JP2856441B2 - Method for producing water-resistant pulp sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pulp sheet which is excellent in water resistance and mechanical strength and easily disintegrates in an acidic or alkaline liquid. More specifically, the present invention relates to a pulp sheet obtained by subjecting a carboxyethyl cellulose alkali metal salt to bi-decomposition with a trivalent or higher inorganic metal salt and via ionic crosslinking, and having water resistance, mechanical strength (particularly, bending strength, It has excellent toughness and air permeability, and has the unique property of being able to be defibrated for reuse of waste paper and waste paper. For example, toughness is required for materials for solid-liquid separation, air filters, speaker cone paper, etc. The present invention relates to a sheet useful for a material to be used, a packaging material, and the like.

[Conventional technology and issues]

In general, so-called paper produced by making wood pulp has the greatest drawback of poor water resistance and toughness. These disadvantages derive from the fact that the inter-fiber bonds of the cellulose fibers depend only on hydrogen bonds. These sheets, which are mainly made of wood pulp, maintain their strength by the hydrogen bonds of the cellulose chains of the pulp fibers, but break the bonds between fibers when wet with water, and are used for applications such as packaging materials. There is a limit in the case of In recent years, the printing method has shifted to offset printing, and dimensional change of a sheet due to squeezing water during printing is a cause of trouble.

As a means of preventing the swelling of fibers and the breakage of hydrogen bonds between fibers due to water molecules penetrating between the cellulose molecules, wet-strengthened resins and the like have been conventionally used. There is a disadvantage that the papermaking speed is reduced due to the need for a curing process. Furthermore, as a result of paper treated with these resins, the fibers are bonded to each other,
Re-disintegration with water etc. becomes impossible This not only hinders the collection and reuse of waste paper in the papermaking process,
Regarding the production of waste paper pulp, which accounts for 50% of papermaking raw materials,
It is supposed to cause extremely serious obstacles.

Also, by chemically modifying the surface of the pulp fiber,
Efforts have been made to address this weakness. For example, for carboxymethylcellulose (hereinafter referred to as CMC), low DS (Degree of Substitution)
The method of forming CMC sheets into sheets and the strength of sheets replaced with polyvalent metal ions have been compared and studied (KK Talwa
r, Tappi, vol. 41, No. 5, 207 (1958); PFNelson et al ,,
Tappi, vol. 47, No. 3, 170 (1964)].

Furthermore, carboxyethylcellulose (hereinafter CE)
Some technologies relating to sheeting (referred to as C) have also been proposed in connection with CMC. For example, a blend of viscose and carboxyethylated regenerated cellulose or fibrous CEC
No. 3,116,119 (1
963); Canadian Pat. 705,292 (1965); US Pat.
84 (1967)]. Baker et al. Also studied the properties of CEC-Na and its cation-exchanged sheets (free acid, calcium ions, and thorium ions) as paper [DLBaker et al., Pulp and Paper Mag. Can., Vol. .66
(9), T449 (1965)].

However, these methods have a significant difference particularly in the mechanical strength of the sheet, especially in the burst strength, but have not yet achieved the provision of water resistance and toughness.

Japanese Patent Publication No. 43-28766 discloses a teletype paper prepared by mixing carboxyethylcellulose aluminum salt having a degree of etherification of 0.6 as a method for producing a paper which is rapidly dispersed in water (Example 4). ). However, this method does not have water resistance at all because the DS is so high that water solubility is required so much that it cannot be used as so-called general paper.

[Means for solving the problem]

That is, the present invention relates to 5 parts by weight of cellulose per 100 parts by weight.
~ 10 parts by weight of a pulp alkali metal salt having a carboxyethyl group in the side chain, aluminum ions, zirconium ions and other trivalent or more inorganic metal salts, metathesis,
An object of the present invention is to provide a method for producing a water-resistant pulp sheet formed by agglomeration.

Thus, the pulp sheet of the present invention is a pulp sheet made of CEC and a trivalent or higher inorganic metal and imparted with water resistance through ionic crosslinking.
A pulp sheet characterized by being easily disaggregated by a mineral acid such as hydrochloric acid or sulfuric acid or an aqueous alkali solution such as sodium hydroxide or potassium hydroxide. In addition, carboxyethylated modified pulp is used alone, but a small amount of components may be mixed.

