JPH04261401A - Water-soluble celurose acetate and preparation thereof - Google Patents

Abstract

PURPOSE: To efficiently obtain the subject compd. forming an aq. soln. high in transparency by acetylating a cellulosic raw material with acetic acid anhydride, acetic acid and an acidic catalyst and subsequently neutralizing the catalyst and hydrolyzing the acetylated raw material to age the same and further adding the acidic catalyst to the reaction mixture and hydrolyzing the raw material.

CONSTITUTION: A cellulosic raw material is activated and 200-400 pts.wt. of acetic acid anhydride, 20-350 pts.wt. of acetic acid and 0.5-5 pts.wt. of an acidic catalyst are added to 100 pts.wt. of the activated cellulose and the whole is held at 50-85°C for 5-20 min to acetylate the cellulose to form a primary cellulose acetate and, after the acidic catalyst is neutralized, this mixture is hydrolyzed at 110-170°C by a water-containing system to age the primary cellulose acetate to obtain a secondary cellulose acetate with an acethylation degree of 1.5-2.6, and 10-1,000 pts.wt. of acetic acid and 1-10 pts.wt. of the acidic catalyst are added to 100 pts.wt. of this cellulose, and the cellulose is hydrolyzed at 50-90°C in the presence of water to age the secondary cellulose acetate to obtain a product with an acetylation degree of 0.4-0.9, a water insoluble content of 1.5 wt.% and a wt. average mol.wt. of 5×10³-3×10⁵.

COPYRIGHT: (C)1992,JPO

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides water-soluble cellulose acetate, which contains few water-insoluble substances and has high transparency when dissolved in water.
The present invention also relates to a method of performing an acetylation step and a ripening step at high temperatures in producing this type of water-soluble cellulose acetate.

0002

[Prior Art] Among cellulose acetate, which is classified as an organic acid ester of cellulose, the degree of substitution by acetyl groups, that is, the number of hydroxyl groups substituted with acetyl groups among the three hydroxyl groups of the glucose ring, is from 0.4 to 0.4. 0
．． 9, low-substituted cellulose acetate is soluble in water. Such water-soluble cellulose acetate has many uses,
For example, it can be used as a coating agent for pharmaceuticals, a binder for tablets, and a glue, making it an industrially important semi-synthetic polymer.

The production of this type of water-soluble cellulose acetate is
Typically, (1) cellulose is acetylated to form primary cellulose acetate in a mixture of acetic acid as a reaction solvent, acetic anhydride as an acetylating agent, and sulfuric acid as a catalyst at a temperature of about 30°C to 50°C; (2) The acetyl groups of the primary cellulose acetate contained in the reaction mixture obtained in the acetylation step are hydrolyzed at a temperature of 100°C or lower, thereby aging the primary cellulose acetate and acetylating it. forming secondary cellulose acetate having a degree of 1.5 to 2.6 (first ripening step); (3) to the reaction mixture containing the secondary cellulose acetate obtained in the first ripening step;
Aging the secondary cellulose acetate by adding an acid mixture consisting of acetic acid, sulfuric acid, and water to hydrolyze the secondary cellulose acetate to form cellulose acetate with a degree of acetylation of about 0.4 to 0.9. (second ripening step), and (4
) The method includes the steps of recovering cellulose acetate from the reaction mixture obtained in the second ripening step by performing separation, precipitation, washing with water, and drying.

Regarding such water-soluble cellulose acetate, US Pat. No. 2,129,052 describes 10
0 parts by weight of secondary cellulose acetate with a degree of acetylation of 1.18, 60% of 1000 parts containing 2 parts by weight of sulfuric acid
It was dissolved in acetic acid, hydrolyzed at 38°C for 192 hours as in the second ripening step (3) above, and water-soluble cellulose acetate with a degree of acetylation of 0.43 was obtained in the recovery step (4) above. A method for obtaining the information is disclosed. The aqueous solution of water-soluble cellulose acetate obtained by this method contains a large amount of water-insoluble matter due to the heterogeneity of the reaction.

