HK1035691B - Method for making a blister pack with indicia - Google Patents

Description

Method for producing embossed blisters

Technical Field

The present invention relates to a method of forming an embossed blister using a laminate film in which an object can be cast. Such blisters are typically constructed from a thin polymer film.

Background

Blister films are particularly suitable for casting fragile articles including chemicals which are usually processed by lyophilization or freeze-drying, although techniques such as solid state dissolution may be used. After the liquid material is poured into the water bath, various treatments are performed in the water bath. The finished products will remain in the blisters until they are removed for use and, at this stage, the products are easily removed.

A disadvantage of polymer blister films is their permeability. Thus, no matter how well the individual blister is sealed, there is always a potential storage problem if the contents of the blister must be isolated (protected) from the surrounding atmosphere. For this reason, laminated water-bubble films have been developed which are less permeable than films composed solely of polymers. However, some known films may deform when subjected to heat treatment, thereby causing irregularities in the poured product and making subsequent blister pack handling more difficult. Although laminates have been developed which are more reliable under heat treatment conditions, for example as described in european patent nos.0646367 and 0710101 of the present company, none of these laminates are substantially suitable for blister thermoforming thereon. Metal foil layers, which are typically constructed of aluminum, are more suitable for cold forming.

There is an urgent need to provide a technique for imparting a permanent mark on the product formed in the above blister film. To this end, an imprint may be formed on the inner surface of a thermoformed blister and then transferred to the surface of the product being cast.

In our co-pending international patent application filed on our same day and based on priority british patent application nos.9717491.6 and 9718382.6, we have emphasized the difficulty of forming blisters themselves and simultaneously forming indicia in the bottoms of the formed blisters with the laminated film to which the present invention relates. In the above application, problems are encountered in the second stage of the two-stage process taken to form the imprint, wherein the bubbles themselves are formed in the first stage.

Disclosure of Invention

It is therefore an object of the present invention to provide a method of making an embossed blister wherein the embossed blister is formed in a single step by combining the blister and impression formation while controlling the stretching of the laminate film. Therefore, the possibility of occurrence of a damaged, weakened, or broken region or the like in the laminated film can be reduced.

To achieve the above objects, the present invention provides a method of forming an embossed blister using a laminated film comprising a metal foil and a polymer layer on either side of the metal foil, the blister having a protruding imprint on the base thereof for embossing onto a cast object within the blister, wherein the method comprises feeding and pressing a punch in a direction transverse to the plane of the film onto a platen having imprint-forming dies to cold form the blister, the end face of the punch forming an imprint die complementary to the imprint-forming dies on the platen, the punch moving towards the platen primarily stretching the film around the blister to minimise stretching of the film at the base of the blister.

According to the present invention, the aforementioned two-stage forming process can be performed by a single pass of the blister forming punch or punch while effectively controlling the stretching (stretching) of the laminate film during blister formation. According to the invention, blisters are cold formed by advancing a punch in a direction transverse to the plane of the film and pressing it against a platen with an imprint mold. The end face of the punch is formed with a marking die complementary to the die on the platen and the film around the blister is stretched primarily as the punch moves towards the platen, thereby minimizing stretching of the film at the bottom of the blister. As a result, less recovery time is required before the film at the bottom is further stretched to form the mark, which can be formed in the final stage of one pass of the punch or punch.

To ensure that the film around the blister is stretched primarily when the punch begins to move rather than the film at the bottom of the blister, a large frictional contact can be made between the periphery of the end face of the punch and the laminated film. To the extent that the end face surrounding the die is substantially flat, this can be achieved by the die structure on the end face of the punch. Of course, it is even more effective if the end face around the die is designed to be slightly concave, so that a circumferential edge is formed, which may provide an additional clamping action.

