JPH0610233B2 - Method for removing free formaldehyde in urea resin particle dispersion - Google Patents

Description

The present invention relates to a method for removing free formaldehyde contained in a urea resin particle dispersion liquid.

Urea resin particles having an average particle diameter of 1.5 to 10 µ, which are formed by agglomeration of urea resin particles having an average particle diameter of 0.1 to 1.0 µ, are reinforced and filled with natural rubber, synthetic rubber, polyethylene and other thermoplastic resins. Can be used as an agent, white pigment,
In particular, it is already known that it is useful as a filler for improving the whiteness of paper, opacity, and preventing strike-through of printing.

Usually, the urea resin particle dispersion liquid is obtained by the condensation reaction of urea, which is the main raw material, with formaldehyde, but after the reaction is completed, it contains unreacted formaldehyde (hereinafter abbreviated as FF) usually called free formaldehyde. This F
Since F has an irritating odor peculiar to formaldehyde, an FF removing step is added to the production of urea resin particles. For example, a method of washing with water, a method of removing urea by adding urea, and a method of removing ammonia by adding ammonia or a salt thereof and reacting them are known. However, the method of removing FF by washing with water is carried out by repeating dispersion of urea resin particles in water and excessive or centrifugal separation, but the drainage of the liquid generated by this is required to be treated, which requires a great deal of cost. There is a drawback. The method of adding urea and reacting it to remove it is that the reaction product of FF and urea is deposited on the urea resin particles and fills the voids of the particles, and the function of the voids of the particles is as a paper filler. When applied, it has the drawback of lowering the printing strike-through prevention function.

Further, in the method of adding ammonia or ammonium salt and reacting it to remove it, since the reaction product of FF and ammonia or ammonium salt becomes a compound having an unpleasant odor, the urea resin particle dispersion containing this unpleasant odor compound is dispersed. Of course, when this liquid is applied to paper as a white pigment or a filler, this odor is generated from the processed paper obtained.

The present inventors do not require a large amount of waste water treatment equipment, do not reduce the function of the voids of the particulate matter, and yet do not generate an unpleasant odor. As a result of continuing diligent research on the method of removing formaldehyde, FF was added by adding sulfite or sulfite.
The present invention has been achieved by finding that a method of reacting with and adjusting the final pH is suitable for this purpose.

That is, the present invention is characterized in that 0.5 to 1.5 mol of sulfurous acid or sulfite is added to 1.0 mol of FF contained for reaction, and the final pH is adjusted to 4 to 10 to disperse a urea resin particle body. This is a method of removing FF in the liquid.

Hereinafter, a typical embodiment of the method of the present invention will be described in the order of steps.
First, a known method, for example, the method of JP-A-54-135893
A dispersion of urea resin particles containing F is produced. That is, formaldehyde solution, urea, carboxymethylcellulose and water are mixed and then pH is adjusted with a caustic soda solution.
It is adjusted to 7 and reacted to obtain an initial condensate. An aqueous solution of this initial condensate and an aqueous solution of several percent of sulfuric acid are continuously mixed with an in-line mixer, and fed onto an acid-resistant endless belt before the condensate starts to solidify. The mixed solution is solidified on the belt and simultaneously cured. The solid matter thus obtained is collected in a container, water is added and stirred to form a slurry (hereinafter referred to as a slurry forming step). Then, it is finely pulverized with a colloid mill (hereinafter referred to as a pulverization step) to obtain a urea resin particle dispersion liquid containing FF.

After that, a predetermined amount of sulfurous acid or sulfite is added, and the pH is adjusted to 5 to 9 and preferably 6 to 9 with an aqueous solution of caustic soda or an aqueous solution of sulfuric acid which is stirred at 0 to 90 ° C for 3 to 30 minutes (hereinafter referred to as FF removal reaction). (Hereinafter referred to as pH adjusting step) is a method for removing FF in the urea resin particle dispersion liquid of the present invention, whereby a urea resin particle dispersion liquid from which FF has been removed can be obtained.

