JP5060728B2 - Cellulose ester and method for producing the same - Google Patents

Description

  The present invention relates to a cellulose ester (such as a mixed fatty acid cellulose ester) having little insoluble matter and bright spot foreign matter (foreign matter causing bright spots) despite its high molecular weight (ie, high degree of polymerization), and a method for producing the same, and The present invention relates to an optical film (a protective film for a polarizing plate, a retardation film, an optical compensation film, a color filter, a film for a photographic material, etc.).

  Cellulose acetate has high optical isotropy and is excellent in toughness and flame retardancy. Therefore, various photographic materials and optical materials such as retardation films, polarizing plate protective films, optical compensation films, antireflection films, etc. It is used as an optical film. In particular, when a film is used for a display device having a small pixel size and a large number of pixels (so-called dot number) such as a liquid crystal display device, a new problem such as a bright spot caused by abnormal refraction of transmitted light due to a foreign matter is generated. Optical defects are a problem. It is considered that the foreign substance that gives this bright spot is caused by cellulose esters having different degrees of esterification. That is, a cellulose ester having a low degree of esterification (sometimes referred to as low esterified cellulose) is produced as a by-product in the esterification step of the production of cellulose ester, and based on the difference in refractive index from cellulose having a high degree of esterification, When used as an optical film such as a polarizing plate protective film, it is recognized as a bright spot foreign material because the polarization is changed.

  Low esterified cellulose remains as an insoluble component when a solution (dope) is prepared by dissolving cellulose ester. Therefore, the low esterified cellulose becomes a filtration residue, and may pass through the filter medium depending on the size and shape of the low esterified cellulose. Therefore, the said subject cannot be solved by filtration of a cellulose-ester solution.

  In particular, compared to cellulose acetate, mixed fatty acid esters (cellulose acetate propionate, cellulose acetate butyrate, etc.) produce bright spot foreign matter because the reactivity of propionic anhydride and butyric anhydride is inferior to acetic anhydride. easy.

JP-A-2001-188128 (Patent Document 1) discloses an optical film containing a fatty acid cellulose ester having an acetyl group and a propionyl group and having a retardation value in the thickness direction of 60 to 300 nm. In this document, fatty acid fatty acid cellulose ester having a total of 2.1 to 2.8 acetyl group substitution degree and propionyl group substitution degree, acetyl group substitution degree 1.5 to 2.3, and propionyl group substitution degree 0.6. -1.2 Fatty Acid Cellulose Esters are disclosed, and it is also described that there are 200 or less foreign matters having a size of 5 to 50 μm per 250 mm ^{2 and} 0 foreign matters exceeding 50 μm that are recognized in a polarized crossed Nicol state. Yes. However, the mixed fatty acid cellulose ester described in this document has a low degree of substitution of acyl groups other than acetyl groups. Further, in the esterification reaction, since the reactivity of propionic anhydride is lower than that of acetic anhydride, low esterified cellulose is likely to be generated, and the generation of low esterified cellulose cannot be sufficiently suppressed.

  In JP-A-2005-307055 (Patent Document 2), 10 to 90% by mass of input cellulose is in an undissolved state, and dissolved cellulose and undissolved cellulose present at the solution interface are in the first stage. An acylation reaction is carried out, then undissolved cellulose is dissolved, and the second stage acylation reaction is carried out with an acylating agent (propionylating agent or butyrylating agent) different from the first stage acylating agent (acetylating agent). A method for producing cellulose acylate is disclosed. However, when producing a mixed fatty acid cellulose ester containing an acetyl group by this method, due to the difference in reactivity of the carboxylic acid, if an acetylating agent is used in the first stage reaction, the degree of acetyl group substitution accounted for in the total substitution degree. The ratio tends to increase, and it is difficult to increase the substitution degree of acyl groups other than acetyl groups while the substitution degree of acetyl groups remains low. On the other hand, when other carboxylic anhydrides other than acetic anhydride are used for the first stage reaction, the reactivity of the carboxylic anhydride used for the first stage reaction is inferior to that of acetic anhydride. It becomes difficult to obtain a mixed fatty acid ester having a polymerization degree. In the production of cellulose ester, when water is rapidly added after the esterification reaction to deactivate the organic carboxylic acid anhydride, the temperature of the reaction system rapidly increases and depolymerization occurs. For this reason, it has been proposed to gradually stop the esterification reaction. For example, in JP-A-10-45804 (Patent Document 3), sulfuric acid is used as a catalyst, cellulose is esterified with acetic anhydride and an organic acid anhydride having 3 or more carbon atoms, and the average substitution degree of acetyl groups is 2. A cellulose mixed fatty acid ester having an average substitution degree of 0 to 2.95, an acyl group having 3 or more carbon atoms of 0.05 to 0.8, and an average substitution degree of total acyl groups of 2.6 to 3.0 is produced. In the method, a method for adjusting the maximum temperature of the esterification reaction to 35 to 50 ° C. is disclosed. This document describes that a reaction terminator is added over 4 to 30 minutes after the esterification reaction in order to obtain a cellulose ester having a high degree of polymerization. However, in this method, since an acylating agent that is less reactive than acetic anhydride is used, the production of low esterified cellulose cannot be suppressed. Moreover, the mixed fatty acid cellulose ester has a low degree of substitution of acyl groups other than acetyl groups.

  It should be noted that prevention of lowering of the degree of polymerization and reduction of insoluble components and foreign matters are in a trade-off relationship, and it is extremely difficult to achieve both. In other words, prevention of a decrease in the degree of polymerization can be realized by shortening the esterification time, but the amount of insoluble components inevitably increases and the bright spots due to foreign substances increase. On the other hand, reduction of the amount of insoluble components can be achieved by lengthening the esterification time or raising the esterification temperature, but inevitably the degree of polymerization (molecular weight) of the cellulose ester is lowered. Therefore, when the film is formed by the casting method, the viscosity of the dope is lowered, the smoothness and mechanical strength of the film are lowered, and the productivity is lowered. Such problems are likely to occur when the degree of acyl group substitution is increased. In particular, mixed fatty acid cellulose esters having a high degree of acyl group substitution are produced using acetic anhydride and an acylating agent that is less reactive than acetic anhydride. It happens when you do. Furthermore, when highly crystalline cellulose (for example, linter pulp) with high purity is used, it is difficult to esterify the entire cellulose homogeneously because the acetylating agent is unlikely to enter the crystal part of the cellulose. In particular, when a mixed fatty acid cellulose ester is produced, an acylating agent that is less reactive than acetic anhydride is used, and therefore the production of low esterified cellulose cannot be suppressed.

In addition, the cellulose ester film is usually obtained by casting a cellulose ester solution (dope) onto a peelable support (metal support such as a rotating drum), partially drying, then peeling the wet sheet from the support and drying. If necessary, it is prepared by stretching the sheet. Therefore, the cellulose ester is also required to be peelable from the support.
JP 2001-188128 A (Claims) Japanese Patent Laying-Open No. 2005-307055 (Claims) Japanese Patent Laid-Open No. 10-45804 (claims, paragraph number [0017])

  Accordingly, an object of the present invention is to provide a cellulose ester (particularly, a mixed fatty acid cellulose ester) with little impurities even when the degree of polymerization is high, and a method for producing the same.