In order to obtain a pulp sheet having water resistance, the present inventors have the following three factors: 1) chemical bonding (binding energy), 2) intermolecular force (cohesive energy), 3) surface chemistry (hydrophilicity). -Hydrophobic balance). That is, in the production of a water-resistant pulp sheet, each of these three factors is, specifically, 1) the bonding between fibers is high due to the transfer of electrons, 2) the cohesive energy between the fibers is high, and 3) The surface of the pulp sheet was considered to be required to be more hydrophobic. As a result of intensive studies on the conditions, it was found that an ion-binding pulp sheet composed of carboxyethylcellulose anian and a metal cation having a valence of 3 or more such as aluminum or zirconium was excellent in water resistance and toughness. In particular, the key of the present invention is the cohesive force due to the ionic bond of a metal having a valence of 3 or more and the effect of hydrophobicity due to the introduced ethylene group.

In the paper making process, the pulp concentration gradually increases as the process proceeds to the coach, press, and dryer parts, and when paper is finally produced, inter-fiber bonds are formed through hydrogen bonds. In the case of cellulose, its cohesion is developed by charge transfer interactions. There is no suitable example of a polymer mainly based on electrostatic interaction, which is a stronger interaction, so that its cohesive energy is about two orders of magnitude higher than that of an inorganic salt. Therefore, as a polymer aggregate, it is considered that a system composed of an acidic polymer and a polyvalent metal ion has a higher aggregation energy.

Carboxymethylation (CM conversion) is often performed to make cellulose fibers into acidic polymers, but a sheet having desired properties could not be obtained by CM conversion. Therefore, the present inventors have conducted intensive studies, and as a result, have found that the balance between the hydrophilic part and the hydrophobic part of the carboxyalkyl group to be introduced is an important factor, leading to the present invention. That is, the hydrophobic portion is more important than the hydrophilic carboxyl group introduced to the pulp surface. In the case of CM conversion, the introduced hydrophobic moiety is one methylene group per one carboxyl group,
When the hydrophobic portion is further increased, the hydrophilic-hydrophobic balance is inclined toward the hydrophobic side as a whole. Moreover, it is expected that a polymer effect as a whole polymer chain is exhibited, rather than an effect per one functional group. Therefore, in order to provide water resistance, the methylene group has one more C than CMC.
EC is considered effective.

On the other hand, when a carboxypropyl group having one more methylene group than CEC was introduced into pulp, a modified pulp having elasticity was obtained, and a desired pulp sheet was not obtained.

From the above, it was possible to produce a pulp sheet provided with water resistance from the CEC alkali salt and the trivalent or higher inorganic metal salt. The pulp sheet obtained here could be redissolved with a mineral acid or aqueous alkali solution. This indicates that the bonding of this sheet is made up of ionic crosslinks. The optimum degree of carboxyethyl group substitution was good for 5 to 10 parts by weight of carboxyethyl group per 100 parts by weight of cellulose. That is, the degree of substitution that satisfies the condition that the bulk modified pulp is fibrous and that the alkali metal salt thereof is partially soluble is important. In addition, the cellulose fiber does not contain hemicellulose such as cotton linter and regenerated cellulose, and those containing lignin such as mechanical pulp cannot be used to obtain a pulp sheet having toughness and water resistance by the method of the present invention. Was. Further, the pH during papermaking was effective at 4 to 5.5.

 Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 80 g of sheet-like cellulose pulp (LBKP) was immersed in 550 g of water in a two-volume three-necked flask, and an alkaline aqueous solution in which 100 g of sodium hydroxide was dissolved in 200 g of water was added at room temperature. Alcerization was performed by stirring with a mechanical stirrer for 30 minutes.

Next, a solution prepared by dissolving 125 g of acrylamide in 250 g of water was added, the temperature was raised to 95 ° C. over 30 minutes, and the mixture was kept for 1 hour to carry out an etherification reaction and an amide hydrolysis reaction. After the completion of the reaction, the system was cooled, washed with methanol and dried at 60 ° C.

The obtained carboxyethyl cellulose (sodium salt) was fibrous, and the average DS was measured.
(7.3 parts of carboxyethyl group based on 100 parts by weight of cellulose)
Parts by weight).

