JPH0571719B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a paper filler. Specifically, the present invention relates to a paper filler made of a urea-formaldehyde crosslinked resin that has a significantly large linseed oil absorption. (Prior art and problems) Traditionally, in the paper industry, kaolin,
Inorganic fillers such as talc and white carbon are widely used. However, these inorganic fillers do not have a sufficient effect on improving paper whiteness, opacity, etc., and because they have poor fixability to paper, they tend to generate paper dust, and they also tend to damage printing equipment due to abrasion. There are drawbacks. On the other hand, it is also known to use a urea formaldehyde crosslinked resin as an alternative to inorganic fillers. For example, in Japanese Patent Publication No. 51-23601, the molar ratio of urea formaldehyde is 1:1 to 1:2.
The use of insoluble, infusible and non-porous fine urea formaldehyde polymers with a BET specific surface area of 5 to 100 m ² /g as paper fillers is described. However, although the conventionally known filler made of urea-formaldehyde crosslinked resin has a large effect on improving paper whiteness, opacity, etc., there is a problem in that the effect on improving opacity after printing is not sufficient. Furthermore, with conventional fillers, it has been difficult to improve the three important optical properties of paper, namely whiteness, opacity, and post-printing opacity, in a well-balanced manner. (Means for Solving the Problems) The present inventors have improved the conventionally known paper filler made of urea formaldehyde crosslinked resin.
The present invention was achieved as a result of extensive research into improving the optical properties of paper products, particularly the opacity after printing. That is, the gist of the present invention is to provide carboxymethylcellulose, an initial condensate obtained by reacting urea and formaldehyde in a neutral to weakly alkaline aqueous medium at a molar ratio of formaldehyde to urea of 1:1.9 to 1:2.4. or a salt thereof, a mixture mainly consisting of water and an acidic catalyst in an amount of 5 to 15 times the weight of the initial condensate,
The linseed oil absorbent is obtained by stirring the whole mixture uniformly, stopping stirring for at least 5 minutes, reacting at 35 to 65°C to form a solid urea formaldehyde crosslinked resin, and then finely pulverizing this. Paper fillers with a content of 800% or more. Next, the present invention will be explained in detail, and "%" in the following description indicates "% by weight" unless otherwise specified. The paper filler of the present invention consists of finely ground urea-formaldehyde crosslinked resin particles and has a linseed oil absorption of 800% or more. According to studies by the present inventors, all conventionally known fillers made of urea-formaldehyde crosslinked resin particles have a small linseed oil absorption amount. Linseed oil absorption is one measure of printing ink absorption, and it is considered that the larger the value, the greater the printing ink absorption. Therefore, if the same type of filler is used, paper made using a material with a higher absorption of linseed oil will have better absorption of printing ink into the filler dispersed in the paper, resulting in lower opacity etc. after printing. It is thought that the optical properties are improved. From the above points, the paper filler of the present invention has a linseed oil absorption of 800% or more, preferably
Consists of more than 1000% urea-formaldehyde crosslinked resin particles. It is necessary that the urea formaldehyde crosslinked resin be finely ground. Usually the average particle size is
Grind to 10μm or less. It is preferably ground to an average particle size of 2 to 9 μm, particularly 3 to 6 μm. Generally, finer pulverization improves the performance as a filler, but on the other hand, the cost of pulverization increases. The filler made of the urea-formaldehyde crosslinked resin according to the present invention is preferably an aggregate consisting essentially of primary particles having a particle size of 1 μm or less, that is, secondary particles.
