The use of radiation-curable compositions containing from 0.5 to 100% by weight of carbonate (meth)acrylates, based on the overall amount of radiation-curable compounds, as coating compositions for exterior applications.

The invention relates to the use of radiation-curable compositions comprising from 5 to 100% by weight, based on the overall amount of radiation-curable compounds, of carbonate (meth)acrylates as coating compositions for exterior applications.
Radiation-curable compositions have to date been used predominantly for the coating of wood, paper and plastics in the interior sector. Exterior applications require resistance to the effects of weathering, which for example means low yellowing tendency, stability to hydrolysis, mechanical stability under weathering conditions, especially stability to cracking, and also acid and other chemical resistance.
In addition to the required weathering stability there is a desire for good processing properties, such as minimal odor nuisance and high reactivity, and also good mechanical properties in the resultant coatings, such as high flexibility and hardness.
Radiation-curable compositions known to date, as disclosed for example by JP 62-132570 and WO 92/17337, do not go far enough toward meeting the above requirements.
EP-A-92 269 and DE-A-27 57 086 disclose carbonate (meth)acrylates. Exterior applications are not described.
It is an object of the present invention to provide weathering-resistant, radiation-curable compositions for exterior applications, having high weathering stability, good processing properties and, at the same time, good mechanical properties.
We have found that this object is achieved by the use of the above compositions.
The radiation-curable compositions contain from 0.5 to 100% by weight, preferably from 5 to 80% by weight and, with particular preference, from 10 to 50% by weight of carbonate (meth)acrylates. These percentages by weight are based on the sum of radiation-curable compounds.
The carbonate (meth)acrylates contain on average preferably from 1 to 5, in particular from 1 to 3, and, with particular preference, 2 or 3 carbonate groups.
The carbonate (meth)acrylates contain on average preferably from 1 to 5, in particular from 2 to 4 and, with particular preference, 2 or 3 (meth)acrylic groups, and with very particular preference 2 (meth)acrylic groups.
The number-average molecular weight Mn of the carbonate (meth)acrylates is preferably less than 3000 g/mol, with particular preference less than 1500 g/mol and, with very particular preference, less than 800 g/mol (as determined by gel permeation chromatography using polystyrene as standard and tetrahydrofuran as solvent).
The carbonate (meth)acrylates are readily obtainable by transesterifying carbonic esters with polyhydric, preferably dihydric, alcohols (diols, such as hexanediol) and subsequently esterifying the free OH groups with (meth)acrylic acid or else by a transesterification with (meth)acrylic esters, as is described, for example, in EP 92 269. They can also be obtained by reacting phosgene, urea derivatives with polyhydric alcohols, such as dihydric alcohols, for example.
Particularly preferred carbonate (meth)acrylates are those of the formula:
where R1 is H or CH3, X is a C2-C18 alkylene group and n is an integer from 1 to 5, preferably from 1 to 3.
R 1 is preferably H, and X is preferably C2-C10 alkylene, with particular preference C4-C8 alkylene. With very particular preference, X is C6 alkylene.
These compounds are preferably aliphatic carbonate (meth)acrylates.
In addition to the carbonate (meth)acrylates the radiation-curable composition may include further radiation-curable compounds.
Particularly suitable are urethane (meth)acrylates, epoxy (meth)acrylates and melamine (meth)acrylates.
Urethane (meth)acrylates, for example, are obtainable by reacting polyisocyanates with hydroxyalkyl (meth)acrylates with or without chain extenders such as diols, polyols, diamines, polyamines or dithiols or polythiols. Urethane acrylates which can be dispersed in water without the addition of emulsifiers additionally comprise ionic and/or nonionic hydrophilic groups, which are introduced into the urethane acrylate by means, for example, of structural components such as hydroxycarboxylic acids.
The urethane (meth)acrylates preferably have a number-average molecular weight Mn of from 500 to 20,000, in particular from 750 to 10,000 and, with particular preference, from 750 to 3000 g/mol (as determined by gel permeation chromatography using polystyrene as standard).
The urethane (meth)acrylates preferably have a content of from 1 to 5, with particular preference from 2 to 4, mols of (meth)acrylic groups per 1000 g of urethane (meth)acrylate.
Preferred structural components of the urethane (meth)acrylates are
C1-C8-hydroxyalkyl (meth)acrylates,
C2-C8-alkanediols or -polyols or C2-C8-alkylamines as chain extenders; the urethane acrylates can also include polyesterols or polyetherols as structural components; preferred polyisocyanates are
dicyclohexylmethane 4,4xe2x80x2-diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, tetramethylene diisocyanate, trimethylhexamethylene diisocyanate, adducts of such isocyanates with polyhydric alcohols such as trimethylolpropane, dimers or trimers of the isocyanates, such as biurets or isocyanurates.
Preference is given to aliphatic polyisocyanates, the term aliphatic being intended to include nonaromatic alicyclic compounds as well.
Preferred urethane (meth)acrylates are aliphatic urethane acrylates, which contain aromatic ring systems if at all, in minor amounts of, for example, less than % by weight, based on the urethane acrylates, and which with particular preference contain no aromatic ring systems.
Epoxide (meth)acrylates are obtainable by reacting epoxides with (meth)acrylic acid. Examples of suitable epoxides are epoxidized olefins or glycidyl ethers, examples being bisphenol A diglycidyl ether, or aliphatic glycidyl ethers, such as butanediol diglycidyl ether.
Melamine (meth)acrylates are obtainable by reacting melamine with (meth)acrylic acid.
The epoxy (meth)acrylates and melamine (meth)acrylates preferably have a number-average molecular weight Mn of from 500 to 20,000, with particular preference from 750 to 10,000, and, with very particular preference, from 750 to 3000 g/mol; the content of meth(acrylic) groups is preferably from 1 to 5, with particular preference from 2 to 4, mol per 1000 g of epoxy (meth)acrylate or melamine (meth)acrylate (gel permeation chromatography, PS standard, THF solvent).
Preferred radiation-curable compositions comprise from to 80% by weight, with particular preference from to 50% by weight, of carbonate (meth)acrylates a) and from 20 to 95% by weight, with particular preference from 50 to 90% by weight, of urethane (meth)acrylates, epoxy (meth)acrylates or melamine (meth)acrylates b).
In addition to the above (meth)acrylic compounds the radiation-curable composition may include other ethylenically unsaturated, free-radically polymerizable compounds.
Mention may be made in particular of compounds c), which have at least one (meth)acrylic group but are different from the above (meth)acrylic compounds a) and b).
Suitable compounds c) are poly(meth)acrylates of aliphatic polyols, especially di- to pentahydric alcohols, which other than the hydroxyl groups contain no further functional groups or, at best, ether groups.
Examples of such alcohols are bifunctional alcohols, such as ethylene glycol, and propylene glycol, and the representatives with higher degrees of condensation, such as diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, etc., butanediol, pentanediol, hexanediol, neopentyl glycol, cyclohexanedimethanol, trifunctional alcohols and alcohols of higher functionality, such as glycerol, trimethylolpropane, butanetriol, trimethylolethane, pentaerythritol, ditrimethylolpropane, dipentaerythritol, sorbitol, mannitol and the corresponding alkoxylated alcohols, especially ethoxylated and propoxylated alcohols.
Suitable poly(meth)acrylates in particular have a molecular weight of less than 1000 g/mol, with particular preference of less than 600 g/mol, and have from 2 to 4 (meth)acrylic groups in the molecule; in other words, they are di-, tri- or tetraacrylates.
Further compounds c) having at least one (meth)acrylic group and being different from a) and b) are, for example, polyester (meth)acrylates, or else mono(meth)acrylates, such as butyl acrylate, cyclohexyl acrylate, etc. Monoacrylates are employed in particular as additional reactive diluents.
With all of the above compounds, the acrylic compounds are fundamentally preferred over the methacrylic compounds.
The radiation-curable compositions may also comprise radiation-curable compounds d) without acrylic groups. Suitable examples are vinyl- or alkyl-containing compounds, such as vinyl esters, aromatic vinyl compounds, such as styrene, vinyl ethers, their oligomers or polymers, and also unsaturated polyesters, etc.
Preferably, the overall amount of the radiation-curable compounds is composed as follows:
from to 80, with particular preference from 10 to 50% by weight of a),
from 20 to 95, with particular preference from 50 to 90% by weight of b),
from 0 to 50, with particular preference from 0 to % by weight of c),
from 0 to 50, with particular preference from 0 to 10% by weight of d).
Preferably, the radiation-curable compositions contain little if any aromatic components. The content of aromatic carbons (that is, carbons which are part of an aromatic ring system) is preferably below 5% by weight, with particular preference below 2% by weight, and, with very particular preference, below 0.5% by weight based on the overall amount of the radiation-curable compounds. In particular it is 0%.
The radiation-curable compounds can be present in the radiation-curable compositions in solvent-free form, dissolved in organic solvents, or dispersed in water.
Preference is given to solvent-free systems and especially to aqueous systems.
To this end, the radiation-curable compounds can be dispersed in water with the aid of emulsifiers or protective colloids, where the compounds are not already self-dispersible by virtue of containing hydrophilic groups.
The radiation-curable compositions preferably include at least one photoinitiator for the photochemical polymerization of free-radical polymerizable compounds.
Suitable examples are mono- or bisacylphosphine oxides, benzophenones, hydroxyacetophenones, phenylglyoxylic acid and its derivatives, or mixtures of these photoinitiators.
