FIELD OF THE INVENTION The present invention relates to a process for preparing enteric water- dispersible hydroxypropyl methylcellulose phthalate nanoparticles, in particular, to a process for preparing enteric water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles in a cost-effective and time-saving manner, in which hydroxypropyl methylcellulose phthalate nanoparticles are prepared without using an emulsifier, wherein the residual electrolyte content is adjusted through ion exchange for a short period of time followed by the addition of a plasticizer, thereby the environment-friendly water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles showing excellent film properties and enteric coating properties are prepared.

DESCRIPTION OF THE RELATED ART To date, hydroxypropyl methylcellulose phthalate and acryl copolymer have been widely used as enteric coating materials. However, hydroxypropyl methylcellulose phthalate is not considered advantageous in that an organic solvent should be used during a coating process, thus causing environmental problems. In addition, acryl copolymer, although its water-dispersible product being available, it is also not considered advantageous in that it is a synthetic

polymer rather than a natural material and it has poor film properties compared to those of hydroxypropyl methylcellulose phthalate. Therefore, there has been an urgent need for the development of a novel type of an environment-friendly material.

In this regard, a water-dispersible hydroxypropyl methylcellulose phthalate has been prepared. The conventional method of preparing such water-dispersible hydroxypropyl methylcellulose phthalate comprises: completely dissolving hydroxypropyl methylcellulose phthalate in an organic solvent and dispersing it in water; and removing the organic solvent in the solution to yield a water- dispersible hydroxypropyl methylcellulose phthalate. However, the product obtained by this method has poor stability in water-dispersible phase. Further, the use of an organic solvent causes an increase in production cost, and after emulsification, the organic solvent in the solution is hardly removed, so that the final product contains the organic solvent, thereby causing environmental problems.

U. S. Pat. No. 5,560, 930 discloses a method of preparing particle of about 0.2 pm, by emulsifying hydroxypropyl methylcellulose phthalate in water after dissolving them in acetone and removing the organic solvent through distillation under reduced pressure. U. S. Pat. No. 5,512, 092 suggests a method of dissolving hydroxypropyl methylcellulose phthalate in ethanol and emulsifying it; and U. S.

Pat. No. 5,346, 542 teaches a method of dissolving carboxymethyl ethylcellulose in methyl acetate and emulsifying it in water. Although these methods do not have problems in terms of latex size or dispersion, the product stability after

emulsification is poor and leaves the organic solvent in the final product because it is difficult to completely remove the organic solvent remaining in the solution. In addition, when the water-dispersible hydroxypropyl methylcellulose phthalate in a form of film of 1cm x lcm, prepared according to the above method, was placed for 2 hr in an aqueous solution of pH 1.2, the form of film was disintegrated. Then, the present inventors diluted the water-dispersible hydroxypropyl methylcellulose phthalate to 7 wt% with distilled water and coated it on a tablet using Hi-Coater (HCT Labo). The disintegration test (using Pharmatest PTZ E) showed that the disintegration took place within 2 hr under pH 1.2. For the reasons, the commercialization of the water-dispersible hydroxypropyl methylcellulose phthalate has not been successful.

The present inventors have attempted a method for preparing stable nanoparticles of water-dispersible hydroxypropyl methylcellulose phthalate, which comprise introducing an aqueous emulsification process of hydroxypropyl methylcellulose phthalate and regulating the content of remaining electrolytes through an ion exchange process. The environment-friendly nanoparticles have exhibited some improvements in general properties such as disintegration and dissolution, when used as an enteric coating material. However, although the process is successful in preparing enteric coating materials with improved properties, it still has some shortcomings. That is, the process needs a high-cost emulsifier and a long period of time (4-8 hr) for ion-exchange process to improve properties of film and enteric coating materials. Therefore, there still remains a need for overcoming such disadvantages in process efficiency and cost-

effectiveness.

The present inventors have conducted intensive researches to overcome the problems associated with the use of a high-cost emulsifier and a long period of time for the process in preparing enteric water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles. As a result, the present inventors have found that the hydroxypropyl methylcellulose phthalate nanoparticles with desired enteric properties could be prepared through ion exchange for 1-2 hr, in which hydroxypropyl methylcellulose phthalate is dispersed in water without using a high-cost emulsifier, nanoparticles are ion-exchanged to obtain the suitable electrolyte content and a plasticizer serving as a softener is added.

Accordingly, it is an object of this invention to provide a process for preparing enteric water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles in a cost-effective and time-saving manner, in which the employment of a high-cost emulsifier can be avoided and the ion exchanging step can be performed in a short period of time.

