NO172551B - MAIN Aqueous-free Concentrate Mixture for Gluing Cellulose Fibers - Google Patents

Abstract

An aqueous sizing composition can be made by mixing into water a concentrate that comprises a substantially anhydrous dispersion of a polyelectrolyte in a liquid reactive size.

Description

The invention relates to a mainly water-free, storage-stable concentrate mixture which, after dilution with water, is suitable for gluing cellulose fibres.

During the production of paper, it is necessary to make the natural hydrophilic cellulose fibers hydrophobic, so that penetration of aqueous liquids into the formed sheets is thereby limited and makes it possible to write and print on the sheets. This procedure, which is called gluing, can be carried out by adding an adhesive to the pulp slurry (normally called internal gluing) or the adhesive can be applied to the shaped paper sheet. This invention relates to the internal bonding process.

There are two types of adhesive in common use. One of these is based on resin used in conjunction with alum. The resin is added as a soap solution or as an emulsion,

and alum is added afterwards just before sheet formation to precipitate the resin as fine particles which are retained in the sheet.

The second type of adhesive is a reactive adhesive such as a ketene dimer or an anhydride-based adhesive, which reacts chemically with the cellulose fibers. Preferably it is applied in combination with a polyelectrolyte which will help to retain the adhesive in the sheet.

The reactive adhesive is generally added to the mass in the form of an aqueous emulsion, generally a cationic emulsion. The emulsion can be produced at the mill, but this requires that the mill has emulsification equipment, and thus it would be easier if a concentrated emulsion could be supplied to the mill ready for dilution and use. Unfortunately, reactive adhesives tend to react with water, so an aqueous emulsion will tend to be rather unstable.

Anhydride-based adhesives such as alkenyl succinic anhydride adhesives are

so reactive that their emulsions must be prepared at the mill immediately before use. These glues are normally fed to the mill with a cationic starch which generally must be pre-boiled before emulsification and thus make it easier to shape the emulsification at the mill.

Ketene dimer glue is often sent to the mill in the form of an emulsion, but these emulsions only have a limited lifetime, and the maximum concentration of ketene dimer in the emulsion is rather low, generally below 6%, so that very large volumes of emulsion must be sent to papermaking.

Emulsification of liquid ketene dimers can be achieved using conventional emulsifying equipment, but some of the preferred ketene dimers are solids at room temperature. As described in US patent no. 3,046,186, emulsification of these first necessitates either melting the solid (so that the emulsion is transferred to a dispersion after cooling) or dissolving the solid in a solvent, generally benzene. A typical important ketene dimer is distearyl ketene dimer, and this only has a relatively low solubility in organic solvents, with the result that the solution of that which is emulsified must be rather dilute. For example, it has been found that this dimer is precipitated from a 40% by weight solution in benzene (weight ratio benzenedimer of 1:0.67) and thus any solution in benzene must be more diluted than this. This dimer is also less soluble in other organic solvents than it is in benzene.

As described in US patent no. 3,046,186, the emulsion is generally prepared by emulsifying the dimer in an aqueous solution of a cationic dispersant, although this patent mentions that "in certain cases the emulsifier can be pre-dispersed in the ketene dimer. It is stated that the emulsions can be prepared with any suitable solids content, but is used at 1 to 5% by weight solids.

In each of the examples in US Patent No. 3,046,186, the starting mixture which was prepared and which contained both adhesive and polyelectrolyte was very diluted. For example, in example 1, the initial concentration is 9% by weight based on the total mixture.

In any case, the emulsifying or dispersing agent in US patent 3,046,186 was introduced as an aqueous solution.

In each case, significant amounts of additional water are also included in the starting mixture. The introduction of the emulsifier or dispersant as an aqueous solution necessarily entails significant amounts of water in the mixture. In the case of ketene dimer glue, as in US patent 3,046,186, this is tolerable provided that the starting mixture is not stored for too long.

As mentioned above, it is preferable to use a polyelectrolyte with the reactive adhesive, and it is conceivable that some of the disadvantages in connection with emulsions of reactive adhesives and polyelectrolyte could be minimized if the reactive adhesive and the polyelectrolyte were added separately. However, this entails other disadvantages.

It would therefore be highly desirable if it were possible to supply a stable concentrated mixture which contained both reactive adhesive and polyelectrolyte, and which could be easily diluted with water at the mill.