That is, when the filler according to the present invention is dispersed so that the filler particles do not overlap each other and observed with a scanning electron microscope, the area occupied by the primary particles larger than 1 μm is at most 50% of the projected area of the secondary particles. %, usually 2% or less. Particularly preferred is a filler consisting of secondary particles that do not contain primary particles larger than 1 μm. The paper filler of the present invention can be produced by the method described below. That is, first, a mixture of urea and formaldehyde in a molar ratio ranging from 1:1.9 to 1:2.4 is mixed into an aqueous medium containing carboxymethyl cellulose (abbreviated as CMC) or a salt thereof, such as an alkali metal salt such as a sodium salt. An initial condensate is produced by reacting at a temperature of about 50 to 90°C in neutral to slightly alkaline conditions. The urea and formaldehyde used in this case may be those for ordinary industrial use. As formaldehyde, an aqueous solution with a concentration of 30 to 55% is usually used, but an aqueous solution of a formaldehyde polymer such as paraformaldehyde can also be used. The molar ratio of urea to formaldehyde is 1:1.9
It is necessary that the ratio is in the range of 1:2.4 to 1:2.4, and the range of 1:2.0 to 1:2.2 is particularly preferable. When the molar ratio of formaldehyde to urea is less than 1.9, the linseed oil absorption of the filler obtained by the subsequent treatment of the present invention does not reach 800%, and
When it is larger than 2.4, the yield of filler obtained by the subsequent treatment of the present invention decreases, and the linseed oil absorption does not reach 800%. As a result, when paper is made using these fillers, the desired effect of improving opacity after printing cannot be obtained. CMC or a salt thereof is usually used in an amount of about 0.1 to 10% based on the total amount of urea and formaldehyde. CMC or its salt controls the particle size of the primary particles of the crosslinked resin to prevent the formation of large primary particles when the initial condensate is polycondensed in the presence of an acidic catalyst to cause a crosslinking reaction. It has the effect of Therefore, CMC or a salt thereof may be added later to the initial condensate produced by the above reaction instead of being added during the production of the initial condensate as described above. The liquid property during the production of the initial condensate is maintained at a neutral to weakly alkaline level, for example, pH 7 to 8, by adding caustic alkali or alkali carbonate, for example. The aqueous solution containing the initial condensate obtained by the above method is then heated at a temperature within a predetermined range by adjusting the amount of water to a predetermined range, adding CMC or a salt thereof if necessary, and adding an acidic catalyst. By polycondensation, a urea formaldehyde crosslinked resin is obtained as a solid. Examples of the acidic catalyst include mineral acids such as sulfuric acid and hydrochloric acid, and organic acids such as formic acid, acetic acid, p-toluenesulfonic acid, and sulfamic acid. The amount of water used in the polycondensation reaction of the initial condensate needs to be 5 to 15 times the amount of the initial condensate. Note that the amount of the initial condensate is equal to the total amount of urea and formaldehyde used in the reaction, excluding those that escape from the system. When the amount of water is less than 5 times the amount, the solidified product produced by polycondensation becomes hard, and the linseed oil absorption amount of the filler obtained by the subsequent treatment of the present invention does not reach 800%. . In addition, when the amount of water is more than 15 times the amount, the solidified product produced by polycondensation is too soft, and the linseed oil absorption amount of the filler obtained by the subsequent treatment of the present invention is similarly 800%. % is not reached. As a result, in any case, when paper is made using these fillers, the desired effect of improving opacity after printing cannot be obtained. In addition, the temperature of the polycondensation reaction of the initial condensate is 35 to 65
°C, preferably between 40 and 60 °C; at temperatures below 35 °C, the linseed oil absorption of the filler obtained by the subsequent treatment of the invention decreases.
Does not reach 800%. Moreover, at temperatures higher than 65° C., the yield of filler obtained in the subsequent treatment decreases and the linseed oil absorption does not reach 800%. In the polycondensation reaction, an acidic catalyst is added to an aqueous solution consisting of the initial condensate, CMC or its salt, and water in an amount 5 to 15 times the amount of the initial condensate, stirred to make the whole homogeneous, and heated at 35 to 65°C. This is done by holding it in place. At this time, stir for as short a time as possible.
In addition, it is necessary to not stir for at least 5 minutes after stopping stirring. That is, when an acidic catalyst is added and stirred, the initial condensate solidifies into a gel, but the stirring is stopped before it solidifies into a gel, and the polycondensation reaction is allowed to proceed independently of each other for at least 5 minutes in each part of the gel-like solid. Let it proceed. As a result, the polycondensation reaction in each part proceeds only with the reactant present in that part, producing a crosslinked resin bound to primary particles smaller than 1 μm.
