking process comprising, emulsifying the sizing agent for use in a papermaking process into an aqueous liquid, in which an aqueous dispersion of a water-soluble polymer of N-vinylformamide and/or N-vinylacetamide units is added to either the sizing agent or the aqueous liquid before, during or after emulsification, wherein the dispersion contains, based on 100 parts by weight of water, (A) from 0.1 to 80 parts by weight of the water-soluble polymer containing N-vinylformamide units and/or N-vinylacetamide units, and (B) from 0.02 to 50 parts by weight of at least one polymeric dispersant for the water-soluble polymer (A) selected from the group consisting of polyvinylpyrrolidone, polyvinylpyridine, polyvinylimidazole, polyethyleneimine, and polydiallyl dimethyl ammonium chloride, wherein the N-vinylformamide units and/or N-vinylacetamide units of polymer (A) are hydrolyzed to an extent of 1 to 40 mol %.

2. The method according to claim 1, wherein the sizing agent is alkenyl succinic anhydride (ASA).

3. The method according to claim 1, wherein the dispersion contains, based on 100 parts by weight of water, (A) from 5 to 80 parts by weight of the water-soluble polymer containing N-vinylformamide units and/or N-vinylacetamide units and (B) from 1 to 50 parts by weight of the at least one polymeric dispersant.

4. The method according to claim 3, wherein the dispersion contains, based on 100 parts by weight of water, (A) from 10 to 50 parts by weight of the water-soluble polymer containing N-vinylformamide units and/or N-vinylacetamide units and (B) from 5 to 40 parts by weight of the at least one polymeric dispersant.

5. The method according to claim 1, wherein the dispersion contains as component (A) a homopolymer of N-vinylformamide.

6. The method according to claim 1 wherein 5 to 30 mol % of the N-vinylformamide units and/or vinylacetamide units of the polymer (A) have been converted into vinyl amine units by hydrolysis.

7. The method according to claim 1 wherein the polymer (A) has a K value of 130 to 300.

8. An aqueous emulsion of a sizing agent obtained by the method of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The FIGURE shows a chart, which compares the Cobb 60 values for Alkenyl Succinic Anhydride (ASA) emulsions prepared with different polymers.

DETAILED DESCRIPTION OF THE INVENTION

(2) Aqueous emulsions of sizing agents for the purposes of the present invention are all two-phase and multiphase systems such as dispersions and emulsions in which the sizing agent is in a dispersed phase within an aqueous continuous phase.

(3) Emulsification of the sizing agent can be achieved using conventional equipment and procedures typically used for producing aqueous emulsions of sizing agents. The aqueous dispersion of a water-soluble polymer of N-vinylformamide and/or N-vinylacetamide units can be diluted by the addition of water to a concentration of between 0.75 and 3%, based on dry polymer. The pH of this diluted polymer can desirably be between 3 and 7. The diluted polymer may be added with the sizing agent, either separately or together, to the emulsification equipment. Numerous systems for emulsifying liquids to form an emulsion are known in the literature. Examples include static mixers, rotor-stator devices, high-pressure homogenisers, ultrasound homogenisers, screen or mesh emulsification techniques, and membrane emulsification techniques. Particularly suitable emulsification equipment for making sizing agent emulsions includes a Cavitron or a modified Cavitron. Such systems may employ recirculation of the mixture of diluted polymer and sizing agent. Such equipment may employ a pressure between 5 and 15 bar. A typical energy consumption may be below 30 kW/hour. The final sizing emulsions employed at a paper machine may have a particle size of up to 1 m, for instance between 0.5 and 1 m.

(4) According to the inventors the aqueous dispersion of a water-soluble polymer of N-vinylformamide and/or N-vinylacetamide units is added to either the sizing agent or the aqueous liquid before, during or after emulsification. Preferably this aqueous dispersion of the water-soluble polymer should be present during the emulsification of the sizing agent into the aqueous liquid. This may be achieved by combining said aqueous dispersion with the mixture of sizing agent and aqueous liquid during the emulsification step. It may be desirable to combine the aqueous dispersion with the sizing agent before addition to the aqueous liquid (i.e. into which the sizing agent is emulsified. More preferably the aqueous dispersion of the water-soluble polymer should be combined with the aqueous liquid prior to the addition of the sizing agent.

