The present invention relates to a process for making paper products in which sizing is effected by the use of a hydrophobic cellulose-reactive sizing agent in combination with a sizing promoter. Further the invention relates to a paper sizing composition for use in a process for making paper products, said composition comprising a hydrophobic cellulose-reactive sizing agent and a sizing promoter.

Hydrophobic cellulose-reactive sizes are widely used in the production of paper and carboard. Since they are insoluble in water they are employed in the form of an emulsion. Comparatively large amounts of cellulose-reactive sizing agents have to be used to obtain the desired sizing efficiency and liquid repellancy of the finished paper. However, high additions of hydrophobic cellulose-reactive sizing agents can cause a lot of different problems in a paper making process, e.g. deposits on wires and felts, high levels of hydrolised sizing agent, friction problems and problems with ink toner adhesion on copy paper. Therefore a reduction of the amount of hydrophobic cellulose-reactive sizing agent to be used to obtain the necessary degree of sizing would not only mean great savings in material costs but also overcome or at least considerably lessen the afore-mentioned problems. Further, in liquid/board applications, where smell and taste of the final board is of importance, unwanted substances coming from the size emulsion could be minimised.

In order to reduce the required amount of hydrophobic cellulose- reactive sizing agent it has been proposed in the prior art to

use water-soluble cationic polymers as promoters. However, these strongly cationic polymers have the disadvantage that they considerably impair the effectiveness of optical brightners used to improve the whiteness of the paper, resulting in increased consumption of optical brightners (for details compare German patent 39 20 356) .

It has now been surprisingly found that water-insoluble bases prepared from amines and fatty acids are useful promoters for hydrophobic cellulose-reactive sizing agents.

Thus the present invention relates to a process for making paper products in which sizing is effected by the use of a hydrophobic cellulose-reactive sizing agent in combination with a promoter, wherein the promoter is a water-insoluble base selected from the group consisting of the reaction products formed from the reaction of fatty acids selected from the group consisting of saturated fatty acids, unsaturated fatty acids, hydroxy sub¬ stituted fatty acids, and mixtures thereof and amines selected from the group consisting of alkanoldiamines and aliphatic polyamines.

Further the invention relates to a paper sizing composition for use in a process for making paper products, said composition comprising a hydrophobic cellulose-reactive sizing agent and a promoter, wherein the promoter is a water-insoluble base selected from the group consisting of the reaction products formed from the reaction of fatty acids selected from the group consisting of saturated fatty acids, unsaturated fatty acids, hydroxy substituted fatty acids, and mixtures thereof and amines selected from the group consisting of alkanoldiamines and aliphatic polyamines.

Preferred embodiments of the present invention will become apparent from the following description and the claims.

Hydrophobic cellulose-reactive sizing agents are well known in the art and e.g. disclosed in US patent No. 3 130 118, the disclosure of which is hereby incorporated by reference. Reference is also made to the definition of alkyl ketene dimers useful in paper sizing included in DE-AS 25 33 411 and DE-AS 23 35 756.

Suitable sizing agents for use in combination with the water- insoluble base promoter are selected from the group consisting of :

a) acid anhydrides of the formula:

where R ₂ and R ₃ are the same or different and each represent hydrocarbon radicals containing 7-30 carbon atoms;

b) cyclic dicarboxylic anhydrides of the formula:

O

II

where R ₄ contains 2 or 3 carbon atoms and R ₅ is a hydrocarbon radical having 7-30 atoms;

c) ketene dimers of the formula:

(R ₆ CH=C=0) ₂ where R ₆ is a hydorcarbon radical having 6-30 carbon atoms, preferably alkyl having 6-22 carbon atoms; and

d) isocyanates of the formula:

R ₇ -N=C=0

where R ₇ is a hydrocarbon radical having 7-30 carbon atoms.

A preferred embodiment of the acid anhydrides referred to in section a) is a stearyl anhydride, while a specific example of a suitable cyclic dicarboxylic anhydride from section b) is isooctadekenyl succinic anhydride. As to the ketene dimers of section c), cyclo alkyl and aryl radicals are also useful as said hydrocaron radical, although a saturated radical such as an alkyl radical is most preferred.

Of the above mentioned four groups a)-d) of cellulose-reactive agents, the cyclic dicarboxylic anhydrides of section b) and the ketene dimers of section c) are most preferred, the ketene dimers being especially preferred.

