WO2002081587A1

WO2002081587A1 - Sizing dispersion for improving hydrophobicity

Info

Publication number: WO2002081587A1
Application number: PCT/FI2002/000237
Authority: WO
Inventors: Ari Juppo; Lars Petander
Original assignee: Kemira Chemicals Oy
Priority date: 2001-03-22
Filing date: 2002-03-21
Publication date: 2002-10-17
Also published as: FI20010588A0; FI20010588A; FI117718B

Abstract

The invention relates to a sizing dispersion, containing a sizing agent and a non-ionic surface active monoester of glycerol with a fatty acid, the amount of the monoester being between 0.1 and 25% by weight relative to the amount of the sizing agent. The sizing dispersion may be used in the production of paper or board to improve the hydrophobicity thereof.

Description

Sizing dispersion for improving hydrophobicity

The invention relates to improving the water repellency or hydrophobicity of paper and board using a sizing dispersion containing a sizing agent and an agent improving the distribution of the sizing agent on surfaces of fibres.

As is known, cellulose reactive sizing agents such as alkenyl succinic anhydride (ASA) or alkyl ketene dimer (AKD) are used as sizes in the production of paper under neutral conditions. The sizing chemical is normally added as a dispersion consisting of very small particles during the production of paper and board. The hydrophobicity of the paper produced substantially; _^depends on the retentive power of the fibre surface, the spreading or distribution of the sizes on the fibre surface, and the attachment of the sizes to active sites thereon.

One of the problems is the poor distribution of the size on the fibre surface. Surface reactions proceed only partly and the hydrophobicity of the surface formed is only weak. Further, it is often necessary to carry out aging of the sized surface to make the sizing effective. This prevents the on-machine sizing.

The alkyl ketene dimer (AKD) or alkenyl ketene dimer may preferably be represented by formula (I) wherein Rl and R2 stand for optionally saturated or unsaturated, straight or branched chain hydrocarbon groups having 8 - 36 carbon atoms. Commonly used hydrocarbon groups include molecules having 14 - 18 carbon atoms.

R1 - CH = C - CH - R2

I I (i) o - c = o

As for the particle size of AKD dispersions, mean particle sizes of below 1 μm are generally desired, and thus the dispersions are commonly produced by using high pressure homogenizers in plants specialized in such production. While AKD is reactive and decomposes in aqueous solution to form a ketone, the reaction is slow especially at low pH- values, such as below 4,5 and therefore, AKD dispersions may be supplied to the customer as ready-to-use products.

The reason for forming small particles is not only the wish to obtain a dispersion that is as stable and non-separating as possible, but also the fact that with small particles, the spreading of the active agent in the pulp and on the surface of the fibre material may be enhanced. Spreading is a substantial part of the mechanism for endowing the paper with high water repellency by using AKD. It is shown that about 15% coverage of the fibre surface by AKD is sufficient for achieving almost complete sizing. The degree of sizing, the hydrophobicity, may be expressed for instance as Cobb-values determined according to SCAN-P 12:76 instructions.

The spreading of alkyl ketene dimer in the paper may be visualized with several methods such as atomic force microscopy (AFM), electron spectroscopy for chemical analysis (ESCA), ellipsometrically, and with breath pattern techniques.

At present in the production of AKD dispersions, the emulsifiability may be improved with various anionic and/or cationic surface active agents such as lignosulphonates and sodium salts of napatalene sulphonates, and fatty amine chloride, all of them being physically stable and usable for several weeks. It is further possible to stabilize AKD dispersions for instance by using starch and/or derivatives thereof and optionally polymers such as polyethylene irnine, polyepiamine, polydimethyl diallyl or dicyandiamide compounds, polyacrylic amide or acid in association with starch or separately. As is generally known, the amount of the stabilizing chemicals is between 1 and 200% by weight, relative to the amount of AKD. The use of polymers not only improves the stability of sizing dispersions, but also influences the performance thereof in paper or board.