In EP 0141641 A2 (not published at the priority date of the present application) concentrated mixtures comprising a substantially anhydrous dispersion of a polyelectrolyte in an organic liquid comprising a solution of a reactive adhesive in a hydrophobic solvent are described. The reactive glue concentration in such mixtures is generally over 20%, and although it e.g. can be up to 85%, it is normally lower.

A concentrate mixture according to the present invention is a substantially anhydrous dispersion of a cationic or anionic polyelectrolyte in a liquid, reactive adhesive and is substantially free of solvent and has a content of the adhesive and the polyelectrolyte of at least 80% by weight, and which contains a dispersion promoter selected from insoluble dispersion stabilizers, amphipathic polymeric dispersion stabilizers and water-in-oil emulsifiers, and optionally an oil-in-water emulsifier. The mixture is essentially free of solvent. Preferably there is no solvent, but if the solvent is present, the amount thereof is insufficient to significantly contribute to the physical properties of the mixture, e.g. below 5% and normally below 1% by weight solvent of the mixture.

Although the adhesive in EP 0141641 A2 could be solid or liquid and present in a mixture in solution in the hydrophobic solvent, the adhesive in the present invention must be liquid at the temperature at which the mixture is to be used and stored, preferably room temperature such as 20 to 25°C. Preferably, the glue is liquid at 0°C.

The preferred liquid adhesives for use in the invention are anhydrous, reactive adhesives which in particular contain alkenyl succinic anhydride adhesives. Suitable materials are described in US patent no. 3,102,064.

Various other reactive adhesives are liquid and can be used

in the invention, e.g. certain ketene dimer glues.

The concentrate mixture must be essentially anhydrous so that the reactive adhesive does not react in the mixture during storage. The amount of water is generally not more than the equilibrium moisture content of the polyelectrolyte (ie the water content of the polyelectrolyte if it is exposed in the form of dry powder to room atmosphere) and is preferably lower than this. Normally the water content is not more than 1% or the height 2% by weight of the mixture.

The polyelectrolyte will generally be water-soluble, and an advantage of the invention is that it can have any desired molecular weight and can in particular have a molecular weight that is higher than what is normally possible with existing mixtures. For example, the internal viscosity can be above 1 and generally above 3, e.g. above 6. Although it is generally below 9, it can be higher, e.g. up to 20 or more.

The polyelectrolyte can be formed from a water-soluble ethylenically unsaturated monomer (or a water-soluble mixture of ethylenically unsaturated monomers) and can be cationic or anionic, cationic polyelectrolytes being generally preferred.

Preferred cationic electrolytes are homopolymers or copolymers of diallyl dialkyl (generally dimethyl) ammonium chloride and homopolymers and copolymers of dialkylaminoalkyl acrylates and methacrylates (preferably dimethylaminoethyl acrylates and methacrylates) which are present as acid addition salts or quaternary ammonium salts, generally quaternized with methyl chloride or dimethyl sulfate. Copolymers of such monomers can be formed with acrylamide or methacrylamide and will typically contain at least 10% and normally at least 30% by weight of the cationic monomer. Other cationic acrylamides and methacrylamides can be used. Other cationic polymers that can be used are polyamines and polyimines such as polyamine-epi-halohydrin polymers and dicyandiamide condensates and polyethyleneimines.

Suitable anionic polymers include polymers formed

from monomers containing carboxylic or sulfonic acid groups. These groups can exist as free acid or, more often, as

a water-soluble ammonium or alkali metal (usually sodium) salt. Suitable acids are acrylic acid, methacrylic acid and 2-acrylamido-2-methyl-propane sulphonic acid. Sodium allyl sulfonate can be used. The anionic polymers can be homopolymers of such acids or mixtures thereof or copolymers with e.g. acrylamide. A suitable polymer is polyacrylamide containing up to 25% or more acrylic acid groups.

The particles of the polyelectrolyte are generally below 500 um and preferably below 200 um in size.

The new mixtures can be prepared by mixing powdered polyelectrolyte into the liquid reactive adhesive. In these mixtures, the polyelectrolyte generally has a particle size above 5 and normally above 10 µm, and often the maximum particle size is within the range of 20 to 100 µm.