(5) The dose of the aqueous dispersion of water-soluble polymer of N-vinylformamide and/or N-vinylacetamide units suitably may be between 5% and 100% by weight based on the weight of the sizing agent. Preferably the dose should be between 10% and 95% and more preferably between 20% and 90%, still more preferably between 30% and 85%, particularly between 35% and 80%.

(6) The amount of polymer (A) may be determined as between 1% and 45% by weight calculated on the weight of the sizing agent. Often the amount of polymer (A) may be between 3% and 40%, usually between 7% and 35%, preferably between 10% and 30%.

(7) It is believed that the aqueous dispersion of water-soluble polymer of N-vinylformamide and/or N-vinylacetamide units is functioning as a protective colloid. It is considered that the addition of this aqueous dispersion of polymer helps stabilise the droplets of sizing agent against coalescence.

(8) The aqueous emulsions of sizing agent prepared by the method of the present invention have improved stability by comparison to aqueous sizing agent emulsions prepared using other cationic polymers. The dispersed phase of sizing agent may have particle sizes between 0.5 and 10 m, often between 0.5 and 7 m. Suitably the dispersed phase of sizing agent may be at least 90% below 6 m and may be at least 50% below 3 m. Preferably the dispersed phase may be at least 90% below 2 m and at least 50% below 1 m. The aqueous emulsions of sizing agent exhibit improved storage stability.

(9) The aqueous dispersion of water-soluble polymer of N-vinylformamide and/or N-vinylacetamide units preferably contains, based on 100 parts by weight of water, (A) from 5 to 80 parts by weight of a water-soluble polymer containing N-vinylformamide units and/or N-vinylacetamide units and (B) from 1 to 50 parts by weight of the at least one polymeric dispersant.

(10) The aqueous dispersion of water-soluble polymer of N-vinylformamide and/or N-vinylacetamide units more preferably contains, based on 100 parts by weight of water, (A) from 10 to 50 parts by weight of a water-soluble polymer containing N-vinylformamide units and/or N-vinylacetamide units and (B) from 5 to 40 parts by weight of the at least one polymeric dispersant.

(11) Particularly preferred dispersions are those which contain as component (A) a homopolymer of N-vinylformamide.

(12) N-vinylformamide units and/or N-vinylacetamide units can be illustrated with the aid of the following formula:

(13) ##STR00001##
where R is H or CH.sub.3

(14) The water-soluble polymers containing N-vinylformamide units and/or N-vinylacetamide units can, if required, contain from 1 to 80, preferably from 5 to 30, % by weight of further monomers as co-polymerised units. Such monomers are, for example, monoethylenically unsaturated carboxylic acids of 3 to 8 carbon atoms, such as acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, maleic acid, citraconic acid, methylenemalonic acid, allylacetic acid, vinylacetic acid, crotonic acid, fumaric acid, mesaconic acid and itaconic acid. From this group of monomers, acrylic acid, methacrylic acid, maleic acid or mixtures of said carboxylic acids preferably used. The monoethylenically unsaturated carboxylic acids are used either in the form of a free acids or in the form of their free alkali metal, alkaline earth metals or ammonium salts in the copolymerisation. For neutralisation of the free carboxylic acids, sodium hydroxide solution, potassium hydroxide solution, sodium carbonate, potassium carbonate, sodium bicarbonate, magnesium oxide, calcium hydroxide, calcium oxide, gaseous or aqueous ammonia, triethylamine, ethanolamine, diethanolamine, triethanolamine, morpholine, diethylene triamine, tetraethylenepentamine is preferably used.

(15) Further suitable monomers are, for example, the esters, amides and nitriles of the aforementioned carboxylic acids, e.g. methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxy ethyl acrylate, hydroxy propyl acrylate, hydroxy butyl acrylate, hydroxy ethyl methacrylate, hydroxy propyl methacrylate, hydroxy butyl methacrylate, hydroxy isobutyl methacrylate, mono methyl maleate, dimethyl maleate, monoethyl maleate, diethyl maleate, 2-ethyl hexyl acrylate, 2-ethyl hexyl methacrylate, acrylamide, methacrylamide, N-dimethyl acrylamide, N-tert butyl acrylamide, acrylonitrile, methacrylonitrile, dimethylamino ethyl acrylate, diethylamino ethyl acrylate, dimethyl amino ethyl methacrylate, diethyl amino ethyl methacrylate, and the salts of the last mentioned basic monomers with carboxylic acids or mineral acids and the quaternised products of the basic (meth) acrylates.

