Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-07-27
2002-07-02
Sells, James (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S228000, C156S292000, C156S308400, C156S359000, C156S581000, C156S583100, C156S583400
Reexamination Certificate
active
06413334
ABSTRACT:
The invention relates to a method and an apparatus for the thermal bonding of a base part of a packaging with a cover film, and to a method and an apparatus for packaging contact lenses in accordance with the preamble of the respective independent patent claims.
Methods and apparatuses of the above-mentioned kind are already used today in a large number of variants where a specific article, especially a contact lens, is to be packed in a tightly sealed manner in a packaging. This is generally accomplished by introducing a contact lens into a depression of a base part of a packaging, dispensing a predetermined amount of a preserving solution into the depression, then placing onto the packaging a cover film that can be thermally bonded to the base part of the packaging, and finally thermally bonding the cover film to the packaging. That operation may then be followed by sterilisation. The packaging containing the contact lens can then be delivered to the customer or to the optician or ophthalmologist.
It will be readily apparent that especially in the field of the packaging of contact lenses, but also, for example, in the fields of foodstuffs, pharmaceuticals, medicinal articles and some other fields, certain demands are made of the packaging. Those demands may relate especially to the sealing (against leakage or against the ingress of foreign substances) of the packaging, but they may also relate to the adhesion of the cover film to the base part of the packaging, to the impermeability of the packaging to certain substances, or to the force required to remove the film (peeling force). If a packaging is to be able to meet those demands, the parameters during the thermal bonding of base part and cover film (duration, pressure, temperature) must always remain within predetermined limits.
In packaging technology there are various techniques for joining two materials to one another. These include inter alia adhesive bonding with hot or cold glue, welding and “sealing”. Whereas in adhesive bonding the join is generally only in the form of a point or line, welding or sealing are suitable especially also for joins made over a larger area. The difference between welding and sealing lies in the nature and the characteristics of the materials to be joined. In packaging technology, “welding” is referred to when two identical materials are joined together under the action of pressure and temperature (without the involvement of any other materials). In the case of “sealing”, however, at least one of the partner materials is provided with a sealable coating. In both methods, therefore, the partner materials are joined together under the action of pressure and temperature, but in the case of sealing the materials to be joined to one another are generally different. Sealing is used most commonly in the field of blister packagings, in which primarily clear, deep-drawable plastics films are sealed to a cardboard card, the cardboard generally having been coated with a sealable coating of sealing varnish or, for example, with a polyethylene film.
In the packaging of contact lenses it is customary for a base part, which can be produced, for example, by injection-moulding, to be bonded to a film that has been covered with a sealable coating. The bonding of base part and cover film is effected after the lens has been introduced into a suitable depression in the base part and after a preserving solution, for example saline, has been dispensed into the depression. Such a packaging is described, for example, in EP-A-0 680 895. That packaging is said to be sealed against the ingress of foreign substances from the outside and is said to prevent the saline from leaking out. The adhesion of the cover film to the packaging must be such that the packaging is not damaged during sterilisation, which normally takes place in an autoclave. In addition, the peeling force required to remove the film from the base part, that is to say to open the packaging, should not exceed a maximum value in order that the user is able to open the packaging with a reasonable amount of effort.
Known apparatuses for the thermal bonding of a base part to a cover film, as used, for example, in the sealing of blister packagings, are constructed essentially as follows: a holding device or cradle is provided with a number of depressions for accommodating the base parts. The holding device is connected to an adjusting device which can be moved towards a bonding unit, for example with the aid of a pneumatic drive means. The bonding unit comprises a bulky metal heating plate having a large heat capacity and it too is arranged to be moved towards the holding device or the cradle with the aid of a further adjusting unit which may include, for example, a pneumatic drive means. In the heating plate of the bonding unit there are arranged a number of heating elements which heat the heating plate to a predetermined temperature. Below the heating plate, that is to say facing the holding device or the cradle, a sealing plate is releasably connected to the heating plate. The sealing plate is provided with a number of contact elements, so-called “dies”. The end face of the dies constitutes the actual pressure face that comes into contact with the cover film during sealing. That pressure face determines substantially also the shape of the join along which the cover film is sealed to the base part. Temperature sensors are provided in the heating plate and the sealing plate. Those temperature sensors are connected to a regulating means which is used to control the length of time for which the heating elements are switched on.
That known apparatus operates as follows: the base parts are held ready in the depressions of the holding device (cradle) and the cover film is placed onto those base parts. Using the adjusting units to move the holding device (cradle) and the bonding unit, the latter are moved towards one another until the pressure faces of the dies press the cover film against the base parts at a predetermined pressure. As the film is pressed against the base part by means of the dies, the sealable coating is heated and, under the action of pressure and temperature, base part and cover film are bonded together.
That known apparatus is basically perfectly efficient, but it does still have disadvantages especially in respect of the above-mentioned demands that must be met when packaging contact lenses. The movement of the holding device and/or the bonding unit must be such that those surfaces of the holding device and of the bonding unit which transfer the sealing pressure to the packaging are very exactly parallel to one another. Even very slight fluctuations can result in significant variations in the sealing pressure and therefore in a seal that does not meet the demands mentioned.
Since the sealing pressure is applied directly by way of the adjusting units, the adjusting unit in question, or its drive means, must operate very accurately. According to the nature of the adjusting unit (mechanical, hydraulic or, as mentioned above, pneumatic), the control means required for that purpose may be very expensive.
The heating elements in the heating plate and the pressure face (that is to say the end face of the dies) are a relatively large distance apart. As a result of the large heat capacity (inertia) of the bulky heating plate and as a result of the heat capacity (inertia) of the sealing plate, a relatively long time elapses before a change in temperature occurs at the pressure face. A rapid change in temperature at the point that is crucial for the quality of the seal, namely at the pressure face, is therefore not possible. In addition, the temperature at the pressure face also continues to rise for a considerable period when the heating elements are switched off again after a heating operation.
Even with the aid of the temperature sensors it is very difficult to achieve accurate regulation of the temperature at the pressure face (end face of the die). If the heat supply is regulated solely on the basis of the temperature sensor that is arranged in
Bochmann Bernd
Heinzelmann Kurt
Hornberger Heiner
Kappler Karl
Koch Dieter
Gearhart Richard I.
Meece R. Scott
Novartis AG
Sells James
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