GB2252984A - Novel compositions and their use for sizing paper - Google Patents

Abstract

A new sizing material which may be employed to reduce or eliminate the technical and cost problems associated with the paper sizing with emulsified sizing compounds comprises a blond of from 3 to 50 wt% alkyl ketene dimer and 97 to 50 wt% alkyl or alkenyl cyclic acid anhydride. In a preferred embodiment the invention provides a solution of 3 to 50 wt% alkyl ketene dimer in form 97 to 50 wt% of a liquid alkyl or alkenyl cyclic anhidride.

Description

NOVEL COMPOSITIONS AND THEIR USE FOR SIZING PAPER This invention relates to a new composition and its use for sizing paper or similar products, such as board, cardboard etc., based on cellulose or synthetic fibres. Particularly paper produced under alkaline or neutral conditions.

Paper, board, cardboard and other similar products are produced by first dispersing the cellulose or synthetic fibres in large quantities of water and the dispersion passed to a paper making machine where the water is removed to form the continuous paper web.

According to the nature of the fibres, the type of paper or board to be produced etc, the product is treated with various chemicals which may be injected into the aqueous dispersion of the fibres. One treatment common to most paper making processes is sizing.

Sizing of paper is well known, two typical sizing materials are alkyl-ketene dimers and alkenyl succinic anhydrides.

These products are generally used in emulsion form as described in, for example, Japanese Patent Publications 62-231099; 61-146898; 61-160495; 52-25102; 60-20905.

United Kingdom Patent 1492104 describes the use of polyoxyalkylene alkyl or arylalkyl ethers, or the corresponding mono- and di-ester derivatives to produce emulsions of cyclic acid anhydrides with a low input of shear energy. Such emulsions are used to disperse intimately the anhydrides into the cellulose stock to produce sized paper.

The sizing emulsion can be produced in-situ, within the cellulose stock, or prior to introduction into the cellulose stock.

The emulsions are preferably prepared in the presence of cationised stabilisers such as cationized starches, polyaminoethyl acrylate resins, polyamide resins having free amino groups, reacted or not with epichlorohydrin etc.

The main function of these cat ionic stabilizers is to charge positively the emulsion's particles favouring their absorption by Coulombic attraction on the negatively charged surface of the cellulose fibres.

The use of nitrogen and/or oxygen containing emulsifiers to produce emulsions of cyclic acid anhydride emulsions, in the presence of cationic stabilizers, with a low shear energy input is generally carried out using a concentration of 2.0 to 10.08 emulsifier based on the anhydride. Concurrently, typically 1 to 5 parts of cationic stabilizers are used for 1 part of anhydride.

The emulsions obtained are chemically unstable in water. As a consequence, emulsion particles with sub-micron diameters are quickly hydrolysed. On the contrary, emulsions particles of diameter above 3-4 microns, with too low surface-to-mass ratios lack enough Coulombic attraction to be rapidly deposited onto the cellulose and thus remain suspended in the process water used in the paper making.

Consequently, they are recycled continuously with the process water and are eventually hydrolysed which not only wastes sizing compounds, but causes foam formation and paper machine running problems.

Alkyl ketene dimers are used since they are not hydrolysed by water and thus does not cause foaming. Alkyl ketene dimers however can give the final paper an undesirable plastic feel and they also react with cellulose more slowly than the alkyl succinic anhydride. The emulsion-based sizing technology based on either product suffers from the disadvantage that it produces poorly sized paper due to re-wetting phenomena, caused by the emulsifier and low sizing yields. Re-wetting results from the presence of residual emulsifier in the cyclic acid anhydride absorbed on the cellulose fiber's surface. The emulsifier's polar groups, spread over the surface of the anhydride particle, attract water to the surface thus favouring the anhydride hydrolysis rather than its reaction with the hydroxy groups in the cellulose.

Moreover, the presence of residual emulsifier on the finished paper creates undesirable water affinity in the paper and the consequent decrease of the hydrophobic character of the paper produced by sizing. These difficulties are not eliminated by reducing the emulsifier concentration to below 1.0% and by using high shear mixers in the presence of 1 to 5 parts of a cationic stabilizer for 1 part anhydride. Even by using turbine-type mixers (rotating in the range 10000 to 20000 RPM) it is difficult to control the particle's diameter distribution both in the sub-micron and 3 to 4 micron ranges.

High-shear emulsification techniques based on turbine pumps with inlet-outlet pressure drops as high as 8 to 10 kg/cm2 are needed to obtain emulsion particle diameter distributions for best sizing result. However, the high-shear produced emulsions are characterized by poor stability and they tend to phase out quickly.

