Filter package

Details Filter package Filter package

1999-05-12

2001-01-16

Fortuna, Ana (Department: 1723)

Liquid purification or separation

Filter

Supported, shaped or superimposed formed mediums

C210S636000, C053S434000, C053S469000, C053S079000, C053S167000

Reexamination Certificate

active

06174439

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a filter package containing a filter immersed in a liquid and to a method of forming such a filter package. More particularly, it relates to a filter package the contents of which are sanitized and preferably sterilized.
2. Description of the Related Art
It is common for filters to be stored and shipped in a wet state, immersed in a suitable liquid within a package. There are several reasons for packaging a filter in this manner. Some filters are not readily wettable by the liquid which they are intended to filter and so are usually prewetted with another liquid having a lower surface tension to prepare the filter for filtration. As a service to the customer, some filter manufacturers perform prewetting at the factory where the filter is manufactured. In order to prevent the prewetted filter from drying out during storage or shipment, the filter is packaged in a sealed bag containing a suitable liquid which keeps the filter wetted until it is ready to be used.
Other types of filters, such as ultrafiltration and reverse osmosis membranes, are not “prewetted” by the manufacturer but are nevertheless shipped to the customer in a wet state in order to maintain their permselective properties. These filters are typically stored and shipped in packages containing a humectant such as glycerin which keeps the filter wet.
Another reason for packaging a filter in a wet state is that it is easier to ensure the cleanliness of such a filter than if it is packaged in a dry state. Thus, even filters which do not require prewetting and which do not need to be kept wet to maintain their filtering properties may be packaged in a wet state for reasons of cleanliness.
In order to give a filter package containing a wet filter a suitable shelf-life, hydrogen peroxide or other bactericide is usually added to the liquid within the package in order to prevent bacterial growth between the time of manufacture and the time that the purchaser opens the package.
Even though the amount of the bactericide is relatively small (typically around 3% in the case of hydrogen peroxide), in some applications, and particularly in the manufacture of semiconductors, the bactericide is an undesirable contaminant. Accordingly, there is a need for a filter package containing a filter in a wet state which has a long shelf-life yet which contains substantially no contaminants.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a filter package containing a filter and a noncontaminating liquid with substantially no contaminants, the filter package having a long shelf life without employing bactericides.
It is another object of the present invention to provide a method of preparing such a filter package.
In accordance with one aspect of the invention, a filter package which enables the filter to be stored and shipped in a wet state without the filter drying out comprises a sanitized filter cartridge, a flexible bag which surrounds the filter cartridge, and sanitized water hermetically sealed inside the bag. The filter is capable of removing particulates from a fluid and has a porous filter medium including a plurality of pores through which the first liquid can pass between upstream and downstream sides of the filter during filtration to remove particulates from the fluid. The flexible bag has walls extending between an upper end and a lower end of the bag, and the walls comprise a polymeric material impervious to microorganisms and liquid water. The sanitized water substantially permeates the pores of the filter medium and immerses substantially 100% of a volume of the filter cartridge. The bag is hermetically sealed around the filter cartridge with substantially all air excluded from the bag.
In accordance with another aspect of the invention, a filter package which has a long shelf life and contains substantially no contaminants includes a sanitized filter cartridge, a flexible bag hermetically sealed around the filter cartridge, and sanitized water hermetically sealed inside the bag. The filter is capable of removing particulates from a fluid and has a porous filter medium including a plurality of pores through which the fluid can pass between an upstream side and a downstream side of the filter as particulates are removed from the fluid. The flexible bag has an inside surface, an outside surface, and walls comprising a material impervious to microorganisms and liquid water. The sanitized water contacts the inside surface of the bag, substantially permeates the pores of the filter medium so that the filter will not dry out during storage and shipment, and immerses substantially 100% of the volume of the filter cartridge. Substantially all air is excluded from the bag.
In accordance with a further aspect of the invention, a filter package comprises a flexible bag, a sanitized filter cartridge disposed in the bag, and sanitized water hermetically sealed inside the bag. The flexible bag has an inside surface, an outside surface, and walls comprising a material impervious to microorganisms and liquid water. The sanitized filter includes a filter medium having pores through which a fluid can pass between an upstream side and a downstream side of the filter to be filtered by the filter medium. The sanitized water contacts the inside surface of the bag, substantially permeates the pores of the filter medium, and immerses substantially 100% of a volume of the filter cartridge.
The sanitized water within the bag is preferably one which contains substantially no substances, such as bactericides or other organic or inorganic substances, which could be considered contaminants with respect to the filter or its intended use. For example, the level of contaminants in the sanitized water is preferably at most in the parts per billion range. In preferred embodiments, the sanitized water comprises deionized water having an initial resistivity of at least 18 M&OHgr;-cm.
The bag preferably comprises a thin-walled, flexible bag such as a bag formed from a polymeric material. The walls of the bag may be transparent or translucent.
A filter package according to the present invention is not restricted to one having any particular type of filter. For example, the filter may be either hydrophilic or hydrophobic, it may be a filter for filtration of gases, liquids, slurries, or mixtures of more than one phase, and the mechanism by which is performs filtration is not important. The filter may preferably be a filter cartridge and may include a pleated filter element. A few examples of various types of filters which may be employed in the present invention are particulate filters, particularly for use in the semiconductor industry, coalescers, ultrafiltration membranes, and reverse osmosis membranes.
The present invention also provides a method of preparing a filter package including disposing a filter and a liquid in a container with the filter immersed in the liquid. The liquid and the filter are then sanitized and preferably sterilized while in the container. If desired, the container may be hermetically sealed after sanitizing.
The contents of the filter package of the present invention are at least sanitized, i.e., all or substantially all non-spore producing microorganisms are killed, and preferably the contents of the package are fully sterilized. In this description, “sterilizing” is included within the scope of the term “sanitizing”. Thus, a sanitized filter package according to the present invention may be one which has been fully sterilized or one which has been sanitized without being fully sterilized.
The sanitizing can be performed in any manner which will not damage or degrade the filter or the container. In preferred embodiments, sanitizing is performed by heating the liquid and the filter within the container. When sanitizing is performed by heating, the container may be vented during sanitizing to permit vapor of the liquid to exit from the container and prevent the build-up of pressures which could damage the container.
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