[0005] These water-insoluble substances are presumed to originate from hemicellulose contained as an impurity in wood pulp. This hemicellulose has a high degree of substitution with acetyl groups and is highly hydrophobic, and is produced in the above-mentioned acetylation step (1). This type of hemicellulose is produced in the acetylation step (1) and associates with the highly hydrophobic cellulose triacetate, inhibiting the uniform hydrolysis of the primary cellulose acetate in the first ripening step (2) and causing aggregation. Cellulose acetate with a high degree of acetyl group substitution, which forms a water-insoluble material, is partially produced. Therefore, since the cellulose acetate obtained by the above method contains a large amount of water-insoluble matter, the properties such as the transparency of the solution are significantly impaired, and the filterability in obtaining the final product is reduced. I ended up
The quality of appearance is also impaired.

Regarding the method for producing cellulose diacetate, the present inventors conducted the acetylation reaction in the above acetylation step (1) in the presence of a small amount of sulfuric acid at high temperature for a short period of time to produce cellulose diacetate. We have already proposed a method in which the hydrolysis reaction in the first ripening step (2) is carried out at high temperature and in a short time [JP-A-56-59801 and JP-A-58-93701 (U.S. Pat. No. 4,439,605).
(corresponding to the issue). These methods (1) allow the use of lower grades of pulp in place of high-grade dissolving pulp as the cellulosic feedstock, allowing for a broader range of pulp sources; and (2) the use of sulfuric acid and neutralizing agents. (3) By performing acetylation at a high temperature in the presence of a low concentration of sulfuric acid for a short time, depolymerization can be suppressed and a decrease in the degree of polymerization of cellulose diacetate can be prevented. (4) )
By performing acetylation and hydrolysis at high temperatures, reaction time can be shortened and productivity can be improved.
(5) It is advantageous in that the reaction product has excellent filterability, solution transparency, spinnability, etc.

However, the cellulose diacetate obtained by these methods is
Even if it is supplied to the second ripening step (3) described in the specification, a large amount of water-insoluble matter is still produced, and as a result,
Filterability, clarity and appearance in aqueous solutions are impaired, reducing the commercial value of the product.

[0008]

[Problems to be Solved by the Invention] Therefore, one object of the present invention is to provide a water-soluble solution that has an extremely low content of water-insoluble substances, has excellent filterability, and can form an aqueous solution with excellent transparency and appearance. Our purpose is to provide cellulose acetate. Another object of the present invention is to provide a method for producing water-soluble cellulose acetate having the above-mentioned excellent properties by carrying out the reaction at high temperature in a short time with high productivity.

[0009]

[Means for Solving the Problems] The inventor of the present invention has proposed a method in which the acetylation step is carried out at a high temperature for a short time in the presence of a small amount of an acidic catalyst, and the first ripening step is carried out at a high temperature for a short time. We have discovered that by combining this method with a method in which the second ripening step is carried out at a high temperature for a short time, productivity can be improved by shortening the reaction time, and the formation of water-insoluble substances can be significantly suppressed.
The invention has been completed.

That is, in the present invention, the degree of acetylation is 0.
．． 4 to 0.9, the content of water-insoluble matter is 1.5% by weight or less,
and a water-soluble cellulose acetate having a weight average molecular weight of 5 x 103 to 3 x 105.

[0011] Furthermore, the present invention has a degree of acetylation of 0.4.
~0.9, the content of water insolubles is 1.5% by weight or less, and the weight average molecular weight is 5 x 103 - 3 x 105. (A)
Activation step of activating cellulose raw material (B)
200 to 40 parts by weight of activated cellulose
Add 0 parts by weight of acetic anhydride, 20-350 parts by weight of acetic acid, and 0.5-5 parts by weight of acidic catalyst, and reduce the mixture to 5 parts by weight.
By holding at a temperature of 0 to 85 °C for 5 to 20 minutes,
an acetylation step in which the activated cellulosic feedstock is acetylated to produce primary cellulose acetate; (C) neutralizing the acidic catalyst in a reaction mixture containing primary cellulose acetate; and (C) neutralizing this mixture in a system containing water. 110~1
By hydrolyzing at a temperature of 70 °C, primary cellulose acetate is aged to reach a degree of acetylation of 1.5 to 2.6.
A first ripening step to produce secondary cellulose acetate, (
D) 10 to 100 parts by weight of secondary cellulose acetate
1000 parts by weight of acetic acid and 1-10 parts by weight of acidic catalyst are added and the mixture is heated at 50-90°C in a system containing water.
(E) a recovery step of recovering the produced water-soluble cellulose acetate from the reaction mixture obtained in the second aging step; The present invention provides a method for producing water-soluble cellulose acetate containing:

[0012] In this specification, "degree of substitution by acetyl group", that is, "degree of acetylation" is defined as ASTM D-
871 (1970, Vol. 15, p. 272).

[0013] In this specification, "content of water-insoluble matter" refers to 10 parts by weight of water-soluble cellulose acetate dissolved in 1000 parts by weight of water, and the resulting solution was heated at 50,000 rpm.
, under conditions of 3 hours, L8 with 50.2Ti rotor
-80 means a value determined by ultracentrifugation using a centrifuge (manufactured by Beckman) and weighing the resulting precipitate after drying. The content of water-insoluble substances in water-soluble cellulose acetate is expressed in weight %.

[0014] In this specification, "transmittance" means
The wavelength measured under the condition of a cell optical path length of 1 cm is 500
Assuming that the transmittance of water for light with a wavelength of 500 nm is 100%, dissolve 5 parts by weight of water-soluble cellulose acetate in 95 parts by weight of water, and measure the transmittance of the above solution for light with a wavelength of 500 nm. means the value obtained by

The water-soluble cellulose acetate of the present invention must have a weight average molecular weight of 5 x 103 to 3 x 105, a degree of acetylation of 0.4 to 0.9, and must be water-soluble. The content of water-insoluble substances in water-soluble cellulose acetate must be 1.5% by weight or less, preferably 1.0% by weight.
It is as follows. Water-insoluble matter is usually derived from acetone-insoluble matter. This acetone insoluble material is dichloromethane/
50-95% by weight of components soluble in methanol mixtures and 5-95% by weight of gel components insoluble in dichloromethane/methanol mixtures.
50% by weight. Furthermore, the transmittance of a 5% by weight aqueous solution of water-soluble cellulose acetate is 45% or more, preferably 60% or more.

[0016] In the production of water-soluble cellulose acetate, cellulose raw materials are subjected to an activation step (A), an acetylation step (B), a first ripening step (C), and a second ripening step (
D) and recovery step (E). The activation conditions in the activation step (A), the acetylation conditions in the acetylation step (B), and the first ripening step (
Regarding the conditions for the first ripening in C), see JP-A-56-5
No. 9801 and JP-A-58-93701 (U.S. Pat.
No. 605).

The activation step (A) is an acetylation step (
B) is important as a pretreatment for uniformly acetylating cellulose in the presence of a small amount of sulfuric acid catalyst. Examples of methods that can be used in the step of activating cellulosic raw materials include conventional methods, such as a one-step treatment method in which acetic acid is sprayed on cellulose and mixed uniformly;
A two-step process in which the cellulose is sprayed with acetic acid and then the cellulose is sprayed with acetic acid containing sulfuric acid; a method in which a sheet of wood pulp is wetted with acetic acid or acetic acid containing sulfuric acid and the sheet is then disintegrated; and Digesting wood pulp in water or a dilute aqueous acetic acid solution to form a slurry;
Examples include a slurry pretreatment method in which solvent removal and acetylation are repeated. In this activation step, 100
It is necessary to activate the cellulose by treating parts by weight of cellulosic raw material with 25 parts by weight or more of acetic acid.