Foam, with its large air-liquid interface, favours evaporation of the recycle liquids with the formation of fatty deposits both on the paper and in the water recycle tank. These can also cause paper machine running problems.

Thus, more frequent cleaning operations may be needed which tend to disrupt the process and to increase the production costs. A further negative cost item is represented by the use of the emulsion's cationic stabilizers.

A number of problems encountered by the paper industry when using emulsions of cyclic acid anhydrides in sizing paper-are described in: 1987 Sizing Short Course, April 8-10 1987, Atlanta, Ga., TAPPI Press 1987.

1985 Alkaline Papermaking, April 17-19, 1985, Denver, CO., TAPPI Press 1985, ISSN 0738-1190.

Thus, although sizing paper may be achieved by using emulsified reactive synthetic products, the disadvantages are sizing compound waste due to hydrolysis, poorly sized paper due to re-wetting phenomena, low sizing yields, foaming, fatty deposits formation in the water recycle tank and paper machine running problems.

It is the main purpose of this invention to provide a new sizing material which may be employed to reduce or eliminate the technical and cost problems associated with the paper sizing with emulsified sizing compounds.

The present invention therefore provides a blend of from 3 to 50 wt% alkyl ketene dimer and 97 to 50 wt% alkyl or alkenyl cyclic acid anhydride. In a preferred embodiment the invention provides a solution of 3 to 50 wt% alkyl ketene dimer in form 97 to 50 wt% of a liquid alkyl or alkenyl cyclic anhydride.

The invention further provides the use for the sizing of paper of a blend of from 3 to 50 wt% of alkyl ketene dimer and from 97 to 50 wt% of an alkyl or alkenyl cyclic anhydride, it is preferred that the alkyl or alkenyl cyclic anhydride be liquid and the alkyl ketene dimer be dissolved therein.

The blends of the present invention are prepared by simple mixing of the two components. When the blend is to be used for paper sizing it is preferably a liquid and it is prefered that the alkyl or alkenyl cyclic ahhydride be a liquid and the blend be prepared by heating the two components together at a temperature above the melting point of the alkyl ketene dimer, generally above 35"C.

The blends of the present invention are useful for sizing paper in particular in a process which uses neat size or solution thereof without the need for emulsifier.

The blends are particularly useful as the size in the process we describe in our European Application 89306178.8 which comprises of the following steps: - production of a cellulose stock water slurry.

- cationization of such slurry.

- dispersing the synthetic size, neat or in solution with non active compounds such as gases or solvents, in form of fine droplets into the cellulose stock before, during or after the paperweb formation whether or not said paperweb is dry or wet.

- drying the paperweb.

and the improvements thereof as described in our UK Patent Applications 9001435; 9001436; 9068334 and 9008335 and the European Patent Application claiming priority therefrom.

In the preferred embodiment of this improved technology the size is injected by means of a piston pump through one or more nozzels imersed in the aqueous system and if the dispersion of the size is improved if it is preheated before injection into the cellulose stock/water slurry. As a preferred feature of these Patents the size is mixed with a small amount of water prior to injection into the cellulose stock/water slurry.

Accordingly the present invention also provides a process to size paper and similar products comprising: - forming a cellulose water slurry; - preheating a blend of from 3 to 50 wt % alkyl ketene dimer and from 97 to 50 wt % of an alkyl or alkenyl cyclic anhydride either neat or in solution, and injecting the mixture in droplet form into said cellulose water slurry before, during or after the paper web formation, wherein the cellulose water slurry and/or the size is treated with a cationizing compound - drying the paper web In a prefered embodiment the blend is injected into a stream of preheated water which carries the size blend into the cellulose water slurry.The preferred temperature to which the blend should be preheated depends upon the nature of the size, it should however be above the melting point of the alkyl ketene dimer, generally above 40"C. We also prefer that the water with which the preheated size is mixed be heated to a temperature in the range 30-650C.

When the slurry is cationised it is generally treated with mineral charges after mixing with the size.

Further benefits of the use of the process of the invention will become apparent in the detailed description of some procedures needed to implement it. Such procedures are described to explain the invention and are not meant to be a limitation thereof.

According to the preferred procedure to implement the invention, the reactive synthetic sizing compound mixed with water is continuously dispersed in the form of fine droplets into the wet-end of the paper machine, preferably in places where the cellulose stock water slurry is under high turbulence, to obtain rapid and complete contact of the sizing compound with the paper stock.

