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Plastic coating of the end-inner area of a cap

Plastic coating of the end-inner area of a cap description/claims

The invention relates to a method for forming compound layers in a sealing cap comprised of substantially a metal material. Such sealing caps, also referred to as “caps”, are used for sealing containers, in particular glass containers, by welding, the upper front end portion of which is provided with scams radially outwards, each of which extending in a tilted manner and being restricted in the perimeter, in order to allow to convert a rotational motion of the “cap” into an axial motion for sealing the container with the described cap and for removing the cap. Thus, the caps are used for the repeated sealing of a container.

The invention relates to a method for manufacturing such a sealing cap, in particular to the fabrication of the compound layer in the peripheral or edge area of the cap, wherein the compound layer forms a seal with the front end of the container and also acts as a mechanical closure at the lateral periphery of the upper end portion of the container. Hence, this area has the double function of sealing and closing such that this area is to be referred to as a sealing and closing or tightening area of the cap (radially outward of a cap level or panel).

The invention also relates to the cap formed by the method (cap, claim 14), which comprises the cap level and the edge area, referred to as “panel area” and “edge area”. These areas blend together via transfer zone, which is to be referred to as cap level edge area.

The invention finally relates to a form mould for positioning and forming an applied compound (as a pre-form) in the cap edge area {claim 20}.

A wide variety of caps is known in the art. One type of cap to be mentioned here is the PT cap as described in EP-B 844 972 (Taber, White Cap), cf. column 1, paragraphs [03], [04], which are here incorporated for the explaining of PT caps. These caps are provided with a compound at the edge area or periphery, which provides for a tightening or closing function and for a sealing function. An axial portion of the compound serves for tightening or closing by an axial pressure, wherein the screw cams of the container to be sealed penetrate the compound, resulting in a mechanical locking, which may be disengaged during use by a rotation only. The “P” represents the axial pressing or closing (P-closing) and the “T” represents the rotational opening (T-opening), cf., claim 14, preamble.

For manufacturing such caps two basically distinct techniques for applying the compound are used. The “lining compound” technique and the “moulded compound” technique, which are explained with reference to FIGS. 1 and 2, alternatively a mixture may be used, as described in U.S. Pat. No. 5,686,040 (Taber, White Cap), cf., the abstract. In the latter reference the application of the sealing material is performed by means of a nozzle in the form of stripes along the perimeter, which corresponds to the lining technique. Additionally, in this method an imprint technique is used for changing the position and the shape of the applied compound while it is in a deformable state, which corresponds to the moulded-compound technique. Two types of caps may be distinguished among the described caps, that is, caps having a closed “channel” in their periphery or edge area, wherein the channel comprises a substantially flat bottom, cf., EP-B 844 972, FIG. 29, and caps having, in the cross section, a wedge shaped channel in the circumference, cf., U.S. Pat. No. 5,413,234 (Hekal), cover sheet, upper figure and associated abstract.

It is an object of the invention to provide a cap having a sealing behavior identical to conventional systems, wherein the amount of compound used is to be reduced in order to reduce costs. In particular, present and future requirements imposed by the sealing of containers to be filled with foods should be met; moreover, within the concept for meeting these requirements a new type of application technique should not be introduced, which may cause additional costs; rather, known methods appropriately to be adapted should be used. The purpose of the invention is to use the conventional technique as much as possible in order to transit to the novel method, cap and moulds as smoothly as possible, while at the same time providing the previously described features of the new cap.

The object is solved by a method, in which two layers of compound are applied in the edge area {claim 1, claim 14}. The two layers of compound are preferably two different types of compound {claim 19, claim 1}, wherein the difference may be of chemical nature or may relate to physical properties. One of the compounds may be an inexpensive one and its food compatibility does not need to be very pronounced, when the compound is used in the radial outward direction with a great distance in the closure area of the sealing and closing area. The second compound may have a higher quality and may thus be more expensive, but it is used in its radial extension in a restricted form, that is, in an area forming a seal with the container at its front end, wherein the second compound may be in contact with the food with its radial inner rim in the sealed state.

