GB2257387A - Moulding a breast prosthesis - Google Patents

Abstract

Before the moulding operation takes place, a bag (21) is made by sealing of two polyurethane sheets together and is filled (7) with the components of curable silicone resin, and is then mounted under vacuum conditions (8) for removal of excess air. The bag is then sealed (10) and is used immediately, or after storage, in the moulding operation. Because a bag is filled before moulding, there is no need to inject silicone under pressure to the mould and inexpensive moulds may be used, and mounting under vacuum conditions avoids air inclusion problems during moulding. Before moulding between cavities (42, 44), the film around the sealed edges of the bag is stretched and further, because silicone is not injected under pressure creasing does not occur very often. <IMAGE>

Description

The invention relates to a process for manufacturing a breast prosthesis.

At present, most prosthesis are manufactured using two silicone components which are capable of a cross-linking addition reaction. This mixture is moulded between sheets of plastic film and is subsequently heated to vulcanise the silicone. Such processes are disclosed in United States Patent Specification Nos. 4,247,351 and 4,249,975 (RECHENBERG). In such processes the silicone mixture is charged under pressure into the mould, which is then placed in a heating oven for vulcanisation. In both cases, because the mixture is charged under pressure, the presence of air between the plastic sheets is a problem and creasing of the sheets is difficult to avoid. In addition, control of the amount injected is very difficult to achieve to the required accuracy.Further, because the moulds must be suitable for reception of silicone gel injected under pressure, they must be of strong construction and are thus expensive. Thus, to produce a wide range of sizes of prosthesis, it would be necessary to manufacture a large number of expensive moulds.

Finally, because the moulding operation is an integral part of the silicone mixing and dispensing operations, a fault in a mixing or dispensing machine results in considerable downtime.

The present invention is directed towards providing a process for producing a breast prosthesis which requires relatively inexpensive moulds, is simple to carry out and which involves a relatively low defect rate.

According to the invention, there is provided a process for manufacturing a breast prosthesis comprising the steps of: coating two sheets of polyurethane film with an adhesion promoter; sealing the two sheets together to form a bag having an open neck; injecting a mixture of two silicone gel components and a pigment into the bag while continuously monitoring weight of the bag to verify the quantity injected; expelling air from the filled bag by mounting in a vacuum chamber; sealing the neck of the bag; moulding the filled and sealed bag by carrying out the sub-steps of: placing the bag in one half of a mould; stretching excess film away from the bag; and pushing the second mould half over the bag and holding it in position; heating the mould containing the pressed bag to vulcanise the silicone; removing the moulded prosthesis from the mould and trimming away the excess film.

Ideally, the first mould half has an aperture at its lowermost portion and a vacuum is applied to the bag through the aperture while the second half is pressed against the bag.

Preferably, the film is stretched by inserting the film on each side of the big onto a rotatable shaft and rotating each shaft to stretch the film.

In one embodiment, the empty bag is filled via a tube having a valve operatively connected to a weighing machine for automatic shut off when the desired weight is reached.

In another embodiment, the sheets of film are sealed together by application of a heating die at a temperature of approximately 2000C for a time period in the range 2.5 to 3.0 seconds.

The filled and sealed bag may be stored in a freezer at a temperature in the range of -10 C to -180C before moulding.

The invention will be more clearly understood from the following description of some preferred embodiments thereof, given by way of example only with references to the accompanying drawings in which: Fig. 1 is a flow diagram illustrating a manufacturing process of the invention; Fig. 2 is a plan view showing a pair of sheets of film when sealed; Fig. 3 is a diagrammatic view of a silicone dispensing apparatus used in the process and a sketch showing a weighing device in more detail; and Fig. 4 is a perspective view of a mould used in the process.

Referring to the drawings, there is illustrated a process of the invention for the manufacture of a breast prosthesis. At the beginning of the process, two sets of operations are carried out in parallel. In one sequence, in step 1 rolls of polyurethane film mounted on a backing sheet are received and inspected. Subsequently, in step 2 the film is cut to a desired sheet size, namely, 17" square. This is carried out by cutting each roll to a width of 17", mounting the roll on a spool and drawing film from the roll and cutting off 17" lengths. Before each length is cut, the backing sheet is separated from the film and adhesion promoter is applied to the film.

