JPH0564164B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing urea resin crosslinked polymer particles. (Field of Industrial Application) The urea resin crosslinked polymer particles obtained by the production method of the present invention exhibit an excellent effect on improving the opacity of paper, and therefore can be advantageously used as a filler for paper manufacturing. (Prior Art) Urea resin crosslinked polymer particles are known as paper-making fillers that improve the optical properties of paper, such as whiteness and opacity. The urea resin crosslinked polymer particles used for such applications have a primary particle size of 0.1
It is already known that an agglomerated structure with a particle diameter of ~1μ and a secondary particle size of 5 to 15μ can produce excellent effects on improving the optical properties of paper. Conventionally, in order to produce crosslinked urea resin polymer particles used for such purposes, an acidic substance is added to an aqueous solution of a precondensate that has been condensed to a water-soluble level to cause a crosslinking gelation reaction, and the resulting gelled resin is was coarsely pulverized to form a slurry liquid, neutralized with an alkaline substance, and further deagglomerated to form crosslinked polymer particles with a primary diameter of 0.1 to 1 μm (Japanese Patent Laid-Open No. 55-36231). However, this conventional method has the following drawbacks. That is, if the degree of condensation of the precondensate is increased, it becomes water-insoluble, and if an acidic substance is added to it, water is separated by a condensation reaction and it becomes a solidified body, but does not become a gelled resin. Further, if the degree of condensation is low, the precondensate is water-soluble, but when an acidic substance is added to it, gel crosslinking reaction, crosslinking reaction, and condensation reaction occur simultaneously, resulting in a gelled resin containing many solidified substances.
Therefore, in this method, formaldehyde is precondensed at a low molar ratio of about 1.3 to 1.7 moles to 1 mole of urea, increasing the degree of condensation within the water-soluble range. The urea resin crosslinked polymer particles have a low content of methylol-formaldehyde present as methylol groups, and the paper cellulose polar groups (-OH group, -COOH group)
It was difficult to form hydrogen bonds with the group), and the effect of improving the opacity of the paper was insufficient. (Problems to be Solved by the Invention) The present invention provides a method for easily producing urea resin crosslinked polymer particles that exhibit excellent effects in improving the optical properties of paper, particularly opacity, when used as a paper filler. We aim to provide the following. (Means for solving the problem) The present inventors first prepared a mixed aqueous solution of urea, formaldehyde, and sulfamic acid or ammonium sulfamate under alkaline conditions.
If the condensation reaction is then carried out under acidic conditions, a urea resin initial condensate having a high degree of condensation and freely soluble in water can be obtained, and if this initial condensate is left without being neutralized with an alkaline substance. It was discovered that the cross-linking gelation reaction occurs and gelation occurs, and that if this initial condensate is neutralized with an alkaline substance, the cross-linking gelation reaction does not proceed (Japanese Patent Application Laid-Open No. 1986-1999).
Publication No. 79114). As a result of further research into such urea resin condensates, the present inventors found that
If this initial condensate is neutralized and then dissolved in water, an aqueous solution of an acidic substance is added, and the mixture is allowed to stand under acidic conditions to cause a crosslinking reaction. The present invention was achieved based on the knowledge that crosslinked polymer particles can be obtained that exhibit a remarkable effect in improving opacity. That is, the method for producing urea resin crosslinked polymer particles of the present invention involves a condensation reaction of a mixed aqueous solution of urea, formaldehyde, and sulfamic acid and/or ammonium sulfamate under alkaline conditions, and then a condensation reaction under acidic conditions to produce urea. The methylene formaldehyde content bound to urea is 50% of the total formaldehyde content bound to urea.
A method characterized by preparing the water-soluble urea resin initial condensate as described above, adding an acid to an aqueous solution of the obtained water-soluble urea resin initial condensate, and solidifying the same resin initial condensate by standing still under acidic conditions. It is. In the condensation reaction for obtaining the urea resin initial condensate of the present invention, first, urea, formaldehyde,
Further, an alkaline aqueous solution such as sodium hydroxide or aqueous ammonia is added as a catalyst to the mixed aqueous solution of sulfamic acid and/or ammonium sulfamate, and the reaction is started under alkaline conditions at a pH of 8.5 to 9.5. The reaction molar ratio in this reaction is 1.6 to 2.6 mol, preferably 1.8 to 2.4 mol, of formaldehyde to 1 mol of urea, and sulfamic acid and/or
Or ammonium sulfamate is 0.01 to 0.05 mol. When such a mixed aqueous solution is gradually heated to 70 to 90°C, preferably 75 to 85°C while stirring, the PH gradually decreases as the condensation reaction progresses, but in the present invention, the condensation reaction During the reaction, the pH is appropriately adjusted using ammonium sulfamate, formic acid, sodium carbonate, etc., and in the latter stages of the reaction, the pH is maintained at 4.0 to 5.8, preferably 4.4 to 5.4. The reaction time under alkaline conditions in the first stage is usually 40 to 120 minutes, preferably 60 to 120 minutes.
