JP2002204951A - Aqueous cellulose gel and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an aqueous cellulose gel which is superior in viscosity, stability, and feel to the touch more than one obtained by prior art and exhibits excellent water retentivity, dispersion stability, and thickening effects when used in pasty or gelatinous food, medicines, or cosmetics or in aqueous coating materials, ink, or adhesive pastes. SOLUTION: A water-insoluble, alkali-soluble cellulose ether with a low degree of substitution is dissolved in an aqueous alkali solution. The resultant solution is neutralized by the addition of an acid. During or after the neutralization, the solution is subjected to shear milling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous gel of low-substituted cellulose ether which is suitably used as a dispersion stabilizer and a viscosity modifier for foods, pharmaceuticals, cosmetics, aqueous paints, inks, pastes, and the like. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Conventionally, an aqueous cellulose gel containing microcrystalline cellulose as a main component has been known. This is because microcrystalline cellulose as a gel-forming component forms a network structure in water, and water-insoluble substances and gases are stably incorporated into the gel. Therefore, additives for various paste-like or gel-like foods, pharmaceuticals, cosmetics, etc. Further, they are used for dispersion stabilizers such as water-based paints, inks and pastes, viscosity regulators, flow improvers, foam stabilizers and the like.

However, gels made from microcrystalline cellulose alone have insufficient water retention or thickening effects. Therefore, sodium carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose and the like are thickened. It is often added in combination as an auxiliary agent, and CMC-Na powder is mixed in advance with the starting microcrystalline cellulose.

On the other hand, JP-B-56-54292, JP-B-62-61041, and JP-B-6-497.
No. 68 discloses a method for producing an aqueous gel, which comprises dispersing a low-substituted cellulose ether powder in water and subjecting the powder to shear grinding.

[0005]

In the above-mentioned technique, a low-substituted cellulose ether of a ground solid powder is dispersed in an aqueous solvent and this is sheared and ground. However, although this method provides a certain effect, it is difficult to produce at the actual production level due to insufficient viscosity and strong shearing force, and a relatively short time after dispersion. In this case, sedimentation and water separation were observed, and when applied to the skin, there were problems such as poor touch feeling.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an aqueous cellulose gel which is highly viscous, stable, has a good tactile feel, and can be produced even on an actual production scale, and a method for producing the same.

[0007]

Means for Solving the Problems and Embodiments of the Invention As a result of diligent studies to achieve the above object, the present inventor has found that instead of dispersing cellulose ether powder in water, the cellulose ether is once alkalized. It has been found that the above-mentioned problems can be solved by shear-milling a solution neutralized by dissolving in water or by shear-milling while gradually neutralizing, and completed the present invention.

That is, the present invention relates to a method comprising dissolving a low-substituted cellulose ether which is insoluble in water but soluble in an alkali, in an aqueous alkali solution, and then neutralizing by adding an acid or shear-milling the neutralized liquid. The present invention provides a method for producing an aqueous cellulose gel and an aqueous cellulose gel obtained by the method.

The present invention is different from the conventional technique of simply dispersing a low-substituted cellulose ether powder in water and shear-milling it, and is characterized in that it is always dissolved in an alkali. In the solution obtained by neutralizing the alkaline solution of cellulose ether, polymer lumps are precipitated, and from this point,
It was thought that the effect would not be the same as putting the powder product in water as it was and shearing it, but contrary to expectation, the polymer mass that precipitated and existed in the neutralized solution passed through the dry grinding process The present inventor has found that a gel having a higher viscosity and a more stable gel is obtained at a lower shearing force than an aqueous dispersion of powder.

Hereinafter, the present invention will be described in more detail.
In the method for producing an aqueous cellulose gel of the present invention, a low-substituted cellulose ether is used as a raw material.

The low-substituted cellulose ether of the present invention has the property of being insoluble in water but soluble in an alkaline solution. In general, cellulose is insoluble in water, but when a hydrogen atom of a hydroxyl group of a glucose ring constituting cellulose is substituted with an alkyl group or a hydroxyalkyl group, the cellulose becomes water-soluble depending on the degree of the substitution. However, those having a low degree of substitution have no solubility in water, but often have the property of dissolving in an alkaline solution.

In many cases, when the low-substituted cellulose ether powder is dispersed in water, a part of the powder is swollen. When the degree of substitution increases, the compound becomes water-soluble and loses the property of dissolving in alkali. By using such a water-soluble cellulose ether, the aqueous gel of the present invention cannot be obtained.

The desirable substitution degree of the main low-substituted cellulose ether used in the present invention is 0.05 to 0.05.
1.0, and the range of the desirable weight% of the substituent is as follows. Low-substituted methylcellulose: methoxyl group 3 to 15% Low-substituted hydroxyethyl cellulose: hydroxyethoxyl group 3 to 15% Low-substituted hydroxypropylcellulose: hydroxypropoxyl group 4 to 20% Low-substituted hydroxypropylmethylcellulose: methoxyl group 3 to 12%, hydroxypropoxyl group 4-2
0% Low-substituted carboxymethylcellulose and its sodium salt: carboxymethyl group 3 to 15%

Such a low-substituted cellulose ether is insoluble in water, but is soluble in an alkaline aqueous solution and has a property of swelling by absorbing water. As a more typical example,
Low-substituted hydroxypropylcellulose; this substance is currently marketed by Shin-Etsu Chemical Co., Ltd. under the trade name of L-HPC, is listed in the Japanese Pharmacopoeia, and is particularly formulated into tablets in the field of pharmaceutical materials. It is widely used as a disintegrant.

Methods for producing these low-substituted cellulose ethers are known, and are described, for example, in Japanese Patent Publication No. 57-53100. For production, it is necessary to prepare alkali cellulose first. This is performed by immersing a sheet-like pulp as a starting material in an alkaline aqueous solution, for example, caustic soda, or mixing a crushed pulp with an alkaline solution as it is, or dispersing pulp powder in an organic solvent. It is prepared by adding an alkali or the like. Next, alkali cellulose is charged into a reactor, an etherifying agent such as propylene oxide, ethylene oxide or the like is added, and the mixture is heated and reacted to obtain cellulose ether. After completion of the reaction, the crude cellulose ether is transferred to another tank, the alkali is neutralized with an acid, and the solid is washed, dried, and pulverized to obtain a final product as a powder.
Alternatively, the crude cellulose ether immediately after the reaction may be completely or partially dissolved in water and then neutralized, and the precipitated polymer may be separated, washed, dried and pulverized.

In the method for producing an aqueous cellulose gel according to the present invention, a low-substituted cellulose ether is dissolved in an aqueous alkali solution, and then neutralized, or after neutralization, subjected to shear-milling. Even if the low-substituted cellulose ether powder once obtained as the final product in the above-described method is dissolved in an aqueous alkali solution, the same effect can be obtained even if the crude cellulose ether is dissolved in water immediately after the reaction. . In the latter case, since the crude cellulose ether contains alkali, the solvent to be dissolved may be only water,
An alkali may be added to ensure dissolution. Either method is included in the present invention.

The alkali used for dissolution includes caustic potash, caustic soda, and the like. The concentration of the alkali varies depending on the type of the substituent and the degree of substitution of the cellulose ether used. same as below),
Particularly, it is 3 to 15%. As a typical example, a low-substituted hydroxypropylcellulose having a substitution degree of 0.2 is 10%.
% Caustic soda. Note that, depending on the difference in the distribution of the substituents, a transparent solution may be obtained, or the solution may not be completely transparent. In the latter case, any apparent increase in viscosity is considered to be dissolved.

The neutralization of the alkaline solution is carried out by using an equivalent amount of hydrochloric acid, sulfuric acid,
Acetic acid or the like may be used. Place the alkaline solution in a shear grinder and grind while gradually adding acid to neutralize,
Alternatively, an equivalent amount of an acid is added first to neutralize, and the liquid in which the precipitated polymer is present is directly sheared and ground.

In the method of shearing and grinding, an alkaline solution of cellulose ether having a suitable concentration or a solution obtained by neutralizing the alkaline solution is ground with a device such as a vibration ball mill, a colloid mill, a propeller homogenizer, and a high pressure homogenizer manufactured by Gorin Co., Ltd. At this time, in the case of an alkaline solution, add hydrochloric acid,
Grinding is performed while gradually adding an acid such as sulfuric acid or acetic acid.
The conditions for shearing and grinding are not particularly limited, but for example, a propeller-type homogenizer may be 3,000 to 15,000 r.
pm, especially 10,000 to 15,000 rpm, and a high-pressure homogenizer with a pressure of 100 to 2,000 kg /
cm ² , particularly preferably 200 to 2,000 kg / cm ² .

The concentration of cellulose ether in the solution upon shearing and grinding is preferably 0.01 to 20% by weight, particularly preferably 0.1 to 1% by weight. At higher concentrations,
Viscosity may increase excessively, making grinding difficult.

In the prepared gel, salts produced by the neutralization are present. If necessary, these salts are removed by a technique such as centrifugation or dialysis.

The aqueous cellulose gel obtained according to the present invention may optionally contain other additives such as a nonionic surfactant or an ionic surfactant, a fragrance, a flavoring agent, a thickener, and a film forming agent. A water-soluble organic solvent such as alcohol may be added as needed.

The particle size of the cellulose ether in the aqueous gel obtained by the method of the present invention is generally 100 μm or less, preferably 50 μm or less. The lower limit is not particularly limited, but is usually 1 μm or more, particularly 5 μm or more. Although the particle size changes depending on the shearing force, if the particle size is excessively large, the stability is deteriorated and the tactile sensation is also reduced. The average particle size can be measured by a wet laser diffraction method. However, the size of the particle size does not make much sense in comparison with an aqueous gel prepared by a conventional method. In general, it is considered that the smaller the particle size, the higher the stability of the dispersion system. It was recognized that. This seems to be because the stability is affected not only by the particle size but also by the difference in swellability of the particles with water. This indicates that the present invention is more stable than the conventional method regardless of the size of the particles.

[0024]

EXAMPLES Next, examples and comparative examples will be given, but the present invention is not limited to these examples. In addition,%
Indicates% by weight.

Example 1 7.5 g of a low-substituted hydroxypropylcellulose powder (L-HPC manufactured by Shin-Etsu Chemical Co., Ltd., substitution degree: 0.2) was dissolved in 425 g of a 6.3% NaOH aqueous solution. The solution neutralized by adding hydrochloric acid was added to the solution by using a homogenizer (AM-10, Nippon Seiki Seisaku-sho, Ltd.).
Sheared at 00 rpm for 10 minutes. The obtained gel was centrifuged at 5,000 rpm for 10 minutes, and the supernatant was discarded.
New pure water was added to the precipitate to redisperse the solid content to 3%. Table 1 shows the physical properties of the obtained aqueous gel.

The physical properties of the aqueous gel were evaluated as follows. 1) The viscosity is a value measured at 20 ° C. using a B-type viscometer. All cellulose ether concentrations are 3% by weight. 2) Stability is the result of visual observation of a sample placed in a vial and left at room temperature (up to 1 month). 3) The average particle size is determined by wet laser diffraction method (Horiba LA-70).
0). 4) The touch was evaluated by applying an appropriate amount to the skin.

Example 2 7.5 g of low-substituted hydroxypropylcellulose powder (L-HPC manufactured by Shin-Etsu Chemical Co., Ltd., substitution degree 0.2, average particle size 100 μm) was added to 6.3% Na
Dissolved in 425 g of an aqueous OH solution. Using a homogenizer (AM-10, Nippon Seiki Seisakusho), the solution was made into 5,000
Neutralizing equivalent acetic acid was added dropwise from a small hole of the vessel over 5 minutes while shearing at 0 rpm. After neutralization, one more
Shear milling was continued at 000 rpm for 10 minutes. The obtained gel was centrifuged at 10,000 rpm for 10 minutes, the supernatant was discarded, and the precipitate was redispersed by adding new pure water to a solid concentration of 3%. Table 1 shows the physical properties of the obtained aqueous gel.

