FI104339B - Improved papermaking process - Google Patents

Description

104339

The invention relates to a process for making paper or a similar fibrous product, such as cardboard. The method can improve the quality of fine paper and the runnability of a papermaking machine compared to normal neutral sizing by treating the pulp stock used in paper making with peracid before neutral sizing. The invention further relates to the use of peracid in the treatment of bleached pulp prior to neutral sizing.

In the pulp gluing of paper or similar fibrous product, such as cardboard, under neutral or mildly alkaline conditions, alkyl ketene dimer (AKD) or alkenyl ketene dimer and / or alkenyl / alkyl succinic anhydride (ASA 02), as disclosed in WO-94/13883, GB-A-2 252 984, EP-B-220 941, EP-B-228 576 and WO-97/35068. AKD and ASA 20 are dispensed into the pulp before the headbox. Because the substances are oil-soluble and insoluble in water, they are emulsified into an aqueous dispersion prior to administration.

The purpose of chemical pulp bleaching is to complete the removal of residual lignin from the pulp after 25 boils. Bleaching! * Is often started by oxygen delignification according to known methods, followed by further bleaching by various methods. In TCF (total chlorine-free) bleaching, pulp bleaching is carried out completely without chlorine-chemical cabbages. oxygen chemicals such as ozone, peracetic acid or hydrogen peroxide under acidic or alkaline conditions.

ECF (elementary chlorine free) bleaching uses chlorine-35 dioxide steps and an alkaline step between them. ECF bleaching is also increasingly used for so-called "bleaching". oxygen chemicals to enhance bleaching.

104339

The use of peracids, especially peracetic acid in pulp bleaching has long been known, TCF bleaching being its most important application. Peracetic acid (PAA) is a highly selective delignification chemical that can maintain the strength properties of pulp 5. When using peracetic acid, the optimum pH is about 4-7.

Peracetic acid is generally prepared by mixing concentrated acetic acid with hydrogen peroxide. After sufficient reaction time, a solution is formed containing peracetic acid plus 10 inert vinegar, hydrogen peroxide and water. This so-called. the equilibrium solution can be used either as such or it can be purified by distillation, whereby unreacted starting materials can be reused in the process. Distilled peracetic acid, which does not contain significant amounts of free peroxide or 15 acetic acid, is currently the most commonly used peracetic acid product for bleaching chemical pulps. It has been found advantageous to use distilled peracetic acid in peracetic acid bleaching, as disclosed, for example, in JP 57-21591 and EP 578 304. It has also been found that peracetic acid can be used to increase the whiteness of already bleached pulps. Such a method is described in Applicant's Finnish Patent Application FI 974575. The method is a post-bleaching process with peracid and a solution of alkaline earth metal to increase the whiteness and whiteness of the pulp to the desired level. In this case, the peracid renders the chromophore groups of the pulp, mainly carbohydrates, colorless. When using the method, only a few pounds of PAA can increase the luminance of the pulp by 1.5 to 2% ISO ver-30, from a lightness level of 89-91% ISO to 91-92% ISO. At the same time, post-bleaching compensates for changes in the lightness of the bleached pulp.

Nowadays, the major application of neutral adhesives such as AKD and ASA 35 is fine paper, which also produces problems caused by AKD and ASA, such as various adhesion problems, paper slippage, and the slow development of bonding. Many of these problems are related to the retention of 104,339 AKD and ASA. Retention is important for successful bonding. The glue that enters the zero water cycle will hydrolyze and the hydrolyzed glue can cause various sticking and dirt problems. Dirt problems are manifested in the deterioration of the brightness, color, strength, and bonding of the paper and in the increase in porosity. Improved retention of AKD and ASA reduces the amount of AKD and ASA entering the zero-water cycle, and thus also reduces the amount of hydrolyzed adhesive and reduces the risk of precipitation.

10

In addition, the lightness, pH and, at the same time, the charge state of the pulp coming from the bleaching mill of the pulp mill to the fine paper machine often vary so that it causes problems in gluing the paper. Brightness fluctuations also cause problems in the administration of op-15 brighteners, which increases the system's sensitivity to interference.

In integrated paper mills, the pulp entering the fine paper machine is often quite low, up to 2.5-3. In order to narrow the pH difference in the paper machine's hot water, some mills are subjected to object neutralization with a slurry pH of 4.5-5.5. Thus, malfunctions in the control or mixing system and buffer capacity of the pulp stock can easily cause pH to escape into the undesired range. This ai-25 results in a variation in pH which in turn also results in a charge-phase variation. Since the retention of AKD and ASA depends on pH and charge state, pH and charge state play an important role in the adhesive retention and its smoothing would also result in a significant ease of adhesion.

