JP2002234925A - Method for preparation of urea-formaldehyde resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stable preparation of a urea-formaldehyde resin having an appropriate hot water extraction rate. SOLUTION: In this preparation method of urea-formaldehyde resin, a urea- formaldehyde initial condensate aqueous solution having not more than 1 mass % of free formaldehyde is reacted with urea, then it is methylenized using an acidic substance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a urea-formaldehyde condensate having excellent decomposition characteristics.

[0002]

2. Description of the Related Art Urea-formaldehyde condensates are used as molding materials, adhesives, paints, processing agents for paper and textiles, foaming agents for construction, coagulants, casting agents, soil strengthening agents for soil improvement or civil engineering work, fertilizers. Used in other fields. Conventionally, as a method for producing a urea-formaldehyde condensate having these various uses, urea, formaldehyde, and water are subjected to a methylolation reaction in the presence of an alkaline catalyst, followed by a methyleneation reaction using an acidic substance. Manufacturing methods are known.

[0003] Examples of such a production method include Japanese Patent Publication No. 2-25880 and Japanese Patent Publication No. 2-39476. In Japanese Patent Publication No. 2-39476, an initial urea-formaldehyde having a water-soluble condensation degree is used. A method for producing a urea-formaldehyde condensate having a suitable decomposability by producing a condensate, further adding urea to an aqueous solution of the initial condensate, and then subjecting it to a methylene reaction using an acidic substance is disclosed. .

When the urea-formaldehyde condensate obtained by this production method is applied to soil, the nitrogen-containing compound is released for a long period of time, for example, as long as 3 years or more, without adversely affecting the germination of seeds. Because
It is said that the fertilizing effect lasts longer than conventional slow-release nitrogen fertilizers, coated fertilizers, and the like, and that it is not necessary to add nitrogen sources.

However, in these conventional methods, it is necessary to select appropriate reaction conditions and strictly control the reaction in order to obtain a urea-formaldehyde condensate having an appropriate hot water elution rate. The urea having an appropriate hot water elution rate within a certain range, for example, the hot water elution rate of the urea-formaldehyde condensate may be as low as about 3% by mass.
It is difficult to obtain a formaldehyde condensate stably.

[0006] The hot water elution rate is an index of the decomposition rate, which affects the initial fertilizing effect and also affects the long-term decomposition characteristics. Fertilizers are required to have different performances when used, and 3
There is a need for a method for producing a urea-formaldehyde condensate having a hot water elution rate higher than mass%. Moreover,
In a tea plantation or the like, it is required that about 60% be decomposed in one year, and a urea-formaldehyde condensate having a hot water elution rate of 5 to 15% by mass is useful as a urea-formaldehyde condensate having such a decomposition rate. Therefore, a stable manufacturing method is demanded.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a method for stably supplying a urea-formaldehyde condensate having an appropriate hot water elution rate.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the problems, and as a result, have found a method for solving the above-mentioned problems, and have completed the present invention. That is, the present invention includes the following inventions. (1) Production of a urea-formaldehyde condensate characterized by reacting an aqueous solution of a urea-formaldehyde initial condensate having an amount of free formaldehyde of 1% by mass or less with urea, and then subjecting it to a methylation reaction using an acidic substance. Method. (2) The urea-formaldehyde condensate having a hot water elution rate of 5 to 15% by mass (anhydrous basis).
The manufacturing method as described. (3) The production method according to the above (1) or (2), wherein the urea-formaldehyde condensate has a total nitrogen content (based on anhydride) of 30% by mass to 40% by mass. (4) A urea-formaldehyde condensate obtained by the production method according to any one of (1) to (3).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the present invention, the urea-formaldehyde condensate has the same meaning as that generally called a urea resin, and is a thermosetting resin obtained by condensing urea and formaldehyde. The term “elution rate of hot water” as used in the present invention refers to the elution rate (based on anhydride) when immersed in water at a temperature of 80 ° C. for 30 minutes, and is calculated by the method described in Examples.

The production method of the present invention is particularly effective for a urea-formaldehyde condensate having a hot water elution rate of 5 to 15% by mass, preferably 7 to 10% by mass. When the hot water elution rate is 5 to 15% by mass, the decomposition rate of nitrogen is controlled. When the hot water dissolution rate is too low, the amount of fertilizer is too low because the fertilizing effect is too low, and it is preferably 5% by mass or more, more preferably 7% by mass or more. Also, if the hot water dissolution rate is too high, when used as fertilizer, the amount of nitrogen that flows out without being absorbed by plants increases, thereby reducing the sustainability of the effect and reducing environmental pollution such as groundwater due to nitrogen outflow. From the perspective of causing
It is preferably at most 15% by mass, more preferably at most 10% by mass. The urea-formaldehyde precondensate used in the present invention refers to one having a degree of condensation that is substantially soluble or dispersible in water.