  Another object of the present invention is to provide a method and a cellulose ester capable of producing a cellulose ester having a high degree of polymerization and a small amount of insoluble components and luminescent spots even when a plurality of acylating agents having different reactivities are used. .

  Still another object of the present invention is to produce a homogeneous cellulose ester (particularly, a mixed fatty acid cellulose ester) with little foreign matter, even when cellulose having a high degree of crystallinity (especially cellulose having a high degree of crystallinity and polymerization) is used. It is to provide a method and a cellulose ester thereof.

  Another object of the present invention is to provide a cellulose ester (particularly, a mixed fatty acid cellulose ester) exhibiting high peelability to a support (such as a metal support) and a method for producing the same.

  Still another object of the present invention is a cellulose ester (such as a mixed fatty acid cellulose ester) that is stretchable and useful for preparing an optical film (such as a retardation film, an optical compensation film, and a polarizing plate protective film), and An object of the present invention is to provide a method capable of producing the cellulose ester quickly and efficiently.

  Another object of the present invention is to provide an optical film that has a small dimensional change with respect to a change in humidity, a small change in in-plane retardation and out-of-plane retardation, and may be stretched.

  The present inventors analyzed the relationship between the depolymerization of cellulose and the reaction modes of esterification and hydrolysis reactions from the point of view that has never been focused on in the production of cellulose esters (especially mixed fatty acid cellulose esters). As a result, they have found that cellulose depolymerization is greatly affected by the reaction termination method in the esterification reaction termination step (quenching step). As a result of intensive studies to achieve the above-mentioned problems based on these findings, the present inventors have found that when a specific reaction termination method is used, a high degree of polymerization is obtained even with a mixed fatty acid ester having a high degree of acyl group substitution. It discovered that the production | generation of a low esterified cellulose can be suppressed with keeping, and completed this invention.

  That is, in the method of the present invention, the step of activating cellulose with an activating agent, and esterifying cellulose with an acylating agent having at least 2 carbon atoms (particularly at least 3 carbon atoms) in the presence of an acylation catalyst. A method for producing a cellulose ester comprising a step and a step of saponifying and ripening the produced cellulose ester, wherein after the esterification step, the esterification reaction terminator is added to 1 mol of the acylating agent remaining in the reaction system. The cellulose ester is produced by adding at a rate of 0.3 to 10 equivalents / minute. The reaction terminator usually contains at least water. The reaction terminator may contain water and at least one component selected from a neutralizing agent for neutralizing the organic carboxylic acid and the esterification catalyst. The esterification reaction terminator may be added to the reaction system in about 0.1 to 3 minutes. Moreover, addition of the reaction terminator to the reaction system is often performed at a temperature of 100 ° C. or less. In the reaction, the step of activating treatment may comprise a step of activating cellulose with an activating agent and a step of activating cellulose with sulfuric acid and an activating agent. In general, the activator is composed of an organic carboxylic acid, the acylating agent is composed of an organic carboxylic acid anhydride, and the acylation catalyst is composed of sulfuric acid.

At least one and more specifically, a first activation step of activating the cellulose with at least one activating agent selected from C _1-5 alkanoic acids, selected from sulfuric acid and C _1-5 alkanoic acid A second activation step of activating the cellulose with an activator of the method, and in the presence of sulfuric acid, the activated cellulose is selected from acid anhydrides corresponding to C _2-6 alkanecarboxylic acids and carbon Esterification with a plurality of acid anhydrides having different numbers to produce a mixed fatty acid cellulose ester, and 0.5 to 5 equivalents of an esterification reaction terminator for 1 mole of acid anhydride remaining in the reaction system Through a step of adding at a rate of / min to deactivate at least the acid anhydride, and an aging step of aging the produced mixed fatty acid cellulose ester in the presence of sulfuric acid or residual sulfuric acid. Suesuteru (mixed fatty acid cellulose ester) can be produced.

By such a method, the production | generation of an impurity (low esterified cellulose) can be prevented, suppressing the fall (depolymerization) of the polymerization degree of a cellulose. Therefore, the present invention includes a step of activating cellulose with an activating agent, a step of esterifying cellulose with an acylating agent having at least 2 carbon atoms (particularly at least 3 carbon atoms) in the presence of an acylation catalyst, And a step of saponifying and aging the produced cellulose ester, and after the esterification step, the esterification reaction terminator is added at a rate of 0.3 to 10 equivalents / minute with respect to 1 mol of the acylating agent remaining in the reaction system. And a method of reducing the production of insoluble matter while suppressing a decrease in the degree of polymerization of the cellulose ester. In particular, even when cellulose having a high degree of crystallinity is used, an acid anhydride of an alkanecarboxylic acid having 3 or more carbon atoms, which is less reactive than acetic acid, can penetrate or diffuse into the crystalline region, resulting in a decrease in the degree of polymerization of cellulose. Generation of impurities (low esterified cellulose) can be prevented while suppressing polymerization. Therefore, the present invention is made of cellulose having an α-cellulose content of 98% or more and an average polymerization degree of 1000 to 3000 (for example, purified cotton linter, linter pulp), and is composed of at least a C _3-6 alkanecarboxylic acid anhydride. Suitable for esterification with acylating agents.

  The present invention also includes cellulose esters (particularly mixed fatty acid cellulose esters), for example, cellulose esters obtained by the above method. In this cellulose ester (particularly, mixed fatty acid cellulose ester), at least an acyl group having 2 or more carbon atoms (particularly at least 3 carbon atoms) is substituted, the average substitution degree of the entire acyl group is 2.5 to 3, and 6 glucose units. Cellulose ester having an average substitution degree of the acyl group of 0.7 to 1, and a viscosity average polymerization degree of 120 to 400 (for example, 190 to 400), a mixed solution of methylene chloride and methanol (methylene chloride / methanol = 9/1 (weight ratio)) insoluble component amount is 0.1% by weight or less. The acyl group may be an alkylcarbonyl group having 3 to 6 carbon atoms. Furthermore, the acyl group may contain an acetyl group. For example, a mixed fatty acid cellulose ester having an alkylcarbonyl group having 2 or more carbon atoms, wherein the substitution degree (A) of the acetyl group and the substitution degree (B) of the alkylcarbonyl group having 3 or more carbon atoms are represented by the following formula (I) ) To (III) may be mixed fatty acid cellulose ester. More specifically, the mixed fatty acid cellulose ester may be cellulose acetate propionate or cellulose acetate butyrate.

2.50 ≦ A + B ≦ 2.90 (I)
0.00 ≦ A ≦ 1.90 (II)
0.60 ≦ B ≦ 2.90 (III)
The present invention further includes a molded body composed of the cellulose ester. The molded body may be a film, for example, an optical film selected from a protective film for a polarizing plate, a retardation film, and an optical compensation film.

