Apparatus for manufacturing prophylactic devices

Details Apparatus for manufacturing prophylactic devices Apparatus for manufacturing prophylactic devices

1999-09-21

2001-08-14

Davis, Robert (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Means applying electrical or wave energy directly to work

Electro-static or inductive field

C425S272000, C425S275000

Reexamination Certificate

active

06273702

ABSTRACT:

FIELD OF THE INVENTION
The field of the present invention relates to apparatus and methods for making prophylactic devices, and more particularly to making such prophylactic devices from polyurethane.
BACKGROUND OF THE INVENTION
Prophylactic devices are used to prevent the transfer of infection, bacteria and viruses from an environment to a body member on which the device is mounted. Prophylactic devices include but are not limited to catheters, valves, gloves, and so forth. For example, condoms are used to protect the user from venereal diseases and for birth control, and surgical gloves are used to protect the user from infection. In order to allow the protected body member to move freely and to respond to external stimulus, the device must be as thin as possible, but this reduces the protection it provides. For many years prophylactic devices have been made of latex rubber, but when a latex condom is sufficiently thin, it reduces overall strength, is subject to breakage, and there is an increased risk that it will have pin holes that are large enough to permit the passage of viruses such as the HIV. Accordingly, latex condoms must be manufactured and tested with great care and consequent expense. Also, some people are allergic to latex.
It has been found that prophylactic devices made of polyurethane, in contrast to latex, can be very thin so as to provide a good sense of feel while at the same time being very strong, and free from pinholes. Also, polyurethane due to its synthetic nature is typically more nonallergenic than latex.
In U.S. Pat. No. 4,684,490 a method for manufacturing condoms is described in which a mandrel having the general shape and dimensions of a condom is dipped into a solvent solution of a polyurethane polymer and heated in air after being withdrawn therefrom so as to dry the polyurethane. The dried polyurethane which now forms a condom is then removed from the mandrel.
SUMMARY OF THE INVENTION
In accordance with the overall method used in this invention, mandrels having the general shape of the prophylactic device being manufactured are cleaned and subjected to cooling before being dipped into polyurethane or other suitable polymers dissolved in tetrahydrofuran (THF) for example. Other solvents or carriers such as dimethylfluorene (DMF), methyl ethyl ketone (MEK), dimethyl sulfoxide (DMSO), dimethylacetimide (DMAC), alcohols, chlorinated hydrocarbons, ketones, ethers, water (H
2
O), or any other organic solvents known in the art, and blends of such solvents, can also be used. THF is preferred for use in this invention partly because of its high solubility and easy removal or release from the finished film.
After dipping, the mandrels are rotated so as to produce a uniform film of a desired thickness profile and subjected to an elevated temperature so as to drive off the solvent. In a preferred method, the process is repeated starting with progressive cooling, followed by a second dip so that a second film of polyurethane is formed with the first film on the mandrel. The two films tend to become homogenous. Since THF tends to be highly flammable and potentially explosive in an oxygen atmosphere, the steps just described are carried out in a pressurized explosion resistant atmosphere maintaining oxygen below levels to support combustion.
The invention also includes a system for carrying out the aforesaid method in which pallets having mandrels mounted therein are transported through cleaning stations before being transported through a plurality of progressive cooling chambers to a dipping chamber in which there is a reservoir of polyurethane material dissolved in tetrahydrofuran. The viscosity of the solution is maintained in a desirable range by mixing or agitating it at a controlled temperature and keeping the concentration of THF within a given range. It is important that the rate at which the mandrels are lowered into and raised from the solution be precisely controlled, smooth and that there be no vibration. The pallets of mandrels are then rotated as much as 360° about an axis in the plane of the pallet, first in the dipping chamber, and then in a rotation chamber. Bidirectional rotation may be used in some applications. While in these chambers the mandrels themselves are also rotated about their respective axes. The polyurethane film formed on the mandrels by their having been dipped into the polyurethane solution is dried in evaporation ovens at successively higher temperatures, respectively. After the pallets emerge from the last evaporation oven, they are preferably subjected to a repeat of the process just described for a second dipping of the mandrels.
After this is done, the pallets are transported to a series of stations in an air atmosphere that respectively form one or more permanent rings at the open ends of the condoms on the mandrels, apply powder and remove the condoms from the mandrels. Alternatively, a wet takeoff system can be used. The pallets of mandrels freed of condoms are washed in one station, and rinsed in another, before being transported via a staging conveyor to an inspection and redress station. After completion of the inspection and redress, the pallets and mandrels are transported to a drying oven station. After drying, the pallets and associated mandrels are ready to be passed through the chambers just described starting with the cooling chambers, for another cycle making condoms.
Because of the high flammability and explosiveness of the solvent, THF, means are provided for keeping the oxygen concentration below given levels in each of the chambers referred to by introducing N
2
, and operating with the THF in a substantially oxygen free atmosphere. The expense of the operation is reduced by recovering THF from the atmosphere expelled from the chambers by utilizing a closed-loop system that passes through a condensing or absorption system. With this process the N
2
is reused, and heat exchangers are employed for extracting heat for use in the process. In this manner, through recovery of THF, N
2
, and heat, the process is made highly economic, and environmentally friendly. Also, any imperfect polyurethane condoms can be recycled back into the system.
Since the stations in the section where the final product is removed from the mandrels, and the mandrels are cleaned, inspected, redressed, and dried, respectively, are in the ambient or air atmosphere containing oxygen, and the chambers in the section where the product is formed on the mandrels in a nitrogen and oxygen reduced atmosphere, the mandrels are passed from one section to the other via an air lock.


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