JPH0670116B2 - Method for producing urea formaldehyde polymer-particle aggregate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a white pigment for yarn production obtained by reacting urea with formaldehyde, and particularly to a printing paper that requires high opacity after printing. And a useful method for producing a urea-formaldehyde polymer particle aggregate.

[Conventional technology]

The average particle size is 0.05 to 0.5μ and the average aggregate size is 1 to 15
It has already been known that an aggregate of μ formaldehyde polymer particles is useful as a pigment for preventing whiteness, opacity and strike-through after printing of paper (Japanese Patent Laid-Open Publication No. S60-242242).
54-135893, JP-A-55-36231, JP-A-56-131658).
In these conventional techniques, a crosslinkable urea-formaldehyde polymer particle aggregate (by mixing an initial condensate having a molar ratio of urea and formaldehyde in the range of 1: 1 to 1: 2 and an acidic aqueous solution and solidifying the mixture is used. (Hereinafter referred to as polymer particle aggregates), the polymer particle aggregates are added to a pulp slurry for paper making, or mixed with an adhesive and coated on a paper surface to obtain white paper. It has already been attempted to reduce the weight of paper and improve printability by improving the degree, opacity and opacity after printing.

[Problems to be solved by the invention]

The basis weight of newspaper roll paper has changed from 52 g / m ² to 46 g / m ² , and 43
The weight of paper used for printing is being reduced so that it will be g / m ² . The technology required to reduce the weight of paper is the opacity of the paper itself (hereinafter referred to as white opacity,
The degree is referred to as white paper opacity), prevention of strike-through after printing (hereinafter referred to as opacity after printing, the degree is referred to as opacity after printing), and maintenance of strength, and especially opacity after printing and strength. Maintenance is important. Usually, when a conventional polymer particle association is added to a pulp slurry for the purpose of improving opacity after printing and paper is obtained by papermaking, the opacity after printing is improved as the amount of the polymer particle association added to the pulp is increased. However, the strength of the paper is reduced.

[Means for solving problems]

In order to solve these drawbacks, the present inventor has earnestly studied in order to obtain a high polymer opacity after printing with a small amount of addition, and further, a decrease in strength due to the addition, and as a result of research, It was found that the polymer particle aggregate obtained by adding urea to the initial condensate of urea and formaldehyde in the presence thereof, and then mixing with an acidic aqueous solution and solidifying the mixture achieves these objects.

That is, in the present invention, urea (U ₂ ) is further added to the initial condensate of urea (U ₁ ) and formaldehyde (F) to form a homogeneous mixed liquid, which is then mixed with an acidic aqueous solution to be solidified and further cured. In the method, protective colloid agents are urea (U ₁ ) and (U ₂ )
And the weight of the reaction component with formaldehyde (F)
0.1 to 10% by weight was added by adding an additive during or urea stages or urea precondensate (U ₂₎ (U ₂₎ after a homogeneous liquid mixture, further molar ratio U ₁ + U _2: F is 1: 1 to 1: 2, and U ₂ / (U
₁ + U ₂ ) is 1.10 to 0.70, which is a method for producing urea formaldehyde polymer particles.

The molar ratio of total urea to formaldehyde used in the present invention is 1: 1 to 1: 2. If this molar ratio is less than 1.0, the yield of polymer particle aggregates obtained from urea and formaldehyde used as raw materials is low, and the degree of improvement in opacity after printing of paper to which this is added is small. This molar ratio is 2.
When it is greater than 0, the yield of polymer particle aggregates is low, and the degree of improvement in opacity after printing of the paper to which this is added is also small. The preferred molar ratio of total urea used to formaldehyde is 1: 1.3 to 1: 1.8.

Urea Urea contained in the initial formaldehyde condensate (U ₁ : hereinafter referred to as condensed urea) and urea added to this (U ₂ :
Hereafter, the ratio of urea added is U ₂ / (U ₁ + U ₂ ).
It is set to be 0.10 to 0.70. U ₂ / (U ₁ + U ₂ ) is
When the polymer particle association obtained by being less than 0.10 is added to the paper, the degree of improvement in the opacity after printing of the paper containing the polymer is low and the strength is largely decreased. Also U ₂ /
When (U ₁ + U ₂ ) exceeds 0.70, the yield of polymer particle aggregates is low, and the degree of improvement in opacity after printing of the paper containing this is low. Preferred values of _{U 2 / (U 1 + U} 2) is 0.20 to 0.60.