To form a bag, two sheets of film to which adhesion promoter has been applied are placed together with the surfaces having adhesion promoter in contact. The pair of sheets are placed on a plate and a sealing die is applied at a temperature of approximately 2000 for 2.5 to 3.0 seconds. This causes the two films to be sealed together along a seal 22 as illustrated in Fig. 2. It will be noted that there is a neck opening 23 in the seal 22. In this drawing the film sheets are represented by the numerals 21(a) and 21(b) and the bag generally by 21.

The second sequence of operations which is carried out in parallel comprises a step 5 of inspecting and storing silicone and subsequently is step 6 mixing silicone components and a pigment together. Referring to Fig. 3, there is illustrated a mixing vessel 28 having a cylindrical housing 29 above which there is a piston 30 having an air vent tube 31. The vessel 28 is mounted on a frame 32 and the apparatus for dispensing of silicone further comprises a weighing device 33, which supports the bag 21. A flexible dispensing tube 35 from the vessel 28 is provided for insertion in the neck 23 of the bag 21 and this has a valve 36 operatively connected to a weigh controller 37.

The silicone components and pigment are mixed under vacuum with a cover, not shown, over the housing 29. Thereafter, the piston 30 is brought into position over the mixture and used for dispensing.

As the silicone mixture is dispensed from the housing 29 under the pressure of the piston 30, the bag 21 is continually weighed using the weigh bar 33 and the weigh controller 37.

When the desired weight is reached, the valve 36 is automatically shut off by the controller 37. The correct weight will have been programmed into the controller 37 beforehand and this allows filling of bags to a very wide range of desired sizes in a simple and convenient manner. It is only necessary to have the bag size formed between the heat seal line correspond to the desired weight. When the dispensing operation is complete, the bag 21 is removed from the weigh bar 33 and its weight is checked on a separate weighing machine. If underweight or overweight, mixture is either applied or removed using a syringe inserted through the neck 23 of the bag 21.

When a batch of bags have been filled, in step 8 they are each stretched on a frame and placed in a vacuum chamber vacuum for approximately 30 minutes. This ensures that any excess air is been removed through the neck 23. When the bag 21 is removed from the vacuum chamber it is inspected in step 9. There may be bubbles of air collected at the neck 23 and these are easily removed by simply pressing the film together to expel the air through the neck 23. These bubbles of air generally gather while the bag is under vacuum as a result of migration of air from the silicone towards the neck. When all air has been removed, the neck of the bag is sealed in step 10 using an impulse heating bar.

The filled and sealed bag may then be brought directly to a moulding station or it may be stored in a freezer. The freezer is at a temperature in the range of -10 C to -18 C and under these conditions, a filled and sealed bag 21 may be stored for up to four weeks while sufficiently retarding the cross linking reaction. This is a very important aspect of the invention as a large number and wide variety of different sizes of bag may be prepared and stored ready for moulding whenever the demand arises. Further, final production is not dependent on operation of the mixing and dispensing machines.

The step of storing the bags is indicated by the numeral 11.

In step 12, the bag is moulded to the shape of a prosthesis.

A mould 40 used for this is illustrated in Fig. 4. The mould 40 comprises a first mould half 41 having a cavity 42 shaped to the desired size. The first mould half 41 has a pin hole at its lowermost portion. The mould 40 also comprises a second mould half 43 having a formation 44 corresponding to the shape of the back of a prosthesis. At each side of the first mould half 41 there is a split bar 45 which is rotatably mounted and at each end of the first mould half 41 there is an upstanding bolt 46 for engagement with apertures 47 in the second mould half 43.