The obtained carboxyethylcellulose (sodium salt) was dispersed in water to form a 0.5% slurry, a certain amount of which was taken, further diluted to 0.018% with water, and then concentrated.
9.3M alum was added at pH 4.8, and paper was formed on a 150-mesh, 16-cm diameter wire mesh with gentle stirring. 4.2kg / cm ² after papermaking
And then air-dried. The obtained sheet is 65% R
The physical properties after humidity control were measured in a constant temperature and humidity chamber at H and 20 ° C.

As a comparative example, an untreated LBKP beaten to a freeness of 385 ml (Comparative Example 1), a urea-formaldehyde resin as a wet paper strength enhancer to which 1% of pulp was added (Comparative Example 2), and a carboxylate solvent method were used. Methylated LBKP (DS0.17, sodium salt) (Comparative Example-3)
Was also made in the same manner as above, and the physical properties were measured.

Table 1 shows the results. However, the physical property test of the paper was measured according to the following method.

Burst strength JIS P 8112-63 Tensile strength JIS P 8113-52 MIT bending strength JIS P 8115-63 Air permeability JIS P 8117-63 Density JIS P 8118-63 The water resistance test was performed by saturating a piece of paper in water, a 3% aqueous solution of sulfuric acid, and a 0.5% aqueous solution of caustic soda, and then evaluating the degree of disaggregation after stirring with a disintegrator for 1 minute.
Table 2 shows the results.

Note that the sample of Example 1 did not disintegrate at all even after stirring for one month in water.

Example 2 According to the method of Example 1, carboxyethyl cellulose (sodium salt) having a higher degree of etherification was produced,
The paper was agglomerated with zirconium sulfate. That is, 60 g of sheet-like cellulose pulp (LBKP) was immersed in 275 g of water in a two-volume three-necked flask, and an alkaline aqueous solution in which 133 g of sodium hydroxide was dissolved in 266 g of water was added at room temperature. Alcerization was performed by stirring with a mechanical stirrer for minutes. Next with acrylamide
A solution prepared by dissolving 158 g in 316 g of water was added, the temperature was raised to 95 ° C. over 30 minutes, and the mixture was kept for 1 hour to carry out an etherification reaction and an amide hydrolysis reaction. The product was washed and dried at 60 ° C. The average DS of the obtained fibrous carboxyethyl cellulose (sodium salt) was 0.19 (8.7 parts by weight of carboxyethyl group based on 100 parts by weight of cellulose).

This was adjusted to pH 4.4 using 9.3 M zirconium sulfate.
And the physical properties thereof were examined. For comparison, physical properties and water resistance were also obtained for a carboxyethylated pulp sheet having a degree of etherification of 2.0% by weight (Comparative Example 4) and a carboxyethylated pulp sheet having a degree of etherification of 13.5% by weight (Comparative Example 5). Was examined. Table 3 shows the results.

With respect to Comparative Example 5, a film-like brittle sheet was obtained, and measurement was impossible.

The water resistance test was performed by saturating a piece of paper in water and then evaluating the degree of disaggregation after stirring with a disintegrator for 1 minute.
Table 4 shows the results.

Example 3 According to Example 1, carboxyethylated pulp (NBKP) having a degree of etherification of 9.9% by weight was coagulated with alum, paper-made, and tested for water resistance. As a comparison, the water resistance of a sheet made of carboxyethylated cotton linter having a degree of etherification of 6.5% by weight and alum was also tested (Comparative Example 6). Table 5 shows the results.

[Effects of the Invention] Since the present invention is configured as described above, carboxyethylcellulose is formed by ionic crosslinking via a trivalent or higher inorganic metal, and has water resistance and mechanical strength (particularly, bending strength,
It is possible to obtain a pulp sheet having excellent toughness and air permeability, and further having properties of being capable of being defibrated. For example, it can be used as a material for solid-liquid separation, an air filter, speaker cone paper, a material requiring toughness, a packaging material, and the like.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) D21H 11/20

Claims (1)

(57) [Claims] An alkali metal salt of pulp having 5 to 10 parts by weight of a carboxyethyl group in a side chain per 100 parts by weight of cellulose is metathesized with a trivalent or more inorganic metal salt such as aluminum ion and zirconium ion. And a method for producing a water-resistant pulp sheet obtained by coagulation.