JPH0223638B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing water-soluble paper with excellent weather resistance and strength by acid-treating a water-soluble sheet made of fibrous carboxymethyl cellulose and containing residual alkali under specific conditions. More specifically, by coating and impregnating conventional water-soluble paper with a solution of an acid having an acid index in water above a certain level, and by adjusting the degree of base saturation of fibrous carboxymethyl cellulose to a certain level or above during coating and impregnation, The present invention relates to a method for producing water-soluble paper having superior weather resistance and strength compared to other products. Conventionally, water-soluble paper has been used for writing and printing confidential documents, labels, etc., as an industrial material that is dissolved and washed away after use, and as a sanitary material for women and infants. However, conventional water-soluble paper inherently has low strength and has high moisture absorption and desorption properties, making it difficult to process.Also, a small amount of alkali such as soda carbonate and caustic soda remains in the water-soluble paper, making it difficult to process during paper storage. ,
In particular, it discolors or sticks during storage and transportation during high temperature and high humidity periods in the summer, it corrodes amphoteric metals such as aluminum and zinc, so its use as an industrial material is limited, and it is harmful to the skin of women and infants. It has been pointed out that neutral to weak acidity is preferable. Conventional water-soluble paper is made from fibrous cellulose glycolic acid (hereinafter referred to as CMC-H), as disclosed in Japanese Patent Publication No. 48-27605, and alkali such as soda carbonate or caustic soda is added to the wet paper after the press part. It is manufactured by applying a liquid, impregnating it, ion-exchanging it to make sodium salt (hereinafter referred to as CMC-Na), dehydrating it, and drying it. At this time, a slightly excessive amount of alkaline solution is added to complete the ion exchange between H ⁺ and Na ⁺ and to ensure uniform solubility of the paper, so the pH of the resulting water-soluble paper is around 10 to 11. It has become alkaline. In order to obtain neutral water-soluble paper, for example, it is possible to apply a dilute solution of hydrochloric acid to water-soluble paper while adjusting its pH, but this method may cause problems due to non-uniformity of the paper structure,
Due to the difficulty of uniform coating due to the precision of the coating roll, there appeared areas where the reverse reaction of CMC-Na to CMC-H occurred significantly, and the resulting paper could not be uniformly dissolved. In order to improve the strength, it is also possible to increase the basis weight or incorporate a large amount of chemical pulp, but the former will increase the cost and the latter will result in a large amount of insoluble fibers being mixed in the solution, so it is not suitable for the intended use. I don't really like it. The present inventors conducted repeated research on the acid resistance and base saturation of CMC-Na in water-soluble paper, with the aim of obtaining water-soluble paper with excellent properties as described above without impairing the solubility of water-soluble paper. As a result, it was discovered that there is a certain relationship between these and solubility, and the present invention was achieved. Here, the solubility of water-soluble paper is defined as the extent to which the solution exhibits colloidal form when observed with the naked eye using the test method described below. It may also contain a fibrous gel. This is because there is no practical problem. In the water-soluble paper of the present invention, in order to neutralize the residual alkali in the water-soluble sheet that is the base material and to improve the weather resistance and strength of the water-soluble paper, an excess of a specific acid is added in excess of the neutralization equivalent. is neutral to weakly acidic. The free acid partially reacts with CMC-Na, but if the amount of carboxyl groups generated by ion exchange is below a certain level, in other words, if the base saturation of CMC-Na is above a certain level, the present invention The effect of improving weather resistance and strength without inhibiting the solubility of water-soluble paper can be obtained. Thus, according to the invention, 50-100% fibrous carboxymethylcellulose and 0-50% papermaking fibers
In the acid treatment of a water-soluble sheet containing residual alkali, a solution in which an acid with an acid index in water of 3 or more is dissolved in a mixed solvent of an organic solvent and water is added to the neutralizing equivalent of the residual alkali in the sheet. Provided is a method for producing water-soluble paper with excellent weather resistance and strength, which comprises coating, impregnating, and acid-treating the base saturation of the fibrous carboxymethyl cellulose in the sheet in a range of 35% or more. be done. Hereinafter, the configuration of the present invention will be explained in detail using experimental examples. Experimental Example 1 The following experiment was conducted to find out the relationship between the acid resistance and base saturation of CMC-Na. Fibrous CMC-H (manufactured by Nichirin Chemical Co., Ltd. with a degree of etherification of 0.43) was purified using a conventional method, and then placed in a mixed solution of caustic soda, methanol, and water, and subjected to base exchange using a conventional method. CMC
-Na was prepared. In order to treat CMC-Na with 100% base saturation with an acid solution, we prepared 8 types of mixed solutions of ethanol:water (1:1 parts by weight) each containing 1 mole of organic acid by changing the type of organic acid. did. Each organic acid has a different water acid index (pka).