The radiation-curable compositions contain preferably from 0.1 to parts by weight of photoinitiators, with particular preference from 1 to 3 parts by weight of photoinitiators, based on 100 parts by weight of radiation-curable compounds.
In addition to the photoinitiators and radiation-curable compounds, the radiation-curable compositions may comprise further constituents. Particular mention may be made of pigments, flow control agents and stabilizers. For applications in the exterior sectorxe2x80x94that is, for coatings which are directly exposed to daylightxe2x80x94the compositions will in particular comprise UV absorbers and free-radical scavengers.
UV absorbers convert UV radiation into thermal energy. Known UV absorbers are hydroxybenzophenones, benzotriazoles, cinnamic esters, and oxalanilides.
Free-radical scavengers bind free radicals which form as intermediates. Important free-radical scavengers are sterically hindered amines, which are known as HALS (Hindered Amine Light Stabilizers).
For exterior applications, the content of UV absorbers and free-radical scavengers is preferably in each case from 0.1 to 5 parts by weight, with particular preference from 0.5 to 3 parts by weight and, with very particular preference, from 2 to 3 parts by weight per 100 parts by weight of the radiation-curable compounds.
In addition, the radiation-curable composition may, as well as radiation-curable compounds, include other compounds which contribute to curing by means of different chemical reactions. Suitable examples are polyisocyanates, which crosslink with hydroxyl groups or amino groups.
The radiation-curable compositions are suitable for use as coating compositions which are employed in the exterior sector and which, therefore, are exposed to daylight.
Examples of such applications are the exterior coating of buildings or parts of buildings, especially facings or roof tiles, coatings on vehicles, especially on motor vehicles such as passenger cars, and trucks (in short, automobiles), rail vehicles, and aircraft.
The radiation-curable compositions are used in particular as a clearcoat (also called topcoat) of motor vehicles. The clearcoat of a motor vehicle is the outermost finish coat, which is exposed to weathering.
In this context, the radiation-curable compositions can be used to coat vehicle bodies or individual parts of vehicles consisting, for example, of metal or plastic. The radiation-curable compositions can also be coated onto films and these films can in turn be bonded adhesively to the vehicle, e.g., to the bodywork or parts of a vehicle.
The substrates to be coated can be metallic substrates, plastics, especially in the form of films and sheets, wood, or ceramic substrates.
The radiation-curable coating compositions can be applied to the coating substrates by known methods. Application techniques such as spraying, rolling and knife coating are particularly appropriate.
Curing can take place by radiation curing with UV light, with the UV fraction of daylight possibly being sufficient under certain circumstances. Preferably, however, commercial UV lamps are used for radiation curing. Curing can also take place by means of electron beams.
The coatings produced with the radiation-curable compositions exhibit high resistance to the effects of weathering, in particular a low yellowing tendency, high stability to hydrolysis, and very good mechanical properties, especially high flexibility and hardness.

Radiation-curable weather-resistant compositions comprising carbonate (meth) acrylates


Chemical pulp is produced from a slurry of comminuted cellulosic fibrous material using a beneficial additive such as AQ, or polysulfide. In the first treatment zone the effective alkali concentration and temperature conditions are such so that substantially no alkali degradation of the cellulose occurs, but so that the material is effectively impregnated with the additive. Then the material is treated with an alkaline cooking liquor, at cooking temperature, to produce a chemical cellulose pulp with higher yield or strength than if the low temperature, low alkali, additive pretreatment was not practiced. Typical alkali and temperature conditions in the first zone are less than 10 g/l expressed as NaOH, and between about 80-130xc2x0 C., e.g. about 80-110xc2x0 C. The first zone is preferably a feed system (which may include a separate impregnation vessel) for a continuous digester, while cooking is in a continuous digester.

Co-pending patent application 09/248,009 now U.S. Pat. No. 6,241,851 filed on Feb. 10, 1999 (the complete disclosure of which is included by reference herein), discloses a method of treating comminuted cellulosic fibrous material with a beneficial additive prior to chemical digestion. This additive is preferably a strength- or yield-enhancing additive, such as athraquinone [AQ] or polysulfide [PS] and their derivatives or equivalents. The present invention comprises a further method and apparatus for effecting the pretreatment of comminuted cellulosic fibrous material, typically wood chips (though the invention is equally applicable to the treatment of other forms of cellulose), to improve the properties [e.g. strength] of the resulting pulp or to improve the effectiveness [e.g. yield] of the pulping process.
It has been discovered that the pretreatment of comminuted cellulosic fibrous material, for example, wood chips, can be more effective if, among other things, the heating and cooking of the chips after pretreatment is essentially isolated from the pretreatment process. That is, a more effective pretreatment can be obtained if the pretreatment process is performed at a cooler temperature, with or, preferably substantially without, the presence of alkali, and the heating of the chips to cooking temperature is performed after the pretreatment (impregnation of the cellulose material) is essentially completed. In one aspect of this invention the additive is added earlier in the treatment process, and the content of cooking chemical, for example, kraft white liquor, is reduced or diverted from this earlier stage of pretreatment and introduced during later stages of pretreatment or in the formal cooking treatment. Thus, according to the present invention, possibly longer, cooler, less alkaline pretreatment is provided so that the cooking additive more effectively treats the chips prior to heating to cooking temperature, that is, to a temperature greater than 140xc2x0 C.
According to one aspect of the present invention there is provided a method of continuously producing chemical cellulose pulp from a comminuted cellulosic fibrous material slurry, comprising substantially continuously: (a) Impregnating the material with a solution containing yield or strength-enhancing additive at effective alkali and temperature conditions so that substantially no alkali degradation of the cellulose occurs, and so that little or substantially no acid hydrolysis occurs. And, (b) after (a), treating the material with an alkaline cooking liquor, at cooking temperature, to produce a chemical cellulose pulp with higher yield or strength than if (a) were not practiced.
In the method (a) may be practiced so that there also is substantially no dissolution of lignin from the material. At the end of (a), the material has been impregnated with the yield or strength enhancing additive (such as AQ or its derivatives or equivalents) so that the problems associated with conventional higher temperature additive impregnation are avoided. For example specifically with respect to AQ, it is a large molecule and needs a longer time to diffuse into the wood chips, or like cellulose material, than does, for example, alkali, and it needs to be reduced in order to dissolve so that it can diffuse. Therefore sometimes AQ is used in its reduced form (commonly referred to as SAQ). However also typically about 80% of the AQ reacts with dissolved lignin and thus is not capable of performing its intended yield and strength enhancing function, leaving only about 20% of the AQ for performing the desired functions. By utilizing the invention a much higher percentage of the AQ (up to substantially all) that is added actually impregnates the wood chips and performs its yield or strength enhancing function, and the AQ may or may not be added in reduced form. When the AQ successfully impregnates the chips it keeps the hemicellulose from being dissolved during cooking, and thus increases yield, and utilizes other mechanisms to enhance strength. Other materials may also be utilized to facilitate penetration of the chips with the additive, such as the use of a surfactant.
In the method as described above (a) may be practiced at an alkali concentration between 0-less than 10 g/l expressed as NaOH, and at a temperature of between about 80-130xc2x0 C., typically less than about 120xc2x0 C., and preferably about 110xc2x0 C. or less. The amount of alkali is most desirably substantially zero, but preferably at most less than about 5 g/l expressed as NaOH.
In the method (a) may be practiced in a feed system of a continuous digester and (b) in a continuous digester. Exactly where in the feed system (a) is practiced may be widely variable. For example a chip bin could be located in a wood yard, and the additive could be sprayed or otherwise applied to the wood chips even prior to entry into the chip bin, or while they were entering the chip bin, or while they were in the chip bin. Then the wood chips could be pumped from the wood yard to the digester using primarily or substantially exclusively water as the slurrying medium (with no intentional significant alkali addition) so that the chips would be at desirable low temperature, low alkali, impregnation-facilitating conditions for a significant period of time. In a typical situation impregnation in (a) will take at least about 20 seconds, e.g. between about 2-60 minutes at superatmospheric pressure (which superatmospheric pressure may be provided in any conventional manner including by a level of liquid above the chips, pumping, and/or in a pressure vessel). Alternatively the additive may be introduced after the chip bin and before a pump and/or high pressure feeder, in a separate treatment vessel such as an impregnation vessel, or any other location in the feed system that proves advantageous for any reason.
The invention may also comprise substantially immediately after impregnation in (a) adding between about 35-100% of the alkali used to treat the material, including in (b), to the material. Alternatively the alkali can be added far downstream. Also the method may further comprise (c), between (a) and (b), treating the material in a second zone with a solution containing additive at an effective alkali concentration of about 5-less than 15 g/l expressed as NaOH and greater than in (a), and at a temperature of between about 110-130xc2x0 C. and higher than in (a)
In the method (a) may be practiced using as the additive at least one of AQ or its derivatives or equivalents, polysulfide or its derivatives or equivalents, or sulfite in the form of sulfur dioxide, NaHSO3, or Na2SO3. A suitable amount of additive may be used; for example if AQ or its derivatives or equivalents are used, typically (a) is practiced with a total additive concentration of between about 0.02-0.5% on wood, typically between about 0.02-0.1% on wood.
Additive may also be added during the digesting process, as is conventional.