The first feature of the present invention is that the acetylation step (
B) Depolymerization of cellulose can be suppressed by carrying out the acetylation reaction in the presence of a small amount of an acidic catalyst at a high temperature for a short period of time. That is, to 100 parts by weight of activated cellulose, 200 to 40 parts by weight
0 parts by weight of acetic anhydride, 20-350 parts by weight of acetic acid (
(preferably glacial acetic acid) and 0.5 to 5 parts by weight of an acid catalyst (preferably sulfuric acid), and the mixture is heated to 50 to 85 parts by weight.
Primary cellulose acetate is formed by an acetylation reaction that involves holding at a temperature of 5 to 20 minutes. The primary cellulose acetate produced in this process is mainly cellulose triacetate. To maintain the reaction mixture at the above reaction temperature and to prevent the degree of polymerization of cellulose acetate from decreasing due to acetylation at high temperatures, a mixture of acetic anhydride and acetic acid may be added, depending on the amount of acidic catalyst used. It is necessary to adjust the temperature in advance to about 15°C to -5°C. When activated cellulose is supplied to a mixture controlled at this temperature, it becomes possible to increase the temperature of the reaction system at a substantially constant rate even in the exothermic acetylation reaction. It is desirable to raise the temperature of the reaction system to 50 to 85°C over 20 to 60 minutes.

In the first ripening step (C), the reaction mixture containing the primary cellulose acetate obtained in the acetylation step (B) is neutralized and then hydrolyzed. The second feature of the present invention is that this hydrolysis is carried out at high temperature and in a short time. The neutralization step uses a neutralizing agent that is capable of neutralizing the acidic catalyst in the reaction mixture containing the primary cellulose acetate and also capable of hydrolyzing excess acetic anhydride. Examples of neutralizing agents include carbonates, acetates, hydroxides and oxides of calcium, magnesium, iron, aluminum and zinc. For complete neutralization, an amount of neutralizing agent is used in excess of 10 to 50% over the stoichiometric amount calculated from the amount of acidic catalyst.

[0020] In the first ripening step, the reaction mixture containing primary cellulose acetate is hydrolyzed in a water-containing system at a temperature of 110 to 170°C, so that the degree of acetylation is 1.5 to 2.6. form secondary cellulose acetate. Hydrolysis is carried out by transferring the reaction mixture containing primary cellulose acetate to a closed reaction vessel and increasing the temperature of the reaction mixture in a pressurized system by introducing pressurized steam to hydrolyze the primary cellulose acetate. conduct. The reaction time for this hydrolysis can be determined depending on the reaction temperature, and is not particularly limited as long as it is long enough to form secondary cellulose acetate having a degree of acetylation of 1.5 to 2.6. More specifically, hydrolysis is approximately 11
Approximately 2 to 10 hours at 0 to 120 °C, or 125 to 1
It can be carried out at 70°C, preferably about 140-160°C for 30 minutes to 6 hours. In these methods, high-pressure steam is supplied to the reaction system, thereby supplying the water necessary for hydrolysis, and the formation of gel-like acetone-insoluble matter is significantly suppressed by the effect of aeration and stirring. Furthermore, since the hydrolysis is carried out at a high temperature, the decomposition of the acetylated hemicellulose formed in the above-mentioned acetylation step (B) can proceed efficiently. Hydrolysis is
The reaction can be advanced not only by supplying high-pressure steam to the reaction system, but also by adding water to the reaction system with stirring and heating the reaction system by external heating means.

[0021] Hydrolysis in the first ripening step
It can be substantially stopped by cooling to below 00°C.

In the second ripening step (D), 1 to 10 parts by weight of an acidic catalyst (preferably sulfuric acid) is added to 100 parts by weight of secondary cellulose acetate, and the mixture is incubated in a water-containing system.
Hydrolysis is carried out at a temperature of 50-90°C, preferably 60-90°C. The third feature of the present invention is that the hydrolysis in the second aging step is carried out for a short time at a temperature higher than the conventional hydrolysis temperature in the presence of a small amount of acidic catalyst. In order to make the degree of substitution by acetyl groups more uniform, hydrolysis is carried out by adding 10 to 1000 parts by weight, preferably 250 to 750 parts by weight, of acetic acid to 100 parts by weight of secondary cellulose acetate. The water present in the reaction system can be derived from the water supplied in the above-mentioned first ripening step, or can be derived from newly added water. The reaction time for this hydrolysis can be arbitrarily set as long as the degree of acetylation can be set to 0.4 to 0.9. Although the reaction time varies depending on the reaction temperature, it is usually about 10 to
It is 48 hours. Hydrolysis can be substantially stopped by cooling the reaction system to a temperature below 40°C. This hydrolysis makes it possible to equalize the number of hydroxyl groups on the glucose ring substituted by acetyl groups. Furthermore, since a small amount of acetylated hemicellulose remaining can be decomposed, the amount of water-insoluble substances can be significantly reduced. Furthermore, in the second aging step described above, hydrolysis is performed at a lower temperature than the hydrolysis in the first aging step, so it is possible to suppress a decrease in the degree of polymerization.

