Background of the invention

Waste paper has in later years become more and more impor¬ tant as raw material for paper pulp manufacture. One reason is that the supply of cellulose does not correspond to the demand of the paper industry, i.e. one compensates the shortage of pulp fibers by using waste paper. Another impor¬ tant reason is that the energy cost has become increasingly higher. Besides the collecting of waste paper has increased, since people are more conscious about environmental aspects today. The increased use of more complex printing ink and the increasing energy costs makes it necessary to develop more cost efficient deinking chemicals.

In order to remove printing ink from waste paper there are mainly two methods that are used, viz. the washing process and the flotation process. These two methods differ mainly in the separation of the ink.

The flotation process is most common in Europe and in South¬ east Asia. It gives a high yield of fibers and filler. Other advantages are environmental aspects, such as a closed water system, a low water consumption and that contaminants are obtained in concentrated form. Disadvantages with this process are the relatively high capital - and chemical costs. These costs are however compensated by the high yield, so that as a whole an economically advantegeous system is achieved. The flotation process requires a careful supervision, i.e. depending on that it is sensitive to variations in the composition of the waste paper pulp. The method is mainly used when the recovered fiber mass is to be used for manufacture of newsprint paper.

The washing process is dominating in the United States and

Canada. In this process filler and fine material are also removed besides the printing ink. This is a drawback in the manufacture of newsprint paper, since the yield is bad. However it is an advantage when soft paper for sanitary purposes is to be produced. An advantage with this method is its insensitiveness for differences in the composition of the waste paper pulp. Besides the capital- and chemical costs are lower than for the flotation process.

In the washing process it is important that the printing ink is kept as dispersed and stable as possible, which is pro¬ vided by high admixture of non-ionactive tensides. Washing is performed by diluting the pulp mixture to low concentra¬ tions and then watering it down to higher concentrations in a water extractor, a washing filter.

The flotation process comprises several steps, the most important of which are: 1. release of ink from the fibers. 2. dispersion of the ink particles.

3. separation of ink from the fiber - ink - suspension, i.e. flotation.

In the dissolver the ink is removed from the fibers. The waste paper is here mixed with water' and chemicals. The paper is disintegrated into separate fibers with adhering printing ink. The added caustic liquid gives a saponifica- tion of the surface layer of the binding agent of the printing ink, which contributes to an electrostatic repul- sion between the carboxylic groups in the printing ink and on the surfaces of the fibers. This together with the softe¬ ning provided by the ink components, facilitates the release of the printing ink. At the same time mechanical energy is supplied.

The caustic liquid also helps to disperse the ink to small ink particles, but a good wetting of the ink is also requi-

red. This is achieved by a wetting agent, which can be a non-ionic tenside, which helps the liquid to penetrate the paper. The tenside is also absorbed on the ink particles and stabilizes these so that reprecipitation is avoided. However dispersion and stabilization may not occur to well, since in such case flotation can be made difficult. This is the next step in the process.

In order to enable separation of dispersed ink particles their surface properties must be changed, which is made by a collector agent. The collector increases the hydrophobic character and creates an electro - chemical attraction to the air bubbles. The flotation is made in a flotation cell. Air is blown into the pulp and the ink particles then colli- de with and stick to the air bubbles, which, flow to the surface. A foam layer is created there, which is then sepa¬ rated.

The following chemicals are used in the deinking:

Sodium hydroxide (NaOH).

Sodium hydroxide is one of the most important deinking chemicals. In high concentration the caustic liquid contri¬ butes to break hydrogen bonds, swell the fibers and release the printing ink. The NaOH saponifies the surface layer of the binding agent of the printing ink, i.e. an alkaline hydrolysis takes place. This involves electrostatic repul¬ sion between the carboxylic groups in the printing ink and on the fiber surface. The printing ink is released and dispersed. At the flotation pH is raised to 10 - 11 by adding the caustic liquid.

Hydrogen peroxide (H ₂ 0 ₂ )

Hydrogen peroxide is used both for bleaching the fibers and for oxidizing possible organic contaminants. It has a great importance for the deinking process, since it contributes to breaking the strong bonds in the printing ink. At high

temperatures the instable hydrogen peroxide decomposes.

Water glass (Sodium silicate Na ₂ Si0 ₃ )

Water glass effects the flotation process in many different ways. It acts as a wetting agent, printing ink dissolver, pH buffer, corrosion inhibitor and complex former which bonds different metals. When adding water glass the collecting effect of the fatty acids are considerably increased and the reprecipitation of the printing ink on the fibers are redu- ced. The instable hydrogen peroxide is stabilized by water glass.

Surfactants

The surfactants have different functions: * the wetting agent; reduces the surface tension

* the frothing agent; stabilized the air bubbles

* the collector; agglomerates and hydrophobizes the printing ink.