30

According to the invention, it has now been found that the adhesive treatment of the pulp can be greatly improved by treating the pulp with peracid before neutral gluing. Characteristic features of the invention will be apparent from the appended claims 1-12.

During adhesive runs, clear synergistic effects were observed between neutral adhesives and peracid treatment.

104339

Butyric acid treatment can modify the properties of the fibers to be particularly suitable for neutral bonding. The pH of the pulp is buffered and at the same time the charge state of the pulp is stabilized by treatment. Together, these provide great benefits in terms of fine paper quality and paper machine runnability. The greatest advantage achieved is the stabilization of the wet head and thus the runnability of the paper machine. In addition to smoother, better paper quality, the need for optical brighteners is reduced. An additional benefit is the reduced microbial activity of mik-10 in the process due to residual peracid. The difference with the normal use of peretics in bleaching as a delignification chemical is that the treatment is already done on a completely bleached pulp with a very low kappa number or lignin content. It is therefore not a delignification term.

Specifically, peracid treatment can smooth out the lightness of the pulp, buffering the pH, and smoothing the charge so that the subsequent gluing on the paper machine will be op-20.

The peracid can be added to the pulp after the bleaching steps in the pulp tube, storage tower and / or paper machine, preferably before the headbox. The peracid can also be added to the final chlorine dioxide step in the bleaching plant. Suitable amounts of peracid use are about 0.1 to 5 kg / tonne, preferably 0.5 to 3 kg / ton. Suitable stabilizers may be added to the peracid treatment, such as, for example, alkaline earth metal salts or complex form. The treatment can be carried out at a consistency of 0.5 to 30%. The pH may be in the range of 2.5 to 9, preferably 4 to 7, and the temperature 20 to 100 ° C.

Various organic or inorganic peracids or mixtures thereof may be used in the process. Peracetic acid is particularly suitable for this purpose. The peracid may also be mono-sulfuric acid (Caronic acid) or a mixture of Caronic acid and a percarboxylic acid. Peracetic acid can be 104339 either in the so-called. equilibrium solution or a solution prepared by distillation or other means which does not contain significant amounts of free vinegar and / or hydrogen peroxide. The manner in which the peracetic acid solution is prepared is not essential to the operation of the invention.

In the process of the invention, the paper is made using a neutral adhesive which is an alkyl ketene dimer, an alkenyl ketene dimer, an alkenyl succinic anhydride or an alkyl succinic anhydride. The neutral adhesive is added to the pulp in an amount of 0.01-0.6% by weight based on the dry solids content. The neutral adhesive is usually added to the pulp as an aqueous dispersion.

15 The applicability of the process is not affected by other chemicals or fillers used in the paper machine, such as e.g. retention agents, optical brighteners, dyes and foaming agents. The retention agents may include e.g. cationic polymers and starch and bentonite and silica and aluminum based sols and gypsum used in combination therewith. Also, the raw material of the pulp or the cooking process has no effect on the performance of the invention. It is also self-evident that the placement of the neutral adhesive or the order of addition of the paper chemicals or the other running parameters of the paper machine as such will not affect the operation of the invention. In the invention, it is essential that the bleached chemical pulp is subjected, after treatment with peracid, to a papermaking process using a neutral adhesive for gluing.

The invention is illustrated by the following examples

Example 1.

In a factory test, the peracid treatment of softwood and birch pulp was made with 2.5 kg / tm PAA. The peracetic acid polar solution used was distilled and contained 38% peracetic acid and less than 2% free peroxide. The temperature in the storage tower ranged from 55 to 60 ° C and the delay for pulp and paper mill 104339 was 2 to 30 hours depending on the production rate. The lightness of the pulp increased from 90% ISO, 1.5% ISO with birch pulp and 1.9% ISO with softwood pulp. . At the same time, the standard deviation of the lightness measurements was reduced by 30% (reference 1.0, during PAA 5 the deviations of 0.7 were the same for both mass grades). At the same time, the pH was found to be buffered to about 5, thereby stabilizing the pH of the pulp going to the papermaking machine. As the experiment continued, the brightness was restored to its original level by raising the beaker, and then the brightness at pH-10 and the pH-buffering effect remained unchanged.

In addition, during the experiment, the need to add optical brightener to the pulp was noticeably reduced (80%) due to the increase in brightness. At the same time, it was observed that the adhesive content of tap water in the water exiting the machine was reduced, meaning that the retention of AKD in the paper web was significantly improved. Microbial concentrations in the headbox were also reduced by more than 99%.

Example 2.

