FI66943C - FOERFARANDE FOER FRAMSTAELLNING AV PAPPER MED HOEG VAOTSTYRKA - Google Patents

Abstract

1. A process for the production of paper exhibiting high wet strenght by adding a melamine-formaldehyde resin colloid to the paper stock and dewatering the paper stock on the paper machine, wherein the melamine-formaldehyde resin colloid used is a product which has been obtained by continuously mixing a 40 to 80% strength aqueous solution of an optionally modified methylol melamine with water and acid in a mixing zone under conditions of turbulent flow at a temperature of from 40 to 110 degrees C and a pH of 2 to 4, the time which elapses between mixing of the components and addition of the mixture to the paper stock being from 1 to 300 seconds, the solids content of the melamine-formaldehyde resin colloid solution being from 5 to 20% by weight.

Description

1 66943

Method for making high wet strength paper

It has long been known to add colloidal aqueous solutions of melamine / formaldehyde resins prepared by dissolving optionally modified methylol melamine in aqueous acid and aging the resulting solution to papermaking raw materials to improve the wet strength of the paper. The pH of the colloidal resin solution is in the range from 0.5 to 5, with a solids content of not more than 15% by weight. With a higher solids content, the colloidal resin solutions become unstable.

DE-AS 10 90 078 discloses the improvement of the potency of melamine / formaldehyde resin colloids by adding formaldehyde and then aging the solutions obtained. In this case, an improvement in the wet strength of the paper is achieved. In hitherto known methods for preparing melamine / formaldehyde resin colloids, it has been necessary to age the solutions for a certain time after the addition of the acid, usually 3 to 12 hours, before using the solutions as a wet strength agent in papermaking. In practice, storage tanks are required to age the acidified melamine / formaldehyde resin colloids. In addition, in the discontinuous preparation of melamine / formaldehyde resin colloids, it has always been necessary to use a mediation between the efficiency of the resin colloid and the storage stability of the colloidal solutions. For example, if an attempt is made to shorten the ripening time by changing the pH or temperature, the effectiveness of the aged solution will be reduced after a short time.

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a method for producing high wet strength paper by adding melamine / formaldehyde resin colloids to a paper raw material and removing water from the paper raw material in a paper machine, thereby no longer being forced to age melamine / formaldehyde resin colloids for long periods of time. storage tanks can be dispensed with and the efficiency of the 2 66943 resin colloid solutions can be easily adjusted.

According to the invention, the object is achieved by using as melamine / formaldehyde resin colloid a product obtained by continuously mixing a 40-80% aqueous solution of optionally modified melamine with water and acid in a stirred state using a vortex flow at a temperature of 40-110 ° C, pH 2- 4 and a residence time from the mixing state to the papermaking agent addition point of 1 to 3000 seconds, wherein the solids content of the melamine / formaldehyde-10 resin colloid solution is about 5 to 20% by weight.

Since the process according to the invention uses highly concentrated, possibly modified melamine solutions, preferably 60-70% aqueous solutions, a significant reduction in transport costs is achieved compared with known processes. All methylol melamines used for this purpose as well as modified methylol melamines are suitable for the preparation of resin colloidal solutions. Preferably, methylol melamines are used in which the molar ratio of melamine to formaldehyde is between 1: 2 and 1: 6. The preparation of aqueous solutions of methylol melamines and corresponding modified methylol methalamines is known. Usually, to prepare methylol melamine, an aqueous solution of melamine is heated to a temperature between 70 and 95 ° C and formaldehyde, for example formalin or para-formaldehyde, is added. The pH of the reaction mixture is regularly adjusted to between 7.5 and 11. Methylol melamines are known to be stable in the alkaline pH range. They can be etherified very easily in an acidic pH range with alcohols. Methanol, ethanol and n- or iso-propanol or n- or iso-butanol are preferably used for the etherification. Etherification with methanol is particularly simple and thus also recommended. It is possible to partially or completely etherify methylol melamine. The products 35 thus formed may contain 1-6, preferably 2-5, ether groupings. After etherification, the pH of the aqueous solution is adjusted to greater than 3,66943 to prevent condensation. If desired, etherified methylol melamines are already prepared in high concentrations, for example in 40-80% aqueous solutions. They can also be obtained by concentrating dilute solutions.