To mould the prosthesis, the filled and sealed bag 21 is placed into the cavity 22 of the first mould half 41. As illustrated in Fig. 4, there is an excess of film and this is cut so that on each of the four sides of the bag 21, a sufficient width of excess film may be placed into the relevant split bar 45. Further, slits are made in the film for reception of the bolts 46. When the bag 21 fits neatly into the cavity 42, the split bars 45 are rotated in the sequence of opposing split bars being rotated firstly so that the film is stretched evenly over the mould cavity 42. When this has been done, the second mould half 43 is placed over the first mould half 41 with the bolts 46 engaging the apertures 47. A vacuum source is then applied to the aperture at the bottom of the first mould half 41. This urges the bag 21 tightly against the surface of the cavity 42.The second mould half 43 is then pushed downwardly and secured in place using wing nuts on the bolts 46. The mould is then put aside to a batch.

When a batch of moulds has been prepared (and inspected in step 13), the batch is placed in an oven in step 14. The oven is heated to approximately 1000C and the batch of moulds is left there for approximately 10 hours. When the mould is removed form the oven, the mould halves are separated and the bag is removed. In step 15, excess film is cut away to provide a neat appearance of the prosthesis.

It will be appreciated that the process of the invention avoids the need for injecting silicone under pressure into a mould. Accordingly, the moulds may be of inexpensive construction such as fibreglass. This considerably reduces costs. Further, by mixing the silicone under vacuum conditions, slowly dispensing the silicone into the bag before moulding, and subsequently mounting the filled bag under vacuum conditions to remove excess air, problems of air inclusion in the bag during the moulding process are significantly reduced. It will be appreciated that this is a substantially more effective process than that of charging silicone under pressure into the mould, which often results in the inclusion of air. It will also be appreciated that because the bag is pre-filled and stretched before moulding, creasing of the film is avoided.Further, by pre-filling bags and storing under low temperature conditions, a very wide range of bag sizes may be ready for final production and prosthesis' may be produced in a short lead time. It is important that demand for various sizes of prosthesis can be met in a very short length of time. Further, a very wide range of sizes are made possible by the fact that the moulds are inexpensive. Also, because the moulds are inexpensive experimentation with different shaped moulds is inexpensive.

This is important for product development.

In summary therefore, it will be appreciated that the invention considerably improves throughput quality and thereby efficiency, involves use of inexpensive equipment and allows for continuing production in the event of machine faults and short lead times.

The invention is not limited to the embodiments hereinbefore described, but may be varied in construction and detail.

Claims (7)

1. A process for manufacturing a breast prosthesis comprising the steps of: coating two sheets of polyurethane film with an adhesion promoter; sealing the two sheets together to form a bag having an open neck; injecting a mixture of two silicone gel components and a pigment into the bag while continuously monitoring weight of the bag to verify the quantity injected; expelling air from the filled bag by mounting in a vacuum chamber; sealing the neck of the bag; moulding the filled and sealed bag by carrying out the sub-steps of: placing the bag in one half of a mould; stretching excess film away from the bag; and pushing the second mould half over the bag and holding it in position; heating the mould containing the pressed bag to vulcanise the silicone; and removing the moulded prosthesis from the mould and trimming away the excess film.

2. A process as claimed in claim 1 wherein, the first mould half has an aperture at its lowermost portion and a vacuum is applied to the bag through the aperture while the second mould half is pressed against the bag.

3. A process as claimed in claims 1 or 2 wherein, the film is stretched by inserting the film on each side of the bag onto a rotatable shaft and rotating each shaft to stretch the film.

4. A process as claimed in any preceding claim wherein, the empty bag is filled via a tube having a valve operatively connected to a weighing machine for automatic shut-off when the desired weight is reached.

5. A process as claimed in any preceding claim wherein the sheets of film are sealed together by application of a heating die at a temperature of approximately 2000C for a time period in the range 2.5 to 3.0 seconds.

6. A process as claimed in any preceding claim, wherein the filled and sealed bag is, if required, stored in a freezer at a temperature in the range of -10 C to -180C before moulding.

7. A breast prosthesis whenever prepared by a process as claimed in any preceding claim.