JP2516775B2 - Improved pulp and its production method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improved pulp and a method for producing the pulp. More particularly, it relates to an improved pulp comprising a urea-formaldehyde crosslinked resin modified with glyoxal.

(Prior art and problems) Conventionally, in the papermaking industry, a method of adding an inorganic filler such as kaolin, talc, white carbon, etc. in order to improve optical properties such as whiteness and opacity of paper has been widely used. Is being done. However, these inorganic fillers do not sufficiently improve the whiteness and opacity of the paper, and are liable to generate paper powder due to low fixability to paper, and are liable to damage printing equipment due to wear. There are disadvantages.

On the other hand, it is also known to use urea-formaldehyde crosslinked resin particles as an alternative to inorganic fillers. For example, Japanese Patent Publication No. 51-23601 discloses an insoluble, infusible and nonporous fine urea having a molar ratio of urea formaldehyde of 1: 1 to 1: 2 and a BET specific surface area of 5 to 100 m ² / g. It describes that formaldehyde polymer particles are used as a filler for paper, and has an effect of improving whiteness, opacity and the like of paper.

However, with the increase in papermaking speed in the papermaking industry,
Since the fine added particles and pulp fibers fall off and the yield decreases, inorganic or organic polymer electrolytes such as aluminum sulfate and polyacrylamide are added thereto to control the electric charge of the papermaking system. Attempts have been made to improve the yield of fine particles and fibers. However, in these methods, pulp flocking occurs and the texture tends to deteriorate. Further, under high shearing force during high-speed papermaking, such flocs are easily broken because of low cohesive force, and the yield of fine particles and fibers (hereinafter referred to as fine materials) is likely to be reduced.

In addition to the above, there is known a papermaking pulp in which urea and formaldehyde are reacted in the aqueous slurry of ordinary raw pulp in the presence of an acidic catalyst to fix a urea-formaldehyde crosslinked resin on pulp fibers. However, even such improved pulp has not been satisfactory in the yield of fine materials during high-speed papermaking.

(Means for Solving the Problems) The present inventors have solved the above-mentioned problems, and have a high yield of fine materials even under a high shearing force at the time of high-speed papermaking. As a result of intensive studies with the aim of obtaining an improved pulp capable of improving the mechanical properties,
A urea-formaldehyde cross-linked resin modified with glyoxal is fixed on pulp fibers obtained by mixing a small amount of glyoxal-modified urea-formaldehyde precondensate with an aqueous slurry of pulp, adding an acidic catalyst, and performing a polycondensation reaction. Papermaking using the improved pulp integrated with the pulp improves the yield of fine materials under high shearing force and finds that the obtained paper has an excellent effect of improving the optical properties, particularly the opacity of white paper. The present invention has been achieved.

That is, the gist of the present invention is an improved pulp characterized in that a urea-formaldehyde cross-linked resin modified with glyoxal of 0.5 mol times or less per 1 mol of urea is fixed on and integrated with pulp fibers and the improved pulp. Be in the manufacturing method.

To explain the present invention in detail, the improved pulp of the present invention comprises:
A urea-formaldehyde crosslinked resin modified with glyoxal is bonded to pulp fibers.

When observed with a microscope, the improved pulp of the present invention substantially retains the shape of the raw pulp, and the urea-formaldehyde cross-linked resin modified with glyoxal covers the surface of the pulp fiber and is integrated therewith. It is believed that the crosslinked resin is bonded to the pulp fibers in the same manner as the bond. The method for producing the improved pulp will be described below.

The improved pulp in the present invention is obtained by adding a glyoxal-modified urea-formaldehyde initial condensate to an aqueous slurry of a raw pulp and mixing the mixture uniformly, and then adding an acidic catalyst and mixing similarly to cause a polycondensation reaction. It is manufactured by producing a crosslinked resin and then neutralizing.

The urea-formaldehyde precondensate modified with glyoxal used in the present method can be obtained by reacting glyoxal, urea and formaldehyde in an aqueous solution. Glyoxal is usually used as an aqueous solution having a concentration of 40% by weight, and formaldehyde is used as an aqueous solution having a concentration of 30 to 55% by weight.

The quantitative ratio of these three components is usually 0.05 to 0.5 mol of glyoxal and 0.8 to 0.8 mol of formaldehyde to 1 mol of urea.
It is preferred to use 1.6 moles.

When the molar ratio of glyoxal to urea is less than 0.05, it is difficult to achieve an improvement in the yield of fine materials when the resulting improved pulp is made under high shearing force. On the other hand, if the molar ratio of glyoxal exceeds 0.5, the improved pulp is colored grayish brown, and the whiteness of the paper made by using this is reduced.

On the other hand, the molar ratio of formaldehyde to urea is 0.8
If it is less than 1.6 or more than 1.6, unreacted urea or formaldehyde remains and the yield of the initial condensate decreases, which is not preferred.

