ROSIN EMULSIONS

Abstract: Aqueous rosin dispersion paper sizing compositions containing an ammonium salt or a precursor thereof, such as urea, a chemically-modified urea or a precursor of the latter.

Description: This invention relates to paper sizing compositions, methods for making such compositions, processes for sizing paper products using these compositions and products which have been sized with the compositions. More particularly, this invention relates to aqueous paper sizing compositions, methods for their manufacture, processes for their use and sized products made by use of the compositions, the compositions being in the form of rosin dispersions. Rosin comprises a complex mixture of cyclic terpene carboxylic acids and is relatively insoluble in water. In order to be usable in the form of aqueous sizing compositions, rosin must either be taken into solution (as a rosin soap) or dispersed as fine droplets in water (as a rosin dispersion). Rosin soap solutions comprise systems in which the rosin acid functionality has been almost completely neutralised with a base, which enables the insoluble rosin acids to be taken into solution. In practice, the degree of neutralisation employed is usually of the order of 90% of the available acidity, the unsaponified acid components remaining and any neutral components present in the rosin being held in the soap structure. Rosin dispersions comprise fine particles of rosin and also include a stabiliser which acts to prevent destabilisation of the dispersion. The stabiliser is commonly a surface-active agent (which may be a soap, in particular a rosin soap, a protective colloid or a mixture of the two). Where a rosin soap is employed, the dispersion may be formed by neutralising from about 1% to about 10% of the total rosin acids present. It has been now been found that rosin dispersions which have not been reported previously nor, it is believed, even formed can be made and are very suitable for use as paper sizing compositions. The ability of urea and various chemically-modified derivatives of urea to act as precursors for ammonia or ammonium salts or to serve as useful ingredients in conjunction with ammonia and ammonium salts in rosin soap sizing compositions has been described in the art. For example, US-A-4022634 and US-A-4093779 describe sizing compositions comprising a rosin soap and a reaction product of urea with an acid selected from sulphamic acid, phosphoric acid, trichloracetic acid, nitric acid, sulphuric acid, hydrochloric acid, stearic acid and acetic acid. US-A-4141750 describes similar compositions, in which urea has been reacted with a Lewis acid, such as paratoluene-sulphonic acid. US-A-4025354 describes sizing compositions which comprise a rosin soap and a chemically-modified urea, the preferred form of which is the product obtained by reacting urea with sulphamic acid. US-A-4437894 describes sizing compositions which comprise a rosin soap and the product obtained by reacting urea with formic acid. US-A-4605445 describes sizing compositions which comprise rosin, a soap and urea. It has been discovered that the addition of chemically modified urea (or a precursor thereof) to rosin dispersion sizing compositions is advantageous. In particular it has not only been found that the addition of these compounds is beneficial because they exhibit a degree of sizing activity when present in such dispersion sizing systems, but also because, surprisingly, the dispersions are stabilised by their addition rather than being destabilised as might have been expected. According to one aspect of the invention, therefore, a paper sizing composition which comprises an aqueous rosin dispersion is provided and is characterised in that it also contains a chemically modified urea. Rosin is a solid resinous material which occurs naturally in the oleoresin of pine trees. It is obtained from one of three main sources, namely the oleoresin exudate of living pine trees, the oleoresin contained in the aged stumps of pine trees and from the tall oil produced as a by-product in the kraft paper industry. In addition to cyclic terpene carboxylic acids, rosin also includes a small amount of non-acidic components. A major constituent of rosin is abietic acid, which is a tricyclic doubly-unsaturated mono-carboxylic acid. Abietic acid undergoes Diels-Alder addition reactions with dienophiles. Rosin may therefore be reacted with dienophilic carboxylic acids and their derivatives, such as maleic acid, maleic anhydride and fumaric acid, and so forms tetracyclic polycarboxylic acids. This reaction between rosin and dienophiles is commonly termed "fortification" and the reaction product is commonly termed a "fortified" rosin. Fortified rosin dispersions are used as sizing compositions in the paper sizing industry. Rosin dispersions according to the present invention may be based either upon rosin or a fortified rosin or a mixture of the two. It is also possible to employ fortified rosins which have been treated with formaldehyde in order to enhance their stability. Esterified or disproportionated rosins may also be used in the compositions of this invention. Esterified rosins are rosins which have been reacted with an alcohol, preferably a polyol such as glycerol. Disproportionated rosins are rosins which have been treated by a catalytic process in order to improve their stability to oxidation. Mixtures of any of these types of rosin may be used in the compositions of this invention. The preferred rosin for use in the composition of this invention are fortified rosins. The preferred fortified rosins are those wherein the rosin has been reacted with an amount of a dienophile in the range from 5% to 50% by weight and generally about 10% by weight of the weight of the rosin. The most preferred type of rosin is fortified tall oil rosin. The rosin dispersions according to the invention preferably