AU593245B2 - Compositions for sizing paper - 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

1 i>~«i COMMONWEALTH' OF AUSTRALIA PATENT ACT 1952 COMPLETE SPECIFICATION (Original) FOR OFFICE USE 593 Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: Related Art: Thi.- doc m-ient cor-.i-s ^r I S -ts 'i\t 0 ,,Name of Applicant: 9* 4 Address of Applicant: Actual Inventor(s): S address for Service: 0 ALLIED COLLOIDS LIMITED P.O. Box 38, Low Moor, Bradford, West Yorkshire, BD12 OJZ John LANGLEY David FARRAR DAVIES COLLISON, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

Complete Specification for the invention entitled: "COMPOSITIONS FOR SIZING PAPER" The following statement is a full description of this invention, including the best method of performing it known to us -1- %la Allied CollOids Limited 60/2456/02 Copwpositions for Sizing Paper The invention rela;-es to the sizing of cellulosic fibres and to compositions for use in this, and to their manufacture.

During the manufacture of paper it is necessary to render the naturally hydrophilic cellulosic fibres hydrophobic so that penetration of aqueous liquids into the formed sheets is limited thereby making writing and printing on the sheets possible. This process, known as sizing, can be carried out by adding a sizir* agent to the pulp slurry (usually termed internal sizing) or the sizing agent can be applied to the formed paper sheet.

This invention is concerned with the internal sizing .15 process.

There are two types of sizing agent in general use.

One of these is based on rosin which is used in conjunction with alum. The rosin is added as a soap solution or as an emulsion and alum is added afterwards 20 just prior to sheet formation to precipitate the rosin as a fine particulate which is retained by the sheet.

The second type of size is a reactive size, such as 7 9 25, a ketene dimer or an anhydride-based size, which reacts 0 tic chemically with the cellulosic fibres. Preferably it is S, 25 applied in combination with a polyelectrolyte which will help to retain the size in the sheet.

The reactive size is generally added to the pulp in the form of an aqueous emulsion, generally a cationic i •emulsion. The emulsion can be prepared at the mill but this necessitates the mill having emulsifying equipment and so it would be more convenient if a concentrated emulsion could be supplied to the mill ready for dilution and use. Unfortunately reactive sizes tend to react with water so that an aqueous emulsion is liable to be rather unstable.

i r 1 ii a i ir r:; Anhydride based sizes, such as alkenyl succinic anhydride sizes, are so reactive that their emulsions have to be prepared at the mill just prior to use. These sizes are normally supplied to the mill with a cationic starch which generally has to be precooked before emulsification, thus making it even less convenient for the emulsion to be formed at the mill.

Ketene dimer sizes often are supplied to the mill in the form of an emulsion but these emulsions have only limited shelf-life and the maximum concentration of ketene dimer in the emulsion is rather low, generally below s' that very large volumes of emulsion have to be supplied to the paper manufacture.

Emulsification of liquid ketene dimers can be 15 achieved using conventional emulsification equipment but some of the preferred ketene dimers are solids at ambient temperature. As described in U.S. Patent Specification 3,046,186, emulsification of these necessitates initially either melting the solid (so that upon cooling the emulsion is converted to a dispersion) or dissolving the solid in a solvent, generally benzene. A typical important ketene dimer is distearyl ketene dimer and this only has relatively low solubility in organic solvents with the result that the solution of it that is *4* 25 emulsified must be rather dilute. For instance we have found that this dimer precipitates from a 40% by weight solution in benzene (weight ratio benzene:dimer of 1:0.67) and so any solution in benzene must be much more dilute than this. Also this dimer is less soluble in other organic solvents than it is in benzene.

As described in U.S. 3,046,186 the emulsions are generally prepared by emulsifying the dimer into an aqueous solution of cationic dispersing agent although that patent does mention that "in certain instances the emulsifying agent may be predispersed in the ketene r9 0 04* 00 0 dimer". It is stated that the emulsions may be prepared at any convenient solids content but are used at 1 to solids by weight.

