Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-02-24
2003-12-02
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S047000, C524S503000, C524S313000, C524S297000, C524S050000, C524S052000
Reexamination Certificate
active
06656984
ABSTRACT:
The present invention relates to a hydrophobic polymer dispersion according to the preamble of claim 1.
Such a dispersion contains modified starch dispersed in a liquid phase together with admixtures which are used in dispersions and known as such.
The invention also relates to a process according to the preamble of claim 16 for the formation of a hydrophobic polymer dispersion.
The emphasis on an environmentally friendly attitude and green values is opening up new markets for products based on renewable natural resources. Such trends are emerging in the fields of, among others, the packing industry, the sanitary product industry and the adhesive industry, where recyclability, reuse, compostability, biodegradability and lack of environmental stress are demands of today. The trend of replacing products based on petrochemistry by processed biopolymer products is also accentuated. Starch and its derivatives constitute a particularly interesting starting material for the production of biodegradable polymer products.
Polymer dispersions are used, e.g., to coat paper and board so as to improve their water resistance. In addition to fillers, dispersions used within the paper industry today also contain various synthetic latexes which are quite poorly decomposed in a biological environment.
Solutions are previously known in which modified starch components are used for the preparation of paper coating dispersions. Thus, a coating composition is known from WO Published Application No. 93/11300, based on a polymer dispersion containing a starch derivative having a polymer grafted thereto containing styrene and butadiene monomers. Therefore. this solution makes no use of such biodegradable components which are compatible with the demands on recyclability set on the products.
The present invention aims at achieving a hydrophobic dispersion most or preferably essentially all of whose components are biodegradable. The invention particularly aims at producing a dispersion whose polymer component mainly comprises a biodegradable polymer, advantageously starch or a derivative thereof. Furthermore, the invention seeks to provide a process for the production of hydrophobic dispersions.
The invention is based on the surprising observation that many biodegradable polymers can advantageously be dispersed in water by first plasticizing them and by dispersing the plasticized melt in water using dispersion admixtures. Thereby no solvents are required for producing the dispersion. Thus, according to the present process,
as the polymer, a biodegradable polymer is used, first mixed with a plasticizer in order to obtain a plasticized blend,
the blend is mixed with admixtures and water in optional order so as to obtain a dispersion, whereby the mixing is carried out at an elevated temperature, and
if desired, the dispersion is homogenized.
In more detail, the dispersion according to the invention is mainly characterized by what is stated in the characterizing part of claim 1.
The process according to the invention. then, is characterized by what is stated in the characterizing part of claim 16.
The invention provides considerable benefits. Thus, the base materials of the starch dispersion according to the invention are mainly based on renewable natural resources and are biodegradable/compostable. The starch component may be derived from any native starch: it need not be, e.g. a starch rich in amylose. No solvents requiring removal by evaporation are needed for the formation of the dispersion instead, the dispersion may be carried out by means of a melt processing apparatus, whereby the consumption of plasticizer is simultaneously considerably reduced. The films formed from the dispersion have a high water repellence and can be used to improve the water resistance of paper or board by at least 40 to 50%.
The new polymer dispersions may be used for coating paper or board, as a primer or as a component in labelling adhesives or paint. They are also suited for the production of hydrophobic cast films and for use as binders in materials based on cellulose fibres.
A particularly interesting embodiment comprises use of polymer dispersions for coating, for instance, medicinal preparations in tablet form.
The coating of medicinal preparations in tablet form is as such a very commnon process within the pharmaceutical industry. The purpose of the coating is either to cover the disagreeable taste or smell of the drug, to protect the drug against external factors during storage or dosage, to facilitate the packaging, identification or dosage of the tablets, or to control the release of active substance from the tablet. The most demanding ground for coating pharmaceutical tablets is the aim of obtaining controlled, usually retarded release of the active substances. The purpose is to achieve a desired rate of absorption by the body of the active substance over a longer time span. The purpose may, however, even lie in achieving the release and absorption of an active substance in a certain part of the digestive tract, this being the optimal part for the absorption of the medicinal preparation in question.
As a pharmaceutical process, the coating of tablets with a polymer film is carried out by spraying a solution or dispersion containing the coating polymer onto the tablets and by then evaporating the solvent or medium by means of pressurized air. Traditionally, polymers dissolved in organic solvents have been used for coating tablets containing medicinal preparations. Typical examples comprise ethyl cellulose and hydroxypropyl methyl cellulose. During the past few years, this technology has been developed especially for water-based coatings. In such a case the coating polymer is either soluble in water or dispersible in water. Polymers which are dispersible in water offer a wider range of possible uses from the point of view of controlling the release of active substances than do those soluble in water. Ethyl cellulose, among others, is available in the form of aqueous dispersions.
The use of aqueous dispersions is aimed at because organic solvents are environmentally less friendly and cause more problems for those dealing with them at work. The change is, however, not entirely free from complications, because the elaboration of dispersion processes is most demanding and not nearly all of the currently used polymers can be used to yield a dispersion. Furthermore, industrial processes for the preparation of drugs often have such dissimilar details that the same coating methods and equipment cannot be used in all cases. In addition, the properties of polymer films made from aqueous dispersions are often essentially different from those of films made from organic solutions.
The present invention can be used to obtain polymer dispersions particularly suited for coating pharmaceutical preparations. The dispersions are especially well suited for coating solid pharmaceutical preparations, such as pharmaceutical preparations with prolonged effect. As examples of pharmaceutical preparations subjected to coating, tablets, capsules and pellets may be cited, as well as particle-shaped drug carrier and allocator systems, such as nanoparticles, nanocapsules, microparticles, and colloidal dispersions. The release rate of a pharmaceutical substance may be controlled by regulating the thickness of the polymer film formed. By modifying the dispersion formulation, an optimal release profile for the medicinal preparation is easily obtained.
The invention is examined in more detail in the following in the light of a detailed description and a number of working examples.
The annexed FIGURE is a graphic pesentation of the release of active substance from dicalcium phosphate tablets coated with dispersions according to the present invention.
Hydrophobic starch dispersions can be produced by means of the process described herein. containing as the starch component a starch ester, starch ether, mixed ester/ether of starch or grafted starch made from native starch, hydrolyzed starch, oxidized starch, crosslinked starch, or gelatinized starch. Hyd
Haasmaa Kristiina
Heikkilä Maija Elina
Paronen Timo Petteri
Peltonen Soili
Urtti Arto Olavi
Oy Polymer Corex Kuopio Ltd.
Rajguru U. K.
Seidleck James J.
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