EP1724000A1

EP1724000A1 - Multiple layered membrane with thin fluorine containing polymer layer

Info

Publication number: EP1724000A1
Application number: EP06252601A
Authority: EP
Inventors: Thomas Edward Frankel
Original assignee: Frankel Thomas Edward
Current assignee: Frankel Thomas Edward; Hong-suk Kim; Kang Seoungil; RITTER, TODD DAVID
Priority date: 2005-05-18
Filing date: 2006-05-18
Publication date: 2006-11-22
Anticipated expiration: 2026-05-18
Also published as: EP1724000B1; DE602006020656D1; ATE501783T1

Abstract

A multi-layer membrane includes a fluorine containing layer and a substrate which are joined by a primer layer or primer component added to the fluorine coating before its application and heat treatment in a multi-step technique. Fluorine containing layer applied by spray coating.

Description

The present application relates to membrane layers.
It is known to provide membrane layers and an example is given in US Patent Application Number 10/711607 . This application shows a thin-film fluorine containing layer of 0.3mm or less bonded through cross linking in a mould to substrate such as EPDM or Nitrile rubber to improve upon the substrate's physical and chemical resistance properties. The improvements in the invention are that the surface of the fluorine containing layer can be made smoother through the application of a spray-coated fluorine containing layer rather than through the previous moulding method, and that the fluorine containing layer has been specifically formulated to optimize the efficiency of the product. The previous method did not offer such flexibility in formulation.
Spray coating methods of applying fluorine containing dispersions onto substrates such as EPDM and Nitrile rubber already exist. They are typically combined with primers such as but not limited to polyamide-imide, polyether sulfones and sprayed onto a substrate that may have been pretreated with. Methyl-ethyl Ketone, N-Methyl Pyrrolidone, plasma or corona treatment to improve adhesion of the primer to the substrate. Following surface preparation and priming, they are coated with a fluorine containing dispersion coating, and are then cured on-line or off-line in an oven. However such methods have not previously been applied to a diffuser membrane for use in water treatment plants, which is a difficult application.
This improvement is of particular importance in application of such a coating to a diffuser membrane used in the sewage and industrial wastewater treatment industries. Diffuser membranes are typically made from perforated non-fluorinated elastomers or polymers, which are perforated with small slits and, when inflated, produce a plume of bubbles which are released into waste water. The efficacy of such diffusers is measured primarily in their ability to produce small bubbles in great quantity, such that the combined surface area of the bubbles is large. A large quantity of small bubbles transfers much more oxygen to the process than do a smaller quantity of large bubbles and oxygen mass transfer is desirable. Manufacturers of diffusers typically spend a great deal of time and energy formulating elastomeric compounds that produce small bubbles, The slightest compound formulation change may result in a vastly different bubble size. Furthermore, where diffuser membranes are submerged in dirty water, surface contamination from foulants such as biofilm, calcium and gypsum can cause an increase in bubble size over time, just as fats, oils, greases and solvents can penetrate traditional membranes causing chemical oxidation of the rubber. This can result in either a failed part or increased bubble size. The coating of a non fluorine containing membrane with a smooth fluorinated layer that is specifically designed to produce small bubbles, and to withstand thousands of perforations and a constant state of flux while submerged in waste water, is a novel invention and provides a universal solution to both fouling and efficiency issues.
Aspects of the present invention apply to flexible diffuser membranes which are used in the aeration of waste water and which is spray coated with a fluorine containing surface layer.
A diffuser membrane is produced from blended EPDM rubber, Nitrite rubber, or Neoprene rubber, the surface is roughened either through corona, plasma, or Methyl-ethyl Ketone, and a primer and fluorine containing surface layer are applied through spray coating. Alternately a blended primer and fluorine containing surface layer are applied through spray coating.
When treated in this way, the membrane becomes significantly more resistant to surface fouling, chemical oxidation, and its oxygen transfer efficiency is acceptably high by industry standards.
Embodiments of the present invention are described by way of example and with reference to the attached drawings wherein:

Fig. 1 is a cross-sectional view of a multi layered disc membrane;
Fig. 2 is a cross-sectional view of a membrane onto which layers have been applied;
Fig. 3 is a cutaway view of a multi layered tube membrane;
Fig. 4 is a cross-section of an air diffuser assembly;
Fig. 5 is a cross-section of a membrane; and,
Fig. 6 is a schematic illustration of a manufacturing process.

