Starch particles and the use thereof in the wet-end of paper and cardboard preparation
Technical field
The present invention relates to process for preparing paper or cardboard by adding to the pulp starch particles. The productivity of said papermaking process is improved and the obtainable paper has improved quality.
Background of the invention
In the production of paper, cellulose is pulped in a slurry, this slurry is then sent to a paper machine wherein the pulp is applied to a wire to retain the fibres and to drain away the liquid. After leaving the wire, the paper sheet is squeezed in the press section between rolls to reduce its water content. The remaining water is then evaporated on heated rolls to further reduce its water content.
The strength of the paper is dependent on the nature of the pulp, on the process conditions and on the level of the additives. Virgin pulp typically gives a stronger paper than pulp from a re-pulped paper.
There is an overall trend, i.e. an environmental demand, to use recycled fibres in the paper composition, and the need for improving the general characteristics of the paper becomes more important. However, the recycled fibres are weakened by successive treatments. The fibres of the paper tend to become shorter and weaker. Reduced interactions (e.g. hydrogen bonds) are also encountered after the paper drying. Up to a limited amount, the weakened strength can be overcome by increasing the amount of starch added into the paper. However, after recycling a number of times, usual ways of improvement can no longer compensate for the loss of strength and paper having an inferior strength is thus produced.
Therefore, there is an increasing interest in finding new additives, which could increase the strength of the paper without affecting the productivity.
Furthermore, there is a trend for producing cheaper packaging paper, which can be achieved by the addition of high amount of a cheap filler e.g. gypsum, or calcium
carbonate. These increased quantities of filler again result in a deterioration of paper strength.
It is known that the strength of paper can be increased by adding starch to the pulp by wet end addition or in the sheet by means of a size press.
Addition of the starch, polymers or a combination of both in the wet-end stage is only effective if the material is retained, in one way or another, onto the fibres which form the basis of the paper or cardboard. In order to achieve this, the efficiency of the starch or polymers can be improved by introducing cationic or anionic groups onto it. Through electrostatic bonds, the self-retention of the starch and its bonding with the cellulosic fibres are improved. However, the maximum amount of these ionic polymers is limited by the flocculation of particles and the subsequent sheet formation.
Secondly, it is possible for adding more starch when the paper sheet has been formed and dried. This is commonly done in a size press.
However, the application of native starch (which can be enzymatically or thermochemically converted) or thinned starch, at the size press stage has different limitations. The main disadvantage is the reduction of the machine speed caused by the re- wetting of the paper during this application. It additionally consumes a lot of energy for the subsequent second drying process of the paper.
For the aforementioned reasons, a replacement of the size press by higher addition levels of starch and/or polymer in the wet-end would help to significantly increase productivity.
GB 2 292 394 relates to a method for improving the strength of paper pulp by the use of flocculents and starches in charged form.
US 4,243,480 relates to a process for production of paper and paperboard wherein water-insensitive starch particles, produced by extrusion of a starch dispersion into a coagulating solution are employed to replace all or part of the cellulosic or other pulp conventionally employed.
WO 94/09190 relates to a device and process for producing fibrous starch materials for use in the production of paper and cardboard.
GB 2 258 251 relates to a starch pulp adapted in particular to be used in the manufacture of paper and cardboard and to a process for its preparation. Said process provides a starch pulp adapted to be used in a high concentration in paper, in addition to cellulose.
There has been a continuing need to improve strength of paper by applying a process which is not limited in its runnability due to the addition of charged polymers and wherein the size press operation is eliminated to increase efficiency (= productivity) and decrease investment and operation costs, and wherein low quality fibres are allowed.
The current invention provides such a process.
Summary of the invention
The present invention relates to a process for preparing paper or cardboard comprising the following steps: a) Preparing a pulp of cellulosic fibres, b) Optionally adding cationic starch for obtaining a completed pulp, c) Delivering the pulp or completed pulp to the wire, d) Dewatering for obtaining a sheet format, e) Drying for obtaining paper or cardboard and, said process is characterised in that starch particles comprising starch and coagulating agent wherein at least 90% by weight of said particles have a particle size of from 20 microns to 200 microns measured by Coulter Counter technology and a thickness of smaller than 5 microns determined by Malvern method, are added either to the pulp of cellulosic fibres, and/or said starch particles are sprayed on to the wire during sheet formation.