In each of the examples in U.S. 3,046,186 the initial composition that was prepared and that contained both size and polyelectrolyte was very dilute. For instance in Example 1 the initial concentration is about 9% by weight size based on the total composition.

In every instance the emulsifying or dispersing agent in U.S. 3,046,186 was introduced as an aqueous solution. Also, in every instance, substantial amounts of additional water are included in the initial composition. The introduction of the emulsifying or dispersing agent as an aqueous solution inevitably 15 incorporates substantial amounts of water into the composition. With ketene dimer sizes, as in U.S.

3,046,186, this is tolerable provided the initial composition is not stored for too long.

As mentioned above, it is preferred to provide a polyelectrolyte with the reactive size and it might be thought that some of the disadvantages associated with providing emulsions of reactive size and polyelectrolyte could be minimised if the reactive size and the polyelectrolyte were supplied separately. However this incurs other disadvantages.

It would therefore be very desirable if it was possible to supply a stable concentrated composition that contained both reactive size and polyelectrolyte and which was readily dilutable with water at the mill.

In EP 0141641 A2 (not published at the priority date hereof) we have described concentrated compositions comprising a substantially anhydrous dispersior of a polyelectrolyte in an organic liquid comprising a solution of a reactive size in a hydrophobic solvent.

The reactive size concentration in such compositions is

?I

i ij^ 4- 1 generally above 20% and although it may be up to, for 2 instance, 85% it is usually lower.

3 The present invention provides a substantially 4 anhydrous, storage stable, concentrate composition suitable, upon dilution with water, for sizing cellulosic fibres and 6 which is a substantially anhydrous dispersion of a cationic 7 or anionic polyelectrolyte in a liquid reactive size and 8 which is substantially free of solvent and has a content of 9 the size and the polyelectrolyte of at least 80% by weight.

Whereas in EP 0141641 A2 the size could be solid or 11 liquid and was present in the composition in solution in the 12 hydrophobic solvent, in the present invention the size must 13 be liquid at the temperature at which the composition is to 14 be used and stored, typically ambient temperatures such as 20 to 25 0 C. Preferably the size is liquid at O°C.

16 The preferred liquid sizes for use in the invention are o 17 anhydride reactive sizes, including especially alkenyl 18 succinic anhydride sizes. Suitable materials are described 19 in U.S. Patent No. 3,1092,064.

Various other reactive sizes are liquid and can be used 21 in the invention, for instance certain ketene dimer sizes.

22 The concentrate composition may be substantially 23 anhydrous in order that the reactive size does not react in 24 the composition upon storage. The amount of water is generally not more than the equilibrium moisture content of 26 the polyelectrolyte the water content of the 27 polyelectrolyte if it is exposed in the form of dry powder 28 to the ambient atmosphere) and is preferably below this.

29 Normally the water content is not more than or at the most by weight of the composition.

31 32 33 34 36 37 0 Z 891120,c-dat.O66"allied2.1.4 YKr V I r 71 L i C- 9, 0* 9 9 9C 9.9 i 9 9 99 9 9 99 9 9* 99 9 *9* The polyelectrolyte will generally be water soluble and an advantage of the invention is that it can have a any desired molecular weight and in particular can have a molecular weight that is higher than is conveniently possible with existing compositions. For instance the intrinsic viscosity can typically be above 1 and generally above 3, above 6. Although it is generally below 9 it can be higher, up to 20 or more.

The polyelectrolyte may be formed from a water soluble ethylenically unsaturated monomer (or a water soluble blend of ethylenically unsaturated monomers) and may be cationic, anionic Qr n-ice, the cationic polyelectrolytes generally being preferred.