  In the present specification, the “insoluble component” means a low-substituted cellulose having poor solubility in unreacted cellulose and a solvent, and means a component that acts optically as a fine foreign substance. , Synonymous with insoluble matter, low esterified cellulose and the like. In the calculation of the equivalent amount of the reaction terminator, water as the reaction terminator is calculated as a monovalent compound, and the carbon number of the acid anhydride is the carbon number of the free carboxylic acid corresponding to the acid anhydride. means.

  In the present invention, since the esterification reaction is rapidly stopped, a cellulose ester (particularly, a mixed fatty acid cellulose ester) with few impurities can be obtained even if the degree of polymerization is high. In particular, even when the acyl group substitution degree is increased by using a plurality of acylating agents having different reactivity (especially acetic anhydride and an acylating agent having a low reactivity of 3 or more carbon atoms), the degree of polymerization is high and insoluble components and A mixed fatty acid cellulose ester with less bright spot foreign matter can be produced. Further, an acylating agent (particularly an acylating agent having 3 or more carbon atoms) having low diffusibility or permeability to the crystalline region of cellulose is used, and cellulose having a high degree of crystallinity (particularly, a high degree of crystallinity and a high degree of polymerization). Even if the cellulose is esterified, a homogeneous cellulose ester (particularly, a mixed fatty acid cellulose ester) with few foreign substances can be produced. Further, when cellulose having a high degree of crystallinity is used as a cellulose source, the releasability of cellulose ester from a support (such as a metal support) can be improved. Cellulose esters (such as mixed fatty acid cellulose esters) can be stretched and are suitable for preparing optical films (such as retardation films, optical compensation films, and polarizing plate protective films). In addition, cellulose esters (such as mixed fatty acid cellulose esters) have a small dimensional change with respect to a change in humidity, a small change in in-plane retardation and out-of-plane retardation, and prepare an optical film that may be stretched. Also suitable for.

  The method of the present invention includes an activation step for activating cellulose, a step of esterifying the activated cellulose with an acylating agent, and a step of saponifying or hydrolyzing the produced cellulose ester and aging. It consists of Moreover, although the general manufacturing method of mixed fatty acid cellulose ester is described in "Fiber-based resin" (Kazuo Utada, Kaoru Marusawa publication, Nikkan Kogyo Shimbun), this invention is demonstrated below.

[Activation process]
In the activation step, cellulose is treated with an activator to activate the cellulose. Usually, since raw material cellulose is often supplied in the form of a sheet, the cellulose is pulverized in a dry manner and activated (or pretreated).

[cellulose]
As the raw material cellulose, various cellulose sources such as wood pulp (coniferous pulp, hardwood pulp) and cotton linter pulp can be used. These pulps usually contain foreign components such as hemicellulose. Therefore, in the present specification, the term “cellulose” is used in the sense that it also contains different components such as hemicellulose.

  As wood pulp, at least one selected from hardwood pulp and softwood pulp can be used, and hardwood pulp and softwood pulp may be used in combination. Also, linter pulp (such as refined cotton linter) and wood pulp may be used in combination. In the present invention, cellulose having a high degree of polymerization, such as linter pulp, particularly cotton linter pulp, can be exemplified, and it is preferable to use cellulose composed of at least linter pulp. The α-cellulose content, which is an index of the crystallinity of cellulose, is 98% or more (for example, 98.5 to 100%, preferably 99 to 100%, more preferably about 99.5 to 100%).

Cellulose has a high molecular weight and degree of polymerization, such as a viscosity average molecular weight of about 15 × 10 ⁴ to 50 × 10 ⁴ , an average degree of polymerization of 500 to 3000, preferably 600 to 2500, and more preferably about 700 to 2000. A preferable average degree of polymerization of cellulose is about 1000 to 3000, and pulp having an average degree of polymerization of about 600 to 1000 can also be used. The average molecular weight and average polymerization degree of cellulose are described in EOKvaemer, WDLansing, J. Phys. Chem., 39, 164 (1935). In addition, you may adjust the said polymerization degree range by using the said linter pulp and wood pulp together.

  In addition, acetic anhydride used as an acylating agent for the synthesis of cellulose acetate has a high permeability or diffusibility to the crystalline region of cellulose. Therefore, in the case of acetic anhydride, there is not much problem. However, when an acylating agent having 3 or more carbon atoms is used, uniform esterification becomes difficult because the permeability to the crystalline region of cellulose is low. In particular, when the quantitative ratio of the acylating agent having 3 or more carbon atoms is large, it becomes difficult to obtain a cellulose ester having a uniform composition. In particular, linter pulp has a dense crystal structure, and carboxylic anhydride as an acylating agent is difficult to diffuse or penetrate. Therefore, when esterification is performed by combining linter pulp and an acylating agent having 3 or more carbon atoms, it becomes difficult to obtain a cellulose ester such as a mixed fatty acid ester having a uniform composition.

  It is known that cellulose usually contains some carboxyl groups in a state of being bonded to cellulose molecules and / or hemicellulose molecules. This carboxyl group content (concentration) can be quantified by various methods such as TAPPI Standard T237 om-83. The carboxyl group content in the pulp (cellulose) defined in the present invention is a value determined by this TAPPI Standard T237 om-83.

  Although there is no restriction | limiting in particular in the carboxyl group content of a cellulose, As a preferable form, cellulose with little carboxyl group content can be used, and the carboxyl group content (concentration) in the cellulose ester produced | generated by esterification can also be reduced. In the case of hardwood pulp, the carboxyl group content of cellulose is 1 meq / 100 g or less (for example, 0 to 1 meq / 100 g, particularly 0.001 to 1 meq / 100 g), preferably 0.8 meq / 100 g or less (for example, 0.001 to 0.001). 0.8 meq / 100 g), more preferably 0.6 meq / 100 g or less (for example, 0.001 to 0.6 meq / 100 g). In linter pulp, the carboxyl group content is even smaller. Particularly preferably, the carboxyl group content is preferably 0.7 meq / 100 g or less (for example, 0.001 to 0.7 meq / 100 g), more preferably 0.4 meq / 100 g or less (for example, 0.001 to 0.4 meq). / 100 g).

  The method for producing cellulose having a low carboxyl group content as described above is not particularly limited. For example, a method for suppressing oxidation by a bleaching agent in a pulp bleaching step (for example, bleaching under mild conditions), a specific linter pulp is used. Obtained by a method of selecting, a method of reducing the content of hemicellulose, a method of extracting a carboxyl group-containing component in the pulp bleaching step, a method of producing pulp using raw materials having low carboxyl groups (wood tree species, linter species, etc.), etc. Can do.

[Activator]
As the activator for activating cellulose, a solvent for acylation reaction (acylation solvent) is usually used. As the acylation solvent, organic carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid are used. And an aliphatic carboxylic acid (linear or branched C _1-6 alkanoic acid) such as valeric acid. These activators can be used alone or in combination of two or more. Among these activators (organic carboxylic acid), more easily penetrates or diffuses into the cellulose interior molecule is small, because the more effectively it is possible to activate the cellulose, C _1-4 alkanoic acid, especially readily available C _1-2 alkanoic acid (formic acid, acetic acid) is preferable from the viewpoints of properties and recoverability.