Preferably the hydrocarbon radicals R ₂ , R ₃ , R ₆ and R ₇ are satu¬ rated linear chain radicals which may, however, contain unsatu- rated and cyclic or aromatic substituents. R ₅ preferably is a saturated linear chain or branched alkyl radical. Further, R ₂ , R ₃ , R ₆ and R ₇ should preferably have 14-22 carbon atoms, and R ₅ should preferably have 14-30 carbon atoms. The hydrocarbon groups R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , and R ₇ in each of the above formulae may also be substituted, e.g. with halogen, for example chlorine, where a special effect is desired.

The water-insoluble base promoters useful in the present invention are reaction products formed from the reaction of fatty acids and amines. These compounds are known and often referred to as wax amines. Furthermore they have been proposed for paper sizing (compare DE-AS 1 012165, DE-AS 1 030 671, EP-A-0 005 201, EP-B-0 008 761, and US-A-5 393 334). However, these wax amines have never been proposed to be used in paper sizing in combina¬ tion with hydrophobic cellulose-reactive sizing agents, particu¬ larly alkyl ketene dimers (AKD) , alkenyl succinic acid anhydrides (ASA), and fatty isocyanates, which are the preferred sizing agents in the process and the composition according to the present invention.

Useful fatty acids to be reacted with amines for preparing the water-insoluble base promoters are in general fatty acids with a carbon chain length of of C ₆ to C ₂₂ . They can be unbranched or branched. Preferred are fatty acids with a carbon chain length of C ₁₂ to C ₁₈ . Examples of useful saturated fatty acids include myristic acid, palmitic acid and stearic acid. Examples of useful unsaturated fatty acids are oleic acid, linoleic acid, linolenic acid and eleostearic acid. A suitable hydroxy substituted fatty acid is ricinoleic acid. Of course, mixtures of fatty acids can be used.

Useful amines to be reacted with the fatty acids are alkanol diamines (diamine aliphatic alcohols) like aminoethylethanolami- ne, aminobutylethanolamine, aminopropylethanolamine and other alkyl substituted aminoethanolamines, and aliphatic polyamines like triethylenetetramine or diethylenetriamine.

The water-insoluble bases prepared from fatty acids and amines preferably have a melting point of below 100 °C.

Generally fatty acids and amines are reacted in amounts corre- sponding to molar ratios of 0.5:1 to 10:1, preferably 1:1 to 2:1.

The reaction of fatty acids and amines for forming the water- insoluble bases takes place at high temperatures, preferably about 200 °C, but lower temperatures down to 150 °C can also be used. Lower temperatures just require longer times to complete the reaction. The reaction product is then allowed to cool. If the obtained wax amine is a solid, then it is preferred to further process the solid product into a particulate form like flakes, prills, powder etc. for easy handling. With regard to further details of the preparation of the water-insoluble bases useful in the present invention reference is made to the above cited prior art documents from which suitable reaction conditions and further suitable reaction components can be gathered.

As the base promoters according to the present invention are water-insoluble they need to be emulsified or dispersed. The water-insoluble base and the hydrophobic cellulose-reactive size are both emulsified and added separately or as a combined product to the paper making process. In this context it is important to note that the emulsion or dispersion of the water-insoluble bases can be prepared without the use of surfactants which is a further advantage since surfactants often impair sizing efficiency and paper quality.

The weight ratio of hydrophobic cellulose-reactive sizing agent and water-insoluble base can vary within broad ranges like 1:100 to 100:1, preferably 30:100 to 100:30. Generally the hydrophobic cellulose-reactive sizing agent is used in an amount of up to 10 kg per tonne paper, preferably 0.2. to 5 kg per tonne paper and the water-insoluble base is used in an amount of up to 10 kg per tonne paper, preferably 0.2 5 to 2 kg per tonne paper.

In practising the present invention the water-insoluble base is dispersed or emulsified in water in amounts ranging from 5 to 15 % by weight, preferably 8 to 10% by weight. Acid like organic acids as acetic acid or formic acid is used as pH controlling agent. Optional ingredients of the aqueous dispersion or emulsion

of the water-insoluble base are thickening agents like derivati¬ ves of guar gum (anionic, non-ionic or cationic) or xanthan gums; viscosity controlling agents like sodium acetate or sodium chloride or other types of salts; antifoamers and preservatives. Of course, also other additives useful in paper making processes can be added provided they do not interfere with the hydrophobic cellulose-reactive sizing agent and the water-insoluble base and adversly affect the paper sizing efficiency of the combination of the present invention.

