SIZE COMPOSITION, METHOD FOR ITS PREPARATION, AND USE THEREOF

Abstract: A size composition in the form of an aqueous emulsion or dispersion comprises hydrophobic cellulose-reactive particles, which exist as a physical mixture of at least two hydrophobic, cellulose-reactive sizing agents, comprising alkyl keten dimer (AKD) and alkenyl succenic acid anhydride (ASA) as well as starch and/or synthetic polymer.

Description: SIZE COMPOSITION, METHOD FOR ITS PREPARATION, AND USE THEREOF TECHNICAL FIELD The invention relates to a new composition which is useful as a so called size composi¬ tion in connection with manufacturing of paper, board, paper board and similar prod¬ ucts. The invention also relates to a method for the preparation of the said composition and to a use thereof, namely in connection with a method for the manufacturing of sized paper, sized board, or sized paper board. Finally, the invention relates to sized paper, sized board, or sized paper board, wherein the paper, board or paper board has been manufactured according to the said method. More precisely, the invention relates to a composition in the form of an aqueous (water based) emulsion or dispersion comprising at least any hydrophobic, cellulose-reactive sizing agent and at least a natural and/or synthetic polymer. BACKGROUND OF THE INVENTION As far as most paper, board and paper board grades are concerned, there is a need to reduce the rate of liquid penetration into the structure ofthe paper, board, or paper board through the addition of hydrophobic substances during the paper manufacturing process. Copying paper, writing and printing papers, papers for so called ink-jet printers, and paper board for packages for juice, milk and other liquids are examples of such paper, board, and paper board grades. These, g. rades for their proper use need to have some liquid repellent features. Different methods are available or the achievement of that effect. One of them includes the addi¬ tion of an emulsion for dispersion of a hydrophobic material during the paper manufac¬ turing process. Aqueous emulsions and dispersions of hydrophobic cellulose-reactive type are previ¬ ously known per se. These emulsions and dispersions, however, are manufactured of only a single hydrophobic, cellulose-reactive sizing agent. Many different hydrophobic materials can be used. The so called hydrophobic, cellu- lose-reactive sizing agents belong to the most efficient ones. It is believed that the - drophobic effect, when using that type of agent, is achieved through a reaction between the hydrophobic material and the hydroxyl groups o the cellulose. 1 he hydrophobic, cellulose-reactive materials which are most commonly used in con¬ nection with neutral or weakly alkalic conditions during the paper or paper board manu¬ facturing process are alkyl keten dimer (in the following called AKD) or alkenyl succe¬ nic acid anhydride (in the following called ASA) Alkyl keten dimer, which are used in the first place when the demands on a durable and permanent hydrophobation are g reat, can react with the cellulose when the paper or the paper board is being dried wherein beta-ketoesters are established In the figure be¬ low, the reaction between AKD and cellulose and the hydrolyse reaction are illustrated 2 R 1 -CH- R 1 -CH 2 -C-CH 2 -R2 + C*0 2 (g) The reaction is slow at low pH values and in practice AKD can not be used other than in the neutral or weakly alka k pH range Instead of reacting with the fibre duπng the pa¬ per or paper board manufacturing, AKD also can be hydrolysed such that an unstable beta-keto acid is obtained, which can be decarbonated to corresponding ketone The hydrolyse products which are formed during the paper manufacturing process, 1 e the ketone products that are obtained, are very disturbing for certain types of photo copying apparatuses, in which these ketones may form depositions The degree of the hydrolyse reaction for AKD, however, is substantially smaller in comparison with ASA This implies that AKD usually is supplied to the paper or board mill in the form oi a dispersion or emulsion which has a particle size of between 0 2 to 2 micrometers The dispersion or emulsion usually is stabilised by means of a cation-active polymer This polymer, which also gives the particles their charge, usually consists of cation-actn e starch but also use of anion-active or amphoteπc starches or synthetic polymers occui AKD has a melting point of between 15-60°C, depending on the length ofthe fatty tail. The commercial products which are most commonly used so far often have a mixture of C j 4, Ci 6, and Ci hydrocarbons, implying a melting point of between 40-60°C. AKD is particularly sensitive in the presence of extractive agents of the fatty acid type, because such agents