Title of Invention	PROCESS FOR PRODUCING A DESIRED BREAKING POINT ON A GLASS BODY
Abstract	A process for producing a desired breaking point for breaking the glass wall of a glass body, in particular a break-open ampoule or a tube, or for separating parts out of a pane of glass by generating microcracks in the breaking zone is described, in which process the microcracks are generated in the interior of the- glass wall or the pane of glass.

Full Text

i Process for producing a desired breaking point on a glass body The present invention relates to a process in accordance with the preamble of Patent Claim l. Glass ampoules are widely used for storing and , transporting medicinal preparations. The reasons for this are firstly that they hermetically seal the contents of the ampoules with 'respect to the outside world, and secondly they can be sealed quickly and easily by being fused together and can also be opened again relatively easily by breaking off the ampoule tip which adjoins the ampoule neck. A further advantage is the ease of optical inspection of the ampoule contents through the transparent glass wall. The opening of ampoules (so-called break-open ampoules) has already formed the subject-niatter of numerous patents and patent applications. However, the processes described therein are all subject to a greater or lesser extent to disadvantages. The broken edge, which is often jagged, on the ampoule, which has to be handled further after being broken open,! causes a certain risk of injury, which is increased still further by the fact that the breaking forces, which vary within a relatively wide range, may often reach rather high values, with the result that' the hands, which at that moment are subject to a very high level of strain, can move in an uncontrolled manner after the ampoule breaks open, resulting in injuries on the jagged broken edge. Finally, there is also the problem that the breaking line penetrates into the main body of, the ampoule, making it unusable. Moreover, broken glass which is formed during the breaking operation may contaminate the preparation situated in the ampoule. The problems described above arise to an increased extent in conventional processes which mechanically generate a more or less defined incipient crack using a file, cutting wheel, diamond or the like as a desired breaking point on the surface of the ampoule in the region of the ampoule neck. The causes of this are, for example, fluctuations in the breaking force as a result of tool wear and as a result of sensitivity of the processes to inevitable production-related fluctuations in the geometry of the ampoulefe. One attempt which has been made to allow the breaking of ampoules to proceed in a more controlled manner is the production of so-called breaking ring ampoules, in which the desired breaking line is marked with an enamel paint. The different coefficients of expansion of the ampoule glass and the enamel paint mean that a network of microcracks is produced on. the surface of the glass in the region of the marked ampoule neck during subsequent heat treatment of the ampoule, which network is used to initiate breaking. A drawback of this process is that there is still, a risk, as previously, of broken glass being formed and of the preparation being contaminated with heavy metal particles from the paint when the ampoule is broken open. More recent processes use laser radiation as a contact - free tool which can be employed with very reproducible results and a high service life to generate incipient cracks. DE 35 37 434 Al describes such a crack formation operation for break-'open ampoules. Pulsed lasers (CO, Nd: YAG) generate defined incipient crack holes at predetermined distances on the surface of the ampoule neck. According to this publication, this measure is said to ensure a controlled break (i.e. defined breaking forces and burr-free broken edges). DE 43 00 730 C1 describes the use of a TEA-CO2 high-power laser for the same purpose. A process for generating a breaking stress as a desired breaking point by means of high-power electromagnetic irradiation with a high power density (Er: YAG laser) is described in DE 42 14 _59. In all the processes which have just been ' described, the glass is heated locally until it becomes a molten liquid by single pulses or multiple pulses in the region of the laser spot. The subsequent very rapid cooling ot the molten zone generates tensile forces which are sufficiently high to produce the spontaneous (or forced: DE 43 00 730 C1) formation of microcracks. These microcracks represent the desired breaking point. . In order for microcracks to be reliably generated, the tensile stress range has to exceed a minimum level, requiring a minimum volume of heated glass. This volume of glass has different physical and chemical properties from the starting material, which properties cannot be fully reversed even after a subsequent "annealing (an extreme example is the appearance of so-called reboil blisters) . The result can be an increased- risk of broken glass during breaking or an uncontrolled Extent of breaking. A further drawback of the laser processes described is that the incipient cracks, which lie on the surface or extend as far as the surface are exposed to environmental effects, e.g. moisture, during the further handling of the ampoules. It is thus possible for undesirable crack propagation to occur, leading to leakage or premature breakage of the ampoule. Moreover, the loading of the glass surface with glass particles or products of evaporation is undefined and is undesirable to the