  In the activation treatment, an aqueous medium containing water is used as the activator. This aqueous medium may be an aqueous medium containing an organic carboxylic acid. In consideration of substituting the aqueous medium from the cellulose raw material with the carboxylic acid used in the reaction prior to the reaction following the activation treatment, it is economical. It is preferable to use many organic carboxylic acids. On the other hand, when the cellulose is in an absolutely dry state, when the organic carboxylic acid concentration exceeds 90%, the activation effect decreases rapidly. For example, when 100% of the organic carboxylic acid is used, the cellulose ester targeted by the present invention is used. Is often not obtained. Therefore, a mixed liquid of water and organic carboxylic acid is usually used as the activator. The water content in the activator is 0 to 50% by weight, preferably 1 to 30% by weight, and more preferably about 5 to 25% by weight. In many cases, cellulose actually contains water at a ratio of about 3 to 12% by weight (for example, 5 to 10% by weight).

  The activation process is not limited to a single activation process, and may be composed of a plurality of activation processes. In a single activation step, the cellulose may be treated with at least an activator, and the cellulose may be treated with an activator containing an acylation catalyst (a strong acid such as sulfuric acid). The plurality of activation steps can be performed using an activator, an activator including an acylation catalyst, and an activator having different acylation catalyst concentrations. For example, the acylating catalyst may be composed of a first activating step for activating cellulose with an activating agent and a second activating step for activating cellulose with an activating agent containing an acylating catalyst. You may comprise in the 1st process of processing cellulose with the activator with a low density | concentration, and the 2nd process of processing cellulose with the activator with the high density | concentration of an acylation catalyst.

  The amount of the activator used is, for example, about 25 to 150 parts by weight, preferably 30 to 125 parts by weight, and more preferably about 50 to 100 parts by weight (for example, 70 to 100 parts by weight) with respect to 100 parts by weight of cellulose. It may be.

  The activation treatment may be performed by treating cellulose with an activator, spraying the activator on cellulose, or immersing cellulose in the activator. Usually, raw material cellulose is often added to the activator to form a slurry. The activation treatment temperature can be selected from the range of 0 ° C to 100 ° C. In order to perform the activation treatment without applying an industrial load, it is usually 10 ° C to 40 ° C, preferably about 15 ° C to 35 ° C. It is. The activation treatment time can be selected in the range of 0.1 hours to 72 hours, and is usually about 0.1 hours to 3 hours, preferably about 0.2 hours to 2 hours.

[Esterification process]
After the activation treatment of cellulose, the esterification step is performed by esterifying cellulose with an acylating agent having at least 2 carbon atoms (for example, an acylating agent having an alkylcarbonyl group) in the presence of an acylation catalyst. be able to. The acylation catalyst is often composed of a strong acid, particularly sulfuric acid. The amount of the acylation catalyst (particularly, sulfuric acid catalyst) is usually 1 to 15 parts by weight (for example, 3 to 14 parts by weight, preferably 5 to 13 parts by weight, more preferably 7 parts by weight with respect to 100 parts by weight of cellulose. 5 to 12.5 parts by weight), but in a preferred embodiment of the present invention, it is 2 to 20 parts by weight, preferably 4 to 15 parts by weight, more preferably about 5 to 12 parts by weight.

The acylating agent may be an organic acid halide such as acetic acid chloride, propionic acid chloride, butyric acid chloride, but is usually an acid anhydride of an alkanecarboxylic acid having 2 or more carbon atoms, such as acetic anhydride or propionic anhydride. C _2-6 alkanecarboxylic acid anhydrides such as butyric anhydride and valeric anhydride can be used. In the present invention, since acylation can be efficiently carried out using an acylating agent that is less reactive than acetic anhydride, the acylating agent may be an acid anhydride of an alkanecarboxylic acid having 3 or more carbon atoms, alone or in combination. You may use it in combination.

As the acylating agent, an acid anhydride of an alkanecarboxylic acid having at least 2 carbon atoms may be used, and a plurality of acid anhydrides selected from acid anhydrides corresponding to C _2-6 alkanecarboxylic acids and having different carbon numbers are used. You may use thing. For example, propionic anhydride and butyric anhydride may be used in combination. Preferred acylating agents are C _2-4 alkanecarboxylic anhydrides, such as acetic anhydride alone, a combination of acetic anhydride and propionic anhydride, a combination of acetic anhydride and butyric anhydride, acetic anhydride, propionic anhydride and butyric anhydride It is a combination. In particular, acetic anhydride alone, a combination of acetic anhydride and propionic anhydride, and a combination of acetic anhydride and butyric anhydride are preferable.

When producing a mixed fatty acid cellulose ester using a plurality of acylating agents, in the esterification step, a plurality of acylating agents may coexist in the reaction system, and cellulose is esterified with a specific acylating agent. Then, the cellulose may be esterified with another acylating agent. In the production of mixed fatty acid cellulose esters, transesterification can be achieved by using highly reactive acylating agents (especially acetic anhydride) and organic carboxylic acids (especially acetic acid) in the esterification step and subsequent steps (ripening step, etc.). By the reaction, another acyl group (C _3-6 acyl group) is substituted with an acetyl group. Therefore, in order to introduce an acetyl group, it is not always necessary to use acetic anhydride, and the reaction may be carried out in the presence of acetic acid.

  The amount of the acylating agent used in the esterification step is, for example, 1.1 to 4 equivalents, preferably 1.1 to 2 equivalents, more preferably about 1.3 to 1.8 equivalents relative to the hydroxyl group of cellulose. is there.

  In the acylation step, an acylation solvent (organic carboxylic acid such as acetic acid, propionic acid, butyric acid) is usually used as a solvent or diluent. The amount of the acylating solvent (organic carboxylic acid) used is, for example, about 50 to 700 parts by weight, preferably 100 to 600 parts by weight, and more preferably about 200 to 500 parts by weight with respect to 100 parts by weight of cellulose. In addition, acylation reaction can be performed on conventional conditions, for example, 0-50 degreeC, Preferably it is 5-35 degreeC, More preferably, it is about 10-30 degreeC.

[Esterification reaction stopping step]
In the present invention, after the esterification reaction is completed, a reaction terminator is added to the reaction system at a specific quantitative ratio in order to deactivate the quenching agent remaining in the reaction system. In addition, when cellulose triacylate is generated by reaction with acylating agent, the reaction system becomes uniform and then the uniform system is maintained. Therefore, the esterification reaction is completed when the reaction system forms a uniform dope (solution). Can be determined. More precisely, since an acylation catalyst exists in the esterification reaction system, in the esterification reaction system, the esterification reaction in which the substitution degree of the acyl group with respect to cellulose increases and the depolymerization reaction in which the glycosidic bond is cleaved compete. However, the esterification reaction occurs preferentially. Therefore, when a uniform reaction system is formed, it can be determined that the esterification reaction has ended. The completion (or end point) of the esterification reaction is also the start (or start point) of the hydrolysis reaction.