1 g of bone-dried CMC-Na was immersed in 50 ml of each organic acid solution, stirred for 2 hours, separated, and the residue was washed in a conventional manner to remove residual organic acids, followed by drying under reduced pressure at 60°C. Next, in order to measure the base exchange capacity and base saturation, 0.5 g of the purified CMC-H and the above acid-treated sample were each taken, and 20 ml of 0.5N caustic soda was added thereto. After stirring for 2 hours, pure water Add 10ml and perform potentiometric titration with 0.5N hydrochloric acid, and calculate this titration value as Aml.
And so. In a blank test, the same operation was performed without using a sample, and this titration value was taken as Bml. The base exchange capacity and base saturation were determined using the following formula. Base exchange capacity (meq/g) = (B-A) x 0.5 x f/1000 x 1/W x 1000 f: 0.5NHCl factor W: Sample bone dry weight (g) Base saturation (%) = Base exchange Capacity - exchangeable H ⁺ amount / base exchange capacity x 10
0 = Exchangeable base amount / Exchangeable base amount + Exchangeable H ⁺ amount ×
100 These results are shown in Table 1 along with the water acid index (pka). The acid index in water is the logarithm of the reciprocal of the dissociation constant of the electrolyte in water. In the present invention, it is essential to use a mixed solvent of an organic solvent and water to dissolve the acid, so it is preferable to use the pka in a non-aqueous solvent as an index. (referred to as an index) is used. Among the acids shown, those with dibasic acids or higher showed a pka value of ₁ .

【table】

[Table] As is clear from Table 1, when CMC-Na is treated with a mixed solution of organic acids in ethanol and water, ion exchange occurs and the degree of base saturation decreases, but the rate of this decreases as the organic acid has a higher acid index. That is, the degree of base saturation is high, and a large proportion of CMC-Na remains as CMC-Na. In experiments conducted by the present inventors in which acid treatment was carried out under the same conditions as above using an aqueous solution of an organic acid, such a tendency was not observed, and the degree of base saturation was approximately 5% or less regardless of which acid was used. It became. From these results, it was determined that in a mixed solvent of an organic solvent and water, dissociation was not as large as in an aqueous solution, and ion exchange was suppressed, resulting in the above-mentioned tendency. The water-soluble paper of the present invention can be obtained by using the above relationship between the acid index and the base saturation as one factor and adding other factors to adjust the base saturation to a desired level. Experimental Example 2 Next, the base material was treated with the acid constant and the concentration of acetic acid (pka 4.756) varied, and the relationship between base saturation and solubility of acid-treated paper was investigated and is shown in Table 2. The base material was the same fibrous material used in Experimental Example 1.
A certain amount of paper with a basis weight of 80 g/m ² was produced by making paper using 100% CMC-H and adding a sodium carbonate solution, and acid treatment was performed according to Experimental Example 1 to determine the base exchange capacity and base saturation. was measured. Solubility was determined by putting about 1 g of a test piece into 300 ml of water, rotating it with a magnetic stirrer, and measuring the number of seconds it took for the test piece to dissolve. Those with small fiber lumps remaining even after 120 seconds were classified as poorly soluble, and those whose sheet form did not collapse were classified as insoluble. The acid-treated paper also showed solubility after being heat-treated at 105°C for 10 minutes after drying under reduced pressure, but this was done in consideration of the fact that it would be dried with hot air in the actual manufacturing process.

[Table] Ivy.
According to Table 2, it was found that no significant change in solubility was observed when the base saturation was 35.3% or higher.
Note that, as mentioned above, the solubility is limited to within 120 seconds, so it has been found that the base saturation that satisfies this condition may be 35% or more. Experimental Example 3 Next, in actual manufacturing, the acid treatment of the water-soluble sheet that is the base material is performed by coating and impregnating with a roll coater rather than by dipping, and the coating and impregnating time is several seconds, so the on-site conditions The solubility, pH of the solution, whiteness, etc. were measured for samples obtained by coating and impregnating various acids under conditions similar to those described above. For whiteness, heat treatment at 105°C for 10 minutes was also performed. This is to know the changes over time. In addition, only solid acids were tested as acids, but solid acids exist as solid acid salts and free solid acids after the solution is applied and dried, and as long as they are not hygroscopic or deliquescent, ion exchange is not possible. This is because the reaction is suppressed, which is more preferable for achieving the object of the present invention.