It is necessary that the mixture be used while the polyelectrolyte is substantially uniformly distributed throughout the liquid reactive adhesive. If the mixture has a tendency to settle, it should therefore be used before serious formation of a non-redispersible sediment occurs. Settling can be minimized or prevented by incorporating an effective amount (eg, 0.1 to 10%) of a dispersion promoter. For example, dispersion stabilizers which are insoluble in the reactive adhesive such as clays and silica-based dispersion stabilizers which are known to stabilize dispersions in oil can be used. Preferred stabilizers for this purpose are organophilic clays such as the materials sold under the trade name "Bentone". Stabilizers that are stable in the glue can also be used.

Preferred mixtures according to the invention, however, have polyelectrolyte with a maximum particle size below 10 µm, preferably below 3 µm. Although a dispersion promoter may be added to the mixture, the amount required is normally low. Further addition of e.g. camps are generally unnecessary. The particles are preferably produced by reverse phase polymerization, preferably in the presence of a dispersion stabilizer of the type known for use in reverse phase polymerization. The presence of residues of this on the polymer particles will generally be sufficient to stabilize the mixtures in the invention.

Particularly preferred mixtures are prepared by mixing into the liquid adhesive a substantially anhydrous dispersion of polyelectrolyte in a volatile organic liquid and then evaporating the organic liquid. The volatility of the liquid must be such that it can evaporate from the dispersion in liquid reactive glue at a temperature below that at which an unwanted chemical reaction can occur.

The particle size in this dispersion in organic liquid should be below 10 and often below 3 um. Preferably it is below 2 µm, often mainly in the range of 0.05 to 1 µm. It can be produced by reverse phase polymerization, generally reverse phase suspension polymerization of water-soluble monomer or monomer mixture dispersed in water-immiscible organic liquid. The reverse phase polymerization can be carried out in the presence of an oil-soluble polymer, generally an amphipathic polymer, as a dispersion stabilizer, and this stabilizer can also increase the stability of the final dispersion in the liquid adhesive. Reverse phase polymerization can also be carried out in the presence of a water-in-oil emulsifier. Materials and methods for reverse phase polymerization are well known and are e.g. described in EP 0126528. Suitable organic liquids which can be used for the dispersion are volatile aliphatic hydrocarbons.

After preparation of the dispersion of polyelectrolyte in organic liquid by reverse phase polymerization, the dispersion is dried to an essentially anhydrous state in the usual way, generally by azeotropic distillation.

If desired, the content of continuous organic phase can be changed after polymerization in a known manner so that the organic liquid (it must be evaporated from the dispersion of polyelectrolyte in liquid glue and organic liquid) has the optimal volatility.

The mixtures according to the invention are substantially free of solvent or other diluents and at least 80%, preferably at least 85% or at least 90% consists of the polyelectrolyte and the liquid adhesive. Preferred compositions contain at least 45, preferably 60 to 80% by weight reactive adhesive, 10

to 50%, preferably 20 to 40% by weight polyelectrolyte and 0 to 15%, preferably 5 to 10% additives such as the described insoluble or soluble stabilizers or water-in-oil emulsifiers.

Preferably, the additives contain oil-in-water emulsifier which serves to promote the emulsification of the concentrate in water at the time of use. Instead of introducing the oil-in-water emulsifier into the concentrate, it can be present in the water in which the concentrate is emulsified. If suitable mixing equipment is available, adequate emulsification can be achieved without the use of an oil-in-water emulsifier, but this is normally less preferred.

The concentrate is transferred to an emulsion in water before use.

The water in which the emulsion is formed can be the water in the cellulose pulp suspension to be treated, but preferably the concentrate is first transferred into an aqueous emulsion to give a reaction

tive glue concentration from 0.01 to 5%, preferably 0.5 to 1%

in relation to the weight of the aqueous solution.

This emulsion can then be added to the aqueous cellulose pulp, and paper can be produced from it in the usual way. The amount of reactive glue in the aqueous mass is generally from approx. 0.0.1 to approx. 1% by weight in relation to the dry weight of the mass. After adding the pulp slurry, the glue/oil droplets are actively held by the polymer on the fibers and the glue reacts with the fibers. The glue that is released from an emulsion in this way gives at least as good results as those obtained with the usual ketene dimer emulsions.

