Starch based formulations - Patent Review 5427614

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It is known to process starch under applied pressures and to manufacture pressure-formed molded bodies therefrom, e.g. by means of injection molding. Preferably, such molded bodies are manufactured for fillint with pharmaceuticals, comestibles, chemicals and others, particularly as pharmaceutical capsules for the dosed processing of medicaments. Such vessels consist as a rule of a container part and a closure part, both parts fitting exactly into one another in the closed state and resulting in a tightly sealed vessel.

The manufacture of such pressure-formed vessels from natural starch is known from European Patent Application No. 84 360 940.8 (Publn. No. 118 240).

In the industrial fabrication it is necessary to manufacture the pressure-formed articles, in particular the very thin-walled pharmaceutical capsule parts, with the greatest precision and at high speed. In addition, during manufacture a minimum of defective parts should arise in order to minimize subsequent controls and interruptions in the filling machines.

Mastering these problems of processibility has proved to be surprisingly difficult. With the manufacture of very thin-walled parts, for example with wall thicknesses of under 0.5 mm, these problems intensify.

In particular a very good flow behavior of the starch mixture is necessary, both with reference to the starting powder (freely flowing starch-based starting mixture), as well as during the total injection molding process as far as the fluid state. The molten mass should, to avoid high pressures, flow as easily as possible and should, with reference to the temperature and the intermixing with the additives and the water, show as homogenous a distribution as possible.

Furthermore, the injection-molded parts should be easily removable from the mold, as well as having a good dimensional stability, in order to avoid adherence to the wall in the tool or deformation on ejection.

Surprisingly, the problems can be solved, if 1. a starch starting mixture which is particulate and free-flowing at room temperature is used, which results under the processing conditions in a molded article with practically amorphous wall structure, 2. the viscosity of the molten mass at 90.degree.-240.degree. C. and particularly 140.degree.-190.degree. C. lies between 2500 and 50 Pa.s (=Pascal.times.second), preferably 2000 and 50 Pa.s, in particular 1500-50 Pa.s, and 3. the glass transition point of the mixture heated in a closed vessel to 140.degree.-190.degree. C. lies at 25.degree. C. at least, preferably at 45.degree. C. at least and in particular at about 65.degree. C. These conditions are achieved with the composition defined in the following.

The composition specified in the following permits injection-molding machines to be driven in continuous 24-hour operation with little chance of process defects and without the above-mentioned disadvantages.

The present invention relates in this sense to basic starch-based formulations for processing under applied pressure which are particulate and free-flowing at room temperatures, characterized in that these contain:

______________________________________ quantity ______________________________________ (a) chemically non-modified starch 72-89.58 parts (b) at least one lubricant/release agent 0-5 parts (c) at least one melt-flow accelerator 0-5 parts (d) texturing agent 0.02-1 parts (e) water 10-22.0 parts ______________________________________

(i) the components (b) and (c) together always result in at least 0.4 parts and at most 5 parts and

(ii) the sum of the components (a), (b), (c), and (d) and (e) always is 100 parts.

It has further been found that these formulations are suitable for the use in the processing under applied pressures e.g. pressure molding, injection molding, blow molding, extrusion etc.

These basic formulations can contain further components, as is described further below. Parts always mean weight parts.

By chemically non-modified starch, naturally occurring plant carbohydrate is to be understood, which mainly consists of amylose and amylopectin. This starch is obtained for example from potatoes, rice, tapioca, corn, rye, oats, wheat and other plants. The term starch with modified physical structure is to be understood to refer to gelatinized or pre-cooked starch and highly water-soluble starch, e.g. starch with a reduced average molar mass. Such starch or a mixture of such starches can be processed in the specified composition under pressure and elevated temperature to compact molded bodies.

Preferably, the proportion of physically altered starch to the natural starch is not higher than 50%, more preferably not higher than 20%. Most preferred is natural starch.

The starch (a) is present in the basic formulation in a quantity of 72-89.58 parts, more preferably 75-85 parts and most preferably around 79-83 parts, related to 100 parts of this composition.

The starch has preferably an amylose content of 0-70% and amylopectin of 100-30%. The type of starch most preferred is potato starch.

A suitable lubricant/release agent (b) for example may be comprised of animal and vegetable fats individually or in a mixture, in particular, hydrogenated fats are suitable, preferably such as are solid at room temperature. Preferably they have a melting point of over 50.degree. C. As a rule, these fats are triglycerides with a proportion of C.sub.14 -, C.sub.16 - and C.sub.18 -acids, for example C.sub.18 (around 65%), C.sub.16 (around 30%), C.sub.14 (around 5%).

The amount of lubricant/release agent employed is preferably 0-5 parts, more preferably 0-3.0 parts and most preferably 0.6-1.2 parts related to 100 parts of the basic formulation.

These lubricant/release agents act simultaneously as softening agents and viscosity depressants so that the addition of these other agents is unnecessary.