20

Peracid treatment of softwood and birch pulp was done with a PAA dose of 2 kg / tm. The temperature in the storage tower was 40 -

O

60 C and a delay of 2 to 24 hours depending on the pulp and paper mill production rate. The lightness of the pulp increased from 89% ISO to 1.4% ISO with birch pulp and from 90% ISO to 1.7% during processing. ISO with softwood. The pulp slurry going to the paper machine contained about 50% of the original 2 kg / tm dose, i.e. 1 kg / tm.

30 Before the PAA treatment, the paper machine had added optical brighteners to the pulp. Thanks to PAA treatment, it was possible to: - * completely add optical brighteners to the pulp. The following table shows the results for the trial period.

35 104339 7

Table 1.

Concentrations of bound and free AKD in the paper during the test period. The adhesive used was a commercial alkyl ketene-5 dimer based wax dispersion product called HYDRORES 551, MD. The active ingredient of the adhesive was cationic AKD wax (20%) and was supplied at a dry solids content of 22% with a dispersion pH of 3.7. The peracetic acid used in the experiment was a distilled solution of Pere acetic acid containing 38% PAA, 4% acetic acid-10 polo and 1.5% H 2 O 2.

7Z i Π AKD- Optical TTT _ “Free / Committed. . ..,. PAA dose.

Roller No Dispensing, Brightener,,. .., lL Note! AKD. ". stock tonnage, kg / h ___ kg / h ___ 580 3.2 1.5 1.3 No Reference 584 3.0 1.5 1.3 No Reference 963 2.9 1.8 2.0 No Reference 982 3.1 1.7 3.2 No Reference 322 3.3 2.1 No Reference 336 3.0 2.1 No Reference 814 2.4 1.7 0.0 2.0 818 2.2 1.7 0.0 2 , 0 964 1.5 1.6 0.0 2.0 780 1.5 1.7 0.0 2.0 _

As can be seen in the table, the ratio of bound to free AKD significantly improved. Due to the improved and even lightness of the pulp and the improved color tone, the dispensing of the opt-15 brightener to the pulp could also be dispensed with.

• · 'The microbial concentrations were also reduced in the paper machine so that the total dose of biocides could be reduced by an average of 50% during the experiment.

Example 3.

The ECF bleached conifer sulphate pulp was treated by the process of the invention. In order to verify the beneficial effect of the method on AKD bonding, the zeta potential of 25 pulp stock was measured. The peracid treatment was carried out at 50 ° C for an hour's reaction, the PAA dose was θ 104339 3 kg (38% distilled peracetic acid product), and the pH was buffered during the reaction to 5 (5). is made from a stock suspended in ion exchange water: 5 bleaching zeta potential

ECF -3.8 mV

ECF + Peracetic Acid (3 kg / tn) -7.5 mV

After bleaching 10 ECF, the surface charge of the fibers can be increased by the use of peracet. Increasing the zeta potential on the fiber surface increases the retention of the cationic adhesive on the fiber surface. The cationicity of the adhesive may be achieved by cationic starch, polymers or polyaluminium compounds.

Claims (12)

104339 A process for the production of paper or similar fibrous product, characterized in that the bleached pulp stock is treated with peracid to modify the properties of the fiber before the addition of the neutral glue to the pulp stock. 2. A method according to claim 1, characterized in that the pulp has a lightness of at least 85% ISO before treatment with the fly. Process according to claim 1 or 2, characterized in that the pulp kappa number before treatment with peracid is not more than 4. 15 Process according to one of the preceding claims, characterized in that the amount of peracid used for the treatment of peracid is 0.1-5 kg / tm, preferably 0.5-3 kg / tm. 20 Process according to claim 4, characterized in that the peracid is peracetic acid. Process according to any one of the preceding claims, characterized in that the pH of the peracid solution is in the range of 2.5-9, preferably 4-7. 7. A process according to claim 1, characterized in that the neutral adhesive is an alkyl ketene dimer, an alkenyl ketene dimer, an alkenyl succinic anhydride or an alkyl succinic anhydride. A process according to claim 1 or 7, characterized in that the neutral size is added to the mass in an amount of 0.01 to 0.6% by weight based on the dry matter content of the mass. 10 104339 Method according to one of the preceding claims 1, 7 or 8, characterized in that the neutral adhesive is added as an aqueous dispersion. Method according to one of the preceding claims, characterized in that the peracid treatment is carried out after the bleaching steps in a pulp tube, storage tower and / or on a paper machine, preferably before the headbox. Process according to any one of the preceding claims, characterized in that the peracid treatment is carried out on a paper machine or elsewhere in the paper mill. Use of a solution containing peracid for treating bleached pulp at a paper mill 15 before adding neutral glue. • · ♦ Patentkrav 104339