A 140 g/m ² water-soluble sheet manufactured using 100% of the same CMC-H used in Experimental Example 2 was used as the base material, and the acid solution was a mixture of 50% by weight of solid acids with different acid indices in ethanol. It was prepared by dissolving it in water. The concentration of the acid solution was based on 10% by weight, but it was adjusted for each acid so that the pH of the acid-treated paper solution was approximately 5. Add a certain amount of water-soluble sheets to each acid solution.
The sample was immersed for ~3 seconds, pulled out, dehydrated under pressure, and dried at 80°C to obtain a test sample. The measurement items and test results are as shown in Table 3.

[Table] According to Table 3, solubility is related to the ranking of acid index; from malic acid with an acid index of 3.460, dissolution time increases as the acid index decreases, and when the acid index falls below tartaric acid with an acid index of 3.036, the PH increases to 5. It was found that the acid-treated paper after heat treatment becomes poorly soluble or insolubilized in the vicinity. In addition, although the dissolution time of citric acid-treated paper with an acid index of 3.128 after heat treatment was slightly longer, its base saturation was considered to be within the limit value of 35% or more. It was also found in comparison with a control product that the color fastness was significantly improved by acid treatment. According to this table, the acid index branching point at which acid-treated paper becomes poorly soluble or insoluble is 3.036, but CMC-H with an etherification degree of 0.25 to 0.65 is normally used for water-soluble paper, and in this experiment. The acids that can be used in the present invention are acids with an acid index of 3 or more, and solid acids with an acid index of 3.5 or more are preferable because CMC-H with an index of 0.43 is used and acid resistance increases as the degree of etherification increases. In addition to the acids listed in Table 3, solid acids such as adipic acid (pka 4.430) and glutaric acid (pka 4.343), and liquid acids such as butyric acid (pka 4.820) and lactic acid (pka 3.858) are also suitable. This can be exemplified as an example. Note that inorganic acids are also included within the technical scope of the present invention as long as they meet the requirements of the present invention. Further, a sodium salt of the acid to be coated and impregnated may be added to the acid solution as a PH buffer. Next, the water-soluble sheet used as the base material of the present invention will be explained. Fibrous carboxymethyl cellulose is a short fiber of a monovalent metal salt such as sodium or potassium of cellulose glycolate, and the sodium salt is usually used. The water-soluble sheet made of CMC-Na may contain other known fiber raw materials and is produced by a known method. For example, special public relations
The inventive method disclosed in No. 27605 is abbreviated as CMC-
Paper is made from a mixed paper stock of 100% H or CMC-H and 40% by weight or less of bleached kraft pulp, and an alkaline aqueous solution is added to the wet paper web on the press felt to produce CMC-H.
It is manufactured by converting it into CMC-Na, dehydrating it, and drying it.
The degree of etherification of CMC-H can be in the range of 0.2 to 1.0, but it is usually 0.25 to 0.65, and 0.40 to 0.65 from the viewpoint of paper making properties, paper solubility, strength, etc.
