JPH0629309B2 - Manufacturing method of paper filler - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a paper filler, and particularly to a method for continuously producing a paper filler comprising urea formaldehyde crosslinked resin particles having improved performance.

The paper filler comprising urea formaldehyde cross-linked resin particles obtained according to the present invention can improve the optical properties of the paper product such as whiteness, opacity, and opacity after printing when filled in the paper product. It can be used to advantage.

<Prior Art> In the fields of newsprint, telephone directory paper, coated base paper, and the like, weight reduction has been remarkably advanced in recent years. Generally, the weight reduction of paper is achieved by reducing the amount of pulp material used, that is, the basis weight, but because of that, the strength (rigidity) and other strength decreases, the optical characteristics decrease, and the printability decreases. Various problems occur. On the other hand, in order to improve optical properties such as whiteness, opacity and opacity after printing of paper, fine particles of inorganic substances such as kaolin, talc and white carbon, and fine urea-formaldehyde cross-linking resin are used as fillers. Is formulated as.

Various methods have been known so far regarding the method for producing a fine urea-formaldehyde cross-linked resin used as a filler for paper. For example, an initial condensate of urea and formaldehyde is reacted in the presence of a protective colloid agent at room temperature to 100 ° C. with sulfamic acid or the like as a catalyst to form a crosslinked resin, which is roughly pulverized, neutralized, and dried. A method of crushing is known (Japanese Patent Publication No. 46-28087).

Further, as a method for industrially continuously producing a urea-formaldehyde crosslinked resin, an initial condensate and an acidic catalyst aqueous solution are continuously mixed in an in-pipe mixer, and gelation is performed in an extrusion screw, A method of post-curing the obtained gel for another 30 minutes has been proposed (Japanese Patent Publication No. S49-49).
2350). A method has also been proposed in which the initial condensate and the acidic aqueous solution are continuously mixed, the mixture is supplied onto a rotating endless belt, and the mixture is solidified on the belt (JP-B-57).
-26686).

<Problems to be Solved by the Invention> As described above, various methods for producing a urea-formaldehyde cross-linking resin by mixing and reacting an initial condensate of urea and formaldehyde with an aqueous acidic catalyst solution are known. The urea-formaldehyde cross-linking resin industrially obtained by the above method is not always satisfactory in improving the paper quality by filling it in the paper, particularly in improving the optical properties of the paper. That is, the whiteness, opacity and post-printing opacity of the paper are usually important as the optical properties of the paper.
The filler composed of the urea-formaldehyde cross-linking resin has a large effect of improving whiteness and opacity, but the effect of improving opacity after printing was insufficient.

Generally, when various kinds of fillers are compounded and filled in the paper, the effect of improving the optical properties is correspondingly increased by increasing the compounding amount, but conversely, other properties such as the strength of the paper are deteriorated. Also,
Conventional fillers generally have a low yield during papermaking, and it is difficult to perform uniform and high-level filling especially in a papermaking machine such as a twin-wire papermaking machine that has a high speed and a high shearing force.

That is, as the properties required for the filler for improving the optical properties of the paper, the whiteness of the paper, the opacity and the opacity after printing can be improved in a well-balanced manner by adding a smaller amount, and the yield at the time of papermaking can be improved. The cost is high, and the appearance of fillers satisfying these required properties is expected.

When the urea-formaldehyde cross-linked resin is prepared by mixing the initial condensate of urea and formaldehyde and the aqueous acid catalyst solution, the reaction mixture first becomes a soft gel, and then the reaction progresses to a cured product. It is not preferred to stir the reaction mixture. This is one of the obstacles to the industrially stable production of a filler composed of a urea-formaldehyde cross-linked resin having excellent quality.

That is, if it is attempted to carry out the reaction by mixing the initial condensate of urea and formaldehyde and the acidic catalyst aqueous solution without stirring in a normal batch type reaction tank,
After completion of the reaction, stirring cannot be performed, or it becomes difficult to efficiently discharge the reaction product from the reaction tank. On the other hand, although industrial continuous methods have been conventionally known, among these methods, in the method of Japanese Patent Publication No. 49-2350, the initial condensate and the acidic catalyst aqueous solution are continuously mixed in a pipe mixer. However, when performing gelation in the extrusion screw, the resulting gel and aqueous phase are separated in the extrusion screw, it is difficult to produce a preferred hydrous gel, as a result, the effect of improving the optical properties of the paper It had the drawback of being insufficient.

