BACKGROUND

1. Field of the Invention

The present invention relates generally to the production of pharmaceutical glass containers as primary packing means for pharmaceutical active ingredients for example of glass bottles (vials), cartridges, or syringe bodies, and relates in particular to a device and a method for relaxing such glass containers.

2. Description of Related Art

Methods for the continuous heat treatment of pharmaceutical glass containers in order for residual stresses in the glass material to be dissipated in a targeted manner are known from the prior art. To this end, the glass containers initially typically pass through a heating zone in which the glass containers are heated to a maximum temperature. The glass containers subsequently cool to room temperature without active cooling measures. However, the conditions when cooling without active cooling measures are not controlled in an open-loop manner.

FIG. 1shows a typical temperature profile which the glass containers herein pass through in a relaxation oven according to the prior art, for example subsequently to a hot forming process in which the glass containers are produced from glass tubes by hot forming. The temperature in the heating zone and cooling zone herein is illustrated so as to be plotted over time inFIG. 1, wherein the afore-mentioned temperature must not be confused with the actual temperature of the glass containers.

At the beginning of the heat treatment, the glass containers herein are often already almost at room temperature again. Upon running into an entry region (period t0to t1), the temperature in the heating zone I is ramped up as fast as possible until a maximum temperature has been reached, the latter in the case of a borosilicate glass being approximately 615° C., for example. For glass vials having a nominal volume of 2 ml, for example, said maximum temperature is maintained during approximately 29 s (zone II, period t2to t3), thus during a very short time, so that it is reliably prevented that the glass temperature is above the glass transition temperature (Tg) for too long. The temperature in the zone III is subsequently ramped down at a substantially constant cooling rate (period t3to t4), this inFIG. 1being illustrated by a linear temperature profile. For glass vials having a nominal volume of 2 ml, this cooling takes for example approximately 340 s.

EP 0 960 863 A2 discloses a device for the continuous heat treatment of pharmaceutical glass containers in which device the glass containers between an entry region and an exit region are conveyed by means of a specially designed conveyor belt. The glass containers herein pass through a first heating zone in which the glass containers are heated to a maximum temperature, and subsequently thereto pass through a cooling zone in which the glass containers are to rapidly cool. An active ventilation in the cooling zone is used here in order for the cooling rate to be increased.

U.S. Pat. No. 3,259,481 A discloses a device for the continuous heat treatment of glass containers. The glass material to be cooled is brought to a very high temperature in a first region. Cooling at a first cooling rate which gradually decreases is subsequently performed. Cooling at a higher cooling rate is subsequently performed. The use of separating plates that are capable of being inductively heated is not disclosed.

U.S. Pat. No. 1,974,058 A discloses a comparable device. The use of separating plates that are capable of being inductively heated is not disclosed.

U.S. Pat. No. 1,071,331 A discloses a further device for the continuous heat treatment of glass containers that is conceived as a heat tunnel.

The heating elements for heating the glass containers are usually disposed at a minor spacing directly above the conveyor belt. Temperature variations of the heating elements therefore lead directly to process variations when relaxing the glass containers. Because the heating elements in the direct environment thereof cause very high temperature gradients, the requirements set for the neighboring materials are also very high, this often resulting in material flaking from and contaminations of the glass containers guided therebelow.

With a view to the further increasing requirements set for the product quality of glass containers for use as primary packing means for pharmaceutical active ingredients, attention must however also be paid to a suitable stress profile in the material of the glass containers.

There thus exists further room for improvement in the continuous heat treatment of pharmaceutical glass containers

SUMMARY

It is an object of the present invention to further improve the conditions in the continuous heat treatment of pharmaceutical glass containers. It is in particular an object of the present invention to provide an improved method and an improved device for the continuous heat treatment of pharmaceutical glass containers, by way of which a heat treatment is possible at consistent conditions with a reduced risk of contaminations.

According to the present invention, a method for the continuous heat treatment of pharmaceutical glass containers is provided in which method the glass containers by means of a conveying installation are continuously conveyed from an entry region to an exit region, wherein the glass containers between the entry region and the exit region first pass through a heating zone in which the glass containers are heated to a maximum temperature, and subsequently to the heating zone pass through a first cooling zone in which the glass containers cool at a first cooling rate.

According to the invention, at least one separating plate made from an electrically conductive material which for separating the glass containers in the heating zone and at least in the first cooling zone from heating installations or combined heating and cooling installations and for preventing an ingress of contaminations into the conveying gap is provided above the conveying installation or above and below the conveying installation, wherein the at least one separating plate is inductively heated by the heating installations or combined heating and cooling installations so as to supply heat to the glass containers in the heating zone and at least in the first cooling zone.

