JPS6051481B2 - Method for producing low viscosity cellulose ethers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production and wet granulation method of low-viscosity cellulose ethers, and its purpose is not only to produce low-viscosity cellulose ethers but also to produce high-grade cellulose ethers with excellent whiteness. The first objective is to provide a method for producing cellulose ethers, and the second objective is to provide them in a granular or acicular shape suitable for practical use.

At least a portion of the three hydroxyl groups per anhydroglucose unit of cellulose is -OCnrunC00H group (n is 1 to 5
It is known that carboxyalkyl cellulose derivatives substituted with ether groups (an integer of
-35393, JP-A-55-9040).

However, from a practical standpoint, it is of course necessary to have a suitable viscosity in terms of coating suitability and enteric function, and in addition, in terms of appearance, high whiteness in the solid state and From the viewpoint of handling suitability, the product form is required to be granulated into granules or needles rather than powder.

That is, an object of the present invention is to industrially provide a high-grade, low-viscosity carboxyalkyl cellulose derivative that meets the above needs.

Although various methods have been proposed for reducing the viscosity of cellulose derivatives, oxidation or acid-based main chain scission methods are generally employed.

Among these, the depolymerization method using an acid has drawbacks such as requiring a complicated operation and a neutralizing agent to remove the acid used as a reaction catalyst. The present inventors have previously proposed a novel method for producing a low-viscosity cellulose ether based on such technical standards (Japanese Patent Application Laid-Open No. 108401/1983). This method is related to lowering the viscosity of carboxymethylethylcellulose, which is a type of cellulose ether. The high viscosity compound is uniformly dissolved in an aqueous solution of a lower alkanol having 1 to 4 atoms, and the alkanol is recovered and removed from the resulting solution by heat treatment at 60°C or the boiling point of the system, resulting in excellent whiteness and product solubility. It was now possible to obtain a high-quality, low-viscosity product.

The present inventors have further improved the method described in JP-A-55-108401, and have not only obtained a product with even higher whiteness, but also obtained a product that is granulated into granules or needles that are easier to handle. As a result of intensive studies on the production method of low-viscosity cellulose ethers with high commercial value and having a morphology of In a method of depolymerizing a highly viscous carboxyalkylcellulose derivative substituted with a 2-ter group with hydrogen peroxide, the carboxyalkylcellulose derivative is uniformly dissolved in an aqueous solution of a lower alkanol having 1 to 4 carbon atoms, and then the carboxyalkylcellulose derivative is peroxidized. The pH of the system is adjusted when the low viscosity carboxyalkyl cellulose derivative is precipitated and obtained by heat treatment with hydrogen at 3 (60'C or the boiling point of the system) and then collecting and removing alkanol from the reaction solution after reaction treatment. The present invention has been completed by discovering that the object can be fully achieved by carrying out the method by adjusting the solvent composition and solid content concentration of the system.

That is, the present invention is a method for producing low-viscosity cellulose ethers with good whiteness and a wet granulation method, which are based on the following two points. 40 (1) At least a portion of the three hydroxyl groups per anhydroglucose unit of cellulose are -0CnH2nC00H groups (n is an integer of 1 to 5)
In a method of depolymerizing a highly viscous carboxyalkylcellulose derivative substituted with an ether group with hydrogen peroxide, the carboxyalkylcellulose derivative is uniformly dissolved in an aqueous solution of a lower alkanol having 1 to 4 carbon atoms, and then hydrogen peroxide is added. When a low viscosity carboxyalkyl cellulose derivative is precipitated and separated by heat treatment at 60° C. or the boiling point of the system and then removing alkanol from the reaction solution after the reaction treatment, the pH of the system is set to 2.
A method for producing low viscosity cellulose ethers, which is carried out while adjusting the viscosity to 5 to 4. (2) In item (1), the lower alkanol is isopropyl alcohol, and the step of removing isopropyl alcohol after reaction treatment and precipitating and separating low-viscosity carboxyalkylcellulose is performed when the isopropyl alcohol/water ratio in the system is A concentration step of concentrating the reaction solution so that the weight ratio is 65/35 to 53/47 and the carboxyalkyl cellulose derivative solid content concentration is 20 to 30% by weight, and water is added to the concentrated solution obtained by the concentration step. When added, the isopropyl alcohol/water ratio in the system is 43/57 to 10 by weight.
/90, and after adjusting the solid content concentration of the carboxyalkyl cellulose derivative to 7 to 1% by weight, the low viscosity carboxyalkyl cellulose derivative is made into granules or needles by further removing residual isopropyl alcohol. A method for producing cellulose ethers, that is, a wet granulation method, characterized by comprising a two-stage reprecipitation step in which cellulose ethers are obtained by precipitation and separation.

