Cellulose acetate and producing method therefor

Patent metadata

Field	Value
Publication number	US-10927189-B2
Application number	US-201716327054-A
Country	US
Kind code	B2
Filing date	Aug 21, 2017
Priority date	Aug 22, 2016
Publication date	Feb 23, 2021
Grant date	Feb 23, 2021

Abstract

The purpose of the present invention is to provide a cellulose acetate which can be used to obtain an optical film having a very small amount of bright spot foreign matters, with excellent production efficiency, even when cellulose containing a small amount of hemicellulose components and having a high degree of crystallinity is used as a raw material. A cellulose acetate in which a content ratio by mole of mannose units to a sum of xylose units, mannose units and glucose units, which are sugar chain components, is 0.04 mol % or less, and a filtration index K measured by the following measurement method is 30 mL −1 or less. (Measurement method) The cellulose acetate is dissolved in a mixed solvent containing methylene chloride and methanol at a weight ratio of methylene chloride/methanol of 9/1 to obtain a solution with a solid concentration of 16% by weight. The temperature of the solution is adjusted to 25° C., and the solution is subjected to constant-pressure filtration under a pressure of 3 kg/cm 2 using a cloth obtained by stacking three sheets of calico (s 618) (diameter: 15 mm, filtration area: 1.77 cm 2 ). At this time, the filtration index k (mL −1 ) is calculated from the following expression, where P 1 represents the amount of filtration (mL) up to 20 minutes after the start of filtration, and P 2 represents the amount of filtration (mL) from 0 to 60 minutes.

Filtration
⁢

⁢
index
⁢

⁢
K

=

2
-

P
2

/

P
1

P
1

+

P
2

×

10
4

[

Mathematical
⁢

⁢
Formula
⁢

⁢
1

]

First claim

The invention claimed is:

1. A cellulose acetate in which a content ratio by mole of mannose units to a sum of xylose units, mannose units and glucose units, which are sugar chain components, is 0.04 mol % or less, and a filtration index K measured by a measurement method is 30 mL −1 or less;
wherein the measurement method comprises:
dissolving the cellulose acetate in a mixed solvent containing methylene chloride and methanol at a weight ratio of methylene chloride/methanol of 9/1 to obtain a solution with a solid concentration of 16% by weight;
adjusting a temperature of the solution to 25° C.;
subjecting the solution to constant-pressure filtration under a pressure of 3 kg/cm 2 using a cloth obtained by stacking three sheets of calico (s 618) with diameter: 15 mm and filtration area: 1.77 cm 2 ;
calculating a filtration index k (mL −1 ) from the following expression, where P 1 represents an amount of filtration (mL) up to 20 minutes after a start of filtration, and P 2 represents the amount of filtration (mL) from 0 to 60 minutes

Filtration
⁢

⁢
index
⁢

⁢
K

=

2
-

P
2

/

P
1

P
1

+

P
2

×

10
4

.

2. The cellulose acetate according to claim 1 , wherein a number of insoluble foreign matters having an equivalent spherical diameter of 20 μm or less, among foreign matters insoluble in dichloromethane/methanol, with a weight ratio of 9:1, measured by FlowCAM (registered trademark) analysis is 70 or less per 1 mg of cellulose acetate.

3. The cellulose acetate according to claim 1 , wherein a number of insoluble foreign matters having an equivalent spherical diameter of 10 μm or less, among foreign matters insoluble in dichloromethane/methanol, with a weight ratio of 9:1, measured by FlowCAM (registered trademark) analysis is 60 or less per 1 mg of cellulose acetate.

4. The cellulose acetate according to claim 1 , wherein the cellulose acetate has a calcium content of 40 ppm or more and 80 ppm or less, a magnesium content of 1.0 ppm or more and 5.0 ppm or less, and a molecular weight distribution Mw/Mn of 2.30 or less and 2.05 or more.

5. A method for producing the cellulose acetate according to claim 1 , the method comprising:
a step of grinding linter pulp through a primary grinding step and a secondary grinding step,
performing pretreatment and activation by adding acetic acid or acetic acid containing sulfuric acid in an amount of 1% by weight or more and 10% by weight or less to the ground linter pulp; and
performing acetylation at 20 to 55° C.,
wherein
the primary grinding step is a step of grinding water-free linter pulp into pulp pieces having an average area of 45 cm 2 or less by a disc refiner or a hammer mill,
the secondary grinding step is a step of grinding the pulp pieces under an impact action of an airflow grinder which includes a casing provided with an inlet and an outlet and having a cylindrical shape, and a rotor facing an inner peripheral surface of the casing and having a plurality of blade portions provided on an outer peripheral portion of the rotor; and
wherein the step of performing pretreatment and activation includes a first pretreatment step and a second pretreatment step, the first pretreatment step including adding acetic acid to the ground linter pulp and holding for 15 minutes to 24 hours at a temperature of 0° C. to 100° C., the second pretreatment step including adding more than 60 parts by weight and 100 parts by weight or less of acetic acid containing sulfuric acid in an amount of 1% by weight or more and 10% by weight or less to 100 parts by weight of the linter pulp subjected to the first pretreatment step left standing at a temperature of 10° C. to 40° C.

Assignees

• Daicel Corp

Inventors

• Tsuda Maiko
• Higuchi Akihiro

Classifications

• C08B3/06 Primary

  Cellulose acetate {, e.g. mono-acetate, di-acetate or tri-acetate} · CPC title

• B02C13/04

  with beaters hinged to the rotor; Hammer mills · CPC title

• B02C7/16

  Driving mechanisms · CPC title

• C08B1/02

  Rendering cellulose suitable for esterification {(esterification per se, C08B3/00, C08B5/00, C08B7/00 or C08B9/00)} · CPC title

• B08B3/06 Primary

  using perforated drums in which the article or material is placed {(B08B3/042 takes precedence)} · CPC title