100 minutes, and the reaction time under acidic conditions in the latter stage is
Usually 20 to 200 minutes, preferably 30 to 180 minutes. In this condensation reaction, if 2.0 mol or less of formaldehyde is used per 1 mol of urea, a white turbidity will occur when a drop of the product in the middle of the reaction is dropped into water at a temperature of 5 to 20°C. but,
If the condensation reaction proceeds further, cloudiness will no longer occur. Regarding this cloudy phenomenon, in this specification, for example, when a drop of a reaction product is dropped into water at 5 to 20°C and cloudiness occurs, the highest temperature of the water at which the cloudiness occurs is referred to as the "white cloudiness point". That's what I will say. On the other hand, when 2.1 moles or more of formaldehyde is reacted with 1 mole of urea, such a cloudy point does not appear. In either case, the viscosity increases slowly as the condensation reaction progresses,
The resulting condensate is transparent and soluble in water in any proportion. When the condensation reaction reaches a desired degree, for example, when the viscosity of the reaction product reaches a predetermined viscosity, an aqueous solution of an alkaline substance such as sodium hydroxide or sodium carbonate is added to the reaction product so that the pH becomes 7.0 to 8.5. Add, neutralize and cool to room temperature. Such neutralization is carried out because the condensate obtained by such a method is acidic, and if left as it is, it will undergo a crosslinking gelation reaction and gelatinize as described above. The urea resin initial condensate obtained by the condensation reaction of the present invention is a transparent opalescent product at any condensation stage and is soluble in water. Therefore, there are no particularly strict restrictions on the end point of the reaction. However, normally, when the nonvolatile content of the urea resin initial condensate reaches 40 to 50% by weight, or when the viscosity of the urea resin initial condensate reaches 25℃,
It is desirable to stop the reaction when the pressure reaches 50 to 250 cps, since this facilitates the subsequent coagulation step with acid. Of course, the reaction may be stopped before or after reaching such a condensation step. Urea, formaldehyde, sulfamic acid, and ammonium sulfamate used in the present invention may all be industrial grade products. The formaldehyde used is usually 37 to 50% by weight formalin. In addition, sodium hydroxide for adjusting the pH of the reaction system is usually 30 to 45% by weight of industrial grade, and ammonia, sulfamine, ammonium sulfamate, formic acid, sodium carbonate, etc. are prepared in advance as a 10 to 15% by weight aqueous solution. It is preferable to use the The molar ratio of this condensation reaction is as described above.
Formaldehyde is 1.6 to 2.6 moles per mole,
Preferably it is 1.8 to 2.4 mol, and sulfamic acid and/or ammonium sulfamate is 0.01 to 2.4 mol.
If the proportion of formaldehyde is too small, clouding will occur during the reaction, making it impossible to obtain a clear water-soluble condensate. Moreover, if the proportion of formaldehyde is too large, the amount of unreacted formaldehyde, that is, the loss of formaldehyde will increase. Furthermore, if the proportion of sulfamic acid or ammonium sulfamate is too small, the condensate will become insoluble in water, and if it is too large, the time required to obtain the desired condensate, that is, the time required to reach the desired viscosity, will be significantly shortened. This makes it difficult to control the end point of the reaction. To explain in detail the PH of the reaction system in the condensation reaction of the present invention, when the reaction is started by setting the PH of the reaction system to 8.5 to 9.5 as in the production of general urea resin, the PH of the reaction system remains unchanged. However, in the present invention, in the later stages of the reaction, it gradually decreases.