In other words, the present inventors found that the carboxyalkylcellulose derivatives described above are not soluble in water alone, but have 1 to 1 atom atoms.
Mixed solution with lower alkanol of No. 4 Focusing on the solubility property of dissolving in a certain solution, the carboxyalkyl cellulose derivative was dissolved uniformly in the alkanol aqueous solution by adding hydrogen peroxide i and heating. The knowledge that it not only promotes polymerization but also has a bleaching effect (for example, as disclosed in JP-A-55-10840 proposed earlier by the present inventors)
As a result of further investigation based on 1 No. 1, it was found that the composition of the alkanol aqueous solution which is the PHL solvent of the system; To adjust the range, the previously proposed Unexamined Japanese Patent Publication No. 5
To obtain a product which not only has an even better whiteness than the product obtained by the method described in No. 5-108401, but also has a granular or needle-like granulated form that has excellent handling suitability. The present invention has been completed by discovering that this can be done.

By implementing the present invention, it is possible to perform depolymerization, bleaching, and even granulation processes in the same process,
Moreover, since the depolymerization is carried out in a homogeneous system, high-grade, low-viscosity cellulose ethers can be obtained economically.

By the way, the greatest advantage of the present invention is that it is possible to obtain a product with high whiteness, and at the same time, it is possible to efficiently granulate the target cellulose ether alone without adding a second component such as a binder. be.

Generally, the carboxyalkyl cellulose derivatives referred to in the present invention are useful compounds as enteric protective coating agents, and are always dissolved in some kind of coating solvent when used.

It is well known that for handling purposes, it is preferable for a polymer compound to be granulated in some form rather than a fine powder, and for use as an enteric protective coating agent. Cellulose ethers are no exception. In order to achieve this purpose, a dry granulation method using a fluidized bed granulator or the like is generally adopted, but in this method, for example, a second component such as hydroxypropylcellulose, hydroxypropylmethylcellulose, or methylcellulose is used as a binder. It is extremely difficult to granulate the desired product as a single component, as it is commonly added.

Furthermore, when the cellulose ethers referred to in the present invention are subjected to dry granulation using such a fluidized bed granulator, there is a technical problem in that efficient granulation is difficult due to static electricity generated during the drying process. It also has points. From the above viewpoint, the wet granulation method, which is the second objective of the present invention, has the following advantages compared to the dry granulation method:
It is possible to granulate the target cellulose ether as a single component without adding a second component such as a binder, and since it is a wet method, there is no risk of deterioration in granulation efficiency due to static electricity. Needless to say, it is advantageous in terms of quality and economy.

To explain the method of the present invention in more detail, the cellulose ethers referred to in the present invention mean that at least a portion of the three hydroxyl groups per anhydroglucose unit of cellulose is -0CnH.
It is a carboxyalkyl cellulose derivative substituted with a 2nC00H group (n is an integer of 1 to 5) and an ether group, and includes, for example, carboxymethylethylcellulose, carboxyethylethylcellulose, carboxybutylethylcellulose, carboxypropylmethylcellulose, etc., and is generally a cellulose derivative. The degree of substitution of carboxyalkyl group per anhydroglucose unit is about 0.3 to 11, the degree of substitution of other ether groups is about 0.3 to 11, and the degree of substitution of other ether groups is about 1 to 2.4. It is enteric-coated.

To carry out the present invention, first, a highly viscous cellulose ether is uniformly dissolved in an aqueous solution of a lower alkanol having 1 to 4 carbon atoms.