After 5 minutes have elapsed, stirring may be performed, but usually the reaction is completed without stirring. The reason why the crosslinked resin has such a structure consisting of an aggregate of primary particles is unknown, but the polycondensate produced from the aqueous solution of the initial condensate as the polycondensation reaction progresses precipitates to form primary particles. It is thought that these particles aggregate in the process of further growth to generate secondary particles. Since such a skeletal structure of primary particles and secondary particles is formed relatively quickly, it is considered that even if stirring is restarted after 5 minutes have elapsed, the structure of the produced crosslinked resin will not be affected. The solidified urea formaldehyde crosslinked resin obtained as described above is then pulverized. In the pulverization process, for example, the solidified material is first coarsely pulverized, then water is added to give a concentration of about 8 to 10%, and then the average particle size is pulverized using a suitable pulverizer, such as a mixer-type high-speed rotary pulverizer. 10μm or less, preferably 2~
Process to make it 9μm. If the cost of pulverization is not considered, it is generally preferable to pulverize the particles to an average particle size of 3 to 6 μm. The slurry after pulverization is neutralized with an alkali, filtered, thoroughly washed with water to obtain a white cake, and optionally dried to obtain a product. (Examples) Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. Furthermore, in the description of Examples, "parts" indicate "parts by weight." In addition, in the present invention, the linseed oil absorption amount, the particle size of the crosslinked resin, the yield of the crosslinked resin, and the filler yield are as follows:
It was measured by the method below. Linseed oil absorption: Measure according to JIS K5101 (1978) method.
That is, about 1 g of a dry sample is placed on a glass plate, and boiled linseed oil is added dropwise from a biuret to the center of the sample little by little, and kneaded using a spatula on the glass plate.
Read the amount of boiled linseed oil added until the sample becomes fluid with one drop of boiled linseed oil, and calculate the oil absorption (%) using the following formula. All operations are performed at room temperature (approximately 25°C). G=H/S×100 [G: Oil absorption amount (%), H: Droplet amount of linseed oil (ml), S: Mass of sample (g)] In addition, the sample is prepared by keeping the sample in a wet state, Pour this into 10 times the volume of methanol and let it stand for 30 minutes at room temperature.
Stir for a minute. Next, suction filtration is performed, and the filter cake is dried at 40° C. and 750 mmHg for 8 hours. Particle size of crosslinked resin: Measured by light transmission method using Stokes' law. That is, crosslinked resin particles are dispersed in distilled water,
Changes in turbidity due to particle sedimentation are measured as changes in light transmittance, a weight cumulative distribution curve (semi-logarithm) is determined from this measured value, and 50% of the curve is defined as the average particle diameter. When calculating the weight cumulative distribution curve,
True specific gravity of sample: 1.45, specific gravity of distilled water (20℃):
Use the following values: 0.998 and viscosity: 1.005. In the following examples, the measuring device used was a Micron Photo Sizer (SKC-
2000S) with a maximum particle size of 50 μm. 50ml of distilled water and 100 samples in a beaker
mg into an ultrasonic disperser (output 20W, frequency 40K)
Hz) for 5 minutes. When this is put into the measurement cell, the absorbance [-log(I ₀ /I)]
The sample was diluted with distilled water to a value of 1.3 to 1.4 and used as a measurement sample. Yield of crosslinked resin: The weight of the wet cake after each step of crushing, neutralization, filtration, and washing with water is K, and the yield when this wet cake is dried at 120°C for 2 hours is A%. The total amount of formaldehyde and urea used is calculated by the following formula as B. Yield of crosslinked resin (%)=K×A/B Filler yield: The nitrogen content (weight) in paper and papermaking slurry is measured by the Kjeldahl method, and calculated by the following formula. Filler yield = Nitrogen in paper/Nitrogen in slurry Example 1 41.0 parts (0.5 mol) of a 37% concentration formaldehyde aqueous solution and 43.1 parts of water were mixed, and this was added to the mixture under stirring.
0.7 parts of CMC sodium salt [CMC manufactured by Daicel Corporation]
Daicel 1193] was dispersed, the pH was adjusted to 7.4 by adding caustic soda, and then 15.2 parts (0.25 mol) of urea was added, heated, and reacted at 70°C for 1.5 hours to form an aqueous solution of the initial condensate (urea A formaldehyde molar ratio of 1:2.0) was obtained. The pH of this initial condensate aqueous solution as measured by BTB test paper was 7.2. 100 parts of the aqueous solution of the initial condensate obtained above was heated to 40°C, and 104 parts of 3.6% sulfuric acid at the same temperature was quickly added and mixed. It became cloudy after 30 seconds and solidified after 45 seconds. The amount of water coexisting during the solidification reaction is 5.6% of the initial condensate.