As is known, surface active agents are used to reduce the surface tension between oil and water. The properties of non-ionic surface active agents are often illustrated with the hydrophile - lipophile balance (HLB value) thereof. Surface active agents having a low HLB value are lipophilic, whereas those having a high HLB value are hydrophilic. With this value, various surface active agents may be classified as suitable for different applications. Surface active agents having a HLB value between 4 and 6 may be used to emulsify water in oils. Those having a HLB value between 7 and 9 are suitable as wetting agents, that is, they contribute to the spreading of water on surfaces. Those surface active agents having a HLB value between 8 andi.8 are generally useful to emulsify oily substances in water. For instance surface active agents having a HLB value between 13 and 15 are suitable as detergents.

As is known, the spreading of sizing agents on fibre surfaces is accelerated by the low melting point of the size and high storage temperature of the sized paper. Publication JP-57112498 A provides a sizing dispersion containing a ketene dimer and di- and/or trigryceride. The glyceride is preferably a triglyceride of a saturated 16-18C fatty acid, the amount thereof being preferably from 10 to 50% of the amount of the ketene dimer. The publication teaches that a sizing effect is attained in a short period of time by using this sizing dispersion.

Patent EP 580 405 of Hercules aims at improving the resistance to hot hydrogen peroxide of liquid packaging board, and particularly the permeability of cut edges by using a sizing mixture consisting of cellulose reactive size e.g. AKD, cellulose non-reactive size e.g. bistearin amide or fatty acid ester having a melting point of above 70 °C, and a thermosetting resin, for instance a reaction product of epichlorohydrin and polyamino amide or polyalkyl amine, in the sizing of board. Triglyceryl ester, a very hydrophobic waxy compound found naturally in fats, is preferably used as the fatty acid ester.

Now it has been surprisingly found that particularly the spreading of the sizing agent on fibre surfaces may be improved by using a sizing agent in combination with a relative low amount of a monoester of glycerol with a fatty acid, this compund acting as a promoter of the sizing performance of the size.

According to the invention, there is provided a sizing dispersion containing a sizing agent and a non-ionic surface active monoester of glycerol with a fatty acid, the amount of the monoester being between 0.1 and 25% by weight relative to the amount of the sizing agent.

Monoesters of glycerol with a fatty acid having one fatty acid molecule esterified with one glycerol molecule belong to a group having a HLB value below 6. The HLB value of laurin or 1-lauroyl glycerol or glyceryl monolaurate (GML) is 4.9, the HLB value of glyceryl monooleate is 3.3 and that of glyceryl monostearate is 3.4.

In monoesters of glycerol with a fatty acid used according to the invention, the individual fatty acid moiety may be a saturated or unsaturated moiety preferably containing 10 to 20 carbon atoms.

Examples of preferable monoesters of glycerol with a fatty acid having a HLB value below 6 include glyceryl monolaurate, glyceryl monopalmitate, glyceryl monostearate, and glyceryl monooleate. Also mixtures thereof are useful.

The amount of said monoesters of glycerol with a fatty acid in the sizing dispersion is preferably between 1 and 5% relative to the amount of the sizing agent. In the sizing dispersion of the invention, the sizing agent used may be any cellulose reactive sizing agent mentioned above in the description. Alkyl ketene dimers (AKD) are preferable. Total numer of the carbon atoms in AKD is preferably 20 to 44. In a particularly preferable AKD, the alkyl groups are from paltimic acid or stearic acid or mixtures thereof.

The sizing dispersion of the invention preferably contains 0.1 to 20% by weight, particularly preferably 1 to 5% by weight of a sizing agent, preferably AKD as mentioned above.

Moreover, the sizing dispersion of the invention may contain one or several of the following constituents:

starch based agents, synthetic polymers, anionic surface active agents, such as alkyl sulphonates, naphtalene sulphonates or formaldehyde condensation products thereof, or lignosulphonates, cationic surface active agents such as primary, secondary, tertiary, or quaternary fatty amines. Cationic surface active agents may be mono-, di-, or triamines, or various combinations thereof.

According to the present invention, there is also provided a process for producing above sizing dispersions by mixing a monoester of glycerol with a fatty acid to the other constituents of the sizing dispersion. In a preferable procedure, said monoester is first mixed to an oily sizing agent followed by the addition of the other constituents of the dispersion. Said monoester may also be mixed to the aqueous phase followed by the addition of the other constituents of the dispersion. It is also possible to mix said monoester to a final sizing dispersion.