According to another aspect of the present invention there may be provided a method of treating comminuted cellulosic fibrous material comprising substantially continuously: (a) Treating a slurry of comminuted cellulosic fibrous material with a first liquid comprising primarily or substantially exclusively water containing a beneficial additive at a maximum effective alkali concentration of less than 10 g/l, and at a first temperature of about 80-130 degrees C., for at least about 20 seconds, e.g. between about 2-60 minutes under superatmospheric pressure. And, (b) after (a), treating the material in the slurry with a second liquid having an initial effective alkali concentration greater than 10 g/l (preferably greater than 15 g/l and most desirably greater than 20 g/l) expressed as NaOH, and at a second temperature greater than 130xc2x0 C. (e.g. greater than 140xc2x0 C.), to produce a chemical cellulose pulp.
The method as described above may further comprise (c), between (a) and (b), treating the slurry with a third liquid containing the beneficial additive at a maximum effective alkali concentration greater than the first liquid and less than the second liquid, and at a third temperature, higher than the first temperature and less than 140 degrees C.
Another embodiment of the present invention may be a method of treating comminuted cellulosic fibrous material consisting of or comprising: (a) treating (e.g. pretreating) a slurry of comminuted cellulosic fibrous material with a liquid containing a beneficial additive at a first alkali content (e.g. from 0-less than 10 g/l) at a first temperature; (b) after (a), treating the slurry with a second liquid containing a beneficial additive at a second effective alkali content [greater than zero, and preferably at least 10% greater than the first effective alkali content] at a second temperature higher than the first temperature; and (c) after (b), treating [possibly, although not necessarily, after displacement of substantially all of the additive therefrom] the slurry with a third liquid having an effective alkali content (i.e. concentration) greater than the first and second effective alkali contents and a temperature greater than the first and second temperatures and greater than 130xc2x0 C. (e.g. greater than 140xc2x0 C.) to produce a chemical cellulose pulp.
As described above, the beneficial additive used in steps (a) and (b) may be AQ (most desirably SAQ), polysulfide, sulfur, surfactants, and combinations thereof. The first alkali content, expressed as xe2x80x9ceffective alkalixe2x80x9d (EA) as NaOH, is preferably less than 10 g/l, and may be less than about 5 g/l, or the first liquid may contain no alkali at all. For example, the first liquid may be mill water, steam condensate, or washer filtrate containing little or no alkali content. The first temperature of treatment (a) is preferably a relatively cool temperature, that is, a temperature less than 130xc2x0 C., preferably less than about 120xc2x0 C., for example, the first temperature may range from about 90 to 110xc2x0 C., or be even lower.
Procedure (a) may be performed using the methods and apparatuses described in U.S. Pat. Nos. 5,476,572; 5,622,598; and 5,632,025, that is the system marketed under the trademark LO-LEVEL(copyright) feed system by Andritz-Ahlstrom Inc. of Glens Falls, N.Y. The LO-LEVEL(copyright) feed system, that is a system employing a chip pump and not using a horizontal xe2x80x9csteaming vesselxe2x80x9d, is particularly suited for treatment according to the present invention since this system allows for the feeding and treatment of chips at lower temperatures than can be handled by conventional feed systems. Other conventional equipment and processes may also be used to perform the present invention, for example, those not including a chip pump and including a horizontal steaming vessel.
The second liquid of step (b) preferably contains at least some alkali, for example, the second liquid contains less than 15 g/l EA, typically about 5 to 10 g/l EA. This alkali content may be supplied by kraft white, green, or black liquor, or from combinations of white, green, or black liquor and water or washer filtrate. The second temperature is also preferably less than 140xc2x0 C., for example, less than about 120xc2x0 C., and is typically between about 110 and 130xc2x0 C. The procedure (b) is typically performed in the upper part of continuous digester, for example, a Kamyr(copyright) continuous digester as also sold by Andritz-Ahistrom Inc. of Glens Falls, N.Y.
Procedure (c), the formal pulping process, may be any form of chemical pulping process, but is preferably one or more of the processes described in U.S. Pat. Nos. 5,489,363; 5,536,366; 5,547,012; 5,575,890; 5,620,562; 5,662,775 and others. The processes and apparatuses described in these patents are marketed under the name LO-SOLIDS(copyright) Pulping by Andritz-Ahlstrom.
According to another aspect of the present invention there is provided a method of continuously producing chemical cellulose pulp from a comminuted cellulosic fibrous material slurry, comprising continuously: (a) In a first treatment zone treating the material with a solution containing yield or strength-enhancing additive at effective alkali and temperature conditions so that substantially no alkali degradation of the cellulose occurs (and so that the material and additive flow in contact with each other for a period of time). (b) After (a), treating the material in a second zone with a solution containing additive at an effective alkali concentration of about 5-less than 15 g/l expressed as NaOH, and at a temperature of between about 110-130xc2x0 C. and higher than in (a). And (c) after (b) (and possibly, but not necessarily desirably, after removing substantially all of the additive from contact with the material), treating the material with an alkaline cooking liquor, at cooking temperature, to produce a chemical cellulose pulp with higher (e.g. at least 2% higher) yield or strength than if (a) and (b) were not practiced.
In the method preferably (a) is practiced in a feed system of a continuous digester, (b) is practiced in a top zone of the continuous digester, and (c) is practiced in the continuous digester below the top zone. Also, preferably (a) is practiced at an alkali concentration between 0-less than 10 g/l expressed as NaOH, and less than in (b), and at a temperature of between about 80-110xc2x0 C. At least 50% of the additive may be introduced in (a), or about 40% may be introduced in (a) and 60% of the additive introduced elsewhere, for primary use in (b). In an embodiment wherein the additive is AQ or its derivative or equivalents, and wherein (a) and (b) are practiced with a total additive concentration of between about 0.05-0.15% on pulp.
The apparatus used in practice of the present invention is primarily conventional apparatus, except, for some aspects, for the additive additions to the feed system, and to the top zone of a continuous digester, and the potential recirculation of additive withdrawn from the top zone (including a screen at a transition between the top zone and the cooking zone of the continuous digester) and introduction to the feed system.
According to another aspect of the present invention there is provided a cellulose slurry treatment system comprising: An upright continuous digester having an inlet adjacent the top and an outlet adjacent the bottom thereof. A feed system for the digester including a slurry pump. A yield or strength-enhancing additive conduit for introducing yield or strength-enhancing additive into the slurry before the slurry pump. A top treatment zone of the digester, and a screen assembly adjacent the bottom of the top treatment zone, and a cooking zone below the screen assembly. The screen assembly providing a temperature transition within the digester. Means for introducing or re-circulating liquids into the digester so as to establish upward flow of liquid in the digester above the screen. And means for introducing yield or strength-enhancing additive into the top zone and/or feed system of the digester.
In the system, the means for introducing additive into the feed system may comprise conventional conduits, nozzles, venturis, or other conventional structures capable of introducing a liquid into a flowing liquid or slurry. The means for introducing liquid into the digester to ensure upward flow immediately adjacent the screen assembly (which preferably comprises the second screen in the digester going from the top to the bottom) comprises any conventional structure that will accomplish that purpose, including re-circulation conduits with central pipes connected to pumps, etc. The invention also preferably comprises means for re-circulating additive withdrawn from the top zone of the digester to the additive introduction means associated with the feed system. Such re-circulation means may comprise conventional conduits, and/or pumps, valves, or like fluid structures for that purpose, and may also include separation equipment for separating the additive from some of the liquid with which it is re-circulated. The preferred additives are those described in co-pending application Ser. No. 09/248,009.
It is the primary object of the present invention to provide for the effective treatment of comminuted cellulosic fibrous material so as to increase the strength, yield, and/or other advantageous properties of the pulp or the treatment process. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.

Method of pretreating pulp with yield or strength-enhancing additive


Apparatus for detecting light emitted by assay samples is provided, in which light emitted by the sample is collected for transmission to a charge coupled device camera (74) by an optical fiber bundle. The cross-sectional area of the optical fiber bundle corresponds to the area of the sample, the end of which is located close to the sample for detecting any light emitted therefrom, and selected fibers (30) of those making up the bundle are separated from the remainder and extend to a source of excitation radiation (76) and serve to convey excitation radiation (if required) directly to a corresponding plurality of points distributed over the are of the end face of the bundle and therefore over the area of the sample. The remaining fibers (32, 38) of the bundle serve to collect emitted light (whether generated by fluorescence caused by excitation or otherwise) and provide a light path to the change coupled device camera, wherein the ends of the excitation fibers and the ends of the emitted light collecting fibers area distributed uniformly over the area of the fiber bundle presented to the reaction site.

This invention concerns methods and apparatus for imaging, and particularly the imaging of luminescence samples of the type in which the sample is illuminated with excitation radiation such as ultra-violet light, or where the sample is activated by some suitable chemiluminescent or bioluminescent means, and is interrogated for any resulting emission light due for example to fluorescence within the sample. The invention is particularly concerned with multipath (or multichannel) systems in which a large number of samples can emit light and need to be interrogated at the same time.
PCT Application No. WO 98/0144 describes a fluorescence assay imaging system in which excitation radiation is supplied to the assay sample via an annular sleeve fitted around the end of a fibre optic bundle the end of which is in close proximity to the assay sample. The fibres collect emitted light due to fluorescence induced by the excitation radiation. It has been found that using an annular source of radiation does not produce the most uniform and sufficiently intense illumination of the assay reaction site, fan it is an object of the present invention to improve the uniformity and intensity of excitation illumination over the p resented area of each assay reaction site, without prejudicing any light collecting efficiency of the fibres.