Preferred cationic electrolytes include homopolymers or copolymers of diallyl dialkyl (generally dimethyl) ammonium chloride and homopolymers and Jopolymers of dialkylaminoalkyl acrylates and methacryla.es (preferably dimethylaminoethyl acrylates and methacrylates) present 20 as acid addition salts or quaternary ammonium salts, generally quaternised with methyl chloride or dimethyl sulphate. Copolymers of such monomers may be formed with acrylamide or methacrylamide and will typically contain at least 10%, and usually 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 polyethylene imines.

qit-Ahi p nnn-inninpolymPr inclndri pnlyacrylamide.

Suitable anionic polymers include polymers formed from monomers including carboxylic or sulphonic acid groups. These groups may be prescE.t as free acid or, more usually, as a water soluble ammonium or alkali metal (generally sodium) salt. Suitable acids are acrylic r

I:

6 acid, methacrylic acid and 2-acrylamido-2-methyl-propane sulphonic acid. Sodium allyl sulphonate may be used.

The anionic polymers may be homopolymers of such acids, or mixtures thereof, or copolymers with, for instance, acrylamide. A suitable polymer is polyacrylamide containing up to 25% or more acrylic acid groups.

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

The novel compositions can be obtained by mixing powdered polyelectrolyte intu the liquid reactive size.

In these compositions the polyelectrolyte generally has a particle size above 5, and usually above 10 Am, and often the maximum particle size is within the range 20 to 100 AIm.

It is necessary that the composition should be used whilst the polyelectrolyte is substantially uniformly dispersed throughout the liquid reactive size. If the composition has a tendency towards settlement it should therefore be used before serious formation of a non-redispersable sediment occurs. Settlement can be minimised or prevented by the inclusion of an effective amount 0.1 to 10%) of a dispersion promoter. For instance dispersion stabilisers that are insoluble in the reactive size, such as the clays and silica based dispersion stabilisers known for stabilising dispersions in oil, may be used. Preferred stabilisers for this purpose are organophilic clays such as the materials sold under the trade name Bentone. Stabilisers that are soluble in the size may also be used.

Preferred compositions according to the invention however have the polyelectrolyte with a maximum particle size below 10 jm, preferably below 3 Am. Although a dispersion promoter can be added to the composition the required amount is usually low. Deliberate addition of, for instance, clays is generally unnecessary. The r 1 Els i: *o 9 8* o 1I 4 (t 8 981 *s 0 9 particles !are preferably made by reverse phase polymerisation preferably in the presence of a dispersion stabiliser of the type known for use in reverse phase polymerisation. The presence of residues of this on the polymer particles will generally be sufficient to stabilise the compositions of the invention.

Particularly preferred compositions are made by blending into the liquid size a substantially anhydrous dispersion of polyelectrolyte in a volatile organic liquid and then evaporating this organic liquid. The volatility of the liquid must be such that it can be evaporated from the dispersion in liquid reactive size at a temperature below that at which undesired chemical reaction might occur.

The particle size of this dispersion in organic liquid should be below 10, and often below 3 4m.

Preferably it is below 2 4m, often mainly in the range 0.05 to 1 um. It may be made by reverse phase polymerisation, generally reverse phase suspension 20 polymerisation, of water soluble monomer or monomer blend dispersed in water immiscible organic liquid. The reverse phase polymerisation may be conducted in the presence of an oil soluble polymer, generally an amphipathic polymer, as a dispersion stabiliser and this 25 stabiliser may also promote the stability of the final dispersion in the liquid size. The reverse phase polymerisation may also be conducted in the presence of a water in oil emulsifier. Materials and processes for reverse phase polymerisation are well known and are 30 described in, for instance, EP 0126528. Suitable organic liquids that can be used for the dispersion include volatile aliphatic hydrocarbons.

After making the dispersion of polyelectrolyte in organic liquid by reverse phase polymerisation the dispersion is dehydrated to a substantially anhydrous 904*4: OR 4 4 r :1 2 :IIYca. SIl *I I

(L

1.

I fIC *I Ifc f state in conventional manner, generally by azeotropic distillation.

If desired the content of continuous organic phase can be altered after polymerisation in known manner in order that the organic liquid (that has to be evaporated from the dispersion of polyelectrolyte in liquid size and organic liquid) has the optimum volatility.

