A method for determining which way of an N-way set associative cache should be filled with replacement data upon generation of a cache miss when all of the ways contain valid data. A first choice for way selection and at least one additional choice for way selection are generated. If the status of the way corresponding to the first choice differs from a bias status, a way corresponding to one of the additional choices is designated as the way to be filled with replacement data. Otherwise, the way corresponding to the first choice is designated as the way to be filled with replacement data. Status information for a given way may include any data which is maintained on a cache line by cache line basis, but is preferably data which is maintained for purposes other than way selection. For example, status information might include indications as to whether a cache line is shared or private, clean or dirty. The algorithm for generating the first choice for way selection is preferably a random or round robin approach, but may be any other algorithm. Any algorithm may also be used for generating the additional choices for way selection. However, the additional choices are preferably generated as functions of the first (e.g., the first choice plus different constants). The bias status which is used to select between the first and at least one additional choices can be programmed to yield different results in different systems.

The invention pertains to methods and apparatus for improving computer system performance by improving cache utilization.
Most computer systems include a processing unit and a memory. The speed at which the processing unit can execute instructions and consume data depends upon the rate at which the instructions and data can be transferred from memory to the processing unit. In an attempt to reduce the time required for the processing unit to obtain instructions and data from main memory, many computer systems include a cache memory which is physically and logically located between the processing unit and main memory.
A cache memory is a small, high-speed buffer memory which is used to temporarily hold those portions of the contents of main memory which it is believed will be used in the near future by the processing unit. The main purpose of a cache is to shorten the time necessary to perform memory accesses, either for data or instruction fetch. Cache memory typically has access times which are several times faster than those of a system""s main memory. The use of cache memory can significantly improve system performance by reducing data access time, therefore enabling a processing unit to spend far less time waiting for instructions and data to be fetched and/or stored.
A cache memory comprises many lines of data which have been copied from a system""s main memory. Associated with each cache line is a cache tag. A line""s tag provides information for mapping the cache line""s data to its main memory address. Each time a processing unit requests an instruction or data from memory, an address tag comparison is made to see if a copy of the requested data resides in the cache. If the desired data is not in the cache, the requested data is retrieved from the main memory, stored in the cache, and supplied to the processing unit. Commonly used mapping functions for cache data storage include direct mapping and associative mapping techniques.
In an N-way set associative cache, a single index is used to simultaneously access a plurality of data arrays. A data array may be implemented by one or more random access memory integrated circuits. A set is a collection of all cache lines addressed by a single cache index. The number of data arrays addressed by a single cache index indicates the xe2x80x9cwayxe2x80x9d number of a cache. For example, if in a cache a single cache index is used to access data from two data arrays, the cache is a 2-way set associative cache. Similarly, if in a cache a single cache index is used to access data from four data arrays, the cache is a 4-way set associative cache.
When a multi-way cache access is made, a tag comparison is made for each data array or way. If a tag comparison indicates that the desired line of data resides in a particular data array, the line of data is output from the cache for subsequent use by the processing unit which requested the data.
Since there are a finite number of lines in a cache, it is frequently necessary to replace the information stored in a cache as new information is needed. However, each time a new line of data is retrieved from main memory, a determination must be made as to which line of data in the cache will be replaced. For an N-way set associative cache, this determination involves selecting the way in which the new line of data will be stored. If one or more ways hold invalid data, then it usually makes sense to fill an invalid way with valid data. However, if all of the ways hold valid data, a line of data must be bumped from the cache. In an ideal cache, it would be desirable to 1) retain valid lines of data which are most likely to be used again by a processing unit, 2) retain valid lines which are expensive to move around, and 3) replace valid lines which are inexpensive to move around. Since replacement of cache data is a relatively slow process in comparison to cache data retrieval, it is desirable to make as meaningful of a way selection as is possible given one""s speed, space and budget constraints.
There are many algorithms for improving cache utilization via better way selection for replacement data. However, one of three general approaches is commonly used. The first approach is a xe2x80x9crandomxe2x80x9d approach, in which new information is written into a randomly or pseudo-randomly selected way. Another approach is a xe2x80x9cround robinxe2x80x9d approach, in which the way to be filled with replacement data is simply the previously replaced way plus some constant. A third approach is to replace the xe2x80x9cleast recently usedxe2x80x9d way with replacement data. The first two methods yield acceptable results with a minimal performance penalty, little hardware, and little cost. The least recently used method achieves better performance, but with significant and costly hardware.
What is needed is a new method for determining which way of an N-way set associative cache should be filled with replacement data upon generation of a cache miss when all of the ways contain valid data. The new method needs to provide better cache utilization than a simple random or round robin approach, but needs to be less costly to implement than a least recently used approach.
In achievement of the foregoing need, the inventor has devised new methods and apparatus for determining which way of an N-way set associative cache should be filled with replacement data upon generation of a cache miss when all of the ways contain valid data. As previously stated, when some way contains invalid data, that way is the preferred target for replacement.
The methods and apparatus generate a first choice for way selection and at least one additional choice for way selection, and then use status information associated with the cache line corresponding to the first choice to determine whether the first choice or one of the at least one additional choices should be used to designate the way which will be filled with replacement data. Status information may comprise any data which is maintained on a cache line by cache line basis, but is preferably data which is maintained for purposes other than way selection. For example, status information might comprise indications as to whether a cache line is shared or private, clean or dirty.
In one embodiment of the invention, a first choice for way selection is generated using any available method. However, the method is preferably one that is simple and cost-effective to implement (e.g., random or round robin). A second choice for way selection is then derived from the first (e.g., the first choice plus some fixed constant). If the status of the way corresponding to the first choice differs from a bias status, the way corresponding to the second choice is designated as the way to be filled with replacement data. Otherwise, the way corresponding to the first choice is designated as the way to be filled with replacement data.
The bias status which is used to select between the first and second choices can be programmed to yield different results in different systems. For instance, a computer system with limited memory bus bandwidth relative to its processing unit""s capacity to execute instructions and consume data might perform better if the bias status favors replacing clean lines over dirty lines, or shared lines over private lines.
In a system comprising two or more processors which operate on data stored in a shared main memory, where data produced by one processor is consumed by another, it might be beneficial to program the bias status so that dirty lines are favored for replacement. In this manner, data needed by the second processor is more likely to be found in main memory rather than the first processor""s private cache, and the second processor can retrieve the data more readily.
These and other important advantages and objectives of the present invention will be further explained in, or will become apparent from, the accompanying description, drawings and claims.

Cache line replacement using cable status to bias way selection


Use, as modifier resin for rubber mixtures, of novolaks ABC plastified with terpene-type olefinically unsaturated natural substances C, where the ratio of the molar amount of the phenol or phenol derivative B and the molar amount of the natural substance C in the modified novolak is from 1:6 to 6:1, process for increasing the tear propagation resistance and reducing the compression set of rubber vulcanizates by adding these modifier resins to rubber mixtures, and components molded from vulcanizates thus prepared.

The invention relates to a method of use of plastified novolaks as additive to rubber mixtures, leading to higher tear propagation resistance and also to lower compression set in the vulcanizates produced therefrom.
For a higher service life or durability of rubber items made from natural or synthetic rubber it is desirable to maximize tear propagation resistance, and also to have low compression set, alongside the required mechanical properties such as Shore hardness, elongation at break, ultimate tensile strength, and moduli.
Examples of rubber vulcanizates are vehicle tires (e.g. for cars or trucks), and also industrial rubber goods, such as V-belts, tubes, toothed belts, membranes, conveyor belts, and substrate matrices for abrasives and frictional linings, etc.
Some attempts to achieve an ideally balanced combination of the abovementioned properties for a particular application of rubber vulcanizates are known from the prior art. Examples of systems described are: use of short fibers as reinforcing agent (Short Polyester Fiber Reinforced Natural Rubber Composites; Senapati, A. K.; Kutty, S. K. N.; Pradhan, B.; Nando, G. B. in Int. J. Polym. Mater. 12(3), pp. 203-224, 1989); rubber-modified polyethylene foam for sports shoe soles (WO-A 88/08860); preparation of mixtures made from natural rubber and lignins (Compounding of Natural Rubber with Lignins; Kumaran, M. G. and De, S. K. in Kautschuk+Gummi Kunststoffe, Volume 30, No. 12, pp. 911-915); Comparison of Rubber Reinforcement Using Various Surface-Modified Precipitated Silicas; Thammathadamikul, V. O.; O""Haver; Harwell, J. H.; Osuwan, S.; Na-Ranong, N. and Waddell, W. H., J. Appl. Polym. Sci., 59(11), 1741-1750 (1996); A New Binary Acceleration System for Rubber Vulcanisation, Kuriakose, A. P.; Mathew, G., Indian J. Technol., 26(7), 344-347 (1988).
When short fibers are used, very marked anisotropy effects arise. For example, the tear propagation resistance and the compression set parallel to the preferred orientation of the fibers is higher than in the direction perpendicular thereto. In addition, a very complicated mixing technique is needed to prepare these rubber vulcanizates comprising short fibers. The literature also discloses that the folding of, and passage of, the rubber mill bands through the narrow gap between the rolls always has to take place in the same direction, and using an ideal number, which has to be predetermined, of passages through the rolls. These complex mixing procedures require complicated monitoring when converting from laboratory to production scale. However, the rubber industry often uses internal mixers which are not particularly likely to give the fibers any desired orientation. As fiber concentration rises, furthermore, the incorporation time inevitably rises, the consequence being a drastic lowering of mixing capacity. In addition, the xe2x80x9cscorch timexe2x80x9d becomes markedly shorter, and this is in turn equivalent to an increase in risk associated with the processing of the mixtures.