The reaction is carried out while maintaining the pH within the range of 4.0 to 5.8, preferably 4.4 to 5.4. If the PH at the start of the reaction is lower than 8.5, the rate of PH decrease will be too fast, and if the PH at the start of the reaction is higher than 9.5, the rate of PH decrease will be too slow. PH4.4
PH to maintain favorable reaction conditions of ~5.4
This is not preferable because the adjustment operation becomes complicated. Ammonium sulfamate, formic acid, sodium carbonate, or the like is appropriately used to adjust the pH in the latter stage to maintain the reaction conditions of 4.0 to 5.8, preferably 4.4 to 5.4. If the pH in the subsequent reaction is too low, especially below 3.8, the condensation reaction will proceed rapidly, the viscosity of the reaction product will rapidly increase, and gelation will occur during the reaction. In addition, if the pH becomes too high, especially 6.8 or higher, sulfamic acid and/or ammonium sulfamate will not react with terminal methylol groups, etc., resulting in poor water solubility of the product, resulting in a urea resin initial condensate. becomes water-insoluble, becomes cloudy, and separates and precipitates. The urea resin initial condensate obtained by the condensation reaction as described above is water-soluble and dissolves in water at any ratio, and the content of methylene formaldehyde bonded to urea in the condensate is extremely high. That is, the initial condensate has a methylene formaldehyde content of 50% or more relative to the total formaldehyde content bonded to urea. Next, in the present invention, the urea resin precondensate obtained by the condensation reaction and neutralization is
Water is added and dissolved to form an aqueous solution of the desired concentration, and then an aqueous solution of an acidic substance is added to the solution to make it acidic, and the mixture is allowed to stand for a crosslinking reaction to solidify the condensate. The coagulation process using acid will be explained in detail based on a typical example.
Water at 30 to 70°C is placed in a mixer (mixer, etc.), and the neutralized urea resin condensate is poured into the water and stirred to completely dissolve the initial condensate in the water. Next, while stirring the aqueous solution of the initial condensate, add an aqueous solution of an acidic substance in an amount sufficient to make the pH of the entire system acidic between 0.5 and 3.0, immediately stop stirring, and leave it still. It is left to stand for a crosslinking reaction and solidify. The time from when the aqueous solution of the acidic substance is added until the stirring is stopped is long enough for the aqueous solution of the acidic substance to be mixed throughout the system and to achieve a uniform pH, and should be as short as possible. is desirable. The time varies depending on the capacity of the coagulation tank, etc., but is usually within a range of several seconds to several tens of seconds. 5 to 60 minutes after the above-mentioned stirring is stopped, the transparent liquid becomes opaque due to solidification of the initial condensate, and gradually changes into a yogurt-like state. And 30~70℃
If the system is left in this static state for 3 to 12 hours at a temperature of , the entire system becomes an elastic white coagulate uniformly containing a large amount of water. This coagulated product is a hydrous coagulated product of urea resin crosslinked polymer particles obtained by the production method of the present invention. Next, start the stirrer in the coagulation tank containing this water-containing coagulum, add an appropriate amount of water to it to make a slurry, and then add an aqueous solution of an alkaline substance to this slurry to adjust the pH to 7 to 8. The homogeneous slurry is transferred to a centrifuge, dehydrated and washed while pouring water, and the coagulated product is taken out as a white water-containing cake. If water is added to this cake again and deagglomerated using a wet milling machine using media, such as an attritor, the primary particle size will be 0.1 to 1μ.
A slurry of urea resin crosslinked polymer particles having a secondary particle size of 5 to 15 μm is obtained. The slurry is filtered, for example, through a glass filter to remove free water, resulting in a cake-like product. When the cake thus obtained is dried at, for example, 120°C for 1 hour, it is found to be a wet cake product containing 10 to 20% by weight of urea resin crosslinked polymer particles as a solid content and 80 to 90% by weight of bound water. . Acidic substances used in the coagulation step of the present invention include inorganic acids and their salts, such as sulfuric acid, sulfamic acid, acidic ammonium sulfate, ammonium sulfate, and ammonium sulfamate. Although one type of these acidic substances may be used alone, a combination of two or more types may be effective in making the particle size of the polymer particles uniform. Also,
The acidic substance is preferably added as a 5 to 20% by weight aqueous solution. In addition, examples of alkaline substances used to neutralize the coagulum slurry include sodium carbonate,
Examples include sodium hydroxide, aqueous ammonia, guanidine carbonate, etc. These alkaline substances
It is conveniently added as a 30% by weight aqueous solution. The concentration of the aqueous solution of the urea resin initial condensate used in the coagulation step is such that the weight ratio of water to the nonvolatile content of the initial condensate (hereinafter simply referred to as "water ratio") is 1.5 to 5.5 times, preferably 2.0
A value within the range of ~5.0 is desirable. When the same water magnification is larger than 5.5 times, the primary particle size of the obtained crosslinked polymer particles tends to be larger than 1μ, and when the same water magnification is smaller than 1.5 times, the primary particle size of the crosslinked polymer particles is smaller than 0.1μ. In either case, it tends to be an inferior filler for paper. The temperature of the coagulation system where acidic substances are added and left to stand is 30
A temperature range of ~70℃ is desirable, and the pH of the coagulation system is 3.0.