The present invention relates to a process wherein said starch particles have a particle size of from 40 microns to 100 microns measured by Coulter Counter technology, and a thickness of between 0.2 to 0.8 microns, preferably a thickness of between 0.3 and 0.5 microns determined by Malvern method.
The present invention relates to a process wherein said starch particles are comprising a coagulating agent selected from the group consisting of ammonium
k
sulphate, aluminium sulphate, ammonium phosphate, potassium chloride, sodium sulphate, sodium carbonate, sodium bicarbonate, ammonium chloride and mixtures thereof, preferably ammonium sulphate.
The present invention further relates to a process wherein the starch particles are added in an amount of from 1 to 10%, preferably 2 to 8% and more preferably 3 to 6% based on the weight of dry pulp.
The present invention relates to a process wherein in step a) said pulp of cellulosic fibres is virgin pulp, pulp from re-pulped paper, pulp from de-inked paper, and/or mixtures thereof.
Furthermore, the present invention relates to a process wherein in step b) from 0.3 to 3% cationic starch is added based on weight of dry pulp.
The current invention relates to the use of starch particles comprising starch and a coagulating agent wherein at least 90% by weight of said particles have a particle size of from 20 microns to 200 microns measured by Coulter Counter technology and a thickness of smaller than 5 microns determined by Malvern method in papermaking process without applying size press.
Furthermore, it relates to the use of the starch particles in papermaking process wherein the productivity of said papermaking process is increased with at least 10%, preferably with 20%, more preferably 40%, in comparison to a process applying size press.
Furthermore, the present invention relates to the use of starch particles in papermaking process wherein the energy consumption of said papermaking process is reduced with at least 40%, in comparison to a process applying size press.
Detailed description of the invention
The present invention relates to a process for preparing paper or cardboard comprising the following steps: a) Preparing a pulp of cellulosic fibres, b) Optionally adding cationic starch for obtaining a completed pulp, c) Delivering the pulp or completed pulp to the wire, d) Dewatering for obtaining a sheet format,
e) Drying for obtaining the paper or cardboard, and said process is characterised in that starch particles comprising starch and coagulating agent wherein at least 90% by weight of said particles have a particle size of from 20 microns to 200 microns measured by Coulter Counter technology and a thickness of smaller than 5 microns determined by Malvern method, are added to the pulp of cellulosic fibres and/or said starch particles are sprayed onto the wire during sheet formation. At least three ways of running the process are comprised.
After preparation of the pulp of cellulosic fibres, said starch particles are added. Alternatively, said starch particles are added solely during the sheet formation. Furthermore, said starch particles may be added in both steps, i.e. after preparation of the pulp of the cellulosic fibres and during the sheet formation.
In addition, in each of these processes it is an option to add cationic starch for obtaining a completed pulp.
The present invention relates to a process wherein said starch particles have a particle size of from 40 microns to 100 microns measured by Coulter Counter technology, and a thickness of between 0.2 to 0.8 microns, preferably a thickness of between 0.3 and 0.5 microns determined by Malvern method. In said process no size press is applied.
Coulter Counter Technology is a method known in the art for measuring particle size. The Malvern Mastersizer is used for determining the thickness of the particles. The particle thickness is given by dividing the average particle size of the surface distribution by the aspect ratio wherein the aspect ratio is the ratio between the actual volume concentration presented to the Mastersizer and the volume concentration calculated by the Mastersizer.