Ultimate tensile strength and elongation at break of fiber-filled rubber vulcanizates are known to vary in opposite directions. For example, when comparison is made with the initial mixture (with no fiber content) comparable ultimate tensile strengths parallel to the orientation of the fibers are achieved only at fiber contents of 20 phr (parts per hundred resin; 20 g for 100 g of the rubber) and above, whereas acceptable elongations at break of from 100 to 300% are found here only for the transverse (perpendicular) direction. For example, the elongation at break falls from 650 to 30% in parallel orientation on addition of 10 phr of fibers. Although the tear propagation resistance can be increased by various levels of addition (from 10 to 40 phr) of the fibers from 23 N/mm to 116 N/mm for parallel orientation and from 25 N/mm to 97 N/mm for transverse orientation, this is achieved at the cost of a drastic reverse, as described above, in elongation at break, from 650 to 30%. In addition, a no less drastic rise in initial hardness occurs, from 41 to 92 Shore A.
The mechanical properties of short-fiber-reinforced natural rubber mixtures are thus dependent on the fiber orientation, the fiber concentration, and the ratio of length and diameter in the fibers used.
In WO-A 88/08860, Kozma et al. describes a rubber-modified polyethylene foam for sports shoe soles. The polyethylene used in the foam is EPDM-modified and crosslinked with peroxides. When comparison is made with an unmodified fine EPDM foam material, the result of the modification is, inter alia, an improvement in compression set.
Other studies (Kumaran and De) concern the incorporation of lignin, a by-product of papermaking, into rubber mixtures, in particular natural rubber mixtures. The rubber mixtures or the vulcanizate prepared therefrom exhibit a drastic drop in tear propagation resistance and an increase in compression set.
In the abovementioned article by O""Haver et al. (Comparison of Rubber Reinforcement Using Various Surface-Modified Precipitated Silicas), the authors study the effect of modified silicas on vulcanization curve, and also on the mechanical properties of a natural rubber mixture of the vulcanizates prepared therefrom. The modification described of the silicas by means of in-situ polymerization with styrene/isoprene or styrene/butadiene as comonomers is very complicated, however. For example, the in-situ polymerization comprises four reaction steps:
Adsorption of the surface-active substance (hexadecyltrimethylammonium bromide) onto the silica particles, adsorption of the monomers via a solution procedure, polymerization of the monomers, and removal of the surface-active substance by bleaching. This time-consuming and expensive procedure is balanced by improved tear propagation resistances and compression setsxe2x80x94with lowered elongation at break.
The authors Mathew and Kuriakose succeeded in improving ultimate tensile strength and tear resistance by using a two-component accelerator system [1-phenyl-2,4-dithiobiuret/TMTD (tetramethylthiuram disulfide)]. However, mechanical tests also showed that rebound resilience and compression set remain unchanged when comparison is made with the standard vulcanization conditions.
In EP-A 0 362 727, modified novolaks are disclosed comprising terpenes and unsaturated carboxylic acids, and/or derivatives of these compounds, the mass ratio between the terpenes and the unsaturated carboxylic acids being from 98.2:2.5 to 2.5:98.5, and the ratio of the mass of the phenolic component and the total mass of the modifiers being from 95:5 to 5:95, preferably from 10:90 to 90:10. Addition of these modified novolaks to other mixtures brings about a rise in hardness and moduli. Nothing is said concerning the effect on tear propagation resistance and compression set.
Surprisingly, it has now been found that the desired high tear propagation resistance can be obtained together with low compression set in vulcanizable rubber mixtures or vulcanizates prepared therefrom by incorporating certain plastified novolaks, and also the usual curing agents for curing the same, e.g. hexamethylenetetramine (HMT) or hexamethoxymethylmelamine (HMMM).
The present invention therefore provides a method of use, as modifier resin for rubber mixtures, of novolaks ABC plastified using terpene-type olefinically unsaturated natural substances C, such as rosin or rosin derivatives, comprising admixing the said components ABC to rubber mixtures the ratio between the amount of substance of the phenol or phenol derivative B and the amount of substance of the natural substance C in the modified novolak being from 1:6 to 6:1, and the melting point of the modified novolak being above 90xc2x0 C.
The preparation of the plastified novolaks is based on the known methods, for example as described in DE-C 22 54 379.
For preparing the plastified novolaks ABC according to the invention, it is in principle possible to use any of the phenolic compounds which have at least one reactive hydrogen atom on the aromatic ring and are at least monofunctional in their reactivity with aldehydes. Examples of these include mononuclear or polynuclear phenolic compounds which may be monofunctional, bifunctional, trifunctional, or have even higher functionality in their reactivity with aldehydes such as formaldehyde. Examples of compounds which may be used individually, in succession one after the other, or as a mixture are therefore: phenol itself, the various isomers of cresol and of xylenol, the ethylphenol isomers, the propylphenol and isopropylphenol isomers, and also p- or o-substituted alkylphenols having up to 18, in particular up to 15, carbon atoms in the side chain. It is also possible to use unsaturated phenols, e.g. o- or p-vinylphenol, p-isopropenylphenol, or phenolic structures reacted with DCPD (dicyclopentadiene) and/or with styrene and/or with rosin. It is also possible to use polynuclear phenols, e.g. dihydroxybiphenyl, or isomers of diphenylolmethane (bisphenol F), of diphenylolethane, or of diphenylolpropane (bisphenol A). It is also possible to use polyfunctional mononuclear phenols, e.g. resorcinol, pyrocatechol, and hydroquinone.
Oxo compounds A which may be used are in principle any of the aldehydes and/or compounds containing keto groups or compounds providing these groups, where these are reactive toward phenols having active hydrogen atoms on the aromatic ring and can form condensation products with these. Among the oxo compounds which can be used as starting components, and may be used individually or in succession one after the other, or in a mixture, preference is given to the use of the aliphatic aldehydes, such as formaldehyde, acetaldehyde, and the homologs or isomers of these having up to 18 carbon atoms per molecule, in particular up to 12 carbon atoms per molecule. The use of aqueous formaldehyde solutions is particularly preferred. It is also possible to use ketones having up to 18, preferably up to 12, carbon atoms. Examples of preferred compounds are acetone, methyl ethyl ketone, diethyl ketone, and camphor.
The unsaturated terpene-type natural substances C are in particular resin acids and naturally occurring mixtures of these, for example abietic acid, neoabietic acid, levopimaric acid, pimaric acid, isopimaric acid, palustric acid, and also hydrogenated and dehydrogenated forms of these. The naturally occurring mixtures of these acids, the composition of which can vary greatly depending on origin, are termed rosin. This is produced as distillation residue during the production of turpentine oil (balsam resin), distillation residue during the production of tall oil (tall resin), or extract from conifer stumps (conifer root resin). The naturally occurring types of rosin also comprise admixtures of fatty esters, of terpene alcohols, and of hydrocarbons.
The novolaks may be prepared using acidic catalysts, either by the conventional process, i.e. under reflux at from 95 to 102xc2x0 C., or else by what is known as the recycle process (U.S. Pat. No. 5,089,589). The acidic catalysts used preferably comprise strong mineral acids and/or their acidic derivatives, in particular sulfuric acid, hydrogen sulfates, or half esters of sulfuric acid, or organic acids, in particular oxalic acid dihydrate and p-toluenesulfonic acid.
The composition of the plastified novolaks used according to the invention as rubber component can be varied within a wide range. The ratio of the amounts of substance of its constituents phenol and aldehyde is from 1:0.4 to 1:1, in particular from 1:0.5 to 1:0.9. Particularly preferred constituents here are phenol itself and formaldehyde.
The ratio of the amounts of substance between phenol and the unsaturated terpene-type natural substances, in particular rosin, is from 1:6 to 6:1, in particular from 5:1 to 1:1.
Further characterization of the plastified novolak resins ABC is possible by stating their melting point and the viscosity of their solutions in a suitable organic solvent, these values being in the ranges conventional for novolaks:
Melting point (capillary, to DIN 53181): about 100xc2x0 C. (from 60 to 120xc2x0 C.)
Dynamic viscosity (DIN 53177/23xc2x0 C.); 50% strength in methoxypropanol: from 350 to 1100 mPa.s
Preference is given to the use of resins ABC which under standard conditions of temperature and humidity are in solid, small-particle form. The melting point here should be at least sufficiently high to prevent the products from clumping on storage at room temperature and during transport. Preference is given here to a melting point of above 90xc2x0 C. for the novolak.
The plastified phenolic resins ABC may be used according to the invention in a very wide variety of vulcanizable rubber mixtures.
Preferred examples of suitable sulfur-vulcanizable rubber types which may be used are natural rubber (NR), polyisoprene (IR), polybutadiene (BR), styrene-butadiene rubber (SBR), acrylonitrile rubber (ACM and ANM), butyl rubber (IIR), chlorobutyl rubber, ethylene-propylene-diene terpolymer rubber (EPDM), and mixtures of these, as conventionally employed in the vehicle tire industry or for producing industrial rubber goods. Examples of the other conventional constituents are fillers, such as carbon blacks, silicas, chalk, kaolins, and also inorganic or organic pigments, such as titanium dioxide and iron oxide, and phthalocyanine dyes. Examples of other conventional constituents are vulcanizing agents selected from the group consisting of sulfur and sulfur-donating compounds, and also vulcanization agents, e.g. accelerators and activators. It is also conventional to use additives, e.g. those selected from the group consisting of stearic acid, zinc oxide, antioxidants, tackifying resins, and metal compounds for additional improvement of adhesion of the rubber to steel cord, for example the cobalt or nickel salts of monobasic carboxylic acids, preferably naphthenic acids or isooctanoic acids. Mineral oils and plasticizers, e.g. phthalic esters, are also conventional additives for improving processability.
The mixtures of rubber and modifier resin ABC preferably also comprise curing agents D. The curing of the modified novolak resins ABC used according to the invention takes place here via elimination of formaldehyde from the curing agents D at an elevated temperature during the vulcanization of the mixtures of rubber and modifier resin. Examples of suitable curing agents are hexamethylenetetramine and what are known as methylene donors in the form of triazine resins, in particular melamine-formaldehyde resins of suitable composition. These melamine resins may be used undiluted as crystalline or liquid products or, preferably, as advantageously processable free-flowing products after prior adsorption on suitable solid substrate materials, such as finely divided silicas.