To produce a urea-formaldehyde precondensate modified with glyoxal, glyoxal and urea are first reacted under acidic conditions, and then the reaction product is reacted with formaldehyde under neutral to alkaline conditions. . The reaction of urea with formaldehyde followed by glyoxal makes it difficult to obtain a precondensate that gives improved pulp with the desired optical properties.

The reaction between glyoxal and urea is preferably carried out at about 30 to 60 ° C. under acidic conditions at a pH of about 3 to 5. Under alkaline conditions, the Cannizzaro's reaction increases the amount of glyoxal that does not react with urea, causes the precondensate to turn yellow, and reduces the whiteness of the modified pulp. If the reaction temperature is too low, a long time is required for the reaction. If the reaction temperature is too high, coloring due to side reactions and loss of glyoxal are undesirably caused.

The reaction between the glyoxal and urea reaction products obtained above and formaldehyde is carried out under a neutral pH of about 7 to 9.
It is preferably carried out at a temperature of about 30 to 100 ° C., which is weakly alkaline. Under acidic conditions, the rate of the methylene reaction is higher than that of the methylolation reaction with formaldehyde, so that a stable initial condensate cannot be obtained.If the pH exceeds 9, the initial condensate obtained is colored yellow, and the improved pulp is colored. Cause.

In order to produce the improved pulp of the present invention, first, a grease-modified urea-formaldehyde precondensate modified with glyoxal prepared as described above is added to an aqueous slurry of raw pulp maintained at a temperature of about 20 to 60 ° C. And mix well enough. Subsequently, the mixture is uniformly mixed with an acidic catalyst at the same temperature with stirring to carry out a polycondensation reaction, and then neutralized by adding an alkaline substance.

The raw material pulp is not particularly limited, and examples thereof include mechanical pulp such as GP, RGP, and TMP, chemical pulp such as SP and KP, and recovered pulp such as DiP, and chemical treatment such as bleaching. May be applied. The pulp concentration of the reaction system is 0.5 to 30%, preferably 2 to 15%.

The urea-formaldehyde precondensate modified with glyoxal is added to the pulp in a weight ratio of 0.5 to 10, preferably 0.7 to 5 (the weight of the precondensate is lost to the outside of the system. Excluding glyoxal, urea and formaldehyde used in the reaction).

When the use ratio of the initial condensate is less than 0.5 with respect to the pulp, it is difficult for a crosslinked resin exhibiting desired optical properties to be formed on the pulp surface. Conversely, if this ratio is greater than 10, the pulp will be linked together by the crosslinked resin. As a result, the releasability of the produced improved pulp becomes poor, and the "texture" of the paper made by using the improved pulp decreases.

Examples of the acidic catalyst include mineral acids such as sulfuric acid, hydrochloric acid, phosphoric acid, and sulfamic acid, and organic acids such as formic acid, acetic acid, and paratoluenesulfonic acid, and diluted with water to a concentration of about 5 to 20%. Is done. These acidic catalysts are preferably used in such an amount that the liquidity of the slurry after the addition becomes pH 3 or less.

Examples of the alkaline substance used for neutralization include ordinary caustic alkalis such as sodium hydroxide, potassium hydroxide, sodium carbonate, and ammonium carbonate or alkali carbonates.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples and Reference Examples, but the present invention is not limited thereto unless it exceeds the gist thereof. In the following Examples and Reference Examples, “parts” means “parts by weight”.

Example 1 Production of Initial Condensate 29 parts of a 40% aqueous glyoxal solution, 60 parts of urea and 90 parts of water were mixed with stirring. The liquid property of the mixed solution was pH 3.35. After maintaining at 50 ° C. for 2 hours with stirring, the pH was adjusted to 9.0 by adding an aqueous sodium hydroxide solution, and then 81 parts of a 37% formaldehyde aqueous solution was added thereto with stirring.
The pH after the addition of formaldehyde was 7.9. 2 at 50 ° C
After stirring for an hour, the mixture was cooled to 25 ° C to obtain a urea-formaldehyde initial condensate modified with glyoxal.

[Production of improved pulp] 230 parts of the aqueous solution of the initial condensate obtained above was treated with
It was added to 600 parts of 5% aqueous GP and stirred at 30 ° C. for 30 minutes.
The ratio of pulp to precondensate is 1: 1. Then, with vigorous stirring, 70 parts of 10% strength sulfuric acid was added thereto (pH 1.
8) After keeping at 30 ° C. for 2 hours, 2700 parts of water was added, and while stirring, 5% aqueous sodium hydroxide solution was added to adjust pH 7
By the neutralization, an improved pulp bonded to a urea-formaldehyde crosslinked resin pulp fiber modified with glyoxal was obtained.