The polymer particle aggregate of the present invention is easily manufactured by any known method after adding post-added urea to the initial condensate to form a homogeneous mixed solution. That is, the homogeneous mixed solution is mixed with an acidic aqueous solution and solidified to form an aggregate of polymer particles. Then proceed with curing, and select and combine steps such as neutralization, removal of unreacted formaldehyde, pulverization, dehydration, drying, etc., and polymer particles with an average aggregate diameter of 2 to 10 μ are in the form of slurry, cake or powder. Obtained in the form of.

The acidic aqueous solution that can be used in the method for producing a particle aggregate according to the present invention is an aqueous solution of an arbitrary acidic compound, and the acidic compound is, for example, sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid or less than 4.
Included are moderate organic acids with PK values such as formic acid, oxalic acid, maleic acid, succinic acid, and chloroacetic acid and the like. Further, water-soluble ammonium hydrogensulfate of sulfamic acid or the formula: RNH ₃ SO ₄ H (wherein R is hydrogen, an alkyl group, a cycloalkyl group, a hydroxyalkyl group, an aralkyl group, an aryl group or the like) can also be used. The water-soluble ammonium hydrogensulfate includes methylammonium hydrogensulfate, ethylammonium hydrogensulfate, hydroxyethylammonium hydrogensulfate, phenylammonium hydrogensulfate, benzylammonium hydrogensulfate and the like.

Further, an advantageous method for producing the polymer particle aggregate of the present invention will be described in detail. The initial condensate composed of condensed urea and formaldehyde is used as an aqueous solution, and the total concentration of condensed urea, formaldehyde and other additives is about 20 to 75% by weight.
(Hereinafter, all% are weight% unless otherwise specified). The initial condensate is obtained by carrying out the reaction at a temperature of about 30 to 100 ° C. and a pH value of about 5 to 9 for about 10 minutes to 4 hours. The pH of this initial condensate is adjusted to 6 to 8 with an acid or alkali compound when long-term storage is required.

When post-added urea is added to the initial condensate to form a homogeneous solution, the urea used is preferably an aqueous solution of 10 to 40%. The initial condensate and the post-added urea are mixed within 1 hour under stirring and mixed with an acidic aqueous solution. In this case, the concentration of the homogeneous solution of the initial condensate and the post-added urea is 10 to 40%,
The concentration of the acidic aqueous solution is preferably 1 to 10% from the viewpoint that uniform mixed liquefaction can be achieved in a short time. The concentration of urea and the condensation product of urea and formaldehyde contained in the mixed solution of the homogeneous solution of the initial condensate and the post-added urea and the acidic aqueous solution is usually 5 to 35%, and the concentration of the acidic compound is usually 0.5 to 5%. It is the concentration of the mixed solution. This mixture is usually at room temperature to
Solidifies within about 50 seconds at about 100 ° C.

Also in the method for producing a polymer particle aggregate of the present invention, as already known, a water-soluble organic polymer having a protective colloid function for the purpose of forming favorable particles is used to form a water-soluble initial stage of condensed urea and formaldehyde before solidification. It is advantageous to add the condensate or the post-added urea or a mixed aqueous solution of the post-added urea and the initial condensate. The water-soluble organic polymer having a protective colloid function is a natural substance such as starch, gelatin, glue, tragacanth gum, kanten and acacia, alkali metal salts of sodium and potassium carboxymethyl cellulose, methyl cellulose, ethyl cellulose. , Β-hydroxyethylcellulose, modified natural products such as alkali metal salts of alginic acid, polyvinyl alcohol, polyvinylpyrrolidone, polymers of acrylic acid or methacrylic acid and alkali metal salts thereof, copolymers of maleic acid with styrene and butylene. Alternatively, salts thereof, salts of vinylpyridine homopolymers and copolymers, and the like. The amount of protective colloid agent used depends on its type, but is generally about 0.1-10% by weight, based on the weight of urea and formaldehyde reactive components,
It is preferably in the range of 0.5 to 5%.

When the amount of the protective colloid agent is less than 0.1% by weight and 10% by weight or more, the yield of polymer particle aggregates is low, the effect of improving opacity as a white pigment for papermaking is not obtained, and the strength is reduced.