are saponificated at alkalic pH values and also because they com¬ pete with the distribution on the cellulose surface. A poor AKD distribution will result in a poor chemical reaction with the fibre. Gorundwood, thermo-mechanical pulps and chemi-mechanical pulps therefor are difficult to hydrophobate by means of AKD. The most pronounced drawback with AKD, however, is that the hydophobicity is devel¬ oped slowly. A completely developed sizing is not achieved until after several days after the manufacturing in the paper or the board machine Another drawback is that a too large dosage of AKD causes friction problems in con¬ nection with the paper or the board/paper board. AKD also impairs the toner addition in connection with the photocopying processes as well as the adherence of the plastic layer in connection with the manufacturing of plastic laminated materials. Alkenyl succenic acid anhydride (ASA) is another example of a so called cellulose- reactive hydrafobation agent. The anhydride can react with the hydroxyl groups of the cellulose, wherein a transesterification takes place. In comparison with AKD, ASA has a much higher reactivity with the cellulose and hence also with water, wherein hydrolysis of the product is a greater problem for ASA than for AKD. ASA is delivered to the paper mill in the form of oil, sometimes with emulgator added. Emulsification takes place in a special emulsification equipment in connection with the paper or board manufacturing machine (so called in situ production) and cationic. ani¬ onic or amphoteric starch or other polymer is used as a stabiliser and charge carrier. The particle size of the emulsion usually is 1-5 micrometers. Larger particles are hydrolysed more slowly but smaller particles provides a better distribution on the cellulose fibres, wherefore there exists an optimal particle size. ASA thus is hydrolysed quickly and the hydrolysis product and its salts with Ca 2+ are sticky and frequently give rise to deposi¬ tions in the paper or paper board manufacturing process. The hydrolysis as well as the reaction velocity are increased with increased pH, but the reaction is fast over the entire pH range. The hydrophobicity is developed fast and is usually fully developed is the finishing part ofthe paper and paper board manufacturing process. Below, the reaction between ASA and cellulose is illustrated: where R or R' is an alkenyl. In connection with the more and more common use of precipitated calcium carbonate, so called PCC, as a filler during the paper and paper board manufacturing, the need of a hydrophobic sizing agent is increased considerably for the achievement ofthe same de¬ gree of sizing as is achieved in a corresponding process where e. g. chalk is used as a filler. Moreover, often problem occur which have to do with the fact that the hydropho- bation effect is reduced after a period of time. To sum up, one can thus state that both the two hydrophobation agents have specific advantages and drawbacks when used in the paper or paper board manufacturing process as well as in the finished paper or paper board product. DISCLOSURE OF THE INVENTION The purpose ofthe invention is to provide a size composition where the above men¬ tioned problems have been eliminated or restricted. This can be achieved therein that the hydrophobic, cellulose-reactive particles ofthe emulsion or dispersion exist as a physi- cal mixture of at least two hydrophobic, cellulose-reactive sizing agents. More particu¬ larly, the invention according to the elected embodiment is characterised in that said at least two hydrophobic, cellulose-reactive sizing agents comprise at least alkyl keten di¬ mer (AKD) and alkenyl succenic acid anhydride (ASA). By means of this composition there are achieved effects which substantially reduce or eliminate many of the shortcom- ings which can be related to the known technique. Among these known problems can be mentioned, i. e., slow development ofthe hydrophobation effect, poor adherence of toner and deposition hydrolysis products in connection with photocopying and reduced efficiency during the paper and paper board manufacturing process because of stops in connection with the formation of hydrolysis products. The size composition is manufac- tured according to a so called in situ method, i. e. in close connection to the use of the composition, i. e. in practise in connection to the machine or those machines which are used for the manufacturing of the paper, the board, or the paper board. This also can be expressed such, that the size composition, according to the invention, in the form of the aqueous emulsion or dispersion is prepared not more than 4 hours, preferably not more than 1 hour, suitably not more than 30 minutes, before the use of the composition in the