The yield and whiteness of the fine pulp obtained above are shown in Table 2 below.

The yield and whiteness of the refined pulp were measured as follows.

[Measurement of fine pulp yield] The improved pulp was adjusted to have a solid content of 0.5% by adding water, and this pulp slurry was subjected to TAPPi T261.
According to -pm-79, the yield of fine particles in the slurry was measured with a brit jar device.

In addition, the brit jar device is widely used as a device capable of measuring the yield of fine materials in a papermaking device such as a twin wire papermaking machine under high shearing force in a laboratory.

[Measurement of whiteness of improved pulp] The improved pulp has a basis weight of 60 g by a method based on JIS P8209.
/ m ² was obtained, and then its whiteness was measured by a method based on JIS P8123.

Examples 2 to 5 The initial condensate was produced in the same manner as in Example 1 except that the molar ratio of glyoxal, urea and formaldehyde was varied as shown in Table 1 during the production of the initial condensate in Example 1. Then, an improved pulp was produced in the same manner as in Example 1 using the obtained initial condensate. In each case, the ratio of pulp to precondensate was 1: 1.

With respect to the obtained improved pulp, the yield and whiteness of fines were measured by the method described in Example 1. Table 2 shows the results.

Comparative Example 1 An initial condensate was prepared and obtained in the same manner as in Example 1, except that the molar ratios of glyoxal, urea and formaldehyde were changed as shown in Table 1 during the preparation of the initial condensate in Example 1. Pulp was treated in the same manner as in Example 1 using the precondensate. The ratio of pulp to precondensate was 1: 1. With respect to the obtained improved pulp, the yield and whiteness of fines were measured by the method described in Example 1. Table 2 shows the results.

Comparative Example 2 A mixture of 60 parts of a water-containing GP having a pulp concentration of 15%, 100 parts of water, 6 parts of urea and 8.1 parts of a 37% aqueous formaldehyde solution was mixed at 30 ° C.
For 30 minutes. Then, with vigorous stirring, add 10
Then, 7 parts of sulfuric acid at a concentration of 7% was added and the mixture was kept at 30 ° C. for 1 hour. To this, 265 parts of water was added, and 14 parts of a 5% aqueous sodium hydroxide solution was added with stirring to neutralize the mixture, thereby obtaining an improved pulp having a crosslinked resin of urea and formaldehyde fixed thereto. With respect to the obtained improved pulp, the yield and whiteness of fines were measured by the method described in Example 1. Table 2 shows the results.

Reference Example Preparation of Compounded Paper Containing Improved Pulp 10 parts NBKP, 20 parts GP, 30 parts TMP, 30 parts DiP and 10 parts of the improved pulp obtained in each of Examples 1 to 5 and Comparative Examples 1 and 2 were blended and beaten. A 1% aqueous pulp slurry having a degree of 230 ml (CSF) was prepared. To 1000 parts of this pulp slurry, 3 parts of a 10% aqueous solution of aluminum sulfate was added, and the mixture was stirred for 1 minute. Then, paper was formed using a 25 × 25 cm TAPPi square sheet machine.

Next, press dewatering was performed at 3.5 kg / cm ² , and the surface temperature was 105
After drying with a rotary dryer at ~ 110 ° C for 3 minutes,
The paper was calendered at a linear pressure of 40 kg / cm, and seasoned for 24 hours in a thermo-hygrostat at a temperature of 20 ° C. and a relative humidity of 65% to prepare a compounded paper. Table 3 shows the opacity of the obtained compounded paper. The whiteness of the treated pulp used in this example is also shown.

(Effect of the Invention) As shown in Examples and Reference Examples, the improved pulp of the present invention has a high yield of fine materials even under high shearing force during high-speed papermaking, and has excellent whiteness. The optical properties, especially opacity, of the paper obtained by papermaking can be improved.

Claims (4)

(57) [Claims] 1. An improved pulp characterized in that a urea-formaldehyde cross-linked resin modified with glyoxal of 0.5 mol times or less per mol of urea is fixed to pulp fibers and integrated therewith. 2. An aqueous slurry of pulp is mixed with an initial condensate of urea / formaldehyde modified with glyoxal of 0.5 mole times or less per mole of urea and an acidic catalyst to cause a polycondensation reaction, followed by neutralization. Characteristic improved pulp manufacturing method. 3. After reacting urea with glyoxal of 0.5 mol times or less with respect to the urea under acidic conditions, 0.8 to 1.6 times mol of formaldehyde with respect to urea supplied to the reaction product is neutralized to neutral. 3. The method for producing an improved pulp according to claim 2, wherein an initial condensate obtained by reacting under alkaline conditions is used. 4. The method according to claim 3, wherein glyoxal is reacted with 0.05 to 0.5 times mol of urea.
The method for producing an improved pulp according to the above item.