comprise from 2.5% to 8.0% by weight of a soap, which is preferably a rosin acid soap, based upon the total weight of solids in the dispersion. The rosin acid soap may be prepared by saponification of a rosin acid or a fortified rosin acid with an organic or an inorganic base. Alternatively, the soap may be formed in situ by the neutralisation of a part of the total acidity of the rosin, again using either an organic or an inorganic base. Preferably, such procedures involve the neutralisation of an amount in the range from 1% to 10% and, more preferably from 3% to 6%, of the total acidity of the rosin acids. The rosin dispersions may be formulated using any of the conventional techniques and ingredients known in the art. In particular, the dispersions may comprise one or more stabilisers in addition to the urea derivative or precursor thereof. A variety of surface-active agents or emulsifiers may be used to stabilise the dispersions, either in admixture with one another or with other known emulsifying agents or in conjunction with other known auxiliary stabilising agents. A preferred class of auxiliary stabilising agents are the protective colloids, such as casein, and compositions comprising rosin, ammonia or an ammonium salt or precursor thereof, a stabiliser and a protective colloid form a preferred aspect of this invention. Anionic, nonionic, cationic or amphoteric surfactants may be utilised as stabilisers in the dispersions of this invention. In general, anionic or nonionic surfactants are preferred. Examples of surface-active agents or surfactants which find use in the compositions of this invention include: (i) salt of sulphonic acids having the general formula: where R' represents a hydrocarbon residue having from 4-18 carbon atoms, m is an integer having a value of 1 or 2, n is an integer having a value of 4 to 25, X represents a hydrogen atom or a hydroxyl group and M represents a monovalent cation; (ii) salts of sulphuric acid half esters having the general formula: wherein R² represents a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms, A represents a straight-chain or branch-chain alkylene group having 2 or 3 carbon atoms, p is an integer having a value of from 4 to 25 and Q is a monovalent cation, including all such compounds described in US-A-4309338; (iii) alkyl-benzene sulphonates wherein the alkyl substituent comprises from 8 to 24 carbon atoms, including all such compounds described in US-A-4157982; (iv) sulphosuccinate half esters of fortified rosin having the formula: wherein R is a fortified rosin acid tricarboxylate group, m has an average value of from 1.5 to 3 and n has an average value from 4.5 to 25, including all such compounds described in EP-A-159794; (v) compounds having one or other of the formulae: wherein R represents an alkyl group containing from 4 to 18 carbon atoms, R' represents an alkyl or alkenyl group containing from 4 to 18 carbon atoms and n is an integer having a value from 4 to 25, including all those described in US-A-4199369; (vi) sulphosuccinate salts of ethylene oxide condensates having the general formula: wherein R represents an alkyl group containing from 4 to 18 carbon atoms and n is an integer having a value of from 4 to 25, including all those compounds described in US-A-4203776. (vii) organic phosphate enters having one or other of the general formulae: and mixtures thereof, wherein R represents an alkyl, alkyl-phenol, alkenyl or alkaryl group containing form 5 to 20 carbon atoms, n has a value of from 5 to 20 and X represents a monovalent inorganic or organic cation or hydrogen. Cationic resin dispersant systems may also be used to stabilise the rosin dispersions of this invention. Examples of suitable materials include water-soluble polyaminopolyamide/epichlorohydrin resins, water-soluble alkylenepolyamine/epichlorohydrin resins and poly(diallylamine)/ephichlorohydrin resins. Examples of compounds which are especially useful in the compositions of this invention include thiourea, biuret, melamine, water-soluble urea/formaldehyde and melamine/formaldehyde resins and acid and Lewis acid derivatives of urea, especially those reaction products obtained by reacting urea with an acid selected from sulphamic acid, phosphoric acid, trichloroacetic acid, nitric acid, sulphuric acid, hydrochloric acid, stearic acid and acetic acid, as described in US-A-4022634 and US-A-4093779, the reaction products of urea with a Lewis acid, such as a p-toluene sulphonic acid, as described in US-A-4141750, the reaction products of urea and sulphamic acid, as described in US-A-4025354 and the products obtained by the reaction of urea and formic acid, as described in US-A-4437894. The preferred sources of ammonia or ammonium salt for use in the compositions of the present invention are the products obtained by the reaction of urea with sulphamic acid, including all those products which are described in US-A-4025354. These modified ureas may be produced by combining urea with sulphamic acid and water. Ideally, the parts by weight of water equal the parts by weight of urea plus sulphamic acid, although the urea may be treated with the sulphamic acid in conjunction with more water or with little or no water. The urea-sulphamic acid solution may be heated to a temperature which causes a change in the pH, for example a rise in the pH at least to about 7.5. When little or no water is used, the temperature affecting the pH may be higher. In one preferred embodiment, however, a 50% water-50% urea/sulphamic acid solution is used, and it has been found that a temperature of about 212° to 235°F, (100°-113°C) preferably about 215° to 230°F, increases the pH at least up to about 7.9. Generally, the solution boils at the temperature which changes the pH and heating should be continued until after boiling has stopped in order to effect an irreversible pH change. Although the pH range is an important