paper, paper board, or board manufacturing process. All known shortcomings in con¬ nection with the tecnique known so far, can surprisingly substantially be reduced or eliminated through the invention without impairing the favourable features which char¬ acterise the two hydrophobic, cellulose-reactive sizing agents taken alone. Surprisingly, one has also found that the new size composition substantially reduces the sizing problems, such as low hydrophobation effect and reduction of the hydrophobation effect by time, which occur when precipitated calcium carbonate, so called PCC, is used as filler in the paper and paper board manufacturing process. A main purpose ofthe invention therefor is to provide a new and improved composition which can be used for sizing paper, board, paper board and similar products. Another purpose ofthe invention is to provide a new size composition which is more efficient than previously known compositions, therein that reduced quantities of the sizing agent are required for the achievement of a hydrophobation degree similar to or corresponding to that ofthe previously known compositions. Still another object ofthe invention is to provide a new size composition, the sizing in¬ fluence or sizing ability of which is developed faster than with the previously known compositions. Another purpose ofthe invention is to provide a new size composition with which the unfavourable effects on the hydrophobation effect are considerably reduced or elimi¬ nated in connection with use of precipitated calcium carbonate. Still another purpose is to provide a new size composition, wherein the amount of the undesired hydrolysis products which are obtained in the paper or paper board manufac¬ turing process when the known size compositions are used, are considerably reduced or eliminated. Further there is an object of the invention to bring about an improved method for the manufacturing of a size composition as described above. Further there is an object to bring about an improved method for the manufacturing of a sized paper or board or paper board, including the use of the new composition of the invention Another object of the invention is to provide sized paper or sized board or sized paper board having improved features by the use of the new composition and the improved process at the manufacturing thereof According to the invention these and other objectives are achieved through the provision of a size composition in the form of an aqueous (water based) dispersion or emulsion, in which the hydrophobic, cellulose-reactive partides of the emulsion or dispersion exist as a physical mixture of at least two hydrophobic, cellulose-reactive sizing agents, wherein the emulsion also contains starch or other natural polymer and/or at least any synthetic polymer, e g polyacrylamide Preferably, said at least two hydrophobic, cellulose- reactive sizing agents consist of particles of alkyl keten dimer and alkenyl succenic acid anhydride, wherein the dispersed or emulsified size composition is prepared in connec¬ tion with the paper and paper board manufacturing process, I e shortly before the com¬ position shall be used, preferably not more than 4 hours, suitably not more than 1 hour and most preferably not more than 30 minutes before the use As far as the new size composition of the invention is concerned, it should be under¬ stood that it also may contain further ingredients if desired or if considered suitable, wherein such further ingredients may be chosen according to known principles Al¬ though such ingredients need not be particularly descπbed here in order to make it pos- sible to carry out the invention, it may, however, be mentioned that among normal addi¬ tions can be mentioned e g dispersing agents, aluminium compounds such as alum (aluminium sulphate) and poly-alumimum chloride The starch or synthetic polymer existing in the dispersion or emulsion may have a cation-active or anion-active or am- photeπc character EXAMPLE The above described size composition can be prepared in the following way 25 parts of a wax consisting of alkyl keten dimer (AKD) is melted The wax usualK has a melting point between 30-60°C, depending on the length of the fatty chains in the raw material Wax with a melting point down to 15°C also can be used l o this melt there is added 25 parts of an oil consisting of alkenvl succenic acid anhydride (ASA) The mixture is stirred such that a homogenous, physical mixture is achieved This mixture of AKD and ASA, during stirring, is added to a solution of 100 parts of cation-active starch and 2 parts of an anion-active dispersion agent and 2500 parts of water in a disper¬ sion/emulsifying device in which it is subjected to so high shear forces that a dispersion or, alternatively, an emulsion