The high viscosity cellulose ethers mentioned here are those obtained by the methods described in, for example, Japanese Patent Publication No. 53-8751, Japanese Patent Application Publication No. 55-4333, and Japanese Patent Application Publication No. 55-118901. As long as it is insoluble but soluble in the lower alkanol aqueous solution, the present invention can be applied regardless of its production method. Examples of the lower alkanol include methanol, ethanol, isopropyl alcohol, etc., and the mixing ratio with water may be any ratio as long as the mixed liquid has the ability to dissolve the high viscosity cellulose ethers. In view of the solubility of the alkanol/water, the weight ratio (alkanol/water) is preferably 95/5 to 70/30 from an economic standpoint. The amount of hydrogen peroxide added is 0.0% based on the solid weight of cellulose ether.
It is desirable to set it as 1-50%, preferably 1-30%. The reaction temperature is preferably 60'C or higher; below this temperature the reaction rate is too low to be practical.

In particular, it is preferable to carry out the reaction at the boiling point of system 5 because temperature control during the reaction is easy. Further, the solid content concentration of cellulose ether during the reaction can be varied over a wide range, but 5 to 5% by weight is a practical range.

O After the reaction is completed, the alkanol is recovered and removed from the reaction solution to precipitate and separate the desired low-viscosity cellulose ether.

A method for separating the target product from the reaction solution is a general method for separating a polymer from a polymer solution, that is, a method of adding a large amount of precipitant (for example, water in the case of cellulose ethers in the present invention). However, it is difficult to recover the alkanol with such a method and it is difficult to say that it is economical.

Therefore, as a method for separating the desired low-viscosity cellulose ether from the reaction liquid, the alkanol is recovered and removed by distillation of the reaction liquid to lower the alkanol concentration in the reaction liquid (i.e., to reduce the ratio of water in the medium). (approximately 100%), it is preferable to adopt a process in which the target substance insoluble in water is separated by precipitation.

When recovering and removing alkanol from the reaction solution by distillation, it may be distilled as it is, but the
More preferably, 3 parts by weight of water is added all at once or in portions before or during distillation.

The above operations are basically the same as the method described in JP-A-55-108401 previously proposed by the present inventors; To achieve this goal, the pH of the slurry system must be adjusted to 2.5 to 4 when collecting and removing alkanol from the reaction solution and precipitating the desired low-viscosity cellulose ether. It is important to adjust it so that it is within the range of .0. This is the first feature of the present invention. To adjust the pH, use a weak base such as sodium acetate.
It is desirable to use a compound or a weakly acidic compound such as acetic acid. Next, to explain the wet granulation process, which is the second feature of the present invention, the depolymerization and bleaching steps are basically the first step.
The method is the same as in the characteristics of wet manufacturing. ``In order to achieve granules, the type of alkanol used, the alkanol recovery process, the alkanol concentration in the system, the solid content concentration, and the pH of the system are important factors.

First, regarding the type of alkanol used, in the case of the present invention, where the purpose is to granulate into particles or needles, it is necessary to use isopropyl alcohol.

Next is the alkanol recovery process from the reaction treatment solution, and the step of removing isopropyl alcohol after reaction treatment and precipitating and separating the target product is the process in which the isopropyl alcohol/water ratio in the system is 65/ 35-53/4
7, and the cellulose ether solid content concentration is 20~
(9) A concentration step of concentrating the reaction solution so that the concentration is % by weight, and water is added to the concentrated solution obtained by the concentration step so that the isopropyl alcohol/water ratio in the system is 43/57 to 43/57 by weight.
10/90, and after adjusting the solid content concentration of the cellulose ether to 7 to 1% by weight, the residual isopropyl alcohol is further collected and removed to precipitate the target product in the form of granules or needles. It is important to use a two-stage reprecipitation process. In addition, if the isopropyl alcohol concentration in the concentration step and reprecipitation step is higher than the above range, the product obtained will be in the form of fine powder.
If they become small, they will become lumpy and it will be impossible to achieve the goal together. Similarly, if the solid content concentration is higher than the above range, it will become lumpy, and if it is lower, it will be fine powdery, making it impossible to achieve the purpose. 1.Also, if the purpose is simply granulation, there is no need to particularly adjust the pH within the system.
To obtain a product with high whiteness, the pH should be adjusted to 2 in the reprecipitation process.
．． It is more preferable to adjust it to 5 to 4.0.