A range of ~0.5 is desirable. Even if the temperature of the coagulation system is lower than 30°C or the pH is higher than 3.0, the coagulation time becomes significantly longer. Also, the temperature
Even if the temperature is higher than 70°C or the pH is lower than 0.5, the coagulation time is significantly shortened. The urea resin crosslinked polymer particles obtained by coagulating over a long period of time or within a very short time have a primary particle size in the range of 0.1 to 1μ and a secondary particle size in the range of 0.1 to 1μ. They tend to be outside the range of 5 to 15 μm, and therefore tend to be inferior as fillers for paper. In addition, if a coagulation system in which an aqueous solution of an acidic substance is added to an aqueous solution of a urea resin initial condensate is coagulated in a fluid state while stirring (for example, while stirring continuously without stopping the rotation of the Juicer mixer), it is possible to obtain The crosslinked polymer particles contain particles having a primary particle size of 1 to 2 microns, and therefore the effect of improving the opacity of the paper is significantly inferior. The urea resin crosslinked polymer particles obtained by the production method of the present invention described in detail above have a substantially perfect spherical shape with a primary diameter of 0.1 to 1 μm, and have an agglomerated structure with a secondary particle diameter of 5 to 15 μm. Then, the slurry deagglomerated with the above-mentioned attritor was passed through a glass filter, and the cake was heated to 60°C.
The urea resin crosslinked polymer particles dried under reduced pressure ⁱⁿ
According to chemical analysis, the ratio of the amount of methylol formaldehyde to the total amount of formaldehyde is 5 to 8%, and the content of methylol formaldehyde is extremely high. (Effect of the invention) The urea resin crosslinked polymer particles obtained by the production method of the present invention have a remarkable effect of improving the opacity of paper when used as a paper filler, compared to the crosslinked polymer particles obtained by the conventional method. Are better. The reason for this is thought to be mainly as follows. (i) First, in the water-soluble urea resin condensate obtained by the condensation reaction of the production method of the present invention, the content of methylene formaldehyde bonded to urea is 50% or more of the total formaldehyde content bonded to urea; The same ratio obtained by the condensation reaction of the method is 10
High methylene formaldehyde content compared to ~20% urea resin precondensate. Therefore, in the urea resin crosslinked polymer particles obtained by the production method of the present invention, the ratio of the methylol formaldehyde content to the total formaldehyde content is 5.
~8%, compared to less than 1% for the same proportion of crosslinked polymer particles obtained by conventional methods.
extremely high (see Examples and Comparative Example 1 in Table 1). In the crosslinked polymer particles obtained by the production method of the present invention, this methylol group contained therein is the cellulose polar group (-OH group, -COOH group) of the paper.
Because it forms a hydrogen bond with the phosphor group), it has an excellent effect of improving the opacity of paper. (ii) In addition, in the production method of the present invention, since sulfamic acid and ammonium sulfamate are condensed, -CONHSO ₃ NH ₄ group, -CH ₂
Since OSO ₂ NH ₂ groups, -CH ₂ OSO ₂ Na groups, etc. are generated, the crosslinked polymer particles obtained by the production method of the present invention are likely to bond to paper cellulose through these anionic groups. it is conceivable that. (iii) The effects of () and () above are that the yield rate of polymer particles obtained by the production method of the present invention when used as a paper filler is significantly higher than that of the conventional method. This is supported by the fact that it is high. (iv)k Furthermore, in the polymer particles obtained by the production method of the present invention, true spherical primary particles with a particle size of 0.1 to 1μ are aggregated into an agglomerated structure with a secondary particle size of 5 to 15μ,
Also, it has a large BET specific surface area.