Surfactants thus contribute to release the printing ink from the fibers and then prevent that the printing ink is repre- cipitated thereon.

The collector shall destabilize the effect of the dispersant on the printing ink, before flotation of the pulp. The added collector increases the hydrophobic character of the ink particles and creates electro - chemical attraction to the air bubbles. The function of the collector is thus to agglo¬ merate and hydrophobize the printing ink effectively.

There are different types of :

* Soap

* Synthetic collectors (advanced synthesis technique)

* Semisynthetic collectors (further refinement of fatty acids).

The border - line between synthetic and semisynthetic col-

lectors is however diffuse.

When soap is used as collector there is one requirement. The fatty acids must be treated with calcium - and magnesium ions in order to function effectively. These ions can later in the process cause problem in the process. Up to now soap is the collector that has caused the best brightness, i.e. the best deinking result. Soap is relatively cheap and there are many distributors.

One of the disadvantages is that at least 30% of the added soap goes along with the paper, which gives poor runnability and coatings. Soap is besides difficult to handle. Use of soap causes high fiber losses, which means that the amount of raw material to the process has to be increased.

Both synthetic and semisynthetic collectors have the advan¬ tage of being independent on the water hardness, i.e. cal¬ cium ions is no requirement. Therefore a better runuability can be provided. The collector gives a lower brightness and are more expensive than soap, but they often give effective deinking at a lower dose. The msot common synthetic collec¬ tors consist of strongly hydrophobic non-ionic tensides, e.g. etoxylated fatty acids.

The mechanism of the collector could be explained in two ways. Synthetic collectors can function as a small wetting and in this way catch the printing ink, but there is then a risk that also fibers are catched. The collector can also due to there hydrophobic properties collect the printing ink to aggregates. The are a number of factors which influence the effect of the.

The molecular weight is an important parameter, which pro- bably should be between 3000 - 10000. This can be controlled in e.g. a GPC (gel permeation chro atography) , after finis¬ hed synthesis.

The acid value is a measure of the number of carboxylic groups in the product (=mg potassium hydroxide per g samp¬ le). The acid value is reduced during the progress of the reaction. A low acid value indicates that most carboxylic groups have reacted which involves a hydrophobic product, which is desireable.

The hydrophobity is important for enabling the collector to selectively collect the ink particles, i.e. without bringing the fibers along. In order to regulate the hydrophobity the length of the carbon chain can be varied.

Object: and most important features of the invention

The object of the present invention is to provide a collec¬ tor, which fulfils the following requirements. The collector should function without admixture of calcium ions. It should not detoriate the backwater purity with time, and thus permit recirculation of the water without detoriating the brightness of the pulp. The collector should function selectively without negatively influencing the other chemicals. The dosing requirement must not be so exact that small variations influence the deinking process. The collector should be simple to handle and cheap to manufac- ture. Besides it should not give any side effects on the environment, i.e. at least partly be based on naturally occuring substances and be decomposeable.

This has according to the invention been provided by a polyester produced by reaction between 1) polyalkylene glycol, 2) di - and/or tricarboxylic acid and/or anhydrides thereof and 3) tall oil, said polyester having a molecular weight between 3000-10000.

Description of the drawings

Figure 1 is a block diagram showing the increase of bright-

ness at flotation tests with the collector according to the invention, a commercial collector and soap. Figure 2 shows flotation graphs for the collector according to figure 1. Figure 3 shows flotation graphs for the collector according to the invention in different additive amounts.

Theoretical background

A polyester is an organic compound formed through reaction between alcohols and acids. The polyester is defined as a polymer with ester bond in the main chain:

-R-COO-R'-00C-R-C00-R'- or -RC00-RC00-RC00-

There are different polyesters available: linear saturated or unsaturated polyesters, branched saturated or unsaturated polyesters and saturated and unsaturated network polyesters.

There are two types of polymerisation reactions, namely chain - and step polymerisation. For producing polyesters step polymerisation is used, so called condensation polyme¬ risation. The step polymerisation is characterized by the following:

* all molecules, irrespective of size, can react with each other.

* during the whole reaction there are all molecular sizes present, i.e. there is a broad molecular weight distribu¬ tion (MPD).

* the monomers disappear early from the reaction mixture.

* the molecular weight increases continuously during the progress of the polymerisation. * long reaction time and high transformation are required for achieving high molecular weight and degree of polyme¬ risation (and by that a low acid value).

In order to obtain a polymer the monomers have to be at least bifunctional, i.e. they should contain two functional groups per molecule. Direct esterification with such raono- mers gives: n HO-R-OH-n HOOC-R'-COOH

H0-(R-0C0-R'-C00) _n -H + H ₂ 0

Examples of acids are maleic acid, fumaric acid and adipic acid. Common diols are ethylene glycol, propylene glycol and 1,4 - butane diol. By varying the acids and diols polyesters with different properties are obtained.