The above is the second feature of the present invention. By the way, it is also possible to perform depolymerization and bleaching treatment from the beginning under conditions corresponding to the concentration step in the present invention, and in this case, the so-called concentration step can be omitted and the re-precipitation step can be performed directly. Although possible, such a method basically falls within the scope of the present invention and does not exceed the scope of the present invention in any way.

As mentioned above, wet granulation, which is the second feature of the present invention, utilizes the solubility characteristics of the cellulose ether in alkanol/water.

Among the lower alkanols having 1 to 4 carbon atoms, the reason why isopropyl alcohol is particularly suitable for such granular or acicular granulation method is not certain, but it can be inferred from the vapor-liquid equilibrium relationship between various alkanols and water. It is thought that the conditions for precipitation as a precipitate having a morphology that is balanced between the change in the liquid phase composition in the concentration step and the reprecipitation step and the solubility of the cellulose ether are likely to be easily satisfied. EXAMPLES Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Note that the viscosity and whiteness were measured according to the following method.

(1) Viscosity of reaction solution 200ml of reaction solution was taken and measured at 25°C using a B-type viscometer.

(2) Product viscosity The cellulose ether referred to in the present invention was dried at 105°C for 2 hours, dissolved in an ethanol/water mixed solvent (weight ratio 8:2) to prepare a 5% by weight solution, and measured using a B-type viscometer at 25% by weight. Measured in °C.

(3) Whiteness Measured using a spectrophotometer at a wavelength of 480 rnμ using standard clay as 100% of a well-pulverized product (200 mesh through product).

Further, in the following examples, parts and % indicate parts by weight and % by weight, respectively, unless otherwise specified. Example 1 Product viscosity 30 (1X) PSl whiteness 70% carboxymethylethyl cellulose 80 g 1 isopropyl alcohol 80 g 1 isopropyl alcohol 306 g and water 13
1 g was placed in a 1' three-necked flask equipped with a stirrer, condenser and thermometer, and completely dissolved at 70°C.

After dissolving, 16 g of 35% hydrogen peroxide was added and the reaction was continued at the boiling point of the system until the viscosity of the reaction solution reached 250 CpS. Then isopropyl alcohol/water = 24.7175.3
and water was added to make the system a slurry so that the solid content concentration was 6%, and the pH of the system was further adjusted to 3.5 with 1M sodium acetate.
Adjusted to. Next, isopropyl alcohol was distilled and recovered until the internal temperature of the flask reached 98°C to precipitate low-viscosity carboxymethylethylcellulose.

After suctioning this material and thoroughly washing it with warm water, it was heated to 70°C.
It was dried to a constant weight. The purified carboxymethylethyl cellulose obtained is in the form of a fine powder and has a product viscosity of 15.
2CPS1 whiteness was 94.3%. Examples 2 to 3 and Comparative Examples 1 to 2 The same carboxymethylethyl cellulose and the same equipment as those used in Example 1 were used, and the treatment conditions were as shown in Table 1. After treatment, purified carboxymethylethyl cellulose was obtained.

The results are shown in Table 1, and it can be seen that by implementing the present invention, products with good whiteness can be obtained.
Example 4 Purified carboxyethyl ethyl cellulose was obtained in the same manner as in Example 1 except that 80 g of carboxyethyl ethyl cellulose having a product viscosity of 420 CPS and whiteness of 75.0% was used.

The product form of this product is fine powder, and the product viscosity is 14.5.
CPS1 whiteness was 93.5%. Comparative Example 3 After the reaction was completed, the same procedure as in Example 4 was carried out except that ethanol was directly distilled and recovered without adjusting the pH of the slurry by adding water to obtain purified carboxyethyl ethyl cellulose in the form of fine powder. .