The reaction mixture obtained in the second ripening step is subjected to the usual precipitation, separation, washing, stabilization, and drying in the recovery step (E), so that the degree of acetylation is 0.4.
~0.9 water-soluble cellulose acetate can be obtained.

[0024] To summarize the present invention as described above, the present invention provides water-soluble cellulose acetate which has a low content of water-insoluble substances and is highly transparent when dissolved in water, and which is capable of acetylation and aging at high temperatures. The present invention provides a method for producing such water-soluble cellulose acetate, which is characterized by the following.

[0025]

Effects of the Invention The water-soluble cellulose acetate of the present invention has a significantly low content of water-insoluble substances, and has excellent filterability, transparency, and appearance when made into an aqueous solution, which are necessary for processing cellulose acetate into final products. The quality above is excellent. The method for producing water-soluble cellulose acetate of the present invention yields water-soluble cellulose acetate having the excellent properties described above. This is due to the combination of the step of hydrolyzing cellulose acetate at high temperature for a short time, and the second ripening step for hydrolyzing cellulose acetate at high temperature for a short time.

[0026]

EXAMPLES The invention will be explained in more detail below with reference to examples, but the invention is in no way limited to these examples.

Example 1 Activation step (A): Wood pulp containing 97% α-cellulose was crushed and dried until the moisture content was 5%. The crushed pulp was fed into a pretreatment device, and 25 parts by weight of glacial acetic acid per 100 parts by weight of α-cellulose was added to the pulp and mixed at 50° C. for 30 minutes to activate the cellulose.

Acetylation step (B): Transfer the activated cellulose to a kneader type acetylation device and preheat it to 10°C.
280 parts by weight of acetic anhydride and 450 parts by weight, which had been cooled to
Parts by weight of glacial acetic acid were added to the acetylation apparatus. Then 5 parts by weight of concentrated sulfuric acid were added and the entire mixture was mixed. Since the reaction accumulates heat in the contents, acetylation is carried out while controlling the temperature of the system by cooling so that the temperature of the system increases from an initial temperature of 10°C to 68°C at a nearly constant rate over 50 minutes. , the temperature of the system was maintained at 68° C. for 10 minutes.

First ripening step (C): In a system at 68°C, 2
4 parts by weight of a 20% by weight aqueous magnesium acetate solution was added. The amount of magnesium acetate added was stoichiometrically excessive than the amount required to neutralize sulfuric acid in the system. Transfer the completely neutralized mixture to an autoclave until the gauge pressure is 5 kg.
/cm2 of water vapor was bubbled into the mixture while it was stirred and heated to 120°C. The mixture was held at this temperature for 130 minutes for a first ripening. reaction mixture
The mixture was rapidly cooled to below 100°C, transferred to a precipitation tank equipped with a stirring device, and water was added to this tank. The produced cellulose acetate was precipitated, centrifuged to remove the solvent, transferred to a washing tank, thoroughly washed with water in this tank, taken out from the tank and dried.

The degree of acetylation of the obtained flaky secondary cellulose acetate was 1.97.

Second ripening step (D); 5 parts by weight of acetic acid and 1.95 parts by weight of water are added to 1 part by weight of the secondary cellulose acetate obtained above, and the mixture is stirred for 2 to 3 hours. to dissolve the secondary cellulose acetate. This solution contains 0.
05 parts by weight of sulfuric acid was added and the resulting solution was heated to 80°C for 20
．． Hydrolysis was carried out by holding for 7 hours. Water was added to the system in two portions to prevent cellulose acetate from precipitating during hydrolysis. That is, once cellulose diacetate has been hydrolyzed to a degree of acetylation of 2.2, 0.67 parts by weight of water is added to the system for 2 to 3 minutes as the first portion, until cellulose acetate has a degree of acetylation of 2.2. Once hydrolyzed to 1.72, a second portion of 1.33 parts by weight of water was added to the system over a 2-3 minute period. The second addition of water was carried out by 1/3 of the time required for hydrolysis starting from the start of the reaction.