measurement of reaction completion, a more important consideration is the acidity of the first stage product measured as parts of water (ppm). When the sulphamic acid is heated with the urea, undetermined reactions occur which not only raise the pH to a basic value, but also effect the acidity of the solution. The desired minimum acidity is at least 1,000 ppm, with a preferred minimum of 4,300 ppm. The actual amount of sulphamic acid most desirably employed is probably at least 0.1% by weight of the urea, with preferred amounts ranging from 0.2% to 8.0%, by weight. The maximum amount of sulphamic acid needed is generally 15% or, at most, 20% by weight of the urea, to achieve the desired results. It has been found that 5% sulphamic acid produces an acidity of about 86,000 ppm with a pH in the range from 7.9 to 8.3, when processed in a 50% water/50% urea plus sulphamic acid solution. Accordingly, sulphamic acid at 0.25% by weight of urea produces a first stage product with an acidity of 4,300 ppm. As indicated, the amount of sulphamic acid added to the solution is not as important as its resulting acidity in defining the first stage product of the size compositions of this embodiment. The proportion of urea derivative to rosin or fortified rosin is desirably in the range from 5% to 60% and preferably from 10% to 35% by weight. The dispersions of the invention will normally be formulated as relatively concentrated compositions, which are either diluted prior to their use in a sizing process or can be added in a concentrated form depending upon the conditions. In general, the dispersions advantageously comprise concentrates which contain from 20% to 60% and more desirably and usually from 30% to 45% by weight of the combined weight of the rosin and the urea derivative. The compositions of the invention may be employed as internal sizes or as surface sizes. Their use as an internal size forms a preferred aspect of the present invention. Internal sizing processes comprise the dilution of the concentrated composition with water and the addition of the diluted composition to a pulp suspension. A flocculant such as, preferably, papermakers alum, aluminium sulphate or polyaluminium chloride may be added to the pulp suspension prior to, simultaneously with or subsequent to the size composition. The amount of size composition employed is generally in the range from 0.1% to 5.0% by weight of solids based on the weight of fibres in the pulp slurry. The compositions of the present invention may be prepared using the phase inversion process. The rosin, preferably a fortified rosin, optionally treated with paraformaldehyde in the presence of paratoluene-sulphonic acid to inhibit crystallisation, and optionally one which has been at least partially saponified with concentrated sodium or potassium hydroxide or with a volatile base such as ammonia, may be melted and the stabilising agent or mixture of stabilising agents may then be added as a concentrated (e.g. 50% by weight solids) aqueous solution. Sufficient water is stirred in to form a creamy water-in-oil emulsion (e.g. 20% to 40% based on the weight of rosin). On dilution with water, the emulsion inverts to provide a stable oil-in-water emulsion, typically having a solids content in the range from 20% by weight up to the maximum achievable oil-in-water concentration (often about 80% by weight solids) and preferably from 30% to 50% by weight solids. The rosin content of the emulsion or dispersion usually includes at least 90% of unsaponified rosin acids. The emulsions may then be blended with an aqueous solution of a urea derivative or a precursor thereof. The emulsions may be used for sizing paper, including alumed paper. The emulsions may contain at least one biocide, such as bactericides, slimicides and/or fungicides, and/or diluents, such as wax. The invention is illustrated by the following non-limitative Examples: Example 1 grm Tall oil rosin treated with fumaric acid 350 Caustic potash 3.5 Casein 17 Sodium tetraborate 4 The fortified rosin at 160°C was cooled to 100°C and the caustic potash was added in a minimum of water. A concentrated solution of the casein and borax was added and the mass immediately inverted. This was mixed for 5 minutes and diluted with water to a solids content of 50% by weight. The final product was mixed with modified urea solution prepared by heating a solution of urea and sulphamic acid to its boiling point and cooling the product. The rosin emulsion and modified urea solution were mixed in such a proportion that 25% of fortified rosin had been replaced by the modified urea. Example 2 Laboratory handsheets were prepared from bleached sulphite pulp beaten to a Schopper-Reigler value of 40 at 2% consistency. The pulp was treated with known quantities of the preferred size or a known industry standard dispersion size (ROSCOL A & W LTD.) and a standard level of aluminium sulphate, the pH was adjusted to 4.9-5.0 and sheets were made on a standard sheet former, pressed and dried by passing around a photographic drier set at 100°C. After conditioning overnight, the sheets were tested for sizing by the Cobb test. As the figures for Cobb value are grams of water picked up per square metre of sheet under the test conditions, a lower value represents improved sizing. The following results were obtained: The extended product shows an improved sizing performance although the level of active content (rosin) is lower than the standard. Example 3 Stability of the rosin dispersions was tested by an accelerated sedimentation test, which subjects the product to high gravitational force for a set time and measures the extent of deposition. This is a test which has long been used and correlates well with storage under normal conditions. The extent of sedimentation reflects the extent of deposition likely to occur if the emulsion is stored normally for three months.