Thus, with the invention, gluing results are obtained that are at least as good as those obtained by using known mixtures,

and at the same time, for the first time, it is possible to add storage-stable, concentrated mixtures which the user can easily transfer into aqueous solutions, and which contain the polyelectrolyte and the glue and which are essentially free of other components than the glue and the polyelectrolyte.

The following are examples of the invention.

EXAMPLE 1

A sizing concentrate was prepared containing alkenyl succinic anhydride as the active sizing ingredient by dispersing a powdered polyelectrolyte into the liquid sizing ingredient to which an oil-in-water emulsifying surfactant had been added.

The chosen alkenyl succinic anhydride was liquid at room temperature and did not require melting for the dispersion to take place.

The polyelectrolyte, a copolymer of methyl chloride-quaternized dimethylaminoethyl methacrylate and acrylamide (25:75 weight ratio) was prepared by bulk solution polymerization. The resulting gel was cut into particles less than 5 mm in dimension, dried on a fluidized bed dryer and then ground down to the required dimension of less than 53 µm.

The mixture consisted of 65 g alkenyl succinic anhydride, 10 g oil-in-water emulsifying surfactant, 12.5 g polyelectrolyte which gives a 74.3% active adhesive mixture. The mixture was apparently free of water.

EXAMPLE 2

2.7 g of the concentrate mixture prepared in Example 1 was added to 197.3 g of water with stirring to give a 1% active alkenyl succinic anhydride emulsion which was used to perform the 1 minute Cobb test. This emulsion was labeled A.

For this sample, 100 g of towels were made from a bleached sulphate/bleached birch stock containing 7% calcium carbonate on a standard laboratory sheet making machine. Before the sheet formation, the required amount of 1% alkenyl succinic anhydride emulsion prepared as above was added to 600 ml of 1% consistency raw material. After stirring, towels were produced on a standard towel making machine. The sheets were cut from the sheet machine in the normal manner, placed on gloss plates and pressed at 3.4 atmospheres for 5 minutes before drying on rings at 110°C for 1 hour. After conditioning at room temperature, the degree of bonding achieved was measured by the standard 1-minute Cobb test. The results are shown in the table below.

EXAMPLE 3

A similar concentrate as in example 1 was prepared by using, instead of the chopped gel polymer, a globular polymer produced by reverse phase globular polymerization followed by azeotropic distillation and separation of the globules from the oil in which they were formed.

EXAMPLE 4

To give the concentrate from example 1 long-term storage stability, a corresponding amount of "Bentone" 38 can be added.

EXAMPLE 5

Preparation of a dispersion of a cationic copolyacrylamide in alkenyl succinic anhydride.

A copolymer of 75 parts by weight of acrylamide and 25 parts by weight of trimethyl B-acryloxyethyl ammonium chloride was first prepared in a hydrocarbon liquid with a boiling range of 154-168°C (Shell SBP11) by ordinary reverse phase polymerization as follows. 287.4 g of a 52.2% aqueous solution of acrylamide, 0.05 g of azo-bis-isobutyronitrile and 160.2 g of water were mixed to give a solution whose pH was adjusted to 4.6 with sodium hydroxide solution (46 wt%), then 71.0 g of a 70.4% aqueous solution of trimethyl B-acryloxyethyl ammonium chloride was mixed in to form the aqueous monomer solution. An oil phase was prepared comprising 363.3 g of SBP11, 14.2 g of a 2 to 1 molar copolymer of stearyl methacrylate and methacrylic acid as a suspension polymerization stabilizer (as described in GB 1.4 82,515) and 7.8 g of Span 80.

The aqueous phase was homogenized with the oil phase and deoxygenated with nitrogen gas, then polymerized by stirring in 1.5 ml of a 5% solution of sodium metabisulfite in water followed by a 1% solution of tertiary butyl hydroperoxide in SBP11 added at a rate of 0.25 ml per minute until polymerization was complete.

The resulting aqueous polymer gel dispersion was azeotropically dried under reduced pressure by recycling SBP11.

A portion of SBP11 was then distilled off, leading to an anhydrous polymer dispersion at a concentration of 40% by weight of polymer in SBP11.