At technical production of polyesters, which often takes place at temperatures between 150°C and 200 ^c C,. one usually directly esterifies the acids with a certain excess of diol. At the same time water is removed through distillation. This is made in order to prevent a return reaction and for obtai¬ ning high polymerisation degrees. Excess of one of the monomers gives a stoicheiometric unbalance, which involves a limited molecular growth, i.e. control of chain length and molecular weight is obtained. Other ways of controlling this is by means of monofunctional compounds, monovalent acid or monovalic alcohol, which stops the reaction (so called chain stopper). In all esterification reactions H ₂ S0 ₄ can be used as catalyzer.

If instead of bifunctional monomers multifunctional monomers are used, i.e. trifunctional, no linear polymers are obtai- ned. The multifunctional monomers contain more reactive groups, and thus give branching points, which can contribute to branching and netting at the polymerisation. The final product is then a network polymer.

Ex . A

A-A + B-B + ^ A A triol

A

B

\

One here speaks of a certain functionality f , e. g . f = 3 .

A λ

A A At a certain yield (transformation) the polymer becomes sparingly soluble and forms a gel. This occurs at the so called gel point, which can be determined when the func¬ tionality is known. When 100% transformation is achieved the network consists of one single polymer molecule.

Under conditions that functional groups of the same kind are equally reactive and that the reactivity is independent of the molecular size, one can calculate in the same way as for bifunctional monomers. There are however exceptions, i.a. glycerol, where the secondary alcohol group is less reactive than the two primary groups.

The following chemicals have been used at the preparation of the collector according to the invention. 1) Polyalkylene glycol, e.g.

Polyethylene glycol PEG HO-(CH ₂ -CH ₂ 0) _n -H

359

10

PEG occurs in many different molecular weights. We have used the mean molecular weight 300, 400 and 600, which all are liquids and PEG 1500, which is a solid compound.

Polypropylene glycol, PPG HO-CCH ₂ -CH ₂ -CH ₂ 0) _n -H.

This also occurs in different molecular weights. PPG 400, 600, 1200, 2000 and 4000 have been used. All are liquids.

2) Di- and tricarboxylic acid or its anhydrides in e.g. Maleic acid (cis-form) HC=CH

HOOC ^ COOH

Fumaric acid (trans-form) COOH HC=CH

HOOC ^

Adipic acid HOOC-(CH ₂ )„-COOH

COOH

I Citric acid HOOC-CH ₂ -C(OH)-CH ₂ -COOH

Oxalic acid HOOC-COOH

Sebacic acid HOOC-(CH ₂ ) ₈ -COOH

3) Tall oil which contains i.a. varying amounts of fatty acids and resin acids.

The final product is a polymer (polyester) with a mean molecular weight of 3000-10000, preferably 5000-10000.

By using bifunctional alcohols and acid the molar ratio should be close to 1. Tall oil is used for controlling the chain length of the final polymer.

Since we have used a simple one-stop synthesis no residual products are obtained, which should be taken care of in the manufacturing process. Only aliphatic carboxylic acids have been used, which are more easily decomposeable and less toxic (cancerogenic) as compared to aromatic compounds.

Description of embodiments

A member of different collectors were prepared having the following composition of raw material:

D

Collector 14 Collector 15A Maleic acid PPG 600 Tall oil

Collector 15B Maleic acid PPG 1200 Tall oil

Collector 16B Maleic acid PPG 2000 Tall oil

Collector 17B Maleic acid Maleic acid 102 g PPG 4000 PEG 400 461 g Tall oil Unitol (Tall oil) 35 g

At the manufacture of all the above collectors 1 ml sulphu¬ ric acid has been used as catalyst.

Synthesis of the collector

The solid and liquid initial chemicals were mixed together with the catalyst in a flange falsk. Nitrogen gas was intro¬ duced into the mixture in order to provide stirring and avoid oxidation. The vacuum suction device was then started in order to reduce the pressure.

When the pressure was sufficiently reduced the flask was heated from room temperature to 150 - 200°C.

The synthesis was continued for about 3 hours, and was con¬ trolled at regular intervals. This was made for measuring the acid value, which showed how far the reaction had pro¬ ceeded. When the acid value was sufficiently low the synthe¬ sis was interrupted.

Another way of controlling how far the reaction has pro¬ ceeded was to measure the amount of water given off, as it is a condensation reaction.

Flotation tests with the collector

Magazine papers and daily papers were cut in pieces of about 3,5 cm. We used the same numbers of both journal papers and daily papers in all tests.

Correct amounts were weighed and put in a beater together with a part of the deinking chemicals.