(16) Other suitable copolymerisable monomers are furthermore acrylamido glycolic acid, vinyl sulphonic acid, allyl sulphonic acid, meth allyl sulphonic acid, styrene sulphonic acid, 3-sulphopropyl acrylate, 3-sulphopropyl methacrylate and 2-acrylamido-2-methyl propane sulphonic acid and monomers containing phosphonic acid groups, such as vinyl phosphonic acid, allyl phosphonic acid, and 2-acrylamido-2 methyl propane phosphonic acid. The monomers containing acid groups can be used in the polymerisation in the form of free acid groups and in a form partially or completely neutralised with bases.

(17) Further suitable copolymerisable compounds are N-vinylpyrrolidone, N-vinyl caprolactam, N-vinyl imidazole, N-vinyl-2-methyl imidazole, diallyl ammonium chloride, vinyl acetate, vinyl propionate and styrene. It is of course also possible to use mixtures of said monomers. The said monomers when polymerised alone do not give water-soluble polymers, the polymers containing N-vinylformamide units and/or N-vinylacetamide units containing these comonomers as polymerised units only in amounts such that the copolymers are still water-soluble. In contrast to water in oil polymer emulsions, no organic solvents are required for the aqueous dispersions. If you know from the prior art that concentrated solutions of inorganic salts are a conventional medium for the preparation of aqueous dispersions of water-soluble polymers. As a result, the known dispersions have a very high salt load. The aqueous dispersions of water-soluble polymers used in the method of the present invention tend to be virtually salt free by comparison to conventional dispersions of water-soluble polymers.

(18) The aqueous dispersions of water-soluble polymers of N-vinylformamide units and/or N-vinylacetamide units employed in the method of the present invention preferably have a high polymer content and preferably containing polymers having high molar masses in combination with low viscosity. The molar masses of the polymers containing N-vinylformamide units and/or N-vinylacetamide units are, for example, at least 50,000 DALTONS, such as at least 200,000 DALTONS and preferably at the 1 million DALTONS. The molar masses of the polymers may range between 50,000 DALTONS and 10 million DALTONS, for instance 200,000 DALTONS to 8,000,000 DALTONS, preferably 1,000,000 DALTONS to 5,000,000 DALTONS, such as 2,000,000 DALTONS to 3,000,000 DALTONS.

(19) The molar masses of the polymers of N-vinylformamide units and/or N-vinylacetamide units can be characterised with the aid of the K values according to Fikentscher. The K values are up to 300 and preferably in the range from 130 to 180. From light scattering experiments, it follows that a K value of 250 corresponds to an average molar mass of about 7 million dalton.

(20) The K values should be determined according to H. Fikentscher, Cellulose-Chemie, 13 (1932), 58-64 and 71-74, in aqueous solution at 25 C. and that a concentration which depending on the K value range, of from 0.1 to 5% by weight. The viscosity of the dispersion can for instance be measured in each case in a Brookfield viscometer using a no. 4 spindle at 20 rpm and a 20 C.

(21) The polymeric dispersant (B) can contain at least one functional group selected from ether, hydroxyl, carboxyl, sulphone, sulphate ester, amino, imino, tertiary amino and/or quaternary ammonium groups. Examples of such compounds are: carboxymethylcellulose, water-soluble starch and starch derivatives, starch esters, starch xanthates, starch xanthogenates, starch acetates, dextran, polyalkylene glycols, polyvinyl acetate, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl pyridine, polyethylenimine, polyvinylimidazole, polyvinylsuccinimide and polydiallyl dimethyl ammonium chloride.

(22) It may be possible that the dispersant (B) also can provide certain functional benefits in the formation and stability of the sizing emulsion.

(23) The aqueous dispersions of N-vinylformamide units and/or N-vinylacetamide units contain from 0.02 to 50, preferably 1 to 50, more preferably from 5 to 40, parts by weight, based on 100 parts by weight of water, of at least one of the above-mentioned polymeric dispersants (B).