250 g of this 40% copolymer dispersion was mixed with 500 g of alkenyl succinic anhydride and distilled under reduced pressure to remove SBP11. The final distillation conditions were 95°C at a pressure of 10 Torr. The resulting product was a stable dispersion of 100 g of polymer in 500 g of liquid reactive adhesive. It could be made self-emulsifying by adding high HLB surfactants.

EXAMPLE 6

The concentrate described in example 5 was used to prepare a corresponding aqueous solution with a 1% by weight active adhesive content by pouring the corresponding amount of dispersion into water. This emulsion was further diluted to 0.1 wt% active adhesive content and labeled B.

As a control, a common alkenyl succinic anhydride emulsion was prepared as follows. A 12% aqueous dispersion of a cationic starch was boiled at 95°C for 20 minutes with constant stirring. The boiled starch was cooled and diluted to 9% activity. Two parts by weight of alkenyl succinic anhydride were added to 3 parts by weight of cationic starch with stirring. High shear mixing with a Silverson mixer was continued to achieve a fine particle size emulsion. This emulsion was diluted with water to 0.1 wt% active glue content and labeled C.

100 G.s.m. towels were made from a bleached sulphate/bleached birch stock containing 10% calcium carbonate on a standard laboratory sheet making machine. Before sheeting, the required amount of 0.1% emulsion marked B was added to 600 ml of 1.0% consistency raw material. After mixing, towels were prepared, pressed at 3.4 atmospheres for 5 minutes before drying at 110°C for 1 hour. After conditioning at room temperature, the degree of adhesion was measured by the standard 1-minute Cobb test.

Control sheets were prepared in the same way as described above, but with emulsion C replacing emulsion B. The results are shown below:

Claims (10)

1. Mainly water-free, storage-stable concentrate mixture which, after dilution with water, is suitable for gluing cellulose fibres, characterized in that it is a substantially anhydrous dispersion of a cationic or anionic polyelectrolyte in a liquid, reactive adhesive and is substantially free of solvent and has a content of the adhesive and the polyelectrolyte of at least 80% by weight, and which contains a dispersion promoter selected from insoluble dispersion stabilizers , amphipathic polymeric dispersion stabilizers and water-in-oil emulsifiers, and optionally an oil-in-water emulsifier. 2. Mixture according to claim 1, characterized in that it contains at least 45% by weight of the reactive adhesive and from 10 to 50% by weight of the polyelectrolyte, and where the combined weight of polyelectrolyte and adhesive is at least 85% by weight. 3. Mixture according to claim 1, characterized in that it contains 5 to 10% by weight of additives selected from emulsifiers and dispersion stabilizers. 4. Mixture according to claims 1 to 3, characterized in that the polyelectrolyte has a particle size below 500 µm and the mixture is prepared by mixing the polyelectrolyte with the liquid, reactive adhesive and with an added dispersion stabilizer. 5. Mixture according to claims 1 to 3, characterized in that the polyelectrolyte has a particle size below 10 µm. 6. Mixture according to claim 5, characterized in that the polyelectrolyte is produced by reverse phase polymerization in the presence of a dispersion stabilizer which serves as the only dispersion stabilizer in the mixture. 7. Mixture according to claims 1 to 6, characterized in that the adhesive is an alkenyl succinic anhydride adhesive which is liquid at 20°C. 8. Mixture according to claims 1 to 7, characterized in that the polyelectrolyte is selected from polymers formed from at least one monomer selected from dialkylaminoalkyl acrylates and methacrylates and their acid addition salts and their quaternary ammonium salts; diallyl-dialkylammonium chlorides; -acrylamide; acrylic acid, methacrylic acid and 2-acrylamide-2-methylpropanesulfonic acid and water-soluble salts; and sodium allyl sulfonate, and from polyamine and polyimine polymers. 9. Mixture according to claims 1-8, characterized in that it is produced by mixing into the liquid, reactive adhesive an essentially anhydrous dispersion of the polyelectrolyte in a volatile, organic liquid and then evaporating the organic liquid. 10. Mixture according to claim 9, characterized in that the essentially anhydrous dispersion of polyelectrolyte in a volatile, organic liquid is a dispersion produced by reverse-phase polymerization of a water-soluble, ethylenically unsaturated monomer, or a water-soluble mixture of ethylenically unsaturated monomers, in a non-water-miscible bar, volatile, organic liquid, and the polyelectrolyte has a particle size below 2/itm.