DETAILED DESCRIPTION OF THIS INVETNION In an aspect of this invention, there is provided a process for preparing enteric water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles, which comprises : a step of adding a neutralizing agent to hydroxypropyl methylcellulose phthalate to obtain a nanoparticle containing a residual electrolyte content of 10.0-12. 0 mS; a step of ion-exchanging the nanoparticles to adjust the

residual electrolyte content to 7. 0-9.0 mS; and a step of adding a plasticizer to the nanoparticle to soften the nanoparticle.

The present invention will be described in more detail hereunder.

The present invention provides a process for preparing nanoparticles of enteric water-dispersible hydroxypropyl methylcellulose phthalate in a cost-effective and time-saving manner, in which the electrolyte content is adjusted to have a predetermined value, preferably, 7. 0-9.0 mS during the ion-exchanging step and a plasticizer as a softener is used instead of a high-cost emulsifier used in the conventional process. Such features could lead to the production of nanoparticles with improved enteric properties to prevent the detachment of film in the presence of gastric acid at pH 1.2.

Hereunder is given a more detailed description of the present process.

The first step of the method disclosed in the present invention is to obtain nanoparticles of hydroxypropyl methylcellulose phthalate containing a residual electrolyte content of 10.0-12. 0 mS by adding a neutralizing agent to hydroxypropyl methylcellulose phthalate.

As a source of hydroxypropyl methylcellulose phthalate, AnyCoat-P <BR> <BR> (Samsung Fine Chemicals Co. , Ltd. , Korea) with a weight-average molecular weight of 40,000-60, 000 was used. Any conventional neutralizing agent can be used in this invention, however, an aqueous ammonia is preferred as a neutralizing agent because it can be easily removed from the final product and also inexpensive.

Preferably, the neutralizing agent is used in the amount of 7-14 wt% based on the weight of hydroxypropyl methylcellulose phthalate. If the amount is less than 7

wt%, the size of particles becomes larger during their dispersion in water to render the particles instability and the presence of remaining unreacted hydroxypropyl methylcellulose phthalate would result in the decrease in solid content. If the amount is more than 14 wt%, the offensive odor of ammonia is generated and nanoparticles cannot be formed because hydroxypropyl methyl cellulose phthalate is completely dissolved. The conditions for the first step of producing nanoparticles may vary depending on the type of neutralizing agents and the reaction amount.

The second step is an ion exchange process to adjust the residual electrolyte content of nanoparticles to be 7.0-9. 0 mS by using ion exchange resin or a membrane.

For ion exchange resin, any general cation exchange resins can be used. The nanoparticles obtained are preferred to stay for 1-2 hr in the resin to adjust the residual electrolyte content to 7.0-9. 0 mS, more preferably, 7. 0-8. 0 mS. If the residual electrolyte content is less than 7.0 mS, the time for removing electrolytes becomes longer and the overall yield is decreased because there will be a loss in product due to ion exchange. If the residual electrolyte content is maintained at the level of more than 8.0 mS, the final product coated on the drug is very likely to be disintegrated in the gastric acid at pH 1.2, although the nanoparticles are added with a plasticizer.

The third step is to add a plasticizer to the nanoparticles for the purpose of softening the nanoparticles.

The plasticizer used in the present invention permits the nanoparticles of hydroxypropyl methylcellulose phthalate to have enteric coating properties and excellent physical properties of film. In addition, the plasticizer allows the film of hydroxypropyl methylcellulose phthalate nanoparticles to have improved physical

properties such as compactness and glossiness. The plasticizer can be selected from a group consisting of polyvinyl alcohol, polyethylene glycol, glycerin, propylene glycol, diethyl phthalate, triacetin, cetyl alcohol, triethyl citrate or a hydrophilic plasticizer, more preferably, polyvinyl alcohol or polyethylene glycol. It is preferred that the plasticizer be used in the amount of 10-30 wt% based on the weight of hydroxypropyl methylcellulose phthalate. If the amount is less than 10 wt%, the film of hydroxypropyl methylcellulose phthalate nanoparticles may be swelled or partially detached when applied to a drug; in contrast, if the amount exceeds 30 wt%, there will be a heavy aggregation among tablets during coating the coating process and the drying process proceeds so slowly that the coating capacity is sharply decreased.

After going through with the above three steps, the hydroxypropyl methylcellulose phthalate nanoparticles having a size of 20050 nm, an acid number of 130-150 and a pH of 4. 5+1. 0 are finally obtained.

