JPH0357237B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a pulp and a method for producing the same, and more particularly to an improved pulp containing crosslinked melamine formaldehyde resin particles and a method for producing the improved pulp. [Prior art] Fine particles such as kaolin, talc, white carbon, and fine urea resin are blended as fillers for the purpose of improving optical properties such as paper whiteness, opacity, and opacity after printing. It is well known to do so. For example, by adding a urea resin having an aggregate structure of insoluble, infusible, and nonporous fine particles with a molar ratio of urea and formaldehyde of 1:1 to 1:2 as a filler, the whiteness of paper can be improved. A method to improve transparency has been proposed (Special Publication No. 51-23601). Another method for improving the optical properties of paper is to react urea and formaldehyde in a water-based pulp slurry in the presence of an acidic catalyst to form a methylene urea precipitate on the fiber structure, either mechanically or chemically. A method has been proposed in which paper products are produced by fixing the paper and making paper from it (Japanese Patent Laid-Open No. 46-2410). [Problems to be Solved by the Invention] In the method of Japanese Patent Publication No. 51-23601, in the case of printing paper such as newsprint, when printing is applied to the paper, the printed image can be seen through the back side. That is, there was a drawback that the effect of improving opacity after printing was insufficient. Furthermore, even with the method of JP-A-46-2410, the effect of improving opacity after printing was still insufficient. Generally, in the method of adding microscopic crosslinked particles obtained by reacting urea with formaldehyde or microscopic inorganic particles as a filler to paper products, thereby improving the optical properties of the paper, the filler is If the amount added is increased, the improvement effect will increase. However, increasing the amount of filler added leads to a decrease in the strength of the paper, and conventional fillers do not improve the whiteness, opacity, and post-printing opacity, which are important optical properties of paper, in a well-balanced manner. That was difficult. In addition, conventional fillers have a low yield during papermaking, and there is also the problem that it is difficult to uniformly and highly fill the paper in a papermaking machine such as a twin-wire papermaking machine that requires high speed and high shear. [Means for Solving the Problems] The present inventors have made extensive studies on pulp that can solve the above-mentioned conventional problems and improve the optical properties of paper products, especially the opacity after printing. As a result, we discovered that excellent effects can be obtained by fixing and incorporating melamine formaldehyde resin crosslinked particles of a specific particle size into pulp,
The present invention has been completed. That is, the present invention provides an improved pulp that can produce paper products that have excellent optical properties such as whiteness, opacity, and opacity after printing, and also have extremely high retention during papermaking, and the improved pulp. The present invention provides a method for producing a pulp containing substantially spherical crosslinked melamine formaldehyde resin particles with a particle size of 1 μm or less, the particles being chemically fixed to the fibers of the pulp, and an aqueous slurry of the pulp. , by adding a water-soluble melamine resin obtained by reacting melamine and formaldehyde at a molar ratio of 1:1.5 to 1:6 and an acidic catalyst, the ratio of the total concentration of melamine and formaldehyde to the pulp concentration is 0.3: Obtain a mixed solution of 1 to 1.5:1, and heat the mixed solution at 30 to 90°C at a pH of 6 or less.
The gist of the present invention is to provide a method for producing pulp, which is characterized by reacting at a temperature of 100 mL and then neutralizing the pulp. The present invention will be explained in detail below. In this specification, "%" indicates "% by weight" unless otherwise specified. The improved pulp of the present invention contains a melamine formaldehyde resin crosslinked product, particularly a fluid melamine formaldehyde resin crosslinked product having a substantially spherical shape with a particle size of 1 μm or less, which is chemically fixed to pulp fibers. The improved pulp of the present invention can be produced industrially advantageously, for example, according to the pulp production method of the present invention. A method for producing the improved pulp of the present invention according to the pulp production method of the present invention will be described below. In the present invention, the raw material pulp is not particularly limited, and examples include mechanical pulps such as GP and RGP, chemical pulps such as SP and KP, as well as recovered pulps such as DIP. Further, the pulp may be subjected to chemical treatment such as bleaching. As an aqueous slurry of these pulps, the pulp concentration is 2.