  The reaction terminator need only be capable of deactivating the acylating agent and contains at least water. The reaction terminator may be composed of water and at least one selected from acylating solvents (such as organic carboxylic acids) and neutralizing agents. More specifically, examples of the reaction terminator include water alone, a mixture of water and organic carboxylic acid, a mixture of water and neutralizing agent, a mixture of water, organic carboxylic acid and neutralizing agent, and the like. it can.

  Examples of the neutralizing agent include an acylation catalyst (particularly sulfuric acid) or a base capable of neutralizing a part of the acylating agent, for example, an alkali metal compound (for example, hydroxide such as sodium hydroxide or potassium hydroxide, sodium carbonate) And carbonates such as potassium carbonate, organic acid salts such as sodium acetate and potassium acetate), alkaline earth metal compounds (eg, hydroxides such as calcium hydroxide, carbonates such as calcium carbonate, organics such as calcium acetate) Acid salt). These bases may be used alone or in combination of two or more.

  In a preferred embodiment, the reaction terminator contains a neutralizing agent in a proportion that neutralizes a part (especially a very small part) of the acylation catalyst (particularly sulfuric acid), or does not contain a neutralizing agent. A preferable reaction terminator may be water alone, but is a mixed solution of water and an acylating solvent (such as an organic carboxylic acid such as acetic acid) in order to prevent precipitation of the produced cellulose ester. When such a reaction terminator is used, the acylation catalyst can be left at a relatively high concentration.

  Conventionally, it has been considered that a significant increase in temperature due to the decomposition of an acylating agent such as acetic anhydride when the esterification reaction is stopped would lead to a decrease in the molecular weight of the cellulose ester. It was common to add a reaction terminator gradually while heating. On the other hand, according to the study by the present inventors, the depolymerization reaction proceeds remarkably in a low moisture content reaction system in the process of transition from esterification to aging, and an acylating agent (an acid anhydride). When hydrolyzed in a short time and deactivated, the water content in the system is increased and the acidity of the acylation catalyst (especially sulfuric acid) is rapidly reduced, thereby suppressing the decrease in the degree of polymerization. I found it. And by utilizing this fact and adjusting the esterification time appropriately, when the amount of low esterified cellulose (unreacted cellulose and cellulose ester having low solubility) is the same as the conventional method, the degree of polymerization is high. A cellulose ester can be produced, and when obtaining a cellulose ester having the same degree of polymerization as that of the conventional method, the amount of low esterified cellulose can be reduced, and the contradictory properties can be achieved. The method for adding a reaction terminator of the present invention was found as a result of detailed investigation of the polymerization degree lowering behavior of the cellulose ester in the reaction termination operation. In order to suppress the depolymerization reaction, the esterification reaction was stopped. It is designed for a short time.

  When cellulose is esterified by increasing the proportion of the acylating agent having a large carbon number, particularly the acylating agent having a large carbon number in the acylating agent, these acylating agents have a lower diffusion rate than acetic anhydride, The reaction proceeds without sufficiently relaxing the crystalline region of cellulose, and insoluble matter is generated. In order to solve this problem, if the amount of acylation catalyst (particularly sulfuric acid catalyst) added in the esterification step is increased and the addition rate of the reaction terminator is increased in the reaction termination step, an excess acylating agent (anhydrocarbon anhydride) is obtained. Acid, etc.) can be quickly removed from the reaction system, the water content in the system can be increased, and the acidity of the acylation catalyst (especially sulfuric acid) can be reduced quickly, thereby reducing the low esterified cellulose and maintaining a high degree of polymerization. Thus, cellulose esters (such as mixed fatty acid esters) can be obtained. The amount of the neutralizing agent used to partially neutralize the acylation catalyst is 0.1 to 0.9 equivalent, preferably 0.2 to 0.00, per 1 equivalent of the acylation catalyst (particularly, sulfuric acid catalyst). It can be selected from the range of about 8 equivalents, more preferably about 0.3 to 0.7 equivalents.

  The addition rate of the esterification reaction terminator is 0.3 to 10 equivalents / minute (for example, 0.5 to 9) with respect to 1 mol of the acylating agent (particularly acid anhydride such as acetic anhydride) remaining in the reaction system. Equivalents / minute), preferably 0.7-8 equivalents / minute (e.g. 1-7 equivalents / minute), more preferably 1.5-6 equivalents / minute (e.g. 1.7-5 equivalents / minute), In particular, it may be about 2 to 5 equivalents / minute. In order to deactivate at least the acid anhydride, the esterification reaction terminator is 0.5 to 5 equivalents / minute (for example, 1.5 to 4 equivalents / minute) with respect to 1 mole of the acid anhydride remaining in the reaction system. In many cases, it is added at a rate of about min. The amount of acylating agent remaining in the reaction system is calculated by converting the amount of cellulose used to glucose units, and the number of glucose units having three hydroxyl groups (number of glucose units × 3 mol) as the number of moles of acylating agent used. Can be calculated as the number of remaining moles.

  The addition time of the esterification reaction terminator to the reaction system can be selected according to the capacity of the reaction vessel (reaction mixture amount) and the like, for example, from about 0.1 minutes (about 6 seconds) to about 3 minutes. You can choose. A preferable addition time is 15 seconds to 2 minutes and 30 seconds, more preferably about 30 seconds to 2 minutes, and usually within 1 minute. In addition, in order to add a reaction terminator rapidly, an auxiliary tank can be provided, and it can also be added in a short time from this auxiliary tank to a reaction system. These addition times can also be applied in industrial production equipment, for example, 5 to 25 parts by weight of a reaction terminator (for example, 7.5 to 20 parts by weight, preferably about 1000 parts by weight of the reaction mixture in the reaction system). The addition time for adding about 10 to 15 parts by weight) may be used.

  Furthermore, if the reaction system generates heat with the addition of the reaction terminator, the cellulose chain may be cleaved as the temperature rises. Therefore, the addition of the reaction terminator to the reaction system is preferably performed at a temperature of about 100 ° C. or less (for example, 10 to 75 ° C., preferably 15 to 60 ° C., more preferably 20 to 50 ° C.).

[Saponification aging process]
After the esterification reaction is stopped, the produced cellulose ester is saponified and ripened (deacylated or hydrolyzed) to obtain a cellulose ester with adjusted acylation degree and substitution degree distribution. In this reaction, a part of the acylation catalyst (especially sulfuric acid) used for esterification may be neutralized, and the remaining acylation catalyst (especially sulfuric acid) may be used as an aging catalyst. Sulfuric acid) may be neutralized. In the saponification aging reaction (deacylation reaction), if necessary, another acid catalyst (proton acid, Lewis acid) may be used, or a part of the acylation catalyst (particularly sulfuric acid) may be used. It may be neutralized and saponified and aged.