The present invention is particularly useful in the production of paper products comprising fillers such as chalk, precipitated calcium carbonate, clay, kaolin, talc and the like. The amount of filler used in paper may vary considerably, but in general does not exceed 30% by weight. For example, a fine paper usually contains 15 to 25% by weight filler.

The combination of hydrophobic cellulose-reactive sizing agent and water-insoluble base exhibits a considerable synergistic effect, i.e the paper sizing efficiency of the combination is considerably higher than the combined efficieny of the single components (see the Examples below). Accordingly the sizing efficiency of a predetermined dosage of a hydrophobic cellulose- reactive sizing agent is improved by the addition of base promoter. Alternatively a lower dosage of hydrophobic cellulose- reactive sizing agent is needed to reach the same sizing level. Further, the water-insoluble base promoters do not impair the effectiveness of optical brightners which is an important advantage over known water-soluble cationic promoters (see above) .

Example 1

Into a 5 1 neck round bottom flask (fitted with a Dean-Stark trap, condenser, temperature probe, mechanical stirrer and nitrogen sweep) was placed 2187 g (7.95 moles) of tallow fatty

acid mixture. The flask was then heated to 100 °C under a nitrogen atmosphere and the tallow fatty acid allowed to melt. To the hot melt was added 520.75 g (5.0 moles) aminoethylethano- lamine as rapidly as possible. The temperature of the melt rose to 130 °C as a result of the addition. The flask was then heated to 200 °C to 205 °C and held at that temperature until water evolution ceased. The total amount of water collected was 170 g. The pale yellow residual liquid product was then cooled to 125 °C and poured into large pyrex baking pans and allowed to cool to room temperature. The cream coloured waxy solid was then broken up and comminuted. The melting point was 58 to 60 °C.

40 g of the above prepared amine wax, 13.6 g acetic acid (98 %) and 266.4 g tap water were mixed and heated to 80-100 °C under stirring. The mixture was stirred for 30 minutes. Then the mixture was dispersed for 1 minute at 20 000 rp using an Ultra Turrax. After dispersion, 79.8 g of a 0.5 % water solution of cationic guar gum were added to the mixture as stabilizer. A small amount of a preservative was also added. The dispersion was quickly cooled to room temperature. The final pH was 3.5 and the final viscosity was 110 mPas.

Example 2

The pH of a bleached sulphate pulp of 50% pine and 50% birch was adjusted to about 8 and the concentration of the pulp was about 0.7 %. A two component system, Hydrocol from Allied Colloids (cationic polyacry1amide and bentonite) was used as a retention aid. Chalk from Faxe Chalk was used as filler and the ash content in the prepared paper sheets was about 15%. A conventional AKD based neutral size formulation was used as sizing agent. The emulsion of AKD prepared from a mixture of stearic acid and palmitic acid was obtained in the following manner:

56 g of cationic corn starch was added to 1438 g of water. The slurry was heat d to 95 °C and this temperature was maintained

for 30 minutes to cook the starch. 5.5 g of an emulsifier, namely a sulphonate containing polymer, and 500 g of AKD were added under stirring and the mixture was then passed through a high- pressure homogeniser (Rannie, Piston type) at a pressure of 120 bar. The homogenised premix was diluted with water to an AKD content of 20%. Small amounts of aluminium sulphate and a preservative were added to keep the formulation stable. A dilution of this AKD emulsion was used for preparing paper sheets.

The chemicals were added to the pulp as follows (concentrations relate to active ingredients) :

Time (seconds) Chemical

0 Chalk (ash content about 15%) 20 Emulsion of AKD (0.5-1.0 kg/tonne paper)

30 Cationic polyacrylamide, Hydrocol 852

(0.4 kg/tonne paper)

165 Bentonite, Hydrocol SH (2 kg/tonne paper)

180 The sheet was formed.

Hand sheets were formed in a Rapid Kδthen sheet former. The sheets were dried (90 °C, 5 min.) and cured (120 °C, 10 min). The

Cobb 60 values were measured. Cobb 60 relates to the amount of water taken up by a unit area of paper in one minute (method reference:SCAN-P 12:64). The lower the value, the better the sizing. The following results were obtained:

AKD Wax amine Cobb 60

(kg/tonne) (kg/tonne) (g/πt ² )

1 0 20.5

0.8 0 27.7

0.7 0 51.4

0.6 0 97.4 0.5 0 123.5

The same pulp system and the same chemicals were used except that

1.0 kg/tonne paper of the wax amine of Example 1 was also added to the pulp slurry.