Adhesion between a spray coated fluorine containing layer and a substrate is accomplished through substrate surface treatment, priming, coating and curing.
Firstly, a substrate layer such as membrane 3 is moulded.
Secondly, a roughing agent such as corona, plasma, methyl-ethyl ketone or N-Methyl Pyrrolidone is applied to the surface to be coated as needed depending on the quality of the substrate.
Thirdly, a primer layer 2 of less than 10 microns is sprayed onto the substrate surface. This primer is then heat treated at 100 degrees C for 15 minutes. The primer layer may contain Polyamide-Imide or Polyether Sulfone. Alternately, the primer is blended with a fluorine containing dispersion layer and this layer is sprayed onto the substrate surface, then heat treated.
Fourthly, if using separate primer and fluorine containing dispersion layers, the fluorine containing dispersion layer 1 of less than 20 microns is sprayed over the cured primer, and is heat treated at 120 degrees C for 20 minutes. The fluorine containing dispersion layer may contain fluoride acryl resin, xylene, toluene, bentonite, titanium dioxide, carbon black, 2-lsocyanatoethyl 2, 6-diisocyanatohexanoate, 2, 6-Diisocyanatohexanoic acid 2-isocyanatoethyl ester and/or ethyl acetate.
From the foregoing it will be seen that this invention is one well adapted to attain all ends and objectives hereinabove set forth together with the other advantages which are obvious and which are inherent to the structure.
It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.
Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative, and not in a limiting sense.
This invention is about the multi-layered membrane of disk typed and tube typed membrane air diffuser. This system can be installed in the aeration tanks of the sewage and waste water treatment system that is used to make the air, which was supplied from the blower, fine bubbles to spray them so that the oxygen in the air can be efficiently dissolved into the sewage and waste water. By doing it, this system analyses and removes the biochemical oxygen demand and suspended solids biologically, and enables to be appropriately mixed so that the sedimentation within the aeration tank can be prevented.
Referring to Figs. 4 to 6 of the drawings in which:-

Fig. 4 represents the cross section of an assembled air diffuser according to this invention.
Fig. 5 is a cross section illustrating a membrane with the PTFE, which was prepared for both surfaces of membrane for air diffuser according to this invention.
Fig. 6 represents a process where the PTFE is coated on the membrane for air diffusers according to this invention.

Within these drawings the following reference numeration is used:

11 : Base
12 : Retaining unit
13 : Multi layered membrane
21 : EPDM membrane
22 : Primer
23 : PTFE (polytetrafluoroethylene) coating layer

The purpose of the invention is a device that sprays the air, taken from a blower, through the membrane infinitesimally for various processes that supply oxygen to the micro organisms in an aeration tank to purify waste and related processes where sewage and waste waters are biologically processed. The membrane used for this purpose are the ones composed of single material and single layer such as EPDM, SILICON and NITRIL.
In this invention, the membrane may be manufactured by coating the PTFE on the multi layer structure or both surfaces of the conventional EPDM or NITRIL membrane (MEMBRANE 22), so that the acid-resistance, resistance to chemical, heat resistance, and the function that can prevent foreign elements from being adhered, which are the functions not owned by EPDM and NITRIL membrane, can be provided.
The invention for achieving the above purposes has the following characteristics:
This invention coats PTFE on both surfaces of membrane whose main material is EPDM or Nitril. It adds the characteristics of PTFE based on the physical property of EPDM membrane so that the functions and durability of the membrane within the sewage and waste water can increase.
Generally, in case of the multi-layered membrane with coating of EPDM and PTFE, the PTFE coating layer is likely to peel from the EPDM surface if there is no pre-treatment In aspects of PTFE layer coated after pre-treatment, the layer was processed through a hardening process from heat treatment so that PTFE coating layer should not rise during the manufacturing process of bending the layer or punching a pore.
The air diffuser of PTFE coating membrane of this invention has the characteristics as follows, it prevents suspended solids from being adhered under water during a process where air is sprayed within the aeration tank of the sewage and surface water treatment system. Also, it has superior acid resistances and strong resistance to chemical.
Figs. 4 to 6 provide illustrations of a practical example according to this invention as shown below.
The compositions of the membrane air diffuser according to this invention are represented. The multi layered membrane (membrane 13) is assembled into the air diffuser (Base 11) and this assemble is tightened by a retaining nut (retaining nut 12). As for the function of the membrane air diffuser, the multilayered membrane (membrane 13) tightened by a retaining nut and expanded by the air supplied through the orifice of the air diffuser base and at this time many slits, which were made by punching over the effective surface of the membrane, are opened while vomiting equal fine bubbles of 1-2mm sizes.
The manufacturing process of a membrane in which PTFE has been coated is described with reference to Fig. 6, wash and dry both surfaces of EPDM or NITRIL membrane (21) and press them by (primer 22) and then heat them for about thirty minutes in a heat treatment furnace,.
Afterwards, coat a membrane which was cooled off, with PTFE and plasticize it in the heat treatment furnace for over 20 minutes at over 100 degrees for plasticity of the membrane.
As described above in detail, the air diffuser of multi layer membrane of PFTE according to this invention has the following effects; it has strong resistance to chemical substances of strong corrosiveness flown into along with sewage or waste water. Also, it is safely prevented from the suspended solids such as CaC1₂ that is easily adhered to the EPDM membrane surface, and it has acid resistance.
The membrane can be used in a number of applications and for example.