Highly concentrated, modified methylol melamine solutions can also be modified with alkali sulfites, alkali bisulfides or amines. The molar ratio of methylol melamine to sulfite or bisulfite is preferably in the range of 1: 0.5 to 1: 5. Suitable amines are, in particular, ammonium-10, primary and secondary alkylamine, di- and polyamine and, for example, mono-, di- and triethanolamine. The molar ratio of methylol melamine to amine is then preferably in the range 1: 0.5 to 1: 5.

The concentrated aqueous solution of the optionally modified methylol melamine is continuously stirred in a stirred space with the addition of water and acid - whereby the second reaction component may be premixed with water at -40-110 ° C, preferably 70-90 ° C, so that the in a flow-through residence vessel, if desired, the polycondensation of the modified methylol melamine takes place in the shortest possible time. When using temperatures above 100 ° C, work on pressure equipment.

When stirring both reaction components continuously - or if the other has already been premixed with water, only one reaction component, preferably an acid - a homogeneous solution must be formed in the shortest possible time - without concentration gradients - because methylmelamine, possibly modified due to high reaction rate would polymerize in a few seconds to an insoluble resin.

The mixing thus takes place in mixing vessels with a small mixing volume 35. The ingredients to be mixed flow strongly turbulent through the mixing space.

4,66943 Under these conditions, the components to be mixed together are affected by high energy densities. For example, the following commercial mixing devices are suitable for the process according to the invention: a) Syringe mixer - Mixing with high-speed liquid jets, preferably using water or a modified aqueous solution of methylol melamine if desired, b) Line mixer (pipeline-mounted vane mixer), c) static mixer and 10 d) mixer.

Preferably, the reaction ingredients are mixed with water in a syringe mixer, after which a residence time zone is placed - as a reaction tube or tank.

To obtain the required mixing energy in the syringe mixer, water or, preferably, a pre-mixed, optionally modified methylol-melamine solution with water is used, the spraying being carried out in a vortex flow at a speed of 5-50 m / s, preferably 10-20 m / s, by means of a syringe mixer nozzle. The energy-20 heys in the mixing space is at least 20 kW / m3 and is preferably greater than 50 kW / m 3.

The resin solution, if not already premixed with water, as well as the acid required to initiate the condensation reaction, can also be fed through 25 nozzles - in this case formed as a multi-material nozzle - or via separate supply pipes next to the nozzle or on the side of the mixing pipe. under.

Due to the impulse exchange between the spray beam and the surrounding reaction solution, rapid and efficient mixing takes place in the mixing state formed into a tube. The ratio of the diameters of the auxiliary tube is 2-20, preferably 3-6; ratio of pipe length to pipe diameter lpipe! dpipe is 5 "20 · 35 The components leave the pipe evenly mixed. Due to the short mixing time and the high energy density of 5 66943 fed to the mixing device, 50-7000, preferably 50-2000 kW / m3, it is possible to shorten the required reaction time to optimal to achieve maturation by adjusting the appropriate reaction conditions (pH 3-4, temperature 40-100 ° C) to 1-300 seconds without interference from flocculation due to excessive condensation or reduced efficiency due to too short a residence time.

The Cyp / Ignition - optionally polycondensation of the modified methylolime-10 laminin - takes place in the mixing state and the subsequent residence state, preferably in a vortex flow reaction tube connected to a syringe stirrer. After leaving the mixing device, a homogeneous solution flows - regardless of the mixing device used - through the pipe 15 or additionally through the tank, where the desired residence time is obtained. The residence time required is from a few seconds to several minutes, preferably from 15 seconds to one minute, depending on the reaction conditions (temperature, pH, if desired, the content and quality of the modified methylolimine).