The production of the sizing dispersion comprises the dispersion and stabilizing of the sizing agent in water using suitable constituents as mentioned above. The dispersion may be produced with a high pressure homogenizer, such as Rannie, or a rotor-stator dispersing apparatus, such as Ultraturrax. The dispersing technique is known as such. The nature and technique of the production have no substantial effect on the performance of the sizing dispersion.

According to the present invention, there is also provided a method for producing sized paper or board, comprising the addition of the sizing dispersion described above to the pulp for paper or board, preferably to the stock during the production of paper or board. In the paper or board machine, the sizing dispersion may be metered either directly or in a prediluted form to the circulating water.

According to the invention, the sizing dispersion is preferably added to the fibre mass in an amount corresponding to a sizing agent concentration of 0.01 - 0.4% by weight relative to the dry matter of the mass.

According to the invention, one or more promoters of the sizing such as highly cationic fragmented starch with an electric charge of 1 to 2 meq/g and having a viscosity of 2500 to 5000 mPas as a 30% aqueous solution, chitosan, cationic polymers, for instance polyethylene imine, polyepiamine, polyvinyl amine, polydimethyl diallyl or dicyandiamide compounds, or polyacryl amide or anionic polyacrylic acid or salts thereof, or aluminium compounds, for instance polyaluminium chloride, sulphate or nitrate or alum may be used. Said compounds may be incorporated into the sizing dispersion or separately dosed to the stock.

With the dispersion of the invention, chemicals normally added to the mass in the production of paper and board, such as retention aids, optical brighteners, dyes and antifoam agents may be used.

Retention aids may for instance include cationic polymers and starch, as well as bentonite, and silica and aluminium based sols used in combination therewith.

The performance of the invention is neither influenced by the other chemicals such as starch or calcium carbonate used in the production, nor by the order of addition thereof in the paper machine, the nature of the mass, or other operation parameters of me machine.

As already stated above, the sizing dispersion of the invention is used in the production of paper and board to improve the hydrophobicity thereof.

Still another object of the invention is the use of the monoester of glycerol with a fatty acid described above in the production of paper and board to enhance the spreading of the size on the fibre surfaces. In this case, said monoester of glycerol with a fatty acid may be incorporated into the sizing dispersion described above.

The advantage of the invention is the improved spreading of the size on a hydrophilic surface such as on the fibre surface or silica surface serving as a model agent. Due to this improved spreading, the paper or board produced from this fibre mass has a superior water repellency. The invention is now illustrated with the following examples.

Example 1

The spreading of alkyl ketene dimer (AKD) size was monitored with the breath pattern technique shown to be a suitable method. The AKD used was produced from a mixture of palmitic and stearic acids in a ratio of 1 : 1.

In the method used, an AKD droplet having a diameter of about 1 mm was placed on the surface to be tested, such as a silica surface. The sample was placed in a chamber with an atmosphere having a relative humidity adjusted to 50%. The temperature was elevated to 50 °C for 48 hours. The extent of the spreading is determined by wetting the tested surface with water vapour and measuring the non- wetted area. Then, the area of spreading is obtained by subtracting the initial droplet area from this non-wetted area. To the melted AKD, glycerides shown in Table 1 were added in an amount of 20% of the weight of the mixture.

Table 1

Sizing mixtures used

As may seen from Table 1, the spreading may be improved by adding a glycerol monoester to the sizing agent compared to the sizing agent alone or to a sizing agent with added diester.

Example 2

An alkyl ketene dimer having a melting range of 45 to 50 °C, was melted at 60 °C and glyceryl monolaurate was added thereto (Grindtek ML90, Grindsted Products). AKD without the glyceryl ester was used as the control.

AKD rnixtures were dispersed into cooked starch cationized with quaternary nitrogen, and having a nitrogen content of 0.35% by weight, using a high pressure homogenizer (Rannie). The AKD and starch contents of the dispersion were respectively 1% and 1.5%.

Mean particle size was measured with an instrument based on laser diffraction, Coulter LS 120.