Achieving uniformity over the reaction site has been found to be even more difficult to achieve where the sample is a very thin layer of cells or is contained or upon a thin gel or membrane.
The problems identified above become even greater as the area of each reaction site decreases. This is tending to occur as greater numbers of samples and therefore reaction sites, are accommodated in a sample supporting device such as a multi-well plate, multi-site membrane or gel or wafer, or chip of silicon or like material.
The invention endeavours to provide an improved illumination and collection system which allows sufficient excitation radiation to be introduced if required by the assay, and emitted light to be collected from reaction sites such as those in a 96 well plate for which the earlier imaging system of Wo 98/01744 is generally adequate, as well as the much smaller reaction sites such as now exist in high format multiple sample plates.
The invention is applicable to any luminescence producing assay.
Light emitting luminescence processes, including fluorescence, chemiluminescence and bioluminescence, and/or a combination of these processes, can be used in the measurements of biomedical and chemical assays. The wavelengths of excitation and emission for these processes are characteristic of the fluorescent and/or luminescent molecules and moieties being used. Wavelength ranges used are in the UV, visible, red and infra-red parts of the spectrum. A typical excitation range is 260-800 nm, a typical emission range is 320-1100 nm.
In the present application, the luminescent processes being measured include fluorescence, chemi- and bioluminescence.
In normal fluorescence, a fluorescent molecule or flurophore is excited by external radiation, such that it absorbs light energy and re-emits light at a longer wavelength.
The fluorescence may occur almost immediately, or later in time in which event it is referred to as time-delayed fluorescence.
In an alternative luminescent process, involving what is generally known as fluorescence or chemiluminescence energy transfer, energy is transferred from a donor molecule or moiety to an acceptor molecule or moiety, via a non-radiative mechanism. This mechanism can occur, eg via resonance or via electron transfer between atoms and molecules. Such luminescent donor and acceptor molecules may be fluorescent or chemi- or bioluminescent. The donor or acceptor molecules are generally different, and more than one molecule type may be used in either the donor or acceptor stage of the process.
The activation of the donor molecules may be via excitation light in the case of fluorescence or via chemical activation in the case of chemi- or bioluminescence. With fluorescence activation there may be a short delay between the excitation of the donor and the emission of the acceptor, in the range microseconds to milliseconds.
Energy transfer only takes place over very short distances (typically 10 nm and therefore the donor and acceptor molecules need to be in very close proximity. This can be achieved by direct bonding (eg covalent) of the donor and acceptor molecules, or linking of the two molecules by a biochemical bridge (eg via a peptide link). Alternatively, the molecules may be coated or bonded onto a solid phase, such that they are in close proximity (eg a microplate or bead). In a further example, the energy transfer from the donor may be via a reactive intermediate product, eg singlet oxygen or some excited chemical radical, which diffuses, eg in a fluid, to interact with the acceptor molecule.
Where no energy transfer takes place between the donor and the acceptor molecules, the donor molecule itself, when activated, will release energy directly as light, with emission wavelength characteristic of that molecule itself. When energy transfer occurs, the emission wavelength is characteristic of the acceptor molecule. Where the donor and acceptor molecules are different, the light emission from the acceptor molecules may be of a longer or shorter wavelength to the emission characteristic of the donor molecule.
When used in biomedical or chemical assays, to measure the presence or activity of a compound or agent, these luminescent processes may be used as an indicator of the presence or activity of such a compound or agent. The increase or decrease in light emission, from the donor or acceptor molecules, may be used as an indicator of the unknown compound being assayed. For example, the unknown compound might interact directly or indirectly with the energy transfer process, eg break the bridge between the donor and acceptor molecules or otherwise inhibit the transfer process. This would result in a change in the relative intensity of light emission of the donor and acceptor molecules, which could be detected by measurement, for example, at the two or more wavelengths which are characteristic of each molecule. Thus a ratiometric measurement involving various pairs of wavelengths characteristic of the molecules used may be appropriate.
EP 0580362 A1 describes a fluorescence detecting apparatus in which some of the fibres terminating below a sealed sample holder 7 convey excitation radiation to the sample, and others convey the fluorescence radiation away to a detector. On pages 3 and 4, a preferred arrangement for weak fluorescence is described, in which the excitation fibres are concentrated in the centre of the bundle presented to the sample and those for receiving and conveying away from the fluorescence radiation are located annularly around the central excitation fibre core.
It was no doubt thought that by concentrating the excitation radiation fibres into a central region of the sample, and collating the weak emitted fluorescence from an annular region of the central core, much of the unwanted excitation radiation reflected or refracted back towards the fibres by the sample (or the reaction site), would thereby not be collected by the fibres leading to the detector.
However it has been found that this creates a virtual dead region in the centre of the reaction site where the product of excitation and light collection for any point is very low or zero (due to the annular arrangement of the collecting fibres), and genuine signals cannot be distinguished from background noise emanating from a large central area of the reaction site.
The present invention seeks to overcome this problem since for reliable and accurate assay evaluation, not only is it Li necessary for good uniformity of response to exist between one well and another over the entire well plate, but it is also very important that there is a high degree of uniformity of response across the area of each assay reaction site so that if the latter can be considered to be divided into a large number of tiny adjacent areas the product of excitation incident on and light collection from each of those tiny areas should be substantially the same over the whole area of the assay.
According to the present invention, there is provided apparatus for detecting luminescence in a sample, in which light emitted by the sample is collected for transmission to photosensitive detector means by an optical fibre bundle the cross-sectional area of which corresponds to the area of the sample and one end of which is located close to but spaced from the sample for directly illuminating the sample and collecting light emitted therefrom, selected ones of the fibres making up the bundle are separated from the remainder and extend to a light source to convey the light for direct illumination of the sample, and other fibres of the bundle serve to collect light emitted from the sample due to luninescence and provide a light path therefor to the photosensitive detector means, wherein the light collecting fibres are divided into a plurality of groups for conveying light to different regions of the detector meqns, thereby providing parallel light paths from the sample to the detector, and a wavelength selective filter is located in each of the said light paths to permit only selected wavelengths of light to reach the region of the detector means associated with each light path, and wherein the fibres in the bundle are arranged in a symmetrical pattern 80 that in the end face of the bundle presented to the sample, each sample illuninating fibre is surrounded by a ring of six light collecting fibres which, around the ring, successively constitute fibres appertaining to the respective groups of said light collecting fibres, whereby the sample illuminating fibres and the light collecting fibres are distributed uniformly over the area of the fibre bundle presented to the sample.
The detector may comprise a CCD array, a cooled CCD camera, an intensified CCD (ICCD) array, or an array of photodiodes or PMT""s, or a or similar device.
Preferably the filters are interference filters.
In the preferred arrangement one third of the fibres in the bundle can convey light radiation to the sample, another third of the fibres collect and convey emitted radiation via a first wavelength selective filter to a first region of the photosensitive detector, and the remaining third of the fibres collect and convey emitted radiation via a second wavelength selective filter to a second region of the detector. Except for peripheral regions of the fibre bundle area, each emission collecting fibre will be a member of each of three separate but intersecting rings of emission collecting fibres, centered on three light conveying fibres which are immediate neighbours of one another.
By distributing the light conveying fibres uniformly over the end of the bundle presented to the sample, and likewise distributing the emission collecting fibres in a similar uniform manner, there is a greater chance that light transmitted to the sample will penetrate to sites in the sample which are capable on stimulation/excitation of emitting light, and there is also a good chance that the very small quantities of light emitted in response to such stimulation or excitation will be collected by emission collecting fibres and conveyed to the photosensitive detector.
Typically the samples are contained in small wells arranged in a matrix in a plate known as a well plate, at least one end of each of the wells being closed so as to retain a liquid sample therein, but in which the closed end is transparent and forms a window to enable light to penetrate into the sample to excite the latter and not to impede light emitted from the sample due to fluorescence or energy transfer, from passing in the return direction therethrough.
Assay analysis often involves studying reactions which have occurred in hundreds or thousands of samples and it is commonplace for well plates to be constructed having a matrix of some many hundreds or thousands of wells. One typical well plate contains 3456 wells which is conveniently interrogated by investigating the luminescence from 96 wells at a time using a presentation plate which aligns 96 fibre bundles with 96 of the 3456 wells in the well plate, and stepping the presentation plate 36 times relative to the well plate so as to interrogate all 3456 wells.
In the case of a 3456 well plate having circular wells, typically each well has a diameter of 1mm. In the case of a well plate having a smaller number of wells, each well can be larger. The wells can in fact be of any cross-sectional shape but normally are circular or square.
According to a preferred feature of the invention the two groups of emission gathering fibres from each of the 96 bundles are collated into two collections each of 96 bundles, and each of the two collections is presented to one of two wavelength selective interference filters, each of which has a different wavelength filtering characteristic from the other, and two further bundles of optical fibres downstream of the filters separately collect and transfer light which is transmitted by the two filters, to two discrete regions of the detector.
The collections of fibres are preferably re-arranged as required so as to optimally utilise the area of the filter, and fibres leading from the filters to the detector are preferably re-arranged, if required, so as to optimally occupy the active area of the detector.
In general this will entail re-arranging the downstream fibres so as to conform to the aspect ratio of the detector if the latter is different from the aspect ratio of the filter.