According to the invention, no contaminations, for example material flakes of heating elements or the direct environment thereof, can thus come into contact with the glass containers. Contaminations or even mechanical damage to the glass containers can thus be effectively prevented. For this purpose, at least the separating plate above the conveying installation is preferably configured so as to be continuous and without interruptions or openings.

The separating plates herein are composed of an electrically conductive material, in particularly from a current-conducting metal, so that said separating plates can be heated inductively, by way of the eddy current losses generated therein, by the heating installations or combined heating and cooling installations. The heating elements can thus be disposed directly above or below, respectively, the moving glass containers so as to cover a comparatively narrow conveying gap and to spatially separate said conveying gap from the heating installations or combined heating and cooling installations. The comparatively minor spacing assists in saving energy costs and minimizes temporal delays when controlling the temperature profiles in a closed-loop or open-loop manner. In the case of inductive heating being chosen, particularly aggressive temperature profiles having high temperature variation rates can in particular be implemented in order for the glass containers be very rapidly heated in the heating zone and the first cooling zone.

According to a further embodiment, the glass containers subsequently to the first cooling zone and prior to reaching the exit region pass through a second cooling zone in which the glass containers cool at a second cooling rate which is higher than the first cooling rate.

By using two directly successive cooling zones the conditions when relaxing the glass containers can be set in a more suitable manner. Attention herein is paid on the cooling of the glass containers at temperatures above the lower annealing point being performed in a relatively slow manner, because the plasticity of the glass in this temperature range is increasingly lost during cooling. Consequently, the cooling of the glass has to be performed in as homogenous a manner as possible in order for no new internal stresses be incorporated in the glass. After undershooting the lower annealing point the glass henceforth can only deform in an elastic manner, so to speak, so that a very much higher second cooling rate can be set according to the invention after the lower annealing point has been undershot. The first cooling rate in the first cooling zone is thus chosen so as to be relatively low so that almost no new internal stresses are incorporated into the glass on account of an excessively rapid cooling. The thermal conditions in the first cooling zone are in particular expediently chosen such that no new (secondary) internal stresses are induced on account of an excessively rapid cooling when passing through the first cooling zone. In particular also such that the residual stress in the glass containers when exiting the first cooling zone does not exceed a limit value of 2-3 MPa.

Upon exiting the first cooling zone, thus once the temperature of the glass containers has slightly undershot the lower annealing point, a significantly higher second cooling rate is chosen such that the glass containers are cooled to approximately room temperature, in particular to a temperature in a range between approximately 20° C. and approximately 100° C., as rapidly as possible but without any build-up of additional stresses in the material.

According to the invention, the overall length of the relaxation oven can be minimized in this way. Taking into account that the glass containers pass through the relaxation oven by means of a conveyor belt at a constant speed, a shorter overall time for relaxation corresponds to a shorter overall length of the relaxation oven, which assists in saving space. This space saving according to the invention can be significant.

However, the duration required for suitably changing process parameters of the hot forming machine situated upstream by means of the results of an inspection of the cooled glass containers, in particular of a video inspection, which is performed downstream of the relaxation oven, when this is deemed necessary by means of the results of the inspection, can also be reduced in this way. Up to the point of inspection a multiplicity of glass containers have already passed through the relaxation oven, said glass containers optionally not being of a suitable quality. Because it is possible to react faster through quality variations of the glass containers by virtue of the shorter overall length of the relaxation oven according to the invention, the amount of rejects can thus also be reduced according to the invention, and a consistently high quality of the glass containers can be guaranteed.

According to a further embodiment, the separating plate for supplying heat to the glass containers in the heating zone and at least in the first cooling zone is inductively heated by the heating installations or combined heating and cooling installations. The separating plates by virtue of the relatively high mass thereof lead to a further homogenization of the temperature conditions in the conveying direction of the glass containers as well as perpendicularly to said conveying direction. According to the invention, temperature conditions which are much more homogenous can thus be set in the heating and cooling zones. To this end it is preferable for the separating plates to possess a sufficient thermal mass.

According to a further embodiment, the glass containers are heated in the heating zone such that the temperature of the glass containers for a short time is higher than the glass transition temperature. Residual stresses in the glass can be particularly effectively dissipated in this range. The aforementioned period herein is in the magnitude of only a few seconds, and is, for example, at most 3 seconds, or more preferably at most 2 seconds, this depending on parameters of the glass containers, in particular on the wall thickness of said glass containers, thus on the duration until the very high temperature has also reached the internal surface of the glass containers.