pharmacist. For the reasons mentioned above, laser processes for generating desired breaking points in ampoules have not yet become fully established. The object of the invention is to form a desired breaking point in a break-open ampoule in the region of the breaking zone in such a manner as to allow reproducible and safe opening of the break-open ampoule. In particular, it is intended to avoid injuries which can occur when opening ampoules which are difficult to break open and to preclude impairment to the medicament caused by opening the ampoule. This object is achieved by means of the1 process described in Patent Claim 1. According to the present invention, the desired breaking point is produced by the fact that microcracks are formed in a controlled manner in the interior of the glass wall of the ampoule- In contrast to the prior i art discussed at the outset, in which in each case the glass wall is weakened by*microcracks from its surface, the surfaces in question remain undamaged when using the process according to the invention. The generation of microcracks in the interior of a glass body has hitherto been disclosed only for the purpose of marking these bodies. Thus, for example, DE 44 07 547 Al describes a process for marking the interior of a body made of a transparent material by means of an Nd:YAG laser (one or more pulses),1 with a network of punctiform microcracks, which may be as small as 0.01 mm and are no longer visible to the naked eye, being formed within spatially limited regions. During the stress-relieving treatment, the residual stresses disappear, but the microcracks are permanent. EP 0 743 128 Al describes a similar process, in which the interior of transparent materials can be marked by means of a laser whose wavelength is not absorbed by the material. A common feature of all these marking processes is that they are aimed at making the markings as visible as possible while simultaneously retaining the mechanical stability of the glass body. EP 0 743 128 Al even emphasizes that it is a particular advantage of the process that the stability of the glass is not impaired by the markings which are made. 4 ' It has now surprisingly been found that the use of the process according to the invention not only allows the stability of a glass wall against breakage, to be reduced considerably, but also that this reduction can be set in a controlled and reproducible manner.. The fact that the microcracks are situated in the interior of the glass wall means that there is no risk of the interaction with the environment mentioned at the beginning, which can lead to a change in the crack formation. As a result, a hitherto unattainable stability of the breaking properties of the ampoule when stored under widely differing conditions is achieved. Furthermore, generating the microcracks beneath the surface of the glass is also advantageous because there is generally a prestressing in the glass which produces a compressive stress zone at the surface and a tensile stress zone, which is usually weak, in the interior of the glass. When the process according to the invention is employed, the tensile stress zone can, as described below, be utilized to produce defined crack formation, whereas in the cracking processes in accordance with the prior art, which act from the surface, it is necessary to penetrate through or compensate for the compressive stress zone near to the surface, so as to prevent the microcracks from healing out in the compressive stress region. Advantageously, according to the invention the microcracks are generated by means of concentrated laser irradiation; in the case! of ampoules, as is known from the prior art, this takes place in the region of the ampoule neck. It has proven advantageous here to focus the laser beam with a diameter of least semi-transparent. By suitably selecting the laser parameters, the person skilled in the art can regulate the formation and propagation of the microcracks, e.g. the length and geometric arrangement thereof, in a controlled manner. Finding suitable parameters to do this does not require any inventive step, and they can readily be determined by the person skilled in the art, for example by means of suitable routine experiments. As is clear from the above, it is also readily possible to adapt the process parameters to different geometries of the glass bodies (e.g. for ampoules). The formation of the microcracks can take place using a single laser pulse or a series of laser pulses with a repetition frequency of approx. 10 to 1000 Hz. The crack formation may in addition be regulated further by a controlled local prestressing of the glass. It has been found that in the case of ampoules a prestressing which generates a tensile stress in the axial direction of the ampoule in the region of the laser spot leads to the preferential formation of microcracks which are aligned in the circumferential direction of the tube. This . crack geometry leads to a particularly good quality of break with minimum broken glass. The tensile stress may, for example, be generated in a manner known per se by means of burners (DE 36 15 287 C2) , forming tools, additional laser beams or by applying mechanical bending moments during the laser treatment. In order to guarantee the stability cf an ampoule even during relatively prolonged storage and transportation, the extent of Lhe cracks perpendicular to the surface of the glass should not exceed approx. 