Patent Publication Number: US-4550238-A

Title: Apparatus and method for sealing capsules

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an apparatus and method for sealing capsules and more particularly using laser radiation sources with means to control the amount of radiation and methods for bonding such capsules. 
     The capsules utilized in the present invention are hard shell, telescopically joined capsules, having coaxial cap and body parts. The capsules are made of gelatin or other hydrophilic polymer materials whose properties are pharmaceutically acceptable. 
     While lasers have been used for many years to machine metals, utility in the polymers field has been limited. These limitations with polymers have involved the degregates of the material irradiated; disposition producing a residue; and discoloration of the polymers materials. 
     BRIEF DESCRIPTION IN DETAIL OF PRESENT INVENTION 
     The apparatus of the present invention includes a coherent source of mono-chromatic radiation, means, such as mirrors and lenses, to direct the radiation to select portions of hydrophilic capsules, such as gelatin and the like, and for means to control the amount of radiation at selected portions of the capsules. Lasers of helium-neon, carbon dioxide and argon types are suitable. Other laser types capable of providing the necessary energy within desirable time frames may obviously be substituted. The laser may be of the continuous or pulsed laser type, although the pulsed laser is preferred due to the relatively large amount of energy usually required. The pulsed laser may be operated using a control of the Q-switching, mode dumping or cavity dumping type. 
    
    
     FIG. 1 is a schematic of a preferred system according to the present invention; 
     FIG. 2 is a side view, partly in section of a capsule and holder embodiment for providing continuous seams; and 
     FIG. 3 is a view in cross-section illustrated as a modified structure for the embodiment of FIG. 1. 
    
    
     Referring to FIG. 1, a high power laser directs a beam 1 of mono-chromatic coherent radiation along an axis. One portion of beam 1 continues through beam splitter 2 and is deflected by mirror 3 toward joined capsule 4. Between mirror 3 and capsule 4, the beam is spread by negative lens 5 and converged along a single meridian by cylinder lens 6. The other portion of beam 1, is reflected by beam splitter 2 and then diverted by mirrors 7 and 8 toward capsule 4. Similarly, negative lens 5a spreads the beam which is then converged along one meridian by cylinder lens 6a. If a pulsed type laser is utilized it may be desirable to utilize a low power laser for alignment of the system. This can be accomplished by moving mirror 9 onto the axis of beam 1 into dotted position. The system, thus described, is suitable for simultaneously bonding a capsule at two points. Alternatively, a mirror 10 could be substituted for beam splitter 2, as illustrated, and alternated between the positions of mirror 10 and beam splitter 2. The bonding would be provided sequentially first along the axis deflected by mirror 3 and then along the axis of mirrors 7 and 8. The power for such apparatus, is regulated through the control by selecting a wattage and energy duration suitable to melt the adjacent surfaces of capsule 4. The lowest energy level sufficient to bond the capsule portions is selected to avoid excessive discoloration of the capsule, deleterious affects of the capsule contents, and/or decomposing the capsule at the bond site which could leave a undesirable residue. 
     Referring to FIG. 2, capsule 104 is supported by holder 105, which in turn is rotated by gear 106 driven by the motor. Laser beam 101, which is directed at joint 111 of capsule components 112 and 113 as capsule 104 is rotated forms seam 114. In the structure shown in FIG. 2, it is not necessary to use the beam deflecting optics shown in FIG. 1 and the laser would normally be operated in the continuous mode. 
     Referring to FIG. 3 capsule 204 is shown partly in cross-section. Beam 201 is spread by negative lens 205 and converged in one meridian by cylinder lens 206, A small quantity of water or plasticol 215 and 215a is placed at joint 211 by hollow needle 216 which is moved into position by solenoid 217. The liquid supply is connected to needle 216 by flexible tubing 218. The amount and timing of the liquid dispensed is controlled by conventional metering apparatus (not shown). Some of the liquid is drawn by capillary action into the overlapping portion of capsule components of 212 and 213. In Table 1 the melting temperatures of gelatin at given water contents are shown: 
     
                       TABLE 1                                                     
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MELTING TEMPERATURE OF GELATIN                                            
AT VARIOUS WATER CONTENTS                                                 
Melting Temperature                                                       
                 %                                                        
°Celsius  Water Content                                            
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130               8                                                       
175              10                                                       
88               15                                                       
65               20                                                       
57               25                                                       
52               30                                                       
50               35                                                       
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     Thus if water is used, some gelatin is dissolved to form a thin film of gelatin components 212 and 213 at the adjacent surfaces of joint 211 to significantly reduce by nearly 50% the temperature required to bond this gelatin capsule at the two locations. If a plasticol is used the amount of energy is again significantly reduced, since the energy need only evaporate the solvent. 
     The energy normally required to bond the capsule components can vary over a considerable range. Normally energy levels of 0.05 to 10 Joules/MM 2  are sufficient. Using an argon laser of 280 milliwatts, a satisfactory bond was obtained using apparatus equivalent to that shown in FIG. 1 having a bonded area of 1×7 MM with a 3 to 4 second radiation time. The embodiment of FIG. 2 provided a satisfactory bond using a C0 2  laser of 400 milliwatts with a 1 MM circular beam cross-section and a rotation speed of 4 RPM.