Further, according to the method of Japanese Patent Publication No. 57-26686, when the charging molar ratio of urea and formaldehyde forming the initial condensate is close to 2, the reaction on the belt is too slow and the curing is slow and stable operation can be performed. On the other hand, when the charging molar ratio is 1.5 or less, the curing rate on the belt is large and stable operation is possible, but the characteristics of the obtained urea-formaldehyde cross-linking resin are not preferable, and the effect of improving the optical characteristics of paper is insufficient. There was a problem.

<Means for Solving Problems> The inventors of the present invention have conducted various studies in order to solve the problems of the conventional method, and produced paper by using urea formaldehyde crosslinked resin particles having high linseed oil absorption as a filler. It was found that the optical properties of the resulting paper, especially the opacity of the paper after printing, were significantly improved, and a patent application was filed therefor (filed April 1, 1987).

However, there are various problems in producing such a filler having a high oil absorption amount of linseed oil, and particularly continuous production has been extremely difficult. The present inventors have studied in detail the process of forming the urea-formaldehyde crosslinked resin immediately after mixing the initial condensate and the acidic catalyst. In the case of the initial condensate used in the present invention, the mixture becomes cloudy after about 30 seconds. It has been found that there is an important step in determining the particle characteristics within about 1 minute after starting. The gel formation that occurs immediately after mixing and after the lapse of about 1 minute is an early stage in the overall reaction, and the gel obtained at this stage is still extremely flexible. The present inventors have conducted various studies on a method for industrially advantageously continuously carrying out this initial stage, and as a result, in order to obtain urea formaldehyde crosslinked resin particles having a high linseed oil absorption, a rotary volume type was used. The present invention has been reached by finding that a uniaxial eccentric screw pump is effective.

That is, according to the present invention, an initial condensate obtained by reacting urea and formaldehyde in a molar ratio of 1: 1.9 to 1: 2.4 and an acidic catalyst are converted into carboxymethyl cellulose or a salt thereof and an initial condensate. On the other hand, when a cross-linking reaction is performed at 35-65 ° C. in the presence of 5 to 20 times by weight of water to produce a paper filler, the reaction raw material is passed through a rotary positive displacement uniaxial eccentric screw pump to cause a cross-linking reaction. The urea-formaldehyde crosslinked resin particles having a high oil absorption amount can be industrially advantageously produced.

Hereinafter, the present invention will be described in detail.

In the present specification, “%” and “part” represent “% by weight” and “part by weight” unless otherwise specified.

Urea in the present invention is produced by a known method, and as the formaldehyde in the present invention, an aqueous formaldehyde solution having a formaldehyde concentration of 30 to 55% is usually used, but other formaldehyde is paraformaldehyde. Water-soluble formaldehyde polymers such as

In the present invention, the initial condensate of urea and formaldehyde is a mixture of urea and formaldehyde at a predetermined ratio, and is neutral to weakly alkaline at 60 to 90 ° C. and 30 to 12 ° C.
It is a water-soluble urea-formaldehyde resin obtained by reaction for 0 minutes, and usually has a concentration of about 10 to 60%. The proportion of urea and formaldehyde charged in producing the initial condensate was 1: 1.9 in terms of the molar ratio of urea and formaldehyde.
˜1: 2.4, preferably 1: 2.0 to 1: 2.2. When the amount of formaldehyde is less than 1: 1.9, the urea-formaldehyde crosslinked resin particles obtained have a small oil absorption, and the effect of improving the optical properties of paper is not sufficient. If the amount is large, the reaction yield is lowered, which is not economical, and the oil absorption amount is also small, and the effect of improving the optical characteristics of the paper is not sufficient.

The urea-formaldehyde crosslinked resin particles of the present invention have a particle size of 1 μm.
In the production method of the present invention, for the purpose of producing primary particles of such minute urea-formaldehyde cross-linked resin, carboxymethylcellulose or a protective colloid agent is used as a protective colloid agent during the reaction. It is necessary to make the salt coexist. Examples of the carboxymethylcellulose salt include carboxymethylcellulose sodium salt and carboxymethylcellulose potassium salt, and those produced by a known method having an etherification degree (DS) of 0.4 to 0.7 can be used. The amount of these carboxymethyl cellulose alkali metal salts used is usually about 0.1 to 10%, preferably 0.5 to 2%, based on the initial condensate. Further, the addition method is not particularly limited, carboxymethyl cellulose alkali metal salt is previously dissolved in water and mixed with either urea or formalin, and added to the reaction system when the initial condensate is produced. Is advantageous.

Examples of the acidic catalyst in the present invention include mineral acids such as sulfuric acid and hydrochloric acid, organic acids such as formic acid, acetic acid, sulfamic acid and paratoluenesulfonic acid. Further, since these acidic catalysts improve the mixing, it is advantageous to add them after diluting them with water to about 5 to 20%. PH during the reaction is 3
It is necessary to keep below, preferably 2 or less.

In the present invention, when the precondensate of urea and formaldehyde and the acidic catalyst are mixed and reacted, 5 to 20 parts of water must be made to coexist with 1 part of the precondensate. When the amount of coexisting water is less than 5 parts or more than 20 parts, the obtained urea formaldehyde crosslinked resin particles have a small oil absorption amount and the effect of improving the optical properties of paper is not sufficient. In the present invention, the weight of the initial condensate is equal to the total weight of urea and formaldehyde used in the reaction, excluding those that have escaped to the outside of the system.

The rotary displacement type uniaxial eccentric screw pump referred to in the present invention is as follows. That is, it is composed of two elements, a stator and a rotor. The stator is a double female screw whose cross-section perpendicular to the axis is a rectangle with semicircles on both ends, while the rotor has a cross-section perpendicular to the axis. It is a coiled single screw. Further, when the rotor is mounted on the stator, a space equal to the rotor volume remains in any cross section inside the stator, and the pump is designed to move as the rotor rotates. For example, "Mono Pump" manufactured by Hyōjin Kikai Co., Ltd. and "Snake Pump" manufactured by Mitsubishi Heavy Industries Ltd. Hiroshima Seiki Co., Ltd. can be mentioned.

As a mode for carrying out the present invention, first, when an aqueous solution of an initial condensate and an aqueous solution of an acidic catalyst are mixed, 5 to 20 parts of water is added to 1 part of the initial condensate in the mixed solution. Prepare to include. Then, this solution is introduced into an in-line mixer and continuously mixed. The mixture discharged from the in-line mixer is immediately introduced into the suction port of the pump and reacted while being transported in the pump. that time,
The temperature of the mixture is 35-65 ° C, preferably 45-60 ° C
Set to keep.

When the reaction temperature is lower than 35 ° C, the oil absorption of the obtained urea-formaldehyde cross-linked resin particles is small, while the temperature of 65 ° C is low.
If it is higher, the reaction yield decreases.

Usually, it is desirable that the reaction temperature is set high when the ratio of water to the total amount of urea and formaldehyde in the mixed solution is large, and set low in the opposite case.

The residence time in the pump is preferably 1 minute or more. That is, the step of determining the particle characteristics of the resulting crosslinked resin is preferably passed through in a pump. The residence time in the pump can be represented by the moving speed of the space generated by the rotor and the stator, but it can be practically measured as follows. That is, the residence time is measured by measuring the time until the inhalant is first discharged at the start of the operation at the set shaft rotation speed.

The hydrogel-like reaction product discharged from the pump is led to a hopper or the like, and the residence time in the hopper is 2
When the reaction is continued for 0 to 60 minutes and the post-reaction is continued, the yield is improved, which is desirable. As another mode for continuing the post-reaction, a method in which a pipe having the same pipe diameter is connected to the discharge port of the pump and the inside of the pipe is retained for a desired post-reaction time while retaining the plug flow is cited. You can

After the post-reaction, the reaction product is neutralized. Neutralization is
It can be carried out with a commonly used alkaline substance such as caustic soda, sodium carbonate, etc., and is neutralized to a pH of about 4.5 to 7. At the time of neutralization, it is possible to improve efficiency by adding water, or by adding water and then stirring with a stirrer.

After neutralization, the reaction product is separated by filtration, washed with water if necessary, pulverized, adjusted to a desired particle size and filled in paper.

The paper filler comprising the urea-formaldehyde cross-linked resin particles of the present invention usually has an average particle size of 2 to 9 μm, preferably 3 μm.
Adjust the particle size to be ~ 6μ.

When the paper is filled with the urea-formaldehyde cross-linked resin particles obtained by the method of the present invention, it can be made into paper by an ordinary method, and as a pulp raw material for producing paper, it is usually used as a raw material for paper. GP and RG used
P, SP, KP, DIP, etc. can be used.

<Examples> The present invention will be described in detail below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist.

The linseed oil absorption, particle size, and filler yield were measured by the following methods.