This is thought to be the reason for the excellent effect of improving the opacity of paper. (Examples, etc.) Hereinafter, the present invention will be further described in detail with reference to Examples and Comparative Examples. In these examples, "part" means part by weight, and "%" means % by weight unless otherwise specified. Example 1 Production of urea resin initial condensate: A reactor was charged with 729 g (9.0 mol) of 37% formalin, 15 g (0.132 mol) of ammonium sulfamate, and 18 g of a 30% aqueous sodium hydroxide solution.
Add 300 g (5.0 mol) of urea while stirring in step 9.2.
The temperature was raised to 85°C over 30 minutes. When the condensation reaction was carried out at the same temperature for 60 minutes, the pH dropped to 6.8, so
At this point, 50% ammonium sulfamate aqueous solution was added dropwise to adjust the pH to 5.0, and the reaction temperature was adjusted to 77°C.
When the condensation reaction was carried out for another 20 minutes,
The pH dropped to 4.6 and a cloudy point of 5°C appeared. Subsequently, when the condensation reaction was carried out at the same temperature for an additional 10 minutes, the cloudy point disappeared. When the condensation reaction was continued for another 30 minutes, the viscosity reached F as measured by a Gardner bubble viscometer, so a 10% aqueous sodium carbonate solution was added to neutralize the mixture to pH 7.5, and the mixture was cooled to room temperature. This urea resin initial condensate has a viscosity of 150 cps/25
℃, and the nonvolatile content was 45.1%. Total formaldehyde in this condensate was analyzed by the phosphoric acid decomposition method, methylol formaldehyde by the iodine method, and free formaldehyde by the ammonium chloride method, and the ratio of the methylene formaldehyde content to the total formaldehyde content bound to urea was calculated. The results were as shown in Table 1. Coagulation and production of product cake: Urea resin initial condensate obtained as above
500 g (non-volatile content: 255 g) was placed in a Juicer mixer containing 740 g of water at 30° C., and stirred to dissolve. The water magnification in this case is 4.5 times.
While stirring this initial condensate aqueous solution, the pH is 1.5.
5% sulfuric acid was added so that Stirring was stopped 15 seconds after the addition of sulfuric acid. Five minutes after the stirring was stopped, the mixture became opaque, and after 30 minutes it became yogurt-like. After this mixed solution was allowed to stand at 30° C. for 12 hours, 500 ml of water was added to the resulting coagulated product while stirring to form a uniform slurry. Next, 25% aqueous ammonia was added to neutralize the pH to 8.0, and the mixture was transferred to a centrifuge and centrifuged while washing with water to obtain a water-containing coagulum. A portion of this water-containing coagulate was placed as a media in an attritor containing alumina balls, water was added thereto, the mixture was rotated at high speed to deagglomerate, and the mixture was passed through a glass filter to form a product cake. This product cake has a solid content of urea resin crosslinked polymer particles after drying at 120℃ for 2 hours.
It was 15.3%. The yield based on the total amount of urea and formaldehyde was 64.4%. The product cake was dried under reduced pressure to obtain a sample with a solid content of 90-95% and a volatile content of 10-5%. Regarding this sample, the primary particle size was measured using a scanning electron microscope, the secondary particle size was measured using an optical microscope, and the specific surface area was measured using the BET method. Furthermore, the methylol formaldehyde content of this sample was measured by chemical analysis. The results were as shown in Table 1. Paper making test: The above product cake was added to a pulp slurry at a slurry concentration of 1% solids, and paper was made using a round large sheet machine under the following paper making conditions in accordance with JIS P-8209. Pulp composition Softwood kraft pulp 20% Thermomechanical pulp 30% Chemical ground pulp 20% Deinked pulp 30% Pulp softness 240ml Product cake solid content addition Bone dry pulp 3% Basis weight 46-47g/ ^m2 obtained The opacity of the paper was measured in accordance with JIS P-8138. The paper was also analyzed using a Kjeldahl nitrogen analyzer, and the filler retention rate was calculated from the N content. The results were as shown in Table 1. In addition,
The opacity of the unfilled paper was 91.0%. Example 2 Production of urea resin initial condensate: A reactor was charged with 811 g (10.0 mol) of 37% formalin, 10 g (0.103 mol) of sulfamic acid, 13 g of 30% sodium hydroxide, and 27 g of 28% aqueous ammonia, and the pH was 8.5. 300g (5.0mol) of urea under stirring
was added and the temperature was raised to 85°C. When the condensation reaction was carried out at this temperature for 100 minutes, the pH dropped to 4.2 and a cloudy point of 10°C appeared. At this point, a 10% aqueous sodium hydroxide solution was added dropwise to adjust the pH to 5.2, and the condensation reaction was continued for 30 minutes at the same temperature while measuring the viscosity. During this time, the cloudy point disappeared. Next, 10% aqueous sodium hydroxide solution was added dropwise to neutralize the pH to 7.2.