Thus in the case of a square detector, the fibres leading from the interference filter are preferably re-arranged in two rectangular arrays which when arranged side by side make up a square corresponding to the square proportions of the detector.
Although rearrangement of the fibre bundles occurs, by maintaining fixed registration between the 192 fibre bundle ends presented to the detector with the 192 fibre bundles derived from the 96 well inspecting bundles, the presence of emitted light from any one well can be determined by interrogating the X,Y coordinate positions in the detector array corresponding to the images of two fibre bundles in the two groups of 96 bundles presented to the detector, which correlate to the two groups of fibres from the fibre bundle inspecting the particular well.
According to a preferred aspect of the invention, each of the fibre optic bundles presented to each well site, is made up of 45 Ge-doped silica clad, silica fibres, each typically of a diameter of 100-200 microns, 15 of which are separated out as a sub-bundle and combined with similar sub-bundles from each of the other 96 bundles, and which extend to a source of excitation radiation such as UV light. One or more filters may be located between the UV source and the sub-bundles. The remaining 30 fibres from each of the 96 bundles are divided into two further sub-bundles each of 15 fibres. This produces a total of 192 emission collecting sub-bundles, 96 of which lead to discreet positions at the input of a first interference filter, and the other 96 of which lead to discreet positions at the input of a second interference filter, which transmits different wavelengths from those transmitted by the first filter.
Light transmitted by the interference filters, enters one or the other of two downstream groups of 96 sub-bundles arranged on a one to one basis with each of the two arrangements of 96 sub-bundles upstream of the filters, and the downstream sub bundles are merged to form an array of 192 sub-bundles having the same aspect ratio as that of the detector.
Where the aspect ratio of the detector is approximately square, the 192 sub-bundles are conveniently arranged into 14 rows, the first and last of which contain 12 sub-bundles and with each of the intermediate 12 rows, containing 14 sub-bundles. The array of rows and columns thereby defines what is essentially a square area with each of the corners missing, for presentation to a generally square aspect ratio detector.
Typically the interference filters are circular and have a diameter of approximately 80 mm.
Typically a square input window of a CCD camera has 27 mm long sides.
The invention also lies in a method of detecting emitted luminescence from an assay sample in which a fibre optic bundle having a cross-sectional area commensurate with the area of the sample is located with one end close to the latter, and fibres which are to collect and transmit emitted light are uniformly distributed over the cross-section of the bundle amongst other fibres in the bundle through which light can be conveyed to the sample, if required.
The method may include the further step of dividing the detected light into two or more channels by arranging that the light collecting fibres are split into two or more sub-bundles of similar numbers of fibres, each sub-bundle serving to convey light to one of a corresponding plurality of interference filters having differing pass bands, causing the filtered light to fall onto differently addressable regions of a photosensitive detector, and comparing the electrical signals from the differently addressable regions to permit a comparison to be made as between the quantity of light transmitted by one of the filters and that transmitted by the other.
PCT Application WO 98/01744 describes an imaging system for light emitting assays in which an interference filter is used to enable highly selective transmission of the radiation which is to reach the imaging device such as a camera.
Whilst an interference filter has a very sharp cut-off and allows virtually 100% transmission of desired wavelengths and virtually zero transmission of unwanted wavelengths, breakthrough can occur if light of a non acceptable wavelength is incident on the filter at a sufficiently large angle to satisfy the transmission criterion for the interference filter, ie the relationship between wavelength and angle of incidence for the interference filter.
By using optical fibres to transmit light from the sample to the interference filter, and shielding the fibre ends from extraneous light as much as possible, rogue rays will in general be restricted to reflected or refracted excitation light and this will in general be of a fixed wavelength. Rays of such light which are capable of being transmitted via the optical fibres and are of such large angle as to be capable of breaking through the interference filter would probably be Skew rays and it has already been proposed to position an angle collimator between the interference filter and the camera to reduce the transfer to the camera of Skew rays issuing from the interference filter.
According to another preferred aspect of the present invention, in apparatus as aforesaid, an additional optical filter is provided in the light path to the detector, preferably between the assay sample and the interference filter, and the characteristics of the additional optical filter are such that light of a wavelength corresponding to that emitted by the sample will be transmitted by the filter but light of a wavelength equivalent to that employed to excite the sample will be strongly attenuated or xe2x80x9cblockedxe2x80x9d by the filter before reaching the interference filter, irrespective of the angle of incidence of the radiation on the filter.
The additional filter may be located immediately in advance of the interference filter between it and the ends of the optical fibres transmitting light from the assay sample to the interference filter.
A primary purpose of the additional filter is to remove rays of excitation radiation and particularly skew rays of excitation radiation that would otherwise be transmitted through the interference filter and could have a very high intensity at the detector as compared with the intensity of any radiation arising at the detector as a result assay luminescence.
The characteristics of the emission filters required for detection of these types of luminescent processes, especially where the emission wavelengths of the acceptor molecules may be shorter or longer than the wavelengths of the donor molecule, has to be considered.
In the case of fluorescein, which produces normal fluorescence, excitation light of, eg 485 nm produces fluorescent light emitted at longer wavelength, eg 530 nm.
Any excitation light appearing at a 530 nm band pass interference filter, with an angle to the filter satisfying the Fabry-Perot condition, will be transmitted. This is the case, eg for 485 nm light arriving at xe2x88x9254xc2x0. In the case of fibre optic components, skew rays can be transmitted and enter the filter at such an angle. A blocking filter is needed to eliminate any light which might be transmitted by virtue of the Fabry-Perot condition, or by punch-through.
In the case of fluorescence energy transfer assays, where the excitation light is used to activate the donor molecules, and is say of wavelength 480 nm, and is of shorter wavelength than the light emitted by the acceptor molecule, eg 540 nm, then the same situation applies. This means that a blocking filter is required to absorb the 480 nm excitation light that would otherwise be transmitted by the Fabry-Perot condition for the interference filter which is chosen to transmit the 540 nm emission light. The blocking filter also helps to eliminate any punch-through of the 480 nm light.
In the case of energy transfer assays where chemi- or bioluminescent activation of the donor molecules occurs, and hence no excitation light is used, there is still the problem arising from the donor or acceptor molecules having different emission wavelengths, and hence the need to detect the longer wavelength in the presence of the shorter wavelength, where the intensity of the shorter wavelength is significantly greater than the intensity of the longer wavelength.
This is particularly the case where the emission wavelength of the acceptor is shorter than the emission wavelength of the donor, and where the energy transfer process has resulted in significant amplification of the signal generated by the acceptor molecules. Again a blocking filter is desirable to prevent light of the shorter wavelength being passed by the interference filter for the longer wavelength light, by virtue of the shorter wavelength light being transmitted through the filter by satisfying the Fabry-Perot condition, or by punch-through.
In a typical example of apparatus embodying the invention, blue is excitation light having a wavelength of 485 nm is employed to excite green fluorescence having a wavelength of the order of 530 nm. Any blue light finding its way down fibres which should only transmit emitted green fluorescence, for example by reflection from the bottom of a sample plate containing the assay, may exit the fibres in a cone of Skew rays of sufficiently large angle to satisfy the transmission criterion of the interference filter, and an intense ring of blue light will be presented to the detector.
Without the presence of the additional filter proposed by the invention, this unwanted light will be conveyed via the remaining fibre optics to the camera. Unless this ring of blue light is eliminated by an angle collimating device ahead of the camera as already proposed, the ring of light will swamp the camera around a region of the camera sensor to which low level green light due to fluorescence will be conveyed if present.
Although an angle collimator will reduce the intensity of such a ring, it is not a complete solution to the problem, and in the presence of strong Skew rays, sufficient swamping can still occur to render green light at the camera virtually indistinguishable from noise etc, and if the assay emits light for example by fluorescence, the small spot of green light attributable to the fluorescence can be surrounded by and essentially swamped by the ring of intense blue light produced by the unwanted breakthrough of excitation radiation even in the presence of an angle collimator. A supplementary filter, as proposed by the invention, fitted ahead of, or downstream of, or both ahead and downstream of the interference filter, reduces this significantly.
In order to reduce Skew ray incidence on the interference filter the additional filter must be located ahead of the interference filter. It may be in contact therewith.
To be effective the additional filter should have a sharp cut-off between transmission and attenuation, and a high attenuation of wavelengths beyond the cut-off point. In the example given above where the blue light wavelength is 485 nm and the emitted radiation due eg to fluorescence, has a wavelength of 530 nm, a filter having a cut-off at 515 nm would be appropriate, thereby transmitting wavelengths of the order of 530 nm but inhibiting wavelengths of the order of 485 nm.
A filter having such a characteristic is a Schott filter, Type OG515. This transmits wavielengths above approximately 515 nm but severely attenuates any wavelengths significantly below 515 nm. Such filters constitute blocking filters.
The use of an additional filter provided by the invention does not obviate the need for an angle collimator as already proposed, but is preferably used in combination therewith.
The angle collimating device further reduces Skew rays and in practice is comprised of a fused fibre optic plate of the order of 5-10 mm thickness, which is mounted in advance of the camera input. Preferably it is made from glass fibres of relatively low numerical aperture (NA) typically of the order of 0.30. Such a device transmits wanted rays within the numerical aperture 0.22 of the bundle of fibres, but greatly reduces Skew rays that would otherwise be transmitted by the bundle.
By inserting the plate in front of the detector (eg before a camera input face plate) any tendency for spreading or cross-talk between the fibres and the detector is reduced.
