TECHNICAL FIELD

The present invention relates to a cellulose acetate composition for thermoforming, a molded article, and a method for producing a cellulose acetate composition for thermoforming.

BACKGROUND ART

In recent years, there has been an increased demand for Reduced Risk Products that do not use fire. Reduced Risk Products are generally divided into two types: with one type (an e-cigarette), a solution that contains nicotine dissolved in an organic solvent is heated and the resulting aerosol or gas is inhaled by a user; and with another type (a heated tobacco product), tobacco leaves (the tobacco leaves including artificial tobacco leaves such as processed tobacco leaves or substrates impregnated with a tobacco component) are heated (but not burned) and then the diffusing nicotine-containing aerosol is inhaled by a user. However, in Japan, nicotine itself is designated as a pharmaceutical product, and the handling of nicotine is regulated. For example, the sale of nicotine is prohibited, in principle. In such cases, the e-cigarette, with which a solution that contains nicotine dissolved in an organic solvent is heated and the resulting aerosol or gas is inhaled, cannot be sold. Further, the e-cigarette is designated as a pharmaceutical product also in many countries besides Japan. Note that iQOS (trade name), available from Philip Morris International Inc., is a heated tobacco product with which tobacco leaves of a dedicated cigarette are heated and then the diffusing nicotine-containing aerosol is inhaled by a user.

Patent Document 1 describes, as an example of a cigarette for use in a heated tobacco product, one having a structure in which a mouthpiece, an aerosol-cooling element, a support element, and an aerosol-forming substrate are arranged in this order from a side close to a mouth-end, and also describes that the cigarette includes a cellulose acetate tow filter as the mouthpiece, a polylactic acid sheet as the aerosol-cooling element, a hollow cellulose acetate tube as the support element, and tobacco as the aerosol-forming substrate.

In the case of heated tobacco products in which tobacco leaves is heated, members other than the tobacco leaves of a dedicated cigarette remain after smoking is finished. Thus, environment issues can arise due to the remaining members being thrown away. To address the environment issues, a biodegradable polylactic acid is used as a material for a cooling part of the cigarette for use in a heated tobacco product, as described above.

From the perspective of excellent biodegradability, in general, cellulose acetates that are used in cellulose acetate tow filters and cellulose acetate tubes preferably have a lower degree of acetyl substitution, but must have a certain degree of acetyl substitution because of ease of processing by thermoforming and less influences on the taste. Furthermore, additives such as a plasticizer may be added to a cellulose acetate for the purpose of achieving superior thermoformability and physical properties (Patent Document 2 to 6).

CITATION LIST

Patent Document

Patent Document 1: JP 2015-503335 APatent Document 2: JP H07-076632 APatent Document 3: JP 2002-030182 APatent Document 4: WO 2015/194186Patent Document 5: JP 2015-140432 APatent Document 6: JP 2000-219776 A

SUMMARY OF INVENTION

Technical Problem

As described in Patent Document 2, a phthalic acid ester may be used as a plasticizer to be typically added to a cellulose acetate. However, phthalic acid esters release strong irritating odors during heat processing such as thermoforming. Also, they are strongly suspected of being endocrine disruptors (in other words, “environmental hormones”), and invite a concern about harmfulness to the human body and a large load on environments. In particular, when a phthalic acid ester is added during processing of known tobacco filters and the respective members of heated tobacco products (smoking-related members including a member for use in a mouth-end such as a cellulose acetate tow filter, a member as an aerosol-cooling element, and a member as a support element such as a hollow cellulose acetate tube), there is a concern about harmfulness to the human body and influences on the taste.

Patent Document 3 describes a cellulose acetate having a degree of acetyl substitution ranging from 1.9 to 2.6, and Patent Document 4 describes a cellulose acetate having a degree of substitution of 2.5. However, cellulose acetates having a degree of acetyl substitution of greater than 2.0 (e.g., ranging from 2.1 to 2.6) do not have excellent biodegradability.

As described in Patent Document 5, polyethylene glycol may be used as a plasticizer to be added to a cellulose acetate having a degree of acetyl substitution ranging from 0.5 to 1.0. However, in particular, addition of polyethylene glycol during processing of known tobacco filters and the respective members of heated tobacco products arouses a concern about influences on the taste. When polyethylene glycol is used as a plasticizer to be added to a cellulose acetate having a degree of acetyl substitution ranging from 1.4 to 1.8, the thermoformability imparted to the cellulose acetate by the polyethylene glycol is not satisfactory. Furthermore, depending on the difference in degree of polymerization, the polyethylene glycol may be in a liquid form in the case of a low degree of polymerization and in a solid form in the case of a high degree of polymerization, at room temperature. A liquid-form polyethylene glycol is preferred because of being easily dispersed uniformly in a cellulose acetate, but the liquid-form polyethylene glycol easily bleeds out from the cellulose acetate. A solid-form polyethylene glycol, on the other hand, arouses a concern about difficulty in uniformly dispersing in a cellulose acetate. Thus, it is not substantially easy to handle the polyethylene glycol as a plasticizer for cellulose acetates.