Example 3 A pulp sheet was made of 49% NaO
H, soaked in alkali cellulose,
It was cut into a chip of × 1 cm. 100 g of this was charged into a reactor, and 11 g of propylene oxide was added. The reactor was purged with nitrogen, sealed, and stirred at 60 ° C.
For 5 hours. A small amount of the reaction product was sampled, and the measured value of the degree of substitution after neutralization washing and drying was 0.2. Separately, 7 g of the reaction product was dissolved in 400 g of water, and this was neutralized by gradually adding acetic acid from the small hole of the chamber for 5 minutes while rotating at 5,000 rpm using a homogenizer of the same type as described above. 10,000 rpm after neutralization
For 5 minutes. The obtained aqueous gel was used for 10.0
After centrifugation at 00 rpm for 10 minutes, the supernatant was removed, re-dispersed by adding 350 g of pure water again, and centrifuged again to remove the supernatant. The same operation was repeated once to purify the gel. Further, the concentration was adjusted by adding water so that the concentration of cellulose ether became 3%. Table 1 shows the physical properties of the obtained aqueous gel.

[Embodiment 4] L-HPC similar to that in Embodiment 1
15 g was dissolved in 1000 g of a 10% aqueous NaOH solution.
This is a high pressure homogenizer manufactured by Gorin (15M8TA).
And the solution was circulated at a pressure of 250 kg / cm ² for 15 minutes, at which time a neutralization equivalent of acetic acid was gradually added. Table 1 shows the physical properties of the obtained gel.

[Examples 5 to 7] L-HPCs were substituted with low-substituted methylcellulose (degree of substitution 0.28) and low-substituted hydroxypropylmethylcellulose (degree of methyl substitution 0.13, degree of hydroxypropyl substitution 0.18). ), And an aqueous gel was prepared in the same manner as in Example 1, except that hydroxyethyl cellulose (substitution degree: 0.2) was used. Table 1 shows the physical properties.

Comparative Example 1 15 g of low-substituted hydroxypropylcellulose similar to that of Example 1 was dispersed in 1000 g of water. This is a high pressure homogenizer (1
The solution was circulated at a pressure of 250 kg / cm ² for 15 minutes using 5M8TA). Table 1 shows the physical properties of the obtained gel.

[Comparative Example 2] The same procedure as in Comparative Example 1 was carried out except that the pressure was 500 kg / cm ² . Table 1 shows the physical properties of the obtained gel. Although a more stable gel was obtained than in the other comparative examples, the pressure used was the highest level of this experimental machine, and difficulties are expected in an actual production machine.

Comparative Example 3 Low-substituted hydroxypropylcellulose fine powder (L-HPC, LH manufactured by Shin-Etsu Chemical Co., Ltd.)
A gel was prepared in the same manner as in Comparative Example 2 using -31, a degree of substitution of 0.2, and an average particle size of 17 µm). Table 1 shows the physical properties of the obtained gel.

Comparative Example 4 Ultra-fine powder of hydroxypropyl cellulose having a low degree of substitution (degree of substitution: 0.2, average particle size: 2 μm)
And a gel was prepared in the same manner as in Comparative Example 2. Table 1 shows the physical properties of the obtained gel.

[0035]

[Table 1]

[0036]

The aqueous cellulose gel according to the present invention is superior in viscosity, stability and touch to those of the prior art, and is in the form of paste, gel, food, medicine, cosmetics, water-based paint, ink, When used as a paste or the like, they have excellent effects in water retention, dispersion stability and thickening action. Further, it can be prepared with a grinding device having a simple mechanism, and can be used for actual production.

Claims (3)

[Claims] Claims 1. A low-substituted cellulose ether which is insoluble in water but soluble in alkali is dissolved in an aqueous alkali solution.
A method for producing an aqueous cellulose gel, which comprises subjecting a neutralized liquid to shearing grinding while adding or neutralizing an acid. 2. The method for producing an aqueous cellulose gel according to claim 1, wherein the low-substituted cellulose ether is a low-substituted hydroxypropyl cellulose having a substitution degree of 0.05 to 1.0. 3. An aqueous cellulose gel obtained by the production method according to claim 1.