The radially inner compound is enhanced with respect to its food compatibility, is, however, reduced in amount, while the compound located radially more outwardly may be optimised with respect to its mechanical strength without having to provide the feature of the food compatibility. This does not exclude that both compounds are of the same chemical and physical nature, however, they will be applied via two different methods to the edge area of the cap in order to cause an interface therebetween, which allows to recognize that a cap {claim 14} formed according to the method {claim 1} is provided with two different compound layers, even though they may be comprised of the same compound material.

With respect to the two methods on the one hand, the previously described method “moulded compound” is used (for the compound located farther radially outwardly), and the lining method (as previously described) is used for the layer of compound located radially further inwardly. Hereby, an overlap zone is created between these two subsequently applied compounds, which causes the above-mentioned intermediate layer, which may be identified in the cross section upon an analysis. Preferably, the compound on the outer edge area with an axially extending tapering more expanded compared to the compound located radially more inwardly, which provides for the front side sealing with the front end of the container.

By referring to the compounds as a first compound and a second compound {claim 1} no ordering is intended, in which these compound layers are applied to the edge area of the cap as a layer (levels). It is only intended to distinguish that the first compound is applied by a first method and the second compound is applied by a second method, wherein both methods are explained.

The order of these methods may be changed. First the layer located in the apron area may be applied. On the other hand, the compound layer located radially more inwardly may be applied first, which is applies according to the lining method. According to the sequence of the methods used there is an overlap zone, in which both compounds overlap and which is preferably located near the circumferential groove {claim 14, feature (a)}. The two methods may also be described such that the radially outer layer does not extend (or does substantially not extend) beyond the inner radial end of the circumferential groove {claim 14, feature (a)}. Alternatively/cumulatively, the compound layer located radially more inwardly may not extend further radially outwardly than the radially outer end of the circumferential groove or the “channel” in the cap {claim 14, feature (b)}.

Furthermore, alternatively/cumulatively the two layers may be distinguished such that one layer extends in a substantially radial manner and the other layer extends in a substantially axial manner, wherein, however, both layers have a given thickness that is adapted to the respective purpose. The substantially radially disposed layer is adapted to the front end sealing of the container. The substantially axially disposed layer is provided for the closing zone so as to cooperate with the screw scams of the container. Both layers together form the sealing and closing zone located at the edge area, which may not necessarily occupy the entire edge area of the cap.

Provided between the edge area and the panel area of the cap (the cap level) is an intermediate zone, which extends radially within the circumferential groove or channel. The compound layer located radially more inwardly does practically no, and preferably not at all, extend into this area so that as less a contact as possible is accomplished with respect to the food sealed in the interior of the container.

The three sub areas of the described sealing and closing zone in the edge area of the cap may be oriented such that they may be referred to as “area 1”, “area 2” and “area 3”. The first area, “area 1”, is in contact with the fill material, thus it is located in the intermediate area (transit zone) between the panel and the edge area. The second area, “area 2”, is the sealing area, which mainly acts as a sealing together with the front end of the container. The third area, “area 3”, serves for embedding the screw thread and for providing for the mechanical closure and the support, respectively, of the sealed cap, after it has been sealed with an axial pressing in order to be opened by screws in a re-sealable manner.

The compound layers applied by the different application methods occupy different geometrical areas in the edge area, that is, the closing area and the sealing area {claim 1}; an overlap zone {claim 9}. By the specific application of the two compound layers different characteristics in the sealing and closing area may be created. Each section of this sealing and closing zone may be given dedicated characteristics. The application of the compounds by the combined use of the Moulded Compound and the Lining Compound serves for the precise alignment of the respective used compound with respect its specific purpose at its specific location within the edge area of the cap {claim 8}.

The lining method is accomplished by injection moulding of a compound, wherein the cap is rotating. After introduction of the compound into a circumferential channel a mechanical post-forming by means of a ring imprint die may be omitted {claim 2}. A rotation of the cap takes place during or after the application inducing a displacement effect, wherein the still flow-like just introduced compound is moved radially outwardly, however only in a restricted amount {claim 1 ;claim 14, feature (b)}. This radial displacement may already begin during the injection.