Claims: A paper sizing composition Comprising an aqueous rosin dispersion wherein the rosin includes at least 90% of unsaponified rosin, characterized in that the composition also contains a chemically modified urea. A composition according to claim 1, wherein the chemically modified urea is thiourea, biuret, melamine, a water soluble urea/formaldehyde or melamine/formaldehyde resin or a urea derivative obtained by reacting urea with an acid or Lewis acid. A composition according to claim 2, wherein the chemically modified urea is a reaction product of urea and sulphamic acid. A composition according to claim 3, wherein the reaction product is made by heating urea and sulphamic acid to a temperature at which a change in pH occurs. A composition according to any of claims 1 to 4, wherein the proportion of chemically modified urea to rosin in the aqueous dispersion is in the range from 5% to 60% by weight. A composition according to claim 5, wherein the proportion is in the range from 10% to 35% by weight. A composition according to any of the preceding claims, wherein the rosin comprises fortified rosin, formaldehyde-treated rosin, esterified rosin, disproportionated rosin or a mixture of one or more thereof. A composition according to claim 7, wherein the dispersion comprises a fortified rosin in which the rosin has been reacted with an amount of dienophile in the range from 5% to 50% by weight of the weight of the rosin. A composition according to any of the preceding claims, wherein an amount in the range from 2.5% to 8% by weight of rosin acid soap, based upon the total weight of solids in the dispersion, is present. A composition according to any of the preceding claims, wherein casein is included as a stabiliser. A composition according to any of the preceding claims, which is in the form of a concentrate suitable for dilution prior to use and containing 20% to 60% by weight of rosin and chemically modified urea. A composition according to claim 11, which contains 30% to 50% by weight of rosin and chemically modified urea. A method of making a paper sizing composition which comprises preparing an aqueous dispersion of rosin by melting the rosin, the rosin including at least 90% of unsaponified rosin, adding at least one stabiliser, agitating the mixture in the presence of an amount of water suitable for the formation of a water-in-oil emulsion, diluting the emulsion with water to cause it to invert to a stable oil-in-water dispersion and blending the dispersion with a chemically modified urea. A method according to claim 13, wherein the chemically modified urea that is blended with the dispersion is thiourea, biuret, melamine, water-soluble urea/formaldehyde and melamine/formaldehyde resins and urea derivatives obtained by reacting urea with an acid or Lewis acid. A method according to claim 14, wherein the chemically modified urea comprises the reaction product of urea and sulphamic acid. A method according to any of claims 13 to 15, wherein the proportion of chemically modified urea to rosin in the aqueous dispersion is in the range from 5% to 60% by weight. A method according to any of claims 13 to 16, wherein the rosin comprises fortified rosin, formaldehyde-treated rosin, esterified rosin, disproportionated rosin or a mixture of one or more thereof. A method according to claim 17, wherein the dispersion comprises a fortified rosin in which the rosin has been reacted with an amount of dienophile in the range from 5% to 50% by weight of the weight of the rosin. A process for the manufacture of a sized paper product, wherein a paper sizing composition is employed as a surface size or is added as an internal size to a pulp suspension, if required after dilution with water, a flocculant is added to the pulp suspension before, during or after addition of the sizing composition and a paper product is made therefrom, the paper sizing composition being a composition as defined in any of claims 1 to 10 or made by a method according to any of claims 11 to 14. A process according to claim 19, wherein the sizing composition is employed as an internal size in the range from 0.1% to 5.0% by weight of solids based upon the weight of fibres in the pulp.

Inventors: BRITTON, ROBERT JOHN, BUSSELL, WILLIAM ROBERT, HISKENS, IAN RICHARD, MORGAN, NICHOLAS STUART
Applicants: EKA NOBEL AB
Application year: 1988
Main classification: D21H17
IPC codes: D21H17