After a period of rest the paper pieces were refined to a pulp in the beater. More chemicals were mixed in and the pulp was allowed to rest for about 1 hour. The pulp was further disintegrated in another beater. The collector was

ED

added and the slurry was brought to the cell, after which the flotation was started. Samples were taken at regular intervals from the flotation cell, said samples were later used for analysis. We controlled pH before and after the flotation.

At the tests were used 100 g daily paper, 45 g magazine paper, 4 1 water (40°C), 13 ml water glass, 30 ml NaOH (6,8%) and 2 ml 2% Bimex (R) (nonion tenside). The pulp was allowed to rest for 10 min and was beaten in a beater for 20 min.

Then 2 ml 2% Bimex(R) and 25 ml water glass was added. The pulp was stirred and was allowed to rest 1 hour. 6 1 water (40°C) was added and the pulp was disintegrated during 2 minutes.

The collector (0,73 g) was added. Full dosis is 0,5% of the dry weight of paper pulp. In cases where soap was used as collector 3,6 g CaCl ₂ had to be added.

About 4 1 water was further added when the cell is filled up.

Hand-sheet for optical tests

From the flotation cell was taken 500 ml mass and pH was adjusted to pH 5 with diluted sulphuric acid. The pulp is sucked off in a Buchner funnel with filter paper of 11 cm diameter. Then the sheets are rolled 10 times with a stain¬ less roller (3 clean blotting papers below and above resp. ) and are allowed to dry in room temperature with a lattice weight on top. The hand sheet are made from pulp from 0, 4, 4, 8 and 16 minutes flotation time. These are used for opti- cal tests.

Ink sludge

Ink sludge is collected between the times 0-4, 4-8, 8-16 minutes of flotation. The volume was measured on the respec- tive fraction. The filter paper was dried and weighed on a balance scale. From a fraction was taken 250 ml of well mixed sludge, which was sucked off in a Bϋchner funnel on a filter paper that was weighed beforehand. The content in the Buchner funnel was removed and transferred to the sheet, air-dried with a lattice weight on top and weighed.

Backwater purity

Settled filtrate from the following dewaterings:

50 ml filtrate from 0 min. flotation (handsheet for optical tests) ^

50 ml filtrate from 16 min. flotation (handsheet for optical tests) .

These were micro-filtrated (1,2 μm) with a membrane filter device (with water suction device). Optical tests were then performed on these microfliters.

The results of these optical tests (absolute values) are given in table 1.

The increase of brightness (A-brightness) for the different collectors is given in table 2.

Determination of acid value

About 2 g sample was weighed in a 300 ml E-flask. 100 ml ethanol (denaturated) was added to a E-flask and 15-20 drops of phenolphtalein solution was added. The ethanol was titra¬ ted to light rose colour change by means of 0,1 M KOH (only one or a few drops). The ethanol was added to the sample and the flask was shaken until the sample was dissolved. The sample solution was filtered to rose-red colour change with 0,1 M KOH and the amount of KOH needed for the change was determined. The titration must take place quickly, since C0 ₂ in the air consumes KOH. A long lasting titration gives the result of a higher acid value.

In the formula below the determined values of volume and mass are inserted:

Acid value = (M«K«ml)/m mg KOH/g solution M = molecular. weight k = concentration KOH (0,1M) ml = ml KOH required for the titration m = mass of sample (g)

Result

The test results prove that a collector based on maleic acid, polyethylene glycol with a mean molecular weight of 400, and tall oil gave the best deinking result. The in¬ crease of brightness after 16 min. flotation was 7,4 units (according to Hunter Lab.). Corresponding values for soap was 5,6 and for commercial collector (KAO) 6,7. The increase of brightness for the collector according to the invention was thus 10% higher for the commercial collector.

Besides the flotation was functioning better with the col¬ lector according to the invention as compared to soap and commercial collector.

In fig. 1 is shown in the form of block diagram the bright¬ ness increase after 16 minutes flotation for the collector according to the invention based on maleic acid, polyethyle- ne glycol and tall oil and for soap and commercial collector resp.

In fig. 2 is shown flotation graphs showing the brightness as a function of time for the collector according to the invention, soap and commercial collector.

The backwater purity with the collector according to the invention was besides higher.

Tests for determining the influence of different dosing amounts on the deinking result have also been performed. To every flotation there has been used 2 kg Bimex 400/ton and varying amounts of collector 1 A according to above. The added amounts were 1, 2, 3, 4 and 5 kg collector resp./ton pulp. In fig. 3 is shown flotation graphs (brightness as a function of time) for the different admixture amounts. An admixture amount of 5 kg collector/ton pulp gave about: 5% better brightness than an admixture amount of 1 kg collector /ton pulp.

As a summary it can be stated that the polyester according to the invention provides a collector which is very effec¬ tive and gives improved deinking results as compared to soap and commercial synthetic collectors. It is besides harmless to the environment due to its composition.