Recovery step (E) After hydrolysis was carried out for 20.7 hours, the temperature of the reaction system was cooled to below 45° C., and the reaction mixture was added to 15 parts by weight of acetone to form a precipitate. A precipitate was collected from the mixture and washed five times with 10 parts by weight of acetone. The washed precipitate was further washed with acetone containing 0.01 parts by weight of potassium acetate to neutralize it and dried.

The obtained low-substituted cellulose acetate has a degree of acetylation of 0.61 and a weight average molecular weight of 2.5×104
The content of water-insoluble matter was 0.67% by weight, and the transmittance was 71%.

Comparative Example 1 Activation step (A); 0.85 parts by weight of sulfuric acid, 0.85 parts by weight
A mixture of 16 parts by weight of water and 60 parts by weight of glacial acetic acid
Two parts by weight of the wood pulp for cellulose acetate were added and the resulting mixture was homogenized by stirring briefly. Next, this mixture was allowed to stand at 25° C. for 2 hours to activate cellulose.

Acetylation step (B): After activation, the reaction mixture was transferred to an acetylation apparatus, 410 parts by weight of acetic anhydride and 560 parts by weight of acetic acid were added, and the mixture was heated at 35 to 45°C for 1.5 hours. Acetylation was performed.

First ripening step (C): After adding magnesium carbonate or magnesium acetate in an amount equivalent to half the amount of sulfuric acid added above to the reaction system, 66.5 parts by weight of water is added to the reaction system. The reaction mixture was heated to 90° C. with stirring while supplying steam until the amount of water reached 162 parts by weight. Magnesium carbonate or magnesium acetate was further added to the system in an amount such that the amount of magnesium salt in the mixture was 0 to 0.05% by weight (in terms of magnesium oxide). Transfer this mixture to an autoclave and weigh 5-6 kg.
First ripening was carried out by maintaining the temperature at 80 to 90° C. for 2 hours under a pressure of /cm 2 . The reaction mixture was then recovered from the autoclave and added to water to obtain a degree of acetylation of 2.5.
6 secondary cellulose acetate was precipitated.

[0037] Second ripening step (D) and recovery step (E)
The obtained secondary cellulose acetate was subjected to the same second ripening step and recovery step as in Example 1 to obtain low-substituted cellulose acetate.

The obtained low-substituted cellulose acetate has a degree of acetylation of 0.63 and a weight average molecular weight of 4.0×10 4
The content of water-insoluble matter was 5.0% by weight, and the transmittance was 19%.

Comparative Example 2 Lowly substituted cellulose acetate was obtained in the same manner as in Example 1, except that the second ripening step of Example 1 was carried out using 60% sulfuric acid containing 2 parts by weight of sulfuric acid. By dissolving 100 parts by weight of secondary cellulose acetate with a degree of acetylation of 1.97 obtained in the first ripening step in 1,000 parts by weight of acetic acid, and hydrolyzing the cellulose acetate at 38°C for 192 hours. went. The obtained low-substituted cellulose acetate has a degree of acetylation of 0.64 and a water-insoluble content of 7.0% by weight.
, the transmittance was 15%.

Example 2 Low-substituted cellulose acetate was obtained in the same manner as in Example 1, except that wood pulp containing 98% α-cellulose was used in the activation step. The obtained low-substituted cellulose acetate has a degree of acetylation of 0.63 and a content of water-insoluble matter of 1.
3% by weight, and the transmittance was 48%.

Comparative Example 3 Low-substituted cellulose acetate was obtained in the same manner as in Comparative Example 1, except that wood pulp with an α-cellulose content of 98% was used in the activation step. The obtained low-substituted cellulose acetate had a degree of acetylation of 0.60, a water-insoluble content of 4.0% by weight, and a transmittance of 23%.