The sizing compound dispersion is conveniently obtained with a spraying nozzle, which produces droplets in the water of predetermined dimensions and a predetermined particle diameter distribution. The spraying nozzle type and spraying angle may change depending on the type of paper machine and on the place, within the paper machine, where it will be positioned for best results.

The number of spraying nozzles used may be chosen according to the type of paper machine and the type of paper or paper product being manufactured.

We have found that good dispersion of the size into the voluminous aqueous systems may be achieved by pumping the size with a piston pump through one or more nozzles immersed in the aqueous system.

Spray-mixing will then occur due to the large pressure differential created at the nozzle tip between the size and the paper stock. Such differential accelerates the disintergration of the liquid jet, issuing at high speed from the nozzle tip, into small spherical particles by impingement on the surrounding fluid.

The reactive synthetic sizing compound may be delivered to the spraying nozzle through a pressurized piping system and the spraying pressure can be generated with metering micro-pumps. Alternatively, the compound may be delivered to the spraying nozzle from storage tanks which are pressurized with an inert dry gas, and the compound can be metered with calibrated microvalves.

The storage tanks, the piping system, the nozzles, the valves and the metering micro-pumps can conveniently be thermostated to maintain the size at the desired temperature. Convenient thermostating may be achieved with water at the selected temperature.

Thermostating controls the viscosity of the sizing compound and produces droplets with predetermined diameters when exiting the spraying nozzle.

The viscosity control which is especially useful when reactive sizing compounds which are solid or highly viscous at room temperature, are used. For instance, this could be the case with cyclic anhydrides substituted with palmityl (or heavier) or linear rather than branched groups or the use of alkyl ketene dimers.

In the preferred process the preheated size is injected into a stream of water at substantially the same temperature as the size shortly before the stream of water is itself injected into the bulk cellulose stock. This water stream can also be used to introduce other additives into the paper stock such as defoamers, proteins, natural gums, synthetic polyhydroxylated hydrocarbons, alum and cationic starch.

Products to micro-encapsulate the size and thus inhibit its hydrolysis may also be included in the water.

The sizing product pressurization in the storage tank can be obtained, at or about room temperature, with dried gases such as air, nitrogen, argon, methane, propane, butane, chlorofluoro hydrocarbons, carbon dioxide, nitrogen protoxide. Some of said gases are soluble in the reactive sizing compounds at the storage temperature.

The absorption of the sizing compound droplets on the cellulosic fibres is aided by the cationizing treatment. The fibres may have undergone a previous cationisation either on-line or in the paper stock preparation tubs.

Alternatively the size itself may be applied together with the cationsing agent. Such cationization is a standard technique in paper production to favour the retention of wet-strength resins, of mineral charges, etc, which otherwise would be in large part lost.

The cationization is generally carried out with long chain fatty amines, synthetic polymers containing amines, cationic modified starches, polyamide-amine resins and other cationized products. Typically 0.02 to 3.50 wt% of cationizing agent based on the weight of dry fibre is used.

The time of contact between the process water and the reactive synthetic sizing compound in dispersed droplet form is very small, depending on the turbulence of the machine wet-end and on the cationizing treatment. These factors can be varied to obtain the desired deposition rates of the size droplets on the fibres.

The combined action of the extremely low contact time with the process water and the natural hydrophobicity of the sizing compound prevent its hydrolytic degradation and the resulting waste. Moreover, by lowering the droplets diameter the interactions with the cellulose fibres and the sizing compound absorption can be improved thus increasing the sizing yield to a level beyond that achieved with the current emulsion technology.

In another procedure to implement this invention, solutions of certain gases, such as methane, propane, butane, chlorofluoro hydrocarbons, carbon dioxide, etc., in the synthetic sizing compound are sprayed in form of fine droplets directly into the wet-end of the paper machine or onto the formed paper web before the machine drying section, or in the size press.

When the spraying technique is used we prefer that the nozzle(s), or any similar device, connected with a pressurized piping system to the storage tank containing the sizing compound solution, may be used to disperse the sizing compound solutions into the cellulose-water slurry.

Preferably the injection system is controlled by the rate of paper reduction and consists of a preheated vessel which feeds a low pressure feed pump which itself feeds, preferably through a filter, a metering pump which is conventiently a 4 to 6 cylinder metering pump operating at pressures in the range 50 to 300 atmospheres, preferably 120 to 200 atmospheres, the pump being controlled by a signal from the paper stock flow to maintain the constant ratio of size to stock.

The pump injects the size through one or more nozzles into the water stream and hence into the stock at the determined rate to give appropriate sizing. Any gas evaporates or it is dissolved by the process water, favouring the droplets dispersion without affecting in any other way the paper production process.