Hereinafter, the production method of the present invention will be described. First, an aqueous urea-formaldehyde precondensate solution having an amount of free formaldehyde of 1% by mass or less is reacted with urea. The aqueous solution of the urea-formaldehyde precondensate can be produced by a known method using an aqueous solution of urea and formaldehyde.
3-75241 and JP-B-62-19767.

In the present invention, the amount of free formaldehyde is 1
An aqueous urea-formaldehyde precondensate solution having a mass% or less is used. When the amount of free formaldehyde in the urea-formaldehyde precondensate aqueous solution exceeds 1% by mass,
This is a problem because the hot water elution rate of the obtained urea-formaldehyde condensate is 5% by mass or less. The amount of free formaldehyde in the aqueous urea-formaldehyde precondensate used in the present invention is preferably 1% by mass or less.
The aqueous solution of the urea-formaldehyde precondensate used in the present invention has a cold water soluble content of usually 50% by mass or more, preferably 80% by mass or more. Here, “cold water” refers to water at 20 to 30 ° C.

The amount of free formaldehyde in the aqueous urea-formaldehyde precondensate solution is determined according to JIS K6801-
Urea resin wood adhesive of 1995 Measured by the method of measuring free formaldehyde described in 6.5. As the substance contained in the aqueous urea-formaldehyde initial condensate aqueous solution, in addition to free formaldehyde, urea, and methylolated urea, water-soluble or dispersible linear or branched condensate having a degree of condensation of about 1 to 4, or And cyclic condensates.

The nonvolatile content in the urea-formaldehyde precondensate aqueous solution is preferably 30% by mass or more, and more preferably 40% by mass or more, from the viewpoint of preventing a decrease in productivity due to an increase in water evaporation. Is more preferred. The nonvolatile content is measured according to JIS K6833 6.4 (nonvolatile content).

The viscosity of the aqueous solution of the urea-formaldehyde precondensate is adjusted by stirring and mixing with urea.
The viscosity of a B-type viscometer (60 rpm) at 25 ° C. is 2000 m
Pa · s or less, preferably 500 mPa · s
Or less, and more preferably 200 mPa · s or less. As an example, JIS K6 in which the amount of free formaldehyde is 1% by mass or less.
801-1995, and specifically, Suisobond 50 manufactured by Nippon Kasei Co., Ltd.
3i. Urea may be used as a solid,
Alternatively, it may be used as a high-concentration urea solution using water or the like as a solvent.

The urea to be added has a total nitrogen content (based on anhydride) of the formed urea-formaldehyde condensate of 30% by mass.
It is preferable to add an amount of ４０40% by mass. If the total nitrogen content is less than 30% by mass, the effect as a nitrogen fertilizer is reduced, which is not preferable. .

The reaction between the urea-formaldehyde precondensate aqueous solution and urea (methylolation reaction) is carried out at 40 ° C.
The reaction is preferably performed at a temperature in the range of 100 ° C, more preferably at 70 to 90 ° C. From the viewpoint of shortening the reaction time, the reaction temperature is preferably higher. The reaction time may be appropriately set according to the reaction temperature, and is usually 0.5 to 6.0 hours, more preferably 1.0 to 3.0 hours.

Next, an acidic substance is added to the reaction solution produced above to carry out a methylene reaction. Examples of the acidic substance include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, formic acid, and acetic acid.
Among them, strong acids such as sulfuric acid, hydrochloric acid and nitric acid are preferred because of their high curing speed. These acids may be used alone or in combination of two or more.

The amount of the acidic substance to be added is preferable from the viewpoint that a large amount of the acid substance accelerates the methyleneation reaction.
It is preferable that the amount of addition is small from the viewpoint that the water-soluble site derived from the salt can be reduced. , Preferably 1: 0.005-0.05, more preferably 1:
The amount is 0.01 to 0.02. When an acidic substance other than sulfuric acid is used, it is preferable to add an acidic substance in the same equivalent range as that of sulfuric acid. Note that a 2% by mass aqueous solution of the reaction solution during the methyleneation reaction (2% by mass of the reaction solution) was used.
g is added to 98 g of water and the solution is stirred), the pH is preferably 4 to 7, and more preferably 5 to 6.