are most commonly used. If the value is 0.65 or more, the fibers will swell significantly and become difficult to form into paper, but depending on the type of acid to be treated, the base material used in the present invention may have a value of 0.65 to 1.0 to increase acid resistance. 0.25
The following CMC-H is easy to make into paper, but the solubility of the product is poor. There are no particular restrictions on the types of papermaking fibers other than CMC-H, and general cellulose pulp, semi-synthetic fibers such as rayon, synthetic pulps such as polyethylene, synthetic fibers such as polyacrylonitrile, etc. are selected depending on the purpose of use. Chemical pulp such as bleached kraft pulp, bleached sulfite pulp, dissolving pulp, and rayon are usually used. Further, its usage ratio is preferably 50% by weight or less of CMC-H. This is because if the content exceeds 50% by weight, fibers tend to bunch together in water. In preparing the acid solution used in the present invention, when the acid is a solid acid, a predetermined amount is dissolved in a mixed solvent of water and an organic solvent that is compatible with water. As organic solvents that are compatible with water, alcohols such as methyl alcohol, ethyl alcohol, butyl alcohol, and propyl alcohol, and ketones such as acetone, ethyl methyl ketone, and methyl propyl ketone can be used. When the acid is a solid acid or liquid acid with a relatively low pka value, it is preferable to use an aqueous solvent with a high mixing ratio of organic solvent in order to suppress its dissociation and obtain a water-soluble paper with the desired base saturation. . Usually, a mixed solvent of 50% by weight is used in consideration of production costs. The mixing ratio of the organic solvent is determined in consideration of the degree of etherification of CMC-H, the type and blending ratio of fiber raw materials, the type of acid, the basis weight of the water-soluble paper, etc., but it must be at least 30% by weight. The dissolved concentration of acid, both solid acid and liquid acid, is such that the amount of the acid coated and impregnated on the water-soluble sheet as a base material exceeds the neutralization equivalent of the residual alkali in the water-soluble sheet, and the base saturation of CMC-Na is determined. It is necessary to set the degree to 35% or more, usually 0.3 to 10
From the weight percent range, a concentration is selected that satisfies the above requirements. The factors that vary the base saturation of CMC-Na in the water-soluble paper of the present invention include the degree of etherification of CMC-Na, the type of acid, the acid index, the composition of the solvent, the acid concentration in the solution, the coating speed, etc., but are constant. If the same material is used and the coating speed is the same, it is determined by the acid concentration. For coating and impregnation with an acid solution, the acid solution is applied to the base material after drying on the paper machine using a size press, or after paper making, it is applied using a roll coater of a coating machine, and then dried at 80 to 120°C. All organic solvents are evaporated by drying. The water-soluble paper produced according to the present invention became neutral to weakly acidic by the above-mentioned means, improved in color fastness, and improved in strength by more than 10%. The reason for this is that in the present invention, usually an excess amount of acid exceeding the neutralization equivalent of the alkali remaining in the base material is coated and impregnated, so that a portion of CMC-Na is absorbed into CMC-Na to the extent that it does not impair water solubility. This is thought to form hydrogen bonds during drying, increasing the dry strength of the sheet. Due to the same reason, paper moisture (20℃, 65%RH)
It was thought that this could contribute to the improvement of processability as well as the increase in paper strength. As explained above, according to the method of the present invention, improvements such as an increase in paper strength, prevention of discoloration, and decrease in paper moisture can be obtained compared to conventional water-soluble paper, as well as corrosion of amphoteric metals such as aluminum and zinc. Since it is neutral to weakly acidic and is suitable for the skin of women and infants, it can contribute to industry by solving the problems associated with water-soluble paper. Hereinafter, the present invention will be explained in detail with reference to examples.
-A water-soluble sheet made of 100% Na was used as the base material.
In addition, since Examples 2 and 3 were intended for use as industrial materials and sanitary materials, respectively, a water-soluble sheet made of paper stock mixed with wood pulp was used as the base material in order to satisfy the processing suitability and product characteristics. did. Therefore, the solubility of the water-soluble papers of the present invention in Examples 2 and 3 was expressed as dissolution and dispersion properties. Note that the present invention is not limited to these examples. Example 1 A paper stock consisting of 100 parts of fibrous CMC-H (manufactured by Nichirin Chemical Co., Ltd.) with a degree of etherification of 0.43 was made into paper, and a 10% concentration sodium carbonate aqueous solution was applied to the wet paper web on the paper machine.
A water-soluble sheet of approximately 120 g/m ² was produced by impregnation and drying. The surface pH of this water-soluble sheet was 10.6, and the pH of the solution was 10.2. The acid solution was prepared by dissolving succinic acid and sodium succinate as a buffer in a mixed solution of ethanol and water (1:1 parts by weight). The succinic acid concentration was 1.5% and the sodium succinate concentration was 1.2%. A water-soluble paper of the present invention was produced by coating and impregnating a base material with an acid solution using a roll coater and drying with hot air at 80°C. When a bromcresol purple PH indicator was applied to the surface of this paper, the entire surface showed an even coloration of around PH6.0, confirming that there was no residual sodium carbonate. The base exchange capacity of the base material was 2.49meq/g. Furthermore, when succinic acid and sodium succinate were removed from the water-soluble paper of the present invention, the base saturation was measured and found to be 75.5%. Tests were conducted on the conventional water-soluble paper and the water-soluble paper of the present invention, paying special attention to whiteness and paper strength, and the results are shown in Table 4. The heat treatment test was conducted under fairly severe conditions, taking into account long-term product inventory and transportation during high-temperature periods.