is formed. The temperature ofthe starch solution should be a few °C higher than the melting point ofthe AKD/ASA mixture. The dispersion or emulsion thereafter is cooled rapidly. A temperature less than 20°C is preferable. As previously mentioned, the AKD/ASA ratio can vary very much depending on the features which are desired in the first place. At a low AKD/ASA ratio, the mixture of AKD and ASA is liquid at room temperature which facilitates the preparation ofthe emulsion. If desired, the AKD/ASA mixture can be prepared by the supplier of these raw materials. The mixture in that case may be delivered e. g. in a container, wherein the mixture is heated to liquid state e. g. by means of an immersion-heater at a higher AKD/ASA ratio. The mixture also can be delivered as a bulk cargo, wherein its tem- perature is just above the melt temperature of the mixture during transport and storing. In both these cases the AKD/ASA mixture can be delivered to the user in a concentrated form in order to be prepared at the user's place by being mixed also with starch or other natural polymer and/or with synthetic polymer and being emulsified or dispersed in an aqueous medium shortly before use. In the above described example, it may, as has been previously mentioned, in certain cases be more suitable to use anion-active starch or amphoteric starch or synthetic polymer instead of cation-active starch. Also other additions, such as for example polyaluminium chloride or alum (aluminium sulphate) may be advantageous. The sizing dispersion or sizing emulsion thus obtained is a milky liquid having a low viscosity, which after dilution is dosed to the stock during the course ofthe paper, board or paper board manufacturing process. Suitably, the size composition may be dosed at any dosage point between the mixing through and the head box. The amount of dosage may vary depending on different process parameters, such as type of used pulps and fillers, temperature in the system and existence of disturbing substances. Usually the amount of dosage may vary from 0.4 to 1.4 kg total solid content/ton paper, board or paper board.

Claims: PATENT CLAIMS 1. Size composition in the form of an aqueous emulsion or dispersion comprising at least any hydrophobic, cellulose-reactive sizing agent and at least one natural and/or synthetic polymer, characterized in that the hydrophobic, cellulose-reactive par¬ ticles ofthe emulsion or dispersion exist as a physical mixture of at least two hydro¬ phobic cellulose-reactive sizing agents. 2. Size composition according to claim 1, characterized in that said at least two hydrophobic, cellulose-reactive sizing agents comprise at least alkyl keten dimer (AKD) and alkenyl succenic acid anhydride ASA. 3. Size composition according to claim 2, characterized in that the ratio between alkyl keten dimer and alkenyl succenic acid anhydride, AKD/ASA, is at least 1/100 and not more than 100/1. 4. Size composition according to claim 3, characterized in that the ratio between alkyl keten dimer and alkenyl succenic acid anhydride, AKD/ASA, is at least 5/100 and not more than 100/5. 5. Size composition according to any of claims 1-4, characterized in that it is prepared in a dispersion or emulsifying equipment according to a so called in situ proc¬ ess. 6. Method for the manufacturing of sized paper, sized board or sized paper board, wherein a sizing agent is added during the manufacturing of said paper or board or paper board, suitably to the stock prior to dewatering thereof, characterized in that the size composition according to any of claims 1-5 is used as said sizing agent. 7. Method according to claim 6, characterized in that the size composition is added in an amount of at least 0.25 kg and at most 4 kg of total solid content per ton paper, board or paper board. 8. Method according to claim 7, characterized in that the size composition is added in an amount of at least 0.4 kg and at most 1.4 kg of total solid content per ton paper, board or paper board. 9. Method according to any of claim 6-8, characterized in that the size composi¬ tion is prepared not more than 4 hours before it is added during the manufacturing of said paper, board or paper board, suitably to the stock before dewatering thereof. 10. Method according to claim 9, characterized in that the size composition is prepared not more than 1 hour, preferably not more than 30 minutes before it is added during the manufacturing of said paper, board or paper board, suitably to the stock be¬ fore dewatering thereof.

Inventors: HAAKANSSON PHILIP, HAAKANSSON, PHILIP
Applicants: HAAKANSSON PHILIP, STORA KOPPARBERGS BERGSLAGS AB, HAAKANSSON, PHILIP, STORA KOPPARBERGS BERGSLAGS AKTIEBOLAG (PUBL)
Application year: 1997
Main classification: D21H21
IPC codes: D21H17, D21H21