a) a disc typed membrane for air diffusers that prevents the suspended solids from being adhered under water by coating PTFE in the multi layer structural on both surfaces of EPDM or NITRIL membranes and that has acid resistance, resistance to chemical, and heat resistance.
b) related to application 1m the multi layered tube type membrane for air diffusers whose membrane is made in a tube form.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

A multi-layer membrane comprising:
a first layer comprising a polymer layer on a membrane and a second layer over said first layer comprising a dispersion layer wherein said dispersion layer is a fluorine containing dispersion layer.
A multi-layer membrane as claimed in claim 1, wherein said first layer comprises a fluoroelastomer.
A multi-layer membrane as claimed in claim 1 or claim 2 wherein said dispersion layer further includes a primer and a fluorine containing dispersion.
A multi-layer membrane as claimed in claims 1 to 3, wherein said first layer further includes material selected from a group consisting of neoprene rubber, ethylene propylene diene monomer (EPDM) and nitrile rubber.
A multi-layer membrane as claimed in any preceding claim, wherein said first layer further includes a primer layer and wherein said primer layer is less than 10 microns.
A multi-layer membrane as claimed in any preceding claim, wherein said membrane is selected from a group consisting of a tubular shaped membrane, a disc shaped membrane and a panel shaped membrane.
A multi-layer membrane as claimed in claim 5, wherein said primer layer comprises material selected from a group consisting of Polyamide-Imide and Polyether Sulfone.
A multi-layer membrane as claimed in any preceding claim, wherein said second layer is less than 20 microns.
A multi-layer membrane as claimed in any preceding claim, wherein said second layer is less than 20 microns and said second layer is heat treated at a temperature of greater than 120 degrees C.
A multi-layer membrane as claimed in any preceding claim, wherein said second layer further comprises material selected from a group consisting of fluoride acryl resin, xylene, toluene, bentonite, titanium dioxide, carbon black, 2-Isocyanatoethyl 2,6-diisocyanatohexanoate. 2,6-Diisocyanatohexanoic acid 2-isocyanatoethyl ester and ethyl acetate.
A multi-layer membrane as claimed in any preceding claim, wherein said first layer is a non-fluarinated polymer.
A mulfi-layer membrane as claimed in any preceding claim, wherein a primer and said fluorine containing dispersion is applied onto said first layer in a single application.
A multi-layer membrane as claimed in any preceding, wherein said second layer is applied through a spray, and is cured using a method selected from a group consisting of an on-line and an off-line oven.
A multi-layer membrane as claimed in any preceding claim, wherein said first layer further includes materials selected from a group consisting of fluoride acryl resin, methyl-ethyl ketone, xylene, toluene and carbon black.
A multi-layer membrane as claimed in any preceding claim, wherein said membrane is pretreated with plasma, corona, N-Methyl Pyrrolidone or methyl-ethyl ketone prior to coating of said first layer.
A multi-layer membrane as claimed in any preceding claim, wherein said membrane is pretreated prior to coating of said first layer.
A multi-layer membrane as claimed in any preceding claim wherein the dispersion layer is polytetrafluorothene (PTFE).
A process for preparing a multi layer membrane wherein said membrane comprises a polymer layer consisting of a fluorine containing polymer, a substrate, wherein a bond between said first layer and said second layer is formed first via a degreasing step, followed by a primer, heat treatment of said primer, spray coating of a fluorine containing dispersion, and finally heat treatment of said coating,
A process for preparing a multi layer membrane wherein said membrane comprises a polymer layer consisting of a fluorine containing polymer, a substrate, wherein a bond between said first layer and said second layer is formed first via a degreasing step, followed by a spray coating of combined primer and fluorine containing dispersion, and finally heat treatment of said combined primer and said coating.
A process for preparing a multi layer membrane wherein said membrane comprises a polymer layer consisting of a fluorine containing polymer, a substrate, wherein a bond between said first layer and said second layer is formed via a spray coating of combined primer and fluorine containing dispersion, and finally heat treatment of said combined primer and said coating.
A process for preparing a multi layer membrane wherein said membrane comprises a polymer layer consisting of a fluorine containing polymer, a substrate, wherein a bond between said first layer and said second layer is formed via a spray coating of a primer, heat treatment of said primer, spray coating of fluorine containing dispersion, and finally heat treatment of said coating.
A process as claimed in any of claims 10 to 21 wherein the fluorine containing polymer is polytetrafluorethene (PTFE)