The composition of the mass used was as follows: 40% of chemical pulp from birch, 40%) of chemical pulp from pine and 20% of calcium carbonate as a filler, and further, 5 kg/ton of mass starch. The amount of AKD was 1 kg/ton. Test sheets having a grammage of 80 g/m2 were prepared from the mass according to Scan-C 26:76 -instructions. Cobb 60 values of the sheets were determined after ageing at 105 °C for 10 minutes. The Cobb values obtained are presented in Table 2.

Table 2

As seen from Table 2, higher glyceryl monolaurate addition improved the Cobb 60 value, reducing the particle size at the same time.

Example 3

Glyceryl monolaurate (Grindtek ML90) was added into a cooked starch solution. AKD having a melting range of 45 to 50 °C was dispersed therein according to Example 2. Cobb 60 values of the sheets were determined after ageing at 105 °C for 10 minutes. The Cobb values thus obtained are presented in Table 3.

Table 3

While in the arrangement of the invention the particle size increases with a high glyceryl monolaurate amomit, sizing performance is however improved with respect to the control.

Example 4

Glyceryl monooleate (Capmul GMO-K, Karlshamn) was mixed into the melted AKD followed by the dispersion thereof to the starch solution as described in Example 2. Test sheets were made as described in Example 2. The results obtained are presented in Table 4.

Table 4

The results show that also a glycerol monoester obtained from a fatty acid with 18 carbon atoms improves the sizing power of AKD.

Claims

1. Sizing dispersion, characterized in that it contains a sizing agent and a non- ionic surface active monoester of glycerol with a fatty acid, the amount of the monoester being between 0.1 and 25% by weight relative to the amount of the sizing agent.

2. Sizing dispersion of Claim 1, characterized in that said monoester of glycerol with a fatty acid has a HLB value below 6.

3. Sizing dispersion of Claim 1 or 2, characterized in that the amount of said monoester of glycerol with a fatty acid is between 1 and 5% by weight relative to the amount of the sizing agent.

4. Sizing dispersion of any of the above Claims, characterized in that the individual fatty acid moiety of said monoester is a saturated or unsaturated moiety containing 10 to 20 carbon atoms.

5. Sizing dispersion of any of the above Claims, characterized in that said monoester is a glyceryl monolaurate, glyceryl monopalmitate, glyceryl monostearate, or glyceryl monooleate.

6. Sizing dispersion of any of the above Claims, characterized in that said sizing agent is an alkyl ketene dimer.

7. Sizing dispersion of Claim 6, characterized in that the alkyl groups of said alkyl ketene dimer are from palmitic or stearic acid or a mixture thereof.

8. Sizing dispersion of any of the above Claims, characterized in that it contains 0.1 to 20%) by weight, preferably 1 to 5% by weight of said sizing agent.

9. Sizing dispersion of any of the above Claims, characterized in that it further contains a starch based substance and/or a synthetic polymer.

10. Process for producing the sizing dispersion of any of the Claims 1 to 9, characterized in that a monoester of glycerol with a fatty acid is mixed to the other constituents of the sizing dispersion such as to an oily sizing ingredient, or to water phase.

11. Process of Claim 10, characterized in that said monoester is first mixed to the sizing agent, followed by the addition of the other constituents of the dispersion.

12. Method for producing sized paper or board, characterized in that it comprises the addition of a sizing dispersion according to any of the Claims 1 to 9 to the pulp for paper or board, preferably to the stock during the production of paper or board.

13. Method of Claim 12, characterized in that the sizing dispersion is added in such an amount that the pulp for paper or board, preferably stock, contains 0.01 -

0.4%) by weight of the sizing agent relative to the dry matter of the pulp.

14. Use of a sizing dispersion of any of the Claims 1 to 9 in the production of paper or board to improve the hydrophobicity thereof.

15. Use of a monoester of glycerol with a fatty acid in the production of paper or board to enhance the spreading of the sizing agent on the fibre surafces.

16. Use of Claim 15, characterized in that said monoester of glycerol with a fatty acid is incorporated into the sizing dispersion defined in any of the Claims 1 to 9.