In order to make the necessary temperature control during the mixing operation, all the ingredients to be mixed together can either be preheated to this temperature or only the water used for dilution can be heated and then to a higher temperature so that the temperature in the mixing range is within a given range. This can be done, for example, by introducing steam into the dilution water.

As the acids, hydrochloric acid and phosphoric acid or carbonic acids such as formic acid, acetic acid and propionic acid are preferably used.

This gives a highly effective melamine / formal-dehyde resin colloid solution with a solids content of about 5-20% by weight and which can be added directly to the papermaking raw materials or also after continuous or non-continuous further dilution with water in a weight ratio of 1:10 to 1:20. add to the paper stock suspension. The colloidal solutions prepared in this manner are effective and are preferably used directly after leaving the mixer. However, they can also be stored for a few hours, however, they lose their effectiveness as a wet reinforcing agent over a relatively long period of time.

The parts mentioned in the examples are parts by weight, the percentages given are determined by the weight of the substances. The dry crack length was determined according to DIN 53 112, sheet 1 and the wet crack length according to DIN 53 112, sheet 2.

The alkali resistance of the paper was determined in terms of the wet-tear length according to the procedure, however, the standard paper strips were stored in the 3% sodium hydroxide solution instead of water for 5 minutes at 80 ° C.

Preparation of etherified methylol melamine solution in water: 127 parts (about 1 mole) of melamine were mixed with 365 parts of a 37% aqueous solution of formaldehyde (about 4.5 moles of Cl 2 O). The mixture was adjusted to pH 8.5 with sodium hydroxide solution and heated to 70 ° C until the melamine was completely dissolved. The reaction was allowed to proceed for an additional 5 minutes at 70 ° C and then 640 parts (about 20 moles) of methanol were added. The pH of the solution was then adjusted to about 4.0 with phosphoric acid and maintained at 40 ° C for 30 minutes. After raising the pH of the solution to about 7 with sodium hydroxide solution, the solution was concentrated in vacuo (about 10 mbar) at 60 ° C to a solids content of 70% and then rapidly cooled to 20 ° C. The 70% solution had a viscosity of about 500 mPas (Brookfield, 20 / min) and can be diluted indefinitely with water.

Example 1

226 kg / h of water at 80 ° C and 38.3 kg / h of a 70% aqueous solution of the above etherified methylol melamine and 3.8 kg / h of 35 concentrated hydrochloric acid (37%) were stirred continuously in a syringe mixer, consisting of a binary nozzle with an inner bore 7 66943 2 mm in diameter and an annular gap 1 mm wide and terminating in a mixing tube 100 mm long and 20 mm in diameter with an impact plate 85 mm from the end of the nozzle, 5 that a spray velocity of 20 m / s (turbulent flow) was obtained for the water sprayed as a beam through the inner borehole. Etherified methylol melamine solution was added through the ring gap and concentrated hydrochloric acid was fed laterally into the mixing tube at the height of the nozzle head.

In the mixing space formed into a tube, the ingredients mix together efficiently and rapidly into a homogeneous solution. The energy density in the mixing room was 470 kW / m. To complete the polycondensation (maturation), there was a residence space connected to the mixing tube in the form of a reaction tube. The inner diameter of the reaction tube was 10 mm and the length was 30 m.

The residence time of the reaction mixture in the mixing space and then in the reaction tube until the papermaking was added to the raw materials was 30 seconds, the temperature was 75 ° C and the pH of the mixture was 3.0.

In this way, a 10% resin colloid solution was obtained, which was added directly to the papermaking raw materials in a long-wire test paper machine with a working width of 75 cm, corresponding to a 5% addition of the resin colloid solution based on the dry paper material. The operating speed of the Pa-25 machine was 66 m / min. The paper consisted of bleached sulfite cellulose and had an area-2 weight of 60 g / m 2. The pH of the material suspension was adjusted to 4.5 by the addition of 2% aluminum sulfate and dilute sulfuric acid. The degree of grinding was 35 ° SR. Sulphite cellulose was fed to the paper machine at 3 kg / min. The properties of the obtained paper are shown in Table 1.