The hydroxypropyl methylcellulose phthalate prepared according to the present process shows no particle sedimentation when stored for a long period of time in water and is not dissolved at pH 1.2, a condition similar to that of gastric acid, when it is coated on tablet. Therefore, it can be used as an environment-friendly enteric coating material.

The following specific examples are only intended to be illustrative of the invention and they should not be construed as limiting the scope of the invention as defined by appended claims.

EXAMPLE 1 400 g of purified water and 100 g of hydroxypropyl methyl cellulose phthalate were placed in a 2L reactor equipped with a stirrer and stirred at a rate of 300 rpm. To the solution, an aqueous ammonia was slowly added to yield water- dispersible hydroxypropyl methyl cellulose phthalate nanoparticles containing the electrolyte content of 10.0-12. 0 mS. The resultant was allowed to stand for 1-2 hr, and then its residual electrolyte content was adjusted to 7.0-9. 0 mS using ion-exchange resin. Thereafter, 10 g of polyvinyl alcohol as a plasticizer was added and stirred to give water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles of interest.

Thus prepared water-dispersible hydroxypropyl methylcellulose phthalate showed the particle size of 20050 nm, an acid number of 130-150 and a pH of 4. 51. 0.

EXAMPLE 2 The water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles were prepared according to the procedures in Example 1, except that the amount of polyvinyl alcohol used was 20 g.

Thus prepared water-dispersible hydroxypropyl methylcellulose phthalate showed a particle size of 20050 nm, an acid number of 130-150 and a pH of 4. 51. 0.

EXAMPLE 3 The water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles

were prepared according to the procedures in Example 1, except that 10 g of polyethylene glycol was used instead of 10 g of polyvinyl alcohol.

Thus prepared water-dispersible hydroxypropyl methylcellulose phthalate showed a particle size of 20050 nm, an acid number of 130-150 and a pH of 4. 51. 0.

EXAMPLE 4 The water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles were prepared according to the procedures in Example 1, except that 20 g of polyethylene glycol was used instead of 10 g of polyvinyl alcohol.

Thus prepared water-dispersible hydroxypropyl methylcellulose phthalate showed a particle size of 20050 nm, an acid number of 130-150 and a pH of 4. 51. 0.

EXAMPLE 5 The water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles were prepared according to the procedures in Example 1, except that 25 g of glycerin was used instead of 10 g of polyvinyl alcohol.

Thus prepared water-dispersible hydroxypropyl methylcellulose phthalate showed a particle size of 20050 nm, an acid number of 130-150 and a pH of 4. 51. 0.

EXAMPLE 6 The water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles were prepared according to the procedures in Example 1, except that 25 g of propylene glycol was used instead of 10 g of polyvinyl alcohol.

Thus prepared water-dispersible hydroxypropyl methylcellulose phthalate showed a particle size of 20050 nm, an acid number of 130-150 and a pH of 4. 51. 0.

EXAMPLE 7 The water-dispersible hydroxypropyl methyl cellulose phthalate nanoparticles were prepared according to the procedures in Example 1, except that 20 g of diethyl phthalate was used instead of 10 g of polyvinyl alcohol.

Thus prepared water-dispersible hydroxypropyl methylcellulose phthalate showed a particle size of 20050 nm, an acid number of 130-150 and a pH of 4. 51. 0.

EXAMPLE 8 The water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles were prepared according to the procedures in Example 1, except that 30 g of triacetin was used instead of 10 g of polyvinyl alcohol.

Thus prepared water-dispersible hydroxypropyl methylcellulose phthalate showed a particle size of 20050 nm, an acid number of 130-150 and a pH of 4. 51. 0.

EXAMPLE 9 The water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles were prepared according to the procedures in Example 1, except that 15 g of cetyl alcohol was used instead of 10 g of polyvinyl alcohol.

Thus prepared water-dispersible hydroxypropyl methylcellulose phthalate showed a particle size of 20050 nm, an acid number of 130-150 and a pH of 4. 51. 0.

EXAMPLE 10 The water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles were prepared according to the procedures in Example 1, except that 20 g of triethyl citrate was used instead of 10 g of polyvinyl alcohol.

Thus prepared water-dispersible hydroxypropyl methylcellulose phthalate showed a particle size of 200+50 nm, an acid number of 130-150 and a pH of 4. 51. 0.

