Hydrophilic polymer compositions for injection molding

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BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a moldable hydrophilic polymer composition, preferably gelatin, for use in an injection molding device preferably with a microprocessor, to produce capsules. The present invention utilizes gelatin made from various types of gelatin, including acid or alkaline processed ossein, acid processed pigskin, or alkaline processed cattle hide. Said types of gelatin have a molecular mass range of 10,000 to 2,000,000 Dalton or a molecular mass range of 10,000 to 2,000,000 and 10,000,000 to 20,000,000 Dalton. The method for determination of the molecular mass distribution of the various types of gelatin used in the present invention is described in the following references:

I. Tomka, Chimia. 30, 534-540 (1976)

I. Tomka, et al, Phot. Sci. 23, 97 (1975)

Gelatin having a molecular mass range between 10,000 and 2,000,000 Dalton, was found to give less deformation of capsule parts after ejection from a capsule mold,

When in the following description the term "gelatin" is used, other hydrophilic polymer compositions whose properties are acceptable as capsule materials are also included. Hydrophilic polymers are polymers with molecular masses from approximately 10.sup.3 to 10.sup.7 Dalton carrying molecular groups in their backbone and/or in their side chains and capable of forming and/or participating in hydrogen bridges. Such hydrophilic polymers exhibit in their water adsorption isotherm (in the temperature range between approximately 0.degree. to 200.degree. C.) an inflection point close to the water activity point at 0.5. Hydrophilic polymers are distinguished from the group called hydrocolloids by their molecular dispersity. For the maintenance of the molecular dispersity of said hydrophilic polymers a fraction of water--according to the working range of the present invention--of 5 to 25% by weight of said hydrophilic polymers must be included provided that the temperature of said hydrophilic polymers is in the working range between 50.degree. C. and 190.degree. C. of the present invention.

There are other hydrocolloids, not hydrophilic polymers in the sense of this definition, which contain more or less spherical or fibrous particles whereby those particles are composed of several macromolecules of a hydrophilic polymer within the molecular mass range of 10.sup.3 -10.sup.7 Dalton giving rise to particle sizes between 0.01-10 microns which is the typical range of colloidal particles. It is a primary object of the present invention to utilize hydrophilic polymer compositions in the production of capsules.

REFERENCES TO COPENDING PATENT APPLICATIONS

Concurrently with this application please also refer to patent application U.S. Ser. No. 490,057 filed Apr. 29, 1983, now U.S. Pat. No. 4,591,475 and to patent application U.S. Ser. No. 362,430 filed Mar. 26, 1982, now abandoned, both of which are copending with this application.

Description of the Prior Art

Capsule-making machines have been developed to utilize dip-molding technology. Such technology involves the dipping of capsule-shaped pins into a gelatin solution, removing the pins from the solution, drying of the gelatin upon the pins, stripping off the gelatin capsule parts from the pins, adjusting for length, cutting, joining and ejecting the capsules. Prior art capsule-making machines have utilized the combination of mechanical and pneumatic elements to perform these functions at speeds up to about 1,200 size 0 capsules per minute. While the above described apparatus are in general suitable for the intended purposes, it is desirable to produce capsules at considerably higher speed, over 15,000 size 0 capsules per minute, while at the same time precisely controlling the properties of the gelatin in order to produce the capsules hygienically and with minimum dimensional deviations so that the capsules can be filled on high speed equipment.

A prerequisite for any material to be moldable by an injection process is its ability to pass a glass transition point at a temperature compatible with the thermal stability of the material and the technical possibilities of an injection molding device.

Shirai et al. in U.S. Pat. Ser. No. 4,216,240 describes an injection molding process to produce an oriented fibrous protein product. The fibrous product as obtained by this process differs fundamentally from the transparent glasslike material of the capsules obtained from the present invention. Furthermore to obtain a flowable mass for the molding process, the protein mixtures used by Shirai et al. have to be denatured and thus lose their capacity to undergo dissolution.

Nakatsuka et al. in U.S. Pat. No. 4,076,846 uses binary mixtures of starch with salts of protein materials to obtain an edible shaped article by an injection molding process. With the present invention shaped articles from protein materials, preferably gelatin and other hydrophilic polymers can be produced without the addition of starch.

Heusdens et al. in U.S. Pat. No. 3,911,159 discloses the formation of filamentous protein structures to obtain edible products of improved tenderness. With the present invention shaped articles are produced without a filamentous protein structure.

The use of an injection molding device for producing capsules of gelatin and other moldable hydrophilic polymers with similar properties is new and has not been suggested in the technical literature.