It is important that the angle colimating device is placed after the interference filter since at that position it does not matter if the material from the which the collimating device is constructed itself produces any fluorescence. It is for example difficult to obtain a fused fibre optic plate of non-fluorescent material such as silica.
Reference has been made to Skew rays. In this connection the numerical aperture of a fibre is the cone-angle for the rays that are transferred with high efficiency by the fibre. In an ideal sense the condition only applies to meridional rays, ie those which pass along a plane including the axis of the fibre. The fibre is normally assumed to be a long cylinder.
In practice such rays are vanishingly few and the light transmitted by a fibre is normally considered to be all the rays within the same cone angle but entering the fibre at any point on the entry face of the fibre, since all these rays will also be transmitted with relatively high efficiency.
Skew rays are therefore those that enter at any point on the end face of the fibre but at an angle greater than sinxe2x88x921 NA. The conditions for such rays to be transmitted are complicated and difficult to satisfy but in some situations up to half the rays transmitted by a fibre can be Skew rays.
In single channel assay systems, Skew rays are less of a problem since the light path in a single channel system can be highly collimated so as to more effectively remove them. The problem is more noticeable in multi-channel systems where there is insufficient space between the channels to allow optical collimating mechanisms to be accommodated.
In apparatus as aforesaid, the photosensitive detector is preferably a CCD, an ICCD, a cooled CCD, or photodiode or PMT array. Whatever device is chosen, it should have good spatial resolution after centroiding so as to be able to resolve individual fibre bundles in the final image to give minimal cross-talk between channels. A preferred spatial resolution is 10-20 microns.
The detector should have good quantum efficiency (QE).
Typically an ICCD will have a QE of 15% in the blue, falling to a few percent in the red.
A cooled CCD will have better QE rising to approximately 30% in the red.
When the optical system presenting light to the camera collects light from the sample via small diameter fibres (typically of the order of 100 microns diameter or less), and maintains this resolution throughout to the input of the photodetector, such as a CCD camera, and where the camera has a spatial resolution of the order of 10-20 microns, inspection of the area of the CCD array on which any light from one sample is incident, will allow light from individual fibres in the bundles conveying light from the sample to the camera to be identified. This for example enables light from a clump of cells in a sample to be observed, as distinct from separated individual cells, which can be useful.
Where this requires a focusing of the light passing through the interference filter region, a Grin lens or other device may be used, such as is described in our aforementioned PCT Application WO 98/01744.
It is to be understood that the present invention can be incorporated in all such systems, including those incorporating different detectors, and sub-well imaging using Grin lenses.
It is also to be understood that whereas the various aspects of the invention have so far been described in relation to well plates, each of the aspects of the invention is equally applicable to assay systems in which the samples occupy discrete areas of a membrane or gel or are distributed in the matrix of a sample support such as a wafer or chip of silicone or thin glass slide or sheet.
The invention will now be described by way of example with reference to the accompanying drawings, in which:
In FIGS. 1 and 1A, a well plate 10 is shown located above a presentation plate 12. The drawing is an exploded perspective view and the spacing implied by the drawing is an exaggeration of the actual spacing. In practice the presentation plate 12 will be very close to the underside of the well plate 10.
Well plates have tended to be constructed with either 96 wells typically arranged in 8 rows of 12 columns, but in recent years higher density plates have been constructed and a typical high density plate may contain, say, 36 times as many wells as the 96 well plate. However tie area of the plate is the same as is the basic matrix. The only difference in this case is that the well size has been decreased enabling six wells to be located along each row and six wells down each column in place of a single well in the original array. This means that instead of there being twelve wells along each row, there are now 72 and instead of there being eight rows, there are now 48 rows.
To take advantage of this and to simplify the indexing of a 96 aperture presentation plate, the latter is formed with openings which correspond in position to each of the original 96 wells of a 96 well plate, but equal in size to that of the wells in the 3456 well plate; This means that 96 of the 3456 wells can be inspected simultaneously by aligning the presentation plate 12 so that the first of the 96 apertures (14) coincides with the first of the 3456 wells, at position 60 in the well plate. This means that the second aperture 18 in the presentation plate aligns with the seventh well 20 along the first row, and so on.
Shifting the presentation plate 12 by a distance equal to the distance between apertures 16 and 22 (the next well in the first row adjacent 16) means that all of the 96 apertures in the presentation plate 12 will now be aligned with a new set of 96 of the wells in the well plate 10. By moving the presentation plate successively through six steps parallel to the rows containing wells 16, 22 and 20, and for each step six positions perpendicular to that row, in each case each movement corresponding to the distance between adjoining wells in the well plate measured perpendicular to the first row, (ie the distance between well 16 and well 24), so every one of the 3456 wells can be interrogated by 36 relative movements between the presentation plate and the well plate.
In practice, the well plate is moved relative to the presentation plate.
Each of the apertures such as 14 in the presentation plate 12 serves as a termination for a fibre bundle made up of 45 individual fibres. The fibres are shown terminating in two of the apertures for illustration only, one designated 26 and the other 28.
Each bundle of 45 fibres is made up of three groups of 15, one group such as 30 extending to an excitation light source, one group such as 32 conveying fluorescence light from a well aligned with the aperture 26 to an aperture 34 in a presentation disc 36. The third group of 15 fibres 38 extends to another opening 40 in a second presentation disc 42, for conveying fluorescence light to that other opening 40.
The three groups of 15 fibres making up the other illustrated bundle leading to and from aperture 28 are denoted by reference numerals 44, 46 and 48 respectively and these extend from the excitation light source in the case of group 44 and to two other apertures 50 and 52 respectively in the two presentation discs 36 and 42.
Each of the latter includes 96 apertures arranged regularly over the circular area of each disc, and similar discs 36xe2x80x2 and 42xe2x80x2 are aligned with the discs 36 and 42. Suitable optical filter discs 54 and 56 are sandwiched between discs 36 and 36xe2x80x2, and discs 42 and 42xe2x80x2.
Apertures in the two discs 36, 36xe2x80x2 (42, 42xe2x80x2) are aligned on a one to one basis and fibres lead from each of the aligned apertures such as 34xe2x80x2 in disc 36xe2x80x2 to unique apertures in two groups of 96 apertures arranged in a rectilinear matrix in an output plate generally designated 58. The first such matrix is designated 60 and the second 62 and the fibres such as 64 from aperture 34xe2x80x2 and 50xe2x80x2 lead to apertures 34xe2x80x3 and 50xe2x80x3 in the matrix region 60 and the fibres 68 and 70 from apertures 40xe2x80x2 and 52xe2x80x2 in disc 42xe2x80x2 lead to apertures such as 40xe2x80x3 and 52xe2x80x3 in matrix 62.
The two matrixes 60 and 62 together form a generally square outline which conforms approximately to the square aspect ratio of an input window illustrated at 72 in a camera 74.
The excitation light source is denoted by reference numeral 76 and between it and the 96 groups of 15 fibres such as 30 and 44 is located a filter 78. The arrangement of the apertures such as 34 and 50 and 40 and 52 on each of the plates 36 and 42 is as shown in FIG. 2. Two of the openings are arbitrarily shown at 34 and 36.
The arrangement of the two groups of 96 fibre ends in the two matrices 60 and 62 is shown in FIG. 3. The camera typically has a generally square aspect ratio and the arrangement of the 192 apertures making up the two matrices 60 and 62 makes the best use of the available generally square outline.
In accordance with a particularly preferred feature of the invention, the three groups of 15 fibres making up the bundle of fibres at each presentation plate aperture such as 16, is as shown in FIG. 4. Here the solid black fibre ends correspond to those in the excitation bundle 30, the clear circles correspond to those in the fibre bundle 32 leading to the first filter path containing filter 54, and the shaded circle corresponds to the fibres in the bundle 38 leading to the other wavelength selective path containing the second filter 56.
Each of the fibres illustrated in FIG. 4 is typically of the order of 100-200 microns diameter and comprises a pure silica core having a lower refrective index cladding, typically formed from doped silica cladding. Typically germanium is used as the dopant, although other materials may be employed. The resulting fibre has a numerical aperture of the order of 0.22.
Preferably the fibre also includes a coating around the cladding. The coating may for example be a polyamide or a material in the form of a thin layer such as obtained by metallisation of the surface of the cladding.
Materials for the core, cladding and any coating, preferably possess a very low tendency to fluoresce, so as to minimise the generation of unwanted light, which appears as background illumination, from which it may be difficult or impossible to distinguish light emitted by the array, due to similarity of wavelength and/or merely due to the relative amplitudes of the emitted and background light.
Experiments have shown that fibres as defined in the preceding paragraphs, permit a wide range of wavelength (including UV, visible and beyond into the infra red) to be accommodated, and low level background luminescence to result.
The numerical aperture can be increased by selecting different dopants and/or particular dopant properties, for the cladding material.
Using fibres of this size means that when bundled into a generally circular cross-section array the outside diameter of the bundle will be approximately 1.7 mm.
The particular arrangement of fibres shown in FIG. 4 has been found to be of considerable merit for ensuring high intensity of illumination from excitation light by ensuring that excitation fibre ends are uniformly distributed over the whole of the circular area of the fibre bundle and by uniformly arranging fibres leading to the two different wavelength selective paths equally uniformly throughout the remaining space, so an optimal excitation/collection characteristic is obtained for each well.