Urea is added to the urea-formaldehyde initial condensate to form a uniform solution, which is then mixed with an acidic aqueous solution for solidification. The solidification reaction is carried out in an extruder, in a mixing screen, or on an endless belt. After the solidification reaction, a curing reaction is usually performed at room temperature to 100 ° C for at least 30 minutes to accelerate the reaction between urea and formaldehyde. This reaction is publicly known (Japanese Patent Publication No.
2350) stirred tank cascade reactor, stirred multichamber tube reactor or endless belt. The curing reaction carried out by these devices is carried out in the form of pellets containing water or in the form of a solid plate, but it is also possible to add water to this to make a slurry to proceed the curing reaction in a tank equipped with a stirrer. After the curing reaction, if necessary, perform preliminary pulverization with a pulverizer capable of coarsely pulverizing the polymer particle association such as a pelletizer or a hammer mill to a diameter of 1 to 2 mm, and add water with stirring to adjust the concentration of the polymer particle association. Make a 5-10% slurry.

The slurry of this polymer particle aggregate is subjected to neutralization, removal of free formaldehyde, dehydration, pulverization, etc. to obtain a polymer particle aggregate having an average aggregate diameter of 2 to 10 μ (hereinafter referred to as final polymer particle aggregate). Neutralization, removal of free formaldehyde, dehydration, re-slurry, pulverization step sequence is used when obtaining the final polymer particle association in the form of a slurry, and neutralization when obtaining the final polymer particle association in the form of a cake, The process sequence of removal of free formaldehyde, pulverization and dehydration is used, and when the final polymer particle aggregate is obtained in the form of powder, the process sequence of neutralization, removal of free formaldehyde, dehydration, drying and pulverization is used.

The neutralization is carried out using an aqueous solution of an alkali such as caustic soda and caustic potash, but the removal reaction of free formaldehyde and the neutralization can be carried out simultaneously by using ammonia or sulfite. The removal of free formaldehyde is carried out by washing with water after neutralization, or by adding ammonia, sulfite, sulfite, thiosulfate, urea or the like as mentioned above and reacting with free formaldehyde.

Dehydration is performed by a method such as excess or centrifugal dehydration, and usually a cake-like product containing about 20% of polymer particle aggregates is obtained. The cake is redispersed in water to obtain a slurry having a concentration of 5 to 10%. In the case of wet dispersion, this slurry is pulverized by a precision pulverizer such as a colloid mill, a free pulverizer, a sand grinder, etc. to obtain a slurry of the final polymer particle aggregate. When the final polymer particle aggregate is obtained as a cake, it is pulverized before dehydration and then dehydrated to form a cake. When the final polymer particle aggregate is obtained in powder form, the dehydrated cake is dried by a conventional method such as air drying, and then the impact mill,
Grind with a dry grinder such as an air mill or a ball mill.

[Action]

The urea-formaldehyde polymer particle association thus obtained can be used not only as a white pigment for papermaking but also when used as a filler for internal addition, imparts high opacity after printing, and It has the characteristic that there is little decrease in strength. By adding urea to the initial condensation product of urea formaldehyde, the distribution of the molecular chain length of the reaction product of urea formaldehyde immediately before solidification becomes broad, or it becomes a mixture of relatively large molecular weight and small molecular weight. It is speculated that this is due to the fact that when it is mixed with an acidic aqueous solution, it has a reaction structure different from that in the case of using a conventional initial condensate that is simply uniformly condensed.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

In the following,% and parts also represent% by weight and parts by weight except for the opacity of the processed paper after printing. Further, various measurement and calculation methods were performed according to the following points.

The yield of polymer particle aggregates is the number of parts when the formaldehyde contained in the homogeneous mixed solution of urea and the formaldehyde precondensate used is added with urea and other additives such as a protective colloid agent, when the dehydration reaction occurs, The total solid equivalent raw material part number is calculated by adding the urea and protective colloid agent parts. Then, the number of white cakes obtained by neutralizing the polymer particle aggregates obtained by mixing and solidifying the homogeneous mixed solution and the acidic aqueous solution and further curing (W part) and JIS K-6801
The concentration of the cake (A%) is measured in accordance with the above.

The yield of polymer particle aggregates is calculated by the formula (W × A / total solid equivalent raw material parts).

Opacity after printing is J.TAPPI paper pulp test method No.45-84
I followed him.

The tensile strength was measured according to JIS (P-8113).