The present invention distinguishes from the known as described above, by the nature of the compositions and by the recognition that gelatin and other hydrophilic polymers possess a dissolution point within a temperature range usable for an injection molding process, provided the water content of the gelatin and other hydrophilic polymers lies within a characteristic range, giving allowance to avoid any essential drying or humidification processes of the capsules.

SUMMARY OF THE INVENTION

The present invention covers an improved hydrophilic polymer composition, preferably gelatin, for use in an improved automatic injection molding device combined with a microprocessor to control the optimum time, temperature, pressure and water content of the composition in formed shaped parts. The composition has a molecular mass range of 10,000 to 2,000,000 Dalton or a molecular mass range 10,000 to 2,000,000 and 10,000,000 to 20,000,000 Dalton.

The composition has a water content range of approximately 5 to 25% by weight.

It is therefore a primary object of the present invention to provide a new and improved moldable composition of hydrophilic polymers for use with an injection molding-microprocessor apparatus which alleviates one or more of the above described disadvantages of the prior art compositions.

It is another object of the present invention to provide a new and improved moldable composition of hydrophilic polymers for use with an injection molding-microprocessor apparatus in method of molding capsules by continuous monitoring and control of the pertinent parameters in order to prevent degradation of the moldable composition of hydrophilic polymers and deformation of the capsules.

It is a further object of the present invention to provide a moldable composition of hydrophilic polymers for use with an injection molding-microprocessor apparatus in a method of molding capsules at high speed and with precision in order to use the capsules with high speed filling equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention both as to its organization and method of operation together with further objects and advantages thereof will best be understood by reference to the following specifications and taken in conjunction with the accompanying drawings.

FIG. 1 is a layout of the reciprocating screw injection molding device for making capsule parts;

FIG. 2 is a schematic of the injection molding work cycle for making capsule parts;

FIG. 3 is a schematic of the combined injection device-microprocessor apparatus for capsule parts;

FIG. 4 is an expanded schematic of the exit end of the injection molding device;

FIG. 5 is the diagram of dependence of shear viscosity of gelatin within the pertinent ranges of the shear rate in the present invention;

FIG. 6 is the diagram of molding area for gelatin within the ranges of time, temperature, pressure and water content of gelatin for the present invention;

FIG. 7 is the diagram of dependence of glass transition temperature range and melting temperature range for the pertinent water content ranges of the gelatin;

FIG. 8 is the diagram of dependence of differential calorimeter scan in which the heat consumption rate of the gelatin is plotted for the pertinent temperture range of the present invention;

FIG. 9 is a diagram of dependence of the logarithmic bulk elastic storage module of the gelatin for the pertinent temperature range of the present invention;

FIG. 10 is a diagram of dependence of equilibrium water content of the gelatin in the entire water activity range; and

FIG. 11 is a diagram of dependence of differential heat of water adsorption in the pertinent range of water content of the gelatin of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1 the injection molding device 27 generally consists of three units: a hopper unit 5, an injection unit 1 and a molding unit 2.

The function of the hopper unit 5 is receiving, storing, maintaining and feeding gelatin 4 at a constant temperature and at a constant water content. The hopper unit 5 comprises a vertical cylinder 30 having a closed top 31 with an inlet 32 therein to receive gelatin 4. At the bottom of the vertical cylinder 30 is a closed conical funnel 33 and a discharge outlet 34 to feed gelatin 4 into an inlet 34 of the injection unit 1. There is an air duct 35 communicating between the closed top 31 and the conical funnel 33 wherein air is circulated by a blower 36, the air temperature is maintained by a thyristor 37 and the air relative humidity is maintained by a steam injector 38.

The function of the injection unit 1 is melting, dissolving in water, and plasticizing in the extruder barrel 17 the gelatin 4 fed from the hopper unit 5 into the extruder inlet 54 and injecting the plasticized gelatin 14 into the molding unit 2.

The function of the molding unit 2 is automatically holding, opening and closing the mold 6 having capsule shaped cavities 19 therein, and ejecting the capsule parts 7 therefrom.

Within the injection unit 1 the screw 8 both rotates and undergoes axial reciprocal motion. When the screw 8 rotates, it performs the functions of melting, dissolving in water, and plasticizing the gelatin 4. When the screw 8 moves axially, it performs the function of injecting by transporting and ramming the plasticized gelatin 14 into the mold 6. The screw 8 is rotated by a variable-speed hydraulic motor and drive 10, and its axial motion is reciprocated by a duplex hydraulic cylinder 9.