The compositions according to the invention are substantially free of solvent or other diluents and at least 80%, preferably at least 85% or at least consists of the polyelectrolyte and the liquid size.

Preferred compositions contain from 45 to 90%, preferably to 80%, by weight reactive size, 10 to 50%, preferably to 40%, by weight polyelectrolyte and 0 to 15 preferably 5 to 10% of additives such as the described insoluble or soluble stabilisers or water-in-oil emulsifiers.

Preferably the additives include oil-in-water emulsifying agent that serves to facilitate emulsification of the concentrate into water at the point of use. Instead of incorporating oil-in-water emulsifying agent into the concentrate it may be present in the water into which the concentrate is emulsified.

If appropriate mixing apparatus is available, adequate 25 emulsification may be achieved without the use of an oil-in-water emulsifying agent, but this is usually less preferred.

The concentrate is converted to an emulsion in water prior to use.

The water in which the emulsion is formed may be the water of the cellulosic pulp suspension that is to be treated but preferably the concentrate is first converted into an aqueous emulsion to give a reactive size concentration of from 0.01 to preferably 0.05 to 1%, based on the weight of the aqueous solution.

4, i i i r i i i ii ~Ii r 4b ii This emulsion may then be added to the aqueous cellulosic pulp, and paper may be made from it, in the usual way. The amount of reactive size in the aqueous pulp is generally from about 0.01 to about 1% by wright based on the dry weight of the pulp, Upon addition to the pulp slurry, the active size/oil droplets are retained by the polymer on the fibres and the size reacts with the fibres. The size released from an emulsion in this way produces results at least as good as those obtained with the conventional ketene dimer emulsions.

Thus by the invention we obtain sizing results at least as good as those obtained using known compositions and yet for the first time we have the ability to supply storage stable concentrated compositions that the user 15 can easily convert into aqueous solutions, and that contain both the polyelectrolyte and the size and that are substantially free of components other than the size and the polyelectrolyte.

The following are examples of the invention.

Example 1 A sizing concentrate was prepared, including alkenyl succinic anhydride as the active sizing constituent, by dispersing a powdered polyelectrolyte into the liquid sizing component to which had been added an oil-in-water 25 emulsifying surfactant.

The chosen alkenyl succinic anhydride was a liquid at ambient temperature and did not require melting to allow tl'e dispersion to take place.

The polyelectrolyte, a copolymer of methyl chloride quaternised dimethyl aminoethylmethacrylate and acrylamide (25.75 by weight), was prepared by bulk solution polymerisation. The resulting polymer gel was cut into particles less than 5 mm in dimension dried on a fluid bed drier and then gound down to the required dimension of less than 53 microns.

I a i~L 3:785::irW~~I~7-; The composition comprised 65 g of alkenyl succinic anhydride, 10 g of oil-in-water emulsifying surfactant, 12.5 g of polyelectrolyte to give a 74.3% active sizing composition. The composition was ostensibly free from water.

Example 2 2.7 g of the concentrate composition made 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 carry out 1 minute Cobb tests. This emulsion was labelled A.

For this test 100 gsm handsheets were prepared, from a bleached sulphate/bleached birch stock containing calcium carbonate loading, on a Standard Laboratory sheet making machine. Prior to sheet formation the required amount of 1% alkenyl succinic anhydride emulsion as prepared above was added to 600 mls of 1.0% consistency stock. After stirring, handsheets were prepared on the standard sheet-making machine. The sheets were couched off the sheet-machine in the normal manner placed on glazing plates and pressed at 50 psi for 5 minutes prior to drying on rings at 1101C for 1 hour. After conditioning at room temperature the degree of sizing achieved was measured by the standard 1 minute Cobb test.

Thu results are shown in the table below.

Emulsion Dose Level of Alkenyl Succinic 1 Minute Anhydride based on Dry Fibre Cobb Value and Filler (g.m2) iA A 0.23% 18.1 A 0.34% 15.9 A A 0.57% 13.4 Example 3 A concentrate similar to Example 1 is made using, instead of the comminuted gel polymer, a bead polymer made by reverse phase bead polymerisation followed by '-in azeotropic distillation and separation of the beads from the oil in which they were formed.

Example 4 In order to impart long term storage stability to the concentrate of Example 1 an appropriate amount of Bentone 38 can be added.

Example Preparation of a Dispersion of a Cationic Co-Polyacrylamide in Alkenyl Succinic Anhydride A copolymer of 75 parts by weight acrylamide and parts by weight of trimethyl B-acryloxyethyl ammonium chloride was first prepared in a hydrocarbon liquid of boiling range 154-168°C (Shell SBP11) by conventional reverse phase polymerisation as follows. 287.4 gms of a 52.2% aqueous solution of acrylamide, 0.05 gms of azo-bis-isobutyronitrile and 160.2 gms of water were mixed to form a solution whose pH was adjusted to 4.6 with sodium hydroxide solution (46% wt/wt) then 71.0 gms of a 70.4% aqueous solution of trimethyl E-acryloxyethyl ammonium chloride was mixed in to form the aqueous monomer solution. An oil phase was prepared comprising 363.3 gms of SBP11, 14.2 gms at a 2 to 1 molar copolymer Sof stearyl methacrylate and methacrylic acid as Ssuspension polymerisation stabiliser (as described in GB S 25 1,482,515) and 7.8 gms Span The aqueous phase was homogenised with the oil phase and deoxygenated with nitrogen gas then polymerised by stirring in 1.5 mis of a 5% solution of sodium

S

f metabisulphite in water followed by a 1% solution of tertiary butyl hydroperoxide in SBP11 added at a rate of 0.25 mis per minute until polymerisation was complete.

The resulting aqueous polymer gel dispersion was azeotropically dehydrated under reduced pressure by recycling the SBP1l. Part of the SBP11 was then distilled off resulting in an anhydrous polymer dispersion at a concentration of 40% polymer by weight in

A

SBPll.

250 gms of this 40% copolymor dispersion was mixed with 500 gms of alkenyl succinic anhydride and subject to distillation under reduced pressure to remove the SBP11.

Final distillation conditions were 950C at a pressure of Torr. The resultant product was a stable dispersion of 100 grams polymer in 500 grams liquid reactive size.

It could be rendered self emulsifying by the addition of high HLB surfactants.

Example 6 The concentrate described in Example 5 was used to prepare a corresponding aqueous emulsion, having a 1% by weight active size content, by stirring the appropirate amount of dispersion into water. This emulsion was further diluted to 0.1% by weight active size content and labelled B.

As control, a conventional alkenyl succinic anhydride emulsion was prepared as follows. A 12% aqueous dispersion of a cationic starch was cooked at 0 C for 20 minutes with constant stirring. The cooked starch was cooled and diluted to 9% activity. 2 parts by weight of alkenyl succinic anhydride was added to 3 parts by weight of cationic starch with agitation. 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% by weight active size content and labelled C.

S100 g.s.m. handsheets were prepared from a bleached sulphate/bleached birch stock containing 10% calcium carbonate loading on standard laboratory sheet making machine. Prior to sheet formation, the required amount of 0.1% emulsion labelled B was added to 600 mls of consistency stock. After stirring, handsheets were prepared, pressed at 50 p.s.i. for 5 minutes prior to drying at 11oC for 1 hour. After conditioning at room temperature, the degree of sizing was determined by the standard 1 minute cobb test.

Control sheets were prepared in the same manner as described above, but with emulsion C replacing emulsion B. The results are shown below: Emulsion Dose Level of Alkenyl 1 Minute Cobb -2 Succinic Anhydride Based Value (g.m on Dry Fibre and Filler B 0.25% 22.1 B 0.35% 16.4 B 0.5% 13.7 C 0.25% 27.2 C 0.35% 20.1 C 0.5% 15.6 20 tt SI 3i I rig tlp° o 1hu. fe I eprtrtedge fsKn a eemndb h

Claims (14)

1. A substantially anhydrous, storage stable, concentrate composition suitable, upon dilution with water, for sizing cellulosic fibres and which is a substantially anhydrous dispersion of a cationic or anionic polyelectrolyte in a liquid reactive size and which is substantially free of solvent and has a content of the size and the polyelectrolyte of at least 80% by weight.