It was double the amount. After mixing with sulfuric acid, the mixture was allowed to stand at 40° C. for 30 minutes, and then the solidified material was collected, crushed, and crushed for 2 minutes with 100 parts of water using a mixer (MX-270G manufactured by Toshiba). After the pulverization treatment, aqueous caustic soda solution was added to neutralize the mixture to obtain 250 parts of a slurry containing about 10% solids. Next, pass the slurry through a glass filter (25G4)
The resulting cake was poured into 250 parts of water again, stirred, and filtered to collect the cake. This cake was dried in an oven at 120° C. for 2 hours, and the average particle size was 4.7 μm. Further, the particle size of the primary particles of this product was 0.1 to 0.3 μm when observed with a scanning electron microscope. In addition, the filter cake before drying obtained above was mixed with methanol, stirred for 30 minutes, filtered with suction through a glass filter (25G4), and the residue was dried at 40°C for 8 hours under reduced pressure. The oil absorption amount was 1200%. Examples 2 to 4 and Comparative Examples 1 to 4 The molar ratio (F/U) of urea and formaldehyde during the production of the initial condensate in Example 1, the amount of water during the polycondensation reaction of the initial condensate (hereinafter referred to as bath ratio) ),
The same treatment as in Example 1 was carried out except that the temperature and time were changed as shown in Table 1 to obtain fillers having the particle size and linseed oil absorption shown in Table 1, respectively. In addition, when producing the initial condensate in Example 1,
When the same treatment as in Example 1 was carried out without using CMC sodium salt (Comparative Example 1), the temperature during the polycondensation reaction of the initial condensate in Example 1 was
When the treatment was carried out according to Example 1 except that the temperature was 75°C (Comparative Example 2), the molar ratio of urea to formaldehyde (F/U) during the production of the initial condensate in Example 1 was 1.5. , and when the process was carried out according to Example 1 except that the bath ratio during the polycondensation reaction was 4.0 (Comparative Example 3), and during the polycondensation reaction of the initial condensate in Example 1. Table 1 also shows the results of the case where the treatment was carried out in accordance with Example 1 (Comparative Example 4), except that the time during which stirring was stopped (=standing time) was 3 minutes.

[Table] Reference example: Preparation of paper quality evaluation paper: 15 copies of NBKP, 25 copies of TMP, 30 copies of RGP, and 30 copies of DIP
1 part of pulp with a freeness of 300ml (csf) mixed with
To 1000 parts of the % slurry, 10 parts of the aqueous filler dispersions obtained in Examples 1 to 4 and Comparative Examples 1 to 4, which had been adjusted to a concentration of 5.0% in advance, were added and stirred for 2 minutes.
Subsequently, 3 parts of 10% aluminum sulfate aqueous solution was added and stirred for an additional 2 minutes to prepare a filler-containing slurry for paper making. This was then processed using a TAPPI square sheet machine (25
After press dehydration at 3.5Kg/ ^cm2 , drying with a rotary dryer at a surface temperature of 105-110℃ for 3 minutes, and calendering at a linear pressure of 40Kg/cm2. After that, relative humidity 65%, 20
Paper for paper quality evaluation was prepared by seasoning for 24 hours in a constant temperature and humidity room at ℃. Evaluation of paper quality: Various optical properties of the paper prepared above were investigated. That is, the whiteness was measured according to JIS P-8123, the opacity was measured according to JIS P-8138, and the opacity after printing was measured according to J.TAPPI.No.45-84. The optical properties of paper and the yield of filler when using the fillers obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were as shown in Table 2. In addition, the case where no filler was added is also shown as Comparative Example 5.

[Table] (Effects of the invention) The paper filler of the present invention has a linseed oil absorption of 800% when produced by a combination of the above specific conditions.
It consists of the above-mentioned microscopic urea-formaldehyde crosslinked resin particles, and as shown in the reference example, when this is used for paper making, the resulting paper has excellent whiteness and opacity, and furthermore, the filler dispersed in the paper is It absorbs printing ink well, so that the opacity of the paper after printing is significantly improved. In addition, the yield of filler is high and efficient.

Claims (1)

[Claims] 1 Initial condensate obtained by reacting urea and formaldehyde in a neutral to weakly alkaline aqueous medium at a molar ratio of formaldehyde to urea of 1:1.9 to 1:2.4, carboxymethylcellulose or a salt thereof, the initial condensation 5 for things
A mixture mainly consisting of ~15 times the weight of water and an acidic catalyst is stirred until the whole is homogeneous, and then the stirring is stopped for at least 5 minutes.
A paper filler with a linseed oil absorption of 800% or more, which is obtained by reacting at ℃ to form a solid urea-formaldehyde crosslinked resin and then finely pulverizing it.