Although bundles of very tiny fibres are required between the presentation plate 12 and each of the presentation discs 36 and 42, the fibres leading from the discs 36xe2x80x2 and 52xe2x80x2 to the output plate 58 do not need to be made up of bundles of fibres but can be single fibres. Thus 64 for example may be a bundle of tiny fibres or a single fibre in each case having a typical outside diameter of 2 mm.
An angle collimating device 76 in the form of a thin plate may be located between the matrix array of fibre ends 34xe2x80x3, 50xe2x80x3 etc and the input window 72 of the camera 74.
The filters 54 and 56 are typically interference filters and preferably are interchangeable to allow different wavelengths to be selected.
Although the examples shown in the drawings are of a well plate, it is to be understood that the samples may be contained in any other supporting device such as a multi-well plate, multi-site membrane gel or wafer or chip of silicon or like material.
As indicated in FIG. 1 the area of presentation plate can be significantly less than the area of the well plate where there is a high ratio of samples to inspection apertures in the presentation plate. Also provided the arrangement and spacing and number of inspection apertures is suitable to align with groups of samples, and the one can be stepped relative to the other to obtain differing registrations, the aspect ratio and size of the sample support and the presentation plate can be quite different.
Additional filters 80, 82 for blocking Skew rays may also be incorporated, as shown in dashed line in FIG. 1, for the Purpose hereinbefore described.
As referred to herein, interference filters may comprise a large number of thin layers of dielectric materials, having differing refractive indices to produce constructive and destructive interference in transmitted light. Such filters can be designed to transmit a specific waveband only (a band pass filter) and can also be made to provide a very steep slope cut-on or cut-off at a particular wavelength, and to produce an edge filter.
Metallic layers may also be incorporated in such devices and in auxiliary blocking structures. Broadband interference filters usually contain a metallic layer.
Narrowband bandpass interference filters can be considered to be a Fabry-Perot interferometer, operating in the first order.


Apparatus and methods are disclosed for simultaneously tracking multiple finger and palm contacts as hands approach, touch, and slide across a proximity-sensing, multi-touch surface. Identification and classification of intuitive hand configurations and motions enables unprecedented integration of typing, resting, pointing, scrolling, 3D manipulation, and handwriting into a versatile, ergonomic computer input device.

A. Field of the Invention
The present invention relates generally to methods and apparatus for data input, and, more particularly, to a method and apparatus for integrating manual input.
B. Description of the Related Art
Many methods for manual input of data and commands to computers are in use today, but each is most efficient and easy to use for particular types of data input. For example, drawing tablets with pens or pucks excel at drafting, sketching, and quick command gestures. Handwriting with a stylus is convenient for filling out forms which require signatures, special symbols, or small amounts of text, but handwriting is slow compared to typing and voice input for long documents. Mice, finger-sticks and touchpads excel at cursor pointing and graphical object manipulations such as drag and drop. Rollers, thumbwheels and trackballs excel at panning and scrolling. The diversity of tasks that many computer users encounter in a single day call for all of these techniques, but few users will pay for a multitude of input devices, and the separate devices are often incompatible in a usability and an ergonomic sense. For instance, drawing tablets are a must for graphics professionals, but switching between drawing and typing is inconvenient because the pen must be put down or held awkwardly between the fingers while typing. Thus, there is a long-felt need in the art for a manual input device which is cheap yet offers convenient integration of common manual input techniques.
Speech recognition is an exciting new technology which promises to relieve some of the input burden on user hands. However, voice is not appropriate for inputting all types of data either. Currently, voice input is best-suited for dictation of long text documents. Until natural language recognition matures sufficiently that very high level voice commands can be understood by the computer, voice will have little advantage over keyboard hot-keys and mouse menus for command and control. Furthermore, precise pointing, drawing, and manipulation of graphical objects is difficult with voice commands, no matter how well speech is understood. Thus, there will always be a need in the art for multi-function manual input devices which supplement voice input.
A generic manual input device which combines the typing, pointing, scrolling, and handwriting capabilities of the standard input device collection must have ergonomic, economic, and productivity advantages which outweigh the unavoidable sacrifices of abandoning device specialization. The generic device must tightly integrate yet clearly distinguish the different types of input. It should therefore appear modeless to the user in the sense that the user should not need to provide explicit mode switch signals such as buttonpresses, arm relocations, or stylus pickups before switching from one input activity to another. Epidemiological studies suggest that repetition and force multiply in causing repetitive strain injuries. Awkward postures, device activation force, wasted motion, and repetition should be minimized to improve ergonomics. Furthermore, the workload should be spread evenly over all available muscle groups to avoid repetitive strain.
Repetition can be minimized by allocating to several graphical manipulation channels those tasks which require complex mouse pointer motion sequences. Common graphical user interface operations such as finding and manipulating a scroll bar or slider control are much less efficient than specialized finger motions which cause scrolling directly, without the step of repositioning the cursor over an on-screen control. Preferably the graphical manipulation channels should be distributed amongst many finger and hand motion combinations to spread the workload. Touchpads and mice with auxilliary scrolling controls such as the Cirque®™ Smartcat touchpad with edge scrolling, the IBM®™ ScrollPoint™ mouse with embedded pointing stick, and the Roller Mouse described in U.S. Pat. No. 5,530,455 to Gillick et al. represent small improvements in this area, but still do not provide enough direct manipulation channels to eliminate many often-used cursor motion sequences. Furthermore, as S. Zhai et al. found in "Dual Stream Input for Pointing and Scrolling," Proceedings of CHI '97 Extended Abstracts (1997), manipulation of more than two degrees of freedom at a time is very difficult with these devices, preventing simultaneous panning, zooming and rotating.
Another common method for reducing excess motion and repetition is to automatically continue pointing or scrolling movement signals once the user has stopped moving or lifts the finger. Related art methods can be distinguished by the conditions under which such motion continuation is enabled. In U.S. Pat. No. 4,734,685, Watanabe continues image panning when the distance and velocity of pointing device movement exceed thresholds. Automatic panning is, stopped by moving the pointing device back in the opposite direction, so stopping requires additional precise movements. In U.S. Pat. No. 5,543,591 to Gillespie et al., motion continuation occurs when the finger enters an edge border region around a small touchpad. Continued motion speed is fixed and the direction corresponds to the direction from the center of the touchpad to the finger at the edge. Continuation mode ends when the finger leaves the border region or lifts off the pad. Disadvantageously, users sometimes pause at the edge of the pad without intending for cursor motion to continue, and the unexpected motion continuation becomes annoying. U.S. Pat. No. 5,327,161 to Logan et al. describes motion continuation when the finger enters a border area as well, but in an alternative trackball emulation mode, motion continuation can be a function solely of lateral finger velocity and direction at liftoff. Motion continuation decays due to a friction factor or can be stopped by a subsequent touchdown on the surface. Disadvantageously, touch velocity at liftoff is not a reliable indicator of the user's desire for motion continuation since when approaching a large target on a display at high speeds the user may not stop the pointer completely before liftoff. Thus it would be an advance in the art to provide a motion continuation method which does not become activated unexpectedly when the user really intended to stop pointer movement at a target but happens to be on a border or happens to be moving at significant speed during liftoff.
Many attempts have been made to embed pointing devices in a keyboard so the hands do not have to leave typing position to access the pointing device. These include the integrated pointing key described in U.S. Pat. No. 5,189,403 to Franz et al., the integrated pointing stick disclosed by J. Rutledge and T. Selker in "Force-to-Motion Functions for Pointing," Human-Computer Interaction—INTERACT '90, pp. 701-06 (1990), and the position sensing keys described in U.S. Pat. No. 5,675,361 to Santilli. Nevertheless, the limited movement range and resolution of these devices, leads to poorer pointing speed and accuracy than a mouse, and they add mechanical complexity to keyboard construction. Thus there exists a need in the art for pointing methods with higher resolution, larger movement range, and more degrees of freedom yet which are easily accessible from typing hand positions.
Touch screens and touchpads often distinguish pointing motions from emulated button clicks or keypresses by assuming very little lateral fingertip motion will occur during taps on the touch surface which are intended as clicks. Inherent in these methods is the assumption that tapping will usually be straight down from the suspended finger position, minimizing those components of finger motion tangential to the surface. This is a valid assumption if the surface is not finely divided into distinct key areas or if the user does a slow, "hunt and peck" visual search for each key before striking. For example, in U.S. Pat. No. 5,543,591 to Gillespie et al., a touchpad sends all lateral motions to the host computer as cursor movements. However, if the finger is lifted soon enough after touchdown to count as a tap and if the accumulated lateral motions are not excessive, any sent motions are undone and a mouse button click is sent instead. This method only works for mouse commands such as pointing which can safely be undone, not for dragging or other manipulations. In U.S. Pat. No. 5,666,113 to Logan, taps with less than about 1/16″ lateral motion activate keys on a small keypad while lateral motion in excess of 1/16″ activates cursor control mode. In both patents cursor mode is invoked by default when a finger stays on the surface a long time.