~30% is preferable, and the pulp freeness is preferably about 100 to 500 ml in terms of Canadian Standard Freeness (hereinafter abbreviated as "CSF"). In the method of the present invention, first, a water-soluble melamine resin is added to an aqueous pulp slurry and thoroughly mixed. Next, add the acidic catalyst, but in order to mix thoroughly, the acidic catalyst should be mixed with water at a ratio of 5 to 20%.
It is preferable to add it after diluting it to a certain concentration. The water-soluble melamine resin used in the present invention contains melamine and formaldehyde in a molar ratio of 1:1.5.
It is a melamine resin obtained by reacting at a ratio of 1:6 to 1:6, preferably 1:2 to 1:4. Such melamine resin is usually made by mixing a predetermined ratio of melamine and formaldehyde in a neutral to weakly alkaline solution of 60 to 60%.
Obtained by reacting at 90°C for 20 to 60 minutes. If the molar ratio of formaldehyde to melamine is less than 1.5, or if this molar ratio is 6.
If it is larger, the reaction yield will decrease, and
A sufficient improvement effect on opacity cannot be obtained after printing. Note that the melamine used in the production of water-soluble melamine resin may be produced by a known method, and as the formaldehyde, an aqueous formaldehyde solution with a formaldehyde concentration of 30 to 55% is usually used, but other Water-soluble formaldehyde polymers such as formaldehyde can also be used. In the present invention, the water-soluble melamine resin has a ratio of the total concentration of melamine and formaldehyde to the pulp concentration in a mixed solution obtained by adding the water-soluble melamine resin and an acidic catalyst to an aqueous pulp slurry of 0.3:1 to 1. Add at a ratio of 1.5:1. In order to obtain the improved pulp of the present invention, this ratio is an extremely important requirement, and if the concentration ratio is less than 0.3, it is possible to form a cross-linked melamine formaldehyde resin in a substantially spherical shape with a particle size of 1 μm or less in the fibers of the pulp. cannot be formed. For example, there is a method of using melamine resin for the purpose of increasing paper strength, but in this case, the above concentration ratio is usually 0.02~
0.05:1, and under these conditions the resin crosslinks produced by the melamine resin under acidic conditions act as an adhesive at the contact points of the pulp fibers, but do not improve the optical properties of the paper. No particle formation occurs. On the other hand, if the concentration ratio is greater than 1.5, a crosslinked resin with an irregular shape is formed over the entire surface of the pulp, making it impossible to obtain good optical properties. In addition, in the method of the present invention, it is preferable that the total concentration of melamine and formaldehyde in the mixed solution and the pulp concentration are each 2% or more. If the concentration is less than 2%, not only the reaction yield is low, but also particles of crosslinked melamine formaldehyde resin having a suitable shape may not be formed. On the other hand, examples of the acidic catalyst include mineral acids such as sulfuric acid and hydrochloric acid, and organic acids such as formic acid, acetic acid and para-toluenesulfonic acid. In the present invention, these acidic catalysts are used in the mixed solution obtained.
It is added so that the pH, that is, the pH during the reaction, is maintained at 6 or less, preferably 5 or less. In the present invention, various protective colloid agents may be present during the reaction in order to form preferable approximately spherical crosslinked melamine resin particles from the pulp fibers. As a protective colloid,
Natural products such as gum arabic, carboxymethylcellulose alkali metal salts, alginate alkali metal salts, etc. and their modified products, polyacrylic acid, polymethacrylic acid, copolymers of maleic acid and styrene and their alkali metal salts, aqueous combinations of polyvinyl alcohol, etc. Polymers and the like can be mentioned. The amount of these protective colloids added is preferably approximately 0.1 to 10% based on the total amount of melamine and formaldehyde. Although the method of addition is not particularly limited, it is advantageous to dissolve melamine in the reaction system when melamine and formaldehyde are reacted to produce a water-soluble melamine resin. The mixed solution obtained by adding a water-soluble melamine resin and an acidic catalyst to an aqueous slurry of pulp is maintained at a temperature of 30 to 90°C, and the water-soluble melamine resin is added to the aqueous slurry of pulp under acidic conditions. Make it react. After the reaction, the reaction mixture is neutralized to a pH of preferably about 4.5 to 7 using a commonly used alkaline substance such as caustic soda or soda carbonate. According to the method of the present invention, a high-quality pulp can be obtained in which fine crosslinked melamine formaldehyde resin particles having a particle size of 1 μm or less and having a substantially spherical shape are chemically fixed on the surface of pulp fibers. By the way, in the present invention, the fixing mode when the melamine formaldehyde resin crosslinked body (melamine resin) particles are fixed on the pulp fibers is as follows:
The following mechanism can be considered. Fixation by chemical bonding force Fixation is mainly done by hydrogen bonds that occur between the hydroxyl groups in the cellulose molecules of the pulp and the amino groups or hydroxyl groups in the melamine resin molecules.
In addition, a portion of the melamine resin is fixed by direct bonding between molecules such as cellulose, hemicellulose, and lignin that constitute the pulp and the functional groups of the melamine resin. Fixation by chemical bonding force During the reaction process, as a polycondensation reaction occurs with an acidic catalyst added to the resulting water-soluble melamine resin, a polymer colloid with a positive charge is generated, and this polymer colloid has a negative charge. It is easily adsorbed to the charged pulp fibers, and is fixed while growing as approximately spherical particles using the deposit as a core. This fixation factor is an electrical bonding force, and can also be called physical fixation, but it is more commonly seen as being in the category of chemical fixation. Fixation by physical bonding force In the reaction slurry system, condensation polymerization may proceed in the liquid phase rather than on the surface of the pulp, forming approximately spherical resin particles. It is physically fixed by being buried in a certain ``indentation'' or ``interference'' created by the entanglement of pulp fibers. Among the above-mentioned fixation modes, in the present invention, the melamine formaldehyde resin crosslinked particles are fixed to the pulp fiber surface mainly by chemical fixation. That is, with the melamine/formaldehyde ratio and the melamine and formaldehyde/pulp ratio of the present invention, there is a relatively small possibility that condensation polymerization will proceed only in the liquid phase to form approximately spherical resin particles. For this reason, physical fixation of , hardly occurs, and chemical fixation of . In fact, in Examples 1 to 4 described below, almost no particles were found embedded and fixed in the "hollows" or "interspaces" of the pulp fibers. In order to produce paper using the pulp of the present invention containing such a crosslinked melamine formaldehyde resin, the pulp of the present invention must be added to the absolute dry weight of the paper.
It is desirable to mix the pulp of the present invention with other pulps to make paper so that the blending ratio is 0.5 to 50%, especially 2 to 40%. If the content of the pulp of the present invention is less than 0.5%, the effect of improving optical properties will not be sufficient;
Even if the amount is greater than 50%, it is not economical because a commensurate improvement effect cannot be obtained. Note that papermaking can be carried out according to a conventional method, and other pulps that can be blended with the pulp of the present invention include those that are usually used as raw materials for paper, such as GP, RGP, SP, KP, and DIP. These can be used alone or in combination of two or more. In addition, the particle diameter of the melamine formaldehyde resin crosslinked product on the pulp fibers in the present invention is measured by the following method. That is, the product obtained by the reaction and neutralization is filtered through a filter paper and washed with water if necessary. The filtration residue obtained by filtration or washing with water after filtration (hereinafter referred to as "pulp pad")
That's what it means. ) contains about 80% water, so
First, put the pulp pad into about 100 times its weight of acetone and stir well for 10 minutes at room temperature to replace the solvent. The pulp pad that has undergone solvent replacement is filtered and then vacuum dried at room temperature to completely remove the acetone contained therein. The dried pulp that has undergone the above treatment is fixed on a sample stage using double-sided tape, gold is evaporated to a thickness of approximately 10 nm using an ion coater, and magnified 10,000 times using a scanning electron microscope using a conventional method. , and measure the particle size by observing. [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 thereof. Note that in the following, "parts" indicate "parts by weight." Example 1 Preparation of improved pulp In a flask equipped with a stirrer, add 1147 ml of water.
