KR19980086226A - Coated cellulose fine particles for the production of homogeneous cellulose solution and preparation method thereof - Google Patents

Abstract

The present invention comprises the steps of (a) finely powdering cellulose, (b) concentrating an aqueous N-methylmorpholine-N-oxide solution to prepare an N-methylmorpholine-N-oxide solution for coating, and (c) Solid N-methylmorpholine-N- having a water content of 5 to 15% by weight, prepared by coating the cellulose fine powder obtained in step (a) with the solution obtained in step (b) in a coating machine. A cellulose fine particle for producing a homogeneous cellulose solution coated with an oxide and a homogeneous cellulose solution prepared from the particles. According to the present invention, since the cellulose fine particles are uniformly coated in a constant composition with an N-methylmorpho-N-oxide solvent, a homogeneous cellulose solution can be prepared immediately by a simple process in a short time.

Description

Coated cellulose fine particles for the production of homogeneous cellulose solution and preparation method thereof

The present invention relates to cellulose fine particles coated with N-methyl morpholine-N-oxide (hereinafter referred to as NMMO), a preparation method thereof, and a highly homogeneous cellulose solution prepared from the cellulose fine particles. It is about. The high homogeneous cellulose solution prepared by the present invention can be used to prepare cellulose fibers or cellulose films.

Since a method for preparing a cellulose solution using a tertiary amine oxide solvent is first known by US Pat. No. 2,179,181 to Graenacher et al., A method of producing a more efficient and economical cellulose solution, as described below. Have been presented.

U.S. Patent Nos. 4,142,913, 4,144,080, 4,196,282 and 4,246,221 disclose, for example, firstly in aqueous tertiary amine oxide solutions (nonsolvents for cellulose) in which cellulose cannot be dissolved with a moisture content of at least 22% by weight. Methods for producing a cellulose solution by vacuum distillation to dissolve cellulose are disclosed by swelling cellulose to obtain a slurry and then removing excess water contained in the slurry by distillation under reduced pressure. However, these methods of preparing the cellulose solution are complicated because the solution is prepared through a long time under reduced pressure distillation, and the problem is that the solution discolors due to thermal decomposition of the solvent and cellulose and wastes time and energy due to long time under reduced pressure distillation. It has

European Patent No. 356,419 to Stefan et al. Discloses a process for continuously producing 72 kg of cellulose solution per hour using a concentration process. This patent swells cellulose using a 40% water content of NMMO solution and suggests a method for producing a cellulose solution by distilling the swollen cellulose slurry under reduced pressure in a presser using a fan-shaped screw. Doing. In addition, International Patent No. WO94 / 06530 to Quigley discloses a method for preparing a solution using a thin film distillator which is a vacuum distillation apparatus. However, these methods have a disadvantage in that a high-viscosity cellulose slurry has to be concentrated, which not only reduces the production efficiency but also requires a complicated apparatus because of the distillation under reduced pressure.

U.S. Patent No. 4,211,574 discloses immersion and swelling of a cellulose pulp sheet at 85 to 95 DEG C in a liquid tertiary amine oxide solvent (solvent to cellulose) capable of dissolving cellulose in a water content of 5 to 15%. A method of preparing a cellulose solution by stirring and heating as it is without a concentration process is proposed. However, since the amine oxide solvent partially swells only the surface of the cellulose pulp sheet and forms a film on the surface, the amine oxide solvent does not penetrate deeply into the pulp so that the cellulose remains undissolved in the solution of the prepared cellulose. do. If a film is formed on the pulp sheet, a uniformly dissolved solution cannot be produced even by vigorous stirring or heating. Therefore, the method of preparing a solution according to the patent has a disadvantage in that a uniform cellulose solution cannot be prepared.

On the other hand, US Patent No. 4,416,698 proposes a method of simply mixing the cellulose powder and the solid NMMO cellulose solution powder to be transferred to an extruder to dissolve. However, since this method simply mixes the cellulose powder and the solid solvent, when a large amount of the mixture is prepared, the cellulose powder and the solid NMMO solvent powder are not uniformly mixed with each other. Thus, this method has a disadvantage in that a uniform cellulose solution cannot be prepared because undissolved cellulose particles are present in the finally prepared solution.