Measurement of linseed oil absorption (JIS K5101) Slurry obtained by neutralization (about 50 g as cross-linked resin)
Is suction-filtered with a glass filter (G4), the residue is again put into 2 liters of water, and after stirring well, again,
Suction filtration was performed to obtain a water-containing cake (solid content: about 20%). To 30 g of this cake, add 70 ml of water to prepare a slurry of about 6%, and use a home-use juice mixer to prepare 2
After crushing for minutes, suction filtration was performed again with a glass filter to obtain a water-containing cake (solid content: about 20%). 20 g of this cake-like substance was put into 200 ml of methanol, and the mixture was stirred at room temperature for 30 minutes, and then, a glass filter (G
Suction filtration was performed in 4). Then, the filtration residue was vacuum dried at 40 ° C. for 8 hours to obtain a white powder.

1 g of this white powder was taken on a glass plate, linseed oil was dropped little by little, kneaded with a spatula on a glass plate, and the titer of linseed oil when the sample was in a fluidized state was read. The linseed oil absorption was determined.

Here G: linseed oil absorption (%) H: linseed oil amount (ml) S: sample mass (g) Measurement of average particle size of urea formaldehyde crosslinked resin particles Measured by light transmission method using Stokes' law did.
That is, the crosslinked resin particles are dispersed in distilled water, the change in turbidity due to the sedimentation of the particles is measured as the change in light transmittance, and the weight cumulative distribution curve (one logarithm) is determined from the measured values.
The% particle size is defined as the average particle size. When calculating the weight cumulative distribution curve, the true specific gravity of the sample: 1.45, distilled water (20
(° C) specific gravity: 0.998, viscosity: 1.005. The maximum particle size was 50 μm.

To prepare the sample, put 50 ml of distilled water and 100 mg of the paper quality evaluation sample (solid) in a beaker, and use an ultrasonic disperser (output 2
Dispersion treatment was carried out for 5 minutes at 0 W and a frequency of 40 kHz, and when this was placed in a measurement cell, the absorbance [-10 g (I
o / I)] was 1.3 to 1.4 and diluted with distilled water to obtain a measurement sample.

As a measuring device, a Micron Fort Sizer (SKC-2000S) manufactured by Seishin Co., Ltd. was used.

Filler yield The filler yield was calculated by the following formula by measuring the nitrogen content in the paper and papermaking slurry by the Kjeldahl method.

Example 1 <Preparation of initial condensate> 25.9 parts (0.319 kg-mol) of 37% formalin, water 27.
2 parts were placed in a flask equipped with a hot water bath and a stirrer, and stirred while carboxymethylcellulose sodium salt ["CMC Daicel 1193" manufactured by Daicel Corp.] 0.42
Parts were dispersed, the pH was adjusted to 7.4 with caustic soda, and then 9.6 parts (0.16 kg-mol) of urea was added and the temperature was raised. After the temperature was raised to 70 ° C., the reaction was carried out for 1.5 hours, and then the flask was transferred to a water bath and cooled to obtain an aqueous solution of an initial condensate (a molar ratio of urea and formaldehyde of 1: 2.0). This product has a total concentration of urea and formaldehyde of 30%.
The pH by TB test paper was 7.2.

The aqueous solution of the initial condensate was further diluted with water to prepare a liquid A having an initial condensate concentration of 18%. Further, 10% diluted sulfuric acid was prepared and used as solution B. The liquid A and the liquid B were mixed by the following method.

A cylinder having a diameter of 25 mm and a length of 200 mm is filled with glass beads having a diameter of about 3 mm, and liquid A and liquid B are injected from one end at a rate of 360 and 80 ml / mm, respectively, and the mixture is injected from the other end. I got it.

<Cross-linking reaction using rotary displacement type eccentric screw pump> Using "Monopump" 2NEL-20 type manufactured by Hyōjin Kikai Co., Ltd., warm the inside of the pump to 60 ° C through warm water before starting operation, and rotate the pump shaft. Was set to 33 rpm.

The liquids A and B, which were kept at 55 ° C. in advance, were passed through a mixing device, and the mixed liquid was directly introduced to the inlet of the pump to start the operation of the pump. The first discharge was confirmed 2 minutes after the start of the operation (residence time in the pump: 2 minutes). Continue running for about 10 minutes,
Emissions were sampled from the pump for 2 minutes from 8 minutes to 10 minutes after the start of operation. At this time, the pump inlet liquid temperature was 53 ° C and the discharge temperature was 63 ° C. In addition, the total amount of liquids A and B fed was 880 g, and the yield of the reaction product (exhaust) was 870 g, which were almost in balance, and the total amount of the discharged product was a soft gel.

After collecting this reaction product, it was left in a receiver at an average temperature of 35 ° C. for 50 minutes and then put into 4 liters of water,
After crushing with a stirrer, neutralization with a 10% sodium hydroxide solution gave a slurry.