The shape of the punch also greatly affects the manner in which the film is stretched as the punch moves toward the platen. It has been found that two or more successively adjacent frustoconical portions are preferred, preferably with the apex angle of the frustoconical portions adjacent the end faces being substantially 60 and the apex angle of the frustoconical portions adjacent thereto being substantially 30.

Another way to achieve different film stretching effects when forming blisters is to use different materials on the punch face and sides. In the method of the present invention, the material used for the punch is preferably stainless steel or Polytetrafluoroethylene (PTFE). Alternatively, the punch and the end face are made of stainless steel, and the side face of the punch is coated with Polytetrafluoroethylene (PTFE).

Drawings

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a side view showing a punch positioned over a laminate film and platen in accordance with one embodiment of the present invention;

fig. 2, 3 and 4 are side views showing a series of progressive sequential positions of the punch over the laminate film and platen during manufacture.

Detailed Description

In fig. 1, a punch or punch 2 is arranged above a film 4 according to the invention, the film 4 comprising a metal foil coated on either side with a polymer layer. Towards the lower end of the punch 2 there are two adjacent frustoconical sides 6 and 8 inclined towards the end face 10, on which end face 10 there is a die to form an imprint in the bottom of the final formed blister.

The film 4 is clamped in a known manner and, as shown in figure 2, the punch 2 is pressed against a platen 12 with an imprint-forming die 14. At the start of the process as shown in figure 2, the stretching of the film is relatively uniform, although the edge of the end face 10 remains in contact with the film 4 under increasing pressure. Thus, when the punch reaches the final position shown in FIG. 3, the stretching of the bottom of the blister formed is minimal, while the film is stretched from the area surrounding the blister. As a result, during the final depression of the punch against the platen 12, the blister itself is shaped while at the same time an imprint is formed in its bottom. This occurs primarily during the last few millimeters of movement of the punch, typically during the last 0.3 to 0.5 millimeters of movement. The depth of the imprint is also typically in this range.

Fig. 4 shows the situation when the punch is removed and shows the laminate film springing back up and rising from the platen 12. It should be noted that the platen 12 and the surrounding base 16 defining the recess in which the blister is formed do not themselves constitute a mold from which the laminate film is formed. The punch 2 determines the overall shape of the blister, only the imprint being pressed from both sides through the opposite surfaces.

It is to be understood that the method of the invention for transferring an imprint to a surface of a cast object is to be understood in its broadest sense. Thus, the imprint shall include forms, in particular those that include pure functionality, such as an imprint that forms a break line. The break lines are typically used on oral tablets because in special cases only a portion of the tablet needs to be taken. The invention is therefore of particular value in providing an imprint (which has or includes a line of disruption) on the surface of a cast product in a blister pack. In this regard, it should be understood that the break line may be formed by a series of indentations or dimples; of course, the dimples need not be continuous in all cases. It is important to form a line of weakness in the cast product so that the product can be easily broken into one or more pieces defined by the line of weakness.

Claims (6)

1. A method of forming an embossed blister using a laminated film comprising a metal foil and a polymer layer on either side of the metal foil, the blister having a protruding footprint at the base thereof for moulding onto a cast object in the blister, characterised in that the method comprises advancing and pressing a punch in a direction transverse to the plane of the film onto a platen having a footprint forming die for cold forming the blister, the end face of the punch forming a footprint die complementary to the footprint forming die on the platen, the punch moving towards the platen causing substantial stretching of the film around the blister to minimise stretching of the film at the base of the blister.

2. The method of claim 1, wherein the end face and the side face of the punch are made of different materials.

3. A method according to claim 1 or 2, characterized in that the side faces of the punch are designed to come into contact with the film step by step starting from the end face.

4. A method according to claim 3, wherein the punch is formed by at least two successive frustoconical portions adjacent the end face.

5. A method according to claim 1 or claim 2, wherein the face of the punch surrounding the die is flat.

6. A method according to claim 1 or claim 2, wherein the face of the punch surrounding the die is concave and forms a peripheral edge.