As described above, the conventional method for producing a cellulose solution can be divided into a technique for producing a homogeneous cellulose solution using an NMMO aqueous solution (nonsolvent for cellulose) and a technique for using NMMO solvent powder. The use of NMMO aqueous solution has the drawback that NMMO is unnecessarily hydrolyzed while removing excess moisture, and the technique using NMMO solvent powder has the drawback that undissolved cellulose particles remain. In order to solve the drawbacks of using NMMO solvent powder, U.S. Patent No. 5,584,919 describes a pulp and solvent particle in which NMMO penetrates cellulose using the heat generated by grinding and mixing pulp and solid NMMO solvent together. A method for producing a constructed pelletized mixed powder is presented.

An object of the present invention is to prepare a cellulose solution using a tertiary amine oxide-based NMMO solvent, unlike the conventional manufacturing process of a complex solution, is prepared by a simple process in a short time, the composition between the cellulose and the solvent is very uniform And a cellulose fine particle coated with NMMO solvent which can be used to prepare a highly homogeneous cellulose solution having the advantage of increasing the bulk density of the cellulose fine powder, and a method for preparing the particle. To provide a highly homogeneous cellulose solution prepared using the particles.

1 is a process chart for producing the cellulose fine particles of the present invention.

Figure 2 is an illustration of a typical block diagram of a fluidized bed spray apparatus which is a coating machine used to make cellulose fine particles of the present invention.

Figure 3 is a process diagram for producing a homogeneous cellulose solution from the cellulose fine particles of the present invention and for producing a cellulose fiber or film from the solution.

Explanation of symbols for the main parts of the drawings

1: N-methylmorpholine-N-oxide solution

2: spray nozzle

3: discharge of cellulose particles coated with solvent

4: release of fine particles

5: discharge of air

6: re-insertion of separated particles

7: collector

8: injection of air for fluidization

Cellulose fine particles for producing a homogeneous cellulose solution according to the present invention is characterized in that the water content is coated with a solid NMMO solvent of 5 to 15% by weight.

The cellulose fine particles according to the present invention,

(a) finely powdering cellulose,

(b) concentrating the aqueous NMMO solution to produce a coating NMMO solution,

(C) can be prepared through the process of coating the cellulose fine powder obtained in the step (a) with the solution obtained in the step (b) in the coating device.

More specifically, the cellulose fine particles according to the present invention,

(a) finely powdering fibrillated cellulose;

(b) concentrating the aqueous NMMO solution to produce an NMMO solution having a water content of 5 to 25% by weight,

(c) coating the cellulose fine powder obtained in the step (a) with the NMMO solution maintained at a temperature of 50 to 130 ° C. in a coating apparatus such as a fluidized bed spray coating tower, a rotary drum or a rotary pan. Can be.

In addition, by dissolving the cellulose fine particles according to the present invention only by heating without a separate swelling process, it is possible to obtain a very homogeneous cellulose solution that can be used for the production of cellulose fibers, films or separators.

Hereinafter, a method for preparing cellulose fine particles for preparing a homogeneous cellulose solution, and a method for preparing a homogeneous cellulose solution therefrom, which are coated with a solid NMMO solvent having a water content of 5 to 15 wt% according to the present invention, refer to the accompanying drawings. It will be described in more detail.

Cellulose, for example a cellulose sheet, is finely powdered using a blade mill equipped with a ring sieve to obtain a fibrillated cellulose fine powder having small particles. In order to prepare a homogeneous cellulose solution, it is preferable that the particle size of the cellulose fine powder is 1,000 μm or less, because larger particle sizes may result in gel particles in which cellulose is not dissolved in a solvent. In addition, when the particles are large, such as cellulose sheets, not only is it difficult to fluidize in the coating apparatus during coating of the NMMO solvent, but it is coated only on the surface of the cellulose sheet so that in the later dissolution, the cellulose is not directly dissolved in the solvent, but rather the solvent on the surface Since the film is formed, it is difficult to produce a uniform cellulose solution.

The aqueous NMMO solution is concentrated in a conventional manner to lower its water content to 5 to 25% by weight, which acts as a solvent to dissolve the cellulose fine powder.