(24) The aqueous dispersions of N-vinylformamide units and/or N-vinylacetamide units may be prepared according to the teaching of US 2006 116448.

(25) By eliminating formyl groups from polymers containing N-vinylformamide units and by eliminating the group CH.sub.3CO from polymers containing N-vinylacetamide units, polymers containing vinyl amine units are formed into each case. Elimination may be effected partially or completely. If the hydrolysis is carried out in the presence of acids, the vinyl amine units of the polymers are present as ammonium salts. The hydrolysis can also be carried out with the aid of bases, or example of metal hydroxides, in particular of alkali metal and alkaline earth metal case hydroxides. Preferably, sodium hydroxide or potassium hydroxide is used. In particular cases, hydrolysis can also be carried out with the aid of ammonia or amines. In the case of the hydrolysis in the presence of bases, the vinyl amine units are present in the form of free bases.

(26) Suitable hydrolysis agents preferably mineral acids, such as hydrogen halides, which may be used in gaseous form or as an aqueous solution. Concentrated hydrochloric acid, sulphuric acid, nitric acid or phosphoric and organic acids, such as C.sub.1- to C.sub.5-carboxylic acids, and aliphatic or aromatic sulphonic acid are preferably used. For example, from 0.05 to 2, in particular from 1 to 1.5, molar equivalent of acid are required per equivalent of formyl groups in the polymers containing polymerised N-vinylformamide units. Hydrolysis of the N-vinylformamide units takes place significantly more rapidly than that of the polymers having N-vinylacetamide units. If copolymers of the suitable vinylcarboxamides with other comonomers are subjected to the hydrolysis, the comonomer units contained in the copolymer can also be chemically modified. For example, vinyl alcohol units are formed from vinyl acetate units. In hydrolysis, acrylic acid units are formed from methyl acrylate units, and acrylamide or acrylic acid units are formed from acrylonitrile units. The hydrolysis of the N-vinylformamide units and/or N-vinylacetamide units of the polymers (A) can be carried out to an extent from 1 to 100% on a molar basis, for instance 1 to 40%, preferably 5 to 30%, more preferably 5 to 20%, for instance between 10 and 20%.

(27) The water-soluble polymer (A) with or without hydrolysis of N-vinylformamide units and/or N-vinylacetamide units is desirably in the form of particles in the aqueous dispersion. Suitably the particle diameter may between 50 nm and 10 m, for instance 50 nm to 2 m, such as 100 to 700 nm. Preferably, the particle diameter is between 1 and 10 m.

Example 1

(28) Alkenyl Succinic Anhydride (ASA) Emulsification in a Laboratory

(29) Trial 1

(30) A mixture containing Polymin VT (aqueous dispersion polymer containing vinyl formamide units (component A) and containing a polymeric dispersant (component B) supplied by BASF) 37.5 g and water 262 g was stirred using a domestic blender (Osterizer pulse matic 10 manufactured by J Oster Company) set at a low speed (speed level 5) for 1.5 min and then ASA (Kemsize 220, supplied from Sellukem) 50 g was added followed by increasing the speed to the highest speed setting level 9 for 1 min. Finally the speed of the domestic blender was reduced to level 3 and then water was added to bring the mixture up to a volume of 1000 ml.

(31) Trial 2

(32) Trial 1 was repeated except using the following components:

(33) TABLE-US-00001 ASA (Kemsize 220) 50 g Polymin VT 20 g Water 280 g
Trial 3

(34) Trial 1 was repeated except using the following components:

(35) TABLE-US-00002 ASA (Kemsize 220) 50 g Polymin VT 5 g Water 295 g
Trial 4

(36) Trial 2 was repeated except using the following components:

(37) TABLE-US-00003 ASA (Kemsize 220) 50 g Polymin VZ 20 g Water 280 g

(38) Stability of the emulsions produced in the trials are shown in Table 1

(39) TABLE-US-00004 TABLE 1 Particle size distribution in microns over time (Malvern Mastersizer) Immediately After about 30 min % distribution Trial No <50% <90% <50% <90% 1 0.809 1.834 0.805 1.942 2 2.116 3.892 2.122 4.056 3 not stable not stable not stable not stable 4 2.446 5.351 2.579 5.257

(40) The results show that good stability is maintained over the period of 30 min.