Time (seconds) Chemical

0 Chalk (ash content about 15%)

10 Wax amine emulsion (1.0 kg/tonne paper)

20 Emulsion of AKD (0.5-1.0 kg/tonne paper)

30 Cationic polyacrylamide, Hydrocol 852 (0.4 kg/tonne paper)

165 Bentonite, Hydrocol SH (2 kg/tonne paper)

180 The sheet was formed

The following results were obtained:

AKD Wax amine Cobb 60

(kg/tonne) (kg/tonne) (g/m ² )

1 1 18.8

0.8 1 21.3

0.7 1 21.1

0.6 1 20.8

0.5 1 22.3

0.4 1 24.5

0.3 1 32.4

0.2 1 118.9

It can be seen that a dosage of 1.0 kg/tonne paper of wax amine will improve the efficiency of the AKD based size. A lower dosage of AKD is needed to reach the same sizing level.

Example 3:

To demonstrate the synergistic effect obtained by using the combination of hydrophobic cellulose-reactive sizing agent and water-insoluble base according to the invention the test described in Example 2 was repeated three times. In Test 1 no emulsion of AKD was added but the amount of wax amine was varied

between 0.5 and 1.0 kg/tonne paper. In Test 2 no wax amine was used and the dosage of the AKD emulsion was varied between 0.5 and 1.0 kg/tonne paper. In Test 3 the dosage of AKD emulsion was varied between 0.1 and 1.0 kg/tonne paper, while the dosage of wax amine was maintained constant at 1.0 kg/tonne paper. The wax amine was a commercial product available under the trade name Reactopaque R 100. The results of all three tests are summarized in Fig. 1.

As can be seen from the test results the wax amine does not provide any sizing when used alone (Test 1). The AKD emulsion results in sizing as expected (Test 2). The combination of AKD emulsion and wax amine provides a clear synergistic effect as demonstrated by the results of Test 3.

Example 4

In this example the impact of the promotor according to the invention on the whiteness of the paper was investigated. The optical brightening agent (OBA) used was Tinopal ABP (tetrasulp- hur compound; typically 20% active material), manufactured by Ciba.

Sizing tests as described in Example 2 were performed in which only AKD, AKD + 1 kg water-insoluble base or AKD + 1 kg traditio¬ nal water-soluble promoter was used. The water-insoluble base and its emulsion was prepared as described in Example 1. The water- soluble traditional promoter was a cationic nitrogen containing polymer which is made from dicyanodiamide and formaldehyde.

The chemicals were added to the pulp as follows (concentrations relate to active ingredients, if not stated otherwise):

Time (seconds) Chemical

0 Chalk (ash content about 15%)

10 OBA, Tinopal ABP (10 kg commercial product/tonne paper) 20 Nothing/water-insoluble promoter/water- soluble promoter (1 kg/tonne paper)

30 Emulsion of AKD (0,2 - 1,2 kg/tonne paper)

40 Cationic polyacrylamide, Hydrocol 852 (0,4 kg/tonne paper)

165 Bentonite, Hydrocol SH (2 kg/tonne pulp)

180 The sheet was formed.

The results are summarized in Fig. 2. The effect of the use of water-insoluble base is as already demonstrated in the above examples, i.e. the dosage of AKD can be reduced to about half when 1 kg/tonne water-insoluble base is added. In contrast the traditional water-soluble promoter (1 kg/tonne paper) resulted in Cobb ₆₀ values which were about the same as those for AKD alone at full curing.

The whiteness index was measured on the sheets prepared using a spectracolourimeter, X-Rite 948 (lamp: D65, angle: 10°). The results are shown in Fig. 3 and demonstrate that the whiteness index is strongly influenced by the traditional water-soluble promoter. In contrast the water-insoluble promotor according to the invention did not seem to influence the whiteness index to any considerable extent.

Example 5:

Similar tests as described in Example 3 were performed but instead of AKD an alkenyl succinic acid anhydride (ASA) was used. In Test 4 no ASA was added but the amount of wax amine was varied between 0.6 and 1.2 kg/tonne paper. In Test 5 no wax amine was used and the dosage of ASA was varied between 0.6 and 1.2

kg/tonne paper. In Test 6 the dosage of ASA was varied between 0.6 and 1.2 kg/tonne paper, while the dosage of wax amine was maintained constant at 1.0 kg/tonne paper. The wax amine was that of Example 1. The results of all three tests are summarized in Fig. 4.

It is obvious that the results were similar as in Example 3.