COMPARATIVE EXAMPLE 1 400 g of purified water, 1. 0 g of Pluronic F-68 as an emulsifier and 100 g of hydroxypropyl methylcellulose phthalate (Mw 40,000-60, 000, Samsung Fine Chemicals Co. , Ltd. , Korea) were placed in a 1 L reactor equipped with a stirrer and stirred at a rate of 300-350 rpm. 28% NH40H (8 g) was slowly added to this solution and the temperature was elevated to 60 °C. After stirring for another 4-5 hr while maintaining the temperature, the residual electrolyte concentration was adjusted to 2.0 mS using ion-exchange resin (Dowex MR-3, Dow Chemicals, USA).

Thus prepared water-dispersible hydroxypropyl methylcellulose phthalate showed a pH of 4. 61. 0, a solid content of 255%, an acid number of 1405 and a particle size of 30050 nm.

COMPARATIVE EXAMPLE 2 400 g of distilled water and 100 g of hydroxypropyl methyl cellulose phthalate were placed in a 2 L reactor equipped with a stirrer and stirred at a rate of

300 rpm. To the solution, an aqueous ammonia was slowly added to yield water- dispersible hydroxypropyl methyl cellulose phthalate nanoparticles containing the electrolyte content of 10.0-12. 0 mS and the residual electrolyte content was adjusted to 7.0-9. 0 mS using ion-exchange resin, thereby giving water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles of interest. However, the process was performed without using a plasticizer.

Thus prepared water-dispersible hydroxypropyl methylcellulose phthalate showed a particle size of 200+50 nm, an acid number of 130-150 and a pH of 4. 5+1. 0.

EXPERIMENTAL EXAMPLE The water-dispersible hydroxypropyl methylcellulose phthalate obtained in Examples 1-10 and Comparative Examples 1-2 was processed into 1 cm X 1 cm film and allowed to stand for 2 hr in an aqueous buffer solution of pH 1.2. Then, the film sample was taken out and the occurrence of disintegration was observed, and the results are shown in Table 1.

In addition, the water-dispersible hydroxypropyl methyl cellulose phthalate was diluted to 7 wt% with distilled water and coated on tablets using Hi-Coater (HCT Labo, Freund, Japan). The disintegration test using Pharmatest PTZ E was performed, and the results are shown in Table 1.

TABLE 1 Items Plasticizer (g) Disintegration (pH 1.2, 2 hr) 1 cm x 1 cm film Coated tablet Exam. 1 Polyvinyl alcohol (10) No occurrence No occurrence Exam. 2 Polyvinyl alcohol (20) No occurrence No occurrence Exam. 3 Polyethylene glycol No occurrence No occurrence (10) Exam. 4 Polyethylene glycol No occurrence No occurrence (20) Exam. 5 Glycerin (25) No occurrence No occurrence Exam. 6 Propylene glycol (25) No occurrence No occurrence Exam. 7 Diethyl phthalate (20) No occurrence No occurrence Exam. 8 Triacetin (30) No occurrence No occurrence Exam. 9 Cetyl alcohol (15) No occurrence No occurrence Exam. 10 Triethyl citrate (20) No occurrence No occurrence Comp. Exam. 1-No occurrence No occurrence Comp. Exam. 2 No occurrence 100 min, disintegration

As shown in Table 1, the films and tablets of the water-dispersible hydroxypropyl methylcellulose phthalate prepared using the plasticizer according to the present invention in Examples 1-10 were not disintegrated over 2 hr in the artificial gastric juice of pH 1.2, thus showing an improved enteric property. Such improved enteric property is similar to that of the known water-dispersible hydroxypropyl methylcellulose phthalate prepared using an emulsifier (Comparative Example 1).

In addition, the film of Comparative Example 2 without using a plasticizer

was not disintegrated unlike those of Examples; however, its coated tablet was observed to be disintegrated at pH 1.2. Accordingly, it would be understood that the use of plasticizer imparts the enteric property enabling to prevent disintegration for at least 2 hr at pH 1.2.

Consequently, instead of using a high-cost emulsifier, the introduction of a low-price plasticizer into the production process of water-dispersible hydroxypropyl methylcellulose phthalate nanoparticles is also successful in the production of enteric products with excellent coating properties. In addition, the use of a low-cost plasticizer enables to shorten the period of time for the process.

INDUSTRIAL APPLICABILITY As described previously, the water-dispersion process of this invention comprises the step of treating with a plasticizer instead of a high-cost emulsifier used in conventional processes, which is responsible for shortening the period of time for ion exchanging and producing hydroxypropyl methylcellulose phthalate nanoparticles with excellent film properties and enteric coating properties in a cost- effective as well as time-saving manner, thereby enabling to provide environment- friendly enteric coating material.