Patent Application
20070269350
In
In
Valve in the claims means any device that can be used to let in and remove a sample from a bag.
Referring now to
It is not essential to heat seal all four edges of the sampling bag. For example, the synthetic polymer sheet material may be folded to form one edge, and the other three edges may then be heat sealed. If the sheet material is folded, care should be taken not to entrap more than a very small amount of air at the fold.
In
Any device for securing the hollow stem to the bag side may be used instead of fastener 8; for example, a rivet or friction insert.
Saranex® laminated film is described by the manufacturer, Dow Chemical Company, as a layer of Saran® integrally coextruded between outer layers of polyolefins, having overall thicknesses ranging from 2 mils to 4 mils (0.002 to 0.004 inch). We are aware of at least fifteen varieties or grades of Saranex® laminated films, the differences being primarily in the type of polyolefins (frequently low density polyethylene), the thicknesses of the layers, and the number of plies or layers. Saranex® laminated films are widely used for various types of barrier and protective applications, including various medical applications. Considerable data are available as to their chemical resistance and barrier properties for many chemicals. Any of them are useful in our invention; more generally, we may use any flexible film comprising Saran® film coextruded or compressed between rolls with thin layers of polyolefin sheet. As is known in the art, Saran® is a film of polyvinylidene chloride frequently copolymerized with vinyl chloride, and we include materials of the generic description for use in our invention. That is, when we use the term polyvinylidene chloride, we mean to include all the commercially available variations of Saran® polymers of vinylidene chloride and its copolymers with vinyl chloride and/or other comonomers having high barrier capabilities for VOC's. A favored version of Saranex® laminated film in our invention is known as Saranex® 14 plastic film, which is a five layer coextruded barrier film 2 mil in thickness, with a structure of LDPE/EVA/PVDCE/EVA/LDPE—that is, a structure wherein a thin layer of ethylene vinyl acetate is inserted or coextruded between the Saran® film and the low density polyethylene film on each side. The high barrier coextruded or laminated multi-ply films useful in our invention may be laminated in a manner described by Vilutis in U.S. Pat. No. 3,329,549—that is, in addition to careful alignment of the films during lamination, using electrostatics to facilitate the clinging of one layer to another during manufacture, and/or partially evacuating the air available to the two layers of film at the point of contact during roll pressurization, in order to minimize the possibility of even minute quantities of air becoming enclosed between the layers.
Clear-Lay Rigid PVC Film
“Clear-Lay”™ is a polyvinyl chloride film available from Grafix Plastics of Cleveland, Ohio. Various filters or additives used to modify the physical appearance and/or surface properties may be present. Actual formula is proprietary. The films can be transparent to opaque. It is an odorless film that is chemically stable and resistant to water. The film used in our studies is manufactured by GRAFIX Plastics in Cleveland Ohio.
Teflon
Teflon® FEP is a fluorinated ethylene propylene resin/film. These films are manufactured by DuPont. They are known for their excellent chemical resistance which makes them extremely suitable for sampling bags. Teflon also provides outstanding temperature toughness and in general good durability. This film is a transparent, thermoplastic film that can be heat sealed, thermoformed, vacuum formed, heat bonded, welded, metalized, laminated-combined with dozens of other materials.
Because the bag bodies are chosen from material constructed without the use of adhesives that include organic solvents, they enable the manufacture of very stable, low-background containers for gas samples, without further treatment. Likewise, the lubricant we use to help seal the interfaces of the fittings and the bag body is chosen for its almost complete absence of volatile organic compounds—For this we use poly 1-decene. However, the fittings must be heat treated (baked) to remove volatile organic compounds (VOC's). To further keep the background of the bag low, low bleed septa, HT-X septa are used for this invention. However, the septa, fittings, and o-rings must be heat treated (baked) to remove some trace volatile organic compounds (VOCs).
We employ a vacuum degassed oven (that is, an oven under a negative pressure) to heat treat the hollow stem, inlet body, septum and related parts. Efficient times and temperatures are shown in the following list:
In spite of the fact that the fittings, o-rings, septa, and Teflon cap are heated to drive off any residual VOCs, in spite of our use of 1-decene as the lubricant, and in spite of our use of Clear-Lay™ rigid PVC Film, Teflon™ FEP, and Saranex as the material of choice for the bag bodies, we may regularly perform a test to determine the effectiveness of our method of making bags and may find trace levels of VOCs. In this test, a finished sampling bag is filled with air of a given or tested purity and analyzed for a contaminant suspected of entering the sample from the sampler itself. Concentration of the contaminant in the air prior to entering the sampler is compared to concentration after it enters the bag. Similar comparisons can be made using carbon dioxide analyzed before and after placement in the sampling bag. Following are the results of such tests:
Our sampling bags are also subjected to stability tests. In this test, the finished sampling bag is filled with air; then a volatile organic compound, (frequently two of them), is injected into the bag and the gas in the bag is analyzed more than once over a period of hours, for example 48 hours or up to 10 days, but usually not longer than 3 days as recommended by the EPA guidelines. The gas is not under significant pressure—only enough, usually about one atmosphere, to assure that the bag will hold a sample approximately of the bag's capacity, such as one liter. A desirable target stability is at least 80% after two days. Following are results of such VOC stability tests using bags made of “Clear-Lay” vinyl and Saranex® 14.
Our invention is not limited to a particular size bag or one of a particular capacity. The sampling bag may vary in capacity from 0.5 to 200 liters. Our sampling bag material has a VOC stability after two days of at least 80% for heptane, ethyl acetate, trichloroethylene, methyl ethyl ketone, methylene chloride, toluene, and isopropyl alcohol. Such a material may be called a barrier film.
In
For testing, where a source of pure air, or air having minor known quantities of known constituents is used to fill the sampling bag, the background VOC's may be determined by difference. Our bag will have no more than two parts of background VOC (total of all types) per million parts of air. The background components come from (a) the very small amount of air present, already containing the VOC's, in the flattened empty bag such as is illustrated in
To use the device as shown in
Various changes could be made in the above construction and method without departing from the scope of the invention as defined in the claims below. It is intended that all matter contained in the above description as shown in the accompanying drawings shall be interpreted as illustrative and not as a limitation.
This application claims the benefit of U.S. Provisional Application No. 60/747,380 filed May 16, 2006 which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60747380 | May 2006 | US |