When the acidic substance is used as a solution such as an aqueous solution, the concentration of the acidic substance is not limited, but is usually 2 to 50% by mass, preferably 2 to 50% by mass, from the viewpoint of easy handling and reduction of the amount of excess water to be evaporated. 5 to 20% by mass.
It is preferred that the methyleneation reaction is carried out by heating and mixing while stirring, from the viewpoint that the reaction proceeds uniformly and a powdery urea-formaldehyde condensate with good handleability is obtained.

The apparatus for heating and mixing may be of any shape and structure as long as it can continuously stir and mix these workpieces and homogenize them. Preferred examples thereof include various kneaders, A heating kneader such as a ribbon mixer may be used. Since the reaction solution at the time of the methylene reaction first changes from an aqueous solution state to a slurry state and paste state to a powder state finally, the methylolation reaction solution and the acid After charging the substance, a methylene reaction is carried out while mixing the contents while heating, and moisture in the reaction solution is removed by evaporation.

The temperature during the methylene reaction is preferably 70 ° C. or higher from the viewpoint of shortening the reaction time, and more preferably 80 to 100 ° C. If the reaction temperature is low, the progress of the methylene formation is slow, the drying efficiency is poor, and this is disadvantageous for industrial production. In addition, it hardens when heated, and a product with good handleability cannot be obtained. Also, when the reaction time is shortened by increasing the efficiency of water removal, the resulting urea-formaldehyde condensate may be reduced in spite of the same water content of the resulting product.
Since the pH of the aqueous solution by mass decreases, it is not preferable in terms of storage stability. Therefore, the reaction time of the methylene reaction is preferably 1 to 6 hours, more preferably 2 to 4 hours.

The urea-formaldehyde condensate of the present invention preferably has a pH of 4 to 8, more preferably 5 to 7, when a 2% by mass aqueous solution thereof is used. Outside this range, storage stability is undesirably reduced.

When drying, the water content is preferably in the range of 10 to 60% by mass. If the water content is too low, the powder is easily blown by the wind, and if the water content is too high, the powder becomes sticky. In any case, the handleability is lowered, which is not preferable. Furthermore, 20-40
The range of mass% is preferred.

The fertilizer containing the urea-formaldehyde condensate of the present invention has a total methylol content of 1.0% by mass in the urea-formaldehyde condensate from the viewpoint of not adversely affecting the germination of seeds when applied to soil. The following is preferred.

[0026]

The present invention will be described below in more detail with reference to examples and comparative examples. The method used for evaluating the obtained urea-formaldehyde condensate will be described below. About 2 g (W1) of a water sample is precisely weighed and dried for 3 hours in a hot-air dryer at a temperature of 105 ° C. to obtain a weight W2 (g) after cooling. Moisture (%) = [(W1-W2) / W1] x 100

Hot water dissolution rate About 4 g of a sample was precisely weighed and poured into 80 ml of water.
After immersion for 30 minutes while maintaining the temperature at 0 ° C. with occasional stirring, filtration (for example, using No. 131 filter paper manufactured by Advantech Co.) is performed. The weight of the sample dissolved in the filtrate (W2) is determined, and the percentage of the weight (W1) of the sample (anhydrous equivalent) used in the test is determined as the amount of hot water eluted in the sample. The weight of the sample dissolved in the filtrate is determined by dispensing 20 ml of the filtrate and drying at 105 ° C. for 3 hours. The anhydride conversion of the sample used for the test is determined by the following formula. Prepared sample anhydride equivalent weight (g) = Prepared sample weight (g) x (1
(00-moisture) / 100

After 2 g of a pH sample is added to 98 g of water and stirred, the pH of the aqueous solution is measured. Total methylol content Total methylol content in the hydrated cured product (hydrate basis) by the iodine method. Oxidize formaldehyde with iodine in the presence of alkali, then acidify to release unreacted iodine,
It is back titrated with sodium thiosulfate. This method
Unreacted formaldehyde and methylol groups in the reaction system of urea and formaldehyde completely react with each other, so that the sum of the two can be obtained. (Calculation formula) Total methylol amount (%) = {(AB) × f × 0.0015 × 100} / weight of sample (g) A: consumption of sodium thiosulfate in blank test (ml) B: thiosulfate in sample Sodium consumption (ml) F: Factor of sodium thiosulfate 0.0015: N / 10 Na ₂ S ₂ O ₃ 1 ml = 0.0015 g HCHO

The total nitrogen was measured by the sulfuric acid decomposition Kjeldahl method (the method described in Soil Nutrient Analysis (Soil Nutrient Measurement Method Committee, 8th edition), pages 171 to 176). The value is converted to anhydride. Mineralization test (method of measuring mineralization rate) Using 100 g of dry soil as a sample equivalent to 100 mg of nitrogen (N) in the surface layer, humus black soil (equivalent to 50 g of dry soil)
Into each Erlenmeyer flask, mix well with the soil, add demineralized water to adjust the soil moisture to about 60% of the maximum capacity, and leave it in a 30 ± 1 ℃ incubator. I do. The weight is measured every two weeks, the weight loss due to water evaporation is calculated, and the necessary water is replenished.