Another important function of the dissolved gas when used is to protect the surface of the droplets from water's hydrolytic action, and to produce in-situ a fresh surface on the droplets as the gas evaporates or dissolves into the process water.

A range of gas sizing compound mixtures may be used, the preferred composition may depend from the type of paper produced in a given machine and from the process parameters.

In general, the dissolved gas concentration may be in the range 20 to 50% on the sizing compound although for economic reasons it is preferable that gas concentrations be kept in the range 1 to 19%. The sizing compound gas solutions could also be obtained by previously mixing gas types with low and high solubility into the sizing compound, such as nitrogen and carbon dioxide, nitrogen and methane.

In another procedure, the reactive synthetic sizing compound is first dissolved in an anhydrous, aprotic, water-soluble, inert solvent. The solution, is sprayed with one or more nozzles as fine droplets directly into the water-cellulose slurry at the paper machine wet-end. In this case, the inert solvent is dissolved by the process water thus protecting the reactive sizing compound droplets from water's hydrolytic action and generating in-situ a fresh surface in the presence of cellulose.

As a further embodiment inert gases may be dissolved in the aprotic solvent, as previously specified (for example carbon dioxide).

Examples of useful aprotic compounds include ketones, esters, ethers, aromatic and aliphatic hydrocarbons, (for example acetone, methylethyl ketone, acetonyl acetone, methyl acetate, ethylene glycol diacetate, dioxane, etc). A range of solvent concentrations in the solutions with the sizing compound can be considered.

The preferred composition will be determined by experiment depending on the process parameters. Cost considerations would indicate that solvent concentrations in the range 1 to 19% may be preferred to concentrations in the range 20 to 50% or higher, use of these lower concentrations will also avoid solvent accumulation in the water recycle system.

In another preferred procedure to implement the invention, the reactive sizing compound is dissolved in an anhydrous, protic, water soluble compound immediately before being sprayed and transformed in fine droplets.

Preferred concentrations of the protic anhydrous solvent with the reactive sizing compound are as previously disclosed in the case of the aprotic solvents. Classes of such solvents include alcohols, etheralcohols, esteralcohols (e.g. methyl alcohol, ethyl alcohol, 2-butoxyethanol, ethylene glycol monoacetate, 2-(2 butoxyethanol), etc.

0.005 to 2.08 weight of size on dry fibres is preferably used. Subsequent to application of the size, the paper web is dried by heating to temperatures in the range 90 to 1200C which also promotes the reaction between the reactive sizing compound and the hydroxyl groups of the cellulose. This may be performed by the heated cylinders which provide also the pressure needed to impregnate the paper web with the reactive sizing compound.

According to an alternative procedure to implement the invention, the synthetic sizing compound is sprayed onto the formed paperweb with one or more nozzles having small spraying angles. They could spray in the direction of one side of the paperweb, or in the opposite side or on both sides simultaneously.

With this technique, the spraying can be extended to the whole surface of the paperweb or can be limited to some parts of the surface, either when still wet or in a size press, or in both positions.

When spraying in a size press, the final drying cylinders used to dry the paper should exert enough pressure and reach a temperature high enough to ensure both the impregnation by the sizing compound of the paper wet thickness and the reaction with the hydroxyl groups of the cellulose.

When the sizing compound is applied in the size press, its concentration could reach values above 2% weight on dry fibres. Higher concentrations are possible with consequences on the cost.

A certain period of time will be required to achieve such reaction when the sizing compound concentration is in the higher ranges.

The preferred cyclic acid anhydrides of the general formula

Where R1 is an organic hydrophobic group. More preferred are the liquid cyclic acid anhydrides in which R1 is a branched chain C8-C16 alkenyl group. The preferred alkyl ketene dimers are preparred from acid chlorides by for example the method described by R. Adams, Organic Reactions Vol III page 129 John Wiley & Sons Inc New York 1946 and J.C.

Saner Journal of the American Chemical Society Vol 69 page 2444 1947. The mixture of acid chlorides being chosen to give a product of desired melting point.

Typical examples of cellulose that may be treated with the sizing compounds are derived from hardwoods and softwoods, bleached or not bleached, semi-chemical, groundwood and combination thereof. Synthetic rayon or regenerated cellulose fibres may also be used as well as waste paper and cardboard.