The starch particles can be prepared according to a process similar as the one described in WO 94/09190, but particle size of starch particles and thickness of the particles are controlled. The starch particles can be prepared by the extrusion of a dispersion or aqueous solution of starch material in a flow of saline coagulant agent, and the starch particles have a particle size of 20 to 200 microns measured by Coulter Counter Technology and a thickness of less than 5 microns determined by Malvern. In
said process the coagulating agent is selected from the group consisting of ammonium sulphate, aluminium sulphate, ammonium phosphate, potassium chloride, sodium sulphate, sodium carbonate, sodium bicarbonate, ammonium chloride and mixtures thereof, preferably ammonium sulphate. Alcoholic solutions can be used as well, but they may show a particular restriction with respect to safety.
The starch used for the preparation of the starch particles is preferably native starch such as starch from maize, rice, tapioca, potato or slightly thinned starch. Furthermore modified starch such as ionic starch, oxidized starch, etherified, esterified and/or mixtures of these can be used as well. Particularly preferred is starch widely available on the local market, where the production of the starch particles is carried out.
The starch particles can be added dry or in slurry form at any stage of the wet-end process of papermaking. The wet-end of the papermaking process refers to the stages of the papermaking process, wherein a pulp of fibres obtained from cellulose based materials, such as wood, recycled, de-inked paper, used paper and/or mixtures thereof, is being processed for obtaining a paper sheet. The starch particles are added in the process preferably at temperature between 20 and 50°C and preferably between 30°C and 40°C.
High quality and improved strength of the paper and cardboard is already obtained by the addition of starches particles in an amount of from 1 to 10%, preferably from 2 to 8% and more preferably from 3 to 6% by weight of the dry pulp.
The starch particles do not affect the Zeta potential of the pulp and do not disturb the flocculation during the paper sheet formation. Due to the well-designed shape of the particles with respect to their particle size and thickness, such particles have particular good mechanically retention behaviour. Furthermore, homogeneous distribution of the particles in the paper is obtained and maximum bonds between the cellulose fibre and starch particles are obtained.
The current invention further discloses a process wherein in step a) said pulp of cellulosic fibres is virgin pulp, pulp from re-pulped paper, pulp from de-inked paper, and/or mixtures thereof. Preferably, re-pulped, de-inked paper pulp is used. In fact, by applying said starch particles to cellulosic fibres with a low quality such as re-pulped and de-inked paper, it is possible for obtaining good quality paper.
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Further improvement of the process and consequently increased paper strength can be obtained by adding in step b) of the process 0.3 to 3% cationic starches based on the weight of the dry pulp. Additionally fillers, and/or polymers may be added in step b).
The current invention relates to the use of starch particles comprising starch and a coagulating agent wherein at least 90% by weight of said particles have a particle size of from 20 microns to 200 microns measured by Coulter Counter technology and a thickness of smaller than 5 microns determined by Malvern method in papermaking process without application of size press.
Furthermore, it relates to the use of starch particles in papermaking process wherein the productivity of said papermaking process is increased with at least 10%, preferably with 20%, more preferably 40% in comparison to a process applying a size press.
Furthermore, the present invention relates to the use of said starch particles in papermaking process wherein the energy consumption of said papermaking process is reduced with at least 40% in comparison to a process applying a size press.
The current invention has the following advantages: by applying the currently disclosed process undesirable interactions during papermaking e.g. flocculation, are avoided.
The current process results in improved runnability and improved quality which cannot be reached by conventional non-ionic starches. - The process can apply pulp of low quality and yet a high quality of paper or cardboard can be obtained.
The thus obtained paper has improved paper strength.
The process is running without size press for obtaining paper of high quality.
The productivity of the process is increased.
The drying energy consumption is reduced with 40% of the total consumption of energy on the paper machine.
The invention is illustrated by way of the following examples.
Example 1 :
Wet end conditions:
1000 kg of pulp consisting of 100% recycled paper of corrugated boxes and printed papers.
Normal recycling of machine brakes.
Cationic starch: 0.0%.
C' Chart-Bi (Cerestar) (% based on pulp dry substance - see table 1).
(= starch particles having particle size between 20 to 200 microns and thickness of smaller than 5 microns) Temperature of the pulp 38°C.
Machine conditions:
No Size Press.
The type of former was a Fourdrinier one for production of a 1 layer paper.
Speed of the machine: 290 m/min.