Compression of the plasticized gelatin 14 in front of the rotating screw 8 forces back the screw assembly 20 containing the screw 8, the drive 10 and the cylinder 9. When the screw assembly 20 reaches a pre-setback position a limit switch 12 is contacted. When a defined time has elapsed during which the gelatin 4 becomes fully plasticized gelatin 14 the hydraulic cylinder 11 brings the screw assembly 20 forward and uses the screw 8 as a ram for the plasticized gelatin 14 to be injected through a valve body assembly 50 (FIG. 4) including a one-way valve 15, a needle valve 23, nozzle 22 and an outlet port 21 into the molding unit 2. The one-way valve 15 prevents the plasticized gelatin 14 from going back over the helical flutes 16 of the screw 8. The extruder barrel 17 has steam heating coils 18 to heat the gelatin 4 while it is being compressed by the screw 8 into plasticized gelatin 14. It is desirable for the plasticized gelatin 14 to be heated at the lowest possible temperature and to be transported with the lowest possible speed of the screw 8. The speed of the screw 8 and the heating of the plasticized gelatin 14 within the extruder barrel 17 by the steam heating coils 18 control the quality and the output rate of the plasticized gelatin 14 injected into the molding unit 2. The molding unit 2 holds the mold 6 having capsule shaped cavities 19 into which the plasticized gelatin 14 is injected and maintained under pressure. Refrigerant cooling conduits 24 encircle the mold 6 so that when the plasticized gelatin 14 in the mold 6 has cooled and sufficiently solidified, the molding unit 2 opens, the mold 6 separates and the capsule parts 7 are ejected.

Referring now to FIG. 1 and also to FIG. 2 which depicts the injection molding work cycle for gelatin 4 (containing approximately 17% water by weight) plotted against time. In general the work cycle of gelatin 4 is as follows in the injection molding device 27 of the present invention:

a. gelatin 4 is fed into the hopper unit 5 where it is received, stored and maintained under conditions of temperature ranging from ambient to 100.degree. C., pressure ranging from 1-5.times.10.sup.5 Newtons per square meter (N.times.m.sup.-2) and water content ranging from 5 to 25% by weight of gelatin,

b. the stored gelatin is melted under controlled condition of temperature ranging from 50.degree. to 190.degree. C., water content ranging from 5 to 25% by weight of gelatin and pressure ranging from 600 to 3000.times.10.sup.5 N.times.m.sup.-2,

c. the molten gelatin is dissolved in water under controlled conditions of temperature ranging from 50.degree. to 190.degree. C. pressures ranging from 600 to 3000.times.10.sup.5 N.times.m.sup.-2, and water content ranging from 5 to 25% by weight of gelatin.

d. the dissolved gelatin is plasticized under controlled conditions of temperature ranging from 50.degree. to 190.degree. C., pressure ranging from from 600 to 3000.times.10.sup.5 N.times.m.sup.-2 and water content ranging from 5 to 25% by weight of gelatin.

e. the plasticized gelatin is injected into the mold 6 under controlled conditions of temperature below 50.degree. C., injection pressure ranging from 600 to 3000.times.10.sup.5 N.times.m.sup.-2 and a clamping force of the mold 6 below approximately 600,000 Newton, and

f. the capsule-shaped parts 7 are ejected from the molded gelatin within the mold 6.

Beginning at point A of FIG. 2 the screw 8 moves forward and fills the mold 6 with plasticized gelatin 14 until Point B and maintains the injected plasticized gelatin 14 under high pressure, during what is called the hold time from point B until Point C of FIG. 2. At Point A the one-way valve 15 at the end of the screw 8 prevents the plasticized gelatin 14 from flowing back from the nozzle 22 onto the screw 8. During hold time, additional plasticized gelatin 14 is injected, offsetting contraction due to cooling and solidification of the plasticized gelatin 14. Later, the outlet port 21, which is a narrow entrance to the molding unit 2 closes, thus isolating the molding unit 2 from the injection unit 1. The plasticized gelatin 14 within the mold 6 is still at high pressure. As the plasticized gelatin 14 cools and solidifies, pressure drops to a level that is high enough to ensure the absence of sinkmarks, but not so high that it becomes difficult to remove the capsule parts 7 from the capsule-shaped cavities 19 within the mold 6. After the outlet port 21 closes, at Point C, screw 8 rotation commences. The plasticized gelatin 14 is accommodated in the increased cylindrical space in front of the screw 8 created by its backward axial motion until Point D. The flow rate of the plasticized gelatin 14 is controlled by the speed of the screw 8 and the pressure is controlled by the back pressure (i.e., the hydraulic pressure exerted on the screw assembly 20) which in turn determines the pressure of the plasticized gelatin 14 at the nozzle 22 in front of the screw 8. After plasticized gelatin 14 generation for the next shot into the mold 6, the screw 8 rotation ceases at Point D. The gelatin 4 on the stationary screw 8 continues to melt from Points D to E by heat conduction from the steam heating coils 18 on the extruder barrel 17. This period is called soak time. Meanwhile, the solidified capsule parts 7 are ejected from the mold 6. Thereafter, the mold 6 closes to accept the next shot of plasticized gelatin 14. All of these operations are automated and controlled by a microprocessor as hereinafter described.