Example 1 A mixture of 37% aqueous formaldehyde solution 42.18 parts, urea 18.73 parts, carboxymethylcellulose soda salt (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., trade name Serogen F-3H) 0.76 parts, and water 55.33 parts were mixed with a 20% caustic soda solution. While adjusting the pH to 7.0 ± 0.5, the reaction was carried out at 70 ° C. for 2.5 hours to obtain an aqueous solution of the initial condensate. Then, 100 parts of this initial condensate aqueous solution is taken and added to this.
% Urea aqueous solution (5.93 parts) was added and stirred to obtain a uniform mixed solution. The molar ratio of formaldehyde (F) to condensed urea (U ₁ ) and post-added urea (U ₂ ) in the initial condensate of this homogeneous mixed solution is U ₁ + U ₂ : F = 1: 1.5, and U ₂ / ( U ₁ + U ₂ ) is 0.10. The total concentration of formaldehyde, urea and carboxymethylcellulose soda salt in the initial condensate aqueous solution is
At 30%, the total organic matter concentration in the homogeneous mixed solution obtained by adding post-added urea to this is also 30%. The ratio of carboxymethyl cellulose soda salt to the total amount of urea and formaldehyde is 2.04%. The temperature of this homogeneous mixed solution is adjusted to 45 ° C., and 1.28 parts of 98% sulfuric acid is rapidly and uniformly mixed with a solution diluted with 48.72 parts of water. Solidification occurs after about 12 seconds, at which time the temperature of the reaction mixture rises to 59 ° C. Then, the temperature is maintained at 60 ° C. for 1 hour to accelerate the curing reaction.

Next, this hardened product is roughly crushed to a particle association size of 1 to 2 mm with a cutter granulator, 143 parts of water is added to make a slurry, and the pH is neutralized to 7.5 with a 20% caustic soda aqueous solution. The obtained slurry is finely pulverized with a pulverizer, dispersed in 1,000 parts of water, and then super-dehydrated to obtain a white cake. This was further washed with water to disperse it in 1,000 parts of water and then superdehydrated to obtain 116.75 parts of a white cake (hereinafter referred to as the cake of Example 1). The nonvolatile content of this cake is 20.7%
Therefore the yield is 24.17 parts. On the other hand, since the total solid equivalent raw material parts of the homogeneous mixed solution used is 24.66 parts, the yield of polymer particle aggregates is 98.0%. The average diameter of the polymer particle aggregate was 5.2 μm by the Coulter counter method.

The total concentration of urea and formaldehyde in the reaction mixture solidified by mixing the homogeneous mixed solution and the sulfuric acid solution was 19.96%, and the sulfuric acid concentration was 0.80%.

Examples 2 to 5 In Example 1, the ratio of the post-added urea (U ₂ ) to the total (U ₁ + U ₂ ) of the post-added urea (U ₂ ) and the condensed urea (U ₁ ), that is, U ₂ / (U ₁ + U ₂ ) is different from 0.20, 0.40, 0.60, 0.70 except that the same conditions and operations as in Example 1 are applied to Example 2 (U ₂ / (U ₁ + U ₂ ) is 0.20) and Example 3 (U ₂ / (U ₁ + U ₂ )
Referred but 0.40), Example _{4 (U 2 / (U 1} + U 2) is 0.60) and Example _{5 (U 2 / U 1 +} U 2) is 0.70) cake (hereinafter Examples 2-5 Cake ) Got. These yields were measured and calculated in the same manner as in Example 1 and shown in Table 1.

Comparative Examples 1 to 3 Production examples in which U ₂ / (U ₁ + U ₂ ) is outside the scope of the present invention in Example 1 are shown as comparative examples. That is, in Example 1, the ratio of post-added urea (U ₂ ) to the total (U ₁ + U ₂ ) of post-added urea (U ₂ ) and condensed urea (U ₁ ), that is, U ₂ / (U ₁ + U ₂ ) is Comparative Example 1 (U ₂ / (U ₁ + U ₂ ) was prepared under exactly the same conditions as in Example 1 (for example, U ₁ + U ₂ : F in a molar ratio of 1: 1.5) except that the values were 0, 0.50 and 0.80. 0), Comparative Example 2 (U ₂ / (U ₁ +
U ₂ ) of 0.05) and Comparative Example 3 (U ₂ / (U ₁ + U ₂ ) of 0.80) were obtained as cakes (hereinafter referred to as Comparative Examples 1 to 3 cakes). These yields were measured and calculated in the same manner as in Example 1 and shown in the table.
Shown in 1.