The drying section was equipped with 26 cylinders and the temperature profile was comprised between 92°C and 112°C.
The available steam pressure was 2.3 bars maximum.
Application: Fluting paper
Table 1
Grammage C*Chart-Bi CMT 30 % increase
(g/m2) (% on pulp d.s.) (N) paper strength
120 0 166
3.0 214 28.9
3.5 220 32.5
4.2 234 41.0
105/110 0 128
3.8 165 28.9
4.3 175 36.7
5.0 186 45.3
By applying the same machine speed, the paper strength, as expressed by CMT 30 value in Newton, is increased by at least 29%, and up to 45%.
Example 2:
Wet end conditions:
1000 kg from pulp consisting of 100% recycled paper of old corrugated containers.
Normal recycling of brakes.
Ash content: about 17% in the paper.
Retention system: PolyAcrylAmid
Cationic starch 0.3% C*Bond 35809 (Cerestar).
CιϊrChart-Bi(Cerestar) (% based on pulp dry substance - see table 2).
Temperature of the pulp: 43 °C.
Machine Conditions:
No Size Press.
The type of former was a Fourdrinier one for production of a 1 layer paper.
Speed of the machine: 290 m/min.
The drying section was equipped with 26 cylinders and the temperature profile was comprised between 92°C and 112°C.
The available steam pressure was 2.3 bars maximum.
Application: Fluting paper
Table 2
Grammage C"&Chart-Bi Burst Mullen CIS g/m2 % on pulp ds % increase vs Blank
112 0.0 0 0 0
5.7 38 36 16
105 0.0 0 0 0
2.9 28 28 33
150 0 0 0 0
5.4 28 28 33
An increase of 16 to 33% paper strength, as expressed by CMT30 value in Newton, is obtained.
Example 3:
Wet end conditions:
Prepare 1000 kg of 100% Recycled paper.
Normal recycling of brakes.
Ash content: about 17% in the paper.
Retention system: PolyAcrylAmid
Cationic starch: 0.6% C ϋrBond 35809 (Cerestar), (based on pulp dry substance) when applying C*Chart-Bi and 1.3% C#Bond 35809 in process without C*Chart-Bi addition
Temperature of the pulp : 43°C.
Machine Conditions:
No Size Press.
The type of former was a Fourdrinier one for production of a 1 layer paper.
Speed of the machine: 290 m/min.
The drying section was equipped with 26 cylinders and the temperature profile was comprised between 92°C and 112°C.
The available steam pressure was 2.3 bars maximum.
The results are displayed in Table 3.
Application: Liner paper
Table 3
Grammage C*Chart-Bi Burst Mullen CMT30
(g/m2) (% on pulp ds) (% increase vs Blank) (N)
112 0.0 0 0 0
5.7 38 36 16
According to CTM30 value the paper strength is increased with 16%) while only 0.6% cationic starch instead of 1.3% cationic starch has been added.
Example 4:
Wet end conditions:
Prepare 1000 kg of 100% Recycled paper « de-inked »
Normal recycling of brakes.
Filler: about 42% in the white top layer.
Retention system: Bentonit
Cationic starch: 0.3% C*Bond 35809 (Cerestar)
Temperature of the pulp : 43°C.
C' Chart-Bi (Cerestar) (% based on pulp dry substance - see table 4)
M
Machine Conditions:
The type of formers was a Fourdrinier one for production of a 2 layer paper.
Speed of the machine: 340 m/min.
No Size Press.
The temperature profile was comprised between 59°C and 104°C.
The available steam pressure for drying was 2.3 bars maximum.
The results are displayed in Table 4.
Application: White top liner (double layer paper: 45g/m2 + 95g/m2)
Table 4
Grammage C*Chart-Bi Burst Mullen Dennison
(g/m2) (% on pulp ds) (% increase vs Blank) (-) •
140 0.0 0 0 13
5.0 5.6 6.9 16
The properties of the obtained paper are expressed in Burst, Muller, Dennison. Meanwhile the property expressed by Scottbond is increased with 65%.