  The sulfuric acid component as the saponification ripening catalyst may be residual sulfuric acid remaining in the reaction system, for example, free sulfuric acid, or bonded sulfuric acid bonded to cellulose (sulfuric acid bonded in the form of sulfate ester). May be.

  The deacylation reaction (aging or hydrolysis step) can be performed, for example, at a temperature of 20 ° C to 90 ° C, preferably 25 ° C to 80 ° C, more preferably about 30 ° C to 70 ° C. The deacylation reaction may be performed in an inert gas atmosphere or an air atmosphere.

[Stop aging reaction]
After producing a predetermined cellulose ester, the aging reaction is stopped. That is, after the deacylation reaction, a neutralizing agent composed of the base (preferably the alkali metal compound and / or the alkaline earth metal compound, particularly at least a calcium compound) may be added as necessary.

  The reaction product (a dope containing a cellulose ester) may be added to a precipitation solvent (water, aqueous acetic acid solution, etc.) to separate the produced cellulose ester, and free metal components and sulfuric acid components may be removed by washing or the like. In addition, a neutralizing agent can also be used in the case of washing with water.

  By such a method, the production | generation of an insoluble matter or a low solubility component (unreacted cellulose, low esterified cellulose, etc.) can be reduced, suppressing the fall of the polymerization degree of a cellulose ester.

[Cellulose ester]
The cellulose ester of the present invention is substituted with at least an acyl group having 2 or more carbon atoms, and is a cellulose ester corresponding to the acylating agent, such as cellulose triacylate (for example, cellulose triacetate, cellulose tripropionate, cellulose triacetate). Cellulose tri C _2-6 acylates such as butyrate), mixed fatty acid cellulose esters (eg, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate propionate butyrate, cellulose acetate fats such as cellulose acetate hexanoate) Group C _3-6 acylate, cellulose mixed C _3-6 acylate such as cellulose propionate butyrate) and the like. In the mixed fatty acid cellulose ester, the acyl group often has an acetyl group and an acyl group having 3 or more carbon atoms. Such a cellulose ester can be obtained by the method described above.

Preferred mixed fatty acid cellulose esters are preferably mixed fatty acid cellulose esters having at least an acetyl group (for example, cellulose acetate C _3-6 acylate), particularly cellulose acetate propionate and cellulose acetate butyrate. Such a cellulose ester not only has high film formability by the casting method and melt extrusion molding method, but can improve stretchability, and therefore can impart various properties to the film.

  The total average substitution degree of the entire acyl group (total average substitution degree of acyl groups substituted at the 2, 3 and 6 positions of glucose units constituting cellulose) is within a range where high moisture resistance can be imparted, for example, 2.5 to 3 (For example, about 2.5 to 2.9) can be selected from 2.6 to 2.99, preferably 2.65 to 2.98, more preferably about 2.7 to 2.97. Also good. The total average substitution degree of the entire acyl group may be about 2.60 to 2.96 (eg, 2.64 to 2.95).

  In the mixed fatty acid cellulose ester, the substitution degree ratio of different acyl groups (especially acyl groups having different carbon numbers) can be appropriately selected depending on the use, for example, in the cellulose mixed acid ester (cellulose acetate acylate) having at least an acetyl group The average substitution degree of the acetyl group may be 0 (about 0 to 1.9), 0.01 to 1.9, preferably 0.3 to 1.5, and more preferably 0.5 to 1. .3, particularly about 0.7 to 1.2. In particular, in cellulose acetate acylate, if the degree of substitution of the acetyl group is relatively large, it is effective in reducing unreacted cellulose, but the stretchability tends to decrease. Moreover, when the average substitution degree of an acetyl group is small, it is disadvantageous for reducing unreacted cellulose, but stretchability is improved. Therefore, the average substitution degree of an acetyl group and another acyl group can be selected according to the use of a cellulose ester.

  The acyl group other than the acetyl group is, for example, about 0.60 to 2.90, preferably 1.00 to 2.5, more preferably 1.30 to 2.00, and particularly about 1.50 to 1.90. May be.

  That is, in the mixed fatty acid cellulose ester, the substitution degree (A) of the acetyl group and the substitution degree (B) of the alkylcarbonyl group having 3 or more carbon atoms often satisfy the following formulas (I) to (III).

2.50 ≦ A + B ≦ 2.90 (I)
0.00 ≦ A ≦ 1.90 (II)
0.60 ≦ B ≦ 2.90 (III)
In the cellulose acetate acylate, the ratio (molar ratio) between the acetyl group and the acyl group having 3 or more carbon atoms is the former / the latter = 50/50 to 1/99 (for example, 55/45 to 2/98). 30/70 to 3/97, more preferably about 20/80 to 5/95 (for example, 25/75 to 10/90).

The average degree of substitution (degree of acylation) can be measured by a conventional method. For example, the degree of acetylation (degree of acetylation) is in accordance with the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate etc.). It can be calculated by measuring the number of moles of acyl groups per unit weight and further measuring the ratio of each acyl group liberated by saponification by liquid chromatography. The acylation degree can also be analyzed by ¹ H-NMR and ¹³ C-NMR.

  And the cellulose ester of this invention has the characteristics that the fall of a polymerization degree is small and there is also little by-product amount of an insoluble matter. That is, the viscosity average polymerization degree of cellulose ester (including mixed fatty acid ester) can be selected from a range of 100 or more (for example, 120 to 800), for example, 150 to 500 (for example, 160 to 400), preferably 190 to It may be 400 (for example, 200 to 400), more preferably 250 to 350 (for example, 270 to 330), particularly about 290 to 320. In particular, the viscosity average polymerization degree of the mixed fatty acid cellulose ester is, for example, a viscosity average polymerization degree of 120 to 400, preferably 130 to 350 (for example, 140 to 300), more preferably about 150 to 250 (for example, 170 to 250). It may be. In the mixed fatty acid cellulose ester, when the degree of acetyl substitution is relatively large, a cellulose ester having a large average degree of polymerization tends to be obtained.

The viscosity average degree of polymerization can be measured by Uda et al.'S limiting viscosity method (Kazuo Uda, Hideo Saito, Journal of Textile Science, Vol. 18, No. 1, pages 105-120, 1962). The solvent can be selected according to the degree of substitution of cellulose ester (including mixed fatty acid cellulose ester). For example, a cellulose ester is dissolved in a mixed solution of methylene chloride / methanol = 9/1 (weight ratio) to prepare a solution having a predetermined concentration c (2.00 g / L), and this solution is injected into an Ostwald viscometer. Measure the time t (seconds) for the solution to pass between the viscometer markings at 25 ° C. On the other hand, for the mixed solvent alone, the passage time t ₀ (seconds) is measured in the same manner as described above, and the viscosity average polymerization degree can be calculated according to the following formula.

η _rel = t / t ₀
[Η] = (lnη _rel ) / c
DS = [η] / (6 × 10 ⁻⁴ )
(Where t is the solution transit time (second), t ₀ is the solvent transit time (second), c is the cellulose triacetate concentration (g / L), η _rel is the relative viscosity, and [η] is the intrinsic viscosity. DS represents the average degree of polymerization).