In coating the NMMO solution thus obtained onto cellulose fine powder, various coating apparatuses such as a fluidized bed spray tower type, a rotary drum type, or a rotary fan type can be used. The method of coating the cellulose fine powder by finely spraying the NMMO solution in the fluidized bed spray tower is most preferred. Looking more specifically at the method of coating the powder using such a fluidization, since the so-called 'Wurster' process (Canada Patent No. 676,215, 1963) was introduced, various methods of modifying it have been described in US Patent No. Numerous patents have been reported in various fields, including 5,395,449. This fluidized bed method is used in both batch and continuous mode and is suitable for small to large volume production (see J.F. Davidson et al., Fluidization 2nd ed., Academic Press, 1985).

Cellulose fine powder prepared from the mill as described above is conveyed by using a closed feed pipe and a hose feeder (force feeder). In order to suppress the generation of static electricity, it is preferable to use a transfer pipe that is antistatically treated. The transfer pipe is connected to the coater and described with reference to a coater using a fluidized bed among coating machines as follows.

The cellulose fine powder is introduced into a fluidized bed spray coating apparatus and then fluidized. When uniform flow is achieved, the NMMO solution is sprayed through the nozzle. The NMMO solution used to coat the cellulose fine powder is for liquid phase with a water content of 5 to 25% by weight, which is obtained by concentrating the NMMO aqueous solution in a conventional manner. At this time, the NMMO solution in the spray nozzle is maintained at 50 to 130 ℃. The liquid NMMO is sprayed into the fluidized bed through a nozzle at a constant speed, dried and applied to the flowing cellulose powder. The moisture content of the coated NMMO is 5 to 15% by weight. In the coated cellulose particles, the composition ratio of cellulose is about 5 to 20% by weight, preferably 10 to 17% by weight based on the coated cellulose particles.

On the other hand, the fluidized bed spray coating apparatus used to prepare the NMMO solvent-coated cellulose particles of the present invention has the structural features illustrated in FIG. The process can be both batch and continuous and the fluidized bed spray coating apparatus used in the present invention will be described in more detail as follows.

After injecting cellulose powder into the fluidized bed spray coating tower, the cellulose powder is fluidized to be a cyclic flow by injecting air through (8). A liquid NMMO (1) having a water content of 5 to 25% by weight is sprayed onto the cellulose powder through the spray nozzle (2). At this time, the position of the nozzle can be both the top or bottom of the fluidized bed. The injected NMMO solution is maintained at 50 to 130 ° C. The liquid NMMO is sprayed into the fluidized bed through the nozzle at a constant speed to reach the surface of the cellulose powder, and is applied while partially evaporating and solidifying the water contained in the NMMO solution through heat exchange with air. By controlling the temperature and humidity of the air used, the moisture in the solution which solidifies on the surface of the particles is adjusted to 5 to 15% by weight. Due to the flow of these particles in the fluidized bed, the aggregation between the particles is less, and the aggregated particles are also minimized due to the collision between the particles. The coated particles have a difference in specific gravity of the particles depending on the amount of the coated particles, so that the size of the reflux flow is changed so that the coated particles are located at the bottom of the tower. The solvent is applied to a constant thickness according to the repetitive circulation in the column, and the composition ratio of the coated particles to the solvent controls the residence time so that the concentration of cellulose is 5 to 20% by weight. Particles coated with a constant composition are discharged through (3). A radial fan is used to blow air upward in the discharge pipe, and the role of the air flow promotes cooling of the coated particles and reverses the direction of air flow and discharge of the particles, so that the coated particles having a specific composition have a specific gravity. Allow only the discharge. Fine particles leaving the fluidized bed through (4) are collected through the collector (7), and the particles separated by the collector are reintroduced into the fluidized bed through (6) and the air containing no powder is discharged through (5). . The coated cellulose fine particles thus prepared are not only easy to store, but also have better fluidity than the cellulose fine powder before coating, which is advantageous for the subsequent process such as transporting, and is used to manufacture fibers, films, and separators through a processing machine such as an extruder. Provide a homogeneous solution.

The cellulose fine particles coated with the NMMO solvent prepared as described above are dissolved and become a homogeneous cellulose solution simply by heating it without a separate swelling process. Such heat melting is preferably performed in an extruder or an injection machine. That is, when the cellulose fine particles according to the present invention are put into an extruder or an injection machine and heated, the cellulose fine particles are completely dissolved in the extruder or the injection machine to form a homogeneous cellulose solution, and extruded to produce a fiber, a film or a separator as a final product. .

Cellulose fine particles and a method for producing a cellulose solution using the same according to the present invention as described above has the following advantages.