According to the invention, the modified phenolic resins ABC are used in vulcanizable rubber mixtures which can be prepared in the conventional way, e.g. in (heatable) internal mixers or on (heatable) mixing rolls. It can be advantageous here to increase the mixing temperature to a value above the melting range of the resin added during a freely selectable mixing phase in order to improve distribution of the resins. It is also important that the hardeners are incorporated as near as possible to the end of the mixing procedure at temperatures which are not excessive (from 80 to 100xc2x0 C.), to avoid premature reaction with the crosslinkable resin components.
A preferred mixing procedure has two mixing stages. In the first mixing stage, the rubber or the various types of rubber and the modifier resin ABC are mixed at temperatures of up to about 160xc2x0 C. (preferably in an internal mixer) with the additives conventional in rubber technology, for example carbon black, antioxidants, ZnO, expelled oil, and silica. This mixture is then mixed, in a second mixing step at temperatures of from 80 to 100xc2x0 C., with the vulcanization agents, e.g. vulcanization accelerators and sulfur, and also with the curing agents D.
In other respects, known criteria may be used for selection of the components and establishing their mass fractions in the vulcanizable rubber mixtures. Mixing of the components at relatively high temperatures may likewise take place in a known manner, e.g. at from 100 to 160xc2x0 C. Vulcanization of the rubber mixtures may also take place in a known manner at conventional temperatures in conventionally heatable apparatus, where appropriate under pressure.
The mass fraction of the plastified novolaks ABC in the vulcanizable rubber mixtures may preferably be up to 20%, in particular up to 15%, particularly preferably from 0.5 to 10%, based on the mass of the vulcanizable rubber mixture (=100%). It is generally also possible to make concomitant use of other known phenolic resins (reinforcing resins or vulcanization resins), e.g. Alnovol(copyright) PN 320 or, respectively, 160, as long as they do not cause or have any disadvantageous or detrimental effects.
The vulcanizable rubber mixtures modified according to the invention, which can be prepared, processed, and vulcanized by known methods, are very well suited for the production of industrial rubber goods, preferably those exposed to high mechanical loads. They may in particular be used for producing tubes, drive belts, such as V-belts, transmission belts, and toothed belts, gaskets with reinforcement, conveyor belts, and vehicle tires, e.g. for cars, trucks, earth-moving machinery, tractors, and aircraft, since they have excellent elongation at break and tear propagation resistance together with low compression set. They are also suitable for producing rubber coatings on solid bodies for protection from mechanical damage or corrosion.
The examples below provide further clarification of the invention.

Plastified novolaks as additive to rubber mixtures


A technique that is usable with a fuel cell stack includes providing a fuel flow and using at least some of the fuel flow to produce power with the fuel cell stack. A request is received to charge a battery. In response to the request, the technique includes determining if the remainder of the fuel flow is sufficient to produce additional power to charge the battery. Based on the determination, the remainder of the fuel flow is used to produce the additional power to charge the battery.

The invention generally relates to a technique to control the charging of a battery using a fuel cell.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a polymer electrolyte membrane (PEM), often called a proton exchange membrane, that permits only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is reacted to produce hydrogen protons that pass through the PEM. The electrons produced by this reaction travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions are described by the following equations:
H2xe2x86x922H++2exe2x88x92 at the anode of the cell, andxe2x80x83xe2x80x83Equation 1
O2+4H++4exe2x88x92xe2x86x922H2O at the cathode of the cell.xe2x80x83xe2x80x83Equation 2
A typical fuel cell has a terminal voltage near one volt DC. For purposes of producing much larger voltages, several fuel cells may be assembled together to form an arrangement called a fuel cell stack, an arrangement in which the fuel cells are electrically coupled together in series to form a larger DC voltage (a voltage near 100 volts DC, for example) and to provide more power.
The fuel cell stack may include flow plates (graphite composite or metal plates, as examples) that are stacked one on top of the other, and each plate may be associated with more than one fuel cell of the stack. The plates may include various surface flow channels and orifices to, as examples, route the reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells. Electrically conductive gas diffusion layers (GDLs) may be located on each side of each PEM to form the anode and cathodes of each fuel cell. In this manner, reactant gases from each side of the PEM may leave the flow channels and diffuse through the GDLs to reach the PEM.
A fuel cell system may include a fuel processor that converts a hydrocarbon (natural gas or propane, as examples) into a fuel flow for the fuel cell stack. For a given output power of the fuel cell stack, the fuel flow to the stack must satisfy the appropriate stoichiometric ratios governed by the equations listed above. Thus, a controller of the fuel cell system may determine the appropriate output power from the stack and based on this determination, estimate the fuel flow to satisfy the appropriate stoichiometric ratios. In this manner, the controller regulates the fuel processor to produce this flow, and in response to controller determining that the output power should change, the controller estimates a new rate of fuel flow and controls the fuel processor accordingly.
The fuel cell system may provide power to an external load, such as a load that is formed from residential appliances and electrical devices that may be selectively turned on and off to vary the power that is consumed by the load. Thus, the power that is consumed by the load may not be constant, but rather, the power that is consumed by the load may vary over time and abruptly change in steps. For example, if the fuel cell system provides power to a house, different appliances/electrical devices of the house may be turned on and off at different times to cause the power that is consumed by the load to vary in a stepwise fashion over time.
The fuel cell system may include a battery to temporarily supplement the power that the fuel cell stack provides to the load during times when the fuel processor does not provide a sufficient level of fuel to the stack to maintain the above-described stoichiometric equations. The battery may frequently need to be charged. However, the battery may need to be charged during times when the fuel cell stack is already providing the maximum amount of power that is possible with a given level of fuel flow from the fuel processor.
Thus, there is a continuing need for an arrangement and/or technique to address one or more of the problems that are stated above.
In an embodiment of the invention, a technique that is usable with a fuel cell stack includes providing a fuel flow and using at least some of the fuel flow to produce power with the fuel cell stack. A request is received to charge a battery. In response to the request, the technique includes determining if the remainder of the fuel flow is sufficient to produce additional power to charge the battery. Based on the determination, the remainder of the fuel flow is used to produce the additional power to charge the battery.
Advantages and other features of the invention will become apparent from the following description, drawing and claims.

Technique and apparatus to control the charging of a battery using a fuel cell


To provide a photosensitive paste that permits pattern formation with a high aspect ratio and a high accuracy and to provide a plasma display comprising said photosensitive paste, by using a photosensitive paste that comprises, as essential components, an inorganic particles and an organic component that contains a photosensitive compound with the difference between the average refractive index of the organic component and the average refractive index of the inorganic particles being 0.1 or less.

The present invention relates to a novel photosensitive paste, a plasma display produced thereof, and a production method thereof.
The photosensitive paste of the present invention is used for pattern formation for various displays, including plasma display and matrix-addressed plasma liquid crystal display, and circuit materials. Such a plasma display can be used in large-size TV sets and computer displays.
In the fields of display and circuit material, demands are recently very high for techniques for highly accurate pattern formation with inorganic materials.
As increasingly small, fine-definition products have been developed in the field of display, demands are very high for advanced techniques for accurate pattern formation. For the production of a barrier rib that divides the pixels on the plasma display panel, for example, it has been hoped to develop a material that serves for pattern formation with an inorganic material, such as glass, with a high level of accuracy and a high aspect ratio.
In the field of circuit material, on the other hand, useful techniques have been needed for accurate processing of ceramic substrates on which IC""s are to be mounted. Screen printing and punching are currently used for the pattern formation, but more advanced techniques are needed for highly accurate pattern formation as smaller circuit devices are developed.
Conventionally, pattern formation with inorganic material has been frequently performed by screen printing using a paste consisting of inorganic particles and an organic binder, followed by firing. Screen printing, however, is disadvantageous in forming accurate patterns. Another disadvantage is that the formation of a pattern with a high aspect ratio requires many processing steps since multiple-layer printing is necessary.
To solve this problem, U.S. Pat. No. 4,885,963, U.S. Pat. No. 5,209,688, and JP-A-05-342992 have proposed to perform photolithography using a photosensitive paste. Since the photosensitive paste is low in sensitivity and resolution, however, it is impossible to produce a high-definition barrier rib with a high aspect ratio, and therefore, a long process consisting of several steps (coating, exposure, development, etc.) is required to form a pattern on a barrier rib up to a large thickness of, for example, 80 xcexcm or more.
U.S. Pat. 5,209,688 has also proposed a method in which transfer paper is coated with a photosensitive paste, followed by transferring transfer film onto a glass substrate, and JP-A-03-57138 has proposed a method in which grooves on a photoresist layer are filled with a dielectric paste to form a barrier rib. Also, U.S. Pat. No. 5,116,271 has proposed the use of photosensitive organic film to form a barrier rib. These methods, however, have disadvantages arising from the use of transfer film, photoresist, or organic film which require additional manufacturing processes. It should also be noted that a high-definition barrier rib with a high aspect ratio has not been obtained with these methods.
Furthermore, manufacturing of plasma displays sometimes requires pattern formation of the insulator layer or dielectric layer in addition to the barrier rib, and results in problems similar to those with the barrier rib processing.
The object of the invention is to provide a photosensitive paste that permits pattern formation with high accuracy and a high aspect ratio, which is made possible by controlling the refractive index of the organic and inorganic components in the photosensitive paste in order to reduce the reflection and scattering at the interface between the organic and inorganic components. Another object of the invention is to provide a high-definition plasma display and a method for the production thereof.
The objects of the invention are achieved by a photosensitive paste comprising, as essential components, inorganic particles and an organic component that contains a photosensitive compound, wherein the average refractive index of the inorganic particles, N1, and the average refractive index of the photosensitive organic component, N2, meet the following equation:
xe2x88x920.1xe2x89xa6N1xe2x88x92N2xe2x89xa60.2
The objects of the invention are also achieved by a photosensitive paste comprising, as essential components, inorganic particles and an organic component that contains a photosensitive compound, wherein the average refractive index of the inorganic particles is in the range of 1.5-1.7.
Furthermore, the objects of the invention are also achieved by a plasma display and its production method wherein the barrier rib is produced by coating a glass substrate with the paste, followed by exposure, development, and firing.