  The cellulose ester of the present invention has a remarkably low content of foreign matter (non-soluble component). In the present specification, such an insoluble component or insoluble component (fine foreign matter) is defined as a component that does not dissolve in a mixed solvent of methylene chloride / methanol (weight ratio) = 9/1. The details of such insoluble components are not clear and are not particularly limited unless dissolved in the mixed solvent, but usually do not react in the synthesis of raw material cellulose or cellulose-derived by-products, mainly cellulose esters. Examples thereof include unreacted cellulose, low-substituted cellulose ester, a bond-formation product in which cellulose esters are bonded to each other via bonded sulfuric acid and a metal component (such as calcium), and a mixture thereof.

  Insoluble component amount (insoluble matter amount) with respect to a mixed solution of methylene chloride and methanol (methylene chloride / methanol = 9/1 (weight ratio)) is 0.1 wt% or less (for example, 0 to 0.09 wt%, preferably 0.0001 to 0.07% by weight, more preferably 0.0005 to 0.05% by weight, particularly about 0.001 to 0.01% by weight). The amount of insoluble matter in the cellulose ester can be measured as follows.

  When cellulose ester is synthesized using sulfuric acid as a catalyst, the cellulose ester usually contains a remaining sulfuric acid component as described in “Acetic acid fiber” (published by Wadano Motomaru Maruzen Co., Ltd.). Most of the remaining sulfuric acid component is bound sulfuric acid bonded to cellulose in the washed cellulose ester. The bound sulfuric acid is preferably as little as possible because it can be a by-product of a cellulose ester bond due to ionic bonds with the metal component, resulting in fine foreign matter. However, simply reducing the amount of catalyst sulfuric acid used tends to produce unreacted cellulose, low-substituted cellulose esters, and the like, and thus the amount of insoluble components cannot be reduced. Therefore, in this invention, an insoluble component is reduced significantly by adjusting manufacturing conditions.

[Heat-resistant treatment]
In the cellulose ester production process (for example, the final stage of the production process), it is desirable to perform heat treatment. That is, the cellulose ester usually undergoes hydrolysis in an environment where heat acts and moisture exists. Therefore, stabilizers such as alkali metals (lithium, potassium, sodium, etc.) or salts or compounds thereof, alkaline earth metals (calcium, magnesium, strontium, barium, etc.) are used to improve thermal stability and wet heat stability. Alternatively, by adding a salt thereof or a compound thereof, the sulfate group may be inactivated and heat resistant stability may be imparted. The stabilizer content may be large excess with respect to the residual sulfuric acid component.

[Cellulose ester solution (dope)]
The cellulose ester may be dissolved in a solvent to prepare a cellulose ester solution (dope). Examples of the solvent include organic solvents such as halogenated hydrocarbons (such as methylene chloride), ketones (such as acetone), esters (such as methyl acetate), and the like. The cellulose ester of the present invention is not only excellent in solubility in a halogen-containing solvent such as methylene chloride, but can also be prepared using a non-halogen solvent.

  The cellulose ester solution of the present invention can be prepared using a dope preparation method and apparatus in a general solvent cast method. A relatively low concentration solution can be obtained by stirring at room temperature. In a high-concentration solution, it is preferable to prepare it by stirring under pressure and heating conditions. Specifically, the cellulose ester and the solvent are put in a pressure vessel and sealed, and stirred while heating to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 60 ° C. or higher, preferably 80 ° C. to 110 ° C.

  Additives may be added to the cellulose ester solution depending on its use. Examples of the additive include plasticizers, ultraviolet inhibitors and deterioration inhibitors (for example, antioxidants, peroxide decomposers, radical inhibitors, metal deactivators, acid scavengers, amines).

  Examples of plasticizers include phosphate ester plasticizers such as triphenyl phosphate (TPP), diphenylbiphenyl phosphate, tricresyl phosphate (TCP), phthalic acid plasticizers such as dioctyl phthalate (DOP), and O-acetyl citrate. Citric acid plasticizers such as tributyl acid (OACTB) and acetyl triethyl citrate are included. The cellulose ester of the present invention has an advantage that a small amount of plasticizer may be added as compared with the conventional cellulose ester. For this reason, even if the amount of the plasticizer is 15% by weight or less, a plastic effect can be obtained.

[paint remover]
The optical film of the present invention comprises at least one acid (citric acid and the like) having an acid dissociation index pka of 1.93 to 4.50 in an aqueous solution, an alkali metal salt of the acid, and an alkaline earth metal of the acid At least one selected from salts can be included as a release agent. The release agent can be added before casting the cellulose ester solution, and may be contained in the cellulose ester.

[Production of cellulose ester film]
As a method and equipment for producing a cellulose ester film, a solution casting film forming method and a solution casting film forming apparatus for use in conventional cellulose triacetate film production can be used. For example, the cellulose ester solution is cast on a smooth band or drum as a support. A plurality of cellulose ester films may be produced by sequentially casting or co-casting a plurality of cellulose ester solutions.

  The mixed fatty acid cellulose ester is also excellent in melt moldability. Therefore, not only the solution casting method but also a melt casting method, an extrusion molding method, and the like can be used, which is environmentally useful.

[Stretching of optical film]
The cellulose ester film of the present invention may be stretched. The stretching method is not particularly limited, and uniaxial stretching or biaxial stretching can be adopted for stretching the film. The stretch ratio of the film (ratio of increase due to stretching relative to the original length) may be 10 to 600%, preferably 10 to 300% (for example, 15 to 100%), more preferably 10 to 70. % (For example, 20 to 50%), particularly about 10 to 30%. In addition, a draw ratio can be selected in consideration of film characteristics (such as optical characteristics). A general optical film may have a stretch ratio of 20 to 40% (for example, 25 to 35%).

[Molded body]
The molded body composed of cellulose ester may be a two-dimensional form such as a fiber, a two-dimensional form such as a film or a sheet, or a three-dimensional form such as a curve or a three-dimensional shape. The molded body is usually a film or a sheet in many cases. In such a molded body (especially a film), dimensions and optical characteristics may change depending on humidity while expressing a wide range of in-plane retardation and out-of-plane retardation which have been difficult to realize in the past. Absent.

  Since the cellulose ester of the present invention is excellent in optical properties, an optical film such as a polarizing plate protective film, a retardation film, an optical compensation film, a color filter, a viewing angle widening film, an antireflection film, a film of a photosensitive material, etc. Can be used as In particular, it is useful as an optical film selected from a protective film for a polarizing plate, a retardation film, and an optical compensation film. Referring to the optical compensation film, the cellulose ester film of the present invention includes a support for an optical compensation sheet of a VA type liquid crystal display device having a VA mode liquid crystal cell, an OCB type liquid crystal display device having an OCB mode liquid crystal cell, or a HAN mode. It is preferably used as a support for an optical compensation sheet of a HAN type liquid crystal display device having a liquid crystal cell and an optical compensation sheet for an ASM type liquid crystal display device having a liquid crystal cell of ASM (Axially Symmetric Aligned Microcell) mode.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In each example, the chemical properties and physical properties of the cellulose ester, its solution and film were measured and calculated as follows.