The sulfurous acid used in the present invention is a sulfurous acid aqueous solution obtained by absorbing sulfurous acid gas and water. Sulfite is a sodium, potassium or ammonium salt of sulfite or acidic sulfite. These may be used alone or in combination of two or more. Generally, sodium sulfite, acidic sodium sulfite, etc. are used, and about 5 to 20% by weight (hereinafter, all% are% by weight).
It is easy to handle when used in an aqueous solution.

In the present invention, the amount of sulfite or sulfite added is in the range of 0.5 to 1.5 mol with respect to 1.0 mol of FF contained in the urea resin particle dispersion liquid. Addition amount is 0.5
If it is less than the molar amount, the formaldehyde odor is not sufficiently removed. The reason for limiting the amount added to 1.5 mol or less is that there is no FF already when the amount added is 1.5 mol.
This is because the usefulness of the added amount of 5 mol or more is not recognized. From this tendency, the addition amount is preferably 0.75 to 1.2.
It is in the range of 5 mol.

The FF content of the urea resin particle dispersion liquid before the FF removal reaction is usually 1000 to 3000 ppm, and the FF content is 5
If it is less than 00ppm, the pungent odor of formaldehyde becomes almost undetectable. Therefore, the lower limit of the amount of sulfite or sulfite added to 1.0 mol of FF is FF content of 500 ppm.
The amount of FF contained before the FF removal reaction can be reduced to 10
This is the case of 00 ppm, and when the content of the urea resin particle dispersion liquid before the FF removal reaction is 1000 ppm or more, the addition amount needs to be 0.5 mol or more.

In order to achieve the object of the present invention, it is necessary to prevent the reaction product of FF and sulfite or sulfite from decomposing during storage to generate FF. For this purpose, the final pH of the urea resin particle dispersion liquid after removing FF by the above method is adjusted to be in the range of 5 to 9, preferably 6 to 8.

In order to achieve the object of the present invention, it is necessary to prevent decomposition of the bisulfide compound, which is a reaction product of FF and sulfite or sulfite, during storage to generate FF. The aqueous solution of the bisulfide compound is most stable in neutrality, and as acidity or alkalinity increases, the rate of decomposition to formaldehyde increases.

Therefore, the final pH of the urea resin particle dispersion liquid after removing FF using sulfite or sulfite is adjusted to 5-9.
When the pH is outside this range, the bisulfide compound is decomposed, and the FF content is increased to 500 ppm or more and the pungent odor of formaldehyde can be detected by, for example, storage for 7 days. Therefore, a more preferred final pH is 6-8.

When the sulfur resin or sulfite salt is added to and reacted with the urea resin particle dispersion liquid containing the FF, the dispersion liquid is preliminarily adjusted to pH 5 to 9 with a caustic soda aqueous solution, and then the FF removal reaction is performed, and then the final reaction is performed. The order of performing pH adjustment is more preferable because sulfurous acid is less likely to be vaporized as a gas from the FF removal reaction system and the FF removal reaction can be efficiently performed. In particular, when sulfite is used rather than sulfite, the order in which the FF removal reaction is performed after the preliminary pH adjustment is preferable.

Further, in the slurrying step, the crushing step, the FF removing step and the pH adjusting step in the order of the steps of the representative aspect of the present invention shown above, the step order of performing the crushing step after the FF removing step or after the pH adjusting step. It is also possible to

The FF-free urea resin particle dispersion liquid obtained by the method of the present invention is usually a dispersion liquid having a concentration of 15% or less, but it is necessary to have a high concentration for convenience of use, transportation, storage and the like. In this case, it can be dehydrated into a cake having a concentration of about 25%, or further dried to obtain a powder.

According to the method of the present invention, it is possible to remove the formaldehyde odor without leaving an unpleasant odor, and when applied to paper, it is confirmed that it does not cause a reduction in the opacifying action of the paper, especially the strike-through prevention action of printing. Was given.

Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 38.4 parts by weight of a 37% aqueous solution of formaldehyde (all parts below are by weight), 18.9 parts of urea, 0.7 parts of carboxymethyl cellulose and 42.0 parts of water were mixed, and the pH was adjusted to 7 with a 20% aqueous sodium hydroxide solution. The reaction was carried out at ℃ for 2 hours to obtain about 100 parts of urea-formaldehyde initial condensate. To this condensate, 180 parts of 2.7% sulfuric acid aqueous solution was added and mixed, and the mixture was mixed at 60 ° C.
Left for hours. Next, the obtained gel-like material was roughly crushed into a shape having a diameter of about 2 mm and stirred to make a slurry. The pH of this slurry liquid is 1.5, and FF in the aqueous phase
The amount was 4400 ppm, which had an extremely strong pungent formaldehyde odor. After finely pulverizing this slurry liquid with a colloid mill, 13.55 parts of a 15% acidic sodium sulfite aqueous solution was added to 100 parts of this FF-containing urea resin particle dispersion liquid (hereinafter referred to as FF-containing dispersion liquid in Example 1) (at this time). The molar amounts of acidic sodium sulfite and FF are equimolar), 5 at 25 ° C
The FF removal reaction was performed by stirring for 1 minute. Subsequently, 7.2 parts of 20% aqueous sodium hydroxide solution was added to adjust the pH to 7.5. The FF content in the aqueous phase of the thus obtained urea resin particle dispersion liquid of the present invention (hereinafter referred to as “Example 1 dispersion liquid”) is
It was 100 ppm, and no formaldehyde odor could be detected.
The concentration of urea resin particles in the dispersion was 7.2%. This Example I dispersion was added to 100 parts of L.BKP dry pulp at a ratio of 138.9 parts (urea resin particles to pulp: 10 parts: 100 parts) to prepare a paper. The opacity of the dispersion-added paper obtained in Example 1 and the strike-through prevention rate of printing were measured by opacity after printing, and the results are shown in Table 1.

The FF in the aqueous phase of the urea resin particle dispersion liquid was measured by measuring the FF amount in the liquid obtained by passing the dispersion liquid through paper. The FF amount was quantified by the sodium sulfite titration method. It was carried out by. The paper is made with a TAPPI square paper machine and the basis weight is 4
It was 5 g / m ² . The opacity of paper conforms to JIS (P-8138),
The opacity after printing was carried out according to the method described in the literature (Paper Technology Times, September 1977, p1-13).

Example 2 15% acidic sodium sulfite aqueous solution 1 in the above Example 1
Instead of adding 3.55 parts 22.75% aqueous sodium sulfite solution 1
Urea resin from which FF was removed under exactly the same conditions and procedures except that 3.55 parts were used (the molar ratio of sodium sulfite to FF was 1.25: 1.0) and 2.2 parts of 20% aqueous sodium hydroxide solution were used. A particle dispersion liquid (hereinafter referred to as the dispersion liquid of Example 2) was obtained. FF content in the aqueous phase of this dispersion is 0 pp
m and pH was 6.9. The urea resin particle concentration was 6.9%. This urea resin particle dispersion is
4.9 parts (10 parts: 100 parts urea resin particles to pulp)
Example 2 dispersion-added paper was obtained under exactly the same conditions and procedures as in Example 1, except that the opacity of the paper and the opacity after printing were measured and the results are shown in Table 1. .

Example 3 Example 1 Until the FF-containing dispersion liquid was obtained, the FF-containing urea resin particle dispersion liquid 10 was obtained under exactly the same conditions and procedures as in Example 1.
Preliminary pH by adding 7.2 parts of 20% caustic soda aqueous solution to 0 parts
After the adjustment, 1.0 part of sulfurous acid gas was absorbed with stirring (the molar ratio of sulfurous acid gas to FF at this time was 0.8: 1.
FF removal reaction was performed at 25 ° C. for 10 minutes. Subsequently, 3.1 parts of a 20% aqueous sodium hydroxide solution was added to adjust the pH to 7.2. The FF content in the aqueous phase of the thus-obtained urea resin particle dispersion liquid of the present invention (hereinafter referred to as the dispersion liquid of Example 3) was 250 ppm, and formaldehyde odor was hardly perceivable. The concentration of urea resin particles in the dispersion was 7.9%. An example was carried out under exactly the same conditions and procedures as in Example 1, except that 126.6 parts of this urea resin particle dispersion liquid was used per 100 parts of dry pulp (10 parts: 100 parts of urea resin particle to pulp). The 3 dispersion-added paper was obtained, and the opacity of the paper and the opacity after printing were measured in the same manner, and the results are shown in Table 1.