The photosensitive paste of the invention comprises inorganic particles and an organic component containing a photosensitive compound, and forms an inorganic pattern when sintered after a pattern is formed by photolithography with the photosensitive organic component.
The content of the inorganic particles in the paste should be in the range of 50-98 wt. %, preferably more preferably 70-95 wt. %, in order to reduce the shrinkage in the firing process to minimize the deformation caused by the firing.
The present inventors have carried out detailed studies and found that a pattern with a high aspect ratio can be produced easily by reducing the difference between the average refractive index of the organic component and the average refractive index of the inorganic particles to 0.1 or less, more preferably 0.07 or less.
Also, a pattern with a high aspect ratio can be produced accurately by allowing the average refractive index of the inorganic particles in the photosensitive paste, N1, and the average refractive index of the photosensitive organic component, N2, meet the following equation:
xe2x88x920.05xe2x89xa6N1xe2x88x92N2xe2x89xa60.1
more preferably,
xe2x88x920.01xe2x89xa6N1xe2x88x92N2xe2x89xa60.07
Also, since the organic component can increase in refractive index when polymerized, a pattern with a higher aspect ratio is produced when the following equation is met.
0xe2x89xa6N1xe2x88x92N2xe2x89xa60.07
A pattern with a higher aspect ratio can be produced when the refractive index of the organic component polymerized by light irradiation, N3, and the refractive index of the inorganic particles, N1, meet the following equation:
xe2x88x920.03xe2x89xa6N1xe2x88x92N3xe2x89xa60.03
Any ordinary inorganic material can be used as the inorganic particles. Preferred ones include glass, ceramics (alumina, cordylite, etc.), and metals (gold, platinum, silver, copper, nickel, palladium, tungsten, ruthenium oxide, and alloys thereof). Glass and ceramics containing, as an essential component, an oxide of silicon, an oxide of boron, or an oxide of aluminum are particularly preferred. Being insulators, they can be effectively used for producing patterned Insulation materials, Including barrier ribs for plasma displays and matrix-addressed plasma liquid crystal displays.
For the diameter of the inorganic particles, a suitable value is selected by considering the shape of the pattern to be formed. For effective pattern formation, however, it is preferable to use inorganic particles with a 50 wt. % particle diameter of 0.1-10 xcexcm, a 10 wt. % particle diameter of 0.4-2 xcexcm, and a 90 wt. % particle diameter of 4-10 xcexcm, and with a specific surface of 0.2-3 m2/g.
The use of spherical inorganic particles permits patterning with a high aspect ratio. Specifically, the sphericity coefficient should preferably be 80% or more. It is more preferred that the average particle diameter, the specific surface, and the sphericity coefficient be 1.5-4 xcexcm, 0.5-1.5 m2/g, and 90% or more, respectively.
The sphericity coefficient to defined as the proportion of those particles which look spherical or ellipsoidal under a microscope. That is, they are observed as round or elliptical objects under an optical microscope.
A pattern with a more accurate shape can be obtained by using glass particles that are produced by crushing glass that is 50% or more in transmittance (3 mm thick) for light with a wavelength of 436 nm.
To produce a space plate for a plasma display or a matrix-addressed plasma liquid crystal display, glass particles with a thermal softening temperature (Ts) of 350-600xc2x0 C. should preferably be used at 60 wt. % or more because a pattern has to be formed on a glass substrate with a low thermal softening temperature.
To prevent warping from taking place in the glass substrate during firing, the glass particles used should preferably have a linear thermal expansion coefficient of 50-90xc3x9710xe2x88x927, more preferably 60-90xc3x9710xe2x88x927.
Concerning the composition of the glass particles, the content of silicon oxide should preferably be in the range of 3-60 wt. %. If it is less than 3 wt. %, the denseness, strength and stability of the glass layer will deteriorate, and the thermal expansion coefficient will be out of the preferred range, possibly causing poor contact with the glass substrate. Furthermore, a content of 60 wt. % or less will lead to a low thermal softening temperature, permitting sintering onto a glass substrate.
When included at up to 5-50 wt. %, boron oxide can act to enhance some electrical, mechanical and thermal characteristics such as electric insulation, strength, thermal expansion coefficient, and denseness of the insulation layer. The glass will deteriorate in stability if the boron oxide content exceeds 50 wt. %.
A glass paste with thermal properties suitable for pattern formation on a glass substrate can be produced by using glass particles that contain at least one of the following bismuth oxide, lead oxide, lithium oxide, sodium oxide, or potassium oxide, at 5-50 wt. %. If the content exceeds 50 wt. %, the thermal resistance of the glass will deteriorate, making sintering onto the glass substrate difficult. In particular, the use of glass containing bismuth oxide at 5-50 wt. % is advantageous since the pot life of the paste will become long.
Such a glass containing bismuth oxide should preferably contain up to 50 wt. % or more of an oxide mixture with the following composition in terms of oxide contents:
bismuth oxide: 5-50 wt. %
silicon oxide: 3-60 wt. %
boron oxide: 5-50 wt. %
Glass material that is usually used as insulation material has a refractive index in the range of 1.5-1.9. If the average refractive index of the organic component is largely different from the average refractive index of the inorganic particles, strong reflection and scattering will occur at the interface between the inorganic particles and the photosensitive organic component, leading to failure in producing a high-definition pattern. Since a typical organic compound has a refractive index of 1.45-1.7, the inorganic particles and the organic component can be matched in terms of refractive index if the inorganic particles have a refractive index of 1.5-1.7. More preferably, the latter should be in the range of 1.55-1.65 to permit an organic component to be selected from a wide choice.
The use of glass particles containing oxides of alkali metals, such as lithium oxide, sodium oxide, and potassium oxide, at 3-20 wt. % in total not only facilitates the control of the thermal softening temperature and thermal expansion coefficient, but also reduces the average refractive index of glass, allowing the difference in refractive index between the glass particles and the organic component to be decreased easily. To increase the stability of the paste, the content of the oxide of alkali metals should preferably be 20 wt. % or less, more preferably 15 wt. % or less.
In particular, of the various alkali metals, the use of lithium oxide can increase the stability of the paste to a relatively high level, and potassium oxide, even when added in small amounts, can serve to control the refractive index. Thus, among other alkali metals, lithium oxide and potassium oxide can work very effectively.
As a result, it becomes easy to provide inorganic particles that have a thermal softening temperature suitable for sintering onto a glass substrate and an average refractive index of 1.5-1.7 which permits a decreased difference in refractive indices of the inorganic particles and the organic component.
Glass containing lead oxide or bismuth may be preferred because they can increase the thermal softening temperature and water resistance. However, glass particles containing lead oxide and/or bismuth at 10 wt. % or more may often have a refractive index of more than 1.6. Thus, the combined use of alkali metal oxides, such as lithium oxide, sodium oxide, and potassium oxide, with lead oxide and/or bismuth oxide can facilitate the control of the thermal softening temperature, thermal expansion coefficient, water resistance, and refractive index.
The hardness and workability of glass particles can be improved by adding aluminum oxide, barium oxide, calcium oxide, magnesium oxide, titanium oxide, zinc oxide, and/or zirconium oxide. In particular, aluminum oxide, barium oxide, and zinc oxide are effective. To maintain a required thermal softening temperature, thermal expansion coefficient, and refractive index, their respective content should preferably be 40 wt. % or less, more preferably 30 wt. % or less, with their total content being 50 wt. % or less.
The shrinkage that may occur during firing can be controlled by adding to the paste of the invention glass particles or ceramic particles with a thermal softening temperature of 600-900xc2x0 C. and an aluminum oxide, barium oxide, calcium oxide, magnesium oxide, titanium oxide, zinc oxide, and/or zirconium oxide content of 40 wt. % or less. To ensure high-accuracy pattern formation, the difference in refractive index among the particles used should preferably be 0.1 or less, more preferably 0.05 or less.
As for circuit materials, particularly for materials for multiple-layer substrates, ceramics as well as glass can be used as substrate material. Thus the thermal softening temperature may not necessarily be 600xc2x0 C. or less, so a high-strength substrate can be produced by using material with an aluminum oxide content of 25-75 wt. %.
The Becke method can be used to measure the refractive index of inorganic particles used for the present invention. To ensure high accuracy, measurement should be carried out at a wave length equal to that of the light used for exposure that is performed after the coating with the paste. In particular, measurement should preferably be conducted by using light with a wave length in the range of 350-650 nm. It is further preferred that refractive index be measured with i-ray (365 nm) or g-ray (436 nm).
A colored pattern can be obtained after firing by adding various metal oxides. For example, a black pattern can be produced by adding black metal oxides to the photosensitive paste up to a content of 1-10 wt. %.
In selecting black metal oxides to be used to produce such a black pattern, at least one, preferably three or more, of the following group of oxides should be used: Cr, Fe, Co, Mn, and Cu. In particular, a highly black pattern can be obtained by adding Fe and Mn, each up to 0.5 wt. % or more.
Further, patterns of various other colors other than black can be produced by employing a paste containing inorganic pigments that can cause coloring in red, blue, green, etc. Such colored patterns can be effectively used in such products as color filters for plasma display.
Particles used for the invention can be a mixture of several sets of particles with different compositions. In particular, the shrinkage caused during firing can be controlled by using several sets of glass particles and ceramic particles with different thermal softening temperatures.
To ensure high-accuracy pattern formation, however, the difference in refractive index among the several sets of inorganic particles with different compositions used in this case should preferably be 0.1 or less, more preferably 0.05 or less.
The organic component used in the present invention as stated herein refers to the organic component of the paste that contains the photosensitive organic material (i.e., the remainder that is obtained after removing the inorganic components from the paste).
The organic component may contain:
(a) 10-90 wt. % of an oligomer or a polymer having a weight-average molecular weight of 500-100,000, which oligomer or polymer has a carboxyl group, an unsaturated double bond or both in its molecular structure;
(b) 10-80 wt. % of a multifunctional acrylate compound and/or methacrylate compound; or
(c) at least one moiety selected from the group consisting of benzene ring, naphthalene ring and sulfur atom with a total content of 10-60 wt. %.