Comparative Examples 4 and 5 Same as Example 1 except that the soda salt of carboxymethyl cellulose in Example 1 was changed to 0% (Comparative Example 4) or 12% by weight (Comparative Example 5) with respect to the total amount of urea and formaldehyde. By the operation of, each cake-like material (hereinafter referred to as Comparative Examples 4 to 5 cakes) was obtained. These yields were measured and calculated in the same manner as in Example 1 and shown in Table 1.

Example 6 32.34 parts of 37% aqueous formaldehyde solution, 12.49 parts of urea, 0.67 parts of carboxymethylcellulose soda salt (trade name: serogen F-3H) and 38.25 parts of water were mixed and adjusted to pH 7.0 ± 0.5 with 20% caustic soda solution. While reacting at 70 ° C. for 2.5 hours, an aqueous solution of an initial condensate was obtained. Then, 75.13 parts of an aqueous solution of this initial condensate was taken, and 24.87 parts of a 30% aqueous urea solution was added thereto and stirred to obtain a homogeneous mixed solution. The molar ratio of formaldehyde (F) to condensed urea (U ₁ ) and post-added urea (U ₂ ) in the initial condensate of this homogeneous mixed solution is U ₁ + U ₂ : F = 1: 1.
At 15, U ₂ / (U ₁ + U ₂ ) is 0.40. Further, the total concentration of formaldehyde, urea and carboxymethyl cellulose soda salt in the aqueous solution of the initial condensate is 30%, and the total organic matter concentration in the homogeneous mixed solution obtained by adding urea to this is also 30%.
The ratio of carboxymethyl cellulose soda salt to the total amount of urea and formaldehyde is 2.04%. The temperature of this homogeneous mixed solution was adjusted to 45 ° C, and 1.28 parts of 98% sulfuric acid was added to water.
Promptly homogenize the 48.72 parts diluted solution. About 13
Solidification occurs in seconds, at which time the temperature of the reaction mixture rises to 57 ° C. Thereafter, the curing reaction and the like were carried out in the same manner as in Example 1 to obtain 112.30 parts of a white cake-like material (hereinafter referred to as the cake of Example 6). The non-volatile content of this cake is 21.3%, so the yield is 23.92 parts. On the other hand, since the total solid equivalent raw material parts of the homogeneous mixed solution used is 24.28 parts, the yield of polymer particle aggregates is 98.5%. The average particle diameter of the polymer particle aggregate was 5.1 μm. The total concentration of urea and formaldehyde in the reaction mixture solidified by mixing the homogeneous mixed solution and the sulfuric acid solution was 19.60%, and the sulfuric acid concentration was 0.85%.

Examples 7 to 10 In Example 6, the molar ratio of U ₁ + U ₂ : F consisting of formaldehyde (F) from the initial condensate and condensed urea (U ₁ ) and post-added urea (U ₂ ) in the homogeneous mixed solution was 1: 1.35, 1: 1.6, 1:
Conditions other than 1.75 and 1: 1.9, namely reaction temperature, pH, U
₂ / (U ₁ + U ₂ ) value, formaldehyde in the initial condensate,
Total concentration of urea and carboxymethyl cellulose soda salt, total organic matter concentration in homogeneous mixed solution, ratio of carboxymethyl cellulose soda salt to total amount of urea and formaldehyde, urea in reaction mixture solidified by mixing homogeneous mixed solution and sulfuric acid solution The total concentration of formaldehyde, the concentration of sulfuric acid, etc. were exactly the same as in Example 6 and the operation was performed in Example 7 (molar ratio of U ₁ + U ₂ : F 1: 1.35) and Example 8 (U ₁ +).
U ₂ : F molar ratio is 1: 1.6), Example 9 (U ₁ + U ₂ : F molar ratio is 1: 1.75) and Example 10 (U ₁ + U ₂ : F molar ratio is 1: 1.9).
The following cakes (hereinafter referred to as Examples 7 to 10 cakes) were obtained. These yields were measured and calculated in the same manner as in Example 6, and are shown in Table-2.

Comparative Examples 6 and 7 In Example 6, the molar ratio of U ₁ + U ₂ : F consisting of formaldehyde (F) and urea (U ₁ ) from the initial condensate in the homogeneous mixed solution and urea (U ₂ ) after-added was the same. A production example outside the scope of the invention is shown as a comparative example. That is, in Example 6, U ₁
Comparative Example 6 (U ₁ +) under exactly the same conditions and operations as in Examples 6 to 10 except that the + U ₂ : F molar ratio was 1: 0.9 and 1: 2.1.
U _2: 1 F molar ratio: 0.9) and Comparative Example 7 (U ₁ + U _2: F is 1 in molar ratio to obtain 2.1) cake of (hereinafter referred to as Comparative Example 6-7 cake). These yields were measured and calculated in the same manner as in Example 6, and are shown in Table-2.