Example 2

(41) Aqueous emulsions of ASA (Kemsize 220) were prepared using a competitor cationic polymer, a liquid cationic starch with a DS of 0.035, or either of Polymin VT (according to the invention) or Polymin VZ (according to the invention) in an analogous method to Example 1.

(42) TABLE-US-00005 TABLE 2 Cationic Polymer Employed Ratio of ASA:Polymer Competitor polymer 1:1.5 Polymin VT 1:0.75 Polymin VT 1:0.4 Polymin VZ 1:0.75 Polymin VZ 1:0.4

(43) Paper hand sheets were prepared in three separate data runs from a commercial papermaking stock employing each of the ASA emulsions as the sizing agent. The Cobb 60 values were measured and the results are shown in the FIGURE. For information sizing results improve with decreasing Cobb 60 value.

(44) It can be seen that on the whole the Cobb 60 values comparable for the Polymin VT and Polymin VZ as the cationic polymer to the Cobb 60 values of the competitor products which is used as at least twice the dose of the products of the invention.

Example 3

(45) A series of ASA emulsions were made using different ratios of ASA (Kemsize 220) and either Polymin VT or Polymin VZ by an analogous method to Example 1 as indicated in Table 3.

(46) TABLE-US-00006 TABLE 3 Emulsion No Ratio of ASA:Polymin Dispersion polymer employed 1 1:0.75 Polymin VT 2 1:0.5 Polymin VT 3 1:0.3 Polymin VT 4 1:0.75 Polymin VZ 5 1:0.5 Polymin VZ 6 1:0.3 Polymin VZ

(47) Paper hand sheets of 80 g/m.sup.2 were prepared from a cellulosic papermaking stock (B19 Furnish) employing a retention agent each of the emulsions as sizing agents immediately on preparation of the emulsion and then 60 min of the preparing the emulsions. The retention agent was Percol 8385 X and Polymin VT Polymix at a concentration of 0.22% and at a dose of 1.05 kg/tonnes. The hand sheets were produced an a hand sheet former (Rapid-Kthen). Cobb 60 values were measured for each paper hand sheet prepared. The results are shown in Tables 4 and 5.

(48) TABLE-US-00007 TABLE 4 Using emulsions immediately after preparation Coulter Coulter dosage dosage dosage LS 230 LS 230 Cobb 60 amount amount amount Polymer D 50 D 90 (app. 6-7% Cobb 60 Emulsion ASA l/h Polymin water conc. in % [m) [m) moisture) dry 1 117 88.35 1182 7.5 33 23 2 117 58.9 1222 4.8 1.795 27.47 36 29 3 117 35.34 1253 2.8 2.584 33.3 38 21 4 117 88.35 1182 7.5 1.517 3.352 23 23 5 117 58.9 1222 4.8 2.317 22.19 21 18 6 117 35.34 1253 2.8 2.788 30.16 19 27

(49) TABLE-US-00008 TABLE 5 Using emulsions one hour after preparation Coulter Coulter dosage dosage dosage LS 230 LS 230 Cobb 60 amount amount amount Polymer D 50 D 90 (app. 6-7% Cobb 60 Emulsion ASA l/h Polymin water conc. in % [m) [m) moisture) dry 1 117 88.35 1182 7.5 1.257 2.115 33 23 2 117 58.9 1222 4.8 1.404 11.92 33 21 3 117 35.34 1253 2.8 2.291 22.35 41 36 4 117 88.35 1182 7.5 1.478 3.837 24 26 5 117 58.9 1222 4.8 1.617 3.959 30 27 6 117 35.34 1253 2.8 1.999 6.101 21 22

(50) For determining the degree of sizing of the surface-sized papers, the Cobb.sub.60 value according to DIN EN 20 535 was determined. The water absorbing of the paper sheet in g/m.sup.2 after contact with water and a contact time of 60 s is defined as the Cobb.sub.60 value. The lower the Cobb.sub.60 value, the better is the sizing effect of the dispersion used.

(51) It is evident from the results that excellent Cobb 60 values are obtained from the emulsions with no significant loss of effect even after one hour.