However, fast touch typing on a surface divided into a large array of key regions tends to produce more tangential motions along the surface than related art filtering techniques can tolerate. Such an array contains keys in multiple rows and columns which may not be directly under the fingers, so the user must reach with the hand or flex or extend fingers to touch many of the key regions. Quick reaching and extending imparts significant lateral finger motion while the finger is in the air which may still be present when the finger contacts the surface. Glancing taps with as much as ¼″ lateral motion measured at the surface can easily result. Attempting to filter or suppress this much motion would make the cursor seem sluggish and unresponsive. Furthermore, it may be desirable to enter a typematic or automatic key repeat mode instead of pointing mode when the finger is held in one place on the surface. Any lateral shifting by the fingertip during a prolonged finger press would also be picked up as cursor jitter without heavy filtering. Thus, there is a need in the art for a method to distinguish keying from pointing on the same surface via more robust hand configuration cues than lateral motion of a single finger.
An ergonomic typing system should require minimal key tapping force, easily distinguish finger taps from resting hands, and cushion the fingers from the jarring force of surface impact. Mechanical and membrane keyboards rely on the spring force in the keyswitches to prevent activation when the hands are resting on the keys. This causes an irreconcilable tradeoff between the ergonomic desires to reduce the fatigue from key activating force and to relax the full weight of the hands onto the keys during rest periods. Force minimization on touch surfaces is possible with capacitive or active optical sensing, which do not rely on finger pressure, rather than resistive-membrane or surface-acoustic-wave sensing techniques. The related art touch devices discussed below will become confused if a whole hand including its four fingertips a thumb and possibly palm heels, rests on the surface. Thus, there exists a long felt need in the art for a multi-touch surface typing system based on zero-force capacitive sensing which can tolerate resting hands and a surface cushion.
An ergonomic typing system should also adapt to individual hand sizes tolerate variations in typing style, and support a range of healthy hand postures. Though many ergonomic keyboards have been proposed, mechanical keyswitches can only be repositioned at great cost. For example, the keyboard with concave keywells described by Hargreaves et al. in U.S. Pat. No. 5,689,253 fits most hands well but also tends to lock the arms in a single position. A touch surface key layout could easily be morphed, translated, or arbitrarily reconfigured as long as the changes did not confuse the user. However, touch surfaces may not provide as much laterally orienting tactile feedback as the edges of mechanical keyswitches. Thus, there exists a need in the art for a surface typing recognizer which can adapt a key layout to fit individual hand postures and which can sustain typing accuracy if the hands drift due to limited tactile feedback.
Handwriting on smooth touch surfaces using a stylus is well-known in the art, but it typically does not integrate well with typing and pointing because the stylus must be put down somewhere or held awkwardly during other input activities. Also, it may be difficult to distinguish the handwriting activity of the stylus from pointing motions of a fingertip. Thus there exists a need in the art for a method to capture coarse handwriting gestures without a stylus and without confusing them with pointing motions.
Many of the input differentiation needs cited above could be met with a touch sensing technology which distinguishes a variety of hand configurations and motions such as sliding finger chords and grips. Many mechanical chord keyboards have been designed to detect simultaneous downward activity from multiple fingers, but they do not detect lateral finger motion over a large range. Related art shows several examples of capacitive touchpads which emulate a mouse or keyboard by tracking a single finger. These typically measure the capacitance of or between elongated wires which are laid out in rows and columns. A thin dielectric is interposed between the row and column layers. Presence of a finger perturbs the self or mutual capacitance for nearby electrodes. Since most of these technologies use projective row and column sensors which integrate on one electrode the proximity of all objects in a particular row or column, they cannot uniquely determine the positions of two or more objects as discussed in S. Lee, "A Fast Multiple-Touch-Sensitive Input Device," University of Toronto Masters Thesis (1984). The best they can do is count fingertips which happen to lie in a straight row, and even that will fail if a thumb or palm is introduced in the same column as a fingertip.
In U.S. Pat. Nos. 5,565,658 and 5,305,017, Gerpheide et al. measure the mutual capacitance between row and column electrodes by driving one set of electrodes at some clock frequency and sensing how much of that frequency is coupled onto a second electrode set. Such synchronous measurements are very prone to noise at the driving frequency, so to increase signal-to-noise ratio they form virtual electrodes comprised of multiple rows or multiple columns, instead of a single row and column, and scan through electrode combinations until the various mutual capacitances are nulled or balanced. The coupled signal increases with the product of the rows and columns in each virtual electrodes, but the noise only increases with the sum, giving a net gain in signal-to-noise ratio for virtual electrodes consisting of more than two rows and two columns. However, to uniquely distinguish multiple objects, virtual electrode sizes would have to be reduced so the intersection of the row and column virtual electrodes would be no larger than a finger tip, i.e., about two rows and two columns, which will degrade the signal-to-noise ratio. Also, the signal-to-noise ratio drops as row and column lengths increase to cover a large area.
In U.S. Pat. Nos. 5,543,591, 5,543,590, and 5,495,077, Gillespie et al measure the electrode-finger self-capacitance for row and column electrodes independently. Total electrode capacitance is estimated by measuring the electrode voltage change caused by injecting or removing a known amount of charge in a known time. All electrodes can be measured simultaneously if each electrode has its own drive/sense circuit. The centroid calculated from all row and column electrode signals establishes an interpolated vertical and horizontal position for a single object. This method may in general have higher signal-to-noise ratio than synchronous methods, but the signal-to-noise ratio is still degraded as row and column lengths increase. Signal-to-noise ratio is especially important for accurately locating objects which are floating a few millimeters above the pad. Though this method can detect such objects, it tends to report their position as being near the middle of the pad, or simply does not detect floating objects near the edges.
Thus there exists a need in the art for a capacitance-sensing apparatus which does not suffer from poor signal-to-noise ratio and the multiple finger indistinguishability problems of touchpads with long row and column electrodes.
U.S. Pat. No. 5,463,388 to Boie et al. has a capacitive sensing system applicable to either keyboard or mouse input, but does not consider the problem of integrating both types of input simultaneously. Though they mention independent detection of arrayed unit-cell electrodes, their capacitance transduction circuitry appears too complex to be economically reproduced at each electrode. Thus the long lead wires connecting electrodes to remote signal conditioning circuitry can pickup noise and will have significant capacitance compared to the finger-electrode self-capacitance, again limiting signal-to-noise ratio. Also, they do not recognize the importance of independent electrodes for multiple finger tracking, or mention how to track multiple fingers on an independent electrode array.
Lee built an early multi-touch electrode array, with 7 mm by 4 mm metal electrodes arranged in 32 rows and 64 columns. The "Fast Multiple-Touch-Sensitive Input Device (FMTSID)" total active area measured 12″ by 16″, with a 0.075 mm Mylar dielectric to insulate fingers from electrodes. Each electrode had one diode connected to a row charging line and a second diode connected to a column discharging line. Electrode capacitance changes were measured singly or in rectangular groups by raising the voltage on one or more row lines, selectively charging the electrodes in those rows, and then timing the discharge of selected columns to ground through a discharge resistor. Lee's design required only two diodes per electrode, but the principal disadvantage of Lee's design is that the column diode reverse bias capacitances allowed interference between electrodes in the same column.
All of the related capacitance sensing art cited above utilize interpolation between electrodes to achieve high pointing resolution with economical electrode density. Both Boie et al. and Gillespie et al. discuss compultattion of a centroid from all row and column electrode readings. However, for multiple finger detection, centroid calculation must be carefully limited around local maxima to include only one finger at a time. Lee utilizes a bisective search technique to find local maxima and then interpolates only on the eight nearest neighbor electrodes of each local maximum electrode. This may work fine for small fingertips, but thumb and palm contacts may cover more than nine electrodes. Thus there exists a need in the art for improved means to group exactly those electrodes which are covered by each distinguishable hand contact and to compute a centroid from such potentially irregular groups.
To take maximum advantage of multi-touch surface sensing, complex proximity image processing is necessary to track and identify the parts of the hand contacting the surface at any one time. Compared to passive optical, images, proximity images provide clear indications of where the body contacts the surface, uncluttered by luminosity variation and extraneous objects in the background. Thus proximity image filtering and segmentation stages can be simpler and more reliable than in computer vision approaches to free-space hand tracking such as S. Alimad, "A Usable Real-Time 3D Hand Tracker," Proceedings of the 28th Asilomar Conference on Signals, Systems, and Computers—Part 2, vol. 2, IEEE (1994) or Y. Cui and J. Wang, "Hand Segmentation Using Learning-Based Prediction and Verification for Hand Sign Recognition," Proceedings of the 1996 IEEE Computer Society Conference on Computer Vision and Pattern Recognition, pp. 88-93 (1996). However, parts of the hand such as intermediate finger joints and the center of the palms do not show up in capacitive proximity images at all if the hand is not flattened on the surface. Without these intermediate linkages between fingertips and palms the overall hand structure can only be guessed at, making hand contact identification very difficult. Hence the optical flow and contour tracking techniques which have been applied to free-space hand sign language recognition as in F. Quek, "Unencumbered Gestural Interaction," IEEE Multimedia, vol. 3, pp. 36-47 (1996), do not address the special challenges of proximity image tracking.
Synaptics Corp. has successfully fabricated their electrode array on flexible mylar film rather than stiff circuit board. This is suitable for conforming to the contours of special products, but does not provide significant finger cushioning for large surfaces. Even if a cushion was placed under the film, the lack of stretchability in the film, leads, and electrodes would limit the compliance afforded by the compressible material. Boie et al suggests that placing cornnressihle insulators on top of the electrode array cushions finger impact. However, an insulator more than about one millimeter thick would seriously attenuate the measured finger-electrode capacitances. Thus there exists a need in the art for a method to transfer finger capacitance influences through an arbitrarily thick cushion.