0.5 x wall thickness of the glass. Two possible practical embodiments of the process according to the invention are described below with reference to the ampoule example: 1) The desired breaking point may, for example, be generated at a point on the circumference of the constriction of the ampoule by means of one or more microcrack zones arranged in the circumferential direction along the desired parting line. This process (one point cut) requires marking of the desired breaking point in order to align the ampoule when it is broken open. 2) Furthermore, the desired breaking point may be generated along the desired parting line so as to run around the ampoule neck (in a similar manner to a so-called breaking ring ampoule) . In this case, the ampoule can be broken open without prior alignment. There is no need to mark the preferred, direction of breaking. For a defined breaking process, the angular interval of the desired breaking points must not exceed 30degrees. By comparison with the laser processes described in DE 42 14 159 CI and DE 35 37 434 Al, the quality of break when the process according to the invention is used is improved considerably by the fact that the modulation of the breaking front by the desired breaking points, which are arranged along the breaking line, is considerably reduced. This is because the residual stress areas in the, region of the laser spots in the processes described in DE 42 14 159 CI and DE 35 37 434 Al generally do not bring about the desired radial course of a crack front through the centre of a laser spot, but'rather cause the crack to deviate so that the crack front in each case runs around i * ! ' i the centre of the spots on a semicircle segment. A crack course of this nature increases the risk of broken glass and injury. cracks for numerous other applications, e.g. when cutting- glass tubes. The process may even be "employed advantageously for special cutting processes in the field of flat glass (e.g. breaking glass pieces of any desired shape (watch glasses) out of a pane of glass). An exemplary embodiment of the invention is illustrated in the drawing and described in more detail below. In the drawing: Fig. 1 shows a diagrammatic layout of a station for generating a desired breaking point in a break-open ampoule in accordance with the invention. In Fig. 1, a desired breaking point is generated in a 2 ml ampoule 1 made of borosilicate glass in the region of the ampoule neck 2 (constriction) . The constriction was formed previously ; in the production process of the ampoule on a turret machine with a forming tool to a diameter of 6.5 mm and a wall thickness of 0.8 mm. The desired breaking point is applied in the further processing line illustrated diagrammatically in Fig. 1, where the ampoule 1 is lifted out of the chain cqnveyor and against a stop roller 4 using a lifting device 3. The ampoule is » i ' mounted on the roller table 5, 6 in such a manner that the roller 6 tracks the forming tool. A Q-switched Nd: YAG laser 7 with a pulse duration of approx. 10 ns and a pulse energy of 25 mJ is used to generate the desired -breaking point. The laser beam is focused onto the centre of the glass wall using a laser lens 8 with a focal length of 50 mm: it has a' diameter of about 0.1 mm. In order to ensure that the' desired breaking point is generated in the centre of the glass wall, the diameter of the constriction 2 may have a tolerance of at most 0.1 mm. With a laser repetition frequency of 10 Hz, desired breaking points are applied to the ampoule neck 3 at a spacing of 1 mm along the , circumferential direction. The rotation of the ampoules which is required to achieve this is brought about by the drive of the roller 4. The three desired breaking points are visible under a microscope and allow the ampoule 1 to be broken cleanly and mechanically. 1. Process for producing a desired breaking point for breaking the glass wall of a glass body, in particular a break-open ampoule or a tube, or for separating parts out of a pane of glass' by generating microcracks in the breaking zone, characterized in that the microcracks are generated in the interior of the glass wall or the pane of glass. 2. Process according to Claim 1, characterized in that the microcracks are generated by means of laser irradiation. , 3. Process according to Claim 1 or j 2, characterized in that the laser radiation used has a wavelength at which the glass is transparent of at , least semi-transparent and the duration , of i a laser pulse is 4. Process according to at least one qf; Claims 1 to 3, characterized in that the size of the microcracks is set by irradiation with a series of laser pulses. 5. Process according to at least one of Claims 1 to 3, characterized in that the size of the microcracks is set by means of a subsequent heat treatment. 6. Process according to at least one of Claims 1 to 5, characterized in that the formation of the microcracks is controlled by means of a targeted pre-stressing of the glass. ' 7. Process according to at least one of Claims 1 to 6, characterized in that the extent of the micro--cracks perpendicular to the surface does not exceed 0.5 x thickness of the glass wall. 8. Process for producing a desired breaking point for breaking the glass wall of a glass body, substantially as herein described and exemplified.

Documents:

1457-mas-1998-abstract.pdf

1457-mas-1998-claims duplicate.pdf

1457-mas-1998-claims original.pdf

1457-mas-1998-correspondence others.pdf

1457-mas-1998-correspondence po.pdf

1457-mas-1998-description complete duplicate.pdf

1457-mas-1998-description complete original.pdf

1457-mas-1998-drawings.pdf

1457-mas-1998-form 1.pdf

1457-mas-1998-form 3.pdf

1457-mas-1998-other documents.pdf