To ensure a high degree of photosensitivity, the photosensitive component in a photosensitive paste as used in the invention should preferably account for 10 wt. % or more, more preferably 30 wt. % or more, of the organic component.
The organic component should contain at least one of the following photosensitive materials: photosensitive monomers, photosensitive oligomer, and photosensitive polymers. In addition, it may contain, as necessary, such additives as binders, photopolymerization initiators, ultraviolet ray absorbents, sensitizers, sensitization assistants, polymerization inhibitors, plasticizers, viscosity improvers, organic solvents, antioxidants, dispersing agents, organic or inorganic suspending agents, and leveling agents.
There are photo-insolubilizing type and photo-solubilizing type photosensitive materials. A photo-insolubilizing type photosensitive material may contain:
(A) functional monomers, oligomers, or polymers that have one or more unsaturated groups in each molecule,
(B) a photosensitive compound such as an aromatic diazo compound, or an aromatic azide compound, an organic halogen compound, or
(C) a so-called diazo resin such as a condensation product of diazotized amine and formaldehyde.
A photo-solubilizing type photosensitive material may contain:
(D) a complex of an inorganic salt of a diazo compound and a organic acid, a quinonediazo compound, etc., or
(E) a product of a quinonediazo compound bonded with a polymer binder, such as naphthoquinone-1,2-diazide-5-sulfonate of phenol or novolak resin.
Any of the photosensitive components listed above can be used for the present invention. In particular, those specified under (A) are preferred as a component of a photosensitive paste because they can be used conveniently in combination with inorganic particles.
The useful photosensitive monomers include compounds with an unsaturated carbon-carbon bond, such as methylacrylate, ethylacrylate, n-propylacrylate, isopropylacrylate, n-butylacrylate, sec-butylacrylate, sec-butylacrylate, iso-butylacrylate, tort-butylacrylate, n-pentylacrylate, allylacrylate, benzilacrylate, butoxyethylacrylate, butoxytriethylene glycolacrylate, cyclohexylacrylate, dicyclopentanylacrylate, dicyclopentenylacrylate, 2-ethylhexylacrylate, glycerolacrylate, glycidylacrylate, heptadecafluorodecylacrylate, 2-hydroxyethylacrylate, isobonylacrylate, 2-hydroxypropylacrylate, isothexylacrylate, isooctylacrylate, laurylacrylate, 2-methoxyethylacrylate, methoxyethylene glycolacrylate, methoxydiethylene glycolacrylate, octafluoropentylacrylate, phenoxyethylacrylate, stearylacrylate, trifluoroethylacrylate, allylated cyclohexyldiacrylate, 1,4-butanedioldiacrylate, 1,3-butylene glycoldiacrylate, ethylene glycoldiacrylate, diethylene glycoldiacrylate, triethylene glycoldiacrylate, polyethylene glycoldiacrylate, dipentaerythritol hexaacrylate, dipentaerythritol monohydroxypentaacrylate, ditrimethylol propanetetraacrylate, glycerol diacrylate, methoxylated cyclohexyldiacrylate, neopentyl glycoldiacrylate, propylene glycoldiacrylate, polypropylene glycoldiacrylate, triglycerol diacrylate, trimethylol propanetriacrylate, acryl amide, aminoethylacrylate, phenylacrylate, phenoxyethylacrylate, benzilacrylate, 1-naphthylacrylate, 2-naphthylacrylate, bisphenol-A-diacrylate, a diacrylate of an addition product of bisphenol-A-ethyleneoxid, a diacrylate of an addition product of bisphenol-A-propyleneoxide, thiophenolacrylate, and benzilmercaptanacrylate; monomers formed by replacing 1-5 of the hydrogen atoms in the aromatic ring of the above compounds with chlorine or bromine atoms; styrene, p-methylstyrene, o-methylstyrene, m-methylstyrene, chlorinated styrene, brominated styrene, xcex1-methylstyrene, chlorinated xcex1-methylstyrene, brominated xcex1-methylstyrene, chloromethylstyrene, hydroxymethylstyrene, carboxymethylstyrene, vinylnaphthalene, vinylanthracene, and vinylcarbazole; above-mentioned acrylates with one or all acrylate parts replaced with methacrylate parts; xcex3-methacryloxypropyl trimethoxysilane, and 1-vinyl-2-pyrolidone. For the purposes of the present invention, these compounds can be used alone or in combination.
In addition to these, an unsaturated acid such as an unsaturated carboxylic acid may be added to improve the developing performance after light irradiation. Such unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, vinylacetic acid, and anhydrides of these acids.
The useful binders include polyvinyl alcohol, polyvinylbutyral, methacrylate polymers, acrylate polymers, acrylate-mathacrylate co-polymers, xcex1-methylstyrene polymers, and butylmathacrylate resins.
Further, oligomers and polymers that are produced by polymerizing at least one of said compounds having a carbon-carbon bond can also be used.
In polymerizing them, these monomers may be copolymerized with other photosensitive monomers in such a way that the content of the former is 10 wt. % or more, more preferably 35 wt. % or more.
The developing performance after light irradiation can be improved by using an unsaturated acid such as an unsaturated carboxylic acid as the monomer for copolymerization. Useful unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, vinylacetic acid, and anhydrides of these acids.
The resultant polymers or oligomers having acid groups such as carboxyl group in their side chains should preferably have an acid value in the range of 50-180, more preferably 70-140. The developable range will be narrow if the acid value is less than 50. If the acid value exceeds 180, on the other hand, the unexposed portions will be small in solubility to the developing solution, but the use of a developing solution with an increased concentration will cause the removal of exposed portions, making it difficult to produce high-definition patterns.
Useful photosensitive polymers or photosensitive oligomers can be produced by adding photosensitive groups to the side chains or the molecular ends of the polymers or oligomers listed above.
Photosensitive groups having an ethylenically unsaturated group are preferred. Such ethylenically unsaturated groups include vinyl, allyl, acryl, and methacryl.
The addition of such side chains to oligomers or polymers can be carried out by allowing a glycidyl- or isocyanate-containing ethylenically unsaturated compound, acrylic acid chloride, methacrylic acid chloride or allylchloride to undergo addition reaction with the mercapto group, amino group, hydroxyl group, or carboxyl group in the polymers.
Such ethylenically unsaturated compounds with glycidyl groups include glycidyl acrylate, glycidyl methacrylate, allylglycidyl ethers, glycidyl ethylacrylate, crotonic glycidyl ethers, iso crotonic glycidyl ethers.
Useful ethylenically unsaturated compounds with isocyanate groups include (meth)acryloyl isocyanate, and (meth)acryloyl ethylisocyanate.
Such aglycidyl- or isocyanate-containing ethylenically unsaturated compound, acrylated chloride, methacrylated chloride, and allyl chloride should preferably be added up to 0.05-1 equivalent to the mercapto, amino hydroxy, or carboxy group in the polymer.
Useful photopolymerization initiators include benzophenone, o-methyl benzoylbenzoate, 4,4-bis(dimethylamine)benzophenone, 4,4-bis(diethylamino)benzophenone, 4,4-dichlorobenzophenone, 4-benzoyl-4-methyldiphenylketone, dibenzilketone, fluorenone, 2,2-diethoxyacetophenon, 2,2-dimethoxy-2-phenyl-2-phenylacetophenon, 2-hydroxy-2-methylpropiophenon, p-t-butyldichloroacetophenon, thioxanthone, 2-methylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, diethylthioxanthone, benzil, benzildimethyl ketanol, benzilmethoxyethyl acetal, benzoin, benzoinmethyl ether, benzoinbutyl ether, anthraquinone, 2-t-butylanthraquinone, 2-amylanthraquinone, xcex2-chloroanthraquinone, anthrone, benzanthrone, dibenzosuberone, methyleneanthrone, 4- azidebenzalacetophenon, 2,6-bis(p-azidebenzylidene)cyclohexanone, 2,6-bis(p-azidebenzylidene)-4-methylcyclohexanone, 2-phenyl-1,2-butadione-2-(o-methoxycarbonyl)ozime, 1-phenyl-propanedione-2-(o-ethoxycarbonyl)ozime, 1,3-diphenyl-propanetrione-2-(o-ethoxycarbonyl)oxime, 1-phenyl-3-ethoxy-propanetrione-2-(o-benzoyl)ozime, Michler""s ketone, 2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propanone, naphthalenesulfonylchloride, quinolinesulfonylchloride, N-phenylthioacridone, 4,4-azobisisobutyzonitril, diphenyldisulfide, benzthiazoledisulfide, triphenylphosphine, camphorquinone, carbon tetrabromide, tribromophenylsulfone, and benzoin peroxide; and combinations of such photoreducing pigments as eosin and methylene blue with reducing agents such as ascorbic acid and triethanolamine. For the purposes of the invention, one or more of these can be used in combination. A photopolymerization initiator should preferably be added to 0.05-10 wt. %, more preferably 0.1-5,wt. %, of the photosensitive component. Photosensitivity can be insufficient if the amount of the polymerization initiator added is too small, while the persistence rate of the exposed portions can be too small if the amount of the polymerization initiator added is too large.
The addition of an ultraviolet ray absorbent can be effective. A high aspect ratio, high definition, and high resolution may be achieved by adding a compound with high ultraviolet ray absorbing performance. The preferred ultraviolet ray absorbents include organic dyes and organic pigments, particularly red organic pigments that absorb ultraviolet ray in the wavelength range of 350-450 nm. Specifically, they include azo dyes, aminoketone dyes, xanthene dyes, quinoline dyes, aminoketone dyes, anthraquinone dyes, benzophenone dyes, diphenylcyanoacrylate dyes, triazine dyes, and p-aminobenzoic acid dyes. Organic dyes are preferred because even when added as light absorbers they will not remain in the fired insulation film, minimizing the deterioration in the performance of the insulation film. Of the dyes listed above, azo dyes and benzophenone dyes are particularly preferred. The content of such an organic dye should preferably be 0.05-5 parts by weight. The effect of the ultraviolet ray absorbent will not be sufficient if the content is less than 0.05 wt. %, while the performance of the fired insulation film will not be sufficient if the content is above 5 wt. %. It is more preferred that the content be in the range of 0.05-1 wt. %. A typical process of adding an ultraviolet ray absorbent comprising an organic dye is as follows: the organic dye is dissolved in an organic solvent to form a solution, followed either by kneading it into a paste, or by adding inorganic particles to the organic solvent and drying it. By the latter method, so-called encapsulated particles in which the surface of each organic particle is coated with the organic compound are produced.
In some embodiments of the invention, such metals as Pb, Fe, Cd, Mn, Co, and Mg or their oxides contained in the inorganic particles may react with the photosensitive component of the paste to cause quick gelation of the paste, making it impossible to use it for coating. To prevent such a reaction, it is preferred that a stabilizing agent be added to inhibit the gelation. Preferred stabilizing agents include triazole compounds. In particular, preferred triazole compounds include benzotriazole derivatives, of which benzotriazole can work effectively. A typical surface treatment of glass particles with benzotriazole as performed for the invention is as follows: a required amount benzotriazole relative to the amount of inorganic particles is dissolved in an organic solvent such as methyl acetate, ethyl acetate, ethyl alcohol, or methyl alcohol, and the particles are immersed in the solution for 1-24 hours to ensure adequate immersion, followed by air drying preferably at a temperature of 20-30xc2x0 C. to evaporate the solvent, thus producing triazole-treated particles. The amount of the stabilizing agent used (stabilizing agent/inorganic particles) should preferably be 0.05-5 wt. %.
A sensitizer is added to improve the sensitivity. Specifically, such sensitizers include 2,4-diethylthioxanthone, isopropylthioxanthone, 2,3-bis(4-diethylaminobenzal)cyclopentanone, 2,6-bis(4-dimethylaminobenzal)cyclohexanone, 2,6-bis(4-dimethylaminobenzal)-4-methylcyclohexanone, Michler""s ketone, 4,4-bis(diethylamino),-benzophenone, 4,4-bis(dimethylamino)chalcone, 4,4-bis(diethylamino)chalcone, p-dimethylaminocinnamylideneindanone, p-dimethylaminobenzylideneindanone, 2-(p-dimethylaminophenylvinylene)-isonaphthothiazole, 1,3-bis(4-dimethylaminobenzal)acetone, 1,3-carbonyl-bis-,(4-diethylaminobenzal)acetone, 3,3-carbonyl-bis(7-diethylaminocoumalin), H-phenyl-N-ethylethanolamine, N-phenylethanolamine, N-tolyldiethanolamine, N-phenylethanolamine, dimethylaminoisoamyl benzoate, diethylaminoisoamyl benzoate, 3-phenyl-5-benzoylthiotetrazole, and 1-phenyl-5-ethoxycarbonylthiotetrazole. One or more of these can be used for the purposes of the invention. Some sensitizers can also work as phoptopolymerization initiators. When a sensitizer is added to a photosensitive paste as used for the invention, its content should preferably be 0.05-10 wt. %, more preferably 0.1-10 wt. %, relative to the photosensitive component. The sensitivity to light may not be improved significantly if the amount of the sensitizer is too small, while the persistence rate of the exposed portions can be too small if the amount of the sensitizer is too large.
A polymerization inhibitor is added to improve the thermal stability during storage. Specifically, such polymerization inhibitors include hydroquinone, monoesterified compounds of hydroquinone, N-nitrosodiphenylamine, phenothiazine, p-t-butylcatechol, N-phenylnaphthylamine, 2,6-di-t-butyl-p-methylphenol, chloranil, and pyrogallol. When a polymerization inhibitor is added, its content should preferably be 0.001-1 wt. % of the photosensitive paste.
Useful plasticizers include dibutylphthalate, dioctylphthalate, polyethylene glycol and glycerin.
An antioxidant is added to prevent the oxidation of an acrylate co-polymer during storage. Specifically, such antioxidants include 2,6-di-t-butyl-p-cresol, butylated hydroxyanisole. 2,6-di-t-4-ethylphenol, 2,2-methylene-bis-(4-methyl-6-t-butylphenol), 2,2-methylene-bis-(4-ethyl-6-t-butylphenol), 4,4-bis-(3-methyl-6-t-butylphenol), 1,1,3-tris-(2-methyl-6-t-butylphenol), 1,1,3-tris-(2-methyl-4-hydroxy-t-butylphenyl)butane, bis[3,3-bis-(4-hydroxy-3-t-butylphenyl)butyric acid] glycol esters, dilaurylthiodipropionate, and triphenylphosphite. When an antioxidant is added, its content should preferably be 0.001-1 wt. % of the paste.
When the viscosity of the solution is to be controlled, an organic solvent may be added to the photosensitive paste of the invention. The useful organic solvents for this include methylcellosolve, ethylcellosolve, butylcellosolve, methylethylketone, dioxane, acetone, cyclohexanone, cyclopentanone, isobutyl alcohol, isopropyl alcohol, tetrahydrofuran, dimethylsulfoxide, xcex3-butyrolactone, bromobenzene, chlorobenzene, dibromobenzene, dichlorobenzene, bromobenzoate, chlorobenzoate, and mixtures of organic solvents containing one or more of them.
The refractive index of the organic component is defined as the refractive index of that organic component in the paste at the time of exposure of the photosensitive component to light. When exposure is to be performed after the paste-coating and drying processes, the refractive index is defined as the refractive index of the organic compound in the paste after the drying process. In a typical method, the glass substrate is coated with a paste and then dried at 50-100xc2x0 C. for 1-30 min, followed by the measurement of the refractive index.
For the purposes of the present invention, common refractive index measurement methods such as the ellipsometric method or the V block method are preferred, and the measurement should be performed at the same wavelength as that of the light used for the exposure. In particular, measurement should preferably be carried out using light with a wavelength in the range of 350-650 nm. Further, measurement of the refractive index should preferably be performed by using i-ray (365 nm) or g-ray (436 nm).
The refractive index of the organic component polymerized by light irradiation can be measured by irradiating only the organic component with the same light as that used for the light irradiation of the pasta.
Glass particles containing 10 wt. % or more bismuth oxide or lead oxide that can be fired onto a glass substrate can have a refractive index of 1.6 or more, and in such a case, the organic compound should have a high refractive index.
In such a case, a substance with a high refractive index should be added to the organic component. To increase the refractive index, the addition of a compound that contains sulfur atoms, bromine atoms, iodine atoms, naphthalene rings, biphenyl rings, anthracene rings, or carbazole rings at 10 wt. % or more to the organic component is effective. The refractive index can also be increased by adding benzene rings at up to 20 wt. %.
In particular, the refractive index of the organic component can be easily increased by adding more than 10 wt. % of sulfur atoms or naphthalene rings. If the content is 60 wt. % or more, however, the sensitivity to light may decrease undesirably, so the total content of the sulfur atoms and naphthalene rings should preferably be in the range of 10-60 wt. %.
An effective method for introducing sulfur atoms, bromine atoms, and naphthalene rings into the organic component is the use of a compound consisting of photosensitive monomers or binders that contain sulfur atoms or naphthalene rings. Typical polymers produced from monomers containing sulfur atoms in their molecular structure include those expressed by formulae (a), (b) and (c) below, where R in the structural formulae denotes a hydrogen atom or a methyl group.
A sensitizer to be used should absorb light of the exposure wavelength. With such a sensitizer, the refractive index extremely increases in the vicinity of the wavelength where absorption occurs, so the refractive index of the organic component can be increased by adding a sensitizer in large amounts. In such a case, the sensitizer can be added 0.5-10 wt. %, more preferably 1-6 wt. %, of the paste.
To produce a paste, the required components such as inorganic particles, ultraviolet ray absorbent, photosensitive polymer, photosensitive monomer, photopolymerization initiator, glass frit, and solvent are prepared to provide a mixture of a required composition, followed by processing by means of a three-roll mill or a kneading machine to ensure homogeneous mixing and dispersion.
The viscosity of the paste is adjusted, as required, by controlling the amounts of the inorganic particles, viscosity improver, organic solvent, plasticizer, and suspending agent to be added. Its range should be 2,000-200,000 cps (centipoise). When the spin coating method is used to coat glass substrates, the viscosity should preferably be 200-5,000 cps. It should preferably be 50,000-200,000 cps when the screen printing method is used to apply a single coat with a thickness of 10-20 xcexcm, while it should preferably be 1,000-20,000 cps when a blade coater or a dye coater is used.
Some examples of using photosensitive pastes for pattern formation are described below, but they should place no limitations on the invention.
A photosensitive paste is applied over the entire surface or a part of a glass substrate, a ceramic substrate, or a polymer film. A common method such as screen printing, bar coater, roll coater, dye coater, or blade coater can be used for the coating. The coat thickness can be adjusted by using an appropriate number of coats, coater gap, screen mesh, and past viscosity.
When a paste is applied over a substrate, the surface of the substrate may be treated to achieve a close contact between the substrate and coat. Useful agents for such surface treatment include silane coupling agents, such as vinyl trichlorosilane, vinyl trimethoxy silane, vinyl triethoxy silane, tris-(2-methoxyethoxy)vinyl silane, xcex3-glycidoxypropyl trimethoxy silane, xcex3-(methacryloxypropyl)trimethoxy silane, xcex3(2-aminoethyl)aminopropyl trimethoxy silane, xcex3-chloropropyl trimethoxy silane, xcex3-mercaptopropyl trimethoxy silane, and xcex3-aminopropyl triethoxy silane; and organic metal compounds such as organic titanium compounds, organic aluminum compounds, and organic zirconium compounds. Such silane coupling agents or organic metal compounds are used as a 0.1-5% solution in such an organic solvent as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol. Then, the surface treatment liquid is applied uniformly over a substrate by means of a spinner etc., followed by drying at 80-140xc2x0 C. for 10-60 min to achieve surface treatment.
When a paste is applied to a film, the exposure may be performed either after drying the paste on the film, or after adhering the film on a glass or ceramic substrate.
A photosensitive green sheet for circuit materials or displays can be produced by applying the photosensitive paste of the invention over such materials as polyester film. A photosensitive paste layer with a uniform thickness can be produced by transferring this green sheet onto a glass substrate.
After the coating, light exposing equipment is used to perform exposure. Exposure to generally carried out with the masked exposure method using a photomask, as in ordinary photolithography. The mask used may be of a negative type or a positive type depending on the photosensitive organic component.
Direct pattern formation by means of a red or blue visible laser beam or Ar ion laser beam may be performed instead of using a photomask.
Exposure devices such as stepper exposer or proximity exposer may be used. For light exposure of a large area, a photosensitive paste may be applied over a glass or other substrate, followed by performing exposure while conveying the substrate to allow a large area to be exposed by means of a light exposer with a small light source.
The active light sources that can be used effectively include visible light, near ultraviolet light, ultraviolet light, electron beam, X-ray, and laser beam. Of these, ultraviolet light is preferred, and such sources as low-pressure mercury lamp, high-pressure mercury lamp, extra-high pressure mercury lamp, halogen lamp, and germicidal lamp can be used. Of these, the extra-high pressure mercury lamp is preferred. The optimum exposure conditions depend on the coat thickness, but an extra-high pressure mercury lamp with an output of 1-100 mW/cm2 should preferably be used for exposure for 0.5-30 min.
Oxygen barrier film may be provided over the applied photosensitive paste to improve the shape of the pattern. Useful materials for such oxygen barriers include PVA membrane, cellulose membrane, and polyester film.
PVA membrane may be produced by coating a substrate uniformly with 0.5-5.0 wt. % aqueous solution using a spinner etc., followed by drying at 70-90xc2x0 C. for 10-60 min to evaporate water. It in preferred that a small amount of alcohol be added to the aqueous solution to improve the wettability with the insulation film, thus facilitating the evaporation. The PVA solution should more preferably be in the concentration range of 1-3 wt. %. A concentration in this range will further improve the sensitivity. It is thought that the PVA coating can improve the sensitivity because of the following mechanism: oxygen in the atmosphere is believed to reduce the sensitivity for photo-curing, but the PVA membrane can block undesirable oxygen to improve the sensitivity to light exposure.
When transparent films such as polyester, polypropylene, or polyethylene are used, such film may be adhered over the applied photosensitive paste.
After the light exposure, development is carried out by making use of the difference in solubility to developing solution between the exposed and unexposed portions. Such a method as dipping, spraying, or brushing may be used for this purpose.
An organic solvent that can dissolve the organic component in the photosensitive paste can be used for the development solution. Water may be added to the organic solvent as long as its dissolving power is not reduced significantly. Alkaline aqueous solution may be used when the photosensitive paste contains a compound with an acid group such as carboxyl. Although the alkaline aqueous solution can be a metallic-alkaline solution such as sodium hydroxide solution, sodium carbonate solution, or calcium hydroxide solution, the use of an organic alkaline solution is preferred because the alkaline components can be removed easily at the time of firing.
Common amine compounds can be used as such organic alkaline compounds. Specifically, they include tetramethylammonium hydroxide, trimethylbenzylammonium hydroxide, monoethanol amine, and diethanol amine. The concentration of said alkaline solution should generally be 0.01-10 wt. %, more preferably 0.1-5 wt. %. The soluble portions will not be removed if the alkali concentration is too low, while an excessively high alkali concentration will cause peeling of patterned portions and corrosion of soluble portions.
At the time of development, the developing temperature should preferably be 20-50xc2x0 C. to facilitate process control.
Firing is then performed in a kiln. The atmosphere and temperature used for the firing depend on the paste and substrate. Firing is generally performed in such an atmosphere such as air, nitrogen, or hydrogen. The kiln to be used may be a batch-type kiln or a belt-type continuous kiln.
The firing temperature should be 400-1,000xc2x0 C. When pattern formation is performed on a glass substrate, it should be maintained at 520-610xc2x0 C. for 10-60 min to ensure firing.
Each of the processes for coating, light exposure, development, and firing may include a heating step at 50-300xc2x0 C. for such purposes as drying and preliminary reaction.
A glass substrate with a space plate as produced by the above processes may be used at the front or rear of a plasma display. It may also be used as the substrate provided for electric discharge from the addressed portions in a matrix-addressed plasma liquid crystal display.
Phosphor is applied between the barrier ribs produced above, followed by sandwiching them between a front and a rear glass substrate, and sealing them up with such a rare gas as helium, neon, or xenon, to produce a panel for plasma display.
Then, driver ICs are installed to complete the plasma display.
The size of each pixel has to be reduced to enhance the definition of the plasma display, i.e., to increase the number of pixels in a display of the same size. The pitch of the barrier rib has to be reduced to achieve this, but a decreased pitch will cause a decrease in the discharge space and a decrease in the phosphor-coated area, resulting in a reduced brightness. Specifically, a 42-in. high-resolution display for TV (1920xc3x971035 pixels) or a 23-in. display for office-automation equipment (XGA: 1024xc3x97768 pixels) will require a 450xc3x97450 xcexcm pixel size and a 150 xcexcm pitch for the barrier rib to divide pixels of each color. In this case, a large line width in the barrier rib will make it impossible to maintain a sufficient discharge space and decrease the phosphor-coated area, thus making it difficult to improve the brightness.
The present inventors have found that the technology given in the present invention serves to reduce the line width in the barrier rib.
In particular, the technology serves to produce a plasma display comprising a stripe-type barrier rib with a spacer width of 20-40 xcexcm. Thus the technology is effective for improving the brightness.
Further, by producing a high-definition barrier rib with a height of 100-170 xcexcm and a pitch of 100-160 xcexcm, a high-definition plasma display useful for high-resolution TVs and computer displays can be provided.
Examples are given below to illustrate the invention more concretely. The examples, however, are not intended to place any limitations on the invention. The concentrations (t) in examples and comparative examples are in percentage by weight unless otherwise specified.
A photosensitive paste containing inorganic particles and an organic component is produced in each example. Its production process is as follows: the materials of the organic component are heated at 80xc2x0 C. with xcex3-butyrolactone to ensure dissolution, followed by adding inorganic particles and kneading them in a kneading machine to produce a paste. Its viscosity was adjusted by controlling the amount of the solvent added. The solvent (xcex3-butyrolactone) was added up to 10-40% of the paste.
Subsequently, several coats were applied by screen printing on a 30xc3x9730 cm soda-lime glass or quartz glass substrate at a thickness of 100 xcexcm, 150 xcexcm, or 200 xcexcm, followed by drying at 80xc2x0 C. for 30 min.
Then, the substrates were exposed to light through either of the two photo-masks listed below.
(1) Chromium negative mask with a pitch of 220 xcexcm and a line width of 50 xcexcm
(2) Chromium negative mask with a pitch of 150 xcexcm and a line width of 20 xcexcm
Light exposure was performed with 2-10 J/cm2 of ultraviolet ray from a extra-high pressure mercury lamp with an output of 50 mW/cm2.
Subsequently, the substrate was immersed in a 0.5% solution of monoethanol amine for development.
The resultant glass substrate was then dried at 80xc2x0 C. for one hour, and fired at a maximum temperature of 560xc2x0 C. or 850xc2x0 C. (maximum temperature maintained for 30 min)
The resultant substrate was cut into specimens and their cross-sections were observed under a scanning electron microscope to determine whether a good pattern had been produced on the barrier rib. Results are shown in Table 3, where xe2x80x9c∘xe2x80x9d indicates that a good pattern was produced and xe2x80x9cxxe2x80x9d indicates that a good barrier rib was not obtained due to missing/destroyed portions in the pattern or due to insufficient development that left unexposed portions unremoved.
The refractive index of the organic component was adjusted only by controlling the organic component in the paste, and it was measured after coating and drying with the ellipsometric method using light with a wavelength of 436 nm at 25xc2x0 C.

Photosensitive paste, a plasma display and a method for the production thereof


A push side pool cleaner (1) has a spheroidal overall shape, within this shape two outer segments (9, 10) serve as wheels and a central zone (8) carries a suction passage (33) and a debris collector (32) also located entirely within the overall shape. The wheels are driven directly by water jets (44, 45) without any gears or other transmission. A flow splitter is provided in the cleaner (1) to divide push side water flow between the jets (44, 45) which drive the wheels and jets (43) which provide impulsion to the suction passage (33).

This invention lies in the field of pool cleaners which are driven by water circulated by a pump. The invention is not necessarily limited to xe2x80x9cautomatic pool cleanersxe2x80x9d, depending on what precisely is understood by this term, but the term xe2x80x9cautomatic pool cleanersxe2x80x9d is often used in the context of pool cleaners with which this invention is primarily concerned. Although the words xe2x80x9cpool cleanersxe2x80x9d will be used for convenience in this specification, they are to be interpreted broadly, as not limited to cleaning of domestic pools, but to include other bodies of water in which a cleaning and/or stirring action is required. The art in this field is divided into two parts, namely suction side cleaners and push side cleaners, referring to the suction and push sides respectively of a pump system which circulates water in the pool. The present invention lies primarily though not exclusively, in the push side part of the art, the term xe2x80x9cpressure side cleanersxe2x80x9d is also used to refer to the same push side cleaners.
Push side pool cleaners are distinguished from suction side cleaners, for various reasons known in the art; an example of a push side cleaner is described in South African patent 85/0648, granted to Alopex Industries, marketed as the xe2x80x9cPOLARISxe2x80x9d (trademark).
Whereas suction side cleaners have an effective wiping or rubbing action on the pool surfaces, this is a shortcoming with push side pool cleaners of the present art which run on wheels with a venturi passage passing over the pool surfaces with a clearance between the mouth of the venturi and the pool surface.
Again, whereas suction side pool cleaners have few moving parts, the cleaner moving over the pool surfaces under impulsion of intermittent water flow caused by an oscillating tongue, or a suction tube whose wall collapses intermittently, for example, certain push side pool cleaners of the art have the disadvantage that they are moved by means of a water turbine driving the wheels through a drive train consisting of many gears and shafts.