The compound pre-form also applied by the lining method that is located radialy more outwardly compared to the above-described lining-application is deformed after application {claim 3} by an imprint die, which is a ring or annular die {claim 20}. This second compound is first positioned (during the application by a rotation of the cap), does not exhibit a rotation deformation but a die induced deformation, which extends only into a portion of the sealing and closing zone that comprises at least the closing zone of the cap. This is a substantially axially extending deformation including moderate amounts of a radial deformation when the circumferential channel of the metal shell (the cap raw form) is concerned {claim 15}. As far is the compound extends into the sealing zone {claim 4}, this compound layer is covered by a subsequent lining deformation in the form of rotative application and rotative displacement such that the surface of the sealing zone is formed in the edge area of the cap by the compound applied as the second compound. The resulting overlap zone is then configured such that in axial direction towards to the closing area of the container provided at the front side only the second compound is exposed, while the underlying first compound is covered.

When the order of the methods used is inverted, the second compound geometrically deformed by the moulded compound method does no extend into the sealing zone, but remains in the closing area {claim 3, claim 14, feature (a) and (c)}.

When the compound applied as the second compound also extends into the sealing zone {claim 4}, it is covered there—as previously explained—by the first compound applied afterwards, which is displaced, starting from the radial inner region, by the rotation of the cap.

In other words, the displacement of the two compounds after their respective application in the form of a circumferentially extending toroidal compound string is restricted {claim 5}. This restriction may effected by a ring-like barrier in such a manner that this barrier is located in the cap groove {claim 7, claim 25, claim 27}, or is provided by the annular die form {claim 6}, at the front side of which the barrier is provided as a front side protrusion, like a fin, or is provided as an outer peripheral relatively sharp edge.

During the respective deforming displacement of the second compound either the die or the annular barrier in the circumferential groove of the cap acts as a resistance at a predefined position for the radially inwardly directed flow of the deformed compound and restricts this flow {claim 5}. The flow therefore extends at most into the sealing zone with respect to the point in time of the end of the flow of the second compound caused by the annular die. This inner border does not mean that this inner flow should always extend to the inner end, but it may be completed earlier, for instance by the radially widely outwards located edge of the annular die {claim 21}, the flow may also be ended in a later stage when the flow is restricted by the radially inwardly located edge of the circumferential groove. Intermediate positions are possible {claim 6, 7}, caused by the axial protrusion at the annular die {claim 22} or an annular barrier in the circumferential groove of the cap, as a circumferential fin having a height that is less than a depth of the circumferential groove. Preferably, this barrier is used within the circumferential groove for such a shape of the circumferential groove which has a substantially flat horizontally disposed bottom. In an alternative groove, which substantially extends in wedge-like manner without a flat bottom the circumferential barrier for the radial inward displacement of the second compound (by the die induced deformation) given or barred by the shape and geometry of the annular die.

Further improvements for the structure, the adhesion and also for the other properties of the double layer are obtained by using an additional die that may also provide the compound layer applied radially more inwardly, that is, the first compound, with a pressure force {claim 10}. This application of the pressure force may occur prior to or after the application of the second compound. Upon the axial pressure a more uniform axial height is obtained. The first compound that is displaced radially outwardly in a too intensive manner caused by rotation, thereby resulting in a too large height (thickness), is pushed back to a substantially uniform axial height or thickness, resulting in a two-fold advantage. Created bubbles are reduced and the adhesion between the two compound layers or the adhesion of the first compound layer to the tin cap in the circumferential groove is enhanced. The improvement with respect to the reduction of bubbles and the adhesion occurs in the circumferential stripe forms. A border line of the compound located radially more inwardly, that is, the radially outermost border line is enhanced in view of its non-uniformity (“tail formation”) and may be made more uniform by the additional effect of the die {claim 11}.

• Provisional Patent
• Utility Patent

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