Cooled to room temperature. This urea resin initial condensate has a viscosity of 210 cps/25
℃, and the nonvolatile content was 46.3%. In addition, Example 1
The results of the same chemical analysis were as shown in Table 1. Coagulation and production of product cake: Using the urea resin initial condensate produced as above, the water ratio was increased to 3 times, and a 10% mixed aqueous solution containing 1 part of sulfamic acid and 1 part of ammonium sulfamate as the acidic substance was added. The pH of the coagulation system is
2.5, and after stopping stirring, transfer to a constant temperature water bath at 45℃.
Crosslinked polymer particles were produced in accordance with the method of Example 1 except that the slurry was allowed to stand for a period of time to solidify, and an aqueous sodium hydroxide solution was used to neutralize the slurry. The resulting product cake had a solid content of urea resin crosslinked polymer particles of 15.8%, and the yield was 68.8%. In addition, the results of measuring the primary particle size, secondary particle size, BET specific surface area, and methylol formaldehyde content are shown in Table 1. Paper making test: Using this crosslinked polymer as a filler, paper was made in the same manner as in Example 1, and the opacity of the paper and the filler retention rate were examined in the same manner, and the results were as shown in Table 1. . Example 3 Production of urea resin initial condensate: In a reactor, 973 g (12.0 mol) of 37% formalin, 20 g (0.175 mol) of ammonium sulfamate, 30%
Add 21g of % sodium hydroxide aqueous solution and 28g of 28% ammonia water, adjust the pH to 9.1, and add urea while stirring.
300 g (5.0 mol) was added and the temperature was raised to 85°C. When the condensation reaction was carried out at the same temperature for 90 minutes, the pH dropped to 7.2 and became constant, so a 10% aqueous formic acid solution was added dropwise to lower the pH to 6.4. Continue at the same temperature
When the condensation reaction was carried out for 50 minutes, the pH dropped to 6.2 and became constant, so 10% formic acid aqueous solution was added.
When the pH was adjusted to 5.4 and the condensation reaction was carried out at the same temperature for 80 minutes, the pH dropped to 4.2, so a 10% aqueous sodium carbonate solution was added dropwise to adjust the pH to 5.2. Continue to perform a condensation reaction for 30 minutes while measuring the viscosity at the same temperature, and then adjust the pH to 7.8 with a 10% aqueous sodium carbonate solution.
and cooled to room temperature. This urea resin initial condensate has a viscosity of 75 cps/25℃,
The nonvolatile content was 41.3%, and the results of chemical analysis similar to those in Example 1 were as shown in Table 1. Coagulation and production of product cake: Using the above urea resin initial condensate, double the water ratio, use sulfamic acid as the acidic substance to adjust the pH of the coagulation system to 0.8, and leave it at 60°C for 4 hours. Using sodium hydroxide aqueous solution to neutralize the slurry,
Other than that, crosslinked polymer particles were produced according to the method of Example 1. The resulting product cake had a crosslinked polymer particle solid content of 14.2% and a yield of 73.5%. Also,
The primary particle size, secondary particle size, BET specific surface area, and methylol formaldehyde content were as shown in Table 1. Paper making test: Using this product cake as a filler, paper was made in the same manner as in Example 1, and the opacity of the paper and the retention rate of the filler were examined. The results are shown in Table 1. Comparative Example 1 This example is an example of a conventional method. Production of urea resin initial condensate: 396 g (4.9 mol) of 37% formalin and water in a reactor.
Add 420 g of sodium carboxymethyl cellulose and 7 g of sodium carboxymethyl cellulose salt, dissolve uniformly with stirring, add 20% aqueous sodium hydroxide solution to adjust the pH to 8.7, and dissolve urea 177
g (3.0 mol) and then heated to 70℃ for 30 minutes.