The product viscosity of Example 5 was 14.8 cpS, but the whiteness was 88.0%, which was inferior to Example 4. Example 5 80 g of the same carboxymethylene ethyl cellulose as used in Example 1 was mixed with 30 g of isopropyl alcohol.
After completely dissolving 6 g and 131 g of water using the same apparatus as in Example 1, 16 g of 35% hydrogen peroxide solution was added and the reaction was carried out at the boiling point of the system until the viscosity of the reaction liquid reached 250 CpS.

Next, isopropyl alcohol/water in the system = 60.9
Isopropyl alcohol was distilled and recovered so that the solid content concentration was /39.1 and 23.9%, and the reaction solution was concentrated.

Then isopropyl alcohol/water = 22.8/77.
2, and water was added to make the system a slurry so that the solid content concentration was 10.9%, and the pH of the system was further adjusted with 1M sodium acetate.
was adjusted to 3.5. Next, isopropyl alcohol was distilled and recovered until the internal temperature of the flask reached 98° C., and low-viscosity carboxymethylethyl cellulose was precipitated.

After suctioning this material and thoroughly washing it with warm water,
Dry to constant weight at °C. The purified carboxymethylethyl cellulose obtained has a length of 2 to 57 r0! It was granulated into acicular shape *8. (See Figure 1). The product viscosity of this purified carboxymethylethylcellulose was 15.3CpS1 and the whiteness was 94.0. Examples 6 to 10 and Comparative Examples 4 to 5 Each of the second
The results listed in the table were obtained. By carrying out the present invention, it is possible to obtain a product granulated into granules or needles, but if conditions are outside the scope of the present invention, it may not be possible to obtain a product in the desired shape. is clear.

Comparative Example 6 Undried low-viscosity carboxymethylethyl cellulose 6k9 (water content 58.1% W.C.) obtained under the same conditions as Example 2.
B. ) was dried at a moisture content of 1.6%W. B. Dry until .

As drying progressed, adhesion to the wall due to static electricity was noticeable. This dried product 2.4k9 was added to a fluidized bed drying granulator W.
Hydroxypro-4/Vylcellulose (product name 11PC-M manufactured by Nippon Soda) was prepared in the SG-5 type (manufactured by Okawara Seisakusho).
Granulation was attempted using a 3% aqueous solution of 3K9 as a granulation binder at a hot air temperature of 60°C. While the binder solution was being sprayed, it grew into fine particles, but most of them disintegrated again during the drying process, making it difficult to achieve the desired goal (
(See Figure 6).

[Brief explanation of the drawing]

1 to 3 are photographs showing the granules obtained in Examples 5, 6, and 9, respectively.

Claims (1)

[Scope of Claims] 1 At least a portion of the three hydroxyl groups per anhydroglucose unit of cellulose is -OCnH_2nCOOH group (n
is an integer of 1 to 5) and a high viscosity carboxyalkyl cellulose derivative substituted with an ether group is depolymerized with hydrogen peroxide in a lower alkanol aqueous solution having 1 to 4 carbon atoms. Dissolve uniformly and heat with hydrogen peroxide at 60℃
The pH of the system is adjusted to 2.5 to 4 when the low viscosity carboxyalkylcellulose derivative is precipitated and obtained by heat treatment at the boiling point of the system and then removing alkanol from the reaction solution after reaction treatment. A method for producing low viscosity cellulose ethers, characterized in that the method is carried out. 2. The lower alkanol is isopropyl alcohol, and the step of removing isopropyl alcohol after reaction treatment and precipitating and separating low viscosity carboxyalkyl cellulose is performed when the isopropyl alcohol/water ratio in the system is 65/35 to 53 by weight. /47, and a concentration step of concentrating the reaction solution so that the carboxyalkyl cellulose derivative solid content concentration is 20 to 30% by weight, and adding water to the concentrated solution obtained in the concentration step to remove isopropyl alcohol in the system. /water ratio is 43/57 to 10/90 by weight,
and a two-stage reprecipitation step in which the carboxyalkyl cellulose derivative solid content concentration is adjusted to 7 to 19% by weight, and then residual isopropyl alcohol is further removed to obtain particles or needles by precipitation. A method for producing low-viscosity cellulose ethers according to claim 1, which comprises: