A system for automatic detection of authenticity of security documents by measuring reflected components of incident energy in three or more optical wave bands. The system involves the use of UV-visible light source, an optional near infra red light source, photodetectors and associated sensing circuitry. Photoelectric signals generated by photodetectors from the reflected energy received from a security document are used to verify its authenticity under UV-visible along with optional near infra red illumination. The process involves measurement of energy reflected as photoelectric signals from a security document in at least three optical wavebands by suitably located photodetectors with appropriate wave band filters and the electronic signal processing to distinguish between a genuine document from a fake one for ultimate LED indicator display and audio-visual alarms, hence the detection of fake security document.

All the prior arts describe systems for verification of currency notes claiming that the systems can be applied for other security documents also. Accordingly, in the following analysis of prior arts the word currency note is used rather than generic term security document. Presently available currency detectors can be classified into two categories, namely viewer type and automated type. All the viewer type instruments rely on subjective visual assessment of authenticity. Few of the viewers display a magnified view of micro-features under visible light. In some the viewers, a currency note is illuminated by UV light to display fluorescent security features like fibres, UV fluorescent printed pattern. Most automatic type detection systems are currency counters also. The verification in some automated type systems is based on UV measurement of fluoresced/reflected UV radiation from a narrow strip of the currency note; the data are collected by moving the note across a detector and measuring the energy from a small area at a time i.e. by scanning and sampling technique. The measured energy is converted into an electrical signal. Data acquired from a genuine currency notes is set as reference. Any deviation of the measured signal from this reference value is indicative of counterfeit. The few of the automatic verifiers measure reflected/fluoresced UV light from UV fluorescent security feature(s). Some currency verifiers are based on scanning a part of the printed pattern and looks for inconsistent locations of the small dots of the printing material. With the advent of technology, art of counterfeiting is also progressing rapidly. Earlier, fake currencies were produced either by colour scanning followed by high-resolution printing (alternatively colour photocopying) or by crude printing on non-security papers. The today's bank notes incorporate several security features like intaglio printing, optically variable ink (OVI) features, and UV fluorescent features including fluorescent fibres. Clever counterfeiters are now attempting to duplicate these features including fluorescent properties of the paper. A very thin line of demarcation now exits between a counterfeit currency note and an authentic one. At least two different modes of verification are imperative to assess the authenticity. The visual and UV fluorescent security features incorporated in a currency note vary from country to country and also denomination dependent. The judgement of authenticity of a currency note relying either on visual assessment or on rapid opto-electronic detection 'on-the-fly' technique based on scanning the light reflected or transmitted from a narrow zone may likely to yield misleading conclusions. A suitable apparatus providing the combination of integrated reflected as well as transmitted energy, received from a large area of a currency note, measurement facilities in at least three different wavebands both for the reflected and transmitted components, in static condition of the currency note, which can be adopted for the currencies from various countries of different denominations or in various physical conditions of the note to be inspected is not available.
Analysis of Prior Art
The following basic principles are used to verify the genuineness of a currency note:                i Visually observing the UV fluorescent features, printed or embedded, of the currency note        ii Reading the magnetically recorded code by a magnetic sensor        iii Assessing the quality of print by studying the mis-registration        iv Assessing the currency paper quality by measuring the quantum of UV light reflected/transmitted        v Assessing the currency paper quality by measuring the quantum of UV light fluoresced        vi Assessing a electronically recorded image        vii Multifunctional apparatus for discrimination and authentication
All the above cited prior arts rely on one of these principles—variations are in the techniques of data collection and the area of the currency note from where data are collected. The drawbacks of the prior arts are discussed below.
The paper used in currency notes has cotton based fibres as the base material that shows very little UV fluorescent property. Other types of paper convert incident UV radiation into visible light. The amount of UV light reflected and fluoresced are complimentary as higher is the quotient of fluorescence, less is the amount reflected and vice versa. So, the measurement one or the other provides similar information. Transmittance also depends on fluorescence since, if large fluorescence will reduce the transmitted components. Accordingly, principles mentioned under (iii) and (iv) above are some similar in nature, data interpretations. All the existing prior arts employing the principals (ii) and (iii) differ in the measurand, and technique of scanning and the zone of data acquisition. These have common limitations. The drawbacks of the all the prior arts are discussed below, apparatuses are classified in accordance with their principle of operation.
Visually Observing the Printed or Embedded UV Fluorescent Features
Prior arts listed in the U.S. Pat. No. 5,942,759 and US2001054644 belongs to this category. These are basically viewers where in the operator exposes the currency note to UV radiation and looks for the presence or absence of printed or embedded UV fluorescent features like serial no., floral or other patterns, thread and fibres etc. These instruments rely on two dimensional image capabilities of human eye and data processing power of the brain. Drawbacks are:                Decision is subjective and needs a priori knowledge about an authentic currency note identical in all respect, except physical conditions, to the one under verification.        It is practically impossible to stock standard samples either as images in the brain or physically corresponding currency notes of different denominations from various countries.
Modern counterfeits incorporate many UV fluorescent printed features to fool an operator relying on visual inspection only. Viewer types are not relevant to the present invention.
Magnetic Sensor Based Equipment
Prior arts listed in the U.S. Pat. No. 4,464,787 and U.S. Pat. No. 5,874,742 fall under this category. The drawbacks are:                Magnetic code readers are basically currency discriminators—magnetic code can be duplicated easily and hence not a reliable method of authentication        Currency notes from many countries do not contain magnetic codes. Genuineness of currency notes from these countries can not be assessed.        Magnetic code of a currency note may be wiped out due to accidental exposure to strong magnetic field, magnetic sensor based instruments would fail to authenticate such a note.        Some machines scan the currency note to determine its dimensions for hence authentication. Dimensional data is unreliable.
These apparatuses are also not closest prior art.
Instruments Based on Assessing the Quality of Print by Studying the Mis-Registration
Prior arts listed in the U.S. Pat. No. 4,482,971 belong to this category. Currency notes counterfeited by high resolution scanning and printing or colour photocopying process. The instruments scan and look for presence of small dots of printing ink inconsistent with the printed pattern. The main drawback is:                Modern counterfeited currency notes are printed in sophisticated notes duplicating most of the processes employed to print authentic currency notes without any discernable mis-registration error. These types of notes cannot be authenticated by studying the mis-registration error.
These apparatuses are also not closest prior art.
Instruments Based on of the Quantum of UV Light Fluoresced/Reflected/Transmitted Energy Measurement
Prior arts listed in the U.S. Pat. No. 4,482,971 and FR2710998 belongs to this category. All of these scan a narrow zone, sampling a small area at a time, while the currency note moves below or over the photodetector. Measurand is either the reflected or transmitted or fluoresced component of incident UV light (there is only one patent, FR2710998, which measures transmitted energy and the rest measure the reflected energy). UV light is either blocked (fluorescent measurement) or rest of the optical spectrum is blocked only UV light is allowed to pass (UV reflectance/transmittance measurement) by a filter. The drawbacks are:                Measured fluoresced/reflected/transmitted energy data corresponding to UV region of the spectrum alone cannot reliably characterize the paper quality. Cleverly counterfeited currency notes can mimic UV fluoresce/reflection/transmission coefficient sufficiently close to that of a currency paper.        The source is kept very close to the moving currency note, so the data are collected from a very small area. The measured energy from each small sampled area is either compared to a reference data (collected from similar type authentic currency note) or summed up to compare with similar data collected from a reference sample. Soiling and or mutilations of the currency under authentication would cause substantial amount of data distortion to reliably assess authentication.        It is known that an accidentally washed genuine note in certain detergent develops UV fluorescent quality. Such a note would be indicated as a counterfeit.        This principle needs motion of the currency note, and performs only first order verification during stacking/counting of unsoiled notes of similar type. It is not a compact and cheap system.        Some apparatuses measure the fluorescent energy emanated from certain printed features, e.g. thread. These need accurate placement of the said feature(s) under the photodetector. Since currency notes of different denominations from different countries contain UV sensitive features at different locations, instruments based on measuring UV fluorescence (by any printed pattern) can be usefully employed for US Dollars only, as all US Dollars have same size and are reasonably similar.
There is only one U.S. Pat. No. 4,618,257 which uses multiple sources emitting different waveband to illuminate a very small zone of the currency note under verification and a single detector collects the energy for each waveband in sequential manner. Since the data corresponds to a small zone, local physical condition, like soiling, mutilation etc. would severely affect the proper authentication process.
Assessing a Electronically Recorded Image
The patent US20030169415 uses a CCD camera to record the image and by tri-chromatic colour analysis technique judges the authenticity. The drawbacks are:
Soiling, mutilation, physical damage etc. would lead to erroneous results
Expensive and complex
Basically designed for passport and similar kinds of documents.
Multifunctional Apparatus for Discrimination and Authentication
US20030081824A1, claims for an improved fake currency detector using different kinds of sensor output. A brief description of is principle of operation and drawbacks are given below:
A multifunctional apparatus is using multiple magnetic and optical sensors. The magnetic sensors scan and generate a magnetic code. Optical sensors scan the currency note in terms reflected energy in two wave bands. Colour matching scheme is also has been claimed to be employed. The two types filters used are used, namely UV pass and UV blocking. UV blocking visible pass filter is made a combination of two filters namely a blue filter passing 320 nm to 620 nm with a peak at 450 nm and a yellow filter passing 415 to 2800 nm. So, the visible light sensor sees 415 nm to 620 nm i.e. it senses blue to a small part of red colour.
The drawbacks are:                Authentication is largely dependent on magnetic and optical scanning. Currency notes of many countries do not have any magnetic code.        In many countries, old notes have threads which do not contain any special optical feature. Such notes would be identified as fake, even if genuine.        The optical authentication is based on thread parameters. Currency notes of many countries, including India, have different series of same denomination with a wide variation in thread locations. The tolerance limit of 0.05 inch permissible in the patent application would reject authentic currency notes.        A genuine note accidentally discoloured due to bleaching etc. would be indicated as fake.        The principle used can not properly authenticate genuine currency notes having no fluorescence feature (text or thread), such as Asoka pillar Indian currency series of Rs.50 and Rs.100 denomination notes, still in wide circulation in India.        The optical authentication is based on printed image pattern and thread data. Clever counterfeiter can duplicate printed patterns.        The apparatus can not detect NIR sensitive features likely to incorporate in the currency notes of various countries.        The apparatus is complex, expensive and not portable.
Another prior art U.S. Pat. No. 4,618,257 incorporates two LEDs positioned at such angles that they illuminate a common target area and a broad band photo detector to measure the light reflected from the target area. As the currency note is transported under the LEDs, each of the LEDs is switched on sequentially with a pre-determined 'on-time' and 'delay time'. The preferred LED pair is comprised of one narrow band red LED and the other narrow band green LED having peak emission wavelengths of 630 nm and 560 nm respectively. The patent suggests the alternative use of yellow or infrared LED. The measured signals in terms of voltages are compared with the corresponding reference values stored in a memory. The drawbacks of this apparatus are:                It does not collect any data corresponding to the reflectance or fluorescence of UV or blue colour. Reflectance information is confined to only about half of the optical spectral range of 350 to 750 nm. Our experiment has shown, as explained later in Example 1, that UV-blue reflectance property of a currency note is a strong indicator of its genuineness due to the very basic nature of the currency paper.        Due to various reasons including local conditions of a currency note, reflected data from a small area may not be the true representative of the bulk properties.        The apparatus collects data from a specified small target area making it highly position sensitive particularly in case of currency notes of varied sizes.
All known automated currency verifiers require transport mechanism, and cannot operate in stationary condition of the document under verification. These verifiers pick up one document from a stack of multiple number of similar documents, transport it from one place to other and verify authenticity on the fly by scanning it. Such systems are suitable basically for currency note with a number of currency notes stacked in a pile, but can not properly handle one off a kind documents like bank draft, security bond and other bank instruments where each document is likely very different from the other in shape, size and other similar parameters. There is no patent sealed or filed till date wherein one off a kind documents like, bank drafts, security bonds and other bank instruments and security documents which require manual feeding can be authenticated by a unique automatic detection mode.
There is no patent sealed or filed till date, which embodies automatic opto-electronic detection techniques using at least three optical wavebands to generate reflectance/fluorescence data by measuring reflected/fluoresced energy together with a provision visual inspection under UV-visible-near infra red light.
There is no patent sealed or filed till date, which embodies automatic opto-electronic detection technique using more than one optical wavebands to obtain reflectance/fluorescence data by spatially integrating energy received from a large area of the document under verification.
There is no known prior art claiming to authenticate polymer based currency notes, passport, visa, various bank instruments visually as well as automatically.
The present invention circumvents the drawbacks of existing prior arts by providing two independent methods of verification and more than one optical band to detect authenticity in automatic mode in a stationary condition of the document under authentication by performing large area spatial and temporal integrations simultaneously. However, the automatic detection module of the invention can be adopted in a currency note counting machine by collecting dynamic data at various scanning points. The present invention provides an apparatus that can be used to authenticate paper and polymer based currency note, bank drafts, security bonds and other bank instruments and security documents without any need to modify system hardware.

Fake currency detector using visual and reflective spectral response

Council of Scientific & Industrial Research


Coated rollers (10) with a hard, high release, non-marking, coating with excellent non-stick properties are disclosed for use as idler rollers, or as laminating, coating or printing rollers. The release coating comprises an outermost coat (15) which includes a silicone-epoxy emulsion in a water-based curing system that is sprayed or brushed on a roller core and then allowed to cure at room temperature. The release coating further comprises a primer coat (16) of silicone-epoxy in a water base that is also sprayed or brushed on the roller to form a coat and then allowed to cure at room temperature. Methods for making such rollers are also disclosed.

Rollers with good non-stick (high-release, low energy) surfaces are required in the processing and handling of adhesives, inks, toners, coatings and other materials for a wide variety of applications. The materials to be released may be liquids or solids. Release may be achieved either by using materials with low surface energies, or by coating, wrapping or impregnating the surface with low energy materials.
Generally, materials that have good release properties tend to be relatively soft and need improvement in the area of abrasion resistance and durability. This is exemplified by silicones and Teflon which are two of the most widely used materials for high release applications. Silicones tend to have good release properties (low surface energy) but not good wear resistance. A use of an improved coating based on a fluoropolymer resin (DuPont "Supra Silverstone") for a fuser roller is disclosed in Chen et. al., U.S. Pat. No. 5,547,759. Such coatings may have improved durability, but may not exhibit the high release characteristics of silicone materials.
Rollers used for transporting solid webs, or used in nip positions generally need to be resistant to wear and abrasion in addition to providing high release properties.
A general object of the invention is to provide improved coatings for idler rollers and laminating rollers, in which the coatings provide excellent wear resistance, excellent release characteristics, are non-marking, and provide a variety of surface finishes. The coatings should also be easy to apply in manufacture of the rollers.

High release coatings for printing and coating rollers


A bladed expander for recovery of thermal energy from a working fluid, comprising a stator provided with an inlet port and an outlet port for the working fluid, a rotor housed within the stator, and a plurality of blades set between the rotor and the stator so as to delimit between them a plurality of compartments with variable volume that increases between the inlet port and the outlet port. The stator and the rotor are subjected to a heat exchange with a hot fluid so as to carry out a transformation of expansion during which the working fluid receives thermal energy from outside.

As is known, in some types of machines (for example, internal-combustion engines for vehicle applications or for the generation of mechanical or electrical energy), of industrial plants and systems for the production of energy (for example, geothermal systems defined as "low-enthalpy systems" or for exploitation of the thermal energy produced by biomasses, which still present thermal flows that usually constitute waste but are potentially useful) the problem of recovering the thermal energy of a hot fluid at a relatively low temperature and of converting it into mechanical energy is posed.
For this purpose, it is known to use a Rankine cycle or Hirn cycle in which a working fluid in the liquid state is pressurized, heated via a heat exchange with the fluid from which the thermal energy is to be recovered up to total or partial vaporization, superheated or not, and then expanded in an expander that produces mechanical power available at its own output shaft (which can be exploited directly or converted into electrical energy via a generator driven by said shaft).
Given the low temperatures, the working fluid is generally constituted by an organic fluid, such as for example a chlorofluorocarbon in pure form or in mixture or a fluorocarbon, etc., in which case the cycle is usually referred to as ORC (Organic Rankine Cycle).
As expander, it is known to use a dynamic bladed expander or a volumetric expander, in this latter case, of the bladed type or some other type.
If the thermal power recovered from the working fluid is of limited intensity and temperature, there exist known technological and constructional difficulties regarding:
a) the production of a high-efficiency dynamic expander (turbine): the low flow rates of working fluid and the low enthalpies would lead to a general layout of the turbine (areas of passage, heights of blading, etc.) that prevents high (adiabatic, isoentropic) efficiency;
b) the contact between the hot working fluid and the surfaces of the machine causes a cooling of the working fluid and its condensation on the surfaces themselves, with loss of efficiency of conversion;
c) in the case of bladed volumetric expanders, the difficulties referred to in point a) cease to exist, even though the difficulties referred to in point b) remain, albeit to not such an important degree;
d) the frictions due to contact between the stator blades and the rotor blades, which are intensified in the presence of fluid vapours that expand, are the cause of a reduction of the efficiency of the machine; there derives therefrom the need for a technological improvement of the expanders with respect to the current state of the art.

Expander for recovery of thermal energy from a fluid


An integral, monolithic frame-membrane is disclosed, such frame-membrane having a semi-permeable membrane portion and integral therewith a frame portion, the frame portion having one or more cavities, each cavity juxtaposed to the membrane portion, each cavity having at least one fluid entrance conduit communicating with an entrance manifold aperture and at least one fluid exit conduit communicating with an exit manifold aperture. The integral, monolithic frame-membrane may be used in apparatus for carrying out gas-separation; microfiltration; ultrafiltration; nanofiltration; reverse osmosis (i.e. hyperfiltration); diffusion dialysis; Donnan dialysis; electrodialysis (including filled-cell electrodialysis; i.e. electrodeionization); pervaporation; piezodialysis; membrane distillation; osmosis; thermo osmosis; and electrolysis with membranes. Also disclosed are pillows prepared from ion exchanging films or fabrics (which may be porous or non-porous), the pillows filled with ion exchange structures such as beads, fibers, fabrics or rods. The pillows may be used with the integral, monolithic frame-membranes, with separate frames and membranes or with frames only.

In "multi-compartment electrodialysis" ("ED") many ion exchange ("IX") membranes are arranged between a single pair of electrodes. The membranes are of two types: cation exchange membranes ("CXM") and anion exchange membranes ("AXM"). The CXM are relatively permeable to positively charged, low molecular weight ions and relatively impermeable to negatively charged ions and to high molecular weight neutral molecules whereas AXM are relatively permeable to negatively charged, low molecular weight ions and relatively impermeable to positively charged ions (and also to high molecular weight neutral molecules). The CXM and AXM alternate between the above mentioned single pair of electrodes. Spaces are left between the membranes through which are passed aqueous solutions. When a direct electric current is passed between the electrodes, positively charged ions in the solutions ("cations", generally metallic ions such as sodium, magnesium, calcium) are pulled toward the negatively charged electrode ("cathode"). Small cations easily pass through CXM but not through AXM. Simultaneously negatively charged ions in the solutions ("anions", generally non-metallic ions such as chloride, nitrate, bicarbonate, fluoride, sulfate) are pulled toward the positively charged electrode ("anode"). Small anions easily pass through AXM but not through CXM. As a result, spaces which are on the cathode side of AXM (on the anode side of CXM) are at least partially deionized by the direct electric current. Such spaces are generally called "diluting" spaces. Spaces which are on the anode side of AXM (on the cathode side of CXM) accumulate the ions removed from the diluting spaces. Such enriched spaces are generally called "concentrating" spaces. ED is made continuous by flowing the solutions between the membranes. In such case the spaces must be enclosed by frames ("spacers") to prevent mixing of the solution in the diluting spaces ("dilute solution" or "dilute") with that in the concentrating spaces ("concentrate solution" or "concentrate"). Holes are provided in the membranes registering with similar holes in the frames thereby forming (internal) manifolds to distribute the solutions to the appropriate spaces (cavities in the frames) and to collect separately the dilute and concentrate solutions. Channels in the frames which enclose the concentrating spaces connect such spaces with the concentrate solution manifolds, and channels in the frames which enclose the diluting spaces connect the latter spaces with the dilute solution manifolds. The channels and/or frames are arranged (designed) so that the flows of solutions are uniform over the surfaces of the membranes. Regions in the diluting spaces in which the solution velocity is lower than average will be more highly deionized than the average extent of deionization. Regions in the concentrating spaces in which solution velocity is lower than average will be more enriched (concentrated) than average. If the solution being deionized contains sparingly soluble salts (such as calcium sulfate or calcium bicarbonate) then such salts may precipitate on or in those membrane surfaces in contact with regions in the concentrating spaces having velocities lower than average.
Roughly 95% of the direct electric current passing through CXM is carried by cations passing from the diluting spaces to the concentrating spaces (the remaining 5% carried by anions passing through the CXM from the concentrating spaces to the diluting spaces). The fraction of the current carried by a given ion is referred to as the "transport number". In the above case the transport number of CXM for cations is approximately 0.95. Similarly the transport number of AXM for anions is approximately 0.95 (and the transport number for cations passing through the AXM from the concentrating spaces to the diluting spaces is about 0.05). In aqueous solutions of mineral salts, the transport number for both anions and cations is roughly 0.5, that is roughly half the current is carried by anions and half by cations. For example, in the case of aqueous solutions of sodium chloride, 40% of the electric current is carried by positively charged sodium ions (i.e. transport number 0.4) and 60% by negatively charged chloride ions. Hence while 95% of the electric current is carried by sodium ions through a CXM (in the case of sodium chloride solutions) only 40% of the current is carried to the CXM by sodium ions. At the interface between the dilute solution and the CXM there is therefore a deficit in sodium ion transport equivalent to 95-40=55% of the current. Such deficit leads rapidly (in roughly one second) to a reduction in the sodium chloride concentration at the above mentioned interface to such a value that the missing 55% of the current is brought to the interface by diffusion. A mass balance leads to ##EQU1## where "i" is the current density in amperes per cm.sup.2, t is the transport number for sodium ions in the CXM (0.95), t is the transport number for sodium ions in aqueous solutions of sodium chloride (0.40), D is the diffusion coefficient (in cm.sup.2 per second) for sodium chloride (not sodium ions) in aqueous solution (1.36.times.10.sup.-5 at 18.degree. C., 64.degree. F.), F is the quantity of current required to transport one gram-equivalent of any ion at a transport number of exactly 1 (96, 480 amperes per gram-equivalent per second, called Faraday's constant), ##EQU2## is the concentration gradient built up because of the deficit in electrical transport of sodium ions, C.sub.m is the concentration (in gram-equivalents per cm.sup.3) at the above mentioned interfaces, .delta. is the distance (in cm) from the interface to the plane in the aqueous solution (parallel to the membrane) where the concentration is C. If the flow is in the streamline (laminar flow) region then .delta. is half the distance from the CXM through the diluting space to the AXM. Even when the general flow is not in the streamline region, a layer of solution adjacent to the CXM membrane remains in the streamline region, in which case .delta. is the thickness of such layer and C is the concentration outside such layer, essentially the bulk concentration. The above mass balance equation may be rearranged to: ##EQU3## where ##EQU4## it is the quantity of sodium ions (in gram-equivalents per second per cm.sup.2) transported by a current having a density of i amperes per cm.sup.2. Inspection of this equation shows ##EQU5## increases as D (the specific rate of diffusion) increases. D is inversely proportional to the viscosity of the solution and directly proportional to the absolute temperature and therefore in the case of aqueous solutions increases at a compound rate of about 2.25% per .degree.C. Therefore there is an advantage to operating at elevated temperatures. The electrical energy consumption (in watt-seconds per gram-equivalent of sodium ion removed through a CXM) is IRF/t where (as mentioned above) i is in amperes per cm.sup.2, F is the quantity of current required to remove 1 gram-equivalent per second of sodium ion through a CXM having a transport number of exactly 1 (96,480 amperes per gram-equivalent per second), t is the actual transport number of the CXM and R is the sum of the electrical resistances per cm.sup.2 of one CXM, one AXM, one diluting space and one concentrating space. R decreases at a compound rate of about 2% per .degree.C. (i.e. the same rate at which the viscosity of water decreases), increasing the importance of operating at elevated temperatures. Almost all of the electrical energy consumption goes into heating the dilute and concentrate solutions. Therefore it is often practical to warm those solutions by recuperative heat exchangers, transferring heat from the effluent solutions to the influent solutions. If the electrical energy used in ED is generated locally (e.g. by a diesel electric generator or a packaged stream electric generator) then the waste heat may be used to elevate the temperatures of the influent solutions at least enough to make recuperative heat exchange practical.
Further inspection of the above equation (2) shows that it/F increases as t/(t-t) increases as illustrated in the following table:
______________________________________ Relative Relative Relative t t/(t - t) it/F i Energy ______________________________________ 0.95 1.73 1.00 1.00 1.00 0.85 1.89 1.09 1.22 1.37 0.75 2.14 1.24 1.57 1.99 0.65 2.60 1.51 2.20 3.22 0.55 3.67 2.12 3.67 6.33 0.45 9.00 5.21 11.00 23.2 ______________________________________
The third column in the above table ("Relative i t/F") is the relative amount of sodium ion removed per cm.sup.2 per second, other things on the right hand side of above equation (2) being equal (i.e. C, C.sub.m, D (which is a constant for sodium chloride dependent only on temperature) and .delta.). The fourth column ("Relative i") is the relative current density (in amperes per cm.sup.2) corresponding to t and it/F while the last column ("Relative Energy") is the relative energy (watt-seconds per gram-equivalent sodium ion removed) other things on the right hand side of equation (2) being equal. It will be seen that, except for the case where very few gram-equivalents of sodium must be removed, it may not be practical to increase it/F (the rate of removal of sodium ion) by increasing t/(t-t). (Water having 584 ppm sodium chloride has 10 gram-equivalents of sodium per cubic meter (1 cubic meter=1 metric tonne=264 U.S. gallons)).
Inspection of equation (2) also shows that it/F (the rate of removal of sodium ion in gram-equivalents per cm.sup.2 per second) increases as .delta. decreases. (.delta. is the distance (in cm) from the interface between the CXM and the solution to the plane in the aqueous solution (parallel to the membrane) where the concentration is C). In many respects, .delta. is only an adjustable constant which correlates the data and cannot otherwise be measured. It correlates with a similar ".delta." (but is not the same as) derived from liquid momentum transfer to the membrane (viscosity loss due to friction at the membrane). It also correlates with (but is not the same as) a similar .delta. derived from heat transfer from solution to the membrane. .delta. for diffusion of sodium chloride to a membrane, is about 0.05 cm for non flowing solutions (apparently due to gravitational convection caused by density differences, in turn caused by concentration and temperature differences). If the distance from the CXM through the dilute solution to the AXM is 0.01 cm then, even when the flow of dilute solution is in the streamline (laminar flow) region, .delta. will be 0.005 cm. (Such CXM/AXM separation seems never to have been tried; no doubt there are interesting engineering problems associated with such small separation but there are no fundamental reasons why such is not possible). Values of .delta. of 0.005 cm are achieved in tortuous path spacers in use commercially from 1954. Such spacers have thicknesses of 0.1 cm (the distance from the CXM to the AXM is 0.1 cm) and have rectangular barriers 0.05 cm thick spaced about 1.4 cm from each other. The barriers alternate from the CXM side to the AXM side. Other spacers are in use or have been in use which use no barriers at all or use barriers provided by screens, expanded plastic sheet or perforated and corrugated plastic sheet. Non-woven screens having a close spacing between strands and oriented to make the flow direction change very frequently by 90.degree. angles, easily result in .delta. of about 0.001 cm (and therefore in much increased it/F, other things in equation (2) being equal). Spacers may be rated by the pressure loss per linear cm to achieve a certain .delta.. on such basis the tortuous path spacers, referred to above, are quite inefficient. This is apparently due to the relatively large pressure losses at the trailing edge of the rectangular barriers, the turbulence resulting therefrom being rapidly damped out before the next barrier in the flow path is reached. The non-woven screens referred to above (oriented to cause frequent 90.degree. changes in flow direction) are much more efficient in terms of it/F achieved for a given pressure loss per cm flow path length. Most efficient seem to be spacers without any barriers operating in the turbulent flow regime for which .delta. of 0.0005 cm seems readily achievable. .delta. is apparently insensitive to temperature.
Additional inspection of equation (2) shows that it/F increases as C.sub.m (the concentration at the membrane-solution interface) decreases. C.sub.m can, in principle, never be less than zero. When C.sub.m is so small that it can be neglected in terms of C for practical purposes, then equation (2) may be written ##EQU6## it/FC is then said to have its "limiting value". Equation (3) points out that when C.sub.m may be neglected in terms of C then it/FC is determined only by D (the diffusion coefficient of sodium chloride), t (the transport number of sodium ions in the CXM), t (the transport number of sodium ions in solution) and .delta. (the thickness of the laminar flow layer adjacent to the CXM or half the distance to the AXM, whichever is smaller). When D, t, t and .delta. are constant, i (said in this case to be the "limiting i") is proportional to C (the concentration of sodium chloride at the mid point between the CXM and the AXM in the diluting space). It is apparent experimentally that C.sub.m never actually becomes zero. The concentration gradient across the laminar flow layer adjacent to the CXM is constant, i.e. the concentration of sodium chloride decreases linearly with distance to the CXM through such layer. As a result, when C.sub.m may be neglected compared to C, there is a (non-linear) electrical potential drop of a few tenths of a volt across the laminar flow layer. The on-set of such a potential drop is most easily seen by plotting E/i versus 1/i (where E/i is the apparent resistance of a cell pair (one diluting space, one CXM, one concentrating space and one AXM)). Such a technique was first used by Cowan and Brown. A plot of E/i versus 1/i shown in FIG. 1A.
The i corresponding to the inflection point (1) is generally referred to as the "limiting current density" and may be regarded as the current density at which C.sub.m first becomes negligible compared to C. C.sub.m actually reaches its steady-state value (close to but not at zero) at inflection point (2). FIG. 1A shows that as i increases (1/i decreases), it reaches a "plateau" at point (1) where it is essentially constant while E (and R) increase (E by a few tenths of a volt as mentioned above). As i increases beyond inflection point (2) (1/i decreases below such point) the current continues to increase but at a voltage level higher by a few tenths of a volt. At such latter current, the situation in the laminar flow layer may be regarded as an essentially constant concentration gradient (C.sub.m, the concentration at the interface between the CXM and the diluting solution being close to zero) and therefore resulting in an essentially constant electrical resistance. (The derivative d E/ d i will be essentially constant). The voltage difference between a 1 normal (1 gram equivalent per liter) solution of hydroxide ion and a 1 normal solution of hydrogen ion at room temperature is about 0.8 volts. Therefore as the voltage difference at the CXM-dilute solution interface approaches a few tenths of a volt, hydrogen ions from the dissociation of water will accompany the sodium ions passing from the diluting solution into the concentrating solution, an equal number of hydroxide ions passing from the interface into the diluting solution. The concentrating solution will then become slightly acidic and the diluting solution slightly alkaline. However the rate at which water can dissociate is relatively small compared to the rate at which sodium ions are typically transferred and therefore the changes in acidity and alkalinity respectively are quite small.
The above discussion seems to have covered all that can be learned from equation (2). However i is the current density locally per cm.sup.2 of membrane area. If the membrane is planar and smooth then the local area is that which may be measured with a straight edge. (It is possible that, if a membrane which appears flat and smooth to the "naked eye", were looked at by an electron microscope it would appear rough on a scale of a micrometer or less. However if such roughness is small compared to .delta., then with respect to equation (2) the membrane is still "flat and smooth"). If the membrane has a surface texture the roughness of which is comparable with or larger than .delta., then the area which must be used to calculate i is not the straight edge area but the "actual area" including such roughness. (Such roughness may also contribute to converting pressure loss into decreased .delta.). The "actual area" of a CXM may be increased also by filling the diluting space between the CXM and the AXM with cation exchange beads ("CXB"). The increase in area may be easily calculated from the diameter of such beads. Such filling can increase the limiting value of it/FC by an order of magnitude or more. (The limiting value of it/FC is that value at which for practical purposes, C.sub.m (the concentration at the interface between the CXM (and the CXB)) becomes negligible compared to C).
The above discussion of phenomena taking place at the interface between an ion exchange membrane and a dilute solution was confined to CXM. The phenomena at an AXM are quite similar, with two exceptions. The first exception arises because the transport number of chloride ions in aqueous solution is 0.6 whereas (necessarily) the transport number of sodium ions is 0.4. Using equation (2), ##EQU7## where in this case i t/F is the rate of transfer of chloride ions through an AXM, D (as before) is the diffusion constant of sodium chloride in aqueous solution, t is 0.6, the following table may be constructed:
______________________________________ Relative Relative i Compared to t t/(t - t) it/F i CXM at t = 0.95 ______________________________________ 0.95 2.71 1.00 1.00 1.57 0.85 3.40 1.25 1.40 2.20 0.75 5.00 1.84 2.33 3.67 0.65 13.00 4.79 7.00 11.00 ______________________________________
The last column shows that, comparing an AXM having t=0.95 with a CXM having t=0.95, C, C.sub.m, D and .delta. being the same, the current density at the AXM is 57% higher than in the case of a CXM. This means that the current density at an AXM can, in this case, be 57% higher before C.sub.m becomes negligible for practical purposes compared to C.sub.m. Column 3 (Relative it/F) shows that utilizing an AXM having t of 0.75 increases the relative transport of chloride ions (compared to t=0.95) by a factor of 1.84 (i.e. by 84%) whereas utilizing a CXM having t of 0.75 (compared to a CXM having t=0.95) resulted in an increase of sodium ion transport of only 24%. (Comparing an AXM having t=0.75 with a CXM having t=0.75, the transport of chloride ion compared to sodium ion at the same C, C.sub.m and .delta. is 57% greater).
The second exception of AXM compared to CXM arises as the voltage difference at the AXM-dilute solution interface approaches a few tenths of a volt. In this case hydroxide ions from the dissociation of water accompany the chloride ions passing from the diluting solution into the concentrating solution, an equal number of hydrogen ions passing from the interface into the diluting solution. The concentrate solution becomes alkaline and the dilute solution acidic. (The changes in alkalinity and acidity as measured by pH changes can be masked by the presence of carbon dioxide and/or bicarbonate which are pH change buffers). As the electric current is increased, in this case, the rate at which water dissociates becomes relatively large compared to the rate at which chloride ions are transferred and in fact most of the increase in current is carried by hydroxide ions passing into the concentrate solution. Therefore the changes in alkalinity and acidity can be quite large. The increase in alkalinity in the concentrate stream can result in precipitation of calcium carbonate on the concentrate side of the AXM if (as is frequently the case in "real" aqueous solutions) calcium bicarbonate is present. It is not that somehow the inherent rate of water dissociation has increased at an AXM but rather that AXM contain and/or have absorbed on their surfaces substances which catalyze the dissociation of water at the high voltage drops which exist at the AXM-dilute solution interface.
Examples are: ##STR1## In equations (4) the ##STR2## (benzyl dimethyl amine) groups result from the decomposition off ##STR3## (benzyl trimethyl ammonium) groups in the surface of the AXM. --COO.sup.-- (carboxylate groups) are present, for example, in the tannin like substances (generally called "humic" and "fulvic" acids) found in natural surface waters. Such tannin like substances are negatively charged and are transported (just like other anions) by the electric current to the AXM where they are strongly adsorbed, in part by multiple electrostatic attractions between positively charged groups ##STR4## in the membrane and negatively charged groups in the tannin like substance (--COO--). Colloidal metal oxides and hydroxides (e.g. iron hydroxide) present in water are also negatively charged and behave as weak acids. It is found that AXM, containing no amine groups (other than quaternary ammonium groups) and processing water free from tannin like substances and colloidal metal oxides and hydroxides, dissociate water in essentially the same amounts as CXM. Commercial CXM contain sulfonic acid groups (--SO.sub.2 H) which are strongly dissociated so that reaction (5a) does not take place, Most aqueous solutions do not contain positively charged organic or inorganic colloids so reactions similar to reaction (4) above do not generally occur from absorbed substances. It is possible however to make CXM which do catalyze water dissociation by incorporating in the CXM weakly basic and/or weakly acid groups. Whether in AXM or CXM, the most effective catalytic groups have ionization constants which are equal to the square root of the ionization constant of water (10.sup.-14), that is to 10.sup.-7. This may be seen by noting that 10.sup.-7 makes the rates of reactions (4b) and (4c) equal. It is possible to make AXM which do not have weakly basic (or weakly acid) groups and in which the bound positively charged anion exchange groups do not decompose into weakly basic (or weakly acid) groups. Such membranes, when processing clean water, will dissociate water only to the same extent as commercial sulfonate type CXM. Negatively charged organic and inorganic colloids may be removed by pretreatment of the solution with ultrafiltration or salt regenerated anion exchange with highly porous anion exchange resin granules.
The "actual area" of an AXM may be increased by filling the diluting space between the AXM and the adjacent CXM with anion exchange resin beads ("AXB"). Such filling can increase the limiting value of it/FC by an order of magnitude or more. (The limiting value of it/FC is that value at which for practical purposes C.sub.m, the concentration at the interface between the solution and the AXM (and the AXB), becomes negligible compared to C). The diluting space may be filled with AXB by pumping a dilute slurry of AXB into such diluting space or by filling the space with AXB before assembling the cell pair. (A "cell pair" consists of one AXM, one diluting space, one CXM and one concentrating space). Since water dissociation is most important at AXM (and AXB) there is merit in filling the diluting space solely with AXB. If it is desired to utilize both AXB and CXB granular resins in the diluting space then it is important to have as many AXB paths back to the AXM and CXB paths back to the CXM respectively, as possible. When the diluting space is filled before assembly of the cell pair such maximization of paths may be accomplished by spreading a layer of AXB on the AXM and then a layer of CXB on the AXB (or, of course, CXB on the CXM and AXB on the CXB). When the diluting space is filled by pumping, such maximization of paths may be accomplished by alternating dilute slurries of AXB and CXB, the resulting filled space then consisting of alternating layers of AXB and CXB (in the direction of fluid flow), each layer perhaps only a few beads thick. Alternatively the space between the AXM and CXM in the diluting space may be divided by a highly porous screen, expanded plastic sheet or diaphragm and AXB pumped in on the AXM side and CXB on the CXM side.
Even with such filling of the diluting space with ion exchange resin beads, it is still possible to arrive at current densities at which the concentration of salt at the membrane-dilute solution and bead-dilute solution interfaces approaches zero. If the current density is increased still further water will be dissociated at the solution-AXB and solution-AXM interfaces into hydroxide ions and hydrogen ions as discussed above. The hydrogen ions will enter the CXB and CXM along with other cations. Another, closely related, mechanism for water dissociation also exists which may be visualized by imagining a diluting space of zero thickness, i.e. the distance between the AXM and the CXM is zero. This is equivalent to a diluting space which is essentially instantly deionized and C.sub.m at the AXM-CXM interface approaches zero essentially instantly. When the voltage drop at such interface reaches a few tenths of a volt water will be dissociated at the AXM surface into hydroxide ions and hydrogen ions, the former ions passing through the AXM and the hydrogen ions through the CXM. (Such a zero thickness diluting space is called a "bipolar junction" and the pair of AXM and CXM with zero gap is called a "bipolar" membrane. Commercial bipolar membranes contain at the interface between the AXM and the CXM a thin layer of colloidal metal oxides and/or polymeric organic weak bases and/or weak acids to catalyze water splitting). A similar situation exists whenever there is an interface between AXM or AXB and CXM or CXB in which the AXM or AXB is generally on the anode (positive electrode) side of such interface (junction) and the voltage drop across such interface is several tenths of a volt. (If the AXM or AXB is generally on the cathode (negative electrode) side of such junction, then the junction acts like a zero gap concentrating space and very concentrated salt solution (e.g. 15%) will accumulate at the junction). There seem to have been no experiments to determine which water dissociation mechanism predominates at current densities much above the limiting it/FC, that is, which predominates: water dissociation (a) at AXM and/or AXB-solution interfaces or (b) at AXM and/or AXB junctions with CXM and/or CXB.
In commercial ED apparatus in which the diluting spaces are filled with IX resin beads, such beads seem always to have been a random mixture of equal gram-equivalents of AXB and CXB, that is about 60 parts of AXB to 40 parts CXB, apparently on the impression that such filled diluting spaces are an electrically regenerated mixed bed ion exchange deionizer. It is true that when the current density is far above that corresponding to the limiting it/CF (so that most of the electric current is carried by hydroxide and hydrogen ions) then the AXB and CXB will be largely in the hydroxide and hydrogen ion forms respectively. This may be proved by turning off the electric current whereupon solution passing through the filled diluting space will continue to be deionized (if the solution is dilute, then for some hours). However it is clear that when the dilute space is filled with a random mixture of IXB the objective is to maximize the number of AXB which are connected to the AXM and simultaneously the number of CXB which are connected to the CXM. If the AXB and the CXB have the same size such maxima clearly occurs (in a random mixture) when the volume (or number) ratio is 1:1. (Preferably the conductivities of the AXB and CXB will be the same under actual use conditions. The conductivities depend in known ways on the ionic form of the IXB, the water content and ion exchange capacity. Since the ionic form of the IXB may vary substantially from the entrance of a filled dilute space to the exit of such space, it may be preferred to vary continuously or step-wise the water content and IX capacity of the IXB from the entrance to the exit. It is also advantageous if one or both IXB are short-diffusion-path IXB ("SDP" or shell-and-core IXB), i.e. IXB in which the outer regions contain a normal concentration of groups and the inner regions contain a much lower (including zero) concentration). If the diameter of the beads is the same as the distance between the AXM and the CXM then all the beads are in contact with both membranes. For other ratios of bead diameter to AXM-CXM gap and for given ratios of number of AXB to CXB a computer program can be devised to calculate the number of AXB which are connected (through other AXB) to the AXM, the number of CXB connected to the CXM and the (harmonic) mean length of the AXB and CXB paths. *It may be possible to study such problem experimentally, for example by using a mixture of AXB and inert beads of the same diameter between a single pair of AXM, measuring the electrical resistance as a function of membrane gap and the ratio of the number of beads of each type. (It may also be possible to study the problem by using a mixture of copper beads and insulating glass or ceramic beads between a pair of copper plates).
It is generally accepted that whatever IXB are used, the diameters should all be the same. It is also clear that the surface area of IXB per cm.sup.3 of beads is inversely proportional to the diameter of the beads. The pressure drop per unit flow path length obviously also depends inversely upon bead diameter. IXB used for water softening or chemically regenerated deionization typically have diameters of about 0.05 cm. (Such typical bead size is obviously a compromise among practical pressure loss in an IX bed; duration of exhaustion run; and limiting exchange rate (i.e. avoiding control of such rate by diffusion in the IXB). Filled cell ED clearly involves a different compromise). Although such diameters (0.05 cm) have also been typically used in ED having diluting spaces filled with IXB, it is not clear that such diameters are optimum for ED. Very much smaller diameters are used for chromatographic analysis.
IXB are available in so called "gel" types in which the beads are transparent (but generally colored) and in "macroporous" ("macroreticular") types in which the beads are opaque. The gel types have water and IX groups more or less uniformly distributed throughout the bead. The (tortuous) pores typically have diameters of about 0.002 micrometer, varying however with the water content.
The macroporous types have comparatively large pores (e.g. 0.1 to 1 micrometer), the IX resin with its IX groups forming the walls of such pores. Diffusion in the large pores is very rapid. The water content of the resin of the pore walls is not generally reported though in principle it is measurable. The water content of the gel type IXB is generally varied by varying the amount of crosslinking monomer (for example divinyl benzene) used during suspension polymerization of the beads (for example from a mixture of styrene and divinyl benzene). The polymerized beads are treated with sulfuric acid to introduce sulfonic acid groups thereby producing CXB or with chloromethyl methyl ether and subsequently with a tertiary amine (e.g. trimethyl amine or hydroxyethyl dimethyl amine (also called dimethyl ethanol amine)) to introduce quaternary ammonium groups (e.g. ##STR5## Beads containing such IX groups swell when immersed in water, the loser the amount of crosslinking and the higher the concentration of IX groups the greater the amount of swelling. The most widely used gel type CXB are made from a mixture of styrene and 8% divinyl benzene (100% basis) although such CXB are also available commercially with 1 to 12% or more DVB. It has been shown that only about half the DVB in such beads is actually involved in crosslinking. However during polymerization as described above, the growing polymer chains become heavily entangled with each other, such entanglement also reducing swelling in water. The most widely used gel type AXB are made from a mixture of styrene and 6% divinyl benzene (100% basis) although such AXB are also available commercially with less or with more DVB. The same comments with respect to efficiency of use of DVB and entanglement apply also to AXB. In addition the treatment with chloromethyl methyl ether (chloromethylation) introduces some methylene crosslinks depending upon the treatment conditions e.g. the catalyst used. (It is also possible to introduce sulfone crosslinks in CXB, depending upon the method of sulfonation used). It is also possible to make gel type IXB by diluting the styrene and divinyl benzene with a non-polymerizable solvent such as diethyl benzene and using comparatively larger amounts of DVB. In such case the swelling of the IXB in water is determined by such solvent, the volume of water absorbed being essentially equal to the volume of solvent used. The efficiency of use of DVB is also roughly only 50% but the amount of polymer entanglement is not important.
In dilute solutions IXB generally prefer doubly charged ions (such as Ca.sup.++ and Mg.sup.++ or SO.sub.4.sup.=) to singly charged ions (such as Na.sup.+ respectively Cl.sup.- or NO.sub.3.sup.-) and triply charged ions (such as Sc.sup.+3 (scandium) or Fe(CN).sub.6.sup.-3 (ferricyanide anion)) to doubly charged ions. There is much confusion between "doubly charged" and "divalent" and between "triply charged" and "trivalent". Amphoteric metal hydroxides (that is metal hydroxides which can behave either as weak acids or weak bases such as cupric hydroxide, nickelous hydroxide, ferrous hydroxide, nickelic hydroxide, ferric hydroxide, aluminum hydroxide) have the same charge as their valence only in acid solutions (e.g. +2 for cupric, nickelous, ferrous, +3 for nickelic, ferric and aluminum). The alkaline earth cations (Mg.sup.+2, Ca.sup.+2, Sr.sup.+2, Ba.sup.+2) are divalent and doubly charged in essentially neutral solutions and the rare earth cations (including Sc.sup.+3 (scandium cation) and La.sup.+3 (lanthanum cation) are trivalent and triply charged in essentially neutral solution. The preference for multiply charged ions compared to singly charged ions may be illustrated by the following reaction:
(6) Ca.sub.s.sup.++ +2Na.sub.r.sup.+ .fwdarw.Ca.sup.++.sub.r +2Na.sub.s +where the subscript "s" refers to solution and the subscript "r" refers to the CXB resin phase. One can write an equilibrium constant:
(7) ##EQU8## where the quantities in parentheses are expressed in gram-moles per kilogram of water (or, what is the same, milligram-moles per gram of water). The equation may be rearranged to: ##EQU9## where K ##EQU10## is defined as "Y" (not a constant) for ease in manipulation. The ion exchange capacity of the CXB in gram-equivalents per kilogram water (i.e. the molality) is given by: EQU Q=2(Ca.sub.r.sup.++)+(Na.sub.r.sup.+). (9)
Then ##EQU11## This is a quadratic equation which has the solution: ##EQU12## For example if Y is 250 (liters/mole), corresponding for example to K=1, Ca.sub.s.sup.++ =40 ppm and Na.sub.s.sup.+ =46 ppm, then the following table may be constructed:
______________________________________ Q 2 Ca.sub.r.sup.++ /Q % H.sub.2 O ______________________________________ 0.1 0.87 97 1.0 0.96 78 10 0.99 26 ______________________________________
The second column (2Ca.sub.r.sup.++ /Q) is the fraction of the CXB which is in the Ca.sup.++ form, the remainder being in the Na.sup.+ form. The third column (%H.sub.2 O) is the percent by weight of water in a CXB having a dry weight capacity of 3.5 milligram equivalents per gram of dry CXB, a typical value. The effect of Y (defined as K ##EQU13## may be seen by setting Y=25 l/mol (consistent with K=1, Ca.sub.s.sup.++ =400 ppm, (Na.sup.+).sub.s =460 ppm) from which the following table may be constructed:
______________________________________ Q 2 Ca.sub.r .sup.++ /Q % H.sub.2 O ______________________________________ 0.1 0.64 97 1.0 0.87 78 10 0.96 26 ______________________________________
Although the ratio of Ca.sup.++ to Na.sup.+ in solution in the latter table is the same as in the former table, this total concentration in solution is 10 times greater in the latter table resulting in loss of preference for Ca.sup.++ compared to Na.sup.+ in the CXB. K for Ca.sup.++ and Na.sup.+ is not exactly 1 and in addition K is not exactly constant. Nevertheless the above simple calculation illustrates the principles involved. The conductivity per ion (equivalent conductivity) in the case of the CXB having only 26% water is very much less than that having 97% water (the latter having an ion conductivity essentially the same as that of water) because of friction between the ions and the polymer of the CXB in the former case (low water content) and the necessity of ions to follow a tortuous path through such resin. The ratio of the conductivity of Ca.sup.++ ion to Na.sup.+ ion is less in the CXB having 26% water than in that having 97% water, in part because of the electrostatic attraction of the doubly charged ion for the fixed sulfonic acid groups. Nevertheless, in ED without filling in the diluting spaces or with filling in which the CXB portion is prepared from styrene-divinyl-benzene mixtures having 8% DVB, Ca.sup.++ is generally preferentially removed compared to Na.sup.+, at least at current densities such that C.sub.m (the total concentration at the CXM and/or CXB solution interface) is not far removed from C (the concentration outside the laminar flow layer adjacent to the CXM or CXB).
Similar considerations apply to the comparative absorption and conductivity of doubly charged sulfate anions compared to singly charged chloride anions or nitrate anions in AXM or AXB. (K for nitrate ions compared to chloride ions is about 2 for most AXM or AXB). However it appears that bulky quaternary ammonium groups such as ##STR6## (benzyl tributyl ammonium) exclude sulfate compared to chloride (or nitrate) as compared with the common commercial quaternary group ##STR7## (benzyl trimethyl ammonium). Such exclusion appears to be due in part to the lack of ability of the doubly charged sulfate ion to approach closely the positively charged nitrogen atom.
The electrodialytic performance of IXM and IXB is however not determined solely by the equilibrium absorption of ions by the IXM or IXB or by the relative conductivities of the ions in the membranes or beads. It is possible to make thin skins on the surfaces of IXM and IXB which skins retard the passage of doubly and triply charged ions. (The skins have low ion exchange capacities, low water contents and low dielectric constants). Such membranes are called "univalent ion selective membranes" and are typically used to prepare 18 to 20% sodium chloride brine by ED from sea water, permitting the passage of sodium and chloride ions and inhibiting the passage of magnesium, calcium and sulfate ions. (The use of the term "univalent ion selective" is not accurate; it would be better to say "selective for singly charged ions" but since the membranes are almost always used to separate ions which have the same charge as their valency (but what is the "valency" of sulfate?) there is no practical harm in the former term). In the above concentration of seawater by ED using such skinned membranes, the current density used is far less (e.g. 50% or less) than that corresponding to the "i" in the limiting value of it/FC (that is to the "i" at which C.sub.m is negligible compared to C, the bulk concentration in the diluting space). At or above the limiting it/FC what goes through a membrane is essentially what is presented to the membrane by diffusion and conduction in the laminar flow layer adjacent to the membrane. The ratio of the ions arriving at the membrane is the ratio of the limiting it/FC that is the ratio ##EQU14## Univalent anion selective membranes have been used selectively to remove nitrate from water containing also sulfate and/or bicarbonate or (with CXM which are not univalent ion selective) selectively to remove calcium chloride from water containing sodium, calcium, chloride, sulfate and bicarbonate ions. In each case the it/FC actually used is 50% or less than the limiting it/FC.
It was noted above that the ratio of the conductivity of doubly charged ions compared to singly charged ions is less in IXB having low water contents than in IXB having high water contents, in part because of the electrostatic attraction of the doubly charged ions for the fixed (singly charged) ion exchange groups. It was also pointed out that bulky, quaternary ammonium anion exchange groups tend to exclude doubly charged sulfate ions in part due to the inability of the doubly charged ions to approach closely the positively charged nitrogen atom in the quaternary ammonium exchange group. One might therefore expect that such diminished electrostatic attraction would lead to greater conductance per sulfate ion at the same water content and same AXB molality (gram-equivalents of fixed, anion exchange groups per kilogram of water in the AXB). A recent report seems to confirm that sulfate is more mobile in an AXB having ##STR8## AX groups than in an AXB having ##STR9## groups.
Sulfate mobility may be even higher in AXB having ##STR10## (benzyl tributyl ammonium) groups. However, as noted above, the latter groups highly exclude sulfate and therefore the relative transport of sulfate versus chloride from solutions containing both ions (at it/FC substantially less than the limiting it/FC) may be poor even though the sulfate ion mobility is comparatively high. It would appear that "pleasingly plump" (rather than "bulky") groups are indicated. In addition to (CH.sub.3).sub.2 N.sup.+ CH.sub.2 CH.sub.2 OH groups, these may include: ##STR11## Commercial AXB are available having N.sup.+ CH.sub.2 CH.sub.3).sub.3 groups. Such AXB appear to be macroporous and it is not known whether sulfate mobility will be the same in a macroporous AXB having such groups as compared to a gel type AXB with such groups.
All commercial ED apparatus having IXB in the diluting spaces use a mixture of AXB and CXB. All such apparatus use as CXB gel type beads having ##STR12## as the exchange groups, known for example as Dowex 50 (Dow Chemical Co.) or Amberlite IR120 (Rohm and Haas Co.). Most such apparatus use as AXB gel type beads having ##STR13## exchange groups (known as Type I groups) for example Dowex 1 or Amberlite IRA 400. The remaining commercial apparatus used (at least originally) AXB gel type beads having ##STR14## exchange groups (known as Type II groups) for example Dowex 2 or Amberlite IRA 410. In the 1960's, an in-house apparatus used a macroporous (macroreticular) AXB having Type I AX groups (Dowex 21K was actually used; similar AXB are available from other manufacturers) to supply deionized water for laboratory use.
(Macroporous (macroreticular) IXB are made, for example, from a mixture of styrene and divinyl benzene with a diluent which is a solvent for the styrene and DVB and a poor solvent for the polymer of styrene and DVB. As a result, as polymerization proceeds the polymer precipitates from solution leaving macropores. The size of the macropores depends upon the quantity of the diluent and its solubility for the polymer. A diluent may be used consisting of a mixture of a good solvent for the polymer and a poor solvent. The amount of DVB used may be the same as used in gel type IXB or less because the polymer in macroporous IXB tends to be highly entangled, the extent depending on the diluent used. With some polymeric diluents it is possible to use no DVB).
Almost all of the above discussion has pertained to the diluting space in an ED apparatus. The design of the concentrating space cannot, however, be neglected. The concentrating space should contain structure to keep the adjacent IXM flat and against whatever structure (turbulence promoting spacer or IXB) may be present in the adjacent diluting spaces. The structure in the concentrating space should also assist the adjacent IXM to resist whatever hydraulic pressure difference there may be from the diluting side of the membranes to the concentrating side. (It is common to operate the diluting space at a higher pressure than the concentrating space in order to avoid possible leaks of concentrate solution into the dilute solution). The concentrating space may be identical in structure to the diluting space e.g. have the same thickness, the same turbulence promoting structure or the same IXB. In such case the choice of which electrode of the pair (discussed above) is positive and which is negative is arbitrary. If the solution processed in the diluting space contains organic or inorganic colloidal matter and/or poorly soluble salts, then the colloidal matter can accumulate at one or the other of the diluting surfaces of the IXM and/or IXB and the poorly soluble salts at one or the other of the concentrating surfaces of the IXM and/or IXB. Regular, periodic reversal of the polarity of the electrodes will then convert a diluting space into a concentrating space and a concentrating space into a diluting space, generally effectively removing accumulated colloids and poorly soluble salts. Cycle times of 30 minutes to 2 weeks are used commercially depending upon the severity of accumulation of colloids and poorly soluble salts (that is reversing polarity every 15 minutes to one week). It is not necessary that such reversal be symmetric (that is, that each space spend equal time as a diluting space and a concentrating space). It is equally possible to operate very asymmetrically say 15 minutes in one direction and 15 seconds in the other. In the case of substantially symmetric reversal whatever structure is optimal for diluting and concentrating spaces in one direction is obviously also optimal in the opposite direction and therefore the structure (e.g. non-woven screen or IXB) should be the same in both spaces. In the case of asymmetric or no reversal the structure in the two types of spaces need not be the same. For example the distance between the AXM and the CXM in the concentrating space can be very much less than such distance in the diluting space and such thin concentrating space can have structure enabling a single pass of concentrate solution through the concentrating space without recycle (nevertheless at a pressure loss which is only slightly less than that in the diluting space) thereby avoiding the investment and operating cost of concentrate solution recycle. A single pump can be used to feed both concentrating and diluting spaces while still maintaining the desired ratio of effluent flows (i.e. percent of feed which is recovered as deionized product). Instead of (or in addition to) using concentrating spaces which are thinner than the diluting spaces (to eliminate the need for recycle of concentrate) it is possible to fill the concentrate space with IXB having a smaller mesh size (smaller diameter) than the IXB used in the diluting spaces, the smaller diameter resulting in greater hydraulic resistance. Of course attention must be paid to achieving the necessary .delta. in the concentrating space to assure adequate mass transfer of poorly soluble electrolytes (e.g. silicic acid (silica), calcium bicarbonate and calcium sulfate) from the interfaces between the IXM (and IXB, if such are used in the concentrating space) and the concentrating solution into the bulk of such solution.
If the diluting solution being deionized is already very dilute (e.g. 6 ppm as sodium chloride) then, even at 90% recovery of deionized dilute solution the conductivity of the concentrating solution effluent will be only about 100 micro Siemens/cm. If in such case IXB filling is used in the diluting space (which will be highly desirable to increase the effective current density in the diluting space and to decrease the electrical resistance of such space), then the principal electrical resistance of the cell pair will be in the concentrating space and it will be desirable to use IXB filling also in the latter space. Such IXB filling need not be the same as the filling in the diluting space. For example in the above mentioned filled cell ED apparatus used in-house in the 1960's, it was found advantageous to fill the concentrating spaces solely with weak base AXB.
The above discussion has concentrated on the use of IXB as filling in the diluting and/or concentrating spaces. The literature also reports apparatus in which the surface of AXM was corrugated at an angle of 45.degree. to the direction of flow, the CXM corrugated at -45.degree. and the corrugations of the AXM were in contact with those of the CXM. The flow was thereby forced to make frequent 90.degree. changes in direction. Apparatus is also reported in which AX fabric was placed against the AXM in the diluting space and CX fabric against the CXM in the same space. The fabrics were knit from IX fibers. CX fibers are most easily made from polyethylene mono- or multi-filaments by soaking the latter in a mixture of styrene, divinyl benzene and free radical catalyst, polymerizing the monomers and subsequently sulfonating. AX fibers may be made by substituting vinyl benzyl chloride for the styrene and finally treating the filaments with an appropriate tertiary amine as discussed above. (IX fibers and filaments may also be made by sulfo-chlorinating polyethylene fibers and filaments, subsequently hydrolyzing or aminating and quaternizing). Such IX monofilaments may be easily bonded together by moderate heat and pressure to give non-woven screens. The latter can obviously be made on automatic machinery. The literature reports that the highest values of limiting it/FC were obtained when there was some interpenetration of the AX knitted fabric with the CX knitted fabric. IX monofilaments or multifilaments having a diameter equal to the spacing between the AXM and the CXM may also be arranged in alternation parallel to the direction of flow.
In the above discussion limiting values of it/FC were used as the basis of discussion since such ratio reflects the actual transfer of ions ##EQU15## In engineering practice it is common to use the ratio ##EQU16## because it relates the easily measurable i and C. It does not however relate to the performance of the ED apparatus.

Membrane-frame for processes including electrodialysis


An agricultural vehicle is described having a chassis and a cab mounted on the chassis. A suspension system for reducing the accelerations transmitted from the vehicles tires or tracks through the frame, into the cab, and ultimately through to the operator is provided. By reducing the accelerations, the ride quality is greatly improved, allowing operators to operate a vehicle for longer periods of time without excessive fatigue.

1. Field of the Invention
Various aspects of the present invention relate to a suspension system linkage arrangement for an agricultural vehicle having a cab resiliently supported on the chassis of the vehicle.
2. Description of Related Art
The ride quality and operator comfort of a work vehicle is adversely affected by vibrations or movement transmitted from the frame or chassis of the vehicle to the operator's cab. As the cab typically is built separately from, and later mounted on, the frame, and because the cab is separate from the frame, movement of the frame may be transmitted through and amplified by the connections between the cab and the frame.
As the work vehicle travels across a surface, movement of the frame/chassis induces the operator's cab to pitch, roll and bounce. Movement of the cab can be particularly severe in agricultural and construction equipment vehicles (e.g., tractors, combines, backhoes, cranes, dozers, trenchers, skid-steer loaders, etc.), because such vehicles typically operate on off-road surfaces or fields having a high level of bumpiness.
Operator comfort may also be adversely affected by the operation of various systems on a work vehicle. In particular, operation of various work vehicle systems can cause forces to be applied to the chassis of the vehicle which, in turn, are transmitted to the cab. Examples of these forces include: draft forces exerted on the hitch of an agricultural tractor by an implement (e.g., a plow), which can cause the cab to pitch; normal forces applied to a work vehicle as the vehicle turns in response to a steering device, which can cause the cab to roll; clutch forces generated when a work vehicle clutch (e.g., a main drive clutch; four-wheel drive clutch) is engaged or disengaged, which can cause the cab to pitch; gear shift forces generated when a transmission of a work vehicle is shifted, which can cause the cab to pitch; braking forces generated as brakes of a work vehicle are operated, which can cause the cab to pitch; and acceleration forces generated when a speed actuator changes the speed of a work vehicle which can cause the cab to pitch.
The movement of the cab caused by surface bumps and the operation of vehicle systems cause both qualitative and quantitative problems. An operator of such a vehicle experiences increased levels of discomfort and fatigue caused by the vibrations. Productivity is decreased when an operator is forced to rest or shorten the work day, or is unable to efficiently control the work vehicle. The operator is also less likely to be satisfied with a work vehicle that provides poor ride quality. Under certain conditions, the frequency and magnitude of cab movement may force the operator to decrease driving speed, further decreasing productivity.
It is common for the cab, or operator station, to be mounted directly on the chassis and to rely only on springing in the operator's seat to improve operator comfort. This, however, is not entirely satisfactory, and therefore the cab can be supported on rubber mounts that provide an improved degree of cushioning.
Another known suspension system enables the cab to be resiliently mounted on the vehicle chassis. Stabilizer linkages are provided on the tractor fore and aft of the cab to limit the movement of the pivotal connection of the stabilizer linkages to the cab to essentially a vertical movement that lies in a vertical plane including the longitudinal centers of the vehicle chassis and the cab. A sway or yaw limiting mechanism as well as a pitch limiting mechanism are provided to limit the pitch and roll of the cab as it moves through the vertical plane relative to the vehicle chassis.
The present invention improves upon the known cab suspension systems, and thus it is to such a system that the present invention is primarily directed.


A fuel cell system, which may include a fuel processing subsystem for converting hydrocarbons into a hydrogen-rich gas, is designed so that at least some of the components of the fuel cell system are contained inside at least one housing. The housing contains a recombiner to convert hydrogen and oxygen into water. The housing may also contain a temperature sensor in the vicinity of the recombiner.

1. Field of Invention
The invention relates to a fuel cell system, which may further include a fuel processing subsystem for converting hydrocarbons into a hydrogen-rich gas, whereby components of the fuel cell system are arranged in at least one housing.
2. Description of the Related Art
A fuel cell system, in particular one that is equipped with a fuel processing subsystem for converting hydrocarbons into a hydrogen-rich gas, is often enclosed in a housing which is suitable for isolating it from the surrounding environment. As a result, in the event of a leak originating from the fuel processing subsystem, the fuel cell or any of the conduits, the leaked fluid (e.g., the hydrogen-rich gas) will accumulate within the volume of the housing. Typically, there are small accumulations of hydrogen in the housing, as hydrogen leaks cannot in most cases be entirely prevented, hydrogen being a permeating gas.
German Patent Application DE 100 31 238 discloses a fuel cell system and a method for operating the fuel cell system. The fuel cell system is equipped with a ventilated housing, whereby fans, designed so as not to constitute an ignition source, are used as ventilating means. The ventilated housing addresses the potential safety hazard, which can be posed by the accumulation of explosive mixtures, such as hydrogen and oxygen, within the fuel cell system environment. German Patent DE 100 01 717 further discloses a fuel cell system where flow amplifiers are used in various locations of the fuel cell system to address the safety hazard posed by hydrogen accumulation.
The article entitled "Self-limiting Catalytic Hydrogen/Oxygen Recombiner" (Journal of Power Sources, Vol. 8, pages 211-227, 1982) discloses the use of recombiners in lead storage battery applications. The recombiners are used to convert the gases produced by the chemical reaction within the battery—typically hydrogen and oxygen—into water. As a result, the water-refill requirement for lead storage batteries equipped with such recombiners is considerably reduced. Recombiners typically comprise the following components: acid separator, carbon filter, catalyst, condenser, gas storage, and valves. German Patent Application DE 198 52 951 A1 similarly discloses use of recombiners to catalytically convert hydrogen and oxygen into water, but in the context of nuclear power plant technology, where recombiners are used in the processing of escaped gases resulting from accidents in boiling water reactors and pressurized water reactors.
Accordingly, there while advances have been made in this field, there remains a need for systems to address potential accumulation of reactive mixtures, such as hydrogen and oxygen mixtures, within the fuel cell system environment, particularly within the housing that encloses such system. The present invention fulfills this need and provides further related advantages.


The high-frequency module of the present invention is formed of two sections: first high-frequency circuit 5 having a first filter circuit; and second high-frequency circuit 6 having a second filter circuit. At least any one of the two high-frequency circuits has a conductive case. The structure is highly effective in attenuating a spurious signal, thereby solving the problem that the output level of the spurious signal fed from the high-frequency module is undesirably increased.

In a high-frequency circuit, a spurious signal generated in a mixing circuit and a matching circuit is removed by a filter circuit. Such a high-frequency circuit has conventionally been configured as a single module. FIG. 6 shows a conventional high-frequency module. In the conventional high-frequency circuit block, mixing circuit 12 mixes a baseband signal fed from baseband section 31 with a local signal fed from oscillator 41. A spurious signal produced by mixing circuit 12 is attenuated by first filter 13 and second filter 22 of filter circuit 18. A desired high-frequency signal has thus been obtained.
In the prior-art high-frequency module, however, due to the structure configured in one module, a spurious signal produced by matching device 14 connected to the input side of first filter 13 directly goes, without passing through first filter 13, matching device 17, and second filter 22, into matching device 24. In the module, matching device 17 is connected to the output side of first filter 13 and the input side of second filter 22, and matching device 24 is located to the output side of second filter 22.
Therefore, in matching device 24, the spurious signal directly come from matching device 14 has an output level greater than that of the spurious signal given attenuation by first filter 13 and second filter 22, accordingly, the resultant spurious signal cannot maintain a desirable attenuation level. As a result, the output level of the spurious signal fed from the high-frequency module has undesirably increased.

High frequency module and radio device using the same

Matsushita Electric Industrial Co., Ltd.


A method of playing a golf-type game at the facility comprises placing a ball at one of the starting points, hitting the ball toward the appropriate target, and determining the surface type on which further play continues or determining the score based upon where the ball lands relative to scoring zones. A facility for playing a golf-type game includes a plurality of short-shot holes, each short-shot hole comprising a starting box on which a ball can be placed, and a target comprising a cup for receiving a ball hit from the starting box, and a plurality of scoring zones surrounding the cup; the target zones having indicia for scoring.

There is a year round demand for golf course play and practice facilities, particularly in colder climates where weather conditions prevent year round play. However, it would be difficult and expensive to provide an indoor golf course driving range. Amateur golfers primarily practice at outdoor driving ranges, which allow practice of golf's long game, but do not provide practice of golf's short game which comprises as much as two-thirds of the shots in a typical round of golf. Furthermore, there is no practice facility that allows golfers to practice their short game skills, such as pitches, chips and sand trap shots, and actually "hole out".

Compact golf facility and a method of playing a golf game


In accordance with this invention, an RPE cell membrane associated protein which has a molecular weight of about 32 kd, as determined by SDS-PAGE, has been discovered. This protein, referred to an "p32," forms an oligomeric protein complex with the previously characterized p63 protein, a component of the membrane receptor for RBP. A nucleic acid molecule which codes for the p32 protein has also been isolated and sequence analysis shows that the p32 protein belongs to the family of short chain alcohol dehydrogenases, and exhibits 11-cis retinol dehydrogenase activity, the enzyme which catalyzes conversion of 11-cis-retinol into 11-cis retinaldehyde.

Retinoids (vitamin A-derivatives) have important physiological functions in a variety of biological processes. During embryonic growth and development, as well as during growth and differentiation of adult organisms, retinoids act as hormones and participate in the regulation of gene expression in a number of cell types. See Lied et al. Trends Genet., 17:427-433 (1992). It is believed that the effects of these molecules are mediated through two classes of nuclear ligand-controlled transcription factors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs), Benbrook et al., Nature, 333:669-672 (1988); Brand et al., Nature, 332:850-853 (1988); Giguere et al., Nature, 330:624-629 (1987); Mangelsdorf et al., Nature, 345:224-229 (1990); Mangelsdorf, et al. Genes Dev. 6:329-344 (1992); Petkovich et al. Nature 330:440-450 (1987); and Zelent et al., Nature 339:714-717 (1989).
Apart from their role as hormones in cellular growth and differentiation, retinoids are also involved in the visual process as the stereo isomer 11-cis retinaldehyde of retinaldehyde is the chromophore of the visual pigments. See, e.g. Bridges, The Retinoids, Vol. 2, pp 125-176, Academic Press, Orlando, Fla., (1984).
Under normal physiological conditions most cells, both ocular and non-ocular, obtain all-trans retinol as their major source of retinoids. Despite the many different metabolic events taking place in different tissues, it is known that a common extracellular transport machinery for retinol has evolved. Specifically, in plasma, retinol is transported by plasma retinol binding protein (RBP). See Goodman et al., The Retinoids, Academic Press, Orlando Fla., Volume 2, pp. 41-88 (1984). The active derivatives of retinol, i.e., retinoic acid in non-ocular tissues and mostly 11-cis retinaldehyde for ocular tissues, are generated by cellular conversion of trans-retinol, using specific mechanisms. To date, none of these mechanisms have been fully defined at the molecular level and several of the enzymes involved have only been identified by enzymatic activities. See Lion et al., Biochem. Biophys. Acta. 384:283-292 (1975); Zimmermann et al., Exp. Eye Res. 21:325-332 (1975); Zimmermann, Exp. Eye Res. 23:159-164 (1976) and Posch et al., Biochemistry 30:6224-6230 (1991).
Polarized retinal pigment epithelial cells (polarized RPE) are unique with regard to retinoid uptake since all-trans retinol enters these cells via two different mechanisms. Retinol accumulated from RBP is taken up through the basolateral plasma membrane, while all-trans retinol, presumably taken up from the interstitial retinol-binding protein (IRBP) following bleaching of the visual pigments, may enter through the apical plasma membrane. See Bok et al., Exp. Eye Res. 22:395-402 (1976); Alder et al., Biochem. Biophys. Res. Commun. 108:1601-1608 (1982); Lai et al., Nature 298:848-849 (1982); and Inu et al., Vision Res. 22:1457-1468 (1982).
The transfer of retinol from REP to cells is not fully understood. In a number of cell types, including RPE, specific membrane receptors for RBP have been identified. This is consistent with a receptor-mediated uptake mechanism for retinol. For example isolated retinal binding protein receptors, nucleic acid molecules coding for these receptors and antibodies binding to the receptor have been taught, in references relating to the first of the two mechanisms. See Bavik et al., J. Biol. Chem. 266:14978-14985 (1991); Bavik, et al. J. Biol. Chem. 267:23035-23042 1992; Bavik et al., J. Biol. Chem. 267:20540-20546 (1993); and copending U.S. application Ser. No. 083,539 and International Publication WO 93/23538, all of which are incorporated by reference herein. See also Heller, J. Biol. Chem. 250:3613-3619 (1975); and Bok et al., Exp. Eye Res. 22:395-402 (1976).
Retinol uptake on the apical side of the RPE for the regeneration of 11-cis retinaldehyde, is less well characterized. Regardless of the origin of all-trans retinal, however, the synthesis and apical secretion of 11-cis retinaldehyde seems to be the major pathway for accumulated retinal in the RPE. At present, it is not known whether similar mechanisms are used with regard to cellular retinal uptake through the basolateral and the apical plasma membranes. Available data do show that functional receptors for RBP are exclusively expressed on the basolateral plasma membrane of RPE-cells. Bok et al., Exp. Eye Res. 22:395-402 (1976).
It is also known that RPEs express a 63 kDa protein (p63). This molecular weight, and all others, is by reference to SDS-PAGE, unless stated otherwise. It has also been shown by chemical cross-linking that this protein may be part of an oligomeric protein complex which functions as a membrane receptor for plasma retinol-binding protein (RBP) in RPEs, or a component of the retinoid uptake machinery in RPE cells. See Bavik et al, J. Biol. Chem. 266:14978-14875 (1991); Bavik et al., J. Biol, Chem. 267:23035-23042 (1992), U.S. patent application Ser. No. 083,539 and PCT application WO93/23538. The p63 protein has been isolated and the corresponding cDNA cloned. See Bavik et al., J. Biol. Chem. 267:20540-20546 (1993). Nothing in these references suggests the existence of the protein which is a feature of this invention.

Isolated nucleic acid molecule which codes for a 32 kDa protein having 11-cis retinol dehydrogenase activity, and which associates with P63, a portion of a retinol binding protein receptor


A fluorinated ether compound which has a poly(oxyperfluoroalkylene) chain (αβ) having a structure of block (α)-block (β) or a structure of block (β)-block (α)-block (β), formed by linking a block (α) comprising at least three C1-3 oxyperfluoroalkylene units of at least one type and a block (β) having C4-15 oxyperfluoroalkylene units of at least one type, wherein the proportion of the C4-15 oxyperfluoroalkylene units is at least 30 mol % among all oxyperfluoroalkylene units constituting the block (β), and which has a hydrolysable silyl group on at least one terminal of the poly(oxyperfluoroalkylene) chain (αβ) via a linking group. Also, a fluorinated ether composition and a coating liquid, whereby it is possible to form a surface-treated layer which has high initial water/oil repellency and which is excellent in abrasion resistance and finger print stain removability, and a substrate having a surface-treated layer and a method for its production.

A fluorinated compound is useful as a surface treating agent since it has high lubricity, water/oil repellency, etc. By imparting water/oil repellency to a substrate surface by such a surface treating agent, stains on the substrate surface will easily be wiped off, and stain removability will be improved. Among such fluorinated compounds, a fluorinated ether compound having a poly(oxyperfluoroalkylene) chain in which an ether bond (—O—) is present in the middle of a perfluoroalkyl chain is particularly excellent in the fat and oil stain removability.
A surface treating agent containing such a fluorinated ether compound is useful in applications wherein it is desired to maintain a performance (abrasion resistance) whereby the water/oil repellency is less likely to be reduced even if repeatedly rubbed by fingers, and a performance (fingerprint stain removability) whereby fingerprints deposited on a surface can easily be removed by wiping, for a long period of time, e.g. as a surface treating agent for a member constituting a surface to be touched by a finger, of a touch panel.
As such fluorinated ether compounds, specifically, fluorinated ether compounds of the following (1) to (4) are known.
(1) A fluorinated ether compound having a structure wherein (CF2O) units and (CF2CF2O) units are randomly linked, and having a hydrolysable silyl group at a terminal (Patent Document 1)
(2) A fluorinated ether compound having a structure wherein at least two types of units selected from the group consisting of (CF2O) units, (CF2CF2O) units, (CF2CF2CF2O) units and (CF(CF3)CF2O) units are randomly linked, and having a hydrolysable silyl group at a terminal (Patent Documents 2 to 5)
(3) A fluorinated ether compound having a structure wherein only (CF2CF2CF2O) units or (CF(CF3)CF2O) units are linked, and having a hydrolysable silyl group at a terminal (Patent Documents 6 and 7)
(4) A fluorinated ether compound having a structure wherein only (CF2CF2CF2CF2O) units are linked, and having a hydrolysable silyl group at a terminal (Patent Document 8)

Fluorinated ether compound, fluorinated ether composition and coating liquid, and substrate having surface-treated layer and method for its production