Also, whereas suction side cleaners remove very small particles from the pool because the particles picked up are passed through the main pool filter, push side pool cleaners of the art do not pass particles through the main pool filter, but through a bag filter attached to the cleaner; dust size particles pass the apertures of bag type filters to re-enter the pool water, so that these cleaners must rely on stirring up these dust size particles so that they remain sufficiently in suspension to be drawn into the pool weir and thence to the main pool filter.
Whereas suction side cleaners are xe2x80x9cadd onxe2x80x9d products, which the owner of an existing pool and filtering system can add on without technical assistance, most push side cleaners of the present art are initially set up by a technically capable person, where they are connected to a booster pump in the main pool filter circulation system, or into a dedicated water circulation system. Hence push side pool cleaners of the art tend to be sold via contractors who are building a pool and circulation system.
Although push side pool cleaners do have potential for less interference with the desirable randomness of movement over the pool surfaces, due to a smaller diameter hose being acceptable, than suction side cleaners, much of this potential advantage is lost by the wheeled drive of these cleaners of the push side cleaner art which tend to provide straight line travel. The POLARIS cleaner has three wheels asymmetrically arranged to try to reduce this effect, for example. There is a continuing need in the art for better randomness of movement of the cleaner over the pool surfaces, leading to better cleaning.
The push side water flow is given a bypass valve at the pool side allowing water flow to the cleaner to be adjusted by increasing or decreasing the bypass, so as to get an acceptable speed of movement of the cleaner over the pool surfaces. A disadvantage of this arrangement of the art is that the energy of the bypassed flow is discarded.
Finally, all present pool cleaners have limitations as to the shallowness at which they will operate and as to their ability to negotiate formations like stairs in pools without becoming stuck in one position. It is desirable that pool cleaners work in shallower regions and thus negotiate formations like stairs better.
Thus there exists a need to address these limitations and problems in push side cleaners of the art at least to some extent.
The present invention provides a push side cleaner which is generally spherical or prolate or otherwise spheroidal in the shape of its outer surfaces (or otherwise expressed, the cleaner outer surfaces conform with a conceptual outer envelope of spherical or prolate spheroidal shape). The invention can also be implemented in an outer shape which conforms to two truncated cones both tapering outwardly from a central region of the cleaner, for convenience the term xe2x80x9cbi-conicalxe2x80x9d will be used in the description and claims to briefly refer to this shape. The invention can also be implemented in a cylindrical shape.
These shapes can comprehensively be described as a family of solids of revolution and other similar shapes, lying between the spherical/spheroidal, conical and cylindrical are also accommodated within the scope of the invention. In this description the term spheroidal only will henceforward be used for convenience, comprehending within its scope also the meaning indicated in the preceding sentence.
A central zone of the spheroidal shape bounded by two segments of the spheroid on each side will form the total outer shape. The central zone will have a push side hose connected to it and the two segments will be rotatively driven on either side to provide impulsion to the cleaner for moving it over the pool surfaces to be cleaned. The central zone will have a clearance from the pool surfaces and will accommodate a venturi or other suction passage for drawing in debris from the pool surfaces.
The two segments may be independently driven, or there may be advantage in linking them by a shaft so that they rotate being fixed relative to each other.
Thus a feature of the cleaner of this invention is that the spheroidal surfaces of the two segments will provide impulsion to move the cleaner over the pool surface, wherever these surfaces engage the pool surfaces and in whatever orientation the cleaner happens to be. In this sense, then, the cleaner of this invention is capable of providing impulsion to the cleaner in three dimensions; by contrast, the pool cleaners of art, both of the push side and of the suction side types, are confined to impulsion only in two dimensions. The cleaners of art must remain oriented with their wheels or foot against the pool surfaces, if they capsize, they are, like a conventional vehicle, unable to move, until righted. By contrast the cleaner of this invention can turn any way round relative to the pool surfaces, be they horizontal or vertical, and still provide impulsion. Furthermore, this three dimensional character of the motivation capability of the cleaner of this invention provides a dramatic enhancement of the ability to achieve more random movement over pool surfaces. The spheroidal surface interacts with the pool surfaces with an additional dimension of randomness i.e. the third dimension in addition to the two dimensions of the pool surface. The cleaner is in fact more unstable than one on wheels or a foot (a foot is used in suction side cleaners) and gives better randomness. For example, when the cleaner engages a wall of the pool surfaces, it has the capacity for the axis on which the two segments were rotating over the pool floor, to swing with three dimensions of freedom to a new orientation, giving enhanced randomness of movement. In a practical embodiment which has been subjected to extensive testing, the three dimensional movement can be described to occur with respect to an axis of the push side hose connection : these are, firstly around the axis, secondly swinging the axis to left and right and thirdly swinging the axis up and down. The randomness of movement is known in the art to be important, in order to result in cleaning of all of the surface to be cleaned, over a period of time, non-random movements leave xe2x80x9cdeadxe2x80x9d spots which remain uncleaned.
Portions of the spheroidal surfaces of the segments may have brush like formations, e.g. bristles, on them, to give a brushing effect.
Preferably the pool cleaner having the features of this invention is made with a specific gravity closer to 1 than is appropriate in cleaners of the art. This is made possible by the three dimensional character of the movement of the cleaner of this invention.
The effective or net force acting on the cleaner, when the cleaner is under water, may be made to pass through a point located on the opposite side of the axis of rotation of the cleaner as a mouth of the suction passage. This may be done with floats, e.g. sealed volumes containing air) located on the same side of the axis of rotation of the cleaner as the mouth. The cleaner may still have a centre of gravity when outside water which centre is on the same side of the axis as the mouth. However, when submerged, the buoyancy of the floats reverses the position of the net force acting on the cleaner to the opposite side of the axis as the mouth. The effective or net force acting on the cleaner when submerged can be assessed by constructing the vector sum of the gravitational forces and the buoyancy forces.
This counter intuitive approach results in a less stable device under water, which is tolerable by virtue of the spheroidal shape of the cleaner of this invention. The lower stability results in more random movement over the pool surface which in turn gives the advantage, as mentioned, of less tendency for the cleaner to repeatedly miss some areas, leaving them uncleaned.
A feature of this invention, whether the floats are used, or not, is that the centre of gravity is made closer to the axis of rotation of the cleaner than is appropriate in cleaners of conventional design. This feature again reduces stability and as a result brings the beneficial advantage of greater randomness than is achieved in conventional cleaners. This is possible simply for the reason already stated, that spheroidal shape gives the advantage that the cleaner can not xe2x80x9ccapsizexe2x80x9d into a position in which it can no longer move, like a conventional vehicle.
The degree of buoyancy of the hose may be selected, for example, to achieve a desirable balance between a tendency to work well on the bottom surfaces of the pool, on the one hand, and also on the wall surfaces, on the other.
The cleaner of this invention may be given a jet which impels the cleaner against the pool surfaces with a mouth of the suction passage in proximity to the pool surfaces, achievable both on upright as well as horizontal parts of the pool surfaces.
Preferably the passage is given a direction, at least near the mouth of the passage, which has a tangential component as well as a radial component. In other words, the venturi passage, at least near its mouth, is preferably not normal (at right angles) to the spheroidal outer surfaces of the cleaner. The passage is oriented so that the mouth is directed in the direction in which the cleaner moves. This gives a degree of scooping action, helpful to lifting debris from the pool surfaces. Jets which provide the suction action in the suction passage, given this tangential component of direction, also assists in the forward impulsion of the cleaner, by jet reaction forces.
This invention further provides a pool cleaner which is driven by direct impulsion of water jets from the push side supply onto vanes on wheels of the cleaner. No drive train is provided or required, there are no gears or drive shafts transmitting a drive to wheels. The spheroidal shaped cleaner, as described above, provides the wheels in the form of the outer segments of the spheroidal shape.
Preferably, this drive feature is provided in the cleaner having a spheroidal outer shape, as described above. The vanes are provided at an inner edge of each segment, with the water jets issuing from nozzle formations provided on the central zone. Low energy losses giving more efficient use of the water energy can be achieved by the judicious application of this aspect of the invention. An advantage that is achievable as a result is that more of the total water energy available from the push side supply can be devoted to the suction function while still leaving sufficient for impulsion of the cleaner. Wearing parts in a drive train are eliminated.
A further feature of the invention, which is preferably implemented with the features described above, is the location of a debris collector inside the spheroidal shape of the cleaner. Conveniently, the debris collector is confined to within the central zone, because this makes it simple to lift the debris collector out of the cleaner to empty it, from time to time. Thus the suction passage leads to the debris collector which is located in the central zone. The debris collector can includes a sump region and must include sieve or screen surfaces to allow the water to exit the collector and retain the debris. The suction passage is therefore preferably curved, leading from the mouth which is oriented with a tangential component of direction, to the collector.
A still further feature of the invention relates to the splitting or division of the water which is supplied to the cleaner via the push side hose between the jets which provide the suction action within the suction passage and the jets which provide the direct impulsion onto the vanes on the wheels. In accordance with the invention, a water flow splitter is provided which comprises two passages which have adjacent entrance mouths, a movable occluding element which is movable to selectable position settings in which one entrance mouth is occluded more or less than the other entrance mouth. The preferred structure for the adjacent entrance mouths is a circular tube with a diametral dividing wall and for the occluding element a cylindrical cup shaped element rotatable in the tube with a bottom of the cup located against the diametral dividing wall and the bottom having a semicircular opening and movable by rotation of the cup shaped element. The occluding element can have markings on it to indicate various optional settings which provide different splits between the driving jets and suction generating jets. There may be grooves and ridges on the occluding element and the adjacent mouths to retain selected settings and the manufacturer or supplier may provide a selected setting to the user.
These splitting arrangements still allow for the water supplied by the push side hose to the cleaner to be provided to a third use, namely the jet which issues external to the cleaner to provide an impulsive force assisting the forward motivation of the cleaner and/or the attachment to a surface to be cleaned.
A beneficial effect of a pool cleaner designed according to this invention, is that a positive pressure is created inside the spheroidal cleaner other than in the suction passage, so that debris which might otherwise accumulate in unwanted spaces does not do so.