Referring now to FIG. 2 and and also to FIG. 3. The injection molding work cycle of FIG. 2 is accomplished on the injection molding device 27 of FIG. 3 by hydraulic and electrical components and the corresponding circuits controlled by the microprocessor 28 of FIG. 3.

Through the use of solid-state circuitry and speed, temperature, limit and pressure switches for the electric and hydraulic systems, the microprocessor 28 of the present invention utilized command signals in its memory 51 for the parameters of time, temperature and pressure conditions of Table 1 below for the injection molding work cycle of FIG. 2 to be accomplished by the injection molding device 27 of FIG. 3 in producing gelatin capsule parts 7.

__________________________________________________________________________ POINTS A B C D E __________________________________________________________________________ Time 10.sup.-2 -1 .sup. 10.sup.-2 -1 10.sup.-2 -1 10.sup.-2 -1 10.sup.-2 -1 (seconds) Temperature ambient-100 50-190 50-190 50-190 50-190 (.degree.Celsius) Pressure 1-5 600-3000 600-3000 0-3000 600-3000 (10.sup.5 .times. N .times. m.sup.-2) (Newtons per square meter) __________________________________________________________________________

Referring now to FIG. 3 illustrating the combined injection molding device 27 and microprocessor 28 utilizing the method of present invention.

The combined injection molding device 27 and microprocessor 28 comprises six control circuits of which five are closed-loop, fully analog, and one is on-off. Starting at molding cycle Point A in FIG. 2, the injection molding work cycle operates as follows:

When sufficient plasticized gelatin 14 has accumulated in front of the screw 8 (microprocessor time controlled) and also when the screw assembly 20 carrying the screw 8, drive 10 and hydraulic motor 9 has been pushed far enough backwards against a constant back-pressure as controlled by control circuit 3, limit switch 12 will be actuated by position sensing circuit 14. Upon these two conditions control circuit 4 is actuated causing the hydraulic fluid to flow into the forward portion of the hydraulic cylinder 11. This rams the screw assembly 20 forward, thus injecting the plasticized gelatin 14 into the mold 6 as molding cycle Point B of FIG. 2 is reached, and, as controlled by the microprocessor 28, the screw 8 remains stationary in this forward position under high pressure for a certain period of time until Point C.

From molding cycle Point B of FIG. 2 onwards the plasticized gelatin 14 cools down in the mold 6 and the port 21 closes at molding cycle Point C of FIG. 2.

At molding cycle Point C of FIG. 2 the screw 8 starts to rotate again and the hydraulic pressure reduced from the forward portion of the hydraulic cylinder 9 to a pressure slightly less than the pressure set for the backward portion of the hydraulic cylinder 9.

The barrel 17 is kept under constant pressure towards the mold 6 by the pressure in the back position of the hydraulic cylinder 11. This is achieved by means of the control circuit 2 where a proportional hydraulic valve is controlled by a pressure sensor circuit I.sub.2.

As the screw 8 rotates a recharge of gelatin 4 is made from the hopper 5. During a certain time period and at a defined rotating speed of the screw 8, controlled by control circuit 3, a precise amount of gelatin 4 is fed into the extruder barrel 17. Control circuit 3 is actuated by speed sensor circuit I.sub.3 measuring the rotating speed of the screw 8 and sensing back to a hydraulic proportional flow control valve 0.sub.3 controlled by control circuit 3, thus assuring a constant rotating speed of the hydraulic motor 10, irrespective of the changing torque resulting from introduction of the gelatin 4 recharge.

When the load time is completed, the screw 8 rotation is stopped and molding cycle Point D of FIG. 2 is reached. The soak time from molding cycle Points D to A of FIG. 2 allows for the gelatin 14 to plasticize completely under controlled temperature conditions as controlled by control circuit 1.

A temperature sensor circuit I.sub.1 senses a thyristor heat regulator 0.sub.1 heating the extruder barrel 17 as directed by control circuit 1.

During the time interval from molding cycle Points B to E on FIG. 2, the mold 6 has cooled down sufficiently so that the finished capsule parts 7 can be ejected from the mold 6.

After ejection of the capsule parts 7, the work cycle returns to Point A of FIG. 2 where a certain volume of plasticized gelatin 14 has accumulated in front of the screw 8 (sensing circuit I.sub.4 is actuated and time has