[Table] According to Table 4, each strength of the product sheet was improved by at least 10%. In particular, the results of a heating test conducted to observe changes over time showed that the brittleness of bending (folding strength) that existed in conventional water-soluble paper was significantly improved. Although the reduction in whiteness cannot be completely prevented, as shown by the numerical values, conventional water-soluble papers turn brown due to heat treatment and lose their commercial value, but the present invention retains sufficient whiteness. This water-soluble paper did not leave any residue after dissolution, so it was suitable as writing and printing paper for confidential documents. In addition, in order for conventional water-soluble paper to have the folding strength of the present invention, it is necessary to mix 10 to 20% of bleached kraft pulp.
A clean solution cannot be obtained. In addition, water (20
℃, 65% RH) decreased from 16.3% to 13.4%, so it is expected that the range of moisture absorption and release during the wet and dry periods will become smaller, and this is thought to contribute to improving processing suitability. Example 2 The purpose was to produce water-soluble paper that does not corrode aluminum. Wet paper consisting of 80 parts of fibrous CMC-H (manufactured by Nichirin Chemical Co., Ltd.) with a degree of etherification of 0.54 and 20 parts of bleached kraft pulp was coated with a 10% sodium carbonate aqueous solution on a paper machine to produce a basis weight of 120 g/ ^m2. A water-soluble sheet was produced. As the acid, acetic acid and citric acid were mixed at a weight ratio of 2:3, and a mixed solvent of methanol and water (1:3) was used.
1 part by weight) to prepare a solution with a concentration of 1.25% by weight. Coat and impregnate the base material using a roll coater.
Water-soluble paper was produced by drying with hot air at 80°C. The amount of acid attached was 1.9g/ ^m2 , the pH of the paper surface was 5.8, and the amount of acid attached was 1.9g/m2.
The pH was 7.2, and the dissolution and dispersion time was 13 seconds, compared to 6 seconds for the base material. The base exchange capacity of the base material is 2.79meq/g
(Calculated value) The base saturation of the water-soluble paper of the present invention was 65.1%. The aluminum corrosion test was conducted on conventional water-soluble paper, water-soluble paper of the present invention, and reagent grade 1 CMC as a reference. In each case, an aluminum wire was immersed in a dissolution dispersion (solution) having a concentration of 1% by weight, and the surface condition was visually judged after 7 days. As a result, the aluminum wire immersed in the dissolved dispersion liquid of the conventional water-soluble paper turned considerably black, but the water-soluble paper of the present invention, with a grade 1 reagent.
In all cases of CMC, almost no discoloration was observed. Therefore, it is suitable for applications in which the water-soluble paper of the present invention is made into a tape, wound around an aluminum wire, and then dissolved and washed away. Example 3 The purpose was to produce water-soluble paper for sanitary materials.
A water-soluble sheet with a basis weight of 40 g/m ^{2 was produced in the same manner as in Example 2 using a paper stock consisting of 80 parts of fibrous CMC-H (manufactured by Nichirin Chemical Co., Ltd.) with a degree of etherification of 0.65 and 20} parts of dissolving pulp. was used as the base material. As the acid, lactic acid was dissolved in a mixed solvent of ethanol and water (2:1 parts by weight) to prepare a solution having a concentration of 1.5% by weight. Coating and impregnating using a roll coater,
It was dried with hot air at 80°C to produce water-soluble paper. The amount of lactic acid applied was 0.7 g/m ² , the paper surface pH was 6.3, and the amount of lactic acid applied was 0.7 g/m 2 .
The pH was 7.4, and the dissolution and dispersibility was within specifications and good. The base exchange capacity of the base material is 3.25meq/g (calculated value),
The base saturation of the water-soluble paper of the present invention was 74.6%. This water-soluble paper has a moist and soft texture,
Since it was acid-treated with lactic acid, it did not irritate the skin of women and infants and was suitable for use as a sanitary material.

Claims (1)

[Claims] 1 Fibrous carboxymethyl cellulose 50-100
In acid treatment of a water-soluble sheet consisting of 0% to 50% of papermaking fibers and containing residual alkali, a solution of an acid with an acid-in-water index of 3 or more dissolved in a mixed solvent of an organic solvent and water is Excellent weather resistance and strength, characterized by coating and impregnating and acid treatment in a range that exceeds the neutralization equivalent of residual alkali in the sheet and that the base saturation of the fibrous carboxymethyl cellulose in the sheet is 35% or more. A method for producing water-soluble paper.