As described in Patent Document 6, in the production of a resin composition containing a cellulose acetate having a combined acetic acid ranging from 34 to 47 wt. % and a biodegradable plasticizer, a mixture containing 13 wt. % of dissolving pulp, 2 wt. % of sulfuric acid, 35 wt. % of an acetic anhydride, and 50 wt. % of glacial acetic acid is acetylated at 36° C. for 3 hours, and, after the reaction, the reaction product is neutralized with potassium acetate, and then hydrolyzed (Examples). However, the acetylation reaction is likely to proceed because sulfuric acid is used in a large amount relative to the dissolving pulp in the acetylation, but also increases the amount of bound sulfuric acid in the resulting cellulose acetate. The sulfate bound to the cellulose acetate becomes a salt by neutralization after the acetylation, and therefore stabilizes and becomes difficult to hydrolyze. Therefore, prolonged hydrolysis is required after the acetylation. As a result, the obtained cellulose acetates are nonuniform and vary in degree of acetyl substitution, and resin compositions formed from such a cellulose acetate and a plasticizer become cloudy and/or contain residual unmelted substances, and have insufficient thermoformability and processability.

Methods of adding a known plasticizer can increase the thermoformability of cellulose acetates to some extent, but cannot achieve both the biodegradability and sufficient thermoformability of the resulting cellulose acetate compositions. An object of the present invention is to provide a cellulose acetate composition for thermoforming, which has excellent biodegradability, is less cloudy, contains less residual unmelted substances, and has excellent thermoformability.

Solution to Problem

A first aspect of the present invention relates to a cellulose acetate composition for thermoforming containing a cellulose acetate and a glycerin ester-based plasticizer, wherein the cellulose acetate has a degree of acetyl substitution of 1.4 or greater and 2.0 or less, a compositional distribution index (CDI), as defined below, of 4.0 or less, and a total sulfur content of 15 mg/kg or greater and less than 150 mg/kg:
CDI=(Measured value of half-height width of compositional distribution)/(Theoretical value of half-height width of compositional distribution)

wherein

the measured value of a half-height width of compositional distribution is a half-height width of compositional distribution determined by HPLC analysis of cellulose acetate propionate obtained by propionylating all residual hydroxyl groups of cellulose acetate (sample); and the theoretical value of a half-height width of compositional distribution is defined by:

Theoretical⁢value⁢of⁢half-height⁢width⁢of⁢compositional⁢distribution=2.354823*DPw*(DS/3)*(1-DS/3)/DPw[Equation⁢1]

where DS represents a degree of acetyl substitution; and

DPw represents a weight average degree of polymerization (a value determined by GPC-light scattering method using cellulose acetate propionate obtained by propionylating all residual hydroxyl groups of cellulose acetate (sample)).

In the cellulose acetate composition for thermoforming, a content of the glycerin ester-based plasticizer may be 5 parts by weight or greater and 40 parts by weight or less, per 100 parts by weight of the total amount of the cellulose acetate and the glycerin ester-based plasticizer.

In the cellulose acetate composition for thermoforming, the glycerin ester-based plasticizer may be an ester compound of glycerin and acetic acid.

In the cellulose acetate composition for thermoforming, the glycerin ester-based plasticizer may be triacetin.

In the cellulose acetate composition for thermoforming, the cellulose acetate may have a degree of acetyl substitution of 1.4 or greater and 1.8 or less.

A second aspect of the present invention relates to a molded article formed by molding the cellulose acetate composition for thermoforming.

The molded article may be a film.

The molded article may have a hollow cylindrical shape.

The molded article may be a cigarette member of a heated tobacco product.

A third aspect of the present invention relates to a method for producing a cellulose acetate composition for thermoforming, including:

dispersing or dissolving a glycerin ester-based plasticizer in a dispersion medium or a solvent to prepare a dispersion or a solution;

mixing the dispersion or the solution with a cellulose acetate; and

vaporizing the dispersion medium or the solvent from a mixture obtained by the mixing,

wherein the cellulose acetate has a degree of acetyl substitution of 1.4 or greater and 2.0 or less, a compositional distribution index (CDI), as defined above, of 4.0 or less, and a total sulfur content of 15 mg/kg or greater and less than 150 mg/kg.

In the method for producing a cellulose acetate composition for thermoforming, the dispersion medium or the solvent may be water, ethanol, or a mixed solution of water and ethanol.

In the method for producing a cellulose acetate composition for thermoforming, a content of the glycerin ester-based plasticizer may be 5 parts by weight or greater and 40 parts by weight or less, per 100 parts by weight of the total amount of the cellulose acetate and the glycerin ester-based plasticizer.

In the method for producing a cellulose acetate composition for thermoforming, the cellulose acetate may have a degree of acetyl substitution of 1.4 or greater and 1.8 or less.

Advantageous Effects of Invention

The present invention can provide a cellulose acetate composition for thermoforming, which has excellent biodegradability, is less cloudy, contains less residual unmelted substances, and has excellent thermoformability.