Example 3 Low-substituted cellulose acetate was obtained in the same manner as in Example 1, except that wood pulp containing 96% α-cellulose was used in the activation step. The obtained low-substituted cellulose acetate has a degree of acetylation of 0.62 and a content of water-insoluble matter of 0.
．． 8% by weight, and the transmittance was 65%.

Example 4 Low-substituted cellulose acetate was obtained in the same manner as in Example 1, except that wood pulp containing 93% α-cellulose was used in the activation step. The obtained low-substituted cellulose acetate has a degree of acetylation of 0.59 and a content of water-insoluble matter of 1.
．． 2% by weight, and the transmittance was 50%.

Example 5 Low-substituted cellulose acetate was obtained in the same manner as in Example 1, except that wood pulp containing 92% α-cellulose was used in the activation step. The obtained low-substituted cellulose acetate has a degree of acetylation of 0.73 and a content of water-insoluble matter of 0.
．． 8% by weight, and the transmittance was 65%.

Claims (10)

[Claims] [Claim 1] The degree of acetylation is 0.4 to 0.9,
A water-soluble cellulose acetate having a water-insoluble content of 1.5% by weight or less and a weight average molecular weight of 5 x 103 to 3 x 105. 2. The water-soluble cellulose acetate according to claim 1, wherein the content of water-insoluble matter is 1.0% by weight or less. [Claim 3] 5 for light with a wavelength of 500 nm
The cellulose acetate according to claim 1, which has a permeability of 45% or more in a wt% aqueous solution. [Claim 4] 5 for light with a wavelength of 500 nm
The cellulose acetate according to claim 3, which has a permeability of 60% or more in a wt% aqueous solution. [Claim 5] The degree of acetylation is 0.4 to 0.9,
In producing water-soluble cellulose acetate having a water-insoluble content of 1.5% by weight or less and a weight average molecular weight of 5 x 103 to 3 x 105, (A) an activation step of activating a cellulose raw material; (B) 100 parts by weight of activated cellulose, 200-400 parts by weight of acetic anhydride, 20-350 parts by weight of acetic acid, and 0.5 parts by weight.
an acetylation step in which the activated cellulosic feedstock is acetylated to produce primary cellulose acetate by adding ~5 parts by weight of an acidic catalyst and holding the mixture at a temperature of 50 to 85°C for 5 to 20 minutes; C) ripening the primary cellulose acetate by neutralizing the acidic catalyst in a reaction mixture containing the primary cellulose acetate and hydrolyzing this mixture in a water-containing system at a temperature of 110-170°C; A first ripening step of producing secondary cellulose acetate having a degree of acetylation of 1.5 to 2.6, (D) 100
By adding 10 to 1000 parts by weight of acetic acid and 1 to 10 parts by weight of an acidic catalyst to parts by weight of secondary cellulose acetate and hydrolyzing this mixture at a temperature of 50 to 90 °C in a water-containing system. , a second aging step of aging the secondary cellulose acetate, and (E) a recovery step of recovering the produced water-soluble cellulose acetate from the reaction mixture obtained in the second aging step. . 6. The method for producing water-soluble cellulose acetate according to claim 5, wherein the acetylation step includes a step of treating 100 parts by weight of the cellulosic raw material with 25 parts by weight or more of acetic acid. 7. The method for producing water-soluble cellulose acetate according to claim 5, wherein the acetylation step includes a step of increasing the temperature within the reaction system to 50 to 85° C. at a substantially constant rate over 20 to 60 minutes. Claim 8: In the first ripening step, 110-1
The method for producing water-soluble cellulose acetate according to claim 5, wherein the hydrolysis is carried out at a temperature of 20°C. 9. The first ripening step includes a step of maintaining the temperature at 140 to 160° C. by supplying high pressure steam to the reaction mixture in the pressurized system obtained in the acetylation step. A method for producing water-soluble cellulose acetate. 10. The method for producing water-soluble cellulose acetate according to claim 5, wherein the acidic catalyst is sulfuric acid.