The following example illustrates the present invention. In this example the content of all materials reported refers to weights on dry cellulose and the following materials are used: A) Bleached sulphate cellulose (60% hardwood, 40% softwood) of freeness 350SR and concentration 40 g per litre in tap water (hardness 17 French degrees) is treated with 0.25 to 0.50% hydrated aluminium sulphate (alum) as a 100 g per litre solution in tap water.

B) Cationized potato starch (Roquette Fr. HICAT 180 brand), of concentration around 5% in demineralized water, is cooked at 85-900C for 30 minutes and subsequently diluted about 5 times. Limited amounts of starch are cooked and normally used within 12-24 hours from cooking to prevent ageing effects.

C) Calcium carbonate (Craie Micronic 0 brand) is pre-slurried in tap water at the concentration 350 g per litre.

D) Alkenyl succinic anhydride (Exxon Chemical Co. brand), having a C12 branched side chain.

E) Alkyl Ketene dimer (AKD) of melting point 39*C as measured by differential scanning calorimetry.

F) Polyacrylamide (Schimmer & Schwartz FO4550BPM brand), dissolved in water at the concentration 0.038 %, is used as flocculating retention aid.

G) Sodium polysilicate Na2Si3o7,.3H2O as a 42%wt water solution is added without modifications. Colloidal polymerized silica containing 0.3% Na20 as a 15% water dispersion (EKA-KEMI Compozil BMA Brand) is added without modification.

H) Diethylene triaminopentamethylene phosphonic acid (Monsanto Dequest 2060 S) containing 0.1 wt% Na2O as a 20 wtt water solution. The product is believed to be of the formula

EXAMPLE A An amount of the paper stock A is fed to a paper machine constructed by SICMA, Terni, Italy. It is fitted with a Fourdrinier net width 0.56m and a series of 22 steam-heated drying cylinders, running at the speed of 40 m.min'l and producing about 100 kg paper per hour. The grammage is kept at about 80-85 g.m2 B. The paper stock amount is limited to about 1 hour of machine feed.

25% calcium carbonate slurried in water is metered on-line into the paper stock on the suction side of the fan pump The paper stock pH after calcium carbonate addition is in the range 7.2-7.6.

0.038% polyacrylamide F is finally added to the paper stock just before it enters the head box.

A piston metering pump, connected to a spraying nozzle, is used to spray-mix a mixture of 92.7 wt % D and 73 wt % E into a stream of cationized potato starch in demineralized water at the concentration of 1.3% at the rate of 0.38 m3.Ton-1 dry cellulose.

Sodium polysilicate G (COMPOZIL) is metered on-line into the paper stock at the rate of 0.33 parts of commercial material per 100 parts of cellulose on the suction side of the fan pump together with calcium carbonate slurried in water.

Finally, 0.25 parts of alum are metered into the paper stock just before the head box and no polyacrylamide is added.

The paper web is dried in the machine drying section, whose steam-heated cylinders are programmed to reach temperatures in the range 50-llO'C, before being wound up.

The following paper machine parameters are observed when equilibrium is attained.

Run No. 1 2 Head box paper stock conc. g 3.6 3.6 First pass retention all solids % 96.5 97.1 First pass retention Ca carbonate % 83.8 88.3 Ashes at 425 C % 21.5 22.8 Zeta potential white waters mV +1.9 +2.8 Felt+Wire/2 Cobb 60" (50% RH, 230C) 19 17 Hercules Sizing Test 287 350 Grammage g.m2 80 80 No foam is produced and no white pitches are observed in both runs and the dark spots in the paper produced is 1-5 per lOm2.

Claims (1)

1) A blend of from 3 to 50 wt% alkyl ketene dimer and 97 to 50 wt% alkyl or alkenyl cyclic acid anhydride.

2) A blend according to Claim 1 in which the alkyl ketene dimer is dissolved in the alkyl or alkenyl anhydride.

3) The use for the sizing of paper of a blend of from 3 to 50 wt% of alkyl ketene dimer and from 97 to 50 wt% of an alkenyl cyclic anhydride.

4) A process to size paper and similar products comprising: - forming a cellulose water slurry; - preheating a blend of from 3 to 50 wt% alkyl ketene dimer and from 97 to 50 wt% of an alkyl or alkenyl cyclic anhydride either neat or in solution, and injecting the mixture in droplet form into said cellulose water slurry before, during or after the paper web formation; wherein the cellulose water slurry and/or the size is treated with a cationizing compound; - drying the paper web 5) A process according to claim 4 in which the blend is injected into a stream of preheated water which carries the size blend into the cellulose water slurry.

6) A process according to claim 5 in which the blend is heated to above the melting point of the alkyl ketene dimer, generally above 40'C.