1 part, 41 parts of melamine, 52 parts of 37% formalin aqueous solution [melamine: formaldehyde = 1:2]
(molar ratio)] and carboxymethylcellulose sodium salt (“CMC Daicel” manufactured by Daicel Corporation)
120 parts of a 1% aqueous solution (1193) was added, heated in a water bath, and raised to 65°C while stirring, and reacted for 1 hour to obtain a water-soluble melamine resin solution. Into this flask, 500 parts of water-containing Refiner Ground Pulp (hereinafter abbreviated as "RGP") with a pulp concentration of 20% was added, and stirring was continued for 30 minutes (total concentration of melamine and formaldehyde:
ratio of pulp density = 0.6:1). After that, transfer the contents to a beaker and add 10% while stirring vigorously.
After adding 140 parts of concentrated dilute sulfuric acid and further stirring for about 3 minutes, the pH of the contents was measured and found to be 3. This beaker was immersed in a water bath kept at 65°C, and the contents were stirred approximately every 20 minutes to allow reaction for 5 hours. Next, remove the beaker from the hot water bath and add 3000 ml of water.
About 90 parts of a 10% aqueous solution of caustic soda was gradually added with stirring to neutralize the mixture to pH 7 to obtain a slurry with a pulp concentration of 2.93%. A small amount of this slurry was taken, dried, and the solid content was measured.The solid content of the slurry was 146.5.
It was confirmed that it corresponds to the Department. Paper Preparation Paper was prepared using the improved pulp obtained in . Pulp formulation: 10 parts of NBKP, 30 parts of TMP
300 ml of improved pulp (improved RGP) with 30 parts DIP and 25 parts RGP.
(CSF) to 1000 parts of 1% pulp slurry, 10%
Three parts of aluminum sulfate aqueous solution was added and stirred for 1 minute to obtain a prepared slurry. Then 25cm x 25
The paper is made using a TAPPI square sheet machine with a size of 3.5 cm.
After press dehydration at Kg/ ^cm2 , surface temperature 105
Drying was performed in a rotary dryer at ~110°C for 3 minutes. Next, the paper was calendered at a linear pressure of 40 kg/cm, and then seasoned for 24 hours in a constant temperature and humidity chamber at a relative humidity of 65% and a temperature of 20°C to obtain paper for paper quality evaluation. The optical properties of the paper obtained in the evaluation of paper quality were investigated.
Whiteness is JIS P-8123, opacity is JISP-
8138, the opacity after printing was measured according to J.TAPPI No. 45-84. In addition, as a method for measuring opacity after printing,
Apply offset ink to 1/2 side of the paper using a two-part roll according to the measurement method of J.TAPPI No. 45-84 to make a test paper. , the reflectance of the ink-applied surface (J.
Based on the measurement method of TAPPI No.45-84) is 9~
Take out the 13% sample, place it on a brown flat plate with the ink-coated side facing down, and visually determine the boundary line between the ink-coated area and the non-inked area from a position 1 m above it. did. The boundary line was determined in the following four stages. The border line is almost invisible. ...4 Slightly visible. ...3 〃 It is quite visible. ...2 〃 Can be clearly seen. ...1 Note that the judgment was made by five subjects and the average value is shown. The results are shown in Table 2. Examples 2 to 4, Comparative Example 1 Improved pulp preparation conditions such as the molar ratio of formaldehyde to melamine in the water-soluble melamine resin, the mixing ratio of the water-soluble melamine resin and pulp, and the pulp composition during paper preparation are shown in Table 1. Paper was obtained and evaluated in the same manner as in Example 1, except for the changes as shown. In addition, in Example 3, carboxymethylcellulose sodium salt was not used.
The results are shown in Table 2. Comparative Example 2 Paper was prepared and evaluated in the same manner as in Example 1, except that the improved pulp of the present invention obtained above was not used and instead a large amount of RGP was blended. The results are shown in Table 2. Comparative Example 3 In a beaker equipped with a stirrer, pulp concentration
20% hydrated RGP 1000 parts, water 863 parts, urea 40 parts, 37
Add 55 parts of formalin at a concentration of 30% at 30°C.