2. A composition according to claim 1 containing from to 90% by weight of the reactive size and from 10 to 50% by weight of the polyelectrolyte and in which the combined weight of polyelectrolyte and size is at least 85% by weight.

3. A composition according to claim 1 containing 60 to by weight reactive size, 20 to 40% by weight polyelectrolyte and 5 to 10% by weight additives selected from emulsifiers and dispersion stabilisers.

4. A composition according to any preceding claim in which the polyelectrolyte has a particle size of from 5 to 500pm and the composition is made by blending the polyelectrolyte with the liquid reactive size and with an added dispersion stabiliser.

A composition according to any of claims 1 to 3 in which the polyelectrolyte has a particle size below

6. A composition according to claim 5 in which the polyelectrolyte has been made by reverse phase polymerisation in the presence of a dispersion stabiliser which serves as the only dispersion stabiliser in the composition.

7. A composition according to any preceding claim which has been made by blending into the liquid size a c 891120,cadat.066,allied2 .1,14 1/ ;i i I 1 substantially anhydrous dispersion of polyelectrolyte in a 2 volatile organic liquid and then evaporating the organic 3 liquid. 4

8. A composition according to claim 7 in which the 6 substantially anhydrous dispersion of polyelectrolyte in a 7 volatile organic liquid is a dispersion made by reverse 8 phase polymerisation of a water soluble ethylenically 9 unsaturated monomer, or a water soluble blend of ethylenically unsaturated monomers, in a water immiscible 11 organic liquid and the polyelectrolyte has a particle size 12 below 2pm. 13 S 14

9. A composition according to any preceding claim in which the size is an alkenyl succinic anhydride size that is 16 liquid at 20 0 C. 17 18

10. A composition according to any preceding claim in which 19 the polyelectrolyte is selected from polymers formed from at least one monomer selected from dialkylaminoalkyl acrylates 21 and methacrylates and their acid addition salts and their 22 quaternary ammonium salts; diallyl dialkyl ammonium 23 chlorides; acrylamide; acrylic acid, methacrylic acid and 24 2-acrylamido-2-methyl propane sulphonic acid and water soluble salts; and sodium allyl sulphonate, and from S26 polyamine and polyimine polymers. 27 28

11. A composition according to any preceding claim S 29 additionally including an oil-in-water emulsifier. t 31

12. A method of making an aqueous sizing composition 32 comprising dispersing into water a concentrate according to 33 any preceding claim in an amount sufficient to give a 34 reactive size concentration in the water of from 0.01 to by weight. 36 37

13. A method in which cellulosic fibres are sized by 38 treating aqueous cellulosic pulp, or cellulosic paper made 891120,c adat.066,allied2,1,15 i hh.. .i F ;:9 le~ i ii- 16 from such pulp, with an aqueous sizing composition that has been made by dispersing into water a concentrate according to any of claims 1 to 11 in an amount sufficient to give a reactive size concentration in the water of from 0.01 to by weight.

14. A method of making a composition according to claim 1 comprising blending into the liquid reactive size a substantially anhydrous dispersion of the polyelectrolyte in a volatile organic liquid and then evaporating the organic liquid. A sizing concentrate, a method of making same, a sizing composition, a method of making a sizing composition and a method of sizing substantially as hereinbefore described with reference to any one of the Examples. DATED THIS 20th November, 1989 DAVIES COLLISON Fellows Institute of Patent Attorneys of Australia. Patent Attorneys for the Applicant f cT C1 C C C CII,' o C CC C C S38 891120,cuxdat.066,allied2.1.16 i i :Cari