The melt-flow accelerator (c) may be selected from solid mono- and diglycerides, preferably long-chained acids such as the C.sub.14 -, C.sub.16 -, C.sub.18 -fatty acids, which are preferred and phosphatides, in particular lecithin is most preferred. Preferred additive quantities are 0-5.0 parts, more preferably 0.1-2.0 and most preferably 0.2-1.0 parts, of such individual compounds or a mixture of such compounds related to 100 parts of the basic formulation.

The sum of the components (b) and (c) always amounts to at least 0.4 parts and preferably 0.8-2.0 parts related to 100 parts of the basic formulation.

The texturing agent (d) is titanium dioxide or silicon-dioxide or a mixture of these compounds. It was found that such compounds guarantee a free flowing of the starting material as a powder at room temperature and further prevent the formation of bridges in the hopper and at the screw during processing, which hinder the feeding of the starting material onto the screw. Through the addition of these components the dosing of the starch material takes place consistently and rapidly from cycle to cycle.

It is thus not necessary to granulate or otherwise pretreat the starting material.

The quantity of the texturing agent is preferably 0.02-1 parts, related to 100 parts of the basic formulation. For titanium dioxide the optimum addition quantity lies at around 0.4 parts and for silicon dioxide at around 0.1 parts both values related to 100 parts of the basic formulation. Naturally more titanium dioxide or silicon dioxide can be added. The excess then acts as a filler and can also influence negatively the properties of the product.

The water (e) is present in a quantity of 10-22 parts, preferably 10-20 parts, more preferably 15-19 parts related to 100 parts of the basic formulation. In the manufacture of thin-walled articles the preferred ranges are most applicable.

The process conditions depend principally on the starch used, the components (b) to (e) and the additives mentioned further below, which are present in addition if necessary.

The higher the water content, the lower are the temperatures and pressures which can be selected in the injection-molding process; the lower the water content, the higher the pressures and temperatures to be selected. The selection of suitable pressures and temperatures is simple and can be easily determined by one of ordinary skill in the art. The pressures suitable in the manufacture of thicker-walled articles are in the range of from 300.times.10.sup.5 N/m.sup.2 to about 3000.times.10.sup.5 N/m.sup.2 and for thinner-walled articles in the range of about 600.times.10.sup.5 N/m.sup.2 to about 3000.times.10.sup.5 N/m.sup.2 preferably about 900.times.10.sup.5 to about 1500.times.10.sup.5 N/m.sup.2.

Extrusion molding pressures of less than 10 bars are suitable, dpending on the water content. Suitable temperatures lie predominantly in the range from about 80.degree.-240.degree. C., preferably at about 130.degree.-210.degree. C. and in particular at about 150.degree.-190.degree. C.

Other known techniques, such as injection-molding machines or extruders, may also be used.

Depending on the same water content, potato starch can be processed more easily, i.e. with lower pressure and temperature conditions, than wheat starch. The degree of difficulty grows in the order of potato starch, wheat starch, corn starch, and rice starch. Preferred is potato starch and wheat starch, in particular potato starch.

In the above mentioned starch based formulations, starch can be replaced up to 50% but preferably not higher than 20% by one or a mixture of other hydrophilic material. Such other hydrophilic materials are polymers such as gelatin and vegetable proteins such as: sunflower protein, soybean proteins, cotton seed proteins, peanut proteins, rape seed proteins, blood proteins, egg proteins, acrylated proteins; water-soluble polysaccharides such as: alginates, carrageenans, guar gum, agar-agar, gum arabic and related gums (gum ghatti, gum karaya, gum tragacanth), pectin; water-soluble derivatives of cellulose: alkylcelluloses hydroxyalkylcelluloses and hydroxyalkyl-alkylcelluloses, such as: methylcellulose, hydroxy-methylcellulose, hydroxyethylcellulose, hydroxypropyl-cellulose, hydroxyethylmethylcellulose, hydroxypropyl-methylcellulose, hydroxybutylmethylcellulose, cellulose esters and hydroxyallylcellulose esters such as: celluloseacetylphthalate (CAP), hydroxypropyl-methylcellulosephthalate (HPMCP); carboxyalkylcelluloses, carboxyalkylcellulose esters, carboxyalkylcellulose esters such as: carboxymethylcellulose and their alkali metal salts; water-soluble synthetic polymers such as: polyacrylic acids and polyacrylic acid esters, polymethacrylic acids and polymethacrylic acid esters, polyvinylacetates, polyvinylalcohols, polyvinylacetatephthalates (PVAP), polyvinylpyrrolidone, polycrotonic acids; also suitable are phthalated gelatin, gelatin succinate, crosslinked gelatin, shellac, water soluble chemical derivatives of starch, cationically modified acrylates and methacrylates possessing, for example, a tertiary or quaternary amino group, such as the diethylaminoethyl group, which may be quaternized if desired; and other similar polymers.

Preferably the starch is replaced by not more than by about 3-10% of these compounds.