(1) Degree of substitution of cellulose ester The DSester (degree of acyl substitution) of cellulose ester can be measured by ¹ H-NMR (nuclear magnetic resonance) method using deuterated chloroform (CDCl ₃ ) as a measurement solvent.

(2) Amount of insoluble matter
[Insoluble matter amount]
In a mixed solvent of methylene chloride: methanol = 9: 1 (weight ratio), the cellulose ester is dissolved at a solid content concentration of 2% by weight, and the obtained solution is filtered using a glass filter (pore size 5 to 10 μm). . As a glass filter, “G-4” manufactured by Mutual Science Glass Co., Ltd. can be used. The residue adhering to the filter and the dope are washed with a mixed solvent of methylene chloride: methanol = 9: 1 (weight ratio). The filtration residue is dried together with the glass filter until a constant weight is obtained. The weight of the glass filter before and after filtration is measured, and the amount of insoluble matter is calculated from the following formula (W1 is the weight of the glass filter before filtration (g), W2 is the weight of the glass filter after filtration (g), and S is Cellulose ether acetate weight (g) is shown).

Insoluble matter amount (% by weight) = [(W2-W1) / S] × 100
(3) Degree of polymerization Using a mixed solution of methylene chloride / methanol = 9/1 (weight ratio), the viscosity average degree of polymerization was measured by the intrinsic viscosity method.

Examples 1-3 and Comparative Examples 1-3
The cellulose is activated in two stages under the conditions shown in Table 1, and after esterification using acetic anhydride, butyric anhydride and / or propionic anhydride in the presence of a sulfuric acid catalyst, an acetic acid / water mixture is used as a reaction system. Addition to stop the esterification reaction, saponification aging, stop the reaction by adding magnesium acetate / acetic acid / water mixture, inject the resulting reaction mixture into water / acetic acid solution to precipitate the cellulose ester The cellulose ester was obtained by washing.

  The results are shown in Table 1.

  As is apparent from Table 1, compared to the comparative example, in the examples, cellulose esters having a high degree of polymerization can be obtained even if the degree of substitution of the butyryl group or propionyl group is large.

Claims (15)

A step of activating cellulose with an activating agent, a step of esterifying cellulose with an acylating agent containing acetic anhydride and an anhydride of an alkanecarboxylic acid having 3 or more carbon atoms in the presence of an acylating catalyst, and a produced cellulose ester Mixed fatty acid cellulose ester comprising a step of saponifying and saponifying, and a precipitation step of separating the mixed fatty acid cellulose ester containing an acetyl group and an alkylcarbonyl group having 3 or more carbon atoms by adding the saponified and aged cellulose ester to a precipitation solvent A mixed fatty acid cellulose ester in which an esterification reaction terminator is added at a rate of 0.3 to 10 equivalents / minute with respect to 1 mol of the acylating agent remaining in the reaction system after the esterification step Manufacturing method.   The method according to claim 1, wherein the reaction terminator contains at least water.   The process according to claim 1, wherein the esterification reaction terminator is added to the reaction system in 0.1 to 3 minutes.   The process according to claim 1, wherein the reaction terminator is added to the reaction system at a temperature of 100 ° C or lower.   The method of claim 1, wherein the activator comprises an organic carboxylic acid and the acylation catalyst comprises sulfuric acid. The α-cellulose content is 98% or more, cellulose having an average polymerization degree of 1000 to 3000 is used, and an acylating agent composed of at least a C _3-6 alkanecarboxylic acid anhydride is used. Method.   The method according to any one of claims 1 to 6, wherein the cellulose is a purified cotton linter. A first activation step of activating cellulose with at least one activator selected from C _1-2 alkanoic acid, and at least one activator selected from sulfuric acid and C _1-5 alkanoic acid A second activation step for activating cellulose, and a plurality of acids selected from acid anhydrides corresponding to C _2-6 alkanecarboxylic acids and having different numbers of carbon atoms in the presence of sulfuric acid. Esterification with an anhydride to produce a mixed fatty acid cellulose ester, and an esterification reaction stopper added at a rate of 0.5 to 5 equivalents / minute per mole of acid anhydride remaining in the reaction system The method according to claim 1, further comprising a step of deactivating at least the acid anhydride and a ripening step of aging the mixed fatty acid cellulose ester produced in the presence of sulfuric acid or residual sulfuric acid. A step of activating cellulose with an activating agent, a step of esterifying cellulose with an acylating agent containing acetic anhydride and an anhydride of an alkanecarboxylic acid having 3 or more carbon atoms in the presence of an acylating catalyst, and a produced cellulose ester A saponification and aging step, and a saponification and aging cellulose ester is added to a precipitation solvent to separate a mixed fatty acid cellulose ester containing an acetyl group and an alkylcarbonyl group having 3 or more carbon atoms. After that, an esterification reaction terminator is added at a rate of 0.3 to 10 equivalents / minute with respect to 1 mol of the acylating agent remaining in the reaction system, while suppressing a decrease in the degree of polymerization of the mixed fatty acid cellulose ester. A method for reducing the generation of insoluble matter.   An acyl group containing an acetyl group and an alkylcarbonyl group having 3 or more carbon atoms is substituted, the average substitution degree of the entire acyl group is 2.5 to 3, and the average substitution degree of the acyl group at the 6-position of the glucose unit is 0.7 to 1 is a mixed fatty acid cellulose ester, wherein the alkylcarbonyl group having 3 or more carbon atoms has an average substitution degree of 1.30 to 2.00, a viscosity average polymerization degree of 120 to 400, a mixed solution of methylene chloride and methanol Mixed fatty acid cellulose ester in which the amount of insoluble components in (methylene chloride / methanol = 9/1 (weight ratio)) is 0.1% by weight or less.   The mixed fatty acid cellulose ester according to claim 10, which has an acetyl group and an alkylcarbonyl group having 3 to 6 carbon atoms. The mixed fatty acid cellulose ester according to claim 10, wherein the average substitution degree (A) of the acetyl group and the average substitution degree (B) of the alkylcarbonyl group having 3 or more carbon atoms are mixed fatty acid cellulose esters satisfying the following formulas (I) to (III). Fatty acid cellulose ester.
2.50 ≦ A + B ≦ 2.90 (I)
0.00 ≦ A ≦ 1.90 (II)
1.50 ≦ B ≦ 1.90 (III)   The mixed fatty acid cellulose ester according to claim 10, wherein the mixed fatty acid cellulose ester is cellulose acetate propionate or cellulose acetate butyrate.   The molded object comprised with the mixed fatty acid cellulose ester in any one of Claims 10-13.   The molded article according to claim 14, which is an optical film selected from a protective film for a polarizing plate, a retardation film, and an optical compensation film.