According to a further embodiment, the ambient temperature in the heating zone is at least 65° C., more preferably at least 85° C., higher than the glass transition temperature. In the case of a borosilicate glass, the ambient temperature in the heating zone can be at least 590° C. and more preferably at least 605° C. For vials, suitable ambient temperatures in the range from 630° C. to 660° C. in the heating zone have been determined by experiments, this being in particular also dependent on the vial size and the cycle rate, this corresponding to a temperature differential of 65° C. to 95° C. in relation to Tg (565° C.). By of the aggressively implemented temperature conditions the glass containers reach the maximum temperature thereof particularly rapidly, this resulting in a further reduction in the overall length of the relaxation oven. The temperature in the heating zone which the glass containers pass through here in can be higher than the glass transition temperature during a duration of at most 25 s, more preferably during a duration of at most 20 s.

According to a further embodiment, the glass containers in the first cooling zone cool to a temperature which corresponds to the lower annealing point or slightly under shoots the latter, for example by a few ° C. More specifically, the temperature profile in the first cooling zone, the overall length of the first cooling zone, and the conveying speed of the glass containers are mutually adapted such that the lower annealing point is reached toward the end of the first cooling zone. The overall length of the first cooling zone can thus also be further reduced. The temperature profile in the first cooling zone herein is expediently chosen such that residual stresses in the glass do not exceed a predetermined limit value of, for example, 2-3 MPa.

According to a further embodiment, the first cooling zone is subdivided into at least two, preferably into at least three, cooling sub-zones having in each case constant temperatures of the assigned combined heating and cooling installations, the temperature of the glass containers in said cooling sub-zones being lowered step-by-step to the range of the lower annealing point.

According to a further embodiment, the cooling is sub-zones of the first cooling zone are mutually thermally separated for example by means of separations in the form of sheet-metal panels or plates which are conceived for preventing or at least significantly minimizing a convection between the cooling sub-zones such that the temperatures of sub-zones of the first cooling zone thus formed can be set in a substantially mutually independent manner. A temperature differential between the ambient temperature in a first cooling sub-zone, when viewed in the conveying direction, and the ambient temperature in the heating zone herein is greater than a temperature differential between the ambient temperature in the first cooling sub-zone, when viewed in the conveying direction, and a neighboring second cooling sub-zone, or a temperature differential of the ambient temperatures in two neighboring cooling sub-zones. In other words, the glass containers in terms of temperature are subjected to the greatest temperature leap in the first sub-zone of the first cooling zone, when viewed in the conveying direction. The glass containers when entering the subsequent sub-zones of the first cooling zone in terms of temperature are subjected to further temperature leaps, the latter however becoming in each case smaller.

According to a further embodiment, the temperature in the first cooling zone, in particular in the cooling sub-zones of the first cooling zone, is lowered not by active cooling, for example by a cooling airflow. Rather, the temperature is suitably set by controlling in a closed-loop manner heating installations above and below the conveying installation.

According to a further embodiment, the second cooling rate in the second cooling zone is set such that the build-up of additional stresses in the glass of the glass containers when cooling in the second cooling zone is avoided.

According to a further embodiment, the temperature in the second cooling zone is lowered actively by an airflow in a closed air circuit. The overall length of the second cooling zone can thus be further reduced, because higher cooling rates can be achieved by way of active cooling by an airflow. For this purpose, an airflow is preferably suitably guided through the second cooling zone and controlled in an open-loop manner or in a closed-loop manner. The second cooling rate herein can be suitably set by varying an airflow in the closed air circuit and/or by additionally switching heat exchangers. Furthermore, an air flow in the closed air circuit can be filtered for reducing a particle load in the second cooling zone.

According to a further embodiment, a dwell time of the glass containers in the first cooling zone is in the range between 73 s and 93 s, more preferably in the range between 78 s and 88 s. The dwell time of the glass containers in the second cooling zone herein can be in the range between 87 s and 117 s, more preferably in the range between 95 s and 109 s.

According to a further aspect of the present invention, a corresponding device for the method of the present invention is also disclosed herein.

A further aspect of the present invention relates to the use of a method or a device, respectively, as disclosed herein, for the continuous heat treatment of pharmaceutical glass containers, in particular of vials, cartridges, or syringe bodies from glass.