First, in the case of particles obtained by coating an NMMO solvent on the cellulose fine powder as in the present invention, since the composition between NMMO solvent and cellulose containing 5 to 15% by weight of water is constant and uniform, the coated particles are constituted. The cellulose is easily dissolved in a solvent coated on the surface by heating only afterwards, so that cellulose is not produced by undissolved.

Second, since the fibrillated cellulose fine powder is coated with a solvent to control the particle size, solid particles which are easy to transport are produced, and the processability is improved by increasing the apparent density.

Third, the conventional method for producing a cellulose solution by vacuum distillation is severely decomposed of cellulose and a solvent because it is prepared through a vacuum distillation process of a pulp slurry over a long time, but in the present invention, in the process of removing water directly from an NMMO aqueous solution. By using a NMMO solution with a water content of 5 to 25% by weight as a solvent, it only needs to be coated on the cellulose fine powder and then heated, so that the cellulose solution can be easily prepared in a simple process in a shorter time than the conventional method.

Fourth, it is easy to add and remove water efficiently according to the operating conditions in the coating equipment, the water content of the NMMO solution used for coating is 5 to 25% by weight, 5 to 5 of the NMMO solvent coated on the final cellulose fine particles Higher than the water content of 15% by weight. As such, the use of a high moisture content of NMMO in the coating has the advantage of lowering the concentrated load of the NMMO aqueous solution. In addition, the higher the moisture content of the NMMO used for coating, the easier the liquefaction of the NMMO, so the temperature in the delivery pipe of the NMMO solution for the coating can be lowered, so that less energy consumption and less decomposition of the NMMO.

Fifth, when the fluidized bed spray coating apparatus for spraying the solution is used, the solution is injected into the air through the nozzle and fluidized, so that the solution is solidified on the surface of the cellulose powder by rapid heat exchange, so that the exposure time at high temperature is shortened, resulting in short cellulose and NMMO. Less decomposition of

Hereinafter, the contents of the present invention will be described by way of examples, but the present invention should not be limited by the following examples.

The evaluation method performed in the Example is as follows.

a) cellulose DPw (weight average degree of polymerization)

The change in molecular weight of cellulose that occurred during the preparation of the cellulose solution was measured by the following method.

The intrinsic viscosity of cellulose was measured in a concentration range of 0.1 to 0.6 g / dl using a 0.5 M cupriethylenediamine hydroxide solution prepared according to the method of ASTM (D 539-51T). Viscosity was measured using Ubbelohde viscometer No. 1 (manufactured by Fisher) at 25 ± 0.01 ° C. The intrinsic viscosity (IV) of the sample was calculated | required from following formula (1) using the value of specific viscosity (eta _sp ) with respect to each density | concentration (c). The weight average degree of polymerization (DPw) is determined from the intrinsic viscosity obtained from Equation 2 below. Immergut, “Polymer Handbook”, 3rd ed., V144, Wiley-Interscience, New York, 1989).

[Equation 1]

[Equation 2]

[Iv] = 0.98 × 10 ^-2 DP ^0.9

b) concentration of colored impurities

The change in NMMO produced during the preparation of the cellulose solution was measured by 30% NMMO aqueous solution reaching equilibrium by separating 10 g of solution from the prepared cellulose solution and immersing in 16.17 ml of distilled water for 60 minutes. At this time, the concentration of colored impurities in the recovered NMMO aqueous solution was measured using a UV-Visible spectrophotometer (Model: Hewlett Packard HP8453). The absorbance of the solution according to solvent decomposition was measured at 450 nm, and the absorbance of the measured solution was expressed as the optical denisty of amine oxide (AOD) containing 1% NMMO in weight ratio. The AOOD of the 50% NMMO aqueous solution used in this experiment showed 0.0006.

c) homogeneity of the solution

The homogeneity of the solution prepared in the present invention was evaluated from the presence of undissolved cellulose particles in the solution passed through the extruder. At this time, the undissolved particles were evaluated by observing with a Zeiss polarization microscope.