<Preparation of sample for paper quality evaluation> Slurry obtained by neutralization (about 50 g as crosslinked resin)
Was suction-filtered with a glass filter (G4), the residue was again put into 2 liters of water and well stirred, and then suction-filtered again to obtain a water-containing cake (solid content: about 20%). To 30 g of this cake, add 70 ml of water and add about 6
% Slurry was prepared and ground in a home juice mixer for 2 minutes.

<Preparation of Paper> Paper was prepared as follows using the above-mentioned sample for paper quality evaluation as a filler. As a pulp formulation, NBKP15
Part, TMP 25 parts, DIP 30 parts, RGP 30 parts 1% pulp slurry 10 with a beating degree of 280 ml (CSF)
To 100 parts, add 10 parts of an aqueous dispersion of the filler, which has been adjusted to a concentration of 5.0% in advance, and stir for 2 minutes, then add 3 parts of 10% aluminum sulfate aqueous solution, and stir for another 2 minutes. To obtain a prepared slurry. 25cm x 25cm TA
Paper was made using a PPI square sheet machine, press-dehydrated at 3.5 kg / cm ² , and then dried for 3 minutes with a rotary dryer having a surface temperature of 105 to 110 ° C. Then line pressure 40
After calendering at kg / cm, relative humidity 65%,
Seasoning was carried out for 24 hours in a thermo-hygrostat at a temperature of 20 ° C. to obtain paper for paper quality evaluation.

<Evaluation of paper quality> The whiteness of the paper obtained as described above is JIS P812.
3, opacity is JIS P-8138, and opacity after printing is J.TAP
The measurement was performed according to PI No. 45-84.

The results are shown in Table 1.

Comparative Example 1 The liquids A and B of Example 1 were mixed in the same manner as in Example 1 and then a cross-linking reaction was carried out using an extruder. As an extruder, Ikegai Tekko Co., Ltd. "Horizontal twin-screw extruder PCM45-30"
Mold (screw diameter 45 mm, length 1350 mm (L / D = 3
0) Use 15 split-type screws, set the barrel temperature to 70 ° C on average, and rotate the screw at 30 rpm.
Set to.

Liquids A and B, which were previously kept at 55 ° C., were passed through a mixing device at a rate of 400 and 90 ml / mm, respectively, and the mixed liquid was introduced directly into the inlet of the extruder to start the operation. The first discharge was confirmed 1 minute after the start of the operation (residence time in the extruder: 1 minute). Continue operation for about 10 minutes, and after operation starts 8
The extruder effluent was sampled for 2 minutes from 10 minutes to 10 minutes. At this time, the temperature of the liquid at the inlet of the extruder is 55
The discharge temperature was 65 ° C. In addition, the total amount of the fed liquids A and B was 980 g, and the yield of the reaction product (exhaust product) was 985 g, which were almost balanced, and the discharged product was discharged in the state where the gel-like material and the aqueous solution were separated.

After collecting this reaction product, it was left in a receiver at an average temperature of 35 ° C. for 50 minutes and then put into 4 liters of water,
After crushing with a stirrer, it was neutralized with a 10% sodium hydroxide solution to obtain a slurry. Using this neutralized slurry, Example 1
A paper quality evaluation sample was prepared and paper quality was evaluated in the same manner as in. The results are shown in Table 1.

<Effects of the Invention> According to the examples and comparative examples, the paper filler produced by the production method of the present invention has a well-balanced improvement in the optical properties of whiteness, opacity, and opacity after printing. It can be seen that the yield on paper is high and that it is excellent.

Claims (3)

[Claims] 1. An initial condensate obtained by reacting urea and formaldehyde in a molar ratio of 1: 1.9 to 1: 2.4 and an acidic catalyst are added to carboxymethyl cellulose or a salt thereof and an initial condensate in an amount of 5: 1. In producing a paper filler by cross-linking at 35 to 65 ° C. in the presence of ˜20 weight times of water, the reaction raw material is cross-linked while passing through a rotary positive displacement eccentric screw pump. Method for manufacturing filler. 2. The method for producing a paper filler according to claim 1, characterized in that a product obtained by reacting urea and formaldehyde in the presence of carboxymethyl cellulose or a salt thereof is used as an initial condensate. how to. 3. The method for producing a paper filler according to claim 1 or 2, wherein the residence time of the reaction raw material in the rotary positive displacement uniaxial eccentric screw pump is 1 minute or more. Method.