[Applications] The usefulness of the polymer particle aggregates obtained according to the above-mentioned examples will be described below.

Application Examples 1 to 10 and Comparative Application Examples 1 to 7 NB.KP 25 parts, TMP 30 parts, RGP 20 parts and newspaper deinking waste paper 25 parts 1% pulp slurry with a beating degree (CSF) of 330 ml 2
To 0.00 parts of the cake of Example 1 was added 40 parts of a slurry in which the concentration of the polymer particle association was adjusted to 5% with water (10% association volume based on dry pulp), and the mixture was stirred for 5 minutes. Obtain a prepared slurry. Then, the wet paper obtained by making paper with a TAPPI square sheet machine and performing press dehydration has a surface temperature of 110 ° C.
After drying with a drum dryer of No.2, pass it twice at a linear pressure of 40 kg / cm, and keep it in a humidity-controlled room at a humidity of 65% and a temperature of 20 ° C for 24 hours.
The processed paper of Example 1 cake was obtained through the seasoning. The basis weight of this processed paper was 45.0 g / m ^{2 and the} tenacity was 0.64 g / cm ³ , and the tensile strength and opacity after printing were measured and calculated. The results are shown in Table-1.

Example 1 In the production of processed paper for cake, the processed paper of Examples 2 to 10 and the processed papers of Comparative Examples 1 to 7 were obtained by the same operation except that the cake of Example 1 was changed. Further, the processed paper of Comparative Example 8 was obtained by the completely same operation except that the aggregate was not added in the method for obtaining the processed paper of Example 1 cake.
The processed papers of Examples 2 to 10 and the processed papers of Comparative Examples 1 to 7 and Comparative Example 6 were also measured and calculated in the same manner as the processed paper of Example 1 cake, and the results are shown in Table- Shown in 1 and 2. The processed paper had a basis weight of 45.0 ± 0.1 g / m ² and a tenacity of 0.64 ± 0.01 g / cm ³ .

[Advantages of the Invention] From Table 1, U ₂ / (U ₁ + U ₂ ) having a small value of 0 or 0.05 shows a small improvement in opacity after printing and a large decrease in strength of the processed paper. On the other hand, beyond the _{U 2 / (U 1 + U} 2) 0.70 0.80
If so, the yield of polymer particle aggregates will be low, and the degree of improvement in opacity after printing will be small. That is, U ₂ / (U ₁ + U ₂ ) is 0.1
It is clear that 0 to 0.70, preferably 0.20 to 0.60, is excellent in terms of yield of polymer particle aggregates, opacity after printing of processed paper and tensile strength. Further, when the amount of the protective colloid agent is 0 or 12.0%, there is no effect of improving the opacity after printing and the strength is lowered. Also, from Table-2, the total molar ratio of condensed urea and post-added urea to formaldehyde is
When the ratio is 1: 0.9, the yield of polymer particle aggregates is low, and the degree of improvement in opacity of the processed paper after printing is small. The same applies to the case of 1: 2.10, and the molar ratio within the scope of the present invention, that is, 1: 1 to 1: 2, preferably 1: 1.3 to 1: 1.8, is the yield of polymer particle aggregates, printing of processed paper. It is clear that the post opacity and tensile strength are excellent.

The polymer particle aggregate of the present invention, which is characterized in that the high opacity-providing power after printing and the reduction in paper strength are small, is particularly useful as a filler for reducing the weight of printing paper such as newspaper roll base paper.

Claims (1)

[Claims] 1. Urea (U ₂ ) is further added to the initial condensate of urea (U ₁ ) and formaldehyde (F) to form a homogeneous mixed liquid, which is then mixed with an acidic aqueous solution to solidify and further harden. In the method, the protective colloid agent is added to the reaction components of urea (U ₁ ) and (U ₂ ) and formaldehyde (F) in an amount of 0.
1 to 10% by weight is added at the stage of the initial condensate or when urea (U ₂ ) is added or after urea (U ₂ ) is added to form a homogeneous mixed liquid, and the molar ratio U ₁ + U ₂ : F is 1: 1 to 1: 2, and U ₂ / (U ₁
+ U ₂₎ are provided methods for producing the urea-formaldehyde polymer particles characterized in that 0.10 to 0.70.