Comparative Example 1 To 100 parts of the FF-containing urea resin particle dispersion liquid obtained in exactly the same manner as in the conditions and procedures for obtaining the dispersion liquid of Example 1, 4.96 parts of a 30% aqueous urea solution was added (the mole of urea to FF at this time). The ratio is 2: 1), after stirring for 30 seconds, 4.0 parts of a 20% aqueous sodium hydroxide solution was added to adjust the pH to 2.5 and 40
The mixture was stirred at 0 ° C for 30 minutes. Then, 3.5 parts of 20% aqueous sodium hydroxide solution was added to adjust the pH to 7.5. The FF content in the aqueous phase of the thus obtained urea resin particle dispersion liquid of Comparative Example 1 (hereinafter referred to as Comparative Example 1 dispersion liquid) was 320 ppm.
The concentration of urea resin particles in this dispersion was 8.0%. This Comparative Example 1 Dispersion 1 to 100 parts of dry pulp
Comparative Example 1 dispersion-added paper was obtained under exactly the same conditions and procedures as in Example 1 except that 25 parts (urea resin particles to pulp: 10 parts: 100 parts) were used, and the opacity of the paper was similarly obtained. The opacity after printing was measured and the results are shown in Table 1.

Comparative Example 2 2.8 parts of 20% ammonia water was added to 100 parts of the FF-containing urea resin particle dispersion liquid obtained by exactly the same conditions and procedures as those for obtaining the dispersion liquid of Example 1 (ammonia to FF at this time). The molar ratio was 2: 1) and the mixture was stirred at 40 ° C. for 1 hour while adjusting the pH to 7.0 with a 20% aqueous sodium hydroxide solution. The FF content in the aqueous phase of the thus obtained urea resin particle dispersion liquid of Comparative Example 2 (hereinafter referred to as Comparative Example 2 dispersion liquid) is
It was 250 ppm. Although the formaldehyde odor was not perceived, the unpleasant odor of trimethylenehexamine was felt, and it was confirmed that the work environment was unsuitable. The concentration of urea resin particles in this dispersion was 8.2%. 100 dry pulp
Comparative Example 2 dispersion-added paper was prepared under exactly the same conditions and procedures as in Example 1 except that 121.95 parts of this Comparative Example 2 dispersion (10 parts by weight of urea resin particles to 100 parts by weight of pulp) was used for each part. Then, the opacity of the paper and the opacity after printing were measured in the same manner, and the results are shown in Table 1.

Comparative Example 3 In Example 1, a urea resin particle-added paper was obtained under exactly the same conditions and procedures except that the FF-containing dispersion liquid of Example 1 was not used, and the opacity of the paper and the opacity after printing were similarly obtained. The measurement was performed and the results are shown in Table 1.

As shown in Table 1, FF contained in the urea resin particle dispersion liquid according to the method of the present invention was removed more than the known method, and there was no unpleasant odor, and even when it was used as a filler for paper. It was found to have a high opacifying effect and an opacifying effect after printing.

The difference between the opacity of the dispersion-added paper in Example 1 of 89.2% and that of Comparative Example 1 of 85.8% is the difference between the paper basis weight of 45 g / m ² and 52 g / m ² , that is, 7 g. / m is equivalent to paper thickness increment of ^2, the effect is great considering that improvements in the state of the newspaper from 49 g / m ² to 46 g / m ² is very difficult to achieve effort targets .

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Claims (1)

[Claims] 1. Urea characterized in that 0.5 to 1.5 mol of sulfurous acid or sulfite is added to 1.0 mol of free formaldehyde contained for reaction, and the final pH is adjusted to 5 to 9. A method for removing free formaldehyde in a resin particle dispersion.