Softening agents may also be added to the basic formulation, in quantity of preferably 0.5-10 parts, in particular 0.5-5 parts, related to the specified 100 parts. The starting materials may also be mixed with liquid additives until they are completely absorbed and a firm flowable mixture arises. An excess or a sticking of the individually mixed particles must be avoided. Suitable softening agents are for example polyalkylene oxides, like polyethyleneglycols, polypropyleneglycols, polyethylenepropyleneglycols; low-molecular organic softening agents like glycerin, glycerin mono-, di- and triacetate; propyleneglycol, sorbitol, sodium diethyl sulfosuccinate, triethyl-citrate, tributylcitrate and mixture thereof.

The sum of the weight parts of water and softening agent should preferably not surpass the specified maximum contents for water. Preferably, therefore, the sum of water and softening agent amounts to 10-22, preferably 10-20 and preferably 15-19 parts related to 100 parts of the basic formulation.

The mixture can also be dyed. Suitable dyestuffs are for example known azo dyes or organic or inorganic pigments, or naturally occurring dyestuffs. Preferred are inorganic pigments, like the oxides of iron or of titanium which are known per se in a concentration of 0.001-10%, preferably 0.5-5%, related to the weight of all the components.

As mentioned above, the formulation of the present invention can be used in all types of molding techniques under applied pressures such as pressure molding, injection molding, blow molding or extrusion and it is possible to produce articles such as containers, bottles, sheets, sacs, films, packaging materials, tubes, rods, pharmaceutical capsules etc. in all the numerous variations known.

The following examples are provided for illustrative purposes. It is readily understood that variations in the materials used and/or processing parameters followed are intended to be within the scope of the present invention. The examples are therefore for demonstration effect only and should not be regarded as limiting the spirit and scope of the invention as recited in the claim that follow.

EXAMPLE 1

A composition consisting of 81 parts of natural potato starch, one part of the hydrated triglyceride containing the fatty acids C.sub.18 :C.sub.16 :C.sub.14 in a ratio of 65:31:4 weight percent, 0.7 parts lecithin, 0.3 parts titanium dioxide and 17 parts water is mixed in a powder mixer for 10 minutes. Thereafter a freely flowing powder is obtained. This powder is fed into the hopper of an injection-molding machine and, at a temperature of 180.degree. C. and a pressure of 1500 bar, injected into an injection molding tool for capsule body and cap parts whose mold wall temperature lies at 40.degree. C. After cooling and ejecting from the mold a dimensionally stable capsule body and cap part is obtained, which can easily be processed on a filling machine.

With this mixture the injection molding machine can easily be driven in 24-hour operation without interruptions to the machine a strongly reduced number of defects to the capsule parts being detectable.

Analogous results are obtained by using the following formulations according to table 1:

TABLE 1 __________________________________________________________________________ STARCH COMPONENT b) COMPONENT c) COMPONENT d) WATER OTHERS No. Type % Type % Type % Type % % Type % __________________________________________________________________________ 1 Potato 75.00 hydrated 1.25 Lecithin 1.5 TiO.sub.2 0.25 22.0 -- -- vegetable fat 2 Potato 80.00 hydrated 1.0 " 0.9 " 0.1 18.0 -- -- vegetable fat 3 Potato 88.6 hydrate 0.8 " 0.5 SiO.sub.2 0.1 10.0 -- -- vegetable fat 4 Wheat 78.0 hydrated -- Monoglyceride, 5.0 " 3.04 19.0 dyestuff 0.96 vegetable fat C.sub.18 5 Wheat 79.0 hydrated 2.05 -- -- TiO.sub.2 /SiO.sub.2 0.95 18.0 -- -- vegetable fat 6 Wheat 85.0 hydrated 2.80 -- -- TiO.sub.2 0.20 12.0 -- -- animal fat 7 Maize 75.0 hydrated 4.80 Monoglycerid, 0.2 " 0.15 17.0 pre-cooked 2.85 animal fat C.sub.18 starch 8 Maize 78.0 hydrated 3.0 Monoglycerid, 1.0 " 0.05 14.0 pre-cooked 3. animal fat C.sub.18 starch 9 Rice 79.0 -- -- Monoglycerid, 2.0 SiO.sub.2 1.0 17.5 dyestuff 0.5 C.sub.18 10 Rice 80.25 " 0.9 Diglyceride, 0.6 " 0.25 15.0 Glycerin 3 C.sub.18, C.sub.16 11 Tapioca 75.2 " 0.9 Diglyceride, 0.6 " 0.3 21.0 HMPCP 2 C.sub.18, C.sub.16 12 Potato 73.96 " 2.0 Diglyceride, 2.0 " 0.04 17.0 PEG 5000 C.sub.18, C.sub.16 13 Potato 75.25 " 1.5 Diglyceride, 1.0 TiO.sub.2 0.25 18.0 PEG 4000 C.sub.18, C.sub.16 14 Potato 75.25 vegetable fat 1.5 Lecithin 1.0 " 0.25 18.0 Sorbitol 4 15 Wheat 60.00 " 1.5 " 1.2 " 0.25 17.0 Polyacrylic 20.05 acid __________________________________________________________________________

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