Example 2

148.3 kg / h of water at 80 ° C and 28.8 kg / h of a 70% aqueous solution of the etherified 35 methylol melamine described above were continuously added to the suction side of the centrifugal pump, mixed in the pump and fed to a syringe boiler through a single-substance nozzle. the diameter was 2 mm, at an injection speed of 15 m / s (vortex flow) 3 corresponding to an energy density of 200 kW / m. 2.8 kg / h of concentrated hydrochloric acid were added to the 5 mixing conditions shown in Example 1. The dimensions of the reaction tube were the same as in Example 1. The residence time of the reaction mixture until it was added to the paper material was 50 seconds, the temperature was 75 ° C, and the pH of the mixture was 3.0.

This 10% resin colloid solution was added in 10 paper machines to the same material mixture as in Example 1, 10%, based on dry fibrous material. The properties of the paper obtained in this case are shown in Table 1.

Comparative Example 84.5 kg of water was heated to 40 ° C in a 250 liter heated tank equipped with a stirrer. The temperature was kept constant and 1.4 kg of concentrated hydrochloric acid (from 37%) and, when a dilute acid solution had formed, 14.3 kg of the 70% aqueous solution of etherified methylol melamine described above were added. To mix the reactants, the solution was mixed at an energy density of 0.4 kW / m3. Stirring is complete after about 5 minutes.

Stirring was then stopped and the mixture was aged at 40 ° C for 3 hours. The pH of the mixture was 2.2. To examine the melamine / formaldehyde resin colloid solution as a wet reinforcing agent, an amount of resin colloid of 150 g / min (corresponding to 5%) based on the dry fibrous material of the paper raw material was added. The pH of the material suspension was adjusted to 4.5 by the addition of 2% aluminum sulfate and further dilute sulfuric acid. This degree of grinding of the material suspension was 35 ° SR and water was removed from it in the paper machine shown in Example 1 at a speed of 66 m / min. In this case, about 3 kg / min of paper was made from bleached sulfite cellulose with a basis weight of 35 to 60 g / m 2. The paper properties are shown in Table 1.

9 66943

Comparative Example 2

Comparative Example 1 was repeated except that 300 g / xn, corresponding to 10% of the fibrous material based on a 10% melamine / formal-5 dehyde resin colloid solution, was used for the papermaking materials. The properties of the paper thus obtained are shown in Table 1.

Table 1 10% Resin Colloid Solution Continuous Discontinuous 10 Without Example Comparative Example

Addition increase 1 2 12

Dry penetration length fmj 5θ4θ 5700 5950 5710 5900 Wet penetration length Cm) 80 1350 1750 1290 1700 Wet penetration length (m) 255 1780 2200 1690 1950 15 after aging 5 min, at 130 ° C

Alkali resistance (m) 0 860 1200 850 1120

Alkali resistance (m) 105 1170 1390 1100 1300

after aging the paper for 20 min, 130 ° C

Claims (3)

10 66943 A process for producing high wet strength paper by adding melamine / formaldehyde-resin-5 colloids to a stock and removing water from the stock in a paper machine, characterized in that a product obtained by continuously mixing 40% of the optionally modified methylol melamine is used as the melamine / formaldehyde resin colloid. aqueous solution with water and acid in a mixing zone in a vortex flow, at a temperature of 40-110 ° C, at a pH of 2-4, with a time between mixing the components and adding the product to the stock, and wherein the melamine / formaldehyde -resin colloid solution has a solids content of about 5-20% by weight. Process according to Claim 1, characterized in that the time between mixing the components and adding the product to the stock is 15 to 60 seconds. Method according to Claim 1 or 2, characterized in that the energy density in the mixing zone is at least 20 kW / m.