Stir for a minute. (The urea:formaldehyde molar ratio is 1:1, and the total concentration of urea and formaldehyde:pulp concentration ratio is 0.3:1.) Then, the contents of the beaker are mixed with 10% dilute sulfuric acid while stirring vigorously. Added 80 copies. Furthermore, after stirring for about 3 minutes, the pH of the contents was measured and found to be 1. Immerse the beaker in a hot water bath kept at 30°C, and
The reaction was allowed to proceed for 3 hours while stirring the contents every 20 minutes. Next, the beaker was taken out from the water bath, 3000 parts of water was added, and while stirring, a 10% aqueous solution of caustic soda was gradually added to neutralize the beaker to pH 7 to obtain a slurry. Using the pulp obtained as described above in place of the improved GRP of the present invention in Example 1, paper was prepared in the same manner as in Example 1 with the pulp composition shown in Table 1, and the paper quality was evaluated. . The results are shown in Table 2.

【table】

【table】

[Table] It is clear from Table 2 that the paper using the improved pulp of the present invention exhibits excellent properties in terms of whiteness, opacity, and opacity after printing. In addition, a part of the pulp slurry containing the melamine formaldehyde resin crosslinked particles obtained in Examples 1 to 4 and Comparative Example 1 was taken, filtered with filter paper, and then washed and filtered with water to take about 1 g of pulp pad. A sample was prepared by putting it into 100 ml of acetone to replace the solvent, and then drying it under vacuum. When the sample was observed under a scanning electron microscope at a magnification of 10,000 times, it was found that the results of Examples 1 to 4 were The particles are approximately spherical in shape and have a particle size of
Solid particles of 1μ or less were formed on the surface of the pulp. On the other hand, in Comparative Example 1, solid matter was attached to the surface of the pulp, but the shape was amorphous, and the pulp in which melamine formaldehyde resin crosslinked particles with a particle size of 1 μm or less were fixed to the pulp fibers was I wasn't getting it. Example 5 Water was added to the pulp slurries obtained in Examples 1 to 4 and Comparative Example 3, and the solid content concentration was 0.5.
%. In addition, a 0.5% slurry of RGP used in Comparative Example 2 was separately prepared. For each slurry, the retention of fine particles in the slurry was measured using a britzer device in accordance with TAPPI, T261pm-79. The britzier device is used as a test device that can predict the retention in the papermaking equipment used in actual production in the laboratory (Paper and Paper Technology Association Journal, 34 , 24, 1980), and the retention is determined by the following. I asked like this. R=T-S/T×100 R: Retention of fine matter T: Total amount of fine matter in 500 ml of slurry (g) S: 500 ml equivalent of the amount of fine matter contained in white water at a given rotation speed (g) Also, retention The measurements are 800, 1000,
Each was performed at a rotation speed of 1200 rpm. The measurement results are shown in Table 3. From Table 3, it is clear that all the samples according to the present invention exhibit high retention.

【table】

[Table] [Effects of the Invention] As detailed above, the pulp of the present invention contains melamine formaldehyde resin particles with a particle size of 1 μm or less by a specific method, and by using the pulp of the present invention, paper The whiteness, opacity, and opacity after printing can be improved in a well-balanced manner, and in particular, paper products with improved opacity after printing can be easily produced. Moreover, since the dynamic retention during papermaking is extremely high, it is extremely advantageous for high-speed papermaking using twin wires or the like. Therefore, the paper obtained using the pulp of the present invention has extremely excellent optical properties such as whiteness, opacity, and printing opacity, especially opacity after printing. Therefore, such excellent pulp of the present invention can be produced extremely easily by the production method of the present invention.

Claims (1)

[Scope of Claims] 1. A pulp comprising substantially spherical crosslinked melamine formaldehyde resin particles with a particle size of 1 μm or less, and the particles are chemically fixed to the fibers of the pulp. 2. A water-soluble melamine resin obtained by reacting melamine and formaldehyde at a molar ratio of 1:1.5 to 1:6 and an acidic catalyst are added to an aqueous pulp slurry to determine the total concentration of melamine and formaldehyde and the pulp. The ratio to the concentration is 0.3:1 to 1.5:
A mixed solution of 1 was obtained, and the mixed solution was heated to a pH of 6 or below from 30 to
A method for producing pulp, which comprises reacting at a temperature of 90°C and then neutralizing it.