Example 1

Sheet-type cellulose (Cellunier-F, ITT Co., Ltd.) having a cellulose polymerization degree (DPw) of 660 was placed in a grinder with a 0.35 nm screen ring body and ground to prepare a powder having a diameter of 180 µm or less. 300 g of this cellulose powder was passed through an antistatic treatment tube, and injected into a batch type fluidized bed spray coating tower in the form of a Walster. Dry air at room temperature was injected from the bottom to allow the cellulose powder to flow uniformly in the tower for 10 minutes. 2,200 g of 80% NMMO solution was sprayed with the dried air through a nozzle located at the bottom of the fluidized bed spray coating tower at a rate of 50 g per minute. The temperature at the nozzle is maintained at 90 ° C and the injected NMMO solution contains 0.2% by weight of propylgallate fine powder as an antioxidant.

From the bottom of the fluidized bed spray coating column, cellulose fine particles coated with a solid NMMO solvent having a water content of 15% by weight were obtained. The composition ratio of cellulose was 12% by weight based on the coated cellulose particles.

Example 2

The cellulose fine particles obtained in Example 1 were transferred to an extruder (30 mm in diameter, L / D 40) and heated and dissolved in this extruder to obtain a cellulose solution.

The degree of polymerization of the cellulose collected from this cellulose solution was 630, and the AOOD of the solvent was 0.013. The solution observed from the microscope was in a very homogeneous state, and no cellulose particles of undissolved water were observed.

Example 3

Sheet-type cellulose (ITT, Inc., RAYONEX-P) having a cellulose polymerization degree (DPw) of 1,000 was placed in a grinder with a 1 mm screen ring body and ground to prepare a powder having a diameter of 500 µm or less. 2,000 g of this cellulose powder was passed through an antistatic treatment tube to be supplied to a continuous fluidized bed spray coating tower, and dry air at room temperature was injected from the bottom of the tower to uniformly flow the cellulose powder in the tower for 10 minutes. Cellulose powder was injected from the cellulose storage tank into the fluidized bed at a rate of 100 g per minute. In this case, the coated cellulose fine particles were prepared by spraying and injecting 87 wt% of liquid NMMO maintained at 100 ° C. at a rate of 840 g per minute with dry air in a fluidized bed at two nozzles positioned in the middle of the fluidized bed spray coating tower. Particles are coated while refluxing with respect to the center of the tower in the fluidized bed spray coating tower, and the specific gravity increases depending on the degree of coating, so that the flow width decreases and settles toward the center of the bottom of the tower. Discharged continuously. The fine particles leaving the fluidized bed suppress the discharge through the nonwoven filter, the separated particles are re-introduced into the fluidized bed, and the air containing no particles is discharged through the discharger.

Thus, cellulose fine particles coated with a solid NMMO solvent having a moisture content of 11% by weight were obtained. The composition ratio of cellulose was 12% by weight based on the coated cellulose particles.

Example 4

The cellulose fine particles obtained in Example 3 were dissolved using an extruder (30 mm in diameter, L / D 40) to obtain a homogeneous cellulose solution. The degree of polymerization of the cellulose collected from this cellulose solution was 950, and the AOOD of the solvent was 0.015. The solution observed from the microscope was in a very homogeneous state, and no cellulose particles of undissolved water were observed.

Since the cellulose fine particles according to the present invention are uniformly coated with a constant composition with NMMO solvent, it is possible to prepare a homogeneous cellulose solution immediately by a simple process in a short time.

Claims (7)

A cellulose fine particle for producing a homogeneous cellulose solution, which is coated with a solid N-methylmorpholine-N-oxide having a water content of 5 to 15% by weight. The particle size according to claim 1, wherein the cellulose fine particles have a composition ratio of 5 to 20% by weight. (a) finely powdering cellulose, (b) concentrating an aqueous N-methylmorpholine-N-oxide solution to prepare an N-methylmorpholine-N-oxide solution for coating, and (c) coating the cellulose fine powder obtained in the step (a) with the solution obtained in the step (b) in a coating machine. The method according to claim 3, wherein the cellulose fine powder obtained in the step (a) is a fibrillated cellulose fine powder having a particle size of 1,000 µm or less. The method according to claim 3 or 4, wherein the coating N-methylmorpholi-N-oxide solution is a liquid solution having a water content of 5 to 25% by weight and a temperature of 50 to 130 ° C. The method according to claim 3 or 4, wherein the coating device is one of a fluidized bed spray coating tower, a rotary drum or a rotary fan. A homogeneous cellulose solution for producing cellulose fibers or films by heating and dissolving cellulose fine particles according to claim 1.