The temperature was raised to . At the same temperature, a 20% aqueous sodium hydroxide solution was added dropwise at appropriate times to maintain the pH between 6.8 and 7.2, and the condensation reaction was carried out for 2 hours, followed by cooling to room temperature. This initial condensate had a viscosity of 50 cps/25°C and a nonvolatile content of 28.0%. Further, this condensate was chemically analyzed in the same manner as in Example 1, and the results were as shown in Table 1. Coagulation and production of product cake: 100 g of the above condensate in a plastic volume of 500 ml.
Add 144g of 2.7% sulfuric acid while stirring,
It was left standing at ℃ for 30 minutes. Next, 40 g of water was added and stirred at room temperature to form a slurry. After stirring for 2 hours, 25 g of 20% urea solution was added and stirred for 20 minutes. The pH of this slurry was 0.8. Then,
A 30% aqueous sodium hydroxide solution was added to this slurry to neutralize it to pH 7.8, followed by deagglomeration using an attritor containing alumina balls as a media, and passing through a glass filter to obtain a product cake. This cake had a solids content of urea resin crosslinked polymer particles of 20.2% and a yield of 81%. Further, the primary particle size, secondary particle size, BET specific surface area, and methylol formaldehyde content were examined in the same manner as in Example 1, and the results were as shown in Table 1. Paper making test: Using the crosslinked polymer particles as a filler, paper was made in the same manner as in Example 1, and the opacity of the paper and the retention rate of the filler were examined. The results are shown in Table 1. Comparative Example 2 Production of urea resin initial condensate: Add 4 g (0.04 mol) of sulfamic acid and heat at 10°C.
An initial condensate was produced in the same manner as in Example 2, except that when a cloudy point appeared, a 10% aqueous sodium hydroxide solution was added dropwise to neutralize the pH to 7.2. The obtained initial condensate had a viscosity of 32 cps/25°C and a nonvolatile content of 45.8%, and the chemical analysis results were as shown in Table 1. Coagulation and production of product cake: The product cake had a solids content of 28.3% and a yield of 55.5%. In addition, the primary particle size, secondary particle size, BET specific surface area, and chemical analysis results were as shown in Table 1. Paper making test: Using this product cake as a filler, Example 1
Paper was made in the same manner as in , and the opacity and filler yield of the paper obtained were examined, and the results are shown in Table 1. Comparative Example 3 Coagulation and production of product cake: Using the aqueous solution of the initial condensate obtained in the manufacturing process of the urea resin initial condensate of Example 1,
The crosslinking reaction was carried out while continuously stirring for 1 hour without stopping the stirring of the mixer, and then the stirring was stopped and the mixture was allowed to stand at 30°C for 11 hours, otherwise the crosslinked polymer particles were produced in the same manner as in Example 1. did. The resulting cake had a solid content of 25.3% and a yield of 58.8%. The primary particle size, secondary particle size, BET specific surface area, and chemical analysis results are as shown in Table 1 below. Paper making test: Using this product cake as a filler, Example 1
Paper was made in the same manner as in , and the opacity and filler yield of the paper obtained were examined, and the results are shown in Table 1.

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Claims (1)

[Claims] 1 A condensation reaction of a mixed aqueous solution of urea, formaldehyde, and sulfamic acid and/or ammonium sulfamate under alkaline conditions,
Next, a condensation reaction is performed under acidic conditions to obtain a water-soluble urea resin initial condensate in which the content of methylene formaldehyde bonded to urea is 50% or more of the total formaldehyde content bonded to urea, and the resulting water-soluble urea resin initial condensation product is 1. A method for producing crosslinked urea resin polymer particles, which comprises adding an acid to an aqueous solution of the product and leaving it to stand under acidic conditions to solidify the initial condensate of the resin. 2. The production method according to claim 1, wherein the reaction molar ratio of urea and formaldehyde is 1.6 to 2.6 formaldehyde to 1 urea. 3 The weight ratio of water to resin nonvolatile content in the urea resin initial condensate aqueous solution used in the coagulation process is
Claim 1 within the range of 1.5 to 5.5 times
or the manufacturing method described in paragraph 2. 4. The manufacturing method according to claim 1, 2, or 3, wherein the urea resin initial condensate aqueous solution left to stand in the coagulation step has a pH of 0.5 to 3.0.