On each predetermined examination day, the Erlenmeyer flask to be examined in the incubator is taken out, ammonia nitrogen and nitrate nitrogen are quantified, and the mineralization rate is calculated by the following equation. Mineralization rate (%) = (Quantitative nitrogen value on specified survey date / Nitrogen quantitative value at start of test) x 100 Nitrogen quantitative value = Ammonia nitrogen + Nitrate nitrogen Inorganic nitrogen (ammonia nitrogen and nitrate nitrogen) The measurement method was the soil nutrient analysis method (edited by the Soil Nutrient Measurement Method Committee, Chapter 8
The microdiffusion analysis method (extracted by the Bremner method) described on pages 184 to 200 of the edition was used.

Cold water solubility: About 20 g of the urea formaldehyde precondensate was precisely weighed, poured into 200 g of ion-exchanged water at 20 to 30 ° C., stirred for 30 minutes, and the solution was filtered with a 0.45 μm filter. Filter. The weight of the sample dissolved in the filtrate (W2) was determined from the nonvolatile content of the filtrate (measured by JIS K6833 6.4), and this was used as the amount of cold water eluted in the sample. %) Is calculated.

Example 1 The amount of free formaldehyde in a urea formaldehyde precondensate aqueous solution Sisobond 503i (manufactured by Nippon Kasei Co., Ltd.) was measured and found to be 0.6% by mass. In addition, B type viscometer No2 rotor, viscosity at 60 rpm is 36
mPa · s, the nonvolatile content was 51.8% by mass, and the pH was 7.0. In addition,
The cold water solubility of the Swissobond 503i was measured to be 75% by mass.

In a 1 L separable flask, 50
598g of 3i (51.8% by mass of non-volatile content) and 102g of urea are mixed, 80 ℃
For 60 minutes. The obtained reaction product was transferred to a 1L jacketed kneader in which warm water of 95 ° C was passed through a jacket,
While mixing, 47 g of 10% sulfuric acid was added and mixed (methyleneation reaction treatment). After the addition of sulfuric acid, the reaction solution was hardened and turned into a paste-like powder. Take it out of the kneader after 160 minutes,
480 g of a white powder was obtained. Table 1 shows the physical properties of the obtained white powder.
Table 2 shows the results of the mineralization test.

(Comparative Example 1) In a 1 L separable flask, 37
% Formalin 353.5g, urea 172.7g, ion exchange water 80g, 3
0.9 g of a 0% aqueous NaOH solution was mixed. The pH at this time was 9.3. This mixture was heated and stirred at 80 ° C. for 60 minutes. The pH of the obtained reaction product was 6.8. The amount of free formaldehyde in this reaction solution was 2.5% by mass. Further, 102 g of urea was added, and the mixture was heated and stirred at 80 ° C. for 60 minutes. The pH after the reaction was 6.9. The obtained reaction product was subjected to a methylene treatment in the same manner as in Example 1 to obtain 475 g of a white powder. Table 1 shows the physical properties of the obtained white powder. Table 2 shows the results of the mineralization test.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

According to the present invention, it is possible to provide a urea-formaldehyde condensate having a controlled decomposition rate and a method for producing the same. The urea-formaldehyde condensate of the present invention is useful for fertilizers and the like because the decomposition rate is adjusted.

Claims (4)

[Claims] 1. A urea-formaldehyde condensate comprising reacting an aqueous urea-formaldehyde precondensate having an amount of free formaldehyde of 1% by mass or less with urea, and then subjecting the urea to a methylation reaction using an acidic substance. Manufacturing method. 2. The method according to claim 1, wherein the urea-formaldehyde condensate has a hot water elution rate of 5 to 15% by mass (based on anhydride). 3. The process according to claim 1, wherein the urea-formaldehyde condensate has a total nitrogen content (based on anhydride) of 30% by mass to 40% by mass. 4. A urea-formaldehyde condensate obtained by the production method according to claim 1. Description: